Rocking/wobbling/shaking when ICE turns off?

[SoCalGuy]

Does anyone notice sometimes at stop light, the Karma wobbling when the engine turns off? Doesn't happen all the time, but probably 1/3 of the time at extended stops.

[brian]

Yeah, that happens all the time for me. I'm pretty sure it's a result of the generator momentum causing a twisting action on the entire car as it comes to a stop. That generator is essentially a big flywheel, so when the engine shuts down the momentum of the flywheel is essentially trying to cause the car to spin in the opposite direction.

-Brian

[SoCalGuy]

Hmmm so you think it's a known design issue not just a fixable oddity? It is a little embarrass g when it happens and you have passengers in the car.

[brian]

Assuming that it's the generator's momentum that's causing it then I don't think there's any way to prevent it unless there's some mechanism for slowing the thing down less abruptly. But since it's bolted right onto the engine, once the engine shuts off that flywheel action is going to be pretty abrupt. All of the energy of the spinning generator gets passed into the engine block and thus to the body of the car.

-Brian

[doug]

There's no clutch to decouple the two? There are plenty of ways to solve that problem. They could have the engine throttle down briefly before stopping to avoid a harsh cutoff. Or simply adjust the load on the generator at cutoff to damp out the oscillation.

At any rate, this is the sort of thing that should have been accounted for at the design phase. If they didn't, there's a chance it could be fixed in software.

[marcus]

There must be a fix because i don't have the problem.

[Don A]

I haven't noticed a problem either. Based on my rather limited experience I would say the off cycle is no more noticeable then my Lexus hybrid was and the on cycle is much less noticeable.

[siliconkiwi]

I've seen/felt it, and really hope they can fix it. You only notice it if your ICE happens to fully turn off when stopped e.g. At a stop light. Then it is really embarrassing :-(

[SoCalGuy]

Yes, and not to state the obvious, but once you get into charge sustain mode (i.e. less than 26 miles of battery range), the engine works much harder/louder than it did north of 26 mile battery range. In fact, since the last weekend was the first time I had the battery above 26 miles and went into Sport mode, its understandable when the reviewers say you can barely hear the ICE in Sport - in charge deplete mode, the ICE revs so low that it is barely audible. But pop into Sport mode with 15 miles battery range and accelerate onto a freeway onramp and you'll definitley notice it - not an unpleasant sound, but certainly noticeable.

So perhaps those of you that haven't noticed the wobble, haven't really used Sport in charge-sustain mode where the engine works harder to generate the electrons to power the car.

[doug]

That's good news then. If it's as SoCalGuy suspects, and those that haven't noticed "the wobble" haven't created the necessary conditions, then it should be possible to program it away in the engine control software.

Not sure where that would fall on the priority list, though.