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I12 Chassis and Suspension 4. Brakes 22 4.1. Introduction Overview of the I12 brake system Index Explanation 1 Dynamic Stability Control (DSC) 2 Electrical vacuum pump 3 Brake fluid expansion tank 4 Brake servo 5 Brake pad wear sensor, rear 6 Wheel speed sensor, rear right 7 Electromechanical parking brake actuator on right 8 Electromechanical parking brake actuator on left 9 Electromechanical parking brake (EMF) control unit 10 Brake pad wear sensor, front 11 Wheel speed sensor, front left

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I12�Chassis�and�Suspension4.�Brakes

22

4.1.�Introduction

Overview�of�the�I12�brake�system

Index Explanation1 Dynamic�Stability�Control�(DSC)2 Electrical�vacuum�pump3 Brake�fluid�expansion�tank4 Brake�servo5 Brake�pad�wear�sensor,�rear6 Wheel�speed�sensor,�rear�right7 Electromechanical�parking�brake�actuator�on�right8 Electromechanical�parking�brake�actuator�on�left9 Electromechanical�parking�brake�(EMF)�control�unit10 Brake�pad�wear�sensor,�front11 Wheel�speed�sensor,�front�left

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At�the�front�and�rear�axle�of�the�I12�lightweight�brake�discs�with�internal�ventilation�comprising�ofan�aluminum�hub�plate�and�a�grey�cast�iron�friction�ring�are�used.�It�has�been�possible�to�reduce�theweight�of�the�brake�discs�and�brake�pads�by�using�less�material�at�the�friction�ring.�Normally,�if�lessmaterial�is�used�the�service�requirements�are�higher�as�the�components�reach�their�wear�limits�sooner.Through�the�brake�energy�regeneration�at�both�axles,�braking�decelerations�up�to�about�2.5 m/s²�canbe�performed�using�pure�electric�means�and�thus�wear-free�via�the�electrical�machine�and�the�high-voltage�starter�motor�generator.�This�means�that�the�wear�of�the�brake�discs�and�brake�pads�will�belower�than�for�conventional�vehicles.

The�front�brakes�can�be�cooled�via�air�ducts�if�required.�The�DSC�control�unit�detects�a�sporty�drivingstyle�and�requests�the�opening�of�the�air�flaps�at�the�cooling�module.

4.2.�Brake�energy�regenerationIn�the�I12�brake�energy�regeneration�(energy�recovery)�takes�place�both�via�the�front�and�rear�axle.Overall,�power�of�60 kW�can�be�recovered.�However,�in�this�case�the�high-voltage�starter�motorgenerator�only�generates�low�power.�The�braking�torque�of�the�high-voltage�starter�motor�generatoris�added�with�the�engine�drag�torque�of�the�combustion�engine.�Based�on�the�driving�dynamics,�themajority�of�the�energy�is�recovered�via�the�electrical�machine�at�the�front.

I12�Chassis�and�Suspension4.�Brakes

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System�overview�for�brake�energy�regeneration�in�the�I12

I12�Chassis�and�Suspension4.�Brakes

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Index ExplanationA Hydraulic�brakingB Signal�pathC Regenerative�braking1 Accelerator�pedal�module2 Data�log�with�accelerator�pedal�angle3 Digital�Engine�Electronics�(DME)4 High-voltage�battery�unit5 Electrical�machine�electronics�(EME)6 Range�Extender�Electrical�Machine�Electronics�(REME)7 Electrical�machine�(front�axle)8 Energy�recovery,�front�axle�(electrical�machine)9 Front�wheel�brake10 Rear�wheel�brake11 Energy�recovery,�rear�axle�(high-voltage�starter�motor�generator)12 High-voltage�starter�motor�generator13 Dynamic�Stability�Control�(DSC)14 Data�log�with�brake�pedal�angle15 Brake�pedal�with�brake�booster

There�are�primarily�two�input�variables,�which�determine�the�level�of�deceleration�in�alternator�mode.The�accelerator�pedal�angle�(2)�and�the�brake�pedal�angle�(14).�If�the�DME�(3)�detects�an�acceleratorpedal�(1)�which�has�not�been�operated,�the�Electrical�Machine�Electronics�(EME)�(5)�and�the�RangeExtender�Electrical�Machine�Electronics�(REME)�(6)�are�requested�to�start�an�energy�recovery�incoasting�(overrun)�mode�by�correspondingly�activating�the�Electrical�Machine�(7)�and�the�high-voltagestarter�motor�generator�(12).�Electrical�power�is�fed�to�the�high-voltage�battery�(4).

If�the�driver�indicates�a�stronger�deceleration�request�by�pressing�the�brake�pedal�(15),�the�DSC(13)�detects�the�level�of�the�desired�deceleration�by�the�brake�pedal�travel�sensor�at�the�brake�pedaland�transmits�the�information�to�the�DME�(3).�The�DME�(3)�calculates�the�power�requirement�at�theelectrical�machine�(7)�and�the�high-voltage�starter�motor�generator�(12)�based�on�the�decelerationrequest�and�sends�the�activation�via�data�bus�signals�to�the�electrical�machine�electronics�(5)�andthe�range�extender�electrical�machine�electronics�(6).�The�wheel�brakes�are�not�operated�until�themaximum�regenerative�deceleration�of�about�2.5 m/s²�has�been�reached.�Only�for�a�higher�decelerationrequest,�are�the�wheel�brakes�also�used.

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4.2.1.�Energy�recovery�without�operating�the�brake�pedalThe�brake�energy�regeneration�generally�functions�in�coasting�(overrun)�mode�similar�for�the�familiarBMW�hybrid�cars.�An�accelerator�pedal�which�has�not�been�operated�is�detected�by�the�DME�whichthen�sends�an�activation�to�the�EME�and�REME.�They�activate�the�electrical�machine�and�the�high-voltage�starter�motor�generator�accordingly.

A�special�feature�in�the�I12�is�the�use�of�brake�energy�regeneration�in�overrun�phases�in�varyingdegrees.�The�level�of�deceleration�is�primarily�dependent�on�the�respective�driving�mode.�For�example,in�SPORT�driving�mode�a�deceleration�up�to�roughly�0.8 m/s²�can�be�achieved.�This�is�necessaryto�maintain�the�high-voltage�battery�at�a�state�of�charge�at�which�there�is�always�sufficient�energyavailable�for�the�electric�motor.�In�contrast,�in�the�driving�modes�COMFORT,�ECO�PRO�and�MaxeDRIVE�only�roughly�0.6 m/s²�is�recovered.�The�I12�thus�decelerates�slightly�more�than�conventionalvehicles�in�overrun�phases.

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4.2.2.�Energy�recovery�with�operation�of�brake�pedal

Overview�of�hydraulic�system

The�following�hydraulic�circuit�diagram�shows�the�components�in�the�DSC�hydraulic�control�unit.

I12�Hydraulic�circuit�diagram

I12�Chassis�and�Suspension4.�Brakes

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Index Explanation1 Brake�pedal�travel�sensor2 Brake�booster3 Separator�valve�(brake�circuit�1)4 Intake�valve�(front,�right)5 Discharge�valve�(front,�right)6 Wheel�brake�(front,�right)7 Discharge�valve�(rear,�left)8 Intake�valve�(rear,�left)9 Wheel�brake�(rear,�left)10 Low�pressure�accumulator11 Intake�valve�(rear,�right)12 Discharge�valve�(rear,�right)13 Wheel�brake�(rear,�right)14 Discharge�valve�(front,�left)15 Intake�valve�(front,�left)16 Wheel�brake�(front,�left)17 Changeover�valve�(brake�circuit�2)18 6-piston�hydraulic�pump19 Separator�valve�(brake�circuit�2)20 Brake�pressure�sensor21 Changeover�valve�(brake�circuit�1)

Hydraulic�functions�during�energy�recovery

With�the�brake�system�of�the�I12�a�larger�brake�pedal�travel�can�be�used�for�regenerative�braking.�Thisis�enabled�by�a�clever�functional�sequence�in�the�DSC�hydraulic�control�unit.�This�results�in�a�naturalpedal�feel�during�regenerative�braking,�which�only�differs�slightly�to�conventional�vehicles.

At�very�high�driving�speeds,�above�160 km/h�(100�mph),�there�is�no�energy�recovery�so�as�not�tooverload�the�respective�components.�The�energy�recovery�is�also�reduced�at�low�driving�speeds�sothat�the�vehicle�is�only�braked�hydraulically�below�about�10 km/h�(6�mph).�This�serves�for�the�ridecomfort�as�the�electrical�machine�would�otherwise�decelerate�irregularly.�In�the�transitional�phasesregenerative�braking�power�is�reduced�and�the�hydraulic�braking�power�increased�in�order�to�guaranteeeven�braking.�The�reduction�of�regenerative�braking�is�thus�compensated�by�hydraulic�braking.

The�processes�in�the�DSC�hydraulic�control�unit�during�regenerative�braking�are�shown�on�thefollowing�graphics�using�an�example�for�a�wheel�brake.�The�red�arrow�shows�the�main�function�in�therespective�braking�situation.

I12�Chassis�and�Suspension4.�Brakes

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I12�DSC�function�during�brake�energy�regeneration

I12�Chassis�and�Suspension4.�Brakes

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Index ExplanationA Pure�regenerative�brakingB Regenerative�and�hydraulic�brakingC Suppressing�the�regenerative�part1 Wheel�brake2 Low�pressure�accumulator3 DSC�hydraulic�pump4 Brake�fluid�expansion�tank5 Tandem�brake�master�cylinder6 Separator�valve7 Intake�valve8 Discharge�valve

Situation�A:�Pure�regenerative�braking

Up�to�a�certain�point�the�brake�pedal�only�serves�for�reading�the�deceleration�request�by�theDSC�control�unit.�The�brake�fluid�volume�suppressed�by�the�tandem�brake�master�cylinder�(5)�isincorporated�by�a�low�pressure�accumulator�(2)�in�the�DSC�unit.�The�discharge�valve�(8)�is�open�for�thispurpose.�Using�the�brake�pedal�travel�sensor�the�driver's�braking�request�is�read�and�calculated�into�abraking�torque�by�the�DSC�control�unit.�This�information�is�forwarded�to�the�DME�via�the�FlexRay�databus.�The�DME�distributes�the�braking�torque�to�the�electrical�machine�at�the�front�and�the�high-voltagestarter�motor�generator.�The�electrical�machine�at�the�front�is�activated�by�the�electrical�machineelectronics�and�the�high-voltage�starter�motor�generator�by�the�range�extender�electrical�machineelectronics.

Situation�B:�Regenerative�and�hydraulic�braking

If�the�maximum�braking�power�in�alternator�mode�is�achieved�and�the�brake�pedal�travel�continues�toincrease,�the�discharge�valve�(8)�is�closed�and�hydraulic�pressure�is�built�up�unchecked.�The�brakingeffects�of�the�electrical�machines�and�the�hydraulic�brake�are�added�to�this.

Situation�C:�Suppressing�the�regenerative�part

Here�regenerative�braking�is�replaced�with�the�hydraulic�brake.�The�6-piston�hydraulic�pump�(3)transports�the�brake�fluid�collected�in�the�low�pressure�accumulator�(2)�to�the�wheel�brakes�(1)�andensures�pressure�build-up,�which�corresponds�to�the�current�deceleration�request.�This�circuit�isclosed�by�the�separator�valve�(6).�If�the�driver�wants�to�increase�the�brake�force,�this�is�possible�via�thenon-return�valve�at�the�separator�valve�(6).�If�a�fault�occurs,�with�which�the�regenerative�braking�effectsuddenly�ceases,�the�necessary�brake�pressure�is�generated�immediately�by�the�6-piston�hydraulicpump�in�the�DSC�unit.

I12�Chassis�and�Suspension4.�Brakes

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Fault�with�the�regenerative�brake�system

In�the�event�of�a�fault�with�the�regenerative�brake�system�the�entire�braking�is�done�via�the�hydraulicallyoperated�wheel�brakes.�There�are�no�noticeable�impairments�to�the�driver.�The�following�warning�lightsin�the�instrument�cluster�indicate�a�fault�to�the�driver:

Warning�light�for�regenerative�brake�system

In�addition,�a�corresponding�message�appears�in�the�instrument�cluster.

4.3.�Service�brake

I12�Diagonal�split�brake�system

The�I12�features�a�hydraulic�dual-circuit�brake�system�with�diagonal�split.�With�this�split�brakingsystem,�the�front�brake�on�the�left�together�with�the�rear�brake�on�the�right�and�front�brake�on�the�righttogether�with�the�rear�brake�on�the�left�respectively�are�combined�into�one�brake�circuit.�In�the�eventof�a�failure�of�a�brake�circuit,�a�wheel�of�the�front�axle�can�also�generate�the�braking�forces.�This�is�anadvantage�as�the�front�axle�can�contribute�more�to�braking�than�the�rear�axle�thanks�to�the�dynamicaxle-load�distribution�during�braking.

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4.3.1.�Unlocking�the�engine�compartment�lidThe�area�underneath�the�(front)�engine�compartment�lid�provides�no�additional�storage�space�for�thecustomer.�The�technical�components�located�here�can�only�be�accessible�to�Service�employees.�Thisis�why�the�I12�only�has�one�unlocking�feature�for�Service.

Unlocking�the�(front)�engine�compartment�lid�of�the�I12

Index Explanation1 Engine�compartment�lid�catch2 Cable�for�unlocking�the�engine�compartment�lid

In�order�to�unlock�the�engine�compartment�lid,�the�cables�at�the�A-pillar�on�the�right�and�left�must�beoperated.�The�cables�are�located�behind�covers.

It�is�generally�recommended�to�have�two�people�open�the�engine�compartment�lid,�oneemployee�for�each�side�of�the�vehicle.

More�information�can�be�found�in�the�BMW�workshop�diagnosis�and�information�system�ISTA.

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4.3.2.�Level�sensor

I12�Brake�fluid�level�sensor�in�brake�reservoir

The�brake�fluid�level�sensor�has�been�moved�from�the�sealing�cap�to�the�brake�reservoir.�The�sealingcap�is�no�longer�permanently�connected�to�the�vehicle�via�a�cable.�This�means�the�sealing�cap�can�beput�in�a�safe�place�when�filling�the�brake�reservoir.

Brake�fluid�poses�a�danger�to�health�when�it�comes�into�contact�with�the�skin�and/or�isswallowed.�Wear�protective�gloves�and�safety�goggles�when�handling�brake�fluid.�Avoidcontact�with�the�eyes�and�skin.

Brake�fluid�destroys�paint.�Make�sure�when�filling�the�brake�fluid�expansion�tank�that�brake�fluid�doesnot�come�into�contact�with�the�surface�of�the�vehicle.

Do�not�use�extractors�containing�mineral�oils�when�draining�excess�brake�fluid;�mineral�oils�candamage�the�rubber�seals�of�the�brake�system.

4.3.3.�Brake�pad�wear�indicatorThe�I12�is�not�equipped�with�a�Condition�Based�Service�display�for�brake�pad�wear.�The�remainingbrake�pad�thickness�must�therefore�be�determined�manually�in�Service.�Single-stage�brake�pad�wearsensors�are�installed�on�the�front�left�and�rear�right�wheel�brakes.�As�soon�as�the�conductor�path�ofthe�brake�pad�wear�sensor�has�worn�out�due�to�reaching�its�wear�limit,�a�Check�Control�symbol�isdisplayed�for�the�driver�in�the�instrument�cluster�(KOMBI).�When�the�wear�limit�is�reached�about�5%�ofthe�brake�pad�thickness�is�still�available�to�the�customer.

I12�Chassis�and�Suspension4.�Brakes

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The�Check�Control�symbol�is�displayed�in�red�with�the�text�message�"Brake"�in�the�US�market�oncethe�brake�pad�wear�limit�has�been�reached.

I12�US�market�specific�Check�Control�symbol�upon�reaching�the�brake�pad�wear�limit

In�addition�to�the�warning�lights,�a�note�appears�in�the�central�information�display.

4.3.4.�Brake-servo�assistanceAlthough�the�I12�has�a�combustion�engine,�the�vacuum�to�enable�brake-servo�assistance�is�generatedpurely�by�electric�means.�Due�to�weight�reasons,�the�installation�of�an�additional�mechanical�vacuumpump�(similar�to�other�BMW�hybrid)�cars�was�waived.

Overview�of�the�I12�brake�vacuum�supply

Index Explanation1 Electrical�vacuum�pump2 Dynamic�Stability�Control�(DSC)3 Brake�vacuum�line4 Brake�vacuum�sensor5 Brake�servo6 Electrical�machine�electronics�(EME)

I12�Chassis�and�Suspension4.�Brakes

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The�brake�pedal�force�generated�by�the�driver�is�augmented�using�a�brake�servo.�The�necessaryvacuum�for�the�brake�servo�is�generated�with�the�assistance�of�an�electrical�vacuum�pump�as�required.To�ensure�that�sufficient�brake�power�assistance�is�available�at�all�times,�a�brake�vacuum�sensor�isfitted�to�the�brake�servo�of�the�I12�in�order�to�monitor�the�available�vacuum.

The�brake�vacuum�sensor�is�designed�as�a�differential�pressure�sensor�that�measures�the�existingvacuum�in�the�brake�servo�relative�to�existing�atmospheric�pressure.

The�Electrical�Machine�Electronics�(EME)�evaluates�this�signal�for�the�purpose�of�activating�theelectrical�vacuum�pump�according�to�the�requirements.�The�implementation�of�requirement-orientedactivation�saves�energy�which�in�turn�is�available�for�the�drive.

If�a�fault�develops,�this�is�communicated�to�the�Dynamic�Stability�Control�(DSC).

I12�Signal�shape�of�brake�vacuum�supply

Index ExplanationA Information�inputB Information�outputC Voltage�output1 Brake�vacuum�sensor

I12�Chassis�and�Suspension4.�Brakes

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Index Explanation2 Electrical�Machine�Electronics�(EME)3 Dynamic�Stability�Control�(DSC)4 Electrical�vacuum�pump5 Instrument�cluster�(KOMBI)

The�brake�vacuum�sensor�is�supplied�with�voltage�from�the�Electrical�Machine�Electronics�(EME)�andreturns�a�voltage�signal�depending�on�the�pressure�in�the�brake�servo.�This�analogue�sensor�signalis�processed�by�the�EME,�which�decides�based�on�the�sensor�signal�and�various�dynamic�handlingcharacteristics,�(such�as�the�driving�speed),�whether�the�electrical�vacuum�pump�is�to�be�switchedon.�In�addition,�the�function�logic�in�the�EME�takes�a�history�of�past�inputs�into�account�so�that�theelectrical�vacuum�pump�is�not�continuously�switched�on�and�off.�Instead,�it�remains�switched�on�until�arequested�minimum�level�of�the�brake�vacuum�is�reached.

The�EME�incorporates�an�output�stage�(semiconductor�relay)�which�assists�with�switching�the�12 Vsupply�voltage�of�the�electrical�vacuum�pump�on�and�off.�When�switching�on,�the�output�voltage�ofthe�DC/DC�converter�is�connected�directly�to�the�electrical�vacuum�pump.�Switch-on�currents�of�upto�30 A�can�occur�in�the�process.�To�protect�the�output�stage�and�the�cable,�the�current�level�is�limitedelectronically.�The�power�or�speed�of�the�electrical�vacuum�pump�is�not�controlled.�Instead,�it�is�onlyswitched�on�and�off.

System�faults�can�have�the�following�consequences:

• When�the�brake�vacuum�sensor�malfunctions,�the�EME�receives�no�information�about�thevacuum�in�the�brake�servo.�The�electrical�vacuum�pump�is�now�activated�by�the�DynamicStability�Control�(DSC)�based�on�information�such�as�the�brake�pressure�or�the�brake�lightswitch.�As�requirement-oriented�control�is�no�longer�possible�without�the�sensor�signal�fromthe�brake�vacuum�sensor,�the�EME�switches�the�electrical�vacuum�pump�on�and�back�offaccording�to�a�time�pattern�when�it�detects�a�braking�requirement.

• If�the�electrical�vacuum�pump�malfunctions,�there�is�no�other�option�for�the�EME�to�createa�vacuum�for�the�brake�servo.�When�a�braking�request�is�detected,�a�DSC�subfunction�isthen�activated�to�compensate�for�the�lack�of�brake�power�assistance.�A�hydraulic�(instead�ofvacuum-based)�brake-servo�assistance�is�now�being�implemented�with�the�help�of�the�DSC.This�DSC�function�is�activated�automatically.

If�system�faults�occur,�the�EME�arranges�for�a�Check�Control�message�to�be�displayed�at�theinstrument�cluster�(KOMBI)�to�inform�the�driver�about�the�fault�status.

In�the�US�market,�system�faults�are�indicated�by�the�red�symbol�shown�below.

I12�Check�Control�symbol�for�US�market�when�the�vacuum�supply�malfunctions

If�this�fault�occurs,�the�brake�pedal�travel�and�brake�pedal�force�are�not�the�same�as�they�would�be�inthe�normal�condition.�However,�the�customer�can�still�decelerate�the�vehicle�safely�using�the�brakepower�assistance,�and�also�use�the�DSC�if�required�for�stabilizing�interventions.

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4.3.5.�Wheel�speed�sensor

I12�Wheel�bearing�unit

Index Explanation1 Wheel�bearing�unit2 Wheel�speed�sensor3 Multi-pole�sensor�gear4 Spur�gearing

The�wheel�speed�signals�are�used�by�numerous�systems�such�as�the�engine,�transmission,�navigationor�suspension�control�systems.�The�I12�is�equipped�with�four�active�wheel�speed�sensors�which�candetect�the�direction�of�rotation.�The�DSC�control�unit�can�use�these�wheel�speed�sensors�to�determinethe�current�wheel�speeds�and�directions�of�rotation.�The�wheel�bearing�unit�can�only�be�replaced�as�acomplete�unit.�This�means�it�is�no�longer�possible�to�mix-up�the�installation�position�of�the�multi-polesensor�gear.

The�wheel�hub�hole�pattern�on�the�wheel�bearing�unit�is�5�x�112 mm.�Due�to�the�new�hole-circle�diameter,�Service�requires�a�modified�clamping�adapter�to�clamp�the�wheel�rims�on�abalancing�machine.

The�drive�shaft�is�connected�to�the�wheel�bearing�unit�via�the�spur�gearing.

The�wheel�bearing�units�are�the�same�at�the�front�and�rear�axles.

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4.3.6.�System�wiring�diagram

I12�System�wiring�diagram�for�DSC�and�EPS

I12�Chassis�and�Suspension4.�Brakes

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Index Explanation1 Wheel�speed�sensor,�front�left2 Power�distribution�box,�front3 Electronic�Power�Steering�(EPS)4 Wheel�speed�sensor,�front�right5 Dynamic�Stability�Control�(DSC)6 Body�Domain�Controller�(BDC)7 Power�distribution�box�in�the�passenger�compartment8 Parking�brake�button9 Brake�pad�wear�sensor,�rear�right10 Wheel�speed�sensor,�rear�axle�right11 EMF�actuator,�right12 EMF�control�unit13 EMF�actuator,�left14 Wheel�speed�sensor,�rear�axle�left15 DTC�button16 Steering�column�switch�cluster�(SZL)17 Accelerator�pedal�module18 Charging�interface�module�(LIM)19 Electrical�machine�electronics�(EME)20 Brake�fluid�level�switch21 Brake�pad�wear�sensor,�front�left

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4.4.�Parking�brake

4.4.1.�Overview

System�overview�of�the�I12�electromechanical�parking�brake�(EMF)

Index Explanation1 Dynamic�Stability�Control�(DSC)2 Instrument�cluster�(KOMBI)3 Parking�brake�button4 EMF�control�unit5 Parking�brake�actuator,�right6 Parking�brake�actuator,�left

The�I12�is�equipped�with�an�electromechanical�parking�brake�(EMF).�The�EMF�is�operated�andmonitored�by�the�EMF�control�unit.�The�EMF�control�unit�also�includes�a�terminating�resistor�forthe�PT-CAN.�The�EMF�control�unit�receives�the�driver's�instruction�to�apply�the�parking�brake�fromthe�parking�brake�button,�which�is�hard-wired�to�the�EMF�control�unit.�If�there�is�a�request�to�applythe�electrical�parking�brake�from�the�parking�brake�button,�the�EMF�control�unit�checks�whether�allpreconditions�are�satisfied�for�activation�of�the�EMF�actuators�in�the�current�vehicle�condition.�TheEMF�control�unit�has�a�vehicle�electrical�system�connection�for�this�purpose.�If�all�preconditions�aresatisfied�for�activating�the�EMF�actuators,�they�are�activated�by�the�EMF�control�unit.

The�structure�and�the�precise�function�of�the�EMF�actuators�at�the�brake�calipers�are�known�frommany�current�BMW�models�and�are�not�dealt�with�in�detail�here.�Further�information�on�this�topic�canbe�found�in�the�"F10�Chassis�and�Suspension"�training�material�available�on�ICP�and�TIS.

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Advantages�of�an�electromechanical�parking�brake:

• Dispensing�with�the�parking�brake�lever�in�the�center�console�makes�space�for�new�equipmentfeatures.

• Contact�pressure�of�brake�pads�correctly�adjusted�at�all�times.• Automatic�release�of�the�Automatic�Hold�brake�upon�request�from�driver�to�drive�off.• Dynamic�emergency�braking�function�is�ensured�by�way�of�the�control�systems�(ABS)�even�on

surfaces�with�a�low�coefficient�of�friction.

4.4.2.�Functions

Dynamic�emergency�braking

The�law�requires�that�there�are�two�operating�facilities�for�the�brakes.�In�the�I12�the�second�operatingunit�after�the�brake�pedal�is�the�parking�brake�button�in�the�center�console.�If�the�parking�brake�buttonis�pulled�up�while�the�vehicle�is�moving,�a�defined-sequence�dynamic�emergency�braking�operation�isperformed�by�the�DSC�system.�This�function�is�intended�for�emergency�situations�in�which�the�driveris�not�able�to�brake�the�vehicle�using�the�brake�pedal.�Other�occupants�can�also�bring�the�vehicle�to�astandstill�in�this�way�if,�for�example,�the�driver�suddenly�falls�unconscious.

If�the�parking�brake�button�is�operated�during�the�journey�above�a�defined�driving�speed,�the�DSC�unitinitiates�a�dynamic�emergency�braking�operation.�During�dynamic�emergency�braking,�brake�pressureis�generated�hydraulically�at�all�four�wheel�brakes.�The�DSC�functions�are�fully�active�and�the�brakelights�are�operated.�The�slip�limits�of�all�wheels�are�monitored�with�the�assistance�of�the�four�wheelspeed�sensors�to�ensure�a�stable�braking�operation�until�the�vehicle�comes�to�a�standstill.�The�twoactuators�of�the�electromechanical�parking�brake�are�activated�as�soon�as�the�vehicle�comes�to�astandstill.�Now�only�the�parking�brake�secures�the�vehicle�to�prevent�it�from�rolling�away.

Releasing�the�parking�brake

The�parking�brake�is�released�by�pressing�the�parking�brake�button�down.�However,�for�the�parkingbrake�to�actually�be�released,�Terminal�15�must�be�ON�and�at�least�one�of�the�following�preconditionssatisfied:

• Brake�pedal�applied,�or• Automatic�transmission�parking�lock�engaged

This�prevents�the�vehicle�starting�to�roll�when�not�intended,�e.g.�if�another�occupant�apart�from�thedriver�presses�the�parking�brake�button.�Once�the�parking�brake�is�released,�the�red�indicator�light�onthe�instrument�cluster�and�the�red�LED�in�the�parking�brake�button�go�out.

Automatic�release�of�the�parking�brake

This�function�allows�the�driver�to�drive�off�when�the�parking�brake�is�applied�without�operating�theparking�brake�button.

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42

Prerequisites�for�automatic�release�of�the�EMF:

• All�doors�are�closed• Driver's�seat�belt�is�fastened• Driving�readiness�established• EMF�operated• Drive�position�engaged• Accelerator�pedal�operated

4.4.3.�Brake�test�standThe�I12�has�a�test�stand�mode�for�checking�the�braking�power�of�the�electromechanical�parking�brakeon�a�brake�test�stand.�The�test�stand�mode�must�be�activated�manually�via�the�Service�menu�in�theinstrument�cluster.�Automatic�rolling�detection�is�not�possible.�When�the�test�stand�mode�is�activated,the�vehicle�is�decelerated�via�the�actuators�of�the�electromechanical�parking�brake�when�the�parkingbrake�button�is�pressed.�A�DSC�pressure�build-up�in�all�four�wheel�brakes�does�not�occur.�This�makesit�possible�to�determine�the�brake�forces�of�the�electromechanical�parking�brake.

After�activation�of�test�stand�mode�the�system�is�in�test�stand�mode.�The�parking�brake�indicator�lightof�the�electromechanical�parking�brake�(EMF)�acknowledges�this�status�by�flashing�at�a�frequencyof�1�hertz.�Using�the�parking�brake�button�the�EMF�can�be�applied�in�five�stages.�In�this�case,�thebraking�varies�between�the�minimum�braking�power�in�the�first�stage�and�the�maximum�braking�poweronce�the�parking�brake�button�has�been�pressed�five�times.�If�the�button�is�operated�continuously,�thesystem�increases�the�braking�power�automatically�incrementally�up�to�the�maximum�braking�power.The�flashing�frequency�of�the�parking�brake�indicator�light�changes�from�1�hertz�to�3�hertz�when�theparking�brake�button�is�pressed�in�test�stand�mode.

I12�Parking�brake�indicator�light

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43

4.4.4.�Service

Overview�of�the�I12�brake�caliper,�rear�axle

Index Explanation1 Housing�of�the�EMF�actuator2 Drive�belt3 Reduction�gear�in�actuator�housing4 Roller�bearing5 Spindle�and�spindle�nut6 Brake�piston7 Electric�motor8 Electrical�connection

For�a�change�of�the�brake�pads�it�is�possible�that�the�workshop�mode�has�to�be�set�via�a�function�in�theIntegrated�Service�Technical�Application�(ISTA).

As�long�as�the�EMF�control�unit�is�in�workshop�mode,�the�Automatic�Hold�brake�cannot�be�applied�forsafety�reasons.�Nevertheless,�if�the�parking�brake�button�is�operated,�the�EMF�indicator�light�on�theinstrument�cluster�flashes�yellow.

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Exiting�workshop�mode:

• ManualThe�Service�employee�deactivates�the�workshop�mode�manually�via�the�service�function.

• AutomaticA�driving�speed�of�3 km/h�was�exceeded�and�the�Automatic�Hold�brake�was�closed�andreopened.

For�various�servicing�it�may�be�necessary�to�teach�in�the�EMF�again�using�an�initialization�process.

The�initialization�run�must�be�performed�after�carrying�out�the�following�work:

• Workshop�mode�has�been�exited• The�EMF�control�unit�was�replaced

The�purpose�of�the�initialization�run�is�to�adjust�the�travel�distance�of�the�spindle�in�the�floatingcaliper.�It�can�be�carried�out�manually�and�without�the�diagnosis�system�ISTA.�For�this,�the�parkingbrake�button�must�be�operated�once�when�operating�the�foot�brake.�Then�the�actuators�of�theelectromechanical�parking�brake�are�activated�several�times.�The�control�unit�detects�based�on�thepower�consumption�when�the�brake�pad�is�fully�in�contact�with�the�brake�disc.�The�spindle�is�then�onlyopened�wide�enough�to�allow�the�brake�disc�to�turn�freely.�In�the�final�step,�the�parking�brake�is�fullyapplied.�If�the�foot�brake�is�released�during�the�initialization�run,�the�initialization�run�stops�and�the�note"Apply�foot�brake.�Release�parking�brake."�appears.�The�initialization�run�must�then�be�restarted.�If�theinitialization�run�is�not�performed,�the�yellow�parking�brake�indicator�light�lights�up�in�the�display.

I12�Parking�brake�indicator�light

4.4.5.�Emergency�releaseTo�release�the�electromechanical�parking�brake�in�emergencies,�the�actuator�must�be�removed�and�thespindle�turned�back�mechanically�via�the�spindle�drive.�For�details�of�the�emergency�release�procedurefor�the�electromechanical�parking�brake,�refer�to�the�current�repair�instructions.

Caution:�Danger�to�life�by�following�the�incorrect�emergency�release�procedure��Before�performing�theemergency�release�of�the�electromechanical�parking�brake,�the�vehicle�must�be�secured�to�prevent�itfrom�rolling�away�