Rack shaft for steering device, manufacturing method thereof, and steering device

Abstract

To provide a rack shaft for a steering device having a rack side slide plane which elongates in the axial direction and in which an axial end overlaps a female screw hole in the radial direction at both ends of an object rack in the tooth width direction, and being easy to ensure the peripheral wall thickness of the female screw hole, and a manufacturing method therefor, and a steering device with the rack shaft,.SOLUTION: A first shaft part (an assist side shaft part 55) includes: a first female screw hole (an assist side female screw hole 58), an object rack (an assist side rack 29), a rack side slide plane 59, and an overhanging surface part 60 which is at a second side end in the axial direction and projects further outward than the object rack (29) in the radial direction at a portion to be in phase with the object rack (29) in the circumferential direction of an outer-peripheral surface in an axial range including an axial range in which at least the first female screw hole (58) exists.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to a steering device, a rack shaft constituting the device, and a method for manufacturing the same. [Background technology]

[0002] An automobile steering device is configured to transmit the rotation of the steering wheel, which is rotated by the driver, to the steering-side pinion shaft of the steering gear unit via a steering shaft, an intermediate shaft, etc., and to apply a steering angle to the left and right steered wheels by converting the rotational movement of the steering-side pinion shaft into axial linear movement of the rack shaft of the steering gear unit, which meshes with the steering-side pinion shaft.

[0003] In the field of steering devices, electric power steering devices that are configured to apply an assist drive force to a steering force transmission path in order to reduce the force required to turn a steering wheel are widely used. There are various types of electric power steering devices that differ in the way in which the assist drive force is applied to the steering force transmission path.

[0004] Among these, a conventionally known dual-pinion electric power steering device described in International Publication No. 2017 / 010345 (Patent Document 1) has a configuration as shown in FIG. 17, for example.

[0005] The dual-pinion electric power steering device 100 shown in Figure 17 includes an assist-side pinion shaft 103 in addition to a steering-side pinion shaft 102 as pinion shafts that mesh with the rack shaft 101. In the following description of Figure 17, the left-right direction refers to the width direction of the vehicle. The left-right direction coincides with the axial direction of the rack shaft 101. One side in the axial direction of the rack shaft 101 is the left side in Figure 17, and the other side in the axial direction of the rack shaft 101 is the right side in Figure 17.

[0006] The rack shaft 101 is disposed inside a housing 111 fixed to the vehicle body so as to be able to move linearly in the axial direction. The rack shaft 101 has a steering-side rack 104 on a circumferential portion of the outer circumferential surface of one axial side portion and an assist-side rack 105 on a circumferential portion of the outer circumferential surface of the other axial side portion, and both axial ends are connected to the left and right steered wheels via a link mechanism including a spherical joint 106 and a tie rod 107. The rack shaft 101 has, at both axial ends, a steering-side female threaded hole 108 and an assist-side female threaded hole 109 that are open only at the axial end faces and are arranged coaxially with each other. The spherical joints 106 on both axial sides are fixed to the rack shaft 101 by threading their respective male threads 110 into the steering-side female threaded hole 108 or the assist-side female threaded hole 109.

[0007] The steering side pinion shaft 102 is supported inside the housing 111 so as to be rotatable only, has a steering side pinion 112 on its outer circumferential surface that meshes with the steering side rack 104, and is rotationally driven by rotating the steering wheel. The assist side pinion shaft 103 is supported inside the housing 111 so as to be rotatable only, has an assist side pinion 113 on its outer circumferential surface that meshes with the assist side rack 105, and is rotationally driven by an electric motor. When driving a vehicle, an assist driving force is applied from the electric motor to the rack shaft 101 via the assist side pinion shaft 103, thereby reducing the force required to rotate the steering wheel.

[0008] Such an electric power steering device 100 further includes a steering-side rack guide 114 and an assist-side rack guide 115 assembled to the housing 111. The steering-side rack guide 114 is disposed in a position where the rack shaft 101 is sandwiched between it and the steering-side pinion shaft 102, and elastically presses the outer peripheral surface of the rack shaft 101 toward the steering-side pinion shaft 102. This reduces backlash at the meshing portion between the steering-side pinion 112 and the steering-side rack 104, thereby suppressing the generation of abnormal noise at the meshing portion. The assist-side rack guide 115 is disposed in the same manner as the steering-side rack guide 114 and functions in the same manner. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2017 / 010345 Brochure Summary of the Invention [Problem to be solved by the invention]

[0010] In the conventional structure shown in FIG. 17 , the assist drive force acting on the meshing portion between the assist-side rack 105 and the assist-side pinion 113 is much larger than the steering force acting on the meshing portion between the steering-side rack 104 and the steering-side pinion 112. As a result, the assist-side rack guide 115 receives a much larger load from the rack shaft 101 than the steering-side rack guide 114. For this reason, if the pressing portions of the steering-side rack guide 114 and the assist-side rack guide 115 are configured with sliding surfaces that slide against the outer circumferential surface of the rack shaft 101, the frictional force acting between the outer circumferential surface of the rack shaft 101 and the pressing portion of the assist-side rack guide 115 is likely to be large. As a result, the resistance to linear movement of the rack shaft 101 in the axial direction is likely to be large, and wear is likely to occur on the sliding surfaces of the rack shaft 101 and the assist-side rack guide 115.

[0011] To solve this problem, it is conceivable to configure the pressing portion of the steering-side rack guide 114 in the conventional structure shown in Fig. 17 as a sliding surface that slides against the outer circumferential surface of the rack shaft 101, while configuring the pressing portion of the assist-side rack guide 115 as a rolling surface that comes into rolling contact with the outer circumferential surface of the rack shaft 101. By adopting such a configuration, it is possible to reduce the frictional force acting between the outer circumferential surface of the rack shaft 101 and the pressing portion of the assist-side rack guide 115. This reduces the resistance force against linear movement of the rack shaft 101 in the axial direction, and also reduces the amount of wear at the contact portion between the outer circumferential surface of the rack shaft 101 and the pressing portion of the assist-side rack guide 115.

[0012] When such a configuration is adopted, it is easy to ensure that the sliding surface, which is the pressing portion of the steering-side rack guide 114, has a large dimension in the tooth width direction of the steering-side rack 104 (the vertical direction in FIG. 17), and therefore it is easy to ensure the ability to suppress displacement of the rack shaft 101 in the tooth width direction. In contrast, it is difficult to ensure that the rolling surface, which is the pressing portion of the assist-side rack guide 115, has a large dimension in the tooth width direction of the assist-side rack 105 (the vertical direction in FIG. 17), and therefore it is difficult to ensure the ability to suppress displacement of the rack shaft 101 in the tooth width direction.

[0013] 17, it is preferable to assemble a cylindrical rack bush 116 near the assist-side rack guide 115 in the housing 111, and to support the outer circumferential surface of the rack shaft 101 slidably in the axial direction by the inner circumferential surface of the rack bush 116, and to suppress displacement of the rack shaft 101 in the tooth width direction of the assist-side rack 105. For this purpose, it is preferable to provide rack-side slide flat surfaces 117 extending in the axial direction on both end portions in the tooth width direction of the assist-side rack 105 of the outer circumferential surface of the rack shaft 101 that is in sliding contact with the inner circumferential surface of the rack bush 116, and to provide bush-side slide flat surfaces 118 that are in sliding contact with the rack-side slide flat surfaces 117 on the inner circumferential surface of the rack bush 116.

[0014] By using the steering-side rack guide 114 and the rack bush 116 to support the rack shaft 101 at two axially separated locations, it is preferable to position the rack bush 116 as far away from the steering-side rack guide 114 as possible in the axial direction in order to sufficiently suppress tilt of the rack shaft 101 in the left-right direction. Specifically, as shown in FIG. 17 , it is preferable to position the rack bush 116 near the other axial end of the housing 111. In this case, it is preferable to form the rack-side slide flat 117 of the rack shaft 101 at least near the other axial end of the rack shaft 101, that is, up to a position where it radially overlaps with the assist-side female threaded hole 109, so that the rack-side slide flat 117 of the rack shaft 101 and the bush-side slide flat 118 of the rack bush 116 are in sliding contact with each other even when the amount of movement of the rack shaft 101 toward one axial side is maximized.

[0015] In recent years, there has been a demand for further weight reduction and higher output in dual-pinion electric power steering devices. To meet these demands, it has been considered to increase the tooth width of the assist-side rack without increasing the weight of the rack shaft, that is, to increase the meshing area of ​​the assist-side rack with the assist-side pinion, thereby improving the strength of the assist-side rack. Specifically, it has been considered to achieve this by forming the cross-sectional contour of the portion of the rack shaft, which has a substantially cylindrical shape, where the assist-side rack is formed, into a substantially D-shape, thereby increasing the tooth width of the assist-side rack.

[0016] An assist-side rack with such a large tooth width can be formed, for example, as follows. First, a round bar-shaped base material 119 shown in FIG. 18( a) is subjected to flat forging at least in the axial direction where the assist-side rack 105 is to be formed, thereby forming a flat surface portion 120 having a width dimension larger than the diameter of the base material 119 in that portion, as shown in FIG. 18( b). Specifically, the base material 119 is set in a mold cavity with the circumferential portion of its outer circumferential surface where the assist-side rack 105 is to be formed facing upward, and the circumferential portion is pressed with a punch to form the flat surface portion 120. Next, the axial portion of the flat surface portion 120 where the assist-side rack 105 is to be formed is subjected to tooth forming by forging and / or cutting, thereby forming the assist-side rack 105 as shown in FIG. 18( c). Furthermore, as shown by the imaginary line (two-dot chain line) in FIG. 18( c), an assist-side internally threaded hole 109 is formed in the axial end portion by cutting.

[0017] 18(b), when forming the flat surface portion 120 with a punch, the flat surface portion 120 may be formed continuously to the other axial end, and at the same time, rack-side slide planes 117 may be formed using a mold on both ends in the tooth width direction of the assist-side rack 105, so as to continue to the other axial end. In this way, the processing cost for forming the rack-side slide planes 117 can be reduced.

[0018] However, if the flat surface portion 120 is formed continuously to the end on the other axial side as shown in Figures 18(b) and 18(c), that is, if the flat surface portion 120 is formed continuously to a position where it radially overlaps the assist-side female threaded hole 109, the thickness T of the portion located between the flat surface portion 120 and the assist-side female threaded hole 109 will be reduced, as shown in Figure 19(a), and the strength of that portion will be reduced. In contrast, if the position of the assist-side female threaded hole 109 is shifted in a direction away from the flat surface portion 120 as shown in Figure 19(b), the thickness T of the portion located between the flat surface portion 120 and the assist-side female threaded hole 109 can be ensured, but on the other hand, the central axis of the assist-side female threaded hole 109 will be misaligned with the central axis of the steering-side female threaded hole 108. From the viewpoint of appropriately changing the steering angle of the left and right steered wheels, it is preferable that these central axes coincide with each other with high precision.

[0019] The problem described above is not limited to dual-pinion electric power steering devices, but can also occur in various types of steering devices when increasing the tooth width of the target rack provided on the rack shaft without increasing the weight of the rack shaft.

[0020] The present invention aims to provide a rack shaft for a steering device that has rack-side slide planes that extend axially at both ends in the tooth width direction of the target rack and whose axial ends overlap radially with female thread holes, and that make it easy to ensure sufficient wall thickness around the female thread holes, a method for manufacturing the same, and a steering device equipped with the rack shaft. [Means for solving the problem]

[0021] A rack shaft for a steering device according to one aspect of the present invention includes a first shaft portion having a target rack on a first side in the axial direction, and a second shaft portion on a second side in the axial direction.

[0022] The first shaft portion has a first female threaded hole provided at an end on a first side in the axial direction and opening only to the end face on the first side in the axial direction, the target rack provided on a circumferential portion of a portion located on the second side in the axial direction from the first female threaded hole, rack-side slide planes provided on both ends of the outer peripheral surface in the tooth width direction of the target rack, extending in the axial direction and having ends on the first side in the axial direction overlapping radially with the first female threaded hole, and a protruding surface portion provided at the end on the first side in the axial direction and provided on a portion of the outer peripheral surface in the axial range including at least the axial range in which the first female threaded hole is present, which is in the same phase as the target rack in the circumferential direction and protruding radially outward from the target rack.

[0023] The second shaft portion is provided at an end portion on a second side in the axial direction, and has a second female threaded hole that opens only to an end face on the second side in the axial direction and is arranged coaxially with the first female threaded hole.

[0024] In one embodiment (first embodiment) of the rack shaft for a steering device of the present invention, the target rack is an assist side rack, and the second shaft portion has a steering side rack provided on a circumferential portion of a portion located on a first axial side of the second female threaded hole.

[0025] In one embodiment (second embodiment) of the rack shaft for a steering device of the present invention, the target rack is a steering-side rack, and the second shaft portion has a ball screw shaft portion provided in a portion located on the first axial side of the second female threaded hole.

[0026] In one embodiment of the rack shaft for a steering device of the present invention, the width dimension of the protruding surface portion in the tooth width direction of the target rack is equal to or less than the width dimension of the first shaft portion in the tooth width direction of the axial range in which the protruding surface portion exists.

[0027] A rack shaft for a steering device according to one aspect of the present invention includes a connection portion that connects an end portion on a second axial side of the first shaft portion and an end portion on a first axial side of the second shaft portion.

[0028] A method for manufacturing a rack shaft for a steering device according to one aspect of the present invention is directed to manufacturing the rack shaft for a steering device according to one aspect of the present invention, a step of setting a round bar-shaped base material in a mold having a slide plane forming portion for forming the rack side slide plane; a step of obtaining an intermediate material having the rack-side slide plane, the flat surface portion, and the protruding surface portion by pressing a first punch, which is placed in a position where the base material is sandwiched between the first punch and the mold, the dimension in the axial direction of the base material being shorter than the mold, and the flat surface forming portion for forming a flat surface portion having a width dimension greater than the diameter of the base material, where the target rack will be formed, and a second punch, which is placed in a position where the base material is sandwiched between the mold and the first punch, the dimension in the axial direction of the base material being shorter than the mold, and the protruding surface forming portion for forming the protruding surface portion, toward the mold and the base material; forming the target rack on the flat surface portion of the intermediate material; and forming the first female screw hole in an end portion of the intermediate member on a first side in the axial direction.

[0029] A steering device according to one aspect of the present invention comprises: a rack shaft including a steering-side rack and an assist-side rack; a steering-side pinion shaft that meshes with the steering-side rack and is rotationally driven by the rotation of a steering wheel; an assist-side pinion shaft that meshes with the assist-side rack and is rotationally driven by an electric motor; a steering-side rack guide disposed at a position sandwiching the rack shaft between itself and the steering-side pinion shaft, the steering-side rack guide having a pressing portion that elastically presses an outer peripheral surface of the rack shaft toward the steering-side pinion shaft and is in sliding contact with the outer peripheral surface; an assist-side rack guide disposed at a position sandwiching the rack shaft between itself and the assist-side pinion shaft, the assist-side rack guide having a pressing portion that elastically presses an outer peripheral surface of the rack shaft toward the assist-side pinion shaft and is in rolling contact with the outer peripheral surface; a rack bushing that supports an outer peripheral surface of the rack shaft so as to be slidable in the axial direction; a housing in which the rack shaft, the steering side pinion shaft, the assist side pinion shaft, the steering side rack guide, the assist side rack guide, and the rack bush are assembled, The rack shaft is a rack shaft for a steering device according to one aspect (the first aspect) of the present invention, The rack bushing is disposed on a first side of the assist-side pinion shaft in the axial direction of the rack shaft, and has a bushing-side slide flat surface that is in sliding contact with the rack-side slide flat surface of the rack shaft.

[0030] A steering device according to one aspect of the present invention comprises: a rack shaft including a steering-side rack and a ball screw shaft portion; a steering-side pinion shaft that meshes with the steering-side rack and is rotationally driven by the rotation of a steering wheel; a ball nut that engages with the ball screw shaft portion via a plurality of balls and is rotationally driven by an electric motor; a steering-side rack guide disposed at a position sandwiching the rack shaft between itself and the steering-side pinion shaft, the steering-side rack guide having a pressing portion that elastically presses an outer peripheral surface of the rack shaft toward the steering-side pinion shaft and is in rolling contact with the outer peripheral surface; a rack bushing that supports an outer peripheral surface of the rack shaft so as to be slidable in the axial direction; a housing in which the rack shaft, the steering side pinion shaft, the ball nut, the steering side rack guide, and the rack bush are assembled, The rack shaft is a rack shaft for a steering device according to one aspect (the second aspect) of the present invention, The rack bushing is disposed on a first side of the steering-side pinion shaft in the axial direction of the rack shaft, and has a bushing-side slide flat surface that is in sliding contact with the rack-side slide flat surface of the rack shaft.

[0031] A steering device according to one aspect of the present invention comprises: a rack shaft having a steering-side rack that is a target rack; a steering-side pinion shaft that is engaged with the steering-side rack, is rotationally driven by the rotation of the steering wheel, and receives an assist driving force from an electric motor; a steering-side rack guide disposed at a position sandwiching the rack shaft between itself and the steering-side pinion shaft, the steering-side rack guide having a pressing portion that elastically presses an outer peripheral surface of the rack shaft toward the steering-side pinion shaft and is in rolling contact with the outer peripheral surface; a rack bushing that supports an outer peripheral surface of the rack shaft so as to be slidable in the axial direction; a housing in which the rack shaft, the steering side pinion shaft, the steering side rack guide, and the rack bush are assembled, The rack shaft is a rack shaft for a steering device according to one aspect of the present invention, The rack bushing is disposed on a first side of the steering-side pinion shaft in the axial direction of the rack shaft, and has a bushing-side slide flat surface that is in sliding contact with the rack-side slide flat surface of the rack shaft.

[0032] In a steering device according to one aspect of the present invention, the rack-side slide plane exists only in a range in which it comes into sliding contact with the bush-side slide plane of the rack bush when the rack shaft is moved from one end to the other end of the range in which it can be moved axially. [Effects of the Invention]

[0033] According to one aspect of the present invention, it is possible to provide a rack shaft for a steering device, which has rack-side slide planes at both ends in the tooth width direction of the target rack, which extend in the axial direction and whose axial ends overlap radially with the female thread holes, and which makes it easy to ensure the wall thickness around the female thread holes, a method for manufacturing the same, and a steering device equipped with the rack shaft. [Brief explanation of the drawings]

[0034] [Figure 1] FIG. 1 is a schematic diagram showing a steering device according to a first embodiment of the present invention. [Figure 2]FIG. 2 is an exploded perspective view showing some members extracted from the steering device of the first example. [Figure 3] FIG. 3 is a cross-sectional view showing one axial side portion of the rack shaft of the first example and members arranged around the portion. [Figure 4] FIG. 4 is a cross-sectional view showing the other axial side portion of the rack shaft of the first example and the members arranged around it. [Figure 5] FIG. 5 is a cross-sectional view taken along line AA in FIG. [Figure 6] FIG. 6 is a cross-sectional view taken along line BB in FIG. [Figure 7] FIG. 7 is a cross-sectional view taken along line CC in FIG. [Figure 8] Figure 8(a) is a plan view of the rack shaft of the first example, Figure 8(b) is a DD cross-sectional view of Figure 8(a), Figure 8(c) is an EE cross-sectional view or FF cross-sectional view of Figure 8(a), Figure 8(d) is a GG cross-sectional view of Figure 8(a), and Figure 8(e) is an HH cross-sectional view of Figure 8(a). [Figure 9] FIG. 9 is a perspective view of the other axial end of the rack shaft of the first example. [Figure 10] 10(a) and 10(b) are diagrams showing the manufacturing method of the steering-side shaft portion of the first example in the order of steps. [Figure 11] 11(a) to 11(c) are diagrams showing the manufacturing method of the assist-side shaft portion of the first example in the order of steps. [Figure 12] Figure 12(a) is a view of the axis of Figure 11(a) from below, Figure 12(b) is a view of the axis of Figure 11(b) from below, and Figure 12(c) is a view of the axis of Figure 11(c) from below. [Figure 13] FIG. 13 is a perspective view of a forging device used in the first and second steps of the manufacturing method of the assist-side shaft portion of the first example. [Figure 14] FIG. 14 is a schematic diagram showing a steering device according to a second embodiment of the present invention. [Figure 15] FIG. 15 is a schematic diagram showing a steering device according to a third embodiment of the present invention. [Figure 16]FIG. 16 is a schematic diagram showing a steering device according to a fourth embodiment of the present invention. [Figure 17] FIG. 17 is a schematic diagram showing a conventional steering device. [Figure 18] 18(a) to 18(c) are diagrams showing the order of steps in a part of the manufacturing method of the rack shaft that was devised in the process of completing the present invention. [Figure 19] FIG. 19(a) is a diagram showing the axial end face of the rack shaft shown in FIG. 18(c), and FIG. 19(b) is a diagram showing a structure in which the assist-side female screw hole is positioned away from the flat surface portion in comparison with the structure shown in FIG. 19(a). DETAILED DESCRIPTION OF THE INVENTION

[0035] [Example 1] A first embodiment of the present invention will be described with reference to FIGS. 1 to 13. FIG.

[0036] In the following description, the front-rear direction refers to the front-rear direction of the vehicle, the up-down direction refers to the up-down direction of the vehicle, and the left-right direction refers to the width direction of the vehicle. The left-right direction corresponds to the axial direction of the rack shaft 11 and the rack housing unit 14, which will be described later. One side in the axial direction of the rack shaft 11 and the rack housing unit 14 is the left side in FIGS. 1, 3, 4, and 8(a), and the other side in the axial direction of the rack shaft 11 and the rack housing unit 14 is the right side in FIGS. 1, 3, 4, and 8(a). In this example, one side in the axial direction of the rack shaft 11 corresponds to the second side, and the other side corresponds to the first side.

[0037] The steering device of this example is an electric power steering device 1 of a dual pinion type. That is, the electric power steering device 1 of this example is equipped with one rack shaft 11, a steering-side pinion shaft 10, and an assist-side pinion shaft 13, and is an electric power steering device of a type in which a steering force is input from the steering-side pinion shaft 10 to the rack shaft 11, and an assist driving force is input from the assist-side pinion shaft 13 to the rack shaft 11. The electric power steering device 1 of this example is equipped with a steering-side rack guide 24 for reducing backlash at the meshing portion between the rack shaft 11 and the steering-side pinion shaft 10, an assist-side rack guide 37 for reducing backlash at the meshing portion between the rack shaft 11 and the assist-side pinion shaft 13, a rack bush 53 for slidably supporting the outer peripheral surface of the rack shaft 11, and a housing 7 in which these are assembled.

[0038] As shown in FIG. 1, the electric power steering device 1 of this example includes a steering wheel 2, a steering shaft 3, a steering column 4, a pair of universal joints 5a and 5b, an intermediate shaft 6, a housing 7 (not shown in FIG. 1, see FIG. 2), a steering mechanism 8, and an assist mechanism 9.

[0039] The steering shaft 3 is rotatably supported inside a steering column 4 supported on the vehicle body. A steering wheel 2 that is rotated by the driver is attached to the rear end of the steering shaft 3. The front end of the steering shaft 3 is connected to a steering-side pinion shaft 10 that constitutes a steering mechanism 8 via a universal joint 5a, an intermediate shaft 6, and another universal joint 5b. As a result, the rotational motion of the steering wheel 2 is transmitted to the steering-side pinion shaft 10. The rotational motion of the steering-side pinion shaft 10 is converted into linear axial motion of a rack shaft 11 that constitutes the steering mechanism 8. As a result, a steering angle corresponding to the amount of rotation of the steering wheel 2 is applied to the left and right steered wheels 12. The electric power steering device 1 reduces the steering force required for the driver to rotate the steering wheel 2 by applying an assist driving force to the rack shaft 11 via an assist-side pinion shaft 13 that constitutes an assist mechanism 9.

[0040] In this example, the housing 7 is a casting made as a single unit by die-casting a light alloy such as an aluminum alloy, and is fixed to the vehicle body. When implementing the present invention, the housing can also be configured by joining and fixing a plurality of parts to each other. In this example, as shown in FIG. 2, the housing 7 includes a rack accommodating portion 14, a steering-side pinion accommodating portion 15, an assist-side pinion accommodating portion 16, a steering-side guide accommodating portion 17, an assist-side guide accommodating portion 18, a gear housing portion 19, and a plurality of mounting portions 20a, 20b.

[0041] The rack housing portion 14 is a portion that houses an axially intermediate portion of the rack shaft 11 that constitutes the steering mechanism portion 8, and has a cylindrical shape that extends in the left-right direction.

[0042] The steering side pinion accommodating portion 15 is a portion that accommodates the tip half of the steering side pinion shaft 10, and is arranged in a circumferential portion of one axial side portion of the rack accommodating portion 14. More specifically, the steering side pinion accommodating portion 15 is arranged in a front portion of one axial side portion of the rack accommodating portion 14, and has a bottomed cylindrical shape with only the upper end open. The steering side pinion accommodating portion 15 is arranged in a twisted positional relationship with respect to the rack accommodating portion 14. In other words, the central axis of the steering side pinion accommodating portion 15 and the central axis of the rack accommodating portion 14 are in a twisted positional relationship. When viewed from the front-to-rear direction, which is a direction perpendicular to both the central axis of the rack accommodating portion 14 and the central axis of the steering side pinion accommodating portion 15, the central axis of the steering side pinion accommodating portion 15 is not arranged in a direction perpendicular to the central axis of the rack accommodating portion 14, but is inclined with respect to the perpendicular direction. The internal space of the steering-side pinion accommodating portion 15 communicates with the internal space of the rack accommodating portion 14 .

[0043] The assist-side pinion accommodating portion 16 accommodates the assist-side pinion shaft 13 and is disposed at a circumferential portion of the other axial side portion of the rack accommodating portion 14. More specifically, in this example, the assist-side pinion accommodating portion 16 is disposed at the front side of the other axial side portion of the rack accommodating portion 14 and has a cylindrical shape with both ends in the vertical direction open. The assist-side pinion accommodating portion 16 is disposed in a twisted position relative to the rack accommodating portion 14. That is, the central axis of the assist-side pinion accommodating portion 16 and the central axis of the rack accommodating portion 14 are in a twisted positional relationship. When viewed from the front-rear direction, which is a direction perpendicular to both the central axis of the rack accommodating portion 14 and the central axis of the assist-side pinion accommodating portion 16, the central axis of the assist-side pinion accommodating portion 16 is not disposed in a direction perpendicular to the central axis of the rack accommodating portion 14 but is inclined relative to the perpendicular direction. The internal space of the assist-side pinion accommodating portion 16 is in communication with the internal space of the rack accommodating portion 14. When carrying out the present invention, the central axis of the assist-side pinion accommodating portion can also be disposed in a direction perpendicular to the central axis of the rack accommodating portion.

[0044] The steering side guide accommodating portion 17 is a portion that accommodates a steering side rack guide 24, which will be described later, and is arranged in a portion of the rack accommodating portion 14 that is diametrically opposite to the steering side pinion accommodating portion 15. That is, in this example, the steering side guide accommodating portion 17 is arranged in the rear portion of the rack accommodating portion 14 at the same axial position as the steering side pinion accommodating portion 15. The steering side guide accommodating portion 17 has a cylindrical shape and extends in radial directions about the central axis of the rack accommodating portion 14. That is, in this example, the steering side guide accommodating portion 17 extends in the front-rear direction. The internal space of the steering side guide accommodating portion 17 also communicates with the internal space of the rack accommodating portion 14.

[0045] The assist-side guide accommodating portion 18 is a portion that accommodates an assist-side rack guide 37, which will be described later, and is disposed in a portion of the rack accommodating portion 14 that is diametrically opposite the assist-side pinion accommodating portion 16. That is, in this example, the assist-side guide accommodating portion 18 is disposed in the rear portion of the rack accommodating portion 14 at the same axial position as the assist-side pinion accommodating portion 16. The assist-side guide accommodating portion 18 has a cylindrical shape and extends in radial directions about the central axis of the rack accommodating portion 14. That is, in this example, the assist-side guide accommodating portion 18 extends in the front-rear direction. The internal space of the assist-side guide accommodating portion 18 also communicates with the internal space of the rack accommodating portion 14.

[0046] The gear housing portion 19 is a portion that accommodates a worm reducer 38 (described later) that constitutes the assist mechanism portion 9, and includes a worm accommodating portion 21 and a wheel accommodating portion 22.

[0047] The wheel accommodating portion 22 is a portion that accommodates the worm wheel 50 that constitutes the worm reducer 38, and is disposed adjacent to the assist side pinion accommodating portion 16 in the axial direction of the assist side pinion accommodating portion 16. Specifically, in this example, the wheel accommodating portion 22 is disposed above the assist side pinion accommodating portion 16. The wheel accommodating portion 22 has a substantially cylindrical shape, and is disposed coaxially with the assist side pinion accommodating portion 16.

[0048] The worm accommodating section 21 is a section that accommodates the worm 49 that constitutes the worm reducer 38, and is disposed at a portion of the wheel accommodating section 22 in the circumferential direction. Specifically, in this example, the worm accommodating section 21 is disposed at the front portion of the wheel accommodating section 22. The worm accommodating section 21 has a cylindrical shape with a bottom, and in this example, has an opening at one end in the axial direction of the rack accommodating section 14. The worm accommodating section 21 has a mounting flange 23 that protrudes radially outward at the end on the opening side, i.e., at one end in the axial direction of the rack accommodating section 14. The internal space of the worm accommodating section 21 and the internal space of the wheel accommodating section 22 are in communication with each other.

[0049] The multiple mounting portions 20a, 20b are used to secure the housing 7 to the vehicle body. In this example, the multiple mounting portions 20a, 20b consist of two mounting portions 20a arranged on the front side of both axial ends of the rack housing portion 14, and two mounting portions 20b arranged on the rear side of the axial middle portion of the rack housing portion 14. The housing 7 is secured to the vehicle body using fastening members such as bolts or studs inserted through the mounting portions 20a, 20b, respectively.

[0050] The steering mechanism 8 has a steering-side pinion shaft 10, a rack shaft 11, and a steering-side rack guide 24, and converts the rotational movement of the steering wheel 2 into linear movement in the axial direction of the rack shaft 11.

[0051] The steering-side pinion shaft 10 is a shaft member made of a metal such as carbon steel. As shown in Figures 1 and 5, the steering-side pinion shaft 10 has a steering-side pinion 25 on the outer peripheral surface of its tip half that meshes with the steering-side rack 28 of the rack shaft 11.

[0052] The steering side pinion shaft 10 is rotatably supported inside the steering side pinion accommodating portion 15 using bearings 26a and 26b. The central axis of the steering side pinion shaft 10 is arranged coaxially with the central axis of the steering side pinion accommodating portion 15. The steering side pinion shaft 10 is connected to the steering wheel 2 via universal joints 5a and 5b and an intermediate shaft 6, and is rotationally driven by the rotation of the steering wheel 2. The rotational movement of the steering side pinion shaft 10 is converted into linear movement of the rack shaft 11, which pushes and pulls tie rods 27 connected to both axial ends of the rack shaft 11. This imparts a steering angle to the left and right steered wheels 12.

[0053] The rack shaft 11 is a rod-shaped member made of a metal such as carbon steel. The rack shaft 11 is disposed with its axial direction facing the left-right direction. As shown in FIGS. 8(a) to 8(e), the rack shaft 11 includes a steering-side shaft portion 54 having a steering-side rack 28 in one axial half portion, and an assist-side shaft portion 55 having an assist-side rack 29 in the other axial half portion. In this example, the steering-side shaft portion 54 corresponds to the second shaft portion, the assist-side shaft portion 55 corresponds to the first shaft portion, and the assist-side rack 29 corresponds to the target rack.

[0054] In this example, in consideration of ease of manufacturing the rack shaft 11, a structure is adopted in which the rack shaft 11 can be manufactured separately into a steering-side shaft portion 54 and an assist-side shaft portion 55. Specifically, in this example, the rack shaft 11 has a connection portion 56 that connects the other axial end of the steering-side shaft portion 54 to one axial end of the assist-side shaft portion 55. That is, the rack shaft 11 of this example is formed by manufacturing the steering-side shaft portion 54 and the assist-side shaft portion 55 separately, and then connecting the other axial end of the steering-side shaft portion 54 to one axial end of the assist-side shaft portion 55 by the connection portion 56. In this example, the connection portion 56 is formed by friction welding. However, when implementing the present invention, any connection portion can be used as the connection portion 56, such as a welded joint, a friction stir welded joint, or a caulked joint, as long as the necessary strength for the connection portion 56 can be ensured. Also, when implementing the present invention, the rack shaft can be manufactured from a single round bar-shaped base material.

[0055] The steering-side shaft portion 54 has a steering-side female screw hole 57 in addition to the steering-side rack 28. In this example, the steering-side female screw hole 57 corresponds to the second female screw hole. The steering-side female screw hole 57 is provided at one end portion in the axial direction of the steering-side shaft portion 54 and opens only on the end face on one side in the axial direction of the steering-side shaft portion 54. The central axis of the steering-side female screw hole 57 coincides with the central axis of the steering-side shaft portion 54, that is, the central axis of the rack shaft 11. The steering-side rack 28 is provided on a part of the circumferential direction of the axial intermediate portion, which is a portion of the steering-side shaft portion 54 located on the other side in the axial direction than the steering-side female screw hole 57. In this example, the steering-side rack 28 is disposed on the front side surface of the steering-side shaft portion 54, that is, the front side surface of the rack shaft 11.

[0056] In this example, as shown in Fig. 8(b), the contour shape of the cross section in the axial range where the steering-side rack 28 is formed in the steering-side shaft portion 54 is such that the portion where the steering-side rack 28 is formed is linear and the remaining portion is arc-shaped, that is, the whole is an oval shape with a missing part. As shown in Fig. 8(c), the contour shape of the cross section in the axial range outside the steering-side rack 28 in the steering-side shaft portion 54 is circular. The diameter d of the circumscribed circle in the axial range where the steering-side rack 28 is formed in the steering-side shaft portion 54 is equal to the diameter d in the axial range outside the steering-side rack 28 in the steering-side shaft portion 54. The tooth width W1 of the steering-side rack 28 is smaller than the diameter d (W1 < d). The diameter d is the same as the diameter of the round bar-shaped base material 62 (see Fig. 10(a)) used to make the steering-side shaft portion 54 of this example.

[0057] The assist-side shaft portion 55 has an assist-side female screw hole 58, a pair of rack-side slide planes 59, and an overhanging portion 60 in addition to the assist-side rack 29. In this example, the assist-side female screw hole 58 corresponds to the first female screw hole.

[0058] The assist-side female threaded hole 58 is provided at the other axial end of the assist-side shaft portion 55, and is open only to the other axial end face of the assist-side shaft portion 55. The central axis of the assist-side female threaded hole 58 coincides with the central axis of the assist-side shaft portion 55, i.e., the central axis of the rack shaft 11. In other words, the assist-side female threaded hole 58 is arranged coaxially with the steering-side female threaded hole 57.

[0059] The assist-side rack 29 is provided on a circumferential portion of an axially intermediate portion of the assist-side shaft portion 55, which is a portion located on one axial side of the assist-side female threaded hole 58. In this example, the assist-side rack 29 is disposed on the front side of the assist-side shaft portion 55, i.e., the front side of the rack shaft 11. In other words, in this example, the steering-side rack 28 and the assist-side rack 29 are arranged in the same phase with respect to the circumferential direction of the rack shaft 11. However, when implementing the present invention, the steering-side rack 28 and the assist-side rack 29 may be arranged in different phases with respect to the circumferential direction of the rack shaft 11.

[0060] In this example, the assist-side shaft portion 55 has flat surface portions 61 on the front side surface thereof that are adjacent to both axial sides of the assist-side rack 29. These flat surface portions 61 exist in the same imaginary plane as the tooth tip surfaces of the assist-side rack 29. Of these flat surface portions 61, the flat surface portion 61 on the other axial side is located on one axial side of the assist-side female threaded hole 58.

[0061] The rack-side slide flat surfaces 59 constituting the pair of rack-side slide flat surfaces 59 are provided on both end portions of the outer peripheral surface of the assist-side shaft portion 55 in the tooth width direction of the assist-side rack 29 (the up-down direction in FIG. 8( a)), i.e., on the upper and lower surfaces, and extend in the axial direction. These rack-side slide flat surfaces 59 are provided continuously in the axial direction from the same axial position as the assist-side rack 29 to an axial position where they radially overlap with the assist-side female threaded hole 58. In particular, in this example, these rack-side slide flat surfaces 59 are provided continuously from the same axial position as the edge portion on one axial side of the flat surface portion 61 on one axial side to the same axial position as the edge portion on the other axial side of the assist-side shaft portion 55. In this example, these rack-side slide flat surfaces 59 are slightly inclined in a direction approaching each other as they move away from the assist-side rack 29 (the right side in FIGS. 8( d) and 8(e)).

[0062] The protruding surface portion 60 is provided at the end on the other axial side of the assist-side shaft portion 55, on the front side, which is a portion of the outer peripheral surface in an axial range including at least the axial range in which the assist-side female threaded hole 58 is present, that is, in phase with the assist-side rack 29 in the circumferential direction, so as to protrude radially outward, i.e., forward, from the assist-side rack 29. In this example, the protruding surface portion 60 is provided over a wider axial range including the axial range in which the assist-side female threaded hole 58 is present. In other words, the end on one axial side of the protruding surface portion 60 is located on one axial side of the bottom of the assist-side female threaded hole 58. The protruding surface portion 60 is arranged adjacent to the other axial side of the flat surface portion 61 on the other axial side.

[0063] In this example, the protruding surface portion 60 has a partial cylindrical surface shape centered on the central axis of the assist-side female screw hole 58. As a result, the wall thickness (radial thickness) of the portion of the periphery of the assist-side female screw hole 58 that is in the same phase as the assist-side rack 29 in the circumferential direction is made substantially the same as the wall thickness of the portion of the periphery of the assist-side female screw hole 58 that is out of phase with the assist-side rack 29 in the circumferential direction. In other words, the wall thickness around the assist-side female screw hole 58 is made substantially constant over the entire circumference. Note that the shape of the protruding surface portion can be any shape as long as the wall thickness around the assist-side female screw hole can be ensured.

[0064] The width dimension X (see FIG. 8(e)) of the protruding surface portion 60 in the tooth width direction of the assist-side rack 29 is smaller (X < Y) than the width dimension Y (see FIG. 8(e)) of the axial range where the protruding surface portion 60 exists in the assist-side shaft portion 55 in the tooth width direction, in other words, the distance Y (see FIG. 8(e)) between the respective rack-side slide planes 59 that constitute the pair of rack-side slide planes 59. The protruding surface portion 60 and the flat surface portion 61 on the other axial side are connected by a stepped surface facing the one axial side.

[0065] In this example, in the axial range of the assist-side shaft portion 55 where the assist-side rack 29 and the flat surface portion 61 are formed, the contour shape of the cross section is, as shown in FIG. 8(d), the portion (front side) where the assist-side rack 29 and the flat surface portion 61 are formed, and the portions (upper side and lower side) where the respective rack-side slide planes 59 that constitute the pair of rack-side slide planes 59 are formed are linear, and the portion (rear side) located on the back side of the assist-side rack 29 and the flat surface portion 61 is arc-shaped, that is, D-shaped as a whole. In the axial range of the assist-side shaft portion 55 that is located on the one axial side of the flat surface portion 61 on the one axial side, the contour shape of the cross section is circular as shown in FIG. 8(c). In the axial range of the assist-side shaft portion 55 where the protruding surface portion 60 is formed, the contour shape of the cross section is the same as the contour shape of the cross section shown in FIG. 8(d), except that the portion where the protruding surface portion 60 is formed is arc-shaped, as shown in FIG. 8(e).

[0066] In this example, the width dimension Y of the assist-side rack 29 in the tooth width direction of the assist-side shaft portion 55 in the axial range where the assist-side rack 29, the flat surface portion 61, and the protruding surface portion 60 are formed is constant over the entire axial length (see FIGS. 8(d) and 8(e)). The width dimension Y is larger than the diameter d of the assist-side shaft portion 55 in the axial range located on one axial side of the flat surface portion 61 on one axial side (Y>d). The diameter d is the same as the diameter d of the round bar-shaped base material 63 (see FIGS. 11(a) and 12(a)) used to produce the assist-side shaft portion 55 of this example. In this example, the diameter d of the base material 63 is the same as the diameter d of the base material 62 (see FIG. 10(a)) used to produce the steering-side shaft portion 54. Therefore, in this example, the tooth width W2 of the assist-side rack 29 is larger than the tooth width W1 of the steering-side rack 28 (W2>W1).

[0067] The rack shaft 11 is supported inside the rack housing 14 so as to be able to move back and forth in the axial direction, with both axial ends protruding from both left and right openings of the rack housing 14. Both axial ends of the rack shaft 11 are connected to tie rods 27 via spherical joints 31. That is, a male threaded portion 32 provided at the base of the spherical joint 31 is threadedly engaged with a steering-side female threaded hole 57 and an assist-side female threaded hole 58 provided at both axial ends of the rack shaft 11, and the base end of the tie rod 27 is supported so as to be able to swing at the tip of the spherical joint 31. The rack shaft 11 is connected to the left and right steered wheels 12 via a link mechanism including the spherical joint 31 and the tie rod 27.

[0068] The steering side rack guide 24 is disposed at a position where the rack shaft 11 is sandwiched between it and the steering side pinion shaft 10, and in this example, it is disposed inside the steering side guide accommodating portion 17. As shown in Figures 3 and 5, the steering side rack guide 24 in this example is a sliding type rack guide, and includes a pad 33 and an elastic member 34.

[0069] The pad 33 has a generally cylindrical shape and is disposed inside the steering-side guide accommodating portion 17 so as to be movable toward and away from the rack shaft 11. The pad 33 has a pressing surface 35, which is a concave cylindrical surface and has a shape that matches the rear side surface of the rack shaft 11, on the surface facing the convex cylindrical rear side surface of the rack shaft 11. The pressing surface 35, which serves as the pressing portion, is made of a synthetic resin or the like that has excellent slip properties. In the illustrated example, the elastic member 34 is a torsion coil spring and is sandwiched in an elastically compressed state between the pad 33 and a steering-side cap 36 that closes the opening of the steering-side guide accommodating portion 17. In this way, the elastic member 34 presses the pad 33 toward the rack shaft 11.

[0070] The steering side rack guide 24 faces the rear side surface, which is the outer peripheral surface of the rack shaft 11, toward the steering side pinion shaft 10 and elastically presses it based on the elastic force of the elastic member 34, thereby reducing backlash at the meshing portion between the steering side pinion 25 and the steering side rack 28. This suppresses the generation of abnormal noise at the meshing portion between the steering side pinion 25 and the steering side rack 28.

[0071] The assist mechanism 9 applies an assist driving force to the rack shaft 11, thereby reducing the steering force required for the driver to rotate the steering wheel 2. The assist mechanism 9 includes an assist side pinion shaft 13, an assist side rack guide 37, a worm reducer 38, an electric motor 39, and a torque sensor 40.

[0072] The assist-side pinion shaft 13 is a shaft member made of a metal such as carbon steel. As shown in Figs. 1 and 6, the assist-side pinion shaft 13 has an assist-side pinion 41 on the outer peripheral surface of the tip half that meshes with the assist-side rack 29 of the rack shaft 11.

[0073] The assist side pinion shaft 13 is rotatably supported inside the assist side pinion accommodating portion 16 using bearings 42a and 42b. The central axis of the assist side pinion shaft 13 is arranged coaxially with the central axis of the assist side pinion accommodating portion 16. The assist side pinion shaft 13 is rotationally driven by an electric motor 39 via a worm reducer 38. In this example, an opening of the assist side pinion accommodating portion 16 on the opposite side of the wheel accommodating portion 22 in the axial direction is closed by a cap 51.

[0074] The assist-side rack guide 37 is disposed at a position where the rack shaft 11 is sandwiched between it and the assist-side pinion shaft 13, and in this example, is disposed inside the assist-side guide accommodating portion 18. As shown in FIGS. 4 and 6 , the assist-side rack guide 37 is a rolling-type rack guide, and has a roller 43, a holder 44, a pin 45, a rolling bearing 46, and an elastic member 47.

[0075] The roller 43 has a generally annular shape and is rotatably supported relative to the holder 44 via a pin 45 and a rolling bearing 46, whose axial direction is oriented vertically. As a result, the outer peripheral surface of the roller 43, which serves as a pressing portion, is in rolling contact with the middle portion of the rear side of the rack shaft 11 in the width direction. The outer peripheral surface of the roller 43 has a generatrix-like concave arc shape that generally matches the contour shape of the rear side of the rack shaft 11. The holder 44 is disposed inside the assist-side guide accommodating portion 18 so as to be able to move toward and away from the rack shaft 11. In the illustrated example, the elastic member 47 is a disc spring and is disposed between the holder 44 and an assist-side cap 48 that closes the opening of the assist-side guide accommodating portion 18. The elastic member 47 presses the holder 44 toward the rack shaft 11.

[0076] The assist-side rack guide 37 faces the rear side surface, which is the outer peripheral surface of the rack shaft 11, toward the assist-side pinion shaft 13 and elastically presses it based on the elastic force of the elastic member 47, thereby reducing backlash at the meshing portion between the assist-side pinion 41 and the assist-side rack 29. This suppresses the generation of abnormal noise at the meshing portion between the assist-side pinion 41 and the assist-side rack 29.

[0077] As shown in FIG. 6, the worm reducer 38 includes a worm 49 and a worm wheel 50, and reduces the rotation speed of the electric motor 39, that is, increases the drive torque of the electric motor 39, and transmits it to the assist-side pinion shaft 13.

[0078] The worm 49 has worm teeth on its outer circumferential surface and is rotatably supported inside the worm accommodating portion 21. The base end of the worm 49 is connected to the motor output shaft of the electric motor 39 via a coupling or the like (not shown) so as to transmit torque.

[0079] The worm wheel 50 has wheel teeth on its outer circumferential surface that mesh with the worm teeth, and is disposed inside the wheel accommodating portion 22. The worm wheel 50 is fitted and fixed to the base end of the assist-side pinion shaft 13 so as not to rotate relative to the assist-side pinion accommodating portion 16. In this example, an opening of the wheel accommodating portion 22 on the opposite side of the assist-side pinion accommodating portion 16 in the axial direction is closed by a cap 52.

[0080] The electric motor 39 is fixed to the mounting flange 23 of the worm housing portion 21 .

[0081] The torque sensor 40 is disposed around the steering side pinion shaft 10 and detects the magnitude and direction of the torque input to the steering side pinion shaft 10. As a result, the torque sensor 40 outputs a signal corresponding to the torque input to the steering side pinion shaft 10 to the electronic control unit of the electric motor 39. As the torque sensor 40, various types of torque sensors can be used, such as a non-contact torque sensor that utilizes the magnetostrictive effect.

[0082] The assist mechanism 9 controls the driving of the electric motor 39 based on the output signal of the torque sensor 40. As a result, the driving torque generated by the electric motor 39 is transmitted as an assist driving force to the rack shaft 11 via the worm reduction gear 38 and the assist-side pinion shaft 13. As a result, the steering force required for the driver to turn the steering wheel 2 is reduced.

[0083] The rack bushing 53 (see FIGS. 4 and 7) is made of a synthetic resin such as polyacetal resin or polyamide resin, has a generally cylindrical shape, and is fitted into the rack housing 14 near the opening on the other axial side. The rack bushing 53 supports the outer peripheral surface of the rack shaft 11 so that it can slide in the axial direction. The rack bushing 53 has, on its inner peripheral surface, a pair of bushing-side sliding flats 64 that come into sliding contact with a pair of rack-side sliding flats 59 of the rack shaft 11. The rack bushing 53 effectively suppresses displacement of the rack shaft 11 in the tooth width direction of the assist-side rack 29 (the up-and-down direction in FIG. 7) based on the engagement between the pair of bushing-side sliding flats 64 and the pair of rack-side sliding flats 59.

[0084] The structure of this example includes an annular spacer 30 that is fitted and fixed to the rack bush 53 in a position adjacent to the opening on the other axial side of the rack housing section 14. The spacer 30 is made of a material that is stronger than the synthetic resin that makes up the rack bush 53, such as metal.

[0085] In this example, the rack shaft 11 can be linearly moved in the axial direction within a range from a position where a circular abutment surface 65 facing the other axial side, which is provided at the radially outer end of the spherical joint 31 (see FIG. 3) on one axial side, abuts against a stopper surface 66a facing one axial side and provided near the opening on one axial side of the rack housing 14, to a position where a circular abutment surface 65 facing one axial side, which is provided at the radially outer end of the spherical joint 31 (see FIG. 4) on the other axial side, abuts against a stopper surface 66b, which is a side surface on the other axial side of the spacer 30. In this example, a limit range for the rotational operation amount of the steering wheel 2 is set by adjusting this range. In this example, the limit range is set to a range of approximately 1.5 rotations (540° rotation angle) on each side from the neutral position of the steering wheel 2.

[0086] Next, a method for manufacturing the rack shaft 11 of this embodiment will be described.

[0087] The manufacturing method of the rack shaft 11 in this example includes a step of manufacturing the steering-side shaft portion 54, a step of manufacturing the assist-side shaft portion 55, and a step of connecting the other axial end of the steering-side shaft portion 54 and the one axial end of the assist-side shaft portion 55 by friction welding to form a connection portion 56.

[0088] In the process of manufacturing the steering-side shaft portion 54, as shown in Figure 10(a), teeth are formed by forging and / or cutting on a circumferential portion of an axially intermediate portion of a metal round bar-shaped base material 62 to form the steering-side rack 28. Furthermore, a cutting process is performed on one axial end of the base material 62 to form a steering-side internally threaded hole 57. This results in the steering-side shaft portion 54 as shown in Figure 10(b).

[0089] The process for manufacturing the assist-side shaft portion 55 will now be described.

[0090] First, in the first step, a metal rod-shaped base material 63 as shown in Figures 11(a) and 12(a) is set in a mold 67 (see Figure 13) equipped with a pair of slide plane forming portions 71 for forming a pair of rack-side slide planes 59.

[0091] The mold 67 has a U-shaped cross section and includes a cavity 72 that is open on both axial sides and the top. A pair of slide plane forming portions 71 for forming a pair of rack-side slide planes 59 are provided on the inner surface of the cavity 72, on both widthwise sides of the upper end. A portion of the inner surface of the cavity 72 that is located below the pair of slide plane forming portions 71 is provided with a partially cylindrical surface forming portion 73 having a curvature radius equal to or slightly larger than half the diameter d of the base material 63. In a first step, the portion of the base material 63 extending from the axial middle portion to the other axial end is set in the cavity 72 of the mold 67.

[0092] Next, in a second step, the base material 63 is press-forged using a die 67, a first punch 68 (see FIG. 13), and a second punch 69 (see FIG. 13) to obtain an intermediate material 70 having a pair of rack-side slide planes 59, a flat surface portion 61z, and a protruding surface portion 60, as shown in FIGS. 11(b) and 12(b). Here, the width dimension of the flat surface portion 61z is greater than the diameter d of the base material 63. The first punch 68 is positioned to sandwich the base material 63 between itself and the die 67, has a dimension in the axial direction of the base material 63 shorter than that of the die 67, and includes a flat surface forming portion 74 for forming the flat surface portion 61z, which is the portion where the assist-side rack 29 will be formed. The second punch 69 is positioned to sandwich the base material 63 between itself and the die 67, has a dimension in the axial direction of the base material 63 shorter than that of the die 67, and includes an protruding surface forming portion 75 for forming the protruding surface portion 60. In the second step, the base material 63 is pressed toward the cavity 72 of the die 67 by the first punch 68 and the second punch 69 to obtain the intermediate material 70.

[0093] Continuing with the third work About In the third step, teeth are formed by forging and / or cutting in the middle of the flat surface portion 61z of the intermediate material 70 to form the assist-side rack 29. In the third step, both side portions of the flat surface portion 61z where the assist-side rack 29 is not formed become the flat surface portions 61 adjacent to both axial sides of the assist-side rack 29.

[0094] Then, in the fourth step, the end of the intermediate material 70 on the axial side where the protruding surface portion 60 is present, i.e., the end on the other axial side, is cut to form the assist-side female screw hole 58. This results in the assist-side shaft portion 55 as shown in Figures 11(c) and 12(c).

[0095] In the structure of this example, the assist drive force acting on the meshing portion between the assist-side rack 29 and the assist-side pinion 41 is much greater than the steering force acting on the meshing portion between the steering-side rack 28 and the steering-side pinion 25. As a result, the assist-side rack guide 37 receives a much greater load from the rack shaft 11 than the steering-side rack guide 24. In consideration of this situation, in this example, the pressing portion of the steering-side rack guide 24 is configured as a sliding surface that slides against the outer circumferential surface of the rack shaft 11, while the pressing portion of the assist-side rack guide 37 is configured as a rolling surface that comes into rolling contact with the outer circumferential surface of the rack shaft 11. This makes it possible to reduce the frictional force acting between the outer circumferential surface of the rack shaft 11 and the pressing portion of the assist-side rack guide 37. This reduces the resistance force against linear movement of the rack shaft 11 in the axial direction and suppresses the amount of wear at the contact portion between the outer circumferential surface of the rack shaft 11 and the pressing portion of the assist-side rack guide 37.

[0096] In the structure of this example, the pressing surface 35, which is the pressing portion of the steering-side rack guide 24, can easily be ensured to have a large dimension in the tooth width direction of the steering-side rack 28 (the vertical direction in FIG. 5), and therefore it is easy to ensure the ability to suppress displacement of the rack shaft 11 in the tooth width direction. In contrast, it is difficult to ensure a large dimension in the tooth width direction of the assist-side rack 29 (the vertical direction in FIG. 6) for the outer circumferential surface of the roller 43, which is the pressing portion of the assist-side rack guide 37, and therefore it is difficult to ensure the ability to suppress displacement of the rack shaft 11 in the tooth width direction. In consideration of these circumstances, in the structure of this example, as shown in FIGS. 4 and 7, a cylindrical rack bushing 53 is assembled in the housing 7 near the assist-side rack guide 37. Furthermore, on the outer peripheral surface of the rack shaft 11 that is in sliding contact with the inner peripheral surface of the rack bush 53, rack-side slide flat surfaces 59 that extend in the axial direction are provided at both end portions in the tooth width direction of the assist-side rack 29 (the front-to-back direction of the paper in FIG. 4, the up-and-down direction in FIG. 7), and a bush-side slide flat surface 64 that is in sliding contact with the rack-side slide flat surface 59 is provided on the inner peripheral surface of the rack bush 53. Therefore, displacement of the rack shaft 11 in the tooth width direction of the assist-side rack 29 near the assist-side rack guide 37 can be suppressed.

[0097] In particular, in the structure of this example, the rack bushing 53 is disposed near the opening on the other axial side of the rack housing portion 14, at a location where the axial distance from the steering-side rack guide 24 is greater than that of the assist-side rack guide 37. This makes it possible to ensure a sufficient axial distance between the steering-side rack guide 24 and the rack bushing 53, effectively preventing the rack shaft 11 from tilting in the tooth width direction relative to the left-right direction.

[0098] In the structure of this example, the rack bushing 53 is disposed near the opening on the other axial side of the rack accommodation portion 14. Therefore, when the amount of movement of the rack shaft 11 toward one axial side reaches a maximum, that is, when the rack shaft 11 moves toward one axial side to a position where the abutting surface 65 of the spherical joint 31 (see FIG. 4) on the other axial side abuts against the stopper surface 66 b of the spacer 30, the portion of the outer circumferential surface of the rack shaft 11 that radially overlaps with the assist-side female threaded hole 58 enters the inner diameter side of the rack bushing 53. In consideration of this situation, in this example, the rack-side slide flat surface 59 is formed continuously in the axial direction up to the position where it radially overlaps with the assist-side female threaded hole 58. Therefore, even when the amount of movement of the rack shaft 11 toward one axial side reaches a maximum, the rack-side slide flat surface 59 remains in sliding contact with the bushing-side slide flat surface 64.

[0099] In the structure of this example, the assist-side rack 29 of the assist-side shaft portion 55 is given a tooth width W2 that is larger than the diameter d of the base material 63 by forging the base material 63. Therefore, the meshing area of ​​the assist-side rack 29 with the assist-side pinion 41 can be increased without increasing the weight of the rack shaft 11, and the durability of the assist-side rack 29 can be improved.

[0100] In this example, the base material 63 is forged to form the flat surface portion 61z, where the assist-side rack 29 is to be formed and which has a width dimension larger than the diameter d of the base material 63, and the protruding surface portion 60. At the same time, the pair of rack-side slide planes 59 are formed by the pair of slide plane forming portions 71 provided in the mold 67. Therefore, the processing cost of the pair of rack-side slide planes 59 can be reduced compared to when the pair of rack-side slide planes 59 are formed by separate cutting. Furthermore, in this example, forming the rack-side slide planes 59 by forging forms a work-hardened layer on the surface of the rack-side slide planes 59, making it easier to ensure the wear resistance of the rack-side slide planes 59 compared to when the rack-side slide planes 59 are formed by cutting.

[0101] In this example, when the flat surface portion 61z is formed by forging the base material 63, the flat surface portion 61z is not formed up to the end portion on the other axial side where the assist-side female threaded hole 58 is formed. That is, in this example, at this time, of the end portion on the other axial side where the assist-side female threaded hole 58 is formed, the protruding surface portion 60 that protrudes radially outward from the flat surface portion 61z is formed in a portion that is in phase with the flat surface portion 61z in the circumferential direction. Therefore, in the structure of this example, under the condition that the steering-side female threaded hole 57 and the assist-side female threaded hole 58 are coaxially arranged, it is possible to ensure a sufficient thickness in the portion around the assist-side female threaded hole 58 that is in phase with the assist-side rack 29, compared to when the flat surface portion 61z is formed up to the end portion on the other axial side where the assist-side female threaded hole 58 is formed.

[0102] Furthermore, according to the manufacturing method of this example, the shape accuracy of the rack-side slide plane 59 can be improved. That is, in the structure of this example, as shown in FIG. 12(b), the rack-side slide plane 59 has a first portion existing in the same axial range as the flat surface portion 61z and a second portion existing in the same axial range as the protruding surface portion 60. As a method for forming such a rack-side slide plane 59 by forging, for example, a method is conceivable in which a base material is pressed by a first punch 68 against a first die having a first-portion forming portion for forming the first portion to form the flat surface portion 61z and the first portion, and then the base material is pressed by a second punch 69 against a second die having a second-portion forming portion for forming the second portion to form the protruding surface portion 60 and the second portion. However, when the first portion and the second portion are formed by forging using different dies (first die, second die) in this way, a step is inevitably formed at the boundary between the first portion and the second portion. In contrast, in the manufacturing method of this embodiment, the first and second portions of the rack-side slide plane 59 are formed by forging using a single die 67 having a slide plane forming portion 71 that is continuous over the entire length. This prevents a step from being formed at the boundary between the first and second portions, improving the shape accuracy of the rack-side slide plane 59. Moreover, as described above, a work-hardened layer is formed on the surface of the rack-side slide plane 59, making it possible to form a rack-side slide plane 59 that not only has good shape accuracy but also excellent wear resistance.

[0103] In the structure of this example, the rack-side sliding plane 59 is formed continuously from the same axial position as the edge portion on one axial side of the flat surface portion 61 on one axial side to the same axial position as the edge portion on the other axial side of the assist-side shaft portion 55. However, when implementing the present invention, it is sufficient that the rack-side sliding plane is formed in a range that comes into sliding contact with the bush-side sliding plane of the rack bush when the rack shaft is moved from one end to the other end of the range in which it can be moved in the axial direction, and therefore it can be formed only in that range.

[0104] That is, when the rack shaft 11 is moved axially toward the other side by rotating the steering wheel 2 to a position where the abutment surface 65 of the spherical joint 31 (see FIG. 3) on one axial side abuts against the stopper surface 66 a of the housing 7, it is not necessary to form the rack-side slide flat surface 59 on a portion of the assist-side shaft portion 55 that is located on one axial side of the rack bush 53. Furthermore, when the rack shaft 11 is moved axially toward the other side by rotating the steering wheel 2 to a position where the abutment surface 65 of the spherical joint 31 (see FIG. 4) on the other axial side abuts against the stopper surface 66 b of the spacer 30, it is not necessary to form the rack-side slide flat surface 59 on a portion of the assist-side shaft portion 55 that is located on the other axial side of the rack bush 53, specifically, on the end portion on the other axial side that is located on the inner diameter side of the spacer 30.

[0105] [Example 2] A second embodiment of the present invention will be described with reference to FIG.

[0106] The steering device of this example is a ball screw type electric power steering device 1a. In this example, one side of the rack shaft 11a in the axial direction corresponds to a first side, and the other side corresponds to a second side.

[0107] In this example, the rack shaft 11a includes, in one axial half, a steering-side shaft portion 54a having a steering-side rack 28a, and, in the other axial half, an assist-side shaft portion 55a having a ball screw shaft portion 76. In this example, the steering-side shaft portion 54a corresponds to the first shaft portion, the assist-side shaft portion 55a corresponds to the second shaft portion, and the steering-side rack 28a corresponds to the target rack.

[0108] In this example, the steering side shaft portion 54a has the same configuration as the assist side shaft portion 55 of the first example (see Figures 8(a), 8(d), 8(e), and 9), but the axial direction when in use is opposite to that of the assist side shaft portion 55a of the first example.

[0109] That is, the steering-side shaft portion 54a has, at one axial end, a steering-side female threaded hole 57 having the same configuration as the assist-side female threaded hole 58 of the first example. In this example, the steering-side female threaded hole 57 corresponds to the first female threaded hole. The steering-side shaft portion 54a has a steering-side rack 28a having the same configuration as the assist-side rack 29 of the first example in a circumferential part of an axially intermediate portion, which is a portion located on the other axial side of the steering-side female threaded hole 57. The steering-side shaft portion 54a has a pair of rack-side slide flat surfaces 59, the same as in the first example, on both end portions in the tooth width direction of the steering-side rack 28a of its outer peripheral surface. The steering-side shaft portion 54a has, at one axial end, a protruding surface portion 60, the same as in the first example, on a portion of the outer peripheral surface in the axial range including the axial range in which the steering-side female threaded hole 57 is present, which is in the same phase as the steering-side rack 28a in the circumferential direction. Other parts of the steering-side shaft portion 54a also have the same configuration as the assist-side shaft portion 55a of the first example.

[0110] In this example, the assist-side female threaded hole 58 provided at the other axial end of the assist-side shaft portion 55a corresponds to the second female threaded hole. In this example, the assist-side shaft portion 55a has a ball screw shaft portion 76 in an axially intermediate portion, which is a portion located on one axial side of the assist-side female threaded hole 58. The ball screw shaft portion 76 has a spiral male ball screw groove on its outer circumferential surface for engaging a plurality of balls 77.

[0111] In this example, the steering-side rack guide 24a has the same configuration as the assist-side rack guide 37 (see FIG. 6) of the first example. That is, in this example, the steering-side rack guide 24a has a pressing portion that elastically presses the outer peripheral surface of the rack shaft 11a toward the steering-side pinion shaft 10 and is in rolling contact with the outer peripheral surface.

[0112] The structure of this example includes a rack bushing 53 (see FIG. 7) having the same configuration as the first example, and the rack bushing 53 is fitted into the housing 7a near an opening on one axial side thereof. In this state, the rack bushing 53 supports the outer circumferential surface of the rack shaft 11a with its inner circumferential surface to allow sliding in the axial direction, and effectively suppresses displacement of the rack shaft 11a in the tooth width direction of the steering-side rack 28a based on the engagement between a pair of bushing-side slide flats 64 and a pair of rack-side slide flats 59.

[0113] The structure of this example further includes a cylindrical rack bushing 53a, which is fitted into the housing 7a near the opening on the other axial side thereof. In this state, the rack bushing 53a supports the outer circumferential surface of the rack shaft 11a with its inner circumferential surface so as to be slidable in the axial direction.

[0114] The structure of this example includes a cylindrical ball nut 78 that is disposed around a ball screw shaft portion 76. The ball nut 78 has a spiral female ball screw groove on its inner peripheral surface for engaging with a plurality of balls 77. The ball nut 78 engages with the ball screw shaft portion 76 via a plurality of balls 77 that are disposed between the female ball screw groove and a male ball screw groove provided on the outer peripheral surface of the ball screw shaft portion 76. In this example, the ball nut 78 can be rotated by an electric motor 39 that is supported by the housing 7a.

[0115] In this example as well, when the driver rotates the steering wheel 2, the electric motor 39 is controlled and driven based on the output signal of the torque sensor 40. As a result, the driving torque generated by the electric motor 39 is applied as an assist driving force to the ball screw shaft 76 via the ball nut 78 and the plurality of balls 77. As a result, the steering force required for the driver to rotate the steering wheel 2 is reduced.

[0116] In the electric power steering device 1a of this example having the above-described configuration, the face width of the steering-side rack 28a can be increased without increasing the weight of the rack shaft 11a. Also, the steering-side rack 28a has rack-side slide flat surfaces 59 at both ends in the face width direction, which extend in the axial direction and whose axial ends radially overlap the steering-side female threaded hole 57, and it is easy to ensure a sufficient wall thickness around the steering-side female threaded hole 57. The other configurations, functions, and effects are the same as those of the first example.

[0117] [Example 3] A third embodiment of the present invention will be described with reference to FIG.

[0118] The steering device of this example is a pinion-assist (single-pinion) electric power steering device 1b. In this example, with respect to the axial direction of the rack shaft 11b, one side corresponds to the first side, and the other side corresponds to the second side.

[0119] In this example, one axial half of the rack shaft 11b is configured with the steering-side shaft portion 54a as in Example 2, and the other axial half of the rack shaft 11b is configured with an assist-side shaft portion 55b that has an assist-side female threaded hole 58 at the end on the other axial side and has a cylindrical outer peripheral surface over the entire axial length. In this example, the steering-side shaft portion 54a corresponds to the first shaft portion, and the assist-side shaft portion 55b corresponds to the second shaft portion.

[0120] The structure of this example includes a worm reducer 38a attached to the steering-side pinion shaft 10. In this example, the steering-side pinion shaft 10 can be rotated via the worm reducer 38a by an electric motor 39 supported by the housing 7b.

[0121] In this example as well, when the driver rotates the steering wheel 2, the electric motor 39 is controlled and driven based on the output signal of the torque sensor 40. As a result, the driving torque generated by the electric motor 39 is applied as an assist driving force to the steering-side pinion shaft 10 via the worm reduction gear 38a. As a result, the steering force required for the driver to rotate the steering wheel 2 is reduced. The other configurations and effects are the same as those of the first and second examples.

[0122] [Example 4] A fourth embodiment of the present invention will be described with reference to FIG.

[0123] This example is an example in which the present invention is applied to a column-assist type electric power steering device 1c. Note that the column-assist type refers to an electric power steering device in which an assist driving force is applied directly to the steering shaft 3 using an electric motor connected to the steering column 4. In this example, one side of the rack shaft 11b in the axial direction corresponds to the first side, and the other side corresponds to the second side.

[0124] In this example, the rack shaft 11b has the same configuration as in the third example.

[0125] The structure of this example includes an electric assist device 79 fixed to the front end of the steering column 4. The electric assist device 79 includes a torque sensor, an electric motor, and a worm reduction gear.

[0126] In this example, when the driver rotates the steering wheel 2, the torque sensor in the electrically powered assist device 79 detects the direction and magnitude of the torque applied from the steering wheel 2 to the steering shaft 3. The electric motor is controlled and driven based on an output signal related to the torque detected by the torque sensor. As a result, the drive torque generated by the electric motor is transmitted as an assist drive force to the steering shaft 3 via the worm reduction gear. That is, in this example, the assist drive force from the electric motor is transmitted to the steering-side pinion shaft 10 via the steering shaft 3, universal joint 5a, intermediate shaft 6, and universal joint 5b. As a result, the steering force required for the driver to rotate the steering wheel 2 is reduced. The other configurations, functions, and effects are the same as those of the first and third examples.

[0127] The present invention can be implemented by appropriately combining the configurations of the above-described embodiments within the scope of not causing any contradiction. [Explanation of symbols]

[0128] 1, 1a, 1b, 1c Electric power steering device 2 steering wheels 3 Steering shaft 4 Steering column 5a, 5b universal joint 6 Intermediate shaft 7, 7a Housing 8 Steering mechanism 9 Assist mechanism 10 Steering side pinion shaft 11, 11a, 11b rack shaft 12 steering wheel 13 Assist side pinion shaft 14 Rack storage area 15 Steering side pinion housing 16 Assist side pinion housing 17 Steering side guide housing 18 Assist side guide housing 19 Gear housing 20a, 20b Mounting parts 21 Worm housing 22 Wheel housing 23 Mounting flange 24, 24a Steering side rack guide 25 Steering side pinion 26a, 26b bearings 27 tie rod 28, 28a Steering rack 29 Assist side rack 30 spacer 31 Spherical joint 32 Male thread 33 Pad 34 Elastic member 35 Pressing surface 36 Steering side cap 37 Assist side rack guide 38, 38a Worm reducer 39 Electric Motor 40 Torque sensor 41 Assist side pinion 42a, 42b bearings 43 Laura 44 Holder 45-pin 46 Rolling bearings 47 Elastic member 48 Assist side cap 49 Warm 50 worm wheel 51 Cap 52 Cap 53, 53a Rack bush 54, 54a Steering side shaft 55, 55a, 55b Assist side shaft 56 Connection 57 Steering side female thread hole 58 Assist side female thread hole 59 Rack side slide plane 60 Overhanging surface part 61 Flat surface part 62 Base material 63 Base material 64 Bush side slide plane 65 Abutment surface 66a, 66b Stopper surface 67 Mold 68 First Punch 69 Second Punch 70 Intermediate material 71 Slide plane forming section 72 Cavity 73 Partial cylindrical surface forming part 74 Flat surface forming part 75 Overhanging surface forming part 76 Ball screw shaft 77 balls 78 Ball nut 79 Electric assist device 100 Electric power steering device 101 Rack axis 102 Steering side pinion shaft 103 Assist side pinion shaft 104 Steering rack 105 Assist side rack 106 Spherical joint 107 tie rod 108 Steering side female thread hole 109 Assist side female thread hole 110 Male thread 111 Housing 112 Steering side pinion 113 Assist side pinion 114 Steering side rack guide 115 Assist side rack guide 116 Luck Bush 117 Rack side slide plane 118 Bush side slide plane 119 Base material 120 Flat surface section

Claims

1. a first shaft portion having a target rack on a first side in the axial direction, and a second shaft portion on a second side in the axial direction; the first shaft portion has: a first female threaded hole provided at an end on a first side in the axial direction and opening only at an end face on the first side in the axial direction; the target rack provided in a circumferential part of a portion located on the second side in the axial direction from the first female threaded hole; rack-side slide planes provided on both ends of the outer peripheral surface in the tooth width direction of the target rack, extending in the axial direction and having ends on the first side in the axial direction overlapping with the first female threaded hole in the radial direction; and a protruding surface portion provided at the end on the first side in the axial direction and provided in a portion of the outer peripheral surface in the axial range including at least the axial range in which the first female threaded hole is present, which is in the same phase as the target rack in the circumferential direction and protruding radially outward from the target rack, the second shaft portion is provided at an end portion on a second side in the axial direction, and has a second female threaded hole that opens only to an end surface on the second side in the axial direction and is arranged coaxially with the first female threaded hole; Steering rack shaft.

2. the target rack is an assist-side rack, The second shaft portion has a steering-side rack provided at a circumferential part of a portion located on a first side in the axial direction relative to the second female threaded hole. The rack shaft for a steering device according to claim 1.

3. the target rack is a steering-side rack, the second shaft portion has a ball screw shaft portion provided at a portion located on a first side in the axial direction relative to the second female screw hole, The rack shaft for a steering device according to claim 1.

4. 4. The rack shaft for a steering device according to claim 1, wherein a width dimension of the protruding surface portion in the tooth width direction of the target rack is equal to or less than a width dimension of the first shaft portion in the tooth width direction of an axial range in which the protruding surface portion exists.

5. 5. The steering device rack shaft according to claim 1, further comprising a connecting portion that connects an end portion of the first shaft portion on a second side in the axial direction and an end portion of the second shaft portion on a first side in the axial direction.

6. A method for manufacturing a rack shaft for a steering device according to any one of claims 1 to 5, a step of setting a round bar-shaped base material in a mold having a slide plane forming portion for forming the rack side slide plane; a step of obtaining an intermediate material having the rack-side slide plane, the flat surface portion, and the protruding surface portion by pressing a first punch, which is placed in a position where the base material is sandwiched between the first punch and the mold, the dimension in the axial direction of the base material being shorter than the mold, and the flat surface forming portion for forming a flat surface portion having a width dimension greater than the diameter of the base material, where the target rack will be formed, and a second punch, which is placed in a position where the base material is sandwiched between the first punch and the mold, the dimension in the axial direction of the base material being shorter than the mold, and the protruding surface forming portion for forming the protruding surface portion, toward the mold and the base material; forming the target rack on the flat surface portion of the intermediate material; and forming the first female screw hole at an end portion of the intermediate material on a first side in the axial direction. Manufacturing method of a rack shaft for a steering device.

7. a rack shaft including a steering-side rack and an assist-side rack; a steering-side pinion shaft that meshes with the steering-side rack and is rotationally driven by the rotation of a steering wheel; an assist-side pinion shaft that meshes with the assist-side rack and is rotationally driven by an electric motor; a steering-side rack guide disposed at a position sandwiching the rack shaft between itself and the steering-side pinion shaft, the steering-side rack guide having a pressing portion that elastically presses an outer peripheral surface of the rack shaft toward the steering-side pinion shaft and is in sliding contact with the outer peripheral surface; an assist-side rack guide disposed at a position sandwiching the rack shaft between itself and the assist-side pinion shaft, the assist-side rack guide having a pressing portion that elastically presses an outer peripheral surface of the rack shaft toward the assist-side pinion shaft and is in rolling contact with the outer peripheral surface; a rack bushing that supports an outer peripheral surface of the rack shaft so as to be slidable in the axial direction; a housing in which the rack shaft, the steering side pinion shaft, the assist side pinion shaft, the steering side rack guide, the assist side rack guide, and the rack bush are assembled, The rack shaft is a rack shaft for a steering apparatus according to claim 2 or claim 4 or 5 which relies on claim 2, the rack bush is disposed on a first side of the assist-side pinion shaft in an axial direction of the rack shaft, and has a bush-side slide flat surface that is in sliding contact with the rack-side slide flat surface of the rack shaft. Steering device.

8. a rack shaft including a steering-side rack and a ball screw shaft portion; a steering-side pinion shaft that meshes with the steering-side rack and is rotationally driven by the rotation of a steering wheel; a ball nut that engages with the ball screw shaft portion via a plurality of balls and is rotationally driven by an electric motor; a steering-side rack guide disposed at a position sandwiching the rack shaft between itself and the steering-side pinion shaft, the steering-side rack guide having a pressing portion that elastically presses an outer peripheral surface of the rack shaft toward the steering-side pinion shaft and is in rolling contact with the outer peripheral surface; a rack bushing that supports an outer peripheral surface of the rack shaft so as to be slidable in the axial direction; a housing in which the rack shaft, the steering side pinion shaft, the ball nut, the steering side rack guide, and the rack bush are assembled, The rack shaft is a rack shaft for a steering apparatus according to claim 3, or claim 4 or 5 which relies on claim 3, the rack bush is disposed on a first side of the steering-side pinion shaft in an axial direction of the rack shaft, and has a bush-side slide flat surface that is in sliding contact with the rack-side slide flat surface of the rack shaft. Steering device.

9. a rack shaft having a steering-side rack that is a target rack; a steering-side pinion shaft that is engaged with the steering-side rack, is rotationally driven by the rotation of the steering wheel, and receives an assist driving force from an electric motor; a steering-side rack guide disposed at a position sandwiching the rack shaft between itself and the steering-side pinion shaft, the steering-side rack guide having a pressing portion that elastically presses an outer peripheral surface of the rack shaft toward the steering-side pinion shaft and is in rolling contact with the outer peripheral surface; a rack bushing that supports an outer peripheral surface of the rack shaft so as to be slidable in the axial direction; a housing in which the rack shaft, the steering side pinion shaft, the steering side rack guide, and the rack bush are assembled, The rack shaft is a rack shaft for a steering apparatus according to claim 1 or claim 4 or 5 which relies on claim 1, the rack bush is disposed on a first side of the steering-side pinion shaft in an axial direction of the rack shaft, and has a bush-side slide flat surface that is in sliding contact with the rack-side slide flat surface of the rack shaft. Steering device.

10. 10. The steering device according to claim 7, wherein the rack-side slide plane exists only in a range in which the rack shaft makes sliding contact with the bush-side slide plane of the rack bush when the rack shaft is moved from one end to the other end of an axially movable range.

Images