US3448229A - Snap-acting pressure operated switch device with magnet control - Google Patents

Description

June 3, 1969 M. D. WILSON ETAL 3,448,229 SNAP-ACTING PRESSURE OPERATED SWITCH DEVICEWITH MAGNET CONTROL Filed March 24, 1967 V 29 30 W I 3|a I I I g?) p H l4 E, a l3 3" ax A 1 INVENTOR MORTIMER D WILSON WILLIAM HGLASS ATTORNEY United States Patent 3,448,229 SNAP-ACTING PRESSURE OPERATED SWITCH DEVICE WITH MAGNET CONTROL Mortimer D. Wilson, Turtle Creek, and William H. Glass, Pittsburgh, Pa., assignors to Westinghouse Air Brake Company, Wilmerding, Pa., :1 corporation of Pennsylvania Filed Mar. 24, 1967, Ser. No. 625,658 Int. Cl. H01h 35/24, 35/38 U.S. Cl. 200-82 11 Claims ABSTRACT OF THE DISCLOSURE A switch device having a contact member actuated by a fluid pressure controlled piston into and out of contact with a stationary contact member, wherein permanent magnet means resiliently mounted in coaxial alignment with the face of the piston exerts magnetic attraction on the piston in a switch-opening direction and in a switchclosing direction such that snap-action movement of the movable contact member occurs responsively to increasing and decreasing fluid pressure forces acting on the piston. The permanent magnet means is mounted in coaxial alignment with the piston by resilient mounting means, attached to the body of the switch device. The resilient mounting means enables self-alignment of the magnet means to insure coplanor contact of the face of the magnet means with the face of the piston and consequent maximum magnetic attraction force thereon.

Background 0 the invention Motor-driven fluid compressors are commonly provided with an electric control switch for starting and stopping the motor thereof responsively to attainment of minimum and maximum pressures in a reservoir charged by the compressor. Control of the switch device is usually effected via a conventional compressor governor, such as the well-known Westinghouse Air Brake Company Type S governor, which has predetermined minimum and maximum pressure settings at which it supplies fluid pressure to and releases fluid presure from a switch operating piston to effect closing and opening of the switch device.

Various expedients and arrangements have been devised for imparting a snap-action to the opening of the switch contact members to prevent excessive arcing and consequent burning of the contact members, particularly as may occur in the event of improper operation of the usual valves of the governor due to faulty seating thereof caused by the pressure of dirt or moisture, in which circumstances, leakage of fluid under pressure into the actuating piston chamber of the control switch at a slow rate effects a slow or creeping separation of the contact members resulting in undesired arcing therebetween and burning thereof.

Summary of the invention tion until establishment of a desired predetermined fluid pressure in the switch operating piston chamber sufficient to overcome the magnetic force exerted by the magnet means and produce a complete rapid opening of the contact members, thereby minimizing arcing and consequent burning of the switch contact members.

3,448,229 Patented June 3, 1969 In the accompanying drawing:

FIG. 1 is a diagrammatic view of a common fluid compressor system including an enlarged sectionalized view of the fluid pressure operated motor control switch device embodying permanent magnet means according to the invention.

FIG. 2 is an exploded view, showing separately the components of the permanent magnet means utilized in the control switch device of FIG. 1.

Description Referring to FIG. 1 of the drawing, the fluid compressor motor control apparatus shown includes a fluid pressure operated switch device 1. The switch device 1 is utilized in the motor control apparatus in cooperation with a standard compressor governor 2 to control energization of the armature circuit of a DC motor 3 for driving a compressor 4. A reservoir 5 is charged with fluid under pressure supplied from the compressor 4 under the control of the governor 2 by utilizing the switch device 1 to open or close the armature circuit of the motor 3. The armature circuit includes a voltage source, illustrated as a battery 6, a negative wire 7, and a positive wire 8, respectively connected to a terminal screw 9 and a terminal cap nut 10 on the switch device 1. The terminal screw 9 is connected to a movable main contact member 11 by way of a flexible metallic strap 12 secured to the terminal cap nut 13. The terminal cap nut 10 is connected to a stationary main contact member 14. A manually operated switch 15 is connected in the positive wire 8 for connecting or disconnecting positive wire 8 in the armature circuit when the apparatus is respectively to be put in or taken out of service. 1

The compressor governor 2 shown in outline -is of the WABCO type (S), similar to that disclosed in U.S. Patent 1,615,365 (assigned to the assignee of this application) with a single control passage connection between the governor 2 and the switch device 1 as described hereinafter.

The switch device 1 comprises the usual components including the aforementioned stationary main contact member 14 and movable main contact member 11 mounted on the free end of a contact arm 16 which is pivotally mounted on a pin 17 that is secured to the switch body 18 by a cotter pin 19. The switch device 1 also includes a movable abutment in the form of a piston 20 movable to different positions within a bore 21 responsively to a supply of fluid under pressure thereto to operate cooperatively with the piston stem 22 to pivot the contact arm 16 and cause the main contact members 11 and 14 to be engaged or disengaged accordingly.

The main contact members 11 and 14 are the replaceable type so as to be renewed when badly burned or pitted by arcing therebetween. The movable main contact member 11 is fastened to a contact body 23, of insulating material pivotally mounted on the contact area 16. A threaded terminal stud 24 is molded in the body 23 with the terminal cap nut 13 screwed on the stud to secure the strap 12 and contact member 11 thereto. A contactinsuring spring 25 biases the contact body 23 pivotally so as to firmly engage the two main contact members 11 and 14 when in their circuit-closing position and maintain said contact members closed during initial movement of said piston 20 during opening operation described hereinafter. The stationary main contact member 14 is secured by the terminal cap nut 10 to a terminal stud 26 that is molded in a stationary insulating block 27. The stationary insulating block 27 is of molded glass-filled polyester or similar insulating material and is secured to the switch body 18 by a suitable means (not shown) in a manner to eletcrically insulate the main contact member 14 from the switch body 18.

' Above and adjacent to the main contact members 11 and 14 is a suitable arc suppressing means shown herein as an arc diffusing bracket 29 having downwardly extending diffusing fingers 30 for breaking-up any arc that may possibly occur between the main contact members. This diffusion bracket is secured to the insulating block 27 by snap spring means 31. A cover 31a. is removably attached to the body 18.

The switch operating piston 20 is located in the lower part of the switch device 1 within the cylindrical bore 21 preferably having a bushing or liner in the switch body 18 With a piston stem 22 extending slidably through a bore 32 coaxial to and of a diameter smaller than the bore 21. The piston 20 is slidably positioned within bore 21 in a manner to form a piston chamber 33 at one side of the face of said piston (the right side as shown in the drawing). The opposite side of piston 20 has the piston stem 22 extending coaxially therefrom into the bore 32 in an annular chamber 34. A spring 35 encircling stem 22 in chamber 34 between piston 20 and a lip 36 of the bore 32 biases the piston toward the chamber 33. An O-ring 37 contained in a peripheral groove 38 in piston 20 serves to maintain a seal on the wall of the bore 21 between the piston chamber .33 and the spring chamber 34. The face of piston 20 is tapered at the outer circumference thereof to permit passage of fluid past the piston to the chamber 33 via a port 39' in the switching body 18 and a port 40 in the liner or bushing in the bore 21.

Forming part of the piston chamber 33 is a piston chamber end cover 41 secured to the switch body 18 by suitable means not shown. A bore 43 formed in the end cover 41 houses a resiliently mounted permanent magnet member 44, adapted to magnetically engage the face of said piston 20 in perfect self-alignment when the piston chamber 33 is vented.

The components of the resiliently mounted permanent magnet member 44 are shown in the exploded view of FIG. 2.

Referring to FIG. 2, the permanent magnet device 44 includes a permanent magnet 45 of cylindrical shape which is secured by a screw 46 within a pair of soft iron pole pieces 47 and 48. Pole pieces 48 has a bore 49 in which a brass bushing or liner 50 is fitted tightly to divert the flow of magnetic flux from said permanent magnet 45 to said pole pieces at the outer faces thereof. A self-aligning resilient mounting piece 51 is suitably bonded to the magnetic pole piece 48. A circular threaded mounting disc means 52 is secured by suitable bonding material to the outer end of the mounting block 51 such that a screw 53 may be inserted through a hole in the cover 41 to maintain the magnet assembly secured thereto in a substantially horizontal position. With the magnet assembly secured thusly, the resilient mounting piece 51 enables the outer face (left side) of the pole piece 47 and the outer extremity of the cup-shaped pole piece 48 to be moved out of the horizontal position a slight degree as might be necessary to fully engage the face of piston 20 even when the piston stem 22 is not in a true horizontal position due to bailing action with arm 16 or due to imprefections in machining the piston 20 or bore 21. Thus, the resilient mounting enables the above-mentioned portions of pole pieces hereinafter referred to as the face of the magnet assembly to be constantly maintained in full contact with the face of the piston 20 and thereby receive the maximum magnet attraction therebetween from the magnetic lines of flux from the magnet passing from the outer extremity of the pole piece 48 to the pole piece 47 around the bushing 50 to tend to maintain the piston 20 in a closed position as explained hereinafter.

When the compressor is initially ready for operation with the system not being charged with fluid under pressure, the piston chamber 33 is void of fluid under pressure.

Thus, the piston 20 is initially in the extreme right-hand position in which it is shown in FIG. 1, with the face of piston 20 engaging the magnet member 44. The combined forces of spring 35 acting through the medium of piston 20 and the magnetic force exerted by the magnet member 44 maintain the piston face in close engagement with the magnet member 44 and causes the contact arm 16 to be pivoted clockwise about the pin 17 to its closed position with the movable main contact member 11 in tight engagement with the stationary main contact member 14.

To initially start the compressor, the switch 15 is closed to complete the armature circuit for the motor 3, said circuit being traced from the positive terminal of the battery 6 via the closed switch 15, positive wire 8, terminal stud 26 and cap nut 10 on the stationary main contact member 14, contact member 11, terminal stud 24 and cap nut 13, strap 12 to a terminal screw 9, and negative wire 7 to the motor armature and back to the negative side of the battery 6 to thereby start the motor 3 which in turn drives compressor 4.

With no pressure in the reservoir 5, the governor 2 operates in the usual well-known manner with the high pressure valve (not shown) remaining closed to permit a build-up of fluid under pressure in said reservoir. It is in this period when the compressor is operating to build up the fluid pressure in the reservoir that any leakage past the high pressure valve of the governor would cause undesired build-up of pressure in the piston chamber 33. In any prior switch device this leakage would effect an undesired partial opening of the main contact members 11 and 14 resulting in arcing therebetween and consequent burning and pitting thereof to eventually render the main contacts ineffective to properly engage and complete the motor armature circuit. In the apparatus shown herein, fluid leakage past the high pressure valve of the governor 2 via pipe 54, volume 55, and port 39 to the piston chamber 33 would effect a slow build-up of pressure therein which, in turn, would tend to cause the piston 20 to move slowly to the left to effect slow opening of the main contacts. However, the combination of the biasing forces of the spring 35 and the magnetic attraction between the face of the piston 20 and the magnet member 44 prevents any movement of the piston 20 to the left, slow or othenwise, until the pressure in said chamber 33 builds up to a high degree sufficient to overcome these combined forces.

When the fluid pressure in the reservoir 5 and the con nected governor 2 builds up to the predetermined desired maximum pressure (regulated as desired by the usual appropriate adjustment of governor settings), the governor high pressure valve snaps open in a well-known manner to permit a sudden surge of high pressure through the pipe 54 and then to the volume 55 and on to the piston chamber 33. The sudden surge of fluid pressure rapidly builds up to a predetermined pressure necessary to overcome the combined biasing forces of the spring 35 and the magnetic attraction between the piston face and the magnet member 44 to cause the piston 20 to move to the left in the bore 21 with a rapid snap action described hereinafter to thereby open the main contact members 11 and 14 with a very rapid motion to limit the arcing therebetween. It will be apparent that as the fluid pressure in the chamber 33 builds up the resultant pressure acting on the face of piston 20 attempts to move said piston to the left, such pressure initially causes said piston to move only a very slight distance away from the magnet member 44. The resulting slight movement of arm 16 does not shift the main contact 11 away from contact member 14 and they remain in firm engagement due to the biasing force of the spring 25 pivoting the contact body 23 in a clockwise direction to maintain the main contact member 11 firmly against the main contact member 14. Increased buildup of fluid pressure in chamber 33, however, causes the piston 20 to be moved to the left a further degree out of the magnetic field of the magnet member 44, at which time the magnetic attraction of the magnet member on the piston is suddenly reduced or lost, thereby leaving only the force of spring 34 to resist movement of the piston. With the sudden reduction in resistance to movement of piston 20, the high pressure built up in chamber 33 causes a rapid snap-action of the piston 20 to the left a distance sufficient to shift arm 16 and the main contact member 11 thereon to a position in which the contact member 11 is completely separated from the main contact member 14.

From the above description, it will be seen there can be no partial slow opening of the main contact members 11 and 14 due to leakage of the fluid pressure into the piston chamber as has been the case in previous switch devices. On the contrary, no matter how slowly the pressure builds up in chamber 33, contact members 11 and 14 cannot be separated except by complete snap-opening when the fluid pressure in the piston chamber 33 is sufficient to overcome the aforementioned strong magnetic attraction of the piston face to the magnet member 44.

With the main contact members 11 and 14 separated, the previously traced circuit energizing the compressor motor 3 is interrupted, thereby stopping the compressor 4 until the pressure of fluid in the reservoir 5 is normally depleted, through usage, to a predetermined minimum value. With the pressure of fluid in the reservoir depleted to a predetermined minimum pressure, the governor 2 operates in its usual manner to position the governor high pressure valve to vent the piston chamber 33 and volume 55 to atmosphere, and permit the spring 35 to start returning the piston 20 to the right-hand position as shown in the drawing. As the piston 20 moves toward the righthand position due to the force of the spring 35, it moves into the magnetic field of the magnet device 44 where the strong magnetic attraction causes the piston to rapidly snap to the right, in reverse of the action previously described to cause the arm 16 to shift main contact member 11 into contact with main contact member 14, simultaneously rocking the contact body 23 in a counterclockwise direction and compressing the spring 25. This rapid snapping action to close the main contact members 11 and 14 reduces any arcing therebetween during the closing action and thereby prevents burning of the contact members. When the main contact members 11 and 14 are reclosed and the spring 25 compressed such that the main contact members are firmly engaged as just described, the circuit for starting the motor 3 is again complete to start the compressor and thereby due to increasing build up of pressure in reservoir 5 cause a reseating of the governor high pressure valve to permit normal operation of the compressor.

It can thus be seen that the magnet device prevents slow opening or closing of the main contacts 11 and 14. Moreover, the resilient self-aligning mounting for said magnet member 44 prevents misalignment of the face of piston 20 with the face of said magnet member as might occur due to bailing action of the piston resulting from movement of the pivotal connection of the end of piston stem 22 with contact arm 16 through an arc. Accordingly, a perfect seating of the face of magnet member 44 with the face of control piston 20 is effected to prevent loss of the magnetic forces and insure maximum effective attractive forces therebetween.

Having now described the invention, what we claim as new and desire to secure by Letters Patent is: 1. An electric switch device comprising: (a) a pair of cooperating switch contact members, and (b) a movable abutment of magnetic material subject to the force of a spring and to fluid pressure acting on opposite faces thereof in opposing relation for actuating one of said pair of contact members into and out of engagement with the other of said contact members, wherein the improvement comprises:

(c) permanent magnet means mounted in coaxial alignment with said movable abutment subject to fluid pressure when said contact members are in engagement, so as to exert a magnetic attractive force on said abutment to resist separation of the contact members until the fluid pressure on said abutment exceeds a certain value, and

(d) means resiliently mounting said magnet means such that the face of said magnet means is selfaligned with the face of said movable abutment subject to fluid pressure.

2. An electric switch device comprising:

(a) a pair of cooperating switch contact members, and

(b) a movable abutment of magnetic material subject to the force of a spring and to fluid pressure acting on opposite faces thereof in opposing relation for actuating one of said pair of contact members into and out of engagement with the other of said contact members, wherein the improvement comprises:

(c) permanent magnet means mounted in coaxial alignment with said movable abutment subject to fluid pressure when said contact members are in engagement, so as to exert a magnetic attractive force on said abutment to resist separation of the contact members until the fluid pressure acting on said abutment exceeds a certain value, and as to exert a magnetic attractive force on said abutment as it moves said contact member toward said other contact member to effect a sudden rapid closing movement of said one contact member into engagement with the said other contact member as the fluid pressure acting on said abutment means reduces below a certain value, and

(d) means resiliently mounting said permanent magnet means such that the face of said magnet member is self-aligned with the face of said movable abutment subject to fluid pressure.

3. An electric switch device as claimed in claim 1,

wherein said permanent magnet means comprises:

(a) a cylindrical member of magnetic material having a recess open at one end,

(b) a disc member of magnetic material secured to said cylindrical member in a position to substantially close the open end of said recess, and

(c) an annular permanent magnet disposed in the recess in said cylindrical member and secured in contact with said cylindrical member and said disc member.

4. An electric switch device as claimed in claim 1,

wherein said permanent magnet means comprises:

(a) a cylindrical member of magnetic material having a recess open at one end,

(b) a disc member of magnetic material secured to said cylindrical member in a position to substantially close the open end of said recess, and

(c) an annular permanent magnet disposed in the recess in said cylindrical member and secured in contact with said cylindrical member and said disc member.

5. An electric switch device as claimed in claim 3, further characterized by bushing means of non-magnetic material encircling the periphery of said annular permanent magnet for magnetically insulating the periphery of said permanent magnet from said cylindrical member.

6. An electric switch device as claimed in claim 1, wherein said permanent magnet means comprises:

(a) a cylindrical member of magnetic material having a recess open at one end,

(b) a disc member of magnetic material secured to said cylindrical member in a position to substantially close the open end of said recess,

(c) an annular permanent magnet disposed in the recess in said cylindrical member and secured in contact with said cylindrical member and said disc member, and

(d) wherein said means resiliently mounting said permanent magnet comprises a resilient block of rubber material by which said permanent magnet member is supported in coaxial juxtaposition to said movable abutment.

7. An electric switch device as claimed in claim 3, wherein a resilient block of rubber material bonded to said cylindrical member supports said permanent magnet member in coaxial juxtaposition to said movable abutment.

8. An electric switch device comprising:

(a) a stationary switch contact member,

(b) a movably mounted switch contact member for movement into and out of circuit closing contact with said stationary contact member,

(c) a piston device operably moved to different positions responsively to build up or release of fluid under pressure in a pressure chamber at one side of the piston device,

(d) means operably connecting said piston device to said movably mounted switch contact member whereby to effect movement of the movably mounted contact member out of circuit closing contact with the stationary contact member upon the supply of rfluid under pressure to said pressure chamber, and conversely to effect movement of said movably mounted contact member into circuit closing contact with said stationary contact member upon release of fluid under pressure from said pressure chamber, and

(e) resilient biasing means resisting movement of said piston device in a direction to effect separation of the movably mounted contact member from the stationary contact member and biasing said piston device in an opposite direction to cause engagement of the movably mounted contact member with the stationary contact member, wherein the improvement comprises magnet means exerting magnetic attraction to said piston device to assist said resilient biasing means in opposing movement of said piston device responsively to build up a fluid pressure in said pressure chamber until the fluid pressure exceeds a certain pressure and then suddenly releasing the magnetic attraction on the piston device, thereby causing a sudden reduction in the force opposing movement of said movably mounted contact member by fluid pressure force on said piston device and causing a sudden rapid separation of said movably mounted contact member from said stationary contact member.

9. In an electric switch device, as claimed in claim 8, the improvement wherein the said magnet means becomes effective, while said movable mounted contact member approaches the stationary contact member responsively to movement of said piston device by said resilient means upon reduction of fluid pressure in said pressure chamber, for suddenly exerting an attracting force on said piston device in assistance of said resilient means to suddenly and rapidly actuate the piston device to cause engagement of said movably mounted contact member with said stationary contact member.

10. In an electric switch device comprising;

(a) a stationary switch contact member,

(b) a pivotally mounted contact arm,

(c) a second switch contact member movably mounted on said pivotally mounted contact arm and having limited movement relative thereto,

(d) biasing means for biasing said second switch contact member in one direction towards one limit of its relative movement with respect to said contact arm,

(e) a piston device operably moved to diiferent positions responsively to build up or release of fluid under pressure in a pressure chamber at one side of the piston device,

(f) means operably connecting said piston device to said pivotally mounted contact arm whereby movement of said piston device efiects corresponding movement of said second contact arm,

(g) resilient biasing means acting on said piston device in a direction to effect movement of said contact arm in a direction to cause engagement of the second switch contact member with the stationary switch contact member and yieldingly resisting movement of said piston device in an opposite direction resultant from a supply of fluid under pressure to said pressure chamber to cause movement of said contact arm to eifect separation of said second switch contact member from said stationary switch contact member, the improvement comprising magnet means exerting magnetic attraction to said piston device to assist said resilient biasing means in opposing movement of said piston device responsively to build up of rfluid pressure in said pressure chamber until the fluid pressure exceeds a certain pressure and then suddenly releasing the magnetic attraction on the piston device, thereby causing a sudden reduction in the force opposing movement of said contact arm by fluid pressure force on said piston device and causing a sudden rapid movement of the contact arm to etfect separation of said second switch contact member from said stationary contact member.

11. An electric switch device, as claimed in claim 10, further characterized in that said magnet means suddenly loses its magnetic attraction for said piston device upon movement of said piston device in opposition to said resilient means an amount sufficient to permit the said contact arm to pivotally move correspondingly while said second switch contact member remains in contact with said stationary switch contact member under the influence of said biasing means until it reaches the said one limit of its relative movement with respect to said contact arm.

References Cited UNITED STATES PATENTS 2,189,653 2/1940 Luthe. 3,042,771 7/ 1962 Oliveau. 3,089,008 5/ 1963 Shirey 200-82 ROBERT K. SCHAEFER, Primary Examiner.

H. *BURKS, Assistant Examiner.

US. Cl. X.R.

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