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Seamless Gearboxes


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#1 24gerrard

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Posted 18 February 2012 - 12:30

http://www.youtube.c...p;v=oBfUPKN-m1E

Here is a u tube video of this years Caterham F1 car testing at Jerez.
Nice video.
It shows absolutely that the gearbox in the car is NOT seamless in its operation.
In fact I firmly believe that a manualy operated gearbox with a dog engagement can be operated as fast.
But then I have driven such racing dog boxes and not just played on computer games.
Mind you I dont have a degree in marketing or for that matter basket weaving so perhaps I am behind the times?

Edited by 24gerrard, 18 February 2012 - 13:18.


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#2 Wolf

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Posted 18 February 2012 - 14:29

My uneducated™ guess is that when you have a car traveling at speed v and engine revving at revs n, and (instantly and without power interruption) change gear ratio from i1 to i2, you will have a mismatch between engine and vehicle speed- and that it will force the clutch to slip until the two are in sync again... Nevertheless, it would be interesting to see how 'seamless shift' would compare against 'ideally executed shift with power interruption', both in terms of performance and component wear.

#3 24gerrard

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Posted 18 February 2012 - 14:56

My uneducated™ guess is that when you have a car traveling at speed v and engine revving at revs n, and (instantly and without power interruption) change gear ratio from i1 to i2, you will have a mismatch between engine and vehicle speed- and that it will force the clutch to slip until the two are in sync again... Nevertheless, it would be interesting to see how 'seamless shift' would compare against 'ideally executed shift with power interruption', both in terms of performance and component wear.


The most important and almost forgotten fact that allows a rapid gear shift in an F1 car and other high end racing vehicles, is the very low mass of the rotating engine components.
When one gear is disengaged and another engaged there is a difference in engine rpm for the same road speed.
This means that the engine must be slowed (upshift) by this amount in rpm.
This is fairly easy to achieve with an F1 engine, it is far more difficult with road engines with heavy flywheels and clutches.
There is no clutch slip changing gear in an F1 car, the clutch is only used for the start.
The mechanisms used between the gears in the synchronising hub are designed to slow the engine to a rotating speed (rpm) that matches the new gear ratio/road speed. The boxes have two selector drums, one for odd gears and one for even, so the disengageing gear is never on the same syncro hub as the one engageing. The engine management also assists by either cutting the engine or reducing the engine torque at the shift overlap.
The gear shifts are very fast BUT NOT SEAMLESS. This is purely marketing hype.

With a road car with heavy flywheel and clutch etc, it is impossible to get close in terms of gear shift speed to any racing powertrain with light weight rotating components even with a dog engagement system.
However, all else being equal, I am prepared to bet that it IS possible to match the gear shift speeds of a modern F1 'so called' seamless gearbox with a manual dog engagement gearbox.
Of course the work load on the driver would begin to come back to times gone by and I personaly would not be able to do it for more than half a lap at the most but it could be done.
The other thing is that changing gear manualy would risk far more in the way of missed shifts and gearbox damage, it would of course sort out the men from the Hamiltons but few modern drivers would instantly master the skills anyway.

Edited by 24gerrard, 18 February 2012 - 14:58.


#4 Wolf

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Posted 18 February 2012 - 15:29

Oh, I didn't think they used synchromesh, or something like that in F1... :blush:

As for low and high inertia rotating components, it's an interesting observation, yet I think that when the whole drivetrain is taken into account the tyres might not see much of a difference (say, 3x the engine revs will require 9x smaller rotating masses to have the same inertial 'effect', at certain road speed). In the gearbox, though, it might make a lot of difference- so a synchrons might not see that big loads...

#5 24gerrard

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Posted 18 February 2012 - 18:37

Oh, I didn't think they used synchromesh, or something like that in F1... :blush:

As for low and high inertia rotating components, it's an interesting observation, yet I think that when the whole drivetrain is taken into account the tyres might not see much of a difference (say, 3x the engine revs will require 9x smaller rotating masses to have the same inertial 'effect', at certain road speed). In the gearbox, though, it might make a lot of difference- so a synchrons might not see that big loads...


It makes no difference what the rear wheels see, unless it breaks traction or locks the wheels.
It is what the engine sees and this is what most people do not realise.
If there is a small inertia it is a simple matter to drag engine RPM down in a micro second.
You can do it with a fancy marketed item like a 'zero shift device' or you can do it equaly as well with a dog ring and a good driver on the end of a level.

#6 Wolf

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Posted 18 February 2012 - 20:38

Well, I think what the engine sees is important to power delivery, but in terms of grip, it's all about what wheels see... (it may not be the case here, and it probably isn't because of synchronization, but I was thinking to compare it with missed upshift or unsynched revs- one moment you're driving the wheels, and the next the wheels are trying to bring the engine up to revs; it's bound to unsettle the car, seeing that tractive force will not only change available lateral force, but slip angle as well)

It's a bit like doomed project I was working on a while back- they were doing some calculations of acceleration of a car, calculated road loads &c, but omitted power requirements to accelerate drivetrain and engine rotataing masses... And those are said in case of that type of vehicle to be possibly equal or even greater to those they've calculated (admittedly, only in lowest gear). The devil is sometimes in details.

And speaking of dogs and clutches, ISTR hearing that Clark once finished a Monaco GP after his clutch failed at third of a race distance (or something like that)... Now, that's skill and determination, if you ask me.

#7 24gerrard

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Posted 18 February 2012 - 21:03

With full automatic control over a current F1 layshaft box, it is possible very easily to control the transfer of torque to meet all requirements including balancing KERS regeneration, front to rear demands for braking and of course perfect traction limiting.
It is the regulations that fix the amount of control and the development allowed.
This is artificial and it is all masked by high downforce anyway.

F1 is nothing but a control formula today, powertrain development is only allowed within a very very small box and is all but stagnant.
After 2014 KERS and other energy recovery ideas will be tightly controlled to meet the demands of the marketing men and those engineers who play with upside down model aeroplanes. This keeps things conveniently under the control of the media and other outside vested interests. The days of the 'garagista's has long gone, corporate marketing is the face of F1 today.
Chunky is turning in his grave, I know that much.

I have a much more efficient 'electric shift energy recovery unit' that could replace current 19th century F1 gearboxes but it is unlikely ever to see the light of day.

Jim Clark learned to use a dog ring manual gearbox like we all did racing in those times. With any layshaft gearbox it is possible to learn to change gear without using the clutch. I once drove a rally escort from Wales to London after the Red Dragon Rally without a clutch and without much in the way of brakes either. Jim Clark was a fantastic driver with skills few modern F1 stars can call on.

Edited by 24gerrard, 18 February 2012 - 21:05.


#8 faaaz

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Posted 18 February 2012 - 21:37

How is it not 'seamless' though?

#9 24gerrard

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Posted 18 February 2012 - 22:14

The definition seamless means without a seam, a seam meaning a join,usualy between two pieces of cloth.
The marketing people have taken the term 'seamless' and applied it to a layshaft gearbox gearshifting mechanism.
The term DOES NOT APPLY TO THIS TECHNOLOGY AT ALL, it is a very bad engineering statement.

The layshaft stepped gearbox CANNOT transfer torque at a continual level through a change between one gear ratio and another.
There has to be a 'torque spike' as the gears change.
If you listen to the sound track in the video in the first post you will clearly hear this during all up and downshifts.
If the definition SEAMLESS, was correct which it is not, this torque spike would constitute a SEAM, or a gap between gears (very small yes, micro seconds in fact but STILL a gap).
Therefore NO layshaft gearbox can be 'SEAMLESS'.
Why do people accept the marketing people describing F1 gearbox operation as if it were a piece of clothing?
Sign of the weedy times I suppose.

Edited by 24gerrard, 18 February 2012 - 22:17.


#10 faaaz

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Posted 18 February 2012 - 22:56

So what do you think of this

#11 24gerrard

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Posted 19 February 2012 - 08:26

So what do you think of this


I thought I had spent the last few posts explaining 'exactly' what I think of 'this'.
It is a mechanism to 'speed up' the gearshift to a speed that compares with the ultimate manual dog ring gear change.
It does NOT replace the gear change and there is STILL a gap in transfering full torque on upshifts.
The name is an incorrect technical definition and is wrong.

#12 Kelpiecross

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Posted 19 February 2012 - 12:38

I thought I had spent the last few posts explaining 'exactly' what I think of 'this'.
It is a mechanism to 'speed up' the gearshift to a speed that compares with the ultimate manual dog ring gear change.
It does NOT replace the gear change and there is STILL a gap in transfering full torque on upshifts.
The name is an incorrect technical definition and is wrong.


You are right - it is misleading to call these gearboxes "seamless" - fast changing but not uninterrupted.

In theory it seems to be possible to propose an arrangement that has a continuous change in ratios between two fixed ratios - but very likely not really practical.



#13 rory57

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Posted 19 February 2012 - 14:44

Motorcycle gearboxes seem entirely successful in their application. Why is this sort of 'box never used in road cars, not even real sports cars?

(obviously they are not seamless either, but much quicker changing than synchromesh gearboxes)



#14 Bloggsworth

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Posted 19 February 2012 - 15:29

The only driver any team would want back if manual gearshifts were reintroduced would me Michele Alboreto...

I can change more quickly from 6th to 2nd in my MX5 than my mate can in his Porsche Boxter with flappy paddles...

Edited by Bloggsworth, 19 February 2012 - 15:30.


#15 24gerrard

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Posted 19 February 2012 - 19:20

Motorcycle gearboxes seem entirely successful in their application. Why is this sort of 'box never used in road cars, not even real sports cars?

(obviously they are not seamless either, but much quicker changing than synchromesh gearboxes)


Motorcycle gearboxes are also layshaft gearboxes.
They use ratchet shift. True sequential operation, where as the current regs in F1 simply demand sequential operation 12345677654321, when the boxes could actualy choose any gear.
I suggested a similar sequential ratchet mechanism to Garry Anderson at Jordan and it was fitted to the Jordan because Eddie did not have the budget for the new semi automatic at the time, which was pioneered by Mansel in the Ferrari I was consulted on. The Jordan box also used 7 gears and established the later FIA regulations for the gear maximum of 7. At the time I was developing multi speed bevel epicyclic geartrains with up to 25 gears for F1, full or semi auto. The regulations killed this off.
Motorcycles on the whole have very light clutches with next to no flywheel and very small light gears.
This results in the faster shifting capability but unfortunately the benefits are lost by continueing to make the rider change gear with an ancient foot lever resembling a banana in a bowl of custard.

All layshaft gearboxes are ancient technology masking huge potential in geartrain development simply to save manufacturers money.

Edited by 24gerrard, 19 February 2012 - 19:21.


#16 24gerrard

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Posted 19 February 2012 - 19:25

You are right - it is misleading to call these gearboxes "seamless" - fast changing but not uninterrupted.

In theory it seems to be possible to propose an arrangement that has a continuous change in ratios between two fixed ratios - but very likely not really practical.


I have a design patented for a stepped gearbox (7 gears if used in F1) that can actualy INCREASE the amount of torque transfered during the gearshift.
It is also a KERS unit in the same package.
It is called an Electric Shift Energy Recovery Unit and is suitable for Kers, Hybrid and full electric use.

#17 gruntguru

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Posted 20 February 2012 - 00:22

It does NOT replace the gear change and there is STILL a gap in transfering full torque on upshifts.

I agree the Zeroshift mechanism is not seamless due to the inevitable torque spike, but there is no gap in torque delivery.

#18 gruntguru

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Posted 20 February 2012 - 00:23

All layshaft gearboxes are ancient technology masking huge potential in geartrain development simply to save manufacturers customers money.

Fixed.

Edited by gruntguru, 20 February 2012 - 00:24.


#19 GreenMachine

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Posted 20 February 2012 - 00:46

All layshaft gearboxes are ancient technology masking huge potential in geartrain development simply to save manufacturers money.


Get over it Gerard. If there was a better mousetrap, it would be made, because those who can make money from it would take it up. Better as in cheaper, more reliable, more efficient, lower running/whole of life costs etc. Either your marketing sucks, or your 'market' is not that of the manufacturers. Yes I know about the inertia of big organisations, and changeover costs, and the other impediments to innovation, but for the right innovation, the right innovator, these can, have been, and will be overcome.


/rant off :rolleyes:

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#20 Engineguy

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Posted 20 February 2012 - 00:56

Get over it Gerard. If there was a better mousetrap, it would be made...


GreenMachine, silly boy, you're overlooking the quashing by the American oil compnies, the American auto companies, the American government, and the Murdochs.

/sarc

Edited by Engineguy, 20 February 2012 - 00:56.


#21 bigleagueslider

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Posted 20 February 2012 - 02:27

......Jim Clark learned to use a dog ring manual gearbox like we all did racing in those times. With any layshaft gearbox it is possible to learn to change gear without using the clutch. Jim Clark was a fantastic driver with skills few modern F1 stars can call on.


24gerrard,

Funny you should mention that about Clark. I once had a chat with an old Lotus race engineer about transmissions. He said that when they would tear down the gearboxes, the dog rings in Clark's transmission would always show amazingly little wear compared to the other driver's.

Regards,
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#22 24gerrard

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Posted 20 February 2012 - 14:41

GreenMachine, silly boy, you're overlooking the quashing by the American oil compnies, the American auto companies, the American government, and the Murdochs.

/sarc


You said it Engineguy and today there is no chance of a better mousetrap.
Environmental health, cruelty to animals and health and safety would stop development before it even started.
Much like the Euro regulations on vehicles and the FIA regulations in F1.
One of their priorities now is keeping the Murdochs happy.
American auto companies have yet to enter the 21st century and the oil companies are waiting for their next war.
Will it be in the middle east or the South Atlantic.
I see you understand my problem.

#23 24gerrard

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Posted 20 February 2012 - 14:47

I agree the Zeroshift mechanism is not seamless due to the inevitable torque spike, but there is no gap in torque delivery.


I tell you what gruntguru, you try to apply anything other than torque from rotational inertia as the torque path changes, at the instant of shift from one gear to another and see what happens.
I have done it a few times on a test bed and a couple of those times I was dodging the flying shrapnel.

#24 24gerrard

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Posted 20 February 2012 - 21:45

24gerrard,

Funny you should mention that about Clark. I once had a chat with an old Lotus race engineer about transmissions. He said that when they would tear down the gearboxes, the dog rings in Clark's transmission would always show amazingly little wear compared to the other driver's.

Regards,
slider


Sadly the skill that made up at least half of a race drivers ability, gearchanging, has been replaced with a kind of x-box control pad that requires hardly any co-ordination or hand and feet sensitivity.
Drivers are pretty superfluous to requirements these days.

#25 gruntguru

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Posted 20 February 2012 - 22:51

I tell you what gruntguru, you try to apply anything other than torque from rotational inertia as the torque path changes, at the instant of shift from one gear to another and see what happens.
I have done it a few times on a test bed and a couple of those times I was dodging the flying shrapnel.

Not a relevant response to my post.

Any shrapnel from a zero-shift box would be due to a torque "spike" not a torque "gap". The torque spike itself is only due to inertia. Reduce the inertia of the driving or driven ends and the torque spike reduces proportionally.

#26 cheapracer

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Posted 21 February 2012 - 05:33

Any shrapnel from a zero-shift box would be due to a torque power "spike" not a torque power "gap". The torque power spike itself is only due to inertia. Reduce the inertia of the driving or driven ends and the torque power spike reduces proportionally.


Fixed.


#27 MatsNorway

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Posted 21 February 2012 - 10:46

Hehe.

#28 24gerrard

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Posted 21 February 2012 - 12:13

Fixed.



:up:
'The music goes round and round oh yea yea yea and it comes out here'.
At the conveniently chosen and placed measuring devices, so as to help promote the wrong concept of seamless/zeroshift for the marketing boys.
They of course are not the ones dodging shrapnel by the test beds.

Edited by 24gerrard, 21 February 2012 - 12:13.


#29 Wolf

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Posted 21 February 2012 - 12:13

Cheapracer- are you sure your corrections are OK? (or are you making a point of a sort- like a jab from some sort of torque vs power argument?) Methinks Gruntguru had phrased it right- when changing gear one adjusts revs to match output torque, and therefore power must 'spike' during gearchange... If power should remain constant, one shzould not change revs during gearshift, and I don't think it's a very wise thing to do.

Gruntguru, OTOH- if spike (or jerk, as I would put it) came only from rotational inertia... that would mean you were saying exactly what Gerrard is saying? The jerk should obviously come from both inertia and unmatched revs (or as is referred to- torque spike)- and the implication is that power is then indeed not transferred during the shift.

#30 24gerrard

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Posted 21 February 2012 - 12:40

Cheapracer- are you sure your corrections are OK? (or are you making a point of a sort- like a jab from some sort of torque vs power argument?) Methinks Gruntguru had phrased it right- when changing gear one adjusts revs to match output torque, and therefore power must 'spike' during gearchange... If power should remain constant, one shzould not change revs during gearshift, and I don't think it's a very wise thing to do.

Gruntguru, OTOH- if spike (or jerk, as I would put it) came only from rotational inertia... that would mean you were saying exactly what Gerrard is saying? The jerk should obviously come from both inertia and unmatched revs (or as is referred to- torque spike)- and the implication is that power is then indeed not transferred during the shift.


You change gear so as to match component RPM.
Transfering torque is a different requirement.
Of course you want to change gear as fast a possible and to transfer torque for as long as possible.
The two things are not the same.
Can grunt explain how it is possible to measure the torque on the baulking components at each gear at the moment of gearshift?
Measuring the output (at the diff or wheel) does not take into account the complex forces within the gearbox at the relevent components.
Let me help.
It is possible to measure the twist (Torque) of the closest input shaft and output shaft to the two gears under shift investigation.
This requires electric contact strips lengthways on the shafts and the sensors measure the linear accuracy of these strips, as this measurement changes with torque applied and how much the shafts twist.
Of course the torque can only be measured if there is a load to apply the force against.
The spike that the marketing boys show, occurs at the central point of the gear shifts where both the gears in question are at their very least engaged state.
and the (so called zero shift or seamless parts) are at their weakest geometry for transfering high torque levels.
So ask yourselves this, 'why is there a so called spike at this point'?
If it were maximum torque from the engine at near Maximum RPM, this would without doubt grenade the geartrain.
No as cheapy corrected it can only be a 'power' spike as a result of rotational inertia.
This being the case, it PROVES, that NO torque can possibly be being transfered from input of the gears to output at the mid point of gearshifting where the spike appears.


#31 Wolf

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Posted 21 February 2012 - 13:37

Gerrard, you do have some points (e. g. about rev matching), with some maybe I would not agree (torque may not be measured if there is no load, but it can be indirectly measured, e.g. change of shaft speed, or power from rotational inertia*), but we're in danger of starting to talk in circles.

Anyways, I do not think that gearchange can be at the same time without power interruption and seamless (smooth). It's in contradiction with conditions at the beginning of the gearchange and at its end...

* IMHO the proper way of looking at it is that rotating parts represent the torque that resists acceleration (theoretically they cannot produce power, but consume it when their speed has to be changed)

#32 24gerrard

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Posted 21 February 2012 - 13:52

Gerrard, you do have some points (e. g. about rev matching), with some maybe I would not agree (torque may not be measured if there is no load, but it can be indirectly measured, e.g. change of shaft speed, or power from rotational inertia*), but we're in danger of starting to talk in circles.

Anyways, I do not think that gearchange can be at the same time without power interruption and seamless (smooth). It's in contradiction with conditions at the beginning of the gearchange and at its end...

* IMHO the proper way of looking at it is that rotating parts represent the torque that resists acceleration (theoretically they cannot produce power, but consume it when their speed has to be changed)


It is much more complicated than that Wolf but you are right there are a number of ways to look at gearbox operation.
The one thing I think is essential to be aware of, that is the output shaft side of any gearbox. It is driven by the road wheels and this is contant the whole time the vehicle is in motion. The output shaft RPM rises with road speed but it has no steps and will not slow down for almost anything.

As you say it is possible to 'indirectly' 'measure' the torque at any component but it is very very difficult.
Be careful not to mix up 'calculating' torque from measuring it.

Edited by 24gerrard, 21 February 2012 - 13:55.


#33 Wolf

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Posted 21 February 2012 - 14:25

Yep, that's what I meant with indirectly measuring it- calculating it from measured values... As for output shaft, that's the main reason for my claim in second paragraph (and in original post).

As I've said-I'm no expert on either engines or gearboxes (some would say I'm not expert on pretty much everything, and I'd have a hard time disagreeing)... But pls let me ask if I got it right. Let's say we have a car accelerating, we're in second gear and change into third. At the beginning, we're at max revs perfectly matched to road speed. What happens as the third gear is engaged? Output shaft rotates at the same speed it was rotating a moment ago, but all of the sudden (because of reduced transmission/gear ratio) engine/output shaft has to be revved down to revs matching the output shaft. How does this happen? I'd venture a guess, that during the synchronization the output shaft will slow the engine down, through synchronizing mechanism (and aided by it), and you seem to agree that the other way around is pretty much impossible. But if I'm right about it, that means the 'power flow' is reversed- instead of engine power accelerating the wheels, the situation is that kinetic energy of the car is used to rev down the engine to appropriate revs (and for that to happen the car would have to slow down, probably by infitensimaly small amount, but actually decelerate). And to me, uninterrupted means that engine power drives the wheels before, during and after the gearchange; same as seamless does not involve power 'flowing' one way, then the other, and back again... :confused:

#34 24gerrard

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Posted 21 February 2012 - 14:47

The engine does indeed have to reduce in RPM to achieve a higher ratio during an upshift.
Of course if the vehicle is already accelerating hard, this acceleration will continue because of the vehicle inertia.
This will cancel out some of the required reduced rpm needed to match the higher gear road speed.
Just one point of hundreds.

#35 Tony Matthews

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Posted 21 February 2012 - 14:48

Wolf, you may be interested in this:-

Posted on: Apr 25 2011, 07:08 by Rachael
In F1 two gears ARE routinely engaged at the same time and the upshift IS made whilst accelerating in the lower gear. Post upshift the engine indeed must slow to drive the higher gear but it is still transmitting positive torque - the torque transducer on the input shaft between gearbox and engine does not record a negative torque during the shift.




#36 24gerrard

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Posted 21 February 2012 - 14:51

Wolf, you may be interested in this:-


Engaged to what Tony?

If both gears are Fully engaged there is no gearshift to make because all you will have is a pile of bits.

Nagative torque Tony?

Edited by 24gerrard, 21 February 2012 - 21:27.


#37 Wolf

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Posted 21 February 2012 - 15:16

You guys are hell bent on confusing poor old moi, hahaha. Thanks Tony, a food for thought... :)

Gerrard, but I thought that's the point- they're never fully engaged at the same time. I pictured the situation as one synchron fully engaged, and one fully disengaged at the start, with reversed situation at the end: so during the shift both gears are partially engaged through their respective synchrons- and, as I understand, synchrons by their nature would allow slippage until fully engaged. Or am I getting something wrong again?

* as for vehicle accelerating- yes, but the rate of the acceleration would IMHO have to drop during the shift (at least, I think so), so the deceleration I spoke of would translate to (partial) decrease of acceleration

#38 MatsNorway

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Posted 21 February 2012 - 16:00

The acceleration would only drop on average(longer time than one gearshift takes) if there is engine cut during gearshifts.




#39 OfficeLinebacker

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Posted 21 February 2012 - 16:06

Separating the men from the Hamiltons.

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#40 Wolf

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Posted 21 February 2012 - 16:36

Mats, it's not the only possible interpretation (and I'm, in light of post that Tony kindly quoted, trying to understand what and how it happens). The acceleration will drop if e.g. power provided by the engine drops a fraction, below the level needed to sustain the acceleration. In order to keep the same level of acceleration the engine must deliver constant power through the shift- and I'm struggling to see how the engine could keep delivering the same amount of power while dropping the revs...

Yet, seeing no reason whatsoever to belie Rachael's post (admittedly, I spotted a thing in it that intrigued me), I must seek explanation elsewhere; and I think the gearbox design itself should explain why there is no negative torque at the clutch...

EDIT: d'oh... if acceleration decreases, but still exists, there is no reason for existence of negative torque at the clutch :blush: (that doesn't mean I'm right... just that my interpretation is not in contradiction with that fact :p I still think it'll require some consideration on my part to get to grips with the whole thing)

Edited by Wolf, 21 February 2012 - 16:42.


#41 MatsNorway

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Posted 21 February 2012 - 19:01

you don`t need over time to have constant engadgement to have no acceleration lost in total.

If the engine revs konstantly it will only rise in rpm when it goes out of one gear and drop down again when it goes into another. there will be a spike on the "graf" but the average would be the same.

this is only in teory, in the real world i guess to not go of the throttle would demand a clutch and that gobbles up power during engaging. due to friction -> heat -> loss of power

blabla lots of other options. Gerrard should have it covered i would think.

#42 Engineguy

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Posted 21 February 2012 - 22:08

... Of course if the vehicle is already accelerating hard, this acceleration will continue because of the vehicle inertia. ...


Vehicle inertia can maintain velocity (very briefly)... it cannot maintain acceleration. Physics 101.


#43 gruntguru

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Posted 21 February 2012 - 22:28

Gruntguru, OTOH- if spike (or jerk, as I would put it) came only from rotational inertia... that would mean you were saying exactly what Gerrard is saying? The jerk should obviously come from both inertia and unmatched revs (or as is referred to- torque spike)- and the implication is that power is then indeed not transferred during the shift.

24G said there was a "gap" in the torque delivered. There is no "gap" only a "spike".

#44 GeoffR

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Posted 21 February 2012 - 22:33

Found another interesting thread that discusses this topic, but I suspect that gerrard already knows about it.

http://www.f1technic...c...?f=4&t=8914

Years ago when participating in the odd drag race, it was common to hold the accelerator flat, briefly dip the clutch and slam the gear lever through to the next gear (not very mechanically sympathetic!). Does this qualify as a 'seamless shift'? ;)

#45 gruntguru

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Posted 21 February 2012 - 22:50

The spike that the marketing boys show, occurs at the central point of the gear shifts where both the gears in question are at their very least engaged state.
and the (so called zero shift or seamless parts) are at their weakest geometry for transfering high torque levels.
So ask yourselves this, 'why is there a so called spike at this point'?
If it were maximum torque from the engine at near Maximum RPM, this would without doubt grenade the geartrain.
No as cheapy corrected it can only be a 'power' spike as a result of rotational inertia.
This being the case, it PROVES, that NO torque can possibly be being transfered from input of the gears to output at the mid point of gearshifting where the spike appears.

Nonsense. Prior to the shift, engine torque is transferred to the rear wheels via the lower-range gearset. When the dogs connect the next gearset (remember the previous gearset is still connected so there is no reduction in torque - the next gearset actually has to begin turning the output shaft faster than the previous gear before the previous gear can dis-engage so there has to be a (tiny) torque increase if only for this to occur) the engine now has to slow down to match the roadspeed in this higher gear. To slow the engine down requires dissipation of its rotational kinetic energy. This will go initially into elastic energy in the drivetrain and mounts (windup) and then into vehicle speed and possibly wheelspin (and possibly drivetrain failure). Drivetrain windup alone is indicative of increased torque.

Measuring torques and stresses in individual components is possible these days using a myriad of techniques, but isn't needed to answer this topic. Transfer of torque to the final drive can be measured or inferred much more simply. Accurate measurement of the transmission output shaft speed is entirely sufficient.

#46 24gerrard

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Posted 22 February 2012 - 10:32

Nonsense. Prior to the shift, engine torque is transferred to the rear wheels via the lower-range gearset. When the dogs connect the next gearset (remember the previous gearset is still connected so there is no reduction in torque - the next gearset actually has to begin turning the output shaft faster than the previous gear before the previous gear can dis-engage so there has to be a (tiny) torque increase if only for this to occur) the engine now has to slow down to match the roadspeed in this higher gear. To slow the engine down requires dissipation of its rotational kinetic energy. This will go initially into elastic energy in the drivetrain and mounts (windup) and then into vehicle speed and possibly wheelspin (and possibly drivetrain failure). Drivetrain windup alone is indicative of increased torque.

Measuring torques and stresses in individual components is possible these days using a myriad of techniques, but isn't needed to answer this topic. Transfer of torque to the final drive can be measured or inferred much more simply. Accurate measurement of the transmission output shaft speed is entirely sufficient.



the next gearset actually has to begin turning the output shaft faster than the previous gear before the previous gear can dis-engage

And just how does it do this with the output shaft connected to the rear wheels which control the rpm the output shaft turns at??????????????????

#47 24gerrard

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Posted 22 February 2012 - 10:50

Zero shift and so called seamless baulking concepts are simply mechanical clutches between two rotating components.
They derive their speed of operation and their ability to transfer a limited amount of torque up to and just beyond the actual shift, by operating partly using slip between components and partly by direct baulking action.
They are simply clever mechanical geometry to improve the action of a baulk ring or a dog ring.
However there still has to be a gap or seam between the full engagement of the two gears involved in the gearshift.

#48 Engineguy

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Posted 22 February 2012 - 11:18

the next gearset actually has to begin turning the output shaft faster than the previous gear before the previous gear can dis-engage

And just how does it do this with the output shaft connected to the rear wheels which control the rpm the output shaft turns at??????????????????


Surely you realize increasing the rpm of the output shaft (i.e. acceleration) is the actual point of shifting gears? While the output shaft may drag down the engine rpm, the engine power/engine inertia/flywheel & input geartrain inertia simultaneously drags the output shaft rpm up... as evidenced by wheelspin and/or vehicle acceleration. The previous gear is immediately overrun/unloaded.

#49 24gerrard

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Posted 22 February 2012 - 11:22

Vehicle inertia can maintain velocity (very briefly)... it cannot maintain acceleration. Physics 101.


Thanks for reminding me.
I was wrong, there is no benefit to be had of a smaller rpm drop between gears from vehicle inertia because acceleration stops at the moment energy other than inertia is removed.
It does show that a slow gearshift will widen that rev drop, making the gearshift more difficult to achieve with matching shaft speeds as the inertia tails off and the vehicle rapidly starts to slow down.
It will also result in a bigger chance of jerky shifts as the input/output rpm gap increases between gears.

Best way to experience this is to drive a vintage vehicle with a 'crash' gearbox with no syncromesh at all. (or even some post war heavy lorries)
Here you have to clutch the gearbox into neutral and then wait for the engine to slow down, so its rpm matches the input rpm through the next gear you wish to select. Get it wrong and you knock teeth off the gears.
Downshifts on these 'crash' gearboxes are even more difficult. You have to rev the engine up in neutral to increase engine rpm to match the higher input rpm of the lower gear to be selected.
This is real double de-clutching without ANY form of syncromesh.
Try adding braking at the same time and then use the heel and the ball of the feet on different pedals. Heel and toeing.
Dont forget this is on a vintage car not a later rally developed car with dog rings.
It doesnt help when some of these vehicles have the pedals in a different order either.
I have driven and competed with many such vehicles and you tend to learn a fair bit about how the powertrains in them work.
In modern vehicles most of these skills is not needed and the way the powertrain works is for the most part masked from the driver.

#50 24gerrard

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Posted 22 February 2012 - 11:32

Surely you realize increasing the rpm of the output shaft (i.e. acceleration) is the actual point of shifting gears? While the output shaft may drag down the engine rpm, the engine power/engine inertia/flywheel & input geartrain inertia simultaneously drags the output shaft rpm up... as evidenced by wheelspin and/or vehicle acceleration. The previous gear is immediately overrun/unloaded.


Incorrect
The purpose of changing gear is to match the rpm of the engine to the road speed. (the process occurs over a range of operation from full acceleration to full vehicle deceleration).
It is the input shaft of a layshaft gearbox, through the engaged direct clutch that drags down the engine rpm, not the output shaft.
In an F1 gearbox it is the engine management system that changes the ignition and fueling to assist this process at the point of shift overlap.
This happens as the 'so called' seamless shift mechanical components undertake the gearchange baulking action.

The previous gear is immediately overrun/unloaded. This makes no sense.

As to increasing the output shaft speed (acceleration), you achieve this by transfering torque from the engine to the rear wheel.
You CANNOT do it using small mechanical components between the shafts and gears especialy when these parts are at their least engaged and least torque capable geometric condition, one set on one gear and one set on another. The available torque has to be reduced to allow the change in ratio to be achieved and a new safe path for torque transfer established.

All you have to do is learn to listen to understand this. The video of the Catterham in the first post will pose you one very importsnt question.
If full torque is being transfered seamlessly as you keep trying to say is happening during gearshifts, then why in hells teeth is there a reduction in engine noise at the point of the gearshift.

Edited by 24gerrard, 22 February 2012 - 11:55.