DRUM BRAKE HAVING COMPENSATION OF BRAKE-SHOE TRANSVERSE OFFSET

Abstract

A drum brake for an electrical motor vehicle brake system wherein actuator means, a transmission means and a spreading device are in a force flow with movably mounted drum brake shoes that are suitable and designed to cooperate with a brake drum. The force flow, in a electromechanically actuatable drum brake such that closed-loop electrical brake control in conjunction with simple actuator control is made possible with reduced outlay over the entire wearing service life of the brake shoe. Transverse offset compensation is provided by way of, a joint-disk-type/joint-socket-type bearing geometry such that a friction lining bearing support geometry with profiling allowing mutual articulation such that transversely oriented lining displacement with respect to the a direction is at least reduced.

Claims

1. A drum brake (1) for a motor vehicle brake system, wherein actuator means, specifically in particular an electrical geared motor drive module including a rotation-translation converter gearing stage, a transmission means and/or a spreading device (2) including an actuating element (15, 16), optionally supported on an abutment (3), are in a force flow, via support bearings, with movably mounted brake shoes (7, 8) that are suitable and designed to cooperate with a brake drum (5), characterized in that a compensation device for brake shoe transverse offset is provided adjacent to the spreading device (2) and/or to the abutment (3), wherein the compensation device is incorporated, laterally adjacent to the spreading device (2) and/or to the abutment (3), into the force flow of the brake shoe (7, 8) of the drum brake (1).

2. The drum brake (1) for a motor vehicle brake system as claimed in one or more of the preceding claims, characterized in that the compensation device is positioned in a brake drum interior space.

3. The drum brake (1) for a motor vehicle brake system as claimed in one or more of the preceding claims, characterized in that the compensation device is incorporated in form-fitting fashion directly into an interface between abutment (3) and brake shoe (7, 8) and/or between actuating element (15, 16) and brake shoe (7, 8).

4. The drum brake (1) for a motor vehicle brake system as claimed in one or more of the preceding claims, characterized in that the compensation device is incorporated in form-fitting fashion indirectly, in particular with the aid of at least one adapter component, into an interface between spreading device (2) and brake shoe (7, 8) and/or abutment (3).

5. The drum brake (1) for a motor vehicle brake system as claimed in one or more of the preceding claims, characterized in that the compensation device has, in its mutual contact region, a joint-like or movable bearing arrangement with a positive guide.

6. The drum brake (1) for a motor vehicle brake system as claimed in one or more of the preceding claims, characterized in that the positive guide of the compensation device between spreading device (2)/actuating element (15, 16) and brake shoe (7, 8) and/or abutment (3) is implemented as a track guide with a 2-dimensionally curved arcuate shape in the manner of a joint disk/joint socket.

7. The drum brake (1) for a motor vehicle brake system as claimed in one or more of the preceding claims, characterized in that the curved guide arranged in the manner of a joint has one or more circular arc segments.

8. The drum brake (1) for a motor vehicle brake system as claimed in one or more of the preceding claims, characterized in that the different paired circular arc segments are in nestled contact, with respective curvatures oriented in the same direction, but are of different radius R.

9. The drum brake (1) for a motor vehicle brake system as claimed in one or more of the preceding claims, characterized in that, in a mutual relationship, a (master) radius R positioned on an actuating element is dimensioned to be gradually smaller than a (slave) radius R positioned on a brake shoe.

10. The drum brake (1) for a motor vehicle brake system as claimed in one or more of the preceding claims, characterized in that a (master) radius R positioned on an actuating element has, in each case in relation to the brake drum diameter, at least approximately 0.6-1.5× the brake drum diameter, wherein the paired counterpart of the (slave) radius R on a brake shoe has at least approximately ¼- 1/20× the brake drum diameter.

11. The drum brake (1) for a motor vehicle brake system as claimed in one or more of the preceding claims, characterized in that one or more centers of radii R are positioned so as to be offset in the transverse direction toward a wheel axis of rotation Ax by a determined, in particular predefined, offset Y1c; Y1d.

12. The drum brake (1) for a motor vehicle brake system as claimed in one or more of the preceding claims, characterized in that all brake shoes (7, 8) are assigned at least one or more compensation devices for brake shoe transverse offset for all brake drum directions of rotation U, U′.

13. The drum brake (1) for a motor vehicle brake system as claimed in one or more of the preceding claims, characterized in that each brake shoe (7, 8) is assigned a compensation device for brake shoe transverse offset for one brake drum direction of rotation U, U′.

14. The drum brake (1) for a motor vehicle brake system as claimed in one or more of the preceding claims, characterized in that the compensation device for brake shoe transverse offset is assigned exclusively to one brake drum direction of rotation U, U′ and exclusively to the one or more trailing drum brake shoe(s) (7, 8).

15. The drum brake (1) for a motor vehicle brake system as claimed in one or more of the preceding claims, characterized in that the compensation device is fixed, adjacent to a load measuring device and within a brake drum, to an anchor plate.

16. The drum brake (1) for a motor vehicle brake system as claimed in one or more of the preceding claims, characterized in that an electrical motor vehicle brake system is configured with a control unit (ECU) for open-loop and/or closed-loop control of the drum brake (1).

17. The drum brake (1) for a motor vehicle brake system as claimed in one or more of the preceding claims, characterized in that the electrical motor vehicle brake system has at least one or more electromechanically and/or electrohydraulically actuatable wheel brakes.

18. The drum brake (1) for a motor vehicle brake system as claimed in claim 17, characterized in that the motor vehicle brake system formed has at least one disk brake.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In the drawing, for the most part in sketch form diagrammatically by way of example:

[0016] FIG. 1 illustrates wear-induced transverse offset/support bearing contact point “displacement” by way of example on a drum brake shoe (at approximately half scale) with a gradually rounded support bearing;

[0017] FIG. 2 depicts the transverse offset on a drum brake with compensation means/support bearing profiling (“shell-disk design”);

[0018] FIGS. 3 and 4 show another further development as an exemplary embodiment with an offset with respect to the axis illustrated in FIG. 3 in the non-worn, new state and with the maximum degree of wear in FIG. 4; and

[0019] FIG. 5 shows the support bearing with geometrically implemented transverse offset compensation by way of example on the basis of the detail V in FIG. 2.

DETAILED DESCRIPTION

[0020] FIG. 1 illustrates wear-induced transverse offset/support bearing contact point “displacement” by way of example on a drum brake shoe (at approximately half scale) with a gradually rounded support bearing. The trailing brake shoe 7 is subject, at its support bearings/contact points (in relation to a preferential direction of rotation U), to a very great transverse offset Y1a/Y1b (by way of comparison, for example approximately 7.9/7.5 mm) over the friction lining service life under consideration.

[0021] FIG. 2 depicts how the transverse offset improves for example on a drum brake with compensation means/support bearing profiling (“shell-disk design”). Over the friction lining service life, the transverse offset at the support bearing contact point accordingly decreases, at the trailing brake shoe 7, by approximately a factor of 4, that is to say the displacement movement is reduced to, for example, approximately 1.77/1.91 mm—in relation to an initial design as in FIG. 1. A person skilled in the art furthermore identifies the design in which the center of the relevant lining shoe radius is offset from its starting point by only the distance Y1c/Y1d.

[0022] FIGS. 3 and 4 show another further development as an exemplary embodiment. This includes the variant with an offset of Y1c/Y1d with respect to the axis Rk (illustrated in FIG. 3 in the non-worn, new state). Owing to this offset, the contact point lies above said axis “Rk” by Y1a/Y1 b. With increasing lining wear, the contact point shifts, over the axis center of Rk, as far as Y1′a/Y1′b, with the maximum degree of wear (cf. FIG. 4). Owing to the offset, the maximum spacing (Y1a/Y1b/Y1′a and Y1′b) about the axis of Rk is smaller by approximately ½ than illustrated in FIG. 2.

[0023] FIG. 5 shows the support bearing with geometrically implemented transverse offset compensation on the basis of the detail V in FIG. 2, for example.

[0024] A drum brake 1, or an electronic brake system having one or more drum brake(s) 1 is designed for a motor vehicle. This may in principle be an electrical service brake apparatus that is designed to be open when electrically deenergized, or an electrical immobilizing brake apparatus that is designed to impart an immobilizing action when electrically deenergized, and a combination based on a combined immobilizing brake and service brake apparatus is likewise possible.

[0025] In this context, the schematic drawing illustrates, in principle, a drum brake 1 which, by way of example and for the purposes of simplification, is of special simplex type, and is thus illustrated as a simple service brake, wherein, for simplicity, the illustration does not show the immobilizing brake device, which is additionally possible in principle and which is to be provided so as to impart an immobilizing action when electrically deenergized. Yet further types of brakes (for example dual servo, duplex, dual duplex) are ultimately also possible in principle from a design aspect.

[0026] For the purposes of actuation, the drum brake 1 may have, on a front side, a spreading device 2 which is hydraulically and/or electromechanically actuatable and which has at least one or as illustrated two actuating elements 15, 16, which are displaceable in translational fashion in relation to the anchor plate 4, and an abutment 3, which actuating elements and abutment are each fixed to a front side F of the anchor plate 4, wherein the anchor plate 4 with its components and attachment parts fixed to the anchor plate, which may include an electromechanical wheel brake actuator on the anchor plate rear side, which electromechanical wheel brake actuator is actuatable on a wheel-specific basis and can be fixed as a wheel brake actuating device to the anchor plate 4 so as to be fixed with respect to the vehicle and non-rotatable. The brake shoes 7, 8 are also mounted movably on the anchor plate 4, which brake shoes cooperate with a brake drum pot 6 of a brake drum 5 that is arranged fixedly with respect to the wheel, that is to say so as to be rotatable, relative to the anchor plate 4. Each brake shoe 7, 8 has a substantially rigid carrier for friction linings 9, 10, which are illustrated as having become gradually worn, and restoring springs 11, 12 may also be braced in elastically preloaded fashion between the brake shoes 7, 8 in order to, in principle, impart a restoring force to the brake shoes 7, 8, or retain the brake shoes 7, 8—proceeding from an unworn and non-actuated starting point “0”—in a non-actuated end position.

[0027] The arrangement is based on the realization that the friction lining wear, which is non-uniform for technical reasons, in cooperation with the brake drum leads, in the case of conventional drum brakes, to a geometrical transverse offset in the region of support bearing contacts 13, 13′, 14, 14′, with the consequence that a support bearing contact point is displaced, so to speak, orthogonally, transversely with respect to the spreading axis S of the actuating elements 15, 16 of the spreading device 2. Accordingly, in the region of spreading device 2 and abutment 3, the increasingly mutually transversely offset support/contact of the brake shoes 7, 8 can give rise to force couples, with the consequence that the spreading device 2 is not free from transverse forces, that is to say torque is introduced, as a result of which a gradually increasing transverse force load acts in the force flow of the spreading device 2. The arrangment and allows transverse force compensation or a reduction of the detrimental effects thereof.

[0028] In the case of an electric drum brake, the electromechanical geared motor drive is designed such that each drum brake may in principle be equipped with an individually associated electromechanical wheel brake actuator means for the purposes of wheel-specific closed-loop control, and it is likewise possible for multiple drum brakes to be equipped, via Bowden cable, with a common electromechanical actuator. A central electronic control unit may be provided for the electrical supply/actuation/closed-loop control of the actuator means, and it is likewise possible for each wheel brake module to have a local electronic control unit, which may be interlinked with further electronic control units. The drum brake 1 may have a force sensor means.

[0029] In the case of the drum brakes according to the known prior art, in the event of wear (from new to fully worn linings), the contact point that the brake shoes form with the spreading unit shifts significantly along the contact line, which leads to a large lever arm about the axis center of the spreading unit (see also FIG. 1). Furthermore, for example for electromechanically actuated drum brakes, no optimized design with regard to a central introduction of force from the brake shoes into the spreading unit has been realized.

[0030] The introduction of force by the lining may be as central as possible. Owing to the fact that force is conducted more centrally, piston jamming events which are possible in the case of existing hydraulic brake drum cylinders (and which lead to increased residual torques), and increased friction, are prevented or reduced. This leads to higher efficiency of the spreading unit. This introduction of force from the linings into the spreading unit is helpful for example in the case of electromechanical spreading units (for example ball screw or ball ramp systems). Aside from the higher efficiency, the transverse forces can be absorbed owing to shorter guide lengths. This consequently leads to smaller dimensioning of the electromechanical spreading units. Further, improved detection of values by correspondingly designed displacement/force measuring units at force transfer points, such as used in “dry” brake systems for brake torque monitoring. Here, transverse forces lead, for example, to transverse deflections that falsify the measured value.

[0031] In the case of the “contact design” pursued here with regard to the force contact point from drum brake lining to spreading unit, the lining displacement is greatly reduced by way of a “shell-disk design” (see also FIG. 3). This form must be selected such that the unavoidable transverse forces are kept as low as possible and are supported in a favorable manner. In the case of an embodiment with an additional “offset”, the shift of the lining out of the axis center can be reduced yet further by virtue of the “start point” of the contact surface being displaced over the axis center. Thus, in the event of wear, the force contact point shifts over the axis center to the end point (fully worn linings).

[0032] The design may also be implemented in each case mirror-symmetrically at the contact surfaces.

[0033] The arrangement allows a reduction of the transverse forces and the shift of the force contact point on drum brake linings. As a result of this reduction, in the components involved, the transverse forces are reduced, whereby said components no longer need to be designed to be as robust with regard to said forces.

[0034] In particular, for new dry brake systems, which use for example spindle or ball/ramp systems to apply the spreading force, the spindles are subjected to lower transverse forces, and in the case of ball/ramp systems, the individual balls are more uniformly loaded. The guide systems of said spreading units can be shortened. This can be used to design smaller components and thus smaller spreading units. In the case of dry systems, the lining support is indeed also used for force/torque determination. Here, too, a central introduction of force provides for the accuracy of the force/torque determination, as already described. This furthermore also benefits existing hydraulic systems with guided pistons. In these, the transverse forces are reduced, and possible piston jamming events are thus prevented.

[0035] The embodiments can in principle improve applications for all drum brake systems in which drum brakes are present (simplex, duplex, dual duplex, . . . ).

[0036] As an embodiment, as small a radius as possible may be selected for Rk, and as large a radius as possible (even a straight line) should be selected for Rg. Owing to the fact that Rg shifts, it must be ensured in the case of Rg that, in the main range of use, as small an angle 1a°/1b°/1′a° and 1′b° as possible arises (see FIGS. 3a/b) if it is sought to reduce the transverse force as far as possible. This is for example possible with an offset as shown. In the case of Rk, the smallest radius is limited by the material properties.

[0037] It is possible in principle for the support bearings (contact points) to be provided universally at different components that are to be paired with one another, that is to say at drum brakes/drum brake shoes. It is likewise possible for the refinement to be provided only at very particular drum brake linings, such that, for example, only a preferential direction of rotation, whereas other contact points, which may be subject to a different loading profile, may be configured differently. The contact points may be configured mirror-symmetrically with respect to one another to a certain degree. Furthermore, the “shell-disk design” may also, instead of circular shapes, be replaced with different curvatures or approximated geometries. Furthermore, the abovementioned principle may also be implemented in a differential design in which the lining carrier and the abutment are configured as multiple parts.