Quote:
Originally Posted by Daox
. . . Honda and Toyota both use them in their hybrids. Thats kind of what I'm aiming at I guess.
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The Honda CVTs have a metal belt that goes between two cones. Beyond that, I have no idea of the control mechanism. The Toyota CVT is quit a bit different.
The Toyota CVT uses a planetary gear with two inputs and one output:
- sun gear - MG1 working as a generator but sometimes a motor
- planetary gears and carrier - the engine drive shaft spins the gear carrier
- ring gear - the output that drives the rest of the drive train
With the engine running and MG1 in 'electrical neutral', the engine spins but no torque goes to the ring gear. The engine rotation is spinning MG1 rapidly in the reverse direction and the car is in neutral.
To move forward, the MG1 electronics put it in 'generator mode.' This causes a counter torque to the planetary gears forcing the ICE torque to rotate the ring gear and the car moves forward. But this leaves a problem ... what to do with the power generated by MG1?
Toyota routes the MG1 electrical power to MG2, another motor generator on the drive train, and MG1 electrical power then adds to the engine power back to the drive train. This is the power-split function of the planetary gear, the power-split device (PSD.)
Now the interesting part is the amount of torque MG1 produces is entirely under electronic control as is the engine throttle. What this means is some truly amazing rpm-torque combinations are possible. For example, low power operation varies the torque without changing the ICE rpm along any scale. We don't get the normal engine rpm pitch changes that indicate the amount of power being generated:
There is a whole other area, the energy recirculation mode, that is used at high speeds to reduce the engine rpm. In this mode, power flows from MG2 to MG1 to 'push against' the engine and put it in a lower rpm mode. Without computer control, none of this would be possible.
Believe me, it took a long time before I could wrap my mind about how it works. Even now, the most recent SAE paper I read about it has it wrong. It truly is an amazing technology.
Bob Wilson