BMW G12 Product Information page 127

G12￿Driver￿Assistance￿Systems
19.￿Cruise￿Control
• Disruptive￿and￿overly￿restrictive￿interventions￿are￿avoided￿if￿the￿driver￿himself￿would￿also￿prefer
high￿lateral￿acceleration.
• Useful￿interventions￿and￿therefore￿also￿significant￿limitations￿in￿dynamics￿are￿effected￿at￿high
speeds.￿Most￿drivers￿find￿an￿overly￿high￿lateral￿acceleration￿in￿these￿situations￿unpleasant,
which￿is￿why￿a￿lower￿limit￿value￿is￿used.
The￿output￿variable￿for￿the￿cornering￿cruise￿control￿is￿also￿used￿as￿a￿set-point￿value￿for￿the￿longitudinal
acceleration.
Prioritization￿of￿the￿partial￿set-point￿value
The￿set-point￿value￿with￿the￿highest￿priority￿according￿to￿the￿situation￿is￿selected￿from￿the￿longitudinal
acceleration￿set-point￿values￿for￿the￿control￿functions￿referred￿to￿above.￿Signals￿are￿filtered￿to￿prevent
abrupt￿jumps￿when￿adjusting￿the￿set-point￿values.
Estimation￿of￿disturbance￿force
An￿acceleration￿or￿brake￿force￿must￿be￿calculated￿in￿order￿to￿be￿able￿to￿apply￿the￿prioritized
longitudinal￿acceleration￿with￿the￿assistance￿of￿the￿actuators.￿Example:￿more￿driving￿power￿is￿required
to￿achieve￿the￿same￿longitudinal￿acceleration￿during￿an￿uphill￿journey￿than￿on￿the￿flat.￿If￿the￿vehicle
needs￿to￿decelerate￿when￿travelling￿up￿hill,￿less￿braking￿force￿is￿required￿compared￿to￿driving￿on￿the
flat.￿In￿order￿to￿be￿able￿to￿correctly￿calculate￿the￿forces￿required,￿the￿precise￿value￿of￿the￿gradient￿and
also￿the￿weight￿of￿the￿vehicle,￿the￿rolling￿resistance,￿the￿drag￿and￿other￿acceleration￿forces￿must￿be
known.￿As￿a￿sensor￿system￿that￿can￿monitor￿all￿of￿these￿disturbances￿does￿not￿exist,￿an￿estimated
value￿is￿calculated￿instead￿by￿comparing￿the￿following￿two￿variables:
• actual￿movement￿variables￿of￿the￿vehicle
• anticipated￿movement￿variables￿of￿the￿vehicle￿as￿a￿result￿of￿the￿driving￿power￿and￿braking
forces￿currently￿acting￿on￿the￿vehicle.
The￿extent￿of￿the￿disturbing￿force￿determined￿using￿this￿method￿is￿taken￿into￿account￿during
subsequent￿processing￿of￿the￿longitudinal￿acceleration￿setpoint￿value￿by￿means￿of￿addition￿or
subtraction.
19.2.2.￿Activation￿of￿the￿actuators
Driving￿power￿and/or￿braking￿forces￿must￿be￿introduced￿in￿order￿to￿produce￿the￿longitudinal
acceleration￿calculated￿by￿the￿control￿functions￿and￿thus￿compensate￿for￿disturbing￿forces￿acting
on￿the￿vehicle.￿To￿accelerate￿the￿vehicle,￿a￿setpoint￿value￿for￿the￿drive￿is￿usually￿transmitted.￿In
exceptional￿cases￿during￿downhill￿driving￿on￿a￿steep￿gradient,￿it￿may￿be￿necessary￿to￿activate￿the￿brake
to￿ensure￿the￿acceleration￿does￿not￿exceed￿a￿specific￿value.
If￿the￿vehicle￿needs￿to￿be￿decelerated,￿the￿extent￿of￿the￿contribution￿that￿may￿be￿required￿by￿the￿drive
towards￿the￿deceleration,￿and￿therefore￿the￿braking￿effect￿of￿the￿engine￿and￿transmission,￿is￿initially
determined.￿This￿value￿is￿output￿to￿the￿Digital￿Motor￿Electronics￿(DME)￿or￿and￿electronic￿transmission
control￿(EGS).￿If￿this￿value￿cannot￿be￿achieved￿by￿the￿drivetrain￿alone,￿the￿additional￿amount￿required￿is
transmitted￿to￿the￿Dynamic￿Stability￿Control￿(DSC).
The￿vehicle's￿brake￿lights￿are￿also￿switched￿on￿if￿the￿brakes￿are￿noticeably￿actuated￿in￿order￿to
produce￿the￿desired￿deceleration.
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