AUTOMATIC BRAKE ADJUSTER

Abstract: A brake actuator shaft has a clutch on an inner end (48) which drives a splined sleeve (50). The splined sleeve (50) engages an inner projection (64) to turn one piston part (44) on another piston (42) part and to effectively lengthen the piston part (40). When the shaft (14) is turned by a brake lever (10), it operates an actuator (22) which presses on the piston part (44) and inward projection (64) and which prevents further relative rotation of the piston parts (42, 44), causing the clutch to slip. A gear (88) on an outer surface of the rotating portion of the piston engages a pinion connected to a manual adjuster. A ratchet in the manual adjuster prevents rotation of the pinion and the gear in the piston shortening direction.

Description: The present invention relates to an automatic brake adjuster for disc brakes of the type defined by the precharacterizing portion of claim 1. Automatic brake adjusters for all types of brakes and especially for disc brakes are known. Usually the brake adjuster operates by a moving portion of the brake engaging a fixed portion of the brake apparatus to prevent excessive return movement of the brake applying member. Disc brakes present a special problem because the clearance between the brake pad or brake shoe and the disc when the brake is not applied is very small. For that reason, the adjustment must be very small and automatic adjustment must occur in a very short movement of the brake apparatus. An automatic brake adjuster of the type referred to at the beginning is disclosed in EP-A-0 008 452. Herein a brake lever turns an actuator element connected to the lever and expands the actuator in an axial direction so that the actuator pushes against a piston. The piston pushes against a brake pad which in turn pushes against the disc face. An opposite reaction causes the caliper in which opposing pads are mounted to move axially, squeezing the disc between two opposing pads to apply the brakes. To keep the axial movement small, the brake is automatically adjusted during its use. A friction clutch means at the end of the actuator shaft turns a screw on the piston only in a direction to reduce the clearance between the brake pad and the disc until axial pressure of the actuator against the piston prevents turning of the screw. The present invention proceeds from the prior art represented by EP-A-0 008 452 and aims at providing a simpler and compact structure of the brake adjuster. According to the present invention, an automatic brake adjuster is provided which is defined in claim 1. In a specific embodiment of the invention a lever is connected to the first end of a shaft for rotating the shaft. Friction clutch means mounted on the second end of the shaft and annular spline means mounted on the second end of the shaft adjacent the friction clutch means rotate with the shaft until another force overrides the clutch and causes the spline means to slip on the shaft. A brake applying piston has first and second concentric portions which are connected by helical adjusting threads which permit relative turning of the elements in adjustment when the piston is not loaded. When brake applying force is applied to the piston, the helical threads lock the piston portions against turning. The turnable piston portion has an inward projection with teeth which engage the spline means which is mounted on the second end of the shaft. As the spline means turns with the shaft, the inward projection turns the turnable piston portion with respect to the non-turnable piston portion. The relative turning of the piston portions effects adjustment. The adjustment is prevented when actuator applies brake applying force to the piston, whereupon the spline means and friction clutch slip as the brake applying shaft is further turned. The spline means comprises a sleeve mounted on a second end of the shaft with radially extending splines on the sleeve. The inward projection on the turnable piston portion is a flat circular plate which faces the actuator and which has inward projecting teeth to engage the spline means on the sleeve. The friction clutch is a Belville spring positioned between the stop means and the sleeve for encouraging the sleeve to rotate with the shaft, stop means, and Belville spring. In a preferred embodiment of the invention, the inward projection on the turnable piston portion is positioned adjacent the actuator. In a preferred embodiment, a washer is mounted on the second end of the shaft and a compression spring extends between a washer and tends to push the adjustable portion of the piston in the direction of the actuator. That spring has several functions, one of which is to tend to encourage the engagement of the piston with the actuator to prevent slop. Another function of the spring is the movement of the rotatable piston portion in an actual direction away from the brake applying direction so that the rotatable piston portion may freely turn on threads interconnecting it to the slideable piston portion until brake applying force is applied by the actuator. In one preferred embodiment, the rotating portion of the piston has a relatively large gear with radially extending teeth on its outer perimeter. The gear engages a relatively small pinion on the manual brake adjuster. The manual brake adjuster includes a ratchet which prevents rotation of the pinion, and thus, prevents rotation of the gear in a direction which would tend to shorten the piston. Because of the relatively large size of the gear and the relatively small size of the pinion, a small angular rotation of the gear effects a relatively large angular rotation of the pinion which is sufficient to move the ratchet to the new locking position. In one preferred embodiment, a friction means is mounted on a face of the inward projection facing the actuator means whereby the actuator means prevents the inward projection and the piston portion from turning upon the transmission of axial force between the actuator means and the piston means. These and further objects and features of the invention will become more clearly apparent upon reference to the following detailed specification taken in connection with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an elevational view partionally in cross section of a disc brake apparatus showing the actuator and adjusting device. Figure 2 is a cross-sectional detail of a manual adjuster showing a pinion and ratchet which permit adjustment of the brake only in the piston lengthening sense of rotation. Figures 3 and 4 are details of the brake actuator shown in Figure 1, Figure 3 being taken along line 3-3 in Figure 4 and Figure 4 being taken along line 4-4 in Figure 3. DETAILED DESCRIPTION OF THE DRAWINGS Referring to Figure 1, a disc brake apparatus is generally referred to by the numeral 1. Disc 2 is braked by opposing pads 4 which are mounted in a caliper generally indicated by the numeral 6. The caliper assembly 6 is mounted on a spider 8. The brake is actuated by rotating lever 10 which is spline 12 to shaft 14. Shaft 14 is splined 18 to the first element 20 of an actuator generally indicated by the numeral 22. A second element 24 of the actuator is splined 26 to the brake housing so that the second element can not rotate as the shaft 14 is rotated. Rollers 28 are mounted in a cage 30 between the first actuator element 20 and the second actuator element 24. As lever 10 and shaft 14 rotate the first actuator 20, rollers 28 ride up cam surfaces 32 and 34, which causes the actuator elements 20 and 24 to move axially apart. Actuator element 20 is supported by roller bearings 36 which prevent axial movement. Actuator element 24 pushes a pressure member 38 against piston 40, which tightens the caliper and squeezes brake pads 4 on opposite faces of rotor 2. Over long use, the brake pads 4 wear. The length of piston 40 is adjustable to compensate for that wear. Piston 40 has two parts, an inner element 42 and an outer element 44 which are interconnected by adjusting threads 46. Turning the outer member 44 on inner member 42 in one direction causes the piston to elongate. Helical threads 46 have slope which locks the piston elements 42 and 44 against rotation when brake applying force is applied to the piston 40. Shaft 14, which has splines 12 on its first end, has a second end 48 which has a reduced diameter. A splined sleeve 50 with radially directed axially extending splines 52 is mounted for rotation on the reduced shaft second end 48. The extreme second end 54 of the shaft 14 is threaded to receive a nut 56 which holds a washer 58 on the shaft. A Belville spring 60 acts as a friction clutch to encourage the collar 50 to rotate with the shaft. Outer piston member 44 has welded thereto at its end facing the actuator 22 an inward projecting plate 62 with inward extending teeth 64 which engage the splines 52 on collar 50. As the friction clutch 60 turns the collar 50 with shaft 14, the inner projection 62 turns the outer piston member 44 on the inner piston member 42, tending to elongate the piston 40. Compression spring 66 extends between the washer 58 and the inward projection 62, tending to move the piston 40 in the direction of actuator 22 and tending to unload the threads 46 so that the piston members 44 and 42 may relatively turn. When actuator element 26 presses against inward projection 62 and piston member 44, the piston applying force locks threads 46, preventing further rotation of the piston members. Belville spring friction clutch 60 then permits adjusting collar 50 to remain in position while shaft 14 turns within the adjusting collar. As shown in Figure 1, the two elements 72 and 74 of the housing 70 are held together with bolts 76. Lubrication fitting 78 supplies lubricating channels 80 which in turn supply roller bearings 82 which support shaft 14 in housing 70 and which supply thrust roller bearings 36 and sleeve 50. As shown in Figure 2, manual adjustment mechanism 84 contains a ratchet 86 which prevents relative rotation of piston member 44 on piston member 42 in a direction which would tend to shorten the piston. As shown in 51, the piston member 44 is formed with a large outward extending gear 88, which engages a relatively small pinion 90. Pinion 90 is splined to adjusting shaft 92 which is fixed to the ratchet 86. As gear 88 turns pinion 90 in a direction which tends to elongate the piston, ratchet 86 turns to permit movement of the pinion and gear. Ratchet 86 prevents turning in the opposite sense of direction, and thus, prevents turning of pinion 90 and gear 88 in a direction which would tend to shorten the piston. Spring 94 permits shaft 92 to move axially to release the ratchet as it is being turned. Shaft 92 may also be turned manually by inserting a wrench in socket 96. Figures 3 and 4 are details of the actuator 22. Rollers 28 move up cam surfaces 32 and 34 as actuator element 20 is rotated with the actuator shaft by the splines 18. That movement of the rollers 28 on the cam surfaces 32 and 34 causes the element 24 to slide axially. Splines 26 prevent rotation of element 24. While the invention has been described with reference to specific embodiments, modifications and variations of the invention may be constructed without departing from the scope of the invention as defined in the following claims.

Claims: Internal automatic brake adjuster apparatus (1) for disc brakes comprising, a shaft (14) having first and second ends, lever means (10) connected to a first end of the shaft (14) for rotating the shaft, friction clutch means (60) mounted on the second end of the shaft (14) and annular spline means (50, 52) mounted on the shaft (14) adjacent the second end and in contact with the friction clutch means (60) whereby the friction clutch means (60) turns the annular spline means (50, 52) with the shaft (14) until the annular spline means (50, 52) encounters resistance whereupon the shaft (14) turns with respect to the annular spline means (50, 52), piston means (40) having a radial inward first portion (42) with a brake applying force and a radial outward second portion (44) and adjusting threads (46) interconnecting the portions whereby turning one of the portions on the other of the portions lengthens the piston means (40) and inward projection means (62) connected to one of the portions, and the inward projection means (62) having inward splines (64) for engaging splines (52) on the spline means (50, 52) and actuator means (22) mounted on the shaft (14) and engaging the piston means (40) for moving the piston means (40) in a brake applying direction upon turning of the shaft (14) whereby turning the shaft causes the clutch means (60) to turn the spline means (50, 52) and the spline means to turn the inward projection (62) and the inward projection to turn the inward piston portion (44) within the outward piston portion (42) until the actuator means (22) forces the piston means (40) in the brake applying direction, whereupon the clutch (60) slips and the spline means (50, 52) no longer turns the inward projection (62), characterized in that the inward piston portion (42) has an axially extending cavity in which the second end of the shaft means (14) is received and wherein the second end of the shaft means (14) comprises a spindle portion (48) and a stop means (56, 58) mounted at an end of the spindle portion (48) in a direction of the brake engaging face of the inward piston portion (42) wherein the spline means (50, 52) comprises a sleeve (50) mounted on the spindle portion (48) and having radially projecting and axially extending splines (52) on the sleeve (50) and wherein the clutch means (60) comprises Belville spring means mounted between the stop means (56, 58) and the face of the sleeve adjacent the stop means (56, 58) with the axial force sufficient to turn the sleeve (50) with the shaft means (14), wherein the second portion (44) of the piston means (40) comprises an outer collar having internal threads for engaging external threads on the inward piston portion (42) and wherein the inward projection means (62) comprises an annular plate having an annular outward portion permanently connected to a face of the outer piston portion (44) in a direction of the first end of the shaft means (14), the annular plate having a central opening with said radially inward projecting splines (64) for engaging the splines (52) on the sleeve (50) whereby the clutch means (60) turns the sleeve (50) and the sleeve turns the plate and the outward piston portion (44) to turn the outward piston portion (44) with respect to the inward piston portion (42) and adjust the piston length, and wherein a helical compression return spring means (66) is mounted between the stop means (56, 58) and the plate of the inward projection means (62) for pushing this plate axially with respect to the stop means (56, 58) thereby pushing the inward piston portion (42) and the outward piston portion (44) in the direction of the actuator (22) to provide brake clearance when the brake is not being applied. The apparatus of claim 1 wherein the inward projection means (62) is positioned between the piston means (40) and the actuator means (22). The apparatus of any one of the foregoing claims further comprising ratchet means (86) connected to the outward piston portion (44) of the piston means (40) to which the inward projection (62) is connected for preventing turning of that outward piston portion (44) with respect to the inward piston portion (42) when the shaft (14) is turned in a non-brake actuating direction. The apparatus of any one of the foregoing claims further comprising friction means (38) mounted on a face of the inward projection (62) facing the actuator means (22) whereby the actuator means (22) prevents the inward projection (62) and the outward piston portion (44) from turning upon the transmission of axial force between the actuator means (22) and the piston means (40). The apparatus of any one of the foregoing claims wherein brake clearance is controlled by controlling arcuate clearance between the splines (52) on the sleeve (50) and the inward projecting splines (64) on the inward projection means (62). The apparatus of any one of the foregoing claims wherein the stop means (56, 58) comprises a washer (58) mounted on a reduced portion (54) of the shaft means (14).

Inventors: WEBER, JAMES LEO
Applicants: ROCKWELL INTERNATIONAL CORPORATION
Application year: 1985
Main classification: F16D65
IPC codes: F16D65