Idling speed control device of an internal combustion engine

An idling speed control device for an internal combustion engine having an intake passage for delivering combustion air to the engine, a throttle valve arranged in the intake passage, a bypass passage having a first end connected to the intake passage upstream of the throttle valve and a second end connected to the intake passage downstream of the throttle valve, a valve member arranged in the bypass passage, a valve shaft connected to the valve member, and drive means for axially moving the valve shaft for controlling the flow area of the bypass passage in response to at least one engine operating condition, wherein said drive means comprises:

• a step motor comprising a motor housing, a stator fixed in said motor housing, a rotor rotatably mounted in said motor housing, the rotor having an internally threaded bore coaxial with its axis of rotation and matingly engaging an externally threaded portion of said valve shaft, the motor housing having a bearing receiving hole;
• and bearing means having an outwardly projecting arm engaging an inner wall of said bearing receiving hole having a contour shape the same as that of the bearing for fixedly mounting the bearing means in said motor housing, said bearing means having a bearing hole of non-circular cross section and said valve shaft having a portion of complementary non-circular cross-section slidably received in said bearing hole, whereby rotation of said rotor is converted to linear motion of said valve shaft.