[kennyb]

I looked on Toyota's website.

Part of the time the engine is running it gives power to the generator, which then sends electricity to the little motors. The motors power the wheels.

Isn't this a waste of efficiency? Why not power the wheels directly with the engine? Why go the long way around?

Also, does the engine have constant rpms? It's supposed to be in some kind of "efficiency band"...does that mean flat constant or does it shift around (in rpms) a bit.

How does the gear thing work if the rpms are constant? Is there an easy diagram that shows how constant rpms and non-constant speed is possible?

 

[finman]

power split device...

try this site:
http://home.earthlink.net/~graham1/MyTo ... Frames.htm
Click on 'understanding your Prius' on the left side. Also do a search here or at Priuschat.com. Lots of info out there. Love my Prius!

 

[Daniel]

The site finman gives is the best place in the world to learn how the Prius works.

A short answer is that there is one gas engine and two motor-generators connected to the wheels via a power-split device (diagrams on that web page). The torque from the engine is split in a fixed ratio between the wheels and MG1. The computer decides whether to send the output of MG1 to the battery or to MG2, and when to send current from the battery to MG2. MG2 drives the wheels directly (along with part of the power from the engine.) MG1 is usually a generator but is also the starter motor, and MG2 usually drives the wheels but is also a generator for regen braking. The display in the car oversimplifies by showing only one MG.

The double conversion mechanical to electrical and back to mechanical (engine to MG1 to MG2) contains inherent effeciency loss, but the system allows the engine to spin in its efficient range even when the car is moving slowly, and the gain in engine efficiency more than makes up for the conversion inefficiency. At slow speeds the engine can spin fast, turning MG1 to power MG2. At higher speeds a greater proportion of the power goes directly from the engine to the wheels. This is determined by the physics of the power-split device.

This is just the short answer. See Graham's web page. It is fascinating!!!

 

[RSnyder]

Why not power the wheels directly with the engine? Why go the long way around?

Graham's site is essential to understanding why the Prius configuration works so well. But you're question is still valid. You're describing the Honda approach. The whole hybrid field is still young and both companies are making great strides, leap-frogging each other every 1-2 years. Who knows for sure where it will all end up, but it's great that both companies are working so hard.

 

[Daniel]

I really really really wanted to stay with Honda, after 15 trouble-free years with my old Civic, and being treated so well by the Honda service department. But the Honda approach to hybridization seemed crackerjack to me, while the Toyota method struck me as a thousand times more elegant. Also, I didn't like the idea of auto-stop without Toyota's radically-different starting method. I was seduced away from Honda to Toyota, and 7 months later I'm still happy with my decision. If Honda comes out with something better, I could switch back. But I don't forsee that happening any time soon. Honda seems committed to its "mild" hybridization concept, and I'm pushing for ever-more electricization (if that's a word... or even if it's not).

 

[washozephyr]

Thanks, Finman, for the great website link...My non-tech mind still doesn't understand it all, but I can confound myself for hours reading it.

 

[Ken Herrick]

2004 block diagram & explanation

See my post under Technical/2004 block diagram.

Ken Herrick