Steering device
In a steering device ( 200 ), a first motor ( 34 a ) operates in accordance with a steering operation of a steering handle ( 12 ), a first steering shaft ( 52 ) steers one of the pair of wheels ( 58 ), and a first conversion unit converts a rotation of a first rotor ( 31 a ) as a rotation element of the first motor ( 31 a ) into an axial-direction movement of the first steering shaft ( 52 ). A second motor ( 34 b ) operates in accordance with the steering operation of the steering handle ( 12 ), a second steering shaft ( 53 ) is separated from the first steering shaft ( 52 ) and steers the other of the pair of wheels ( 58 ), and a second conversion unit converts a rotation of a second rotor ( 31 b ) as a rotation element of the second motor ( 34 b ) into an axial-direction movement of the second steering shaft ( 53 ). A coupling unit ( 60 ) couples the first rotor ( 31 a ) and the second rotor ( 31 b ) together and cancels the coupling of the first rotor ( 31 a ) and the second rotor ( 31 b ).
1. A steering device which steers a pair of wheels in accordance with a steering operation of a steering handle, comprising:
a first motor operating in accordance with the steering operation of the steering handle;
a first steering shaft steering one of the pair of wheels;
a first conversion unit converting a comparatively low torque rotation of a first rotor as a rotation element of the first motor into an axial-direction movement of the first steering shaft with a comparatively high thrust;
a second motor operating in accordance with the steering operation of the steering handle;
a second steering shaft which is separated from the first steering shaft and steers the other of the pair of wheels;
a second conversion unit converting a comparatively low torque rotation of a second rotor as a rotation element of the second motor into an axial-direction movement of the second steering shaft with a comparatively high thrust; and
a coupling unit coupling the first rotor and the second rotor together and canceling the coupling of the first rotor and the second rotor.
2. The steering device according to claim 1 wherein the coupling unit comprises a differential unit providing a differential operation between the first rotor and the second rotor, and a locking unit locking the differential unit.
3. The steering device according to claim 2 wherein the differential unit has a planetary gear mechanism comprising: a first solar gear connected with the first rotor and rotatably supported; a first internal gear rotatably supported and coaxially with the first solar gear; a first planet gear engaged with the first solar gear and the first internal gear; a second solar gear connected with the second rotor and rotatably supported; a second internal gear disposed coaxially with the second solar gear in which rotation of the second internal gear is inhibited; and a second planet gear engaged with the second solar gear and the second internal gear and rotatably connected with the first planet gear and coaxially with the first planet gear, and
wherein the locking unit locks rotation of the first internal gear so that the differential unit is locked.
4. The steering device according to claim 3 wherein the differential unit comprises a third motor which drives the first internal gear.
5. The steering device according to claim 4 wherein the locking unit has a torque transmission unit provided between the first internal gear and the third motor, and the torque transmission unit is provided to transmit an input torque to the first internal gear when the input torque is given from the third motor, and provided to inhibit transmission of an input torque to the third motor and locks rotation of the second internal gear when the input torque is given from the second internal gear.
6. The steering device according to claim 1 further comprising a motor problem detecting unit which detects a problem in any of the first motor and the second motor, and the coupling unit is provided to cancel coupling of the first rotor and the second rotor when no problem in both the first motor and the second motor is detected by the motor problem detecting unit, and provided to couple the first rotor and the second rotor together when a problem in at least one of the first motor and the second motor is detected by the motor problem detecting unit.
7. The steering device according to claim 6 wherein, when a problem in one of the first motor and the second motor is detected by the motor problem detecting unit, the other of the first motor and the second motor is operated in accordance with the steering operation of the steering handle.
8. The steering device according to claim 4 further comprising a rotation angle detection unit which detects a difference between a rotation angle of the first motor and a rotation angle of the second motor, wherein, before the first rotor and the second rotor are coupled together by the coupling unit, the third motor is operated so that the rotation angle difference detected by the rotation angle detection unit is set to zero.
9. The steering device according to claim 1 further comprising:
an input shaft connected with the steering handle;
an output shaft connected with either the first steering shaft or the second steering shaft through a steering gear; and
a transfer ratio varying unit having a differential generating mechanism and a motor, the transfer ratio varying unit operating the differential generating mechanism by driving the motor, and varying a transfer ratio between the input shaft and the output shaft.