spacecraft

Ok, here's the behaviour I'm talking about (4wd 2008 RX400h):
When I brake, the car goes in regenerating mode and both electric motors recharge the batteries.
This happens from the moment when I start braking, till the car is ALMOST completely stopped.
I'm stressing "almost" because when I progressively reduce the effort on the braking pedal (to smoothen the braking), there is a point when the front electric motor starts pulling, instead of regenerating.
This seems to happen when:
1) the car speed is extremely low - not even measurable on the tacho, AND
2) the brake pedal is pressed just a tiny bit.
In these conditions, I can arrive to stopping completely the car (again, with the brake pedal only slightly pressed), and see on the display that the electric motor is still trying to pull forward.
This doesn't happen if I press the brake pedal a bit further.

In other words, it seems that the car doesn't "sense" the brake pedal at the beginning of its excursion, when it's only pressed just a tiny bit.
Have you ever experienced the same in your RX?
And is there maybe some part (like a sensor of the brake pedal position, or anything else) which should be registered to avoid the above?

Thanks in advance for any suggestion!

Driver125

Hi,
Since this isnt a traditional engine/transmission setup, if u had the gas pedal pressed on hard right before braking, the the engine would continue to rev at high rpm to level off with the cvt and pull the car while you try to brake. This gives that "pulling" sensation and is normal. If thats not the case, then I suggest you have it checked out because it might be a sensor problem.

spacecraft

Nope, I'm talking of "normal" decelerations, as when you see a red light from some distance: you take your foot off the gas pedal first (hence the thermal engine goes off, and the electric motors start regenerating), then you start braking gently.
The thermal engine has nothing to see with what I previously described, it's the electric motor that after regenerating (till the car is almost stopped) begins pulling, if the brake pedal is pressed just a bit.
In "Info screen" terms, I see the light blue arrows for the whole duration of the coasting/braking, and when the car speed gets close to zero, with just a light touch on the brake, the front electric motor shows the yellow arrow. And continues to show it even with the car completely stopped, unless I press the brake pedal further.

maseace

Below 9 mph, the regenerative braking stops and the normal friction brake pads engage. All the Toyota/Lexus hybrids do this, and it's part of the hybrid system design. You can sometimes feel a lurch on slippery or uneven pavement during this transition. Also, when braking hard at any speed, the friction brakes will engage. The regenerative braking can only do so much, using the motors as generators.

katzjamr

I have also noticed that if i am stopped at a light or stop sign and not pushing hard on the brake, the arrows are moving on the display, and if you push harder they stop moving. Just because the arrows are moving on the screen i dont think you have 'pulling' or energy going to the wheels. This is normal in the 92,000 miles i have on my hybrid. It is nothing to worry about.

spacecraft

Thanks maseace & katzjamr.
I wasn't aware of the 9mph limit, and yes, my RX behaves exactly as katzjamr describes.

Driver125

Yes. I have also experienced this. It is completely normal. Something else to note: if you have your foot on the brake lightly, then the brake lights don't come on... You must depress the brake harder to the point where the "info screen" shows no energy coming from the wheels when at a complete stop... (And so you could warn any vehicles behind you that you"re stopped.)

spacecraft

Happy to hear that it's not a problem of my own RX.
But on the other hand, I can't understand the reason for such behaviour.
Wouldn't it make more sense if even the slightest touch to the brake pedal would release the electric motor and turn on the stop lights...

joedaddy1

iTrader: (1)

i know what you are talking about.. and i don't think it's an issue...

i know for sure if you weren't looking at the info screen of the NAV, you probably can't even tell.. right?

spacecraft

That's correct.
But it doesn't change the fact that it can't see any logic in it, or am I missing something?
Even more so, now that Driver125 told us that also the stop light don't come on when the brake pedal is pressed lightly...
Btw, I'll check that also on my RX. So far, I only noticed looking at the info screen, as you said.

joedaddy1

iTrader: (1)

i don't agree with this.. the brake lights will come on every time you step on the brake pedal AND brake is being applied. If it didn't come on, that would be a MAJOR safety flaw. This would be almost as bad as unintended acceleration.

If your foot is not putting enough pressure on the brake pedal, the light will not come on, but at the same time your car will not have any brake power. Say example, i know my foot is lightlyon my brake pedal in downtown areas to stop for jaywalkers and car doors to be thrown open. I wouldn't want the guy behind me to think i am stopping/riding on my brakes..

spacecraft

Today I checked the brake lights behaviour, and I can confirm that my RX does NOT behave as Driver125 described.
I mean, by pressing the brake pedal very lightly, I can manage to stop the car, and keep it stopped, with the info screen still showing the yellow arrow from the front electric motor to the front wheel.
BUT in such condition, the brake lights do come on. If I press the brake pedal further, the yellow arrow disappear and the brake lights (obviously) remain on.
There's no way I could stop the car (or keep it stopped) in D without having the brake lights coming on.

maseace

The brake light on the RX hybrid is the same as any other car - there's a switch behind the brake pedal arm that senses when the pedal is pressed, and it can be adjusted if it doesn't come on at the right time. It's connected directly to the 12V battery via a fuse, so it works whether the car is on or off, and it's not part of the hybrid system.

There is a separate brake pedal stroke sensor that IS related to the hybrid system, and stablity control, skid control, etc. It senses how hard and quickly the pedal is pressed.

I verified this using the repair manual wiring diagrams.

spacecraft

Funny you mention it, because before posting this thread I had a look at the brake pedal, thinking that I could have seen something attached to it, but found nothing.
I mean, the pedal pushes a small piston, which goes inside the engine compartment, but that's all I could see...
Out of curiosity, does the manual say where that switch is located?
Besides, is the repair manual you're talking about downloadable from somewhere?

maseace

See the stop light switch in the diagram. It's from the repair manual I bought on CD on eBay.

Manual link on eBay.