Steering System

“The steering system allow the driver to guide the car along the road & turn left or right as desired.” 

The system includes the following: 

1. The steering wheel 

2. The steering gear 

3. The steering linkage 

The steering system configuration depends upon the vehicle design (the drive train & suspension system used). 

Function of Steering System

1. The primary function of the steering system is to achieve angular motion of the front wheels to negotiate a turn. 

2. To provide directional stability of the vehicle when going straight ahead. 

3. To minimize wear & tear of the tires. 

4. To absorb a major part of the road shocks thereby preventing them to get transmitted to the hands of driver. 

5. To provide perfect rolling motion of the road wheels at all times.

Requirement of good steering system 

1. Very accurate. 

2. Easy to handle. 

3. Provide directional stability. 

4. Multiply the turning effort applied on the steering wheel by the driver. 

5. Irreversible to certain degree, so that the shock of the road surface encountered by the wheels are not transmitted to driver’s hands. 

Parts of Steering System

The main parts of the steering system are:- 

1. Steering Wheel 

2. Steering Column 

3. Steering Shaft 

4. Steering Gear Box 

5. Steering Drop Arm 

6. Pull & Push Rod (Drag link) 

7. Knuckle Arm 

8. Tie Rod & Tie Rod End

1. Steering Wheel :- 

Its made of steel ring welded together on the hub with the help of 2, 3 or 4 spokes. The steering wheel may be fixed position or tilted position. The steering wheel is pulled out with the help of puller. 

2. Steering Column:- 

This is hollow steel pipe in which steering shaft is housed. One end of the pipe is fixed into the steering box & other end is usually held with the help of bracket under the instrument panel. 

3. Steering Shaft:- 

Its made of good quality steel.one end is fixed in the steering wheel with the help of splines or key & kept tight by nut. The other end with worm is secured in steering box with the help of bearing placed both top & bottom. 

4. Steering Gear Box:- 

Its function to convert rotary motion of the wheel to-&- fro motion of drop arm so that drag link tie up with drop arm can pushed & pulled resulting into moving stub axle to right or left as desired by driver. 

5. Drop arm:- 

Its forged out of good quality steel. Its one side is provided with splines which match the splines of sector shaft & held on sector shaft by nut.

6. Pull & Push Rod (Drag link) :-

A drag link converts rotary motion from a crank arm, to a second bell crank, usually in an automotive steering system. one end of the drag link is connected via the Pitman arm and steering gearbox to the steering wheel (providing the connection between the driver and the steering system); the other end is attached to the steering linkage, by the steering arm.

7. Knuckle Arm :-

In automotive suspension, a steering knuckle is that part which contains the wheel hub or spindle, and attaches to the suspension and steering components. It is variously called a steering knuckle, spindle, upright or hub, as well.

8. Tie Rod & Tie Rod End :-

The tie rod is a part of the steering mechanism in a vehicle. A tie rod consists of an inner and outer end. The tie rod transmits force from the steering center link or rack gear to the steering knuckle. This will cause the wheel to turn. The outer tie rod end connects with an adjusting sleeve, which allows the length of the tie rod to be adjustable. This adjustment is used to set a vehicle’s alignment angle.

Types of Steering Gear Box

The steering gear box are following types :- 

1. Worm & worm wheel type 

2. Worm & Nut type 

3. Worm & roller type 

4. Recirculating ball type 

5. Rack & pinion type 

6. Cam & lever type.

1. Worm & worm wheel type 

In this type of steering gear box there will be worm at the bottom end of steering inner column. This worm meshes with a wheel in steering gear box housing. When steering wheel turned, the steering column revolves and the wheel is rotated along with it. This causes the drop arm to move and thereby drag link and other steering linkages like tie rods king pin etc. This steering commonly used in Tractor.

2. Worm & Nut type 

In this type of steering gear box worm is an integral part of steering column. Worm is mesh with a nut arrangement. When worm rotate the nut is able to move. This movement take place along the axis of the column either up or down. This enable the cross shaft to rotate an arc. This in turn helps the drop arm to also move in an arc. This arm transmits the steering to all wheels.

3. Worm & roller type 

In this steering gear, there will be a worm at the bottom end of inner column and a roller is there in the steering gear box. When the worm rotates, the roller which is attached to it also rotates causing the roller to rotate and thereby moving drop arm. This type of steering gear fitted in the Leyland vehicles & American Passenger Cars.

4. Recirculating ball type

 In this steering gear there will be some steel balls in the grooves of steering inner column which move along with the steering worm. This enables to control the friction among them and there by reducing noise. It increases the mechanical advantage of the operator for easy and smooth operation of steering. This type of steering gears is used by Tata, Dodge/Fargo & standard 20 vehicles.

5. Rack & pinion type 

In this steering gear, a pinion is mounted at the end of the steering inner column. It engages the rack which has ball joints at each end to allow the raise and fall of the wheel, the rods are connected with ball joint to the sub axles. The rotary movement of steering wheel turn the pinion which moves the rack sideways parallel to tie rod. This type of gears used in Maruti 800.

6. Cam & lever type

In this type of steering gear, a special worm called Cam is located at the end of inner column which it attached to column in the steering gear. When the worm is rotated, the lever is also moved in the groove provided in the worm. This causes the lever to swing through an arc.

Steering Ratio

“The steering ratio is number of degree that the steering wheel must be turned to pivot the front wheel 1 degree.” 

For example- if steering wheel must be turned 18 degree to pivot the front wheels 1 degree. Therefore the steering ratio is 18:1. The steering ratio generally used with present day steering gear vary from about 12:1 for small vehicle to 35:1 for heavy vehicle. 

Wheel Alignment

“wheel alignment refer to the positioning of the front wheels & steering mechanism that gives the vehicle directional stability, promotes ease of steering & reduces tire wear to a minimum.” 

The front wheel alignment depends upon the following factors:- 

1. Factor pertaining the steering geometry:- 

1. Camber 

2. King pin alignment 

3. Caster 

4.Toe-in 

5. Toe-out 

2. Factor pertaining to front wheel condition:- 

1. Balance of wheel 

2. inflation of tires 

3. brake adjustment 

1. Factor pertaining the steering geometry:- 

1. Camber 

“Camber is tilting in & tilting out of the front wheels from the vertical when viewed from the front of vehicle.” 

If the top of the wheel is tilts out, it has “Positive camber". If the top of the wheel is tilts in, it has “Negative Camber". The amount of tilt measured in degree from the vertical, is called “Camber Angle”. The amount of camber, positive or negative, tends to cause uneven or more tyre wear on one side than on the other side. Its not exceed 2 degree.

2. King pin alignment 

“The King pin inclination is the angle between the vertical line & centre of the king pin or steering axle, when viewed from the front of the vehicle.” 

Its absolutely necessary due to following reasons: 

1. It helps the car to have steering stability. 

2. It make the operation of the steering quite easy particularly when the vehicle is stationary. 3. It helps in reducing the wear on the tyres.

The combined camber & King pin inclination is called the “Included angle.”

3. Caster 

“The angle between the King pin centre line & the vertical, in the plane of wheel is called Caster Angle.” 

If the king pin centre line meets the ground at a point ahead of the vertical centre line is called “Positive Caster” while if its behind the vertical wheel centre line is called “Negative Caster”. The caster angle in the modern vehicles ranges from 2 degree to 8 degree . 

4.Toe-in 

“when the position of front wheels is less than the distance between them at the rear. The front wheels point inward is called Toe-in.” 

The purpose of the toe-out is to give correct turning alignment & to prevent excessive wear.

5. Toe-out 

“when the distance between front wheels at the front end is grater than the distance between them at the rear when the car is stationary , this position of front wheels is called Toe-out.” 

The Toe-in serves the following purpose. 

1. It ensure parallel running of the front wheels. 

2. It stabilizes steering. 

3. It prevent the side slipping & excessive wear of the tyres. 

The Toe-in provides in the vehicles usually few millimeters (3 to 5 mm).

 

Steering Mechanism

“The steering mechanism is used for changing the direction of two or more of the wheel axles with reference to the chassis, so as move the automobile in any desired path.” 

The condition for the correct steering is that all the four wheels must turn about the same instantaneous centre. To avoid skidding the two front wheels must turn about the same instantaneous centre which is lie on the axis of rear wheels. 

Let a= Wheel Track 

b = Wheel Base 

c = Distance between the pivot A & B of the front axle. 

Now, from IBM 

Cot θ = BM/IM 

from IAM 

Cot Ø = AM/IM = (AB+BM)/IM 

Cot Ø = (AB/IM) + (BM/IM) 

Cot Ø= (c/b) + cot θ 

Cot Ø – Cot θ = c/b 

This is fundamental equation for correct Steering. 

The turning circle radius for different wheels can also be written 

1. For the inner front wheel 

RIF = b/Sin θ (a-c/2) 

2. For the outer front wheel 

ROF = b/Sin Ø + (a-c/2) 

3. For the inner rear wheel 

RIR = b/tan θ - (a-c/2) 

4. For the outer rear wheel 

ROR = b/tan Ø + (a-c/2)

Types of Steering Gear Mechanism

The steering gear mechanism are the following two types:- 

1. Davis steering gear 

2. Ackermann steering gear 

1. Davis steering gear:- 

The Davis steering gear has sliding pairs. Since sliding pair has more friction therefore this type of gear will wear out earlier & become inaccurate after sometime. Its theoretically correct. It consists of cross link CD sliding parallel to another link AB & is connected to the stub axles of the two front wheel by means of two similar bell crank levers LAC & MBD pivoted at A & B. The cross link CD slides in the bearing & carries pairs at its ends C & D. 

when the wheel is running straight the gear is said to be in its mid position. The short arms AC & BD are inclined at an angle (900 + a)  to their stub axles AL & BM. 

The correct steering depends upon the suitable section of cross arm angle a & is given by 

tan a = c/ 2b 

where c/b= 0.4 to 0.5 

Where c= distance b/w the pivots of front axles.

b = wheel base. 

Where a is lies between 11.3 to 14.1.

2. Ackermann steering gear:-

Its has turning pairs. Its consists of cross link CD connected to the short axles AL & BM of the two front wheels through the short arms AC & BD forming bell crank lever LAC & MBD. When the wheel is running straight, the cross link CD is parallel to AB, the short arm AC & BD both makes angle a to the horizontal axis of chassis. 

Sin (a+ q) + Sin (a-Ø) = 2 sin a

For correct steering Cot Ø - Cot θ = c/ b 

The value of c/ b lies between 0.4 to 0.555. There are three values of θ which gives the correct steering of the vehicles- 1st while turning right, 2nd - while turning left & 3rd -while in running straight.

Understeer & Oversteer

The angle through which the wheel has to turn sustain the side force is called slip or Creep angle. 

“when the slip angle of the front wheel is grater than the rear wheel, the wheel turns at the radius larger than that intended & the driver has to keep steering into turn. This condition is known as Understeer.” 

“When the slip angle of the rear wheel is grater than front wheel the vehicle tends to Oversteer that is to turn into more than driver indented. 

“When the front & rear slip angles are the same neutral steer occurs”

Advantages of Steering System

1. Better Steering Response – Your vehicle will respond faster to the steering that you perform overall. This allows your steering to be more precise and controllable on the road.

2. Cornering Stability – When you’re going around a corner in a vehicle, four-wheel steering will give you control and stability as you drive. This especially comes in handy if the road is wet.

3. Smaller Radius While Turning – Because you can turn the rear wheels in the opposite direction of the front wheels, this allows you to make smaller circular turns at lower speeds.

4. Better on Tougher Terrains – If you live in an area with a lot of dirt roads or possibly snowy roads in the winter, then you’ll want a vehicle with four-wheel steering to help you drive better on these difficult terrains.

5. Straight Line Stability – If you’re driving your vehicle down a straight road, the four-wheel steering will give you the best stability you could ever want. This helps when you have potholes and high winds within the environment.

6. Easy Lane Changing – If you’re traveling fast on the interstate and you need to change lanes quickly, you can easily do so with a four-wheel steering vehicle without having to turn the steering wheel too much.

Disadvantages of Steering System

1. Expensive – As great as four-wheel steering systems are, they also require many more components in their construction than two-wheel steering systems. Because of this, vehicles with four-wheel steering are more expensive.

2. Bigger Chance of Problems – Due to the fact that four-wheel steering systems have many components, especially electronic components, the entire system could become inoperable if just one of these components malfunctions. This means you’ll spend more time repairing or replacing components in a four-wheel steering system vehicle.