P85D - Electric Mechanical Braking System

[neroden]

You know, I'm a bit conservative -- I miss the fully mechanical emergency brake connected by a chain. Worked when *everything* failed. When they design this drive-by-wire stuff, do they actually do safety cases, running through single point of failure and dual point of failure possibilities?

 

[EarlyAdopter]

You know, I'm a bit conservative -- I miss the fully mechanical emergency brake connected by a chain. Worked when *everything* failed. When they design this drive-by-wire stuff, do they actually do safety cases, running through single point of failure and dual point of failure possibilities?

Maybe you missed my post earlier up-thread, but the new system isn't drive-by-wire. There's a direct mechanical linkage from your foot to the booster. This is actually a step better than traditional hydraulic brake systems where your foot is connected to the master cylinder via a hydraulic line, another potential point of failure.

This Wards article has some good information on the fail-safe aspects of the new "iBooster" system.

Braking suppliers such as Bosch introduced electrohydraulic braking systems years ago as the initial foray into brake-by-wire. Bosch worked with Daimler in developing the Sensotronic brake system, introduced on the Mercedes SL in 2001.

That system replaced the conventional master cylinder with a hydraulic high-pressure reservoir and a piston pump driven by an electric motor. When the brake was applied, an electronic control unit calculated the desired brake pressure on each individual wheel, for improved stability.

But there were technical difficulties, and Mercedes recalled some 2 million vehicles with the system in 2004 and 2005. The auto maker eventually dropped the system. Toyota is conducting a similar brake recall.

The Mercedes recall illustrated that brake-by-wire may need more development time, Steiger says. As a result, the new iBooster still integrates with full hydraulic braking and a conventional master cylinder.

“We said we always need direct control from the driver so we developed the iBooster, which has a direct link between the pedal and the master cylinder,” he says. “So if something goes wrong, if there is a failure, we still have the ability to brake by your own foot.”

 

[PlanB]

@techiesjc: did you have the "ticking" noise issue prior to getting the iBooster replaced? (See issues on new cars). I have the ticking on my P85, which I took delivery of on 9/28, one day before you did. Haven't taken it in for service yet since the consensus on the other thread was that this was "normal"... maybe not!

It's not normal, they have open graded it. Your local SC should be aware of this.

 

[JRP3]

You know, I'm a bit conservative -- I miss the fully mechanical emergency brake connected by a chain. Worked when *everything* failed.

I've encountered enough emergency brakes where the cables were frozen or broken. Nothing is fail safe.

 

[ratsbew]

Also, don't forget the difference between an emergency brake and a parking brake. Many cars have the ratcheting foot pedal to apply a parking brake. A parking brake is not meant to stop a car in motion.

 

[JRP3]

If that's all there is it's better than nothing, and becomes your emergency brake.

 

[green1]

I've encountered enough emergency brakes where the cables were frozen or broken. Nothing is fail safe.

Not fail safe, but completely separate from everything else to the largest possible degree. That's worth something.

 

[thecloud]

It's not normal, they have open graded it. Your local SC should be aware of this.

Thanks. Not familiar with that term, but in any case I will be making a visit to the SC soon.

 

[PlanB]

Thanks. Not familiar with that term, but in any case I will be making a visit to the SC soon.

Not sure why I said "graded". The ibooster was replaced on my brand new P85. They wanted to do this before autopilot was released so it is a known issue.

- - - Updated - - -

Replace Electromechanical Brake Booster

Pay Type: Warranty

Corrections: Replace Electromechanical Brake Booster
Replaced electromechanical brake booster per bulletin.
Part Quantity
iBooster - Model S (1037123-00-A) 1
NUT HFPT M8x1.25 [10]-ZnNi (2007104-00-
B)
4
SWITCH,BRAKE ON/OFF (1005124-00-A) 1
HYDRAULIC FLUID DOT 4 (2001936) 3

 

[neroden]

Maybe you missed my post earlier up-thread, but the new system isn't drive-by-wire. There's a direct mechanical linkage from your foot to the booster.

Why yes, I did miss it! Thank you very much for the link. Fascinating and great system design.

 

[PeterK]

Umm my point is that Tesla probably includes this functionality on the Ds that will be delivered in December. The "software development, integration and testing" for the simple function of using the brake pedal to trigger add'l regen is already done. It could be part of the reason for the increased range in addition to the power curve of the additional motor.

Those on this thread saying the Tesla can't do what they imagine (incorrectly) that Toyota could not do (use the brake pedal to trigger add'l regn) will probably be shown wrong in December. (They were actually shown wrong with the Toyota/Tesla RAV4 EV already many months ago.)

It is so amusing to see the hand wringing and fretting about the looming prospect of regen from the brake pedal.

No one ever said Tesla can't do regen on the brake pedal, we just did not feel it was worth the effort for a minor incremental amount of regen, nor did we want to risk negatively affecting the brake feel (I used to own a Toyota hybrid and I found the brake transition from regen to friction brake very noticeable).

Now that these cars have been on the road for some six months, can anyone answer whether the iBoosters are doing brake pedal regen?

 

[mspohr]

Not fail safe, but completely separate from everything else to the largest possible degree. That's worth something.

The emergency brake is a completely separate system from the switch to separate calipers.

 

[Todd Burch]

Now that these cars have been on the road for some six months, can anyone answer whether the iBoosters are doing brake pedal regen?

They are not--all regen is definitely tied purely to the go pedal.

 

[bhzmark]

Or tied to tacc. But I agree now. The brake pedal can only make dust-- not electricity.

 

[webman22]

Hi, the link with the presentation doesn't work anymore. Do you or anybody else in this forum has it stored and could send it to me? I'm very interessted in the iBooster but there aren't many information.
Thanks

 

[JRP3]

If you Google "Bosch ibooster" and select "Video" there are a number of different videos available.

https://www.youtube.com/watch?v=Uzx1Hj7WmVY

http://videoportal.bosch-presse.de/clip/_/-/-/iBooster-Footage--1?category=IAA-2013-PKW

 

[steph280]

We had the SBC (Sensotronic Brake Control) in our 2005 Mercedes E320 (W211). While they made a big deal about it in marketing material, nobody knew its existence other than the frequent loud primer pump noise, even when you are not driving the car. The frequency of the pump startups apparently caused some premature failure, which Mercedes promptly issued a free extended warranty to the specific pump. This system was abandoned in later US E-class models.

Driving dynamic was no different than old hydraulic brakes. Except there is a second motorcycle sized 12V battery as backup system. And there was warning to the DIY group to disconnect ALL POWER when changing brake pads, as the calipers can activate when car detects potential usage (like opening a door).