Electric power steering device and method for manufacturing electric power steering device

Abstract

To provide an electric power steering device and a method for manufacturing the electric power steering device that reduce processing costs during manufacturing and suppress the generation of abnormal noise.SOLUTION: An electric power steering device has a rack bar 22 having rack teeth 23, a rack housing 50 that houses the rack bar 22, and a pressing portion 60 disposed in the rack housing 50 that presses the rack teeth 23 against a pinion gear 21 by exerting a force on the rack bar 22. An inner circumferential surface 51 of the rack housing 50 has a diameter-expanding portion 52 whose size of the opening area when viewed in the longitudinal direction of the rack housing 50 increases toward a predetermined direction in the longitudinal direction of the rack housing 50. In the diameter-expanding portion 52, in a cross section of the position where the pressing portion 60 is disposed in the circumferential direction of the rack housing 50 cutting along the longitudinal direction of the rack housing 50, a second line L2 of the inner circumferential surface 51 passing through a position different from the position where the pressing portion 60 is disposed is inclined relative to a first line L1 of the inner circumferential surface 51 running through the position where the pressing portion 60 is disposed and extending along the longitudinal direction.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to an electric power steering device and a method for manufacturing an electric power steering device. [Background technology]

[0002] An electric power steering device mounted on a vehicle has a pinion gear that rotates due to the rotational torque generated when the steering wheel is steered, a rack bar that has rack teeth that mesh with the pinion gear, and a rack housing that houses the rack bar. The rack housing is formed in a substantially cylindrical shape, and is often manufactured by casting.

[0003] For example, the gear housing described in Patent Document 1 is cast by using a concave mold corresponding to the outer shape of the gear housing and two rod-shaped cores having an outer shape corresponding to the inner surface of the gear housing, and pouring molten metal between the outer surfaces of the cores and the inner surface of the mold while arranging the tips of the two cores in contact with each other inside the mold. Also, the cores in Patent Document 1 have a tapered shape, and the inclination toward the tip forms a casting gradient, which makes it easy to remove the cores from both ends of the molded product after casting is completed.

[0004] Furthermore, the electric power steering device is provided with a mechanism for pressing the rack teeth of the rack bar against the pinion gear. For example, the steering device described in Patent Document 2 is provided with a rack guide that biases the rack shaft toward the pinion shaft by the elastic force of a biasing member. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2000-6823 A [Patent Document 2] JP 2017-132438 A Summary of the Invention [Problem to be solved by the invention]

[0006] Here, when the rack housing is formed by casting as in Patent Document 1, the core used for casting has a draft angle, so that the inner peripheral surface of the rack housing is formed in a tapered shape in which the diameter of the inner peripheral surface changes toward the axial direction of the rack housing. Therefore, after the rack housing is cast, the inner peripheral surface is cut to form a straight cylindrical shape. However, since the rack housing is formed in a long shape, when the inner peripheral surface is cut, the length of the portion to be cut also becomes long, which tends to increase the processing cost.

[0007] Furthermore, when the rack bar is pressed against the pinion gear as in Patent Document 2, a pressing member that presses the rack bar is brought into contact with the rack bar inside the rack housing, thereby applying a pressing force from the pressing member to the side of the rack bar where the pinion gear is located. However, when the rack housing is formed by casting and then the inner peripheral surface of the rack housing is cut, the distance between the inner peripheral surface of the rack housing and the rack bar becomes large, so that the pressing member tends to protrude from the inner peripheral surface of the rack housing. When the pressing member protrudes from the inner peripheral surface of the rack housing too much, the pressing member tends to tilt.

[0008] In other words, when the pressing member protrudes from the inner peripheral surface of the rack housing, 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, so that, for example, when the rack bar performs a linear motion, the pressing member is likely to tilt due to the movement of the rack bar. When the pressing member tilts, it becomes difficult for the pressing member to appropriately apply a pressing force to the rack bar, so the pressing force pressing the rack bar against the pinion gear becomes smaller, and backlash at the meshing portion between the rack bar and the pinion gear becomes large. When the backlash at the meshing portion between the rack bar and the pinion becomes large, abnormal noise is likely to occur from the meshing portion. For these reasons, the conventional rack housing has room for improvement in terms of the processing cost during manufacturing and the abnormal noise that is likely to occur due to the tilt of the pressing member.

[0009] The present disclosure has been made in consideration of the above, and aims to provide an electric power steering device and a manufacturing method for an electric power steering device that can reduce processing costs during manufacturing and suppress the generation of abnormal noise. [Means for solving the problem]

[0010] The electric power steering device of the present disclosure includes a rack bar having rack teeth that mesh with a pinion gear, a rack housing formed in a cylindrical shape and storing the rack bar inside its inner circumferential surface, and a pressing portion disposed on the rack housing and pressing the rack teeth against the pinion gear by applying a biasing force to the rack bar, wherein the inner circumferential surface of the rack housing has an expanding portion in which the size of an opening area formed by the inner circumferential surface when viewed in the longitudinal direction of the rack housing increases toward a predetermined direction in the longitudinal direction of the rack housing, and the inner circumferential surface of the expanding portion extends along the longitudinal direction of the rack housing at a position in the circumferential direction of the rack housing where the pressing portion is disposed, and the inner circumferential surface is inclined with respect to the longitudinal direction of the rack housing at a position different from the position in the circumferential direction of the rack housing where the pressing portion is disposed.

[0011] According to this configuration, in a cross section cut along the longitudinal direction of the rack housing at the position where the pressing portion is arranged in the circumferential direction of the rack housing, the first line of the inner peripheral surface of the expanded portion of the rack housing, which passes through the position where the pressing portion is arranged, extends along the longitudinal direction of the rack housing. Therefore, the position where the pressing portion is arranged on the inner peripheral surface can be made into a surface extending along the longitudinal direction of the rack housing without cutting the inner peripheral surface of the rack housing. This makes it possible to suppress the distance between the position where the pressing portion is arranged on the inner peripheral surface and the rack bar from increasing due to the cutting of the inner peripheral surface of the rack housing, and to suppress the protrusion of the pressing portion from the inner peripheral surface from increasing. Therefore, it is possible to suppress the generation of abnormal noise caused by the protrusion of the pressing portion from the inner peripheral surface of the rack housing from increasing. In addition, since the position where the pressing portion is arranged on the inner peripheral surface can be made into a surface extending along the longitudinal direction of the rack housing without cutting the inner peripheral surface of the rack housing, it is possible to suppress the increase in processing costs due to the cutting. As a result, it is possible to suppress the processing costs during manufacturing and the generation of abnormal noise.

[0012] In a preferred embodiment, the inner circumferential surface of the rack housing is cylindrical at a position in the longitudinal direction of the rack housing where the pressing portion is disposed.

[0013] According to this configuration, the inner peripheral surface is cylindrical at the position where the pressing portion is arranged in the longitudinal direction of the rack housing, so that the distance between the inner peripheral surface of the rack housing and the rack bar can be reduced, and the protrusion of the pressing portion from the inner peripheral surface can be reduced. This makes it possible to suppress the generation of abnormal noise caused by the large protrusion of the pressing portion from the inner peripheral surface of the rack housing. In addition, the cutting range for cutting the inner peripheral surface of the rack housing is a part of the range including the part where the diameter of the inner peripheral surface of the rack housing after casting is the smallest, so the cutting range can be reduced. This makes it possible to suppress an increase in processing costs due to the cutting process. As a result, it is possible to suppress the processing costs during manufacturing and the generation of abnormal noise.

[0014] In a preferred embodiment, the opening area of ​​the enlarged diameter portion increases from a position where the pressing portion is disposed in the longitudinal direction of the rack housing toward an end of the rack housing.

[0015] According to this configuration, the opening area of ​​the enlarged diameter portion increases from the position where the pressing portion is disposed in the longitudinal direction of the rack housing toward the end of the rack housing, so that the core for forming the enlarged diameter portion can be easily removed when the rack housing is cast. This makes it easy to manufacture the rack housing by casting. As a result, the manufacturing cost can be reduced.

[0016] In a preferred embodiment, the opening area of ​​the expanded diameter portion increases from one end side to the other end side in the longitudinal direction of the rack housing.

[0017] According to this configuration, the expanded diameter portion of the rack housing is formed such that the opening area of ​​the inner peripheral surface increases from one end side to the other end side in the longitudinal direction of the rack housing, so that when the rack housing is cast, the inner peripheral surface can be molded with one core. This makes it easy to manufacture the rack housing because only one core is needed when casting the rack housing. As a result, manufacturing costs can be reduced.

[0018] In a preferred embodiment, the first line is parallel to an axis of the rack bar.

[0019] According to this configuration, the first line on the inner peripheral surface of the rack housing that passes through the position where the pressing portion is arranged is parallel to the axis of the rack bar, so that the position on the inner peripheral surface where the pressing portion is arranged can be made into a surface that extends parallel to the axis of the rack bar without cutting the inner peripheral surface. This makes it possible to prevent the distance between the position on the inner peripheral surface where the pressing portion is arranged and the rack bar from increasing due to cutting the inner peripheral surface of the rack housing, and to prevent the generation of abnormal noise caused by the large protrusion of the pressing portion from the inner peripheral surface of the rack housing. In addition, since the position on the inner peripheral surface where the pressing portion is arranged can be made into a surface that extends parallel to the axis of the rack bar without cutting the inner peripheral surface of the rack housing, it is possible to prevent the increase in processing costs due to cutting. As a result, it is possible to reduce processing costs during manufacturing and prevent the generation of abnormal noise.

[0020] In a preferred embodiment, the expanding portion has a first expanding portion whose opening area increases from a position where the pressing portion is located in the longitudinal direction of the rack housing toward one end side in the longitudinal direction of the rack housing, and a second expanding portion whose opening area increases from an end position of the first expanding portion in the longitudinal direction of the rack housing toward the other end side in the longitudinal direction of the rack housing.

[0021] According to this configuration, the expanded diameter portion of the inner peripheral surface of the rack housing has a first expanded diameter portion and a second expanded diameter portion, so that the direction in which the opening area increases as the rack housing moves in a predetermined direction in the longitudinal direction can be different between the first expanded diameter portion and the second expanded diameter portion. This makes it possible to prevent the diameter of the inner peripheral surface from becoming too large due to the expanded diameter portion whose opening area increases as the rack housing moves in a predetermined direction in the longitudinal direction. As a result, the rack housing can be made smaller.

[0022] In a preferred embodiment, the rack teeth include first rack teeth and second rack teeth arranged at positions different from the first rack teeth in the longitudinal direction, the pinion gear includes a first pinion gear meshing with the first rack teeth and a second pinion gear meshing with the second rack teeth, and the pressing portion includes a first pressing portion that applies a biasing force to the rack bar to press the first rack teeth against the first pinion gear, and a second pressing portion that applies a biasing force to the rack bar to press the second rack teeth against the second pinion gear. and a second pressing portion that applies a pressure to the first expanding portion, wherein an arrangement position in the longitudinal direction of the first expanding portion includes a position in the longitudinal direction where the first pressing portion is arranged, and the inner circumferential surface extends along the longitudinal direction at a position in the circumferential direction where the first pressing portion is arranged, and an arrangement position in the longitudinal direction of the second expanding portion includes a position in the longitudinal direction where the second pressing portion is arranged, and the inner circumferential surface extends along the longitudinal direction at a position in the circumferential direction where the second pressing portion is arranged.

[0023] According to this configuration, the first enlarged diameter portion is formed at a position in the circumferential direction of the rack housing where the first pressing portion is disposed, with the inner peripheral surface extending along the longitudinal direction of the rack housing, and the second enlarged diameter portion is formed at a position in the circumferential direction of the rack housing where the second pressing portion is disposed, with the inner peripheral surface extending along the longitudinal direction of the rack housing. This makes it possible to reduce the protrusion of both the first pressing portion and the second pressing portion from the inner peripheral surface. Therefore, the first enlarged diameter portion can suppress the generation of abnormal noise caused by the large protrusion of the first pressing portion, and the second enlarged diameter portion can suppress the generation of abnormal noise caused by the large protrusion of the second pressing portion, so that when two pinion gears are provided, the generation of abnormal noise at the meshing portion of both pinion gears can be suppressed. As a result, the generation of abnormal noise in a dual pinion type electric power steering device can be suppressed.

[0024] In a preferred embodiment, the rack housing has an outer circumferential surface that is inclined with respect to the longitudinal direction in accordance with the inclination of the inner circumferential surface at the expanded diameter portion with respect to the longitudinal direction.

[0025] According to this configuration, the rack housing has an outer peripheral surface that is inclined along the inclination of the enlarged diameter portion of the inner peripheral surface, so that the thickness of the rack housing having the enlarged diameter portion can be made uniform. This ensures the flowability of the molten material during casting of the rack housing, and prevents defects such as manufacturing defects and the occurrence of portions with insufficient strength due to deterioration of the material flowability. As a result, the rack housing can be appropriately manufactured by casting.

[0026] The manufacturing method for the electric power steering device disclosed herein includes the steps of inserting a core having a tapered shape and for molding the inner surface of the rack housing inside an outer mold for molding the outer surface of the rack housing, injecting molten material between the outer mold and the core, and releasing the outer mold and the core after the material has solidified, and in the step of inserting the core inside the outer mold, the core is inserted in a direction such that a portion of the circumferential position of the core on the inclined surface of the tapered shape extends along the longitudinal direction of the rack housing.

[0027] According to this configuration, in the step of inserting the core into the inside of the outer mold used for casting, the core is inserted in such a way that a part of the circumferential position of the core on the tapered inclined surface extends along the longitudinal direction of the rack housing, so that a part of the circumferential position of the inner circumferential surface can be made into a surface extending along the longitudinal direction of the rack housing without cutting the inner circumferential surface. This makes it possible to suppress the distance between the inner circumferential surface and the rack bar from increasing due to the cutting of the inner circumferential surface of the rack housing, and to suppress the protrusion of the pressing part from the inner circumferential surface from increasing when the pressing part is disposed on the rack housing. Therefore, it is possible to suppress the generation of abnormal noise caused by the protrusion of the pressing part from the inner circumferential surface of the rack housing becoming large. In addition, since a surface extending along the longitudinal direction of the rack housing can be formed without cutting the inner circumferential surface of the rack housing, it is possible to suppress the increase in processing costs due to the cutting process. As a result, it is possible to suppress the processing costs during manufacturing and the generation of abnormal noise. Effect of the Invention

[0028] The electric power steering device and the manufacturing method for the electric power steering device according to the present disclosure have the advantage of being able to reduce processing costs during manufacturing and to suppress the occurrence of abnormal noise. [Brief description of the drawings]

[0029] [Figure 1]FIG. 1 is a schematic diagram of an electric power steering device according to a first embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view of the rack bar shown in FIG. 1 and a rack housing that stores the rack bar. [Diagram 3] FIG. 3 is a cross-sectional view taken along line AA of FIG. [Figure 4] FIG. 4 is an explanatory diagram showing a state in which a rack housing is molded using an outer mold and a core. [Diagram 5] FIG. 5 is a schematic diagram of the rack housing after the outer mold and the core have been separated. [Figure 6] FIG. 6 is an explanatory diagram showing an example of a conventional method for manufacturing a rack housing, in which a core is aligned with the axis of the rack housing during casting. [Figure 7] FIG. 7 is an explanatory view showing a state in which the core shown in FIG. 6 has been removed. [Figure 8] FIG. 8 is an explanatory diagram of cutting performed on a portion of the rack housing shown in FIG. 7 having a small inner diameter. [Figure 9] FIG. 9 is an explanatory diagram showing a state in which the rack bar and the pressing portion are arranged in the rack housing shown in FIG. [Figure 10] FIG. 10 is an explanatory diagram of a rack housing of the electric power steering device according to the second embodiment. [Figure 11] FIG. 11 is an explanatory diagram showing a state in which the rack bar and the pressing portion are arranged in the rack housing shown in FIG. [Figure 12] FIG. 12 is an explanatory diagram of a rack housing of the electric power steering device according to the third embodiment. [Figure 13] FIG. 13 is a schematic diagram of an electric power steering device according to the fourth embodiment. [Figure 14] FIG. 14 is a schematic cross-sectional view of a rack housing that stores the rack bar shown in FIG. [Figure 15] FIG. 15 is a schematic cross-sectional view of the rack housing shown in FIG. 14, showing a state in which the rack bar is stored in the rack housing. [Figure 16] FIG. 16 is a schematic cross-sectional view of a rack housing at a position including the first pressing portion and the first pinion gear, showing a modified example of the electric power steering device according to the fourth embodiment. [Figure 17] FIG. 17 is a cross-sectional view of the rack housing at a position different from that in FIG. 16, and is a schematic cross-sectional view of the rack housing at a position including the second pressing portion and the second pinion gear. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Hereinafter, the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the following modes for carrying out the invention (hereinafter, referred to as embodiments). Furthermore, the components in the following embodiments include those that a person skilled in the art can easily imagine, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the components disclosed in the following embodiments can be appropriately combined.

[0031] [First embodiment] Fig. 1 is a schematic diagram of an electric power steering device 10 according to a first embodiment. As shown in Fig. 1, the electric power steering device 10 includes, in the order in which a force applied by an operator is transmitted, a steering wheel 11, a steering shaft 12, a torque sensor 31, an electric motor 32, a reduction gear 33, a universal joint 15, an intermediate shaft 16, and a universal joint 17, which are joined to a stub shaft 18.

[0032] A steering wheel 11 is attached to one end of the steering shaft 12, and an intermediate shaft 16 is connected to the other end of the steering shaft 12 via a universal joint 15. The steering shaft 12 rotates by torque input from the steering wheel 11. The steering shaft 12 includes an input shaft 13, an output shaft 14, and a torsion bar (not shown). The torsion bar is connected to both the input shaft 13 and the output shaft 14, and the input shaft 13 and the output shaft 14 are connected to each other via the torsion bar. The steering wheel 11 is attached to the steering shaft 12 by being connected to one end of the input shaft 13, and a torsion bar extends from the other end of the input shaft 13 toward the side where the output shaft 14 is located. A torsion bar extends from one end of the output shaft 14, and the other end of the output shaft 14 is connected to the intermediate shaft 16 via a universal joint 15. Rotational torque is transmitted between the input shaft 13 and the output shaft 14 via the torsion bar connected to both of them.

[0033] A universal joint 15 and a universal joint 17 are disposed on both ends of the intermediate shaft 16 in the extending direction. One end of the intermediate shaft 16 is connected to the universal joint 15, and the other end is connected to the universal joint 17. Of the universal joint 15 and the universal joint 17, the universal joint 15 connects the intermediate shaft 16 to the steering shaft 12. The universal joint 17 connects the intermediate shaft 16 to a stub shaft 18. One end of the stub shaft 18 is connected to the universal joint 17, and the other end is connected to a steering gear 20. The intermediate shaft 16 has one end connected to the steering shaft 12 and the other end connected to the stub shaft 18 via the universal joint 15 and the universal joint 17. The universal joint 15 and the universal joint 17 are, for example, a Cardan joint. The rotation of the steering shaft 12 is transmitted to the stub shaft 18 via the intermediate shaft 16. Therefore, the intermediate shaft 16 can rotate together with the steering shaft 12.

[0034] The steering gear 20 includes a pinion gear 21 and a rack bar 22. The pinion gear 21 is connected to the stub shaft 18. The rack bar 22 meshes with the pinion gear 21. The steering gear 20 converts the rotational motion transmitted to the pinion gear 21 into linear motion by the rack bar 22. The electric power steering device 10 according to the first embodiment is of a single pinion assist type in which the rack bar 22 performs linear motion by the rotational motion transmitted from the pinion gear 21. The rack bar 22 is connected to a tie rod 24. The angle of the wheels changes as the rack bar 22 moves. That is, the electric power steering device 10 is a rack-and-pinion type electric power steering device.

[0035] The electric power steering device 10 further includes an ECU (Electronic Control Unit) 30 and a vehicle speed sensor 35. The electric motor 32, the vehicle speed sensor 35, and the torque sensor 31 are electrically connected to the ECU 30. The reduction gear 33 is attached to the electric motor 32. The torque sensor 31 outputs the steering torque transmitted to the input shaft 13 to the ECU 30 via CAN (Controller Area Network) communication. The vehicle speed sensor 35 detects the traveling speed (vehicle speed) of the vehicle body on which the electric power steering device 10 is mounted. The vehicle speed sensor 35 is provided on the vehicle body, and outputs the vehicle speed to the ECU 30 via CAN communication.

[0036] The ECU 30 controls the operation of the electric motor 32. The ECU 30 acquires signals from each of the torque sensor 31 and the vehicle speed sensor 35. When the ignition switch 36 is on, the ECU 30 is supplied with power from a power supply device 37 (e.g., an on-board battery). The ECU 30 calculates an auxiliary steering command value based on the steering torque and the vehicle speed. The ECU 30 adjusts the value of power supplied to the electric motor 32 based on the auxiliary steering command value. The ECU 30 acquires information on the induced voltage of the electric motor 32 or information output from a resolver or the like provided in the electric motor 32. The force required to operate the steering wheel 11 is reduced by the ECU 30 controlling the electric motor 32.

[0037] Fig. 2 is a schematic cross-sectional view of the rack bar 22 shown in Fig. 1 and a rack housing 50 that stores the rack bar 22. The rack bar 22 shown in Fig. 1 is formed in a substantially cylindrical, shaft-like shape extending in a predetermined direction, and has rack teeth 23 that mesh with the pinion gear 21. The rack teeth 23 are formed on the surface of the rack bar 22 at a predetermined position in the longitudinal direction. The rack bar 22 is stored in a rack housing 50 that covers the rack bar 22. The rack housing 50 is formed in a cylindrical shape, and stores the rack bar 22 inside an inner circumferential surface 51. The rack housing 50 is formed from a material such as aluminum or magnesium.

[0038] The pinion gear 21 is disposed in a rack housing 50 that stores the rack bar 22, and thereby meshes with the rack teeth 23 of the rack bar 22. More specifically, the pinion gear 21 is disposed in the rack housing 50 such that the extension direction of the pinion gear 21 intersects with the extension direction of the rack bar 22. The pinion gear 21 is disposed in a position in the longitudinal direction of the rack housing 50 where the rack teeth 23 of the rack bar 22 are located in the longitudinal direction of the rack housing 50. The rack bar 22 stored in the rack housing 50 is disposed such that the rack teeth 23 face the pinion gear 21. As a result, the rack teeth 23 of the rack bar 22 and the pinion gear 21 mesh with each other inside the rack housing 50.

[0039] Further, the rack housing 50 is provided with a pressing portion 60 that applies a biasing force to the rack bar 22. More specifically, the rack housing 50 is provided with a through hole 57 in which the pressing portion 60 is disposed, on the opposite side of the side where the pinion gear 21 is positioned with respect to the rack bar 22, at the position where the pinion gear 21 is disposed in the longitudinal direction of the rack housing 50. The through hole 57 is a hole that penetrates the inside and outside of the rack housing 50, and the pressing portion 60 is disposed on the inside of the through hole 57. For this reason, the pressing portion 60 is disposed in a positional relationship in which the rack bar 22 is sandwiched between the pressing portion 60 and the pinion gear 21, and is disposed with respect to the rack bar 22 on the opposite side to the surface on which the rack teeth 23 of the rack bar 22 are formed.

[0040] In this way, a biasing force toward the rack bar 22 is applied by a biasing means (not shown) to the pressing portion 60 arranged in the through hole 57 of the rack housing 50. The biasing means is, for example, a compression spring (not shown) arranged on the side of the pressing portion 60 opposite to the side on which the rack bar 22 is arranged, and the compression spring applies a biasing force to the pressing portion 60 from the side of the pressing portion 60 opposite to the side on which the rack bar 22 is located. As a result, the pressing portion 60 is pressed against the rack bar 22 by the biasing force applied by the compression spring.

[0041] Since the pressing portion 60 is disposed on the surface of the rack bar 22 opposite to the surface on which the rack teeth 23 are formed, the pressing portion 60 is pressed against the rack bar 22 by the compression spring, thereby pressing the rack bar 22 in a direction pressing the rack teeth 23 against the pinion gear 21. As a result, the pressing portion 60 applies a biasing force to the rack bar 22 by the biasing force of the compression spring, which is a biasing means, thereby pressing the rack teeth 23 of the rack bar 22 against the pinion gear 21. The rack teeth 23 of the rack bar 22 continue to mesh with the pinion gear 21 regardless of the operating states of the pinion gear 21 and the rack bar 22, as the rack teeth 23 are pressed against the pinion gear 21 by the pressing portion 60.

[0042] The inner peripheral surface 51 of the rack housing 50 that stores the rack bar 22 has an expanded diameter portion 52. The expanded diameter portion 52 is formed in a tapered shape in which the size of the opening area by the inner peripheral surface 51 when viewed in the longitudinal direction of the rack housing 50 increases toward a predetermined direction in the longitudinal direction of the rack housing 50. The predetermined direction here refers to a predetermined direction in the longitudinal direction of the rack housing 50, or a predetermined direction in the axial direction of the rack bar 22 stored in the rack housing 50, and does not include the radial direction of the rack housing 50. The expanded diameter portion 52 is formed such that the opening area increases from the position where the pressing portion 60 is disposed in the longitudinal direction of the rack housing 50 toward the end 56 of the rack housing 50, for example.

[0043] Specifically, the enlarged diameter portion 52 is formed in a substantially truncated cone shape, and the axis IA of the truncated cone is formed in a direction close to the longitudinal direction of the rack housing 50. For this reason, the size of the opening area of ​​the inner peripheral surface 51 of the enlarged diameter portion 52 when viewed in the longitudinal direction of the rack housing 50 changes depending on the position in the longitudinal direction of the rack housing 50. That is, the size of the opening area of ​​the inner peripheral surface 51 of the enlarged diameter portion 52 when viewed in the longitudinal direction of the rack housing 50 increases from the bottom surface side of the truncated cone, which is the shape of the enlarged diameter portion 52, where the diameter is smaller, to the bottom surface side of the truncated cone, which is the shape of the enlarged diameter portion 52. The diameter of the bottom surface of the truncated cone, which is the shape of the enlarged diameter portion 52, where the diameter is smaller, is larger than the diameter of the rack bar 22, which is formed in a substantially cylindrical shape.

[0044] The expanded diameter portion 52 of the inner peripheral surface 51 of the rack housing 50 has a truncated cone axis IA that is inclined with respect to the longitudinal direction of the rack housing 50. In other words, the truncated cone axis IA of the expanded diameter portion 52 is inclined with respect to the axis HA of the rack housing 50 and the axis of the rack bar 22 stored in the rack housing 50.

[0045] In this case, the axis HA of the rack housing 50 coincides with the axis of the rack bar 22 stored in the rack housing 50 and extends in the longitudinal direction of the rack housing 50. In other words, the longitudinal direction of the rack housing 50 coincides with the extension direction of the axis HA of the rack housing 50.

[0046] The expanded diameter portion 52 formed in a substantially truncated cone shape on the inner peripheral surface 51 of the rack housing 50 is formed in such a direction that the inner peripheral surface 51 extends along the longitudinal direction of the rack housing 50 at the position where the pressing portion 60 is disposed in the circumferential direction of the rack housing 50. Therefore, the expanded diameter portion 52 has the inner peripheral surface 51 inclined with respect to the longitudinal direction of the rack housing 50 at a position different from the position where the pressing portion 60 is disposed in the circumferential direction of the rack housing 50. In other words, in the cross section of the expanded diameter portion 52 on the inner peripheral surface 51 of the rack housing 50, in which the position where the pressing portion 60 is disposed in the circumferential direction of the rack housing 50 is cut along the longitudinal direction of the rack housing 50 as shown in FIG. 2, the first line L1 of the inner peripheral surface 51 passing through the position where the pressing portion 60 is disposed extends substantially parallel to the longitudinal direction of the rack housing 50, and extends substantially along the longitudinal direction of the rack housing 50. A first line L1 of the inner circumferential surface 51 passing through a position where the pressing portion 60 is arranged is preferably parallel to the axis of the rack bar 22. On the other hand, a second line L2 of the inner circumferential surface 51 passing through a position in the expanded diameter portion 52 different from the position where the pressing portion 60 is arranged in the same cross section of the rack housing 50 is inclined with respect to the first line L1 of the inner circumferential surface 51 and the longitudinal direction of the rack housing 50.

[0047] That is, in the expanded diameter portion 52, the axis IA of the truncated cone is inclined with respect to the axis HA of the rack housing 50 and the axis of the rack bar 22 at an angle such that the inner peripheral surface 51 extends along the longitudinal direction of the rack housing 50 at a position where the pressing portion 60 is disposed in the circumferential direction of the rack housing 50. In other words, in the expanded diameter portion 52, the axis IA of the truncated cone is inclined with respect to the axis HA of the rack housing 50 and the axis of the rack bar 22 at an angle equal to the inclination angle of the side surface with respect to the axis IA of the truncated cone. The inclination angle θ of the axis IA of the expanded diameter portion 52 with respect to the axis HA of the rack housing 50 coincides with the inclination angle θ of the axis CA of a core 110 (see FIG. 4 ) used in manufacturing the rack housing 50, described later, with respect to the axis HA of the rack housing 50.

[0048] In addition, the portion of the expanded diameter section 52 formed in a direction extending along the longitudinal direction of the rack housing 50 at the position in the circumferential direction of the rack housing 50 where the pressing section 60 is disposed does not have to strictly extend along the longitudinal direction of the rack housing 50. The portion of the expanded diameter section 52 formed in a direction extending along the longitudinal direction of the rack housing 50 at the position in the circumferential direction of the rack housing 50 where the pressing section 60 is disposed may be inclined, for example, within a range of about 0.5°, with respect to the longitudinal direction of the rack housing 50 in a direction away from the axis HA of the rack housing 50 as it moves from the pressing section 60 side toward the end section 56 side of the rack housing 50.

[0049] 3 is a cross-sectional view taken along line AA in FIG. 2. Since the expanded diameter portion 52 is formed in a substantially truncated cone shape, the shape of the expanded diameter portion 52 when viewed in the longitudinal direction of the rack bar 22 is substantially circular, and the opening area of ​​the circle changes depending on the position in the longitudinal direction of the rack housing 50. Since the axis IA of the truncated cone of the expanded diameter portion 52 is inclined with respect to the axis HA of the rack housing 50, the shape of the expanded diameter portion 52 when viewed in the longitudinal direction of the rack bar 22 is elliptical. That is, the shape of the expanded diameter portion 52 when viewed in the longitudinal direction of the rack bar 22 is an ellipse whose major axis is the direction in which the axis IA of the truncated cone of the expanded diameter portion 52 is inclined with respect to the axis HA of the rack housing 50.

[0050] Since the inclination angle of the expanded diameter portion 52 relative to the axis HA of the rack housing 50 is small, the shape of the expanded diameter portion 52 when viewed in the longitudinal direction of the rack bar 22 is close to a circle as shown in Figure 3, but is formed into an elliptical shape.

[0051] The expanded diameter portion 52 of the inner peripheral surface 51 of the rack housing 50 has a first expanded diameter portion 52a and a second expanded diameter portion 52b. The first expanded diameter portion 52a and the second expanded diameter portion 52b are both formed in a substantially truncated cone shape, and the axis IA of the truncated cone is disposed inclined with respect to the axis HA of the rack housing 50. In the first embodiment, the first expanded diameter portion 52a and the second expanded diameter portion 52b have the inner peripheral surface 51 extending along the longitudinal direction of the rack housing 50 at a position where the pressing portion 60 is disposed in the circumferential direction of the rack housing 50. The first expanded diameter portion 52a and the second expanded diameter portion 52b are disposed at different positions in the longitudinal direction of the rack housing 50.

[0052] Of the first and second enlarged diameter portions 52a and 52b, the first enlarged diameter portion 52a is formed so that the opening area increases from the position where the pressing portion 60 is disposed in the longitudinal direction of the rack housing 50 toward one end side in the longitudinal direction of the rack housing 50. In the first embodiment, the first enlarged diameter portion 52a is disposed such that a position near the bottom surface on the side with a smaller diameter in the truncated cone is located at the position where the pressing portion 60 is disposed in the longitudinal direction of the rack housing 50, and is disposed from the position where the pressing portion 60 is disposed to one end side in the longitudinal direction of the rack housing 50.

[0053] The second expanded diameter portion 52b is formed so that the opening area increases from the end position of the first expanded diameter portion 52a in the longitudinal direction of the rack housing 50 toward the other end side in the longitudinal direction of the rack housing 50. In other words, the first expanded diameter portion 52a and the second expanded diameter portion 52b are connected at the bottom surfaces on the smaller diameter sides of the respective truncated cones, and the size of the opening area increases as they move away from the other expanded diameter portion 52. For these reasons, the opening area of ​​both the first expanded diameter portion 52a and the second expanded diameter portion 52b is largest at the end position 56 in the longitudinal direction of the rack housing 50.

[0054] Moreover, the rack housing 50 is formed with an outer peripheral surface 55 inclined with respect to the longitudinal direction in accordance with the inclination of the inner peripheral surface 51 at the expanded diameter portion 52 with respect to the longitudinal direction. That is, the outer peripheral surface 55 of the rack housing 50 is formed substantially parallel to the inner peripheral surface 51. Therefore, the thickness of the rack housing 50 between the inner peripheral surface 51 and the outer peripheral surface 55 is nearly constant.

[0055] Next, a manufacturing method of the electric power steering device 10 will be described. Fig. 4 is an explanatory diagram showing the state in which the rack housing 50 is molded using an outer die 100 and a core 110. The rack housing 50 of the electric power steering device 10 is manufactured by casting using the outer die 100 which molds the outer peripheral surface 55 of the rack housing 50, and the core 110 which molds the inner peripheral surface 51. The outer die 100 and the core 110 are each made of iron, for example.

[0056] The outer die 100 has an inner peripheral surface formed in a shape capable of forming the outer peripheral surface 55 of the rack housing 50, and the core 110 has an outer peripheral surface formed in a shape capable of forming the inner peripheral surface 51 of the rack housing 50. The outer die 100 is, for example, split into two, and formed into a cylindrical shape by joining the two halves together. The outer die 100 has an inner peripheral surface formed in a shape capable of forming the outer peripheral surface 55 of the rack housing 50 when formed into a cylindrical shape by joining the two halves together in this manner.

[0057] When manufacturing the rack housing 50, first, the core 110 is inserted inside the outer mold 100. The core 110 is capable of forming the inner peripheral surface 51 of the rack housing 50 having the expanded diameter portion 52. For this reason, the core 110 has a tapered shape in which the diameter increases from one end side to the other end in the axial direction of the core 110.

[0058] In the first embodiment, since the inner peripheral surface 51 of the rack housing 50 has the first enlarged diameter portion 52a and the second enlarged diameter portion 52b, the core 110 uses a first core 110a for forming the first enlarged diameter portion 52a and a second core 110b for forming the second enlarged diameter portion 52b. The first core 110a and the second core 110b each have a tapered shape. That is, the first core 110a and the second core 110b are each formed in a shape of a substantially truncated cone. The diameter of the bottom surface of the truncated cone of the first core 110a and the second core 110b is larger than the diameter of the portion of the rack bar 22 where the bottom surface of the truncated cone of the first core 110a and the second core 110b is located in the longitudinal direction of the rack housing 50.

[0059] When manufacturing the rack housing 50 according to the first embodiment, the first core 110a and the second core 110b are inserted into the outer mold 100. The first core 110a and the second core 110b are inserted into the outer mold 100 in such a way that the bottom surfaces of the truncated cones with smaller diameters face each other. That is, the first core 110a and the second core 110b are inserted into the outer mold 100 in such a way that the bottom surfaces of the truncated cones with smaller diameters face each other and the bottom surfaces of the truncated cones with larger diameters face each other on the opposite side to the side where the other core 110 is located. Therefore, the first core 110a and the second core 110b arranged inside the outer mold 100 are arranged in such a way that the diameters become larger as they move away from the other core 110.

[0060] At this time, the core 110 is inserted in a direction such that a portion of the tapered inclined surface in the circumferential direction of the core 110 extends along the longitudinal direction of the rack housing 50. In other words, the core 110 is inserted into the inside of the outer mold 100 with the axis CA of the core 110 inclined at an angle equal to the inclination angle of the tapered inclined surface with respect to the axis CA of the core 110, relative to the longitudinal direction of the portion of the outer mold 100 that forms the outer peripheral surface 55 of the rack housing 50. As a result, the core 110 is inserted in a direction such that a portion of the inclined surface, which is the outer peripheral surface of the core 110, in the circumferential direction of the core 110 extends along the longitudinal direction of the portion of the outer mold 100 that forms the outer peripheral surface 55 of the rack housing 50. In other words, the core 110 is inserted in such a direction that a portion of the inclined outer peripheral surface of the core 110 in the circumferential direction of the core 110 extends along the axis HA of the rack housing 50 to be molded by the outer mold 100.

[0061] In detail, the outer die 100 has a through hole forming section 101 which forms a through hole 57 for arranging the pressing section 60 in the rack housing 50. The through hole forming section 101 is disposed at a partial position in the circumferential direction of a portion of the outer die 100 which forms the outer peripheral surface 55 of the rack housing 50. The core 110 is inserted inside the outer die 100 in a direction in which a slope of the core 110 which is positioned at the same position in the circumferential direction as the through hole forming section 101 of the outer die 100 extends along the longitudinal direction of a portion of the outer die 100 which forms the outer peripheral surface 55 of the rack housing 50.

[0062] Regarding the inclination angle of the core 110 when the core 110 is inserted inside the outer mold 100, for example, if the inclination angle of the slope of the core 110 relative to the axis CA of the core 110 is 0.5°, the core 110 is inserted inside the outer mold 100 with the axis CA of the core 110 inclined by 0.5° relative to the axis HA of the rack housing 50.

[0063] It is not necessary to incline core 110 strictly in accordance with the inclination angle of the slope of core 110. When the inclination angle of the slope of core 110 relative to axis CA of core 110 is 0.5°, the inclination angle θ of axis CA of core 110 relative to axis HA of rack housing 50 may be within a range of about 0°<θ<1.5°, and is preferably θ=0.5°.

[0064] Furthermore, in order to ensure the removability of core 110, the inclination angle θ of axis CA of core 110 relative to axis HA of rack housing 50 may be smaller than the inclination angle of the tapered slope of core 110 relative to axis CA of core 110. For example, if the inclination angle of the slope of core 110 relative to axis CA of core 110 is 0.5°, the inclination angle θ of axis CA of core 110 relative to axis HA of rack housing 50 may be set within the range of 0°<θ<0.5°. As a result, the portion of the tapered slope of core 110 that is oriented to extend along the longitudinal direction of rack housing 50 is also slightly inclined while extending along the longitudinal direction of rack housing 50, so that a slight draft gradient of core 110 can be ensured, and removability can be ensured.

[0065] The inclination angle of the core 110 may be different depending on the material used for casting. For example, when the rack housing 50 is made of a magnesium material, the adhesion of the magnesium material to the core 110 made of an iron-based material is small, so the draft angle of the core 110 may be smaller than that when the rack housing 50 is made of an aluminum material. That is, for example, when the rack housing 50 is made of an aluminum material, a portion of the tapered slope of the core 110 that extends along the longitudinal direction of the rack housing 50 is slightly inclined in order to ensure the draft angle of the core 110, whereas when the rack housing 50 is made of a magnesium material, this portion of the core 110 may be made to extend substantially along the longitudinal direction of the rack housing 50 without being inclined.

[0066] Moreover, it is preferable that the axis CA of the core 110 is inclined with respect to the axis HA of the rack housing 50, and that the abutting surfaces 111 of the first core 110a and the second core 110b are perpendicular to the direction of movement of the core 110 by the actuator that moves the core 110. In this case, the abutting surfaces 111 of the cores 110 are the surfaces of the two cores 110 that come into contact with the other core 110, and correspond to the bottom surface of the side with the smaller diameter in the truncated cone shape of the cores 110. In other words, the abutting surface 111a of the first core 110a is the end surface of the first core 110a facing the second core 110b, and the abutting surface 111b of the second core 110b is the end surface of the second core 110b facing the first core 110a. It is preferable that the core 110 is formed such that the axis CA of the core 110 is inclined relative to the axis HA of the rack housing 50, and that the abutting surfaces 111 are oriented perpendicular to the axis HA of the rack housing 50 and the axis of the rack bar 22, i.e., perpendicular to the direction of movement of the core 110 by the actuator.

[0067] After the core 110 is inserted inside the outer die 100, a molten material for forming the rack housing 50 is then injected between the outer die 100 and the core 110. In other words, the outer diameter of the core 110 is smaller than the inner diameter of the outer die 100, and therefore, when the core 110 is inserted inside the outer die 100, the inner peripheral surface of the outer die 100 and the outer peripheral surface of the core 110 are separated from each other, and a gap is formed between the inner peripheral surface of the outer die 100 and the outer peripheral surface of the core 110. The molten material is injected into the gap formed between the inner peripheral surface of the outer die 100 and the outer peripheral surface of the core 110 in this manner.

[0068] 5 is a schematic diagram of the rack housing 50 after the outer die 100 and the core 110 have been released. When the molten material injected into the gap between the inner peripheral surface of the outer die 100 and the outer peripheral surface of the core 110 has solidified, the outer die 100 and the core 110 are released after the material has solidified. That is, when the material injected into the gap between the inner peripheral surface of the outer die 100 and the outer peripheral surface of the core 110 has solidified and been molded into the shape of the rack housing 50, the outer die 100 and the core 110 are released.

[0069] When releasing the outer die 100 from the core 110, the two halves of the outer die 100 are separated from each other to remove the outer die 100. Furthermore, the core 110 is removed from the molded rack housing 50 by solidifying the material.

[0070] At that time, because core 110 is formed in a tapered shape, core 110 is moved in the direction in which the diameter of the tapered shape is larger to remove core 110 from rack housing 50. Therefore, core 110 can be easily removed because core 110 is removed by moving it to the side of expanded diameter portion 52 of inner circumferential surface 51 of rack housing 50 formed by core 110 that has a larger diameter than the diameter of core 110. In other words, the tapered shape of the outer circumferential surface of core 110 forms a so-called cast draft when core 110 is removed during casting, so that core 110 can be easily removed.

[0071] The rack housing 50 of the electric power steering device 10 is formed by casting using the outer mold 100 and the core 110 as described above.

[0072] Next, the operation of the electric power steering device 10 will be described. When the steering wheel 11 is operated while driving a vehicle equipped with the electric power steering device 10, the steering force applied to the steering wheel 11 is transmitted from the steering wheel 11 to the steering shaft 12. The steering force transmitted to the steering shaft 12 is transmitted as steering torque from the steering shaft 12 to the intermediate shaft 16, and from the intermediate shaft 16 to the pinion gear 21 via the stub shaft 18. As a result, the steering gear 20 having the pinion gear 21 converts the rotational motion transmitted from the pinion gear 21 into linear motion of the rack bar 22, and operates the tie rod 24.

[0073] The electric power steering device 10 according to the first embodiment also has an electric motor 32 that generates an auxiliary steering torque to assist the driver in steering. The electric motor 32 generates the auxiliary steering torque based on the steering torque detected by a torque sensor 31 disposed between the input shaft 13 and the output shaft 14 of the steering shaft 12.

[0074] The torque sensor 31 detects the steering torque applied from the steering wheel 11 to the steering shaft 12 based on the angle of relative rotation between the input shaft 13 and the output shaft 14. The torque sensor 31 transmits the detected steering torque to the ECU 30 as an electric signal.

[0075] The ECU 30 operates the electric motor 32 based on the electric signal transmitted from the torque sensor 31, and causes the electric motor 32 to generate an auxiliary steering torque. That is, the ECU 30 acquires a steering torque signal from the torque sensor 31, acquires a vehicle speed signal from the vehicle speed sensor 35, and further acquires operation information of the electric motor 32 from a rotation detection device provided in the electric motor 32, and causes the electric motor 32 to generate an auxiliary steering torque based on the operation information, steering torque, and vehicle speed signal. The auxiliary steering torque generated by the electric motor 32 is transmitted to the output shaft 14 of the steering shaft 12 via the reduction gear 33. As a result, the steering force applied to the steering wheel 11 by the driver is assisted by the auxiliary steering torque generated by the electric motor 32.

[0076] When steering using the electric power steering device 10, the rotational motion of the pinion gear 21 is converted into linear motion of the rack bar 22 to operate the tie rod 24 and change the direction of the wheels, but the rack teeth 23 of the rack bar 22 are pressed against the pinion gear 21 by the pressing portion 60. The meshing portion between the rack teeth 23 and the pinion gear 21 meshes with backlash minimized due to the pressing force applied from the pressing portion 60 to the rack bar 22 in this manner. This suppresses the generation of abnormal noise during operation at the meshing portion between the rack teeth 23 and the pinion gear 21, which is caused by backlash at the meshing portion.

[0077] Here, the expanded diameter portion 52 of the inner peripheral surface 51 of the rack housing 50 extends along the longitudinal direction of the rack housing 50 at a position where the pressing portion 60 is disposed in the circumferential direction of the rack housing 50. For this reason, the pressing portion 60 that applies a pressing force to the rack bar 22 has a relatively small protrusion from the inner peripheral surface 51 of the rack housing 50. In other words, when the axis of the core 110 used in manufacturing the rack housing 50 is aligned with the axis of the rack housing 50, it is necessary to cut the portion of the rack housing 50 with a small inner diameter after casting, which tends to increase the protrusion of the pressing portion 60.

[0078] Fig. 6 is an example of a conventional manufacturing method for the rack housing 50, and is an explanatory diagram of a case where casting is performed by aligning the core 110 with the axis of the rack housing 50. Fig. 7 is an explanatory diagram showing the state where the core 110 shown in Fig. 6 has been removed. In the conventional manufacturing method for the rack housing 50, when casting the rack housing 50, the core 110 having a tapered shape is inserted inside the outer mold 100 with the axis CA of the core 110 aligned with the axis HA of the rack housing 50. After the core 110 is inserted inside the outer mold 100, a molten material is injected between the outer mold 100 and the core 110, and after the injected material has solidified, the outer mold 100 and the core 110 are released from each other.

[0079] In this way, when the rack housing 50 is cast by aligning the axis CA of the core 110 with the axis HA of the rack housing 50, the rack housing 50 is cast in a state in which the axis IA of the inner circumferential surface 51 is aligned with the axis HA of the rack housing 50. For this reason, the inner circumferential surface 51 of the rack housing 50 is cast at an inclination with respect to the axis HA of the rack housing 50 in all parts. In other words, when the rack housing 50 is cast by aligning the axis CA of the core 110 with the axis HA of the rack housing 50, in a cross section cut along the longitudinal direction of the rack housing 50 at the position of the through hole 57 in which the pressing portion 60 is arranged in the circumferential direction of the rack housing 50 as shown in FIG. 7, both the first line L1 of the inner circumferential surface 51 passing through the position of the through hole 57 and the second line L2 of the inner circumferential surface 51 passing through a position different from the position of the through hole 57 are cast at an inclination with respect to the longitudinal direction of the rack housing 50. In a conventional method for manufacturing the rack housing 50, after the rack housing 50 is cast, the inner peripheral surface 51, which is inclined with respect to the axis HA of the rack housing 50, is cut.

[0080] FIG. 8 is an explanatory diagram of cutting performed on a portion of the rack housing 50 shown in FIG. 7 where the inner diameter is small. In the conventional manufacturing method of the rack housing 50, after the rack housing 50 is cast, the cut portion 58 of the inner circumferential surface 51 is cut. In this case, the cut portion 58 of the inner circumferential surface 51 is a portion where the diameter of the inner circumferential surface 51 is smaller than a predetermined size. In the conventional manufacturing method of the rack housing 50, the cut portion 58 is cut to reduce a portion of the inner circumferential surface 51 that is inclined with respect to the axis HA of the rack housing 50. That is, in the conventional manufacturing method of the rack housing 50, the inner circumferential surface 51 of the rack housing 50 after casting is inclined with respect to the axis HA of the rack housing 50 even at the position where the through hole 57 for arranging the pressing portion 60 is formed. Therefore, by cutting the cut portion 58, the portion of the inner circumferential surface 51 where the through hole 57 is located is made into a surface along the axis HA of the rack housing 50.

[0081] FIG. 9 is an explanatory diagram showing a state in which the rack bar 22 and the pressing portion 60 are arranged in the rack housing 50 shown in FIG. 8. When the inner peripheral surface 51 of the rack housing 50 is cut, the diameter of the inner peripheral surface 51 of the rack housing 50 becomes large. Therefore, when the rack bar 22 is stored in the rack housing 50 whose inner peripheral surface 51 has been cut, and the pressing portion 60 that applies a pressing force to the rack bar 22 is arranged in the through hole 57, the pressing portion 60 protrudes from the inner peripheral surface 51 to a large extent. In other words, when the inner peripheral surface 51 of the rack housing 50 is cut, the diameter of the inner peripheral surface 51 becomes large, so that the distance between the inner peripheral surface 51 and the rack bar 22 stored in the rack housing 50 becomes large. Therefore, the pressing portion 60 that abuts against the rack bar 22 and applies a pressing force to the rack bar 22 protrudes from the inner peripheral surface 51 to a large extent as the distance between the inner peripheral surface 51 and the rack bar 22 becomes large.

[0082] When the pressing portion 60 protrudes greatly from the inner peripheral surface 51 of the rack housing 50, the portion of the pressing portion 60 that enters the through hole 57 of the rack housing 50 is reduced, and therefore the portion supported by the through hole 57 is reduced. When the pressing portion 60 protrudes greatly and the portion of the pressing portion 60 that is supported by the through hole 57 is reduced, there is a risk that the pressing portion 60 will be dragged by the rack bar 22 and tilted when the rack bar 22 against which the pressing portion 60 abuts moves linearly (see, for example, FIG. 7 of Patent Document 2).

[0083] If the pressing portion 60 is tilted, it becomes difficult for the pressing portion 60 to appropriately press the rack bar 22, and difficult for the pressing portion 60 to press the rack teeth 23 of the rack bar 22 against the pinion gear 21. In this case, it becomes difficult for the pressing portion 60 to reduce the backlash at the meshing portion between the rack teeth 23 and the pinion gear 21, and therefore it becomes difficult to suppress the generation of abnormal noise during operation caused by the backlash at the meshing portion between the rack teeth 23 and the pinion gear 21.

[0084] In addition, since the rack teeth 23 are formed at an angle with respect to a direction perpendicular to the axis of the rack bar 22, when the rack bar 22 moves linearly due to the steering torque transmitted from the pinion gear 21, the rack bar 22 also moves in a direction perpendicular to the axis. The linear motion of the rack bar 22 and the movement of the rack bar 22 in a direction perpendicular to the axis also change when the steering direction changes, but when the pressing part 60 is inclined and in contact with the rack bar 22, the inclination direction of the pressing part 60 also changes. At that time, the inclination direction of the pressing part 60 changes while being pressed against the rack bar 22, so that a so-called stick-lip phenomenon occurs at the contact surface between the pressing part 60 and the rack bar 22, and abnormal noise may occur. When the pressing part 60 contacts the rack bar 22 while inclined, the stick-lip phenomenon may continue to occur even while the rack bar 22 is moving linearly, and abnormal noise may continue to occur.

[0085] Furthermore, when the pressing portion 60 tilts, the pressing portion 60 becomes more likely to come into contact with the through hole 57 that holds the pressing portion 60 in the rack housing 50, and therefore a collision noise may be generated when the pressing portion 60 comes into contact with the through hole 57 of the rack housing 50. When the pressing portion 60 tilts due to a large protrusion of the pressing portion 60 from the inner peripheral surface 51 of the rack housing 50, abnormal noise is more likely to be generated due to various factors such as those mentioned above.

[0086] In contrast, in the first embodiment, the expanded diameter portion 52 of the inner circumferential surface 51 of the rack housing 50 extends along the longitudinal direction of the rack housing 50 at the position where the pressing portion 60 is disposed in the circumferential direction of the rack housing 50. Therefore, in the first embodiment, the position on the inner circumferential surface 51 where the pressing portion 60 is disposed can be made into a surface that extends along the longitudinal direction of the rack housing 50 without cutting the inner circumferential surface 51 of the rack housing 50 having the expanded diameter portion 52. This makes it possible to reduce the protrusion of the pressing portion 60 from the inner circumferential surface 51 of the rack housing 50.

[0087] For this reason, a large portion of the pressing portion 60 is supported by the through-hole 57 of the rack housing 50. Therefore, even if the rack bar 22 with which the pressing portion 60 abuts moves linearly, the pressing portion 60 is less likely to be dragged by the rack bar 22 and therefore is less likely to tilt, and the pressing portion 60 can appropriately press the rack bar 22.

[0088] As a result, the pressing portion 60 can press the rack teeth 23 of the rack bar 22 against the pinion gear 21, and the backlash at the meshing portion between the rack teeth 23 and the pinion gear 21 can be reduced by the pressing portion 60. Therefore, the pressing portion 60 disposed in the through hole 57 of the rack housing 50 can suppress the generation of abnormal noise caused by the backlash at the meshing portion between the rack teeth 23 and the pinion gear 21.

[0089] In addition, since the pressing portion 60 is less likely to tilt, it is possible to suppress the occurrence of the stick lip phenomenon on the contact surface between the pressing portion 60 and the rack bar 22. Furthermore, since the pressing portion 60 is less likely to tilt, the pressing portion 60 is less likely to come into contact with the through hole 57 that holds the pressing portion 60 in the rack housing 50, and it is possible to suppress the occurrence of a collision sound caused by the pressing portion 60 coming into contact with the through hole 57 of the rack housing 50.

[0090] As a result, when the direction of the wheels is changed using the electric power steering device 10, the direction of the wheels can be changed while suppressing the generation of abnormal noises caused by backlash at the meshing portion between the rack teeth 23 of the rack bar 22 and the pinion gear 21, abnormal noises caused by the stick lip phenomenon, and abnormal noises caused by the pressing portion 60 colliding with the through hole 57 of the rack housing 50.

[0091] As described above, in the electric power steering device 10 according to the first embodiment, the expanded diameter portion 52 of the inner circumferential surface 51 of the rack housing 50 has a first line L1 of the inner circumferential surface 51 passing through the position where the pressing portion 60 is arranged, extending along the longitudinal direction of the rack housing 50 in a cross section taken along the longitudinal direction of the rack housing 50 at the position where the pressing portion 60 is arranged in the circumferential direction of the rack housing 50. Therefore, the position on the inner circumferential surface 51 where the pressing portion 60 is arranged can be made into a surface extending along the longitudinal direction of the rack housing 50 without cutting the inner circumferential surface 51.

[0092] This makes it possible to prevent the distance between the rack bar 22 and the position at which the pressing portion 60 is disposed on the inner peripheral surface 51 from increasing due to the cutting process of the inner peripheral surface 51 of the rack housing 50, and to prevent the pressing portion 60 from protruding too much from the inner peripheral surface 51. Therefore, it is possible to prevent the generation of abnormal noise caused by the pressing portion 60 protruding too much from the inner peripheral surface 51 of the rack housing 50.

[0093] Furthermore, since the position on the inner circumferential surface 51 where the pressing portion 60 is disposed can be made to be a surface that extends along the longitudinal direction of the rack housing 50 without cutting the inner circumferential surface 51 of the rack housing 50, it is possible to suppress an increase in processing costs that would otherwise be caused by cutting. As a result, it is possible to suppress processing costs during manufacturing and the generation of abnormal noise.

[0094] In addition, the opening area of ​​the expanded diameter portion 52 increases from the position where the pressing portion 60 is disposed in the longitudinal direction of the rack housing 50 toward the end portion 56 of the rack housing 50, so that the core 110 that forms the expanded diameter portion 52 can be easily removed when the rack housing 50 is cast. This makes it easy to manufacture the rack housing 50 by casting. As a result, the manufacturing cost can be reduced.

[0095] In addition, since the first line L1 of the inner peripheral surface 51 of the rack housing 50 passing through the position where the pressing portion 60 is arranged is parallel to the axis of the rack bar 22, the position where the pressing portion 60 is arranged on the inner peripheral surface 51 can be made into a surface extending parallel to the axis of the rack bar 22 without cutting the inner peripheral surface 51. This makes it possible to suppress the distance between the position where the pressing portion 60 is arranged on the inner peripheral surface 51 and the rack bar 22 from increasing due to cutting the inner peripheral surface 51 of the rack housing 50, and suppresses the generation of abnormal noise caused by the large protrusion of the pressing portion 60 from the inner peripheral surface 51 of the rack housing 50. In addition, since the position where the pressing portion 60 is arranged on the inner peripheral surface 51 can be made into a surface extending parallel to the axis of the rack bar 22 without cutting the inner peripheral surface 51 of the rack housing 50, it is possible to suppress the increase in processing costs due to cutting. As a result, it is possible to suppress the processing costs during manufacturing and the generation of abnormal noise.

[0096] In addition, since the expanded diameter portion 52 of the inner peripheral surface 51 of the rack housing 50 has the first expanded diameter portion 52a and the second expanded diameter portion 52b, the direction in which the opening area increases toward a predetermined direction in the longitudinal direction of the rack housing 50 can be different between the first expanded diameter portion 52a and the second expanded diameter portion 52b. This makes it possible to prevent the diameter of the inner peripheral surface 51 from becoming too large by the expanded diameter portion 52 whose opening area increases toward a predetermined direction in the longitudinal direction of the rack housing 50. As a result, the rack housing 50 can be made smaller in size.

[0097] Furthermore, since the outer peripheral surface 55 of the rack housing 50 is inclined with respect to the longitudinal direction of the rack housing 50 along the inclination of the expanded diameter portion 52 of the inner peripheral surface 51 with respect to the longitudinal direction of the rack housing 50, the thickness of the rack housing 50 having the expanded diameter portion 52 can be made uniform. This ensures the flowability of the molten material when the rack housing 50 is cast, and prevents defects such as manufacturing defects due to deterioration of the material flowability and the occurrence of portions with insufficient strength. As a result, the rack housing 50 can be appropriately manufactured by casting.

[0098] Furthermore, in the manufacturing method for the electric power steering device 10 of the first embodiment, in the step of inserting the core 110 inside the outer mold 100 used for casting, the core 110 is inserted in a direction such that a portion of the circumferential position of the core 110 on the tapered inclined surface extends along the longitudinal direction of the rack housing 50. Therefore, without performing cutting processing on the inner surface 51, a portion of the circumferential position of the inner surface 51 can be made into a surface extending along the longitudinal direction of the rack housing 50.

[0099] This makes it possible to prevent the distance between the inner peripheral surface 51 and the rack bar 22 from increasing due to the cutting process of the inner peripheral surface 51 of the rack housing 50, and to prevent the pressing portion 60 from protruding too much from the inner peripheral surface 51 when the pressing portion 60 is disposed in the rack housing 50. Therefore, it is possible to prevent the generation of abnormal noise caused by the pressing portion 60 protruding too much from the inner peripheral surface 51 of the rack housing 50.

[0100] In addition, since the surface extending along the longitudinal direction of the rack housing 50 can be formed without cutting the inner peripheral surface 51 of the rack housing 50, it is possible to suppress an increase in processing costs due to cutting. As a result, it is possible to suppress the processing costs during manufacturing and the generation of abnormal noise.

[0101] Furthermore, by forming the abutment surface 111 of the core 110 in a direction perpendicular to the axis HA of the rack housing 50 and the axis of the rack bar 22, the rack housing 50 can be easily manufactured in an appropriate shape. In other words, the core 110 is inserted into the outer mold 100 with the axis CA of the core 110, which is formed in a substantially truncated cone shape, inclined with respect to the axis HA of the rack housing 50, so that when the first core 110a and the second core 110b are inserted from opposite sides, the abutment surfaces 111 may be misaligned. In contrast, in this embodiment, the abutting surfaces 111 of the cores 110 are formed in a direction perpendicular to the axis HA of the rack housing 50 and the axis of the rack bar 22, so that when the two cores 110 are inserted into the outer mold 100 from opposite sides with the axes CA of the cores 110 inclined relative to the axis HA of the rack housing 50, the abutting surfaces 111 are abutted against each other, thereby preventing the abutting surfaces 111 of the cores 110 from misaligning in the radial direction. This makes it easy to align the axes of the two cores 110 with each other when the axes CA of the cores 110 are inclined relative to the axis HA of the rack housing 50.

[0102] Furthermore, by forming the abutment surfaces 111 of the core 110 in a direction perpendicular to the axis HA of the rack housing 50 and the axis of the rack bar 22, the abutment surfaces 111 can be brought into contact with each other with uniform pressure when they are abutted against each other, thereby preventing stress concentration. This prevents deformation of the core 110 due to stress concentration on the abutment surfaces 111. As a result, the rack housing 50 can be easily manufactured in an appropriate shape when the rack housing 50 is manufactured, and the core 110 can be protected.

[0103] [Second embodiment] Next, an electric power steering device 10 according to a second embodiment will be described. The same components as those in the first embodiment will be given the same reference numerals and the description thereof will be omitted. The following description will focus on the differences from the first embodiment.

[0104] 10 is an explanatory diagram of a rack housing 50 of an electric power steering device 10 according to the second embodiment. In the electric power steering device 10 according to the second embodiment, as in the first embodiment, an inner circumferential surface 51 of the rack housing 50 has an expanded diameter portion 52, and the expanded diameter portion 52 is formed such that the inner circumferential surface 51 extends along the longitudinal direction of the rack housing 50 at a position where a pressing portion 60 is disposed in the circumferential direction of the rack housing 50.

[0105] In the second embodiment, the diameter of the core 110 (see FIG. 4) for forming the inner circumferential surface 51 of the rack housing 50 having a tapered shape is smaller than the diameter of the core 110 for forming the inner circumferential surface 51 of the rack housing 50 in the electric power steering device 10 according to the first embodiment. As a result, in the cast rack housing 50, the diameter of the smallest portion of the inner circumferential surface 51 is smaller than the diameter of the rack bar 22 stored in the rack housing 50. For this reason, in the second embodiment, after the rack housing 50 is cast using the outer mold 100 (see FIG. 4) and the core 110, cutting is performed on the vicinity of the portion of the inner circumferential surface 51 where the diameter is small.

[0106] Specifically, also in the second embodiment, the core 110 for forming the inner circumferential surface 51 of the rack housing 50 has a first core 110a (see FIG. 4) and a second core 110b (see FIG. 4), and the bottom surfaces of the first core 110a and the second core 110b on the side with the smaller diameter of the truncated cone are located near the through hole 57 for disposing the pressing portion 60 in the longitudinal direction of the rack housing 50. Therefore, the inner circumferential surface 51 of the cast rack housing 50 has the smallest diameter near the through hole 57 in the longitudinal direction of the rack housing 50.

[0107] Therefore, in the second embodiment, a position on the inner circumferential surface 51 of the rack housing 50 near the through hole 57 in the longitudinal direction of the rack housing 50 is defined as a cutting range 54, and the inner circumferential surface 51 is cut. In the cutting process, the inner circumferential surface 51 in the cutting range 54 is cut to increase the diameter of the inner circumferential surface 51 in the cutting range 54. At that time, the inner circumferential surface 51 in the cutting range 54 is cut so as to have a uniform diameter that is larger than the maximum diameter of the portion of the rack bar 22 that will be located in the cutting range 54.

[0108] FIG. 11 is an explanatory diagram showing a state in which the rack bar 22 and the pressing part 60 are arranged in the rack housing 50 shown in FIG. 10. The rack bar 22 is stored inside the rack housing 50 in which the cutting range 54 of the inner circumferential surface 51 has been cut, and the pressing part 60 is arranged in the through hole 57 of the rack housing 50 in which the cutting range 54 of the inner circumferential surface 51 has been cut. In the second embodiment, the inner circumferential surface 51 of the rack housing 50 near the through hole 57 in the longitudinal direction is cut to have a uniform diameter, so that the inner circumferential surface 51 of the rack housing 50 becomes cylindrical at the position where the pressing part 60 is arranged in the longitudinal direction of the rack housing 50. That is, the rack housing 50 has a cylindrical part 53 where the inner circumferential surface 51 becomes cylindrical at the position where the pressing part 60 is arranged in the longitudinal direction of the rack housing 50.

[0109] In the second embodiment, a core 110 used to mold the rack bar 22 has a smaller diameter than that in the first embodiment, and the inner circumferential surface 51 is cut only in the vicinity of the smallest diameter of the inner circumferential surface 51 to form the cylindrical portion 53. Therefore, at the position of the cylindrical portion 53 on the inner circumferential surface 51, the distance between the inner circumferential surface 51 and the rack bar 22 is small.

[0110] The pressing portion 60 is disposed in a portion where the cylindrical portion 53 is located in the longitudinal direction of the rack housing 50, and therefore abuts against the rack bar 22 at a position where the distance between the inner peripheral surface 51 and the rack bar 22 is small. As a result, the pressing portion 60 abuts against the rack bar 22 in a state where the protrusion from the inner peripheral surface 51 of the rack housing 50 is small, and applies a pressing force to the rack bar 22 that presses the rack teeth 23 against the pinion gear 21.

[0111] In the second embodiment, since the inner circumferential surface 51 has the cylindrical portion 53 at the position where the pressing portion 60 is disposed in the longitudinal direction of the rack housing 50, the distance between the inner circumferential surface 51 of the rack housing 50 and the rack bar 22 can be reduced, and the protrusion of the pressing portion 60 from the inner circumferential surface 51 can be reduced. This makes it possible to suppress the generation of abnormal noise caused by the large protrusion of the pressing portion 60 from the inner circumferential surface 51 of the rack housing 50.

[0112] Furthermore, the cutting range 54 where the inner circumferential surface 51 of the rack housing 50 is cut is a portion of the range including the portion where the diameter of the inner circumferential surface 51 of the rack housing 50 after casting is smallest, so the cutting range can be made small. This makes it possible to suppress an increase in processing costs due to the cutting process. As a result, the processing costs during manufacturing can be suppressed, and the generation of abnormal noise can be suppressed.

[0113] In addition, the inner diameter of the rack housing 50 is small enough that the diameter of the smallest portion of the inner circumferential surface 51 of the cast rack housing 50 is smaller than the diameter of the rack bar 22, and therefore the outer diameter of the rack housing 50 can also be reduced accordingly. As a result, the rack housing 50 can be made smaller in size.

[0114] [Third embodiment] Next, an electric power steering device 10 according to a third embodiment will be described. The same components as those in the first embodiment will be given the same reference numerals and the description thereof will be omitted. The following description will focus on the differences from the first embodiment.

[0115] 12 is an explanatory diagram of a rack housing 50 of an electric power steering device 10 according to a third embodiment. In the electric power steering device 10 according to the third embodiment, as in the first embodiment, an inner circumferential surface 51 of the rack housing 50 has an expanded diameter portion 52, and the expanded diameter portion 52 is formed by extending the inner circumferential surface 51 along the longitudinal direction of the rack housing 50 at a position where a pressing portion 60 is disposed in the circumferential direction of the rack housing 50. In the third embodiment, the expanded diameter portion 52 of the inner circumferential surface 51 of the rack housing 50 is formed so that the opening area of ​​the inner circumferential surface 51 becomes larger from one end side to the other end side in the longitudinal direction of the rack housing 50.

[0116] That is, in the third embodiment, unlike the first embodiment, the expanded diameter portion 52 does not have two expanded diameter portions 52, the first expanded diameter portion 52a and the second expanded diameter portion 52b, but is formed in the shape of a single substantially truncated cone formed from one end side to the other end side in the longitudinal direction of the rack housing 50. For this reason, the expanded diameter portion 52 is formed in a tapered shape in which the opening area of ​​the inner circumferential surface 51 increases from one end 56 side to the other end 56 side in the longitudinal direction of the rack housing 50.

[0117] In the third embodiment, the opening area of ​​the inner surface 51 of the expanded diameter portion 52 increases from the end portion 56 close to the through hole 57 in which the pressing portion 60 is disposed in the longitudinal direction of the rack housing 50 toward the end portion 56 away from the through hole 57.

[0118] In the third embodiment, the expanded diameter portion 52 of the rack housing 50 is formed so that the opening area of ​​the inner circumferential surface 51 increases from one end side to the other end side in the longitudinal direction of the rack housing 50, so that when the rack housing 50 is cast, the inner circumferential surface 51 can be molded with one core 110. As a result, only one core 110 is handled when casting the rack housing 50, so that the rack housing 50 can be easily manufactured. As a result, the manufacturing cost can be reduced.

[0119] [Fourth embodiment] Next, an electric power steering device 10 according to a fourth embodiment will be described. The same components as those in the first embodiment will be given the same reference numerals and the description thereof will be omitted. The following description will focus on the differences from the first embodiment.

[0120] 13 is a schematic diagram of an electric power steering device 10 according to a fourth embodiment. The electric power steering device 10 according to the fourth embodiment includes a steering wheel 11, a steering shaft 12, a universal joint 15, an intermediate shaft 16, a universal joint 17, a stub shaft 18, a steering gear 20, a tie rod 24, a torque sensor 31, and an electric motor 32, similar to the first embodiment.

[0121] In the fourth embodiment, unlike the first embodiment, the pinion gear 21 of the steering gear 20 has a first pinion gear 21a and a second pinion gear 21b. Unlike the first embodiment, the torque sensor 31 is disposed between the stub shaft 18 and the second pinion gear 21b. That is, the torque sensor 31 is connected to the stub shaft 18 at one end and connected to the second pinion gear 21b of the steering gear 20 at the other end.

[0122] The second pinion gear 21b is a shaft-shaped member having a gear that meshes with the rack bar 22 formed at the end opposite to the side connected to the stub shaft 18, and the stub shaft 18 and the second pinion gear 21b are connected via a torsion bar (not shown). One end of the torsion bar is connected to the stub shaft 18 and the other end is connected to the second pinion gear 21b, and the torsion bar transmits rotational torque between the stub shaft 18 and the second pinion gear 21b. The torque sensor 31 detects the rotational torque transmitted between the stub shaft 18 and the second pinion gear 21b via the torsion bar.

[0123] Unlike the first embodiment, the electric motor 32 is connected to the first pinion gear 21a via a reduction gear (not shown) and rotates the first pinion gear 21a via the reduction gear. The first pinion gear 21a is rotated by the driving force transmitted from the electric motor 32.

[0124] The steering gear 20 converts the rotational motion transmitted to the second pinion gear 21b and the first pinion gear 21a into linear motion by the rack bar 22 disposed inside the rack housing 50 (see FIG. 14). The electric power steering device 10 according to the fourth embodiment is of a dual pinion assist type in which the rack bar 22 performs linear motion by the rotational motion transmitted from the second pinion gear 21b and the first pinion gear 21a.

[0125] In the fourth embodiment, the steering force of the driver input to the steering wheel 11 is transmitted to the second pinion gear 21b. The steering force transmitted to the second pinion gear 21b is transmitted to the tie rod 24 via the steering gear 20, displacing the wheels.

[0126] In addition, the steering force input by the driver to the steering wheel 11 is transmitted to a torque sensor 31 arranged on a steering force transmission path from the steering wheel 11 to the second pinion gear 21b. At this time, the ECU 30 obtains the steering torque from the torque sensor 31 and also obtains a vehicle speed signal from a vehicle speed sensor 35. Then, the ECU 30 controls the operation of the electric motor 32. The auxiliary steering torque generated by the electric motor 32 is transmitted to the first pinion gear 21a.

[0127] The auxiliary steering torque transmitted to the first pinion gear 21a is transmitted to the tie rod 24 via the steering gear 20, displacing the wheels. That is, the electric power steering device 10 according to the fourth embodiment displaces the wheels by transmitting the auxiliary steering torque of the electric motor 32 via the first pinion gear 21a to the rack bar 22 at a position different from the second pinion gear 21b that transmits the steering force of the driver to the rack bar 22. The electric power steering device 10 according to the fourth embodiment is thus a dual pinion type electric power steering device in which an assist force is applied via the first pinion gear 21a different from the second pinion gear 21b.

[0128] FIG. 14 is a schematic cross-sectional view of a rack housing 50 that stores the rack bar 22 shown in FIG. 13. FIG. 15 is a schematic cross-sectional view of the rack housing 50 that shows a state in which the rack bar 22 is stored in the rack housing 50 shown in FIG. 14. In the fourth embodiment, the rack bar 22 has, as the rack teeth 23 that mesh with the pinion gear 21, first rack teeth 23a that mesh with the first pinion gear 21a and second rack teeth 23b that mesh with the second pinion gear 21b. The first rack teeth 23a and the second rack teeth 23b are disposed at different positions in the longitudinal direction of the rack bar 22. Therefore, the rack bar 22 meshes with the first pinion gear 21a and the second pinion gear 21b at different positions in the longitudinal direction of the rack bar 22.

[0129] In the fourth embodiment, the pressing portion 60 that applies a biasing force to the rack bar 22 includes a first pressing portion 60a and a second pressing portion 60b. The first pressing portion 60a applies a biasing force to the rack bar 22 that presses the first rack teeth 23a against the first pinion gear 21a, and the second pressing portion 60b applies a biasing force to the rack bar 22 that presses the second rack teeth 23b against the second pinion gear 21b. Since the pressing portion 60 includes the first pressing portion 60a and the second pressing portion 60b, the rack housing 50 is provided with a first through hole 57a that is the through hole 57 in which the first pressing portion 60a is disposed, and a second through hole 57b that is the through hole 57 in which the second pressing portion 60b is disposed.

[0130] The first through hole 57a is formed on the opposite side of the side where the first pinion gear 21a is located with respect to the rack bar 22, at the position where the first pinion gear 21a is arranged in the longitudinal direction of the rack housing 50. For this reason, the first pressing portion 60a is arranged in a positional relationship in which the rack bar 22 is sandwiched between the first pressing portion 60a and the first pinion gear 21a, and is arranged on the surface side of the rack bar 22 opposite to the surface on which the first rack teeth 23a of the rack bar 22 are formed.

[0131] Further, the second through hole 57b is formed on the opposite side of the rack bar 22 from the side where the second pinion gear 21b is located, at the position where the second pinion gear 21b is located in the longitudinal direction of the rack housing 50. For this reason, the second pressing portion 60b is disposed in a positional relationship in which the rack bar 22 is sandwiched between the second pressing portion 60b and the second pinion gear 21b, and is disposed on the surface of the rack bar 22 opposite to the surface on which the second rack teeth 23b of the rack bar 22 are formed.

[0132] In FIG. 15, for convenience, the first pressing portion 60a and the second pressing portion 60b are arranged at the same position in the circumferential direction of the rack housing 50, but the first pressing portion 60a and the second pressing portion 60b may be arranged at different positions in the circumferential direction of the rack housing 50. That is, the first through hole 57a and the second through hole 57b of the rack housing 50 shown in FIG. 14 and FIG. 15 may be arranged at different positions in the circumferential direction of the rack housing 50. In other words, in FIG. 15, the first rack tooth 23a and the second rack tooth 23b of the rack bar 22 are arranged at the same position in the circumferential direction of the rack bar 22, but the first rack tooth 23a and the second rack tooth 23b may be arranged at different positions in the circumferential direction of the rack bar 22.

[0133] In the fourth embodiment, the inner peripheral surface 51 of the rack housing 50 also has a first expanded diameter portion 52a and a second expanded diameter portion 52b. The first expanded diameter portion 52a is disposed at a position in the longitudinal direction of the rack housing 50 that includes a position in the longitudinal direction of the rack housing 50 where the first pressing portion 60a is disposed.

[0134] In the fourth embodiment, the first expanded diameter portion 52a is located such that the bottom surface of the side with the smaller diameter of the truncated cone is located near the position of the second through hole 57b in the longitudinal direction of the rack housing 50. The opening area of ​​the first expanded diameter portion 52a defined by the inner circumferential surface 51 increases from near the position of the second through hole 57b in the longitudinal direction of the rack housing 50 toward the side where the end portion 56 closer to the first through hole 57a in the longitudinal direction of the rack housing 50 is located.

[0135] The first enlarged diameter portion 52a is formed at a position in the circumferential direction of the rack housing 50 where the first pressing portion 60a is disposed, with the inner circumferential surface 51 extending along the longitudinal direction of the rack housing 50.

[0136] The second expanded diameter portion 52b is disposed closer to the end 56 side of the rack housing 50 opposite the end 56 on the side where the first expanded diameter portion 52a is located in the longitudinal direction than the first expanded diameter portion 52a. The opening area of ​​the inner peripheral surface 51 of the second expanded diameter portion 52b increases from the position of the end on the side located near the arrangement position of the second through hole 57b in the first expanded diameter portion 52a toward the end 56 on the opposite side to the side where the first expanded diameter portion 52a is located in the longitudinal direction of the rack housing 50.

[0137] In the fourth embodiment, the expanded diameter portion 52 of the inner circumferential surface 51 of the rack housing 50 has a first expanded diameter portion 52a and a second expanded diameter portion 52b, and the first expanded diameter portion 52a extends along the longitudinal direction of the rack housing 50 at a position where the first pressing portion 60a is disposed in the circumferential direction of the rack housing 50, so that the protrusion of the first pressing portion 60a from the inner circumferential surface 51 can be reduced. This makes it possible to prevent the first pressing portion 60a from tilting due to an increase in the protrusion of the first pressing portion 60a from the inner circumferential surface 51, and to suppress the generation of abnormal noise due to an increase in the protrusion of the first pressing portion 60a.

[0138] In particular, the first pressing portion 60a is a pressing portion 60 that imparts a biasing force to the rack bar 22 that presses the first rack teeth 23a against the first pinion gear 21a, and the first pinion gear 21a transmits the driving force generated by the electric motor 32 to the rack bar 22. For this reason, the torque transmitted from the first pinion gear 21a to the first rack teeth 23a of the rack bar 22 is greater than the torque transmitted from the second pinion gear 21b to the second rack teeth 23b of the rack bar 22. As a result, with regard to abnormal noises caused by backlash at the meshing portion between the pinion gear 21 and the rack teeth 23, abnormal noises at the meshing portion between the first pinion gear 21a and the first rack teeth 23a tend to be greater than abnormal noises at the meshing portion between the second pinion gear 21b and the second rack teeth 23b.

[0139] Therefore, by preventing the first pressing portion 60a from protruding too much from the inner peripheral surface 51 of the rack housing 50, it is possible to prevent the generation of abnormal noise caused by backlash at the meshing portion between the first pinion gear 21a and the first rack teeth 23a, which is prone to generate loud abnormal noise, and thus the generation of loud abnormal noise can be suppressed. As a result, it is possible to prevent the generation of abnormal noise at the meshing portion between the first pinion gear 21a and the first rack teeth 23a, which is prone to generate loud abnormal noise.

[0140] [Variations] In the above-described fourth embodiment, the second expanded diameter portion 52b of the rack housing 50 is positioned at a position in the longitudinal direction of the rack housing 50 different from the pressing portion 60, but the position of the second expanded diameter portion 52b in the longitudinal direction of the rack housing 50 may include the position where the pressing portion 60 is positioned.

[0141] FIG. 16 is a modified example of the electric power steering device 10 according to the fourth embodiment, and is a schematic cross-sectional view of the rack housing 50 at a position including the first pressing portion 60a and the first pinion gear 21a. FIG. 17 is a schematic cross-sectional view of the rack housing 50 at a position different from that of FIG. 16, and is a schematic cross-sectional view of the rack housing 50 at a position including the second pressing portion 60b and the second pinion gear 21b. For example, the second enlarged diameter portion 52b may be disposed at a position including the position where the second pressing portion 60b is disposed in the longitudinal direction of the rack housing 50. In FIG. 16 and FIG. 17, the boundary portion 53c between the first enlarged diameter portion 52a and the second enlarged diameter portion 52b is disposed between the position where the first pressing portion 60a is disposed and the position where the second pressing portion 60b is disposed in the longitudinal direction of the rack housing 50. In other words, when casting the rack housing 50, the butt surface 111 (see Figure 4) of the first core 110a (see Figure 4) and the second core 110b (see Figure 4), which form the inner surface 51, is positioned between the positions of the first through hole 57a and the second through hole 57b in the longitudinal direction of the rack housing 50, and casting is performed.

[0142] In this way, when the second expanded diameter portion 52b is disposed at a position including the position where the second pressing portion 60b is disposed, the second expanded diameter portion 52b is preferably formed with the inner circumferential surface 51 extending along the longitudinal direction of the rack housing 50 at the position where the second pressing portion 60b is disposed in the circumferential direction of the rack housing 50. That is, as shown in Figs. 16 and 17, when the first pressing portion 60a and the second pressing portion 60b are disposed at positions different from each other in the circumferential direction of the rack housing 50, it is preferable that the positions where the first expanded diameter portion 52a and the second expanded diameter portion 52b are formed extending along the longitudinal direction of the rack housing 50 in the circumferential direction of the rack housing 50 are also different from each other in accordance with the first pressing portion 60a and the second pressing portion 60b.

[0143] Furthermore, it is preferable that the boundary 53c between the first expanded diameter portion 52a and the second expanded diameter portion 52b, i.e., the abutting surface 111 between the first core 110a and the second core 110b, is located closer to the second pinion gear 21b in the longitudinal direction of the rack housing 50. In other words, it is preferable that the boundary 53c between the first expanded diameter portion 52a and the second expanded diameter portion 52b, or the abutting surface 111 between the first core 110a and the second core 110b, is located closer to the second pinion gear 21b that transmits the steering force input to the steering wheel 11 than to the first pinion gear 21a that transmits the auxiliary steering torque generated by the electric motor 32.

[0144] The second expanded diameter portion 52b is formed at a position where the second pressing portion 60b is disposed in the circumferential direction of the rack housing 50, with the inner circumferential surface 51 extending along the longitudinal direction of the rack housing 50, thereby making it possible to reduce the protrusion of the second pressing portion 60b from the inner circumferential surface 51. This makes it possible to prevent the second pressing portion 60b from tilting due to an increase in the protrusion of the second pressing portion 60b from the inner circumferential surface 51, and to suppress the generation of abnormal noise due to an increase in the protrusion of the second pressing portion 60b.

[0145] Therefore, the first enlarged diameter portion 52a can suppress the generation of abnormal noise caused by the increased protrusion of the first pressing portion 60a, and the second enlarged diameter portion 52b can suppress the generation of abnormal noise caused by the increased protrusion of the second pressing portion 60b, so that in the case where there are two pinion gears 21, it is possible to suppress the generation of abnormal noise at the meshing portion of both pinion gears 21. As a result, it is possible to suppress the generation of abnormal noise in the dual pinion type electric power steering device 10.

[0146] Moreover, by positioning the butt surface 111 between the first core 110a and the second core 110b on the second pinion gear 21b side, it is possible to efficiently manufacture the rack housing 50 suitable for storing the rack bar 22 of the dual pinion type electric power steering device 10. That is, in the dual pinion type electric power steering device 10, the shape of the rack bar 22 near the first rack teeth 23a to which the auxiliary steering torque from the electric motor 32 is transmitted tends to be larger than the shape near the second rack teeth 23b, so that the maximum diameter of the first rack teeth 23a side of the rack bar 22 is larger than that of the second rack teeth 23b side. Accordingly, the inner diameter of the inner peripheral surface 51 of the rack housing 50 is also larger on the first rack teeth 23a side than on the second rack teeth 23b side.

[0147] Therefore, by positioning the abutting surface 111 between the first core 110a and the second core 110b on the second pinion gear 21b side and forming the expanded diameter portion 52 so that the diameter of the inner circumferential surface 51 of the rack housing 50 increases from the second pinion gear 21b side toward the first pinion gear 21a side, it is possible to increase the inner diameter of the position on the inner circumferential surface 51 of the rack housing 50 where the first rack teeth 23a of the rack bar 22 are arranged. As a result, it is possible to efficiently manufacture the rack housing 50 suitable for storing the rack bar 22 of the dual pinion type electric power steering device 10.

[0148] Note that, since burrs may occur at the position of the abutment surface 111 between the first core 110a and the second core 110b when the rack housing 50 is cast, it is preferable to position the abutment surface 111 at a position close to the end 56 in the longitudinal direction of the rack housing 50 in order to cut and remove these burrs. By positioning the abutment surface 111 between the first core 110a and the second core 110b at a position close to the end 56 in the longitudinal direction of the rack housing 50, even if burrs occur at the position of the abutment surface 111, it is possible to easily cut the burrs from the end 56 of the rack housing 50.

[0149] Furthermore, the abutment surface 111 between the first core 110a and the second core 110b does not necessarily have to be located near the through hole 57 in which the pressing portion 60 is disposed in the longitudinal direction of the rack housing 50. The abutment surface 111 between the first core 110a and the second core 110b may be located closer to the end portion 56 of the rack housing 50 than the through hole 57 in the longitudinal direction of the rack housing 50, or may be located on the inner side in the longitudinal direction of the rack housing 50.

[0150] 16 and 17, the inner circumferential surface 51 of the rack housing 50 is provided with the expanded diameter portion 52 at both the position where the first pressing portion 60a is disposed and the position where the second pressing portion 60b is disposed in the longitudinal direction of the rack housing 50, but the expanded diameter portion 52 of the inner circumferential surface 51 does not have to be provided at both positions where these pressing portions 60 are disposed. For example, the expanded diameter portion 52 of the inner circumferential surface 51 may be provided only at the position where the first pressing portion 60a is disposed in the longitudinal direction of the rack housing 50, and the inner circumferential surface 51 may be formed to have a constant inner diameter without having the expanded diameter portion 52 at the position where the second pressing portion 60b is disposed in the longitudinal direction of the rack housing 50.

[0151] In the dual pinion type electric power steering device 10, by positioning the expanded diameter portion 52 of the inner circumferential surface 51 in a range where the first pressing portion 60a that imparts to the rack bar 22 a biasing force for pressing the first rack teeth 23a of the rack bar 22 against the first pinion gear 21a that transmits the auxiliary steering torque from the electric motor 32 is disposed, it is possible to suppress the protrusion of the first pressing portion 60a from the inner circumferential surface 51 of the rack housing 50 and suppress the generation of abnormal noise. In other words, in the dual pinion type electric power steering device 10, the backlash at the meshing portion between the first pinion gear 21a and the first rack teeth 23a, which is prone to generate large abnormal noise at the meshing portion due to large transmission torque, can be suppressed by suppressing the protrusion of the first pressing portion 60a from the inner circumferential surface 51 of the rack housing 50. As a result, it is possible to suppress the generation of abnormal noise at the meshing portion between the first pinion gear 21a and the first rack teeth 23a, where loud abnormal noise is likely to occur in the dual pinion type electric power steering device 10.

[0152] Furthermore, in the above-described third embodiment, similarly to the second embodiment, the diameter of the core 110 for forming the inner peripheral surface 51 of the rack housing 50 may be reduced, and cutting may be performed only partially after the rack housing 50 is cast. In other words, the diameter of the core 110 may be reduced to such an extent that the diameter of the end portion 56 side of the core 110 close to the through hole 57 in which the pressing portion 60 is disposed becomes smaller than the diameter of the rack bar 22, and after the rack housing 50 is cast, cutting may be performed only near the end portion 56 on the inner peripheral surface 51 close to the through hole 57 to ensure an inner diameter capable of storing the rack bar 22.

[0153] In this case, the cutting process of the inner peripheral surface 51 is performed only near the end portion 56 in the longitudinal direction of the rack housing 50, so that the cutting tool can be easily performed without penetrating deep inside the rack housing 50. Therefore, the number of cores 110 handled when casting the rack housing 50 is one, so that the manufacturing of the rack housing 50 can be easily performed, and the outer diameter can be reduced by reducing the inner diameter of the rack housing 50, and further, the cutting process associated with reducing the inner diameter of the rack housing 50 can be easily performed. In addition, since the cutting tool can be easily performed without penetrating deep inside the rack housing 50, the machining can be performed while suppressing the vibration width of the tool during the cutting process from becoming large, so that the deterioration of the machining accuracy can be suppressed. As a result, the manufacturing cost can be suppressed, the rack housing 50 can be miniaturized, and the machining accuracy during the cutting process can be ensured.

[0154] Although the preferred embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments. The configurations described as the embodiments and modified examples may be combined as appropriate. [Explanation of symbols]

[0155] 10. Electric power steering device 11 Steering Wheel 12 Steering shaft 13 Input shaft 14 Output shaft 15, 17 Universal joint 16 Intermediate shaft 18 Stub shaft 20 Steering gear 21 Pinion gear 21a 1st pinion gear 21b 2nd pinion gear 22 Rack Bar 23 rack teeth 23a 1st rack tooth 23b 2nd rack tooth 24 Tie rod 30 ECU 31 Torque sensor 32 Electric motor 33 Reducer 35 Vehicle speed sensor 36 Ignition switch 37 Power supply 50 Rack Housing 51 Inner surface 52 Expanded diameter part 52a 1st enlarged diameter section 52b 2nd enlarged diameter section 53c Boundary 53 Cylindrical section 54 Cutting range 55 Outer surface 56 End 57 Through hole 57a 1st through hole 57b 2nd through hole 58 Cutting part 60 Pressing part 60a First pressing part 60b Second pressing portion 100 External mold 101 Through-hole molding part 110 Core 110a 1st core 110b 2nd core

Claims

1. a rack bar having rack teeth that mesh with the pinion gear; a rack housing formed in a cylindrical shape and storing the rack bar inside an inner circumferential surface; a pressing portion disposed in the rack housing and configured to apply a biasing force to the rack bar to press the rack teeth against the pinion gear; Equipped with the inner circumferential surface of the rack housing has an expanding portion in which a size of an opening area of ​​the inner circumferential surface when viewed in a longitudinal direction of the rack housing increases toward a predetermined direction in the longitudinal direction of the rack housing, The expanded diameter portion is an electric power steering device in which, in a cross section taken along the longitudinal direction of the rack housing, a position in the circumferential direction of the rack housing where the pressing portion is located is inclined relative to a first line of the inner surface that passes through the position where the pressing portion is located and extends along the longitudinal direction of the rack housing.

2. The electric power steering device according to claim 1 , wherein the inner circumferential surface of the rack housing is cylindrical at a position in the longitudinal direction of the rack housing where the pressing portion is disposed.

3. The electric power steering device according to claim 1 , wherein the opening area of ​​the enlarged diameter portion increases from a position where the pressing portion is disposed toward an end of the rack housing in the longitudinal direction of the rack housing.

4. The electric power steering device according to claim 1 , wherein the opening area of ​​the expanded diameter portion increases from one end side to the other end side in the longitudinal direction of the rack housing.

5. The electric power steering device according to claim 1 , wherein the first line is parallel to an axis of the rack bar.

6. The enlarged diameter portion is a first enlarged diameter portion in which the opening area becomes larger from a position in the longitudinal direction of the rack housing where the pressing portion is disposed toward one end side of the rack housing in the longitudinal direction; 2. The electric power steering device according to claim 1, further comprising a second enlarged diameter portion in which the opening area increases from an end position of the first enlarged diameter portion in the longitudinal direction of the rack housing toward the other end side of the rack housing in the longitudinal direction.

7. The rack teeth include first rack teeth and second rack teeth arranged at a position different from the first rack teeth in the longitudinal direction, the pinion gear includes a first pinion gear that meshes with the first rack teeth and a second pinion gear that meshes with the second rack teeth, the pressing portion includes a first pressing portion that imparts to the rack bar a biasing force that presses the first rack teeth against the first pinion gear, and a second pressing portion that imparts to the rack bar a biasing force that presses the second rack teeth against the second pinion gear, The first expanding portion has an arrangement position in the longitudinal direction including a position where the first pressing portion is arranged in the longitudinal direction, and the inner circumferential surface extends along the longitudinal direction at a position where the first pressing portion is arranged in the circumferential direction, 7. The electric power steering device according to claim 6, wherein the second expansion portion has an arrangement position in the longitudinal direction that includes a position in the longitudinal direction where the second pressing portion is arranged, and the inner circumferential surface extends along the longitudinal direction at a position in the circumferential direction where the second pressing portion is arranged.

8. The electric power steering device according to claim 1 , wherein the rack housing has an outer circumferential surface that is inclined with respect to the longitudinal direction in accordance with an inclination of the inner circumferential surface of the expanded diameter portion with respect to the longitudinal direction.

9. inserting a core having a tapered shape and for forming an inner peripheral surface of the rack housing into an outer mold for forming an outer peripheral surface of the rack housing; injecting a molten material between the outer mold and the core; releasing the outer mold and the core after the material has solidified; Including, A manufacturing method for an electric power steering device, wherein in the step of inserting the core inside the outer mold, the core is inserted in a direction such that a portion of the circumferential position of the core on the tapered inclined surface extends along the longitudinal direction of the rack housing.

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