Air disc brake pad

Abstract

An air disc brake pad 10 for inserting into a brake pad carrier, the brake pad including a backplate 14 and a friction material 16 mounted on one side of the backplate, the pad periphery 30 including

Description

08 03 24 The present invention relates to an air disc brake pad and to a method of providing a poka-yoke to prevent incorrect insertion of a brake pad to a brake caliper. BACKGROUND TO THE INVENTION 5 In an air disc brake for a commercial vehicle, including a heavy goods vehicle, brake calipers actuate brake pads against a rotating disc during braking. The brake pads are a wearable component and need replacing when the friction material on the brake pad wears to a predefined limit. It is important that the replacement brake pads are assembled correctly to the brake caliper. 10 As shown in Figure 1, brake calipers include brake pad carriers which receive the brake pads. Brake pads may be common inboard and outboard brake pads (i.e. can be inserted on both the inside face and outside face of the brake disc) and symmetrical. This means it is possible for the brake pads to be assembled in the brake pad carrier incorrectly, where the pad may be inserted with the backplate facing the brake disc. 15 To prevent this, it is known to poka-yoke (i.e. fool-proof) the pad assembly. As seen in DE102004002571A1, this is generally achieved by providing a finger and notch arrangement. The interface at the carrier (e.g. the ‘finger’) requires additional cast material on the carrier. The additional cast material increases both the weight of the carrier and the 20 cost. Furthermore, the form and location of the finger can increase the material stresses during brake operation, reducing the life of the carrier. Some solutions may also entail having either a non-symmetrical pad or carrier. This can result in unusual pad wear patterns or non-uniform stresses when the brake is operating in opposite directions (e.g. where brake calipers are fitted to different sides of a vehicle). 25 Furthermore, if the permissible pad and disc wear allowance is exceeded, then the worn pad can be at risk of slipping between the disc and brake pad carrier, thereby being ejected from the brake. This is shown in Figures 2a and 2b. It is an object of the present invention to reduce or substantially obviate the aforementioned problems. 30 STATEMENT OF INVENTION 08 03 24 According to the present invention there is provided an air disc brake pad for inserting into a brake pad carrier, the brake pad including a backplate and a friction material mounted on one side of the backplate, the pad periphery including an inner side, an 5 outer side and first and second ends; in which at least a portion of the pad periphery includes a thickened edge, the thickened edge extending in a direction opposing the friction material; and at least one rear protrusion is provided, the at least one rear protrusion extending from the backplate in a direction opposing the friction material; 10 in which the depth of the at least one rear protrusion being greater than the depth of the thickened edge; in which the air disc brake pad includes first and second abutment tabs for providing horizontal abutment with the brake pad carrier, the first abutment tab extending from the first end and the second abutment tab extending from the 15 second end; and in which at least a portion of the thickened edge extends along at least a portion of one of the first and second ends and a corresponding abutment tab. The at least one rear protrusion can be used to prevent the brake pad being inserted 20 into a brake caliper back-to-front (i.e., with the backplate facing the brake disc). The rear protrusion may be received in a corresponding space in a backplate facing side of the brake caliper. The depth of the at least one rear protrusion may cause the rear protrusion to abut a top edge of the brake disc during insertion if the brake pad is inserted with the backplate facing the brake disc, preventing further insertion of the 25 brake pad. This poka-yokes or “fool-proofs” the correct method of assembly. The insertions of the brake pad is poka-yoked without requiring additional material on the brake pad carrier. Providing a thicker edge on the backplate mitigates the risk of the brake pad slipping 30 between the brake disk and brake pad carrier if the permissible pad and disc wear allowance is exceeded. The at least one rear protrusion may further mitigate the risk of the brake pad slipping between the brake disk and brake pad carrier. 08 03 24 The at least one rear protrusion may have a depth of at least 4 mm. For example, the at least one rear protrusion may have a depth of at least 5 mm. For example, the at least one rear protrusion may have a depth of at least 6 mm. The thickened edge may have a depth of at least 3 mm. For example, the thickened 5 edge may have a depth of at least 4 mm. For example, the thickened edge may have a depth of at least 5 mm. The at least one rear protrusion may protrude from the thickened edge. The thickened edge and the at least one rear protrusion may be spaced apart. In other words, a gap may be provided between the at least one rear protrusion and the 10 thickened edge. The at least one gap may be a region of the backplate which has a thickness equal to the rest of the backplate. In other words, there may be at least one gap provided in which the edge is not thickened. The at least one gap may reduce the weight and material required during manufacture of the backplate. 15 The at least one rear protrusion may be disposed substantially adjacent to the inner side of the backplate. The at least one rear protrusion may be disposed substantially adjacent to the first and / or second end of the backplate. Where the at least one protrusion is disposed substantially adjacent to the inner side and one or both of the first and second ends, the rear protrusion can be received in a space in a backplate 20 facing side of a number of brake calipers already on the market. In other words, the brake pad can be inserted into existing brake pad carriers without altering the brake pad carrier. The at least one rear protrusion may be positioned substantially adjacent to the first 25 and / or second end of the backplate to allow the pads to be stacked on top of each other whilst keeping face of the friction material are parallel to each other. The at least one rear protrusion may have a depth which allows the pads to be stacked on top of each other whilst keeping face of the friction material are parallel to each other. For example, the depth of the at least one rear protrusion may be less than the thickness 30 of the friction material. The thickened edge may be disposed adjacent to at least one of the first and second ends of the backplate. 08 03 24 During use, the first and second abutment tabs may provide horizontal abutment with brake pad carrier. During use, the first and second abutment tabs may rest on at least one brake pad carrier horn of the brake pad carrier. Providing the at least one rear protrusion in a space in a backplate facing side of brake 5 pad calipers may mitigate the distance the brake pad can drop should the abutment tabs fracture. For example, the abutment tabs may fracture when under excessive vibrational loading. Reducing the distance that the brake pad drops following the fracture may ensure alignment between the brake pad and disc is maintained. At least a portion of the thickened edge may be disposed at the point at which the 10 brake pad horizontally abuts the brake pad carrier. At least a portion of the thickened edge is disposed on the first and second abutment tabs. At least a portion of the thickened edge may be substantially L-shaped. At least a portion of the thickened edge extends along at least a portion of one of the first and second ends and corresponding abutment tab. 15 The brake pad may be substantially symmetrical. The symmetry may be about a central vertical axis extending from the inner side to the outer side. The symmetry of the brake pad may mitigate against the development of unusual wear patterns. The symmetry between the first and second ends may mitigate against non-uniform stresses being applied to the brake pad when the brake is operating in opposite 20 directions (e.g. where the brake pad is fitted to an opposite side of a vehicle). The brake pad may be provided as part of a pair of common inboard and outboard pads. The brake pads may be for original equipment brake assemblies. The brake pads may be replacement brake pads. According to an unclaimed second aspect of the present invention, there is provided 25 an air disc brake pad for inserting into a brake pad carrier, the brake pad including a backplate and a friction material mounted on one side of the backplate, the pad periphery including an inner side, an outer side and first and second ends; in which the brake pad carrier includes first and second abutment tabs for providing horizontal abutment with the brake pad carrier, the first abutment tab 30 extending from the first end and the second abutment tab extending from the second end; and at least one rear protrusion extending from the backplate in a direction opposing the friction material. 08 03 24 The at least one rear protrusion can be used to prevent the brake pad being inserted into a brake caliper back-to-front (i.e., with the backplate facing the brake disc). 5 As described above with reference to the first aspect of the present invention, providing the at least one rear protrusion in a space in a backplate facing side of brake pad calipers may mitigate the distance the brake pad can drop should the abutment tabs fracture. For example, the abutment tabs may fracture when under excessive vibrational loading. Reducing the distance that the brake pad drops following the 10 fracture may ensure alignment between the brake pad and disc is maintained. The brake pad may have any feature or combination of features described in the first aspect of the present invention. According to a third aspect of the present invention, there is provided a method of providing a poka-yoke to prevent incorrect assembly of an air disc brake pad to a brake 15 caliper; the method comprising providing an air disc brake as described in the first aspect of the present invention, in which the at least one rear protrusion can only be accommodated by a corresponding gap in a backplate facing side of the brake caliper. The method can be used to prevent incorrect assembly of a brake pad to a brake caliper. The method cab be used to prevent a brake pad being fitted to a brake pad 20 caliper where the backplate faces the brake disc (i.e. back-to-front). BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the present invention, and to show more clearly how it 25 may be carried into effect, reference will now be made by way of example only to the accompanying drawings, in which: Figure 1 shows a conventional brake pad inserted into a conventional brake pad carrier; 30 Figures 2a and 2b show plan views of conventional brake pads in brake calipers that are unworn and worn; 08 03 24 Figure 3 shows a perspective view of an air disc brake pad according to the present invention; Figure 4 shows a front view of a brake pad assembly including the brake pad of Figure 5 3 inserted into a brake pad carrier; Figure 5a and Figure 5b show plan views of a cross-section of a brake pad assembly including a pair of brake pads of Figure 3 correctly and incorrectly fitted to a brake pad caliper; 10 Figures 6a and 6b show plan views of a cross-section of a brake pad assembly including a pair of brake pads of Figure 3 that are unworn and worn; and Figure 7 shows a plurality of brake pad backplates of Figure 3 arranged in a stack including a close-up of the abutment between two adjacent brake pad backplates. 15 DESCRIPTION OF PREFERRED EMBODIMENTS Referring firstly to Figures 3 and 4, an air disc brake pad according to the present invention is generally shown at 10. During use, the air disc brake pad 10 is disposed 20 inside a brake carrier 12 as shown in Figure 4. The air disc brake pad carrier 12 is part of an air disc brake. The air disc brake pad carrier 12 is part of a pair of brake pad carriers in the air disc brake. The air disc brake pad carriers 12 are disposed on opposite sides of a brake disc (100, see Figures 5a and 6a). 25 The brake pad carrier 12 has a base or inner side. The brake pad carrier has a first side wall formed from a first carrier horn 40. The first carrier horn 40 extends substantially perpendicular from a first end of the base. The brake pad carrier 12 has a second side wall formed from a second carrier horn 42. The second carrier horn 42 extends substantially perpendicular from a second end of the base. The second carrier 30 horn 42 opposes the first carrier horn 40. The base and side walls define a brake pad receiving region. The carrier horns 40, 42 provide bearing surfaces for “ears” of the backplate, described further below. The brake pad 10 includes a backplate 14. The brake pad 10 also includes a friction 35 material 16. The friction material 16 is mounted to a disc-facing side of the backplate 14. 08 03 24 The brake pad 10 has a pad periphery 30. The pad periphery 30 extends around the periphery of the backplate 14. The pad periphery 30 has an inner side 20, the lower side of the pad as viewed in Figure 3. The inner side 20 of the pad periphery 30 faces an inner side of the brake pad carrier 12 during use. The pad periphery 30 has an outer 5 side 18. The outer side 18 of the pad periphery 30 opposes the inner side 20 of the brake pad periphery 30. The pad periphery 30 includes a first end 22. The first end 22 of the pad periphery 30 faces and lies adjacent to the first carrier horn 40 of the brake pad carrier 12 during use. The pad periphery 30 includes a second end 24. The second end 24 of the pad periphery 30 faces and lies adjacent to the second carrier horn 42 10 of the brake pad carrier 12 during use. First and second rear protrusions 26, 28 are provided on the backplate 14 of the brake pad 10. The protrusions 26, 28 are added to the backplate 14 casting. In this embodiment, the rear protrusions 26, 28 extend by 5 to 6 mm from the backplate 14. 15 However, it will be appreciated that in other embodiments, the depth of the rear protrusions 26, 28 can be tailored to the brake caliper. The first and second rear protrusions 26, 28 are disposed adjacent to the inner side 20 and the first and second ends 22, 24 respectively. In other words, the rear protrusions 20 26, 28 are disposed in bottom left and right-hand corners of the backplate 14, as viewed in Figure 3. As can be seen in Figure 5a, when the brake pad 10 is correctly inserted into the brake caliper, the rear protrusions 26, 28 are accommodated in a space between the brake 25 pad 10 and the brake caliper. When inserted with the backplate 14 facing the brake disc 100, the rear protrusions 26, 28 abut the brake disc 100. Full insertion of the brake pad 10 into the brake caliper is prevented, as shown in Figure 5b. In other words, the rear protrusions 26, 28 poka-yokes the incorrect insertion of the brake pad 10 into the brake caliper. 30 The brake caliper can slide axially (i.e. in a direction towards and away from the brake disc 100) to accommodate wear of the friction material 16. The extent of movement of the brake caliper is limited to prevent insertion of the rear protrusions 26, 28 when the brake pad 10 is inserted incorrectly (i.e. back-to-front). 35 As the friction material 16 wears, the effectiveness of the poka-yoke reduces. The depth of the rear protrusions 26, 28 can be tailored to provide an appropriate poka- 08 03 24 yoke for the friction material 16 used and / or the space provided in the brake caliper. For example, a greater depth of the rear protrusions 26, 28 may be provided to increase the effectiveness of the poka-yoke over the wear of the pad. 5 Referring again to Figures 3 and 4, the brake pad 10 includes first and second abutment tabs 32, 34 or “ears”. The abutment tabs 32, 34 protrude from the first and second ends 22, 24 of the brake pad 14. During use, the abutment tabs 32, 34 sit above the first and second carrier horns 40, 42. The abutment tabs 32, 34 provide horizontal abutment, i.e., fix the position of the depth of engagement between the brake 10 pad 10 and the brake pad carrier 12. During use, the rear protrusions 26,28 mitigate the distance the brake pad 10 can drop should the abutment tabs 32, 34 fracture. For example, the abutment tabs 32, 34 may fracture when under excessive vibrational loading. Reducing the distance that the 15 brake pad 10 drops following the fracture may ensure alignment between the brake pad 10 and brake disc 100 is maintained. Portions of the pad periphery 30 contact the first and second carrier horns 40,42 during use. Portions of the pad periphery 30 includes first and second thickened edges 36, 38. A portion of the first thickened edge 36 is disposed on the first abutment tab 32. A 20 portion of the second thickened edge 38 is disposed on the second abutment tab 34. The thickened edges 36, 38 are disposed where the pad periphery 30 horizontally abuts the carrier horns 40, 42. In other words, the edges of the backplate are locally thickened where the brake pad 10 horizontally abuts the first and second carrier horns 25 40,42. The first thickened edge 36 extends along a portion of the first end 22. The second thickened edge 38 extends along a portion of the second end 24. The thickened edges 36, 38 are disposed where the pad periphery 30 vertically abuts the carrier horns 40, 30 42. Each thickened edge 36, 38 has a substantially L-shaped profile. A gap is provided between each of the thickened edges 36, 38 and the corresponding rear protrusions 26, 28. The thickened edges 36, 38 have a thickness greater than the majority of the backplate 35 14. The thickened edges 36, 38 have a depth of between 3 to 5 mm extending from 08 03 24 the backplate 14. The thickened edges 36, 38 have a depth less than the depth of the rear protrusions 26, 28. Referring now to Figures 6a and 6b, a gap is shown between the brake caliper and the 5 brake disc 100. Figure 6a shows an unworn brake pad 10 in a brake caliper and Figure 6b shows a worn brake pad 10 in a brake caliper. That is to say, the friction material 16 of the brake pad 10 in Figure 6b has worn away during use. As one or both of the friction material 16 and brake disc 100 wears, a distance between the carrier abutments 40, 42 and brake disc 100 increases. As the distance between the carrier 10 abutments 40, 42 and brake disc 100 increases, the risk that the brake pad 10 slips between the carrier abutments 40, 42 and brake disc 100 increases. The depth of the thickened edges 36, 38 compensate for the increased distance between the carrier abutments 40, 42 and brake disc 100. The thickened edges 36, 38 mitigate the risk of the brake pad 10 from slipping between the gap between the brake caliper and the 15 brake disc 100. Referring now to Figure 7, the backplate 14 is shaped to allow even stacking of a plurality of backplates 14. 20 As discussed above, the rear protrusions 26, 28 have depth greater than the depth of the thickened edges 36, 38. The difference in depth between the rear protrusions 26, 28 and thickened edges 36, 38 is generally shown at 44 in Figure 7. A portion of the thickened edge additionally extends from the opposite side of the backplate 14. The extent of the thickened edge from the opposite side is shown at 46 in Figure 7. The 25 difference in depth between the rear protrusion and thickened edge 44 and the extent of the thickened edge 46 are substantially the same length. That is to say that the backplate 14 has a total thickness at the thickened edges 36, 38 that is substantially the same as the total thickness of the backplate 14 at the rear protrusions 26, 28. The substantially same thicknesses allow the plurality backplates 14 to be stacked in a 30 parallel arrangement. When a first backplate 14 is stacked on top of a second backplate 14, the thickened edges 36, 38 of the first backplate 14 and the rear protrusions 26, 28 of the second backplate 14 support the first backplate 14 parallel to the second backplate 14. The 35 backplates 14 may be stacked evenly where each backplate 14 is level. Keeping the backplates 14 parallel when stacked is advantageous in manufacturing. A significant advantage of the brake pad assemblies described above is that the brake pads can only be fully inserted into brake pad carriers in the correct orientation. The insertion of a brake pad with the backplate facing the brake disc cannot be fully inserted into a brake pad carrier. Where a brake pad cannot be fully inserted, the 5 operator is alerted to the fact that the brake pad is being inserted back-to-front thereby “fool-proofing” the correct assembly of the brake pad assembly. Furthermore, when the pads are worn, even if the ears fracture, the thickened edges hold the pad in the carrier, preventing a total loss of braking. 10 The embodiments described above are provided by way of example only, and various changes and modifications will be apparent to persons skilled in the art without departing from the scope of the present invention as defined by the appended claims. 08 03 24

Claims

08 03 241. An air disc brake pad for inserting into a brake pad carrier, the brake pad including a backplate and a friction material mounted on one side of the backplate, the pad periphery including an inner side, an outer side and first and 5 second ends;in which at least a portion of the pad periphery includes a thickened edge, the thickened edge extending in a direction opposing the friction material; andat least one rear protrusion is provided, the at least one rear protrusion extending from the backplate in a direction opposing the friction material;10 in which the depth of the at least one rear protrusion being greater than thedepth of the thickened edge;in which the air disc brake pad includes first and second abutment tabs for providing horizontal abutment with the brake pad carrier, the first abutment tab extending from the first end and the second abutment tab extending from the 15 second end; andin which at least a portion of the thickened edge extends along at least a portion of one of the first and second ends and a corresponding abutment tab.

2. An air disc brake pad as claimed in claim 1, in which the at least one rear protrusion has a depth of at least 4 mm.20 3. An air disc brake pad as claimed in any preceding claim, in which the at leastone rear protrusion has a depth of at least 5 mm.

4. An air disc brake pad as claimed in any preceding claim, in which the at least one rear protrusion has a depth of at least 6 mm.

5. An air disc brake pad as claimed in any preceding claim, in which the thickened 25 edge and rear protrusion are spaced apart.

6. An air disc brake pad as claimed in any preceding claim, in which the at least one rear protrusion is disposed substantially adjacent to the inner side of the backplate.

7. An air disc brake pad as claimed in any preceding claim, in which the thickened edge is disposed adjacent to at least one of the first and second ends of the backplate.

8. An air disc brake pad as claimed in any preceding claim, in which at least a 5 portion of the thickened edge is substantially L-shaped.

9. An air disc brake pad as claimed in any preceding claim, in which the air disc brake pad is substantially symmetrical about a central vertical axis extending from the inner side and the outer side.

10. A method of providing a poka-yoke to prevent incorrect assembly of an air disc 10 brake pad to a brake caliper; the method comprising providing an air disc brakeas claimed in any preceding claim, in which the at least one rear protrusion can only be accommodated by a corresponding gap in a backplate facing side of the brake caliper.08 03 24

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