As a result of these reflections, the concept of power steering was born in the 19th century. After the appearance of heavy-duty steam-powered buses on city streets, it became necessary to make the work of the drivers operating them easier. The search for design solutions began, allowing to reduce the effort when turning the steering wheel.
In 1925, Francis Davis was one of the first in the United States to patent a hydraulic power steering, and in 1933, General Motors was already planning to install it on its Cadillac with a twelve-cylinder engine. By 1951, Chrysler had mastered the production of power steering and since then has been equipping many of its models with it. Fiat was the first car manufacturer to offer power steering as an optional extra for the 519 model. Nowadays, as a result of the advent of front-wheel drive cars, the use of larger and heavier tires, and suspension with complex kinematics, there is a need to use power steering even on small cars. As the name suggests, this device is based on the principle of hydraulics. The pressure in the system, filled with a special liquid, is created by a hydraulic pump driven by the engine crankshaft. The design includes 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 rack). Initially, power steering designs were imperfect and had a number of shortcomings. For example, they reduced the effort required to control the car so much that the steering was no longer informative. Such systems were installed on cars until the 80s. It is easy to imagine how dangerous it is to "overdo it" when manipulating the steering wheel while turning at high speed.
This is where the basic requirements for the power steering mechanism come from. The task is to make turning easy when maneuvering at low speeds and more noticeable in terms of steering force when driving at higher speeds, so that driving the car becomes as safe as possible.
Most hydraulic power steering systems have a constant gain regardless of the vehicle speed. However, an increasing number of cars entering the market today are equipped with variable gain systems, in which the gain level changes depending on the vehicle speed. They provide precise and fast response when the vehicle is turning 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 achieve this, the pitch and pitch diameter of the teeth change along the rack, while the pitch of the teeth on the pinion remains constant. When the wheels of the car are set to move straight ahead, the steering 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. Computer-controlled power steering is also no longer something unusual. Such steering systems process information from the car's speedometer. Their operation is determined not only by the engine speed, but also by the speed of the car. The computer's microprocessor analyzes the signals coming from the sensor and calculates the gain required at each moment, which is realized using an electrohydraulic converter.
The idea behind these systems is to take the best of both worlds - making the steering as light as possible at parking speeds, and reducing the power assist when driving at high speeds so that the system operates almost like a conventional manual steering system without power assist.
Material based on data from the portal (MERCEDESMAN)