US3752947A

US3752947A - Auxiliary mechanism for operating handle of circuit breaker

Info

Publication number: US3752947A
Application number: US00275454A
Authority: US
Inventors: A Strobel
Original assignee: ITE Imperial Corp
Current assignee: Siemens Energy and Automation Inc; ITE Imperial Corp
Priority date: 1972-07-27
Filing date: 1972-07-27
Publication date: 1973-08-14
Anticipated expiration: 1990-08-14

Abstract

An auxiliary handle mechanism for operating a multipole circuit breaker is provided with a pair of links that transmits operating forces from a relatively long main operating handle to a relatively short circuit breaker handle extension. The main handle and links move in planes generally parallel to the front of the circuit breaker, and the circuit breaker handle moves in a plane generally perpendicular to the front of the circuit breaker. The links are interconnected by a pin-roller means including a follower portion disposed in a cam slot. The latter is designed so that the relative effective lengths of the links change by virtue of the changing position of the connecting pin means relative to the fixed pivots of both links as for different positions of the main handle. The configuration of the cam slot is such that the mechanical advantage achieved by the auxiliary mechanism increases and decreases as the force requirements for operating the contact operating mechanism increase and decrease. As the mechanical advantage is reduced, the motion disadvantage is also reduced.

Description

United States Patent [1 1 Strobel 1 AUXILIARY MECHANISM FOR OPERATING HANDLE OF CIRCUIT BREAKER [75] Inventor: Albert Strobel, Cherry Hill, NJ.

[73] Assignee: I-T-E Imperial Corporation,

Philadelphia, Pa.

221 Filed: July 27,1972

211 Appl.No.:275,454

[52] US. Cl. 200/172 A, 74/99 R Primary Examiner-J. V. Truhe Assistant Examiner-William J. Smith Atlorney- Sidney G. Faber, Bernard Gerb and Jerome M. Berliner et a1.

[ 51 Aug. 14, 1973 57 ABSTRACT An auxiliary handle mechanism for operating a multipole circuit breaker is provided with a pair of links that transmits operating forces from a relatively long main operating handle to a relatively short circuit breaker handle extension. The main handle and links move in planes generally parallel to the front of the circuit breaker, and the circuit breaker handle moves in a plane generally perpendicular to the front of the circuit breaker. The links are interconnected by a pin-roller means including a follower portion disposed in a cam slot. The latter is designed so that the relative effective lengths of the links change by virtue of the changing position of the connecting pin means relative to the fixed pivots of both links as for different positions of the main handle. The configuration of the cam slot is such that the mechanical advantage achieved by the auxiliary mechanism increases and decreases as the force requirements for operating the contact operating mechanism increase and decrease. As the mechanical advantage is reduced, the motion disadvantage is also reduced.

12 Claims, 6 Dining Figures Patented Aug. 14, 1973 5 Sheets-Sheet 1 Patented Aug. 14, 1973 5 Sheets-Sheet 2 Patented Aug. 14, 1973 s Sheets-Sheet 3 Patented Aug. 14, 1973 5 Sheets-Sheet 4 Patented Aug. 14, 1973 5 Sheets-Sheet 5 "I" n My. Z4; 2 Z52 I i I I M @60/ K AUXILIARY MECHANISM FOR OPERATING HANDLE F CIRCUIT BREAKER This invention relates to molded case circuit breakers in general and more particularly relates to a novel auxiliary handle mechanism in which mechanical advantages are varied in accordance with the forces required to load the contact operating springs for different positions of the circuit breaker handle.

Molded case circuit breakers are usually constructed with a spring powered overcenter toggle mechanism for contact operation. This mechanism is operable by means of a molded insulating handle which is, in essence, an extension of the operating member in the mechanism for moving the contacts to open and closed positions. As the current ratings of circuit breakers increase, the required contact operating and pressure forces increase so that the forces provided by the operating mechanism must also increase.

Since it is desirable to maintain the overall size of a circuit breaker to a minimum, the available space within the mechanism for obtaining operating leverage is very restricted especially when the operating springs required become larger and larger with increased force requirements. As the forces required to operate the circuit breaker handle increase, the prior art often pro vided a molded extension handle to keep the force that had to be applied by the operator within a reasonable range.

Recently the current capacity and force requirements of molded case circuit breakers have reached such high levels that mere extension handles no longer appear to be practical. Thus, an auxiliary mechanism must be provided to obtain the necessary leverage to reduce forces that must be applied by the operator. Usually these auxiliary mechanisms are partially incorporated in the circuit breaker cover, with a spring loaded member providing the connection to the primary contact operating mechanism. This makes removal of the circuit breaker cover fairly difficult, and may create insulating problems.

In accordance with the instant invention, an auxiliary handle mechanism having a very shallow housing is bolted directly to the outside of the circuit breaker cover. A pair of spaced rollers in the auxiliary mechanism positioned on opposite sides of the circuit breaker handle extension engage a roller on the extension to provide the driving connection between the auxiliary mechanism and the circuit breaker handle.

The auxiliary mechanism includes a pair of slotted links or levers interconnected by roller means guided by a cam slot so that the position of the roller means changes with respect to both of the lever pivots for different positions of the auxiliary mechanism handle, and as the position of this roller means changes the relative effective lengths of the levers also change. The cam means is so constructed that as the forces required to operate the circuit breaker mechanism increase for different positions of the circuit breaker handle, the mechanical advantage achieved by the auxiliary mecha nism also increases.

Accordingly, a primary object of the instant invention is to provide a novel auxiliary handle mechanism for a molded case circuit breaker.

Another object is to provide an auxiliary mechanism of this type in which the effective lengths of the operat ing levers are varied in a controlled manner so that the mechanism provides increased mechanical advantages as the forces required to operate the circuit breaker mechanism increases.

Still another object is to provide an auxiliary mechanism of this type that is relatively compact and is of simplified construction.

A further object is to provide a mechanism of this type which is readily mounted to :a circuit breaker.

These objects as well as other objects of this invention will become readily apparent after reading the following description of the accompanying drawings in which:

FIG. 1 is a plan view of a circuit breaker constructed in accordance with teachings of the instant invention.

FIG. 2 is a longitudinal cross-section taken through line 2-2 of FIG. 1, looking in the direction of arrows 2--2, and including an auxiliary handle operating mechanism not shown in FIG. 1.

FIG. 3 is an exploded perspective of one overcenter toggle mechanism and selected elements connected thereto.

FIG. 4 is an exploded perspective of the movable contact structure for one phase.

FIG. 5 is an enlarged longitudinal cross-section of the auxiliary handle operating mechanism taken at right angles to the section of FIG. 2.

FIG. 6 is a cross-section taken through line 6-6 of FIG. 5 looking in the direction of arrows 6--6.

Now referring to the figures. Three phase molded case circuit breaker 25 of FIGS. 1 and 2 includes an individual overcenter spring-powered toggle operating mechanism. Prior art examples of circuit breakers having more than a single operating mechanism for all phases are disclosed in U.S. Pat. Nos. 2,067,935 and 3,125,653.

Circuit breaker 25 includes a molded housing constructed of base 26 and removable cover 27 joined along line 28, and provided with longitudinal internal partitions 31, 32 which divide

housing

26, 27 into three longitudinally extending compartments, one for each phase of circuit breaker 25. Cover 27 isprovided with aperture 29 through which stubby bifurcated extension 33 of operating handle means 30 extends. Each section of handle extension 33 receives an individual pin 34 extending upwardly from the web portion of inverted generally U-shaped operating yoke member 35 of the center phase. Operating members 35 of the outer phases are. each secured to handle means 30 by a pair of screws 152.

Member 35 is pivoted to the spaced arms of generally U-shaped operating mechanism frame 36 at outwardly extending lugs 37. Bolts 48, received by threaded apertures of inturned edges 36a'at the bottom of frame 36,

fixedly secure the latter to base 26. Transverse tie member 49 is riveted to the arms of frame 36 to maintain spacing therebetween and to stabilize the frame structure.

Four-tensioned coil springs 38, each connected at one end thereof to the web oi operating member .35, combine to constitute the main operating spring means for the overcenter toggle-type contact operating mechanism. The other ends of springs 38 are connected to spaced

plates

39, 39 that are pivotally mounted to tog gle knee pin 4). connecting upper and lower 43 tog gle links. The upper ends of upper toggle links 42 are pivotally connected to the spaced arms oi latchablc cradle 40 at pins 44, and the lower ends of lower toggle iinks 43 are pivotally connected to contact carrier 45 by rod 46 that extends between the spaced arms of contact carrier 45. The spaced arms of cradle 40 are positioned adjacent the inner surfaces of the spaced arms of frame 36 and are pivotally connected thereto by pins 47 that are secured to frame 36.

Under normal operating conditions plate 51, secured to web 40a of cradle 40, is in engagement with forward latching surface 52 of auxiliary latch 53. The latter is loosely mounted to pivot rod 55 extending between the spaced arm of mechanism frame 36 and slightly outboard thereof. The coiled end sections of torsion spring member 56 are wound about pivot rod 55, with the ends of these sections bearing against rod 57 and auxiliary latch 53 to bias the latter counterclockwise against stop rod 58. The ends of rods 57 and 58 are supported by the arms of frame 36. Leaf spring 73 secured to auxiliary latch 53 bears against pivot rod 55 biasing latch 53, so that rod 55 will normally lie at the central portion of V-shaped notch 74 of primary latch 53.

The ends of rod 55 projecting outboard of mechanism frame 36 are engaged by the hooked portions at the forward extensions of the arms for U-shaped trip unit frame 60, whose web portion is seated on a forward surface of load strap 61, being secured thereto by bolts 62 that extend through clearance apertures in strap 61 and are received by threaded inserts molded in base 26.

Rear latch tip 54 engages latch tip 63 at the U-shaped forward arm of primary latch 65, whose rear latch tip 64 is engaged by latch plate 67 mounted on one leg of L-shaped carrier 66. Primary latch 65 is pivotally mounted to trip unit frame 60 at stub shaft 69, and the carrier is pivoted on rod 68 to frame 60. Tension spring 75 biases primary latch 65 in a clockwise direction about pivot 69. The other leg' of carrier 66 is provided with transversely extending pin 71 that projects into triangular window 72 of primary latch 65 at a portion thereof near rear latch tip 64, for a reason to be hereinafter explained. Tension spring 76, connected between frame 60 and carrier extension 66a, biases carrier 66 in a counterclockwise direction about its pivot 68 toward latching position.

When automatic tripping occurs, carrier 66 in the faulted phase is moved clockwise either by the deflection of bimetal 77 or movement of magnetic armature 78, causing latch plate 67 to release primary latch 65, which in turn releases secondary latch 53 and permits main operating springs 38 to rotate cradle 40 in a counterclockwise direction to break

toggle

42, 43. The force from main spring 38 acts through cradle 40, primary latch 53, and secondary latch 65 to drive cam surface 78, bounding opening 72, against extension 71 to rotate carrier 66 clockwise, with surface 79 thereof engaging ear 81 of extension 82 on tripper bar 80 which extends between all three phases. This causes tripper bar 80 to rotate in a counterclockwise direction, so that extensions 82 in the non-faulted phases rotate counterclockwise with cam surfaces 83 thereof engaging transversely extending pin 84 of carriers 66 in the nonfaulted phases, rotating them clockwise or in the tripping direction. to release the cradle latching systems in the non-faulted phases, so that the contacts of all three phases are open.

in order to prevent closing of the contacts of any one phase before the operating mechanisms of all phases are latched, circuit breaker 25 is provided with a defeater latching system including defeater latch 80' and defeater lever 90. Latch is pivotally mounted upon rod 55 and includes protrusion 81 extending over the rear of cradle 40 when the latter is in latched position. Latch 80' further includes protrusion 82 extending over the forward end of defeater lever in slot 91 thereof. Coiled tension spring 83 is connected between stop rod 57 and latch 80', passing partially around rod 55, to bias latch 80 in a counterclockwise direction about its pivot 55 and maintaining this pivot in the basic position at the right end of slot 84' in latch 80'. This basic position is established through the engagement of latch stop surface 86 and stop rod 57.

Slot 91 is in the web of the U-shaped forward portion of latch lever 90, with the U arms having pivot pin 69 for lever 90 extending therethrough. Rear portion 89 of lever 90 is positioned below and in interfering relationship with transverse pin 71 mounted to latch plate carrier 66.

During normal relatching of circuit breaker 25, inwardly protruding portions of the operating member 35 arms engage outboard portions of pin 44 to pivot cradle 40 clockwise, whereby the latter cams defeater latch 80' away and moves below auxiliary latch 53. Upon release of the circuit breaker operating handle 30, the elements of the

latch train

53, 65, 66 move into place. However, should'any ofthese elements fail to properly engage or should cradle 40 not have been moved far enough to engage auxiliary latch 53, cradle 40 will pick up defeater latch protrusion 81', causing clockwise rotation of defeater latch 80'. In turn, this causes defeater latch protrusion 82' to engage defeater lever 90 and rotate the latter counterclockwise, with the rear end 89 thereof contacting carrier extension 71 so that latch plate carrier 66 is pivoted in a clockwise or latch train releasing direction. During this releasing movement of carrier 66, surface 79 thereof engages nose 81 of one trip bar extension 82 to rotate common tripper bar 80 in a counterclockwise direction, with the other extensions 82 on bar 80 engaging pins 84 on the latch plate carriers 66 of the other poles, thereby causing the latch systems of all other poles to be released.

The lower end of bimetal 77 is fixedly secured to shading coil 99, and these elements are fixedly secured to molded frame member secured to trip unit frame 60. The horizontal leg of inverted U-shaped stationary magnetic frame member 98 passes through the center of coil 99. Member 98 is secured to the rear of frame 60, with the vertical legs of member 98 being on opposite sides of load strap 61. The other U-shaped magnetic frame member 96 is secured directly to load strap 61, with the ends of the arms for frame members 96 and 98 confronting one another in spaced relationship. Thus, current flowing in load strap 61 generates flux in magnetic frame 96, 98 which induces current flow in shading coil 99 and thereby generates heat that is conducted to bimetal 77 for heating thereof. Coiled tension spring 97, connected between armature 78 and an element mounted to the rear transverse part 60a of frame 60, biases the former away from two spaced legs 98a extending upward from the horizontal leg of member 98, and is drawn downward toward legs 98a when overload currents generate sufficient magnetic flux in

magnetic frame

78, 96, 98.

With particular reference to FIG. 4, it is seen that the movable contact structure for each phase of circuit breaker 25 includes eight main contacts 103-110 and a single arcing contact 101. The latter contact 101 is mounted at the forward end of arm 112, which is pivotally mounted to carrier 45 at toggle connecting rod 46. Main contacts 103-110 are arranged in two parallel rows positioned to the rear of arcing contact 101 and disposed at right angles to the plane of movement of arcing contact arm 112.

Main contacts 103-106 in the forward row are mounted to individual contact arms 113-116 respectively, all pivotally mounted to carrier 45 on rod 46. Main contacts 107-110 in the rear row are mounted to the forward end of the respective contact arms 117-120, respectively, pivotally mounted to carrier 45 on rod 102. All of the contact arms 112-120 are connected to load strap 61 by means of individual stacks 121 of flexible sheet conductors. Contact arms 113-116 are in alignment with and extend over the respective contact arms 117-120, so that the latter group of arms 117-120 block downward movement of the former group of arms 113-116 to establish the open circuit position of contacts 103-106 in a manner which will hereinafter be seen. The open circuit position for arcing contact arm 112 is established through engagement thereof with aligned pins 123, 124 which mount the respective pairs of

main contacts

117, 118 and 119, 120 to

auxiliary carriers

125, 126 respectively. Notch 122 along the lower edge of arcing contact arm 112 provides clearance for pins 123, 124.

Auxiliary carrier 125 is an inverted U-shaped member whose arms extend downwardly through

cutouts

131, 132 in the web portion of contact carrier 45 and straddle four

contact arms

113, 114, 117, 118. Pin 123 secures contacts 1 17, 118 to the lower ends of the arms comprising auxiliary carrier 125. The web of auxiliary carrier 125 is biased towards the web of contact carrier 45 by coiled compression spring 127, which is wound around the threaded body of bolt 128 whose head is positioned below the web portions of contact carrier 45. Self-locking nut 133 mounted to bolt 128 is rotated to adjust the loading of spring 127 with the rectangular shoulder of bolt 128 cooperating with rectangular cutout in carrier 45 to prevent rotation of bolt 128. Thus, in the open circuit position, spring 127 biases the web of auxiliary contact carrier 125 against the web of contact carrier 45, and when the contacts are closed there is a space between the webs of these

contact carriers

45, 125, so that the force exerted by spring 127 acts to bias

contacts

107, 108 into firm electrical engagement with their respective cooperating contact portions on line strap 136.

The mounting of

contact arms

119, 120 to auxiliary contact carrier 126 and mounting of the latter to contact carrier 45 is the same as the mounting of

contact arms

117, 118 and auxiliary carrier 125, so that this de scription will not be repeated.

Binsing forces for each of the contacts 103-106 in the forward row are provided by individual coiled compression springs 138, and each of these springs is mounted in the same way so that only the mounting of one of these springs will be described. The lower end of spring 138 extends into depression 139 in the upper surface of main contact arm 115, and the rear of spring 138 extends into tubular support 141 through the open bottom thereof. Support 141 is mounted to the upper surface of carrier 45 at the web portion thereof, and its upper end is threaded to receive adjusting screw 142 whose lower end bears against disc 143 abutting the upper end of spring 138. It screw 142 is adjusted to set the contact pressure exerted by spring 138, lock nut 144 is tightened to lock this adjustment.

In order to increase the area of engagement between main contacts 103-110 and their respective cooperating stationary main contacts in the very limited space available, it is noted that each of the main contacts is provided with a portion extending outward of its respective contact arm. That is, in order to utilize the space below arcing contact 112,

main contacts

104, 105, 108, 109 have been extended beyond their

respective contact arms

114, 115, 118, 2119 to project below arcing contact arm 112. Similarly,

main contacts

103, 106, 107, have been extended outboard from their respective contact arms 113, 1 16, 117, 120, to lie in the space below the outboard arms of

auxiliary contact carrier

125, 126 and other elements used to connect the movable contact structure to the contact operating mechanism.

The forward end of arcing contact arm 1 12 is biased downward away from the web portion of contact carrier 45 by coiled compression spring 171 whose lower end is positioned by pin 172 extending upward from am 112. The upper end of spring 171 extends into tubular member 173, on the upper surface of the carrier 45 web portion, through the bottom of member 173 and abuts the closed upper end thereof.

The spaced arms of contact carrier 45 are provided with

rearward extensions

45a, 45b that are spaced by and secured to shouldered cylindrical tube 146. After all contact structures, operating mechanisms, latching devices, and automatic trip units are mounted to base 26, and all adjustments to these mechanisms have been made, the contact structures of all phases are operated to the closed circuit position, so that the tubular members 146 of all phases are axially aligned and are positioned above barriers 31, 32 and the longitudinal sides of base 26. Thereafter, cylindrical tie bar 147 is driven longitudinally in the members 146 of all phases to constitute a rigid mechanical connection between the movable contact structures of all phases. The fit between tie rod 147 and tubular members 146 is tight enough to prevent unintentional axial movement of tie rod 147, yet permits tie rod 147 to be removed for convenient servicing and replacement of parts. Mechanism frame 36 is provided with aligned elongated slots 148 to provide clearances for movement of rod 147 during opening and closing of the movable contact structures.

Auxiliary handle operating mechanism (FIGS. 2, 5 and 6) is mounted directly to the front of cover 27 by four screws 251 located at opposite corners of shallow rectangular molded housing 252. Molded main operat* ing handle 253 is positioned outside of housing 252 and is keyed to stub shaft 254 so as to be pivotable in a plane parallel to the front of housing 252. Shaft 254 is journaled by circular apertures in closely spaced parallel support plates 257 and 258. Plates 257 and 258 are secured together as part of an assembly which, for the most part, is disposed within housing 252 and is secured thereto by four bolts 259.

Parallel closely spaced plate-lilte sections 2560, 2562 forming drice link 256 are joined at: their left ends (with respect to FIGS. 5 and 6) at connecting part 256a, and at this region drive link 256 is keyed to shaft 254. Main link 260 is freely mounted at its right end (with respect to FIGS. 5 and 6) on stub shaft 261 whose ends are held in circular apertures of support plates 257, 258.

Links

256, 260 extend toward one another and are provided at their respective free ends with longitudinally extending

slots

263, 264 which receive roller portions of connecting means 265. Other roller portions of connecting means 265 act as followers, being disposed in aligned cam slots 266 in support plates 257, 258.

The central portion of main link 260 is provided with cutout 267 wherein spaced

rollers

268, 269 are disposed.

Stub shafts

271, 272, whereon the

respective rollers

268, 269 are freely mounted, are disposed within circular apertures of retainer plates 273 secured on opposite surfaces of main link 260 by four rivets 274. Roller 222, mounted on extension 33 of circuit breaker handle 30, is disposed between

rollers

268, 269 so as to be engageable thereby for transfer of motion from main operating handle 253 to circuit breaker handle 30.

Thus, it is seen that a force supplied to pivot arm 253 is applied directly to drive link 256 which acts through connecting means 265 to pivot main link 260. This motion of link 260 causes the arcuate surface of one or the other of

rollers

268, 269 to engage the arcuate surface of roller 222 on circuit breaker handle extension 33 to thereby pivot circuit breaker handle 30 for opening and closing of circuit breaker 25 depending upon the direction of movement of main operating handle 253.

It is noted that cam slots 266 force pin-roller connecting means 265 to travel along a predetermined path, and in this manner the effective relative lengths of

links

256, 260 are varied in accordance with the position of handle 253. The effective lengths of

links

256, 260 are the distances between the connecting means 265 and the respective fixed

pivots

254, 261. In the embodiment illustrated, cam slot 266 is an arc drawn about a center located to the left of fixed pivot 254 as seen in FIGS. and 6. The shape of cam slot 266 and its location with respect to fixed

pivots

254, 261 are chosen so that the mechanical advantage afforded by main operating handle 256 and

link system

256, 260 varies in accordance with the force required to operate the contact operating mechanism.

The force that must be applied to handle 253 is also minimized by having the driving connection between auxiliary mechanism 250 and circuit breaker operating handle 30 take place between roller 222 and

rollers

268, 269, all of which are freely rotatable. This essentially eliminates frictional engagement. This arrangement also permits

rollers

222, 268, 269 to be of substantially uniform diameters throughout the lengths thereof.

It is noted that because of high magnitude current flow in circuit breaker 25, the magnetic fields generated are very strong. In order to reduce adverse effects of these magnetic fields, many of the frame parts and operating mechanism parts are constructed of nonmagnetic stainless steel.

For those features of construction in circuit breaker 25 that have not been described in detail herein, reference is made to one or more of the copending applica tions Ser. Nos. [D2028], [D2029]. [D2030], [D2031], [D2032], [D2034], [D2035], [D2036], [D2037], [D2039], [D2040], [D2044], [D2045], and [D2047], all filed of even date herewith, and all assigned to the assignee of the instant invention.

Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now become apparent to those skilled in the art. Therefore, this invention is to be limited not by the specific disclosure herein but only by the appending claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. The combination comprising a circuit breaker and an auxiliary handle mechanism mounted thereto; said circuit breaker including an enclosure having a front wall, and a spring powered overcenter toggle contact operating mechanism including a contact operating handle having an extension projecting through an opening in said front wall and mounted for movement in a first plane; said auxiliary handle mechanism including support means, a main link mounted at one end thereof to a first pivot fixed on said support means, a drive link mounted at one end thereof to a second pivot fixed on said support means, connecting means drivingly connecting said links to one another at intersecting portions thereof located in a region generally between said pivots, main operating handle means for applying an operating force to pivot said drive link about said second pivot in a plane generally perpendicular to said first plane with this operating force being transmitted through said connecting means to pivot said main link in a plane generally perpendicular to said first plane, and engaging means carried by said main link at a point intermediate said first pivot and said connecting means to transmit operating force from said main link to said extension of said contact operating handle; and guide means for directing movement of said connecting means in an operating path displaced from arcuate paths about either of said pivots as a center to change the relative effective lengths of said links in a predetermined relationship as the angular position of said drive link changes.

2. A combination as set forth in claim 1 in which the predetermined relationship is dictated primarily by differing forces required to move said contact operating handle at different positions thereof.

3. A combination as set forth in claim 1 in which the guide means comprises cam means on said support means, and said connecting means includes a follower portion in operative engagement with said cam means.

4. A combination as set forth in claim 3 in which the connecting means includes additional portions riding in first and second longitudinally extending slots in said main and said drive links, respectively.

5. A combination as set forth in claim 4 in which the follower and additional portions of said connecting means comprise roller means.

6. A combination as set forth in claim 4 in which the main and drive links comprise plate-like elements.

7. A combination as set forth in claim 6 in which the support means includes a shallow housing; said main operating handle being disposed in front of said housing and said link being disposed behind said main operating handle and within said'housing.

8. A combination as set forth in claim 7 in which the predetermined relationship is dictated primarily by differing forces required to move said contact operating handle at different positions thereof.

9. A combination as set forth in claim 7 in which the support means also includes first and second spaced parallel plates disposed within said housing in planes generally perpendicular to the first plane; said links being disposed between said plates.

rollers mounted on axes perpendicularto the planes of said plates; and said extension of said contact operating handle including another roller disposed between said spaced rollers and engageable thereby as said main link is pivoted; said another roller being mounted on an axis perpendicular to said first plane.

t k t III

Claims

7. A combination as set forth in claim 6 in which the support means includes a shallow housing; said main operating handle being disposed in front of said housing and said link being disposed behind said main operating handle and within said housing.

10. A combination as set forth in claim 9 in which the cam means comprises aligned slots in said plates.

11. A combination as set forth in claim 10 in which the predetermined relationship is dictated primarily by differing forces required to move said contact operating handle at different positions thereof.

12. A combination as set forth in claim 11 in which the engaging means comprises first and second spaced rollers mounted on axes perpendicular to the planes of said plates; and said extension of said contact operating handle including another roller disposed between said spaced rollers and engageable thereby as said main link is pivoted; said another roller being mounted on an axis perpendicular to said first plane.