BMW F12 2011 Technical Training Manual page 17

F12￿Chassis￿Dynamics
3.￿Chassis￿and￿suspension
3.5.￿Tire￿Pressure￿Monitor￿System
3.5.1.￿System￿function
The￿Tire￿Pressure￿Monitor￿System￿is￿installed￿in￿the￿F12.
The￿direct￿measuring￿TPM￿system￿(RDC)￿consists￿of￿the￿TPMS￿control￿unit￿with￿integrated￿reception
aerial￿and￿four￿wheel￿electronics.￿It￿was￿possible￿to￿reduce￿the￿number￿of￿components￿and￿cost￿of￿the
TPM￿system￿by￿integrating￿the￿reception￿antenna￿in￿the￿TPMS￿control￿unit.
The￿four￿wheel￿electronics￿transmit￿the￿tire￿pressure￿and￿temperature￿to￿the￿TPMS￿control￿unit￿via
radio￿communication￿(433￿MHz).￿Once￿the￿wheel￿electronics￿have￿been￿woken￿up,￿(vehicle￿speed￿>
20￿km/h),￿a￿total￿of￿25￿telegrams￿are￿transmitted￿once￿at￿two￿second￿intervals.￿Providing￿the￿pressure
does￿not￿drop,￿individual￿telegrams￿are￿then￿sent￿every￿18￿seconds￿from￿the￿wheel￿electronics￿to￿the
TPMS￿control￿unit.￿As￿a￿prerequisite￿for￿the￿wheel￿electronics￿to￿go￿to￿sleep,￿the￿wheel￿must￿be￿at￿a
standstill￿for￿more￿than￿five￿minutes.
Resetting￿the￿tire￿pressure￿values
The￿tire￿pressure￿values￿are￿reset￿via￿the￿instrument￿panel￿(KOMBI)￿or￿Central￿Information￿Display
(CID).￿The￿TPMS￿text￿message￿appears,￿or￿the￿permanent￿TPMS￿indicator￿light￿lights￿up,￿in￿the￿instru-
ment￿panel￿(KOMBI)￿when￿the￿teach-in￿process￿starts.
Teach-in￿process
During￿the￿teach-in￿process,￿the￿wheel￿electronics￿identification￿numbers￿(IDs)￿are￿transmitted￿to￿the
TPMS￿control￿unit.￿The￿TPMS￿control￿unit￿can￿identify￿the￿wheel￿position￿of￿the￿corresponding￿wheel
electronics￿via￿the￿identification￿numbers￿once￿the￿teach-in￿process￿is￿complete.
Two￿acceleration￿sensors￿are￿installed￿in￿each￿of￿the￿wheel￿electronics￿in￿order￿to￿be￿able￿to￿determine
their￿positions.￿The￿acceleration￿sensors￿determine￿the￿wheel's￿direction￿of￿rotation.￿This￿means￿that
it￿is￿possible￿to￿differentiate￿between￿the￿positions￿of￿the￿right/left￿wheel￿electronics￿at￿the￿vehicle.
The￿high￿frequency￿signals￿received￿are￿evaluated￿in￿order￿to￿determine￿whether￿the￿wheel￿electronics
are￿at￿the￿front￿or￿rear￿axle.￿The￿TPMS￿control￿unit￿with￿integrated￿receiver￿is￿installed￿in￿the￿luggage
compartment.￿The￿level￿of￿the￿signals￿received￿by￿the￿TPMS￿control￿unit￿from￿the￿wheels￿on￿the￿rear
axle￿is￿higher￿than￿the￿level￿of￿signals￿sent￿by￿the￿wheel￿electronics￿on￿the￿front￿axle.￿This￿means￿it￿is
possible￿to￿determine￿whether￿the￿wheel￿electronics￿are￿at￿the￿front￿or￿rear￿of￿the￿vehicle.
The￿entire￿teach-in￿process￿takes￿between￿roughly￿one￿and￿twelve￿minutes￿at￿the￿most.￿The￿following
factors￿influence￿the￿time￿it￿takes￿to￿complete￿the￿process:
• The￿condition￿of￿the￿road￿(smooth￿or￿rough￿surface)
• The￿current￿mode￿of￿the￿wheel￿electronics￿(awake/gone￿to￿sleep)
• The￿RDC￿control￿unit￿already￿knows￿what￿the￿IDs￿of￿the￿wheel￿electronics￿are.
13