Thank you Bob and Soopahman for your detailed explanations!

I read the link that Soopahman provided in his post for an explanation on Torque and HP. I could gather a little info from that article ...

So, basically, for what we think as "engine powe", all that matters is torque .. the turning force! .. so, that begs one more question .. what does the torque curve for the Prius engine look like? At what RPM is it producing its max torque .. would that point not be its most optimum/fuel efficient? So, we should be aiming at getting that torque when the ICE is on in Prius .. is my understanding correct?

Thank you again for your answers!

Regards.

 

I am specifically referring to this section in the article: " In contrast to a torque curve (and the matching pushback into your seat), horsepower rises rapidly with rpm, especially when torque values are also climbing. Horsepower will continue to climb, however, until well past the torque peak, and will continue to rise as engine speed climbs, until the torque curve really begins to plummet, faster than engine rpm is rising. However, as I said, horsepower has nothing to do with what a driver *feels*."

So, we need to see the Torque-vs-RPM curve ... right? Anyone?

Thanks!

 

It turns out that a Graham scanner can provide the data:

• MG1 torque - is 28% of the ICE torque
• ICE rpm - read directly

The following graph comes from a test performance last September with my NHW11, 03 Prius:
The left axis is the ICE torque in Newton-meters calculated from the MG1 torque based upon the gearing. The bottom axis is ICE rpm and the right axis is the scale for HP.

These curves were used to map the specific fuel consumption but they also show how the Prius engine works in the vehicle. Traditionally folks have used engine charts from a dynometer test stand. The actual performance in a vehicle, especially with an automatic transmission / transaxle can be quite different.

Bob Wilson

 

Bob, every time I see that graph I am reminded of the Beatles' Yellow Submarine album.

DAS

 

Thanks Bob for the wonderful chart .. I remember seeing it in some other thread .. (or may be in this thread, but a few pages earlier ..).

I did not realize that this is was Torque vs RPM chart .. and even I did, I would not have realized the significance of it. Thanks again for going through your experimentation and providing us with this chart ..

But you know what .. (I sound so silly here ..) you would need to interpret that for me as well ..because I am confused as to how to read the most optimum point from the graph ....


Regards.

 

Hi Bob and all,

Bob placed a power distribution picture of ICE yesterday, but Graham Davies wrote that the ICE torque is always distributed 28% to sun gear(MG1) and 72% to ring gear(wheels).
http://prius.ecrostech.com/original/...plitDevice.htm
I think I must agree with Graham.

Regards,
Ken@Japan

 

Hi,

It a challenge to figure out how to show all of the elements but the simple rule is this:

- smaller circles are better
- red-dots are the best

You'll notice the red-dots are to the left; then the orange dots; light blue; and finally the big blue dots, the least efficient samples. So what happens is we find the largest amount of power relative to fuel burned (injector time) occurs at the lower rpm. The general rule is:

- up to 2,400 rpm, pretty darn good
- 2,400-3,200 rpm, Ok but not as good
- 3,200+ rpm, burning a lot of fuel for the power

Bob Wilson

 

Hi Ken,

The 28% ratio is critical because the inverse times the MG1 torque is the ICE torque. But after carefully checking the rotational and torque directions, I agree that yours is more accurate:


The one suggestion is the lower right text should read:

"ICE+MG2" should read either:

"28%ICE + 72%ICE"
or
"28%ICE(MG) + 72%ICE(PSD)"

NOTE: While editing, I decided to use "100%ICE", "28%ICE", "72%ICE" and back to "100%ICE". I also sized the vectors to be proportional to the power they represent.

One aspect of this chart is we can look at the mechanical efficiency of the gears and chain separate from the mechanical efficiency of the MG1+MG2 pair. This is important if doing transaxle oil studies.

Thank you for the correction, I'd made a mistake and will correct my original drawing.

Bob Wilson

 

Does that mean when you're just trying to get the most momentum out of the gas that MG2 is always bleeding off 28% of that momentum? At best that can be converted to electricity and then back to momentum via MG1... conversion losses the whole way.

I always assumed that at some levels of demand MG2 was shorted-out to avoid it holding back any ICE power from the wheels.

Fuel efficiency of 91-96% is somewhat amazing, and it's interesting that the best efficiency numbers posted at both 1650rpm and 2600rpm are some of the engine's best torque numbers as well.

Bob, do you think the outlier at 3400rpm is in error?

 

Hi Bob,

Thank you for your correction of the original drawing.

Back to your original post...
I have never seen such MG2->MG1 power flow on any material.
http://www.toyota.co.jp/en/tech/envi.../ths2/how.html

Would you please show us the reference pointer for the MG2->MG1 power flow?

Thanks in advance.
Ken@Japan