Does anyone else notice anything like this or is it just my MiEV? This usually happens at very low speeds; like crawling. Most often when I am stopped in traffic. I will let off the go pedal but not apply the brakes. I will let the car slowly inch forward on idle. However, as the cars in front of me start to move, I will lightly rest my foot on the go pedal. If I barely depress the pedal, as though I want to move forward just a tiny little bit, I feel this stuttering/shaking in the powertrain. As soon as I accelerate more, it goes away. But if I stay in this pseudo idling forward state with my foot barely pressing the pedal, the stuttering will kind of flutter in and out. Thoughts?
Acceleration/Transmission Stuttering?
- Thread starter RobbW
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All the cars do this - It's the result of the super soft motor mounts. Once you get used to it, you'll prevent it from happening any longer by changing the way you modulate the brake pedal
There's a video here somewhere taken under the car which shows how much the motor/transmission moves around as the car is driven. It moves a surprising amount
Don
There's a video here somewhere taken under the car which shows how much the motor/transmission moves around as the car is driven. It moves a surprising amount
Don
+2, and I'm pretty sure it happens less in Eco than B mode, so I shift to Eco in stop-n-go, confident that I can still stomp it to get full passing power.
Don is right about the soft motor mount causing this. We have a electric motor that has a rotor with high energy magnets inside it. If you happen to stop the car with the rotor magnetic poles between the stator winding poles the creep mode will try to pull the motor to the next pole position. We have a device called a resolver on the end of the motor shaft. It is located under the sheet metal cover on the motor which has a bunch of wires coming out of it. The resolver tells the inverter drive system where the rotor is in its rotation sequence, which way it is rotating and how fast. When you are stopped, the rotor tries to move to the next stator pole but because it can move the vehicle, it moves the torque arm instead. That movement tells the resolver that the rotor has moved and the inverter reduces the current on the stator causing the torque arm to relax starting the whole sequence over again. If you just let the brake off and let the car move just little bit, you will get out of this position and the car will settle down. Many A/C drive electrics shut current completely off to the stator when the rotor stops with the brake applied---it appears it does not on the I-MiEV. Another problem with permanent magnet rotor motors is at very slow speeds, the inverter is running at a low frequency causing the rotor to jump between poles. This is known as "cogging". There are inverter circuits to smooth this out and the I-MiEV is pretty good at this. My old RAV-4 cogged like crazy making you want to get up to a few miles per hour quite quickly. Anybody on this forum that has or had a RAV4-EV knows what this is.
aarond12
Well-known member
One of the things I noticed was at a stop light, if you don't have your brake pedal fully depressed, the car's electric motor is still trying to "crawl" the car forward. Pressing the brake pedal fully causes the car to change attitude slightly -- the rear of the car raises slightly as power is cut to the motor.
I noticed also that my power gauge shows a little power being used at a stop unless the brake pedal is fully depressed. Takes practice to stop that way. I always used to put only the amount of pressure needed to stop the vehicle.
I noticed also that my power gauge shows a little power being used at a stop unless the brake pedal is fully depressed. Takes practice to stop that way. I always used to put only the amount of pressure needed to stop the vehicle.
You may be right . . . . but I drive in B mode 100% of the time and I can't remember the last time I experienced this 'studdering' so I think it's something you can avoid with learned behavior. I don't press on the go pedal at all until after the car begins to move on it's own in the creep mode - A couple inches is all you need. I think that small initial movement preloads the soft motor mounts and mostly eliminates the problemjray3 said:
Don
