Steering device

Abstract

To fully motorize application of steering assist force to the front first axle side of two front axles and apply steering assist force to the rear second axile by a simple configuration.SOLUTION: A steering device configured to turn steering wheels 2, 2, 3, 3, which form respective front and rear pairs on a front two-axle vehicle 1, includes: a first electric motor 12 configured to apply steering assist force to a steering shaft 9; and a hydraulic device 56 configured to apply steering assist force to a rear second axle 5 of the front two-axle vehicle 1 via a link mechanism 15. The hydraulic device 56 includes: a hydraulic cylinder 60 configured to apply steering assist force to the rear second axle 5; a hydraulic pump capable of supplying hydraulic pressure to the hydraulic cylinder 60; a second electric motor 58 configured to drive the hydraulic pump; and a second ECU controller 59 configured to control driving of the second electric motor 58 based on steering torque detected by a torque sensor 27.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] 2. Description of the Related Art A steering device disclosed in Patent Document 1 below is known as a steering device used in a vehicle with two front axles.

[0003] In the steering device described in Patent Document 1, hydraulic pressure is generated by a pump driven by an engine or other device and supplied to a steering housing including a steering shaft. The hydraulic pressure is then passed from the steering housing through an actuator changeover valve and selectively used to control the front steered wheels or the rear steered wheels of the front two axles.

[0004] Furthermore, in recent years, there has been a trend toward the spread of so-called electric vehicles, which are fully electrically powered, in typical small automobiles that have a single front axle and are driven by an engine, in order to curb global warming caused by carbon dioxide in the exhaust gas. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2011-201540 A Summary of the Invention [Problem to be solved by the invention]

[0006] Furthermore, there is a trend to electrify relatively large automobiles with two front axles in order to curb global warming. As one step toward this trend, there is a need to fully electrify the steering assist force to at least the first front axle of the two front axles, and to provide steering assist force to the second rear axle with a simple configuration. [Means for solving the problem]

[0007] The present invention relates to a steering device for steering a pair of steerable wheels, front and rear, of a front two-axle vehicle. This steering device is equipped with a first electric motor that imparts a steering assist force to a steering axle, and a hydraulic device that imparts a steering assist force to the rear axle of the front two-axle vehicle via a link mechanism, the hydraulic device having a hydraulic cylinder for imparting the steering assist force to the rear axle, a hydraulic pump capable of supplying hydraulic pressure to the hydraulic cylinder, a second electric motor that drives the hydraulic pump, and a second control device that drives and controls the second electric motor based on the steering torque detected by a torque sensor. Effect of the Invention

[0008] According to the present invention, the steering assist force can be applied completely electrically to the first axle, which is the front of the two front axles, and the steering assist force can be applied to the second axle, which is the rear axle, by a simple configuration. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic top view of a vehicle including a steering device according to an embodiment; [Diagram 2] 1 is a vertical cross-sectional view of a steering device according to an embodiment of the present invention; [Diagram 3] FIG. 4 is a schematic explanatory diagram of a hydraulic device that applies a steering assist force to a second axle. [Figure 4] 1 is a cross-sectional view of a hydraulic device taken along the longitudinal direction of a hydraulic cylinder. FIG. [Diagram 5] FIG. 5 is a cross-sectional view of the hydraulic pump taken along line AA in FIG. 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a steering device according to the present invention will be described with reference to the drawings.

[0011] Fig. 1 is a schematic top view of a vehicle including a steering device of an embodiment. Fig. 2 is a longitudinal sectional view of the steering device of an embodiment. In Fig. 1, a part of the chassis of a front twin-axle vehicle 1 is shown by a two-dot chain line, but there are other parts of the chassis that are not shown in addition to the part shown by the two-dot chain line. In Fig. 2, the side (upper side in the figure) that is linked to the steering wheel 8 (see Fig. 1) in the direction along the rotation axis P of the steering shaft 9 is described as "one end" and the side (lower side in the figure) to which the ball screw mechanism 10 is attached is described as "the other end."

[0012] The steering device is configured to steer a pair of steerable wheels 2, 2, 3, 3 at the front and rear of the front twin axle 1. The front twin axle 1 has, as the front wheel side shafts, a first axle 4 on which the steerable wheels 2, 2 located at the front side in the longitudinal direction of the vehicle are provided, and a second axle 5 on which the steerable wheels 3, 3 located at the rear side in the longitudinal direction of the vehicle are provided, and also has, as the rear wheel side shafts, a third axle 7 on which the steerable wheels 6, 6 are provided.

[0013] The steering device is mainly composed of a steering shaft 9 linked to the steering wheel 8, a sector gear 11 used for steering the steered wheels 2, 2, 3, 3 via a ball screw mechanism 10, a first electric motor 12 for applying a steering assist force to the steering shaft 9, and a reducer 13 for reducing the rotation speed of the first electric motor 12. The sector gear 11 is connected to the steered wheels 2, 2, 3, 3 via a pitman arm 14 and a link mechanism 15 connected to the pitman arm 14.

[0014] The steering shaft 9 is arranged so as to penetrate through a cylindrical first housing 16, a cylindrical second housing 17 to which the first housing 16 is attached, and an annular bearing holding member 18 provided at the end of the second housing 17 opposite to the first housing 16, and is inserted into a bottomed cylindrical third housing 19. The steering shaft 9 includes an input shaft 20 to which a rotational force from the steering wheel 8 is transmitted, and an output shaft 22 connected to the input shaft 20 via a torsion bar 21. The outer periphery of one end of the input shaft 20 is rotatably supported by a first ball bearing 23, which is a bearing provided on the inner periphery of the first housing 16. The other end of the input shaft 20 is arranged in a recess 22b recessed in the direction of the rotation axis P from an axial end 22a on one end of the output shaft 22. The output shaft 22 is connected at one end to the input shaft 20 via the torsion bar 21 so as to be rotatable relative to the input shaft 20, and is used to input a steering assist torque of the first electric motor 12 connected to the outer periphery via the reduction gear 13. The output shaft 22 is rotatably supported by a second ball bearing 24 , which is a bearing provided on the inner periphery of the bearing holding member 18 .

[0015] Here, for convenience of the following explanation, the direction along the rotation axis P of the steering shaft 9 is defined as the "axial direction", the direction perpendicular to the axial direction is defined as the "radial direction", and further, the direction around the steering shaft 9 is defined as the "circumferential direction".

[0016] The first housing 16 is formed in a cylindrical shape from a metal material, for example, an aluminum alloy. The first housing 16 is disposed on one end side of the steering shaft 9, and is attached and fixed to the second housing 17 by a fastening member, for example, a bolt 25, as shown in FIG. 2. As shown in FIG. 2, the first housing 16 has a small diameter portion 16a located on one end side of the steering shaft 9, and a large diameter portion 16b formed integrally with the small diameter portion 16a and having a larger diameter than the small diameter portion 16a. In the space inside the small diameter portion 16a, a dust seal 26 is disposed adjacent to the one end side of the first ball bearing 23 in the axial direction of the steering shaft 9 together with the first ball bearing 23, and prevents dust and the like from entering the first housing 16 from the outside. In addition, a torque sensor 27 for detecting a steering torque corresponding to the rotation of the steering shaft 9 is disposed in the space inside the large diameter portion 16b. The torque sensor 27 is accommodated in a sensor accommodating member 95 provided in the first housing 16.

[0017] The second housing 17 is made of a metal material, such as an aluminum alloy, and accommodates the reducer 13 that reduces the rotation speed of the first electric motor 12, which is driven and controlled by a first ECU controller, which is a first control device (not shown).

[0018] The bearing retaining member 18 is formed from a metal material, for example, an aluminum alloy, and the above-mentioned second ball bearing 24 is provided on the inner periphery thereof.

[0019] The third housing 19 is made of a metal material, for example, an aluminum alloy. The third housing 19 has a ball screw mechanism accommodating portion 19a that accommodates the other end side of the output shaft 22 and the ball screw mechanism 10, and a gear accommodating portion 19b that accommodates the sector gear 11 adjacent to the ball screw mechanism 10.

[0020] The torque sensor 27 is mainly composed of a permanent magnet 28, a holder member 29, a pair of first and second yokes 30, 31, a pair of first and second magnetic flux collecting rings 32, 33, and a magnetic sensor (not shown). The permanent magnet 28, the holder member 29, the first and second yokes 30, 31, and the magnetic flux collecting rings 32, 33 are all arranged substantially concentrically with the rotation axis P of the steering shaft 9.

[0021] The permanent magnet 28 is a magnetic member made of a magnetic material and formed into a substantially cylindrical shape, and attached and fixed to the outer periphery of one end of the output shaft 22. The permanent magnet 28 is configured such that N poles and S poles are alternately arranged (magnetized) along the circumferential direction of the permanent magnet 28.

[0022] The holder member 29 is formed in a substantially cylindrical shape, and is attached and fixed to the outer periphery of the input shaft 20 at the axial center thereof.

[0023] The pair of first and second yokes 30, 31 are each made of a soft magnetic material and formed into a substantially cylindrical shape, and are connected to the input shaft 20 via a holder member 29, with the other end side facing radially opposite the permanent magnet 28. The first and second yokes 30, 31 are fixed to the holder member 29 by welding with an annular welding plate (not shown).

[0024] The pair of magnetic flux collecting rings 32, 33 are substantially annular rings that collect, within a predetermined range, magnetic flux from the permanent magnets leaking to one end sides of both yokes 30, 31. The magnetic flux collecting ring 32 is disposed on the outer periphery side of the torque sensor 27, while the magnetic flux collecting ring 33 is disposed on the inner periphery side of the torque sensor 27 so as to face the magnetic flux collecting ring 32. A magnetic flux collecting portion 32a having a flat surface (not shown) is provided at a predetermined circumferential position of the magnetic flux collecting ring 32, while a magnetic flux collecting portion 33a having a flat surface (not shown) parallel to the flat surface of the magnetic flux collecting portion 32a is provided at a position of the magnetic flux collecting ring 33 facing the magnetic flux collecting portion 32a in the circumferential direction.

[0025] The magnetic sensor is composed of a Hall element (not shown) accommodated and arranged in a radial gap between the flat surface of the magnetic flux collector 32a and the flat surface of the magnetic flux collector 33a, and a connection terminal (not shown) for connecting the Hall element to a substrate (not shown). The magnetic sensor detects the magnetic flux passing between the opposing flat surfaces of the magnetic flux collectors 32a, 33a by using the Hall effect of the Hall element, and outputs a signal corresponding to the magnetic flux to the substrate (not shown). This allows the calculation of the relative rotation angle between the input shaft 20 and the output shaft 22 on the substrate and the calculation of the steering torque based on the relative rotation angle. In the calculation of the relative rotation angle, a calculation is performed based on the steering direction, which is the rotation direction of the input shaft 20, so that the steering direction of the steering shaft 9 can be specified. Therefore, the steering direction of the steering shaft 9 can be detected using the torque sensor 27.

[0026] The ball screw mechanism 10 is composed of an output shaft side ball screw groove 22b which is a helical groove provided on the outer periphery of the output shaft 22, a nut side ball screw groove 34a which is a helical groove provided on the inner periphery of the nut 34, and a plurality of balls 35 arranged between the ball screw grooves 22b, 34a. The balls 35 support the nut 34 so as to be rotatable relative to the output shaft 22. The outer periphery of the nut 34 is in slidable contact with the inner periphery of the ball screw mechanism accommodating portion 19a. This allows the nut 34 to slide along the rotation axis P of the output shaft 22 within the ball screw mechanism accommodating portion 19a.

[0027] Further, a plurality of rack teeth 34b are formed on the outer periphery of the nut 34 on the sector gear 11 side. These rack teeth 34b are adapted to mesh with the teeth portion 11a of the sector gear 11.

[0028] The sector gear 11 is provided in the gear housing portion 19b so as to be able to swing. One axial end of the sector gear 11 is connected to a nut 34 via a toothed portion 11a, and the other axial end is linked to the steered wheels 2, 2, 3, 3 via a pitman arm 14 and a link mechanism 15.

[0029] The reducer 13 reduces the rotation speed from the first electric motor 12 and is composed of a worm gear formed by meshing a worm shaft 36 fixed to the motor shaft of the first electric motor 12 with a worm wheel 37.

[0030] The worm wheel 37 has a generally cylindrical metal core 37a and a gear forming portion 37b made of synthetic resin provided on the outer periphery of the core 37a. The gear forming portion 37b meshes with a worm formed on the worm shaft 36.

[0031] The first electric motor 12 is connected to the output shaft 22 via the reduction gear 13, and is configured as a three-phase AC brushless motor that applies a steering assist torque to the output shaft 22 according to the amount of torsion of the torsion bar 21. As shown in FIG. 2, the first electric motor 12 is configured integrally with a first EPS controller (not shown) that is a first control device that controls the first electric motor 12 based on the steering torque from a torque sensor 27.

[0032] 1, the link mechanism 15 connects the sector gear 11 to the first axle 4 and the second axle 5 of the front two-axle vehicle 1. The link mechanism 15 includes a first-axle side link component 15a that transmits the steering assist force, which is the output from the sector gear 11, to the first axle 4 via the pitman arm 14, and a second-axle side link component 15b that transmits the steering assist force, which is the output from the sector gear 11, to the second axle 5 via the pitman arm 14.

[0033] The first-shaft link component 15a has a first drag link 38 and a first knuckle arm 39. One end of the first drag link 38 is rotatably supported by the pitman arm 14 via a first joint 40, while the other end of the first drag link 38 is rotatably supported by one end of the first knuckle arm 39 via a second joint 41. An intermediate portion 39a of the first knuckle arm 39 is attached to one of the pair of steered wheels 2, 2. The other end of the first knuckle arm 39 is rotatably supported by one end of the first shaft 4 via a third joint 42. The other end of the first shaft 4 is rotatably supported by one end of a second knuckle arm 44 via a fourth joint 43. The other end of the second knuckle arm 44 is attached to the other of the pair of steered wheels 2, 2.

[0034] The second-shaft link component 15b has a second drag link 45, an intermediate link 46, a third knuckle arm 47, and a branch link 48. One end of the second drag link 45 is rotatably supported by the pitman arm 14 via a fifth joint 49, while the other end of the second drag link 45 is rotatably supported by one end of the intermediate link 46 and one end of the branch link 48 via a sixth joint 50. The other end of the intermediate link 46 is rotatably supported by one end of the third knuckle arm 47 via a seventh joint 51. The other end of the branch link 48 is rotatably supported by a portion of the chassis (not shown) via an eighth joint 52. A link mounting member 87 at one end of a hydraulic cylinder 60 of a hydraulic device 56 (described later) is attached to the center of the branch link 48. A connection portion 60c at the other end of the hydraulic cylinder 60 is rotatably supported by a portion of the chassis (not shown). An intermediate portion 47a of the third knuckle arm 47 is attached to one of the pair of steered wheels 3, 3. The other end of the third knuckle arm 47 is rotatably supported to one end of the second shaft 5 via a ninth joint 53. The other end of the second shaft 5 is rotatably supported to one end of a fourth knuckle arm 55 via a tenth joint 54. The other end of the fourth knuckle arm 55 is attached to the other of the pair of steered wheels 3, 3.

[0035] Fig. 3 is a schematic explanatory diagram of a hydraulic device 56 used to apply a steering assist force to the second shaft 5. Fig. 4 is a cross-sectional view of the hydraulic device 56 cut along the longitudinal direction of the hydraulic cylinder 60. In Fig. 4, for the sake of simplicity, cross sections of the second electric motor 58, the second ECU controller 59, the first check valve 65, and the second check valve 67, as well as the first tank 64 and the second tank 66 are omitted. Fig. 5 is a cross-sectional view of the hydraulic pump 57 cut along the line AA in Fig. 4.

[0036] The hydraulic device 56 applies a steering assist force to the second rear axle 5 of the front twin axle vehicle 1 via the second axle side link component 15b of the link mechanism 15. The hydraulic device 56 includes a hydraulic pump 57, a second electric motor 58, a second ECU controller 59, and a hydraulic cylinder 60.

[0037] The hydraulic pump 57 is configured as an internal gear pump capable of supplying hydraulic pressure to the hydraulic cylinder 60 and capable of switching hydraulic pressure between two directions according to the rotation direction of the second electric motor 58. The hydraulic pump 57 may be configured as an external gear pump instead of an internal gear pump. The hydraulic pump 57 is not limited to an internal gear pump or an external gear pump, and may be another type of pump capable of switching between two directions. The hydraulic pump 57 includes a housing member 61, a drive gear 62, a driven gear 63, a first tank 64, a first check valve 65, a second tank 66, a second check valve 67, a gear ring member 68, and a cover member 69.

[0038] The housing member 61 is formed in a generally cylindrical block shape, and has a circular recess 61b formed in an end face 61a of the housing member that faces the cover member 69. The driving gear 62, the driven gear 63, the first check valve 65, the second check valve 67, and the gear ring member 68 are mainly housed in this circular recess 61b.

[0039] The drive gear 62 is fixed to the outer periphery of the motor shaft 58a of the second electric motor 58. As shown in Fig. 5, the outer periphery of the drive gear 62 is formed with a plurality of teeth 62a (six in this embodiment) that are equally spaced apart along the circumferential direction of the drive gear 62.

[0040] The driven gear 63 has an annular shape and is provided around the drive gear 62. As shown in FIG. 5, a plurality of (seven in this embodiment) toothed portions 63a are formed on the inner periphery of the driven gear 63 at equal intervals along the circumferential direction of the driven gear 63. When the drive gear 62 rotates, the driven gear 63 rotates in the same direction as the drive gear 62 through meshing between the toothed portions 62a and the toothed portions 63a. As shown in FIG. 5, a space is provided between the four toothed portions 63a arranged in the circumferential direction of the driven gear 63 and the four toothed portions 62a arranged in the circumferential direction of the drive gear 62. When the second electric motor 58 rotates right (clockwise in FIG. 5) as shown in FIG. 5, oil in the first tank 64 on the low pressure side is supplied to the space between the toothed portions 62a, 63a via the first check valve 65, flows along the oil flow direction X, which is the right rotation direction, and flows into the second flow passage 72 on the high pressure side, which will be described later. On the other hand, when the second electric motor 58 rotates to the left (counterclockwise in FIG. 5), the low pressure section and the high pressure section are switched, and oil in the second tank 66 on the low pressure section side is supplied to the space between the teeth portions 62a, 63a via the second check valve 67, flows in the direction opposite to the oil flow direction X, and flows into the first flow path 71 on the high pressure section side, which will be described later.

[0041] The gear ring member 68 has an annular shape and accommodates therein the drive gear 62 fixed to the motor shaft 58a of the second electric motor 58, and the driven gear 63 surrounding the drive gear 62. End faces 68a, 62b, 63b of the gear ring member 68, the drive gear 62 and the driven gear 63 on the cover member 69 side are flush with the accommodation member end face 61a.

[0042] The cover member 69 is disk-shaped and is provided so as to close the opening surface of the recessed portion 61b of the housing member 61 while being adjacent to each end face 68a, 62b, 63b and the housing member end face 61a. A first flow passage inlet portion 73 having an L-shaped cross section is formed in a portion of the inside of the cover member 69 on the first check valve 65 side facing the boundary portion between the driving gear 62 and the driven gear 63. The first flow passage inlet portion 73 is connected to a first relay portion 74 which also constitutes a part of the first flow passage 71 and has an internal passage 74a which communicates with the first flow passage inlet portion 73. The first relay portion 74 is connected to a first pipe portion 75 which also constitutes a part of the first flow passage 71. The first pipe portion 75 is connected to a second relay portion 76 which also constitutes a part of the first flow passage 71 and has an internal passage 76a which communicates with the first pipe portion 75. The second relay portion 76 communicates with a first cylinder chamber 60a of the hydraulic cylinder 60, which will be described later.

[0043] In addition, a second flow passage inlet portion 77 having an L-shaped cross section is formed in a portion of the inside of the cover member 69 on the second check valve 67 side facing the boundary between the drive gear 62 and the driven gear 63. The second flow passage inlet portion 77 also constitutes a portion of the second flow passage 72 and communicates with a third relay portion 78 having an internal passage 78a communicating with the second flow passage inlet portion 77. The third relay portion 78 communicates with a second pipe portion 79 which also constitutes a portion of the second flow passage 72. The second pipe portion 79 also constitutes a portion of the second flow passage 72 and communicates with a fourth relay portion 80 having an internal passage 80a communicating with the second pipe portion 79. The fourth relay portion 80 communicates with a second cylinder chamber 60b of the hydraulic cylinder 60, which will be described later.

[0044] The second electric motor 58 is configured as a three-phase brushless motor similar to the first electric motor 12, and drives the hydraulic pump 57. The second electric motor 58 is controlled by a second ECU controller 59.

[0045] The second ECU controller 59 receives information on the required motor torque (motor torque required to drive the hydraulic cylinder 60) calculated by the first ECU controller associated with the first electric motor 12 based on the steering torque and steering direction via CAN communication. The second ECU controller 59 controls the drive of the second electric motor 58 in accordance with the motor torque based on the steering torque and steering direction, so that the hydraulic pressure required for the steering assist of the second shaft 5 by the hydraulic cylinder 60 is supplied to the first cylinder chamber 60a or the second cylinder chamber 60b of the hydraulic cylinder 60.

[0046] In addition, the second ECU controller 59 may directly receive the steering torque and steering direction from the torque sensor 27, instead of receiving information from the first ECU controller on the first electric motor 12 side, to independently detect the driver's intention and calculate the motor torque required to drive the hydraulic cylinder 60.

[0047] The hydraulic cylinder 60 serves to apply a steering assist force to the rear second axle 5. The hydraulic cylinder 60 includes a cylinder tube 81, a piston 82, a rod 83, a second closing member 84, a third closing member 85, a rubber boot 86, and a link mounting member 87.

[0048] The cylinder tube 81 has a cylindrical shape. A first insertion hole 81b, into which the second relay portion 76 of the first flow passage 71 is inserted, is formed penetrating the outer periphery of the cylinder tube 81 near one end 81a along the radial direction of the cylinder tube 81. A second insertion hole 81d, into which the fourth relay portion 80 of the second flow passage 72 is inserted, is formed penetrating the outer periphery of the cylinder tube 81 near the other end 81c along the radial direction of the cylinder tube 81.

[0049] The piston 82 is disk-shaped with an outer diameter slightly smaller than the inner diameter of the cylinder tube 81, and is slidably provided in the cylinder tube 81. A hole 82a into which a bolt 89 for attaching the other end 83b of the rod 83 is inserted is formed in the center of the piston 82 along the thickness direction of the piston 82. The piston 82 divides the inside of the cylinder tube 81 into a first cylinder chamber 60a located on the second relay portion 76 side and a second cylinder chamber 60b located on the fourth relay portion 80 side. In addition, an annular groove is formed on the outer circumferential surface of the piston 82 in which an annular first seal member 88 is accommodated. The first seal member 88 provides a liquid-tight seal between the outer circumferential surface of the piston 82 and the inner circumferential surface of the cylinder tube 81.

[0050] The rod 83 has a long and thin cylindrical shape. One end 83a of the rod 83 is provided with a link mounting member 87 to which the branch link 48 (see FIG. 1) is attached. The other end 83b of the rod 83 is fixed to the piston 82 via a fixing member, for example, a bolt 89.

[0051] The second blocking member 84 is annular, and a through hole 84a into which the rod 83 is slidably inserted is formed in the center thereof along the thickness direction of the second blocking member 84. A first annular protrusion 84b is formed on the outer circumferential surface of the second blocking member 84, protruding from the outer circumferential surface toward the radially outer side of the second blocking member 84. One end 81a of the cylinder tube 81 abuts against the surface of the first annular protrusion 84b on the piston 82 side. The first annular protrusion 84b is attached and fixed to a first flange 81e provided on one end 81a of the cylinder tube 81 via a fixing member, for example, a bolt 90. An annular groove into which an annular second seal member 91 is fitted is formed on a portion of the inner circumferential surface of the second blocking member 84 (the inner circumferential surface of the through hole 84a) close to the rubber boot 86. The second seal member 91 provides a liquid-tight seal between the inner circumferential surface of the second blocking member 84 and the outer circumferential surface of the rod 83. Further, an annular groove into which an annular third seal member 92 is fitted is formed in a position on the outer circumferential surface of the second closing member 84 near the first cylinder chamber 60a. The third seal member 92 provides a liquid-tight seal between the outer circumferential surface of the second closing member 84 and the inner circumferential surface of the cylinder tube 81.

[0052] The third closing member 85 is formed in a generally cylindrical shape. A second annular protrusion 85a is formed on the outer peripheral surface of the third closing member 85 at a portion adjacent to the second cylinder chamber 60b, protruding from the outer peripheral surface of the third closing member 85 toward the radially outward side of the third closing member 85. The other end 81c of the cylinder tube 81 abuts on the piston 82 side surface of the second annular protrusion 85a. The second annular protrusion 85a is attached and fixed to a second flange portion 81f provided on the other end 81c of the cylinder tube 81 via a fixing member, for example, a bolt 93. In addition, an annular groove into which an annular fourth seal member 94 is fitted is formed at a position of the third closing member 85 near the second cylinder chamber 60b. The fourth seal member 94 provides a liquid-tight seal between the outer peripheral surface of the third closing member 85 and the inner peripheral surface of the cylinder tube 81.

[0053] The rubber boot 86 is made of a rubber material and formed into a bellows shape, and is provided at a position adjacent to the second closing member 84 between the second closing member 84 and the link mounting member 87. The rubber boot 86 prevents foreign matter from entering the gap between the outer circumferential surface of the rod 83 and the inner circumferential surface of the second closing member 84 from outside the hydraulic cylinder 60.

[0054] In the hydraulic device 56 configured in this manner, the hydraulic cylinder 60 applies a steering assist force to the second shaft 5 so as to compensate for a shortage of the steering assist force to the second shaft 5 by the first electric motor 12. More specifically, when the driver steers the steering wheel 8, the steering assist force by the first electric motor 12 is transmitted to both the first shaft 4 and the second shaft 5 via the output shaft 22 of the steering shaft 9, the ball screw mechanism 10, the sector gear 11, the pitman arm 14, the first shaft side link component 15a, and the second shaft side link component 15b. At this time, the steering assist force transmitted to the first shaft 4 is larger than the steering assist force transmitted to the second shaft 5. Therefore, the shortage of the steering assist force to the second shaft 5 relative to the steering assist force to the first shaft 4 is compensated for by the hydraulic cylinder 60.

[0055] In this hydraulic device, when the driver steers the steering wheel 8 in a left rotation direction, the second electric motor 58 rotates in the left rotation direction (counterclockwise rotation direction in FIG. 5), and as a result, the oil in the second tank 66 flows into the first cylinder chamber 60a through the second check valve 67, the space between the teeth portion 62a and the teeth portion 63a, and the first flow path 71. Then, due to an increase in the hydraulic pressure in the first cylinder chamber 60a, the piston 82 is pressed toward the other end 81c of the cylinder tube 81, and accordingly, the rod 83 also moves toward the other end 81c of the cylinder tube 81. As a result, the branch link 48 shown in FIG. 1 is pulled in a direction approaching the hydraulic cylinder 60, and one of the steered wheels 3 (the steered wheel 3 on the right side in FIG. 1) is steered to the left via the intermediate link 46 and the third knuckle arm 47. At the same time, the other steered wheel 3 (the steered wheel 3 on the left side in FIG. 1) is also steered to the left via the second shaft 5 and the fourth knuckle arm 55.

[0056] Also, when the driver steers the steering wheel 8 in the right direction, the second electric motor 58 rotates in the right direction (clockwise direction in FIG. 5), and as a result, the oil in the first tank 64 flows into the second cylinder chamber 60b through the first check valve 65, the space between the teeth 62a and the teeth 63a, and the second flow path 72. Then, due to an increase in the hydraulic pressure in the second cylinder chamber 60b, the piston 82 is pressed toward the one end 81a of the cylinder tube 81, and accordingly, the rod 83 also moves toward the one end 81a of the cylinder tube 81. As a result, the branch link 48 shown in FIG. 1 is pressed in a direction away from the hydraulic cylinder 60, and one of the steered wheels 3 (the steered wheel 3 on the right side in FIG. 1) is steered to the right via the intermediate link 46 and the third knuckle arm 47. At the same time, the other steered wheel 3 (the steered wheel 3 on the left side in FIG. 1) is also steered to the right via the second shaft 5 and the fourth knuckle arm 55.

[0057] Furthermore, when the first electric motor 12 fails, the second ECU controller 59 continues to drive and control the second electric motor 58, and actuates the hydraulic cylinder 60. Here, the second ECU controller 59 drives and controls the second electric motor 58 so as to stably steer the steered wheels 3, 3 on the second axle 5 side via the second axle side link component 15b of the link mechanism 15, at least until an emergency stop of the vehicle occurs. At this time, in conjunction with the steering of the steered wheels 3, 3, the steered wheels 2, 2 on the first axle 4 side are also steered until an emergency stop of the vehicle occurs.

[0058] As described above, in this embodiment, the steering device includes the first electric motor 12 capable of transmitting a steering assist force to both the first axle 4 and the second axle 5 via the output shaft 22 of the steering shaft 9, the ball screw mechanism 10, the sector gear 11, the pitman arm 14, the first axle side link component 15a and the second axle side link component 15b by applying a steering force to the steering shaft 9, and the hydraulic device 56 that applies a steering assist force to the rear second axle 5 of the front twin axle vehicle 1 via the second axle side link component 15b of the link mechanism 15. The hydraulic device 56 includes a hydraulic cylinder 60 that is used to apply the steering assist force to the rear second axle 5, a hydraulic pump 57 that is capable of supplying hydraulic pressure to the hydraulic cylinder 60, a second electric motor 58 that drives the hydraulic pump 57, and a second control device that drives and controls the second electric motor 58 based on the steering torque detected by the torque sensor 27. With the steering device configured in this manner, the generation of the steering assist force in the housing including the steering shaft 9 (the housing including the first housing 16, etc.) is completely electrically generated by the first electric motor 12, without using a hydraulic pump driven by the engine. Therefore, the application of the steering assist force to the front first axle 4 of the two front axles can be completely electrically generated, and the application of the steering assist force to the rear second axle 5 can be performed by a simple configuration. In other words, the application of the steering assist force to the first axle 4 is completely electrically generated, while the application of the steering assist force to the rear second axle 5 is performed by applying the steering assist force by the first electric motor 12 via the second axle side link component 15b of the link mechanism 15, and further, the shortage of the steering assist force can be compensated for by using the hydraulic cylinder 60, which has a relatively simple configuration.

[0059] In this embodiment, the first ECU controller associated with the first electric motor 12 calculates the steering direction of the steering wheel 8 and the motor torque of the second electric motor 58 corresponding to this steering direction based on the steering torque detected by the torque sensor 27. The hydraulic cylinder 60 can switch the hydraulic pressure in both directions by the movement of the piston 82 corresponding to the motor torque. Therefore, the steering torque used to control the first electric motor 12 is also used to control the hydraulic cylinder 60 via the second electric motor 58, so that the steering assist force can be applied to the second shaft 5 more efficiently than when the motor torque is calculated using other parameters.

[0060] Furthermore, in this embodiment, when the first electric motor 12 fails, the second ECU controller 59 continues drive control of the second electric motor 58 and operates the hydraulic cylinder 60 to stably steer the steered wheels 3, 3 on the second axle 5. As a result, even when the first electric motor 12 fails, the steered wheels 3, 3 on the second axle 5 are steered, and accordingly the steered wheels 2, 2 on the first axle 4 are also steered, so that the front two-axle vehicle 1 can be brought to a safe emergency stop. [Explanation of symbols]

[0061] Reference Signs List 1 front two axles, 2 steered wheels, 3 steered wheels, 4 first axle, 5 second axle, 9 steering axle, 12 first electric motor, 13 reduction gear, 15a first axle side link component, 15b second axle side link component, 27 torque sensor, 45 second drag link, 46 intermediate link, 47 third knuckle luer a hydraulic system, 48 branch link, 56 hydraulic device, 57 hydraulic pump, 58 second electric motor, 59 second ECU controller, 60 hydraulic cylinder, 60a first cylinder chamber, 60b second cylinder chamber, 71 first flow path, 72 second flow path, 81 cylinder tube, 82 piston, 83 rod

Claims

1. A steering device for steering a pair of front and rear steered wheels of a front two-axle vehicle, comprising: a steering shaft to which rotation from a steering wheel is input; a sector gear to which rotation of the steering shaft is transmitted; a link mechanism connecting the sector gear to a front shaft and a rear shaft of the front two-axle vehicle; a torque sensor that detects a steering torque corresponding to a rotation of the steering shaft; a first electric motor that applies a steering assist force to the steering shaft and transmits the steering assist force to both the front shaft and the rear shaft; a first control device that controls the first electric motor based on the steering torque detected by the torque sensor; a hydraulic device that applies a steering assist force to a rear axle of the front twin-axle vehicle via the link mechanism, the hydraulic device having a hydraulic cylinder that is used to apply the steering assist force to the rear axle, a hydraulic pump that can supply hydraulic pressure to the hydraulic cylinder, a second electric motor that drives the hydraulic pump, and a second control device that drives and controls the second electric motor based on the steering torque detected by the torque sensor; A steering device comprising:

2. 2. The steering device according to claim 1, the first control device or the second control device calculates a steering direction of the steering wheel based on the steering torque detected by the torque sensor and a motor torque of the second electric motor corresponding to the steering direction; The steering device according to claim 1, wherein the hydraulic cylinder is capable of switching hydraulic pressure in both directions by movement of a piston corresponding to a steering direction of the steering wheel and a motor torque of the second electric motor.

3. 2. The steering device according to claim 1, The second control device continues to control the drive of the second electric motor when the first electric motor fails, and operates the hydraulic cylinder to steer the steered wheels attached to the rear axle of the front two-axle vehicle via the link mechanism.

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