Ball screw assembly and electric power steering assembly

Abstract

Ball screw assembly (10) comprising: a helical path (14) for guiding a plurality of balls (16), the helical path (14) extending from a first end (20) to a second end (22); a return path (24) extending from a first transition point (26) to a second transition point (28), the first transition point (26) being located near the first end (20) of the helical path (14) to transfer the plurality of balls (16) from the helical path (14) to the return path (24), and the second transition point (28) being located near the second end (22) of the helical path (14) to transfer the plurality of balls (16) from the return path (24) to the helical path (14), the return path (24) comprising: a first segment (30), which is defined by a first arc segment of a first ellipse (32);a second segment (36) defined by a second arc segment of the first ellipse (32); and a third segment (40) defined by an arc of a second ellipse (42), wherein the first ellipse (32) and the second ellipse (42) are arranged in a common plane; wherein the second ellipse (42) comprises a major axis (44) extending from a first end (46) of the major axis (44) to a second end (48) of the major axis (44); wherein the first end of the third segment (40) is arranged at an intersection of the first ellipse (32) with the second ellipse (42); and wherein the second end of the third segment (40) is arranged at an intersection of the first ellipse (32) with the second ellipse (42).

Description

BACKGROUND OF THE INVENTION

[0001] The embodiments described here relate to ball screw arrangements and in particular to a ball return path for ball screw arrangements.

[0002] Some vehicle power steering systems use an electric motor that interacts with a ball screw assembly, which converts the rotary motion of the electric motor into linear motion. The ball screw assembly includes a ball return tube that follows a path with an elliptical trajectory.

[0003] Although the arrangement described above is functionally effective and reduces noise, it has limitations in terms of packaging size and manufacturing. In particular, a large envelope is required to fit around the ball return tube that encloses the ball return path. This large envelope limits the pitch of the ball raceway available to designers, eliminating the possibility of designs with a smaller pitch due to a potential conflict between the ball return path and adjacent ball raceways of a helical path through which the load-bearing balls travel. Furthermore, the complex geometry of the associated interface with the spindle nut complicates manufacturing process capacities. SUMMARY OF THE INVENTION

[0004] In accordance with one aspect of the disclosure, a ball screw assembly includes a helical path for guiding a plurality of balls, the helical path extending from a first end to a second end. The ball screw assembly also includes a return path extending from a first transition point to a second transition point, the first transition point being located near the first end of the helical path to transfer the plurality of balls from the helical path to the return path, and the second transition point being located near the second end of the helical path to transfer the plurality of balls from the return path to the helical path. The return path includes a first segment defined by a first arc segment of a first ellipse.The return path also includes a second segment defined by a second arc segment of the first ellipse. The return path further includes a third segment defined by an arc of a second ellipse, with the first and second ellipses lying in a common plane.

[0005] In accordance with another aspect of the disclosure, an electric power steering arrangement of a vehicle includes a motor for assisting steering maneuvers of the vehicle, a rack and pinion assembly, and a ball screw assembly for converting a rotary motion of the motor into a linear motion to assist the rack and pinion assembly. The ball screw assembly includes a helical path for guiding a plurality of balls, the helical path extending from a first end to a second end. The ball screw assembly also includes a return path extending from the first end of the helical path to the second end of the helical path. The return path includes a first segment defined by a first arc segment of a first ellipse.The return path also includes a second segment defined by a second arc segment of the first ellipse. The return path further includes a third segment defined by an arc of a second ellipse, with the first and second ellipses lying in a common plane.

[0006] These and other advantages and features will become clearer from the following description in conjunction with the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The subject matter considered to be the invention is specifically set forth and claimed separately in the claims at the end of the description. The foregoing and further features and advantages of the invention will become apparent from the following detailed description in conjunction with the accompanying drawings, in which:

[0008] Fig. 1 is a perspective view of a spindle nut arrangement;

[0009] Fig. 2 is a front view of the ball screw assembly, showing a sketch of the packaging environment;

[0010] Fig. 3 is a perspective view of the ball screw assembly;

[0011] Fig. 4 is a sectional view of a segmented ball recirculation path of the ball screw assembly;

[0012] Fig. 5 is a perspective view of the segmented ball return path of the ball screw assembly;

[0013] Fig. 6 is a schematic representation of a return path of the ball screw assembly; and

[0014] Fig. Figure 7 is a schematic representation of the appropriate envelope curve of a return opening. DETAILED DESCRIPTION

[0015] With reference to the figures, the invention being described with reference to specific embodiments without limiting them, a return path of a ball screw, such as those used in electric power steering assemblies of vehicles, is provided to reduce the envelope of the overall structure required to accommodate the entire ball screw assembly, as will be established from the disclosure herein.

[0016] With reference to Fig. 1– Fig. 5 and Fig. 7 is a ball screw assembly 10 illustrated. In some embodiments, the ball screw arrangement is 10 It is used in a vehicle power steering system that assists the user in performing steering maneuvers. In these embodiments, an electric motor interacts with the ball screw assembly. 10, which converts a rotary motion of the electric motor into a linear motion. The linear motion is applied to a rack and pinion assembly, which indirectly controls the steering position of at least one wheel of a vehicle. Components located between the rack and pinion assembly and the wheel(s) include, for example, tie rods and an axle. Although described above as follows, the ball screw assembly 10 When used in a power steering system of a vehicle, it should be noted that the ball screw assembly described here is 10 can be used in numerous other applications.

[0017] The ball screw assembly 10 contains a threaded screw 12 with a spiral path 14 , along which a multitude of balls 16 is guided. The multitude of spheres 16carries a load during movement and drives a spindle nut 18 along the threaded screw 12 on. The spiral path 14 extends spirally from a first end 20 to a second end 22 It can be observed that the balls 16 depending on the direction in which the ball is moving 18 It is supposed to move in both directions along the spiral path. 14 They can move. For discussion, one direction of movement of the balls is considered here. 16 described as being from the second end 22 towards the first end 20 of the spiral path 14 move.

[0018] To avoid the large number of balls 16 upon reaching the first end 20 of the spiral path 14 from the spiral path 14 Falling out, a return path will be established. 24for the balls 16 provided. The return path 24 extends from a first crossing point 26 , which are near the first end 20 of the spiral path 14 is ordered to proceed to a second crossing point 28 , which are near the second end 22 of the spiral path 14 is ordered. At the first crossing point 26 will the balls 16 from the spiral path 14 on the return path 24 transferred. When a ball passes the first transition point 26 Once reached, the balls behind it push the ball further along the overall path and into the return path. 24 into. At the second crossing point 28 will the balls 16 from the return path 24 on the spiral path 14 transferred. The ball return tube 58 , 60 is at the return openings62 , 64 on the spindle nut 18 fastened. The return openings 62 , 64 set the appropriate envelope 56 for the ball return tube 58 , 60 ready.

[0019] With reference to now Fig. 6 is the return path 24 presented in greater detail. In particular, illustrated Fig. 6. geometrically define the return path 24 in specific detail. The return path 24 It is formed from three segments. A first segment 30 is formed by a first arc segment of a first ellipse 32 defined. The first segment 30 extends along an elongated section of the first ellipse 32 , so that it is in an essentially, but not entirely, linear orientation. The first segment 30 extends from the first crossing point 26 until an end34 of the first segment. The return path also contains a second segment. 36 , relative to the first segment 30 is similarly oriented, but on an opposite side of the first ellipse 32 is arranged. In particular, the second segment 36 through a second arc segment of the first ellipse 32 defined. The second segment 36 extends from the second crossing point 28 to an end 38 of the second segment.

[0020] In contrast to return paths that continue to follow an elliptical trajectory, such as that of the first ellipse, the return path described here contains 24 a third segment 40 , that of the first ellipse 32 deviates to form the first segment 30 and the second segment 36 to connect. Such a deviation reduces the overall packaging environment. 66the ball screw assembly 10 , while maintaining the functional advantages of the overall arrangement. In particular, the third segment extends 40 between the end 34 of the first segment and the end 38 of the second segment. The trajectory of the third segment. 40 agrees with an arc segment of a second ellipse 42 agree, lying completely in the same plane as the first ellipse 32 is arranged. The term "complete," as used here, describes the arc of the third segment. 40 essentially within a common plane with the first ellipse 32 lies.

[0021] The second ellipse 42 contains a main axis 44 , which extend from a first end 46 the main axis to a second end 48 the main axis extends. The main axis 44is essentially parallel to a secondary axis 54 the first ellipse 32 As described above, the third segment extends between the end 34 of the first segment and the end 38 of the second segment. Each of the ends 34 , 38 The segments are located at an intersection of the first ellipse. 32 with the second ellipse 42 arranged. The arrangement is defined such that the second ellipse 42 the first ellipse 32 at the ends 34 and 38 which cuts the segments tangentially.

[0022] As shown, the second ellipse 42 a center point that leads to an axis 52 is offset, around which the balls are arranged. 16 within the spiral path 14 move. The special geometric dimensions of the first and second ellipses 32 , 42can vary depending on the specific application, but the length of the main axis 50 the first ellipse 32 is larger than that of the main axis 44 the second ellipse 42 This aspect, in combination with the tangential interfaces of the ellipses, represents the reduction of the overall packaging environment of the ball screw assembly. 10 ready.

[0023] The geometric configuration of the segments of the return path 24 represents a reduced, suitable envelope 56 the return openings 62 , 64 Ready. The appropriate envelope. 56 It is geometrically defined as a cylinder. This is achieved by the first and second segments 30 , 36 along arc segments of the elongated first ellipse 32, which has a high eccentricity. In combination with this reduced dimension, another dimension (e.g., height) is reduced by the third segment. 40 of the return path 24 along an arc segment of the second ellipse 42 is oriented to cover the first and second segments 30 , 36 to connect in the manner described in detail above.

[0024] Although the invention has been described in detail in connection with only a limited number of embodiments, it is easy to understand that the invention is not limited to these disclosed embodiments. Instead, the invention can be modified to include any number of variations, alterations, substitutions, or equivalent arrangements not described above, but which are consistent with the spirit and scope of the invention. While various embodiments of the invention have been described, it is also understood that aspects of the invention may only include some of the described embodiments. Consequently, the invention should not be interpreted as being limited to the foregoing description.

Claims

[1] Ball screw assembly comprising: a spiral path for guiding a multitude of spheres, the spiral path extending from a first end to a second end; a return path extending from a first transition point to a second transition point, wherein the first transition point is located near the first end of the spiral path to transfer the plurality of balls from the spiral path to the return path, and wherein the second transition point is located near the second end of the spiral path to transfer the plurality of balls from the return path to the spiral path, the return path comprising: a first segment defined by a first arc segment of a first ellipse; a second segment defined by a second arc segment of the first ellipse; and a third segment defined by an arc of a second ellipse, wherein the first ellipse and the second ellipse are arranged in a common plane. [2] Ball screw assembly according to claim 1, wherein the second ellipse comprises a principal axis extending from a first end of the principal axis to a second end of the principal axis. [3] Ball screw assembly according to claim 2, wherein the first end of the third segment is arranged at an intersection of the first ellipse with the second ellipse. [4] Ball screw assembly according to claim 2, wherein the second end of the third segment is arranged at an intersection of the first ellipse with the second ellipse. [5] Ball screw arrangement according to claim 2, wherein the first end of the third segment and the second end of the third segment are each oriented tangentially to the first ellipse. [6] Ball screw assembly according to claim 2, wherein the first segment extends from the first transition point to the first end of the third segment. [7] Ball screw assembly according to claim 2, wherein the second segment extends from the second transition point to the second end of the third segment. [8] Ball screw assembly according to claim 1, wherein a center point of the ellipse is offset to an axis of the spiral path. [9] Ball screw assembly according to claim 1, wherein the ball screw assembly is arranged in an electric power steering assembly of a vehicle. [10] Electric power steering arrangement of a vehicle, comprising: a motor to assist with the vehicle's steering maneuvers; a rack and pinion arrangement; a ball screw assembly for converting a rotary motion of the motor into a linear motion to support the rack and pinion assembly, wherein the ball screw assembly comprises: a spiral path for guiding a multitude of spheres, the spiral path extending from a first end to a second end; a return path extending from the first end of the spiral path to the second end of the spiral path, wherein the return path includes; a first segment defined by a first arc segment of a first ellipse; a second segment defined by a second arc segment of the first ellipse; and a third segment defined by an arc of a second ellipse, wherein the first ellipse and the second ellipse are arranged in a common plane. [11] Electric power steering arrangement of a vehicle according to claim 10, wherein the first transition point is arranged near the first end of the spiral path to transfer the plurality of balls from the spiral path to the return path, wherein the second transition point is arranged near the second end of the spiral path to transfer the plurality of balls from the return path to the spiral path, and wherein the second ellipse has a principal axis extending from a first end of the principal axis to a second end of the principal axis. [12] Electric power steering arrangement of a vehicle according to claim 11, wherein the second ellipse comprises a principal axis extending from a first end of the principal axis to a second end of the principal axis. [13] Ball screw assembly according to claim 12, wherein the first end of the third segment is arranged at an intersection of the first ellipse with the second ellipse. [14] Ball screw assembly according to claim 11, wherein a center point of the ellipse is displaced to an axis of the spiral path. [15] Ball screw assembly according to claim 11, wherein the ball screw assembly is arranged in an electric power steering assembly of a vehicle.

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