Question on sprint car transmissions 1

[ebola]

Hi.Im looking for transmission solution for compact race car.And I found interesting transmission for sale on ebay, wich is not realy suitable for me, but very interesting as a device.It was sprint car variable torque multiplicator, just one gear, like direct drive coupled with pump and torque converter.Owner of the transmission told me, that it has torque multiplication of 2.5:1 ratio at low speed, wich comes to 1:1 in linear while speed of vehickle is increasing.I was looking for info at internet about these transmissions, but couldnt find any decent technical explanation, on how converter multiplies torque. As much as I understand, what converter does, it just "slips" until certain impeller speed is reached (stall speed), and then it "locks" at some point(I fully realise its not 100% lock in conventional turbine).
So desired stall speed usualy is either low for efficient drive or higher for max motor torque speeds, but its very difficult for me to realise, that is does multiply torque in any similar way as conventional gear ratio transfer does.
It is simple to understant for me,that 2.5 turbine revolutions via hydraulic effects transfers enough torque to turn output wheel once, and since output shaft load decreases(with vehicle speed increase), ie there is lesser resistance between turbine and stator, and it makes transfer come to 1:1.But I dont see there any torque multiplication!? Its just a slippage, ordinary slippage in mechanical way! I do hope I dont know anything about these devices, and I need more knowledge, because these hydraulic direct drives look very symphatic for me, and Id like to make one suitable for my special case.
If you guys anybody would give me some link, or guidance to any usefull technical link about these things, Id appreciate very very much. Thanks.Andrius

 

[BrianPetersen]

What you have seen is nothing special. Every torque converter in every conventional automatic transmission has a torque-multiplication when the output shaft is held stopped or is operating at a low speed.

I think what you are missing is the torque reaction from the stator. Visualize the fluid from the input pump turbine being flung in a "forward" direction. The output turbine takes that "forward" flinging fluid and changes its momentum (this is where the output torque is coming from) so that the fluid is now flinging "backward". The stator takes the "backward" flinging fluid and bends the flow so that it is now flinging "forward a little bit". Then the input turbine only has to change "forward a little bit" to "forward".

The torque multiplication is the maximum with the output turbine held stopped. As the output turbine accelerates, there is less and less "backward-flinging" on the inside (discharge) of the output turbine that the stator can change the direction of, so there is less and less torque multiplication. Eventually the fluid coming off the turbine is spinning "forward" fast enough that the stator can't change its direction any more. Beyond this point, the stator (which is mounted on a one-way clutch) begins freewheeling. At this point, there is no longer any torque multiplication, and the device operates as a fluid coupling.

Torque converters are nowhere near as efficient as gears, neither in torque-multiplication mode nor in coupling mode.

 

[BrianPetersen]

By the way, look up "torque converter" on howstuffworks.com - there are some decent photos and explanations there.