This application relates to and incorporates herein by reference Japanese Patent Application No. 10-340440 filed on Nov. 30, 1998.
1. Field of the Invention
The present invention relates to an electrical motor used for an electrical device and its manufacturing method.
2. Related Art
Small-sized electrical motors which are used for vehicular electrical devices, audio devices or the like have a bottomed cylindrical yoke and a rotor disposed within the yoke. The yoke holds permanent magnets therein and forms a part of a magnetic circuit. The yoke is shaped by deep-drawing a metal plate. A bearing is fixed on the bottom of the yoke to support a rotary shaft of the rotor to enable rotation of the rotor.
In manufacturing the yoke, the metal plate is first deep-drawn into a bottomed cylindrical shape, and then the bearing is fixed after flushing the deep-drawn yoke to remove the machining oil used in the deep-drawing, machining debris and the like.
If the deep-drawn yoke is subjected to the flushing process after the bearing is fixed to the yoke, oil provided in the bearing will also be unnecessarily removed thus lessening the function of the bearing. Further, the bearing cannot be fixed before or during the deep-drawing process, because the thickness of the metal plate changes between before and after the deep-drawing process. Thus, the conventional motor requires an increased number of manufacturing processes and thus lowers the manufacturing efficiency.
It is therefore an object of the present invention to provide an electrical motor manufacturing method which reduces the number of manufacturing processes and increases manufacturing efficiency.
According to the present invention, a flat metal plate is die-cut into a base plate shaped to include a bottom wall and a side wall unitary with the bottom wall. A bearing member for supporting a rotary shaft of an electrical motor is fitted substantially in a center of the bottom wall of the base plate.
The base plate is bent at a junction between the bottom wall and the side wall, and the side wall is bent in correspondence with an outer peripheral configuration of the bottom wall, thereby forming a bottomed cylindrical yoke of the electrical motor.
Preferably, a through hole for passing the rotary shaft therethrough is formed in the center of the bottom wall of the base plate at the same time as the die-cutting of the metal plate. A central part of the bottom wall of the base plate is plastically deformed to provide a bearing holder in the bottom wall for rotatably accommodating the bearing member in the bearing holder.
Preferably, the bearing member is placed on the bottom wall of the base plate, a resilient member is placed on the bearing member, and the resilient member is tightly fixed to the bottom wall of the base plate to resiliently bias the bearing member toward the bottom wall of the base plate.