[DBris]

We are finding that when the gas motor is running and the regen braking kicks in there is quite a bit of vibration. This is a problem only when driving around town when we have no battery power left. It is really bad when driving in L (so we don't), less bad when driving in D and using the regen paddle, and almost gone when driving in D and using the foot brakes as you can 'feather' them to not apply much pressure.
It is also worse when the engine is reving hard (which it does randomly). It is almost like the engine and the braking are fighting each other.
I took it into the dealer and they contacted GM but I didn't really get a satisfactory answer.
The regen works very well and smoothly when on battery power - it is only when the gas engine is running that we have this problem.

Anyone else having this problem when the gas engine is on?
David

 

[quirkySquirt]

Are you saying there is vibration in the car in general or is the brake pad pulsating (similar to warped rotors on non-regen braking)?

I use the ICE everyday for about 10-25 miles of freeway driving and typically don't brake to a stand still since it's freeway (always switch to NORMAL mode when getting off freeway, which shuts off the ICE within seconds of mode switch).

Can you describe exactly how to reproduce the symptoms? Like, road type (flat, incline, decline), weather conditions, SOC, HOLD mode or Charge Sustaining mode (aka, you used up all electric power and are on ICE), speeds?

BTW, what did the dealer tell you was the reason?

 

[llninja]

It's not the brakes. It's got to be something in the "transmission" assembly that brings the 2 generators and ice in sync when regenerating (yes when you hit the brake pedal, regen happens first and the friction brakes only kick on near the very end of the stop or when you are panic stopping). It could also be electronic, one of the systems controlling the "transmission"

 

[DBris]

The only conditions needed to produce the symptoms is to have the gas engine running. If we are on the highway or are able to 'coast' in D in town long enough for the gas engine to turn off then there is no problem - just as there isn't when the car is being driven in electric mode.
However, if we have to brake while the gas engine is running then we have the vibration. The whole car vibrates, it is not just a vibration one can sense in the brake pads.

The dealer (who has not sold many Volts) didn't know anything about this so I took the Service Manager out to show him. He then phoned GM and they really didn't give a reason. They just said things like 'Don't drive in L around town" and "It must be because the pads are wearing in" . The last one is ridiculous as the car is only 4 months old and it has done it since we got it.

I think LLniga (post below) may be onto something, as I said in my original post it feels like the gas engine and the brakes are 'fighting' each other when it happens. So, it may be in fact more to do with the transmission than the brakes/regen themselves.
I'm still hoping that some one out there has had a similar problem and GM has been able to fix it.

 

[llninja]

So just to be clear, are you sure you can't get the car to do this at all in D or L at varying speeds and varying levels of braking or regen? But then you can always reproduce this when the ICE is running? Have you tried it in hold or mountain modes? Does it do the same thing or do either mode not cause vibration?

As a software tester in a previous profession, I would make a little two dimensional matrix and put different symbols into that matrix to show when it happens (always, sometimes, never) with one axis as Normal D, Normal L, Hold, Mountain, Sport (and maybe expand to every permutation of these at highway speeds, slow city speeds), then the other axis would be lifting accelerator in D, lifting in L, regen paddle, light braking, heavy braking, panic stopping (engaging the ABS...in a safe area where someone won't rear end you). That might give us more clues as to what is going on. Too bad you're too far away for some hands-on testing.

Alas, I'm a bit worried that testing the extremes might make things even worse. violent shaking in the transmission might be the car fighting itself when it shouldn't be. We need WOT (or resident GM employee) to chime in.

 

[quirkySquirt]

Hmm, I've had ICE running both in HOLD and Charge Sustaining mode while on freeway and on neighborhood streets. Breaking during gradual slow down (with ICE revving) and during panic braking (also with ICE revving, I remember because the loud revving scared me in addition to an idiot driver cutting me off).

I've never felt what I thought was the ICE fighting the regenerative braking. I could hear the ICE rev up a bit but it typically died down a few seconds before I came to a gradual stop or a few seconds after I came to an abrupt stop. You're definitely seeing something weird.

 

[DBris]

Not sure why I would want to be putting the regen or brakes on at varying speeds. I only put them on when I am already slowing down (on the highway) or going at a relatively slow speed in town. I really don't want to do an emergency stop if I don't have to in case I did do some damage.

As for Mountain Mode I have never used it as I don't have any mountains around where I live.

As far as varying levels of regen I don't know anyway to alter those levels. When driving in L once my foot is off the gas the regen kicks in automatically and when in D and I pull the paddle the regen just comes on - there is no 'feathering' as there can be with the brake peddle.
When I use the brake peddle I can cut down on the vibration by using just the smallest amount of pressure.

I can only reiterate that this never happens on battery power or if the gas motor has shut itself down during a "coast'. It only happens when the gas motor is running and it is worse when the motor is reving high.

In order not to do any possible damage we have developed 'work arounds' to cut down on this happening such as:
Not using L in town when we have no battery power
Saving battery power on trips to use in towns
Taking our foot off the gas well before needing to stop so that the gas engine cuts out before we need to use regen paddle or brakes.

Doing this means that we don't have the problem often (only if we need to slow quickly or if it is cold enough that the gas engine comes on automatically). However, even though this minimizes the problem I would still like to have it 'fixed' if possible.

I would love for someone from GM to comment on this!

 

[quirkySquirt]

When you brought it to the dealer, were you able to reproduce it with one of their techs riding with you? Did you present any recordings of the phenomenon happening? If not, you might consider bringing along a dealer rep/tech and/or record the event happening.

Maybe mount a camera on the windshield or passenger headrest. Heck, just stick it in your cup holder. I vote to find a smooth stretch of road and to turn off any anti-shaky cam feature of your camera. Drive for a bit to establish a baseline, smooth recording then start demonstrating the effect.

 

[Arcanox]

"Don't drive in L around town" and "It must be because the pads are wearing in"

Sounds like they missed the part where he said he was talking about a Volt. Driving around town in "L" mode is intentional behavior (I call it "Tesla mode" because that's how its regenerative brakes work), and "the pads" don't do anything unless you really MASH the brake pedal.

I notice quite a bit of engine vibration when braking, but usually the engine shuts off right as I start braking (before which it revs up for a second or two). ERDTT is really the only time when I notice extended braking vibration.

 

[Arcanox]

I should also mention that I do notice what you might be thinking is the ICE "fighting regeneration," which is mechanically impossible. What it actually is is the engine still being connected to MGA (thus generating power to the battery) while braking, so the regenerative brakes can't do as much. Reproduce this by getting up to 60-70 MPH in C/S mode and immediately applying the regen paddle. The battery current gauge on the left should go all the way negative (green) but the car won't really start slowing down much until the engine shuts off.

 

[DBris]

Thanks for this Kinetic Blue (that's also the colour of our car!) Can you explain some of your 'short hand'. I don't understand ERDTT and C/S mode.
What you say does make me think that I am not making things up!
Your comment about driving in L was exactly my comment to the service manager when he told me what the GM person had said.

 

[TSquare]

Thanks for this Kinetic Blue (that's also the colour of our car!) Can you explain some of your 'short hand'. I don't understand ERDTT and C/S mode.
What you say does make me think that I am not making things up!
Your comment about driving in L was exactly my comment to the service manager when he told me what the GM person had said.

I can take that one.
ERDTT = Engine Running Due To Temperature
C/S Mode = Charge Sustaining Mode (Battery depleted, running on the generator)
And here is the link to the list of the most common ones:
http://gm-volt.com/forum/showthread.php?60457-Acronym-Guide-What-do-they-all-mean

 

[DBris]

Thanks for the link and the explanations.
I agree, when ERDTT that is when the vibration is the worst. Largely because the engine is doing its own thing due to temperature, so there is no way to "turn it off" by coasting or anything else.

 

[quirkySquirt]

You can at least defer the ERDTT via a setting in your Volt when it's on (the vehicle settings page is greyed-out if off). I forget the temperature cut offs, but I think if you set it to "deferred", it will drop the cut off by another 20F before engaging ERDTT. If you park in a garage, you might also want to turn off the precondition setting that uses the ICE for sped up heating of the cabin.

I just googled Cobourg and it appears fairly cold, but I think the deferred ERDTT should minimize your ICE running.

 

[DBris]

Not sure why my yesterday's reply isn't showing up so I"ll try again.

I do have the ERDTT deferred setting set as low as it will go. The ERDTT was only an issue so far on one trip that we had to friends who live quite a bit further north than we do.

Cobourg is in the 'banana belt' - at least as far as Ontario concerned

 

[Arcanox]

Thanks for this Kinetic Blue (that's also the colour of our car!) Can you explain some of your 'short hand'. I don't understand ERDTT and C/S mode.
What you say does make me think that I am not making things up!
Your comment about driving in L was exactly my comment to the service manager when he told me what the GM person had said.

TSquare explained most of the acronyms I used excellently. The one I used that's not in the acronym guide is "MGA", which I should have explained.

MGA is Motor/Generator A; it's what starts the engine, and what generates electricity from the engine's power.
MGB (Motor/Generator B), on the other hand, is what propels the wheels of the car during acceleration, and what generates electricity by slowing down the car during regenerative braking.

 

[wordptom]

Re: CD and CS, perhaps it should be clarified that the Volt has but two operating modes, Electric Mode and Extended Range Mode. In Electric Mode the vehicle uses grid power stored in the battery, depleting the available supply, i.e., Charge Depleting (CD) Mode. Extended Range Mode uses the ICE to generate electricity to sustain the battery state of charge level at the fully-depleted soc, or at the driver-chosen Hold point soc, or at the Mountain Mode soc, i.e., Charge Sustaining (CS) Mode.

 

[Patog23]

I’m having the same issue.. does anyone know what this could be now we are few years later ?

 

[SammyG]

Hello All!

I would definitely see how this can be unsettling when one isn’t used to this and I do find it quite odd that GM didn’t figure this out as it’s fairly simple when your understand the powertrain.

The second I saw you mention that “the engine is fighting the braking” I knew exactly what you were describing.

So there isn’t any fighting going on there and while yes the engine may rev up, it is not producing any power. Rather it is absorbing power through engine braking. This is accomplished by using MGA (motor/generator A) to spin up the engine while the injection & ignition are disabled. This is analogous to what one could do in a traditional car by downshifting to increase engine RPM & provide said engine braking.

This is a typical behaviour of petro-electric drive trains, such as locomotives. It can, however, be seen in many automobiles. I believe the best example is Toyota/Lexus’ Hybrid Synergy Drive. This occurs when the shifter is put in the “B mode”.

This occurs mostly in cases where A: driving in CS mode and the battery is already full or B: driving in CS mode and the required deceleration provides more current than the battery can accept; in which case that extra electricity is rerouted to MGA to spin up the ICE and get the engine braking. In very high braking demands, the system can blend regen, dynamic & service braking systems together. In any case, it seems that the absolute requirement is that the engine has been warmed up prior to this. It seems that it will never do it in pure EV mode (in that case it prioritizes regen & service brakes).

I have never experienced this in my 1st gen Volt, but was pleasantly surprised to find out that it happens in the 2nd gen, this Thursday.

So worry not, fellow Volt drivers. While it may be unusual at first, it is totally normal.

-Sam

 

[kamil.niedzielski]

Has any of the group members already found a solution to this problem? I have an ampera from 2013 polift version and I have exactly the same symptoms. In addition, if, for example, I stand at the traffic lights and the internal combustion engine works and the revolutions are at a certain level, you can feel such vibrations from time to time. What could it be.