STEERING SYSTEM IN VEHICLE

STEERING SYSTEM IN VEHICLE

Introduction

The most conventional steering arrangement is to turn the front wheels using a hand–operated steering wheel which is positioned in front of the driver, via the steering column, which may contain universal joints (which may also be part of the collapsible steering column design), to allow it to deviate somewhat from a straight line.

Other arrangements are sometimes found on different types of vehicles, for example, a tiller or rear–wheel steering. 

Tracked vehicles such as bulldozers and tanks usually employ differential steering — that is, the tracks are made to move at different speeds or even in opposite directions, using clutches and brakes, to bring about a change of direction.

The steering effort passes to the wheels through a system of pivoted joints. These are designed to allow the wheels to move up and down with the suspension without changing the steering angle.They also ensure that when cornering, the inner front wheel - which has to travel around a tighter curve than the outer one - becomes more sharply angled.The joints must be adjusted very precisely, and even a little looseness in them makes the steering dangerously sloppy and inaccurate.

What is Steering system?
The steering system in automobiles, steering wheel, gears, linkages, and other components used to control the direction of a vehicle's motion. 
The steering system converts the rotation of the steering wheel into a swiveling movement of the road wheels in such a way that the steering wheel rim turns a long way to move the road wheels a short way.


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Steering system consists of 2 types:-

    1)The Steering-box system type
          -The Rack-and-Pinion steering system(commonly used)
          -Worm-and-Peg steering and Recirculating-ball steering(used in old vehicles)

    2)Power-assisted steering system type


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1) STEERING-BOX SYSTEM TYPE

Rack-and-Pinion gear

The pinion is closely meshed with the rack, so that there is no backlash in the gears. This gives very precise steering.

At the base of the steering column there is a small pinion (gear wheel) inside a housing. Its teeth mesh with a straight row of teeth on a rack - a long transverse bar.

Turning the pinion makes the rack move from side to side. The ends of the rack are coupled to the road wheels by track rods.This system is simple, with few moving parts to become worn or displaced, so its action is precise.

A universal joint in the steering column allows it to connect with the rack without angling the steering wheel awkwardly sideways.

RACK-AND-PINION STEERING LINKAGE

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Worm-and-Peg steering

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Recirculating ball steering

WORM AND PEG STEERING GEAR

At the base of the steering column there is a worm gear inside a box. A worm is a threaded cylinder like a short bolt. Imagine turning a bolt which holding a nut on it; the nut would move along the bolt. In the same way, turning the worm moves anything fitted into its thread.

• Depending on the design, the moving part may be a sector (like a slice of a gear wheel), a peg or a roller connected to a fork, or a large nut.
• The nut system has hardened balls running inside the thread between the worm and the nut. As the nut moves, the balls roll out into a tube that takes them back to the start; it is called a recirculating-ball system.
• The worm moves a drop arm linked by a track rod to a steering arm that moves the nearest front wheel.
• Older designs use two main principles: the worm and sector design and the screw and nut. Both types were enhanced by reducing the friction; for screw and nut it is the recirculating ball mechanism, which is still found on trucks and utility vehicles. The steering column turns a large screw which meshes with nut by recirculating balls.



RECIRCULATING BALL STEERING GEAR

• The nut moves a sector of a gear, causing it to rotate about its axis as the screw is turned; an arm attached to the axis of the sector moves the Pitman arm, which is connected to the steering linkage and thus steers the wheels.
• The recirculating ball version of this apparatus reduces the considerable friction by placing large ball bearings between the screw and the nut; at either end of the apparatus the balls exit from between the two pieces into a channel internal to the box which connects them with the other end of the apparatus, thus they are "recirculated".

• Recirculating ball has same mechanism as that of worm gear type.
• The recirculating ball mechanism has the advantage of a much greater mechanical advantage, so that it was found on larger, heavier vehicles while the rack and pinion was originally limited to smaller and lighter ones; due to the almost universal adoption of power steering, however, this is no longer an important advantage, leading to the increasing use of rack and pinion on newer cars.
• The recirculating ball design also has a perceptible lash, or "dead spot" on center, where a minute turn of the steering wheel in either direction does not move the steering apparatus; this is easily adjustable via a screw on the end of the steering box to account for wear, but it cannot be entirely eliminated because it will create excessive internal forces at other positions and the mechanism will wear very rapidly. 
• This design is still in use in trucks and other large vehicles, where rapidity of steering and direct feel are less important than robustness, maintainability, and mechanical advantage.

• The worm and sector was an older design, used for example in Willys and Chrysler vehicles, and the Ford Falcon (1960's). To reduce friction the sector is replaced by a roller or rotating pins on the rocker shaft arm.
• A central track rod reaches to the other side of the car, where it is linked to the other front wheel by another track rod and steering arm. A pivoted idler arm holds the far end of the central track rod level. Arm layouts vary.
• The steering-box system has many moving parts, so is less precise than the rack system, there being more room for wear and displacement.

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Power-assisted steering

Power steering helps the driver of a vehicle to steer by directing some of its power to assist in swiveling the steered road wheels about their steering axis.

Power steering normally use an engine driven pump and a hydraulic system to assist steering action.

Three major types of power steering systems:

1)Integral-piston linkage system

2)External power steering system

3)Rack and pinion system

          1)Integral power piston steering system (most commonly used)

          2)External power piston steering system

On a heavy car, either the steering is heavy or it is inconveniently low geared - the steering wheel requiring many turns from lock to lock.

Heavy gearing can be troublesome when parking in confined spaces. Power-assisted steering overcomes the problem. The engine drives a pump that supplies oil under high pressure to the rack or the steering box.

Valves in the steering rack or box open whenever the driver turns the wheel, allowing oil into the cylinder. The oil works a piston that helps to push the steering in the appropriate direction.

As soon as the driver stops turning the wheel, the valve shuts and the pushing action of the piston stops.

The power only assists the steering - the steering wheel is still linked to the road wheels in the usual way.

So if the power fails, the driver can still steer but the steering becomes much heavier.

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CHECK THIS VIDEO

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by MECHANICAL ENGINEERING 

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