Electromechanical brake

Abstract

The invention relates to an electromechanical brake (10) for braking a motor vehicle. The electromechanical brake (10) comprises an electric motor (14) having a shaft (22) via which a transmission unit (26) can be driven for the purposes of adjusting a brake actuator (30). The transmission unit (26) comprises a worm and helical gear transmission (38) having a worm (42) and having a plastics helical gear (46), wherein the worm (42) is arranged on the shaft (22) of the electric motor (14), and wherein a worm axis (50) and an axis (54) of the plastics helical gear (46) are oriented differently to one another.

Description

[0001] Description

[0002] Title:

[0003] Electromechanical brake

[0004] The present invention relates to an electromechanical brake for braking a motor vehicle. The invention also relates to a motor vehicle having such a brake.

[0005] State of the art

[0006] Typically, the service brake is a brake in which a brake piston, together with a brake pad, is pressed onto a brake disc via brake fluid to slow the vehicle. With the increasing electrification of motor vehicle components, the service brake is also being designed as an electromechanical brake, eliminating the need for brake fluid and the associated complex valve and line assembly. Such an electromechanical brake could also significantly reduce maintenance requirements.

[0007] DE 10 2022 120373 A1 discloses an electromechanical brake with a drum brake. The electromechanical brake comprises an electric motor that drives a first gear. This first gear is operatively connected to a second gear, so that the second gear is driven via the first gear. A shaft is formed on the second gear, on which a worm is arranged. The worm meshes with a worm wheel, forming a worm gear with it. The worm wheel drives a spindle drive unit of a brake actuator, via which two brake pads of the drum brake can be applied to the drum for braking. The object underlying the invention is to provide an electromechanical brake that can be arranged in a space-saving manner and that can be manufactured economically.

[0008] The object is achieved by an electromechanical brake having the subject matter of patent claim 1. Preferred embodiments can be found in the dependent claims.

[0009] Disclosure of the invention

[0010] The invention specifies an electromechanical brake for braking a motor vehicle. The electromechanical brake comprises an electric motor with a shaft, via which a gear unit can be driven for adjusting a brake actuator. The gear unit comprises a worm-helical gear with a worm and a plastic helical gear. The worm is arranged on a shaft of the electric motor, and a worm axis and an axis of the plastic helical gear have a different orientation from one another.

[0011] A worm-helical gear drive is a gear consisting of a worm and a helical gear, which are arranged at different angles to each other. This results in point-like contact between the worm and the helical gear. In contrast, a worm gear is a gear with linear flank contact. This means that the worm gear and worm are at an angle of 90° to each other. A worm axis and the axis of the plastic helical gear, however, can have an angle other than 90°. The advantage of a worm-helical gear drive over a worm gear is that, due to the point-like contact, a worm-helical gear drive is less sensitive to tolerance deviations in the components or during installation. This makes it more economical to manufacture an electromechanical brake with a helical gear drive.

[0012] A worm gear has the additional advantage that the position of the electric motor is not fixed at 90°. This allows for more variable positioning of the electric motor, allowing for specific installation conditions. Furthermore, the electric motor can be positioned more efficiently on the housing, allowing for a more compact design of this type of electromechanical unit.

[0013] According to the invention, the helical gear is designed as a plastic helical gear. The plastic helical gear can therefore be easily manufactured using an injection molding process. Compared to a metal helical gear, this ensures that tolerances are permanently maintained, thus minimizing the number of rejects and thus reducing manufacturing costs. Furthermore, a plastic helical gear saves weight and material costs. The unsprung mass on the wheel can be reduced. This also improves the handling of the vehicle.

[0014] The plastic helical gear is advantageously made of polyoxymethylene (POM), polyamide 6.6 (PA66), polyamide 4.6 (PA46), or polyetheretherketone (PEEK). Such plastics exhibit good tribological properties. These plastics exhibit favorable elasticity, so that contact with the worm results in a flattening of the surface. This increases the contact area and reduces surface tension during contact. Furthermore, this results in favorable tolerance sensitivity to positional tolerances of the gear and worm.

[0015] Particularly preferably, the plastic helical gear is made of an unreinforced plastic. In other words, the plastic does not contain any reinforcing fibers. Aside from the fact that an unreinforced plastic is more economical than a reinforced plastic, this also ensures that the surface can be flattened.

[0016] In an advantageous embodiment, the electromechanical brake is a service brake. Particularly preferably, the brake actuator is designed as a disc brake. In a further preferred embodiment of the invention, the helical gear has a gear ratio between 6 and 50. Such a gear ratio is realized in just one stage. With such a gear ratio, it is possible to use a more cost-effective, smaller and lighter electric motor. Accordingly, the installation space required for the electromechanical brake is further reduced. The lighter electric motor further reduces the mass arranged on the wheel, thereby improving the driving characteristics of the motor vehicle. Advantageously, the electric motor has a diameter of less than or equal to 65 mm and a length of less than 30 mm. Particularly preferably, the diameter is less than 50 mm.

[0017] Preferably, the axis of the plastic helical gear and the worm axis are at an angle of between 60° and 120°. This angle ensures that friction between the plastic helical gear and the worm is kept to a minimum, thus preventing the service life of such a gear from being reduced due to wear.

[0018] In an advantageous refinement, the plastic helical gear has a semi-globo-shaped design. With a semi-globo-shaped design, one shoulder of the gear is raised. This increases the contact area with the worm in one direction of rotation, thus reducing the surface load. This design increases the tooth stiffness, thereby increasing the load-bearing capacity of the plastic helical gear. Cost-effective production using injection molding without complex sliding elements is maintained.

[0019] Advantageously, the screw pitch angle is greater than 6°. This prevents self-locking of the screw. This has the advantage that if the electric motor fails while the brake is applied, the brake can be released again.

[0020] In an advantageous design, the worm is designed as a multi-start worm. A multi-start worm has more than one worm tooth winding around the shaft. A multi-start worm is more efficient than a single-start worm. Furthermore, the tendency toward self-locking is reduced.

[0021] In another advantageous design, the plastic helical gear has straight teeth. In contrast to a helical gear, a straight-toothed plastic helical gear is more economical and precise to manufacture. Furthermore, a straight-toothed injection-molded part is easier to remove from the injection mold.

[0022] According to a practical design, the helical gear is directly connected to a spindle gear, via which a brake piston can be axially displaced. Thus, no additional gear components are arranged between the helical gear and the spindle gear. This allows for a reduction in the number of parts and the installation space for such an electromechanical brake. Furthermore, the play in the gear unit, which increases with each gear element, is minimized. This type of gear unit thus has a better response time for rapid braking maneuvers, such as ABS braking.

[0023] Advantageously, the electric motor shaft and the worm are designed as separate parts that can be connected to each other. Although the shaft and worm can also be designed together as a single part, they are designed separately. This allows the worm to be manufactured more independently, simplifying production. If a manufactured worm fails to meet the tolerance dimensions, only the worm needs to be rejected. By designing the parts separately, manufacturing these parts can be carried out more economically and simply.

[0024] Preferably, the electric motor shaft and the worm gear are formed as a single piece. This eliminates the need for couplings and bearings between the two shafts. Compared to mounting the worm gear on the motor shaft, the worm gear diameter can be kept small. This increases the efficiency of the worm gear, which is advantageous for the motor power required, thus reducing the cost and installation space of the motor and the power required for braking.

[0025] Additionally, a motor vehicle is provided which features the electromechanical brake according to the invention. Such a motor vehicle has the advantages described above.

[0026] Embodiments of the invention are illustrated in the drawing and explained in more detail in the following description. It shows:

[0027] Figure 1 Perspective view of an electromechanical brake according to an embodiment of the invention, and

[0028] Figure 2 Sectional view of the electromechanical brake.

[0029] Figure 1 shows a perspective view of an electromechanical brake 10 according to an embodiment of the invention. The electromechanical brake 10 comprises an electric motor 14, which is attached to a housing 18 of the electromechanical brake 10. The electric motor 14 has a shaft 22 that projects into the housing 18. A gear unit 26 is driven via the shaft 22. A brake actuator 30, which in this embodiment is designed as a disc brake (see Figure 2), is adjustable via the gear unit 26. By adjusting brake pads 34 of the disc brake 30, these can be applied to a brake disc (not shown here), thereby braking the motor vehicle.

[0030] The gear unit 26 has a worm-helical gear 38. A worm 42 of the worm-helical gear 38 is formed on the shaft 22 of the electric motor 14. The worm 42 engages with a plastic helical gear 46. In the illustrated embodiment, a worm axis 50 is arranged almost orthogonally to an axis 54 of the plastic helical gear 46. The plastic helical gear 46 is designed as a straight toothed gear without a semi-globoid. Figure 2 shows a sectional view of the electromechanical brake 10. This figure shows that the gear unit 26 additionally comprises a spindle gear 58. In this embodiment, the spindle gear 58 is designed as a ball spindle gear. The spindle gear 58 comprises a spindle 62, which is directly connected to the plastic helical gear 46.Thus, no additional gear components are arranged between the plastic helical gear 46 and the spindle gear 58, allowing the gear unit 26 to be designed compactly. The spindle 62 is operatively connected to a spindle nut 66, so that a rotational movement of the spindle 62 results in a translational movement of the spindle nut 66. A brake piston 70 is moved axially via the spindle nut 66, via which a force is applied to the brake pad 34.

Claims

Claims 1. Electromechanical brake (10) for braking a motor vehicle, comprising an electric motor (14) with a shaft (22), via which a gear unit (26) can be driven for adjusting a brake actuator (30), characterized in that the gear unit (26) comprises a worm helical gear (38) with a worm (42) and a plastic helical gear (46), wherein the worm (42) is arranged on the shaft (22) of the electric motor (14), and wherein a worm axis (50) and an axis (54) of the plastic helical gear (46) have a different orientation to one another.

2. Electromechanical brake (10) according to claim 1, characterized in that the brake actuator (30) is designed as a disc brake.

3. Electromechanical brake (10) according to claim 1 or 2, characterized in that the worm gear (38) has a gear ratio between 6 and 50.

4. Electromechanical brake (10) according to one of the preceding claims, characterized in that the axis (54) of the plastic helical gear (46) and the worm axis (50) have an angle between 60° and 120° to one another.

5. Electromechanical brake (10) according to one of the preceding claims, characterized in that the plastic helical gear (46) is semi-globoidal.

6. Electromechanical brake (10) according to one of the preceding claims, characterized in that a pitch angle of the worm (42) is greater than 6°.

7. Electromechanical brake (10) according to one of the preceding claims, characterized in that the plastic helical gear (46) has straight teeth.

8. Electromechanical brake (10) according to one of the preceding claims, characterized in that the plastic helical gear (46) is directly connected to a spindle gear (58) via which a brake piston (70) is axially displaceable.

9. Electromechanical brake (10) according to one of the preceding claims, characterized in that the electric motor (14) has a diameter of less than or equal to 65 mm and a length of less than 30 mm.

10. Electromechanical brake (10) according to one of the preceding claims, characterized in that the shaft (22) of the electric motor (14) and the worm (42) are formed together in one piece.

11. Electromechanical brake (10) according to one of claims 1 to 9, characterized in that the shaft (22) of the electric motor (14) and the worm (42) are designed as separate parts which can be connected to one another.

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

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