GB2152294A

GB2152294A - Cover plate

Info

Publication number: GB2152294A
Application number: GB08431505A
Authority: GB
Inventors: Shinichi Matsuda
Original assignee: Mabuchi Motor Co Ltd
Current assignee: Mabuchi Motor Co Ltd
Priority date: 1983-12-14
Filing date: 1984-12-13
Publication date: 1985-07-31
Also published as: GB2152294B; JPS6099854U; GB8431505D0

Abstract

A thin resin film 11 integral with a retainer 9-3 for the rotor shaft rotary bearing of a motor and formed on a metallic base plate 7 forming part of a cover plate for the motor serves with the adjacent region of the base plate as a thrust bearing for the rotor shaft. Brush gear for the motor is mounted via insulating means in electrically insulating relation with respect to the base plate. The insulating means may be integrally moulded with the bearing retainer and thin film from synthetic resin. <IMAGE>

Description

SPECIFICATION Cover plate This invention relates to cover plates for electric motors.

It has previously been proposed to manufacture so-called "miniature electric motors" with a cover plate forthe motor case formed of a metallic plate adapted to shield electromagnetic noises generated within the motor. It has generally been the practice heretofore for the metallic cover plate itself to serve as a thrust bearing limiting axial movement of the rotor shaft. As we shall explain below, we have found this arrangement to be insufficiently satisfactory.

Attempts to overcome the problems by employing a specific thrust bearing such as a plate made of synthetic resin or of relatively soft material are also not fully satisfactory for reasons which we shall explain.

In accordance with the present invention, we provide a cover plate for an electric motor, comprising: a metallic base plate; insulator means mounted on said base plate and adapted to mount brush gear for the motor in an electrically insulated relation with respect to the base plate; and a bearing retainer made of a synthetic resin and mounted on said base plate generally centrallythereof, the bearing retainer being adapted to retain a bearing for rotatably supporting one end of the rotor shaft of the motor, the bearing retainer further including an integrally formed portion thereof comprising a thin synthetic resin film formed on the metallic base plate in a region therofwherethe axial end of the rotor shaft tends to come into contact therewith, the said region and the said integrally formed portion being adapted together to act as a thrust bearing for the rotor shaft.

The invention is hereinafter more particularly described by way of example only with reference to the accompanying drawings, in which: Fig. lisa side elevational view partly in section illustrating a miniature electric motor employing a previously proposed form of cover plate; Fig. 2A is an enlarged cross-sectional view illustrating the bearing arrangements for the end ofthe rotor shaft in the embodiment of Fig. 1; Fig. 28 is a viewgenerallysimilarto Fig. 2A showing an alternative prior proposed arrangement; Fig. 3A is a plan view of an embodiment of cover plate in accordance with the present invention; Fig. 3B is a side elevational view of the plate of Fig.

3A, partly in section; Fig.4Aisan enlarged view of the central portion of Fig. 3A; and Fig. 48 is an enlarged cross-sectional view of the bearing retainer portion of the cover plate illustrating the insertion ofthe bearing.

Referring first to the previously proposed arrangements of Figs. 1 to 2B, the motor comprises a rotor 1 and a commutator 2 mounted on a rotatable shaft 3.

The shaft 3 is supported in bearings4-1 and 4-2.

Permanent magnets 5 are mounted interiorly of the cylindrical motor case 6, in the closed end of which is supported the bearing 4-1. The bearing 4-2 is supported by a cover plate for the motor case. The cover plate includes a metallic base plate 7 from which the brush gearforthe motor is mounted. As shown in Fig.

1 the brush gear comprises integral brushes which include a terminal 8-1 and a brush proper 8-2 which makes contact with the commutator 2. The brush gear is mounted on the cover plate in electrically insulating relation with respect to the metallic base plate 7 by insulating means, which here comprise insulators 9-1 and 9-2 on opposite sides of the base plate 7. The insulators 9-1 and 9-2 in this embodiment are integrally formed, a nd also integrallyformed with the insulators is a bearing retainer9-3forthe bearing 4-2.

The term "cover plate" as used in relation to this embodiment, and throughout this specification, is intended to include both the base plate 7 and the parts mounted or solid therewith, namely the insulator means.

When voltage is applied to the terminals 8-1 of the miniature motorshown in Fig. 1, current is fed to the rotor via the brushes8-2 and the commutator2 and the rotor is thereby caused to rotate in a predetermined direction by the interaction of the magnetic flux caused by the magnet 5 and the current flowing in the rotor 1.

When an external mechanical load is applied to the rotor shaft, as for example when a gear wheel is press-fitted to the rotor shaft, the resultant axial thrust must be absorbed so that there is no axial movement.

In the arrangement of Fig. 1, and as best shown in the enlarged view of Fig. 2A, axial thrust ofthe rotor shaft 3 is prevented by the metallic base plate 7, suitably formed of sheet steel, where the axial end of the rotor shaft 3 comes into contact with the base plate 7 at the region (1). We have found that such contact between the rotatable shaft and the metallic cover plate tends to cause flaws, deformation and wear resulting in vibration and mechanical noise in use of the motor.

In an attemptto overcome this problem, the arrangement shown in Fig. 2B was devised. When a thrust bearing plate 10 made of a synthetic resin or of a relatively soft metal is inserted between the axial end ofthe shaft 3 and the metallic base plate 7 as shown in the region (2) of Fig. 2B, the problem encountered with the arrangement of Fig. 2A is largely prevented so far as relatively small axial thrusts are concerned. However,the insertion and fitting ofthethrust plate 10during assembly of the miniature motor represents an unacceptable assembly and labour expense and severely affects the efficiency of assembly.

When a relatively thick synthetic resin thrust bearing plate 10 as shown in Fig. 2B is employed, we find that relatively large forces exerted on thrust bearing plate 10,forexample,when press-fitting ageartothe opposite end of the shaft 3, may cause a recess to be formed on the thrust bearing plate 10, resulting in mechanical noise and vibration.

We have found that the problems can be effectively overcome by employing a thin synthetic resin film on the metallic base plate. In particular, we have found that this arrangement appears to have good wear resistance and is capable of withstanding deformation due to thrust pressure ofthe rotating shaft 3 against the base plate.

Referring now to Figs. 3A to 4B which illustrate an embodiment incorporating this arrangement, it will be seen that, where applicable, we have employed like reference numerals as in the arrangements of Figs. 1 to 28 for like parts. The synthetic resin film is illustrated at 11 and suitably has a thickness in the range of 0.2 to 0.5 mm.This range isthatwhich we have found to be of practical untility in that a film much thinnerthan this is difficult to form, while if the synthetic resin is much thickerthan 0.5 mm., there is the danger of deformation due to thrust pressure of the rotating shaft 3 as in the arrangement of Fig. 28.

We have found that by employing a synthetic resin film 11 generally within this range, no recess or other defect tends to be formed on the resin film or on the rotating shaft 3 even when a relatively large force is applied to the shaft by press-fitting a gear to the opposite end thereof. Additionally, manufacture of cover plates as shown in Figs. 3A to 4B is extremely easy since the synthetic resin film 11 is integrally formed with the bearing retainer 9-3.

Referring more particularly to Figs. 4A and 4B, it will be seen thatthe bearing retainer 9-3 is integrally formedwiththefirstinsulator9-1 and hasa plurality of flexible part spherical fingers adapted to clasp the external part spherical surface of the bearing 4-2. As indicated schematically in Fig. 4B, the bearing 4-2 can simply be pressed into place in its bearing retainer.

In order to form the thin film 11, special consideration is given to the construction of the mould so as to faciiitate formation of a smooth and thin synthetic resin film. Thus, in order to form the first insulator9-1, the thin synthetic resin film 11 and other components on the metallic base plate 7, a mould having a construction such thaw fluid resin at high temperature and pressure can easily flow through the bearing retainer 9-3 into the bottom thereof to form a thin film is employed.

We have found that by employing a construction of cover plate as described and illustrated in Figs. 3Ato 48, we can obtain a miniature motorwith significantly less mechanical noise and vibration as compared with the prior proposed arrangements of Figs. 1 to 2B, and at the same time wear between the end of the rotor shaft and the cover plate or other axial thrust bearing is reduced providing for longereffectiveworking life.

Claims

1. A cover plate for an electric motor, comprising: a metallic base plate; insulator means mounted on said base plate and adapted to mount brush gearfor the motor in an electrically insulated relation with respect two the base plate; and a bearing retainer made of a synthetic resin and mounted on said base plate generally centrally thereof, the bearing retainer being adapted to retain a bearing for rotatably supporting one end of the rotorshaftofthe motor, the bearing retainerfurtherincluding an integrally formed portion thereof comprising a thin synthetic resin film formed on the metallic base plate in a region thereofwherethe axial end of the rotorshafttendsto come into contact therewith, the said region and the said integrally formed portion being adapted together to act as a thrust bearing forthe rotor shaft.

2. Acover plate according to Claim 1, wherein the thickness of the said thin synthetic resin film is from 0.2 to 0.5 mm.

3. A cover plate according to Claim 1 or Claim 2, wherein the bearing retainerandthe integral thin film portion are formed by moulding.

4. A cover plate according to Claim 3, wherein the bearing retainer and its integral thin film portion are formed using a mould which allows fluid synthetic resin at high temperature and pressure to flow through the bearing retainerwithinthe mould into the bottom of said bearing retainertotherebyformsaid thin film portion.

5. A cover plate according to Claim 3 or Claim 4, wherein the said insulator means is integral with the bearing retainer and its said integral thin film portion, the insulator means, bearing retainer and integral thin film portion being moulded in situ on the metallic base plate.

6. Acoverplateforanelectricmotorsubstantially as hereinbefore described with reference to and as shown in Figs. 3A to 4B of the accompanying drawings.

7. An electric motor including a cover plate according to any preceding claim.