Composite brake drum

Abstract

Composite brake drum, comprising a connecting section (2) oriented perpendicular to the axis of rotation (X) of the composite brake drum (1) and designed to connect the composite brake drum (1) to a wheel to be braked, comprising an annular shell section (5) supported by the connecting section (2) and rotating around the axis of rotation (X) of the composite brake drum (1), and comprising a friction ring (6) supported by the shell section (5), which also rotates around the axis of rotation (X) of the composite brake drum (1) and has a friction surface (16) on its free inner circumferential side, which is rotationally symmetrical to the axis of rotation (X) of the composite brake drum (1), wherein the connecting section (2) is made of a light metal material and the friction ring (6) is made of a cast iron material, wherein the friction ring (6) has a structure on its outer circumferential surface,the structure is formed by protrusions (17) and depressions (18) which are at least partially bounded by the protrusions (17), and wherein the material of the shell section (5) has penetrated into the depressions (18) of the structure, characterized in that the friction ring (6) has a thickness (D1) in a first edge region (12), which is bounded by its end face (7) facing the connection section (2), which is smaller than the thickness (D2) that the friction ring (6) has in its second edge region (14), which is bounded by the end face (10) facing away from the connection section (2), and that the thickness (D1) of the first edge region (12) increases continuously from its edge associated with the connection section (2) towards the second edge region (14) and the thickness (D2) of the second edge region (14) increases continuously up to the end face (10) facing away from the connection section (2).that the increase in thickness (D2) over the second edge region (14) is greater than the increase in thickness (D1) over the first edge region (12) and the proportion of the width of the second edge region (14) to the width (BR) of the friction ring (6) is greater than the proportion that the width of the first edge region (12) occupies to the width (BR) of the friction ring (6) and that at least some of the protrusions (17) extend parallel to the axis of rotation (X) of the composite brake drum (1)..

Description

The invention relates to a compound brake drum according to the preamble of claim 1.When the "thickness of the friction ring" is mentioned here, this means the material thickness of the friction ring measured in the radial direction with respect to the axis of rotation of the respective composite brake drum. The "width" of the friction ring, on the other hand, is measured axially parallel to the axis of rotation of the composite brake drum.An example of a compound brake drum of the type specified at the beginning is known from DE 79 13 595 U1. The known brake drum has a bowl-like drum housing which is formed from a light metal material, in particular an aluminium alloy, and is provided on the inner circumferential surfaces of its casing section with at least one composite profile which consists of a carrier profile consisting of light metal and at least one steel support. The carrier profile and the steel support together form a friction ring which rotates about the axis of rotation of the brake drum and on the inner circumferential side of which, present on the steel support, the friction surface is formed against which the brake shoes of the respective brake device with their brake pads act during use. The friction ring formed in this way as a composite profile is placed in an associated annular receptacle formed into the inner circumferential surface of the drum housing by welded seams, by shrink fitting in a force-fitting manner or by notches or the like in a form-fitting manner to the drum housing. In this case, because the drum housing consists of a light metal material, a considerable saving in weight is achieved compared to brake drums made of solid material.In the case of the composite brake drum likewise known from EP 0 002 581 B1, the casing section running around the axis of rotation of the brake drum is cast from an aluminum material, while the connection section consists of a stamped sheet metal, onto which the casing section is cast. Projections provided on the circumference of the connecting section and projecting radially therefrom engage in the material of the jacket section and thus ensure a positive, rotationally fixed connection even under the high torques occurring during braking. On the inner circumferential side of the jacket section, a friction ring is also seated in this known brake drum, which friction ring is cast from cast iron material in this case. The casing section is also cast onto the friction ring. In order to ensure a permanently secure connection, the friction ring is provided on its outer circumferential surface facing the casing section with a rough rib or ridges spaced apart from one another, which protrude into the light metal of the casing section.In EP 0 879 975 A2 a brake drum assembly has also been proposed, which consists of a pot-shaped brake drum, which is fastened in a rotationally fixed manner to a hub of a vehicle axle, and a friction ring, which is arranged in a rotationally fixed manner on the brake drum and against which at least one brake shoe radially abuts when a brake is actuated. In order to permanently secure the friction ring within the brake drum, the brake drum material and the friction ring material are specifically matched to one another in such a way that they have an almost identical coefficient of thermal expansion and, in addition, electrochemical corrosion between the friction ring and the brake drum that may possibly result due to their material properties is avoided.Thus, characteristic of composite brake drums of the type in question here is a pot-like shape, the bottom of which is formed by the connecting portion oriented normally to the axis of rotation and the circumferential wall of which is formed by the jacket portion which runs around the axis of rotation and is held by the connecting portion, on the inner circumferential surface of which the friction ring is held, on the free inner circumferential surface of which the friction surface is formed, against which the brake pads of the brake device press during use.In the article "Tabs de frein en alliage leger" mentioned in the introduction to the description of the above-mentioned EP 0 002 581 B1, published in "Revue de l'Aluminum", Vol. 37, no. 273, it has already been explained that composite brake drums are subjected to deformations during braking, in particular when their casing sections consist of a light metal material or are designed with a comparably small wall thickness, due to the non-uniform contact of the brake pads on the friction surface of the friction ring that results in this case. Thus, in the region of the edge of the jacket section of the brake drum facing away from the connecting section of the respective drum, expansion occurs due to the pressure forces directed in the radial direction against the friction surface of the friction ring, whereas the jacket surface in the region of its connection to the connecting section can only yield to a reduced extent to the pressure forces. Starting from the connecting portion, the jacket portion is then deformed in the manner of a funnel, with the result that the contact pressure exerted by the brake shoes is significantly lower in the edge region of the friction ring remote from the connecting portion than in its edge region directly assigned to the connecting portion. Due to this non-uniformity of the force distribution, the forces applied by the respective brake device cannot act optimally during a braking operation and a correspondingly non-uniform wear of the friction ring occurs.As further explained in the article mentioned, this phenomenon can be minimized by a rib which extends around the outer circumference and is arranged close to the edge of the jacket section facing away from the connection section. However, in many modern composite brake drum constructions, the installation space required for this purpose is not available. Minimized wall thicknesses are also required with regard to a maximum weight reduction, in particular in the connection section and casing section of a composite brake disc.In addition, DE 10 2011 054 484 A1 is known from the prior art, said document discloses a brake drum and a method for producing a brake drum of this type.From the prior art is also known GB 896 553 A, which discloses improvements to or in relation to a wheel and brake drum assembly.The prior art also discloses U.S. Pat. No. 3,005,259 A, which discloses a method for producing brake drums.From the prior art, U.S. Pat. No. 1,978,563 A is also known, which discloses a brake drum.Against the background of the prior art explained above, the object has been to create a compound brake drum of the type mentioned at the beginning that a substantially uniform distribution of tension is established in the friction ring during braking over the entire width of the friction ring.The invention has achieved this object by a composite brake drum having at least the features specified in claim 1.Advantageous embodiments of the invention are specified in the dependent claims and are explained in detail below, like the general concept of the invention.A composite brake drum according to the invention accordingly has, in accordance with the prior art explained at the beginning, a connecting portion which is aligned normally with the axis of rotation of the composite brake drum and is provided for connecting the composite brake drum to the wheel to be braked in each case, an annular casing portion which is supported by the connecting portion and rotates about the axis of rotation of the composite brake drum, and a friction ring which is supported by the casing portion and likewise rotates about the axis of rotation of the composite brake drum and has, on its free inner circumferential side, a friction surface which is aligned rotationally symmetrically with the axis of rotation of the composite brake drum.According to the invention, in such a composite brake drum, the friction ring is bounded in an edge region by its end side facing away from the connection portion, and has a thickness which is greater than the thickness which the friction ring has in its edge region bounded by the end side facing the connection portion.A composite brake drum according to the invention thus also has the basic shape of a pot, the base of which is formed by the connection section and the circumferential side wall of which is formed by the casing section. In a composite brake drum according to the invention, the friction ring is designed in such a way that it counteracts the edge region of the casing section which occurs during a braking operation and is directed in the radial direction in the free edge region of the casing section which is remote from the connection region. For this purpose, the friction ring is thickened in its edge region assigned to the relevant edge region of the casing section compared to its other edge region assigned to the connection region. The thicker edge region in this case optimally runs around the friction ring, so that continuous stiffening is achieved.In this case, it is understood, in view of the fact that the friction ring has on its free inner circumferential side the cylindrical friction surface for the brake shoes acting against the friction surface during braking operation, that the portions of the edge regions of the friction ring which have the different thicknesses preferably extend outwards in a radial direction with respect to the axis of rotation of the brake disk, so that a uniformly cylindrically shaped contact surface is formed on the inner circumferential side of the friction ring over the entire width thereof.Practical investigations have shown that the shaping according to the invention makes it possible to provide brake drums which can be produced in a simple and cost-effective manner and, with a minimized space requirement in practical brake application, exhibit a behavior which is at least equivalent to the behavior of one-piece brake drums cast conventionally in one piece from an iron casting material and known composite brake drums. The invention takes into account the per se known finding that the surface pressure of the brake shoes on the friction surface of the friction ring in conventional brake drums typically follows a regular, for example cycloid, function and that the forces which during braking act against the friction surface and, associated therewith, on the friction ring and on the casing section of the brake drum carrying the friction ring occur in an uneven distribution. In order to counter the non-uniform loads resulting from this circumstance, the invention proposes a brake drum which is composed of at least two molded bodies, of which one molded body is the friction ring and the other is a brake drum main body formed by the connecting portion and the casing portion, wherein the friction ring is designed such that it counteracts the deformation conditions of the brake drum axially by virtue of its thickness being varied over the width of the friction ring.Since in a brake drum according to the invention the shell portion is substantially only given the function of holding and bonding the friction ring to the connection portion of the brake drum, the wall thicknesses of the shell portion can be minimized, in particular in the region in which the friction ring is seated on its inner circumferential surface. This results in a particularly compact and simultaneously stable embodiment of a composite brake drum according to the invention if the receptacle provided for the friction ring is formed by a shoulder formed in the shell section, on which the friction ring is seated.The variation in thickness of the friction ring proceeding from the edge region which is assigned to the connection section is adapted to the loads which occur during braking operation and act in the radial direction in such a way that uniformly distributed stresses occur in the friction ring over the entire width of the friction ring. In this way, the deformation of the friction ring that is unavoidable under the load of the braking is also uniformly distributed over its width, so that the friction ring optimally deforms exactly in its edge region assigned to the connecting portion of the brake drum as in its edge region facing away from the connecting portion. The thickness profile suitable for this purpose can be determined by examining the deformation behavior of a conventionally shaped friction ring intended for a composite brake drum under the loads occurring during braking. From the result of this examination and taking into account the geometry of the connecting section and the casing section of the brake drum, it is then possible to determine how the thickness of the friction ring has to be varied over its width so that during braking a uniform stress distribution and, along with this, a uniform deformation in the radial direction is established.A variant of the thickness distribution of the friction ring provides, for example, that the thickness of the friction ring increases steadily starting from the end face of the friction ring assigned to the connection section as far as the end face of the friction ring facing away from the connection section. This variation takes into account the case that the braking forces during braking occur uniformly distributed over the width of the friction surface.In the variant explained above, the edge regions with the different thicknesses merge into one another. According to another embodiment, the thickness increase according to the invention is, on the other hand, not uniformly distributed over the width of the friction ring. Rather, in this case the edge region of the friction ring assigned to the connection section extends over a first part of the width of the friction ring and the edge region of the friction ring facing away from the connection section extends over a second part of the width of the friction ring, wherein the thickness increase of the one edge region follows a different condition than the thickness increase of the other edge region.In order to avoid a sudden, sudden change in the thickness of the edge regions and, associated therewith, a stress distribution in the case of braking, a transition region can be formed between the edge regions of the friction ring, via which transition region the increase in thickness between the edge region assigned to the connection portion and the edge region of the friction ring facing away from the connection portion is adapted.A soft, in particular jump-free transition of the thickness of the one edge region to the thickness of the other edge region of the friction ring can also be accomplished, for example, by the thickness of the edge region of the friction ring assigned to the connection portion increasing in the direction of the second edge region of the friction ring following a continuous function up to the thickness of the second edge region. For example, the thickness of the edge region of the friction ring assigned to the connection section can thus increase linearly in the direction of the end face of the friction ring facing away from the connection section. Although the thickness profile increases over its edge region assigned to the connection portion as far as the second edge region facing away from the connection portion, the increase in thickness is greater in the second edge region than in the first edge region. The thickness of the second edge region facing away from the connection portion may increase from the boundary to the other edge region of the friction ring in the direction of the end face of the composite brake drum facing away from the connection portion.In cases in which the thickness over the one edge region follows a different specification than the thickness over the other edge region of the friction ring, for example the part of the width of the friction ring over which the edge region of the friction ring assigned to the connection section extends can assume 15-30% of the total width of the friction ring.The particular advantage of the invention is that during the production of a composite brake drum according to the invention, the separately prefabricated, in particular precast, friction ring can be cast without problems into the casing section which carries it and can simultaneously be cast in one piece with the connecting section.In order to ensure optimum bonding of the friction ring to the material of the casing section during production by casting in this way, the friction ring has a structure on its outer circumferential surface which is formed by elevations and depressions delimited at least in sections by the elevations, wherein the material of the casing section has penetrated into the depressions of the structure. For this purpose, it may be sufficient if the structure extends exclusively over the edge region of the friction ring assigned to the connection section and the optionally present transition section. In order to ensure that the torques occurring during a braking operation are reliably absorbed by the casing section and by the connection section of the composite brake drum according to the invention, at least some of the elevations extend axially parallel to the axis of rotation of the composite brake drum. In this case, uniform force transmission can be achieved by distributing the elevations at regular angular distances about the axis of rotation.The particular advantage of a composite brake drum according to the invention is that at least the connecting portion can consist of a light metal material, wherein, as already mentioned above, the casing portion and the connecting portion are preferably produced in one piece. The light metal material can be any material already known for these purposes in the prior art, wherein in particular aluminum materials are possible which can be shaped by casting to form the casing section and the connecting section. By using light metal material for at least the connecting section, advantageously also the casing section, a considerable weight reduction can be achieved compared to conventional brake drums consisting of cast iron. The friction ring is advantageously made of cast iron material, which is known and proven for the production of conventional brake drums or brake disks. It has proven particularly favorable in this case if the thickness of the friction ring is 20-30% of the greatest thickness of the jacket or connecting section cast in each case from the light metal material.The invention is explained in more detail below with reference to a drawing showing an exemplary embodiment. They show in each case schematically: FIG. 1 shows a composite brake drum in a longitudinal section; FIG. 2 shows the composite brake drum in a section along the section line A-A in FIG. 1 ; FIG. 3 shows the composite brake drum in a frontal view.The composite brake drum 1 has a connecting portion 2 oriented normally to its axis of rotation X, which connecting portion has a central opening 3 via which a wheel bearing or the like is accessible when the composite brake drum 1 is fastened to a vehicle axle, not shown here. In addition, five threaded openings 4 are formed in the connecting portion 2 in a conventional manner, distributed at uniform angular distances about the axis of rotation X, into which threaded openings rim screws, not shown here, can be screwed for fastening a wheel of the vehicle, likewise not shown here.Integrally formed on the connecting portion 2 is a jacket portion 5 which extends axially parallel to the axis of rotation X and runs around the axis of rotation X.In the jacket section 5, a friction ring 6 is held which likewise extends around the axis of rotation X and is aligned with its end face 7 facing away from the connection section 2 flush with the free end face 8 of the jacket section 5 aligned normally to the axis of rotation X. The friction ring 6 is seated in a receptacle 9 formed into the casing section 5 and is supported with its end face 10 assigned to the connection section 2 on a circumferential shoulder 11.The friction ring 6 has been cast as a separate part from a cast iron material already known for these purposes, which can be, for example, the material known under the standard designation GJL 150 or the material known under the standard designation GG 225.The friction ring 6 has a first edge region 12 assigned to the connecting portion 2 of the composite brake drum 1, which first edge region begins on the end face 10 of the friction ring 6 facing the connecting portion 2 and extends over approximately two thirds of the total width BR of the friction ring 6. The first edge region 12 is adjoined in the axial direction XR by the end face 7 facing away from the connection section 2 by a transition region 13 of the friction ring 6, which is followed by a second edge region 14 facing away from the connection section 2, which ends at the end face 7 of the friction ring 6 facing away from the connection section 2. This second edge region 14 takes up approximately a quarter of the total width BR of the friction ring 6, while the transition region 13 extends over the remainder of the total width BR not taken up by the edge regions 12, 14.The thickness D 1 of the first edge region 12 facing the connection section 2 increases steadily starting from the end face 10 facing the connection section 2 in a shallow increase following a linear function until the beginning of the transition region 13, so that the thickness D 1 of the first edge region 12 at its boundary to the transition region 13 is approximately 1.1 to 1.2 times its thickness D 1 at the end face 10.The circumferential surface of the transition region 13 is shaped circumferentially in a fillet-like manner about the axis of rotation X, so that the circumferential surface of the first edge region 12 transitions without sudden changes into the second edge region 14 of the friction ring 6.Starting from its boundary to the transition region 13, the thickness D 2 of the edge region 14 facing away from the connection portion 2 likewise increases steadily following a linear function until it has reached its maximum value at the free end face 7 of the friction ring 6, which corresponds approximately to 1.2 to 1.3 times the thickness D 2 of the edge region 14 at the boundary to the transition region 13.On its inner circumferential side 15, a cylindrical friction surface 16 running around the axis of rotation X has been produced on the friction ring 6 in a manner known per se by machining. In use, the brake linings, not shown here, of a braking device, likewise not shown, of the respective vehicle on which the composite brake drum 1 is mounted act against the friction surface 16.On its outer circumferential side, the first edge region 12 of the friction ring 6 facing the connection portion 2 is provided with a structure which extends in a wave-like manner around the axis of rotation X and is formed by elevations 17 which each extend in the axial direction XR axially parallel to the axis of rotation X and by depressions 18 which are laterally bounded in each case by adjacent elevations 17. Both in the region of the depressions 18 and in the region of the elevations 17, the thickness D 1 of the first edge region 12 increases in the manner described above starting from the end face 10 of the friction ring 6, wherein the transition to the thickness D 2 of the second edge region 14 takes place in each case likewise in the manner described above. The circumferential surface 19 of the edge region 14 facing away from the connection section 2, on the other hand, is formed uniformly conically and free of a corresponding surface structure, so that the edge region 14 rotates around the axis of rotation X in the manner of a stiffening ring.During the production of the composite brake drum 1, the connecting portion 2 and the casing portion 5 connected integrally thereto have been cast onto the friction ring 6 in a manner known per se. For this purpose, the friction ring 6 has been placed in a suitably shaped casting mold, into which a molten aluminum has subsequently been poured. The aluminum melt, which is made of an Al material known for these purposes, penetrates into the depressions 18 of the structure on the outer side of the first edge region 12 and covers the elevations 17 on the outer circumferential side of the jacket section 5. In this way, an intensive positively locking clamping of the friction ring 6 with the casing section 5 is achieved, by means of which the braking forces acting on the friction ring 6 during braking operation are reliably transmitted to the unit formed from the casing section 5 and the connecting section 2 and from there to the wheel of the respective vehicle which is connected to the composite brake drum 1 and is not shown here. The Al material here can be the one known under the names EN AC-43400 (EN AC-AlSi10Mg(Fe)), EN AC-44300 (EN AC-AlSi12(Fe)), EN AC-46000 (EN AC-AlSi9Cu3(Fe)), EN AC-46500 (EN AC-AlSi9Cu3(Fe)(Zn)), EN AC 47100 (EN AC-AlSi12Cu1(Fe)) or EN AC-51200 (EN AC-AIMg9).The course of the thicknesses D 1, D 2 of the friction ring 6 provided over the edge regions 12, 14 is adapted to the distribution of the loads occurring over the total width BR of the friction ring 6 during braking in such a way that a substantially uniform distribution of stress is established in the friction ring 6. As a result, the friction ring 6 widens as far as possible uniformly with respect to its width BR, wherein the greater increase in thickness in the region of the edge region 14 prevents excessive widening of the composite brake drum 1 in the region of the free end sides 8, 10 of the casing section 5 and the friction ring 6.REFERENCE NUMERALS1 Composite brake drum 2 Connection section of the composite brake drum 1 3 Central opening of the composite brake drum 1 4 Threaded openings of the composite brake drum 1 5 Shell section of the composite brake drum 1 6 Friction ring of the composite brake drum 1 7 End face of the friction ring 7 8 which is remote from the connection section 2 Free end face of the shell section 5 9 Receptacle of the shell section 5 10 End face of the friction ring 6 11 which is associated with the connection section 2 Circumferential shoulder of the shell section 5 12 First edge region of the friction ring 6 13 Transition section of the friction ring 6 14 Second edge region of the friction ring 6 15 Inner circumferential side of the friction ring 6 16 Friction surface of the friction ring 6 17 Elevations of the structure on the outer circumferential side of the first edge region 12 of the friction ring 6 18 The friction ring 6 has a circumferential surface of the second edge region 14D 1 facing away from the connecting portion 2, a thickness of the first edge region 12D 2 facing away from the connecting portion 2, a thickness of the second edge region 14BR facing away from the connecting portion 2, a total width of the friction ring 6X a rotational axis of the composite brake drum 1XR an axial direction

Claims

Composite brake drum, having a connection section (2) which is oriented perpendicularly to the axis of rotation (X) of the composite brake drum (1) and is provided for connecting the composite brake drum (1) to a wheel which is to be braked in each case, having an annular casing section (5) which is supported by the connection section (2) and rotates about the axis of rotation (X) of the composite brake drum (1), and having a friction ring (6) which is supported by the casing section (5) and also rotates about the axis of rotation (X) of the composite brake drum (1) and has, on its free inner circumferential side, a friction surface (16) which is oriented rotationally symmetrically to the axis of rotation (X) of the composite brake drum (1), wherein the connection section (2) is composed of a light metal material and the friction ring (6) is composed of an iron casting material, wherein the friction ring (6) has a structure on its outer circumferential surface which is formed by elevations (17) and depressions (18) delimited at least in sections by the elevations (17), and wherein the material of the casing portion (5) has penetrated into the depressions (18) of the structure, characterized in that the friction ring (6) has a thickness (D1) in a first edge region (12), which is delimited by its end side (7) facing the attachment portion (2), which is smaller than the thickness (D2) which the friction ring (6) has in its second edge region (14) delimited by the end side (10) facing away from the attachment portion (2), the thickness (D1) of the first edge region (12), starting from its edge assigned to the connecting portion (2), in the direction of the second edge region (14) and the thickness (D2) of the second edge region (14), increase steadily up to the end face (10) facing away from the connecting portion (2), the increase in the thickness (D2) over the second edge region (14) is greater than the increase in the thickness (D1) over the first edge region (12) and the proportion of the width of the second edge region (14) to the width (BR) of the friction ring (6) is greater than the proportion, which the width of the first edge region (12) at the width (BR) of the friction ring (6) assumes, and that at least some of the elevations (17) extend axially parallel to the axis of rotation (X) of the composite brake drum (1).Composite brake drum according to Claim 1, characterized in that the friction ring (6) is seated in a receptacle (9) delimited at least in sections by the casing section (5).Composite brake drum according to Claim 2, characterized in that the receptacle (9) is formed by a shoulder (11) which is formed into the casing section (5) and on which the friction ring (6) is seated.Composite brake drum according to one of the preceding claims, characterized in that a transition region (13) is formed between the edge regions (12, 14) of the friction ring (6), via which transition region the increase in thickness between the first edge region (12) assigned to the connection portion (2) and the second edge region (14) of the friction ring (6) facing away from the connection portion (2) is adapted.Composite brake drum according to one of the preceding claims, characterized in that the thickness (D1) of the first edge region (12) of the friction ring (6) assigned to the connection portion (2) increases in the direction (XR) of the second edge region (14) of the friction ring (6) following a continuous function up to the thickness (D2) of the second edge region (14).Composite brake drum (1) according to Claim 1, characterized in that the elevations (17) are distributed at regular angular spacings about the axis of rotation (X).Composite brake drum (1) according to Claim 1, Claim 5 or Claim 6, characterized in that the structure extends exclusively over the edge region (12, 14) of the friction ring (6) assigned to the connection portion (2) and the optionally present transition portion (13).

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