[Axel16]

Does somebody of you had problems with the brakes of the Fisker?
I am asking this because the breaking performance of my Fisker is real strange. Most of the time the grip of the brakes are strong as expected. But sometimes in random occasions the breaking maneuver is scaring. When using the breakes, the response I get is weak and fading for 1 oder two seconds, than the regular grip steps in.
There is no reason or sign recognizable, when or why this happens. This phenomenon appeared the first time, when I switched from winter to summer tires. I have no idea, whether there is a correlation between these incidents.

Can you help; any idea, what to do ?

Thanks

Axel:s

 

[Fabulist]

Does somebody of you had problems with the brakes of the Fisker?
I am asking this because the breaking performance of my Fisker is real strange. Most of the time the grip of the brakes are strong as expected. But sometimes in random occasions the breaking maneuver is scaring. When using the breakes, the response I get is weak and fading for 1 oder two seconds, than the regular grip steps in.
There is no reason or sign recognizable, when or why this happens. This phenomenon appeared the first time, when I switched from winter to summer tires. I have no idea, whether there is a correlation between these incidents.

Can you help; any idea, what to do ?

Thanks

Axel:s

@Axel16 As you probably already know, the Karma's brakes start out as regenerative and then switch to standard friction braking depending on how hard you press the pedal. In my experience, if the HV battery is full (49 Miles or higher), then the regenerative braking does not actually slow the car down and you need to press a bit harder to get to the friction braking. But if there is any capacity in the HV battery, then the brakes start out very strong and you can feel it slowing down the car.

I live on top of a big hill and when I leave the house with the HV battery fully charged, the initial application of the brakes does not do a whole lot and I have to press harder to get to the friction brakes. But if I leave the house with my battery below 49 miles, the initial application of the brakes is very noticeable and I don't need to press too hard to slow the car down.

I don't know if this relates to your situation, but next time the initial brake press does not seem to work, check your HV battery level to see if it is nearly full.

The original Karma specification avoided this problem by using the power generated by the brakes the turn the GM engine without fuel to use the engine compression to use up the electrical charge if the battery was already full. But I don't think this feature was ever implemented, so now there is a soft braking spot when the HV is full.

 

[Karma 2012]

My experience is that from 50 down to 47 miles, I do not feel much regenerative braking. Any remaining miles under 47 is when I can feel a significant slow down when let go of the power peddle.

 

[FiskerPhilly]

Yes, and temperature is a big factor as well. In colder climates and extreme winter conditions it is very difficult to charge a frozen battery or likewise a very hot one.

 

[Axel16]

Fabulist,
Thank you very much. I have thought that there might be a correlation between the friction brakes and the regenerative brakes, but I do not have that much technical knowledge, to find out the exact reasons. No hints or solutions in the car's manual. So I checked for potential mechanical defect and also the breaking fluid. Everything was fine.
I am wondering, why I haven't made the experience with the brakes before. That has upset and worried me. I drive the Karma since May 2012, almost 40.000 Kilometer on the clock.

Thanks again!

 

[Fabulist]

Fabulist,
Thank you very much. I have thought that there might be a correlation between the friction brakes and the regenerative brakes, but I do not have that much technical knowledge, to find out the exact reasons. No hints or solutions in the car's manual. So I checked for potential mechanical defect and also the breaking fluid. Everything was fine.
I am wondering, why I haven't made the experience with the brakes before. That has upset and worried me. I drive the Karma since May 2012, almost 40.000 Kilometer on the clock.

Thanks again!

Hard to say. It's very situation-dependent and it's not always easy to observe the correlation between braking force and the battery charge level. I noticed it very early on since I had to drive down the big hill every day to go to work, but that may not be your situation.

 

[ghost2]

The first thing to check is if there are any brake warning lights on the instrument cluster, either red or yellow telltales. This would indicate a problem which could be fixed. If there aren't any waring lights, then the brake system is probably working as intended. The system is basically an adaptation of a very well-engineered and tested system from the Chevy Tahoe hybrid and Chevy Volt PHEV, and the brake controller hardware is extremely reliable. Any real issues will be mostly in wiring of various external sensors or brake system power supply. The self-diagnostics are very sophisticated though, so if there is an issue the driver will be warned in the cluster.

I never considered lift-throttle drag to be regen braking, although technically it can regen energy. It was supposed to feel like a conventional automatic transmission vehicle. Lifting your foot off the accelerator pedal would trigger coast drag, which goes to almost nothing when the battery is full as noted in the prior post. So that's the one condition where it won't feel like a conventional vehicle, because the Powertrain development team never finished their work with the "simulated engine braking mode".

However, whenever the driver puts their foot on the brake pedal, that's what triggers braking and the brake controller does the work to divide up braking by the powertrain and friction. The amount of torque delivered should be consistent whether the battery can accept charge or not, since the brake controller will dial up extra friction torque when the battery is full. Braking torque is only proportional to the brake pedal travel. If your battery is full, then the driver should naturally apply additional braking force to slow the car down, in that unique mode where there's reduced lift-throttle coast drag torque. It's similar to how a driver brakes harder when stopping downhill versus stopping uphill. The transition should be seamless. Assuming no fault codes, I would suspect the owner here is noticing the transition when the coast drag suddenly kicks back in after the battery is slightly discharged, and so suddenly the braking effort required drops a lot. The brakes feel more powerful, but in actuality the they are the same but the pedal effort to achieve a certain deceleration decreased. My 2 cents! Best of luck.

 

[Sigurd]

@ghost2, that is some useful information. Thanks!

 

[FiskerPhilly]

I do recognize the feeling Axel16 is getting. It is frequent up here in the winter only. Ive felt it on decel when braking you get fading response then suddenly bam, brakes kick in. You can actually see it on the generation gauge on the DIS. Ive only had one client complain of it but I do feel it quite often moreso the colder it is. I attributed it to a cold hv battery not accepting high amperage regen charging such as a slightly frozen battery as it does seem to go away after some extended driving.

 

[ct-fiskerbuzz]

... Ive felt it on decel when braking you get fading response then suddenly bam, brakes kick in. ...

I've had that happen once (so far—if all goes well and we move to this house I'm trying to buy, I will be near the top of a big hill, around 1000 ft ASL vs downtown at maybe 10-30 ft ASL, so who knows after that ). All in all, though, the regen vs friction braking is essentially seamless. It's one of the best features of the Karma, some other hybrids definitely do worse.

(Edit: PS, for anyone wondering: ASL = Above Sea Level, basically a way of measuring elevations)

 

[CA_MP4]

@ghost2 - thanks for your very useful explanation, and kudos to the engineers that implemented this complex, yet completely smooth integration of regen and friction braking in the Fisker, it works so well, we take it for granted.

 

[ElectricRocket]

I have experienced the exact problem that Axel 16 is describing and that FiskerPhilly confirms. I've only had this issue when I'm on the winter tires. So FiskerPhilly, did you also have winter tires on when you had this problem. I am wondering if the problem only comes up with the winter tires on?? I had thought not to run with the winter tires this year to see if the problem comes up purely due to cold weather. It really sucks. You're going along and press the breaks then no real response then bang they kick in. Not good. Any thoughts comrades?

 

[FiskerPhilly]

Not tire related at least for me anyway. Its certainly temp related though. Most likely curable with a software refinement in future.

 

[AlJOHN]

If I may piggy-back on the Breaking Topic a bit. Does anyone know whether the brake Lights activate in "hill 2" mode automatically when decelerating. The car does "brake" as sorts. I read that the Tesla does activate the brake lights, since the car slows rapidly in the highest regen mode.

 

[Sandy Eggo]

If I may piggy-back on the Breaking Topic a bit. Does anyone know whether the brake Lights activate in "hill 2" mode automatically when decelerating. The car does "brake" as sorts. I read that the Tesla does activate the brake lights, since the car slows rapidly in the highest regen mode.

I was told that the brake lights do not light up in either Hill 1 or 2 mode.

 

[ct-fiskerbuzz]

The brake lights on my old stick shift did not light up when I downshifted into a low gear, either.

Incidentally, can some moderator fix the spelling of the title, it's "brake" (slow down, stop, halt, etc) not "break" (smash violently, cease to function, etc). (The misspelling bothers my OCD )

 

[Fabulist]

If I may piggy-back on the Breaking Topic a bit. Does anyone know whether the brake Lights activate in "hill 2" mode automatically when decelerating. The car does "brake" as sorts. I read that the Tesla does activate the brake lights, since the car slows rapidly in the highest regen mode.

I was told that the brake lights do not light up in either Hill 1 or 2 mode.

They definitely do not. Which means that you need to keep a close eye on the car tailgating you when you use Hill mode going down a hill, or the way I used it, in heavy traffic.

 

[Fabulist]

The brake lights on my old stick shift did not light up when I downshifted into a low gear, either.

Incidentally, can some moderator fix the spelling of the title, it's "brake" (slow down, stop, halt, etc) not "break" (smash violently, cease to function, etc). (The misspelling bothers my OCD )

I noticed that, but I thought it was word play, as in if there is a problem with braking, there will be lots of things breaking.