Ball screw drive and method for operating a ball screw drive

Abstract

The invention relates to a ball screw drive (1), in particular for a parking brake, comprising a threaded spindle (2), a spindle nut (3) and rolling elements (5), i.e. balls, which are arranged in the thread turns (4) between the threaded spindle (2) and the spindle nut (3), wherein, in addition, spring elements (8, 9) are arranged in the thread turns (4) between the nut-side stop (6, 7). At least one setting of the threaded spindle (2) and the spindle nut (3) exists, in which the balls (5) and the spring elements (8, 9) are arranged in the thread turns (4) in a play-free manner.

Description

Technical Field

[0001] This invention relates to a ball screw drive suitable for use in electromechanical actuators according to the preamble of claim 1. Furthermore, this invention relates to a method for operating a ball screw drive. Background Technology

[0002] For example, a general-purpose ball screw drive intended for operation in an electromechanically actuated parking brake of a motor vehicle is known from EP 2 207 982 B1. The known ball screw drive has balls as rolling elements, arranged in the threaded turns of the ball screw drive such that the balls can move to a certain extent. Here, a spring element in the form of a helical spring is arranged between the stop and the rolling elements. Furthermore, at least one intermediate spring element is provided, arranged between the rolling elements and designed as a helical compression spring or an elastomeric spring. If several intermediate spring elements are present, they are evenly distributed between the rolling elements to reduce the friction between the rolling elements.

[0003] Another ball screw actuator is described in DE 10 2014 223 021 A1. Compared to the ball screw actuator according to the cited patent specification EP 2 207 982 B1, this other ball screw actuator also involves a floating caliper type disc brake, equipped with a rigid separator instead of an intermediate spring element. The separator reduces the friction between the balls of the ball screw actuator. DE 10 2014 223 021 A1 mentions a non-elastic plastic as a material that can be used to produce the separator. The separator can be a separator ball with a diameter smaller than the diameter of the ball used as the rolling element.

[0004] A ball screw drive with a spring element is also described in DE 10 2017 127 404 B4, which is inserted into a threaded turn and applies force to the balls of the screw drive. In this case, the stop for the spring element is formed by a molded portion of the threaded nut connected to the ball screw drive. Summary of the Invention

[0005] The present invention is based on the following objective: to further develop, among other things, a ball screw drive suitable for parking brakes of motor vehicles, compared with the prior art mentioned above, such that there is a particularly favorable ratio between production cost, required installation space and friction generated during operation of the ball screw drive.

[0006] According to the present invention, this objective is achieved by a ball screw drive. This objective is also achieved by a method for operating the ball screw drive. The embodiments and advantages of the invention described below with respect to the operating method also apply to the apparatus, i.e., the ball screw drive, and the embodiments and advantages of the invention described with respect to the apparatus, i.e., the ball screw drive, also apply to the operating method.

[0007] In its basic known structure, a ball screw drive includes a threaded spindle, a spindle nut, and rolling elements, i.e., balls, arranged in threaded turns between the threaded spindle and the spindle nut. Additionally, spring elements are arranged in threaded turns between stop members on the nut side. A stop member for two spring elements, or a threaded spindle or spindle nut securely connected to such a stop member, can be configured as the rotary drive element of the ball screw drive, while another component of the screw drive, the spindle nut or threaded spindle, serves as a movable output element of the ball screw drive that is secured to prevent torsion.

[0008] In principle, a ball screw drive can also be driven by the linear displacement of one of the mentioned components, where, in this case, i.e., in the formation of a linear rotary transmission, the output element of the screw drive is a rotating element. Regardless of which component of the ball screw is the driving component, the thread of the ball screw can, in principle, be designed as a single-start thread or a multi-start thread.

[0009] There exists at least one configuration of the ball screw, namely the positioning of the spindle nut relative to the threaded spindle, in which the rolling elements and spring elements are arranged in the threaded turns with clearance. Clearance can be formed between the different elements of the ball screw, particularly between the individual rolling elements and / or between the spring elements and the rolling elements. Simultaneously, clearance can exist at one, two, or more points within the ball-spring strand formed between the two stops; the ball-spring strand is also referred to as a ball-spring pack, or, for simplicity, a ball chain.

[0010] The ball screw drive can be operated as follows: starting from a first position where exactly one of the two spring elements is tensioned (i.e., compressed), the ball screw drive is first moved to a center position, in which both springs are relaxed and the balls are arranged in the threaded turns with clearance. The term "center position" does not necessarily mean that the position is exactly centered between the two stop positions. Instead, the center position can also be positioned eccentrically between the two stop positions. In either case, the ball screw drive can move from the center position to a second setting, in which, compared to the first setting, the second spring element is tensioned and the first spring element is relaxed.

[0011] Due to the gapped arrangement of the balls in the threaded turns, slippage of the balls in the central section of the ball screw's adjustment range is acceptable. On the other hand, towards the ends of the adjustment range, the balls roll with almost no slippage as the force increases. There is no annular closed ball channel for the balls to return. Therefore, ball screw drives are designed for applications with short adjustment paths, such as those commonly used in electromechanical parking brakes. In such applications, the spring-loaded balls roll in the threaded turns both when clamping and releasing the brake, allowing for simultaneous hydraulic preload.

[0012] The rolling elements of a ball screw drive can be arranged in several groups, with a spacer element arranged between each group. Smaller balls than the rolling elements of the ball screw drive, i.e., the bearing balls, i.e., spacer balls, are particularly suitable as spacer elements. For example, the diameter of each spacer ball, i.e., the spacer ball, is at least 80% and at most 95% of the diameter of each bearing ball of the screw drive.

[0013] Regarding material selection, the spacer element can be made of the same material as the rolling elements, or it can be made of a different material, such as a metal with different compositions and / or that has been heat-treated in different ways, or even a plastic material. In typical applications, the rolling elements of a ball screw drive are metal rolling elements. In principle, ceramic rolling elements can also be considered.

[0014] For example, regardless of the materials used to manufacture the rolling elements and spacer elements, each group of rolling elements consisting of at least two and at most four rolling elements is separated from each other by spacer elements, particularly spacer balls.

[0015] For example, the group of rolling elements adjacent to the first spring element comprises exactly three rolling elements, while the group of rolling elements adjacent to the second spring element comprises exactly two rolling elements. At least one spacer element, and typically multiple spacer elements, particularly multiple spacer balls, are arranged between these outermost groups of rolling elements. The first spring element is also referred to as an adjusting spring, and the second spring element as a pre-compression spring. Both spring elements are typically designed as helical compression springs. According to possible embodiments, the first spring element—measured in the direction of extension of the threaded turns—is longer than the second spring element.

[0016] A total of at least twelve and at most 30 sets of rolling elements are arranged between the pre-compression spring and the readjustment spring, wherein each set of rolling elements includes no more than four bearing balls.

[0017] The total length of the free space formed in the direction of extension of the threaded turn—equivalent to the gap present in the ball-spring assembly—measured at least 0.2% and at most 5% of the total length of the threaded turn measured, for example, between two stops on the nut side, when the spring element is relaxed.

[0018] In particular, the advantage of the present invention lies in the fact that, compared with conventional ball screw drives with preload in the ball-spring bundle, a particularly high efficiency can be achieved in ball screw drives where there is no ball return due to the gap in the ball-spring bundle, without additional equipment costs, wherein this does not produce any practically related disadvantages, such as disadvantages in terms of wear behavior or acoustic behavior. Attached Figure Description

[0019] In the following description, exemplary embodiments of the present invention will be illustrated in more detail with the aid of the accompanying drawings. In the drawings: Figure 1 The ball screw drive is shown in cross-section. Figure 2 The abstract representation shows the basis Figure 1 The components of the ball screw. Detailed Implementation

[0020] The ball screw drive, generally indicated by reference numeral 1, is intended for use as a rotary linear transmission device in the parking brake of a motor vehicle and includes a threaded spindle 2 and a threaded nut 3. The threaded turns of the ball screw drive 1 are indicated by reference numeral 4. Between the threaded spindle 2 and the threaded nut 3, balls, as rolling elements 5, roll within the threaded turns 4. For the main function of the ball screw drive 1, refer to the prior art cited at the beginning. The parking brake of a motor vehicle is combined with a hydraulic disc brake in a manner known per se.

[0021] The threaded nut 3, also known as the spindle nut, contains a first nut-side stop 6 and a second nut-side stop 7. Roller return is not provided, for example, roller return in the form of external deflection is not provided. Therefore, it is impossible to use the ball screw 1 for applications with long travel distances.

[0022] The threaded turn 4 contains a first spring element 8 that can impact the first stop 6 and a second spring element 9 that can be supported on the second stop 7. Both spring elements 8 and 9 are designed as helical springs.

[0023] In addition to the rolling elements 5, i.e., the bearing balls, there are also several spacer elements 10 in the threaded turn 4. The spacer elements 10 are balls with a diameter smaller than that of the rolling elements 5. Regarding the arrangement of the various balls 5 and 10 in the threaded turn 4, refer to [reference needed]. Figure 2The symbolic representation is shown below. Immediately following the first spring element 8, which is significantly longer than the pre-compression spring 9 (i.e., the adjusting spring), the arrangement shown contains a ball arrangement structure 11, which is configured in a defined manner by groups of rolling elements 5 and spacer elements 10: groups of three rolling elements 5 and a single spacer element 10 are alternately inserted into the threaded turn 4. In general, the ball arrangement structure 11, shown only partially, consists of 19 groups of three rolling elements 5—that is, a total of 57 rolling elements 5—and an additional 19 spacer balls 10. This ball arrangement structure 11 is followed by a final ball arrangement structure 12, which is formed by only two rolling elements 5. In the exemplary embodiment, the diameter of the rolling elements 5 in both the ball arrangement structure 11 and the final ball arrangement structure 12 is 2.778 mm, and the diameter of the spacer element 10 is 2.5 mm. The dimensional difference between the rolling elements 5 and the spacer balls 10 is magnified in both figures. The purpose of the spaced balls 10 is to reduce friction within the ball screw drive 1 compared to a ball screw drive with only balls of the same size.

[0024] As can be seen from the two figures, a free space FR is formed in the threaded turn 4 as a further measure to reduce friction and thus improve efficiency. This is equivalent to the fact that even when both spring elements 8 and 9 are fully relaxed, the rolling element 5 and the spacer element 10 are arranged in the threaded turn 4 with a gap, wherein the gap is related to the direction of extension of the threaded turn 4. The total length of the free space FR, measured in the specified direction, is at least 0.2% and at most 5% of the total length of the threaded turn 4, and this free space can be divided into multiple segments, i.e., in the form of a single free segment. Once one of the two spring elements 8 and 9 is tensioned while the other spring element 9 and 8 remain fully extended, the free space FR increases.

[0025] According to Figure 2 In the arrangement, the free space FR between the final ball bearing arrangement 12 and the pre-compression spring 9 is not drawn to scale. If, starting from this arrangement, the threaded nut 3 is adjusted to the left relative to the thread spindle 2, this means… Figure 2 The free space FR indicated in the diagram becomes smaller, and both spring elements 8 and 9 are relaxed, and this relaxation occurs between the first spring element 8 and / or within the ball arrangement structure 11—as shown in the diagram. Figure 1As indicated in the diagram, this creates additional free space FR. Therefore, in this state, the rolling element 8 is not under spring preload. Under no-load or low-load conditions, this could cause the rolling element 5 to slip. On the other hand, if the rolling element 5 shifts against one of the spring elements 8 or 9, the force within the ball screw drive 1 increases, where the first spring element 8 contacts the ball arrangement structure 11 or the second spring element 9 presses against the end ball arrangement structure 12. The resulting force, including the spring force, ensures that the rolling element 5 rolls almost kinematically ideally. Therefore, under high load conditions, the behavior of the ball screw drive 1 hardly deviates from that of a conventional ball screw drive with permanently spring-preloaded rolling elements; however, especially within the central adjustment range, the ball screw 1 can be adjusted with low friction, and thus achieves particularly high efficiency overall.

[0026] Explanation of reference numerals in the attached figures 1. Ball screw driver 2. Threaded spindle 3. Threaded Nuts 4. Thread turns of the threaded spindle 5. Rolling elements, balls 6 First Nut Side Stop 7 First Nut Side Stop 8 First Spring Element 9 Second spring element 10 spacer elements, ball bearings 11 ball arrangement structure 12. End of ball bearing arrangement structure FR stands for Free Space.

Claims

1. A ball screw drive (1) comprising a threaded spindle (2), a spindle nut (3), and rolling elements (5), i.e., balls, wherein the balls are arranged in a threaded turn (4) between the threaded spindle (2) and the spindle nut (3), wherein, Furthermore, a spring element (8, 9) is arranged in the threaded turn (4) between the nut-side stop members (6, 7), characterized in that at least one configuration of the threaded spindle (2) and the spindle nut (3) exists, in which the ball (5) and the spring element (8, 9) are arranged in the threaded turn (4) with a gap.

2. The ball screw driver (1) according to claim 1, characterized in that, Spacer elements (10) are arranged between the multiple sets of rolling elements (5).

3. The ball screw driver (1) according to claim 2, characterized in that, A ball smaller than the rolling element (5) is configured as the spacer element (10).

4. The ball screw driver (1) according to claim 3, characterized in that, The diameter of each of the spacer elements (10) is at least 80% and at most 95% of the diameter of each ball of the rolling element (5).

5. The ball screw driver (1) according to claim 2, characterized in that, Groups of at least two and at most four of the rolling elements (5) are separated from each other by the spacer elements (10).

6. The ball screw driver (1) according to claim 5, characterized in that, The group of rolling elements (5) adjacent to the first spring element (8) comprises exactly three rolling elements (5), and the group of rolling elements (5) adjacent to the second spring element (9) comprises exactly two rolling elements (5), wherein at least one of the spacer elements (10) is arranged between these outermost groups of rolling elements.

7. The ball screw driver (1) according to claim 6, characterized in that, The first spring element (8) is longer than the second spring element (9) when measured in the extension direction of the threaded turn (4).

8. The ball screw drive (1) according to any one of claims 1 to 7, characterized in that, A total of at least twelve and at most 30 sets of rolling elements (5) are arranged between two spring elements (8, 9).

9. The ball screw drive (1) according to any one of claims 1 to 7, characterized in that, When the spring elements (8, 9) are relaxed, the total length of the free space (FR) measured in the extension direction of the threaded turn (4) is at least 0.2% and at most 5% of the total length of the threaded turn (4) measured between the two nut-side stops (6, 7).

10. A method for operating a ball screw drive (1), the ball screw drive comprising: The ball (5) is arranged as a rolling element in a threaded turn (4) formed between a threaded spindle (2) and a spindle nut (3); and spring elements (8, 9) are arranged in the threaded turn (4), characterized in that, starting from a first setting in which exactly one of the spring elements (8, 9) of the ball screw drive (1) is tensioned, the ball screw drive (1) enters a second setting in which two of the spring elements (8, 9) of the threaded spindle (2) and the spindle nut (3) are relaxed, and is then tensioned.

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