US3523288A - Brush wear indicator - Google Patents

Description

Aug. 4, 1970 l H. A. THOMPSON 3,523,288

BRUSH WEAR INDICATOR Filed March 20, 1968 2 Sheets-Sheet l Fig. I3

INVENTOR. Harris A. Thompson A fr0/ME Ys Aug. 4, 1970 H. A. THcMPsoN 3,523,233

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33 ,6' 32 3o 34 35 B/ 3l 32 \l6 16/ Fig. Fly-f2 4 I INVENTOR. Harris A. .771 ompson BYWM A TTOR/VEYS 4United States Patent O- i 3,523,288 BRUSH WEAR INDICATOR Harris A. Thompson, P.O. Box 916, Boulder, Colo. 80302 Filed Mar. 20, 1968, Ser. No. 714,555 Int. Cl. G08b 21/00; H01h 1/36 U.S. Cl. 340-267 13 Claims ABSTRACT OF THE DISCLOSURE A brush wear indicator for an electric motor including a switch means having one portion contacting a motor brush. This switch means trips to initiate a warning device. When the brush is nearly worn out, the contacting portion drops over the edge of the brush and the switch is tripped. A switch may be used with one or with each brush and when used with both, either will trip to actuate the warning device. The warning device may be a light adapted to flash whenever the switch is tripped.

This invention relates to Wear indicating devices, and more particularly to brush wear indicators in electric motors.

A primary object of the invention is to provide a novel and improved brush wear indicator for an electric motor which will actuate a suitable Warning signal whenever the brush becomes suiiiciently worn as to require replacement.

The present invention is especially useful in artificial respiration devices, especially those which must be run continuously to assist a patient in breathing. In such cases, should the apparatus be stopped because of a breakdown, the life of the patient may be in danger and every reasonable precaution must be taken to prevent such an occurrence. In such devices, the motor is usually a 12-volt type, which is normally operated by an alternating current supplied by a regular 11G-volt A C. power source, with the voltage being reduced by a transformer. However, in case of an emergency, the motor may also be operated by a direct current power source such as a storage battery.

By keeping a storage battery available for emergency uses, a power supply is assured, and the only possibility of a breakdown will be in the mechanisms of the respirator itself. However, by the selection of good components, the respirator mechanisms can be designed to operate reliably over long periods of time, with the only wear occuring on the commutator brushes of the electrical motor driving the blower. Ordinarily, this brush Wear can be predicted and after several thousand hours of operation, the motor will be inspected, serviced and the brushes replaced even though they may be only partially worn.

Naturally, such a procedure does not allow for contingencies such as an extraordinary rate of brush wear. Also, where a motor will run for several thousand hours without attention, the individuals relying upon the mot-or often lose track of time, with the result that the brushes will be worn out and the motor will stop, often at a very inconvenient time. Also, arcing will occur across a commutator before the motor stops to cause serious damage to the motor.

3,523,288 Patented Aug. 4, 1970 There is a real and definite need for an improved brush Wear indicator in a situation such as that above indicated, where an electric motor must run continuously and where the brush wear is the component which requires the most frequent periodic attention. The above invention was conceived and developed with such a need in view, and comprises in essence, an auxiliary switch built into the brush assembly which is adapted to remain in a normally closed, or open, position until such time as the brush becomes worn. Thereupon, the switch trips to open or close to initiate a. warning signal, preferably a ashing light, which will operate continuously thereafter until the motor brushes are replaced.

Accordingly, another object of the invention is to provide a novel and improved brush wear indicator for an electric motor which will include a Warning device to warn users that the brushes are almost worn out and must be replaced before they are completely worn out.

Another object of the invention is to provide a novel and improved brush wear indicator which will emit a continual warning signal when the brush is about to be Worn out, so that the brushes may be replaced at any time withinseveral Weeks after the warning signal commences as at a time when it is also convenient for a regular serviceman to check and service the motor and other mechanisms in the apparatus.

Another object of the invention is to provide a novel and improved brush wear indicator which is especially adapted to use an electrical flashing system, of the type where the hashing light will attract attention until the matter is taken care of.

Another object of the invention is to provide a novel and improved brush wear indicator which is especially adapted to be used in electrical motors of the type having unitized brushes and brush carriers for certain components of the indicator may be advantageously incorporated into the unitized brush carriers as a part of a factory-produced item.

Other objects of the invention are to provide a novel and improved brush wear indicator which is a simple, reliable, 10W-cost arrangement, and is easily incorporated into equipment such as respirator devices or also, into similar equipment where it is important to keep the electrical motors continuously running.

vWith the foregoing and other objects in view, my present invention comprises certain constructions, cornbinations and arrangements of parts and elements as hereinafter described, deiined in the appended claims, and illustrated in preferred embodiment by the accompanying drawing in which:

FIG. 1 is an isometric view of a respirator, of a type which can advantageously use the invention, formed as an enclosed container, having controls and indicators on its upper face and a blower within it as shown by broken lines.

FIG. 2 is an isometric View of a blower, such as is used in the respirator shown at FIG. l, and showing the motor portion of the blower wherein the brush wear indicators are incorporated according to the present invention.

FIG. 3 is a plan view of a portion of the motor, as from the indicated arrow 3 at FIG. 2, but on an enlarged scale, to show the commutator and one brush within its holder bearing against the commutator.

FIG. 4 is a side elevational view of the portion of the motor shown at FIG. 3.

FIG. 5 is a longitudinal sectional view as taken from the indicated line 5 5 at FIG. 3, but on an enlarge scale.

FIG. 6 is a sectional fragment of the brush and its holder similar to a portion of the showing at FIG. 5, but on a greatly enlarged scale and with the brush being worn to the point where the improved brush wear indlcator becomes operative.

FIG. 7 is a portion of the circuit diagram of the electric motor modified to include a circuit for a brush wear indicator, having a light which will burn steadily while the brushes are of an operative length, but which will flash when one or both of the brushes are nearly worn out. f

FIG. 8 is a circuit diagram similar to FIG. 7, but with an arrangement having a light which will flash fora few minutes when the motor starts, but thereafter will not burn while the motor is running and the brushes are of an operative length, but which will ash when one or both of the brushes are nearly worn out.

FIG. 9 is a plan view similar to FIG. 3, but showing a modified type of brush holder.

FIG. 10 is a side elevational view of the construction shown at FIG. 9.

FIG. 11 is a longitudinal sectional view of the brush and its carrier similar to FIG. 5, but showing yet another arrangement wherein the electrical contact mechanism of the wear indicator is reversed from the arrangement shown at FIG. 5.

FIG. l2 is a circuit diagram similar to that of FIG. 7, but being modied to use the indicator shown in FIG. 11, using a separate light for each brush which will not burn while the motor is running and the brushes are of an operative length, but which flash when the brush is nearly worn out.

FIG. 13 is yet another circuit diagram modified to provide a wear indicator is one brush only, to provide for a continuously burning pilot light which goes out when the brush is nearly worn out, and to provide for a manual switch to test the pilot light.

Referring more particularly to the drawing, FIG. l illustrates a typical respirator R which is one example of an apparatus wherein the present invention may be incorporated. This respirator is formed as a box-like case 15 having a power supply lead 16 extending into the case to drive various mechanisms therein, such mechanisms including a motorized air blower A and control components not shown. A switch 17 and suitable gages and control knobs 18 are located on the surface of the case 15 for turning the unit on and for adjustments during its operation. Also, a blower tube 19 extends from a side of the case for attachment to respiratory equipment, not shown.

In the present invention, a brush wear indicator is incorporated in the electrical motor of the blower A and it includes a signal means which will actuate whenever one, or both, of the brushes become worn to the point where replacement is required, all as will be hereinafter described in detail. Preferably, such a signal means is a light L which is conveniently mounted upon the resiprator case 15 and which will light up, go out or continually flash whenever it is actuated depending upon the type of circuit used with the light. The purpose of the light, regardless of the manner in which it operates, is to call to the attention of the users, the need for brush replacement and a periodic check of the apparatus to prevent a breakdown at an inopportune time, and thereby assure a long period of continuous operation of the apparatus.

The air blower A, as illustrated at FIG. 2, includes a cylindrical shell 20 wherein a centrifugal blowing mechanism is housed, with a suitable discharge tube 21 extending from one side of the shell to connect with the blower tube 19. lIt includes also, an electrical motor M outstanding from an end of the shell and in axial alignment therewith. The motor shaft 22 shown in dotted lines at FIG. 2, extends into the shell 20 to carry the rotor of the blower.

The motor M is a conventional arrangement housed within a suitable cylindrical frame 23 aixed to the shell 20 as by a transition 24. This frame includes a spider 25 at its outward end to carry a bearing 26 for the end of the shaft 22. The shaft carries the rotor windings 27 and a commutator 28. The eld windings 29 are mounted within the frame about the rotor and two diametrically opposed brush carriers B are mounted upon the edges of the frame 24 so that the brushes 30 within them bear against the commutator 28. Power leads 16' extend to this motor through the frame to connect with the field windings 27 and the brushes 30 to render the unit operative.

The present invention is concerned with indicating the wear of the brushes 30 as they bear against the commutator and the invention includes a normally closed, or normally open switch which will be opened, or closed, by the position of the brush within its carrier B just before the brush is worn out.

The carrier B must insulate the brush 30 from the motor frame and thus, the construction on various types of electric motors is quite similar. In the construction illustrated, the carrier is generally formed as a deep cup-like body 31 of a plastic or similar insulating material. A short metallic tube 32, closed at one end, approximately one-third longer than the body and essentially rectangular in cross section, is mounted within the body to form a socket with the forward portion thereof extending beyond the body 31. The brush 30 slidably fits in this socket and a spring 33 also lies within this socket behind the brush and is adapted to urge the brush outwardly. A pliable feeder wire 34 is mounted in the tube within the embrace of this spring 33, and is secured to the bottom of the tube 32 and to the back of the brush 30. This wire 34 thus connects the brush with the tube to provide a better electrical contact between the two and also, limits the outward movement of the brush from the tube when it is worn out. To complete this assembly, a lead wire 16l is attached to the outer face of the metallic tube as by a clip 35, tightly fitting into a small space between the body 31 and tube 32 as best illustrated at FIG. 5.

This body 31 is mounted upon a shelf portion 32a on the rim of the motor body 23 by a clamp 36 extending over the body 31 and being held in position by mounting screws 37 turned into socketed studs 38 upstanding from the shelf 23a. So mounted, the axis of the body is radially oriented wit-h respect to the commutator axis with the mouth of the socket formed by the tube 32 being comparatively close to the commutator 28. Accordingly, the major portion of the brush 30 will slidably extend into the tube 32 with its outward end 39 projecting therefrom to contact the commutator, as clearly illustrated at FIG. 5. It follows that as the brush is worn, the spring 33 urges it outwardly from the socket and against the commutator, and that when the brush is worn to the point where it is considered worn out, the retaining wire 34 is stretched taut preventing further movement of the brush. It must then be replaced or else the motor will soon stop running. Before it stops, however, the arcing from t-he brush to the commutator can damage the commutator.

To modify this brush carrier B and the brush 30 within it, to indicate when the brush is nearly Worn out, an indi-r cator switch S for each brush is mounted upon the respective carriers B. In the construction illustrated at FIGS. 2 through 6, the indicator switch S includes a resilient arm 40, of fiat spring brass, or the like, which lies upon the top of the body 31 to extend longitudinally thereupon with the forward extended end being cantilevered over the portion of the tube 32 extending beyond the body 31. This arm 40 is held in position by the clamp 36, but with a flat insulator pad y41 between the arm 40 and clamp 36 to completely insulate the arm from the frame of the motor. A lock strap 42 may also be wrapped about the portion of the body 31 which extends outwardly from the frame ledge 23a, to extend also about the arm 40 and insulator pad 41 as shown.

The indicator switch S also includes a slide pin 43 carried in an insulator button 44 which fits with a press fit in an opening in the top surface of the extended end of the tube 32 directly underneath the cantilevered end of the arm 40. The button 44 has a central passageway through it wherein the body of the pin 43 slidably fits to extend through it and bear against the brush 30. The top of the pin includes an enlarged head 45 which is contacted by the undersurface of the arm 40. The length of the pin is such as to hold the arm 40 in a lifted position and biased against the pin when the bottom of the pin within the insulated button 43 is bearing against the top of the brush within the tube 32, as best illustrated at FIG. 5.

Accordingly, in the arrangement, a continuous electrical circuit extends through the normally closed switch S, lead 50 wheren the light L is located and this lead 50 extending from the brush 30, to and through the pin 43, and to and through the arm 40. The outward end of this arm, opposite the pin contact end, is upturned as at 46, to provide a connector clip for the attachment of a lead wire 47 as by a drop of solder 48. The lead 47 is part of a signal means circuit as hereinafter described.

The switch S, thus described, is normally closed and the signal means will be actuated when the switch is tripped to open and interrupt the circuit through it. Tripping may be effected by locating the insulator button and pin at a position on the tube 32 where the rear inner edge of the brush will pass as it approaches the worn-out position so that the pin will drop away from the brush. However, because of the chance that the pin might accidentally contact the spring 33, it is preferred that the pin drop into a hole 49 drilled into the top of the brush 30 near its inner, rearward end as illustrated at FIG. 6. The hole 49 is several times as large as the pin and it is to be noted that when the pin is dropped into this hole 49, the undersurface of the head 45 abutting against the button 44 limits the depth to which the pin may drop so that it will not contact the bottom of the hole. It is also to be noted that the size of the hole 49 is such that some brush wear will occur before the pin moves from the edge of the hole, its position when it first drops into the hole, to the middle of the hole as illustrated. Thus, the circuit may be open to permit the signal means to operate for several weeks before the motor stops.

The location of the hole 49 is correlated with the length of the restraining wire 34 so that as brush wear causes the hole 49 to shift to the position shown at FIG. 6, or shortly therebeyond, the restraining wire wire become taut to prevent further brush movement and to eventually stop the motor.

One or both brush carriers B may be provided with switches S, and various signal circuits may be used in connection therewith as will now be described.

Where two indicator switches S are used, a circuit such as that illustrated at FIG. 7 may be used. This circuit shows that portion of the motor circuit associated with the brushes. The two power leads 16 to the motor connect to the field coils and extend to the brushes 30 as lead 16". Since each switch S is normally closed by contacting its brush, the opposing leads 47 form a shunt connecting with a lead 40 wherein the signal light L is mounted, between the leads 47. Thus, as llong as both switches S are closed, the signal light will emit a steady, glowing light whenever the motor is running. The steady light will indicate that the apparatus is turned on and is functioning properly.

Each end of the lead 50 also connects with a lead 451 in parallel with the shunt lead 47 and the lead 51 connects to the power supply lead 16 back of the brush 30. Each lead 51 includes a asher generator F, of any suitable type such as, for example, a Tungsol unit, Type 616, manufactured by Tung Sol Electric Co. Accordingly, it follows that whenever either indicator switch S opens because the brush wear permits the pin 43 to drop into a hole 49, the flow through the shunts 47 and lead 50 is interrupted and the light L goes out. Then the current must flow through a lead 51 and this flow will actuate the flasher generator F and cause the light L to flash to indicate that it is necessary to replace a brush.

Another circuit, which may be used where it is desirable to have the light L burn only when flashing is desired, is illustrated at FIG. 8. The leads 47 from each switch S are connected to a resistor 52, the heating element of a thermal relay of the type which uses a bimetallic switch 53, which is normally closed and opens responsive to heat from resistor 52. One commercial unit having such components is an Amperite 5CT3 manufactured by Amperite Co., Inc. This switch 53 is in a circuit lead 54 which includes a flasher generator F and the signal light L in a series arrangement. The lead l54 is connected directly to the opposite power leads 16 back of the brushes 30, so that whenever the switch 53 is closed, the flasher F causes the light L to flash. In operation, with the motor running and the indicator switches S properly contacting their respective brushes, the resistor 52 is heated to hold the switch 53 open. The switch 53 closes whenever a switch S opens as when a brush is worn out or when the motor is turned off. The light L will flash for a short period of time immediately after the motor starts and before the resistor 52 is heated, but such is not significant and actually is desirable since it serves as an indication that the flasher is operative.

FIGS. 9 and 10 illustrate a modified form of a brush carrier B'. In this construction, the plastic body 31 has a pair of opposing lugs 55 and it is held in position by clips 56 mounted on a flat shelf 23a of the motor body as by mounting screws 37. The arm 40 is mounted upon a pad 57 and secured in place by pins 58 which extend through both the arm and pad. To supplement the pins, a lock strap 42 embraces the assembly about the pad as illus` trated.

FIG. 1l illustrates one manner in which the arc indicator switch S' may be mounted upon the brush carrier B to function as a normally open, rather than a normally closed, switch to be closed only when the brush is worn. In this construction, the components forming the brush carrier B, the body 31, the tube 32, spring 33, conductor wire 34 and circuit connecting clip 35 are the same as hereinbefore described. Likewise, certain components of the switch S and the components which hold it in position are the same as hereinbefore described. An arm 40 of a slightly modified construction, cantilevers from the body 31 to overlie the inward end of the tube 32 and be held in position upon the body by a U-strap 36 with an insulator pad 41 between the arm and strap 36. Likewise, a lock strap 42 may fasten the arm 40 to the body 31 and the outer end 46 of the arm may be connected to a lead wire 47, as illustrated.

The button 44 is not an insulator button, but a conductor button, of metal, and is soldered or otherwise fastened to the tube 32. The slide pin 43', on the other hand, is a simple, cylindrical member formed of an insulating, nonconductor material. This pin does not carry a head, but instead, a suitable contact button 60 is affixed to the underside of the end of the arm 40. The length of the pin 43 is such that when it is within the passage way of the button 44 and bears against the top of the brush, the contact button 60 on the arm is lifted above the conductor button 44. However, when it drops into the socket 49', the contact 60 rests upon the Ibutton 44 making contact to close the circuit. It is to be noted that the socket 49', as illustrated in FIG. 11, can be slotformed instead of being a hole and also, it can be eliminated with the pin 43' being adapted to drop over the rear edge of the brush since the insulated pin will not cause an undesirable circuit if it contacts a spring 33.

FIG. 12 is a circuit which may be used with the construction illustrated at FIG. 8. The lead 47' from each switch S is conected to an individual light L, a flasher F and to the power input circuit 16 at the opposite side of the motor, Therefore, whenever a normally open switch S is closed, the circuit is closed and the light L will commence to flash. It is to be noted that individual lights L and individual flashers F will be required for each circuit lead, however, special lights can be used having separate filaments.

PIG. 13 is a circuit which produces a burning light as long as the brushes are in good condition and which goes out to warn the user of the apparatus when the brushes are worn. Also, this figure shows a circuit which uses a switch S on only one brush B". The use of the single switch S is desirable in an electric motor where the wear of one brush is always faster than the wear of the other, a condition comon in many types of motors. Accordingly, the switch S is located at the faster wearing brush B", and the lead 47 therefrom, connects with a extends, thence, to the power circuit lead 16l opposite the brush B".

The circuit is closed and the light burns whenever the motor in operating and until the switch kS opens because of brush wear. To ascertain whether or not the light goes out for this reason or is merely burnt out, a check circuit lead 65 having a normally open manual switch 66, shunts the switch S. Closing switch 66 will cause the light to turn on if brush wear is the cause of its going out.

The invention has been described for a twobrush, single-phase unit; however, it could be easily applied to a three-brush, three-phase unit if desired. Moreover it is obvious that others skilled in the art can build and devise similar alternate and equivalent constructions which are nevertheless within the spirit and scope of my invention. Hence, I desire that my protection be limited not by the constructions illustrated and described, but only by the proper scope of the appended claims.

I claim:

1. A brush wear indicator system for an electric motor having a commutator and a brush slidably contained within a socketed carrier with its leading edge extending therefrom to contact the commutator, said brush being resiliently based to be moved from the carrier and against the commutator as it wears, and comprising in combination therewith:

a circuit generally shunting the brush and commutator;

a switch means in said circuit adapted to be tripped from a normal position and to thereby disrupt the circuit;

a signal means actuated responsive to a disruption of the circuit; and

a holding means associated with the switch means and with the brush holding the switch means in its normal position when the brush is normally within its carrier, but shifting to trip the switch means when the brush has moved towards the commutator to a position where it is nearly worn out, whereby to disrupt the circuit and actuate the signal means.

2. The organization set forth in claim 1, wherein:

said signal means is a light in said circuit; and

in said circuit which opens upon tripping;

said signal means is a light in said circuit; and

a shunting lead having a flasher, shunting said nor mally closed switch, whereby, when the switch is closed, the light will burn steadily responsive to current flow through the said circuit, but when the switch opens, the light will flash responsive to an intermittent current flow through the said shunting lead about the switch.

3. In the organization set forth in claim 1, wherein:

said switch means includes a normally closed switch in said circuit which opens upon tripping;

a switch control in said circuit; and

a second powered circuit including said signal means and a control switch adapted to be actuated by said switch control, said switch control being adapted to hold said control switch open whenever the first said normally closed switch is closed, 'but to close whenever the rst said switch is opened.

4. In the organization set forth in claim 1, wherein said holding means includes:

a pin mounted upon said carrier to project normally into the socket portion thereof to bear against a side of the brush when the brush is normally within the socket, but to drop behind a rearwardly disposed edge of the brush surface when the brush is moved toward the comutator and is nearly worn out.

5. In the organization set forth in claim 4, wherein the brush includes a hole in its side near its rearward end in alignment with the pin to constitute said rearwardly disposed edge so that the pin will drop into the hole.

6. In the organization set forth in claim 1, wherein said switch means includes a resilient arm mounted upon the carrier having an end biased towards the socket therein, and said holding means includes a pin carried in a passageway extending through a hole in the wall of the carrier and into the socket, said pin having its inner end bearing against a side of the brush and its outward end contacting the arm to hold the arm away from the carrier when the brush is in a normal condition, but to have its inner end drop over an edge of the brush when the brush is moved close to its worn out position to release the arm and permit it to move towards the carrier.

7. In the apparatus set forth in claim 6, wherein the pin is a conductor and said circuit extends through the brush and pin, and said switch means in thus normally closed whenever the pin bears upon the brush, but is adapted to be opened whenever the pin drops away from the brush.

8. In the organization set forth in claim 6, wherein the pin is an insulator and said switch means includes an electrical contact on the carrier adjacent to the pin which is adapted to be conducted by the arm whenever the pin drops away from the brush.

9. An indicator control switch means for indicating the wear of the brush of an electric motor of the type having a commutator and a socketed carrier wherein the brush is slidably mounted and is resiliently biased to be urged therefrom and against the motor commutator, said switch means being held in a normal position when the brush is normally within its socket, but tripped when the brush is moved towards the commutator to a position indicative of its being nearly worn out, and including in combination therewith:

a resilient means mounted upon the side of the carrier and being resiliently biased toward the side thereof;

a passageway through the carrier wall aligned with said resilient means; and

a pin slidably carried in this passageway with its outer end being held by the resilient means and being urged inwardly by the resilient means and with its inner end being held against a side of the brush when the brush is in a normal condition, but with its inner end being adapted to drop from an edge of the brush when the brush approaches its worn out condition to thereby release the resilient means and permit the same to move towards the carrier.

10. In the organization set forth in claim 9, wherein a hole is formed in the face of the brush near its edge, and the pin is adapted to drop from the side of the brush and from an edge of the hole and thereinto.

11. In the organization set forth in claim 9, wherein:

the resilient means is a conductor; and

the pin is a conductor forming a continuous circuit between the brush and to the resilient means when the brush is in a normal condition, to permit the same to function as a normally closed switch adapted to be opened when the pin drops away from the References Cited brush. 12. In the organization set forth in claim 9, wherein: UNITED STATES PATENTS the resilient means is a conductor; 2,613,258 10/1952 Azno 340-282 the pin is an insulator member to hold the switch 5 En@ t l 310 239 l -turrows e va means 111 a normal Y 013611 190511011, and 3,350,617 10/1967 Firth 340 267 X a contact means is mounted on the carrier adapted to contact the resilient means and close the switch when ALVIN H. WARING, Primary Examiner the Pin drops away from the brush' P. PALAN, Assistant Examiner 13. In the organization set forth in claim 7, wherein 10 the resilient means is an arm attached to the carrier with U'S' C1' X'R' one end cantilevered from its point of attachment. 20G-164; 310-239, 245; 340--282 UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No 3 523,288

Harris A. Thompson August 4, 1970 It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 7y line 6l, "said signal means is a light in said circuit; and" should read said switch means includes a normally closed switch Signed and sealed this 23rd day of February 1971.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

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