US3609270A

US3609270A - Electric reversing switch

Info

Publication number: US3609270A
Application number: US3045A
Authority: US
Inventors: Jorgen Jorgensen; Tage S Basse
Original assignee: Danfoss AS
Current assignee: Danfoss AS
Priority date: 1969-02-14
Filing date: 1970-01-15
Publication date: 1971-09-28
Anticipated expiration: 1988-09-28

Abstract

The invention relates to an electric reversing switch assembly having at least one fixed contact and a pair of movable contacts. The assembly includes a main contact actuating arm and a snapaction spring, such as an omega spring, attached to the actuating arm. The movable contacts have lugs and are resiliently biased towards the fixed contact. An actuating element connected to the actuating arm lifts one of said movable contacts from the fixed contact while allowing the other of the movable contacts to abuttingly engage the fixed contact.

Description

United States Patent lnventors Jorgen Jorgensen Sonderborg; Tage S. Basse, Nordborg, both 01 Denmark Appl. No. 3,045 Filed Jan. 15, 1970 Patented Sept. 28, 1971 Assignee Danfoss A/S Nordborg, Denmark Priority Feb. 14, 1969 Germany P 19 67 418.1

ELECTRIC REVERSING SWITCH 1 Claim, 5 Drawing Figs.

11.8. C1 200/67 D, 200/166 A Int. Cl ..1 0l11 13/36 Field of Search 200/67 D,

166.1, 166 A, 83 MW,67 A, 67,176

[56] References Cited UNITED STATES PATENTS 2,924,684 2/1960 Claesson 200/l66.1 UX 3,032,626 5/1962 Payne 200/67 D UX FOREIGN PATENTS 549,661 4/1932 Germany ZOO/166.1 UX 1,528,450 4/1968 France 200/166 H UX 1,127,435 4/1962 Germany 200/67 D UX Primary ExaminerDavid Smith, Jr. AttorneyWayne B. Easton ABSTRACT: The invention relates to an electric reversing switch assembly having at least one fixed contact and a pair of movable contacts. The assembly includes a main contact actuating arm and a snap-action spring, such as an omega spring, attached to the actuating arm. The movable contacts have lugs and are resiliently biased towards the fixed contact. An actuating element connected to the actuating arm lifts one of said movable contacts from the fixed contact while allowing the other of the movable contacts to abuttingly engage the fixed contact.

PATENTED SEPZB um SHEET 1 OF 2 ELECTRIC REVERSING SWITCH The invention relates to an electric reversing switch in which a middle contact is selectively brought into contact with one of two outer contacts and which is actuated by a snap-action system which comprises a main arm and a snap-action spring.

ln the known reversing switches of this kind the two outer contacts are fixed, whereas the middle contact is connected to or guided by a movable part of the snap-action system, e.g. the main arm. These switches suffer considerable rebound when the contacts close; they also exhibit variable contact pressure which alters when the snap-action system is adjusted, e.g. when the difference is set, or it even changes simultaneously with the actuating force, a slow seperating movement of the contacts often occuring, especially in the case of small snapaction systems; furthermore, these known reversing switches cannot readily be suited to special operating conditions, e.g. when it is required that the current shall not be interrupted during reversal.

A particularly simple form of snap-action system is one comprising two parts consisting only of a main arm and an omega spring, which parts are interconnected by way of a linkage point, whereas the two free ends rest in links secured to the casing. In this arrangement, the fact that the omega spring can apply a force not only in the direction of the main arm but also at right angles thereto is exploited. When the last-mentioned force is overcome by the other forces applied to the main arm, particularly the variable actuating force, the system snaps over, a stop preventing the dead center position of the omega spring from being passed. Only a simple on-off switch can be actuated by the main arm of a snap-action system of this kind.

The object of the present invention is to provide an electric reversing switch of the initially described kind which constitutes a considerable improvement over the known reversing switches from the design and functional points of view, and, in particular enables the above-described disadvantages to be overcome.

According to the invention this object is achieved by the middle contact being fixed and the two outer contacts being resiliently urged toward it in their at rest position, and by a lifting element moving, with a lost-motion action, between the carriers of the two outer contacts, which element is connected to the main arm in such manner that one of the outer contacts is lifted from the middle contact in the first position of the snap-action system and the other outer contact in the second position of the snap-action system.

In this arrangement, the electric reversing system and the snap-action system are constructionally separate from each other. Any changes in the snap-action system, e.g. due to adjustment of the difference, have no effect upon the reversing system. The contact pressure is therefore constant for each of the two reversing positions. As a result of the use of two movable outer contacts, the mass of the parts of the snap-action system moved when reversal takes place can immediately detach itself from the contact carrier when contact occurs; the still effective mass of the contact and contact carrier can then be designed to be largely free from rebound. The spring force of the particular contact that is lifted imparts additional acceleration to the lifting element when the snapover action takes place, so that after it has passed through the lost-motion stage it strikes the carrier of the other contact with considerable force and pulls it away from the fixed middle contact with considerable velocity. By varying the lost-motion it is possible to lift the second contact selectively before or after the other pair of contacts has closed.

A reversing switch of particularly simple construction is obtained if, using a known two-part snap-action system, consisting of a main arm and an omega spring, the limiting stops of the snap-action system are so arranged that the direction in which the force of the omega spring is applied is reversed when the snapover action occurs. Since the omega spring is enabled to pass through its dead center position with a snapping movement, symmetrical conditions can be established, so that the two outer contacts of the reversing switch are acted upon in opposite directions but in a manner that is otherwise the same. With an arrangement of this kind, it is only necessary to provide for reversal of the direction of the sum of the actuating forces acting on the main arm. This can be readily achieved, however, e.g. by using a bimetal member as the force-applying means, by employing a nominally rated spring counteracting a pressure capsule, and so on.

Fully symmetrical conditions can be achieved if the limiting stops are disposed symmetrically with respect to the dead center position of the snap-action system. To achieve this in an accurate manner, the limiting stops can also be displaceable.

Expediently, the lifting element engages the outer contact carriers in the immediate vicinity of the contracts. This ensures that the lifting forces can act on the contacts without being reduced.

In a preferred embodiment, the carriers for the outer contacts are spring arms which are clamped at one end and are stiffened over a considerable part of their length in such manner that their spring action is largely limited to the area immediately adjacent the clamping point. This results in extremely little rebound.

Furthermore, for the purpose of clamping at one end, the contact carriers can be pushed between three knife-edged bearings, two of which engage on one side and the other ongages between them on the other side. This leads to very simple assembly, since the contact carriers can be held in a completely secure manner after having pushed into the knife edge bearings.

If at least one knife edge bearing is displaceable transversely of the contact carrier, the spring tension of this contact carrier can be easily set to any required value. Here it is often sufficient if the adjustable knife edge bearing is replaced by the end of a setscrew. In particular, the screw can constitute the bearing that faces the contact.

In a preferred construction, the three contact carriers for the fixed middle contact and the two movable outer contacts are held in a one-piece casing of synthetic material having four substantially parallel walls on which the knife edge bearings are formed. This casting of synthetic material can be prefabricated to incorporate the contact carriers and can be fitted in the switch unit independently of the snap-action system. The forming of the knife edge hearings on four parallel walls results in a construction that occupies very little space.

in this arrangement, that end of the contact carrier remote from the contact can be bent over at right angles and can bear against a stop. in this way the correct axial positions of the contacts is ensured. The bend end can even be welded on to the stop so that the latter can constitute a connector.

In a modified form of the reversing switch of the invention, the middle contact carrier carries two fixed contacts offset relatively to each other, and the two outer contacts, when in their at rest position, bear resiliently at the same level against the fixed contacts and can be lifted in synchronism by the lifting element. This double switch is of exactly the same simple construction as the above-described reversing switch.

The invention will now be described in more detail by reference to embodiments illustrated in the drawing, in which:

FIG. 1 is a longitudinal section through a reversing switch in accordance with the invention on the line A-A of FIG. 2,

FIG. 2 is a cross section through the reversing switch on the line B-B of FIG. 1, but with the upper part, including the omega spring, removed,

FIG. 3 is a longitudinal section through the casing of the reversing system,

FIG. 4 shows a perspective view, on a greater scale, of a contact carrier for an outer contact, and

FIG. 5 shows a modification of the switching system of FIG. 3.

A snap-action system 2 and an electric reversing system 3 are provided alongside each other in a box 1.

The box consists of a base 4 and three

sidewalls

5, 6, and 7. It is closed at the top by a plate 8 and a cover 9. 1n the base is an inlet 10 for a medium under pressure, e.g. the vapor of a thermostatic sensor, and an inlet 11 for the electric leads.

The snap-action system incorporates a main arm 12 and an omega spring 13, which bear against each other at the linkage point 14. By means of raised portion 15, the main arm is supported on a knife edge bearing 16 formed on the cover plate 9. The omega spring 13 is supported on a fixed bearing 17, which is mounted on a slide 18 which can be pushed towards and away from the main arm 12 with the help of a setting knob 19. The cover plate 8 also carries two

setscrews

20 and 21, which act as limiting stops for the main arm 12.

The force from a bellows 23, the interior 24 of which is pressurized by the medium under pressure, acts on. the main arm through a plunger 22. The outer case of the bellows is secured to the base. At a distance therefrom, a nominally rated spring 25 acts on the main arm 12, a plate 26 being interposed. The nominally rated spring is backed by a ring 27, which is axially displaeeable on a threaded rod 28 when the latter is rotated, for which purpose a setting knob, for example, can be fitted on its upper end.

Furthermore, a lifting element 30 is secured to the main arm 12 by means of a screw 29, this element establishing the connection with the electric reversing system 3.

This reversing system comprises a casing 31 having four

parallel walls

32, 33, 34 and 35, between which are clamped three

contact carriers

36, 37 and 38 by their being inserted from the side. The middle contact carrier 37 carries a fixed double contact 39, and the two

outer contact carriers

36 and 38 each carry a movable

outer contact

40 and 41. Each contact carrier is clamped by three bearing points formed on the walls; in the case of the contact carrier 36 a knife edge bearing 42 is provided on the wall 33 and, on both sides thereof, a knife edge bearing 43 is provided on the wall 32 and a bearing 44 is provided in the form of a setscrew 45. The

outer contact carriers

36 and 38 also have raised portions 46 and 47 immediately alongside the

contacts

40 and 41, which portions can be engaged by the lifting element 30 with a lost-motion action. At the opposite

end connecting tabs

48, 49 and 50 are provided in the casing, which tabs on the one hand are used for the fitting of connecting screws 51 and, on the other, constitute a bearing surface for an angled part 52 of each of the

contacts carriers

36, 37, and 38; each part 52 can also be welded on to this bearing surface.

FIG. 4 shows the contact carrier 36 on a larger scale. The carrier consists of a piece of resilient sheet metal which is stiffened by upstanding edges 53 over the major part of its free length beginning at the bearing point 44. Thus, there is left over only a portion a at which the contact carrier 36 can execute a spring action.

In the position illustrated, the main arm 12, is biassed in the clockwise direction by the omega spring 13. This load is counteracted by the lower strength of the raised outer contract carrier 36. The resultant force holds the system in the position illustrated. The system remains in this position until the other forces applied to the main arm reach a force of equal magnitude applied in the opposite direction. This is the case when the pressure in the bellows 23 drops to such an extent that the excess force of the nominally rated spring 25 exceeds the resultant force. Then the omega spring snaps through dead center into the other end position determined by the setscrew 21. During the snapover movement, the lifting element 30 moves towards the other outer contact carrier 38. As soon as the contact 40 strikes the contact 39, the lifting element 30 is released from the contact carrier 36, so that the mass and rigidity of this carrier are alone responsible for the actual rebound. Shortly thereafter, the lifting element 30 strikes the other contact carrier 38 and lifts its contact 41 from the fixed contact 30 at great velocity. Reversal is then possible only when the pressure in the bellows 23 has reached such a level that it exceeds the strength of the nominally rated spring by an amount such that the resultant force of the omega spring 13 and of the contact carrier 38, occuring in this end position is overcome.

By displacing the threaded rod 28 it is possible to adjust the strength of the nominally rated spring and thus to set the working point of the reversing switch. By shifting the slide 18 it is possible to vary the characteristic curve of the omega spring 13, so that the difference can be set, i.e. that pressure difference is established in the bellows 23 that is necessary for moving from one snap operation to the other. The distance travelled by the main arm 12 can be fixed with the help of the

screws

20 and 21. Finally, by means of the screws A5 on the two

outer contact carriers

36 and 38 each individual movable contact can be so adjusted as to establish a minimal tendency toward rebound.

in the modified form shown in H0. 5, the same casing 31 is used; the only difference is that the bearing 44 constituted by the screw 45 is replaced by a fixed knife edge bearing 54. The form of the outer contact carrier 36 remains unchanged. The middle contact carrier 37 has at its outer end a Ushaped portion 55, on each of the two parallel limbs of which are fitted fixed

contacts

56 and 57 facing towards the same side. At its front end the outer contact carrier 38 has a contact 58 and a raised portion 59 which extend in the opposite direction compared with the arrangement of HO. 3. A lifting element 60 having two arms engages the raised

portions

46 and 59 so that the two

contacts

40 and 58 are simultaneously separated from the fixed

contacts

56 and 57 when the snap-action system moves into the other position. in this system too, the

contact carriers

36, 37 and 38 need only be pushed from the side into the casing 31. They are then held securely and firmly by the knife edge bearings.

The embodiments illustrated can be modified in numerous ways depending upon requirements without thereby departing from the basic idea behind the invention. For example, a bimetal spring can be used as the force-applying means instead of the bellows 23. if it is required that the pair of

contacts

40, 39 should close only after the pair of

contacts

39 and 41 have opened, it is only necessary to make the lifting elemen! 30 thicker, i.e. the lost motion must be somewhat less. The limiting screws 20 and 21 can also be so set that the snap action occurs only on one side of the dead center plane of the main arm 12 and the omega spring 13.

We claim:

1. An electric reversing switch assembly comprising a frame, a fixed middle contact and a pair of movable contact on opposite sides of said fixed contact, a main arm, a snap action spring connected to said main arm, said pair of contacts having lugs and being resiliently biased towards said fixed contact, an actuating element connected to said main arm, said main arm being movable so that said actuating clement alternately lifts one of said movable contacts from said fixed contact while allowing the other of said movable contacts to abuttingly engage said fixed contact, spring arms connected to said contacts, each of said spring arms being clamped to said frame at one end with a substantial portion of the entire length thereof being relatively immobile, setscrews in threaded holes in said frame, said spring arms each having one side thereof in clamping engagement with at least one of said setscrews.

Claims

1. An electric reversing switch assembly comprising a frame, a fixed middle contact and a pair of movable contacts on opposite sides of said fixed contact, a main arm, a snap action spring connected to said main arm, said pair of contacts having lugs and being resiliently biased towards said fixed contact, an actuating element connected to said main arm, said main arm being movable so that said actuating element alternately lifts one of said movable contacts from said fixed contact while allowing the other of said movable contacts to abuttingly engage said fixed contact, spring arms connected to said contacts, each of said spring arms being clamped to said frame at one end with a substantial portion of the entire length thereof being relatively immobile, setscrews in threaded holes in said frame, said spring arms each having one side thereof in clamping engagement with at least one of said setscrews.