Rx400h Brakes

[bikeandsail]

My RX400h has about 4000 miles on it and recently I have noticed what I think is a change in the braking, a problem? Normally the braking is part regenerative until about 10 mph and then regineration stops.

On a few occasions while stopping and passing through 30 or 40 mph over bumps I have felt what seems like sudden acceleration. After better observation I have noticed that when braking starts there is regeneration and then the regineration stops and the brake pedel must be pushed harder to get the same brake effect. There is no actual acceleration just a feeling of that.

It's is almost like there is a loose wire that the bumps sometimes effect and cause the regeneration to stop prematurely.

Has anyone else noticed this. This only happens ocasionally and took serveral times before I noticed the stop of regeneration seemed to be the problem.

Ron

[wwest]

If the batteries happen to be nearly, or fully charged then regeneration cannot be effected.

[ericner]

I have noticed the same thing. It acts almost like ABS braking where it catches and then releases intermittently. I think what we're experiencing is a "feature".

[wwest]

The EBD on my 2001 RX300 does that, feels almost the same as ABS except very light, with light braking down a slight incline.

[RX400h]

I have noticed this too on occasion, mostly while going down an incline. It does almost feel as if there is sudden acceleration. However, it happens so infrequently that I haven't worried about it too much.

[wwest]

I have noticed this too on occasion, mostly while going down an incline. It does almost feel as if there is sudden acceleration. However, it happens so infrequently that I haven't worried about it too much.

←

What I was referring to is the "throbbing" effect, seemingly of the EBD function.

The "sudden acceleration" that you refer to is most likely the lockup torque converter being released so the vehicle can "freewheel" down the incline. Nothing I have found indicates that there is no engine compression braking in the higher gears but the shop manual incates that technicians should only test for engine compression braking in 1st and 2nd. Also torque converter lockup is only used in 3rd, 4th and 5th.

Sorry, this is completely OFF-TOPIC, but I'll leave it here for RX330 owners who might stumble by.

In the RX400h the effect might be the result of the batteries already being fully charged (no requirement for regenerative "braking") and the ECU slipping the CVT into a higher gear to allow "freewheeling".

[bikeandsail]

Since I started this thread I'd like ot get it back on track.

The key word is BUMP.

The action, loss of regenerative braking at high speed, I describe in the first note only occurs when going over a hard bump in the road. It is repeatable if the bump/pothole is hard enough.

By the way RX400h doesn't have torque converter.

Ron

[goofygrin]

Since I started this thread I'd like ot get it back on track.

The key word is BUMP.

The action, loss of regenerative braking at high speed,  I describe in the first note only occurs when going over a hard bump in the road. It is repeatable if the bump/pothole is hard enough.

By the way RX400h doesn't have torque converter.

Ron

←

I know in my other cars (haven't driven the 400h -- wife's car) that have ABS, then I go over a bump at speed, while breaking, I'll feel something like the ABS kick in (but not the ABS I think). As soon as I release the brakes and hit them again, all is ok.

Now I've been in my 400h when coming to a stop and felt some "jerkyness" as we came to the complete stop. My wife swears it's not her... I think it's the car switching from regenerative to real brakes.

[stonecutter]

By the way RX400h doesn't have torque converter.

Ron

←

This may be off thread, but why doesn't the 400h need a torgue converter ?

[bikeandsail]

The regineration normally stops at about 10mph and you can feel the change.

[wwest]

The primary purpose of a torque converter is to replace the functionality of a clutch in a manual transmission car. Secondarily it multiplies the engine torque by a significant factor. At low engine RPMs, at or near idle, the "coupling" from a torque converter's input shaft to its output is intentional "loose", poor. This prevents the engine from being stalled as you come to a stop.

The Prius, Rx400h, Hybrid HL and the Ford Escape hybrid all have CVT's which are implemented using a planetary gear style differential. This CVT really is as close to a manual transmission as one might get in that there is NO method for mechanically uncoupling the engine driveline from the output shaft.

If the engine is idling at ~800 RPM the A/C motor driving the other diff'l (CVT) input shaft simply neutralizes the engine's output drive by turning its diff'l (CVT) input shaft in the "opposite" direction at the exact same speed.

You can see it happening by jacking up both drive wheels of a vehicle without Trac. Start the engine, put the transmission in drive and the driven wheels will start turning, or at least the one with the least frictional resistance will. If you hold one wheel steady then the opposite wheel will turn at twice the normal rate. If you turn a wheel by hand fast enough you can completely negate the rotation of the opposite wheel.

[patt]

My RX400h has about 4000 miles on it and recently I have noticed what I think is a change in the braking, a problem? Normally the braking is part regenerative until about 10 mph and then regineration stops.

←

I don't notice the bump you are talking about, though the roads around here are pretty free of potholes and bumps. One day I when I had to break relatively hard on a wet pavement I felt typical ABS type pulsations. Other than that the braking is pretty smooth.

Do you really only see regenerative braking up to 10 mph? How have you determined that? I see regeneration happen any time I let off the gas or step slightly on the brake regardless of speed. If I hit the brakes harder (to the point where the power meter arrow stops moving more negative) then I assume it moves in to regeneration plus using the brake pads.

If you aren't seeing regeneration above 10 mph, it sounds like something is broken.

I haven't been on a long enough downslope yet to fully charge the battery so I don't know if at that point it would go to pads only or continue to run the generator and dump the power to a load resistor. From what some others have posted, it sounds like it might do the former.

[wwest]

BUMP?

As in Speed Bump....??

If you happen to be on the brakes as the rear wheels "climb" over the speed bump I could see where the ABS might see the slightly disparate F/R rotational rate as a momentary wheel lockup and activate the ABS system for a very brief period.

As your rear wheels "climb" over the speed bump they must rotate slightly faster than the front, already over and now traveling on the flat. To the ABS ECU, brakes applied, the front wheels going slower than the rear just momentarily might fool the ECU into thinking front wheel lockup is impending.

[bikeandsail]

BUMP?

As in Speed Bump....??

If you happen to be on the brakes as the rear wheels "climb" over the speed bump I could see where the ABS might see the slightly disparate F/R rotational rate as a momentary wheel lockup and activate the ABS system for a very brief period.

As your rear wheels "climb" over the speed bump they must rotate slightly faster than the front, already over and now traveling on the flat. To the ABS ECU, brakes applied, the front wheels going slower than the rear just momentarily might fool the ECU into thinking front wheel lockup is impending.

←

BUMP as in salt induced pothole in the road. This is not a momentary event. Once the regeneration stops it stays stopped untill the vehicle is stopped even if event starts at 40 mph.

Ron

[bikeandsail]

My RX400h has about 4000 miles on it and recently I have noticed what I think is a change in the braking, a problem? Normally the braking is part regenerative until about 10 mph and then regineration stops.

←

I don't notice the bump you are talking about, though the roads around here are pretty free of potholes and bumps. One day I when I had to break relatively hard on a wet pavement I felt typical ABS type pulsations. Other than that the braking is pretty smooth.

Do you really only see regenerative braking up to 10 mph? How have you determined that? I see regeneration happen any time I let off the gas or step slightly on the brake regardless of speed. If I hit the brakes harder (to the point where the power meter arrow stops moving more negative) then I assume it moves in to regeneration plus using the brake pads.

If you aren't seeing regeneration above 10 mph, it sounds like something is broken.

I haven't been on a long enough downslope yet to fully charge the battery so I don't know if at that point it would go to pads only or continue to run the generator and dump the power to a load resistor. From what some others have posted, it sounds like it might do the former.

←

I didn't make myself clear. Regeneration normally occurs from a high speed stop untill the speed decreases to about 10 mph and then the regneration stops as indicated the KW meter.

Ron

[patt]

Okay, now I understand.

I don't think regeneration stops below 10 mph, but at that speed the regenerated power is pretty small so the needle is only a little below 0. Since there isn't an exact 0 mark on the scale, it is easy to not see the deflection at all.

The CVT doesn't provide an infinite range of gearing. As the wheels slow, it reaches a point where the generator just isn't turning fast enough to generate max power and the regeneration starts to drop off. If I release and press the brake pedal when rolling at a few miles per hour, I do see a small movement in the power meter needle so regeneration is happening but it is pretty tiny.