Split from:

https://www.greenhybrid.com/discuss/...ed=1#post32783


This could get interesting. CGame-dude I've come to respect your knowledge but in this case one of us is way off in our understanding. As far as I know the Toyota does not work as you describe. Further even if it did work the way you describe there would be no advantage to converting mechanical energy to electrical energy and then converting back to mechanical energy again. You lose a little everytime you convert.

The Toyota only sends about 28% of the engine torque down the electrical path and 72% is fed down the mechanical path. Please see:

http://home.earthlink.net/~graham1/MyToyotaPrius/Understanding/PowerSplitDevice.htm

 

lakedude, I am going by the car's own fuel consumption display and by one or two articles I remember reading on it. I'm almost positive I remember the FCD showing the engine charging the battery but not driving the car directly; only the motors were. And I know I've read the advantage to that is the engine can operate more efficiently than it can when driving the car directly, which offsets the loss in energy from generating electricity and using that electricity to drive the car.

See, electric motors are very efficient at any speed, but gasoline motors are not. When you think about it, if you were right about the Prius' drive being inefficient, then it would never ever charge the battery from the engine and would rely solely on regenerative braking, since the energy put into charging the battery will be less than the energy gained back when using the battery for the electric motors.

Furthermore -- and I admit I don't understand much of the physics of this, just the fact that it's what the car does -- even when the engine is directly driving the car, it's also recharging the battery while the electric motors use the battery to drive the car. So some of the engine's power drives the car while the rest is used to generate electricity that then... drives the car. Unlike Honda's hybrids that use only the ICE during high-speed cruising, the Prius and Ford Escape hybrids use the electric motors at all times.

 

This is at least somewhat inaccurate. You can't have the ICE charging the batteries while both electric motors are driving the car. The ICE charges the batteries by driving at least one of the electric motors in reverse, i.e. as a generator. That motor cannot be driving the car and charging batteries at the same time. It's either consuming electricity or generating electricity.

 

Well yes, I shouldn't have used the plural. I was thinking there was a dedicated generator -- absent-minded of me.

 

You are getting confused between torque and power. The torque split is constant between the output and generator, but the power split is continuously variable. Think about the car just idling (as it's warming up for example) there's 0% power moving through the mechanical path, 100% moving through the electrical path (into the battery until the car starts to move) but the torque split is still 28%/72%. The Prius does in fact use the motor generators as a torque converter as CGP explained because there are no gears to multiply the torque between the engine and the output of the transmission. What Honda's CVT or manual tranny is doing is multiplying the output power of the engine into enough torque to accelerate the car, but in doing so there are energy losses, just like the electrical path in the HSD system.

 

The Honda does the exact same thing at idle. Since the car is not moving zero power is being used for moving the car. The IMA is still working while the engine is running and can charge both batteries without moving the car.

 

Yes, I realize that, but I wasn't trying to compare the IMA to HSD in that example, just trying to explain the difference between power split and torque split.

 

Hi Lakedude:

___Kind of a funny story … At the Marathon Attempt, HBO needs some footage of the cars interior and Dave B.’s Prius II was the video mule. Its SoC was pretty low for whatever reason and Dave said to me, bring her up. I Pulsed out of the hotel parking lot and grabbed some heavy regen into a light, turned around and did the same over ~ 2 minutes. It wasn’t full but it wasn’t pink either. Dave asked what the hell I was doing and I said bringing up your SoC. He said you don’t have to drive it; you can do the same sitting in the parking lot. I am still not exactly sure what he meant but I saw him and Dan perform this SoC loading while parked and I think they just held the brake, brought up the RPM’s, and MG1 starting pushing for all she was worth into the pack. At least that is what I think they were doing

___Good Luck

___Wayne R. Gerdes

 

It think you can do that in Park, don't necessarily have to be in drive with the brake on. Neutral won't charge though, plenty of warnings about how evil neutral is in the manual.

 

Schwa

CGameProgrammer said:

Quote:

only Toyota's hybrids can run the engine to recharge the batteries while the electric motors alone power the car

Then I said:

Meaning that whenever the engine is running it is trying to push the car, even when the car is not moving.

I'm not getting confused between power and torque, I was only pointing out the error in CGP's statement. It is true of course that the Prius can move on electric power alone but not if the engine is running. I don't care what the display shows, if the engine is running it is helping push the car period (unless I understand it wrong).