Electronic Suspension and Steering Systems

2. Chapter 14 Electronic Suspension and Steering Systems

3. Objectives • Identify the components of electronic suspension systems. • Explain the operation of electronic suspension systems. • Identify types of electronic suspension systems. • Explain the operation of electronic steering systems. • Identify the components of electronic steering systems.

4. Electronic Suspension System Fundamentals • Electronic suspension system uses electronic components to control parts of suspension system • Systems vary according to: • Type and number of input sensors • Whether air compressor is present • Number of wheels controlled

5. Electronic Suspension System Fundamentals • All systems control operation of shock absorbers or strut cartridges • Most air-operated systems control ride height and quality by increasing or decreasing air in air shocks • Air shock systems always contain an air compressor • Hydraulic systems: • Have no compressor • Control ride quality but not ride height • Regulate hydraulic flow through shock absorber internal parts

6. Electronic Suspension System Fundamentals • Basic suspension components of electronic suspension identical to those on conventional suspension systems

7. Electronic Suspension Input Sensors • Variety of input sensors used • Most systems use one or more: • Height sensors • Vehicle speed sensors • Acceleration sensors • Steering wheel rotation sensors • Switches

8. Height Sensors • Height sensor converts position of vehicle body and axle into electrical signal • Some vary electrical resistance as distance changes • Some vary magnetic field of current passing through sensor as distance changes (Buick)

9. Height Sensors • When current flow varies, voltage varies • Control module reads change in voltage as change in height • Sensor usually installed on body or frame • Linkage connects sensor to axle or control arm • When weight added or removed from vehicle, body moves in relation to axle

10. Height Sensors • When system compensates for weight change: • Lever moves in opposite direction • Movement tells control module that ride height correct • Common systems use: • Two sensors on front suspension • Attached to lower control arm and body • One on rear • Attached to rear axle and body

11. Height Sensors • Height sensor: • Records position of suspension part it is attached to • Sends information to control module • Control module • Interprets sensor signal vehicle height

12. Height Sensors • Advantage of system: • Control module can monitor height at all four wheels • Make changes to keep vehicle level

13. Vehicle Speed Sensor • Vehicle speed sensor either attached: • To output shaft of transmission or transaxle • In differential of rear-wheel drive vehicle • Consists of: • Toothed wheel • Small coil • Uses magnetism to create AC signal (Toyota)

14. Vehicle Speed Sensor • Some speed sensors wired to engine control module (ECM) or body control module (BCM) • ECM or BCM controls engine factors such as fuel mixture and ignition timing based partially on signal from speed sensor • ECM also directs speed input to suspension control module

15. Acceleration Sensor • Acceleration sensor or accelerometer: • Measures speed of vehicle acceleration or deceleration • Input from sensor used to calculate suspension firmness • Keeps vehicle body level during heavy acceleration or braking

16. Acceleration Sensor • Some sensors, are lateral accelerometers: • Mount at right angle to centerline of vehicle • Detect body roll when vehicle turns sharply (Bosch)

17. Acceleration Sensor • Modern accelerometer consists of: • Piezoelectric crystal • Weight • Changes in speed and direction cause weight to press on crystal • Crystal produces small electrical currently • Signal is sent to control module

18. Steering Wheel Rotation Sensor • Some vehicles use steering wheel rotation sensor as input to suspension system • Sensor determines: • Which direction steering wheel is turned • How quickly steering wheel is turned (Nissan)

19. Review Questions 1. All of the following are electronic suspension input sensors, except: A. speed sensor. B. height sensor. C. temperature sensor. D. acceleration sensor. C. temperature sensor.

20. Switches • Switches are on-off devices that send specific signal to control module • Most are two position switches • Usually on-off • Some have several positions (Corvette)

21. Switches • Switches include: • Brake pressure switches • Manual control switches • Suspension service switches • Door switches

22. Brake Pressure Switches • Brake system hydraulic pressure increases when vehicle brakes hard • Brake pressure switch closes at preset pressure • When switch closes, voltage signal is sent to module • Tells module vehicle braking is severe

23. Brake Pressure Switches • Brake switch located in brake hydraulic system • Many ride control systems do not use brake pressure input

24. Manual Control Switches • Manual control switches: • Driver-accessible switches mounted on dashboard • Used to move between soft and firm positions when desired • Manual switches usually have two or three positions

25. Suspension Service Switches • Suspension service switch: • Used to disable electronic suspension system before vehicle raised on lift • System would attempt to compensate for suspension changes when wheels drop • If system not disabled with wheels off ground, vehicle height will be incorrect when wheels back on ground

26. Suspension Service Switches • Suspension service switch usually located in trunk • Switch may be called on-off switch by some manufacturers (Lexus)

27. Review Questions 2. True or False? The suspension service switch must be put in the Off position before the vehicle is raised on a frame lift. True.

28. Door Switches • Door switch: • Type of input switch • Informs ride control system that someone is entering or leaving vehicle • Most electronic suspension systems do not use door switch input

29. Electronic Suspension Control Module • Control module: • Computer • Processes signals (inputs) from input sensors and sends command signals (output) to output devices • Examples: Air compressor and flow control actuators

30. Electronic Suspension Control Module (Cadillac)

31. Electronic Suspension Control Module • Microprocessor • Uses control loop principle • Compares input information from sensors with preset information • Decides whether output devices should be activated

32. Electronic Suspension Control Module • Control module has delay mechanism that prevents system activation for 5-10 seconds • Delay mechanism keeps system from operating excessively when vehicle driven over rough roads

33. Electronic Suspension Control Module • Most modern modules have data link connector • Some electronic suspension systems electrically connected to ECM or PCM • Diagnostic connector of ECM/PCM retrieves suspension system trouble codes and other information

34. Electronic Suspension Control Module • Control module can be located anywhere on vehicle • Under the hood • Dashboard • Under a seat • In trunk • Ride-height suspension modules may be single units with height sensor • Some vehicles do not have separate module

35. Electronic Suspension Control Module • Suspension control is part of ECM or PCM • ECM or PCM receives sensor inputs and makes ride control decisions based on inputs

36. Review Questions 3. The electronic suspension _____ processes signals (inputs) from input sensors and sends command signals (output) to output devices. control module

37. Electronic Suspension Output Devices • Output of electronically controlled suspension system may be either: • Air pressure system similar to that of conventional air shock system • Hydraulic controls located directly at shock absorber or strut • Some use air and hydraulic components

38. Electronic Suspension Output Devices • Air-operated system components • Hydraulic system components • System lights

39. Air-Operated System Components • Output devices found in air-operated suspension systems include: • Air compressor • Control relay • Exhaust valve and solenoid • Air drier • Air lines and fittings • Air springs • Air shock absorbers/struts

40. Air Compressor • Most common air compressor used in air-operated systems: • Single-piston compressor driven by small electric motor • Compressor consists of: • Piston and cylinder • Two check valves at top of cylinder

41. Air Compressor • Check valves arranged so that: • When piston moves down in cylinder, inlet valve opens by atmospheric pressure • When piston moves up, pressure increase closes inlet valve

42. Air Compressor • Outlet valve: • Remains closed when piston moves downward • Opens by pressurized air when piston moves upward (General Motors)

43. Air Compressor • Compressor assembly contains either: • Pressure relief valve • Pressure relief switch • When preset pressure value reached: • Valve opens to relieve pressure • Switch opens to de-energize motor • When pressure drops, switch closes and voltage supplied to motor • Switch may be replaced by relay

44. Review Questions 4. How many pistons does the typical air suspension compressor have? The typical air suspension compressor has one piston.

45. Control Relay • Some compressors operated by relay • Control module energizes relay • Relay sends power to compressor • Relays may be: • Electromechanical (contact point) • Power transistors

46. Exhaust Valve and Solenoid • Air exhaust valveoperated by exhaust valve solenoid • Solenoid: • Controlled by module • Energized to release pressure from system when ride height excessive (Chevrolet)

47. Exhaust Valve and Solenoid • Air may be exhausted either: • Directly to atmosphere • Through air drier (General Motors)

48. Air Drier • Air drier keeps moisture from entering shock absorbers • Contains chemical called desiccant • Desiccant absorbs moisture • Air entering system from compressor passes through drier and moisture removed

49. Air Drier • Filter keeps desiccant from entering other parts of system • When air is released from system, it passes through drier and takes some moisture with it • Keeps desiccant from being overloaded with moisture

50. Air Drier • Some driers installed ahead of compressor • Check valve in drier maintains set pressure in system