US3758732A

US3758732A - E spring adjustment means fluid pressure actuated snap-action switch with differential and rang

Info

Publication number: US3758732A
Application number: US00266066A
Authority: US
Inventors: Olsen J Hagedorn
Original assignee: Danfoss AS
Current assignee: Danfoss AS
Priority date: 1971-06-26
Filing date: 1972-06-26
Publication date: 1973-09-11
Anticipated expiration: 1990-09-11
Also published as: JPS5126622B1; DE2131858C3; BR7204180D0; DE2131858A1; DE2131858B2; AU468975B2; GB1389477A; FR2143744A1; AR198789A1; DK137207B; DK137207C; AU4306572A; DD98176A5; IT959075B; FR2143744B1

Abstract

The invention relates to a snap action switch assembly comprising a snap action system which incorporates a main arm which is movable between two stops and to which the force of a pressurized working element and of an adjustable range defining spring is applied. A snap action arm is linked with said main arm and hinged in a bearing at its other end. This bearing is spring urged towards the snap action arm and the spring force thereof is likewise adjustable. The switch also comprising a contact system in which a movable contact is spring biased against a fixed contact and can be lifted by a drive element associated with the main arm.

Description

United States Patent n 1 Hagedorn-Olsen 1 1 FLUID PRESSURE ACTUATED SNAP-ACTION SWITCH WITH DIFFERENTIAL AND RANGE SPRING ADJUSTMENT MEANS [75] Inventor: Jens Hagedorn-Olsen,Nordborg,

Denmark [73] Assignee: Danfoss A/S, Nordborg, Denmark [22] Filed: June 26, 1972 [21 Appl. No.1 266,066

[ Sept. 11, 1973 Primary Examiner-Robert K. Schaefer Assistant Examiner Robert A. Vanderhye Attorney-Wayne B. Easton [57] ABSTRACT The invention relates to a snap action switch assembly comprising a snap action system which incorporates a main arm which is movable between two stops and to which the force of a pressurized working element and of an adjustable range defining spring is applied. A snap action arm is linked with said main arm and hinged in a bearing at its other end. This bearing is spring urged towards the snap action arm and the spring force thereof is likewise adjustable. The switch also comprising a contact system in which a movable contact is spring biased against a fixed contact and can be lifted by a drive element associated with the main arm.

PATENTEU 1 3.758.732

SHEET 2 0F 2 l 33 L73 3739 I917 FLUID PRESSURE ACTUATED SNAP-ACTION SWITCH WITH DIFFERENTIAL AND RANGE SPRING ADJUSTMENT MEANS The invention relates to a snap action switch comprising a snap action system which incorporates a main arm which is movable between two stops and to which the force of a pressurized working element and of an adjustable range defining spring is applied, and a snap action arm linked with said main arm and hinged in a hearing at its other end, which bearing is spring urged towards the snap action arm and the spring force of which is likewise adjustable, the switch also comprisng a contact system in which a movable contact is spring biased against a fixed contact and can be lifted by a drive element associated with the main arm.

Recently snap action switches of this kind have been disclosed in which the snap action system consists of only two parts, i.e., the main arm and a snap action arm in the form of a spring in the shape of the Greek letter omega. The omega spring not only has a force component directed towards the main arm, but also a component directed transversely of this arm. In the working range this latter component has a negative characteristic curve. The snap action system therefore remains in one of its end positions until the difference between the forces applied by the working element and the range defining spring overcomes the transverse force. Then the system snaps into the other end position and thereby actuates the contact system. The return movement takes place in a similar manner.

A snap action switch of this kind is often known as a force proportional switch, to differentiate it from the distance proportional snap action switches in which a snap action system, usually comprising three parts, switches over when the dead center of the system is passed, usually by the displacement of one of the arms.

In distance proportional pressure responsive switches of this kind it has usually been the practice to fix one of the switching points by setting the range defining spring, and the other switching point by setting a differential spring, and to achieve clearly defined switching pressures, the two settings were not intended to influence each other. Furthermore, pressostats have to be adjustable within very wide pressure ranges. A highpressure pressostat for refrigerating installations, for example, has a range setting of 6 30 atmosphere and a differential setting of 3 8 atmoshpere. Within these setting ranges, not only should the required independence of the settings be achieved, but also the greatest possible linearity in the work characteristic curves. This has led to complicated and expensive constructions.

In the case of force proportional snap action switches too, it is possible to set a certain value at which response is required to occur with the aid of the range defining spring, and to vary the differential between the two switching points by adjusting the omega spring. Generally however, the differentials and changes in differentials are small. Furthermore, each adjustment of the differential also leads to displacement of both switching points. For this reason, snap action switches of this kind, despite their simple construction, are only used with thermostats in which a small differential suffices and the alteration of the two switching points occurring when the differential is changed can be accepted.

Also known is a temperature responsive snap-action switch in which three thermostatic working elements, arranged in parallel, engage the main arm, the snap action arm is an extension of the main arm and is of rigid design and is held in a bearing which is formed on a lever pivotable about a fixed point. The lever is loaded by an adjustable spring, the tension of which can be varied. One of the end positions of the main arm is determined by a stop, whilst its other end position is determined by the fixed contact of the switch, the movable contact of which is moved through a lost motion zone by the main arm. This temperature responsive snap action switch too is intended only for small differentials. Contact bounce also occurs.

, The object of the present invention is to provide a pressure responsive switch which can be set in all of the ways possible in the known distance responsive pressostat switches, but which is of considerably simpler construction.

In a snap-action switch of the initially mentioned kind and, applying this switch to a pressostat, this object is achieved, according to the invention, by making thesnap action arm rigid and holding it in a bearing which is formed on a lever which is pivotable about a fixed point and is loaded by a differential spring, one of the stops limiting the movement of the main arm near the dead center of the snap action system.

In this construction, differentials of any required magnitude can be set, since the differential spring engaging the bearing lever, in contrast to an inherently resilient snap action arm, can be adjusted over very considerable distances. These adjustments do not generally lead to large deviations in the linearity of the work characteristic curves. If one of the stops for the main arm is located near the dead center line, the transverse force produced by the differential spring is approximately zero. This value is retained even when the differential spring is displaced. Therefore, if the switching point that is to be set with the aid of the range defining spring is associated with this position of the main arm, the other switching position can be determined with the aid of the differential spring without the two settings influencing each other. This results in a pressostat switch of very simple construction.

Particular advantage accrues if the two stops are interconnected and aremade adjustable in such manner that one or other of them can be selected to limit the movement of the main arm near the dead center. In this way a temperature responsive switch is provided with which, when it has been set in the factory or at the point where it is fitted, it is possible to determine whether the upperswitching point has been set with the aid of the range defining spring or the associated lower switching point with the aid of the differential spring, or conversely whether the lower switching point has been set with the aid of the range defining spring or the upper switching point with the aid of the differential spring.

Furthermore, the bearing lever may be a double armed lever and may engage the spring by that of its ends remote from the bearing, i.e., at a greater distance from the fixed pivot pin. This results in a saving in space and also in a stepping up of the force, so that a relatively weak differential spring can be used or larger differentials can be set with the help of a given differential spring.

A particularly advantageous arrangement is that in which the bearing lever is a two armed toggle lever and the differential spring extends parallel with the range defining spring. This enables the springs to be fitted alongside each other in a narrow space. They may also be adjusted by means of set screws arranged parallel with each other. This also facilitates indication of the particular setting.

In some cases it is advantageous if the differential spring engages the bearing lever at an angle other than 90. In this way it is possible to offset non linearity which can occur, for example, if the main arm has to cover a greater distance of swing before reaching the stop located beyond the dead center point, and this can also be of importance when setting large differentials.

The bearing lever may be in two parts and the position of the two parts in relation to each other can be adjusted by means of a set screw. It is possible in this way to adjust the differential spring, e.g., to suit a particular scale.

In a preferred arrangement, a set screw for the rangedefining spring, a set screw for the differential spring and a screw carrying the two stops can be mounted parallel with each other on a common carrier plate. All three possible setting operations can therefore be carried out from the same side. Thus, it is only necessary to make sure that this side is accessible when fitting the switch.

In particular, the main arm can be positioned close to the carrier plate and the set screws for the range defining and differential springs can extend through it.

Also, the set screws can carry backing elements for the springs, which elements are used as indicators in two parallel slots which disclose scales and are formed in a side wall of the casing.

Considerable saving in space is achieved if the working element and the range defining spring are arranged coaxially and engage a plate which acts on the main arm by way of a bar which bridges the range-defining spring.

In a particularly recommended arrangement, the working element and the range defining spring are arranged approximately in the central plane in the switch casing, the snap action arm, bearing lever and differential spring are laterally offset therefrom towards the edge, and the contact system is fitted in the remaining space beside the last mentioned parts. This results in a pressure responsive switch of smaller dimensions than those hitherto obtainable in such switches.

Advantageously, the main arm has, near one of its ends, a bearing, solid with the casing, and near the other a bearing for the snap-action arm which extends towards the bearing solid with the casing, and the bearing lever is likewise angled in this direction; also the differential spring isv fitted adjacent the range limiting spring positioned near the end mounted solidly on the casing. In this arrangement the differential spring lies close beside the range defining spring, so that a considerable portion of the rest of the casing is available for the contact system.

The invention will now be described in greater detail by reference to an embodiment illustrated in the drawing, in which:

FIG. 1 is a front view of a pressure responsive snapaction switch in accordance with the invention,

FIG. 2 is a view of the snap action switch with the casing carrying the front wall removed,

FIG. 3 is a view, partly in section, of the switch with the contact system removed,

FIG. 4 is a side view of the snap action switch as seen from the left of FIG. 2,

FIG. 5 is a side view of the snap action switch as seen from the right of FIG. 2, and

FIG. 6 is a horizontal section through the snap action switch of FIG. 2 below the upper carrier plate.

The pressure responsive snap action switch illustrated has a substantially U-shaped frame 1 comprising a rear wall 2, an upper carrier plate 3 and a base 4. The frame is completed by a front plate 5 which is secured to the upper carrier plate 3 and the base 4. A casing 6 is pushed from the front over this frame and is secured thereto by means of a screw 7; the front wall 8 of the casing contains two slots 9 and 10 which disclose a scale and which register with corresponding slots 11 and 12 in the front plate 5. The front wall 8 and the side walls of the casing are solid, and the upper and lower walls may contain openings.

A main arm 13 is mounted by one of its ends on a rod 14. This is held in the rear wall 2, the front wall 5 and a bracket 15 connected to the front wall. Near its other end the main arm has a knife-edge bearing 16 in which a snap action arm 17 is held. The snap action arm extends towards the fixed bearing rod 14 and is held at the other end in a bearing 18 which is carried by a double armed bearing lever 19. This lever can pivot about a fixed pin 20. The two

arms

21 and 22 of the lever are interconnected in a mechanically positive manner. Their relative lengths can be varied by means of an adjusting screw 23. A tension spring which constitutes the differential spring 24 engages the arm 22 and urges the bearing 18 towards the snap action arm 17. The point of engagement of the differential spring 24 with the lever 19 is at a greater distance from the pivot pin 20 than is the bearing 18. The bearing 18 is positioned substantially vertically above the pivot pin 20. The arm 22 extends obliquely downwards at an angle of approximately 45, so that the differential spring 24 also engages the bearing lever 19 at an angle of approximately 45.

The end plate 25 of a working element 26 constituted by a bellows is secured to the base 4. The pressure is supplied through a pipe 27. The working element 26 acts on a plate 28, the other side of which is loaded by a range defining spring 29. The plate is connected by way of a bridging rod 30 to a drive element 31 which acts on the main arm 13 in the downward direction. Also, the bridging rod contains a slot 32.

Extending through the carrier plate 3 is a set screw 33, the outwardly projecting end of which has a rotatable knob 34. A backing element 35 can be screwed on to this set screw and this element provides support for the range defining spring 29. A compression spring 36 holds the main arm 13 against the drive element 31. A further set-screw 37 is mounted in the carrier plate 3. At its lower end this set screw 37 has a backing element 38 in which the differential spring 24 is fixed. The two set

screws

33 and 37 extend through complementary openings in the main arm 13.

Furthermore, the upper plate 3 carries the set-screw 39 having an upper stop 40 and a lower top 41. This element likewise extends into an opening in the main arm 13 and determines the upper and lower end positions of said arm.

FIG. 6 shows that the set screw 33 and thus the range-defining spring 29 and the work element 26 are located approximately in the central plane of the switch but that the set screw 37 together with the differential spring 24, the snap action arm 17 and the bearing lever 19 are offset therefrom towards the rear edge of the main arm 13. Space is therefore available for fitting a contact system 42 beside the last mentioned parts. This system is secured to the frame 1 by means of a screw 43. The contact system comprises a fixed middle contact 44 and two

movable contacts

45 and 46, each contact having a connector 47. The

movable contacts

45 and 46 are mounted on

spring blades

48 and 49, between the ends of which engages a drive element 50 which is secured to the main arm 13. In the illustrated position the lower contact 46 is lifted from the fixed contact 44. When the main arm snaps over into its upper position, the pair of

contacts

46 and 44 close, whereas the

pair

44 and 45 are opened. The

backing elements

35 and 38 have

extensions

51 and 52 which extend through the slots 11 and 12 in the plate 5 and through the slot 32 in the bridging bar 30 and are visible through the slots 9 and as indicators cooperating with the scale.

FIG. 3 shows that the main arm 13 and the snapaction arm 17 are only able to move on one side of the dead center line, i.e., from a point immediately alongside this line and determined by the stop 41 to a point which is well beyond the dead center line and which is determined by the stop 40. In the position illustrated in FIG. 3, the differential spring 24 can be adjusted as required without any substantial alteration to the value at which the snap action system responds, which value is largely predetermined by the setting of the range defining spring 29, since in this position the transverse component of the snap action force, produced by the differential spring 24, is practically zero. If however the snap action system has moved into its other end position, the differential set by means of the spring 24 becomes fully effective, so that the second change over point is thus defined. Both the range defining spring 29 and the differential spring 24 can be adjusted to cover a wide range of values without any interference factors being superimposed.

If the set-screw 39 is screwed down to such an extent that the upper stop 40 bears on the main arm 13 near the dead center line, then very similar conditions result but with the difference that the change over from the upper position of the main arm 33 is determined by the range defining spring 29, and the change over from the lower end position is determined by the differential spring 24.

In this way a pressure responsive switch which occupies little space is obtained by using a relatively small' number of components and all the adjustments and settings that require to be carried out at the point where the switch is fitted can be effected by means of set screws accessible from the top of the switch.

I claim:

1. A snap action switch assembly comprising a housing, a main arm hinged at one end thereof to said housing, stop means engaging said arm to limit the pivotal movement thereof to a desired range, a pressure operated element biasing said arm in a first direction, a range defining spring biasing said element in a second direction opposite to said first direction, a lever having a fixed pivot point and oppositely extending arms, a snap action arm attached to one of said lever arms and being engageable with said main arm, differential spring means for biasing said lever and causing said snap action arm to be biased into engagement with said main arm, said stop means including two separately adjustable stops with either stop being adjustable to provide a limit for the movement of said main arm near its dead center position.

2. A snap action switch assembly according to claim 1 wherein said lever arms are of unequal length and said differential spring is attached to the longer of said lever arms.

3. A snap action switch assembly according to claim 2 wherein said range defining spring and said differential spring means extend in parallel relation to each other.

4. A snap action switch assembly according to claim 1 wherein said differential spring is attached to one of said lever arms at an angle other than ninety degrees.

5. A snap action switch assembly according to claim 1 wherein said lever arms are individually pivoted relative to said fixed pivot point, and set screw means for adjusting the position of said lever arms relative to each other.

6. A snap action switch assembly according to claim 1 including threaded backing elements for said range defining spring and for said differential spring means, set screws being threaded in said elements for adjusting said spring and said spring means, slots in said housing, said backing elements being adjacent said slots and visible therethrough as position indicators.