Our 2006 Highlander Hy has, on more than one occassion, "slipped" as we brake. We have experienced this feeling when applying the brake going down hill (both in town and coming down from the local ski hill). You press the brake (not pumping) and after a second or so, you get the feeling of the brakes "locking up" for a second and than engaging as normal. It is not consistant and the local Toyota Dealer has no experience with the issue nor have they been able to duplicate the feeling when they test drove the unit. Any feedback would be appreciated.

ps... Winter driving conditions but no snow or ice on the road; speeds at 15kmh to 60 kmph.

 

During the slipping event, did the power meter initially begin to dip down into the blue range as normal when braking (to signify regenerative braking) but abruptly the power gage needle swung back up to the neutral position while still braking steadily at speeds over 20 mph?

If so, the regenerative braking abruptly shut down, and after a time lag, the friction braking engaged and took over. During the transition from abrupt regenerative braking shut-down to friction brake ramp up, the vehicle feels as if braking was momentarily lost even though your foot pressure on the brake pedal has not changed. The transition is unfortunately not very seamless. This compels you to press harder on the brake pedal to compensate.

If the road is slippery, one or more wheels may have begun to skid causing the ABS to engage. When the ABS engages, the regenerative braking is shut down and the friction brakes take over. If the road is particularly bumpy or even has one significant bump that the wheels bounce over while braking, the wheel bounce can cause a momentary wheel slippage which again triggers the ABS system which shuts down regen braking.

However, I have experienced this regen shut down on smooth dry roads intermittently. Typically the battery charge level as indicated on the multi function display is within one to two bars of max charge when it happens - but not always. Maybe the regen shuts down if the battery is close to max charge also.

The battery charge level tends to be higher with cold ambient temperatures than when the weather is warm due to the engine running much more of the time when stopped or coasting below 40 mph.

I am not yet sure if occurrence on smooth dry roads could be a sign of abnormal brake function.

 

I've experienced it too! What i've noticed is that it occurs right when the engine turns off as well. If you live in a colder climate (i'm in MN), it is especially apparent w/ the heater on. I suggest turning off the radio, and when decelerating listen and time the braking sequence with the engine shutting off. I don't know what to do though.

 

I've noticed something similar with my HH, but I've noticed mine to happen when I hit a bump or rough road while braking. It is more pronunced when cold. If you are not expecting it it can be very exciting

 

That has to do with the ABS system. Regen braking interferes with normal ABS operation. When the system anticipates an emergency braking situation, it will cut off regen. One doesn't realize how much the regen slows the car down until it gets cut off.

I've noticed that cold weather also affects ABS/regen. If it's below freezing, the car will not regen in the "blue" range until things warm up. I know that Ford has tech papers on this; and remember Ford and Toyota both get their hybrid tranny parts from Aisin.

 

The pause is usually the slight lag between regen braking and conventional braking kicking in. The system is actually quite conservative about braking. If you hit a decent size pothole while braking the regen will kick off.

 

THANKS TO ALL OF YOU... On the response you gave on the HyHy braking system; if you ever need a letter of reccomendation for a job as a "Toyota total care provider" I'll give you one.

 

I've noticed this several times in our '08 RXh. I agree anything triggering the ABS would likely switch the car over to friction braking, but don't believe that explains the situations when I've noticed it which were typically on good pavement. Nor was I braking particularly hard, since I tend to make long, gentle decels, light enough to push the 'power' gauge towards the bottom of the blue, but not enough to peg it. (I've been assuming the bottom of the blue is the max that can be re-gen'd and anything beyond that is friction braking. Is that correct?)

Likewise, I think I've tried coming off the brakes and back on, and found it to return to re-gen braking, so don't think it's trying to protect against over-charging the HV pack.

I had an alternate theory to try out -- some luxo cars can detect moisture (dew even, doesn't take a *wet* road) on the brakes and will drag the pads to dry 'em. I wondered if maybe it was doing this?

Benton 21may08

 

The bottom of the blue range is a panic stop for me. I try to keep it close to the top of the blue range when possible. The slower you stop, the more efficient the regeneration. Batteries do not like accepting charge quickly.

The regenerative drop out will occur due battery charging parameter limits being reached. If you release the brake upon drop out and immediately reapply it, regeneration will again engage but may again drop out shortly thereafter depending on conditions.

 

My guess would be that the colder it is outside the more sensitive the Anti-lock system will be at detecting that the "RATE" at which the braked wheels are decelerating indicates an impending lockup.

Note that the braked wheel(s) need not actually reach lockup to cause the ABS to "activate".

According to Ford's US patent on this matter upon the first indication of impending lockup ABS itself does not activate but instead regen mode is instantly disabled in favor of friction braking only.

Only then will ABS actually activate and release/modulate braking capability if impending lockup is subsequently detected.