Guide Assembly for a Disc Brake

Abstract

A guide assembly for a disc brake, the guide assembly comprising a bore disposed in a disc brake caliper for receiving a guide pin. The bore comprises a first bore portion with a substantially circular cross-sectional profile and a second bore portion with a substantially circular cross-sectional profile arranged sequentially along the length of the bore and tangentially offset such that the bore is defined by the overlap of the first bore portion and second bore portion and has a lens-shaped cross-sectional profile.

Claims

1-15. (canceled)

16. A guide assembly for a disc brake, the guide assembly comprising: a disc brake caliper having a bore for receiving a guide pin, wherein the bore has a substantially circular cross-sectional profile; and a guide bush member mounted in the bore, the guide bush member being a strip of metal formed into a tube having a substantially circular cross-sectional profile, and including first and second thinned strip regions arranged on opposing sides of an inner face of the guide bush member.

17. The guide assembly of claim 16 wherein the first and second thinned strip regions are spaced apart from each other.

18. The guide assembly of claim 16 wherein the first and second thinned strip regions are predetermined locations of the strip that have been broached or machined to be thinner with respect to a remainder of the strip.

19. The guide assembly of claim 16 wherein the first and second thinned strip regions are arranged in a circumferential direction.

20. The guide assembly of claim 16 wherein the guide bush member includes third and fourth sliding strip regions on opposing sides of the inner face of the guide bush member, wherein the third and fourth sliding strip regions extend radially inward further than the first and second thinned strip regions.

21. The guide assembly of claim 20 wherein the third and fourth sliding strip regions are arranged in a tangential direction.

22. The guide assembly of claim 20 wherein the third and fourth sliding strip regions separate the first and second thinned strip regions from each other.

23. The guide assembly of claim 20 wherein the third and fourth sliding strip regions have recesses.

24. The guide assembly of claim 23 wherein the recesses are disposed between and spaced apart from the first and second thinned strip regions and extend radially outward from an inside surface of the guide bush member toward an outside circumference of the guide bush member.

25. A disc brake comprising: a disc brake caliper having a bore, wherein the bore has a substantially circular cross-sectional profile; a guide bush member mounted in the bore, the guide bush member being a strip of metal formed into a tube having a substantially circular cross-sectional profile, and including first and second thinned strip regions arranged on opposing sides of an inner face of the guide bush member; and a disc brake carrier that has a guide pin arranged to be received in the guide bush member.

26. A method of forming a guide bush member for receiving a guide pin of a disc brake, the method comprising: providing a strip of metal; broaching or machining two portions of the strip so as to thin the two portions with respect to a remainder of the strip; and forming the strip into a tube with a substantially circular cross-sectional profile such that the two portions are located on opposing inner faces of the tube.

27. The method of claim 26 further comprising inserting the guide bush member into a bore disposed in a disc brake caliper of the disc brake, wherein the bore has a substantially circular cross-sectional profile.

28. The method of claim 27 wherein inserting of the guide bush member includes inserting the guide bush member into the bore such that the two portions are arranged in a circumferential direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0029] FIG. 1 is an isometric view of a disc brake having the guide assembly of a first embodiment of the present invention and sectioned through the guide assembly;

[0030] FIG. 2 is an enlarged isometric cross-sectional view of the guide assembly shown in FIG. 1;

[0031] FIG. 3 shows a cross-sectional view of the bore of the guide assembly of FIG. 1;

[0032] FIG. 4 shows schematically the cross-sectional profile of the bore of the guide assembly of FIG. 1 normal to the cross-section of FIG. 3;

[0033] FIG. 5 shows a perspective, cross-sectional view of guide assembly of a second embodiment of the present invention;

[0034] FIG. 6 shows a cross-sectional view of the bore of the guide assembly of FIG. 5;

[0035] FIG. 7 shows schematically a cross-sectional profile of the bush of the guide assembly of FIG. 5 normal to the cross-section of FIG. 6;

[0036] FIG. 8 shows a cross-sectional profile a bush of a guide assembly of a third embodiment of the present invention; and

[0037] FIG. 9 shows a perspective, cross-sectional view of the bush of FIG. 8.

DETAILED DESCRIPTION

[0038] As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

[0039] Referring to FIGS. 1 to 7, a guide assembly for a disc brake 8 according the present invention is indicated generally at 10. The guide assembly is provided in the disc brake 8 to slidably mount a caliper 20 of the disc brake with respect to a brake carrier 30 of the disc brake.

[0040] In a first embodiment of the guide assembly 10 as shown in FIGS. 1 to 4, the guide assembly 10 comprises a guide pin 11 along which the caliper 20 can slide and a bore 12 disposed in the caliper for receiving the guide pin.

[0041] The guide pin 11 comprises a fastener to secure the guide pin to the brake carrier. In the first embodiment depicted in FIGS. 1 to 4, the fastener is a bolt 11a that affixes to the brake carrier by screwing into a threaded bore in the brake carrier 30.

[0042] With particular reference to FIG. 2, the guide pin 11 further comprises a guide sleeve 11b at least substantially surrounding the fastening means and over which the caliper 20 slides. The sleeve is a hollow, thin-walled tube with a substantially circular cross-sectional profile. The outer surface of the sleeve may be coated with PTFE to aid the sliding action of the caliper along the guide pin.

[0043] When attached to the brake carrier 30, the guide pin 11 extends in an axial direction A. Direction A is parallel to an axis R of rotation of a rotor 40 (shown in part) of the disc brake 8 and parallel to the transverse axis of the disc brake.

[0044] The bore 12 of the guide assembly 10 is an elongate hole extending from a first caliper side (inboard) 20a to the second caliper side 20b (outboard) of the caliper. The caliper 20 is slidably mounted with respect to the brake carrier 30 by sliding the guide pin 11 through the bore 12. Hence, when the disc brake is actuated, the caliper 20 is able to slide in the axial direction A along the guide pin 11.

[0045] The bore 12 comprises a first bore portion 12a with a first substantially circular cross-sectional profile and a second bore portion 12b with a second substantially circular cross-sectional profile. The first bore portion 12a and second bore portion 12b are arranged sequentially along the bore and offset in a tangential direction Y. Direction Y is tangential to a circle described by the rotation of the rotor 40 of the disc brake 8, perpendicular to the axial direction A, perpendicular to the longitudinal axis of the disc brake and parallel to the direction in which brake pads 50a, 50b are inserted or removed from the brake carrier 30.

[0046] Due to the sequential and tangentially offset arrangement of the first bore portion and second bore portion the cross-sectional profiles of each of the bore portions intersect such that the bore subsequently has a stepped longitudinal profile as shown in FIG. 3 and a quasi-oval cross-sectional profile, where the two bore portions 12a and 12b overlap as shown in FIG. 4. The smallest cross-sectional dimension of the bore extends in the tangential direction Y. The largest cross-sectional dimension of the bore extends in a generally circumferential direction X. Direction X is perpendicular to the axial direction A, perpendicular to the tangential direction Y and parallel to the longitudinal axis of the disc brake.

[0047] To allow the caliper to slide along the guide pin, the diameter of the guide pin 11 is selected to correspond approximately to the tangential diameter of the bore 12. Therefore, the clearance between the bore 12 and the guide pin 11 in the tangential direction is minimised, vibration is reduced and so the undesirable effects of noise, stress and excess wear are restricted. Whereas, the greater clearance provided between the bore and the guide pin in the circumferential direction X provides sufficient lateral play to allow for manufacturing tolerances and deflections of the brake carrier and guide pin due to the braking torque. In practice this results in the guide pin being in potential sliding contact with the lower part of bore portion 12a and the upper part of bore portion 12b only, because these are the surfaces that form the lens-shaped profile.

[0048] The sequential and tangentially offset bore portions 12a, 12b can be formed by machining the first bore portion into the caliper from the first caliper side 20a with a predetermined diameter and depth and machining the second bore portion into the caliper from the second caliper side 20b with a predetermined diameter, depth and offset displacement until they intersect. Due to the circular cross-sectional profiles of the bore portions, the bore portions may be machined using conventional drilling techniques. Hence, the bore 12 can be formed simply, quickly and cost effectively. The bore may be treated or coated after machining in order to improve its wear performance.

[0049] The first bore portion and second bore portion may have different diameters or substantially the same diameter. The first bore portion and second bore portion may have different lengths or substantially the same length. The first bore portion and second bore portion may be offset solely in the tangential direction Y.

[0050] In the first embodiment depicted in FIGS. 1 to 4, the first bore portion 12a has a cross-sectional circular profile with diameter D and length L1, the second bore portion has a cross-sectional circular profile with diameter D and length L2 and the centreline C1 of the first bore portion is offset solely in the tangential direction to the centreline C2 of the second bore portion by displacement O. The centrelines C1 and C2 are substantially parallel. The resulting bore has a length L=L1+L2 and has a quasi-oval, overlapping cross-sectional profile where the minimum diameter in the tangential direction TD=DO and the maximum diameter in the circumferential direction RD=D.

[0051] In geometric terms, the overlap may be considered a symmetric lens, although given the limited offset with respect to the diameters of the bores, the shape 25 approximates sufficiently to an oval of the prior art bush to be functionally equivalent.

[0052] In addition to the features of the first embodiment of the guide assembly a second embodiment of the guide assembly as shown in FIGS. 5 to 7 also includes a bush 13 to guide the guide pin within the bore. This arrangement is preferred as it improves the durability and serviceability of the guide assembly 10. The bush comprises a first bush member 13a and a second bush member 13b. The first bush member 13a has a substantially circular cross-sectional profile that is configured to form a close fit with the first bore portion 12a and act as an inner liner in the first bore portion. Likewise, the second bush member 13b has a substantially circular cross-sectional profile that is configured to form a close fit with the second bore portion 12a and act as an inner liner in the second bore portion. For heavy vehicle applications the internal diameter of the bush members are typically in a range of 25-40 mm.

[0053] Due to the substantially circular profiles of the bore portions, the guide bush members may comprise solid sleeved, hollow tubular bush members having a substantially circular cross-sectional profile. The bush members may be manufactured from steel, bronze, plastic, rubber or a composite of any of these, and may include a low friction coating such as PTFE. The bushes may have a plain inner surface or a suitable pattern of depressions to assist in the sliding of the caliper. In a preferred embodiment the bushes may be the same as the bushes used for a circular guide pin arrangement used at the circumferentially opposite side of the brake caliper on the brake (see below).

[0054] Due to the sequential and offset arrangement of the bore portions 12a, 12b, the cross-sectional profiles of the first bush member 13a and the second bush member 13b overlap such that the bush within the bore has a stepped longitudinal profile (see FIG. 6) and an quasi-oval cross-sectional profile (see FIG. 7).

[0055] The first bush member 13a may be inserted into the first bore portion 12a from the first caliper side 20a. The second bush member 13b may be inserted into the second bore portion 12b from the second caliper side 20b.

[0056] When a bush is provided in the bore, the diameter of the guide pin is selected to correspond to the smallest cross-sectional dimension of the bush overlap. Accordingly, the clearance gap between the guide pin and the bush in the tangential direction Y is minimal and so vibration, noise, stress and excess wear are reduced. The largest cross-sectional dimension of the bush provides a greater clearance gap between the guide pin and the bush in the circumferential direction X to allow for play due to manufacturing tolerances, heat expansion and brake torque.

[0057] The embodiments of the guide assembly are suitable for use in any type of disc brake, including pneumatic, hydraulic, electrically and mechanically actuated disc brakes. However, the embodiments are believed to be particularly beneficial in air-actuated disc brakes for heavy commercial vehicles, where rotors typically have a diameter of between 30-60 cm, meaning that the torque and heat effects may be more significant than in hydraulic disc brakes for smaller, lighter vehicles.

[0058] FIG. 1 depicts an embodiment of a disc brake 8. The disc brake comprises a caliper 20 slidably mounted with respect to a brake carrier 30 by two guide pin assemblies. The caliper 20 has a housing typically formed from cast iron or steel. The brake carrier 30 is typically also formed from cast iron or steel.

[0059] The brake carrier 30 carries an inboard brake pad 50a and an outboard brake pad 50b. A rotor 40, rotatable about an axis extending in the axial direction A, is positioned between the brake pads. An air actuator (not shown) is provided to move the inboard brake pad 50a into frictional contact with the rotor. When the inboard brake pad 50a is pushed towards and contacts the rotor, the caliper 20 slides inboard along the guide pins of the guide pin assemblies. As the caliper slides inboard it moves the outboard brake pad 50b towards the rotor. Hence, the rotor 40 becomes clamped between the inboard and outboard brake pads and the rotation of the rotor is frictionally inhibited. So as to accommodate installation and deflection constraints, the first guide assembly is a guide assembly 10 according to the first embodiment of the invention in which the bore has a lens-shaped cross-sectional profile. The second guide assembly is a conventional guide assembly 6 comprising a guide pin (not shown), a bore (not shown) with a circular cross-sectional profile to receive the guide pin and at least one guide bush member (not shown) with a circular cross-sectional profile to guide the guide pin within the bore. These bushes may be the same as the first and second bush members 13a and 13b, thereby minimising the number of parts required to assemble and service the brake. The guide pin of the second guide assembly 6 is preferably longer than the guide pin of the first guide assembly 10 to provide a more positive attachment and guidance to the brake carrier and location for the caliper.

[0060] In an alternative embodiment of guide assembly, a conventional cylindrical bore (not shown) may be formed in the caliper by a machining operation and at least one bush 113 shown in FIGS. 8 and 9 then inserted therein. The bush is initially provided as a rectangular plate of suitable material (e.g., brass). The plate is thinned at predetermined locations 115 in a broaching or other suitable machining operation, and may also have recesses 117 formed in a sliding surface 119 thereof. The plate is then formed into the tubular bush illustrated in FIGS. 8 and 9 such that the thinned locations are on opposing sides of an inner face of the bush, and act in conjunction with a circular guide pin to provide the required amount of play in the X direction.

[0061] Advantageously, the guide pin receiving bore with a lens-shaped cross-sectional profile allows for free sliding of a guide pin and eliminates the need for an oval bush formed by a costly process, such as sintering. The manufacture of the guide pin receiving bore with the lens-shaped cross-sectional profile in overlap can be achieved in a simple and cost effective manner. In addition, the construction and insertion of guide bush members in a guide pin receiving bore having sequential and tangentially offset bore portions so as to provide a guide bush within the guide pin receiving bore with the lens-shaped cross-sectional profile is straightforward and inexpensive.

[0062] Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.