US3375335A - Safety circuit switch with a pneumatic time delay return - Google Patents

Description

March 26, 1968 w, F, SCHULTZ 3,375,335

SAFETY CIRCUIT SWITCH WITH A PNEUMATIC TIME DELAY RETURN Filed Nov. 22, 1965 I N VENTOR.

.'' ATTORNEY 3,375,335 Patented Mar. 26, 1968 3,375,335 SAFETY CIRCUIT SWITCH WITH A PNEUMATIC TIME DELAY RETURN Werner 1F. Schultz, Flint, Mich, assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Nov. 22, 1965, Ser. No. 509,135 4 Claims. (Cl. 200-33) ABSTRACT OF THE DECLOSURE An electric switch which includes a fluid time delay return so as to remain actuated by a periodic motion.

My invention relates generally to a safety switch and more specifically to a safety switch with a pneumatic time delay return so as to be maintained in a closed position by periodic actuation. A nonlimiting example of the utility of my invention is in connection with a pump driven by an electric motor. In such a system, it is desirable to shut down the electric motor in case of a defect or mechanical breakdown in the pump. One of the easiest ways of accomplishing this shutdown is to provide a switch which can be actuated by a cam, eccentric or other device on the pump motor combination which produces a periodic motion. A problem associated with the use of a periodic actuator, however, is thatthe actuator may stop in its extended position which would maintain the switch closed even though the motor had stopped.

My invention then is specifically directed toward providing a switch which will be maintained closed by a periodic motion and which will open when this periodic motion ceases irrespective of the position of the actuator. In a broader sense, my invention is capable of use in any application where it is desirable to provide a signal or a control responsive to a periodic actuating motion.

The exact nature of this invention as well as other objects and advantages thereof will be readily apparent from consideration of the following specification relating to the annexed drawing in which:

FIGURE 1 is a longitudinal cross section of a safety circuit switch with a pneumatic time delay return in accordance with my invention showing the switch in its unactuated position.

FIGURE 2 is a section taken on a line 2--2 of FIG- URE 1 and looking in the direction of the arrows.

FIGURE 3 is a view similar to FIGURE 1 showing the switch in its first stage of actuation with the switch in its switch open position.

FIGURE 4 is a view similar to FIGURE 1 showing the switch and the time delay means fully actuated.

FIGURE 5 is a view similar to FIGURE 1 showing the switch maintained in the switch closed position by the time delay means after the removal of the switch actuating means.

Referring to FIGURE 1 in detail, my safety switch comprises a cylindrical housing 12 which has a somewhat recessed end wall 16 provided with an aperture 18. The aperture 18 is closed by a one-way flapper valve 20 mounted on the end wall by a snap ring 22 which is disposed between the fiapper valve 20 and a circumferential bead 24 on the end wall 16. A first piston 26 is slid-able within the cylindrical housing 12 such that an air gap 28 is provided therebetween. The reciprocable piston 26 and the housing 12 form a first chamber 30. A coil spring 32 is disposed within the chamber between the end wall 16 and the piston 26 to urge the piston toward the right as viewed in the drawings. The piston 26 is hollow and has a second piston 34 reciprocably disposed within it. Again an air gap 36 is provided between the two pistons and the two pistons form a second chamber 38 with a second lighter coil spring 40 disposed in this chamber. The spring 40 urges the piston 34 to the right with respect to piston 26. An axially extending annular flange 42 extends from the forward face of the piston 34 into the chamber 38. The face of the second piston 34 has an aperture 44 closed by a one-way flapper valve 46 which is held against the face of the piston by the coil spring 40. The piston 34 is also hollow and receives a push rod 48. The first piston 26 has a cap member 50 which abuts radially outwardly extending wings 52 formed by an enlarged forward portion 54 on the push rod and fixes the extreme right hand relative position of piston 34 with respect to piston 26. The cap member 50 is a metallic conductor and bridges a pair of spaced contacts 56 mounted within the cylindrical housing 12 to close a circuit when the piston 26 is in the switch closed position. (See FIGURE 4). The right hand end of the push rod 48 extends through an annular boss 58 on the housing closure cap 14 with a gap 59 therebetween and into abutment with a cam 60. The cam 60 is merely representative of any periodic motion actuation source. With the above-described structural details in mind, the operation of my switch will now be described.

As the cam 60 rotates from the position shown in FIGURE 1 to that shown in FIGURE 3, the push rod 48 and piston 34 will move to the left to the position shown in FIGURE 3. This movement will be against the action of the light coil spring 40 and will compress the air entrapped within the chamber 33. The entrapped air thus compressed produces a differential pressure across the piston 26 which causes it to move toward the left against the action of coil spring 32. Continued rotation of the cam to its high point pneumatically moves piston 26 further to the left until the end wall of the piston 26 abuts the cylinder end wall 16. This leftward movement of piston 26 evacuates chamber 30 through the one-way flapper valve 20 and the conductor cap 50 on piston 26 is moved to a bridging position where it electrically connects the spaced contacts 56. The contacts 56 are on resilient arms 57 and the right hand ends of the contacts 56 are ramped at the right hand ends 56' so that as the conductor cap 50 moves to its bridging position, the contacts 56 are spread radially. The contacts 56 then are biased radially inwardly into contact with the outer circumference of the cap 50 in the switch closed condition The relative position of the parts in my switch in this condition are shown in FIG- URE 4. While I have shown the above motion of the two pistons 26 and 34 in two distinct steps, it is to be understood that this was for purposes of clarity only. In actual operation, the motion of the pistons occur simultaneously, however, in the leftward or switch closed direction the motion of piston 34 lags that of piston 26 because of the spring forces. I

Referring now to FIGURE 5, as the cam continues rotation from its high point to the solid line position shown therein, the push rod 48 and the inner second piston 34 will move toward the right under the influence of spring 40 and the pressure of the air entrapped in chamber 38. The piston 26, however, will remain in the left hand position where the cap 50 bridges the contacts 56 because the chamber 30 is below atmospheric pressure. As the cam 60 rotates further to the dotted line position, the push rod 48 and the piston 34 will not move further toward the right because the wings 52 on the push rod 48 abut the cap member 50. This action prevents the inner piston 34 from being withdrawn too far out of the outer piston 26. The time delay means just described is of limited duration as air enters the evacuated chamber 30 through the longitudinal air gap 28 to increase the pressure toward atmospheric. As the pressure builds up, the differential pressure force across piston 26 which opposes the force of spring 32 decreases. Before the pressure increases to a point where piston 26 will have started to move toward the right, the cam 60 will have rotated back to the position shown in FIGURE 3 to repeat the actuation chain of motion as described above and thus the switch is maintained closed. This action repeats itself as long as there is a periodic motion actuating force acting on push rod 48.

When the reciprocating driver cam 60 stops, the switch will open after the limited duration of the time delay as described above. Should the drive cam have stopped in the position of FIGURE 4 where the cam is in the same position as shown in FIGURE 3, the push rod 48 and the piston 34 will be held inwardly toward the left and chamber 38 is pressurized. The pressure in chamber 30 will increase to atmospheric, as before, because of air supplied through the gap 28. When this occurs, the force of spring 32 is sufficient to move piston 26 toward the right against the force of spring 40 and the differential pressure force acting on piston 26. The parts will then be as shown in FIGURE 3. Eventually, the pressure in chamber 38 will diminish to atmospheric because of its communication with the atmosphere through gaps 36 and 59. Upon renewed movement of the cam 60 from the position of FIGURE 3 to the position of FIGURE 1, the piston 34 will first be returned to its extreme right hand position. In this action, air is admitted to the chamber 38 via the oneway flapper valve 46. The switch then resumes the sequence as originally described.

Thus it can be seen that I have invented a safety switch which is maintained closed by a periodic actuation and which will open upon cessation of the periodic actuation irrespective of the position of the actuator.

It should be understood, of course, that the foregoing disclosure relates to only a preferred embodiment of the invention and that it is intended to cover all changes and modifications of the example of the invention herein chosen for the purposes of the disclosure, which do not constitute departures from the spirit and scope of the invention.

I claim:

1. An electrical switch comprising in combination, a closed cylindrical housing having end walls, a pair of spaced fixed contacts resiliently mounted on said housing, said fixed contacts each having a ramp means, a first hollow piston reciprocable within said housing and forming a first chamber with one of said end walls, one-way valve means on said one end wall, a conductor on said first piston, said conductor bridging said spaced contacts in one position of said first piston and abutting said otherv 'end wall in a second position of said first piston, first spring means in said first chamber urging said first piston toward said other end wall, a second piston reciprocable in said first hollow piston and forming a second chamber therewith, second spring means in said second chamber, second one-way valve means on said second piston, and rod means on said second piston extending through said other end wall whereby movement of said rod means toward said one end wall pressurizes said second chamber to move said first piston and conductor to said one position camming said contacts into biasing abutment therewith and bridging said contacts, said first chamber being evacuated to delay return of said first piston upon depressurization of said second chamber,

2. An electric switch comprising:

a first hollow piston,

a second piston reciprocably mounted therein,

a conductor carried by one of said pistons,

a housing including a cylindrical surface,

said one piston reciproca'bly engaging said cylindrical surface and forming a chamber therewith,

a fixed contact mounted on said housing so as to be spaced from said conductor in a first position of said one piston and contacted by said conductor in a second position of said one piston, said one piston being moveable to one of said positions by a fluid force created by movement of said other piston in a direction toward said one position, and

fluid time delay means including said chamber which is exhausted by movement of said one piston to said one position, said fluid time delay means delaying the movement of said one piston away from said one position after movement of said other piston in a direction away from said one position whereby said switch is adopted to be actuated by a periodic motion.

3. The electric switch as defined in claim 2 which further includes a'first spring means between said pistons urging said pistons away from each other, and second spring means between said housing and said one piston urging it toward said other position, said first spring means being lighter than said second spring means.

4. An electric switch comprising,

a housing including'a cylinder with an end wall,

a first hollow piston,

a second piston reciprocably mounted within said first piston forming a first chamber, a first one-way valve opening into said'first chamber, one of said pistons reciprocably mounted within said cylinder forming a second chamber,

second one-way valve opening out of said second chamber,

a pair of contacts carried by said housing,

a conductor carried by said one piston, said conductor spaced from said contacts in a first position of said.

one piston, and bridging said contacts in a second position of said one piston,

first resilient means in said first chamber biasing said pistons away from each other, and

second resilient means in said second chamber biasing said one piston toward said first position whereby said one piston is moved from said first position to said second position by movement of said other piston toward said second position, said movement exhausting said second chamber and delaying the return of said one piston to said first position after said other piston reverses direction whereby said switch is adapted to be closed by a periodic motion.

References Cited UNITED STATES PATENTS Re. 25,631 8/1964 Forwald 200-82 1,954,427 4/1934 Platz 20082 BERNARD A. GILHEANY, Primary Examiner.

F, BELL, Assistant Examiner.

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