BMW F97 Technical Training Manual page 51

F97/F98￿Complete￿Vehicle
5.￿Chassis￿and￿Suspension
M￿Servotronic￿is￿that￿3￿stages￿can￿be￿selected￿in￿comparison￿to￿2￿stages￿in￿the￿production￿vehicles,
and￿it￿has￿a￿separate￿button￿in￿the￿M￿driving￿dynamics￿button￿panel￿in￿the￿center￿console.￿Using￿the
button￿or￿via￿the￿M1/M2￿buttons,￿the￿driver￿can￿switch￿between￿"Comfort",￿"Sport"￿and￿"Sport+".
Here￿the￿corresponding￿characteristic￿curve￿is￿activated￿and￿in￿Sport￿direction￿the￿power￿steering
support￿is￿also￿noticeably￿withdrawn.￿The￿program￿selection￿can￿also￿be￿preconfigured￿in￿the￿head
unit￿HU￿and￿selected￿using￿the￿M1/M2￿buttons￿on￿the￿steering￿wheel.
M￿drive￿dynamic￿control￿switch,￿program￿description,￿M￿Servotronic:
• "COMFORT":￿Focus￿on￿light￿and￿comfortable￿steering￿torques￿with￿perfect￿feedback￿from￿the
road￿surface￿at￿the￿same￿time.
• "SPORT":￿Greater￿rise￿in￿the￿steering￿force￿and￿perceptibly￿more￿feedback￿for￿sporty￿M
dynamic￿driving,￿both￿for￿every￿day￿use￿and￿at￿the￿dynamic￿driving￿limit.
• "SPORT+":￿Even￿greater￿rise￿in￿the￿steering￿force￿and￿high￿steering￿force￿level￿for￿the￿greatest
possible￿feedback￿and￿clear￿sporty￿steering￿sensation.
5.1.3.￿Steering￿angle￿sensor
The￿information￿on￿the￿steering￿angle￿in￿the￿F97/F98￿is￿not￿recorded￿by￿the￿Electronic￿Power￿Steering
(EPS)￿and￿not￿via￿a￿separate￿sensor￿on￿the￿steering￿wheel￿and￿instead￿is￿computed￿based￿on￿the
motor￿position￿angle￿of￿the￿EPS￿motor￿in￿relation￿to￿the￿steering￿wheel.
The￿EPS￿delivers￿the￿position￿of￿the￿rack￿via￿FlexRay￿to￿the￿M￿Dynamic￿Stability￿Control￿(M￿DSC).
During￿this￿process,￿the￿EPS￿calculates￿the￿absolute￿position￿of￿the￿rack￿based￿on￿the￿current￿motor
position￿of￿the￿EPS￿motor￿and￿the￿number￿of￿complete￿revolutions￿performed￿by￿the￿motor￿starting
from￿the￿zero￿position￿(straight-ahead￿driving￿position).
Taking￿this￿position￿as￿the￿starting￿point,￿the￿M￿Dynamic￿Stability￿Control￿(M￿DSC)￿determines￿the
wheel-specific￿steering￿angle￿among￿other￿things￿using￿the￿stored￿ratio￿parameters￿(rack￿to￿wheel-
specific￿steering￿angle)￿and￿transmits￿this￿via￿FlexRay.￿This￿wheel-specific￿steering￿angle￿is￿used
by￿the￿M￿Dynamic￿Stability￿Control￿(M￿DSC)￿among￿other￿things￿as￿a￿reference￿variable￿for￿internal
control￿functions.
In￿cases￿where￿the￿absolute￿value￿is￿not￿available￿from￿the￿EPS￿(loss￿of￿terminal￿30,￿flash￿process),￿the
absolute￿value￿is￿determined￿through￿interaction￿between￿the￿M￿Dynamic￿Stability￿Control￿(M￿DSC)
and￿EPS￿using￿an￿adaption￿function￿in￿which￿the￿steering￿wheel￿is￿turned￿from￿end￿stop￿to￿end￿stop
(e.g.￿straight-ahead￿position￿->￿left￿->￿right￿->￿straight-ahead￿position).
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