560 replies to this topic

[24gerrard]

Machins graphs are all valid but depend on what the question is.
Try this.

Is it possible to increase acceleration from stationary by adding multiple gears lower in ratio than the current first gear being used?

I think this might also show that torque is a more versatile measure than bhp.

Edited by 24gerrard, 07 July 2011 - 10:39.

[machin]

24gerrard, on Jul 7 2011, 11:37, said:

Is it possible to increase acceleration from stationary by adding multiple gears lower in ratio than the current first gear being used?

If you allow the driver of my example "typical motorsport" gearbox to slip the clutch (as they do in real life) then the answer is NO. The clutch slippage takes the exact place of a lower gear. The rate of acceleration at low speeds is limited by the grip available up to the point where the grip is higher than the force/power/torque developed by the car at the wheels, after which point the engine output will be the limiting factor. By your own admission your own car, even with slicks, would spin its wheels right up to its top speed. This means that you are grip limited at all times and therefore your acceleration is limited at all times to the level dictated by the grip. Adding lower gears does not add to the grip!

One advantage of having a lower "launch" gear is that it will be more efficient than slipping the clutch. For such a short amount of time (once, maybe twice, per race) most people can live with this loss of efficiency. It won't increase the acceleration of the car in my example, and you will still need to modulate the throttle to ensure you don't break traction.

Quote

Now imagine your car with at least two lower gears than your second gear but with the ability for instant, constant torque gear shifting. I dare say the reason you cant use lower gears for your hill climbing is because you do not have enough of them and you cannot change gear fast enough if you did.

Even assuming that the gear changes are INSTANT your slow speed acceleration is still limited by how fast the car can accelerate whilst actually in those gears (whether its 1, 2 or 1000 of them). Since the force that is used to accelerate the car whilst in the gear is limited by the grip available then you won't accelerate any quicker.

Quote

I think this might also show that torque is a more versatile measure than bhp.

The answer is the same whichever method of analysis you do (Force or Energy). It is easier to see it on a force-based chart because the numbers at low road speeds are higher on a force based graph then they are on power-based graph, but the fundamental answer is exactly the same.

Edited by machin, 07 July 2011 - 12:31.

[machin]

To be absolutely fair to 24Gerrard, if the initial selection of first gear were wrong (i.e. too long), then of course adding additional lower gears would be beneficial. (otherwise it would be like trying to start in 5th gear).

Your first gear should be selected such that it can just about break traction, and only require clutch slippage at low road speeds in order to maximise the grip available. If you achieve this then adding additional gears won't help your acceleration. It is for this reason that the typical Quaife/Hewland close ratio box has a long first gear -because the typical "short-first" found on road car gearboxes is too short -and simply creates too much force at the contact patch (i.e. it causes wheel spin too easily)

Without sounding like a broken record; The answer here is that maximising the use of the grip available is the name of the game -providing any more than that (with an ultra low gear ratio) is pointless as you are still limited by the grip. There is no magic formula using a "multiple ratio, instant shifting, constant torque" gearbox to overcome this grip issue.

Edited by machin, 07 July 2011 - 13:42.

[murpia]

24gerrard, on Jul 5 2011, 13:48, said:

...
Slipping the clutch from zero to just below 25 mph can be done of course.
However controlling this and balancing it against traction break away and wheel spin is next to impossible.
In F1 they are well aware of this, it is one of the most difficult things to get right, as we all know.
...

The stepped fulcrum clutch goes a long way to making controlled clutch slip possible.

I thought I had read an AP press release announcing it, but I can't find it anywhere on their website.

Essentially it introduces a wide zone of slave cylinder position for a constant slip torque. If tuned accurately this slip torque is just above the expected tyre limit. Combined with a very 'stretchy' pedal torque map over the last 20% of travel in 1st gear, the driver can easily modulate the rear wheel torque as required.

Regards, Ian

[24gerrard]

murpia, on Jul 7 2011, 14:59, said:

The stepped fulcrum clutch goes a long way to making controlled clutch slip possible.

I thought I had read an AP press release announcing it, but I can't find it anywhere on their website.

Essentially it introduces a wide zone of slave cylinder position for a constant slip torque. If tuned accurately this slip torque is just above the expected tyre limit. Combined with a very 'stretchy' pedal torque map over the last 20% of travel in 1st gear, the driver can easily modulate the rear wheel torque as required.

Regards, Ian

So the purpose of the clutch is to slip away available torque until a speed is reached for a gear ratio that does not go over the 'grip' curve can be used?
Why?

[24gerrard]

machin, on Jul 7 2011, 14:31, said:

To be absolutely fair to 24Gerrard, if the initial selection of first gear were wrong (i.e. too long), then of course adding additional lower gears would be beneficial. (otherwise it would be like trying to start in 5th gear).

Your first gear should be selected such that it can just about break traction, and only require clutch slippage at low road speeds in order to maximise the grip available. If you achieve this then adding additional gears won't help your acceleration. It is for this reason that the typical Quaife/Hewland close ratio box has a long first gear -because the typical "short-first" found on road car gearboxes is too short -and simply creates too much force at the contact patch (i.e. it causes wheel spin too easily)

Without sounding like a broken record; The answer here is that maximising the use of the grip available is the name of the game -providing any more than that (with an ultra low gear ratio) is pointless as you are still limited by the grip. There is no magic formula using a "multiple ratio, instant shifting, constant torque" gearbox to overcome this grip issue.

I agree up to a point but why do any lower gears have to be used with torque levels from the engine that go over the grip curve?
If there is no reason then why cannot a number of lower gears be used?
If the shifts are constant torque, the larger number of gears used the closer it would bring the torque transfer curves (saw tooths) as near as dammit to the maximum possible grip curve.
Far better than clutch slip.
The only theoreticaly ideal gear ratio is 1: infinite, where there is no clutch and maximum torque is from stationary.
Voila, electric traction!!! In this case the torque is controlled (TC) using an electronic control systems, to be at maximum grip and no higher.
On my mini gearbox with very low (crawler) gears it was controlled with the right foot.

[machin]

24gerrard, on Jul 7 2011, 22:15, said:

So the purpose of the clutch is to slip away available torque until a speed is reached for a gear ratio that does not go over the 'grip' curve can be used?

No. That is a common misconception; The purpose of the clutch when used during starts is to temporarily increase the ratio between the engine speed and the road wheel speed -increasing torque available (at the driven wheels) at low road speeds and hence increasing the motive force at the tyre contact patch to fill in the yellow area of the curve below . The driver has to balance clutch slip and throttle to make sure he doesn't get too much force and go over the grip line -this would cause wheel spin and less forward motion.

24gerrard, on Jul 7 2011, 22:30, said:

I agree up to a point but why do any lower gears have to be used with torque levels from the engine that go over the grip curve?
If there is no reason then why cannot a number of lower gears be used?
If the shifts are constant torque, the larger number of gears used the closer it would bring the torque transfer curves (saw tooths) as near as dammit to the maximum possible grip curve.
Far better than clutch slip.
The only theoreticaly ideal gear ratio is 1: infinite, where there is no clutch and maximum torque is from stationary.
Voila, electric traction!!!

You can use lower gears if you want.. but (assuming the original "first" gear was appropriate in the first place) at full throttle these new lower gears will cause force at the contact patch to go over the grip line -unless you reduce the amount of throttle....
On this example (below) I added just one gear (orange) that was about 33% shorter than the original first gear, and it put the maximum motive force way above the grip line (I'm guessing that you'd need about 66% of full throttle with this gear to avoid spinning wheels in this example)... if you added a couple more even lower gears like this you'd need even less throttle in those gears to avoiding spinning the wheels. So my point is that additional gears won't add anything to performance (but will increase complexity of the gearbox).

Quote

On my mini gearbox with very low (crawler) gears it was controlled with the right foot.

Yes indeed, (you're earlier posts said that your special gearbox would not slip, but no matter, I forgive you ;) ) -so as you can see its still a balancing act you have to play. You either balance clutch and throttle with a "normal" gearbox, or you have a gearbox with more gears (read; more expensive and heavier) and you still have to balance the throttle.... or......

Quote

In this case the torque is controlled (TC) using an electronic control systems, to be at maximum grip and no higher.

Easier said than done.... the grip level is very much dependant on the road surface, ambient temperature, gradient, tyre pressure, etc etc.... getting electronics to work perfectly can be a major nightmare... that's why most 0-60mph road-tests are conducted with traction control off -its simply not as good as can be achieved by the driver.



I also want to make it clear that I'm not suggesting that a high multi-ratio gearbox can't be beneficial to certain engines -engines that are very "peaky" need to have lots of gears simply because they only work over a very narrow band. However the typical road-car derived engine, especially a modern 4 valve per cylinder engine, has a fairly decent torque curve width (which results in a nice fat Power curve), and really doesn't need more than 6 gears, and that's why the typical "motorsport" gearboxes have the ratios they do -"its horses for course" (as my old lecturer used to say!). For proof, look at the SBD 2 litre Duratec -in maximum tune it puts out over 300bhp naturally aspirated, and the torque curve is flat and wide giving a real fat power curve, amazing.

Edited by machin, 08 July 2011 - 06:30.

[gruntguru]

24gerrard, on Jul 8 2011, 07:15, said:

So the purpose of the clutch is to slip away available torque until a speed is reached for a gear ratio that does not go over the 'grip' curve can be used?

This might sound picky but a clutch does not "slip away available torque". The clutch simply allows a speed mismatch between drive and driven shafts while also transferring 100% of the torque from drive to driven shaft. Sure you can use the clutch to reduce the torque transferred to the driven shaft, but the mechanism for this is increased energy storage in the flywheel ie. You push the clutch in a little more to reduce torque -> the torque in both drive and driven shafts is reduced equally to a new lower level -> the engine speeds up because of the reduced load. If it speeds up enough it will reach the RPM where its torque output matches the clutch setting and hold those revs. This is the second phase of "torque reduction" as employed by top fuel dragsters with their slipper clutches.

The real (usual) purpose of a clutch is to allow the engine speed to be high enough to avoid stalling, at road speeds where the lowest gear available still requires the engine speed to be too low. Note that this condition will always exist, regardless of how low you make the lowest gear ratio. As Machin points out, it is beneficial to match the lowest gear ratio to the grip limit during launch conditions. The downside (and I think this is Gerrard's point) is this may require excessive clutch slipping or wheel spin until the vehicle speed is sufficient for the engine to produce enough torque to approach the traction limit with the clutch fully engaged (particularly with "peaky" race engines.)

[gruntguru]

machin, on Jul 8 2011, 08:47, said:

Easier said than done.... the grip level is very much dependant on the road surface, ambient temperature, gradient, tyre pressure, etc etc.... getting electronics to work perfectly can be a major nightmare... that's why most 0-60mph road-tests are conducted with traction control off -its simply not as good as can be achieved by the driver.

Half-decent traction control will outperform any driver. Unfortunately most traction control systems have trouble in the "yellow" area where clitch slip or wheelspin is necessary. The system may also have trouble transitioning from the yellow area to normal operation if the driver is employing (as he should) clutch slipping techniques in the yellow zone.

[bigleagueslider]

gruntguru, on Jul 7 2011, 16:14, said:

This might sound picky but a clutch does not "slip away available torque".......

gruntguru,

I would agree that an engine's friction clutch does not "slip away available torque". What it does is limit power transfer. The clutch slippage converts excess power into heat, via sliding friction. The excess power absorbed by the clutch at a given interval is defined by the transmitted torque (in ft-lbs) x the speed delta (in rpm) / 5252.

So what's important is power transfer. While the clutch may be manipulated to slip at a certain level of input torque during a standing start, that input torque level can be rapidly increased as the car's wheel speed becomes synchronized with the transmission input speed. While most cars can spin the tires at 2mph, just how many cars can also spin the tires at 100mph? The difference is due to power, not torque.

[gruntguru]

bigleagueslider, on Jul 8 2011, 13:51, said:

gruntguru,

I would agree that an engine's friction clutch does not "slip away available torque". What it does is limit power transfer. The clutch slippage converts excess power into heat, via sliding friction. The excess power absorbed by the clutch at a given interval is defined by the transmitted torque (in ft-lbs) x the speed delta (in rpm) / 5252.

All true but quite irrelevent to the point I was making.

bigleagueslider, on Jul 8 2011, 13:51, said:

While the clutch may be manipulated to slip at a certain level of input torque during a standing start, that input torque level can be rapidly increased as the car's wheel speed becomes synchronized with the transmission input speed.

No. The input torque will need to be roughly constant with increasing speed (in line with grip). The power required will of course increase linearly with speed.

[machin]

gruntguru, on Jul 8 2011, 05:33, said:

The power required will of course increase linearly with speed.

I'm with you on this... the job of the driver is to make sure it goes up linearly along the grip line; thereby maximising acceleration.

[24gerrard]

gruntguru, on Jul 8 2011, 00:22, said:

Half-decent traction control will outperform any driver. Unfortunately most traction control systems have trouble in the "yellow" area where clitch slip or wheelspin is necessary. The system may also have trouble transitioning from the yellow area to normal operation if the driver is employing (as he should) clutch slipping techniques in the yellow zone.

Traction control either using the right foot or a control system is a piece of cake with 'crawler' gears.

[24gerrard]

Quote

'gruntguru' date='Jul 8 2011,
The real (usual) purpose of a clutch is to allow the engine speed to be high enough to avoid stalling, at road speeds where the lowest gear available still requires the engine speed to be too low. Note that this condition will always exist, regardless of how low you make the lowest gear ratio. As Machin points out, it is beneficial to match the lowest gear ratio to the grip limit during launch conditions. The downside (and I think this is Gerrard's point) is this may require excessive clutch slipping or wheel spin until the vehicle speed is sufficient for the engine to produce enough torque to approach the traction limit with the clutch fully engaged (particularly with "peaky" race engines.)

Machin is correct in his conclusions, the main one being the added weight, complexity and packaging needs of extra crawler gears.
This is a major consideration in layshaft designs.

My Mini automatic clutchflite gearbox for quarter mile oval racing, was not built for the benefits of low 'crawler' gears to be achieved however.
It was built to make use of a more efficient geartrain than the layshaft type and to gain performance from rapid torque constant gearshifts that needed very little effort to achieve, either automaticaly or manualy by the driver.
The conventional practice with layshaft gearboxes fitted to short oval cars is still to use 'one' gear or two at a push.
This is a direct result of the limitations of the manualy shifted layshaft gearbox, which prevents the drivers from being able to shift gears in the time available.
My AP based automatic gearbox allowed up to five gears to be used in the same road speed range (and corners) as the one or two used before.
The performance increase was high and the benefits of better clutch control on the 'few' non rolling starts was also very noticable.

I concede that an F1 style auto/semi auto layshaft gearbox would equal the shift speed and control requirements.
It would still not be as efficient a geartrain however and would be way to expensive for short oval cars.
It would also not be strong enough at realy low ratios, this is another reason I chose the AP 'bevel epicyclic' train.
Short oval one ratio cars use second gear as a base gear with a low diff ratio.
My box matched the maximum engine rpm in this ratio, to the top gear in the AP with up to four gears evenly spread under it.
It went rather well.
Today I have a far better system ready for development.

Edited by 24gerrard, 08 July 2011 - 11:11.

[machin]

24gerrard, on Jul 8 2011, 11:48, said:

Traction control either using the right foot or a control system is a piece of cake with 'crawler' gears.

Not only does the theory disagree (theory says its the same whether you have "crawler" gears, or are using the clutch -you need to module the throttle to match the grip) my own experience, and that of my competitors doesn't agree with this view either.... My car already has a "crawler" gear since it is based on a standard road car gearbox, and therefore has a short first gear. Experience shows that 64ft time (the time taken from the moment the car starts moving to the time it takes to cover 64ft -a commonly recorded time on hillclimbs and sprints) is unaffected by starting in second. Also since this then requires an additional gearchange (at about 30 to 35mph -after the 64ft line) using the short first has a negative effect.

Indeed as has been stated on this thread many times -a common upgrade is to change to a gearbox which does not have the short first gear. Non of my competitors have suffered from extended 64ft times as a result of making this change.

(If you had an instant shifting gearbox this would remove the negative effect of the additional gear chaneg, but still wouldn't help with the issue of balancing the power to the grip).

Edited by machin, 08 July 2011 - 11:16.

[machin]

24gerrard, on Jul 8 2011, 12:02, said:

My Mini automatic clutchflite gearbox for quarter mile oval racing, was not built for the benefits of low 'crawler' gears to be achieved however.
It was built to make use of a more efficient geartrain than the layshaft type and to gain performance from rapid torque constant gearshifts that needed very little effort to achieve, either automaticaly or manualy by the driver.

In this application I can see the point of your mini gearbox -as you have said before:-

1, You use a highly tuned small capacity engine, which I'm guessing has a very poor power/torque curve, although produced a very healthy 140bhp (for such a small engine). So you need multiple ratios to keep it "in the power band".
2, The circuits are short, so changing gears can be a pain, -hence why the auto up-shift helps.
3, Your competitors you said used big V8 engines... probably with nice wide power bands -this meant they don't need the additional gears.

[24gerrard]

machin, on Jul 8 2011, 12:10, said:

Not only does the theory disagree (theory says its the same whether you have "crawler" gears, or are using the clutch -you need to module the throttle to match the grip) my own experience, and that of my competitors doesn't agree with this view either.... My car already has a "crawler" gear since it is based on a standard road car gearbox, and therefore has a short first gear. Experience shows that 64ft time (the time taken from the moment the car starts moving to the time it takes to cover 64ft -a commonly recorded time on hillclimbs and sprints) is unaffected by starting in second. Also since this then requires an additional gearchange (at about 30 to 35mph -after the 64ft line) using the short first has a negative effect.

Indeed as has been stated on this thread many times -a common upgrade is to change to a gearbox which does not have the short first gear. Non of my competitors have suffered from extended 64ft times as a result of making this change.

(If you had an instant shifting gearbox this would remove the negative effect of the additional gear chaneg, but still wouldn't help with the issue of balancing the power to the grip).

You wont know until you try it Machin.

[machin]

24gerrard, on Jul 8 2011, 12:24, said:

You wont know until you try it Machin.

I've tried starting in my car's 1st gear many times ... makes no difference to starting in second at slow speeds, and has a detrimental effect at 35mph because of the additional gear change.

Anyone can prove this... go out in your car (off the public road ) put it in second, give it loads of revs, slip the clutch and see if you can break traction -if you can then you don't actually need to start in 1st because you can evidentally create enough motive force to overcome traction without it! (for increased clutch life of your "daily" driver though you should start in 1st!!!!)

[24gerrard]

machin, on Jul 8 2011, 12:15, said:

In this application I can see the point of your mini gearbox -as you have said before:-

1, You use a highly tuned small capacity engine, which I'm guessing has a very poor power/torque curve, although produced a very healthy 140bhp (for such a small engine). So you need multiple ratios to keep it "in the power band".
2, The circuits are short, so changing gears can be a pain, -hence why the auto up-shift helps.
3, Your competitors you said used big V8 engines... probably with nice wide power bands -this meant they don't need the additional gears.

Not a direct comparison but close.
The car was a Hot Rod and was raced mainly against Ford Escorts with a limit of 1600 cc pushrod engines.
The Fords has an extra 20 to 25 bhp and we could out corner them but had less speed on the straits. (the conventional manual minis)
This was a benefit for the Fords, as any overtaking we made was usualy in the corners until I fielded my auto system.
Then I was usualy at least a lap ahead.

I did race against super stocks using large American V8s on a number of venues on occasion.
The drivers were very fair and realised the dangers to us in the event of a collision.
A solid steel chassis superstock would not do a mini much good on impact.
I also raced large saloons like Jaguars, Mustangs, and many others.
My mini always set faster lap times.
One of the larger saloons was responsible for loosing its rear end and spinning me backwards into the fence as I was overtaking it on the outside of a bend. The fence post ended next to my seat and I still suffer from back ache today from it. Impact was over 60 mph.
Oval racing takes tough drivers.

http://oi49.tinypic.com/28sr429.jpg

My three car hot rod team my car on the right, all 1430cc S motors full race.

[24gerrard]

machin, on Jul 8 2011, 12:33, said:

I've tried starting in my car's 1st gear many times ... makes no difference to starting in second at slow speeds, and has a detrimental effect at 35mph because of the additional gear change.

Anyone can prove this... go out in your car (off the public road ;) ) put it in second, give it loads of revs, slip the clutch and see if you can break traction -if you can then you don't actually need to start in 1st because you can evidentally create enough motive force to overcome traction without it! (for increased clutch life of your "daily" driver though you should start in 1st!!!!)

I fully agree and I would choose the same set up as you within the regulation restraints and the layshaft capability.
However, I was suggesting the use of a multi speed constant shift auto/semi auto box for the job, not just confirming that which we all already know about the downsides of using a low gear with a one to two wide ratio spread for competition.

[machin]

24gerrard, on Jul 8 2011, 12:51, said:

However, I was suggesting the use of a multi speed constant shift auto/semi auto box for the job

My point has always been that there is no performance advantage of using additional low ratio gears if you can already spin your wheels with the gear ratios you have....

...if you can't "just about spin your wheels" then your 1st gear is too long.

Even if I were designing a brand new gearbox I wouldn't add more parts if there were no performance advantage of doing so.... more parts = more parts to go wrong IMO. 1st gear should be as long as possible -but still short enough that it is just about able to break traction without too much clutch slipping.

Edited by machin, 08 July 2011 - 12:44.

[24gerrard]

machin, on Jul 8 2011, 13:42, said:

My point has always been that there is no performance advantage of using additional low ratio gears if you can already spin your wheels with the gear ratios you have....

...if you can't "just about spin your wheels" then your 1st gear is too long.

Even if I were designing a brand new gearbox I wouldn't add more parts if there were no performance advantage of doing so.... more parts = more parts to go wrong IMO. 1st gear should be as long as possible -but still short enough that it is just about able to break traction without too much clutch slipping.

You have a few problems choosing your first gear ratio then Machin.
For a start, if it has to be capable of 'just' spinning the drive wheels, there is no accurate way that you can calculate variations in road surface or weather conditions.
More ratios and less clutch slip is far 'more' predictable for a start.
It is also far more controlable in the real world.

[machin]

24gerrard, on Jul 8 2011, 13:55, said:

You have a few problems choosing your first gear ratio then Machin.

Not really; you set the gear ratio to give you a bit of a margin for dry road conditions. This is fairly easily calculatable.

Quote

For a start, if it has to be capable of 'just' spinning the drive wheels

Not really, a bit of a margin is more than acceptable, if you're a little bit over that, so what, you use a little bit less throttle.

Quote

More ratios and less clutch slip is far 'more' predictable for a start. It is also far more controlable in the real world.

My experience (and I guess even your own experience if you'll admit it) shows this not to be true -infact -starting in a higher gear reduces the sensitivity of the throttle application. A really low gear gives you too much force at the contact patch. A really low gear would be like trying to start on ice with a normal road car's first gear -not easy, so you use 2nd or 3rd instead.

Edited by machin, 08 July 2011 - 14:00.

[24gerrard]

I think you are 'playng' both ends here Machin.;)
You now say a 'bit of a margin is acceptable', when describing the calculation for wheelspin.
Both ways can't work, or allow a fair conclusion.
Which do you want, your fixed graphs using limited data, or the real world and a debate on driving skills and techniques?

With very low 'crawler' gears, the clutch can be 'dumped' with almost no slip at all (at tick over if you like in some applications).
This allows very fine use of the throttle for traction control, manualy or electronicaly.
It is only the inability to undertake gearshifts both fast enough and with constant torque transfer that prevents such low gear use with a layshaft gearbox of ordinary design.

Edited by 24gerrard, 08 July 2011 - 15:07.

[kikiturbo2]

it would be interesting to see your "crawler gear" solution, however as you make gearing lower, the "internal" moment of inertia (engine/transmission inertia) starts being more of an issue during acceleration..

[murpia]

24gerrard, on Jul 7 2011, 22:15, said:

Quote

The stepped fulcrum clutch goes a long way to making controlled clutch slip possible.

I thought I had read an AP press release announcing it, but I can't find it anywhere on their website.

Essentially it introduces a wide zone of slave cylinder position for a constant slip torque. If tuned accurately this slip torque is just above the expected tyre limit. Combined with a very 'stretchy' pedal torque map over the last 20% of travel in 1st gear, the driver can easily modulate the rear wheel torque as required.

Regards, Ian

So the purpose of the clutch is to slip away available torque until a speed is reached for a gear ratio that does not go over the 'grip' curve can be used?
Why?

No, the purpose of the stepped fulcrum is to limit the torque to a reasonably consistent value (with the clutch lever anywhere between 1/3rd and 2/3rds released).

The engine torque modulation means the engine revs can be controlled by the driver in a resonably consistent way.

So the launch proceeds thus:

Engine is revved to it's launch rev zone (start of power-band).
Clutch lever is opened to the slip region.
Rear wheel torque is then approximately controlled by the level of the stepped fulcrum torque, the various inertias and the friction characteristics of the clutch material.
(This seems to be a stable system, as there seem to be inherent negative feedbacks in the system that mean the driver can keep control - limiting wheelspin and / or engine rev rise).
Engine revs remain roughly stable.
Rear axle revs 'catch up' engine and driver releases clutch lever fully so clutch fully engaged.

Regards, Ian

[machin]

24gerrard, on Jul 8 2011, 16:04, said:

I think you are 'playng' both ends here Machin.;)
Which do you want?

I have never disputed the fact that the "ideal" gearbox would be a cvt, with 100% efficiency, be smaller, just as robust and weigh less than a convential 'box. This would allow the engine to put 100% of its horsepower to the roads at all times except when the grip is the limiting factor. This whole conversation started because you said that you could use a lower ratio gear to put all the engine's power to the road at low speed without spinning wheels. I hope that I have adequately shown both yourself and anyone reading this that it is not possible to put more power or torque or motive force to the road than is allowed by the grip, regardless of what fancy gearbox you have.

Quote

It is only the inability to undertake gearshifts both fast enough and with constant torque transfer that prevents such low gear use with a layshaft gearbox of ordinary design.

As I've shown mathematically a lower gear does not improve acceleration where you are grip limited anyway, and you can use the clutch to fill in the gaps at lower road speeds if necessary. My experience confirms this, but I implore anyone reading this not to take my word for it but to try it for themselves... can you make your car wheelspin from a standing start? If you can already do this it proves that you don't need a lower gear since your performance is grip limited anyway.

kikiturbo2, on Jul 8 2011, 16:16, said:

it would be interesting to see your "crawler gear" solution, however as you make gearing lower, the "internal" moment of inertia (engine/transmission inertia) starts being more of an issue during acceleration..

Indeed this fact was conveniently disregarded when I brought it up some time ago:-

machin said

must also account for the inertia of any parts which rotate on the car as a function of the road speed (wheels, tyres, props shaft, clutch, gears, engine etc). On a light weight car in low gears this can account for a significant proportion of the total value of the "m" in F=mA. The gearing matters because in low gears the engine/clutch etc turn much faster compared to the road wheels than they do in higher gears. You can work out what the equivalent "static" mass is for a rotating part using the kinetic energy equations of KE = 1/2mv^2 and KE = 1/2Iw^2. But for a typical car in low gears it can be around 20 to 30% of the static mass, dropping to 5to 10% in higher gears.

24Gerrard I don't think there's anything more to say on the subject...... I think we're boring everyone now.

Edited by machin, 08 July 2011 - 17:22.

[24gerrard]

kikiturbo2, on Jul 8 2011, 16:16, said:

it would be interesting to see your "crawler gear" solution, however as you make gearing lower, the "internal" moment of inertia (engine/transmission inertia) starts being more of an issue during acceleration..

Yes, you can use it to accelerate the vehicle without using engine power and without slipping the clutch.
Just think of all that stored flywheel energy that usualy gets burnt away with clutch slip.
With a realy low first you can drive off with high acceleration with no throttle on at all.
Then ease the throttle on just under that so important red grip curve.
Voila.

Edited by 24gerrard, 08 July 2011 - 19:22.

[24gerrard]

Question:

Why is it Machin, that a one manpower pushbike with very low gearing and a grip footprint smaller than my palm,
can out accelerate any car over 10 feet?

Must draw a graph.;)

Oh I forgot, is everyone getting bored?

Edited by 24gerrard, 08 July 2011 - 19:47.

[machin]

24gerrard, on Jul 8 2011, 20:38, said:

Question:Why is it Machin, that a one manpower pushbike with very low gearing and a grip footprint smaller than my palm,
can out accelerate any car over 10 feet?

Push bikes? Now we're talking! Best invention ever IMO.

Easy. Better weight distribution and lighter weight and softer tyres means that the grip curve for a push bike is actually steeper than that for a car relative to its total power:weigt ratio. That means that the push bike can "cope" with a much lower gear (relatively) without breaking traction (although believe me, you can spin tyres on a push bike so there is still a limit to how low the gearing needs to go.. going lower than that won't improve acceleration; same as the car -the exact same rules of physics apply!!!!). The low inertia also helps. That means you can accelerate faster than a car for a few feet. However, you are very soon limited by the actual power that a man on a pushbike can create and not by the grip, and that's when the car goes past you -as it has much better power to weight, despite being grip limited for another 50ft or so.

Do you want a graph? Because I'm "a bit keen" on bicycles I even have my own power output chart (what can I say, I'm a geek)!

Edited by machin, 08 July 2011 - 20:35.

[Fat Boy]

machin, on Jul 8 2011, 21:33, said:

Do you want a graph? Because I'm "a bit keen" on bicycles I even have my own power output chart (what can I say, I'm a geek)!

I'd like to see that. What kind of wattage can you put out? I'm good for 1160 watts for 5 seconds, but it falls off pretty quickly after that, and that's starting from a 110 rpm cadence.

machin, I have to say, I am terribly impressed with the depth of your patience. You not only have a perfect grasp of the issue, but the ability to not get fed up with a complete imbecile. Well done.

[gruntguru]

24gerrard, on Jul 9 2011, 05:38, said:

Why is it Machin, that a one manpower pushbike with very low gearing and a grip footprint smaller than my palm, can out accelerate any car over 10 feet?

Any car? Come on! I don't even need to go to dragsters to blow that statement away. Fit any AWD hot hatch with a set of soft slicks and bye bye push bike.

Top fuel dragster? 6G+ for the first 10 ft = 0 - 10ft in 0.3 seconds.

I think a sprinter would beat a bicycle over 10 feet.

[Tony Matthews]

Fat Boy, on Jul 9 2011, 03:09, said:

machin, I have to say, I am terribly impressed with the depth of your patience. You not only have a perfect grasp of the issue, but the ability to not get fed up with a complete imbecile. Well done.

[Magoo]

gruntguru, on Jul 8 2011, 23:58, said:

Any car? Come on! I don't even need to go to dragsters to blow that statement away. Fit any AWD hot hatch with a set of soft slicks and bye bye push bike.

Top fuel dragster? 6G+ for the first 10 ft = 0 - 10ft in 0.3 seconds.

The first 60 feet in .86 seconds. With significant wheelspin. Since you clever lads are so desperately in need of something to do, maybe you could nail down how that is accomplished. Show your work.

http://www.youtube.c...feature=related

[carlt]

Magoo, on Jul 9 2011, 12:45, said:

The first 60 feet in .86 seconds. With significant wheelspin. Since you clever lads are so desperately in need of something to do, maybe you could nail down how that is accomplished. Show your work.

http://www.youtube.c...feature=related

I always found slipping the tyres instead of the clutch as a quicker way of getting off the line [ 1380 BMC 'A' series, twin cam head - British Hillclimb - ie not a lot of Power or Torque !!! ]

sorry , thats as far as my 'workings' go

[24gerrard]

Tony Matthews, on Jul 9 2011, 08:01, said:

I am glad you both agree, that tells me a great deal.

[Canuck]

There's some merit in what 24 is saying about crawler gears. Anyone who has used the "low range" selection of a 4 wheel drive vehicle's transfer case has been there. The torque output becomes massive yet there's less wheelspin even on low-traction surfaces because the exceedingly low ratio provides for a very low wheel rpm to engine rpm.

I grew up just outside the arctic circle in northern Canada and learned to drive in the snow as my birthday falls in the middle of winter (not to mention snow from October to late April). I've a pretty solid background of driving in the stuff in all sorts of conditions and scenarios from a high-powered, low-traction Hotrod on the frozen highway @ -50c to the aforementioned 4-wheel drive in low range, in my case with a small snow plow attachment (that could double as a steering input device while off the ground at highway speeds :-) ). Anyway, I spent more than the odd night plowing snow with the truck - doubly traction-challenged environment where you're operating on a frozen pavement surface at best (snow-packed ice more likely) and trying to push a large amount of heavy snow around. Like a tractor pull, the farther you managed to drive with the blade down, the heavier the load got as the snow piled up in front of the blade. Despite having more than enough power to spin all 4 tires in 3rd gear (in the snow obviously - the 300/6 wasn't exactly a monster), the traction solution wasn't a higher gear, but using the low-range selection of the transfer case. A full-throttle mash in low-range / 1st gear would try to snap your head off it's spindly post but just for an instant and then it was all over - you might travel all of 6 or 8 feet in that gear before you'd swept through from idle to redline and were out of breath. A steady application of throttle would leave you chugging along at a crawl, engine reving at 4000 rpm and snow piles being pushed where needed. Normal tractive force was enough to keep the tires from spinning in this low gear except with the largest of resistive loads applied to the plow. I find the notion of starting in 2nd gear in low-traction situations as was mentioned above amusing. Any normal road car can easily spin it's wheels in a winter situation even at highway speeds and the higher the gear, the higher the instantaneous delta between your tires and the road. In fact as a kid, the man who hooked me on cars used to put on quite a show by running his LS-7 powered 1st Gen Camaro up to 7000 rpm and dumping the clutch with the trans in 4th. The ensuing violence would literally liquidate the rear tires (and kill any mosquitoes in a 20 block radius) and left a mighty impression on a 5 year old boy.

Edited by Canuck, 09 July 2011 - 15:41.

[carlt]

Canuck, on Jul 9 2011, 16:36, said:

There's some merit in what 24 is saying about crawler gears. Anyone who has used the "low range" selection of a 4 wheel drive vehicle's transfer case has been there. The torque output becomes massive yet there's less wheelspin even on low-traction surfaces because the exceedingly low ratio provides for a very low wheel rpm to engine rpm.

I can understand the principle with the crawler gears [ I do a lot of off road competitive driving ]

But as I asked in an earlier post -

If 24's revolutionary gearbox was So stunningly good and gave such a massive competitive advantage , Where are the thousands in use today ? [ remember this was developed and running in 1978 ! ]

I suspect there are too many unmentioned negatives involved [ don't mention cost of production - this is motorsport - cost is generally irrelevant when a winning advantage is concerned

[24gerrard]

carlt, on Jul 9 2011, 17:31, said:

I can understand the principle with the crawler gears [ I do a lot of off road competitive driving ]

But as I asked in an earlier post -

If 24's revolutionary gearbox was So stunningly good and gave such a massive competitive advantage , Where are the thousands in use today ? [ remember this was developed and running in 1978 ! ]

I suspect there are too many unmentioned negatives involved [ don't mention cost of production - this is motorsport - cost is generally irrelevant when a winning advantage is concerned

I think I explained why.
I was working up a 15 speed auto/semi auto gearbox for F1 when the regulations where changed to allow only 7 stepped ratios.
I suggested the electronic control of layshaft dog engagement systems and John Barnard used some of this information that I discused at Ferrari in the late 80's and early 90's, to develop the first 'Ferrari' automatic layshaft system for Nigel Mansel's car.

There were competition applications other than F1 and British Leyland loaned me a number of vehicles to modify.
John Davenport was their competitions manager at the time and was a great help.
I also built a Range Rover with help from British Leyland in which we undertook record trips across the Sahara.
I also build a road mini with electronic gear shifting in 1978, far earlier than the current ones were even thought of.
I also understand the benefits of crawler gears in low traction environments from work I did on the Range Rover powertrains.
If you want to read up on the 'first' practical 4x4 system, check out the Ferguson system and the Jenson FF.
My friend Ginger Baker had three of them and I worked on all three. One was driven to North Africa in 1973 and was a far better set up than Audis Quatro, which was a bad copy of the 4x4 system on the Jensen.
The planetary gear sets I modified and developed would still be capable of better torque transfer than any current layshaft gearboxes with flap or button shift.
All the prototypes had promise.
British Leyland then closed.

I retired from both motor sport and gearbox development in the mid 90's.
I was for one thing annoyed because F1 had become a spec formula that only benefited engineers in aero, the rest had been emaciated.
I have watched all the attempts by manufacturers to apply electronics to vehicles and reduce the potential for driver skill and ability with amusement for nearly two decades.
All that has happened is that road cars now look all the same and the driving experience has been all but destroyed.

My interest today is in hybrid and electric powertrains, which I see as the future both for road and competition.
The transmission side of this 21st century vehicle development has huge scope for new ideas.
I have a system being considered at the moment.

[carlt]

24gerrard, on Jul 9 2011, 18:28, said:

There were competition applications other than F1
All the prototypes had promise.

thank you for you breif resume 24

I was not questioning the fact you had a viable working product - more the fact that If it was such a competitive advantage Someone surely would have taken on the production for motorsport application ?

are you saying you didn't approach the likes of Hewland / Quaife et al ,

you simply retired ?

Or are there a few negatives to this planetary gearset , instant gearshift wonderbox


Apologies for the Thread derailment -

[gruntguru]

Magoo, on Jul 9 2011, 21:45, said:

The first 60 feet in .86 seconds. With significant wheelspin. Since you clever lads are so desperately in need of something to do, maybe you could nail down how that is accomplished. Show your work.

acc = 2 x dist/(t x t) = 2 x 60 / (0.86 x 0.86) = 162 ft/s/s = 5.1 G

So - it is accomplished by the equivalent of 5.1G constant acceleration for the first 60 ft. With no aero effects (drag, wing-downforce or exhaust downforce), no dynamic effects (vertical weight transfer due to tyre growth or rearward weight transfer under acceleration) but with 100% of vehicle weight on the drive wheels, this would require a tyre friction coefficient of 5.1.

If we consider exhaust downforce reputed to be 1000 lbs on a 2,300 lb car, the required friction coefficient drops to 5.1 x 2300/3300 = 3.55.

If we consider wing downforce - reputed to be 12,000 lbs at 324 mph (Wikipedia), the required friction coefficient drops to 3.32. (Can't show the working for this step as I used a moderately complex spreadsheet to do the calcs).

If we consider aerodynamic drag (estimated at 65% of the DF ie 7,800 lb at 324 mph), the required friction coefficient increases to 3.34 which shows how little effect aero drag has in "drag" racing. The power required for this 60' time is about 3,000 hp. Increasing the power to 8,000 hp (which does nothing for the traction-limited 60' time) gives the following (modelled) stats.

400m time - 4.17 sec
400m speed - 324 mph
60' time - 0.86 sec
60' speed - 100.5 mph
Absolute top speed 340 mph. (Removing the wing and fairing the tyres and engine would probably double that figure)
Launch acceleration - 4.7 G
Lowest acceleration - 0.6 G (at end of run doing 324 mph)
Peak acceleration - 8.8 G (after 1.2 sec, 123 ft, 158.5 mph) this is (theoretically) where the slipper clutch should lock up as the car transitions from "traction-limited" to "power-limited". In reality the clutch locks up near peak torque RPM as the car has to complete the run in the same gear (I think)

It is possible to produce those 60' times with lower tyre friction coefficients if the contact patch normal force can be momentarily increased at launch. Many classes of drag car do this by "jacking" - momentarily raising the centre of gravity at launch - using either suspension design or tyre growth (or both). I don't know if a coefficient of 3 is realistic but I wouldn't be surprised.

EDIT. BTW "significant wheelspin" needs to be kept under about 20% of wheelspeed or grip goes out the window. Most slick tyres make optimum longitudinal grip at about 10% slip.

Edited by gruntguru, 10 July 2011 - 23:11.

[machin]

Nice workings Gruntguru!

Back to the subject of crawler gears momentarily; the thing is travelling at a constant 2mph (crawling) and full bore acceleration are different beasts... The answer to the question: 'can lower gears improve low speed acceleration of a grip limited car?' is no. The average racer can balance the throttle and clutch to maximise use of the grip, so why have a heavier gearbox?

On the crawler box; some may say: 'if it doesn't spin its wheels what harm is using full throttle?' well in an acceleration case it would spin its wheels if it was asked to try and accelerate faster than the grip. Imagine a 100 gear launch gearbox... In first gear full throttle is applied and the wheel spins 1mm more than the car moves, so the gearshift changes up a gear 'slightly' early, in second gear the same thing happens, but now the slip is 10mm, 3rd gear, 100mm... Etc etc and 'voila' (to coin a phrase) full-on wheel slip is developed. 'use a traction control system!' I hear you cry? Yes indeed, but what acceleration rate are you limited to in order to avoid the runaway situation? You guessed it: the level dictated by the grip....

[carlt]

gruntguru, on Jul 10 2011, 08:31, said:

EDIT. BTW "significant wheelspin" needs to be kept under about 20% of wheelspeed or grip goes out the window. Most slick tyres make optimum longitudinal grip at about 10% slip.

is this a general figure for 'slicks'
or is it for 'drag slicks'

[24gerrard]

I completely agree Machin as I do with GGs figures for the dragster.
Interestingly, I had a 'Herridge' framed dragster in which I ran a number of engines.
A Chevy 289 cu in a Ford 351 cu inch and a 1000cc supercharged Cooper S sngine on one of my Ap boxes.
The Cooper S was faster over the first 60 feet.
Of course that was 30 years ago.
Modern fuel dragsters and funny cars have very well developed tyres, clutches and gear systems.

[24gerrard]

Quote

Can lower gears increase acceleration of a 'grip' limited car?

Of course not! Daft question, 'grip limited' presumably means what it says.

The question should be.
Can lower gears continualy achieve the maximum acceleration of a 'grip' limited car?


Conventional high gearing at start, can only achieve the maximum possible acceleration, if everything in the powertrain works as designed and the driver retains full control of it and every other outside variable.
It is rarely achieved by the established and accepted means but is far more likely to be achieved most of the time using lower gears.

It is a bit like aero in F1.
If the majority are brainwashed enough to accept that aero is the greatest thing in F1, rather than the main thing that is dragging it down, then it is very difficult to prevent the lemmings going over the cliff.
Right Tony.

Edited by 24gerrard, 10 July 2011 - 15:48.

[gruntguru]

carlt, on Jul 10 2011, 19:42, said:

is this a general figure for 'slicks' or is it for 'drag slicks'

I am only familiar with circuit racing slicks. Not sure about drag slicks but I would guess they fall in the 10% - 20% range.

[GrpB]

Magoo, on Jul 9 2011, 11:45, said:

The first 60 feet in .86 seconds. With significant wheelspin. Since you clever lads are so desperately in need of something to do, maybe you could nail down how that is accomplished. Show your work.

Ooh, I know this one:

1) Clutch guy covers clutch assembly, takes covered assembly into trailer
2) Chanting, chicken squawking that ends very suddenly, strange smells (incense?)
3) Clutch guy comes back out, clutch goes in, fuel car does 60' in 0.86 sec.
Note: I think I've seen some stray bloody feathers on the bottom of clutch guy's shoes.

Well, am I right?

[gruntguru]

I have seen the traction curve! No human could program a pneumatic circuit and a handful of solenoinds - to clamp a slipping clutch - to follow that traction curve - to pull that 0.86 60' time. It has to be witchcraft.

Yes you are right.

[24gerrard]

gruntguru, on Jul 11 2011, 23:38, said:

I have seen the traction curve! No human could program a pneumatic circuit and a handful of solenoinds - to clamp a slipping clutch - to follow that traction curve - to pull that 0.86 60' time. It has to be witchcraft.

Yes you are right.

Bet I could do it with electric traction and my ESERU.
Hehehe.
I must look around for my old witches hat I used to wear in the paddock at Santa Pod.
One run at Samhain that should do it.

Edited by 24gerrard, 12 July 2011 - 07:04.

[faaaz]

machin, on Jul 2 2011, 16:13, said:

Ok, so I thought I might have a go at helping some people out with the power vs torque thing.

An engine/motor etc essentially just wants to accelerate its flywheel (and any load attached to it) as fast as possible until it can't accerlerate it any more because it either can't produce enough effort or it runs out of revs (reaches its rev limit). We can describe its ability to accelerate its crank shaft (and any load attached to it) in one of two ways; either its torque curve, or its power curve. You can use either, it doesn't matter, the result will be the same but the maths inbetween is obviously very different.

The thing to bear in mind is that it is the Power or the Torque at the road wheels which is important, not at the flywheel.

Simple things are beautiful, right? Well the beauty with power is that it is the same at the flywheel as it is at the roadwheels (if we neglect losses due to transmission efficiency -which affect power or torque in the same way so can safely be ignored for the purposes of this discussion). This makes comparisons between cars with different engines very easy.

The "problem" with torque is that the torque at the road wheels is affected by the gear ratio between the road wheels and the engine flywheel, and that makes comparisons between different engines a bit more difficult. Not impossible, just more difficult.

Lets take two cars, both travelling at a road speed such that their road wheels are turning at say 1000rpm. Now lets say one car produces 100lbft at 2000rpm at the flywheel. In order to match 2000rpm at the flywheel to the 1000rpm wheels the gear ratio between the engine and the road wheels must be 2:1 (two turns of the engine for one turn of the road wheels). That 2:1 gear ratio means the flywheel torque is multiplied by 2, so at the road wheels it has 200lbft to accelerate it.

Now take the second car, also travelling at a road speed such that its road wheels are turning at 1000rpm. Lets say that its engine has only 50lbft of torque, but it produces it at 6000rpm. In order to match the 6000rpm to the 1000rpm road wheels it needs a gear ratio of 6:1 in betweeen. That 6:1 ratio means the flywheel torque is multipled by 6, so it actually has 300lbft of torque to accelerate the car. Since that is more than the first car's 200lbft it will accelerate faster.

Hopefully that has shown that it is dangerous to compare the flywheel torque of one engine to another, unless you also know at what speed that torque is produced. Even knowing the speeds doesn't help instantly because you have to do a little multiplication in your head.. is 200lbft at 4500rpm better than 195lbft at 4800rpm..? hang on let me just get my calculator.... The beauty with power is that the calculation is already done for you since Power is simply (Torque) x (RPM at which that Torque is produced).

So lets take the same two cars again, but look in terms of power... the first one has 2000rpmx100lbft = 200000 lbft.rpm or divide by 5252 to get the bhp (38bhp). The second one has 6000rpmx50lbft = 300000lbft.rpm again divide by 5252 to get BHP (57bhp). Again, the second car has more horsepower and hence can accelerate faster. Different method, same result.

The final point to bear in mind is that the peak torque or power figures only give us the acceleration at one road speed for each gear that is fitted to the car (so peak power or peak torque in a 6 gear car only determines the acceleration at 6 different road speeds). Again, taking one of the cars above (I'll choose the one which accelerated faster since I like fast cars!)... for the same 6:1 gear ratio in order to know what power or torque is available at a road speed equivalent to 900rpm at the road wheels we need to know the engine's power or torque at 5400rpm (900rpm/1000rpm x 6000rpm), for a road wheel speed of 800rpm we need to know the power or torque at 4800rpm (800/1000 x 6000rpm) etc etc.

I blame the motoring press and the manufacturer's glossy advertising for the majority of the confusion since they always quote peak power and peak torque figures (basically equivalent to starting to speak in english and then finishing to speak in german -both valid forms of communication, but confusing if you start in one and finish in another). My preference, since it is easy to compare one car to another would be for manufacturer's to quote a peak power figure, and also a second power figure at say 50% of the peak power revs. This would allow you to make a much easier comparison between cars, regardless of whether one revs to 20,000rpm and the other to only 2,000rpm. The problem is that diesel manufacturers love telling us that their engines can make twice the torque of an equally sized petrol engine... do they also know that the typical cyclist can generate more torque at the pedals than a 600cc sportsbike engine can make at the flywheel???!!!

I've got a little calculator-thing on my website with a few examples to show the effect of different engine output curves on the power or torque available at the road wheels.... which hopefully might be further illustrative....

http://www.competiti...ower_Torque.htm



Hope that's helped clear things up for some people?

Thanks mate.