Acceleration pedal calibration problems ?

[garygid]

Unless (even if) it is reported by many, when it finally causes an accident, it will be blamed on the driver "mashing" on the accelerator rather than the brake.

If you can reproduce this "Drag-Racer" feature (sudden throttle to modest depression from stop ... leads to a fast ramp up to maxinum power ... even when reducing pressure on the go-faster ... and it continues until the foot is entirely off the pedal), take a dealer Service Rep/Tech for a ride and demonstrate. Then, have them sign and date an accurate description, and get a copy to send to Nissan (and, if ignored, to the NTSB).

Example:
Toyota never recognized a non-reproducable BUG in their (at least 2010) Prius start-up sequence: After turning the Prius ON, when starting to release pressure on the brake, instead of creeping forward/backward as expected, the car would accelerate strongly f/r instead.

In spite of many reported accidents, the NTSB judged it "user error" because many/most of the reported events happened to older drivers in parking lots.

Yes, exactly where it would happen, and the user-group that would be most affected. However, it has happened to ME at least 6 times, and it is a REAL, accident-producing BUG!

Because it cannot be reproduced on demand, and is "rare" (perhaps less than a 1% happening), Toyota never even recognized this accident-CAUSING BUG.

We do not need this "Drag-Racer" feature in the LEAF.

 

[TickTock]

[moving over from the other thread]

I never noticed the runaway accel before, but I looked for it this morning and can confirm that my car exhibits it too. Seems to ramp proportionally to how much you press. At one light I *very* lightly touched the pedal (but did it quickly). It took longer, but I did eventually get to 80kW power to the motor.

I think Ingineer mentioned that the throttle was simply proportional to torque (which is proporitonal to the motor current). If so, this is expected behavior. Since power is torque X rpm, if you hold constant torque/current, the power will increase linearly with speed. What is weird, though is why when you are cruising already at speed, the same throttle position reaches equilibrium at a lower power output.

I was capturing a can log a the time so I will try to ferret out the actual throttle position and power as registered on the can bus tonight and see if we can actually quantify these observations.

 

[turbo2ltr]

Since power is torque X rpm, if you hold constant torque/current, the power will increase linearly with speed.

yes and no. Speed in this case is increased *because* of torque, so it's not quite the same thing.

The pedal controls torque. X pedal position should give you Y torque (which for the purpose of this discussion, we'll say draws Z amps, though in reality current draw is also a function of motor speed as well as the requested torque). If Y torque is greater than the negative force applied by the sum of the rolling resistance plus the drag (plus other negative forces), then the car will accelerate. The more it is greater than that negative torque, the harder you will accelerate. When the Y torque exactly equals the negative force, the car will maintain that speed. If you add more torque the car will accelerate once again, until the negative forces asserted on the car equal the motor output.

But here, clearly the relationship between the motor torque an pedal position is skewed and actively changes in an odd manner producing a motor torque output similar to slowly flooring the pedal even though you haven't moved the pedal, and in some cases, even while backing off the pedal.

Bottom line is, just as in an ICE, at no time should requested motor torque increase when there is a negative delta in throttle positions.

 

[TickTock]

OK. It looks like the pedal, when in "D," is not constant torque... at least not constant current. Below is a plot of the throttle position (blue), battery amps (red), and speed (green). I had the heater on which is why the amps was positive before I even touched the pedal. I quickly applied ~40% throttle, watched the energy screen ramp to 80kW and then stomped the pedal to the floor twice to show the max throttle setting. As you can see, the car delivered full current immediately - even at the 40% throttle setting. Looks like once I hit 80kW and the car was still accelerating, the car started to back off on the current to keep the hp from exceeding limits.

 

[Nubo]

As you can see, the car delivered full current immediately - even at the 40% throttle setting.

Did you notice all of the "bubbles" lite up along with this?

 

[TickTock]

I didn't. Was too busy watching the power meter and for traffic. I need to do another log, I think, where I log full pedal from a stop for comparison instead of after I am already at speed. So I'll watch the bubbles, too, this go around... and turn off the heater.

 

[TickTock]

I did this morning and can confirm the bubble max out, too. I'll plot the logs tonight. I want to also change me wording in the original post. I said the throttle was not constant torque. The flat current response suggests otherwise. What I meant to say and should have said was the torque was not a linear and constistant function of the throttle position.

 

[TickTock]

OK. Here's a nice capture. I actually got a lot of examples of full throttle and light throttle, but this was a nice section of my commute with one of each close to each other. Looks like the amps to the motor is indeed a consistent current for a given throttle position - only tapering off once you reach maximum hp. So my first explanation appears correct. The steady increase in the power (kw) is simply due to constant torque and steadily increasing rpm. Even letting off the throttle will not reduce the power unless you reduce the current faster then you are increasing your speed (why it still climbs even when backing off). You *are* reducing the torque (and acceleration), but you are still accelerating and acceleration means torque and power = torque X rpm.

Another interesting thing to note is just before the full throttle experiment, you can see three spikes in the amps. That is me pressing the brake hard three times to mark the start of an experiment. Take-away: Don't press hard on the brake while sitting at a light - it consumes a significant amount of power!

 

[turbo2ltr]

The steady increase in the power (kw) is simply due to constant torque and steadily increasing rpm.

I'm not understanding what you are trying to explain. What steady increase in power are you referring to?

 

[turbo2ltr]

BTW, when you stop, you will see the power go to zero. As soon as you let up a little on the brakes, a small torque is applied for "creep torque". This is an effort to save battery at a stop while still providing creep torque. Pressing the brakes hard doesn't waste power....but letting up on the brakes will trigger the creep torque. You can sometimes feel the creep torque being applied as there is a very subtle "lurch" the instant you start to let up on the brakes, if you were already holding the brakes very lightly.

 

[TickTock]

The steady increase in the power (kw) is simply due to constant torque and steadily increasing rpm.

I'm not understanding what you are trying to explain. What steady increase in power are you referring to?

I was referring to the observation that although the throttle is held steady at a low position (or even letting off slightly), the car continues to accellerate and power continues to ramp to max (80kW).

 

[TickTock]

BTW, when you stop, you will see the power go to zero. As soon as you let up a little on the brakes, a small torque is applied for "creep torque". This is an effort to save battery at a stop while still providing creep torque. Pressing the brakes hard doesn't waste power....but letting up on the brakes will trigger the creep torque. You can sometimes feel the creep torque being applied as there is a very subtle "lurch" the instant you start to let up on the brakes, if you were already holding the brakes very lightly.

Ah yes - I had forgotten about that. Makes more sense.

 

[TickTock]

Here's another plot of a longer section. I'm rushing out the door so I'll just post it for others to comment.

 

[johnr]

...motor torque increase when there is a negative delta in throttle positions.

Best summary I've read, right there. This is the only vehicle I know of where power output can get stuck at 100% and not decrease when you let up on the pedal (until you back off all the way and enter regen mode).

Also, when this happens, momentarily flooring it resets the algorithm back to normal:

starting from a stop, pedal pressure at about 10% -- power output: 100%
while accelerating, momentarily increase pedal pressure to 100% -- power output: 100%
decrease pedal pressure to about 20% -- power output: about 50% (as expected in D)

 

[TickTock]

...motor torque increase when there is a negative delta in throttle positions.

Best summary I've read, right there. This is the only vehicle I know of where power output can get stuck at 100% and not decrease when you let up on the pedal (until you back off all the way and enter regen mode).

Also, when this happens, momentarily flooring it resets the algorithm back to normal:

starting from a stop, pedal pressure at about 10% -- power output: 100%
while accelerating, momentarily increase pedal pressure to 100% -- power output: 100%
decrease pedal pressure to about 20% -- power output: about 50% (as expected in D)

I have not seen torque increase with a negative delta in throttle. Power increase, yes, but not torque.

 

[QueenBee]

After seeing this thread one thing I've noticed is that I can have all power bubbles lit without having the pedal all the way down. My casual observation is that doesn't seem right? I've never gotten the feeling like the accelerator wasn't working like it should though...

Which after reading Turbo's description is what is happening. Odd but I think people are a bit sensitive if they consider it a safety issue, let off the pedal if you are accelerating too fast