Electromechanical drum brake

Abstract

The invention relates to an electromechanical drum brake, in particular an electromechanical drum brake (10) for a motor vehicle, comprising a brake drum (22), in which brake shoes (46) are arranged, and an adjusting device (42), which is arranged between the brake shoes and is driven by a drive unit (14), by means of which the brake shoes can be expanded for braking. The adjusting device has a rack (66) which is driven by the drive unit and is supported in a floating manner between the brake shoes and which meshes with a coupling gear (74) which acts on the first brake shoe (46a) via a push rod (82) connected thereto. An actuation rack (94) acting on a second brake shoe (46b) meshes with the coupling gear on a side of the coupling gear opposite the rack, and the coupling gear is freely movable between the brake shoes on the rack such that a difference in force occurring between the brake shoes can be balanced by rotation of the coupling gear.

Description

Technical Field

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

[0002] Drum brakes with different types of actuation are known in today's vehicles. For passenger vehicles, drum brakes are usually hydraulically actuated. Here, hydraulic pressure is built up in a double piston, which expands and thus exerts a force on each brake shoe of the drum brake. The design with pistons that are movable on both sides and coupled via a fluid ensures that the forces exerted on both brake shoes are always of the same magnitude. For future passenger vehicles, hydraulic actuation may be replaced by electromechanical actuation. There are many variants for mechanical actuation.

[0003] In the field of heavy-duty vehicles, drum brakes are usually operated pneumatically, wherein the pneumatic piston is arranged outside the brake, so that the actual actuation takes place mechanically. In this design, the actuation is carried out using an S-cam and a wedge. Usually, these designs have an actuation with equal stroke of the brake shoes, without force balancing. With mechanical actuation, this usually involves considerable mechanical outlay to ensure an actuation with force balance. This is because the low-friction movement of the individual parts of the actuation mechanism usually has to be ensured using additional mechanical elements and cannot be achieved by pressure balancing in the hydraulic fluid, as in hydraulic brakes.

[0004] Patent document US10,001,186B2 discloses a drum brake assembly having a brake drum in which two brake shoes are arranged. At one end of the brake shoes, the brake shoes 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 or a worm gear transmission, or directly connected to the shaft. Summary of the invention

[0005] The invention is based on the object of providing an electromechanical drum brake which has an improved braking effect and requires less structural effort.

[0006] This object is achieved by an electromechanical drum brake having the subject matter of claim 1. Preferred embodiments are derived from the dependent claims.

[0007] The invention provides an electromechanical drum brake for a motor vehicle. The electromechanical drum brake comprises a brake drum in which brake shoes are arranged, and an adjustment device arranged between the brake shoes and driven by a drive unit, by means of which the brake shoes can be expanded for braking. The adjustment device has a rack driven by the drive unit and floatingly supported between the brake shoes, the rack meshing with a coupling gear, which acts on a first brake shoe via a push rod connected to the coupling gear. An actuating rack acting on a second brake shoe meshes with the coupling gear on the side of the coupling gear opposite to the rack, and the coupling gear can be freely moved on the rack between the brake shoes, so that the difference in forces occurring between the brake shoes can be balanced by the rotation of the coupling gear.

[0008] The adjusting device is a device that can exert a force on the brake shoe so that the brake shoe rests on the brake drum. The adjusting device is preferably arranged at the upper end of the brake shoe. Preferably, the drive unit comprises an electric motor. Floating bearing is understood to mean that the rack is not fixed relative to the brake drum, but can be moved relative to the brake drum, for example via a bearing. The rack can be moved along its longitudinal extension so that it moves between the brake shoes. The coupling gear can also be freely moved between the brake shoes.

[0009] The coupling gear is displaced accordingly between the brake shoes, so that a force balance is achieved between the brake shoes. This makes it possible to compensate for tolerances and eccentricities in the drum brake. As a result, the brake shoes can be optimally placed against the brake drum, so that their self-energizing properties are brought into play. This improves the braking effect of the drum brake. By balancing the forces applied to the brake shoes, the bearing forces present at the adjustment device are significantly reduced. This allows the mechanical strength of the bearing mechanism to be significantly reduced and to be designed more simply. The structural expenditure on such a drum brake can thus be reduced.

[0010] The coupling gear can not only push the brake shoes away from each other, but also, by appropriately actuating the toothed rack, a tensile force can be exerted on the brake shoes so that they can be separated from the brake drum after the braking process. This can prevent wear of the brake shoes after the braking process. It can also separate stuck brake shoes, which can occur in drum brakes after long-term operation.

[0011] In a preferred embodiment of the invention, the coupling gear is designed as a multiple gear, and the rack and the actuating rack mesh with different toothed rings of the multiple gear, thereby forming a gear change. Therefore, the toothed ring can be designed according to the required requirements. This increases the flexibility of the drive of the actuating rack and the drive of the coupling gear.

[0012] In another preferred embodiment of the present invention, the actuating rack is configured to be forked in the region of the coupling gear, and each part of the forked actuating rack meshes with a toothed ring having the same number of teeth. The forked configuration of the actuating rack is understood to mean that the actuating rack is divided along its longitudinal extension, wherein the two parts of the actuating rack are spaced apart from each other. The forked actuating rack meshes symmetrically at the coupling gear here. Thus, the application of torque to the coupling gear during the braking process is avoided. In addition, by the forked engagement of the actuating rack at the coupling gear, the additional support of the coupling gear can be eliminated. This simplifies the structural construction of the electromechanical drum brake constructed in this way.

[0013] Preferably, the push rod has a joint which allows a movement of the push rod orthogonal to the axis of rotation of the coupling gear and a movement orthogonal to the longitudinal extension of the push rod. The push rod is therefore not rigidly arranged at the coupling gear. Since the brake shoe moves in the brake drum during braking, this possibility of movement is ensured by such a joint. As a result, the brake shoe can assume an optimal position in the brake drum to improve the braking effect.

[0014] In an advantageous improvement, the drive unit is driven in a torque-controlled manner. By adjusting the drive unit in terms of torque rather than in terms of travel, it can be ensured that a predetermined braking force is permanently applied to the brake shoe. This also compensates for the wear of the brake lining arranged at the brake shoe.

[0015] Advantageously, the rack is driven by a drive pinion, the diameter of which is smaller than the diameter of the coupling gear. By using a small drive pinion, a smaller electric motor can be used, which is also lighter. The overall weight and size of the electromechanical brake can thereby be reduced.

[0016] In a further advantageous embodiment, the actuating rack is designed to apply a force to the second brake shoe at the height of the axis of the coupling gear. By designing the actuating rack accordingly, the force of the push rod is at the same height as the force of the actuating rack. This avoids applying a moment to the coupling gear. Such a moment would lead to an uneven force distribution at the brake shoe. The force balance between the brake shoes can be improved by a suitable design.

[0017] The invention also provides a motor vehicle having an electromechanical drum brake according to the invention. The motor vehicle has the above-mentioned advantages and functions. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Embodiments of the present invention are shown in the drawings and explained in more detail in the following description.

[0019] Figure 1 An electromechanical drum brake according to an embodiment of the invention is shown,

[0020] Figure 2A diagram showing a brake drum according to an embodiment of the invention,

[0021] Figure 3 a diagram showing an adjustment device according to an embodiment of the invention, and

[0022] Figure 4 Shown according to Figure 3 A three-dimensional diagram of the adjustment device. DETAILED DESCRIPTION

[0023] Figure 1 An electromechanical drum brake 10 according to an embodiment of the invention is shown. The electromechanical drum brake 10 comprises a drive unit 14, which is arranged at the rear wall 18 of the brake drum 22. The drive unit 14 comprises an electric motor 26 which drives a transmission unit 30. The transmission unit 30 is driven on the input side by a worm 34 extending from the electric motor 26. The transmission unit 30 is formed here by a plurality of spur gears 38. On the output side, the transmission unit 30 drives an adjustment device 42 of the brake drum 22.

[0024] Figure 2 2 shows a diagram of a brake drum 22 according to an embodiment of the present invention. Figure 1 The adjustment device 42 shown in FIG. 4 is arranged in the brake drum 22. In addition, a brake shoe 46 is arranged in the brake drum 22, which cooperates with the brake drum 22 for braking. The adjustment device 42 is arranged at the upper end 50 of the brake shoe 46. For braking, the adjustment device 42 acts on the brake shoe 46 so that the brake shoe 46 expands and presses against the brake drum 22. A support element 58 is arranged at the lower end 54 of the brake shoe 46, via which the two brake shoes 46 are connected. In addition, a spring 62 is arranged between the brake shoes 46, by which the brake shoe 46 can be separated from the brake drum 22 after the braking process.

[0025] Figure 3 1 shows a diagram of an adjustment device 42 according to an embodiment of the invention. The adjustment device 42 comprises a floatingly supported rack 66 meshing with a drive pinion 70. The drive pinion 70 is driven by the drive unit 14. By rotating the drive pinion 70, the rack 66 can be moved between the brake shoes 46. The adjustment device 42 also comprises a coupling gear 74 meshing with the teeth of the rack 66. A push rod 82 is arranged at the axis 78 of the coupling gear 74, which acts on the first brake shoe 46a of the drum brake 10.

[0026] In the exemplary embodiment shown here, the coupling gear 74 is designed as a multiple gear, wherein the first toothed ring 86 meshing with the toothed rack 66 has a diameter d 1 Greater than the diameter d of the second gear ring 90 2The gear shifting is achieved by the different diameters. In the embodiment shown here, the diameter d of the drive pinion 70 is R Smaller than the diameter d of the first gear ring 86 1 As a result, the size and thus the weight of the electric motor 26 can be reduced.

[0027] The adjustment device 42 also includes an actuating rack 94 which meshes with the second toothed ring 90 on the side of the coupling gear 74 opposite the rack 66. The actuating rack 94 has a bent section 98 which is configured such that a section 102 acting on the second brake shoe 46b exerts a force F on the second brake shoe 46b at the height of the axis 78. A This prevents the second toothed ring 90 from being subjected to a torque. The force F of the actuating rack 94 A Here, the force F of the push rod 82 D At the same height. Accordingly, the force F between the brake shoes 46 can be improved A 、F D balance.

[0028] Figure 4 Shown according to Figure 3 3D view of the adjusting device 42 of FIG. It can be seen here that the actuating rack 94 is designed in the shape of a fork in the region of the coupling gear 74. The actuating rack 94 meshes in the second gear ring 90 on both sides of the first gear ring 86. The second gear ring 90 is arranged on both sides of the first gear ring 86 accordingly. This prevents the application of torque to the coupling gear 74. In the embodiment shown here, the push rod 82 has a joint 106, via which a movement orthogonal to the axis 78 of the coupling gear 74 and a movement orthogonal to the extension of the push rod 82 is allowed. Movements of the brake shoe 46 can be compensated by means of this joint 106.

Claims

1. An electromechanical drum brake (10) for a motor vehicle, comprising a brake drum (22) in which brake shoes (46) are arranged, and an adjustment device (42) arranged between the brake shoes (46) and driven by a drive unit (14), by means of which the brake shoes (46) can be expanded for braking, It is characterized in that The adjusting device (42) has a toothed rack (66) driven by the drive unit (14) and floatingly supported between the brake shoes (46), the toothed rack meshing with a coupling gear (74), the coupling gear acting on the first brake shoe (46a) via a push rod (82) connected to the coupling gear, wherein an actuating toothed rack (94) acting on the second brake shoe (46b) meshes with the coupling gear (74) on the side of the coupling gear (74) opposite to the toothed rack (66), and the coupling gear (74) can move freely on the toothed rack (66) between the brake shoes (46), so that the difference in force occurring between the brake shoes (46) can be balanced by the rotation of the coupling gear (74).

2. The electromechanical drum brake (10) according to claim 1, characterized in that The coupling gear (74) is constructed as a multiple gear, and the rack (66) and the actuating rack (94) mesh with different toothed rings (86, 90) of the multiple gear, thereby forming a speed change.

3. The electromechanical drum brake (10) according to claim 2, characterized in that The actuating rack (94) is configured to be forked in the region of the coupling gear (74), and each portion of the forked-configured actuating rack (94) meshes with a gear ring (90) having the same number of teeth.

4. An electromechanical drum brake (10) according to any one of the preceding claims, characterized in that The push rod (82) has a joint (106) which allows movement of the push rod (82) orthogonal to the axis (78) of the coupling gear (74) and movement orthogonal to the longitudinal extension of the push rod (82).

5. An electromechanical drum brake (10) according to any one of the preceding claims, characterized in that The drive unit (14) is driven in a torque-controlled manner.

6. An electromechanical drum brake (10) according to any one of the preceding claims, characterized in that The rack (66) is driven via a drive pinion (70) having a smaller diameter than the coupling gear (74).

7. An electromechanical drum brake (10) according to any one of the preceding claims, characterized in that The actuating rack (94) is configured to apply a force (F A ) is applied to the second brake shoe (46b) at the height of the axis (78) of the coupling gear (74).

8. Motor vehicle comprising an electromechanical drum brake (10) according to any one of the preceding claims.

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