Steering System

Steering system

Requirements of Vehicle Steering System

   -  It should be able to turn the vehicle with more mechanical advantage and less efforts.

   -  it should turn the wheel within shortest possible time

   -  It should be certain degree irreversible so that the shocks of the roads surface are not transmitted to the hands of the driver.

   -  The steering mechanism should be very accurate and easy to handle.

   -  The effort required to steer should be minimal and must not be tiresome to the driver.

   -  The steering mechanism should also provide directional stability. This implies that the vehicle should have a tendency to return to its straight-ahead position after turning.

Types of Steering Gear

    1. Worm and wheel steering gear

    2. Worm and roller steering gear

    3. Worm and sector steering gear

    4. Rack and pinion steering gear

    5. Re-circulating ball steering gear

       1)      Worm and wheel steering gear

       worm gears are special gears used in automobile steering mechanisms and rolling mills.

A worm gear drive consists of two elements:

Driving element → Screw

Driven element → Helical gear

In this type of steering gear the steering wheel shaft is attach with worm & worm is attach with the worm wheel And worm wheel is attach with drop arm. When the steering is rotate the worm arm is also rotate and worm arm is rotate the worm wheel and worm wheel is connected with drop arm and it convert the rotary motion in angular motion and vehicle take turn.

 The worm (screw) continuously rotates and drives the worm wheel (meshed with it). Worm and worm gear form a lower pair as they have sliding contact with each other.

In a worm gear drive, power is always transmitted from worm to worm wheel. Power cannot be transmitted from worm wheel to worm. This phenomenon is called self-locking. It is highly useful in many applications.

Velocity ratio is determined by the number of teeth on worm gear and the number starts on worm. Power transmission decreases with increase in velocity ratio. Mostly use in tractors.

Advantages of Worm Drives

       -          Worm gear drives operate silently and smoothly.

       -          They are self-locking.

       -          They occupy less space.

       -          They have good meshing effectiveness.

       -          They can be used for reducing speed and increasing torque.

       -          High velocity ratio of the order of 100 can be obtained in a single step.

Disadvantages of Worm Drives

       -          Worm gear materials are expensive.

       -          Worm drives have high power losses and low transmission efficiency.

       -          They produce a lot of heat.

         2)      Worm and roller steering gear

In this gear box the steering gear shaft is attach with worm. When the worm rotates, the roller which is attached to Worm also rotates causing the Roller to rotate and there by moving drop arm.

       3)      Worm and sector steering gear

Figure shows the Worm and sector steering gear. In warm and sector steering gear shaft is attach with warm and warm is attach with drop arm shaft selector & drop arm shaft selector are attach with drop arm. so when we take turn the shaft rotate the drop arm shaft selector and drop arm shaft selector is convert the rotary motion of drop arm shaft selector in to angular motion of drop arm and vehicle take turn.

       4)      Rack and pinion steering system

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 wheels, the rods are connected with ball joints to the sub axles. The rotary movement of steering wheel turn the pinion which moves the rock sideways parallel to tie rod.

       5)      Re-circulating ball steering gear

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 thereby reducing noise. It increases the mechanical advantage of the operator for easy and smooth operation of steering.

Steering geometry, Caster, Camber, Kingpin inclination, toe-in and toe-out.

Steering Geometry: It refers to the positioning of the front wheel sand steering mechanism that gives the vehicle directional stability, promotes ease of steering and reduces tire wear to a minimum. It also refers to the angular relationship between the front wheels and parts attached to the front wheel, frame of the vehicle. It depends upon the following terms. Caster angle, camber angle, King Pin inclination, Toe-in Toe-Out on turn.

Caster angle: It is the angle of tilting the king pin axis either forward or backward from the vertical line. This tilting is known as Caster. The angle between the vertical line and the king pin center line in the plane of the wheel (When viewed from the side) is called the Caster angle.

When the top of the king pin is backward, the caster angle is positive, and when it is forward, the caster angle is negative. Usually the caster angle in modern vehicles ranges from 2 to 8 degrees.

The main purpose of caster angle is to create self-centering effect in the steering. It provides the directional stability. Its positive caster increases the efforts required to steer and tries to keep the wheels straight ahead. In heavy duty trucks negative caster is preferred. This makes the steering easier.

Camber Angle: It is the angle between the center line of the tire and the vertical. When viewed from the front of the vehicle when the angle is outward, so that the wheels are farther apart at the top the camber is “Positive” when the angle is inward, so that the wheels are closer together at the top, the camber is “Negative”. The usual value of camber angle should not exceed 2 degree.

When the camber angle is positive, it causes slip out prevention lightens the perpendicular load and lessen the required steering effort. If it is a Zero camber, it prevents uneven wear of tires. When the camber angle is negative, the camber thrust increase with increase in tire inclination relative to the road surface.

King Pin Inclination or steering Axis Inclination

It is the angle between the vertical line and the center of the King pin the steering axis when viewed from the front. The Kingpin inclination, in combination with caster angle, is used to provide directional stability. It also reduces steering effort particularly when the vehicle is stationary. It reduces tyre wear also. The kingpin inclination in modern vehicle ranges from 4 Degree to 8 Degree. It is also known as steering Axis inclination.

Toe-In: It is the inward tilting of front wheels at the front so that the distance between the front wheels at the front is less than the distance between at the front wheels at the rear when viewed from the top. The Amount of the Toe-in is usually 3 to 5 mm.

The toe-in is provided to ensure parallel rolling of the front wheels to stabilize steering and prevent side slipping of front wheels and thereby prevent excessive tire wear.

Toe-Out: Toe-out is the difference in angles between the two front wheels and the car frame during turns. The steering system is designed to the turn the inside wheel through a larger angle than the outside wheel when making a turn. The toe-out is secured by providing the proper relationship between steering knuckle arms, tie rods and pitman arm (drop arm).

Power steering

In motor vehicles, a power steering system helps drivers steer the vehicle be augmenting steering effort needed to turn the steering wheel, making it easier for the driver to turn.

Hydraulic or electric actuators add controlled energy to the steering mechanism, so the driver can provide less effort to turn the steered wheels when driving at typical speeds, and reduce considerably the physical effort necessary to turn the wheels when a vehicle is stopped or moving slowly. Power steering can also be engineered to provide some artificial feedback of forces acting on the steered wheels.

Hydraulic power steering systems for cars augment steering effort via an actuator, a hydraulic cylinder that is part of a servo system. These systems have a direct mechanical connection between the steering wheel and the linkage that steers the wheels. This means that power-steering system failure (to augment effort) still permits the vehicle to be steered using manual effort alone.

Electric power steering systems use electric motors to provide the assistance instead of hydraulic systems. As with hydraulic types, power to the actuator (motor, in this case) is controlled by the rest of the power-steering system.

TYPES OF POWER STEERING SYSSTEM

1) Electric Power Steering Systeem (EPS)

2) Hydrolic Power Steering System

1) Electric power steering (EPS)

By eliminating the power steering pump which can use up to 10 hp under load, an EPS system provides up to a 2% increase in fuel economy over the conventional system. Another benefit of having an electric steering system is that it eliminates the use of hoses and fluid, therefore eliminating power steering leaks as well as a reduction in weight.

Electronic power steering systems are becoming widely popular among auto manufacturers due to the fact that they provide a more refined feel that can be adjusted as needed.

The EPS system consists of four major components: the EPS control module which collects data from the EPS components and sends out the required information; the EPS motor, its speed strength and direction controlled by the EPS Control Unit; the reduction gear, which inputs the power assist to the steering rack assembly; and torque sensor, which monitors the driver’s input and the EPS system’s mechanical output.

The EPS is powered by a permanent magnet alternating current motor and is not dependent on the engine for its power source so steering feel is not affected when the engine is shut off. The torque sensor itself has two independent coils of wire. One of the coils determines if a right-hand turn is being made, the other coil determines if a left is being made. The signal is then sent from the EPS module to the appropriate coil, which will assist the vehicle in steering.

A hybrid type of electronic power steering has been in place for some time now, but that included the use of an electric motor to drive a hydraulic pump.

The new version of EPS is all electronic. The system works by incorporating information with the EPS control unit, EPS motor, reduction gear and torque sensor.

An EPS system works by using a pinion gear assist that provides the power assist by rotating the pinion gear. The reduction gear is press fitted onto a set of splines on the pinion shaft and delivers the assist to the rack gear instead of pushing on the rack gear as in a hydraulic system.

The steering gear itself is a manual rack with an electric motor mounted on the steering column or the rack. When the driver turns the wheel, a steering sensor detects the position and rate of rotation of the steering wheel. This information along with input from a torque sensor mounted in the steering shaft is sent to the power steering control module. The system also uses other inputs from vehicle speed sensors and the traction control system which are factored in to determine how much steering assist is required. The control module then tells the motor to rotate the required amount.

Attached to the motor is the motor resolver sensor, which measures the rotation of the motor and sends the data to the EPS control module.

Different surfaces will require different amounts of steering assist. For example, a vehicle traveling on pavement will require much less steering assist than a vehicle traveling on sand or snow. With the EPS system working with other sensors, it can much more easily provide the required assistance for any kind of terrain and vehicle speed.

Electric power steering modes

Normal mode:-  Left and right assist is provided in response to inputs and vehicle speed. During normal operation power assist levels will decrease as the vehicle speed increases.

Assist limitation:- Will occur if there is a problem with the information going back to the EPS control module, overheating of the EPS module or a malfunction with the controller area network.

Assist off:-  System is turned off if there is a problem with any of the major EPS components.

2) hydraulic power steering system

Figure shows the hydraulic power steering system.

In hydraulic power system when we move the steering wheel the power steering pump is attach with steering wheel rack. When we rotate the steering wheel the power steering pump pressurized the hydraulic fluid and move towards the hydraulic piston cylinder arrangement.

When we take right turn the hydraulic pump transfer the fluid to the hydraulic piston

And hydraulic fluid push the piston to right so the vehicle take turn easily. After completing turn steering wheel return in its original position due to positive camber.