GB2463447A

GB2463447A - Thermostat control device

Info

Publication number: GB2463447A
Application number: GB0811933A
Authority: GB
Inventors: John Edwin Tooke
Original assignee: Diamond H Controls Ltd
Current assignee: Diamond H Controls Ltd
Priority date: 2008-07-01
Filing date: 2008-07-01
Publication date: 2010-03-17
Also published as: EP2304517A2; WO2010001110A2; WO2010001110A3; GB0811933D0

Abstract

A thermostat control device (1) comprises a housing (2) within which there is provided a diaphragm (4) and temperature sensor (5) coupled via a capillary system (6). A drive screw (12) is threadingly engaged to a correspondingly threaded diaphragm head (7) which moves the drive screw (12) in response to temperature changes at the sensor, bringing a striker arrangement (15) into and out of engagement with a moveable contact (18) to "break" and "make" electrical connection with a fixed contact (19). A rotatable user control spindle (30) receives a tabbed end (25) of the drive screw (12) within a receiving slot (27) allowing rotation of the drive screw with respect to the diaphragm (4) without imparting axial movement to the user control spindle (30). Calibration of the device is achieved by adjusting the depth of engagement between the drive screw (12) and the diaphragm head (7) thereby eliminating the need for a conventional calibration screw mechanism.

Description

IMPROVEMENTS TO THERMOSTAT CONTROL DEVICES

Field of the Invention

The present invention relates to thermostatic control devices, particularly electro-mechanical thermostat devices such as temperature limiters or thermally operated switches for the control of power to a load. The invention more particularly relates to thermally operated switches which include a temperature-sensing probe coupled to a bellows or diaphragm, the movement of which causes the connection and disconnection of an electrical circuit, thereby regulating the operating temperature of domestic or commercial heating systems or boilers and cooking appliance loads, such as hot plates, hobs, grills, ovens and the like.

Background to the Invention

There are a wide variety of theniially operated switches, however, in the field of thermal control of domestic and commercial heating systems or boilers and cooking appliance controls, a familiar type of control is traditionally used. Such controls have a rotatable user control for setting the temperature at which switching is to occur and a temperature sensor within or adjacent the boiler, oven, grill or the like. The temperature sensor comprises a probe including phial of expansible fluid. The phial communicates with a sealed unit located within the body of the control device via a capillary system. The sealed unit comprises a diaphragm connected to an actuator.

Temperature changes sensed by the phial produces a change in the volume of the filling liquid or a pressure change in the filling gas or vapour. These expansion movements are communicated via the capillary system to the diaphragm where

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they are converted to a linear movement within the body of the control device causing the connection and disconnection of electrical contacts.

It will be understood by the skilled addressee that a reference to a temperature sensor or probe is intended to include other comparable means for effecting a temperature depended linear movement at a diaphragm or equivalent means known in the art. In the description which follows, reference to a hydraulic or fluid filled temperature sensor is not intended to be in any way limiting or to exclude other systems capable of effecting temperature dependent linear movement.

Exemplifying of prior art control devices is an electro-mechanical thermostat device such as that produced by the present Applicant (Diamond H Controls Limited, 40TH and 50TH Series thermostat controls). Hydraulic expansion of a fluid within a probe is used to produce a mechanical action within a control housing. The effect of the mechanical action (which is small) is regulated by a cam surface to adjust the sensitivity of a spring switch mechanism to the action produced by the fluid expansion. In such devices the temperature range over which accurate detection andlor reguJation is relatively small (say 50 350C) and response times may be slow. More particularly, the component count and the manufacturing tolerances for the hydraulic circuit within such controllers tend to make them particularly expensive.

The thermal expansion of the hydraulic fluid is converted to mechanical movement by the separation of opposed diaphragm walls (or skins) and the movement is transmitted via an actuator element or striker arrangement to engage a switch blade. The force applied to the switch blade results in an electrical connection being broken and establishing an electrical separation between contact terminals.

Normally, the striker arrangement comprises a lever system where a diaphragm head on the moving wall or skin of the diaphragm actuates one side of a lever which transfers the diaphragm head movement to a striker element, which in turn breaks the switch blade from electrical contact with a load terminal. Electrical --)-power to a load is then broken. The temperature at which the movement of the diaphragm head actuates the switch blade is dependent on the position of an actuator element or striker, the position in turn being controlled via the rotatable user control knob.

Each of the known controls ("profile cam" and "lead screw") has disadvantages associated with reliability, component count and cost which are immediately apparent to those skilled in the art.

Calibration of sensors due to manufacturing inconsistencies and the sensitivity of known sensors and the components to which they are connected also increase the end costs to a user. Devices which are self-calibrating or those which are manufactured to have specific fixed response characteristics are desirous but often unrealisable. Most typically, calibration of the thermostat control is made either via a calibration screw on the lever or an adjustment screw machined into the striker or actuating element.

One of the perceived disadvantages from the perspective of an appliance designer and an end user of existing lead screw thermostat control devices is that there is axial movement of the control knob to and from a mounting plate or face as the control knob is rotated. The axial movement occurs when the control spindle abuts control surfaces within the thermostat device housing and these movements cause a visible gap between the knob and the mounting plate or face.

A further disadvantage is the complexity of components required to ensure connection between electrical contacts remain broken even when ambient room temperature falls substantially, for example, to -20C (minus 20 degrees Centigrade). Thus, there remains a requirement for a guaranteed safe "OFF" position.

It is an object of the present invention to seek to alleviate the disadvantages associated with such prior art thermostatic cojitrol devices and to provide an improved electro-mechani cal thermostat control device.

it is a particular object of the invention to provide a lead screw thermostat control device having no externally perceived axial movement at the control knob during rotation thereof Et is a further object of the invention to provide a thermostat control device having direct linear action between a diaphragm and a switch actuator element and to reduce overall component count to improve reliability and decrease cost.

It is a yet further object of the present invention to provide a thermostat control device having a guaranteed safe "OFF" position at low ambient temperatures It is i yet further object of the present invention to provide simplified calibration 0 of the control device and to eliminate the calibration screw mechanism used on

prior art devices.

Summary of the Invention

Accordingly, the present invention provides a thermostat control device comprising: a housing; a resiliently deformable member in operable connection with a temperature sensor; a drive screw axially moveable under the influence of the deformable member in response to temperature changes at the sensor: and a rotatable user control spindle in communication with and adapted to move the drive screw with respect to the deforrnable member, wherein the deformable member operably moves the drive screw to bring a striker arrangement into and out of engagement with a nioveable contact to "break" and "make" electrical connection with a fixed contact.

Conveniently, the resiliently deformable member comprises a diaphragm having a profiled diaphragm head adapted to engage the drive screw.

In a preferred arrangement, the drive screw has an externally threaded end which mates with an internally threaded cylindrical portion of the diaphragm head, so that the axial position of the drive screw is determined by the depth of threaded reception within said threaded portion of the diaphragm head.

Advantageously, the depth of threaded reception of the drive screw within the diaphragm head is determined by the rotational adjustment of the user control spindle.

Preferable, the rotatable user control spindle receives a tabbed end of the drive screw within a receiving slot thereof allowing rotation of the drive screw with respect to the deformable member without imparting axial movement to the user control spindle.

Preferably, the striker arrangement comprises a collar located on the drive screw and includes an actuating surface thereon which engages a switch blade carrying the nioveable contact.

In an advantageous arrangement, the collar includes an overthrow surface adapted to engage a striker pin extending radially from the drive screw, so as to provide additional axial movement to the collar with respect to the drive screw to maintain a "break" position.

Ideally, the switch blade carrying the nioveable contact comprises a leaf spring element having an over-centre snap action.

Advantageously. calibration of the device is achieved by adjusting the depth nf engaierneiit between the drive screw and the diaphragm head, thereby eliminating the need fbr a conventional calibration screw mechanism.

Calibration may also be achieved by adjusting the interface of the temperature sensor (specifically it's capillary system) and the diaphragm, whereby an offset value for the deflection of the diaphram at a given temperature is selected.

User settings are selected by means of a control knob secured on the control spindle to which a stop plate is fixed. A radial projection on the stopplate abuts a control surface in the housing to limit rotation of the control spindle.

Ideal]y, rotation of the control spindle has a range of from 0 to 330 angular degrees.

Brief Descriptjoi-i of the Drawings The Invention will now be described more particularly with reference to the accompanying drawings which show, by way of example only, one embodiment of thermostat control device in accordance with the invention. In the drawings: Figure 1 is a sectional side elevation of the control device; Figure 2 is a detailed sectional side elevation of striker overthrow feature; and Figure 3 is an exploded assembly view of the control device.

Detailed Description of PrefelTed Embodiments

Referring to the drawings and initially to Figure 1, a thermostat control device denoted generally by reference numeral 1, comprises a main housing 2 to which there is attached a diaphragm assembly 3 defining the base of the housing. The diaphragm assembly 3 comprises a diaphragm 4 in sealed communication with a thermal probe 5 which indude a phial of expansible fluid, such as hydraulic liquid known in the art. The liquid is constrained within a capillary system 6 so that thermal expansion of the hydraulic liquid is converted to movement at the diaphragm 4.

The diaphragm 4 includes a diaphragm head 7 which has an internally threaded cylindrical receiver 8 into which a correspondingly threaded end 11 of a drive screw 12 is operably engaged. Thus, the axial position of the drive screw within the housing is determined by the depth of threaded reception within said threaded receiver 8.

Along the axial length of the drive screw 12 a striker assembly comprises a collar 15 seated on a radial land or shoulder 16 of the drive screw 12 and includes an activating surface adapted to abut the underside of a switch blade 17 carrying a first electrical contact 18 which is brought into and out of electrical connection with a second static electrical contact 19, defining "make" and "break" conditions.

thereby defining the switch mechanism.

The switch blade 17 comprises a leaf spring element anchored at one end and has an over-centre snap action to facilitate automatic resetting thereof when the actuating surface of the collar is no longer in abutting contact.

The striking collar 1 5 also includes an overthrow feature operating between the drive screw 12, the striker collar 1 5 and the switch blade 1 7 to assure the switch blade does not re-establish electrical contact in low ambient temperatures (typically determined to be in the region of -20C), without human intervention, to provide a guaranteed safe "OFF" position. As shown in detail in Figure 2. an overthrow surface 22 on the underside of the striker collar 15 abuts a pin 23 extending radially from the drive screw so as to provide additional axial movement to the collar with respect to the drive screw 1 2 to maintain a "break" position.

A top portion 20 of the housing provides an electrical insulator and protection of the switch mechanism within the main housing 2 and the first and second external connecting terminal tabs (not shown) are secured in the main housing 2. The line terminal is further mechanical supported by the top portion 20 to prevent movement, At the other end of the drive screw 12. a flattened axial region is formed to provide a tab 25 adapted to slidingly engage with a receiving groove 27 of a user control spindle 30. The user control spindle 30 is rotatable within a hearing 32 which is retained within a fixing plate 33 which in turn is secured during assembly to the top portion 20 of the housing, as illustrated in Figure 3.

The depth to which the threaded end 11 of the drive screw 12 is engaged in the diaphragm head receiver 8 is determined by the rotational adjustment of the user control spindle 30. As the drive screw 1 2 moves, its axial movement is taken up within the receiving groove 27, thereby eliminating any axial movement to the user control spindle 30. User settings are selected on a control knob (not shown) which is secured to the free end of the user control spindle 30. A stop plate 35 is fixed to the control spindle to limit the range of rotation of the control knob to between 0 and 330 angular degrees. The limitation is realised by having a radial projection on the stop plate which abuts a control surface within the fixing plate 33 or the top portion 20 of the housing.

In use, the temperature probe 5 is located within or adjacent an oven, boiler or any other body the temperature of which is to be regulated by the thermostatic control device I connected to an electrical load, specifically a heater circuit. When the temperature increases, the hydraulic fluid in the probe 5 expands and via the capillary system 6 forces the diaphragm 4 to expand. This expansion is transmitted into linear movement at the diaphragm head 7 and from there through the drive screw 1 2. As the position of the diaphragm head 7 is predetermined by the expansion of the hydraulic fluid at any given temperature (within in operational range), the relative position of the drive screw 1 2 with respect to the other components of the control device (and particularly the switch blade 1 7) is determined by the depth to which the threaded end 11 of the drive screw 12 is retained within the correspondingly threaded receiver 8 of the diaphragm head 7.

This critical depth is in turn determined by the rotation of the user control spindle which slidingly in the axial direction engages the opposite end 25 of the drive screw 12. The sliding relationship between the drive screw and user control spindle means that the axial movement of the drive screw is not transferred to the user control spindle 30. Thus, the user control spindle can be fixed in the axial direction so that there is no increase or decrease in gap presented between the control knob (not shown) and the fixing plate 33 during rotation of the control knob to determine the temperature at which the striker arrangement, attached to the drive screw activates the switch blade 17, thereby breaking electrical contact between the load contacts 18,19.

In the light of this disclosure, modifications of the described embodiment, as well as other embodiments, will now become apparent to persons skilled in this art.

It will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible within the scope of the appended claims.

Claims

CLAIMS: I. A thermostat control device comprising: a housing; a resiliently deformable member in operable connection with a temperature sensor; a drive screw axially moveable under the influence of the deformable member in response to temperature changes at the sensor; and a rotatable user control spindle in communication with and adapted to move the drive screw with respect to the deformable member, wherein the deformable member operably moves the drive screw to bring a striker arrangement into and out of engagement with a moveable contact to "break" and "make" electrical connection with a fixed contact.
2. A thermostat control device as claimed in Claim 1. in which the resiliently deformable member comprises a diaphragm having a profiled diaphragm head adapted to engage the drive screw.
3. A thermostat control device as claimed in Claim I or Claim 2, in which the drive screw has an externally threaded end which mates with an internally threaded cylindrical portion of the diaphragm head, so that the axial position of the drive screw is determined by the depth of threaded reception within said threaded portion of the diaphragm head.
4. A thermostat control device as claimed in Claim 3. in which the depth of threaded reception of the drive screw within the diaphragm head is determined by the rotational adjustment of the user control spindle.
5. A thermostat control device as claimed in any one of the preceding claims.in which the rotatable user control spindle receives a tabbed end of the drive -ii-screw within a receiving slot thereof allowing rotation of the drive screw with respect to the deformable member without imparting axial movement to the user control spindle.
6. A thermostat control device as claimed in any one of the preceding claims, in which the striker arrangement comprises a collar located on the drive screw and includes an actuating surface thereon which engages a switch blade carrying the moveable contact.
7. A thermostat control device as claimed in Claim 6. in which the collar includes an overthrow surface adapted to engage a striker pin extending radially from the drive screw, so as to provide additional axial movement to the collar with respect to the drive screw to maintain a "break" position.
8. A thermostat control device as claimed Claim 6 or CIaim7, in which the switch blade carrying the moveable contact comprises a leaf spring element having an over-centre snap action.

1 5
9. A thermostat control device as claimed in any one of Claims 2 to 8, in which calibration of the device is achieved by adjusting the depth of engagement between the drive screw and the diaphragm head, thereby eliminating the need for a conventional calibration screw mechanism.
1 0. A thermostat control device as claimed in any one of the preceding claims.in which calibration is achieved by adjusting the interface of the temperature sensor and the diaphragm, whereby an offset value for the deflection of the diaphragm at a given temperature is selected.
11. A thermostat control device as claimed in any one of the preceding claims.in which user settings are selected by means of a control knob secured on the control spindle to which a stop plate is fixed.
1 2. A thermostat control device as claimed in Claim 11, in which a radial projection on the stop plate abuts a control surface in the housing to limit rotation of the control spindle.
13. A thermostat control device as claimed in any one of the preceding claims, in which rotation of the control spindle has a range of from 0 to 330 angular degrees.
14. A thermostat control device substantially as herein described, with reference to and as shown in the accompanying drawings.