steering systems - goodheart-willcox · pdf fileall steering systems contain several common...

After studying this chapter, you will be able to:� Identify and explain the operation and components of steering wheels, columns, and related

parts.� Explain the operation of conventional steering systems.� Identify the components of conventional steering systems.� Explain the operation of rack-and-pinion steering systems.� Identify the components of rack-and-pinion steering systems.� Explain the operation of power steering systems.� Identify the components of power steering systems.� Identify the major types of power steering systems.� Explain the operation of four-wheel steering systems.� Identify the components of four-wheel steering systems.

Technical Terms

167

Chapter 9

Steering Systems

Telescoping steering columnsSteering armSteering stopsBall socketsTie rod endsSteering ratioRack-and-pinion steeringConventional steering systemsPitman armRelay rodDrag linkConnecting rod Idler arm

ReservoirPower steering pumpFlow regulatorPressure regulatorPower pistonRotary valveLinear control valveFour-wheel steeringHydraulic/electronic four-wheelsteering system

Electromechanical four-wheel steering

Road feelSteering wheelMaster splineHorn switchAir bagClockspringSteering shaftsCollapsible shaftTelescoping shaftsSteering couplerUniversal jointsAdjustable steering columnsTilt steering wheel

This sample chapter is for review purposes only. Copyright © The Goodheart-Willcox Co., Inc. All rights reserved.

168 Auto Suspension and Steering

Introduction

The steering system components are a commonsource of driver complaints. Tire wear is almost completelydependent on the condition and adjustment of the steeringcomponents. This chapter covers the construction andoperation of both conventional and rack-and-pinion steering systems. Study this chapter carefully.

Note: Chapters 13 and 14 will cover electronically controlled steering systems.

The Job of the Steering System

The steering system is a group of parts that transmitthe movement of the steering wheel to the front, and sometimes the rear, wheels. The primary purpose of thesteering system is to allow the driver to guide the vehicle.When a vehicle is being driven straight ahead, the steeringsystem must keep it from wandering without requiring thedriver to make constant corrections.

The steering system must also allow the driver to havesome road feel (feedback through the steering wheel aboutroad surface conditions). The steering system must helpmaintain proper tire-to-road contact. For maximum tirelife, the steering system should maintain the proper angle

between the tires both during turns and straight-ahead driving. The driver should be able to turn the vehicle with little effort, but not so easily that it is hard to control.

Common Steering System Parts

All steering systems contain several common parts.Every steering system, no matter what type, will have asteering wheel, a steering shaft and column, a flexible coupler, universal joints, steering arms, and ball sockets.These parts are discussed below.

Steering WheelsThe only part of the steering system the average driver

is familiar with is the steering wheel. Older wheels aremade of hard plastic, are larger in diameter, and are relatively thin when compared to modern steering wheels.The modern steering wheel is generally padded. Moststeering wheels have two or three spokes or a large centersection that connects the wheel portion to the hub. To prevent slippage, the steering wheel hub has internalsplines, which match external splines on the steering shaft.Some shafts and steering wheels have a master spline,which is larger than the others. The master spline preventsthe installation of the wheel in the wrong position. A largenut holds the hub to the steering shaft, Figure 9-1.

Steering wheel hubretaining nut

Steering wheel

SIR coil andcombination

switch assembly

Steering shaft

Column cover

Steering column

Steeringshaftjoint

Ignitionswitch

Column cover

Hub

Air bag(when used)

Figure 9-1. A large nut holds the steering wheel hub to the steering shaft. (General Motors)

Chapter 9 Steering Systems 169

Steering Wheel SizeThe steering wheel size has an effect on the effort

expended by the driver to turn the vehicle. The larger thewheel, the less effort needed to turn it. This is due to theleverage exerted by the larger wheel.

Steering Wheel AttachmentsSteering wheels contain other parts, which are

discussed below. While not directly related to the steeringsystem, these parts may require removal when the steeringwheel is serviced.

Horn SwitchThe horn switch, or horn pad, is always mounted on

the steering wheel, Figure 9-2. When an emergencyoccurs, the driver’s hands are already on the steeringwheel, and little movement is required to reach and pressthe horn switch. Some horn switches are easily observablebuttons, while others are built into the steering wheel andare operated by squeezing or pressing the vinyl cover overthe wheel or the spokes.

A horn switch has electrical contacts that connect therotating steering wheel components to the rest of the vehicle’s electrical system. Stationary brass or copper ringsin the steering column touch sliding or rolling contacts inthe wheel assembly. The sliding or rolling contacts brushagainst the rings as the wheel is turned, maintaining electrical contact at all times.

Air BagIn most late-model vehicles, the center of the steering

wheel also contains an air bag, Figure 9-3. Air bag is a general term given to devices that inflate to protect thevehicle’s occupants during a collision. In most manufac-turers’ service literature, however, an air bag is referred toas a supplemental inflatable restraint, or SIR. The air baginflates rapidly (within 1/10 of a second) if the vehicle isinvolved in a collision. Air bag inflation is often calleddeployment.

In addition to the steering wheel-mounted air bag,many vehicles have an additional air bag mounted in thedashboard on the passenger side of the vehicle. Somemodern vehicles are equipped with side air bags, whichwill deploy if the vehicle is struck from the side.

Most air bag systems are designed to deploy only ifthe vehicle is involved in a frontal collision (within a certain number of degrees of its centerline). During animpact, electronic impact sensors, which are oftenmounted in the front portion of the vehicle, tell the air bagcontrol module that a collision has occurred. The controlmodule then sends a current to an air bag squib. The squibgenerates heat, igniting a flammable substance in the bag.As the flammable substance burns, it creates a largeamount of a harmless gas. The gas expands and causes thebag to inflate. The sequence of events that results in air baginflation is shown in Figure 9-4.

To prevent unnecessary air bag deployment, atleast two impact sensors must indicate a collision. Mostvehicles have at least one primary impact sensor, aswell as a safing sensor, which confirms a collision hastaken place. On some newer vehicles, the impact sen-sors are mounted in the air bag control module in thepassenger compartment.

Air bag control modules often contain a reservepower supply that allows the air bag system to operateeven if the rest of the vehicle loses electrical power. Thereserve power supply can retain power for up to 30 min-utes after the ignition is switched off.

Most steering wheel–mounted air bags use a clockspring to provide an electrical connection between the steering wheel and the steering column. See Figure 9-5. The clockspring consists of a flat wire,sometimes called a ribbon wire, wound into a coil. Thewire coil is called a clockspring because it resembles themainspring of a mechanical clock. One end of the clock-spring is attached to the air bag system electrical connector in the stationary steering column. The other endof the clockspring is attached to the air bag electrical connector in the steering wheel. The clockspring coils and

Horn pad/air bag

Air bag wire lead

Wire connector

Steeringwheel nut

Airbag

Horn wireSteering wheel

Figure 9-2. The horn buttons or pad is mounted on the steeringwheel. (Jeep)


uncoils as the steering wheel is turned. Using a clockspringensures that there is always a complete electrical circuitbetween the air bag squib and the rest of the air bag system, regardless of the position of the steering wheel.

Steering Columns and ShaftsThe steering shaft is installed in the steering column.

Bearings are generally used to hold the shaft in position.The shaft and column assembly is usually removed andreplaced as a unit. However, individual parts are oftenreplaced without removing the shaft or column. In this section, we will discuss the individual parts that make upthe steering column and shaft assembly.

Shaft DesignModern steering shafts are made of two sections of

steel rod. One section is hollow and the other is solid. Thesolid section slides into the hollow section. See Figure 9-6.

Air bag

Air bag warninglight

Frontimpactsensor

Clockspringassembly

Air bag control moduleFront impactsensor

Figure 9-3. Typical air bag system. Note the location of the impact sensors, the air bag control module, and the clockspring assembly. (Toyota)

Powersource

Ignitioncontrol &

drive circuit

Frontimpact

sensors

Safingsensors

Squib

Gasgenerant

InflatorAir bag

ImpactCollision

Air bag system diagram

Figure 9-4. Air bag activation sequence. At least one front impact sensor and the safing sensor must be triggered to cause deployment. (Toyota)

Clockspring

Air bag lead

Figure 9-5. Cutaway of an air bag clockspring. This type ofclockspring is common. (Toyota)


This design allows the steering shaft to collapse whenthe vehicle is in a collision. For this reason it is called a collapsible shaft. Collapsible shafts are often referred to astelescoping shafts, since the shaft length is reduced as onesection of the shaft slides into the other in the same way aportable telescope is collapsed.

During normal driving, the two halves of the steeringshaft are held in position by shear pins. Shear pins are purposely made of a relatively weak material, usually plastic. Their purpose is to break when sufficient pressureis placed on them, preventing injury to the driver. If a collision occurs that is severe enough to cause the driver tostrike the steering wheel, the shear pins break, allowing theshaft to collapse.

Steering CouplersA flexible steering coupler is installed at the bottom of

the steering shaft, just before the steering gear. This couplerallows for slight variations in the alignment between theshaft and steering gear. It also absorbs vibrations. The disc coupler is usually a flexible rubber disc, as shown in Figure 9-7. The steering shaft contains a yoke that is connected to the disc at two points opposite each other

(180° apart). Another yoke is connected to the disc at 90°from the shaft connection. This yoke is attached to the stubshaft that leads into the steering gear, or it may be attachedto an intermediate steering shaft. The rubber disc transmitsturning effort while absorbing small vibrations from theother parts of the steering system. The yokes are designedto provide a connection if the flexible coupling breaks.Some vehicles with one or more universal joints do not usea steering coupler.

Steering UniversalsOn many newer cars, there is not enough clearance to

allow the steering shaft to make a straight connection withthe steering gear. Therefore, the upper and lower shaftsmust be offset through the use of universal joints. Steeringshaft universal joints allow the shaft to turn through anangle. Universal joints consist of a center cross that connects two yokes. Each yoke is connected to one part ofthe steering shaft. The yokes can twist as they rotate. Thisallows the centerline of the steering shaft to change. Figure 9-8 shows a typical universal joint installed on asteering shaft.

Figure 9-6. A two-piece steering shaft assembly. (General Motors)

Attaching yoke(to upper

steering shaft)

Crossstrap

Flexiblecoupler

Cross strap

Yoke

Lower steering shaft

Figure 9-7. A flexible rubber steering coupler. (General Motors)

Coupling shield

Flexiblecoupling

Bolt

Lowerintermediate

shaft

Seal Spring

Nut

Jointcoupling

Bolt

Upper intermediateshaft


Column DesignThe steering column is the support and cover for the

steering shaft and other steering wheel–mounted components and wiring. Shaft bearings are ball or rollerbearings installed at the top and bottom of the steering column to allow the steering shaft to turn with no resist-ance. The steering column is attached to the underside ofthe dashboard, usually through studs and nuts. Many of the column attachment holes are slotted to allow for steering column adjustment. On some vehicles, the bottomof the column is attached to the firewall.

The upper part of the steering column is usually somewhat larger in diameter to hold the driver-operatedcomponents, as well as the air bag clockspring. The steering column usually contains the turn signal indicatorstalk, Figure 9-9. In addition to controlling the turn signals,the modern turn signal stalk may also be used to operatethe cruise control, the windshield wipers, and the high-beam selector.

On most modern vehicles, the ignition switch isinstalled inside the steering column. The ignition lockassembly is installed on the column and connected to the

switch by a metal rod. On some vehicles, the steering column contains the gearshift indicator and selector lever.Neutral safety switches and vacuum parking brake releaseswitches may also be located on the lower portion of thesteering column.

The steering column is collapsible, although its designis somewhat different from that of the steering shaft. Thelower section of the steering column is perforated andresembles a heavy screen, Figure 9-10. If the driver hits thesteering wheel during an accident, the perforated area willbend, allowing the column to collapse.

Universaljoint


Uppersteering shaft

Columnassembly

Figure 9-8. This steering shaft assembly uses a universal joint.(Toyota)

Steeringcolumn

Cover

Turn signalindicator

stalk

Cruise controlwire connections

Figure 9-9. Cutaway view of a steering column showing the turnsignal stock (lever) assembly. Stock assemblies vary in function,shape, etc. (General Motors)

Perforated section ofsteering column

Positionarm

PRNDL cable

Adjustable Steering ColumnsSome steering columns can be adjusted to change the

position of the steering wheel. Adjustable steeringcolumns make driving more comfortable for people whoare shorter or taller than average. Changing the wheel posi-tion can also make long trips more comfortable.

On a tilt steering wheel, the steering column is sectioned at the top and can pivot. The upper part of thesteering shaft is equipped with a universal joint. There maybe an extra bearing at the tilt mechanism to further supportthe shaft. A lock holds the steering column in position asthe vehicle is driven. A lever mounted on the steering column releases the lock when the driver wants to changethe steering wheel position. The design of a typical tiltsteering column is shown in Figure 9-11.

Telescoping steering columns are designed so that thesteering wheel can be moved either toward or away fromthe driver. The telescoping parts of a steering columninclude a solid steering shaft section inside a hollow shaftsection. This assembly is called a telescopic shaft. Duringnormal driving, a locking mechanism holds the telescopicshaft in position. Moving a lever on the steering columnallows the driver to release the lock and move the steeringwheel. When the lever is released, the column is locked inthe new position. See Figure 9-12.

Figure 9-10. This collapsible steering column has a perforatedsteering column tube. (Chrysler)


Clock-spring

Turn signalswitch

Wiper/dimmer switch

Turn signal cancel cam

Shaft lock

Steering columnhousing assembly

Lock housing

Steering shaftassembly

Interlock solenoid

Shifttube

Gearshiftlever bowl

Column supporthousing assembly

Columnjacket

Ignitionswitch

Bearingassembly

Figure 9-11. Exploded view of an adjustable steering column (tilt steering wheel). This column is equipped with a clockspring, whichconnects to the air bag. Study the construction. (General Motors)


steering stops are adjustable, but most are not. See Figure 9-16. A few manufacturers locate the steering stopson the pitman arm, Figure 9-17.

Ball SocketsSince many parts of the steering linkage move in

relation to each other, it is necessary to have a flexible connection between them. Ball sockets are used to makethis flexible connection. The internal parts of the ballsocket resemble those of a ball joint, Figure 9-18. Thebearing surfaces of the ball socket form a sliding surface forthe transfer of motion. To reduce wear and vibration, ballsockets are preloaded (placed under tension). A smallspring or rubber ring is installed under one of the bearingsurfaces to create this tension.

Like ball joints, ball sockets are used to transfer loadswhile rotating and moving both horizontally and vertically.Unlike ball joints, ball sockets do not transfer vehicleweight downward. Instead, they transfer steering effortsideways. Therefore, the loads placed on a ball socket arehorizontal (side to side) rather than vertical (up and down).

Some ball sockets are self-contained units, such as theassembly shown in Figure 9-19. The ball socket is attachedto the steering knuckle by a threaded and tapered stud. Theother end is a threaded section, which is installed intomatching threads in another part of the steering linkage.The threaded section can have internal or external threads,depending on the linkage design. Ball sockets used to connect the steering linkage to the steering knuckle arecalled tie rod ends.

Grease fitting

NutSteering

arm

Axlehousing

Steeringknuckle

Bolt

Figure 9-14. This steering arm is bolted to the steering knuckle.(General Motors)

Steeringarm

Steering knuckle

Hub assembly

Figure 9-15. In this steering knuckle assembly, the steering armis an integral part of the knuckle. (Corvette)

Projection oncontrol arm

Contactpoints

Movableknuckle

Figure 9-16. This vehicle has nonadjustable steering stops on both the steering knuckle and the control arm. (General Motors)


Steering Arms and Ball SocketsAll vehicles use steering arms and ball sockets to

transmit motion from the steering gear, through the steeringlinkage, and into the steering knuckles.

Steering ArmThe steering arm converts the linear (back-and-forth)

motion of the steering linkage to the rotating motion of thesteering knuckle. See Figure 9-13. The steering arms oneach side of the vehicle are shaped to allow the relativeposition of the wheels to change as the vehicle is turned.This position change, called toe out on turns, will be dis-cussed in more detail in Chapters 15 and 16. Asteering arm can be bolted to the steering knuckle, Figure 9-14, or may be cast as an integral part of the steering knuckle, Figure 9-15.

The steering arm usually contains the steering stops,or tie stops. These are projections on the arm that keep thewheels from being turned too far in either direction. Some

Pivot point

Lock pin

Tilt lever

Telescopic lever

Standard position

Telescopic shaft Threadedportion

Lock shaft

Telescopic leverLock key

Steering shaft

Figure 9-12. Telescopic steering column.

Steering lowershaft

Tie rod

Drag rodPitman

arm Steeringgear box

Steering upper shaft

Steeringwheel

Steeringarm

Figure 9-13. Turning the steering wheel to the right or leftmoves the tires in the desired direction. The steering gear pit-man arm changes rotational motion to a linear (side-to-side)motion through the use of steering linkage. (Suzuki)


Ball sockets are used on other parts of the steeringlinkage. The ball and socket section is often part of the linkage component, and the entire component must bereplaced when the ball socket wears out.

Types of Steering Systems

Two main types of steering systems are used on modern cars and light trucks: the rack-and-pinion systemand the conventional, or parallelogram linkage, steeringsystem. On automobiles, the conventional system was theonly type used until the 1970s. It has been almost completely replaced by rack-and-pinion steering. Manylight trucks continue to use the conventional system. Thetwo types of systems are discussed below.

Note: The steering gear assembly isreferred to by many names. For clarity, wewill refer to the mating internal gears, the

related internal parts, and the housing as the steeringgear.

Steering RatioSteering ratio is the relative number of turns of the

steering wheel compared to the movement of the wheels.If the steering wheel must be turned one revolution to turnthe front wheels one sixteenth of a turn, the steering ratiois 1 to 1/16. Reversing the numbers gives a ratio of 16 to 1,or 16:1. Although the steering ratio is not as critical onmodern vehicles with power steering, it must be carefullyselected as a compromise between handling and steeringeffort. The average steering ratio on modern vehiclesranges from 12:1 to 24:1. A heavy vehicle will have ahigher ratio than a lighter vehicle. If the vehicle has powersteering, the ratio will be lower than that on the same vehi-cle with manual steering.

Steering ratio affects the response of the front wheelsto the movement of the steering wheel (handling) and theease of turning the wheel. A small steering ratio means thatslight steering wheel movement will turn the front wheels,but the effort required to turn the steering wheel will be relatively high. A large steering ratio means that more turnsof the steering wheel are needed to turn the front wheels,but that the steering effort is less. A relatively high steeringratio also helps to absorb shocks from the road. If forinstance the steering ratio is 16:1, road shocks are transmitted to the steering wheel at 1/16 of their originalintensity.

Steering ratio, as well as overall handling and ease ofsteering, is determined by many factors. The size of thesteering wheel was already mentioned. The relative size of

Steering gear

Framebracket

Pitman armstop bolt

ClearancesettingPitman

arm

Tie rodLocknut

Cotter pin

Dust boot

Ball socket

Tensionspring

Grease fittingTie rod end

Housing

Nut

Figure 9-17. Adjustable pitman arm stop bolts and lock nuts.This setup calls for a 0.20″ (5 mm) clearance for the propersteering angle. (General Motors)

Figure 9-18. Cutaway view of a typical ball socket. Note theinternal components. (General Motors)

Threads

Taper

Tie rod end

Figure 9-19. Typical self-contained ball socket. Note thetapered ball stud. (Moog)


the gears in the steering gear, the size and shape of thesteering arms, and the angles formed by the linkage allaffect the steering action. The percentage of vehicle weightplaced on the front wheels and whether the vehicle hasfront- or rear-wheel drive are also factors.

Rack-and-Pinion SteeringRack-and-pinion steering is a simple system that

directly converts the rotation of the steering wheel tostraight line movement at the wheels. Figure 9-20illustrates the principle of the rack-and-pinion steeringgear. The steering gear consists of the rack, pinion, andrelated housings and support bearings. Turning the steering

wheel causes the pinion to rotate. Since the pinion teethare in mesh with the rack teeth, turning the pinion causesthe rack to move to one side. The rack is attached to thesteering knuckles through linkage, so moving the rackcauses the wheels to turn.

Steering RatioThe size of the pinion gear and the number of teeth on

the gear determine the rack-and-pinion steering ratio. Alarge pinion gear with many teeth would turn quickly butwould require a large steering effort. A small gear with afew teeth would turn easily, but require many revolutionsof the steering wheel to make a turn.

A

Pin

4-way valve

Pinion shaft

Pinionholder

Power cylinders

Steering rack

Pinion holder

Pinion center Pinion gear

Pinion holdercenter

Steering rackreaction

Steeringrack

4-way valvePin

Gear housing

B

Figure 9-20. A—Rack-and-pinion steering system cutaway showing the pinion shaft and the rack. B—Steering rack reaction in rela-tion to the direction the pinion shaft and teeth are turned. This particular unit is powered with hydraulic fluid. (Honda)

Cotter pin

Nut

Bolt

Crossmember

One-piecebushing

Retainer

Nut

Inner tie rod end

LocknutOuter tierod end

Ball joint

Steeringknuckle

Figure 9-22. Rack-and-pinion steering linkage. Note the outer rod ends, which are attached to the steering knuckle with a ball joint.This unit is hydraulic power unit. (Moog)


Rack-and-Pinion ConstructionThe body of a rack-and-pinion steering gear is usually

an aluminum casting. The rack is often held to the vehiclebody or frame by two U-shaped brackets that are bolted inplace. Other units are bolted directly to the vehicle with aseries of bolts and nuts that pass through holes in the rackbody and the vehicle’s frame. The pinion assembly is ahardened steel gear supported by bearings at the top andbottom. The rack is also made of hardened steel and movesin slide bearings. Seals keep the steering gear lubricantfrom leaking out of the rack-and-pinion assembly. Figure 9-21 shows a typical manual rack-and-pinion gear.Power rack-and-pinion gears will be discussed later in thischapter.

Rack-and-Pinion LinkageRack-and-pinion linkage connects the gear to the

steering knuckles. Rack-and-pinion linkage is simple, consisting of inner and outer tie rods, Figure 9-22. Designof the outer tie rod was discussed earlier in this chapter.One end of the inner tie rod is inside the steering gear andis usually threaded into the end of the rack. A plastic ormetal shear pin keeps the tie rod from loosening. Some tierods are held in place by a crimp on the inner part of thetie rod assembly. The inner tie rod is protected from the elements by a flexible rubber bellows, sometimes called abellows boot or a boot. The outer part of the inner tie rodis a threaded shaft. The outer tie rod is threaded onto thisshaft and held in place by a locknut, Figure 9-23.

Bolt

To steeringwheel

Universaljoint

Pinion gear shaft

Boot

Outer tierod end

Nut

Cotter pin

Grommet

Mounting bracket

Bolt

Nut

Bracket

Grommet

Cotter pin

Ball joint

Inner tie rod end

Gear housingassembly

Figure 9-21. One type of manual rack-and-pinion steering assembly. Styles will vary. (Toyota)


Conventional SteeringConventional steering systems are sometimes referred

to as parallelogram steering, Figure 9-24. The conven-tional steering system has more components than the rack-and-pinion system. The basic design and components ofthe conventional steering system are discussed below.

Conventional Steering GearsAll steering gears used on conventional steering

systems appear similar when viewed from the outside. Allcontain a worm shaft, or worm gear, which is turned bythe steering shaft, and a sector gear, which is turned by theworm gear. The interaction of the worm and sector gearconverts the rotation of the worm into movement at the pitman arm while turning the steering effort 90°.

One difference between conventional and the rack-and-pinion steering gears is that the conventional gear canbe adjusted. There are two adjusting devices built into theconventional gearbox, as shown in Figure 9-25. Theadjuster at the top of the sector shaft is used to adjust theclearance between the sector gear and worm gear. Theworm gear adjuster is used to adjust the bearing preload ofthe worm gear. The worm gear adjuster can also be

Locknut

Outer tie rod

Inner tie rod

Threads

Figure 9-23. Exploded view of a manual rack-and-pinion steer-ing gear assembly. Note that the inner tie rod end threads(screws) into the outer tie rod end and is secured with a locknut.(General Motors)

Steering wheel

Steering column


Pitman arm

Center linkTie rodSteeringknuckle

Idlerarm Parallelogram

steering linkage Steering gear

Tie rod

Figure 9-24. Parallelogram steering system. (General Motors)

Toe adjustment is made by loosening the locknut and turning the inner rod to shorten or lengthen the tie rodassembly.


removed to gain access to the worm gear and nut duringoverhaul. The adjuster can be located at either end of theworm gear shaft.

Steering RatioThe number of worm gear threads in relation to its

length determines the steering ratio of a conventional steering gear. If there are many threads per inch, the wormgear will be easy to turn (lower steering effort), but the handling will be slow. If there are relatively few threads perinch, handling will be quick, but steering effort will behigh. For example, to move the sector gear about 1/4 turn,the steering wheel is turned about 4 turns. This gives asteering ratio of about 16 to 1 (4 turns at the wheel dividedby 1/4 turn at the sector gear equals 16).

Variable Ratio SteeringSome conventional steering gears are equipped with

variable ratio steering. Variable ratio steering gears use specially designed nut and sector gears. These gears taperas the sector gear moves away from the center position.See Figure 9-26. The sector is moved a relatively smallamount when it is in the center of its travel, which elimi-nates overreaction when the steering wheel is first turned,and reduces wander when traveling straight ahead. As the sector gear moves further, the increasing taper of the meshing gears increases the steering ratio. This makes hardturns easier, especially in low speed situations such asparking.

Types of Conventional Steering GearsThree types of conventional steering gears have been

used in the recent past. They all make use of a worm gearand a sector gear. The most common type is the recirculat-ing-ball steering gear. Variations of the recirculating-ballsteering gear are used on all modern vehicles. An older,less-used type is the worm-and-roller, which may be foundon some older cars, usually imports. A rare type is the camand worm, which is found only on older imported cars.

Manual steering versions of each type are discussed below.Power steering versions of these gears will be covered laterin this chapter.

Recirculating-Ball Steering GearThe recirculating-ball steering gear is commonly used

on modern vehicles. This steering gear is known by manynames, depending on the manufacturer. Common namesfor this type of steering gear include worm and nut, wormand ball, and recirculating nut and worm. No matter whatthe name, the basic design is the same. The basic principleof this type of steering gear is shown in Figure 9-27. Theworm gear is the screw, and the ball nut rides up and downas the screw turns. Teeth on one side of the ball nut contactmatching teeth on the sector gear. When the steering shaftturns the worm gear, the ball nut moves on the worm gearshaft. Teeth on the ball nut cause the sector gear to turn.

The ball bearings between the threads of the wormgear and ball nut reduce friction between the worm andthe nut. The steering gear is called a recirculating-ball

Jam nutSector gear–worm gearclearance (lash)

adjuster

Adjusternut

Wormgear

(preload)adjuster

Steering gear Worm shaft

Figure 9-25. A conventional steering gear box showing two separate adjustment points. Always follow the manufacturer’srecommended adjustment procedures. (General Motors)

Equallengthteeth

Longtooth

Nutgear

Pitman shaftsector

Constant ratio Variable ratio

Figure 9-26. Conventional steering gear box setup. This illustrates the difference between a constant ratio gear and avariable ratio gear. Note that the variable ratio pitman shaft sector has a longer center tooth with a shorter tooth on eachside. (General Motors)

Balls andguides

Adjusterplug

Locknut

Wormbearing(lower)

Sector gearBall nut

Wormbearing(upper)

Oilseal

Worm gear(worm shaft)

Figure 9-27. Cutaway of a recirculating ball steering gear. Noteas the sector gear moves, the nut travels with it, causing theworm gear to rotate. (Dodge)


steering gear because the ball bearings move in a loop, orcircuit, as the worm gear moves the ball nut. The ball bear-ings can recirculate because of ball guides installed on topof the ball nut assembly.

The worm and sector gears ride on ball or roller bear-ings to reduce friction. The steering gear may be lubricatedby 90–140 weight gear oil, or it may require automatictransmission fluid. Seals at the input shaft and sector shaftkeep lubricant from leaking out of the steering gear. Theworm and sector gears contain thrust washers and spacersfor proper clearance.

Worm-and-Roller Steering GearThe worm-and-roller steering gear is found on Asian

vehicles, as well as some older Jeep vehicles and Europeancars. Figure 9-28 is an illustration of a typical worm-and-roller steering gear. Unlike the recirculating-ball steeringgear, the worm-and-roller steering gear does not use a ballnut. Instead, the worm gear turns against a roller installedin the sector gear. Turning the worm gear causes the sectorgear to move. The rolling action between the worm gearand the sector roller reduces friction. Note that the wormgear is tapered, with the end sections being larger than thecenter. This worm gear design results in constant full contact between the worm and roller, no matter what thesector position. The worm-and-roller steering gear mayhave a provision for adjustment.

WormRoller

Pitman shaftLock washer

Nut

Pitman arm

Bushings

Locknut

Adjustingscrew

Bearing

Shims

Bearing

Roller assembly

Bearing

Case

Worm

Figure 9-28. Exploded view of a worm-and-roller steering gearassembly. The roller gear engages the worm gear and shaft.(Toyota)

Adjusting screw stop

Follower peg screw

Follower peg

Gasket

Top cover

Capscrew

Adjustingscrew

Locknut

WasherFiller plug

Worm gear

Capscrew

Nut

Seal

End coverAdjusting shims

Gasket

Races

Bearings

Castellated nutand cotter pin

Washer

Pitman arm

Dust excluder

Oilseal

Steering boxbracket

Steeringbox

Innercolumn

Figure 9-29. An exploded view of a worm and tapered pin (peg) steering box assembly. The pin travels in the worm gear.(British-Leyland)

Worm-and-Follower Steering GearThe worm-and-follower steering gear is found on

older European cars. Figure 9-29 shows a typical worm-and-follower steering gear. This design may be


called the worm-and-peg, worm-and-cam, or worm-and-pin steering gear. Note that the worm gear works directlyon the follower, causing the sector shaft to turn as the follower moves on the turning worm gear.

Pitman ArmsThe pitman arm is attached to the sector gear at the

steering gear. It converts the turning movement of the sec-tor gear to linear (back-and-forth) motion and transfers thismotion to the steering linkage.

Note: The sector gear shaft is sometimescalled the pitman shaft.

The pitman arm has internal splines, Figure 9-30.These splines match the external splines on the bottom ofthe sector gear shaft. The splines are slightly tapered to create a tight fit. The pitman arm is held to the sector shaftby a large nut and a lock washer. The linkage end of the pitman arm may contain the ball socket. Other pitmanarms have a hole to accept the ball socket shaft.

Relay RodsThe relay rod, or drag link, is used to transmit the

steering motion from the pitman arm to the inner tie rodson each side of the vehicle. Figure 9-31 shows thearrangement of a typical relay rod. The relay rod may haveball sockets permanently installed, or may have holes forinstallation of the ball socket studs attached to other linkage parts.

Some vehicles have an additional piece of linkagecalled a connecting rod. The connecting rod attaches therelay rod to the pitman arm, Figure 9-32.

Another system uses two long pieces of linkageinstead of a center relay rod and tie rods. This design isshown in Figure 9-33.

Idler ArmsIf the linkage were not supported on the side of the

vehicle opposite the pitman arm, the linkage would flexinstead of moving the wheel on that side. To preventunwanted flexing, an idler arm is installed on the frameacross from the pitman arm. One end of the idler arm isattached to the frame through a metal bushing, whichallows the arm to turn. The other end of the idler arm isattached to the relay rod through a ball socket. Figure 9-34shows an idler arm as it is installed on most vehicles. Somelarge vans and pickup trucks have two idler arms. The idlerarm will usually have grease fittings on both the ball socketand the bushing ends. Some vehicles have two idler arms,Figure 9-35.

Ballsocket Pitman arm

Internal splines

Figure 9-30. A pitman arm with internal splines. These splinesmate with those on the sector gear shaft, locking the twotogether. (Moog)

Nut

Steeringknuckle

Ball joint

Nut

Inner tie rod

Relay rod

Inner tie rod

Adjuster sleeve

Nut

Steering knuckle

Ball jointClampNut

Figure 9-31. Steering linkage illustrating the relay rod in relation to the other linkage parts. (General Motors)


Tie RodsA tie rod assembly is attached to each end of the relay

rod. The tie rod assembly consists of inner and outer tierods that are usually connected through an adjustingsleeve. See Figure 9-36.

Hydraulic DamperSome vehicles have a hydraulic damper installed

between the relay rod and the frame or axle, Figure 9-37.The hydraulic damper resembles a shock absorber. Its

function is to absorb road shocks. A hydraulic piston insidethe damper allows small amounts of hydraulic fluid to passthrough calibrated holes. This absorbs the energy fromroad shocks before they reach the steering gear.

Power Steering Systems

Power steering is a steering system feature thatreduces driver effort by providing extra force to steer thevehicle. The use of power steering has increased to thepoint that all but the smallest cars are equipped with powersteering as standard equipment. Power steering systems areused on both rack-and-pinion and conventional steeringsystems. Principles of power steering are discussed in thefollowing sections.

Pressure Development and ControlThe basic operating principle of power steering is that

liquids (in this case power steering fluid) cannot be compressed. Therefore, liquids can be used to transmitpressure and movement. Systems that make use of liquidsto transfer pressure are called hydraulic systems, and thepressure exerted by the liquid is called hydraulic pressure.Observe the closed hydraulic system in Figure 9-38.Hydraulic pressure is transmitted through the hose to oneside of the piston. This pressure causes the piston to move.

Pitmanarm

Relay rod

Connecting rod

Figure 9-32. This connecting rod is located between the pitmanarm and the relay rod. (General Motors)

Hydraulic steeringdamper

Nut

Drag link

Tie rod

Washer

Pitman arm

Figure 9-33. In some systems, two long linkage rods are used instead of a relay rod and tie rods. (Chrysler)


Support

Mountinghole

Seal

GreasefittingBushing

Idler arm

Center link

Idler arm assembly

Frame

Stabilizer bar

Shock absorber

Upper control arm

Ball joint

Steering knuckle

Coil spring

Spindle

Ball joint

Tie rodends

Lower control arm

Figure 9-34. Idler arm and layout. Note its relationship to the other steering components. (Moog and Sun)

Idler arm

Relay rod

Idler arm

FRONT

Sleeve

Tie rods

Clamp

Figure 9-36. These tie rods are connected together with anadjusting sleeve and clamps. (Dodge)

Figure 9-35. This particular system uses two idler arms, whichare connected to the relay rod and the frame. (General Motors)

Front

Wheelspindle

Front axle

Wheel stopscrewRelay

rod

Hydraulicdamper

assembly

Figure 9-37. A hydraulic damper assembly is used on somevehicles to minimize road shock transferred to the steeringsystem. (Chrysler)

Fluid controlvalve

Relief portLow pressure

Power cylinder Piston

Highfluid

pressure

Returnhose

Pump

Figure 9-38. A closed power steering hydraulic system. Highpressure is pushing on the piston, forcing it to the left. (Lexus)


In a power steering system, pressure is created by apump and transmitted to the steering gear or, in a fewcases, a separate power piston. This pressure is used to help the driver move the wheels. Pressures in a powersteering system can rise to over 2000 psi (13,450 kPa) dur-ing hard turns.

Power Steering FluidThe average power steering system contains less than

two pints (0.95 liters) of hydraulic fluid. A few systems useslightly more. This fluid must transfer pressure, lubricateparts, and remove heat. Most power steering fluid isintended to last the life of the vehicle, providing lubricationwithout breaking down into sludge or acids.

Many older power steering systems used automatictransmission fluid as hydraulic fluid. Newer systems, however, are filled with special power steering fluids.These fluids contain additives designed to increase thesmoothness of power steering system operation and prolong the life of the power steering parts. Specific fluidrequirements vary from one manufacturer to the next. Dueto the extreme forces placed on the fluid, it is importantthat the correct fluid be used.

Power Steering ReservoirThe power steering system must be full of fluid at

all times. Any air that enters the system will cause malfunctions. The power steering reservoir stores extrafluid for use by the other system components. Some reser-voirs are installed around the pump assembly, Figure 9-39.The pump draws fluid directly from the reservoir. A largeO-ring is used to seal the pump and reservoir mating surfaces. Other reservoirs are separate from the pump andare connected by low-pressure hoses, as in Figure 9-40. Afiller cap installed on the top of the reservoir allows fluid tobe added when necessary.

Power Steering PumpThe engine operates the power steering pump.

A pulley on the engine crankshaft turns a belt that turns apulley on the power steering pump, Figure 9-41. Theengine may have to provide as much as 5 horsepower tocreate pump pressure during maximum power assist.

Most power steering pumps are vane-type pumps,Figure 9-42. This type of pump has an internal chamberwith suction and pressure sides. Flat metal vanes turninside the chamber to draw in and pressurize fluid. To keepthe vanes in contact with the chamber walls, pressure isdirected to the area at the center of the pump. This pressureenters behind the vanes and pushes them against the wallsof the chamber.

Refer to Figure 9-43 as you read the following section.In the suction chamber, the vanes move apart and the areabetween the vanes increases. This creates a partial vacuumthat sucks fluid into the chamber from the reservoir. Thefluid is carried around to the pressure side of the chamber.On the pressure side, the area between the vanes becomessmaller and the fluid is pressurized. The pressurized fluidthen exits to the other parts of the system.

A similar type of pump is the slipper pump. Theoperating principles are similar to those of the vane pump,but spring-tensioned slippers are used instead of vanes.The spring tension keeps the slippers in contact with thepump wall. Figure 9-44 shows a typical slipper pump. Anolder design uses rollers in place of the slippers. See Figure 9-45.

A few vehicles have dual gear power steering pumps.The dual gear pump, Figure 9-46, creates pressure usingtwo gears. As the gear teeth move apart on one side of thepump housing, they create a suction that draws in fluid.The fluid is carried around with the pump gears and thencompressed as the gear teeth move together.

Some late-model vehicles are equipped with hydro-boost brake systems. In these systems, the power steeringpump produces power assist for both the steering systemand the brake system.

Cap Cap Cap

Reservoirattachedto pump

Reservoircontains

pumpReservoircontains

pump Pumpbolt

Pump(submerged type)

Line connections

Pump(submerged type) Pump

(nonsubmerged type)

Figure 9-39. Three different styles of power steering pumps with fluid reservoirs installed around them. (General Motors)


Flow and Pressure RegulatorsTo control the output of the pump, a flow regulator

and a pressure regulator are used. Each has a separatefunction. A few pumps have only one regulator.

Reservoir cap

Remotely mountedfluid reservoir

High-pressure hose

High-pressure switch

Pump drive pulley

Mounting bracket

Low-pressure hose

Metal tubing

Mountingbracket

Steeringgear

Power steering pump

Figure 9-40. A power steering pump which uses a separate, remotely mounted fluid reservoir. (Nissan)

Pump mount

Power steeringvane pump assemb

Pulley

Ribbeddrive belt

Figure 9-41. This power steering pump is belt driven. The beltis driven by the crankshaft pulley (not shown), and in turn drivesthe pump pulley.

Rotor

Cam ring

Pumphousing

Vane

Figure 9-42. A belt-driven vane-type power steering pump.(Honda)


Flow Control Valve The flow control valve allows the pump to produce

maximum flow for assist at low speeds, while reducingflow at high speeds to preserve road feel. Allowing thepressurized fluid to enter the inlet also reduces pump wearand fluid temperatures. The goal of the flow control valveis to keep the flow constant as the pump speed and thefluid demands of the system change.

The flow control valve consists of a tapered pininserted into a small orifice. A spring holds the valve in theclosed position, Figure 9-47. Note that in the closed position, fluid can still flow to the power steering gear.

As the engine and pump speed increases, excess fluidflow through the orifice causes a low-pressure condition(called the venturi effect) on the spring side of the valve.Lower pressure on the spring side causes the valve to compress the spring and begin moving. Valve movementuncovers a passage to the pump inlet, and fluid is returnedto the pump. With more fluid bypassing back to the pump,less flows through the steering gear, reducing sensitivity.The tapered pin helps to control the amount of venturiaction, allowing the valve to move more or less dependingon the amount of fluid flowing. This helps to avoid suddenchanges in flow.

Inlet portDischarge

port

Start of fluid intake: Fluid intake: Fluid discharge:Fluid movement:

The vanes are pushed ontothe inner circumference ofthe cam ring.

The volume of the vane chamber increases so that fluid is sucked in.

The sucked-in fluid movestoward the discharge port.

As the vanes return to theiroriginal position on the innerside, the volume of the vane chamber decreases so the fluid is discharged from thedischarge port.

Figure 9-43. Study the operation of this vane-type power steering pump. (Honda)

Cam ring

Drive shaft

Slipper Housing/reservoir

Figure 9-44. Exploded view of a slipper-type power steeringpump. (Moog)

CamRoller

Housing/reservoir

Roller carrier

Drive shaft

Figure 9-45. Exploded view of a roller-type power steeringpump. (Moog)

Port housing

Housing seal

Pumphousing

Drivegear

Drivengear

Dowel pins

Figure 9-46. One type of dual-gear power steering pump. Theyoperate much like an engine gear oil pump. (Honda)


Cap stick

Reservoir

Retaining clips

Pressure platespring

O-ringSleeve

Dowel pin

Pump housing

Flow control spring

Flow control valve

O-ring seal

Fitting outlet

O-ring seal

Pressure plate

Dowel pins

Vanes

Pump rotor

Pump ring

O-ring seal

Thrust plate assembly

Thrust plate retaining ring

Retaining ring

Bearing

Driveshaft

O-ringseal

Seal

Housing

Figure 9-47. Exploded view of a vane-type power steering pump illustrating the flow control valve, spring, and cover fitting.(General Motors)


Pressure RegulatorThe purpose of the pressure regulator is to bleed off

high pressures that could damage power steering components. The pressure regulator is a check ball or asmall valve that is held closed by a spring. The pressureregulator may be built into the pump housing or may bepart of the flow regulator. If system pressure becomesgreater than the spring tension, the ball is pushed awayfrom its seat. This opens a passage to the reservoir andallows fluid to return to the reservoir.

The spring holds the valve closed during normal operation. However, if the steering wheel is turned completely left or right, fluid cannot flow through the steering gears and dead ends in the pump. When flowstops, fluid pressure increases and overcomes valve springpressure. The valve opens and fluid is dumped into thereservoir, reducing the pressure. When pressure returns tonormal, the spring pushes the valve closed.

Power Steering HosesSince the power steering pump is installed on the

engine and the power steering gear is mounted on the vehicle’s frame, there will be relative motion between thepump and the gear when the engine moves on its mounts.To supply the steering gear with fluid, flexible hoses areneeded. The hose that directs the pressurized fluid to thesteering gear is called a high-pressure hose. High-pressurehoses are made of several layers of reinforced rubber, withtubing fittings solidly attached to each end. The ends of thetubing are double-flared fittings or ISO (InternationalStandards Organization) fittings to withstand high systempressures. Some high-pressure hoses use banjo-type fittings. See Figure 9-48.

The return hose is used to return fluid to the reservoirand is usually a low-pressure hose. Most low-pressurehoses have much less reinforcement than high pressures.Instead of using high-pressure threaded fittings, low-pressure hoses are usually clamped to tubing that is brazedor threaded into the steering gear and the reservoir cover,Figure 9-49.

Power Steering Pressure SwitchSome vehicles have a pressure switch installed on the

power steering high pressure hose, Figure 9-50, or on thegearbox. This on-off–type pressure switch sends signals tothe ECM. This switch and the ECM work together to raisethe engine idle when the power steering system puts anextra load on the engine. The switch contains a flexiblediaphragm and two electrical contacts. When the wheels

Pressure feed tube

Air control valve

Banjo fitting

Vane pumpassembly

Pulley

Unionbolt

Gasket

Figure 9-48. This high-pressure power steering hose uses abanjo fitting. The fitting is secured to the pump with a union bolt(bolt that allows fluid to flow through it) and is sealed with twogaskets. (Toyota)

High-pressure hose

Outlet pipe

Power steering gearFrame

Low-pressure hose

Clamp

Pump

Figure 9-49. Power steering system showing both high- andlow-pressure hoses. Note that the low pressure hose is connected with clamps. (General Motors)

Figure 9-50. The power steering pressure switch tells the ECMwhen the steering wheel is locked. The ECM can then increaseengine speed to compensate for the extra load.


are turned to lock (their maximum turning position ineither direction), the power steering pump produces maxi-mum pressure. This pump pressure increases the load inthe engine. When maximum pressure is reached, the pres-sure switch diaphragm deflects enough to close the con-tacts and the switch sends an electrical signal to the ECM.The ECM then compensates for the extra load by raisingengine idle. On some vehicles, the ECM may also deacti-vate the air conditioning compressor when signaled by thepressure switch.

Power Steering CoolersPressurizing the power steering fluid creates heat. If

this heat is not removed, it will overheat the fluid, causingoxidation and sludge formation. Excessive heat will alsocause hardening of the hoses and other rubber parts. Powersteering systems used on smaller vehicles generate lessheat than those used on larger vehicles, and the fluid temperature does not become dangerously high. Manylarger vehicles have enough airflow through the enginecompartment to remove excess power steering systemheat.

However, some vehicles develop high power steeringsystem temperatures and have cramped engine compart-ments with low airflow. On these vehicles, an oil cooler isused to prevent fluid overheating. Some oil coolers aresimply extra lengths of aluminum tubing installed on thebottom of the frame where air can pass over them, asshown in Figure 9-51. Other coolers are finned heatexchangers installed ahead of the radiator, Figure 9-52.

Rack-and-Pinion Power SteeringA rack-and-pinion power steering gear is similar in

design to a conventional system. A self-contained power piston is added to the rack assembly. The power piston creates two pressure chambers in the rack-and-pinion housing. A control valve is installed in the pinionsection. The operation of each of these units is explainedin the following sections.

Pressure passages may be built into the rack assembly,or the unit may have external piping to deliver the pressurewhere it is needed. Seals are more complex and stronger toseal under power steering pressures and to hold in the thin-ner power steering fluid.

Power PistonThe rack-and-pinion power piston is installed inside

the rack housing and is directly connected to the rackassembly, Figure 9-53A. Seals prevent pressure from crossing between the two sides of the piston. When thevehicle is not being turned, there is no pressure on eitherside of the power piston.

When the driver begins a turn, pump pressure isdirected to one side of the power piston. This causes a pressure differential, meaning that there are unequalamounts of pressure on each side of the piston. The piston

will move toward the side with the least pressure, takingthe rack with it. This provides the power assist. Fluid on theside of the power piston that is not pressurized is exhaustedinto the pump reservoir.

During a left turn, pressure enters the left turn side ofthe power piston, Figure 9-53B. No fluid pressure is delivered to the right side. This causes the power piston tomove the rack, assisting with steering effort in that direction. During a right turn, Figure 9-53C, fluid pressureis delivered to the right turn side of the power piston, causing it to move.

Control ValveThe power steering control valve is called a rotary

valve. It is composed of a spool valve inside a valve body.Since the valve body turns in the rack-and-pinion gearhousing, it is equipped with sealing rings. The turning effortfrom the steering wheel passes through the valve assembly

Fan shroud

Oil cooler

Steeringgear

Returnhose

Pump

Figure 9-51. A power steering fluid cooler pipe assembly is commonly mounted to the vehicle frame. Styles vary.(General Motors)

Reservoirhose

Pumppulley Power

steeringpump

Inlethose

Outlethose

Bumpersupport

plate

Finned coolerassembly

FRONT

Cooler outlethose

Figure 9-52. A finned heat-exchanger unit. Study the construc-tion and layout of the parts. (General Motors)


before reaching the pinion gear. The spool valve is con-nected to the valve body through a torsion bar that allowsthe valve to rotate slightly inside the valve body beforetransferring motion to the valve body. Figure 9-54 is a crosssection of a typical control valve. Note the relationship ofthe fluid passages in the spool valve and valve body. Fluidflow through the rotary valve depends on how the passagesin the spool valve and the valve body are aligned.

When the steering wheel is in the straight ahead, orcentral, position, pressure from the pump circulatesthrough the valve assembly and returns to the reservoir.When the steering shaft turns the valve assembly, the spoolvalve moves in relation to the valve body before the turning effort passes through the valve body to the piniongear. Note in Figure 9-55A the spool valve has turnedslightly to the left. Fluid passages in the spool valve arealigned with passages in the valve body that direct fluid tothe side of the power piston that assists a left turn.Pressurized fluid enters the left turn side of the power piston, assisting the driver with a left turn. Fluid on the right

turn side of the power piston exhausts through the valveand valve body passages to the pump reservoir.

In Figure 9-55B the spool valve has turned slightly tothe right. Fluid passages in the spool valve are aligned withholes in the valve body that direct fluid to the right turnside of the power piston. Pressurized fluid enters the rightturn side of the power piston, assisting the driver with aright turn. Fluid on the left turn side of the power pistonreturns to the pump reservoir through the valve passages.

When the driver returns the steering wheel to thestraight ahead position, the spool valve returns to its central position inside of the valve body and fluid pressureis exhausted from the power piston.

Conventional Linkage Power SteeringTwo kinds of power steering are used on conventional

linkage steering systems. The self-contained steering geardesign is in almost universal use. Linkage types are foundon a few vehicles.

Tie rod

Boot Powerpiston

Rackassembly

Rack housing

Tube

Power piston Rack housing

Tie rod

Power piston Rack housing Boot

Figure 9-53. A—Power piston installed inside the rack housingcylinder. B—Power piston movement during a left turn.C—Power piston movement during a right turn. (Hunter)

A

B

C

Torsion bar

Dust cover

Seal

Tubingconnections

Bearing

Cap

Spring

Rack guide

Rack guide seat

Rack housing cap

Nut

Bearing

Gearhousing

O-ring

Controlvalve

Bearing

Figure 9-54. A cross-sectional view of a typical control valveand valve body. (Lexus)


Worm

Spool valve

Torsionbar

Lower shaft

Valve body

Oil return portOil pressureport

To upper sideof rack-piston

High pressure

Low pressureA

Worm

Spool valve

Torsionbar

Lower shaft

Valve body

Oil return portOil pressureport

High pressure

Low pressureTo lower side of rack-pistonB

Figure 9-55. A—Spool valve has turned slightly to the left. It is now in a left turn position. (General Motors) B—The spool valve hasrotated slightly to the right and is now in a right turn position.


Self-Contained Steering GearThe self-contained power steering gear is a conven-

tional recirculating-ball steering gear that contains a powerpiston and a control valve.

Power PistonsA piston with Teflon® seals is attached to the ball nut,

dividing the interior of the steering gear into upper andlower chambers, Figure 9-56. Pressure directed to either ofthe power chambers causes it to move the ball nut. Movingthe ball nut moves the sector gear.

When the driver makes a left turn, pressure is directedto the upper chamber, creating a pressure differentialbetween the upper and lower chambers. This pressure differential assists the driver effort in moving the ball nutdown. See Figure 9-57A. The fluid in the lower chamberexhausts through the passages in the rotary valve.

In Figure 9-57B the vehicle is making a right turn.Pressure is directed to the lower chamber, causing the ballnut to be assisted in moving up. Fluid in the lower cham-ber exits through the rotary valve to the pump reservoir.

Rotary Control ValveMost self-contained power steering gears use a rotary

valve similar to that used on rack-and-pinion power steer-ing. The valve assembly consists of a spool valve inside avalve body. The spool valve can turn a small amount insideof the valve body. Passages in the valve and valve bodydirect fluid to the power chambers. The outer valve spoolturns the stationary steering gear housing, and Teflon®sealing rings seal the pressure passages

The series of illustrations in Figure 9-58 shows theaction of the rotary valve. Note that when the steeringwheel is in the straight ahead position, fluid circulatesthrough the valve with no effect on either power chamber.When the steering wheel is turned to the left, fluid passages

in the valve align with passages in the valve body to directfluid to the upper chamber. This presses on the top of thepower piston. Fluid in the lower chamber exhausts throughthe valve passages to the pump reservoir.

When a right turn is begun, the valve moves slightlyto the right. Fluid passages in the valve and valve bodyalign to direct fluid to the lower chamber. Pressurized fluidagainst the lower end of the power piston assists the driverwith the turn. Fluid in the upper chamber returns to thepump reservoir through exhaust passages in the rotaryvalve.

When the driver returns the steering wheel to thestraight ahead position, the valve twists to the straightahead position inside of the valve body and fluid pressureis exhausted from the power chambers.

Linear Control Valve Another power steering gear uses a linear control

valve. The linear control valve assembly is a small spoolvalve that can move in a linear direction (back and forth)in a valve bore. A lever connected to the steering shaftmoves the linear valve. A typical linear valve steering gearis shown in Figure 9-59. The operation of the power chambers and pistons is identical to the operation of thepower chambers and pistons used in the rotary valve power steering gear. This steering gear was used on someolder cars and on pickup trucks until the early 1990s.

When the steering wheel is turned, the resistance ofthe sector gear against the ball nut causes the shaft to moveeither up or down according to whether the wheel is beingturned right or left. This causes the lever to pivot and movethe valve in its bore. The valve then directs fluid to theproper power chamber as necessary. Turning the steeringwheel in the opposite direction causes the lever to pivotand return the valve to the centered position.

Linkage-Mounted Power SteeringLinkage-mounted power steering is a conventional

steering system with a separate power piston and controlvalve mounted on the linkage. The steering gear is a manual design, although it may have a different steeringratio than one used with manual steering. Linkage powersteering was the first kind of power steering, but it has notbeen used on cars since the late 1980s. Pressure from thepower steering pump is delivered to the valve assemblythrough high-pressure hoses.

Power CylinderThe power cylinder is a machined cylinder containing

an internal piston connected to an output rod. The powercylinder is attached to the steering linkage, usually at thecenter of the relay rod. The cylinder output rod is attachedto the vehicle frame, usually through a double bushing.Hydraulic fluid enters the power piston through high pressure hoses from the valve. See Figure 9-60.

O-ring

Valvespool

Teflon rings (4)

O-rings (4) - installedunder teflon rings

Valve body ball nut

Stub shaft

Figure 9-56. An exploded view of one particular power pistonassembly. Styles will vary. (General Motors)

steering systems - goodheart-willcox · pdf fileall steering systems contain several common...

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