Two MG1 Questions

Check this video out.

 

Hi Jonny Zero

Yes! Both electric motors work as a motor and as a generator. When the ICE is stationary the main motoring duty is taken by MG2, but MG1 delivers a small amount of torque, so both work as motors.

In this post I describe the energy flow within the Prius and in following picture you may see the mechanical energy flow (both ways) of MG1 and MG2 in the cold days of this post:




The net energy of MG2 is very small 67Kj acting as a generator, but it comes from two much bigger numbers 2104Kj acting as a motor and 2171Kj acting as a generator.

The net energy of MG1 is 1585Kj acting as a generator. It comes from two big numbers 2158Kj acting as generator and 573Kj acting as a motor.

Big hugs from Frank

 

Hi Frank,

I've skimmed both of your referenced posts, and it's clear that you have a great understanding of what's going on here... so, i have one "simple" (?) question: IF the ICE is stationary - doesn't that require that MG1 Delivers zero torque? Said another way: If MG1 were to deliver any torque, wouldn't that result in rotation of the ICE?

I'm almost certain that I'm missing something here, as your analysis is far more well-considered than my own...

Thanks,
Eric

 

If you want to search for it, MG1 helps power the car in Heretical mode

Here is one write up
Whats Going On As I Drive?

This mode allows high throttle opening, low RPM operation (top gear, full throttle in a manual, but hard to achieve in an automatic or true CVT) Think 'overdrive'

 

Thanks!

So that's what Heretical mode is.... I remember reading something about that some time ago, but it then left me...

Is the ICE stationary? (I'll soon find out when I read the post you referenced).

 

A hard concept for me is that the ICE is pushing on the planet carrier. Even when that is stationary, the planet gears themselves can pass energy from the sun to the ring and vice versa.

Toyota Prius - Power Split Device

You can leave the ICE off and each planet gear rotates on its axis as you move MG2 slider, then you move the ICE slider all four gears rotate around the Sun gear.

 

I think that if ICE is stationary - MG1 can not contribute... (I think Heretical Mode includes ICE motion...)???

 

yes - I love that website!

 

Hi Eric,

Yes, MG1 has zero torque when ICE is stationary, only MG2 is delivering the torque. See attached image circled in orange.



To start the ICE, MG1 will function as a motor to apply positive torque (see above time at 15.113 sec).

Vincent

 

OK - got it - and that is a bit contradictory to Frank's statement above:

When the ICE is stationary the main motoring duty is taken by MG2, but MG1 delivers a small amount of torque, so both work as motors.
not that I'm looking to start an argument -as it is very clear that Frank has much more knowledge on this topic than I do - I'm just trying to cement my own understanding...

 

Vincent,

How did you generate those great graphs?
You have another OBD interface device?

Thanks,
Bob Wilson

 

It is generated by Techstream. I 've the mini-VCI but the data was actually captured by Paja using his Tactrix cable on a Gen3. He sent me his log file and I can replay it in TS.

Vincent

 

You asked the right question, we'll wait for Frank to response...

As per my understanding, MG1 cannot apply any torque in order to keep ICE stationary. MG1 only apply torque when ICE need to be started.

Vincent

 

When the engine is not running, the spider gears are spinning like mad sandwiched between MG1 sun gear and outer ring gear connected to MG2. No torque is needed to keep the engine from rotating after the initial stop.

If you'll look at Vincent's graph, you will see two little blips just before and at the end of the zero ICE speed:

1. Initial pulse to stop the engine - there are reports this puts the engine in a specific, stopped configuration, but I haven't seen that data.
2. Initial pulse to start the engine - the engine needs a quick pulse to start running.

MG1 provides the counter-torque, what the engine pushes against, to transfer power to the ring-gear and on to the wheels. But it comes in two modes:

1. Low-speed, under ~25 mph - MG1 works like a generator to provide the counter torque. But since it has just generated a bunch of electrical power, it is routed primarily to MG2 and adds to the power going to the wheels. This is often called 'normal mode.' More about the battery later.
2. High-speed, above ~25 mph - MG1 works like a motor to force the engine to spin at a slower speed . . . in effect it has shifted into a higher gear. It gets this energy by having MG2 work like a generator and sending the power to MG1. This transition is electronic which means instantly. This is called "energy recirculate" mode in the Toyota SAE papers or 'heretical mode' by the early adopters who first saw it in the data.

Now the battery provides an 'energy well' during the sub-millisecond transmission shifts between the two modes. It is also an energy source providing the additional torque the Atkinson cycle, engine lacks. But these longer duration, torque shortfalls, are typically events when the engine is spinning up to a new power level or the engine is at maximum power. These torque addition events are typically measured in 10s of seconds up to a 100 seconds.

Sad to say, the energy flow display does not have units or bars sized for the actual amount of energy flowing. This gives a false equivalency between 'house keeping' and 'serious energy flows.' You really have to use a data recording OBD scanner, spreadsheets, modeling, and aspirin to really understand what is going on . . . it is awesome.

Bob Wilson

 

Bob, would it be fair to say that the stronger ones accelerates (higher RPM), the less "energy recirculation" happens and more energy travels from ICE to wheels via mechanical link? If so, that would explain how better efficiency happens with quick acceleration (whether that is pulse and glide or not).

 

I would rather do some metrics before making that claim. I have data that shows the two modes have some overlap in the 25 mph range but (from memory) there is about a 10 mph 'slop'.

One of these days I may try to do some energy studies on how to minimize fuel burn from 0-50 mph at different throttle settings BUT the problem is how to calibrate the throttle request.

We know there is a metric called "requested power" that appears to be what the HV and engine ECUs use to determine what the engine does. However, it might be simpler just to hold engine RPMs to narrow ranges during the acceleration tests. Because of the manual input and feedback, it is not a trivial problem and making credible, reproducible measurements is hard given what we have for controls.

Bob Wilson

 

You asked for it.



MG1 first exert a more negative torque, negative rpm (Generator Motor mode) then gradually decreases to slow down ICE speed so as to reduce the "shock".

Vincent

 

Thank you!

I wasn't clear in that I'd heard the engine was stopped at a specific angle . . . something that might be seen by setting up a remote camera and taking a photo of the stopped crankshaft angle using either a 'timing mark' or 'paint spot.' Given it is a four-stroke, I would expect the crank shaft to always stop in two locations 180 degrees apart. The only way to really know if there is a specific stop location would be to record the camshaft sensor timing but now we're getting really anal-retentive(*). Still, you've captured something I've long wondered about with some excellent, high-speed samples (sample rate?)

The stopping and starting pulses have a specific magnitude and duration. It should be possible to calculate the kWhr or specific energy needed to start and stop the crank, pistons, and cam shaft. The difference between these two is the internal engine 'drag' or 'overhead'. A similar number can be measured in the 'cold start' energy. Now what possible use could we make of this:

• Study effects of 0W-20, 0W-30, 5W-30, or other oil weights on engine 'overhead'.
• Study effects of credible oil additives on engine 'overhead.'
• Study effects of oil level, especially overfill, on engine 'overhead'.
• Remove spark plugs and measure the non-compression, starting 'overhead' compared to just oil pump, cam shaft, and valve overhead.

Now is any of this useful to the owner? Perhaps just to end speculations and establishing bragging rights. But there are some things that I look at and when I weigh what it takes to perform the experiment versus the potential pay-back . . . well sometimes I'm a little lazy or have other more interesting problems to pursue. <grins>

Bob Wilson

* - Many years ago, I had just joined an engineering team supporting network operations at NASA HQ. About three weeks into my new job, they were 'giddy' about 'Mike N.' who had just been hired to rejoin our team. So I asked Don B. 'why are you so happy about Mike N.?' and he said,

"Oh you'll like Mike, he is as anal retentive as you are."

Don was right!

If you are going to have major medical, legal, or other significant work done . . . look for the anal retentive professional. <GRINS>