Technical training. Product information. F25 Chassis Dynamics Edited for the U.S. market by: BMW Group University Technical Training ST1106 2/1/2011 V_/ BMW Service General information Symbols used The following symbol is used in this document to facilitate better comprehension or to draw attention to very important information: A Contains important safety notes and information that needs to be observed strictly in order to guaran¬ tee the smooth operation of the system. Information status and national-market versions BMW Group vehicles meet the requirements of the highest safety and quality standards. Changes in requirements for environmental protection, customer benefits and design render necessary continu¬ ous development of systems and components. Consequently, there may be discrepancies between the contents of this document and the vehicles available in the training course. This document basically relates to left-hand drive vehicles with European specifications. Some con¬ trols or components are arranged differently in right-hand drive vehicles than shown in the graphics in this document. Further differences may arise as the result of the equipment variations used in specific markets or countries. Additional sources of information Further information on the individual topics can be found in the following: • Owner's Handbook • Integrated Service Technical Application. ©2010 BMW AG, Munich Reprints of this publication or its parts require the written approval of BMW AG, Miinchen The information contained in this document form an integral part of the technical training of the BMW Group and is intended for the trainer and participants in the seminar. Refer to the latest relevant infor¬ mation systems of the BMW Group for any changes/additions to the Technical Data. Status of the information: July 2010 VH-23/lnternational Technical Training F25 Chassis Dynamics Contents 1. Introduction.1 1.1. Driving dynamics and comfort.1 1.2. Bus overview.2 2. Models.5 2.1. Comparison.5 3. Chassis and suspension.6 3.1. Front axle.6 3.1.1. Technical Data F25.7 3.1.2. Service Information.8 3.2. Rear axle.9 3.2.1. Technical data.11 3.2.2. Notes for Service.11 3.3. Wheels and tires.12 3.4. Tire Pressure Monitoring.13 3.4.1. Operating principle.13 3.4.2. System overview of TPM.15 3.4.3. System wiring diagram.16 3.4.4. Notes for Service.17 3.5. Suspension/dampers.19 4. Brakes.20 4.1. Service brakes.20 4.2. EMF Electromechanical Parking Brake.21 4.2.1. System overview.22 4.2.2. System wiring diagram.24 4.2.3. System structure.25 4.2.4. System function.26 4.2.5. Check Control messages.34 5. Steering.40 5.1. Electronic Power Steering EPS.40 5.1.1. System overview.42 5.1.2. System wiring diagram.43 5.1.3. Steering angle sensor.44 5.2. Variable sport steering.44 5.2.1. System overview.45 5.3. Steering column.46 5.3.1. Steering column adjustment.46 F25 Chassis Dynamics Contents 6. Driving stability control systems.47 6.1. Directions of action.47 6.2. Integrated Chassis Management (ICM).47 6.2.1. System overview.47 6.2.2. System function.48 6.3. Dynamic Stability Control DSC.49 6.3.1. System overview.50 6.3.2. System wiring diagram.51 6.4. xDrive.55 6.4.1. System overview.55 6.4.2. VTG control unit system wiring diagram.57 6.4.3. Drive function.58 6.5. Performance Control.60 6.6. Dynamic Cruise Control DCC.60 6.7. Electronic Damper Control (EDC).62 6.7.1. System overview.62 6.7.2. System wiring diagram.63 6.7.3. System function.64 6.7.4. Service information.65 6.8. Driving dynamics control switch.65 F25 Chassis Dynamics 1. Introduction 1.1. Driving dynamics and comfort F25 Chassis and suspension Index Explanation 1 Dynamic Stability Control (DSC) 2 Suspension/dampers 3 Electronic Power Steering (EPS) 4 EMF Electromechanical Parking Brake 5 Five-link rear axle 6 Wheels 7 Brakes 8 Two-joint spring strut front axle with trailing links The chassis and suspension of the F25 is a further development of the E83 at the front axle. A version of the established HA5 five-link rear axle used in the E84 has been improved and adapted to the F25 and is used at the rear axle. The chassis and suspension sets new standards when it comes to driving dynamics and comfort. 1 F25 Chassis Dynamics 1. Introduction 1.2. Bus overview (SB ttli i ! [SB El !; H S S S « * £ innnr B I I 2 O 20 km/h/12mph), a total of 25 telegrams are transmitted once at two second intervals. Providing the pres¬ sure has not dropped, individual telegrams are then sent every 18 seconds from the wheel electronics to the TPM 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 or Central Information Display CID. The TPM text message appears, or the permanent TPM indicator light lights up, in the instrument panel when the teach-in process starts. Teach-in process During the teach-in process, the wheel electronics identification numbers (ID) are transmitted to the TPM control unit. The TPM 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 right/left differentiation of the wheel electronics positions at the vehicle is possible. The high frequency signals received are evaluated in order to determine whether the wheel electron¬ ics are at the front or rear axle. The TPM control unit with integrated receiver is mounted in the outer area of the luggage compartment well above the rear axle. The level of the signals received by the TPM control unit from the wheels on the rear axle is higher than the level of signals sent by the wheel elec¬ tronics 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 duration: • The condition of the road (e.g. cobbles) • The current mode of the wheel electronics (awake/gone to sleep) • The TPM control unit already knows what the IDs of the wheel electronics are. 13 F25 Chassis Dynamics 3. Chassis and suspension O ~ |a »*C 4 4 bar ^^^ 4 * 30 «»« 30t SSBEEZESEHHHHHBi F25 TPM, teach-in process complete Once the teach-in process is complete, the TPM text message or solid TPM indicator light are can¬ celled. The green tire symbols subsequently appear in the CID. Pressure drop F25 TPM pressure drop Once the teach-in process is complete, the wheel electronics send the pressure, temperature and also the identification numbers of the tires to the TPM control unit at regular intervals when driving. If a pressure change of > 20 kPa (0.2 bar, 2.9 psi) is identified within two successive pressure measure¬ ments, the wheel electronics for the relevant wheel immediately assumes a fast transmitting mode. It then sends information to the control unit at one-second intervals. If the pressure drop is higher than 25%, the TPM text message "Tire Low" appears. 14 F25 Chassis Dynamics 3. Chassis and suspension 3.4.2. System overview of TPM F25 System overview of TPMS Index Explanation 1 Wheel electronics (battery-operated sensor with transmitter unit 433MHz) 2 Instrument panel (KOMBI) 3 Control unit with integrated reception antenna 15 F25 Chassis Dynamics 3. Chassis and suspension 3.4.3. System wiring diagram © ® < 3 » F25 System wiring diagram, TPMS 16 TF100008 F25 Chassis Dynamics 3. Chassis and suspension Index Explanation 1 Wheel electronics, front left 2 Wheel electronics, front right 3 Power distribution box, luggage compartment 4 Wheel electronics, rear right 5 Tire pressure monitoring control (TPM) 6 Wheel electronics, rear left 7 Central gateway module ZGM 8 Instrument panel (KOMBI) 9 Central Information Display (CID) 10 Headunit 11 Central operating element KI.30B Terminal 30, time-dependent 3.4.4. Notes for Service Teach-in process The wheel electronics must be taught in under the following circumstances: • The tire pressure has been changed • A tire has been changed • Wheels are replaced axle-wise. The driver can start the teach-in process via the Central Information Display CID and the controller. For more information, refer to the vehicle Owner's manual. Service life of batteries for wheel electronics The service life of the batteries installed in the wheel electronics is roughly 7.5 years. The current val¬ ue of the service life counter in the batteries of the wheel electronics can be read out via the diagnosis system. If the battery is fully discharged or defective, an TPM fault message is displayed. Remove/install wheel electronics The following points must be observed when removing/installing the wheel electronics of the tire pres¬ sure control (TPM): 17 F25 Chassis Dynamics 3. Chassis and suspension Do not use high pressure cleaners to clean wheel rim with the wheel electronics installed when the tire has been removed Replace the wheel electronics if tire sealant has been used Clean the valve and valve seat thoroughly before installing the wheel electronics Do not apply solvents or cleaning agents to the wheel electronics, or clean them with com¬ pressed air To clean the wheel electronics, simply wipe down with a clean cloth. F25 Wheel electronics, TPM Index Explanation 1 Data Matrix Code 2 BMW part number 3 FCC ID = approval for wireless operation 4 Wheel electronics ID 5 Transmission frequency (433MHz) 6 Pressure sensor 7 Production date of wheel electronics 8 Tightening torque 9 Width across flats of union nut 18 F25 Chassis Dynamics 3. Chassis and suspension 3.5. Suspension/dampers The F25 is fitted with steel springs on the front and rear axle. The damping action is provided by con¬ ventional shock absorbers as standard. The Electronic Damper Control EDC (SA 223) is available as optional equipment. The EDC is a sub¬ function of the Vertical Dynamics Management VDM. The damper characteristics stored in the VDM control unit can be selected via the driving dynamics control switch in the center console. For additional information on the EDC, refer to Chapter 6.7 - EDC. 19 F25 Chassis Dynamics 4. Brakes F25 Service brake Index Explanation 1 Dynamic Stability Control, DSC 2 Brake fluid expansion tank 3 Brake servo 4 Electromechanical parking brake actuator 5 Brake caliper 6 Brake pedal 7 Brake disc 4.1. Service brakes The F25 has a hydraulic dual-circuit brake system with front/rear split. Conventional internally ventilat¬ ed brake discs are installed at the front and rear axle of all F25 engine versions. Grey cast iron floating caliper brakes are installed at the front and rear axle. In this instance, the EMF actuator on the rear axle is integrated in the brake caliper. The familiar brake pad wear monitoring function for the Condition Based Service display continues to be used. Brake pad wear sensors are therefore installed at the front left and rear right wheel brakes. The brake dimensions of the F25 are listed in the following table. Front axle xDrive28i/35i Brake disc diameter mm/in 328 mm/12.9 in Brake disk thickness mm/in 28 mm/1.10 in Brake piston diameter mm/in 57 mm/2.24 in 20 F25 Chassis Dynamics 4. Brakes Rear axle xDrive28i/35i Brake disc diameter mm/in 330 mm/13 in Brake disk thickness mm/in 20 mm/0.78 in Brake piston diameter mm/in 42 mm/1.65 in 4.2. EMF Electromechanical Parking Brake On the F25 there is an EMF integrated in the rear brake calipers. The use of the electromechanical parking brake offers the following advantages: • Operation via an ergonomically designed button in the center console • Safe and reliable application and release of the parking brake under all pre-conditions • Automatic Hold function (ACC Active Cruise Control) • Dynamic emergency braking function ensured by way of the control systems (ABS), even with a low coefficient of friction • Discontinuation of the parking brake lever in the center console makes room for new equip¬ ment features. 21 F25 Chassis Dynamics 4. Brakes 4.2.1. System overview F25 System overview, EMF 22 TF09-1959 F25 Chassis Dynamics 4. Brakes Index Explanation A DSC unit B Brake caliper, front left C Brake caliper, front right D Brake caliper, rear right E Brake caliper, rear left 1 Parking brake button 2 Wheel speed sensor, front left (not used for the EMF) 3 Wheel speed sensor, front right (not used for the EMF) 4 Wheel speed sensor, rear right 5 Wheel speed sensor, rear left 6 EMF actuator, rear left 7 EMF actuator, rear right KOMBI Instrument panel (KOMBI) ZGM Central gateway module DSC Dynamic Stability Control PT CAN Drive train Controller Area Network EMF Electromechanical parking brake 23 F25 Chassis Dynamics 4. Brakes 4.2.2. System wiring diagram F25 EMF system wiring diagram 24 TF ID-0805 F25 Chassis Dynamics 4. Brakes Index Explanation 1 Central gateway module (ZGM) 2 Dynamic Stability Control (DSC) 3 Advanced Crash Safety Module 4 Junction box power distribution box 5 Integrated Chassis Management (ICM) 6 Parking brake button 7 Instrument panel (KOMBI) 8 Car Access System (CAS) 9 Footwell module (FRM) 10 EMF actuator, rear left 11 EMF control unit 12 Power distribution box, luggage compartment 13 EMF actuator, rear right 14 Wheel speed sensor, rear right 15 Wheel speed sensor, rear left Terminal 30 Terminal 30 Terminal 15 wake-up Wake-up with terminal 15 ON 4.2.3. System structure The EMF control unit receives the driver's instruction to apply the parking brake from the parking brake button. The vehicle condition is queried/detected via the electrical system connection and the bus systems. The EMF control unit decides whether all the pre-conditions for the parking brake se¬ quence are satisfied. If so, the two EMF actuators on the rear brake calipers are operated. 25 F25 Chassis Dynamics 4. Brakes F25 Operating principle of EMF Index Explanation 1 Instrument panel (KOMBI) 2 Information flow 3 Parking brake button 4 EMF actuator 5 EMF control unit 6 Battery 4.2.4. System function Due to the spindle's self-locking facility, the clamping force remains securely applied even when no power supply is connected, and the vehicle is thus securely held. Once the required force is reached, the parking brake applied status is indicated by a red indicator lamp on the instrument panel and an additional red LED in the parking brake button. If the vehicle's parking brake is already applied, pulling the parking brake button again has no effect. The driver applies the vehicle's parking brake by pulling out the parking brake button. The operating direction of the button is the same as the operating direction for a mechanical parking brake lever. The signal from the parking brake button is read by the EMF control unit. The EMF control unit operates the EMF actuators on the rear brake calipers individually. The parking brake can be applied in any logical terminal status. Parking brake application in Terminal 0 status is made possible by the connection from Terminal 30 to the EMF control unit. If the driver op¬ erates the parking brake button in Terminal 0 status, the EMF control unit is woken up. The EMF con- 26 F25 Chassis Dynamics 4. Brakes trol unit then wakes up the other control units on the vehicle. Only then does the EMF control unit re¬ ceive the essential information about vehicle standstill. In addition, the change of parking brake status can also be indicated once the system has been woken up. F25 Indicator lamp for parking brake applied Design and function of EMF actuator F25 Design of EMF actuator (?) ® ® ® i Index Explanation 1 Plug connection 2 Electric motor 3 Drive belt 4 Planetary gear train 5 Housing 6 Connection to spindle The EMF actuator is fixed to the brake caliper and acts directly on the brake piston. 27 F25 Chassis Dynamics 4. Brakes The force is transmitted to a two-stage planetary gear train (4) by an electric motor (2) and a belt drive system (3). The spindle illustrated in the graphic below is driven via the connection to the spindle (6). © F25 Spindle and spindle nut in brake piston Index Explanation 1 Groove 2 Spindle nut with anti-twist lock 3 Brake piston 4 Spindle 5 Spindle end stop 6 Connection to planetary gear train 28 F25 Chassis Dynamics 4. Brakes Index Explanation A Current flow B Force flow 1 Applying parking brake 2 Parking brake applied 3 Releasing parking brake __ to- a. ®— 0 - ®“ 1 ^-® © F25 Overview of EMF actuator and brake caliper Index Explanation 1 Plug connection 2 Electric motor 3 Drive belt 4 Planetary gear train 5 Housing 6 Brake piston 7 Spindle and spindle nut 8 Roller bearing 29 F25 Chassis Dynamics 4. Brakes Index Explanation 1 Drive belt 2 Planetary gear train 3 Brake piston 4 Dust boot 5 Sealing ring 6 Spindle nut 7 Electric motor 8 Spindle 9 Roller bearing 10 Sealing ring 11 Housing 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 control unit is used as the input variable for roll-away detection. As soon as that signal indicates that the vehicle is starting to roll during the detection window, the EMF actuators are immediately 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 30 F25 Chassis Dynamics 4. Brakes to roll again, the retightening process is repeated (up to three times). If rolling of the vehicle is still de¬ tected after retightening the parking brake three times, the function terminates with a fault entry 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 change takes place, the higher of the two brake disc temperatures is applied for temperature monitoring purposes. The temperature ranges and corresponding 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: • Brake pedal applied, or • Automatic transmission parking lock engaged. That prevents the vehicle starting to roll when not intended, e.g. if another occupant apart from the driver presses the parking brake button. Once the parking brake is released, the red indicator lamp on the instrument panel and the red LED in the parking brake button go out. Activation of the EMF actuator sets the spindle in motion. The rotation of the spindle moves the spin¬ dle nut a small, defined distance away from the brake piston. Dynamic emergency braking The law requires that there are two operating facilities for the brakes. On the F25, the second operat¬ ing facility after the brake pedal is the parking brake button in the center console. If the parking brake button is pulled up while the vehicle is moving, a dynamic emergency braking operation with a defined procedure is performed by the DSC system. This function is intended for emergency situations in which the driver is not able to brake the vehicle using the brake pedal. Other occupants can also bring the vehicle to a standstill in this way if, for example, the driver suddenly falls unconscious. During dynamic emergency braking, brake pressure is generated hydraulically at all four wheel brakes. The DSC functions are fully active and the brake lights are operated. That represents a fundamental advantage over manual parking brakes. 31 F25 Chassis Dynamics 4. Brakes The dynamic emergency braking sequence only remains in effect while the parking brake button is be¬ ing pulled. The level of deceleration applied by the DSC is steeply increased. During dynamic emer¬ gency braking the EMF indicator light on the instrument panel is activated. In addition, a Check Control message is displayed along with an acoustic signal in order to draw the driver's attention to the special situation. If the driver simultaneously brakes by pressing the brake pedal and pulling the parking brake button, the DSC control unit prioritizes. The greater deceleration demand is put into effect. If dynamic emer¬ gency braking is continued until the vehicle is at a standstill, the vehicle remains braked even after the parking brake button is released. The EMF indicator light on the instrument panel remains on. The driver can then release the parking brake (see "Releasing the parking brake"). Parking brake fault If a fault occurs on the parking brake, the EMF indicator lamp on the instrument panel shows yellow. A Check Control message is displayed. PARK (®> F25 Indicator light showing parking brake fault Emergency release Emergency release of the parking brake by the customer is not provided for. The parking brake can be released by unscrewing the EMF actuators and manually screwing back the spindle. Replacing brake pads To replace the brake pads the EMF actuator must be in the fully released position so that the brake piston can be pressed back. The EMF actuators can be activated via the diagnosis system and moved to the fully released position. That position is required in order to be able to change the brake pads. Once the installation position is reached, installation mode is automatically activated. 32 F25 Chassis Dynamics 4. Brakes A_ As long as the EMF control unit is in installation mode, the parking brake cannot be applied for safe¬ ty reasons. If the parking brake button is nevertheless operated, the EMF indicator lamp on the instru¬ ment panel (KOMBI) flashes yellow. Installation mode can be cancelled in two ways: • By executing the service function "Reset installation mode" with the aid of ISTA • By driving the vehicle and exceeding a programmed minimum speed. Brake test stand detection The EMF control unit detects that the vehicle is on a brake test stand by means of a plausibility check (comparison of wheel speeds) and switches to brake test stand mode. Identification takes about. 6 seconds. Pulling the parking brake button several times in sequence sets the parking brake to the following po¬ sitions: Brake pads in contact Force level 1 for brake test stand Force level 2 for brake test stand Target force. Alternatively, the parking brake button can be held continuously in the pulled-out position while brake test stand mode is active. The parking brake is then moved to the individual defined positions in se¬ quence at intervals of 3 seconds. 33 F25 Chassis Dynamics 4. Brakes When brake test stand mode is active and the EMF actuators are released, the parking brake indicator light flashes slowly. When brake test stand mode is active and the EMF actuators are partially applied, the parking brake in¬ dicator light starts to flash more quickly. When the vehicle is on a brake test stand, the parking brake can be released without having to press the brake or clutch pedal. Brake test stand mode is automatically cancelled when the vehicle is driv¬ en off the brake test stand. It is also deactivated if the parking brake button is pressed in or if a fault is present. 4.2.5. Check Control messages EMF indicator light Check Control symbol Description EMF is applied mechanically Check control message - Central Information Display - EMF indicator light Check Control symbol PARK (©> Description EMF is in installation mode - the parking brake button is operated simultaneously Check control message - Central Information Display - EMF indicator light Check Control symbol Description Brake test stand detected - actuator released Check control message - Central Information Display - 34 F25 Chassis Dynamics 4. Brakes EMF indicator light Check Control symbol Brake test stand detected - actuator in interme¬ diate position Check control message Central Information Display EMF indicator light Check Control symbol Description EMF is applied mechanically - the driver at- tempts to drive off at the same time Check control message Release parking brake! Central Information Display - EMF indicator light Check Control symbol Description Parking brake button is applied during the jour¬ ney (dynamic emergency braking) Check control message Release parking brake! Central Information Display - Description 35 F25 Chassis Dynamics 4. Brakes EMF indicator light Check Control symbol Description The driver attempts to release the EMF without having depressed the brake pedal - the selector lever is not in position P Check control message Press foot brake as well! Central Information Display - EMF indicator light Check Control symbol Description The driver attempts to release the EMF - the se¬ lector lever is not in position P Check control message Also engage transmission P Central Information Display To release parking brake, also engage transmis¬ sion position R EMF indicator light Check Control symbol Description The driver attempts to release the EMF - the brake or clutch pedal are not operated Check control message Press foot brake or clutch pedal! Central Information Display Also press foot brake or clutch pedal to release the parking brake. 36 F25 Chassis Dynamics 4. Brakes EMF indicator light Check Control symbol Description "New" fault occurs at parking brake button OR Fault pending at parking brake button with si¬ multaneous operation Check control message - Central Information Display - EMF indicator light Check Control symbol Description Fault detected at parking brake button - no re¬ striction in functionality at present Check control message Availability of parking brake restricted Central Information Display Availability of parking brake restricted Have vehicle checked by your BMW Service au¬ thorized workshop. PARK (®> PARK (®) EMF indicator light Check Control symbol Description At least one speed signal is no longer available - no restriction in functionality at present Check control message Availability of parking brake restricted Central Information Display Availability of parking brake restricted Have vehicle checked by your BMW Service au¬ thorized workshop. PARK <©) PARK (®) 37 F25 Chassis Dynamics 4. Brakes EMF indicator light Check Control symbol 1 Description Check control message Central Information Display Dynamic emergency braking no longer available Availability of parking brake restricted Availability of parking brake restricted Parking brake can be applied and released using button when stationary. It is not possible to brake the vehicle when it is in motion using the parking brake. Have vehicle checked by your BMW Service au¬ thorized workshop. EMF indicator light Check Control symbol 1 ^ mm Description Mechanical application of the parking brake is no longer available OR Dynamic emergency braking and mechanical parking brake application are no longer available Check control message Central Information Display Parking brake has failed Parking brake has failed To park, secure vehicle to prevent it rolling. Have vehicle checked by your BMW Service au¬ thorized workshop. 38 F25 Chassis Dynamics 4. Brakes EMF indicator light Check Control symbol PARK PARK (© (©> Description Mechanical application of the parking brake is no longer available OR Dynamic emergency braking and mechanical parking brake application are no longer available Check control message Parking brake has failed! Central Information Display Parking brake has failed. To park, secure vehicle to prevent it rolling. Have vehicle checked by your nearest BMW Service authorized workshop. 39 F25 Chassis Dynamics 5. Steering 5.1. Electronic Power Steering EPS The F25 xDrive is the first mass-produced vehicle with xDrive to be equipped with Electronic Power Steering EPS (electromechanical power steering) which replaces the conventional hydraulic power steering. In contrast to hydraulic power steering, with EPS steering the servo forces are applied to the rack via an electric motor and a reduction gear. This has achieved an average reduction in fuel consumption of roughly 0.3 I per 100 km when com¬ pared to conventional hydraulic power steering. That helps to reduce the carbon dioxide emissions. As there is no oil in the EPS, it is environmentally cleaner and more service friendly than conventional hy¬ draulic power steering. Compared to conventional hydraulic power steering, the installation and maintenance cost has been significantly reduced thanks to the compact design of the steering box with integrated electric motor and control electronics. With EPS steering, the steering servo (steering forces) and also the return characteristics are freely configurable. This means that the steering and drivability can be adapted optimally to the relevant driv¬ ing situation (e.g. when driving in the city or on the highway). Servotronic, i.e. steering servo dependent on vehicle speed, is available as optional equipment (SA 216). If a driving dynamics control switch is installed - two different settings, "Normal" or "Sporty" can be accessed with the following optional equipment: • EDC (SA 223) • Sports steering (SA 2VL) • Servotronic (Standard) • Steptronic sport automatic transmission (SA 2TB) Although Active Steering is not provided for in the F25, "Variable sport steering" (SA 2VL) is available as the optional equipment. 40 F25 Chassis Dynamics 5. Steering F25 EPS steering components Index Explanation 1 Electronic Power Steering EPS 2 Steering column 3 Steering wheel 41 F25 Chassis Dynamics 5. Steering 5.1.1. System overview F25 EPS steering box Index Explanation 1 Reduction gear 2 Steering-torque sensor 3 Track rod 4 EPS control unit 5 Electric motor with rotor position sensor 42 F25 Chassis Dynamics 5. Steering 5.1.2. System wiring diagram F25 EPS system wiring diagram F25 Chassis Dynamics 5. Steering Index Explanation 1 Electronic Power Steering (EPS) 2 Power distribution box, engine compartment 3 Dynamic Stability Control (DSC) 4 Junction box power distribution box 5 Integrated Chassis Management (ICM) 6 Steering column switch cluster (SZL) 7 Instrument panel (KOMBI) 8 Central gateway module (ZGM) 9 Digital Motor Electronics (DME) KI.30 Terminal 30 KI.15N Ignition (after-run) LIN bus Local interconnect network bus 5.1.3. Steering angle sensor In the F25, information on the steering angle is not acquired via the Electronic Power Steering EPS from a separate sensor at the steering wheel and is instead deduced from the motor position angle of the EPS motor in relation to the steering wheel. The EPS reports the position of the rack via FlexRay to the ICM control unit. In this case the EPS cal¬ culates the absolute position of the rack based on the current position of the EPS motor rotor and the number of full rotor revolutions from the neutral position (corresponds to straight-ahead driving). Taking this position as the starting point, the ICM control unit determines, among other things, the steering angle in relation to the wheel using the stored gear ratio parameters (between the rack and steering angle in relation to wheel) and transmits these via FlexRay. This wheel-specific steering angle is used by the Dynamic Stability Control and other systems as a reference variable for internal control functions. In cases where the absolute value is not available from the EPS (terminal 30 loss, flashing process), the absolute value is determined through interaction of the ICM and EPS via a teach-in function by steer¬ ing from end stop to end stop (e.g. straight-ahead position -> left -> right -> straight-ahead position). 5.2. Variable sport steering The optional equipment "Variable sport steering" (SA 2VL) is available for the F25 as an alternative to the basic version of the EPS. This is the first steering system available on the market to combine the benefits of an extremely direct, variable steering gear ratio with the operating principle of EPS steering. The variable sport steering increases ride comfort and also agility. The direct ratio reduces the total steering angle, i.e. the number of steering wheel revolutions from steering stop to steering stop, by roughly 25%. This therefore increases comfort during driving manoeuvres that require larger steering angles, e.g. when parking, turning off or turning. 44 F25 Chassis Dynamics 5. Steering Compared to the basic version of the EPS steering, the vehicle responds more directly and has greater agility owing to the more direct steering gear ratio and the resulting lower required steering angle. This is effective during avoidance manoeuvres, for example. The variable steering gear ratio is achieved by using a displacement-dependent rack gearing geome¬ try. When roughly in the center position of the steering box, the steering responds precisely with stable directional stability. As the steering angles move out of the center position, the ratio becomes increas¬ ingly more direct. 5.2.1. System overview w umimmm F25 Comparison between steering gear ratio of EPS steering basic version and variable sport steering Index Explanation 1 Rack, EPS basic version (constant gearing geometry) 2 Rack, variable sport steering (variable gearing geometry) A More indirect steering gear ratio (variable sport steering) B More direct steering gear ratio (variable sport steering) X Steering angle y Steering gear ratio 45 F25 Chassis Dynamics 5. Steering 5.3. Steering column 5.3.1. Steering column adjustment The length and height of the steering column of the F25 can be mechanically adjusted. This is re¬ quired for the driver to achieve an optimum ergonomic driving position. 46 F25 Chassis Dynamics 6. Driving stability control systems 6.1. Directions of action Direction of action Longi¬ tudinal Pitch Lateral Yaw Vertical Roll DSC • • • • EDC • • • • • DCC • Driving stability control systems are differentiated according to their basic effective directions. Dynam¬ ic handling control systems may act along as well as around an axis of the vehicle coordinate system (X, Y or Z). 6.2. Integrated Chassis Management (ICM) 6.2.1. System overview 6 F25 ICM control unit ICM 47 F25 Chassis Dynamics 6. Driving stability control systems Index Explanation 1 ICM control unit The ICM control unit is installed on the center console by means of a holder. It contains the driving dy¬ namics sensor system and central sensor system for the airbag. 6.2.2. System function Influence of the ICM control unit on driving stability control in detail: • Performance Control (SA 2VG) Selective braking at the rear inner cornering wheel makes a more neutral self-steering re¬ sponse possible and reduces the tendency to understeer. For the duration of braking interven¬ tion, the output of the engine is increased proportionally so this is not perceived as decelera¬ tion. The setpoint is calculated in the ICM control unit and put into action in the Dynamic Sta¬ bility Control. (For more information!, refer to sections 6.4 and 6.5 of this training material.) • Driving dynamics control The driver can use the operating elements DTC button or driving dynamics control switch (DTC mode, Dynamic Stability Control OFF) to activate the driving dynamics control FDR. The function mode is displayed via the instrument panel (KOMBI). Evaluation of the DTC button and driving dynamics control switch as well as the changeover logic, including communication with the systems involved (including DSC), takes place in the ICM control unit. In addition, the ICM control unit incorporates system monitoring of part¬ ner functions that changes back to normal mode when one of the functions being monitored drops out (DSC ON). • Hill Descent Control HDC The purpose of HDC is to support the driver when driving downhill. When the driver activates this function by pushing the button, the vehicle travels on downhill gradients at a constant speed defined by the driver of between roughly 5 and 25 km/h. If the actual speed is not the same as the reference speed set by the driver, the HDC attempts by means of harmonious control to match the two speeds. The driver is supported by the DSC control functions during this process. A If the driver operates the HDC button, the ICM control unit checks this operation against the current states of the other assist systems. • Dynamic Cruise Control The Dynamic Cruise Control DCC is a road speed controller that incorporates brake interven¬ tion. The DCC function in the ICM control unit acts on the powertrain and brake via the corre¬ sponding interfaces. In addition, interfaces for display and operating elements and for the driv¬ ing dynamics sensor system exist. (For more information, refer to section 6.6.) 48 F25 Chassis Dynamics 6. Driving stability control systems The ICM control unit contains the following sensors, depending on the vehicle equipment: Function Vehicles with out Vehicles with EDC EDC The information from these sensors is used to calculate the following signals which are made available to the Dynamic Stability Control DSC via FlexRay: • Yaw rate • Lateral acceleration • Longitudinal acceleration • Steering angle. 6.3. Dynamic Stability Control DSC The Dynamic Stability Control DSC is at the heart of suspension control systems that are designed to increase active safety. It optimizes driving stability under all driving conditions and also traction when driving off and accelerating. In addition, it detects unstable driving conditions such as understeering or oversteering and helps keep the vehicle safely on course. To this end the current driving conditions are permanently recorded by the highly sensitive sensors of the DSC. The information acquired comes from the wheel speed, steering angle, lateral acceleration, longitudinal acceleration, pressure and yaw sensors (rotation around the vertical axis of the vehicle), for example. The single-track model calculated from this information in the DSC control unit serves as the basic parameter for regulatory intervention by the DSC. During this process, a comparison is made be¬ tween the corresponding driver input (steering wheel angle and vehicle speed). If the measured actual condition deviates from the calculated reference condition, action is taken to improve stability and/or traction. This involves selective actuation of the engine and brake manage¬ ment as well as the xDrive. The driving stability can be ensured once again or a traction request can be implemented by selectively reducing or increasing the engine torque (with active engine drag torque control or Performance Control) or brake intervention at individual wheels. 49 F25 Chassis Dynamics 6. Driving stability control systems 6.3.1. System overview ® 2 ® F25 System overview, DSC u. I- Index Explanation 1 Dynamic Stability Control DSC 2 Center console operating facility 3 Integrated Chassis Management ICM 50 F25 Chassis Dynamics 6. Driving stability control systems 6.3.2. System wiring diagram F25 System wiring diagram, DSC 51 TF 10.0807 F25 Chassis Dynamics 6. Driving stability control systems Index Explanation 1 Brake pad wear sensor, front left 2 Wheel speed sensor, front left 3 Brake fluid level switch 4 Digital Motor Electronics (DME) 5 Junction box power distribution box 6 Dynamic Stability Control (DSC) 7 Front right wheel speed sensor 8 Rear right brake pad wear sensor 9 Rear right wheel speed sensor 10 Luggage compartment power distribution box 11 EMF control unit 12 Wheel speed sensor, rear left 13 Brake light switch 14 Steering column switch cluster (SZL) 15 Instrument panel (KOMBI) 16 Car Access System CAS 17 Footwell module FRM 18 Central Gateway Module 19 Junction box electronics 20 Center console operating facility 21 Parking brake button 22 Central operating element 23 Integrated Chassis Management ICM Function Sub-function Designation ABS Antilock Brake System EBV Electronic brake force distribution CBC Cornering Brake Control DBC Dynamic Brake Control ASC Automatic Stability Control ADB-X Automatic Differential Brake MMR Engine torque control MSR Engine drag control BMR Braking torque control DSC Dynamic Stability Control 52 F25 Chassis Dynamics 6. Driving stability control systems Function Sub-function Designation AKR Anti-tilt control Trailer Stability Control (Not for US) DTC Dynamic Traction Control Performance Control HDC Hill Descent Control HDC The DSC can be operated in three modes: • Dynamic Stability Control ON • Dynamic traction control, DTC • DSC OFF Function DSC DTC DSC ON OFF 53 F25 Chassis Dynamics 6. Driving stability control systems Symbol Explanation • Function active - Function not active X Function with adapted control thresholds * Can be switched on and off by the driver A Adopting a suitably adapted driving style always remains the responsibility of the driver. Not even DSC can overcome the laws of physics. The additional safety features of the system should not be diminished by risky driving. 54 F25 Chassis Dynamics 6. Driving stability control systems 6.4. xDrive 6.4.1. System overview F25 xDrive system overview Index Explanation 1 Transfer box (VTG) control unit 2 Actuator for transfer box coupling 3 Instrument panel (KOMBI) 4 DSC sensor (lateral acceleration, longitudinal acceleration and yaw sensor) 55 TF10-1096 F25 Chassis Dynamics 6. Driving stability control systems Index Explanation 5 Steering angle sensor 6 DSC hydraulic unit 7 DSC control unit 8 Run Flat Indicator button 9 HDC button 10 DTC button 11 Brake fluid level switch 12 Wheel speed sensor 13 Electronic transmission control (EGS) 14 Digital Motor Electronics (DME) The intelligent BMW xDrive four-wheel drive permanently distributes the drive torque between the front and rear axle via an electronically-controlled multi-disc clutch. The F25 features the new ATC 450 transfer box which has been optimized in terms of effectiveness and efficiency. 56 F25 Chassis Dynamics 6. Driving stability control systems 6.4.2. VTG control unit system wiring diagram F25 VTG system wiring diagram F25 Chassis Dynamics 6. Driving stability control systems Index Explanation 1 VTG control unit 2 Dynamic Stability Control (DSC) 3 Junction box power distribution box 4 Integrated Chassis Management (ICM) 5 Central gateway module (ZGM) 6 Car Access System (CAS) 7 Footwell module (FRM) KI.30 Terminal 30 KI.30B Terminal 30, time-dependent 6.4.3. Drive function The drive torque is distributed variably in terms of driving dynamics and traction as the situation de¬ mands through networking with the dynamic stability control DSC. Due to its optimized design, the xDrive adaptation in the F25 makes a further contribution towards enhancing the driving experience. Understeering xDrive shifts more drive torque to the rear axle as the understeering tendency increases. This allows the front axle to build up more traction which reduces understeering. At the same time the Performance Control (SA 2VG) ensures, through braking intervention at the inner rear cornering wheel and by increasing the drive torque of the engine, that the vehicle adopts a neutral drivability without slowing it down. F25 xDrive, intervention during understeering 58 F25 Chassis Dynamics 6. Driving stability control systems Index Explanation red arrow Performance Control intervention green arrow xDrive intervention 1 On the approach to the bend, xDrive adjusts the distribution of drive torque so the emphasis is slightly towards the rear 2 and 3 During cornering, xDrive shifts more drive torque to the rear axle; Performance Control counteracts understeering 4 As the understeering tendency reduces, more drive torque is directed to the front axle and the intervention by Performance Control diminishes 5 xDrive re-establishes the standard distribution, intervention by Performance Control is no longer required Oversteering In an oversteering driving situation, xDrive distributes the drive torque so that the load on the rear axle is reduced as much as possible. At the same time, the DSC ensures, through additional brake intervention at the outer rear wheel dur¬ ing cornering, that the vehicle is quickly stabilized and that neutral drivability is restored. F25 xDrive, intervention in the event of oversteering o 6 59 F25 Chassis Dynamics 6. Driving stability control systems Index Explanation red arrow Performance Control intervention green arrow xDrive intervention 1 On the approach to the bend, xDrive adjusts the distribution of drive torque so the emphasis is slightly towards the rear 2 If an oversteering tendency exists, xDrive shifts more drive torque to the front axle 3 As the oversteering tendency increases, Performance Control (SA 2VG) further stabilizes the vehicle through braking intervention at the outer rear wheel during cornering 4 As the oversteering tendency reduces, less drive torque is directed to the front axle and the intervention by Performance Control diminishes 5 xDrive re-establishes the standard distribution, intervention by Performance Control is no longer required 6.5. Performance Control The F25 features Performance Control (SA 2VG), the DSC functionality of the xDrive. To increase the agility of the xDrive vehicle, the understeering tendency and the required steering an¬ gle are reduced. This is implemented by varying the torque distribution at the rear axle. The Perfor¬ mance Control brakes the rear inner cornering wheel when the vehicle is being driven with a sporty driving style. At the same time, the drive torque of the engine is increased to compensate for the brak¬ ing torque produced. Due to the driving dynamics, the Performance Control is withdrawn at high speeds. 6.6. Dynamic Cruise Control DCC The Dynamic Cruise Control DCC is a road speed controller that incorporates brake intervention. The DCC maintains a constant set speed at speeds higher than roughly 30 km/h - as opposed to con¬ ventional speed control with the following additional functions: • Active brake intervention - if the engine drag torque is insufficient to maintain the selected speed in coasting (overrun) mode, the vehicle is decelerated automatically by means of addi¬ tional controlled brake intervention. • Curve-Speed-Limiter CSL - depending on the lateral acceleration that currently exists, the speed in the longitudinal direction is reduced during controlled cornering as necessary. When exiting the corner, the speed is adjusted until the required speed is obtained once again. 60 F25 Chassis Dynamics 6. Driving stability control systems • Comfort-Dynamic-System CDS - the driver can use an operating element at the steering wheel to permanently accelerate or decelerate the vehicle in two dynamic stages respective¬ ly in "Hand throttle mode". This means the required speed will be reached more quickly. The driver can accelerate or decelerate in traffic flow without estimating the target speed before¬ hand. • Controlled downhill driving - in order to reduce fuel consumption, downhill driving is con¬ trolled by means of overrun fuel cutoff. To reduce the load on the wheel brakes when driving downhill, gear downshifts are modified and torque is distributed between the front and rear axle. In the DSC brake control system, corresponding leakage compensation and torque distri¬ bution measures are applied using a substitute temperature model. This counteracts any leak¬ age in the brake control circuit. The desired speed is displayed in the instrument panel (KOMBI) by a movable marker around the speed reading. When the control system is active, this marker lights up green. When the DCC function is deactivated, the marker lights up orange and the resume speed is displayed. If the desired speed has been adjusted or if the DCC function is activated, the updated digital value is displayed briefly as a checkback signal for the operator. 61 F25 Chassis Dynamics 6. Driving stability control systems 6.7. Electronic Damper Control (EDC) 6.7.1. System overview Driving dynamics control switch Electromagnetic setting valve Index Explanation © F25 EDC system overview Electronic adjustable damper Wheel acceleration sensor EDC control unit 62 F25 Chassis Dynamics 6. Driving stability control systems 6.7.2. System wiring diagram © F25 EDC system wiring diagram 63 TF10-0809 F25 Chassis Dynamics 6. Driving stability control systems Index Explanation 1 Sensor, vertical wheel acceleration, front left 2 Electromagnetic setting valve, front left 3 Dynamic Stability Control (DSC) 4 Electromagnetic setting valve, front right 5 Sensor, vertical wheel acceleration, front right 6 Junction box power distribution box 7 Luggage compartment power distribution box 8 Electromagnetic setting valve, rear right 9 Vertical Dynamics Management (VDM) 10 Electromagnetic setting valve, rear left 11 Integrated Chassis Management (ICM) 12 Center console operating facility 13 Footwell module (FRM) 14 Central gateway module (ZGM) KI.30B Terminal 30, time-dependent KI.15N Ignition (after-run) KI.30 Terminal 30 6.7.3. System function The EDC is a variable, electronically controlled shock absorber adjustment system that controls the vertical dynamics. EDC adapts the damping forces of the shock absorber more or less instantly to changing road or driving conditions. The EDC consists of • four electronic adjusting dampers • the EDC control unit • two wheel acceleration sensors on the front axle to determine the wheel movement • a sensor cluster integrated in the ICM control unit to determine the movements of the body (pitch, vertical, roll). The sensors in the vehicle permanently measure • the body and wheel acceleration • the current lateral/longitudinal acceleration • the vehicle speed • the steering wheel position. 64 F25 Chassis Dynamics 6. Driving stability control systems The EDC control unit uses this measured data in conjunction with the road profile and driving situa¬ tion to calculate the wheel-specific control commands for the electromagnetic valves in the shock ab¬ sorbers. The damping forces delivered will therefore always match the requirements. This improves ride comfort and at the same time enhances driving dynamics. • Increased body stability and agility • Improved driving safety by minimizing wheel load fluctuation and reduced stopping distance. The driver can use the driving dynamics control switch to change between a comfortable or sporty as¬ pect of the vehicle's character according to his individual requirements. 6.7.4. Service information Other separate lines exist between the dampers, including front axle sensors and the wiring harness. These are not shown in the system wiring diagram. These lines can be replaced individually when car¬ rying out repairs. 6.8. Driving dynamics control switch F25 center console Index Explanation 1 Driving dynamics control switch 2 Controller The driving dynamics control switch is installed in the center console operating facility. Three areas (characteristic curves) for driving dynamics can be selected via the driving dynamics control switch: Normal, Sport, Sport+. The Sports mode can be adapted by means of the Controller. 65 F25 Chassis Dynamics 6. Driving stability control systems F25 Sports mode adaptation It is possible to specify whether the Sports mode applies only to the chassis and suspension, only to the drivetrain, or to both. Normal Sport Sport+ Drivetrain Accelerator character¬ istic Normal Sports Sports Shift program Normal Sports Sports Shift speed Normal Sports Sports Chassis and sus¬ pension systems Steering servo Normal Sports Sports Dynamic Stability Control DSC on DSC on DTC Electronic Damper Control (EDC) Normal Sports Sports 66 Bayerische Motorenwerke Aktiengesellschaft Handlerqualifizierung und Training RontgenstraBe 7 85716 UnterschleiBheim, Germany