Power steering system, speed reduction mechanism and bearing holder

A speed reduction mechanism comprising:

• a first gear housed in a housing and rotated by an actuator;
• a second gear adapted to mesh with the first gear;
• a bearing adapted to rotatably support at least one end of the first gear;
• a bearing holder having a substantially cylindrical holding portion formed to enclose and fit onto the bearing for holding the bearing;
• and
• a preloading means located in the bearing holder for preloading the bearing in a direction that the first gear and the second gear are brought into meshed-engagement with each other,
• wherein a first gear housing portion is defined in the housing for housing the first gear inside of the housing;
• a holder housing portion is provided at one axial end of the first gear housing portion for housing the bearing holder;
• the holder housing portion has a restriction wall arranged coaxially with the first gear housing portion for restricting a movement of the bearing holder at least in an opposite direction, which is opposite to the direction that the first gear and the second gear are brought into meshed-engagement with each other, and in a direction perpendicular to the opposite direction, and
• an inner peripheral surface of the holder housing portion, defined by the restriction wall, is formed into a substantially circular shape in lateral cross-section, and a central axis of the inner peripheral surface of the holder housing portion and a central axis of an inner peripheral surface of the first gear housing portion are configured to substantially coincide with each other.

A bearing holder for holding a bearing installed on one end of a wormshaft adapted to mesh with a worm wheel, comprising:

• a substantially cylindrical holding portion formed to enclose and fit onto the bearing and housed and retained in a holder housing portion, which is arranged coaxially with a shaft housing portion defined in the housing for housing the wormshaft;
• a guide portion provided in an inner circumference of the holding portion for permitting a movement of the bearing in a direction that the wormshaft and the worm wheel are brought into meshed-engagement with each other, and for restricting a movement of the bearing in a direction perpendicular to the direction of meshed-engagement;
• and
• a preloading means provided for preloading the bearing in the direction that the wormshaft and the worm wheel are brought into meshed-engagement with each other,
• wherein an inner peripheral surface of the holder housing portion is formed into a substantially circular in lateral cross-section and a central axis of the inner peripheral surface of the holder housing portion and a central axis of an inner peripheral surface of the shaft housing portion are configured to substantially coincide with each other.