Electric power steering device

Abstract

To provide an electric power steering device that is able to prevent emission of abnormal noise and is able to prevent an increase in the size of a rack housing.SOLUTION: An electric power steering device includes: a rack bar 30 having a rack tooth forming portion 31; a rack housing 10 configured to store the rack bar 30; and a pressing portion 60 configured to apply an urging force to the rack bar 30. In a rack-teeth forming portion 31, a maximum width in a direction orthogonal to a longitudinal direction of the rack bar 30 is larger than a width in a direction orthogonal to the maximum width. The rack housing 10 has a large-diameter housing portion 11 having a large-diameter through-hole 12 and a small-diameter housing portion 21 having a small-diameter through-hole 22. In the large-diameter through-hole 12, a maximum width in the same direction as a direction of the maximum width of the rack-teeth forming portion 31 is larger than a width in a direction orthogonal to the maximum width of the large-diameter through-hole 12. An amount of protrusion of the pressing portion 60, from an inner circumferential surface of the large-diameter housing portion 11 is substantially equal to or less than a gap between an inner circumferential surface of the small-diameter housing portion 21 and the rack bar 30.SELECTED DRAWING: Figure 13

Description

[Technical Field]

[0001] The present disclosure relates to an electric power steering device. [Background technology]

[0002] An electric power steering device has a pinion gear that rotates due to the rotational torque generated when the steering wheel is steered, a rack bar with rack teeth that mesh with the pinion gear, and an electric motor that generates an assist force to supplement the steering force. For example, the steering device described in Patent Document 1 has a steering mechanism that steers the steered wheels based on the driver's operation of the steering wheel, and an assist mechanism that assists the driver's steering operation, and the assist mechanism has a motor that is a source of the assist force. Also, the steering device described in Patent Document 2 has a steering mechanism unit that has a steering-side pinion shaft and a rack shaft, and an assist mechanism unit that has an electric motor, and the assist mechanism unit transmits the drive torque generated by the electric motor to the rack shaft as a steering assist force.

[0003] Furthermore, electric power steering devices are equipped with a mechanism for pressing the rack against the pinion. For example, the steering device described in Patent Document 1 is provided with a rack guide that uses the elastic force of a biasing member to bias the rack shaft toward the pinion shaft. Furthermore, the steering device described in Patent Document 2 has a steering-side rack guide that includes a pad and an elastic member, and the steering-side rack guide presses the pad toward the rack shaft with the elastic member, thereby pressing the rack shaft toward the steering-side pinion shaft. In this way, the electric power steering device maintains meshing between the rack teeth and the pinion teeth by pressing the rack against the pinion with the rack guide. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-132438 [Patent Document 2] Japanese Patent Application Publication No. 2022-134190 Summary of the Invention [Problem to be solved by the invention]

[0005] Here, in order to enable a rack bar having rack teeth that mesh with a pinion to bear a large force between the rack bar and the pinion, the portion of the rack bar where the rack teeth are arranged may be made into an irregular shape to ensure a sufficient tooth width for the rack teeth.For example, in the steering device described in Patent Document 1, the cross-sectional contour shape of the assist-side rack portion is made into a substantially D-shape in order to improve the strength of the assist-side rack teeth, and the assist-side rack teeth are provided on a straight portion of the front side surface.

[0006] Furthermore, in some conventional electric power steering devices, when the portion of the rack bar where the rack teeth are arranged is given an irregular shape to ensure the tooth width of the rack teeth, the portion where the rack teeth are arranged is formed so that it is larger than the diameter of the rack bar. In this way, when the portion of the rack bar where the rack teeth are arranged is formed to be an irregular shape, the rack housing that stores the rack bar needs to have an inner diameter of a portion that stores the irregularly shaped portion of the rack bar that is larger than the inner diameter of the portion of the rack bar other than the irregularly shaped portion, i.e., the portion that stores the round bar-shaped portion.

[0007] In this way, when the inner diameter of the portion of the rack housing that stores the irregularly shaped portion of the rack bar is increased, the distance between the inner circumferential surface of the rack housing and the portion of the rack bar that abuts against a pressing member such as a rack guide tends to increase at the irregularly shaped portion of the rack bar. When the distance between the inner circumferential surface of the rack housing and the rack bar is large, the pressing member abuts against the rack bar with a large protrusion from the inner circumferential surface of the rack housing, and applies a pressing force to the rack bar.

[0008] However, if the pressing member protrudes significantly from the inner peripheral surface of the rack housing, the pressing member is more likely to tilt. In other words, if the pressing member protrudes significantly from the inner peripheral surface of the rack housing, the proportion of the pressing member supported by the rack housing relative to the overall size of the pressing member becomes relatively small. For example, when the rack bar performs linear motion, the pressing member is more likely to tilt due to the movement of the rack bar. If the pressing member tilts, it becomes difficult for the pressing member to appropriately apply a pressing force to the rack bar, so the pressing force pressing the rack bar against the pinion decreases, and backlash at the meshing portion between the rack bar and pinion increases. If backlash at the meshing portion between the rack bar and pinion increases, abnormal noise is more likely to occur from the meshing portion.

[0009] Furthermore, because the rack teeth formed on the rack bar are formed at an angle relative to the direction perpendicular to the axial direction of the rack shaft, when the steering wheel is steered, not only a force in the axial direction of the rack bar but also a force perpendicular to the axial direction acts on the rack bar, causing the rack bar to move parallel to the direction perpendicular to the axial direction. Therefore, if the pressing member protrudes significantly from the inner peripheral surface of the rack housing, the pressing member is also tilted in the direction perpendicular to the axial direction of the rack bar due to the movement of the rack bar in the direction perpendicular to the axial direction when the steering wheel is steered. Furthermore, when the steering wheel is steered, the forces perpendicular to the axial direction of the rack bar act in opposite directions depending on the steering direction of the steering wheel. Therefore, when the steering direction is changed, the direction of movement of the rack bar in the axial direction changes, and the direction of movement of the rack bar in the direction perpendicular to the axial direction of the rack bar also changes, causing the pressing member to change its tilt direction in the direction perpendicular to the axial direction and also its tilt direction in the direction perpendicular to the axial direction.

[0010] At this time, the pressing member changes its tilt direction while being pressed against the rack bar, which can cause a so-called stick-lip phenomenon at the contact surface between the pressing member and the rack bar, resulting in abnormal noise. When the pressing member contacts the rack bar while tilting, the stick-lip phenomenon can continue to occur even while the rack bar is moving linearly in the axial direction, resulting in continuous abnormal noise. Furthermore, when the pressing member tilts, it becomes more likely to come into contact with the portion of the rack housing that holds the pressing member, which can result in a collision noise when the pressing member comes into contact with the rack housing.

[0011] Furthermore, if the inner diameter of the portion of the rack housing that accommodates the irregularly shaped portion of the rack bar is increased, the outer diameter of the rack housing also increases accordingly, which may result in the rack housing becoming larger.For these reasons, in an electric power steering device having a structure in which the rack bar is pressed against the pinion by a pressing member, if the portion of the rack bar where the rack teeth are arranged is made irregularly shaped, there is room for improvement in terms of the likelihood of abnormal noise being generated due to the inclination of the pressing member, and the likelihood of the rack housing becoming larger by increasing the inner diameter of the rack housing.

[0012] The present disclosure has been made in view of the above, and aims to provide an electric power steering device that can suppress the generation of abnormal noise and prevent the rack housing from becoming larger. [Means for solving the problem]

[0013] The electric power steering device of the present disclosure includes a rack bar having a rack tooth forming portion where rack teeth that mesh with a pinion gear are arranged, a cylindrical rack housing that stores the rack bar inside its inner circumferential surface, a pressing portion that is arranged on the rack housing and presses the rack teeth against the pinion gear by applying a biasing force to the rack bar, and a steering assist device that applies a steering assist force to the pinion gear or the rack bar, wherein the rack tooth forming portion has a back portion located on the back side of the rack teeth that is formed in an arc shape when viewed in the longitudinal direction of the rack bar, and the maximum width in a direction perpendicular to the longitudinal direction of the rack bar at the rack tooth forming portion is the rack housing has a large diameter housing portion having a large diameter through hole that stores the rack tooth forming portion of the rack bar, and a small diameter housing portion having a small diameter through hole that stores a portion of the rack bar different from the rack tooth forming portion, and the large diameter through hole has a maximum width in the same direction as the direction in which the rack tooth forming portion has its maximum width, at the portion that stores the rack tooth forming portion, that is larger than the width of the large diameter through hole in the direction orthogonal to the maximum width, and the amount of protrusion of the pressing portion from the inner peripheral surface of the large diameter housing portion is approximately the same as or less than the gap between the inner peripheral surface of the small diameter housing portion and the rack bar.

[0014] According to this configuration, the maximum width of the large-diameter through-hole of the rack housing in the direction corresponding to the maximum width of the rack-tooth-forming portion is greater than the width of the large-diameter through-hole in the direction perpendicular to the maximum width. Therefore, the amount of protrusion of the pressing portion from the inner circumferential surface of the large-diameter housing portion is equal to or less than the gap between the inner circumferential surface of the small-diameter housing portion and the rack bar. This prevents the pressing portion from being tilted by being dragged by the rack bar during linear motion of the rack bar, and allows the pressing portion to press the rack teeth of the rack bar toward the pinion gear. This reduces backlash at the meshing portion between the rack teeth and the pinion gear, thereby suppressing noise caused by backlash, noise due to stick-lip, and noise caused by the pressing portion colliding with the hole in the rack housing where the pressing portion is located. Furthermore, the width of the large-diameter through-hole in the large-diameter housing portion of the rack housing in the direction perpendicular to the maximum width of the large-diameter through-hole is smaller than the maximum width of the large-diameter through-hole. This allows the size of the portion of the rack housing that accommodates the rack-tooth-forming portion of the rack bar to be reduced, thereby enabling the rack housing to be made more compact. As a result, the generation of abnormal noise can be suppressed and the size of the rack housing can be prevented from increasing.

[0015] In a preferred embodiment, the rack teeth include first rack teeth and second rack teeth arranged at positions different from the first rack teeth in the longitudinal direction, the second rack teeth are arranged on the rack tooth forming portion, the rack bar has a small diameter portion having the first rack teeth and a large diameter portion having the rack tooth forming portion and a diameter larger than that of the small diameter portion, the small diameter housing portion houses the small diameter portion of the rack bar, the large diameter housing portion houses the large diameter portion of the rack bar, and the pinion gear is a first pinion gear that meshes with the first rack teeth. and a second pinion gear that meshes with the second rack teeth, the pressing portion having a first pressing portion disposed in the small diameter housing portion and applying a biasing force to the rack bar to press the first rack teeth against the first pinion gear, and a second pressing portion disposed in the large diameter housing portion and applying a biasing force to the rack bar to press the second rack teeth against the second pinion gear, and the amount of protrusion of the second pressing portion from the inner circumferential surface of the large diameter housing portion is equal to or less than the amount of protrusion of the first pressing portion from the inner circumferential surface of the small diameter housing portion.

[0016] According to this configuration, the amount of protrusion of the second pressing portion from the inner circumferential surface of the large-diameter housing portion is approximately the same as or less than the amount of protrusion of the first pressing portion from the inner circumferential surface of the small-diameter housing portion. Therefore, when the rack bar moves linearly, the second pressing portion is not pulled by the rack bar and tilted, and the second pressing portion can press the second rack teeth toward the second pinion gear. This reduces backlash at the meshing portion between the second rack teeth and the second pinion gear, thereby suppressing the generation of abnormal noise due to backlash. Furthermore, because tilting of the second pressing portion can be suppressed, the generation of abnormal noise due to the stick-lip phenomenon and the generation of abnormal noise due to the second pressing portion colliding with the hole in the rack housing where the second pressing portion is located can be suppressed. As a result, the generation of abnormal noise can be suppressed.

[0017] In a preferred form, the large diameter through hole has a substantially elliptical shape when viewed in the longitudinal direction of the rack housing, and the rack bar is stored inside the rack housing with the direction in which the rack tooth forming portion has the greatest width aligned with the major axis of the elliptical shape of the large diameter through hole.

[0018] According to this configuration, by forming the large-diameter through-hole of the large-diameter housing portion in a substantially elliptical shape and arranging the pressing portion on an extension of the minor axis of the elliptical shape of the large-diameter through-hole, it is possible to reduce the distance between the rack bar and the vicinity of the position where the pressing portion is located on the inner circumferential surface of the large-diameter housing portion. This reduces the amount by which the pressing portion protrudes from the inner circumferential surface of the large-diameter housing portion, thereby preventing the pressing portion from tilting. As a result, it is possible to reduce the generation of abnormal noise caused by the pressing portion tilting.

[0019] In a preferred embodiment, the rack tooth forming portion has protruding portions on both sides in the direction of the maximum width of the rack tooth forming portion that protrude in the direction in which the maximum width of the rack tooth forming portion increases, and the large diameter through hole has an arc portion on the inner circumferential surface of the large diameter through hole that has an arc shape when viewed in the longitudinal direction of the rack bar, and protruding portion storage portions located on both sides in the same direction as the direction of the maximum width of the rack tooth forming portion that store the protruding portions, and the protruding portion of the rack bar is stored in the protruding portion storage portion of the large diameter through hole, and the back portion of the rack tooth forming portion is stored inside the rack housing in an orientation facing the arc portion of the large diameter through hole.

[0020] According to this configuration, the large-diameter through-hole of the large-diameter housing portion has an arc portion and a protrusion-receiving portion, allowing the inner circumferential surface of the large-diameter housing portion to conform to the shape of the surface of the rack bar. This reduces the gap between the inner circumferential surface of the large-diameter housing portion and the rack bar, thereby reducing the amount of protrusion of the pressing portion from the inner circumferential surface of the large-diameter housing portion. This allows the amount of protrusion of the pressing portion to be the same as or smaller than the gap between the inner circumferential surface of the small-diameter housing portion and the rack bar. Therefore, when the rack bar moves linearly, the pressing member is not pulled by the rack bar and tilted, and the pressing portion can press the rack teeth toward the pinion gear. This reduces the generation of abnormal noise caused by tilting of the pressing portion. Furthermore, by conforming the shape of the inner circumferential surface of the large-diameter housing portion to the shape of the rack-tooth-forming portion of the rack bar, the outer shape of the large-diameter housing portion can also be conformed to the shape of the rack bar, thereby enabling the large-diameter housing portion to be made smaller. As a result, the generation of abnormal noise can be reduced and the rack housing can be prevented from becoming larger.

[0021] In a preferred embodiment, bolt holes for attaching ball joints to which tie rods are connected are arranged at both longitudinal ends of the rack bar, the rack bar is arranged at a position where the central axis of the bolt hole arranged in the small diameter portion coincides with the central axis of the small diameter through hole, and the large diameter portion of the rack bar is connected to the small diameter portion at a position where the central axis is shifted toward the side where the second pressing portion is located with respect to the central axis of the bolt hole arranged in the small diameter portion.

[0022] According to this configuration, the large-diameter portion of the rack bar is connected to the small-diameter portion at a position where its central axis is offset toward the second pressing portion relative to the central axis of the bolt hole in the small-diameter portion. This reduces the gap between the rack bar and the portion of the inner circumferential surface of the large-diameter housing portion where the second pressing portion is located. This reduces the amount of protrusion of the second pressing portion from the inner circumferential surface of the large-diameter housing portion, making the amount of protrusion of the second pressing portion equal to or less than the amount of protrusion of the first pressing portion. Therefore, when the rack bar moves linearly, the second pressing portion is not pulled by the rack bar and tilted, and the second pressing portion can press the second rack teeth toward the second pinion gear. As a result, noise caused by tilting of the second pressing portion can be suppressed.

[0023] In a preferred embodiment, the large diameter housing portion is connected to the small diameter housing portion at a position where the central axis of the large diameter through hole in the large diameter housing portion is shifted toward the side where the second pinion gear is located relative to the central axis of the small diameter through hole in the small diameter housing portion.

[0024] According to this configuration, the large-diameter housing portion of the rack housing is connected to the small-diameter housing portion at a position where the central axis of the large-diameter housing portion is offset toward the side where the second pinion gear is located relative to the central axis of the small-diameter housing portion. This reduces the gap between the rack bar and the portion of the inner circumferential surface of the large-diameter housing portion where the second pressing portion is located. This reduces the amount of protrusion of the second pressing portion from the inner circumferential surface of the large-diameter housing portion, making the amount of protrusion of the second pressing portion equal to or less than the amount of protrusion of the first pressing portion. Therefore, when the rack bar moves linearly, the second pressing portion is not pulled by the rack bar and tilted, and the second pressing portion can press the second rack teeth toward the second pinion gear. As a result, noise caused by tilting of the second pressing portion can be suppressed.

[0025] In a preferred embodiment, the first rack teeth are formed within the range of a projected shape of the small diameter portion when the small diameter portion is viewed in a direction along the central axis.

[0026] According to this configuration, the first rack teeth of the rack bar are formed within the projected shape of the small-diameter portion, thereby minimizing the inner diameter of the small-diameter housing portion of the rack housing that houses the small-diameter portion. This reduces the protrusion amount of the first pressing portion, which is disposed in the small-diameter housing portion and presses the first rack teeth against the first pinion gear by abutting against the small-diameter portion of the rack bar. Therefore, when the rack bar moves linearly, the pressing member of the first pressing portion can press the first rack teeth of the rack bar toward the first pinion gear without being dragged by the rack bar and tilting. Therefore, the pressing force applied from the first pressing portion to the rack bar can reduce backlash at the meshing portion between the first rack teeth and the first pinion gear, thereby suppressing the generation of abnormal noise due to backlash. Furthermore, suppressing tilting of the pressing member of the first pressing portion can suppress the generation of abnormal noise due to the stick-lip phenomenon and the generation of abnormal noise due to the first pressing portion colliding with the hole in the rack housing that holds the first pressing portion. As a result, the generation of abnormal noise caused by backlash can be suppressed.

[0027] In a preferred embodiment, the rack tooth forming portion has protruding portions on both sides in the direction of the maximum width of the rack tooth forming portion that protrude in the direction in which the maximum width of the rack tooth forming portion increases, and the protruding portions have chamfers at both ends in a direction perpendicular to the longitudinal direction of the large diameter portion on the side where the back portion is located.

[0028] According to this configuration, the protruding portion of the rack tooth-forming portion of the rack bar has chamfered ends on the side where the rear portion is located. Therefore, by offsetting the large-diameter portion and small-diameter portion of the rack bar when connecting the rack bar or the large-diameter housing portion and small-diameter housing portion of the rack housing, the protruding portion of the rack tooth-forming portion is less likely to abut against the inner circumferential surface of the large-diameter housing portion when the large-diameter portion of the rack bar approaches the second pressing portion. Therefore, the large-diameter portion of the rack bar can be connected to the small-diameter portion at a position offset from the small-diameter portion toward the side where the second pressing portion is located, or the large-diameter housing portion of the rack housing can be connected to the small-diameter housing portion at a position offset from the small-diameter housing portion in a direction that allows the large-diameter portion of the rack bar to approach the second pressing portion, without the protruding portion of the rack tooth-forming portion abutting against the inner circumferential surface of the large-diameter housing portion. This reduces the gap between the rear portion of the rack tooth-forming portion of the rack bar and the inner circumferential surface of the large-diameter housing portion, thereby reducing the amount of protrusion of the second pressing portion from the inner circumferential surface of the large-diameter housing portion. Therefore, when the rack bar moves linearly, the second pressing portion is not pulled by the rack bar and does not tilt, and the second pressing portion can press the second rack teeth toward the second pinion gear, which can suppress the generation of abnormal noise caused by the second pressing portion tilting.

[0029] In a preferred embodiment, the inner surface of the large diameter housing portion has an expanding diameter portion in which the size of the opening area of ​​the inner surface when viewed in the longitudinal direction of the rack housing increases toward a predetermined direction in the longitudinal direction of the rack housing, and in a cross section taken along the longitudinal direction of the rack housing, a position in the circumferential direction of the rack housing where the second pressing portion is located, a second line of the inner surface that passes through a position different from the position where the second pressing portion is located is inclined relative to a first line of the inner surface that passes through the position where the second pressing portion is located and extends along the longitudinal direction of the rack housing.

[0030] According to this configuration, the inner circumferential surface of the large-diameter housing portion has an expanded-diameter portion in which a first line on the inner circumferential surface passing through the position where the second pressing portion is disposed extends along the longitudinal direction of the rack housing. Therefore, the position on the inner circumferential surface where the second pressing portion is disposed can be aligned along the longitudinal direction of the rack housing without cutting the inner circumferential surface. This reduces the distance between the inner circumferential surface of the rack housing and the rack bar at the position where the second pressing portion is disposed, thereby reducing the amount of protrusion of the second pressing portion from the inner circumferential surface of the rack housing. Furthermore, the expanded-diameter portion has an inclined second line on the inner circumferential surface that passes through a position different from the position where the second pressing portion is disposed in the same cross section of the rack housing as the cross section of the rack housing where the first line appears. This ensures a draft angle for the core when manufacturing the rack housing by casting. This makes it easier to remove the core used to form the expanded-diameter portion during casting of the rack housing, facilitating the manufacturing of the rack housing by casting. As a result, manufacturing costs can be reduced and the generation of abnormal noise can be suppressed. [Effects of the Invention]

[0031] The electric power steering device according to the present disclosure has the effect of suppressing the generation of abnormal noise and suppressing an increase in the size of the rack housing. [Brief explanation of the drawings]

[0032] [Figure 1] FIG. 1 is a schematic diagram for explaining an electric power steering device according to a first embodiment. [Figure 2] FIG. 2 is an explanatory diagram showing the configuration of the steering gear and its surroundings. [Figure 3] FIG. 3 is a plan view of the rack bar shown in FIG. [Figure 4] FIG. 4 is a perspective view of the rack bar shown in FIG. [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 the line BB in FIG. [Figure 7] 7 is a perspective view of the rack bar including the cross section BB of FIG. 3. FIG. [Figure 8] FIG. 8 is a cross-sectional view of a rack housing and a rack bar of an electric power steering device, taken at a position including a cross section of an assist rack tooth. [Figure 9] FIG. 9 is a cross-sectional view of a rack housing and a rack bar of an electric power steering device, taken at a position including a cross section of the steering rack teeth. [Figure 10] FIG. 10 is a detailed view of part C in FIG. [Figure 11] FIG. 11 is a detailed view of part D in FIG. [Figure 12] FIG. 12 is a schematic cross-sectional view of the rack housing and the rack bar in the first embodiment. [Figure 13] FIG. 13 is a view taken along the arrow EE in FIG. [Figure 14] FIG. 14 is a schematic diagram showing a case where the large diameter through hole of the large diameter housing portion is formed in a substantially circular shape. [Figure 15] FIG. 15 is a view seen from the direction of the arrow FF in FIG. [Figure 16] FIG. 16 is a schematic cross-sectional view of a rack housing and a rack bar of an electric power steering device according to the second embodiment. [Figure 17] FIG. 17 is a view taken along the arrows GG in FIG. [Figure 18] FIG. 18 is a cross-sectional schematic view of a rack housing and a rack bar of an electric power steering device according to a third embodiment. [Figure 19] FIG. 19 is a view taken along the arrow JJ in FIG. [Figure 20] FIG. 20 is a cross-sectional view of a rack tooth forming portion of a rack bar provided in an electric power steering device according to a third embodiment. [Figure 21] FIG. 21 is a cross-sectional schematic view of a rack housing and a rack bar of an electric power steering device according to a fourth embodiment. [Figure 22]FIG. 22 is a view taken along the arrow KK in FIG. [Figure 23] FIG. 23 is a cross-sectional view of a rack housing and a rack bar that an electric power steering device according to a fifth embodiment has, and is a schematic cross-sectional view of the rack housing at a position including the second pressing portion and the second pinion gear. [Figure 24] FIG. 24 is a cross-sectional view of the rack housing at a position different from that in FIG. 23, and is a schematic cross-sectional view of the rack housing at a position including the first pressing portion and the first pinion gear. [Figure 25] FIG. 25 is a schematic cross-sectional view of a rack housing according to the fifth embodiment. [Figure 26] FIG. 26 is a schematic cross-sectional view of the rack housing shown in FIG. 25, showing a state in which the rack bar is stored in the rack housing. [Figure 27] FIG. 27 is a cross-sectional view taken along line MM of FIG. [Figure 28] FIG. 28 is a cross-sectional view taken along line NN of FIG. [Figure 29] FIG. 29 is a cross-sectional view taken along the line RR in FIG. [Figure 30] FIG. 30 is a cross-sectional view taken along line SS in FIG. [Figure 31] FIG. 31 is a schematic diagram of an electric power steering device according to a sixth embodiment. [Figure 32] FIG. 32 is a schematic cross-sectional view of a rack housing and a rack bar in the sixth embodiment. [Figure 33] FIG. 33 is a view taken along the arrow TT in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0033] The present disclosure will be described in detail below with reference to the drawings. Note that the present disclosure is not limited to the following modes for carrying out the invention (hereinafter referred to as embodiments). Furthermore, the components in the following embodiments include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the components disclosed in the following embodiments can be combined as appropriate.

[0034] [First embodiment] Fig. 1 is a schematic diagram for explaining an electric power steering device 80 according to a first embodiment. As shown in Fig. 1, the electric power steering device 80 includes, in the order in which a force applied by an operator is transmitted, a steering wheel 81, a steering shaft 82, a universal joint 84, an intermediate shaft 85, a universal joint 86, a stub shaft 87, a steering gear 90, and a tie rod 94. The electric power steering device 80 also includes a control device (hereinafter referred to as an ECU (Electronic Control Unit)) 100, a torque sensor 101, and an electric motor 102. A vehicle speed sensor 103 is provided in the vehicle and outputs a vehicle speed signal V to the ECU 100 via CAN (Controller Area Network) communication.

[0035] The steering shaft 82 is connected to the steering wheel 81 at one end and to a universal joint 84 at the other end.

[0036] Intermediate shaft 85 is connected at one end to universal joint 84 and at the other end to universal joint 86. Stub shaft 87 is connected at one end to universal joint 86 and at the other end to torque sensor 101. Torque sensor 101 is connected at one end to stub shaft 87 and at the other end to first pinion gear 92 of steering gear 90.

[0037] 2 is an explanatory diagram showing the configuration around the steering gear 90. The first pinion gear 92 is a shaft-shaped member having a gear 92a that meshes with the rack bar 30 formed on the end opposite to the side connected to the stub shaft 87, and the stub shaft 87 and the first pinion gear 92 are connected via a torsion bar (not shown). One end of the torsion bar is connected to the stub shaft 87 and the other end is connected to the first pinion gear 92, and the torsion bar transmits rotational torque between the stub shaft 87 and the first pinion gear 92.

[0038] Torque sensor 101 is a torque detection device that detects torque acting on a shaft connected to torque sensor 101, and detects rotational torque transmitted between stub shaft 87 and first pinion gear 92 via a torsion bar. In other words, stub shaft 87 and first pinion gear 92, which are connected via a torsion bar, are the shafts that are the detection targets when torque is detected by torque sensor 101.

[0039] The steering gear 90 includes a pinion gear 91 and a rack bar 30 on which rack teeth 35 that mesh with the pinion gear 91 are arranged. The rack teeth 35 include steering rack teeth 48 that are first rack teeth and assist rack teeth 43 that are second rack teeth. The pinion gear 91 includes a first pinion gear 92 that meshes with the steering rack teeth 48 and a second pinion gear 93 that meshes with the assist rack teeth 43. The first pinion gear 92 is connected to the stub shaft 87 via a torsion bar. The steering rack teeth 48 mesh with a gear 92a of the first pinion gear 92. The assist rack teeth 43 are arranged on the rack bar 30 at a position on the rack bar 30 that is different from the position at which the steering rack teeth 48 are arranged in the longitudinal direction of the rack bar 30. Therefore, the rack bar 30 meshes with the second pinion gear 93 at a position different from the position where the rack bar 30 meshes with the first pinion gear 92 .

[0040] An electric motor 102 is connected to the second pinion gear 93 via a worm reduction gear 95, and the second pinion gear 93 is rotated by a driving force transmitted from the electric motor 102. The electric motor 102 rotates the second pinion gear 93 via the worm reduction gear 95. The electric motor 102 is, for example, a brushless motor, but may also be a motor including brushes (sliders) and a commutator (commutator). The electric motor 102, the worm reduction gear 95, and the second pinion gear 93 constitute a steering assist device 110 that applies a steering assist force to the rack bar 30.

[0041] The steering gear 90 converts the rotational motion transmitted to the first pinion gear 92 and the second pinion gear 93 into linear motion by the rack bar 30 arranged inside the rack housing 10 (see FIG. 8). The electric power steering device 80 according to the first embodiment is of a dual pinion assist type in which the rack bar 30 performs linear motion by the rotational motion transmitted from the first pinion gear 92 and the second pinion gear 93. The tie rod 94 is connected to the rack bar 30. In other words, the electric power steering device 80 according to the first embodiment is a rack-and-pinion type electric power steering device 80.

[0042] The torque sensor 101 detects the steering force of the driver transmitted to the steering shaft 82 via the steering wheel 81 as a steering torque. The vehicle speed sensor 103 detects the traveling speed (vehicle speed) of the vehicle on which the electric power steering device 80 is installed. The electric motor 102, the torque sensor 101, and the vehicle speed sensor 103 are electrically connected to the ECU 100.

[0043] The ECU 100 controls the operation of the electric motor 102. The ECU 100 also acquires signals from a torque sensor 101 and a vehicle speed sensor 103. That is, the ECU 100 acquires a steering torque T from the torque sensor 101 and a vehicle speed signal V of the vehicle from the vehicle speed sensor 103. When an ignition switch 104 is in an on state, the ECU 100 is supplied with power from a power supply device (for example, an on-board battery) 105. The ECU 100 calculates an assist steering command value of an assist command based on the steering torque T and the vehicle speed signal V. The ECU 100 then adjusts the power value X to be supplied to the electric motor 102 based on the calculated assist steering command value. The ECU 100 acquires, as operation information Y, information on an induced voltage from the electric motor 102 or information output from a rotation detection device such as a resolver provided in the electric motor 102.

[0044] The steering force of the operator (driver) input to the steering wheel 81 is transmitted to the first pinion gear 92. The steering force transmitted to the first pinion gear 92 is transmitted to the tie rod 94 via the steering gear 90, displacing the wheels.

[0045] Furthermore, the steering force input by the operator to the steering wheel 81 is transmitted to a torque sensor 101 arranged in a steering force transmission path from the steering wheel 81 to the first pinion gear 92. At this time, the ECU 100 acquires the steering torque T from the torque sensor 101 and acquires a vehicle speed signal V from a vehicle speed sensor 103. Then, the ECU 100 controls the operation of the electric motor 102. The auxiliary steering torque generated by the electric motor 102 is transmitted to the second pinion gear 93.

[0046] The assist steering torque transmitted to the second pinion gear 93 is transmitted to the tie rod 94 via the steering gear 90, displacing the wheels. That is, the electric power steering device 80 displaces the wheels using not only the steering force of the operator transmitted to the rack bar 30 via the first pinion gear 92, but also the assist steering torque of the electric motor 102 transmitted to the rack bar 30 via the second pinion gear 93. The electric power steering device 80 according to the first embodiment is a dual pinion type electric power steering device in which an assist force is applied to the second pinion gear 93 in this way.

[0047] 3 is a plan view of the rack bar 30 shown in FIG. 2. FIG. 4 is a perspective view of the rack bar 30 shown in FIG. 2. FIG. 5 is a cross-sectional view taken along line AA in FIG. 3. FIG. 6 is a cross-sectional view taken along line BB in FIG. 3. The rack bar 30 has a large diameter portion 41 and a small diameter portion 46 that have different maximum widths in a direction perpendicular to the longitudinal direction of the rack bar 30. The large diameter portion 41 has a maximum width Wa in a direction perpendicular to the longitudinal direction of the rack bar 30 that is larger than the maximum width Wb of the small diameter portion 46 in a direction perpendicular to the longitudinal direction of the rack bar 30. The large diameter portion 41 and the small diameter portion 46 are connected to each other in the longitudinal direction of the rack bar 30. The large diameter portion 41 and the small diameter portion 46 are joined by, for example, friction welding. In the first embodiment, the large diameter portion 41 and the small diameter portion 46 have approximately the same length in the longitudinal direction of the rack bar 30.

[0048] The small diameter portion 46 has steering rack teeth 48 that mesh with a gear 92a of the first pinion gear 92 (see FIG. 2). The small diameter portion 46 has the steering rack teeth 48 formed on a small diameter round bar portion 47 that is shaped like a round bar. Therefore, the steering rack teeth 48 are formed within the range of the projected shape of the small diameter portion 46 when the small diameter portion 46 is viewed in a direction along the central axis of the small diameter portion 46, i.e., in a direction along the central axis of the small diameter round bar portion 47. As a result, the maximum width Wb of the small diameter portion 46 in a direction perpendicular to the longitudinal direction of the rack bar 30 is equal to the diameter of the small diameter round bar portion 47.

[0049] The large diameter portion 41 has assist rack teeth 43 that mesh with the second pinion gear 93 (see FIG. 2). The assist rack teeth 43 of the large diameter portion 41 are formed facing in a different direction from the steering rack teeth 48 of the small diameter portion 46. The large diameter portion 41 has a large diameter round bar portion 42 in the shape of a round bar having a diameter larger than that of the small diameter round bar portion 47, and a rack tooth forming portion 31 in which the assist rack teeth 43 are arranged. The large diameter round bar portions 42 are arranged on both sides of the rack tooth forming portion 31 in the longitudinal direction of the rack bar 30. The rack tooth forming portion 31 is formed so that the maximum width Wa of the rack tooth forming portion 31 in a direction perpendicular to the axial direction of the large diameter round bar portion 42 is larger than the width Wc of the rack tooth forming portion 31 in a direction perpendicular to the maximum width Wa.

[0050] In the first embodiment, the steering rack teeth 48 and the assist rack teeth 43 are formed at mutually different positions in the circumferential direction of the small diameter round bar portion 47 and the large diameter round bar portion 42 of the rack bar 30. In other words, the steering rack teeth 48 and the assist rack teeth 43 are formed to face mutually different directions in the circumferential direction of the small diameter round bar portion 47 and the large diameter round bar portion 42.

[0051] 7 is a perspective view of the rack bar 30 including the cross section BB of FIG. 3. The rack-tooth-forming portion 31 of the large-diameter portion 41 of the rack bar 30 is formed by crushing the surface of the large-diameter round bar portion 42, on which the assist rack teeth 43 are formed, in a direction perpendicular to the axial direction of the large-diameter round bar portion 42. By being crushed in this manner in a direction perpendicular to the axial direction of the large-diameter round bar portion 42, the rack-tooth-forming portion 31 has two protruding portions 33 that protrude in opposite directions in the direction perpendicular to the axial direction of the large-diameter round bar portion 42. The rack-tooth-forming portion 31 is formed into a shape having the protruding portions 33 by, for example, crushing a round bar in a direction perpendicular to the axial direction by forging. The maximum width Wa of the rack-tooth-forming portion 31 (see FIG. 6) is the distance between the ends of the two protruding portions 33 that are opposite the ends where the other protruding portion 33 is located. The assist rack teeth 43 are formed on the flat surface formed by crushing the large diameter round bar portion 42 in this way, and are formed across the two protruding portions 33 .

[0052] Furthermore, in the rack-tooth forming portion 31, the large diameter round bar portion 42 is crushed in only one direction, and therefore the surface of the rack-tooth forming portion 31 opposite to the surface where the assist rack teeth 43 are formed is formed in a shape that is continuous with the large diameter round bar portions 42 located on both sides of the rack-tooth forming portion 31. In other words, the back surface portion 32, which is the surface of the rack-tooth forming portion 31 opposite to the surface where the assist rack teeth 43 are formed, has a shape when viewed in the longitudinal direction of the rack bar 30 that has a radius of curvature that is substantially the same as the radius of curvature of the outer circumferential surface of the large diameter round bar portion 42, and is formed in an arc shape whose central axis coincides with the central axis of the large diameter round bar portion 42. The back surface portion 32 of the rack-tooth forming portion 31 is located between two protruding portions 33 on the surface of the rack-tooth forming portion 31 opposite to the side where the assist rack teeth 43 are formed.

[0053] Furthermore, by crushing the large diameter round bar portion 42, the two protruding portions 33 of the rack tooth forming portion 31 are formed to protrude in opposite directions perpendicular to the axial direction of the large diameter round bar portion 42. That is, the protruding portions 33 of the rack tooth forming portion 31 are arranged on both sides in the direction of the maximum width Wa of the rack tooth forming portion 31, and are formed to protrude in the direction in which the maximum width of the rack tooth forming portion 31 increases. For this reason, the maximum width Wa of the rack tooth forming portion 31, which is the distance between the ends of the two protruding portions 33 on the opposite sides to the side where the other protruding portion 33 is located, is larger than the width Wc of the rack tooth forming portion 31 in the direction perpendicular to the maximum width Wa.

[0054] As a result, the rack tooth forming portion 31 is formed so that its cross section has an irregular cross section when viewed in the longitudinal direction of the rack bar 30. In other words, the large diameter round bar portion 42 is formed so that its cross section has a circular cross section when viewed in the longitudinal direction of the rack bar 30, whereas the rack tooth forming portion 31 is formed so that its size in the direction in which the two protruding portions 33 protrude in the cross section when viewed in the longitudinal direction of the rack bar 30 is larger than the size in the direction perpendicular to the direction in which the two protruding portions 33 protrude.

[0055] In the first embodiment, the assist rack teeth 43 formed in the rack tooth forming portion 31 have a maximum width Wa in a direction perpendicular to the longitudinal direction of the rack bar 30 that is larger than the diameter of the large diameter round bar portion 42 located in the portion of the large diameter portion 41 other than the assist rack teeth 43. The maximum width Wa of the rack tooth forming portion 31 formed in this manner is the maximum width Wa of the large diameter portion 41 in a direction perpendicular to the longitudinal direction of the rack bar 30.

[0056] By forming the protruding portions 33 in two locations in this manner, the assist rack teeth 43 are formed in the rack-tooth forming portion 31, whose maximum width Wa is greater than the diameter of the large-diameter round bar portion 42. This allows the length of the assist rack teeth 43 to be longer than when the assist rack teeth 43 are formed directly in the large-diameter round bar portion 42. Furthermore, because the assist rack teeth 43 are formed in the rack-tooth forming portion 31 of the large-diameter portion 41 in this manner, the length of the teeth is longer than the length of the steering rack teeth 48 formed in the small-diameter portion 46.

[0057] FIG. 8 is a cross-sectional view of the rack housing 10 and the rack bar 30 of the electric power steering device 80, taken at a position including a cross section of the assist rack teeth 43. FIG. 9 is a cross-sectional view of the rack housing 10 and the rack bar 30 of the electric power steering device 80, taken at a position including a cross section of the steering rack teeth 48. The rack bar 30 is stored in the rack housing 10. The rack housing 10 is formed in a cylindrical shape and stores the rack bar 30 inside its inner circumferential surface. More specifically, the rack housing 10 has a small-diameter housing portion 21 in which a small-diameter through hole 22 is formed, and a large-diameter housing portion 11 in which a large-diameter through hole 12 is formed, the large-diameter through hole 12 communicating with the small-diameter through hole 22 and having an inner diameter larger than the inner diameter of the small-diameter through hole 22. The large-diameter housing portion 11 and the small-diameter housing portion 21 are each formed in a substantially cylindrical shape and are connected to each other in the axial direction.

[0058] The rack housing 10 stores the rack bar 30 in the internal space between the large diameter through hole 12 and the small diameter through hole 22, with the axial direction of the large diameter through hole 12 and the small diameter through hole 22 aligned with the longitudinal direction of the rack bar 30. When storing the rack bar 30 in the rack housing 10, the rack bar 30 is stored with the large diameter portion 41 of the rack bar 30 positioned on the large diameter housing portion 11 of the rack housing 10 and the small diameter portion 46 of the rack bar 30 positioned on the small diameter housing portion 21 of the rack housing 10. Therefore, the large diameter through hole 12 formed in the large diameter housing portion 11 of the rack housing 10 mainly stores the large diameter portion 41 of the rack bar 30, and the small diameter through hole 22 formed in the small diameter housing portion 21 of the rack housing 10 mainly stores the small diameter portion 46 of the rack bar 30.

[0059] The large diameter through hole 12 formed in the large diameter housing portion 11 mainly accommodates the large diameter portion 41 of the rack bar 30, and therefore accommodates the rack tooth forming portion 31 of the large diameter portion 41 of the rack bar 30. Therefore, the small diameter through hole 22 formed in the small diameter housing portion 21 accommodates a portion of the rack bar 30 other than the rack tooth forming portion 31.

[0060] The small diameter through-hole 22 of the rack housing 10 has a substantially circular shape when the substantially cylindrical small diameter housing portion 21 is viewed in the axial direction, and is a hole that penetrates the small diameter housing portion 21. The minimum diameter of the small diameter through-hole 22 is larger than the maximum width Wb of the small diameter portion 46 of the rack bar 30. In other words, the inner diameter of the small diameter housing portion 21 of the rack housing 10 is larger than the maximum width Wb of the small diameter portion 46 of the rack bar 30.

[0061] Furthermore, the small diameter through-hole 22 of the rack housing 10 that houses the small diameter portion 46 of the rack bar 30 has a minimum diameter that is smaller than the maximum width Wa of the large diameter portion 41 of the rack bar 30. In other words, the maximum width Wa of the large diameter portion 41 of the rack bar 30 is larger than the minimum diameter of the small diameter through-hole 22 of the rack housing 10. Furthermore, the small diameter through-hole 22 of the rack housing 10 has a minimum diameter that is smaller than the size of the large diameter round bar portion 42 of the large diameter portion 41 of the rack bar 30.

[0062] Unlike the small diameter through holes 22, the large diameter through holes 12 of the large diameter housing portion 11 of the rack housing 10 have a shape other than a circle when viewed in the axial direction of the large diameter housing portion 11, that is, are formed in an irregular shape. The shape of the large diameter through holes 12 will be described later.

[0063] A ball joint accommodating portion 15 is formed in the large diameter housing portion 11 of the rack housing 10 at the end opposite to the side where the small diameter housing portion 21 is located. The inner diameter of the ball joint accommodating portion 15 formed in the large diameter housing portion 11 is larger than the size of the large diameter through hole 12. In this way, the ball joint accommodating portion 15 formed in the large diameter housing portion 11 is formed to protrude on the side opposite to the side where the small diameter housing portion 21 is located, beyond the portion of the large diameter housing portion 11 where the large diameter through hole 12 is formed.

[0064] Similarly, a ball joint accommodating portion 25 is formed in the small diameter housing portion 21 of the rack housing 10 at the end opposite to the side where the large diameter housing portion 11 is located. The inner diameter of the ball joint accommodating portion 25 formed in the small diameter housing portion 21 is larger than the inner diameter of the small diameter through hole 22. In this way, the ball joint accommodating portion 25 formed in the small diameter housing portion 21 is formed to protrude toward the side opposite to the side where the large diameter housing portion 11 is located, beyond the portion of the small diameter housing portion 21 where the small diameter through hole 22 is formed.

[0065] Bolt holes 55 are arranged at both longitudinal ends of the rack bar 30 stored in the rack housing 10, and ball joints 50 to which tie rods 94 are connected are attached. The bolt holes 55 are arranged such that the central axis Cb (see FIG. 12) of the bolt hole 55 arranged in the small diameter portion 46 and the central axis Ca (see FIG. 12) of the bolt hole 55 arranged in the large diameter portion 41 are positioned on an extension line of each other. The ball joint 50 has a bolt portion 52 that screws into the bolt hole 55 formed in the rack bar 30. The ball joint 50 is attached to the rack bar 30 by screwing the bolt portion 52 into the bolt holes 55 formed in both longitudinal end portions of the rack bar 30. As a result, a ball joint 50 is arranged at each longitudinal end of the rack bar 30.

[0066] The ball joints 50 arranged on both ends of the rack bar 30 each have a joint portion 51 on the side opposite to the side attached to the rack bar 30. The joint portion 51 of the ball joint 50 has a recessed portion formed on the side opposite to the side where the bolt portion 52 that screws into the bolt hole 55 of the rack bar 30 is located, and the end of the tie rod 94 can fit into the recessed portion of the joint portion 51. This makes it possible for the tie rod 94 to be connected to the ball joint 50, and the tie rod 94 is connected to the rack bar 30 via the ball joint 50.

[0067] Furthermore, a gear box 17 of the worm reduction gear 95 is provided in the large diameter housing portion 11 of the rack housing 10. A second pinion gear 93, a worm wheel 96 that transmits the driving force generated by the electric motor 102 to the second pinion gear 93, and the like are arranged inside the gear box 17. The second pinion gear 93 is arranged to mesh with the assist rack teeth 43 formed on the rack tooth forming portion 31 of the large diameter portion 41 of the rack bar 30. As a result, the second pinion gear 93 can transmit the driving force generated by the electric motor 102 and transmitted via the worm wheel 96 to the assist rack teeth 43, and can transmit the driving force generated by the electric motor 102 to the rack bar 30.

[0068] Additionally, a pressing portion 60 is disposed in the rack housing 10, which applies a biasing force to the rack bar 30 to press the rack teeth 35 against the pinion gear 91. The pressing portion 60 has a first pressing portion 61 and a second pressing portion 66. The first pressing portion 61 is disposed in the small diameter housing portion 21 of the rack housing 10, and applies a biasing force to the rack bar 30 to press the steering rack teeth 48 against the first pinion gear 92. The second pressing portion 66 is disposed in the large diameter housing portion 11 of the rack housing 10, and applies a biasing force to the rack bar 30 to press the assist rack teeth 43 against the second pinion gear 93.

[0069] Figure 10 is a detailed view of portion C in Figure 9. On the small diameter housing portion 21 side, the rack housing 10 supports a first pinion gear 92 in mesh with steering rack teeth 48 formed on the small diameter portion 46 of the rack bar 30. That is, the first pinion gear 92 is disposed in the small diameter housing portion 21. A through hole 26 that penetrates the small diameter housing portion 21 from the inside to the outside of the small diameter housing portion 21 is formed in the small diameter housing portion 21 at a position opposite to the side on which the steering rack teeth 48 of the rack bar 30 are formed. The first pressing portion 61 is disposed in the through hole 26 formed in the small diameter housing portion 21.

[0070] The first pressing portion 61 has a pressing member 62, a spring 63, and a sealing member 64, and the pressing member 62, spring 63, and sealing member 64 of the first pressing portion 61 are housed in a through hole 26 formed in the small diameter housing portion 21. A portion of the pressing member 62 is exposed from the through hole 26 of the small diameter housing portion 21, and protrudes from the inner circumferential surface 23 of the small diameter housing portion 21. The pressing member 62 protruding from the inner circumferential surface 23 of the small diameter housing portion 21 abuts against the rack bar 30 on the inside of the small diameter housing portion 21, from the side opposite to the side on the rack bar 30 where the first pinion gear 92 is located. The sealing member 64 is disposed at the opening of the through hole 26 and seals the opening.

[0071] The spring 63 is a compression spring, and is disposed between the sealing member 64 and the pressing member 62 in a state in which it is compressed between the sealing member 64 and the pressing member 62. Therefore, the pressing member 62 is pressed against the rack bar 30 by the biasing force of the spring 63, and the surface of the small diameter portion 46 of the rack bar 30 on which the steering rack teeth 48 are formed is pressed against the gear 92a of the first pinion gear 92 by the biasing force of the pressing member 62. This causes the rack bar 30 to maintain a state in which the steering rack teeth 48 are meshed with the gear 92a of the first pinion gear 92.

[0072] 8. The rack housing 10 supports a second pinion gear 93 on the large diameter housing portion 11 side by meshing it with assist rack teeth 43 formed on the large diameter portion 41 of the rack bar 30. That is, the second pinion gear 93 is disposed in the large diameter housing portion 11. A through hole 16 that penetrates the large diameter housing portion 11 from the inside to the outside of the large diameter housing portion 11 is formed in the large diameter housing portion 11 at a position opposite to the side on which the assist rack teeth 43 of the rack bar 30 are formed. The second pressing portion 66 is disposed in the through hole 16 formed in the large diameter housing portion 11.

[0073] The second pressing portion 66 has a pressing member 67, a spring 68, and a sealing member 69, and the pressing member 67, spring 68, and sealing member 69 of the second pressing portion 66 are housed in a through hole 16 formed in the large-diameter housing portion 11. A portion of the pressing member 67 is exposed from the through hole 16 of the large-diameter housing portion 11 and protrudes from the inner circumferential surface 13 of the large-diameter housing portion 11. The pressing member 67 protruding from the inner circumferential surface 13 of the large-diameter housing portion 11 abuts against the rack bar 30 on the side opposite to the side on the rack bar 30 where the second pinion gear 93 is located, inside the large-diameter housing portion 11. Specifically, the pressing member 67 abuts against the back surface portion 32 of the rack-tooth forming portion 31 on the large-diameter portion 41 of the rack bar 30. The sealing member 69 is disposed at the opening of the through hole 16 to seal the opening.

[0074] The spring 68 is made of a compression spring, and is disposed between the sealing member 69 and the pressing member 67 in a state in which it is compressed between the sealing member 69 and the pressing member 67. Therefore, the pressing member 67 is pressed against the back surface portion 32 of the rack tooth forming portion 31 in the large diameter portion 41 of the rack bar 30 by the biasing force of the spring 68. The large diameter portion 41 of the rack bar 30 has a surface on which the assist rack teeth 43 are formed in the rack tooth forming portion 31 pressed against the second pinion gear 93 by the biasing force of the pressing member 67. This maintains the rack bar 30 in a state in which the assist rack teeth 43 mesh with the second pinion gear 93.

[0075] Fig. 12 is a cross-sectional schematic diagram of the rack housing 10 and the rack bar 30 in the first embodiment. Fig. 13 is a view taken along the arrow EE in Fig. 12. Note that in the first embodiment, the first pinion gear 92 and the second pinion gear 93 are disposed at different positions in the circumferential direction about the central axes of the small diameter round bar portion 47 and the large diameter round bar portion 42 of the rack bar 30, but in Fig. 12, the first pinion gear 92 and the second pinion gear 93, as well as the first pressing portion 61 and the second pressing portion 66, are illustrated on the same plane for convenience.

[0076] The large diameter through hole 12 formed in the large diameter housing portion 11 of the rack housing 10 has a substantially elliptical shape when viewed in the longitudinal direction of the rack housing 10. That is, unlike the small diameter through hole 22 formed in the small diameter housing portion 21, the large diameter through hole 12 formed in the large diameter housing portion 11 has a substantially elliptical shape rather than a substantially circular shape when viewed in the longitudinal direction of the rack housing 10. Therefore, the large diameter through hole 12 has a width Da in the major axis direction of the ellipse when viewed in the longitudinal direction of the rack housing 10 that is larger than a width Db in the minor axis direction of the ellipse.

[0077] Because the large diameter through hole 12 is formed in a generally elliptical shape as described above, the maximum width of the large diameter through hole 12 when viewed in the longitudinal direction of the rack housing 10 is a width Da in the long axis direction of the ellipse. The maximum width Da of the large diameter through hole 12 is larger than a maximum width Wa (see FIG. 6) of the rack tooth forming portion 31 housed in the large diameter through hole 12. Furthermore, a width Db of the large diameter through hole 12 in the short axis direction of the ellipse is larger than a width Wc (see FIG. 6) of the rack tooth forming portion 31 in a direction perpendicular to the maximum width Wa.

[0078] The large diameter housing portion 11, which has a substantially elliptical large diameter through hole 12, is connected to the small diameter housing portion 21 at a position where the central axis Ha of the large diameter through hole 12 is on an extension of the central axis Hb of the small diameter through hole 22 in the small diameter housing portion 21. In this case, the central axis Ha of the large diameter through hole 12 is the central axis of the ellipse of the large diameter through hole 12 that is a substantially elliptical hole that passes through the large diameter housing portion 11, and the central axis Hb of the small diameter through hole 22 is the central axis of the circle of the small diameter through hole 22 that is a substantially circular hole that passes through the small diameter housing portion 21.

[0079] Specifically, the central axis Ha of the large diameter through hole 12 in the large diameter housing portion 11 is the central axis of an ellipse at a position in the large diameter through hole 12 that accommodates the rack tooth forming portion 31 of the large diameter portion 41 of the rack bar 30. Furthermore, the central axis Hb of the small diameter through hole 22 in the small diameter housing portion 21 is the central axis of a circle at a position in the small diameter through hole 22 that accommodates the portion where the steering rack teeth 48 formed on the small diameter portion 46 of the rack bar 30 are located.

[0080] The rack bar 30 stored in the rack housing 10 formed as above has the large diameter portion 41 and the small diameter portion 46 connected at a position where the central axis Ba of the large diameter portion 41 and the central axis Bb of the small diameter portion 46 are on extensions of each other. In this case, the central axis Ba of the large diameter portion 41 of the rack bar 30 is the central axis of the large diameter round bar portion 42 that the large diameter portion 41 has, and the central axis Bb of the small diameter portion 46 is the central axis of the small diameter round bar portion 47 that the small diameter portion 46 has.

[0081] Furthermore, the rack bar 30 is stored inside the rack housing 10 in an orientation such that the direction of the maximum width Wa (see FIG. 6) of the rack tooth forming portion 31 of the rack bar 30 is the direction along the major axis of the ellipse that is the shape of the large diameter through hole 12. In other words, the rack bar 30 is stored in the rack housing 10 in an orientation such that the direction of the maximum width Wa of the rack tooth forming portion 31 is the direction along the width Da in the major axis direction of the ellipse that is the shape of the large diameter through hole 12, and the direction of the width Wc of the rack tooth forming portion 31 that is perpendicular to the maximum width Wa is the direction along the width Db in the minor axis direction of the ellipse that is the shape of the large diameter through hole 12.

[0082] In this case, the width Da of the large diameter through hole 12 in the major axis direction of the ellipse that is the shape of the large diameter through hole 12 is larger than the width Db of the small axis direction of the ellipse. Therefore, in the portion of the large diameter through hole 12 that stores the rack tooth forming portion 31, the maximum width Da in the same direction as the maximum width Wa of the rack tooth forming portion 31 is larger than the width Db in the direction perpendicular to the maximum width Da of the large diameter through hole 12. In other words, in the portion of the large diameter through hole 12 that stores the rack tooth forming portion 31, the width Db in the direction along the width Wc that is perpendicular to the maximum width Wa of the rack tooth forming portion 31 is smaller than the maximum width Da of the large diameter through hole 12. Therefore, the distance between the inner circumferential surface 13 of the large diameter through hole 12 and the rack bar 30 in the direction along the width Wc that is perpendicular to the maximum width Wa of the rack tooth forming portion 31 is less likely to become large compared to when the large diameter through hole 12 is formed in a circular shape.

[0083] Here, the second pressing portion 66 is arranged at a position where the pressing member 67 abuts against the back surface portion 32 of the rack tooth forming portion 31 of the large diameter portion 41 of the rack bar 30, and therefore the second pressing portion 66 is arranged on the minor axis of the ellipse that is the shape of the large diameter through hole 12 in the large diameter housing portion 11. In other words, the through hole 16 (see FIG. 11) of the large diameter housing portion 11 is formed on the minor axis of the ellipse that is the shape of the large diameter through hole 12, and the second pressing portion 66 is arranged in the through hole 16 located on the minor axis of the ellipse that is the shape of the large diameter through hole 12.

[0084] For this reason, the second pressing portion 66 is disposed at a position that is in a direction along the direction of width Db that is perpendicular to the maximum width Da of the large diameter through hole 12 that the large diameter housing portion 11 has. As a result, the second pressing portion 66 is disposed at a position where the distance between the inner circumferential surface 13 of the large diameter housing portion 11 and the back surface portion 32 of the rack tooth forming portion 31 of the rack bar 30 is unlikely to become large, that is, at a position where the distance between the inner circumferential surface 13 of the large diameter housing portion 11 and the back surface portion 32 of the rack tooth forming portion 31 is small. In other words, the second pressing portion 66 is disposed in a state where the distance from the back surface portion 32 of the rack tooth forming portion 31 is smaller than when the large diameter through hole 12 is formed in a circular shape.

[0085] Here, the second pressing portion 66 protrudes from the inner circumferential surface 13 of the large diameter housing portion 11 into the inside of the rack housing 10, thereby coming into contact with and pressing the rack bar 30 stored in the rack housing 10. Similarly, the first pressing portion 61 disposed in the small diameter housing portion 21 of the rack housing 10 also protrudes from the inner circumferential surface 23 of the small diameter housing portion 21 into the inside of the rack housing 10, thereby coming into contact with and pressing the rack bar 30. In other words, the first pressing portion 61 presses the rack bar 30 by having the pressing member 62 protrude from the inner circumferential surface 23 of the small diameter housing portion 21 into the inside of the rack housing 10, and the second pressing portion 66 presses the rack bar 30 by having the pressing member 67 protrude from the inner circumferential surface 13 of the large diameter housing portion 11 into the inside of the rack housing 10.

[0086] In this case, the inner diameter of the small diameter housing portion 21 of the rack housing 10 is larger than the maximum width Wb of the small diameter portion 46 of the rack bar 30, but the maximum width Wb (see FIG. 3) of the small diameter portion 46 of the rack bar 30 is the diameter of the small diameter round bar portion 47 (see FIG. 3) of the rack bar 30. Therefore, the distance between the small diameter portion 46 of the rack bar 30 stored in the small diameter housing portion 21 and the inner circumferential surface 23 of the small diameter housing portion 21 is approximately the same at any position in the circumferential direction about the central axis Hb of the small diameter housing portion 21. Therefore, by reducing the difference between the inner diameter of the small diameter housing portion 21 of the rack housing 10 and the diameter of the small diameter round bar portion 47 of the rack bar 30, it is possible to reduce the protrusion amount Pb from the inner circumferential surface 23 of the small diameter housing portion 21 of the first pressing portion 61 that protrudes from the inner circumferential surface 23 of the small diameter housing portion 21 and comes into contact with the rack bar 30.

[0087] In contrast, the maximum width Wa (see FIG. 6) of the large diameter portion 41 of the rack bar 30 stored in the large diameter housing portion 11 of the rack housing 10 is the maximum width Wa at the position of the rack tooth forming portion 31 (see FIGS. 6 and 7), and the rack tooth forming portion 31 is formed in a shape having two protruding portions 33 formed by crushing the large diameter round bar portion 42 (see FIG. 7) of the large diameter portion 41. For this reason, when the large diameter through hole 12 of the large diameter housing portion 11 that stores the large diameter portion 41 of the rack bar 30 is formed in a substantially circular shape, the distance between the inner circumferential surface 13 of the large diameter housing portion 11 and the large diameter portion 41 of the rack bar 30 varies depending on the position in the circumferential direction about the central axis Ha of the large diameter housing portion 11.

[0088] FIG. 14 is a schematic diagram of the large-diameter through hole 12 of the large-diameter housing portion 11 when the large-diameter through hole 12 is formed in a substantially circular shape. FIG. 15 is a view taken along the arrow FF in FIG. 14 . For example, if the large-diameter through hole 12 of the large-diameter housing portion 11 is formed in a substantially circular shape when viewed in the longitudinal direction of the rack housing 10, the large-diameter housing portion 11 will be formed with an inner diameter larger than the maximum width Wa of the rack-tooth forming portion 31 of the rack bar 30, i.e., the maximum width Wa of the large-diameter portion 41 of the rack bar 30. In this case, the distance between the inner circumferential surface 13 of the large-diameter housing portion 11 and the rack bar 30 is smallest in the direction along the maximum width Wa of the rack-tooth forming portion 31 of the large-diameter portion 41 of the rack bar 30. In other words, the distance between the inner circumferential surface 13 of the large-diameter housing portion 11 and the rack bar 30 is smallest when the distance between the inner circumferential surface 13 of the large-diameter housing portion 11 and the protruding portion 33 of the rack-tooth forming portion 31 is smallest.

[0089] On the other hand, the distance between the inner peripheral surface 13 of the large diameter housing portion 11 and the rack bar 30 is greater in a direction other than the direction along the maximum width Wa of the rack tooth forming portion 31 in the circumferential direction centered on the central axis Ba of the large diameter portion 41 of the rack bar 30 than in the direction along the maximum width Wa. That is, when the large diameter through hole 12 of the large diameter housing portion 11 is formed in a circular shape whose inner diameter is larger than the maximum width Wa of the large diameter portion 41 of the rack bar 30, the distance between the inner peripheral surface 13 of the large diameter housing portion 11 and the rack bar 30 is greater in the direction along the width Wc (see FIG. 6 ) perpendicular to the maximum width Wa of the rack tooth forming portion 31 than in the direction along the direction of the maximum width Wa of the rack tooth forming portion 31. Therefore, the distance between the inner surface 13 of the large diameter housing portion 11 in the rack housing 10 and the back portion 32 of the rack tooth forming portion 31 in the large diameter portion 41 of the rack bar 30 is greater than the distance between the inner surface 13 of the large diameter housing portion 11 and the protruding portion 33 of the rack tooth forming portion 31.

[0090] Therefore, the protrusion amount Pc from the inner peripheral surface 13 of the large diameter housing portion 11 of the second pressing portion 66, which protrudes from the inner peripheral surface 13 of the large diameter housing portion 11 and comes into contact with the back surface portion 32 of the rack tooth forming portion 31 in the large diameter portion 41 of the rack bar 30, is greater than the protrusion amount Pb of the first pressing portion 61 from the inner peripheral surface 23 of the small diameter housing portion 21, as shown in Fig. 14. For example, if the protrusion amount Pb of the first pressing portion 61 is 2.5 mm, the protrusion amount Pc of the second pressing portion 66 will be approximately 4 to 5 mm.

[0091] 12 and 13 , in the first embodiment, the large-diameter through-hole 12 of the large-diameter housing portion 11 has a maximum width Da in the same direction as the direction in which the rack-tooth forming portion 31 has a maximum width Wa, which is larger than a width Db of the large-diameter through-hole 12 in a direction perpendicular to the maximum width Da. In other words, the large-diameter through-hole 12 of the large-diameter housing portion 11 is formed in a substantially elliptical shape, so that the width Db in the minor axis direction of the ellipse, which is the direction in which the second pressing portion 66 is arranged, is smaller than the width Da in the same direction as the direction in which the rack-tooth forming portion 31 has a maximum width Wa. For this reason, the distance between the back surface portion 32 of the rack-tooth forming portion 31 in the large-diameter portion 41 of the rack bar 30 and the inner circumferential surface 13 of the large-diameter housing portion 11 in the rack housing 10 is smaller than when the large-diameter through-hole 12 of the large-diameter housing portion 11 is formed in a substantially circular shape, as shown in FIGS. 14 and 15 .

[0092] As a result, the amount of protrusion Pa from the inner circumferential surface 13 of the large diameter housing portion 11 of the rack housing 10 of the second pressing portion 66 that protrudes from the inner circumferential surface 13 of the large diameter housing portion 11 in the rack housing 10 and comes into contact with the back surface portion 32 of the large diameter portion 41 of the rack bar 30 is smaller than when the large diameter through hole 12 of the large diameter housing portion 11 is formed in a substantially circular shape, as shown in Figures 14 and 15. In other words, the amount of protrusion Pa from the inner circumferential surface 13 of the large diameter housing portion 11 of the rack housing 10 of the pressing member 67 of the second pressing portion 66 in the first embodiment is smaller than when the large diameter through hole 12 of the large diameter housing portion 11 is formed in a substantially circular shape, as shown in Figures 14 and 15.

[0093] 12 , in the first embodiment, the amount of protrusion Pa of the second pressing portion 66 from the inner circumferential surface 13 of the large diameter housing portion 11 is set to be equal to or smaller than the gap Ga between the inner circumferential surface 23 of the small diameter housing portion 21 and the rack bar 30. In this case, the gap Ga between the inner circumferential surface 23 of the small diameter housing portion 21 and the rack bar 30 is the gap Ga between the inner circumferential surface 23 of the small diameter housing portion 21 and the portion of the rack bar 30 opposite the side on which the steering rack teeth 48 are arranged. For this reason, in the first embodiment, the amount of protrusion Pa of the pressing member 67 of the second pressing portion 66 from the inner circumferential surface 13 of the large diameter housing portion 11 is set to be equal to or smaller than the amount of protrusion Pb of the pressing member 62 of the first pressing portion 61 from the inner circumferential surface 23 of the small diameter housing portion 21. For example, if the protrusion amount Pb of the pressing member 62 of the first pressing portion 61 is 2.5 mm, it is preferable that the protrusion amount Pa of the pressing member 67 of the second pressing portion 66 is 2.5 mm, and more preferably, the protrusion amount Pa is ideally about 1 mm.

[0094] In these cases, the protrusion amount Pb of the first pressing portion 61 is the protrusion amount Pb of the pressing member 62 of the first pressing portion 61 from the inner surface 23 of the small diameter housing portion 21, and the protrusion amounts Pa, Pc of the second pressing portion 66 are the protrusion amounts Pa, Pc of the pressing member 67 of the second pressing portion 66 from the inner surface 13 of the large diameter housing portion 11.

[0095] Next, the operation of the electric power steering device 80 will be described. When the steering wheel 81 is operated while driving a vehicle equipped with the electric power steering device 80, the steering force applied to the steering wheel 81 is transmitted from the steering wheel 81 to the steering shaft 82. The steering force transmitted to the steering shaft 82 is transmitted as steering torque from the steering shaft 82 to the intermediate shaft 85, and from the intermediate shaft 85 via the stub shaft 87 to the first pinion gear 92. As a result, the steering gear 90 having the first pinion gear 92 converts the rotational motion transmitted from the first pinion gear 92 into linear motion of the rack bar 30, causing the tie rod 94 to operate.

[0096] Furthermore, the electric power steering device 80 according to the first embodiment includes a steering assist device 110 that applies a steering assist force to the rack bar 30 to assist the driver in steering, and the steering assist device 110 has an electric motor 102 that generates an auxiliary steering torque used as the steering assist force. The electric motor 102 generates the auxiliary steering torque based on the steering torque detected by a torque sensor 101 that is disposed between the stub shaft 87 and the first pinion gear 92.

[0097] Torque sensor 101 detects the steering torque applied to stub shaft 87 based on the angle of relative rotation between stub shaft 87 and first pinion gear 92. That is, because stub shaft 87 and first pinion gear 92 are connected via a torsion bar (not shown), when steering torque is applied to stub shaft 87, the steering torque is transmitted between stub shaft 87 and first pinion gear 92 via the torsion bar. At that time, the torsion bar is slightly twisted, causing relative rotation between stub shaft 87 and first pinion gear 92. Torque sensor 101 detects the relative rotation between stub shaft 87 and first pinion gear 92 caused by the slight twisting of the torsion bar, and transmits the detected rotation to ECU 100 as an electrical signal.

[0098] The ECU 100 operates the electric motor 102 based on the electrical signal transmitted from the torque sensor 101, causing the electric motor 102 to generate an assist steering torque. In other words, the electrical signal transmitted from the torque sensor 101 to the ECU 100 changes based on the steering torque T acting between the stub shaft 87 and the first pinion gear 92. Therefore, the ECU 100 uses the electrical signal transmitted from the torque sensor 101 as information that changes depending on the steering torque T acting on the stub shaft 87 and the first pinion gear 92, and adjusts the power value X supplied to the electric motor 102 based on the electrical signal transmitted from the torque sensor 101, causing the electric motor 102 to generate an assist steering torque.

[0099] That is, ECU 100 acquires a signal of steering torque T from torque sensor 101, acquires a vehicle speed signal V of the vehicle from vehicle speed sensor 103, and further acquires operation information Y of electric motor 102 from a rotation detection device provided in electric motor 102. Based on this operation information Y, steering torque T, and vehicle speed signal V, ECU 100 causes electric motor 102 to generate auxiliary steering torque. The auxiliary steering torque generated by electric motor 102 is transmitted to second pinion gear 93. Steering gear 90 having second pinion gear 93 converts the rotational motion transmitted from second pinion gear 93 into linear motion of rack bar 30. As a result, the steering force applied to steering wheel 81 by the driver is assisted by the auxiliary steering torque generated by electric motor 102.

[0100] More specifically, when the driver turns the steering wheel 81, the stub shaft 87 and the first pinion gear 92 rotate due to the transmission of steering force. When the first pinion gear 92 rotates, the steering torque of the first pinion gear 92 is transmitted from the first pinion gear 92 to the steering rack teeth 48 of the rack bar 30 that mesh with the first pinion gear 92. As a result, the rack bar 30 moves linearly in the axial direction while being supported by the rack housing 10.

[0101] Furthermore, the driving force generated by the electric motor 102 is transmitted to the second pinion gear 93 via the worm reduction gear 95, and the second pinion gear 93 is rotated by the driving force generated by the electric motor 102. When the second pinion gear 93 rotates, the auxiliary steering torque of the second pinion gear 93 is transmitted from the second pinion gear 93 to the assist rack teeth 43 of the rack bar 30 that meshes with the second pinion gear 93. As a result, the rack bar 30 performs linear motion while the linear motion caused by the steering torque from the first pinion gear 92 is assisted by the auxiliary steering torque from the second pinion gear 93.

[0102] In this case, the rack bar 30 has a rack-tooth forming portion 31 where the assist rack teeth 43 are formed, whose maximum width Wa is larger than the width Wc in a direction perpendicular to the maximum width Wa and is larger than the diameter of the large-diameter round bar portion 42. In other words, the tooth width of the assist rack teeth 43 in the direction along the maximum width Wa is larger than the diameter of the large-diameter round bar portion 42. This allows the rack bar 30 to receive the large assist steering torque caused by the driving force generated by the electric motor 102 at the assist rack teeth 43, and causes linear movement while receiving the large assist steering torque.

[0103] The linear motion of the rack bar 30 is transmitted from the ball joints 50 arranged on both ends of the rack bar 30 to the tie rods 94 connected to the ball joints 50, and the direction of the wheels is changed in accordance with the movement of the tie rods 94.

[0104] When the driver turns the steering wheel 81 as described above to change the direction of the wheels, the rack bar 30 moves linearly, and the steering force when the steering wheel 81 is turned and the driving force generated by the electric motor 102 are transmitted to the rack bar 30 by the first pinion gear 92 and the second pinion gear 93. In the rack bar 30, to which these forces are transmitted via the first pinion gear 92 and the second pinion gear 93, the steering rack teeth 48 are pressed against the first pinion gear 92 by the first pressing portion 61, and the assist rack teeth 43 are pressed against the second pinion gear 93 by the second pressing portion 66.

[0105] The meshing portion between the steering rack teeth 48 and the first pinion gear 92 and the meshing portion between the assist rack teeth 43 and the second pinion gear 93 mesh with as little backlash as possible due to the pressing forces applied to the rack bar 30 from the first pressing portion 61 and the second pressing portion 66. This suppresses the generation of abnormal noise during operation at the meshing portion between the steering rack teeth 48 and the first pinion gear 92 and the meshing portion between the assist rack teeth 43 and the second pinion gear 93, which is caused by backlash at the respective meshing portions.

[0106] Here, the rack tooth forming portion 31 of the large diameter portion 41 of the rack bar 30 stored in the large diameter housing portion 11 of the rack housing 10 in which the second pressing portion 66 is arranged has a maximum width Wa in a direction perpendicular to the longitudinal direction of the rack bar 30 that is larger than the width Wc in a direction perpendicular to the maximum width Wa of the rack tooth forming portion 31.

[0107] On the other hand, the second pressing portion 66, which applies a pressing force to the rack bar 30 in a direction that presses the assist rack teeth 43 against the second pinion gear 93, comes into contact with the back surface portion 32 of the large diameter portion 41 of the rack bar 30 and presses the back surface portion 32. The portion of the back surface portion 32 of the large diameter portion 41 of the rack bar 30 to which the pressing force from the second pressing portion 66 is applied is located in the direction of a width Wc that is narrower than the maximum width Wa and perpendicular to the maximum width Wa of the rack tooth forming portion 31.

[0108] That is, the second pressing portion 66, which applies a pressing force to the rack bar 30 by pressing the rear surface portion 32 of the rack tooth forming portion 31, contacts the rear surface portion 32 of the rack tooth forming portion 31 from the direction of a width Wc that is perpendicular to the maximum width Wa of the rack tooth forming portion 31 and is narrower than the maximum width Wa. For this reason, as shown in Fig. 14, if the large diameter through hole 12 of the large diameter housing portion 11 is formed in a substantially circular shape when viewed in the longitudinal direction of the rack housing 10, the second pressing portion 66, which contacts the rear surface portion 32 of the rack tooth forming portion 31 in the large diameter portion 41, is likely to protrude by a large amount Pc from the inner circumferential surface 13 of the large diameter housing portion 11.

[0109] Therefore, the amount of protrusion Pc from the inner circumferential surface 13 of the large diameter housing portion 11 of the second pressing portion 66, which protrudes from the inner circumferential surface 13 of the large diameter housing portion 11 and comes into contact with the back surface portion 32 of the rack tooth forming portion 31 in the large diameter portion 41 of the rack bar 30, tends to be greater than the amount of protrusion Pb of the first pressing portion 61 from the inner circumferential surface 23 of the small diameter housing portion 21, as shown in Fig. 14. In other words, when the large diameter through hole 12 of the large diameter housing portion 11 is formed in a substantially circular shape, the amount of protrusion Pc of the pressing member 67 (see Fig. 11) of the second pressing portion 66 from the inner circumferential surface 13 of the large diameter housing portion 11 tends to be greater.

[0110] When the amount of protrusion Pc of the pressing member 67 of the second pressing portion 66 from the inner peripheral surface 13 of the large-diameter housing portion 11 is large, a smaller portion of the pressing member 67 enters the through-hole 16 (see FIG. 11 ) of the large-diameter housing portion 11, and therefore a smaller portion of the pressing member 67 is supported by the through-hole 16. When the amount of protrusion Pc of the pressing member 67 is large and the portion of the pressing member 67 supported by the through-hole 16 is small, there is a risk that the pressing member 67 will be dragged by the rack bar 30 and tilted when the rack bar 30, against which the pressing member 67 abuts, moves linearly (see, for example, FIG. 7 of Patent Document 1).

[0111] If the pressing member 67 is tilted, it becomes difficult for the pressing member 67 to appropriately press the large diameter portion 41 of the rack bar 30, and it becomes difficult for the pressing member 67 to press the assist rack teeth 43 of the rack bar 30 against the second pinion gear 93. In this case, it becomes difficult for the second pressing portion 66 to reduce the backlash at the meshing portion between the assist rack teeth 43 and the second pinion gear 93, and therefore it becomes difficult to suppress the generation of abnormal noise during operation that is caused by the backlash at the meshing portion between the assist rack teeth 43 and the second pinion gear 93.

[0112] Furthermore, because the assist rack teeth 43 are formed obliquely with respect to a direction perpendicular to the central axis Ba of the large diameter portion 41 of the rack bar 30, when the rack bar 30 makes linear motion while being assisted by the auxiliary steering torque from the second pinion gear 93, the rack bar 30 also moves in a direction perpendicular to the central axis Ba. The linear motion of the rack bar 30 and the movement of the rack bar 30 in a direction perpendicular to the central axis Ba also change direction when the steering direction changes. However, if the pressing member 67 is tilted and abuts against the rack bar 30, the direction of tilt of the pressing member 67 also changes. At that time, the tilt direction of the pressing member 67 changes while being pressed against the rack bar 30, which can cause a so-called stick-lip phenomenon at the contact surface between the pressing member 67 and the rack bar 30, resulting in noise. The stick-lip phenomenon that occurs when the pressing member 67 contacts the rack bar 30 while tilting may continue even while the rack bar 30 is moving linearly, and may result in continuous abnormal noise.

[0113] Furthermore, when the pressing member 67 of the second pressing portion 66 tilts, the pressing member 67 is more likely to come into contact with the through-hole 16 that holds the pressing member 67 in the rack housing 10, which may cause a collision noise when the pressing member 67 comes into contact with the through-hole 16 of the rack housing 10. When the pressing member 67 tilts due to the large protrusion amount Pc of the pressing member 67 of the second pressing portion 66, abnormal noise is more likely to occur due to various factors such as those mentioned above.

[0114] In contrast, in the first embodiment, the large diameter through hole 12 in the rack housing 10 that accommodates the rack tooth forming portion 31 of the rack bar 30 has a maximum width Da in the same direction as the direction of the maximum width Wa of the rack tooth forming portion 31 that is larger than a width Db in the direction perpendicular to the maximum width Da of the large diameter through hole 12 (see FIG. 13 ). For this reason, the second pressing portion 66 disposed in the large diameter housing portion 11 of the rack housing 10 is disposed in a direction of width Db that is perpendicular to the direction of the maximum width Da of the large diameter through hole 12 and is narrower than the maximum width Da, and is disposed on a line perpendicular to the direction of the maximum width Da of the large diameter through hole 12. In other words, the second pressing portion 66 disposed in the large diameter housing portion 11 is disposed on an extension of the minor axis of the elliptical shape that is the shape of the large diameter through hole 12 of the large diameter housing portion 11 when viewed in the longitudinal direction of the rack housing 10.

[0115] As a result, the distance between the rear surface 32 of the rack tooth forming portion 31 in the large diameter portion 41 of the rack bar 30 and the inner surface 13 of the large diameter housing portion 11 of the rack housing 10 becomes smaller, and the second pressing portion 66 that contacts the rear surface 32 in the large diameter portion 41 of the rack bar 30 protrudes less Pa from the inner surface 13 of the large diameter housing portion 11.

[0116] That is, the amount of protrusion Pa of the pressing member 67 (see FIG. 11) of the second pressing portion 66 from the inner peripheral surface 13 of the large diameter housing portion 11 becomes smaller, and a larger portion of the pressing member 67 is supported by the through hole 16 of the large diameter housing portion 11. Therefore, even when the rack bar 30 against which the pressing member 67 abuts moves linearly, the pressing member 67 of the second pressing portion 66 is less likely to be dragged by the rack bar 30 and therefore less likely to tilt, and the pressing member 67 can appropriately press the large diameter portion 41 of the rack bar 30.

[0117] As a result, the pressing member 67 of the second pressing portion 66 can press the assist rack teeth 43 of the rack bar 30 against the second pinion gear 93, and the backlash at the meshing portion between the assist rack teeth 43 and the second pinion gear 93 can be reduced by the second pressing portion 66. Therefore, the second pressing portion 66, which is disposed in the large diameter housing portion 11 of the rack housing 10, can suppress the generation of abnormal noise caused by backlash at the meshing portion between the assist rack teeth 43 and the second pinion gear 93.

[0118] Moreover, since the pressing member 67 of the second pressing portion 66 is less likely to tilt, it is possible to suppress the occurrence of a stick-lip phenomenon at the contact surface between the pressing member 67 and the rack bar 30. Furthermore, since the pressing member 67 of the second pressing portion 66 is less likely to tilt, the pressing member 67 is less likely to come into contact with the through-hole 16 that holds the pressing member 67 in the rack housing 10, and it is possible to suppress the occurrence of a collision sound caused by the pressing member 67 coming into contact with the through-hole 16 in the rack housing 10.

[0119] As a result, when the direction of the wheels is changed using the electric power steering device 80, the direction of the wheels can be changed while suppressing abnormal noise caused by backlash at the meshing portion between the assist rack teeth 43 of the rack bar 30 and the second pinion gear 93, abnormal noise caused by the stick-lip phenomenon, and abnormal noise caused by the pressing member 67 colliding with the through hole 16 of the rack housing 10.

[0120] As described above, in the electric power steering device 80 according to the first embodiment, the rack-tooth forming portion 31 of the rack bar 30 has a maximum width Wa in a direction perpendicular to the longitudinal direction of the rack bar 30 that is larger than the width Wc in a direction perpendicular to the maximum width Wa, and the large-diameter through-hole 12 that houses the rack-tooth forming portion 31 in the rack housing 10 has a maximum width Da in the same direction as the direction in which the rack-tooth forming portion 31 has a maximum width Wa that is larger than the width Db in the direction perpendicular to the maximum width Da of the large-diameter through-hole 12. As a result, the second pressing portion 66 that is disposed in the rack housing 10 and applies a biasing force to the rack bar 30 to press the assist rack teeth 43 against the second pinion gear 93 has a protrusion amount Pa of the second pressing portion 66 from the inner circumferential surface 13 of the large-diameter housing portion 11 that is approximately the same as or smaller than the gap Ga between the inner circumferential surface 23 of the small-diameter housing portion 21 and the rack bar 30.

[0121] Therefore, when the rack bar 30 moves linearly, the pressing member 67 of the second pressing portion 66 is not pulled by the rack bar 30 and tilted, and the pressing member 67 can press the assist rack teeth 43 of the rack bar 30 toward the second pinion gear 93. This makes it possible to reduce backlash at the meshing portion between the assist rack teeth 43 and the second pinion gear 93, thereby suppressing the generation of abnormal noise caused by backlash. Furthermore, because the pressing member 67 of the second pressing portion 66 can be prevented from tilting, it is possible to suppress the generation of abnormal noise due to the stick-lip phenomenon and the generation of abnormal noise due to the pressing member 67 hitting the through-hole 16 of the rack housing 10.

[0122] Furthermore, the large diameter through-hole 12 of the large diameter housing portion 11 of the rack housing 10 has a width Db in a direction perpendicular to the maximum width Da of the large diameter through-hole 12 that is smaller than the maximum width Da of the large diameter through-hole 12, so the size of the portion of the rack housing 10 that stores the large diameter portion 41 of the rack bar 30 can be reduced. This allows the rack housing 10 to be made smaller and therefore lighter. As a result, the generation of abnormal noise can be suppressed and the rack housing 10 can be prevented from becoming larger.

[0123] Furthermore, since the protrusion amount Pa of the second pressing portion 66 from the inner circumferential surface 13 of the large-diameter housing portion 11 is equal to or less than the protrusion amount Pb of the first pressing portion 61 from the inner circumferential surface 23 of the small-diameter housing portion 21, the pressing member 67 can press the assist rack teeth 43 toward the second pinion gear 93 without being dragged by the rack bar 30 and tilting when the rack bar 30 moves linearly. This reduces backlash at the meshing portion between the assist rack teeth 43 and the second pinion gear 93, thereby suppressing the generation of abnormal noise due to backlash. Furthermore, since tilting of the pressing member 67 of the second pressing portion 66 can be suppressed, the generation of abnormal noise due to the stick-lip phenomenon and the generation of abnormal noise due to the pressing member 67 colliding with the through-hole 16 of the rack housing 10 can be suppressed. As a result, the generation of abnormal noise can be suppressed.

[0124] Furthermore, the large-diameter through-hole 12 of the large-diameter housing portion 11 has a substantially elliptical shape when viewed in the longitudinal direction of the rack housing 10, and the rack bar 30 is stored inside the rack housing 10 with the direction of the maximum width Wa of the rack-tooth forming portion 31 aligned along the major axis of the ellipse. This reduces the amount of protrusion Pa of the second pressing portion 66 from the inner circumferential surface 13 of the large-diameter housing portion 11. In other words, by forming the large-diameter through-hole 12 of the large-diameter housing portion 11 in a substantially elliptical shape and arranging the second pressing portion 66 on an extension of the minor axis of the ellipse that defines the shape of the large-diameter through-hole 12, the distance between the rack bar 30 and the vicinity of the position where the second pressing portion 66 is arranged on the inner circumferential surface 13 of the large-diameter housing portion 11 can be reduced. This reduces the amount of protrusion Pa of the second pressing portion 66 from the inner circumferential surface 13 of the large-diameter housing portion 11, thereby preventing the pressing member 67 of the second pressing portion 66 from tilting. As a result, the generation of abnormal noise caused by the pressing member 67 tilting can be suppressed.

[0125] Furthermore, because the steering rack teeth 48 of the rack bar 30 are formed within the range of the projected shape of the small diameter portion 46 when the small diameter portion 46 is viewed in the direction along the central axis Bb, the inner diameter of the small diameter housing portion 21 of the rack housing 10 that houses the small diameter portion 46 can be made as small as possible. This makes it possible to reduce the protrusion amount Pb of the first pressing portion 61 that abuts against the small diameter portion 46 of the rack bar 30. Therefore, when the rack bar 30 moves linearly, the pressing member 62 of the first pressing portion 61 can press the steering rack teeth 48 of the rack bar 30 toward the first pinion gear 92 without being dragged by the rack bar 30 and tilting. Therefore, the pressing force applied to the rack bar 30 by the pressing member 62 of the first pressing portion 61 can reduce backlash at the meshing portion between the steering rack teeth 48 and the first pinion gear 92, thereby suppressing the generation of abnormal noise caused by backlash. Furthermore, since tilting of the pressing member 62 of the first pressing portion 61 can be suppressed, it is possible to suppress the generation of abnormal noise due to the stick-lip phenomenon and the generation of abnormal noise due to the pressing member 62 colliding with the through-hole 26 of the rack housing 10. As a result, the generation of abnormal noise can be suppressed.

[0126] [Second embodiment] Next, an electric power steering device 80 according to a second embodiment will be described. The same components as those in the first embodiment will be assigned the same reference numerals and descriptions thereof will be omitted. The following description will focus on the differences from the first embodiment.

[0127] Fig. 16 is a cross-sectional schematic diagram of a rack housing 10 and a rack bar 30 included in an electric power steering device 80 according to the second embodiment. Fig. 17 is a view taken along the arrows G and G in Fig. 16. In the second embodiment, the rack bar 30 also has a large diameter portion 41 and a small diameter portion 46, and the large diameter portion 41 has a rack-tooth forming portion 31 on which the assist rack teeth 43 are arranged. As in the first embodiment, the rack-tooth forming portion 31 has, on both sides in the direction of the maximum width Wa of the rack-tooth forming portion 31, protruding portions 33 that protrude in the direction in which the maximum width Wa of the rack-tooth forming portion 31 increases, and the back surface portion 32 located on the back side of the assist rack teeth 43 is formed in an arc shape when viewed in the longitudinal direction of the rack bar 30 (see Fig. 6).

[0128] The rack housing 10 that stores the rack bar 30 has a large diameter housing portion 11 and a small diameter housing portion 21, and the rack tooth forming portion 31 of the rack bar 30 is stored in the large diameter housing portion 11. Unlike the first embodiment in which the large diameter through hole 12 of the large diameter housing portion 11 has a substantially elliptical shape when viewed in the longitudinal direction of the rack housing 10, in the second embodiment, the inner circumferential surface 13 of the large diameter through hole 12 has an irregular shape with an arc portion 13a and a protrusion portion storage portion 13b.

[0129] The overhang portion storage sections 13b of the large diameter through hole 12 are located on both sides in the same direction as the direction of the maximum width Wa of the rack tooth forming section 31 when the rack tooth forming section 31 is stored in the large diameter housing section 11, and are capable of storing the overhang portion 33. For this reason, the overhang portion storage sections 13b are located at two locations on both sides in the direction of the maximum width Da of the large diameter through hole 12 when viewed in the longitudinal direction of the rack housing 10, and are formed as spaces that protrude in the direction in which the maximum width Da of the large diameter through hole 12 increases. Because the overhang portion storage sections 13b are capable of storing the overhang portion 33 of the rack tooth forming section 31, their shape when viewed in the longitudinal direction of the rack housing 10 is formed to follow the overhang portion 33 of the rack tooth forming section 31.

[0130] The arc portion 13a of the large diameter through hole 12 is disposed between the two protrusion storage portions 13b when viewed in the longitudinal direction of the rack bar 30, and its shape when viewed in the longitudinal direction of the rack bar 30 is formed as an arc that convex toward the outside of the rack housing 10. More specifically, the arc portion 13a is formed in an arc shape centered on the position of the central axis Ba of the large diameter portion 41 of the rack bar 30 when the rack tooth forming portion 31 is stored in the large diameter housing portion 11. The arc portion 13a of the large diameter through hole 12 is formed to include a position in the large diameter housing portion 11 where the second pressing portion 66 is to be disposed. Therefore, the pressing member 67 of the second pressing portion 66 protrudes toward the inside of the large diameter housing portion 11 from the position of the arc portion 13a of the large diameter through hole 12.

[0131] When viewed in the longitudinal direction of the rack housing 10, the large diameter through hole 12 of the large diameter housing portion 11 formed in this manner has a maximum width in the direction in which the two protrusion portion storage portions 13b protrude, which is the maximum width Da of the large diameter through hole 12 in a direction perpendicular to the longitudinal direction of the rack housing 10. For this reason, the width Db of the large diameter through hole 12 in a direction perpendicular to the direction in which the large diameter through hole 12 has the maximum width Da when viewed in the longitudinal direction of the rack housing 10, and which includes the position where the arc portion 13a is arranged, is smaller than the maximum width Da of the large diameter through hole 12.

[0132] In this case, the width Db of the large diameter through hole 12 is the width Db of the large diameter through hole 12 in a direction passing through the center position of the maximum width Da and the center position in the longitudinal direction of the arc portion 13a. The second pressing portion 66 is thus disposed on a line that passes through the center position of the maximum width Da of the large diameter through hole 12 and the center position in the longitudinal direction of the arc portion 13a, and that is along the width Db of the large diameter through hole 12 and is perpendicular to the direction of the maximum width Da of the large diameter through hole 12. In other words, the second pressing portion 66 is disposed at a position that includes the center position in the longitudinal direction of the arc portion 13a.

[0133] The rack bar 30 stored in the rack housing 10 formed in this manner has the protruding portion 33 of the rack tooth forming portion 31 stored in the protruding portion storing portion 13b of the large diameter through hole 12, and is stored inside the rack housing 10 with the back portion 32 of the rack tooth forming portion 31 oriented to face the arc portion 13a of the large diameter through hole 12. Therefore, in the rack housing 10, when the rack tooth forming portion 31 of the rack bar 30 is stored inside the large diameter housing portion 11, the inner circumferential surface 13 of the large diameter housing portion 11 in the range spanning the two protruding portions 33 and the back portion 32 of the rack tooth forming portion 31 is formed in a shape that follows the surface of the rack bar 30.

[0134] Because the inner peripheral surface 13 of the large diameter housing portion 11 is formed in a shape that follows the surface of the rack bar 30 in this way, the minimum gap between the inner peripheral surface 13 of the large diameter housing portion 11 and the rack bar 30 is about 1 mm. Therefore, the gap between the arc portion 13a of the large diameter through hole 12 and the back surface portion 32 of the rack tooth forming portion 31 is about 1 mm, and the pressing member 67 of the second pressing portion 66 that protrudes from the arc portion 13a of the large diameter through hole 12 and abuts against the back surface portion 32 of the rack tooth forming portion 31 also protrudes by an amount Pa of about 1 mm from the arc portion 13a.

[0135] In the second embodiment, the large diameter through hole 12 of the large diameter housing portion 11 has the arc portion 13a and the protruding portion storage portion 13b as described above, and by storing the protruding portion 33 of the rack tooth forming portion 31 in the protruding portion storage portion 13b and arranging the back portion 32 of the rack tooth forming portion 31 to face the arc portion 13a, the inner circumferential surface 13 of the large diameter housing portion 11 can be made to conform to the shape of the surface of the rack bar 30. This makes it possible to reduce the gap between the inner circumferential surface 13 of the large diameter housing portion 11 and the rack bar 30, thereby reducing the protruding amount Pa of the second pressing portion 66 from the inner circumferential surface 13 of the large diameter housing portion 11 and making the protruding amount Pa of the second pressing portion 66 approximately the same as or smaller than the protruding amount Pb of the first pressing portion 61. Therefore, when the rack bar 30 moves linearly, the pressing member 67 is not pulled by the rack bar 30 and tilted, and the pressing member 67 can press the assist rack teeth 43 toward the second pinion gear 93, thereby suppressing the generation of abnormal noise caused by the pressing member 67 tilting.

[0136] Furthermore, by providing the arc portion 13a and the protrusion storage portion 13b in the large-diameter through-hole 12 of the large-diameter housing portion 11 and by shaping the inner circumferential surface 13 of the large-diameter housing portion 11 to conform to the shape of the rack-tooth forming portion 31 of the rack bar 30, the large-diameter housing portion 11 can be made more compact. In other words, by shaping the inner circumferential surface 13 of the large-diameter housing portion 11 to conform to the shape of the rack bar 30, the outer shape of the large-diameter housing portion 11 can also conform to the shape of the rack bar 30, thereby making the large-diameter housing portion 11 more compact. In other words, by shaping the inner circumferential surface 13 of the large-diameter housing portion 11 to conform to the shape of the rack bar 30, the size of the space inside the large-diameter housing portion 11 can be minimized, and the overall size of the large-diameter housing portion 11 can be minimized. As a result, the generation of abnormal noise can be suppressed and the rack housing 10 can be prevented from becoming larger.

[0137] [Third embodiment] Next, an electric power steering device 80 according to a third embodiment will be described. The same components as those in the first embodiment will be assigned the same reference numerals and descriptions thereof will be omitted. The following description will focus on the differences from the first embodiment.

[0138] Fig. 18 is a cross-sectional schematic view of a rack housing 10 and a rack bar 30 included in an electric power steering device 80 according to the third embodiment. Fig. 19 is a view taken along the arrow JJ in Fig. 18. In the third embodiment, the rack bar 30 also has a large diameter portion 41 and a small diameter portion 46, and the large diameter portion 41 has a rack tooth forming portion 31 on which assist rack teeth 43 are arranged. As in the first embodiment, the rack tooth forming portion 31 has protruding portions 33 on both sides in the direction of the maximum width Wa of the rack tooth forming portion 31 that protrude in the direction in which the maximum width Wa of the rack tooth forming portion 31 increases.

[0139] The rack housing 10 has a large diameter housing portion 11 and a small diameter housing portion 21, and the rack tooth forming portion 31 of the rack bar 30 is housed in the large diameter housing portion 11. The large diameter through hole 12 of the large diameter housing portion 11 is formed so that its shape when viewed in the longitudinal direction of the rack housing 10 is substantially elliptical, similar to the first embodiment.

[0140] In the third embodiment, the rack bar 30 stored in the rack housing 10 configured as above has the large diameter portion 41 and the small diameter portion 46 connected together with the central axis Ba of the large diameter portion 41 misaligned with the central axis Bb of the small diameter portion 46. In this case, the central axis Ba of the large diameter portion 41 of the rack bar 30 is the central axis of the large diameter round bar portion 42 of the large diameter portion 41, and the central axis Bb of the small diameter portion 46 is the central axis of the small diameter round bar portion 47 of the small diameter portion 46. Furthermore, since the central axis of the large diameter round bar portion 42 coincides with the central axis of the arc that forms the shape of the back surface portion 32 of the rack tooth forming portion 31, the central axis Ba of the large diameter portion 41 also becomes the central axis of the arc that forms the shape of the back surface portion 32 of the rack tooth forming portion 31. The large diameter portion 41, which is connected to the small diameter portion 46 with its central axis Ba shifted relative to the central axis Bb of the small diameter portion 46, is connected to the small diameter portion 46 with its central axis Ba shifted relative to the central axis Bb of the small diameter portion 46 toward the side where the second pressing portion 66 is located.

[0141] On the other hand, the bolt holes 55 arranged at both ends in the longitudinal direction of the rack bar 30 are arranged so that the central axis Cb of the bolt hole 55 arranged in the small diameter portion 46 and the central axis Ca of the bolt hole 55 arranged in the large diameter portion 41 are located on extensions of each other. In other words, although the large diameter portion 41 and the small diameter portion 46 of the rack bar 30 are connected to each other with their respective central axes Ba and Bb offset from each other, the bolt holes 55 arranged at both ends of the rack bar 30 are arranged in a positional relationship such that the central axes Ca and Cb are on extensions of each other.

[0142] For this reason, of the bolt holes 55 arranged at both ends of the rack bar 30, one bolt hole 55 is arranged at a position that coincides with the central axis of the rack bar 30 in which the bolt hole 55 is formed, and the other bolt hole 55 is arranged at a position that is offset from the central axis of the rack bar 30 in which the bolt hole 55 is formed. In the third embodiment, the bolt hole 55 formed in the small diameter portion 46 is arranged at a position where the central axis Cb of the bolt hole 55 coincides with the central axis Bb of the small diameter portion 46, and the bolt hole 55 formed in the large diameter portion 41 is arranged at a position where the central axis Ca of the bolt hole 55 is offset from the central axis Ba of the large diameter portion 41. Therefore, in the third embodiment, the large diameter portion 41 of the rack bar 30 that is connected at a position that is offset from the small diameter portion 46 is connected to the small diameter portion 46 at a position where the central axis Ba of the large diameter portion 41 is offset toward the side where the second pressing portion 66 is located with respect to the central axis Cb of the bolt hole 55 arranged in the small diameter portion 46.

[0143] Note that, because the rack-tooth-forming portion 31 of the large-diameter portion 41 is formed by forging, the central axis of the arc of the back surface portion 32 may be misaligned with the central axis of the large-diameter round bar portion 42. In this case, the central axis Ba of the large-diameter portion 41 may be the central axis of the radius of curvature of the apex of the arc that forms the back surface portion 32 of the rack-tooth-forming portion 31. In other words, the large-diameter portion 41 may be connected to the small-diameter portion 46 with the central axis of the radius of curvature of the apex of the arc that forms the back surface portion 32 of the rack-tooth-forming portion 31 misaligned with the central axis Bb of the small-diameter portion 46.

[0144] Furthermore, when the central axis of the large diameter round bar portion 42 and the central axis of the back surface portion 32 of the rack-tooth forming portion 31 are misaligned, it is sufficient that either the central axis of the large diameter round bar portion 42 or the central axis of the back surface portion 32 of the rack-tooth forming portion 31 is misaligned with the central axis Bb of the small diameter portion 46 of the large diameter portion 41. In other words, it is sufficient that at least one of the central axes of the large diameter round bar portion 42 and the central axis of the back surface portion 32 of the rack-tooth forming portion 31 is misaligned with the central axis Bb of the small diameter portion 46 of the large diameter portion 41. In other words, it is sufficient that at least one of the central axes of the large diameter round bar portion 42 and the central axis of the back surface portion 32 of the rack-tooth forming portion 31 is set as the central axis Ba of the large diameter portion 41, and that the central axis regarded as the central axis Ba of the large diameter portion 41 is misaligned with the central axis Bb of the small diameter portion 46.

[0145] The rack bar 30 formed in this manner is stored in the rack housing 10 at a position where the central axis Bb of the small diameter round bar portion 47 of the small diameter portion 46 coincides with the central axis Hb of the small diameter through hole 22 of the small diameter housing portion 21 of the rack housing 10. Therefore, the rack bar 30 is stored in the rack housing 10 at a position where the central axis Ba of the large diameter round bar portion 42 of the large diameter portion 41 is eccentric with respect to the central axis Ha of the large diameter through hole 12 of the large diameter housing portion 11 of the rack housing 10. In other words, the rack bar 30 is stored in the rack housing 10 at a position where the central axis Ba of the large diameter portion 41 is eccentric with respect to the central axis Ha of the large diameter through hole 12 of the large diameter housing portion 11, on the side where the second pressing portion 66 is located.

[0146] The rack bar 30 is stored in the rack housing 10 at a position where the central axis Bb of the small diameter portion 46 coincides with the central axis Hb of the small diameter through hole 22 of the small diameter housing portion 21, and therefore the bolt hole 55 arranged in the small diameter portion 46 is arranged at a position where the central axis Cb coincides with the central axis Hb of the small diameter through hole 22. Furthermore, the bolt hole 55 arranged in the large diameter portion 41 of the rack bar 30 is also arranged at a position where the central axis Ca coincides with the central axis Ha of the large diameter through hole 12 of the large diameter housing portion 11.

[0147] The bolt holes 55 arranged at both ends of the rack bar 30 have central axes Ca and Cb that are located on extensions of each other, and therefore the ball joints 50 (see FIG. 8) whose bolt portions 52 (see FIG. 8) screw into these bolt holes 55 are also arranged in a positional relationship such that the central axes of the ball joints 50 are located on extensions of each other. In the third embodiment, the ball joints 50 arranged at both ends of the rack bar 30 are arranged at positions where the center lines of the respective ball joints 50, i.e., the central axes of the bolt portions 52 of the ball joints 50, are aligned on the central axis Bb of the small diameter portion 46 of the rack bar 30.

[0148] The rack bar 30 is stored in the rack housing 10 with the central axis Ba of the large diameter portion 41 eccentric to the side where the second pressing portion 66 is located with respect to the central axis Ha of the large diameter through hole 12 of the large diameter housing portion 11. For this reason, the large diameter portion 41 of the rack bar 30 is stored with the distance from the inner circumferential surface 13 of the large diameter housing portion 11 on the back surface portion 32 side, which is the surface opposite the assist rack tooth 43 side, being smaller than the part of the large diameter portion 41 on the assist rack tooth 43 side. In other words, since the back surface portion 32 of the rack tooth forming portion 31 of the rack bar 30 faces the second pressing portion 66 arranged in the rack housing 10, in a state where the central axis Ba of the large diameter portion 41 is eccentric to the side where the second pressing portion 66 is located with respect to the central axis Ha of the large diameter through hole 12, the large diameter portion 41 of the rack bar 30 is stored with the distance from the inner circumferential surface 13 of the large diameter housing portion 11 being smaller on the back surface portion 32 side than on the assist rack tooth 43 side.

[0149] Fig. 20 is a cross-sectional view of the rack tooth forming portion 31 of the rack bar 30 of the electric power steering device 80 according to the third embodiment. Note that Fig. 20 is a cross-sectional view of the rack bar 30 of the electric power steering device 80 according to the third embodiment, taken at the same position as the cross section BB in Fig. 3. In the electric power steering device 80 according to the third embodiment, the large diameter portion 41 of the rack bar 30 has chamfers 34 at both ends in a direction perpendicular to the longitudinal direction of the large diameter portion 41 on the side where the back surface portion 32 of the portion where the assist rack teeth 43 are arranged is located.

[0150] The chamfers 34 are formed on the side where the rear surface portion 32 of the rack tooth forming portion 31 is located, near the end of each of the two overhanging portions 33 that the rack tooth forming portion 31 of the large diameter portion 41 of the rack bar 30 has, opposite the side where the other overhanging portion 33 is located. That is, the two overhanging portions 33 that the rack tooth forming portion 31 has have chamfers 34 on both ends in a direction perpendicular to the longitudinal direction of the large diameter portion 41, on the side where the rear surface portion 32 is located. The chamfers 34 are formed over the entire rack tooth forming portion 31 in the longitudinal direction of the rack bar 30.

[0151] In the third embodiment, a chamfer 34 is formed on the protruding portion 33 of the rack tooth forming portion 31 of the rack bar 30, and therefore, the large diameter housing portion 11 of the rack housing 10 can easily ensure a distance between the large diameter portion 41 of the rack bar 30 stored in the large diameter housing portion 11 and the inner circumferential surface 13 of the large diameter housing portion 11. That is, in the third embodiment, the rack bar 30 is stored in the rack housing 10 with the central axis Ba of the large diameter portion 41 eccentric to the side where the second pressing portion 66 is located with respect to the central axis Ha of the large diameter through hole 12, but since the chamfer 34 is formed on the protruding portion 33 of the rack tooth forming portion 31, the large diameter portion 41 of the rack bar 30 is less likely to come into contact with the inner circumferential surface 13 of the large diameter housing portion 11.

[0152] As a result, the large diameter portion 41 of the rack bar 30 is connected to the small diameter portion 46 without coming into contact with the inner circumferential surface 13 of the large diameter housing portion 11, with the central axis Ba of the large diameter portion 41 shifted toward the side where the second pressing portion 66 is located with respect to the central axis Cb of the bolt hole 55 arranged in the small diameter portion 46. Therefore, the back surface portion 32 of the rack tooth forming portion 31 of the large diameter portion 41 of the rack bar 30 is closer to the inner circumferential surface 13 of the large diameter housing portion 11, so the protrusion amount Pa of the second pressing portion 66 from the inner circumferential surface 13 of the large diameter housing portion 11 can be reduced.

[0153] As described above, in the third embodiment, the large diameter portion 41 of the rack bar 30 is connected to the small diameter portion 46 at a position where the central axis Ba is shifted toward the side where the second pressing portion 66 is located with respect to the central axis Cb of the bolt hole 55 arranged in the small diameter portion 46. This reduces the gap between the rack bar 30 and the portion of the inner circumferential surface 13 of the large diameter housing portion 11 where the second pressing portion 66 is located. This reduces the protrusion amount Pa of the second pressing portion 66 from the inner circumferential surface 13 of the large diameter housing portion 11, making it possible to make the protrusion amount Pa of the second pressing portion 66 approximately the same as or smaller than the protrusion amount Pb of the first pressing portion 61. Therefore, when the rack bar 30 moves linearly, the pressing member 67 is not pulled by the rack bar 30 and tilted, and the pressing member 67 can press the assist rack teeth 43 toward the second pinion gear 93. As a result, the generation of abnormal noise caused by tilting of the pressing member 67 can be suppressed.

[0154] Furthermore, the overhanging portion 33 of the rack tooth forming portion 31 of the rack bar 30 has chamfers 34 at both ends on the side where the back surface portion 32 is located, so when the large diameter portion 41 of the rack bar 30 is connected to the small diameter portion 46 at a position shifted toward the side where the second pressing portion 66 is located relative to the small diameter portion 46, the overhanging portion 33 of the rack tooth forming portion 31 is less likely to come into contact with the inner circumferential surface 13 of the large diameter housing portion 11. Therefore, the rack bar 30 can be connected to the small diameter portion 46 at a position shifted toward the side where the second pressing portion 66 is located relative to the small diameter portion 46, without the overhanging portion 33 of the rack tooth forming portion 31 coming into contact with the inner circumferential surface 13 of the large diameter housing portion 11. This makes it possible to reduce the gap between the back surface portion 32 of the rack tooth forming portion 31 of the rack bar 30 and the inner circumferential surface 13 of the large diameter housing portion 11, and to reduce the amount of protrusion Pa of the second pressing portion 66 from the inner circumferential surface 13 of the large diameter housing portion 11. Therefore, when the rack bar 30 moves linearly, the pressing member 67 is not pulled by the rack bar 30 and tilted, and the pressing member 67 can press the assist rack teeth 43 toward the second pinion gear 93. As a result, it is possible to suppress the generation of abnormal noise caused by the pressing member 67 tilting.

[0155] [Fourth embodiment] Next, an electric power steering device 80 according to a fourth embodiment will be described. The same components as those in the first embodiment will be assigned the same reference numerals and descriptions thereof will be omitted. The following description will focus on the differences from the first embodiment.

[0156] Fig. 21 is a cross-sectional schematic view of a rack housing 10 and a rack bar 30 included in an electric power steering device 80 according to a fourth embodiment. Fig. 22 is a view taken along the arrow KK in Fig. 21. In the fourth embodiment, the rack bar 30 also has a large diameter portion 41 and a small diameter portion 46, and the large diameter portion 41 has a rack tooth forming portion 31 on which assist rack teeth 43 are arranged. As in the first embodiment, the rack tooth forming portion 31 has protruding portions 33 on both sides in the direction of the maximum width Wa of the rack tooth forming portion 31 that protrude in the direction in which the maximum width Wa of the rack tooth forming portion 31 increases.

[0157] The rack housing 10 has a large diameter housing portion 11 and a small diameter housing portion 21, and the rack tooth forming portion 31 of the rack bar 30 is housed in the large diameter housing portion 11. The large diameter through hole 12 of the large diameter housing portion 11 is formed so that its shape when viewed in the longitudinal direction of the rack housing 10 is substantially elliptical, similar to the first embodiment.

[0158] In the fourth embodiment, the large diameter housing portion 11 and the small diameter housing portion 21 of the rack housing 10 are disposed in a positional relationship in which the central axis Ha of the large diameter housing portion 11 is offset from the central axis Hb of the small diameter housing portion 21. More specifically, the large diameter housing portion 11 of the rack housing 10 is coupled to the small diameter housing portion 21 at a position in which the central axis Ha of the large diameter through hole 12 in the large diameter housing portion 11 is offset from the central axis Hb of the small diameter through hole 22 in the small diameter housing portion 21 toward the side where the second pinion gear 93 is located.

[0159] On the other hand, the rack bar 30 has the large diameter portion 41 and the small diameter portion 46 connected in a positional relationship in which the central axis Ba of the large diameter portion 41 and the central axis Bb of the small diameter portion 46 are on extensions of each other. The rack bar 30 stored in the rack housing 10 is disposed at a position where the central axis Bb of the small diameter portion 46 of the rack bar 30 coincides with the central axis Hb of the small diameter housing portion 21 of the rack housing 10. Therefore, the large diameter housing portion 11, which is disposed at a position where the central axis Ha is offset from the central axis Hb of the small diameter housing portion 21, is connected to the small diameter housing portion 21 in a position where the central axis Ha of the large diameter housing portion 11 is offset from the central axis Ba of the large diameter portion 41 of the rack bar 30 stored in the large diameter housing portion 11. In other words, when the large diameter portion 41 of the rack bar 30 is stored inside the large diameter housing portion 11, the large diameter housing portion 11 stores the large diameter portion 41 at a position where the central axis Ba of the large diameter portion 41 is eccentric with respect to the central axis Ha of the large diameter housing portion 11.

[0160] The direction in which the central axis Ha of the large diameter housing portion 11 deviates from the central axis Hb of the small diameter housing portion 21 is the side on which the second pinion gear 93 is located, and therefore the direction in which the central axis Ha of the large diameter housing portion 11 deviates from the central axis Ba of the large diameter portion 41 of the rack bar 30 is the side on which the second pinion gear 93 is located. In other words, the large diameter portion 41 of the rack bar 30, which is stored in the large diameter housing portion 11 at a position eccentric to the central axis Ha of the large diameter housing portion 11, is stored inside the large diameter housing portion 11 in a state where it is eccentric to the side opposite to the side on which the second pinion gear 93 is located with respect to the large diameter portion 41. As a result, the large diameter portion 41 of the rack bar 30, which is stored in the large diameter housing portion 11, is stored with the distance from the inner circumferential surface 13 of the large diameter housing portion 11 being smaller on the back surface portion 32 side, which is the surface opposite to the assist rack teeth 43 side, than on the portion of the large diameter portion 41 on the assist rack teeth 43 side.

[0161] In the fourth embodiment, similarly to the third embodiment, chamfers 34 are formed on the protruding portions 33 of the rack tooth forming portions 31 of the large diameter portion 41 of the rack bar 30. That is, the chamfers 34 are formed on the sides where the back surface portions 32 of the rack tooth forming portions 31 are located, near the ends of the two protruding portions 33 of the rack tooth forming portions 31 of the large diameter portion 41 of the rack bar 30, opposite to the sides where the other protruding portion 33 is located.

[0162] For this reason, in the fourth embodiment, as in the third embodiment, the large diameter housing portion 11 of the rack housing 10 makes it easier to ensure the distance between the large diameter portion 41 of the rack bar 30 stored in the large diameter housing portion 11 and the inner surface 13 of the large diameter housing portion 11.

[0163] As a result, the large diameter housing portion 11 of the rack housing 10 is connected to the small diameter housing portion 21 at a position where the central axis Ha of the large diameter through hole 12 is shifted toward the side where the second pinion gear 93 is located with respect to the central axis Hb of the small diameter through hole 22 in the small diameter housing portion 21, without coming into contact with the rack tooth forming portion 31 of the large diameter portion 41 of the rack bar 30. Therefore, the portion of the inner circumferential surface 13 of the large diameter housing portion 11 where the second pressing portion 66 is located is closer to the back surface portion 32 of the rack tooth forming portion 31 of the large diameter portion 41 of the rack bar 30, so the protrusion amount Pa of the second pressing portion 66 from the inner circumferential surface 13 of the large diameter housing portion 11 can be reduced.

[0164] As described above, in the fourth embodiment, the large-diameter housing portion 11 of the rack housing 10 is connected to the small-diameter housing portion 21 at a position where the central axis Ha of the large-diameter housing portion 11 is shifted toward the side where the second pinion gear 93 is located with respect to the central axis Hb of the small-diameter housing portion 21. This reduces the gap between the rack bar 30 and the portion of the inner circumferential surface 13 of the large-diameter housing portion 11 where the second pressing portion 66 is located. This reduces the protrusion amount Pa of the second pressing portion 66 from the inner circumferential surface 13 of the large-diameter housing portion 11, making the protrusion amount Pa of the second pressing portion 66 approximately the same as or smaller than the protrusion amount Pb of the first pressing portion 61. Therefore, when the rack bar 30 moves linearly, the pressing member 67 is not pulled by the rack bar 30 and tilted, and the pressing member 67 can press the assist rack teeth 43 toward the second pinion gear 93. As a result, the generation of abnormal noise caused by tilting of the pressing member 67 can be suppressed.

[0165] [Fifth embodiment] Next, an electric power steering device 80 according to a fifth embodiment will be described. The same components as those in the first embodiment will be assigned the same reference numerals and descriptions thereof will be omitted. The following description will focus on the differences from the first embodiment.

[0166] FIG. 23 is a cross-sectional view of the rack housing 10 and the rack bar 30 included in an electric power steering device 80 according to the fifth embodiment, and is a schematic cross-sectional view of the rack housing 10 at a position including the second pressing portion 66 and the second pinion gear 93. FIG. 24 is a cross-sectional view of the rack housing 10 at a position different from that shown in FIG. 23, and is a schematic cross-sectional view of the rack housing 10 at a position including the first pressing portion 61 and the first pinion gear 92. In the fifth embodiment, the rack bar 30 also has a large diameter portion 41 and a small diameter portion 46, and the large diameter portion 41 has a rack-tooth forming portion 31 on which the assist rack teeth 43 are arranged. As in the first embodiment, the rack-tooth forming portion 31 has protruding portions 33 (see FIG. 6) on both sides in the direction of the maximum width Wa of the rack-tooth forming portion 31 that protrude in the direction in which the maximum width Wa of the rack-tooth forming portion 31 increases.

[0167] The rack housing 10 has a large diameter housing portion 11 and a small diameter housing portion 21, and the rack tooth forming portion 31 of the rack bar 30 is stored in the large diameter housing portion 11. As in the second embodiment, the large diameter through hole 12 of the large diameter housing portion 11 has an irregular shape when viewed in the longitudinal direction of the rack housing 10, with an arc portion 13a and a protrusion portion storing portion 13b on the inner circumferential surface 13 of the large diameter through hole 12 (see FIGS. 28 and 29).

[0168] Fig. 25 is a schematic cross-sectional view of the rack housing 10 according to the fifth embodiment. Fig. 26 is a schematic cross-sectional view of the rack housing 10 showing a state in which the rack bar 30 is stored in the rack housing 10 shown in Fig. 25. Note that in the fifth embodiment, the first pressing portion 61 and the second pressing portion 66 are arranged at different positions in the circumferential direction of the rack housing 10, but in Figs. 25 and 26, the first pressing portion 61 and the second pressing portion 66, and the first pinion gear 92 and the second pinion gear 93 are illustrated as being located on the same plane for convenience.

[0169] In the fifth embodiment, the inner peripheral surface of the rack housing 10 that stores the rack bar 30 has an expanded diameter portion 28. The expanded diameter portion 28 is formed in a tapered shape such that the size of the opening area of ​​the inner peripheral surface when viewed in the longitudinal direction of the rack housing 10 increases toward a predetermined direction in the longitudinal direction of the rack housing 10. The minimum gap between the tapered expanded diameter portion 28 and the rack bar 30 is about 1 mm.

[0170] The predetermined direction here refers to a predetermined direction in the longitudinal direction of the rack housing 10 or a predetermined direction in the axial direction of the rack bar 30 stored in the rack housing 10, and does not include the radial direction of the rack housing 10. The expanded diameter portion 28 is formed so that the opening area increases from a position near where the pressing portion 60 is located in the longitudinal direction of the rack housing 10 toward the end of the rack housing 10 in the longitudinal direction.

[0171] In the fifth embodiment, the expanded diameter portion 28 includes a first expanded diameter portion 28a located closer to the small diameter housing portion 21 in the longitudinal direction of the rack housing 10 and a second expanded diameter portion 28b located closer to the large diameter housing portion 11. That is, the inner circumferential surface 23 of the small diameter housing portion 21 includes the first expanded diameter portion 28a, in which the size of the opening area of ​​the inner circumferential surface 23 when viewed in the longitudinal direction of the rack housing 10 increases toward a predetermined direction in the longitudinal direction of the rack housing 10. Similarly, the inner circumferential surface 13 of the large diameter housing portion 11 includes the second expanded diameter portion 28b, in which the size of the opening area of ​​the inner circumferential surface 13 when viewed in the longitudinal direction of the rack housing 10 increases toward a predetermined direction in the longitudinal direction of the rack housing 10.

[0172] A boundary 28c between the first expanded diameter portion 28a and the second expanded diameter portion 28b is located between the positions of the first pressing portion 61 and the second pressing portion 66 in the longitudinal direction of the rack housing 10. More specifically, the boundary 28c between the first expanded diameter portion 28a and the second expanded diameter portion 28b is located near the position of the first pressing portion 61, between the positions of the first pressing portion 61 and the second pressing portion 66. That is, the boundary 28c between the first expanded diameter portion 28a and the second expanded diameter portion 28b is located between the through hole 26 in which the first pressing portion 61 is disposed and the through hole 16 in which the second pressing portion 66 is disposed. Therefore, the entire first expanded diameter portion 28a is located in the small-diameter housing portion 21, and forms the small-diameter through hole 22. In contrast, the second expanded diameter portion 28b is located across the large diameter housing portion 11 and the small diameter housing portion 21, and forms not only the large diameter through hole 12 but also part of the small diameter through hole 22 (see FIG. 23).

[0173] These first expanded diameter portion 28a and second expanded diameter portion 28b are formed by a core (not shown) used when manufacturing the rack housing 10 by casting. The tapered shape of expanded diameter portion 28 is formed as a so-called draft angle for withdrawing the core from the rack housing 10 in the longitudinal direction of the rack housing 10 after the rack housing 10 is cast. The cores include a core for forming first expanded diameter portion 28a and a core for forming second expanded diameter portion 28b, and boundary portion 28c is the abutting portion between the core for forming first expanded diameter portion 28a and the core for forming second expanded diameter portion 28b when the rack housing 10 is cast.

[0174] The position of boundary 28c between first expanded diameter portion 28a and second expanded diameter portion 28b may be a position other than a position between the positions of first pressing portion 61 and second pressing portion 66 in the longitudinal direction of rack housing 10. The position of boundary 28c between first expanded diameter portion 28a and second expanded diameter portion 28b may be, for example, the same position as the position where first pressing portion 61 is arranged in the longitudinal direction of rack housing 10, or may be located on the opposite side of the position where second pressing portion 66 is located relative to the position where first pressing portion 61 is arranged in the longitudinal direction of rack housing 10.

[0175] The small diameter through hole 22 has a substantially circular shape when viewed in the longitudinal direction of the rack housing 10. Therefore, the first expanded diameter portion 28a is formed in a substantially truncated cone shape, with the opening area increasing from the position of the boundary portion 28c toward the side where the ball joint accommodating portion 25 (see FIG. 24) of the small diameter housing portion 21 is located. That is, the opening area of ​​the first expanded diameter portion 28a when viewed in the longitudinal direction of the rack housing 10 is smallest at the position of the boundary portion 28c and largest at the end on the ball joint accommodating portion 25 side.

[0176] Furthermore, second expanded diameter portion 28b, which forms part of small diameter through hole 22 and large diameter through hole 12, has an opening area that increases from the position of boundary portion 28c toward the side where ball joint accommodating portion 15 (see FIG. 23) of large diameter housing portion 11 is located. That is, when viewed in the longitudinal direction of rack housing 10, the opening area of ​​second expanded diameter portion 28b is smallest at the position of boundary portion 28c and largest at the end on the ball joint accommodating portion 15 side.

[0177] The tapered expanded diameter portion 28 is formed so that, at the position in the circumferential direction of the rack housing 10 where the pressing portion 60 is disposed, the inner circumferential surface of the rack housing 10 extends along the longitudinal direction of the rack housing 10. In other words, the tapered axis IA (see FIG. 25), which is the shape of the expanded diameter portion 28, is inclined with respect to the central axes Ha, Hb (see FIG. 25) of the rack housing 10, and the inner circumferential surface of the rack housing 10 that passes through the position where the pressing portion 60 is disposed extends along the longitudinal direction of the rack housing 10.

[0178] In this case, the central axes Ha and Hb of the rack housing 10 coincide with the central axis of the rack bar 30 stored in the rack housing 10 and extend in the longitudinal direction of the rack housing 10. In other words, the longitudinal direction of the rack housing 10 coincides with the extension direction of the central axes Ha and Hb of the rack housing 10.

[0179] As described above, the tapered axis IA of the expanded diameter portion 28 of the rack housing 10 is inclined with respect to the central axes Ha and Hb of the rack housing 10, and therefore the inner circumferential surface of the rack housing 10 is inclined with respect to the longitudinal direction of the rack housing 10 at a position different from the position where the pressing portion 60 is disposed in the circumferential direction of the rack housing 10. As a result, the expanded diameter portion 28 can reduce the distance between the inner circumferential surface of the rack housing 10 at the position where the pressing portion 60 is disposed and the rack bar 30 stored in the rack housing 10, while ensuring the draft angle of the core when the rack housing 10 is cast. In other words, the expanded diameter portion 28 can ensure the draft angle of the core when the rack housing 10 is cast, while preventing the distance between the inner circumferential surface of the rack housing 10 and the rack bar 30 from increasing due to the draft angle of the core when the rack housing 10 is cast.

[0180] 26 , in the first expanded diameter portion 28a, a first line L1 of the inner circumferential surface 23 that passes through a position where the first pressing portion 61 is disposed extends substantially parallel to the central axis Hb of the rack housing 10. The first line L1 of the inner circumferential surface 23 that passes through a position where the first pressing portion 61 is disposed in the first expanded diameter portion 28a is preferably parallel to the axis of the rack bar 30. On the other hand, a second line L2 of the inner circumferential surface 23 that passes through a position in the first expanded diameter portion 28a different from the position where the first pressing portion 61 is disposed is inclined with respect to the first line L1 of the inner circumferential surface 23 and the central axis Hb of the rack housing 10.

[0181] 24 , in a cross section taken along the longitudinal direction of the rack housing 10, where the position in the circumferential direction of the rack housing 10 where the first pressing portion 61 is disposed, the first line L1 of the inner circumferential surface 23 passing through the position where the first pressing portion 61 is disposed extends approximately parallel to the longitudinal direction of the rack housing 10, and extends substantially along the longitudinal direction of the rack housing 10. It is preferable that the first line L1 of the inner circumferential surface 23 passing through the position where the first pressing portion 61 is disposed in the first enlarged diameter portion 28a is parallel to the axis of the rack bar 30.

[0182] On the other hand, a second line L2 of the inner circumferential surface 23, which passes through a position in the first expanded diameter portion 28a different from the position where the first pressing portion 61 is disposed, in the same cross section of the rack housing 10, is inclined with respect to the first line L1 of the inner circumferential surface 23 and the longitudinal direction of the rack housing 10. In other words, the second line L2 of the first expanded diameter portion 28a is inclined with respect to the first line L1 and the longitudinal direction of the rack housing 10 in a direction in which the distance from the first line L1 of the first expanded diameter portion 28a increases as the second line L2 moves from the boundary portion 28c side toward the side where the ball joint accommodating portion 25 of the small diameter housing portion 21 is located.

[0183] As a result, the first expanded diameter portion 28a can ensure the draft angle of the core when casting the rack housing 10, while reducing the distance between the inner circumferential surface 23 of the rack housing 10 at the position where the first pressing portion 61 is disposed and the rack bar 30 stored in the rack housing 10. Therefore, the first expanded diameter portion 28a can reduce the protrusion amount Pb (see FIG. 16 ) of the first pressing portion 61 from the inner circumferential surface 23 of the rack housing 10, while ensuring the draft angle of the core when casting the rack housing 10.

[0184] In other words, when the inner circumferential surface 23 of the rack housing 10 has the first expanded diameter portion 28a and thus has a draft gradient for the core, if the distance from the boundary portion 28c in the longitudinal direction of the rack housing 10 to the position where the first pressing portion 61 is disposed is large, the distance between the portion of the inner circumferential surface 23 of the rack housing 10 where the first pressing portion 61 is disposed and the rack bar 30 tends to increase. In this case, the protrusion amount Pb of the first pressing portion 61 from the inner circumferential surface 23 of the rack housing 10 also tends to increase. However, in the fifth embodiment, the first line L1 of the first expanded diameter portion 28a extends substantially parallel to the longitudinal direction of the rack housing 10, and therefore, the distance between the portion of the inner circumferential surface 23 of the rack housing 10 where the first pressing portion 61 is disposed and the rack bar 30 can be prevented from increasing. As a result, the first expanded diameter portion 28a can reduce the protrusion amount Pb of the first pressing portion 61 from the inner circumferential surface 23 of the rack housing 10 while ensuring the draft gradient for the core.

[0185] 26 , in the second expanded diameter portion 28b, a first line L1 of the inner circumferential surface 13 that passes through the position where the second pressing portion 66 is disposed extends substantially parallel to the central axis Ha of the rack housing 10. The first line L1 of the inner circumferential surface 13 that passes through the position where the second pressing portion 66 is disposed in the second expanded diameter portion 28b is preferably parallel to the axis of the rack bar 30. On the other hand, a second line L2 of the inner circumferential surface 13 that passes through a position in the second expanded diameter portion 28b different from the position where the second pressing portion 66 is disposed is inclined with respect to the first line L1 of the inner circumferential surface 13 and the central axis Ha of the rack housing 10.

[0186] 23 , a first line L1 of the inner circumferential surface 13 of the second expanded diameter portion 28b, which passes through the position in the circumferential direction of the rack housing 10 where the second pressing portion 66 is disposed, in the large diameter through hole 12, extends approximately parallel to the longitudinal direction of the rack housing 10, and substantially extends along the longitudinal direction of the rack housing 10. The first line L1 of the inner circumferential surface 13 of the large diameter through hole 12, which passes through the position in the second expanded diameter portion 28b where the second pressing portion 66 is disposed, is preferably parallel to the axis of the rack bar 30.

[0187] On the other hand, a second line L2 of the inner circumferential surface 13 of the large diameter through hole 12, which passes through a position in the same cross section of the rack housing 10 that is different from the position where the second pressing portion 66 is disposed in the second expanded diameter portion 28b, is inclined with respect to the first line L1 of the inner circumferential surface 13 and the longitudinal direction of the rack housing 10. In other words, the second line L2 of the large diameter through hole 12 in the second expanded diameter portion 28b is inclined with respect to the first line L1 and the longitudinal direction of the rack housing 10 in a direction in which the distance from the first line L1 of the large diameter through hole 12 in the second expanded diameter portion 28b increases from the boundary portion 28c side toward the side where the ball joint accommodating portion 15 of the large diameter housing portion 11 is located.

[0188] As a result, the second expanded diameter portion 28b can ensure the draft angle of the core when casting the rack housing 10, while reducing the distance between the inner circumferential surface 13 of the rack housing 10 at the position where the second pressing portion 66 is disposed and the rack bar 30 stored in the rack housing 10. Therefore, the second expanded diameter portion 28b can reduce the protrusion amount Pa (see FIG. 16 ) of the second pressing portion 66 from the inner circumferential surface 13 of the rack housing 10, while ensuring the draft angle of the core when casting the rack housing 10.

[0189] In other words, when the inner circumferential surface 13 of the rack housing 10 has the second expanded diameter portion 28b and thus has a draft gradient for the core, if the distance from the boundary portion 28c in the longitudinal direction of the rack housing 10 to the position where the second pressing portion 66 is disposed is large, the distance between the portion of the inner circumferential surface 13 of the rack housing 10 where the second pressing portion 66 is disposed and the rack bar 30 tends to increase. In this case, the protrusion amount Pa of the second pressing portion 66 from the inner circumferential surface 13 of the rack housing 10 also tends to increase. However, in the fifth embodiment, the first line L1 of the second expanded diameter portion 28b extends substantially parallel to the longitudinal direction of the rack housing 10, and therefore, the distance between the portion of the inner circumferential surface 13 of the rack housing 10 where the second pressing portion 66 is disposed and the rack bar 30 can be prevented from increasing. As a result, the second expanded diameter portion 28b can reduce the protrusion amount Pb of the second pressing portion 66 from the inner circumferential surface 13 of the rack housing 10 while ensuring the draft gradient for the core.

[0190] In the fifth embodiment, similarly to the first embodiment, the steering rack teeth 48 and the assist rack teeth 43 of the rack bar 30 are formed at mutually different positions in the circumferential direction of the small diameter portion 46 and the large diameter portion 41, and therefore the first pressing portion 61 and the second pressing portion 66 are also disposed at mutually different positions in the circumferential direction of the rack housing 10 corresponding to this. Therefore, the first line L1 of the first enlarged diameter portion 28a and the first line L1 of the second enlarged diameter portion 28b are also disposed at mutually different positions in the circumferential direction of the rack housing 10 corresponding to the first pressing portion 61 and the second pressing portion 66.

[0191] Furthermore, the first line L1 of the first expanded diameter portion 28a and the second expanded diameter portion 28b does not necessarily have to extend strictly along the longitudinal direction of the rack housing 10. For example, the first line L1 of the first expanded diameter portion 28a and the second expanded diameter portion 28b may be inclined with respect to the longitudinal direction of the rack housing 10 within a range of about 0.5° in the opposite direction to the inclination direction of the second line L2 with respect to the longitudinal direction of the rack housing 10.

[0192] Furthermore, the angle of the first line L1 of the first expanded diameter portion 28a and the second expanded diameter portion 28b may differ depending on the material of the rack housing 10. For example, when the rack housing 10 is made of a magnesium material, the draft angle of the core may be smaller than when the rack housing 10 is made of an aluminum material because magnesium material has low adhesion to a core made of an iron-based material. That is, when the rack housing 10 is made of an aluminum material, the first line L1 of the first expanded diameter portion 28a and the second expanded diameter portion 28b may be slightly inclined with respect to the longitudinal direction of the rack housing 10 to ensure the draft angle of the core. However, when the rack housing 10 is made of a magnesium material, the first line L1 of the first expanded diameter portion 28a and the second expanded diameter portion 28b may be aligned substantially along the longitudinal direction of the rack housing 10 without being inclined.

[0193] 27 is a cross-sectional view taken along line MM of FIG. 24. FIG. 28 is a cross-sectional view taken along line NN of FIG. 24. FIG. 29 is a cross-sectional view taken along line RR of FIG. 24. FIG. 30 is a cross-sectional view taken along line SS of FIG. 24. Here, the second expanded diameter portion 28b forms the large diameter through hole 12 and a part of the small diameter through hole 22. Therefore, the opening shape of the second expanded diameter portion 28b when viewed in the longitudinal direction of the rack housing 10 varies depending on the position in the longitudinal direction of the rack housing 10. For example, as shown in FIG. 30, the portion of the second expanded diameter portion 28b that forms the small diameter through hole 22 has an approximately circular opening when viewed in the longitudinal direction of the rack housing 10. Similarly, as shown in FIG. 27, the portion of the large diameter housing portion 11 that forms the ball joint accommodating portion 15 also has an approximately circular opening when viewed in the longitudinal direction of the rack housing 10.

[0194] 28 and 29, the opening shape of the portion of the second expanded diameter portion 28b that forms the large diameter through hole 12, as viewed in the longitudinal direction of the rack housing 10, is irregular, having an arc portion 13a and an overhang portion storage portion 13b, similar to the large diameter through hole 12 of the second embodiment. Therefore, when viewed in the longitudinal direction of the rack housing 10, the large diameter through hole 12 has a maximum width Da in the direction in which the two overhang portion storage portions 13b are arranged, which is larger than a width Db in a direction perpendicular to the maximum width Da of the large diameter through hole 12. In other words, when viewed in the longitudinal direction of the rack housing 10, the width Db of the large diameter through hole 12 in a direction passing through the center position of the maximum width Da of the large diameter through hole 12 and the center position in the longitudinal direction of the arc portion 13a is smaller than the maximum width Da of the large diameter through hole 12 in the direction in which the two overhang portion storage portions 13b are arranged.

[0195] At this time, the size of the opening area of ​​second expanded diameter portion 28b increases from the position of boundary portion 28c toward the side where ball joint accommodating portion 15 of large diameter housing portion 11 is located. Therefore, width Db and maximum width Da of large diameter through hole 12 vary in size depending on the position in the longitudinal direction of rack housing 10. For example, as shown in FIGS. 24 and 28, width Dbn and maximum width Dan of large diameter through hole 12 at a position in second expanded diameter portion 28b closer to ball joint accommodating portion 15 are larger than width Dbr and maximum width Dar of large diameter through hole 12 at a position in second expanded diameter portion 28b closer to boundary portion 28c as shown in FIGS. 24 and 29.

[0196] In other words, the second expanded diameter portion 28b maintains the irregular shape having the arc portion 13a and the protrusion portion storage portion 13b within the range where the large diameter through hole 12 is formed, and the opening area when viewed in the longitudinal direction of the rack housing 10 increases from a position closer to the boundary portion 28c in the longitudinal direction of the rack housing 10 toward the side where the ball joint accommodating portion 15 is located.

[0197] In the fifth embodiment, the large diameter through hole 12 has an irregular shape having the arc portion 13a and the protrusion storage portion 13b as in the second embodiment, so that it is possible to reduce the protrusion amount Pa (see FIGS. 16 and 17) of the second pressing portion 66 that protrudes from the inner circumferential surface 13 of the large diameter housing portion 11 and abuts against the back surface portion 32 of the rack tooth forming portion 31 of the rack bar 30. This makes it possible to suppress the generation of abnormal noise caused by the pressing member 67 of the second pressing portion 66 tilting.

[0198] Furthermore, by forming the large diameter through hole 12 in an irregular shape having the arc portion 13a and the protrusion storage portion 13b, the shape of the inner peripheral surface 13 of the large diameter housing portion 11 can be made to match the shape of the rack tooth forming portion 31 of the rack bar 30. This allows the outer shape of the large diameter housing portion 11 to also match the shape of the rack bar 30, making it possible to minimize the overall size of the large diameter housing portion 11 and thereby minimizing the size of the large diameter housing portion 11.

[0199] As described above, in the fifth embodiment, the inner circumferential surface 13 of the large-diameter housing portion 11 has the expanded diameter portion 28, and in a cross section taken along the longitudinal direction of the rack housing 10 at a position in the circumferential direction of the rack housing 10 where the second pressing portion 66 is to be disposed, the first line L1 of the inner circumferential surface 13 passing through the position where the second pressing portion 66 is to be disposed extends along the longitudinal direction of the rack housing 10. Therefore, without performing cutting on the inner circumferential surface 13, the position on the inner circumferential surface 13 where the second pressing portion 66 is to be disposed can be made into a surface that extends along the longitudinal direction of the rack housing 10, and the distance between the inner circumferential surface 13 of the rack housing 10 and the rack bar 30 at the position where the second pressing portion 66 is disposed can be reduced. Therefore, the protrusion amount Pa of the second pressing portion 66 from the inner circumferential surface 13 of the rack housing 10 can be reduced, and noise caused by tilting of the pressing member 67 of the second pressing portion 66 can be suppressed.

[0200] Furthermore, in the same cross section of the rack housing 10 where the first line L1 appears, the second line L2 of the inner circumferential surface 13 of the expanded diameter portion 28 is inclined, which passes through a position different from the position where the second pressing portion 66 is disposed, so that the draft angle of the core can be ensured when manufacturing the rack housing 10 by casting. This makes it easier to remove the core that forms the expanded diameter portion 28 when casting the rack housing 10, facilitating the manufacturing of the rack housing 10 by casting. As a result, manufacturing costs can be reduced and the generation of abnormal noise can be suppressed.

[0201] It is preferable that boundary 28c between first expanded diameter portion 28a and second expanded diameter portion 28b be located near an end in the longitudinal direction of rack housing 10. That is, boundary 28c is the abutment portion between the core that forms first expanded diameter portion 28a and the core that forms second expanded diameter portion 28b, and burrs may be generated at the abutment portion between the cores when casting rack housing 10. For this reason, it is preferable that the abutment portion between the core that forms first expanded diameter portion 28a and the core that forms second expanded diameter portion 28b, i.e., boundary 28c between first expanded diameter portion 28a and second expanded diameter portion 28b, be located near an end in the longitudinal direction of rack housing 10 so that burrs generated during casting can be removed by cutting. By positioning the butt joint between the core that forms the first expansion section 28a and the core that forms the second expansion section 28b at a position close to the longitudinal end of the rack housing 10, even if a burr occurs at the butt joint, it becomes easier to cut off the burr from the end of the rack housing 10.

[0202] Furthermore, the inner peripheral surface 13 of the rack housing 10 may be formed by reducing the diameter of the core used to form the inner peripheral surface 13, and only a portion of the inner peripheral surface 13 may be machined after the rack housing 10 is cast. That is, the diameter near the joint between the core used to form the first expanded diameter portion 28a and the core used to form the second expanded diameter portion 28b may be made smaller than the diameter of the rack bar 30, and after the rack housing 10 is cast, the area near the boundary 28c between the first expanded diameter portion 28a and the second expanded diameter portion 28b may be machined to ensure an inner diameter large enough to accommodate the rack bar 30. This allows the overall size of the inner peripheral surface 13 of the rack housing 10 to be made as small as possible.

[0203] Furthermore, when performing cutting near the boundary 28c between the first enlarged diameter portion 28a and the second enlarged diameter portion 28b, it is preferable to position the boundary 28c close to the longitudinal end of the rack housing 10. As a result, even when performing cutting near the boundary 28c between the first enlarged diameter portion 28a and the second enlarged diameter portion 28b, cutting of the inner circumferential surface 13 can be performed near the longitudinal end of the rack housing 10. This allows cutting to be performed without the cutting tool having to penetrate deep into the rack housing 10, making cutting easier. Furthermore, because cutting can be performed without the cutting tool having to penetrate deep into the rack housing 10, cutting can be performed while suppressing an increase in tool vibration during cutting, thereby suppressing a decrease in machining accuracy. This improves machining accuracy when cutting the inner circumferential surface 13 of the rack housing 10.

[0204] [Sixth embodiment] Next, an electric power steering device 80 according to a sixth embodiment will be described. The same components as those in the first embodiment will be assigned the same reference numerals and descriptions thereof will be omitted. The following description will focus on the differences from the first embodiment.

[0205] 31 is a schematic diagram of an electric power steering device 80 according to a sixth embodiment. The electric power steering device 80 according to the sixth embodiment includes a steering wheel 81, a steering shaft 82, a universal joint 84, an intermediate shaft 85, a universal joint 86, a stub shaft 87, a steering gear 90, a tie rod 94, a torque sensor 101, and a steering assist device 110, similar to the first embodiment.

[0206] In the sixth embodiment, unlike the first embodiment, the steering shaft 82 has an input shaft 82a and an output shaft 82b, and the input shaft 82a and the output shaft 82b are connected via a torsion bar (not shown). Unlike the first embodiment, the torque sensor 101 is disposed between the input shaft 82a and the output shaft 82b of the steering shaft 82, and detects the rotational torque transmitted between the input shaft 82a and the output shaft 82b.

[0207] Moreover, unlike the first embodiment, the steering gear 90 does not have a second pinion gear 93 (see FIG. 1), but has one pinion gear 91. The pinion gear 91 is provided integrally with the stub shaft 87.

[0208] Unlike the first embodiment, the steering assist device 110 has a worm reduction gear 95 connected to the output shaft 82b of the steering shaft 82. Therefore, the steering assist device 110 transmits the assist steering torque generated by the electric motor 102 to the output shaft 82b via the worm reduction gear 95. Therefore, in the sixth embodiment, the assist steering torque generated by the electric motor 102 is transmitted to the output shaft 82b and applied to the pinion gear 91 via the intermediate shaft 85 and the stub shaft 87. In other words, the steering assist device 110 applies a steering assist force to the pinion gear 91. The electric power steering device 80 according to the sixth embodiment is a single pinion assist type in which the rack bar 30 performs rectilinear motion by rotational motion transmitted from one pinion gear 91.

[0209] In the sixth embodiment, the steering force of the driver input to the steering wheel 81 reaches the pinion gear 91. The steering force transmitted to the pinion gear 91 is transmitted to the tie rod 94 via the rack bar 30, displacing the wheels.

[0210] Furthermore, the steering force input by the driver to the steering wheel 81 is transmitted to a torque sensor 101 arranged in a steering force transmission path from the steering wheel 81 to the pinion gear 91. At this time, the ECU 100 acquires the steering torque from the torque sensor 101 and also acquires a vehicle speed signal from a vehicle speed sensor 103. The ECU 100 then controls the operation of the electric motor 102. The auxiliary steering torque generated by the electric motor 102 is also transmitted to the output shaft 82b of the steering shaft 82 via the worm reduction gear 95, and then to the pinion gear 91 via the intermediate shaft 85 and the stub shaft 87.

[0211] As a result, the electric power steering device 80 according to the sixth embodiment assists the steering force of the driver by transmitting the auxiliary steering torque of the electric motor 102 to the pinion gear 91, which transmits the steering force of the driver to the rack bar 30. The electric power steering device 80 according to the sixth embodiment is a single-pinion type electric power steering device in which an assist force is applied to the pinion gear 91 that transmits the steering force of the driver to the rack bar 30 in this way.

[0212] Figure 32 is a cross-sectional schematic diagram of the rack housing 10 and the rack bar 30 in the sixth embodiment. Figure 33 is a view taken along the arrow TT in Figure 32. In the electric power steering device 80 according to the sixth embodiment, the pinion gear 91 does not have a second pinion gear 93 but has one pinion gear 91, and therefore the rack bar 30 does not have assist rack teeth 43 (see Figure 2) which are second rack teeth but has one rack tooth 35. In other words, the rack bar 30 has one rack tooth 35 that meshes with one pinion gear 91.

[0213] The rack bar 30 has a large diameter portion 41 and a small diameter portion 46, as in the first embodiment, and the rack teeth 35 are arranged on the large diameter portion 41. That is, the large diameter portion 41 has a rack tooth forming portion 31 with a protruding portion 33, as in the first embodiment, and the rack teeth 35 are arranged on the rack tooth forming portion 31. On the other hand, in the sixth embodiment, the rack teeth 35 are not provided on the small diameter portion 46 of the rack bar 30, and the small diameter portion 46 is formed by a small diameter round bar portion 47.

[0214] The rack housing 10 has a large diameter housing portion 11 and a small diameter housing portion 21, similar to the first embodiment, and the rack tooth forming portion 31 of the rack bar 30 is stored in the large diameter housing portion 11. Also, a pinion gear 91 that meshes with the rack teeth 35 of the rack tooth forming portion 31 is disposed in the large diameter housing portion 11 and meshes with the rack teeth 35 inside the large diameter housing portion 11. The large diameter through hole 12 of the large diameter housing portion 11 is formed so that its shape when viewed in the longitudinal direction of the rack housing 10 is substantially elliptical, similar to the first embodiment.

[0215] The rack bar 30 is stored inside the rack housing 10 with the direction of the maximum width Wa (see FIG. 6) of the rack tooth forming portion 31 oriented along the major axis of the ellipse that is the shape of the large diameter through hole 12, i.e., along the direction of the maximum width Da of the large diameter through hole 12. In other words, the rack bar 30 is stored inside the rack housing 10 with the direction of the width Wc (see FIG. 6) that is perpendicular to the maximum width Wa of the rack tooth forming portion 31 oriented along the minor axis of the ellipse that is the shape of the large diameter through hole 12, i.e., along the direction of the width Db that is perpendicular to the maximum width Da of the large diameter through hole 12.

[0216] Unlike the first embodiment, the sixth embodiment has one pinion gear 91 and one rack tooth 35. Therefore, in the sixth embodiment, one pressing portion 60 is also arranged on the rack housing 10. More specifically, the rack teeth 35 and the pinion gear 91 arranged on the rack bar 30 mesh with each other inside the large-diameter housing portion 11 of the rack housing 10, and therefore the pressing portion 60 is arranged on the large-diameter housing portion 11. The pressing portion 60 arranged on the large-diameter housing portion 11 presses the rack teeth 35 against the pinion gear 91 by having the pressing member 60a abut against the back surface portion 32 of the rack-tooth forming portion 31 and applying a biasing force to the rack bar 30 toward the side where the pinion gear 91 is located.

[0217] At this time, the rack bar 30 is stored inside the rack housing 10 with the direction of the width Wc, which is perpendicular to the maximum width Wa of the rack tooth forming portion 31, oriented along the minor axis of the ellipse that is the shape of the large diameter through-hole 12, and therefore the pressing portion 60, where the pressing member 60a abuts against the back surface portion 32 of the rack tooth forming portion 31, is positioned on the minor axis of the ellipse. As a result, the portion of the inner circumferential surface 13 of the large diameter housing portion 11 of the rack housing 10 where the pressing portion 60 is positioned is close to the rack bar 30.

[0218] For example, the gap between the rack bar 30 and the portion of the inner circumferential surface 13 of the large diameter housing portion 11 where the pressing portion 60 is arranged is equal to or smaller than the gap Ga between the inner circumferential surface 23 of the small diameter housing portion 21 and the rack bar 30. Therefore, the amount Pa of protrusion of the pressing member 60a from the inner circumferential surface 13 of the large diameter housing portion 11 in the pressing portion 60 is equal to or smaller than the gap Ga between the inner circumferential surface of the small diameter housing portion 21 and the rack bar 30.

[0219] Even in the sixth embodiment, which is a single-pinion type electric power steering device 80, by reducing the protrusion amount Pa of the pressing member 60a of the pressing portion 60, the pressing member 60a is not pulled by the rack bar 30 and tilted when the rack bar 30 moves linearly, and the pressing member 60a can press the rack teeth 35 of the rack bar 30 toward the pinion gear 91. This makes it possible to reduce backlash at the meshing portion between the rack teeth 35 and the pinion gear 91, thereby suppressing the generation of abnormal noise caused by the backlash. Furthermore, because tilting of the pressing member 60a of the pressing portion 60 can be suppressed, it is possible to suppress the generation of abnormal noise due to the stick-lip phenomenon and the generation of abnormal noise due to the pressing member 60a colliding with the through-hole 16 of the rack housing 10.

[0220] Furthermore, in the sixth embodiment, which is a single-pinion type electric power steering device 80, the width Db in the direction perpendicular to the maximum width Da of the large diameter through hole 12 of the large diameter housing portion 11 is also smaller than the maximum width Da of the large diameter through hole 12, so the size of the portion of the rack housing 10 that stores the large diameter portion 41 of the rack bar 30 can be reduced. This allows the rack housing 10 to be made more compact, and therefore the weight of the rack housing 10 can be reduced. As a result, the generation of abnormal noise can be suppressed, and an increase in the size of the rack housing 10 can be prevented.

[0221] [Variations] In the first, third, fourth, and sixth embodiments described above, the large diameter through hole 12 of the rack housing 10 has a substantially elliptical shape when viewed in the longitudinal direction of the rack housing 10, and in the second and fifth embodiments, the large diameter through hole 12 has a shape including the arc portion 13a and the protruding portion storage portion 13b when viewed in the longitudinal direction of the rack housing 10, but each embodiment and the large diameter through hole 12 may be combined as appropriate. For example, in an embodiment in which the large diameter through hole 12 has the arc portion 13a and the protruding portion storage portion 13b when viewed in the longitudinal direction of the rack housing 10 as in the second embodiment, the large diameter portion 41 and the small diameter portion 46 may be connected with their central axis Ba and central axis Bb of the large diameter portion 41 and the small diameter portion 46 of the rack bar 30 misaligned as in the third embodiment.

[0222] Furthermore, in a single-pinion electric power steering device 80 as shown in the sixth embodiment, the large-diameter through-hole 12 when viewed in the longitudinal direction of the rack housing 10 may be formed to have a shape including an arc portion 13a and a protrusion storage portion 13b, as in the second embodiment. Furthermore, in a single-pinion electric power steering device 80 as shown in the sixth embodiment, the inner circumferential surface of the rack housing 10 may have an expanded diameter portion 28, as in the fifth embodiment.

[0223] In the first embodiment described above, the rear surface portion 32 of the rack tooth forming portion 31 formed on the large diameter portion 41 of the rack bar 30 is formed in a shape that matches the shape of the outer circumferential surface of the large diameter round bar portion 42, but the rear surface portion 32 of the rack tooth forming portion 31 may have a shape different from that of the outer circumferential surface of the large diameter round bar portion 42. The rear surface portion 32 of the rack tooth forming portion 31 may be larger or smaller than the shape of the outer circumferential surface of the large diameter round bar portion 42.

[0224] Furthermore, in the first embodiment described above, the large diameter portion 41 of the rack bar 30 has round bar-shaped large diameter round bar portions 42 arranged on both sides of the rack tooth forming portion 31, but the large diameter portion 41 does not have to have the large diameter round bar portions 42. In other words, in the rack bar 30, the shapes of the large diameter round bar portions 42 located on both sides of the rack tooth forming portion 31 in the first embodiment may be formed in the same shape as the rack tooth forming portion 31.

[0225] Although the preferred embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments. The configurations described as the embodiments and modified examples may be combined as appropriate. [Explanation of symbols]

[0226] 10 Rack Housing 11 Large diameter housing part 12 Large diameter through hole 13, 23 Inner surface 13a Arc section 13b Extension storage section 15, 25 Ball joint housing 16, 26 through holes 17 Gearbox 21 Small diameter housing part 22 Small diameter through hole 28 Expanded diameter part 28a 1st enlarged diameter section 28b 2nd enlarged diameter section 28c Boundary 30 Rack Bar 31 Rack tooth forming part 32 Rear part 33 Overhang 34 Chamfering 35 rack teeth 41 Large diameter section 42 Large diameter round bar section 43 Assist rack teeth 46 Small diameter section 47 Small diameter round bar section 48 steering rack teeth 50 ball joint 51 Joint 52 Bolt section 55 bolt holes 60 Pressing part 60a, 62, 67 pressing members 61 First pressing part 63, 68 Springs 64, 69 Sealing member 66 Second pressing part 80 Electric power steering device 81 Steering wheel 82 Steering shaft 82a Input shaft 82b Output shaft 84, 86 universal joint 85 Intermediate shaft 87 Stub shaft 90 Steering gear 91 Pinion gear 92 1st pinion gear 92a Gear 93 2nd pinion gear 94 tie rod 95 Worm reducer 96 Worm Wheel 100 ECU 101 Torque sensor 102 electric motor 103 Vehicle speed sensor 104 Ignition switch 105 Power supply 110 Steering assist device

Claims

1. a rack bar having a rack tooth forming portion on which rack teeth that mesh with the pinion gear are arranged; a rack housing formed in a cylindrical shape and storing the rack bar inside an inner circumferential surface thereof; a pressing portion disposed on the rack housing and configured to apply a biasing force to the rack bar to press the rack teeth against the pinion gear; a steering assist device that applies a steering assist force to the pinion gear or the rack bar; Equipped with the rack tooth forming portion has a rear surface portion located on the rear side of the rack teeth, which is formed in an arc shape when viewed in the longitudinal direction of the rack bar, and a maximum width in a direction perpendicular to the longitudinal direction of the rack bar is larger than a width of the rack tooth forming portion in a direction perpendicular to the maximum width, the rack housing has a large-diameter housing portion having a large-diameter through-hole that accommodates the rack tooth forming portion of the rack bar, and a small-diameter housing portion having a small-diameter through-hole that accommodates a portion of the rack bar different from the rack tooth forming portion, a maximum width of the large diameter through hole in a portion that accommodates the rack tooth forming portion in the same direction as the direction in which the rack tooth forming portion has a maximum width is larger than a width of the large diameter through hole in a direction perpendicular to the maximum width, An electric power steering device, wherein the amount of protrusion of the pressing portion from the inner peripheral surface of the large diameter housing portion is equal to or less than the gap between the inner peripheral surface of the small diameter housing portion and the rack bar.

2. The rack teeth include first rack teeth and second rack teeth that are arranged at positions different from the first rack teeth in the longitudinal direction, The second rack teeth are arranged on the rack tooth forming portion, the rack bar has a small diameter portion having the first rack teeth and a large diameter portion having the rack tooth forming portion and having a diameter larger than that of the small diameter portion, the small diameter housing portion accommodates the small diameter portion of the rack bar; the large diameter housing portion accommodates the large diameter portion of the rack bar; the pinion gear includes a first pinion gear that meshes with the first rack teeth and a second pinion gear that meshes with the second rack teeth, the pressing portion includes a first pressing portion disposed in the small diameter housing portion and applying a biasing force to the rack bar to press the first rack teeth against the first pinion gear, and a second pressing portion disposed in the large diameter housing portion and applying a biasing force to the rack bar to press the second rack teeth against the second pinion gear, 2. The electric power steering device according to claim 1, wherein the amount of protrusion of the second pressing portion from the inner circumferential surface of the large diameter housing portion is equal to or less than the amount of protrusion of the first pressing portion from the inner circumferential surface of the small diameter housing portion.

3. the large-diameter through-hole has a substantially elliptical shape when viewed in the longitudinal direction of the rack housing, 3. The electric power steering device according to claim 1, wherein the rack bar is stored inside the rack housing with the direction in which the rack tooth forming portion has the greatest width aligned with the major axis of the ellipse that is the shape of the large-diameter through hole.

4. the rack-tooth forming portion has, on both sides in a direction of maximum width of the rack-tooth forming portion, protruding portions that protrude in a direction in which the maximum width of the rack-tooth forming portion increases, the large diameter through hole has an arc portion on an inner peripheral surface of the large diameter through hole that has an arc shape when viewed in the longitudinal direction of the rack bar, and overhang portion storage portions that store the overhang portion and are located on both sides in the same direction as the direction in which the rack tooth forming portion has the maximum width, 3. The electric power steering device according to claim 1, wherein the rack bar is stored inside the rack housing with the protrusion stored in the protrusion storage portion of the large diameter through hole, and the back surface of the rack tooth forming portion is oriented to face the arc portion of the large diameter through hole.

5. Bolt holes for attaching ball joints to which tie rods are connected are arranged at both ends of the rack bar in the longitudinal direction, the rack bar is disposed at a position where a central axis of the bolt hole disposed in the small diameter portion coincides with a central axis of the small diameter through hole, 3. The electric power steering device according to claim 2, wherein the large diameter portion of the rack bar is connected to the small diameter portion at a position where a central axis thereof is shifted toward a side where the second pressing portion is located with respect to a central axis of the bolt hole arranged in the small diameter portion.

6. 3. The electric power steering device according to claim 2, wherein the large diameter housing portion is connected to the small diameter housing portion at a position where a center axis of the large diameter through hole in the large diameter housing portion is shifted toward a side where the second pinion gear is located with respect to a center axis of the small diameter through hole in the small diameter housing portion.

7. 3. The electric power steering device according to claim 2, wherein the first rack teeth are formed within a range of a projected shape of the small diameter portion when the small diameter portion is viewed in a direction along the central axis.

8. the rack-tooth forming portion has, on both sides in a direction of maximum width of the rack-tooth forming portion, protruding portions that protrude in a direction in which the maximum width of the rack-tooth forming portion increases, The electric power steering device according to claim 2, wherein the protruding portion has chamfers at both ends in a direction perpendicular to the longitudinal direction of the large diameter portion on the side where the back portion is located.

9. the inner circumferential surface of the large-diameter housing portion has an expanding diameter portion in which the size of an opening area of ​​the inner circumferential surface when viewed in the longitudinal direction of the rack housing increases toward a predetermined direction in the longitudinal direction of the rack housing, 3. The electric power steering device according to claim 2, wherein, in a cross section taken along the longitudinal direction of the rack housing at a position where the second pressing portion is located in the circumferential direction of the rack housing, a second line on the inner surface of the expanded diameter portion is inclined relative to a first line on the inner surface that passes through the position where the second pressing portion is located and extends along the longitudinal direction of the rack housing.

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