GB2233160A - Commutated electric motor with suppression element - Google Patents

Abstract

In a rotor for an electric motor a suppression element eg a varistor 1 has apertures, surrounded by conductive silver pads, which receive extensions 12a of tangs 12 of commutator segments 10. The extensions 12a serve to locate the varistor mechanically on the commutator and form an electrical connection therewith. Alternatively, in a commutator arrangement having insulation piercing terminals, connectors 45 may engage varistor 50 via holes 52 and pads 53. The armature connections may be wrapped around the portions 45b which have insulation cutting edges 48 (Fig 5). The terminal housings 25 may be circumferentially enlarged to permit angular adjustment of the segments 29 during assembly. <IMAGE>

Description

ECTRO MOTOR wT:-: SUPPRESSION ~EN.Elim The present invention relates to an electric motor with a suppression element, such as a varistor.

Varistors in the form of discs are electrically connected across the commutator segments in PMDC motors in order to suppress the electrical interference produced by the operating motor.

This is particularly important when the motors are used in modern automobiles. Automobiles may have over twenty such motors for operating door locks, windows, airconditioning vents etc., and also have sophisticated electronic control systems for controlling the enne performance and the brakes. Any electrical interference may adversely affect the electronic control systems and so the efficient operation of the motor suppression is of considerable importance. Hence a variety of spark quenching suppress on elements is used in such motors to reduce sparking at the brush commutator interface.

A first aspect of the present invention provides a rotor for an electric motor, comprising a shaft and an armature and commutator mounted on the shaft, the commutator comprising a plurality of segments mounted on an electrically insulating base, the segments being electrically connected to coils of the armature, and a spark quenching suppression element electrically connected across two or more commutator segments, wherein the suppression element is electrically connected to a said segment by means of an electrically conducting tab which is mounted on the commutator in electrical connection with the segment and which extends through an aperture or slot in the suppression element and is electrically connected thereto.

In this way the mechanical connection of the suppression element on the commutator can be enhanced, this reducing the risk of the suppression element becoming electrically disconnected from the commutator segments.

Preferably the suppression element is a varistor.

A second aspect of the present invention provides a varistor which is annular in shape and has a plurality of apertures therein for the passage of a connecting element for electrically connecting the varistor to a commutator.

Other preferred features and advantages of the invention will be apparent from the following description and the accompanying claims.

The invention will be further described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a varistor in accordance with the invention; Figure 2 shows the varistor of claim 1 mounted on a commutator of a PMDC motor in accordance with the invention; Figure 3 is partial side view of the arrangement of Figure 2; Figure 4 is an exploded perspective view of a commutator forming part of a rotor according to a further embodiment of tne invention; Figure 5 is a longitudinal section through the commutator of Figure 1 when assembled; Figure 6 is a plan view of a commutator segment in blank form, and Figure 7 is a side view of the rose-like terminal support of Figure 4 with one of the housings shown in section.

Figure 1 shows a varistor 1 which can be of sintered ceramic material such as silicon carbide or titanium oxide. The varistor 1 is annular and has a central aperture 2. Three silver pads 3 are provided on a face 4 of the varistor for electrical connection to tangs of commutator segments (vide hereinafter).

Apertures 5 extend through the body of the varistor and the pads 3. The apertures 5 are arranged to receive tabs on a commutator, the tabs serving to locate the varistor on the commutator and electrically connect the varistor to segments of the commutator.

Figure 2 shows the varistor 1 of Figure 1 mounted on an assembled commutator 6 in a rotor of a fractional horsepower PMDC motor. The commutator 6 comprises an electrically insulating cylindrical base 7 on a motor shaft 8. A collar 9 at one end of the base 7 extends radially outward. Commutator segments 10 are mounted on the base 7 and have brush contacting portions 11 and tangs 12. The tangs i2 are supported on the collar 9.

A wound armature 13 having a laminated core 14 and a wire winding 15 is also mounted on the shaft 8. Wire 16 of the winding 15 is wound about a tang 12 before passing back into the armature coils. The wire 16 may be broken at the tang 12, the two ends overlapping at the tang. The tang is bent over onto the wire and forged or soldered to the wire in the usual way.

The tangs 12 each have an extension or tab 12a which projects over the brush contacting portions 11, clear of the collar 9. The varistor 1 is slid over the brush contacting portions 11, the apertures 5 passing over respective tabs 12a. The silver pads 3 on the varistor 1 are then soldered to the tabs 12a. By passing the tabs 12a through the apertures 5 the tabs serve to secure the varistor in position mechanically to supplement the soldered connection to the tangs 12.

The tabs 12a need not be integrally formed extensions of the tangs 12. They may be formed, for example, by providing other outwardly extending formations on the commutator, which may be integrally formed with the segments. The tabs 12a may be soldered to silver pads 3 on a side of the varistor distal of the collar 9, also the tabs may be bent to further secure the varistor in position.

The invention will be further exemplified by reference to Figures 4 to 7 of the drawings.

In our British Patent No. 2128818B, for example, we described a connection between an armature winding and a commutator segment which avoids the application of heat to effect the connection and which utilises the principle of insulation displacement in which a wire having an insulating cover is forced into a slot narrower than the wire diameter to form a clean metal to metal contact between the wire and a terminal portion of the commutator segment.

Some motor armatures have windings of very thin wire. This very thin wire is flimsy and hence prone to breakage. Moreover, it is difficult to manufacture commutator segments with slots narrow enough to form a clean metal to metal contact with this very thin wire.

Referring first to Figures 4 and 5 of the drawings, there is shown therein a commutator base 30 and a commutator segment 31. The segment 31 has an integral terminal portion 32 at one end and an integral lug 33 at its other end with a brush contacting portion 29 therebetween. The base 30 comprises a rose-like terminal support 34 including five housings 35, each of which has a recess 35a receiving a terminal portion 32 of a commutator segment 31, and a cylindrical support 36 on which the brush contacting portions 29 of the commutator segments 31 are seated.

The terminal portion 32 of the commutator segment blank shown in Figure 6 is generally rectangular with its minor axis coincident with the longitudinal axis of the brush contacting portion 29 of the commutator segment. The terminal portion 32 comprises a central part 38 and two end parts 39 and 40. The central part 38 has a central cut out portion 37 which reduces from its largest width at the centre to two elongate slots 41 which terminate either end of the cut out.

The closed end of each slot 41 is enlarged to ensure that the edges of the slot 41 have a certain resilience to separation.

A triangular barb 42 is provided on either side of the minor axis of the central part 38 along the edge furthest from the brush contacting portion 29 of the commutator segment. These barbs 42 grip the housing 34 (Figures 4 and 5) and therefore retain the terminal portion 32 in the housing 34, as will be explained hereinafter.

The brush contacting portion 29 of the commutator segment 31 is of arcuate form to conform to the external radius of the support 36. The terminal portion. 32 is bent upright from the commutator segment 31 and the central part 38 of the terminal portion is bent at 900 in areas 43 to form the arms t4 (Figure 1) which extend parallel to each other and to the longitudinal axis of the commutator segment 31, and forward along the length thereof.

The commutator segments 31 are seated on the support 36 and located thereon by the lugs 33 which extend into respective recesses in the end of the support 36 remote from the terminal support 34.

As shown in Figures 4, 5 and 6, an electrical connector 45 is supported by each housing 35 of the terminal support 34. The connectors 45 are L-shaped pins each having a first limb 45a which extends across the housing 35 at a tangent to an imaginary circle centered on the axis 46 of the support 34 and which is located in an aligned pair of slots 47 in the housing 35, and a second limb 45b which extends parallel to the axis 46. The limb 45a of the connector 45 is generally cylindrical and has a diameter slightly greater than the width of each slot 41 in a respective terminal portion 32. The second limb 45b is flat and has sharp edges 48 around which is wound a connector portion 49 of a thin wire armature winding, the sharp edges 48 breaking through insulation on the wire.The limbs 45b project over the brush contacting portions 49 of the assembled commutator of the armature assembly.

A varistor 50 (Figures 1 and 2) is of annular shape and has a central aperture 51 which slides over the brush contacting portions 49. Five apertures 52 extend through the varistor and are sized and spaced to receive the limbs 45b. Silver pads 53 are provided around each aperture 52.

The rotor is assembled as follows.

A lamination stack (not shown) is first mounted fast on a shaft. The rose-like terminal support 34, having a connector 45 extending across each housing 35, is then mounted fast on the shaft against the lamination stack. The armature is then wound in conventional manner and connector portions 49 of the winding are wound around the respective second limbs 45b of the connectors 45 a multiplicity of times to guarantee the integrity of each joint and ensure that the electrical resistance between each connector portion 49 and the respective connector 45 is low, the edges 48 cutting through the insulation on the connector portions 49.

The commutator segments 31 are pre-assembled on the cylindrical support 36 and after the armature has been wound the support 36 is mounted on the shaft.

The commutator segments 31 are mounted on the support 36 in angularly spaced apart relationship with the brush contacting portions 29 seated on the peripheral surface of the support 36. The segments 31 are located with respect to the support 36 by the lugs 33 which are press fitted into respective recesses in one end of the support 36.

When mounting the cylindrical support 36 on the shaft, the support 36 is moved towards the rose-like terminal support 34 and the terminal portions 32 enter respective housings 35. As each terminal portion 32 enters its respective housing 35 the first limb 45a of the connector 45 enters the slots 41 in the terminal portion 32 to establish and maintain electrical contact between the connector 45 and the commutator segment 31. Also the barbs 42 bite into the housing 35 to firmly secure the terminal portion 32 in the housing 35.

With such an arrangement it is possible on the one hand to assemble the commutator segments 31- on the support 36 and on the other hand wind the armature in remote locations and to then connect the commutator segments 31 to the armature winding by a sliding mechanical connection between the terminal portions 32 and the electrical connectors 45.

Moreover, by making the circumferential extent of each housing recess 35a greater than the circumferential extent of a respective terminal portion 32 the angular positions of the commutator segments 31 with respect to the terminal housings 35 can be selected during assembly of the armature to provide for a desired commutation angle. In this case the first limbs 45a of the electrical connectors 45 may be of arcuate shape to facilitate connection between the terminal portion 32 and the electrical connector 45 in a desired angular relationship.

Instead of slots 47 each housing could be provided with a pair of aligned holes to locate the respective connector 45.

The varistor 50 is then slid over the brush contacting portions 49, so that the limbs 45b penetrate the apertures 52. The limbs 45b may then be soldered to the silver pads 53. The outer ends of the limbs 45b may also be bent to enhance the mechanical mounting of the varistor on the assembled commutator.The invention is equally applicable to other spark quenching suppression elements, such as resistors, as well as varistors.

The above embodiment is given by way of example only and various other modifications will be apparent to persons skilled in the art without departing from the scope of the invention as defined by the appended claims.

Claims (18)

Claims

1. A rotor for an electric motor, comprising a shaft and an armature and commutator mounted on the shaft, the commutator comprising a plurality of segments mounted on an electrically insulating base, the segments being.electrically connected to coils of the armature, and a spark quenching suppression element electrically connected across two or more commutator segments, wherein the suppression element is electrically connected to a said segment by means of an electrically conducting tab which is mounted on the commutator in electrical connection with the segment and which extends through an aperture or slot in the suppress ion element and is electrically connected thereto.

2. A rotor as claimed in claim 1, wherein the tab is integral with the said segment.

3. A rotor as claimed in claim 2, wherein the tab is formed by an extension on a tang of the commutator segment.

4. A rotor as claimed in claim 3, wherein the armature has coils wound from wire and the wire is electrically connected to a said tang by hot forging or soldering to the tang.

5. A rotor as claimed in any one of claims 1 to 4, wherein the tab extends through an aperture in the suppression element.

6. A rotor as claimed in any one of claims 1 to 5, wherein the conmutator segments form a cylindrical brush contacting portion, and the suppress ion element is in the form of an annulus which is slid over the brush contacting portion.

7. A rotor as claimed in any one of claims 1 to 6, wherein the suppression element is a varistor.

8. A rotor as claimed in any one of claims 1 to 7, wherein the tab is soldered to the suppression element.

9. A rotor as claimed in claim 8, wherein a silver pad is provided on a face of the suppression element, and the tab is soldered to the pad.

10. A rotor as claimed in claim 1, wherein the commutator base has a plurality of commutator segments, each having an integral terminal portion, a commutator base having a plurality of housings which are respectively formed with housing recesses for terminal portions of the commutator segments, and an electrical connector supported with respect to each of the housings, each connector having a first part disposed within the housing and a second part disposed externally of the housing, each terminal portion having a slot which straddles and grips the first part of a connector in a respective housing to form an electrical connection therewith, and the second part of each connector being received in a said aperture or slot of a suppress ion element and forming an electrical connection therewith.

11. A rotor as claimed in claim 10, wherein the electrical connectors are rigid.

12. A rotor as claimed in claim 10 or claim 11, wherein the first part of each connector extends across a respective housing recess.

13. A rotor as claimed in claim 10, 11 or 12, wherein each terminal portion has at least two spaced parallel arms each comprising a slot which straddles and grips a first part of a connector.

14. A rotor as claimed in any one of claims 10 to 14, wherein each terminal portion has a barb for retaining the terminal portion in a respective housing.

15. A rotor as claimed in any one of claims 10 to 14, wherein the commutator base comprises a first part which includes said housings and a second part on which brush contacting portions of the commutator segments are seated.

16. A rotor as claimed in any one claims 10 to 15, wherein the circumferential extent of each housing recess is greater than the circumferential extent of a respective terminal portion so that the angular position of the commutator segments with respect to the terminal housings can be selected during assembly of the armature.

17. A rotor substantially as hereinbefore described with reference to Figures 1 to 3 or Figures 4 to 6 of the accompanying drawings.

18. An electric motor equipped with a rotor as set forth in any one of the preceding claims.