GB1598115A - Snap-action mechanism for an electromechanical timelapse relay - Google Patents

Abstract

The intermittent mechanism has a transmission which is driven by a synchronous motor. A sequence wheel (1) is coupled to the transmission output. A pre-clamping lever (9) is connected between an intermittent-action lever (8) and a clamping cam (17) on the sequence wheel (1). The pre-clamping lever (9) is constructed as a rocker, as is the intermittent-action lever (8). The pre-clamping lever (9) engages with the intermittent-action lever (8) via a compression spring (10). The pre-stressing lever (9) can be moved relative to the intermittent-action lever (8) in order to prestress the compression spring (10). The intermittent-action lever (8) can be locked by a locking lever (3). The locking lever (3) can be operated by a release cam (19) on the sequence wheel (1). The release cam (19) causes the intermittent-action lever (8) to unlock, via the locking lever (3). High return accuracy of the switching time can be achieved using the intermittent mechanism, with a constant switching rate. <IMAGE>

Description

(54) A SNAP-ACTION MECHANISM FOR AN ELECTROMECHANICAL TIME-LAPSE RELAY (71) We, SCHLEICHER GmbH & Co.

RELAIS-WERKE KG., a German company, of Pichelswerder Strabe 3-5 D-1000 Berlin 20, German Federal Republic, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a snap-action mechanism for an electromechanical timelapse relay. In known such arrangements gearing is driven by a synchronous motor and a time-lapse wheel is connected to the gearing output. A trip cam and a rocker forming a snap-action lever for actuating at least one actuating member are provided. A prestressed spring operates the snap-action lever.

A snap-action mechanism of the aforesaid type is described in German Patent Specification 2 160 301. Electromechanical timelapse relays generally comprise contact members which operate instantaneously upon excitation of the magnetic system as well as contact members which operate with a timelapse. The latter come into operation only after the lapse of a pre-selected period of time.

It is important with contact members of the time-lapse type, that the switching instant of the snap-action contact member can be accurately repeated and that creeping contact-making is prevented. The snap-action contact member must carry out the switching operation rapidly. It is also important that the switching operation always takes place after exactly the same time-lapse.

In the afore-described snap-action mechanism a snap-action contact member which is constructed as a spring member is used. This spring member can be pre-stressed by a set screw which retains it in an extreme position.

The snap-action lever actuated by a trip cam moves so as to bear against the pre-stressed snap-action contact member. The snap-action contact member jumps into the other extreme position at the instant when a pre-set pre-stressing force has been overcome by the snap-action lever and thus carries out the switching operation. Creeping contact-making is avoided due to this arrangement of the snap-action mechanism.

The use of pre-stressed contact-member constructed as a spring has the disadvantage that the pre-stress of the spring and thus the switching instant can vary for several reasons. At a constant adjustment of the setscrew, the spring stress of the snap-action contact alters with varying ambient temperature. The switching instant therefore changes, since a different force is required to bring the snap-action contact member into the switching position. The electromecham- cal time-lapse relay thus carries out the switching operation at varyirg instants depending on the ambient temperature. A further drawback is that pre-stressed leaf springs used as snap-action contact members lose their original elasticity after a relatively small number of switching cycles.

It is an object of the invention to obviate or at least mitigate the above disadvantages.

According to the invention there is provided a snap-action mechanism for an electromechanical time-lapse relay comprising a synchronous motor, gearing driven by the motor, a time-lapse wheel connected to an output of the gearing, a trip cam provided on the time lapse wheel, a rocker forming a snap-action lever for actuating at least one contact member, a pre-stressing lever interposed between the snap-action lever and a stressing cam on the time-lapse wheel such that the pre-stressing lever is movable by the stressing cam during movement of the wheel, the pre-stressing lever being in engagement with the snap-action lever by way of a compression spring and being movable relatively to the snap-action lever by the stressing cam to pre-stress said spring, the snap-action lever being lockable by a locking lever, and the locking lever being arranged to be moved by the trip cam during movement of the wheel so that the locking lever moves from a position in which the locking lever locks the snap-action lever to a position allowing release of said snap-action lever.

The invention makes it possible to improve the known snap-action mechanism for an electromechanical time-lapse relay such that a constant switching speed and high repetition accuracy of the switching instant may be achieved.

It is an advantage of the invention that a special member is used for pre-stressing the spring. This member is not used for tripping the switching operation. The actuating member by which the switching instant is tripped is therefore completely relieved of the role of producing pre-stressing. In this way, each member is able to perform its own operation without further operations being made dependent on it.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Fig. I is a fragmentary side view partly in section of one embodiment of the snapaction mechanism according to the invention for an electromechanical time-lapse relay, seen in the direction of arrow I in Fig. 2, and Fig. 2 is a fragmentary plan view partly in section of the snap-action mechanism in Fig.

1 seen in the direction of arrow II in Fig. 1.

In the drawings, a time-lapse wheel driven by a synchronous motor is designated generally by the reference numeral 1 (Fig. 2). This time-lapse wheel 1 is mounted on an output shaft 2 of gearing. A locking lever 3 mounted on a pin 4 engages with a leaf spring 5 which is held under stress by a pin 6. The locking lever 3 is thereby pivoted against one wall 7 of a housing only a small portion of which is shown.

At right-angles to the locking lever 3, a snap-action lever 8 (Fig. 1) is pivotally mounted on a pin 24 of the housing. The snap-action lever 8 is provided with a further pivot pin on which a pre-stressing lever 9 is pivotally mounted. The snap-action lever 8 and the pre-stressing lever 9 are both constructed as rockers. A compression spring 10 is located at one end of the pre-stressing lever 9. This compression spring bears at one end in a recess in the pre-stressing lever 9 and at the other end bears against one face of the snap-action lever 8. The pre-stressing lever 9 is able to pivot relative to the snap-action lever 8 on the pivot pin of the latter, its angle of traverse being limited by a stop face 11.

A second compression spring 12 is located on the opposite side of the pin 24 from the compression spring 10. One end of the compression spring 12 bears against a wall 13 of the housing and its other end bears against the snap-action lever 8. The spring 12 thus pushes the snap-action lever 8 against a stop 23 on the housing. This position in which the snap-action lever 8 is pushed against the stop 23 on the housing will be referred to hereinafter as the inoperative position of the snapaction lever 8.

The snap-action lever 8 comprises actuating surfaces 14. Switching members which are actuated either directly or by way of actuating members 15 are located opposite the actuating surfaces 14. In the inoperative position of the snap-action lever 8, the switching members or their actuating members 15 are not in contact with the associated actuating surfaces 14 of the snap-action lever 8.

In a modification (not shown), the snapaction lever is provided with actuating members attached thereto in place of the actuating surfaces.

In the inoperative position, the snapaction lever 8 is not in contact with the end of the locking lever 3. Guide grooves 16 are provided in the housing. Projections of the snap-action lever 8 are guided in the grooves 16 in order to facilitate high return accuracy.

A stressing cam 17 is provided on the timelapse wheel 1 illustrated in Fig. 2.

During the rotation of the time-lapse wheel 1 in the direction of the curved arrow, the stressing cam 17 meshes with an actuating pin 18 on the pre-stressing lever 9. A trip cam 19 is also attached to the time-lapse wheel 1. At the tripping instant, the cam 19 comes into engagement with an actuating pin 20 formed on the locking lever 3.

The operation of the time-lapse relay will now be described in detail: The time-lapse wheel 1 is rotated by the synchronous motor by way of the gearing, in the direction of the curved arrow. Shortly before the switching instant, the stressing cam 17 comes to bear against the actuating pin 18 of the pre-stressing lever 9. Upon further movement the stressing cam 17 pivots the pre-stressing lever 9 and the snap-action lever 8, by means of the actuating pin 18, about the pin 24. This pivoting movement occurs until the snap-action lever 8 comes into contact with the locking lever 3. Upon further rotation of the time-lapse wheel 1 and therefore a further movement of the stressing cam 17, the snap-action lever 8 in contact with the locking lever 3 is locked thereby and does not move further, but the pre-stressing lever 9 pivots further on the pivot pin of the snap-action lever 8. The compression spring 10 is thus compressed (i.e. pre-stressed) between the pre-stressing lever 9 and the snap-action lever 8. At this instant, the trip cam 19 of the time-lapse wheel comes into engagement with the actuating pin 20 of the locking lever 3.

Upon further rotation of the time-lapse wheel 1, the trip cam 19 pivots the locking lever 3 in Fig. 2 in the clockwise direction about the pin 4. This pivotal movement occurs until the surface 21 at one end ofthe locking lever 3 comes into alignment with the opposite inner surface 22 of the snap-action lever 8. At this instant the snap-action lever 8 is released by the locking lever 3, and due to the force of the pre-stressed compression spring 10 the snap-action operation of the snap-action lever takes place. The snapaction operation of the snap-action lever 8 is transmitted by way of the surfaces 14 on the snap-action lever to the actuating rods 15, which in turn operate sets of contacts. One of these sets of contacts stops the motor so that the gearing and time-lapse wheel are stopped.

If the connection between the gearing and the time-lapse wheel 1 is interrupted, then due to a torsion spring (not shown), the timelapse wheel 1 rotates back to a pre-set time value. The snap-action lever 8 and prestressing lever 9 are returned by the compression spring 12 to the inoperative position, so that the snap-action lever 8 comes to bear against the stop 23. The leaf spring 5 returns the locking lever to its position in readiness to lock the snap-action lever.

WHAT WE CLAIM IS: 1. A snap-action mechanism for an electromechanical time-lapse relay comprising a synchronous motor, gearing driven by the motor, a time-lapse wheel connected to an output of the gearing, a trip cam provided on the time-lapse wheel, a rocker forming a snap-action lever for actuating at least one contact member, a pre-stressing lever interposed between the snap-action lever and a stressing cam on the time-lapse wheel such that the pre-stressing lever is movable by the stressing cam during movement of the wheel, the pre-stressing lever being in engagement with the snap-action lever by way of a compression spring and being movable relatively to the snap-action lever by the stressing cam to pre-stress said spring, the snap-action lever being lockable by a locking lever, and the locking lever being arranged to be moved by the trip cam during movement of the wheel so that the locking lever moves from a position in which the locking lever locks the snap-action lever to a position allowing release of said snap-action lever.

2. A snap-action mechanism for an electromechanical time-lapse relay, substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (2)

**WARNING** start of CLMS field may overlap end of DESC **. the force of the pre-stressed compression spring 10 the snap-action operation of the snap-action lever takes place. The snapaction operation of the snap-action lever 8 is transmitted by way of the surfaces 14 on the snap-action lever to the actuating rods 15, which in turn operate sets of contacts. One of these sets of contacts stops the motor so that the gearing and time-lapse wheel are stopped. If the connection between the gearing and the time-lapse wheel 1 is interrupted, then due to a torsion spring (not shown), the timelapse wheel 1 rotates back to a pre-set time value. The snap-action lever 8 and prestressing lever 9 are returned by the compression spring 12 to the inoperative position, so that the snap-action lever 8 comes to bear against the stop 23. The leaf spring 5 returns the locking lever to its position in readiness to lock the snap-action lever. WHAT WE CLAIM IS:

1. A snap-action mechanism for an electromechanical time-lapse relay comprising a synchronous motor, gearing driven by the motor, a time-lapse wheel connected to an output of the gearing, a trip cam provided on the time-lapse wheel, a rocker forming a snap-action lever for actuating at least one contact member, a pre-stressing lever interposed between the snap-action lever and a stressing cam on the time-lapse wheel such that the pre-stressing lever is movable by the stressing cam during movement of the wheel, the pre-stressing lever being in engagement with the snap-action lever by way of a compression spring and being movable relatively to the snap-action lever by the stressing cam to pre-stress said spring, the snap-action lever being lockable by a locking lever, and the locking lever being arranged to be moved by the trip cam during movement of the wheel so that the locking lever moves from a position in which the locking lever locks the snap-action lever to a position allowing release of said snap-action lever.

2. A snap-action mechanism for an electromechanical time-lapse relay, substantially as hereinbefore described with reference to the accompanying drawings.