Drum brake

Abstract

A drum brake (1), in particular for a commercial vehicle, comprises a brake drum (2) rotatably mounted about an axis of rotation (AR), at least two brake linings (3) mounted in a receiving space (22) of the brake drum (2), each with a friction lining carrier (32) and a friction lining (31) arranged thereon, and a clamping device arranged non-rotatably on an anchor housing (6) with a wedge ring (5) displaceable on a cylindrical sleeve (61) of the anchor housing (6) parallel to the axis of rotation (AR) of the brake drum (2), with which the brake linings (3) can be pressed radially to the axis of rotation (AR) of the brake drum (2) via a respective pressure piston (34), wherein the pressure pistons (34) are arranged about the axis of rotation (AR) of the brake drum (2) in such a way as tothat, starting from a radial axis (Tr2) of a first printing die (34), a first angular distance (W12) to a radial axis (Tr1) of a second printing die (34) adjacent in a circumferential direction (U) is not equal to a second angular distance (W23) to a radial axis (Tr3) of a printing die (34) adjacent opposite to the circumferential direction (U), wherein the ratio of the smaller of the angular distances (W12) to the larger of the angular distances (W23) does not exceed the limit of 0.8 and does not fall below the limit of 0.6.

Description

The invention relates to a drum brake according to the preamble of claim 1.Drum brakes generally have a cylinder drum-shaped rotor with friction surfaces arranged on an inner side of the rotor, also referred to as a brake drum. A braking force is generated with brake pads which are pressed against the inner friction surface of the brake drum.According to the present state of the art, in drum brakes for utility vehicles, the introduced actuating force is generally amplified by means of an S-cam in order to generate the necessary braking torques.In this case, as a rule, two brake shoes, which are mounted rotatably on one side, are pressed against the inner wall of the brake drum in a force-enhanced manner by means of the eccentric action of the S-cam. By using two brake shoes, the system is relatively stable with respect to its eigenmodes with respect to noise generation.In the generic drum brakes considered here, the force transmission of which is configured such that a force introduced axially with respect to the axis of rotation is amplified by deflecting the latter such that the reaction force acts radially on the friction surface of the brake drum, the brake pads are pressed on by means of a wedge which is displaceable in the direction of the axis of rotation.The reaction force can be divided by actuating a plurality of plungers.In these drum brakes, it is significantly more likely to meet the eigenmodes of the system with respect to noise generation.This is primarily due to the fact that the introduction of force must take place more centrally with respect to the brake lining and the possible expansion of a brake lining in the circumferential direction is thus limited.Consequently, in this system, at least three brake pads are usually necessary so that the system is not overloaded with regard to surface pressure of the friction material and thermal load.Due to the higher number of force introduction points, the system is, however, more unstable with respect to the generation of audible or perceptible oscillations, the so-called NVH behavior (noise vibration").It is an object of the present invention to provide a drum brake of the generic type with improved NVH behavior.The object set is achieved by a drum brake having the features of claim 1.The drum brake according to the invention, in particular for a commercial vehicle, has a brake drum mounted rotatably about an axis of rotation.The drum brake furthermore has a number of at least two brake linings mounted in a receiving space of the brake drum, with a respective friction lining carrier and a friction lining arranged on the latter.Furthermore, the drum brake has a brake application device which is arranged on an armature housing in a rotationally fixed manner and has a wedge ring which is displaceable on a cylinder sleeve of the armature housing parallel to the axis of rotation of the brake drum and by means of which the brake pads can be pressed via a respective pressure plunger onto a casing inner surface of the brake drum which is designed as a friction surface radially with respect to the axis of rotation of the brake drum.The printing punches are arranged about the axis of rotation of the brake drum in such a way that, starting from a radial axis of movement of a first of the printing punches, a first angular distance from a radial axis of movement of a second printing punch adjacent in a circumferential direction is not equal to a second angular distance from a radial axis of movement of a printing punch adjacent opposite to the circumferential direction.The ratio of the smaller of the angular distances (W 12) to the larger of the angular distances (W 23) does not exceed the limit value of 0.8 and does not fall below the limit value of 0.6.The following applies here to the smaller of the angular distances:For the larger of the angular distances, the following applies: where N w is the number of pressure rams or brake pads.The asymmetry in the arrangement of the brake pads within the brake drum which is provided in this way makes it possible to avoid eigenmodes of the system, which leads to significantly lower noise development than in the case of a uniform distribution of the brake pads.In addition, this makes it possible to avoid relative micro-movements between the pad carrier plates of the brake pads and the armature housing.Advantageous embodiment variants of the invention are the subject matter of the dependent claims.According to an advantageous embodiment variant, the number of brake pads and plungers is four or six, wherein the plungers are arranged opposite one another in pairs relative to the axis of rotation.Due to the brake linings arranged opposite one another in pairs, forces exerted on the brake drum during a braking operation can cancel one another out.According to a further advantageous embodiment variant, a brake pad length viewed in the rotational direction and a support height of the brake pads viewed in the radial direction are dimensioned such that the quotient of length and support height is greater than / equal to 6 and less than / equal to 22.According to an advantageous development, with a friction radius R of the brake drum of 150 mm≤R<175 mm, the brake lining length is not more than 200 mm, with a friction radius of 175 mm≤R<200 mm is not more than 240 mm and with a friction radius of 200 mm≤R<230 mm is not more than 280 mm.According to a further advantageous development, for a friction radius of the brake drum of 150 mm≤R<175 mm and a maximum brake lining length of 200 mm, the quotient of length L and supporting height H applies:With a friction radius of the brake drum of 175 mm≤R<200 mm and a maximum brake lining length of 240 mm, the quotient of length L and supporting height H applies accordingly:With a friction radius of the brake drum of 200 mm≤R<230 mm and a maximum brake lining length of 280 mm, the quotient of length L and supporting height applies:According to a further advantageous embodiment variant, the brake lining width B, viewed in the direction of the axis of rotation in the installed state: wherein A Drum is defined as the free surface of the brake drum without its flange region.Preferred exemplary embodiments are explained in more detail below with reference to the attached drawings. The following are shown: FIG. 1 shows a schematic isometric view of an embodiment variant of a drum brake according to the invention, FIG. 2 shows a schematic sectional view of the drum brake shown in FIG. 1 through a sectional plane denoted by II in FIG. 3, FIG. 3 shows a side sectional view of the drum brake shown in FIG. 1 in a sectional plane denoted by III in FIG. 2, FIG. 4 is an enlarged fragmentary sectional view of FIG. 2 showing the angular spacing of adjacent brake pads; and FIG. 5 shows a further enlarged detail of the sectional view shown in FIG. 2 for illustrating the relative dimensions of the brake pads.In the following description of the figures, terms such as top, bottom, left, right, front, rear etc. refer exclusively to the exemplary illustration and position of the drum brake, of the brake drum, of the brake linings, of the bearing housings, of the wedge ring, of the printing rams and the like selected in the respective figures. These terms are not to be understood as limiting, i.e. these references can change due to different working positions or the mirror-symmetrical design or the like.In FIGS. 1, 2 and 3, reference numeral 1 designates overall an embodiment variant of a drum brake according to the invention, in particular for use on a commercial vehicle.The drum brake 1 has a brake drum 2 which is mounted rotatably about an axis of rotation AR and is connected in a rotationally fixed manner via an armature housing 6 to a hub, not shown here, of a wheel axle.A plurality of brake pads 3, in the exemplary embodiment shown four brake pads 3, are arranged in a receiving space 22 within the brake drum 2, with a respective friction pad carrier 32 and a friction pad 31 arranged on the latter. The brake linings 3 are arranged with their friction linings 31 facing an inner jacket surface 21 of the brake drum 2, as is illustrated by way of example in FIGS. 2 to 5.On the armature housing 6, a brake application device is arranged with a wedge ring 5 which is displaceable on a cylinder sleeve 61 of the armature housing 6 parallel to the axis of rotation AR of the brake drum 2 and by means of which the brake pads 3 can be pressed against the casing inner surface 21 of the brake drum 2 which is designed as a friction surface radially with respect to the axis of rotation AR of the brake drum 2 (direction r shown in FIG. 1 ), as can be seen clearly in FIG. 3.For transmitting the movement of the wedge ring 5 to the brake pads 3, a respective pressing wedge 33 is arranged as part of a respective brake pad 3 on a side of the friction pad carriers 32 facing away from the friction pad 31. The pressure wedge 33 is connected to the friction lining carrier 32 via a pressure ram 34.The pressure wedge 33 lies on a pressure surface 51 of the wedge ring 5, as can be seen in FIG. 3.The wedge ring 5 is displaceable, for example, via a brake piston parallel to the axis of rotation AR of the brake drum 2 from a non-braking position into a braking position in a direction z, shown in FIG. 3.Between the wedge ring 5 and the pressing wedge 33 of the brake lining 3, a slide 4 with a plurality of rolling bodies 41 is arranged in order to reduce the friction between the pressing surface 51 of the wedge ring 5 and the pressing wedge 33 of the brake lining 3.The number N w of the brake pads 3 arranged in the receiving space 22 within the brake drum 2 depends primarily on the maximum transmittable force of the components located in the force flow, the dimensioning of which is in turn limited by the installation space available.The surface pressure on the friction material of the friction lining 31 is determined by the force introduced per pressure ram 34 with the friction surface available per brake lining 3.Particularly preferably, four brake pads 3 are installed in the receiving space 22 within the brake drum 2.Depending on the requirement for the resulting braking torque, two, three or even five, six or more brake pads 3 are also conceivable, for example.The arrangement of the brake linings 3 is in principle most advantageous with regard to its force distribution to the components lying in the force flow in the case of a uniform distribution within the brake drum 2. This would mean an angular division of 4×90°=3604 in the case of four printing punches 34. For the NVH behavior, however, a uniform distribution is always in the range of eigenmodes and is thus worst.With regard to the force-transmitting components, however, it is advantageous to choose a force transmission that is evenly distributed, since opposing forces cancel one another out at the bearing.Therefore, to reduce audible or perceptible oscillations and to enable the most homogeneous possible introduction of force, an even number of plungers 34 or brake pads 3 is preferred, wherein the plungers 34 or brake pads 3 are arranged opposite one another in pairs offset from one another by 180°, but have a different angle to their respective adjacent plungers 34.The ratio of a smaller of the angular distances W 12 to a larger of the angular distances W 23 is selected such that it does not exceed the limit value of 0.8 and does not fall below the limit value of 0.6.Thus, in the exemplary embodiment shown in FIG. 4 with four pressure rams 34 or four brake pads 3, the angular spacing W 1,2 of the radial axes between a first of the pressure rams 34 and an adjacent second of the pressure rams 34 is 75°, the angular spacing W 2,3 of the radial axes between the second of the pressure rams 34 and an adjacent third of the pressure rams 34 is 105°. The angular distance between the third and fourth printing punches 34 again corresponds to the angular distance W 1,2 and the angular distance between the fourth and first printing punches 34 again corresponds to the angular distance W 2,3.The ratio between the smaller of the angular distances W 1,2 and the larger of the angular distances W 23 is therefore approximately 0.7 here.For the smaller of the angular distances (W 12) the following applies depending on the number of brake linings 3 or pressure rams 34 arranged in the brake drum:The same applies to the larger of the angular distances (W 23) depending on the number of brake pads 3 or pressure rams 34 arranged in the brake drum:In addition to the asymmetry of the adjacent angles (angular distances W 12, W 23) in order to avoid resonances on account of the eigenmodes, the so-called servo effect plays a decisive role in the attenuation of the noise development.The servo effect arises due to the opposite direction of the radial force vectors of the tangential forces occurring at the friction pairing of brake drum 2 to the friction material of friction lining 31 of brake lining 3.Because the force introduced is introduced in the central region of the brake pads 3, the brake pad 3 is divided into two regions.The ascending region of the brake lining 3 is understood to mean the region in which the brake drum 2 first passes the location of the introduction of force in the direction of rotation and then the contact side of the friction lining 31 of the brake lining 3.In the trailing region of the brake lining 3, on the other hand, the brake drum 2 first passes the contact side of the friction lining 31 of the brake lining 3 in its rotational direction and then impinges on the location of the introduction of force.Important here is a necessary minimum lever arm H, which, as is shown in FIG. 5, lies between the contact of the lining carrier plate 32 of the brake lining 3 with the housing 6 and the force introduction surface of the lining carrier plate 32 at the interface with the printing die 34.In this case, the available supporting torques are considered as counter-torques to the torque introduced by the servo effect. With sufficiently high supporting torques, a stable state is established.If the servo moment becomes greater than the existing opposing moments, the situation becomes unstable, which in the microscopic range leads to a flutter of the brake lining 3 at the supporting point in the housing 6 and thus significantly to the generation of undesirable noises.Thus, the brake pad length L viewed in the direction of rotation U and the support height H of the brake pads 3 viewed in the radial direction r are preferably dimensioned such that the quotient of the brake pad length L and the support height H applies:In a preferred exemplary embodiment, with a friction radius R of the brake drum 2 of 150 mm≤R<175 mm, the brake lining length L is a maximum of 200 mm.With a friction radius R of the brake drum 2 of 175 mm≤R<200 mm, the brake pad length L is preferably at most 240 mm and with a friction radius R of the brake drum 2 of 200 mm≤R<230 mm, the brake pad length L of 280 mm is preferably not exceeded.Particularly preferably, with a friction radius R of the brake drum 2 of 150 mm≤R<175 mm and a maximum brake lining length L of 200 mm, the quotient of brake lining length L and support height H applies:In the case of a friction radius R of the brake drum 2 of 175 mm≤R<200 mm and a maximum brake lining length L of 240 mm, the quotient of length (L) and supporting height (H) is preferably:In the case of a friction radius R of the brake drum 2 of 200 mm≤R<230 mm and a maximum brake lining length L of 280 mm, the quotient of length (L) and supporting height (H) is preferably:In the following, the width B of the brake lining 3 describes its extent parallel to the axis of rotation AR of the brake drum 2.The surface coverage ratio is understood to mean the percentage of the friction surface of the brake drum that is covered with the surface of the friction material of the friction lining of the brake linings.Since in the above-described type of force transmission the advantages of a disc brake with regard to its friction pairing is to be transferred to the principle of the drum brake, the conditions prevailing there serve as a comparison value for the design described herein.In the case of disc brakes for commercial vehicles, there is a surface coverage ratio of approximately 16%. Usually, the pure friction surface of the rotor is considered here. Since in drum brakes, contrary to the brake linings resting on both sides in the case of disc brakes, the friction surface is only loaded under pressure on one side, a larger surface of the rotor must be taken into account here. Likewise, in operation, with comparable use, the brake drums are at a lower temperature level compared to the brake disks, since a larger area is available for the heat emission. For this reason, a slightly higher area coverage ratio of 20% is set.It should be noted that, due to the given application space, the free surface of the brake drum 2 is approximately constant and is only slightly influenced by the varying brake lining width B. The free surface A Drum of the brake drum 2 takes into account the surface of the brake drum 2 minus the area of the flange portion 23.For the brake lining width (B), viewed in the installed state in the direction of the axis of rotation (AR), the following applies preferably:The maximum permissible brake pad width B is, for example, 162 mm for a friction diameter R of 213.5 mm, a number N w of 4 brake pads, a brake pad length L of 200 mm and a free surface A Drum of the brake drum 2 of 6760 cm 2 thus.It should be noted that the maximum permissible width B increases with increasing free surface area A Drum of the brake drum 2 and decreases with increasing brake lining length L.List of reference characters1 Drum brake 2 Brake drum 21 Casing inner surface 22 Receiving space 23 Flange region 3 Brake lining 31 Friction lining 32 Friction lining carrier 33 Pressure wedge 34 Pressure plunger 4 Slide 41 Rolling bodies 5 Wedge ring 51 Pressure surface 52 Bearing surface 53 End stop 54 Inner periphery 55 Undercut 6 Armature housing 61 Cylinder sleeve 62 Lining receptacle AR Axis of rotation U Circumferential direction of the brake drum R Friction radius of the brake drum r Direction z Direction T r1 Radial axis T r2 Radial axis T r3 Radial axis N w Number of brake linings L Brake lining length B Brake lining width H Support height

Claims

Drum brake (1) for a commercial vehicle, having - a brake drum (2) mounted rotatably about an axis of rotation (AR), - a number (N w) of at least two brake pads (3) mounted in a receiving space (22) of the brake drum (2), having a respective friction pad carrier (32) and a friction pad (31) arranged thereon, - a brake application device arranged rotationally fixedly on an armature housing (6) and having a wedge ring (5) displaceable on a cylinder sleeve (61) of the armature housing (6) parallel to the axis of rotation (AR) of the brake drum (2), with which the brake pads (3) can be pressed via a respective pressure plunger (34) onto a casing inner surface (21) of the brake drum (2) designed as a friction surface radially to the axis of rotation (AR) of the brake drum (2), characterized in that, the printing rams (34) being arranged about the axis of rotation (AR) of the brake drum (2) in such a way that, starting from a radial axis (T r2) of a first of the printing rams (34), a first angular distance (W 12) to a radial axis (T r1) of a second printing ram (34) adjacent in a circumferential direction (U) is not equal to a second angular distance (W 23) to a radial axis (T r3) of a printing ram (34) adjacent counter to the circumferential direction (U), wherein the ratio of the smaller of the angular spacings (W 12) to the larger of the angular spacings (W 23) does not exceed the limit value of 0.8 and does not fall below the limit value of 0.6, - and wherein the smaller of the angular spacings (W 12) is to be considered: 320 ° N W ≥ W 12 ≥ 270 ° N W - and wherein the larger of the angular spacings (W 23) is to be considered: 400 ° N W ≥ W 23 ≥ 450 ° N W. Drum brake (1) according to Claim 1, characterized in that the number (N w) of the brake pads (3) and the pressure rams (34) is four or six, the pressure rams (34) being arranged opposite one another in pairs relative to the axis of rotation (AR).Drum brake (1) according to Claim 1 or 2, characterized in that a brake pad length (L) as viewed in the direction of rotation and a supporting height (H) of the brake pads (3) as viewed in the radial direction are dimensioned such that the quotient of length (L) and supporting height (H) is 6 ≤ L H ≤ 22 Drum brake (1) according to Claim 3, characterized in that, with a friction radius (R) of the brake drum (2) of 150 mm ≤ R < 175 mm, a brake lining length (L) of 200 mm is exceeded, with a friction radius (R) of the brake drum (2) of 175 mm ≤ R < 200 mm, a brake lining length (L) of 240 mm is not exceeded, and with a friction radius (R) of the brake drum (2) of 200 mm ≤ R < 230 mm, a brake lining length (L) of 280 mm is not exceeded.Drum brake (1) according to Claim 4, characterized in that a) for a friction radius (R) of the brake drum (2) of 150 mm ≤ R < 175 mm and a maximum brake lining length (L) of 200 mm applies to the quotient of length (L) and supporting height (H): 6.4 ≤ L H ≤ 16 ; b) for a friction radius (R) of the brake drum (2) of 175 mm ≤ R < 200 mm and a maximum brake lining length (L) of 240 mm applies to the quotient of length (L) and supporting height (H): 6.3 ≤ L H ≤ 15 ; _ner16_c) and, with a friction radius (R) of the brake drum (2) of 200 mm≤R<230 mm and a maximum brake lining length (L) of 280 mm, the quotient of length (L) and supporting height (H) holds: 6.2≤L H≤14. Drum brake (1) according to one of the preceding claims, characterized in that the following applies to the brake lining width (B) viewed in the direction of the axis of rotation (AR) when installed: B ≤ 20% × A D r u m 2 asin ( L 2 R ) R N W where A Drum is defined as the free surface of the brake drum (2) without its flange region (23).

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