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BOEING / GoFly contest: Oh, BOEING


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#51 gruntguru

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Posted 26 August 2019 - 04:27

Most would say the same of many less-useful contraptions out there - wing suits, jet packs, assault rifles . . 

 

I would have a go at flying it - if it looked stable and controllable (ie handlebars fitted  :lol: )



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#52 pierrre

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Posted 26 August 2019 - 08:25

on the topic of bad weather the vehicle's body would naturally point towards the oncoming force. rather than being blown away or tilted sideways away from the force.. it might look to go against it and straightened.. could this be a positive? i think it is. don't know why the competition didn't see your application go further

how do you see it handle bad weather conditions? maybe you can do a go fund me page manolis? I'd love to see this materialize

Edited by pierrre, 26 August 2019 - 08:27.


#53 manolis

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Posted 26 August 2019 - 13:51

Hello Kelpiecross.

 

Flying with a Portable Flyer 2 meter (6 ft) above the sea seems to me as safer than driving a motorcycle on the road (as long as not many flying fishes come the opposite direction).

Even the best – ever – Variable Valve Timing system needs a car maker or motorcycle maker to put it in the market.

 

Thanks

Manolis Pattakos



#54 manolis

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Posted 26 August 2019 - 13:51

Hello Pierrre.

 

Nice video.

 

But without Newton’s laws, how can be calculated the 2nd order force, and how can be drawn a plot of the 2nd order force vs the crankshaft angle?

 

The total force (from 1:05) seems as looking permanently upwards. Is this correct?

 

The balance web is to partially cancel out the 1st order inertia force coming from the piston reciprocation, and can do nothing at all for the 2nd order force (they are of different frequencies).

 

Thanks

Manolis Pattakos



#55 manolis

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Posted 26 August 2019 - 13:54

Hello Gruntguru.

 

I wish I had a few Gruntguru around the world to read, understand, think and write down their justified objections.

 

 

When it will fly?

I hope it will fly well before the final Fly-Off of the GoFly-BOEING contest (February 2020 according their latest postponement).

 

 

Who will fly it?

When we applied to the contest, they wanted US250$ for one-person teams, and US500$ for teams. So I put only myself.

 

 

The casting was/is a delay (a lot of time-consuming “try and error” lessons), but as I see it now, it was worth the cost.

Now it seems possible the mass production at an affordable – for everyone – cost.

 

 

As for the handlebars for your Flyer, what do you preffer: handlebars from a Harley or from a Ducati Panigale?

 

Thanks again

Manolis Pattakos  



#56 pierrre

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Posted 26 August 2019 - 15:47

Hello Pierrre.

 

Nice video.

 

But without Newton’s laws, how can be calculated the 2nd order force, and how can be drawn a plot of the 2nd order force vs the crankshaft angle?

 

The total force (from 1:05) seems as looking permanently upwards. Is this correct?

 

The balance web is to partially cancel out the 1st order inertia force coming from the piston reciprocation, and can do nothing at all for the 2nd order force (they are of different frequencies).

 

Thanks

Manolis Pattakos

thanks for the compliment, the overall force is the black arrow, 1:05 is just the beginning when forces were about to be added to the model

i forgot to credit the animation though, will do it on the caption



#57 manolis

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Posted 26 August 2019 - 16:36

Helo Pierrre.

 

You write:

"on the topic of bad weather the vehicle's body would naturally point towards the oncoming force. rather than being blown away or tilted sideways away from the force.. it might look to go against it and straightened.. could this be a positive? i think it is. don't know why the competition didn't see your application go further

how do you see it handle bad weather conditions?"

 

 

Quote from the "Device Technical Report" (at https://www.pattakon...GoFly/DTR_1.pdf ) as filed in the GoFly-BOEING contest:

 

 

Safety and high speed

. . .

Flying in adverse conditions, like sudden weather change, gusts of wind, rain etc is a big risk in case of underpowered flying devices having large surfaces exposed to the wind.

 

The ability for high speed flights is mandatory for the safety; at windy weather a big size / slow moving (“hovering”) flying device is a “feather in the wind”.

 

A personal flying device having 30 kts maximum speed and flying along a sea shore, has a big safety risk when the wind starts blowing towards the sea at, say, 35kts.

 

Because every flying object is at the mercy of any gust of the wind, the most important characteristics for safety seem to be: the small frontal area, the small drag coefficient, the high power to weight ratio, and the ratio of the power to the product of the frontal area times the drag coefficient. 

 

The human body is very well streamlined when hovering vertically and when cruising near horizontal.

 

If the PORTABLE FLYER can fly way faster than the wind, the strong wind and the strong wind gusts are not a problem any longer."

 

End of Quote.

 

 

 

 

For the animation: you do not need to credit the animation.

 

Thanks

Manolis Pattakos



#58 gruntguru

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Posted 26 August 2019 - 21:57

on the topic of bad weather the vehicle's body would naturally point towards the oncoming force. rather than being blown away or tilted sideways away from the force.. it might look to go against it and straightened..

In hover mode, provided the centre of aerodynamic pressure is lower than the centre of gravity, the flyer-pilot system will tilt towards the wind gust. Yes - a good thing.


Edited by gruntguru, 26 August 2019 - 22:04.


#59 gruntguru

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Posted 26 August 2019 - 22:03

As for the handlebars for your Flyer, what do you preffer: handlebars from a Harley or from a Ducati Panigale?  

 

:lol:   :lol:   :lol:

 

It needs inexpensive, lightweight handlebars. https://www.wish.com...egaAkqaEALw_wcB

 

The handles should be waist high.

 

Crowdfunding sounds like a great idea.


Edited by gruntguru, 26 August 2019 - 22:15.


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#60 Kelpiecross

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Posted 27 August 2019 - 04:22

Hello Kelpiecross.

 

Flying with a Portable Flyer 2 meter (6 ft) above the sea seems to me as safer than driving a motorcycle on the road (as long as not many flying fishes come the opposite direction).

Even the best – ever – Variable Valve Timing system needs a car maker or motorcycle maker to put it in the market.

 

Thanks

Manolis Pattakos

 

 

  Your valve gear ideas are certainly not the best ever  -  every  type is a variation on a already-known  principle.  But some are better arrangements than some presently in use  examples from car makers.

 

 Your "Flyer" is hugely compromised by your insistence on using such small diameter propellers.   Like the H4 the minimum practical propeller diameter would need to be 13 to 15 feet - and then two this size.  You could easily rearrange your design  so  each  engine drove a central coaxial  propeller  system of a much bigger diameter.  

 

  And of course it needs to be of the "sit-down" variety.  You claim that the whole arrangement weighs 20kg?   I would guess probably twice that.   But even at  20Kg it is probably too heavy (and top-heavy) for a normal  person to comfortably wear and put on - it would need  and assistant.   Whereas a  "sit-down"  (H4) layout would need no assistance. 

 

  I hate to be critical of someone who is so productive of ideas - but your main problem with all your ideas is continually insisting that your particular idea is the "best ever"  and refusing even minor changes.


Edited by Kelpiecross, 27 August 2019 - 04:23.


#61 manolis

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Posted 27 August 2019 - 10:28

Thank you Kelpiercoss.

 

 

You write:

“Your valve gear ideas are certainly not the best ever”

 

I did not write the pattakon VVA’s are the best ever.

 

But, please let me know which VVA is the best ever, and I will tell you its problems.

 

Take, for instance, the MultiAir / TwinAir of FIAT, Chrysler, Alfa Romeo, INA.

It is a hydraulic electronically controlled VVA; maybe, the most advanced today.

The PatAir (at https://www.pattakon...ttakonHydro.htm) , which is the MultiAir with different cam lobe profiles and different programming, provides all the modes of operation of the MultiAir plus an infinity of additional modes which can realize the Atkinson / Miller cycle for better efficiency at partial loads.

 

 

 

You also write:

“Your "Flyer" is hugely compromised by your insistence on using such small diameter propellers. Like the H4 the minimum practical propeller diameter would need to be 13 to 15 feet - and then two this size.  You could easily rearrange your design  so  each  engine drove a central coaxial  propeller  system of a much bigger diameter.”

 

The size of the rotors / propellers is not small.

The disk-loading is less than that of the Osprey V-22.

While the heavy disk-loading requires more power for the vertical take-off and landing, at high speeds it is a blessing (actually for really high speeds it is mandatory).

 

Compare the OSPREY V-22 (small diameter rotors, heavy disk loading):

 

Ossprey.jpg

 

 with the Chinook CH-47 (big diameter propellers and light disk loading):

 

photo2542_large.jpg

 

The first has almost double cruising speed, double range and substantially higher mileage.

 

I.e. the small diameter propellers of the OSPREY V-22 offer great advantages (even though it sacrifices the autorotation and the safety it offers).

 

 

With the small propellers the downwash speed is high.

 

With the pilot / rider of the Portable Flyer into the high speed downwash, the Portable Flyer has more control options.

 

Portable_Flyer_Accel_Decel_small.png

 

Besides the “weight displacement control” of the GEN-H-4, it has also true aerodynamic control (like Yves Rossy Delta Wing JetPack).

 

In the future the diameter of the propellers of the Flyer will be reduced for the sake of even higher speeds.

 

 

You also write:

“And of course it needs to be of the "sit-down" variety.  You claim that the whole arrangement weighs 20kg?   I would guess probably twice that.   But even at  20Kg it is probably too heavy (and top-heavy) for a normal  person to comfortably wear and put on - it would need  and assistant.   Whereas a  "sit-down"  (H4) layout would need no assistance.”

 

The 20Kg total weight is for normal materials (aluminum and steel).

With better / exotic / expensive materials the total weight reduces.

 

 

You also write:

“I hate to be critical of someone who is so productive of ideas - but your main problem with all your ideas is continually insisting that your particular idea is the "best ever"  and refusing even minor changes.”

 

Please keep on being critical.

Criticism is the best contribution in a technical discussion.

It helps to correct errors and it gives ideas for rethinking.

 

 

 

The complete application for the Portable Flyer in the GoFLy-BOEING contest is at https://www.pattakon...GoFly/DTR_1.pdf and https://www.pattakon...oFly/index.html

 

Please read it, be critical and let me know all your objections to help me improve it.

 

Thanks

Manolis Pattakos



#62 Slumberer

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Posted 27 August 2019 - 12:33

How do you transition from high speed cruising to braking?

It would seem to me that the only way would be to throttle back but that might just reduce your altitude and that might not be a great option.



#63 manolis

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Posted 27 August 2019 - 15:53

Hello Slumberer.

 

You write:

"How do you transition from high speed cruising to braking?"

 

 

See in the following video, from 1':52'' to 2':02'', Fraky Zapata accelerating and then decelerating with his FlyBoard Air.

  

 

To accelerate, Zapata leans forwards, so that the exhaust gas from his jet turbines exits downwards - backwards pushing him upwards - forwards.

To decelerate / brake, Zapata leans backwards, so that the exhaust gas from his jet turbines exits downwards - forwards pushing him upwards - backwards.

 

 

 

Quote from https://www.pattakon...GoFly/DTR_1.pdf

 

Zero vibrations, zero gyroscopic rigidity, zero reaction torque: 

 

• The symmetry of the engine, the zero phase difference between the two synchronized and counter-rotating crankshafts, the common combustion chamber (same instant pressure on the piston crowns of the two opposed pistons, same (and opposite) instant torque on the two crankshafts), and the symmetrical load (two counter-rotating symmetrical propellers) rids the saddle (and the pilot) of all kinds and orders of vibrations (zero free inertia forces, zero free inertia moments, zero free inertia torques, and zero combustion vibrations of all kinds). This is an absolute requirement when a powerful high revving engine is to be tightened to the body of a person. 

 

• The reaction torque is also permanently zero: no matter how wide the “throttle” is opened, or how abruptly the “throttle” opens or closes, there is no reaction torque (the only that happens is the increase or the decrease of the thrust force provided by the propellers). 

 

• The symmetry and the counter-rotation of the propellers and of the crankshafts maintains the gyroscopic rigidity of the PORTABLE FLYER zero. Even when only the one engine is running (for instance due to a malfunction of the other engine), the gyroscopic rigidity is zero. Zero gyroscopic rigidity means that the pilot “instantly” and “effortlessly” can vector the engine/propellers (i.e. the thrust force) towards the desirable direction, which is an absolute requirement for a safe, accurate and instantaneous control of the flight. 

 

• Without zero inertia and combustion vibrations, without zero gyroscopic rigidity, and without zero reaction torque at the changes of the “throttle”, the control of the flight becomes slow, inaccurate, unsafe, uncomfortable and exhausting.

 

End of Quote

 

 

Similarly to Zapata:

  • in order to accelerate towards a direction, the pilot / rider of the Portable Flyer leans towards that direction: the rotors provide an upwards force that takes the weight of the pilot / Flyer, and a horizontal force that accelerates the pilot / Flyer towards the selected direction.
  • in order to decelerate, the pilot /rider of the Portable Flyer leans backwards: now the rotors provide an upwards force that takes the weight of the pilot / Flyer, and a backwards force that decelerates the Flyer.

 

If it is not clear, please let me know to further explain.

 

Thanks

Manolis Pattakos 



#64 Kelpiecross

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Posted 30 August 2019 - 06:49

 Manny - various comments etc.:  

 The Flyer is dangerous.    Imagine the Flyer at take off -  a bloke staggering about  with a screaming engine, four propellers/twelve blades  spinning at around 5,000rpm balanced precariously on his (her) shoulders. Not dangerous?  I think it is self-evident - bloody dangerous both to the pilot and anybody within a hundred yards or so..

 

 The weight of the Flyer:  20kg all up? - and the rest.  The similar (in intended purpose)  H4 claims 70 kg empty/dry weight - allow 10 or 15 kg  for the additional structure - it is still about three times heavier than the Flyer.  With the Flyer you would have to add  10-15 kg for the fuel tank and fuel alone, plus carby/fuel injection  throttle cable and other controls,  starter motor/battery/generator, harness and some structure for the pilot and I am sure there are other items I have forgotten.    50kg  at least I would guess and probably a lot more.

 

 Insufficient lifting power:  I can only refer to previous practice with this.  If you look through all the available information on the internet etc.  you will not find even one example of an unshrouded/non-ducted propeller of this diameter being used. There are a few examples of ducted propellers of this size being used - but generally not very successfully.   The duct apparently adds 40% to 50% extra thrust for the same power and propeller diameter.   

This is a very good  example:           https://www.bing.com...26F38&FORM=VIRE

 Notably- even without a pilot or dummy it still couldn't lift itself off the ground.  The Mythbusters  didn't give the all-up weight - just that it was less than 500lbs. The MBs with their apparently unlimited budget and  engineering assistance  can only manage a weight like this - and yet you claim something approaching 1/10 of this weight.  

 

 You make a lot of comparisons between and Flyer and the Osprey  - I not sure it is valid to make such comparisons between two such widely varying in size airframes.   In any case - the vertical  performance aspect of the Osprey really is pretty terrible  compared to a conventional helicopter -  probably because of its  small rotor diameter.      

 

 Despite all the above the Flyer is an interesting project and topic.  

 

 On the subject of variable valve timing etc.:  I am referring only to VVT systems that are strictly mechanical  (maybe hydraulics or electrickery  to operate it - but the main principle is mechanical).  This rules out your MultiAir (or whatever it is called)  and all similar arrangements and hydraulic/pneumatic/solenoid (or combinations thereof) in general.  Also I rule out two-step systems (even though some of these are very good and very practical).  

  The only (and I mean only) contender I think (and I admit to a slight conflict of interest here) is the Helical Camshaft.    

 

 

 

 

 

.   


Edited by Kelpiecross, 30 August 2019 - 06:54.


#65 manolis

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Posted 30 August 2019 - 16:35

Thank you Kelpiecross.

 

 

You write:

“ Insufficient lifting power:  I can only refer to previous practice with this.  If you look through all the available information on the internet etc.  you will not find even one example of an unshrouded/non-ducted propeller of this diameter being used. There are a few examples of ducted propellers of this size being used - but generally not very successfully.   The duct apparently adds 40% to 50% extra thrust for the same power and propeller diameter.   

This is a very good  example:           

https://www.bing.com...26F38&FORM=VIRE

 Notably- even without a pilot or dummy it still couldn't lift itself off the ground.  The Mythbusters  didn't give the all-up weight - just that it was less than 500lbs. The MBs with their apparently unlimited budget and  engineering assistance  can only manage a weight like this - and yet you claim something approaching 1/10 of this weight.”

 

 

The following video:

 

 

shows the Martin JetPack in China, 2015, flying controllably for five minutes.

 

Worth mentioning:

in the video the pilot is tightly strapped onto the casing as a “dead weight” (neither ability for “weight displacement control”, nor for aerodynamic control by means of pilot’s limbs). The only control is some sets of flaps at the bottoms of the ducted rotors.

 

Specifications:

200Kg (440lb) empty weight,

320Kg (700lb) total take-off weight,

150kW (200PS) from a V-4 2,000cc 2-stroke engine,

two ducted rotors, 0.8m diameter (2 ft 7 in) each,

total “rotor disk area” 1m2,

disk loading: 320Kg/m2 (in comparison, the “non-ducted” Osprey V-22 has three times lower disk loading: 102Kg/m2).

 

According your:

 

The duct apparently adds 40% to 50% extra thrust for the same power and propeller diameter”,

 

and in case the propellers of the Martin JetPack were un-ducted:

 

with the existing (0.8m) diameter of the rotors the total take-off weight would drop to ~200Kg (so it could not take-off),

or,

for the existing 320Kg total take-off weight (and with the same 200PS power), the “rotor disk area” should increase by 50%, i.e. the rotor diameter should increase from 0.8m to 1m (1.5*(0.8^2)=1^2) to make it capable for take-off.

 

So, with 1m diameter un-ducted rotors and 200PS power, the 320Kg Martin JetPack would take-off and fly.

 

The total weight of the Portable Flyer is 1/3 of that of the Martin JetPack, while the power of each engine of the Portable Flyer is about 1/3 of the power of the Martin JetPack, and its rotors are 1m diameter each (as in the un-ducted version of the Martin JetPack).

 

I.e. even with the one engine and the one pair of counter-rotating propellers, the Portable Flyer can take-off and fly (just like the Martin JetPack).

 

With one more engine and one more pair of counter-rotating rotors, the Portable Flyer not only takes-off, but can accelerate upwards with 1g.

The take-off at full power (both engines) would be like falling to the sky, with 1g upwards.

This cannot be called “insufficient lift power”.

 

 

More important is the control:

 

With the pilot having free his limbs / head, and being permanently (from take-off to landing) into the high speed downwash, the control can be any combination of “weight displacement control” (like GEN-H-4) and of “aerodymanic control” (say, like Yves Rossy DeltaWing JetPack).

 

The most difficult moments are when the feet of the pilot are about to touch the ground during the landing, and when the feet of the pilot are un-touching (leaving) the ground during a take-off.

 

In both cases the downwash air stream is directly hitting the limbs / head of the pilot (enabling "aerodynamic control") and combined with the body’s re-posing (enabling "weight displacement control") provide over-control (redudancy of control for errors correction).

 

As for pilot’s legs / feet, they are the most adjustable and sensitive landing gear.  

 

 

 

You also write:

“The weight of the Flyer:  20kg all up? - and the rest.  The similar (in intended purpose)  H4 claims 70 kg empty/dry weight - allow 10 or 15 kg  for the additional structure - it is still about three times heavier than the Flyer.  With the Flyer you would have to add  10-15 kg for the fuel tank and fuel alone, plus carby/fuel injection  throttle cable and other controls,  starter motor/battery/generator, harness and some structure for the pilot and I am sure there are other items I have forgotten.    50kg  at least I would guess and probably a lot more.”

 

Here they are shown the two engines of the videos (previous post) from the ignition side:

 

Tilting_Flyer_both_A.jpg

 

Tilting_Flyer_both_B.jpg

 

and from the sprockets (power output) side:

 

Tilting_Flyer_both_C.jpg

 

Tilting_Flyer_both_D.jpg

 

With 2  carburetors each, and with their ignitions on, the total weight is 21Kg.

 

No extra attention has been paid, so far, for the weight reduction (only from the sprockets / synchronizing gearing can be removed a couple of Kg, while from the cylinder liners (they were made too thick because too much aluminum had to be removed from the cast casings) can be removed more than one more kg).

 

What is not shown is:

the saddle,

the propellers (with their sprockets and toothed belts)

and the pipes whereon the propellers are rotatably mounted.

 

The cranking is to be manual.

Neither electric generator, nor battery are required.

 

The above make the 20Kg total weight for the Portable Flyer feasible (without using special / expensive materials).

 

 

 

You also write:

“The Flyer is dangerous.    Imagine the Flyer at take off -  a bloke staggering about  with a screaming engine, four propellers/twelve blades  spinning at around 5,000rpm balanced precariously on his (her) shoulders. Not dangerous?  I think it is self-evident - bloody dangerous both to the pilot and anybody within a hundred yards or so..”

 

For those who fly (with airplanes, helicopters, paragliders etc), the real danger is the hit the ground after an uncontrolled fall.

The rotors (which rotate at less than 4,000rpm) are the most reliable (and extremely lightweight) part.

 

 

Thanks

Manolis Pattakos



#66 Kelpiecross

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Posted 31 August 2019 - 10:06

  Interesting stuff.

 

  I don't think the Flyer will get off the ground -  you think it will accelerate upwards at 1g.   I think something 

we can both agree on,  and be certain of,  is that the Flyer's performance will lie somewhere between these two limits.  



#67 manolis

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Posted 12 September 2019 - 11:30

Hello all.

 

A few pistons and rods going for the heat treatment:

 

Tilting_Pistons_Rods_before_heat_treatme

 

and here the one prototype (without the aluminum pulley) revving low and high:

 

 

Thanks

Manolis Pattakos



#68 manolis

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Posted 18 November 2019 - 05:33

Hello all.
 
In the following photos:
 
Tilting_Fly_Blocks_1.jpg
 
and
 
Tilting_Fly_Blocks_2.jpg
 
a few OPRE_Tilting blocks, almost finished, are shown.
 
 
 
Yesterday they were added at https://www.pattakon...ttakonDesmo.htm two demo videos for the DVVA (Desmodromic VVA):
 
]
 
and
 
 
The central control shaft varies the duration of the intake valves from 0 to 300+ degrees, while the side control shaft varies the intake valves lift (from 0 to more than 12+mm), all "on the fly".
 
In the Formula1 the Rotary Valves are banned since 2004.
Are the Desmodromic, and/or the Fully Variable valve systems also banned?
 
Thanks
Manolis Pattakos

Edited by manolis, 18 November 2019 - 05:41.


#69 gruntguru

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Posted 18 November 2019 - 22:24

Are the Desmodromic, and/or the Fully Variable valve systems also banned?

 
Thanks
Manolis Pattakos

 

 

Yes. They can't even run camshaft phasers.

 

Beautiful mechanism Manolis!


Edited by gruntguru, 18 November 2019 - 22:26.


#70 manolis

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Posted 10 December 2019 - 17:12

Hello Kelpiecross.

 

You wrote (30 August 2019):

“On the subject of variable valve timing etc.:  I am referring only to VVT systems that are strictly mechanical  (maybe hydraulics or electrickery  to operate it - but the main principle is mechanical).  This rules out your MultiAir (or whatever it is called)  and all similar arrangements and hydraulic/pneumatic/solenoid (or combinations thereof) in general.  Also I rule out two-step systems (even though some of these are very good and very practical).  

The only (and I mean only) contender I think (and I admit to a slight conflict of interest here) is the Helical Camshaft.”

 

 

The DVVA (Desmodromic Variable Valve Actuation, more at https://www.pattakon...ttakonDesmo.htm ) complies with the above limitations (strictly mechanical, continuously variable etc).

 

DVVA_lower_upper_head.jpg

 

 

For the Helical Camshaft VVA Wikipedia writes:

 

“A helical camshaft is a type of mechanical variable valve actuation (VVA) system. More specifically it is a camshaft that allows the valve opening duration to be varied over a wide, continuous, step-less range, with all of the added duration being at full valve lift.

. . .

The Helical Camshaft's typical 250 degree to 350 + degree duration range basically means that a suitably robust engine could “pull” strongly from about 1500 RPM to maybe 20,000 + RPM and still idle smoothly at 500 or 600 RPM.”

 

 

 

Let’s compare the DVVA with the the Helical Camshaft VVA.

 

 

VARIABILITY

 

The DVVA is more variable than the Helical Camshaft because:

 

The DVVA varies the valve duration from a maximum to zero, while the Helical Camshaft cannot go to small valve durations.

 

The DVVA varies the valve lift, too, from zero to a maximum (not possible for the Helical Camshaft VVA that operates at constant valve lift).

 

The DVVA varies independently the valve lift and the valve duration (for instance, a 300 crankshaft degrees valve duration can be combined with 0mm valve lift, also with 4mm valve lift, also with 8mm valve lift, also with 12mm valve lift, also with 7.4mm valve lift and so on; and vice versa, a 5mm valve lift can be combined with 100 degrees valve duration, also with 150 degrees valve duration, also with . . .).

 

The state-of-the-art / mass production VVAs (BMW’s valvetronic, Toyota’s ValveMatic, Nissan’s VVEL etc) and the Helical Camshaft VVA can combine each valve duration with only a unique valve lift.

In comparison, the DVVA combines each valve duration with infinite valve lifts (and vice-versa).

This makes the DVVA infinite times more variable than the state-of-the-art VVA’s and than the Helical Camshaft.

 

 

HIGH REVVING

  

While the Helical Camshaft opens positively the poppet valves, valve springs are necessary to restore the valves back to their valve seats.

At higher revs the valve springs must be stiff (the inertia forces increase with revs square).

The constant valve lift the Helical Camshaft VVA operates, means that even at idling, the strong (for the higher revs) valve springs have to be fully compressed (friction loss, wear, idling smoothness etc).

 

The cam-lobe profile of the original camshaft on which the Helical Camshaft is based on, may have ramp and “nose” curves not proper for high revs.

 

Here is a Helical Camshaft valve lift profile of a modified Suzuki (from Wikipedia):

 

Helical_Camshaft_Wiki.png   

 

The trapezoidal valve lift profile may be good for low revs, but as the revs increase it can’t work; it has to be modified to a smoother one, say like:

 

DVVA_smooth.png

 

otherwise the valve will bounce.

But, again, if you modify the cam lobe profile to a smoother one, the minimum allowed duration of the Helicam Camshaft VVA gets longer spoiling the low revs operation.

 

A set of “sport” valve-springs is not cheap.

In order to go from 10.5mm valve lift (of the original B16A2  VTEC engine) to 12mm valve lift, and from 8,000rpm (wherein the red line of the original Honda 1,600cc VTEC engine is) to 9,000rpm, we had to pay 460 Euro to TODA for a set of sport valve springs (more at https://www.pattakon...attakonVVAs.pps )

 

im14.jpg

 

ValveLifts.gif

 

In the high revving engines the valve lift vs the crank angle is near sinusoidal, which lowers the inertia loads.

Compare the two red curves (exhaust and intake valve lift profiles with the high rpm cam-lobes) of the original Honda B16A2 V-TEC engine with the trapezoidal curves of the modified to Helical Camshaft Suzuki (above)

 

 

Without valve springs, the DVVA opens positively and closes positively the valves, allowing higher revs and more power, but also efficient, clean, friction-less and wear-less operation at medium, low and very low revs.

 

 

The DVVA is not only the most variable mechanical VVA, but it is also a true desmodromic valve train, way more desmoromic than the single-mode (non VVA) DESMO of Ducati; the Panigale cylinder head cannot operate without the big springs shown here:

 

Ducati_Panigale_valve_train.jpg

 

 

THROTTLE-LESS OPERATION

 

The DVVA needs not a throttle to control the load (the intake valves, which open as little as necessary, do this job; for instance, the intake valve lift at idling can be 0.15mm, while the maximum intake valve lift is well above 12mm).

 

The Helical Camshaft needs a throttle for the load control.

 

For sport / racing engines an independent throttle body (ITB) is an expensive part.

In the case of the VVA-roller (the father of the DVVA) its cost is zero:

 

im16.jpg

 

 

 

PS.

 

According the previous analysis,

the trapezoidal valve lift profile of the Helical Camshaft VVA creates extreme inertia loads at high revs, and needs super-extra-stiff valve springs in order to keep the valves from bouncing,making the following quote from Wikipedia:

 

“The Helical Camshaft's typical 250 degree to 350 + degree duration range basically means that a suitably robust engine could “pull” strongly from about 1500 RPM to maybe 20,000 + RPM and still idle smoothly at 500 or 600 RPM.”

 

nothing more than nonsense.

 

Thanks

Manolis Pattakos


Edited by manolis, 10 December 2019 - 17:21.


#71 Kelpiecross

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Posted 15 December 2019 - 09:57

  Manny - this is the first time I have had a serious look at the DVVA - I had not realised that the DVVA was so "all-singing/all dancing"  (meaning it can do everything).  It is certainly very ingenious that you have been able to make the DVVA so capable with linkages etc.  What reasons did the car companies give for not taking it up? (Typically they give no reason).

 My personal criticisms of the DVVA is that it is clearly very complex (hard to imagine it running at very high RPM)  and a lot of its features really are unnecessary.  For instance; being desmodromic is probably more of  a hindrance rather than an advantage - with modern cams and cam springs etc. it really is just not needed.  I think it is generally accepted that Ducati only keeps it on as a sales gimmick - conventional cams/springs etc. would be better. (As an aside here,  I think you would need clearance and springs like the Ducati).  Also the desmo requires that the driving crankshaft  is needed so that the operation is "double-acting" - a driving cam would be better - there is a lot of lost motion with the crankshaft arrangement.  The making of the "curved slot"  would be tricky to make accurately  so as to achieve  soft valve landings etc.  

  Essentially, the DVVA is very clever but I wouldn't like the job of trying to make it all work.        

 

The  HC  on the other hand (compared to the DVVA) is meant to be very simple - it is a cam only system rather than a whole VVA setup like the DVVA.  The HC ends at the follower - the drive train from the cam on is conventional - whether it be plain, roller, hydraulic or whatever. (I don't think the DVVA could be made hydraulic easily?).  The general thinking behind the HC  was that, as a normal "fixed" cam does a pretty good job, all that was needed was the most important variable - to have a large range of variable duration.  As long as there is adequate lift, variable lift is of much less importance - and desmo etc. should be avoided like the plague.  

  Anyhow have a look at this - I found this a few weeks ago on YouTube:

 

 I have to admire young Matthew's good taste and engineering acumen.  I should point out that neither I, or anyone at Helical Cams  previously knew this bloke or even knew of his YouTube channel.  

  Also, his general videos on various engineering subjects are well worth having a look at: 

https://www.youtube....BeOMA/playlists

 Despite the slightly Guy Martin - esque  accent, the videos are very good and almost addictive to watch - and there bloody hundreds of them.

 

PS - recent developments have made the machining/hardening etc. of the HC  really quite straightforward, albeit a little complex - despite what Matthew says.         


Edited by Kelpiecross, 15 December 2019 - 10:06.


#72 manolis

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Posted 16 December 2019 - 19:18

Hello Kelpiecross.

 

You write:

“Manny - this is the first time I have had a serious look at the DVVA - I had not realised that the DVVA was so "all-singing/all dancing"  (meaning it can do everything).  It is certainly very ingenious that you have been able to make the DVVA so capable with linkages etc.”

 

Thanks.

 

The deeper you will “dive” in the DVVA, the more you will “discover”.

 

It would be useful if you, as a third party, explain to the rest forum members how the DVVA works.

 

 

 

You also write:

“What reasons did the car companies give for not taking it up? (Typically they give no reason)”

 

I suppose they didn’t get how it works and how many things it can do.

The DVVA is difficult to understand, but easy to make.

The PatRoVa rotary valve is easy to understand, but is hard to make (because it needs high precision manufacturing and DLC coating).

 

 

 

You also write:

“As an aside here,  I think you would need clearance and springs like the Ducati)”

 

No.

The only spring is the “washer spring” that takes the lash (say, 0.2mm) and keeps the valve tightly closes on its seat.

 

 

 

You also write:

“Also the desmo requires that the driving crankshaft  is needed so that the operation is "double-acting" - a driving cam would be better - there is a lot of lost motion with the crankshaft arrangement.”

 

What is presented as a problem is actually an advantage of the infinite mode DVVA as compared to the single mode Desmo of Ducati.

 

In the Desmo there are two independent mechanisms that keep the valve between them. Other “finger followers / cam-lobes” open the valve, and other “finger followers / cam lobes” restore the valve.

The valve is like a tennis ball that oscillates / rebounds between two rackets. At higher revs wherein the inertia forces get strong, things become hard fro the Desmo.

 

In the DVVA the same linkage that opens positively the valve, the same exactly linkage closes positively the valve.

 

Worth mentioning here:

While the Desmo is based on sliding friction, the DVVA is based on rolling friction. The difference in friction loss and wear is more than significant (when Honda launched their S2000 VTEC with the roller bearings, they claimed some 75% reduction of the friction loss in the valvetrain).

 

 

 

You aso write:

“My personal criticisms of the DVVA is that it is clearly very complex (hard to imagine it running at very high RPM)”    

 

The linkage that opens and closes the valves in the DVVA is, more or less, the typical “crankshaft / connecting rod / piston” mechanism, which is extremely robust and reliable in actuating big pistons at long strokes, at high revs and under extreme gas pressure and inertia loads.

In the case of the DVVA the same mechanism / linkage has a by far easier work to do, which allows the valve to operate at very high RPM reliably.

 

Throwing away the top half of the valve stem and the valve spring:

 

DVVA_short_valve_stem.jpg

 

what is left is lightweight, i.e. for high and extreme revs.

 

 

 

You also write:

“The making of the "curved slot"  would be tricky to make accurately  so as to achieve  soft valve landings etc.”

 

The track (curved slot) is easy to design (for soft landing etc) and cheap to make with a CNC 2-axes milling machine (excluding the two tracks, all the rest parts of the prototype were made with an old lathe; drilling the “ends” of each pair of “connecting rods” together (i.e. the one part over the other), their “center to center” distance are exactly the same).

 

 

 

You also write:

“I don't think the DVVA could be made hydraulic easily?).”

 

It can, and it is easy (but meaningless for extreme rpm).

More details at https://www.pattakon...attakonVVAs.pps (page 52).

 

Application of the DVVA on side-cam engines (like Harley V-2, American V8 etc):
 

DVVA_side_cam.gif

 

At left it is shown the conventional mechanism (constant duration, constant lift, camshaft, valve restoring spring).
At right it is shown the modified-to-desmodromic mechanism: the duration is selected by rotating, about the cross, the DLC track; then the lift is aligned by rotating, about the same cross, the LC pin.

The rocker-arm pivot of the DVVA embodies the hydraulic lash adjuster.

 

 

 

You also write:

“As long as there is adequate lift, variable lift is of much less importance - and desmo etc. should be avoided like the plague.”

 

At https://www.mcnews.c...-panigale-v4-r/ it is presented the new Ducati Panigale V4 R:

 

2019-Ducati-Panigale-V4-R-2-640x960.jpg

 

Panigale_V4_R.png

 

221bhp/lt specific power, provided at 24.6m/sec mean piston speed.

 

Estimated price: ~50,000 euro.

Plague?

 

 

 

You also write:

“The  HC  on the other hand (compared to the DVVA) is meant to be very simple - it is a cam only system rather than a whole VVA setup like the DVVA.”

and

“the HC ends at the follower”

 

 

Strictly technical thoughts and questions:

 

I suppose the HC needs a control mechanism (a linkage?) for the accurate (and lash free) axial displacement of the several rotating semi-cam-lobes of the Helical Camshaft.

 

Any photos of the control mechanism for a typical straight-four 16-valve engine modified to HC?

 

Is the control mechanical or hydraulic?

Is it simple and durable?

Are there any thrust-roller bearings between the sliding semi-cam-lobes and the control “linkage”?

 

In “your” video, the 3D-printed blue semi-cam-lobe seems as supported exclusively at one side (I mean the complete rings at its one end). Is this support adequate and durable?

 

Isn’t a problem the need for a minimum “constant lift region” (of some 40 crank degrees?)?

 

Isn’t a problem (friction, wear) that at high revs the “constant lift” portion of the cam-lobe is heavily loaded by the fully compressed valve springs? (with the valve immovable, there is no inertia to reduce the load from the valve spring).

 

In the HC it is required a fast deceleration on the valve just before the constant lift portion of the lobe, and a fast acceleration on the valve at the end of the constant lift portion of the cam lobe.

Doesn’t this mean that for the same rev limit, stiffer valve springs are necessary when an engine is modified to Helical Camshaft?

 

Can the HC with its trapezoidal valve lift profile rev at high rpm reliably?

 

 

 

At the end:

 

The DVVA is more variable than the HC (and than the state-of-the-art mass production VVA’s).

The DVVA is more desmodromic than the DESMO of Ducati.

The DVVA is for higher revs than both, the HC and the DESMO.

The DVVA has simple pure-mechanical control (a few degrees of rotation of the control shaft(s) and the valves follow another valve lift profile from the infinite-infinities available.

 

Even if the DVVA were way more complicated and expensive than the HC and the DESMO, it would be worthy to be in production because it can make more.

 

But judging from the manufacturing of the demonstration prototype, I can say that the DVVA is simple, cheap and easy to built.

 

Thanks

Manolis Pattakos



#73 Kelpiecross

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Posted 17 December 2019 - 12:12

The blue and pink  3D-printed model  was made by the bloke in the video.   There are plenty of images and running videos of the "real"  steel HC on the internet if you look.  

  

 To quote from the video:

  

 "I f-------  love it, it gives me the horn". 

 

 I suggest that the DVVA  would have the opposite effect on most blokes. 



#74 manolis

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Posted 18 December 2019 - 12:23

Hello all.

 

In this video:

 

 

a wingsuiter flying at 142mph (230Km/h = 64m/sec) passes though a 10ft (3m) wide rock hole.

 

 

Judging from the trees and the horizon, his angle of descent is some 30 degrees (1.7:1 glide ratio).

 

His vertical speed is 64m/sec * sin(30degrees) = 32m/sec (i.e. his weight is descending at a 32m/sec speed).

 

With a total weight of 165lb (75Kp, 750Nt), the power consumed is: 32m/sec * 750Nt = 24kW = 33bhp.

 

 

Thus,

if the wingsuiter had a prime mover (say, some jet turbines like those of Rossy or Browning or Mayman or Zapata) providing 33bhp of push (or pull) power, then the wingsuiter could sustain a horizontal cruise speed of 230Km/h.

 

 

With a propeller efficiency of, say, 75%, the required power output from the engines of the Portable Flyer is 44bhp for 230Km/h horizontal cruise.

 

For 300Km/h speed, the required engine power is 44bhp * (300/230)^3 = 100bhp (50bhp per engine).

 

PatTol_axial_pilot3.gif

 

Thanks

Manolis Pattakos



#75 manolis

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Posted 21 December 2019 - 05:20

Hello Kelpiecross

 

Quote from Wikipedia at https://en.wikipedia...elical_camshaft  :

 

“There is no physical reason why a Helical Camshaft could not be the “driving” cam in a Valvetronic-type oscillating cam setup. (But it would be quite complex and the Valvetronic part of the arrangement would limit the Helical Camshaft's high RPM capabilities). 

The result would be an almost unbelievable array of possible duration/lift combinations”

 

End of quote.

 

 

The DVVA (desmodromic VVA, more at https://www.pattakon...ttakonDesmo.htm) alone:

 

DVVAphoto.jpg

 

does exactly this, providing “an almost unbelievable array of possible duration/lift combinations”:

 

DVVA_profiles.png

 

without the limitations of either the Helical Camshaft VVA (and has a lot: post #72 bottom) or of the BMW Valvetronic VVA.

 

 

Worth to note:

 

The DVVA needs neither rotating cams nor orcillating cams.

 

The "slow" pure-mechanical angular displacement (for a few degrees) of the "track" (inside which the roller bearing is trapped and rolls) defines the duration, while the "slow" pure-mechanical angular displacement of the other "control shaft" defines the lift.

 

Thanks

Manolis Pattakos



#76 Kelpiecross

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Posted 09 January 2020 - 06:07

Manny - this may be of interest to you: 

 

  https://www.bing.com...eos&FORM=HDRSC3

 

  This video is relevant to the Helical Camshaft's  ability (or lack of ability) to operate at very high RPM with its "trapezoidal" (as you put it) profile.  The variable cam in this Daihatsu engine  has an identical base shape and  "expands" its duration in the same way - that is; by moving the closing flank away from the opening flank by adding to the constant nose radius.  This cam has a "circumferential" movement as opposed to the HC's "helical" movement.  Thus it is limited to about  40 crankshaft degrees in duration increase rather than  the HC's  100 plus degrees.   I think it is fairly clear that it is not particularly rev-limited  - whether it would rev to 20,000RPM or so is another question - but possibly it could.

 

  I am told that this short sequence is part of a much longer video (about 90 mins)  about this cam and the HC.  The full length video was apparently made at the request of a big (the biggest?) automotive parts maker in the US who were asking for much information about both cam types over a period of about a year.   It is said that the whole company (from the vice-president down) watched the video and loved it - but didn't love it  enough apparently to take it up for further development.  

 

 I also heard unofficially that,  years later,  a MG engineer said that they  would have used one of these cam types in the MGF if they had known about it at the time when they were developing their own odd  (but very clever)  system of variable duration  valve system.      



#77 manolis

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Posted 10 January 2020 - 15:04

Hello Kelpiecross.

 

You write:

“Manny - this may be of interest to you: 

   https://www.bing.com...eos&FORM=HDRSC3

   This video is relevant to the Helical Camshaft's  ability (or lack of ability) to operate at very high RPM with its "trapezoidal" (as you put it) profile.  The variable cam in this Daihatsu engine  has an identical base shape and  "expands" its duration in the same way - that is; by moving the closing flank away from the opening flank by adding to the constant nose radius.  This cam has a "circumferential" movement as opposed to the HC's "helical" movement.  Thus it is limited to about  40 crankshaft degrees in duration increase rather than  the HC's  100 plus degrees.   I think it is fairly clear that it is not particularly rev-limited  - whether it would rev to 20,000RPM or so is another question - but possibly it could.”

 

 

Congratulations to the guy who modified the engine of the video.

 

Strictly technically, now:

 

 

HIGH REVVING

 

To show the high revving capacity of a modified valve train, you need a high revving engine (alternatively, you can drive the camshaft of the cylinder head with an electric motor, keeping the crankshaft and the pistons immovable; this is what we did with the PatRoVa Rotary Valve prototype which “operated” for a few minutes at 11,000rpm (corresponding to 22,000rpm of the crankshaft / engine) without being hot).

 

The engine of the video is an old (1980 or so) 1,000cc 3-cylinder 2-valve-per-cylinder engine (Daihatsu Charade).

 

Its peak power is provided at 5,600rpm.

 

At 8,000rpm the inertia loads on the connecting rods double ((8/5.6)^2=2) as compared to those at the peak power revs; the same for the inertia forces in the valve train.

 

At 20,000rpm the inertia loads (in the bottom end and in the valve train) become more than a dozen times heavier than in the peak power revs.

 

 

 

CONTROL SYSTEM

 

The control system is a centrifugal “governor” that changes “automatically” the valve duration according the engine revs (but not according the engine load or other parameters).

 

To control the valve duration in a modern 4-in-line 16-valve engine is not easy for the HC: the control mechanism may be more complex / expensive than the Helical Camshaft itself.

 

 

 

WIKIPEDIA

 

At Wikipedia’s Helical Camshaft page (wherein the heading writes: “This article contains content that is written like an advertisement”) I tried to add a link to the DVVA (Desmodromic VVA) and a line of explanatory text.

 

Unfortunately the moderators of Wikipedia considered inappropriate the readers of Wikipedia to know that there are other VVA’s that can do what the HC does (and more), and in a few hours the link / text was deleted (censored).

 

 

 

TRAPEZOIDAL PROFILE

 

The increase of the inertia loads (and of the required valve spring stiffness) due to the trapezoidal valve lift profile of the Helical Camshaft is not an assumption or an accusation. It results by applying Newton’s laws in the geometry of the HC system.

 

I am sure that Greg Locock, who is a Mechanical Engineer experienced in various engine projects, can – in no more than three lines - explain the issues a trapezoidal valve lift profile brings.

 

Thanks

Manolis Pattakos



#78 Greg Locock

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Posted 10 January 2020 - 19:59

Thanks for the shout out but I've never worked on the top end of engines! Crankshafts, main bearings, conrods and pistons and TV dampers and bending dampers and calibration, but no camshafts ever. Having said that, the camshaft boys pay a lot of attention to mm s-3, ie jerk, which your trapezoidal profile will have a lot of.



#79 Kelpiecross

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Posted 12 January 2020 - 02:55

  I would have thought that the high-revving section of the video would be convincing enough  -  that is clearly an engine that is happy with its cam timing.   I wasn't present for that test run - but I have actually seen that engine rev quite a bit higher than that.   By this stage the people concerned  these variable camshafts were becoming a little circumspect about standing next to a screaming engine and that bloody deadly-looking  "un-cased"  controller.  

 

  The main criticism and argument about these two varieties of variable duration  camshaft  (which both use basically the same  "trapezoidal"  profile) is that the rates of valve acceleration, jerk etc. would be excessively high.   The true fact is actually the opposite.  The whole basic principle of the cams is that they use the standard profile and lift  - which is split at the lobe nose to have variable amounts of constant lift  added or subtracted.   Just how the rates of accel etc.  compare to a F1 engine (or similar) I have no idea  - very much less I would have guessed in the sense of  mm of lift per degree of rotation.

 

 Anyhow I think the whole argument/criticism is based around the fact that  a typical "all-out"  racing cam profile strives to get the ultimate possible lift.  Clearly these variable cams don't strive for ultimate lift  - but -   (and this is the most important point of all ) -  they "trade off" a  lack of lift against  the fact that they can add whatever  "area under the lift curve" they lack through lower lift  by adding  to it through whatever amount of  extra duration is needed.  

 

 Would very high lift and variable duration be better? - possibly - but ultimately you can only achieve  about 100%  VE  anyhow - the extra lift may not be an advantage.  

 

 If the automotive world had wanted a practical and useful variable duration system 20 years ago - they could have had it.  Maybe the time and circumstances were not quite  right?  Quite possibly it could still happen -  but it's a bit unlikely the HC Co. (or anybody else) will make a quid out of it.  



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#80 manolis

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Posted 14 January 2020 - 05:51

Hello Kelpiecross.

 

You write:

“The main criticism and argument about these two varieties of variable duration  camshaft  (which both use basically the same  "trapezoidal"  profile) is that the rates of valve acceleration, jerk etc. would be excessively high.   The true fact is actually the opposite.  The whole basic principle of the cams is that they use the standard profile and lift  - which is split at the lobe nose to have variable amounts of constant lift  added or subtracted.   Just how the rates of accel etc.  compare to a F1 engine (or similar) I have no idea  - very much less I would have guessed in the sense of  mm of lift per degree of rotation.”

 

 

When you split a normal lobe nose in two halves and put a bridging section of “variable duration / constant lift” between them, the breathing may improve but not the high revving capacity / capability of the valve train mechanism.

 

 

GEOMETRY

 

While this modification (just split and bridge) appears simple and straightforward, it is not:

 

A normal cam lobe has a maximum eccentricity (it is the point where you split it to make the HC camshaft).

At that point the acceleration (or more correctly: the deceleration) of the valve is – typically – maximized.

In the constant lift section of the modified to HC camshaft, the acceleration of the valve is zero.

This means that at the transmission point the acceleration makes a “step change” (from maximum to zero), which creates an extreme jerk.

The only you can do is to modify the original cam lobe before and after its maximum eccentricity point to progressively reduce the acceleration till zero at exactly the maximum eccentricity point.

 

 

HIGH REVVING

 

A standard profile is designed for normal revs, say till 8,000rpm (which is well above engine’s red line in most cases).

 

Until 8,000rpm the velocity, the acceleration and the jerk remain within some reliability limits.

 

The resulting inertia loads along the valve actuation mechanism are proportional to the acceleration, while the jerk says how much impact (hammering) the inertia loads are.

 

If you double the engine revs (from 8,000 to 16,000rpm):

the velocity doubles,

the acceleration gets four times larger,

while the jerk becomes eight times larger.

 

If you increase 2.5 times the engine revs (to reach 20,000 rpm):

the velocity multiplies by 2.5,

the acceleration multiplies by 6.25,

and the jerk becomes some 15 times larger.

 

Even if you achieve to run the engine at some high revs without valve - piston collision, the contact surfaces between the various parts of the valve actuation mechanism (cam-lobe, cam follower, pivot pin, valve, valve seat etc) will start wearing where the jerk exceeds some limit.

 

In order to go to really high revs, you have to smooth out the cam-lobe so that the resulting valve lift profile keeps low the maximum acceleration and jerk everywhere.

But if you do so, you will change substantially the initial valve lift profile and the behaviour of the engine at low / medium revs.

 

In this plot:

 

Scissor_Cam.png

 

the red curve is the valve lift profile of a high revving engine (either VVA or not), while the blue curve is the same curve after scissoring the peaks (i.e. more or less what the Helical Camshaft does).

 

The red curve provides not only increased valve-time-area (better breathing), but also substantially lower inertia loads (and so it needs less stiff valve springs for the same revs):

 

In the red curve the fast opening valve (point B) continues its opening motion till the peak point A and then starts closing by the compressed valve spring, gathering speed (point D). The time (or crank angle) the valve decelerates is from B to D.

 

In the blue curve, at the point B the fast opening valve decelerates strongly (by the compressed valve spring) in order a few degrees later (point E) to be completely stopped, then remains stopped (along the C horizontal line) until the point F wherein the valve spring needs to apply a strong force to accelerate the valve till the point D.

 

In the second case you need a substantially stiffer valve spring to keep the cam lobe in contact with the cam follower.

 

 

A reasonable question:

 

If with softer valve springs I can have higher valve lifts, weaker forces (and hammering) in the valve train mechanism (i.e. better reliability, longevity etc) and increased valve time area (i.e. better breathing), 

then why to cut off the peaks of the valve lift curves and go to a like HC solution?

 

The Desmodromic VVA (DVVA) does the above.

But it is complicated, I hear you saying.

 

 

SIMPLICITY

 

The HC needs a control mechanism to displace precisely the various rotating parts.

I still wait for a drawing or photo of such a control mechanism (the centrifugal governor is not a good one).

 

The DVVA has everything (the control mechanism too) inside it and fits with multicylinder engines as it is.

 

Which is really the simpler one and which is the complicated?

 

 

VARIABILITY

 

Then it is the variability.

 

The presentation of the HC in Wikipedia recognizes / proposes the benefits of the fully variable VVA’s (wherein the valve lift is also varied) over the variable duration / constant lift VVA’s.

In order the variability of the Helical Camshaft VVA to be as that of the DVVA, it needs to cooperate with another VVA (like the valvetronic); imagine the complexity of the combination and its rev limit.

 

Thanks

Manolis Pattakos


Edited by manolis, 14 January 2020 - 06:07.


#81 gruntguru

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Posted 14 January 2020 - 23:24

Hi Manolis. A cam profile with dwell at maximum lift would ideally not be produced by "scissoring" a higher lift profile. Rather you would start with a workable profile (like the red curve or a smaller version of it) and add a dwell period at max lift. Of course this does not address the jerk problem so further modification would still be required.



#82 manolis

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Posted 15 January 2020 - 07:01

Hello Gruntguru.

 

In this plot:

 

HC_GruntGuru.png

 

the red curve of my last post (which is a "workable profile") splits in two halves with a flat (constant lift) region (or part) between them (it is the purple / violet curve).

 

But then it comes another valve lift profile, the green curve, having (as compared to the violet profile) higher valve lift, larger valve-time area, smaller maximum acceleration and jerk, softer valve springs and is capable for higher revs .

 

 

To limit the valve lift with a "constant lift" or dwell region makes no good; everything worsens.

 

 

On the other hand,

the DVVA can "simulate" the Helical Camshaft, whereas the opposite is impossible.

 

Thanks

Manolis Pattakos



#83 Kelpiecross

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Posted 15 January 2020 - 11:14

  My main argument (and the HC Co.s)  is that both types of flat-topped profile VVA systems clearly just bloody "work".   The later (as yet unmentioned)  VVA system  for  3.9l  E-Series Ford engine worked very well - making 30 to 50% more power at only a few hundred RPM over the stock peak - I'll see if I can get the dyno graphs from the HC mob.

 

 I think it is a bit deceptive  just looking at the flat-topped valve lift graphs  -  they look to have a violent discontinuity on the graph  (you can't really see the "flat" area  when actually holding the cam) -  but look at the accel/jerk etc.  on Wiki and you will see that it is not that excessive and could be "massaged", "fettled" etc. to be normal or near normal stock.    The HC in particular has plenty of "wiggle" room  - the 34 degree helix angle giving 3.4 crankshaft  degrees of duration per mm could be halved (to 17 degrees)   meaning that the nose "flat" area becomes almost  negligible  (but at the expense of doubling the axial movement needed for adjustment to 30mm or so).    

 

  The company in the US actually liked the centrifugal controller  (of course it needs a casing for safety)  -  even after they decided not to develop the HC - they enquired about the use of the controller on some unrelated project.  

 

  Complex controller on the HC?    It could hardly be simpler I would have thought.  A simple circular hydraulic cylinder to move the outer shaft back and forth  maybe 15-16mm.  


Edited by Kelpiecross, 15 January 2020 - 11:16.


#84 manolis

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Posted 16 January 2020 - 06:20

Hello Kelpiecross.

 

Here is a section of a MultiAir cylinder head :

 

MultiAir_Text.jpg

 

A, B: two intake valves of a cylinder,

C, D: the valve springs of the intake valves A and B,

E: the “piston” actuating the intake valve B,

F, G: electromagnet and release valve,

H, I: oil passageways,

J, K: hydraulic piston and its restoring spring,

L: intake cam lobe (it actuates the hydraulic piston J),

M: spark plug,

N, O: exhaust valve springs (neighbor cylinder),

P, Q: exhaust valves hydraulic bucket lifters,

R, S: exhaust cam lobes,

T: a journal of the camshaft,

U: dump holes,

W, V: electromagnet and release valve of the other neighbor cylinder,

Y: intake valve.

 

It may seem complicated, yet it is not:

 

The unique camshaft drives the exhaust valves the conventional way (bucket lifters).

 

On the same camshaft, for each pair of intake valves (A, B) there is one intake cam lobe that actuates a piston (J) having a restoring spring (K). The piston (J) displaces oil that displaces the intake valves to open (like, say, an “oil column” push rod). When the electromagnet (F) is triggered by the ECU, the release valve (G) opens and the two intake valves restore under the action of their springs (C, D) and seat smoothly on their valve seats.

 

The only variable in the mechanism is the time (or crank angle) of the electromagnet triggering.

 

 

The MultiAir needs only one camshaft for 16 valves.

 

It is a true electronically controlled VVA that provides variable timing, variable lift and variable duration of the intake valves (the valve lift / duration can be quite small, i.e. no need for a throttle valve).

 

Its control is not only accurate (more accurate than in any mechanical VVA), but it is also simple / straightforward and independent in each cylinder.

 

Each electromagnetic valve is triggered by the ECU the right moment, and opens the release valve allowing the respective pair of intake valves to close.

The feedback from the high-speed Oxygen sensor (i.e. how rich or lean the specific cylinder runs) is received from the ECU that aligns the time of the next “trigger” to the electromagnet of the specific cylinder.

 

The MultiAir operates based on the ingoing air control.

 

The modification of the MultiAir to PatAir:

 

air.gif

 

mito_cam_lifts.gif

 

Mito_Camshafts.jpg

 

Mito_MultiAir_PatAir_camlobes.gif

 

Mito_new_camshaft.jpg

 

 

keeps the existing modes of the MultiAir adding an infinity of additional modes (outgoing air control, LIVC, Atkinson / Miller cycle), say, like those of the mechanical Helical Camshaft.

 

The MultiAir system is in mass production for several years and is used in the FIAT, Chrysler and Alfa Romeo car engines. No reliability issues have been reported, as far as I know.

 

After understanding how the MultiAir works, try to get how the PatAir works and then compare to the Helical Camshaft.

 

 

At idling, in the Outgoing Air Control mode (PatAir) the noise of Alfa Romeo Mito engine is like a quiet whispering (you can hardly say the engine is running):

 

RenaultMito.jpg

 

 

Thanks

Manolis Pattakos



#85 Kelpiecross

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Posted 17 January 2020 - 11:42

 Manny - I think you meant to write:  "It may look complicated - and it bloody is".

 

 The lift graph of the MultiAir  looks very much like the much- maligned (in some circles)  the lift graph of the HC.

 Only 3.8mm lift (from graph) -  what's the lift at the valve?   



#86 manolis

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Posted 17 January 2020 - 14:56

Hello Kelpiecross.

 

You write:

“Only 3.8mm lift (from graph) -  what's the lift at the valve?”

 

 

Here is the original cylinder head of the Alfa Romeo MITO:

 

MITO_Rocker_Arm_2.jpg

 

and here is the same cylinder head modified to PatAir:

 

MITO_Rocker_Arm_1.jpg

 

The only difference is the intake cam-lobes.

 

A is an intake cam lobe,

B is the roller cam follower of the A,

C is the rocker arm wherein the B is mounted,

D is the “hydraulic piston”; the D is actuated by the C; the D actuates through an “oil column” a pair of intake valves, not shown).

 

E and F are two exhaust cam lobes.

 

 

The “only” 3.8mm cam-lift of the intake cam-lobe is multiplied by the rocker arm “ratio”. I.e. the hydraulic piston has about 7mm stroke.

But this says actually nothing, because the larger the diameter of the hydraulic piston, the shorter the required intake-cam-lift for the same intake-valve-lift.

 

 

According the https://www.pattakon..._Simulation.pdf article of FIAT (wherefrom the following drawing is):

 

MultiAirValveLift.gif

 

the intake valve lift is 8mm:

 

 

 

 

Quote from https://www.pattakon...ttakonHydro.htm:

 

The MultiAir mechanism:
 

An "oil push rod" is interposed between the valve and the cam.
The cam pushes the "oil push rod" and the "oil push rod" pushes the valve.
At the right moment a solenoid valve opens, the "oil push rod" collapses and the valve closes under the restoring action of the valve spring.
By a "hydraulic braking mechanism" the landing of the valve on the valve seat becomes acceptably smooth.

 

The "Ingoing Air Control" (MultiAir / TwinAir) has some inbuilt disadvantages.

After the intake valve closing, the piston continues to move towards the BDC. The charge (air or mixture) inside the cylinder undergoes an expansion. The expansion causes the charge temperature to drop increasing the heat absorption from the hotter walls (cylinder, piston crown, cylinder head, intake and exhaust valves). After the BDC the piston compresses a hotter charge and restores less mechanical energy than the mechanical energy consumed to expand the charge.

 

PumpingLoss.gif

 

That is, pure mechanical energy (yellow) from the crankshaft-flywheel is consumed inside the cylinder, with only result the increase of the charge temperature. The lighter the load, the bigger this "mechanical energy loss" and the higher the temperature of the cycle. The lighter the load, the more "expensive" the mechanical energy consumed, because it was generated at high BSFC.

The early closing of the intake valve leaves more time to the charge turbulence and swirl to fade before the combustion. The slower the combustion, the less efficient and the less clean the operation of the engine.


The PatAir system

 

The PatAir system operates either according the pattakon "Outgoing Air Control", or according the Fiat MultiAir / TwinAir "Ingoing Air Control".

According the "Outgoing Air Control" pattakon cycle, the later the intake valve closes, the more "outgoing" air is left to escape from the cylinder back to the intake manifold as the piston moves towards TDC (compression stroke).”

 

End of Quote

 

 

 

MECHANICAL CONTROL versus ELECTRONIC CONTROL

 

Quote from https://www.pattakon...Adv.htm#pattair

 

“The PatAir, based on very similar hardware (only the duration of the camshaft needs to change), works according:

either the "Ingoing Air Control" of Fiat,
or according the "Outgoing Air Control" of pattakon wherein the load is controllably increased by preventing more "Outgoing Air" from leaving the cylinder. The sooner the intake valve closes after BDC, during the compression stroke, the heavier the load.
 

The thermodynamic cycles of the "Ingoing Air Control" (Fiat) and of the "Outgoing Air Control" (pattakon) are different.
 

The "Outgoing Air Control" cycle avoids not only the underpressure, under part load, into the intake manifold (as the throttle-less VVAs, like the Fiat MultiAir and the BMW valvetronic, do) but it also avoids the underpressure into the cylinder by avoiding the expansion of the charge before the compression.
 

By minimizing the pumping-loss, by avoiding the consumption of mechanical-energy to just expand and warm the charge, by keeping alive the turbulence and swirl during combustion and by improving the mixture homogeny the "Outgoing Air Control" minimizes the mechanical-energy loss and optimizes the combustion.
 

The PatAir is an evolution of the MultiAir because it can operate not only according the infinite available modes of Fiat MutliAir cycle, but also according the infinite modes of pattakon "Outgoing Air Control" cycle.

The extremely accurate, instant, flexible, cheap and easy electronic control is the key advantage of the MultiAir, as well as of the PatAir.

The VVA system is not based, any longer, on an extreme construction accuracy of the hardware.

The ECU, based on the feedback, controls independently the operation of each cylinder by just aligning the opening and closing times of the solenoid valves.
It is simple to modify and control complicate engines like the V-8 and the V-12.
The side cam American V-8 engines can easily turn to efficient and clean engines.

The electronic control offers flexibility: for instance, a PatAir four inline engine is easy to operate with one cylinder deactivated, with another cylinder running at full load, with another cylinder running at medium load according the "Ingoing Air Control" cycle and with another cylinder running at medium load according the "Outgoing Air Control" cycle. It is also easy to swap, a few dozens of times per second, the above modes among the cylinders.”

 

End of Quote

 

 

 

You also write:

“Manny - I think you meant to write:  "It may look complicated - and it bloody is".”

 

 

Even if the PatAir (and MultiAir) cylinder head was “bloody” complicated, the extra complication would be justified, among others:

by its variability,

by the flexibility its electronic control offers (an example of which is given in the last paragraph of the above quote),

by its ability to independently control each cylinder,

by its feed back control / alignment.

 

No mechanical VVA can offer such accuracy of control and “flexibility”.

 

BLOODY COMPLICATED?

 

What I see in the PatAir (MultiAir) cylinder head is a conventional single-piece camshaft, conventional cam followers, conventional valves and valve springs.

The only difference from a conventional non-VVA cylinder head is four small hydraulic pistons, some oil holes / passageways and four solenoids (electromagnets).

The rest complication has to do with the ECU and its programming.

 

Thanks

Manolis Pattakos

 



#87 Kelpiecross

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Posted 18 January 2020 - 04:22

  Manny - you make  a  big thing about the incredible range  of variation  and fine adjustment  of valve timing and lift etc.   of your various designs - and fair enough - they do appear to have these qualities that you claim - but ( a big but)  it is my personal opinion that this huge variety of adjustment etc. really does very little and is not worth the extra complication.  The "Law of Diminishing Returns"  etc.  

 

 After all - a totally "dumb"  fixed timing cam  does a pretty good job  (and has done for more than a hundred years)  - all you need is  a wide range of available durations and Robert is your father's brother.   Variable lift is a bit pointless.  

 

 Personal opinions - of course.   But I know from experience that manufacturers  are wary of even the slightest mechanical complexity.


Edited by Kelpiecross, 18 January 2020 - 04:22.


#88 manolis

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Posted 19 January 2020 - 05:33

Hello Kelpiecross

 

You write:

“But I know from experience that manufacturers are wary of even the slightest mechanical complexity.”

 

 

BMW (with their Valvetronic VVA), Toyota (with their Valvematic VVA), Nissan with their VVEL) etc, etc don’t seem to agree.

 

There are millions of VVA engines on the roads.

The benefits they offer (efficiency, power, emisions, driver friendly, torquey etc) justifies their added cost, complexity, limitations etc.

 

Here is an interesting comparison:

 

LostMotionCompare.gif

 

of three “lost-motion” VVAs.

 

The by-far simplest of the three, animated at low, medium and high duration and lift:

 

LM_high_lift.gif

 

LM_medium_lift.gif

 

LM_low_lift.gif

 

Does anybody see an advantage of the BMW valvetronic (in functionality, in high revving, in simplicity, in cost etc) over the animated one?

 

Thanks

Manolis Pattakos



#89 Kelpiecross

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Posted 19 January 2020 - 11:58

 Manny - A very neat design indeed  - by far the best I have seen in the "oscillating cam"   general class.  

 

 Do all the graphs etc. on the "time attack" thread  refer to the   Pattakon  "Lost Motion VVA"?  

 

 Why was it never tested on a chassis dyno?

 

 I can assure you that some manufacturers  think the Valvetronic  (and the Mahle too, I would assume)  to be ridiculous.    A popular theory is that BMW and Honda both consider themselves to be the leader in engine technology - when Honda announced the VTEC,  BMW had to counter with their own system which had to be different to the  VTEC - and thus the Valvetronic.  .    



#90 gruntguru

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Posted 19 January 2020 - 21:45

VTEC is primitive compared to the three lost-motion systems pictured. Two camshaft profiles and a switching system.



#91 Kelpiecross

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Posted 20 January 2020 - 03:52

VTEC is primitive compared to the three lost-motion systems pictured. Two camshaft profiles and a switching system.

 

 Two of the "lost-motion"  designs above are absolute  crap  - one is verging on the brilliant.   "Credit where credit's due".  

 

 "Two-step"  systems  are primitive  but effective.


Edited by Kelpiecross, 20 January 2020 - 09:49.


#92 manolis

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Posted 20 January 2020 - 05:20

Hello all.

 

Here is another pattakon-VVA:

 

VTS10.JPG

 

It is the "Rod Roller" version and controls the intake valves of a Citroen/Peugeot 1600 cc,16 valve engine.

 

The following animations show how it works:

 

image002.gif

 

image003.gif

 

image004.gif

 

Here they are shown some more details "stereoscopically":

 

image006.jpg

 

 

The control shaft is directly connected to the gas pedal by the gas cable. The deeper the gas pedal is pressed, the more the control shaft rotates increasing the valve stroke. When the gas pedal is released the normal intake valve springs restore the control shaft to its “idling” position.
 

image005.gif

 

Depending on the control shaft angular position, the valve lift profile varies continuously from zero (for valve deactivation if desirable), to tiny (for idling), to mild, to medium, to racing (top curve), all in the same engine, all instantly available:

 

image007.jpg

 

The quick moving parts are "true" lightweight.
 

VTS14.JPG

 

Even with the toughest valve springs, the engine at low to medium revs "feels" (as regards friction, wear, resistance of the camshaft to rotate etc) way softer valve springs than conventional. At short lifts (say 1mm) one can rotate the camshaft pulley (sprocket) by his small finger.

The intake valves make the "throttling" (ideal for efficient and cheap ITB).
The lash adjusters can be mechanical or hydraulic.

 

 

In these short videos:

 

 

 

the camshaft is driven by an electric drill while the control shaft is angularly displaced.

 

The plan was to put the cylinder head on a racing car (having light pistons, connecting rods etc) and test it in races.

 

For more: https://www.pattakon...onRodRoller.htm

 

Thanks

Manolis Pattakos


Edited by manolis, 20 January 2020 - 05:56.


#93 Kelpiecross

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Posted 20 January 2020 - 09:51

 I like the one in Post  88 better.  



#94 gruntguru

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Posted 20 January 2020 - 21:43

Isn't it the same?



#95 manolis

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Posted Yesterday, 04:16

Hello Gruntguru.

 

The one in post #88 is a “Lost Motion” VVA:

 

LMVVA.gif

 

The other, in post #92, is a “Constant Duration” VVA.

 

CDVVA.gif

 

The first “cuts” valve duration as the lift decreases (say, the valve lift and the valve duration are proportional).

 

The second keeps a “constant” duration; how much “constant” depends on “where” it is measured; for instance, if you measure the duration at 1/4” (6mm) 0.025" (0.6mm) valve lift, then the lowest valve lift profile in the following plot has zero duration, while the nearest curve (that with maximum valve lift 1mm) has a duration of ~120 crank decrees, and while the top valve lift curve has a duration of ~280 crank degrees:

 

image005.gif

 

In the typical Lost Motion VVA’s, at small valve lifts the opening / closing of the valve happens around the middle stroke of the piston (where the cam lift maximizes); this means that a “fast responding” wide-angle VVT (Variable Valve Timing system or phaser) is necessary to shift angularly the valve lift near the TDC. This adds complication and cost, and worsens the response and the feeling.

 

BMW’s valvetronic is a Lost Motion VVA and uses the Vanos (a wide angle VVT) in order to phase properly the valve opening.

 

A Constant Duration VVA does not need a “fast responding” “wide angle” VVT and this makes it simpler and cheaper without sacrificing any functionality or efficiency.

 

 

Here is shown stereoscopically the Constant Duration VVA of post #92:

 

imge010.jpg

 

and in the following quote from https://www.pattakon...onRodRoller.htm is the Lost Motion version of the same VVA:

 

“With a different control shaft the above "Constant Duration VVA" changes to a "Lost Motion VVA" as shown below (the axis of rotation of the control shaft goes from the "top center" to the "bottom center" of the rods) .
BMW's "Valvetronic" is a "Lost motion VVA": decreasing the valve stroke, the valve duration - in crankshaft degrees - is also decreased.
Compare BMW's Valvetronic to Pattakon's Rod Roller Lost Motion VVA in functionality, simplicity, accuracy (number of "joints" interposed), height, lightweight, inertia loads, cost and capability for high revs (specific output).

 

LostMotion.gif

 

End of quote.

 

Thanks

Manolis Pattakos


Edited by manolis, Yesterday, 05:56.


#96 manolis

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Posted Yesterday, 04:49

Hello Kelpiecross.

 

You like the Lost Motion VVA of post #88, some others may like the Constant Duration VVA of post #92 (maybe because it has the lightest moving parts).

 

 

What I like is the DVVA (Desmodromic VVA) because it can do everything and better:

 

It can be a Constant Duration VVA,

 

It can be a Lost Motion VVA,

 

It can be a Constant Lift VVA,

 

It can be any combination of these,

 

It varies independently the lift and the duration (each valve duration combines with infinite valve lifts and each valve lift is combined with infinite valve durations),

 

Its fast moving parts are lightweight and rid of bending loads,

 

It has not “oscillating cams” (an oscillating cam cannot be lightweight, which means it creates heavy inertia loads at high revs, which limits the rev limit); the only “cam” it uses is the “track” wherein the roller bearing is trapped and moves / rolls, and this “cam” / track moves only when a different valve lift profile is desirable.

 

It has not valve springs to restore the valves: the valves open poisitvely and close positively; without valve springs the oscillating mass per valve reduces to about half.

 

The valve stems can be half in height, further reducing the “oscillating mass”.

 

Etc, etc.

 

 

From https://www.pattakon...ttakonDesmo.htm  (actually from the patent granted for the DVVA):

 

DVVA_mechanism1.gif

  

A track 4 is provided having a lost motion portion and an actuation portion. Track 4 is pivotally mounted about a pivot at 12. A first link 9 is pivotally mounted at one end about a pivot 150 on the valve actuator 10. The link 9 is pivotally mounted at its other end about a pivot 151.
A second link 154 is pivotally mounted at one end about the pivot 151. The link 154 is pivotally mounted at its other end to a pivot 156.

 

 

Thanks

Manolis Pattakos



#97 Kelpiecross

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Posted Today, 03:50

 I would still class the DVVA  as  being in the "oscillating  cam"  class - the follower and cam still oscillate relative to each other - no rotary motion.   

 

  No matter how many times I see the DVVA  explained etc.  - it still doesn't look really practical.

 

  The DVVA  design looks (all this is personal opinion of course)  unnecessarily "fussy"  and "busy" - especially compared to the neat economy of design of   No. 88.   (I refuse to use a "#"  instead of "No.").  

 

 I think there is no point in  "desmodromic".  Conventional "valve spring" layouts can run to over 20,000 RPM and last at least half a million miles plus - a "desmo" can really do no better  - and does have some characteristic problems - like being noisy etc.

 

 You  think the very short valve stems are advantageous  - I don't - I think valve stems have evolved to their  typical present length out of necessity  - for sideways support  and heat transfer etc.

 

 Overall - I think the DVVA tries to do too much  - every valve function known to enginekind  is not needed - just the basics.   Trying to achieve too many functions has lead to excessive complication of the design.            

 

  

  

   

.  


Edited by Kelpiecross, Today, 03:52.


#98 manolis

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Posted Today, 05:54

Hello Kelpiecross.

 

It is good you like the No. 88.

 

 

You write:

“I would still class the DVVA  as  being in the "oscillating  cam"  class - the follower and cam still oscillate relative to each other - no rotary motion.”

 

 

No matter how the “oscillating cam class” is defined, the cam (actually the track 4 of the figure in my last post) of the DVVA is not an oscillating cam with the absolute meaning of the term.

During a cycle the track 4 (or cam) of the DVVA remains actually immovable.

It rotates slightly only when a different valve duration is desirable, and this slight rotation may last for, say, 100 engine cycles.

 

 

Take the BMW’s Valvetronic.

 

Valvetronic.png

 

The “J” shape part 13 (intermediate lever) has at its lower side a secondary “cam” (6) (the primary cam is on the camshaft (5)).

 

During each cycle of the engine the secondary cam performs a complete wide-angle oscillation, with the roller of the rocker arm (12) abutting / rolling / sliding on it.

 

The “foot” of the intermediate lever acts as a true cam and needs to be strong and inflexible; i.e. it cannot be lightweight, and needs a strong restoring spring (3).

 

Depending on the angular displacement of the control shaft (14), the valve duration and lift can vary from a maximum to zero:

 

Vue-de-profil-du-BMW-Valvetronic-et-diff

 

The intermediate lever has 3 roller bearings, one at its center (it abuts on the camshaft) and two on top (the one abutting on the control shaft (14), the other on the cylinder head roof (4)). Adding the roller bearing of the rocker arm, it makes a total of 4 roller bearings per intake valve.

 

The intermediate lever is a true “oscillating cam”.

 

The track (the purple / violet part) of the Desmodromic VVA (DVVA):

 

DVA.gif

 

is not an “oscillating cam”. If it were, the rev limit of the DVVA would be a couple of thousand rpm, or so.

 

 

You write:

“I think there is no point in  "desmodromic".  Conventional "valve spring" layouts can run to over 20,000 RPM and last at least half a million miles plus - a "desmo" can really do no better  - and does have some characteristic problems - like being noisy etc.”

 

Conventional valve springs cannot go to 20,000 rpm.

Only unconventional racing valve springs can afford such revs.

Besides the valve, they have to restore their own mass; during the calculation of the reciprocating mass and of the created inertia loads, about half of the spring mass has to be added to the reciprocating mass of the valve).

 

As for their longevity, the racers have to replace their valve springs regularly; a set of racing valve springs has a surprisingly high cost.

 

Regarding the noise:

 

The DVVA is not like the DESMO of Ducati (wherein the valve oscillates between two independent mechanisms (one for opening it and one for closing it), like a tennis ball that oscillates between two rackets).

 

In the DVVA the same mechanism (and parts) that opens positively a valve, the same mechanism closes positively the valve. The difference is more than significant and has to do with the longevity of the valve train, with the noise and with the time between lash adjustments.

 

 

You also write:

“You  think the very short valve stems are advantageous  - I don't - I think valve stems have evolved to their  typical present length out of necessity  - for sideways support  and heat transfer etc.”

 

As in the conventional valves, similarly in the DVVA valves the heat transfer happens through the valve seat and through the valve guide. The valve stem above the valve guide (which is that part eliminated in the DVVA) is there only to make space for the valve spring. .

 

Take the case of the sport Honda VTEC B16A2 engine:

Intake valve: 45 gr,

Intake valve springs: 50 gr,

Intake valve + (Intake valve springs)/2 + Retainer = 85 gr

 

If you achieve to decrease the total reciprocating mass of the poppet valve at half, it is a great step and brings only advantages.

This is what the DVVA does, because it eliminates the valve springs and a part of the valve stem (which also reduces the cylinder head and the engine height).

 

 

You also write:

“ Overall - I think the DVVA tries to do too much  - every valve function known to enginekind  is not needed - just the basics.   Trying to achieve too many functions has lead to excessive complication of the design.”

 

Forget its variability (which is in another class) and compare the DVVA complication with that of BMW’s valvetronic (or Toyota’s valvematic, or Nissan’s VVEL, or Ducati’s DESMO).

 

Without the infrastructure of a car maker, the valvetronic (and the rest) cannot be manufactured.

 

In a typical machine shop the DVVA can be manufactured in fucntional quality.

 

So, where do you see the “excessive complication” of the DVVA?

If you see it on the infinite infinites of modes it offers, you can simply use only a few of them (say, operate it as a Lost Motion VVA, or as a COnstant Duration VVA or ...).

 

The most difficult part I see is the track, and this is quite cheap and easy to make in a simple 2-axis milling machine.

 

I really want to know which part you think is difficult to be made / machined?

 

 

 

From a different viewpoint:

 

Take a supercar, say a Ferrari or a Bugatti or, and replace its cylinder heads for DVVA ones.

 

Along with having higher power, it will also be more driver friendly, far greener, with better mileage, better longevity etc (simply because the engine makers of the supercars can’t help sacrificing these qualities for the sake of the absolute power).

 

And if a buyer can be found to pay for the original cylinder heads, a good net amount of money will be profited / gained / won.

 

Thanks

Manolis Pattakos


Edited by manolis, Today, 06:56.


#99 gruntguru

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Posted Today, 07:42

KC I think the following animations from the Pattakon website better illustrate the operation of the DVVA. The first illustrates the "low lift and duration" setting and the others illustrate progressively increasing lift and duration. This accomplished by simply rotating the cyan "track" to a new position. The centre of rotation of the cyan track is in the same location as the point where 3 links (green orange and blue) join - with the valve closed. Image 2 shows also a different position of the second control shaft. Control shaft #1 (apologies for the #) ie the pink tracks, are in the maximum duration position as in image 3. Image 2 has less lift but the same duration as image 3.

 

DVA3.gifDVA2.gifDVA1.gif

Manolis. My apologies if I have undersold your invention in any way. It is an ingenious system.



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#100 manolis

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Posted Today, 08:19

Hello Gruntguru.

 

The same animation was used in the presentation for the "pattakon-VVA's" at Engine Expo International, Stuttgart Germany, wherefrom the following slide is:

 

DVVA_and_Rod_VVA.gif

 

The lower part of the DVVA mechanism is quite similar to the Rod-VVA mechanism, while the upper part of the DVVA mechanism is quite similar to roller-VVA mechanism.

 

RenaultHonda1.jpg

 

 

The DVVA is a combination - evolution of the rod-VVA (that in the white Renault) and of the roller-VVA that in the black Honda).

 

 

Having the experience from the manufacturing and the road-tests / use of DVVA's "grand father" (the rod-VVA at https://www.pattakon...pattakonRod.htm ) .

 

image002.jpg

 

having also the experience from the manufacturing, tuning and road- testing / use of DVVA's "father" (the roller VVA at https://www.pattakon...takonRoller.htm ) .

 

im6.jpg

 

the manufacturing of a fully functional DVVA is not something special.

 

 

Judging from the driving experience and the reliability of DVVA's "father" and "grandfather", the DVVA would be a unique experience on the road.

 

Thanks

Manolis Pattakos