Drum brake

Abstract

A drum brake (1), in particular for a commercial vehicle, has 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) with a respective friction lining carrier (32) and a friction lining (31) arranged on the carrier, 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 towards an axis of rotation (AR) of the brake drum (2) against an inner surface (21) of the brake drum (2) designed as a friction surface, wherein the wedge ring (5) is mounted on at least two axial bearings (7a, 7b) spaced apart from each other in the circumferential direction of the cylindrical sleeve (61) and movable parallel to the axis of rotation (AD).

Description

[0001] The invention relates to a drum brake according to the preamble of claim 1.

[0002] Drum brakes generally have a cylindrical drum-shaped rotor with friction surfaces arranged on the inside of the rotor, also known as the brake drum. Braking force is generated by brake pads that are pressed against the inner friction surface of the brake drum.

[0003] According to the current state of the art, the actuating force applied to drum brakes for commercial vehicles is usually amplified by means of an S-cam in order to generate the necessary braking torque.

[0004] In the generic drum brakes considered here, whose power transmission is designed in such a way that a force introduced axially to the axis of rotation is amplified by its deflection so that the reaction force acts radially on the friction surface of the brake drum, the brake pads are pressed by means of a wedge that can be moved in the direction of the axis of rotation.

[0005] The reaction force can be divided by activating several pressure pistons.

[0006] It is advantageous to make the wedge as stiff as possible, otherwise the deformation due to the transmission ratio will greatly increase the stroke.

[0007] It is also desirable to keep the hysteresis of the system as low as possible.

[0008] In conventional types of axial bearings, e.g. using plain bearing sleeves, the deformation of the bearing shell due to the required small gap dimensions ensures high friction values, especially under uneven loads.

[0009] Since several punches usually have to be arranged radially, an alternative bearing arrangement using rolling bearings is very difficult, since the positional tolerances of several bearing points relative to each other can only be maintained by very costly manufacturing processes.

[0010] The object of the present invention is to provide a cost-effective drum brake which enables reliable application with low hysteresis.

[0011] The stated object is achieved by a drum brake having the features of claim 1.

[0012] The drum brake according to the invention, in particular for a commercial vehicle, has a brake drum mounted so as to be rotatable about a rotational axis. The drum brake further comprises at least two brake pads mounted in a receiving space of the brake drum, each having a friction pad carrier and a friction pad arranged thereon.

[0013] Furthermore, the drum brake has an application device arranged on an armature housing in a rotationally fixed manner with a wedge ring which can be moved on a cylinder sleeve of the armature housing parallel to the axis of rotation of the brake drum and with which the brake pads can be pressed radially to the axis of rotation of the brake drum against an inner surface of the brake drum designed as a friction surface.

[0014] The wedge ring is movably mounted on at least two axial bearings spaced apart from each other in the circumferential direction of the cylinder sleeve, parallel to the axis of rotation of the brake drum.

[0015] The support of the wedge ring on at least two axial bearings spaced apart from each other in the circumferential direction of the cylinder sleeve and movable parallel to the axis of rotation enables reliable axial mobility of the wedge ring with, at the same time, low hysteresis due to the reduction of the bearing load.

[0016] Advantageous embodiments of the invention are the subject of the subclaims.

[0017] According to an advantageous embodiment, the axial bearings are held frictionally and / or positively on the cylinder sleeve or the wedge ring.

[0018] This allows easy mounting of the axial bearings on the cylinder sleeve or the tapered ring.

[0019] According to a further advantageous embodiment, the positions of the axial bearings on the wedge ring viewed in the circumferential direction are selected such that when a force acts on the wedge ring, a radial distance between bearing surfaces on the inner circumference of the wedge ring and the cylinder sleeve increases.

[0020] According to an advantageous embodiment, each of the axial bearings has a bearing shell, a plurality of rolling elements arranged one behind the other in the bearing shell parallel to the axis of rotation of the brake drum, and a rolling element cage holding the rolling elements to the bearing shell.

[0021] In an advantageous further development, the wedge ring and the axial bearings together form a form-fitting subassembly, which simplifies the assembly of the drum brake overall.

[0022] According to an advantageous further development, the bearing shells can be deformed radially in the direction of the friction surface by elastic deformation of the wedge ring when the brake pads are pressed against the inner surface of the brake drum.

[0023] The radial expansion of these bearing shells advantageously reduces the Hertzian pressure, so that the overall size of the axial bearings can be significantly reduced.

[0024] The axial bearings are preferably designed as ball bearings with rolling elements designed as balls.

[0025] In an advantageous design variant, the rolling element cages are arranged stationary on the respective bearing shell and movable parallel to the rotation axis of the brake drum and radially stationary on the wedge ring.

[0026] The rolling element cages preferably have stops for regulating the axial distances of the rolling elements, the clearance of which is at least 0.5 times the possible axial stroke of the wedge ring.

[0027] In order to prevent the rolling elements, which are preferably designed as balls, from falling out, according to a preferred development an end stop is formed on the wedge ring, against which the last ball of the axial bearing in the direction of movement rests when the drum brake is not actuated.

[0028] According to an alternative design variant, the rolling element cages are arranged stationary on the wedge ring and movable parallel to the rotation axis of the brake drum and radially stationary on the respective bearing shell.

[0029] In this design variant, end stops are preferably formed on the bearing shells to allow the required clearance of the rolling elements and to prevent the rolling elements from falling out.

[0030] Preferred embodiments are explained in more detail below with reference to the accompanying drawings. They show: Fig. 1 a schematic sectional view of a drum brake through a Fig. 2 cutting plane marked I, Fig. 2 a side sectional view of the Fig. 1 shown drum brake in a Fig. 1 cutting plane marked II, Fig. 3 a schematic isometric view of the drum brake with the brake drum hidden, Fig. 4 a further sectional view through an armature housing of the drum brake and the wedge ring movably guided on it by an axial bearing, Fig. 5 a projection view of the Fig. 4 shown assemblies with six axial bearings for supporting the wedge ring on a cylinder sleeve of the armature housing, Fig. 6a a schematic enlarged detail of a Fig. 5 section marked Vla, Fig. 6b one of the Fig. 6a corresponding representation of a Fig. 5 section marked VIb showing an alternatively designed axial bearing, Fig. 7 an isometric view of the Fig. 5 shown assemblies, Fig. 8a an isometric view of the thrust bearing according to Fig. 6a, Fig. 8b an isometric view of an axial bearing according to Fig. 6b, Fig. 9 a plan view of a variant of a wedge ring, Fig. 10 a plan view of the Fig. Bearing shell shown in 8a, Fig. 11 a sectional view of the Fig. 10 shown bearing shell, Fig. 12 a front view of the rolling element cage according to Fig. 8a, Fig. 13 a plan view of the rolling element cage according to Fig. 8a, Fig. 14 a plan view of the axial bearing consisting of bearing shell, rolling elements and rolling element cage according to Fig. 8a, Fig. 15 to 19 den Fig. 10 to 14 corresponding representations of the axial bearing according to Fig. 8b, Fig. 20 one of the Fig. 5 corresponding representation of the armature housing with wedge ring in a design variant with four instead of six axial bearings and Fig. 21 a schematic enlarged detail of a Fig. 5 section marked Vla under force to show the curvature of the bearing shells.

[0031] In the following description of the figures, terms such as top, bottom, left, right, front, rear, etc., refer exclusively to the exemplary representation and position of the drum brake, brake drum, brake pads, bearing housing, tapered ring, thrust bearing, and the like chosen in the respective figures. These terms are not to be understood as limiting; i.e., these references may change due to different operating positions or the mirror-symmetrical design, etc.

[0032] In the Fig. 1 and Fig. 2, the reference numeral 1 denotes an embodiment variant of a drum brake according to the invention, in particular for use on a commercial vehicle.

[0033] The drum brake 1 has a brake drum 2 which is mounted so as to be rotatable about a rotation axis AR and which is connected in a rotationally fixed manner to a hub of a wheel axle (not shown here) via an armature housing 6.

[0034] In a receiving space 22 within the brake drum 2, a plurality of brake pads 3 are arranged, each with a friction lining carrier 32 and a friction lining 31 arranged thereon. The brake pads 3 are arranged with their friction linings 31 facing an inner surface 21 of the brake drum 2, as is shown for example in the Fig. 1, Fig. 2 in Fig. 3 is shown.

[0035] On the armature housing 6, shown as an example in Fig. 3, an 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 rotational axis AR of the brake drum 2, with which the brake pads 3 are applied to the inner surface 21 of the brake drum 2, which is designed as a friction surface, radially to the rotational axis AR of the brake drum 2 (direction r in Fig. 1) can be pressed on.

[0036] In order to transmit the movement of the wedge ring 5 to the brake pads 3, a respective pressure wedge 33 is arranged as part of a respective brake pad 3 on a side of the friction pad carrier 32 facing away from the friction pad 31.

[0037] This pressure wedge 33 rests on a pressure surface 51 of the wedge ring 5, as shown in the Fig. 1 and Fig. 2 is clearly visible.

[0038] The wedge ring 5 is, for example, via a rod coupled to a brake piston parallel to the rotation axis AR of the brake drum 2 from a non-braking position into a braking position in a direction z, shown in Fig. 2, movable.

[0039] A slide 4 with a plurality of rolling elements 41 is arranged between the wedge ring 5 and the pressure wedge 33 of the brake pad 3 in order to reduce the friction between the pressure surface 51 of the wedge ring 5 and the pressure wedge 33 of the brake pad 3.

[0040] How further, especially in Fig. 2, in order to reduce the friction between the cylinder sleeve 61 of the armature housing 6 and the wedge ring 5, at least two axial bearings 7a, 7b spaced apart from one another in the circumferential direction of the cylinder sleeve 61 are arranged for axially displaceable mounting parallel to the axis of rotation AR.

[0041] In the preferred embodiments shown, the axial bearings 7a, 7b are designed as ball bearings. The tapered ring 5 is supported on the cylindrical sleeve 61 of the armature housing 6 by means of the axial bearings 7a, 7b at at least two, preferably at least three, bearing points distributed around the circumference.

[0042] The maximum possible number of bearing points is determined by the deformation of the wedge under load.

[0043] So in the Fig. 4 and Fig. 5 shows an embodiment with a total of 6 axial bearings 7a, 7b. In Fig. 20 shows an embodiment with a total of 4 axial bearings 7a, 7b.

[0044] The positioning of the axial bearings 7a, 7b is preferably such that the wedge ring 5 is stabilized by the multi-sided application of force by the plurality of pressure wedges 33 of the brake pads 3 distributed over the circumference, which introduce force onto the wedge ring 5 during a braking operation, analogous to a pipe under external pressure.

[0045] The axial bearings 7a, 7b are preferably held frictionally and / or positively on the cylinder sleeve 61 or, as shown in the embodiments shown, on the wedge ring 5.

[0046] Furthermore, the axial bearings 7a, 7b are preferably designed as ball bearings with rolling elements designed as balls 72.

[0047] Each of the axial bearings 7a, 7b has, as shown in the Fig. 7, Fig. 8a and Fig. 8b, a bearing shell 71a, 71b, a plurality of rolling elements arranged one behind the other in the bearing shell 71a, 71b parallel to the rotational axis AR of the brake drum 2, in the embodiments shown balls 72, and a rolling element cage 73a, 73b holding the rolling elements on the bearing shell 71a, 71b, designed as a ball cage in the embodiments shown.

[0048] The use of the plurality of axial bearings 7a, 7b together with the use of balls 72, which are guided on bearing surfaces 52 of the wedge ring 5, which are shaped as ball tracks concave to the balls 72, on the one hand, and on running surfaces 712a, 712b in the bearing shells 71a, 71b, which are shaped as ball tracks, on the other hand, enables tolerance compensation, in particular of the positional tolerance on the cylinder sleeve 61 of the armature housing 6, on which the undersides of the bearing shells 71a, 71b, facing away from the running surfaces 712a, 712b, rest, and on the wedge ring 5.

[0049] The curvature of the bearing surfaces 52 of the wedge ring 5 and the running surfaces 712a, 712b in the bearing shells 71a, 71b is less than the curvature of the spherical surface of the balls 72.

[0050] The position tolerance is compensated by the rotational degree of freedom of the bearing shells 71a, 71b during assembly.

[0051] Furthermore, the bearing play is compensated by the fact that the balls 72 can move parallel to the rotation axis AR of the brake drum 2 relative to the wedge ring 5 and the bearing shells 71a, 71b.

[0052] The geometry of the wedge ring 5 is designed such that the bearing surfaces 52 in the wedge ring 5 move away from the balls 72 under load. Accordingly, the bearing shells 71a, 71b are radially deformable when the brake pads 3 are pressed against the inner surface 21 of the brake drum 2 due to the elastic deformation of the wedge ring 5 described above.

[0053] The positions of the axial bearings 7a, 7b on the wedge ring 5 viewed in the circumferential direction are preferably selected such that when a force acts on the wedge ring 5, a radial distance between bearing surfaces 52 on the inner circumference 54 of the wedge ring 5 and the cylinder sleeve 61 increases.

[0054] This relief on the axial bearings 7a, 7b greatly reduces the hysteresis, since the axial bearings 7a, 7b are largely load-free when actuated.

[0055] In the non-actuated case, however, the wedge ring 5 is optimally supported against vibration loads, since the bearing clearance on all axial bearings 7a, 7b is very small.

[0056] When designing the wedge ring 5, it is important to ensure that the expansion on the bearing shell 71a, 71b, as shown in Fig. 21, is as elastic as possible in the radial direction (expansion R) under load.

[0057] In the circumferential direction, elastic-plastic deformation is permissible (expansion U in Fig. 21), as long as the curvature of the bearing shell 71a, 71b remains smaller than the curvature of the spherical surface.

[0058] The design of the axial bearings 7a, 7b with rolling element cage 73a, 73b, which is possible in two functional variants, proves to be advantageous.

[0059] For ease of illustration, both variants were Fig. 7 in an assembly. However, in technical applications, only one variant makes sense.

[0060] In one in the Fig. In the variant shown in Figures 10 to 14, the rolling element cages 73a are arranged stationary on the respective bearing shell 71a and movable parallel to the rotation axis AR of the brake drum 2 and radially stationary on the wedge ring 5.

[0061] The fixed fixing to the respective bearing shell 71a is preferably carried out by means of a clamping connection in a retaining groove 713a, as shown in the Fig. 8a and Fig. 14 is shown.

[0062] In addition, a geometry provided on the rolling element cage 73a, preferably in the form of a clamping leg 731a, engages in a geometry attached to the wedge ring 5, preferably an undercut 55, as shown in the Fig. 6a, Fig. 6b and Fig. 21 shows that the wedge ring 5 and the axial bearings 7a together form a form-fitting subassembly, but are mounted axially movable relative to the wedge ring 5.

[0063] The resulting subassembly consisting of wedge ring 5, bearing shells 71a, rolling element cages 73a and balls 72 can thus be assembled as a whole in the subsequent assembly steps.

[0064] When designing the rolling element cage 73a, in this embodiment, the first ball 72 viewed from the direction of movement z rests against the rolling element cage 73a, whereby the last ball 72 in the direction of movement z requires a clearance of at least 0.5 times the maximum stroke to the rolling element cage 73a, as shown in Fig. 14 is shown.

[0065] In this version, the last ball 72 in the direction of movement z rests against an end stop 53 in the wedge ring 5 when the drum brake 1 is not actuated (see Fig. 4), otherwise the balls 72 would be shaken out of position.

[0066] Since the end stops in this design variant are mounted in two different components, a design clearance must be provided to cover the tolerance position.

[0067] In one in the Fig. 6b, Fig. 8b and 15 to 19, the rolling element cage 73b is locked radially and axially stationary on the wedge ring 5, ideally by clamping the joined geometries (see Fig. 6b).

[0068] The connection of the rolling element cage 73b to the bearing shell 71b, however, is only radially secured, but is mounted so as to be freely displaceable axially.

[0069] This in turn creates the subassembly already described in the previously described design variant.

[0070] The rolling element cage 73b is provided with stop geometries such as a stop 713b, shown in Fig. 8b, which are located in front of the balls 72 in the direction of movement z. The rolling element cage 73b, which is axially fixed in the wedge ring 5, travels twice the distance relative to the balls 72 within one stroke. Thus, for the Fig. 19 shown condition: ball diameter ≥ distance ≥ 0.5 times stroke.

[0071] Due to the required clearance, in this design variant of the axial bearing 7, an end stop 713b is provided on the bearing shell 71b for the first ball 72, as is also the case in Fig. 15 is shown. List of reference symbols 1 drum brake 2 brake drums 21 Shell inner surface 22 Recording room 3 brake pad 31 Friction lining 32 friction lining carriers 33 Pressure wedge 4 sleds 41 rolling elements 5 wedge ring 51 pressure surface 52 storage areas 53 End stop 54 inner circumference 55 undercut 6 armature housings 61 Cylinder sleeve 62 Pad holder 7a Thrust bearing 71a bearing shell 711a side edge 712a tread 713a retaining groove 72 ball 73a Rolling element cage 731a clamping leg 732a slot 733a Holding bridge 7b Thrust bearing 71b bearing shell 711b side edge 712b tread 713b stop 72 ball 73b Rolling element cage 731b clamping leg 732b Long hole 733b Holding bridge AR rotation axis D Diameter ball r direction z direction f outdoor access

Claims

[1] Drum brake (1), in particular for a commercial vehicle, comprising - a brake drum (2) mounted so as to be rotatable about an axis of rotation (AR), - at least two brake pads (3) mounted in a receiving space (22) of the brake drum (2) with a respective friction pad carrier (32) and a friction pad (31) arranged thereon, - an application device arranged on an armature housing (6) in a rotationally fixed manner, 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), with which the brake pads (3) can be pressed against an 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 by , that - the wedge ring (5) is movably mounted on at least two axial bearings (7a, 7b) spaced apart from one another in the circumferential direction of the cylinder sleeve (61) parallel to the axis of rotation (AD). [2] Drum brake (1) according to claim 1, characterized by that the axial bearings (7a, 7b) are held frictionally and / or positively on the cylinder sleeve (61) or the wedge ring (5). [3] Drum brake (1) according to claim 1 or 2, characterized by that the positions of the axial bearings (7a, 7b) on the wedge ring (5) viewed in the circumferential direction are selected such that when force is applied to the wedge ring (5), a radial distance between bearing surfaces (52) on the inner circumference (54) of the wedge ring (5) and the cylinder sleeve (61) increases. [4] Drum brake (1) according to one of the preceding claims characterized by that each of the axial bearings (7a, 7b) has a bearing shell (71a, 71b), a plurality of rolling elements arranged one behind the other in the bearing shell (71a, 71b) parallel to the axis of rotation (AR) of the brake drum (2), and a rolling element cage (73a, 73b) holding the rolling elements on the bearing shell (71a, 71b). [5] Drum brake (1) according to one of the preceding claims, characterized bythat the wedge ring (5) and the axial bearings (7a, 7b) together form a form-fitting subassembly. [6] Drum brake (1) according to claim 4 or 5, characterized by that the bearing shells (71a, 71b) are radially deformable by elastic deformation of the wedge ring (5) when the brake pads (3) are pressed against the inner surface (21) of the brake drum (2). [7] Drum brake (1) according to one of the preceding claims, characterized by that the axial bearings (7a, 7b) are designed as ball bearings with rolling elements designed as balls (72). [8] Drum brake (1) according to one of claims 4 to 7, characterized by that the rolling element cages (73a) are arranged stationary on the respective bearing shell (71a) and movable parallel to the axis of rotation (AR) of the brake drum (2) and radially stationary on the wedge ring (5). [9] Drum brake (1) according to 8, characterized bythat the rolling element cages (73a) have stops for regulating the axial distances of the rolling elements, the clearance of which is at least 0.5 times the possible axial stroke of the wedge ring (5). [10] Drum brake (1) according to 9, characterized by that an end stop (53) is formed on the wedge ring (5). [11] Drum brake (1) according to one of claims 4 to 7, characterized by that the rolling element cages (73b) are arranged stationary on the wedge ring (5) and movable parallel to the axis of rotation (AR) of the brake drum (2) and radially stationary on the respective bearing shell (71b). [12] Drum brake (1) according to claim 11, characterized by that an end stop (713b) is formed on the bearing shells (71b).

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