US3793837A

US3793837A - Wax element diaphragm and seal

Info

Publication number: US3793837A
Application number: US00279467A
Authority: US
Inventors: W Biermann; J Rice
Original assignee: Controls Company of America
Current assignee: Eaton Corp
Priority date: 1972-08-10
Filing date: 1972-08-10
Publication date: 1974-02-26
Anticipated expiration: 1991-02-26

Abstract

The flanged end of the plunger guide which fits into the enlarged end of the wax element cup has a chamfer which seats against the internal shoulder when the clamping is completed. Inside the chamfer is a flat leading to a downwardly radiused clamp portion which develops maximum compression of the elastomeric diaphragm. The radius and the chamfer both force the elastomer to flow outwardly to effect a superior seal. The diaphragm face remote from the wax charge has a generally annular recess (which appears to dis-appear after clamping) to reduce the friction between the diaphragm and the guide to thereby facilitate stretching the diaphragm over a maximum area.

Description

United States Patent [1 1 Biermann et al.

[ Feb. 26, 1974 WAX ELEMENT DIAPHRAGM AND SEAL [75] Inventors: William A. Biermann, Brookfield; John S. Rice, Milwaukee, both of Wis.

[73] Assignee: Controls Company of America,

Schiller Park, Ill.

[22] Filed: Aug. 1.0, 1972 [21] Appl. No.: 279,467

[52] US. Cl. 60/527, 73/3683 [511 m. l-..we9m2t 1/Qe /1 58 Field of Search 60/23; 73/3683; 9 236/100; 337/117, 320; 92/98 R, 99

[56] References Cited UNITED STATES PATENTS 2,986,936 6/1961 Vernet 73/3683 3,180,150 4/1965 Horne 3,696,611 10/1972 Noakes et a1. 60/23 3,719,085 3/1973 Sliger 73/3683 Primary Examiner-Edgar W. Geoghegan Assistant Examiner-H. Burks, Sr. Attorney, Agent, or Firm-Michael, Best & Friedrich [5 7 ABSTRACT The flanged end of the plunger guide which fits into the enlarged end of the wax element cup has a chamfer which seats against the internal shoulder when the clamping is completed. Inside the chamfer is a flat leading to a downwardly radiused clamp portion which develops maximum compression of the elastomeric diaphragm. The radius and the chamfer both force the elastomer to flow outwardly to effect a superior seal. The diaphragm face remote from the wax charge has a generally annular recess (which appears to dis-appear after clamping) to reduce the friction between the diaphragm and the guide to thereby facilitate stretching the diaphragm over a maximum area.

7 Claims, 1 Drawing Figure BACKGROUND OF THE INVENTION 1. Field of the Invention In the wax element actuator art the generally accepted device has a cup portion which contains a wax charge which will melt at a predetermined temperature and expands considerably upon melting. The actuator also includes a guide for a plunger which is actuated in response to the expansion of the wax acting on a diaphragm positioned between the guide and the cup. The guide is generally secured to the cup in such a way as to clamp the periphery of the diaphragm. These actuators generally work in a liquid medium and any failure on the part of the diaphragm to seal will permit liquid to migrate into the wax charge and adversely affect the calibration of the unit. The seal is one aspect of the present invention.

The other aspect of the present invention is related to the necessary stretching of the diaphragm as it deflects to transmit motion to the plunger. In theory, the elastomer diaphragm will stretch uniformly. In practice, however, this does not appear to be the case since the operating pressures obtained in these units are sufficient to cause a very considerable load acting to hold the diaphragm against the adjacent surface of the guide and this is particularly pronounced in the flat portion of the guide more or less normal or perpendicular to the motion of the piston. Here the forces seem to obtain such magnitude as to virtually preclude stretching the diaphragm at this area notwithstanding the fact it is an elastomer and presumably will stretch.

2. Description of the Prior Art Most of the prior art diaphragm seals are simply clamps which permit leaks to develop in the course of 2 tion with a substantial risk of rupturing. With this added area effectively stretching, the danger. of rupturing the diaphragm is substantially reduced.

DESCRIPTION OF THE DRAWING The single FIGURE is, in effect, a split FIGURE; one half representing the parts before clamping and the other half showing the parts after clamping.

DESCRIPTION OF THE PREFERRED EMBODIMENT The actuator assembly has a cup portion 10 which is filled with a predetermined amount of the desired wax or wax/metal, etc., composition 12 having the characteristic of melting at a desired temperature and at that time expanding considerably to provide the motive power for the actuator. The cup 10 has an enlarged portion 14 which provides an annular seat 16 upon which the periphery of diaphragm l8 rests. The upstanding wall of the enlarged portion 14 is provided with a small internal shoulder 20 which functions as a seat for the chamfered surface 22 of the flanged end 24 of the plunger guide 26. The guide end 24 is sized to just fit within the open end of the cup until it seats on the shoulder 20. This, then, dimensionally locates the guide relative to the cup with the corner of the shoulder 20 engaging the chamfered surface in what might be considered line contact. The outside corner of the guide is radiused at 28 to form a surface over which the wall 14 is rolled or bent during the clamping action.

It will be noted the chamfered surface leads to a flat annular surface 30 on the face ,of the guide confronting the diaphragm. Inside the flat surface 30 there is a radius 32 which terminates at surface 34 which is the clamping surface. It will be noted that surface 34 slopes time. Some few prior art devices employ constructions which tend to develop outward flow of the diaphragm but any benefit of such outward flow is cancelled by the fact thatthe diaphragm is caused to flow outwardly into engagement with a cup which then fits within another cup and, hence, there is no assured leak prevention.

As for obtaining more uniform stretch of the diaphragm over the entire diaphragm surface, the prior art seems to have ignored this problem insofar as obtaining practical solutions are concerned.

SUMMARY OF THE INVENTION ness of the diaphragm is reduced at this point with a consequent reduction in force holding the diaphragm against the generally flat area of the guide inside of the clamp ring. This. then, permits the elastic nature of the diaphragm to be more evident and, hence, some stretching can occur in this annular portion which experience with the prior art shows does not normally stretch to any substantial extent. Hence, the prior art diaphragm tends to stretch primarily in the center secvery slightly away from the wax diaphragm to the radius 36 leading to, cylindrical bore 38 in which an elastomer plug may be mounted. This plug is not shown and can take various configurations including having a converging section corresponding to the convergence of the guide bore at 40 which leads to the bore 42 in which the piston is mounted. The details of the plug and of the piston form no part of this invention and are not shown.

When the open end ofthe cup is rolled onto the distal portion of guide flange 24 as illustrated at 44, the guide is drawn down tightly with the chamfer 22 seating firmly on the corner of internal shoulder 20. The portion of the flange closest to the cup 10, i.e., inside radius 32, might be considered a clamp ring. The maximum compressive force on the diaphragm 18 is obtained at this area. The clamping action causes the radius 32 to push the elastomer material of the diaphragm outwardly into intimate contact with the inside wall of the enlarged portion of the cup. The flat annular portion 30 just outside the radius 32 exerts a considerable clamping action on the diaphragm while the chamfered portion causes the elastomer material to flow outwardly and upwardly to fill the space between the chamfer 22 and the inside of the cup. This method of clamping the diaphragm forces the elastomer outwardly into intimate contact with the cup to form a superior seal while the clamp ring will resist any tendency of the diaphragm to migrate inwardly as it is repeatedly stretched in operation. Therefore the diaphragm remains in intimate contact with the wall and prevents liquid in which the device is operating from migrating into the wax charge.

As noted heretofore, the prior art appears to have been primarly concerned with achieving good clamping action on the diaphragm with the expectation that this, therefore, would effect the seal whereas practice has shown that the seal thus obtained is inadequate. The present construction forces the elastomer material outside the actual clamping area into a good sealing relation with the cup. In effect, therefore, this construction separates the sealing and clamping functions and provides a sound solution to each function. When the assembly is completed the seal radially outside the clamp ring portion and radius 32 will function to prevent liquid from migrating to the clamp area and the wax charge.

In the relaxed condition of the diaphragm (i.e., before clamping) it will be noted the diaphragm has a generally annular recess 46 on the diaphragm face which confronts the flanged end of the guide 26. This recess is of increasing depth from the inside to the outside of the annular recess. The inside of the annular recess corresponds approximately to the point where radius 36 begins while the outside of the recess is in general alignment with the inside wall of cup 10. This, therefore, permits the maximum clamping action on the diaphragm to occur between the outside of the recess and the start of radius 32. It will be noted that the central portion of the diaphragm is somewhat domed to provide adequate elastomeric material to withstand the stretching to which the diaphragm will be subjected.

When the wax melts, the pressure acting on the diaphragm will function to stretch the diaphragm and actuate the piston. It has always been assumed that the elastomer diaphragm will stretch over its entire unsupported area. This does not appear to be the case and it is thought that the high pressure acting on the diaphragm portion overlying the annular recess in the diaphragm would, absent the recess, so hold the diaphragm to the face of the guided flange that the resulting friction virtually precludes stretching of the elastomer in this area. By providing the recess 46 the initial compression of the elastomer in this area is substantially reduced. In the drawing the recess appears to be non-existent after the clamping operation and this corresponds to physical samples. In practice, however, there is not any substantial preload of the elastomer in the annular portion which is recessed. This results in a reduction in the frictional engagement between the diaphragm and the guide in the area of the recess. The reduction in frictional engagement in this annular portion results in the diaphragm being stretched more readily at that portion. As a result the central portion of the present diaphragm does not have to stretch as much. it is kept within reasonable limits with a consequent reduction in field failures attributable to diaphragm rupture.

We claim:

1. A wax element actuator including,

a housing having a cup portion and an enlarged portion with an annular ledge therebetween,

a fusible material in said cup portion,

a diaphragm dimensioned to fit snugly within the enlarged portion and overlying the fusible material and said ledge,

a shoulder inside the enlarged portion and spaced from said ledge a distance greater than the thickness of the periphery of the diaphragm in its natural state,

a piston guide having a flanged end dimensioned to fit within said enlarged portion and seat on said shoulder,

the flanged end having a face confronting the diaphragm,

said face having an annular clamping portion spaced radially inwardly of the outside of the flanged end,

said face including a surface outside the clamping ring sloping outwardly and away from the diaphragm,

the axially outer edge of the enlarged portion being formed inwardly over the flanged end of the guide to firmly retain the flanged end in engagement with said shoulder with the diaphragm firmly retained between the clamping ring and said ledge and said sloping surface functioning to force the adjacent diaphragm material radially outwardly into sealing engagement with the ledge and the inside of said enlarged portion between said shoulder and the ledge.

2. An actuator according to claim 1 in which the diaphragm face confronting the guide is provided with an annular recess adjacent and inside of the diaphragm portion engaged by said clamping portion.

3. An actuator according to claim 2 in which the guide has a central cylindrical portion joined to the flanged end by a radiused portion,

said recess in said diaphragm confronting the portion of the flanged end lying between said radiused portion and said clamping portion.

4. An actuator according to claim 3 in which the depth of said recess increases with increasing radius of the recess.

5. An actuator according to claim 1 in which the outside of the clamping portion is defined by a curved surface leading to a flat annular portion generally parallel to said ledge whereby the curved surface acts on the diaphragm to force the diaphragm material radially outwardly, said flat annular portion being spaced from said ledge a distance which requires substantial compression of the diaphragm therebetween whereby sealing force is maintained.

6. An actuator according to claim 5 in which the portion of the flanged end which seats on said shoulder is chamfered from said flat annular surface to the outside diameter of the flanged end whereby line contact seating is obtained and the chamfered portion forces diaphragm material outwardly into sealing contact with the inside of the enlarged portion of the housing.

7. An actuator according to claim 1 in which the portion of the flanged end which seats on said shoulder is a chamfered surface having a line contact seat on the surface and acting on the diaphragm material to force the material radially outwardly into sealing contact with the interior of the enlarged portion of said hous-

Claims

1. A wax element actuator including, a housing having a cup portion and an enlarged portion with an annular ledge therebetween, a fusible material in said cup portion, a diaphragm dimensioned to fit snugly within the enlarged portion and overlying the fusible material and said ledge, a shoulder inside the enlarged portion and spaced from said ledge a distance greater than the thickness of the periphery of the diaphragm in its natural state, a piston guide having a flanged end dimensioned to fit within said enlarged portion and seat on said shoulder, the flanged end having a face confronting the diaphragm, said face having an annular clamping portion spaced radially inwardly of the outside of the flanged end, said face including a surface outside the clamping ring sloping outwardly and away from the diaphragm, the axially outer edge of the enlarged portion being formed inwardly over the flanged end of the guide to firmly retain the flanged end in engagement with said shoulder with the diaphragm firmly retained between the clamping ring and said ledge and said sloping surface functioning to force the adjacent diaphragm material radially outwardly into sealing engagement with the ledge and the inside of said enlarged portion between said shoulder and the ledge.

3. An actuator according to claim 2 in which the guide has a central cylindrical portion joined to the flanged end by a radiused portion, said recess in said diaphragm confronting the portion of the flanged end lying between said radiused portion and said clamping portion.

7. An actuator according to claim 1 in which the portion of the flanged end which seats on said shoulder is a chamfered surface having a line contact seat on the surface and acting on the diaphragm material to force the material radially outwardly into sealing contact with the interior of the enlarged portion of said housing.