US3826942A

US3826942A - Brush assembly for a slip ring

Info

Publication number: US3826942A
Application number: US00300445A
Authority: US
Inventors: J Twarog
Original assignee: Avco Corp
Current assignee: Avco Corp
Priority date: 1972-10-25
Filing date: 1972-10-25
Publication date: 1974-07-30
Anticipated expiration: 1991-07-30

Abstract

A slip ring, mounted on a rotating shaft, is contacted by four pairs of spring loaded, pressure activated, gas cooled brushes. The brush assembly is supported in one-half of a seal housing, the other half of which provides conventional shaft sealing. The housing for the brush assembly is an annulus having end walls and inner and outer peripheral walls, the inner peripheral wall surrounding the ring and having a plurality of circumferentially spaced openings. The brush assemblies are mounted within the housing and are driven through the apertures into contact with the ring. The brushes are supported from the ends of a leaf spring, the center of which is in turn supported by a support spring which is gas pressure actuated.

Description

United States Patent 1 Twarog, Jr.

[11] 3,826,942 July 30, 1974 BRUSH ASSEMBLY FOR A SLIP RING [73] Assignee: Avco Corporation, Stratford, Conn.

[22] Filed: Oct. 25, 1972 [21] Appl. No.: 300,445

3,278,777 10/1966 Grooms 310/240 Primary Examiner-R. Skudy Attorney, Agent, or Firm-Charles M. Hogan; lrwin P. Garfinkle [5 7 ABSTRACT A slip ring, mounted on a rotating shaft, is contacted by four pairs of spring loaded, pressure activated, gas cooled brushes. The brush assembly is supported in one-half of a seal housing, the other half of which provides conventional shaft sealing. The housing for the brush assembly is an annulus having end walls and inner and outer peripheral walls, the inner peripheral wall surrounding the ring and having a plurality of circumferentially spaced openings. The brush assemblies are mounted within the housing and are driven through the apertures into contact with the ring. The brushes are supported from the ends of a leaf spring, the center of which is in turn supported by a support spring which is gas pressure actuated.

7 Claims, 3 Drawing Figures 1 BRUSH ASSEMBLY FOR A SLIP RING BACKGROUND The use of slip rings for transferring electrical energy between rotating and stationary components is very old, but most applications have been limited to relatively low speeds. Recent developments have resulted in significant improvements and some slip rings used in gas turbine engines satisfactorily transmit signals in the order of millivolts at shaft speeds as high as 100,000 r.p.m. with contact velocities of 6,5000 feet per minute. Certain of these slip rings have had life expectancies ranging from 5 to 50 hours of use.

The present invention seeks to improve the prior art slip ring by permitting operation with contact velocities up to 20,000 feet per minute with improved life expectancies. In addition, this invention improves the prior art by positioning a pair of slip rings in one-half of the housing of a conventional engine seal so that the sealing function and the slip ring function are simultaneously accommodated.

In order to obtain good signal transfer over a period of time and a variety of speeds, general slip ring requirements are as follows:

l. Low electrical resistance variations due to'rubbing contact.

2. Low electrical resistance variations due to brush bounce.

3. Low wear of rubbing components.

4. Limitation of heat generation to prevent destruction of contact materials.

5. Elimination of loose material generated by rubbing cont-act.

6. Protection from foreign material.

This invention improves the prior art slip rings and meets all of the foregoing requirements. These results are accomplished by mounting the contacting brushes in pairs, four pairs being used around the periphery of the ring. The pairs are spring loaded and are piston operated in response to air pressure so that the brushes are in running contact with the ring only when signals are being transferred. The system also provides gas flow cooling and cleaning, thus further reducing wear.

THE DRAWINGS For a better understanding of the precise nature of this invention reference should now be made to the attached drawings in which:

FIG. 1 is an end view, partly in section, of a preferred embodiment of this invention;

FIG. 2 is a section taken through the line 2-2 of FIG. 1; and

FIG. 3 is a section taken through the line 3--3 in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The slip rings provided in accordance with this invention are supported within one-half of a conventional seal housing normally used for sealing a rotating shaft 11. The spring loaded carbon seal 12 is conventional and, as shown in FIGS. 2 and 3, occupies the right half of the seal housing 10. The remainder of the housing 10 is occupied by two sets of slip ring assemblies. Although two such assemblies are shown, any number capable of accommodation by the housing l0 \M; may be 'iis'ed. Since the slip ring assemblies are identical, only one is described.

Each of the two slip rings assemblies includes a conducting ring 13 imbedded in a non-conducting insert 14 on the shaft 11. The conducting rings 13 are each electrically connected by means of a lead 15 to a signal source (not shown) such as a strain gage or other sensor secured to the shaft.

Each ring 13 is contacted by a set of four identical brush assemblies 17 mounted in the housing 10 and spaced from the seal 12 between insulating disc spacers 16. Each of the brush assemblies 17 consists of two spring-loaded brushes l8 and 19 which are electrically interconnected by a leaf spring 20. The assemblies 17 also include a brush lifting and actuating spring 22 connected to the spring 20 by a piston 24. An electrical connection to the brushes is made through the piston 24 and a lead 26.

The brush lifting and actuating spring 22 provides the support for the brushes l8 and 19 and in addition transmits the contacting forces to the brushes. It is supported within the housing between adjacent inlet manifolds 28 positioned apart within the housing, and each spring 22 extends axially between the spacers 16. The space between the outer periphery of the housing 10, the spring 22, and the spacers 16 provides an annular chamber 27 into which pressurized air is admitted for actuating the spring.

The housing 10 has an inner peripheral wall 29 around which the brush assemblies are located. The wall 29 is provided with two sets of apertures. Apertures 30 permit the radial travel of the brushes from a non-contacting position into a ring contacting position. Apertures 31 provide a gas inlet to the surface of the rings 13. Air of freon supplied to the inlet manifolds 28 is directed through ports 32 in the manifold and through aperture 31 onto the surface of the respective ring 13 for cooling and cleaning the rings and brushes.

Normally the brushes l8 and 19 are biased out of contact with their associated ring 13 by the spring action of spring 22 and are driven into contact with the ring by admitting brush actuating air under pressure to the chamber 27 via a valve 34 and an airinlet 36. The pressurized air serves to apply gas pressure to all of the brush actuating springs 22 thereby driving the" springs 22, along with the attached pistons 24 and brush supporting leaf springs 20, radially inward. This action drives the brushes l8 and 19, through the apertures 30, into contact with an associated ring. Since the leaf springs 20 and the associated pistons 24 travel to a positive stop against the inner peripheral wall 29, the contact pressure of the brushes against the ring 13 is determined solely by the amount of prestressing of leaf spring 20.

SUMMARY In summary, two sets of slip ring assemblies are installed in the housing 10 of conventional carbon seals in the position normally occupied by one of the seals. Four brush-segment assemblies per set are used with two brushes l8 and 19 per assembly 17. Thus 8 brushes contact each ring 13, and this redundancy of brush contacts substantially eliminates contact resistance variations on the rings. The use of dual contacts per assembly insures efficiency of contact by providing an out-ofphase brush vibration frequency. Brush and ring wear is reduced to a minimum by the brush lifting springs 22 which hold the

brushes

18 and 19 out of contact with rings 13 when the assembly is not activated by air pressure. All brushes l8 and 19 are actuated into contact with the rings 13 by pressurizing the annular chamber 27 above the brush lifting spring 22 which deflects to a positive stop. With the

springs

22 and 20 bottomed, a high natural frequency is attained since the assembly mass is reduced to the mass of the

brushes

18 and 19 and leaf spring 20. Initial brush contact pressure is predetermined by fixing the allowable leaf spring deflection. Brush cooling is accomplished by air leakage past the support springs 22, and by the admission of pressurized air or freon channeled to the four manifolds 28 which direct flow to the slip rings 13.

The brushes l8 and 19 are driven into contact with the rings 13 only when it is desired to make a reading ser number may be used depending on the system requirements. Furthermore, the slip ring need not be used in combination with the seals but may be used separately, or the particular embodiment may be readily modified to add additional rings and associated brush assemblies.

I claim:

1. A slip ring assembly for providing an electrical connection to a conductive ring fixedly mounted on the periphery of a rotating shaft, the combination comprismg:

a stationary annular housing having axially spaced end walls and outer and inner peripheral walls, said housing being coaxial with said shaft, said inner wall surrounding said conductive ring and being spaced therefrom, and having a plurality of circumferentially spaced openings;

4 a plurality of radially displaceable circumferentially extending leaf springs supported within said housmg; 4 first and second electrically conductive contact brushes mounted on the respective ends of said leaf springs; and

means for radially driving said leaf spring toward said axis to drive each of said brushes through said openings and into contact with said ring.

2. The invention as defined in claim 1 and a support for each of said leaf springs, said support comprising a plurality of relatively heavy support springs extending circumferentially within said housing, the ends of said support springs being fixed, the spaces between said support springs and the outer peripheral wall of said housing defining a chamber, the center of said support spring being connected to the center of said leaf spring, said support spring being radially inwardly deflectable to deflect said leaf spring and drive said brushes into contact with said ring.

3. The invention as defined in claim 2 wherein said means for deflecting said leaf spring comprises means for admitting gas under pressure to said chamber for radially deflecting said support spring.

4. The invention as defined in claim 3 and a plurality of gas inlet manifolds in said housing, the ends of said support springs being fixed against said manifolds, and gas passageways through said manifold and said inner peripheral wall to admit gas from said manifold to said ring to cool and clean said ring and said brushes.

5. The invention as defined in claim 1 wherein said housing is a conventional seal housing and wherein said brush assemblies occupy one end of said housing, the other end of said housing being occupied by a set of shaft seals.

6. The invention as defined in claim 1 wherein said means for deflecting said leaf spring is a source of pressurized gas admitted to said housing.

7. The invention as defined in claim 1 wherein the center of said leaf spring is normally driven against said inner wall to a positive stop.

mg?" UNITED STA'IES PATENT omen CERTIFICATE OF CORRECTION Patent No. 3,826,942 Dated July 30, 1974 lnven tofls) John J. Twarog, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

' Column 1, li ne 11, "6,5000" should read 6,500

Signed and sealed this 29th day of October 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. 0. MARSHALL DANN V Attesting Officer Commissioner of Patents .J

mg? v UNITED S'IA'IES PATENT ormcm CERTIFICATE OF CORRECTION Ratent No. 3,826,942 Dated July 30, 1974 Invcotofls) John J. Twarog, Jr.

It is certified that error appears in the above-identified patent end that said Letters Patent are hereby corrected as shown below:

- Column 1, li e 11, "6,5000" should read 6,500

Signed and sealed this 29th day of October 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. I C. MARSHALL DANN Attesting Officer Commissioner of Patents

Claims

1. A slip ring assembly for providing an electrical connection to a conductive ring fixedly mounted on the periphery of a rotating shaft, the combination comprising: a stationary annular housing having axially spaced end walls and outer and inner peripheral walls, said housing being coaxial with said shaft, said inner wall surrounding said conductive ring and being spaced therefrom, and having a plurality of circumferentially spaced openings; a plurality of radially displaceable circumferentially extending leaf springs supported within said housing; first and second electrically conductive contact brushes mounted on the respective ends of said leaf springs; and means for radially driving said leaf spring toward said axis to drive each of said brushes through said openings and into contact with said ring.