Electronic Suspension and Steering Systems

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

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 system

Systems vary according to:Type and number of input sensors

Whether air compressor is present

Number of wheels controlled

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

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

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

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)

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

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

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 wheels

Make changes to keep vehicle level

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)

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

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 vehicle

Detect body roll when vehicle turns sharply

(Bosch)

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

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 module

Most are two position switches

Usually on-off

Some have several positions

(Corvette)

Switches

Switches include:Brake pressure switches

Manual control switches

Suspension service switches

Door switches

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

Brake Pressure Switches

Brake switch located in brake hydraulic system

Many ride control systems do not use brake pressure input

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

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 trunk

Switch 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.

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

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

(Cadillac)

MicroprocessorUses control loop principle

Compares input information from sensors with preset information

Decides whether output devices should be activated

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

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

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

Suspension control is part of ECM or PCM

ECM 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 system

Hydraulic controls located directly at shock absorber or strut

Some use air and hydraulic components

Electronic Suspension Output Devices

Air-operated system components

Hydraulic system components

System 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 cylinder

Two check valves at top of cylinder

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

Air Compressor

Outlet valve:Remains closed when piston moves downward

Opens by pressurized air when piston moves upward

(General Motors)

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

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 relay

Control module energizes relay

Relay sends power to compressor

Relays 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 atmosphere

Through air drier

(General Motors)

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

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

Air Drier

Some driers installed ahead of compressor

Check valve in drier maintains set pressure in system

Review Questions

5. An air _____ contains a material called desiccant.

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)

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)

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

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 chambers

When used on struts, chambers sometimes called air bladders

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

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

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 firmness

Unlike air-operated systems, these systems cannot control ride height

Hydraulic systems consist of two major components:

Flow control actuators

Ride relays

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)

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

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 switch

Modify 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 selected

Lights usually consist of LEDs (light emitting diodes) mounted on switch itself (Lexus)

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

Warning Lights

Some system use dashboard-mounted warning lights

Light may be:Standard automotive bulb

Light operated by suspension control module

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)

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

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

Air pressure to either type is:Increased by air compressor

Decreased by exhaust valve

Electronic control system operates:Compressor

All associated valves and switches

Typical sensor inputs include:Ride height

Vehicle speed

Output devices are:Air compressor

Exhaust valve

Control module:Processes inputs

Issues commands to air compressor and exhaust valve solenoid

Height-sensitive system

Speed-sensitive system

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)

Distance between axle and body decreases when weight added

Height sensor lever movesTelling module that height has decreased

Module energizes compressor motorCausing compressor to send pressurized air to air springs or air shocks

Increased pressure raises vehicle body in relation to axle

When 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 solenoid

Height-sensitive system may also be used as part of combination system

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)

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

Amount vehicle is lowered varies with engine speed

System 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:

Accelerometer

Speed sensor

Brake pressure sensor

Steering 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 other

Helpful when cornering or hard braking

Manual control systems

Automatic control systems

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

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

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

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

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

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

Electronic Steering Control Systems

Electronic steering control system:Provides maximum power assist at low speeds

Reduces assist at high speeds

Increases road feel and steering stability

System functions by monitoring:Vehicle speed

Speed 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 affected

Power steering system operates normally

Dashboard mounted light warns driver of system failure

Control system components

Control system operation

Electric power steering systems

Control System Components

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

Gearbox

Connecting hoses

Control System Components

Electronic components used to modify operation of basic parts

Common electronic components:Input devices

Control module

Output devices

Input Devices

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

Vehicle speed sensor

Steering wheel rotation 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

Steering wheel rotation sensor installed in steering column

Two basic types:Electromagnetic sensor

Optical sensor(Lexus)

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

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

Photo cell

Photo diode

Shutter assembly

Photo diode creates light signal that is picked up by photocell

Photocell converts light beam to electrical signal

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

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 sensors

Sends output command to flow control solenoid

Module usually installed near steering wheel

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

Output Devices

Output devices include:Flow control solenoid

Inlet hose check valve

Pressure control solenoid

Electromagnet

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

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 valve

If 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 hose

Reduces kickback by allowing fluid in gear to absorb some shock

Not all systems use this valve

Pressure Control Solenoid

Controls pressure to steering gear valve

Increases or decreases steering effort

Solenoid located on rack-and-pinion steering gear

(General Motors)

Electromagnet

Some systems use electromagnet assembly

Assembly located at power steering valve in rack-and-pinion steering gear

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)

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

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

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

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

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

Electric solenoid:Operated by control module

Regulates 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 effort

Improving road feel

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

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

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

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

Permission granted to reproduce for educational use only.131

All electric power steering systems operate on same principles

Computer controls overall system operation

Computer bases decisions on inputs from sensors

Sensor on steering column provides inputs on:

Turning effort

Speed 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 shifting

Anti-lock brake (ABS) operation

Computer:Processes inputs

Sends 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 assist

At 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.

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