Brake Release Going Over Bump

[chand3]

I've had my 2006 RX400 for just over a month now and have noticed the following odd brake behavior. When I apply constant brake pressure to slow the car down, the car decelerates at a controlled rate as I would expect any car too. However, if while braking I go over a bump in the road (I.e. rail road tracks, speed pump, pot hole), the car all of a sudden surges faster as if the brakes suddenly release it's grip somewhat. This is kinda scary because I then have to compensate by pressing the brake pedal further down. Also when I brake i try to brake with light to medium pressure to allow the generator motor to work at it's peak. Any one else notice this?

[cduluk]

I notice the same EXACT thing in my 08... No idea why though.

I know half of the braking power is controlled by the computer and brake regenerator, i guess when it senses an obstruction it relieves that energy...

[lemon]

What it is, is the regenerative braking (electric motors) ceasing and the regular braking (hydraulic / calipers) taking over. There can be no ABS with the regenerative braking - calipers are needed and the calipers are also much more powerful than the regenerative when heavy braking is needed.

In your case, I'm guessing going over the bump in the road lessens the load on a wheel enough that it momentarily locks up or slows enough in comparison to the other wheels that the system thinks it needs or will need ABS. So it disengages the regenerative and activates fully the hydraulic braking circuit to activate or prepare to activate the ABS.

If you slam the brakes on in an emergency stop, you'll see that the regenerative is not activated at all (watch your power meter) and only the traditional hydraulic brakes are used.

My car does the same thing now and again. It would have been nice if Toyota could have made this function more seamless.

I'm at work, but at home I have a shop manual that explains this. I can post a more technical (and probably more accurate) explanation if you really want it.

[chand3]

What it is, is the regenerative braking (electric motors) ceasing and the regular braking (hydraulic / calipers) taking over. There can be no ABS with the regenerative braking - calipers are needed and the calipers are also much more powerful than the regenerative when heavy braking is needed.

In your case, I'm guessing going over the bump in the road lessens the load on a wheel enough that it momentarily locks up or slows enough in comparison to the other wheels that the system thinks it needs or will need ABS. So it disengages the regenerative and activates fully the hydraulic braking circuit to activate or prepare to activate the ABS.

If you slam the brakes on in an emergency stop, you'll see that the regenerative is not activated at all (watch your power meter) and only the traditional hydraulic brakes are used.

My car does the same thing now and again. It would have been nice if Toyota could have made this function more seamless.

I'm at work, but at home I have a shop manual that explains this. I can post a more technical (and probably more accurate) explanation if you really want it.

Wow, that totally makes sense to me. However, it's a rather weird and potentially unsafe way of doings things. I agree, it could have been more seemless. If you have the "more technical" explanation handy, I wouldn't mind reading your post of it. Thanks.

[RX400h]

After driving our RX400h for almost 5 years, I must say that this scenario occurs very infrequently, so I don't worry about it.

[chand3]

After driving our RX400h for almost 5 years, I must say that this scenario occurs very infrequently, so I don't worry about it.

I wonder if it's because you live in beautiful CA where the roads are perfect. We here in Winnipeg Canada have pretty bad roads. I would say I encounter this more often than not.

[lemon]

Yeah, potholes and bumps etc might cause this more often. The freeze/thaw cycle in the winter just wreaks havoc on the road. Funny though I haven't been experiencing this very much lately. It seemed more often in the fall for some reason.

[RX400h]

After driving our RX400h for almost 5 years, I must say that this scenario occurs very infrequently, so I don't worry about it.

I wonder if it's because you live in beautiful CA where the roads are perfect. We here in Winnipeg Canada have pretty bad roads. I would say I encounter this more often than not.

Well, I wouldn't call them perfect, but they surely beat the roads in many cold climate areas! Regarding the weather: We are currently experiencing the most rainfall I can ever remember. So far, it's been raining every day this week. Last night, it was raining so intensely that my neighbor's two plastic garbage cans were picked up by a stream of water and slammed against my son's car. Bizarre sight for San Diego.....

[LexRexBlue]

The worst was potholes at the bottom of the hill with a STOP sign. Letting the car coast down the hill (straight) recharged the battery didn't use gas, etc. but the car wouldn't Stop because of the holes at the Stop sign. After much angst the township repaired the holes. I feel much safer now.