Table of Contents Electronic Dampening Control (EDC) Subject Page Purpose of the System.3 System Components E38 System Components E31/E32 Acceleration Sensors.6 Steering Angle Sensors. 6 Control Module.7 Program Switch.7 Road Speed Input.8 Solenoid Controlled Dampers.8 Basic Damper Operation.9 E38 Damper Operation.10 E31/E32 Damper Operation.11 l-P-0 E38 .12 l-P-0 E31/E32.13 Electronic Damper Control Functions.14 Safety Monitoring.16 Special Tools.17 Initial Print Date: 1/03 Revision Date Model: E31 8501, 850Ci, 850CSi f 840i 1991-1997 E32 750iL, 735i/iL, 740i/iL 1988-1994 E38 750iL, 7401/iL from 1995-2001 Production: All with EDC Objectives: After completion of this module you should be able to: Identify EDC System Components Locate EDC System Components Understand EDC System Operation 2 Electronic Dampening Control Purpose of the System The EDC III is a fully automatic adjusting damper control system available on the E31, E32 and E38 vehicles. It also allows the driverto choice of two damping programs (comfort and sport) Conventional non-adjustable systems have damper (shock absorber) settings which pro¬ vide an acceptable damping action over as wide of range of speeds and loads as possible. This means a compromise between a high standard of ride comfort on one hand, and a margin of safety on the other. Modern technology enables this trade off to be resolved with variable damping, and this principle has been adopted on the EDC III system. The system uses various input parameters directly relating to road condition, load on the car and driving style to select one of three damping characteristics, (soft, medium or hard). The result is optimum damping over a wide range of speeds and loads, and definite gains in both ride comfort and safety. EDC III is a further development of the variable damping systems already used on BM Ws in other markets. The purpose of any damping force adjustment is to reduce oscillations as perceived by the car's occupants, without affecting either handling or driving safety. This is achieved by continuously matching the damping force to road conditions, vehicle load and driving style. 3 Electronic Dampening Control System Components E38 The EDC system on the E38 consists of the following components Front-axle acceleration sensor - This is installed on the right side of the wheel housing, close to the right-hand upper spring strut mount. Rear-axle acceleration sensor - This is installed on the right rear wheel arch, on top of the spring strut mount EDC III control module . Mounted on right side of trunk. (Behind Glovebox from 99 M odel Year) Steering angle sensor - On lower section of steering column Solenoid valves - Integrated in the strut housing. Program switch - Located on dash in center below IHKA panel ACCELERATION SENSOR ACCELERATION SENSOR 4 Electronic Dampening Control System Components E31/E32 The EDC system on the E32/E31consists of the following components: Front-axle acceleration sensor - This is installed on the right side of the wheel housing, close to the right-hand upper spring strut mount. Rear-axle acceleration sensor - This is installed on the right rear wheel arch, on top of the spring strut mount. EDC III control module and power relay - Both units are mounted in trunk on right side. Longitudinal acceleration sensor - On the left rear wheel arch. Steering angle sensor- On the steering column (similar component on the E31, E32 but not interchangeable) Solenoid valve - Two valves are mounted at the base of each strut assemb y. Program switch - Located on center console. 5 Electronic Dampening Control Components Acceleration (Motion) Sensors There are three acceleration sensors: one each for the front and rear axles (vertical motion), and one for forward/aft motion. All sensors are solid state, piezo ceramic elements. Vehicle movement on the sensors is converted into an electric signal. The control module uses these inputs to detect road surface condition, vehicle loading and degree of motion. The loading of the vehicle influences ver¬ tical motion and is therefore detected by the sen¬ sors. The E38 acceleration sensors are identical to the E31/E32 sensors, the longitudinal sensor has been deleted on the E38. The dynamic longitudi¬ nal forces on the vehicle are calculated from the inputs of the front wheel speed sensors. The following inputs are used to detect dynamic forces acting on the vehicle; Vertical acceleration Fore and aft acceleration Steering wheel angle Vehicle road speed Steering Angle Sensor The steering angle sensor is identical for all vehicles The rotating double potentiometer provides two variable resis¬ tance signals for turn recogni¬ tion. The EDC control module used this input to increase the damping rate when corning. 6 Electronic Dampening Control Control Module One basic control module is used for the E38. Selecting the proper damping curves is carried out via the DISplus or GT-1. The E31/E32 also use a basic control module which must be coded for proper vehi¬ cle application. Referto the EPC forthe propercontrol module. Program Switch The E38 uses a momentary switch to select comfort or sport. Low for comfort and high for sport. The E31 and E32 use a two position rocker switch to select comfort or sport. E31/E32 Comfort Program When the comfort program is selected, the priority setting is for soft damping. Any changes to dynamic movements detected by the sensor will allow the system to switch to either medium or hard depending on how severe the dynamic changes are. The system will auto¬ matically switch back to the soft setting when conditions warrant. This results in an ideal combination of maximum comfort and optimum driving safety. Sport Program When the sport program is selected only the medium and hard damping settings are used. The control unit selects the medium setting until dynamic changes require a higher damp¬ ing force to maintain stability. The program characteristics allow the hard setting to be selected sooner and held longer than the comfort program. 7 Electronic Dampening Control Vehicle Road Speed The road speed comes from the ABS/ASC or DSC control module on the E38. The E31 signal comes from the EKM and the instrument cluster sup¬ plies the signal for the E32. Solenoid Controlled Dampers E31/E32 and E38 The EDC system utilizes solenoid valves to change the valving in the damper to relieve the oil flow through additional valves and create a softer damper value. The E38 solenoids are mounted internally The E31/E32 use dampers with the solenoid valves mounted external¬ ly of the dampers. Front axle twin-tube, gas pressurized dampers and rear single tube dampers are used on all EDC vehicles. Two solenoid valves are used for each strut assembly These valves pro¬ vide an additional passage for the flow of oil in the soft and medium settings. Both valves are never energized simultaneously. Damping can be varied front to rear, but not side to side. E38 wiring for control runs up through piston. EXTERNALLY P"^ MOUNTED SOLENOID VALVES PRE E38 EDC 3+ E38 REAR SHOCK 8 Electronic Dampening Control Basic Damper Operation When the vehicle bounces the damper travels thru the compression and rebound stages. The damper as illustrated corresponds to the EDC sport damper setting because the oil basic dampers transfer uses only a mechanical one-way valve. The EDC III system can pro¬ vide softer damping rates (soft, medium) by energizing solenoid valves which allow addi¬ tional oil volume to transfer. COMPRESSION REBOUND 9 Electronic Dampening Control E38 Solenoid Controlled Damper Operation There are three passages for oil transfer in the strut assembly. The first is the main oil trans¬ fer valve. This valve is always open. The second and third valves are controlled by the EDC solenoids. Through the two different orifices, the solenoids can vary the throughput of hydraulic oil transfer thereby regulating the damping force. Soft Setting - In this setting the "soft solenoid in each shock is energized allowing oil trans¬ fer through the mechanical orifice and larger diameter "soft” orifice. The soft setting pro¬ vides oil transfer with the least restriction and the struts are set to the softest damping force. Medium Setting - When the EDC control module's processing calls forthe medium setting, the soft solenoid is de-energized and the "M edium" solenoid is energized so thatthe oil now flows through the smaller valved orifice. This restricted oil flow increased the damping force of the strut. Hard Setting - When the EDC control module's processing requires the hard setting, the medium solenoid is switched "OFF''. This closes the solenoid controlled orifices and only allows oil transferthrough the main valve. The struts are now set to the maximum firmness. This is also the failsafe setting of the EDC III system. With no power applied to the struts, the system will be in the hard setting. SOFT MEDIUM HARD 10 Electronic Dampening Control E31/E32 External Solenoid Damper Operation The EDC III solenoid operation is identical for both soft and medium settings. The soft sole¬ noid has a larger orifice so more oil can pass through the energized solenoid. Soft Setting = Soft solenoid energized = M aximum oil transfer Medium Setting = Medium solenoid energized = Moderate oil transfer Hard Setting = No solenoids energized = No oil transfer through solenoids Compression Stage Rebound Stage EDC III Control Unit EDC III Control Unit 11 Electronic Dampening Control E38 l-P-0 DFEttAIINS PUWER TYVO SOLENOIDS TWO SOLENOIDS SPORT PROGRAM SIGNAL. LER AND RIGHI FHON r DAMPERS fRONT AXLE ACCELERATION SENSOR LEFT and RIGHT RFAR HAMPERS REAR AXLE ACCELERATION SENSOR TWO SOLENOIDS DUAL STEEP NO ANGLE SIGNALS TWO SOLENOIDS □I MM ‘NG, SIGNAL FOR SWITCH SPORT ..ED ILLUMINATION ruiru DIAGNOSIS VEHICLE SPEEO 12 Electronic Dampening Control E31-E32 l-P-0 KL 30 KL 15 KL 31 STEERING ANGLE SENSOR FRONT VERTICAL ACCELERATION REAR VERTICAL qyj ACCELERATION LONGITUDINAL ACCELERATION PROGRAM SWITCH VEHICLE SPEED SIGNAL KL 58 EDC III + E-31 CONTROL MODULE FRONT SOLENOIDS REAR SOLENOIDS PROGRAM SWITCH DIAGNOSIS 13 Electronic Dampening Control Electronic Damper Control Functions Automatic Load compensation (/> w to +■» o +■* o > to +■* o > in > > m ■ > in o in CM o . -o _>» q C ~o o ro ■o 5 1 1 1 jeduiBQ 14 Electronic Dampening Control Secondary Roads Primary Roads Highway EDC III Ride Program Comparison "O 0) CO 0 0 0 Q Q- > 0 CO ^ t w I 2 ■§ i-S ™ I E m -E c -o X o c 0 CD < o o 01U|J J.O % O CO o CO uiejBojd ViojuiOQ tuejBojd iJods 15 Electronic Dampening Control mph 60 40 mph 75 40 mph 120 Safety Monitoring All operating cycles and sensor inputs are checked by the control unit for plausibility and function. Any faults that might occur are stored in the defect memory according to there p rio rity, In the event of certain faults, the control module selects the "medium" damping setting. Steering angle sensor e.g. bent wiper in sensor (signals do not match; max. deviation 30deg.) or tempo¬ rary signal disturbed. Steering angle sensor e.g. contact difficulties, wiper on conductor of potentiometer, loose contact in con¬ ductor. Steering angle sensor e.g. broken locating pin (sensor always supplies same signal), steering angle sen¬ sor not fitted. Defective road speed signal e.g. break in wire to EDC module. Defective acceleration sensor e.g. signals not within working range. If the soft solenoid fails, the medium setting is selected. If the medium solenoid valve circuit or control module fails, the solenoids are de-ener- gized which results in the hard or fail-safe setting. 16 Electronic Dampening Control EDC Special Tools E38 Adapter Harness EDC Shock Solenoids P/N 90 88 6 616 041 Special adapter harness plugs into shock harness fortesting purposes. Shock Assembly Removal Socket P/N 90 88 6 312 210 Special socket for disassembly of shock absorber with new solenoid harness. 17 Electronic Dampening Control