| 摘要 |
A starter motor for an internal combustion engine comprising an electric motor capable of rotating a shaft. A pinion gear wheel carried by the shaft, and rotatable therewith, the gear wheel also being movable axially relative to the shaft. An electromagnet including an armature which is coupled to the pinion gear wheel so that the two can move axially relative to the shaft. The electromagnet also includes a plurality of electromagnet poles which are equi-angularly spaced around the shaft in a plane at right angles to the axis of the shaft, and which are spaced apart by an amount such that the armature can enter between the poles. In the rest position of the armature there is a clearance between the poles and the armature in the direction of movement of the armature. The shaping of each pole is such that the surface of the pole presented to the armature includes regions which are spaced from the armature by different distances in the direction of movement of the armature, and which are equally spaced from the shaft in a radial direction. The electromagnet further includes a member which magnetically interconnects the poles and a winding associated with the poles so that when energised there is a flow of magnetic flux between the poles and the armature, within the armature at right angles to the direction of movement thereof, and between the poles by way of said member, such that the armature is attracted to the poles. The arrangement of said regions of the pole surfaces is chosen to achieve a predetermined attraction between the poles and the armature during the movement of the armature towards the poles. |
