BMW F12 2011, Technical Training Manual, Page: 33 / 68

F12�Chassis�Dynamics
4.�Brakes
29
The�"applied"�status�is�indicated�by�a�red�indicator�light�in�the�instrument�panel�(KOMBI)�and�an�addi-
tional�red�LED�in�the�parking�brake�button.�Once�the�parking�brake�is�on,�pulling�the�parking�brake�but-
ton�again�has�no�effect.
F12�Indicator�lamp�for�parking�brake�applied
Roll-away�detection�while�parking�brake�applied
The�roll-away�detection�function�is�designed�to�prevent�the�vehicle�rolling�away�while�the�parking�brake
is�applied.�The�roll-away�detection�function�is�always�activated�whenever�the�parking�brake�status
changes�from�"released"�to�"applied"�and�terminates�after�a�defined�period�of�time�from�that�change�of
status.
A�signal�from�the�DSC�is�used�as�the�input�variable�for�roll-away�detection.�As�soon�as�that�signal�in-
dicates�that�the�vehicle�is�starting�to�roll�during�the�detection�window,�the�EMF�actuators�are�immedi-
ately�further�tightened.�That�is�achieved�by�applying�maximum�current�to�the�EMF�actuators�for�100
ms�in�order�to�increase�the�clamping�force.�The�system�then�waits�for�400�ms.�If�the�vehicle�starts�to
roll�again,�the�retightening�process�is�repeated�(up�to�three�times).�If�rolling�of�the�vehicle�is�still�detect-
ed�after�retightening�the�parking�brake�three�times,�the�function�terminates�and�a�fault�is�entered�in�the
fault�memory.
Temperature�monitoring
The�temperature�monitoring�function�ensures�that�the�loss�of�parking-brake�force�that�occurs�when
hot�brake�discs�cool�down�is�compensated�for.�The�temperature�monitoring�function�is�activated�if�the
temperature�is�above�a�defined�value�on�a�change�of�parking�brake�status�from�"released"�to�"applied".
The�temperature�of�the�brake�discs�is�calculated�individually�for�each�wheel�by�the�DSC�control�unit
and�communicated�to�the�EMF�control�unit.�When�the�status�changes,�the�higher�of�the�two�brake�disc
temperatures�is�used�for�temperature�monitoring�purposes.�The�temperature�ranges�and�correspond-
ing�retightening�periods�are�stored�in�a�characteristic�map.
The�appropriate�retightening�periods�from�the�characteristic�map�are�applied�according�to�the�temper-
ature�on�change�of�status.�Once�the�first�retightening�period�has�elapsed,�the�parking�brake�is�retight-
ened�for�the�first�time.�After�expiry�of�the�second�retightening�period,�the�parking�brake�is�retightened
again,�and�again�after�the�third�period�has�elapsed.�The�characteristic�map�may�also�contain�the�value
0�for�one�or�more�retightening�periods.�In�that�case,�the�corresponding�retightening�sequences�do�not
take�place.�The�function�terminates�when�the�last�retightening�sequence�has�been�completed.
Releasing�the�parking�brake
The�parking�brake�is�released�by�pressing�the�parking�brake�button�down.�However,�for�the�parking
brake�to�actually�be�released,�Terminal�15�must�be�ON�and�at�least�one�of�the�following�preconditions
satisfied: