So WHY does the regen have to cut out?

That is the only time I've encountered this. I turned into a parking lot where the entrance has a ridge running parallel with the street. I came in too fast and at an angle so the passenger side wheel was in the air as I went over the crest of ridge.

I would not want to do it again, but it seems less jarring than banging into a pothole.

 

I am leaning towards a mechanical rationle as well for the cut out since 1 sec is a loooooong time for anything electrical.

 

Probably, they did not want the ABS "fighting" the Regen-Braking in a skid.

Presumably, the new firmware handles the "skid" differently?

 

Switching from regenerative braking to friction braking during wheel slip makes perfect sense to me, if nothing else because only with hydraulically operated friction braking can the ABS control unit get all wheels spinning at the same speed again: By modulating the hydraulic pressure to each of the wheels it can allow them to gain traction again and it doesn't want the drag from the generator to interfere with that.

Regenerative braking can only control the total drag (negative torque) via the generator, which then gets split between the two front wheels by the front differential. If the left and the right wheel turn at different speeds because only one has hit a pot hole or if both spin at different speeds from the rear wheels there is really no alternative but to remove the regenerative drag on the driving wheels to get them spinning again, or the car could lose directional control.

However, this does not explain to me why it would take as long as 800 ms to get braking force again. It should not take the ABS unit 800 ms to build up hydraulic pressure. It does so very quickly and impressively when you quickly move your foot from the accelerator to the brake pedal and depress it. If one wheel develops slip or even both, the ABS could still engage the brakes on the other three or two wheels hydraulically.

As a software engineer, this long delay with no brake action does not make any sense to me. Personally I can not feel easy about the firmware update until I understand what exactly the reason for the 800 ms interval was and how it is being addressed under the new algorithm.

 

I don't really need to know what Toyota has changed with the fix, but I sure would *like* to know. It's hard to imagine that the 800 ms delay was an oversight. On the other hand, who would consider that acceptable?

I hope we eventually find out the details.

Tom

 

Not sure if this has been discussed elsewhere, but I found this NHTSA complaint posted on the a Tesla owners' club site. It involves a braking problem on a 2008 Roadster that sounds similar to the 2010 Prius. I don't know if later model Roadsters handle regen differently than the 2008.

 

Wayne,

I've been thinking about the HSD protection theory for the regeneration and acceleration cutout when a wheel spins. Toyota put a torque limiter (AKA clutch) between the ICE and the HSD for protection. They could have done the same at both half shafts to protect the HSD and then simplified their SW routines if HSD protection is the driving force.

JeffD (an EE playing ME)

 

Evan: here is a link to the complaint on the NHTSA site:

Complaints Summary


This is the link on the Tesla club site that references the complaint. (My first time posting links. Hope they work.)

NHTSA Complaint wrt Regen and TC - Tesla Motors Club Forum

 

I'm sure protection of the HSD is a factor, but likely more important is being able to control the rate of deceleration of the two front wheels independently. Something that can't easily be done at the HSD level. I think that is why the "affect" is so easy to reproduce on a bumpy surface at moderate to slow speeds. Even if the car only might need to vary breaking strength to the two front wheels independently, regenerative breaking would certainly get in the way and therefore must be bypassed just in case.

 

well, by now someone has told you the 2010 regen does not cut out. i have seen regen on the HSI screen as low as 3 mph