Correct again. The drawing was in error and the resulting description. However, there is the proverbial "heretical" mode that requires an unusual power flow. How would we show the power flows in 'heretical' mode?

Bob Wilson

 

It is more accurate to see it as power that takes another path to the wheels. Both paths have power losses by different means.

Not shorted but sometimes, MG2 works as a generator and the energy is stored in the battery. This is called regenerative braking.

That percentage is relative to the highest fuel efficiency observed, not an absolute. The absolute numbers from a 530 mile trip indicate we're seeing ~31% ICE efficiency converting gasoline energy to shaft power.

There are outliers due to the sampling nature of the monitor. Each data item is captured at separate times but to calculate things like fuel burn, you have to combine injector-time and ICE rpm. For power, the product of MG1 Nm and ICE rpm. There are transient states such as acceleration and braking where even with interpolation of the data, it gives an outliner. The data has to be treated as a sets of samples.

There folks doing original work with direct data capture from injector wiring and current sensing of MG1 and MG2. By using such 'real time' data sources, the problem of outliers can be greatly minimized.

 

Hi Bob,

I'm not sure what does 'heretical' mode mean.
Would you please explain?

Ken@Japan

 

It was introduced in "Prius_Technical_Stuff" in reference to "heretical mode" or Prius "overdrive" (search the messages.) It is not an area I've tried to investigate or document although there have been a lot of discussions in the Yahoogroup.

Now I may not understand all of what they've discussed but one claim is that at high speeds MG2 may work as a generator to make the current needed to drive MG1. The claim is MG1 is driven to keep the ICE in a high-torque, low-rpm mode. That in fact was what my original drawing depicted BUT my experiments and data have yet to demonstrate "heretical mode."

I like the corrected drawing because it closely matches the SAE papers describing Prius operation. There are some subtleties that have to deal with the angular rates and power generation but we have enough data from the Dept. of Energy studies to answer those questions. It is much simpler system if MG1 is always used as a generator and the source of counter-torque for the ICE.

The miniscanner does a great job of showing current in and out of the battery. But it doesn't show AC current flow in and out of MG1 and MG2. However, my experiments with audio recording has shown the signature of generation versus motor mode in the profile. I just haven't tried to find and document the elusive "heretical mode," yet.

One option, I need to check is the availability of MG2 torque from the miniscanner. MG1 torque tells us when it is running as a generator or motor. MG2 torque should do the same. There is a fairly direct relationship between MG1/MG2 torque and current.

Bob Wilson

ps. I've expanded the mechanical description in the corrected drawing. Eventually, I'll work up a series that starts from the schematic and power flows and morphs into the physical layout.

 

I don't know if he was the first, but Graham Davies describes heretical mode (and others) here:

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

 

Due to frames, you have to click on "Understanding your Prius" where you'll find:
I have no data supporting or opposing this point of view. It sounds reasonable but it isn't important unless one is drawing a schematic power flow chart. But this morning I'll check to see if the miniscanner records MG2 torque. If MG2 torque changes sign, not associated with regenerative braking, we'll have direct evidence of 'heretical mode.'

Bob Wilson

 

Oops, sorry. I knew that, I just went too hurriedly with the post.

 

Hi,

This morning, I reconfigured the Graham scanner and directly observed both modes:

1. normal mode - power split device uses MG1 as a generator to pass power to MG2
2. heretical mode - MG2 runs as a generator to make power for MG1, which the PSD combines

As a general rule, "normal" mode occurs when accelerating and "heretical" mode occurs at steady-state speeds above 42 mph. But I wasn't recording the data, just doing a quick sanity check. I was able to see the torque sign change on MG2 both with regenerative braking and in cruise.

What I need to do is refine my Prius schematic and show the various power modes with data samples from the Graham scanner. This will cover the principles of operation and refine the models. Then I need to add a series of charts that morphs the 'linear' Prius schematic into the compressed version and ends with photos of the parts. This will help folks more quickly understand what is going on. I'll probably post the drafts in "Prius_Technical_Stuff" for peer review and then share the final product here.

Of course one interesting question is can we operate our Prius with neutral MG2 power? I don't think so because there would be no power for MG1 to give the counter torque needed by the ICE. However, mapping the operational ranges and transitions between "normal" and "heretical" may lead to new understandings.

Bob Wilson

 

I think "heretical mode" needs a new name ;O)

What's interesting about the set of spins you describe is that in the Prius PSD simulators online you can actually arrive at this scenario relatively simply in just normal playing with the sliders - but, because none of those demos worry about Torque, it doesn't tell the whole story.

One thing I can't get a straight answer out of my Engineer friends about is what exactly the addition is when the sun gear spins one way and the ICE the other - do you add the torque of the 2? Or does the ICE only provide torque above what the sun gear is already providing?

It sounds like what's being accomplished is that the sun gear is in a low-rpm, high torque state and the ICE is in a moderate-rpm, moderate torque state, but when cruising the car doesn't need all that torque so it bleeds off a lot of torque with MG2 with minimal impact to RPM, and a constant flow of electricity that can variably go to MG1 or the battery to provide a range of cruise gear ratios.

This PSD is one simple-looking, complex device.

 

Hi,
On proposal was "electric overdrive" but in truth, I'm not sure there is a good term to use.

AMEN!!! What is needed is some kind of 'coloration' of the teeth showing torque that move the car forward as opposed to torque that is a consequence of generating shaft power.

This is the 'headache' exercise. The key is the planetary gears are driven by the ICE shaft. As they rotate, the ring-gear side is providing positive torque to move the car forward. The sun-gear side is being balanced by MG1 whose torque is also in the direction of moving the car forward. What I mean is if the ICE shaft broke and the planetary gears froze on their shafts, the forward torque of MG1 would move the car forward.

I'm not sure I follow this. Let me suggest that once I get my charts published and reviewed, I'll bring them here and it will hopefully make more sense.

I suspect the part that will be really confusing for some is that in some modes, the MG1 torque that allows the ICE power to move the car forward comes from generating power. In other modes, the MG1 torque comes from power generated by MG2 and sent to MG1. The reason for this has to do with the reactive force from MG1 being very speed dependent. BUT let me get the charts and data together and hopefully it will become clear.

AMEN!!! Someone once posted something about needing a PHD to understand the HSD/TSD. For sure, it has taken me a while to reach my understanding and Ken's posting helped clarify and lead to better experimental data. It is non-trivial, which means I have no envy for those adjudicating the patent dispute although I'd love to see all of evidence.

Bob Wilson