lurch when braking - GreenHybrid

earthgrrl · #1 (**permalink**) 01-31-2006, 02:27 PM

Does anyone else feel a slight lurch forward when braking (when you're almost at a stop)?

Susan

Sledge · #2 (**permalink**) 01-31-2006, 02:34 PM

At a certain point, the electric motor will stop trying to regen and all your braking will be done by the friction brakes. You can see your CHRG bar disappear right before you come to a stop.

AZMerf · #3 (**permalink**) 01-31-2006, 08:18 PM

Also, sometimes on backing up. Also, sometimes if you almost come to a stop and then press the accelerator.

sparksongs · #4 (**permalink**) 02-01-2006, 05:24 AM

I've found that once the car warms-up enough for auto-stop to start working, this "lurching" no longer occurs. However, until that happens, it is really an annoying problem (and obviously somewhat dangerous).

subnivean · #5 (**permalink**) 02-01-2006, 10:07 AM

Quote:

Originally Posted by sparksongs

...it is really an annoying problem (and obviously somewhat dangerous).

I don't know about dangerous - the only time it does this 'mode shifting' between regen braking and friction braking is when you're decelerating relatively slowly. I'm sure that if you really stomp on the break pedal, the car's computer will take note and tell the battery 'Whoa! Gotta stop *NOW*! No regen for you!" and go right to the friction brakes.

livvie · #6 (**permalink**) 02-01-2006, 12:45 PM

Yeup keep in mind there are points where hitting the brakes doesn't translate to your actual brakes clamping down on your rotor (or shoe in drum), the car's engine and electric regen mode are slowing you down. When this gets negated at slower (near stop speed) then your real brakes do the braking... so the lurch is the transistion between the engine stopping you to know the brakes having to make up the difference.... hence you have to put more pressure on the brakes.

ElanC · #7 (**permalink**) 02-01-2006, 04:30 PM

Quote:

Originally Posted by subnivean

I don't know about dangerous - the only time it does this 'mode shifting' between regen braking and friction braking is when you're decelerating relatively slowly. I'm sure that if you really stomp on the break pedal, the car's computer will take note and tell the battery 'Whoa! Gotta stop *NOW*! No regen for you!" and go right to the friction brakes.

It's not an either-or situation. Regen alone is used as long as it provides enough braking power. If you press harder on the brake pedal, you get the addition of the conventional brakes, but regen doesn't stop. Regen is stopped when the vehicle is moving so slowly that the electric motor, working as a generator, can no longer utilize a significant amount of torque.

subnivean · #8 (**permalink**) 02-01-2006, 04:45 PM

Quote:

Originally Posted by ElanC

It's not an either-or situation. Regen alone is used as long as it provides enough braking power. If you press harder on the brake pedal, you get the addition of the conventional brakes, but regen doesn't stop. Regen is stopped when the vehicle is moving so slowly that the electric motor, working as a generator, can no longer utilize a significant amount of torque.

Point taken. Do you think the 'lurch' is when the friction brakes start to take hold, or when the regen stops, or something else?

Anyway, I was talking about stomping on the brakes so hard that the wheels lock up immediately and the ABS kicks in. In that case, if there is indeed any regen still going on, I doubt you would feel any 'lurch' in the braking due to the regen/friction brake split. That seemed to be the implication of the post I originally replied to - that this 'lurch' was some fault in the braking system that might make it hard to stop. I was just saying if you *really* want the car to stop, and stop quickly, it will stop quickly.

ElanC · #9 (**permalink**) 02-01-2006, 04:52 PM

Quote:

Originally Posted by subnivean

I'm talking about stomping on the brakes so hard that the wheels lock up immediately and the ABS kicks in. In that case, if there is indeed any regen still going on, I doubt you would feel any 'lurch' as the regen stopped. That seemed to be the implication of the post I originally replied to - that this 'lurch' was some fault in the braking system that might make it hard to stop. I was just saying if you *really* want the car to stop, and stop quickly, it will stop quickly.

Yeah, sure it will. The problem is not that severe. But when you're slowing down to a stop light, and there's a car stopped in front of you, and suddenly when you're ten feet away and almost stopped the brakes go to half-power, you might just hit the car in front of you if you're not paying close attention.

subnivean · #10 (**permalink**) 02-01-2006, 04:57 PM

Quote:

Originally Posted by ElanC

Yeah, sure it will. The problem is not that severe. But when you're slowing down to a top light, and there's a car stopped in front of you, and suddenly when you're ten feet away and almost stopped the brakes go to half-power, you might just hit the car in front of you if you're not paying close attention.

That's possible, I suppose