US2993965A - Timing devices - Google Patents

Description

July 25, 1961 D. L. MORGAN TIMING DEVICES Filed June 27, 1957 Fig. I

34v 42 "7 22 20 I8 36 f? ,21

Fig.

TEMPERATURE C IN VEN TOR.

DAVID L. MORGAN ATYUKA [Y United States Patent 2,993,965 TIMING DEVICES David L. Morgan, Shelton, Conn., assignor to Robertslraw-Fulton Controls Company, Richmond, Va., a corporation of Delaware Filed June 27, 1957, Ser. No. 668,390 2 Claims. (Cl. 20034) This invention relates to timing devices and more particularly to hydraulic timing devices which are compensated for changes in viscosity of the fluid caused by changes of temperature.

In the usual form of hydraulic timing devices, a fluid is forced from an expansible chamber through a capillary tube to a reservoir by applying pressure to the expansible chamber. Accordingly, a time delay is established corresponding to the time required to displace the fluid from the expansible chamber to the reservoir.

Such devices are subject to an inherent disadvantage in that the viscosity of the fluid changes with the temperature thereof. It will be apparent that if the viscosity of the fluid changes, the rate of flow of the fluid from the expansible chamber will also vary, causing variations in the time delay.

It is an object of this invention to utilize a fluid to produce a time delay substantially unaffected by temperature variations of the fluid.

Another object of this invention is to compensate a hydraulic timing device for variations in viscosity of the fluid.

In the preferred embodiment of the invention, a pair of expansible elements are connected by a capillary tube and filled with a suitable fluid. Means are provided for biasing one of said elements to a contracted condition, and means are provided for actuating the other of said elements to force the fluid therein into the one element to expand the same against its bias to thus establish a time delay determined by the time required for the fluid to return to said other element under the force of said biasing means. A volume of fluid is used so that a change in viscosity of the fluid as a result of a temperature change is compensated for by the thermal expansion of the fluid in response to the temperature change.

Other objects and advantages will become apparent from the following description taken in connection with the accompanying drawing wherein:

FIG. 1 is a longitudinal sectional view in somewhat schematic form of a control device embodying this invention; and

FIG. 2 is a graph illustrating the operation and result achieved by the invention.

Referring more particularly to the drawing, the timing device comprises a casing having mounted therein a pair of spaced parallel expansible and contractible bellows member 12, 14. The bellows member 12 defines an expansible chamber 13 and has one end sealed to a plate 16 fixed to'the bottom wall of the casing 10 and its other upper end sealed to a disc 18. An actuating plunger 20 extends from the disc 18 and is slidably mounted in a suitable opening 22 in the upper wall of the casing 10, in axial alignment with the bellows member 12. A flange 24 is formed on the upper end of the plunger 20 to enable the plunger 20 to be manually actuated axially toward the bellows member12. The plunger 20 provides a means for manually contracting the bellows member 12. It will be apparent that if the plunger 20 is manually depressed, the upper end of the bellows member 12 will be moved axially toward the bottom wall of the casing 10 to reduce the volume of the chamber 13.

The other bellows member 14 defines an expansible chamber 25 and has one end sealed to a suitable plate 26 fixed to the bottom wall of the casing 10 and the other end thereof sealed to a disc 27 engaging the bottom wall of a cup-shaped member 28, the member 28 substantially enclosing the bellows member 14. The lower end of the cup-shaped member 28 terminates in a flange 30 providing a seat for a spring 32 mounted in compression between the flange 30 and the upper wall of the casing 10. The spring 32 serves to bias the bellows member 14 downward tending to contract the same to decrease the volume of the chamber 25.

An actuating stem 34 extends upwardly from the end wall of the cup-shaped member 28 and is slidably mounted in a suitable opening 36 formed in the upper wall of the casing 10. The upper portion of the actuating stem 34 is reversely bent at 38 and carries an electrical contact 40 on the end thereof for cooperation with a fixed contact 42 fixed to an abutment on the exterior surface of the upper wall of the casing 10. The contacts 40, 42 may be connected by suitable lead wires (not shown) to an electrical device (not shown) to be controlled.

In the position shown in FIG. 1, the contact 40 is out of engagement with the contact 42. However, the contact 40 will move into engagement with the contact 42 upon downward axial movement of the actuating stem 34 during contraction of the bellows member 14 under the bias of spring 32 to engage the contact 42.

The chamber 25 of the bellows member 14 communicates with the chamber 13 of the bellows member 12 by means of a capillary tube 44 which has the ends thereof sealed within the bottom wall of the casing 10 in communication with the chambers 13, 25, respectively. The capillary tube 44 is reduced in diameter at 46, preferably at its medial portion, to define a restricted flow passage 48. The bellows members 12, 14 and capillary tube 44 define a closed system filled with a viscous fluid, such as heptane. In addition, the bellows members 12, 14 and capillary tube 44 operate in conjunction with the parts described in connection therewith to form a hydraulic timing device, the operation of which may be described as follows.

In operation of the timing device, the plunger 20 is manually depressed to the position shown in FIG. 1. This movement of the plunger 20 will serve to compress the bellows member 12 and force fluid from the chamber 13 through the capillary tube 44, passage 48 and into the chamber 25 of the bellows member 14. This forcing of fluid into the bellows member 14 causes expansion of the same against the bias of the spring 32 and-movement of the actuating stem upward to the position shown, e.g., wherein the contact 40 is disengaged from the contact 42 The sequence of operation discussed thus far will condition the timing device to effect a delayed closing of contacts 40, 42. More particularly, when the plunger 20 is released in its depressed position illustrated in FIG. 1, the bellows member 14 will contract under the bias of the spring 32 to undergo reduction in volume and force fluid from the chamber 25 through the capillary tube 44 to the bellows member 12. The rate of contraction of the bellows member 14 is determined by the biasing force of the spring 32, the volume of the bellows member 14, the size of restricted passage 48, and the viscosity of the fluid filling the system.

After a predetermined time delay which is determined by the foregoing factors, the bellows member 14 will have contracted sufficiently to cause engagement of the contact 40 with the contact 42 and to have returned the plunger 20 to its uppermost position. Normally, a temperature change causing a change in viscosity of the fluid filling the bellows members 12, 14, and capillary tube 44 would vary the time delay established as above described since, as the fluid becomes more viscous, the flow rate thereof through the orifice 48 will decrease.

However, the physical variables in the device have been so selected so as to compensate for any change in viscosity of the fluid as the result of a change in temperature of the fluid. More particularly, it has been found that by accurately selecting the volume of the fluid, a change in viscosity can be offset or balanced by a change due to thermal expansion of the fluid as a result of the temperature increase.

Referring to FIG. 1, it will be apparent that when the plunger 20 is depressed to the position shown, the spacing between the two contacts 40, 42 willvary with the temperature of [the fluid due to the thermal expansion of the fluid in response to a temperature increase. This variation in volume of the fluid with temperature will depend on the total volume of the fluid and the thermal coeflicient of expansion of the fluid. Thus, it will be apparent that at a predetermined temperature, a portion of the fluid sufiicient to expand the bellows member 14 to open the contacts 40, 42 and having a predetermined viscosity will flow through the orifice or passage 48 in a time which may be determined from the following equation:

where t is time delay at temperature T v is volume of fluid flowing through the orifice at temperature T n is the viscosity at temperature T;

K is a constant for varying temperature.

Assuming now a temperature increase of the fluid to a temperature T the following equation may be written:

where the new terms are:

t is time delay at temperature T V is the total volume of fluid in the system at T n is the viscosity at temperature T a is the thermal coeflicient of expansion of the liquid.

If the ratio of t to t is determined, the following equation results:

When the ratio of t to t is unity, the last equation becomes:

From this last equation, it will be apparent that the time delay at two different temperatures can be made substantially constant by a proper choice of For purposes of illustration, assume that it is desired that the time delays t and t be equal at temperature of 50 C. and +50 C. when the liquid is heptane. The following tabulation gives the necessary values:

n 1.177 .3128 density .7420 .6583

From the above density data (a may be calculated as a n as tfl m R Tm For heptane AE=1897 calories and R=l.987 calories. It is evident that since viscosity is an exponential function of T and volume is almost a linear function of T that the ratio can be exactly unity at only two given values of T for a certain ratio of Referring to the graph illustrated in FIG. 2, the ratio of t to t, for heptane is plotted between the temperature of 75 C. and C. From the graph it can be seen that with heptane, the range of 58 C. to +100 C. results in not more than i-l0% variation in time delay.

From the foregoing it will be apparent that by properly selecting the volume of the liquid filling the bellows members '12, 14 and tube 44 as illustrated for the above equations, a time delay is obtained which is substantial- 1y constant during normal variations in temperature of the fluid used.

While only one embodiment of the invention has been shown and described herein, it will be apparent that many modifications and changes may be made without departing from the scope of the invention as defined in the appended claims.

I claim:

1. In a fluid actuated constant delay timing device exposed to a variable ambient temperature, the combination comprising a support means, first and second hollow expansible and contractible elements secured to said support means and being spaced adjacent to each other, a capillary tube connected to each of said first and second elements and being adapted to communicate with the hollow interiors of said first and second elements, said hollow interiors of said first and second elements and said capillary tube forming a chamber of a predetermined volume and proportional to the volume of liquid flow through said capillary tube for a given ambient temperature range, a viscous fluid filling said fluid chamber, a positive displacement actuating means operativelyconnected to said second element for displacing a predetermined amount of fluid, biasing means adapted for exerting a substantially constant contracting force on said first element, said biasing means being responsive to the release of said actuating means to cause the return of said predetermined amount of fluid from the hollow interior of said first element to the hollow interior of said second element via said capillary tube, and contact means operatively associated with said first element for controlling an electrical circuit, said fluid being adapted to expand and contract said first element in response to different temperature ambients to variably adjust said contact means, the viscosity of said fluid varying in response to variable ambient temperatures whereby said first element compensates for changes in total volume and viscosity of said fluid upon changes in said ambient temperature to obtain uniform time response to adjust said contact means when said actuating means is released.

2. A timing device as Claimed in claim 1 wherein said first and second elements and said capillary tube are constructed in accordance with the equation v is the volume of fluid flowing through said capillary 10 tube upon release of said fluid at T n is the viscosity of fluid at T and a is the thermal coefiicient of expansion of said fluid.

References Cited in the file of this patent UNITED STATES PATENTS Youngman May 6, 1884 Kellett June 27, 1933 Turner Apr. 27, 1948 Davison et a1 May 5, 1953 Troendle May 5, 1953 OTHER REFERENCES Germany Jan. 28, 1927

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