This invention relates generally to a miniature motor used in audio and video equipment, and automotive electrical equipment, and more particularly to a miniature motor which can be manufactured in small sizes, assembled easily, and in which electrical noise can be reduced.
FIG. 1 is a partially cross-sectional side view illustrating an example of miniature motor to which this invention is applied. In FIG. 1, reference numeral 31 refers to a housing made of a metallic material, such as mild steel, formed into a bottomed hollow tubular shape and having a permanent magnet 32 of an arc-segment shape, for example, fixedly fitted to the inner circumferential surface thereof. Numeral 33 refers to an end cap made of a thermoplastic resin material, for example, and formed in such a fashion as to engage with an open end of the housing 31. Next, numeral 34 refers to a rotor consisting of an armature 35 facing the permanent magnet 32 and a commutator 36, and rotatably supported by bearings 37 and 38 each provided on the housing 31 and the end cap 33.
Numeral 39 refers to a brush arm made of an electrically conductive material, formed into a strip shape, having a brush 40 making sliding contact with the commutator 36, and provided inside the end cap 33. Inside the end cap 33 also provided are a pair of terminals 41 and 41 electrically connected to the brush arms 39 and 39 so that power can be fed from an external d-c power source to the armature 35 via the brush arms 39 and 39, the brushes 40 and 40 and the commutator 36.
With the aforementioned construction, when power is fed to the armature 35, rotating force is imparted to the armature 35 placed in a magnetic field formed by the permanent magnet 32 fixedly fitted to the inner circumferential surface of the housing 31, causing the rotor 34 to rotate, driving various pieces of equipment connected to the rotor 34.
As means for reducing electrical noise in the aforementioned miniature motor, there can be a construction where the housing 31 is connected to one terminal 41 via a ground terminal 42 made of an electrical conductive material and formed into a flat sheet shape. As another such means, there can also be a construction where a capacitor 44 is connected across a pair of the terminals 41 and 41 via a lead wire 43, as shown in FIG. 3.
Examples of public knowledge include EP 509683, GB 2172754, GB 2173648, and GB 2103042.
In the construction shown in FIGS. 2 and 3, where the ground terminal 42, the capacitor 44 and other component members for reducing electrical noise are provided, an excess space has to be provided inside the equipment or system which is driven by the miniature motor. Furthermore, a space larger than necessary may have to be provided because the shape, size and mounting position of the component members for reducing electrical noise are uncertain.
Since the component members for reducing electrical noise have no interchangeability, separate jigs, tools and personnel have to be provided if multiple types of component members are needed. This could lead to lowered production efficiency.
In the construction shown in FIG. 3, the operation of connecting the lead wire 43 of the capacitor 44 to the terminal 41 is extremely troublesome, the soldering operation inevitably needed for wire connections, and the placement and cutting of the lead wires 43 involve a high degree of skills because of a very limited space around the location at which the capacitor 44 is installed. This could result in increased assembly time and manhours, leading to increased manufacturing cost. In addition, soldering in a limited space tends to cause unstable wire connections, lowering the strength of wire connections to vibration or impact during service. This could lead to deteriorated reliability of electrical connections.