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 adjusting device the brake shoes (14) can be expanded for braking. According to the invention, the adjusting device (18) is fixed to a rear wall (22) of the drum brake (10), the rear wall (22) being designed to be resilient such that it allows a movement at least in the range of expected out-of-roundness and eccentricity.

Description

Technical Field

[0001] The invention relates to an electromechanical drum brake for a motor vehicle. Background Art

[0002] Drum brakes with different types of actuation are known in today's vehicles. Usually, drum brakes are hydraulically actuated. Here, hydraulic pressure is generated in a double piston, which expands thereby generating a force on each brake shoe of the drum brake. The brake shoes are usually only roughly positioned by means of support bearings and return springs and can find their position in the brake drum depending on tolerances and wear conditions.

[0003] US10 001 186 B2 discloses a drum brake device with a brake drum, in which two brake shoes are arranged. At one end of the brake shoes, they are connected to each other in a pivotable manner. An S-shaped cam is arranged between the second ends of the brake shoes, which expands the brake shoes by rotation, so that the brake shoes engage with the brake drum and achieve a braking effect. The shaft of the cam is driven by an electric motor. Here, the electric motor can be connected to the shaft via a planetary gear transmission, a worm gear transmission, or directly connected to the shaft. Summary of the invention

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

[0005] This 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.

[0006] The invention provides an electromechanical drum brake (electromechanical drum brake) for a motor vehicle. The electromechanical drum brake comprises brake shoes, a drive unit and an adjustment device arranged between the brake shoes and driven by the drive unit, by means of which the brake shoes can be expanded for braking. The adjustment device is fixed to the rear wall of the drum brake, wherein the rear wall is designed to be elastic so that it allows movement at least within the expected range of out-of-roundness and eccentricity.

[0007] The adjusting device is a device that can exert a force on the brake shoe so that the brake shoe is pressed against the brake drum. The adjusting device is preferably arranged at the upper end of the brake shoe. The drive unit preferably comprises an electric motor. The rear wall is here a wall that closes the brake drum in the axial direction and separates the brake shoe from the drive unit.

[0008] Despite the fact that the adjusting device is firmly connected to the rear wall, the elasticity of the rear wall allows the adjusting device to move in the brake drum. The elasticity of the rear wall is designed to compensate for out-of-roundness and eccentricity. The elasticity of the rear wall can be set by adjusting various parameters such as the wall thickness or the material or the shape of the rear wall. The movement of the adjusting device takes place entirely in the elastic region of the rear wall, so that the rear wall cannot be damaged during operation.

[0009] By mounting the adjustment device firmly on the rear wall, the mechanical complexity of the electromechanical drum brake can be significantly reduced. It is therefore not necessary to provide the adjustment device with separate movability by means of additional components. This makes it possible to produce such an electromechanical drum brake more economically. At the same time, such a drum brake is also lighter due to the omission of separate components, so that the unsprung masses at the wheel can be reduced and driving comfort can be increased.

[0010] In a preferred embodiment of the invention, the rear wall is made of a sheet material. The advantage of using a sheet material as the rear wall is that the rear wall is easy to manufacture, thereby reducing the cost of the electromechanical drum brake.

[0011] In another preferred embodiment of the present invention, the adjusting device is configured as an S-shaped cam. The advantage of using a cam is that expansion can be achieved by simply rotating the cam. Therefore, the transmission device of the drive unit can be designed as a pure rotation. The cam can save complex and expensive components for rotation-translation conversion.

[0012] The S-shaped cam is advantageously formed in the shape of an Archimedean spiral. The advantage of using an Archimedean spiral is that it ensures an approximately linear relationship between the rotation angle and the expansion path. Due to the linear relationship between the rotation angle and the expansion path, the adjustment of the braking force is particularly easy and the actuator has the same characteristics (including wear) over the entire operating path. By using such an Archimedean spiral, the wear of the brake shoe can therefore be determined based on the determined rotation angle. This also makes it possible to warn the driver in good time before the brake lining is completely worn out.

[0013] In an advantageous development, the adjustment path of the cam is designed such that it takes into account the wear of the brake shoes. By designing the cam in this way, a separate device for wear adjustment can be omitted. The complexity of the electromechanical drum brake can thereby be reduced. At the same time, the weight on the unsprung wheel can also be reduced. Overall, such an electromechanical drum brake can thus be manufactured more economically. Furthermore, the air gap of the brake can be set as desired depending on the driving state, in order to minimize the losses due to residual friction in any case and to achieve adequate response dynamics of the brake.

[0014] Advantageously, the brake shoes each have a roller carrier at the end facing the cam, on which rollers are arranged that are in contact with the cam. The rollers roll on the surface of the cam. By using a roller carrier to which the rollers are fixed, the rotational resistance of the adjustment device can be reduced. As a result, the adjustment device can expand the brake shoes with a smaller torque. As a result, the electric motor for driving the adjustment device can be designed to be smaller and therefore lighter.

[0015] In a further advantageous embodiment, the drive unit has a transmission unit which is designed to be unlocked. The transmission unit therefore has no self-locking mechanism. After braking, the brake lining can be released again automatically by the forces generated in the brake drum. This allows the brake to be released in a de-energized state (e.g., in the event of a fault). Such an electromechanical drum brake can therefore also be used as a service brake in passenger cars.

[0016] According to an expedient embodiment, the drive unit has a transmission unit comprising at least one worm and spur gear stage. Such a worm and spur gear stage has a high transmission ratio and requires little installation space. Thus, a drive unit having such a worm and spur gear stage can be used in the wheel rim region.

[0017] According to another advantageous embodiment, the worm wheel is made of a plastic material. The advantage of plastic materials is that they can be easily manufactured by injection molding. In addition, plastic materials are lightweight and much cheaper than metals. By cleverly selecting the plastic material, a self-lubricating surface can be provided at the same time. This makes it possible to dispense with a separate lubricant. Advantageously, polyoxymethylene (POM) is used as the plastic material. In addition, due to its low noise generation, it is optimal to use a transmission stage made of plastic as the first transmission stage with a high rotational speed. In addition, due to the greater distance to the brake drum, the thermal load is lower.

[0018] Preferably, the drive unit has a transmission unit with spur gears. Spur gears are usually avoided due to high noise generation, but due to the low rotational speed, their use in the second transmission stage is not a problem. This avoids axial forces on the shaft, thereby simplifying its support. In addition, spur gears are more economical to manufacture. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Embodiments of the present invention are shown in the drawings and explained in more detail in the following description.

[0020] Figure 1 An electromechanical drum brake according to an embodiment of the invention is shown,

[0021] Figure 2 Shown according to Figure 1 Magnified view of the cam and roller carrier of the electromechanical drum brake,

[0022] Figure 3a diagram showing a drive unit and a cam according to an embodiment of the invention, and

[0023] Figure 4 Further illustrations show drive units and cams according to embodiments of the invention. DETAILED DESCRIPTION

[0024] Figure 1 An electromechanical drum brake 10 according to an embodiment of the invention is shown. The drum brake 10 comprises two brake shoes 14 and an adjustment device 18 arranged between the brake shoes 14, by means of which the brake shoes 14 can be expanded for braking. In the embodiment shown, the adjustment device 18 is designed as an S-shaped cam. Here, the adjustment device 18 is fixed (attached) to a rear wall 22 of the drum brake 10. The rear wall 22 is designed to be elastic, so that it allows the cam 18 to move, so that out-of-roundness or eccentricity can be compensated.

[0025] Figure 2 An enlarged view of the cam 18 and the roller carrier 26 of the electromechanical drum brake 10 is shown. The roller carrier 26 is arranged at the end of the brake shoe 14 facing the cam 18. The roller 30 is rotatably fixed (attached) to the end of the roller carrier 26. The roller 30 runs on the surface 34 of the cam 18, thereby achieving a low-friction rotation of the cam 18.

[0026] Figure 3 A diagram of a drive unit 38 and a cam 18 according to an embodiment of the invention is shown. The drive unit 38 comprises a transmission unit 42, which drives the cam 18 after reducing the rotational speed of an electric motor 46 of the drive unit 38. In the embodiment shown, the transmission unit 42 comprises a spur gear 50, by which the noise generated by the transmission unit 42 can be reduced. Such a spur gear 50 can also be manufactured economically.

[0027] Figure 4 A further illustration of the drive unit 38 and the cam 18 is shown. This figure shows that the electric motor 46 of the drive unit 38 drives a worm 54, which in turn interacts with a spur gear stage formed by a spur gear 50. Such a transmission unit 42 configured as a worm and spur gear stage has a high transmission ratio and a small installation space.

Claims

1. An electromechanical drum brake (10) for a motor vehicle, comprising brake shoes (14) and an adjustment 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 expanded for braking, It is characterized in that The adjustment device (18) is fixed to a rear wall (22) of the drum brake (10), wherein the rear wall (22) is designed to be elastic so that it allows movement at least within the range of expected out-of-roundness and eccentricity.

2. The electromechanical drum brake (10) according to claim 1, characterized in that The rear wall (22) is made of a plate.

3. The electromechanical drum brake (10) according to claim 1 or 2, characterized in that The adjusting device (18) is designed as an S-shaped cam.

4. The electromechanical drum brake (10) according to claim 3, characterized in that The S-shaped cam (18) is formed in the shape of an Archimedean spiral.

5. The electromechanical drum brake (10) according to claim 3 or 4, characterized in that The adjustment path of the cam (18) is designed so that it takes into account the wear of the brake shoe (14).

6. The electromechanical drum brake (10) according to any one of claims 3 to 5, characterized in that The brake shoes (14) each have a roller carrier (26) at the end facing the cam (18), on which a roller (30) is arranged, which is in contact with the cam (18).

7. An electromechanical drum brake (10) according to any one of the preceding claims, characterized in that The drive unit (38) has a transmission unit (42) which is designed to be lock-free.

8. An electromechanical drum brake (10) according to any one of the preceding claims, characterized in that The drive unit (38) has a transmission unit (42) including at least one worm and a spur gear stage (58).

9. The electromechanical drum brake (10) according to claim 8, characterized in that The worm gear is made of plastic material.

10. An electromechanical drum brake (10) according to any one of the preceding claims, characterized in that The drive unit has a transmission unit including a spur gear with straight teeth.

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