Abstract:
A separately-excited fractional-horsepower electric motor in which a field coil is connected to one of the brushes by means of a brush retainer which is formed with a plug portion such that, on fitting the brush retainer to the brush holder, the plug portion penetrates and engages a socket connected to the field coil.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to the provision of a plug-in field coil connector in a fractional-horsepower electric motor to facilitate assembly of the motor. 
     A typical fractional-horsepower electric motor comprises at least one field coil which has one end for connection to a first terminal member; a first terminal member to which said one end is connected; at least two brushes; a brush holder for each brush; guide means formed on one of the brush holders; and a brush retainer movable, on the guide means, into and out of a retaining position in which the brush retainer is electrically connected to and retains a brush in said one of the brush holders. 
     To connect the brush retainer to a field coil in a motor such as this, it is normal practice to solder one end of an electrical lead to the brush retainer and to connect the other end of the lead to the field coil either by soldering or by means of a second terminal member which is cooperable with the first terminal member to form an electrical connection. Clearly, this is a time-consuming, labor intensive process. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a fractional-horsepower electric motor with a plug-in field coil connector to facilitate assembly of the motor. 
     This is achieved by providing the brush retainer with a second terminal member which is movable into and out of engagement with the first terminal member on movement of the brush retainer into and out of its retaining position. 
     Thus, according to the invention, there is provided a fractional-horsepower electric motor in which at least one field coil is connected to a first terminal member; a brush retainer is movable on guide means formed on a brush holder, into and out of a retaining position in which the retainer is electrically connected to and retains a brush in the brush holder; and the brush retainer is provided with a second terminal member which is movable into and out of engagement with the first terminal member on movement of the brush retainer into and out of the retaining position. 
     Conveniently, the guide means may comprise two side extensions projecting transversely on opposite sides of an axial plane through the brush holder and two abutment surfaces respectively formed on the side extensions and facing inwardly and away from the radially outer surface of the brush holder. 
     In this case, the brush retainer may comprise a retaining portion engaging the radially outer surface of the brush holder; grips on opposite sides of the retaining portion engaging the two abutment surfaces formed on the side extensions of the brush holder so as to permit guided movement of the brush retainer along the two side extensions; and a connecting portion extending laterally from one side of the retaining portion and carrying, at its free end, the second terminal member which is engageable with the first terminal member connected to the field coil. 
     The brush retainer may be of sheet metal and, to help secure the brush retainer in its retaining position, a concavity having a wall extending transversely of the axis of the motor may be formed in the radially outer surface of the brush holder and at least one retaining strip pressed out of the retaining portion may be disposed within the concavity so that the free end of each retaining strip lies adjacent the wall of the concavity for abutment with the wall to prevent withdrawal of the brush retainer from its retaining position. Preferably, there are two or more retaining strips and the wall of the cavity lies in a plane extending perpendicular to the axis of the motor. This ensures that the brush retainer is held squarely in place. 
     The first and second terminals may constitute the members of a plug and socket connection and, in a preferred embodiment of the invention, a moulded plastics end ring is provided adjacent the brush holders, the first terminal is a socket comprising a metal-lined aperture formed in the end ring with an axis extending parallel to the axis of the motor and the second terminal comprises a plug engageable in this socket. 
     In a typical motor according to the invention, two field coils are respectively provided with ends for connection to first terminal members; two first terminal members are connected, respectively, to two of said ends; guide means are formed on each of the brush holders; two brush retainers are respectively movable, on the guide means, into and out of retaining positions in which the brush retainers are respectively connected to and retain the two brushes in the brush holders; and the two brush retainers are respectively provided with two second terminal members which are respectively movable into and out of engagement with said two first terminal members on movement of the brush retainers into and out of their retaining positions. 
     In this case, the guide means on each brush holder may comprise two side extensions projecting transversely on opposite sides of an axial plane through the brush holder and two abutment surfaces respectively formed on the side extensions so as to face inwardly and away from the radially outer surface. In addition, each brush retainer may comprise a retaining portion engaging the radially outer surface of a brush holder, grips on opposite sides of the retaining portion engaging the two abutment surfaces on the side extensions of the brush holder so as to permit guided movement of the brush retainer along the two side extensions, and a connecting portion extending laterally from one side of the retaining portion and carrying, at its free end, one of the two second terminal members. 
     In an alternative form of motor according to the invention in which two field coils are respectively provided with ends for connection to first terminal members; two first terminal members are connected, respectively, to two of said ends; and two second terminal members are respectively movable into and out of engagement with the two first terminal members on movement of the brush retainer into and out of its retaining position, the two second terminal members are provided on only one of the brush retainers. In this case, the guide means on said one of the brush holders may comprise two side extensions projecting transversely on opposite sides of an axial plane through the brush holder and two abutment surfaces respectively formed on the side extensions so as to face inwardly and away from the radially outer surface of said one of the brush holders. In addition, the brush retainer may comprise a retaining portion engaging the radially outer surface of the brush holder, grips on opposite sides of the retaining portion engaging the two abutment surfaces on the side extensions of the brush holder so as to permit guided movement of the brush retainer along the two side extensions, and two connecting portions extending laterally from opposite sides of the retaining portion and respectively carrying, at their free ends, the two first terminal members. 
     In practice, in both of the alternative forms of the invention hereinbefore described, four terminal members are connected, respectively, to the four ends of the two field coils, but only two of these terminal members constitute first terminal members which contribute to the present invention. 
     Thus, in a preferred embodiment of the invention, a moulded plastics end ring is provided adjacent the two brush holders, the two first terminal members are sockets comprising metal lined apertures formed in the end ring with axes extending parallel to the axis of the motor, and the two second terminal members comprise plugs engageable in these sockets. 
     In another preferred electric motor according to the invention, a stator comprises a stack of field laminations, moulded plastics end rings adjacent at opposite ends of the stack, two field coils, and brush gear at one end of the stack; a rotor incorporating a commutator is mounted in the stator for rotation about the axis of the motor; the end ring the brush gear is formed with at least two apertures having axes extending parallel to the axis of the motor and at least two further apertures are formed in at least one of the two end rings; the two apertures in the end ring adjacent the brush gear are provided with metal lining to form two first terminal sockets and two of the remaining apertures are provided with metal lining to form two main terminal sockets for receiving lead terminals connected to external circuit leads; and one end of each field coil is connected to the metal lining of one of the two first terminal sockets, one end of the other field coil is connected to the metal lining of the other first terminal socket, and the other ends of the two field coils are respectively connected to the two main terminal sockets. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention are hereinafter described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a part-sectional end view of a universal electrical motor embodying the present invention; 
     FIGS. 2 and 3 are plan and side views of the motor shown in FIG. 1; 
     FIG. 4 is an isometric view of a brush holder forming part of the motor shown in FIGS. 1 to 3; 
     FIGS. 5 to 7 are plan, side and sectional end views of a brush retainer forming part of the motor shown in FIGS. 1 to 3; and 
     FIGS. 8 and 9 are plan and side views of a modified form of the brush retainer shown in FIGS. 5 to 7. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The universal electrical motor shown in FIGS. 1 to 3 has two field coil 1. Each field coil 1 has two ends 2 respectively connected to a first terminal member 3 and a main terminal member 4. The two first terminal members 3 (one for each field coil) and the two main terminal members 4 (also one for each field coil) consist of metal lined sockets molded integrally with a first plastic end ring 5. Two such end rings 5 and 6 are provided and form part of a spool structure for supporting the field coils 1 within the field laminations 7 of the motor. 
     As shown in FIG. 1, first terminal members 3 connected to the field coils 1 are connected to the brushes 8 of the motor by means of brush retainers 9 and brush springs 10. Two electrical leads 11, each provided with a lead terminal member 12 in the form of a plug, are connected, respectively, to the two field coils 1 through diagonally opposite main terminal members or sockets 4 which receive the lead terminal members 12. 
     Each brush 8 and its spring 10 are slidably mounted in a passageway 13 formed in a brush holder 14. At its radially outer end, each brush holder 14 is formed with guide means in the form of side extensions 15. As shown in FIG. 4, two abutment surfaces 16, respectively formed on the side extensions 15 face inwardly and away from the radially outer surface 17 of the brush holder 14. Each brush retainer 9 is pressed from sheet brass and, as shown in FIGS. 5 to 7, has a retaining portion 18, a connecting portion 19 and a second terminal member 20 in the form of a plug which is receivable in one of the first terminal members or sockets 3. Grips 21 on opposite sides of the retaining portion 18 are shaped to cooperate with the side extensions 15 of the brush holder 14 by engaging the abutment surfaces 16 and so, with the retaining portion 18, provide a &#34;C&#34;-section for gripping the brush holders 14. The connecting portion 19 extends from one side of the retaining portion 18 and the second terminal member 20 depends from the free end of the connecting portion 19. When mounted, each brush retainer 9 traps a brush spring 10 between its retaining portion 18 and a brush 8, to press the brush 8 against the commutator 22 (FIG. 3), and the second terminal member or plug 20 is received in the first terminal member or socket 3 of one of the field coils 1 to thereby electrically connect the coil 1 to the brush 8. 
     Connection of the coil 1 to the brush 8 can therefore be easily accomplished by sliding the retaining portion 18 of the brush retainer 9 along the radially outer surface 17 of the brush holder 14 so that the grips 21 on opposite sides of the retaining portion 18 ride over the side extensions 15 of the brush holder 14. At the same time, because of the shape and size of the connecting portion 19, this single translational movement causes the second terminal member or plug 20 to penetrate and engage the first terminal member or socket 3. 
     As shown in FIG. 4, to hold the brush retainer 9 more securely in place, the radially outer surface 17 of the brush holder 14 is formed with a concavity 23 having a transversely extending end wall wall 24 which extends perpendicular to the axis of the motor, adjacent the axially outer surface 25 of the brush holder 14. The concavity 23 accommodates retaining strips 26 which, as shown in FIGS. 5 to 7, are pressed out of the retaining portion 18 of the brush retainer 9. As shown more clearly in FIG. 7, the free end 27 of each strip 26 is disposed inwardly of the remainder of the retaining portion 18 and, as the brush retainer 9 is pressed onto the brush holder 14, the free ends 27 of the strips 26 are deflected outwards as they ride over the radially outer surface 17 of the brush holder 14. Then, when the free ends 27 reach the side wall 24 of the concavity 23, the strips 26 move into the concavity 23, as a result of their resiliency, and the free ends 27 engage the end wall 24 of the concavity 23 to hold the brush retainer 9 in place and resist its removal from the brush holder 14. 
     The brush retainer 9 is also formed with a hook 28 which is pressed from the sheet metal of the brush retainer 9, during formation of the brush retainer 9, for the optional attachment of electrical components such as a capacitive suppressor (not shown). As shown in FIGS. 5 and 6, the hook 28 is pressed from the grip 21 on the opposite side of the retaining portion 18 to the connecting portion 19. 
     In the electric motor shown in FIGS. 1 to 3, the two field coils 1 are respectively connected in series with the two brushes 8 by means of two brush retainers 9. However, in motors of different electrical configuration, in which both field coils 1 are connected in parallel to one of the brushes 8 (and neither is directly connected to the other brush 8), a different form of brush retainer is required. A modified brush retainer 29, such as this, is shown in FIGS. 8 and 9. 
     As shown in FIGS. 8 and 9, the modified brush retainer 29 has a retaining portion 18 provided with grips 21 and, on one side, a connecting portion 19 and a second terminal member 20 which are similar in all respects to the retaining portion 18, the connecting portion 19 and the second terminal member 20 of the brush retainer 9 shown in FIGS. 5 to 7. However, the modified brush retainer 29 differs from the brush retainer 9 in that, instead of being provided with a hook 28 on the side of the retaining portion 18 opposite to that of the connecting portion 19 and second terminal member 20, it is provided with a further connecting portion 19 and second terminal member 20. 
     Thus, as the modified brush retainer 29 is mounted on a brush holder 14, by sliding the retaining portion 18 over the radially outer ends of the brush holder 14 so that the grips 21 ride over the guide means provided by the side extensions 15, the two second terminal members 20, on opposite sides of retaining portion 18, penetrate and engage with respective first terminal members 3 to thereby connect the two field coils 1 directly to the brush 8 retained by the modified brush retainer 29.