GB1566355A - Air applied disc brake - Google Patents

Description

PATENT SPECIFICATION

( 11) 1 566 355 ( 21) Application No 12380/78 ( 62) Divided out of No 1566353 ( 31) Convention Application No.

( 22) Filed 22 Jun 1977 703933 ( 32) Filed 9 Jul 1976 in ( 33) United States of America (US) ( 44) Complete Specification Published 30 Apr 1980 ( 51) INT CL 3 F 16 D 65/56 ( 52) Index at Acceptance F 2 E LX ( 54) AIR APPLIED DISC BRAKE ( 71) We, WAGNER ELECTRIC CORPORATION, a corporation of the State of Delaware, United States of America, having its offices at 100 Misty Lane, Parsippany, New Jersey 07054, United States of America, do hereby declare this inventionfor which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:-

The present invention relates to disc brakes.

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 commerical highway and off-road vehciles 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, caused by variation in the brake lining friction, is magnified by this energization Brake torque imbalance could cause steering pulls.

The modern trend to higher stopping rates for trucks, coupled with the requirment 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 automotive applications where higher braking performance, better straight-line stopping ability and reduction in brake fading was desired.

United States Patent Nos 3,536,166, 3,768,604 and 3,835,962 in the name of E J.

Falk teach hydraulically operated disc brakes suitable for automotive applications.

Similar use of disc brakes has not been made on articulated highway vehicles.

The invention consists in a disc brake for a vehicle, the disc brake having: first and second friction members disposed adjacent opposed faces of a rotatable brake disc; a caliper; a cam carrier between said first friction member and said caliper, a contacting surface on said cam carrier contacting said first friction member; cam means for urging said contacting surface against said first friction member to urge said first friction member to move into frictional contact with a first face of said rotatable brake disc, said caliper including a transverse member operative to urge said second frictional member to move into contact with said rotatable brake disc whenever force is applied to said caliper; an adjuster nut mounted in said cam carrier; an adjusting screw engaged in said adjuster nut; connecting means for bearing said ajusting screw against said caliper whereby, whenever said first friction member is urged into frictional contact with said first face of said rotatable brake disc, force is also applied to said caliper through said adjusting screw; and an automatic brake adjuster for adjusting said adjusting screw to compensate for wear on the frictional contacting parts, said automatic brake adjuster comprising ratchet means mounted on said ajusting screw and unidirectional means for transmitting the motion applied to said friction members to said ratchet means on said adjusting screw whereby said screw is advanced towards said caliper.

Methods of performing the invention will ( 19) 1 566 355 now be described with reference to the accompanying diagrammatic drawings, in which:Figure 1 shows one embodiment of the air-operated disc brake mounted in its operating position at the front wheel of a highway vehicle.

Figure 2 shows a view of the invention looking outward from the center of the vehicle.

Figure 3 shows a longitudinal cross section of the S-type cam.

Figure 4 shows a cross-sectional view of the disc brake taken along 4-4 in Figure 2.

Figure 5 shows a cross-sectional view taken along 5-5 in Figure 2.

Figure 6 shows an exploded view of a portion of the air actuated disc brake.

Figure 7 shows an exploded view of the disc brake illustrating the assembly of major subassemblies.

Figure 8 shows a view of the air chamber in Figure 7 rotated 90 degrees about its axis.

Figure 9 shows a top view of a portion of the assembled brake taken along 9-9 in Figure 2.

Figure 10 shows a close-up view of the spring retainer and slotted washer.

Figure 11 shows a perspective view of the adjusting mechanism.

Figure 12 shows a cross-sectional view of the star wheel and adjusting screw showing the method of keying these parts together.

Figure 13 shows an alternate embodiment of the disc brake.

Figure 14 shows an embodiment in which the air brake chamber is supported at the end of a cantilever.

The air-applied disc brake system is shown generally at 10 in Figure 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 therethrough of the vehicle axle (not shown) A brake disc 18 is rotatably 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 conventionally 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 outboard side of the brake disc 18, to be shown and described later, are held in relationship with portion 22 within the disc brake caliper 20 In the brakes-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 torque 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 the brake shoes into frictional contact with the inboard and outboard 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 torque plate 12 directly into the axle flange of the vehicle.

Referring now to Figure 2, a chamber push rod 26 is connected to the lever arm 28 of an S-type cam 30 The S-type cam 30 applies equal and opposite forces to a pull-lever 32 and a push-lever 34 The pull-lever 32 and push-lever 34 transmit their input forces to disc brake friction members located within the brake 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 38 a to which are rigidly mounted a brake support plate 40 and the air-brake chamber 24.

Figure 3 shows 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 This force tends to cause the S-type cam 30 to rotate clockwise about its pivot 46 A permanently lubricated type sleeve 48 encircles the pivot 46 and provides a reduced-friction bearing 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 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 Figure 2, the push and pull forces along rods 52 nd 64 are connected to cam levers 34 and 32 using hemispheric collars 70 and 72 and cooperating hemispheric cavities 74 and 76, all respectively.

Permanently lubricated inserts 75 and 77 1 566 355 may be located between the bearing surfaces of collar 70 and cavity 74 and between collar 72 and cavity 76, respectively.

Referring to Figures 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 permanently 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 receives an adjusting screw 94 in a threaded hole 96 A star wheel 98 is positioned in keyed relationship with the adjusting screw 94 A reduceddiameter 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.

The upper surface 108 of the adjusting screw guide 104 is dome shaped 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 shaft 100 enable attachment of a wrench thereto for manual adjustment of the brake.

A transverse member 118 transmits force applied to the caliper 112 at the socket 110 on two reaction legs 120, 120 a on the opposite side of the brake disc 18 The two reaction legs 120, 120 a are positioned adjuacent to an outboard shoe plate 122 The outboard shoe plate 122 is connected 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 inboard brake lining 128 are located adjacent to the inboard parallel surface 129 of the brake disc 18 The cam carrier 81 has its bearing surface 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 62, the cams 78 and 80 rotate about their pivots 84 and 86 in the direction shown by the curved arros The cam lips 88 and 92 bear upward against the underside of the adjusting nut 90 A downward force is thereby transmitted through the pivots 84 and 86 and the cam carrier 81 is the inbored shoe plate 126; and an equal upward force is 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 reactions legs 120, 120 a to the outboard shoe plate 122 Equal and opposite normal forces are thereby transmitted to the outboard and inboard brake linings 124 and 128 which are thus brought into frictional contact with the outboard and inboard parallel surfaces 129 a and 129 of the brake disc 18.

Also in Figure 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 member 118 and reaction leg a is seen to partially encircle the brake disc 18 and the force-developing elements previously described.

The entire assembly shown in Figures 4 and 5 is free to translate normal to the parallel surfaces of the brake disc 18 is order to apply equal forces to the two parallel surfaces 129, 129 a.

Figure 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, 138 a and the circular hole 114 and socket 110 is its closed end 140 Holes 138, 138 a 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 of the caliper 112 by lifting and tilting the cam carrier assembly 136 so that the ends of the cam levers 34 and 32 fit throigh the holes 138, 138 a As the cam and carrier assembly 136 is nested inside the closed end 140, the end of the reduced diameter shaft 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, 142 a in the sides of the cam carrier 81 are aligned adjacent to a second pair of grooves 144, 144 a in the sides of the closed end 140 of the caliper 112 A third pair of grooves 146, 146 a in the outside surfaces of the reaction legs 120, 120 a are aligned with the first and second pair of grooves 142, 142 a and 144, 144 a respectively.

The support plate 40 is in a general U shape having two opposed end portions 148, 148 a 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, 152 a to form a forward pair of parallel surfaces 154, 154 a and a rear pair of parallel surfaces 156, 156 a The forward surfaces 154, 154 a are so spaced and the material thickness is such that a sliding fit of the forward surfaces 154, 154 a into the grooves 144, 142 and 144 a, 142 a is possible Similarly, the rear surfaces 156, 156 a are capable of a sliding fit within the grooves 146, 146 a When so assembled, the tongue-in groove connection holds the cam and carrier assembly 136 correctly aligned within the caliper 112 but allows lateral 1 566 355 sliding movement of the assembled parts on surfaces 154, 154 a and 156, 156 a.

The inboard and outboard brake shoes 158, 160 are inserted through the opening provided by the openings 152, 152 a The inboard brake shoe 158 is moved toward the closed end 140 of the caliper 112 until the grooves 162 and 162 a in the inboard shoe plate 126 engage the forward surfaces 154, 154 a The inboard brake shoe 158 is moved along forward surfaces 154, 154 a until it comes to rest against the cam and carrier assembly 136 Similarly, two grooves 164, 164 a on the outboard brake shoe plate 122 are fitted on the rear pair of parallel surfaces 156, 156 a and moved outward until the outboard shoe Plate 122 bears against the reaction legs 120, 120 a 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 brake disc 18 (see also Figures 4 and 5) when finally assembled and installed as will be described The S-type cam 30 is preassembled to the ends of the pull rod 64 and push rod 52 which interconnect the caliper assembly 35 with the S-type cam 30 which may be preassembled to form cam and caliper assembly 136, Figure 7, a major subassembly to be mounted on the vehicle.

Referring further to Figure 7, the preassembled caliper and support plate 40 with attached S-type cam is mounted upon anchor flanges 38, 38 a 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, 154 a and 156, 156 a 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 pulurality of holes 174 The circular opening 16 accommodates the passage therethrough of the shaft and wheel hub (not shown) 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 flange 176 containing bolt hols 178 provides a mounting location for an air-brake chamber bracket 180 The airbrake chamber 24 is mounted to the airbrake chamber bracket 180 using a pair of threaded studs 182, 182 a and cooperating nuts 184, 184 a In the isolated view of the air-brake chamber 24 shown in Figure 8, the threaded studs 182, 182 a are symmetrically located on either side of the chamber push rod 26 A clevis 186 is attached to the end of the chamber push rod 26.

Referring now to Figure 9, the air-brake chamber bracket 180 has bearing holes 188, 188 a passing through two side plates 190 and a The S-type cam 30 is pivotally secured between the side plates 190, 190 a 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 188 a in the second sideplate 190 a 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, 202 a through the two arms 204, 204 a of the clevis 186 A bearing pin 206, inserted through the bearing holes 202, 202 a 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 Figures 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 (in and out of the page in Figure 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 claiper assembly 35.

Refer to Figure 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, 208 a, or anti-scuff springs, are connected between the cam carrier 81 and the caliper 112 Each end of the cam carrier 81 has a hole 210, 210 a having an enlarged lower diameter 212, 212 a forming a stepped bore The bottom ends 214, 214 a of the springs 208, 208 a are enlarged to a diameter greater than the holes 210, 210 a but smaller than the enlarged diameters 212, 212 a forming a stepped diameter The bottom end 214, 214 a of the springs 208, 208 a are consequently retained in the cam carrier 81 At thier upper ends, the springs 208, 208 a pass into aligned holes 216, 216 a or bores in the caliper 112 and are connected to the lower lobes 218, 218 a of spring retainers 220, 220 a The spring retainers 220, 220 a are captured by slotted washers 222, 222 a which bear against mating surfaces on the caliper 112.

An isolated view of a spring retainer 220 and its associated slotted washer 222 is shown in Figure 10 The spring retainer 220 has a narrow waist region 224 between the lower lobe 218 and an upper lobe 226 The 1 566 355 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 S 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 228 until the waist region 224 is level with the slotted washer 222 The spring retainer 220 is then turned degrees and released The shoulders 232, 232 a 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 Figure 4, when the brakes are released, the return springs 208, 208 a 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 positively removed, the brake shoes 160 and 158 are free to be moved away from the brake disc 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 Figure 11 The star wheel 98 and adjusting screw 94 are fixed together such that rotary motion of the star wheel 98 is imparted to the adjusting screw 94 One method of fixing the two together which has been reduced to practice is shown in Figure 12 The adjusting screw 94 contains two vertical slots 234, 234 a at loctions 180 degrees diametrically opposed The slots 234, 234 a are of regular trapezoidal cross section in which the shorter base of the trapezoids 236, 236 a are nearer the axis of rotation of the adjusting screw 94 The star wheel 98 has similarly shaped trapezoidal inward projections 238, 238 a which fit loosely into the slots 234 234 a 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 Figure 11, 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 aforementioned 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 counterclockwise 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 horizonfal 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 adjusting 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 surface of the star wheel 98 The retainer tab 266 restrains the star wheel 98 from sliding up the adjusting screw 94, and keeps the star wheel 98 loosely adjacent to the upper surface of the adjusting nut 90.

It will be evident 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 th right 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 of the time, full brake actuation fails to move the finger 252 far enough rightward 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 is thus advanced a small increment to compensate for brake wear.

The consequent tightening of the brake adjustment reduces 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.

Note that the teeth 256 on the star wheel 98 have rounded tips This allows the automatic adjustment to be overridden by manual adjustment using a wrench on the flats 116 (shown at Figure 5) at the end of the adjusting screw 94 When the adjusting screw 94 is manually rotated, the flexible finger 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 1 566 355 brake is shown in Figure 13 in which internal and attachment details are identical to the embodiment previously described Two cam levers 268 and 270 protrude from the caliper 112 An airbrake 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 chamber 24 is pivotally connected to a hole 276 near the end of cam lever 270 A return spring 278 is connected to tabs 280 and 282 on the cam levers 268 and 270 respectively.

When the air brakes are applied, the chamber 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 analogously 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 chamber push rod into the air brake chamber 24.

Figure 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 bolted to the mounting flange 174 on the torque plate 12 The air brake chamber 24 is bolted to support flange 286, 286 a at the unsupported 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 diameter 293 near its end, thereby forming a shoulder 294 A hole 295 is 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 cooperating 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 convenient length which is required to displace the air-brake chamber 24 to a non-interferring location.

It will be undestood that the claims are intended to cover all changes and modifications of the preferred embodiments of theinvention, herein chosen for the purpose of illustration which do not consitute departures from the 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 158 operated by the levers and cams of any of the described embodiments could be substituted without departing from the scope of the invention.

Further features of disc brakes are described and claimed in our copending U K.

Patent Application No 26062/77 (Serial No.

1566353).

Claims (8)

WHAT WE CLAIM IS:-

1 A disc brake for a vehicle, the disc brake having: first and second friction members disposed adjacent opposed faces of a rotatable brake disc; a caliper; a cam carrier betwen said first friction member and said caliper, a contacting surface on said cam carrier contacting said first friction member; cam means for urging said contacting surface against said first friction member to urge said first friction member to move into frictional contact with a first face of said rotatable brake disc, said caliper including a transverse member operative to urge said second frictional member to move into contact with said rotatable brake disc whenever force is applied to said caliper; an adjuster nut mounted in said cam carrier; an adjusting screw engaged in said adjuster nut; connecting means for bearing said adjusting screw against said caliper whereby, whenever said first friction member is urged into frictional contact with said first face of said rotatable brake disc, force is also applied to said caliper through said ajusting screw; and an automatic brake adjuster for adjusting said adjusting screw to compensate for wear on the frictional contacting parts, said automatic brake adjuster comprising ratchet means mounted on said adjusting screw and unidirectional means for transmitting the motion applied to said friction members to said ratchet means on said adjusting screw whereby said screw is advanced towards said caliper.

2 A brake as claimed in Claim 1, wherein said means on said adjusting screw comprises a star wheel, and means for relatively non-rotating connection of said star wheel to said adjusting screw.

3 A brake as claimed in Claim 2, wherein said unidirectional means comprises a spring finger forming a ratchet mechanism with said star wheel, and wherein means are provided for connecting the mechanical motion applied to said friction member to said spring finger.

1 566 355

4 A brake as claimed in Claim 3, including a control arm, an outer end of which is disposed adjacent to the teeth of said star wheel, and means for connecting the mechanical motion applied to said frction member to said control arm, said outer end being pressed into frictional bearing relationship with the teeth of said star wheel when the brakes are applied.

5 A brake as claimed in Claim 3, or Claim 4, wherein said means for relatively non-rotative connection of said star wheel to said adjusting screw comprises at least one axially directed slot in the surface of said adjusting screw, and at least one inward projection on said star wheel, said at least one inward projection fitting into said at least one axially directed slot.

6 A brake as claimed in Claim 1, including a star wheel on said adjusting screw, a relatively non-rotating connection between said star wheel and said adjusting screw, a spring finger forming a ratchet mechanism with said star wheel, and a connection between the mechanical motion applied to said friction member and said spring finger, the arrangement being such that said adjusting screw rotates relative to said adjuster nut when said star wheel is rotated by said spring finger.

7 A brake as claimed in Claim 6, including manual means for rotating said adjusting screw whereby said automatic adjuster mechanism is overridden.

8 A brake as claimed in Claim 1, wherein said automatic brake adjuster is as illustrated in Figure 11 of the accompanying diagrammatic drawings.

For the Applicants, G F REDFERN & COMPANY, Marlborough Lodge, 14 Farncombe Road, Worthing, West Sussex, BN 11 2 BT.

Printed for Her Majesty's Stationery Office, by Croydon Printing Company Limited, Croydon, Surrey, 1980.

Published by The Patent Office, 25 Southampton Buildings, London WC 2 A IAY, from which copies may be obtained.