Table of Contents E46 TRACTION AND STABILITY CONTROL SYSTEMS Subject Page MK20EIASC 4 Corner Braking Control (CBC).5 Electronic Brake Proportioning (EBV). 6 Diagnosis.6 DSC III MK20 7 System Overview.8 DSC Control Overview.9 Components Control Module/Hydraulic Unit.11 Wheel Speed Sensors.12 Brake Light Switch.12 Brake Fluid Level Switch.13 DSC Button.13 Steering Angle Sensor..14 CAN Interface.15 Rotation Rate Sensor..16 Lateral Acceleration Sensor..17 I.P.O.18 Hydraulic System Components Charge Pump.19 M aster Cylinder/Fluid Resevoir..20 Pressure Sensors.20 DSC Hydraulic Operation.21 Diagnosis.22 TEVES DSC III MK60 Purpose of the System I.P.O. System Components. Control umt/Hydraulic unit CAN Interface. Tandem Master Brake Cylinder. .23 24 25 26 27 29 30 Subject Page Expansion Tank and Brake Fluid Level Switch.30 Brake Pressure Sensors.31 Wheel Speed Sensors.32 Rotation Rate Sensor..35 Steering Angle Sensor..36 Transverse Acceleration Sensor..37 DSC Button.38 Instrument Cluster Warning Indicators.39 Principle of Operation.40 ABS.40 ASC.44 DSC.48 Workshop Hints.55 MK20EI ASC Model: E46/4 Production Dates: 6/98 to 6/99 Objectives After completing this module you should be able to: Q Identify the communication link between ASC and DM E. D Understand the CBC function of ASC. Q Understand the EBV function of ASC. MK20EI ASC ASC was standard equipment on both the 1999 323i and 328i M odels. The Teves - Mark 20 El system is used for the E46. The theory/operation of the slip control system is unchanged from the previous ASC system. The major changes of the Mark 20 El are: Q The electronic control module is integrated into the hydraulic unit. Q The throttle reduction operation is carried out through the DME activation of the MDK motor. Q The ASC control module communicates with the AGS and DME control modules over the CAN Bus. 4 E46 Traction and Stability Control Systems The Mark 20 El system includes the Cornering Brake Control (CBC) utilized in the Bosch ASC 5 system. This feature reduces pressure build-up on the inside rear brake circuit while cornering, if the threshold values for activation are exceeded. 5 E46 Traction and Stsbility Control Systems ELECTRONIC BRAKE PROPORTIONING (EBV) A new feature of the Mark 20 El system is the Electronic distribution of the braking force (EBV). This feature will adjust the braking force to the rear wheels based on the vehicle's loading to maximize the braking force at all wheels. The control module monitors the wheel speed sensor inputs, when the brakes are applied, to determine vehicle loading. The control module compares the rate at which the front and rear axles are slowing down. If the rear axle is slowing at a rate similar to the front it indicates that the vehicle is loaded and more braking force can be applied to the rear calipers to stop the vehicle. If the decel rate of the rear wheels is far less than the front, it indicates a lightly loaded vehi¬ cle. At this point, if the same braking force were applied to the front and rear axles, the vehi¬ cle would become unstable. If this difference exceeds the threshold values programmed in the control module, EBV is activated. The control module will cycle the inlet valves to the rear brakes to regulate the braking force. DIAGNOSIS Diagnosis of the slip control system is carried out with the DI5 or MoDiC using the fault symptom driven troubleshooting procedures. 6 E46 Traction and Stability Control Systems DSC III MK20 Model: E46 all versions except all-wheel drive Production Dates: 6/99 to 9/00 Objectives After completing this module you should be able to: Q List the components used in the DSC III system. Q Explain the intervention the DSC III can execute to control oversteer or understeer. Q Describe the calibration required when replacing a steering angle sensor. Q Explain the reason why a pre-charge pump is necessary. INTRODUCTION The DSC III system was introduced for the E46, beginning with Model Year 2000 produc¬ tion (E46/2: 6/99, E46/4: 9/99). The system is similar to the DSC III used on the E38 and E39 vehicles, however it is manufactured by Teves for use in the E46. The system incorporates all of the features of the previous Teves slip control system and adds the lateral dynamic control of the DSC III system already installed on the E38/E39s. The Teves DSC system is designed to maintain the lateral locating forces for the following: Q ABS braking control Q ASC +T traction control □ DSC - Dynamic Stability Control for oversteer and understeer conditions SYSTEM OVERVIEW The E46 DSC III system consists of the following components: 0 Control module/Hydraulic Unit (combined) Q Four wheel speed sensors Q Charge pump Q Tandem Brake M aster Cylinder Q Steering Angle Sensor Q Yaw Rate Sensor Q Lateral Acceleration Sensor Q Two Brake Pressure Sensors Q Brake Fluid Level Switch Q DSC Button Q DSC Warning Indicator □ CAN Interface (DME/AGS) 8 E46 Traction and Stability Control Systems DSC CONTROL OVERVIEW The Teves DSC system maintains the lateral location forces during all phases of operation through; □ ABS - Hydraulic intervention preventing the wheels from locking during hard brak¬ ing D ASC +T - Engine drive torque reduction and/or hydraulic intervention on the drive wheels to ensure straight line traction (acceleration - driving and deceleration) Q DSC - Engine drive torque reduction and/or hydraulic intervention on any wheel brake during cornering to minimize oversteer and understeer conditions DSC control can aid the driver in controlling the vehicle while driving but can not overcome the laws of physics if the vehicle is being driven beyond the range of DSC control. UNDERSTEER/OVERSTEER CONDITIONS 3. VEHICLE COMES OUT OF TURN SUCCES- FULLY UNDERSTEER CORRECTION WITH DSC III 1. VEHICLE APPROACHES TURN: - Driver steers into turn - Brakes are applied WITHOUT DSC - regulated brake slows wheel down (and helps to reduce vehicle speed). Wheel on outside of curve speeds up due to power transfer thru differential. Vehicle pivots in favor of curve. Combined, this forces the vehicle into the turn. 9 E46 Traction and Stability control systems 3. VEHICLE COMES OUT OF TURN SUCCESFULLY WITH DSC OVERSTEER CORRECTION 1. VEHICLE APPROACES TURN AT HIGH RATE OF SPEED: - Driver steers into turn and applies brakes to slow down. 2D. The torque reduction and rear brake regulation should stabilize the vehicle at this point. If not the left front wheel has a high degree of lateral locating force and is momentarily regulated. This action deliberately causes the wheel to shed a calculated degree of it's locating force. This counteracts oversteer yaw at this wheel and also aids in slowing the vehicle down to correct it. 2B. Driver tries to compensate by oversteering which diminishes lateral locating force even further. Simultaneously, rear of car starts to slide out. 2C. DSC III determines an OVERSTEER condition. Engine torque is reduced via CAN Bus signalling. Outside rear wheel is momentarily regulated to counteract severe yaw angle (also helps to reduce drive torque further.) 10 E46 Traction and Stability Control Systems COMPONENTS CONTROL MODULE/HYDRAULIC UNIT The control module is installed in the engine compartment, on the right side, in the battery well. Both the control module and the hydraulic unit are replaceable as separate components. All processing functions for ABS/A5C or DSC regulating functions are carried out in the one control module. The module is linked to the CAN bus forcommunication with the DM E and AGS control modules. Additionally the CAN bus is used forcommunication with the steer¬ ing angle sensor and for illumination of the ABS and DSC indicator lamps in the instrument cluster. The hydraulic unit consists of the follow Q Four inlet solenoids 0 Four outlet solenoids [|Two changeover solenoids Q Two charge solenoids 11 E46 Traction and Stability control systems WHEEL SPEED SENSORS The E46 DSC III system uses the same inductive wheel speed sensors from the ASC system. BRAKE LIGHT SWITCH The brake light input signal is used by the control module to interrupt an ASC regulation control if the driver steps on the brakes during its operation. This interruption does not take place during DSC regulation. 12 E46 Traction and Stability Control Systems BRAKE FLUID LEVEL SWITCH Fluid level switch is incorporated into the brake master cylinder reservoir. If the fluid level is correct, the switch provides a ground signal to the DCS control module. If the fluid level drops below the specified level, the switch opens and the ASC/DSC func¬ tions are switched off. DSC BUTTON The DSC system comes on every time the vehicle is switched on. The DSC button can be used to switch the system off. The warning indicator lamp comes on when the system is manually switched off 13 E46 Traction and Stability control systems STEERING ANGLE SENSOR The steering angle sensor is mounted at the bottom of the steering column, in front of the flexible coupling. It utilizes two potentiometers to determine steering angle and the rate of steering change. These signals are processed in the steering angle sensor and a digital out¬ put signal is passed over the CAN bus to the DSC control module. The sensor requires calibration after repairs to the steering or suspension system. The sen- soris calibrated using the DIS or MoDiC. Once calibrated, the sensorsends an ID number to the DSC control module. The ID provides confirmation to the module that the angle sen¬ sor is properly calibrated. Installing a new sensor or exchanging sensors with another vehicle will require that this ca ibration procedure is carried out. POTENTIOMETER HOUSING \ CAN BUS MICROPROCESSOR 14 E46 Traction and Stability Control Systems CAN INTERFACE The DSC control module communicates over the CAN line for the following Q Steering angle from the steering angle sensor Q Engine control module for engine intervention Q Transmission control module for shift intervention Q Instrument cluster for illumination of the warning indicator lamps GS 20 MS 42.0 INSTRUMENT CLUSTER SPLICE CONNECTIONS FOR TWISTED PAIR CAN 15 E46 Traction and Stability control systems ROTATION RATE SENSOR The rotational rate sensor is mounted underthe driver's seat. It provides a signal to the DSC control module that corresponds to the vehicle's rotational speed around its axis (yaw speed). The sensor receives its operating power (5 volts) from the DSC control module and pro¬ vides an output voltage of approx. 0.25 to 4.65 volts depending on the amount of yaw exerted on the vehicle. The sensor operates on the Coriolis effect to produce the output voltage. The element of the sensor is a micromechanical double quartz tuning fork. A frequency of 11 Hertz is applied to one side of the fork and as the vehicle turns on its axis, vibrations are induced into the tips at the other end. The sensor processes the signals produced by the fork and produces an analog voltage signal that is proportional to the amount of yaw. Based on the control module's programming parameters, the DSC will activate a DSC reg¬ ulation cycle to ensure that the vehicle remains stable under all driving conditions. ROTATION RATE SENSOR 16 E46 Traction and Stability Control Systems LATERAL ACCELERATION SENSOR The lateral acceleration sensor is mounted in the left "A" pillar. The sensor provides the DSC control module with an input signal that corresponds to the degree of lateral acceleration ("G" forces) acting on the vehicle. The sensor is a capacitive type with two capacitive plates (one fixed and one moving). Under the effect of lateral acceleration, the one plate moves in relation to the fixed plate. This results in a voltage signal being produced in proportion to the degree of lateral accel¬ eration. The voltage signal output of the sensor to the DSC control module ranges from 0.5 to 4.5 volts. When the vehicle is stationary, The standing voltage from the sensor is approximate¬ ly 1.8 volts. This signal is used in conjunction with the yaw sensor input to determine the degree of DSC regulation required to maintain the vehicle's stability. 17 E46 Traction and Stability control systems ECM MAIN RELAY KL 30 KL 15 r ■ 1 i" * . ,_ ■. ~. i * * \ . i ■ 1 i" ■ ■ |" 1 S ■ 1 ■ 1 s . DSC SWITCH — i ■ ■ | . _■ 1 i ■ 1 i r \AT •— U i- 1 WHEEL «=D 1 1 SPEED «=D 1 1 1 SENSORS i TAT CHARGE PRESSURE SENSOR CHARGE PRESSURE SENSOR REFERENCE VOLTAGE SIGNAL VOLTAGE SIGNAL VOLTAGE ROTATION RATE SENSOR + SIGNAL VOLTAGE LATERAL ACCELERATION SENSOR ELECTRONIC BRAKE LIGHT SWITCH i TO LCM PARK BRAKE SWITCH DSC E46 KL 15 POWER SUPPLY POWER SUPPLY PUMP INLET (4X) OUTLET (4X) CHANGEOVER (2x) PRE-LOAD (2x) — 'iflfiflflur DSCIII HYDRAULIC UNIT POWER SUPPLY GROUND SENSOR TEST ROTATION RATE SENSOR CHARGE PUMP CONTROL STEERING ANGLE SENSOR WITH INTEGRAL MICRO¬ PROCESSOR CAN T DME WHEEL SPEED X 4 DIAGNOSIS 18 E46 Traction and Stability Control Systems HYDRAULIC SYSTEM COMPONENTS PRE-CHARGE PUMP The pre-charge pump is installed between the master cylinder and the brake fluid reservoir. During DSC controlled regulations that involve brake intervention, the pump ensures that the required volume of fluid is available for the hydraulic unit. When activated, the pre-charge pump draws fluid from the reservoir and delivers it to the master cylinder at a pressure of 10 Bar. 19 E46 Traction and Stability control systems MASTER CYLINDER/FLUID RESERVOIR The master cylinder contains the central valves in both the front and rear brake circuits, 5 imilar to the Bosch DSC system. The central valves allow fluid to transfer during DSC con¬ trolled interventions. The brake fluid reservoir has internal baffles that minimize fluid foaming during controlled interventions. The charge pump pick up is mounted low on the reservoirto prevent airfrom entering the system during regulation. The fluid level switch will signal the control module to cancel DSC regulation if the fluid is below the safety margin level. PRESSURE SENSORS Two pressure sensors are installed on the master cylinder in the outlet ports for the front and rear brake circuits. The sensors provide the DSC control module with an analog volt¬ age signal in proportion to the brake pressure in the master cylinder. 20 E46 Traction and Stability Control Systems DSC HYDRAULIC OPERATION Based on the programming of the DSC control module, hydraulic intervention can be acti¬ vated at any wheel brake as follows: D ABS regulation for any wheel that is in danger of locking - causing the wheel to skid. □ ASC regulation for either or both rear wheels to ensure that the optimum traction is applied to the drive wheels □ DSC regulation for any wheel to correct for dynamic forces that are causing the vehicle to become unstable. The DSC intervention only takes place on one wheel of a corresponding axle. Depending on the hydraulic intervention reguired, the charge pump, return pump, change over valves, charging valves, inlet and outlet solenoids are activated to provide: G Pressure build up for brake application G Pressure hold to slow or stop the wheel G Pressure release to allow the wheel to turn 21 E46 Traction and Stability control systems DIAGNOSIS Troubleshooting the E46 TEVES DSC system is carried out using the DIS or MoDiC. The fault indicators in the instrument panel will illuminate when there is a fault and the sys¬ tem is off line. Follow the diagnostic procedures as outlined with the tester to troubleshoot the E46 Teves DSC system. 22 E46 Traction and Stability Control Systems TEVES DSC III MK60 Model: E46 (except M3 and Xi) and E36/7 Production Date: From 9/00 Objectives After completing this module you should be able to: Q Identify the changes of the M K60 over the previous M K20EI system. Q Understand the operation of the new wheel sensors. 0 Review the operating principles of AB5, A5C and DSC. Q Describe the new ADB and DBC functions. 23 E46 Traction and Stability Control Systems Purpose of the system DSC III M K60 is supplied by Continental Teves and supersedes the Teves DSC III M K20 El system. The M K60 includes all of the features of the previous M K20 El system and incor¬ porates two additional functions: D DBC function Q Modified ADB function The most important changes from the MK20 El are: Q Reduction in size of the control unit/hydraulic Unit. Q Installation of the hydraulic unit close to the master cylinder. Q Elimination of a pre-charge pump. Q Magneto resistive wheel speed sensors. The Teves MK60 system is designed to maintain the vehicles stability during: Q AB5 braking regulation Q ASC+T traction control Q DSC for oversteer and understeer control Additional features are also programmed into the control module to enhance driver safety and comfort. These features are: □ CBC Corner Brake Control Q EBV Electronic Brake Proportioning G MSR Engine Drag Torque Regulation G ADB Automatic Differential Brake G DBS Dynamic Brake System 24 E46 Traction and Stability Control Systems KL 30 DME MAIN RELAY KL 15 1 - 1 - ■ ■ ■ ' *. ■ 1 DSC SWITCH — ■ L i . i * ■ . i ,. ■ . i ■ . i LF RF /^S LR RR •— U •=0 1 - 1 WHEEL 1 , 1 ' •=0 SPEED 1 , 1 ' SENSORS _i BRAKE PRESSURE SENSORS ■|J BRAKE PRESSURE SIGNAL X2 SIGNAL VOLTAGE ROTATION RATE SENSOR SIGNAL VOLTAGE LATERAL ACCELERATION SENSOR BRAKE LIGHT SWITCH TO f * LSZ PARK BRAKE SWITCH i—* SPLICE TO KOMBI i— BRAKE FLUID LEVEL SWITCH DSC MK 60 47 PIN ABS LAMP KL POWER SUPPLY POWER SUPPLY PUMP INLET (4X) OUTLET (4X) CHANGEOVER (2x) INTAKE (2x) mm — mm— MK60 HYDRAULIC UNIT POWER SUPPLY GROUND ROTATION RATE SENSOR REFERENCE VOLTAGE BRAKE PRESSURE SENSORS POWER GROUND LATERAL ACCELERATION SENSOR STEERING ANGLE SENSOR RIGHT REAR LEFT REAR PROCESSED WHEEL SPEED DSC LAMP GENERAL BRAKE WARNING LAMP WHEEL SPEED SENSOR REFERENCE VOLTAGE X 4 25 E46 Traction and Stability Control Systems System Components The Teves DSC III M K60 consists of the following components: Q Integrated Control unit/Hydraulic unit with CAN Interface Q Tandem Master Brake Cylinder Q Brake Expansion Tank with Fluid Level Reed Contact in Cap Q 2 Brake Pressure Sensors Q Brake Light Switch Q 4 Wheel Speed Sensors (active) Q Rotation Rate Sensor (yaw) Q Steering Angle Sensor (LEW) Q Transverse Acceleration Sensor Q DSC Button (part of SZM) Q Instrument cluster Warning indicators • Hand brake Switch Q Wiring Harness 26 E46 Traction and Stability Control Systems Control Unit/Hydraulic Unit The M K60 control unit/hydraulic unit is located in the engine compartment on the left side under the brake master cylinder. Both the control unit and the hydraulic unit are replaceable as separate components. The pre-charge pump used on previous systems is no longer required. Rapid pressure build up is possible because of the close proximity of the hydraulic unit to the master cylinderand improvements in the design of the return pump. The control unit/hydraulic unit itself is 20% smaller and lighter than the previous M K20 El. All processing functions for ABS, ASC or DSC are performed by the combined control unit/hydraulic unit. The M K 60 control unit is also responsible for processing the wheel speed signals and providing them to other control units. The M K60 control unit for MY 2002 incorporates the RDW function into its scope of control, making a separate RDW control unit unnecessary. The operating principle continues to be based on the analysis of wheel speed. 27 E46 Traction and Stability Control Systems MK60 Hydraulic Unit DSC HYDRAULIC UNIT REAR AXLE BRAKE CIRCUITS FRONT AXLE BRAKE CIRCUITS INTAKE VALVE CHANGEOVER VALVE 401 INTAKE VALVE INLET OUTLET VALVE VALVE RUMP m OUTLET INLET VALVE VALVE ir LEFT REAR BRAKE PUMP 'NLET OUTLET VALVE VALVE *K OUTLET INLET VALVE VALVE ir right \ LEFT RIGHT REAR V*. >; ) FRONT FRONT BRAKE -h ^ y BRAKE BRAKE The hydraulic unit consists of an aluminum block containing 12 solenoid valves, 2 pressure accumulators and the return pump. 0 4 inlet solenoid valves (N/0) Q 2 changeover solenoid valves (N/O) Q 4 outlet solenoid valves (N/C) Q 2 Intake solenoid valves (N/C) The solenoid valving ensures that normal braking is possible in the event of a defective control unit. In ABS regulation the pump returns fluid back to the master cylinder circuits. In ASC/D5C regulation with brake intervention, the pump is responsible for building up the brake pressure required for the front and rear hydraulic circuits. Note: N/0= Normally Open N/C= Normally Closed 28 E46 Traction and Stability Control Systems CAN Interface The MK60 is connected to the CAN bus for communication with the AGS, DME control module, Steering Angle Sensor and the Instrument Cluster. The CAN bus allows all of the connected control modules to send and receive information and commands. Communication with the M K60 includes: Q DME - The DME sends current engine torque. M K60 commands the DME to reduce (ASC/DSC) or raise (MSR) engine torque. □ AGS - The M K60 commands the AGS to suppress shifts during regulation. 0 LEW - The M K60 receives steering angle information. 0 KOMBI - The M K60 commands the instrument cluster to activate or deactivate the warning lamps. Q All four wheels speed signals are sent over the CAN bus for use by other modules. INSTRUMENT 29 E46 Traction and Stability Control Systems Tandem Master Brake Cylinder The M K60 system uses a tandem master brake cylinder fitted with central valves as in other DSC master cylinders. The central valves allow fluid to be drawn through the master cylinder during ASC and DSC regulation. The hydraulic circuit is divided front/rear. An inlet for pre-charge pressure is no longer used since the charge pump has been eliminated from the M K60. Both brake pressure sensors are mounted on the master cylinder. Expansion Tank and Brake Fluid Level Switch The brake fluid expansion tank has internal baffles that reduce foaming during return pump operation. The expansion tank includes a pick-up tube for clutch master cylinder fluid supply. The brake fluid level switch is incorporated into the cap. The switch is a reed contact switch. If the brake fluid is at a sufficient level, the switch is closed and switched to ground. If the fluid level drops below a specified level , the reed contacts open and the M K 60 responds by switching off the ASC/DSC functions. Normal braking and ABS operation is unaffected. 30 E46 Traction and Stability Control Systems Brake Pressure Sensors Two brake pressure sensors are mounted on the master cylinder below the outlet ports for the front and rear brake circuits. The sensors are provided a 5V reference voltage by the M K 60 control unit. The sensor provides the control unit with an analog signal proportional to brake pressure. Voltage increases with increasing brake pressure. Plausibility with BLS The signal input from the brake light switch is compared with the pressure sensor values. The pressure sensors must not detect more that 5 bar when the BLS is not actuated. Both signals are used to form a redundant BLS input which is constantly monitored. Note: Refer to the Workshop Hints for instructions on initializing the brake pressure sensors. Brake Light Switch (BLS) The brake switch is an input to the M K 60 to inform it that the brakes are being applied. If the signal is received during an ASC regulation then brake regulation is interrupted. 31 E46 Traction and Stability Control Systems Wheel Speed Sensors (active) With the introduction of the Teves DSC III M K60, active wheel speed sensors that operate on the principle of magnetoresistive effect are used for the first time on BMW vehicles. The sensor element and evaluation module are two separate components within the sensor housing. 1. Metal pulse wheel 6. 2. Magnet 7. 3. Sensor element 8. 4. Evaluation module 9. 5. Support for sensor element 10. Sensor wiring with weather boot Ground contact ring Fastening element Sensor housing Pick-up surface Principle of operation of the magnetoresistive sensor The active sensing of the magnetoresistive sensor is particularly suitable for advanced stability control applications in which sensing at zero or near zero speed is required. A permanent magnet in the sensor produces a magnetic field with the magnetic field stream at a right angle to the sensing element. The sensor element is a ferromagnetic alloy that changes its resistance based on the influence of magnetic fields. 32 E46 Traction and Stability Control Systems As the high portion of the pulse wheel approaches the sensing element, a deflection of the magnetic field stream is created. This causes the resistance to change in the thin film ferromagnetic layer of the sensor element. 1. Metal pulse wheel 2. Magnet 3. Sensor element 4. Evaluation circuit 5. Magnetic field The sensor element is affected by the direction of the magnetic field, not the field strength. The field strength is not important as long as it is above a certain level. This allows the sensor to tolerate variations in the field strength caused by age, temperature or mechanical tolerances. The resistance change in the sensor element affects the voltage that is supplied by the evaluation circuit. The small amount of voltage provided to the sensorelement is monitored and the voltage changes (1 to lOOmV) are converted into current pulses by the evaluation module. inA' 0 Signal High-14mA If, f —. f —, — Q Signal Low-7mA I The sensorevaluation circuit is supplied 12V by the M K60 control unit. Output voltage from the sensor is approximately 10V. The control unit counts the high and low current pulses to determine the wheel speed signal. Front sensors are three wire because they have a separate ground wire. Rear sensors are two wire and use the sensor case as a ground point. 33 E46 Traction and Stability Control Systems Different sensors are used on the left and right side front axle of the vehicle. The difference comes in the length of the harness. The connectors are blue to distinguish them apart from the grey connectors used for sensors on the M K20 El. The DSC III M K60 uses the same metal pulse wheels used with the M K20 inductive sensors. Front axle E46/Z3 Rear axle Z3 Rear axle E46, short There are two types of sensors used in the rear axle of the E46: Q The short sensor is used on the 325i (any transmission) and 330i automatic. Q The long sensor is used on the 330i manual transmission version. The Z3 uses the same sensors for the rear axle, left or right. 34 E46 Traction and Stability Control Systems Rotation Rate Sensor The Rotation Rate Sensor is mounted on a metal bracket under the drivers seat. The sensor provides information to the MK60 concerning the vehicles speed around its main axis (yaw). The sensor has a three pin connector with the following connections: Q 5V reference D Signal D Ground The sensor receives a reference voltage of 5V from the M K60 control unit and provides a signal output of approximately 0.25 to 4.65V depending on the amount and direction of yaw. If the sensor is defective a constant voltage will be sent to the M K60. The sensor element is a micro-mechanical double quartz tuning fork. A frequency of 11 Hertz is applied to one side of the fork and as the vehicle turns on it’s axis, vibrations are induced on the other end. The sensor analyzes the signal produced by the fork and produces an analog voltage signal that is proportional to the amount of yaw. The rotation (yaw) rate is compared to the signal from the Steering Angle Sensor and the Transverse Acceleration Sensor. If physical limits are beginning to be exceeded, the M K60 DSC will begin regulation by engine and brake intervention to attempt to stabilize the vehicle. This is referred to as a GMR regulation. The M K60 DSC III for M ,Y. 2002 incorporates a combined Rotation rate and Transverse Acceleration Sensor. The Sensor is connected to the M K60 control unit by the CAN bus. The Z3 version will retain separate sensors until the E36/7 is replaced by the E46/6. 35 E46 Traction and Stability Control Systems Steering Angle Sensor (LEW) The Steering Angle Sensor is mounted towards the lower end of the steering column, above the flexible coupling. The LEW consists of a potentiometer and a built in microprocessor. The potentiometer has two pickups offset at 90° to one another. The raw potentiometer signal is processed and converted into a digital signal that is transmitted over the CAN bus to the M K60 DSC III control unit. The sensor requires initialization in order to create a zero point default. Once initialized the LEW sends an ID number to the DSC control unit. The ID provides confirmation that the LEW is properly initialized. The total steering wheel angle is determined by combining the CAN telegram signal, the stored zero point default and the actual number of turns to the wheel. In order to prevent the LEW from loosing count, KL 30 is provided to the sensor and it continues to record even after the ignition has been switched off. The M K60 DSC III calculates the drivers desired rate of turn from the steering angle signa POTENTIOMETER HOUSING \ CAN BUS MICROPROCESSOR Pin 1. KL 30 Pin 2. KL 87 Pin 3. CAN high Pin 4. CAN low Pin 5. KL 31 Pin 6. TXD Note: Refer to the Workshop Hints for instructions on coding and initializing the sensor. 36 E46 Traction and Stability Control Systems Transverse (Lateral) Acceleration Sensor The Transverse Acceleration Sensor is mounted in the left "A” pillar behind the driver's foot rest. The sensor provides the M K60 DSC control unit with a signal that corresponds to the degree of transverse acceleration (G forces) acting on the vehicle. The sensor is a capacitive sensor with two plates. One plate is rigidly mounted, the other plate is mounted on a spring. Under the effect of transverse forces acting on the sensor the distance between the plates changes. This change of distance between the plates affects the capacitance of the sensor. The evaluation circuitry converts the signal into an analog voltage that is transmitted to the control unit. The output signal of the sensor is between the range of 0.5 to 4.5 Volts. This corresponds to -1.5 to 3.5g respectively. When the vehicle is stationary the output is 1.8V. The transverse acceleration signal is used in the M K60 DSC III control unit along with the rotation rate and steering angle signal to determine if DSC regulation is required to maintaii the vehicles stability. Note: Refer to Workshop Hints for instructions on initializing sensor. 37 E46 Traction and Stability Control Systems DSC Button The DSC button is located on the SZM, however the SZM provides no processing, it is simply a housing for the button which is hardwired to the M K60 control unit. The DSC Button features two functions that can be set by varying the time the button is held down for: Button activation Function Display Short press <2.5s Only the yaw control of the DSC is deactivated. The ADB and DBC functions remain active. DSC light illuminated A higher slip ratio is allowed up to 42 mph for the purpose of improving traction in slippery conditions. ASC uses different thresholds. Long press >2.5s All ASC, ADB, DSC, GMR (yaw control) and DBC control functions are deactivated. DSC light and general brake warning light (yellow ABL) illuminated. Used for service and use on dynamometers. Pressing the button again returns the system to normal status. It is not possible to go directly from one function to the next without first returning to normal status. 38 E46 Traction and Stability Control Systems Instrument Cluster Warning Indicators Three warning indicator lamps are arranged in the instrument cluster: Q DSC lamp: Indicates fault in DSC or system disabled by the switch. 0 ABS lamp: Indicates a fault in the ABS system. Q ABL"BRAKE" lamp: This lamp is a general brake warning and illuminates two different colors. Q Red indicates low brake fluid or hand brake engaged. Q Yellow indicates DSC/ABS fault orsystem disabled by the switch. The DSC and yellow ABL lamp are controlled by the M K60 DSC III control unit via the CAN bus. The ABS lamp is controlled directly by the M K60 via hardwire. Hand brake Switch The hand brake switch is an input to the M K60 DSC to cancel M SR regulation. 39 E46 Traction and Stability Control Systems Principle of Operation The scope of control for the M K60 DSC III is comprised of three systems: □ ABS □ ASC+T □ DSC Based on signals coming from the various sensors, the M K60 DSC III will determine which system is best suited to maintain control of the vehicle. In addition to the three basic systems, there are several sub-functions which are activated during very specific circumstances. The sub-functions are: □ CBC □ EBV □ M SR □ ADB □ DBC □ MBC System: Anti-Lock Braking System (ABS) The ABS system can prevent wheel lock when braking by comparing the four active wheel speed sensors to the average vehicle speed. If a wheel is locking during braking or has dropped below a speed threshold programmed in the control unit ABS braking will begin. ABS braking is possible when vehicle speeds are above 12 kph (7mph). ABS regulation has three phases: G Pressure Build G Pressure Hold G Pressure Release 40 E46 Traction and Stability Control Systems Pressure Build already occurs during normal braking, so when ABS first intervenes it will start holding pressure by energizing the Inlet Valve. For example, if the right rear wheel is locking up, both Inlet Valves will be energized, regulating both wheels together. This logic is known as Select Low. Front wheels can be regulated individually as needed to prevent lockup. Energizing the Inlet Valve closes the brake fluid passage to the calipers and traps the fluid at the current pressure, thus not allowing the brake pressure to rise any further. If the wheel speed does not increase the Pressure Release phase begins FRONT AXLE BRAKE CIRCUITS CHANGEOVER VALVE ACCUMULATOR i (9 valve