Automotive
Steering Systems

Manual Steering Systems

 •         The steering system is composed of three major subsystems:

–         steering linkage

–         Steering gear

–         Steering column and wheel

•      As the steering wheel is turned by the driver, the steering gears transfer this motion to the steering linkage.

•     The steering linkage turns the wheels to control the vehicle’s directions.

•     Although there are many variations to this system, these three major assemblies are in all steering systems.

Steering Linkage

•     The term steering linkage is applied to the system of pivots and connecting parts place between the steering gear and the steering arms that are attached to the front or rear wheels that controls the direction of vehicle travel.

•      The type of front-wheel suspension (independent wheel suspension as compared with a solid front axle) greatly influences steering geometry.

•      Most passenger cars and many light trucks and recreational vehicles have independent front-wheel suspension systems.

•      Therefore, a steering linkage arrangement that tolerates relatively large wheel movement must be used.

Parallelogram Steering Linkage

•      A parallelogram type of steering linkage arrangement was at one time the most common type used on passenger cars.

•      Now it is found mostly on larger cars, pickups, and larger SUV’s.

•      It is used with the recalculating ball steering gear.

•      It can be classified into two distinct configurations

–         Linkage placed behind the front-wheel suspension. (1)

–        Linkage placed ahead of the front wheel suspension. (2)

Pitman Arm

•      The pitman arm connects the linkage to the steering column through a steering gear located at the base of the column.

•      It transmits the motion it receives from the gear to the linkage, causing the linage to move left or right to turn the wheels in the appropriate direction.

Idler Arm

•      The idler arm is attached on the opposite side of the center link, from the pitman arm and to the car frame, supporting the center link at the correct height.

Links

•      Links, depending on the design application, can be referred to a center links, drag links, of steering links.

Tie Rods

•      Tie rods are actually assemblies that make the final connections between the steering linkage and steering knuckles.

•      They consist of inner tie-rod ends, which are connected to the opposite sides of the center link; outer tie-rod ends, which connect to the steering knuckles; and adjusting sleeves or bolts, which join the inner and outer tie-rod ends, permitting the tie-rod length to be adjusted for correct toe settings.

Rack and Pinion Steering Linkage

Rack and Pinion 

•      Rack and pinion is lighter in weight and has fewer components than parallelogram steering.

•      Tie rods are used in the same fashion on both systems, but the resemblance stops there.

•      Steering input is received from a pinion gear attached to the steering column.

Rack

•      The rack is a toothed bar contained in a metal housing.

•      The rack maintains the correct height of the steering components so that the tie-rod movement is able to parallel control arm movement.

Pinion

•      The pinion is a toothed or worm gear mounted at the base of the steering column assembly where it is moved by the steering wheel.

•      The pinion gear meshes with the teeth in the rack so that the rack is propelled sideways in response to the turning of the pinion.

Tie Rods

•      Tie rods in rack and pinion systems are very similar to those used on parallelogram systems.

•      They consist of inner and outer ends and adjusting sleeves or bolts.

•      The inner tie-rod ends are usually spring-loaded ball sockets that screw onto the rack ends.

Manual Steering Gear

•      The purpose of the steering gear is to change the rotational motion of the steering wheel to a reciprocation motion to move the steering linkage.

•      There are three styles currently in use:

–         recirculating ball

–         worm and roller

–         the rack and pinion

•      The recirculating ball shown here is generally found in larger cars.

•      A sector shaft is supported by needle bearing in the housing and a bushing in the sector cover.

•      A ball nut is used that has threads that mate to the threads of the worm shaft via continuous rows or ball bearings between the two.

•       Ball bearings recalculate through the outside loops, referred to ball return guide tubes.

•      The ball nut has gear teeth cut on one face that mesh with gear teeth on the sector shaft. on the sector shaft.

•      As the steering wheel is rotated, the wormshaft rotates, causing the ball nut to move up or down the wormshaft.

•      Since the gear teeth on the ball unto are meshed with the gear teeth on the sector shaft, the movement of the nut causes the sector shaft to rotate and swing the pitman arm.

Steering Wheel and Column

•      The purpose of the steering wheel and column is to produce the necessary force to turn the steering gear.

•      The exact type of steering wheel and column depends on the year and car manufacture. The steering column also called a steering shaft, relays the movement of the steering wheel to the steering gear.

•       Differences in steering wheel and column designs include fixed column, telescoping column, tilt column, manual transmission, floor shift, and automatic transmission column shift.

Power Steering Systems

•      The power steering unit is designed to reduce the amount of effort required to turn the steering wheel.

•      It also reduces driver fatigue on long driver and makes it easier to steer the vehicle at slow road speeds, particularly during parking.

•      Power steering can be broken down into two design arrangements: Conventional and non conventional or electronically controlled.

•      In the conventional arrangement, hydraulic power is used to assist the driver.

•      In the non conventional arrangement , an electric motor and electronic controls provide power assistance in steering.

•      There are several there are several power-steering systems in use of passenger cars and light-duty trucks.

•     The most common ones are the integral-piston, and power-assisted rack and pinion system.

Components

•      A power-steering gear box is basically the same as a manual recirculation ball gearbox with the addition of a hydraulic assist.

•      A power-steering gearbox is filled with hydraulic fluid and uses a control valve. 

•      Power-assisted rack and pinion component are basically the same as for manual rack and pinion steering except for the hydraulic control housing.

•    The power-steering fluid can be checked either hot of cold.

•      Fluid level will vary with temperature, however, and a more accurate check is done when the engine is warm.

•     The reservoir cap is usually marked for HOT and COLD fluid levels on opposite sides of the dip stick.  If necessary, add fluid to correct the level.  Most manufacturers recommend a specific fluid for use in a power-steering system.

Power Steering Pump

•     The power steering pump is used to develop hydraulic flow, which provides the force needed to operate the power steering.

•     The pump is belt driven from the engine crank, providing flow any time the engine is running.

•     There are four general types of power steering pumps:

•         Slipper

•         Gear

•         Roller

•         Vane

•       Functionally, all pumps operate in the same basic manner.

•       Hydraulic fluid for the power-steering pump is stored in a reservoir.

•      Fluid is routed to and from the pump by hoses and lines.

•      Excessive pressure is controlled by a relief valve.

Electronically Controlled Power-Steering Systems

•      The object of power steering is to make steering easier a low speeds, especially while parking.

•      However, higher steering efforts are desirable at higher speeds in order to provide improved down the road feel.

•      The electronically controlled power-steering system provides both of these benefits.

•      The hydraulic boost of these systems is tapered off by electronic control as road speed increases

Active Steering

•      Active steering improves vehicle stability by turning the wheels more or less sharply than commanded by the turn of the steering wheel during some situations.

•      Through inputs and computer programming, this system can adjust the steering to respond quickly to the threat of skidding.

•      The system also allows for a variable steering ratio dependent on vehicle speed.

•      Current active steering systems are not true steer-by-wire systems.

•      There is still a mechanical connection between the steering wheel and the vehicle’s wheels. 

Electric/Electronic Rack and Pinion Systems

•     The electric/electronic rack and pinion unit replaces the hydraulic pump, hoses, and fluid associated with conventional power-steering systems with electronic controls and an electric motor located concentric to the rack it’s self.

•      The electric/electronic rack and pinion unit replaces the hydraulic pump, hoses, and fluid associated with conventional power-steering systems with electronic controls and an electric motor located concentric to the rack it’s self.

•      The basis of system operation is its ability to change the rotational direction of the electric motor while being able to deliver the necessary amount of current to meet torque requirements at the same time.

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