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Hill Assist

Hill Assist

I really find it strange that in a 2012/2013 car there is no hill-hold feature standart. Does anybody know how the braking system of the Model S works? Is the braking pedal mechanical connected to device (magnetic or hydraulic) that activates and releases the brakes or is the pedal just connected to a sensor that sends an electrical signal to the braking device? In the latter case it should not be difficult to program a delay of 2-3 seconds between the release of the brake pedal and the release of the brake and should not take long to develop and implement.

ye | 19. April 2014

rdalcanto said: "If hill assist doesn't use the motor, why does the orange line move up significantly as soon as you release the brake pedal and hill assist is holding the car still on the incline?"

Interesting. Maybe the ABS uses a lot of electricity? Although, offhand, I don't see why it would.

So far, I still can't tell for sure what's going on.

TFMethane | 19. April 2014

@ye I thought the reason parking brakes traditionally use cable systems is that they double as emergency brakes, and the point is to have a simpler mechanical linkage that works well even if the other system fails. I guess your explanation makes sense, though.

ye | 19. April 2014

DickB said: "It's the parking brake that come on for the hill assist."

How can you tell?

ye | 19. April 2014

TFMethane said: "I thought the reason parking brakes traditionally use cable systems is that they double as emergency brakes, and the point is to have a simpler mechanical linkage that works well even if the other system fails."

That sounds plausible as well.

ye | 20. April 2014

rdalcanto said: "If hill assist doesn't use the motor, why does the orange line move up significantly as soon as you release the brake pedal and hill assist is holding the car still on the incline?"

What does the orange line do if you try it on level ground?

ye | 20. April 2014

Pungoteague_Dave said: "The parking brake does not use an electric motor. It has an electronic servo system that hydraulically activates a second set of standard brake calipers brake pads on the rear brake rotors. No motor involved."

What's an electronic servo system, and how does it differ from an electric motor?

ye | 20. April 2014

Wouldn't it be so much easier if Tesla just told us how it works? :-)

Do the release notes give any hint?

J.T. | 20. April 2014

@ye Wouldn't it be so much easier if Tesla just told us how it works? :-)

The last two issues I've asked Ownership about: do rear guidelines require new hardware and crumple zone integrity if spare tire is placed in frunk, seemed to leave them befuddled.

So, we could ask them but it might be a few weeks before they can find someone who knows. :-)

ye | 20. April 2014

I could see the crumple zone question being tricky to answer. Presumably they haven't actually done any crash tests with a spare tire in the frunk, so it would have to be a more or less educated guess.

The rear guidelines question shouldn't be that hard to find an answer to.

And the hill assist question should be trivial to answer. They designed it themselves, so obviously they know how it works.

SeattleSid | 20. April 2014

What I've noticed, and it's admittedly subtle, is that when I'm stopped on a hill and step on the brake, a little guy pops out of the trunk, leans against the car, then hops back in as soon as I apply power. Never happened before 5.9.

NKYTA | 20. April 2014

@sid, haha.

I've not noticed energy increasing on the dash when using hill assist. Perhaps I need to try a steeper hill.

J.T. | 20. April 2014

I wrote to ownership and expect an answer "soon".

David Trushin | 20. April 2014

I just checked this on my (steep) driveway. Put on the brake. Then i removed my foot from the brake. The car did not move. The energy line did not move. I put on th accelerator and the energy line moved as did the car. I have creep on.

Bighorn | 20. April 2014

My sense is that the regular brakes locked for about a second before letting go. Didn't spend a lot of time listening for the parking brake though. I doubt the motor is involved.

ye | 20. April 2014

Theory: Hill assist uses the brakes to hold the car. rdalcanto has creep on, NKYTA and David Trushin have it off. With creep on, the motor is using power trying to move the car against the brakes.

Either that or somebody is hallucinating. :-)

Bighorn | 20. April 2014

@ye
I think the TM engineers are smart enough to have creep suspended for the hill hold function.

drp | 20. April 2014

It certainly is fantastic that people mention creep, hill assist, etc and soon these all appear for free! What a great company.
I wonder if that's how Maserati, BMW, and other companies respond to customer insights? No, I don't really wonder.....
I sure appreciate the software updates!

Thank you Tesla Team!!!

David Trushin | 20. April 2014

Sorry to contradict, but my post says i have creep on.

David Trushin | 20. April 2014

I agree with drp. When people ask me what's so great about Tesla, i tell them about hill assist.

ye | 21. April 2014

David Trushin said: "Sorry to contradict, but my post says i have creep on."

Indeed it does. I don't know how I missed that.

There goes that theory.

More questions: If the car is in Drive and pointed downhill, does the hill assist hold the car and prevent it from rolling forward? In general, how does the car decide whether to creep or to hold?

Bighorn | 21. April 2014

ye-
I think if the car senses an angle (up or downhill) and has the brake depressed, there is a latency before the brake is released.

David Trushin | 21. April 2014

I would suspect that there is a sensor that determines direction of motion of the wheels. If the wheels are moving (over a period of micro or milliseconds) opposite to the intended direction (as indicated by the shift lever) it leaves the brake engaged until the accelerator is pressed. Otherwise, it releases the brake when you lift your foot. I don't think it mucks with creep. In other words, if creep is selected and the direction of motion is correct, then it releases the brake. If creep is selected and the motion is opposite, then it leaves the brake engaged. This would seem to be the simplest algorithm. And it is independent of the steepness of the hill and whether or not creep is on.

Mark E | 21. April 2014

I wouldn't expect it to be that complicated. If the hold is achieved using either the parking brake or the normal brakes then the logic is extremely easy.

If the car is stopped using the brake then activate hill hold. When the brake is released confine to hold either the brakes or parking brake (I suspect the latter) for 1 second OR until the accelerator is pressed.

Hey presto! Hill hold either forwards or backwards, up or down hill.

Bighorn | 21. April 2014

@Mark
I considered that--but I don't think the prolonged braking is engaged on shallow angles. It will take more time with it to know though.

Mark E | 21. April 2014

@Bighorn
I'd be interested in what you find. I saw from some other posts that you need to brake reasonably firmly to activate it - maybe that's why you haven't noticed it on minor slopes.

I'd be keen to test it when deliveries finally start here in Australia!

ye | 21. April 2014

Bighorn said: "I think if the car senses an angle (up or downhill) and has the brake depressed, there is a latency before the brake is released."

It would need an accelerometer to detect that it's angled up or down. I didn't see why it would already have one, but now that I think about it some more, maybe the stability control system uses one.

ye | 21. April 2014

David Trushin said: "I would suspect that there is a sensor that determines direction of motion of the wheels. If the wheels are moving (over a period of micro or milliseconds) opposite to the intended direction (as indicated by the shift lever) it leaves the brake engaged until the accelerator is pressed. Otherwise, it releases the brake when you lift your foot."

I don't see how that would work. The wheels won't turn at all, because the brakes are already applied. So how would the car know whether or not to release them?

David Trushin | 21. April 2014

When you release the brake, the wheels move, triggering the sensor. Then the brakes get reapplied if necessary. This all happens so quickly you never notice.

But the truth of the matter is that this is all just speculation. Thhe important thing is that it works and works pretty well and the did it with software.

ir | 21. April 2014

@ye: I think it already has an accelerometer for the regen brake lights. Conservation of matter is preserved! ;)

GaryREM.va.us | 21. April 2014

@Pungoteague_Dave

"The parking brake does not use an electric motor. It has an electronic servo system that hydraulically activates a second set of standard brake calipers brake pads on the rear brake rotors. No motor involved."

What's your source for this? Most description of electric parking breaks show them as electromechanical systems since they have to work when power is off. This picture from TMC looks like the electromechanical (not hydraulic) devices I've seen described.

GaryREM.va.us | 21. April 2014

Whoops, sorry about the picture size.

ye | 21. April 2014

ir said: "I think it already has an accelerometer for the regen brake lights."

It doesn't need an accelerometer for that. It can just use (the rate of change of) the speed of the motor or wheels.

ir | 21. April 2014

@ye: just for fun, I coasted to a stop at a traffic light (mostly flat grade) and pressed firmly on the brakes. When I let go, the car drifted backwards due to some unevenness in the road. No hill assist.

If the car was using rate of change, it should have applied the hill assist due to the car drifting backwards.

Keep in mind that when hill assist does kick-in, the car doesn't drift before. So there is no rate of change to detect.

By using the accelerometer, it can tell that it is on an even grade and not apply hill assist. Which is consistent with what I experienced.

Brian H | 22. April 2014
ye | 22. April 2014

ir, based on your experiment, it seems like the car does have an accelerometer and does use it to decide whether to engage hill assist.

In my previous post, I wasn't talking about hill assist. What I meant there was that the car doesn't need an accelerometer in order to illuminate the brake lights during regen. For that purpose, it could look at the speed of the motor or wheels.

TFMethane | 22. April 2014

All cars have had accelerometers for years. It's one of the triggers for airbag deployment, and is one piece of data stored for post-crash investigations (i.e. your car's black box). These have been around in all US cars for a while.

ye | 22. April 2014

I knew that accelerometers were used for triggering airbags, but I thought it likely that the dynamic range of a single accelerometer is not wide enough to measure the very high forces generated in a crash and also the low forces from being on a slight incline. But I don't really know. Maybe the same one can be used for both purposes.

TFMethane | 22. April 2014

It's a fair question. They are all designed differently. The MEMS acellerometers in the airbag systems likely don't have good DC (i.e. constant signal - gravity) response, but I believe the ones under the hood do. In addition, I'm not sure how you can do active suspension properly without a good acellerometer but, then, I'm not an automotive engineer.

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