US2034145A - Operating mechanism - Google Patents

Description

March 17, 1936. J LINDE 2,634,345-

OPERATING MECHANISM Filed 001;. 19, 1933 2 Sheets-Sheet 1 Invencov: -LeonaT-dJ.Linde,

by NH is ttorney.

March 17, 1936. LHJ, LINDE OPERATING MECHANISM Inventor: LeonavdJILinde,

2 Sheets-Sheet 2 Filed Oct. 19, 1933 Patented Mar. 17, 1936 PATENT OFFICE OPERATING MECHANISM Leonard J. Linde, Folcroft, Pa., assignor to General Electric Company, a corporation of New York Application October 19, 1933, Serial No. 694,282

11 Claims.

My invention relates to operating mechanisms, more particularly to operating mechanisms of the type for effecting predetermined travel of an actuated member as in the operation of electric circuit breakers for example, and has for its principal object the provision of an improved operating mechanism which shall be efficient, precise and reliable in operation, simple and compact in design while permitting ready assembly or disassembly of the component parts, and rugged in construction.

My invention will be more fully set forth in the following description referring to the accompanying drawings, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Referring to the drawings, Fig. 1 is a perspective view partly in section illustrating in detail an electric air circuit breaker and its associated operating mechanism embodying the present invention; Fig. 2 is a view, partly in section, of brake structure illustrated in Fig. 1 in the braking position thereof; Fig. 3 is a similar view of the brake structure in non-braking position; Fig. 4 is an elevational view of apparatus illustrated in Fig. 1 in the closed circuit position; Fig. 5' is a similar view illustrating the apparatus in open circuit position before the resetting operation is completed; Fig. 6 is a similar view of the apparatus illustrating the same in the completely reset position; Fig. 7 is an elevational front view oi-the assembled circuit breaker and operating mechanism unit, Fig. 8 is an elevational side view of the unit shown in Fig. 7, and Fig. 9 is a detailed view of a modified form of the resetting means.

Referring more particularly to Fig. 1, there is illustrated operating mechanism l for effecting predetermined travel of the movable element of an electric circuit breaker 2. The operating mechanism I generally comprises suitable motive means as an electric motor 3 and collapsible thrust transmitting means 4 which is operatively connected to the motor in a manner hereinafter described. The thrust transmitting structure 4 is likewise operatively connected to the movable element 5 of the circuit breaker.

The circuit breaker as shown is of the polyphase type, the circuit controlling contacts of each phase including (Figs. 1 and 5) movable arcing and main contacts 6 and i, respectively, which are carried by the movable element 5, and coacting stationary contacts 8 and 9. The detailed construction of the circuit breaker which forms no part of the present invention will be described later.

The power circuit through the circuit breaker 2 includes in general a terminal member ID, a flexible braided conductor ll composed of suitable conducting material as copper interconnecting terminal in and the movable contacts, the pairs of movable and stationary contacts 68 and l9, a magnetic blow-out coil 12 and terminal 13. There are likewise included a pair of transfer or burning contacts I and 9 arranged in shunt with the main and arcing contacts.

Upon opening of the circuit breaker due to pivotal counterclockwise movement of the movable element 5 about a fixed shaft 14, separation of the main contacts I and 9 occurs prior to separation of the transfer and arcing contacts for confining arcing and burning upon opening of the circuit to the latter contacts. The are extinguishing means may comprise any suitable arrangement, as an arcing horn 15 connected to the stationary arcing contact 8 and a magnetic blow-out coil it which is connected in series in the power circuit between the stationary arcing contact 8 and terminal i3.

The operative connection between the motor 3 and the thrust transmitting structure 4 comprises a rotatable shaft ll directly connected to the motor 3, and a rotatable shaft I8 on which is mounted an actuating cam 19 coacting with the thrust transmitting structure 4. The motor shaft H and the cam shaft I8 are interconnected by automatic brake. structure 20 and suitable speed reducing gearing 2|. Energization of the motor 3 efiects rotation of the actuating cam l9 and a circuit closing operation on the circuit breaker 2 through the thrust transmitting structure 4 in a manner hereinafter described.

In mechanism of this character it is highly desirable that over-running or over-travel of the actuating cam be prevented except within comparatively narrow limits so that the operating mechanism may be readily tripped, and reset, if necessary, without interference by the actuating cam. Heretofore upon deenergization of the motor the inertia of the moving parts made it very dimcult to control the final position of the actu ating cam. The problem of mechanical brakin is complicated by the fact that energization of the motor must be continued to a certain point to insure positive closing of the circuit breaker and the braking operation must commence immediately upon deenergization in order that the actuating cam shall be stopped shortly beyond shaft I1.

member 22.

the point where the circuit closing operation is completed.

For the purpose of braking the actuating cam immediately upon deenergization of the motor after the completion of the circuit closing operation, the brake structure 20 is designed so that a brake member is moved to a non-braking position in response to predetermined motor torque and is moved to a braking position in response to decrease of transmitted motor torque below said value. To this end the motor shaft I1 is connected to a brake member 22 by a resilient connection comprising a torsion spring 23 which is connected at one end as at 24 to the brake member 22 and at its other end as at 25 to the motor The shaft l1 likewise is provided with a limited lost motion connection with a hub-like extension 22' of the brake member comprising a pin and slot connection 26-21.

The brake member which comprises a disk or the like having an annular flange as illustrated for receiving the torsion spring 23 is provided with a centrally disposed recess 28 within which the lower end of the motor shaft i1 is freely positioned. Accordingly, it will be noted that the brake member 22 may both rotate and move axially with respect to the motor shaft [1 within certain prescribed limits.

The pin and slot connection 2621 interconnecting the shaft l1 and brake member 22 is arranged so that the pin 26, which is secured to the driving shaft l1, rides in a diagonal slot 21 in the hub member 22 so as to cam the brake member 22 in a direction axially of the shaft I1 depending on the direction of rotation of said shaft. For the purpose of maintaining the brake member 22 in positive driving relation at all times to the driven shaft 29 which is directly connected to the actuating cam I!) through the reducing gearing 2 l, the shaft 29 is provided with a squared extension 29' slidably mounted within a corresponding aperture in the lower end of the hub Accordingly, the brake member 22 is always positively connected to the actuating cam notwithstanding axial movement of the brake member.

The actual braking surface of the brake mem-- ber 22 may comprise any suitable brake lining material secured as at 30 to the lower side of the brake disk. A fixed brake member 3i comprising part of the brake housing 3| surrounds the hub member 22 and is provided with a brake surface 32 adapted to coact with the brake lintransmitted by motor 3 decreases below a certain value. Due to the fact that brake member 22 is positively connected to the shaft 29, it will be apparent that movement of the brake member 22 to its braking position effects direct braking of the actuating cam I9.

Immediately upon energization of the motor tending to rotate shaft I1 in the direction indicated, referring more particularly to Fig. 3,

ber 22.

the torsion of spring 23 is opposed by the motor torque. When the motor torque overcomes the torsion of spring 23, the spring yields permitting rotation of shaft i1 with respect to brake mem- After limited movement of the shaft l1 with respect to the brake member 22 the pin 26 engages the opposite end of the slot so as to constitute a direct and positive driving connection between shaft l1, brake member 22 and shaft 29, movement of the pin to this position in the meantime causing camming of the brake member 22 upwardly to a non-braking position as clearly illustrated in Fig. 3.

While the motor transmits normal torque through shaft H the spring 23 is maintained flexed and under tension and the brake member is maintained in non-braking position. When.

however, the motor is deenergized and the transmitted torque decreases to a certain value the opposing torque of the charged spring 23 causes camming of the brake member 22 downwardly to the braking position illustrated in Fig. 2. Accordingly, there is provided a direct positive drive between the motor and actuating cam when the motor is transmitting the required torque, and likewise an automatic and quick acting brake effective in response to decrease of the motor torque upon completion of the circuit closing operation directly to brake the actuating cam.

The thrust transmitting structure 4 operatively interconnecting the actuating cam 19 and the movable circuit breaker element 5 is of the socalled trip-free type and is adapted to be reset and latched independently of the cam l9. Referring more particularly to Figs. 4, 5 and 6, the thrust transmitting structure comprises toggle members 35 and 36 which are pivotally interconnected at 31. The toggle member 35 is provided with a fixed pivot 38 and an extension 39 having at its outer end a roller 40 coacting with latching and tripping means hereinafter described. The toggle member 36 comprises a triangularly shaped link pivotally supported at an intermediate point, as indicated at 31, by the member 35 and having rollers 4| and 42 mounted at opposite sides of said pivotal support. The roller 4| is arranged to be in the path of the actuating cam l9 when the circuit breaker is to be closed and the roller 42 is arranged to engage an inclined actuating face 43 of a pivoted supporting member 44 of the movable circuit breaker element 5. The member 44 which is pivotally mounted on shaft I 4 is resiliently biased as by a compression spring 45 towards open circuit position.

The mechanism as illustrated by Fig. 4 is in the closed circuit position wherein the toggle 35--36 is overset so as tohold the.element 5 in closed circuit position, the toggle being latched in this position by a pivoted latch member 46 engaging the roller 40. The latch 46 is provided with an extension 46' so as properly to position the latch with respect to the roller 40.

The toggle when latched as shown by Fig. 4

is maintained in an overset thrust-transmitting position by the fact that the reacting force of the circuit breaker is along the line of centers of pins 31 and 42' and that this line is slightly offset with respect to the fixed pivot 38. Accordingly, there is a clockwise movement acting on link 35 which in turn is restrained by latch 46 thereby rigidly positioning pivot 31. The inclined face 43 engaged by roller 42 is normal to the line of centers 31-42 so that link 36 is in deadcenter position with respect to the toggle thrust.

For the purpose of preventing accidental movement of pivot 31 past the line of centers 3B42 due to vibration, thereby causing collapse of the toggle and opening of the circuit breaker, a prop 41 pivotally mounted on shaft I4 is arranged to drop behind and brace the pivot pin 42.

The latch controlling and resetting means comprises an arrangement whereby a comparatively small tripping force is effective to release a charged spring or the like for causing positive and quick release of the main latch 46. In other words, the available tripping force, which may be comparatively small as in the case of alternating current trip coils, efiects release of an intermediate energy-storing device as a spring charged trigger which in turn releases the main toggle controlling latch.

To this end the trip coil 50 coacts with a pivoted catch or latch 5! which is spring biased as at 52 so as normally to be engaged by a roller 53 carried by the trigger member 54. The trigger member 54, which is co-pivotally mounted at 55 with the latch 45, is resiliently biased as indicated at 58 in clockwise direction. The application of the spring compression at 56 is shown as slightly oil-center with respect to the pivot 55 so that the spring force is available immediately to rotate the trigger member 54 clockwise upon releasing movement of catch 5|. A pin 68 carried by the trigger 54 is arranged so that upon clockwise movement of the trigger the pin sharply strikes an extension of the latch 46 so as to rotate the same clockwise to the toggle releasing position.

It will, therefore, be apparent that a much greater releasing force than that delivered by the trip coil 50 is available for releasing the latch 46 since the force required to maintain the spring 58 charged near its dead-center position with respect to pivot 55 is obviouslycomparatively small.

The resetting means for the latch and trigger arrangement above described is best illustrated by Figs. 5 and 6. The arrangement is such that immediately upon collapse of the main toggle 35-36 and circuit opening movement of the element 5, the trigger 54 is reset and the latch 46 positioned so that it is in readiness immediately to latch the main toggle when the roller 40 thereof returns to its initial position. The trigger resetting means may comprise any suitable arrang'ement as a member 58 carried by the ele ment 5 and provided with an extension 58' arranged to engage the trigger 54 and rotate the same counterclockwise as illustrated in Fig. 5. Return of the trigger 54 to its initial position causes it to be latched by the catch 5! which is resiliently biased so that it snaps over the roller 53 as the same is rotated counterclockwise. The resetting operation by the circuit breaker element 5 likewise recharges the spring at 56 by compressing the same against a fixed stop (not shown).

The positioning of the latch for relatching the roller so of the main toggle is accomplished by means of a resilient connection, as a leaf spring 5%, arranged between the trigger 55 and latch illustrated, the spring 59 is secured at one end to the trigger 5d and is flexed so as to engage at its other end the latch and urge the same in counterclockwise direction. The stop pin es limits the counterclockwise rotation of latch 65.

In order further to increase the sensitivity of the tripping means, the toggle member in riding under the latch 45 to its latched position may flex the spring 59 sufficiently so that the trigger spring at 56 is on dead center with respect to pivot 55. In this arrangement the flexing of spring 59 is suificient, upon releasing movement of catch 5|, to move the trigger 54 clockwise oil center so that the trigger is immediately snapped over to actuate the latch 46.

Immediately after collapse of toggle 35-35 and opening movement of the element 5, the toggle member 35 is urged counterclockwise from the position shown in Fig. 5 by a spring Bl until the extension 39 engages a stop 39. When the toggle member 35 is returned to this position the l latch 46 snaps over the roller 40 as illustrated by Fig. 6.

In this position the toggle member 36 may be rotated counterclockwise about the restrained pivot 31 by the actuating cam is so that the roller 42 in riding along the inclined face 43 causes circuit closing movement of the element 5. The cam l9, which rotates clockwise to engage the roller 44, is designed to meet the operating characteristics of the circuit breaker so that the same may always be positively closed without difficulty. The brake mechanism above described is eifective to stop rotation of cam l9 within a few degrees of rotation" after circuit closing movement of the main toggle as illustrated in Fig. 4. The cam in this position is, therefore, free of the thrust transmitting structure and is likewise in a predetermined position for effecting a circuit closing operation by a single revolution thereof.

A modified form of the resetting device for the trigger 54 is illustrated by Fig. 9. In this arrangement the trigger 54 is returned to its latched position notwithstanding limited variations in the final open circuit position of the element 5. The elementv 5 which is biased by spring 45 against the stop member 5' may. due to friction of the apparatus and other causes, come to rest short of the stop member. arrangement shown in Fig. 9, an intermediate member 62 pivotally supported at 63 is adapted to be engaged by a bufier member 64 of the element 5. The member 62 is thereby swung clockwise into engagement with the trigger 54 resetting the same in the manner above described. In the present case. however, the final moternent of the element 5 efiects comparatively small movement of the trigger 54 due to the lengthening of the lever arm with respect to pivot 63. Accordingly, the trigger 54 may be reset during the main part of the opening travel of the element 5, the trigger being unafiected by slight variations in the final position of said element.

In summarizing the operation of the mechanism, it may be briefly stated that the thrust transmitting toggle is held in a thrust transmitting position, both in the closed circuit position illustrated by Fig. i and also during rotation of the toggle member 36 by the actuating cam i by the latch 55 wh ch is in turn controlled by the spring charged trigger 54. The trigger is nicely balanced so that a comparatively small trip force is effective to actuate the same. The tripping impulse at the trip coil 56 actuates the catch 59 causing release of trigger 5t and consequent actuation of latch G5 with the result that the toggle 35-35 is no longer restrained in thrust. transmitting position and collapses under the action of the circuit breaker opening spring Q5 as illustrated by Fig. 5. Immediately upon opening. however, the element In the through the resetting means above described resets the spring charged trigger 55 which in turn through spring 59 positions the latch 56 for resetting so that the lower edge thereof is in the path of the toggle roller 40.

After collapse of the toggle 3536 and opening of the circuit breaker, the toggle spring 5| throws the toggle from the position shown in Fig. 5 to that shown in Fig. 6 wherein the roller 50 engages the restraining face of latch 45. The mechanism is now in readiness for a closing operation which is accomplished by a single clockwise revolution of the actuating cam l9, returning the mechanism to the position illustrated in Fig. 4.

It will be noted that the mechanism is tripfree at all stages of its operation. That is, the occurrence of a tripping impulse during the camming operation causes actuation of the latch 56 in the usual manner and collapse of the toggle 35-36, the element 5 thereupon returning to open circuit position notwithstanding continued rotation of the cam Hi. When the cam comes to rest the toggle spring 5i causes relatching of the toggle 1n the manner above described.

Where manual operation of the circuit breaker, eitheralone or in combination with the motor, is desired, an actuating cam 65 (Fig. 1) similar in design to cam I9 is mounted on a shaft 65 so as likewise to coact with the toggle roller 4!. In the present instance the shaft 65, which is provided with an operating handle 67 at the outer end thereof, extends longitudinally through the hollow motor operated cam shaft l8 so that the handle 67 may be applied to the opposite end of the shaft where necessary. The operation of shafts l8 and 66 are entirely independent of each other.

The shaft 56 is provided with a tripping and positioning member 68 arranged to engage, as by extension 68, a guided member 69 coacting with the extension 66' of the main toggle latch. When tripping of the breaker by the manual means is desired the handle 5] is rotated counterclockwise (as viewed in Fig. l) a short distance so that the member 69 is raised and the latch 46 actuated to release the toggle 3536. A positioning spring 10 coacting with notches in the member 68 serves to maintain the shaft'56 in definite positions.

In Fig. 1 there is likewise illustrated a control system for insuring proper operation of the motor. The motor as shown is energized from a suitable source of power, indicated at H, the motor control circuit including a push button control switch 12, circuit breaker-limit switch l3, and manual control switch Hi. When the manual operating means is in inoperative position and the element 5 of the circuit breaker is in open circuit position the manual switch 15 and the limit switch 13 are both closed. An interconnecting linkage 75 serves to operate the limit switch 73 in accordance with opening and closing movements of element 5.

The control circuit which includes a solenoid 15 may be completed by closing of the push button switch 12. Energization of solenoid I6 is in turn effective to close contacts J1 thereby completing the motor circuit through the manual switch M. Shortly after closing of contacts I1 and energization of the motor, the push button 12 may be released since the plunger of solenoid "I5 is mechanically sealed in contacting position by a cam element I8 mounted on shaft l8. The cam '18 seals in the contacts ll only during normal travel of cam IS, the motor meanwhile being energized from the source H directly through contacts 17 and switch 14. Upon completion of the'circuit closing operation the cam 18 permits the contacts E1 to be biased open thereby deenergizing the motor and stopping theactuating cam 89.

When the switch element 5 is closed the limit switch 13 is open preventing energization of solenoid 16 from source 77 through push button 12. In the case of trip-free operation the actuating cam I9 is rotated to its normal final position due to the sealing-in cam l8. When the manually operated cam 65 is rotated to operative position, the

switch It is opened with the result that energization of the motor 3 from the source H is impossible.

The present invention is not limited to the specific type of circuit breaker shown, it being understood that the movable element 5 is equivalent to the movable element generally of a circuit breaker of either the air or oil type.- The more detailed construction of the air circuit breaker illustrated is as follows:

As previously described the movable contacts of the circuit breaker are carried by the element 5 which includes the pivoted arm 54 on which is mounted an insulating cross-bar 80. Secured to the cross-bar are a plurality of contact supporting members 8|, each member being channelshaped as illustrated and forming a bearing at 82 for the pivot pin of an arcing contact support 83. Each contact support 83 is resiliently biased, as by springs 84, clockwise so as normally to urge the corresponding arcing contact point into engagement with its coacting contact. This movement is limited by a pin 85 adapted to engage a leg 85' forming a part of the member 8|. The main current-carrying contacts I are mounted within the supports 8| for limited reciprocal movement, as by pin and slot connection 8586'. The contacts 1 are biased by a spring 81 so as to provide resilient engagement of the contacts I and 9.

The transfer contacts I are connected to the corresponding contacts i by a current conducting strip 88. Upon opening of the circuit, current through themain contacts I and 9 is first transferred to the contacts I and 9' in order to avoid burning at the main contacts. Heavy currents cannot be shunted directly through the arcing coils without some burning at the main contacts by reason of the inductance of the blowout coil.

The above described circuit breaker and operating mechanism are compactly assembled and designed so that each main component part may be assembled or disassembled as a unit with respect to the associated parts.- In the present instance the motor 3 and brake structure 22 is assembled as a unit with respect to the shaft 29 by simply positioning the motor and brake unit above the shaft and sliding the hub 22' on the squared extension 29' of the shaft. The reducing gearing 2i and a portion of the shaft I8 are likewise removable as a unit by reason of a detachable interlocked connection dividing the shaft l8 into separate sections as indicated at 90. .Upon disassembly, the reducing gearing and associated portion of shaft l8 are slidable longitudinally oif the manually operated shaft 66 after removal of the motor and brake unit.

In view of the fact that the thrust transmitting structure 4 has no permanent connection with the movable element 5, it will be apparent that till this portion of the structure including the actuating cam and the corresponding section of the cam shaft may be constructed and assembled as a unit with respect to the remainder of the mechanism. The same likewise applies to the latch and trigger mechanism. A mechan sm so designed is not only quickly and efficiently assembled but may be produced at comparatively low cost. That is, the component units may be individually constructed so that considerable time is saved as compared with the usual method of having a number of workmen assemble the entire apparatus in a single frame.

The complete circuit breaker and mechanism unit are illustrated by Figs. 7 and 8 wherein a panel 9| has mounted thereon the phase units of the circuit breaker 2 and the operating mechanism therefor including the motor and brake unit indicated at 92, the reduction gearing unit indicated at 93 and the thrust transmitting and tripping and latching units indicated at 94 and 95, respectively. An auxiliary switch unit including the limit switch is indicated at 96. Starting with the motor and brake unit, the mechanism may be readily disassembled by units by merely loosening and removing the clamping bolts provided for securing together the casings of said units where indicated.

. It should be understood that my invention is not limited to specific details of construction and arrangement thereof herein illustrated, and that changes and modifications may occur to one skilled in the art without departing from the spirit of my invention.

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

1. Circuit breaker operating mechanism comprising a motor, means actuated thereby for effecting in a cycle of operation a circuit closing operation, means for deenergizing said motor at the end of said cycle, and a connection between said motor and actuated means including a brake member and resilient means exerting a torque for biasing said brake member towards a braking position upon completion of said circuit closing operation, said motor effecting movement of said brake member to a non-braking position in opposition to said torque while transmitting driving torque for effecting said circuit closing operation.

2. Circuit breaker operating mechanism comprising a motor, a member actuated thereby for efiecting in a cycle of operation a circuit closing operation, means for deenergizing said motor at the end of said cycle. and means interconnecting said motor and member including a brake member, and resilient means under initial tension for biasing said brake member towards a braking position upon completion of said circuit closing operation, said motor during transmission of normal circuit closing torque overcoming the tension of said resilient means for effecting movement of said brake member to a nombrakingf position.

3. Circuit breaker operating mechanism comprising a motor, a rotatable cam for er recting a circuit closing operation, means for deenergizing said motor in accordance with a predetermined position of said cam, and means operatively interconnecting said motor and cam including a brake member and a spring under initial tension for biasing said brake member towards braking position upon deenergization of said motor and completion of said circuit closing operation, the torque of said spring opposing the motor torque, the motor torque for eifecting said circuit closing operation overcoming said spring torque to effect movement of said brake member to a non-braking position.

4. Circuit breaker operating mechanism comprising a motor having a rotatable operating shaft, a coacting rotatable cam shaft for driving a circuit closing member, means for decnergizing said motor in accordance with a predetermined position of said cam shaft, and means interconnecting said shafts comprising a brake member, said brake member having limited axial and r tative movement with respect to one of said shafts, a spring interconnecting said brake member and said shaft arranged so that the circuit closing torque of said motor effects in opposition to the tension of said spring axial movement of said brake member to a non-braking position, decrease of the motor torque below the countertorque of said spring causing movement of said brake member to a braking position.

5. Circuit breaker operating mechanism for effecting predetermined travel of a circuit closing member, comprising a motor having a rotatable shaft. a second rotatable shaft operatively connected to said circuit closing member, means for deenergizing said motor in accordance with predetermined movement of said second shaft, a brake member mounted on and having a pin and slot connection with said motor shaft permitting lirrfited rotatve and axial movement with respect to said motor shaft, said brake member having a driving connection with said econd shaft, a fixed brake member coacting with the first-named brake member, and a tensioned spring interconnecting said motor shaft and said first-named 6. Circuit breaker operating mechanism comi prising a motor having a rotatable operating shaft, a second rotatable shaft for driving a circuit closing cam, means for deenergizing said motor in accordance with predetermined movement of said cam, and means interconnecting said shafts comprising a brake member mounted on said motor shaft for rotation therewith, camming means for efiecting limited axial movement of said brake member on said motor shaft, said brake member having a driving connection with said second shaft, and a spring interconnecting said motor shaft and said brake member arranged so that the circuit closing torque of said motor effects through said camming means in opposition to the tension of said spring axial movement of said brake member to a non-braking position, the tension of said spring efiecting through said camrning means movement of said brake member in the opposite direction to a braking position upon predetermined decrease of said motor torque.

7. An electric circuit breaker unit comprising a supporting frame, relatively movable contact structure, operating mechanism comprising a motor and a rotatable shaft having a cam mounted thereon for closing said contact structure, and means operatively interconnecting said motor and rotatable shaft including a brake for preventing over-travel of said cam upon deenergization of said motor, said motor and brake comprising structurai unit detachably mounted on said frame with respect to said rotatable shaft.

8. A circuit breaker unit comprising relatively movable contact structure operating mechanism comprising a motor and a rotatable shaft having a cam mounted thereon for effecting circuit closing movement of said structure, and means operatively interconnecting said motor and rotatable shaft comprising a brake and reduction gearing, said motor and brake comprising a structural unit having a slidable, detachable connection with respect to a shaft connected to said reduction gearing, and said reduction gearing together with a portion of said rotatable shaft likewisecomprising a structural unit having a detachable sliding connection with respect to the remainder of said rotatable shaft on which said cam is mounted.

9. electric circuit breaker comprising relatively movable contact structure including a movable contact element having a plane actuating face, and operating means for effecting circuit closing movement of said element comprising a motor, a rotatable shaft having an actuating cam thereon, thrust transmitting structure including a roller arranged to engage the actuating face of said element, said cam arranged so as to engage and actuate said thrust transmitting structure, and means operatively connecting said motor and rotatable shaft including a brake .for preventing over-travel of said cam with respect to said thrust transmitting structure upon deenergization of said motor.

10. A circuit breaker comprising relatively movable contact structure and operating mech-.

anism for effecting circuit closing movement of said structure, comprising a motor, a rotatable cam for actuating said contact structure, means for deenergizing said motor in accordance with predetermined movement of said structure, and a driving connection between said motor and cam including a spring biased brake member arranged to brake and prevent over-travel of said cam upon deenergization of said motor and completion of said circuit closing movement, said brake member constituting a rigid driving connection between said motor and cam during said circuit closing movement.

11. An electric circuit breaker comprising relatively movable contact structure and operating mechanism comprising a motor, a cam for effecting circuit closing movement of said structure, means for deenergizing said motor in accordance with predetermined movement of said structure, and a combined driving and braking connection between said motor and cam including a brake member having a lost motion connection with respect to said motor, and a tension spring operatively interconnecting said motor and brake member arranged so that said brake member is moved to braking and non-braking positions in accordance with the torque transmitted by said motor.

LEONARD J. LINDE.

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