Electric power steering device

Abstract

To provide an electric power steering device capable of suppressing generating noise.SOLUTION: An electric power steering device is provided with: a rack bar 30 having a small diameter part 41 having a first pinion gear 91 and a steering rack gear 44 engaging therewith, and a large diameter part 31 having a second pinion gear 92 and an assist rack geer 34 engaging therewith; a rack housing 10 having a small diameter housing part 21 receiving the small diameter part 41 and a large diameter housing part 11 receiving the large diameter part 31; a second pressing part 65 arranged in the large diameter housing part 11 to press the assist rack gear 34 on the second pinion gear 92; and bolt holes 55 arranged at both ends of the rack bar 30 and in which ball joints 50 are attached, wherein the largest width of the assist rack gear 34 is larger than a width in a direction orthogonal to the largest width of the large diameter part 31, and a central axis of the large diameter part 31 is connected to the small diameter part 41 at a position offset from a center axis of the bolt hole 55 arranged in the small diameter part 41 to a side where the second pressing part 65 is positioned.SELECTED DRAWING: Figure 12

Description

Technical Field

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

Background Art

[0002] An electric power steering device includes a pinion gear that rotates by a rotational torque when a steering wheel is steered, a rack bar having rack teeth that mesh with the pinion gear, and an electric motor that generates an assist force for assisting a steering force. For example, the electric power steering device described in Patent Document 1 includes a steering mechanism that steers the vehicle wheels in response to rotation of a steering wheel to which a steering force is input by a driver, and an assist mechanism that assists the driver's steering force. The assist mechanism has an electric motor that is a power source of the assist force. In this electric power steering device, the rack shaft includes a first shaft formed with a first rack that meshes with a first pinion shaft that rotates as the steering wheel is steered, and a second shaft formed with a second rack that meshes with a second pinion that rotates by the electric motor. Of the first shaft and the second shaft, the outer diameter of the first shaft on which a relatively low load acts is smaller than the outer diameter of the second shaft.

[0003] In addition, an electric power steering device is provided with a mechanism for pressing the rack against the pinion. For example, the electric power steering device described in Patent Document 1 includes a first rack guide that presses a first rack forming portion against the first pinion from the back side, and a second rack guide that presses a second rack forming portion against the second pinion from the back side. Further, in the steering device described in Patent Document 2, a rack guide is provided that biases the rack shaft toward the pinion shaft side by the elastic force of a biasing member. In the electric power steering device, by pressing the rack against the pinion by such a rack guide, the meshing between the rack teeth and the pinion teeth is maintained.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2018-167780 [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2017-132438 [Summary of the Invention] [Problems to be Solved by the Invention]

[0005] Here, among electric power steering devices, in the so-called dual pinion type electric power steering device in which the driving force generated by an electric motor is transmitted to a rack bar by a pinion different from the pinion that rotates by the driver's steering force as in Patent Document 1, in order to cope with the high output of the electric motor, the portion on the rack bar where the driving force generated by the electric motor is transmitted is formed in an irregular shape with a large size in the tooth width direction of the rack teeth. That is, in the dual pinion type electric power steering device, the assist side portion, which is the portion on the rack bar where the driving force from the electric motor is transmitted, is formed in an irregular shape.

[0006] When the assist side portion of the rack bar is formed in an irregular shape, the rack housing that stores the rack bar needs to have a larger inner diameter of the portion that stores the assist side portion of the rack bar than the inner diameter of the portion that stores the manual side portion, which is the portion on the rack bar where the driver's steering force is transmitted. Thus, when the inner diameter of the portion of the rack housing that stores the assist side portion of the rack bar is increased, in the assist side portion of the rack bar, the distance between the inner peripheral surface of the rack housing and the portion where a pressing member such as a rack guide on the rack bar abuts tends to increase. When the distance between the inner peripheral surface of the rack housing and the rack bar is large, the pressing member abuts on the rack bar in a state where the protrusion from the inner peripheral surface of the rack housing is large, and applies a pressing force to the rack bar.

[0007] However, if the protrusion of the pressing member from the inner peripheral surface of the rack housing is large, the pressing member is likely to tilt. That is, when the protrusion of the pressing member from the inner peripheral surface of the rack housing is large, the ratio of the portion of the pressing member supported by the rack housing to the overall size of the pressing member becomes relatively small. Therefore, for example, when the rack bar makes a linear motion, the pressing member is likely to tilt following the movement of the rack bar. When the pressing member tilts, it becomes difficult to appropriately apply a pressing force from the pressing member to the rack bar. As a result, the pressing force pressing the rack bar against the pinion becomes small, and the backlash at the meshing portion between the rack bar and the pinion increases. When the backlash at the meshing portion between the rack bar and the pinion increases, abnormal noise is likely to occur from the meshing portion.

[0008] In addition, the rack teeth formed on the rack bar are formed obliquely with respect to the direction orthogonal to the axial direction of the rack shaft. Therefore, when the steering wheel is steered, not only a force in the axial direction of the rack bar acts on the rack bar, but also a force in the direction orthogonal to the axial direction acts, causing the rack bar to translate in the direction orthogonal to the axial direction. For this reason, when the protrusion of the pressing member from the inner peripheral surface of the rack housing is large, the pressing member is tilted in the direction orthogonal to the axial direction of the rack bar following the movement of the rack bar that moves in the direction orthogonal to the axial direction when the steering wheel is steered. Also, the forces in the direction orthogonal to the axial direction of the rack bar during steering of the steering wheel act in opposite directions depending on the direction of steering the steering wheel. Therefore, when switching the steering direction, the moving direction of the rack bar in the axial direction is switched, and the moving direction of the rack bar in the direction orthogonal to the axial direction is also switched. As a result, the direction of tilt of the pressing member in the axial direction of the rack bar is switched, and the direction of tilt in the direction orthogonal to the axial direction is also switched.

[0009] At that time, since the pressing member is tilted while being pressed against the rack bar, the so-called stick-slip phenomenon occurs at the contact surface between the pressing member and the rack bar, and abnormal noise may be generated. The stick-slip phenomenon when the pressing member contacts the rack bar while tilting may continuously occur even while the rack bar is linearly moving in the axial direction, and abnormal noise may continuously occur. Further, when the pressing member tilts, the pressing member is likely to contact the portion of the rack housing that holds the pressing member. Therefore, when the pressing member contacts the rack housing, a collision sound may be generated. For these reasons, in an electric power steering apparatus having a structure in which the rack bar is pressed against the pinion by the pressing member, there is room for improvement from the viewpoint of abnormal noise that is likely to occur due to the tilt of the pressing member.

[0010] The present disclosure has been made in view of the above, and an object thereof is to provide an electric power steering apparatus capable of suppressing the generation of abnormal noise.

Means for Solving the Problems

[0011] The electric power steering apparatus of the present disclosure includes a rack bar having a small-diameter portion with a first rack tooth that meshes with a first pinion gear, and a large-diameter portion having a second rack tooth that meshes with a second pinion gear and has a larger diameter than the small-diameter portion; a small-diameter housing portion in which a small-diameter through-hole for storing the small-diameter portion of the rack bar is formed; and a large-diameter housing portion that stores the large-diameter portion of the rack bar and in which a large-diameter through-hole having an inner diameter larger than the inner diameter of the small-diameter housing portion is formed. The electric power steering apparatus further includes a second pressing portion that is disposed in the large-diameter housing portion and presses the second rack tooth against the second pinion gear, and bolt holes that are disposed at both ends in the longitudinal direction of the rack bar and to which tie rods are connected and in which ball joints are attached. The maximum width of the second rack tooth in a direction orthogonal to the longitudinal direction of the rack bar is larger than the width in a direction orthogonal to the maximum width in a portion of the large-diameter portion where the second rack tooth is formed. The large-diameter portion is connected to the small-diameter portion at a position shifted to the side where the second pressing portion is located with respect to the central axis of the bolt hole whose central axis is disposed in the small-diameter portion.

[0012] According to this configuration, since the central axis of the large-diameter portion of the rack bar is shifted to the side where the second pressing portion is located with respect to the central axis of the bolt hole whose central axis is disposed in the small-diameter portion, the protruding amount of the second pressing portion that abuts against the large-diameter portion of the rack bar can be reduced. Therefore, when the rack bar makes a linear motion, the second pressing portion is not dragged and tilted by the rack bar, and the second pressing portion can press the second rack tooth of the rack bar toward the second pinion gear. For this reason, the backlash at the meshing portion between the second rack tooth and the second pinion gear can be reduced, and the generation of abnormal noise due to the backlash can be suppressed. In addition, since the inclination of the second pressing portion can be suppressed, the generation of abnormal noise due to the stick-slip phenomenon and the generation of abnormal noise due to the second pressing portion colliding with the hole that holds the second pressing portion in the rack housing can be suppressed. As a result, the generation of abnormal noise can be suppressed.

[0013] Desirably, the center axis of the bolt hole disposed in the small-diameter portion and the center axis of the bolt hole disposed in the large-diameter portion of the rack bar are located on the same extension line.

[0014] According to this configuration, a ball joint screwed into the bolt hole disposed in the small-diameter portion of the rack bar and a ball joint screwed into the bolt hole disposed in the large-diameter portion can be arranged at positions symmetrical in the vehicle width direction. As a result, the tie rods connected to the ball joints can also be arranged symmetrically in the vehicle width direction, so that the movement of the wheels with respect to the linear movement of the rack bar during steering can be made the same when steering to the left and when steering to the right. Consequently, it is possible to suppress the occurrence of abnormal noise while suppressing a decrease in the feeling during steering.

[0015] Desirably, 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 on the extension line of the central axis of the small-diameter through hole in the small-diameter housing portion, and the rack bar is arranged at a position where the central axis of the bolt hole disposed in the small-diameter portion coincides with the central axis of the small-diameter through hole.

[0016] According to this configuration, since 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 is on the extension line of the central axis of the small-diameter through hole, and the rack bar is arranged at a position where the central axis of the bolt hole disposed in the small-diameter portion coincides with the central axis of the small-diameter through hole, the rack bar can be stored in a position where the central axis of the large-diameter portion is offset from the central axis of the large-diameter through hole. As a result, the distance between the back surface of the assist rack tooth forming portion of the large-diameter portion of the rack bar and the inner peripheral surface of the large-diameter housing portion of the rack housing can be reduced, and the protruding amount of the second pressing portion that abuts against the back surface of the large-diameter portion of the rack bar can be reduced. Therefore, when the rack bar moves linearly, the pressing member of the second pressing portion is not dragged and tilted by the rack bar, and the assist rack teeth can be pressed toward the second pinion gear by the pressing member. As a result, the occurrence of abnormal noise can be suppressed.

[0017] Desirably, the first rack teeth are formed within the range of the projected shape of the small-diameter portion when viewed in the direction along the central axis of the small-diameter portion.

[0018] According to this configuration, since the first rack teeth of the rack bar are formed within the range of the projected shape of the small-diameter portion, the inner diameter of the small-diameter housing portion of the rack housing that stores the small-diameter portion can be made as small as possible. As a result, the protruding amount of the first pressing portion that 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 can be reduced. Therefore, when the rack bar makes a linear motion, the pressing member of the first pressing portion is not dragged and tilted by the rack bar, and the first rack teeth of the rack bar can be pressed toward the first pinion gear by the pressing member. Accordingly, the backlash at the meshing portion between the first rack teeth and the first pinion gear can be reduced by the pressing force applied from the first pressing portion to the rack bar, and thus the generation of abnormal noise due to the backlash can be suppressed. Also, since the inclination of the pressing member of the first pressing portion can be suppressed, the generation of abnormal noise due to the stick-slip phenomenon and the generation of abnormal noise due to the first pressing portion colliding with the hole that holds the first pressing portion in the rack housing can be suppressed. As a result, the generation of abnormal noise due to the backlash can be suppressed.

[0019] Desirably, the large-diameter portion has chamfers at both ends in the direction orthogonal to the longitudinal direction of the large-diameter portion on the back side of the portion where the second rack teeth are disposed.

[0020] According to this configuration, chamfers are formed on the large-diameter portion of the rack bar, so that interference between the inner peripheral surface of the large-diameter housing portion and the large-diameter portion can be suppressed as much as possible. As a result, when shifting the central axis of the large-diameter portion of the rack bar to the side where the second pressing portion is located with respect to the central axis of the bolt hole disposed in the small-diameter portion, the inner diameter of the large-diameter housing portion can be reduced. Therefore, the inner diameter of the large-diameter housing portion can be reduced while reducing the protruding amount of the second pressing portion from the inner peripheral surface of the large-diameter housing portion. As a result, generation of abnormal noise due to backlash at the meshing portion between the second rack teeth and the second pinion gear, generation of abnormal noise due to the stick-slip phenomenon, and generation of abnormal noise due to the second pressing portion colliding with the hole that holds the second pressing portion in the rack housing can be suppressed, and the weight of the rack housing can be reduced.

Effect of the Invention

[0021] The electric power steering apparatus according to the present disclosure has an effect of being able to suppress generation of abnormal noise.

Brief Description of the Drawings

[0022]

Figure 1

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[0023] Hereinafter, the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited by the following embodiments for carrying out the invention (hereinafter referred to as embodiments). In addition, the constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art, substantially the same ones, and those within a so-called equivalent range. Furthermore, the constituent elements disclosed in the following embodiments can be combined as appropriate.

[0024] [First Embodiment] FIG. 1 is a schematic diagram for explaining an electric power steering apparatus 80 according to the first embodiment. As shown in FIG. 1, the electric power steering apparatus 80 includes, in the order in which the force applied from the 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 93. The electric power steering apparatus 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 by CAN (Controller Area Network) communication.

[0025] The steering shaft 82 is connected to the steering wheel 81 at one end and to the universal joint 84 at the other end.

[0026] The intermediate shaft 85 is connected to the universal joint 84 at one end and to the universal joint 86 at the other end. The stub shaft 87 has one end connected to the universal joint 86 and the other end connected to the torque sensor 101. The torque sensor 101 has one end connected to the stub shaft 87 and the other end connected to a first pinion gear 91 of the steering gear 90.

[0027] FIG. 2 is an explanatory diagram showing the configuration around the steering gear 90. The first pinion gear 91 is a shaft-shaped member having a gear 91a formed at an end opposite to the side connected to the stub shaft 87 and meshing with a rack bar 30. The stub shaft 87 and the first pinion gear 91 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 91, and the torsion bar transmits rotational torque between the stub shaft 87 and the first pinion gear 91.

[0028] The torque sensor 101 is a torque detection device that detects the torque acting on the shaft connected to the torque sensor 101, and detects the rotational torque transmitted between the stub shaft 87 and the first pinion gear 91 via the torsion bar. That is, the stub shaft 87 and the first pinion gear 91 connected via the torsion bar are the shafts to be detected when the torque sensor 101 detects torque.

[0029] The steering gear 90 includes a first pinion gear 91, a rack bar 30, and a second pinion gear 92. The first pinion gear 91 is connected to the stub shaft 87 via a torsion bar. The rack bar 30 has a steering rack tooth 44 which is a first rack tooth meshing with the first pinion gear 91 and an assist rack tooth 34 which is a second rack tooth meshing with the second pinion gear 92. The steering rack tooth 44 meshes with the gear 91a of the first pinion gear 91. The assist rack tooth 34 is arranged on the rack bar 30 at a position different from the position where the steering rack tooth 44 is arranged in the longitudinal direction of the rack bar 30. For this reason, the rack bar 30 meshes with the second pinion gear 92 at a position different from the position where it meshes with the first pinion gear 91.

[0030] An electric motor 102 is connected to the second pinion gear 92 via a worm reduction gear 94, and the second pinion gear 92 is rotated by the driving force transmitted from the electric motor 102. The electric motor 102 rotates the second pinion gear 92 via the worm reduction gear 94. The electric motor 102 is, for example, a brushless motor, but may also be a motor provided with a brush (sliding contact) and a commutator (commutator).

[0031] The steering gear 90 converts the rotational motion transmitted to the first pinion gear 91 and the second pinion gear 92 into a linear motion by a rack bar 30 disposed inside a rack housing 10 (see FIG. 8). The electric power steering apparatus 80 according to the first embodiment is of a dual pinion assist type in which the rack bar 30 performs a linear motion by the rotational motion transmitted from the first pinion gear 91 and the second pinion gear 92. The tie rod 93 is connected to the rack bar 30. That is, the electric power steering apparatus 80 according to the first embodiment is a rack and pinion type electric power steering apparatus 80.

[0032] The torque sensor 101 detects the driver's steering force 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 apparatus 80 is mounted. The electric motor 102, the torque sensor 101, and the vehicle speed sensor 103 are electrically connected to the ECU 100.

[0033] The ECU 100 controls the operation of the electric motor 102. Also, the ECU 100 acquires signals from the torque sensor 101 and the vehicle speed sensor 103, respectively. That is, the ECU 100 acquires the steering torque T from the torque sensor 101 and the vehicle speed signal V of the vehicle from the vehicle speed sensor 103. The ECU 100 is supplied with electric power from a power supply device (for example, an in-vehicle battery) 105 when the ignition switch 104 is in the on state. The ECU 100 calculates an assist command value of an assist command based on the steering torque T and the vehicle speed signal V. Then, the ECU 100 adjusts the power value X supplied to the electric motor 102 based on the calculated assist command value. The ECU 100 acquires information on the 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 as operation information Y.

[0034] The steering force of the operator (driver) input to the steering wheel 81 is transmitted to the first pinion gear 91. The steering force transmitted to the first pinion gear 91 is transmitted to the tie rod 93 via the steering gear 90 to displace the wheels.

[0035] Also, the steering force of the operator input to the steering wheel 81 is transmitted to the torque sensor 101 disposed in the steering force transmission path from the steering wheel 81 to the first pinion gear 91. At this time, the ECU 100 acquires the steering torque T from the torque sensor 101 and also acquires the vehicle speed signal V from the 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 92.

[0036] The auxiliary steering torque transmitted to the second pinion gear 92 is transmitted to the tie rod 93 via the steering gear 90 to displace the wheels. That is, the electric power steering device 80 uses, in addition to the steering force of the operator transmitted to the rack bar 30 via the first pinion gear 91, also the auxiliary steering torque of the electric motor 102 transmitted to the rack bar 30 via the second pinion gear 92 to displace the wheels. The electric power steering device 80 according to the first embodiment is thus a dual pinion type electric power steering device to which an assist force is applied to the second pinion gear 92.

[0037] FIG. 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 sectional view taken along line A-A of FIG. 3. FIG. 6 is a sectional view taken along line B-B of FIG. 3. The rack bar 30 has a large-diameter portion 31 and a small-diameter portion 41 whose maximum widths in a direction orthogonal to the longitudinal direction of the rack bar 30 are different from each other. The large-diameter portion 31 has a maximum width Wa in a direction orthogonal to the longitudinal direction of the rack bar 30, which is larger than the maximum width Wb of the small-diameter portion 41 in a direction orthogonal to the longitudinal direction of the rack bar 30. These large-diameter portion 31 and small-diameter portion 41 are connected to each other in the longitudinal direction of the rack bar 30. The large-diameter portion 31 and the small-diameter portion 41 are joined by, for example, friction welding. In the first embodiment, the large-diameter portion 31 and the small-diameter portion 41 have lengths that are approximately the same in the longitudinal direction of the rack bar 30.

[0038] The small-diameter portion 41 has a steering rack tooth 44 that meshes with the gear 91a of the first pinion gear 91 (see FIG. 2). The small-diameter portion 41 has the steering rack tooth 44 formed on a round bar-shaped small-diameter round bar portion 42. Therefore, the steering rack tooth 44 is formed within the range of the projected shape of the small-diameter portion 41 when looking at the small-diameter portion 41 in a direction along the central axis of the small-diameter portion 41, that is, in a direction along the central axis of the small-diameter round bar portion 42. As a result, the maximum width Wb of the small-diameter portion 41 in a direction orthogonal to the longitudinal direction of the rack bar 30 is the diameter of the small-diameter round bar portion 42.

[0039] The large-diameter portion 31 has an assist rack tooth 34 that meshes with the second pinion gear 92 (see FIG. 2). The assist rack tooth 34 provided on the large-diameter portion 31 is formed to face a direction different from that of the steering rack tooth 44 provided on the small-diameter portion 41. The large-diameter portion 31 has a round bar-shaped large-diameter round bar portion 32 whose diameter is larger than that of the small-diameter round bar portion 42, and an assist rack tooth forming portion 33 on which the assist rack tooth 34 is formed. The large-diameter round bar portion 32 is disposed on both sides of the assist rack tooth forming portion 33 in the longitudinal direction of the rack bar 30. The assist rack tooth forming portion 33 is formed such that the maximum width Wa in a direction orthogonal to the axial direction of the large-diameter round bar portion 32 is larger than the width Wc in a direction orthogonal to the maximum width Wa in the assist rack tooth forming portion 33.

[0040] In the first embodiment, the steering rack teeth 44 and the assist rack teeth 34 are formed at positions different from each other in the circumferential direction of the small-diameter round bar portion 42 and the large-diameter round bar portion 32 of the rack bar 30. That is, the steering rack teeth 44 and the assist rack teeth 34 are formed to face in different directions from each other in the circumferential direction of the small-diameter round bar portion 42 and the large-diameter round bar portion 32.

[0041] FIG. 7 is a perspective view of the rack bar 30 including the B-B cross section of FIG. 3. The assist rack tooth forming portion 33 of the large-diameter portion 31 of the rack bar 30 is formed by crushing the surface on which the assist rack teeth 34 are formed in the large-diameter round bar portion 32 in a direction orthogonal to the axial direction of the large-diameter round bar portion 32. The assist rack tooth forming portion 33 has two projecting portions 36 that project in opposite directions from each other in the direction orthogonal to the axial direction of the large-diameter round bar portion 32 by being crushed in the direction orthogonal to the axial direction of the large-diameter round bar portion 32 in this way. The assist rack tooth forming portion 33 is formed into a shape having the projecting portion 36, for example, by forging a round bar and crushing it in a direction orthogonal to the axial direction. The maximum width Wa (see FIG. 6) of the assist rack tooth forming portion 33 is the distance between the ends on the opposite side of each other's projecting portion 36 at the two projecting portions 36. The assist rack teeth 34 are formed on the surface where the large-diameter round bar portion 32 is crushed into a planar shape and are formed across the two projecting portions 36.

[0042] Further, since the large-diameter round bar portion 32 is crushed only in one direction in the assist rack tooth forming portion 33, the surface on the opposite side of the surface where the assist rack teeth 34 are formed in the assist rack tooth forming portion 33 is formed in a shape continuous with the large-diameter round bar portions 32 located on both sides of the assist rack tooth forming portion 33. That is, the back surface 35, which is the surface on the opposite side of the surface where the assist rack teeth 34 are formed in the assist rack tooth forming portion 33, has a shape that, when viewed in the longitudinal direction of the rack bar 30, has a radius of curvature substantially the same as the radius of curvature of the outer peripheral surface of the large-diameter round bar portion 32, and is formed in an arc shape with the central axis of the arc coinciding with the central axis of the large-diameter round bar portion 32. The back surface 35 of the assist rack tooth forming portion 33 is disposed between two protruding portions 36 on the surface on the opposite side of the side where the assist rack teeth 34 are formed in the assist rack tooth forming portion 33.

[0043] Furthermore, the two protruding portions 36 of the assist rack tooth forming portion 33 are formed to protrude in opposite directions in the direction orthogonal to the axial direction of the large-diameter round bar portion 32 due to the crushing of the large-diameter round bar portion 32. For this reason, in the assist rack tooth forming portion 33, the maximum width Wa, which is the distance between the ends on the opposite sides of each other's protruding portions 36 in the two protruding portions 36, is larger than the width Wc in the direction orthogonal to the maximum width Wa in the assist rack tooth forming portion 33.

[0044] As a result, the assist rack tooth forming portion 33 is formed with an irregular cross-section when viewed in the longitudinal direction of the rack bar 30. That is, the large-diameter round bar portion 32 is formed with a circular cross-section when viewed in the longitudinal direction of the rack bar 30, whereas the assist rack tooth forming portion 33 is formed with an irregular cross-section in which the size in the direction in which the two protruding portions 36 protrude in the cross-section when viewed in the longitudinal direction of the rack bar 30 is larger than the size in the direction orthogonal to the direction in which the two protruding portions 36 protrude.

[0045] In the first embodiment, the maximum width Wa in the direction orthogonal to the longitudinal direction of the rack bar 30 of the assist rack teeth 34 formed in the assist rack tooth forming portion 33 is larger than the diameter of the large-diameter round bar portion 32 located in the portion other than the assist rack teeth 34 in the large-diameter portion 31. The maximum width Wa of the assist rack tooth forming portion 33 formed in this way is the maximum width Wa in the direction orthogonal to the longitudinal direction of the rack bar 30 in the large-diameter portion 31.

[0046] The assist rack teeth 34 are formed in the assist rack tooth forming portion 33 where the maximum width Wa is larger than the diameter of the large-diameter round bar portion 32 by forming the two protruding portions 36 in this way. As a result, the length of the assist rack teeth 34 can be made longer compared to the case where the assist rack teeth 34 are directly formed on the large-diameter round bar portion 32. Further, since the assist rack teeth 34 are formed in the assist rack tooth forming portion 33 of the large-diameter portion 31 in this way, the tooth length is longer than the tooth length of the steering rack teeth 44 formed in the small-diameter portion 41.

[0047] FIG. 8 is a cross-sectional view of a rack housing 10 and a rack bar 30 included in an electric power steering apparatus 80, and is a cross-sectional view at a position including a cross-section of assist rack teeth 34. FIG. 9 is a cross-sectional view of a rack housing 10 and a rack bar 30 included in an electric power steering apparatus 80, and is a cross-sectional view at a position including a cross-section of steering rack teeth 44. The rack bar 30 is stored in the rack housing 10. 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 that communicates with the small-diameter through-hole 22 and has an inner diameter larger than the inner diameter of the small-diameter through-hole 22 is formed. 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. The large-diameter through-hole 12 is a hole that penetrates the large-diameter housing portion 11 with a shape that is substantially circular when the substantially cylindrical large-diameter housing portion 11 is viewed in the axial direction. The small-diameter through-hole 22 is a hole that penetrates the small-diameter housing portion 21 with a shape that is substantially circular when the substantially cylindrical small-diameter housing portion 21 is viewed in the axial direction.

[0048] The minimum diameter of the large-diameter through-hole 12 of the rack housing 10 is larger than the maximum width Wa of the large-diameter portion 31 of the rack bar 30. Also, the minimum diameter of the small-diameter through-hole 22 of the rack housing 10 is larger than the maximum width Wb of the small-diameter portion 41 of the rack bar 30. That is, the inner diameter of the large-diameter housing portion 11 of the rack housing 10 is larger than the maximum width Wa of the large-diameter portion 31 of the rack bar 30, and 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 41 of the rack bar 30.

[0049] The rack housing 10 stores the rack bar 30 in the internal spaces of the large-diameter through-hole 12 and the small-diameter through-hole 22 in such a direction that the axial direction of the large-diameter through-hole 12 and the small-diameter through-hole 22 coincides with the longitudinal direction of the rack bar 30. Further, when storing the rack bar 30 in the rack housing 10, the direction of the rack bar 30 is such that the large-diameter portion 31 side of the rack bar 30 is located on the large-diameter housing portion 11 side of the rack housing 10, and the small-diameter portion 41 side of the rack bar 30 is located on the small-diameter housing portion 21 side of the rack housing 10. For this reason, 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 31 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 41 of the rack bar 30.

[0050] The small-diameter through-hole 22 of the rack housing 10 that stores the small-diameter portion 41 of the rack bar 30 has a minimum diameter of the small-diameter through-hole 22 that is smaller than the maximum width Wa of the large-diameter portion 31 of the rack bar 30. In other words, for the rack bar 30, the maximum width Wa of the large-diameter portion 31 is larger than the minimum diameter of the small-diameter through-hole 22 of the rack housing 10. Further, the small-diameter through-hole 22 of the rack housing 10 has a minimum diameter of the small-diameter through-hole 22 that is smaller than the diameter of the large-diameter round bar portion 32 of the large-diameter portion 31 of the rack bar 30.

[0051] In the large-diameter housing portion 11 of the rack housing 10, a ball joint accommodating portion 15 is formed at an end portion on the side opposite to the side where the small-diameter housing portion 21 is located. The ball joint accommodating portion 15 formed in the large-diameter housing portion 11 has an inner diameter larger than the inner diameter of the large-diameter through-hole 12. Thus, the ball joint accommodating portion 15 formed in the large-diameter housing portion 11 protrudes and is formed on the side opposite to the side where the small-diameter housing portion 21 is located, rather than the portion where the large-diameter through-hole 12 is formed in the large-diameter housing portion 11.

[0052] Similarly, a ball joint housing portion 25 is formed at an end portion of the small-diameter housing portion 21 of the rack housing 10 on the side opposite to the side where the large-diameter housing portion 11 is located. The ball joint housing portion 25 formed in the small-diameter housing portion 21 has an inner diameter larger than the inner diameter of the small-diameter through hole 22. Thus, the ball joint housing portion 25 formed in the small-diameter housing portion 21 protrudes on the side opposite to the side where the large-diameter housing portion 11 is located, beyond the portion where the small-diameter through hole 22 is formed in the small-diameter housing portion 21.

[0053] At both ends in the longitudinal direction of the rack bar 30 stored in the rack housing 10, bolt holes 55 are arranged to which ball joints 50 to which tie rods 93 are connected are attached. 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 at both end portions on both sides in the longitudinal direction of the rack bar 30. Thereby, ball joints 50 are respectively arranged at both ends in the longitudinal direction of the rack bar 30.

[0054] The ball joints 50 arranged at both ends of the rack bar 30 each have a joint portion 51 on the side opposite to the portion on the side where the rack bar 30 is attached. The joint portion 51 of the ball joint 50 is formed in a concave shape at the portion 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 portion of the tie rod 93 can enter the concave-shaped portion of the joint portion 51. Thereby, the tie rod 93 can be connected to the ball joint 50, and the tie rod 93 is connected to the rack bar 30 via the ball joint 50.

[0055] In addition, a gearbox 17 of a worm reduction gear 94 is provided in the large-diameter housing portion 11 of the rack housing 10. Inside the gearbox 17, a second pinion gear 92, a worm wheel 95 for transmitting the driving force generated by the electric motor 102 to the second pinion gear 92, and the like are arranged. The second pinion gear 92 is arranged to mesh with assist rack teeth 34 formed on an assist rack tooth formation portion 33 of a large-diameter portion 31 of the rack bar 30. Thereby, the second pinion gear 92 can transmit the driving force generated by the electric motor 102 and transmitted via the worm wheel 95 to the assist rack teeth 34, and can transmit the driving force generated by the electric motor 102 to the rack bar 30.

[0056] FIG. 10 is a detailed view of part C in FIG. 9. The rack housing 10 supports the first pinion gear 91 in mesh with the steering rack teeth 44 formed on the small-diameter portion 41 of the rack bar 30 on the side of the small-diameter housing portion 21. A first pressing portion 60 for pressing the steering rack teeth 44 against the first pinion gear 91 is arranged in the small-diameter housing portion 21 of the rack housing 10. A through hole 26 penetrating the inside and outside of the small-diameter housing portion 21 is formed at a position on the opposite side of the small-diameter housing portion 21 from the side where the steering rack teeth 44 of the rack bar 30 are formed, and the first pressing portion 60 is arranged in the through hole 26 formed in the small-diameter housing portion 21.

[0057] The first pressing portion 60 includes a pressing member 61, a spring 62, and a sealing member 63. The pressing member 61, the spring 62, and the sealing member 63 included in the first pressing portion 60 are accommodated in the through hole 26 formed in the small-diameter housing portion 21. A part of the pressing member 61 is exposed from the through hole 26 of the small-diameter housing portion 21 and protrudes from the inner peripheral surface 23 of the small-diameter housing portion 21. The pressing member 61 protruding from the inner peripheral surface 23 of the small-diameter housing portion 21 abuts against the rack bar 30 from the side opposite to the side where the first pinion gear 91 is located on the rack bar 30 inside the small-diameter housing portion 21. The sealing member 63 is arranged at the opening of the through hole 26 to seal the opening.

[0058] The spring 62 is a compression spring and is disposed between the sealing member 63 and the pressing member 61 in a state of being compressed between them. Therefore, the pressing member 61 is pressed against the rack bar 30 by the biasing force from the spring 62, and the small-diameter portion 41 of the rack bar 30 is pressed against the gear 91a of the first pinion gear 91 by the biasing force from the pressing member 61 on the surface where the steering rack teeth 44 are formed. Thereby, the rack bar 30 maintains a state in which the steering rack teeth 44 mesh with the gear 91a of the first pinion gear 91.

[0059] FIG. 11 is a detailed view of part D in FIG. 8. The rack housing 10 supports the second pinion gear 92 in mesh with the assist rack teeth 34 formed on the large-diameter portion 31 of the rack bar 30 on the large-diameter housing portion 11 side. A second pressing portion 65 for pressing the assist rack teeth 34 against the second pinion gear 92 is disposed in the large-diameter housing portion 11 of the rack housing 10. A through hole 16 penetrating the inside and outside of the large-diameter housing portion 11 is formed at a position on the opposite side of the large-diameter housing portion 11 from the side where the assist rack teeth 34 of the rack bar 30 are formed, and the second pressing portion 65 is disposed in the through hole 16 formed in the large-diameter housing portion 11.

[0060] The second pressing portion 65 includes a pressing member 66, a spring 67, and a sealing member 68, and the pressing member 66, the spring 67, and the sealing member 68 included in the second pressing portion 65 are accommodated in the through hole 16 formed in the large-diameter housing portion 11. A part of the pressing member 66 is exposed from the through hole 16 of the large-diameter housing portion 11 and protrudes from the inner peripheral surface 13 of the large-diameter housing portion 11. The pressing member 66 protruding from the inner peripheral surface 13 of the large-diameter housing portion 11 abuts against the rack bar 30 inside the large-diameter housing portion 11 from the side opposite to the side where the second pinion gear 92 is located on the rack bar 30. Specifically, the pressing member 66 abuts against the back surface 35 of the assist rack tooth forming portion 33 in the large-diameter portion 31 of the rack bar 30. The sealing member 68 is disposed at the opening of the through hole 16 and seals the opening.

[0061] The spring 67 is a compression spring and is disposed between the sealing member 68 and the pressing member 66 in a state of being compressed between them. For this reason, the pressing member 66 is pressed against the back surface 35 of the assist rack tooth forming portion 33 in the large diameter portion 31 of the rack bar 30 by the biasing force from the spring 67. The large diameter portion 31 of the rack bar 30 is pressed against the second pinion gear 92 by the biasing force from the pressing member 66, such that the surface on which the assist rack teeth 34 are formed in the assist rack tooth forming portion 33. Thereby, the rack bar 30 maintains a state in which the assist rack teeth 34 are engaged with the second pinion gear 92.

[0062] FIG. 12 is a schematic diagram showing the relative positional relationship between the large diameter portion 31 and the small diameter portion 41 of the rack bar 30 in the first embodiment. FIG. 13 is a view taken along the line E-E of FIG. 12. In the first embodiment, the first pinion gear 91 and the second pinion gear 92 are arranged at different positions from each other in the circumferential direction around the central axes of the small diameter round bar portion 42 and the large diameter round bar portion 32 of the rack bar 30. However, in FIG. 12, the first pinion gear 91, the second pinion gear 92, the first pressing portion 60, and the second pressing portion 65 are illustrated on the same plane for the sake of convenience.

[0063] 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 in the large-diameter housing portion 11 is on the extension line of the central axis Hb of the small-diameter through hole 22 in the small-diameter housing portion 21. The central axis Ha of the large-diameter through hole 12 in this case is the central axis of the circle in the large-diameter through hole 12 that is a substantially circular hole and penetrates 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 in the small-diameter through hole 22 that is a substantially circular hole and penetrates the small-diameter housing portion 21. Specifically, the central axis Ha of the large-diameter through hole 12 of the large-diameter housing portion 11 is the central axis at the position in the large-diameter through hole 12 that stores the assist rack tooth forming portion 33 of the large-diameter portion 31 of the rack bar 30. Further, the central axis Hb of the small-diameter through hole 22 of the small-diameter housing portion 21 is the central axis at the position in the small-diameter through hole 22 that stores the portion where the steering rack teeth 44 formed on the small-diameter portion 41 of the rack bar 30 are located.

[0064] In the rack bar 30 stored in the rack housing 10 formed as described above, the central axis Ba of the large-diameter portion 31 and the central axis Bb of the small-diameter portion 41 are displaced. The central axis Ba of the large-diameter portion 31 of the rack bar 30 in this case is the central axis of the large-diameter round bar portion 32 of the large-diameter portion 31, and the central axis Bb of the small-diameter portion 41 is the central axis of the small-diameter round bar portion 42 of the small-diameter portion 41. Further, since the central axis of the large-diameter round bar portion 32 coincides with the central axis of the arc that is the shape of the back surface 35 of the assist rack tooth forming portion 33, the central axis Ba of the large-diameter portion 31 is also the central axis of the arc that is the shape of the back surface 35 of the assist rack tooth forming portion 33. The large-diameter portion 31 where the central axis Ba is displaced with respect to the central axis Bb of the small-diameter portion 41 and is connected to the small-diameter portion 41 is connected to the small-diameter portion 41 at a position where the central axis Ba is displaced to the side where the second pressing portion 65 is located with respect to the central axis Bb of the small-diameter portion 41.

[0065] On the other hand, the bolt holes 55 arranged at both ends in the longitudinal direction of the rack bar 30 are such that the central axis Cb of the bolt hole 55 arranged in the small-diameter portion 41 and the central axis Ca of the bolt hole 55 arranged in the large-diameter portion 31 are located on the same extension line. That is, although the large-diameter portion 31 and the small-diameter portion 41 of the rack bar 30 are connected to each other at positions where the central axes Ba and Bb are displaced, the bolt holes 55 arranged at both ends of the rack bar 30 are arranged in a positional relationship where the central axes Ca and Cb are on the same extension line with respect to each other.

[0066] Therefore, among 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 displaced with respect to the central axis of the rack bar 30 in which the bolt hole 55 is formed. In the first embodiment, the bolt hole 55 formed in the small-diameter portion 41 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 41, and the bolt hole 55 formed in the large-diameter portion 31 is arranged at a position where the central axis Ca of the bolt hole 55 is displaced with respect to the central axis Ba of the large-diameter portion 31. Therefore, in the first embodiment, the large-diameter portion 31 of the rack bar 30 that is connected to the small-diameter portion 41 at a displaced position is connected to the small-diameter portion 41 at a position where the central axis Ba of the large-diameter portion 31 is displaced to the side where the second pressing portion 65 is located with respect to the central axis Cb of the bolt hole 55 arranged in the small-diameter portion 41.

[0067] The rack bar 30 formed in this way is stored in the rack housing 10 at a position where the central axis Bb of the small-diameter round bar portion 42 of the small-diameter portion 41 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. For this reason, 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 32 of the large-diameter portion 31 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. That is, the rack bar 30 is stored in the rack housing 10 at a position where the central axis Ba of the large-diameter portion 31 is eccentric to the side where the second pressing portion 65 is located with respect to the central axis Ha of the large-diameter through hole 12 of the large-diameter housing portion 11.

[0068] Since the rack bar 30 is stored in the rack housing 10 at a position where the central axis Bb of the small-diameter portion 41 coincides with the central axis Hb of the small-diameter through-hole 22 of the small-diameter housing portion 21, the bolt holes 55 disposed in the small-diameter portion 41 are arranged at positions where the central axis Cb coincides with the central axis Hb of the small-diameter through-hole 22. Further, for the bolt holes 55 disposed in the large-diameter portion 31 of the rack bar 30, the central axis Ca is also arranged at a position where it coincides with the central axis Ha of the large-diameter through-hole 12 of the large-diameter housing portion 11.

[0069] Since the central axes Ca and Cb of the bolt holes 55 disposed at both ends of the rack bar 30 are located on the extension lines of each other, the ball joints 50 (see FIG. 8) to which the bolt portions 52 (see FIG. 8) are screwed with respect to these bolt holes 55 are also arranged in a positional relationship where the central axes of the ball joints 50 are located on the extension lines of each other. In the first embodiment, the ball joints 50 disposed at both ends of the rack bar 30 are arranged at positions where the center line of each ball joint 50, that is, the central axis of the bolt portion 52 of the ball joint 50, is on the central axis Bb of the small-diameter portion 41 of the rack bar 30.

[0070] The rack bar 30 is stored in the rack housing 10 with the central axis Ba of the large-diameter portion 31 eccentric to the side where the second pressing portion 65 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, with respect to the second pressing portion 65 disposed in the rack housing 10, the back surface 35 of the assist rack tooth forming portion 33 faces the large-diameter portion 31 of the rack bar 30. Thus, in a state where the central axis Ba of the large-diameter portion 31 is eccentric to the side where the second pressing portion 65 is located with respect to the central axis Ha of the large-diameter through-hole 12, the large-diameter portion 31 of the rack bar 30 is stored with a smaller distance from the inner peripheral surface 13 of the large-diameter housing portion 11 on the back surface 35 side than on the assist rack tooth 34 side.

[0071] Here, the second pressing portion 65 projects from the inner peripheral surface 13 of the large-diameter housing portion 11 to the inside of the rack housing 10, contacts the rack bar 30 stored in the rack housing 10, and presses the rack bar 30. Similarly, the first pressing portion 60 disposed in the small-diameter housing portion 21 of the rack housing 10 projects from the inner peripheral surface 23 of the small-diameter housing portion 21 to the inside of the rack housing 10, contacts the rack bar 30, and presses the rack bar 30. That is, the first pressing portion 60 presses the rack bar 30 when the pressing member 61 projects from the inner peripheral surface 23 of the small-diameter housing portion 21 to the inside of the rack housing 10, and the second pressing portion 65 presses the rack bar 30 when the pressing member 66 projects from the inner peripheral surface 13 of the large-diameter housing portion 11 to the inside of the rack housing 10.

[0072] At this time, 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 41 of the rack bar 30. However, the maximum width Wb (see FIG. 3) of the small-diameter portion 41 of the rack bar 30 is the diameter of the small-diameter round bar portion 42 (see FIG. 3) of the rack bar 30. For this reason, the distance between the small-diameter portion 41 of the rack bar 30 stored in the small-diameter housing portion 21 and the inner peripheral surface 23 of the small-diameter housing portion 21 is approximately the same at any position in the circumferential direction centered on 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 42 of the rack bar 30, the protruding amount Pb of the first pressing portion 60 that protrudes from the inner peripheral surface 23 of the small-diameter housing portion 21 and contacts the rack bar 30 can be reduced.

[0073] On the other hand, the maximum width Wa (see Fig. 6) of the large-diameter portion 31 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 assist rack tooth forming portion 33 (see Figs. 6 and 7). The assist rack tooth forming portion 33 is formed in a shape in which the large-diameter round bar portion 32 (see Fig. 7) of the large-diameter portion 31 is crushed and has two protruding portions 36. Therefore, in the large-diameter housing portion 11 of the rack housing 10 whose inner diameter is larger than the maximum width Wa of the large-diameter portion 31 of the rack bar 30, the distance between the inner peripheral surface 13 of the large-diameter housing portion 11 and the large-diameter portion 31 of the rack bar 30 will vary depending on the position in the circumferential direction centered on the central axis Ha of the large-diameter housing portion 11.

[0074] Fig. 14 is a schematic view when the central axis Ba of the large-diameter portion 31 of the rack bar 30 and the central axis Bb of the small-diameter portion 41 coincide. Fig. 15 is a view taken along the line F-F of Fig. 14. For example, when the central axis Ba of the large-diameter portion 31 of the rack bar 30 and the central axis Bb of the small-diameter portion 41 coincide, the central axis Ba of the large-diameter portion 31 of the rack bar 30 also coincides with the central axis Ha of the large-diameter housing portion 11 of the rack housing 10 that houses the large-diameter portion 31. In this case, the distance between the inner peripheral surface 13 of the large-diameter housing portion 11 formed to have an inner diameter larger than the maximum width Wa of the large-diameter portion 31 of the rack bar 30 and the rack bar 30 is the smallest in the direction along the direction of the maximum width Wa in the assist rack tooth forming portion 33 of the large-diameter portion 31. That is, the distance between the inner peripheral surface 13 of the large-diameter housing portion 11 and the rack bar 30 is the smallest when the distance between the inner peripheral surface 13 of the large-diameter housing portion 11 and the protruding portion 36 of the assist rack tooth forming portion 33 is the smallest.

[0075] 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 larger in a direction different from the direction along the maximum width Wa of the assist rack tooth forming portion 33 in the circumferential direction centered on the central axis Ba of the large-diameter portion 31 of the rack bar 30 than in the direction along the maximum width Wa. That is, since the large-diameter through hole 12 of the large-diameter housing portion 11 has a circular shape with an inner diameter larger than the maximum width Wa of the large-diameter portion 31 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 larger in the direction along the width Wc (see FIG. 6) orthogonal to the maximum width Wa in the assist rack tooth forming portion 33 than in the direction along the maximum width Wa in the assist rack tooth forming portion 33. For this reason, the distance between the inner peripheral surface 13 of the large-diameter housing portion 11 in the rack housing 10 and the back surface 35 of the assist rack tooth forming portion 33 in the large-diameter portion 31 of the rack bar 30 is larger than the distance between the inner peripheral surface 13 of the large-diameter housing portion 11 and the protruding portion 36 of the assist rack tooth forming portion 33.

[0076] Therefore, as shown in FIG. 14, the protruding amount Pc of the second pressing portion 65 that protrudes from the inner peripheral surface 13 of the large-diameter housing portion 11 and contacts the back surface 35 of the assist rack tooth forming portion 33 in the large-diameter portion 31 of the rack bar 30 is larger than the protruding amount Pb of the first pressing portion 60 from the inner peripheral surface 23 of the small-diameter housing portion 21. For example, when the protruding amount Pb of the first pressing portion 60 is 2.5 mm, the protruding amount Pc of the second pressing portion 65 is about 4 to 5 mm.

[0077] In contrast, in the first embodiment, as shown in FIGS. 12 and 13, the large-diameter portion 31 of the rack bar 30 is arranged at a position shifted to the side where the second pressing portion 65 is located with respect to the central axis Bb of the small-diameter portion 41 and the central axis Cb of the bolt hole 55 arranged in the small-diameter portion 41 with the central axis Ba of the large-diameter portion 31. For this reason, the distance between the back surface 35 of the assist rack tooth forming portion 33 in the large-diameter portion 31 of the rack bar 30 and the inner peripheral surface 13 of the large-diameter housing portion 11 in the rack housing 10 is smaller than the case where the central axis Ba of the large-diameter portion 31 of the rack bar 30 and the central axis Bb of the small-diameter portion 41 coincide as shown in FIGS. 14 and 15.

[0078] As a result, the protruding amount Pa of the second pressing portion 65 that protrudes from the inner peripheral surface 13 of the large-diameter housing portion 11 in the rack housing 10 and contacts the rear surface 35 of the large-diameter portion 31 of the rack bar 30 becomes smaller than the case where the central axis Ba of the large-diameter portion 31 of the rack bar 30 and the central axis Bb of the small-diameter portion 41 coincide with each other as shown in FIGS. 14 and 15. That is, the protruding amount Pa of the pressing member 66 of the second pressing portion 65 in the first embodiment from the inner peripheral surface 13 of the large-diameter housing portion 11 in the rack housing 10 becomes smaller than the case where the central axis Ba of the large-diameter portion 31 of the rack bar 30 and the central axis Bb of the small-diameter portion 41 coincide with each other as shown in FIGS. 14 and 15.

[0079] In the first embodiment, as shown in FIG. 12, the protruding amount Pa of the pressing member 66 of the second pressing portion 65 from the inner peripheral surface 13 of the large-diameter housing portion 11 is approximately the same as or less than the protruding amount Pb of the pressing member 61 of the first pressing portion 60 from the inner peripheral surface 23 of the small-diameter housing portion 21. For example, when the protruding amount Pb of the pressing member 61 of the first pressing portion 60 is 2.5 mm, the protruding amount Pa of the pressing member 66 of the second pressing portion 65 is preferably 2.5 mm, and more preferably, the protruding amount Pa is preferably about 1 mm.

[0080] Note that the protruding amount Pb of the first pressing portion 60 in these cases is the protruding amount Pb of the pressing member 61 of the first pressing portion 60 from the inner peripheral surface 23 of the small-diameter housing portion 21, and the protruding amounts Pa and Pc of the second pressing portion 65 are the protruding amounts Pa and Pc of the pressing member 66 of the second pressing portion 65 from the inner peripheral surface 13 of the large-diameter housing portion 11.

[0081] Next, the operation of the electric power steering device 80 will be described. When the steering wheel 81 is operated during the operation of 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 a steering torque from the steering shaft 82 to the intermediate shaft 85, and from the intermediate shaft 85 to the first pinion gear 91 via the stub shaft 87. As a result, the steering gear 90 having the first pinion gear 91 converts the rotational motion transmitted from the first pinion gear 91 into a linear motion of the rack bar 30, and operates the tie rod 93.

[0082] Further, the electric power steering device 80 according to the first embodiment has an electric motor 102 that generates an auxiliary steering torque for assisting the driver's steering. The electric motor 102 generates an auxiliary steering torque based on the steering torque detected by a torque sensor 101 disposed between the stub shaft 87 and the first pinion gear 91.

[0083] The torque sensor 101 detects the steering torque applied to the stub shaft 87 based on the angle of relative rotation when the stub shaft 87 and the first pinion gear 91 rotate relative to each other. That is, since the stub shaft 87 and the first pinion gear 91 are connected via a torsion bar (not shown), when a steering torque is applied to the stub shaft 87, the steering torque is transmitted between the stub shaft 87 and the first pinion gear 91 via the torsion bar. At that time, the torsion bar is slightly twisted, causing the stub shaft 87 and the first pinion gear 91 to rotate relative to each other. The torque sensor 101 detects the relative rotation between the stub shaft 87 and the first pinion gear 91 due to the slight twisting of the torsion bar, and transmits it to the ECU 100 as an electrical signal.

[0084] The ECU 100 operates the electric motor 102 based on the electrical signal transmitted from the torque sensor 101, and generates an auxiliary steering torque in the electric motor 102. That is, 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 91. For this reason, the ECU 100 uses the electrical signal transmitted from the torque sensor 101 as information that changes according to the steering torque T acting on the stub shaft 87 and the first pinion gear 91, and adjusts the power value X supplied to the electric motor 102 based on the electrical signal transmitted from the torque sensor 101, and generates an auxiliary steering torque in the electric motor 102.

[0085] That is, the ECU 100 acquires the signal of the steering torque T from the torque sensor 101, acquires the vehicle speed signal V of the vehicle from the vehicle speed sensor 103, and further acquires the operation information Y of the electric motor 102 from the rotation detection device provided in the electric motor 102, and generates an auxiliary steering torque in the electric motor 102 based on these operation information Y, the steering torque T, and the vehicle speed signal V. The auxiliary steering torque generated in the electric motor 102 is transmitted to the second pinion gear 92. The steering gear 90 having the second pinion gear 92 converts the rotational motion transmitted from the second pinion gear 92 into a linear motion of the rack bar 30. Thereby, the steering force applied by the driver to the steering wheel 81 is assisted by the auxiliary steering torque generated in the electric motor 102.

[0086] Specifically, when the driver steers the steering wheel 81, the stub shaft 87 and the first pinion gear 91 rotate as the steering force is transmitted. When the first pinion gear 91 rotates, the steering torque of the first pinion gear 91 is transmitted from the first pinion gear 91 to the steering rack teeth 44 of the rack bar 30 that meshes with the first pinion gear 91. Thereby, the rack bar 30 linearly moves in the axial direction while being supported by the rack housing 10.

[0087] In addition, the driving force generated by the electric motor 102 is transmitted to the second pinion gear 92 via the worm reduction gear 94, and the second pinion gear 92 rotates by the driving force generated by the electric motor 102. When the second pinion gear 92 rotates, the auxiliary steering torque of the second pinion gear 92 is transmitted from the second pinion gear 92 to the assist rack teeth 34 of the rack bar 30 that meshes with the second pinion gear 92. As a result, the rack bar 30 linearly moves while being assisted by the auxiliary steering torque from the second pinion gear 92 in the linear motion caused by the steering torque from the first pinion gear 91.

[0088] At this time, in the rack bar 30, the maximum width Wa of the assist rack tooth formation portion 33 where the assist rack teeth 34 are formed is larger than the width Wc in the direction orthogonal to the maximum width Wa, and is also larger than the diameter of the large-diameter round bar portion 32. That is, the tooth width of the assist rack teeth 34 in the direction along the direction of the maximum width Wa is larger than the diameter of the large-diameter round bar portion 32. Thereby, the rack bar 30 can receive a large auxiliary steering torque by the driving force generated by the electric motor 102 with the assist rack teeth 34, and linearly moves while receiving the large auxiliary steering torque.

[0089] The linear motion of the rack bar 30 is transmitted from the ball joints 50 arranged at both ends of the rack bar 30 to the tie rod 93 to which the ball joints 50 are connected, and the direction of the wheels is changed as the tie rod 93 moves.

[0090] When changing the direction of the wheels, the rack bar 30 linearly moves when the driver steers the steering wheel 81 in this way. However, the steering force when the steering wheel 81 is steered and the driving force generated by the electric motor 102 are transmitted to the rack bar 30 by the first pinion gear 91 and the second pinion gear 92. The rack bar 30 through which these forces are transmitted via the first pinion gear 91 and the second pinion gear 92 has the steering rack teeth 44 pressed against the first pinion gear 91 by the first pressing portion 60, and the assist rack teeth 34 pressed against the second pinion gear 92 by the second pressing portion 65.

[0091] The meshing portions between the steering rack teeth 44 and the first pinion gear 91, and between the assist rack teeth 34 and the second pinion gear 92 mesh with each other with the backlash minimized as much as possible by the pressing forces applied to the rack bar 30 from the first pressing portion 60 and the second pressing portion 65 in this way. Thereby, in the meshing portions between the steering rack teeth 44 and the first pinion gear 91, and between the assist rack teeth 34 and the second pinion gear 92, the generation of abnormal noise during operation due to the backlash of each meshing portion is suppressed.

[0092] Here, the large-diameter housing portion 11 of the rack housing 10 where the second pressing portion 65 is disposed has an inner diameter larger than that of the small-diameter housing portion 21. The inner diameter of the large-diameter housing portion 11 is set to a size that matches the maximum width Wa of the large-diameter portion 31 of the rack bar 30.

[0093] On the other hand, the second pressing portion 65 that applies a pressing force in the direction of pressing the assist rack teeth 34 against the second pinion gear 92 with respect to the rack bar 30 abuts against and presses the back surface 35 of the large-diameter portion 31 of the rack bar 30. The back surface 35 of the large-diameter portion 31 of the rack bar 30 is smaller than the distance from the central axis Ba of the large-diameter portion 31 of the rack bar 30 in the direction along the maximum width Wa in the portion where the distance from the central axis Ba of the large-diameter portion 31 is the maximum width Wa. For this reason, as shown in FIG. 14, when the central axis Ba of the large-diameter portion 31 of the rack bar 30 stored in the large-diameter housing portion 11 of the rack housing 10 coincides with the central axis Ha of the large-diameter housing portion 11, the second pressing portion 65 that contacts the back surface 35 of the assist rack tooth forming portion 33 in the large-diameter portion 31 is likely to have a large protruding amount Pc from the inner peripheral surface 13 of the large-diameter housing portion 11.

[0094] Therefore, the protruding amount Pc of the second pressing portion 65 that protrudes from the inner peripheral surface 13 of the large-diameter housing portion 11 and contacts the rear surface 35 of the assist rack tooth forming portion 33 in the large-diameter portion 31 of the rack bar 30 is likely to be larger than the protruding amount Pb of the first pressing portion 60 from the inner peripheral surface 23 of the small-diameter housing portion 21, as shown in FIG. 14. That is, when the central axis Ba of the large-diameter portion 31 of the rack bar 30 coincides with the central axis Ha of the large-diameter housing portion 11, the protruding amount Pc of the pressing member 66 (see FIG. 11) of the second pressing portion 65 from the inner peripheral surface 13 of the large-diameter housing portion 11 is likely to be larger.

[0095] When the protruding amount Pc of the pressing member 66 of the second pressing portion 65 from the inner peripheral surface 13 of the large-diameter housing portion 11 is large, the portion of the pressing member 66 that enters the through hole 16 (see FIG. 11) of the large-diameter housing portion 11 becomes smaller, so the portion supported by the through hole 16 becomes smaller. Thus, when the protruding amount Pc of the pressing member 66 is large and the portion of the pressing member 66 supported by the through hole 16 is small, the pressing member 66 may be dragged and tilted by the rack bar 30 when the rack bar 30 in contact with the pressing member 66 moves linearly (see, for example, FIG. 7 of Patent Document 2).

[0096] When the pressing member 66 is tilted, it becomes difficult for the pressing member 66 to appropriately press the large-diameter portion 31 of the rack bar 30, and it becomes difficult to press the assist rack teeth 34 of the rack bar 30 against the second pinion gear 92. In this case, it becomes difficult to reduce the backlash at the meshing portion between the assist rack teeth 34 and the second pinion gear 92 by the second pressing portion 65, so it becomes difficult to suppress the generation of abnormal noise during operation due to the backlash at the meshing portion between the assist rack teeth 34 and the second pinion gear 92.

[0097] Further, since the assist rack teeth 34 are formed obliquely with respect to the direction orthogonal to the central axis Ba of the large-diameter portion 31 of the rack bar 30, when the rack bar 30 moves linearly while being assisted by the auxiliary steering torque from the second pinion gear 92, the rack bar 30 also moves in the direction orthogonal to the central axis Ba. The linear movement of the rack bar 30 and the movement of the rack bar 30 in the direction orthogonal to the central axis Ba change in these directions when the steering direction is switched. However, when the pressing member 66 is tilted and in contact with the rack bar 30, the tilting direction of the pressing member 66 also changes. At that time, since the pressing member 66 is tilted while being pressed against the rack bar 30, a so-called stick-slip phenomenon occurs at the contact surface between the pressing member 66 and the rack bar 30, and abnormal noise may be generated. The stick-slip phenomenon when the pressing member 66 contacts the rack bar 30 while tilting may continuously occur while the rack bar 30 is moving linearly, and abnormal noise may continuously occur.

[0098] Furthermore, when the pressing member 66 of the second pressing portion 65 tilts, the pressing member 66 easily comes into contact with the through hole 16 that holds the pressing member 66 in the rack housing 10. Therefore, when the pressing member 66 contacts the through hole 16 of the rack housing 10, a collision sound may occur. When the pressing member 66 tilts due to the large protrusion amount Pc of the pressing member 66 of the second pressing portion 65, abnormal noise is likely to be generated due to various factors like these.

[0099] In contrast, in the first embodiment, the large-diameter portion 31 of the rack bar 30 is connected to the small-diameter portion 41 at a position where the central axis Ba of the large-diameter portion 31 is shifted to the side where the second pressing portion 65 is located with respect to the central axis Bb of the small-diameter portion 41 and the central axis Cb of the bolt hole 55 disposed in the small-diameter portion 41 (see FIG. 12). For this reason, the central axis Ba of the large-diameter portion 31 of the rack bar 30 is shifted to the side where the second pressing portion 65 is located with respect to the central axis Ha of the large-diameter housing portion 11 of the rack housing 10 that houses the large-diameter portion 31.

[0100] As a result, the distance from the inner peripheral surface 13 of the large-diameter housing portion 11 of the rack housing 10 to the back surface 35 of the assist rack tooth forming portion 33 in the large-diameter portion 31 of the rack bar 30 becomes smaller, and the protruding amount Pa from the inner peripheral surface 13 of the large-diameter housing portion 11 of the second pressing portion 65 that contacts the back surface 35 in the large-diameter portion 31 of the rack bar 30 becomes smaller.

[0101] That is, in the second pressing portion 65, the protruding amount Pa from the inner peripheral surface 13 of the large-diameter housing portion 11 of the pressing member 66 (see FIG. 11) that the second pressing portion 65 has becomes smaller, and the portion of the pressing member 66 supported by the through hole 16 of the large-diameter housing portion 11 increases. Therefore, even when the rack bar 30 with which the pressing member 66 of the second pressing portion 65 comes into contact moves in a linear motion, the pressing member 66 of the second pressing portion 65 is less likely to be dragged by the rack bar 30 and thus less likely to tilt, and the pressing member 66 can appropriately press the large-diameter portion 31 of the rack bar 30.

[0102] As a result, the pressing member 66 of the second pressing portion 65 can press the assist rack teeth 34 of the rack bar 30 against the second pinion gear 92, and the backlash at the meshing portion between the assist rack teeth 34 and the second pinion gear 92 can be reduced by the second pressing portion 65. For this reason, the second pressing portion 65 disposed in the large-diameter housing portion 11 of the rack housing 10 can suppress the generation of abnormal noise due to the backlash at the meshing portion between the assist rack teeth 34 and the second pinion gear 92.

[0103] In addition, since it becomes difficult for the pressing member 66 of the second pressing portion 65 to tilt, the occurrence of a stick-slip phenomenon at the contact surface between the pressing member 66 and the rack bar 30 can be suppressed. Furthermore, since it becomes difficult for the pressing member 66 of the second pressing portion 65 to tilt, the pressing member 66 is less likely to come into contact with the through hole 16 that holds the pressing member 66 in the rack housing 10, and the generation of a collision sound caused by the pressing member 66 coming into contact with the through hole 16 of the rack housing 10 can be suppressed.

[0104] Accordingly, when changing the direction of the wheels using the electric power steering apparatus 80, it is possible to change the direction of the wheels while suppressing the generation of abnormal noises caused by backlash at the meshing portion between the assist rack teeth 34 of the rack bar 30 and the second pinion gear 92, abnormal noises due to the stick-slip phenomenon, and abnormal noises caused by the pressing member 66 colliding with the through-hole 16 of the rack housing 10.

[0105] As described above, in the electric power steering apparatus 80 according to the first embodiment, the large-diameter portion 31 of the rack bar 30 is connected to the small-diameter portion 41 at a position shifted to the side where the second pressing portion 65 is located with respect to the central axis Cb of the bolt hole 55 whose central axis Ba is disposed in the small-diameter portion 41. Thereby, the distance between the rear surface 35 of the assist rack tooth forming portion 33 of the large-diameter portion 31 of the rack bar 30 and the inner peripheral surface 13 of the large-diameter housing portion 11 of the rack housing 10 can be reduced, and the protruding amount Pa of the second pressing portion 65 that abuts against the rear surface 35 in the large-diameter portion 31 of the rack bar 30 can be reduced. Therefore, when the rack bar 30 moves linearly, the pressing member 66 of the second pressing portion 65 is not dragged and tilted by the rack bar 30, and the assist rack teeth 34 of the rack bar 30 can be pressed toward the second pinion gear 92 by the pressing member 66. For this reason, the backlash at the meshing portion between the assist rack teeth 34 and the second pinion gear 92 can be reduced, and the generation of abnormal noises due to the backlash can be suppressed. Further, since the inclination of the pressing member 66 of the second pressing portion 65 can be suppressed, the generation of abnormal noises due to the stick-slip phenomenon and the generation of abnormal noises caused by the pressing member 66 colliding with the through-hole 16 of the rack housing 10 can be suppressed. As a result, the generation of abnormal noises can be suppressed.

[0106] Further, since the rack bar 30 is connected to the small-diameter portion 41 at a position shifted to the side where the second pressing portion 65 is located with respect to the central axis Cb of the bolt hole 55 in which the central axis Ba of the large-diameter portion 31 is disposed in the small-diameter portion 41, more portions of the second pinion gear 92 can be positioned inside the large-diameter housing portion 11. As a result, in the rack housing 10, the portion of the large-diameter housing portion 11 that is deformed from the cylindrical shape to match the second pinion gear 92 in order to store the second pinion gear 92 can be made smaller.

[0107] That is, when the central axis Ba of the large-diameter portion 31 of the rack bar 30 coincides with the central axis Cb of the bolt hole 55 disposed in the small-diameter portion 41, as shown in FIG. 14, the large-diameter housing portion 11 of the rack housing 10 needs to be enlarged in the portion that is deformed from the cylindrical shape to match the second pinion gear 92 in order to secure a portion for storing the second pinion gear 92. In this case, since the amount of deformation of the large-diameter housing portion 11 of the rack housing 10 from the cylindrical shape becomes large, it is conceivable that the strength of the rack housing 10 decreases or the weight increases.

[0108] On the other hand, in the first embodiment, the central axis Ba of the large-diameter portion 31 of the rack bar 30 is shifted to the side where the second pressing portion 65 is located with respect to the central axis Cb of the bolt hole 55 disposed in the small-diameter portion 41, that is, the side opposite to the side where the second pinion gear 92 is located. Therefore, in the first embodiment, as shown in FIG. 12, the size of the portion that is deformed from the cylindrical shape to match the second pinion gear 92 in order to secure a portion for storing the second pinion gear 92 in the large-diameter housing portion 11 can be made smaller compared to the configuration shown in FIG. 14. As a result, since the amount of deformation of the large-diameter housing portion 11 of the rack housing 10 from the cylindrical shape becomes small, it is possible to suppress a decrease in the strength of the rack housing 10 or an increase in weight. As a result, the strength of the rack housing 10 can be ensured and the weight can be reduced.

[0109] Further, since the central axis Cb of the bolt hole 55 disposed in the small-diameter portion 41 of the rack bar 30 and the central axis Ca of the bolt hole 55 disposed in the large-diameter portion 31 are located on the same extension line, the ball joints 50 screwed into these bolt holes 55 can be arranged at symmetric positions in the vehicle width direction. As a result, the tie rod 93 connected to the ball joint 50 can also be arranged symmetrically in the vehicle width direction, so that the movement of the wheels with respect to the linear movement of the rack bar 30 during steering can be made the same when steering to the left and when steering to the right. As a result, it is possible to suppress the generation of abnormal noise while suppressing a decrease in feeling during steering.

[0110] Further, the large-diameter housing portion 11 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 the extension line of the central axis Hb of the small-diameter through hole 22, and the rack bar 30 is arranged at a position where the central axis Cb of the bolt hole 55 disposed in the small-diameter portion 41 coincides with the central axis Hb of the small-diameter through hole 22. Therefore, the rack bar 30 can be stored in the rack bar 30 at a position where the central axis Ba of the large-diameter portion 31 is displaced with respect to the central axis Ha of the large-diameter through hole 12. As a result, the distance between the rear surface 35 of the assist rack tooth forming portion 33 provided in the large-diameter portion 31 of the rack bar 30 and the inner peripheral surface 13 of the large-diameter housing portion 11 of the rack housing 10 can be reduced, and the protruding amount Pa of the second pressing portion 65 that abuts against the rear surface 35 in the large-diameter portion 31 of the rack bar 30 can be reduced. Therefore, when the rack bar 30 makes a linear movement, the pressing member 66 of the second pressing portion 65 is not dragged and tilted by the rack bar 30, and the assist rack teeth 34 can be pressed toward the second pinion gear 92 by the pressing member 66. As a result, the generation of abnormal noise can be suppressed.

[0111] Further, since the steering rack teeth 44 of the rack bar 30 are formed within the range of the projected shape of the small-diameter portion 41 when viewed in the direction along the central axis Bb of the small-diameter portion 41, the inner diameter of the small-diameter housing portion 21 of the rack housing 10 that stores the small-diameter portion 41 can be made as small as possible. As a result, the protruding amount Pb of the first pressing portion 60 that abuts against the small-diameter portion 41 of the rack bar 30 can be reduced. Therefore, when the rack bar 30 moves linearly, the pressing member 61 of the first pressing portion 60 is not dragged and tilted by the rack bar 30, and the steering rack teeth 44 of the rack bar 30 can be pressed toward the first pinion gear 91 by the pressing member 61. Accordingly, the backlash at the meshing portion between the steering rack teeth 44 and the first pinion gear 91 can be reduced by the pressing force applied from the pressing member 61 of the first pressing portion 60 to the rack bar 30, so that the generation of abnormal noise due to backlash can be suppressed. Further, since the inclination of the pressing member 61 of the first pressing portion 60 can be suppressed, the generation of abnormal noise due to the stick-slip phenomenon and the generation of abnormal noise due to the pressing member 61 colliding with the through hole 26 of the rack housing 10 can be suppressed. As a result of these, the generation of abnormal noise can be suppressed.

[0112] [Second Embodiment] Next, the electric power steering apparatus 80 according to the second embodiment will be described. The same reference numerals are given to the same constituent parts as those in the first embodiment, and the description thereof will be omitted. Hereinafter, the description will be centered on the differences from the first embodiment.

[0113] FIG. 16 is a cross-sectional view of the assist rack tooth forming portion 33 in the rack bar 30 included in the electric power steering apparatus 80 according to the second embodiment. Note that FIG. 16 is a cross-sectional view at the same position as the B-B cross section in FIG. 3 in the rack bar 30 included in the electric power steering apparatus 80 according to the second embodiment. In the electric power steering apparatus 80 according to the second embodiment, the large-diameter portion 31 of the rack bar 30 has chamfers 38 at both ends in the direction orthogonal to the longitudinal direction of the large-diameter portion 31 on the back surface 35 side of the portion where the assist rack teeth 34 are arranged.

[0114] The chamfers 38 are formed near the ends on the side opposite to the side where the other protruding portion 36 is located in the two protruding portions 36 of the assist rack tooth forming portion 33 of the large diameter portion 31 of the rack bar 30, on the side where the back surface 35 of the assist rack tooth forming portion 33 is located. The chamfers 38 are formed over the entire area of the assist rack tooth forming portion 33 of the rack bar 30 in the longitudinal direction.

[0115] FIG. 17 is a schematic cross-sectional view of the rack bar 30 and the rack housing 10 included in the electric power steering apparatus 80 according to the second embodiment. FIG. 18 is a view taken along the line G-G in FIG. 17. In the second embodiment, chamfers 38 are formed on the protruding portions 36 of the assist rack tooth forming portion 33 of the large diameter portion 31 of the rack bar 30. The protruding portion 36 of the assist rack tooth forming portion 33 is the portion where the distance from the inner peripheral surface 13 of the large diameter housing portion 11 of the rack housing 10 that houses the large diameter portion 31 of the rack bar 30 is the smallest in the large diameter portion 31 of the rack bar 30. For this reason, the inner diameter of the large diameter housing portion 11 of the rack housing 10 is set based on the distance from the protruding portion 36 of the assist rack tooth forming portion 33 of the rack bar 30.

[0116] In the second embodiment, chamfers 38 are formed on the protruding portions 36 of the assist rack tooth forming portion 33 of the rack bar 30. For this reason, it is easier to secure the distance between the large diameter portion 31 of the rack bar 30 housed in the large diameter housing portion 11 and the inner peripheral surface 13 of the large diameter housing portion 11 of the rack housing 10. That is, in the second embodiment, even if the inner diameter of the large diameter housing portion 11 of the rack housing 10 is made smaller, it is difficult for the inner peripheral surface 13 of the large diameter housing portion 11 to come into contact with the large diameter portion 31 of the rack bar 30.

[0117] As a result, in the second embodiment, the inner diameter HD of the large-diameter housing portion 11 of the rack housing 10 is smaller than the inner diameter of the large-diameter housing portion 11 of the rack housing 10 in the case where the chamfer 38 is not formed on the overhanging portion 36 of the assist rack tooth forming portion 33 of the rack bar 30 as in the first embodiment. That is, when the center axis Ba of the large-diameter portion 31 of the rack bar 30 is shifted toward the side where the second pressing portion 65 is located with respect to the center axis Cb of the bolt hole 55 disposed in the small-diameter portion 41, in the case where the chamfer 38 is not formed on the overhanging portion 36 of the assist rack tooth forming portion 33 as in the first embodiment, it is necessary to increase the inner diameter of the large-diameter housing portion 11 in order to avoid interference between the inner peripheral surface 13 of the large-diameter housing portion 11 of the rack housing 10 and the overhanging portion 36 of the assist rack tooth forming portion 33.

[0118] On the other hand, in the second embodiment, by forming the chamfer 38 on the overhanging portion 36 of the assist rack tooth forming portion 33, interference between the inner peripheral surface 13 of the large-diameter housing portion 11 and the overhanging portion 36 of the assist rack tooth forming portion 33 can be suppressed as much as possible. As a result, in the second embodiment, when the center axis Ba of the large-diameter portion 31 of the rack bar 30 is shifted toward the side where the second pressing portion 65 is located with respect to the center axis Cb of the bolt hole 55 disposed in the small-diameter portion 41, the inner diameter HD of the large-diameter housing portion 11 can be reduced.

[0119] Therefore, in the second embodiment, it is possible to reduce the inner diameter HD of the large-diameter housing portion 11 while reducing the protruding amount Pa of the pressing member 66 of the second pressing portion 65 from the inner peripheral surface 13 of the large-diameter housing portion 11. As a result, it is possible to suppress the generation of abnormal noise due to backlash at the meshing portion between the assist rack teeth 34 and the second pinion gear 92, the generation of abnormal noise due to the stick-slip phenomenon, and the generation of abnormal noise due to the pressing member 66 colliding with the through hole 16 of the rack housing 10, while achieving weight reduction of the rack housing 10.

[0120] In addition, when reducing the inner diameter HD of the large-diameter housing portion 11 of the rack housing 10 by forming a chamfer 38 on the protruding portion 36 of the assist rack tooth forming portion 33 of the rack bar 30, the rack housing 10 may align the central axis Ha of the large-diameter through hole 12 with the central axis Hb of the small-diameter through hole 22, or may shift the central axis Ha of the large-diameter through hole 12 from the central axis Hb of the small-diameter through hole 22.

[0121] [Modification Example] In addition, in the above-described first embodiment, the central axis of the large-diameter round bar portion 32 of the large-diameter portion 31 coincides with the central axis of the arc that is the shape of the back surface 35 of the assist rack tooth forming portion 33. However, since the assist rack tooth forming portion 33 is formed by forging, the central axis of the arc of the back surface 35 may deviate from the central axis of the large-diameter round bar portion 32. In this case, the central axis Ba of the large-diameter portion 31 may be the central axis of the radius of curvature of the top of the arc that is the shape of the back surface 35 of the assist rack tooth forming portion 33. That is, the large-diameter portion 31 may be connected to the small-diameter portion 41 with the central axis of the radius of curvature of the top of the arc that is the shape of the back surface 35 of the assist rack tooth forming portion 33 shifted from the central axis Bb of the small-diameter portion 41.

[0122] Further, in the above-described first embodiment, since the central axis of the large-diameter round bar portion 32 of the large-diameter portion 31 and the central axis of the arc, which is the shape of the back surface 35 of the assist rack tooth forming portion 33, coincide with each other, the central axes of both are offset with respect to the central axis Bb of the small-diameter portion 41. However, as described above, the central axis of the large-diameter round bar portion 32 and the central axis of the back surface 35 of the assist rack tooth forming portion 33 may be offset. In this case, for the large-diameter portion 31 with respect to the central axis Bb of the small-diameter portion 41, it is sufficient if either the central axis of the large-diameter round bar portion 32 or the central axis of the back surface 35 of the assist rack tooth forming portion 33 is offset. That is, for the large-diameter portion 31 with respect to the central axis Bb of the small-diameter portion 41, it is sufficient if at least one of the central axes of the large-diameter round bar portion 32 and the central axis of the back surface 35 of the assist rack tooth forming portion 33 is offset. In other words, for the large-diameter portion 31, at least one of the central axes of the large-diameter round bar portion 32 and the central axis of the back surface 35 of the assist rack tooth forming portion 33 is used as the central axis Ba of the large-diameter portion 31, and it is sufficient if the central axis treated as the central axis Ba of the large-diameter portion 31 is offset with respect to the central axis Bb of the small-diameter portion 41.

[0123] Further, in the above-described first embodiment, the back surface 35 of the assist rack tooth forming portion 33 formed on the large-diameter portion 31 of the rack bar 30 is formed in a shape that coincides with the shape of the outer peripheral surface of the large-diameter round bar portion 32. However, the back surface 35 of the assist rack tooth forming portion 33 may be made different from the shape of the outer peripheral surface of the large-diameter round bar portion 32. The back surface 35 of the assist rack tooth forming portion 33 may be larger or smaller than the shape of the outer peripheral surface of the large-diameter round bar portion 32.

[0124] Further, in the above-described first embodiment, round bar-shaped large-diameter round bar portions 32 are arranged on both sides of the assist rack tooth forming portion 33 on the large-diameter portion 31 of the rack bar 30. However, the large-diameter portion 31 may not have the large-diameter round bar portion 32. That is, in the first embodiment, the shape of the portion of the large-diameter round bar portion 32 located on both sides of the assist rack tooth forming portion 33 of the rack bar 30 may be formed in the same shape as the assist rack tooth forming portion 33.

[0125] In the first embodiment described above, the central axes Ca and Cb of the bolt holes 55 respectively arranged at both ends of the rack bar 30 coincide with the central axes Ha and Hb of the large-diameter through hole 12 and the small-diameter through hole 22 of the rack housing 10. However, the central axes Ca and Cb of the bolt holes 55 do not necessarily coincide with the central axes Ha and Hb of the large-diameter through hole 12 and the small-diameter through hole 22 of the rack housing 10. For example, when the central axis Ha of the large-diameter through hole 12 of the rack housing 10 is offset from the central axis Hb of the small-diameter through hole 22, the central axes Ca and Cb of the bolt holes 55 arranged at both ends of the rack bar 30 may coincide with only one of the central axis Ha of the large-diameter through hole 12 and the central axis Hb of the small-diameter through hole 22.

[0126] As described above, the preferred embodiments of the present disclosure have been described. However, the present disclosure is not limited to those described in the above embodiments. The configurations described as embodiments or modifications may be combined as appropriate.

Description of Reference Numerals

[0127] 10 Rack housing 11 Large-diameter housing portion 12 Large-diameter through hole 13 Inner peripheral surface 15 Ball joint housing portion 16 Through hole 17 Gearbox 21 Small-diameter housing portion 22 Small-diameter through hole 23 Inner peripheral surface 25 Ball joint housing portion 26 Through hole 30 Rack bar 31 Large-diameter portion 32 Large-diameter round bar portion 33 Assist rack tooth forming portion 34 Assist rack teeth 35 Back surface 36 Protruding portion 38 Chamfer 41 Small-diameter portion 42 Small-diameter round bar portion 44 Steering rack teeth 50 Ball joint 51 Joint part 52 Bolt part 55 Bolt hole 60 First pressing part 61, 66 Pressing members 62, 67 Springs 63, 68 Sealing members 65 Second pressing part 80 Electric power steering device 81 Steering wheel 82 Steering shaft 84, 86 Universal joints 85 Intermediate shaft 87 Stub shaft 90 Steering gear 91 First pinion gear 92 Second pinion gear 93 Tie rod 94 Worm reduction gear 95 Worm wheel 100 ECU 101 Torque sensor 102 Electric motor 103 Vehicle speed sensor 104 Ignition switch 105 Power supply device

Claims

1. A rack bar having a small-diameter portion with first rack teeth that mesh with a first pinion gear, and a large-diameter portion having second rack teeth that mesh with a second pinion gear and having a diameter larger than that of the small-diameter portion, a small-diameter housing portion in which a small-diameter through-hole for storing the small-diameter portion of the rack bar is formed, and a large-diameter housing portion in which a large-diameter through-hole for storing the large-diameter portion of the rack bar and having an inner diameter larger than that of the small-diameter housing portion is formed, a second pressing portion disposed in the large-diameter housing portion and pressing the second rack teeth against the second pinion gear, bolt holes disposed at both ends in the longitudinal direction of the rack bar and to which tie rods are connected and in which ball joints are attached, comprising, wherein the maximum width of the second rack teeth in a direction orthogonal to the longitudinal direction of the rack bar is larger than the width in a direction orthogonal to the maximum width at a portion where the second rack teeth are formed in the large-diameter portion, and wherein the large-diameter portion is connected to the small-diameter portion at a position where the central axis is displaced to the side where the second pressing portion is located with respect to the central axis of the bolt hole disposed in the small-diameter portion, an electric power steering apparatus.

2. The electric power steering apparatus according to claim 1, wherein the central axis of the bolt hole disposed in the small-diameter portion and the central axis of the bolt hole disposed in the large-diameter portion are located on the same extension line.

3. 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 on the extension line of the central axis of the small-diameter through-hole in the small-diameter housing portion, and the rack bar is disposed at a position where the central axis of the bolt hole disposed in the small-diameter portion coincides with the central axis of the small-diameter through-hole, the electric power steering apparatus according to claim 1 or 2.

4. The electric power steering apparatus according to claim 1 or 2, wherein the first rack teeth are formed within the range of the projected shape of the small-diameter portion when viewed in a direction along the central axis of the small-diameter portion.

5. The electric power steering apparatus according to claim 1 or 2, wherein the large-diameter portion has chamfers at both ends in a direction orthogonal to the longitudinal direction of the large-diameter portion on the back side of the portion where the second rack teeth are disposed.

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