GB2160369A - Electric motor - Google Patents

Abstract

The brushes of an electric motor are housed in brush boxes (29) to which electrical connections are made by mechanically connecting the terminal portions (31) to leads (32) to terminal portions (30) of the boxes. To facilitate assembly of the motor and to reduce the risk of the leads (32) becoming detached, the brush boxes are mounted on a support member (24) in fixed relationship to the field assembly (23 etc.) of the motor and a cap (1) is fitted in the vicinity of the mechanical connections (30, 31) and prevents the terminal portions (31) of the leads (32) moving to break those connections. <IMAGE>

Description

SPECIFICATION Electric motor This invention relates to an electric motor and to a method of assembling electric motors.

In a previously proposed design of an electric motor, motor brushes are housed in an electrically conducting holder having an integral blade projection defining a male terminal. Electrical connection to the brush box is made by mechanically connecting a suitable female connector on one end of a flexible lead to the blade terminal on the brush box. The other end of the lead may be connected to a field winding of the motor. While an arrangement of this kind is satisfactory from many respects and avoids the need for a soldered connection there is always a risk that the lead will become detached and this can be dangerous, particularly if the end of the lead then happens to make contact with the armature shaft of the motor.

It is an object of the invention to provide an improved electrical motor and an improved method of assembling such a motor.

According to the invention there is provided an electric motor including an armature, a field assembly, a support member in fixed relationship to the field assembly, a pair of brush boxes mounted on the support member and housing brushes for making electrical connections to the armature, and connecting leads for making electrical connections to the brush boxes, the connecting leads including terminal portions mechanically connected to terminal portions of the brush boxes, wherein a cap is fitted in the vicinity of the brush boxes and prevents the terminal portions of the leads moving to a position detached from the brush boxes.

With such a motor the possibility of the lead becoming detached from the brush box is substantially eliminated.

The terminal pc. 'ions of the brushes and leads may be connected together by movement of the lead terminal portions in an axial direction towards the field and the cap may be located on the axially opposite side of the brush boxes to the field in close proximity to the terminal portions of the leads. This is a convenient arrangement suitable for use on an assembly line.

The cap may be fastened to the support member of the motor.

The cap is preferably snap fitted to the electric motor. The snap fit is preferably such that once the cap is fitted it is not readily removed at least without the aid of a special tool.

The cap preferably also includes means for locating at least one wire connected to the field. The locating means may comprise a notch formed in an edge of the cap in which the wire is received. A pair of such wires, which may provide the power supply, may be located in a pair of such notches.

The cap may include one or more cavities for receiving an electrical impedance, for example a capacitor. The or each cavity may be open in a direction facing away from the brush boxes.

By way of example, an electric motor embodying the invention will now be described with reference to the accompanying drawings, of which: Fig. 1 is a top plan view of a cap for the motor; Fig. 2 is an underneath plan view of the cap; Fig. 3 is a sectional view along the line Ill-Ill of Fig. 1; Fig. 4 is a sectional view along the line IV-IV of Fig. 2; Fig. 5 is an enlarged view of part of Fig. 1; Fig. 6 is a side view of the motor with the cap of Figs. 1 to 5 fitted; and Fig. 7 is a plan view of the motor with the cap of Figs. 1 to 5 fitted.

The cap 1 shown in Figs. 1 to 5 is moulded in one piece from plastics material and generally com prises a shaped base part 2 and a pair of resilient flaps 3 having curved inwardly directed feet 4. The base part 2 is formed with a central longitudinal rib 5 on either side of which slots 6 are provided and cavities 7 are formed at opposite ends of the part 2.

The cavities 7 are box-shaped having a bottom wall 8, end wall 9 and side walls 10; the sides of the box opposite the bottom wall 8 and the end wall 9 are open. The side walls 10 are provided with slots 11 which extend inwardly from the top edges of the walls. The base part 2 has a pair of integral extensions 12 located diagonally opposite one another and these extensions have notches 13 formed in them. As most clearly seen Fig. 5, each notch has an outwardly flared outer portion 14, a constant width central portion 15 and a slightly enlarged circular inner portion 16.

A pair of slots 17 are provided in the base part 2.

Reference will now be made also to Figs. 6 and 7 in which the cap 1 is shown fitted to an electric commutator motor 20 of which only the commutator end is shown (the other end being of a suitable conventional construction). The motor 20 has an armature 21 on which a commutator 22 is provided. A field assembly generally comprising a lamination stack 23 and field coils (not visible in Fig.

6) is provided around the armature 21 and a support member 24 moulded from plastics material fixed to the end of the lamination stack. The support member 24 is of generally frustoconical shape having a wide cylindrical portion 25 at the end fixed to the lamination stack and a narrow cylindrical portion 26 at the other end in which a bearing for that end of the armature 21 is mounted. Four bars 27 interconnect the cylindrical portions 25, 26.

Housings 28 for a pair of brush boxes 29 made of metal, are mounted between pairs of bars 27.

Each of the brush boxes 29 has an integral blade 30 projecting in an axial direction away from the lamination stack 23 and defining a male terminal. A respective female terminal 31 on the end of a respective lead 32 is fitted over each of the blade terminals 30. The leads 32 are electrically connected to terminals (not shown) on the field assembly.

The cap 1 is snap fitted over the cylindrical portion 26 of the support member 24 with the feet 4 engaging the inner face of the portion 26 and located between the bars 27. The ends of the base part 2 of the cap are orientated in alignment with the brush boxes 29 with the bottom walls 8 of the boxshaped cavities 7 in close proximity to the connection of the terminals 30 and 31.

A power supply cable for the motor has an outer insulating sheath 33 in which a pair of insulated wires 34 are carried. The sheath 33 terminates short of the motor and the wires 34 pass through the enlarged circular inner portions 16 of the notches 13 and are connected to terminals (not shown) of the field assembly, the insulation of the wires 34 being stripped away only close to the field assembly.

During assembly of the motor the brush boxes 29 are fitted and the terminals 31 of the leads 32 fitted over the blades 30 on the boxes before the cap 1 is fitted. Once the cap 1 is fitted, the terminals 31 are unableto move sufficiently in an axial direction away from the brush boxes 29 to become detached from the blade 30. The wires 34 are thereafter pressed into the notches 13 in which they are a tight fit. All the above operations can readily be performed automatically on an assembly line.

Thus, in the assembled motor the cap 1 serves both to locate the wires 34 connecting the power supply to the field assembly and to retain the brush box connections. Because of the nature of the snap fitting between the cap 1 and the support member 24, the cap cannot be detached except with the aid of a tool that is able to move the feet 4further apart.

The slots 17 in the cap allow a cooling airflow to pass through the cap when the motor is in use.

The motor described above is not provided with any suppressor. If it is desired to provide a capacitor for this purpose (or any other electrical impedance for this or another purpose) one or both of the leads 32 from the brush boxes may be brought up along a side wall 10 of the base part 2 of the cap and through the slot 11 in the side wall 10 into the cavity 7. The impedance may be connected in the lead 32 at this point so that the impedance is housed in the cavity 7 and the lead 32 can pass out of the cavity 7 through the slot 11 in the opposite side wall 10 and then be connected to the field assembly.

While in the invention described the leads from the brush boxes are connected to the field assembly, in the case of a motor provided with a reversing facility or a speed control circuit it may be desirable for the leads from the brush boxes to be led away from the motor for connection to the required circuitry.

Claims (11)

1. An electric motor including an armature, a field assembly, a support member in fixed relationship to the field assembly, a pair of brush boxes mounted on the support member and housing brushes for making electrical connections to the armature, and connecting leads for making electrical connections to the brush boxes, the connecting leads including terminal portions mechanically connected to terminal portions of the brush boxes, wherein a cap is fitted in the vicinity of the brush boxes and prevents the terminal portions of the leads moving to a position detached from the brush boxes.

2. An electric motor according to claim 1 in which the terminal portions of the brushes and leads are connected together by movement of the lead terminal portions in an axial direction towards the field and the cap is located on the axially opposite side of the brush boxes to the field in close proximity to the terminal portions of the leads.

3. An electric motor according to claim 1 or 2 in which the cap is fastened to the support member of the motor.

4. An electric motor according to any preceding claim in which the cap is snap fitted to the motor.

5. An electric motor according to any preceding claim in which the cap also includes means for locating at least one wire connected to the field.

6. An electric motor according to claim 5 in which the locating means comprises a notch formed in an edge of the cap in which the wire is received.

7. An electric motor according to any preceding claim in which the cap includes one or more cavities for receiving an electrical impedance.

8. An electric motor according to claim 7 in which the or each cavity is open in a direction facing away from the brush boxes.

9. An electric motor substantially as herein described with reference to and as illustrated by the accompanying drawings.

10. A method of assembling an electric motor including an armature, a field assembly, a support member in fixed relationship to the field assembly, a pair of brush boxes mounted on the support member and having brushes for making electrical connections to the armature, and connecting leads for making electrical connections to the brush boxes, the connecting leads including terminal portions for mechanical connection to terminal portions of the brush boxes, wherein after the connecting lead terminal portions are mechanically connected to the terminal portions of the brush boxes a cap is fitted in the vicinity of the brush boxes and, once fitted, prevents the terminal portions of the leads moving to a position detached from the brush boxes.

11. A method of assembling an electric motor the method being substantially as herein described with reference to and as illustrated by the accompanying drawings.