Some winter discussion

[Nigel]

This is just some thought for the winter season, even if I knew exactly how to do it, I don’t have the money or expertise to build it. But anyways, for discussion here is something to think about. Fluid couplings are routinely used in industry with variable speed control. The fluid coupling is typically used in constant input speed applications. The fluid coupling also does not multiply torque, but has better coupling efficiency then a torque converter….

I was curious if a similar approach has been used to vary stall speed in an automotive torque converter application as has been used to vary speed in a fluid coupling. A fluid coupling will vary the amount of fluid in the coupling with a devise to drain the fluid to a certain level, which can be varied continuously. The concept actually is used by FB Performance(found via a google search), but with a different implementation. The feed to the torque converter has a step control. So you can stall at one speed, deactivate a solenoid which increases the fluid feed to the torque converter, and reduce the stall and lower the coupling rpm.
http://www.fbperformance.com/Product-Release-Blog/2004/4/Variable-Stall-Control-TM

My thought, an enhancement to the FB performance system would be to continuously modulate the feed so that you could hold a preset rpm. With a turbo car running a large turbo, you could hit the gas, engine comes right up to a preset rpm, and then modulate the fluid flow into the torque converter to hold the rpm as the boost increases. Once up on power, you could allow full normal flow, or tune for the launch.

What you would probably sacrifice is some lost power(due to slip and reduced torque multiplication) on the start with a reduced amount of fluid in the torque converter, but as soon as you hit with full flow, you get it back. Depending on how much power you are making, may not be a draw back.

With a purpose built design you may be able to build a lower rpm coupling capability with the ability to quickly stall a large turbo. Maybe somebody is already doing something similar?

This leads into the next point. If you could practically apply and spool a large turbo, you may be able to use one in which you can hit the crossover point, make more boost pressure then the exhaust back pressure. At this point, instead of having net pumping losses by pumping against more exhaust back pressure, you would have a net pumping gain on the intake stroke with a higher manifold pressure than atmospheric and higher than the exhaust back pressure(better recovered exhaust energy). This also opens the door to different cam grinds and probably a host over things I have no idea about.

Any thoughts?

 

[Gene Van Horn]

Id love to comment, but i have no idea about anything you wrote in that paragraph.

 

[69RSCLONE]

Thought makes sense, but I don't think it would be possible using a standard 2004r trans. GM did do something similar to the th400 back in the 60's called a switch pitch converter. Solenoid switched fluid travel in the converter allowing 2 different stall speeds. If it worked out like it should they would still be using it. As for completely redesigning the coupling ability and make it work with the original fluid passages I don't think it would ever be economical for the gain you would see. You would be better off designing a variable geometry turbo system that would build boost at low rpm and top end. Listen to a new tractor trailer, they sound like they are building boost at idle. They redirect the exhaust to spin the turbo at low flow and open up as exhaust flow increases so there is low restriction like a large turbo. Best of both worlds

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[Nigel]

The thought here is just to dig in a little on what makes a car quick, what are the limitations, and what can be improved. The OEMs spend millions upon millions developing technology, so I would not expect any more than hopefully some interesting discussion. The NLU converters are doing a pretty good job with out the fancy stuff, so just thinking down the road of what an optimal setup might be able to do, and what it would look like.

The ideal would be to have a drag car with a motor that sat at peak horsepower, and the transmission varied and was able to put it all down from start to finish with the motor never coming off of the peak. That is not possible. Tradeoffs have to be made in any design. The VVT technology for an all out drag car probably won't get you there. You need mass flow and velocity to develop the shaft horsepower to drive a turbo. Picking a turbine that gave max power at steady state WOT would have a lot of lag. Picking a converter to spool it would give a converter that would likely not couple well in the rpm range of peak power. Developing a system that allows a turbo to be better optimized for WOT performance with a converter that couples well in the correct RPM range and can spool it quickly enough for the launch.

One of the magazines did a test awhile back on compressed air supercharging, using high pressure air bottles. On 8 psi of manifold pressure, they doubled the power output of a small block chevy. Went from 400ish to 800ish on the power, no other changes other than fuel and timing. The discharge was very cold, but not enough to account for doubling power with 50% more manifold pressure. My guess is they got a good bump from eliminating pumping losses and improved fill and scavenging. Getting back pressure lower than intake will give you some of the same benefits with a turbo, just not the really cold intake temps.

The other benefit to being able to tune the stall speed is you can control the operating speed of the engine with the torque converter at the line and during the launch. You could actually tune between shifts, but I don't know how efficient a partially filled converter is. Once you have this ability, the torque converter design could be further optimized given the new tuning lever. Maybe unforeseen gains there.