USRE22586E - Brake mechanism - Google Patents

Description

Jan. 2, 1945. w P L ET AL Re. 22,586

BRAKE MECHANISM Original Filed April 7, 1941 2 Sheets-Sheetl jwuc-Mou/ a WFZ/idm H JpiZZer Herberz WA/den Hal 0f? [i Super Jan. 2, 1945. w R SPILLER ETAL Re. 22,586

BRAKE MECHANI SM Original Fil d April 7, 1941 2 Sheets-Sheet 2 i V'zllz'am R Spills! He/bert W Alden Ha'Zp/z K 644 06)" Reissued Jan. 2, 1945,

I Re.

mums mechanism- William R. Spiller, Dayton, Ohio, and net-am w.

Alden and Ralph K. Super, Detroit, Micln, assignors to The 'llmken-Detrolt Axle Company, Detroit, Micln, a corporation of Ohio.

Original No. 2,337,069, not Decemlaer 21, 1943,

- Serial No. 387,314, April 1, 1941. Application for reissue October 4, 1944, Serial No. 557,118

24 Claims. (Cl. 188-28) 'l'hepresent invention relates to brake mechanisms, and more particularly to internal expanding drum brakes for automotive vehicles, although it is not limited to such use.

- In a conventional brake, the brake shoe is pivoted on a fixed anchorv pin and rocks about a definite axis, between engaged and disengaged positions. Although in such a. brake there is a direct line relationship between the force applied and the braking torque developed, it is open to the disadvantage that through a phenomenon known as "toe grab," or self-locking, the shoewill often grab and cause uneven braking, and/or uneven-wear oi the brake lining. Circumferential extent or span of the lining in such brakes must be held to small limits; the anchor pin mounting must be maintained closely adjacent the drum; and the coemcient of the lining must be kept comparatively low to avoid toe grab and self-locking oi the shoe. Each of these factors serves to decrease the braking power or torque capacity of the brake.

In the Servo brakes oi the prior art, a pri-' mary shoe is mounted for floating movement and is linked to a secondary-shoe, which in turn is pivoted on an anchor pin. The braking torque of such brakes is greater than a conventional brake oi given size, but they are open'to serious disadvantages. The major diiiiculty of this brake is that it is not completely controllable under all conditions. For one thing, a release of, or reduction in, pedal pressure is not always reflected as a corresponding cessation of, or reduction in,

- braking torque, with the result that the brake is not altogether reliable in operation.

In Hayes et al. Patent No, 2,208,293, granted July 16, 1940, there is disclosed a brake mechanism embodying a shoe assembly mounted for pivotal and sliding movement and designed to overcome the toe grabbing defect of conventional ,pivoted shoes,. and to also permit the braking power to be increased and an appreciable degree of self-energizing action achieved, by shifting the anchor pin inwardly toward the axis of the brake drum, and increasing the degree to which the lining at the toe end of the shoes is extended.

. Although the patented structure represents a substantial advance in the art over the other brake mechanisms 01 theprior art, from the standpoints 01 construction and operation it is not altogether successful and fails short 01 a brake having all of the desired operating characteristics. The Hayes et al. brake, by reason drum in such manner that, when either end of to structural distortion or iailurewhen excessive braking torques are imposed upon the mechanism, and also, because the braking torque is taken solely at one end 01 each shoe, the increased braking torque due to anchor'pin location is achieved for only one direction oi rotation for each shoe. when the drum rotation is reversed the shoe functions substantially the same as the trailing shoe of a conventional anchored brake shoe assembly. Therefore, the improvements made by Hayes et al. are only available for one direction of rotation of each shoe.

It is the major object of this invention to provide-a brake mechanism having all of the advantages of the Hayes et al. brake, and in addiga'gement with the drum; and each shoe possesses substantially the same braking characteristics in both directions 01' rotation of the drum..

A further object is to provide a brake mechanism embodying means for supporting each shoe for floating movement toward and away from the the shoe is engaged with the drum, the opposite end may move toward and bring the full area of the lining into engagement with the drum.

A further object is to provide a novel mount for a floating brake shoe, embodying an inclined abutment assembly at each end of the shoe, for

' imparting predetermined braking characteristics I to the shoe when forward or rearward brake torquing reactions are applied thereto;

The invention also aims to provide a brake mechanism embodying a novel lever assembly designed to operably support each shoe for floating movement, and to also apply actuatingiorces, to

the central portion of the shoe.

Another object is to provide a brake shoe mounting which anchors the shoe at both ends and yet permits iree pivotal movement about each end as well as free translational movements of each end of the shoe toward and away from the A further object is to provide a brake mechanism in which each shoe 'is supported on two anchor pins, symmetrically located with respect to the center of pressure of the resultant, forces or the slotted shoe end construction, is subject as acting on the shoe, the anchor pins beingoperable to impart similar operating characteristics to the shoe in both directions of drum rotation.

Further objects are to provide novel adjusting means, novel level fulcrum means, novel anchor means, and to generally improve and reflne other features of the brake mechanism of the prior art, which will become apparent as the specification proceeds in conjunction with the annexed drawings.

Figure 1 is a fragmental elevational view of a brake mechanism embodying the invention. with the brake drum and certain other parts broken away to more clearly illustrate the construction modified form of brake anchor adjusting mech-- anism which may be used in the construction shown in Figure 1, and also forming part of the invention; and I Figure 6 is asectional view taken substantially along the line 6-6 of Figure 5.

With continued reference to the drawings, wherein like reference characters have been employed to designate likev parts throughout the several views thereof, the brake mechanism broadly comprises a brake drum A, a pair of brakeshoes B and a hydraulic piston and cylinder assembly 0, although it is to be understood that a cam or any well-known form of link construction may be usedinstead of hydraulic or pneumatic pressure for actuating the brake.

The brake assembly is carried by a foundation plate l0, having a central opening ll designed to fit over any suitable form of axle construction and has a plurality of openings l2 through which fastening screws or rivets are inserted to secure the foundation plate to a flange on the axle. Plate i is flanged to provide a dirt-excluding lip l3 and a brake drum i 4 is mounted for rotation on the wheel or hub assembly in cooperative relationship with lip II in well known manner. The brake of the invention embodies both a novel floating'mount for the brake shoes, which imparts improved braking characteristics to the mechanism, and also a novelpressure applying lever assembly. The novel floating brake mount will first be described.

Rigidly secured to backing plate III is a pair of anchor pins l5 and I5. Pin I5 is provided with large and small diameter concentric journal portions 11 and 18, respectively, and an intermediate eccentric portion is. The large diameter journal portion is pulled into tight engagement with plate III by means of a nut 2i, a lock washer 22 and a spacer member 23, The latter is provided with a flange 24, and is located in a cupped portion 25 formed in the foundation plate. Spacer 23 is preferably riveted to the foundation plate, so as to provide a rugged journal for pin l5.

Pin I5 is provided with a squared end 21, so

that by loosening nut 2| the pin may be engaged by a wrench and turned to rotatethe eccentric, I and thereby adjust the brake ina manner to be hereinafter pointed out.

. Upper pin it is provided with a shoulder 29,

which is pulled into tight engagement with a reinforcing plate ll, secured in turn to backing Anchor plus I! and it constitute the sole support for the shoe and lever actuating mechanism and since the two pairs of actuating pins support the two shoes in exactly the same manner, the

right-hand shoe, which is of identical construction, has not been illustrated (Figure l) the description of the left-hand shoe clearly constituting a full disclosure of the invention.v

anchor pins, and by reason of their novel construction, they directly absorb the braking torque reaction of the drum in both directions of rotation. Abutment member 4i is pivoted upon eccentric portion IQ of anchor pin it, so that by rotating the anchor pin the abutment member is correspondingly actuated to advance or retract the lower end of the shoe with respect to the'drum. The upper abutment member 42 is pivoted upon anchor pin It.

.The coasting faces of the abutment members are comparatively long, so as to avoid high 10- calized pressures, and to also insure pivotal movement of the abutment members in response to the application of. drum reaction forces thereto and prevent the abutment members from swinging around and locking the shoes in engaged position.

Preferably resilient means is employed to constantly maintain the ends of the shoes in engagement with their abutment members when the brake is released, as shown in Figure 1. A tension spring 44 'has its opposite ends hooked into openings 45 and 4G in the brake'shoe flange, and

is provided with two coiled portions 41 and 48.

ma l to face 38, thereis no tendency for the spring to slide the shoe end across the face of member 4|. A somewhat difl'erent spring arrangement is employed for maintaining abutment member 42 in engagement with the upper end of the,

brake shoe, and will be describedin conjunction with the description of the lever assembly.

- Although the brake shoes may be actuated toward the brake drum by any suitable actuating mechanism, we preferably employ the following novel lever assembly because it maintains accurate .control over all movement, ofeach shoe, cooperates with the'abutment members to guide the shoe for accurate movement toward and away from the drum, and also applies actuating forces substantially at the mid-portion of the shoe, so as to effect a substantially uniform distribution of braking pressure.

A pair of levers 5i and 52, of substantially identical shape, are secured together in spaced par- I lever assembly is detachably secured in place on the lower anchor pin by means of a washer "'1 and a split ring '1, which is sprung into a groove in the anchorpin. v

' Each lever, adjacent its upper end, is provided with an elongated slot II for clearing the upper anchor pin. The of slot I in lever ll col operatewith the upper anchor 'pin to limit ex-- treme movement of the levers in both directions. Asshowninl igureLthebrakeshoeisinreleased position. and the left-hand end of slot 58 in lever II is engaged with the upper anchor pin.

The upper end of the lever assembly is m: tained in cooperative relationship to the foundation plate by means of a washer II and a snap ringl2 sprung into a groove in anchor pin ll.

The upper end of the lever assembly is accordingly freely rockable in a plane. normal to the upper anchor pin, but is restrained against movement axially of the pin. As seen in Figure 2, a shoulder" on the pin restrains link member 42 site direction;

Each brake shoe is constantly urged toward .35 for each shoe. For instance, if the brake is actuated when the drum is rotating in one direcdisengaging position by means cl 9. novel retracting spring assembly, which also constantly urges abutment face 39 of the brake shoe toward engagement with itsabutment member 42. A

sauce which applies the forces substanflally centrally ofthe shoe andis so'designedastonotinterlere with free rocking movement thereof, thereby permitting the shoe to autmnatically find a seaton I the drum in full surface engagement therewith.

Journalled in a bushing ll in brake shoe flange 31 is a. 'tmnnion member ll having a pair of slots ti and I2 formed therein (Figure 3). Levers I] and I! are each provided with a straight edge II. which slidably coacts with the grooves in the trunnion member. The grooves, being located adjacent the diameter of'the trunnion, provide long bearing surfaces of adequate, area to sustfln the loads imposed by the levers, which are constantly maintained in full surface engag ment with the bottoms of the grooves. v r

The lever assemblies are accordingly operative to apply forces to the central portion of the brake shoe .through trunnion member II, and at the same time individual lever members may freely slide relatively to the shoe in the trunnion member slots, thereby permitting any self-aligning action to freely take place. In order to further insure free sliding movement of the shoe web between the latter, slightly raised bosses N and .5 are provided on the brake shoe web adlacent abutment faces 3! and 3!, reapectiveb,

* and also a circular boss I8 is formed on the web adjacent trunnion member ID. Working clear-r against movement to the right, which in turn reshoes are provided between the bosses and the brake shoe flange, but the parts fit sufllciently close to insure accurate guiding of the shoe.

' The novel brake mechanism of the invention embodies what may be termed a shifting anchor tion, the drum reaction is taken by one set of anchor pins, and when the direction is reversed the drum reaction is taken by the" other pair of short link member I! has one end thereof hooked 40 anchor pins. Also, the mechanism possesses a at the other end is hooked into the corresponding eyes' of the opposite brake shoe and lever assembly. Spring I2, acting through links ll and it, accordingly, constantly urges the brake shoe an away from the drum and toward'the engagement i with its abutment member 42, and also urges the lever assembly into retracted position, in engagement with pin ll. Link Bl confines the pull of spring I2 upon link '5 to a direction substan as tialLv normal to face 80, with the result that there is no tendency to slide the upper end of the shoe across the face of member 42.

The lever assemblies may be actuated y 118- draulic, pneumatic or mechanical means of any on desired character, it only being necessary to spread the upper ends of the lever assemblies to actuate the brake. In the present instance, however, we have illustrated a well-known type of hydraulic mechanism embodying a cylinder ll having a piston in each end thereof. Piston rods I! are provided with forked portions 1!, which fit over, and fulcrum against, the upper spacer pin 55 of each lever assembly.

co din a arent that, when pressure It is ac r 81! pp angular distance, so as to tightly e age its abut ment face it with abutment member I, and if is applied to cylinder ll, rod II will move outwardly and cause the lever assemblies to fulcrum about lower anchor 'pins II as axes. Rocking movement of the lever assembly is tranamitted'to A tension spring as 12 is hooked into eyes I! and H at one end and further highly-desirable function of so functioning that'each shoe functions as a leading shoe I in both directions of drum rotation, with the re suit that controlled degrees of self-energizing action maybe secured.

Operation chor pin I. This action, through trunnion 1|,

forces the brake shoe outwardly'against the action of spring 12 and spring H, which constantly urges the abutment faces of the shoe toward their links. The resulting substantially horizontal movement of the shoe causes slight clearancesto develop between the shoe abutment faces and their links. Whether or not the clearances developed are equal is immaterial because, as soon as contact of the shoe is made with the drum, j the shoe may rock slightly about the axis of trunnion I! and bring its full surface into engagement with the drum, thereby efiectively avoiding "high spots or areas of high localized pressures, and insuring long lii'e of the brake lining. As soon as the shoe has been brought into engagement with the drum as just described, the braking torque reaction carries the shoe a slight for any reason a clearance exists between them member I is automatically rocked so as to bring them into full surface engagement.

Under the conditions just described, and considering the shoe shown-in Figure 1 alone, the brakeisfuilyappliedandthedrumreactimis taken solely by lower anchor pin II. A slight clearance exists between the upper end of the brake shoe and its abutment, member it, because the outward movement of the lever in combination with the drum reaction has separated these surfaces against the action of spring 12. The opposite shoe (not shown) functions in exactly the same way for clockwise rotation of the drum as the illustrated shoe for counterclockwise rotation, since the levers are fulcrumed the same side of the axis of rotation.

In view of the foregoing, it, is apparent that, if the upper or lower end of the shoe should first engage the drum during the initial stage of brake operation, it will merely result in the shoe being bodily rocked into full surface engagement with the drum, and'there is accordingly no possibility of "toe grab" or greater lining wear at one end than the other; i

The brake of the'invention is accordingly free from all of the disadvantages of the prior art, possesses the advantages over the slotted shoe type of brake of applying the pressures approximately centrally of the brake shoe, and in addition each shoe functions as a leading shoe in both directions of rotation, as will now be pointed out.

Assuming that the drum is rotated in the opposite direction, namely, clockwise as viewed in Figure 1, and the brake actuated as before, the

drum reaction torque forces the brake shoe angularly in a clockwise direction, so as to bring its surface 39 into tight engagement with abut- 35 ment member .2. This transmits all of the braking reaction forces applied to the shoe to anchor pin IS. The bodily movement of the shoe in a clockwise direction in response to the torque reaction causes an increased clearance to develop between abutment surface 38 and abutment member ll, against the action of spring 44. This removes anchor pin II from the sphere of action entirely, and the shoe may be regarded during this operation as being floatingly anchored to pin it alone. -In other words, the .eflectual anchor for the brake shoe has been shifted or transposed, through a reversal of rotation of the drum, from pin l5 to pin I6, and all of the advantages of the leading shoe, which includes a desirable degree of self-energization, realized for both directions of drum rotation.

It is also observed that during the braking operation the braking forces are constantly applied to the mid-portion of the shoe, thereby avoiding localized pressure at either end; insuring uniform pressure distribution; and at the same time permitting either end of the shoe to move inwardly and outwardly, so as to compensate for a slightly out-of-round brake drum.

It is, of course, understood that the shoe, on the opposite side of the axis from the shoe illustrated functions in exactly the same way but. at different times; namely, when the drum is rotating clockwise as just discussed, the shoe opposite the one-shown will transmit the braking torque reaction to lower anchor pin II, and when i the drum is rotating in the opposite direction it will transmit the braking torque reaction to upper pin ii. In either event, both shoes possess the operating characteristics of a leading shoe in either direction of rotation of the drum, by reason of the transfer of the braking torque reaction forces from one set of anchor pins to the other upon reversal of drum rotation. Upon conclusion of the braking operation, pressure is released from cylinder II, and springs N and I! return the, shoes and levers to inoperative position, and

there is no tendency. as in the shoe brakes of, f'g' the prior art, for the diseng n operation to 'be delayed.

In order to simplify the disclosure, the foregoing description of the construction mntains no mention of critical angles and dimensions of the parts used in the brake. The various factors which influence the operating characteristics of the brakes will be taken up separately as follows: I I 7 Brake lining span I In the prior pivoted shoe brakes, it is necessary to so limit the span of the liningas to seriously reduce the braking power of the mechanism. If the lining were carried too far at the we end,

serious "toe grab" would occur, and if it were carried too far under the heel of the shoe, little braking action would be obtained from that portion of the lining.

In the present construction the whole shoe is mounted for bodily translational movement, and

the forces are applied approximately centrally of the shoe, so that the lining may be carried as far as is practicable without encountering the difflculties from shoe grab, and at the same time all parts of the lining bear with equal force against the drum. In the brake illustrated the angle E,

indicating the span of the lining, is approximately 114 degrees, which has been found very satisfactory in actual operation. However, it is to be understood that the angular extent or span of the lining -may be increased or decreased with respect to this value without departing from the spirit of the invention.

Abutment face inclination 5 (2) the thrust or torque reaction Q1 or Q: acting at 90 to the particular anchor pin (15 or 16) involved; and (3) the resultant drum reaction R passing through the intersection X of P and Q.

The force diagram may be solved vectorially in well known manner to locate point X. As shown in Figure 1, abutment faces 38 and 39 of theshoe are disposed at right angles to lines Q1 and Q2, respectively, drawn through the axes of the anchor pins and intersection X of lines P, R, Q1

and Q2. As seen in Figure 1, the resulting arrangement is perfectly symmetrical.

The point X isshown in the position illus trated in the drawings only by way of illustration of the theory of the brake, and it is to be under- '0 stood that in practice its location will depend upon the coemcient of friction of the lining.

From the foregoing it is apparent that the invention is not limited to the abutment face inclinations disclosed, because they will vary in accordance with the location of the anchor pins,

but in any event will be disposed normal to lines containing the anchor pin axes and the point of irliltersection of the three forces acting upon the s cc.

7o Anochor pin placement In the brakes of the prior art it has been necessary to locate the anchor pins very close to the inner surface of the drum to avoid self-locking dimculties, especially those which occur through 16 egrab.

In the present construction no dimculties with the phenomena of toe grab or self-locking of the shoe are possible, and therefore the anchor pins may be moved inwardly to achievean appreciable increase in braking power of the mechanism through an additional self nergizing action.

.In the construction ill rated, pin It is' v cated slightly clomr to the axis than pin it, in

order to accommodate the actuating mechanism disclosed. However, since the braking-power is maintained of constant value so long as the pins are maintained on reaction lines Q1 and Q, the braking power will be the same when the drum is rotating counterclockwise as it is when it is rotatingclockwise. Accordingly, the distances of the two anchor pins from the drum axis may be made equal or varied through substantial ranges to suit, any particular layout because in order to achieve satisfactory operation it is only necessary to locate the pins along the lines Q1 and ch, and so shape abutment faces 38 and .39 as to be disposed normal to lines Q1 and Q2, and this will produce equal braking effects directions of drum rotation.

Brake adjustment If after the brake has been in usefor some time the lining becomes so worn as to introduce an undesirable clearance between the lining and the drum, each nut 2| is loosened and pin i5 rotated sufllciently to'cause the eccentric portion, acting through link", to advance the shoe tofor both 5 The term brake 81108.10 the appended claims is intended to embrace the shoe illustrated em-' the shoe proper and lining it, but it is tobe understood that italso covers brake shoes 7 having an integral braking face.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the an pended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. In a brake mechanism, adapted to be operatively associated with a brake drum; a supward the drum and compensate for the lining wear. Nuts 2| are then tightened and the ad- Justment is complete. As seen in Figure 1, rotation of the eccentric in either direction will advance the shoe toward the drum, but the one shown is preferably rotated counterclockwise, and the opposite one rotated clockwise to advance the shoe toward the drum.

In Figures 5 and 6 there is illustrated a modified construction for adjusting thelower anchor .pins, also forming part of the invention. With continued reference to these figures, the parts which are similar to those of the construction Just described will be given the same number with the subscript "a.

In this form of the invention a modified form of anchor pin lid is used, each of which extends through an elongated slot 9| in foundation plate Ida.

Levers Eli; and 52a, together with abutment member a, are pivoted on an enlarged concentric cylindrical portion 92 of each anchor pin lid. The shoulder formed by enlarged portion 92 port adapted to be mounted in cooperative relationship to said brake drum; a brake shoe carried by said support and movable toward and away from said brake drum; means for forcing said shoe toward said drum; an abutment member carried by said support and cooperating with one end of said shoe for restraining it against rotation in response to rotation of said drum in one direction; a second abutment member carried by said support and coacting with the other end of said shoe for restraining it against rota tion in response to rotation of said drum in the opposite direction; one of said abutment members being located closer to the axis of the drum than the other when assembled therewith, and

said brake shoe having flat faces adjacent its ends cooperating with said abutment members, said abutment members each permitting free, substantially radial outward movement of the ends of said shoe, and slight bodily rocking of, said shoe about either of said abutment members as a fulcrum, so as to insure full surface engagement of the shoe with the drum when the latter is rotating in either direction, the flat faces of said brake shoe being inclined differently from the other sufficiently to compensate for the differential placement of said abutment members is adapted to be pulled into tight engagement I with plate Ila by means of a nut 93, a lock washer 84, and an enlarged block member 95 fittin over each anchor pin. As seen in Figure 5, each block III is provided with a portion 98 depending below the anchor pins.

An adjusting member 91, having a central hexagon shaped portion, is provided with oppositelv threaded portions 98 threaded into member Ii. I

By loosening nuts 93, so as to free the anchor pins for sliding movement in slots 9|, member 91 may be rotated to move blocks 95 toward and away from each other so as to increase or decrease the clearance that exists between the brake l ming and the drum. when the adjustment is completed nuts 93 are then tightened to permanently lock the anchor pins in their new positionswith respect to said axis, and effect'similar brak ing characteristics in both directions of drum rotation.

2. The brake mechanism defined in claim 1,

' wherein said shoe is provided with a flat, substantially non-radial face at each end thereof coacting with bers. w

3. In a brake assembly, .a foundation plate; a pair of anchor pins carried by said plate and spaced aparticircumferentially; a brake actuating lever mounted for-pivotal movement on one of said plus; a brake shoe disposed in operative relationship with respect to said plate and being provided adjacent each end with an abutmentface disposed in proximity to said anchor pins; an abutment member pivotally mounted on each of said: anchor pins and coacting with the abutment faces of said brake shoe, and being free to rock into various positions in response to forces applied-thereto; means for rocking said 4 lever about said one pin; and means for transmitting forces from said lever to said brake shoe.

4. In a brake assembly, a foundation plate; a pair of anchor pins carried by said plate and spaced apart circumferentially; a brake actuating lever mounted for pivotal movement on one of said pins, a brake shoe disposed in operative relationship with respect to said plate and being flat faces on said abutment mem- 6. ..provided adjacent each end with an abutment face adjacent said anchor pins: an abutment member pivotally mounted on each of said anchor pins and coacting with the abutment faces of said brake shoe, and beingfree to rock into various positions in response to forces applied thereto; means for rocking said lever about said one pin; and means for-transmitting forces fromsaid lever to said brake shoe, said abutment faces and having a web-like portion disposed between said levers and terminating ateach end in an abutment face adiacent'said anchor pins: an abutment member pivotally mounted on each of said anchor pins coacting with the abutment faces of said brake shoe and being free to rock into various positions in response to forces'applied thereto; means for rocking said levers about said one pin: and means for transmitting forces from said levers to said brake shoe intermediate the ends of the latter.

6. In a brake mechanism, adapted to be operatively associated with a brake drum; a support for said mechanism adapted to be mounted adjacent said drum; a pair of anchor pins carried by said support at circumfcrentially spaced points an abutment member pivotally mounted on each of said pins and each having an abutment face; and a brake shoe adapted to be disposed within said drum intermediate said abutment members and having abutment faces coacting with the abutment faces of said members, and each being disposed substantially at different angles to radii passing through axes of their respective. anchor pins.

7. In a brake mechanism, adapted to be operatively associated with a brake drum; a support for said mechanism adapted to be mounted ads jacent said drum; a pair of anchor pins carried points; an abutment member pivotally mounted on each of said pins, and each having an abutment face: and a brake shoe adapted to be disposed within said drum intermediate said abutment members and having abutment faces coacting with the abutment faces of said members, one of said pins being located closer to the axis of said druinthanthe other, when assembled.

8. In a brake mechanismya support therefor adapted to be mounted in cooperative relationship with a brake drum; a rigid brake shoe adaptinclined with respect to radii intersecting eases shoe being' wholly disposed within an arc of 180 of the brake drum when assembled therewith, said pivoted members constituting the sole means for transmitting brake torque reaction from said shoe to said support, and adapted to be rocked freely about their axes by saidbrake shoe abutment faces, while maintaining surface engagement therewith.

9. In a brake mechanism", a support; a rockable member carried by said support; a pair of spaced levers fulcrumed on said member, said member also having an eccentric portion intermediate said levers; and a brake shoe abutting element fitting over said eccentric portion, and adapted to beadvanced and retracted when said member is rocked, said member beingso designed as to maintain said levers in fixed positions with respect to the axis of said member when the latter is rocked.

'10. In a brake mechanism, a support; a rockablemember carried by saidsupport'a'nd having spaced large and small diameter concentric journal portions; a pair of spaced levers fulcrumed on said large and small diameter portions, said member also having an eccentric portion intermediate said large and small diameter portions;

" and a brake shoe abutting element fitting over said eccentric portion, and adapted to be advanced and retracted'when said member is rocked,'said member maintaining said levers in fixed positions with respect to the axis of said member whenthe latter is rocked.

11. In a brake mechanism, a support; a pair of levers disposed in spaced apart relationship and mounted for pivotal movement on said support; a. brake shoe mounted for floating movement on said support and having a web portion disposed between said levers; a pivot member journalled in the web portion of said brake shoe;

by said support at circumferentially spaced 5 said pivot member having a pair of recesses therein for receiving one side of each of said levers and for transmitting forces from the latter to said brake shoe, said recesses providing large area bearing surfaces for the sides of said lever and permitting free sliding movment of said shoe with respect to said levers.-

' 12. In a brake mechanism, adapted for association witha brake drum mounted for rotation adjacent thereo; a support; a brake shoe carried by said support and mountedfor movement toward and away from said brake drum; a lever pivotally mounted on said support and'having edtobedisposedwithinsaidbrakedrumincoits free enddisposed adjacent one end of said brake shoe; means for transmitting forces from said lever to said shoe intermediate its length;

and common means for urging the free end of b said lever and said one end of said shoe away from said drum and permitting independent movement thereof, comprising a tension spring having independent connections with. said lever and said brake shoe.

13. In a brake mechanism, a support adapted to be mounted adjacent an associated brake drum; two. pairs of circumferentialiy spaced members pivoted for free rocking movement on said support; a brake shoe disposed between each pair of said members and having abutment faces cooperating therewith to restrain said shoe against rotation in response to braking forces; said abutment faces being inclined with respect to lines pas ing through the axis of said drum and said members, adapted to maintain surface engagement with the abutment face of one of said brake 15 members in either direction of drum rotation and;

14. The brake mechanism defined in claim 13,

wherein one member of each pair is adjustable toward andaway' from said drum for compensating for the effects of brake lining wear.

15. In a brake mechanism, a support therefor adapted to be mounted in cooperative relationship with a rotatable brake drum; a pair of anchor pins carried by said support and circumferentially spaced apart: said pins being disposed to the same side of a plane containing the drum axis; a rigid brake shoe disposed in .operative relationship with respect to said support and located to the same side of the drum axis as said pins and being provided adjacent each end with an abutment face disposed in proximity to said anchor pins; an abutment member pivotally mounted on each of said anchor pins and coacting with the abutment faces of said brake shoe, and being free to rock into various positions in response to forces applied thereto by said shoe; a pivoted actuating lever for rocking said shoe; and means' for transmitting forces from said lever to said brake shoe adjacent the mid-portion thereof.

16. In a brake, a support; fulcrum means carried by said support; a lever assembly pivotally mounted on said fulcrum means and comprising a pair of levers secured together in spaced apart relationship; a brake shoe mounted on said support and having a web portion slidably disposed between said levers; means for transmitting forces from said lever assembly to said shoe comprising a force transmitting member having pivotal movement upon a large area curved surface on the web of said brake shoe, and having sliding movement upon a large area flat surface on said lever assembly. a

1']. In a brake, a support; a brake shoe carried by said support and mounted for movement toward and away from an associated rotatable brake drum; a lever pivotally mounted upon said support and having lts'free end disposed adjacent one end of said brake shoe; means for retracting saidbrake shoe and lever, comprising a tension spring; a link connecting one end of said tension spring to'the free end of said lever ass'embly, and, a second link connected to said shoe.

bearing face and passing through the axis of said anchor pins; abutment faces adjacent the ends of said brake shoe having areas substantially coextensive with the area of the bearing faces of said abutment members and operable to coact in full surface engagement with one abutment member when the brake is applied in one direction of drum rotation, and to coact in full surface engagement with the other abutment member when the drum is rotating in the other direction; and lever means for applying braking forces to said brake shoe intermediate'its length.

20. The brake construction defined in claim 19,

wherein said bearingfaces, measured in a direction normal to the drum axis, each have a length materially greater than the distance of said hearing faces from the axis of said anchor pin, for insuring free rocking of said abutment members in response to the application of braking reaction forces thereto by said shoe.

21. The brake construction defined in claim 19, together with means for adjustably decreasing the circumferential spacing of said abutment members, to compensate for the effect of brake lining wear.

22. The brake construction defined in claim 19, wherein one of said abutment members is pivoted upon an eccentric portion provided on its pin, and the latter is mounted for adjustment into a plurality of angular positions, for adjustably varying the circumferential spacing of said abutment members, to compensate for the effect of brake lining wear.

23. In a brake mechanism adapted to be operatively associated with a brake drum, a brake drum; 9. support adapted to be mounted adjacent of said shoe assembly to move toward or away from said drum; a brake shoe actuating lever is. The brake defined in claim 17, wherein said links are disposed at an angle of approximately 90 to each other and the line of action of said spring substantially bisects said angle, whereby the action of the spring upon 'said brake shoe is restricted to a direction substantially normal to said first link.

19. In a brake adapted to be operatively associated with a rotatable brake drum, a support; a pair of substantially axially directed anchor pins carried by said support and disposed in circumferentia'lly spaced relationship; an abutment member moimted for free rocking movement uponeach of said anchor'pins and having a, substantially flat bearing face extending a substantial distance in either from a line normal to said assembly pivoted adjacent one of said anchors; means for transmitting forces from an intermediate portion of said lever assembly to an inter--' mediate portion of said shoe assembly, comprising a force transmitting member having a large area curved surface cooperating in surface engagement with a large area curved surface means on one of said assemblies, and also having a large area flat surface cooperating in sliding engagement with a large area flat surface means on the other assembly; and means for rocking said lever.

24. The brake mechanism defined in claim 23, wherein said lever assembly comprises a pair of spaced levers and said brake shoe comprises a web disposed between said levers, and said flat surface means comprises a flat surface on each of said levers, and said curved surface means coigprises a curved surface on said brake shoe we Y WILLIAM R. SPILLER. HERBERT W. ALDEN.

. RALPH K. SUPER.

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