Most efficient RPM for ICE
 

In several threads a link has been posted that showed the relationship between the two motor/generators and the ICE in the Prius. It was stated that the ICE can be kept at its most efficient speed and MG2 can be varied. I played with the diagrams, holding the ICE rotation at a constant 1500 RPM and varied MG2. I found that the car couldn't go above 77 mph without putting MG1 at red line, which would necessitate increasing the engine's RPM.

I realize this diagram is for a Prius with a different engine, but has anyone heard anything about what speed the TCH's engine is most efficient?

Re: Most efficient RPM for ICE
 

That's an easy one. At ZERO RPM the ICE is 100% efficient.
Somehow I don't think that's the answer you are looking for.
:)
J

Re: Most efficient RPM for ICE
 

That's the kind of wise-a** remark I would make. :embarass: ;)

Re: Most efficient RPM for ICE
 

Does it matter? You can't control the ICEs RPMs. That is done by the control computer. Unless someone comes out with a computer mod chip, you won't be able to control the speed of the ICE.

Re: Most efficient RPM for ICE
 

First, the MG2 rpm is proportional to the vehicle speed. In other words, the vehicle speed is determined by the MG2 rpm.

I'm commenting about Prius, but TCH works under the same concept.
We know Prius(TCH) is the Drive-By-Wire vehicle.
We press the accelerator which means telling the vehicle we need this much of power, then the ECU determines the required torque and rpm using the engine map for the most efficient combination. Please refer to the following pic. (yellow band)

The most efficient rpm is usually the place we see the max torque, however the rpm is just a single spot which means a single combination of torque and rpm.
We can't keep that rpm in the real world.

Anyway, the pic is derived from...
http://www.engin.umd.umich.edu/vi/w4...Miller_W04.pdf
It's worth for reading.

Ken@Japan

http://priusdiy.fc2web.com/image/efficient.jpg

Re: Most efficient RPM for ICE
 

TK, I realize that. Just wondering out of GP.

Ken, that's quite the graph. Don't think I'm going to try and understand it.;)

Re: Most efficient RPM for ICE
 

I believe BSFC stands for Brake Specific Fuel Consumption, which is a measure of fuel consumed per unit of work output. The lower the number, the more efficiently the engine is operating. So that circular region marked with 210...don't know what unit it is...is your sweet spot. As you get farther from that region you are getting less bang for your gallon.

Of course, staying in that high-efficiency region (high load/low RPM) at all times isn't possible since you don't always have a need for all the torque produced by keeping the load high. It just dawned on me that this graph is probably the best illustration of why P&G works! It's all about keeping the engine in or near that sweet spot while its running and turning it off the rest of the time. That's as opposed to a steady cruise, which would put you somewhere below it.