ELECTRIC DRUM BRAKE FOR A ROTATABLE ELEMENT

Abstract

An electric drum brake for a rotatable element of a passenger motor vehicle. The drum brake has a brake drum and a brake surface which is connected rotationally conjointly to the brake drum, and also an electromagnet arrangement, wherein multiple brake shoes can be pushed against the brake drum by the electromagnet arrangement, and wherein the drum brake has a preloading arrangement which preloads the electromagnet arrangement into a position spaced apart from the brake surface.

Claims

1. An electric drum brake for a rotatable element of a passenger motor vehicle, wherein the drum brake comprises: a brake drum which is connected rotationally conjointly to the rotatable element; a brake surface which is connected rotationally conjointly to the brake drum; an electromagnet arrangement which has at least one electrical coil which, when energized, generates a magnetic field which pushes the electromagnet arrangement against the brake surface, such that the electromagnet arrangement is concomitantly rotated to a limited extent by the brake surface; and at least two brake shoes, wherein the electromagnet arrangement and the brake shoes are arranged such that the brake shoes are pushed against the brake drum by the electromagnet arrangement when the electromagnet arrangement is rotated, and wherein the drum brake has a preloading arrangement which preloads the electromagnet arrangement into a position spaced apart from the brake surface.

2. The electric drum brake as claimed in claim 1, wherein the brake surface is formed on the brake drum or is formed on a disk which is separate from the brake drum and which is connected rotationally conjointly to the rotatable element.

3. The electric drum brake as claimed in claim 1, wherein the electromagnet arrangement is of ring-shaped design.

4. The electric drum brake as claimed in claim 1, wherein the electromagnet arrangement has a yoke with an E-shaped or a W-shaped cross section.

5. The electric drum brake as claimed in claim 1, wherein the electromagnet arrangement has two electrical coils.

6. The electric drum brake as claimed in claim 5, wherein each electrical coil is arranged in a respective groove of a yoke of the electromagnet arrangement.

7. The electric drum brake as claimed in claim 1, wherein the preloading arrangement has a number of springs.

8. The electric drum brake (10) as claimed in claim 1, comprising a number of force-measuring devices between the electromagnet arrangement (40) and the brake shoes (30, 35).

9. The electric drum brake as claimed in claim 1, wherein the electromagnet arrangement has a yoke composed of magnetic sheet metal and/or a friction region which is composed of spheroidal graphite cast iron and which in the activated state engages with the brake surface.

10. The electric drum brake as claimed in claim 1, comprising a detent mechanism for mechanically holding the electromagnet arrangement on the brake surface.

11. The electric drum brake as claimed in claim 1, which is partially or entirely arranged in a liquid or in transmission oil.

12. The electric drum brake as claimed in claim 1, wherein the drum brake is a duo-duplex drum brake.

13. The electric drum brake as claimed in claim 1, wherein the electromagnet arrangement has a number of cams which, when the electromagnet arrangement is rotated, engage with the brake shoes so as to actuate the latter.

14. The electric drum brake as claimed in claim 1, wherein the brake drum is composed of aluminum and has an inlaid magnetically conductive brake surface.

15. The electric drum brake as claimed in claim 1, wherein multiple coils are arranged in circularly distributed fashion with axial coil cores.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Further features and advantages will be gathered by a person skilled in the art from the exemplary embodiment described below with reference to the appended drawing. In the drawing:

[0033] FIG. 1: shows an electric drum brake in an exploded view, and

[0034] FIG. 2: shows a sectional view of an electromagnet arrangement.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] FIG. 1 shows an electric passenger motor vehicle drum brake 10 according to an exemplary embodiment of the invention.

[0036] The electric drum brake 10 has a base plate 20. Two projections 22, 24 are formed on said base plate, which projections bear further components that will be described below.

[0037] The drum brake 10 has a first brake shoe 30 and a second brake shoe 35. Respective brake linings 32, 37 are applied to the radially outer side of the brake shoes 30, 35.

[0038] The drum brake 10 has an electromagnet arrangement 40. An electrical coil 50 is arranged in said electromagnet arrangement. The electromagnet arrangement 40 is in the present case of ring-shaped design, with the coil 50 likewise being of ring-shaped design.

[0039] A first cam 42 and a second cam 44, which point toward the base plate 20, are arranged on the electromagnet arrangement 40. When the drum brake 10 is assembled with the components shown in the orientation shown, the cams 42, 44 do not yet engage with the brake shoes 30, 35. However, if the electromagnet arrangement 40 is rotated, the cams 42, 44 push the brake shoes 30, 35 radially outward. This corresponds to an activation of the drum brake 10.

[0040] The drum brake 10 has an intermediate element 60. The intermediate element 60 can in particular be mounted onto the respective wheel bearing.

[0041] The drum brake 10 has a disk 70 on which a brake surface which points toward the base plate 20, and which is thus not visible in FIG. 1, is formed. The disk 70 is mounted onto the intermediate element 60.

[0042] The drum brake 10 furthermore has a brake drum 80.

[0043] When the components shown in FIG. 1 are assembled, the disk 70 is fixedly connected to the brake drum 80, that is to say rotates together with the brake drum 80. The brake drum 80 is furthermore connected to a rotatable element (not illustrated) such as a drive shaft, wherein a braking action of the drum brake 10 is intended to act on said rotatable element. By contrast, the base plate 20 is typically fixedly installed in a vehicle, such that the rotatable element rotates together with the brake drum 80 and the disk 70 relative to the base plate 20.

[0044] The electromagnet arrangement 40 is preloaded into its basic position, such that it is spaced apart from the disk 70, by a preloading arrangement 25 with two schematically illustrated springs 26. Constant friction of the electromagnet arrangement 40 can thereby be avoided. If the coil 50 is energized, it is pulled against the brake surface of the disk 70 owing to the magnetic action. Since the disk 70 rotates, the electromagnet arrangement 40 is thus also concomitantly rotated, specifically owing to the resulting friction. In this way, as already described further above, the two brake shoes 30, 35 are pushed outward, whereby the brake linings 32, 37 engage with the brake drum 80. This generates a braking action.

[0045] It should be mentioned that the friction of the electromagnet arrangement 40 against the brake surface of the disk 70 already creates friction. This also already generates a braking action, such that the two braking actions are added together.

[0046] The design shown corresponds to that of a duo-duplex drum brake.

[0047] FIG. 2 shows a slightly modified form of an electromagnet arrangement 40, which may also be used in the embodiment of FIG. 1. Here, the electromagnet arrangement 40 has a yoke 46 in an E shape, such that two grooves are created in the yoke 46. A respective coil 50, 55 is arranged in each of these grooves, which coils are electrically independent of one another. In the present case, an embodiment with two coils 50, 55 is thus provided. This increases the redundancy.

[0048] Toward the brake surface of the disk 70, the electromagnet arrangement 40 has a friction region 48, which may be formed from a different material than the yoke 46. In particular, spheroidal graphite cast iron may be used for the friction region 48. This has been found to be advantageously particularly durable for the intended use, which causes friction upon every braking operation.

[0049] It is pointed out that, for faster deactivation of the drum brake 10, residual magnetization can be actively reduced. For this purpose, an alternating, falling current amplitude can be applied to the magnet.

[0050] The embodiment shown and described has been found to be an inexpensive electrical actuator which can withstand a long service life and which is resistant to corrosion and/or contamination. Constant friction can be eliminated, as the inventors of this application have found out. The drum brake shown can in particular be of encapsulated design, which leads to a high level of availability. It can be integrated in compact fashion in a series installation space. It may also be designed as a dry brake without hydraulic supply devices, and typically requires only an electrical connection for the purposes of activation.

[0051] It is pointed out that features may be described in combination in the claims and in the description, for example to facilitate understanding, although these may also be used separately from each other. The person skilled in the art will gather that such features may also be combined with other features or feature combinations independently of each other.

[0052] Dependency references in the dependent claims may characterize preferred combinations of the respective features but do not exclude other feature combinations.

LIST OF REFERENCE SIGNS

[0053] 10: Electric drum brake [0054] 20: Base plate [0055] 22: Projection [0056] 24: Projection [0057] 25: Preloading arrangement [0058] 26: Springs [0059] 30: Brake shoe [0060] 32: Brake lining [0061] 35: Brake shoe [0062] 37: Brake lining [0063] 40: Electromagnet arrangement [0064] 42: Cam [0065] 44: Cam [0066] 46: Yoke [0067] 48: Friction region [0068] 50: Coil [0069] 55: Coil [0070] 60: Intermediate element [0071] 70: Disk [0072] 80: Brake drum