US2374651A - Internal shoe drum brake - Google Patents

Description

May l, 1945.

INTERNAL SHOE DRUM BRAKE Filed oct'. 1a, 194s' nf, g

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INTERNAL SHOE DRUM BRAKE Filed Oct. 18, 1945 2 Sheets-Sheet 2 /N VE N TUI? y 5.52/5 6'. (//Qa/A/GS Patented May 11,1945

o f lN'rEnNAL suon DRUM BRAKE Leslie Cyril Chouings, Leamington Spa, England, aosignor to Automotive Products ConmanyV Limited.

Application october 1s, 194s, serial Noisosnas j In Gres: Britain october 9, 1942 s claims. (ci. issrsi This invention relates to internal shoe drum brakes of the kind comprising two arcuate shoes each having an anchorage abutment atone end, both shoes extending from their abutments in the same circumferential ing operated by a single spreading means acting directly on to the free end of one shoe, and through a linkage on to the free end of the sec. ond shoe.

It is the object of the invention to provide a' simple and elcient brake of this kind In a brake which is of the kind referred to and in which the linkage comprises two interconnected bell-crank levers, -the first of which levers is acted upon by the spreading means, while the second the second shoe with one of its ch'aracterised by and engages a iixed abutment arms, the present invention is the fact that the first bell-crank lever is pivotally mounted on the-xed support of the brake, and, through its interconnection with the other bell-crank lever, limits the yinward movement of the second shoe when the brake is released. Y

Preferably the fixed abutment comprises an adjustable stop serving to adjust the drum clearance of the second shoe, said adjustable stop conveniently comprising a strut of variable length operatively connected between the second bell-crank lever and the anchorage abutment of the rst shoe. 'I'he spreading means may act as an anchorage for the first bell-crank lever when the brake is released. Moreover at least one arm of each bell-crank lever is preferably double so as to extend on both sides of a radial web forming part of the second shoe, said bell-crank levers conveniently being connected together by a thrust member comprising a pair of strips held in spaced parallel relationship so as to extend alongside opposite side surfaces of the shoe web. Movement of the shoe in an axial direction is preferably prevented by a spring iinger, which resiliently tact with a shoe-locating projectoncarried by the iixed support of the brake, the shoe-locating projection being provided with a screw-threaded adjustment member against which the shoe web bears slidably. If desired a single adjusting means may serve to move the anchorage of the iirst shoe and the adjustable stop for the second bell-crank lever.

'I'he invention is illustrated in the accompanying drawings, in which:

Figure 1 is an elevation of one construction of brake, the drum being shown in section;

sense and the shoes besectional plan taken ied adjusting device for the lower ends of the is pivoted on the free end of shoes; and l Figure 4 is a fragmentary sectional plan taken on the line l-I of Figure 3.

A drum Il of the usual cylindrical form constitutes the rotating element of the brake, as shown in Figure 1, and is arranged to be engaged by a pair of rigid arcuate brake shoes, the'ilrst of which is indicated at II .and the second at I2. Each shoe is of the usual T shape in cross-section comprising a web' I3 and a curved flange I 4, to which latter the lining I5 of the brake -shoe is attached. The usual xed support of the brake, i. e. that part which does not rotate and 2s pin I9,

maintains said web in con-A serves as a mounting for the brake shoes, comprises a substantially tubular member I6 arranged to be secured to the axle casing or other convenient xed part of the vehicle, said tubular member I6 being formed integrally with a depending bracket I'l and an upwardly extending bracket I8. A circumferentiall'y grooved anchor fixedly mounted upon the bracket Il, is arranged to be engaged by a notch 20 in the end of the web I3 of the shoe said shoe to move angularly into and out of engagement with the interior of the drum I 0. A similar fixed anchor 2I is provided for engagement by the notched portion 22 of the shoe I2. Spreading meansindicated generally at 23, are secured to the lbracket I8 and conveniently com. prise a hydraulic cylinder 24 containing a pair of pistons 25 and 26 adapted to be spread apart by admitting liquid under pressure through an inlet opening 21. The piston 25 is formed with a shoulder 28 arranged to abut against the corresponding end of the cylinder -24 so as to enable said piston to act as an anchorage; in the case of the piston 26 a knurled head 29 provides a shoulder 30 adapted to engage the end of the cylinder for a similar reason, but the head 29 is in addition arranged to serve as an adjustment for the first l'shoe II. Thus a stem member 3|, screw-threaded into the piston 26, is slotted diametrally at 32 to embrace the end of the web I3 of the shoe Il, so that by rotating the head 29 the stem member 3I can be forced outwards to the desired extent in order to adjust the clearance between the lining I5 and thedrum I0. A springnger 33 preserves the adjustment of the .head 29 in the usual manner.

The means used for applying the second shoe I2 comprise a rst bell-crank lever 34 mounted I I, thereby allowing.

' the fixed support. The bell-crank lever 34 comprises an upwardly directed arm 36 engaging with the piston 25, and also a substantially horizontal arm 31 which is double or bifurcated so as to extend on both sides of the web of the shoe I2, said arm 31 beingv formed at its outer end with a notch 38 adapted to engage pivotally with the narrow but rounded upper end of a thrust member 39. This is also of double construction so as' to engage with both parts of the arm 31, and comprises a pair of strips 49 held in parallel relationship by spacing members 4l. The lower end of the thrust member 39 engages with a second bell-crank lever 42. The second bell-crank lever 42 comprises a pair ofvidentical substantially triangular plates 43 disposed one on each side of the web I3 of the shoe I2 and pivoted to the latter by means of a fulcrum pin 44. The lower end of the thrust member 39 pivotally engages with notches 45 in what constitutes the substantially horizontal arm 46 of the bell-crank lever, while a substantially vertical arm, indicated at 41, is formed with a notch 48 which engages pivotally with the end of the bifurcated portion 49 of a fixed abutment device indicated generally at 59.

The fixedabutment device 59, which operates in conjunction with the anchorage I9, is arranged to be adjustable and comprises a nonrotatable bearer member having an arcuate head portion 52 arranged to engage the groove in the anchor pin I9 and a cylindrical spigot 53; mounted rotatably upon the spigot 53 so as to bear against a shoulder 54 is an adjusting sleeve 55 having a knurled head portion 56 engaged by a retaining spring nger `51. The adjusting sleeve 55 is internally screw-threaded for engagement with a corresponding thread upon the outside of a stem 58, which latter extends through a slotted retaining lug 59 and is formed with the bifurcated portion 49 to-embrace the end of the web of the shoe I2. Thus the bifurcated portion 49 serves as a fixed but adjustable anchorage for the arm 41 of the bell-crank lever 42, and, owing to the provision of the slotted lug 59, it also acts to prevent lateral displacement of the lower end of the shoe I2 in a direction parallel with the drum axis.

Lateral displacement of each of the shoes II and I2 is also prevented by a shoe-locating projection 69 secured to the ilxed support I6 by screws 6I. The extremity of the projection 69 is threaded to receive a grub screw 62, against the inner end 63 of which the web I3 of the brake shoe is adapted to bear, as will be seen more clearly in Figure 2. Thev shoe is held resiliently in this position by a spring finger 64 having a reinforced end portion 65, said nger being secured to the projection 69 by a a pair of screws, one of which is indicated at 66. A lock nut 61 preserves the adjustment of the grub screw 62.

The usual two pull-olf springs which draw the shoes together for releasing the brake are indicated at 68 and 69. Each is anchored at one end to a pin 19 projecting from the web of the shoe I2,` and at its other end said spring engages with a dead-centre link in the form of a substantially triangular plate 1I. This plate is pivoted at 12 to the web I3 of the shoe II. The turned-over end of the spring engages with a notch 13 in the plate, so that by rotating said plate the axis of the spring can be caused to pass the axis of the pin 12. The spring naturally tends to move the plate 1I in either direction away from this dead-centre position, but such movement in one direction is prevented by the engagement of the corner portion 14 of the plate with the inside of the flange I4, thus retaining the spring in its operative stretched condition. To release the tension in the spring the corner portion 14 is moved away from the ilange I4, and after the dead-centre position has been passed the tension in the spring can be completely released before the spring is disconnected.

The normal forward direction of drum rotation of the brake shown in Figure l is clockwise, and when the spreading means 23 are operated with the drum rotating in this direction the first shoe II acts as a simple leading shoe taking its abutment upon the anchor pin I9. At the same time outward movement ofthe piston 25 causes the first bell-crank lever 34 to be moved in an anti-clockwise direction, thus moving the thrust member 39 in a downward direction. `The bifurcated portion 49 of the fixed abutment device 59 then acts as an anchorage, so that the second bell-crank lever 42 is caused to move in an f' anti-clockwise .direction about said bifurcated portion, thus forcing the pin 44 towards the left and applying the second shoe I2 to the drum I9; during this action the upper end of the shoe I2 engages the anchor pin 2 I, so that this shoe also acts in a leading sense for forward rotation of the drum. With the drum I9 rotating in an anti-clockwise direction both shoes II and I2 operate as trailing shoes, the shoe I2 being moved outwards into engagement with the drum I9 by the action of the bellcrank levers 34 and 42. As mentioned above, the first shoe II is adjusted by means of the head 29, and it will now be appreciated that the clearance of the shoe I2 is regulated by turning the head 56 so as to vary the operative length of the xed abutment device 59, the bell-crank lever 34 taking its abutment upon the cylinder 24 through the medium of the external part of the hydraulic piston 25.

If desired the xed abutment device 59 may be arranged to eiTect simultaneously the adjustment of both shoes II and I 2, and a modied form of shoe anchorage embodying this feature is shown in Figures 3 and 4. A somewhat V-shaped housing 15 is secured to the bracket I1 by a pair of studs and nuts 16, and is formed with a pair of mutually inclined bores 11 and .19 each containing .a corresponding freely slidable plunger member 19 or 89. The plunger member 19 has a head 8I, which is slotted at 82 to embrace the web of the first shoe II, the base of the slot being convex to engage pivotally with a semi-circular notch 83 formed in the lower end of the shoe Il. The outer end of the plunger member is slotted diametrically, as indicated at 84, so as to receive the web at the lower end of the second shoe I2, the pair of end surfaces 85 being arranged to bear each against a convex surface 86 at the lower part of the corresponding plate 413 constituting the bell-crank lever 42. The adjacent end part of the housing 15 is also slotted at diametrically opposite positions to accommodate the web of the shoe I2, thus locating said shoe against axial displacement. The inner ends of the plungers 19 and 89 are sloped, as indicated at 81, for engagementjwith a cam member 88 having a pair of ears 89 and 99, these being of triangular shape and being arranged to slide within corresponding grooves 9| and 92 formed in the housing 15. The cam member 8B is screw-threaded at its central part and constitutes a nut mounted upon a screw-threaded stem 93 having a head 94 adapted to bear against an annular surface 95 of the housing 15; axial displacement of thestem 93 in an outward direction is prevented by a plate 96. When the brake is in operation the plunger member 'I9 constitutesl the anchorage abutment for the shoe Il, while the plunger member 80 forms a corresponding anchorage for the bell-crank lever I2.

When it is desired to readjust the shoes in order to take up wear of the linings the stem 93 is rotated by means of a suitable key applied to its squared end portion 91, the direction of rotation being such that the ears 89 and 90 of the cam member 88 force apart the plunger members 19 and 80 to the requisite amount. y

It will be understood that the arrangements which have been described are given merely by way of example and that the constructionmay be modified to suit requirements. For instance, various forms of spreading means may be employed, such, for example, asthe mechanical expander device described in United States of America patent specication No. 2,238,361, dated April 15,

The improved brake is more particularly applicable to the steering mechanism of endless. track vehiclesin which brakes are used to retard the movement of the track on one or other side or the vehicle for steering purposes. Itsuse is not, of course, limited to this particular application.

What I claim is:

1. In a Ibrake including a support, a shoe mounted on the support, an actuator, and a fixed abutment device on the support at the opposite end of the shoe from the actuator, means for exerting force against the end of the shoe remote from the actuator comprising two interconnected bell-crank levers, the rst of which is acted upon by the actuator and is pivotally mounted on the support, the second of which is pivoted on the remote end of the shoe and engages the iixed abutment device with one of its arms, the first bell-crank lever being adapted through its interconnection With the other bell-crank lever to limit the inward movement of the shoe when the brake is released, said abutment device including an adjustable stop engaging the second bell-crank lever and which serves to adjust the clearance of the shoe.

2. A brake as claimed in claim 1, wherein the 'mounted on the support, an actuator, and an anchor on thesupport' opposite the actuator, in combination, means'for' exerting force against the end of one shoe near the anchor comprising two interconnected bell-crank levers, the rst of which is acted upon by the actuator and is pivotally mounted on the support, and the4 second of which is pivoted on the remote end of the shoe and engages the anchor with .one of its arms, the rst bell-crank lever being adapted through its interconnectionwith the second bellcrank lever to limit the movement of the shoe when the brake is released, and a single adjusting means serving to move the anchorage ofA crank levers, the first of which is acted upon by movement of the shoe when the brake is reactuator acts as an anchorage for the lrst belly crank lever when the brake is released.

3.x In a brake including a support, two shoes the actuator and is pivotally mounted on the support, the second of which is pivoted on the remote end of the shoe and engages the xed abutment with one of its arms, the iirst bell-crank lever being adapted through its interconnection with the other bell-crank lever to limit the inward movement of the shoe when the brake is released, and means for preventing movement of the shoe in an axial direction comprising a spring finger which resiliently maintains the shoe web in contact with the support.

5. In a brake including a support, a shoe mounted on the support, an actuator, and a iixed abutment on the support at the opposite end of the shoe from the actuator, means for exert-V ing force against the end of the shoe remote from the actuator comprising two interconnected :bellcrank levers, the yfirst of which is acted upon by the actuator and is pivotally mounted on the support, the second of which is pivoted on the remote end of the shoe and engages the fixed abutment with one of its arms, the iirst bell-crank lever being adapted through its interconnection with the other bell-crank lever to limit the inward leased, and means for preventing movement of the shoe in an axial direction comprising a projection on said support having thereon a. screw threaded adjustment member against which the shoe web lbears slidably, and a spring nger which resiliently maintains the shoe web in contact with said adjustment member.

LESLIE CYRIL CHOUINGS.`

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