How is the Steering Rack Arranged?
Steering control ensures the movement of a car in the direction set by the driver. The main components of the steering system are the steering drive and the steering mechanism. Today, car manufacturers install rack-type steering mechanisms in passenger cars, and its foundation is the steering rack.
To ensure a high level of driving comfort, the steering rack is equipped with either a hydraulic power steering (HPS) or an electromechanical power steering (EPS). There are three main types of steering racks:
- Mechanical steering racks.
- Racks with hydraulic power steering (HPS).
- Racks with electromechanical power steering (EPS).
Mechanical Steering Racks
The simplest in design, they represent a direct transfer of torque from the input shaft with a gear to the toothed rack. This type of rack is often used in conjunction with EPS and is installed on the steering column.
Among the main components of a mechanical steering rack, the following can be highlighted:
- Housing made of aluminum, with a special cavity for the corrugated protection to prevent moisture and dirt from entering the mechanism.
- Gear or toothed wheel drive, located inside the steering mechanism housing, held in place by a special bearing.
- Spring with a pressurized piston. Its task is to tightly press the steering rack against the gear, allowing for the maximum engagement of teeth.
- Bushing for the tie rod joint. It operates within a specified interval set by engineers and provides the necessary movement for the mechanical rack.
Steering Racks with Hydraulic Power Steering
The main difference from a mechanical rack is the presence of hydraulic cylinders formed between the toothed rack and the housing. A spool valve installation is provided on the input rack bar.
It is necessary to constantly monitor the condition of the hydraulic drive to prevent leakage of working fluids and their contamination. To remove the steering mechanism, it is necessary to drain the working fluid. During the replenishment of the hydraulic drive with fresh working fluid, it is necessary to remove air from the system.
This type of rack was widely used until 2000. Then there was a transition to racks with electromechanical power steering. Currently, HPS is mainly used in off-road and commercial vehicles. Approximately 98% of all passenger cars produced today are equipped with EPS.
Steering Racks with Electrical Power Steering
In racks of this type, reinforcement is achieved through an electric motor. The operation of the electric motor is controlled by the EPS system.
There are several types of EPS, differing in the way force is transmitted to the rack bar and the location of the control block.
- The most common design involves placing the electric motor next to the rack and assisting in its movement through an additional gear and worm gear.
- Another solution involves placing the electric motor parallel to the rack, with force transmission achieved through a toothed belt.
- The third option is called a direct drive. In such racks, the rack bar moves inside the motor, using a force transmission system with a "screw-nut" pair, making the entire unit the most compact.
Control blocks with electromechanical power steering also differ in location. In European cars, the EPS block is often mounted next to the electric motor or on it, essentially on the rack. In Japanese and Korean cars, the control block is installed closer to the instrument panel. In the first case, the design is more repairable, but there may be mechanical damage to the control block or water ingress. In the second case, the control block is better protected, but if a separate check of the rack is needed, it is necessary to pull several meters of wiring to find the control block itself.
