Slip Ring Assembly And Method Of Making Same

Abstract

A slip ring assembly in which principal components, a molded cylindrical base, conductive rings and terminals are separately manufactured and assembled together. In assembling, the terminals are fitted in diametrically spaced grooves formed on the cylindrical base and the conductive rings are press-fitted on the cylindrical base thereby to bring the conductive rings into pressure contact with the respective terminals and to ensure satisfactory engagement of the conductive rings with the cylindrical base.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a slip ring assembly for use in small-sized rotary electric machines and a method of making such a slip ring assembly.

2. Description of the Prior Art

With the remarkable progress of chemical synthetic materials in recent years, these synthetic materials are widely used in small-sized rotary electric machines to form a part such as a molded cylindrical base of slip ring assemblies.

Conventional slip ring assemblies of this kind have been made by preparing conductive rings separately from terminals, welding the terminals to the respective conductive rings and molding the conductive rings with a molding material to obtain a slip ring assembly or, as disclosed in U.S. Pat. No. 3,435,402, by punching out conductive strips each provided with a terminal from a sheet of conductive material by means of a press, forming these conductive strips into an annular shape to obtain conductive rings, setting two conductive rings on a mold in suitably spaced apart relation from each other, and molding with a thermo-setting molding material such as a polyester resin in such a manner that the outer peripheral surface of the conductive rings is exposed to outside from the molded structure. In such a conventional slip ring assembly, claws must be provided on the conductive rings in order to ensure a better bond between the conductive rings and the molding material and to prevent undesirable deformation of the conductive ring and the molding material due to the thermal contraction of the molding material. Due to the need for provision of such claws, the conductive rings must have a correspondingly greater thickness which results in the wasteful use of the conductive material and is thus uneconomical. In the former slip ring assembly, the terminals are joined to the conductive rings by means of soldering, brazing or electric welding and then the conductive rings are molded with a molding material. Thus, molding pressure is imparted to the terminals during the molding to apply a breaking force to the weld thereby reducing the reliability of the weld. Further, a heating loss occurs generally in the molding material which is therefore subject to shrinkage. This is objectionable for the proper performance of the machine in that an undesirable clearance is produced between the inner peripheral surface of the conductive rings and the outer peripheral surface of the molding material during the operation of the machine and the conductive rings are subject to deformation thereby bringing forth unsatisfactory sliding engagement with the associated brushes.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a slip ring assembly and a method of making same in which individual components are separately prepared and are assembled together by means of press-fitting and pressure engagement so as to improve the productivity thereof.

Another object of the present invention is to provide a slip ring assembly and a method of making same in which a generally U-shaped wire is used to provide the terminals so as to improve the productivity and workability.

A further object of the present invention is to provide a slip ring assembly having a molded cylindrical base which is formed with a plurality of spaced grooves for receiving the terminals therein, each groove including a combination of a portion having a depth larger than the diameter of the terminal and a portion having a depth smaller than the diameter of the terminal so that electrical connection and insulation can be simply carried out on a single line.

These objects are realized according to the present invention by providing a method of making a slip ring assembly comprising the steps of preparing a molded cylindrical base, a plurality of conductive rings and a plurality of wire terminals separately from one another, said molded cylindrical base being formed with a plurality of axially extending grooves each having a deep portion and a shallow portion, disposing said wire terminals in said grooves respectively, and press-fitting said conductive rings on said cylindrical base in spaced apart relationship from each other thereby to electrically and mechanically connect said conductive rings and said wire terminals with each other so as to obtain an assembly of said molded cylindrical base, said conductive rings, and said wire terminals. The present invention also contemplates the assembled slip ring assembly construction according to this method. By virtue of the fact that the components are prepared as individual units, the slip ring assembly can be produced at low cost with a high productivity. The slip ring assembly is free from any deformation of the conductive rings and the molded cylindrical base due to thermal contraction of the molded cylindrical base. Further, the slip ring assembly thus manufactured shows a high reliability due to the fact that the welding of the wire terminals to the conductive rings is unnecessary.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a perspective view of a slip ring assembly made by a method embodying the present invention.

FIG. 2 is a sectional view taken on the line II--II in FIG. 1.

FIG. 3 is a sectional view taken on the line III--III in FIG. 1.

FIG. 4 is an axial sectional front elevation of a molded cylindrical base having conductive rings and terminals set at predetermined positions thereon.

FIG. 5 is an exploded perspective view showing the components of the slip ring assembly.

DESDRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawing, a slip ring assembly according to the present invention comprises a molded cylindrical base 1 of electrically insulating material such as a phenol resin, simple conductive rings 2 and 3, and wire terminals 4 and 5. A pair of diametrically spaced grooves 6 and 7 are formed on the outer peripheral surface of the molded cylindrical base 1 to extend in the axial direction thereof. The grooves 6 and 7 receive the respective terminals 4 and 5 therein so as to electrically connect the conductive rings 2 and 3 with the respective terminals 4 and 5. The conductive rings 2 and 3 have an inner diameter of, for example, 29.0 mm and the molded cylindrical base 1 has an outer diameter of, for example, 29.1 to 29.2 mm so that the conductive rings 2 and 3 are press-fitted on the molded cylindrical base 1. The relation between the conductive rings 2 and 3 and the grooves 6 and 7 will be described with reference to FIGS. 2 to 4. As seen in FIGS. 2 and 4, the portion of the groove 6 underlying the conductive ring 2 has a depth smaller than the diameter of the wire terminal 4 so that the conductive ring 2 press-fitted on the molded cylindrical base 1 can be brought into pressure contact with the wire terminal 4 at this portion, while the portion of the groove 7 underlying the conductive ring 2 has a depth larger than the diameter of the wire terminal 5 so that a space for electrically insulating the conductive ring 2 from the wire terminal 5 can be maintained therebetween and an electrically insulating sleeve 8 can be disposed in the space. On the other hand, as seen in FIGS. 3 and 4, the portion of the groove 6 underlying the conductive ring 3 has a depth larger than the diameter of the wire terminal 4 so that the unnecessary portion of the wire terminal 4 can be easily removed from the groove 6, while the portion of the groove 7 underlying the conductive ring 3 has a depth smaller than the diameter of the wire terminal 5 so that the conductive ring 3 press-fitted on the molded cylindrical base 1 can be brought into pressure contact with the wire terminal 5 at this portion. The length of the deep portion of the groove 7 is different from that of the deep portion of the groove 6 as seen.

The method of assembling such a slip ring assembly will be described with reference to FIGS. 4 and 5. A generally U-shaped wire A to provide the wire terminals 4 and 5 is fitted in the grooves 6 and 7 formed on the molded cylindrical base 1 and then the conductive rings 2 and 3 are successively press-fitted on the molded cylindrical base 1 from one end of the latter, After positioning the conductive rings 2 and 3 at predetermined positions as shown in FIG. 4, the electrically insulating sleeve 8 for preventing short-circuit between the conductive rings 2 and 3 is fitted on the wire A and the wire A is severed at points A.sub.1 and A.sub.2. Finally, the remaining wire portions are bent as required to provide the wire terminals 4 and 5.

It will thus be seen that, according to the method of the present invention, the conductive rings 2 and 3 can be brought into pressure contact and completely electrically connected with the respective wire terminals 4 and 5 at predetermined positions by merely press-fitting the conductive rings 2 and 3 on the molded cylindrical base 1. While a generally U-shaped wire is desirably used in the embodiment of the present invention, it will be understood that a straight wire may be used in lieu thereof to attain the effect similar to that above described.

From the foregoing detailed description, it will be understood that the present invention provides a method of making a slip ring assembly comprising the steps of preparing a molded cylindrical base, a plurality of conductive rings and a plurality of wire terminals separately from one another, said molded cylindrical base being formed with a plurality of axially extending grooves each having a deep portion and a shallow portion, disposing said wire terminals in said grooves respectively, and press-fitting said conductive rings on said cylindrical base in spaced apart relation from each other thereby to electrically and mechanically connect said conductive rings and said wire terminals with each other so as to obtain an assembly of said molded cylindrical base, said conductive rings and said wire terminals. By virtue of the fact that the components are prepared as individual units, the slip ring assembly can be produced at low cost with a high productivity. The slip ring assembly is free from any deformation of the conductive rings and the molded cylindrical base due to thermal contraction of the molded cylindrical base. Further, the slip ring assembly thus manufactured shows a high reliability due to the fact that welding of the wire terminals to the conductive rings is unnecessary.

Slip ring assemblies made by the method of the present invention were subjected to a test under severe conditions including a high temperature and a very low temperature. In the test, one heating ad cooling cycle included heating to 170.degree. C for 23 hours, cooling to -30.degree. C for 1 hour, heating to 80.degree. C for 47 hours at a relative humidity of 80 percent and allowing to stand at room temperature for 1 hour, and the slip ring assemblies were subjected to ten such heating and cooling cycles. The test results showed that the outer diameter of the conductive rings varied in the range of from 0.004 to 0.014 mm which is very small compared with the range of from 0.1 to 0.2 mm in the case of the conductive rings in conventional slip ring assemblies. (In order that the test conditions match the actual operating conditions of electric generators, the molded cylindrical base was subjected to after-curing at 240.degree. C for 4 hours prior to the test to remove moisture and any other volatile matters therefrom for the purpose of sufficient aging.) The tensile strength of the wire terminals lay in the range of 61 to 98 Kg per square mm. It will thus be understood that the variation in the dimension of the molded cylindrical base due to aging is about one-fifth that of conventional slip ring assemblies and the slip ring assembly according to the present invention can operate over a long period of time without any deformation.

Claims

We claim:

1. A method of making a slip ring assembly comprising the steps of separately preparing a base of electrical insulating material having a cylindrical base part, a plurality of conductive rings and a plurality of wire terminals of the same number as that of said conductive rings, the step of preparing said cylindrical insulating base part including forming a plurality of grooves of the same number as that of said conductive rings for receiving said wire terminals therein, axially extending each of said grooves through the overall length of said cylindrical base part, and forming each groove with a shallow portion having a depth substantially smaller than the thickness of said wire terminals at a predetermined position of the cylindrical base part where a corresponding conductive ring is to be press-fitted and with a deep portion having a depth substantially larger than the thickness of said wire terminals at the remaining portion of the groove excepting said shallow portion, disposing one of said wire terminals in each of said respective grooves, and press-fitting said conductive rings onto the respective predetermined positions of said cylindrical base part such that each of said wire terminals is pressed by the corresponding one of said conductive rings to be firmly held between the bottom surface of the shallow portion of the corresponding one of said grooves and the inner peripheral surface of said corresponding conductive ring to thereby electrically connect said wire terminals to said corresponding conductive rings and insulate said conductive rings from each other.

2. A method of a making a slip ring assembly as claimed in claim 1, in which a generally U-shaped wire of electrical conductor is disposed in said terminal receiving grooves, and after press-fitting said conductive rings to engage the outer peripheral surface of said wire, unnecessary wire portions are cut off and removed to provide said wire terminals.

3. A method according to claim 1, further comprising positioning wire insulation in surrounding engagement over a predetermined portion of the length of at least one of said wire terminals prior to disposing said at least one wire terminal in one of said respective grooves, wherein said disposing of said wire terminals includes positioning said one of said wire terminals with the wire insulation extending along the deep portion of the corresponding groove.

4. A method according to claim 1, wherein said base includes an end part adjacent said cylindrical base part which has a greater cross-sectional area than said cylindrical base part, wherein openings are provided in said end part which are aligned with respective ones of said grooves, and wherein said disposing of said wire terminals includes extending portions of said wire terminals through said openings.

5. A method according to claim 4, further comprising bending the extreme ends of said wire terminals extending through said openings to form attachment points for electrical circuitry after said press-fitting.

6. A method according to claim 4, wherein said disposing of said wire terminals includes positioning the legs of a U-shaped piece of wire in two respective grooves, and further comprising cutting off unnecessary portions of said U-shaped piece of wire after said press-fitting.

7. A method according to claim 6, wherein said U-shaped piece of wire is positioned with said legs extending through said openings in the end part of the base.

8. A method according to claim 7, wherein the bridge part of said U-shaped piece of wire is positioned adjacent the cylindrical part of said base, and wherein said cutting includes cutting said wire immediately adjacent the respective press-fitted ring in press-fitting contact with said wire portion being cut.

9. A method according to claim 1, including preparing said cylindrical part with a constant diameter along its length and preparing each of said conductive rings similar inner diameters.

10. A method of making a slip ring assembly comprising the steps of separately preparing a base of electrical insulating material having a first part with constant cross-section along its length, a plurality of conductive rings and a plurality of wire terminals of the same number as that of said conductive rings, the step of preparing said first part including forming a plurality of grooves of the same number as that of said conductive rings for receiving said wire terminals therein, axially extending each of said grooves through the overall length of said first part, and forming each groove with a shallow portion having a depth substantially smaller than the thickness of said wire terminals at a predetermined position of the first part where a corresponding conductive ring is to be press-fitted and with a deep portion having a depth substantially larger than the thickness of said wire terminals at the remaining portion of the groove accepting said shallow portion, disposing one of said wire terminals in each of said respective grooves, and press-fitting said conductive rings onto the respective predetermined positions of said first part such that each of said wire terminals is pressed by the corresponding one of said conductive rings to be firmly held between the bottom surface of the shallow portion of the corresponding one of said grooves and the inner peripheral surface of said corresponding conductive ring to thereby electrically connect said wire terminals to said corresponding conductive rings and insulate said conductive rings from each other.

11. A method according to claim 10, further comprising positioning wire insulation in surrounding engagement over a predetermined portion of the length of at least one of said wire terminals prior to disposing said at least one wire terminal in one of said respective grooves, wherein said disposing of said wire terminals includes positioning said one of said wire terminals with the wire insulation extending along the deep portion of the corresponding groove.

12. A method according to claim 10, wherein said base includes an end part adjacent said first part which has a greater cross-sectional area than said first part, wherein openings are provided in said end part which are aligned with respective ones of said grooves, and wherein said disposing of said wire terminals includes extending portions of said wire terminals through said openings.

13. A method according to claim 12, further comprising bending the extreme ends of said wire terminals extending through said openings to form attachment points for electrical circuitry after said press-fitting.