CA1099221A - Air applied disc brake - Google Patents

Abstract

AIR APPLIED DISC BRAKE

ABSTRACT OF THE DISCLOSURE

An air-actuated disc brake develops the required force magnification to operate disc brakes from an air pressure chamber using push-pull rods driving a pair of cam levers applying normal force to one shoe plate of the disc brake. Clamp action is carried through to an opposing brake shoe plate by a caliper. The entire air applied disc brake is mounted as a unit to the axle flange. An automatic adjuster compensates for brake lining wear.

Description

Thi~ application 1~ ~ divlsion of Canadian Applicatlon Serial ~lo. 280,953 flled June 20, 1977.

BACKGROUND OF THE INVENTION
Air brakes have been almost universally accepted for use in articulated vehicles of the tractor and semi-trailer type. This acceptance has come about because articulated vehicles require means on the tractor which can be used for applying and controlling the semi-trailer brakes. Because of technological advantages such as-flexible hoses and quick connect and disconnect air hose couplers, high pressure air has become virtually the only accepted transmission medium for this purpose.
Air brakes of the drum and shoe type have been satisfactorily used on commercial highway and off-road vehicles for many years. The arcuate shoes of drum type brakes tend to wrap into the brake drums in a stop in the forward direction. This wrapping action causes magnification of the braking force called energization. Brake torque imbalance between the two front wheels, ca~sed by variation in the brake lining friction, is magnified by this energization.
Brake torque im~alance could cause steering pulls.
The modern trend to higher stopping rates for trucks t coupled with the requirement for straight-line stopping, now threatens to exceed the ability of the drum brake~ Disc brakes, both hydraulically operated and vacuum-assisted hydraulically operated, being non-energizing, have found increasing use in passenger auto-motive applications where higher braking performance, better straight-line stopping ability and reduct:;on in brake fadiny was desired. United States Patent Nos.
3,536, 166, 3,768,604 and 3r835/96~ in the name oE E.J.

- 2 -22~

Falk teach hydraulically operated disc brakes suitable for automotive applicationsO Similar use of disc brakes has not been made on articulated highway vehicles.
Until the present invention, prac~ical brake components have limited the use of truck tractor disc hrakes to actuation with aix-applied hydraulic actuators.
This limitation resulted from the need for force multipli-caiion from the approximately 100 psig commonly available from the truck air supply to the approximately 45,000 pounds of normal force at the disc brake caliper in a large truck. Although the equivalent of such force multi-plication was readily obtained using hydraulic cylinders, the hybrid air/hydraulic disc brake was complex and costly because it required both hydraulic and air actuators.
SUMMARY OF THE INVENTION
.
The instant invention teaches a simple rugged disc brake system in which a minimum number of mechanical ele-ments provide force multiplication between a force-generating device and a pair of disc brake friction membexs, The force-generating device can be mechanical linkage or a hydraulic piston but best results are obtained with air actuation. Air actuation on the tractor of an articulated vehicle allows the use of the same control air pressur~
source for both tractor and trailer.
Friction variability in the mechanical path is reduced through permanently lubricated bearings at all rotating friction pivots. Such permanently lubricated bearings reduce friction differences ~ince there is no lubricant depletion with use.
An S-type cam levex, actuated by an air brake ~q~22~L
-chamber, applies equal and opposite forces to the ends of a pair of push-pull ro~s. The push-pull xods, in turn, apply ~orce to a pair of cam levers. The cams connected ~o the cam levers apply normal force to one brake lining, or friction member, of a disc brake. Clamping force is carried through to an opposi.ng brake lining through a brake caliper.
An automatic brake adjuster mechanism is included in one embodiment of the invention~
The invention as defined in the parent application provides, in a disc brake for a vehicle, first and second friction mem~ers retained in a floating caliper and adapted for frictional contact with first and second opposed radial surfaces of a ~rake disc~ a single fluid chamber providing force to a cam carrier durlng brake application, the cam carrier movably disposed between the first friction member and an inside surface of the caliper, cam means in the cam carrier for applying force to the first friction member during the brake application to hold the first friction member against the first opposed radial surface of the brake disc, the cam means also applying reaction force to the floating caliper during braking, the floating caliper being operative -to urge the second friction member into fr~ctional contact with the second opposed radial surface of the brake disc, and resilient means for urging the cam carrier and cam means away from the first friction memher toward the insiae surface during a brakes-off condition.
On the other hand th.e .invention according to the present application provides a vehicular di:sc brake system having at least one friction member retained in a brake caliper and actuated by applying mechanical motion thereto to urge the friction mer~er into frictional contact wlth a rotating frictional surface, and wherein frictional forces ~99~

cause wear on the frictional contactiny par-ts, the improvement of an automatic disc brake adjustor comprising:
a threaded adjusting nut; an adjus~ing screw threadably engaged in the ad]usting nut; a star wheel on the adjustin~
screw; means for relatively non-rotating connec-tion of the star wheel to the adjusting screw; a spring finger resilientl~
connected to the adjustor nut in rachetable contact with the star wheel; means for connecting the mechanical motion applied to the ~riction member to the spring finger; means for compensating for frictional wear when the adjusting screw is rotated by the spring finger; and retainer means attached to said ad~ustor nut for retaining said star wheel adjacent to said adjustor nut.
BRIEF DESCRIPTION OF THE DR~WINGS

_ .. .. _ . ....
FIG. 1 shows one embodiment of the air-operated disc brake mounted in its operating position at the front wheel of a highway vehicle.
FIG. 2 shows a view of the invention looking out-ward from the center of the vehicle.
FIG. 3 shows a longitudinal cross-section of the S-type cam.
FIG. 4 shows a cross-sectional view of the disc brake taken along 4 4 in FIG. 2.
FIG. 5 shows a cross~sectional view taken along 5-5 in FIG. 2.
FIG. 6 shows an exploded view of a portion of the air actuated disc brake.
FIG. 7 shows an exploded view of the disc brake illustrating the assembly of ma~or subassemblies.
FIG. 8 shows a view of the air chamber in FIG. 7 rotated 90 degrees about its axis.
FIG. 9 appearing on tlle same shee-t as FIG. 5, ~ .-- ws/~

shows a top vie~ o-E a portion of the assembled br~ke taken along 9-9 in F~G~ 2.
FIG~ 10 appearing on the same sheet as FIG~ 4, shows a close up view of the spring retainer and slotted washer.

ws/ ~

FIG. 11 shows a perspective view of the ad~usting mechanism.
FIG. 12 shows a cross-sectional view of the star wheel and adjusting screw showing the method of keying these parts together.
FIG. 13 shows an alternate embodiment of the disc brake.
FIG. 14 shows an embodiment in which the air brake chamber is supported at the end of a cantilever .
DETAILED DES~RIPTION OF THE PREFERRED EMBODIMENT
The air-applied disc brake system is shown gener-ally at 10 in FIG. 1 in its operative location at a front wheel 11 of a vehicle. The disc brake system 10 is rigidly and non-rotatably attached to an axle flange (not shown) by a torque plate 12 using/ for example, a plurality of bolts 14. A circular opening 16 in the center of the torque plate 12 provides clearance for the passage there-through of the vehicle axle (not shown~. A brake disc 18 is rotatabl~ mounted inside and coaxial to the wheel 11 and is rigidly fixed to rotate therewith. Retarding forces applied to the brake disc 18 and transmitted to the vehicle wheel 11 are reacted against by the torque plate 12 and provide stopping torque which acts conven-tionally against the road surface to retard the vehicle.
A disc brake caliper 20 encloses a chordal portion 22 of the brake disc 18. A pair of arc-shaped brake shoes, one located on the inboard side of the brake disc 18, the other located on the outboaxd side of the brake disc 18, to be shown and described laterj are held in relationship with portion 22 within the disc brake caliper 20~ In the jrc:~V~

2;~L
b~akes-off condition, the brake shoes apply virtually no frictional force against the brake disc 18.
An air-brake chamber 24 is rigidly bracketed to the toxque plate 12. Upon brake application, air pressure is admitted to the air-brake chamber 24. A chamber push rod 26 is forced outward by the air pressure within the air-brake chamber 24. The chamber push rod 26 applies force to a system of levers and cams which force ~he brake shoes into frictional contact with the inboard and out-board sides of the enclosed portion 22 of the brake disc 18. The frictional forces generated by the brake shoes are transmitted through the caliper 20 and the ~orque plate 12 directly into the axle flange of the vehicle.
Referring now to FIG. 2, a chamber push rod 26 is connected to the lever arm 28 of an S-type cam 30.
The S-type çam 30 applies e~ual and opposite forces to a pull-lever 32 and a push-lever 34O The pull-lever 32 and push-lever 34 transmit their input forces to disc bxake friction members located within the bxake caliper assembly shown generally at 35.
The brake caliper assembly 35 develops frictional forces on the outer opposed parallel surfaces of the brake disc 18. The torque plate 12 is shown in its operative relationship with the brake disc 18. The torque plate 12 contains flanges 38 and 38a to which are rigidly mounted a brake support plate 40 and the air-brake chamber 24.
FIG. 3 shown the S-type cam 30 and its actuating lever arm 28 in isolated cross section for clarity. The chamber push-rod force acts on the lever arm 28 through the pivot 42 in the direction 44~ 'rhis foxce tends to cause the S-typa cam 30 to rotate clockwise about its pivot 46. A

permanently lubricated type sleeve 48 encircles the pivot 46 and provides a reduced-friction beaxiny surface for the S-type cam 30, A hemispheric collar 50 on an actuating push rod 52 fits into a cooperating hemispheric cavity 54 in the S-type cam 30. As the S-type cam 30 rotates clockwise about its pivot, the hemispheric cavity 54 applies compressive force to collar 50. This compressive force is exerted through the push rod 52 in the direction indicated by 56. A hemispheric collar 58 engaged in cooperating hemispheric cavity 60 in the S-type cam 30 applies equal and opposite tension force in the direction shown by 62 to a pull rod 64. Permanently lubricated inserts 51 and 59 may be located between the bearing surfaces of collar 50 and cavity 54 and between collar 58 and cavity 60 respectively.
Returning to FIG~ 2, the push and pull forces along rods 52 and 64 are connected to cam levers 34 and 32 using hemispheric collars 70 and 72 and-cooperating hemispheric cavities 74 and 76, all respec~ively. Permanently lubricated inserts 75 and 77 may be located between the bearing surfaces of collar 70 and cavity 74 and between collar 72 and ca~ity 76, respectively.
Referring to FIGS. 4 and 5, the two cam levers 34, 32 are connected to pivoted cams 78 and 80. The pivoted cams 78, 80 are pivotably engaged with cam carrier 81 by two perm-anently lubricated pivots 84 and 86. A lip 88 on pivoted cam 78 engages the underside of adjusting nut 90. A similar lip 92 on pivoted cam 80 also engages the underside of adjusting nut 90~
Adjusting nut 90 threadably receive 5 an adjusting screw 94 in a threaded hole 96. A star wheel 98 is positioned in keyed relationship with the adjusting screw 94. A reduced-diameter shaft 100 on the adjusting screw 94 fits the axial bore 102 in an adjusting screw guide 104. A shoulder 106 is formed at the point that the reduced diameter shaft joins the upper end of the adjusting screw 94.

Z~21 The upper surface lOi of the adjusting screw guide 104 is dome shapea to engage a similarly shaped socket 110 in the caliper 112. A circular hole 114 in the center of the socket 110 allows the protrusion of the end of the reduced diameter shaft 100 outside the caliper 112. Flats 116 on the end of the reduced diameter sha Et 100 enable attachment of a wrench thereto for manual adjustment of the brake.
A transvèrse member 118 transmits force applied to the caliper 112 at the socket 110 to two reaction legs 120, 120a on the opposite side of the brake disc 18. The two reaction legs 120,120a are positioned adjacent to an out-board shoe plate 122. The outboard shoe plate 122 is con-nected to an outboard brake lining 124 by methods well known in the art such as riveting, adhesive bonding or integral molding.
An inboard shoe plate 126 and an inbo~rd brake lining 128 are located adjacent to the inboard parallel surface 129 of the brake disc 18. The cam carrier 81 has its bearing sur-face 130 in contact with the inboard shoe plate 126.
When application of the brake forces the ends of cam levers 34 and 32 to move outward in the directions 56 and 52, the cams 78 and 80 rotate about their pivots 84 and 86 in the direction shown by the curved arrows. The cam lips 88 and 92 bear upward against the Underside of the adjusting nut 90. A
downward :Eorce is thereby transmitted through the pivots B4 and 86 and the cam carrier 81 to the inboard shoe plate 126;
and an equal upward force i5 simultaneously transmitted through the adjusting screw 94 and adjusting screw guide 104 to the caliper 112. The upward force is transmitted through the transverse member 118 and the two reaction legs 120, 120a to the outboard shoe plate 122. Equal and opposite normal forces are thereby transmitted to the outboard and inboard brake linin~s 124 and 128 which are thus brought into frictional i-~r~ ,^1~.

contact with the outboard and inboard parallel surfaces 129a and 129 of the brake disc 18.
Also in FIG. 5, pivot 86 is a pin having a head 132 at one end and a cotter pin 134, or other means to prevent accidental removal, at the other end. The caliper 112, with its transverse memb~r 118 and reaction leg 120a is seen to partially encircle the brake disc 18 a~d the force-developing elements previously described.
The entire assembly shown in FIGS. 4 and 5 is free to translate normal to the parallel surfaces of the hxake disc 18 in order to apply equal forces to the two parallel surfaces 129, 129a.
FIG. 6 shows an exploded view which will be used to describe how the cam and carrier assembly 136 is fitted into the caliper 112 and the whole is locked together by the support plate 40.
The caliper 112 contains two rectangular holes 138, 138a and the circular hole 114 and socket 110 is its closed end 140. Holes 138, 138a are larger than the cross section of the cam levers 34 and 32. The cam and carrier assembly 136 is fitted inside the closed end 140 of the caliper 112 by lifting and tilting the cam carrier assembly 136 so that the ends of the cam levers ~4 and 32 fit through the holes 138, 138a. As the cam and carrier assembly 136 is nested inside the closed end 140, the end of the reduced diameter shaft 100 protrudes through the circular hole 114 and the adjusting screw guide 104 comes to rest within the cooperating socket 110.
In the nested position of the cam and carrier assembly 136 a first pair of grooves 142, 142a in the sides of the cam carrier 81 are aligned adjacent to a second pair of yrooves 144, 144a in the sides of the closed end 140 of the caliper 112.
A third pair of grooves 146, 146a in the outside surfaces of the reaction leys 120, 120a are aligned with the first and second ~ %z~
pair of grooves 142, 1~2a and 144, 144a respec~ively.
The support plate ~0 is in a general U shape having two opposed end portions 148, 148a connected by a frame portion 150. The insides of the arms of the U are generally parallel and each is interrupted by a rectangular opening 152, 152a to form a forward pair of parallel sur-faces 154, 15~a and a rear pair of parallel surfaces 156, 156a. The forward surfaces 154, 154a are so spaced and the material thickness is such that a sliding fit of the forward surfaces 154, 154a into the grooves 144, 142 and 144a, 142a is possible. Similarly, the rear surfaces 156, 156a are capable of a sliding fit within the grooves 146, 146a. When so assembled, the tongue-in groove con-nection holds the cam and carrier assembly 136 correctly aligned within the caliper 112 but allows lateral sliding movement of the assembled~parts on surfaces 154, 154a and 156,156a.
The inboard and outboard brake shoes 158, 160 are inserted through the opening provided by the openings 152, 152a. The inboard brake shoe 158 is moved toward the closed end 140 of the caliper 112 until the grooves 162 and 162a in the inboard shoe plate 126 engage the forward surfaces 154, 154a. The inboard brake shoe 158 is moved along forward surfaces 154, 154a until it comes to rest against the cam and carrier assembly 136. Similarly, two grooves 164, 16~a on th~
outhoard brake shoe plate 122 are fitted on the rear pair of parallel surfaces 156, 156a and moved outward until the out-board shoe plate 122 bears against the reaction legs lZ0, 120a. In the positions just described, the inboard brake lining 128 faces the outboard brake lining 124 across a gap.
The gap is wide enough to accommodate the ~rake disc 18 (see also FIGS. 4 and 5) when finally assembled and installed as will be describedO The S-type cam 30 is preassembled to ~ ' ~L~951~
the ends of the pull rod 64 and push rod 52 which inter-connect the caliper assembly 35 with the S-type cam 30 which may ~e preassembled to form cam and caliper assembly 136, FIG. 7, a ma jor subassembly to be mounted on the vehicle.
Referring further to FIG. 7, the preassembled caliper and support plate 40 with attached s-type cam is mounted upon anchor flanges 38, 38a using for example a plurality of bolts 168. The cam and caliper assembly 136 and its contained parts remain free to translate along the pairs of parallel surfaces 154, 154a and 156, 156a on the support plate 40 as previously described.
The torque plate 12 contains a circular flange 170 which has a circular opening 16 and a plurality of holes 174 in its perimeter. Flange 170 is adapted for attachment to the axle flange (not shown) of a motor vehicle using for example a plurality of bolts through the plurality of holes 174. The circular opening 16 accornrnodates the pas-sage therethrough of the shaft and wheel hub (not shown)O
The torque plate 12, brake-support plate 40 and caliper 112 in combination, hold the brake shoes or friction members 158, 160, adjacent to the brake disc 18 as previously discussed.
A mounting ~lange 176 containing bolt holes 178 provides a mounting location for an air-brake charnber bracket 180. The air~brake chamber 24 is mounted to the air-brake chamber bracket 180 u5ing a pair of threaded studs 182, 182a and cooperating nuts 184, 184a. In the isolated view of the air~brake chamber 24 shown in FIG. 8, the threaded studs 182, 182a are syr~metrically located on either side of the chamber pu3h rod 26. A clevis 186 is attached to the end of the char~er push rod 26.
Referring now to FIG. 9, the air-brake cha~mber bracket 180 has bearing holes 188, 188a passing through two jrc: ~

2~
side plates 190 and l90a. The S-type cam 30 is pi~ot~lly secured between the side plates 190, l90a by a pin 192 which passes through the bearing hole 188 in the first side plate 190, the pivot hole 194 and through the bearing hole 1~8a in the second side plate l90a. The pin 192 is secured in place by, for example, a cotter pin 196.
The pivot hole 198 at the end of the lever arm 28 of the S-type cam 30 is aligned in position with bearing holes 202~ 202a through the two arms 204, 204a of the clevis 186.
A bearing pin 206, inserted through the bearing holes 202, 202a and the pivot hole 198, connect the S-type cam 30 to the clevis 186. The S~type cam 30 is connected by pull rod 64 and push rod 52 to the cam levers 32 and 34 as previously described.
Referring to FIGS. 2 and 9, it can be seen that the mass of the air-brake chamber 24 is not rigidly attached to the slideably mounted caliper assembly 35. Instead, the air-brake chamber is rigidly mounted to the torque plate 12. The caliper assembly 35 is free to slide along the brake-support plate 40 (in and out of the page i~ YIGo 1) by hinge-like rotation of the hemispheric joints at the ends of the push rod 52 and pull rod 64. Thus the masses of the air-brake chamber 24 and its bracket 180 are not added to the vibration mass of the sliding caliper assembly 35.
Refer to FIG. 4 for the following description. In order to reduce friction between the brake shoes 158 and 160 and the brake disc 18 in the brakes-off condition, two return springs 208, 208a, or anti-scuff springs, are connected be-tween the cam carrier 81 and the caliper 112. Each end of the cam carrier 81 has a hole 210, 210a having an enlarged lower diameter 212, 212a forming a stepped bore. The bottom ends 214, 214a o~ the springs 208, 208a are enlarged to a diameter greater tha~ the holes 210, 210a but smaller than the enlarged diameters 212, 212a forming a stepped diameter. The bottom z~
end 214, 214a of the springs 208, 208a are conseque~tly re-tained in the cam carrier 81. At their upper encls, the springs 208~ 208a pass into aligned holes ~16, 216a or bores in the caliper 112 and are connected to the lower lobes 218, 218a o~ spring retainers 220, 220a. The spring retainers 220, 220a are captured by slotted washers 222, 222a which bear agains~
mating sur~aces on the caliper 112.
An isolated view of a spring retainer 220 and its associated slotted washer 222 is shown in FIG. 10. The spring retainer 220 has a narrow waist region 224 between the lower ]ohe 218 and an upper lobe 226. The slotted washer 222 contains a slot 228 whose long dimension exceeds the width of the upper lobe 226 and whose shorter dimension is wider than the waist region 224. A linear depression 230 is located in the slotted washer 222 at right angles to the slot 228. The spring retainer 220 is engaged in the slotted washer 222 by passing the upper lobe 226 through the slot 2~8 until the waist region 2~4 is level with the slotted washer 222. The spring retainer 220 is then turned 90 degrees and released. The shoulders 232, 232a above the waist region 224 are engaged in the linear depression 230 and are retained thereby the continuing downward force applied by the stretched return spring 208.
Returning to FIG. 4, when the brakes are released, the return springs 208, 208a pull the cam carrier 81 positively away from the inboard brake shoe 158 to the limit of the brake adjustment tolerance. With all cam pressure positivel~ removed, the brake shoes 160 and 158 are free to ~e moved away from the brake di~.c 18 by any axial runout of the brake disc 18. Thus, the fuel economy attainable with drag-free brakes is obtained.
The automatic adjuster mechanism is shown in FIG. 11.
The star wheel 98 and adjusting screw 94 are fixed together jrc: ~

~9;22~
such that rotary motion of the star wheel 98 is imparted to the adjusting screw 94. One method of fixing the two to-ge~her which has been reduced to practice is shown in FIG. 12.
The adjusting screw 94 contains two vertical slots 234, 234a at locations 180 degrees diametrically opposed. The slots 234, 234a are of regular trapezoidal cross section in which the shorter base of the trapezoids 236, 236a are nearer the axis of rotation of the adjusting screw 94. The star wheel 98 has similarly shaped trape~oidal inward projections 238, 238a which fit loosely into the slots 234, 234a. In addition, the hole 240 in the star wheel 98 fits loosely over the outer diameter of the threads of the adjusting screw 94. Thus, if not restrained, the star wheel 98 could be freely slid along the length of the adjusting screw 94.
Returning to FIG. ll, a tang 242 attached to the inner surface of one of the cam levers 32 or 34 engages a slot 244 in an adjuster spring 246. The adjuster spring 246 consists of a horizontal part 248 containing the afore-mentioned slot 244 and two vertical portions. One vertical portion, connected to the horizontal part 248 by a right-angle bend at 250 forms a finger 252. The end 254 of the finger 252 is spring loaded to engage the teeth 256 of the star wheel 98. Because the finger 252 approaches the star wheel 98 at close to a tangential angle, the finger 252 acts like a ratchet, imparting counter-clockwise motion of the star wheel 98, as indicated by an arrow inscribed thereon.
The other vertical portion of the adjuster spring 246 is divided by a horizontal slot 258 into an attachment tab 260 and a control arm 262. The attachment tab 260 is firmly affixed near its outer end to the adjustiny nut 90 using, for example a bolt 264. The outer end of the control arm 262, normally rests adjacent to the teeth of the star wheel 98 and a retainer tab 266 loosely overlaps the upper - I . 1~ --surface of the star wheel 98. The retalner tab 266 restrains the star wheel 98 from sliding up the adjusting screw 94, an~
keeps the star wheel 98 loosely adjacent to the upper surface of the adjusting nut 90.
It will be e~ident that, each time the brake is applied, the cam 78 or 80 rotates clockwise about its pivot 84 or 86. The tang 242 is drawn toward the right by the motion of the cam lever 32 or 34. The rightward motion of the tang 242 causes the attachment tab 260 to bend, thus allowing the finger 250 to move toward the rightO As the attachment tab 260 bends, the control arm 262 is urged against the teeth of the star wheel 98. This pressure against the teeth of the star wheel 98 prevents the star wheel 98 from rotating as the finger 252 is drawn to the right. Most o*
the time, full brake actuation fai.ls to move the f.inger 252 far enough ri~htward for the end 254 of the finger 252 to drop into and engage the next adjacent tooth 256. However, after the brake linings have become slightly worn, the cam lever 32 or 34 and the attached tang 242 and adjuster spring 246 are drawn far enough to the right to allow the end 254 of the finger 252 to drop into and engage the next adjacent tooth on the star wheel 98. When the brake is released, the resulting leftward motion of the finger 252 forces the star wheel 98 to rotate one tooth pitch. The adjusting screw 94 i5 thus advanced a small increment to compensate ~or brake wear. The consequent tightening of the brake adjustment re-duces the travel of the cam lever 32 or 34 to less than the amount required to enable further adjustment. This situation continues until additional wear allows the finger 252 to again engage the next adjacent tooth 256 and add another increment of adjustment to the brake. The adjustment is thus seen to be automatically controlled by the actual amount of wear.

: ~ 15 -z~
Note that the teeth 256 ~n the star wheel 9~ have rounded tips. This allows the automatic adjus~ment to be overridden by manual adjustment USinCJ a wrench on the flats 116 (shown at FIG. 5) at the end of the adjusting screw 94. When the adjusting screw 94 is manually rotated, the flexible ~inger 252 is forced to ride over the tooth 256, and drop into engagement with the next tooth 256. This applies for both directions of rotation of the adjusting screw 94.
An alternate embodiment of the disc brake is shown ~0 in FIG. 13 in which internal and attachment details are identical to the enbodiment previously described. Two cam levers 268 and 270 protrude from the caliper 112. An air-brake chamber 24 is located between the two cam levers 268 and 270. The chamber push rod 26 is pivotally connected to a hole 272 near the end of one cam lever 268.- A mounting lug 274 on the opposite side of the air-brake charnber 24 is pivotally connected to a:hole 276 near the end of cam leyer 270. A
return spring 278 is connected to tabs 280 and 282 on the cam levers 268 and 270 respectively.
2Q When the air brakes are applied~ the charnber push-rod 26 is forced outward from the air-brake chamber 24. The ends of cam levers 268 and 270 are forced apart. Braking forces are developed within the disc brake entirely analog-ously to the operation previously described. When the air brakes are released, the return spring 278 pulls the cam levers 268 and 270 toward each other to aid in the rapid and complete disengagement of the brake. The together~directed force on the cam levers 268 and 270 forces the charnber push rod into the air brake chamber 24.
FIG. 14 shows an embodiment in which the air brake chamber 24 is supported at the end of a cantilever 284. The use of the cantilever 284 is an adaptation made necessary by the interference of suspension springs and other vehicle parts . ~

with an air-brake chamber 24 which is closely connected as in those previously described. The cantilever 284 is bol-te~ to the mounting flange 174 on the tor~ue plate 12. The air brake chamber 24 is bolted to support flange 286, 286a at the un-supportetl end of the cantilever 284.
A cylindrical tube 288, integratedly formed with the cantilever 284 contains a bushing 290 which is preferably of the kind containing lubricant. The cylindrical shaft 292, attached to the S-type cam 30 is slidably fitted into the bushing 290. The shaft 292 is stepped down to a smaller di-ameter 293 near its endO thereby orming a shoulder 294. A
hole 295 in a cam actuating lever 296 is fitted over the smaller diameter 293 and the actuating lever 296 bears against the shoulder 294. A nut 297 and lockwasher 298 rigidly connect the actuating lever 296 to the shaft 292. The other end of the actuating lever 296 is hingeably connected to the clevis 186 of the air-brake chamber using the bearing pin 206 through the clevis 186 and a coopera~ing hole 299 in the actuating lever 296. The jagged lines across the cantilever 284 and associated members indicates that the cantilever 284 can be of any con-venient length which is required to displace the air-brake chamber 24 to a non-interferring location.
It will be understood that the claims are intended to cover all changes and modifications of the preEerred em-bodiments of the invention, herein chosen for the purpose of illustratiorl which do not constitute departures from the spirit and scope of the invention. For example, although a disc brake with two brake shoes forced against opposing sides of the brake disc is shown and described, a fixed caliper 112 containing a single brake shoe 15~ operate~l by the levers and cams of any of the described embodiments could be substituted without departing from the spirit and scope of the inventionO

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Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a vehicular disc brake system having at least one friction member retained in a brake caliper and actuated by applying mechanical motion thereto to urge said friction member into frictional contact with a rotating frictional surface, and wherein frictional forces cause wear on the frictional contacting parts, the improvement of an automatic disc brake adjustor comprising:
(a) a threaded adjusting nut;
(b) an adjusting screw threadably engaged in said adjusting nut;
(c) a star wheel on said adjusting screw;
(d) means for relatively non-rotating connection of said star wheel to said adjusting screw;
(e) a spring finger resiliently connected to said adjustor nut in rachetable contact with said star wheel;
(f) means for connecting the mechanical motion applied to said friction member to said spring finger;
(g) means for compensating for frictional wear when said adjusting screw is rotated by said spring finger; and (h) retainer means attached to said adjustor nut for retaining said star wheel adjacent to said adjustor nut.

2. The improvement of claim 1 wherein said means for compensating for frictional wear comprises:
(a) means for applying force from said adjusting screw to said caliper; and (b) means for applying force from said adjusting nut to said at least one friction member.

3. The improvement recited in claim 1 further comprising manual means for rotating said adjusting screw whereby said automatic adjustor mechanism is overridden.

4. The improvement recited in claim 3 wherein the teeth of said star wheel are rounded, said rounded teeth allowing said finger to slide up and over the teeth during manual rotation.

5. The improvement recited in claim 1 wherein said retainer means is an adjustor spring, said spring finger is affixed to said adjustor spring, and a control arm on said adjustor spring is moveable into frictional contact with said star wheel when said friction member is urged into frictional contact with said rotating frictional surface.

6. The improvement recited in claim 1 wherein said means for relatively non-rotating connection of said star wheel to said threaded adjusting screw comprises:
(a) at least one longitudinal slow in the surface of said adjusting screw;
(b) said star wheel having an axial hole therein adapted to slidably fit over the threads of said adjusting screw; and (c) at least one inward projection on said star wheel into said axial hole said inward projecting into said longitudinal slot whereby relative rotation of said adjusting screw and star wheel is presented.

7. The improvement recited in claim 2 wherein said brake caliper retains two friction members adjacent to the radial surfaces of said brake disc and rotation of said adjusting screw is operative to change the distance between said means for applying force from said adjusting screw to said caliper and said means for applying force from said adjustor nut to at least one friction member ? to compensate for the wear of said two friction members.