Does Gas Engine ever directly drive wheels

If its running it is charging your battery.

 

+1.

Play with the flash simulator and it will answer many questions. You will see with the sliders when each thing happens and the rpm of each along with total speed. Quite ingenious.

 

When you are stopped and the engine is running it's for one of three reasons:
1. The battery is too low and it's being charged.
2. It's cold, and either the cat or the car interior needs to be warmed up.
3. It will -eventually- stop, it's just waiting for a fixed time period to "see" if you need it. I still want my "anticipation switch" to stop it!

 

The Prius does not have a clutch, assuming you don't count the torque damper which includes an emergency clutch to prevent damage under extreme loads. Therefore, yes, without an operable clutch.

Tom

 

That's what I said.

 

Ah, gotcha. Yes, that would be exciting to drive.

Tom

 

David, your explanation is one of the best on this thread. Clear and easy to understand. So perhaps you can tell me what the engine rpm is when driving at a highway speed, say 60 mph, when all motive power is coming from the ICE.

 

In case David doesn't see this right away: in a transmission with fixed gear ratios, you can answer a question like "how many revs does the engine turn at 60 mph in x gear?"

With a continuously-variable transmission (any CVT, not just the weird hybrid kind in a Prius), your question has much less of a definite answer. The car can be moving 60 mph, and the engine can be turning any rpm where it produces enough power to maintain the car's speed under the current conditions. The CVT does the magic to match the two speeds.

The Prius power management computer knows the engine's torque and power curves. When it calculates how much power is needed to move the car in the current driving conditions, it will try to send the engine right to the rpm range most efficient for producing that amount of power, and adjust the transaxle ratio to match that to the car speed.

If you watch your rpms on a ScanGauge, the Torque app, or the like, at 60 mph you might be seeing anywhere from under 2000 (downgrade, tailwind, etc.) to 4000 or higher (steep upgrade, stiff headwind, etc.) or anywhere in between.

-Chap

 

Well, you still can not say that all motive power will come from the ICE. There are two electric motors: MG1 and MG2. MG2 speed is proportional with engine speed, MG1 is totally independent. So we can answere the question "what will engine rpm be when MG1 is not spinning", but then still MG2 can deliver power to propel the car. But ok, this is the closest you'll get and you could short MG2 to make sure it does not deliver power and for ICE rpm this does not matter because when MG1 speed is constant, ICE rpm is proportional to your speed.

Under that condition, ICE rpm is about 5/18 * 143/145 * 120 * speed in mph

 

There seem to be some misconceptions in post #29. MG2 speed is proportional to wheel speed, not to engine speed. MG1 is not totally independent, it's related to both engine speed and MG2/wheel speed by a fixed nomograph that's been posted and discussed widely on PriusChat. Shorting MG2 would not "make sure it does not deliver power", it would strongly resist the car's motion and create serious heating in MG2 (indeed, when that happens on its own through deterioration of the winding insulation, it's one of the known transaxle failure modes).

There are a lot of threads already on PriusChat that accurately describe how the hybrid system works....

-Chap

 

The question asked by eco-one was mostly answered by chapman.

The MGs can spin without actually -pulling- the car. They can actually absorb momentum energy (regenerate mode) or just spin, using minimal power, in "coast mode". And yes, they can help power the car or even contribute all the power to move the car. And in reverse, MG2 is the -only- source of motive power for the car (there is no "reverse" gear so the engine can't drive the car in reverse), though I suppose it's possible MG1 could contribute some power as well, but I don't think that is done in the HSD.

If you try to reverse up a very steep hill you can see this lower power (about 40 HP) in reverse. Once I had to reverse up a very steep hill, and Pearl struggled mightily, but did move, with full throttle. You get quite a surprise when this happens.

 

Here is another perspective: If you do not provide electrical power to M/G2 and M/G1, the engine has nothing to push against and can run all day and you won't go anywhere. This is N on the stick shift.

Once you do provide resistance for the engine to push against by using at least one motor as a Generator (usually the other is a Motor) then 71 % of the torque goes to M/G2 and usually drives the wheels via gearing and 29% goes to M/G1 and make electricity, perhaps also driving M/G2 indirectly.

There is a mode where M/G2 is acting as a generator, cutting into the power supplied by the engine, while M/G1 is acting as a motor, using electricity from M/G2 to slow the engine. This seems very odd, but doing so acts like an overdrive, allowing full throttle at low RPMs. If you are doing 1600 RPM at 60 MPH, this is the mode.

No gears shift, no clutches grab, no physical change in the transaxle, just software controlling the M/Gs.

 

Thank you, Chap. Good explanation. I had read that the CVT transmission was like a single speed transmission, but I recently saw a chart that shows how MG2 often revolves to change the effective ratio of the ICE to the wheels.

 

I should have written MG1, not MG2.

 

Or, using very elementary algebra and the relevant gear ratios in the transmission, you can easily calculate MG2 (or car) speed, MG1 speed, or engine speed, if the other two of those three variables are known. I made a spreadsheet which does that.