Hybrid Transmission Recorded RPM Data Analysis

[plus 3 golfer]

I had a little time today so I analyzed some real time data on my C-Max that I recorded several months ago.  I recorded speed data of the various components of the Hybrid transmission using ForScan to calculate certain fixed ratios so that one can compare the 2013 ratios with newer MY ratios as Ford said that they made “hardware” changes to the transmission for MY 2014.

 

“The upgrades build on powertrain software updates Ford announced last month for the 2013 C-MAX Hybrid. The 2014 C-MAX also will benefit from several hardware changes, including: Gearing changes that result in a more efficient transmission drive ratio” _{- FORD}

 

Of course now we need someone to do the same for MY 2014+ so that my 2013 data can be compared with MY 2014+ data.

The attached chart shows the relationship of the motor, generator, and ICE speeds and calculated speed ratios.

 

1)      Vehicle speed averages 72.2 mph as recorded.  “The hybrid vehicle uses three methods to calculate vehicle speed. The PCM uses the ABS signal if available, and will substitute the motor speed if the ABS signal is missing. The PCM will use the engine and generator speed calculation if both the ABS and motor speeds are unavailable.”

 

2)      Tire speed is calculated based on changing the tire revolutions per mile to yield the 2.51 axle ratio.  The tire revs per mile needed to get a 2.51 ratio was 811.   The spec tire ratio is 803.  This is a difference of 1%.  However, “a tire transitions from an unloaded to loaded state as it rolls, continuously flattening where the tread footprint comes into contact with the road. These continuous transitions result in some tread slippage, again increasing the tire revolutions per mile beyond what simple math would indicate.”

 

3)      (Motor speed / Tire speed) ratio is calculated to be 9.0

 

4)      (Motor speed + Generator speed) / ICE speed) ratio averages 3.55.  The variances from the 3.55 are attributed to variances in scanning frequency when there are large, quick changes in the variables (for example ICE ramping up / down).  The ForScan scan rate averages 83 milliseconds with a standard deviation of 20 milliseconds.  Thus, the time from the first data point scanned to the last data point scanned during the large, quick changes will likely affect the calculated ratio since I'm not using the time stamp associated with each variable but rather the time stamp for the first variable scanned (too difficult to try to sync the time stamps for each variable scanned). 

 

Below are observations from the chart.

 

1)      When ICE speed is 0 rpm, the Motor speed and Generator speed are equal but of opposite sign.

2)      When Generator speed is zero, the overall ICE / Wheel ratio is 2.51 – the axle ratio.

3)      The Generator effectively controls the overall ratio in this case from a numerically high ratio of 3.3 (ICE RPM about 3000) to a low ratio of 1.7 (ICE RPM about 1660).  

Edited October 4, 2016 by Plus 3 Golfer

[fbov]

I had a little time today so I analyzed some real time data on my C-Max ... Below are observations from the chart.

 

1)      When ICE speed is 0 rpm, the Motor speed and Generator speed are equal but of opposite sign.

2)      When Generator speed is positive, the generator is producing power and ICE rpm increases.  This is referred to a “positive split” mode operation.

3)      When Generator speed is negative, the generator is using power and slowing down ICE RPM.   This is referred to as “negative split” mode operation.

4)      When Generator speed is zero, the overall ICE / Wheel ratio is 2.51 – the axle ratio.

5)      The Generator effectively controls the overall ratio in this case from a numerically high ratio of 3.3 (ICE RPM about 3000) to a low ratio of 1.7 (ICE RPM about 1660).  

1) this is a mechanical requirement of the power split device. When the planetary gears are stationary, sun RPM = - ring RPM, or the planetary gears aren't stationary. 

 

2 & 3) Generator rotational direction is not necessarily correlated with power produced. It's too easy to change polarity of the applied field as Generator passes through 0 RPM. Why would the generator would ever use more power than unavoidable parasitic losses? 

 

4 & 5) I don't see how any of this matters when the Motor is running at 9000 RPM. Given that's fixed, Generator and ICE RPM move in a fixed relationship, shown in your data. 

 

Any chance you're looking at the ratios too hard?

Frank

[plus 3 golfer]

1) this is a mechanical requirement of the power split device. When the planetary gears are stationary, sun RPM = - ring RPM, or the planetary gears aren't stationary. 

 

2 & 3) Generator rotational direction is not necessarily correlated with power produced. It's too easy to change polarity of the applied field as Generator passes through 0 RPM. Why would the generator would ever use more power than unavoidable parasitic losses? 

 

4 & 5) I don't see how any of this matters when the Motor is running at 9000 RPM. Given that's fixed, Generator and ICE RPM move in a fixed relationship, shown in your data. 

 

Any chance you're looking at the ratios too hard?

Frank

 

 

Edited October 4, 2016 by Plus 3 Golfer

[fbov]

1) True

2&3) True, but the direction of rotation of the generator is related to the direction of flow of mechanical and electrical power of the Hybrid system in normal driving with ICE. Positive rotation of the generator indicates charging (current out of the generator).  Negative rotation is power consumption (current into the generator) when not in EV mode.  ....

 

...The point is did Ford change any transmission hardware in later MY C-Maxes as stated in the quote in my first post to improve efficiency (I doubt it).  

I now understand your interest in the ratios, but not the first part. 

 

There are two parts to the tractor and generator equations, rotation direction and electric polarity. Please consider that:

- the traction motor produces torque in both forward and reverse directions. 

- the traction motor produces both torque and braking (opposite polarity) forces in the forward direction. Does regen work in reverse, too?

 

All your timeline chart shows regarding the generator is that at ICE = 3000 RPM, gen is at +2K RPM, but when ICE = 2000 RPM, gen is -2K RPM.  That sounds like a reasonable requirement of the power split gearing.  I see no reason to expect a change in polarity of the gen output. Very easy to change applied field polarity going through 0 RPM.

 

As to the phrase "generator motor is reducing engine speed," that sounds like control system effects, not a transfer of mechanical torque; batttery is full, so gen load is low, allowing a low engine speed run mode. while the gen is still spinning fast enough to make power if needed. although that may not be part of the control system, per their diagrams.  

 

And thank you for your continued contributions,

Frank

[plus 3 golfer]

I think we are saying the same.  

 

Here's some excerpts from the manual:

 

"The generator motor is a three phase permanent magnet AC motor connected to the sun gear of the planetary gear set. The generator power inverter is internal to the TCM and receives a DC current from the high voltage traction battery. The DC current is inverted to an AC current, which is controlled by the TCM. The generator is used as a starter for the internal combustion engine, charges the high voltage traction battery, and controls the engine speed. "

 

"The TCM is responsible for torque determination and energy management functions. The TCM monitors gear selector position (PRNDL), brake pedal position (BPP) and accelerator pedal position (APP). The TCM then makes a torque command determination. Positive torque is perceived as vehicle acceleration and negative torque is perceived as braking. Based on the amount of torque requested by the driver, the TCM decides which power source has to deliver the torque to meet the driver demand while the powertrain system is running most efficiently." 

 

"The traction motor is a three phase permanent magnet AC motor connected to the ring gear of the planetary gear set. The traction motor is connected to the drive wheels through a series of gears and rotates whenever the drive wheels rotate. The traction motor power inverter is internal to the SOBMDC and receives a DC current from the high voltage traction battery. The DC current is inverted to an AC current, which is controlled by the TCM. The traction motor delivers positive torque for the vehicle in the forward or reverse direction. The traction motor also provides negative torque during the regenerative braking to function as a generator."

 

"In order to achieve optimum fuel economy and lower emission levels, the TCM torque determination and energy management strategy controls the powertrain system with specified operational conditions. First, the torque determination and energy management strategy determines the torque the driver is requesting and the amount of torque each power source can deliver to the drivetrain. Then applies the most efficient power source for that operational condition. Some of the inputs to the energy management strategy include driver demand, high voltage traction battery state of charge, performance limitations of components, battery life, driveability, ambient temperature, and barometric pressure." 

Edited October 4, 2016 by Plus 3 Golfer

[ptjones]

I seem to remember 5 mph is when regen stops, you can see this slowing down with the Battery coach.  :)

 

Paul

[ptjones]

Tested today and got down to 2 1/2-3 mph

[fbov]

 

I think we are saying the same.  

 

... When you look at the generator current it switches from positive (charging) to negative (still charging, or now supplying torque?, ed.) as rpm crosses zero.  ...

 

... One can change the rotation of the 3 phase generator by swapping any 2 phases. So, as current and generator rpm reach zero, the control algorithm can easily swap two of the phases and the generator will start to spin in the opposite direction...

Too many words for a detailed reply. This is the bit where we differ. 

 

Put another way, the polarity of generator output remains the same if you swap phases moving through 0 RPM, does it not? If so, direction of rotation gives no information about the direction of current and torque flow, and thus no information about charging status. The generator can charge when turning in either direction (but not at 0 RPM!). 

 

I also see no condition under which the generator would transfer torque to the ICE to reduce speed. It's pure waste. That's why I call it "control system speak" to say the generator is slowing the ICE in negative split mode. Providing drive torque, yes, with ICE running at low RPM. It's in the interpretation of the explanation; Ford's not doing wasteful things. 

 

HAve fun,

Frank

[plus 3 golfer]

Yes, a 3 phase motor / generator can rotate in either direction (swapping 2 phases) and can act as a motor or generator in either direction based on the phase angle between the voltage and current.  

 

Papers and Ford use "control system speak" when referring to negative split mode.  They are talking control algorithms for a specific purpose not general operation of a motor / generator. 

 

So, there's no confusion, I edited my previous posts. :)

[fbov]

Thanks for understanding that it's all about understanding.