Automotive Electric Power Steering systems & hydraulic power steering systems
Features of power steering system and inspection method
The power steering system has the role of assisting the force so that the steering wheel can be turned more smoothly. There are two types of power steering systems, electric power steering systems and hydraulic power steering systems. Until now, hydraulic power steering systems have been the mainstream, but now electric power steering systems are the mainstream. Although the power steering system is designed so that the steering wheel can be operated at a minimum even if it breaks down, the steering wheel becomes extremely heavy when the assist force is lost.
The progressive increase in weight, in the dimensions of the cars and in the section of the tires has led over time to an increase in the effort to be exerted on the steering wheel. Compensating for this by raising the steering ratio compromises the handling of the car, since the steering wheel has to be turned more for the same corner. For this reason, all cars have been equipped with power steering for about twenty years.
Birth and spread
Born in the United States in the mid-twenties of the twentieth century, the steering servo initially spread to high-class cars, and then also fitted small cars. A boost to its diffusion was given by the advent of electrical systems, more efficient and economical than hydraulic ones, normally used until a few years ago. The latter, in fact, included a pump driven by the engine by means of a belt, which kept a specific oil under pressure, so as to be able to lighten the effort on the steering wheel, when necessary, by opening special valves which thus sent the oil to hydraulic pistons connected to the steering rack. This entailed the constant absorption of power from the motor by the pump, even in straight-line travel when servicing is not required.
The electric power steering consists of a motor that absorbs energy only when you steer and that engages on the column, near the steering wheel, or directly on the rack. The latter solution is preferred on luxury or sports cars because it ensures more precise and progressive steering behavior. The system also includes a steering wheel rotation sensor and a control unit, which calibrates the engagement according to the speed of the car and other parameters. In fact, in many cases it is possible to modify the amount of power assistance, and therefore the effort to be exerted on the steering wheel, according to one’s tastes or according to other devices, such as the calibration of the shock absorbers.
The electric power steering also allows the adoption of modern driving assistance systems, starting from automatic parking up to semi-autonomous driving: the control electronics are in fact able to operate the electric motor as desired and therefore to optimally calibrate the steering. For legal reasons it is still essential to keep your hands on the wheel and your eyes on the road, but the most advanced cars today are able to travel almost autonomously in many situations.
In case of failure
If the power steering action fails (which is possible for example if the steering wheel angle sensor fails), it is of course possible to control the car as usual, but the effort to be exerted on the steering wheel increases a lot and this can create a situation. dangerous if the breakdown occurs immediately before a low speed maneuver (a turn in the city, a curve on a winding road).
What is an electric power steering system?
The electric power steering system is abbreviated as EPS. There are three types of electric power steering: column assist type, pinion assist type, and rack assist type.Column assist type
The column assist type assists the steering column that connects the steering wheel and gearbox. The column assist type is suitable for small cars because it cannot exert a large amount of force. The disadvantage is that the noise of the motor is easily transmitted to the company.Pinion assist type
The pinion assist type assists the pinion gear shaft of the steering gearbox. Since a general-purpose motor can be used, the advantage is that the cost can be kept low. However, since there are many parts near the pinion, there is often no room for installation, so it is necessary to make the gear part compact.Rack assist type
The rack assist type has the role of assisting the reciprocating motion of the rack, and can realize a large assist force. However, it has the disadvantages of having a large structure and increasing the number of parts, and is generally used in large automobiles.
What is a hydraulic power steering system?
The hydraulic power steering system uses the power of the engine to operate the pump and the hydraulic power generated there to assist. Since the pump is driven by the engine, it has the disadvantage of putting a strain on the engine and wasting energy. Also, it cannot be used in the EV mode of hybrid vehicles or in the idling stop state.
The merit is that the steering inertia is small, so the steering feeling is good, and it is sometimes used in luxury cars.
How to check the power steering
If the power steering system fails, the car can still drive. However, because the steering wheel is heavy, you may not be able to turn the curve completely and you may hit the car, so check it regularly.Inspection of electric power steering system
Electric power steering is OK just by checking the steering wheel operation. Drive straight on a flat surface and check if the steering wheel can be taken to the left or right, and if you can turn the steering wheel smoothly.