Rack bar and electric power steering device

Abstract

To restrict an increase in manufacturing cost.SOLUTION: An electric power steering device includes: a rack bar 30 having an assist-side rack teeth 33 and a steering-side rack teeth 43, the assist-side rack teeth 33 being larger in teeth width than the steering-side rack teeth 43; an assist-side rack guide 61 abutting on an assist-side back surface portion 34 located on a back-surface side of the assist-side rack teeth 33; and a steering-side rack guide 66 abutting on a steering-side back surface portion 44 located on a back-surface side of the steering-side rack teeth 43. The assist-side back surface portion 34 and the steering-side back surface portion 44 are identical in shape as viewed in a longitudinal direction of the rack bar 30. In the assist-side rack guide 61 and the steering-side rack guide 66, a shape of an abutting portion 61a of the assist-side rack guide 61, which abuts on the assist-side back surface portion 34 and a shape of an abutting portion 66a of the steering-side rack guide 66, which abuts on the steering-side back surface portion 44 are identical.SELECTED DRAWING: Figure 7

Description

Technical Field

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

Background Art

[0002] An electric power steering apparatus 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, Patent Documents 1 to 3 describe an electric power steering apparatus that transmits an assist force generated by an electric motor to a rack bar at a position different from a rotational torque when a steering wheel is steered.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, among electric power steering devices that transmit the assist force generated by an electric motor to the rack shaft at a position different from the steering torque applied by the driver, there are those that form rack teeth for receiving the assist force generated by the electric motor on the rack bar, as in Patent Documents 2 and 3. In such an electric power steering device, the rack teeth for receiving the assist force generated by the electric motor are arranged at a position different from the position where the rack teeth for receiving the rotational torque when steering the steering wheel are arranged in the longitudinal direction of the rack bar. Further, among electric power steering devices in which the rack teeth for receiving the assist force generated by the electric motor are formed on the rack bar, there are those in which, as in Patent Document 2, the tooth width of the rack teeth for receiving the assist force is wider than the tooth width on the steering side so as to be able to cope with the high assist force output of the electric motor.

[0005] However, when the tooth width of the rack teeth on the assist side is widened, the shape of the back surface of the rack bar located on the opposite side of the rack teeth on the assist side becomes larger than the shape of the back surface located on the opposite side of the rack teeth on the steering side, as in Patent Document 2. In this case, rack guides arranged to press the rack teeth against the pinion with which the rack teeth mesh are used, and the shapes thereof are different between the assist side and the steering side.

[0006] That is, in many cases, a rack guide is arranged on the rack bar to press the rack teeth against a pinion with which the rack teeth mesh by applying a pressing force to the rack bar from the back side of the portion where the rack teeth are located. For this reason, when the back shape of the portion where the rack teeth on the assist side are located is larger than the back shape of the portion where the rack teeth on the steering side are located, the shape of the portion of the rack bar that contacts the rack guide is different between the assist side and the steering side. Therefore, it is necessary to use rack guides with different shapes for the assist side and the steering side according to the rack bar. Accordingly, in an electric power steering apparatus in which the rack teeth on the assist side are arranged at positions different from those of the rack teeth on the steering side on the rack bar, the manufacturing cost tends to increase due to the use of rack guides with different shapes for the steering side and the assist side.

[0007] The present disclosure has been made in view of the above, and an object thereof is to provide a rack bar and an electric power steering apparatus capable of suppressing an increase in manufacturing cost.

Means for Solving the Problems

[0008] The rack bar of the present disclosure has assist-side rack teeth and steering-side rack teeth, and is a rack bar in which the tooth width of the assist-side rack teeth is wider than the tooth width of the steering-side rack teeth. An assist-side back portion located on the back side of the assist-side rack teeth and a steering-side back portion located on the back side of the steering-side rack teeth have the same shape when viewed in the longitudinal direction of the rack bar.

[0009] According to this configuration, since the assist-side back surface portion and the steering-side back surface portion of the rack bar have the same shape, the assist-side rack guide that contacts the assist-side back surface portion and the steering-side rack guide that contacts the steering-side back surface portion can have the same shape as each other, and the same parts can be used for the assist-side rack guide and the steering-side rack guide. Therefore, when manufacturing the assist-side rack guide and the steering-side rack guide, it is only necessary to manufacture those with the same shape. Thus, compared with the case where these parts have different shapes from each other, the manufacturing can be simplified. Also, by using the same parts for the assist-side rack guide and the steering-side rack guide, the labor for managing these parts can be reduced. As a result, an increase in manufacturing costs can be suppressed.

[0010] As a desirable form, the curvature radius of the assist-side back surface portion and the curvature radius of the steering-side back surface portion are the same size when viewed in the longitudinal direction of the rack bar.

[0011] According to this configuration, since the curvature radius of the assist-side back surface portion and the curvature radius of the steering-side back surface portion are the same size, the forming of the assist-side back surface portion and the steering-side back surface portion can be made relatively easy to perform. Also, since the curvature radius of the assist-side back surface portion and the curvature radius of the steering-side back surface portion are the same size, the same-shaped parts can be used for the assist-side rack guide and the steering-side rack guide. Thus, compared with the case where these parts have different shapes from each other, the manufacturing can be simplified. As a result, an increase in manufacturing costs can be suppressed.

[0012] The electric power steering apparatus of the present disclosure includes an assist-side rack tooth and a steering-side rack tooth, a rack bar having a tooth width of the assist-side rack tooth wider than that of the steering-side rack tooth, an assist-side rack guide that abuts against an assist-side back surface portion located on the back surface side of the assist-side rack tooth, and a steering-side rack guide that abuts against a steering-side back surface portion located on the back surface side of the steering-side rack tooth. The assist-side back surface portion and the steering-side back surface portion have the same shape when viewed in the longitudinal direction of the rack bar, and the assist-side rack guide and the steering-side rack guide have the same shape in a portion that abuts against the assist-side back surface portion in the assist-side rack guide and a portion that abuts against the steering-side back surface portion in the steering-side rack guide.

[0013] According to this configuration, the assist-side back surface portion and the steering-side back surface portion of the rack bar are formed in the same shape, and the shape of the portion that abuts against the assist-side back surface portion in the assist-side rack guide and the shape of the portion that abuts against the steering-side back surface portion in the steering-side rack guide are the same. Therefore, the same parts can be used for the assist-side rack guide and the steering-side rack guide, so that the manufacturing of the assist-side rack guide and the steering-side rack guide can be simplified, and the labor for managing these parts can be reduced. As a result, an increase in manufacturing cost can be suppressed.

[0014] As a desirable form, the radius of curvature of the assist-side back surface portion and the radius of curvature of the steering-side back surface portion are the same size when viewed in the longitudinal direction of the rack bar.

[0015] According to this configuration, since the radius of curvature of the assist-side back surface portion and the radius of curvature of the steering-side back surface portion are the same, the forming of the assist-side back surface portion and the steering-side back surface portion can be made relatively easy. Also, since the radius of curvature of the assist-side back surface portion and the radius of curvature of the steering-side back surface portion are the same, parts of the same shape can be used for the assist-side rack guide and the steering-side rack guide, and the simplification of manufacturing can be achieved as compared with the case where these parts have different shapes from each other. As a result of these, an increase in manufacturing cost can be suppressed.

[0016] As a desirable form, it has a rack housing formed in a cylindrical shape and storing the rack bar inside, and the rack housing has an assist-side rack guide housing portion that houses the assist-side rack guide inside and a steering-side rack guide housing portion that houses the steering-side rack guide inside, and the assist-side rack guide housing portion and the steering-side rack guide housing portion have the same shape of the inner peripheral surface.

[0017] According to this configuration, since the rack housing has an assist-side rack guide housing portion that houses the assist-side rack guide and a steering-side rack guide housing portion that houses the steering-side rack guide, and the shape of the inner peripheral surface is the same, when providing the assist-side rack guide housing portion and the steering-side rack guide housing portion in the rack housing, it can be provided more easily as compared with the case where these shapes are different from each other. As a result, an increase in manufacturing cost can be suppressed.

Effects of the Invention

[0018] The rack bar and the electric power steering apparatus according to the present disclosure have an effect of being able to suppress an increase in manufacturing cost.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Mode for Carrying Out the Invention

[0020] 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 mode for carrying out the invention (hereinafter referred to as the embodiment). 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 the so-called equivalent range. Furthermore, the constituent elements disclosed in the following embodiments can be combined as appropriate.

[0021] [Embodiment] FIG. 1 is a schematic diagram for explaining an electric power steering apparatus 80 according to an 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.

[0022] The steering shaft 82 is connected to the steering wheel 81 at one end and to the universal joint 84 at the other end.

[0023] 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.

[0024] The first pinion gear 91 is a shaft-like member having a gear formed at an end opposite to the side connected to the stub shaft 87 and meshing with the rack bar 30. The stub shaft 87 and the first pinion gear 91 are connected via a torsion bar 88 (see FIG. 8). The torsion bar 88 has one end connected to the stub shaft 87 and the other end connected to the first pinion gear 91, and transmits rotational torque between the stub shaft 87 and the first pinion gear 91.

[0025] 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 88. That is, the stub shaft 87 and the first pinion gear 91 connected via the torsion bar 88 are the shafts to be detected when the torque sensor 101 detects torque.

[0026] 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 the torsion bar 88. The first pinion gear 91 and the second pinion gear 92 mesh with the rack bar 30 at different positions in the longitudinal direction of the rack bar 30, respectively.

[0027] An electric motor 102 is connected to the second pinion gear 92 via a worm reduction gear 94 (see FIG. 7), 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 including a brush (slider) and a commutator (commutator).

[0028] 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 the rack bar 30 disposed inside the rack housing 10 (see FIG. 6). The electric power steering device 80 according to the embodiment is a dual pinion assist system 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 device 80 according to the embodiment is a rack and pinion type electric power steering device 80.

[0029] The torque sensor 101 detects the driver's steering force transmitted to the steering shaft 82 via the steering wheel 81 as steering torque. The vehicle speed sensor 103 detects the traveling speed (vehicle speed) of the vehicle on which the electric power steering device 80 is mounted. The electric motor 102, the torque sensor 101, and the vehicle speed sensor 103 are electrically connected to the ECU 100.

[0030] 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 on. The ECU 100 calculates an auxiliary steering command value of the 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 auxiliary steering 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.

[0031] 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.

[0032] Also, the steering force of the operator input to the steering wheel 81 is transmitted to the torque sensor 101 disposed in the transmission path of the steering force 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 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.

[0033] 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 apparatus 80 displaces the wheels using, in addition to the steering force of the operator transmitted to the rack bar 30 via the first pinion gear 91, the auxiliary steering torque of the electric motor 102 transmitted to the rack bar 30 via the second pinion gear 92. The electric power steering apparatus 80 according to the embodiment is a dual pinion type electric power steering apparatus in which an assist force is applied to the second pinion gear 92 in this way.

[0034] FIG. 2 is a plan view of the rack bar 30 shown in FIG. 1, and is a plan view of the steering side rack teeth 43 viewed from the front. FIG. 3 is a plan view of the rack bar 30 shown in FIG. 1, and is a plan view of the assist side rack teeth 33 viewed from the front. The rack bar 30 has steering side rack teeth 43 that mesh with the first pinion gear 91 and assist side rack teeth 33 that mesh with the second pinion gear 92. The steering side rack teeth 43 mesh with the first pinion gear 91. The assist side rack teeth 33 are arranged on the rack bar 30 at a position different from the position where the steering side rack teeth 43 are 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. As shown in FIGS. 2 and 3, these assist side rack teeth 33 and steering side rack teeth 43 extend in a direction close to a direction orthogonal to the longitudinal direction of the rack bar 30, and a plurality of teeth are arranged side by side in the longitudinal direction of the rack bar 30, respectively.

[0035] The rack bar 30 is formed in a round bar shape except for the portions where the assist-side rack teeth 33 and the steering-side rack teeth 43 are formed, and is a round bar portion 31 extending in the longitudinal direction of the rack bar 30. The assist-side rack teeth 33 are arranged in an assist rack tooth forming portion 32 formed such that the maximum width Wa in the direction orthogonal to the longitudinal direction of the rack bar 30 is larger than the maximum width Wb of the round bar portion 31 in the direction orthogonal to the longitudinal direction of the rack bar 30. That is, in the assist rack tooth forming portion 32, the maximum width Wa in the direction orthogonal to the longitudinal direction of the rack bar 30 is larger than the diameter of the round bar portion 31. The assist rack tooth forming portion 32 is formed in the range where the assist-side rack teeth 33 are arranged in the longitudinal direction of the rack bar 30, and round bar portions 31 are provided on both sides of the assist rack tooth forming portion 32 in the longitudinal direction of the rack bar 30.

[0036] Further, the arrangement position of the assist-side rack teeth 33 in the circumferential direction centered on the central axis AX of the round bar portion 31 is different from the arrangement position of the steering-side rack teeth 43 in the circumferential direction centered on the central axis AX of the round bar portion 31. That is, the assist-side rack teeth 33 and the steering-side rack teeth 43 are arranged facing in different directions from each other in the circumferential direction centered on the central axis AX of the round bar portion 31. Note that the assist-side rack teeth 33 and the steering-side rack teeth 43 may have the same phase in the circumferential direction centered on the central axis AX. That is, the assist-side rack teeth 33 and the steering-side rack teeth 43 may be arranged facing in the same direction from each other in the circumferential direction centered on the central axis AX of the round bar portion 31.

[0037] FIG. 4 is a sectional view taken along line A-A of FIG. 2. The steering-side rack teeth 43 formed on the rack bar 30 are formed within the range of the projected shape of the round bar portion 31 when viewing the rack bar 30 in the longitudinal direction of the rack bar 30, that is, along the central axis AX of the round bar portion 31. For this reason, the maximum width Wb in the direction orthogonal to the longitudinal direction of the rack bar 30 of the portion where the steering-side rack teeth 43 are formed in the longitudinal direction of the rack bar 30 is the same as the maximum width Wb of the round bar portion 31, that is, the diameter of the round bar portion 31. The steering-side rack teeth 43 formed in this way are formed facing a predetermined direction in the circumferential direction of the round bar portion 31.

[0038] Also, in the range where the steering-side rack teeth 43 are formed in the longitudinal direction of the rack bar 30, the portion other than the portion where the steering-side rack teeth 43 are formed in the circumferential direction of the round bar portion 31 is formed in the same shape as the round bar portion 31. For this reason, the steering-side back portion 44, which is the portion located on the back side of the steering-side rack teeth 43 in the range where the steering-side rack teeth 43 are formed in the longitudinal direction of the rack bar 30, is formed such that the shape of the outer peripheral surface is the same as the shape of the outer peripheral surface of the round bar portion 31. That is, the steering-side back portion 44 is formed in an arc shape where the radius of curvature R2 is the same as the radius of the round bar portion 31 when viewed in the longitudinal direction of the rack bar 30.

[0039] FIG. 5 is a sectional view taken along line B-B of FIG. 3. The assist rack tooth forming portion 32 is formed such that the maximum width Wa in the direction orthogonal to the longitudinal direction of the rack bar 30 is larger than the width Wc in the direction orthogonal to the maximum width Wa in the assist rack tooth forming portion 32. Specifically, the assist rack tooth forming portion 32 is formed by crushing the surface on which the assist-side rack teeth 33 are formed in the round bar portion 31 in a direction orthogonal to the axial direction of the round bar portion 31.

[0040] The assist rack tooth forming portion 32 has two protruding portions 35 that protrude in opposite directions in the direction orthogonal to the axial direction of the round bar portion 31 by being crushed in the direction orthogonal to the axial direction of the round bar portion 31 in this way. The maximum width Wa of the assist rack tooth forming portion 32 is the distance between the end portions on the opposite sides of each other on the side where the other protruding portion 35 is located in the two protruding portions 35. The assist side rack teeth 33 are formed on the surface where the round bar portion 31 is crushed and flattened in this way, and are formed across the two protruding portions 35.

[0041] Further, since the round bar portion 31 of the assist rack tooth forming portion 32 is crushed only in one direction, the surface on the opposite side of the surface where the assist side rack teeth 33 are formed in the assist rack tooth forming portion 32 is formed in a shape continuous with the round bar portions 31 located on both sides of the assist rack tooth forming portion 32. That is, the assist side back portion 34 located on the back side of the assist side rack teeth 33 in the assist rack tooth forming portion 32 is formed in an arc shape whose curvature radius in the longitudinal direction of the rack bar 30 is substantially the same as the curvature radius of the outer peripheral surface of the round bar portion 31.

[0042] Therefore, the curvature radius R1 of the assist side back portion 34 when viewed in the longitudinal direction of the rack bar 30 is the same as the radius of the round bar portion 31. In other words, the assist side back portion 34 and the steering side back portion 44 have the same shape when viewed in the longitudinal direction of the rack bar 30, and the curvature radius R1 of the assist side back portion 34 and the curvature radius R2 of the steering side back portion 44 are the same size. The assist side back portion 34 formed in the assist rack tooth forming portion 32 in this way is disposed between the two protruding portions 35 on the surface on the opposite side of the side where the assist side rack teeth 33 are formed in the assist rack tooth forming portion 32.

[0043] Note that since the arrangement positions of the assist-side rack teeth 33 and the steering-side rack teeth 43 are different from each other in the circumferential direction centered on the central axis AX of the round bar portion 31, the arrangement positions of the assist-side back surface portion 34 and the steering-side back surface portion 44 are also different from each other in the circumferential direction centered on the central axis AX of the round bar portion 31. Note that the assist-side back surface portion 34 and the steering-side back surface portion 44 may be arranged at the same position in the circumferential direction centered on the central axis AX of the round bar portion 31. That is, when the phases of the assist-side rack teeth 33 and the steering-side rack teeth 43 in the circumferential direction coincide, the phases of the assist-side back surface portion 34 and the steering-side back surface portion 44 in the circumferential direction centered on the central axis AX may also coincide.

[0044] The assist-side rack teeth 33 are formed across between two protruding portions 35 in an assist rack tooth forming portion 32 where the maximum width Wa is larger than the diameter of the round bar portion 31 due to the formation of the two protruding portions 35. Thereby, the assist-side rack teeth 33 can have a longer length compared to the case where the assist-side rack teeth 33 are directly formed on the round bar portion 31 like the steering-side rack teeth 43. Also, since the assist-side rack teeth 33 are provided in the assist rack tooth forming portion 32 having the two protruding portions 35, the length of the teeth is longer than the length of the teeth of the steering-side rack teeth 43. That is, the assist-side rack teeth 33 have a tooth width, which is the width in the extending direction of the teeth, wider than the tooth width of the steering-side rack teeth 43.

[0045] FIG. 6 is a cross-sectional view of a rack housing 10 and a rack bar 30 included in an electric power steering apparatus 80. The electric power steering apparatus 80 has a rack housing 10 that houses the rack bar 30. The rack housing 10 is formed in a cylindrical shape, and the rack bar 30 is housed inside the rack housing 10 formed in a cylindrical shape.

[0046] 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 that communicates with the small-diameter through hole 22 and in which a large-diameter through hole 12 having an inner diameter larger than that 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 large-diameter housing portion 11 in the shape of a substantially cylinder 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 small-diameter housing portion 21 in the shape of a substantially cylinder is viewed in the axial direction.

[0047] The minimum diameter of the large-diameter through hole 12 of the rack housing 10 is larger than the maximum width Wa of the assist rack tooth forming portion 32 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 round bar portion 31 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 assist rack tooth forming portion 32 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 round bar portion 31 of the rack bar 30.

[0048] 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 a direction in which 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 the rack bar 30 is stored in the rack housing 10, the direction of the rack bar 30 is such that the side on which the assist-side rack teeth 33 of the rack bar 30 are arranged is located on the large-diameter housing portion 11 side of the rack housing 10, and the side on which the steering-side rack teeth 43 of the rack bar 30 are arranged 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 stores the range including the assist-side rack teeth 33 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 stores the range including the steering-side rack teeth 43 of the rack bar 30.

[0049] Further, in the small-diameter through-hole 22 of the rack housing 10, the minimum diameter of the small-diameter through-hole 22 is smaller than the maximum width Wa of the assist rack tooth forming portion 32 of the rack bar 30. In other words, in the rack bar 30, the maximum width Wa of the assist rack tooth forming portion 32 is larger than the minimum diameter of the small-diameter through-hole 22 of the rack housing 10.

[0050] A ball joint accommodating portion 15 is formed at the end of the large-diameter housing portion 11 of the rack housing 10 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.

[0051] Similarly, in the small-diameter housing portion 21 of the rack housing 10, a ball joint housing portion 25 is formed at an end portion on the opposite side of 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 and is formed on the opposite side of the side where the large-diameter housing portion 11 is located, compared to the portion where the small-diameter through hole 22 is formed in the small-diameter housing portion 21.

[0052] Ball joints 50 are respectively arranged at both ends of the rack bar 30 stored in the rack housing 10. The ball joints 50 are attached to the rack bar 30 by screwing into screw holes formed at both ends on both sides in the longitudinal direction of the rack bar 30.

[0053] The ball joints 50 arranged at both ends of the rack bar 30 each have a joint portion 51 on the opposite side of the portion attached to the rack bar 30. The joint portion 51 of the ball joint 50 is formed such that the portion on the opposite side of the side connected to the rack bar 30 is in a concave shape, and the end portion of the tie rod 93 can enter the concave 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.

[0054] FIG. 7 is a cross-sectional view taken along the line C-C of FIG. 6. In the large-diameter housing portion 11 of the rack housing 10, a gear box 17 of the worm reduction gear 94 is provided. Inside the gear box 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 the assist-side rack teeth 33 formed on the assist rack tooth forming portion 32 of the rack bar 30. Thereby, the second pinion gear 92 can transmit the driving force generated by the electric motor 102 and transmitted through the worm wheel 95 to the assist-side rack teeth 33, and can transmit the driving force generated by the electric motor 102 to the rack bar 30.

[0055] Also, in the large-diameter housing portion 11 of the rack housing 10, an assist-side rack guide portion 60 for pressing the assist-side rack teeth 33 against the second pinion gear 92 is arranged. In the large-diameter housing portion 11, a hole-shaped assist-side rack guide housing portion 16 penetrating the inside and outside of the large-diameter housing portion 11 is formed at a position on the opposite side of the side where the assist-side rack teeth 33 of the rack bar 30 are formed. The assist-side rack guide housing portion 16 is formed at a position corresponding to the position where the assist-side rack teeth 33 are arranged in the longitudinal direction of the rack bar 30 in the rack housing 10. The assist-side rack guide portion 60 is arranged in the assist-side rack guide housing portion 16 formed in the large-diameter housing portion 11.

[0056] The assist-side rack guide portion 60 has an assist-side rack guide 61, a spring 62, and a sealing member 63. The assist-side rack guide 61, the spring 62, and the sealing member 63 are housed inside an assist-side rack guide housing portion 16 formed in the large-diameter housing portion 11. A part of the assist-side rack guide 61 is exposed from the assist-side rack guide housing portion 16 of the large-diameter housing portion 11 and protrudes from the inner peripheral surface of the large-diameter through-hole 12 in the large-diameter housing portion 11. The assist-side rack guide 61 protruding from the inner peripheral surface 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 in the rack bar 30 is located. Specifically, the assist-side rack guide 61 abuts against an assist-side back surface portion 34 located on the back side of the assist-side rack teeth 33 in the rack bar 30.

[0057] Therefore, the shape of the contact portion 61a, which is the portion of the assist-side rack guide 61 that contacts the assist-side back surface portion 34, is formed in a shape along the shape of the assist-side back surface portion 34. That is, the shape of the contact portion 61a when viewed in the longitudinal direction of the rack bar 30 is formed in an arc shape along the arc of the assist-side back surface portion 34 when viewed in the longitudinal direction of the rack bar 30.

[0058] The sealing member 63 is disposed at the opening of the assist-side rack guide housing portion 16 to seal the opening. The spring 62 is a compression spring and is disposed between the sealing member 63 and the assist-side rack guide 61 in a state of being compressed between them. For this reason, the assist-side rack guide 61 is pressed against the assist-side back surface portion 34 of the rack bar 30 by the biasing force from the spring 62, and the rack bar 30 is pressed by the biasing force from the assist-side rack guide 61 such that the surface on which the assist-side rack teeth 33 are formed is pressed against the second pinion gear 92. Thereby, the state in which the assist-side rack teeth 33 mesh with the second pinion gear 92 is maintained for the rack bar 30.

[0059] Figure 8 is a cross-sectional view taken along the line D-D of Figure 6. The small-diameter housing portion 21 of the rack housing 10 is provided integrally with the shaft housing 70. A first pinion gear 91 is disposed within the shaft housing 70, and the first pinion gear 91 is connected to a stub shaft 87 via a torsion bar 88 within the shaft housing 70. Also, a torque sensor 101 for detecting the rotational torque transmitted between the stub shaft 87 and the first pinion gear 91 is disposed within the shaft housing 70.

[0060] The first pinion gear 91 disposed within the shaft housing 70 is disposed in mesh with the steering-side rack teeth 43 formed on the rack bar 30. Thereby, the first pinion gear 91 can transmit the steering force of the operator transmitted from the stub shaft 87 side via the torsion bar 88 to the steering-side rack teeth 43, and can transmit the steering force of the operator input to the steering wheel 81 (see Figure 1) to the rack bar 30.

[0061] Also, a steering-side rack guide portion 65 for pressing the steering-side rack teeth 43 against the first pinion gear 91 is disposed on the small-diameter housing portion 21 of the rack housing 10. A hole-shaped steering-side rack guide housing portion 26 that penetrates 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-side rack teeth 43 of the rack bar 30 are formed. The steering-side rack guide housing portion 26 is formed at a position in the rack housing 10 corresponding to the position where the steering-side rack teeth 43 are disposed in the longitudinal direction on the rack bar 30. The steering-side rack guide portion 65 is disposed in the steering-side rack guide housing portion 26 formed on the small-diameter housing portion 21.

[0062] The steering-side rack guide portion 65 has a steering-side rack guide 66, a spring 67, and a sealing member 68. The steering-side rack guide 66, the spring 67, and the sealing member 68 are accommodated inside a steering-side rack guide housing portion 26 formed in the small-diameter housing portion 21. A part of the steering-side rack guide 66 is exposed from the steering-side rack guide housing portion 26 of the small-diameter housing portion 21 and protrudes from the inner peripheral surface of the small-diameter through-hole 22 in the small-diameter housing portion 21. The steering-side rack guide 66 protruding from the inner peripheral surface of the small-diameter housing portion 21 abuts against the rack bar 30 inside the small-diameter housing portion 21, from the side opposite to the side where the first pinion gear 91 is located on the rack bar 30. Specifically, the steering-side rack guide 66 abuts against a steering-side back surface portion 44 located on the back side of the steering-side rack teeth 43 on the rack bar 30.

[0063] Therefore, the shape of the contact portion 66a, which is the portion of the steering-side rack guide 66 that contacts the steering-side back surface portion 44, is formed in a shape along the shape of the steering-side back surface portion 44. That is, the shape of the contact portion 66a when viewed in the longitudinal direction of the rack bar 30 is formed in an arc shape along the arc of the steering-side back surface portion 44 when viewed in the longitudinal direction of the rack bar 30.

[0064] The sealing member 68 is disposed at the opening of the steering-side rack guide housing portion 26 to seal the opening. The spring 67 is a compression spring and is disposed between the sealing member 68 and the steering-side rack guide 66 in a state of being compressed between them. Therefore, the steering-side rack guide 66 is pressed against the steering-side back surface portion 44 of the rack bar 30 by the biasing force from the spring 67, and the rack bar 30 is pressed by the biasing force from the steering-side rack guide 66 such that the surface on which the steering-side rack teeth 43 are formed is pressed against the first pinion gear 91. Thereby, the meshing state of the steering-side rack teeth 43 with the first pinion gear 91 is maintained for the rack bar 30.

[0065] Here, the rack bar 30 is formed such that the radius of curvature R1 of the assist-side back surface portion 34 located on the back side of the assist-side rack teeth 33 and the radius of curvature R2 of the steering-side back surface portion 44 located on the back side of the steering-side rack teeth 43 are the same size. That is, the assist-side back surface portion 34 and the steering-side back surface portion 44 of the rack bar 30 have the same shape when viewed in the longitudinal direction of the rack bar 30. For this reason, the assist-side rack guide 61 and the steering-side rack guide 66 have the same shape in terms of the shape of the contact portion 61a that contacts the assist-side back surface portion 34 in the assist-side rack guide 61 and the shape of the contact portion 66a that contacts the steering-side back surface portion 44 in the steering-side rack guide 66.

[0066] That is, the contact portion 61a of the assist-side rack guide 61 is formed in a shape along the shape of the assist-side back surface portion 34 of the rack bar 30, and the contact portion 66a of the steering-side rack guide 66 is formed in a shape along the shape of the steering-side back surface portion 44 of the rack bar 30. Since the assist-side back surface portion 34 and the steering-side back surface portion 44 of the rack bar 30 have the same shape when viewed in the longitudinal direction of the rack bar 30, the contact portion 61a of the assist-side rack guide 61 and the contact portion 66a of the steering-side rack guide 66, which are formed in shapes along these, also have the same shape when viewed in the longitudinal direction of the rack bar 30.

[0067] In addition, the assist-side rack guide 61 and the steering-side rack guide 66 are formed in the same shape for the portions other than the contact portions 61a and 66a, and the assist-side rack guide 61 and the steering-side rack guide 66 are formed in the same shape as a whole. Further, in the assist-side rack guide portion 60 and the steering-side rack guide portion 65, the spring 62 of the assist-side rack guide portion 60, the spring 67 of the steering-side rack guide portion 65, and the sealing member 63 of the assist-side rack guide portion 60 and the sealing member 68 of the steering-side rack guide portion 65 are also formed in the same shape, respectively. For this reason, common parts can be used for the assist-side rack guide portion 60 and the steering-side rack guide portion 65, and when manufacturing the assist-side rack guide portion 60 or the steering-side rack guide portion 65, it is only necessary to manufacture those with the same shape, so the manufacturing cost can be suppressed.

[0068] Also, since the assist-side rack guide portion 60 and the steering-side rack guide portion 65 are the same shape as each other as described above, the inner peripheral surface shapes of the assist-side rack guide housing 16 that houses the assist-side rack guide portion 60 and the steering-side rack guide housing 26 that houses the steering-side rack guide portion 65 in the rack housing 10 are also formed in the same shape. For this reason, when providing the assist-side rack guide housing 16 and the steering-side rack guide housing 26 in the rack housing 10, they may be provided in the same shape, and thus the manufacturing cost can also be suppressed by this.

[0069] Next, a manufacturing method of the assist rack tooth forming portion 32 of the rack bar 30 will be described. FIG. 9 is a schematic diagram showing a manufacturing process of the assist rack tooth forming portion 32 of the rack bar 30. (a) in FIG. 9 shows a state in which the blank material 200 is set in the lower die 320, (b) shows a state in which the upper die 310 is lowered to crush the blank material 200 from above, and (c) shows the rack bar 30 in which the forming of the assist rack tooth forming portion 32 is completed. The rack bar 30 is formed, for example, by forging. As shown in FIG. 9, the mold 300 used for manufacturing the rack bar 30 includes an upper die 310 and a lower die 320. The upper die 310 is disposed above the lower die 320, and uneven portions are provided on the bottom surface 311 of the upper die 310. The assist side rack teeth 33 of the assist rack tooth forming portion 32 of the rack bar 30 are formed by the uneven portions provided on the bottom surface 311 of the upper die 310.

[0070] The lower die 320 includes a concave portion 321 and an upper surface 322. The concave portion 321 is formed in a shape with a circular arc cross-section on the upper surface 322 side of the lower die 320. The radius of curvature of the arc of the concave portion 321 is larger than the radius of the columnar blank material 200 that becomes the material of the rack bar 30. The diameter of the blank material 200 is the same as the diameter of the round bar portion 31 of the rack bar 30. When forming the assist rack tooth forming portion 32 of the rack bar 30, the blank material 200 of the rack bar 30 is set in the concave portion 321. The upper surface 322 of the lower die 320 other than the portion where the concave portion 321 is formed is a flat surface.

[0071] When forming the assist rack tooth forming portion 32 of the rack bar 30, as shown in FIG. 9(a), first, the blank material 200 of the rack bar 30 is set in the concave portion 321 of the lower die 320. At this time, since the radius of curvature of the concave portion 321 of the lower die 320 is larger than the radius of the blank material 200, it is easy to insert the blank material 200 into the concave portion 321.

[0072] Once the blank material 200 is set in the recess 321 of the lower die 320, next, as shown in FIG. 9(b), the upper die 310 is lowered from above the lower die 320. As a result, the upper die 310 crushes the upper side of the blank material 200 with the bottom surface 311. At this time, since the uneven portions are provided on the bottom surface 311 of the upper die 310, the portion of the blank material 200 that contacts the bottom surface 311 is formed into a shape along the shape of the uneven portions. Thereby, the assist side rack teeth 33 are formed in the portion of the blank material 200 where the bottom surface 311 of the upper die 310 contacts.

[0073] On the other hand, since the recess 321 of the lower die 320 is formed in a shape with a circular arc cross section, the portion of the blank material 200 that enters the recess 321 is difficult to deform, and the portion of the columnar blank material 200 that enters the recess 321 is slightly deformed along the shape of the recess 321 to have a circular arc cross section shape. Thereby, the portion of the blank material 200 that enters the recess 321 has an arc shape when viewed in the longitudinal direction of the rack bar 30, and is formed as the assist side back surface portion 34 located on the back side of the assist side rack teeth 33.

[0074] Also, the portion of the blank material 200 that protrudes upward from the recess 321 of the lower die 320 is crushed and deformed when the upper die 310 is lowered, and is in a state of being sandwiched between the upper surface 322 of the lower die 320 and the upper die 310. In this way, the portion of the blank material 200 that is sandwiched between the upper surface 322 of the lower die 320 and the upper die 310 is formed as the protruding portion 35 in the assist rack tooth forming portion 32. Note that the protruding portion 35 is a portion that bulges to the left and right when pressed by the upper die 310, and the mold 300 is not disposed on the outer peripheral side of the portion.

[0075] While the blank material 200 is being crushed by the upper die 310 and the lower die 320 in this way, the assist-side rack teeth 33 are formed by the bottom surface 311 of the upper die 310, and the assist-side back surface portion 34 is formed by the concave portion 321 of the lower die 320. As a result, as shown in FIG. 9(c), an assist-rack tooth forming portion 32 having the assist-side rack teeth 33, the assist-side back surface portion 34, and the overhanging portion 35 is formed.

[0076] 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 on which the electric power steering device 80 is mounted, 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 is transmitted from the intermediate shaft 85 to the first pinion gear 91 via the stub shaft 87. Thereby, 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.

[0077] Further, the electric power steering device 80 according to the 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 the torque sensor 101 disposed between the stub shaft 87 and the first pinion gear 91.

[0078] 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 the torsion bar 88, 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 88. At this time, the torsion bar 88 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 88 and transmits it to the ECU 100 as an electrical signal.

[0079] 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. Therefore, 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, 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.

[0080] 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 on the electric motor 102, and generates an auxiliary steering torque for 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 by 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 the 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 by the electric motor 102.

[0081] Specifically, when the driver steers the steering wheel 81, the stub shaft 87 and the first pinion gear 91 rotate by the transmission of the steering force. 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-side rack teeth 43 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.

[0082] Also, 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-side rack teeth 33 of the rack bar 30 that meshes with the second pinion gear 92. At that time, since the tooth width of the assist-side rack teeth 33 is wider than the tooth width of the steering-side rack teeth 43, a large auxiliary steering torque based on the driving force generated by the electric motor 102 can be reliably received. Thereby, the rack bar 30 linearly moves while the linear motion due to the steering torque from the first pinion gear 91 is assisted by the auxiliary steering torque from the second pinion gear 92.

[0083] 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 rods 93 to which the ball joints 50 are connected, and the direction of the wheels is changed as the tie rods 93 move.

[0084] When changing the direction of the wheels, the rack bar 30 performs linear motion 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 to which these forces are transmitted via the first pinion gear 91 and the second pinion gear 92 has the steering-side rack teeth 43 pressed against the first pinion gear 91 by the steering-side rack guide portion 65, and the assist-side rack teeth 33 pressed against the second pinion gear 92 by the assist-side rack guide portion 60.

[0085] The meshing portions between the steering-side rack teeth 43 and the first pinion gear 91 and between the assist-side rack teeth 33 and the second pinion gear 92 mesh with each other with the backlash minimized as much as possible by the pressing force applied to the rack bar 30 from the steering-side rack guide portion 65 and the assist-side rack guide portion 60 in this way. As a result, the generation of abnormal noise during operation due to the backlash of each meshing portion is suppressed at the meshing portions between the steering-side rack teeth 43 and the first pinion gear 91 and between the assist-side rack teeth 33 and the second pinion gear 92.

[0086] As described above, for the rack bar 30 according to the embodiment, the assist-side back surface portion 34 located on the back side of the assist-side rack teeth 33 and the steering-side back surface portion 44 located on the back side of the steering-side rack teeth 43 have the same shape when viewed in the longitudinal direction of the rack bar 30. Therefore, the assist-side rack guide 61 that abuts against the assist-side back surface portion 34 and the steering-side rack guide 66 that abuts against the steering-side back surface portion 44 can be made to have the same shape as each other, and the same parts can be used for the assist-side rack guide 61 and the steering-side rack guide 66. For this reason, when manufacturing the assist-side rack guide 61 and the steering-side rack guide 66, it is only necessary to manufacture those with the same shape. Therefore, compared with the case where these parts have different shapes from each other, the manufacturing can be simplified. Also, by using the same parts for the assist-side rack guide 61 and the steering-side rack guide 66, the labor for managing these parts can be reduced. As a result, an increase in the manufacturing cost can be suppressed.

[0087] Further, since the radius of curvature R1 of the assist-side back surface portion 34 and the radius of curvature R2 of the steering-side back surface portion 44 are the same when viewed in the longitudinal direction of the rack bar 30, the forming of the assist-side back surface portion 34 and the steering-side back surface portion 44 can be made relatively easy to perform. Also, since the radius of curvature R1 of the assist-side back surface portion 34 and the radius of curvature R2 of the steering-side back surface portion 44 are the same, the same-shaped parts can be used for the assist-side rack guide 61 and the steering-side rack guide 66. Compared with the case where these parts have different shapes from each other, the manufacturing can be simplified. As a result, an increase in the manufacturing cost can be suppressed.

[0088] In addition, in the electric power steering apparatus 80 according to the embodiment, the assist-side back surface portion 34 and the steering-side back surface portion 44 of the rack bar 30 are formed in the same shape, and the shape of the contact portion 61a that contacts the assist-side back surface portion 34 in the assist-side rack guide 61 is the same as the shape of the contact portion 66a that contacts the steering-side back surface portion 44 in the steering-side rack guide 66. Therefore, since the same parts can be used for the assist-side rack guide 61 and the steering-side rack guide 66, the manufacturing of the assist-side rack guide 61 and the steering-side rack guide 66 can be simplified, and the labor for managing these parts can be reduced. As a result, an increase in the manufacturing cost can be suppressed.

[0089] Further, the rack housing 10 includes an assist-side rack guide housing portion 16 that houses the assist-side rack guide 61 and a steering-side rack guide housing portion 26 that houses the steering-side rack guide 66. Since the shapes of the inner peripheral surfaces are the same, when providing the assist-side rack guide housing portion 16 and the steering-side rack guide housing portion 26 in the rack housing 10, it can be provided more easily compared to the case where these shapes are different from each other. As a result, an increase in the manufacturing cost can be suppressed.

[0090] In this embodiment, the radius of curvature R1 of the assist-side back surface portion 34 of the assist rack tooth forming portion 32 is the same as the radius of the round bar portion 31, and is also the same as the radius of curvature R2 of the steering-side back surface portion 44. Thereby, the tooth width of the assist-side rack teeth 33 is less likely to increase compared to the case where the material system on the assist side of the rack bar 30 is made larger than the material diameter on the steering side, as in Patent Document 3, for example. Therefore, this embodiment is preferably applied to the electric power steering apparatus 80 in which the auxiliary steering torque transmitted from the second pinion gear 92 to the assist-side rack teeth 33 is not so large.

[0091] [Modification Example] In the above-described embodiment, the protruding portion 35 of the assist rack tooth forming portion 32 of the rack bar 30 is formed by being sandwiched between the upper die 310 and the lower die 320 of the die 300 when pressing the blank material 200, but further processing may be performed on the protruding portion 35. FIG. 10 is a modification example of the electric power steering device 80 according to the embodiment, and is an explanatory view of the case where chamfering 36 is performed on the protruding portion 35 of the assist rack tooth forming portion 32. As shown in FIG. 10, chamfering 36 may be performed on the protruding portion 35 of the assist rack tooth forming portion 32 of the rack bar 30.

[0092] That is, the protruding portion 35 of the assist rack tooth forming portion 32 of the rack bar 30 is a portion where the distance from the inner peripheral surface of the large-diameter through hole 12 in the large-diameter housing portion 11 of the rack housing 10 that stores the assist rack tooth forming portion 32 is the smallest in the assist rack tooth forming portion 32. For this reason, the radius RH of the inner diameter of the large-diameter through hole 12 is set based on the distance from the protruding portion 35 of the assist rack tooth forming portion 32 of the rack bar 30. Therefore, by forming chamfering 36 on the protruding portion 35 of the assist rack tooth forming portion 32 of the rack bar 30, the radius RH of the large-diameter through hole 12 can be reduced.

[0093] That is, by forming chamfering 36 on the protruding portion 35 of the assist rack tooth forming portion 32 as shown in FIG. 10, it is possible to easily ensure the distance between the protruding portion 35 of the assist rack tooth forming portion 32 and the inner peripheral surface of the large-diameter through hole 12 in the large-diameter housing portion 11. For this reason, the large-diameter housing portion 11 of the rack housing 10 can reduce the radius RH of the large-diameter through hole 12 without interfering with the large-diameter through hole 12 on the protruding portion 35 of the assist rack tooth forming portion 32 of the rack bar 30, and the large-diameter housing portion 11 can be made smaller. As a result, the rack housing 10 can be miniaturized.

[0094] In the above-described embodiment, the assist rack tooth forming portion 32 of the rack bar 30 is described as being manufactured by forging. However, the assist rack tooth forming portion 32 may be manufactured by other methods than forging. For example, the assist rack teeth 33 may be manufactured by cutting. Further, the rack bar 30 may be manufactured by separately producing the side on which the assist rack teeth 33 are formed and the side on which the steering rack teeth 43 are formed, and then joining them by friction pressure welding or the like. The manufacturing method of the rack bar 30 is not limited as long as the shapes of the assist side back surface portion 34 located on the back side of the assist rack teeth 33 and the steering side back surface portion 44 located on the back side of the steering rack teeth 43 are the same when viewed in the longitudinal direction of the rack bar 30.

[0095] 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 modification examples may be combined as appropriate.

Description of Reference Numerals

[0096] 10 Rack housing 11 Large-diameter housing portion 12 Large-diameter through hole 16 Assist side rack guide housing portion 17 Gearbox 21 Small-diameter housing portion 22 Small-diameter through hole 26 Steering side rack guide housing portion 30 Rack bar 31 Round bar portion 32 Assist rack tooth forming portion 33 Assist side rack teeth 34 Assist side back surface portion 35 Protruding portion 36 Chamfer 43 Steering side rack teeth 44 Steering side back surface portion 50 Ball joint 60 Assist side rack guide portion 61 Assist side rack guide 61a, 66a Contact portion Springs 62 and 67 Sealing members 63 and 68 Steering side rack guide part 65 Steering side rack guide 66 Shaft housing 70 Electric power steering device 80 Steering wheel 81 Steering shaft 82 Intermediate shaft 85 Stub shaft 87 Torsion bar 88 Steering gear 90 First pinion gear 91 Second pinion gear 92 Tie rod 93 Worm reduction gear 94 Worm wheel 95 ECU 100 Torque sensor 101 Electric motor 102 Vehicle speed sensor 103 Ignition switch 104 Power supply device 105 Blank material 200 Mold 300

Claims

1. A rack bar having an assist-side rack tooth and a steering-side rack tooth, wherein a tooth width of the assist-side rack tooth is wider than a tooth width of the steering-side rack tooth, and an assist-side back surface portion located on a back surface side of the assist-side rack tooth and a steering-side back surface portion located on a back surface side of the steering-side rack tooth have the same shape when viewed in a longitudinal direction of the rack bar.

2. The rack bar according to claim 1, wherein a radius of curvature of the assist-side back surface portion and a radius of curvature of the steering-side back surface portion are the same when viewed in the longitudinal direction of the rack bar.

3. A rack bar having an assist-side rack tooth and a steering-side rack tooth, wherein the tooth width of the assist-side rack tooth is wider than the tooth width of the steering-side rack tooth, an assist-side rack guide that abuts on an assist-side back surface portion located on a back surface side of the assist-side rack tooth, a steering-side rack guide that abuts on a steering-side back surface portion located on a back surface side of the steering-side rack tooth, and the assist-side back surface portion and the steering-side back surface portion have the same shape when viewed in the longitudinal direction of the rack bar, wherein the assist-side rack guide and the steering-side rack guide have the same shape in a portion that abuts on the assist-side back surface portion in the assist-side rack guide and a portion that abuts on the steering-side back surface portion in the steering-side rack guide. An electric power steering apparatus.

4. The electric power steering apparatus according to claim 3, wherein a radius of curvature of the assist-side back surface portion and a radius of curvature of the steering-side back surface portion are the same when viewed in the longitudinal direction of the rack bar.

5. having a rack housing formed in a cylindrical shape and storing the rack bar therein, wherein the rack housing has an assist-side rack guide housing portion that houses the assist-side rack guide therein and a steering-side rack guide housing portion that houses the steering-side rack guide therein, and the electric power steering apparatus according to claim 3 or 4, wherein the assist-side rack guide housing portion and the steering-side rack guide housing portion have the same shape in an inner peripheral surface.

Images