The front wheels are turned to the right or left as per the will of the driver through the mechanical advantage of the steering gear and the linkage
There are some disadvantages in manual steering.
v It is bigger and heavier in engines on cars.
v Low pressure types should be used in case of cars.
v The larger steering ratio is required to steer these cars. For this, more turns of the steering wheel are required to move to the desired distance.
v Larger tyres having heavier weight on vehicles make the car more difficult in parking. So, the driver has to apply greater physical strength for driving the vehicles.
v To overcome this difficulty, power – assisted steering has been introduced as shown in fig. They have only power –assisted steering, called power steering.
When a car is steered manually, the driver has to supply all the
v The power steering is to improve driving comfort, most modern automobiles have wide, low pressure tyres with increased the tyre to road surface contact area.
v The power – steering system used in automobiles is actually a modified manual – steering system as show in fig.
v The steering column, steering gear, and steering linkage entirely vary from the manual – steering systems. The main difference between power steering and manual steering system is a power booster attached to assist the driver.
v In this power – assisted steering, the booster is operated when the steering shaft turns. When the steering effort exceeds a certain force, when the steering wheel turns, valves are actuated by this hydraulic pressure to a cylinder. “Then this pressure makes the piston to move and provides most of the steering force.
A simple hydraulic power assisted steering is illustrated in fig
v It consists of a fluid reservoir, hydraulic pump, hydraulic ram, control valve, steering shaft, steering box and steering wheel.
v The engine driven by hydraulic pumps supply oil under pressure from the oil reservoir to the feed lines. A hydraulic control valve provided below the steering measures the input pressure at the steering wheel. Then the pressure is converted in to the hydraulic ram.
v When the steering wheel is stationary, the oil will exert the same pressure on both sides of the piston and retain the piston at rest.
v When the driver turns the steering wheel, the control valve is moved by the steering arm. At that time, one of the ports closes while the other one opens.
v High pressure oil enters one side thereby moving the piston. Then this movement of the piston actuates the steering linkage to move in the required direction.
v This system is used in big cars and heavy commercial vehicles.
v It is very much suitable for low speeds and the vehicle for parking purposes while reversing.