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TRANSCRIPT
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Electronic Suspension and Steering Systems
Chapter 14
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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.
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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
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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
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Electronic Suspension System Fundamentals
Basic suspension components of electronic suspension identical to those on conventional suspension systems
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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
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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)
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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
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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
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Height Sensors
Height sensor:Records position of suspension part it is attached to
Sends information to control module
Control moduleInterprets sensor signal vehicle height
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Height Sensors
Advantage of system:Control module can monitor height at all four wheels
Make changes to keep vehicle level
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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)
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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
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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
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Acceleration Sensor
Some sensors, are lateral accelerometers:
Mount at right angle to centerline of vehicle
Detect body roll when vehicle turns sharply
(Bosch)
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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
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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)
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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.
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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)
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Switches
Switches include:Brake pressure switches
Manual control switches
Suspension service switches
Door switches
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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
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Brake Pressure Switches
Brake switch located in brake hydraulic system
Many ride control systems do not use brake pressure input
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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
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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
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Suspension Service Switches
Suspension service switch usually located in trunk
Switch may be called on-off switch by some manufacturers
(Lexus)
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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.
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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
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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
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Electronic Suspension Control Module
© Goodheart-Willcox Co., Inc.
(Cadillac)
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Electronic Suspension Control Module
MicroprocessorUses control loop principle
Compares input information from sensors with preset information
Decides whether output devices should be activated
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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
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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
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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
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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
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Review Questions
3. The electronic suspension _____ processes signals (inputs) from input sensors and sends command signals (output) to output devices.
control module
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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
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Electronic Suspension Output Devices
Air-operated system components
Hydraulic system components
System lights
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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
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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
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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
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Air Compressor
Outlet valve:Remains closed when piston moves downward
Opens by pressurized air when piston moves upward
(General Motors)
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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
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Review Questions
4. How many pistons does the typical air suspension compressor have?
The typical air suspension compressor has one piston.
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Control Relay
Some compressors operated by relay
Control module energizes relay
Relay sends power to compressor
Relays may be:Electromechanical (contact point)
Power transistors
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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)
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Exhaust Valve and Solenoid
Air may be exhausted either:Directly to atmosphere
Through air drier
(General Motors)
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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
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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
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Air Drier
Some driers installed ahead of compressor
Check valve in drier maintains set pressure in system
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Review Questions
5. An air _____ contains a material called desiccant.
drier
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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)
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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)
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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
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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)
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Air Shock Absorbers/Struts
Air shock absorbers are conventional shock absorbers with sealed air chambers
When used on struts, chambers sometimes called air bladders
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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
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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
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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.
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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
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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)
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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
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Review Questions
7. Flow control actuators are used on _____ ride control systems.
hydraulic
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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
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System Lights
Electronic suspension controls use indicator lights
Installed in instrument panel
These lights used to:Indicate system status
Warn of suspension system problem
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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)
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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
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Warning Lights
Some system use dashboard-mounted warning lights
Light may be:Standard automotive bulb
LED
Light operated by suspension control module
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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)
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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
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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
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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
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Air-Operated Ride and Height Control System
Typical sensor inputs include:Ride height
Vehicle speed
Output devices are:Air compressor
Exhaust valve
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Air-Operated Ride and Height Control System
Control module:Processes inputs
Issues commands to air compressor and exhaust valve solenoid
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Air-Operated Ride and Height Control System
Height-sensitive system
Speed-sensitive system
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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)
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Height-Sensitive System
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
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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
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Height-Sensitive System
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)
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Height-Sensitive System
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
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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)
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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
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Speed-Sensitive System
Amount vehicle is lowered varies with engine speed
System does not operate until vehicle reaches cruising speeds
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Review Questions
8. A speed-sensitive suspension lowers the vehicle body as the vehicle’s speed _____.
increases
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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
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Hydraulic Damping Systems
Input sensors for hydraulic ride control system include:
Accelerometer
Speed sensor
Brake pressure sensor
Steering wheel position sensor
(Lexus)
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Hydraulic Damping Systems
Control module:Processes inputs from sensorsEnergizes solenoids at shocks or struts
Solenoid operation reduces amount of flow through fluid orifices
Firming suspension as necessary
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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
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Hydraulic Damping Systems
Manual control systems
Automatic control systems
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Electronic Steering Control Systems
Control system components
Control system operation
Electric power steering systems
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Control System Components
Basic components of electronic steering systems same as conventional steering system:
Pump
Gearbox
Connecting hoses
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Control System Components
Electronic components used to modify operation of basic parts
Common electronic components:Input devices
Control module
Output devices
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Input Devices
Two most common input sensors used in electronic steering control systems:
Vehicle speed sensor
Steering wheel rotation sensor
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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
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Steering Wheel Rotation Sensor
Steering wheel rotation sensor installed in steering column
Two basic types:Electromagnetic sensor
Optical sensor(Lexus)
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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
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Steering Wheel Rotation Sensor
Optical sensor (or optical disc) senses steering wheel speed using:
Photo cell
Photo diode
Shutter assembly
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Steering Wheel Rotation Sensor
Photo diode creates light signal that is picked up by photocell
Photocell converts light beam to electrical signal
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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
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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.
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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
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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
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Output Devices
Output devices include:Flow control solenoid
Inlet hose check valve
Pressure control solenoid
Electromagnet
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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
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Flow Control Solenoid
Module controls pulse time (or duty cycle) of solenoid
(Toyota)
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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
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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
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Pressure Control Solenoid
Controls pressure to steering gear valve
Increases or decreases steering effort
Solenoid located on rack-and-pinion steering gear
(General Motors)
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Electromagnet
Some systems use electromagnet assembly
Assembly located at power steering valve in rack-and-pinion steering gear
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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)
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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
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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
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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
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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
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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
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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
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Pressure Control Systems
At higher speeds, solenoid allows pressure to pistons to increase:
Increasing steering effort
Improving road feel
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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
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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
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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)
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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
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Electric Power Steering Systems
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(TRW)
A B C
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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
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Electric Power Steering Systems
Sensor on steering column provides inputs on:
Turning effort
Speed of steering wheel movement
Speed sensors provide vehicle speed input
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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
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Electric Power Steering Systems
Computer:Processes inputs
Sends voltage to electric motor
Amount and direction of voltage depends on inputs received from sensors
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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
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Review Questions
10. True or False? Some electric power steering systems have hydraulic components.
True.