Data on "brake loss" (aka "sudden acceleration") after bump

That's good data 2009, you've captured the problem of regen to ABS transition really clearly there.

One question. Is the purple trace roughly proportional to the force on the brake pedal, or is it more related to it's position rather than force?

 

I notice that about 2 seconds after the (partial) loss of deceleration that the brake signal increases about 50% and then the original deceleration rate is restored. Was that a conscious decision to push harder or was that the brake pedal just sinking a bit lower with not much extra force.

The one time I experienced something like this I was descending a long hill with a full (8 green) SOC and near the end it cut out the regenerative braking (because of the high SOC). I wasn't braking hard, just gently as a approached a red traffic light, but I felt the braking effort suddenly reduce a bit and I had to let the brake pedal sink just a little bit further down before I got back to the original deceleration rate.

 

Yes , a person has to be ready for the transition from regen to no regen! By the way how did you capture that data? Was it printed from the black box? Hal

 

Maybe he's got an accelerometer and is the new bwilson4web?

 

I wanted to thank you for this post, but I'm so sick of this subject from previous unending threads that I can't do it. :madgrin:

 

All this info is available over the CAN bus.

 

Humans are very sensitive to changes in acceleration, but not to the value of acceleration. In other words, we can sense small changes, but we can't tell whether acceleration is positive or negative. A drop in deceleration (negative acceleration) feels like acceleration (positive acceleration).

If you want to demonstrate this, have someone make a constant turn in a parking lot while you keep your eyes shut. After a couple of loops around the circuit, have them ease off on the turn, still with your eyes shut. You will swear that they just turned in the opposite direction.

The brake pedal transducers are pressure sensors. They sense pedal pressure and send it to the brake ECU.

Tom

 

Jerk

 

Exactly. Most humans are sensitive to jerks.

(apologies to the non-physicists in the audience)

Tom

 

Yes it's interesting how many people we've seen describe this as a "surge forward" and have been totally adamant about that no matter how many people tried to tell them otherwise.

Allowing for the DC offset in the accelerometer and the fact that the brake signal is decreasing slightly during the interval I'd estimate it to between 25% and 30% loss of deceleration.

 

The "surge forward" and "lurches forward" seemed to mostly be coming from newbie 3rd gen owners. Bwilson4web had accelerometer data on his 3rd gen (prior to the application of SSC-A0B that showed the brake pause was just that.

 

Nice to see a troll free thread regarding this issue with actual data. To me it feels like my Prius is coming out from under me a little bit. I have a spot on my ride home where this happens repeatably. Sort of a washboard of bumps just before I take a corner. It never feels dangerous. I wonder if now that this has been documented if there will be a recall.

 

Are you talking about the 2nd or 3rd gen? Besides Bwilson4web's measurements on the 3rd gen, there was a running thread of known repro locations. He seemed to like collecting them. I contributed one spot myself.

 

There was a TSB to update the braking software. It reduced the sensation by shortening the time to apply ABS.

Other than that, it's not likely that there will be a recall, as you would need to recall the roads, not the car.

Tom

 

I vote for recalling the potholes. :madgrin:

 

If one of the wheels hits a manhole cover or you are braking on a washboardy surface, the FJ Cruiser does the same thing

No regenerative braking here, just ABS that gets easily confused

 

I'm an engineer. you insensitive clod.

(Apologies to non /. ers in the audience)