electronic suspension control module

Permission granted to reproduce for educational use only.1© Goodheart-Willcox Co., Inc.


Electronic Suspension and Steering Systems

Chapter 14


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.


Electronic Suspension System Fundamentals

Electronic suspension system uses electronic components to control parts of suspension systemSystems vary according to:

Type and number of input sensorsWhether air compressor is presentNumber of wheels controlled


Electronic Suspension System FundamentalsAll systems control operation of shock absorbers or strut cartridgesMost 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 compressorControl ride quality but not ride heightRegulate hydraulic flow through shock absorber internal parts


Electronic Suspension System Fundamentals

Basic suspension components of electronic suspension identical to those on conventional suspension systems


Electronic Suspension Input Sensors

Variety of input sensors usedMost systems use one or more:

Height sensorsVehicle speed sensorsAcceleration sensorsSteering wheel rotation sensorsSwitches


Height Sensors

Height sensor converts position of vehicle body and axle into electrical signal

Some vary electrical resistance as distance changesSome vary magnetic field of current passing through sensor as distance changes

(Buick)


Height Sensors

When current flow varies, voltage variesControl module reads change in voltage as change in heightSensor usually installed on body or frameLinkage connects sensor to axle or control armWhen weight added or removed from vehicle, body moves in relation to axle


Height SensorsWhen system compensates for weight change:

Lever moves in opposite directionMovement 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


Height Sensors

Height sensor:Records position of suspension part it is attached to Sends information to control module

Control moduleInterprets sensor signal vehicle height


Height Sensors

Advantage of system:Control module can monitor height at all four wheelsMake changes to keep vehicle level


Vehicle Speed Sensor

Vehicle speed sensor either attached:

To output shaft of transmission or transaxleIn differential of rear-wheel drive vehicle

Consists of:Toothed wheel Small coil

Uses magnetism to create AC signal(Toyota)



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 sensorECM also directs speed input to suspension control module


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


Acceleration Sensor

Some sensors, are lateral accelerometers:

Mount at right angle to centerline of vehicleDetect body roll when vehicle turns sharply

(Bosch)


Acceleration Sensor

Modern accelerometer consists of:Piezoelectric crystalWeight

Changes in speed and direction cause weight to press on crystal

Crystal produces small electrical currentlySignal is sent to control module


Steering Wheel Rotation Sensor

Some vehicles use steering wheel rotation sensor as input to suspension systemSensor determines:

Which direction steering wheel is turnedHow quickly steering wheel is turned

(Nissan)


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.


Switches

Switches are on-off devices that send specific signal to control moduleMost are two position switches

Usually on-off Some have several positions

(Corvette)


Switches

Switches include:Brake pressure switchesManual control switchesSuspension service switchesDoor switches


Brake Pressure Switches

Brake system hydraulic pressure increases when vehicle brakes hardBrake pressure switch closes at preset pressureWhen switch closes, voltage signal is sent to module

Tells module vehicle braking is severe


Brake Pressure Switches

Brake switch located in brake hydraulic systemMany ride control systems do not use brake pressure input


Manual Control Switches

Manual control switches:Driver-accessible switches mounted on dashboardUsed to move between soft and firm positions when desired

Manual switches usually have two or three positions


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


Suspension Service Switches

Suspension service switch usually located in trunkSwitch may be called on-off switch by some manufacturers

(Lexus)


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.


Door Switches

Door switch:Type of input switchInforms ride control system that someone is entering or leaving vehicleMost electronic suspension systems do not use door switch input


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

Permission granted to reproduce for educational use only.30


© Goodheart-Willcox Co., Inc.

(Cadillac)



MicroprocessorUses control loop principleCompares input information from sensors with preset informationDecides whether output devices should be activated



Control module has delay mechanism that prevents system activation for 5-10 secondsDelay mechanism keeps system from operating excessively when vehicle driven over rough roads



Most modern modules have data link connectorSome electronic suspension systems electrically connected to ECM or PCMDiagnostic connector of ECM/PCM retrieves suspension system trouble codes and other information



Control module can be located anywhere on vehicle

Under the hoodDashboardUnder a seatIn trunk

Ride-height suspension modules may be single units with height sensor Some vehicles do not have separate module



Suspension control is part of ECM or PCMECM or PCM receives sensor inputs and makes ride control decisions based on inputs


Review Questions

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

control module


Electronic Suspension Output Devices

Output of electronically controlled suspension system may be either:

Air pressure system similar to that of conventional air shock systemHydraulic controls located directly at shock absorber or strutSome use air and hydraulic components


Electronic Suspension Output Devices

Air-operated system componentsHydraulic system componentsSystem lights


Air-Operated System Components

Output devices found in air-operated suspension systems include:

Air compressorControl relayExhaust valve and solenoidAir drierAir lines and fittingsAir springsAir shock absorbers/struts


Air Compressor

Most common air compressor used in air-operated systems:

Single-piston compressor driven by small electric motor

Compressor consists of:Piston and cylinderTwo check valves at top of cylinder


Air Compressor

Check valves arranged so that:When piston moves down in cylinder, inlet valve opens by atmospheric pressureWhen piston moves up, pressure increase closes inlet valve


Air Compressor

Outlet valve:Remains closed when piston moves downwardOpens by pressurized air when piston moves upward

(General Motors)


Air Compressor

Compressor assembly contains either:Pressure relief valvePressure relief switch

When preset pressure value reached:Valve opens to relieve pressureSwitch opens to de-energize motor• When pressure drops, switch closes and

voltage supplied to motor• Switch may be replaced by relay


Review Questions

4. How many pistons does the typical air suspension compressor have?

The typical air suspension compressor has one piston.


Control Relay

Some compressors operated by relayControl module energizes relayRelay sends power to compressorRelays may be:

Electromechanical (contact point)Power transistors


Exhaust Valve and Solenoid

Air exhaust valve operated by exhaust valve solenoidSolenoid:

Controlled by moduleEnergized to release pressure from system when ride height excessive

(Chevrolet)


Exhaust Valve and Solenoid

Air may be exhausted either:Directly to atmosphereThrough air drier

(General Motors)


Air Drier

Air drier keeps moisture from entering shock absorbers

Contains chemical called desiccantDesiccant absorbs moisture

Air entering system from compressor passes through drier and moisture removed


Air Drier

Filter keeps desiccant from entering other parts of systemWhen air is released from system, it passes through drier and takes some moisture with it

Keeps desiccant from being overloaded with moisture


Air Drier

Some driers installed ahead of compressorCheck valve in drier maintains set pressure in system


Review Questions

5. An air _____ contains a material called desiccant.

drier


Air Lines and Fittings

Air lines connect other air system partsAir lines made of plastic tubingAir line diameter about 1/32'' (0.8 mm)


Air Lines and Fittings

Fitting at end of each air line used to attach line to other componentsFittings:

Keep lines from blowing off under pressureSeal against leaks

(Lexus)


Air Springs

Air springs used in place of both spring and shock absorber in some air-operated systemsBasic component of air spring is rubber diaphragm, or membraneDiaphragm installed between lower control arm and vehicle body


Air Springs

Filling diaphragm with air causes it to expandAs diaphragm expands, it pushes body upwardWhen air removed, diaphragm collapses, allowing body to drop down

(Ford)


Air Shock Absorbers/Struts

Air shock absorbers are conventional shock absorbers with sealed air chambersWhen used on struts, chambers sometimes called air bladders



Compressed air can be added to chambers to:

Compensate for vehicle loadingIncrease ride height

Sealed chamber exerts pressure on shock interiorPressure causes shock to try to expand



As shock expands, it pushes upward against vehicle weight, causing rear of vehicle to riseAir shocks or struts installed in same location as conventional shocks and struts


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.


Hydraulic System Components

On vehicles without air compressor, internal hydraulic system of shock or strut controlled to vary ride firmnessUnlike air-operated systems, these systems cannot control ride heightHydraulic systems consist of two major components:

Flow control actuatorsRide relays


Flow Control Actuators

Electric flow control actuators installed in shocks or struts

Actuator is electric solenoid that operates flow control valveValve controls flow of hydraulic fluid through shock

(General Motors)


Flow Control Actuators

Most flow control solenoids pulse on and offOn for certain percentage of time vehicle is operating

Percentage may be called duty cycleSolenoid and valve assembly located in shock or strut


Review Questions

7. Flow control actuators are used on _____ ride control systems.

hydraulic


Ride Relays

Some systems with flow control solenoids have soft and firm ride relays

Relays energized from dashboard switchModify computer input to compensate for driver preferences


System Lights

Electronic suspension controls use indicator lights

Installed in instrument panel These lights used to:

Indicate system status Warn of suspension system problem


Status Lights

Some vehicles have lights at manual control switch to indicate which ride status or mode has been selectedLights usually consist of LEDs (light emitting diodes) mounted on switch itself (Lexus)


Status Lights

Some status lights used to indicate problemsSystem has defect if:

All lights are on at onceLights flash on and off

Some lights are located on center console


Warning Lights

Some system use dashboard-mounted warning lightsLight may be:

Standard automotive bulbLED

Light operated by suspension control module


Warning Lights

Most warning lights come on briefly when vehicle started to check module and light operationIf light is illuminated at any other time, system has defect

(Nissan)


Types of Electronic Suspension Systems

Three general types of electronically controlled suspension systems:

Air-operated ride and height control systemHydraulic ride control systemCombination system using both air and hydraulic controls


Air-Operated Ride and Height Control System

Air-operated ride and height controls use one of two height adjustment devices:

Air springsAir shock absorbers



Air pressure to either type is:Increased by air compressorDecreased by exhaust valve

Electronic control system operates:CompressorAll associated valves and switches



Typical sensor inputs include:Ride heightVehicle speed

Output devices are:Air compressorExhaust valve



Control module:Processes inputsIssues commands to air compressor and exhaust valve solenoid



Height-sensitive systemSpeed-sensitive system


Height-Sensitive System

Height-sensitive system varies pressure delivered to air springs or air shocks based on ride height inputModule operation of compressor and pressure relief valve solenoid controls ride height

(General Motors)



Distance between axle and body decreases when weight added Height sensor lever moves

Telling module that height has decreasedModule energizes compressor motor

Causing compressor to send pressurized air to air springs or air shocks



Increased pressure raises vehicle body in relation to axleWhen module determines height has returned to normal, it de-energizes compressor motor



When extra weight removed, distance between axle and body increasesHeight sensor lever moves in opposite directionHeight sensor input causes module to energize exhaust valve solenoid

Exhaust valve opens (General Motors)



Air pressure exits systemBody moves downward

When height returns to normal, module de-energizes exhaust valve solenoidHeight-sensitive system may also be used as part of combination system


Speed-Sensitive System

Speed-sensitive suspension lowers vehicle body as speed increasesAccomplished by reducing air pressure in shocks or struts as speed increasesWhen speed is reduced, air compressor energizes, causing vehicle height to increase

(Ford)



Control module receives input directly from vehicle speed sensor or by way of ECM or PCMWhen vehicle reaches preset speed:

ECM or PCM releases air pressure from air springs or shocks Vehicle is lowered



Amount vehicle is lowered varies with engine speedSystem does not operate until vehicle reaches cruising speeds


Review Questions

8. A speed-sensitive suspension lowers the vehicle body as the vehicle’s speed _____.

increases


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



Input sensors for hydraulic ride control system include:

AccelerometerSpeed sensorBrake pressure sensorSteering wheel position sensor

(Lexus)



Control module:Processes inputs from sensorsEnergizes solenoids at shocks or struts

Solenoid operation reduces amount of flow through fluid orifices

Firming suspension as necessary



Control module can control individual solenoids

Results in variations in firmness from one side of vehicle to otherHelpful when cornering or hard braking



Manual control systemsAutomatic control systems


Manual Control Systems

Instrument panel switch controls manual systemSwitch may be:

Two-position, generally on-off switchThree-position switch, with additional “automatic” (or auto) position• Automatic control takes over when selected


Automatic Control Systems

Control module operates automatic system based on inputs from sensorsInputs include:

AccelerometerVehicle speed sensorSometimes steering wheel and brake sensors


Automatic Control SystemsSystem stiffens suspension when sensors signal firmer suspension neededWhen accelerometer input indicates vehicle being braked hard:

Module signals control solenoids, or actuators, in shocks/struts to closeDamping effect increased

Increased shock firmness reduces tendency of vehicle to dive during hard braking


Automatic Control Systems

When input indicates hard braking over:Module signals solenoids to allow normal flow through shocks or strutsRide quality returns to normal settings for maximum passenger comfortSystem performs similar function when vehicle accelerated or cornered hard


Combination Systems

Combination system consists of both:Air-operated shock absorbersHydraulic damping valves

System performs functions of air-operated system:

Height controlLowering at cruising speeds


Combination Systems

System performs functions of hydraulic system:

Control of body level during heavy acceleration, braking, or corneringVarying ride feel

Operation of system similar to operation of individual systems


Electronic Steering Control Systems

Electronic steering control system:Provides maximum power assist at low speedsReduces assist at high speedsIncreases road feel and steering stability



System functions by monitoring:Vehicle speedSpeed at which steering wheel is turned

System uses this information to control output of power steering pump



If electronic steering control system fails:

Power steering pump output is not affectedPower steering system operates normally

Dashboard mounted light warns driver of system failure



Control system componentsControl system operationElectric power steering systems


Control System Components

Basic components of electronic steering systems same as conventional steering system:

PumpGearboxConnecting hoses


Control System Components

Electronic components used to modify operation of basic partsCommon electronic components:

Input devicesControl moduleOutput devices


Input Devices

Two most common input sensors used in electronic steering control systems:

Vehicle speed sensorSteering wheel rotation sensor



Vehicle speed sensor operates in same manner as described earlier

ac signal created in sensorSensor signals ECM or PCMECM or PCM sends speed reading to steering control module



Steering wheel rotation sensor installed in steering columnTwo basic types:

Electromagnetic sensorOptical sensor(Lexus)



Electromagnetic sensor creates variable ac voltageOperates in same manner as wheel speed sensorFrequency sent to control module as steering wheel turning speed signal



Optical sensor (or optical disc) senses steering wheel speed using:

Photo cellPhoto diodeShutter assembly



Photo diode creates light signal that is picked up by photocellPhotocell converts light beam to electrical signal



Shutter:Connected to steering shaftRotates with it

As shutter turns, slits interrupt light beamHow fast light beam interrupted determines electrical signal sent to module


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.


Control Module

Control module:Processes inputs from vehicle and steering wheel speed sensorsSends output command to flow control solenoid

Module usually installed near steering wheel


Output Devices

Several devices used to control steering effort in power steering systemSome mounted on power steering pumpOthers installed on steering gearSystems will have only one type of output device


Output Devices

Output devices include:Flow control solenoidInlet hose check valvePressure control solenoidElectromagnet


Flow Control Solenoid

Flow control solenoid and valve assembly:

Diverts flow to pump reservoirInstalled in outlet line of power steering pumpPulses on and off to control amount of fluid diverted


Flow Control Solenoid

Module controls pulse time (or duty cycle) of solenoid

(Toyota)


Inlet Hose Check Valve

Inlet to power steering gear contains internal inlet hose check valveIf vehicle strikes pothole or bump when flow rate low, severe kickback may be felt in steering wheel


Inlet Hose Check Valve

Check valve:Keeps fluid from backing up through inlet hoseReduces kickback by allowing fluid in gear to absorb some shock

Not all systems use this valve


Pressure Control Solenoid

Controls pressure to steering gear valveIncreases or decreases steering effortSolenoid located on rack-and-pinion steering gear

(General Motors)


Electromagnet

Some systems use electromagnet assemblyAssembly located at power steering valve in rack-and-pinion steering gear


Electromagnet

Electromagnetic assembly consists of:

Permanent magnet attached to input shaft of valveTwo pole pieces (also magnets) attached to output section of valveMagnetic coil installed in pinion gear housing

(General Motors)


Control System Operation

In operation, electronic steering control system components work together:

To control steering system operationRegardless of type of output device used

Flow control systemsPressure control systemsElectromagnetic systems


Flow Control Systems

At low vehicle speeds, module instructs flow solenoid to allow full oil flow to power steering gear

Solenoid opens completelySystem inoperativeControl module still receives and processes inputs from sensors



At high speeds:Rate at which steering wheel turned affects electronic steering system operationAt straight-ahead cruising speeds, module reduces power steering fluid flowing to steering gear



Low fluid flow increases power steering effort

Gives driver more control and road feelWhen 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


Pressure Control Systems

Steering gear valve contains small hydraulic pistonsPistons use power steering pump pressure to oppose movement of steering gearExtra pressure increases steering effort



Electric solenoid:Operated by control moduleRegulates hydraulic pressure to pistons

At low speeds, solenoid reduces pressure to pistons

Results in minimum steering effort



At higher speeds, solenoid allows pressure to pistons to increase:

Increasing steering effortImproving road feel


Electromagnetic Systems

At low speeds:Coil de-energizedPower steering at maximum assist

As speed increases:Module proportionally energizes coilIncreasing current flow builds up magnetic field around magnets in power steering control valve


Electromagnetic Systems

Magnetic field increases resistance between input and output sections of valve

Driver input to steering gear has less effectDriver must put more effort into turning steering wheel to move steering gearIncrease in effort improves road feel


Electric Power Steering Systems

Power steering system on some late-model vehicles operated by electric motorKinds of electric power steering:

Electrohydraulic• Steering conventional

hydraulic type, but pump driven by electric motor, not engine-driven belt

(TRW)



Three electromechanical types have no hydraulic componentsMotor 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



All electric power steering systems operate on same principles

Computer controls overall system operationComputer bases decisions on inputs from sensors



Sensor on steering column provides inputs on:

Turning effortSpeed of steering wheel movement

Speed sensors provide vehicle speed input



Vehicle speed inputs come from same sensors that provide inputs used to control:

Automatic transmission shiftingAnti-lock brake (ABS) operation



Computer:Processes inputsSends voltage to electric motor

Amount and direction of voltage depends on inputs received from sensors



At low speeds or during parking, computer sends high voltage to motor to provide maximum steering assistAt high speeds, computer sends relatively small voltage to motor

Reduces assist to increase road feel


Review Questions

10. True or False? Some electric power steering systems have hydraulic components.

True.

electronic suspension control module

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