Question after test drive - hack software to change regen/friction transition

Deuces, ask the dealer remove the brake pads, that should eliminate the problem.

 

Drive in B (mode)

 

Maybe it was just the car you test drove. Or a matter of you getting smoother with the pedals?

 

By any chance did this coincide with the 7 mph transition from regeneration to purely friction braking?

 

i'm pretty sure that' the effect he's describing, which, as we all know, after you've driven the car a couple of times you just learn to subconsciously feather the pedal and it goes away.

 

Most brakes rust when not used. I live in a damp environment where rust will form overnight. Our Honda cars were particularly aggressive about growing rust on the rotors.

The difference with most cars is that the brakes are used heavily, so they self clean. Prius brakes live an easy life, but that can also mean that surface rust is not consistently removed. If your brakes get noisy or grab, follow Jeff's advice about braking in N.

Tom

 

I've never experienced this.

 

Wash your car, make sure you get the discs nice and wet, leave it over night. in the morning, drive up to 30 mph and then brake moderately to a halt. When regen switches to friction at 7mph (or whatever it is) you will feel a pull and hear a scrape as the pads attack the rust on the discs.

 

There are 2 Gen III in my household. The braking characteristics are different on each car. The transition on my Prius is more noticable than on my wife's Prius. I would try driving several Prii the dealer has on the lot and see which one has a less noticable braking transition if you are that concerned about it. I just got used to it.

 

Aside from the amazement I feel that someone who drove 1 car in 1 test drive thinks they know better than Toyota about how to write software for a safe smooth reliable braking system...

The electric only mod is 1 wire from an existing (empty) pin-out to ground. All the software, wiring and hardware already exist in the car as designed by Toyota. The nav mod is a simple switch in 1 wire. Neither changes software in any way.

I wrote a decompiler for car on-board computer systems. I could probably make one for the chip the Prius uses. It probably wouldn't be more than $100,000 plus full indemnity. Then all you need to do is figure out how to download the existing code, decompile it, figure out what it actually does, make the fix, recompile it, upload it back to the car, test it under all conditions.

Of course, all that ignores the basic problem. The coefficient of friction between the brake rotor and the pad changes. Until force is applied to the mechanical brakes, that can not be determined. It is impossible to match existing decelerating force (regenerative braking) to an undetermined mechanical braking force.

 

The best you could do would be full-feedback inertial control. Even then it would be rough, giving the jerky nature of rusty brakes.

Tom