BALL SCREW DRIVE AND METHOD FOR OPERATING A BALL SCREW DRIVE

Abstract

A ball screw drivel, in particular for a parking brake, comprises a threaded spindle, a spindle nut, and rolling bodies, namely balls, which are arranged in a thread turn between the threaded spindle and the spindle nut, Spring elements are arranged in the thread turn between nut-side stops. There is at least one setting of the threaded spindle and the spindle nut in which the balls and the spring elements are arranged in the thread turn with backlash.

Claims

1. A ball screw drivel, comprising, a threaded spindle, a spindle nut, rolling bodies configured as balls arranged in a thread turn between the threaded spindle and the spindle nut, and spring elements arranged in the thread turn between two nut-side stops, wherein in at least one setting of the threaded spindle and the spindle nut the balls and the spring elements are arranged in the thread turn with backlash.

2. The ball screw drive according to claim 1, further comprises spacer elements arranged between a plurality of groups of balls.

3. The ball screw drive according to claim 2, wherein the spacer elements are configured as balls which are smaller than the rolling bodies.

4. The ball screw drive according to claim 3, wherein a diameter of each spacer element is at least 80% and at most 95% of a diameter of each rolling body.

5. The ball screw drive according to claim 2, wherein groups of at least two and at most four rolling bodies are each separated from one another by a spacer element.

6. The ball screw drive according to claim 5, wherein a first group of rolling bodies adjacent to, a first spring element comprises exactly three rolling bodies and a second group of rolling bodies adjacent to a second spring element comprises exactly two rolling bodies and at least one spacer element is arranged between the first and second groups of rolling bodies.

7. The ball screw drive according to claim 6, wherein the first spring element measured in a direction of extension of the thread turn, is longer than the second spring element.

8. The ball screw drive according to claim 7, wherein a total of at least twelve and at most groups of rolling bodies are arranged between the first and second spring elements.

9. The ball screw drive according to claim 1, total length of a free space measured in a direction of an extension of the thread turn when the spring elements are relaxed is at least 0.2% and at most 5% of total length of the thread turn to be measured between the two nut-side stops.

10. A method for operating a ball screw drive comprising: arranging balls as rolling bodies in a thread turn formed between a threaded spindled and a spindle nut, arranging first and second spring elements in said thread turn such that starting from a first setting of the ball screw drive in which the first spring elements is tensioned, the ball screw drive via a central position of the threaded spindle and the spindle nut, in which the first and second spring elements are relaxed, is brought out into a second setting, in which the second spring element is tensioned.

11. The method of claim 10, wherein in the second setting, the first spring element is relaxed.

12. A ball screw drive, comprising: a threaded spindle, a spindle nut, a first quantity of rolling bodies arranged in a thread turn between the threaded spindle and the spindle nut, and a first spring element and a second spring element arranged in the thread turn between two end stops, and in at least one setting of the threaded spindle and the spindle nut, the first quantity of rolling bodies and the first and second spring elements are arranged in the thread turn with backlash.

13. The ball screw drive of claim 12, wherein the first and second spring elements are helical springs.

14. The ball screw drive of claim 12, further comprising a second quantity of spacer elements arranged amongst the first quantity of rolling bodies.

15. The ball screw drive of claim 14, wherein the first quantity of rolling bodies are balls and the second quantity of spacer elements are balls which are smaller than the first quantity of rolling bodies.

16. The ball screw drive of claim 15, wherein the first quantity of rolling bodies are arranged in groups of consecutive same-sized balls and at least one ball of the second quantity of spacer elements are arranged between the groups.

17. The ball screw drive of claim 16, further comprising: a central setting in which the first and second spring elements are in a relaxed state and backlash is present between the first quantity of rolling bodies, a first setting of the ball screw drive in which the first spring element is tensioned, and a second setting of the ball screw drive in which the second spring element is tensioned.

18. The ball screw drive of claim 17, wherein the groups of consecutive same-sized balls includes a first group having at least two balls, and one of the at least two balls is configured to abut with a first end stop, and another one of the at least two balls is configured to abut with one ball of the second quantity of spacer elements.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In the following, an exemplary embodiment of the disclosure is explained in more detail by means of a drawing. In the drawings:

[0021] FIG. 1 shows a ball screw drive in a sectional representation,

[0022] FIG. 2 shows components of the ball screw according to FIG. 1 in an abstracted representation.

DETAILED DESCRIPTION

[0023] A ball screw drive, identified overall by the reference numeral 1, is intended for use as a rotary-linear transmission in a parking brake of a motor vehicle and comprises a threaded spindle 2 and a threaded nut 3. A thread turn of the ball screw drive 1 is identified by the numeral 4. Between the threaded spindle 2 and the threaded nut 3, balls roll off as rolling bodies 5 in the thread turn 4. With regard to the principal function of the ball screw drive 1, reference is made to the prior art cited at the outset. The parking brake of the motor vehicle is combined with a hydraulic disc brake in a manner known per se.

[0024] In the threaded nut 3, which is also referred to as a spindle nut, there is a first nut-side stop 6 and a second nut-side stop 7. A rolling body return, for example in the form of an external deflection, is not provided. Therefore, using the ball screw 1 for applications with long travel distances is out of the question.

[0025] In the thread turn 4 there is a first spring element 8 which can strike the first stop 6 and a second spring element 9 which can be supported on the second stop 7. Both spring elements 8, 9 are designed as helical springs.

[0026] In addition to the rolling bodies 5, i.e. bearing balls, there are several spacer elements 10 in the thread turn 4. The spacer elements 10 are balls which have a smaller diameter than the rolling bodies 5. As far as the arrangement of the various balls 5, 10 in the thread turn 4 is concerned, reference is made to the symbolized representation according to FIG. 2. Immediately following the first spring element 8, i.e. the adjustment spring, which is significantly longer than the pre-compression spring 9, there is a ball arrangement 11 in the arrangement shown, which is constructed in a defined manner from groups of rolling bodies 5 and spacer elements 10: Alternating groups of three rolling bodies 5 and individual spacer elements 10 are inserted into the thread turn 4. Overall, the ball arrangement 11, only partially shown, is made up of 19 groups of three rolling bodies 5 each, that is to say a total of 57 rolling bodies 5 and an additional 19 spacer balls 10. This ball arrangement 11 is followed by a closing ball arrangement 12 which is formed from only two rolling bodies 5. In the exemplary embodiment, the rolling bodies 5 of both the ball arrangement 11 and the closing ball arrangement 12 have a diameter of 2.778 mm and the spacer elements 10 have a diameter of 2.5 mm. The difference in size between the rolling bodies 5 and the spacer balls 10 is exaggerated in both figures. The purpose of the spacer balls 10 is to reduce the friction within the ball screw drive 1 compared to screw drives, which only have balls of the same size.

[0027] As can be seen from the two figures, a free space FR is formed in the thread turn 4 as a further measure to reduce friction and thus to increase the efficiency. This is equivalent to the fact that the rolling bodies 5 and spacer elements 10 are arranged in the thread turn 4 with backlash even in the completely relaxed state of both spring elements 8, 9, wherein the backlash relates to the direction in which the thread turn 4 extends. The total length of the free space FR to be measured in the specified direction, which can be divided into sections, i.e. in the form of individual free sections, is at least 0.2% and at most 5% of the total length of the thread turn 4. As soon as one of the two spring elements 8, 9 is tensioned while the other spring element 9, 8 remains fully expanded, the free space FR increases.

[0028] In the arrangement according to FIG. 2, the free space FR between the closing ball arrangement 12 and the pre-compression spring 9 is shown—not to scale. If, starting from this arrangement, the threaded nut 3 is adjusted to the left relative to the threaded spindle 2, this means that the free space FR indicated in FIG. 2 becomes smaller, while both spring elements 8, 9 are relaxed and an additional free space FR is created between the first spring element 8 and/or—as indicated in FIG. 1—within the ball arrangement 11. In this state, the rolling bodies 8 are therefore not under spring preload. In a load-free or low-load state, this can lead to rolling bodies 5 slipping. If, on the other hand, the rolling bodies 5 are displaced against one of the spring elements 8, 9 as the forces within the ball screw drive 1 increase, wherein either the first spring element 8 contacts the ball arrangement 11 or the second spring element 9 presses against the closing ball arrangement 12, the forces that occur, including the spring forces, ensure a kinematically almost ideal rolling of the rolling bodies 5. Under conditions of high load, the behavior of the ball screw drive 1 thus hardly deviates from the behavior of a conventional roller screw drive with permanent spring preloading of the rolling bodies, whereas particularly in a central adjustment range, low-friction adjustment of the ball screw 1 is possible and thus a particularly high efficiency is achieved overall.

LIST OF REFERENCE SYMBOLS

[0029] 1 Ball screw drive [0030] 2 Threaded spindle [0031] 3 Threaded nut [0032] 4 Thread turn of the threaded spindle [0033] 5 Rolling body, ball [0034] 6 First nut-side stop [0035] 7 Second nut-side stop [0036] 8 First spring element [0037] 9 Second spring element [0038] 10 Spacer element, ball [0039] 11 Ball arrangement [0040] 12 Closing ball arrangement [0041] FR Free space