623 replies to this topic

[cheapracer]

If I remember right there is nothing in the current rules that abolish a good ol fashion manual box. We're it more efficient they would run those instead of the hugely expensive current boxes.....correct?

They (F1) have been chipping away at seamless boxes since the late 80's. Over later time some of the cheaper teams had no choice but to run manuals on a cost basis - guess where they were on the grid ..

That manual option is even being touted in this century is indicative of this thread.

that the modulation of throttle and clutch, needed for the Zeroshift AMT to work without destroying itself, dumbs down power transfer to where a conventional dogbox might be a better option.

Why is it you consider that 'banging' a dog box Vs a zeroshift into the next gear would be any different or for that matter a synchro box or automatic ...?

For road use they all need modulation for comfort and long service life, for racing they simply need to be engineered for the appropriate service life and control ability such as changing gear mid corner where the torque spike might break traction causing instability.

Many people here consider their thoughts based on road cars as that's all they have experienced but the torque spike disturbance/stress on a race car with ultra-close gear ratios is actually minimal.

My own Mazda 6 auto has a problem of no modulation from 3rd to 4th and has an uncomfortable "BANG" when changing under load when hot (imagine a broken engine mount "bang") it's a known problem ... http://forum.mazda6c...ing-so-far.html

This implies that there is an instant change in the speed of the driven wheels, and the car. There isn't, all that happens 'instantly' is a drop in engine revs.

Oddly enough Tony you claim lower tech knowledge but you have one of the most astute posts here.

[cheapracer]

...the use of such forums as a source of knowledge to our young engineering apprentices.
This particular thread has become more a source of amusement for them recently.

On the other hand education can come about by learning/understanding all the wrong ways to do things too (seriously).

[Kelpiecross]

468 - very important! Understand the railcar analogy and tell me why you think it is wrong.

I like the cable car (not "railcar") analogy. However I am not sure it clears up the matter. Presumably actually gripping the cable would involve a fair bit of slippage (otherwise there would be an enormous jolt to the passengers) - this deliberate slippage would be analogous to clutch slip in a car during a gear change.

I am no longer sure just what this debate is about. There seems little doubt that if you were prepared to put up with the jolt the gear shift in a Zeroshift 'box is certainly "gapless" as the cable grip would be if it was instantaneous.

Is using the clutch etc. to smooth the change in a Zeroshift 'box any different than the action of the clutches in an epicyclic 'box (which 24G seems to favour) or a twin-clutch 'box?

Maybe just what the argument is about should be defined clearly with the aim of possibly bringing this debate to an end. I get the impression that the claims etc. have changed a little since this debate began.

[gruntguru]

On the other hand education can come about by learning/understanding all the wrong ways to do things too (seriously).

I must add, this is best done by doing things the wrong way yourself - to a lesser extent by listening to a supposed expert in the field giving you wrong advice. Best of all is to have a proper understanding of the basic science underlying your particular field then jumping in, making mistakes (and having accidental successes) and being able to correctly identify the reasons for the results obtained.

I was having a similar discussion with a good friend just yesterday, on the skill level of dyno-tuning "experts" around Australia. I have experiened the "wisdom" of a good proportion of them and the majority - although very capable of doing good work - are unable to operate beyond the limits of the "knowledge" they have gained through experience. What is lacking is "understanding" - the next level of wisdom that enables the best in their field to extract a little extra, or cope with situations that deviate from the norm.

[gruntguru]

I like the cable car (not "railcar") analogy. However I am not sure it clears up the matter. Presumably actually gripping the cable would involve a fair bit of slippage (otherwise there would be an enormous jolt to the passengers) - this deliberate slippage would be analogous to clutch slip in a car during a gear change.

I am no longer sure just what this debate is about. There seems little doubt that if you were prepared to put up with the jolt the gear shift in a Zeroshift 'box is certainly "gapless" as the cable grip would be if it was instantaneous.

Just to be clear:

1. A cablecar with friction "grips" to connect it with either cable is analogous to an auto trans - a stepped-ratio gearbox with engagement of one or more gears possible simultaneously via friction devices.

2. A cablecar with one-way "hooks" to connect it with either cable is analogous to a Zeroshift - a stepped ratio gearbox with engagement of one or more gears possible simultaneously via ratcheting devices. This cable car will shift with a "jolt" unless it is equipped with some extra devices - perhaps a spring and damper or a friction damper.

The key point here is that both types (1 and 2) are capable of changing ratio without interruption to drive because they are both capable of engaging both consecutive ratios simultaneously - even if only for a very brief period.

Sure - if the shift occurs with a "jolt" the drive might be unloaded briefly just after the jolt because of "unwinding" ie transient oscillations. This is true of either transmission type - if an auto is shifted with sudden application/release of the friction devices it will also jolt and possibly unwind. This phenomenon does NOT mean either device cannot be classified as capable of changing ratios without interruption to drive.

Is using the clutch etc. to smooth the change in a Zeroshift 'box any different than the action of the clutches in an epicyclic 'box (which 24G seems to favour) or a twin-clutch 'box?

No. Sure it is done differently but the end result is the same ie in terms of a record of torque flow to the rear wheels (as provided by Greg earlier) either transmission is capable of producing a gapless flow of torque.

[24gerrard]

Thank you, it now starts to make sense.
It is time perhaps to square the circle so to speak.

My original statement was that true seamless and zeroshift gearboxes based on layshaft stepped geartrains are not possible.
I stated that there will always be a gap in torque transfer from the input to the output at the shift mechanisem.

I think we can agree on the basic operation of the zeroshift components in the video shown.
I also agree that the shift shown on the graph is true and can be achieved.

Slider has stated that he did not believe there was a stepped ratio gearbox system that could change gear without a gap in the change in torque path from one ratio to a different ratio.
I agree with this.
I believe that most are unsure if this is true or false for the zeroshift.
I believe that for the fierce version of the zeroshift with no torque modulation the gap will be caused by a rebound of the drive train, or there will be a complete break in traction if the torque is high enough.

There is one more component in this mechanism that I am sure many have not fully considered.
The over run ramps/ratchet on the engagement faces of the gears briefly touched on by Sam.
Sam states that the movement of the 2nd gear fork towards first gear when first gear is engaged, is to assist over run.
This tells only part of the reason for the ramps.
Yes, when a non modulated shift is undertaken the 2nd gear engagement allows the 1st gear bullets to over run the ramps and the gear is freewheeled on the ramps by the bullets now driven by 2nd gear via the central hub on the output shaft.
The timing of this over run disengagement is dictated by the spring rate of the 1st gear bullets and the amount of torque applied to 2nd gear.
(the springs operating can also be considered a gap, springs on your hooks for the cable car grunt)

However the main 'gap' dimension is present in most of the actual shifts on the road.
Here, other than for the ultimate 'fierce' shift, the input torque is controlled by reducing engine torque output using engine management and clutch disengagement. There is a range of control which with damping on the drive train results in a smooth and so called 'seamless' shift.
It is a 'smooth' result but at the expense of some of the available torque for drive.

We agree that in the basic shift sequence torque applied from second gear reduces the torque applied (and driving) through first gear, resulting in the 1st gear bullets disengageing (being sprung off by their bullet springs) and running up the over run ramps/ratchet.

The point I have continued to make, is that reducing torque to 1st gear (by modulating torque input) can have the same result, with the 1st gear bullets springing out of engagement, without the need to apply torque through second gear.
This action is essential to achieve a 'smooth' shift.
If it did not work in this way there would still be a fierce engagement of 2nd gear and the input torque modulation would be pointless.

This even gives the possibility for varying the timing of the shift forks relative to one another, so as to control the shift overlap (GAP) directly.
This was a method I experimented with in the late 1970s.
So if you look at the video, you should be able to see this potential for shift fork actuation timing.

There are a number of ways to modulate torque at the shift overlap, I count four in this mechanism.
Engine management, clutch management, drive train damping and the spring rate of the detent bullets.
There may be more not shown.
One could easily be shift fork timing.
Without them you would be driving a sledgehammer, which would however transfer torque more efficiently.

Edited by 24gerrard, 21 March 2012 - 09:56.

[hogits2]

So, no gap on the bench.

In the car, 'induced' gap when driving. Gap induced/introduced/created by the modulation etc. for better comfort/wear etc. Gap not caused by/during handover.

Is this view ok?

Also as several posters have mentioned, forcing a dog box through at WOT and no clutch disengagement is fairly severe. Might this not create gaps when both dogs are disengaged and also when the output etc. bounces/unwinds after higher gear engagement? 2 gaps.

[gruntguru]

The point I have continued to make, is that reducing torque to 1st gear (by modulating torque input) can have the same result, with the 1st gear bullets springing out of engagement, without the need to apply torque through second gear.
This action is essential to achieve a 'smooth' shift.
If it did not work in this way there would still be a fierce engagement of 2nd gear and the input torque modulation would be pointless.

Disagree on this point. The inertial spike is double ended. The greater part of the inertia is due to the rotating mass of the engine on one side and the vehicle mass through the drivewheels on the other side. A relief valve in the form of a slipping clutch can be placed anywhere between these two masses to mitigate the inertial spike. Note that engine output control alone cannot eliminate the inertial spike created by an extremely rapid handover like the Zeroshift, but it will reduce the amount of clutch slippage required.

. . . . so as to control the shift overlap (GAP) . . .

Shift overlap is not a "GAP" in torque delivery.

[24gerrard]

So, no gap on the bench.

In the car, 'induced' gap when driving. Gap induced/introduced/created by the modulation etc. for better comfort/wear etc. Gap not caused by/during handover.

Is this view ok?

Also as several posters have mentioned, forcing a dog box through at WOT and no clutch disengagement is fairly severe. Might this not create gaps when both dogs are disengaged and also when the output etc. bounces/unwinds after higher gear engagement? 2 gaps.

Yes it depends on the skill of the driver both to shift speed and shift modulation.
A very skilled driver can modulate the shifts to meet all conditions on the race track.
A modern seamless shift box cannot fully reproduce these skills. AFAIK
How good the 'seamless' shift will be depends on the design and how well the modulation and timing is set up.

[24gerrard]

[quote]name='gruntguru' date='Mar 21 2012, 10:12' post='5610023']
Disagree on this point. The inertial spike is double ended. The greater part of the inertia is due to the rotating mass of the engine on one side and the vehicle mass through the drivewheels on the other side. A relief valve in the form of a slipping clutch can be placed anywhere between these two masses to mitigate the inertial spike. Note that engine output control alone cannot eliminate the inertial spike created by an extremely rapid handover like the Zeroshift, but it will reduce the amount of clutch slippage required.[/quote]

Your chosen operating parameter above only applies to a slightly modulated racing shift.

[quote]Shift overlap is not a "GAP" in torque delivery.[/quote]

Shift overlap is not of itself a gap in torque delivery.
The result of changing a torque path from one fixed ratio to another creates one.

[gruntguru]

Your chosen operating parameter above only applies to a slightly modulated racing shift.

Not sure what you mean. It is a fact however that a clutch set to a specific clamp pressure will absolutely limit torque to a specific value and this alone will "clip" the torque spike to whatever value the designer chooses. The location of the clutch has no effect on its effectiveness in this role.

Shift overlap is not of itself a gap in torque delivery. The result of changing a torque path from one fixed ratio to another creates one.

Not at all. You yourself said that an auto trans is "gapless" and I demonstrated in post 615 that the zeroshift with clutch-slip can be functionally equivalent.

[REN_AF1]

Not sure what you mean. It is a fact however that a clutch set to a specific clamp pressure will absolutely limit torque to a specific value and this alone will "clip" the torque spike to whatever value the designer chooses. The location of the clutch has no effect on its effectiveness in this role.



Not at all. You yourself said that an auto trans is "gapless" and I demonstrated in post 615 that the zeroshift with clutch-slip can be functionally equivalent.

Now I am going to throw the proverbial spanner in the gearbox so to speak, becourse the thing that really bothers me is that according to the SAE paper the Zeroshift guys have written on the transmission, they shows a chart on page 27 that CLEARLY shows they manitain a 0.3g lateral acceleration while reducing their engine rpm´s.. I for the love of god cannot se where that energy should come from. Mean acceleration is even increasing.

By the way, they also show transducer output for the position of the shift forks during the entire phase to clear out any confusion about this.

Unfortunately they dont show clutch engagement.

R

[Wuzak]

Not sure what you mean. It is a fact however that a clutch set to a specific clamp pressure will absolutely limit torque to a specific value and this alone will "clip" the torque spike to whatever value the designer chooses. The location of the clutch has no effect on its effectiveness in this role.

Off topic here, the Rolls-Royce Merlin and Griffon were not fitted with crankashaft torsional vibration dampers. To protect the supercharger from the vibrations the supercharger drive was via a torsionally flexible shaft, and a predetermined amount of clutch slip in the gearbox.

In the two speed systems each gear had its own clutch. Potentially, then, could this have been a "seamless" gearbox? I do recall seeing reports that the change from M gear to F gear was severe, and was accompanied by a loud bang.

Incidentally, the two speed systems designed by Rolls-Royce used a layshaft arrangement, but with a layshaft for each gear. Packard (at least the later ones) engines were fitted with a Wright designed epicyclic gearbox.

[gruntguru]

Now I am going to throw the proverbial spanner in the gearbox so to speak, becourse the thing that really bothers me is that according to the SAE paper the Zeroshift guys have written on the transmission, they shows a chart on page 27 that CLEARLY shows they manitain a 0.3g lateral acceleration while reducing their engine rpm´s.. I for the love of god cannot se where that energy should come from. Mean acceleration is even increasing.

I assume you are talking about the period immediately after the upshift in which case the reducing kinetic energy of the slowing engine is being utilised to produce a spike in acceleration. The inertial spike that would otherwise occur in the absence of clutch slip has been flattened out and extended in duration.

[NTSOS]

So, as of today, the 1st to 2nd gear handover where the 2nd gear dog rotates around and contacts the 2nd gear drive ring bullet while simultaneously causing the 1st gear drive ring bullet to accelerate away from the 1st gear drive dog is now no longer considered to be the source for an impossible gap or interruption in torque delivery at that exact moment of transfer/handover? 

It's now low torque and a bang.........a moving target perhaps?

You can generate a torque gap if you disengage both drive rings to neutral before engaging 2nd gear. That is of course not how the shift sequence of the ZS mechanism is set up. If for some reason you really wanted a gap in the shift process, you would simply use a single drive ring assembly not the ZS's two ring setup!

John

Edited by NTSOS, 21 March 2012 - 14:04.

[cheapracer]

Half the humour in these threads is that many think that stuff like seamless boxes are something new, here's a 1920's designed seamless and even a sequential shift of type...



The invention patent ...

http://www.google.co...4...lson&f=true

More info ..

http://en.wikipedia....elector_gearbox

[Wuzak]

Half the humour in these threads is that many think that stuff like seamless boxes are something new, here's a 1920's designed seamless and even a sequential shift of type...



The invention patent ...

http://www.google.co...4...lson&f=true

More info ..

http://en.wikipedia....elector_gearbox

Thanks for the info.

Is it me, or does the Cotal gearbox sound like an ESERU without the KERS function?

The Cotal self-changing gearbox of the 1930s was a manually controlled epicyclic, like the Wilson. The difference is that instead of band brakes, it used electromagnetic clutches. These two clutches each consisted of a central rotating disk (a simple steel pole piece) and a pair of coil-carrying rings, one rotating and one fixed (this coil could be considered as either a clutch or a brake). Sliprings were used to transmit electrical power to the rotating clutch elements

[SamSeles]

Any point in carrying on this discussion?

Seems like everyone (else) is comfortable with the principle.

Happy to discuss further if anyone feels like it.

[hogits2]

Away we go....

This may have been covered before but at the point of (ZS) handover, keeping 1st under load until 2nd is loaded must reduce the spike as the in & out shafts won't unload - less oscillations etc. Perhaps won't reduce the spike but should help reduce unwinding.

Also how about the actual shock/spike as the ZS gear starts to drive the bullet and hub. Assuming that inputs etc. are modulated & damped, how similar would the shocks be to say a dog box under the same conditions.

Edited by hogits2, 23 March 2012 - 20:35.

[hogits2]

F1 rotating inertia is so low and ratios so close now that the shock would be very minimal and don't they have need for shock absorption although they certainly did up to the 70's F1 as with this '60's Lotus with it's large rubber donut drives...



and in the '70's the donuts ended up on the outsides for some reason (F3 shown)..

Just a thought here - I was under the impression that donuts were just used to cope with angle & plunge until Mr Lobro came along. Incorporating Hookes joints & splines (especially rollers) was heavy & expensive. I saw a hinged Hooke's joint once on, I think, a 2.5 BRM which looked a bit odd but it obviously coped with some plunge.

Was there a Mr Lobro or is it an acronym?

[SamSeles]

This may have been covered before but at the point of (ZS) handover, keeping 1st under load until 2nd is loaded must reduce the spike as the in & out shafts won't unload - less oscillations etc. Perhaps won't reduce the spike but should help reduce unwinding.

Good point, oscillations are reduced. Depending on the application (car/bike) arguably of greater benefit than the neutral phase of a standard shift.

Also how about the actual shock/spike as the ZS gear starts to drive the bullet and hub. Assuming that inputs etc. are modulated & damped, how similar would the shocks be to say a dog box under the same conditions.

Clutch slip, damping and post engagement engine modulation is required for passenger car applications in order to improve NVH. In a race application where engine is generally cut or ******** with a locked clutch so that the dog ring being driven can be removed (in most cases) the engine will be re-introduced as the dog ring is being transitioned through neutral. The engine flair as a result will increase the speed difference that the engine inertia has to synchronize to. In such a case the synchronization energy in the standard dog box would be even greater than a "ZS". However consideration has to be given to the effect of introducing the spike to a wound drive line vs an unwound drive line at the point of engagement.

[gruntguru]

The comparison is an interesting one. I have had some experience with crash shifting motorcycle dog-ring boxes. It is surprising how smooth the shift can be (full throttle, clutchless upshift with a timed engine cut). My guess is a ZS operated the same way would be even smoother. My reasoning:- As mentioned, the ZS would keep the driveline loaded throughout. That would reduce the opportunity for the driveline to unwind (which certainly happens during the "gap" of a dog-ring upshift). It would also decelerate the engine more rapidly during the "cut" period since there is no "gap" in the load on the engine. That would also mean a reduction in the optimum cut period. (Typically around 50-100ms for a motorcycle box)

[slucas]

http://www.inmotive.com/

It's all beyond me... but I don't think it's seamless either. There is a lot of shuffling going on

[munks]

Looks seamless to me. You can see that the radius of the pulley grows over a short amount of time as a new section rotates from no contact with the belt to partial contact to full contact. Assuming they've spaced the gear teeth right, there's no slippage or anything.