Steering issue under load with track tires

[DocWalt]

In my case it was 100% not something binding as it did it with no end links. Zero rub marks on inner fenders either.

EPS definitely would just give up mid corner under extreme load, or sometimes when trailing into a corner you would just not have any assist.

I had an early 2013 and they "fixed" it on later cars, but it definitely still happens in some cases.

[TRS]

Im digging out this old thread because Im also dealing with the PS cut off issue. After investigating this closely using TechStream live data, I found a trace how this issue is caused.

As commonly known, this issue apears under high load turns especially in cars with sticky tires and aggressiv setup. So my attempt was to monitor the PS motor torque and see what happens. The motor torque in my 2013 EUspec seems to be limited to 7Nm max. Now, since this is a full electric unit, it seems the manufacturer has implemented an intensional "overload cutoff" when the steering is turned against full lock.

This can easily be tested: Start engine on a parked car, turn steering wheel untill full lock towards random direction. When reaching lock, just try to turn the steering wheel further against lock. After about 1s the PS cuts off and stays off, also with no warning sign or fault code deployed, as long as the torque to the steering wheel stays applied. When the "input force" to the steering wheel is reduced by a certain amount, the PS returns service.

Watching this via TechStream data, it can be seen that the "overload cutoff" jumps in once the 7Nm maximum is reached for more then about 1s. This is the same thing what can be observed under high load turns on sticky tires.

Unfortunately the manufacturer seems to not have implemented a steering angle limit failsafe condition. Meaning, it is kind of poor programming, since the steering lock protection feature should only work when steering angle is somewhere below 10% away from maximum value. But this fail check seems to not be implemented.

So, when high load is applied to the steering wheel at any angle and the torque limit is reached for more then 1s, the system quits service. This is kind of crazy, because it is actually dangerous, especially for non spirited drivers possiby entering such a situation unintended. It is redicioulous to just turn of PS support without notice. It would be okay to flash warning lights, to limit support to the max torque or to even slightly reduce it. But switching off intensionally without notice is just damn dump and crazy.

In my point od view this is a tremendous safety issue and should cause a major recall for all vehicles equiped with that system. I dont know If a software update of the PS ECU would be possible without extracting the circuit board, but this beeing said, it's mostly a software issue and Im still looking for a solution.

-The esiest solution would be to raise the max allowed torque. But this ofcourse would just shift the actual issue.

-Maybe this could also bei achieved by an inline resistor in the torque sensor circuit in order to reduce steering support in general. But also this would be a bandaid.

Anyway, the baseline is that someone sopisticated in reading, reverse engineering and reprogramming the PS ECU would be needed. I wasnt able to find any support of this kind yet. So now I want to try my luck here. Maybe @geraldjust could imagine to develop a workarround? Or does someone know about another company or forum member expierienced enough to maybe deal with that issue?

[Opie]

Pretty sure G-Rom Electronics is looking into this, and hopefully a solution.
https://www.facebook.com/GROMElectronics

[Bonburner]

Originally Posted by TRS

Im digging out this old thread because Im also dealing with the PS cut off issue. After investigating this closely using TechStream live data, I found a trace how this issue is caused.

As commonly known, this issue apears under high load turns especially in cars with sticky tires and aggressiv setup. So my attempt was to monitor the PS motor torque and see what happens. The motor torque in my 2013 EUspec seems to be limited to 7Nm max. Now, since this is a full electric unit, it seems the manufacturer has implemented an intensional "overload cutoff" when the steering is turned against full lock.

This can easily be tested: Start engine on a parked car, turn steering wheel untill full lock towards random direction. When reaching lock, just try to turn the steering wheel further against lock. After about 1s the PS cuts off and stays off, also with no warning sign or fault code deployed, as long as the torque to the steering wheel stays applied. When the "input force" to the steering wheel is reduced by a certain amount, the PS returns service.

Watching this via TechStream data, it can be seen that the "overload cutoff" jumps in once the 7Nm maximum is reached for more then about 1s. This is the same thing what can be observed under high load turns on sticky tires.

Unfortunately the manufacturer seems to not have implemented a steering angle limit failsafe condition. Meaning, it is kind of poor programming, since the steering lock protection feature should only work when steering angle is somewhere below 10% away from maximum value. But this fail check seems to not be implemented.

So, when high load is applied to the steering wheel at any angle and the torque limit is reached for more then 1s, the system quits service. This is kind of crazy, because it is actually dangerous, especially for non spirited drivers possiby entering such a situation unintended. It is redicioulous to just turn of PS support without notice. It would be okay to flash warning lights, to limit support to the max torque or to even slightly reduce it. But switching off intensionally without notice is just damn dump and crazy.

In my point od view this is a tremendous safety issue and should cause a major recall for all vehicles equiped with that system. I dont know If a software update of the PS ECU would be possible without extracting the circuit board, but this beeing said, it's mostly a software issue and Im still looking for a solution.

-The esiest solution would be to raise the max allowed torque. But this ofcourse would just shift the actual issue.

-Maybe this could also bei achieved by an inline resistor in the torque sensor circuit in order to reduce steering support in general. But also this would be a bandaid.

Anyway, the baseline is that someone sopisticated in reading, reverse engineering and reprogramming the PS ECU would be needed. I wasnt able to find any support of this kind yet. So now I want to try my luck here. Maybe @geraldjust could imagine to develop a workarround? Or does someone know about another company or forum member expierienced enough to maybe deal with that issue?

should try reporting this to your gov't to file for a safety recall :P

[TRS]

Originally Posted by Bonburner

should try reporting this to your gov't to file for a safety recall :P

Besides the fact that there is no place Id know to place such an report, I dont want to be that guy. 😬

[TRS]

Originally Posted by Opie

Pretty sure G-Rom Electronics is looking into this, and hopefully a solution.
https://www.facebook.com/GROMElectronics

Thx. Texted them right away. Lets see If I can convince them to take care of that topic.

[RedReplicant]

Glad I happened across this thread buried in this small subforum.

DCE makes a kit that replaces the stock motor and EPS controller to fix this, it is $5k. I'll follow this G-ROM thing though I kind of guess from the FB replies that they're not interested in going this deep.

This whole thing just drives me insane, it is easy to drive though but steering wheel feedback when you actually need to feel what the front of the car is doing goes straight to the dumpster.

[geraldjust]

Originally Posted by TRS

Im digging out this old thread because Im also dealing with the PS cut off issue. After investigating this closely using TechStream live data, I found a trace how this issue is caused.

As commonly known, this issue apears under high load turns especially in cars with sticky tires and aggressiv setup. So my attempt was to monitor the PS motor torque and see what happens. The motor torque in my 2013 EUspec seems to be limited to 7Nm max. Now, since this is a full electric unit, it seems the manufacturer has implemented an intensional "overload cutoff" when the steering is turned against full lock.

This can easily be tested: Start engine on a parked car, turn steering wheel untill full lock towards random direction. When reaching lock, just try to turn the steering wheel further against lock. After about 1s the PS cuts off and stays off, also with no warning sign or fault code deployed, as long as the torque to the steering wheel stays applied. When the "input force" to the steering wheel is reduced by a certain amount, the PS returns service.

Watching this via TechStream data, it can be seen that the "overload cutoff" jumps in once the 7Nm maximum is reached for more then about 1s. This is the same thing what can be observed under high load turns on sticky tires.

Unfortunately the manufacturer seems to not have implemented a steering angle limit failsafe condition. Meaning, it is kind of poor programming, since the steering lock protection feature should only work when steering angle is somewhere below 10% away from maximum value. But this fail check seems to not be implemented.

So, when high load is applied to the steering wheel at any angle and the torque limit is reached for more then 1s, the system quits service. This is kind of crazy, because it is actually dangerous, especially for non spirited drivers possiby entering such a situation unintended. It is redicioulous to just turn of PS support without notice. It would be okay to flash warning lights, to limit support to the max torque or to even slightly reduce it. But switching off intensionally without notice is just damn dump and crazy.

In my point od view this is a tremendous safety issue and should cause a major recall for all vehicles equiped with that system. I dont know If a software update of the PS ECU would be possible without extracting the circuit board, but this beeing said, it's mostly a software issue and Im still looking for a solution.

-The esiest solution would be to raise the max allowed torque. But this ofcourse would just shift the actual issue.

-Maybe this could also bei achieved by an inline resistor in the torque sensor circuit in order to reduce steering support in general. But also this would be a bandaid.

Anyway, the baseline is that someone sopisticated in reading, reverse engineering and reprogramming the PS ECU would be needed. I wasnt able to find any support of this kind yet. So now I want to try my luck here. Maybe @geraldjust could imagine to develop a workarround? Or does someone know about another company or forum member expierienced enough to maybe deal with that issue?

Super interesting stuff! Unfortunately the power steering unit is not updatable. There is no way to flash new data into it. Atleast not without taking it out lol. You also need to log the voltage that the alternator is putting out. as the ABS/PS is suuuuper dependent on it. If the voltage drops, it will also cause that behavior. Its not really something to be concerned about that a regular driving situation. What does seem weird is the condition of it happing only 1 second after applying higher end torque than max. My way of thinking is that the physical limitations could be ether the voltage applied to the system may not be high enough, or it runs into a thermal limit. Thermal shutdown sometimes are handles internally by the mosfet packages that do the switching. They have a trip temp and a reset temp. that would make sense on why it would cut off but the module not spit out any error codes. i havent taken the driver module apart, but i might shortly to see how its physically constructed.

[geraldjust]

looked into the spare module i had on a bench and the mosfets looked ok. But i have a strong feeling that its the junction temperature. Please note that junction temp is not the same as operating temp. junction temp is internal to the die package rather than what directly connected to the heatsink . So even if outside was -40c if you overload the mosfet it will thermal trip. The turning off, then on after a while sound exactly this behavior. Their also no temp sensor from the mosfet location into the supporting PCB. So their no way for the module to tell if it trips.

And the only way to figure this out is by putting some data acquisition sensors loggers into the module and testing it out in those extreme conditions.My hunch, its not a software issue, its a physical one.

[RedReplicant]

I saw the EEPROM in there, no idea what is on it though. I assume it is what stores these Battery Voltage Lo, Speed Sig Invalid, etc flags that you can read out in Techstream. Agreed that the MOSFET setup / heat sink looks stout in the BRZ controller.

I've logged the 12v data from car since I'm on Haltech, it doesn't dip when the EPS cuts.

We've seen this happen with the older two wire motor Prius modules and the cut can be solved by soldering the shunt, but the newer three phase modules used by the BRZ/Lexus/etc don't have one onboard. I thought about just swapping the motor / controller from a Prius so I bought spare BRZ and Prius columns w/ controllers... The Prius motor doesn't bolt on due to slightly different flange bolt hole spacing and a different coupler style, which can be easily worked around (see the DCE kit, same same), the issue really becomes that the gear ratios between the BRZ (~18.5 motor turns to one shaft turn) and Prius (~15.25 motor turns to one shaft turn) column are different so the controller software would probably freak out with respect to assist provided / centering / etc.

[TRS]

First Off all, thanks for that great input @geraldjust and @RedReplicant ! (And all Others too ofcourse...)

I can definately confirm that there is no voltage drop. I looked into that very deeply, since my car is swapped and so I was searching for a failure from my side/due to the swap very intense. But voltage not even flickers during that cut off condition. Also, the wiring of the EPS system and also the complete Chassis electrics are 100% factory and where not changed due to the swap.

Im definately no expert in the circuit design and function topic as you are. But I, without having the ability to explain or proof it in any technical way, this behavior seems much too repeatable to be physically inducted by temperature. It can easily be tested on any car with this EPS by just "over turning" against lock. The timespan to cut off is absolutely constant and also the imidiate "kick in" after slightly releasing is repeatable. For me it's hard to Imagine that any overloaded component causes this behavior.

One more reason for that impression: If you monitor the requested torque and keep it slightly below the 7Nm limit, lets say to 6.9Nm, you can hold it there virtually forever without any cut off. I somehow cannot imagine a component behavior which is that dramatically black/white due to a 3-5% load change....

Just sayin', it can hold 95+ % load for minutes but, once you apply 100% it fails in an absolutely constant time span of 1s, independant from any ambient conditions. And after reducing the requested output back to 95% it INSTANTLY cools down and returns service? This somehow does sound far from plausibel in my ears. My conclusion, as said before, would be that this is a programmed behavior. But as said, Im not the expert...

[Ohio Enthusiast]

Originally Posted by geraldjust

And the only way to figure this out is by putting some data acquisition sensors loggers into the module and testing it out in those extreme conditions.My hunch, its not a software issue, its a physical one.

Do you mind sharing some high-res photos of the PCB? Particularly with the component markings visible so we can look up datasheets and see if this theory makes sense. Both sides would be ideal to help with tracing (presuming it's not multi-layer).

[TRS]

Update: I tested the whole thing today on a BRZ FL. Behavior is identical. I was able to further specify the limits. The 7Nm is the max value that the torque sensor can measure for the input on the steering wheel. But the limit for the shutdown is 6Nm. The value jumps then due to the cut off of the support abruptly to 7Nm. (Since one keeps holding the steering wheel...).



The value for "Motor Current requestet" jumps to zero when the input exceeds 6Nm. As soon as the input drops below 5.5Nm the support starts again. Temperature is definitely not the limiting or triggering value. Thermistor temperature increased gradually over several trials. Shutdown occurred at 30°C thermistor as well as at 39°C thermistor. So did the return of support.



Next step will be to test the behavior again on my own vehicle, blocking the steering mechanism near the zero position. If my theory is correct, the behavior at close to zero steering angle will be the same. Next step will then be tests in a driving vehicle with data logger.

[geraldjust]

Originally Posted by RedReplicant

I saw the EEPROM in there, no idea what is on it though. I assume it is what stores these Battery Voltage Lo, Speed Sig Invalid, etc flags that you can read out in Techstream. Agreed that the MOSFET setup / heat sink looks stout in the BRZ controller.

I've logged the 12v data from car since I'm on Haltech, it doesn't dip when the EPS cuts.

We've seen this happen with the older two wire motor Prius modules and the cut can be solved by soldering the shunt, but the newer three phase modules used by the BRZ/Lexus/etc don't have one onboard. I thought about just swapping the motor / controller from a Prius so I bought spare BRZ and Prius columns w/ controllers... The Prius motor doesn't bolt on due to slightly different flange bolt hole spacing and a different coupler style, which can be easily worked around (see the DCE kit, same same), the issue really becomes that the gear ratios between the BRZ (~18.5 motor turns to one shaft turn) and Prius (~15.25 motor turns to one shaft turn) column are different so the controller software would probably freak out with respect to assist provided / centering / etc.

might have a go on reading the eeprom then.
well the voltage does not dip but ive learned that for engine swaps that VSC and PS are sensitive to it. On the stock system, the current draw sensor on the battery knows when too much current is bring pulled. ie, PS or VSC pump. Then the ECU request the alternator for higher current.

So from those older style drivers/motors their DC type with a H-bridge. They can do a good job but electronic wise, but 3 phase AC driving are typically better designs because you can get more torque from them for a given size


@TRS

The temp monitor is not monitoring the junction temp of the mosfets. only in the PCB. So unless you stick a bunch of thermal sensors in the box the temp test is kinda useless.
Is your car swapped?



But il be looking into this further then and so a full diagnosic read on the system then since it peaked my interest now.