Regen Braking Issue When Turning

[hybridbear]

I filed a complaint with the NHTSA, the text is below. The complaint ID # is 10758745. I am also going to contact the dealership with the data I have logged so far & ask them to send it to the Ford Corporate Engineers for help.

 

The regenerative braking will cut out under specific circumstances and the car will feel like it is lurching forward instead of slowing down. The situation is: braking using only regen brakes, no friction brakes; steady pedal pressure; going 15-20 MPH; turning the steering wheel at least 90 degrees left or right; driving on smooth pavement. Data I have logged from the SOBDMC indicates that the traction motor briefly reduces its negative torque which causes the car to surge forward. In one instance that I logged, the negative torque shows around 48 ft-lbs and then suddenly drops to about 8 ft-lbs. The traction motor then gradually increases torque back to the appropriate level. In another instance, the negative torque suddenly went from about 28 ft-lbs to 8 ft-lbs. The drop in torque occurs in 1/10 of one second per my logged data. It takes about 2.5-3.0 seconds for the traction motor to return to the appropriate level of negative torque to stop the vehicle.

This behavior began occurring right after our vehicle was serviced by a local Ford dealership. The work done by the Ford dealership included replacing the 12V battery & 3 recalls: 14S21, 15E03 & 15S14. I believe that this service is responsible for these problems, as this issue was not present before our car went to the dealership.

Edited August 24, 2015 by hybridbear

[lolder]

A few years ago, Prii had a similar problem when they went over grates or manhole covers while turnong. I think it had something to do with the ABS and I believe a software change fixed it. Yours is probably something else.

[hybridbear]

A few years ago, Prii had a similar problem when they went over grates or manhole covers while turning. I think it had something to do with the ABS and I believe a software change fixed it. Yours is probably something else.

Likely. Our issue is on smooth pavement, not when going over bumps. Many cars will behave strangely when going over bumps & braking because the tires momentarily lose contact with the ground.

[hybridbear]

Update from the SA:

 

Ford has no answers or suggestions until we get the vehicle in and do some module checks and programing checks.

I'll take the Energi back to the dealership tomorrow.

[hybridbear]

Today I got FORScan working completely with the Energi. I can only log PIDs from one module at a time, but FORScan has a better refresh rate. I logged data from the SOBDMC. I added Wheel Speed Sensors divided by 10 to make them scale better on the chart. This enables you to clearly see when the car is turning. This data was recorded during a right turn. The charts I posted earlier were both from left turns.

 

You can see that the HVB charge rate decreases in proportion with the decrease in torque from the traction motor. The traction motor RPM doesn't show any abnormal values during this time. The numbers along the X-axis are the time in milliseconds since I began streaming data in FORScan. This time, the reduction in stopping power lasted about 4 seconds. This appears to be longer than any other occurrence that I have logged.

 

Edited August 24, 2015 by hybridbear

[hybridbear]

I did some additional testing tonight. I went to the empty parking ramp at work & tested some various scenarios.

Low Gear Left Turn

 

Low Gear Right Turn

 

Braking Before Turning the Steering Wheel

 

Turning Before Pressing the Brake Pedal

 

Notice how when using Low Gear to slow down when turning the regen doesn't cut out at 15-20 MPH.

[GrySql]

Ford Engineering ought to appreciate those graphs. I doubt that they have ever done anything exactly like this because it is such an unexpected and vague system error. This is excellent work.

 

I think you ought to have FordService get involved here and get Ford Engineering to take a look at this while it's online here on the Forum.

[hybridbear]

Larry tested with his car & determined that the car is supposed to reduce regen during turns. When turning the two front wheels turn at different speeds. Regen braking slows both front wheels at the same rate. Thus friction brakes are needed when braking while turning since each brake pad can be applied with a different amount of force. The issue appears to be that the brake pads are not being applied quickly enough & thus the surge is felt. The regen braking force doesn't come back for quite awhile according to the graphs. So the brake pads must be getting applied shortly after the sharp drop in regen force.

 

Larry postulated that the issue is different modules being at different software levels which are not compatible. Hopefully that will be all it takes to fix it.

 

With this additional information, I wish acdii was still around to get feedback about this issue with his FFH to help figure it out.

[hybridbear]

More info about how the braking is supposed to work:

Regenerative Braking Mode

The ABS module determines the amount of braking torque necessary and sends that info to the PCM along with the current threshold for ABS intervention. The PCM determines how much braking torque the electric motor can provide based on the High Voltage Traction Battery (HVTB) state-of-charge and sends this information back to the ABS module. At the same time, the electric motor is switched to a generator which supplies the determined amount of braking torque. Based on the amount of braking torque the PCM can deliver, the ABS module determines whether it is necessary to apply the friction brakes or if the brake torque from the electric motor is sufficient to safely stop the vehicle.

Friction Braking Mode

Under some circumstances, the brake torque generated by the electric motor is insufficient to bring the vehicle to a safe, controlled stop and requires the assistance of the conventional friction brakes. Additionally, the state-of-charge in the High Voltage Traction Battery (HVTB) may not allow for regenerative braking to take place or the vehicle may be experiencing an ABS or stability control event.

In these instances, the ABS module activates a mechanical relay which supplies power to the brake vacuum pump. At the same time, the ABS module sends a PWM voltage to a solenoid mounted on the brake booster. The solenoid allows vacuum from the vacuum pump to enter the brake booster which moves the booster push rod and applies the conventional friction brakes.

During certain braking events, the friction brakes can be applied directly by the driver. The brake booster push rod is equipped with an adjustable stop, once the brake pedal travels far enough to engage the stop, the brake booster push rod is forced into the master cylinder and the conventional friction brakes are applied.

I believe the issue is a module calibration issue which is causing the friction brakes to not be applied promptly when turning & braking at the same time.

Edited August 25, 2015 by hybridbear

[FordService]

Ford Engineering ought to appreciate those graphs. I doubt that they have ever done anything exactly like this because it is such an unexpected and vague system error. This is excellent work.

 

I think you ought to have FordService get involved here and get Ford Engineering to take a look at this while it's online here on the Forum.

 

Thanks!

 

Update from the SA:

I'll take the Energi back to the dealership tomorrow.

 

Keep me in the loop with how the dealer visit goes, and I'll check out some options on my end. :)

 

Meagan

[hybridbear]

The dealer claims it is fixed. They're coming to pick me up now. We'll see if it is or not.

[hybridbear]

The dealer claims it is fixed. They're coming to pick me up now. We'll see if it is or not.

The car is not fixed. Ford has no answers.

[hybridbear]

Here is what I sent the SA this morning:

 

Dean,

This is the diagram of all the modules involved in controlling the combination of regenerative braking & the friction brakes from section 206-09 Anti-Lock Brake System (ABS) and Stability Control Description & Operation.

According to the description of Regenerative Braking Mode, the ABS module determines the necessary braking force & sends that info to the PCM. The PCM then determines how much braking should be done by the traction motor & sends that info to the TCM (also known as SOBDMC). The SOBDMC controls the behavior of the traction motor for regen braking. When the steering wheel is turned & the wheel speed begins to differ, the SOBDMC cuts the regen braking force. At this time, the PCM should be sending a message to the ABS module to engage the friction brake pads to make up the difference.

Another subheading says:

Brake Modes

Because much of the brake torque required to stop the vehicle can be achieved through regenerative braking, it is not always necessary for the conventional friction brakes to be applied. The brake pedal uses a pedal feel simulator that acts against a curved bracket to give the driver a simulated pedal resistance as the brake pedal is applied. The ABS module uses the driver input on the brake pedal, wheel speed sensor input and the lateral deceleration messages from the RCM to determine the amount of deceleration the driver is requesting and which brake mode is necessary.

 

The blending of friction braking with the reduction in regen braking while turning is what is experiencing a momentary lag. This issue has appeared since the PCM was recently updated per the 15E03 recall & the RCM was replaced per the 14S21 recall. No other modules in the above diagram were updated. I really doubt that Ford has tested all the possible combinations of module calibrations for compatibility issues. It appears that this is a software compatibility issue. The issue could stem from either the new RCM or the updated PCM calibration. Can you please check with the Ford engineers to see if the ABS module, SOBDMC & others that play a key role in braking while turning can be updated to the latest calibration? Perhaps bringing all the modules that are at play in this scenario up to the latest calibration would fix the issue.

Thank you,

Edited August 26, 2015 by hybridbear

[GrySql]

Love it.... Good work HB!

 

:mademyday:

[murphy]

How sharp does the turn have to be and how fast to notice the problem? I have the new RCM but not the PCM update. I have not noticed anything turning into my driveway. I drive most of the time in L so the regen should be there.

[hybridbear]

How sharp does the turn have to be and how fast to notice the problem? I have the new RCM but not the PCM update. I have not noticed anything turning into my driveway. I drive most of the time in L so the regen should be there.

I'm not so sure that the steering wheel angle is all that important. I think it's more about the difference in wheel speed. I notice it most often when making left turns & slowing down, such as when turning into a parking lot or driveway. The lurch seems to happen between 15-20 MPH based on the graphs I've previously posted. I'll be over at my parents' house tomorrow night & I'll do some testing in their C-Max Energi.

[md13ffhguy]

How sharp does the turn have to be and how fast to notice the problem? I have the new RCM but not the PCM update. I have not noticed anything turning into my driveway. I drive most of the time in L so the regen should be there.

What? You do most of your driving in L? What speeds are you driving? Can you provide some more background on that, please?

[murphy]

What? You do most of your driving in L? What speeds are you driving? Can you provide some more background on that, please?

L is not low gear like in most other cars. There are no gears in an eCVT transmission. It causes regeneration when the accelerator pedal is released. In an emergency it means that you are braking as soon as your foot leaves the accelerator pedal long before it reaches the brake pedal. It allows one pedal driving in many cases. The only downside is that the brake lights are not turned on when braking is happening. This is not a new situation. A manual shift car can be slowed down by downshifting to a lower gear with no indication to the car behind that you are slowing. It is the other approach to regenerative braking and is the way a Tesla works. It is not full regenerative braking so more is available when the brake pedal is pushed.

 

I have an FFE so my ICE is hardly ever on. It would not be as useful in an FFH because a full charge in the HVB would mean the ICE comes on in engine braking mode. In an FFE it just charges the battery and the ICE doesn't get involved.

[GrySql]

I filed a complaint with the NHTSA, the text is below. The complaint ID # is 10758745. I am also going to contact the dealership with the data I have logged so far & ask them to send it to the Ford Corporate Engineers for help.

I was looking at the NHTSA website and saw your complaint. Compared to the other complaints yours is the most professional, logical, complete and backed with facts. I don't know how they can ignore something so well presented. I hope it's not just the number of complaints but rather the quality of the complaint that gets their bureaucratic attention.

[hybridbear]

I confirmed that the reduction in regen is operation as designed. The chart below is from my parents' C-Max Energi. Note how regen braking force is reduced when I turn the wheel. However, in the C-Max this transition from regen braking to friction braking is imperceptible.

[gkinla]

L is not low gear like in most other cars. There are no gears in an eCVT transmission. It causes regeneration when the accelerator pedal is released. In an emergency it means that you are braking as soon as your foot leaves the accelerator pedal long before it reaches the brake pedal. It allows one pedal driving in many cases. The only downside is that the brake lights are not turned on when braking is happening. This is not a new situation. A manual shift car can be slowed down by downshifting to a lower gear with no indication to the car behind that you are slowing. It is the other approach to regenerative braking and is the way a Tesla works. It is not full regenerative braking so more is available when the brake pedal is pushed.

 

I have an FFE so my ICE is hardly ever on. It would not be as useful in an FFH because a full charge in the HVB would mean the ICE comes on in engine braking mode. In an FFE it just charges the battery and the ICE doesn't get involved.

 

Murphy, now that you've explained it so eloquently, I won't be afraid to put the trans into low as the OM says you can at any speed. I may try the one pedal driving accasionally. I have had the tac on in the LH display and tried shifting into L, without any increase in RPM. This would be good in slow Los Angeles FWY traffic.

Edited August 31, 2015 by gkinla

[gkinla]

 

Murphy, now that you've explained it so eloquently, I won't be afraid to put the trans into low as the OM says you can at any speed. I may try the one pedal driving accasionally. I have had the tac on in the LH display and tried shifting into L, without any increase in RPM. This would be good in slow Los Angeles FWY traffic.

 

I just completed a short FWY drive and I was wrong about no increase in ICE RPM. At 65 mph the ICE is ususally around 2k rpm with no load. When I dropped the eCVT in L the rpm jumped to 4k. The other times I shifted into L, I was decelerating coming up to a stop light and going very slow. When crusing on a city street at 35, on battery, shifting to L without lifting off the gas, the ICE comes on to 4k rpm. When lifting off the gas, this does slow the car down much faster using both regen and ICE braking. This is what I've experienced, others may experience it differently.

[GrySql]

 

I just completed a short FWY drive and I was wrong about no increase in ICE RPM. At 65 mph the ICE is ususally around 2k rpm with no load. When I dropped the eCVT in L the rpm jumped to 4k. The other times I shifted into L, I was decelerating coming up to a stop light and going very slow. When crusing on a city street at 35, on battery, shifting to L without lifting off the gas, the ICE comes on to 4k rpm. When lifting off the gas, this does slow the car down much faster using both regen and ICE braking. This is what I've experienced, others may experience it differently.

My FFH acts similarly, Low is not useful for freeway driving because the ICE rpm gets so high. I can't imagine doing that as a gas saving technique. Maybe the FFE works a bit different?? In stop and go traffic it may help.

Edited September 1, 2015 by GrySql

[murphy]

The FFE is running on pure electric power. The ICE does not come on unless L is used with a fully charged HVB or it's real cold outside or the HVB is depleted and the car has switched to hybrid mode. In my FFE I am not trying to save gas (the ICE does not run, there is no gas to save). L provides regen braking without touching the brake pedal.

[GrySql]

The FFE is running on pure electric power. The ICE does not come on unless L is used with a fully charged HVB or it's real cold outside or the HVB is depleted and the car has switched to hybrid mode. In my FFE I am not trying to save gas (the ICE does not run, there is no gas to save). L provides regen braking without touching the brake pedal.

Got it, good explanation, thanks.