APPLICATION>Steering System
Steering System
Vehicles have three basic functions: moving, turning and stopping. Turning is the job of the steering system. Steering systems are mechanisms by which turning displacement of the steering wheel is converted to turning of the tires via the steering gear. Various types of rolling bearings are used in the various rotational mechanisms of steering system. The main steering system from the steering wheel to the tires consists of the following components:

>Steering column
>Steering gear
>Hydraulic pump

HCH bearings for steering column
One ball bearing is used on the upper side and the other is on the lower side as column shaft support bearings. Thin series ball bearings are used due to limited space. Because the radial and axial play of the steering wheel should be minimized, the residual radial clearance of the bearing after mounting should be very small even slightly negative. HCH are able to supply these kinds of bearings with optimized clearance. Moreover material with high purity and long service life is heat treated by most advanced machines.

HCH bearings for steering gear
Steering gear bearings are usually for rack-and-pinion type steering. For this application, axial and radial loads are produced by gear reaction. Axial load is supported by the deep groove ball bearing. Since the axial load being placed on the bearing is usually high, and therefore thorough consideration should be given to the allowable axial load of the bearings. In the case of power steering, bearings are also used in the torsion bar, if the clearance after assembly is a source of noise, deep groove ball bearings are used and clearance after assembly is made negative.

HCH bearings for pumps
Ball bearings are used for pulley support of the engine-driven hydraulic pump (vane pump), which serves as the power source for hydraulic power steering. The configuration is shown in the picture. The side of the bearing facing the pulley is exposed to the air in the engine bay, so the bearing must be sealed. Furthermore, the bearing must have a small running toque in order to minimize energy loss. Therefore, HCH has developed a very light contact type seals for this application. However, if the bearing is mounted near the road surface in the engine bay, HCH contact type seals are used so that muddy water can’t get into the bearing if it gets on the bearing from the pulley side.

Electric power steering
Electric power steering (EPS), which uses an electric motor as its power source, is now being used increasingly in the place of enginedriven hydraulic power steering because it reduces energy loss. Regarding the features of column type EPS shown in the picture, because the motor, reduction gear and other parts composing the power assist mechanism are concentrated on the column, a manual steering system can be converted to a power system merely by changing the column unit. Basically, only the motor and the reduction mechanism are added, and therefore column type EPS is much lighter and more compact than a conventional hydraulic power steering system.

HCH bearings for reduction gear and electric motors
Two deep groove ball bearings are used for worm shaft support. The pre-load is applied from the outer ring side of the motor side bearings. The axial and radial loads produced by reaction of the worm gear are supported by the two bearings. Quiet operation is especially important because it is located in the passenger room, and sufficient consideration must be given to noise regarding these bearings.

Brush-less permanent magnets motors will provide better steering feel due to lower rotor inertia. A brush-less approach will typically provide a longer service life than brush equivalent. The usual performance criteria requested for electric motors are:

> Silent running
> Mechanical and electric components compatible with frequent and occasional severe contamination
> Long service life including resistance to knocks and shocks which may occur during vehicle maintenance
> Low friction torque, conserving battery power

Accordingly, HCH endeavor to develop bearings in electric motors for driving hydraulic gear pump or worm gear reducer with following characteristics:

> Torque reduction
> Improved stiffness, under low and high load
> Low friction for reduced energy consumption
> Longer service life with HCH high quality bearing material and advanced heat treatment technology

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