JP2016055796A - Rear wheel steering control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rear wheel steering control device which can have an improved vehicle layout performance.SOLUTION: On the basis of a result of detection of a steering angle sensor AS for detecting a steering angle of a steering wheel SW, a steering angle and so one of a rear side steering wheel RS is calculated in a control unit CU, drive of a hollow motor 30 is controlled by a control current supplied from a battery BT on the basis of the calculation result and a steering torque is inputted to a rear side steering control device RM, whereby a piston 16 of a power cylinder is moved in an axial direction. Thus, a sector shaft 17 engaging with the piston 16 is rotated, and a third pitman arm A3 connected to the sector shaft 17 is oscillated in a vehicle width direction thereby enabling steering of the rear side steering wheel RS.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a rear wheel steering control device that can control a rotary valve used for hydraulic pressure control by a motor, among rear wheel steering control devices that control rear wheel steering by hydraulic pressure.

  As a conventional rear wheel steering control device, for example, a device described in Patent Document 1 below is known.

  In brief, the rear wheel steering control device includes a hydraulic cylinder for assisting steering of the rear wheel, a hydraulic pump for selectively supplying hydraulic oil to the hydraulic chamber of the hydraulic cylinder via a predetermined switching valve, and , And the solenoid valve is controlled based on a control current from the ECU, thereby enabling hydraulic control of the hydraulic cylinder, that is, steering control of the rear wheels.

JP 2001-287656 A

  However, in the conventional rear wheel steering control device, since the hydraulic pump corresponding to the actuator is shared with the front wheel steering control, it is necessary to extend hydraulic piping or the like from the front wheel side. In that respect, it was insufficient.

  The present invention has been devised in view of the actual situation of the conventional rear wheel steering control device, and an object thereof is to provide a rear wheel steering control device capable of improving the vehicle layout.

  The present invention relates to a steering shaft composed of an input shaft that rotates in response to a rotational input, an output shaft connected to the input shaft via a torsion bar, and a steering housing that rotatably supports the steering shaft. A piston that is slidably accommodated in the steering housing, and that divides the interior of the steering housing into a first pressure chamber and a second pressure chamber, and is provided in the steering housing, the input shaft, A rotary valve that selectively supplies hydraulic fluid supplied from an external pump to the first pressure chamber and the second pressure chamber in accordance with relative rotation with the output shaft; and rotation of the output shaft to control rotation of the piston. A ball screw mechanism for converting to axial movement; a transmission mechanism for transmitting axial movement of the piston to a rear steering wheel of a multi-axis steering vehicle; and an input side provided on an outer peripheral side of the input shaft. The motor element is composed of a motor rotor that rotates integrally with the motor rotor, a motor stator provided on the outer peripheral side of the motor rotor, and a motor housing that accommodates the motor element. A rear wheel steering control device comprising: a hollow brushless motor that controls rotation of a shaft.

  According to the present invention, the actuator that rotationally drives the input shaft is a brushless motor, so that it is not necessary to extend a hydraulic pipe or the like from the front wheel side to perform power transmission, and vehicle layout can be improved.

  Further, since the brushless motor is configured as a so-called hollow motor, the apparatus can be miniaturized and the vehicle layout can be further improved. It is characterized by having.

1 is a schematic view of a multi-axis steering vehicle to which a rear wheel steering control device according to the present invention is applied. FIG. 2 is a longitudinal sectional view of the rear wheel steering control device shown in FIG. 1 showing the first embodiment of the rear wheel steering control device according to the present invention. FIG. 3 is a cross-sectional view taken along line AA in FIG. 2, illustrating a neutral state of the input shaft. FIG. 3 is a cross-sectional view taken along the line AA in FIG. It is a longitudinal cross-sectional view of the rear-wheel steering control apparatus showing 2nd Embodiment of the rear-wheel steering control apparatus which concerns on this invention, and represented the neutral state of the piston. FIG. 6 is a view corresponding to FIG. 5 illustrating a state in which the input shaft is rotated 20 ° to the right. FIG. 6 is a view corresponding to FIG. 5 illustrating a state where the input shaft is rotated 20 ° to the left. It is a principal part expansion equivalent figure of Drawing 2 concerning other examples of a 2nd embodiment of the present invention. FIG. 6 is a longitudinal sectional view of a rear wheel steering control device representing a third embodiment of the rear wheel steering control device according to the present invention and representing a neutral state of an input shaft. FIG. 10 is a view corresponding to FIG. 9 showing a state where the input shaft is rotated 20 ° to the right. FIG. 10 is a view corresponding to FIG. 9 showing a state where the input shaft is rotated 20 ° to the left. FIG. 10 is a longitudinal sectional view of a rear wheel steering control device representing a fourth embodiment of the rear wheel steering control device according to the present invention and showing a neutral state of an input shaft. FIG. 13 is a view corresponding to FIG. 12 illustrating a state where the input shaft is rotated 20 ° to the right. FIG. 13 is a view corresponding to FIG. 12 showing a state where the input shaft is rotated 20 ° to the left.

  Hereinafter, embodiments of a rear wheel steering control device according to the present invention will be described with reference to the drawings. In each of the following embodiments, an example is shown in which this rear wheel steering control device is applied as an integral power steering device for a multi-axis steering vehicle such as a large truck.

  FIG. 1 is a schematic view of a multi-axis steering vehicle to which a rear wheel steering control device according to the present invention is applied.

  The multi-axle steering vehicle includes a first front steering wheel FS1 and a second front steering wheel FS2 that are two-axis front steering wheels linked to a front wheel steering control device FM, and a first biaxial rear drive wheel. A rear drive wheel RF1 and a second rear drive wheel RF2, and a one-axis rear steered wheel RS that is arranged at the rearmost part and is linked to the rear wheel steering control device RM to provide a smooth turn. ing.

  The front wheel steering control device FM is a well-known integral type hydraulic power steering device, and is stored in the first reservoir tank T1 by an external first pump PF driven by power transmitted from the engine. The hydraulic fluid is pumped and selectively supplied to a pair of pressure chambers of a hydraulic cylinder (not shown) configured inside the apparatus, so that this hydraulic pressure is input via the steering wheel SW. The driver's steering torque is assisted.

  That is, when a piston (not shown) that separates the pair of pressure chambers moves in the axial direction based on the steering torque from the steering wheel SW and the assist torque by the hydraulic pressure, the piston moves in the axial direction. When the sector shaft SS meshing with the piston rotates and the first pitman arm A1 connected to the sector shaft SS swings in the left-right direction in FIG. 1, the first front steering wheel FS1 is steered. It has come to be. Further, the second front steering wheel FS2 is linked to the first pitman arm A1 via the second pitman arm A2, and the second pitman arm A2 swings as the first pitman arm A1 swings. The first front side steering wheel FS1 is steered in conjunction with the first front side steering wheel FS1.

  The rear wheel steering control device RM is a well-known integral type hydraulic power steering device configured in the same manner as the front wheel steering control device FM described above. The rear wheel steering control device RM is not directly linked to the front wheel steering control device FM but is steered by a hollow motor 30 that is driven and controlled by the electronic control unit CU based on the steering angle of the front wheel steering control device FM. Torque is input, and hydraulic fluid stored in the second reservoir tank T2 is pumped by an external second pump PR that is driven and controlled by the electronic control unit CU based on the steering torque. Is configured to be assisted.

  That is, the rear wheel steering control device RM calculates the steering angle of the rear steering wheel RS in the electronic control unit CU based on the detection result of the steering angle sensor AS that detects the steering angle input by the steering wheel SW. The hollow motor 30 is driven and controlled by the control current supplied from the battery BT based on the calculation result, and the steering torque is input to the rear wheel steering control device RM. A third pitman arm connected to the sector shaft 17 is rotated by a sector shaft 17 meshing with the piston 16 (see FIG. 2), which is not shown in the drawing, in the axial direction based on the torque. The rear steering wheel RS is steered by swinging A3 in the left-right direction in FIG.

  2 to 4 show a first embodiment of a rear wheel steering control device according to the present invention. This rear wheel steering control device RM has one end side connected to a connection member 37 of a hollow motor 30 as shown in FIG. The input shaft 11 is linked and the other end side is accommodated and arranged in the main housing 13 as a steering housing, and the whole is accommodated and arranged in the main housing 13, and one end side is connected to the other end side of the input shaft 11. An output shaft 12 connected to the output shaft 12, a sector shaft 17 linked to a rear steering wheel RS (not shown) and steering in accordance with the axial movement of the piston 16 provided on the outer periphery of the other end of the output shaft 12, The main housing 13 has a first pressure chamber P1 and a second pressure chamber P2 which are a pair of pressure chambers separated by a piston 16, and generates assist torque to assist steering torque. The hydraulic cylinder 18 is provided between the shafts 11 and 12 and the hydraulic fluid supplied from the second pump PR (not shown) according to the relative rotation of the shafts 11 and 12 is supplied to the first and second pressure chambers. A rotary valve 19 which is selectively supplied to P1 and P2 and a rotor 31 which will be described later are provided so as to be fitted to the outer periphery of one end side of the input shaft 11, and rear steering is performed by applying a steering torque to the input shaft 11. A hollow motor 30 for steering the wheel RS and a neutral urging mechanism 40 that is linked to one end of the input shaft 11 and urges the input shaft 11 toward the neutral position.

  In the rear wheel steering control device RM, the input shaft 11 and the output shaft 12 are connected by the torsion bar 10 to constitute the steering shaft of the present invention, and the sector shaft 17 and the third pitman arm linked thereto are configured. The transmission mechanism of the present invention is constituted by A3.

  The main housing 13 has a cylindrical shape that is open at one end and closed at the other end, and closes the first main housing 14 used for the configuration of the pressure chambers P1 and P2 and the one end opening of the first main housing 14. And a second main housing 15 that is a valve housing that accommodates the rotary valve 19 therein, and the two housings 14 and 15 are not shown in the drawing and are arranged at predetermined circumferential positions. It is fastened with a plurality of bolts.

  The first main housing 14 includes a cylinder component 14a formed along the Z1 direction of the piston 16 (hereinafter referred to as a first axis), a cylinder component 14a that is substantially orthogonal to the cylinder component 14a, and A shaft housing portion 14b formed so that a part thereof faces the cylinder constituting portion 14a, and the other end side of the output shaft 12 and the output shaft 12 are provided inside the cylinder constituting portion 14a. A piston 16 is provided on the outer peripheral side so as to be relatively movable via a ball screw mechanism 20, and is separated into a first pressure chamber P 1 on one end side and a second pressure chamber P 2 on the other end side by the piston 16. On the other hand, one end side is linked to the piston 16 and the other end side is linked to the rear steering wheel RS (not shown) via the third pitman arm A3 (not shown) inside the shaft housing portion 14b. Kuta shaft 17 is accommodated arranged.

  Here, teeth 16a, 17a that can mesh with each other are provided on the outer periphery of the piston 16 and the outer periphery of the sector shaft 17, respectively. As a result, the sector shaft 17 is rotated, whereby the third pitman arm A3 (not shown) is pulled in the vehicle body width direction (left-right direction in FIG. 1), thereby changing the direction of the rear steering wheel RS (not shown). It has a configuration. At this time, the working fluid in the second pressure chamber P2 is guided to the shaft accommodating portion 14b, thereby being used for lubrication between the tooth portions 16a and 17a.

  On the inner peripheral side of the second main housing 15, a shaft insertion hole 15 a provided in a step-reduced shape along the first axis Z <b> 1 direction is formed to penetrate from the one axial end side to the other end side. The other end side of the input shaft 11 is inserted into the shaft insertion hole 15a, and one end side of the output shaft 12 in which the torsion bar 10 is accommodated on the outer periphery of the other end side of the input shaft 11 is arranged in an overlapping manner. A rotary valve 19 constituted by overlapping portions of the shafts 11 and 12 is accommodated.

  Further, the reduced diameter portion on the other end side of the shaft insertion hole 15a is connected to a hydraulic pressure source (not shown) through an introduction passage (not shown) and provided on one end side (the overlapping portion) of the output shaft 12. The introduction port 21 for introducing hydraulic fluid from the outside through the first supply / discharge passage L1 and the supply of hydraulic fluid to the second pressure chamber P2 through the second supply / discharge passage L2 extending radially outward. A supply / discharge port 22 used for supply and discharge and a discharge port 23 connected to a reservoir tank (not shown) through a discharge passage (not shown) and used to discharge the working fluid in the pressure chambers P1 and P2 are respectively predetermined. It is provided at an axial position.

  When the steering is neutral, the rotary valve 19 is maintained in an open state so that the introduction port 21 and the discharge port 23 communicate with each other, and in response to the relative rotation of the input shaft 11 and the output shaft 12 generated during steering, The valve is opened and closed in the other direction. That is, when the input shaft 11 is steered to one side by the hollow motor 30, the hydraulic fluid pumped from the second pump PR (not shown) passes through the rotary valve 19 to the one pressure chamber P1 corresponding to the steering direction. , P2 and the hydraulic fluid (surplus) corresponding to the supply amount from the other pressure chambers P1, P2 is discharged to the second reservoir tank T2 (not shown). In this way, the piston 16 is driven with the fluid pressure, and assist torque based on the fluid pressure acting on the piston 16 is applied to the sector shaft 17.

  The hollow motor 30 is a so-called three-phase AC brushless motor, and is a rotor 31 that is a motor rotor that is externally fitted to the outer peripheral portion of the input shaft 11 facing the outside of the main housing 13 so as to be integrally rotatable with a key connection described later. And a stator 32 that is a motor stator disposed on the outer peripheral side of the rotor 31 with a predetermined minute radial gap therebetween, and this motor element is accommodated, and one end side is attached to the main housing 13. A substantially cylindrical motor housing 33 to be mounted and fixed; a first bearing BR1 and a second bearing BR2 which are housed inside the motor housing 33 and rotatably support one end side and the other end side of the rotor 31; And a resolver 36 that detects the rotational position of the input shaft 11.

  The motor housing 33 is configured to be divided into two parts by a predetermined metal material such as an aluminum alloy, and the first motor housing 34 is provided with one end side for receiving the motor element and the other end side for receiving the resolver 36. The first motor housing 34 includes a second motor housing 35 that closes the opening on one end side and serves to connect the motor housing 33 to the main housing 13.

  The first motor housing 34 is provided with a motor element accommodating portion 34a for accommodating the motor element on one end side, and the resolver accommodating portion 34b for accommodating the resolver 36 on the other end side. A second motor housing 35 is fastened to the opening at the other end of the first motor housing 34 by a plurality of bolts B1 so as to close the resolver housing portion 34b. The first motor housing 34 is fastened to one end surface of the second main housing 15 by a plurality of bolts B2.

  The rotor 31 is fitted and fixed to the outer peripheral portion of the input shaft 11 protruding to the outside of the main housing 13, and is connected to the input shaft 11 so as to rotate integrally therewith, and the connection member 37. And a plurality of magnets 31b bonded to the outer periphery of the rotor core 31a. The rotor 31 may have a configuration like an IPM motor in which the plurality of magnets 31b are embedded in the rotor core 31a.

  The connecting member 37 has an inner periphery on an input shaft side engaging portion in which a key 25 as a metal piece is press-fitted and fixed in a groove-like recess 39a formed in the outer peripheral surface of the input shaft 11 along the axial direction. The rotor side engagement part which consists of the keyway 37a notched in the part is engaged, and it is fixed by fitting to the outer periphery of the input shaft 11 with what is called key coupling.

  The stator 32 is formed by laminating a plurality of stator cores 32a into a circular shape, and is press-fitted or shrink-fitted and fixed to the motor element accommodating portion 34a, and teeth projecting from the inner peripheral portion of each stator core 32a. A three-phase (u-phase, v-phase, w-phase) stator coil SC is wound around (not shown).

  The neutral urging mechanism 40 is fastened to the outer peripheral area of the shaft insertion hole 34c through which the input shaft 11 is inserted on one end side of the first motor housing 34 by a plurality of bolts B3, and extends along the radial direction of the first axis Z1. A substantially cylindrical housing 41 that extends and is housed on one end side corresponding to the fixed end side of the housing 41 and is fitted to the outer periphery of one end of the input shaft 11 so that it can rotate integrally with the input shaft 11. A bobbin 42 configured in the above manner, a cable 43 configured to be wound around the outer periphery of the bobbin 42 as the bobbin 42 is rotated, and one end side of the bobbin 42 being rotated. A flange-shaped first seating plate 44 extending to the inner periphery on one end side is disposed opposite to the first seating plate 44 on the other end side of the housing 41 and fixed to the other end side of the cable 43. And a coil spring 46 as a biasing member that is elastically mounted between the two seating plates 44, 45 and biases the other end of the cable 43 away from the bobbin 42. .

  The housing 41 is disposed on one end side and fixed to the first motor housing 34, and is provided with a first housing 47 for housing the bobbin 42, and a second housing 48 disposed on the other end side for housing the coil spring 46. And are integrally configured by being fastened by a plurality of bolts B4 via flange-like connecting portions 47a and 48a provided at opposing portions of the both 47 and 48, respectively.

  The first housing 47 is configured to form an L-shaped space having an inverted vertical cross section, and one end portion of the input shaft 11 enters the inside through a first opening 47b that opens to the first motor housing 34 side. The bobbin 42 is extrapolated to the one end. Further, the other end side of the cable 43 faces the inside of the second housing 48 through a second opening 47 c that opens to the second housing 48 side.

  The second housing 48 is formed in a substantially bottomed cylindrical shape, and the other end side of the cable 43 faces the inside through an opening on one end side, and the second seating plate 45 is at the other end when the cable 43 is longest. The coil spring 46 can be elastically supported by abutting (elastically contacting) the bottom 48b on the side.

  The bobbin 42 is formed with a pair of flange portions 42a and 42a at both ends, and a winding portion 42b used for winding the cable 43 at an intermediate portion extends in the axial direction toward the hollow motor 30 side. Thus, it is formed in a substantially conical taper shape whose outer diameter gradually decreases. Here, the cable 43 is fixed to the maximum diameter portion 42c of the bobbin 42, and is wound from the maximum diameter portion 42c to the minimum diameter portion 42d side during winding.

  The first seating plate 44 is formed in a substantially cylindrical support portion 44a set smaller than the inner diameter of the coil spring 46, and is formed in a flange shape at the outer end portion of the support portion 44a. The fixing portion 44b is fixed in a state of being sandwiched between the connecting portions 47a and 48a of the housings 47 and 48, and is fixed to both the housings 47 and 48 by the bolts B4. With this configuration, the first seating plate 44 seats and supports one end of the coil spring 46 with the inner peripheral portion of the fixing portion 44b while supporting the inner periphery of the one end portion of the coil spring 46 with the support portion 44a. It has become.

  The second seating plate 45 is formed in a substantially bottomed cylindrical shape, and supports the outer periphery of the other end of the coil spring 46 by the peripheral wall 45a, while the other end of the coil spring 46 is supported by the outer peripheral portion of the bottom wall 45b. Is designed to support seating. A cylindrical cable connecting portion 45c extends toward the peripheral wall 45a at the center of the bottom wall 45b of the second seating plate 45, and the cable 43 is connected to the distal end of the cable connecting portion 45c. The other end is connected.

  Hereinafter, the operation of the neutral urging mechanism 40 will be described with reference to FIGS. 3 and 4 are cross-sectional views taken along line AA of the neutral urging mechanism 40 shown in FIG. 2, and FIG. 3 shows a state in which the input shaft 11 is in the neutral position. Indicates a state in which the input shaft 11 is rotated once in the left direction.

  First, as shown in FIG. 3, when the input shaft 11 is in the neutral position, one end of the cable 43 is not wound around the bobbin 42, and the other end is second seated by the biasing force of the coil spring 46. The state where the outer bottom surface of the plate 45 is in contact with the inner bottom surface of the second housing 48 is maintained.

  Subsequently, as shown in FIG. 4, when the input shaft 11 is steered in one direction (leftward in the present embodiment), one end side of the cable 43 is wound in the steering direction, and the other end is wound by this winding amount. The side pulls the second seating plate 45 toward the bobbin 42 against the biasing force of the coil spring 46, and the coil spring 46 contracts and deforms by the amount of movement L1 of the second seating plate 45.

  Here, in this embodiment, since the bobbin 42 is formed in a conical taper shape, there is an advantage that the torque related to winding and rewinding of the cable 43 can be adjusted by changing the outer diameter of the taper.

  In such a configuration, since the cable 43 is connected to the maximum diameter portion 42c of the bobbin 42, a relatively large winding torque can be secured near the neutral position of the input shaft 11, so that the torque generated by the coil spring 46 is reduced. Therefore, the coil spring 46 can be reduced in size, and the neutral urging mechanism 40 can be reduced in size.

  In addition, after the winding of the cable 43 is started, the winding portion of the cable 43 moves toward the small diameter side as the cable 43 is wound. 43 can be wound and unwound more smoothly.

  Subsequently, in the steering state of the rear steering wheel RS, for example, when an abnormality occurs in the electrical system such as the hollow motor 30 has failed, the steering force by the hollow motor 30 does not act on the input shaft 11 while being neutral. On the basis of the biasing force generated by the contraction of the coil spring 46 in the biasing mechanism 40, the steering torque acts in a direction in which the input shaft 11 is returned to the neutral position side (hereinafter abbreviated as “return direction”).

  Then, the input shaft 11 has the steering torque generated by the neutral urging mechanism 40 and the assist torque generated by the relative rotation with the output shaft 12 accompanied by torsional deformation of the torsion bar 10 based on the steering torque. The two seating plates 45 rotate in the return direction until they are brought into contact with the bottom wall 48b of the second housing 48 and restricted in movement. As a result, the input shaft 11 is returned to the neutral position and held at the neutral position, and the rear steering wheel RS is returned to the neutral position and held at the neutral position.

  As described above, in the rear wheel steering control device RM according to the present embodiment, the actuator that rotationally drives the input shaft 11 is configured as a brushless motor (hollow motor 30) that is independent from the front wheel side. There is no need to extend the pressure piping or the like to transmit power, and the vehicle layout can be improved.

  In addition, since the brushless motor is configured as the hollow motor 30, the rear wheel steering control device RM can be further miniaturized, and the vehicle layout of the device RM can be further improved.

  Further, by providing the rear wheel steering control device RM with a neutral urging mechanism 40 that serves for neutral return of the rear steering wheel RS, for example, when the hollow motor 30 has failed, the rear steering wheel RS is made neutral. As a result of being able to return to the position and hold it in the neutral position, compared to the case where the rear steering wheel RS is maintained in the steering state or the free state, the traveling of the vehicle and the subsequent steering are stabilized. Can be made.

  Moreover, in the neutral urging mechanism 40 according to the present embodiment, the input shaft 11 is urged toward the neutral position side, thereby being accompanied by a hydraulic pressure assist based on the relative rotation of the input shaft 11 and the output shaft 12. Since the rear steering wheel RS can be steered, the biasing force applied to the input shaft 11 is sufficient to generate torsional deformation of the torsion bar 10, and the biasing force of the coil spring 46 is minimized. It becomes possible to limit to the limit. As a result, there is an advantage that the coil spring 46 is miniaturized and, in turn, the neutral urging mechanism 40 is miniaturized.

  In addition, since the second pump PR used for hydraulic assist of the rear wheel steering control device RM is driven by the electric motor (not shown) instead of the engine power, the engine driving force is set to the second. It is not necessary to provide a driving force transmission mechanism for transmitting to the pump PR, and the vehicle layout is improved.

  Basically, it is necessary to introduce the hydraulic fluid by the second pump PR when the piston 16 is operated in accordance with the steering by the hollow motor 30. For this reason, in the present embodiment, an electric motor (not shown) that drives the second pump PR is driven and controlled as the hollow motor 30 is driven, that is, the two motors are linked. Thus, the power consumption of the electric motor (not shown) can be reduced.

  5 to 7 show a second embodiment of the rear wheel steering control device according to the present invention, in which the specific configuration of the neutral urging mechanism 40 in the first embodiment is changed. In the following, only the configuration different from that of the first embodiment will be described, and the same configuration as that of the first embodiment will be denoted by the same reference numeral, and the specific description will be omitted.

  That is, the neutral urging mechanism 50 according to the present embodiment is built in the power cylinder 18 and urges the piston 16 toward the neutral position with the urging force of a coil spring 57 described later. The rear steering wheel RS mechanically linked to the piston 16 via the sector shaft 17 or the like is returned to the neutral position and held in the neutral position.

  Specifically, the neutral urging mechanism 50 includes a guide rod 51 fixed to one end of the piston 16 and an inner surface of a locking member 52 fixed to the tip of the guide rod 51. 2 The first seating plate 53 which is a first spring receiver that follows the movement of the other end of the piston 16 by being pressed by the urging portion 52b, and the end wall of the cylinder component 14a in the first main housing 14 A first restricting member 54 that constitutes a first restricting portion 54 a that restricts the maximum movement of the other end of the first seating plate 53, and a base of the guide rod 51 so as to face the first seating plate 53. A second seating plate 55 that is a second spring receiver that follows the movement of one end side of the piston 16 by being pressed by a first urging portion 16 b that is inserted and arranged on the end side and recessed in one end portion of the piston 16. When, A second restricting member 56 constituting a second restricting portion 56a that protrudes from the inner peripheral surface of the Linda constituting portion 14a and restricts the maximum movement of one end side of the second seating plate 55, and the both seating plates 53, 55. It is mainly composed of a coil spring 57 which is a coil spring mounted between them.

  The first seating plate 53 is formed in a substantially plate shape having projections and depressions, and a recess 53a that is recessed toward the second seating plate 55 is formed in the inner periphery of the first seating plate 53, and at the center of the recess 53a. A rod insertion hole 53b through which the guide rod 51 is inserted is formed so as to extend therethrough, and a seating portion 53c on which one end portion of the coil spring 57 is seated extends in the outer peripheral area of the recess 53a. The concave portion 53a is configured to support the inner peripheral portion of the coil spring 57 (first coil spring 57a described later) by the outer peripheral side and to accommodate the locking member 52 on the inner peripheral side. Further, the first seating plate 53 is in contact with a first restricting portion 54 a formed on the inner peripheral edge of the first restricting member 54, thereby restricting the maximum movement of the first seating plate 53 toward one end side. (See FIG. 6).

  The second seating plate 55 has a substantially bottomed cylindrical shape, and a rod insertion hole 55a through which the guide rod 51 is inserted is formed at a substantially central position of the bottom wall on one end side, and an outer peripheral region of the rod insertion hole 55a. However, the other end of the coil spring 57 is configured as a seating portion 55b. In addition, a locking portion 55 c that can be locked to the second regulating member 56 is formed on the outer periphery of the other end portion of the second seating plate 55, and the locking portion 55 c is formed inside the second regulating member 56. The maximum movement of the second seating plate 55 toward one end side is restricted by engaging with the second restricting portion 56a formed on the peripheral edge (see FIG. 7).

  The coil springs 57 are a pair of coil springs arranged in an overlapping manner on the inner and outer peripheries, and are a first coil spring 57a arranged on the inner peripheral side and a second coil arranged on the outer peripheral side. And a spring 57b.

  Further, in the present embodiment, the coupling means between the input shaft 11 and the hollow motor 30 is not key coupling as in the first embodiment, but the input shaft 11 is expanded in diameter by a so-called taper bolt 58 and the inner portion of the connection member 37. It is pressed and joined to the peripheral surface.

  Specifically, one end portion of the input shaft 11 is configured as a hollow cylindrical tubular portion, and the taper bolt 58 is provided on the lower end side 11c of the concave portion 11a formed on the inner peripheral side of the tubular portion. A female screw portion is provided in which the male screw portion is screwed. And the peripheral wall of the axial direction range in which this female thread part was provided is provided with a plurality of not-shown notches formed in the axial direction from one end of the input shaft 11 in the circumferential direction. Is configured as the easily deformable portion 11b.

  With this configuration, the hollow motor 30 tightens the taper bolt 58 screwed into the female thread portion of the input shaft 11, so that the conical taper-shaped head portion 58 a pushes the easily deformable portion 11 b as the taper bolt 58 enters. The input shaft 11 and the connection member 37 (rotor 31) can be rotated integrally by deforming the diameter in a widened manner and the outer peripheral surface of the deformable easily deformable portion 11b pressed against the inner peripheral surface of the connection member 37. It has become.

  The connecting means for the input shaft 11 and the connecting member 37 is not limited as long as the input shaft 11 can be expanded and deformed. In addition to the tapered bolt 58 in which the head portion 58a is tapered, for example, FIG. As shown in FIG. 5, it is also possible to use a taper plug 59 in which the male thread portion is configured in a tapered shape.

  Hereinafter, the operation of the neutral urging mechanism 50 according to the present embodiment will be described with reference to FIGS. 5 shows a state where the piston 16 is in a neutral position, FIG. 6 shows a state where the output shaft 12 is rotated 20 ° to the left, and FIG. 7 shows a state where the output shaft 12 is rotated 20 ° to the right. Yes.

  First, as shown in FIG. 5, when the output shaft 12 is in the neutral position, the first and second coil springs 57a and 57b are stretched to the maximum, and the first seating plate 53 is the first restricting member. The second seating plate 55 is held at the second predetermined position by abutting against the second regulating portion 56a of the second regulating member 56. Is done. As a result, the piston 16 is pushed and pulled by the first and second seating plates 53 and 55 with equal urging forces of the first and second coil springs 57a and 57b. Retained.

  Subsequently, as shown in FIG. 6, when the output shaft 12 rotates leftward in accordance with the input from the hollow motor 30, the piston 16 moves downward in the figure via the ball screw mechanism 20. Then, in the neutral urging mechanism 50, the movement of the other end side of the coil spring 57 is regulated by the first seating plate 53 coming into contact with the first regulating part 54a of the first regulating member 54, The second seating plate 55 approaches the lower side (the first seating plate 53 in the drawing) along the guide rod 51 (first axis Z1) against the biasing force of the coil spring 57 by the amount of movement L2 of the piston 16. In other words, the coil spring 57 contracts and deforms by the amount of movement L2 of the second seating plate 55.

  Here, in the steering state of the rear side steering wheel RS, when an abnormality occurs in the electrical system such as the hollow motor 30 has failed, the second biasing force is generated based on the biasing force due to the contraction of the coil spring 57 in the neutral biasing mechanism 50. As a result of the seating plate 55 being urged toward the other end, the piston 16 is pushed back until the second seating plate 55 is locked to the second restricting portion 56a of the second restricting member 56 and restricted in movement. As a result, the piston 16 is returned to the neutral position and held at the neutral position, and the rear steering wheel RS mechanically connected to the piston 16 via the sector shaft 17 or the like is returned to the neutral position. And held in the neutral position.

  On the other hand, when the output shaft 12 rotates in the right direction, the piston 16 moves upward in the drawing via the ball screw mechanism 20, as shown in FIG. Then, in the neutral urging mechanism 50, the second seating plate 55 is locked to the second restricting portion 56a of the second restricting member 56, so that the movement of one end side of the coil spring 57 is restricted, The first seating plate 53 resists the biasing force of the coil spring 57 by the amount of movement L2 of the piston 16 and moves upward along the guide rod 51 (first axis Z1) in the drawing (the side approaching the second seating plate 55). In conjunction with this, the coil spring 57 is contracted and deformed by the amount of movement L2 of the first seating plate 53.

  Here, in the steering state of the rear steering wheel RS, when an abnormality occurs in the electrical system, such as the hollow motor 30 has failed, the neutral biasing mechanism 50 determines the first based on the biasing force due to the contraction of the coil spring 57. The seating plate 53 is urged toward one end, and the piston 16 is pulled back until the first seating plate 53 comes into contact with the first restricting portion 54a of the first restricting member 54 and is restricted in movement. As a result, the piston 16 is returned to the neutral position and is held in the neutral position, and the rear steering wheel RS mechanically connected to the piston 16 via the sector shaft 17 or the like is moved to the neutral position. It will be returned and held in the neutral position.

  As described above, according to the rear wheel steering control device RM according to the present embodiment, the neutral biasing mechanism 50 biases the piston 16 mechanically connected to the rear steering wheel RS toward the neutral position. In particular, the holding force at the neutral position of the piston 16 based on the biasing force can be directly transmitted to the rear steering wheel RS, so that the vehicle can be driven and steered thereafter. It can be made more stable.

  In particular, in the case of such a configuration, unlike the first embodiment in which the input shaft 11 is urged, it is not necessary to allow the movement of the rear steering wheel RS by the amount of twist of the torsion bar 10. There is a merit for further stabilization of steering.

  In the case of this embodiment, since the neutral urging mechanism 50 is concentrated on one end side of the piston 16, the rear wheel steering control device RM can be downsized and the vehicle layout can be improved. The

  Furthermore, since the neutral urging mechanism 50 is accommodated in the first pressure chamber P1, it is not necessary to provide an independent housing for accommodating the neutral urging mechanism 50, and the rear wheel steering control device RM is simplified. There is also an advantage that can be achieved.

  FIGS. 9-11 shows 3rd Embodiment of the rear-wheel steering control apparatus which concerns on this invention, and changes the specific structure of the neutral biasing mechanism 50 in the said 2nd Embodiment. Hereinafter, only the configuration different from that of the second embodiment will be described, and the same configuration as that of the second embodiment will be denoted by the same reference numeral, and the specific description will be omitted.

  That is, the neutral urging mechanism 60 according to the present embodiment urges the third pitman arm A3 to the neutral position side based on the hydraulic pressure of cylinders (first and second pistons 63 and 64) described later. The rear steering wheel RS mechanically linked to the third pitman arm A3 is returned to the neutral position and is held at the neutral position.

  Specifically, the neutral urging mechanism 60 has a substantially cylindrical cylinder tube 61 whose one end side in the axial direction is connected to the one-side steering wheel, and one end side in the axial direction faces into the cylinder tube 61, and the like. A rod 62 whose end side is connected to the other side steering wheel and a cylinder tube 61 are slidably accommodated, and the inside of the cylinder tube 61 is divided into three spaces (first chamber R1, second chamber R2, and third chamber). A first piston 63 on one side and a second piston 64 on the other side, which are a pair of pistons liquid-tightly separated in the chamber R3), and the first piston 63 or the second piston. And a biased member 65 that biases the third pitman arm A3 toward the neutral position side.

  A connecting member 66 for connecting the cylinder tube 61 and the vehicle body is provided on one end side of the cylinder tube 61, and the first chamber R <b> 1 is separated by the connecting member 66 and the first piston 63. On the other hand, on the other end side of the cylinder tube 61, a guide member 67 through which the rod 62 is inserted and used for sliding guidance of the rod 62 is provided, and the third chamber R3 is formed by the guide member 67 and the second piston 64. It is formed.

  The connecting member 66 has a first hydraulic fluid introduction hole H1 that communicates the outside with the first chamber R1 and introduces hydraulic fluid pumped from the second pump PR into the first chamber R1. The first piston 63 is urged by the hydraulic pressure formed and introduced from the first hydraulic fluid introduction hole H1. On the other hand, on the other end side of the cylinder tube 61, the second working fluid is introduced into the third chamber R3 for introducing the working fluid pumped from the second pump PR through the third chamber R3. A hole H2 is provided, and the second piston 64 is urged by the hydraulic pressure introduced from the second hydraulic fluid introduction hole H2.

  Further, the inner peripheral portion of the cylinder tube 61 is smaller than the first and second pistons 63 and 64 in an approximately middle portion of the axis 62 of the rod 62 (hereinafter referred to as “second axis”) in the Z2 direction. In addition, the inner diameter is set larger than the biased member 65 and the axial width is set to be equal to the axial width of the biased member 65 to restrict the movement of the first and second pistons 63 and 64. Thus, a substantially annular regulating member 68 is provided so as to project and return to the neutral position of the third pitman arm A3.

  With this configuration, when the third pitman arm A3 is in the neutral position, the biased member 65 is accommodated on the inner peripheral side of the restricting member 68, and one end of the restricting member 68 contacts the first piston 63. Thus, the first piston 63 functions as a first locking portion 68a for restricting the movement of the first piston 63 on the third chamber R3 side (right direction in FIG. 9), and the other end of the restricting member 68 is the second piston 64. , And functions as a second locking portion 68b that restricts the movement of the second piston 64 on the first chamber R1 side (the left direction in FIG. 9).

  Hereinafter, the operation of the neutral urging mechanism 60 according to the present embodiment will be described with reference to FIGS. 9 shows a state where the third pitman arm A3 is in a neutral position, FIG. 10 shows a state where the third pitman arm A3 has moved leftward, and FIG. 11 shows a state where the third pitman arm A3 has moved rightward.

  First, as shown in FIG. 9, when the third pitman arm A3 is in the neutral position, the first and second pistons 63 and 64 are respectively connected to the first and second locking portions 68a and 68b of the regulating member 68. The abutted member 65 is completely accommodated on the inner peripheral side of the regulating member 68. At this time, the first and second pistons 63 and 64 are subjected to the same hydraulic pressure introduced into the first chamber R1 and the third chamber R3, respectively. As a result, the first and second pistons 63 and 64 are neutral without being biased to one side. Held in position.

  Subsequently, as shown in FIG. 10, the third pitman arm A3 is moved to the left in accordance with the input from the hollow motor 30, that is, the rod 62 is moved to the left. In the state, when an abnormality occurs in the electrical system, such as the hollow motor 30 has failed, the neutral urging mechanism 60 discharges the pressure from the second pump PR through the first and second hydraulic fluid introduction holes H1, H2 (the same (Discharge pressure) is introduced and the second piston 64 is kept in contact with the second locking portion 68b while the first piston 63 is in contact with the first locking portion 68a and is restricted in movement. The urging member 65 is pressed, and the rod 62 is pushed back through the urging member 65 until the urging member 65 is accommodated in the inner peripheral portion of the regulating member 68. Thus, the biased member 65 is returned to the neutral position and is held in the neutral position, and is mechanically connected to the biased member 65 via the rod 62 and the third pitman arm A3. The rear side steering wheel RS is returned to the neutral position and is held in the neutral position.

  On the other hand, if an abnormality occurs in the electrical system such as the hollow motor 30 has failed while the third pitman arm A3 has moved to the right, the first and second hydraulic fluids are introduced as shown in FIG. Based on the discharge pressure (the same discharge pressure) from the second pump PR introduced into the holes H1 and H2, respectively, the second piston 63 is maintained in a state in which the first piston 63 is in contact with the first locking portion 68a. The biased member 65 is pulled until the piston 64 abuts on the second locking portion 68b and is restricted from moving, and the biased member 65 is retained until the biased member 65 is accommodated in the inner peripheral portion of the regulating member 68. Then, the rod 62 is pulled back through. Thus, the biased member 65 is returned to the neutral position and is held in the neutral position, and is mechanically connected to the biased member 65 via the rod 62 and the third pitman arm A3. The rear side steering wheel RS is returned to the neutral position and is held in the neutral position.

  In the present embodiment, an example using the second pump PR as the hydraulic source is illustrated, but instead of the second pump PR, a hydraulic source other than the second pump PR or an air pressure source is used. You may comprise so that motive power may be acquired.

  As described above, according to the rear wheel steering control device RM according to the present embodiment, in the neutral urging mechanism 60, the third pitman arm A3 mechanically connected to the rear steering wheel RS is moved to the neutral position side. As in the second embodiment, the holding force at the neutral position of the third pitman arm A3 based on the biasing force (hydraulic pressure) is directly transmitted to the rear steering wheel RS. This makes it possible to further stabilize the traveling of the vehicle and the subsequent steering.

  In particular, in the case of such a configuration, as in the first embodiment for biasing the input shaft 11, the hydraulic pressure is applied to both the first chamber R1 and the third chamber R3 regardless of the position of the third pitman arm A3. Since the third pitman arm A3 can be returned to the neutral position by being introduced, it is not necessary to provide a switching control valve or the like, and the neutral urging mechanism 60 can be configured with a relatively simple structure.

  In addition, by adopting a configuration in which the hydraulic fluid is introduced only when the third pitman arm A3 needs to be returned to the neutral position, there is an advantage that the steering load (resistance) by the neutral urging mechanism 60 in the normal state can be suppressed.

  FIGS. 12-14 shows 4th Embodiment of the rear-wheel steering control apparatus which concerns on this invention, and changes the concrete structure of the neutral biasing mechanism 40 in the said 1st Embodiment. In the following, only the configuration different from that of the first embodiment will be described, and the same configuration as that of the first embodiment will be denoted by the same reference numeral, and the specific description will be omitted.

  That is, the neutral urging mechanism 70 according to the present embodiment includes a first coil spring 76a and a second coil spring 76b that are a pair of urging members for a nut 74 described later of the ball screw mechanism 72 linked to the input shaft 11. And by urging the input shaft 11 toward the neutral position with the urging force of the coil springs 76a and 76b, the relative rotation of the shafts 11 and 12 is the same as in the first embodiment. The rear steering wheel RS is returned to the neutral position with the hydraulic pressure assist based on the above, and is held at the neutral position.

  Specifically, the neutral urging mechanism 70 is housed in a cylindrical housing 71 that is bolted to the outer end of the first motor housing 34, and a screw shaft 73 that rotates integrally with the input shaft 11 and the screw shaft 73. A ball screw mechanism 72 in which a plurality of balls 75 are interposed between a nut 74 provided on the outer peripheral side of the screw shaft 73 and the both ends of the nut 74 are arranged, and the nut 74 is arranged along the axial direction. The first coil spring 76a and the second coil spring 76b that are urged in this manner are mainly configured.

  The ball screw mechanism 72 has one end side in the axial direction connected to one end side of the input shaft 11 via a predetermined joint member 80 and the other end side accommodated in the housing 71, and the screw shaft 73. A nut 74 linked to the outer periphery of the other end via the plurality of balls 75, first and second coil springs 76a and 76b elastically mounted on both ends of the nut 74, and both ends of the nut 74 The first seating plate 77 and the second seating plate 78 are provided adjacent to each other and formed to have a diameter larger than that of the nut 74 to provide seating on the inner end side of the first coil spring 76a and the second coil spring 76b. And a substantially annular regulating member 79 for regulating the movement of the first and second seating plates 77 and 78 to return and hold the nut 74 to the neutral position.

  Each of the first and second seating plates 77 and 78 is formed in a substantially disk shape. When the first seating plate 77 moves to one side of the nut 74, the second seating plate 78 serves as the other side of the nut 74. Each of the seating plates 77 and 78 corresponding to the moving direction of the nut 74 is interlocked with the nut 74 by being pressed by the nut 74 at the time of moving to the position.

  The restricting member 79 has a substantially cylindrical shape, is fixed to the inner peripheral surface of the axially intermediate portion of the housing 71, is larger than the outer diameter of the nut 74, and has outer diameters of the first and second seating plates 77 and 78. And an axial width equivalent to the axial width of the nut 74. With this configuration, when the nut 74 is in the neutral position, the nut 74 is accommodated on the inner peripheral side of the regulating member 79, and one end portion of the regulating member 79 abuts on the first seating plate 77, thereby The first seating plate 77 functions as a first locking portion 79a that restricts movement of the first seating plate 77 on the second coil spring 76b side (upward in FIG. 12), and the other end of the regulating member 79 is connected to the second seating plate 78. By contacting, the second seating plate 78 functions as a second locking portion 79b that restricts the movement of the first coil spring 76a side (downward in FIG. 12).

  Hereinafter, the operation of the neutral urging mechanism 70 according to the present embodiment will be described with reference to FIGS. 12 shows a state in which the input shaft 11 is in a neutral position, FIG. 13 shows a state in which the input shaft 11 is rotated 20 ° to the right, and FIG. 14 shows a state in which the input shaft 11 has been rotated 20 ° in the left direction. ing.

  First, as shown in FIG. 12, when the input shaft 11 is in the neutral position, the first and second coil springs 76a and 76b are both stretched to the maximum, and the first and second seating plates 77 are placed. , 78 are in contact with the first and second engaging portions 79a, 79b of the restricting member 79, and the nut 74 is completely accommodated on the inner peripheral side of the restricting member 79. The nuts 74 (first and second seating plates 77 and 78) are sandwiched with equal force by the first and second coil springs 76a and 76b, so that they are held in a neutral position without being biased to one side. The

  Subsequently, as shown in FIG. 13, in the state where the input shaft 11 rotates to the right in accordance with the input from the hollow motor 30 and the nut 74 moves downward, that is, in the steering state of the rear steering wheel RS, When an abnormality occurs in the electrical system, such as the motor 30 has failed, the first seating plate 77 is biased toward the regulating member 79 based on the biasing force generated by the contraction of the first coil spring 76a in the neutral biasing mechanism 70. Thus, the nut 74 is pushed back until the movement of the first seating plate 77 is restricted by being locked to the first locking portion 79a. As a result, the nut 74 is returned to the neutral position and held at the neutral position, and the input shaft 11 is returned to the neutral position via the ball screw mechanism 72 and held at the neutral position. It becomes.

  On the other hand, when an abnormality occurs in the electrical system, such as the hollow motor 30 losing while the nut 74 is moved upward, as shown in FIG. 14, the second coil spring 76b in the neutral urging mechanism 70 is obtained. The second seating plate 78 is biased toward the regulating member 79 based on the biasing force due to the contraction of the nut 74, and the nut 74 is moved until the second seating plate 78 is restrained from moving by contacting the second locking portion 79b. Will be pushed back. As a result, the nut 74 is returned to the neutral position and held at the neutral position, and the input shaft 11 is returned to the neutral position via the ball screw mechanism 72 and held at the neutral position. It becomes.

  As described above, according to the rear wheel steering control device RM according to the present embodiment, the neutral urging mechanism 70 is configured to urge the input shaft 11 toward the neutral position side, so that the first embodiment is configured. In the same manner as described above, the rear steering wheel RS can be steered with a hydraulic pressure assist based on the relative rotation of the shafts 11 and 12, so that the urging force of the first and second coil springs 76a and 76b is minimized. Therefore, it is possible to reduce the size of the apparatus.

  In particular, in the case of this embodiment, since the neutral biasing mechanism 70 is configured by the ball screw mechanism 72, a reduction ratio can be increased, and the biasing force of the first and second coil springs 76a and 76b can be increased. It is possible to reduce the output of the hollow motor 30 that rotates against it.

  Further, as in the present embodiment, the neutral urging mechanism 70 is extended in the first axis Z1 direction, which can contribute to the reduction in size of the apparatus in the radial direction.

  Further, since the neutral urging mechanism 70 is configured such that the nut 74 is urged to the neutral position by a pair of coil springs 76a and 76b, one coil spring is used in both compression and tension forms. Compared to the above, there is also an advantage that the biasing force difference in the rotation direction of the input shaft 11 can be reduced.

  In addition, by using the pair of coil springs 76a and 76b, both the coil springs 76a and 76b can be used only in the compression direction. As a result, the coil springs 76a, 76a, 76b, It also serves to suppress the sag of 76b.

  The present invention is not limited to the configuration of each of the above-described embodiments. For example, a specific example of the rear wheel steering control device RM that is not directly related to the features of the present invention, such as the sector shaft 17 or the third pitman arm A3 as a transmission mechanism. The specific configuration can be freely changed according to the specification, cost, etc. of the vehicle to which the device RM is applied.

10 ... Torsion bar 11 ... Input shaft 12 ... Output shaft 13 ... Main housing (steering housing)
16 ... Piston 17 ... Sector shaft (transmission mechanism)
19 ... Rotary valve 20 ... Ball screw mechanism 30 ... Hollow motor (brushless motor)
31 ... Rotor (motor rotor)
32 ... Stator (motor stator)
33 ... Motor housing P1 ... First pressure chamber P2 ... Second pressure chamber

Claims (16)

A steering shaft composed of an input shaft that rotates in response to a rotational input, and an output shaft connected to the input shaft via a torsion bar;
A steering housing that rotatably supports the steering shaft;
A piston that is slidably accommodated in the steering housing, and that partitions the interior of the steering housing into a first pressure chamber and a second pressure chamber;
A rotary that is provided in the steering housing and selectively supplies hydraulic fluid supplied from an external pump to the first pressure chamber and the second pressure chamber according to relative rotation between the input shaft and the output shaft. A valve,
A ball screw mechanism that converts rotation of the output shaft into axial movement of the piston;
A transmission mechanism for transmitting axial movement of the piston to the rear steering wheel of the multi-axis steering vehicle;
A motor rotor that is provided on the outer peripheral side of the input shaft and that rotates integrally with the input shaft; a motor element that is provided on the outer peripheral side of the motor rotor; and a motor housing that houses the motor element; A hollow brushless motor configured to control the rotation of the input shaft according to the driving situation of the vehicle,
A rear wheel steering control device comprising:   2. The rear wheel steering according to claim 1, further comprising a neutral urging mechanism that urges the input shaft, the piston, or the transmission mechanism to hold the rear steering wheel at a neutral position. Control device.   The rear wheel steering control device according to claim 2, wherein the neutral urging mechanism urges the input shaft toward the neutral position. The neutral biasing mechanism is
A bobbin that rotates as the input shaft rotates,
A cable having one end fixed to the bobbin and wound around the bobbin by rotating the bobbin;
A biasing member that biases the other end of the cable in a direction away from the rotation axis of the bobbin;
The rear wheel steering control device according to claim 3, comprising:   The rear wheel steering control device according to claim 4, wherein the bobbin is formed in a substantially conical taper shape whose outer diameter gradually changes along the axial direction.   6. The rear wheel steering control device according to claim 5, wherein the cable is connected to a larger diameter side of the bobbin and wound toward a smaller diameter side of the bobbin as the number of turns increases. The neutral biasing mechanism is
A screw shaft that has a thread groove on the outer periphery and rotates in accordance with the rotation of the input shaft; a nut that is provided on the outer periphery side of the screw shaft and has the thread groove on the inner periphery; and the nut and the screw shaft; A plurality of balls interposed therebetween, and a ball screw mechanism composed of
A biasing member that biases the nut along the axial direction of the screw shaft so that the screw shaft rotates to a position corresponding to a neutral position of the input shaft;
The rear wheel steering control device according to claim 3, comprising: The biasing member is a pair of coil springs provided on both sides of the nut in the axial direction of the nut,
The rear wheel steering control device according to claim 7, wherein the pair of coil springs are provided so as to bias the nut toward a neutral position.   The rear wheel steering control device according to claim 2, wherein the neutral urging mechanism urges the piston toward the neutral position. The neutral biasing mechanism is
A coil spring provided on one end side of the piston in the first axial direction which is the moving direction of the piston;
A first spring receiver provided on one side of the first axial direction of the coil spring so as to be movable in the first axial direction of the coil spring;
A second spring receiver provided on the other side in the first axial direction of the coil spring so as to be movable in the first axial direction of the coil spring;
A first restricting portion that is provided in the steering housing and restricts movement of the first spring receiver from the first predetermined position to one side in the first axial direction;
A second restricting portion that is provided in the steering housing and restricts movement of the second spring receiver from the second predetermined position to the other side in the first axial direction;
Provided in the piston, and when the piston moves to one side in the first axial direction, the second spring receiver is moved in a state where movement of the first spring receiver is restricted at the first predetermined position. A first urging portion that urges the piston toward the neutral position by a restoring force of the coil spring by urging the coil spring to one side in the first axial direction to compressively deform;
Provided in the piston, and when the piston moves to the other side in the first axial direction, the second spring receiver moves the first spring receiver in a state in which movement is restricted at the second predetermined position. A second urging portion that urges the piston toward the neutral position by a restoring force of the coil spring by urging the coil spring to the other side in the first axial direction;
The rear wheel steering control device according to claim 9, comprising:   The neutral urging mechanism is provided in a first pressure chamber provided on one side of the piston in the first axial direction of the first pressure chamber and the second pressure chamber. Item 13. A rear wheel steering control device according to Item 10. The piston has a plurality of rack teeth along the first axial direction,
The transmission mechanism has a sector gear that meshes with the rack teeth and rotates as the piston moves in the first axial direction, and a pitman arm that swings in conjunction with the sector gear,
The rear wheel steering control device according to claim 2, wherein the neutral urging mechanism urges the pitman arm toward the neutral position. The neutral biasing mechanism is
A cylinder tube formed in a cylindrical shape;
A rod housed in the cylinder tube and connected to the pitman arm;
A pair of pistons slidably accommodated inside the cylinder tube and provided so as to be relatively movable in a second axis direction which is a movement direction of the rod, and the interior of the cylinder tube is divided into three spaces. A first piston and a second piston which are liquid-tightly separated from each other;
A first chamber on one side in the second axial direction that is respectively separated in the cylinder tube and separated by the first piston, and adjacent to the first chamber, the first piston and the second A second chamber defined between the pistons; a third chamber disposed adjacent to the second chamber and defined by the second piston in the second axial direction;
A first hydraulic fluid introduction hole that is provided in the cylinder tube and serves to bias the first piston by introducing hydraulic fluid pumped by an external pump into the first chamber;
A second hydraulic fluid introduction hole that is provided in the cylinder tube and serves to bias the second piston by introducing hydraulic fluid pumped by the external pump into the third chamber;
Provided on the rod, when the first piston moves to one side in the second axial direction, it is urged by the first piston, while the second piston moves to the other side in the second axial direction. A biased member that biases the pitman arm to the neutral position side via the rod by being biased by the second piston when moved,
The first piston is provided on the inner peripheral side of the cylinder tube, and when the first piston biases the biased member to the other side in the second axial direction, the first piston is returned to the neutral position. A first locking portion that restricts movement of the first piston to the other side in the second axial direction by contacting the first piston;
The second piston is provided on the inner peripheral side of the cylinder tube, and when the second piston urges the biased member to one side in the second axial direction, the second piston is moved back to the neutral position. A second locking portion for restricting movement of the second piston to one side in the second axial direction by contacting the second piston;
The rear wheel steering control device according to claim 12, further comprising:   The rear wheel steering control device according to claim 1, wherein the external pump is driven and controlled by an electric motor.   15. The rear wheel steering control device according to claim 14, wherein the electric motor is driven and controlled when the brushless motor is driven. The input shaft includes a recess opening at an axial end opposite to the output shaft, a female screw formed on the inner periphery of the recess, and a plurality of notches provided in the circumferential direction of the recess. Have
The motor rotor has a cylindrical portion into which the input shaft is inserted. When the taper bolt or the taper plug is screwed into the recess of the input shaft, the notch is expanded in the radial direction, and the recess is expanded. The rear wheel steering control device according to claim 1, wherein the rear wheel steering control device is fixed to the input shaft by increasing a frictional force between the outer peripheral surface of the input shaft and the inner peripheral surface of the cylindrical portion with a diameter.

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