Introduction: This system provides the directional change in the movement of an Automobile and maintain in a position as per the driver’s decision without much strain on him.
REQUIREMENTS OF STEERING SYSTEM:
a. It must keep the wheel at all times in to rolling motion with out rubbing on the road.
b. This system should associate to control the speed.
c. It must light and stable.
d. It should also absorb the road shocks.
e. It must easily be operated with less maintenance.
f. It should have self-centering action to some extent
Functions of Steering System:
1. It helps in swinging the wheels to the left or right.
2. It helps in turning the vehicle at the will of the driver.
3. It provides directional stability.
4. It is used to minimize the tyre wear and tear.
5. It helps in achieving self-centering efforts.
6. It absorbs major part of the road shocks.
Main Components of Steering System:
The following are the main components of steering system are
1. Steering Wheel
2. Steering column or shaft
3. Steering Gear
4. Drop Arm or Pitman Arm
5. Drag Link
6. Steering Arm
7. Track-Arms
8. Track Rod or Tie-Rod
9. Adjusting Screws
Types of Steering Gear Boxes:
1. Worm and Wheel Steering Gear.
2. Worm and Roller Steering Gear.
3. Re-circulating Ball type Steering Gear.
4. Rack and Pinion type Steering Gear.
5. Cam and Roller Gear type Steering Gear.
6. Cam and Peg Steering Gear.
7. Cam and Double lever Steering Gear.
8. Worm and Sector Type Steering Gear.
Functions of Steering Gear Box:
1. It converts the Rotary movement of the steering wheel in to the angular turning of the front wheels.
2. It also multiplies drivers efforts and give MEHANICAL ADVANTAGE.
1.Worm and Wheel Type: This type of steering gear has a square cut screw threads at the end of the steering column; which forms a worm, at the end of it a worm wheel is fitted and works rigidly with it. Generally covered shaft is used for the worm wheel. The worm wheel can be turned to a new position the drop arm can be readjusted to the correct working position.
2. Re-circulating Ball Type: In this type of gear box the endless chain of balls are provided between the worm and nut members. The nut form a ring of rack having an axial movement. So that the sector on the rocker shaft racks, the balls roll continuously between the worm and nut. Being provided with
return chambers at the ends of the worm. This method reduces friction between worm and nut members. This type of steering gear is used for heavy vehicles.
3. Rack and Pinion Type: This is common manual type of steering gear box is used in most of the vehicles. In this type of steering a pinion is provided the bottom end of the steering column. The teeth of the pinion wheel in mesh with corresponding teeth provided on the rack, the end of which are connected to the stub axle through the rod. The rotating motion of the pinion operates the rack in FORE and AFT direction which in turn operates the stub axle.
4. Cam and Lever Type: The cam and lever steering uses one or two lever studs fitted in taper roller bearing. When the worm in the form of helical groove rotates the stub axle and it also rotates along with it. This imports a turning motion to the drop arm shaft.
5. Worm and Sector Type: In this type the worm on the end of the steering shaft meshes with a sector mounted on a sector shaft. When the worm is rotated by rotation of the steering wheel, the sector also turn rotating the sector shaft. Its motion is transmitted to the wheel through the linkage. The sector shaft is attached to the drop arm or pitmen arm.
Power Steering: Power steering reduces much strain on the part of the driver while negotiating sharp curves. It makes easy to turn sharp corners. It is usually arranged to be operative when the effort of steering wheel exceeds a predetermined value. It is fitted on heavy commercial vehicles and medium cars.
Steering Linkages: Steering Linkage is a connection of various links between the steering gear box and the front wheels. The motion of the pitman arm and steering gear box is transferred so the steering knuckles of the front wheels through the steering linkages. The swinging movement of the pitman arm from one side to the other side gives angular movement to the front wheel through the steering linkages.
Types of steering Linkages:
1. Conventional steering Linkage.
2. Direct cross type steering linkage
3. Three piece steering linkage
4. center arm steering linkage
5. Relay type steering linkage.
Slip Angle: The angle between direction of the motion of the vehicle and the center plane of the tyre is known as Slip Angle. It ranges from 8º to 10º.
Under steer: When the front slip angle is greater than that of rear, the vehicle tends to steer in the direction of side force. Then it is known as under steer. This provides greater driving stability, especially when there is a side wind.
Over Steer: When the rear slip angle is greater than that of front slip angle, the vehicle tends to mover away from the direction of center path. This is known as over stear. This is advantageous when the vehicle moving on the road having many bends curves.
Steering Gear Ratio or Reduction Ratio: It has been defined as the “ number of turns on the steering wheel required to produce on turn of steering gear cross shaft to which the pitman arm is attached. Generally it varies between
14'.1 and 24'.1.
Turning Radius: It is the radius of the circle on which the outside front wheels moves when the front wheels are turned to their extreme outer position. This radius is 5 to 7.5 m for buses and trucks.
Wheel Alignment: It returns to the positioning of the front wheels and steering mechanism that gives the vehicle directional stability, reduce the tyre wear to a minimum.
Factors effects the wheel alignment:
1. Factors pertaining to wheel:- a. Balance of wheels(Static and Dynamic)
b. Inflation of tyre.
c. Brake adjustments.
2. Steering Linkages.
3. Suspension System
4. Steering Geometry –a. caster b. camber c. king pin inclination d. toe-in and toe-out etc.,
Steering Geometry: It refers to the angular relationship between the front wheels and parts attached to it and car frame.
The steering Geometry includes
1. Caster angle
2. Camber angle
3. King-pin inclination
4. toe-in
5. toe-out etc.,
Caster Angle: This is the angle between backward or forward tilting of the king pin from the vertical axis at the top. This is about 2º to 4º. The backward tilt is called as positive caster. The forward tilt is called negative caster.
Camber: The angle between wheel axis to the vertical line at the top is called camber angle. It is approximately ½º to 2º.
King-pin inclination: It is the angle between vertical line to the king pin axis. The inclination tends to keep wheels straight ahead and make the wheels to get return to the straight position after completion of a turn. The inclination is normally kept 7º to 8º.
