Patent Application
20130199879
The present invention relates to a guide pin for slidably mounting a caliper to a brake carrier of a disc brake, and a disc brake incorporating such a guide pin.
Pneumatic disc brakes are frequently used on heavy vehicles. One typical type of disc brake used is a reaction beam air disc brake, an example (among many) is the Meritor air disc brake D-ELSA 2 indicated generally at 8 in
The conventional guide pins 22 and 24 comprise a guide sleeve 28 and 26 and a bolt 30 and 32 respectively. The bolt is received in the sleeve and attaches the guide pin to the brake carrier 10. The inner surface of the sleeve is a close fit to the bolt, approximately 0.2 to 0.4 mm clearance radially. Two bores are formed in the caliper and bushes 34 and 36 are positioned in the bores. The bushes 34 and 36 receive the respective guide pin. This arrangement permits the caliper to slide on the guide pin, and as such brakes of this type are often described as “sliding caliper”.
A concern with conventional guide pins is the amount of machining required to form the sleeve. A further concern is the amount of metal required by such sleeves, with the associated cost and weight implications.
In at least one embodiment, an aim of the present invention is to alleviate at least some of the problems associated with the guide pins of the prior art.
Accordingly, in a first aspect the invention provides a guide pin for slidably mounting a caliper to a brake carrier of a disc brake, the guide pin having: a fastener for connecting the guide pin to the brake carrier; a hollow tube surrounding the fastener providing a surface along which the caliper can slide; and an elongate insert positioned in the hollow tube occupying a space between the hollow tube and the fastener.
Advantageously the provision of an elongate insert means that the hollow tube can be formed to a near net shape, which reduces the amount of machining required and therefore the waste produced when manufacturing the guide pin, which in turn reduces the cost of manufacture. Provision of an insert also means that additional methods of manufacture are available for manufacture of the tube.
The following describes features that can be optionally combined with the features of the guide pin of the first aspect, either individually or where appropriate in combination.
The elongate insert may be abuttable against the hollow tube so as to maintain the fastener, hollow tube and elongate insert in substantially fixed relative positions when the fastener is tightened.
The elongate insert may be deformable such that it is capable of dampening vibration. A problem with guide pins of the prior art is that when the guide pin or components of the guide pin wear, the guide pin contributes to rattle of the brake, which can be of concern to the user. The use of an elongate insert with damping properties alleviates this problem by reducing and dampening the noise due to rattling of the guide pin. Further advantageously, such a deformable elongate insert improves the robustness of the guide pin to vibration loading.
The elongate insert may be sufficiently deformable and arranged such that sufficient tightening of the fastener to a brake carrier deforms the elongate insert so that the elongate insert contacts the hollow tube. The force exerted by the deformation of the elongate insert on the hollow tube may be sufficient to maintain or partially maintain the elongate insert, the hollow tube and the fastener in fixed relative positions when the fastener is tightened. The elongate insert may alternatively or additionally be held to the hollow tube using either an interference fit between the elongate insert and the hollow tube or using an adhesive.
In the case of an elongate insert sufficiently deformable and arranged such that sufficient tightening of the fastener deforms the elongate insert so that the elongate insert contacts the hollow tube, the tightening load required to cause the elongate insert to deform may be a load equal to or greater than 100 kN. Alternatively, it may be a load equal to or greater than 150 kN. Further alternatively, it may a load equal to or greater than 170 kN.
The hollow tube may be of substantially constant cross section. Advantageously, a substantially constant cross section further reduces the amount of machining required to manufacture the guide pin and offers potential alternative manufacturing methods.
A collar can be positioned at an end of the hollow tube remote from a head of the fastener to contact the brake carrier. The collar may be positionable within a space defined by the hollow tube. The collar may have a flange, and the flange may be positionable axially between the hollow tube and the brake carrier. The collar may be made from mild steel, or stainless steel. The collar may be provided with a protective finish, for example a corrosion resistant coating.
In some embodiments, a washer may be positionable between a head of the fastener and the elongate insert. The washer may be made from mild steel.
The fastener may be a bolt. In some embodiments, the fastener may be a flange-head bolt.
The elongate insert may be made of plastics. Advantageously, manufacturing the elongate insert from a material such as plastic reduces the overall weight of the guide pin compared to comparably sized guide pins of the prior art. This is particularly important for guide pins that are used on disc brakes of heavy vehicles where weight reduction of the vehicle can be advantageous in improving fuel economy and reducing carbon dioxide (CO2) emissions.
The elongate insert may be made from polyhexamethylene adipamide, commonly known as Nylon 66.
In a second aspect, the invention provides a guide pin for slidably mounting a caliper to a brake carrier of a disc brake, the guide pin having: a fastener for connecting the guide pin to the brake carrier; a hollow tube surrounding the fastener providing a surface along which the caliper can slide; and a connector for abutting a surface of the hollow tube; wherein the clearance between the hollow tube and the fastener is greater than 0.5 mm radially.
Advantageously, such spacing between the hollow tube and the fastener means that the guide pin of the second aspect has reduced weight compared to a conventional guide pin of comparable size, and the machining required to manufacture the guide pin is reduced because the components of the guide pin can be formed to net or near net shape. This has the advantage of reducing both waste and the cost of manufacture.
In other embodiments the clearance may be greater than 0.6 mm radially, 0.7 mm radially, 0.8 mm radially, 0.9 mm radially, 1 mm radially or 2 mm radially.
The following describes features that can be optionally combined with the guide pin of the second aspect of the invention.
The connector may be a washer. Alternatively, the connector may be a flange formed as part of the fastener. For example, the fastener may be a flange head bolt.
A collar can be positioned at an end of the hollow tube remote from a head of the fastener to contact the brake carrier. The collar may be positionable within a space defined by the hollow tube. The collar may have a flange and the flange may be positionable axially between the hollow tube and the brake carrier. The collar may be made from mild steel or stainless steel. The collar may be provided with a protective finish, for example a corrosion resistant coating.
The following describes optional features of the first and the second aspect of the invention.
An outer surface of the hollow tube may have a PTFE (polytetrafluoroethylene) coating.
The cross section of the hollow tube may be non-circular, for example oval. Alternatively, the cross section of the hollow tube may be circular.
In a third aspect, the invention provides a disc brake having a brake carrier and a guide pin according to the first or the second aspect.
The fastener may be screwed into the brake carrier so as to compress the elongate insert such that the fastener, hollow tube, and insert are maintained in substantially fixed relative positions.
The disc brake may have two guide pins, one of which is shorter than the other. The shorter guide pin may have an oval cross section and the longer guide pin may have a circular cross section.
The disc brake may further comprise a caliper slidably mounted to the brake carrier by one or more guide pins.
A vehicle may have the guide pin according to the first or the second aspect.
In a fourth aspect, the invention provides a kit of parts for assembly of a guide pin for slidably mounting a caliper to a brake carrier of a disc brake, the kit having: a fastener for connecting the guide pin to the brake carrier; a hollow tube for surrounding the fastener to provide a surface along which the caliper can slide; and an elongate insert for positioning in the hollow tube to occupy a space between the hollow tube and the fastener.
The fourth aspect may optionally have any of, or where compatible combination of, the optional features of the first aspect.
A kit of parts for assembly of a guide pin for slidably mounting a caliper to a brake carrier of a disc brake, may have; a fastener for connecting the guide pin to the brake carrier; a hollow tube for surrounding the fastener so as to provide a surface about which the caliper can slide; and a connector for abutting a surface of the hollow tube; wherein the clearance between the hollow tube and the fastener is greater than 0.5 mm radially.
The kit of parts may optionally have any of, or where compatible any combination of, the optional features of the second aspect.
Embodiments of the invention will now be described, by example only, with reference to the accompanying drawings in which:
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.
Referring to
Surrounding the fastener 42 is a hollow tube 44. In this embodiment, the hollow tube 44 is an elongate thin walled tube made from either mild steel (e.g. with a suitable anti-corrosion treatment such as a galvanised coating) or stainless steel. The hollow tube 44 may have a PTFE coating on its outer surface 45. The hollow tube 44 of the present embodiment has a substantially constant circular cross section. In this embodiment, the hollow tube 44 extends in the axial direction of the fastener 42 and extends past the head of the fastener 42, such that the head of the fastener is axially within the end of the hollow tube 44. However, in alternative embodiments, the head of the fastener 42 may be flush with the end of the hollow tube 44 or may protrude from the hollow tube 44. In a further alternative, the cross section of the hollow tube 44 is oval, or any other suitable shape. In further alternative embodiments the cross section of the hollow tube may not be constant, for example it may have a step on the inner or outer surface of the hollow tube 44.
Positioned at the end of the hollow tube 44, remote from the head of the fastener 42, is a collar 46, which in this example is made from mild steel. A recess 50 is formed in the brake carrier 10 and this recess provides a seat for the collar 46. The collar 46 is annular and has a body and a flange. The body of the collar 46 fits within a radial space formed between the fastener 42 and the hollow tube 44, and the flange of the collar 46 extends over the end of the hollow tube 44 so as to be positioned axially between the brake carrier and the hollow tube. The collar 46 substantially seals the hollow tube 44 and improves the positional fit between the brake carrier 10 and the guide pin 40. The collar 46 also performs the function of locating the fastener 42, in this example concentrically, in the hollow tube 44 and against the brake carrier 10. In alternative embodiments, the collar 46 may not have a flange, and/or the brake carrier 10 may not have a recess 50 to provide a seat for the collar 46. In a further alternative, the collar 46 may be positioned external to the hollow tube 44 so that the collar 46 surrounds the outer side 45 of the hollow tube 44 at one end of the hollow tube 44.
A washer 52 is positioned at an end of the fastener remote from the collar 46. The washer 52 is concentrically aligned with the fastener 42 and the hollow tube 44, and the washer 52 contacts a head of the fastener 42. The washer 52 is made from mild steel in this embodiment. In alternative embodiments, the use of the washer may not be required, and in such examples the fastener 42 may be a flange head bolt.
An elongate insert 48 is positioned axially between the collar 46 and the washer 52. In this embodiment, the elongate insert 48 abuts the collar 46 and the washer 52, and surrounds the fastener 42. In other embodiments the elongate insert 48 may not fully surround the fastener 42 and/or may be provided with perforations, ridges or other formations. In this example, the elongate insert 48 is made from plastic, a suitable plastic being polyhexamethylene adipamide, commonly known as Nylon 66. The elongate insert 48 is annular and the fit between the elongate insert 48 and the hollow tube 44 is a clearance fit and the extent of the clearance depends on the plastic used for the elongate insert 48, the dimensions of the hollow tube 44 and the dimensions of the elongate insert 48.
In this embodiment, the dimensions of the elongate insert 48 should be such that the elongate insert 48 can be compressed in an axial direction, and a compression load caused by the tightening of the fastener 42 causes the elongate insert 48 to deform so as to contact the inner surface of the hollow tube 44, and hold the hollow tube 44 to the elongate insert 48. In alternative embodiments, the deformation of the elongate insert 48 may not cause or wholly cause the hollow tube 44 to be attached to the elongate insert 48, and instead or in addition an interference fit or an adhesive between the elongate insert 48 and the hollow tube 44 may be used.
To connect the guide pin 40 to the brake carrier 10, the guide pin 40 is firstly assembled. In one method of assembly of the guide pin, the hollow tube 44 is placed over the collar 46 such that the body of the collar 46 is positioned within the hollow tube 44 and the flange of the collar 46 extends over an end of the hollow tube 44. The elongate insert 48 is then inserted into the hollow tube 44. Washer 52 is then placed on the elongate insert 48 and the fastener 42 is positioned in a receiving hole formed by the collar 46, elongate insert 48 and hollow tube 44. It will be appreciated that there are other ways in which assembly can be achieved.
The fastener 42 is then screwed into a receiving hole in the brake carrier 10. As the fastener is screwed into the receiving hole, tightening of the fastener 42 applies a compressive load to the elongate insert 48 in an axial direction of the elongate insert 48. In this example the compressive load applied once the fastener 42 is screwed to its limit in the brake carrier 10 is approximately 170 kN, which is the current pre-load used for guide pins 40 of the prior art of a comparable size. At such a compressive load, the elongate insert 48 reduces in axial length but expands in a radial direction, such that the volume of the deformed elongate insert 48 is substantially similar to the volume of the undeformed elongate insert 48. The increase in radial width of the deformed elongate insert 48 causes the elongate insert 48 to push against the inner wall of the hollow tube 44, the elongate insert 48 exerting a sufficient force on the hollow tube 44 to maintain the hollow tube 44 in position.
In use, once the guide pin 40 is attached to the brake carrier 10, a caliper 12 will be mounted on the guide pin 40. The caliper 12 is mounted on the guide pin 40 by positioning one or more bushes 34, 36 into a bore in the caliper 12. These bushes may be steel, bronze, plastic or rubber bushes, or a composite of any of these. The guide pin 40 is greased, and the caliper 12 is slid onto the guide pin 40. In the case of a disc brake 8 having two guide pins 40, for example the Meritor Air Disc Brake D-ELSA 2, ELSA 225 H, ELSA 195 C or ELSA 175 S, one of the guide pins 40 may be shorter than the other guide pin. The shorter guide pin in some cases may be guided in an “oval” (non-round) bush, or have an oval cross section so as to accommodate brake deflection during braking One bush may be positioned in the receiving hole that receives the shorter guide pin, and two bushes may be positioned in the receiving hole that receives the longer guide pin. Both of the pins may be pins according to the invention, or one of the pins may be a conventional pin and the other pin may be a pin according to the invention.
Advantageously, the multi-part construction of the guide pin 40 means that the component parts can be manufactured to a net or near net shape which means there is little machining required and therefore little material wastage. In addition, the use of a plastic elongate insert 48 permits a material of lower density than the hollow tube 44 to be used, in this example Nylon 66, which reduces the weight of the guide pin 40 compared to the guide pins of the prior art. The use of Nylon 66, or another suitable plastic or material has the advantage of exhibiting damping properties which results in reduced rattling when the or components of the guide pin wear, and the construction of the guide pin may be more robust to vibration loading.
An alternative embodiment to the one described above is shown in
Referring to
Advantageously, this embodiment provides a guide pin of reduced weight compared to a comparably sized conventional guide pin. This embodiment also permits component parts of the guide pin to be made to net or near net shape, which reduces the amount of machining required and therefore the material wastage, cost and time to manufacture.
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 12154431.6 | Feb 2012 | EP | regional |
