Method of obtaining a backing plate for a brake pad and backing plate thus obtained

Abstract

Method for obtaining a backing plate (11) for a brake pad (13), comprising the steps of: - provide a strip (113) of a suitable material for manufacturing the backing plate (11): - to perform in said band (113) the die-cutting of the backing plate (11) to define in said backing plate (11) a front surface (11a) and a back surface (11b) essentially parallel to each other, the flat front surface (11a) being of smooth constitution, i.e., lacking roughness, except for microscopic roughness due to the usual manufacturing tolerance, and being adapted to receive a layer of friction material; - to perform on said band (113) the stamping of a plurality of hook recesses (19) on the front surface (11a); - wherein at the end of the die-cutting and stamping operations the front surface (11a) of the backing plate (11) is smooth and is provided with engagement recesses (19), characterized in that the engagement grooves (19) are distributed over the front surface (19a) in a non-uniform manner and according to a predetermined pattern within an engagement portion (23) of said front surface (11a) intended to engage the friction material layer (21) and surrounded, without interruption, by a peripheral zone (25) without engagement grooves.

Description

Method of obtaining a backing plate for a brake pad and backing plate thus obtained Technical field The invention relates to a method for obtaining a backing plate for a brake pad. The invention also relates to a brake pad backing plate obtained by this method. Previous technique A brake pad for a disc brake comprises a backing plate having a dorsal surface and a frontal surface substantially parallel to each other. A layer of friction material is bonded to the frontal surface. The friction material is applied to the frontal surface of the backing plate in a predefined engagement portion that usually occupies most of the available area on that frontal surface. This engagement portion of the frontal plate is further surrounded, without interruption, by a free peripheral zone, i.e., a zone intended not to be covered with the friction material. The peripheral zone, free of friction material, is required primarily for operational reasons.The width of the clearance zone is usually kept to the bare minimum, as it is disadvantageous, primarily for weight reasons, for the total area of ​​the backing plate's frontal surface to be greater than the effective braking area. The minimum width of this clearance zone, usually measured along the longitudinal sides of the backing plate, can vary from a few tenths of a millimeter to several millimeters. During the operation of a brake system, i.e., during braking, the brake pad is pressed against the disc in a direction substantially perpendicular to the disc's rotating surface. During braking, the friction layer of the brake pad is subjected to forces that are primarily tangential to the disc's circular motion. These tangential forces develop in the plane of the brake pad parallel to the disc and tend to remove the friction material by tearing it from the backing plate. In addition to these tangential forces, other forces acting in various directions also occur during braking. In particular, there are forces perpendicular to the brake pad surface caused by vibrations.Vibrations are generated during the action of the brake pad on the disc, for example, as a result of possible misalignment of the moving parts. Furthermore, some of the disc's energy is converted into heat during braking. The heat generated in this way usually causes an increase in the temperature of the brake pad materials. This temperature increase can weaken the bonds that hold the friction material to the backing plate, with a consequent risk of the material detaching. The greater the braking force exerted by the brake assembly on the rotating disc, the greater the forces acting on the friction material during braking.When such forces overcome the counterforces that keep the friction material adhered to the backing plate, a detachment and destruction of the friction material or part of it occurs, thus causing a reduction or loss of the braking effect. Therefore, one of the problems to be solved in the manufacture of a brake pad is how to prevent the friction material from detaching during use. Several solutions are known in the art to promote the adhesion of the friction material to the backing plate. A first solution to the aforementioned problem involves creating projections on the front surface of the backing plate intended to receive the friction material. During brake pad manufacturing, the friction material is deposited onto the surface of the backing plate. As the friction material layer hardens, the projections become embedded within it. Therefore, the projections that penetrate the friction material layer help prevent the friction material from detaching from the backing plate when shear forces, even large ones, are applied. According to the prior art, these projections can be obtained by depositing a material that, for example, can be welded to the front surface of the backing plate. US Patent 4,991,697 describes an example of this type of solution.According to another known solution, protrusions can also be obtained by removing material from the surface of the backing plate, for example, using movable blades. Cutting the surface of the backing plate with movable blades causes a partial removal of material, thus creating corresponding recesses. The material removed by the movable blades is lifted from the surface of the backing plate, but it is not completely detached. Therefore, the removed material remains raised, creating protrusions or ridges. Each protrusion is associated with a corresponding engagement recess, but this is not the primary purpose of working with movable blades. The protrusions and corresponding engagement recesses thus obtained can be distributed randomly, as described, for example, in EP 1484 524 A1, or they can be distributed uniformly, as described, for example, in US 6,431,331 B1.Another solution to the aforementioned problem involves creating only engagement grooves on the surface of the backing plate, without producing any roughness, thus leaving the backing plate surface substantially smooth. This solution is described in US patents 2011 / 0220441 A1 and 2005 / 161297 A1 and involves creating a regular array of engagement grooves with a square cross-section on the front surface of the backing plate. The engagement grooves are pre-cut into the strip of material from which the backing plate will subsequently be cut using known die-cutting methods. According to the teachings in these patents, the engagement groove array has a regular shape that determines a regular distribution of the engagement grooves.According to the teachings of document US 2011 / 0220441 A1, it is further provided that the side walls of the engagement recesses extend perpendicularly to the surface of the backing plate in which said engagement recesses are made, and that the base of the recesses is parallel to the front surface of the backing plate. However, the problem of preventing friction material from detaching is not effectively solved by known solutions. In fact, these solutions generally focus on promoting the adhesion of the friction material to any flat surface. Nevertheless, it has been demonstrated in practice that the problem of friction material detachment does not affect the brake pad surface uniformly. Furthermore, the results obtained with known solutions are not consistent when certain brake pad parameters are varied. The parameters that can influence the behavior of known solutions include, in particular, the grade of steel from which the backing plate is made, the grade of friction material, the size and shape of the backing plate, and the size of the brake disc.The type and thickness of the backing plate determine, for example, its heat dissipation capacity. The shape of the backing plate and the disc shape determine the direction and intensity of the shear forces applied to the friction material. The particle size, density, and binder used in the friction material mixture affect the effectiveness of the methods described above, depending on how these parameters are varied. Therefore, there is a strong need in this field to solve the problem of how to promote the adhesion of the friction material to the backing plate, avoiding peeling phenomena when varying these parameters, thus allowing better and more uniform results to be obtained when varying the type of brake pad that is manufactured. The main object of the invention is to solve the aforementioned problem by providing a method for obtaining a brake pad backing plate that improves the adhesion of the friction material to the brake pad. Another object of the invention is to provide a method of the aforementioned class that is easy and inexpensive to implement and is therefore suitable for large-scale use in industry. Summary of the invention These and other objects are obtained using the method and backing plate claimed in the appended claims. The invention is based on the principle that the engagement recesses machined into the surface of the backing plate, if appropriately distributed, are sufficient to achieve the desired results without the need for any protrusions or roughness. The absence of protrusions or roughness allows the backing plate to be manufactured using a stamping process. Therefore, according to a preferred embodiment of the invention, the engagement surface for the friction material is smooth, i.e., free of roughness, except for microscopic roughness due to usual manufacturing tolerances, and is consequently advantageously easier to use for subsequent manufacturing steps to obtain the brake pad. The stamping punches can be arranged within the same die used for stamping the backing plate.This avoids subsequent workpiece remachining operations, resulting in significant production cost savings. The arrangement of stamping punches within the same die-cutting mold also allows for high flexibility in defining shapes and rabbet distribution. Furthermore, it simplifies shape changes, rabbet distribution adjustments, and mold maintenance. Another advantage of the stamping method is the ability to orient the opening of the rabbets in any desired direction, unlike methods using movable cutting blades that only allow rabbets to be oriented along a single direction of blade feed.Therefore, adopting the stamping method allows the engagement grooves to be distributed across the surface of the backing plate in an optimized and predetermined manner with respect to the applied forces generated by the relevant parameters. Consequently, the backing plate obtained by the method according to the invention will have a non-uniform distribution of engagement grooves that follows a predetermined design (pattern). Another advantage of the invention stems from the fact that the engagement grooves are arranged only where necessary and at an appropriate density, potentially leaving some areas of the backing plate free, resulting in energy savings, reduced tool wear, and lower production costs. Brief description of the drawings Some embodiments of the invention will be given by way of non-limiting examples with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a brake pad; Figure 2 is a mock-up of a mold in a preferred embodiment of the manufacturing method according to the invention; Figure 3A is a perspective view from above of a strip or band from which a backing plate is obtained according to a first embodiment; Figure 3B is a top view of the strip in Figure 3A; Figure 3C is a cross-sectional view taken along line MIC-IIIC of Figure 3B; Figure 4 is an enlarged partial view of a punch holder block; Figure 5 is a perspective view of a backing plate according to an embodiment of the invention; Figure 6A is a plan view of a portion of a backing plate provided with circular engagement recesses; Figure 6B is a cut taken along line VIB-VIB of Figure 6A; Figure 7A is a plan view of a portion of a backing plate provided with hook recesses in the form of circular crowns; Figure 7B is a cross-section taken along line VIIB-VIIB of Figure 7A; Figure 8A is a plan view of a portion of a backing plate provided with rectangular engagement recesses; Figure 8B is a cut taken along the VIMB-VIMB line of Figure 8A; Figure 8C is a cross-section taken along the VINC-VINC line of Figure 8A; Figure 9A is a plan view of a portion of a backing plate provided with slot-shaped engagement recesses; Figure 9B is a cross-section taken along line IXB-IXB of Figure 9A; Figure 9C is a cross-section taken along line IXC-IXC of Figure 9A; Figures 10A to 10E are plan views of as many embodiments of the backing plate; Figure 11A is a perspective view of a backing plate of another embodiment of the invention; and Figures 11B, 11C, 11D are enlarged views of as many portions of Figure 11A. Description of some preferred realizations Referring to Figures 1 to 5, the method according to the invention for obtaining a backing plate 11 for a brake pad 13 will be described. The method according to the invention provides for the use of a mold 111. This mold 111 may be of the traditional type for stamping a backing plate 11 from a strip 113 of suitable material. A suitable material for making the backing plate 11 is typically steel. Still according to the invention, this mold 111 may also be of the type known in this field for obtaining a thin stamped part. The method according to the invention provides for performing at least one stamping step and one die-cutting step. In a preferred embodiment of the invention, the stamping and die-cutting steps are performed with a single mold 111. Furthermore, the mold preferably performs the stamping and die-cutting on a strip of material 113 that is advanced step by step by a feeder (not shown). Therefore, according to this embodiment, a mold portion 115, which performs stamping on the strip 113, and a mold portion 117a, which performs die-cutting of the stamped workpiece to separate it from the strip 113, are arranged in the same mold 111. A first intermediate mold portion 117b may be provided for pre-die-cutting on the strip 113. In addition, a second intermediate mold portion 123 may be provided in mold 111 for creating guide holes 125 in the strip 113.These machining operations are performed simultaneously by means of the single die 111 on different portions of the strip 113. The strip 113 moves forward step by step to reach the subsequent portions of the die 111. In this way, stamping, punching, and possibly the creation of guide holes 125 and / or pre-punching are performed sequentially on the same portion of the strip 113. The portion of the strip 113 on which stamping was performed in one of the preceding steps is punched, and the resulting workpiece is removed from the strip 113. According to this embodiment, it is also possible to provide for stamping to take place in a sequence of stamping steps with punches arranged in different areas of the same die. For example, each of these areas of the die can be provided with groups of punches of different types.At each advance step of belt 113, the same portion of belt is sequentially stamped while the belt is stopped in the mold areas equipped with a different group of punches. In another embodiment, it will be possible to foresee that the stamping and die-cutting are obtained by means of independent molds. In another embodiment, it will be possible to provide a single mold that simultaneously performs stamping and die-cutting on the same portion of the strip. In this way, stamping and die-cutting of the backing plate along the perimeter surrounding the area where stamping is performed simultaneously are carried out in a single operation. According to another embodiment, it can be foreseen that the stamping on the backing plate, after the die-cutting step, is carried out in a re-machining step of the die-cut workpiece, by means of a single stamping die or a plurality of stamping dies. According to a preferred embodiment of the invention, stamping is carried out by means of a mold 111 equipped with a punch block 119 in which blades or punches 121 are mounted. The blades or punches 121 have a shape corresponding to the shape of a corresponding engagement recess 19 to be obtained in the backing plate 11. According to the invention, the engagement recesses 19 obtained by stamping will preferably be blind recesses. Furthermore, the punch block 119 is preferably removable from the mold. This allows the block 119 to be replaced when it is worn or to be replaced with a block having punches capable of producing different recesses or recesses arranged differently. The stamping process allows the backing plate 11 to be formed from the initial strip 113 of suitable material, with a profile that meets the requirements of the brake assembly for which the brake pad 13 is intended. The backing plate 11 thus defines a flat front surface 11a and a flat back surface 11b. Surfaces 11a and 11b are also essentially parallel to each other. Furthermore, the flat front surface 11a is smooth and adapted to receive a layer of friction material 21. The stamping step generates a plurality of engagement grooves 19 on the front surface 11a of the backing plate 11. According to the invention, the engagement grooves 19 are advantageously distributed non-uniformly according to a predetermined design (pattern). Advantageously, the distribution and shape of the engagement grooves 19 are determined primarily based on the following parameters: the grade of steel from which the backing plate is made, the grade of friction material intended for use on the backing plate, the size and shape of the backing plate, and the size of the brake disc for which the backing plate is intended. Furthermore, thanks to the stamping technique, the 19 recesses can be made with high precision within the backing plate mask on band 113. According to the invention, the engagement means for the friction material comprise only the recesses 19 and do not include any engagement protrusions or ridges. Therefore, at the end of the die-cutting and stamping operations, the front surface 11a of the backing plate 11 is smooth and provided with engagement recesses 19. Referring to Figures 3A to 3C, a strip or band 113 is illustrated during the execution of the method according to a preferred embodiment of the invention. The hooking grooves 19 obtained by stamping in a first portion of the strip 113a can be seen in the strip. Guide holes 125 are obtained in portions 113b of the strip 113. The guide holes 125 are adapted to receive corresponding guide pins 126, which are provided, according to the prior art, in the working equipment for the purpose of keeping the strip 113 firmly aligned with the mold 111. In a portion 113c of the strip 113, the corresponding opening left by the die-cutting of the backing plate after it has been removed from the strip 113 by known means can be seen. The deposition of the friction material layer 21 onto the backing plate 11 takes place in such a way as to allow the friction material to penetrate deeply into the engagement recesses 19.The friction material is applied according to known techniques that are not part of the present invention and are therefore not discussed in detail. The engagement recesses 19 are located within an engagement portion 23 of the front surface 11a of the backing plate 11. The engagement portion 23 corresponds to the portion of said front surface 11a intended to engage the friction material layer 21. This portion 23 is surrounded, without interruption, by a peripheral zone 25 without engagement recesses. The peripheral zone 25 is intended to remain free of friction material, and it is advantageous that it does not have engagement recesses 19. Engagement recesses that are not filled, or are only partially filled, with friction material could create cracks and cause the friction material to detach at the peripheral outer edge of the brake pad. The presence of engagement recesses without friction material also leads to an accumulation of dust and other materials that could impair the proper functioning of the brake pad.For the same reasons, between the hitch recesses 19 closest to the periphery of the hitch portion 23 and said periphery, a safety distance (offset) is provided, usually between approximately 1.0 and 3.0 mm. According to one embodiment of the invention, the cross-section of the engagement grooves 19 and, correspondingly, the opening of the engagement grooves 19 on surface 11a can be substantially any shape. However, according to the invention, the preferred shapes for the cross-section are a circular shape, a circular crown shape, a rectangular shape, or a groove shape. The aforementioned shapes, combined with a predetermined distribution of the engagement grooves, effectively determine the best results in terms of resistance to peeling of the friction material. Furthermore, the aforementioned shapes are the optimal choice for the stamping manufacturing process due to the simplicity of the punch shapes that must be provided. According to the invention, the hook recesses 19, provided with a rectangular or slot-shaped cross-section, i.e., for which it is possible to identify a longitudinal plane of symmetry, can be oriented with their long sides arranged in mutually parallel positions or in directions that are not mutually parallel. According to the invention, the cross-section of the engagement recesses 19 can be the same for all engagement recesses 19 obtained in the backing plate 11, or it can be of mixed configurations with engagement recesses 19 having different cross-sections. For example, the cuts can all be circular, or some engagement recesses can have a circular cross-section, some a slot-shaped cross-section, and others a rectangular cross-section, etc. Preferably, according to the invention, all the engagement grooves 19 formed in the front surface 11a of the backing plate 11 are obtained simultaneously in a single stamping step using a single die 111 and a corresponding punch block 119. According to other embodiments, the engagement grooves 19 can be made in a sequence of stamping steps using a single die in which the punches are distributed in different areas reached by the same portion of strip in a sequence of advance steps. In other embodiments, different dies can be provided, each of which is equipped with one or more groups of punches, reached by the same portion of strip in a sequence of advance steps. According to the invention, the engagement recesses 19 extend within the plate material 11 along an axis of symmetry essentially perpendicular to the plane of the front surface 11a. In a preferred embodiment of the invention, the depth of the engagement recesses 19 is between 0.3 and 0.6 mm. According to the invention, the side walls of the engagement recesses 19 are preferably inclined outwards. Therefore, the engagement recesses have side walls that diverge from the lower base of the engagement recess, which is within the backing plate material, outwards, i.e., towards the opening of the engagement recesses in the front surface 11a of the backing plate. Furthermore, the inclination of the side walls of the engagement recesses 19 is preferably constant circumferentially and axially, meaning that it does not vary from the base of the engagement recess 19 towards the surface and does not vary angularly along the periphery of the engagement recess 19 or along any depth of the engagement recess 19.The side walls of the engagement recesses 19 are preferably inclined so that they form an angle α of between approximately 60° and 90° with respect to the plane of the front surface 11a of the backing plate 11. Even more preferably, this angle α is between approximately 75° and 80°. This slight inclination is advantageous for achieving easy and complete penetration, into the engagement recesses 19, of the friction material mixture deposited on the front surface 11a during the manufacturing step of the brake pad 13. Furthermore, the inclination of the engagement recess walls is advantageous because it increases the surface area that counteracts tangential forces and to which the friction material adheres. According to a particular embodiment of the invention, at least one of the engagement recesses 19 has its lower base within the backing plate 11 in a position not parallel to the front surface 11a of the backing plate 11. According to this particular embodiment of the invention, preferably all or most of the engagement recesses 19 obtained by stamping into the backing plate 11 will have a substantially flat base inclined relative to the front surface 11a of the backing plate 11. Advantageously, the engagement recesses 19 with their inclined lower base are obtained by means of stamping punches having an oblique cutting edge. This cutting edge shape allows engagement recesses 19 to be obtained with less effort.Applying less force during the stamping steps results in lower energy consumption and, therefore, reduced production costs and less stress applied to the backing plate material during the stamping process. According to this embodiment of the invention, the planes on which the lower bases of the engagement recesses 19 are located in a backing plate 11 can all be parallel to each other. However, it is possible to provide inclined planes in various ways, either randomly or according to a predetermined order. The inclination of the lower base can also vary according to the area of ​​the backing plate 11 in which the corresponding engagement recess 19 is obtained.The inclined lower base offers two main advantages: firstly, it allows for the maximum depth of the rebate compatible with the material thickness, and secondly, it reduces the force required to cut the rebates. Thanks to this invention, deeper rebates can be made with less effort. Preferably, the inclination of the lower base of the rebates is between approximately 0° and 10° relative to the plane of the front surface of the backing plate. Referring to Figures 6A and 6B, an embodiment of the invention is illustrated in which the engagement recess 19 has a circular cross-section. Furthermore, as can be seen more clearly in Figure 6B, according to this embodiment, the side wall 27 of the circular cross-section engagement recess 19 is inclined at an angle α with respect to the plane of the surface 11a. In the example shown, the angle α is approximately 75°. Preferably, the diameter at the lower base 29 of the circular cross-section engagement recess 19 is between 2.0 and 4.5 mm. In this embodiment, the lower base 29 of the engagement recess 19 is flat and parallel to the front surface 11a of the backing plate 11. However, it is possible to provide for said lower base 29 to be flat and inclined, for example, at approximately 10°, with respect to the front surface 11a of the backing plate 11. Referring to Figures 7A and 7B, an embodiment of the invention is illustrated in which the engagement recess 19 has a circular cross-section. Furthermore, as can be seen more clearly in Figure 7B, in this embodiment the circular cross-section engagement recess 19 comprises a cylindrical outer wall 31 and a cylindrical inner wall 33. The cylindrical inner wall 33 surrounds a cylindrical portion 35 of the backing plate. The portion 35 is within the circular cross-section engagement recess 19 and extends for a length substantially equal to the depth of the engagement recess 19. The cylindrical outer wall 31 of the circular cross-section engagement recess 19 is, moreover, preferably inclined at an angle α with respect to the plane of surface 11a. In the example shown, angle a is around 75°.Preferably, the diameter at the lower base 15 is between 4.0 and 5.5 mm. In this embodiment, the lower base 37 of the engagement recess 19 is also flat and parallel to the front surface 11a of the backing plate 11. However, it is possible to provide for said lower base 37 to be flat and inclined, for example at about 10°, with respect to the front surface 11a of the backing plate 11. Still with reference to this embodiment, the cross-section of the engagement recess 19 and correspondingly the opening of the engagement recess 19 in surface 11a can also have a crown-like shape with the inner and outer perimeters being substantially any shape. According to the invention, the preferred shapes for the crown-like cross-section are circular, square, rectangular, or groove-like. According to other embodiments of the invention, it will also be possible to provide that the shape of the central portion of the backing plate is different from the shape of the cross-section of the recess.For example, there may be cross-sectional shapes of the hook recess where the outer perimeter defines a circle and the inner perimeter defines a square, and vice versa; or shapes where the outer perimeter defines a rectangle and the inner perimeter defines a square, or vice versa; or shapes where the outer perimeter defines a groove and the inner perimeter defines a rectangle, and vice versa. Other combinations of shapes are also possible. Referring to Figures 8A, 8B, and 8C, an embodiment of the invention is illustrated in which the engagement recess 19 has a rectangular cross-section. Furthermore, as can be seen more clearly in the figures, in this embodiment the side wall 39 of the rectangular cross-section engagement recess 19 is inclined at an angle α with respect to the plane of the surface 11a. In the example shown, the angle of inclination α is approximately 75°. Preferably, the lower base 41 of the rectangular cross-section engagement recess 19 has a length between 2.0 and 5.0 mm and a width between 1.0 and 2.0 mm. On the backing plate 11, the rectangular cross-section engagement recess 19 can be oriented in different ways so that its long sides are arranged in mutually parallel positions or are inclined in different ways.In this embodiment, the lower base 41 of the engagement recess 19 is also flat and parallel to the front surface 11a of the backing plate 11. However, it will be possible to provide for said lower base 41 to be flat and inclined, for example at about 10°, with respect to the front surface 11a of the backing plate 11. Referring to Figures 9A, 9B, and 9C, an embodiment of the invention is illustrated in which the engagement recess 19 has a slot-shaped cross-section. The slot shape is defined by a substantially rectangular central portion 43a extending longitudinally into two corresponding semicircular portions 43b and 43c. Furthermore, as can be seen more clearly in Figures 9B and 9C, according to this embodiment, the side walls 45 of the slot-shaped cross-section engagement recess 19 are inclined at an angle α with respect to the plane of surface 11a. In the example shown, the angle of inclination is approximately 75°. The lower base 47 of the slot-shaped cross-section engagement recess 19 preferably has a length between 2.0 and 5.0 mm and is transversely curved with a radius of curvature between approximately 1.0 and 2.0 mm.In this embodiment, the lower base 47 of the engagement recess 19 is also flat and parallel to the front surface 11a of the backing plate 11. However, it will be possible to provide for said lower base 47 to be flat and inclined, for example at about 10°, with respect to the surface 11a of the backing plate 11. According to a particular embodiment of the invention, the engagement recesses 19 are grouped into arrays or rows on the backing plate 11. The arrays may consist of staggered rows or aligned rows. The arrays may be rectangular, square, circular, or have other shapes, including irregular shapes. The rows of engagement recesses may be single rows or multiple parallel rows, rectilinear, curvilinear, or annular, and may follow a predetermined path, for example, parallel to the outer edge of the engagement portion 23. Within each group of engagement recesses 19, i.e., within each array or row, the engagement recesses may have identical cross-sections or mixed cross-sections and may be oriented with their sides mutually parallel or inclined relative to one another. Referring to Figure 10A, an embodiment of the invention is illustrated in which the engagement recesses 19 are distributed according to a predetermined first design (pattern). The design shown provides a rectangular array 49a of engagement recesses 19 arranged in the center of the engagement portion 23, a continuous annular row 49b of engagement recesses 19 arranged on the periphery of the engagement portion 23, and two continuous circular annular rows 49c of engagement recesses 19 arranged symmetrically on the sides of the array 49a. The engagement recesses 19 in the embodiment of Figure 10A have a circular cross-section. Furthermore, still with reference to this embodiment, some of the recesses 19 in the array 49a and row 49b have a circular crown-like cross-section.The remaining portions of the backing plate that do not have the engagement recess groups 49a, 49b, 49c have the front surface 11a free of engagement recesses. Referring to Figure 10B, an embodiment of the invention is illustrated in which the engagement recesses 19 are distributed according to a second predetermined design (pattern). The design (pattern) shown differs from that of Figure 10A in that it does not have the die 49a. In the embodiment of Figure 10B, the engagement recesses 19 also have a circular cross-section, and some recesses 19 are further provided with a cross-section in the form of a circular crown. Referring to Figure 10C, an embodiment of the invention is illustrated in which the engagement recesses 19 are distributed according to a predetermined third design (pattern). The engagement recesses 19 in the embodiment of Figure 10C differ from those in Figure 10A in that they have a slotted cross-section. According to the invention, the slotted engagement recesses 19 can be oriented such that at least two of them are not parallel to each other. In this way, it will be advantageously possible to arrange the slots in a sunburst pattern as in the annular rows 49c of Figure 11C. This arrangement is tolerated by the fact that the hook recesses 19 have been produced by stamping, i.e., by means of punches 121 that strike perpendicularly the surface 11a of the backing plate 11 and not by moving blades that cut tangentially the surface of the backing plate.As illustrated, some of the recesses 19 may also have a crown-like cross-section. The remaining portions of the backing plate that do not have the groups of engagement recesses have the front surface 11a free of engagement recesses. Referring to Figure 10D, an embodiment of the invention is illustrated in which the engagement recesses 19 are distributed according to a predetermined fourth design (pattern). The design (pattern) shown differs from that of Figure 11A in that the engagement recesses 19 have mixed cross-sections. In particular, the recesses in array 49a have a rectangular cross-section, the recesses in row 49b have a slot-shaped cross-section on the longitudinal sides of the backing plate and a circular cross-section on the transverse sides, and the engagement recesses 19 in row 49c have a circular cross-section. Referring to Figure 10E, an embodiment of the invention is illustrated in which the hook recesses 19 are distributed according to a predetermined fifth design (pattern). The design shown provides an array 51a of hook recesses 19 arranged in the center of the hook portion 23, a row 51b of hook recesses 19 arranged along a first longitudinal side of the portion 23, two parallel rows 51c, 51d of hook recesses 19 arranged along a second longitudinal side of the portion 23 opposite the first side, and a row 51e for each transverse side of the portion 23. In the embodiment of Figure 10E, the hook recesses 19 have mixed cross-sections.Specifically, the engagement recesses in array 51a have a circular cross-section, the engagement recesses in rows 51b and 51c have a slotted cross-section, the engagement recesses in row 51d have a rectangular cross-section, and the engagement recesses in row 51e have a circular cross-section. The remaining portions of the backing plate that do not have engagement recess groups 51a, 51b, 51c, and 51d have a face surface 11a free of engagement recesses. As illustrated, some of the engagement recesses may also have a crown-like cut. Referring to Figures 11A to 11D, an embodiment is illustrated in which the engagement recesses 19 have an inclined lower base 53. The embodiment shown comprises engagement recesses 19 with a rectangular cross-section. However, it is possible to provide an inclined lower base for any shape of engagement recess 19. In the illustrated embodiment, the bases 53 of the engagement recesses 19 adjacent to the transverse side of the backing plate 11 are inclined towards the center of the backing plate (Figures 11B, 11C). In addition, an array 55 of engagement recesses 19 with bases inclined in opposite directions, alternating with each other, is arranged in the center of the backing plate 11 (Figure 11D). This arrangement is particularly effective when it is desired to give the brake pad behavior that is substantially independent of the direction of application of tangential forces.In other cases, it is possible to ensure that all or most of the coupling recesses have their bases inclined in the same direction. With this arrangement, the resulting brake pad has greater resistance to the friction material's separation in one direction than in the opposite direction. The recess wall that best counteracts the friction material's separation is the deepest wall. Therefore, by appropriately orienting the inclination of the lower bases of the coupling recesses, it is possible to provide the necessary resistance to separation in all directions or only in the desired direction or directions. Various variants and modifications are possible for the described and illustrated invention, all of which fall within the same inventive principle.

Claims

1. Method of obtaining a backing plate (11) for a brake pad (13), comprising the steps of: - providing a strip (113) of a suitable material for manufacturing the backing plate (11); - stamping the backing plate (11) in said strip (113) to define in said backing plate (11) a front surface (11a) and a back surface (11b) essentially parallel to each other, the flat front surface (11a) being smooth, i.e., lacking roughness except for microscopic roughness due to usual manufacturing tolerances, and being adapted to receive a layer of friction material; - stamping a plurality of engagement recesses (19) on the front surface (11a) of said strip (113); - wherein at the end of the die-cutting and stamping operations the front surface (11 a) of the backing plate (11) is smooth and is provided with engagement recesses (19),characterized in that the engagement grooves (19) are distributed on the front surface (19a) in a non-uniform manner and according to a predetermined pattern within an engagement portion (23) of said front surface (11a) intended to engage the friction material layer (21) and surrounded, without interruption, by a peripheral zone (25) without engagement grooves.

2. Method according to claim 1, wherein the stamping step and the die-cutting step are performed simultaneously by means of a single die (111) on different portions of the strip (113) of material from which the backing plate (11) is made.

3. Method according to claim 1 or 2, wherein the stamping step generates engagement grooves (19) having a circular cross-cut, in the form of a circular crown, rectangular or groove-shaped, or a combination thereof.

4. Method according to claim 1 or 2 or 3,wherein the stamping step generates a group of engagement recesses (19) having a rectangular or slot-shaped cross-section, and wherein at least two of said engagement recesses (19) are oriented in directions that are not mutually parallel.

5. A method according to any of the preceding claims, wherein the engagement recesses (19) extend into the backing plate material (11) along an axis of symmetry essentially perpendicular to the plane of the front surface (11a), and wherein the side walls of the engagement recesses (19) are inclined outwards.

6. A method according to claim 5, wherein the inclination of the side walls of the engagement recesses (19) is circumferentially and axially constant.that is, it does not vary from the lower base of the engagement recess (19) to the surface (11a) and does not vary angularly along the perimeter of the engagement recess (19) or at any depth of the engagement recess (19).

7. Method according to claim 5 or 6, wherein the side walls of the engagement recesses (19) are preferably inclined so as to form an angle α of between approximately 60° and 90° with respect to the plane of the front surface (11a) of the backing plate (11).

8. Method according to any of the preceding claims, wherein a safety distance (offset) is provided between the engagement recesses (19) nearest to the periphery of the engagement portion (23) and said periphery, usually between approximately 1.0 and 3.0 mm.

9. Backing plate (11) for a brake pad (13) comprising a front surface (11a) and a back surface (11b) essentially parallel to each other,wherein the flat front surface (11a) is adapted to receive a layer of friction material (21), said front surface (11a) of the backing plate (11) being smooth, i.e., lacking roughness except for microscopic roughness due to usual manufacturing tolerances, and being provided with engagement recesses (19), characterized in that said engagement recesses (19) are distributed non-uniformly and according to a predetermined pattern within an engagement portion (23) of said front surface (11a) provided for engaging the layer of friction material (21) and surrounded, without interruption, by a peripheral zone (25) without engagement recesses.

10. Backing plate according to claim 9,wherein the engagement recesses are distributed according to a predetermined pattern providing an array (51a) of engagement recesses (19) located in the center of the engagement portion (23) defined on the front surface (11a), at least one row (51b) of engagement recesses (19) located along a first longitudinal side of the engagement portion (23), at least one row (51c) of engagement recesses (19) along a second longitudinal side of the engagement portion (23) opposite the first side, and at least one row (51d) of engagement recesses (19) for each transverse side of the engagement portion (23).

11. Brake pad comprising a backing plate according to any of claim 9 or 10.

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