GB2171158A - Automatic adjusting apparatus for a disc brake - Google Patents

Abstract

A disc brake comprises a brake piston (8) which is slidably accommodated within a brake cylinder and is actuatable by means of a hydraulic actuating device (not shown) and a mechanical actuating device (36, 38, 39), with an adjusting member arranged between the brake piston and the mechanical actuating device and comprising two adjusting elements (14, 20) which are coupled to each other through a thread without self-locking engagement. A friction clutch is formed by conical friction surfaces (24, 26) on adjusting element (20) and part (34) of handbrake piston (30) and serves to retain one of the adjusting elements in the event of mechanical actuation. in order to render possible larger tolerances in the region of the clutch in regard of coaxial alignment, the piston part (34) is mounted on a second piston part (28) for radial movement relative thereto. <IMAGE>

Description

SPECIFICATION Automatic adjusting apparatus for a disc brake This invention relates to an automatic adjusting apparatus for a disc brake, said disc brake comprising a brake piston which is slidably accommodated within a brake cylinder for the purpose of actuation of a brake shoe and which is actuatable by means of a hydraulic and a mechanical actuating device; the adjusting apparatus including an extensible adjusting member which is arranged between the said brake piston and the said mechanical actuating device and comprises two adjusting elements (adjusting spindle and adjusting nut) coupled to each other through a thread free of nonreversibility, and a friction clutch furnished with conical friction surfaces and serving to retain one of the said adjusting elements at the moment of mechanical actuation.

In the automatic adjusting apparatus described in our copending patent application No. 8423683 (Serial No. 2147671), an adjusting spindle provided with a coarse thread free of nonreversibility is coupled non-rotatablyto the bottom of the brake piston. A corresponding mating thread is provided in an adjusting nut which is positioned on the adjusting spindle. At its end facing away from the piston, the adjusting nut is furnished with a radial attachment which forms a conical friction surface. A further conical friction surface which is provided at a handbrake piston interacts with the aforementioned conical friction surface. Operation of this arrangement is very largely satisfactory.Manufacturing problems may, however, originate from the requirement that a highly precise coaxial alignment has to be observed for the parts of the friction clutch, which is difficult to realise in manufacture.

It is, therefore, an object of the present invention to create an automatic adjusting apparatus for disc brakes, of the aforementioned type, in which the admissible tolerances regarding the coaxial alignment in the range of the clutch can be increased.

According to the present invention there is provided an automatic adjusting apparatus for a disc brake, said disc brake comprising a brake piston which is slidably accommodated within a brake cylinder for the purpose of actuation of a brake shoe and which is actuatable by means of a hydraulic and a mechanical'actuating device; the adjusting apparatus including an extensible adjusting member which is arranged between the said brake piston and the said mechanical actuating device and comprises two adjusting elements (adjusting spindle and adjusting nut) coupled to each other through a thread free of nonreversibility; and a friction clutch furnished with conical friction surfaces and serving to retain one of the said adjusting elements at the moment of mechanical actuation, characterised in that one element of said friction clutch has a divided configuration and is provided with an automatic mismatch balance.

Thanks to the inventive solution, the tolerances is coaxial alignment are allowed, in a simple manner, to be selected sufficiently large so as to render possible an economically reasonable manufacture.

According to an advantageous version of the present invention, it is envisaged that an element of a handbrake piston, in particular a clutch disc, straddles a friction surface of the adjusting nut from the outside and that the handbrake piston is designed formed in two parts. In another advantageous embodiment, one part of the handbrake piston is furnished with a supporting element on which the clutch disc comprising the other part, is arranged with radial play. In this configuration, the supporting element is, expediently, constituted by an axial extension at the one part of the handbrake piston, which extension projects into an opening of the clutch disc.

The clutch element formed at the handbrake piston whereby it may itself be considered as divided into two parts, is coupled together again by means of a spring element, with a spring which urges the clutch disc part of the handbrake piston against the other part of the handbrake piston being, expediently, supported at the axial extension.

Embodiments of the invention will now be described with reference to the accompanying sub stantially sectional drawing.

Since except for the clutch developed further by the present invention the adjusting apparatus very largely corresponds to that described in the aforementioned patent application, the description which follows is limited to the essential parts of the adjusting apparatus with their functions. Reference should be made to the description in aforementioned patent application for supplementary information and the basic mode of operation of the adjusting apparatus.

The only figure of the accompanying drawing shows a longitudinal section through a part of a disc brake, only one side of the brake without lining and without disc is, however, illustrated therein. In a brake housing 2, a cylinder bore 4 is provided which is substantially configured with two steps. A brake piston 8 is axially slidably accommodated in bore section 6, which has the largest diameter. Said brake piston 8 has a cup-shaped design, with an open end being positioned within the cylinder bore 4, whereas its closed end projects out of the cylinder bore 4 in order to press against a brake shoe (not shown in the drawing).A so-called rollback seal 10 is positioned in a circular groove 12 of the brake housing 2 in a manner generally known in the art and serves the purpose of sealing off the brake piston 8 with respect to the cylinder bore and, in addition, effects the return of the brake piston 8.

An adjusting spindle 14which extendscoaxially through the cavity formed by the brake piston and up into a bore section 16 having a reduced diameter is coupled non-rotatably to the bottom of the brake piston 8. Said adjusting spindle 14 is furnished with a coarse thread 18 free of nonreversibility (without self-locking engagement). An identical mating thread is provided in an adjusting nut 20 which is located on said adjusting spindle 14. The adjusting nut has a substantially cylindrical shape, but is furnished, at its end facing away from the piston, with a radial attachment 22 which forms a conical friction surface 24. In a special version (not shown in the drawing), the cylindrical main portion and the radial attachment 22 can be designed as two parts and be coupled to each other.

A further conical friction surface 26 which is provided at a handbrake piston 28 interacts with the aforesaid conical friction surface 24. The handbrake piston 28 comprises a cylindrical section 30 which is slidably accommodated within a bore section 32 having a further reduced diameter, and a section 34 which extends substantially in radial direction and at which the aforesaid friction surface 26 is provided.

The section 34 of the handbrake piston 28 straddles the radial attachment 22 of the adjusting nut 20 from the outside, with the handbrake clearance S remaining in between the friction surfaces 24, 26.

Beyond the handbrake piston 28, a mechanical actuating device comprises, in addition, an eccentric apparatus 36 which acts on the handbrake piston 28 through a tappet 39. Said eccentric apparatus 36 consists of a shaft 38 which is rotatably supported in a bore 40 extending transversely of the cylinder bore 4 and to which a handbrake lever is coupled (in a way not shown in the drawing). A recess 42 is provided in said shaft 38 in which one end of the tappet 39 is disposed. The other end of said tappet is received in a recess 44 formed in the handbrake piston 28. Said handbrake piston 28 is retained by means of an anti-rotation guard which is comprised, in the embodiment shown in the drawing, of at least one radial attachment 74 provided at the handbrake piston and extending into a recess 60 in the housing.

The part of the adjusting nut 20 facing the brake piston 8 carries a four-point ball bearing 46 or a three-point ball bearing whose internal ball race is formed by the adjusting nut 20 itself in the embodiment illustrated in the drawing. The external ball race 48 of the ball bearing 46, which ball race 48 is divided into two parts along a plane running at right angles to the axis of rotation, is in abutment against a shoulder 50 of a ring 52 which is fastened in the brake housing 2 and extends in axial direction between the adjusting nut 20 and the wall of the brake piston 8. Against the other side of the external ball race 48, a spring 54 is applied which takes support at a bushing 56 (cup-shaped housing) fixed to said ring 52.

The cylindrical section 30 of the handbrake piston 28 is furnished with an axial extension 80 which projects through a through opening 82 provided in the section 34 which is configured as a clutch disc and extends substantially in radial direction. In this context, the extension 80 and the opening 82 are sized such in diameter that there exists a radial play which permits of an automatic mismatch balance.

The length of the extension 80 is selected in a way that said extension 80 projects from the opening 82 still a sufficient distance on the opposite side so as to allow a spring element 84 to be supported on it. At the outer circumference, said spring element 84 is applied against the clutch disc 34 urging the latter against the cylindrical section 30 of the handbrake piston 28. One spring or a plurality of springs fixed to the outer circumference may also act on the clutch dics.

Claims (6)

1. An automatic adjusting apparatus for a disc brake, said disc brake comprising a brake piston which is slidably accommodated within a brake cylinder for the purpose of actuation of a brake shoe and which is actuatable by means of a hydraulic and a mechanical actuating device; the adjusting apparatus including an extensible adjusting member which is arranged between the said brake piston and the said mechanical actuating device and comprises two adjusting elements (adjusting spindle and adjusting nut) coupled to each other through a thread free of nonreversibility, and a friction clutch furnished with conical friction surfaces and serving to retain one of the said adjusting elements at the moment of mechanical actuation, characterised in that one element (28) of said friction clutch has a divided configuration and is provided with an automatic mismatch balance.

2. An automatic adjusting apparatus as claimed in claim 1, with an element of a handbrake piston, in particular a clutch disc, straddling a friction surface of the said adjusting nut from the outside, characterised in that the said handbrake piston (28) is formed in two parts.

3. An automatic adjusting apparatus as claimed in claim 2, characterised in that one part of the said handbrake piston (28) is furnished with a supporting element (80) on which the said clutch disc comprising the other part is arranged with radial play.

4. An automatic adjusting apparatus as claimed in claim 3, characterised in that the said supporting element (80) is constituted by an axial extension of the one part of said handbrake piston (28), which said extension projects into an opening (82) of the said clutch disc.

5. An automatic adjusting apparatus as claimed in claim 4, characterised in that a spring element (84) which urges the said clutch disc against the one part of said handbrake piston (28) is supported at the said axial extension (80).

6. An automatic adjusting device for a disc brake substantially as herein described with reference to and as illustrated in the accompanying drawing.