Fundamental of steering system in automotive car

© 2012 Delmar, Cengage Learning

Steering Fundamentals

Chapter 65


Objectives• List the parts of steering systems• Describe the principles of operation of steering

systems• Compare linkage systems to rack and pinion• Describe how power steering systems operate


Steering Systems• Steering system works with the suspension

system– Components

• Steering gear• Steering linkage• Steering wheel• Steering column

• Styles of steering– Gear box and parallelogram linkage– Long rack with linkage extending from ends


Steering Gears• Common types

– Recirculating ball and nut steering gear– Rack and pinion steering gear

• Steering ratio– Amount of steering wheel rotation

• Steering wheel turned all the way in one direction: stops against a lock

• Turning radius– Amount of space required for a vehicle to turn

around


Recirculating Ball and Nut Steering Gear

• Sector gear meshes with ball nut– Ball nut rides on bearings on the worm shaft

• Provides smooth steering feel– Ball nut has curved channels– Steering shaft has bearing channels

• Balls rotate and recirculate through tubes


Rack-and-Pinion Steering• Characteristics

– End of steering shaft has a pinion gear • Meshes with the rack gear

– Lighter and easier to install than standard steering gears

– Often has a faster ratio– More easily damaged when front wheels hit a

curb or rock– Transmit more road shock


Steering Linkage• Steering gear is connected to wheels by

steering linkage• Parts vary depending on design

– Tie-rods– Steering arms– Steering-knuckle

• Parallelogram steering design – Most popular – Used with long and short arm suspension


Parallelogram Steering Linkage• Recirculating ball gear uses parallelogram

steering– Name comes from parallelogram shape made by

steering linkage during a turn• Characteristics

– Tie-rods on each side connected by center link– Pitman arm connects steering box to center link– Idler arm supports center link on passenger side


Ball Sockets• Ball sockets connect steering linkage parts

– Allow parts to rotate during a turn– Pivot as the steering deflects during a bump


Tie Rods• Tie-rod ends attached to pivot points at front

wheels– Transmit motion from steering wheel to front

wheels– Maintain correct front wheel toe

• Threaded adjusting sleeve connects inner and outer tie-rods– Right-hand thread on one end

• Left-hand on other


Steering Arm• Tie-rods attach to front wheels at steering arms

– Steering arm is attached to steering knuckle• Includes spindle

• During a turn– Inside wheel must turn sharper than outside

wheel• Steering arms angled inward

– Ackerman angle– Toe-out-on-turns


Rack-and-Pinion Steering Linkage

• Rack and pinion: less complicated – Two tie-rods come out of steering rack– Conventional tie-rod end ball sockets on outer

ends– Inner tie-rod ends are ball sockets enclosed in

rubber bellows or boots• Steering damper

– Minimizes effect of road shocks to steering wheel


Steering Column• Steering wheel splined to steering shaft located

in center of steering column– Locknut retains steering wheel to shaft

• Shaft supported by bearings at top and bottom of column

• Tilt columns allow driver to adjust steering wheel angle– Air bags are installed on steering wheel– There is flexible coupling between steering shaft

and splined input shaft of steering gear


Power Steering• Steering systems on most cars today are power

assisted – Some manual units are still made

• Most power steering is hydraulic– Pressure supplied from crankshaft by belt-driven

pump


Power Steering Pump• Steering pump driven by crankshaft belt

supplies hydraulic pressure to assist steering– Power steering pump types: roller, vane, and

slipper• Operation

– Pump develops more flow at higher speeds– Flow control valve is almost always working– Requires considerable horsepower to operate


Types of Power Steering• Power steering is either rack-and-pinion or

conventional recirculating ball and nut units– Most power steering systems are integral

• Recirculating ball power steering– Gear boxes use pivot lever or torsion bar acting

on spool valve• Rack-and-pinion systems

– Fluid is directed to a chamber on either side of the rack


Electronically Controlled Variable Effort Power Steering

• Reasonable speed: fixed power assist not necessary– Late-model vehicles: vehicle speed determines

amount of power assist– Pump-controlled units: actuator solenoid

changes fluid flow– Steering gear–controlled steering assist: boost is

sensed by module– Four-wheel steering systems: improve handling


Electronically Controlled Steering Systems

• Can be “steering-by-wire” or mechanically connected using electro-hydraulic steering gear– AFS system changes between low and high

speed steering assist• Electric motor–powered steering systems use a

rack-and-pinion steering gear• Electric power steering improves fuel economy

– Controls amount of assist by regulating current• Planetary gear active steering

– Input is sun gear and output is planetary carrier

Fundamental of steering system in automotive car

Automotive

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