CVT manipulation for perfect gear ratios

[Daox]

Does anyone know what kind of signal is used to control a CVT's ratio? Is it something that can be manipulated? I'm thinking some sort of potentiometer that you can adjust to fake out the transmission to make it think that the throttle position is much higher than it actually is. You'd simply have to 'dial in' your tranny ratio for whatever cruising speed you want.

[Frank Lee]

Depends on the CVT. Some use springs, cams and ramps, and weights.

[Daox]

Well, I know Nissan only uses CVTs now. Honda and Toyota both use them in their hybrids. Thats kind of what I'm aiming at I guess.

[DonR]

I believe the production car CVTs are hydraulically controlled by a computer. The signal that goes to the hydraulic cylinder is probably based on engine RPM, axle RPM, throttle position & possibly change in throttle position. There may be position sensors(lvdt) involved as well. you may be able to adjust a signal going into the computer from one or more of the sensors if the mfr. used seperate engne & tranny cpu's.

I wish you luck.

Don

[vinny1989]

Or, buy a CVT gearbox from a breakers yard, rip it open and try and get it controlled by pulling on a cable/rod? More fun..

Manual controlled CVT > auto controlled CVT

[bwilson4web]

Originally Posted by Daox

. . . Honda and Toyota both use them in their hybrids. Thats kind of what I'm aiming at I guess.

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

[dcb]

still sounds a lot more complicated/fragile/expensive/heavy/lossy than a properly spaced manual trans.

[Daox]

Yeah, its definitely a different beast. I didn't know that the planetary setup did the entire work of the tranny. I kind of get what you're talking about Bob. Thanks for the explination.

It is quite an amazing package over all. I took my first drive this weekend in an 04 Prius, and with the wife driving at a steady 65 mph down the highway, we were getting about 55 mpg. Thats pretty hard to beat. No special driving, just a smooth foot on the accelerator.

[NeilBlanchard]

Hi,

I think that some CVT's are computer controlled?

[Christ]

What a CVT should be = two mechanical centrifugal clutches, one that opens with speed, one that closes with speed, and an idler pulley.

This is what my PUG had... 3200 RPM, in high gear, was about 28 MPH.