US3551615A - Pneumatic time delay switch with improved dashpot structure - Google Patents

Description

United States Patent Inventor John J. Dennison Southington, Conn. Appl. No. 827,323 1 Filed May 23, 1969 Patented Dec. 29, 1970 Assignee Arrow-Hart, Inc.

Hartford, Conn.

a corporation of Connecticut PNEUMATIC TIME DELAY SWITCH WITH IMPROVED DASI-IPOT STRUCTURE 4 Claims, 4 Drawing Figs.

US. Cl 200/34, 1 8 8/ 95 Int. Cl H0111 7/03 Field of Search 200/34;

[56] References Cited UNITED STATES PATENTS 2.543090 2/1951 Ballou 200/34 2,866,862 12/1958 Bachi 200/34 2,996,155 8/1961 Priesemuth. ZOO/34X 3,178,524 4/1965 Frisk 200/34 3,268,675 8/1966 Willcox 200/34 Primary ExaminerRobert K. Schaefer Assistant Examiner-.l. R. Scott Attorney-Davis, Hoxie, Faithfull & Hapgood ABSTRACT: An electrical switch includes a pneumatic time delay mechanism to provide a delay between movement of the actuator and transfer of the contacts. The pneumatic mechanism is vented to ambient air pressure until movement of the actuator to insure repeatability of the delay time irrespective of the frequency of actuation.

PNEUMATIC TIME DELAY SWITCH WITH IMPROVED DASIIPOT STRUCTURE The present invention is concerned. with a switch which pneumatically provides an adjustable delay between movement of the actuator and movement of the contacts. The switch contacts can be arranged to make contact, break contact, or change to a second contact after the delay. The switch assembly is useful for motor starting where windings are connected in a time sequence. It also can be used to establish a minimum recycle time for. such applications as refrigeration compressors.

According to the present invention, movement of an actuator frees a'spring loaded bellows to expand at a rate determined by an adjustable air inlet flow-control. The expanding bellows cause the switchcontacts to change their position to accomplish the switching function.

Since the time delay is determined by the rate at which air is permitted to enter the bellows, air remaining in the bellows in their initial or collapsed state will cause a variation in the time of delay dependent upon the completeness of the previous air exhaustion from the bellows. The degree of exhaustion of bellows air depends, in part, upon the frequency of actuation. Long intervals permit the escape of residual air whereas short intervals may not. Thus, the time delay may be irregular.

The present invention provides a solution to the problem of delay irregularity due to residual air by providing a valve structure which opens after completion ofthe delay function to exhaust the bellows thereby insuring that the device is reset to the same initial bellows condition every time the delay function is completed. I

In the drawings:

FIG..1 is an elevational view partially in section of a switch according to the present invention;

FIG. 2 is a sectional view taken along the line 2-2 of FIG. 1; FIG. 3 is a sectional view taken along the line 3-3 of FIG. 2;

and FIG. 4 is a sectional view taken along line 4-4 of FIG. 1.

Referring now to the drawings, particularly FIG. 1, the switch mechanism of the present invention is housed in a three part case comprising alower portion 10, an intermediate portion 11, and an upper portion 12. The housing portions are assembled with screws. Lower portion includes a pair of moving contact blade members 13 associated with a spring 14 which provides toggleaction to bias the moving contact blade members 13 upwardly or downwardly against fixed contacts in a conventional manner. Fixed contact members 16 and 18 are affixed to the lowerponion 10 such that the moving contact blade members can establish spring-biased contact with the fixed contacts. In the switch assembly illustrated in FIG. 1, the normal condition completes the circuit with fixed contacts 16. A vertically reciprocable blade carrier 19 having blade receiving grooves is located between the pair of contact blade members 13 such that downward motion of the blade carrier 19 from the position illustrated in FIG. 1 will cause the contact blade members 13 to snap over to establish contact with fixed contacts 18.

Intermediate housing portion 11 includes a bellows member 20 which is formed of elastomeric material. Within bellows 20 is an actuator spring 22 which acts downwardly against a disc member 24 affixed to or integral with a plunger 26. Spring 22 tends to urge the plunger downwardly to cause actuation of the switch contacts. Another spring 28 bears against an annular washer member 27 associated with the plunger 26. Spring 28 is arranged to bias a movable annular washer member 29 upwardly of the plunger 26' against the lower edge portion 21 between the tapered portion 31 and the bore 34 into which it fits. This clearance provides an air inlet orifice of variable dimension leading to the interior of the bellows member 20. A pad of filter material 38 such as polyurethane foam is included in the upper housing portion 12 and serves to clean the air before it enters the clearance space about the tapered portion 31 of valve member 30. Adjustment of plug valve 30 is accomplished by a screwdriver slot 35 in the protruding threaded portion 32. A cover 36 may be provided to discourage tampering with the adjustment and for protection.

As is best illustrated in FIG. 2, the switch mechanism is actuated by an actuator member 40 having a portion 41 which protrudes from an appropriate opening in the lower housing portion 10 to be engageable by an external device. Actuator member 40 is a rod vertically reciprocable within avertical bore in the housing and is biased upwardly by a spring 42. Blade carrier 19 has a projection 17 which engages a ledge 43 on the actuator 40 such that spring 42 exerts upward force on the blade carrier when the mechanism is returning to its normal position after the actuator is released.

Upper housing member 12 includes a reset valve unit 50 which comprises a valve plate 51 which seats against an elastomeric O-ring 52 and is biased into sealing relationship therewith by means of a spring 53 which exerts a downward force against the valve plate 51. Reset valve 50 is in communication with the interior of the bellows via a passage 15 formed in the upper housing member 12. The valve plate 51 includes a portion 54, best illustrated in FIG. 3, which portion extends horizontally to be engaged by a ledge 44 near the top of the actuator rod 40 such that valve plate 51 may be canted to unseat the plate 51 from the O-ring 52 to open the valve 50 when the actuator 40 has returned to its uppermost or rest position. Small projecting ears or lugs 55 fit within grooves in housing member 12 to retain valve plate 51 in position with respect to O-ring 52 while permitting tilting or canting motion of the plate.

Operation of the device will now be described. The switch mechanism is illustrated in its normal or initial position. Downward movement of actuator 40 initiates the time delay sequence which results in transfer of the moving contact blades 13 from fixed contact 16 to fixed contacts 18. Contact with fixed contacts 18 prevails until the actuator 40 is released. When actuator 40 has been moved downwardly against the spring 42, ledge 43 is moved out of engagement with projection 17 of blade carrier 19 thereby freeing blade carrier 19 for downward movementfSpring 22 within the bellows 20 exerts a downward force on disc 24 and plunger 26 to move the plunger and blade carrier 19 downwardly. This motion is resisted by the extension of the bellows 20 creating therein a subatmospheric pressure. Air is permitted to enter the bellows through the adjustable orifice whose dimensions are determined by the adjustment of inlet air valve 30. Air traversing the clearance between tapered plug portion 31 and bore 34 enters bellows 20 relieving the subatmospheric pressure at a rate determined by the setting of air inlet valve 30. As bellows 20 ispermitted to extend under the urging of spring 22, blade carrier 19 proceeds downwardly causing contact blades 13 to rise to a horizontal position. In so doing, blade spring 14 is stretched. Spring 14 provides an overcentering toggle action which causes the blades 13 to snap upwardly of the bellows member 20 to urge the bellows edge 21 against A against fixed contacts 18 accomplishing the desired contact change. The time between depression of the actuator and snapping of the moving contact blades is the delay time. It is apparent that this time can be set to that desired by adjustment of the valve 30. Switch devices made in accordance with the present invention have delay capabilities of up to about five minutes.

The switch mechanism is returned to its initial condition by release of downward force on actuator 40. Spring 42 urges the actuator upwardly such that ledge 43 engages projection 17 of blade carrier 19. Spring 42 has a spring rate adequate to overcome spring 22 and the downward component derived from spring 14 with the result that blade carrier 19 moves upwardly and plunger 26 collapses bellows 2 0. The moving contact blades 13 snap back to their initial position in contact with fixed contacts 16. The return to the initial condition is rapid.

Air within bellows is compressed as the bellows is collapsed. The resulting superatmospheric pressure deflects bellows edge 21 downwardly against spring biased washer 29. Deflection of edge 21 creates a passage for the compressed air to escape between plunger 26 and the surrounding bellows edge 21. Edge 21, washer 29, spring 28, and the surface of plunger 26 cooperate .to form a check valve which relieves superatmospheric pressure within the bellows but seals against ingress of air when the bellows interior is subatmospheric during the delay function.

' .Because of the elasticity of edge 21 and the bias of spring .28, this check valvewill close before the pressure within the bellows has completely returned to atmospheric pressure. This it ii remaining air pressure must be vented to reestablish the initial condition with certainty.- Without venting provision for this residual air pressure, the residual pressure in the bellows will *only slowly approach atmospheric pressure, thereby creating a 'condition of an initial bellows pressure which is a variable deplate to unseat it from the elastomeric ring 52. A venting passage 15 for residual air pressure in the bellows is thereby opened to reset the bellows to atmospheric pressure. The passage remains open until the actuator 40 is depressed to initiate a new cycle. A small spring 53 recloses reset valve 50 immediat'ely upon actuation.

' Because switch devices are frequently employed in unclean environments, applicant provides filter means 38 which may be polyurethane foam pads to' clean the air prior to its passage through the adjustable inlet valve orifice. To further promote cleanliness, the airused in the pneumatic system recirculates within the system. This 'permits hermetic enclosure of the moving parts of the switch if desired. Where hermetic sealing isnot necessary, recirculation of air obviates the need to introduce unclear external air to the interior of the device. The path of air circulation is illustrated in FIG. 1 by arrows. Air travels past adjustable plug valve 50 into the bellows interior. Upon release of theactuator, air exitsfrom the bellows by passing through an aperture in disc 24 and then passing between edge 21 and plunger 26. At the completion of a cycle, residual air in the bellows is exhausted to the interior of the housing through reset valve 50. The air is drawn from the interior of the housing through passage 55 and'through filter 38 when the bellows are being extended.

The above-describedwdevice .provides'a pneumatic time delay switch havinga repeatable time delay of great accuracy. The delay is adjustableoverawide range of times. By recirculating and filtering the air usedby'thepneumaticsystem. the device is insensitive to the cleanliness of its environment. The arrangement of the moving contact blades provides rapid and positive contact establishment and maintains adequate contact pressure with the resulting benefits of .reduced arcing. contact sticking,.andinsensitivity to shock and vibration.

1. An adjustable delay time electrical switch having first and second positions, at least one of said positions havingfixed electrical contacts, electrical contacts movable between the first position and the second position, a movable actuator member for initiating transfer of the movablecontacts, and a pneumatic time delay'device for effecting a delay of contact transfer subsequent toactuator movement, said time delay device comprising a bellows spring biased to extend sub sequent to actuator movement, said bellows being collapsible upon actuator release said bellows being associated with the movable contacts to effect their movement to the second position upon extension, an inlet orifice to admit air at a selected rate to the interior of the bellows during their extension, the

rate of air admission being determinative of the delay time, a pressure responsive check valve for exhausting air under pressure from the interior of thebello'ws during the collapse, and a reset valve which vents the interior of the bellows to maintain ambient pressure when they are collapsed, said check valve and said reset valve being arranged toclose upon extension of the bellows. A

29A switch according toclaim 1' wherein the reset valve includes a valve plate spring biased toward sealing engagement with a resilient ring surrounding the terminal end of a vent passage in communication with the interior of the bellows, and wherein the actuator member has-a portion adapted to displace said valve plate when the actuator is in its released position to interrupt said sealing engagement.

3. A switch according to claim 2 wherein filtering means are provided on the intake side of said adjustable inlet orifice.

4. A switch according to claim 3 wherein air exhausted through the bellows check valve and the reset valve is recirculated to the adjustable inlet orifice through the filtering means.

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