Electromechanical drum brake

Abstract

The invention relates to an electromechanical drum brake (14) for a motor vehicle. The electromechanical drum brake (14) comprises a drum (10) inside which brake shoes (18, 22) are arranged, and an adjustment device (26) which is placed between the brake shoes (18, 22) and is driven by a drive unit (38) and by means of which the brake shoes (18, 22) can be forced apart to perform a braking action. The adjustment device (26) is connected to a worm gear (34) which is driven via a worm (42) to make the adjustment device (26) rotate, the adjustment device (26) being mounted along with the worm gear (34) so as to be movable between the brake shoes (18, 22) in a force direction (RF) in which a force is to be applied to the brake shoes (18, 22).

Description

[0001] Description

[0002] Title:

[0003] Electromechanical drum brake

[0004] The present invention relates to an electromechanical drum brake for a motor vehicle. Furthermore, the invention relates to a motor vehicle having such an electromechanical drum brake.

[0005] State of the art

[0006] Drum brakes with various actuation types are common in modern vehicles. In cars, drum brakes are typically actuated hydraulically. Hydraulic pressure is built up in a double piston, which is then spread apart, exerting a force on each brake shoe. The design, with pistons that can be moved in both directions and are coupled via fluid, ensures that the forces on both brake shoes are always equal. In future cars, hydraulic actuation could be replaced by electromechanical actuation. There is a wide variety of mechanical actuation options.

[0007] In the truck sector, drum brakes are typically pneumatically actuated, with the pneumatic piston located outside the brake, allowing the actual actuation to occur mechanically. In such designs, actuation with S-cam and wedge has become the standard. These designs typically feature equal-path actuation of the brake shoes without force compensation. With mechanical actuation, ensuring actuation with force compensation generally involves considerable mechanical effort. This is due to the fact that the low-friction movement of individual parts of the actuator system typically has to be ensured with additional mechanical elements and cannot be achieved through pressure compensation in the hydraulic fluid, as is the case with hydraulic brakes.

[0008] 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 to the shaft via a planetary gear, a worm gear, or directly.

[0009] The object underlying the invention is to provide an electromechanical drum brake which has an improved braking effect and which requires less construction effort.

[0010] The object is achieved by an electromechanical drum brake having the subject matter of patent claim 1. Preferred embodiments can be found in the dependent claims.

[0011] Disclosure of the invention

[0012] The invention specifies an electromechanical drum brake for a motor vehicle. The electromechanical drum brake comprises a drum in which brake shoes are arranged, 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 connected to a worm gear of the electromechanical drum brake, which is driven by a worm of the electromechanical drum brake to rotate the adjusting device. The adjusting device is movably mounted between the brake shoes with the worm gear in a direction of force applied to the brake shoes.

[0013] The adjusting device is a device with which a force can be applied to the brake shoes so that they engage the drum. The adjusting device is preferably arranged at an upper end of the brake shoes. The drive unit is preferably designed as an electric motor. The adjusting device is fixedly connected to the worm gear, so that when the worm gear rotates, the adjusting device can also rotate. The worm gear can be straight-toothed or helical-toothed. A straight-toothed worm gear has the advantage of being simpler and more economical to manufacture.

[0014] The direction of force is the direction of a force by which the brake shoes can be spread. Applying this force creates a counterforce on the adjustment device. Because the adjustment device is mobile along the direction of force, the counterforce allows the adjustment device to be moved until a force equilibrium is achieved between the brake shoes. This allows the drum brake to better develop its self-reinforcing effect, resulting in improved braking performance compared to a fixed-mounted adjustment device. Manufacturing tolerance requirements can also be reduced because the adjustment device adjusts itself automatically, thus reducing design effort. The design effort is further reduced by the fact that the forces acting on the adjustment device do not need to be supported.This also reduces the weight of such an electromechanical drum brake on the unsprung wheel, thereby improving driving comfort.

[0015] According to the invention, a worm wheel and a worm are used to drive the adjusting device. Such a worm drive has the advantage of having a high gear ratio and linear transmission behavior. In addition, only a few parts are required. This also reduces the design effort. In a preferred embodiment of the invention, the worm wheel and the adjusting device are connected to one another via a shaft, wherein the shaft is movably arranged in an elongated hole that runs in the direction of force. The worm wheel and the adjusting device are thus arranged at the ends of the shaft. The distance between the worm wheel and the adjusting device is thus determined by the length of the shaft. The shaft is arranged in the elongated hole, which runs in the direction of force. The elongated hole enables movement of the shaft, and thus also of the cam and the worm wheel, in only one direction.By arranging the shaft in the elongated hole, rotation of the shaft and displacement are easily ensured so that the brake shoes can be actuated and a balance of forces between the brake shoes can be achieved.

[0016] In a further preferred embodiment of the invention, the worm wheel and the adjusting device each form a guide section which bears against a component forming the elongated hole in such a way that an axial alignment of the shaft to the drum is fixed. The guide sections are positioned at the ends of the shaft and thus bear against the component forming the elongated hole on both sides of the shaft. This prevents the shaft from tilting in the elongated hole due to a driving force acting on the shaft and the counterforce of the brake shoes. The guide sections therefore only allow a displacement of the shaft in the elongated hole. This permanently achieves a high level of adjustment accuracy and prevents incorrect engagement between the worm wheel and worm due to tilting of the shaft.

[0017] The guide sections preferably have a guide surface that rests against the component forming the elongated hole, wherein a sliding material is applied to the guide surfaces and / or to a component surface of the component that rests against the guide surfaces. The sliding material simplifies displacement of the shaft in the elongated hole. This improves the establishment of a force balance, so that the braking performance is increased. In an advantageous development, the sliding material is PTFE plastic or bronze. By forming a sliding material from bronze, a favorable coefficient of friction can be provided. The sliding material can also be made of polytetrafluoroethylene (PTFE) plastic. Such a plastic is simple and economical to apply. With both materials, a low coefficient of friction is achieved, so that a force balance can be achieved more easily.

[0018] Advantageously, one brake shoe is connected to a pressure roller, which rests against an outer circumferential surface of the adjustment device, and the other brake shoe is connected to the shaft or the guide section via a connecting rod. The pressure roller rolls on the outer circumferential surface, so that the distance between the brake shoes can be increased or decreased. In contrast to the prior art, only one brake shoe is actuated via the contour of the cam. Only when the shaft is displaced is the other brake shoe also deflected. Since only one brake shoe is deflected via the cam, other, more advantageous cam contours can be used.

[0019] In a further advantageous embodiment, the adjustment device is designed as a cam. High forces can be applied via a cam, so that such an electromechanical drum brake can also be used in trucks. This makes such an electromechanical drum brake versatile.

[0020] According to a practical design, the cam is designed as an Archimedean spiral. A cam designed as an Archimedean spiral has the advantage that rotating such a cam allows for linear adjustment of the brake shoes. This allows for more precise adjustment of the brake shoes.

[0021] According to a further practical embodiment, the cam has an adjustment range of up to 360°. In other words, the cam causes the brake shoe to be adjusted within an angular range between 0° and 360°. The longer adjustment range compared to an S-cam reduces the torque required to rotate the cam. The effective transmission ratio of the cam can thus be doubled with the same spread. This allows the use of a smaller drive unit, reducing the weight on the unsprung wheel. This increases driving comfort.

[0022] The invention additionally provides a motor vehicle having the electromechanical drum brake according to the invention. Such a motor vehicle has the advantages and properties described above.

[0023] Embodiments of the invention are illustrated in the drawing and explained in more detail in the following description. It shows:

[0024] Figure 1 View of a drum of an electromechanical

[0025] Drum brake according to an embodiment of the invention,

[0026] Figure 2 Sectional view of the adjustment device and the

[0027] Worm wheel according to Figure 1 ,

[0028] Figure 3 Sectional view of the adjustment device and the

[0029] Worm wheel according to Figure 2.

[0030] Figure 1 shows a view of a drum 10 of an electromechanical drum brake 14 according to an embodiment of the invention. Two brake shoes 18, 22 are arranged in the drum 10 and interact with the drum 10 for braking. The electromechanical drum brake 14 additionally comprises an adjusting device 26, which in this embodiment is designed as a cam. The cam 26 is designed as an Archimedean spiral, which effects an adjustment over a full 360° rotation of the cam 26. The cam 26 interacts with the brake shoes 18, 22 such that the brake shoes 18, 22 can be spread apart with a rotation of the cam 26 for braking. The cam 26 is connected to a shaft 30 to which a worm gear 34 is attached. The worm gear 34 is rotatable via a worm 42 driven by a drive unit 38. In the exemplary embodiment, the drive unit 38 is designed as an electric motor.Together with the worm gear 34, the cam 26 is thus rotated.

[0031] At one end of one of the brake shoes 18, a pressure roller 46 is arranged, which rolls on an outer circumferential surface 50 of the cam 26. A connecting rod 54 is arranged between one end of the other brake shoe 22 and the shaft 30. This connecting rod 54 supports this brake shoe 22 on the shaft 30. By rotating the cam 26, the distance between the brake shoes 18, 22 can be increased or decreased. As a result, a spreading force Fs running in a force direction RF can be applied to both brake shoes 18, 22.

[0032] Figure 2 shows a sectional view of the adjusting device 26 and the worm gear 34 according to Figure 1. This figure shows that the shaft 30 is movably arranged in an elongated hole 62 formed in a drum rear wall 58. The elongated hole 62 runs in the direction of force RF. As a result, a movement of the cam 26 in the elongated hole 62 can establish a force equilibrium between the brake shoes 18, 22. The worm gear 34 and the cam 26 each form a guide section 66, 70, via which a movement of the cam 26 and the worm gear 34 is guided over the drum rear wall 58. Tilting of the shaft 30 is prevented by the guide section 66, 70, which rests against the drum rear wall 58 without play. The shaft 30 can thus be held permanently axially aligned with the drum 10 in the elongated hole 62.

[0033] The guide sections 66, 70 each have a guide surface 74, 78, which is in contact with a surface 82 of the drum rear wall 58. A sliding material is applied to the guide surfaces 74, 78 and the surface 82 of the drum rear wall, which reduces the coefficient of friction. This sliding material improves the balance of forces between the brake shoes 18, 22. Figure 3 shows a sectional view of the adjusting device 26 and the worm gear 34 according to Figure 2. This figure shows the elongated hole 62 again in a side view. The elongated hole 62 runs in a force direction RF of the force Fs applied to the brake shoes 18, 22 via the cam 26.

Claims

Claims 1. An electromechanical drum brake (14) for a motor vehicle, comprising a drum (10) in which brake shoes (18, 22) are arranged, and an adjusting device (26) arranged between the brake shoes (18, 22) and driven by a drive unit (38), via which adjusting device the brake shoes (18, 22) can be spread for braking, characterized in that the adjusting device (26) is connected to a worm wheel (34) which is driven via a worm (42) to rotate the adjusting device (26), wherein the adjusting device (26) is movably mounted between the brake shoes (18, 22) with the worm wheel (34) in a direction of force (RF) to be applied to the brake shoes (18, 22).

2. Electromechanical drum brake (14) according to claim 1, characterized in that the worm wheel (34) and the adjusting device (26) are connected to one another via a shaft (30), the shaft (30) being movably arranged in an elongated hole (62) which runs in the direction of force (RF).

3. Electromechanical drum brake (14) according to claim 2, characterized in that the worm wheel (34) and the adjusting device (26) each form a guide section (66, 70) which bears against a component (58) forming the elongated hole (62) in such a way that an axial alignment of the shaft (30) to the drum (10) is fixed.

4. Electromechanical drum brake (14) according to claim 3, characterized in that the guide sections (66, 70) have a guide surface (74, 78) which bears against the component (58) forming the elongated hole (62), wherein a sliding material is applied to the guide surfaces (74, 78) and / or to a component surface (82) of the component (58) which bears against the guide surfaces (74, 78).

5. Electromechanical drum brake (14) according to claim 4, characterized in that the sliding material is PTFE or bronze.

6. Electromechanical drum brake (14) according to one of claims 2 to 5, characterized in that one brake shoe (18) is connected to a pressure roller (46) which bears against an outer peripheral surface (50) of the adjusting device (26), and the other brake shoe (22) is connected to the shaft (30) or the guide section (66, 70) via a connecting rod (54).

7. Electromechanical drum brake (14) according to one of the preceding claims, characterized in that the adjusting device (26) is designed as a cam.

8. Electromechanical drum brake (14) according to claim 7, characterized in that the cam (26) is designed as an Archimedean spiral.

9. Electromechanical drum brake (14) according to claim 7 or 8, characterized in that the cam (26) has an adjustment path up to a 360° rotation of the cam (26).

10. Motor vehicle comprising an electromechanical drum brake (14) according to one of the preceding claims.

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