Roller screw drive

Abstract

The invention relates to a roller screw drive (1) without a rolling body return, which comprises a threaded spindle (2) as a drive element and a spindle nut (3) as an output element that can be displaced in a housing (17). Rolling bodies (7), in particular balls, are arranged in a rolling body channel (4) formed between the threaded spindle (2) and the spindle nut (3), which rolling bodies are loaded by the force of at least one spring (8), which is likewise placed between the threaded spindle (2) and the spindle nut (3). The spring (8) is supported on a stop element (14, 15) which penetrates the spindle nut (3) and is at the same time an element of an anti-rotation means (9) which acts between the spindle nut (3) and the housing (17).

Description

[0001] rolling thread drive

[0002] The invention relates to a rolling screw drive comprising a threaded spindle as a drive element and a spindle nut as an output element, wherein the spindle nut is displaceable in a housing in a rotationally secured manner.

[0003] EP 2 908 028 B1 discloses an electric linear drive which includes, among other things, a ball screw drive, i.e., a rolling screw drive. In this drive, a nut of the ball screw drive is rotatably, but axially non-displaceably, mounted in a housing. An associated threaded spindle, which is referred to as a worm shaft in EP 2 908 028 B1, is guided axially movable and simultaneously secured against rotation. As an anti-rotation element, EP 2 908 028 B1 proposes a sleeve made of sheet steel, extending in the axial direction of the threaded spindle and the nut, and having a plurality of grooves. This sleeve is pressed into a blind hole in the housing of the linear drive. A guide pin engages in two diametrically opposed grooves of the sleeve. This guide pin is aligned in the radial direction of the ball screw drive and is inserted through a bore in the threaded spindle.

[0004] DE 10 2007 043 391 A1 discloses an actuator with a movable arm. The actuator has a threaded spindle that is rotatably mounted in a housing and interacts with a nut connected to the arm. An anti-rotation device is provided between the nut or the arm on the one hand and the housing on the other. This anti-rotation device comprises an elongated sliding profile which, according to the teaching of DE 10 2007 043 391 A1, is attached to the nut or the arm and is movable in a radial direction with respect to the axis of rotation of the threaded spindle.

[0005] German patent DE 10 2020 202 843 A1 relates to an electromechanical brake pressure generator with a threaded drive assembly, intended for use in a vehicle. A hydraulic piston of the brake pressure generator is moved either by turning a spindle or by turning a spindle nut. The hydraulic piston is secured against rotation within a hydraulic cylinder. The anti-rotation device comprises a sliding element that makes contact over a sliding surface provided by a recess.

[0006] A ball screw drive described in JP 2016-196927 A has a bolt inserted through a threaded spindle, which forms part of an anti-rotation device. In a stop position, the bolt contacts a nut-side stop element of the ball screw drive, which is located on an end face of a nut.

[0007] WO 2009 / 053359 A1 discloses a combined vehicle brake with an electromechanically actuated parking brake. The device according to WO 2009 / 053359 A1 comprises a ball screw drive whose balls, i.e., rolling elements, are movable within a limited range between two stops in one thread, with a spring element arranged between the rolling elements and a stop. Additionally, intermediate spring elements exist, each arranged between two groups of rolling elements.

[0008] The invention is based on the objective of providing a rolling screw drive that is further developed compared to the aforementioned prior art and operates without rolling element recirculation, the rolling elements of which are always or at least in some of all possible operating conditions subjected to the force of a spring, with the aim of achieving a particularly compact, manufacturable design.

[0009] This problem is solved according to the invention by a rolling screw drive with the features of claim 1. In particular, the rolling screw drive is a ball screw drive. Alternatively, the rolling screw drive can have rollers which roll between a spindle and an associated nut. The rolling screw drive according to the application comprises a threaded spindle provided as a drive element and a spindle nut which is displaceable as an output element in a housing which is also part of the rolling screw drive. A rolling element channel is formed between the threaded spindle and the spindle nut. Rolling elements, i.e., balls or rollers, are arranged in this rolling element channel, which are loaded in at least one operating state by the force of at least one spring also located between the threaded spindle and the spindle nut.The spring is supported by a stop element that penetrates the spindle nut, which also serves as an anti-rotation device between the spindle nut and the housing. Compared to the loads that occur during operation of the ball screw drive, particularly those transmitted via the rolling elements between the threaded spindle and the spindle nut, the force exerted by the spring can be very small.

[0010] The stop element thus has a dual function and can be configured in various ways as a bolt-shaped element aligned radially with the roller screw drive. For example, the stop element can be a spring pin. The spring pin can be constructed in one or more parts. Reference is made in this context to documents EP 2 619 464 B1, DE 7 421 844 U, and DE 1 815 882 B. In particular, if the spring pin is constructed in one part, it can have a longitudinal profile and optionally a transverse profile. The spring pin can be hollow or solid. In both cases, the spring pin can be provided with a friction-reducing coating.

[0011] A coating on the spring pin can extend over its entire length or only over a portion of it. In cases where the spring pin is only partially coated with a friction- and / or wear-reducing coating, this coating is present in the section of the spring pin responsible for the anti-rotation function. However, if a coating covers a bolt- or sleeve-shaped base body of the spring pin along its entire length, the coating only exerts its desired friction- and / or wear-reducing function on the outer surface of the spindle nut, i.e., on the anti-rotation side, acting as a friction partner for the guide designed as the anti-rotation device.

[0012] In a geometrically simple design, the stop element can, for example, be a cylindrical pin. Roller-shaped rolling elements, such as needle rollers or cylindrical rollers, are also suitable as stop elements. Regardless of the exact shape of the stop element, which is typically a standard part, inserting a separate, multifunctional stop element into the nut allows for a particularly manufacturing-friendly design of the nut, i.e., the lead screw nut of the ball screw drive. Of particular note here is the possibility of forming at least a section of the nut's outer circumferential surface cylindrically. The lead screw nut, as the output element of the ball screw drive, can be rigidly connected to another machine element.The threaded spindle, which acts as a drive element, can, for example, have a toothed section that contacts a driving gear or a toothed belt. An electric direct drive for the threaded spindle is also conceivable.

[0013] The overall simple design of the spindle nut, particularly its outer contour without protruding elements, allows for the application of both efficient and precise machining methods. Continuous grinding is one example. The bores into which the stop elements are inserted can be easily machined. Furthermore, forming processes, including extrusion, are also suitable for manufacturing the spindle nut, especially for near-net-shape production. Its compact design also ensures exceptional robustness during handling and transport.

[0014] While the section of the stop element protruding outwards from the spindle nut is part of the anti-rotation mechanism, another section of the stop element projects into the spindle nut, acting as a spring stop. The two sections are not necessarily the same length. In particular, the section that secures the spindle nut against rotation within the housing can be longer than the second section, which projects radially inwards.

[0015] Regarding the number of stop elements within the rolling screw drive, various design options exist. For example, if only a single stop element of the type specified in claim 1 is present, the function of retaining the rolling elements in the rolling element channel at the second end of the rolling element-spring row, which is formed between the threaded spindle and the spindle nut, can be realized by a separate element that does not have an anti-rotation function, or by a contour of the nut.

[0016] In numerous embodiments, the rolling screw drive comprises exactly two stop elements, each with a dual function: firstly, to secure the spindle nut against rotation in the housing while simultaneously ensuring its adjustability; and secondly, to support the rolling elements and the at least one spring, which is also located in the rolling element channel. The spring does not necessarily bear directly against the stop element. Rather, it is possible, for example, to insert another element, in particular one of the rolling elements, especially balls, between the spring and the stop element. Instead of a single contact point between the spring and the stop element, there are thus two separate, geometrically distinct contact points: one between the spring and the rolling element, and one between the rolling element and the stop element.

[0017] The bolt-shaped stop element is pressed into a bore located in the spindle nut. In principle, any known fastening technology, such as screw connections or bonded joints (e.g., adhesive, welding, or soldering), can be used to secure the stop element in the spindle nut. The rolling element channel of the ball screw drive can be delimited by two identical or two different stop elements, which can be offset from each other both axially along the screw drive and circumferentially along the spindle nut. Specifically, the circumferential offset is 180 degrees. Rolling element recirculation, i.e., the routing of rolling elements out of the rolling element channel and back to another location within the channel, is not provided, neither as an external deflection nor as a single deflection.

[0018] The rolling screw drive is particularly suitable for applications requiring a small to moderate stroke. This is the case, for example, with electromechanical brakes in vehicles, especially passenger cars. Furthermore, stationary applications of the rolling screw drive are also possible, for example in automation technology.

[0019] Several embodiments of the invention are explained in more detail below with reference to a drawing. This drawing shows:

[0020] Fig. 1 shows a first embodiment of an actuator with a rolling screw drive,

[0021] Fig. 2 shows an actuator with a roller screw drive modified compared to Figure 1,

[0022] Unless otherwise stated, the following explanations refer to both embodiments. Corresponding or essentially equivalent parts are marked with the same reference numerals in all figures.

[0023] An electromechanical actuator, designated 10, is suitable, for example, for use in the braking system of a motor vehicle, particularly a passenger car. The actuator 10 comprises a ball screw drive 1 for converting rotation into linear motion. In the exemplary embodiments, a threaded spindle 2 represents the rotating drive element, and a spindle nut 3 represents the displaceable output element of the ball screw drive 1. A rolling element channel 4 is formed between the thread 5 of the threaded spindle 2 and an internal thread 6 of the spindle nut 3, in which rolling elements 7, i.e., balls, roll. An electric motor for driving the threaded spindle 2 is not shown.

[0024] The ball screw drive 1 is a rolling screw drive without rolling element recirculation. It does not feature individual deflection, i.e., the routing of rolling elements 7 from one turn of the rolling element channel 4 to a directly adjacent turn, nor external deflection. Several springs 8, which are compression springs in the form of helical springs, are arranged in the rolling element channel 4. As shown in Figures 1 and 2, several groups of rolling elements 7 are separated from each other by a spring 8. The springs 8 can be designed differently, depending on whether they are located at the ends or in a central region of the interrupted row of rolling elements 7.

[0025] Depending on the operating state of the rolling screw drive 1, the springs 8 are compressed to varying degrees. Springs 8 arranged at both ends of the rolling element channel 4 contact a stop element 14, 15. In the embodiment according to Figure 1, the stop element 14 is in the form of a profiled spring pin. In contrast, the rolling screw drive 1 according to Figure 2 comprises cylindrical pins 15 as stop elements.

[0026] In each embodiment, the two stop elements 14 and the two stop elements 15 are inserted through bores 13 located in the spindle nut 3. The bores 13, which penetrate the spindle nut 3, are located in the section of the spindle nut 3 that has the internal thread 6. As shown in Figures 1 and 2, this section adjoins a non-profiled section 16 of the spindle nut 3. A cavity 11 is formed by the spindle nut 3, particularly in the non-profiled section 16, into which the threaded spindle 2 penetrates to a greater or lesser extent depending on the operating condition of the rolling screw drive 1.

[0027] The bolt-shaped stop element 14, 15 is part of an anti-rotation device 9. The anti-rotation device 9 is further formed by a groove 12, which is attached to a

[0028] The inner surface of the housing of the roller screw drive 1, designated 17, runs in its longitudinal direction. Each stop element 14, 15 thus has a dual function: Firstly, the springs 8, which exert a force on the rolling elements 7 (i.e., balls) located in the roller channel 4, are supported by the two stop elements 14, 15. Secondly, these same stop elements 14, 15 constitute functional elements of the anti-rotation device 9, which ensures that the spindle nut 3 is guided longitudinally displaceably, but not rotatably, in the housing 17. In the exemplary embodiments, the stop elements 14, 15 are pressed into the bores 13 located in the spindle nut 3. Alternatively, screw-in stop elements 14, 15 are also possible.

[0029] List of reference signs

[0030] rolling screw drive

[0031] threaded spindle

[0032] Spindle nut

[0033] rolling element channel

[0034] Thread of the threaded spindle

[0035] Internal thread of the spindle nut

[0036] rolling elements

[0037] Feather

[0038] Anti-rotation device

[0039] actuator

[0040] cavity

[0041] Nut

[0042] bore in the spindle nut

[0043] Stop element, tension pin

[0044] Stop element, cylindrical pin, unprofiled section of the spindle nut

[0045] Housing

Claims

Patent claims 1. A rolling screw drive (1) without rolling element recirculation, with a threaded spindle (2) as a drive element and a spindle nut (3) as a displaceable output element in a housing (17), and with a rolling element channel (4) formed between the threaded spindle (2) and the spindle nut (3), in which rolling elements (7) are arranged, wherein at least one operating state exists in which the rolling elements (7) are subjected to the force of at least one spring (8) also placed between the threaded spindle (2) and the spindle nut (3), and wherein the spring (8) is supported at least indirectly on a stop element (14, 15) penetrating the spindle nut (3), which is also an element of an anti-rotation device (9) effective between the spindle nut (3) and the housing (17).

2. Rolling screw drive (1 ) according to claim 1 , characterized in that a spring pin is provided as a stop element (14,15).

3. Roller screw drive (1 ) according to claim 1 , characterized in that a cylindrical pin is provided as a stop element (14,15).

4. Rolling screw drive (1 ) according to claim 1 , characterized in that a rolling bearing element with a cylindrical basic shape is provided as a stop element (14,15).

5. Rolling screw drive (1 ) according to one of claims 1 to 4, characterized in that the stop element (14,15) is pressed into a bore located in the spindle nut (3).

6. Rolling screw drive (1 ) according to one of claims 1 to 4, characterized in that the stop element (14,15) is fastened by screwing it into the spindle nut (3).

7. Rolling screw drive (1 ) according to one of claims 1 to 4, characterized in that the stop element (14,15) is materially bonded to the spindle nut (3).

8. Rolling screw drive (1 ) according to one of claims 1 to 7, characterized in that the spring (8) is supported on the stop element (14,15) by means of an intermediate rolling element (7).

9. Rolling screw drive (1 ) according to one of claims 1 to 8, characterized in that the spring (8) is designed as a compression spring in the form of a helical spring.

10. Rolling screw drive (1) according to one of claims 1 to 9, characterized in that it is designed as a ball screw drive.

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