Ball screw drive for electromechanical brake system

Abstract

The invention relates to a ball screw drive for an electromechanical brake system, in which a rotational movement of an electric actuator can be transmitted to the ball screw drive by means of a speed reducer and can be converted into a translational movement by means of the ball screw drive, the invention relates to an electro-mechanical brake system for actuating a brake in a braking direction and for unloading the brake in an unloading direction, which electro-mechanical brake system is rotated in a braking rotational direction for actuating the brake of the electro-mechanical brake system and in an unloading rotational direction for unloading the brake. The ball screw drive mechanism includes a spindle nut and a spindle which together form a helically curved ball channel and balls rolling therein, the ball channel transferring braking and unloading forces between the spindle and the spindle nut. In the braking direction, a braking contact surface of the ball channel, which bears against the ball by the spindle nut and the spindle and transmits a braking force, is larger than an unloading contact surface of the ball channel, which bears against the ball and transmits an unloading force.

Description

Field of the Invention

[0001] The present invention relates to a ball screw drive mechanism for an electromechanical braking system. Furthermore, the present invention relates to a motor vehicle having an electromechanical braking system with such a ball screw drive mechanism. Background Art

[0002] For example, from DE 10 2013 216 327 A1, an electromechanical braking system with a hydraulically actuable service brake is known. The braking system further includes an electromechanical actuator, the rotational movement of which is transmitted to the threaded spindle of the ball screw drive mechanism. The rotational movement of the threaded spindle is converted into a translational movement of the threaded nut via rolling elements arranged in a threaded groove in the form of a thread between the threaded spindle and the threaded nut of the ball screw drive mechanism. To carry out the braking process, the threaded nut bears on a brake piston, whereby the brake piston moves translationally and the brake lining bears against the brake disc. The rotational movement of the electromechanical actuator is decelerated to the threaded spindle via a rod with an intermediate connection of a two-stage worm gear. For this purpose, the worm wheel of the worm gear is connected to the rod or the threaded spindle. Summary of the Invention

[0003] The object of the present invention is to provide a ball screw drive mechanism for an electromechanical braking system, by means of which a higher braking force can be transmitted without increasing the weight of the ball screw drive mechanism.

[0004] This object is solved by a ball screw drive mechanism for an electromechanical braking system according to the present invention.

[0005] The present invention provides a ball screw drive mechanism for an electromechanical braking system. The rotational movement of an electric actuator can be transmitted to the ball screw drive mechanism by means of a speed reducer and can be converted into a translational movement by means of the ball screw drive mechanism for actuating the brake in the braking direction and unloading the brake in the unloading direction, the electric actuator rotating in the braking rotation direction for actuating the brake of the electromechanical braking system and rotating in the unloading rotation direction for unloading the brake. The ball screw drive mechanism includes a spindle nut and a spindle, which together form a helically curved ball channel and balls rolling therein, the ball channel transmitting braking force and unloading force between the spindle and the spindle nut. In the braking direction, the braking contact surface of the ball channel, which is in contact with the balls by the spindle nut and the spindle and transmits the braking force, is larger than the unloading contact surface of the ball channel, which is in contact with the balls and transmits the unloading force.

[0006] Due to the acting force, the contact surface of the ball channel is understood as the surface that abuts against the balls and participates in force transmission due to the geometric orientation related to the acting force. Therefore, the braking contact surface includes the surfaces of the spindle and the spindle nut that abut against the balls during the braking process. Therefore, the unloading contact surface is the surface of the spindle and the spindle nut that abuts against the balls in the unloading direction during the movement of the ball screw drive. Therefore, according to the present invention, the braking contact surface that can be used to transmit the braking force is larger than the unloading contact surface for unloading the force. Since in an electromechanical braking system, the unloading force is usually significantly smaller than the braking force, the ball screw drive can be better adapted to the loads occurring during use. In order to be able to absorb high braking forces, the entire ball screw drive does not have to be constructed larger in order to provide a larger braking contact surface. Thereby, the structural dimensions of such a ball screw drive can be reduced. Higher braking forces can also be transmitted without increasing the size and weight of the ball screw drive.

[0007] Therefore, the weight can be reduced by means of such a ball screw drive. It is also possible to use more suitable materials for the spindle or the spindle nut. Therefore, such a ball screw drive can be manufactured compactly and economically.

[0008] In a preferred embodiment of the present invention, the unloading contact surface is constructed in a point-like manner. The point-like contact between the ball channel and the corresponding balls reduces the friction of the ball screw drive in the unloading direction. Therefore, the ball screw drive can run quickly and with low torque in the unloading direction.

[0009] In a further preferred embodiment of the present invention, a ball return portion is constructed in the spindle nut. In the ball return portion, the balls are conveyed to the opposite axial end of the ball screw drive through a guiding channel. Thereby, it is possible to achieve a larger adjustment path.

[0010] The present invention additionally provides a motor vehicle having an electromechanical braking system with such a ball screw drive. Such a motor vehicle has the above-mentioned advantages and characteristics. Description of the Drawings

[0011] Embodiments of the present invention are shown in the drawings and are explained in detail in the following description. Among them:

[0012] Figure 1 A cross-sectional view of a ball screw drive according to an embodiment of the present invention is shown,

[0013] Figure 2 showing according to [[ID=2,6]] Figure 1 an enlarged view of the ball channel, and

[0014] Figure 3Shows an enlarged view of the ball channel according to a further embodiment of the present invention. Detailed Description

[0015] Figure 1 Shows a cross-sectional view of a ball screw drive mechanism 10 according to an embodiment of the present invention. Here, the ball screw drive mechanism 10 is part of an electromechanical braking system and includes a spindle 14 surrounded by a spindle nut 18. The spindle 14 and the spindle nut 18 form a helically curved ball channel 22 in which a plurality of balls 26 are arranged. The spindle nut 18 additionally includes a ball return portion 30 through which the balls 26 can be conveyed to the axial ends of the ball screw drive mechanism 10. In the embodiment shown here, the spindle nut 18 is driven by a speed reducer (not shown). Thus, the spindle 14 can move axially, so that a braking force F B can be applied to a brake adjuster not shown here.

[0016] Figure 2 Shows according to Figure 1 an enlarged view of the ball channel 22. The figure shows how the braking force F B is transmitted from the driven spindle nut 18 via the balls 26 to the spindle 14. It can be seen here how the flank 34 of the spindle nut thread groove for transmitting the braking force F B on the braking contact surface 36 of the balls 26 extends inwardly through the equator 38 of the balls 26 extending in the axial spindle direction. In other words, the starting point of the gap 42 between the spindle nut 18 and the spindle 14 is arranged between the equator 38 of the balls 26 extending in the axial spindle direction and the inner end of the balls 26 in the radial direction of the ball screw drive mechanism 10. Thus, the gap 42 is not provided above the center of the balls 26. Thereby increasing the braking force F B transmitted from the spindle nut 18 to the braking contact surface 36 of the balls 26.

[0017] In the same way, the braking contact surface 36 of the spindle 14 and the balls 26 for transmitting the braking force F B is also increased. The spindle 14 also forms a spindle thread groove flank 50 which is axially opposed to the correspondingly increased flank 34 of the spindle nut thread groove (in the case of the balls 26 arranged between them) for transmitting the braking force F B . Here, the spindle thread groove flank 50 protrudes beyond the equator 38 of the balls 26 extending in the axial direction in the direction of the outer side in the radial direction. Correspondingly, the starting point of the gap 42 between the spindle 14 and the spindle nut 18 is also arranged here between the equator 38 of the balls 26 extending in the axial spindle direction and the outer end of the balls 26 in the radial direction. Correspondingly, for absorbing the braking force F BThe braking contact surface 36 is thus also increased.

[0018] Figure 2 It is additionally shown how the unloading force F E can be transmitted from the spindle nut 18 to the spindle 14 in the unloading direction 52. The braking regulator is removed from the brake disc in the unloading direction 52. Thus, the unloading force F E is significantly smaller than the braking force F B . Accordingly, the unloading contact surface 54 between the ball 26 and the spindle nut 18 or the spindle 14 in the unloading direction 52 is also constructed to be smaller than the braking contact surface 36 between the ball 26 and the spindle nut 18 or the spindle 14 in the braking direction 58. Accordingly, the flank 34 of the thread groove of the spindle nut related to the transmission of the unloading force F E ends before the axial equator 38 of the ball 26 extending in the spindle direction. Similarly, the flank 50 of the thread groove of the spindle related to the transmission of the unloading force F E ends before the axial equator 38 of the ball 26 extending in the spindle direction.

[0019] Figure 3 An enlarged view of the ball channel 22 according to a further embodiment of the invention is shown. This figure is different from the Figure 2 embodiment shown in that the unloading contact surface 54 between the ball 26 and the spindle 14 or the spindle nut 18 in the unloading direction 52 is only constructed as a point. To construct a point contact, the ball channel 22 is constructed as straight in the region of the unloading force F E . Accordingly, the ball channel 22 has a different radius from the ball 26. Accordingly, the ball 26 only abuts against the ball channel 22 in a point-like manner. The advantage of this construction is that the friction between the ball 26 and the ball channel 22 is reduced by the point contact.

Claims

1. A ball screw drive mechanism (10) for an electromechanical braking system, wherein, The rotational movement of the electric actuator can be transmitted to the ball screw drive mechanism (10) by means of a reduction gear and can be converted into a translational movement by means of the ball screw drive mechanism (10) for actuating the brake in the braking direction (58) and for unloading the brake in the unloading direction (52). The electric actuator rotates in the braking rotational direction for actuating the brake of the electromechanical brake system and rotates in the unloading rotational direction for unloading the brake. The ball screw drive mechanism (10) includes a spindle nut (18) and a spindle (14). The spindle nut and the spindle together form a helically curved ball channel (22) and balls (26) that roll in the ball channel. The ball channel transmits the braking force (F B ) and the unloading force (F E ) between the spindle (14) and the spindle nut (18). Characterized in that, in the braking direction (58), the braking contact surface (36) of the ball channel (22) where the spindle nut (18) and the spindle (14) bear against the ball (26) and transmit the braking force (F B ) is larger than the unloading contact surface (54) of the ball channel (22) that bears against the ball (26) and transmits the unloading force (F E ).

2. The ball screw drive mechanism (10) according to claim 1, characterized in that, The unloading contact surface (54) is configured pointwise in the unloading direction (52).

3. The ball screw drive mechanism (10) according to claim 1 or 2, characterized in that, A ball return section (30) is configured in the spindle nut (18).

4. A motor vehicle, comprising an electromechanical braking system having a ball screw drive (10) according to any one of the preceding claims.

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