US2322061A

US2322061A - Automatic adjusting mechanism for brakes

Info

Publication number: US2322061A
Application number: US391930A
Authority: US
Inventors: Schnell Steve
Original assignee: Wagner Electric Corp
Current assignee: Wagner Electric Corp
Priority date: 1941-05-05
Filing date: 1941-05-05
Publication date: 1943-06-15
Anticipated expiration: 1960-06-15

Description

June 15, 1943. a HNELL' 2,322,061

AUTOMATIC ADJUSTING MECHANISM FOR BRAKES Filed May 5, 1941 2 Sheets-Sheet 1 FIG.I.

38 4 34 f T a v 2 36 37 23 a 42 39 I6 2 27" A 43v 3 I J 5 47 ,.la 5 Q l\:

IO l2 8 I 5 1 rY I x ll

INVENTQR STEVE SCHNELL June 15, 19439 '5. SCHNELL AUTOMATIC ADJUSTING MECHANISM FOR BRAKES Filed May 5, 1941 ZSheetS-Y-Sheet 2 FIG.5.

INVENTOR STEVE SCHNELL TORNE Patented June 15, 1943 AUTOMATIC ADJUSTING MECHANISM FOR BRAKES Steve Sclmcll, Kirkwood, Mo., assignor to Wagner Electric Corporation, St. Louis, Mo.', a corporation of Delaware Application May 5, 1941, Serial No. 391,930

22 Claims. (G. 188-495) My invention relates to brakes and more particularly to the adjustment of brake shoes to compensate for lining wear. I

One of the objects of my invention is to provide improved means for automatically adjusting two brake shoes simultaneously by a single adjusting mechanism controlled by the'lining wear of one shoe.

Another object of my invention is to provide an automatically operable adjusting mechanism for two brake shoes which is controllable by the lining wear of one shoe that the total or com bined off position clearances of both shoes at predetermined points will be substantially constant.

Still another object of my invention is to provide an automatic adjusting means. of the kind referred to which will be controlled by a control member so carried on a shoe that it will be contactable with the drum during braking action and manner as to provide a pocket for receiving a block H pivoted on the anchor pin. The anchor pin extends through opposed radial slots l2 in member ill in order that the shoe end may have radial movement toward the brake drum for adjusting purposes. The end of the shoe abuts directly against the block and is held in frictional engagement withthe block by a leaf spring l3 interposed between the base of the U-shaped member and said block. Thus, by

. means of this construction it is seen that the heel capable of movement relative to the shoe an I Yet another object of my invention is 'to so combine an automatic adjusting means for brake shoes with a mechanical actuating means for said shoes that the actuating means will also be auto matically adfiusted.

Other objects of my invention will become apparent from the following description taken in connection with the accompanying drawings in which Figure 1 is a view .of a brake assembly having associated therewith adjusting mechanism embodying my invention, parts being shown in section and broken away; and Figures 2, 3, 4 and 5 are sectional views showing details, said views being taken on the lines 2-2, 3-3, t-t and 5--5, respectively, of Figure 1.

Referring to the drawings in detail, the numeral l indicates a brake drum which is secured to the wheel of a vehicle and 2 is a support or backing plate secured to a fixed part of the vehicle such as the axle housing. Within the drum for cooperation therewith are two

shoes

3 and 4, each comprising a web 5, a lining carrying flange 5 and lining l. The heel end of shoe 3 is pivotally mounted on the anchor pin 8 carried by the backing plate and an anchor pin-9 also carried by the backing plate has pivotally mounted thereon the heel end of shoe 6. The mounting arrangement of each shoe is the same and of such construction as to permit automatic adjustment of the heel end toward the drum when lining wear occurs. The construction comprises a U-shaped member it welded to the end of the shoe in such end of each shoe may slide radially toward the drum and relatively to the block ll pivoted on the anchor pin. At the same time the shoe may pivot about the anchor pin in order that it may be engaged and disengaged from the drum. A connecting link It extends between

anchor pins

8 and 9 so that the reaction on one pin during braking, will be partially transferred to the other pin.

The toe ends of

shoes

3 and 4 may be actuated into engagement with the drum for service purposes by any suitable actuating means such, for example, as the double piston fluid motor 95, said motor being connected to a master cylinder or other source of pressure not shown. Thus, to actuate the shoes into engagement with the drum, fluid under pressure is transmitted to the fluid motor thereby causing the pistons to spread the toe ends of the shoes apart. When it is desired to release the brake, the fluid pressure is released from the fluid motor. The shoes are retracted from the drum by the action of a return spring it having its ends connected to the .shoes in a manner to be subsequently described.

The shoes 3 and t are provided with steady rests I1 and 58, respectively, each rest embodying friction means for holding the shoe in its oil position. The construction involved is the same for each shoe, the steady rest it being shown in detail in Figure 5. This construction comprises a pin 69 carried by the backing plate and extending through slot 20 in the web of the brake shoe so arranged as to permit pivotal movement of the shoe. The inner end of the pin carries a washer 2 I, and associated with the portion of the pin outside the backing plate is a spring 22 for biasing the washer against the web and holdin the web frlctionally engaged against a block 22' surrounding the pin and interposed between the backing plate and the web.

As best shown in Figures 1 and 3, web 5, flange 6 and lining l of shoe 3 are cut away to provide an opening 23 in which. is positioned a control member or block 24 of wear resisting material.

Secured to this block is an arm which extends inwardly along side of web 5 of the shoe and is supported on the shoe by a pin 26 carried by the web and extending through a slot 21 in the arm, said slot being of such length that the block and arm may move relatively in a radial direction with respect to the shoe. A washer 28 holds the arm on the pin. The rear end of the arm is formed with a flange 29 and interposed between this flange and the pin is a one-wedge portion 30 of a double-wedge adjustingmember 3|. The wedge portion 30 is frictionally held between flange 29 and pin 26 by a relatively strong hairpin spring 32, the legs of which cooperate with pin 26 and arm 25.

Y The other wedge portion 33 of the double-wedge adjusting member 3| extends upwardly along side of web 5 of the shoe and projects between two

blocks

34 and 35. Block 34 is pivoted to web 5 of the shoe by a pin 36. Block 35 carries a pin 31 which extends through a slot 38 in the web and is also pivotally mounted to an end of a rod 39. This rod extends between the toe ends of the shoes just below the fluid motor i5. The said end of this rod is slotted to receive the web with one leg 40 having pin 31 pivoted therein, and the other leg 4| having a semi-cylindrical bearing surface for abutting a. like surface on block 35. A coil spring 42 is connected at one end to block 35 and at its other end to a turned-over portion 43 on the end of wedge portion 30. The other end of rod 39 is connected by a pin 44 to the intermediate portion of a lever 45 lying along side of web 5 of shoe 4 and having one end pivoted to the toe end of the shoe by a pin 45, The lever is of such length that its free end will be positioned adjacent the heel end of shoe 4 and connected to this end is a flexible cable 41 for operating the lever. The lever 45 at a point between the free end and the connecting pin 44 of rod 39 is pro- 54 is provided for the opening to exclude dust and dirt.

The retracting spring i6 previously referred to surrounds the rod 39 and one end of the spring is hooked over the end of pin 35 on shoe 3. The other end of the spring is hooked through a slot 55 in the web of brake shoe 4.

Referring to the operation of the adjusting mechanism, it is flrst necessary to make certain adjustments before the mechanism is ready to operate in a proper manner. With the drum removed the adjusting member 3| is pushed downwardly in the direct on of the arrow Aand against the bias of spring 42. This will permit the block 24 to move outwardly under the action of the hairpin spring 32. Since this latter spring is of such strength as to normally prevent the spring 42 from pulling the adjusting member upwardly in the direction opposite arrow A, the block will remain in its outer position. Next, the cam 49 is turned in the direction indicated by the arrow B and to its starting position; that is, where the shortest radial length is oppos te flange 48 of lever 45. The adjustment of the cam is accomplished by removing the plug 54 in the backing plate and inserting a tool through the opening 53. After these operations have been performed, the drum is now placed in position around the brake shoes and with the drum rotating flrst in one direction and then in the other direction, the brake shoes are applied by the fluid motor l5. This operation automatically causes the heel ends of the two shoes to be automatically adjusted to proper position since they are capable of a radial movement due to the particular mounting means employed.

The application of the shoes results in the control member or block 24 carried by shoe 3 to be pushed back flush with lining 1 of said shoe. Since this increases the space between flange 29 and pin 26, spring 42 will be effective to move the adjusting member 3| upwardly or in the direction opposite that indicated by the arrow A. The wedge portions 30 and 33 of the adjusting member 3| thus assume their starting positions. Next, cam 49 is rotated in the direction opposite that indicated by the arrow B and to a position where the shoes are brought into contact with the drum by the movement of lever 45 and the connecting rod 39. The cam is now rotated in the opposite direction; that is, in the direction of arrow B until the combined retracted clearance of both shoes with respect to the drum is the desired amount, which distance should be twice the distance each shoe should have if each were provided with a. fixed off" position stop on the backing plate as is present practice. After this adjustment has been made, the actuating mechanism for operating lever 45 by means of cable 41 is adjusted so that when in its inoperative position there will be no slack in cable 41.

With the adjusting mechanism now properly set, there is no need for making any additional adjustments throughout the entire life of the brake lining. All subsequent adjustments will be made automatically not only to compensate for wear of the shoe linings but also for taking up slack in the mechanical actuating means for the shoes including the lever 45 and rod 39. As the lining of shoe 3 wears, block 24 will be pushed inwardly since the block does not wear to any appreciable extent as there is no brake actuating pressureholding it in engagement with the drum when the brake shoe is applied. As the block is pushed back, flange 29 is moved farther away,

from pin 26, thus permitting spring 42 to move the adjusting member 3| upwardly in a direction opposite arrow A. This will cause wedge 33 to increase the distance between

blocks

34 and 35. and consequently the distance between the shoes because block 34 is carried by shoe 3 and block 35 is carried on rod 39 connected to shoe 4.

It is to be noted that when any movement of the adjusting member-3| takes place, brake shoe 3 will be n engagement with the drum and, therefore, blocks 34 and 35 will be in such positions that the wedge portion 33 is not clamped between them. Thus the adjusting member is easily moved under the action of spring 42. Since the eifective length of rod 39 is increased when an adjustment is made by the adjusting member, it is seen that the originalinoperative adjustment of the mechanical actuating mechanism will remain the same regardless of lining wear.

In the pivoted shoe type of brake with which the adjusting mechanism is associated, the iming on the forward shoe will wear more rapidly than that on the reverse shoe. Thus, if it is considered that shoe ,3 is the forward ,shoe with a normal forward rotation of the drum, as indicated by the arrow C, the lining on this shoe will asaaooi wear about three times as fast as the lining on the reverse shoe 4. Thus, to maintain the combined or total -off" position clearances of the 'two shoes substantially constant, it is necessary wear of the lining of, the forward shoe 3 will permit such a movement of the wedge portion 33 that it will cause the distance between the retracted positions of the shoes to beincreased one v and one-third times the predetermined wear of the lining of shoe 3. In other words, the arrangement will be such that for each unit of distance the block 2d is pushed back relative to shoe 8, the distance between the shoes in their re tracted positions is increased by one and onethird units. Thus, the difference in wear of both linings is properly compensated for.

In order to prevent the adjusting means from making any adjustment after the lining of shoe 3 approaches a completely worn condition prvision is made to limit inward movement of block 2 3. This is accomplished by predetermining the space X between the block and web 5 of the shoe (see Figure 3). When the block moves inwardly in order to abut the web, it will then wear with the lining and no further adjustment will take place. With no new adjustment taking place, there will be increased pedal travel and the operator will be warned that his brakes need lining and can have this done before the lining is completely worn off the forward shoe.

Although there is no fixed off posit on stop on the backing plate for each of the brake shoes. the brakes will, nevertheless, be held disengaged from the drum when retracted by the spring Hi. This is accomplished by the friction mean v associated with the guides IT and 18. The frict on means prevent the shoes from freely swinging as a unit and causing one shoe to re-engaue w th the drum once the shoes have been retracted. The wiping action of the drum after the brakes have been released will so push the shoes against the friction clamping action that they will be disengaged from the drum. The total clea ance of both shoes will always be substantially the samev although the clearance of each shoe may vary each time the brake shoes are retracted.

In the above described adjusting mechanism it is seen that once the original adjustment has been made, it is not necessary to again make any adjustment until the linings are replaced. The heel ends of both shoes are automatically adjusted by the adjustable anchor mounting. The total or combined off position clearances of the shoes at their. toe ends isalso maintained substantially constant, thus insuring that the brake shoes can always be applied by a given displacement of fluid in the fluid actuating system. Also,

by having the adjusting mechanism which compensates for lining wear associated with the mechanical actuating mechanism so that this actuating mechanism is adjusted simultaneously with.

the lining wear adjustment, the brake can always be applied by the same throw of the lever used to operate the mechanical mechanism. This is important because this mechanism can become a' real dependable emergency actuating mechanism or it can even be employed as the sole actuating' means of the brake shoes without any adjusting requirements,

Being aware of the possibility of modifications in the particular structure herein described without departing from the fundamental principles of my invention, I do not intend that its scope be limited except as set forth by the appended claims.

Having fully described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. In braking mechanism, a support a drum, friction means cooperable with the drum and having two actuatable ends capable of movement into and out of engagement with the drum by an operator-controlled actuating means associated with said ends, anchoring means carried by the support for the friction means, means between said ends independent of the anchoring means for the friction means for limiting the amount of the combined clearances the ends may have with respect to the drum when retracted-therefrom, and means for adjusting said last named means so that the combined clearances will remain substantially constant as both actuatable ends of the friction means wear, said means comprising a single control member engaged by the drum and movable in accordance with the amount of wear of the friction means at one predetermined place.

2. In braking mechanism, a support, a drum, friction means cooperable with the drum and having two actuatable ends capable of 'movement into and out of engagement with the drum by an operator-controlled actuating means associated with said ends, anchoring means carried by the support for the friction means, means between said ends-independent of the anchoring means for the friction means for limiting the amount of the combined clearances the ends may have with respect to the drum when retracted therefrom, means for adjusting said last named means so that the combined clearances will remain substantially constant as both ends of the friction means wear, said means comprising a control member contactable with the drum and capable of having relativemovement with respect to the friction means in accordance with the amount of wear of the friction means at one predetermined place and means comprising a longitu dnally movable wedge having its movement governed by the movement of the control member for adjusting the limiting means.

3. In braking mechanism, a support, a drum, friction means cooperable with the drum and having two actuatable ends capable of movement into and out of engagement with the drum, means for actuating said ends of the friction means into engagement with the drum for braking purposes and comprising means for limiting the distance said ends can be retracted toward each other when the actuating means is in an inoperative position, and automatically operable means associated with the actuating' means for increasing the retracted distance between the ends of the friction device as sa d ends wear so as to maintain the total retracted clearances of both ends with respect to the drum substantially constant, said means comprising a control member contactable with the drum and capable of having relative movement with respect to the friction means in accordance with the amount of wear of the friction means at one predetermined place. said automatically operable means also preventing any slack from developing in the actuating means due to wear of the friction means,

4. In braking mechanism, a support, a drum, friction means cooperable with the drum and having two actuatable ends capable of movement into and out of engagement with the drum, meansfor actuating said ends of the friction means and comprising a lever pivoted to one end of the friction means and a rod operatively connecting the lever to the other end of the friction means, and means for automatically increasing the effective length of said rod in a manner to compensate for wear of the ends of the friction means and maintain the total retracted clearances of said ends with respect to the drum substantially constant, said means comprising a control member contactable with the drum and capable of having relative movement with respect to the friction means in accordance with the amount of wear of the friction means at one predetermined place;

5. In braking mechanism, a support, a drum, friction means cooperable with the drum and having two actuatable ends capable of movement into and out of engagement with said drum by an operator-controlled actuating means associated with said ends, anchoring means carried by the support for the friction means, a connection between the ends independent of the anchoring means for the friction means for limiting the amount of the combined clearances the ends may have with respect to the drum when retracted therefrom, and means for adjusting said connection so that said combined clearances will be substantially constant as both ends of the friction means wear, said means comprising a single control member carried by a part of the friction means for engagement with the drum and capable of movement relative to said friction means in accordance with wear of the friction means adjacent said part thereof.

6. In braking mechanism, a support, a drum,

friction means cooperable with the drum and having two actuatable ends capable of movement into and out of engagement with said drum by an operator-controlled actuating means associated with said ends, anchoring means carried by the support for the friction means, a connection between the ends independent of the anchoring means for the friction means for limiting the amount of the combined clearances the ends may thereto in accordance with wear of the friction means at one point only, a wedge for adjusting the connection, and means governed by the movement of the control member for causing the wedge to have such movement that the connection will be adjusted sufficiently to compensate for the wear on both ends of the friction means.

,8. In braking mechanism, a support, a drum,

' two brake shoes in the drum and pivoted on the support at their heel ends, means for limiting the distance between the toe ends of the shoes when moved toward each other upon retraction from the drum, and means for automatically adjusting said limiting means to increase said distance to compensate for wear of both shoes, said means comprising a control member carried by one of the shoes and movable relatively thereto by contact with the drum as the friction surface of said shoe on which it is mounted wears.

9. In braking mechanism, a support, a drum, two brake shoes in the drum and pivoted on the support at their heel ends, means for limiting the distance between the toe ends of the shoes when moved toward each other upon retraction from the drum, means for automatically adjusting said limiting means to compensate for wear of both shoes, said means comprising a control member so carried by one of the shoes that it is contactable with the drum and capable of movement relative to the shoe as the shoe wears, and means controlled by the movement of said con-' trol member for acting on the limiting means and increasing said distance an amount equal to the wear of both shoes.

10. In braking mechanism, a support, a drum, friction means cooperable with the drum and having two actuable ends capable of movement into and out of engagement with the drum, means between the ends for limiting the total of the clearances said ends may have with respect to the drum when retracted therefrom,

have when retracted from the drum, and means for adjusting said connection so that said combined clearances will be substantially constant as both ends of the friction means wear, said means comprising a control member carried by a part of the friction means and capable of movement relative to said friction means in accordance with wear of the friction means adjae cent said part thereof and a wedge directly controlled by the movement of said control member that it will adjust said connection in a manner to maintain the combined clearances of the ends substantially constant.

7. In braking mechanism, a support, a drum, friction means cooperable with the drum and having two actuatable ends capable of movement into and out of engagement with said drum, anchoring means carried by the support for the friction means, a connection between the ends independent of the anchoring means for the friction means for limiting the amount of the combined clearances the ends may have when retracted from the drum, means for adjusting said connection so that said combined clearances will be substantially constant as both ends of the friction means wear, said means comprising a control member carried by a part of the friction means and capable of relative movement means for adjusting said last named means so that the total of the clearances will be substantially constant as both ends of the friction means wear, said means comprising a control member slidably mounted on the friction means for relative radial movement and having a portion contactable with the drum, a slidable adjusting member for controlling the limiting means, spring means for operating said adjusting memher, and means controlled by movement of the control member for determining the extent of movement of the adjusting member by the spring means, said control member being movable in accordance with wear of the friction means adjacent said drum contacting portion.

11. In braking mechanism, a support, a drum, two brake shoes in the drum and pivoted on the support at their heel ends, means for limiting the distance between the toe ends of the shoes when moved toward each other upon retraction from the drum, means for automatically increasing said distance to compensate for wear of both shoes, said means comprising a control member mounted for relative slidable movement on one shoe and having a portion contactable with the drum in order to cause the control member to move an amount equal to the wear of the shoe, an adjusting member connected to adjust said distance limiting means, spring means for operating said adjusting member, and means for permitting said adjusting member to be moved by the spring means only when the control member is moved relatively to the shoe, the amount of movement of the adjusting memances of said ends when they are retracted from v the drum, and automatically operable means for acting on and so adjusting said actuating means that the total of the clearances of said ends will remain substantially constant as the friction surfaces of said ends wear, said means comprising a control member contactable with the drum and movable in accordance with the amount of wear at a predetermined place on the friction surface of said friction means.

13. In braking mechanism, a support, a drum, two brake shoes in the drum and pivoted on the support at their heel ends, means for spreading the toe ends of the snoes apart and for limiting their movement toward each other when retracted from the drum, and automatically operable means for so adjusting said actuating means that the retracted distance between the toe ends of the shoes will be increased to compensate for the wear of the toe ends of both shoes, said means comprising a control member contactable with the drum and movable in accordance with the amount of wear at a predetermined place on the friction surface of one shoe.

14. In braking mechanism, a support, a drum, two brake shoes in the drum and pivoted on the support at their heel ends, a lever connected to the toe end of one shoe, 9. rod operatively connecting the lever to the toe end of the other shoe, said lever and rod limiting the distance that the toe ends of the shoes may move toward each other when the shoes are retracted from the drum, means for automatically increasing the effective length of said rod to compensate for the wear at the toe ends of both shoes, said means comprising a control member contactable with the drum and movable in accordance with the amount of wear on the friction surface of one shoe and means governed by the movement of the control member for adjusting the rod so that the total of the retracted clearances of the toe ends of both shoes will be substantially constant, and means for moving the lever to actuate the shoes into engagement with the drum.

15. In braking mechanism, a support, a drum, two brake shoes provided with lining and positioned in the drum, means for pivotally mounting the heel ends of the shoes to the support operable adjusting means comprising a control member movable in accordance with the wear of the lining at a predetermined place on one shoe. 16. In braking mechanism, a support, a drum, two brake shoes provided with lining and positioned in the drum, means for pivotally mounting' the heel ends of the shoes to the support so as to'automatically permit said ends to move toward the drum as the lining adjacent thereto wears, a connection between the toe ends of the shoes for limiting the retracted distance between said ends, automatically operable means for adjusting said connection so as to increase the retracted distance as the lining at the toe ends wear and thus maintain the combined retracted clearances of the toe ends with respect to the drum substantially constant, said automatically operable adjusting means comprising a control membe. carried by one shoe so as to be contactable with the drum and movable relatively to the shoe as the lining thereon wears, and means controlled by the movement of the control member and cooperating with the connection for causing it to be adjusted to compensate for wear of the lining on both toe ends.

17. In braking mechanism, a support, a drum, two shoes provided with lining and pivotally mounted on the support at their heel ends, means for actuating the toe ends of the shoes into engagement with the drum, means comprising a connecting rod between the toe ends of .theshoes for limiting the total amount of the drum clear-- ances of the toe ends'when the shoes are retracted from the drum, a control member carried by one shoe for movement relative to said shoe in accordance with lining wear at a predetermined point, said control member having a part contactable with the drum when the shoe is engaged therewith, an adjusting member for increasing the length of said connecting rod, and means controlled by the relative movement of the control member for causing said adjusting member to so increase the length of said connecting rod that the total amount of the clearances of said toe ends of the shoes will be maintained substantially constant.

18. In braking mechanism, a support, adrum, two shoes provided with lining and pivotally mounted on the support at their heel ends, means for actuating the toe ends of the shoes into engagement with the drum, means comprising a connecting rod between the toe ends of the shoes for limiting the total amount of the drum clearances of the toe ends when the shoes are re=- tracted from the drum, a control member carried by one shoe for movement relative to said shoe in accordance with lining wear at a predetermined point, said control member having a part contactable with the drum when the shoe isengaged therewith, an adjusting member for increasing the length of said connecting rod, means controlled by the relative movement of the control member for causing said adjusting member to so increase the length of said connecting rod that the total amount of the clearances of said toe ends of the shoes-will be maintained substantially constant, and means including said rod for actuating the shoes into engagement with the drum independently of the first named actuating means.

19. In braking mechanism, a. support, a drum, two shoes provided with lining and pivotally mounted on the support at their heel ends, means for actuating the toe ends of the shoes into engagement with the drum, means comprising a connecting rod between the toe ends of the shoes for limiting the total amount of the drum clearances of the toe ends when the shoes are retracted from the drum, a control member carried by one shoe for movement relative to said shoe in accordance with lining wear at a predeteramount of the clearances of the toe ends of the shoes substantially constant.

20. In braking mechanism, a support, a drum. two shoes provided with lining and pivotally mounted on the support at their heel ends, means for actuating the toe ends of the shoes into engagement with the drum, means comprising a connecting rod between the toe ends of the shoes for limiting the total amount of the drum clearances of the toe ends when the shoes are retracted from the drum, a control member carried by one shoe for movement relative to said shoe in accordance withlining wear at a predetermined point, said control member having a part contactable with the drum when the shoe is engaged therewith, a wedge for increasing the length of said connecting rod, a spring for operating the wedge, means controlled by the relative movement of the control member for permitting the spring to so move the wedge that the length of the connecting rod will be increased an amount sumcient to maintain the total amount of the clearances of the toe ends of the shoes substantially constant. and means ocmprising a. lever pivoted to the other shoe and cooperating with the rod for actuating the shoes into engagement with the drum independently of the first named actuating means.

21. In braking mechanism, a support, a drum, friction means cooper-able with the drum and having two actuatable ends capable of movement into and out of engagement with the drum,

means for limiting the distance said ends can be retracted toward each other and comprising a lever pivoted to one end of the friction means. a member connected to the lever and abutting the other end of the friction means, and means carried by the friction means and positioned between the portion of the friction means upon which the lever is pivoted and the lever for so adjusting the lever with respect to said portion of the friction means as to vary the distance the ward each other.

22. In braking mechanism, a support, a drum, friction means cooperable with the drum and having two actuatable ends capable of movement into and out of engagement with the drum, and means for actuating the ends and for limiting the distance said ends can be retracted toward each other, said means comprising a lever pivoted at one of its ends to one end of the friction means, a rod connected to an intermediate portion of the lever and abutting the other end of the friction means, a cam carried by theportlon of the friction means upon which the lever is pivoted and cooperating with the lever to so adjust it and the rod that the retracted distance between theends of the friction device can be varied and means connected to the non-pivoted end of the lever for actuatingthe lever and the rod to expand the two ends of the friction means.

STEVE SCHNELL.

ends of the friction device can be retracted 00--