© Goodheart-Willcox Co., Inc.

Electronic Suspension and Steering Systems Chapter 14 Electronic Suspension and Steering Systems © Goodheart-Willcox Co., Inc.

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. © Goodheart-Willcox Co., Inc.

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 © Goodheart-Willcox Co., Inc.

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 © Goodheart-Willcox Co., Inc.

Electronic Suspension System Fundamentals Basic suspension components of electronic suspension identical to those on conventional suspension systems © Goodheart-Willcox Co., Inc.

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 © Goodheart-Willcox Co., Inc.

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) © Goodheart-Willcox Co., Inc.

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 © Goodheart-Willcox Co., Inc.

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 © Goodheart-Willcox Co., Inc.

Height Sensors Height sensor: Control module Records position of suspension part it is attached to Sends information to control module Control module Interprets sensor signal vehicle height © Goodheart-Willcox Co., Inc.

Height Sensors Advantage of system: Control module can monitor height at all four wheels Make changes to keep vehicle level © Goodheart-Willcox Co., Inc.

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) © Goodheart-Willcox Co., Inc.

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 © Goodheart-Willcox Co., Inc.

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 © Goodheart-Willcox Co., Inc.

Acceleration Sensor Some sensors, are lateral accelerometers: Mount at right angle to centerline of vehicle Detect body roll when vehicle turns sharply (Bosch) © Goodheart-Willcox Co., Inc.

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 © Goodheart-Willcox Co., Inc.

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) © Goodheart-Willcox Co., Inc.

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. © Goodheart-Willcox Co., Inc.

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) © Goodheart-Willcox Co., Inc.

Switches Switches include: Brake pressure switches Manual control switches Suspension service switches Door switches © Goodheart-Willcox Co., Inc.

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 © Goodheart-Willcox Co., Inc.

Brake Pressure Switches Brake switch located in brake hydraulic system Many ride control systems do not use brake pressure input © Goodheart-Willcox Co., Inc.

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 © Goodheart-Willcox Co., Inc.

Suspension Service Switches 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 © Goodheart-Willcox Co., Inc.

Suspension Service Switches Suspension service switch usually located in trunk Switch may be called on-off switch by some manufacturers (Lexus) © Goodheart-Willcox Co., Inc.

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. © Goodheart-Willcox Co., Inc.

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 © Goodheart-Willcox Co., Inc.

Electronic Suspension Control Module Computer Processes signals (inputs) from input sensors and sends command signals (output) to output devices Examples: Air compressor and flow control actuators © Goodheart-Willcox Co., Inc.

Electronic Suspension Control Module (Cadillac) © Goodheart-Willcox Co., Inc.

Electronic Suspension Control Module Microprocessor Uses control loop principle Compares input information from sensors with preset information Decides whether output devices should be activated © Goodheart-Willcox Co., Inc.

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 © Goodheart-Willcox Co., Inc.

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 © Goodheart-Willcox Co., Inc.

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 © Goodheart-Willcox Co., Inc.

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 © Goodheart-Willcox Co., Inc.

Review Questions 3. The electronic suspension _____ processes signals (inputs) from input sensors and sends command signals (output) to output devices. control module © Goodheart-Willcox Co., Inc.

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 © Goodheart-Willcox Co., Inc.

Electronic Suspension Output Devices Air-operated system components Hydraulic system components System lights © Goodheart-Willcox Co., Inc.

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 © Goodheart-Willcox Co., Inc.

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 © Goodheart-Willcox Co., Inc.

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 © Goodheart-Willcox Co., Inc.

Air Compressor Outlet valve: Remains closed when piston moves downward Opens by pressurized air when piston moves upward (General Motors) © Goodheart-Willcox Co., Inc.

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 © Goodheart-Willcox Co., Inc.

Review Questions 4. How many pistons does the typical air suspension compressor have? The typical air suspension compressor has one piston. © Goodheart-Willcox Co., Inc.

Control Relay Some compressors operated by relay Control module energizes relay Relay sends power to compressor Relays may be: Electromechanical (contact point) Power transistors © Goodheart-Willcox Co., Inc.

Exhaust Valve and Solenoid Air exhaust valve operated by exhaust valve solenoid Solenoid: Controlled by module Energized to release pressure from system when ride height excessive (Chevrolet) © Goodheart-Willcox Co., Inc.

Exhaust Valve and Solenoid Air may be exhausted either: Directly to atmosphere Through air drier (General Motors) © Goodheart-Willcox Co., Inc.

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 © Goodheart-Willcox Co., Inc.

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 © Goodheart-Willcox Co., Inc.

Air Drier Some driers installed ahead of compressor Check valve in drier maintains set pressure in system © Goodheart-Willcox Co., Inc.

Review Questions 5. An air _____ contains a material called desiccant. drier © Goodheart-Willcox Co., Inc.

Air Lines and Fittings Air lines connect other air system parts Air lines made of plastic tubing Air line diameter about 1/32'' (0.8 mm) © Goodheart-Willcox Co., Inc.

Air Lines and Fittings Fitting at end of each air line used to attach line to other components Fittings: Keep lines from blowing off under pressure Seal against leaks (Lexus) © Goodheart-Willcox Co., Inc.

Air Springs Air springs used in place of both spring and shock absorber in some air-operated systems Basic component of air spring is rubber diaphragm, or membrane Diaphragm installed between lower control arm and vehicle body © Goodheart-Willcox Co., Inc.

Air Springs Filling diaphragm with air causes it to expand As diaphragm expands, it pushes body upward When air removed, diaphragm collapses, allowing body to drop down (Ford) © Goodheart-Willcox Co., Inc.

Air Shock Absorbers/Struts Air shock absorbers are conventional shock absorbers with sealed air chambers When used on struts, chambers sometimes called air bladders © Goodheart-Willcox Co., Inc.

Air Shock Absorbers/Struts Compressed air can be added to chambers to: Compensate for vehicle loading Increase ride height Sealed chamber exerts pressure on shock interior Pressure causes shock to try to expand © Goodheart-Willcox Co., Inc.

Air Shock Absorbers/Struts As shock expands, it pushes upward against vehicle weight, causing rear of vehicle to rise Air shocks or struts installed in same location as conventional shocks and struts © Goodheart-Willcox Co., Inc.

Review Questions 6. True or False? A vehicle with air springs has conventional (not air-operated) shock absorbers. False. A vehicle with air springs does not have any shock absorbers. © Goodheart-Willcox Co., Inc.

Hydraulic System Components On vehicles without air compressor, internal hydraulic system of shock or strut controlled to vary ride firmness Unlike air-operated systems, these systems cannot control ride height Hydraulic systems consist of two major components: Flow control actuators Ride relays © Goodheart-Willcox Co., Inc.

Flow Control Actuators Electric flow control actuators installed in shocks or struts Actuator is electric solenoid that operates flow control valve Valve controls flow of hydraulic fluid through shock (General Motors) © Goodheart-Willcox Co., Inc.

Flow Control Actuators Most flow control solenoids pulse on and off On for certain percentage of time vehicle is operating Percentage may be called duty cycle Solenoid and valve assembly located in shock or strut © Goodheart-Willcox Co., Inc.

Review Questions 7. Flow control actuators are used on _____ ride control systems. hydraulic © Goodheart-Willcox Co., Inc.

Ride Relays Some systems with flow control solenoids have soft and firm ride relays Relays energized from dashboard switch Modify computer input to compensate for driver preferences © Goodheart-Willcox Co., Inc.

System Lights Electronic suspension controls use indicator lights Installed in instrument panel These lights used to: Indicate system status Warn of suspension system problem © Goodheart-Willcox Co., Inc.

Status Lights Some vehicles have lights at manual control switch to indicate which ride status or mode has been selected Lights usually consist of LEDs (light emitting diodes) mounted on switch itself (Lexus) © Goodheart-Willcox Co., Inc.

Status Lights Some status lights used to indicate problems System has defect if: All lights are on at once Lights flash on and off Some lights are located on center console © Goodheart-Willcox Co., Inc.

Warning Lights Some system use dashboard-mounted warning lights Light may be: Standard automotive bulb LED Light operated by suspension control module © Goodheart-Willcox Co., Inc.

Warning Lights Most warning lights come on briefly when vehicle started to check module and light operation If light is illuminated at any other time, system has defect (Nissan) © Goodheart-Willcox Co., Inc.

Types of Electronic Suspension Systems Three general types of electronically controlled suspension systems: Air-operated ride and height control system Hydraulic ride control system Combination system using both air and hydraulic controls © Goodheart-Willcox Co., Inc.

Air-Operated Ride and Height Control System Air-operated ride and height controls use one of two height adjustment devices: Air springs Air shock absorbers © Goodheart-Willcox Co., Inc.

Air-Operated Ride and Height Control System Air pressure to either type is: Increased by air compressor Decreased by exhaust valve Electronic control system operates: Compressor All associated valves and switches © Goodheart-Willcox Co., Inc.

Air-Operated Ride and Height Control System Typical sensor inputs include: Ride height Vehicle speed Output devices are: Air compressor Exhaust valve © Goodheart-Willcox Co., Inc.

Air-Operated Ride and Height Control System Control module: Processes inputs Issues commands to air compressor and exhaust valve solenoid © Goodheart-Willcox Co., Inc.

Air-Operated Ride and Height Control System Height-sensitive system Speed-sensitive system © Goodheart-Willcox Co., Inc.

Height-Sensitive System Height-sensitive system varies pressure delivered to air springs or air shocks based on ride height input Module operation of compressor and pressure relief valve solenoid controls ride height (General Motors) © Goodheart-Willcox Co., Inc.

Height-Sensitive System Distance between axle and body decreases when weight added Height sensor lever moves Telling module that height has decreased Module energizes compressor motor Causing compressor to send pressurized air to air springs or air shocks © Goodheart-Willcox Co., Inc.

Height-Sensitive System Increased pressure raises vehicle body in relation to axle When module determines height has returned to normal, it de-energizes compressor motor © Goodheart-Willcox Co., Inc.

Height-Sensitive System When extra weight removed, distance between axle and body increases Height sensor lever moves in opposite direction Height sensor input causes module to energize exhaust valve solenoid Exhaust valve opens (General Motors) © Goodheart-Willcox Co., Inc.

Height-Sensitive System Air pressure exits system Body moves downward When height returns to normal, module de-energizes exhaust valve solenoid Height-sensitive system may also be used as part of combination system © Goodheart-Willcox Co., Inc.

Speed-Sensitive System Speed-sensitive suspension lowers vehicle body as speed increases Accomplished by reducing air pressure in shocks or struts as speed increases When speed is reduced, air compressor energizes, causing vehicle height to increase (Ford) © Goodheart-Willcox Co., Inc.

Speed-Sensitive System Control module receives input directly from vehicle speed sensor or by way of ECM or PCM When vehicle reaches preset speed: ECM or PCM releases air pressure from air springs or shocks Vehicle is lowered © Goodheart-Willcox Co., Inc.

Speed-Sensitive System Amount vehicle is lowered varies with engine speed System does not operate until vehicle reaches cruising speeds © Goodheart-Willcox Co., Inc.

Review Questions 8. A speed-sensitive suspension lowers the vehicle body as the vehicle’s speed _____. increases © Goodheart-Willcox Co., Inc.

Hydraulic Damping Systems Module varies operation of solenoids to control flow of fluid in shocks or struts Can be done: Manually through instrument panel switch Automatically by control module based on sensor inputs A combination of manual and automatic controls © Goodheart-Willcox Co., Inc.

Hydraulic Damping Systems Input sensors for hydraulic ride control system include: Accelerometer Speed sensor Brake pressure sensor Steering wheel position sensor (Lexus) © Goodheart-Willcox Co., Inc.

Hydraulic Damping Systems Control module: Processes inputs from sensors Energizes solenoids at shocks or struts Solenoid operation reduces amount of flow through fluid orifices Firming suspension as necessary © Goodheart-Willcox Co., Inc.

Hydraulic Damping Systems Control module can control individual solenoids Results in variations in firmness from one side of vehicle to other Helpful when cornering or hard braking © Goodheart-Willcox Co., Inc.

Hydraulic Damping Systems Manual control systems Automatic control systems © Goodheart-Willcox Co., Inc.

Manual Control Systems Instrument panel switch controls manual system Switch may be: Two-position, generally on-off switch Three-position switch, with additional “automatic” (or auto) position Automatic control takes over when selected © Goodheart-Willcox Co., Inc.

Automatic Control Systems Control module operates automatic system based on inputs from sensors Inputs include: Accelerometer Vehicle speed sensor Sometimes steering wheel and brake sensors © Goodheart-Willcox Co., Inc.

Automatic Control Systems System stiffens suspension when sensors signal firmer suspension needed When accelerometer input indicates vehicle being braked hard: Module signals control solenoids, or actuators, in shocks/struts to close Damping effect increased Increased shock firmness reduces tendency of vehicle to dive during hard braking © Goodheart-Willcox Co., Inc.

Automatic Control Systems When input indicates hard braking over: Module signals solenoids to allow normal flow through shocks or struts Ride quality returns to normal settings for maximum passenger comfort System performs similar function when vehicle accelerated or cornered hard © Goodheart-Willcox Co., Inc.

Combination Systems Combination system consists of both: Air-operated shock absorbers Hydraulic damping valves System performs functions of air-operated system: Height control Lowering at cruising speeds © Goodheart-Willcox Co., Inc.

Combination Systems System performs functions of hydraulic system: Control of body level during heavy acceleration, braking, or cornering Varying ride feel Operation of system similar to operation of individual systems © Goodheart-Willcox Co., Inc.

Electronic Steering Control Systems Provides maximum power assist at low speeds Reduces assist at high speeds Increases road feel and steering stability © Goodheart-Willcox Co., Inc.

Electronic Steering Control Systems System functions by monitoring: Vehicle speed Speed at which steering wheel is turned System uses this information to control output of power steering pump © Goodheart-Willcox Co., Inc.

Electronic Steering Control Systems If electronic steering control system fails: Power steering pump output is not affected Power steering system operates normally Dashboard mounted light warns driver of system failure © Goodheart-Willcox Co., Inc.

Electronic Steering Control Systems Control system components Control system operation Electric power steering systems © Goodheart-Willcox Co., Inc.

Control System Components Basic components of electronic steering systems same as conventional steering system: Pump Gearbox Connecting hoses © Goodheart-Willcox Co., Inc.

Control System Components Electronic components used to modify operation of basic parts Common electronic components: Input devices Control module Output devices © Goodheart-Willcox Co., Inc.

Input Devices Two most common input sensors used in electronic steering control systems: Vehicle speed sensor Steering wheel rotation sensor © Goodheart-Willcox Co., Inc.

Vehicle Speed Sensor Vehicle speed sensor operates in same manner as described earlier ac signal created in sensor Sensor signals ECM or PCM ECM or PCM sends speed reading to steering control module © Goodheart-Willcox Co., Inc.

Steering Wheel Rotation Sensor Steering wheel rotation sensor installed in steering column Two basic types: Electromagnetic sensor Optical sensor (Lexus) © Goodheart-Willcox Co., Inc.

Steering Wheel Rotation Sensor Electromagnetic sensor creates variable ac voltage Operates in same manner as wheel speed sensor Frequency sent to control module as steering wheel turning speed signal © Goodheart-Willcox Co., Inc.

Steering Wheel Rotation Sensor Optical sensor (or optical disc) senses steering wheel speed using: Photo cell Photo diode Shutter assembly © Goodheart-Willcox Co., Inc.

Steering Wheel Rotation Sensor Photo diode creates light signal that is picked up by photocell Photocell converts light beam to electrical signal © Goodheart-Willcox Co., Inc.

Steering Wheel Rotation Sensor Shutter: Connected to steering shaft Rotates with it As shutter turns, slits interrupt light beam How fast light beam interrupted determines electrical signal sent to module © Goodheart-Willcox Co., Inc.

Review Questions 9. All of the following are part of a steering wheel rotation optical sensor, except: A. flow control actuator. B. photo cell. C. shutter assembly. D. photo diode. A. flow control actuator. © Goodheart-Willcox Co., Inc.

Control Module Control module: Processes inputs from vehicle and steering wheel speed sensors Sends output command to flow control solenoid Module usually installed near steering wheel © Goodheart-Willcox Co., Inc.

Output Devices Several devices used to control steering effort in power steering system Some mounted on power steering pump Others installed on steering gear Systems will have only one type of output device © Goodheart-Willcox Co., Inc.

Output Devices Output devices include: Flow control solenoid Inlet hose check valve Pressure control solenoid Electromagnet © Goodheart-Willcox Co., Inc.

Flow Control Solenoid Flow control solenoid and valve assembly: Diverts flow to pump reservoir Installed in outlet line of power steering pump Pulses on and off to control amount of fluid diverted © Goodheart-Willcox Co., Inc.

Flow Control Solenoid Module controls pulse time (or duty cycle) of solenoid (Toyota) © Goodheart-Willcox Co., Inc.

Inlet Hose Check Valve Inlet to power steering gear contains internal inlet hose check valve If vehicle strikes pothole or bump when flow rate low, severe kickback may be felt in steering wheel © Goodheart-Willcox Co., Inc.

Inlet Hose Check Valve Check valve: Not all systems use this valve Keeps fluid from backing up through inlet hose Reduces kickback by allowing fluid in gear to absorb some shock Not all systems use this valve © Goodheart-Willcox Co., Inc.

Pressure Control Solenoid Controls pressure to steering gear valve Increases or decreases steering effort Solenoid located on rack-and-pinion steering gear (General Motors) © Goodheart-Willcox Co., Inc.

Electromagnet Some systems use electromagnet assembly Assembly located at power steering valve in rack-and-pinion steering gear © Goodheart-Willcox Co., Inc.

Electromagnet Electromagnetic assembly consists of: Permanent magnet attached to input shaft of valve Two pole pieces (also magnets) attached to output section of valve Magnetic coil installed in pinion gear housing (General Motors) © Goodheart-Willcox Co., Inc.

Control System Operation In operation, electronic steering control system components work together: To control steering system operation Regardless of type of output device used Flow control systems Pressure control systems Electromagnetic systems © Goodheart-Willcox Co., Inc.

Flow Control Systems At low vehicle speeds, module instructs flow solenoid to allow full oil flow to power steering gear Solenoid opens completely System inoperative Control module still receives and processes inputs from sensors © Goodheart-Willcox Co., Inc.

Flow Control Systems At high speeds: Rate at which steering wheel turned affects electronic steering system operation At straight-ahead cruising speeds, module reduces power steering fluid flowing to steering gear © Goodheart-Willcox Co., Inc.

Flow Control Systems Low fluid flow increases power steering effort Gives driver more control and road feel When steering wheel rotation sensor indicates steering wheel moving quickly: Module signals flow control solenoid to move to fully open position Provides full power assist needed to make quick steering maneuver at high speeds © Goodheart-Willcox Co., Inc.

Pressure Control Systems Steering gear valve contains small hydraulic pistons Pistons use power steering pump pressure to oppose movement of steering gear Extra pressure increases steering effort © Goodheart-Willcox Co., Inc.

Pressure Control Systems Electric solenoid: Operated by control module Regulates hydraulic pressure to pistons At low speeds, solenoid reduces pressure to pistons Results in minimum steering effort © Goodheart-Willcox Co., Inc.

Pressure Control Systems At higher speeds, solenoid allows pressure to pistons to increase: Increasing steering effort Improving road feel © Goodheart-Willcox Co., Inc.

Electromagnetic Systems At low speeds: Coil de-energized Power steering at maximum assist As speed increases: Module proportionally energizes coil Increasing current flow builds up magnetic field around magnets in power steering control valve © Goodheart-Willcox Co., Inc.

Electromagnetic Systems Magnetic field increases resistance between input and output sections of valve Driver input to steering gear has less effect Driver must put more effort into turning steering wheel to move steering gear Increase in effort improves road feel © Goodheart-Willcox Co., Inc.

Electric Power Steering Systems Power steering system on some late-model vehicles operated by electric motor Kinds of electric power steering: Electrohydraulic Steering conventional hydraulic type, but pump driven by electric motor, not engine-driven belt (TRW) © Goodheart-Willcox Co., Inc.

Electric Power Steering Systems Three electromechanical types have no hydraulic components Motor in these electromechanical systems is installed: (A) In steering gear and moves rack directly (B) On steering column and operates pinion gear meshed with ring gear attached to steering shaft (C) On rack and next to, and meshing with, pinion gear © Goodheart-Willcox Co., Inc.

Electric Power Steering Systems A B C (TRW) © Goodheart-Willcox Co., Inc.

Electric Power Steering Systems All electric power steering systems operate on same principles Computer controls overall system operation Computer bases decisions on inputs from sensors © Goodheart-Willcox Co., Inc.

Electric Power Steering Systems Sensor on steering column provides inputs on: Turning effort Speed of steering wheel movement Speed sensors provide vehicle speed input © Goodheart-Willcox Co., Inc.

Electric Power Steering Systems Vehicle speed inputs come from same sensors that provide inputs used to control: Automatic transmission shifting Anti-lock brake (ABS) operation © Goodheart-Willcox Co., Inc.

Electric Power Steering Systems Computer: Processes inputs Sends voltage to electric motor Amount and direction of voltage depends on inputs received from sensors © Goodheart-Willcox Co., Inc.

Electric Power Steering Systems At low speeds or during parking, computer sends high voltage to motor to provide maximum steering assist At high speeds, computer sends relatively small voltage to motor Reduces assist to increase road feel © Goodheart-Willcox Co., Inc.

Review Questions 10. True or False? Some electric power steering systems have hydraulic components. True. © Goodheart-Willcox Co., Inc.

Glossary Electronic suspension system — System that uses electronic components to control parts of the suspension system. Height sensor — Device that converts the relative position of the vehicle's body and axle into an electrical signal. Vehicle speed sensor — Sensor consisting of a toothed wheel and a small coil. Acceleration sensor — Sensor used to measure the speed of vehicle acceleration or deceleration. © Goodheart-Willcox Co., Inc.

Glossary Steering wheel rotation sensor — Sensor that determines which direction and how quickly the steering wheel is being turned. Serves as an input to the suspension system. Lateral accelerometers — Acceleration sensor mounted at a right angle (laterally) to a vehicle's centerline and used to detect body roll when the vehicle is turned sharply. Piezoelectric crystal — Crystal that produces a small electric current when pressure is applied to it. © Goodheart-Willcox Co., Inc.

Glossary Brake pressure switch — Electronic suspension system switch that closes at a preset brake system pressure to tell the control module that vehicle braking is severe. Manual control switches — Dashboard mounted driver-accessible switches used to move between soft and firm positions when desired. Suspension service switch — Switch used to disable the electronic suspension system before the vehicle is raised on a lift. © Goodheart-Willcox Co., Inc.

Glossary Control module — Electronic device that processes the signals (inputs) from the input sensors and sends a command signal (output) to the output devices. Air compressor — Component used in load-leveling systems and electronic ride control systems to provide pressurized air to the shocks or air springs. Pressure relief valve — Valve that opens to relieve excess pressure when the air pressure reaches a preset value. Control relay — Relay used to operate the compressor in a few electronic suspension systems. © Goodheart-Willcox Co., Inc.

Glossary Air exhaust valve — Operated by exhaust valve solenoid. Exhaust valve solenoid — Solenoid used in ride-height systems. The solenoid is controlled by the module and is energized to release pressure from the system when the ride height is excessive. Air drier — Component that removes moisture from air entering the air shock absorbers in an electronic suspension system. Desiccant — A chemical that has the ability to absorb moisture. © Goodheart-Willcox Co., Inc.

Glossary Air springs — Air-operated bellows used in place of both the spring and the shock absorber in some air-operated suspension systems. Flow control actuators — Solenoid and valve assembly that controls the flow of hydraulic fluid through the shock absorber. Ride relays — Electronic suspension system relays that are energized when the driver moves a dashboard switch to the soft and firm positions. Duty cycle — The percentage of time a device that is pulsed on and off, such as a flow control solenoid, is on. © Goodheart-Willcox Co., Inc.

Glossary Electronic steering control system — Steering system that provides maximum power assist at low speeds while reducing assist at higher speeds to increase road feel and steering stability. Optical sensor — Sensor that uses a photo cell, a photo diode, and a shutter assembly to sense steering wheel speed. Photo cell — Converts light beam to electrical signal. Photo diode — Creates light signal that is picked up by photocell. © Goodheart-Willcox Co., Inc.

Glossary Shutter assembly — Connected to the steering shaft and rotates with it so that as the shutter turns, slits interrupt light beam. Speed of light beam interruption determines electrical signal sent to module. Flow control solenoid — Solenoid and valve assembly used in an electronic steering control system to divert fluid flow to the pump reservoir. Inlet hose check valve — Valve that keeps fluid from backing up through the inlet hose if the vehicle strikes a pothole or a bump when the flow rate is low. © Goodheart-Willcox Co., Inc.