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Feature for comfort and safety: The power steering
The power steering is a feature designed for comfortable and secure moving and steering of any heavy vehicles. It decouples the force required to rotate the steering wheel from the frictional force of the wheels. This increases with the pressure on the ground. Originally, the power steering was developed for trucks, as they were difficult to steer once a certain size was reached. Today, almost all vehicles are equipped with a power steering system from factory.
How does a steering system work?
A steering system consists of a steering wheel, the steering column and the wheel-steering. In a car's steering system, the rotation from the steering wheel is first converted into a linear movement at the steering gear and then back into a rotation of the wheels. The more pressure is exerted onto the wheels, the more difficult it is to turn the steering wheel. Thus cars were often provided with huge steering wheels prior to the advent of power steering. The intention behind the large lever was creating sufficient torque at the steering column to somewhat comfortably steer the vehicle. Yet, when engines became larger and heavier, especially in American vehicles, this simple solution reached its limits. This is why the hydraulically assisted power steering was invented.
The path of power steering fluid
The steering gear is the point at which the power steering system, also called steering booster, can take effect. Ideally, the linear movement is supported by a hydraulic cylinder at this position. This hydraulic cylinder has a double effect: At the pressure plate in the cylinder, compression is created at one side, and suction at the other, depending on the direction in which one steers. When changing the direction of rotation, a valve called the control bushing, toggles the flow of the hydraulic oil. For the entire system to remain pressurized, a power steering pump delivers a constant pressure. The power steering pump is driven by the engine via a flat belt. The power steering system is filled via a small tank that also serves as a reservoir. The power steering fluid is filled into it. To prevent dirt particles from spreading in the power steering system, a filter is installed in this component's supply system.
Hazard of aging power steering fluid
The power steering fluid and filter should be replaced at least every 150000 km or every 5 years. Just as any mineral oil, the power steering fluid can become obsolete. If it flocculates, becomes emulsified due to condensation or too many dirt particles accumulate, the power steering system's effect suffers significantly. Changing the hydraulic oil can completely restore a power steering system's effect. It is important to change the filter as well.
Changing hydraulic oil
Good power steering fluid is clear and golden brown in color. If the steering is stiff or a whistling noise can be heard when driving, the power steering fluid's fill level should be checked. On some cars the reservoir tank is difficult to find, yet the exact position is always documented in the operating instructions. Oftentimes the provided measuring rod has markings regarding the fill level when the engine is warm or cold. It is important to keep this in mind when filling up. If the hydraulic oil has a dark discoloration and is cloudy, it should be replaced as soon as possible. Depending on the manufacturer, special drain plugs are located at the power steering or a line must be loosened to drain the hydraulic oil. The oil is drained with the engine off, otherwise the servo pump will run on empty. This must be avoided, as it could quickly take damage as a result. If no drain plug is present and provided, the oil can also be removed from the upper tank using a syringe. The servo system requires about 1 liter of hydraulic oil.
It is important to bleed the servo system after changing the oil and replacing the filter. This is achieved by turning the steering wheel all the way to each side multiple times while the reservoir is open and refilling oil if needed. However, ensure not to overfill!