Electromechanical drum brake

Abstract

The invention relates to an electromechanical drum brake (10) for a motor vehicle. The electromechanical drum brake (10) comprises brake shoes (14) and an adjusting device (18) arranged between the brake shoes (14) and driven by a drive unit (38), by means of which the brake shoes (14) can be spread apart for braking. The adjusting device (18) is attached to a rear wall (22) of the drum brake (10), the rear wall (22) being designed to be elastic such that it permits movements at least to the extent of the expected out-of-roundness and eccentricity.

Description

[0001] The present invention relates to an electromechanical drum brake for a motor vehicle. State of the art

[0002] Drum brakes with various actuation types are common in modern vehicles. Drum brakes are typically hydraulically actuated. Hydraulic pressure is built up in a double piston, which then expands, exerting a force on each brake shoe. The brake shoes are often only roughly positioned by a support bearing and return springs and can find their own position within the drum depending on tolerances and wear.

[0003] US 10,001,186 B2 discloses a drum brake assembly with a drum in which two brake shoes are arranged. At one end of the brake shoes, these are pivotally connected to each other. An S-shaped cam is arranged between a second end of the brake shoes. When rotated, this cam spreads the brake shoes apart, causing them to engage the drum and achieve a braking effect. A shaft of the cam is driven by an electric motor. The electric motor can be connected via a planetary gear, a worm gear, or directly to the shaft.

[0004] The object underlying the invention is to provide an electromechanical drum brake for a motor vehicle with which an out-of-roundness and an eccentricity of the drum brake can be compensated and which has a low mechanical complexity.

[0005] The object is achieved by an electromechanical drum brake for a motor vehicle having the subject matter of patent claim 1. Preferred embodiments can be found in the dependent claims. Disclosure of the invention

[0006] The invention specifies an electromechanical drum brake for a motor vehicle. The electromechanical drum brake comprises brake shoes, a drive unit, and an adjusting device arranged between the brake shoes and driven by the drive unit, via which the brake shoes can be spread for braking. The adjusting device is attached to a rear wall of the drum brake, with the rear wall being designed to be elastic, allowing movements at least to the extent of the expected out-of-roundness and eccentricity.

[0007] The adjustment device is a device with which a force can be applied to the brake shoes so that they engage a drum. The adjustment device is preferably arranged at an upper end of the brake shoes. The drive unit preferably comprises an electric motor. The rear wall is a wall that closes the drum in the axial direction and separates the brake shoes from the drive unit.

[0008] Although the adjustment mechanism is firmly connected to the back wall, its elasticity allows for movement within the drum. The elasticity of the back wall is designed to compensate for out-of-roundness and eccentricity. The elasticity of the back wall can be adjusted by adjusting various parameters such as wall thickness, the material of the back wall, or the shape. The movement of the adjustment mechanism lies entirely within the elastic range of the back wall, ensuring that the back wall is not damaged during operation.

[0009] By mounting the adjustment mechanism firmly on the rear wall, the mechanical complexity of the electromechanical drum brake can be significantly reduced. This eliminates the need to provide separate movement for the adjustment mechanism via additional components. This type of electromechanical drum brake is therefore more cost-effective to manufacture. Furthermore, by eliminating the need for separate components, this type of drum brake is also lighter, allowing the unsprung mass on the wheel to be reduced and driving comfort to be increased.

[0010] In a preferred embodiment of the invention, the rear wall is formed from a sheet metal. Using a sheet metal as the rear wall has the advantage that such a rear wall is easy to manufacture, thus reducing the costs of such an electromechanical drum brake.

[0011] In a further preferred embodiment of the invention, the adjusting device is designed as an S-shaped cam. The use of a cam has the advantage that a spread can be achieved by simply rotating the cam. A gear of the drive unit can thus be designed purely rotary. The cam eliminates the need for complex and expensive elements for rotation-translation conversion.

[0012] Advantageously, the S-shaped cam is designed in the form of an Archimedean spiral. The use of an Archimedean spiral has the advantage of ensuring an approximately linear relationship between the angle of rotation and the spreading distance. The linear relationship between the angle of rotation and the spreading distance makes it particularly easy to control the braking force, and the actuator exhibits the same characteristics over its entire operating range (including wear). Using such an Archimedean spiral allows brake shoe wear to be determined based on the detected angle of rotation. This also makes it possible to warn the driver in good time before the brake pad is completely worn out.

[0013] In an advantageous further development, the adjustment path of the cam is designed in such a way that it also includes wear on the brake shoes. This design of the cam eliminates the need for a separate device for wear adjustment. This reduces the complexity of the electromechanical drum brake. Likewise, the weight of the unsprung wheel can be reduced. Overall, such an electromechanical drum brake can be manufactured more economically. Furthermore, it is possible to adjust the brake clearance as required depending on the driving condition in order to minimize losses due to residual drag in every situation and to achieve sufficient brake response dynamics.

[0014] Advantageously, the brake shoes each have a roller carrier at an end facing the cam, on which a roller is arranged, which is in contact with the cam. The roller rolls on a surface of the cam. By using roller carriers to which rollers are attached, the rotational resistance of the adjustment device can be reduced. The adjustment device can therefore spread the brake shoes with less torque. Accordingly, an electric motor for driving the adjustment device can be smaller and thus lighter.

[0015] In a further advantageous embodiment, the drive unit has a gear unit that is designed to be non-locking. The gear unit therefore has no self-locking feature. After braking, the brake pads can be automatically released again by the forces acting on the drum. This allows the brake to be released in a de-energized state, such as a fault condition. Such an electromechanical drum brake can therefore also be used as a service brake in a passenger vehicle.

[0016] According to a practical embodiment, the drive unit has a gear unit comprising at least one worm and spur gear stage. Such a worm and spur gear stage provides a high gear ratio while requiring little installation space. This allows a drive unit with such a worm and spur gear stage to be used in the area of ​​the rim.

[0017] According to a further practical embodiment, the worm gear is made of a plastic material. A plastic material has the advantage that it is easily manufactured by injection molding. In addition, plastic materials are lightweight and significantly cheaper than metals. By cleverly selecting the plastic material, a self-lubricating surface can be provided at the same time. This eliminates the need for a separate lubricant. Polyoxymethylene (POM) is advantageously used as the plastic material. Furthermore, the use of a plastic gear stage as the first gear stage with high rotational speed is optimal due to its low noise generation. In addition, the thermal load is reduced due to the greater distance from the drum.

[0018] The drive unit preferably has a gear unit comprising straight-toothed spur gears. The use of straight-toothed spur gears, which is typically avoided due to increased noise generation, is unproblematic in the second gear stage due to the low rotational speeds. Axial forces acting on the shaft are avoided, simplifying its bearings. Furthermore, straight-toothed spur gears are more economical to manufacture.

[0019] Embodiments of the invention are illustrated in the drawing and explained in more detail in the following description. It shows: Fig. 1 Electromechanical drum brake according to an embodiment of the invention, Fig. 2 Enlarged view of the cam and roller carrier of the electromechanical drum brake according to Fig. 1, Fig. 3 Representation of a drive unit and the cam according to an embodiment of the invention, and Fig. 4 Further illustration of the drive unit and the cam according to an embodiment of the invention.

[0020] In Fig. 1 shows an electromechanical drum brake 10 according to an embodiment of the invention. The drum brake 10 comprises two brake shoes 14 and an adjusting device 18 arranged between the brake shoes 14, via which the brake shoes 14 can be spread for braking. In the illustrated embodiment, the adjusting device 18 is designed as an S-shaped cam. The adjusting device 18 is attached to a rear wall 22 of the drum brake 10. The rear wall 22 is designed to be elastic, allowing movement of the cam 18, thus compensating for any out-of-roundness or eccentricity.

[0021] Fig. Figure 2 shows an enlarged view of the cam 18 and a roller carrier 26 of the electromechanical drum brake 10. The roller carriers 26 are arranged at the ends of the brake shoes 14 facing the cam 18. A roller 30 is rotatably mounted at the end of the roller carrier 26. The roller 30 runs on a surface 34 of the cam 18, enabling low-friction rotation of the cam 18.

[0022] In Fig. Figure 3 shows a diagram of a drive unit 38 and the cam 18 according to an exemplary embodiment of the invention. The drive unit 38 comprises a gear unit 42, which drives the cam 18 after reducing the speed of an electric motor 46 of the drive unit 38. In the exemplary embodiment shown, the gear unit 42 comprises straight-toothed spur gears 50, which can reduce the noise generated by the gear unit 42. Such straight-toothed spur gears 50 can also be manufactured economically.

[0023] A further illustration of the drive unit 38 and the cam 18 is shown in Fig. 4. This figure shows that the electric motor 46 of the drive unit 38 drives a worm 54, which in turn interacts with the spur gear stage formed by spur gears 50. Such a gear unit 42, designed as a worm and spur gear stage, has a high gear ratio and a small installation space. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 10,001,186 B2

[0003]

Claims

[1] Electromechanical drum brake (10) for a motor vehicle comprising brake shoes (14) and an adjusting device (18) arranged between the brake shoes (14) and driven by a drive unit (38), by means of which the brake shoes (14) can be spread for braking, characterized by that the adjusting device (18) is fastened to a rear wall (22) of the drum brake (10), wherein the rear wall (22) is designed to be elastic in such a way that it permits movements at least to the extent of the expected out-of-roundness and eccentricity. [2] Electromechanical drum brake (10) according to claim 1, characterized by that the rear wall (22) is made of a sheet metal. [3] Electromechanical drum brake (10) according to claim 1 or 2, characterized by that the adjusting device (18) is designed as an S-shaped cam. [4] Electromechanical drum brake (10) according to claim 3, characterized bythat the S-shaped cam (18) is shaped in the form of an Archimedean spiral. [5] Electromechanical drum brake according to claim 3 or 4, characterized by that an adjustment path of the cam (18) is designed such that it includes wear of the brake shoes (14). [6] Electromechanical drum brake (10) according to one of claims 3 to 5, characterized by that the brake shoes (14) each have a roller carrier (26) at an end facing the cam (18), on which a roller (30) is arranged, which is in contact with the cam (18). [7] Electromechanical drum brake (10) according to one of the preceding claims, characterized by that the drive unit (38) has a gear unit (42) which is designed to be free of inhibition. [8] Electromechanical drum brake (10) according to one of the preceding claims, characterized bythat the drive unit (38) has a gear unit (42) which comprises at least one worm and spur gear stage (58). [9] Electromechanical drum brake (10) according to claim 8, characterized by that the worm wheel is made of a plastic material. [10] Electromechanical drum brake (10) according to one of the preceding claims, characterized by that the drive unit has a gear unit which comprises straight-toothed spur gears.

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