GB2123147A - Thermostatic control - Google Patents

Abstract

A thermostatic control has a bellows or other temperature responsive actuator (2) acting on a lever (6) in opposition to a first spring (9), and a second spring (20) acting upon the lever (6), in opposition to the first spring (9), through a latchable switch operating member (16) which forms part of a manually operable latching mechanism (28). In a reset or unlatched condition, for normal cycling operation, the switch (15) is opened and closed at sensed temperatures which are predetermined by the opposed forces exerted on the lever (6) by the two springs (9, 20), while in the latched condition of the mechanism (28) the operating member (16) is latched to remove it from engagement with the lever (6), resulting in a single switching cycle, governed solely by the first spring (9), which is terminated by the automatic resetting of the latching mechanism (28) at a sensed temperature higher than the range of normal cycling operation. <IMAGE>

Description

SPECIFICATION Thermostatic control This invention relates to thermostatic controls, and in particularthermostaticcontrols suitableforheating appliances orfor refrigeration apparatus, in which normal cycling control can be suspended by manual intervention to cause the thermostatic control to cycle at a highertemperature than its normal working range.

An object of the present invention is to provide a thermostatic control ofthe aforesaid type which is semi-automatic in that, following manual intervention to cause a single cycle at a higher temperature than the normal working range, the control resets automaticallyto its normal working mode.

According to the present invention there is provided athermostatic control comprising a temperature responsive actuator acting on a lever in opposition to a first spring, a second spring acting upon the lever, in opposition to the influence thereon ofthe first spring, through a latchable switch operating member which forms part of a manually operable latching mechanism having a reset or unlatched condition, for normal cycling operation, in which the switch is opened and closed at sensed temperatures which are predetermined bythe opposed forces exerted on the lever by the two springs, and having a latched condition in which it latches the said member to remove itfrom engagement with the lever, resulting in a single switching cycle governed solely bythefirst spring, which is terminated by the automatic resetting of the latching mechanism at a sensed temperature higher than the range of normal cycling operation.

The control according to the invention has the advantage of mechanical simplicity in that the latching mechanism can be operated manually by, for example, a simple push button. Oncethe latching mechanism has been operated into its latched condition, removing the latchable memberfrom engagement with the lever, the operation of the switch is thereafter prevented until the latching mechanism has been reset. In a preferred embodiment of the invention the latching mechanism is retained in its latched condition by the lever itself until the termination of the single high temperature switching cycle.

As applied to a heating appliance, or an appliance incorporating heating elements, such as, for example, a washing machine or oil burner, the switch operating member controls a switch which is normally closed and which, in normal cyclic operation of the control, is opened in response to a predetermined sensed temperature dependent upon theforces of the two springs, and in which manual operation of the latching mechanism causes the switch to be closed and subsequentlyto be reopened, in response to a temperature higher than said predetermined temperature, only after resetting of the latching mechanism.

Applied in this way the thermostatic control according to the invention allows a user to select at will, by manual operation of the latching mechanism, a single cycle in which the appliance operates to a higherthan normal temperature, for example upon initially switching on a heater or boiler, following which the control reverts automatically to its normal cycling operation.

The thermostatic control according to the invention also finds practical application in controls for refrigerators, in which case the switch operating memberwould control a switch which, in normal cyclic operation of the control, is opened and closed in response to predetermined lower and uppertemperatures defining a normal working range, and in which manual operation ofthe latching mechanism causes the switch to be opened, the switch being subsequently reclosed, in response to a sensed temperature higher than said uppertemperature ofthe normal working range, only after resetting ofthe latching mechanism.Manual operation ofthe latching mechanism results in a single defrosting cycle in which the refrigeratortemperature, normally sensed in the vicinity of the evaporator, reaches a predetermined temperature (forexample justabove 0 C), allowing defrosting ofthe refrigerator evaporator before the thermostat reverts, automatically, to its normal cycling mode.

In preferred embodiments of the invention the force exerted in the lever bythe second spring through the latchable member is adjustable by means of a setting camwhich predeterminesthetemperature range of normal cycling operation ofthe control. When the latching mechanism is operated to disengagethe latchable memberfrom the lever, the force exerted on the lever by the first spring will be independent ofthe setting of the cam, so thatthe temperature reached in the single switching cycle resulting from manual latching ofthe member is independent of the cam setting of the control.

Preferably the latchable member acts on the switch through a displaceable plunger which is operable, at the termination of a said single switching cycle, by the lever acting directly on said plunger. The plunger may for example be carried by and slidable relative to the lever, the plunger having a head orflangewhich is engaged by the lever atthe termination of a said single switching cycle.

The invention will be further described, by way of example only, with reference to the accompanying drawings, in which Figures 1 and 2 are purely diagrammatic sectional views of a thermostatic control according to one embodiment ofthe invention, showing respectively the normal cycling condition, and the latched condition for a single high temperatureswitching cycle.

The thermostatic control illustrated in the drawings is intended for use with a refrigator. The control has a housing 1 one wall of which supports a bellows device 2 constituting a temperature responsive actuator. The bellows device2 communicatesthrough a capillary tube 3 with a bulb 4 which, with the bellows 2, forms a sealed system which isfilled with vapour in equilibrium with a small quantity of liquid, in a conventional manner. The bellows device has a displaceable central button 5which acts on one end of a first lever 6. The lever 6 is pivoted intermediate its ends in the side walls ofthe housing 1,the leverfulcrum being indicated by reference numberal 7 in the drawings.

The lever 6 has an upstanding arm 8to which one end of a first tension spring 9 is attached, the other end of the spring 9 being anchored to a screw-adjustable anchorage located in an end wall of the housing 1. The spring 9 exerts a moment on the lever 6 urging the latter into contact with the displaceable button 5 ofthe bellows device 2.

At its end opposite that which is acted upon by the bellows device 2 the first lever 6 has an aperture 11 which guides the sliding movement of a switch operating plunger 12 of insulating material. The plunger 12 is formed with an enlarged head 13 at its lower end which is larger in diameter than the guide aperture 11. The head 13 bears upon the operating element 14 of a switch 15. In the illustrated embodi menttheswitch 15 has normally open contacts (not shown) which are closed upon depression of the operating element 14.

A latchable second lever 16 is pivoted at one end in the side walls ofthe housing 1 about a fulcrum 17 and is formed at its opposite end with a heel 18 which bears againstthefirst lever 6. Adjacent the heel 1 8the lever 16 is provided with an upstanding arm 19 which provides an anchoragefor one end of a second tension spring 20, the other end of which is anchored to a cam slider 21 through an adjustable screw connection 22. The cam slider 21 is maintained bythe tension in the spring 20 in engagement with a peripheral cam surface carried by a cam disc 23 carried on the inner end of a cam setting shaft 24 which is rotatably mounted in a bush 25 affixed to a wall ofthe housing 1.

The second lever 16 is provided at its pivoted end with a lift arm 26 which cooperates with an operating arm 27 of a latch lever 28. The latch lever 28 is pivoted in the side walls of the housing 1 about a fulcrum 29 and in addition to the operating arm 27 has a trip arm 30 which projects towards the cam setting shaft 24, a latch arm 31 which projects towards the first lever 6, and a biassing arm 32 which provides an anchorage for one end of a helical biassing spring 33, the other end of which is anchored to the housing 1.

A push rod 34 is slidable in an axial bore ofthe cam setting shaft 24 and carries at its outer end a push button 35. At its inner end the push rod 34 has a foot 36 which is engageablewith the trip arm 30 ofthe latch lever 28, the trip arm 30 being maintained in engagementwith the push rod 34 by the tension in the biassing spring 33.

The illustrated control has a normal cycling mode of operation, illustrated in Figure 1, in which the second lever 16 is unlatched by the latch mechanism constituted bythe latch 28 and the push rod 34. In this condition the operating arm 27 of the latch lever 28 is clear of engagement with the lift arm 26 ofthe lever 16, and the latter exerts a force on the first lever 6 through the tension in the second spring 20, this force exerting a moment onthefirst lever 6 which is opposed to the moment exerted by the first spring 9. The switch operating plunger 12 is maintained in engagement with the second lever 16 by virtue of the spring biassing force acting upon the switch operating element 14: in this condition the head 13 of the plunger 12 is clear of engagement with the first lever 6.

In normal cycling operation (Figure 1 ) the operation of the switch 15 is controlled by the second lever 16 acting on the switch operating element 14through the insulating plunger 12. Switch operating movement of the second lever 16 is effected by the first lever 6 in response to temperature changes sensed by the bellows device 2, the switch operating movement of the second lever 16 being influenced by the two springs 9 and 20 acting in opposition to each other.

The temperatures at which the switch 15 is closed and opened in normal cycling operation ofthecontrol will, therefore, be determined by the difference between the forces exerted by the two springs 9 and 20 acting together.Thetemperature range of normal cycling operation can be predetermined by adjusting the tension ofthe spring 20 by rotation ofthe cam setting shaft24, which would normallycarryaknobcooperat- ing with a graduated scale (not shown). Movement of the switch operating plunger 12 acted upon by the second lever 16 is guided bythe sliding ofthis plunger 12 in the aperture 11 ofthefirst lever 6.

When it is desired to effect a single switching cycling at a highertemperature, in the illustrated exampleforthe purpose of defrosting the refrigerator, the push button 35 is depressed, causing the latch lever28to be rotated anti-clockwise, as viewed in the drawings, into the latched condition shown in Figure 2. This latching operation causes the second lever 16 to be lifted out of engagement with the first lever6 by engagement of the operating arm 27 with the lift arm 26 ofthe lever 16, while atthe sametimethe latch arm 31 engages a heel 37 atthe adjacent end of the first lever 6, effectively locking the latching mechanism, includingthe lever 16, in its latched position.The disengagement of the lever 16 from the plunger 12 allows the switch 15to adopt its normally open condition, commencing a defrost cycle. The lever 27 is maintained in its latched positioned bythetension of the springs 33 and 20.

In the latched condition (Figure 2) the first lever 6 is acted upon solely by the spring 9, which has a fixed pre-adjusted tension. The resultant moment exerted upon the lever 6 will therefore be greater than that exerted in the normal cycling mode, when the two springs 9 and 20 act in opposition to each other.

Accordingly, the bellows device 2 will have to sense a highertemperature in orderthattheforce exerted on the lever6 bythe bellows device2 can overcome the force exerted bythe spring 9. When this higher temperature, which is predetermined by adjustment of the tension ofthe spring 9, is reached,thefirst lever 6 will be rotated clockwise sufficiently to disengage the heel 37 of the lever 6from the latch arm 31 of the lever 28. This immediately causes the latch mechan ismto resetundertheaction ofthespring 33 and to resumethe position illustrated in Figure 1. Once the latch mechanism has reset, the switch 15 is operated by the lever 16, and the control then reverts to its normal cycling mode as described previously.

In the application ofthe illustrated thermostatic control to a heating appliance, oran appliance incorporating a heater, such as a boiler, washing machine or space heater, the control would function in exactly the same manner as that described above, butthe switch 15 would be of a different type, having normallyclosed contactswhich are opened upon depressian of the switch operating element 14. In this case the normal cycling mode of the thermostatic control will?again be interrupted by depression of the push button3S,which will have the effect of latching the lever 16, asdescribed previously and as illustrated in Figure 2. VERh the lever 16 latched the switch 15 will adopt its normally closed condition and the associated heater will be energised to perform a single cycle to a highertemperaturethanthatto which the thermostat shaft24 is set.When this higher temperature is reached, thebellows device 2 will have rotated the lever 6 sufFiciently againstthe action ofthe biassing spring 9to disengage the heel 37 from the latch arm 31, resetting the latch mechanism as described previously. Normal cycling operation of the thermostat then resumes.

An important characteristicofthethermostatic control as described and illustrated is that, once the switch operating lever 16 has been latched by depression ofthe push button 35 the associated switch 15 cannot be prematurelyoperated by the lever 6 until the predetermined high temperature of the single switching cycle has been reached. This is because, in normal operation of the control (Figure 1) the head 13 oftheswitch operating plunger 12 is spaced from the lever 6, the plunger being acted upon bythe operating lever 16. Once the lever 16 has been latched the lever 6 tends to rotate anticlockwise (as depicted), underthe influence ofthe spring 9, the counteracting effect of the spring 20 being removed.

This further spaces the lever 6 from the head 13 ofthe plunger 12; upon the subsequent rise in temperature, when the lever 6 rotates (clockwise as depicted) to a position corresponding to the normal operating point of the switch, 15, the lever abutsthe head 13 ofthe plunger 12, as shown in Figure 2, butthe switch 15 is still not operated, because, in normal operating conditions, with the lever 6 in this position, the head 13 is spaced from the lever 6 bytheengagement of the leverl6withthe plunger 12.

The clearance between the head 1 3 of the plunger 12 and the lever 6 in normal operation therefore represents a safety margin: this clearance has to be taken upbythe lever6acting alone beforethelatch mechanism can reset, so that operation ofthe switch is effectively precluded until the defrost temperature has been reached and the latch has been reset. This clearance also compensates for the tolerances which inevitably arise in mass production.

As applied to a refrigeratorthermostatwith a push-button defrost facility, the thermostatic control ofthe present invention affords the practical advantage that the defrost temperature reached is determined by the setting of a single spring (spring 9) and can therefore be preset with some accuracy, normally within + 1 K.

Claims (8)

1. Athermostatic control comprising a temperature responsive actuator acting on a lever in opposition to a first spring, a second spring acting uponthe lever, in opposition to the influence thereon of the first spring, through a latchable switch operating member which forms part of a manually operable latching mechanism having a reset or unlatched condition, for normal cycling operation, in which the switch is opened and closed at sensed temperatures which are predetermined by the opposed forces exerted on the lever by the two springs, and having a latched condition in which it latches the said member to removeitfrom engagementwiththe lever, resulting in a single switching cycle, governed solely bythefirst spring,which is terminated by the automatic resetting ofthe latching mechanism at a sensed temperature higher than the range of normal cycling operating.

2. Athermostatic control according to Claim 1, in which the latching mechanism is retained in its latched condition by the lever itself until the termination ofthe single high temperature switching cycle.

3. Athermostaticcontrol according to Claim 1 or Claim 2,forcontrolling a heating appliance, oran appliance incorporating at least one heating element, in which the switch operating member controls a switch which is normally closed and which, in normal cyclic operation ofthe control, is opened in response to a predetermined sensed temperature dependent upon the forces ofthetwo springs, and in which manual operation ofthe latching mechanism causes the switch to be closed and subsequently to be re-opened, in response to a temperature higher than said predetermined temperature, only after resetting ofthe latching mechanism.

4. Athermostaticcontrol according to Claim 1 or Claim 2, for controlling a refrigerator, in which the switch operating member controls a switch which, in normal cyclic operation of the control, is opened and closed in response to predetermined lower and upper temperatures defining a normal working range, and in which manual operation ofthe latching mechanism causes the switch to be opened, the switch being subsequently reclosed, in response to a sensed temperature higherthan said uppertemperature of the normal working range, only after resetting ofthe latching mechanism.

5. Athermostatic control according to any of Claims 1 to 3, in which the latchable member acts on the switch through a displaceable plungerwhich is operable, at the termination of a said single switching cycle, bythe lever acting directly on said plunger.

6. The thermostatic control according to ClaimS, in which the plunger is carried by and is slidable relative to the lever and has a head orflange which is engaged bythe leveratthetermination of said single switching cycle.

7. Athermostatic control according to any one of Claims 1 to 6, in which the force exerted on the lever by the second spring through the latchable member is adjustable by means of a setting cam which predeterminesthetemperature range of normal cycling operation ofthe control.

8. Athermostatic control substantially as herein described with reference to and as shown in the accompanying drawings.