Electric power steering apparatus

Abstract

An invention relating to an electric power steering device is disclosed. An electric power steering device according to the present invention comprises: a ball screw portion having a spiral outer circumference groove on its outer surface; a ball portion movable along the outer circumference groove; and a ball nut portion surrounding the outer surface of the ball screw portion and having a spiral inner circumference groove through which the ball portion moves. The ball screw portion is characterized by comprising: an on-center portion in which the ball nut portion is disposed on its outer surface; and off-center portions formed on both sides of the on-center portion.

Description

Technology Field

[0001] The present invention relates to an electric power steering device, and more specifically, to an electric power steering device capable of reducing NVH (noise, vibration, and harshness). Background Technology

[0003] The R-MDPS (Rack-type Motor Driven Power Steering) consists of ball screw rack bar components and other parts. The ball screw rack bar component receives manual torque from the driver, converts it into linear motion of the rack bar, and ultimately transmits the load to the tires.

[0004] Ball screw rack bar components are closely related to friction and NVH (noise, vibration, harshness).

[0005] In conventional rack-driven electric power steering systems, NVH is continuously generated, which leads to increased user discomfort. Therefore, there is a need to improve this.

[0006] The background technology of the present invention is disclosed in Korean Registered Patent Publication No. 10-1724170 (Registered on March 31, 2017, Title of Invention: Electric Power Steering Device). The problem to be solved

[0008] The present invention was created to solve the above-mentioned problems, and the objective of the present invention is to provide an electric power steering device capable of reducing NVH. means of solving the problem

[0010] An electric power steering device according to the present invention comprises: a ball screw portion having a spiral outer circumference groove on an outer surface; a ball portion movable along the outer circumference groove; and a ball nut portion surrounding the outer surface of the ball screw portion and having a spiral inner circumference groove through which the ball portion moves, wherein the ball screw portion comprises an on-center portion on which the ball nut portion is disposed on an outer surface; and off-center portions formed on both sides of the on-center portion.

[0011] In the present invention, the outer groove of the on-center portion is formed with an annular radius of a set length, and the outer groove of the off-center portion is formed to be smaller than the annular radius of the on-center portion.

[0012] In the present invention, the outer groove of the on-center portion is formed with an annular radius of a set length, and the outer groove of the off-center portion is formed to be equal to the annular radius of the on-center portion.

[0013] In the present invention, the outer groove of the on-center portion is formed with an annular radius of a set length, and the outer groove of the off-center portion is formed larger than the annular radius of the on-center portion.

[0014] In the present invention, the on-center part and the off-center part are continuously connected.

[0015] In the present invention, the on-center portion and the off-center portion are formed by being pressed by a rolling die. Effects of the invention

[0017] According to the electric power steering device of the present invention, operating noise generated as the ball part moves along the outer groove of the ball screw part can be reduced.

[0018] In addition, according to the present invention, by forming the annular radii of the on-center and off-center portions of the ball screw portion to be the same or different, it is possible to manufacture a product suitable for friction or NVH while varying the clearance with the ball portion. Brief explanation of the drawing

[0020] FIG. 1 is a perspective view schematically showing an electric power steering device according to the present invention. FIG. 2 is a front view schematically showing a ball screw portion according to a first embodiment of the present invention. FIG. 3 is a cross-sectional view schematically showing the off-center portion of a ball screw portion according to the first embodiment of the present invention. FIG. 4 is a front view schematically showing a ball screw portion according to a second embodiment of the present invention. FIG. 5 is a cross-sectional view schematically showing the off-center portion of a ball screw portion according to a second embodiment of the present invention. FIG. 6 is a front view schematically showing a ball screw portion according to a third embodiment of the present invention. FIG. 7 is a cross-sectional view schematically showing the off-center portion of a ball screw portion according to the third embodiment of the present invention. Specific details for implementing the invention

[0021] An electric power steering device according to an embodiment of the present invention will be described below with reference to the attached drawings. In this process, the thickness of lines or the size of components shown in the drawings may be exaggerated for clarity and convenience of explanation.

[0022] Furthermore, the terms described below are defined in consideration of their functions within the present invention, and these may vary depending on the intent or practice of the user or operator. Therefore, the definitions of these terms should be based on the content throughout this specification.

[0024] FIG. 1 is a perspective view schematically showing an electric power steering device according to the present invention, FIG. 2 is a front view schematically showing a ball screw part according to a first embodiment of the present invention, FIG. 3 is a cross-sectional view schematically showing an off-center part of a ball screw part according to a first embodiment of the present invention, FIG. 4 is a front view schematically showing a ball screw part according to a second embodiment of the present invention, FIG. 5 is a cross-sectional view schematically showing an off-center part of a ball screw part according to a second embodiment of the present invention, FIG. 6 is a front view schematically showing a ball screw part according to a third embodiment of the present invention, and FIG. 7 is a cross-sectional view schematically showing an off-center part of a ball screw part according to a third embodiment of the present invention.

[0025] Referring to FIGS. 1 to 7, the electric power steering device according to the present invention includes a ball screw part (100), a ball part (200), and a ball nut part (300).

[0026] The ball screw section (100) is provided with a spiral outer groove (111) on its outer surface. The ball screw section (100) is mounted on the ball nut section (300) and moves in a straight line while rotating. The ball screw section (100) includes an on-center section (A, A', A") and an off-center section (B, B', B"). The ball screw section (100) forms part of the rack bar of the electric power steering device.

[0027] On the on center section (A, A', A"), the ball nut body section (310) of the ball nut section (300) is disposed on the outer surface. The off center section (B, B', B") is formed on each side of the on center section (A, A', A").

[0028] The on-center portion (A, A', A") and the off-center portion (B, B', B") are formed by being pressed by a rolling die. The rolling die consists of two circular dies with a round screw shape. The on-center portion (A, A', A") and the off-center portion (B, B', B") are placed between the rolling die consisting of two circular dies, and as the rolling die rotates, a spiral outer groove (111) is formed.

[0029] The ball portion (200) is formed in a ball shape and is movable along the outer groove (111) of the ball screw portion (100). The ball portion (200) is interposed between the outer groove (111) of the ball screw portion (100) and the inner groove (not shown) of the ball nut portion (300) and is movable along the spiral direction of the outer groove (111) and the inner groove.

[0030] The ball nut portion (300) surrounds the outer surface of the ball screw portion (100). The ball nut portion (300) is provided with a spiral inner groove on its inner surface that faces the outer groove (111) of the ball screw portion (100) and through which the ball portion (200) moves. The inner groove of the ball nut portion (300) provides a path through which the ball portion (200) moves together with the outer groove (111) of the ball screw portion (100).

[0031] The ball nut portion (300) includes a ball nut body portion (310) and a deflector (320). The ball nut body portion (310) surrounds the outer surface of the ball screw portion (100) and is provided with an inner groove formed on the inner surface and an open through hole. The inner groove of the ball nut portion (300) is formed to face the outer groove (111) of the ball screw portion (100). The through hole of the ball nut portion (300) is formed to be open in the ball nut body portion (310) in multiple numbers.

[0032] The deflector (320) is mounted in the through hole of the ball nut portion (300) and guides the ball portion (200) to circulate along the outer groove (111) and the inner groove. The deflector (320) is detachably coupled to the through hole of the ball nut portion (300). The ball portion (200) moves along the inner surface of the deflector (320) in the inner groove of the ball nut portion (300).

[0033] Referring to FIGS. 2 and 3, in an electric power steering device according to the first embodiment of the present invention, the outer groove (111) of the on center portion (A) is formed with an annular radius (D) of a set length.

[0034] The BCD (Ball Circular Diameter) described in Fig. 2 illustrates the center point where the ball (200) performs rolling motion in the outer groove (111) of the on-center part (A) and the outer groove (111) of the off-center part (B).

[0035] In an electric power steering device according to the first embodiment of the present invention, the outer groove (111) of the off-center portion (B) is formed to be smaller than the annular radius (D) of the on-center portion (A). The annular radius of the outer groove (111) of the off-center portion (B) is formed to be smaller by α than the annular radius (D) of the outer groove (111) of the on-center portion (A). That is, the annular radius of the outer groove (111) of the off-center portion (B) is formed as D-α, and the annular radius of the outer groove (111) of the on-center portion (A) is formed as a set length of D.

[0036] The off-center portion (B) may be formed to protrude outward. The off-center portion (B) is formed so that a portion of it protrudes outward from the outer groove (111). Accordingly, the annular radius of the off-center portion (B) is formed to be smaller than the annular radius of the on-center portion (A).

[0037] The off-center portion (B) according to the first embodiment of the present invention is referred to as a convex form. When steering the off-center portion (B) of the above-described configuration, the deformation of the rack bar due to the increase in the actual vehicle rack thrust is advantageous for reducing friction feel, jamming, and snagging sensations.

[0038] Referring to FIGS. 4 and 5, in an electric power steering device according to the second embodiment of the present invention, the outer groove (111) of the on-center portion (A') is formed with an annular radius (D) of a set length, and the outer groove (111) of the off-center portion (B') is formed with the same annular radius (D) as the on-center portion (A'). That is, the annular radius of the outer groove (111) of the off-center portion (B') and the annular radius of the outer groove (111) of the on-center portion (A') are formed with the same set length of D.

[0039] The BCD (Ball Circular Diameter) described in Fig. 4 illustrates the center point where the ball (200) performs rolling motion in the outer groove (111) of the on-center part (A') and the outer groove (111) of the off-center part (B').

[0040] The off-center portion (B') according to the second embodiment of the present invention is called a straight form. When steering the off-center portion (B') of the actual vehicle with the above-described configuration, the noise generated between the ball nut portion (300) and the ball screw portion (100) is reduced, and NVH (Noise, Vibration, Harshness) performance can be improved.

[0041] Referring to FIGS. 6 and 7, in an electric power steering device according to the third embodiment of the present invention, the outer groove (111) of the on center portion (A) is formed with an annular radius (D) of a set length.

[0042] The BCD (Ball Circular Diameter) described in Fig. 6 illustrates the center point where the ball (200) performs rolling motion in the outer groove (111) of the on-center part (A) and the outer groove (111) of the off-center part (B).

[0043] In an electric power steering device according to the third embodiment of the present invention, the outer groove (111) of the off-center portion (B) is formed larger than the annular radius (D) of the on-center portion (A). The annular radius of the outer groove (111) of the off-center portion (B) is formed larger than the annular radius (D) of the outer groove (111) of the on-center portion (A) by α. That is, the annular radius of the outer groove (111) of the off-center portion (B) is formed as D+α, and the annular radius of the on-center portion (A) is formed with a set length of D.

[0044] The off-center portion (B) according to the third embodiment of the present invention is called a straight form (concave form). When steering the actual vehicle off-center portion (B) of the above-described configuration, the noise between the ball nut portion (300) and the ball screw portion (100) is reduced, so that NVH performance can be improved.

[0045] In the present invention, the on-center portion (A) and the off-center portion (B) are continuously connected. That is, the outer groove (111) of the on-center portion (A) and the outer groove (111) of the off-center portion (B) are formed as a continuous curve. In other words, the outer groove (111) of the on-center portion (A) and the outer groove (111) of the off-center portion (B) are formed as a continuous curve without step, so that the occurrence of operating noise, such as noise, can be prevented during the process in which the ball portion (200) moves through the outer groove (111) of the on-center portion (A) and the outer groove (111) of the off-center portion (B).

[0046] According to the electric power steering device of the present invention, the operating noise generated as the ball portion (200) moves along the outer groove (111) of the ball screw portion (100) can be reduced.

[0047] In addition, according to the present invention, by forming the annular radii of the on-center portion (A, A', A") and the off-center portion (B, B', B") of the ball screw portion (100) to be the same or different, a product suitable for friction or NVH can be manufactured while varying the clearance with the ball portion (200).

[0049] Although the present invention has been described with reference to the embodiments illustrated in the drawings, this is merely illustrative, and those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible therefrom. Accordingly, the true technical scope of protection of the present invention should be determined by the claims below. Explanation of the symbols

[0051] 100: Ball screw section 111: Outer groove 200: Ball part 300: Ball nut part 310: Ball nut body 320: Deflector

Claims

Claim 1 An electric power steering device comprising: a ball screw portion having a spiral outer circumference groove on an outer surface; a ball portion movable along the outer circumference groove; and a ball nut portion surrounding the outer surface of the ball screw portion and having a spiral inner circumference groove through which the ball portion moves, wherein the ball screw portion comprises: an on-center portion in which the ball nut portion is disposed on an outer surface; and off-center portions formed on both sides of the on-center portion, wherein the outer circumference groove of the on-center portion is formed with an annular radius of a set length, and the outer circumference groove of the off-center portion is formed smaller than the annular radius of the on-center portion. Claim 2 delete Claim 3 delete Claim 4 An electric power steering device comprising: a ball screw portion having a spiral outer circumference groove on an outer surface; a ball portion movable along the outer circumference groove; and a ball nut portion surrounding the outer surface of the ball screw portion and having a spiral inner circumference groove through which the ball portion moves, wherein the ball screw portion comprises: an on-center portion in which the ball nut portion is disposed on an outer surface; and off-center portions formed on both sides of the on-center portion, wherein the outer circumference groove of the on-center portion is formed with an annular radius of a set length, and the outer circumference groove of the off-center portion is formed larger than the annular radius of the on-center portion. Claim 5 An electric power steering device according to claim 1, characterized in that the on-center portion and the off-center portion are continuously connected. Claim 6 An electric power steering device according to claim 1, characterized in that the on-center portion and the off-center portion are formed by being pressed by a rolling die.

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