@
geraldjust Yes, my car is swapped. But the test decribed in my last post was done on a factory 2018 BRZ. The behavior of this car and my swapped one is fully identical for the test in stopped condition. Ofcourse driving wise it is easier to provocate the cut off in my LS swap due to the higher weight.
I monitored the thermistor temperature during repeating that test on the standing vehicle. I kept the steering torque all the time pretty high to stress the system and also changed direction multiple times. The thermistor temp rised constantly over several minutes, but behavior was same. The cut off jumped in, and as soon as the steering was released slightly, support came back.
It was same when starting the test at 30°C thermistor at the beginning as it was at 40°C in the end. I was provocating cut offs against lock for about 5min. So I highly doubt a mechanical or thermal limitation, since during the complete test run nothing in the basic behavior changed. (Again note: The change request would not be to further increase support, everything needed is to keep that thing running...)
I also was able to define the limits further. The cut off jumps in as soon as the measured steering wheel input torque reached 6Nm. The requested current is reduced to zero in that second.
Then the value just instantly jumps to 7Nm, what seems where the sensor itself tops out, since one still is holding the steering wheel while the motor quits, what inturn results in a instantly higher input torque.
Then, once the steering input torque is slowly reduced, the support kicks in as soon as 5.5Nm is reached. The requested current is then set to the value (or at least ball park) which could be seen during the way towards lock.
This game can be played quick or slow. Means exceeding 6Nm and holding the input torque above 5.5Nm for 10s results in a 9s cut off (about 1s system reaction time...). If you stay above that 5.5Nm for 1.5s, the result is 0.5s cut off. The whole procedure can be repeted in close to 1Hz frequency or any frequency lower then that.
One more observation: The highest current values of above 40+ amps was seen during fast turning of the wheel. Highest current when hitting the lock was about 30-35. So my conclusion: the motor driver is also able to provide even higher amps.
Also the temp is not instantly freaking out, since internal temp sensing keeps in acceptabel range even over longer stress periods and, most important, behavior and values dont change all over the stress test.
The behavior is a simple reaction towards input torque and pretty much doesnt care about any other conditions. Not temp, not current requested, not current controlled, not steering angle nor steering speed. It's a simple and clasic one-variable-condition with hysteressis.
I cannot make any other conclusion but the intension was to create a steering lock overload protection (what absolutely makes sense, no doubt about that), but nobody cared about giving this function a little more then absolute basic logic. This results in a unneccessarily low marging of the EPS system support and the possibility of suddenly losing EPS support during harsh turns and as well the possibility of sudden return of the support, what from my personal expierience, is the far bigger issue towards vehicle stability/control and safety.
The driver is still turning the wheel to stay with the turn, then suddenly support returns and the steering wheel gets "light", what results to a sudden, short inwards turn of the steering wheel due to driver reaction time. This is pretty much like a forced mid-turn-scandinavian-flik.
What actually might be a limitation by physical Design ist the fact, that I was not able to read a steering wheel angle. This somehow triggers me, since the zero position can be calibrated, what draw me to the conclusion that the system must have some kind of knowledge about the steering angle. Though, there is no readable value for that. Only available angle it motor angle. But this can not be easily transfered to a steering angle, since the motor does multiple turns and there is no turn counter. So the absolute position is unknown.
If there actually is no steering angle measured, what somehow makes zero Sense in my head, it's clear that a lock protection has no other option then to relie on input torque only...