US2767262A - Sequential switch - Google Patents

Description

M. L. HEINTZ SEQUENTIAL SWITCH Oct. 16, 1956 2 Sheets-Sheet 1 Filed Feb. 2, 1954 Fig.2.

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Milton L. d

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Oct. 16, 1956 M. 1.. HEINTZ 2,

SEQUENTIAL SWITCH Filed Feb. 2, 1954 I 2 Sheets-Sheet 2 Fig.6.

Inventor:

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United States Patent SEQUENTIAL SWITCH Milton L. Heintz, Broomall, Pa., assignor to General Electric Company, a corporation of New York Application February 2, 1954, Serial No. 407,675

Claims. (Cl. 200-59 This invention relates to sequential switches and, more particularly, to improvements in sequential switches of the general type disclosed in Patent No. 2,627,559, Netzel, issued February 3, 1953, and assigned to the assignee of the present invention The sequential switch of the above-mentioned patent comprises a main switch member and a discharge switch member and is constructed in such a manner that these switch members are separately movable in opposite directions with respect to each other by means of a common reciprocable operating shaft. As a result of this opposite movement of the switch members, one of the switch members is closed while the other is opened and vice versa. To provide for the required overlap in the closing and opening operations of the switch members of the above-mentioned patent, a lost motion connection is provided between the reciprooable operating shaft and the operating linkage for the discharge switch member. The presence of this lost motion connection makes it necessary to provide separate closing springs for moving the discharge switch into closed position during the time that the tripped operating shaft, while moving to open the main switch member, is in lost motion relationship to the operating linkage of the discharge switch unit.

Although these closing springs operate effectively for certain applications, a discharge switch unit which employs such springs is subject to the disadvantage that the closing movement of the discharge switch member, being under the independent influence of the closing springs, can undesirably lag behind the fast tripping opening movement of the main switch member. Additionally, certain parts of the operating linkage for the discharge switch are maintained in a highly stressed condition by bending forces produced by the charged closing springs. Because these stressed parts must be made of insulating material, due to their close association with the live components of the switch, these parts are subject to permanent distortion which may harmfully affect the gap distance of the open discharge switch contacts.

It is, therefore, an object of my invention to construct the operating linkage for the movable discharge switch member of such a sequential switch in such a manner that separate springs are not required to provide the desired closing operation.

It is a further object of this invention to provide a linkage which, under all conditions, insures. positive contact sequencing motion between the main contacts and the discharge contacts.

In carrying out my invention in one form, I provide, in a switch having a pair of reversely-movable switch members coupled together for sequential operation, a toggle connected to one of said switch members and having a 1 art movable in opposite directions to collapse and extend said toggle, thereby respectively opening and closing said one switch member. For operating the toggle, these is provided a reciprocable operating shaft movable from a fully open position to a closed position to extend said toggle and reversely-movable to collapse said toggle,

2,767,262 Patented Oct. 16, 1956 and a lever pivoted intermediate its ends and having one end positively coupled to said operating shaft and having its other end coupled to the toggle actuating part by a linkage including a thrust member having varying effective speeds of toggle-actuating movement during rnovernrent of said operating shaft through its stroke. This thrust member is arranged in such a manner that its highest eifectivc toggle-actuating speed occurs during initial switch member-closing movement of the operating shaft.

Further objects and advantages of my invention will become apparent as the following description proceeds, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and fonning a part of this specification.

For a better understanding of my invention reference may be had to the accompanying drawings wherein Fig. l is a schematic view of the sequential switch of the present invention, the switch being connected to control the energizati-on and discharge of a field winding.

Fig. 2 is a schematic view similar to Fig. 1 but showing the switch contacts in a different position from Fig. 1.

Fig. 3 is a detailed view of the discharge switch unit shown in its fully-open contact position.

Fig. 4- is a detailed view of the discharge switch unit shown in its closed contact position.

Fig. 5 is a modified form of discharge switch unit shown in open-contact position.

6 shows the switch unit of Fig. 5 in closed-contact position.

The circuit breaker illustrated schematically in Fig. 1 comprises a pair of outside poles 1 and 2 and an inside pole 3 mounted intermediate the outside poles. Since the construction of the contact members for each of these poles is substantially identical and corresponds to the contact construction for the circuit breaker shown in the above-mentioned Netz-el patent, only the contact structure for the intermediate pole 3 will be described in detail. As shown in Figs. 3 and 4, this pole 3 comprises a movable contact or switch member 4 pivotally mounted at its lower end on a current conducting pivot pin 4a which electrically interconnects the conductive contact-supporting structure 5 with the contact member 4.

At its upper end the contact member 4 is movable into and out of extended wiping engagement with a c0- operating cont-act finger 6. For providing this extended wiping engagement, the cooperating contact finger 6 is pivotally mounted by means of a rounded bearing projection 7 formed thereof and seating in an open groove formed in the inside surface of a J-shaped conducting member 8. This pivoted contact finger 6 is biased into the path of the cooperating contact member 4 by means of a compression spring 9 urging a slidably mounted pin 9a into engagement with the back surface of the contact finger 6. Since, as previously specified, the contact structure for each of the three poles of the circuit breaker is substantially identical, extended wiping engagement is provided in the outer poles i and 2 in the same general manner as described with respect to the intermediate pole 3.

The movable contacts, or switch members, of the outside poles 1 and 2, being coupled by conventional insulating links ll to a laterally reciprocable operating shaft diagrammatically shown at 12, are simultaneously operable between open and closed position by this reciprocable shaft 12. As will appear hereinafter, the movable contact 4 of the intermediate pole or switch unit 3 is operated in a reverse direction with respect to the outer pole contact member by means of the common operating shaft 12. For guiding the reciprocable operating shaft 12, the circuit breaker housing is provided with a pair of guide slots, indicated at 14, each having opposite ends between which the operating shaft 12 ciprocable to open and close the poles 1, 2, and 3.

For moving the operating shaft 12 at high speed between the ends of guide slot 14, a conventional form of switch operating mechanism (not shown) may be used. Preferably, however, the described switch employs the improved trip-free toggle, latch type of operating mechanism described and claimed in Patent No. 2,549,441, Favre. In such a mechanism, when the operating shaft is positioned at the right hand end of guide slot 14, as shown in Fig. l, the main poles l and 2 are closed and the operating shaft is latched against the bias of opening springs (not shown) tending to force the shaft 12 to the left hand end of the slot 14. When the opening springs are unlatched, they move the operating shaft at high speed from the right hand end of the slot 14 to the left hand end thereof. For moving the shaft 12 from left to right so as to close the main poles 1 and 2, the operating mechanism includes a suitable trip-free toggle linkage.

The circuit breaker, or switch, of the present invention is especially adapted to control the energization and discharge of the field winding for an electrical machine. This is illustrated in Fig. l where the field winding of an electrical machine, such as synchronous generator, is shown connected through the outer poles i and 2 to suitable unidirectional current supply lines L1 and L2. In a manner to be described in greater detail hereinafter, when operating shaft 12 is moved in the fixed guide slots 14 from the position of Fig. l to the position of Fig. 2, the outer poles 1 and 2 are opened and the intermediate pole 3 is closed. Closing of the intermediate pole when the outer poles are opened connects a discharge resistor 16 in series with the field winding 15 and thereby allows the field to be discharged through the resistor 16 so as to prevent excessive build up of voltage in the field winding 15.

The most desirable operation of the field discharge switch from the standpoint of maximum protection requires that there be a certain degree of overlap in the operation of the switch units. Specifically, the field dis charge switch unit 3 should be moved to closed position before the main units 1 and 2 are moved from closed to open position. Similarly, the discharge switch unit should be opened only after the main poles have been closed.

To provide for the desired overlap in the above switch operations, I have provided an improved linkage 2% for operatively interconnecting the main operating shaft 12 and the movable contact member 4 of the field discharge switch unit 3.

Referring to the detailed views of Figs. 3 and 4, this linkage 20 includes a toggle 22 which is extensible to move the pivoted discharge switch member 4 from the open position of Fig. 3 to the closed position of Fig. 4 and is collapsible to move the switch member 4 in a reverse direction from closed to open position. This toggle 22 comprises a first insulating toggle link 23 and a sec ond insulating toggle link 24 pivotally joined at their inner ends by a knee 25. The outer end of link 23 is pivoted on a fixed pivot pin 26, and the outer end of link 24 is pivotally joined to the movable switch member 4 by a pivot pin 27.

The linkage 20 additionally includes an actuating lever 28 of insulating material pivoted intermediate its ends on the fixed pivot pin 26 and coupled at its upper end to the reciprocating operating shaft 12. This coupling between the operating shaft 12 and the lever 28 is substantially free of lost motion and is positive for both directions of translatory movement of the operating shaft. Preferably, the pivot 26 for the actuating lever 28 is located near the upper end of the lever 28 so that a small angular displacement of the upper end of the lever by the operating shaft 12 produces a relatively large displacement of the lower end. At the lower end of actuating lever 28, a thrust link 29 is pivotally mounted on a is repivot pin 30 carried by the actuating lever 28. Also included in linkage 20 is a crank arm 31 which has one of its ends pivotally mounted on a fixed pivot pin 32 and is pivotally joined at its other end by a pin 34 to a connecting link 33 of insulating material, which in turn, is connected to the knee 25 of the toggle 22. Intermediate its ends, the crank arm 31 is pivotally joined to the upper end of the thrust link 2% by a pivot pin 35.

The operating characteristics of the linkage 20 will be apparent from the following description of the closing operation of the discharge switch unit 3. Assume first that the operating shaft 12 is positioned at the right hand end of the guide slot 14 and the contact 4 is in its fully open position, as is shown in Figs. 1 and 3. Now when the shaft 12 moves rapidly to the left under the influence of the tripped opening springs (not shown), the pivoted actuating lever 23 being positively coupled to the operating shaft is immediately pivoted in a counterclockwise direction by the operating shaft 12. This counterclockwise movement of lever 28 pivots the thrust link 29 counterclockwise about its lower pivot 39. This counterclockwise motion of thrust link 29 is transmitted to the crank arm 31 through the pivot pin 35 thereby rotating the crank arm 31 counterclockwise about its fixed pivot 32 whereby to drive the connecting link 33 upwardly. Since the connecting link 33 is coupled to the knee 25 of the toggle 22, upward movement of the connecting link 33 extends the toggle 22 and, accordingly, drives the movable contact 4 into contact-closing engagement with its cooperating contact finger 6.

Referring to Fig. 3, from the above description it may be observed that the component of force which is transmitted through pin 35 to cause actuation of the primary toggle 22 acts in a direction normal to a radius R connecting the axes of pivot pins 32 and 35. It is to be further observed that the velocity component of pin 35 which acts in the above mentioned normal direction is comparatively large when counterclockwise motion of the thrust link 29 about its lower pivot 30 (from the position of Fig. 3) is initiated. However, as the pin 35, in moving to the position of Fig. 4, approaches the centerline S extending between the axis of pins 26 and 30, this toggle-actuating velocity component of pin 35 rapidly diminishes. In accordance with the present invention, the comparatively large toggle actuating velocity which occurs during the first portion of counterclockwise movement of links 28 and 29 is utilized to move contact 4 to closed position during this first portion of movement, whereas the highly diminished toggle actuating velocity which follows permits continued counterclockwise movement of links 28 and 29 through a comparatively large arc with only a slight resulting continuation in the closing movement of the contact 4. It should be apparent from this operational description that the thrust link 29 and the lever 28 together form a tension toggle, i. e., a toggle in which one of the links 28 is placed under tension by movement of the knee 3%} toward toggle center. It will also be apparent that this tension toggle moves toward and into the region of toggle center as the closing stroke progresses, as is evidenced by the movement of pin 35 toward center line S as the closing stroke progresses.

This characteristic of the linkage 20 which permits continued counterclockwise pivoting of lever 23 accompanied by only slight movement of contact 4 once the contact 4 has been moved to closed position, permits the shaft 12 to positively close the switch unit 3 during the first portion of shaft movement from right to left without producing further significant closing movement of the contact member 4 during the last portion of shaft movement from right to left.

The importance of this characteristic will be apparent from the following description of the operation of the complete sequential switch. Assume first that the circuit breaker parts are in the position of Fig. 1, i. c. with the operating shaft 12 positioned at the right hand end of the slot 14 with the main poles 1 and 2 in closed position whereby to connect field 15 across the supply lines L1 and L2, and with the field discharge switch unit 3 in open position. Now if the shaft 12 moved rapidly to the left in response to tripping of the circuit breaker, the shaft 12, being positively coupled by the linkage 20 to the discharge contact member 4 rapidly and in the first portion of its movement, positively drives this contact member 4 to closed position. During the time that this closing operation of discharge switch unit 3 is taking place, the outer main switch contacts have not yet parted for they are still passing through their opening wipe relationship. As the operating shaft 12 continues in its movement toward the left, the operating shaft disengages the main contacts, but not until the discharge contacts have closed, and then rapidly separates the main con tacts until they are moved into the fully open position of Fig. 2. During the time that the main contacts are moving apart after breaking contact, it will be apparent that, as a result of the previously described characteristics of the linkage 20, only slight wiping movement of the discharge switch member 4 in its closed position is occurring. Accordingly, rapid separation of the main contacts over a substantial distance may be effected with negligible corresponding wiping movement of the dis charge switch contacts in their now closed position. It will be apparent that by reason of the construction of the linkage 20, lost motion between the operating shaft 12 and the lever 28 is obviated and, as a result, no separate springs are required to close the discharge switch unit. In the present invention, this closing movement of the discharge contact is effected by a positive drive connection between the operating shaft 12 and the movable discharge contact 4.

It will be further apparent that the movable discharge contact 4 is maintained in closed position by the substantially fully extended toggle 22. This extended toggle effectively holds the movable contact 4 in closed position and serves to prevent the transmission of forces from the movable contact member 4 back through the linkage 2%.

Closing of the main contacts is effected by moving the operating shaft 12 from the left to the right end of guide slot 14. Such movement rapidly closes the contacts of the main poles 1 and 2 but is ineffective to open the discharge switch unit 3 until after closing of these main contacts. This desired delayed opening of the discharge switch results from the fact that the toggle actuating velocity of thrust member 29 is extremely low for initial left to right movement of the operating shaft 12. The slight movement of the movable contact member 4 which occurs during this initial movement is taken up by the contact wipe in the discharge switch unit 3.

Figs. 5 and 6 illustrate a modified form of discharge switch unit constructed in accordance with the present invention. The parts of this switch unit which correspond to similar parts in Figs. 1-4 have been given corresponding reference numerals.

Referring to the drawings it will be observed that the principal difference between the two forms of switches is the construction of the coupling between the lower end of the lever 28 and the thrust member or crank arm 31.

In Figs. 1-4 I have obtained, during movement of the operating shaft 12 through its stroke, a variable angular velocity ratio between the lever 28 and the crank arm 32 by means of thrust link 2?, whereas in Figs. 56 I have obtained this variable angular velocity ratio by providing the crank 31 with an L-shaped cam slot 50, which cooperatively receives a lever pin 51 carried by lever 28.

Fig. 5 illustrates in solid lines the position of the parts when the movable contact 4 is in its fully open position. In such a switch position the pin 51 is disposed in the steep portion 52 of the cam slot 50. Now when the operating shaft 12 is moved from right to left in the guide slot 14, i. e., in a direction to effect closing of the discharge switch unit 3, the pin 51 at the lower end of lever 28 is moved counterclockwise about fixed pivot 26. Since initial movement of the pin 51 takes place in the steep portion 52 of the cam slot 50, a slight initial movement of the pin 51 produces a comparatively large toggle-actuating movement of the thrust member or crank arm 31 and the connecting link 33. This is illustrated by the dotted line positions shown in Fig. 5, wherein it may be seen that when pin 51 has been initially moved only slightly into the dotted line position, the toggle 22 has been extended to a dotted line position in which the contact 4 is almost closed. The cam slot 50 is shaped so that once the contact 4 has been closed by pin movement in the steep portion 52, the pin 51 moves into a flattened portion 53 of the cam slot. In this flattened portion of the slot, continued counterclockwise movement of the pin 51 produces little or no further movement of the contact member 4.

To further describe the shape of cam slot 50, it will be noted that the slope of the flattened portion 53 of the cam slot is more effectively tangential with respect to center of rotation 26 of the lever 28 than is the slope of the steep portion 52 of the slot 50.

From the above description of the characteristics of the cam connection, it will be apparent that the operating shaft 12, once it has driven the discharge contact 4 to closed position, may continue in its movement with negligible corresponding movement of the discharge contact whereby to effect positive sequential opening of the main contacts, as pointed out hereinabove. Fig. 6 illustrates the relationship of the parts when the discharge switch unit 3 is closed and the main switch units (not shown) are fully open.

As in Figs. l-4, reverse movement of the operating shaft 12, i. e., from left to right, rapidly closes the main contacts, but is ineffective to open the discharge switch unit 3 until after closing of the main contacts, at which time the pin 51 moves out from the flattened portion of cam slot 50 and into the effective steep portion 52 thereof. Thus, this return movement of the pin 51 in the steep portion of the cam slot is effective to move the discharge contact 4 back to the initial open position.

While I have shown and described particular embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the invention in its broader aspects and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a switch having a pair of switch members coupled together for mutually reverse circuit controlling movement, a toggle linkage connected to one of said switch members and having an actuating part movable in opposite directions to extend and collapse said toggle linkage thereby respectively closing and opening said one switch member, a laterally reciprocable operating member positively coupled to the other of said switch members and movable through a closing stroke to extend said toggle and reversely movable to collapse said toggle, a lever pivoted intermediate its ends and having one end positively coupled to move with said reciprocable operating member, a thrust member coupled to said toggle actuating part and to said lever and forming with said lever a second toggle which moves toward and into the region of its center position as said closing stroke progresses whereby the highest effective actuating speed of said thrust member occurs during the initial portion of said closing stroke.

2. In a switch having a pair of switch members coupled together for mutually reverse circuit controlling movement, a toggle linkage connected to one of said switch members and having an actuating part movable in 7 opposite directions to extend and collapse said toggle linkage thereby respectively closing and opening said one switch member, a laterally reciprocable operating memberpositively coupled to said other switch member and movable through a closing stroke to extend said toggle and reversely movable to collapse said toggle, a pivoted lever having one portion positively coupled to move with said reciprocable operating member, a thrust member coupled between said toggle actuating part and another portionof said lever and forming with said lever a second toggle which moves toward and into the region of its center position as said closing stroke progresses Whereby the highest effective actuating speed of said thrust member occurs during the initial portion of said closing stroke.

3. In a switch having a pair of contact members coupled together for mutually reverse circuit controlling movement, a toggle linkage connected to one of said contact members and having an actuating part movable in opposite directions to extend and collapse said toggle linkage thereby respectively closing and opening said one contact member, a laterally reciprocable operating member positively coupled to the other of said contact members and movable from a fully-open position to a closed position to extend said toggle and reversely movable to collapse said toggle, a pivoted lever having one portion positively coupled to move with said reciprocable operating member, a crank arm pivotable about a stationary pivot and connected to move said toggle actuating part, a connection between said crank arm and another portion of said lever providing a variable angular velocity ratio between said lever and said crank arm during movement of said operating member through its contact closing stroke, said angular velocity ratio being relatively high during initial contact closing movement of the operating member and diminishing thereafter.

4. In a switch having a pair of contact members coupled together for mutually reverse circuit controlling movement, a toggle linkage connected to one of said contact members and having an actuating part movable in opposite directions to extend and collapse said toggle linkage thereby respectively closing and opening said one contact member, a laterally reciprocable operating member positively coupled to the other of said contact members and movable from a fully-open position to a closed position to extend said toggle and reversely-movable to collapse said toggle, a pivoted lever having one portion positively coupled to move with said reciprocable operating member, a pivotable crank arm connected to move said toggle actuating part, a thrust link pivotally interconnecting said crank arm and another portion of said lever and forming with said lever a second toggle which provides a variable angular velocity ratio between said lever and said crank arm during movement of said operating member through its contact closing stroke, said second toggle being arranged to move toward and into the region of toggle center as said closing stroke progresses whereby said angular velocity ratio is relatively high during the initial portion of the closing stroke and diminishes thereafter.

5. In a switch having a pair of contact members coupled together for reverse circuit controlling movement, a toggle linkage connected to one of said contact members and having an actuating part movable in opposite directions to extend and collapse said toggle linkage thereby respectively closing and opening said one contact member, a laterally reciprocable operating element movable from a fully-open position to a closed position to extend said toggle and reversely movable to collapse said toggle, a pivoted lever member having one portion positively coupled to move with said reciprocable operating element, a pivotable crank member connected to move said toggle actuating part, a slotted cam portion on one of said members, a cooperating projection on the other of said members slidably received in said cam slot, said cam slot having varying efi'ective slopes with respect to the pivot point for said lever member whereby to provide a variable angular velocity ratio between said lever and said crank arm during movement of said operating member through its contact closing stroke, said angular velocity ratio being relatively high during initial contact closing movement of the operating member and diminishing thereafter.

6. In a switch having a pair of contact members coupled together for reverse circuit controlling movement, a toggle linkage connected to one of said contact members and having an actuating part movable in opposite directions to extend and collapse said toggle linkage thereby respectively closing and opening said one contact member, a laterally reciprocable operating member movable from a fully-open position to a closed position to extend said toggle and reversely movable to collapse said toggle, a lever pivoted about a center of rotation and having one portion positively coupled to move with said reciprocable operating member, a pivotable crank arm having a cam slot and connected to move said toggle actuating part, a projection carried by another portion of said pivoted lever and slidably movable within said cam slot from a first position to a second position as said operating member moves from its fully-open to its closed position respectively, the portion of the cam slot adjacent said second position being more effectively tangential with respect to said center of rotation than the cam slot portion adjacent said first position.

7. In a switch having a pair of mutually reverselymovable contact members coupled together for sequential circuit controlling operation, a toggle linkage operatively connected to one of said contact members and having an actuating part movable in opposite directions to extend and collapse said toggle linkage thereby respectively closing and opening said one contact member, a laterally reciprocable operating member positively coupled to the other of said contact member and movable through a closing stroke to extend said toggle and reversely movable to collapse said toggle, a pivoted lever having one portion positively coupled to move with said reciprocable operating member, a pivotable crank connected to move said toggle actuating part, a thrust member pivotally connected between said lever and said crank and forming with said lever a tension toggle which moves toward and into the region of toggle center as said closing stroke progresses whereby the highest effective actuating speed of said thrust member occurs during the initial portion of said closing stroke.

8. In a switch comprising a pair of switch members which are movable in mutually-reverse directions, a common laterally-movable operating member for said switch members, means for positively coupling said operating member to one of said switch members, a crank arm mounted for angular movement about a stationary pivot, a linkage coupling said crank arm to the other of said switch members and operable to close said other switch member in response to angular movement of said crank arm, a lever mounted for angular movement about a stationary pivot and having a portion positively coupled to said operating member, a thrust link pivotally interconnecting said crank arm and another portion of said lever H and forming with said lever a tension toggle which moves toward and into the region of toggle center in response to movement of said operating member in a direction to close said other switch member.

9. In a switch comprising a pair of switch members which are movable in mutually-reverse directions, a common laterally-movable operating member for said switch members, means for positively coupling said operating member to one of said switch members, a crank arm mounted for angular movement about a stationary pivot, a linkage coupling said crank arm to the other of said switch members and operable to close said other switch member in response to angular movement of said crank arm, a lever mounted for angular movement about a stationary pivot and having a portion positively coupled to said operating member, a thrust link pivotally interconnecting said crank arm and another portion of said lever and forming with said lever a toggle which moves toward and into the region of toggle center in response to movement of said operating member in a direction to close said other switch member.

10. In a switch comprising a pair of switch members which are movable in mutually-reverse directions, a common laterally-movable operating member for said switch members, means for positively coupling said operating member to one of said switch members, a crank element mounted for angular movement about a stationary pivot, a linkage coupling said crank element to the other of said switch members and operable to close said other switch member in response to angular movement of said crank element, a lever element mounted for angular movement about a stationary pivot and having a portion positively coupled to said operating member, one of said elements having a slotted cam portion, a cooperating projection on the other of said elements slidably received in said cam slot, said cam slot having varying effective slopes with respect to the pivot point for said lever element whereby to provide a variable angular velocity ratio between said lever element and said crank element during movement of said operating member through a closing stroke for said other switch member, said cam slot being shaped to render said velocity ratio relatively high during first portion of said closing stroke and relatively low thereafter.

References Cited in the file of this patent UNITED STATES PATENTS 1,798,058 Besag Mar. 24, 1931 1,857,220 Thumim May 10, 1932 FOREIGN PATENTS 212,054 Germany July 12, 1909

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