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CART, F1, and rev limiter like throttle

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obanion

Automotive
Jan 1, 2004
101
Do modern champ car and/or F1 engines use a throttle?

I noticed they seem to be either in full power mode, or on some some of rev limiter. Coming out of the pits, they are bouncing off a rev limiter to stay under pit speed, rather than just having less power output from a mostly closed throttle butterfly. Also, they don't seem to idle steady either, seems like a rev limiter is used to keep idle speed.

Also lack of any blow off valve (never heard any anyway) on the champ car turbo engines leads me to think maybe they don't have a throttle.

Is this perhaps a suitable way to run throttleless, on a drag strip car? Obviously not very feasible for driving to work.

The idea is like this. Fuel injection events are set to full or slightly leaner than stoich. Throttle input (electronic), would incrementally control a soft fuel rev limiter. At 0% throttle, 60-70% of the fuel injection "squits" would be skipped, keeping the engine at a idle speed. As you increase throttle input, the % of skipped squirts would go down, increasing power output. By 100% throttle, there would be no skipped squirts.

Would operating a engine this way damage it from the unbalanced operation? Or would it be ok as the skipped squirts will move around between cylinders constantly?
 
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You've reinvented the hit and miss governor, used on stationary gas engines.

When these overspeeded a link is pulled out of the injector drive, so the engine gets no fuel for that cycle.

At a rough guess you'll only be firing about once in every 4 or 10 opportunities, ah except that you will be pumping a lot of air, that might put the load up.

Very interesting idea.







Cheers

Greg Locock
 
I have read in a couple of throttleless experiments, that the increase in compressive work is offset by a greater gain by eliminating throttling losses. So if anything, efficiency should go up a few %.

I just watched F1 qualifying, and paid close attention to the engine note as they entered the corners and backed off the throttle. The engine note changed a lot, getting "rougher," indicating a "hit and miss" load control. Not to be confused with the rough note of traction control, which is rougher still, when they are coming out of the corners.
 
One additional thought. When the term of "compression work" is considered in a engine, that's the work required to move the piston from BDC to TDC on the compression stroke, not counting any work of expansion....correct? If you were to have NO FUEL, and the compressed air is then allowed to expand again in the cylinder, how much work would it create? It will lose some energy from heat transfer, but I'd think 50-80% of the work put into compression, would come back from expansion in this "no fuel power stroke."
 
I imagine a most of the compression energy is regained from expansion, with a little lost to heat transfer, but some is also lost to increased friction in the rings, as the cylinder pressure forces them harder against the cylinder wall.

I have no data nor real feel for the numbers here, but intuition tells me is is quite low in the overall scheme of things.

I am at a bit of a loss as to why throttle-less speed control is seen as an advantage here, as there are no losses at WOT (at least with slide throttles), and part throttle is a deliberate loss in efficiency, so why worry about the loss in efficiency then, unless chasing fuel economy. The part throttle fuel economy savings in an application where most time is spent at WOT would be very small, but I guess cuts a little weight from the car with a full fuel load aboard, and reduces refuelling time by maybe less than 0.10 sec or something like that.

I guess there is a slight weight saving in the manifold and a slight cost saving re investment and maintenance, once the original software is developed.

I expect, as to whether or not I just contradicted myself lies in the detailed analysis of some very marginal numbers.

Thats my 2 cents worth, and I guess it's a two way bet. [ponder] [yinyang]

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
 
Someone with a fuel injected car could get a very quick estimate of the effectiveness of this, just remove the wires to all but one injectors and see how fast the engine will run at full throttle.

Your emission control will be stuffed as you'll have too much oxygen in the exhaust, so only do this in open loop.

Cheers

Greg Locock
 
Oh I have a better way of testing it. The fuel management computer in use by many people (AEMPro), can at least currently be tested. Set the rev limit to 1500RPM, set the Cut rate to 80%, floor it, and adjust the cut rate up and down and see how it changes the acceleration, sound, and feel of the motor.

For race cars with individual air stacks for each cylinder (most hi-po NA motors), this would remove the need for 6-12 little throttle bodies, and all the flow balancing needed as well. This would make individual stacks cheap and easy, instead of complex and expensive. The flow increase without the butterfly in the center would be a couple % I'd think.

Would run cooler, as more air is being pulled through the motor acting as a internal radiator.

You wouldn't need any form of idle control motor. On a turbo car, the BOV wouldn't be needed anymore.

I figured out the frequency of skipped pulses in average use, and it would be enough (cruise would probably drop out 40-60 pulses a second) that it wouldn't cause a uncomfortable vibration. The engine note would just be funny.

I do realize this would make any cat converter stop working, but it's not intended for cars with converters anyway. It would probably "cheat" through a emissions test, with all the extra air to dilute the exhaust gasses.
 
For a drag race car, I expect you only really need start, idle, staging and full throttle settings.

If you have access to program your ECU for speed control like performance to control staging, I guess the ECU can handle start and idle at no throttle, staging at first click, then hand over to traction control at second click.

Is traction control legal in the class you intend to run.

This would also reduce the load on the rods, rod bolts and pins on lift off at high rpm, thereby allowing either slightly higher red line or slightly lighter components in the reciprocating parts and crank.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
 
Well I'd want the ability to drive the car on the street. What I meant by drag car is that a certain level of macro user unfriendlyness is acceptable to me. Since the level of cut is quite adjustable, I'd think it would be suitable under all street situtations. It may be a little rough and vibrate a bit in certain very low load conditions, but I accept that.

I didn't think about the throttling strain on lifting at high RPM. Good point. Throw another thing in the positives column.

I don't plan to run any class at this point. Just gonna go for ET bragging rights, and get noticed for doing things a little different. The car will certainly have a distinctive tone if I used this method.

Gonna ask one last time, anyone think there is some inhenently bad thing in concern of wear about running it in this high speed "hit and miss" style?
 
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