Introduction to Prius Power Flow

[ScottY]

Bob,

WOW, thanks for the nice graphics and explanation. I can observe this energy-recirculation mode on CAN-View. Like Dennis said, while cruising at high way speed, MG1 is showing a positive RPM, I back off the pedal and press light to maintain speed. At that time, MG1 RPM goes negative and engine RPM greatly decrease as well. I observed this for a while and don't know what it means, I do now! Again, Bob, thanks for the great work!

[bwilson4web]

Hi folks,

Graham Davies did some excellent work describing PSD operation:

http://prius.ecrostech.com/original/PriusFrames.htm

For example, Graham explained how to derive the rpm relationships:

MG1 = 3.6 * ICE - 2.6 * MG2

MG1 - MG1 rpm
ICE - ICE rpm
MG2 - MG2 rpm

MG1_torque = 28% * ICE_torque (again from Graham Davies)

Any two rpm values determine the third rpm. Also, the MG1_torque tells the ICE_torque. Using the Graham's mini-scanner data, it was easy to calculate the energy flows.

Bob Wilson

[hobbit]

The throttle isn't actually "wide open" in most modes. Graph the
TPS PID and you'll see.
.
_H*

[bwilson4web]

Thanks H*,
<div class='quotetop'>QUOTE(hobbit @ Mar 29 2007, 08:02 PM) [snapback]414585[/snapback]</div>

The throttle isn't actually "wide open" in most modes. Graph the
TPS PID and you'll see.[/b]

I recorded 35 miles of data with the throttle position and graphed the ICE power vs. throttle%:



There appears to be an unusual, high power, trend at high throttle settings to try and open the throttle plate more but without a significant power increase. But the interesting area is in the 25-35% throttle settings.

In the range of 25-35% throttle,obviously not "wide open," the higher power settings are occurring in energy recirculate (aka., "heretical") mode. This suggests MG1 torque enables higher ICE power output at any given throttle plate position:



This is counter to what I would have expected. I'll edit the first posting to reflect this new information.

Bob Wilson

[okiebutnotfrommuskogee]

<div class='quotetop'>QUOTE(bwilson4web @ Mar 5 2007, 05:13 PM) [snapback]400563[/snapback]</div>

A frustrated automotive engineer once claimed that you had to have a doctorate to understand the Prius transaxle. Learning how it works can lead to a headache but it is understandable. Hopefully, the following charts and data will clear things up.

Bob Wilson
[/b]

One thing is still bothering me. When the car is running on the Electric motor, and since the ICE shaft is connected to the planetary gears, what keeps the engine compression from putting a drag on the system?

[donee]

<div class='quotetop'>QUOTE(okiebutnotfrommuskogee @ Mar 31 2007, 11:10 AM) [snapback]415433[/snapback]</div>

One thing is still bothering me. When the car is running on the Electric motor, and since the ICE shaft is connected to the planetary gears, what keeps the engine compression from putting a drag on the system?
[/b]

Hi Okie,

Nothing. But below 41 MPH, MG1 can run fast enough that the engine is imobilized. Above 41 MPH, MG1 would be overspeeded to imobilized the enigne, so in electric only mode (warp stealth), the engine turns overs, and does drag. There is a net benefit if running the engine would require such a low power level the engine would be inefficiient. Which is probably when the Prius drops into warp stealth. The engine is still less efficient, even at its best efficiency, than the 40 % or so charge battery through inverter, wait, discharge through inverter to motor cycle.

Check out http://eahart.com/prius/psd/ . As long as the nomograph line does not change to red, the condition is valid. Setting MG2 to 41 mph, you will see MG1 at -6500 rpm, with the engine at 0 RPM.




Hi again Okie...,

Using that simulator, and assuming the spin speed of the unfired ICE is about 1100 RPM, which I believe is correct, one can see the fastest electric-only speed is 64 mph. Above that speed the engine will be fed gas (green zone in ICE RPM range in simulator). Which is why I cruise at 63 mph typically.




Oops,

Some of those numbers in that last paragraph may need refining. Need someone with instrumentation to tell us what the true unfired engine speed is. And at 1100 RPM, the fastest speed, without overspeeding the MG1 is 68 mph.

[bwilson4web]

<div class='quotetop'>QUOTE(okiebutnotfrommuskogee @ Mar 31 2007, 09:10 AM) [snapback]415433[/snapback]</div>

One thing is still bothering me. When the car is running on the Electric motor, and since the ICE shaft is connected to the planetary gears, what keeps the engine compression from putting a drag on the system?
[/b]

The planetary gears on the planetary gear carrier are spinning like mad because anytime the car is moving the ring gear is rotating. But with no counter-torque from the sun gear, the planetary gears have nothing to push against. The planetary gears spin but can not apply torque via their bushings to the planetary gear carrier and ICE shaft. So normal friction and compression drag lets the ICE sit there without spinning or transferring any force to slow the vehicle down. The only motions are the ring gear rotation spinning the planetary gears around their bushings and they in turn spin MG1 freely in the opposite direction. Only the planetary gear carrier, connected to the ICE shaft, remains immobile.

Bob Wilson

[okiebutnotfrommuskogee]

<div class='quotetop'>QUOTE(bwilson4web @ Mar 31 2007, 09:37 AM) [snapback]415454[/snapback]</div>

The planetary gears on the planetary gear carrier are spinning like mad because anytime the car is moving the ring gear is rotating. But with no counter-torque from the sun gear, the planetary gears have nothing to push against. The planetary gears spin but can not apply torque via their bushings to the planetary gear carrier and ICE shaft. So normal friction and compression drag lets the ICE sits there without spinning or transferring any force to slow the vehicle down. The only motions are the ring gear rotation spinning the planetary gears around their bushings and they in turn spin MG1 freely in the opposite direction. Only the planetary gear carrier, connected to the ICE shaft, remains immobile.

Bob Wilson
[/b]

Thanks Bob,

It is beginning to make sense.

Warren

[MPG > HP]

<div class='quotetop'>QUOTE(bwilson4web @ Mar 6 2007, 04:47 AM) [snapback]400781[/snapback]</div>

Hi Gary,
With my older NHW11 and the Graham scanner, I have access to over 50, decoded OBD signals:

...It is a complex function dependent upon speed, grade and vehicle maintenance ...
[/b]

Thanks for the detailed response, Bob! Also, when you mention "grade," does the Prius use something like a piezo gyro to measure changes in inclination? Do you have access to that metric with your scanner? Is there a way to tell if programmers have given "preference" to taking or giving battery energy based on inclination and battery charge state? Is programming logic mainly proprietary requiring reverse engineering to determine? Just curious. - Gary

[bwilson4web]

<div class='quotetop'>QUOTE(MPG > HP @ Apr 1 2007, 06:58 PM) [snapback]416177[/snapback]</div>

. . . when you mention "grade," does the Prius use something like a piezo gyro to measure changes in inclination? [/b]

We use topographical maps from our test runs. To the best of my knowledge, there are no built-in altitude measurement devices or systems.

<div class='quotetop'>QUOTE(MPG > HP @ Apr 1 2007, 06:58 PM) [snapback]416177[/snapback]</div>

. . . Is programming logic mainly proprietary requiring reverse engineering to determine? . . . [/b]

Toyota has released a number of engineering papers and several US agencies have done extensive analysis. The rest has been done by individuals trying to expand the envelope of their vehicles. You can't make a change without understanding what you have and how it works.

Bob Wilson