The steering system translates the steering wheel’s rotation into a swivelling movement of the road wheels so that a long turn of the steering wheel rim results in a short angle of the road wheels.
As a result, a driver can use only a small force to steer a heavy vehicle. The rim of a steering wheel that is 15 inches (380 mm) in diameter travels nearly 16 feet (5 m) when the rim of the steering wheel moves four turns from full left lock to full right lock.
The edge of the road wheel moves only slightly more than 12 inches (300 mm). If the driver were to swivel the road wheels directly, he or she would have to push nearly 16 times harder.
The steering effort is transmitted to the wheels through a system of pivoted joints that allow the wheels to move up and down with the suspension without changing the steering angle. The joints accommodate for the inner front wheel turning more sharply than the outer front wheel when cornering.
The joints are adjusted very closely. If the joints are even a little loose, the steering will feel unacceptably sloppy and be dangerously inaccurate.
Two steering systems are commonly used – rack and pinion or steering box.
On larger cars, either of these systems may have been power assisted to further reduce the amount of force needed to move it, especially at low speed.
What is Steering System?
The steering system in a car is a key part of automobile steering control and distinguishes itself by its responsiveness to the driver while in operation. Steering control gives you the driver peace of mind.
The car steering system in the automobile is a process that runs the vehicle in a desired direction by turning, usually, the front wheels. Proper steering is required for proper control of the automobile throughout its speed range with safety.
The system allows a driver to apply only light forces to steer a heavy automobile.
Steering is also accomplished via the rear wheels, but this is typically used at low speeds in slow floor vehicles for lifting transporting heavy parts over a short distance, for example, a forklift.
If you would like to learn all about the car steering system, and how it works, what are the types of steering systems, and how it supports handling, road holding, and drivability, then please continue reading.
Automobiles are always supplied with front wheel steering. Simple sketch of a car steering system.
The Basics of Steering System
Steering a vehicle is easy, right? Do you understand how it works? It looks easy but it’s not. Let’s take a look at your vehicle’s moving parts and see what they are doing.
When you turn the steering wheel, the steering shaft rotates the pinion gear. When the pinion rotates, the pinion gear’s teeth and the steering rack become interlocked.
This rotation will push the rack when the rack moves the rods and the steering knuckles, act as pivots and turn the front tires.
For example, turning the steering wheel left will push the rack to the right and pivot the front tires to the load. That’s it all the more you turn the wheel the more rack is pushed and the sharper the turn will be.
This be confusing of course and you shouldn’t worry you do not have to be mechanic to steer a vehicle but we wanted to give you a visual of exactly what is occurring when you make that turn of the wheel.
With little effort and the help of your steering system, it is easy to steer you vehicle, even though there are many moving parts and words you have probably never heard of.
How does a Car Steering System work?
The steering system will change the steering wheel’s rotary motion into the angular turn of the front wheels.
- The steering wheel rotates the steering column.
- The steering gearbox is attached to the end of the column. So the steering wheel is rotated and the cross shaft oscillates in the gearbox.
- The cross shaft is connected to the drop arm. And the drop arm is connected with a drag link to the steering arms.
- The tie rods connect the steering arms of both wheels to the drag link.
- As the steering wheel operates the knuckles move back and forth, the steering knuckles are connected to the tie rods and drag link.
- One end of the drag link is connected to the tie rod and the other end is connected to the end of the drop arm.
The Purpose of a Steering System
To allow safe and driver-friendly control of the vehicle over its entire speed range on all types of road surfaces, proper steering controls are essential.
To assure vehicle functionality and service, the driver’s control of automobile must be properly maintained with minimal effort while the vehicle is in motion.
Therefore, control of the automobile is made possible by a steering system which provides direction to the automobile.
Function of Steering System
The steering system has the important roles of:
- Allowing the driver to control the vehicle in the way he wants
- Keeping the vehicle stable on the road
- Minimizing tire wear and tear
- Preventing the driver from being affected by road shocks
- Providing self-rightening after taking a turn.
Wheel Alignment
Wheel alignment is the adjustment of the pivot axes that govern wheel movements.
Wheel alignment, specifically, is a measurement for the proper positioning of the front wheel and steering mechanism to allow ease of steering, minimize tire wear, and provide directional stability of the vehicle.
Proper aligned front wheels result in.
- Steering comfort.
- Uniform wear of tyres.
- Minimum energy consumption.
- Minimum vibrations.
- No wheel wobbling.
- Reduce the driver effort to turn the vehicle.
- To achieve self-centring of the wheel after turning.
- To achieve directional stability of the vehicle while running.
Types of The Steering System in an Automobile
Following are the three types of steering systems:
- Bicycle steering.
- Turntable steering or centre pivot steering.
- Ackarman steering or side pivot steering.
#1. Bicycle Steering.
In these steering systems, the rear wheel is not moved and front wheel is steered. For proper turning, the two wheels must roll about the same turning point.
The perpendicular to the front wheel at this point will have the same relationship to the rear wheel, which is referred to as the instantaneous center.
#2. Turntable or Center Pivot Steering
In a four-wheel vehicle, the front of a vehicle consists of the two wheels attached to an axle, the axle is then attached to a turntable with a single pivot. This is an arrangement of an automobile steering where when the front wheels are turned, the whole front axle rotates about the center pivot.
Again, the front and rear wheels also have perpendiculars that will pass through the same point when the vehicle is turning. Thus, the turning is safe and free rolling. This arrangement is commonly used in horse-drawn coaches and trailers.
It is not suitable for a vehicle designed for automobile use at high speeds, and the effect of turntable and center pivot would be unstable at speed.
Also, a center pivot steering arrangement needs a lot of space to turn because an entire axle has to turn.
#3. Ackerman Steering or Side pivot steering
This is the modern steering layout of almost all automobiles. In this steering layout, you can turn each wheel separately about the side pivot/axle. A wheel turns on a stub axle that has located about the axle. Those stub axles are turned by steering arms with a tie rod.
The steering arms are not parallel but are tilted or inclined. The lines produced by the inclined arms will converge at the center line of the rear vehicle axle line at a point creating an angle called the “Ackerman Angle.”
To obtain a good alignment it is necessary to understand the following factors,
- Camber (Wheel rake or Camber angle).
- Caster.
- King Pin inclination.
- Toe-in.
- Toe-out.
Camber
Camber is the angle between the tire’s centerline and a straight line drawn vertically from the front of the vehicle.
Wheels that tilt out at the top have positive camber; wheels that tilt inward have negative camber. Both front wheels of a vehicle have approximately the same camber angle. When loaded, the positive camber makes the wheels verticle, and the tires will have complete road contact, promoting even tire wear.
If the camber is excessive, the outer edge will wear out faster in a positive camber situation, while a negative camber condition will wear out the inner edge faster. If both front wheels have unequal camber, vibration will occur at this wheel position of low vehicle speed. Older vehicles have noticeable camber.
Modern day vehicles have less camber relative to older designs because of better designs and materials. Camber should never be more than 2°. The camber in modern vehicles is adjusted with an eccentric cam on the control arm shaft.
Caster
The Kingpin tilt or steering axle may tilt forward or rearward from vertical. This is known as caster.
Caster Angle: The caster angle is the amount of forward or rearward tilt of the steering axis from the vertical, measured in reference to the side of the wheel.
Rearward tilt is termed positive caster and forward tilt is termed negative caster.
If the caster angle is not equal on both sides, this will create the vehicle pulling to the side with the smaller caster angle. Caster angle in modern vehicles ranges from 2° to 8°.
Purposes of Caster
- To maintain directional stability and control.
- To increase steering stability.
- Reduce drives effort to turn the vehicle.
King Pin Inclination
Kingpin inclination is the angle between the vehicle line and kingpin center or steering axis, viewed from the front of the vehicle.
In modern cars, Kingpin inclination varies from 7° to 8° on either side. It should be equal on both sides. If it is greater on one side than the other, the vehicle will tend to pull towards the side with the greater angle.
The main functions of Kingpin inclination are as follows,
- It helps in self-centring of wheels after taking a turn.
- To provide directional stability.
- It reduces steering effort.
Toe-in
The vehicle’s front wheels tilt slightly inward meaning that the distance from the front wheels at the front (A) is narrower than the distance at the back (B). The measurements (A & B) are taken at the hub level and at the very tread center of each wheel.
This difference in measurements is called the ‘Toe-in’ (B-A) and is usually 2 to 3 mm. The toe is used to help against the negative effects of camber. The tie-rod ends are used to adjust the toe-in.
Toe-out
When a vehicle is turning with Ackerman steering geometry, the inner wheel turns in more degrees than the outer wheel. This is done so perpendiculars can be drawn from all four wheels and the perpendiculars meet at a point when continued to be drawn.
This is called the instantaneous center of the front wheels allowing for all wheel rolling without a scuff on the tires.
Types of Steering System Depending on the Leverage
There are two types of steering, based on the leverage provided between the road wheel and the steering wheel, and the number of shocks and vibrations transmitted from the road wheels to the steering wheels, known as:
- Reversible steering.
- Irreversible steering.
Reversible steering
Reversible steering in which the gear ratio is 1:1 and for example bicycle or scooter steering.
In this gear case any angular movement of the handle causes the same angular movement to the wheel and the wobbling or vibrations of the wheel are faithfully transmitted to the steering handle. This is suitable for only bicycles, motorcycles, scooters etc.,
Irreversible steering.
In this gear reduction between the wheel and handle is very high and for example in road rollers it is about 40:1
Here, very high gear reduction is necessary as the load carried on the wheel is very high. With this type of steering, there will not be any transmission of notion due to wheel vibration from road wheels to steering wheels.
Steering Gears
Directly attaching the steering wheel to the steering linkage would require a lot of effort to turn front wheels. The use of a reduction system assists the driver.
The steering gear is a device that provides a mechanical advantage in converting the rotary motion of the steering wheel to linear motion of the linkage. The steering gear is in a box called the steering gearbox.
Types of Steering Gears
Following are the eight important steering gears:
- Recirculating ball steering gear.
- Rack and pinion steering gear.
- The Worm and sector steering gear.
- Worm and roller steering gear.
- Worm and ball bearing nut steering gear.
- Cam and roller steering gear.
- The Cam and peg steering gear.
- Cam and double lever steering gear.
#1. Recirculating Ball Steering Gear.
The recirculating ball steering gear is similar to the worm and ball bearing. The balls are contained in half nut and a transfer tube.
As the cam or worm rotates, the balls pass from one side of the nut, to the transfer tube to the opposite side.
The nut cannot turn, so the movement of the balls along the track of the cam carry the nut allowing it to rotates the rocker shaft.
#2. Rack and Pinion Steering Gear.
In the Rack and pinion, the pinion is mounted on the end of the steering shaft and meshes with the rack that has a ball joint on each end that will allow for the rise and fall of the wheels. The roads connect the ball joints to the stub excels.
The rotary movement of the steering wheel turns the pinion which moves the rack sideways. The movement of the rack is converted into movement of the wheels.
#3. Worm and Sector Steering Gear.
In the worm and sector steering gear, the worm on the end of the steering shaft meshes with a sector mounted to a sector shaft.
When the worm is rotated by rotation of the steering wheel, the sector turns rotating a sector shaft. It is this motion that is transmitted to the wheel through a linkage.
You will hear that the sector shaft is also known as pitman arm shaft, pitman shaft, roller shaft, steering arm shaft, cross shaft.
#4. Worm and Roller Steering Gear.
In the worm and roller steering gear, a two-toothed roller fastened to the sector or roller shaft so that it meshes with the thread of the worm gear or shaft at the end of the steering shaft or tube.
When the worm shaft is turned is causes the roller to move in an arc so as to rotate the roller shaft and at the same time turning on the pin connecting to the shaft. The roller is mounted on a ball bearing.
The worm shaft is mounted on a bearing designed to resist both radial and end thrust. This steering gear is used widely in American passenger cars.
#5. Worm and Ball Bearing Nut Steering Gear.
The worm and ball bearing nut steering gear has a ball nut that rides on the worm of the steering shaft. The worm and nut have spiraled grooves in which steel balls roll, allowing motion with minimal friction.
Two sets of balls are used, and are independent of one another, with a ball return guide attached to the outer surface of the nut.
When steering shaft is turned left or right, the ball nut is moved up and down by the balls rolling between the worm and the nut.
There is a sector gear mounted on the sector shaft that engages with the ball nut to take motion from the ball nut.
#6. Cam and Roller Steering Gear.
In the cam and roller steering gear, a cam is meshed with the roller, rotating the cam thus rotating the roller and in doing so turning the rocker shaft, moving the drop arm.
The contour of the cam is designed to mesh with the arc made by the roller, maintaining a relatively constant depth of mesh and distributing load and wear evenly on the mating parts.
#7. Cam and Peg Steering Gear.
The cam and peg with the rocker arm has a tapered peg that engages in the cam. As the cam rotates the peg travels along the groove, thus rotating the rocker shaft.
#8. Cam and Double Lever Steering Gear.
In cam and double lever steering gear, a unique worm known as a cam takes the place of the worm found in the two types of worm and sector steering gear and worm and roller steering gear.
The cam has the shape of a cylinder, and its actuating component is a groove of variable pitch, which is thinner in the center than at the ends. This creates non-reversibility in the center of the cam, which is where the majority of the steering is done in the vehicle.
The two levers are mounted on the cross shaft and are positioned with the stubs engaging the cam from the side. When the cam is turned, the stubs are moved along the cam groove causing the lever to swing through an arc, and the cross shaft is then turned.