GB2177171A

GB2177171A - Automatic adjusting; disc brakes; parking brake

Info

Publication number: GB2177171A
Application number: GB08516485A
Authority: GB
Inventors: Anthony C Evans
Original assignee: Kelsey Hayes Co
Current assignee: Kelsey Hayes Co
Priority date: 1984-04-09
Filing date: 1985-06-28
Publication date: 1987-01-14
Anticipated expiration: 2005-06-28
Also published as: GB2177171B; IN165376B; DE3523379A1; GB8516485D0

Abstract

A parking brake actuator and adjuster mechanism 24 is mounted on a caliper (10) of a disc brake assembly and comprises a housing 32 with bores 34, 36 - bore 34 receives an adjusting nut 42 and an adjusting screw 58 threadingly engaging threaded bore 44 in nut 42. Nut 42 has ratchet teeth 47 engaged by adjusting leg 70 of a pivotally mounted pawl 66 while a tracking arm 68 of pawl 66 engages groove 48 on nut 42: pawl 66 is mounted on a plate 76 in bore 36. A lever 26 having tongs 28a, 28b received in holes 13a, 13b on housing 32 is fastened to a toggle pin 52 which communicates with nut 42 by an axial projection 49. Mechanical parking brake application is by means a cable 98 acting on lever 26. Translation of nut 42 occurs during mechanical and hydraulic brake actuation and if predetermined amount of translation occurs, leg 70 of pad 66 advances and rotates nut 42 upon release, arm 68 tracking in groove 48. <IMAGE>

Description

SPECIFICATION Improvements in and relating to self adjusting parking brakes The invention relates to an automatic brake adjuster, to an actuating assembly for a mechanical parking brake having an integral self adjusting feature, particularly suitable for use on rear-axle disc-brake assemblies, and to a disc brake including such an adjuster or such an actuating assembly.

The invention provides a brake-adjuster comprising: a screw; a nut threaded onto the screw and having a ring of teeth; and a pivotally-mounted pawl having a first arm so engaging the nut that axial movement of the nut causes rotation of the pawl and a second arm so engaging the teeth that reciprocation of the pawl over at least a predetermined arc causes rotation of the nut in a sense to advance the screw through the nut.

The invention also provides an automaticallyadjusting parking-brake actuator comprising a brake adjuster according to the invention and means for urging the nut forwards.

The invention further provides a brake comprising a brake-adjuster or an actuator according to the invention so attached to the brake and with the forward end of the screw so engaging a brake-pad of the brake that the screw tends to advance as the brake is applied.

The parking brake actuator is preferably a "bolt-on" type assembly intended for external mounting to a disc brake caliper. Use of a "bolt-on" parking-brake actuating assembly eliminates the necessity of having front and rear axle disc brake assemblies of different design since the parking brake mechanism is not an integral part of the disc brake assembly.

One form of "bolt-on" self-adjusting parking-brake assembly according to the invention comprises an adjustable thrust-screw and adjusting-nut combination mechanically activated by a toggle pin for parking-brake application.

The adjusting nut is acted upon by a ratchetpawl arrangement each time the thrust screw and adjusting nut is activated. Activation of the thrust screw and adjusting nut combination occurs both when the parking brake is mechanically activated and when the hydraulic brake is activated. Thus, adjustment of the parking brake mechanism for friction pad wear is maintained regardless of the frequency of parking brake use.

One form of disc brake including a parkingbrake actuator constructed in accordance with the invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a fragmentary outboard elevation view of a disc brake assembly; Figure 2 is a side elevation view of the disc brake assembly, showing a mechanical parking brake assembly; Figure 3 is a fragmentary elevation view of the disc brake assembly; Figure 4 is a sectional view taken along line 4-4 in Figure 3; Figure 5 is a sectional view taken along line 5-5 in Figure 4 showing an adjusting pawl mechanism in its idle position; Figure 6 is a sectional view taken along line 6-6 in Figure 5; Figure 7 is a sectional view, similar to Figure 5 showing the adjusting pawl mechanism in its applied state; Figure 8 is an exploded view of the mechanical parking brake assembly; and Figure 8a is a perspective view of the adjusting pawl mechanism.

Referring to the accompanying drawings, and initially to Figures 1 to 4, a disc brake assembly, which may be a floating-caliper disc brake similar to that shown in United States Patent No. 4,391,355, comprises a C-shaped floating caliper 10 having an inboard leg 21 and an outboard leg 22, each having attached thereto a brake pad asembly 16 or 18, respectively. Within the inboard leg 21 is a cylinder bore 12 having its longitudinal axis generally perpendicular to the plane of a brake disc 20 and having a brake activating piston 14 slidably disposed therein. In response to hydraulic activation of the brake, the piston 14 exerts a force against the inboard brake pad assembly 16 urging the brake pad into contact with the disc 20.In reaction to the force exerted by the pad 16 against the disc 20, the caliper 10 translates along a mounting pin 11 and the outboard caliper leg 22 urges the outboard brake pad assembly 18 into contact with the outboard face of the disc 20. As the activating hydraulic pressure increases within the bore 12, the clamping force exerted by the piston 14 and the caliper 10 upon the brake pad assemblies 1 6 and 18 increases thus resulting in increasing braking torque.

Referring to Figures 2, 4, and 8, a housing 32 of parking brake actuator and adjuster mechanism 24 is mounted on the caliper 10 by suitable fastening means such as bolts 23 shown in Figure 2. The housing 32 includes intersecting bores 34 and 36. The longitudinal axis of the bore 34 is perpendicular to the plane of rotation of the disc 20 and is configured to include a first, outer, bore of larger diameter 29 extending from the outboard end of the housing 32 and terminating at a shoulder 33; a second, inner, bore of smaller diameter 31 extends from the shoulder 33 to an inboard shoulder 35. Extending from the inboard shoulder 35 and terminating at the inboard surface of the housing 32 is a conically shaped bore 25 which widens from the inboard shoulder towards the surface of the housing.

Positioned at the inboard end of the bore 31 and extending through the conical bore 25 is a toggle pin 52 having its head 54 seated upon the inboard shoulder 35. Externally attached to the toggle pin 52 is a mechanical activating lever 26.

The activating lever 26 comprises side arms 27a and 27b spaced apart by a transverse web 30. The side arms include tangs 28a and 28b which are received in locator holes 1 3a and 13b, respectively, on the housing 32. The web 30 is provided with an opening 38 receiving therethrough the protruding toggle pin 52. The toggle 52 and the activating lever 26 are fastened together by a bellville washer 43 received in a groove 55 on pin the 52 and by a coil spring 15 extending between an eye 57 in the pin 52 and a notch 41 on the lever 26.

A dust boot 90 is provided to prevent the entry of dirt into the conical bore 25. By the action of the washer 43 and the coil spring 15, the tangs 28a and 28b are retained within the locating holes 13a and 13b, and the head 54 of the toggle pin 52 is urged into seating engagement with the shoulder 35.

Extending through the housing bore 34 and into mating engagement with the inner bore 31 is an adjusting nut 42 having a coaxial threaded bore 44 internally therein. The adjusting nut 42 communicates with the toggle pin 52 by an axial projection 49 on the nut 42 extending into abutting engagement with the bottom of a recess 56 within the head 54 of the toggle pin.

An adjusting screw 58 threadingly engages the threaded bore 44 in the adjusting nut 42 and includes an enlarged head 60 which is received and held captive within a cage 62 attached to the inboard brake pad assembly 16 and which mates with the cage in such a way as to prevent rotation of the adjusting screw. A dust boot 92 is provided to prevent dirt and contamination from entering the outer bore 29.

The elements just described serve to activate the parking brake. The automatic adjusting elements will now be described.

Positioned within the intersecting bore 36, in abutting engagement with a shoulder 37 is an adjusting mechanism foundation plate 76.

The plate 76 is provided with a pivot post 78. The post 78 may be provided by upsetting plate metal, as shown, to form the post, by insertion of a roll pin, or any other suitable technique. An adjustment pawl indicated generally by the reference numeral 66 is so mounted on the plate 76, as shown in Figure 8a, that the pivot post 78 is received in a pivot hole 74 in the pawl, with a dog leg 71 of the pawl extending through an aperture 84 in the plate thereby placing an adjusting leg 70 and a tracking arm 68 of the pawl on opposite sides of the foundation plate and generally parallel thereto. A spring 88 is attached to and extends between a tang 86 on the plate 76 and a tang 72 on the pawl 66 and biases the adjustment leg 70 in the counter clockwise direction as seen in Figures 5, 7, 8, and 8a.The foundation plate 76 is axially retained in position in the bore 36 by a snap ring 80 and is restrained from rotation by an anti-rotation tang 75 that seats in a groove in the wall of the bore 36. When positioned within the bore 36, the foundation plate 76 forms an opening bounded by a chordal edge 82 of the plate and the wall of the bore through which ratchet teeth 47 on the adjusting nut 42 protrude and engage the adjusting leg 70 of the pawl 66; the tracking arm 68, in turn, slidingly engages a tracking groove 48 on the adjusting nut shown in Figure 4, 5, and 7.

The parking brake assembly has two operational functions. First, and foremost, the mechanism operates as a mechanical parking brake actuator. Secondly, the mechanism functions as a self-adjusting mechanism preventing loss of effectiveness of the parking brake through wear of the friction pads of the brake pad assemblies 16 and 18. The self-adjusting mechanism has two modes of operation; first and most importantly the self-adjusting mechanism operates to adjust for brake pad wear through normal hydraulic braking activation; secondly, the adjusting mechanism operates upon mechanical activation of the parking brake.

Mechanical actuation of the parking brake is initiated by the vehicle operator applying a tensioning force to a cable 98 by means of a mechanical parking brake actuating mechanism (not shown). A tensioning force in the cable 98 causes the actuator lever 26 to pivot about the locator holes 13a and 13b by the receipt of the tangs 28 therein. As the lever 26 pivots it in turn causes a like pivoting of the toggle pin 52 as shown in Figure 7. The pivoting action of the toggle pin 52 causes axial translation of the adjuster nut 42 and of the adjuster screw 58 threadingly engaged in the nut, applying a brake-actuating force upon the inboard brake pad assembly 16. The outboard brake pad assembly 18 is caused to engage the disc 20 through the reactive force imparted to the caliper 10 through the contact of the head 54 of the toggle pin 52 with the inboard shoulder 35 of the bore 34 in the housing 32. Upon release of the parking brake mechanism (not shown) by the vehicle operator, the activating lever 26 and the toggle pin 52 are returned to their normal idle position (as shown in Figure 4) by the action of the return spring 15. The adjusting nut 42 in combination with the screw 58 are returned to their idle position by the action of the spring 88 in the adjusting mechanism, through the contact of the tracking arm 68 of the pawl 66 with the side of the tracking groove 48 on the adjusting nut.

During normal hydraulic activation of the disc brake, movement of the inboard brake pad assembly 16 relative to the caliper 10 causes a similar axial movement of the adjusting nut 42 and the adjusting screw 58 assembly because the screw head 60 is engaged and entrapped within the bracket 62 fixed to the backing plate of the inboard brake pad assembly 16. Any axial movement of the adjusting nut 42 toward the disc 20, whether by actuation of the hydrulic brake or by the mechanical parking brake, will set in motion the self adjusting mechanism and for a given axial displacement of the adjusting nut 42, representing an amount of brake pad wear requiring adjustment, the adjusting pawl 66 affects rotation of the adjusting nut 42 thereby advancing the advancing the adjusting screw 58 a proportional amount as explained below.

Referring primarily to Figures 5, 6, and 7, as the adjusting nut 42 is caused to translate toward the disc 20, the tracking leg 68 of the adjuster pawl 66, tracking within the groove 48 of the adjuster nut 42, causes pivotal movement of the pawl 66 about the pivot 78.

Compare Figure 5 showing the mechanism in its inactive state and Figure 7 showing the mechanism when the brake is applied. Because Figure 7 depicts mechanical activation of the mechanism, the toggle pin 52 is shown in its tilted position; when the adjusting nut 42 translates because of hydraulic brake activation, the toggle pin 52 remains in its idle position as shown in Figure 5.

If the state of the brake pad assemblies 16 and 18 is such that a wear adjustment of the mechanical brake mechanism is appropriate, as manifested in a predetermined amount of translation of the adjuster nut 42, then the adjusting leg 70 of the pawl 66 is caused to advance upon the adjuster screw ratchet wheel 47 and to engage the next available tooth as seen again by comparing figures 5 and 7.

Upon release of the brake applying mechanism (either the parking brake or hydraulic brake), the energy stored in the spring 88, during brake application, not only acts to restore the pawl 66 to its original position, thereby rotating the adjuster nut 42 in a sense to cause the adjuster screw 58 to advance, but also, through the action of the tracking leg 68 of the pawl in the groove 48 of adjuster nut 42, causes the adjuster nut to return to its idle position as shown in Figure 2 and 5.

Claims

1. A brake-adjuster comprising: a screw; a nut threaded onto the screw and having a ring of teeth; and a pivotally-mounted pawl having a first arm so engaging the nut that axial movement of the nut causes rotation of the pawl and a second arm so engaging the teeth that reciprocation of the pawl over at least a predetermined arc causes rotation of the nut in a sense to advance the screw through the nut.

2. A brake-adjuster as claimed in claim 1, wherein the nut and screw are disposed within a bore in a housing and the pawl is mounted pivotally about an axis fixed in the housing.

3. A brake-adjuster as claimed in claim 2, wherein the nut and screw are reciprocable together between a rearward position in which the nut abuts a surface fixed in the housing and a forward position, and wherein the forward end of the screw projects from the housing.

4. A brake-adjuster as claimed in any one of claims 1 to 3, which comprises means for securing the forward end of the screw nonrotatably to a brake pad of a brake.

5. A brake-adjuster as claimed in any one of claims 1 to 4, wherein the first arm of the pawl engages in an annular groove encircling the nut.

6. An automatically-adjusting parking-brake actuator comprising a brake adjuster as claimed in any one of claims 1 to 5 and means for urging the nut forwards.

7. An actuator as claimed in claim 6 when dependent upon claim 2, wherein the urging means comprises a pin with a head seated against the forward face of a shoulder within the bore and a stalk projecting rearwardly from the housing, the pin being so arranged as to tend to rotate and to urge the nut forwards in response to a transverse force acting on the distal portion of the stalk.

8. An actuator as claimed in claim 7, comprising a lever engaging the housing and the distal portion of the stalk of the pin and arranged to rotate and to urge the pin to rotate in response to an applied force.

9. An actuator as claimed in claim 7 or claim 8 when dependent upon claim 3, wherein the head of the pin, in its rearmost position, defines the said surface fixed in the housing.

10. An automatically-adjusting parking-brake actuator substantially as hereinbefore described with reference to, and as shown in Figs. 2 to 8 and 8A of, the accompanying drawings.

11. A brake comprising a brake-adjuster as claimed in any one of claims 1 to 5 or an actuator as claimed in any one of claims 6 to 10, so attached to the brake and with the forward end of the screw so engaging a brake-pad of the brake that the screw tends to advance as the brake is applied.

12. A brake as claimed in claim 11, which is a floating-caliper disc brake having a disc, inboard and outboard brake-pads, a caliper straddling the disc and the brake-pads and having an outboard leg engaging the outboard brake-pad and an inboard leg, and actuating means arranged in use to urge the inboard leg of the caliper and the inboard brake-pad apart to apply the brake; wherein the said brakeadjuster or actuator is secured to the inboard leg of the caliper and the said forward end of the screw is secured to the inboard brakepad.

13. A floating-caliper disc-brake as claimed in claim 12, wherein the said actuating means comprises a hydraulic cylinder and piston.

14. A floating-caliper disc-brake substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

15. An automatically-adjusting parking-brake actuator for use with an automotive brake assembly, comprising: thrust screw means arranged to be so attached to the friction pad means that in operation the thrust screw translates axially in response to brake-activating movement of the friction pad means; adjusting nut means having an axial threaded bore threadingly receiving the thrust screw, the adjusting nut means including coaxial ratchet teeth and a peripheral groove externally circumscribing it; adjuster pawl means having a pivot, relative to said adjusting nut means, and including an adjusting leg so engaging the ratchet teeth and a camming leg so engaging the peripheral groove that axial translation of the adjusting nut means causes pivotal movement of the adjuster pawl means and rotation of the ratchet teeth and the adjusting nut means relative to the thrust screw means; and means for applying an axial force to the adjusting nut means to urge the adjusting nut means and the thrust screw means axially in a sense to urge the friction pad means into a brake applying mode.

16. An actuator as claimed in claim 15, wherein the means for applying an axial force to the adjusting nut means comprises toggle pin means so communicating with the adjusting nut means that pivotal movement of the toggle pin means applies the said axial force to the said adjusting nut means.

17. An automotive hydraulically-activated disc brake having an automatically-adjusting parking-brake mechanism comprising: a housing juxtaposed to the disc brake assembly, the housing having an elongate bore extending through it; a parking brake adjusting strut assembly including an elongate adjusting nut having a threaded bore therein and a thrust screw threadingly received within the said threaded bore, the adjusting nut having a circumscribing ratchet wheel and a peripheral groove axially separated one from the other, the strut assembly being slidingly retained within the said bore in the housing with the thrust screw extending from a first, open, end of the said bore in the housing; means for so attaching the thrust screw to one friction pad assembly of the said disc brake that the adjusting strut assembly is caused to translate within the elongate bore and in concert with the friction pad assembly; pawl means movably attached to the housing, the pawl means including an adjusting leg so communicating with the ratchet wheel and a camming leg so communicating with the peripheral groove circumscribing the adjusting nut that translation of the adjuster strut assembly through a predetermined distance causes the pawl means adjusting leg to rotate the ratchet wheel and to rotate the adjusting nut in a sense to advance the thrust screw outwardly from the threaded bore in the adjusting nut thereby increasing the axial length of the adjusting strut assembly; and means for applying an axial force to the adjusting strut assembly in a sense to activate the disc brake.

18. A disc brake as claimed in claim 17, wherein the means for applying an axial force to the adjusting strut assembly comprises toggle pin means so arranged in communication with the adjusting strut assembly that pivotal movement of the toggle pin means applies the said axial force to the adjusting strut assembly.

19. Automatic brake-adjusting apparatus comprising: an adjusting strut assembly including adjusting nut means having a threaded bore therein and adjusting nut means having a threaded bore therein and thrust screw means threadingly received within the threaded bore, the adjusting nut means having a circumscribing ratchet wheel and a peripheral groove axially separated one from the other; means for so attaching the adjusting strut assembly to friction pad means of a brake assembly that in use the adjusting strut assembly is caused to move in concert with the friction pad means; pawl means including a first arm communicating with the ratchet wheel, and a second arm communicating with the peripheral groove, and having a pivot between the said first and second arms, and being so disposed that, upon a predetermined axial translation of the adjusting strut assembly, the adjusting strut assembly causes rotational movement of the pawl arms about the pivot sufficient to rotate the ratchet wheel and the adjusting nut means relative to the thrust screw means thereby changing the axial length of the adjusting strut assembly.

20. Automatic brake-adjusting apparatus comprising: an adjusting-strut assembly including adjusting-nut means having a threaded bore therein and thrust-screw means threadingly received within the said threaded bore, the adjusting nut means having a circumscribing ratchet wheel and a peripheral groove axially separated one from the other; means for so attaching the adjusting strut assembly to friction pad means of a brake assembly that in use the adjustingstrut assembly is caused to move in concert with the friction pad means; pawl means including a first arm communicating with the ratchet wheel, a second arm communicating with the peripheral groove and having a pivot therebetween whereby upon a predetermined relative movement between the pivot and the adjusting nut means the first pawl arm is caused to rotate about the pivot sufficiently to rotate the ratchet wheel and the adjusting-nut means relative to the thrust screw means thereby changing the axial length of the adjusting-strut assembly.