GB2146708A - Thermostatic and like controls - Google Patents

Abstract

A thermostatic or like control has a setting shaft (15) (Fig. 3) which is rotatably mounted within a bush (16) (Fig. 2), both the shaft (15) and bush (16) being of resilient plastics material. The shaft (15) which is preferably formed with an integral cam (14) at one end, is snap-engaged in the bush to locate the shaft axially, and the bush itself is snap-engaged in an aperture in the frame of the control. <IMAGE>

Description

SPECIFICATION Thermostatic and like controls This invention relates to thermostatic and like controls.

A known type of thermostatic control has a temperature responsive actuator such as a fluid-filled bellows which acts upon a switch through an operating mechanism. The operat ing mechanism includes a spring which op poses the action of the temperature responsive actuator. The biasing force exerted by the spring predetermines the temperatures at which the thermostatic switch is operated in response to the actuator and this force is normally presettable manually by the angular adjustment of a setting shaft. The setting shaft is rotatable in a bush which is fixed in an aperture of a frame supporting the other components of the control. The shaft carries a cam which acts upon a movable anchorage for the biasing spring to adjust the force exerted by the latter according to the angular setting of the shaft.

In controls of the aforesaid type the setting shaft, the bush and the cam are commonly made of metal. The bush is fixed in the frame, which is also of metal, by a rivetting operation performed on an end of a bush projecting through an aperture in the frame. The shaft is rendered captive within but rotatable relative to the bush by the deformation of a lip carried by the bush into engagement with a profiled circumferential groove in the surface of the shaft. The end of the shaft within the control carries the cam which may in the form of a metal disc of appropriate profile, secured to the end of the shaft by a swaging or rivetting operation.

The assembly of the various components of the control as mentioned above requires a sequence of separate operations in mass production of the control. An object of the present invention is to provide a control in which the operations of assembling the shaft, the bush and the cam are considerably simplified, thereby potentially improving the reliability of the assembled control and the cost of assembly.

According to the present invention there is provided a control of the kind having a setting shaft rotatably mounted in a bush which is fixed in an aperture in a frame, in which the shaft and the bush are both formed of resilient plastics material, the shaft being snapengaged in the bush to locate the shaft axially while permitting rotation of the latter and the bush being snap-engaged in the aperture in the frame to secure the bush 40 the frame.

Preferably the shaft is snap-engaged in the bush, and the bush is snap-engaged in the frame, by axial movement relative to the hole in the frame from the same side of the frame.

This facilitates the assembly of the control, the bush and the shaft being located by snap action without requiring any fixing operations such as upsetting or rivetting, characteristic of known controls with metal bushes and shafts.

Preferably the shaft is formed at one end with an integral cam, so that both the shaft and the cam are of plastics material.

The shaft may have a circumferential notch in which an integral resilient lip projecting inwardly from the bush engages upon insertion of the shaft into the bush. The bush preferably has a circumferential groove in which the edge of the aperture in the frame engages upon insertion of the bush into the aperture from one side of the frame.

In a preferred embodiment the plastics bush has an externally screw threaded portion upon which a nut, also of plastics material, is threaded to secure the bush to the frame.

The bush and the aperture in the frame may have interengaging portions of non-circular cross section which prevent rotation of the bush in the aperture upon its engagement therein. Thus the part of the frame surrounding the aperture may be formed circumferentially with with teeth which engage the bush to prevent rotation thereof.

By providing a shaft and cam of plastics material the manually operable part of the control, that is, the shaft, is inherently insulated electrically from the remainder of the control.

Where reference is made herein to "thermostatic and like controls" it is understood that the invention is not confined in its practical applications to thermostatic controls, but is more generally applicable to any control of the kind having a setting shaft rotatably mounted in a frame. Thus the invention may, for example, find practical application in a manually presettable pressure control.

The invention is applicable to controls having different types of temperature or pressure responsive actuator. In one embodiment of the invention the control includes a sealed bellows device which is fixed in the frame and which, upon assembly of the control, cooperates with a switch-operating mechanism, the interior of the of the bellows device being in communication with a flexible capillary tube for sensing a temperature remote from the control, and in which both the bellows device and the capillary tube are of metal coated with plastics material. By coating the capillary tube, which may be of aluminium, and the bellows device with plastics material the possibility of leakage from the capillary tube or the bellows device is minimised, and the electrical isolation of the control is further enhanced.

The invention will be further described by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic partly cut away side view of a thermostatic control according to one embodiment of the invention; Figure 2 is a side elevational view, partly in axial section, illustrating the plastic bush of the control shown in Figure 1, and part of the frame of the control; Figure 3 is a side elevational view, partly in axial section, of the plastics camshaft which fits into the bush of Figure 2; Figure 4 is a plan view of part of the frame of the control, showing the aperture into which the bush of Figure 2 fits, and Figure 5 is a diagrammatic cross sectional view taken on on line V-V in Figure 4.

The control illustrated in Figure 1 has a frame 1 comprising a sheet metal pressing having a base wall 2 an upstanding side wall 3. A bellows device 4 forming part of a sealed fluid-containing system with a capillary 5 is supported by the side walls 3. The capillary tube 5 is connected to a remote sensing point or bulb (not shown). One of the flexible walls of the bellows device 4 carries a centrai boss 6 which is displaceable,in a direction generally perpendicular to the plane of the base wall 2, upon temperature-responsive deformation of the bellows device 4. Movement of the bellows boss 6 is transmitted through a switch operating lever 7, which is pivotally mounted in the side walls 3 of the frame 1, to an operating member 8 of a snap-action switch device 9 which is supported by the side walls 3 adjacent the bellows device 4.

The switch operating lever 7 has an upstanding lug 10 to which one end of a helical tension spring 11 is anchored. The other end of the helical tension spring 11 has an adjustable screw-anchorage 1 2 connecting the spring 11 to a cam slider plate 1 3 of generally L-shape, the plate 1 3 having a portion which slides parallel to the base wall 2 and which is held by the tension in the spring 11 in engagement with the edge of a disc-like cam 14 arranged generally parallel to the base wall 2.

The cam 14 is carried at one end of a camshaft 1 5 which is rotatably mounted in a bush 1 6 supported in an aperture in the base wall 2, the axis of rotation X of the camshaft 1 5 being perpendicular to the plane of the base wall 2.

In use of the control a temperature setting knob (not shown) is mounted on the externally projecting portion of the camshaft 1 5. Angular adjustment of the shaft by rotation of the setting knob adjusts the angular position of the cam about the axis X , which in turn causes a predetermined displacement of the cam slider 13, according to the profile of the cam 14. This displacement of the cam slider 1 3 adjusts the tension in the spring 11, thereby adjusting the biasing force exerted by the lever 7 on the boss 6 of the bellows device 4. By this means the operating point of the thermostat, that is, the sensed temperature at which the switch device 9 is operated,can be manually preset.

The control as thus far described is of a known type with a conventional arrangement of the component parts. According to the present invention the assembly of the camshaft 1 5 and the bush 1 6 is considerably simplified by arranging that these components are of suitable resilient plastics material, for example "delrin 100" (trade mark).

Referring to Figure 2, the plastics bush 1 6 is designed to be snap-fitted into a generally circular aperture 1 7 in the base wall 2. The bush 1 6 is formed at one end with an integral radial flange 18 and with a bevelled shoulder 1 9 which is spaced from the flange 1 8 and defines therewith a circumferential groove 20 in which the edge of the aperture 1 7 engages upon assembly of the bush 1 6. The external surface of the bush 1 6 adjacent the shoulder 1 9 is provided with a screw-threaded portion 21 designed to receive an internally threaded plastics nut 21A (Figure 1) which serves to anchor the bush to a mounting plate (not shown) of an appliance in use of the control.

At its end opposite the flange 1 8 the bush 1 6 is formed with an integral lip 22 which projects radially inwardly from the internal cylindrical bore 23 of the bush and which also projects in an axial direction away from the flanged end of the bush.

The plastics camshaft 1 5 , shown separately in Figure 3, is formed integrally with the disc-like cam 14. By making the camshaft 1 5 and cam 1 4 in one piece the separate assembly step of fixing a cam disc to a shaft, characteristic of the use of metal components, is avoided. The camshaft 1 5 has an external cylindrical surface the diameter of which is only slightly smaller than the internal diameter of the cylindrical bore 23 of the bush 1 6 into which the shaft fits.A circumferential notch 24 is formed in the cylindrical surface of the shaft 1 5 at a position such that, upon assembly of the shaft 1 5 by pushing it axially into the bush 1 6 from the flanged end of the latter, the lip 22 snap-engages in the notch 24 to render the shaft 1 5 captive in the bush 1 6 while being freely rotatable relative thereto about its axis X.

The plastics bush 1 6 is fitted into the aperture 1 7 in the base wall 2 by pushing the bush 1 6 into the aperture from the inside of the frame 1, with the lip 22 leading. The external surface of the bevelled shoulder 1 9 engages the edge of the aperture 1 7 and upon pushing of the bush 1 6 using a suitable press-tool the shoulder 1 9 is forced through the aperture 17, and snap-engages the edge of the aperture 1 7 so that the bush 1 6 is effectively anchored with the circumferential groove 20 in engagement with the edge of the aperture 17, as shown diagrammatically in Figure 2.

In order to prevent rotation of the assembled bush 16 in the aperture 1 7 the edge of the aperture 16 is formed with inwardly pro jecting teeth 25 (Figure 4)of shallow sawtooth profile which snapengage in corresponding recesses (not shown) in the base of the groove 20 upon twisting of the bush 1 6 about its axis after insertion of the bush 1 6 into the aperture 1 7.

Rotation of the bush 1 6 about its axis in the aperture 1 7 may alternatively be prevented by making the cooperating surfaces of the groove 20 and the aperture 1 7 of suitable non-circular profile.

Before assembly of the control the entire external surface of the bellows device 4 and the capillary tube 5 is coated in plastics material, by a powder-coating method. A thermosetting epoxy resin is preferred as the coating material. This has the effect of sealing the capillary tube 5 externally, particularly where the latter is aluminium and would be prone to corrosion if left unprotected. A thermoplastics powder may alternatively be used as the coating material.

Claims (11)

1. A control of the kind having a setting shaft rotatably mounted in a bush which is fixed in an aperture in a frame, in which the shaft and the bush are both formed of resilient plastics material, the shaft being snapengaged in the bush to locate the shaft axially while permitting rotation of the latter and the bush being snap-engaged in the aperture in the frame to secure the bush to the frame.

2. A control according to Claim 1, in which the shaft is snap-engaged in the bush, and the bush is snap-engaged in the frame, by axial movement relative to the hole in the frame from the same side of the frame.

3. A control according to claim 1 or claim 2, in which the shaft has a circumferential notch in which an integral resilient lip projecting inwardly from the bush engages upon insertion of the shaft into the bush.

4. A control according to Claim 1, Claim 2 or Claim 3, in which the bush has a circum ferentiai groove in which the edge of the aperture in the frame engages upon insertion of the bush into the aperture from one side of the frame.

5. A control according to any one of the preceding claims, in which the shaft is formed integrally with a cam at one end of the shaft.

6. A control according to any one of the preceding claims, in which the plastics bush has an externally screw-threaded portion upon which a nut of plastics material is threaded to secure the bush to the frame.

7. A control according to any one of the preceding claims, in which the bush and the aperture in the frame have interengaging portions of non-circular cross section which prevent rotation of the bush in the aperture upon its engagement therein.

8. A control according to claim 7, in which the frame surrounding the aperture is formed circumferentially with teeth which engage the bush to prevent rotation thereof.

9. A control according to any one of the preceding claims, and further including a sealed bellows device which is fixed in the frame and which, upon assembly of the control, cooperates with a switch-operating mechanism, the interior of the bellows device being in communication with a flexible capillary tube for sensing a temperature remote from the control, and in which both the bellows device and the capillary tube are of metal coated with plastics material.

10. A control according to Claim 9 in which the capillary tube is of aluminium.

11. A control substantially as herein described with reference to and as shown in the accompanying drawings.