LT1 Z51: Do you know: Does the electric power steering run cooler on "Track Setting" than on "Tour Setting"? Does it use less electricity, relatively?

 

It does in so much in that Track mode has less gain on the boost curves (power steering even hydraulic works on the idea that your input torque is multiplied by a value and the system provides that assist).

Boost is a function of mode and speed. Each mode has I think 8 speed curves (with interpolation being done between the curves). Each curve is made by selecting I think 8 torque points, with interpolation being done between.

Regardless you get a 3D-graph of Input Torque (or Driver Torque) and Vehicle Speed being inputs and Output Torque (or Assist Torque) being the output. Between modes the magnitude is changed between these values with Tour having the most gain, Track the least and Sport between the two.

Getting back to your question, electrical draw is a function of that gain transiently. So the quicker the gain increases (driven by the need for fast steering wheel speeds) and the higher the gain (driven by more toque needing to be generated) the more the system will draw current.

Given all other things being equal, such as temperature and voltage, two identical maneuvers, one in Tour the other in Track, the one in Track will take less current. This can however get "washed" out if voltage drops (system compensates to a point by drawing more current) or temperature (system reduces current to cool down electronics).

Typically in a Corvette I'd expect to see "cooler" temps on EPS on the track (due to higher speeds and more airflow), and more voltage unless the engine is heat soaked and running the electric cooling fan excessively. So these as well as the lack of gain in Track mode would on average cause EPS to run better at the track than on the street.

Note: The temperature comments only apply to RWD "Front Mounted" Gears, as any "Rear Mounted" gears are behind the engine and thus right near the exhaust. Which as you know is the hottest thing in the car. All FWD and some RWD cars are like that. Corvette is a "Front Mounted" design.

 

You may not have lost assist. You may have had derated or reduced assist due to overheating.

The software isn't messed up by heat. Rather the MOSFETs will fail at over 125 degrees C, so the system reduces assist to keep the hardware safe. A reduction of assist below 40% will turn on the dash light in a Corvette. This level of reduction WILL feel to the average person like a total loss. It is not, but it's still very uncomfortable.

This type of thing is present in all EPS systems. The threshold for driver notification varies by manufacturer, as does the message on the dash.

 

It's not poor design. It's Physics. The SW does what it needs to do to protect the hardware. EPS has new failures versus HPS, and unfortunately most HPS failures where slow (due to a leak) and had a noticeable physical attribute (a puddle).

EPS being an electronic system doesn't offer those types of warnings. It usually just fails. This is how all electronic systems work. A lot of work is done in mitigating those failures and trying to control the systems reaction after one does happen.

The fact of the matter is with EPS you will never see 100% up time and your failure types will be more noticeable (and probably more annoying) than you were used to with HPS.

 

Mine didn't start acting up until this summer when our day time temps have been in the 110's/1-teens and overnight lows in the upper 80's to low 90's. I think one poster that reported the issue though wasn't in a situation with a high ambient temperature.

 

The Tail of the Dragon would be an interesting test for one of these replaced assemblies to see how prone it is to overheating since it is nearly constant curves but at a moderate speed.

LT1 Z51, do you know if this is a different supplier being used for model year 17?

 

You've got ETC, and on some Automatic Transmissions now Shift by Wire, and don't even think about ABS or ESC. All those things can fail for similar if not identical reasons as the EPS.

EPS is unique though in that the Self-Steer failure must be avoided at all costs, so maybe earlier systems were too "conservative" and removed assist more free than really required.

But one thing is for certain. If at 60 MPH, your engine throttle fails open, you can shift to neutral, and control the car; your brakes fail, you can coast to a stop, and control the car; your steering self-steers, well you don't recover from that, the car will be uncontrollable. So the propensity was to remove assist, thereby removing the self-steer hazard, and keep the car controllable.

Take that as you will, but I'm always more comfortable with a loss of assist versus a self steer.

 

There is no acceptable down time for this system and I cannot believe that GM or any manufacturer would put a product out that said that X percent of downtime on a power steering unit was acceptable. If someone at General Motors signed off on possible power steering failures as being acceptable I need a different brand car.

 

It's still Bosch, formerly ZFLS. I'm unsure if any hardware was changed within the system. I'd need to see two parts side by side and compare some numbers in them (Bosch prints part numbers on the motor and ECU housings as well, those are NOT GM part numbers).

The SW, specifically the calibration, is almost certainly updated. That happens every year. It is possible calibration thresholds were changed year to year, which could manifest in more aggressive reductions or more frequent reductions.

 

You are aware all cars that have electronic parts have this issue.

It's not a matter of GM accepting the downtime. It's a matter of that's how electronics work. All electronics fail, and all of them have a rate of failure.

These failure are not the same as mechanical components which almost always are time, material, and wear rated. You cannot design a perfect electronic part.

If that's your expectation you should stop buying and driving cars.

 

Thanks for the info, it sounds like something certainly changed for the worst.

I am confident Bosch will figure it out quickly unlike GM and Stanadyne did with their injection pumps on the old 6.5L diesel. The fuel solenoid driver transistors were meant to be cooled by the diesel fuel but that didn't work so well and I went through a couple of in-warranty replacement pumps before trading it in. One of the popular after-market accessories was a relocation kit that put the two transistors on a heat sink out in the incoming air stream which seemed to cure the problem. Of course Bosch has had their own issues in recent years with self destructing high pressure diesel pumps for the common rail systems.

 

Power steering units failing is not acceptable under any circumstances. For any reason. If the technology doesn't exist to have them up 100% of the time then they shouldn't exist on motor vehicles. I spent many years in the car business selling very high end automobiles that use electric power steering and I have never once ever had a power steering unit fail

 

Just because you never saw a failure doesn't mean it didn't happen.

I'm also speaking of "design failures" not failures due to a quality spill. ISO 26262 uses FIT (Failures in Time) to describe the robustness of a system to a failure. A FIT is the number of failures in 1 billion hours of that part. It applies to all electronics from resistors to microprocessors.

Most if not all steering systems are sub-10 FIT or ASIL-D in automotive terms for Self-Steer failures as a system. However most current, if not all current systems are QM (the lowest rating) for Loss of Assist. These systems have a FIT rating in the thousands (2000-5000 is typical). This is because a removal of assist and return to manual steering like hydraulic was deemed safe.

The industry after the many steering recalls (notably the Cobalt one), has been moving to increase the FIT rating level. It probably will move closer to 10 FIT like a self steer. However, this does not remove all failure as that is physically impossible.

Hence my comment, if you demand 100% uptime or 0 FIT, then you shouldn't drive any car with any electronics in it.

 

[QUOTE=LT1 Z51;1595181757]Just because you never saw a failure doesn't mean it didn't happen.[QUOTE]

If I don't notice it, I don't care. If it happens when I'm driving and I don't have power steering, or any system for that matter, it's not acceptable.

I really appreciate the explanations on these systems, it's valuable and interesting but I think you're writing as an engineer, not as a consumer/end user. I won't put up with any system in my car failing, intermittently or otherwise, nor should I have too. GM can either get it right or buy it back.

 

I'm writing as both consumer and engineer.

Expectations need to be realistic. Saying you don't want any electronic parts in your car to fail is akin to saying you never want to have to reboot your phone or restart your PC due to it freezing or an error.

Simplistically speaking all electronics have this issue. People are just conditioned to accept it. The only way around it is to have multiple redundancies, like you see in Aerospace and Military applications. However this greatly increases cost.

Basically you could get your way and have a car that would almost certainly never fail (in fact it would but a redundant system would hide that failure from you), but to do that your car would increase in cost 2 to 5 times.

As a consumer I'm not willing to pay that cost, I don't think you are either.

 

^^^
I am always amazed that Bill Gates became the richest man in the world producing a product that crashes and requires workarounds all the time! Guess for computers and cell phones it's acceptable!

That said, power steering going out is scary! Reminds me of an unexpected problem that occurred with a microprocessor MIG welder we sold that was making spot welds in an automated line producing food freezing belts. Watched as our engineer duplicated the problem in our Lab that occurred once in many thousand welds. He could not understand how it happened and went through his software many times.

I asked, "If you can't find it, can you put in code that if it ever happens will shut the system down instead of having the power spike that creates a hole in the belt?" He did! He never understood why it was happening in the first place but prevented a destroyed part the occasional time it did.

Therefore, for the power steering, if it's an intermittent ground issue, for example, why not turn the system back on and have a warning message but not leave it with no power? Just Sayn'.

 

There are some questions as to whether this is heat related. In my case it wasn't.
Both times it happened it was early in the morning low 70's and dry and Ive only been driving for less than 10min.
I drove a lot last sunday (it didn't happen this day) in upper 80's and got caught in a major traffic jam. Stop and go up hill for 20min hot day and no issues. Except my left leg working the clutch.

 

I wonder what the life expectancy is of the electric motor for the power steering.
That motor seems to be pretty busy.
My Radio Control Airplane motors don't last very long. But I guess they are pushed to their limits more often.

 

DC versus AC motors. The Power Steering Motor its self is probably the most robust part of the electronics. It's just a copper wire stator and a permanent magnet rotor. The parts that will most likely fail are the sensors, specifically the torque sensor (which is located on the input shaft, it's the reason for the cable coming out of that side of the gear) that reads your torque (the driver torque) or the motor/rotor sensor which is inside the electronics but measures the movement of the motor (and thus allows for closed loop control of the motor).

Both of those failures are pretty permanent though, you won't recover from them. These failures all are of the type where the system either recovers during the cycle or on the next cycle suggesting they are either temporary (temp or voltage related) or are latched.

If anything were to "burn out" in an AC motor system it would be the power electronics which convert DC to AC. They consist of 6 MOSFETs in a bridge configuration with 3 high side and 3 low side drivers. The MOSFETs are switched on and off in a variable duty cycle to create 3 AC signals which using a space vector control the motor (since it's a 3-phase system not a single phase, think the AC on the power pole versus the AC in your house).

 

You can't mitigate a ground fault because the fault is outside the systems boundaries. The system is running just fine, but then loses the connection and just turns off. When it turns on it can diagnose that it didn't go thru a proper shutdown (this is done usually by flipping a register during a regular shutdown, when power is removed the register isn't flipped so upon reboot the system knows it suddenly lost power). So you can mitigate the recovery of power, and ramp in assist much quicker, but you can't do anything to prevent the loss.

Well not without putting a battery in the steering or a super cap near it (which would protect the system from sudden loss and dips in power for a short duration. Both of those are prohibitively expensive options mind you.