BMW F12 2011 Technical Training Manual page 33

F12￿Chassis￿Dynamics
4.￿Brakes
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:
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