CA1061386A - Temperature or pressure responsive switch units - Google Patents

Abstract

ABSTRACT
A control switch unit adaptable for a number of different purposes has a fluid-filled flexible-walled capsule acting within a housing on a pivoted operating lever arranged to operate a switch located in the housing on the other side of the pivot axis of the lever from the capsule, the lever being biased by a cam-adjustable tensioning spring acting on the opposite side of the operating lever from the capsule and the switch.
Further components such as a manual switch-off control, a pilot lamp operable by an auxiliary switch, or a capsule heater, can be added without rearrangement of the basic unit.

Description

3L06:13~3~

2 This invention relates to control switch units.

3 More particularly the invention concerns temperature

4 or pressure responsive switch units in which a switching

5 operation is effected in response to deformation of a

-6 fluid-filled flexible-walled capsule or power element.

7 A known type of such a control switch unit comprises

8 a housing, a fluid-filled flexible-walled power element

9 or capsule mounted within the housing, an operating

10 lever pivotally mounted in the housing and arranged to

11 operate a switch located in the housing in response to

12 deformation of the capsule, a tension spring located

13 within the housing and acting on the operating lever, i14 the tension spring exerting a moment on the lever in J15 opposition to that exerted thereon by the capsule, and 16 cam means ~or adjusting the tension in the spring to 17 predetermine the operating point of the switch in 18 response to deformation of the capsule.
19 An object of the present invention is to provide 20 a switch unit of the aforesaid type which is of simple 21 construction and assembly while being versatile in 22 its practical applications, and capable of adaptation to 23 a variety of dlfferent uses without radical modification.

25 According to the present invention there is provided 26 a control switch unit comprising:
27 - a housing having a housing wall;
28 - a fluid-filled power element mounted within the 29 housing opposite said housing wall;
30 - an operating lever pivotally mounted in the housing 31 and cooperating with the power element;
32 a switch located in the housing and cooperating with ... .

i :~i 3`l~
1 the operating lever to be operated by the power element 2 through the lever,both the power element and the switch 3 being disposed on the same side of the operating lever 4 and on opposite sides of the pivot axis of the lever;
- a tension spring located within the housing and 6 acting on the opposite side of the operating lever from 7 the power element and the switch, said tension spring 8 exerting a moment on the lever in opposition to the 9 power element;
- cam means acting upon the spring to adjust the 11 tension thereof and to predetermine the operating point 12 of the switch under control of the power element; and .7 13 - a setting shaft connected to the cam means for

14 adjustment of the latter, said setting shaEt being .
rotatable in said housing wall.
16 The arrangement of the switch unit with the cam 17 setting shaft in the wall of the switch housing opposite 18 the power element and the switch itself, with the operating 19 lever pivoted between the power element and the switch, lends itself to easy assembly of the switch unit and 21 moreover can, in preferred embodiments of the invention, 22 leave adequate space within the housing for ancilliary 23 switches or switch operating members, without the necessity 24 to modify the basic components of the switch unit.
Preferably the axis of the setting shaft is perpendicular 26 to the pivot axis of the operating lever.
27 In preferred practical embodiments of the invention 28 the tension spring comprises a helical spring the longitudinal 29 axis of which extends generally-parallel to the operating lever, the spring being anchored at one end to a protuberance 31 on the operating lever and at its other end to a slider 32 which is movable in the direction of the longitudinal axis '; ' ' . . ''''' ~ , ~ , .

~61;~86 1 of the spring under control of the cam means.
2 The cam means permit fine adjustment of the tension in 3 the spring and, therefore, the operating point of the switch, 4 that is, the temperature (or pressure) sensed by the power element at which the switch is operated.
6 It will be understood that in the present context 7 the term "power element" connotes any fluid-filled flexible-8 walled device, such as a bellows, capsule or diaphragm, which 9 exhibits a deformation in response to changes in internal pressur-e, usually associated with temperature changes at a 11 remote sensing point to which the device is connected through 12 a capillary tube. The control switch unit according to the 13 invention would not necessarily be employed for sensing 14 temperature in this way: the switch unit could for example be employed as a pressure responsive switch, in which case 16 the pressure to which the switch unit responds would be 17 the fluid pressure within the power element.
18 To permit adjustment of the setting rangeof the cam 19 means the tension spring preferably has a screw-adjustable anchorage to the cam-operated slider by means of which the 21 tension in the spring can be adjusted independently of 22 the adjustment thereof by the cam means.
23 The operating lever may comprise a plate which is 24 pivotally supported in opposite walls of the housing by lugs on the plate intermediate the points of engagement 26 of the lever with the power element and the switch.
27 The switch in preferred embodiments of the invention 28 comprises an electrically insulating base attached to 29 the housing and supporting a fixed switch contact and a snap-action switch blade carrying a switch contact 31 movable relative to the fixed contact, the switch blade 32 being engageable by the operating lever to effect snap-33 separation and/or snap-closure of the switch contacts.
34 Suitable snap-action switch blades for this purpose are described in Canadian Patent Application Serial No.
36 241734 filed December 15, 1975.
37 Preferably the separation of the switch contact in the 38 open condition of the switch is adjustable by means of 39 an adjustment screw accessible from the outside of the housing. This so-called "differential" adjustment screw ,,'. ' .~., . .
,i ., :

106~86 1 would serve to ad]ust the temperature range (or pressure 2 range in the case of a pressure responsive switch) between 3 the opening and the closing of the switch contacts. In 4 a preferred practical arrangement the snap-action switch blade has a fixed mounting on the insulating base 6 and projects cantilever-fashion from its fixed mounting 7 in a direction generally parallel to the pivot axis of 8 the operating lever.
9 The switch unit according to the invention may be adapted to perform more than one switching operation.
11 For example, in a preferred embodiment, in which the cam 12 means comprises a cam disc located within the housing 13 and attached to a rotatable cam setting shaft pro~ecting 14 from the housing an auxiliary cam may be mounted on the same shaft as the cam disc, this auxiliary cam acting 16 through a cam following lever mechanism on an auxiliary 17 switch within the housing connected in series with the 18 first switch. This auxiliary switch would normally be 19 carried on the same insulating base as the first switch.
The lever mechanism cooperating with the auxiliary 21 cam may, for example, comprise a bell-crank lever 22 one arm of which is engageable by the auxiliary cam 23 and the other arm of which has a hinge connection to 24 a plunger which is displaceable longitudinally within the housing for engagement with an operating part of 26 the auxiliary switch. Preferably both the bell-crank 27 lever and the plunger are formed of plastics material, 28 the hinge connection between the bell-crank lever and 29 the plunger consisting of an irtegral ~lexible portion ,. ~ . . .
: . . ..

~L~61386 1 of the said plastics material.
2 For some practical applications it may not be necessary 3 to provide an externally adjustable cam arrangement for 4 controlling the operating point of the switch, in which case the cam means may be dispensed with. A temperature 6 or pressure responsive switch unit according to such an 7 alternative embodiment of the invention comprises a 8 housing containing a fluid-filled flexible-walled 9 capsule secured to a wall of the housing, an operating lever pivotally mounted in the housing and arranged to 11 operate a switch located in the housing in response to 12 deformation of the capsule, the capsule and the switch 13 being disposed on the same side of the operating lever, 14 a hellcal tension spring acting upon the operating lever and extending generally parallel to the lever 16 on the opposite side thereof from the capsule and the 17 switch, and an adjustable anchorage for the end of the 18 tension spring remote from the operating lever, said 19 adjustable anchorage being connected to or abutting an external wall of the housing and being adjustable 21 from the outside of the housing, the operating lever 22 being pivotally supported in opposite walls of the 23 housing for rocking movement about a transverse pivot 24 axis perpendicular to the longitudinal axis of the helical tension spring.
26 A further lever may be pivotally mounted in the housing 27 and engageable by the switch operating lever in one 28 direction of rocking movement only of the latter, the ~6~;~86 1 further lever being biased by a spring of ad~ustable 2 tension. The biasing spring acting on this :Eurther 3 lever may have an anchorage at its end remote from the 4 further lever which is adjustable by a cam to predetermine the force which the further lever exerts on the switch 6 operating lever when engaged by the latter.

8 The invention will now be further described, by way 9 of example, with reference to the accompanying purely diagrammatic drawings, in which:
11 Figure l is a cross sectional view of a temperature 12 responsive control switch unit according to one embodiment 13 of the invention;
1~ Figure 2 is a partial section taken on line II-II
of Figure l illustrating the switch employed in the 16 switch unit of Figure l;
17 Figure 3 is a cross section of the switch, taken 18 on line III-III of Figure 2;
19 Figure 4 is a sectional view corresponding to Figure l of a modified version of the switch unit shown 21 in Figure l;
22 Figure 5 is a sectional view, corresponding to 23 Figure 3, of a modified switch employed in the switch 24 unit of Figure 4;
Figure 6 is a cross section of the modified switch, ~`
~ 26 taken on line VI-VI of Figure 5;
.. 27 Figure 7 is a cross sectional view corresponding 28 to Figure 2 of a switch employed in a switch unit `l 29 according to a further embodiment of the invention;
Figure 8 is a cross-sectiona.l view corresponding to ',.
..
. - 7 -.

' 6~L3~36 1 Figure 3, taken on the line VIII of Figure 7;
2 Figure 9 is a sectional view corresponding to 3 Figure l of a switch unit according to a further embodiment 4 of the invention, and Figure l0 is a sectional view of a modification 6 of the switch unit shown in Figure 7.

8 The basic control switch unit illustrated in 9 Figure l comprises a housing l formed by a pressed sheet metal frame 2 of U-shaped cross sectional form 11 partially closed on its open side by a pressed sheet 12 metal support plate 3. A power element cornprising a 13 flexible-walled fluid-filled capsule 4 is secured to 14 the support plate 3 and a switch assembly 5 is secured to the housing frame 2 and adjoins the support plate 16 3 to complete the closure of the open side of the frame l.
17 The switch assembly 5 wi1l be described in further 18 detail later with reference to Figures 2 and 3.
19 The switch unit of Figures l to 3 is a temperature-responsive unit. The capsule 4 comprises a vapour-21 filled bellows device formed by two flexible resilient 22 sheet metal walls welded together along adjoining edges 23 to form a sealed capsule which communicates through a 24 capillary tube 6 with a temperature sensing bulb 6a located at a point at which temperature is to be 26 sensed, the bulb, the capillary tube 6 and the capsule 27 4 forming a sealed fluid-filled system the pressure in 28 which is directly dependent upon the temperature 29 of the bulb. The walls of the capsule 4 deform in ~OEil3~36 1 response to changes in the internal pressure and, 2 therefore, in the temperature sensed at the bulb 6a.
3 This deformation is transmitted to a switch operating 4 lever 7 comprising a rigid metal plate pivotally supported in the frame 1 for rocking movement about a transverse 6 axis X. -7 The plate constituting the switch operating 8 lever 7 is not shown in the interests of clarity 9 in Figure 2. The plate has laterally projecting lugs 7a which engage in apertures in the side walls of the 11 frame 1 to define the pivot axis X of the lever 7.
12 On one side of the pivot axis X the lever 7 is 13 formed with a nose 8 which engages a boss 9 welded 14 to the central part of the capsule 4 and reinEorcing the latter so that deformation of the capsule walls takes 16 place in the region between the reinforcing boss 9 and 17 the outer periphery of the capsule. On the other side 18 of the pivot axis X the lever 7 is formed with a 19 protuberance 10, on the same face of the lever plate as the nose 8, which is engageable with an operating 21 tongue 11 (Figures 2 and 3) of a cantilever-mounted 22 snap-action switch blade 12 forming part of the 23 switch asse~bly 5.
24 On the opposite face of the lever plate from the protuberance 10, and on the same side of the pivot axis 26 X, the lever 7 is provided with an upstanding lug 13 27 which provides an anchorage for one end of a helical 28 tension spring 1~, the opposite end of which is anchored to a 29 nut carried by a presetting screw 15. The presetting screw 6~3l36 1 15 has a head 16 which is located in an aperture in a 2 bracket portion 17 of a cam slider 18, the head 16 of 3 the screw 15 being accessible for adjustment purposes 4 through an aperture 19 in an end wall of the housing 1, By adjusting the setting of the scre~J 15 the tension 6 in the spring 19 is adjustable thereby regulating the 7 biasing moment exerted on the switch operating lever 8 7, in an anti-clockwise direction as viewed in Figure 1, 9 and in turn controlling the force with which the lever 7 reacts against the capsule 4 through the boss 9.
11 The cam slider 18 is displaceable linearly in a 12 base wall of the frame 2 and has an end flange 20 which 13 is maintained by the tension spring 14 in engagement 14 with the outer edge of a disc-like cam 21. The cam 21 is attached to a cam setting shaft 22 which is rotatable 16 in a bush 23 secured in the base wall of the housing 17 frame 2, the shaft 22 projecting outwardly from the 18 housing 1. The axis of rotation of the shaft 22 is 19 perpendicular to the transverse pivot axis X of the switch operating lever 7 and also generally perpendicular to 21 the longitudinal axis of the helical tension spring 14.
22 The end of the lever 7 remote from the switch 23 assembly 5 is located in a slot 24 in an end wall of the 24 housing 1 to define the limits of pivotal movement of , 25 the lever 7 about the axis X-X. Ad]acent this end 26 the lever 7 is formed with an upstanding appendix 25 27 which is engaged by the flange 20 of the cam slider 28 in one position of the cam shaft 22 to operate the i ,, .

'' ~-` 106~6 1 switch 5 directly through the lever 7 in an "off"
2 position of the shaft 22.
3 The switch assembly 5 which forms part of the switch 4 unit is self-contained and is assembled separately and fitted to the switch housing 1. The switch assembly 6 5 is shown in Figures 2 and 3 and includes an insulating 7 base 26 moulded in plastics material. Two conductors 8 27, 28 are secured to the base 26 and terminate in 9 respective quick-connect terminals 29, 30 which project beyond the base 26. A fixed switch contact 31 (Figure 3) 11 is carried by the conductor 28 and cooperates with a 12 movable switch contact 32 carried by the snap-action 13 switch blade 12.
14 The snap-action switch blade 12 has an integral outwardly projecting tongue 33 by meansof which the 16 blade 12 is attached cantilever-fashion to the conductor 17 27 and thus to the base 26, the blade 12 extending 18 generally parallel to the base 26 and to the pivot axis 19 X of the lever 7.
The switch blade 12 has two arms 34, 35 which are 21 drawn together by crimping of an integral bridge portion 22 36 interconnecting the two arms remote from the tongue 23 33, thereby pre-stressing the blade so that it adopts 24 a dished deformation in the vicinity of the base of the two arms 34, 35 adjoining the tongues 11, 33. As a 26 result of this pre-stressing of the blade 12 the 27 arms 34, 35 will have a first stable position in which 28 the blade is dished in one sense and the arms 34, 35 are 29 both disposed on one side of the central tongue 11, . and a second stable position in which the blade is ' . ' ~ , ': ~ j ~ ~LCl 6~3~1~
1 dished in the opposite sense and the arms 34, 35 are 2 disposed on the opposite side of the central tongue 3 ll. The intermediate position in which the arms 34, 4 35 are coplanar with the central tongue ll is inherently 5 unstable, so that the blade will undergo snap-deformation 6 between the two stable positions.
7 The movable contact 32 is carried at the centre of 8 the bridge portion 36 and is so arranged relative to the 9 fixed contact 31 that upon snap-deformation of the blade 12 the contact 32 makes a snap movement relative to the 11 fixed contact 31, either in a switch opening or switch 12 closing sense.
13 In an alternative construction of the switch blade 14 12 the bridge portion 36 is constituted by the contact 32 itself, which may comprise a rectangular plate welded 16 to the two arms 34, 35 in such a way as to draw these 17 arms together and prestress the blade.
18 In the illustrated embodiment of thP invention the ¦ 19 switch blade 12 is itself conductive and carries current between the two conductors 27, 28 when the switch is 21 closed. In view of this, the switch operating lever 22 7 is provided with an insulating part 37 formed with the 23 switch operating protuberance lO, so that the switch 2~ operating lever and the associated mechanical parts of the unit are electrically insulated from the current i 26 carrying parts of the switch assembly 5.
'~ 27 In this example the switch assembly 5 is of the ,1 , "!
,.. . . .
, - 12 -.

. ' :, ~;
: .
.,; .

lL3~6 1 normally open type and the switch operating lever 7 2 acts through the protuberance lO on the switch operating 3 tongue ll, d~placing the latter towards the base 26 of 4 the switch (Figure 3) until a point of instability is reached when the switch blade 12 snaps towards its other 6 stable position, bringing the contact 32 into engagement 7 with the fixed contact 31. The position of the contact 8 31 is such that the switch blade 12 does not reach its 9 other stable position, and in conse~uence the central operating tongue ll of the switch blade remains biased 11 towards the operating lever 7. Upon release of the force 12 applied to the tongue ll by the operating lever 7, 13 therefore, the tongue ll moves progressively away from 14 the base 26 as the lever 7 rocks anti-clockwise (as viewed in Figure l) until the point of instability 16 of the blade 12 is again reached, when snap movement 17 of the blade again occurs, removing the contact 32 from 18 engagement with the fixed contact 31 towards its 19 other position of stability. In moving towards this other s-table position the contact 32 is arrested by 21 a stop constituted by a screw 38 which is located in 22 the base 26 of the switch. Adjustment of the screw 23 38 adjusts the gap between the switch contacts 31, 32 Z4 in the open condition of the switch, and the force with which the movable contact 32 abuts the screw 38.
26 This in turn adjusts the temperature differential, as 27 sensed at the bulb 6a connected to the capillary tube 6, 28 between the point at which the switch closes and the point 613~36 1 at which the switch subsequently opens. For this reason 2 the screw 38 will be referred to as the "differential 3 adjustment" screw.
4 By adjusting the angular setting of the cam setting shaft 22 the tension of the biasing spri.ng 14 is adjusted, 6 through the displacement of.the cam slider 18 by the 7 cam 21, and this in turn will adjust the biasing force 8 exerted by the lever 7 on the capsule 4. For each 9 angular setting of the shaft 22, therefore, there will correspond a different switch operating point, so that, 11 a different internal pressure in the capsule 4 and, 12 therefore, a different temperature sensed at the bulb 13 6a, will be necessary to operate the switch for each 14 different cam setting. By adjusting the presetting screw

15 at a given setting of the cam shaft 22 it can

16 be arranged that the switch is operated at a desired

17 temperature (or pressure) sensed by the capsule 4.

18 Thereafter, manual rotation of the cam sha-Et 22 will

19 select the temperature ~or pressure) at which the switch is operated.
21 As described and illustrated with reference to 22 Figures l to 3 the switch unit is particularly applicable 23 to the control of, for example, a refrigerator, in which 24 it is desired to close the switch 5, and thereby 25 energise the compressor motor of the refrigerator, when 26 the temperature sensed by the capsule 4 rises to a pre-27 determined level, and thereafter to open the switch 28 5, cutting off the motor, when the temperature as 29 sensed by the capsule 4 has fallen to a second, lo~er .

~ ' . '' 315~6 1 level. The switch unit will operate to maintain the 2 monitored temperature between the two levels. For 3 this application the cam shaft will carry a manual 4 operating element such as a knob rotatable between "warm" and "cold" settings to determine different 6 operating points for the switch. In addition the cam 7 shaft 22 will usually have an "off" setting corresponding 8 to engagement of the flange 20 of the cam slider 18 9 with the appendix 25 of the switch operating lever, such engagement causing anti-clockwise rocking of the lever 11 7 (as viewed in Figure l) to open the switch.
; 12 In the construction of the switch unit illustrated 13 in Figures l to 3 the capsule 4 is attached to the support 14 plate 3 by riveting or upsetting a cylindrical collar 39 welded to one of the Elexible plates of the capsule 4, 16 as illustrated in Figure l, the capsule 4 being held in 17 position by the abutment of a bulbous portion 40 of the 18 capillary tube 6 against the deformed collar 39.
19 The cam 21 is riveted onto the internal end of the cam shaft 22. The shaft 22 itself is located in 21 the housing l by the bush 23 which has an outer peripheral 22 lip 41 which, after assembly of the shaft 22 and the 23 cam 21 is deformed inwardly to abut a shoulder 42 formed 24 on the shaft 22.
The switch unit illustrated in Figures l to 3 is 26 a basic unit which can be modified to provide a "family"
27 of different switch units for performing a number of :
,.~
, - 15 -'.'' `:~
~, .

~ 613~3~
, ancilliary switching functions by the addition of further 2 components, and with minimal modification of the components 3 of the basic switch unit.
4 Figures 4 to 6 illustràte the modification of the basic switch unit to provide an additional switch, 6 incorporatea in the switch assembly 5, which is connected 7 electrically in series with the switch co~tacts 31, 32 8 of the main switch and serves as an auxiliary or 9 "ON/OFF" switch.
In the embodlment of Figures 4 to 6 the auxiliary 11 switch comprises a resilient spring blade 43 carrying 12 a switch contact 44 which normally engages a fixed 13 contact 45. A point 46 on the switch blade 43 is 14 engageable by a plunger 47 located within the housing l and guided for longitudinal displacement by a tab 48 16 projecting from and integral with the frame 2. The 17 plunger 47 has a hinge connection to a bell-crank lever 18 49 pivotally mounted within the housing l on a transverse 19 shaft 50. Both the bell-crank lever 49 and the plunger 47 are made of thermoplastics material and are connected 21 integrally to each other by a thin ligament 51 which 22 constitutes the hinge connection between the plunger 47 23 and the lever 49. The arm of the bell-crank lever 24 49 which is not connected to the plunger 47 is engaged by an auxiliary cam 52 carried by the same cam shaft 22 26 as the cam 21.
27 The arrangement is such that when the cam shaft 28 22 is rotated into an "OFF" setting the auxiliary cam ^ .

- 16 - .

. . . .

1~613~6 1 52 rocks the bell-crank lever 49 in a clockwise direction 2 as viewed in Figure 4, depressing the plunger 47 sufficiently 3 to displace the spring blade 43 of the auxiliary switch, 4 separating the contacts 44, 45 of the latter.
Since the embodiment of Figures 4 to 6 employs 6 a separate series switch to perform the "OFF" function 7 the raised appendix 25 of the switch operating lever 7 8 is truncated at 53 so that it is not engaged by either 9 of the cams 21, 52.
In both the embodiments described with reference to 11 Figures l to 3 and Figures 4 to 6 -the switch assembly 5 12 may include an auxiliary signal switch mounted on the 13 same base 26 as the main switch 5. A modification of 14 the switch assembly shown in Fiyures 2 and 3 to include an auxiliary signal switch is shown diagrammatically in 16 Figures 7 and 8. The auxiliary signal switch includes 17 a movable contact 54 carried by a cantilever spring 55 18 which is formed with a lateral arm 56 located beneath 19 the central operating tongue ll of the main switch blade 12 (Figure 7). The auxiliary switch has a fixed 21 contact 57 connected to an auxiliary swi-tch terminal 22 57'. The fixed contact 57 will be disposed either above 23 or below the movable contact 54, as viewed in Figure 7, 2~ according to whether the auxiliary switch is to be normally open or normally closed respectively. As 26 illustrated the auxiliary switch is normally open.
27 When the central tongue ll of the switch blade 12 28 is depressed by the action of the switch operating lever 7 ,' '~ \

. . . . . . . ~

:~113613~

1 the tongue ll engages the arm 56, causing the latter to 2 pivot about a fulcrum provided by an adjustment screw 58 3 screwed into the base 26 and thereby causing the movable 4 eontaet 54 to move into engagement with the fixed contaet 57. The eontacts 54, 57 of the auxiliary signal switch 6 can be used to monitor the operation of the main switch 7 in the event of an abnormal increase in temperature, 8 outside the normal range of operation of the main switch, 9 the temperature at which the auxiliary switch operates being determined by the setting of the adjustment screw 11 58.
12 A typical example of the operation of the auxiliary 13 signal switch would be in a refrigerator in which the 14 compressor has ceased to function or is funetioning incorreetly, while the thermostatic control of the main 16 switch is still operating correctly, so that the contacts 17 31 and 32 are closed. Since the compressor is not 18 functioning the sensed temperature will increase, and the 19 tongue ll will be depressed sufficiently to engage the arm 56 and operate the auxiliary switch.
21 If the auxiliary switch contacts 54 and 57 are 22 normally open and connected to a circuit including a 23 pilot lamp, the lamp will be lit when the auxiliary 24 signal switch is operated. Alternatively, if the auxiliary switch eontacts 54 and 57 are normally closed the 26 associated circuit will be open when the auxiliary signal 27 switch is operated.
28 The switeh units hitherto described are suitable "
~,, ;' .

13~ Ei 1 for the control of refrigerators, in which the cyclic 2 operation of the compressOr mo-tor is controlled automatically 3 to maintain the evaporator of the refrigerator within a 4 predetermined temperature range. For some simple applications of the control switch the cyclic temperature variation 6 is effected between fixed predetermined limits, and in 7 this case the temperature selection cam 21 and its 8 associated shaft 22 can be omitted, the anchoring screw 9 15 for the tensioning spring 14 being engaged directly with the frame 2 of the switch unit.
11 In refrigerators of the "two door" type having a 12 freezer and a fresh food compartment with two different 13 evaporators it is common to arrange for each cycle of 14 operation of the compressor to be followed by an automatic defrost cycle of the evaporator located in the fresh food 16 compartment, while the evaporator of the freezer 17 compartment remains in operation. For this purpose the 18 associated control switch must have a "cut-in"
19 (that is, switch closing) temperature above freezlng and a "cut-out" (that is, switch opening) temperature 21 sufficiently low to ensure a suitable temperature in the 22 freezer compartment for conservation of frozen food.
23 The "cut-out" temperature should be capable of selection 24 within limits, while the "cut-in" temperature should always remain constant, and above freezing, to ensure 26 the completion of each defrosting cycle.
27 A switch unit according to the present invention can be 6~386 adapted to meet these requirements, and a modification 2 for this purpose of the switch unit shown in Figure l is 3 illustrated diagrammatically in Figure 9.
4 In addition to the components of the switch unit shown in Figure l there is provided a supplementary 6 biasing spring comprising a leaf spring 59 anchored 7 at one end in the frame 2 of the switGh housing 8 and acting at its other end on a protuberance 60 9 provided on the switch operating lever 7 so as to exert .on the latter an anti-clockwise (as viewed in Figure 9) 11 biasing moment in the same direction as that caused 12 by the biasing spring 14. In this embodiment, however, 13 the anchoring screw 15 for the tension spring 14 14 is anchored in the aperture l9 in the frame l and con-sequently the tension in the spring 14 is adjustable 16 only by means of the cam shaEt 22. Consequently, when 17 the pressure in the capsule 4 increases, in response 18 to an increase in the sensed temperature, the point at 19 which the switch is operated by the lever 7 will always be constant, representing the desired "constant cut-in"
21 operating condition. To provide for variation in the 22 "cut-out"temperature a "cut-out" lever 61 of L-shape 23 is pivotally mounted in the frame 2 of the switch housing 24 at 62, the lever 61 being biased in an anti-clockwise direction, as viewed in Figure 9, by a helical tension 26 spring 63 one end of which is attached to the lever 27 61 and the other-e~d of which is attached to a screw 28 64 the head of which is carried by the bracket portion 29 17 of the cam slider 18. The lever 61 has a .

- 20 -L3~
1 projecting arm 65 which cooperates with a fixed stop 66 2 within the switch housing. In addition the lever 61 has 3 a rounded portion 67 which cooperates with the switch 4 operating lever 7 upon anti-clockwise rotation of the latter, as viewed in Figure 9, the stop 66 preventing 6 the lever 61 from engaging the lever 7 during clockwise 7 rotation of the latter, that is, during the switch closing 8 or cut-in operation. The stop 66 is so positioned that 9 during the anti-clockwise rotation of the switch operating lever 7l and before the opening of the switch 5 occurs, 11 the lever 7 engages the portion 67 of the lever 61~ -12 and thereafter the movement of the lever is resisted by 13 virtue of the tension in the spring 63. Consequently 14 the point at which the switch opens will be determined, at least in part, by the tension in the spring 63 and, 16 therefore, by the angular setting of the cam shaft 22.
17 . The embodiment illustrated in Figure 9 is similar to 18 that shown in Figure l in having an arrangement for opening 19 the switch contacts, that is, turning the switch off, in one setting of the cam shaft 22. In the Figure 9

21 embodiment a further cam 6~ is carried on the cam shaft

22 22 and is engageable with the upstanding appendix 25

23 carried by the switch operating lever 7 to rock the

24 lever anti-clockwise (as viewed in Figure 9) and open the switch in an "off" position of the cam shaft 22.
26 An alternative switch unit, similar to that of 27 Figure 9, is shown in Figure lO, in which a separate "off"

613~36 1 switch is provided for operation by an auxiliary cam 52 2 carried by the cam shaft 22, as described previously 3 with reference to Figures 4, 5 and 6. In other respects 4 the switch unit of Figure l0 is similar to that of Figure 9.
6 If it is desired to provide for variation in the 7 "cut-in" or switch on point of the switch unit the helical 8 tension spring 14 in the embodiments illustrated in 9 Figures 9 and l0 may be anchored to the cam follower slider 18 in a manner similar to the helical spring 63, 11 as illustrated in Figures l and 4. Alternatively, the 12 spring 63 may be anchored to the frame 2 of the housing 13 and the spring 14 may be anchored to the cam slider 18, 14 in which case the switch unit will operate in a manner essentially similar to that of Figure l, but with a 16 wider temperature (or pressure) differential between 17 the limits of its control cycle.
18 To avoid undesirable cross-ambient effects it may 19 be necessary to provide a heater for the capsule 4, to maintain the latter at a constant temperature. One 21 form of such a bellows heater is shown in broken outline 22 in Figure 5 at 69, consisting of a heating resistor 23 connected permanently between the switch terminals 24 29, 30 in parallel with the switch contacts 31, 32 so that current flows through the heating resistor when 26 the switch contacts are open, the heater being 27 effectively short-circuited when the switch contacts 28 are closed. The heating resistor 69 is located for 29 convenience in the switch assembly 5, but is positioned close to the capsule 4 to achiPve the optimum heating 31 effect with a low power heater.

.~ .

Claims (16)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A control switch unit comprising:
- a housing having a housing wall;
- a fluid-filled power element mounted within the housing opposite said housing wall;
- an operating lever pivotally mounted in the housing and cooperating with the power element;
- a switch located in the housing and cooperating with the operating lever to be operated by the power element through the lever, both the power element and the switch being disposed on the same side of the operating lever and on opposite sides of the pivot axis of the lever;
- a tension spring located within the housing and acting on the opposite side of the operating lever from the power element and the switch, said tension spring exerting a moment on the lever in opposition to the power element;
- cam means acting upon the spring to adjust the tension thereof and to predetermine the operating point of the switch under control of the power element; and - a setting shaft connected to the cam means for adjustment of the latter, said setting shaft being rotatable in said housing wall.

2. A switch unit as defined in Claim 1, wherein the axis of the setting shaft is perpendicular to the pivot axis of the operating lever.

3. A switch unit as defined in Claim 1, wherein the tension spring comprises a helical spring the longitudinal axis of which extends generally parallel to the operating lever, the operating lever having a protuberance to which one end of the spring is anchored, and the unit further including a slider engaging the cam means and movable in the direction of the longitudinal axis of the spring under control of the cam means to adjust the tension in the spring.

4. A switch unit as claimed in Claim 3, wherein the helical tension spring has a screw-adjustable anchorage connecting said end of the spring to the cam-operated slider, said adjustable anchorage enabling the tension in the spring to be adjusted independently of the adjustment thereof by the cam means.

5. A switch unit as defined in Claim 1, wherein the housing has opposite walls and the operating lever comprises a plate having lugs pivotally supported in said opposite walls of the housing and disposed intermediate the points of engagement of the lever with the power elements and the switch.

6. A switch unit as defined in Claim 1, wherein the switch comprises an electrically insulating base attached to the housing and supporting a fixed first switch contact, and a snap-action switch blade carrying a second switch contact movable relative to the fixed contact, the switch blade being engageable by the operating lever to effect snap-movement of the second switch contact relative to the first switch contact.

7. A switch unit as defined in Claim 6, including a differential adjustment screw accessible from the outside of the housing for adjustment of the separation of the switch contacts in the open condition of the switch.

8. A switch unit as defined in Claim 6, wherein the snap-action switch blade has a fixed mounting on the insulating base and projects cantilever-fashion from its fixed mounting in a direction generally parallel to the pivot axis of the operating lever.

9. A switch unit as defined in Claim 1, wherein the cam means comprises a cam disc located within the housing and attached to the cam setting shaft, and including a cam slider engaged by the cam disc, said cam slider carrying anchorage means for one end of the tension spring.

10. A switch unit as defined in Claim 9, including an auxiliary cam mounted on the cam setting shaft, a cam following mechanism operatively associated with the auxiliary cam, and an auxiliary switch within the housing, connected in series with the first switch, and engageable by said cam following mechanism.

11. A switch unit as defined in Claim 10, wherein the cam following mechanism cooperating with the auxiliary cam comprises a plunger displaceable longitudinally within the housing and engageable with the auxiliary switch, and a bell-crank lever having a first arm engageable by the auxiliary cam and a second arm having a hinge connection to said plunger.

12. A switch unit as defined in Claim 11, wherein the bell-crank lever and the plunger are formed of plastics material, the hinge connection between the bell-crank lever and the plunger consisting of an integral flexible portion of said plastics material.

13. A switch unit as defined in Claim 1, including a resistive heater associated with the power element to heat the latter, said heater being connected electrically in parallel with the switch.

14. A control switch unit comprising:
a housing;
a fluid-filled power element mounted within the housing;
an operating lever pivotally mounted in the housing and cooperating with the power element;
- a switch located in the housing and cooperating with the lever to be operated by the power element through the lever, both the power element and the switch being disposed on the same side of the operating lever and on opposite sides of the pivot axis thereof;
- a helical tension spring acting upon the operating lever and extending generally parallel to the lever on the opposite side thereof from the power element and the switch;
- adjustable anchorage means for the end of the tension spring remote from the operating lever, said adjustable anchorage means being connected to a wall of the housing and being adjustable from the outside of the housing; and - pivotal mounting means for the operating lever defining a transverse pivot axis perpendicular to the longitudinal axis of the helical tension spring.

15. A switch unit as defined in Claim 14 including a further lever pivotally mounted within the housing and engageable by the switch operating lever in one direction of rocking movement only of the latter, and a biasing spring of adjustable tension acting upon said further lever.

16. A switch unit as defined in Claim 15, wherein the biasing spring acting on the further lever has an anchorage at its end remote from the further lever and cam means engageable with said anchorage to adjust the latter and predetermine the force which the further lever exerts on the switch operating lever when engaged by the latter.