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 Davis 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, in which the amount of gain already varies depending on the speed of the vehicle. They provide precise and fast response when the vehicle is moving around corners and the required effort 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 behind 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 action of the amplifier to such an extent that the system works almost the same as a conventional mechanical steering without power steering.