jumbojake

Hold button function

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I like the 'hold' button feature.... good for stop/start congestion.... seems like a user friendly version of the hill start on my wife's Rx ..... but curious how it works.  

Does anyone know if it actually applies the hand-brake, play with the foot-brake hydraulics or is it some magic in the transmission?

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I think it applies the handbrake. 

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It applies the handbrake electronically.   The handbrake is a pair of old fashioned brake shoes which sit inside the rear brake disc  just like a brake drum but the actuator to pull the shoes on is totally electrically controlled.   The rear brake disc and calliper are conventional looking but the handbrake bits are hidden inside the rear brake disc.  

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ok, interesting, so it's a different technology to use the electric handbrake on the ES, as opposed to whatever they do on the Rx  (which has a manual cable handbrake).

in the ES, I could hear the handbrake winding in/out when I pressed the handbrake button, but didn't hear it when the hold is engaged... perhaps the background noise drowned it.

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I am fairly sure it is using the service brake, I have not heard the EPB actuating or releasing when using the brake hold. It appears there is both an auto and manual hold - the auto hold engages on an incline but only holds the brakes for 2 seconds after you take your foot off the pedal. The manual hold appears to hold "indefinitely" although I am unsure if there is some limit on how long the solenoids in the ABS/ESC actuator can stay switched on.

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I am pretty sure it is not the handbrake, for the simple reasons that 1) you cannot hear the parking break engaging and it would be too slow to release in traffic and 2) the brake lights stay illuminated for however long it is in use.

There is a time limit, which is a few minutes minutes, after which a message comes up asking you to press the pedal and reactivate the holding feature.

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One of our family BMWs have that feature, I've tried it once and it works well - I think you have to get used to it because normally I tend to just use the foot break if the stop is not too long.

It never gets used in the BMW for sure

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I use it every day.  As soon as I start the car I hit the Hold button (it turns off when you turn off the car).  In stop / start traffic it’s excellent.  Car just happily sits on the brakes until I’m ready to move off.

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Adaptive Cruise Control does the same in traffic - will quite happily sit there holding it on the brakes for you, then asks you to press accelerator or the resume button when the car in front moves off.

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46 minutes ago, The_Doctor said:

Adaptive Cruise Control does the same in traffic - will quite happily sit there holding it on the brakes for you, then asks you to press accelerator or the resume button when the car in front moves off.

I only use ACC on the open road where the speed is constant such as a motorway.  I know it’s full range ACC but I usually go to manual control once speed becomes variable.

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CORRECTION.     My error,  the handbrake operation on an ES does clamp the actual disc brake on the rear wheels and not like a 2007   LS460 which did hide a pair of brake shoes inside the rear disc.

I had my wheels off the car today for their fortnightly clean and took a minute to look at the rear disc arrangement.  It's clear that there is a mechanised electric motor that looks like it operates a piston housed in a separate black plastic  housing,  nothing to do with the brake calliper pistons.   The electric motor must engage some sort of piston to force the brake pads to grip the brake disc and hold the car.  If you use the brake hold function like me,  once you press the accelerator the electric motor must receive an electronic signal and  releases the hydraulic pressure and the brake pads release the discs.   No sign of any old fashioned levers or cables.          

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