US 3712421 A
This invention relates to a fluid controlled rotary timer capable of measuring elapsed times ranging from minutes to months and which is insensitive to gravitational forces. A rotary paddle member is operatively positioned within a circumambient housing containing a viscous silicone gum retarding fluid. An external constant torque spiral spring is connected to one end of the paddle member while the other end of this paddle member serves as an output shaft.
Description (OCR text may contain errors)
' 22' Filed:
United States Patent [1 1 Hadfield ROTARY TIMER  Inventor: Harry J. Hadfield, Hunterdon County, NJ.
 Assignee: The United States of America as represented by the Secretary of the Army June 15,1971
[21 Appl.No.: 153,320
 U.S. Cl. ..185/37, 185/40 K, 58/1 R  Int. Cl ..F03g l/00  Field of Search ..185/37, 40 K, 40 M; 92/8;
58/1 R, 46 R, 145 R 56] References Cited UNITED STATES PATENTS 2,063,799 12/1936 Fornelius etal ..185/37 1 Jan. 23, 1973 7/1952 Exline ....58/l R Primary ExaminerEdgar W. Geoghegan Attorneyl-larry M. Saragovitz et a1.
 ABSTRACT This invention relates to a fluid controlled rotary timer capable of measuring elapsed times ranging from minutes to months and which is insensitive to gravitational forces. A rotary paddle member is operatively positioned within a circumambient housing containing a viscous silicone gum retarding fluid. An external constant torque spiral spring is connected to one end of the paddle member while the other end of this paddle member serves as an output shaft.
1 Claim, 3 Drawing Figures PAT-ENTEU-JAH 16 I975 sum 2 0r 2 INVENTOR ROTARY TIMER BACKGROUND OF THE INVENTION Various means are known for making dashpot or fluid controlled retarders or timers. Many of the prior art devices have utilized the principle of pressure flow of a liquid or gas through an orifice to control the rate of linear motion of a piston in a cylinder. Some of these prior art devices, because of their linear motion, are extended in length and therefore do not lend themselves to missile or projectile fusing applications that have severe spacial limitations and require long timing cycles. Another problem encountered with prior art devices is the variability of the timing as a function of changes in the ambient environment. This non-consistency in timing action or retarding function as a result of changes in temperature in prior art devices is mainly due to the temperature dependence of the viscosity of the fluid medium and the resultant variation in flow rate of that medium through an orifice. In applications which require very short timing intervals the use of a gas such as argon as a pressure flow medium while not affected by temperature in its viscosity is nevertheless proportionally responsive to temperature by changes in pressure. These changes in pressure of the gas flow medium through an orifice as a function of temperature limit their use in applications which demand consistency in timing.
Prior art devices are generally less satisfactory than the present invention because of their larger size and their variation in timing or retarding action as function of temperature. q
The present invention provides a reliable means for both relatively short and long timing applications that have spacial limitations and which are not severely temperature dependent.
SUMMARY OF THE INVENTION The present invention relates to a fluid controlled rotary timer which can measure elapsed times ranging from minutes to months. The present device utilizes the retarding action of a viscous fluid upon a spring loaded paddle member to control the rate of rotation of the latter. The viscous fluid and the paddle rotating member are contained in an ring sealed chamber. The 0 rings provide a seal to prevent the extrusion of the viscous medium when the pressure in the containing vessel increases as a result of temperature expansion and also provide a bearing surface for the shaft portions of the paddle member to rotate upon.
In accordance with the present invention a cylindrical housing of rectangular cross section has one closed end and an open end. The opened end is closed by a cover which. is held thereto by crimping the open cylinder-end walls of the housing over the cover. The closed end and the cover have oppositely disposed, and axially aligned shaft bores therein. An "0 ring groove is operatively positioned adjacent to both of the aforementioned shaft bores and contains ineach groove an 0" ring. A paddle member having a plurality of blades symmetrically positioned between two axially aligned paddle shafts is held by the two 0" rings within the cylindrical housing. The paddle shafts protrude through the shaft bore of the closed end of the housing and through the shaft bore of the housing cover. A viscous silicone gum fluid completely fills the voids between the housing and the paddle portion of the paddle member. A suitable silicone gum applicable for this invention may be obtained from Dow Corning Corp., 401 Sylvan Avenue, Englewood Cliffs, N. J. as Dow Corning 401 Gum. The inner convolution of a flat spiral negator spring is mechanically affixed to one end of the protruding paddle shaft and applies a constant rotational torque to the shaft when the spring is prebiased. The rotational output of the other output shaft of the paddle member is affixed to a device which is responsive to its rotation. The number of revolutions in any given period made by the paddle member output shaft will be a function of the energy stored in the negator spring, the frictional losses in the bearing surface, the viscosity of the fluid filling the cavity, and the size of the orifice space that is created between the inner walls of the housing and the peripheral surfaces of the paddle member.
The present invention has been found to be relatively insensitive to changes in temperature. The total change in period as a function of changes in temperature for a specific embodiment subjected to temperatures ranging from 30F to F has been limited to 22 percent over the entire range. An increase of temperature will normally tend to reduce the viscosity of the fluid where the fluid is free to expand; this reduction in viscosity will increase the pressure flow through the fixed orifice and thereby shorten the timing period. However, in the present embodiment, because of the sealed housing construction, as the temperature increases the viscous fluid, which has a coefficient of expansion greater than that of the cylinder, will be put under increased pressure. It is surmised that this pressure increase will increase the density of the viscous fluid and balance the viscosity effects tending to speed up the rotational cycle. When the present invention is subject to an ambient environment which results in a decrease in temperature, the increase in viscosity of the fluid is once again balanced by a decrease'in pressure within the containing vessel, the fluid medium is permitted to expand thereby decreasing the density of the fluid and once again compensating and balancing the temperature effects on viscosity and thereby minimizing the changes in timing. I
One of the objects of this invention is to provide a rotary timer whose timing cycle will remain relatively constant as a function of changing ambient temperatures.
Another object of the present invention is to provide a timer whose mechanical motion is rotational rather than linear.
Another object of the present invention is to provide a rotary timer whose timing cycle is independent of the forces of gravity.
Another object of the present invention is to provide a rotary timer having a long timing cycle that can be reliably manufactured into a small size that is compatible with the space requirements of missiles and projectiles.
For a better understanding of this present invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanyingdrawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational and partial cross-sectional view of the rotary timer.
FIG. 2 is a cross-sectional view of FIG. 1 taken along line 2-2.
FIG. 3 isan expanded partial cross-sectional view of FIG. 1 taken along line 3-3.
Throughout the following description like reference numerals are used to denote like parts in the drawings.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 a flat spiral wound negator biasing spring 10 has the inner winding of a first spiral l2 operatively connected to one end of a rotary spring shaft 14 and a second oppositely wound spiral 13 wound upon atake up shaft 15. The rotary paddle 16 is enclosed in a cylindrical cup shaped member 18 which has a first closed end 20 and an opened end 22 in which a cover 24 is held by the turned over edge 26 of the housing wall 28. The closed end 20 and the cover 24 each have oppositely disposed and axially aligned first and second shaft bores 30-and 32 respectively therein. The rotary paddle 16 has a plurality of symmetrically spaced paddle blades34, 34', 34" and 34" (not so designated in FIG. 1) intermediate to and integrally connected to first and second hubs 38 and 38 and output shaft 36 and spring shaft 14 which are axially aligned with each other. The spring shaft 14 and output shaft 36 each pass'respectively through the aforementioned shaft bores 30 and 32 without touching the bore walls. The whole cavity between the housing inner with a viscous silicone fluid 40. For utilization of this device a suitable gearing arrangement can be coupled to the output shaft to perform a mechanical timing function.
Referring now to FIG. 2 the paddle blades 34, 34, 34" and 34" are shown centrally disposed within the housing 28, free to rotate about its axis in the silicone fluid 40 without touching the inner housing wall 42 nor, as shown in FIG. 1', the inner surface 44 of the closed end 20 nor the inner surface 46 of the cover 24.
In FIG. 3 the expanded partial cross-sectional view along line 3-3, as illustrated in FIG. 1, shows the bearing and sealing configuration in cover 24. A second similar bearing and sealing configuration (not shown in FIG. 3) is located in the closed housing end 20. The O ring groove 50 is positioned midway between the inner surface 46 and the outer surface 48 of cover 24. An ring 52 fits in the O ring groove 50 and forms a bearing surface and seal between the paddle member output shaft 36 and the housingcover 24.
When negator spring is operatively biased to apply a constant rotational torque force to the spring shaft 14 the paddle member 16 will rotate fora fixed number of revolutions in a given period depending upon the number of pre-wound turns on the first negator spiral spring 12. As previously stated the period will be a function of the energy stored in the negator spring 10, the frictional losses between the bearingsurfaces of the O ring 52 and the oppositely disposed O ring 54 and shafts 14 and 36'respectively, the viscosity of the silicone fluid 40, the size of the orifice clearance space between the inner walls of the housing 42, 44, inner wall 46 of cover 24 and the peripheral surfaces of therotary paddle'member 16 which are all dependent on the paddle configuration.
I wish it to be understood that I do not desire to be limited to the exact detail of construction shown and described for obvious modification will occur to a person skilled in the art.
What is claimed is: p
1. A rotary timer for measuring elapsed times ranging from minutes to months which is insensitive to normal gravitational forces which comprises:
a housing means which includes;
a cylindrical cup-shaped member, closed on one end;
a cover closing an open end of said cup-shaped member; I
said cover and said closed end each have a single centrally located shaft bore;
a paddle means operatively positioned in said housing for rotation therein which includes;
a spring shaft;
an output shaft; and
a plurality of radial blades symmetrically positioned with respect to each other and intermediate to said spring shaft and said output shaft, whereby said housing being circumambient to said plurality of blades and a portion of said spring shaft and said output shaft, said spring shaft partially protrudes through said closed end bore and operatively engages said torque biasing means, said output shaft partially protrudes out of said cover shaft bore;
fluid sealing and bearing means for retaining a fluid within'said housing and simultaneously providing a bearing surface for said paddle means which includes; a first 0" ring annular groove intermediate an inner surface and an outer surface of said housing cover and concentrically disposed with respect to said output shaft bore;
a first O ring operatively positioned within said first 0 ring groove fits around said output shaft and forms a bearing surface and seal between said output shaft and said housing cover;
a second O? ring annular groove intermediate an inner surface and an outer surface of said closed end and concentrically disposed with respect to v said spring shaft;
a second 0 ring operatively positioned within said second Of ring groove fits around said spring shaft and forms a bearing surface and seal between said spring shaft and said housing closed end;
a fluid retarding means intermediately positioned between said housing means and said paddle means which includes;
a viscous, silicone-gum, fluid; and
torque biasing means, external to said housing means, operatively connected to said paddle means for rotation thereof which includes;
a flat spiral spring wound in a first direction having an inner convolution operatively connected to said spring shaft and wound in an opposite direction on the other end so that said spring shaft will have a constant rotational torque force exerted thereon.
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