GB2280066A - Securing segment on a commutator of a miniature motor - Google Patents

Abstract

A commutator segment has an end portion 19 positioned in or adjacent a recess 14 in the commutator base 1 and is plastically deformed therein to secure the segment to the body. Engaging elements 6 may be plastically deformed prior to insertion in holes 3 so as to grip therein. <IMAGE>

Description

MINIATURE MOTOR HAVING A BUILT-UP COMMUTATOR This invention relates to miniature d-c motors for driving for example, power tools, automotive rear-view mirrors, and automotive door locks. It relates particularly to such miniature motors having built-up commutators, and to the design of such commutators.

Known commutators and motors for the above uses are usually either of the moulded or the built-up type. Each has its advantages and disadvantages. In the former type, there are difficulties in moulding accuracy, and problems arising from the thermal differences between the conductive material of the commutator segments and the material of the insulative body. In the latter type, there are difficulties in securing the commutator segments to the insulative body, and size and assembly problems.

The present invention addresses the above problems in commutators of the built-up type. According to the invention, a commutator for a miniature motor comprises a plurality of commutator segments of conductive material, each being formed into a substantially cylindrical arc, secured to the outer circumferential surface of a substantially cylindrical body of insulating material with an outwardly directed flange at one end, the flange being formed with axially directed guide grooves, which grooves receive engaging pieces on the ends of the commutator segments. Normally, the distal ends of the engaging pieces project from the flange, and the engaging pieces may be secured to the flange by plastic deformation of the distal ends thereof in the circumferential direction of the cylindrical body.

Conveniently, the distal ends of the engaging pieces are slit to form lanced pieces.

In preferred embodiments of the invention projections are formed on the outer circumferential surface of the guide grooves, whereby the engaging pieces are brought into close contact with the inner circumferential surface of the guide grooves. In another preferred feature, the guide grooves are each formed into a circular arc shape in cross section. In yet another variant, a plurality of recesses are provided on the other end face of the cylindrical body of the commutator, and bent portions for engaging with the recesses are provided on the other end of said commutator segments, the bent portions being secured to the recesses by plastic deformation.

The invention will now be described by way of example and with reference to the accompanying drawings wherein: Figure 1 is a longitudinal sectional view of a commutator embodying the invention; Figure 2 is a end view from the left, of the commutator shown in Figure 1; Figure 3 is a developed view showing the commutator segments in the commutator of Figure 1; Figure 4 is a perspective view of a cylindrical commutator body as shown in Figures 1 and 2; Figure 5 is a perspective view of a commutator segment as shown in Figures 1 and 2; Figure 6 is a perspective view illustrating a commutator segment positioned but not secured on the outer circumferential surface of a cylindrical body; Figures 7 and 8 are developed views showing different forms of guide grooves and engaging pieces in an embodiment of this invention; Figures 9 and 10 are partial perspective views showing different forms of terminal portion; Figure 11 is a longitudinal sectional view of a commutator in another embodiment of the invention; Figure 12 is an end view illustrating a commutator in yet another embodiment of this invention; Figure 13 is a longitudinal sectional view illustrating a modified example of flange and projection; Figures 14 and 15 are longitudinal sectional views illustrating comnutator segments in still other embodiments of this invention; Figure 16 is a cross-sectional development taken along line A-A in Figure 1; Figures 17 and 18 are partially sectional developments illustrating modified examples of guide grooves and engaging pieces according to the invention; Figure 19 is a longitudinal sectional view of a commutator in a further embodiment of the invention; Figure 20 is an end view of yet a further embodiment of the invention; Figure 21 is a cross-sectional view taken along line A-A in Figure 20; Figure 22 is an enlarged sectional view illustrating the fit of an engaging piece in a guide groove; Figure 23 is a side view of the commutator segment shown in Figures 19 and 20; Figure 24 is a bottom view of the commutator segment in Figures 19 and 20; Figure 25 is a right-end view of the commutator segment shown in Figures 19 and 20; Figure 26 is a longitudinal sectional view illustrating a modified example of the engaging piece shown in Figures 19 and 20; Figure 27 is an enlarged cross-sectional view illustrating the bent portion in Figures 20 and 21; Figure 28 is an enlarged cross-sectional view illustrating another modified example of the bent portion in Figures 20 and 21; Figures 29 and 30 are end views illustrating other modified examples of the bent portion in Figure 20; Figures 31 and 32 are enlarged perspective views of the terminal portion shown in Figures 19 and 20; Figure 33 shows in partial section, a known miniature electric motor construction; Figure 34 is a partly sectioned side view of a built-up commutator for use in the motor of Figure 33; and Figure 35 is an end view of the commutators of Figure 34.

A known motor construction will first be described with reference to Figures 33 to 35.

As shown in Figure 33, a motor housing 51 is formed in a cup-shaped hollow cylinder, on the inside surface of which a field magnet 52 is secured. An end plate 53 is fitted to the open end of the motor housing 51. A rotor core 55 and a commutator 58 are fitted to a motor shaft 54, which is rotatably supported by bearings 57 and 58.

A rotor winding 59 is wound on the rotor core 55. A terminal 60 is supported by the end plate 53. A brush arm 61 supports a carbon brush 62, and is electrically connected to the terminal 60. The carbon brush 62 is formed in such a fashion as to make sliding contact with the outer surface of the commutator 56. Thus, current is supplied from the terminal 60 to the rotor winding 59 via the brush arm 61, the carbon brush 62 and the commutator 56. As a result, a rotor 63 existing in a magnetic field formed by the field magnet 52 fixedly fitted on the inside surface of the motor housing 51 is caused to rotate.

There are two types of commutator 56 used in miniature motors of the above type; the moulded type and the built-up type. Depending on the design speed or operating temperature of the motor, the built-up commutator is usually preferred for motors with low design speeds, while the moulded commutator is preferred for higher operating temperatures.

The moulded commutator is usually manufactured by monolithic-mouldiny a thermoset resin into a ring-shaped commutator blank. Such a moulded blank is then machined to form slits between the commutator segments.

However, variations in the width of the slits, improper roundness of the outer circumferential surface of the commutator, and other unwanted phenomena adversely affecting motor performance often occur due to the difference in thermal expansibility between a metallic material of which the commutator segments are made and a thermoset resin of which the cylindrical body is made, or inadequate adhesion between them during moulding.

Further, burrs can be produced around the slits between commutator segments during machining, requiring deburring operations. This results in increased manufacturing costs.

The built-up commutator, in which separately prepared components are mechanically assembled, avoids many of the problems associated with the moulded commutator, but encounters a strength problem and other problems as described below.

In Figures 34 and 35, a commutator segment 56a is made of an electrically conductive material, such as copper, and formed into a circular arc shape in cross section. Three such pieces; ie, three commutator segments 56a are fixedly fitted at radially equal spacings on the outer circumferential surface of a cylindrical body 64 of insulating material, which is formed into a cylindrical shape, via a ring 65 also formed of an insulating material. A terminal portion 56b is used for connecting a lead wire of the rotor winding 59 shown in Figure 33. A slit 66 is formed between the commutator segments 56a.

The built up commutator 56 of the above-mentioned construction has an advantaye in that dimensional accuracy can be improved because the cylindrical body 64, the commutator segment 56a and the ring 65 are manufactured separately. On the other hand, it has the disadvantage of reduced strength in that the commutator segment 56a must be fitted to the body 64. Since the segment 56a is secured to the body 64 only be the pressfitting force of the ring 65, the bonding strength produced by press-fittiny or sandwiching is limited.

This could lead to displacement of the commutator segment 56a, and irregular circumferential widths of slits 66 due to vibration and other external forces.

The built-up commutator 56 which requires the use of the ring 65 to assemble the segments on the cylindrical body poses a cost disadvantage and the width of the ring 65 limits the effective axial length of the commutator segment 56a, requiring an increased axial length of the commutator 56. This presents an obstacle in further reducing the size of the miniature motors.

In recent years, on the other hand, the demands for reducing the size and cost, while increasing the performance and cost of miniature motors of this type have become increasinyly stringent. As a consequence, miniature motors having commutators of the conventional types cannot meet these requirements.

In Figures 1 and 2 a cylindrical body 1 is formed of a thermoset resin, such as phenol or epoxy resin, into a hollow cylindrical shape, and a flange 2 is provided integrally with the cylindrical body 1 in the vicinity of an end thereof.

Guide grooves 3 each in the shape of a circular arc in cross section, pass through the flange 2 at the boundary to the cylindrical body 1 and parallel with the axis thereof. A commutator segment 4 of an electrically conductive material, such as copper, is formed integrally with a base 5, which will be described later, engaging pieces G, and a terminal portion 7.

As shown in Figure 4, grooves 8 are disposed radially at equal spacings in the circumferential direction on the end face of the flange 2, and used for positioning the commutator segments 4, as will be described later. In Figure 5, the base 5 of the commutator segment 4 is formed into a circular arc shape in cross section, corresponding to the outer circumferential surface of the cylindrical body 1 shown in Figure 4. Two engaging pieces 6 are provided on the end edge of the commutator segment 4, and the terminal portion 7 is bent in such a manner as to protrude outwards from the intermediate portion of the engaging piece 6 along the end face of the flange 2 shown in Figure 4.

The assembly of a commutator having the components discussed above will now be described.

As shown in Figures 1 to 3, the commutator segment 4 is disposed on the outer periphery of the cylindrical body 1. The engaging pieces 6 of the commutator segment 4 are inserted into the guide grooves 3 provided on the flange 2. The terminal portion 7 of the commutator segment 4 is engaged with the groove 8 (Figure 4) provided on the end face of the flange 2 to position the commutator segment 4 in the circumferential and axial directions.

As shown in Figure 6, the engaging piece 6 passes through the guide groove 3 on the flange 2 and protrudes from the end face opposite to the flange 2. Next, a cutting and bending blade 9 as shown in Figure 3, is forced in the direction of the arrow in the Figure between the engaging pieces 6 protruding from the end face of the flange 2 to provide a notch 6a as shown by dotted lines in the figure on the engaging piece 6. By causing the notch 6a to deform plastically in the circumferential direction and press-fitting the notch 6a to the flange 2, the commutator segment 4 is fixedly fitted to the cylindrical body 1. During this step, the outer periphery of the base 5 of the commutator segment 4 can be held by a collet chuck, for example.

In Figure 7, the axial length of the flange 2 is made slightly longer than the axial length of the engaging piece 6. By forming the flange 2 in such dimensions, the tip of the engaging piece 6 does not protrude from the flange 2, thus being prevented from making unwanted contact with the rotor winding 59 (Figure 33).

In Figure 8, lanced pieces 6b are plastically deformed to both sides from the notch 6a. By forming the lanced pieces 6b in this way, the width of the engaging piece 6 can be maintained, and a predetermined bonding strength can be effectively maintained in cases where a multi-pole commutator, such as that having more than five commutator segments 4, is required.

In Figures 9 and 10, the terminals 10 and 11 are provided integrally with the tip of the terminal portion 7. The terminals 10 and 11 are for connecting the lead wires of the rotor winding, or installing varistors and other component members.

In Figures 11 and 12, a projection 20 is formed on the outside inner circumferential surface of the guide groove 3 into a width smaller than the circumferential width of the guide groove 3.

With the above-mentioned construction, when the engaging piece 6 is press-fitted into the guide groove 3 provided on the flange 2, it is pushed by the projection 20 toward the axial centre to make close contact with, and become secured to, the inside inner circumferential surface of the guide groove 3. The tip of each engaging piece 6 is slit and deformed plastically in the same manner as shown in Figures 3, 7 and 8.

In Figure 13, a recess 2a is provided at the leftend face of the flange 2. The projection 20 is formed into an axial length smaller than the axial length of the guide groove 3. The tip of the engaging piece 6 is formed in such a manner as not to protrude from the end face of the flange 2. This can avoid unwanted accidents due to the tip of the engaging piece 6 projecting from the end face of the flange 2, as in the case of the examples shown in Figures 7 and 8.

In Figures 14 and 15 a slight taper is provided on the base 5 of the commutator segment 4. In Figure 14, the projection 21 is provided on the inside inner circumferential surface, and on the side of the left-end face of the flange 2 with respect tot he projection 20.

In Figure 15, a taper having an angle e with respect to the cylinder axis is provided on the outer circumferential surface of the cylindrical body 1 corresponding to the base 5 of the commutator segment 4 and the engaging piece 6, and on the inside inner circumferential surface of the guide groove 3.

With the aforementioned construction, a larger pushing force is exerted by the projection 20 provided in the guide groove 3 of the flange 2 in the axial centre direction, and thereby the commutator segment 4 can be brought into close contact with the cylindrical body 1.

The method of slitting the tip of the engaging piece 6 is similar to that in the previous embodiments.

Figures 16 to 18 are partially cross-sectional developments illustrating examples of the guide groove 3 and the engaging piece 6 in various embodiments of this invention.

In Figure 16, the commutator segment 4 is fixedly fitted to the cylindrical body 1 by forcing a staking bar 9, for example, in between the protruding engaging pieces 6 in the direction shown by an arrow in the Figure to cause the engaging piece 6 to plastically deform in the circumferential direction as shown by a dotted line, thereby press-fitting the engaging piece 6 to the flange 2. In this case, the commutator segment 4 is preferably held at the outer periphery thereof by a collet chuck, for example.

In Figure 17, the axial length or width of the flange 2 is made larger than the axial length of the engaging piece 6. By forming the flange 2 in this way, the tip of the engaging piece 6 is prevented from protruding from the flange 2, and thus from making unwanted contact with the rotor winding.

In Figure 18, the engaging piece 6 is provided on one of the commutator segments 4. In this way, the width of the engaging piece 6 can be maintained and a predetermined bonding strength can be maintained in cases where a multi-pole commutator having more than five commutator segments is required.

Other embodiments of this invention will now be described, referring to Figures 19 to 32. In these Figures, a cylindrical body 1 is formed of a thermoset resin, such as phenol or epoxy resin, into a hollow cylindrical shape, and a flange 2 formed into an outside diameter larger than the outside diameter of the cylindrical body 1 is integrally formed therewith in the vicinity of an end of the cylindrical body 1.

Guide grooves 3 each in the shape of a circular arc pass through the flange 2 at the boundary to the cylindrical body 1 and parallel with the axis thereof. A plurality of recesses 14 are provided on the end face opposite to the flange 2 of the cylindrical body 1. The end face of the recess 14 is formed into a triangular or dovetail shape. The recesses 14 are disposed at equal spacings in the circumferential direction.

A commutator segment 4 is made of an electrically conductive material, such as copper, and consists of a base 5, and engaging piece 6, a terminal portion 7 and a bent portion 19. In Figures 23 to 25, the base 5 is formed into a circular arc shape in cross section, corresponding to the outer circumferential surface of the cylindrical body 1 shown in Figures 19 and 20. On an end of the commutator segment 4 provided are engaging pieces 6 and a terminal portion 7. Two engaging pieces 6 are provided along the end edge of the commutator segment 4.

The engaging pieces 6 are bent as shown in Figure 23.

The terminal portion 7 of the commutator segment 4 is formed in such a manner as to protrude from the intermediate part of the engaging piece 6 outwards along the end face and the outer circumferential surface of the flange 2 shown in Figures 19 and 20. The protruded end of the terminal portion 7 is formed into a U shape, for example, as shown in Figure 23. The terminal portion 7 is formed in such a fashion that the width T of the end part thereof is smaller than the width W of the foot part 7a thereof rising from the base 5, that is, T < W (see Figure 25). On the other end of the commutator segment 4 provided is a bent portion 19 whose end face is formed into a triangular or dovetail shape, for example. The bent portion 19 and the engaging portion 6 are formed in such a fashion that the bent portion 19 and the engaging portion 6 are engaged and fitted to the recess 14 and the guide groove 3 shown in Figures 19 through 21.

The assembly of a commutator having the abovementioned construction will now be described.

As shown in Figures 19 and 20, the commutator segment 4 is disposed on the outer periphery of the cylindrical body 1. The engaging piece 6 of the commutator segment 4 is inserted and fitted into the guide groove 3 provided on the flange 2. Since the radial length r from the axial line of the engaging piece 6 is larger than the radial length R from the axial line of the outside inner circumferential surface of the guide groove 3, the engaging piece 6 is caused to be slightly deformed plastically and make close contact with the inner wall of the guide groove 3 as the engaging piece 6 is inserted into the guide groove 3 while being bent in such a manner that the upper surface of the engaging piece 6 becomes concave. Thus, the commutator segment 4 is prevented from coming off in the axial direction.

In Figures 19 through 21, the bent portion 19 is bent and engaged with the recess 14. When a recess 110 as shown in Figure 21 is formed on the bent portion 19 by a tool, like a knife, the bent portion 19 is caused to be deformed plastically in the circumferential direction of the end face due to upsetting or staking, thereby making close contact with, or press-fitting to, the recess 14 provided on the cylindrical body 1. Thus, the commutator segment 4 is secured fitted to the cylindrical body 1.

When upsetting or staking the bent portion 19, the outer periphery of the base 5 of the commutator segment 4 can be held by a collet chuck, for example.

After the commutator segment 4 is fixedly fitted to the cylindrical body 1, the lead wire of the rotor winding is hooked on the terminal portion 7 and connected thereto by resistance welding. In this case, since the foot portion 18a and the end portion 18b of the terminal portion 7 are formed so that the width W of the foot portion 18a is smaller than the width T of the end portion 18b, as shown in Figure 25, the foot portion 18a is prevented from being heated, and the heat is effectively concentrated on the end portion 18b, making the connection easy. When the width T of the end portion 18b is equal to the width W of the foot portion 18a, on the other hand, an area near the foot portion ls a is heated before the lead wire is fused to the end portion 18b. This could cause the covering of the lead wire to be melted away.

In Figure 26, the projection 111 is provided on part of the engaging piece 6 by stamping, for example. In this case, the radial length of the projection 111 from the axial line is of course made similar to that shown in Figure 22. As the engaging piece 6 formed in such a fashion is inserted into the guide groove 3 shown in Figures 19 and 22, the commutator segment 4 is prevented from coming off in the axial direction.

In Figures 27 and 28, the bent portion 19 is formed by bending, for example, in such a fashion that the upper surface of the bent portion 19 become convex, and engaged with the recess 14. After that, when the bent portion 19 is pushed or hit in the direction shown by an arrow as shown in Figure 28, by a jig (not shown), the bent portion 19 is press-fitted to the recess 14 by the plastic deformation thereof, and fixedly fitted to the cylindrical body 1.

Figures 27 and 28 also show the recesses 14 with parallel sidewalls perpendicular to its base. However, the side walls can be divergant, for example at an angle of 20 degrees, so that the engaging piece is held in place by friction only; ie, without deformation.

In Figures 29 and 30, the notch 112 is provided on an end of the bent portion 19. After the bent portion 19 is engaged with the recess 14, as shown in Figure 29, the notch 112 is open apart hy a jiy, as shown in Figure 30, then the bent portion 19 is press-fitted to the recess 14 by the plastic deformation thereof, and fixedly fitted to the cylindrical body 1.

In Figures 31 and 32, the terminal 113 is provided integrally with the terminal portion 7. The terminal 113 is used for installing other component members, such as a varistor, for example.

In the above embodiments, the cylindrical body and the flange are stated to be of a thermoset resin. They may be made of a thermoplastic resin, or any other suitable material. The method of forming them may be injection moulding and other known moulding means. The guide groove provided on the flange may be formed in such a fashion that part or whole of the guide groove passes through the flange. In short, the guide groove may be of any shape and size so long as the engaging piece can be inserted, positioned and fixedly fitted into the guide groove. Furthermore, the recess provided on the end face of the cylindrical body, and the end face of the bent portion engaging with the recess may be of any shape that can be selected in accordance with the specifications required for the commutator.

The invention in its various embodiments can achieve the following effects: 1. Since the commutator segments are fixedly fitted to the cylindrical body, no inconveniences, such as displacement of the commutator segments, irregular slit width, etc. are caused even when vibration due to motor operation and other external forces are exerted.

This results in high-performance and high-reliability miniature motors.

2. Because no ring is required to fixedly fit the commutator segments to the cylindrical body, the number of required components can be reduced, assembly work is facilitated, and manufacturing manhours and cost can be reduced.

3. Since a ring to fixedly fit the commutator segments to the cylindrical body is not needed, the axial length of the commutator segments need not be limited.

This makes it possible to reduce the size of a miniature motor as a whole.

Claims (4)

1. A miniature motor having a commutator comprising a plurality of commutator segments of conductive material, each being formed into a substantially cylindrical arc, secured to the outer circumferential surface of a substantially cylindrical body of insulating material with an outwardly directed flange at one end, the flange being formed with axially directed guide holes which holes receive engaging pieces on the ends of the commutator segments, and a plurality of recesses are provided on the other end face of the cylindrical body, with bent portions for engaging with the recesses provided on the other end of said commutator segments, the bent portions being secured to the recesses by plastic deformation thereof.

2. A miniature motor according to Claim 1 wherein the engaging pieces are plastically deformed such that upon insertion they ma]ce close contact with wall surfaces of the respective holes to hold segments against axial withdrawal from the flange.

3. A miniature motor according to Claim 1 or Claim 2 wherein the end face of each recess and bent portion is substantially triangular.

4. A miniature motor substantially as described herein with reference to Figures 19 to 32 of the accompanying drawings.