US1660620A - Brake - Google Patents

Description

Feb. 28, 1928.

G. w. LAUTRUP BRAKE Filed March 18. 1926 2 Sheeis-Sheet l GM w. Lam INVENTOR m R O m Feb. 28, 1928.

G. w. LAUTRUP BRAKE Filed March 18. 1926 2 Sheets-Sheet 2 us m3 R 0 T N E V N ATTORNEY Patented Feb. 28, 1928.

UNITED STATES 1,660,620 PATENT oFFic GEORGE W. LAUTR'UP, OF YONKERS, NEW YORK, ASSIGNOR .TO OTIS ELEVATOR COM- PANY, 01E JERSEY CITY, NEW JERSEY, A CORPORATION OF NEW JERSEY.

BRAKE.

Application filed March 18, 1926. Serial No. 95,640.

The invention relates to mechanism of the type wherein friction shoes are caused to engage a rotatable drum and particularly to multiple shoe braking mechanism for elevator hoisting machines wherein the bralde shoes are mechanically applied and electrically released.

One feature of the invention is the provision of braking mechanism in which the.

operation of the brake shoes is caused by rotative means, as by a motor, in a simple and efficient manner.

Another feature is the provision of such braking mechanism in which the proper release and application of the brake shoes is assured under all conditions of operation and in which stresses on the parts of the operating means, such as caused by variations of adjustment or by uneven wear, are eliminated.

Still another feature is the provision of such braking mechanism which is of simple construction, quiet in operation and readily adjust-able.

A fourth feature resides in arranging such mechanism so that the force exerted to move one shoe with respect to the drum is counterbalanced by the force exerted to move another shoe with respect to the drum.

Figure 2 is a front elevation of the same,

certain parts bein broken away;

Figure 3 is a p an view of the same, also with portions shown in section; and

Figure 4 is a detail sh wing the arrangement of the bufier.

The brake frame 10, upon which the mechanism is supported, consists of two sides 11 and 12 joined at the top by a web 13 and at their bottoms by the feet'14. Considering only the left half of the mechanism as viewed in Figure 1, the operating lever 15 is pivotally mounted on a pin 16,. supported as by bosses 17 formed on the sides of the brake frame. As illustrated in Figure 2, lever 15 is widened at the support and is formed with an opening 18, the sides of the lever which embrace the opening being designated 20 Other features and advantages will become and 21. These two sides are joined at their lower ends by a yoke 22. The brake shoe 23 is provided with strengthening ribs 24 formed with lugs'25extending into opening18 between the sides 20 and 21. The brake shoe is pivotally mounted on the lever by means of a pin 26 extending through the sides 20, 21 and lugs 25. A spring seat 27 also is pivotally mounted on lever 15 by pin 26, the seat being formed with a lug 28 which extends between lugs 25 on ribs 24 and through which pin 26 extends. The actuator spring 30 extends outwardly into a spring cap 31. The spring cap is secured to the frame 10, as by means of bolts 32 extending through flanges 33 formed on the spring cap and lugs 34- formed on the sides of the frame, so as to permit the adjustment of the compression of spring 30. Considering the right half of the mechanism as viewed in Figure 1, in a simllar manner brake shoe 35 is pivotally mounted on lever 36 by its pivot pin 37 and is provided with an actuator spring 38 extending between spring seat 40 and spring cap 41. The lever is pivotally mounted on pin 42 supported by the sides of the brake frame.

Although any suitable means for producing rotative motion may be employedto cause the action of the mechanism to re ease the brake shoes, it is preferred to utilize an electric torque motor 43. The motor is mounted on a base 44 secured, as by screws 45, to the top of. the brake-frame 10. As illustrated for the left half of the mechanism in Figure 1,

the inner race ,of motor shaft bearing 51 is positioned against a shoulder 52, formed on the motor shaft 47, by a nut 53. A bumper support 54 is keyed to the shaft 47 beyond nut 53, being held in axial position as by a set screw '55. The outer end of the shaft is threaded to form an operating screw 56. An operating nut 57 is provided on this screw and extends into a lubricant housing 48 formed on the bumper support 54. A U shaped link 58 is pivotally mounted on the outer end of operating nut 57, as by means of a pin 60 extending. through the sides of the link and the nut. The link is pivotally secured at its open end to the operating lever 15, as by a pin 61 extending through the forks 62 forming the upper end of the lever, the sides of the link and the nut. Since the lever 15, during operation, swings in an are about pivot pin 16, the diameter of each of the apertures 63, through which pin 61 extends, is made larger than the diameter of the pin to provide sufficient clearance for this arcuate motion. 7

The right hand portion of shaft 47 is similarly provided with a bearing 71 clamped against a spacing sleeve 72 by nut 70. A spring support 73 is keyed to the shaft beyond nut 70, being held in axial position by set screw 74. The outer end of the shaft is threaded, as in the case of the other end of the shaft, to form an operating screw 75. Also an operating nut 76 is provided on the screw and extends into a lubricant housing 77 formed as part of the spring support 7 3. The operating nut 76 and operating lever 36 are connected by a link 78 in the same manner that operating nut 57 and lever 15 are connected by link 58. A torsion spring 80 is arranged on spring support 73, being It is to be noted that the operating screws are oppositely threaded so that, for example, upon the rotation of the operating motor clockwise, as viewed in Figure 2, each operating nut is drawn inwardly by its respective operating screw.

In order that the brake shoes may be maintained substantially concentric with the drum 84 when the brake is released, thus preventing the draggin of any part of the brake shoes, an adjustable abutment is provided on each operating lever above its pivot point and resilient means is provided below each pivot point for holding the brake shoe in engagement with its respective abutment. Thus, in the case of brake shoe 23 for example, a lug 85, formed on the lever 15 and extending downwardly between the sides-20 and 21, is threaded to receive abutment screw 86. A nut 87 is provided for locking screw 86 in adjusted position. The central portion of the connecting yoke 22 at the lower end of the lever is enlarged to form a boss 67. This boss is provided with a threaded aperture for recelvlng an adjusting screw 88 for the spring 90. A nut 91 is provided for locking the screw 88 ,.in adjusted position. Spring extends between a spring seat 92 formed on the innerv end of screw 88 and a spring seat 93 formed on the brake shoe. The compression of the spring 90 is so adjusted as to maintain the boss 94 on the brake shoe in abutting relation with screw 86 when the brake is released. This portion of the apparatus is the same for brakeshoe 35 and will not be described.

An adjustable abutment screw 95 is provided on operating lever 15 for engagement with a stop 96 formed on the frame web as by screws 108, to the bumper support 54. Y

The bumper plate is provided with a lug 110 for engaging the bufl'er during the operation of the motor to release the brake shoes.

The above described bumper and bufi'er arrangement serves to determine the limit of movement of the mechanism during brake releasing operation. To control the brake applying operation, however, it is preferred to employ adjustable retarding mechanism. Such mechanism may comprise a dash pot 111 and a cam and lever arrangement for transmitting the rotary motion of the motor shaft to the dash pot piston 112. The dash pot cylinder cover 113 is formed on the retarder bracket 114. The retarder bracket is secured to the motor base 44 as by screws 115. The dash pot cylinder 116 is secured to the cover 113 as by screws 117. A conical spring 118 is arranged within the cylinder between the piston 112 and the end of the cylinder. A piston rod 120 extends through an aperture 121 in the cylinder cover into a recess 122 formed in piston 112. The outer end of the rod is pivotally secured to an arm 123 of bell crank lever 124 as by a pin 119.

The diameter of aperture 121 is larger than that of the piston rod 120 to permit the flow of air into and out of the cover end of the cylinder during the movement of the piston and to allow for the arcuate motion of arm 123 of hell ,crank lever 124. .Also the end of piston rod 120 extends loosely into the recess 122 in the piston so as to allow for this areuate motion, the piston ordinarily being maintained against the end of the piston rod by the force of spring 118.

The bell crank lever 124 is pivotally mounted on the retarder bracket 114 as by a pin 125. The other arm 126 of the lever is provided with an operating roller 127. The lever is so positioned that the roller is disposed in the path of the retarder cam 128. An extension 129 is formed on the bell crank lever and is disposed opposite arm 126 so as to balance the lever and to aid in returning the piston rod 120 to its outer position. A stop 137 is provided on the retarder bracket for limiting the outward movement of the piston rod. The plate 130 upon which the cam is formed is adjustably secured to bumper support 54 by the screws. 108, the bumper plate 107 being arranged between the cam plate and the bumper support. V

A bushing 144, having a threaded passage 131 is arranged in a. boss 132 formed on the closed end of the dash pot cylinder. A continuation of this passage extendsinto the inside of Y the cylmder. A longitudinally slotted screw 133 is provided for regulating the flow of air out of the cylinder through the passage 131... Nut 134 serves to lock the regulating screw in its adjusted position. The inner end of;the regulating screw is formed into a seat 135 for a ball 136, forming a ball check valve. A longitudinal passage 138 extends through the screw 133 from the ball check valve to the outside of thecylinder.

In operation, the motor 43, upon energization, causes the rotation of operating screws 56 and 75, the direction of rotation being clockwise as viewed in Figure 2. Thus both operating nuts 57 and 7 6 are drawn inward-- 1y, nut 57 acting through link 58 ,to move operating lever 15 about its pivot 16 and nut 76 acting through link 78 to move operating lever 36 about its pivot 42. The inward movement of the upper ends of the operating levers causes the release of the brake shoes against the force of their respective actuator springs. Bumper plate 107 is rotatd along with the screws 56 and 75, being secured to bumper sup ort 54 which is keyed to the. motor shaft. T us, as the rotation of the motor continues, bumper plate lug 110 engages the cover washer 103, the buffer felt yielding to bring the mechanism to 31 511100511 and substantially noisless stop. As the motor remains energized however, the braking mechanism is maintained in released position. It is to be noted that the torsion spring 80, being secured at one end to spring I operation.

Upon the deenergization of motor 43, the torsion spring 80 acts to rotate the motor, and therefore the operating screws, in the reverse direction. This, reverse movement causes the outward-movement of the operating nuts, permitting actuator springs 30 and 38 to apply their respective brake shoes to the drum. The torsion spring 80 also aids the brake actuator springs in. ap lying the brake shoes. Thus the brake appl ying operation may be very accurately controlled since the action of the mechanism may be adjusted by varying the applying force exerted by the torsion spring as well as that exerted by the actuator springs. The actuator springs may be adjusted by means of screws 32. The torsion s ring may be adjusted by connecting it to itlerent lugs 82 on bearing-cover 83.

During the brake applying operation, the cam 128, rotated by the motor shaft, engagesthe bell crank lever roller 127. During the movement of the cam with its oblique surface in engagement with the roller, the bell crank lever is moved counter-clockwise (as viewed in Figure 2). This lever, acting throughpiston rod 120, moves. the piston 112 toward the closed .end of the dash pot cylinder against the force of the conical spring 118. .The cam plate is preferably initially adjusted so that the cam engages the roller just as the brake shoes engage the drum. Thespeed with which the piston may be moved into the dash pot cylinder is governed by the setting of the regulating screw 133. In this manner, the motor shaft is retarded in its reverse rotation and the brake shoesare retarded in their full application to the brake drum. With the brake shoes fully applied, the mechanism is; brought to rest. With the brake shoes applied, roller 127 rests on the curved surfaceof cam 128. Upon the brake shoes being released, as reviously described, the cam is disengaged rom the roller. The spring 118 returns the piston 112 toward the dash pot cylinder cover and, assisted by the extension 129, moves the bell crank lever clockwise about its pivot- (as viewed in Figure 2). 136 of the ball check valve lifts from its seat to permit the free movement of the piston. It is preferred to employ aspring 118 of the conical type to permit the piston to move nearer the closed end of dash pot cylinder.

The initial adjustment for proper clearance between the brake drum 84 and 'the brake shoes may be obtained by means of the operating nuts 57 and 76 and the adjustable bumper plate 107. The operating nuts are arranged to be adjusted, in steps of quarter turns. In order that this may be accomplished, the apertures for the pin 60, which connects the operating nut 57 and link 58, are spaced ninety degrees apart around the periphery of the nut. The apertures 63 for pin 61, which connects the link 58 and operating lever 15, are similarly arranged. The apertures provided in operating nut 76 are arranged in a similar manner. With the brake shoes applied and the rotor of the motor central with respect to the stator, the operating nuts may be turned so that their. apertures are positioned to receive their respective connecting pins. The bumper support is provided with a plurality of threaded apertures, for example eight, arranged on a circle concentric with the motor shaft. vided with apertures arranged on a circle which coincides with the assumed circle on the bumper support. The number of apertures in the bumper plate, however, is difi'ercut, as for example, ten. By this arrangement the angular position of lug 110 may be The ball lot) The bumper plate is proadjusted in steps of nine degrees, i. e., with screws 108 removed, a nine degree angular movement of bumper plate 107 with respect to the bumper support 54 causes the first apertures in the bumper plate, in advance of the apertures in the plate through which screws 108 extended, to coincide with the first apertures in the bumper support in advance of the apertures in the su port which received the screws. Thus wit the brake shoes moved off the brake drum such distance as to give the desired clearance, the bumper plate may be adjusted so that lug 110 is in engagement with the bumper.

The cam plate 130, if desired, may be provided with the same number of apertures as the bumper plate 107. Thus an adjustment of thirty-six degrees is provided for the cam 128. In the event that the cam cannot be set so as to give the desired action with such adjustment, a nine degree adjustment may be obtained by moving the cam plate and bumper plate as a unit in the direction to givegreater clearance for the final setting. The arrangements above described may be employed also to adjust the mechanism after the brake shoes have become worn. It is to be noted that the curved surface of cam 128 is extended to allow forthe wear of the shoes before the adjustment is made. The cam plate and bumper plate are illustrated in theiradjusted positions.

The shaft of motor 43 is preferably mounted for axial freedom, as by dimensioning the bearing housings for the motor shaft bearings so as to permit considerable movement of the shaft and bearings to each side of central position, i. e., the position with the rotor of the motor central with respect to the stator. Thus, as regards bearing 51, for example, considerable axial clearance is provided between the bearing and bearing cover 141 and also between the bearing and the bearing housing hub 142. Axial clearance for bearing 71 is'provided in a similar manner. These bearings have a sliding fit in their .respective housings. This arrangement acts automatically to insure the release and application of both brake shoes under various operating conditions without strain on the bearings 51 and 71 and there fore without strain on the motor framework and mounting. In order that this may be clearly understood, assume first that only slight normal axial clearance is provided for bearings 51 and 71 in their respective housings and that one of the brake shoes, for example, brake shoe 23, has been adjusted improperly so that the clearance between the shoe and brake drum, with the brake shoes released, is too great. This would mean that actuator spring 30, in attempting to force brake shoe 23 into engagement with the brake drum upon each brake applying operation, would exert considerable side thrust "on the bearings to the left (as viewed in force being obtained. Similar conditions might be obtained as the result of unequal wear of the brake shoes.

With the axial clearance provided as previously described, however, such faulty operation is eliminated and the proper application and release of the brake shoes is obtained. Assume again'that improper adjustment has been made so that the clear- M128 between brake shoe 23 and the brake drum, with the brake shoes released and with the motor shaft in central position, is too great. Should the motor shaft be in central position at the time the brake applying operation is initiated, the engagement of brake shoe 35 with the brake drum would occur first. Immediately thereafter, however, brake shoe 23 would be forced into engagement with the brake drum by its actuator spring 30. The a plication of brake shoe 23 under such con itions would be accomplished without the above described side thrusts as the motor shaft and bearings, being free to move axially, would shift to the left, once brake shoe 35 engaged the brake drum, to permit the movement of shoe 2'3 into'engagement with the drum. Similarly, if one brake shoe, for example shoe 23, tended to wear to a greater-"extent than brake shoe 35, the motor shaft and bearings would be gradually shifted to the left during the brake applying operations in which the unequal wear occured, assuring the proper I ap lication of both brake shoes. Since, by this arrangement, the desired application of the brake shoes under operating conditions is obtained and since the operating screw and nut arrangement results in the positive operation of levers 15 and 36, substantially simultaneous release of the brake shoes, is assured during the releasing operation.

The above described arrangement for obtaining axial freedom of the motor shaft, in conjunction with abutment screws 95 and 98 and their stops, also serves to insure the proper operation of the mechanism without strain on the bearings and the motor framework and mounting in the event of considerable unequal adjustment of the actuator springs. Again for convenience of explana tion, assume that only slight normal axial clearance is provided for the bearings and in addition that abutment screws 95 and 98 tightened to the extent of causing actuator spring 38 to exert more force against brake shoe 35 than actuator spring 30 exerts against brake shoe 23. As a result, the motor, upon its energization, would have to exert considerable side thrust on the bearings to the right (as viewed in Figure 1) to effect the release of brake shoe 35 against the force of actuator spring 38. As previously explained, such side thrust might result in damage to parts of the mechanism. With the motor shaft mounted for axial freedom and the abutment screws 95 and 98 and their stops provided, however, such side thrusts due to the unequal forces exerted by the actuator springs are eliminated. In order that this may be clearly seen, assume again that actuator spring 38 isadjusted to exert more force against brake shoe 35 than actuator spring 30 exerts against brake shoe Upon the energization of the motor to release the brake shoes, therefore, operating lever 36 is held stationary by the force of actuator spring 38, causing the motor shaft to be shifted to the right during its turning motion by the action of operating screw in nut 76; Brake shoe 23 is released by the combined effect of the turning motion and shifting of the motor shaft to move operating nut'57 to the right. Upon brake shoe 23 moving a certain distance away from brake drum 84, determined by the adjustment of abutment screw 95, this screw engages its stop 96. As a result, further movement of operating nut 57 in the direction to release brake shoe 23 is prevented and the continued rotation of the motor shaft acts to overcome the force of actuator spring 38. Also the motor shaft is shifted back toward its central, position by the turning of screw 56 in nut 57. Brake shoe 35, therefore, is released by 'the combined effect of the turning motion and .shifting of the armature shaft to move operating nut 76 to the left. If desired, screws 95 and 98 may be employed to serve as a final stop for the releasing operation with felt disc 102 acting as a buffer.

The mounting of the motor shaft so as to be free to move axially further serves to insure the proper operation of the mechanism in the event of such adjustment thereof as would cause the engagement of one of the abutment screws 95 or 98 before the other in the brake releasing operation. With movement of the motor shaft axially prevented, such adjustment might result in stalling the motor during the releasing operation. Such condition would be undesirable because it might leave one of the brake shoes applied or only partially released as well as because of the possibility of damage whlch might result from the attendant side thrusts. For convenience of more specific explanation, assume again that only slight axial clearance is provided for the motor shaft bearings and that the adjustment is such that abutment screw 95 engages its stop in the brake releasing operation before the engagement of abutbefore any appreciable lifting of brake shoe 35 or before the "latter shoe, had been completcly released from the drum. l/Vith the axial clearance provided, however, upon the engagement of abutment screw 95 and its stop as in the above example, the motor shaft would-be shiftedto the left, not only eliminating the stalling of the motor and the attendant side thrusts but also aiding in lifting brake shoe 35 from the drum.

It is to be noted from the preceding description that theforce exerted to effect the movement of each brake shoe with respect to the drum is counterbalanced by the-force exerted to effect the movement of the other.

This is true under all operating conditions regardless of the adjustment of the shoes or the wear on their linings. Although the motor is illustrated with only the rotating parts mounted for axial freedom, it is to be understood that it may be arranged so that. it is free to move longitudinally asa whole.

The torque motor is preferably of the alternating current, induction motor type, wound for slow speed to produce high torque per ampere and designed so that a large percentage of the losses is concentrated in the end rings 139. These rings are brazed to the rotor bars 140 and are locatedoutside the stator windings 143 as indicated in Figure 1. With such construction the heat generated in the end rings is not effective to unduly heat the stator windings.

The motor, being inherently quiet in rotation, aids in minimizing the possibility of noisy operation of the mechanism. No great amount of kinetic energy is imparted to the rotating parts of the mechanism during the brake releasing operation as the motor is rotated only a fraction of one revolution. The use of the dash pot arrangement to retard the mechanism as the brake shoes are being applied, in conjunction with the fact that the manner of pivoting the operating above construction and many apparently widely different embodiments of this invention could be made Without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

WVhat is claimed is:

1. In combination; a rotatable drum; a pair of friction shoes for cooperating with said drum; operating means for each shoe; and rotative means for causing, during its rotative motion, the operation of said operating means to move their respective shoes with respect to said drum, said rotative means being axially free whereby the force exerted on each operating means in causing said movement of said shoes is counterbalanced by the force exerted on the other.

2. In combination; a rotatable drum; a pair of friction shoes for cooperating with said drum; an operating lever for each shoe; a motor interposed between said operating levers; and means associated with said levers and operable by said motor during its rota tive motion to cause pivotal movement of said levers to release their respective shoes from said drum, the motor shaft being axially free whereby the force exerted on each lever during the releasing operation is counterbalanced by the force exerted on the other.

3. In combination; a rotatable drum; a friction shoe for cooperating with said drum; yielding means tending to maintain said shoe in gripping relation with said drum; a lever adapted, upon pivotal movement, to cause the release of said shoe from said drum; a pivotal support for said lever; a motor having a rotatable shaft; a screw formed on said shaft; a nutmovable by said screw during the rotative motion of said motor; and means for transmitting the movement of said nut to said lever to cause the pivotal movement of said lever and thus the release of said shoe from said drum against the force of'said yielding means.

' 4. In combination; a rotatable drum; a pair of levers; a pivotal support for each lever; a friction shoe carried by each lever for cooperation with said drum; yielding means tending to-maintain said shoes in engagement with said drum; a nut operatively connected to each lever; an operating screw for each nut; and a motor for turning said screws, said motor having a shaft upon the ends of which said screws are formed, said screws, upon being turned by said motor,

causing movement of said nuts and therefore the plvotal movement of said levers to re lease said shoes from said drum against the force of said yielding means.

5. In combination; a rotatable means for frictionally engaging said drum;

and means for causing movement of said firstdrum;

named means with respect to said drum, said last named means comprising rotatable actuating means adapted, upon having power supplied, thereto, to cause the release of the first named means from said drum, and a torsion spring, wound up by said actuating means during the releasing operation, for returning said actuating means, upon the discontinuation of the supply of power'thereto,

to a position to permit said first named means to reengage said drum.

6. Braking mechanism comprising; a brake drum; a pair of levers; a pivotal support for each lever; a brake shoe carried by each lever at one end thereof for cooperation with said brake drum; yielding means for each shoe, each yielding means tending to maintain its respective shoe in engagement with said drum; a nut for each lever, each,

sion spring, wound up during the release of said shoes from said drum, for causing, upon the deenergization of said motor, movement of the rotor of said motor, screws, nuts and levers toward positions to permit said shoes to reengage said drum and for aiding both yielding means in causing the reengagement of said shoes with said drum.

7. Braking mechanism comprising; a brake drum; a pair of brake levers; a pivotal support for each lever; a brakeshoe carried by each lever for cooperation with. said drum; yielding means tending to maintain said shoes applied to said drum; mechanism for causing, upon rotative motion in one direction, the pivotal movement of said levers to release said shoes from said drum against the force of said yielding means; means for imparting rotative motion to said mechanism in the other direction to a position to permit the reapplication of said shoes to said drum; and means, operated during the latter part of the rotative motion of said mechanism in said other direction, to retard the application of said shoes to said drum.

8. In combination; a rotatable drum; a pair of friction shoes for cooperating with said drum; operating means for each shoe; rotative means for causing, during its rotative motion, the operation of said operating means to move their respective shoes with respect to said drum; and means for supporting said rotative means for suflicient movement axially to permit the movement of both of said shoes with respect to said drum without receiving axial thrusts in the event movement of one of said shoes occurs before movement of the other.

9. Braking mechanism brake drum; a pair of brake shoes for cooperating with said drum; yielding means for each shoe, each yielding means tending to maintain its respective shoe in engagement with said drum; an operating lever for each shoe; an operating nut for each lever, each nut being operatively connected to its respective lever; a motor having means for supporting its shaft for rotative motion; an operating screw for each nut; said screws being one on each end of the motor shaft; and means for permitting the release of both brake shoes from said drum without the exertion of axial thrusts on the supporting means for the motor shaft in the event that one of said shoes is maintained in engagement with said drum, during the release of the other, by the force exerted by its yielding means, said last named means comprising an abutment carried by each lever, a stop for each abutment, said stops being disposed in the paths of their respective abutments, and means for permitting axial movement of the motor shaft.

10. Braking mechanism comprising; a

brake drum; a pair of brake shoes for cooperating with said drum; an operating member for each shoe; a motor; means movable substantially axially of the motor shaft by the motor during rotative motion thereof to cause the operation of said members to move their respective shoes with respect to said drum; an abutment for each member; a stop for each abutment. each stop being adapted to be engaged by its respective abutment upon operation of the member, for which said abutment is provided, to move its shoe a certain distance away from said drum; and supporting means for the motor shaft arranged to permit sufficient axial movement thereof to allow the release of both of said shoes from said drum in. the event of the engagement of the abutment for one of said members with its stop during the release operation before the operation of the other member to release its shoe.

llaBraking mechanism comprising; a brake drum; a "pair of brake shoes for cooperating with said drum; an operating lever for each shoe; an abutment carried by each lever; a stop for each abutment and disposed in the path thereof; means for operating said levers, said means comprising a nut for each lever and operatively connected thereto and an operating screw for each nut; a motor for turning said screws to cause movement of said nuts and therefore the levers to release said shoes Z from said drum, said screws being formed, one on each end of the shaft of the motor; and supporting means for said shaft arranged to permit.

comprising; a

sufficient axial movement thereof to allow the release of both of said shoes from said drum in the event of the engagement of the stop and abutment for one of them during the releasing operation before the release of the other. 1

12. Braking mechanism comprising; a brake drum; a pair of brake shoes for 00- operating with said drum; anoperating member for each shoe; a motor; means movable substantially'axially of the motor shaft by the motor, during rotative motion thereof in onedirection, to cause the operation of said members to release said shoes from said drum; means for causing the application of said shoes to 'said drum upon rotative motion of themotor in the other direction; and means for permitting sufiicient axial movement of the niotor shaft to allow the second named means to cause the application of both of said shoes to said drum in the event that one of them engages said drum ahead of the other. I

13. Braking mechanism comprising; a brake drum; a pair of levers;-a pivotal support for each lev'er; a brake shoe carried by each lever at one end thereof for coo'peration with said brake drum; yielding means for each shoe, each yielding means tending to maintain its respective shoe in engagement with said drum; a nut for each lever, each nut being operatively connected to its respective lever at the other-end thereof; an operating screw for each nut; an electric motor having a rotatable shaft, said screws being one on each end of said shaft and being adapted, upon being turned by the rotative motion of said shaft in one direction, to cause movement of their respective nuts and therefore the pivotal movement of said levers to release said shoes from said drum against the force of their respective yielding means; a spring for causing, upon the cleenergization of said motor, the rotative motion of said shaft and therefore the turning of said screws in the other direction to cause movement of said nuts and levers toward positions to permit said shoes to engage said drum; and means for permittinglsuflicient axial movement of the\moto'r shaft to allow each yielding means to a plyflits respective brake shoe in the event 0 the prior engagement of the other shoe with said drum 14. Braking mechanism comprising; a brake drum; a pair of brake shoes for cooperating with said drum; an operating member for each shoe; a motor; means movable substantially axially of the motor shaft by the motor, during rotative motion thereof in one direction, to cause the operation of said membersto release said shoes from said drum; means for causing the application of said shoes to said drum upon rotative motion of said motor in the otherdirection; and means for permitting suificient axial movement of the motor shaft to allow the release of both of said shoes from said drum in the event that one 'of them is released ahead of the other and to allow the second named means to cause the aplication of both of said shoes to said drum in the event that one of them engages said drum ahead of the other.

15. Braking mechanism comprising; a brake drum; a pair of levers; a pivotal support for each lever; an abutment carried y each lever; a stop for each abutment and disposed in the path thereof; a brake shoe carried by each lever at one end thereof for cooperation with said brake drum; yielding means for each shoe, each yielding means tending tov maintain its respective shoe in engagement with said drum; a nut for each lever, each nut being operatively connected to its respective lever at the other end there of; an operating screw for each nut; an electric motor having a rotor including a shaft therefor, said screws being formed one on each end of said shaft and being adapted, upon being turned by the rotative motion of said rotor in one direction to cause movement of their respective nuts and therefore the pivotal movement of the levers to release said shoes from said drum against the force of their respective yielding means; a torsion spring, wound up during the rotative motion of said rotor to release said shoes from said drum, for causing, upon the de- *energization of the motor, the rotative motion of said rotor and shaft and therefore the turning of said screws in the other direction to cause movement of said nuts and levers toward positions to permit said shoes to reengage said drum and for aiding both yielding means in causing the reengagement of said shoes with said drum; bearing members forthe motor shaft; and supporting means for said bearing members arranged to permit suflicient axial movement of the rotor, screws and nuts in either direction from central osition of said rotor to allow the release of 0th brake shoes from said drum in the'event of the engagement of the abutment and stop for one of them during the releasing Operation before the release of the other and to allow each yielding means to apply its respective shoe to said drum in the event of the prior engagement of the other.

In testimony whereof, I have signed my name to this s ecification.

EORGE W. LAUTRUP.

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