As a result of these reflections, the concept of power steering was born in the 19th century. After the appearance of heavy-duty buses with a steam engine on the streets of cities, it became necessary to lighten the work of the drivers driving them. A search began for constructive solutions to reduce the effort when turning the steering wheel.
In 1925, in the USA, Francis Daizis was one of the first to patent a hydraulic power steering, and in 1933, the concern "General Motors" already intended to install it on my car "Cadillac" with a twelve-cylinder engine. By 1951 the company "Chrysler" mastered the production of power steering and since that time began to equip many of its models with it. First passenger car manufacturer to offer power steering as an option on a model "519", was a firm "Fiat". Currently, as a result of the emergence of front-wheel drive vehicles, the use of tires of larger size and mass, suspension with complicated kinematics, there is a need to use power steering even on small vehicles. As the name suggests, this device is based on the principle of hydraulics. The pressure in the system filled with a special fluid is created by a hydraulic pump driven by the engine crankshaft. The design provides for a spool valve, which, when the steering wheel is turned, switches the fluid supply to one or another cavity, providing additional impact on the steering actuator (gearbox or rail). Initially, power steering designs were imperfect and had a number of drawbacks. For example, they reduced the effort when driving a car so much that the information content of the steering was lost. Such systems were installed on the car until the 80s. It's not hard to imagine how dangerous "overdo" when manipulating the steering wheel while making a turn at high speed.
This implies the basic requirements that the hydraulic booster mechanism must meet. The goal is to make turning easy when maneuvering at low speeds and more noticeable in terms of steering effort when driving at higher speeds, so that driving is as safe as possible.
For most hydraulic boosters, regardless of the speed of the vehicle, the gain remains constant. However, an increasing number of vehicles entering the market today are equipped with variable gain systems, which already vary in amount of gain with vehicle speed, □neither provide accurate and fast response when the vehicle is cornering and the required force when maneuvering the vehicle at low speed..
One way to achieve this is to use a variable ratio steering rack. To this end, the pitch and diameter of the pitch circle of the teeth change along the length of the rack, and the pitch of the teeth on the gear remains constant. When the wheels of the car are set to move in the forward direction, the steering gear ratio is equal to one and the gain is the smallest, but as the steering wheel approaches its extreme positions, the gear ratio increases and the force required to turn the wheels decreases. Power steering, controlled by a computer, also ceases to be something unusual. Such steering systems process information from the vehicle's speedometer. Their work is determined not only by the number of revolutions of the engine, but also by the speed of the car. The computer microprocessor analyzes the signals coming from the sensor and calculates the gain required for each moment, which is implemented using an electro-hydraulic converter.
The idea of the developers of such systems is to take the best of two types of steering - at speeds typical for parking a car, make the steering as easy as possible, and when driving at high speed, reduce the effect of the amplifier to such an extent that the system works almost the same as a conventional mechanical steering without power steering.
System maintenance
As a rule, the hydraulic booster steering mechanism is highly reliable and does not require complex maintenance during vehicle operation. Even in the event of a failure of the power steering pump, the car can continue to move, although it will require much more effort to turn the steering wheel in this case than even on a car without power steering.
The cause of a complete failure of the hydraulic booster is most often a broken pump drive belt. Check the condition of the belt regularly - it may be worn or loose. One of the signs of a weak belt tension is the appearance of kickback (pushback) on the steering wheel. This is usually most noticeable when starting the car from a place when the wheels are turned to the full.
Maintain the proper amount of fluid in the booster reservoir. If necessary, add fluid only to the brand specified in the service manual. Please note that automatic transmission fluid can not be used for all power steering. There are many different brands of liquids on the market. The wrong fluid can ruin all the seals in the system.
Since the liquid is used not only as a working fluid of the hydraulic system, but also as a lubricant, it is very important that its level does not fall below normal, otherwise the pump may fail. Also keep the fluid clean. Dirty or expired fluid will quickly destroy the pump and rack and pinion hydraulic seals, requiring costly repairs later. Fluid changes are rarely required. If you want to drain the fluid, you must open the cap of the expansion tank, disconnect one of the pipelines of the system and turn the steering wheel from side to side several times to squeeze the fluid out of the hydraulic system. There is usually no special hole for draining the liquid. Filling with new fluid is done through the expansion tank. As a rule, in this case, air plugs are formed in the hydraulic system that disrupt its performance. They should be removed. The easiest way to do this is as follows. Start the engine, open the expansion tank cap and bleed the system by turning the steering wheel several times from one extreme position to another. As the hydraulic system is pumped, the fluid level in the reservoir will decrease. Repeat this procedure until it stabilizes. After that, add liquid to the required level and close the lid, after checking if the vent is not clogged in it (if it exists).
The most common malfunction of hydraulic boosters is fluid leakage. With such a defect, cars usually fail to pass inspection. Some older hydraulic systems allowed some leakage of fluid through bearings, shafts, etc., as it is almost impossible to make them completely tight. Regularly inspect the system components from all sides for the timely detection of possible leaks from pipelines and fittings, as well as from loose pipelines and other parts.
Find out if the tubes and hoses are rubbing against the chassis and suspension parts. A hydraulic line failure can cause fluid to break through the covers. When checking, turn the steering wheel from one extreme position to another. Small leaks can often be repaired by introducing commercially available sealing additives into the fluid. However, this will only be a short-term measure. If the pump fails, it can be repaired using a new seal repair kit. Replacing the seals will do little to fix if the pump is badly worn.
For those who like to do everything themselves, repairing the pump is no big deal. However, before installing the repaired pump on the car, it is advisable to check it on the stand. If you suspect that the pump is worn out, contact a power steering specialist to check its operating pressure and correctly identify the problem. Generally speaking, the numerous advantages of power steering far outweigh the problems posed by its possible malfunctions. It is worth, after you have traveled in a car with a modern system, to change to a car that does not have a power steering system, and you will immediately "feel the difference".