BALL SCREW DRIVE AND ELECTROMECHANICAL ACTUATOR

Abstract

A ball screw drive, in particular for an actuator of a hydraulic brake system, includes two spindle drive elements, namely a threaded spindle and a spindle nut which can be rotated relative to the threaded spindle. One of the spindle drive elements is provided as a rotatable drive element, and the second spindle drive element is provided as an output element which can be moved in a secured manner against rotation. The ball screw drive additionally includes a damping element that is configured as an annular element concentric relative to a central axis of the threaded spindle. The annular element is rigidly connected to one of the two spindle drive elements, and can be simultaneously rotated and moved relative to the other spindle drive element in a play-free manner.

Claims

1. A ball screw drive comprising: a threaded spindle, and a spindle nut configured to be rotated relative to the threaded spindle, and one of the threaded spindle or the spindle nut is a rotatable drive element and a remaining one of the threaded spindle or the spindle nut is an output element configured to move without rotation, and a damping element rigidly connected to the one of the threaded spindle or the spindle nut, the damping element configured to be moved without play relative to the remaining one of the threaded spindle or the spindle nut.

2. The ball screw drive according to claim 1, wherein the threaded spindle is the rotatable drive element and the spindle nut is the output element, and the spindle nut is configured to be axially movable.

3. The ball screw drive according to claim 2, wherein the damping element is mounted to the threaded spindle and engages a piston support rigidly coupled to the spindle nut.

4. The ball screw drive according to claim 1, wherein the spindle nut is the rotatable drive element and the threaded spindle is the output element, and the threaded spindle is configured to be axially movable.

5. The ball screw drive according to claim 4, wherein the damping element is arranged on outer circumferential surface of the spindle nut and simultaneously engages an inner circumferential surface of a hollow piston rigidly connected to the threaded spindle.

6. The ball screw drive according to claim 5, wherein the damping element is fixed on the threaded spindle and simultaneously engages a sleeve-shaped element configured for driving the spindle nut.

7. The ball screw drive according to claim 2, wherein the damping element is held in the spindle nut and simultaneously engages the threaded spindle.

8. The ball screw drive according to claim 1, wherein the damping element is configured as an annular element arranged concentrically to a central axis of the threaded spindle.

9. An electromechanical actuator of a hydraulic brake system, comprising the ball screw drive according to claim 1.

10. The electromechanical actuator of claim 9, further comprising a piston fixed to the one of spindle nut or the threaded spindle and the piston is configured to receive a hydraulic fluid pressure.

11. The ball screw drive according to claim 1, wherein the damping element is an elastic element.

12. The ball screw drive according to claim 11, wherein the damping element is arranged radially between the threaded spindle and the spindle nut.

13. The ball screw drive according to claim 12, wherein the damping element is fastened to the spindle nut and rests directly on a thread of the threaded spindle.

14. The ball screw drive according to claim 3, wherein the damping element is arranged radially between the threaded spindle and the piston support and the damping element slidably engages the piston support.

15. The ball screw drive according to claim 5, wherein the damping element rotates together with the spindle nut and moves axially relative to the hollow piston.

16. A ball screw drive comprising: a threaded spindle, and a spindle nut configured to be rotated relative to the threaded spindle, and one of the threaded spindle or the spindle nut is a rotatable drive element and a remaining one of the threaded spindle or the spindle nut is an output element configured to move without rotation, a piston fixed to one of the threaded spindle or the spindle nut, the piston configured to receive a hydraulic fluid pressure, and an elastic vibration damping element: i) rigidly connected to the one of the threaded spindle or the spindle nut, and ii) configured to be moved without play relative to the remaining one of the threaded spindle or the spindle nut.

17. The ball screw drive of claim 16, further comprising a plurality of balls disposed between the threaded spindle and the spindle nut.

18. The ball screw drive of claim 16, wherein the elastic vibration damping element is annularly shaped.

19. The ball screw drive of claim 16, wherein the piston and spindle nut move together in an axial direction.

20. The ball screw drive of claim 16, wherein the piston and threaded spindle move together in an axial direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Five exemplary embodiments of the disclosure are explained in more detail below by means of drawings. In the figures:

[0020] FIG. 1 shows a comparative design of a ball screw drive with a driven threaded spindle, which is not in accordance with the invention,

[0021] FIG. 2 shows a first design of a ball screw drive with a driven threaded spindle,

[0022] FIG. 3 shows a first design of a ball screw drive with a driven spindle nut,

[0023] FIG. 4 shows a second design of a ball screw drive with a driven spindle nut,

[0024] FIG. 5 shows a third design of a ball screw drive with a driven spindle nut, and

[0025] FIG. 6 shows a further design of a ball screw drive with a driven threaded spindle.

DETAILED DESCRIPTION

[0026] Unless otherwise stated, the following explanations relate to all the exemplary embodiments. Parts that correspond to each other or have basically the same effect are denoted with the same reference signs in all the figures.

[0027] A ball screw drive 1 comprises a threaded spindle 2 as the first spindle drive element and a spindle nut 3 as the second spindle drive element. A ball track 4 for balls 26 as rolling elements is formed between the spindle drive elements 2, 3. A load section of the ball track 4 is designated with 5. In the embodiments according to FIGS. 1 and 2, an external recirculation of the balls 26 is provided. In these cases, return sections of the ball track 4 are designated with 6. In the cases of FIGS. 3 and 4, an internal recirculation of the balls 26 is provided. In these cases, recirculation elements for the internal recirculation are designated with 21. The common central axis of the threaded spindle 2 and the spindle nut 3 and thus of the entire ball screw drive 1 is designated with MA in all cases.

[0028] The ball screw drive 1 moves a piston 16 in a housing 11. A pressure p of a hydraulic fluid acts on the piston 16. Forces acting in the axial direction of the ball screw drive 1 are generally designated with F. The piston 16 is sealed by a seal 18, which is inserted into a groove 17. The groove 17 is located in the piston 16 in the cases of FIGS. 1 and 2 and in the housing 11 in the cases of FIGS. 3 and 4.

[0029] In the designs according to FIGS. 1 and 2, the threaded spindle 2 acts as the driving element of the ball screw drive 1. In the cases outlined, a belt transmission 7 in the form of a belt drive is connected upstream of the ball screw drive 1. Here, a belt pulley 8 of the belt transmission 7 is connected to the threaded spindle 2 for conjoint rotation. A further driving belt pulley of the belt transmission 7 is connected to the motor shaft of an electric motor 9 for conjoint rotation. In the cases outlined in FIGS. 1 and 2, the motor shaft of the electric motor 9 is arranged parallel to the central axis MA. The belt of the belt transmission 7 is designated with 10.

[0030] The threaded spindle 2 or a part connected to the threaded spindle 2 for conjoint rotation, has a cap-shaped end piece 12 projecting beyond the belt pulley 8, which strikes approximately at a point on an inner wall 13 of the housing 11. In a more complex variant of the ball screw drive 1, which is not shown, an axial bearing or an angular contact ball bearing supporting axial forces F could also be arranged at the corresponding point, for example.

[0031] The spindle nut 3 of the ball screw drives 1 according to FIGS. 1 and 2 is secured against rotation in a manner not shown. A tubular piston support 15 is connected to the spindle nut 3, via which compressive forces in particular can be transmitted to the piston 16. A tube that is rigidly connected to the housing 11 and concentrically surrounds the piston support 15 is designated with 14.

[0032] In the comparative design according to FIG. 1, an annular damping element 24 is inserted between the outer circumferential surface of the spindle nut 3 and the tube 14 fixed to the housing. If the threaded spindle 2 rotates, the damping element 24 is moved in the axial direction together with the spindle nut 3. The damping element 24 does not rotate in this case. The distance between the damping ring 24 and the piston 16, which delimits a pressure chamber 25, remains constant with all settings of the ball screw drive 1.

[0033] In the exemplary embodiment according to FIG. 2, the damping ring 24 is fastened on the threaded spindle 2 and is located close to that end of the threaded spindle 2 which faces the piston 16. When the threaded spindle 2 rotates, the damping ring 24 rotates relative to the inherently rigid arrangement of the spindle nut 3, piston support 15 and piston 16, and the damping ring 24 slides on the inner circumferential surface of the piston support 15. Simultaneously, the piston support 15 is moved in the axial direction on the damping element 24.

[0034] In the exemplary embodiments according to FIGS. 3 and 4, the spindle nut 3 is the driving element of the ball screw drive 1. The spindle nut 3 is extended in the axial direction in the form of a drive section 19, which does not have a threaded structure. The section 19 and thus the entire spindle nut 3 is electrically driven by a reduction gear 7, which is not shown in this case. Alternatively, an electric direct drive of the spindle nut 3 is possible. Axial forces F acting on the spindle nut 3 are in any case received by a rolling bearing 20, in particular in the form of an angular contact ball bearing. In the cases shown in FIGS. 3 and 4, the piston 16 is hollow, and not only the threaded spindle 2 but also the spindle nut 3 engages in the cavity formed by the piston 16. A rigid connection between the threaded spindle 2 and the piston 16 is established via an annular element 22 and a cylindrical element 23.

[0035] In the exemplary embodiment according to FIG. 3, the annular damping element 24 is inserted into an annular gap between the outer circumferential surface of the spindle nut 3 and the inner circumferential surface of the piston 16. The damping ring 24 rotates together with the spindle nut 13 and is simultaneously moved in the axial direction relative to the piston 16 when the ball screw drive 1 is actuated. The measurable distance in the axial direction between the damping ring 24 and the surface of the piston 16 delimiting the pressure chamber 25 is therefore variable.

[0036] In the exemplary embodiment according to FIG. 4, the damping ring 24, in principle comparable to the design according to FIG. 2, is fastened on the threaded spindle 2. Simultaneously, in the case of FIG. 4, the damping ring 24 contacts the inner circumferential surface of the cylindrical drive section 19. As the drive section 19 rotates together with the entire spindle nut 3, a relative rotation occurs between the damping ring 24 and the spindle nut 3. The distance between the damping ring 24 and the piston 16 is constant in the case of FIG. 4. In the case of both FIG. 3 and FIG. 4, the arrangement of the threaded spindle 2 and piston 16 is guided in a manner secured against rotation in the housing 11.

[0037] The exemplary embodiment according to FIG. 5 differs from the exemplary embodiment according to FIG. 4, mainly in that the damping ring 24 is fastened in the spindle nut 3. Thus, in this case too, a movement is provided for between the damping ring 24 and one of the two spindle drive elements 2, 3, in this case the threaded spindle 3. In this regard, the flexible damping ring 24, which rotates together with the spindle nut 3, rests on the thread of the threaded spindle 3 under a slight preload.

[0038] In the exemplary embodiment according to FIG. 6, the damping ring 24 is also held in the inner circumferential surface of the spindle nut 3, and in this case, as in the variant according to FIG. 2, the threaded spindle 3 acts as the drive element of the ball screw drive 1. In the constellation according to FIG. 6, the damping ring 24, which is under a slight preload, also contributes in particular to the damping of bending vibrations.

LIST OF REFERENCE SYMBOLS

[0039] 1 Ball screw drive [0040] 2 Threaded spindle [0041] 3 Spindle nut [0042] 4 Ball track [0043] 5 Load section [0044] 6 Return section [0045] 7 Belt transmission [0046] 8 Belt pulley [0047] 9 Electric motor [0048] 10 Belt [0049] 11 Housing [0050] 12 Cap-shaped end piece [0051] 13 Inner wall [0052] 14 Tube fixed to the housing [0053] 15 Piston support [0054] 16 Piston [0055] 17 Groove [0056] 18 Seal, inserted into the groove 17 [0057] 19 Drive section of the spindle nut [0058] 20 Rolling bearing [0059] 21 Recirculation element for internal recirculation [0060] 22 Annular element [0061] 23 Cylindrical element [0062] 24 Annular damping element [0063] 25 Pressure chamber [0064] 26 Ball [0065] F Force [0066] MA Central axis [0067] p Hydraulic pressure