ABC News reports on acceleration problems

[Mike Dimmick]

Originally Posted by Morrisdb

Interesting - I have noticed occasionally in my 2005 Prius this SLIGHT feeling of acceleration when I brake to turn a corner - and it definitely has nothing to do with the floor mat. It is a weird feeling and thought I might have been the only one experiencing it - so you are assured that this is the ABS system??

I get that too. I can be gliding, then lift off the gas pedal completely, then when I press the brake pedal get a slight feeling of acceleration. I seem to recall reading somewhere that no-pedals regeneration is done with MG1 while braking with the brake pedal is done with MG2, though that could have been someone else on here. If that is the case, the slight hesitation could be while it switches from one to the other.

I think it's also subtly transferring control - the brake pedal is read by the Skid Control ECU while the accelerator is read by the Hybrid Vehicle ECU. When you brake with the brake pedal, the Skid Control ECU tells the HV ECU how much regen it wants - perhaps there's a moment where what it tells the HV ECU is actually less than the HV ECU was already doing on its own. As a result it decelerates less, which feels like an acceleration.

You would think that the HV ECU would ignore such a signal but in the case of controlling the braking force over bumps, the Skid Control ECU wants to keep complete control (ABS on friction brakes) and eliminate regen entirely.

[qbee42]

Originally Posted by Morrisdb

Interesting - I have noticed occasionally in my 2005 Prius this SLIGHT feeling of acceleration when I brake to turn a corner - and it definitely has nothing to do with the floor mat. It is a weird feeling and thought I might have been the only one experiencing it - so you are assured that this is the ABS system??

Yes. It happens if one of the front tires loses traction. Normal braking in a Prius is done regeneratively through only the front drive wheels. If one of them slips for any reason - ice, bump, whatever - the traction control system senses this and switches to ABS friction braking on all four wheels.

The loss of traction and transition to ABS friction braking produces a very short interval of reduced braking. When you are already braking, a reduction in braking feels like forward acceleration. You don't really accelerate forward since you are still slowing down, but it feels like acceleration since you are not slowing down as fast. After the short transition braking works as it does in any normal car.

Tom

[sambojoho]

There is a way on the Prius to shift into neutral without much thought, delay, or fiddling around with the shifter. Simply press the Park button while driving and it will kick you instantly into neutral. I have hit the park button a couple of times accidently while driving...