How your car works - Power Assisted Steering

Does your car have Power Assisted Steering and how do you know?
The benefit of power assisted steering is best felt when parking the car or moving it at very slow speeds. When stationary it can actually require considerable effort to turn the wheel from lock to lock without Power Assisted Steering. When the car is moving the tyres offer less resistance to being steered left or right and very little force is required to steer round corners. Power Assisted Steering clearly doesn't change the amount of resistance the tyre has on the road surface it is simply that it is far less noticeable to the driver.

Power Steering was introduced around the 1950s as an optional extra. The need for assistance in steering came about because cars were rapidly gaining weight around this time. American cars were really the first to use the technology, owing to the size of the cars there and public demand for this option.

Now most cars either have it fitted as standard or, where this is not so, it will at least be available as an option. No longer is it just fitted to large or powerful cars but also to small cars where manoeuverability in the town centres or the supermarket car park becomes a key issue.

What types of Power Steering are there?
There are only a few different types in use on today's cars. The most commonly used is the hydraulic type, although electro-hydraulic and pure electric motor assisted powered steering is now being favoured by some motor manufacturers.

Hydraulic Power Steering
The main components that make up this type of Power Assisted Steering system are the steering rack, the hydraulic pump, the fluid, the reservoir containing it and the hydraulic lines connecting it all together.

The operating principle of Hydraulic Power Assisted Steering is quite simple unlike the construction of the system which is more complex. The steering rack assembly is a sealed unit and should never be tampered with as it works at very high pressures. There should be no visible signs of fluid leaking from any part of the system. If there is any sign of fluid leaking then take your car to your local Unipart Car Care Centre for it to be checked over. If caught in time, any damage to the system can be limited. The cost of a replacement Power Steering rack can run into several hundred pounds.

Operationally it is quite simple. The engine drives a belt that powers the hydraulic pump and this gives hydraulic pressure to the system, ready when needed. When you turn the steering wheel in the car the system automatically calls on this pressure to assist in turning the wheels.

Electric Power Steering
Electric Power Steering was first introduced in the mid 1970s to prevent the sudden loss of control caused by the loss of the hydraulic assistance if the engine were to stall with the car still moving. The Electric Power Steering works independently from the engine, taking its power from the car's battery.

Electric Power Steering functions in a very similar way, in that a power source, this time electric only, kicks in when you turn the wheel. This time however the power source is an electric motor.

You will find that this is either itself connected to your steering rack and powers this directly or it is connected to a hydraulic pump that in turn powers the system much as a standard hydraulic system would.

The different types mentioned above are an "electric servo" type, where the electric motor directly drives the gears inside the steering rack, via reducing gears, or an "electro-hydraulic" type, where there is an electric pump providing pressurised hydraulic fluid to the steering rack. The electric servo type does have one tangible advantage since there is no power drain from a pump being driven by the engine and this, incidentally, also means marginally better fuel economy.

The system is powered by electrical current being drawn from the vehicle's electrics. They have a built-in safety device so that if the electrical power supply were to fail, then it will default to a conventional un-assisted steering system. Additionally, if the engine was to stop whilst the car is moving then the electrically assisted steering system will still operate, unlike a conventional hydraulic assisted system.

As for maintenance, the electro-hydraulic systems are sealed units requiring no maintenance except for checking for wear and fluid leaks.

Caring for your Power Steering

• Make sure that the hydraulic fluid is to the correct level within the reservoir. If it is left to run too low it can cause damage to the pump and the system may fail.
• Never attempt a repair to the steering system without having the technical repair instructions and special tools required for a proper repair. There is the possibility of damaging the steering components, which are usually quite expensive to replace and also affecting the road-worthiness of the car.
• It is quite normal to have some noises coming from the car if you move the steering wheel from side to side when stationary. If there are 'squealing' noises coming from the car when stationary (with the wheels pointing straight-ahead) or when moving then do not drive with it for too long before going to your nearest garage for the fault, probably a slipping belt, to be rectified.
• The drivebelt for the pump is driven from the engine crankshaft pulley. Check the condition of this periodically to ensure that is it not split and that it is tight enough. If it is too loose or it is contaminated with oil then it can slip around the pulley and not deliver sufficient drive to the pump.