P & M session

[MadMan]

The Prius 'transmission' is actually quite fascinating. As a transmission mechanic, I had the opportunity once to open one up. Everyone always kept telling me it was a CVT transmission.

In a manner of speaking, I suppose. But no, it was a lie! There's next to nothing inside of them. There's 2 big ass electric motor/generators, the final drive (differential), and then a little planetary gear that is the armature of the 1st motor. There are no clutches, no torque converter, no hydraulics, and no electronics. The engine is directly coupled to the planetary gear, and the way it's set up is that the planetary just freewheels there. Unless the motor is energized, then it sort of holds it, and the engine is 'directly' coupled to the wheels, the amount of 'slip' varying by how much electricity is sent to the motor. Reverse is accomplished electrically.

Fun fact, if you have a Prius, you can use pretty much any oil as a trans fluid. They say it has to be Toyota's basic trans fluid, but really, any old trans fluid is fine, because no hydraulics, and no clutches.