A miniature electric motor

Abstract: A miniature motor comprising a cylindrical case (1) closed at one end and having a permanent magnet (2) fixedly fitted adjacent the inner surface thereof. An end plate (6) closes the open end of the case (1) and has input terminals (8). A rotor (5) is rotatably supported by bearings (9,10) on the case (1) and the end plate (6). Power is fed to the input terminals via a printed-circuit board (31) which is fitted to a connector-unit body (21), itself mounted on the end plate (6), The connector unit (20) has connector pins (22) formed with retainer pieces (25) at one end for printed-circuit boards and contactor pieces (26) at the other ends for the input terminals (8). The connector-unit body (21) is made of an insulating material and formed into a plate shape for fitting the motor end plate (6).

Description: This invention relates to a miniature electric motor of the type in which power is fed to the motor rotor via printed-circuit boards on which control equipment is mounted, or printed-circuit boards connected to control circuits. Typically, in such a motor a printed-circuit board will be connected directly to the motor input terminals. When mounting a printed-circuit board (hereinafter referred to as a "PCB") on a miniature electric motor, electrical connections are normally made directly by soldering to the input terminals of the motor. However, lead wires or separately provided connectors may be used. Alternatively, connector pins for mounting PCBs may be incorporated inside the miniature motor. Soldering PCB connections directly to motor input terminals requires a high level of skill in performing complicated soldering operations in an extremely limited space in a miniature motor. This poses a problem in improving productivity in the mass production of miniature motors. Connecting a PCB to the motor input terminals via lead wires or connectors also normally involves soldering operations, as noted above, making the entire assembly work complex. In addition, the presence of such lead wires between the PCBs and the miniature motor requires additional space. This makes it difficult to make the entire motor unit compact in size. With each of these techniques some additional assembly work is required after a PCB has been mounted. This leads to increased manufacturing cost. When connector pins are incorporated inside miniature motors, a particular design is needed, requiring an increase in the number of production items. This is not suitable for mass production requiring component standardization, and leads to increased cost. Further, since conventional PCB-mounting connector pins are normally made in a resilient material that is caused to bite into a PCB, upon mounting, it is difficult to remove a PCB once mounted, and replace it after removal. This construction cannot easily cope with the need for detachability of PCBs in miniature motors. An electric motor is disclosed in European Specification No. 0,056,756 in which connecting wires leading from the motor stator are attached to a PCB connector. The connector is disposed within the motor case and clips to the edges of an opening in the case. Spring elements are provided on the connector to engage a PCB when inserted through the opening. European Specification No. 0,360,623 describes a splashproof cover for a motor which provides a socket for connection to a power supply. The cover fits over the end cap of a motor. Two conductors are moulded into the cover, each having a slot for receiving a respective motor terminal, and a tongue for fastening to a corresponding slot formed in the motor end cap. The present invention is an adaptation of a known miniature electric motor construction having a cylindrical case closed at one end and a permanent magnet fitted to the inner surface thereof; an end plate closing the open end of case; a rotor rotatably supported by bearings on the case and the end plate; input terminals mounted in the end plate; and means enabling a printed circuit board to be connected to the terminals in an electrical circuit for coupling the rotor to an electric power source. According to the invention a connector unit for a printed circuit board is mounted on the input terminals, which unit comprises a body with connection elements, each element having a contact at one end for engaging a motor input terminal and a retainer piece at the other end, the retainer pieces cooperating to provide a mount for the printed circuit board and extending into an opening in the connector body from one side, which opening defines an insertion hole on the other side of the body for receiving an edge of a printed circuit board. The connector unit is preferably designed to fit adjacent the motor end plate to minimise additional space requirements. The unit would normally be fitted over the motor input terminals external of the motor case, but in some embodiment it can be mounted internally. Thus, the PCB can be connected between the input terminals and the motor rotor connections, such as brushes, commutator etc., or between the power source and the input terminals, which is the preferred arrangement and facilitates the removal and replacement of the PCB. Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings wherein: Figure 1 is a longitudinal partly sectional view of a miniature motor suitable for adaptation according to the present invention; Figure 2 is an exploded perspective view illustrating the installation of a connector unit according to one embodiment of the invention; Figure 3 is an exploded perspective view showing the inner face of the connector-unit body and a connection element of the unit shown in Figure 2. Figure 4 is a cross-sectional view of the connector unit shown in Figures 2 and 3; Figure 5 is a detail cross-sectional view showing the connector unit fitted to the end plate and the connection with a motor input terminal; Figure 6 is another detail cross-sectional view showing the connector unit fitted around a central boss on the end plate; Figure 7 is a partially cross-sectional view illustrating an alternative means by which the connector unit may be fixedly fitted to the end plate; Figure 8 is an exploded perspective view similar to Figure 2, but illustrating another embodiment of the invention; Figure 9 is an exploded perspective view showing the inner face of the connector-unit body and a connection element of the unit shown in Figure 8; and Figure 10 is a perspective view showing the inner face of the assembled unit of Figure 8. As shown in Figure 1, a miniature motor to which this invention may be applied has a case 1 made of a soft magnetic material, such as mild steel, formed into a bottomed hollow cylindrical shape and having a permanent magnet 2 of an arc-segment shape fixedly fitted to the inner surface thereof. A rotor 5 is mounted in the case 1, which rotor comprises an armature 3 facing the permanent magnet 2 and a commutator 4. An end plate 6 made of an insulating material engages and closes the open end of the case 1. Bearings 9 and 10 are fixedly fitted in bearing holders 11 and 12 provided by embossing the bottom part of the case 1 and the end plate 6, respectively, and rotatably supporting a shaft 13, upon which the rotor is mounted. Reference 7 indicates a brush arm made of an electrically conductive material provided on the end plate 6, connected to an input terminal 8. The brush arm 7 makes sliding contact with the commutator 4 as the rotor turns. Thus, as electric current is fed to the input terminals 8 the motor operates in known manner to drive external equipment (not shown) via the rotating shaft 13. The connector unit shown in Figure 2 has a body 21 and connection elements 22. The body 21 is made of an insulating material and formed into substantially a plate shape, with the outer contour thereof substantially similar to that of the end plate 6. The connection elements 22 are made of an electrically conductive material and formed into a strip shape of an almost arc-segment shape, and fitted to the connector-unit body 21, forming a pair. At the ends of each connection element 22 are a retainer piece 25 and a contact 26 formed by bending the ends thereof by pressing means, for example. The retainer pieces 25 cooperate to provide a mount for a printed circuit board (PCB) 31 within a recess 23, as described below. The contacts 26 serve to make electrical connections with the input terminals 8. The body 21 is also formed with a central opening 24 to facilitate the mounting of the unit 20 on the end plate 6. A boss 12 is formed on the external face of the end plate 6 with lateral projections 27. When the unit is mounted, the boss 12 projects through the opening 24, and is held in place by the projections 27, as shown in Figure 6. As shown in Figure 3, recesses 28 are formed on the rear or inner surface of the body 21 to a depth corresponding to the thickness of the connection elements 22, and holes 29 and 30 are provided at the ends of the recesses 28 for receipt of the retainer pieces 25 and contacts 26 respectively. With the elements 22 fitted to the body 21, a PCB 31 can be readily mounted on the unit in the recess 23, as shown in Figure 4. This will normally be effected only after the unit 20 has been fitted to the end plate 6 of the motor. The PCB 31 can be held in position at a predetermined pressure by the elastic deformation of the retainer pieces 25. The PCB can be extracted by exerting a moderate degree of pulling force. In Figure 5 a lanced and raised part 32 formed in the middle of the contact 26 of a connection element 22 is shown resiliently engaged with an input-terminal 8. as the connector unit 20 is mounted on the end plate 6, the lanced and raised part 32 makes contact with the input terminal 8 by a predetermined elastic force, thus establishing and maintaining an electrical connection. Figure 6 shows the mounting of the connector unit 20 on the end plate 6, as described above. Figure 7 illustrates an alternative technique. In Figure 7, engaging pieces formed integrally with the connector-unit body 21, with the tips thereof formed into an arrowhead shape protrude from the connector-unit body 21. Matching insertion holes 34 are provided at locations on the end plate 6 corresponding to the engaging pieces 33 and having locking parts 35. With this arrangement, as the connector unit 20 is mounted on the end plate 6 in the direction shown, the engaging pieces 33 enter the holes 34, and the tips of the engaging pieces 33 are locked by the locking parts 35. In the embodiment of the invention shown in Figures 8 to 10 the input terminals 8 are so-called female terminals existing on the end plate 6, unlike the male terminals shown in Figures 1 and 2. The contacts 26 therefore extend away from the connector body 21 such that they project into the end plate 6 when the unit 21 is mounted to engage the input terminals 8. In other respects, the construction of the unit of Figures 8 to 10 is substantially the same as that previously described. The present invention offers the following particular benefits. (1) PCBs can be mounted on a miniature motor merely by fitting a connector unit as described herein to the end plate of the miniature motor. This leads to a substantial improvement in working efficiency. (2) The miniature motor of this invention has great versatility, and can satisfy both terminal specifications and PCB specifications, depending on customers' needs. This lends itself to standardization of miniature motors and helps reduce manufacturing costs. (3) Since the connector unit is compact in size, little or no modification is needed even after it is incorporated in a miniature motor. this meets the market's needs for downsizing the motors. (4) The PCBs are detachable from the motors which facilitates maintenance of the motors during their working life.

Claims: A miniature motor having a cylindrical case (1) closed at one end and a permanent magnet (2) fitted to the inner surface thereof; an end plate (6) closing the open end of case; a rotor (5) rotatably supported by bearings (9,10) on the case (1) and the end plate (6); input terminals (8) mounted in the end plate (6); and means enabling a printed circuit board to be connected to the terminals in an electrical circuit for coupling the rotor to an electric power source CHARACTERISED IN THAT a connector unit (20) for a printed circuit board (31) is mounted on the input terminals (8), which unit comprises a body (21) with connection elements (22), each element having a contact (26) at one end for engaging a motor input terminal (8) and a retainer piece (25) at the other end, the retainer pieces (25) cooperating to provide a mount for a said printed circuit board (31), the retainer pieces (25) extending into an opening in the connector body (21) from one side, which opening defines an insertion hole (23) on the other side of the body (21) for receiving an edge of a printed circuit board. A miniature motor according to Claim 1 CHARACTERISED IN THAT the connection elements (22) are received in recesses (28) in the connector body (21), each recess being enlarged in the region of the respective contact (26) to receive an input terminal adjacent thereto. A miniature motor according to Claim 1 or Claim 2 CHARACTERISED IN THAT the connector body (21) is substantially equivalent in shape to the motor end plate (6) and made of an insulating material. A miniature motor according to any preceding Claim CHARACTERISED IN THAT each connection element is in the shape of an arcuate plate segment, the contacts (26) and retainer pieces (25) being formed by bending sections from said plate. A miniature motor according to any preceding Claim CHARACTERISED IN THAT the contacts (26) and the retainer pieces (25) project in the same direction into the connector body (21). A miniature motor according to any of Claims 1 to 4 CHARACTERISED IN THAT the contacts (26) and the retainer pieces (25) project in opposite directions with the retainer pieces (25) projecting into the connector body. A miniature motor according to any preceding Claim CHARACTERISED IN THAT a bearing holder forms a projection (12) on the outer end face of the end plate (6), the connector-unit body (21) being formed with a central opening or recess (24) which engages the projection (12) to secure the connector unit thereon. A miniature motor according to any preceding Claim CHARACTERISED IN THAT engaging pieces (33) are formed on the connector unit body (21), which pieces are received in insertion holes (34) formed in the end plate (6) to secure the connector unit on the end plate. A miniature motor according to any preceding Claim CHARACTERISED IN THAT the connector unit (20) is fitted to the end plate (6) externally of the motor case (1).

Inventors: KAJIE NAOSHI, SUZUKI SATOSHI, KAJIE, NAOSHI, SUZUKI, SATOSHI, KAJIE, NAOSHI, MABUCHI MOTOR KABUSHIKI KAISHA, SUZUKI, SATOSHI, MABUCHI MOTOR KABUSHIKI KAISHA
Applicants: MABUCHI MOTOR CO, MABUCHI MOTOR KABUSHIKI KAISHA
Application year: 1992
Main classification: H02K23
IPC codes: H02K5, H02K23