Torque Converter As Variable Ratio Drive?

[aiboart]

I have read somewhere that the torque converter behaves effectively as a variable ratio drive (torque multiplier) as well as a fluid coupling.

Would anyone care to confirm, debunk and or explain if and when this occurs?

Regards,

aa

Edited 24/04/05 12:16 AM by aiboart

[YOOT]

that's what they supposed to do, all autos are the same. Only at certain points though, it locks up in 3rd and 4th like a manual.

The torque multiplying effect is what slipping the clutch on take off in a manual does.

[Turbo6man]

Yes, that is EXACTLY what a torque convertor is.

The maximum multiplier effect occurs under full load at stall speed of the convertor and is theoretically 2:1 or 100%. In practice it is less due to heat loss, friction, oil compression and aeration, among heaps of other things.

Generally the multiplier effect during normal driving is less than 15%.

When the torque convertor locks up, as the Ford does in third and fourth the multiplier is 1:1 or zero%. The new six speed auto has the ability to lock up in all six gears. This will assist in achieving best possible fuel economy because whenever the torque is multiplying, ie. convertor slipping, the engine is revving higher than the physical gearing would dictate (for any particular road speed). That's why the "old" autos (with no lockup) were always noted for being thirstier than their equivalent manual model counterpart.

[xrdreaming]

I will vouch for the non lock up stall, I have a 3000rpm non lock up in the ute and it is a thirsty sucker, fun though.

[aiboart]

Yes, that is EXACTLY what a torque convertor is.

The maximum multiplier effect occurs under full load at stall speed of the convertor and is theoretically 2:1 or 100%. In practice it is less due to heat loss, friction, oil compression and aeration, among heaps of other things.

Generally the multiplier effect during normal driving is less than 15%.

When the torque convertor locks up, as the Ford does in third and fourth the multiplier is 1:1 or zero%. The new six speed auto has the ability to lock up in all six gears. This will assist in achieving best possible fuel economy because whenever the torque is multiplying, ie. convertor slipping, the engine is revving higher than the physical gearing would dictate (for any particular road speed). That's why the "old" autos (with no lockup) were always noted for being thirstier than their equivalent manual model counterpart.

<{POST_SNAPBACK}>

Thanks!

I think I can intuitively see how this would occur with different fluid paths and internal vectors and vane angles and all that.

What is the stall speed, is it related to the stator operation or is it something else again?

As I understand it at the moment, a torque convertor moves between three end states.

State one is when the pump is at low speed and the turbine is static. (low load)

State two is when the pump is at high speed and the turbine is static. (hi load)

State three is when the pump is at high speed and the turbine is approaching turbine speed or is even locking to it. (lockup or near lockup)

The stator rearranges the internal fluid flow of the torque convertor as the system moves from one state to another, to maintain efficiency. Efficient fluid flows in low load state become highly inefficient as the rpm of the pump and the rpm of the turbine increase, either separately or unison.

As far as the variable ratio drive effect goes, this would suggest that if we hold the engine at a fixed rpm the car can, in fact will (if torque is sufficient to overcome drag), accelerate, is this correct?

Is this correct?

Thanks for all the help.

Regards,

aa

Edited 24/04/05 11:06 AM by aiboart

[Turbo6man]

The stall speed is related to state 2 - it is the rpm at which the fluid is "pumping" at it's maximum volume but can produce no more pressure. It is controlled by the vane angles and clearances within the convertor (rotor).

As for the second part, no. First asumption is :- all things being equal and ignoring all external forces; if you hold the engine revs steady with no load on the convertor/engine, the torque convertor will not be producing any pressure and therefore no torque multiplication effect. A torque convertor is actually similar in effect to a turbo - it will only pump under load. If it is freewheeling, ie equal pressure on both sides, it simply doesn't come into effect.

[aiboart]

Thanks Turbo6man.

What happens if say in a car, in a fixed gear (say first gear), you take the pump to stall speed whilst keeping the turbine static, then let go of the brakes thereby releasing the turbine?

If I am understanding this so far.

The torque multiple is at its greatest whilst the turbine is static and at the pump is at stall speed.

Then as the turbine comes up to speed with the pump, the torque multiple is dropping whilst the pump speed is increasing (ignoring pumping losses).

As the car is accelerating in first gear, the torque convertor is in effect behaving as a variable ratio drive.

Is this right?

If it is it is very cool.

Also what would happen if you could alter those vane angles and clearances on the fly?

Can you make a torque convertor more or less 'slippy' on demand, thereby manipulating the torque multiplying effect at will - smearing the gear ratios as it where?

Thanks and Regards.

aa

[xrdreaming]

Should be some info here to explain things.

http://www.dominatorconverter.com.au/

http://www.converter.com/q1.htm

http://auto.howstuffworks.com/torque-converter1.htm

[Turbo6man]

Thanks Turbo6man.

What happens if say in a car, in a fixed gear (say first gear), you take the pump to stall speed whilst keeping the turbine static, then let go of the brakes thereby releasing the turbine?

If I am understanding this so far.

The torque multiple is at its greatest whilst the turbine is static and at the pump is at stall speed.

Then as the turbine comes up to speed with the pump, the torque multiple is dropping whilst the pump speed is increasing (ignoring pumping losses).

As the car is accelerating in first gear, the torque convertor is in effect behaving as a variable ratio drive.

Is this right?

If it is it is very cool.

Yes, that is correct.

Also what would happen if you could alter those vane angles and clearances on the fly?

<{POST_SNAPBACK}>

The latest generation convertors do just that - all ECU controlled.

[aiboart]

Thanks for all the information Turbo6man.

This is such an elegant everyday technology yet most are unaware that it even exists, amazing really.

Regards,

aa