E brake after brake change

[Chippie]

The e89 senses if the car moves with the handbrake applied & applies more force to the ebrake to halt the car
Rob

I'm interested; how does it "sense"? The only other electrics are ABS sensors (I think) on the brakes. Does it use these?

I noticed if you try to move the car with the ebrake applied, it shouts a message on the dashboard to say the parking brake is on

I would hazard a guess that the ECU monitors the current draw when the EPB is applied and knows when it can’t turn anymore

[flybobbie]

The ebrake and the way it works is probably the best system i have seen on a car. No more slack handbrake cables to adjust every time the car approaches the MOT. And simple to work on.

I had a RX7, the most stupid handbrake design, had a rod going into the back of the caliper to press on the piston, that always leaked brake fluid.

[Pondrew]

I would hazard a guess that the ECU monitors the current draw when the EPB is applied and knows when it can’t turn anymore

Yes it must regulate by a current switch, but I can't see how it can apply more if the car moves. The only way it can apply more force is by the motor turning the actuator more. If it has decided, by means of a current switch, that enough pressure is exerted, how can it apply more?

[warmasice]

I did two videos putting the ebrake into workshop mode and back using software



if you're interested in setting up a laptop, pm me

Good to know. Thanks

[Smartbear]

I would hazard a guess that the ECU monitors the current draw when the EPB is applied and knows when it can’t turn anymore

Yes it must regulate by a current switch, but I can't see how it can apply more if the car moves. The only way it can apply more force is by the motor turning the actuator more. If it has decided, by means of a current switch, that enough pressure is exerted, how can it apply more?

Here you go, it’s all clever stuff

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Rob

[flybobbie]

Off course the system needs to recheck the ebrake force, because as the disc cools, it shrinks and so could cause car to roll.
I also assume the abs sensors would sense rotation and reapply brake.

[Smartbear]

Off course the system needs to recheck the ebrake force, because as the disc cools, it shrinks and so could cause car to roll.
I also assume the abs sensors would sense rotation and reapply brake.

The car apparently uses a temperature map to determine cooling times of the discs & applies force accordingly

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Rob

[Pondrew]

I think my problem is that I am a Mechanical Engineer, not an Electronics Engineer.

The electronics still have to convert all that sh*t into a mechanical action. I didn't understand any of the attached cr*p, sorry (and got bored reading it).

A lot of the stuff in Rob's (attached info sheet) post has to be bullsh*t. There are no temperature sensors on the discs, pads or pistons. It HAS to be down to current switches. IE the Ebrake checks after a given period (easily done thru Etimers) and puts a squirt of juice to the motors. If the current switch is made, nothing happens. If not it turns the motor until the switch does make.

I may be wrong, of course. It has happened before (Once)!

[Pondrew]

I've thought about this some more!

When the ebrake motors release it doesn't pull the pistons back (I know this from winding the actuator by hand; the pistons didn't move, I had to physically compress them), it only releases the pressure or EMF which I presume is Electro-Mechanical (or Motive) Force, which will make them retract a tiny amount to free them from the disc otherwise they would bind.

I have noticed that after about ten minutes of the car sitting idle, the red LED goes out on the ebrake; this is allied to all sorts of other "noises", I presume these are cancelling "primed" circuits for driving, maybe fuel pump release and also a "test" of the ebrake. This would make sense to my simple brain.

[Smartbear]

I think my problem is that I am a Mechanical Engineer, not an Electronics Engineer.

The electronics still have to convert all that sh*t into a mechanical action. I didn't understand any of the attached cr*p, sorry (and got bored reading it).

A lot of the stuff in Rob's (attached info sheet) post has to be bullsh*t. There are no temperature sensors on the discs, pads or pistons. It HAS to be down to current switches. IE the Ebrake checks after a given period (easily done thru Etimers) and puts a squirt of juice to the motors. If the current switch is made, nothing happens. If not it turns the motor until the switch does make.

I may be wrong, of course. It has happened before (Once)!

It’s official bmw bullsh*t No temperature sensors, the value is calculated by the dsc unit.
Rob

[Smartbear]

I've thought about this some more!

When the ebrake motors release it doesn't pull the pistons back (I know this from winding the actuator by hand; the pistons didn't move, I had to physically compress them), it only releases the pressure or EMF which I presume is Electro-Mechanical (or Motive) Force, which will make them retract a tiny amount to free them from the disc otherwise they would bind.

I have noticed that after about ten minutes of the car sitting idle, the red LED goes out on the ebrake; this is allied to all sorts of other "noises", I presume these are cancelling "primed" circuits for driving, maybe fuel pump release and also a "test" of the ebrake. This would make sense to my simple brain.

Yes, I think the e89 takes around 30mins to fully go to sleep.
Rob

[Pondrew]

It’s official bmw bullsh*t No temperature sensors, the value is calculated by the dsc unit.
Rob

I tried to iterate (maybe unsuccessfully) that I wasn't implying you were talking bullsh8t. Please don't hate me just cos I don't like your weird fence panels

The value cannot be calculated by the dsc unit; it just can't. The electronics are not that clever.

The amount of expansion (and subsequent contraction) of a steel brake disc is TINY; like thousandths of a mm. These cars do not have sensors that could measure those tiny increments. It MUST be done using current switches and timers. I would love to be proved wrong (for the second time)

[flybobbie]

The motors could have counters, position servo on them, start and finish count would change depending on the disc width due heat.
Certainly if you fiddle with the motors, a code comes up on the reader.

[Pondrew]

The motors could have counters, position servo on them, start and finish count would change depending on the disc width due heat.
Certainly if you fiddle with the motors, a code comes up on the reader.

See we are going back to the OBD reader nonsense. Why would an electro-mechanical motor have a counter? They don't. I promise you.

I have done this in real life, the only thing the motors do is wind further on until they are happy there is piston pressure. If they had as you suggest, my car would be in the river by now

[Smartbear]

It’s official bmw bullsh*t No temperature sensors, the value is calculated by the dsc unit.
Rob

I tried to iterate (maybe unsuccessfully) that I wasn't implying you were talking bullsh8t. Please don't hate me just cos I don't like your weird fence panels

The value cannot be calculated by the dsc unit; it just can't. The electronics are not that clever.

The amount of expansion (and subsequent contraction) of a steel brake disc is TINY; like thousandths of a mm. These cars do not have sensors that could measure those tiny increments. It MUST be done using current switches and timers. I would love to be proved wrong (for the second time)

I don’t mind if you don’t like my wierd railings, that’s fine
The dsc is actually cleverer than that as it calculates individual brake disc temperatures & it uses the hottest one to chose the temperature map it references for the re tensioning times.
Rob