So I have been doing some thinking on this and using my electrical background as I think through it. So I am a part owner of an Electrical Contracting business that does a lot of industrial wiring with PLC controls and what not, including currently working on the new manufacturing plant for Rivian Battery truck/SUV and vans for the Amazon fleet. I am saying all that just to clarify my thoughts. I think this issue is 2 separate safety shutoffs in the equation (maybe Paul can shed some light from the shop manual side of this). I believe that the issue Paul is describing when he was out playing around and overheated his power steering for a few minutes before it came down in temp and came back on-line. And the other situation is when we are driving fine and go to turn on pavement or high traction areas and the PS kicks out for a second then comes back on line. In the first situation Paul is actually overheating the PS pump and that will stay off till the heat gets back in range and that sensor is on the pump it self. The next situation which is intermittent PS failure is due to more of an overcurrent draw issue in my mind. This could more than one possible cause for this situation.....one reason could be that when we are on pavement and trying to turn with the extra traction the current spikes past the parameters set by the controller and then after that current drops and then the PS comes back on-line and it works from there because the initial turn is past the spike. Yes overcurrent causes heat and they are saying that but in this instance a spike does not have enough time to cause enough heat build up to do what Paul had happen in his situation. That's why a breaker can be pushed past its stated amp draw (startup) for a short period of time before it trips. Start up current is always high and then drops so if that delay in reaction to the spike is not figured into the safety parameters in the controller then it will kick out for a short time when there really is not an issue. The other thing that could be causing the spike is if the system ground is not as good as should be then the when the PS motor goes to full amp load (as on pavement), if the return path is not good (loose ground or paint covering the connection) then the current draw will spike above its normal operation draw to over come the weak ground and cause an intermittent shut down of the PS.
These are just thoughts.... I know that in certain instances the AC power and DC power are different in how they work but theory is a lot of the same. Paul curious your feedback as I am brainstorming here! Thanks.
You are somewhat correct. There is no temp sensor on the Motor so the EPS ECU basically "guesses" when the EPS Motor is overheated by monitoring the steering wheel torque and current draw and reduces or even kills the power to the Motor (kind of a limp mode) until it "guesses" again that it has cooled down or out of a bound state. I believe that there is some sort of maximum amperage threshold that the ECU kills the power to protect the entire system. For instance, if you hold the wheel all the way left or right and the torque applied and/or current are over a threshold, it will kill the power to the motor.
After pondering about this a bit, I think the issue most experience is the ECU killing the PS when it senses too much torque applied to the steering wheel. Bigger/wider/stickier tires require more torque and the ECU thinks the driver has either blocked the front tires from turning or has hit the steering stop. Personally, I think the ECU is overly sensitive and is being fooled by the increased friction and prematurely killing the PS.
There may also be an issue with the wire size/length from the ECU to the Motor that is contributing. It appears to be 12 gauge (maybe 10) and is about 15 feet round trip from the ECU to the PS Motor and the ECU is on a 40 amp fuse. Not that the motor draws 40 amps (fuses in 12 volt systems are generally sized at 125%) but for that amp/distance, a 6 gauge wire should be used to maintain a 2% drop. At 2% drop, 12 gauge wire in only good for 11 amps and 10 gauge is only good for 18 amps. 12 gauge is allowed but produces a whopping 10% voltage drop. Doing the math, that means when the motor is drawing 20 amps, the ECU sees more like 23.
Too small of a wire will cause more amperage draw than the motor is actually pulling so my theory is that the undersized wire has too much resistance, causing the current to peak and is "tricking" the ECU into thinking that the Motor is being overworked or overheating when in fact it is not. This "tricking" of the ECU may be causing the PS to go into "limp" mode when it shouldn't.
A couple ways to find out is to either...
-Change all the power wires (including from the fuse and ground to the ECU) to 6 gauge. OR...
-Move the ECU right next to Motor, stretch the small control wires and use the Winch wires for power.
This may prove the wiring is too small or disprove it, I am not willing to go to that much work to find out. Possibly some Amp testing at the battery vs the motor will reveal any loss in the wiring.
If someone can rule out the wiring, then it would only reason that the torque sensor and/or the ECU are just overly sensitive and nothing we can do about that without reprogramming the EPS ECU. I looked at my PV3 and although DynoJet has added many nodes, PS is not one of them (yet???) so there is no way for me to even take a look.
I sent DynoJet an email to see if they are interested in cracking the EPS ECU. I doubt they will but it was worth a try.
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