US3528344A

US3528344A - Passive delay timer

Info

Publication number: US3528344A
Application number: US707592A
Authority: US
Inventors: David W Ravenhorst
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1968-02-23
Filing date: 1968-02-23
Publication date: 1970-09-15
Anticipated expiration: 1987-09-15

Description

United States Patent [72] Inventor David W. Rabenhorst,

Silver Spring, Maryland [21 Appl. No. 707,592 [22] Filed Feb. 23, 1968 [45] Patented Sept. 15, 1970 [73] Assignee By mesne assignments, to the United States of America as represented by the Secretary of the Navy [54] PASSIVE DELAY TIMER 4 Claims, 3 Drawing Figs. [52] US. Cl 92/35, 92/38, 92/84, 92/143, 73/407, 73/410 [51] Int. Cl. .4 F16j 3/00, FOlb 19/04 [50] Field of Search 92/8, 35, 37, 38, 84, 97, 143; 137/78, 8l;73/410, 407; 251/54 [56] References Cited UNITED STATES PATENTS 2,312,201 2/1943 Thompson et al. 92/35X 2,389,412 11/1945 Carlton 92/35X 2,403,186 2/"1946 Leslie 137/81X 2,453,841 11/1948 Gluzek 92/35X 2,466,071 4/1949 Barnes et al. 73/410X 2,469,038 5/1949 Winkler 251/54X Kain 2,580,433 l/1952 251/54X 2,635,581 4/1953 Karig.... 92/35X 2,773,482 12/1956 Dickie 92/35X 2,795,239 6/1957 Eckman et al. 92/37 2,815,705 12/1957 Jensen l37/81X 2,816,561 12/1957 Krueger 137/81 2,963,034 12/1960 Cummins 137/81 2,988,282 6/1961 Hotten Roth 92/35X 3,400,638 9/1968 McEvoy 92/38X Primary Examiner-Martin P. Schwadron Assistant Examiner-Leslie J. Payne Altorneys.lustin P. Dunlavey and John O. Tresansky ABSTRACT: A passive delayed timing device, comprising fluid-containing chambers at standard atmospheric pressure,

which, on exposure to a lower pressure environment such as Patented Sept. 15, 1970 DAVID W. RABENHORST INVENTOR ATTORNEY PASSIVE DELAY TIMER BACKGROUND OF THE INVENTION 1. Field of the Invention Timing devices have long been used aboard spacecraft to perform such necessary functions as initiation of antenna erection, boom deployment, high voltage equipment turn-on, cover removal, and stage separation. Timers now employed are generally electrical or mechanical with certain specific timers utilizing the sublimation properties of substances such as biphenyl. In operation, the subject invention must be considered a passive pneumatic device, its sole input being exposure to an external pressure lower than that pressure initially present within the device.

2. Description of the Prior Art Advantages of the present invention relative to prior devices used for a like purpose will be hereinafter described more completely, along with comments pertinent thereto in the summary of the invention.

The present invention utilizes pressure differentials to actuate a fluid metering delay device. Grant and Hubby in respective U.S. Pat. No. 2,663,153 of December 22, I953, and U.S. Pat. No. 3,152,611 of October 23, 1964, disclose delay timers which use gas pressure to force fluid through a slow metering orifice. However, the delay timers of Grant and Hubby each require a large source of pressurized gas, whereas the subject invention requires only a small capsule of air packaged under ordinary atmospheric conditions. Additionally, the present invention is automatically triggered when exposed to a low-pressure environment, whereas the prior art devices require manual setting. More importantly, the above-mentioned devices of the prior art do not demonstrate the extremely long timing cycles within the capability of the subject invention nor can said devices be of practical use on a spacecraft due to weight considerations.

SUMMARY OF THE INVENTION Work functions aboard a spacecraft mustoften be initiated after launch. Timing cycles aboard the spacecraft or groundinitiated radio signals provide the two major methods for accomplishing actuation of such functions. Self-contained timers possess certain advantages over radio signals in that timers require simpler instrumentation and therefore are less costly, proximity to radio signal transmitting stations is rendered unnecessary, and timers generally weigh less than radio receivers and supporting equipment, thereby conserving weight for payload applications.

Timers now in use range from the traditional electrical and mechanical mechanisms to devices basing their timing cycles on physical or chemical properties of various compounds, such as sublimation switches using biphenyl. The passive timer disclosed herein comprises a pneumatic device whbse sole input is exposure to the vacuum of outer space. Expandible capsules of fluids at differing pressures cause movement of an output shaft, thus providing force for the accomplishment of a work cycle or for the initiation of work cycles through a triggering system which then produces the desired output. In the various embodiments of the present invention, an accurate fluid metering system sensitive to these slight pressure differentials caused by exposure to a low pressure environment is essential.

It is therefore an object of the invention to provide a selfcontained timing device possessing a substantial shelf life even in a launch-ready configuration despite temperature changes, normal handling contamination, humidity changes, and assembly and testing procedures.

It is another object of the invention to provide a passive timing device immune to RF, static, or other electrical background disturbances, and which requires no batteries, Wiring or electrical instrumentation for operation.

It is still another object of the invention to provide a relatively lightweight and compact delayed timing device which has no functional or physical interface with a launch vehicle and which can be integrated into existing spacecraft systems.

It is a further object of the invention to provide an accurate delayed timing device with timing cycles of from a few minutes up to one year, and which may be tested any number of times before launch without its destruction or impairment to its subsequent use.

Further objects and advantages of the invention will become more readily apparent from the following detailed description of the preferred embodiments thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-section of a first embodiment of the invention;

FIG. 2 is a cross-section of a second embodiment of the invention, showing the concentric expandible chamber; and

FIG. 3 is a cross-section of a third embodiment of the inventron.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings and first to FIG. 1 thereof, one embodiment of the invention is shown generally at l and includes a cylindrical casing 2 which defines a first fluid storage chamber 3. The outer end of the casing is closed by a wall plate 4. At its inner end the casing 2 isprovided with a wall plate 5 which is formed with an axial extension 6 that is closed at its free end by a wall plate 7 having a port 8 therein. The extension 6 is substantially one-half the diameter of the casing 2 and defines a second storage chamber 9 which is vented to ambient pressure through the port 8.

Mounted for sliding movement in the extension 6 is an expandible chamber 10, a bellows in the embodiment shown, which is closed at its inner end by a plate 11 that also serves to close the inner end of the chamber 9. The outer end of the chamber 10 is closed by a plate 12, and secured to the plate 12 is a plunger 13 having an actuator rod 14 that slidably extends through the wall plate 7 axially thereof.

A second expandible chamber 15 of bellows configuration is secured to the inner surface of the wall plate 4 within the chamber 3 and is closed at its opposite ends, thereby defining a pressure tight chamber. The chamber 15 is expandible within the chamber 3 and contains a gas, such as air, which is at atmospheric pressure when the bellows of the chamber 15 is in a contracted position.

Positioned within the chamber 3 and connected to the plate 1 1 is a metering valve 16 which communicates between the interior of said chamber and the interior of the expandible chamber 10. The valve 16, which may conveniently be the well-known Viscojet, manufactured by the Lee Company of Westbrook, Connecticut slowly meters a fluid, such as propyl alcohol or a gas such as air, from the chamber 3 into the expandible chamber 10. The fluid used depends principally on the rate of metering desired, since a liquid would pass through the valve 16 at a slower rate than would a gas.

When the passive timer thus described is subjected to an ambient pressure equal to standard atmospheric pressure, pressures in all of the aforementioned chambers are equal and the system is completely passive. If the passive timer is placed in a vacuum, or in an ambient pressure environment wherein the pressure is less than standard atmospheric pressure, such as the vacuum of outer space, gas within the second storage chamber 9 will escape through port 8 and create a low pressure region acting on plate 12 of expandible chamber 10. Expandible chamber 15 containing a gas at a pressure of one atmosphere feels" this pressure differential across expandible chamber 10 and expands slowly, communicating force to the fluid contained in fluid storage chamber 3, and thereby' causing said fluid to be contained at a higher pressure than that fluid in expandible chamber 10. Said fluid is thus metered through the metering valve 16 into expandible chamber 10, creating a force tending to expand said chamber 10. The expandible chamber 10, on overcoming friction, thereby expands and advances plunger 13 toward wall plate 7 which causes the actuator rod 14 to move outwardly of said wall plate 7 and thereby to actuate a trigger mechanism (not shown) which accomplishes boom deployment, equipment turn-on, stage separation, or any other desired effect. The timing cycle as represented by the slow, steady progression of the acutator rod is divorced from the output cycle as represented by the trigger mechanism, since the force of the actuator rod is not employed to perform the work cycle, only to actuate it. Since timing accuracy depends on having a known and reasonably steady load on the actuator rod during the timing cycle, varying forces required to directly produce different work functions could conceivably cause error in the performance of the timer.

The time delay between exposure of the passive timer to a low pressure environment and the subsequent extension of the actuator rod 14 depends upon the total travel designed into the system (which can be adjustable), the metering rate and accuracy of the metering valve 16, the ambient atmospheric pressure, the choice of fluid medium to be contained within fluid storage chamber 3 and expandible chamber 10, and the frictional forces opposing movement of the plunger 13 and actuator rod 14. Through manipulation of the aforementioned factors governing time delays, timing cycles ranging from a few minutes to several days may be effected, depending upon the metering fluid used, and based on a size of less than cubic inches. The amount of force on the actuator rod 14 depends also upon the cross-sectional area of expandible chamber 10. The extension of actuator rod 14 obviously can be utilized to trigger many functions in a space environment, and the parameters mentioned hereinabove affecting the time delay and rate of extension of the rod are all controllable, which further enhances the adaptability of the instant invention to a plurality of desired functions.

The second embodiment of the present invention is shown generally in FIG. 2 at 17 and includes a cylindrical casing 18 which defines a first fluid storage chamber 19. The outer end of the casing is closed by a wall plate 20, while the inner end is provided with a wall plate 21 having an axial opening 22 therein.

A cylindrical first expandible chamber 23 of bellows configuration is contained concentrically within a relatively larger V second expandible chamber 24 which also has walls of bellows shape. Said first and second expandible chambers are sealed at respective opposite ends by

plates

25 and 26, said

chambers

23 and 24 being air-tightly sealed from each other. The plate 25 is attached to the wall plate 21 and has a hub 25a which extends through the opening 22, said hub having a port 25b therein. Plate 26 has an axial extension 27 to which is attached one end of the expandible chamber 23.

An actuator rod 28 is disposed within the expandible chamber 23, and slidably extends through a bore 29 formed in the hub 25a of the plate 25.

A third expandible chamber 30, of bellows configuratiomds secured to the inner surface of the wall plate within the chamber 19 and is closed at its opposite ends, thereby defining a pressure tight chamber. The chamber 30 is expandible within the chamber 19 and contains a gas, such as air, which is at atmospheric pressure when the bellows of the chamber 30 is in a contracted position.

Positioned within the chamber 19 and connected to the plate 26 is a metering valve 31 which communicates between the interior of said chamber 19 and the interior of the second expandible chamber 24 through a T-shaped port 32 located in the extension 27 of the plate 26. The valve 31 may comprise a Lee Viscojet" previously mentioned hereinabove. A fluid, which is preferably a liquid, contained in both fluid storage chamber 19 and the expandible chamber 24, is metered by the valve 31 between the two chambers.

The first expandible chamber 23 is vented to ambient pressure through the port b. Pressure within chamber 23 therefore approaches zero on exposure to a vacuum, such as the vacuum of outer space. Gas at standard atmospheric pressure contained within third expandible chamber transmits its one atmosphere pressure through the fluid in fluid storage chamber 19 and across the frontal area of plate 26 and of first and second

expandible chambers

23 and 24, thereby impressing a force on said

expandible chambers

23 and 24 equal to one atmosphere multiplied by the respective frontal areas of said chambers. If the diameter of the expandible chamber 23 is one-tenth the diameter of expandible chamber 24. a pressure increase of one-tenth atmosphere is experienced in expandible chamber 24. This differential pressure causes fluid flow from the chamber 24 to the fluid storage chamber 19 through the metering valve 31. As the pressure in expandible chamber 24 drops, said chamber 24 contracts, moving the actuator rod 28 through the plate 25. The third expandible chamber 30 then expands to fill the internal volume increase of fluid storage chamber 19. The volume of the expandible chamber 30 is on the order of thirty times the volume of the first expandible chamber 23 so that the pressure within said chamber 30 never drops more than about 3 percent. The entire system returns to neutral, or pre-launch, condition when the ambient pressure is returned to one atmosphere, thus permitting test cycles to be accomplished readily. In-flight temperature changes should have only a moderate effect on performance, about a 1 percent change in time for each [5C change in temperature. This configuration could be made to delay, for a year or more, depending on the metering fluid used and based on a size of less than 10 cubic inches.

A third embodiment, shown in FIG. 3, comprises a casing 33 of cylindrical shape which defines a fluid storage chamber 34 which is sealed at respective ends by

wall plates

35 and 36, plate 36 having an axial opening 360! therein. A cylindrical first expandible chamber 37 of bellows configuration is contained concentrically within a relatively larger second expandible chamber 38 which also is of bellows shape. The

chambers

37 and 38 are sealed at respective ends by

plates

39 and 40, said

chambers

37 and 38 being air-tightly sealed from each other. The plate 39 has an axial extension 41 to which is attached one end of the first expandible chamber 37. The plate 40 is attached to the end wall 36 and has a port 42 therein. The plate 40 also has a hub 40a which extends through the opening 360, said hub having a port 42 therein.

An actuator rod 43 is disposed within the expandible chamber 37, is secured to the extension 41 of plate 39, and slidably extends through a bore 44 in the plate 40.

Positioned within the chamber 34 and connected to the plate 39 is a metering valve 45 which communicates between the interior of said chamber 34 and the interior of the second expandible chamber 38 through a T-shaped port 46 located in the extension 41 of the plate 39. The valve 45 may comprise the Lee Viscojet previously described. A fluid, more preferably a gas in this particular case, contained in both the fluid storage chamber 34 and the second expandible chamber 38, is metered by the valve 45 between said chambers.

The first expandible chamber 37 is vented to ambient pressure through the port 42. Pressure within the chamber 37 therefore approaches zero on exposure to a vacuum, such as would be experienced on a spacecraft in the environment of outer space. By adjusting the frontal areas of the first and second

expandible chambers

37 and 38 varying differential pressures can be applied across the metering valve 45 between fluid storage chamber 34 and the second expandible chamber 38. For example, if the area of second expandible chamber 38 is times that of the volume of first expandible chamber 37, the one atmosphere of pressure in the fluid storage chamber 34 would impress a force of one atmosphere times the frontal area of the two expandible chambers on the plate 39 of said expandible chambers. A resulting increase in pressure of onehundredth atmosphere in the second expandible chamber 38 would be experienced, causing extremely slow internal metering of gas between the fluid storage chamber 34 and the second expandible chamber 38. The only limitation is that the force thus generated must be enough to overcome friction and the spring forces of the bellows. The actuator rod 43 would gradually move on contraction of the second expandible chamber 38 to initiate some work function.

It is believed apparent that many variations and modifications of the present invention are possible in light of the above description. lt is therefore to be understood that, within the scope of the appended claims, the invention is not to be limited to ,the particular construction or uses described in these embodiments, it being considered that minor changes in construction may be permitted within the scope of the appended claims.

lclaim:

l. A passive timer comprising:

casing means defining a chamber of fixed volume;

a fluid medium contained within said chamber at a predetermined pressure;

a first pressure-responsive means disposed within said chamber;

a second pressure-responsive means disposed within said first pressure-responsive means;

said casing means having a port communicating the interior of said second pressure-responsive means with ambient pressure;

an actuator rod carried by the second pressure-responsive means and extending slidably through the casing means; and

metering means disposed internally of the casing means for permitting flow of the fluid medium at a controlled rate between the interior of said casing means and the interior of the first pressure-responsive means, said metering means being operable on exposure of the timer to an environment of lower pressure than that predetermined pressure existing in said casing means, metering of the fluid medium causing actuation of the second pressureresponsive means for actuating said actuator rod.

2. The passive timer of claim 1, wherein said first and second pressure-responsive means comprises expandible bellows.

3. The passive timer of claim 1, and further comprising a third pressure-responsive means disposed within said casing means, said third pressure-responsive means being closed at its opposite ends and defining an expandible chamber.

4. The passive timer of claim 2, wherein said third pressureresponsive means comprises expandible bellows.