Steering system

Abstract

This improves the efficiency of steering assist torque transmission without requiring significant design changes from the pitman arm to the steering wheel side. [Solution] The steering device comprises a conversion mechanism 5 that converts the rotational motion of the input shaft 1 into linear motion along an output shaft 3 perpendicular to the input shaft 1; an assist mechanism 6 that applies steering assist force to the output shaft 3 based on steering torque and steering direction; a pitman arm 7 positioned radially outward from the input shaft; and a link 8 connected to the output shaft 3 and the point of force application P3 of the pitman arm 7, which causes the pitman arm 7 to swing by pushing and pulling the point of force application P3 in conjunction with the application of steering assist force to the output shaft 3. The conversion mechanism includes a gear mechanism 39 having a first bevel gear 41 and a second bevel gear 42, and a ball screw mechanism 40.

Description

Technical Field

[0001] The present invention relates to a steering device.

Background Art

[0002] Patent Document 1 discloses an integral type steering device used for large vehicles and the like. This steering device includes an input shaft, a power cylinder capable of generating a steering assist torque by sliding a piston provided on the outer periphery of the input shaft within a housing, and a sector gear as an output shaft having a tooth portion that meshes with a tooth portion provided on the outer peripheral surface of the piston. The outer peripheral surface of the piston and the inner peripheral surface of the housing are sealed in a liquid-tight manner by an annular seal member. Further, a pitman arm for transmitting the steering assist torque to the steering wheel side is connected to the sector gear. The pitman arm is disposed on the radially outer side of the housing that houses the input shaft.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the steering device of Patent Document 1, due to the resistance between the seal member and the housing during the sliding of the piston, there is a possibility that the transmission efficiency of the steering assist torque in the steering device may decrease. Further, due to the meshing component force between the tooth portion of the sector gear and the tooth portion of the piston, the piston slides within the housing while the outer peripheral surface of the piston is pressed against the inner peripheral surface of the housing, resulting in a problem that the transmission efficiency of the steering assist torque in the steering device decreases. Furthermore, the meshing itself between the tooth portion of the sector gear and the tooth portion of the piston also becomes a factor in reducing the transmission efficiency of the steering assist torque in the steering device.

[0005] Furthermore, in various vehicles having an integral-type steering system like that described in Patent Document 1, the pitman arm is generally constrained by the fact that it is positioned radially outward from the housing that accommodates the input shaft, and the configuration of the link from the pitman arm to the steering wheel is generally uniformly defined. Therefore, if the installation position of the pitman arm or the configuration of the link around it were to be changed, a significant design change would be required, which presents a problem.

[0006] This invention was made in view of these problems, and one of its objectives is to provide a steering device that can improve the efficiency of steering assist torque transmission without requiring significant design changes from the pitman arm to the steering wheel side. [Means for solving the problem]

[0007] The present invention relates to a steering device, the steering device comprising: an input shaft to which rotational force from a steering wheel is input; a conversion mechanism that converts the rotational motion of the input shaft into linear motion in a direction along an output shaft intersecting the input shaft; a torque sensor provided on the input shaft for detecting the steering torque and steering direction of the input shaft; an assist mechanism that applies a steering assist force to the output shaft based on the steering torque and steering direction; a pitman arm positioned radially outward of the input shaft, having a fulcrum that is the center of oscillation, a point where steering assist force from the output shaft is applied, and a point where a force acts toward the steering wheel when the pitman arm oscillates; and a link connected to the output shaft and the point where steering assist force is applied to the pitman arm, which causes the pitman arm to oscillate by pushing and pulling the point where steering assist force is applied to the output shaft. [Effects of the Invention]

[0008] According to the present invention, the efficiency of steering assist torque transmission can be improved without requiring significant design changes from the pitman arm to the steering wheel side. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional view of the steering device of the first embodiment. [Figure 2] This is a cross-sectional view of the steering device of the first embodiment, cut along line AA in Figure 1. [Figure 3] This is a schematic diagram illustrating the assist mechanism used to provide steering assist force to the output shaft. [Figure 4] This is a cross-sectional view of the hydraulic pump cut along line BB in Figure 1. [Figure 5] This is an explanatory diagram showing the oscillation of the pitman arm in the first embodiment. [Figure 6] This is a cross-sectional view of the steering device of the second embodiment. [Figure 7] This is a cross-sectional view of the steering device of the second embodiment, cut along line CC in Figure 6. [Figure 8] This is an explanatory diagram showing the oscillation of the pitman arm in the second embodiment. [Figure 9] This is a cross-sectional view of the steering device of the third embodiment. [Figure 10] This is a longitudinal cross-sectional view of a portion of the steering device of the third embodiment, including the input shaft and its surrounding components. [Figure 11] This is a cross-sectional view of the steering device according to the fourth embodiment. [Figure 12] This is a longitudinal cross-sectional view of a portion of the steering device of the fourth embodiment, including the input shaft and its surrounding components. [Modes for carrying out the invention]

[0010] Hereinafter, embodiments of the steering device of the present invention will be described with reference to the drawings. The steering device of the present invention is used in relatively large vehicles, such as trucks. In this steering device, instead of using a power cylinder or engine-driven pump as in conventional integral-type steering devices, a hydraulic pump 50 driven by an electric motor 51 is used.

[0011] Figure 1 is a cross-sectional view of the steering device of the first embodiment. In Figure 1, the side of the input shaft 1 that is linked to a steering wheel (not shown) along the rotation axis Z (upper side in the figure) is referred to as "one end," and the side where the first bevel gear 41 is formed (lower side in the figure) is referred to as "the other end." Note that Figure 1 shows a cross-sectional view of the steering device when the steering wheel is in the neutral position. Figure 2 is a cross-sectional view of the steering device of the first embodiment, cut along line AA in Figure 1. Figure 3 is a schematic explanatory diagram of the assist mechanism 6 used to apply steering assist force to the output shaft 3. Figure 4 is a cross-sectional view of the hydraulic pump 50, cut along line BB in Figure 1. Figure 5 is an explanatory diagram showing the oscillation of the pitman arm 7 of the first embodiment.

[0012] The steering system mainly consists of an input shaft 1, a torque sensor 2, an output shaft 3, a housing 4, a conversion mechanism 5, an assist mechanism 6, a pitman arm 7, and a link 8.

[0013] The input shaft 1 is housed within a first housing 13, an intermediate member 14, and a second housing 15, described later, the remaining portion of which, excluding the portion including one end, constitutes the housing 4. The input shaft 1 comprises a first shaft 9, a second shaft 10, and a third shaft 11. One end of the first shaft 9 is linked to a steering wheel (not shown) and is used to input steering torque from the driver. The other end of the first shaft 9 is inserted into an opening recess formed on one end of the second shaft 10. One end of the second shaft 10 is connected to the first shaft 9 via a torsion bar 12 so as to be rotatable relative to it. The second shaft 10 is rotatably supported by a bearing, such as a first ball bearing B1, provided on the inner circumference of the intermediate member 14. One end of the third shaft 11 is spline-fitted to the outer circumference of the other end of the second shaft 10. Furthermore, the third shaft 11 is rotatably supported at one end by a bearing, for example, a second ball bearing B2, while the other end is rotatably supported at the other end by a bearing, for example, a third ball bearing B3.

[0014] The first housing 13 is formed in a cylindrical shape from a metal, such as an aluminum alloy or cast iron. The first housing 13 is disposed on one end side of the input shaft 1 and is fixed to a cylindrical intermediate member 14 by a plurality of fastening members, such as screw members (not shown).

[0015] The second housing 15 is formed in a cylindrical shape from a metal, such as an aluminum alloy or cast iron. The second housing 15 has a cylindrical portion 15a that mainly houses the third shaft 11 of the input shaft 1, and a cylindrical protruding portion 15b that communicates with the cylindrical portion 15a and mainly houses a part of the output shaft 3. An end portion 14a on the other end side of the intermediate member 14 is fixed to an axial end portion 15c of the cylindrical portion 15a. Further, an annular bearing holding member 16 that holds the third ball bearing B3 is screwed to the inner peripheral portion of the other axial end portion 15d of the cylindrical portion 15a. The opening of the bearing holding member 16 is closed by a first closing member 17 having a substantially disk shape.

[0016] Further, the cylindrical protruding portion 15b protrudes radially outward of the input shaft 1 from the outer peripheral portion on the other axial end portion 15d side of the cylindrical portion 15a. On the back side (the depth side in FIG. 1) of the cylindrical protruding portion 15b and the cylindrical portion 15a, a mounting portion 18 for mounting the steering device to the vehicle is integrally formed. The mounting portion 18 has a relatively thick rectangular plate shape, and when viewed from a direction orthogonal to the plane of FIG. 1, most of the short side 18a of the mounting portion 18 along the radial direction of the input shaft 1 is located on the side of a boss portion 18b described later. A boss portion 18b for mounting the steering device to the vehicle is provided at a position overlapping with the end portion 14a of the intermediate member 14 in the radial direction of the input shaft 1 in a portion of the mounting portion 18 on the cylindrical protruding portion 15b side. Further, three boss portions 18c, 18d, and 18e for mounting the steering device to the vehicle are provided at a portion of the mounting portion 18 opposite to the cylindrical protruding portion 15b. Further, as shown in FIG. 2, a boss portion 18f for mounting the steering device to the vehicle is provided on the cylindrical protruding portion 15b of the mounting portion 18.

[0017] Also, as shown in FIGS. 1 and 2, the attachment portion 18 has a cylindrical shaft accommodating portion 19 formed at substantially the same position as the boss portion 18d on the opposite side of the cylindrical protruding portion 15b in the axial direction of the input shaft 1 and at a position between the cylindrical protruding portion 15b and the boss portion 18b. One end portion 19a of the shaft accommodating portion 19 is closed by screwing a bottomed cylindrical second closing member 20. A part of an arm fixing shaft 21 to which the pitman arm 7 is fixed is accommodated in the shaft accommodating portion 19.

[0018] The arm fixing shaft 21 has a small-diameter shaft portion 21a, a large-diameter shaft portion 21b formed integrally with the small-diameter shaft portion 21a and having a larger diameter than the small-diameter shaft portion 21a, a medium-diameter shaft portion 21c formed integrally with the large-diameter shaft portion 21b and having a diameter smaller than the large-diameter shaft portion 21b and larger than the small-diameter shaft portion 21a, and a tip portion 21d formed integrally with the medium-diameter shaft portion 21c and having a diameter smaller than the medium-diameter shaft portion 21c.

[0019] On the outer peripheral portion of the small-diameter shaft portion 21a, a bearing for rotatably supporting the small-diameter shaft portion 21a, for example, a fourth ball bearing B4 is provided.

[0020] Also, at a position on the outer peripheral portion of the medium-diameter shaft portion 21c adjacent to the large-diameter shaft portion 21b, a bearing for rotatably supporting the large-diameter shaft portion 21b, for example, a sliding bearing 22 is provided. Also, at a position on the opposite side of the large-diameter shaft portion 21b across the sliding bearing 22, a pair of first sealing members 23 for sealing the inner peripheral surface of the shaft accommodating portion 19 and the outer peripheral surface of the medium-diameter shaft portion 21c are provided. Further, as shown in FIG. 2, a portion of the outer peripheral surface of the medium-diameter shaft portion 21c adjacent to the tip portion 21d is formed in a conical taper shape so as to taper toward the tip portion 21d side, and a serration 21e is formed in this conical taper portion. This tapered serration 21e is fitted into a serration 24a of a shaft fixing hole 24 provided in the pitman arm 7, and by tightening a nut 25, the pitman arm 7 is fixed to the arm fixing shaft 21.

[0021] The axis of the arm fixing shaft 21 configured as described above serves as a fulcrum P1 when the pitman arm 7 swings.

[0022] The torque sensor 2 is configured as a well-known magnetic torque sensor using a magnet portion 26 crimped and fixed to the outer circumferential surface of the first shaft 9, and detects the steering torque and steering direction of the input shaft 1. The torque sensor 2 has a detection unit 27 that detects a signal corresponding to the change in magnetism of the magnet portion 26 which rotates together with the first shaft 9, and a signal processing unit 28 arranged around the detection unit 27 that processes the magnetic flux detected by the detection unit 27 and calculates the steering torque.

[0023] The output shaft 3 is located radially outward of the input shaft 1 at the other end of the input shaft 1. As shown in Figure 1, the output shaft 3 is positioned to intersect with the input shaft 1, or more specifically, to be perpendicular to the input shaft 1. The output shaft 3 has a main shaft 29, a connecting shaft 30, and a nut member 31.

[0024] The main shaft 29 is a long, continuous cylindrical shape along the radial direction of the input shaft 1. The main shaft 29 has one radial end 29a located far from the input shaft 1 and the other radial end 29b located close to the input shaft 1.

[0025] The radial end 29b of the main shaft 29 is connected to one end of the connecting shaft 30 by a spline coupling. Furthermore, a radially enlarged portion 29c is formed near the radial end 29b of the main shaft 29, extending radially from the output shaft 3. A bearing, such as a fifth ball bearing B5, is provided on the outer circumference of this enlarged portion 29c to rotatably support the main shaft 29. An annular first bearing detachment prevention member 32 is provided at a position adjacent to the fifth ball bearing B5 and the second closing member 20 in the radial direction of the input shaft 1 to prevent the fifth ball bearing B5 from detaching. The first bearing detachment prevention member 32 and the enlarged portion 29c of the main shaft 29 are liquid-tightly sealed by a second seal member 33, for example, made of rubber.

[0026] Furthermore, as shown in Figure 1, the majority of the main shaft 29 is housed in a cylindrical cylinder 34 made of metal, such as aluminum alloy or cast iron. Of the two ends 34a and 34b of the cylinder 34 in the longitudinal direction, the end 34a located on the input shaft 1 side is fastened to the outer circumference of the tip of the cylindrical projection 15b of the second housing 15.

[0027] Furthermore, a third closing member 35 is fastened to the end 34b of the cylinder 34. The third closing member 35 is formed in a disc shape. A central hole 35a is formed in the radial center of the third closing member 35, through which a nut member 31 is slidably inserted, along the radial direction of the input shaft 1, that is, along the axial direction of the output shaft 3. The space between the central hole 35a and the nut member 31 is liquid-tightly sealed by a pair of third sealing members 36, which are made of, for example, rubber. In addition, a first hole 35d is formed in the end face 35b of the third closing member 35 facing the inside of the cylinder 34, and the first shaft end 37a of a slender cylindrical guide member 37 is inserted into this first hole 35d. The second shaft end 37b of the guide member 37 is inserted into a second hole 32a provided in the first bearing detachment prevention member 32. The guide member 37 extends parallel to the main shaft 29.

[0028] The connecting shaft 30 is a shaft that connects the third shaft 11 of the input shaft 1 and the main shaft 29 of the output shaft 3. The length of the connecting shaft 30 along the axial direction of the output shaft 3 is shorter than the length of the main shaft 29 along the axial direction of the output shaft 3. A bearing, such as a sixth ball bearing B6, is provided on the outer circumference of the central part of the connecting shaft 30 in the axial direction of the output shaft 3 to rotatably support the connecting shaft 30. An annular second bearing detachment prevention member 38 is provided at a position adjacent to the sixth ball bearing B6 and the third closing member 35 in the axial direction of the output shaft 3 to prevent the sixth ball bearing B6 from detaching.

[0029] The nut component 31 will be described in detail later.

[0030] The conversion mechanism 5 includes a gear mechanism 39 and a ball screw mechanism 40 that convert the rotational motion of the input shaft 1 into linear motion along the output shaft 3 which is perpendicular to the input shaft 1.

[0031] The gear mechanism 39 includes a first bevel gear 41 formed on an annular projection 11b that protrudes radially from the other end 11a of the third shaft 11 of the input shaft 1 and then slopes diagonally upward, and a second bevel gear 42 formed on the outer circumference of the connecting shaft 30 near the end 30a on the input shaft 1 side. The gear mechanism 39 converts the rotational force from the input shaft 1 into the rotation of the output shaft 3 which is perpendicular to the input shaft 1 through the meshing of the first bevel gear 41 and the second bevel gear 42. The speed ratio of the first bevel gear 41 and the second bevel gear 42 is set to, for example, 2:1.

[0032] The ball screw mechanism 40 is composed of a shaft-side ball screw groove 29d, which is a helical groove provided on the outer circumference of the main shaft 29 of the output shaft 3; a nut-side ball screw groove 43, which is a helical groove provided on the inner circumference of the oil chamber compartment 31c formed in the nut member 31; and a plurality of balls 44 arranged between the ball screw grooves 29d and 43. The balls 44 support the nut member 31 so that it can rotate relative to the main shaft 29. The outer circumference of the nut member 31 is in slidable contact with the inner circumference of the cylinder 34. As a result, the oil chamber compartment 31c of the nut member 31 can slide within the cylinder 34 in the radial direction of the input shaft 1, that is, along the axial direction of the output shaft 3.

[0033] The nut member 31 is formed in a bottomed cylindrical shape from a metal material. The nut member 31 has a base portion 31a, a cylindrical tubular portion 31b that extends from the outer edge of the base portion 31a along the axial direction of the output shaft 3 toward the input shaft 1, and a cylindrical oil chamber portion 31c that is connected to the end of the tubular portion 31b opposite to the base portion 31a.

[0034] The base portion 31a is fixed to the support member 46 via a fixing member 45, for example, a screw. This support member 46 is movable in accordance with the rotation of the main shaft 29 and the movement of the nut member 31 due to the supply of oil into the cylinder 34 via the hydraulic pump 50 described later.

[0035] Furthermore, a rubber boot 47, formed in a bellows shape from, for example, a rubber material, is provided between the boot mounting portion 80 on the support member 46 and the third closing member 35. The rubber boot 47 prevents foreign matter from entering the inside of the cylinder 34 through the gap between the inner circumferential surface of the third closing member 35 and the outer circumferential surface of the cylindrical portion 31b of the nut member 31.

[0036] The length of the space along the axial direction of the output shaft 3 within the cylindrical portion 31b and the oil chamber compartment portion 31c corresponds to the length from the tip 32b of the first bearing detachment prevention member 32 to one radial end 29a of the main shaft 29.

[0037] The oil chamber compartment 31c divides the internal space of the cylinder 34 into a first oil chamber R1 located on the input shaft 1 side and a second oil chamber R2 located on the second closing member 20 side. As shown in Figure 1, a through hole 31d is formed through the oil chamber compartment 31c in the portion of the oil chamber compartment 31c that is on the pivot point P1 side of the pitman arm 7, relative to the main shaft 29, along the axial direction of the output shaft 3. A guide member 37 is inserted into this through hole 31d. The guide member 37 prevents the nut member 31 from rotating when the nut member 31 moves and guides the movement of the nut member 31 along the axial direction of the output shaft 3. The space between the outer circumferential surface of the guide member 37 and the inner surface of the through hole 31d is liquid-tightly sealed by an annular fourth seal member 48, for example, made of rubber. Furthermore, the space between the outer circumferential surface of the oil chamber compartment 31c and the inner circumferential surface of the cylinder 34 is liquid-tightly sealed by an annular fifth seal member 49, for example, made of rubber. Furthermore, on the side of the oil chamber compartment 31c opposite to the side where the guide member 37 is provided, a recess 39e is formed that is recessed from the outer circumferential surface of the oil chamber compartment 31c toward the main body shaft 29.

[0038] The assist mechanism 6 applies steering assist force to the nut member 31 of the output shaft 3 based on the steering torque and steering direction detected by the torque sensor 2. The assist mechanism 6 comprises a hydraulic pump 50, an electric motor 51, an ECU controller 52, and a cylinder 34.

[0039] The hydraulic pump 50 is capable of supplying hydraulic pressure to the cylinder 34, which is a hydraulic cylinder, and is configured as an internal gear pump capable of switching hydraulic pressure in two directions according to the rotation direction of the electric motor 51. The hydraulic pump 50 may be configured as an external gear pump instead of an internal gear pump. Furthermore, the hydraulic pump 50 is not limited to an internal or external gear pump, and may be other types of pumps capable of switching in two directions. The hydraulic pump 50 comprises a tank 53, a drive gear 54, a driven gear 55, a first check valve 57, a second check valve 59, a gear ring member 60, and a cover member 61.

[0040] Tank 53 mainly houses a drive gear 54, a driven gear 55, a first check valve 57, a second check valve 59, and a gear ring member 60.

[0041] The drive gear 54 is fixed to the outer circumference of the motor shaft 51a of the electric motor 51. As shown in Figure 4, the outer circumference of the drive gear 54 has a plurality of teeth 54a (six in this embodiment) that are arranged at equal intervals along the circumferential direction of the drive gear 54.

[0042] The driven gear 55 is annular in shape and is positioned around the drive gear 54. As shown in Figure 4, the inner circumference of the driven gear 55 has multiple (seven in this embodiment) teeth 55a arranged at equal intervals along the circumferential direction of the driven gear 55. When the drive gear 54 rotates, the driven gear 55 rotates in the same direction as the drive gear 54 through the meshing of the teeth 54a and teeth 55a. As shown in Figure 4, a space is provided between the four teeth 55a of the driven gear 55 arranged in the circumferential direction and the four teeth 54a of the drive gear 54 arranged in the circumferential direction. Oil discharged from the second relay section 66 and the fourth relay section 71, which will be described later, are supplied to this space. Also, for example, if the volume of oil decreases at low temperatures, oil is supplied to the space from the tank 53 via the first check valve 57 and the second check valve 59.

[0043] The annular gear member 60 is ring-shaped and houses a drive gear 54 fixed to the motor shaft 51a of the electric motor 51, and a driven gear 55 surrounding the drive gear 54.

[0044] The lid member 61 is disc-shaped and is positioned adjacent to the drive gear 54, the driven gear 55, and the gear ring member 60 to close the tank 53. Inside the lid member 61 on the side of the first check valve 57, a first flow path inlet 63 is formed in the portion facing the boundary between the drive gear 54 and the driven gear 55, forming part of the first flow path 62 and having an L-shaped cross-section. The first flow path inlet 63 communicates with a first relay section 64, which also forms part of the first flow path 62 and has an internal passage 64a communicating with the first flow path inlet 63. The first relay section 64 communicates with a first pipe section 65, which also forms part of the first flow path 62. The first pipe section 65 communicates with a second relay section 66, which also forms part of the first flow path 62 and has an internal passage 66a communicating with the first pipe section 65. The second relay section 66 communicates with the first oil chamber R1 of the cylinder 34.

[0045] Furthermore, a second flow path inlet 68, which forms part of the second flow path 67 and has an L-shaped cross-section, is formed in the part of the inside of the lid member 61 on the side of the second check valve 59 that faces the boundary between the drive gear 54 and the driven gear 55. The second flow path inlet 68 is in communication with a third relay section 69, which also forms part of the second flow path 67 and has an internal passage 69a that communicates with the second flow path inlet 68. The third relay section 69 is in communication with a second pipe section 70, which also forms part of the second flow path 67. The second pipe section 70 is in communication with a fourth relay section 71, which also forms part of the second flow path 67 and has an internal passage 71a that communicates with the second pipe section 70. The fourth relay section 71 is in communication with the second oil chamber R2 of the cylinder 34.

[0046] The electric motor 51 is configured as a three-phase brushless motor and drives the hydraulic pump 50. The electric motor 51 is driven and controlled by the ECU controller 52.

[0047] The ECU controller 52 drives the electric motor 51 according to the motor torque based on the steering torque and steering direction, so that the hydraulic pressure necessary for steering assistance of the output shaft 3 by the cylinder 34 as a hydraulic cylinder is supplied to the first oil chamber R1 or the second oil chamber R2 of the cylinder 34.

[0048] In this assist mechanism 6, when the driver steers the steering wheel to the left, the electric motor 51 rotates to the left (counterclockwise rotation in Figure 4), and as a result, the pumping action of the teeth 54a and 55a causes oil to flow into the first oil chamber R1 via the first passage 62. Then, the increase in hydraulic pressure in the first oil chamber R1 causes the oil chamber compartment 31c to be pressed towards the third closing member 35, and consequently, the nut member 31 moves towards the third closing member 35.

[0049] Furthermore, when the driver steers the steering wheel to the right, the electric motor 51 rotates to the right (clockwise rotation direction in Figure 4), and as a result, the pumping action of the teeth 54a and 55a causes oil to flow into the second oil chamber R2 via the second flow path 67. Then, the increase in hydraulic pressure in the second oil chamber R2 causes the oil chamber compartment 31c to be pressed toward the input shaft 1, and consequently, the nut member 31 moves toward the input shaft 1.

[0050] As shown in Figure 1, the pitman arm 7 is positioned radially outward of the input shaft 1, more specifically on the side of the cylindrical portion 15a of the second housing 15 that houses the input shaft 1. As shown in Figure 2, the pitman arm 7 has the aforementioned shaft fixing hole 24 to which the medium diameter shaft portion 21c of the arm fixing shaft 21 is fixed, a first mounting hole 73 to which the one-end shaft portion 72a constituting one end of the drag link 72 is fixed, and a second mounting hole 74 to which the one-end link portion 8a constituting one end of the link 8 is attached.

[0051] The shaft fixing hole 24 is formed near one end 7a in the longitudinal direction of the pitman arm 7.

[0052] The first mounting hole 73 is formed near the other end 7b in the longitudinal direction of the pitman arm 7. In the orientation of the pitman arm 7 shown in Figures 1 and 2, the first mounting hole 73 is located below the shaft fixing hole 24 in the axial direction of the input shaft 1. In other words, in the orientation of the pitman arm 7 shown in Figures 1 and 2, the first mounting hole 73 is located below the shaft fixing hole 24 in the vertical direction (up and down direction of the vehicle). The center of the first mounting hole 73 becomes the point of action P2 that moves the drag link 72 when the pitman arm 7 swings.

[0053] The second mounting hole 74 is formed approximately midway between the shaft fixing hole 24 and the first mounting hole 73 in the longitudinal direction of the pitman arm 7. In the posture of the pitman arm 7 shown in Figures 1 and 2, the second mounting hole 74 is located below the shaft fixing hole 24 and above the first mounting hole 73 in the axial direction of the input shaft 1. In other words, in the posture of the pitman arm 7 shown in Figures 1 and 2, the second mounting hole 74 is located below the shaft fixing hole 24 and above the first mounting hole 73 in the vertical direction (up and down direction of the vehicle). The center of the second mounting hole 74 is the point of force application P3, to which force from the link 8 is applied when the link 8 moves due to the movement of the nut member 31 during the operation of the hydraulic pump 50 of the assist mechanism 6. The point of force application P3 is located below the fulcrum P1 and above the point of application P2 in the vertical direction.

[0054] Link 8 is formed from a metal material into a long, slender rod shape. One end 8a of link 8 is attached to the second mounting hole 74 of the pitman arm 7, while the other end 8b of link 8 is attached to a support member 46 that supports the nut member 31 of the output shaft 3. Link 8 causes the pitman arm 7 to swing by pushing and pulling the point of force P3 of the pitman arm 7 in response to the steering assist force applied to the nut member 31 by the operation of the hydraulic pump 50. For example, when steering the steering wheel in the leftward rotation direction, the increase in hydraulic pressure in the first oil chamber R1 causes the nut member 31 to move toward the third closing member 35 side (right side in Figure 5), and the link 8 is pulled toward the right side in Figure 5. As a result, the point of force P3 of the pitman arm 7, which is in the neutral position shown by the solid line, moves to the position of the point of force y1, and the pitman arm 7 swings counterclockwise in Figure 5 to the position shown by the dashed line L1. On the other hand, when the steering wheel is turned to the right, the increase in hydraulic pressure in the second oil chamber R2 causes the nut member 31 to move toward the input shaft 1 side (left side in Figure 5), pushing the link 8 toward the left side in Figure 5. As a result, the point of force application P3 of the pitman arm 7, which is in the neutral position shown by the solid line, moves to the position of the point of force application y2, and the pitman arm 7 swings clockwise in Figure 5 to the position shown by the dashed line L2.

[0055] As described above, in the first embodiment, the steering device includes a conversion mechanism 5 that converts the rotational motion of the input shaft 1 into linear motion along the output shaft 3 which is perpendicular to the input shaft 1, an assist mechanism 6 that applies steering assist force to the output shaft 3 based on the steering torque and steering direction detected by the torque sensor 2, a pitman arm 7 positioned radially outward from the input shaft 1, and a link 8 that is connected to the nut member 31 of the output shaft 3 and the point of force P3 of the pitman arm 7, and swings the pitman arm by pushing and pulling the point of force P3 in accordance with the application of steering assist force to the nut member 31. Unlike conventional steering devices, the steering device of this first embodiment does not have a piston provided on the outer circumference of the input shaft or a sector gear having teeth that mesh with teeth provided on the outer surface of the piston. Therefore, unlike in the conventional technology, problems such as reduced steering assist torque transmission efficiency due to resistance between the sealing member and the housing during piston sliding, the piston sliding inside the housing while its outer surface is pressed against the inner surface of the housing, and the meshing between the teeth of the sector gear and the teeth of the piston do not occur.

[0056] Furthermore, in this embodiment, the steering wheel is steered by pushing and pulling the pitman arm 7 via the link 8 while maintaining the pitman arm 7 in a desirable design position, which is radially outward from the input shaft 1, more specifically on the side of the cylindrical portion 15a of the second housing 15. Therefore, it is not necessary to significantly change the design from the pitman arm 7 to the steering wheel.

[0057] Therefore, according to the configuration of this embodiment, the efficiency of steering assist torque transmission can be improved without requiring significant design changes from the pitman arm 7 to the steering wheel side.

[0058] Furthermore, in this embodiment, the conversion mechanism 5 includes a gear mechanism 39 having a first bevel gear 41 and a second bevel gear 42 that mesh with each other, and a ball screw mechanism 40 having a shaft-side ball screw groove 29d, a nut-side ball screw groove 43, and a ball 44. Therefore, a relatively large sector gear, as in the prior art, and a piston with teeth that mesh with the teeth of this sector gear are not required. Thus, steering force can be efficiently transmitted from the input shaft 1 to the output shaft 3.

[0059] Figure 6 is a cross-sectional view of the steering device of the second embodiment. Figure 7 is a cross-sectional view of the steering device of the first embodiment, cut along line CC in Figure 6. Figure 8 is an explanatory diagram showing the oscillation of the pitman arm 7 of the second embodiment.

[0060] In the second embodiment, the pitman arm 7 is configured with the positions of the fulcrum P1 and the point of force application P3 swapped compared to the first embodiment. That is, in the second embodiment, the pitman arm 7 is configured such that the point of force application P3 is located above the fulcrum P1 in the vertical direction. Accordingly, in the second embodiment, the axial length of the third shaft 11 of the input shaft 1 and the cylindrical portion 15a of the second housing 15 is shortened. In addition, in this embodiment, the first bevel gear 41 is formed as an annular projection 11c that protrudes radially from the other end 11a of the third shaft 11 of the input shaft 1 and then inclins diagonally downward. Furthermore, in this embodiment, the first closing member 17 of the first embodiment is eliminated, and the bearing holding member 16, bottom wall portion 15e and cylindrical projection portion 15b are integrally provided on the cylindrical portion 15a.

[0061] Mounting portions 18 for attaching the steering device to the vehicle are integrally formed on the bottom wall portion 15e and the cylindrical projection portion 15b. The mounting portion 18 is a relatively thick rectangular plate, and as shown in Figure 6, most of it is located below the bottom wall portion 15e and the cylindrical projection portion 15b in the vertical direction. The boss portion 18b provided on the cylindrical projection portion 15b side is located below the output shaft 3 in the vertical direction and above the point of action P2 of the pitman arm 7.

[0062] As shown in Figure 6, when viewed from the direction of the arm fixing axis 21 (the direction perpendicular to the plane of the paper in Figure 6), the point of force application P3 of the pitman arm 7 is located above the main body axis 29 in the vertical direction and overlaps with the cylindrical projection 15b.

[0063] Furthermore, the pivot point P1 of the pitman arm 7 is located in the vertical direction between the point of force application P3 and the boss portion 18b, closer to the boss portion 18b.

[0064] In this embodiment, for example, when the steering wheel is steered in the leftward direction, the increase in hydraulic pressure in the first oil chamber R1 causes the nut member 31 to move toward the third closing member 35 (right side in Figure 8), and the link 8 is pulled toward the right side in Figure 8. As a result, the point of force application P3 of the pitman arm 7 in the neutral position shown by the solid line moves to the position of point of force application y3, and the pitman arm 7 swings clockwise in Figure 8 to the position shown by the dashed line L3. On the other hand, when the steering wheel is steered in the rightward direction, the increase in hydraulic pressure in the second oil chamber R2 causes the nut member 31 to move toward the input shaft 1 (left side in Figure 8), and the link 8 is pushed toward the left side in Figure 8. As a result, the point of force application P3 of the pitman arm 7 in the neutral position shown by the solid line moves to the position of point of force application y4, and the pitman arm 7 swings counterclockwise in Figure 8 to the position shown by the dashed line L4.

[0065] As described above, in the second embodiment, the input shaft 1 extends vertically, and the point of force application P3 of the pitman arm 7 is located above the fulcrum P1 in the vertical direction. More specifically, the point of force application P3 is located above the output shaft 3 in the vertical direction, and the fulcrum P1 is located below the output shaft 3 in the vertical direction. Due to this positional relationship between the point of force application P3 and the fulcrum P1, compared to the configuration of the first embodiment in which the point of force application P3 is located below the fulcrum P1 in the vertical direction, the axial dimension between the third shaft 11 of the input shaft 1 and the second housing 15 that houses the third shaft 11 can be shortened, the steering device can be miniaturized, and manufacturing costs can be reduced.

[0066] Figure 9 is a cross-sectional view of the steering device of the third embodiment. Figure 10 is a longitudinal cross-sectional view of the portion of the steering device of the third embodiment that includes the input shaft 1 and its surrounding components.

[0067] In the third embodiment, the gear mechanism 39 and ball screw mechanism 40 of the conversion mechanism 5 in the first embodiment are eliminated, and the conversion mechanism 5 is configured as a rack and pinion mechanism having pinion teeth 11d provided on the third shaft 11 of the input shaft 1 and rack teeth 75e provided on the output shaft 3 that mesh with the pinion teeth 11d. Accordingly, in the third embodiment, the output shaft 3 has a single racked shaft 75 instead of a main shaft 29, a connecting shaft 30, and a nut member 31.

[0068] The racked shaft 75 is formed from a metal material into an elongated cylindrical shape. The racked shaft 75 has a base shaft portion 75a and a rack shaft portion 75b which is formed integrally with the base shaft portion 75a. One axial end 75c of the base shaft portion 75a is fixed to a support member 46 via a fixing member 45. The other axial end 75d of the base shaft portion 75a is formed integrally with the rack shaft portion 75b. The portion of the base shaft portion 75a near the other axial end 75d is formed to have a larger diameter than the rest of the portion, and this portion forms an oil chamber compartment portion 31c that divides the inside of the cylinder 34 into a first oil chamber R1 and a second oil chamber R2. Rack teeth 75e that mesh with pinion teeth 11d provided on the third shaft 11 of the input shaft 1 are formed on the outer circumference of the rack shaft portion 75b.

[0069] The opening end 76a of the third housing 76 is fastened to the input shaft 1 side end 34a of the cylinder 34, which houses a portion of the racked shaft 75. The third housing 76 is mainly capable of housing the racked shaft 75 and is formed in an elongated, bottomed cylindrical shape that takes into account the stroke required for the movement of the racked shaft 75 as the input shaft 1 rotates. The third housing 76 is formed integrally with the second housing 15 and the mounting portion 18.

[0070] As shown in Figure 10, a rack retainer housing wall portion 15f is integrally formed on the cylindrical portion 15a of the second housing 15, projecting cylindrically from the outer circumference of the cylindrical portion 15a so as to be perpendicular to the racked shaft 75. Inside the rack retainer housing wall portion 15f, a rack retainer 77, a spring 78 that biases the racked shaft 75 toward the third shaft 11, and a bottomed cylindrical closing cover member 81 that supports the spring 78 are provided. By biasing the racked shaft 75 toward the third shaft 11 with the spring 78 and the rack retainer 77, backlash between the rack teeth 75e on the outer circumference of the racked shaft 75 and the pinion teeth 11d on the outer circumference of the third shaft 11 is suppressed.

[0071] Furthermore, as shown in Figure 10, a cylindrical bearing fixing member 79 is positioned on the outer circumference of the third shaft 11 above the pinion teeth 11d. A bearing, such as a seventh ball bearing B7, which rotatably supports the third shaft 11, is fixed to a circular recessed portion 79a formed on the other end of this bearing fixing member 79.

[0072] In the third embodiment, the system includes a conversion mechanism 5 that converts the rotational motion of the input shaft 1 into linear motion along the output shaft 3 which is perpendicular to the input shaft 1; an assist mechanism 6 that applies steering assist force to the output shaft 3 based on the steering torque and steering direction detected by the torque sensor 2; a pitman arm 7 positioned radially outward from the input shaft; and a link 8 that is connected to the racked shaft 75 of the output shaft 3 and the point of force application P3 of the pitman arm 7, and that swings the pitman arm by pushing and pulling the point of force application P3 in conjunction with the application of steering assist force to the racked shaft 75. Therefore, in this embodiment, since there are no pistons or sector gears as in the prior art, the problem of reduced efficiency in transmitting steering assist torque does not occur.

[0073] Furthermore, in this embodiment, the steering wheel can be steered by pushing and pulling the pitman arm 7 via the link 8 while maintaining the pitman arm 7 in a desirable position, which is radially outward from the input shaft 1, or more specifically, laterally to the cylindrical portion 15a of the second housing 15. Therefore, it is not necessary to significantly change the design from the pitman arm 7 to the steering wheel.

[0074] Therefore, in the third embodiment as well, the efficiency of steering assist torque transmission can be improved without requiring significant design changes from the pitman arm 7 to the steering wheel side.

[0075] Furthermore, in the third embodiment, the conversion mechanism 5 has pinion teeth 11d provided on the third axis 11 of the input shaft 1, and rack teeth 75e provided on the rack shaft portion 75b of the output shaft 3, which mesh with the pinion teeth 11d. Even with such a rack and pinion configuration having pinion teeth 11d and rack teeth 75e, steering force can be efficiently transmitted from the input shaft 1 to the output shaft 3 while suppressing a decrease in the transmission efficiency of steering assist torque, without using a relatively large sector gear as in the conventional technology or a piston having teeth that mesh with the teeth of this sector gear.

[0076] Figure 11 is a cross-sectional view of the steering device according to the fourth embodiment. Figure 12 is a longitudinal cross-sectional view of the portion of the steering device according to the fourth embodiment that includes the input shaft 1 and its surrounding components.

[0077] The fourth embodiment is configured in which the positions of the fulcrum P1 and the point of force application P3 of the pitman arm 7 are swapped compared to the third embodiment. In other words, in the fourth embodiment, the point of force application P3 of the pitman arm 7 is configured to be located above the fulcrum P1 in the vertical direction. Accordingly, in the fourth embodiment, the axial lengths of the third shaft 11 of the input shaft 1, the cylindrical portion 15a of the second housing 15, and the bearing fixing member 79 are shorter compared to the third embodiment. Also, unlike the third embodiment, the mounting portion 18 is formed integrally with the second housing 15 so that most of it is located below the third housing 76.

[0078] As described above, the point of force application P3 of the pitman arm 7 is configured to be located above the fulcrum P1 in the vertical direction. Therefore, this positional relationship between the point of force application P3 and the fulcrum P1 allows for a reduction in the axial dimensions of the third shaft 11 of the input shaft 1, the second housing 15, and the bearing fixing member 79, compared to the configuration of the third embodiment in which the point of force application P3 is located below the fulcrum P1 in the vertical direction, thereby enabling a smaller steering device and reducing manufacturing costs. [Explanation of Symbols]

[0079] 1...Input shaft, 2...Torque sensor, 3...Output shaft, 5...Conversion mechanism, 6...Assist mechanism, 7...Pitman arm, 8...Link, 11d...Pinion teeth, 31...Nut member, 39...Gear mechanism, 40...Ball screw mechanism, 41...First bevel gear, 42...Second bevel gear, 50...Hydraulic pump, 51...Electric motor, 52...ECU controller, P1...Fulfillment point, P2...Point of application of force, P3...Point of effort, 75...Shaft with rack, 75e...Rack teeth

Claims

1. The input shaft receives rotational force from the steering wheel, A conversion mechanism that converts the rotational motion of the input shaft into linear motion along an output shaft intersecting the input shaft, A torque sensor is provided on the input shaft for detecting the steering torque and steering direction of the input shaft, An assist mechanism that applies steering assist force to the output shaft based on the steering torque and steering direction, A pitman arm positioned radially outward from the input shaft, the pitman arm having a pivot point that serves as the center of oscillation, a point where the steering assist force is applied from the output shaft, and a point where a force acts toward the steering wheel when the pitman arm oscillates, A link is connected to the output shaft and the point of force application of the pitman arm, and in conjunction with the application of the steering assist force to the output shaft, the point of force application is pushed and pulled, causing the pitman arm to swing. A steering system equipped with a steering mechanism.

2. A steering device according to claim 1, The aforementioned conversion mechanism includes a gear mechanism and a ball screw mechanism. The gear mechanism includes a first bevel gear formed on the input shaft and a second bevel gear formed on the output shaft that meshes with the first bevel gear. The ball screw mechanism is characterized by having a shaft-side ball screw groove provided on the output shaft, a nut-side ball screw groove provided on a nut member that slides on the outer circumference of the output shaft, and a plurality of balls arranged between the shaft-side ball screw groove and the nut-side ball screw groove.

3. A steering device according to claim 1, The steering device is characterized in that the conversion mechanism has pinion teeth provided on the input shaft and rack teeth provided on the output shaft that mesh with the pinion teeth.

4. A steering device according to claim 2 or 3, The aforementioned input shaft extends along the vertical direction, A steering device characterized in that the point of force application is located below the fulcrum in the vertical direction.

5. A steering device according to claim 2 or 3, The aforementioned input shaft extends along the vertical direction, A steering device characterized in that the point of force application is located above the fulcrum in the vertical direction.

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