GB2160714A

GB2160714A - Improvements in or relating to electric motors

Info

Publication number: GB2160714A
Application number: GB08422604A
Authority: GB
Inventors: Anthony Jonathon Sanders
Original assignee: Black and Decker Inc
Current assignee: Black and Decker Inc
Priority date: 1984-06-22
Filing date: 1984-09-07
Publication date: 1985-12-24
Also published as: GB8415951D0; GB8422604D0

Abstract

An end cap assembly for an electric motor includes a plastics body and an electrical impedance (21A) which is mounted on the plastics body and to which electrical connection is made. The plastics body includes a resilient plastics clamping arm (24) which is resiliently deformed by the impedance (21A) and which bears against the impedance clamping it to the body. This provides a very simple but reliable and effective way to secure the impedance on the end cap assembly. <IMAGE>

Description

SPECIFICATION Improvements in or relating to electric motors This invention relates to electric motors and the design of certain components for such motors. In particular the invention is concerned X ith the mounting of an impedance on the motor.

A difficulty encountered by designers of an electric motor relates to the location of the impedance (capacitor) that is commonly connected across the power supply leads to the motor. In many respects it is convenient to mount the impedance on the motor itself but as this part vibrates during operation of the motor there is a risk of the electrical connections to the impedance breaking.

According to the invention there is provided an end cap assembly for an electric motor, the end cap assembly including a plastics body and an electrical impedance which is mounted on the plastics body and to which electrical connection is made, wherein the plastics body includes a resilient plastics clamping arm which is resiliently deformed by the electrical impedance and which bears against the impedance clamping it to the body.

Such an arrangement provides a very simple but reliable and effective way to secure the impedance on the end cap assembly.

In a typical case the impedance may be a capacitor connected across the power supply to the electric motor.

The clamping arm may have a distal end on which a clamping head is formed, the clamping head having a protuberance for engaging the impedance. The protuberance may have an inclined cam face for engaging the impedance during its installation whereby its clamping arm is resiliently deformed during its installation. The protuberance may have a face disposed at an acute angle to the longitudinal axis of the arm, which face bears against the impedance clamping it to the body.

The invention also provides an electric motor including an armature and a stator assembly wherein the stator assembly includes a lamination stack and an end cap assembly as defined above, the end cap assembly being fixedly mounted relative to the lamination stack. The invention further provides an electric tool, which may be a hedge trimmer, incorporating such an electric motor.

By way of example an embodiment of the invention will now be described with reference to the accompanying drawings, of which: Fig. 1 is a sectional side view of a motor mounted in the body of a hedge trimmer, Fig. 2 is a plan view of an end cap assembly of the motor, Fig. 3 is a sectional view along the lines Ill- 111 of Fig. 2, and Fig. 4 is a side view of a part of the end cap assembly without electrical connectors showing the use of a resilient arm to locate a capacitor on the motor body.

Referring first to Fig. 1, a hedge trimmer has an outer casing 1 of clam shell construction, a motor 2 connectible to a power supply by a cable 3 via a switch 4 in a handle 5. The motor has an armature shaft 6 which drives the blades (not shown) of the trimmer via gears (not shown) mounted in a gearbox housing 7.

The motor 2 has an armature on the armature shaft 6, a commutator 8, a stator assembly 9, an end cap 10 at the gearbox end and an end cap assembly 11 at the commutator end. The end cap 10, end cap assembly 11 and stator assembly 9 are bolted together and the end cap 10 and the gearbox housing 7 are also bolted together. The armature shaft is mounted for rotation at one end in a bearing of the end cap assembly 11 and at the other end in a bearing in the gearbox housing 7.

The present invention is concerned with the structure of the end cap assembly 11 and in particular the mounting of an impedance on the end cap assembly, and it should be understood that the invention may find a wide variety of applications in any case where an electric motor is to be employed. The description below is therefore concerned primarily with those details of the motor 2 and in particular of the end cap assembly 11 that relate to the mounting of the impedance.

Referring now also to Figs. 2 and 3, the end cap assembly 11 comprises a plastics body 12,having an annular endportion 13 in which a bearing (not shown in Fig. 2) for the motor armature shaft is mounted, a pair of brush boxes 1 4 housing brushes 15, three part connecting arrangements 1 6A, 1 6B, 1 6C for making electrical connection between the brush boxes 14 and ends of the field coils of the motor 2, and a pair of strip connectors 1 7 for making electrical connection between a power supply and ends of the field coils. The strip connectors 1 7 are relatively stiff members and therefore retain their shape during normal use.Each three part connecting arrangement comprises a first strip connector 1 6A which connects to a brush box at one end and has a forked end at the other end, a second strip connector 1 6C which connects to a field coil at one end and has a forked end at the other end and a length of wire 1 6B connected between the forked ends of connectors 16A, 16C.

As shown most clearly in Fig. 3, the cap assembly fits around the end of the stator assembly 9 and has screw threaded bores 20 by which it is bolted to the stator assembly and the end cap 1 0.

A capacitor 21 is electrically connected between the connectors 1 7 by soldering the leads of the capacitor to the connectors 1 7.

The capacitor 21 is located in a recess 22 on the body 1 2 and is secured in place by a novel fastening arrangement which will now be described with reference primarily to Fig.

4.

There is shown in Fig. 4 three positions of the fastening arrangement corresponding to a first position without any capacitor received in the arrangement, a second position with a capacitor 21A of a first relatively small size received in the arrangement and a third position with a capacitor 21 B of a second larger size received in the arrangement.

The fastening arrangement is provided on the top of a cylindrical cap part 23 of the body 1 2 and comprises an upstanding integral plastics arm 24, the natural position of which is the extreme right position shown in Fig. 4, and a wall 25 opposite the arm 24.

The arm 24 is formed with a head 26 at its distal end and the head has a steeply inclined cam face 27 and a shallowly inclined shoulder 28 below the face 27. The depth of the arm (that is to say the dimension from left to right in Fig. 4) may be of the order of half the width (that is the dimension into the paper in Fig. 4).

During assembly of the motor, taking the case where for example the capacitor 21A is to be installed, the capacitor 21A is introduced parallel to the armature axis towards the space between the wall 25 and the arm 24. As the capacitor 21A meets the distal end of the arm 24 it engages the cam face 25 thereof camming that end of the arm away from the wall 25 and bending the arm towards a perpendicular position. Once the leading end of the capacitor has passed the head 26 further movement of the arm 24 away from the wall 25 ceases.As the leading end of the capacitor approaches the top of the cylindrical cap part 23 the trailing end passes the most protruding part of the head 26 and the trailing end comes into engagement with the shallowly inclined shoulder 28; at this stage the resilience of the arm causes the arm to spring back towards the wall 25 and the capacitor 21A is pressed down against the top of the cylindrical cap part 23.

The final positions of the capacitor 21A and the arm 24 are shown in Fig. 4, the arm 24 being in the middle one of the three positions shown. In this position the arm 24 is still resiliently deformed and the capacitor 21A is clamped securely between the head 26 of the arm on the one hand and the top of the cap part 23 and the wall 25 on the other hand.

If rather than installing the capacitor 21A it is desired to install the capacitor 21 B the sequence of operations is the same as that described above except that the final position of the arm 24 is the left hand position shown in Fig. 4.

Because the capacitor is securely clamped on the end cap assembly the risk of the electrical connections to the capacitor becominc damaged are very greatly reduced.

Claims

1. An end cap assembly for an electric motor, the end cap assembly including a plastics body and an electrical impedance which is mounted on the plastics body and to which electrical connection is made, wherein the plastics body includes a resilient plastics clamping arm which is resiliently deformed by the electrical impedance and which bears against the impedance clamping it to the body.

2. An end cap assembly as claimed in claim 1 wherein the impedance is a capacitor.

3. An end cap assembly as claimed in claim 1 or 2 wherein the clamping arm has a distal end on which a clamping head is formed, the clamping head having a protuberance for engaging the impedance.

4. An end cap assembly as claimed in claim 3 in which the protuberance has an inclined cam face for engaging the impedance during its installation whereby the clamping arm is resiliently deformed during said installation.

5. An end cap assembly as claimed in claim 3 or 4 wherein the protuberance has a face disposed at an acute angle to the longitudinal axis of the arm, which face bears against the impedance clamping it to the body.

6. An end cap assembly as claimed in any preceding claim wherein the arm is an integral part of the plastics body.

7. An end cap assembly substantially as herein described with reference to and as illustrated by the accompanying drawings.

8. An electric motor including an armature and a stator assembly wherein the stator assembly includes a lamination stack, an end cap assembly as claimed in any preceding claim, the end cap assembly being fixedly mounted relative to the lamination stack.