[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.

 

[Don A]

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.

My experience I was referring to was when the car was at a 1 or 2 mile remaining charge-sustain mode.

 

[SoCalGuy]

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.

My experience I was referring to was when the car was at a 1 or 2 mile remaining charge-sustain mode.

Hmm, interesting. I wish I could test drive your car to be sure and compare. It would be ashame to continue driving my car with such an issue only to find out months/years later that it could be fixed.

 

[Fabulist]

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.

My experience I was referring to was when the car was at a 1 or 2 mile remaining charge-sustain mode.

Hmm, interesting. I wish I could test drive your car to be sure and compare. It would be ashame to continue driving my car with such an issue only to find out months/years later that it could be fixed.

There is a slight shake when the ICE turns off. I have felt it both in Sport and Stealth+ICE modes. In my experience it is not really a big deal but it may vary from car to car so I can't really generalize. A very simple solution would be to energize the generator for a fraction of the second and use it as a motor to wind the system down gradually under power when the ICE shuts off to avoid the vibration of the ICE sputtering to a halt under load. If we know how to safely wind down and stop hard drive motors that are running at 10K RPM smoothly and quietly, this should be no problem.

-- Fab.

 

[LonePalmBJ]

I feel the slight tremor in Sport mode too when I'm at a light for longer than 30 or 45 seconds (I don't know what the threshold is) and the ICE shuts down. Maybe other people are feeling something differently than I am, or maybe people are expecting complete stillness, but the tremor is minor, brief and not at all an issue for me.

 

[doc]

I feel the tremor all the time at 1-2 MPH, whether in sport or stealth. It goes away when taking off, but is of course a little embarassing. It is almost the same feel you get if you start of at a higher gear in a manual transmission car. I addressed this to the dealer, and they said all the cars do this. If you there is a fix or all cars don't do this please let us know.

 

[LonePalmBJ]

I feel the tremor all the time at 1-2 MPH, whether in sport or stealth. It goes away when taking off, but is of course a little embarassing. It is almost the same feel you get if you start of at a higher gear in a manual transmission car. I addressed this to the dealer, and they said all the cars do this. If you there is a fix or all cars don't do this please let us know.

Doc - As far as I know, all Fiskers do this. The electric motor doesn't 'creep' at idle speed as smoothly as a conventional ICE car does. While I'd love for it to go away, it's more in the "quirky" than "unacceptable" camp for me.

 

[Fabulist]

I feel the tremor all the time at 1-2 MPH, whether in sport or stealth. It goes away when taking off, but is of course a little embarassing. It is almost the same feel you get if you start of at a higher gear in a manual transmission car. I addressed this to the dealer, and they said all the cars do this. If you there is a fix or all cars don't do this please let us know.

Doc - As far as I know, all Fiskers do this. The electric motor doesn't 'creep' at idle speed as smoothly as a conventional ICE car does. While I'd love for it to go away, it's more in the "quirky" than "unacceptable" camp for me.

I think we are talking about different issues.

The original thread was talking about the slight shudder that is caused by the ICE+Generator turning off, which is typical for an ICE turning off while it is under load. This is a mechanical issue, and short of adding a clutch between the ICE and generator or redesigning the ICE-Gen interface, it's probably not going away.

What @Doc is talking about sounds more like sound and jerky movements the electric traction motors make moving at very slow speed. This issue, as I understand it, has actually been addressed in the 615 software and the motors are supposed to be a lot smoother at low speed with the new software.

 

[LonePalmBJ]

I think we are talking about different issues.

Yes, I took the thread on a tangent. There's the shudder when the ICE auto-stops when idle, for example at a traffic light, and there's the shudder/jerkiness when creeping along at slow speed. I haven't driven on 6.15 long enough to know if it's better or different.