[carcrazy]

Hi, I'm new to forum have a 2017 volt with 7500 miles on it. Love the car and the savings on gas. I was wondering if any one else feels the same thing I feel while on the highway in cruse control with engine running on hold. It's just a slight shift ,hesitate feel that comes and goes. Not too annoying but doesn't do it on pure electric mode. Also when it moves from electric to engine I feel a shift like a transmission has changing gears. is this normal? Frank

 

[llninja]

It's normal. When cruising there is a mode where the ice jumps in to power the generator and do a little push for efficiency. If you come up on a hill or punch it, the ice will drop out of the picture and the electric motor will do most of the work. Think of it as an overdrive gear, though it really isn't a gear.

This video explains it pretty well. Jump to 4:30 in if you want to skip the background.
https://youtu.be/o3-wGOyT2-I

 

[jcanoe]

Yes, and yes. I have a 2017 with the ACC and sometimes notice the Volt hesitate for a second, it is nothing to be concerned about. Also, when switching from Hold to Normal mode the Volt is changing the way that power is applied to the drive wheels so you may notice as the power to the wheels switches from the ICE being coupled to the wheels to motor generator A (the larger electric motor) takes over powering the drive wheels.

Here is a link to a good explanation of how the Gen II Volt drive train operates. There are a total of 5 different drive modes. I have read this several times and find that I still refer to this article.

http://gm-volt.com/2015/02/20/gen-2-volt-transmission-operating-modes-explained/

 

[carcrazy]

Thank You all for the info it was very helpful. I didn't want to complain to the dealer and waste time. That is why these forums are full of real world users that probably know answers than the dealers do.

 

[jupitermoon]

Hi, I'm new to forum have a 2017 volt with 7500 miles on it. Love the car and the savings on gas. I was wondering if any one else feels the same thing I feel while on the highway in cruse control with engine running on hold. It's just a slight shift ,hesitate feel that comes and goes. Not too annoying but doesn't do it on pure electric mode. Also when it moves from electric to engine I feel a shift like a transmission has changing gears. is this normal? Frank

I think it's the ICE actually transmitting power to the wheels. I am coming to understand that the "power loss" or "chugging" feeling people here talk about is from the ICE/electric motors engaging and disengaging depending on mode, power required, power stored, etc.

From what I'm gathering, mountain mode is a EV mode but the engine is being used purely as a generator to maintain battery power to a certain level through the climb.

In Hold, there is no splitting of power or torque transmitted from the ICE and all of the power goes to driving the wheels.

Don't know..but that's what I'm understanding the difference to be.

 

[obermd]

Normal. What the car is doing is turning the fuel injectors on and off as needed to maintain a steady speed. In GM's pure ICE vehicles this is referred to as Deceleration Fuel Cut Off (DFCO). The ECU detects the load on the engine to maintain the speed and when the load goes to zero for a second or two the fuel injectors are cut off. It's really noticable on "flat" roads that are really very slightly down. At 65 MPH it takes very a descent so small most people won't realize their descending unless they're watching the road closely. The ECU in the Cruze can cycle the fuel injectors about twice a second; I suspect the Volt has a similar cycle time. The result is you can feel the car "pulsing". When the "pulse" results in you sliding forward the injectors have been turned off; when it pushes you back they've been turned back on. When running as pure EV the control the ECU has over the motors is far more accurate and the power applied to the motors is simply reduced to maintain speed. No pulsing occurs as a result.

The Volt appears to implement DFCO but the main traction battery also comes into play by the Volt's ECU always wanting to use the electric motors before the ICE motor, or if the battery SOC is lower than the ECU's target window, recharging the battery.

Mountain mode only recharges the battery to about one bar (5 to 7 miles) and only when the car needs less than about 40KW for propulsion. Hold mode will recharge the car back to the target window as well, but again only when fewer than 40KW are needed for propulsion. I have driven across Kansas with a headwind and watched my battery drop to zero, even in Mountain mode because the car was above the 40KW mark the entire way. In Normal mode the car appears to maintain the battery SOC at 0% at the expense of propulsion.

 

[caskConditionedAle]

The official name for this behavior is the "chuggle." I've heard the dealer has a fix that can reduce the effect. I haven't had mine fixed and to be honest, I don't notice it much anymore. Maybe it lessens as the ICE breaks in or I'm just used to it.

 

[VoltenRock]

Bottom line -- G2 Volt is just not that smooth on gas due to engineering tradeoffs and choices. Unfortunately, this lack of smoothness is "normal" and is inherent in the design that now operates more in parallel than serial.

The 5ET50 in my opinion still needs a bit of tweaking. This is basically the first run of this complete redesign so I suspect (hope) it will be improved. Heck, they finally just recently released an update to take care of the afterfire/backfire issue.

I still get the "rumble strip" sensation under certain speeds/conditions on the highway. It's certainly better than it was originally, and I hear that the new afterfire update adds a bit more smoothness also.

At least it's positive that GM keeps releasing tweaks to improve the drivetrain, given that this is a VERY low volume vehicle.

 

[Sheldon]

Normal. What the car is doing is turning the fuel injectors on and off as needed to maintain a steady speed. In GM's pure ICE vehicles this is referred to as Deceleration Fuel Cut Off (DFCO). The ECU detects the load on the engine to maintain the speed and when the load goes to zero for a second or two the fuel injectors are cut off. It's really noticable on "flat" roads that are really very slightly down. At 65 MPH it takes very a descent so small most people won't realize their descending unless they're watching the road closely. The ECU in the Cruze can cycle the fuel injectors about twice a second; I suspect the Volt has a similar cycle time. The result is you can feel the car "pulsing". When the "pulse" results in you sliding forward the injectors have been turned off; when it pushes you back they've been turned back on. When running as pure EV the control the ECU has over the motors is far more accurate and the power applied to the motors is simply reduced to maintain speed. No pulsing occurs as a result.

The Volt appears to implement DFCO but the main traction battery also comes into play by the Volt's ECU always wanting to use the electric motors before the ICE motor, or if the battery SOC is lower than the ECU's target window, recharging the battery.

Would other ICE cars feel the same "pulsing" as the Volt? I wasn't sure if the pulsing effect was real or it was my imagination. I would think in the Volt, if the load on the ICE goes down, they have the alternative of diverting engine power to the battery which might be equally or more fuel efficient as well.

 

[Eagleco]

Would other ICE cars feel the same "pulsing" as the Volt? I wasn't sure if the pulsing effect was real or it was my imagination. I would think in the Volt, if the load on the ICE goes down, they have the alternative of diverting engine power to the battery which might be equally or more fuel efficient as well.

I think generally speaking ICE's are not always as smooth running as one would ideally like. In an effort to create maximum fuel efficiency I think trade offs occur which can cause pulsing or whatever under certain conditions. The DFCO would be one reason.

We just came back from CA where we rented a 2017 Altima 2.5 CVT. Decent acceleration and good mpg but it was not always smooth running under certain rates of acceleration and conditions. It was noticable enough that it may have bothered me if it was my car, but it's probably normal.

Sent from my SM-G930V using Tapatalk

 

[JRRF]

Normal. Welcome to the dichotomy of ICE and EV driving. EV driving is smooth as silk. ICE driving has never been particularly smooth, and manufacturers have been trying to refine ICEs for decades. The Volt has a little 1.5L 4 banger that does the best it can. Couple that with all the clutches constantly opening and closing, and chuggle is what you get.

 

[obermd]

Would other ICE cars feel the same "pulsing" as the Volt? I wasn't sure if the pulsing effect was real or it was my imagination. I would think in the Volt, if the load on the ICE goes down, they have the alternative of diverting engine power to the battery which might be equally or more fuel efficient as well.

This same question comes up on CruzeTalk periodically, so yes, ICE vehicles that implement Deceleration Fuel Cut Off have this same pulsing. It's actually more noticible in ICE cars than in the Volt but as you discovered, you can feel it. I suspect the Volt's primary electric drive train buffers the car a little.

With my 2012 Cruze Eco Manual I was not only able to feel it but figured out how to see it on the DIC as well.