Rolling screw drive, brake actuator and method for operating a rolling screw drive

Abstract

Rolling screw drive (1), comprising a threaded spindle (2), a spindle nut (6), rolling elements (4) arranged between the threaded spindle (2) and the spindle nut (6), and a spindle bearing (12) including a housing disk (16) for receiving axial forces, and a first axial force transmission contour (11) formed on an end face of the spindle nut (6) opposite the spindle bearing (12), which, including an end face contour of a piston (7) displaceable by means of the spindle nut (6), represents a first pair of non-rotating angle-adjustable guide surfaces (8, 9), characterized in that the housing disk (16) together with a housing component (19) forms a second pair of non-rotating angle-adjustable guide surfaces (22, 23).

Description

[0001] The invention relates to a rolling screw drive designed according to the preamble of claim 1. Furthermore, the invention relates to a brake actuator with a rolling screw drive and a method for operating a rolling screw drive.

[0002] A ball screw drive of this type is known, for example, from EP 2 464 897 B1. A threaded spindle of the known ball screw drive, intended for use in a braking device, has a convex bearing surface that is axially supported on a conically shaped second bearing surface. The component comprising the second bearing surface is a bearing disk that rotates together with the threaded spindle and is capable of wobbling movements. Overall, the device according to EP 2 464 897 B1 is designed as a ball screw drive without ball recirculation.

[0003] Another ball screw drive, which also operates without ball recirculation, is disclosed in DE 10 2015 201 257 B3. In this case, a spring element that generates a restoring force is indirectly supported, namely via a ball, on a cage of the ball screw drive.

[0004] DD 1 57 819 A1 discloses a bearing arrangement for the spindle nut in a screw winch, designed to ensure uniform force transmission under all load conditions. To achieve this, the spindle nut is mounted spherically relative to a crossbeam. Specifically, the disclosure provides either a spherical, convexly curved sliding bearing surface on the spindle nut, upon which a corresponding concave bearing surface of the crossbeam rests with angular movement, or alternatively, the use of an axial spherical roller bearing between the spindle nut and the crossbeam. Furthermore, the spindle nut is secured against rotation in the crossbeam by means of convexly shaped bolts, so that it can perform oscillating movements but cannot rotate with the crossbeam.

[0005] DE 10 2018 211 716 A1 describes a self-aligning threaded spindle module for a motor vehicle brake, which, due to its special geometric design, automatically orients itself into a defined installation position. The threaded spindle module consists of a longitudinally oriented threaded spindle with a threaded nut screwed onto it and is designed as a convex, three-dimensional body with a homogeneous density distribution. The threaded nut has a spherically curved bearing surface that rests in a complementary receptacle. Due to its lower center of gravity and the curved bearing surface, the module self-aligns under the influence of gravity. In this way, the threaded spindle module centers and aligns itself in the receptacle, which significantly simplifies the mounting of the brake caliper and the blind coupling to an actuator.

[0006] US 2015 / 0330487 A1 discloses a ball screw drive, particularly for an electromechanically actuated parking brake of a motor vehicle, with measures to improve the operational reliability of the ball return. The arrangement comprises a threaded spindle and a spindle nut mounted thereon, which together form a helical ball channel in which a series of rolling balls runs. A helical spring is provided along the ball channel to preload this series of balls, bearing against the spindle nut on one side and against the last ball or a ball cage on the other. To prevent this helical compression spring from bending or jamming under compression, a stabilizing rod is integrated within the spring coils. This rod engages in the helix of the spring and supports the coils, thus preventing lateral buckling of the spring under load.In one embodiment, the rod is spring-elastic and bendable to follow the curved shape of the ball channel, and after installation, it automatically straightens out, supported by the spindle nut. Alternatively or additionally, the end of the coil spring can be stiffened by potting or adhesive to prevent kinking at the spring end.

[0007] US 2018 / 0058553A1 describes a ball screw assembly—specifically, a ball screw drive for a brake actuator—with an integrated stop system to limit the relative rotation between the screw and the nut. The screw has two sections of different diameters: a larger, threaded section on which the hollow cylindrical screw nut sits, and an adjacent smaller section. A screw washer is fixed to the smaller screw section. This screw washer has a conical contact surface on its inner surface that fits positively onto a corresponding conical surface of the screw. These conical surfaces transmit the drive torque between the screw and the screw washer and simultaneously allow a slight tilting of the screw washer relative to the screw to compensate for misalignment.On its outer surface, the spindle disc features a radially projecting flange that acts as a stop. This stop flange forms a stop surface which, upon reaching the end stop, abuts a corresponding counter-stop surface on the spindle nut, either axially or circumferentially. This limits the rotational movement or twisting of the spindle nut relative to the spindle in a specific end position and prevents over-tightening or binding. It is noteworthy that these stop surfaces are located entirely outside the ball screw's partial circle diameter, resulting in a compact axial design and enabling the absorption of high torques across the larger radius of the stop.

[0008] US 2023 / 0151864 A1 discloses a brake actuator unit for an electromechanical disc brake in which the ball screw bearing is designed to automatically compensate for misalignment or lateral forces. The unit comprises a brake piston guided in a brake housing and driven by a ball screw, as well as a special bearing arrangement for the drive screw. The ball screw sits with an output-side bearing section in an axial screw bearing that has a spherically curved bearing contact surface. This surface rests against a complementarily shaped surface at the screw end or a transition section of the ball screw. This spherical bearing allows the ball screw to tilt slightly when lateral forces or tilting occur, with the curvature of the bearing surfaces generating a restoring force toward the central axis.In practical terms, this means that even under high reaction forces, the threaded spindle always remains centered and aligned with the brake cylinder axis.

[0009] WO 2008 / 037738 A1 describes a combined vehicle brake with a hydraulic service brake and an electromechanically actuated parking brake, as well as a special ball screw design for converting rotational motion into translational motion. The parking brake acts on the brake piston via a ball screw drive. Unlike conventional ball screws, which require complex return channels for the balls, here the rolling elements are arranged directly in the thread between the screw and the nut without a recirculation channel. WO 2008 / 037738 A1 discloses that the balls are arranged in this thread with limited displacement between two axially spaced stops. A first spring element is positioned at one end of the ball row between the balls and the first stop, and optionally a second spring element can be provided at the opposite end.These spring-loaded buffer elements serve two purposes: When the screw drive is started without significant load, the balls can slide freely because the spring allows for some play. However, as soon as a significant resistance or braking force is applied, the springs are partially compressed, and the balls are supported by the stops, allowing them to roll within the thread. In this way, the screw drive operates highly efficiently under load, like a conventional ball screw drive with rolling friction, while during unloaded adjustment, it enables rapid, low-friction relative movement, for example, to compensate for play in the lining.

[0010] The invention is based on the objective of providing more advanced possibilities for converting a rotation into a translation compared to the prior art, with the aim of achieving applicability in vehicles, particularly in parking or service brakes, within a wide range of conceivable operating conditions.

[0011] This problem is solved according to the invention by a rolling screw drive with the features of claim 1. According to claim 9, the rolling screw drive, in particular in the form of a ball screw drive, is suitable for use in a brake actuator of a motor vehicle. The brake actuator can be designed to actuate a parking brake or a service brake. Furthermore, the problem is solved by a method for operating a rolling screw drive designed according to claim 10. The embodiments and advantages of the invention explained below in connection with the operating method also apply mutatis mutandis to the devices, i.e., the rolling screw drive and the brake actuator, and vice versa.

[0012] The rolling screw drive, in a basic design known per se, comprises a threaded spindle, a spindle nut, and rolling elements, particularly in the form of balls, arranged between the threaded spindle and the spindle nut. A spindle bearing, which includes a housing washer, is provided to absorb axial forces. An axial force transmission contour is located on an end face of the spindle nut opposite the spindle bearing. This contour, together with an end face contour of a piston displaceable by means of the spindle nut, forms a first pair of non-rotating, angularly adjustable guide surfaces.

[0013] According to claim 1, the housing disc, together with a housing component, forms a second pair of non-rotating, angle-adjustable guide surfaces, i.e., a second axial force transmission contour suitable for compensating for angular errors. The two parts belonging to the same axial force transmission contour, which are provided with the contacting guide surfaces that are pivotable relative to each other within limits, are generally also referred to as the first pair of parts or the second pair of parts. The first pair of parts is formed by the spindle nut and the piston, the second pair by the housing disc of the spindle bearing and the housing component.

[0014] None of the four parts of the two pairs are rotating components. Both the spindle nut and the housing washer have contours that prevent rotation of the respective part relative to the housing of the ball screw drive, while in the case of the spindle nut, its movement within a predetermined range is simultaneously permitted.

[0015] The piston, which can be moved by means of the spindle nut, can be a component of a hydraulic system. However, in this case, any other part that is movable together with the spindle nut and, together with the spindle nut, forms a pair of parts suitable for compensating for an angular misalignment, is also referred to as a piston. The axially measured distance between a convexly curved end face of the spindle nut that abuts the piston and the angularly adjustable pairing between the housing disc and the housing component located on the opposite end face of the spindle nut is greater than the distance between the piston-side curved contact surface of the spindle nut and a contact surface between the threaded spindle and a shaft-side component of the spindle bearing.Thanks to this particularly large distance between the two angle-adjustable part pairs, the rolling screw drive exhibits particularly stable operating behavior, especially when used in an electromechanical brake actuator.

[0016] The spindle bearing can be designed as either a plain bearing or a rolling bearing. In the case of a rolling bearing, rolling elements with a cylindrical shape are particularly suitable. Accordingly, the spindle bearing could be, for example, a thrust roller bearing or a thrust needle bearing.

[0017] According to various possible configurations, the guide surface of at least one component of the rolling screw drive, which is neither part of the housing nor the piston, has a radius of curvature that is at least seven times and at most fourteen times the diameter of the spindle nut. This makes the component pairs particularly suitable for compensating for small angular errors, while simultaneously allowing for generously dimensioned contact surfaces.

[0018] Optionally, the radius center of the component of the rolling screw drive exhibiting a radius of curvature is offset from its central axis. This applies particularly to designs in which machine elements of the rolling screw drive and / or its surrounding structure are not rotationally symmetrical.

[0019] Regardless of any potential offset between the central axis of the threaded spindle and the geometric centers of at least one spherically curved guide surface, this guide surface can contact a flat piston- or housing-side guide surface. Alternatively, conical or convex guide surfaces, for example, could be used on the piston- or housing-side.

[0020] One possible further development involves a third pair of guide surfaces, adjustable angularly relative to each other, being formed between the threaded spindle and a shaft disc of the spindle bearing. Unlike the first and second pairs of components, the parts providing the third pair of guide surfaces are rotating parts of the rolling screw drive.

[0021] The patented method for operating a rolling screw drive assumes that a rotation of a threaded spindle is converted into a displacement of a spindle nut. Axial forces acting between the spindle nut and the threaded spindle are transmitted via mutually adjustable guide surfaces at an end face of the spindle nut and between an axial bearing of the threaded spindle located on the opposite side of the spindle nut and a housing component.

[0022] The rolling screw drive can be used not only in brake actuators but also in other electromechanical actuators, such as steering actuators or robotics applications. In all cases, the angle-adjustable thrust transmission contours enable a self-aligning effect. Optionally, the rolling screw drive, particularly in the form of a ball screw drive, can be equipped with sensors, for example, for force measurement and / or for acquiring geometric information, especially position and angle information.

[0023] Two embodiments of the invention are explained in more detail below with reference to a drawing. The drawing shows: Fig. 1 a first embodiment of a rolling screw drive of an electromechanical actuator, Fig. 2 a section of a spindle nut of the rolling screw drive to Fig. 1, Fig. 3 and 4 a housing disc of a spindle bearing of the rolling screw drive according to Fig. 1, Fig. Figures 5 to 8 show a second embodiment of a roller screw drive in analogous views. Fig. 1 to 4.

[0024] Unless otherwise stated, the following explanations apply to all embodiments. Corresponding or essentially equivalent parts are marked with the same reference numerals in all figures.

[0025] A rolling screw drive 1, specifically a ball screw drive, is part of an electromechanical actuator 10, which is used as a brake actuator in a motor vehicle. The actuator 10 can be designed to actuate a parking brake or a service brake. Regarding the basic design and function of the actuator 10, including the ball screw drive 1, reference is made to the prior art cited above. In the present cases, the rolling screw drive 1 is designed as a ball screw drive without ball recirculation.

[0026] A threaded spindle 2 forms the driving element of the rolling screw drive 1. Balls 4 roll as rolling elements in the thread 3 of the threaded spindle 2, simultaneously rolling in an internal thread 5 of a spindle nut 6. The spindle nut 6, as the output element of the rolling screw drive 1, is guided longitudinally displaceably in a housing of the actuator 10. A piston 7, which in this case is part of a hydraulic system, is displaced by the spindle nut 6. Unlike the spindle nut 6, an anti-rotation device is not strictly necessary for the piston 7. At the interface between the spindle nut 6 and the piston 7, the overall annular end face of the spindle nut 6 is designed as a convexly curved guide surface 8, which contacts a flat, annular guide surface 9 of the piston 7. The guide surfaces 8 and 9 together are referred to as the axial force transmission contour 11.The convexly curved shape of the guide surface 8 on the side of the spindle nut 6 ensures limited angular adjustability between the spindle nut 6 and the piston 7. Depending on the setting of the rolling screw drive 1, the threaded spindle 2 can either extend beyond the spindle nut 6 or terminate in the spindle nut 6.

[0027] For supporting the threaded spindle 2, a spindle bearing 12, designed in the present cases as a rolling bearing, is provided. The spindle bearing 12 is located in the area of ​​a bearing section 13 of the threaded spindle 2. A drive section of the threaded spindle 2, provided with a toothed section 21 and through which a torque can be introduced into the threaded spindle 2, is designated 14. The bearing section 13 is located between the threaded section 3 of the threaded spindle 2 and the drive section 14. Components of the spindle bearing 12 are a shaft disk 15 rotating together with the threaded spindle 2, a housing disk 16, and rolling elements 17, namely rollers guided in a cage 18. In both embodiments, the spindle bearing 12 is designed as an axial roller bearing.

[0028] The housing disc 16 is supported by a housing component 19, which is either fixedly installed in the housing of the actuator 10 or formed directly by the housing. To prevent rotation of the housing disc 16 within the housing, a projection 20, also referred to as a finger, is located on the outer circumferential surface of the housing disc 16 and engages in a recess on the housing side. In the case of the spindle nut 6, anti-rotation protection is achieved in these cases by means of lateral flattening.

[0029] Regarding the contact between the housing disc 16 and the housing component 19, there are similarities with the axial force transmission contour 11. The housing disc 16 forms a convexly curved guide surface 22, which rests against a flat guide surface 23 of the housing component 19. Thus, the housing disc 16 is angularly adjustable relative to the housing component 19 to a limited extent, thereby providing a second axial force transmission contour 24 suitable for compensating for angular errors. The diameter of the spindle nut 6, measured at the end face facing the piston 7, i.e., at the guide surface 8, is designated D6. The radius of curvature of the guide surface 8 is designated R8. In the present cases, the radius of curvature R8 corresponds to at least seven times and at most fourteen times the diameter D6.

[0030] In the case of the housing disc 16, its diameter D16 is to be measured without the projection 20. The radius of curvature of the guide surface 22, which is formed on the housing disc 16, is designated R22. The radius of curvature R22 also corresponds to at least seven times and at most fourteen times the diameter D6 of the spindle nut 6. In the present cases, the radii of curvature R8 and R22 are between 100 mm and 500 mm, particularly at 400 mm.

[0031] As a comparison of Fig. 2 to 4 on the one hand and the Fig. As can be seen from Figures 6 to 8, the centers of the guide surfaces 8, 22 lie on the central axis of the roller screw drive 1, designated MA, in the first embodiment, whereas in the second embodiment they are spaced away from the central axis MA. This deliberately chosen asymmetry in the embodiment according to the Fig. Sections 5 to 8 account for load-induced deformations during the operation of the rolling screw drive 1. Asymmetrical load conditions are primarily due to elastic deformations of parts of the hydraulic system.

[0032] Further differences between the embodiment according to the Fig. 1 to 4 and according to the exemplary embodiment Fig. Items 5 to 8 relate to the connection of the threaded spindle 2 to the spindle bearing 12.

[0033] In the exemplary embodiment according to the Fig. In sections 1 to 4, a spherically curved connecting section 25 engages in a correspondingly curved, i.e., concave, recess 26 of the wave disk 15. This forms a third axial force transmission contour 27 suitable for compensating for angular errors. In contrast to the first axial force transmission contour 11 and the second axial force transmission contour 24, the third axial force transmission contour 27 is formed by rotating parts.

[0034] Unlike in the embodiment according to the Fig. 1 to 4 are located in the exemplary embodiment according to the Fig. 5 to 8 of the connecting section 25 with its flat end face abuts the shaft disk 15. In this case, the central axis of the shaft disk 15 always coincides with the central axis MA of the threaded spindle 2. Reference symbol list 1. Roller screw drive, ball screw drive 2 threaded spindles 3 threads of the threaded spindle 4 rolling elements, ball 5 internal threads 6 Spindle nut 7 pistons 8 Guide surface of the spindle nut 9 Piston guide surface 10 Actuator, brake actuator 11 first axial force transmission contour 12 Spindle bearing, axial bearing 13 Storage section 14 Drive section 15 wave washer 16 Housing disc 17 rolling elements, roller 18 cage 19 Housing component 20 lead, fingers 21 Gearing 22 Guide surface of the housing disc 23 Guide surface of the housing component 24 second axial force transmission contour 25 Connection section 26 Exclusion 27 third axial force transmission contour D6 Diameter of the spindle nut D16 Diameter of the housing disc MA Central Axis R8 radius of curvature of the guide surface 8 R22 Radius of curvature of the guide surface 22

Claims

[1] Rolling screw drive (1), comprising a threaded spindle (2), a spindle nut (6), rolling elements (4) arranged between the threaded spindle (2) and the spindle nut (6), and a spindle bearing (12) including a housing washer (16) for receiving axial forces, and a first axial force transmission contour (11) formed on an end face of the spindle nut (6) opposite the spindle bearing (12), which, including an end face contour of a piston (7) displaceable by means of the spindle nut (6), represents a first pair of non-rotating angle-adjustable guide surfaces (8, 9), characterized by , that the housing disc (16) together with a housing component (19) forms a second pair of non-rotating angle-adjustable guide surfaces (22, 23). [2] Roller screw drive (1) according to claim 1, characterized by , that a rolling bearing is provided as the spindle bearing (12). [3] Roller screw drive (1) according to claim 2, characterized by, that the spindle bearing (12) comprises rolling elements (17) with a cylindrical basic shape. [4] Roller screw drive (1) according to one of claims 1 to 3, characterized by , that the guide surface (8, 22) of at least one component which is not attributable to the housing or the piston (7) has a radius of curvature (R8, R22) which is at least seven times and at most 14 times the diameter (D6) of the spindle nut (6). [5] Roller screw drive (1) according to claim 4, characterized by , that the radius center of the component of the rolling screw drive (1) having the aforementioned radius of curvature (R8, R22) is offset from its central axis (MA). [6] Roller screw drive (1) according to claim 4 or 5, characterized by , that the curved guide surface (8, 22) contacts a piston- or housing-side flat guide surface (9, 23). [7] Roller screw drive (1) according to any one of claims 1 to 6, characterized bya third, angle-adjustable axial force transmission contour (27) formed between the threaded spindle (2) and a wave disk (15) of the spindle bearing (12), which rotates with the threaded spindle (2). [8] Roller screw drive (1) according to any one of claims 1 to 7, characterized by that it is designed as a ball screw drive. [9] Brake actuator (10) for a motor vehicle, comprising a roller screw drive (1) according to claim 1. [10] Method for operating a rolling screw drive (1) wherein a rotation of a threaded spindle (2) is converted into a displacement of a spindle nut (6) and axial forces acting between the spindle nut (6) and the threaded spindle (2) at an end face of the spindle nut (6) and between an axial bearing (12) of the threaded spindle (2) arranged on the opposite side of the spindle nut (6) and a housing component (19) are transmitted via guide surfaces (8, 9; 22, 23) that are adjustable angularly relative to each other.

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