Steering device, and control method and control program for steering device

Abstract

This steering device comprises an electric motor (14B) that imparts a steering force to rear wheels (5B) of a vehicle, a motor shaft (30) that extends from the electric motor (14B), a first deceleration mechanism (25) that is connected to the motor shaft (30) and that decelerates the rotation of the electric motor (14B), a ball screw mechanism (26) that converts rotational motion transmitted from the first deceleration mechanism (25) into linear motion, a rack bar (10B) that is connected to the ball screw mechanism (26) and that steers the rear wheels (5B), and an electromagnetic clutch (51) that is provided on the side of the first deceleration mechanism (25) opposite from the electric motor (14B) and is capable of exerting a braking force so as to limit the movement of the rack bar (10B) at an arbitrary steering position.

Description

Steering device, steering device control method, and control program

[0001] The present invention relates to a steering device, a control method for a steering device, and a control program.

[0002] The steering device described in Patent Document 1 has an electric motor that can apply a steering force to the rear wheels of a vehicle. An electromagnetic brake is disposed around the motor shaft of the electric motor to lock the steering of the rear wheels in the event of an electrical failure of the electric motor. The motor shaft is rotatably supported by a pair of bearings provided at both axial ends thereof.

[0003] International Publication No. 2021 / 186932

[0004] In the steering device described in Patent Document 1, the electric motor has a built-in electromagnetic clutch, so the distance between the bearings of the motor shaft is longer than in an electric motor that does not have a built-in electromagnetic clutch. As a result, vibrations are more likely to occur when the electric motor rotates at high speeds, which causes a problem of a worsening steering feel for the driver.

[0005] Furthermore, although Patent Document 1 discloses that the steering of the rear wheels is locked in the event of an electrical failure of the electric motor, no measures are taken to address the deterioration of the steering feel.

[0006] The present invention was devised in consideration of the current situation, and one of its objects is to provide a steering device, a control method for a steering device, and a control program that can suppress deterioration of the steering feel felt by the driver.

[0007] In the present invention, a steering device provided on a vehicle includes a motor that applies a steering force to steered wheels of the vehicle, and a braking mechanism that exerts a braking force so as to limit the movement of a movable member at any steering position. The braking mechanism is provided on the opposite side of the reduction mechanism from the motor.

[0008] According to the present invention, it is possible to suppress deterioration of the steering feel felt by the driver.

[0009] 7 is a schematic diagram of a steering system to which the steering device of the first embodiment is applied. FIG. 8 is a longitudinal sectional view of the rear wheel side steering device of the first embodiment. FIG. 9 is an exploded perspective view of a coupling. FIG. 10 is a process diagram showing a process of adjusting the tension of an endless belt. FIG. 11 is a process diagram showing a process of attaching an electromagnetic clutch to a second housing. FIG. 12 is a system block diagram of a motor control device. FIG. 13 is a flowchart showing the flow of control of the rear wheels after a primary failure of the electric motor in the first embodiment. FIG. 14 is a flowchart showing the flow of returning the rear wheels to neutral in step S4 of FIG. 7. FIG. 15 is a timing chart showing control of the rear wheels in the first embodiment. FIG. 16 is a timing chart showing control of the rear wheels in the second embodiment. FIG. 17 is a schematic longitudinal sectional view of the rear wheel side steering device of the third embodiment.

[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] First Embodiment FIG. 1 is a schematic diagram of a steering system to which a steering device according to a first embodiment is applied.

[0012] The steering system shown in FIG. 1 has a front-wheel steering device 1A used to steer the front wheels 5A, 5A, which are the steerable wheels on the front side of the vehicle, and a rear-wheel steering device 1B used to steer the rear wheels 5B, 5B, which are the steerable wheels on the rear side of the vehicle.

[0013] As shown in FIG. 1, the front wheel steering device 1A includes a steering mechanism 2 that transmits steering force from a driver, and a steering assist mechanism 3 that assists the driver in steering.

[0014] The steering mechanism 2 mechanically connects a steering wheel 4 located in the driver's cab of the vehicle to the front wheels 5A. The steering mechanism 2 includes a first steering shaft 8A having an input shaft 6 to which rotational force from the steering wheel 4 is transmitted and an output shaft 7 connected to the input shaft 6 via a torsion bar (not shown), and a transmission mechanism 9 that transmits the rotation of the first steering shaft 8A to the front wheels 5A. The transmission mechanism 9 is configured with a rack-and-pinion mechanism (rack-and-pinion gear) including a pinion (not shown) provided on the outer periphery of the output shaft 7 and a rack (not shown) provided on the outer periphery of a rack bar 10A, which is a movable member. Both ends of the rack bar 10A are connected to the corresponding front wheels 5A via two tie rods 11A and two knuckle arms 12A.

[0015] The rack bar 10A is provided so as to be movable in the axial direction of the rack bar 10A within a cylindrical rack bar housing 13A made of a metal material, for example, an aluminum alloy material.

[0016] The steering assist mechanism 3 includes an electric motor (actuator) 14A that applies a steering force to the steering mechanism 2, and this electric motor 14A is electrically connected to a motor control device (ECU) 15. Furthermore, the electric motor 14A is connected to the rack bar 10A via a transmission device (not shown). The electric motor 14A rotates a nut (not shown) provided in the transmission device, and as the nut rotates, the rack bar 10A moves in the axial direction.

[0017] The motor control device 15 has the function of storing and executing various control processes, and drives and controls the electric motor 14A based on an external command signal. Here, the external command signal is a signal based on the rotation of the steering wheel 4, which is a steering input device that receives steering operations from the driver, and in this embodiment, is a steering angle signal Ar from a steering angle sensor 16 provided on the first steering shaft 8A, and a steering torque signal Tr from a steering torque sensor 17 also provided on the first steering shaft 8A.

[0018] In this front-wheel steering device 1A, when the driver turns the steering wheel 4, the input shaft 6 rotates and the torsion bar is twisted, and the resulting elastic force of the torsion bar rotates the output shaft 7. The rotational motion of the output shaft 7 is then converted into linear motion along the axial direction of the rack bar 10A by the rack and pinion mechanism, and the knuckle arms 12A, 12A are pushed and pulled in the vehicle width direction via the tie rods 11A, 11A, thereby changing the orientation of the corresponding front wheels 5A, 5A.

[0019] The rear-wheel steering device 1B drives and controls an electric motor 14B based on external command signals, which in this embodiment are a steering angle signal Ar, a steering torque signal Tr, and a displacement signal Dr (described later), to drive a rack bar 10B, which is a movable member, via a first reduction gear mechanism 25 (described later) and a ball screw mechanism 26 (described later) which is a rotary-to-linear conversion mechanism. Furthermore, instead of using the steering angle signal Ar or the like as the external command signal, a command signal for automatic driving may be used. The rear-wheel steering device 1B includes a rack bar 10B, tie rods 11A, knuckle arms 12A, and a rack bar housing 13B which have the same configurations as the rack bar 10A, tie rods 11A, knuckle arms 12A, and rack bar housing 13A of the front-wheel steering device 1A. Both ends of the rack bar 10B are connected to the corresponding rear wheels 5B via two tie rods 11B and two knuckle arms 12B. The rack bar 10B is provided so as to be movable in the axial direction within a cylindrical rack bar housing 13B made of a metal material, such as an aluminum alloy.

[0020] The rack bar 10B is provided with a displacement sensor 18 that detects the axial displacement of the rack bar 10B. A displacement signal Dr detected by the displacement sensor 18 is sent to the motor control device 15.

[0021] In the rear-wheel steering device 1B, the electric motor 14B is drive-controlled based on the steering angle signal Ar, the steering torque signal Tr, and the displacement signal Dr, and the rotational motion of the electric motor 14B is transmitted to a ball screw mechanism 26, which will be described later, via a first reduction gear mechanism 25, which will be described later. The ball screw mechanism 26 then converts the rotational motion of the electric motor 14B into linear motion along the axial direction of the rack bar 10B, and the knuckle arms 12B, 12B are pushed and pulled in the vehicle width direction via the tie rods 11B, 11B, thereby changing the orientation of the corresponding rear wheels 5B, 5B.

[0022] Fig. 2 is a vertical cross-sectional view of the rear-wheel side steering device 1B of the first embodiment. Fig. 3 is an exploded perspective view of the coupling 94. Fig. 4 is a process diagram showing a process of adjusting the tension of the endless belt 47. Fig. 5 is a process diagram showing a process of attaching the electromagnetic clutch 51 to the second housing 22.

[0023] The rack bar 10B is housed in a rack bar housing 19 formed in an elongated cylindrical shape. The rack bar housing 19 has a first housing 20 located on the electric motor 14B side, and a second housing 22 located on the electromagnetic clutch 51 side (described later) and attached and fixed to the first housing 20 via fixing members, such as bolts 21.

[0024] The first housing 20 is made of a metal material and has an elongated cylindrical shape. As shown in FIG. 2 , the first housing 20 includes a first small-diameter cylindrical portion 20a and a first large-diameter cylindrical portion 20b that is integrally formed with the first small-diameter cylindrical portion 20a and has a larger diameter than the first small-diameter cylindrical portion 20a. The first small-diameter cylindrical portion 20a accommodates a portion of the rack bar 10B. The first large-diameter cylindrical portion 20b accommodates a portion of the rack bar 10B, a portion of a nut 45 (described below), a third ball bearing B3, and a portion of the first reduction gear mechanism 25. As shown in FIGS. 2 and 4 , a first protrusion 20c is formed on the outer periphery of the first large-diameter cylindrical portion 20b on the electric motor 14B side, protruding radially outward from the outer periphery of the first large-diameter cylindrical portion 20b. As shown in FIG. 4 , the first protruding portion 20c has a cylindrical first central portion 20d and three generally triangular first hole-forming portions 20e formed at equidistant positions circumferentially from the outer periphery of the first central portion 20d. Each first hole-forming portion 20e has a first elongated hole (first alignment mechanism) 20f extending axially through the rack bar 10B to adjust the tension of the endless belt 47 of the first reduction mechanism 25 (described later). As shown in FIGS. 2 and 4 , the first elongated hole 20f has an oval shape that is elongated in a direction perpendicular to both the rack bar 10B and the motor shaft 30 of the electric motor 14B. A fixing bolt 23, which serves as a fixing member, is inserted through the first elongated hole 20f.

[0025] The second housing 22 is made of a metal material and has a cylindrical shape with an axial dimension smaller than that of the first housing 20. The second housing 22 has a second small-diameter cylindrical portion 22a and a second large-diameter cylindrical portion 22b that is integrally formed with the second small-diameter cylindrical portion 22a and has a larger diameter than the second small-diameter cylindrical portion 22a. The second small-diameter cylindrical portion 22a accommodates a portion of the rack bar 10B. The second large-diameter cylindrical portion 22b accommodates a portion of the rack bar 10B and a first reduction mechanism 25 (described below). As shown in FIGS. 2 and 5 , a second protrusion 22c is formed on the outer periphery of the second large-diameter cylindrical portion 22b, on the electromagnetic clutch 51 side, that protrudes radially outward from the outer periphery of the second large-diameter cylindrical portion 22b. 5, the second protruding portion 22c has a cylindrical second central portion 22d and three generally triangular second hole forming portions 22e formed at equidistant positions in the circumferential direction from the outer periphery of the second central portion 22d. A circular screw hole 22f is formed through each second hole forming portion 22e along the axial direction of the rack bar 10B.

[0026] Rear-wheel steering device 1B has a steering assist mechanism 24 that assists the steering force transmitted to rear wheels 5B, 5B, which are steered wheels, via rack bar 10B. Steering assist mechanism 24 has electric motor 14B, a first reduction mechanism 25 that transmits the rotational motion of electric motor 14B while reducing the rotational speed, and a ball screw mechanism 26 that is a rotary-to-linear motion converting mechanism that converts the rotational motion transmitted from first reduction mechanism 25 into linear motion.

[0027] The electric motor 14B is a three-phase (U-phase, V-phase, W-phase) AC motor consisting of two systems, and is configured integrally with the motor control device 15. Note that the electric motor 14B may be configured to be provided at any location on the vehicle, rather than being configured integrally with the motor control device 15. The electric motor 14B includes a motor housing 27, a stator 28 and a rotor 29 disposed within the motor housing 27, and a motor shaft 30 that rotates integrally with the rotor 29 as the rotor 29 rotates. As shown in FIG. 2 , the motor shaft 30 protrudes from the interior of the motor housing 27 to the exterior of the motor housing 27 and extends toward the electromagnetic clutch 51.

[0028] For convenience of the following explanation, the direction along the longitudinal direction of the motor shaft 30 is defined as the "axial direction," the direction perpendicular to the longitudinal direction of the motor shaft 30 is defined as the "radial direction," and the direction along the periphery of the longitudinal direction of the motor shaft 30 is defined as the "circumferential direction." Note that the motor shaft 30 is disposed parallel to the rack bar 10B, and the axial direction of the motor shaft 30 corresponds to the axial direction of the rack bar 10B.

[0029] The motor housing 27 includes a cylindrical housing member 31 and a first closing member 32 that closes an opening of the cylindrical housing member 31. The cylindrical housing member 31 is formed from a metal material and includes a cylindrical portion 31a, a partition wall portion 31b formed near one axial end of the cylindrical portion 31a, and a housing-side flange portion 31c extending radially outward from the outer periphery of the other axial end of the cylindrical portion 31a.

[0030] The partition wall 31b has a generally circular plate shape and separates the motor housing space Q1, which houses motor components such as the rotor 29, from the control device housing space Q2, which houses the motor control device 15. The partition wall 31b has a partition wall through-hole 31d through which the axial end 30a of the motor shaft 30 passes. An annular protrusion 31f protruding axially inward from the axial inner end surface 31e of the partition wall 31b is formed at a radial position near the partition wall through-hole 31d. A second ball bearing (second bearing) B2 is provided on the inner circumferential surface of the annular protrusion 31f, which is disposed on the side of the sensor magnet 33 provided on the motor shaft 30 and which rotatably supports the outer periphery of the motor shaft 30 near the axial end 30a.

[0031] Although not shown, the housing side flange portions 31c are provided at positions corresponding to the three first hole forming portions 20e of the first housing 20. The housing side flange portions 31c have threaded holes 31g into which the fixing bolts 23 serving as fixing members are screwed.

[0032] The first closing member 32 is made of a metal material and is cylindrical in shape, with a stepped diameter that decreases from one axial end 30a toward the other axial end 30b of the motor shaft 30. The first closing member 32 has a cylindrical small-diameter portion 32a located on the other axial end 30b side of the motor shaft 30, a cylindrical large-diameter portion 32b located on the one axial end 30a side of the motor shaft 30, and an annular connecting portion 32c that connects the small-diameter portion 32a and the large-diameter portion 32b.

[0033] A first ball bearing (first bearing) B1 is disposed on the first reduction mechanism 25 side of the inner circumferential surface of the small diameter portion 32a on the axial other end 30b side of the motor shaft 30. The first ball bearing (first bearing) B1 is a bearing that rotatably supports the outer circumferential portion of the motor shaft 30 near the axial other end 30b. The small diameter portion 32a is disposed within a cylindrical first central portion 20d of the first protruding portion 20c of the first housing 20. The outer diameter of the small diameter portion 32a is smaller than the inner diameter of the first central portion 20d, and the small diameter portion 32a is allowed to move relative to the first central portion 20d before the motor housing 27 is assembled to the first housing 20.

[0034] The outer peripheral surface of the tip of the large-diameter portion 32b and the inner peripheral surface of the cylindrical portion 31a of the cylindrical housing member 31 are airtightly sealed by an annular first seal member 34. Furthermore, a blocking member-side flange portion 32e protruding radially outward is formed on the outer peripheral portion of the large-diameter portion 32b at a location farthest from the rack bar 10B. Although not shown, the blocking member-side flange portion 32e is provided at positions corresponding to the three first hole-forming portions 20e of the first housing 20. Bolt insertion holes 32f are formed through the blocking member-side flange portion 32e in the axial direction of the motor shaft 30. Fixing bolts 23, which serve as fixing members, are inserted into the bolt insertion holes 32f.

[0035] A rotor 29 is connected to the outer periphery of the axial center of the motor shaft 30, and a stator 28 is provided on the outer periphery of the rotor 29. A sensor magnet 33 is attached to one axial end 30a of the motor shaft 30, that is, the end of the motor shaft 30 that extends on the opposite side of the rotor 29 from the first reduction mechanism 25 and is located on the opposite side from the first reduction mechanism 25, by a fixing member, for example, a screw 35. The other axial end 30b of the motor shaft 30 is fixed to a first pulley 44, which will be described later.

[0036] The motor control device 15, which is configured integrally with the electric motor 14B, is disposed in a control device housing space Q2 provided between the partition wall portion 31b and the second closing member 40 and second cover member 41. The motor control device 15 includes a microprocessor (not shown), a first board 36 on which the microprocessor is mounted, a sensor IC 37 mounted on the first board 36, and a second board 38.

[0037] The first substrate 36 is provided at the axial end of the partition wall 31b in an orientation perpendicular to the rotation axis O of the motor shaft 30. The first substrate 36 is made of a non-conductive resin material, such as glass epoxy resin, and has conductor patterns (not shown) formed on both sides thereof, with numerous electronic components, including a microprocessor, mounted on the conductor patterns. A sensor IC 37 that detects changes in the magnetic field of the sensor magnet 33 mounted on the motor shaft 30 is mounted on the surface 36a of the first substrate 36 facing the partition wall 31b, facing the sensor magnet 33. The opposite surface 36b of the first substrate 36 is connected to a battery (not shown) via connectors 40b and 40c integrally formed with the second closing member 40.

[0038] The second board 38 is disposed in the control device accommodating space Q2 so as to be perpendicular to the axial direction of the motor shaft 30 and to face the surface 36b of the first board 36.

[0039] The second closing member 40 is made of a synthetic resin material and is integrally formed with a generally circular plate-like portion 40a that serves to close the control device accommodating space Q2 and connector portions 40b, 40c that serve to supply power, etc. The second closing member 40 is fixed to the tubular housing member 31 via a cylindrical second cover member 41 with a bottom.

[0040] The first reduction mechanism 25 includes a cylindrical first pulley 44 that rotates integrally with the motor shaft 30 of the electric motor 14B, a cylindrical second pulley 46 that rotates integrally with a nut 45 disposed on the outer periphery of the rack bar 10B, and an endless belt 47 that is wound between the first pulley 44 and the second pulley 46 and transmits the rotation from the first pulley 44 to the second pulley 46. As shown in FIG. 2 , the first pulley 44 is fixed to the motor shaft 30 by press-fitting its inner periphery into the outer periphery of the other axial end 30b of the motor shaft 30. As shown in FIG. 4 , the second pulley 46 has an outer diameter larger than that of the first pulley 44. As shown in FIGS. 2 and 4 , the second pulley 46 houses a nut 45 on its inner periphery and is axially fastened to the nut 45 by a plurality of bolts 48 serving as fixing members. The endless belt 47 is made of synthetic rubber and is wound around the first pulley 44 and the second pulley 46 with a predetermined tension.

[0041] Ball screw mechanism 26 has a steered-shaft-side ball screw groove 49 formed in a spiral shape on the outer periphery of rack bar 10B, a nut-side ball screw groove 45a formed in a spiral shape on the inner periphery of nut 45, and a plurality of balls 50 provided between steered-shaft-side ball screw groove 49 and nut-side ball screw groove 45a. Balls 50 support nut 45 so as to be rotatable relative to rack bar 10B.

[0042] Further, a third ball bearing B3 is disposed on one end of the nut 45, which is a bearing that rotatably supports the nut 45 relative to the rack bar 10B.

[0043] Additionally, an electromagnetic clutch 51, which is a braking mechanism capable of exerting a braking force so as to limit the movement of the rack bar 10B at any steering position, is disposed on the opposite side of the first reduction gear mechanism 25 from the electric motor 14B. The electromagnetic clutch 51 includes a clutch shaft 52, a coil holding portion 53, an excitation coil 54, an armature (first clutch member) 55, a clutch plate (second clutch member) 56, a plurality of coil springs 57, a clutch plate mounting member 58, and a braking mechanism housing 59. When the excitation coil 54 is not energized, the electromagnetic clutch 51 restricts the relative rotation of the rotor 29 with respect to the motor housing 27 by engaging the armature 55 with the clutch plate 56.

[0044] The clutch shaft 52 is made of a metal material and is a cylindrical shaft member whose axial length is shorter than that of the motor shaft 30. A motor-side end 52a of the clutch shaft 52, which is the axial end located on the motor shaft 30 side, is connected to the other axial end 30b of the motor shaft 30 via a coupling 94 (described later). Therefore, the axial direction of the clutch shaft 52 coincides with the axial direction of the motor shaft 30.

[0045] The coil holding portion 53 is formed in the shape of a relatively thick circular plate. The coil holding portion 53 constitutes part of the brake mechanism housing 59 and is disposed adjacent to a base wall portion 59a that is perpendicular to the clutch shaft 52. As shown in FIG. 2 , an expanded portion 53a that expands radially outward is formed at a portion of the outer periphery of the coil holding portion 53 adjacent to the base wall portion 59a. A bolt insertion hole 53b is formed in this expanded portion 53a, through which a bolt 60 serving as a fixing member is inserted. The coil holding portion 53 is attached and fixed to the base wall portion 59a by screwing the bolt 60 into the base wall portion 59a through the bolt insertion hole 53b. A shaft through hole 53c, through which the clutch shaft 52 passes, is formed in the radial center of the coil holding portion 53. A coil holding groove 53e that holds the excitation coil 54 is formed at a radially inner position on an axial end surface 53d of the coil holding portion 53 that faces the armature 55.

[0046] The excitation coil 54 is electrically connected to a harness 62 that passes through a relay portion 61 provided on the outer periphery of the coil holding portion 53. The harness 62 is connected to a battery (not shown). A plurality of circular spring accommodating recesses 53f (only one is shown in this embodiment) are provided on an axial end surface 53d of the coil holding portion 53 at positions radially outward of the excitation coil 54 and spaced equally apart around the circumferential direction of the coil holding portion 53. A biasing member, such as a coil spring 57, capable of biasing the armature 55 against the clutch plate 56 is disposed in a compressed state in each spring accommodating recess 53f. One end of each coil spring 57 is connected to the bottom of the spring accommodating recess 53f, and the other end is connected to the opposing surface of the armature 55.

[0047] Furthermore, circular support holes 53g are formed in the coil holding portion 53 at three locations (only one location is shown in the present embodiment) radially outward from the coil holding groove 53e, and extend through the coil holding portion 53 along the axial direction of the clutch shaft 52. The support holes 53g cooperate with the support hole 63a of the circular plate-shaped guide support member 63 to hold a cylindrical guide member 64 that guides the armature 55 along the axial direction of the clutch shaft 52.

[0048] The armature 55 has a circular plate shape and is slidably connected to a guide member 64 via a guide hole 55a provided on the outer periphery of the armature 55 between the coil holding portion 53 and the clutch plate 56. The armature 55 is connected to the coil holding portion 53 via the guide member 64. When the armature 55 is attracted to the excitation coil 54 by the magnetic force generated by the excitation coil 54, the armature 55 is separated in the axial direction from the clutch plate 56. When the armature 55 is not attracted to the excitation coil 54 (when power to the electric motor 14B fails), the armature 55 fastens to a brake lining (not shown) of the clutch plate 56 by the biasing force of each coil spring 57, thereby restricting the relative rotation of the rotor 29 with respect to the motor housing 27.

[0049] The clutch plate 56 is formed in a circular plate shape and is disposed between the armature 55 and the guide support member 63. The clutch plate 56 has a relatively thin plate portion 56a located radially inward and a relatively thick plate portion 56b located radially outward. A fixing hole 66 is formed in the center of the thin plate portion 56a, and the clutch plate 56 is fixed to the outer periphery of a cylindrical clutch plate mounting member 58 via this fixing hole 66. The clutch plate mounting member 58 is attached to the outer periphery of the clutch shaft 52 by fixing members, such as screw members 68, with its rotation relative to the clutch shaft 52 restricted by a key 67.

[0050] The brake mechanism housing 59 has a circular plate-shaped base wall portion 59a and a cylindrical peripheral wall portion 59b that stands upright from the outer edge of the base wall portion 59a along the axial direction of the clutch shaft 52 on the opposite side to the electric motor 14B.

[0051] As shown in FIG. 5, the base wall portion 59a has a shape corresponding to the outer shape of the second overhang portion 22c of the second housing 22. The base wall portion 59a has generally triangular third hole forming portions 59c formed at positions corresponding to the three second hole forming portions 22e of the second overhang portion 22c. As shown in FIG. 2, a second elongated hole 59d serving as a second alignment mechanism for adjusting the tension of the endless belt 47 of the first reduction gear mechanism 25 is formed to penetrate the third hole forming portions 59c along the axial direction of the clutch shaft 52. As shown in FIG. 2, the second elongated hole 59d has an oval shape that is elongated in a direction perpendicular to both the clutch shaft 52 and the rack bar 10B. As shown in FIG. 2, a base wall portion insertion hole 59e is formed to penetrate the radial center of the base wall portion 59a along the axial direction of the clutch shaft 52. The motor-side end 52a of the clutch shaft 52, which is the axial end of the clutch shaft 52 and located on the electric motor 14B side, is inserted through the base wall insertion hole 59e. The base wall insertion hole 59e has a first enlarged diameter portion 59i that is stepped toward the electric motor 14B via a step 59f. A cylindrical protrusion 59g that protrudes toward the electric motor 14B is formed on the axial end surface of the base wall 59a on the electric motor 14B side. The cylindrical protrusion 59g is disposed within the cylindrical second central portion 22d of the second protruding portion 22c of the second housing 22. The outer diameter of the cylindrical protrusion 59g is smaller than the inner diameter of the second central portion 22d, allowing the cylindrical protrusion 59g to move relative to the second central portion 22d before the brake mechanism housing 59 is assembled to the second housing 22.

[0052] The step portion 59f is provided with a fourth ball bearing B4, which is a bearing that rotatably supports the outer periphery of the motor-side end 52a side of the clutch shaft 52. The fourth ball bearing B4 is fixed to the base wall portion 59a by threading a cylindrical fixing member 69 onto the inner periphery of the cylindrical protrusion 59g.

[0053] A pair of breathing valves 72 that can release air from inside the brake mechanism housing 59 to the outside are provided in the peripheral wall portion 59b at positions near the harness 62.

[0054] The opening of the peripheral wall portion 59b is closed by a cylindrical clutch control housing 73 with a bottom. An insertion hole 73a is formed in the radial center of the clutch control housing 73, penetrating along the axial direction of the clutch shaft 52. The non-motor end 52b, which is the axial end of the clutch shaft 52 opposite the motor end 52a, is inserted into the insertion hole 73a. A fifth ball bearing B5, which rotatably supports the outer periphery of the non-motor end 52b of the clutch shaft 52, is press-fitted into the insertion hole 73a.

[0055] A hole 73b is formed in the clutch control housing 73 along the axial direction of the clutch shaft 52 at a position corresponding to the relay portion 74 of the electromagnetic clutch 51. A harness 62 connected to the relay portion 74 is passed through the hole 73b. The harness 62 passes through the clutch control housing 73 and extends to the side of a third closing member 75 that closes the clutch control housing 73.

[0056] A braking mechanism control device 77 that controls the electromagnetic clutch 51 is housed in the space between the clutch control housing 73 and the third closing member 75. The braking mechanism control device 77 houses a microprocessor (not shown) and a third board 78 on which the microprocessor is mounted.

[0057] In this electromagnetic clutch 51, in the event of an electrical failure (primary failure) of the electric motor 14B, the armature 55 is not attracted to the excitation coil 54 and is fastened to the brake lining of the clutch plate 56 by the biasing force of each coil spring 57. This restricts the relative rotation of the clutch shaft 52 with respect to the braking mechanism housing 59. Furthermore, the restriction on the relative rotation of the clutch shaft 52 also restricts the rotation of the motor shaft 30, which is connected to the clutch shaft 52 via the coupling 94. Furthermore, the movement of the rack bar 10B, which is connected to the electric motor 14B via the first reduction mechanism 25 and the ball screw mechanism 26, is also restricted. In other words, the restriction on the relative rotation of the clutch shaft 52 restricts the steering of the rack bar 10B at any axial position of the rack bar 10B, i.e., at any steering position of the rack bar 10B. The fastening of the armature 55 to the brake lining of the clutch plate 56 exerts a braking force at any position in the axial direction of the rack bar 10B, and does not necessarily lock the steering of the rear wheels 5B, 5B at the above-mentioned any position.

[0058] The coupling 94 connects the brake mechanism side end 44a, which is the end of the first pulley 44 located on the electromagnetic clutch side, to the motor side end 52a of the clutch shaft 52. As shown in Figure 3, the coupling 94 has a first coupling member 95, a second coupling member 96, an intermediate member 97, and a web washer 98.

[0059] The first coupling member 95 is made of a metal material and is cylindrically formed so as to be integral with the cylindrical first pulley 44. The first coupling member 95 is formed integrally with the first pulley 44 and has a cylindrical base portion 95a with a larger diameter than the first pulley 44. The first coupling member 95 has a plurality of first teeth 95c (six in this embodiment) that protrude from an end surface 95b of the base portion 95a adjacent to the outer periphery of the base portion 95a toward the second coupling member 96. When viewed axially of the clutch shaft 52, the first teeth 95c are generally triangular. The six first teeth 95c are arranged at equal intervals around the clutch shaft 52.

[0060] The second coupling member 96 is cylindrical and made of metal. The second coupling member 96 is connected to a shaft tooth portion 52c formed on the outer periphery of the motor-side end 52a of the clutch shaft 52. The second coupling member 96 has a large cylindrical portion 96a and a small cylindrical portion 96c that extends from an end surface 96b of the large cylindrical portion 96a on the first coupling member 95 side to the first coupling member 95 side and has a smaller diameter than the large cylindrical portion 96a. A plurality of second tooth portions 96d (six in this embodiment) are formed on the outer periphery of the small cylindrical portion 96c so as to protrude radially outward. The six second tooth portions 96d are arranged at equal intervals around the circumference of the clutch shaft 52.

[0061] The intermediate member 97 is made of a metal material and has an annular shape. The intermediate member 97 is disposed between the first coupling member 95 and the second coupling member 96 to connect them. The inner periphery of the intermediate member 97 has six pairs of tooth retaining portions 97a that sandwich and hold the six second tooth portions 96d of the second coupling member 96. The six pairs of tooth retaining portions 97a are disposed at equal intervals in the circumferential direction of the clutch shaft 52. A gap 99 is provided between two circumferentially adjacent pairs of tooth retaining portions 97a on the inner periphery of the intermediate member 97 to sandwich and hold the first tooth portions 95c of the first coupling member 95. The first tooth portions 95c are inserted through the gap 99 between two circumferentially adjacent second tooth portions 96d of the second coupling member 96.

[0062] The web washer 98 is disposed between the motor side end 52a of the clutch shaft 52 and the base portion 95a of the first coupling member 95, thereby filling the axial gap therebetween.

[0063] Next, a method for adjusting the tension of the endless belt 47 of the first reduction mechanism 25 will be described with reference to FIGS.

[0064] First, the second pulley 46 is attached to the nut 45 provided on the first large-diameter cylindrical portion 20b of the first housing 20, and the small-diameter portion 32a of the first closing member 32 of the motor housing 27 is inserted into the cylindrical first central portion 20d of the first protruding portion 20c of the first housing 20. After inserting the small-diameter portion 32a, the first pulley 44 is press-fitted into the other axial end 30b of the motor shaft 30, which extends through the small-diameter portion 32a, and a portion in the vicinity thereof.

[0065] An endless belt 47 in a loop shape is wound around the first pulley 44 and the second pulley 46 .

[0066] Next, the fixing bolts 23 (see FIG. 2) are threaded through the first elongated holes 20f of the three first hole forming portions 20e of the first housing 20 and the bolt insertion holes 32f of the three closing member side flange portions 32e of the first closing member 32, and into the three threaded holes 31g of the housing side flange portion 31c of the tubular housing member 31. During this threading, the motor housing 27 is not completely fixed to the first housing 20, but rather, room is left for the fixing bolts 23 to be further threaded into the threaded holes 31g. As described above, the outer diameter of the small diameter portion 32a is smaller than the inner diameter of the first central portion 20d, and therefore, before the motor housing 27 is assembled to the first housing 20, or in this embodiment, before the fixing bolts 23 are fully threaded into the threaded holes 31g, the small diameter portion 32a is allowed to move relative to the first central portion 20d. Furthermore, the fixing bolt 23 is allowed to move within the first elongated hole 20f in a direction perpendicular to both the motor shaft 30 and the rack bar 10B (the up and down direction in FIGS. 2 and 4). Therefore, when the fixing bolt 23 moves in a direction perpendicular to both the motor shaft 30 and the rack bar 10B and away from the rack bar 10B, the first pulley 44 fixed to the motor shaft 30 also moves in a direction away from the rack bar 10B. As a result, the endless belt 47 is pulled by the first pulley 44 in a direction away from the rack bar 10B, and the tension of the endless belt 47 is adjusted to be stronger.

[0067] Next, a method of assembling the brake mechanism housing 59 to the second housing 22 will be described with reference to FIGS.

[0068] First, the second housing 22 is attached to the first housing 20 using the bolts 21 .

[0069] Then, the brake mechanism housing 59 having the clutch shaft 52 equipped with the second coupling member 96, the intermediate member 97, and the web washer 98 is assembled to the second overhanging portion 22c of the second housing 22. During this assembly, the fixing bolts 91 are screwed into the respective threaded holes 22f of the three second hole forming portions 22e of the second housing 22 through the respective second elongated holes 59d of the three third hole forming portions 59c of the brake mechanism housing 59. During this screwing, the brake mechanism housing 59 is not completely fixed to the second overhanging portion 22c of the second housing 22, but rather, room is left for the fixing bolts 91 to be further screwed into the threaded holes 22f. As described above, the outer diameter of the cylindrical protrusion 59g is smaller than the inner diameter of the second central portion 22d. Therefore, before the brake mechanism housing 59 is assembled to the second overhanging portion 22c of the second housing 22, or in this embodiment, before the fixing bolt 91 is fully threaded into the threaded hole 22f, the cylindrical protrusion 59g is allowed to move relative to the second central portion 22d. Furthermore, the fixing bolt 91 is allowed to move within the second elongated hole 59d in a direction perpendicular to both the motor shaft 30 and the rack bar 10B. Therefore, when the fixing bolt 91 moves away from the rack bar 10B in a direction perpendicular to both the motor shaft 30 and the rack bar 10B, the first pulley 44, which is connected to the clutch shaft 52 by the coupling 94, also moves away from the rack bar 10B. Therefore, the endless belt 47 is pulled by the first pulley 44 in a direction away from the rack bar 10B, and the tension of the endless belt 47 is adjusted to be stronger.

[0070] After adjusting the tension of the endless belt 47, the fixing bolt 23 is screwed all the way into the screw hole 31g to completely assemble the motor shaft 30 to the first housing 20, and the fixing bolt 91 is screwed all the way into the screw hole 22f to completely assemble the brake mechanism housing 59 to the second protrusion 22c of the second housing 22.

[0071] FIG. 6 is a system block diagram of the motor control device 15.

[0072] The electric motor 14B, controlled by the motor control device 15, includes a first stator coil 100A corresponding to the first system and a second stator coil 100B electrically separated from the first stator coil 100A and corresponding to the second system. The first stator coil 100A is driven by a first control circuit 101A (shown enclosed by a two-dot chain line) provided in the motor control device 15, while the second stator coil 100B is driven by a second control circuit 101B (shown enclosed by a two-dot chain line) provided in the motor control device 15. The first control circuit 101A and the second control circuit 101B are connected to an MCU 102 provided in the motor control device 15. A steering angle signal Ar and a steering torque signal Tr obtained via a CAN driver 103, and a displacement signal Dr detected by a displacement sensor 18 are input to the MCU 102. The MCU 102 calculates a torque command value A for the electric motor 14B based on the steering angle signal Ar, the steering torque signal Tr, and the displacement signal Dr. The MCU 102 is electrically connected to an MCU monitor 104 that monitors the MCU 102 and a power supply circuit 106 that supplies power P from a battery 105 to the MCU 102. The MCU 102 also includes a microprocessor, which has an abnormality determination unit that determines whether an abnormality has occurred within the motor control device 15. In this embodiment, the abnormality determination unit determines whether an electrical failure has occurred in the first and second systems, such as an electrical failure caused by an abnormality or failure in the first inverter 107A, the second inverter 107B, the first stator coil 100A, or the second stator coil 100B. If an electrical failure has occurred in either the first or second system, the abnormality determination unit determines that a primary failure has occurred within the motor control device 15. If the abnormality determination unit determines that a primary malfunction has occurred, the brake mechanism control device 77 controls the electromagnetic clutch 51 to maintain the steering angle of the electric motor 14B and the rear wheels 5B, 5B, which are the steered wheels, in accordance with the command signals from outside, which in this embodiment are the steering angle signal Ar, steering torque signal Tr, and displacement signal Dr.

[0073] It is also possible to provide a first MCU including a first microprocessor and a second MCU including a second microprocessor instead of providing a single MCU 102. In this case, the first microprocessor determines whether or not there is an electrical failure due to an abnormality or failure of the first inverter 107A and the first stator coil 100A, while the second microprocessor determines whether or not there is an electrical failure due to an abnormality or failure of the second inverter 107B and the second stator coil 100B.

[0074] The first control circuit 101A includes a first pre-driver 108A and a first inverter 107A. The first pre-driver 108A is an integrated circuit (IC) that receives a torque command value A from the MCU 102. The first inverter 107A is driven and controlled based on the torque command value A from the first pre-driver 108A. The first inverter 107A converts power P from a battery 105 (as a power source) from DC to three-phase AC and supplies the converted power P as a motor drive current Ad to the electric motor 14B. This motor drive current Ad serves as a control signal that drives and controls the electric motor 14B to control the steering angle of the rear wheels 5B, 5B, which are steered wheels. A first current sensor 109A provided in the first inverter 107A feeds back to the MCU 102 a motor current Ae, which is the current actually flowing through the electric motor 14B. A first-phase potential detector 110A detects a potential Pt between the first inverter 107A and the electric motor 14B and feeds back the detected potential Pt to the MCU 102.

[0075] The second control circuit 101B includes a second pre-driver 108B and a second inverter 107B configured similarly to the first pre-driver 108A and the first inverter 107A. The second pre-driver 108B is an integrated circuit (IC) that receives a torque command value A from the MCU 102. The second inverter 107B is driven and controlled based on the torque command value A from the second pre-driver 108B, and converts the power P of the battery 105 (power source) from DC to three-phase AC and supplies the converted power P to the electric motor 14B as a motor drive current Ad. This motor drive current Ad serves as a control signal that drives and controls the electric motor 14B to control the steering angle of the steered rear wheels 5B, 5B. A second current sensor 109B provided in the second inverter 107B feeds back to the MCU 102 a motor current Ae, which is the current actually flowing through the electric motor 14B. The potential Pt between the second inverter 107B and the electric motor 14B is detected by a second phase potential detector 110B and fed back to the MCU 102 .

[0076] A motor rotation angle sensor 111 that detects a motor rotation angle Am of the electric motor 14B is electrically connected to the electric motor 14B. The motor rotation angle Am detected by the motor rotation angle sensor 111 is transmitted to the MCU 102. The motor rotation angle sensor 111 is also supplied with power P from the power supply circuit 106.

[0077] Next, Fig. 7 is a flowchart showing the flow of control of the rear wheels 5B, 5B after a primary failure of the electric motor 14B. Fig. 8 is a flowchart showing the flow of returning the rear wheels 5B, 5B to neutral in step S4 of Fig. 7.

[0078] First, as shown in FIG. 7, in step S1, an abnormality in the steering of the rear wheels 5B, 5B due to a primary failure of the electric motor 14B is detected.

[0079] Next, in step S2, the steering angle of the front wheels 5A, 5A when the steering of the rear wheels 5B, 5B is abnormal is obtained.

[0080] Then, in step S3, the rear wheels 5B, 5B are locked by the electromagnetic clutch 51.

[0081] Next, in step S4, the rear wheel 5B is returned to neutral.

[0082] Then, in step S5, the rear wheel 5B is locked by the electromagnetic clutch 51.

[0083] Next, the flow of returning the rear wheel 5B to neutral in step S4 of FIG. 7 will be described with reference to FIG.

[0084] First, in step S11, whether or not |AR1| ≥ AR0 is established is determined as a neutral return process execution determination (1). Here, "AR1" is the steering angle value of the rear wheels 5B when an abnormality is detected, and "AR0" is the steering angle threshold value of the rear wheels 5B for determining whether or not to perform the neutral return process. If |AR1| ≥ AR0 is not established, the flow ends.

[0085] If |AR1|≧AR0 is established in step S11, the process proceeds to step S12, where it is determined whether ΔAF<0 is established as a neutral return process execution determination (2). i＋１ |-|AF i It is expressed by the formula "AF i＋１ " is F i＋１ The steering angle of the front wheels 5A at the next moment is "AF i " is the steering angle of the front wheels 5A at a certain moment. Furthermore, step S12 is based on the premise that the vehicle is not in a dangerous state. This state is determined from vehicle state information, such as vehicle speed, yaw rate, lateral G, longitudinal G, ACC valve opening, parking brake, shift range, LSD, etc. If ΔAF<0 is not established, the process returns to the beginning of step S12.

[0086] If ΔAF<0 is established in step S12, the process proceeds to step S13, where the return of the rear wheel 5B to the neutral position is started.

[0087] After the rear wheel 5B starts to return to the neutral position, the electromagnetic clutch 51 is released in step S14.

[0088] Then, in step S15, the rear wheels 5B are steered toward the neutral position.

[0089] Next, in step S16, it is determined whether ΔAF>0 is satisfied to determine whether the neutral return process should be continued. Here, step S16 is premised on the premise that the neutral return process will be stopped if the vehicle changes into a dangerous state. If ΔAF>0 is not satisfied, the process proceeds to step S17, and the rear wheels 5B are locked by the electromagnetic clutch 51. After the rear wheels 5B are locked, the process returns to step S12.

[0090] If ΔAF>0 is established in step S16, the process proceeds to step S18, where it is determined whether |AR|≦AR0 is established as a neutral return completion determination. If |AR|≦AR0 is not established, the process returns to step S15.

[0091] If |AR|≦AR0 is established in step S18, the process proceeds to step S19, where the neutral return process for the rear wheel 5B is terminated.

[0092] 9 is a timing chart showing the control of the rear wheels 5B in the first embodiment. The control of the rear wheels 5B is carried out by the motor control device 15 executing a control program (not shown).

[0093] First, from time T1 to T2, the front wheel steering (AF) and rear wheel steering (AR) increase in phase. More specifically, when the front wheels 5A are steered further, that is, when the driver's steering operation is turned further away from the neutral position, the rear wheels 5B are also steered further in the same manner as the front wheels 5A. At this time, the rear wheel steering command increases by a large amount above 0, and the electromagnetic clutch 51 is turned off.

[0094] Then, when a primary failure of electric motor 14B occurs at time T2, the front wheel steering is increased from time T2 to T3 and then maintained at that position. Meanwhile, from time T2 to T3, the output to the system remaining after the failure of electric motor 14B becomes zero, causing the rear wheel steering command to become zero, and electromagnetic clutch 51 is turned on to maintain the steering angle (steered angle) of rear wheels 5B, locking rear wheels 5B; in other words, the rear wheel steering is maintained constant.

[0095] Next, from time T3 to T4, when the steering of the front wheels 5A is to be returned, that is, when the driver's steering operation results in a return steering operation signal in a direction approaching the neutral position, a control signal is output to the electric motor 14B so that the steering angle (AR) of the rear wheels 5B approaches the neutral position. More specifically, when the steering of the front wheels 5A is to be returned, the rear wheel steering command is decreased at time T3 and then gradually increased until time T4 to a value slightly smaller than 0. Also, from time T3 to T4, the electromagnetic clutch 51 is turned off (disengaged).

[0096] Then, when the driver's steering operation changes from a steering back direction before time T4 to a steering operation signal for maintaining the steering after time T4, the output to the system remaining after the failure of the electric motor 14B is again set to 0, and the electromagnetic clutch 51 is turned on to maintain the steering angle of the rear wheels 5B when the steering is maintained.

[0097] Furthermore, from time T4 to time T7, the front wheel steering based on the driver's steering operation is performed in the order of maintaining the steering, further steering, maintaining the steering, and steering back, as shown in FIG.

[0098] At time T5, the rear wheel steering command is decreased again and then increased to 0 toward time T6. Accordingly, the rear wheel steering is decreased to the neutral position. Also, from time T5 to T6, the electromagnetic clutch 51 is turned off (released).

[0099] After time T6, the rear wheel steering command is maintained at 0, and furthermore, the electromagnetic clutch 51 is turned on, thereby locking the rear wheels 5B, that is, the rear wheel steering is maintained constant.

[0100] Furthermore, the steering of the front wheels based on the driver's steering operation is maintained from time T7 to time T8. After time T8, when the driver's steering operation results in a steering operation signal that turns the wheel further away from the neutral position, the output to the system remaining after the failure of electric motor 14B remains at zero, and electromagnetic clutch 51 is maintained in the on state to maintain the steering angle of rear wheels 5B at the neutral position.

[0101] [Effects of the First Embodiment] As described above, in the first embodiment, the electromagnetic clutch 51 is separate from the electric motor 14B and is provided on the opposite side of the first reduction gear mechanism 25 from the electric motor 14B. Therefore, compared to when the electromagnetic clutch 51 is built into the electric motor 14B, the axial dimension of the motor shaft 30 is shorter by the dimension of the electromagnetic clutch 51 along the axial direction of the motor shaft 30. As a result, when the electric motor 14B rotates at high speed, the amplitude of vibration of the motor shaft 30 is reduced, and the generation of vibration is suppressed. Therefore, it is possible to suppress deterioration of the steering feel felt by the driver.

[0102] Furthermore, if the electromagnetic clutch 51 were located on the motor control device 15 side (see FIG. 9 of Patent Document 1), the motor shaft 30 would extend relatively long in a cantilevered manner on the connector portions 40b, 40c side of the second blocking member 40, making it more likely to vibrate during rotation of the motor shaft 30. This would increase the vibration of the connector portions 40b, 40c, and could result in the wires connected to the connector portions 40b, 40c breaking.

[0103] However, in this embodiment, the electromagnetic clutch 51 is provided on the opposite side of the first reduction gear mechanism 25 from the electric motor 14B, and the axial dimension of the motor shaft 30 is short, so the motor shaft 30 is less likely to vibrate. Therefore, the connectors 40b, 40c are also less likely to vibrate, which makes it possible to prevent breakage of the electric wires.

[0104] Furthermore, in this embodiment, the motor shaft 30 is rotatably supported by the first ball bearing B1 arranged on the first reduction gear mechanism 25 side and the second ball bearing B2 arranged on the sensor magnet 33 side. Therefore, compared to a case in which the electromagnetic clutch 51 is built into the electric motor 14B and furthermore, the electromagnetic clutch 51 is arranged between the first ball bearing B1 and the second ball bearing B2, the bearing-to-bearing distance of the motor shaft 30 between the first ball bearing B1 and the second ball bearing B2 can be shortened, and vibration during high-speed rotation of the electric motor 14B can be suppressed. Therefore, deterioration of the steering feel felt by the driver can also be suppressed.

[0105] Furthermore, in this embodiment, the first pulley 44 of the first reduction mechanism 25 is connected to the motor shaft 30 of the electric motor 14B. Furthermore, on the axial side of the motor shaft 30 opposite the electric motor 14B across the first reduction mechanism 25, a first coupling member 95 formed integrally with the first pulley 44 is connected to the motor-side end 52a of the clutch shaft 52 via an intermediate member 97 and a second coupling member 96. Therefore, the electromagnetic clutch 51, which is a relatively heavy load, is located on the opposite side of the first reduction mechanism 25 from the electric motor 14B. Therefore, when vibrations occur during high-speed rotation of the electric motor 14B, the vibrations are absorbed by the heavy electromagnetic clutch 51 via the first reduction mechanism 25. This makes it possible to suppress an increase in vibrations during high-speed rotation of the electric motor 14B.

[0106] In this embodiment, the first hole forming portion 20e of the first protruding portion 20c of the first housing 20 has a first elongated hole 20f as a first alignment mechanism for adjusting the tension of the endless belt 47 when the motor housing 27 is assembled to the first housing 20. A fixing bolt 23 is inserted into this first elongated hole 20f, and when the fixing bolt 23 moves within the first elongated hole 20f, the endless belt 47 is pulled by the first pulley 44 in a direction away from the rack bar 10B, thereby adjusting the tension of the endless belt 47. Therefore, the tension of the endless belt 47 can be easily adjusted by simply machining the first elongated hole 20f in the first hole forming portion 20e of the first protruding portion 20c of the first housing 20, without providing a new device for adjusting the tension of the endless belt 47.

[0107] Furthermore, in this embodiment, each third hole forming portion 59c of the base wall portion 59a of the brake mechanism housing 59 has a second elongated hole 59d formed therethrough along the axial direction of the clutch shaft 52, for use in adjusting the tension of the endless belt 47 of the first reduction mechanism 25. Similar to the first elongated hole 20f, the tension of the endless belt 47 of the first reduction mechanism 25 can be adjusted by moving the fixing bolt 91 through this second elongated hole 59d, and further, the electric motor 14B and the electromagnetic clutch 51 can be maintained coaxially.

[0108] In this embodiment, the brake mechanism-side end 44a of the first pulley 44 and the motor-side end 52a of the clutch shaft 52 are connected via a coupling 94. When adjusting the tension of the endless belt 47 using the first elongated hole 20f described above, it is difficult to adjust the axis of the motor shaft 30 relative to the first housing 20, resulting in a problem of misalignment of the axis. Similarly, when adjusting the tension of the endless belt 47 using the second elongated hole 59d described above, it is difficult to adjust the axis of the clutch shaft 52 relative to the second housing 22, resulting in a problem of misalignment of the axis. Therefore, by connecting the brake mechanism-side end 44a of the first pulley 44 and the motor-side end 52a of the clutch shaft 52 via the coupling 94, it is possible to absorb the misalignment of the axes of the motor shaft 30 and the clutch shaft 52 and align the motor shaft 30 and the clutch shaft 52 in the axial direction of the motor shaft 30.

[0109] Furthermore, in this embodiment, the motor control device 15 is provided in the motor housing 27, while the brake mechanism control device 77 is provided in the brake mechanism housing 59. Therefore, the motor control device 15 and the motor housing 27 can be assembled together and then easily attached to the first housing 20, and the brake mechanism control device 77 and the brake mechanism housing 59 can be assembled together and then easily attached to the second housing 22.

[0110] Furthermore, in this embodiment, if the abnormality determination unit determines that a primary malfunction has occurred, the brake mechanism control device 77 controls the electric motor 14B and the electromagnetic clutch 51 to maintain the steering angle of the steered rear wheels 5B, 5B, in accordance with external command signals, which in this embodiment are the steering angle signal Ar, steering torque signal Tr, and displacement signal Dr. For example, as shown from time T2 to time T3 in FIG. 9 , when the front wheels are turned further and then maintained at a constant steering angle, the rear wheel steering command becomes zero, and the electromagnetic clutch 51 is turned on to maintain the steering angle (steering angle) of the rear wheels 5B, thereby maintaining the rear wheel steering constant. This prevents deterioration of steering performance that is contrary to the driver's intention, improving vehicle safety. Therefore, the driver's steering feel can be improved.

[0111] Furthermore, in this embodiment, as shown after time T6 in Figure 9, when the rear wheel steering returns to neutral after a primary failure of the electric motor 14B, the electromagnetic clutch 51 is turned on to lock the rear wheels 5B. This allows the amount of control in the lateral direction of the vehicle to be made nearly equal by steering the front wheels 5A, thereby preventing deterioration in the steerability of the steering system. [Second Embodiment] Figure 10 is a timing chart showing the control of the rear wheels 5B in the second embodiment.

[0112] The timing chart of the second embodiment differs from the timing chart of FIG. 9 of the first embodiment in the rear wheel steering commands from time T2 to time T3 and from time T4 to time T5.

[0113] From time T2 to time T3, the front wheel steering increases and then is maintained, i.e., when the driver's steering operation turns the wheel away from the neutral position and then produces a steering operation signal to maintain the steering, a control signal is output to electric motor 14B to move the steering angle of rear wheels 5B toward the neutral position, and electromagnetic clutch 51 is controlled to maintain the steering angle of rear wheels 5B. More specifically, from time T2 to time T3, the rear wheel steering command is decreased to turn on electromagnetic clutch 51. At this time, the rear wheel steering command is set to be smaller than the force of electromagnetic clutch 51. Therefore, the force of electromagnetic clutch 51 from time T2 to time T3 is weaker than in the first embodiment.

[0114] Also, from time T4 to time T5, the rear wheel steering command is maintained at a value smaller than 0 but larger than the rear wheel steering command from time T2 to time T3. [Effects of the Second Embodiment] In the second embodiment, as shown in time T2 to time T3 in FIG. 9, the rear wheel steering is maintained constant when the front wheel steering is further turned and then maintained. This prevents deterioration of steering performance that is contrary to the driver's intention, improving vehicle safety. Therefore, the driver's steering feel can be improved. [Third Embodiment] FIG. 11 is a schematic vertical cross-sectional view of a rear wheel side steering device 1B of a third embodiment.

[0115] The rear wheel side steering device 1B of the third embodiment is configured by replacing the first reduction mechanism 25 and ball screw mechanism 26 of the rear wheel side steering device 1B of the first embodiment with a second reduction mechanism 112 and a rack and pinion mechanism 113, which is a rotary-to-linear motion conversion mechanism.

[0116] The second reduction gear mechanism 112 includes a worm shaft 114 and a worm wheel 115 that meshes with a worm formed on the outer periphery of the worm shaft 114. Of both axial ends 114a, 114b of the worm shaft 114, the axial end 114a located on the electric motor 14B side is connected to the other axial end 30b of the motor shaft 30 via a motor coupling 94. An electromagnetic clutch 51 is attached to the axial end 114b of the worm shaft 114. The worm wheel 115 is fixed to the outer periphery of a second steering shaft 116.

[0117] The rack and pinion mechanism 113 has a pinion (not shown) formed on the outer periphery of the second steering shaft 116 and a rack (not shown) formed on the outer periphery of the rack bar 10B that meshes with the pinion. [Effects of the Third Embodiment] In the third embodiment, the electromagnetic clutch 51 is located on the opposite side of the motor coupling 94 from the electric motor 14B, thereby shortening the axial dimension of the motor shaft 30. When the electric motor 14B rotates at high speed, the amplitude of vibration of the motor shaft 30 is reduced, thereby suppressing the generation of vibration. Therefore, it is possible to suppress deterioration in the steering feel experienced by the driver.

[0118] In the above embodiments, examples have been described in which the present invention is applied to a vehicle equipped with a steering system in which the front-wheel steering device 1A and the rear-wheel steering device 1B are not mechanically connected, but the present invention may also be applied to a vehicle equipped with a similar steering system of another type, for example, a steer-by-wire steering system.

Claims

A steering device provided in a vehicle, a motor that applies a steering force to the steered wheels of the vehicle; a motor shaft extending from the motor; a reduction mechanism connected to the motor shaft and configured to reduce the rotational speed of the motor before transmitting the rotational motion; a rotary-to-linear motion conversion mechanism that converts the rotary motion transmitted from the reduction mechanism into linear motion; a movable member connected to the rotary-to-linear motion conversion mechanism for steering the steered wheels; a braking mechanism that is provided on the opposite side of the speed reduction mechanism from the motor and that is capable of exerting a braking force so as to limit the movement of the movable member at any steering position; A steering device having 　 The steering device according to claim 1, The motor includes a motor housing, a rotor connected to the motor shaft, and a stator coil. the motor shaft extends to a side opposite to the reduction mechanism side with respect to the rotor, and a sensor magnet is provided at an end opposite to the reduction mechanism side; The motor housing supports the motor shaft and is provided with a first bearing disposed on the reduction mechanism side and a second bearing disposed on the sensor magnet side. 　 The steering device according to claim 2, the reduction mechanism includes a first pulley attached to the motor shaft; the braking mechanism includes a braking mechanism housing, a shaft member to which the output of the motor is transmitted, a first clutch member connected to the braking mechanism housing, and a second clutch member connected to the shaft member, a brake mechanism side end of the first pulley and a motor side end of the shaft member are connected to each other; A steering device that restricts relative rotation of the shaft member with respect to the brake mechanism housing by engaging the first clutch member and the second clutch member. 　 The steering device according to claim 1, The motor includes a motor housing, a rotor connected to the motor shaft, and a stator coil. the motor housing covers a portion of the motor shaft; the reduction mechanism includes a first pulley attached to the motor shaft, a second pulley disposed on an outer periphery of the movable member, and an endless belt wound around the first pulley and the second pulley, A steering device having a first housing that accommodates a portion of the movable member and at least a portion of the reduction mechanism and is equipped with a first alignment mechanism for adjusting the tension of the endless belt when assembling the motor housing. 　 The steering device according to claim 4, A steering device, wherein the first aligning mechanism is an elongated hole through which a fixing bolt is inserted. 　 The steering device according to claim 5, the braking mechanism includes a braking mechanism housing, a shaft member to which the output of the motor is transmitted, a first clutch member connected to the braking mechanism housing, and a second clutch member connected to the shaft member, A steering device having a second housing that houses a portion of the movable member and at least a portion of the reduction mechanism and is equipped with a second alignment mechanism for adjusting the tension of the endless belt when the brake mechanism housing is assembled. 　 The steering device according to claim 4 or 6, A steering device, wherein the brake mechanism side end of the first pulley and the motor side end of the shaft member are connected via a coupling. 　 The steering device according to claim 1, The motor includes a motor housing, a rotor connected to the motor shaft, and a stator coil. the braking mechanism includes a braking mechanism housing, a shaft member to which the output of the motor is transmitted, a first clutch member connected to the braking mechanism housing, and a second clutch member connected to the shaft member, a motor control device that controls the motor and a brake mechanism control device that controls the brake mechanism are separate devices; the motor control device is provided in the motor housing, The braking mechanism control device is provided in the braking mechanism housing. 　 A steering device provided in a vehicle, a motor that applies a steering force to the steered wheels of the vehicle; a motor shaft extending from the motor; a reduction mechanism connected to the motor shaft and configured to reduce the rotational speed of the motor before transmitting the rotational motion; a rotary-to-linear motion conversion mechanism that converts the rotary motion transmitted from the reduction mechanism into linear motion; a movable member connected to the rotary-to-linear motion conversion mechanism for steering the steered wheels; a braking mechanism capable of exerting a braking force so as to limit the movement of the movable member at any steering position, the braking mechanism including a braking mechanism housing, a shaft member to which the output of the motor is transmitted, and an electromagnetic clutch that restricts the relative rotation of the shaft member with respect to the braking mechanism housing; a control device for controlling the motor and the electromagnetic clutch, The control device A control signal for controlling the steering angle of the steered wheels is output to the motor based on an external command signal, and the presence or absence of an abnormality occurring within the control device is determined. If an abnormality is determined, controlling the electromagnetic clutch in accordance with the command content of the external command signal to maintain the steering angle of the motor and the steered wheels; Steering device.

10. The steering device according to claim 9, The steering device, wherein the external command signal is a steering operation signal from a steering input device provided in the vehicle and receiving a steering operation from a driver.

10. The steering device according to claim 9, The motor includes a motor housing, a rotor connected to the motor shaft, and a stator coil. the stator coil includes a first stator coil and a second stator coil provided electrically separated from the first stator coil, the control device includes a first control circuit, a second control circuit, a first microprocessor, and a second microprocessor; the first control circuit includes a first inverter; the second control circuit includes a second inverter; the first inverter controls the supply of power to the first stator coil; The second inverter controls the power supply to the second stator coil. 　 The steering device according to claim 10, When the driver's steering operation is a steering operation signal for turning the vehicle further away from the neutral position or for maintaining the steering position, a steering device that controls the electromagnetic clutch so as to set the output to the motor to 0 and maintain the steering angle of the steered wheels; 　 The steering device according to claim 10, When the steering operation by the driver becomes a steering operation signal in a direction approaching a neutral position, the control device a steering device that outputs a control signal to the motor so that the steering angle of the steered wheels approaches a neutral position. 　 A steering device according to claim 13, When the steering operation by the driver becomes a steering operation signal for maintaining the steering after the steering operation in the returning direction, a steering device that sets the output to the motor to 0 again and controls the electromagnetic clutch to maintain the steering angle during the holding steering.

15. The steering device according to claim 14, When the driver's steering operation becomes a steering operation signal for turning the vehicle further in the opposite direction from the neutral position, The steering device again sets the output to the motor to 0 and controls the electromagnetic clutch to maintain the steering angle of the steered wheels at a neutral position. 　 The steering device according to claim 10, When the driver's steering operation is a steering operation signal for turning the vehicle further away from the neutral position or for maintaining the steering position, a steering device that outputs a control signal to the motor so that the steering angle of the steered wheels approaches a neutral position, and controls the electromagnetic clutch to maintain the steering angle of the steered wheels. 　 A control method for a steering device provided in a vehicle, comprising: a motor that applies a steering force to the steered wheels of the vehicle; a motor shaft extending from the motor; a reduction mechanism connected to the motor shaft and converting rotational motion of the motor into linear motion; a rotary-to-linear motion conversion mechanism that converts the rotary motion transmitted from the reduction mechanism into linear motion; a movable member connected to the rotary-to-linear motion conversion mechanism for steering the steered wheels; a braking mechanism capable of exerting a braking force so as to limit the movement of the movable member at any steering position, the braking mechanism including a braking mechanism housing, a shaft member to which the output of the motor is transmitted, and an electromagnetic clutch that restricts the relative rotation of the shaft member with respect to the braking mechanism housing; a control device for controlling the motor and the electromagnetic clutch, The control device A control signal for controlling the steering angle of the steered wheels is output to the motor based on an external command signal, and the presence or absence of an abnormality occurring within the control device is determined. If an abnormality is determined, controlling the electromagnetic clutch in accordance with the command content of the external command signal to maintain the steering angle of the motor and the steered wheels; A method for controlling a steering device. 　 A control program that causes the control device to execute the steering device control method according to claim 17.

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