Patent ID: 12258080

DESCRIPTION OF EMBODIMENTS

A steering system1for a vehicle2according an embodiment of the present invention is described in the following. As shown inFIG.1, the steering system1consists of a steer-by-wire (SBW) steering system. The vehicle2fitted with the steering system1is a four-wheeled vehicle having left and right front wheels3and left and right rear wheels (not shown in the drawings). The left and right front wheels3are supported by a vehicle body8(only the outline of a lower part thereof is shown inFIG.1) via respective knuckles7so that the steered angle α of the front wheels3can be changed, and the front wheels3thus serve as steerable wheels. The steered angle α refers to the angle of the front wheels3with respect to the fore and aft direction in plan view. The steering system1thus changes the steered angle α of the front wheels3.

The steering system1includes a steering member10rotatably provided on the vehicle body8, a steering mechanism11for steering the front wheels3, a steering actuator12for applying a driving force to the steering mechanism11, a reaction force actuator13that applies a reaction torque T to the steering member10, and a control unit15that controls the reaction force actuator13and the steering actuator12. The steering system1may be a redundant system that includes a plurality of sets each of which is provided with a steering actuator12, a reaction force actuator13, and a control unit15.

The steering member10accepts a steering operation by the driver. The steering member10includes a steering shaft18rotatably supported by the vehicle body8and a steering wheel19provided at an end of the steering shaft18. The steering shaft18is rotatably supported by a steering column20provided on the vehicle body8, and has a rear end thereof projecting rearward from the steering column20. The steering wheel19is connected to the rear end of the steering shaft18so as to rotate integrally with the steering shaft18.

The reaction force actuator13consists of an electric motor which is connected to the steering shaft18via a gear mechanism. When the reaction force actuator13is driven, the driving force is transmitted to the steering shaft18as a rotational force. The reaction force actuator13applies a rotational torque to the steering member10. The torque applied to the steering member10by the reaction force actuator13in response to the steering operation is called a reaction torque T.

The steering system1is further provided with a steering angle sensor21that detects the rotational angle of the steering shaft18around the central axis thereof as a steering angle β. The steering angle sensor21may be a per se known rotary encoder. Further, the steering system1is provided with a torque sensor22that detects the torque applied to the steering shaft18as a steering torque Ts. The torque sensor22detects the steering torque Ts applied to a part of the steering shaft18located between the steering wheel19and the reaction force actuator13. The steering torque Ts is determined by the operating torque applied to the steering wheel19by the driver and the reaction torque T applied to the steering shaft18by the reaction force actuator13. The torque sensor22may consist of a per se known torque sensor such as a magnetostrictive torque sensor or a strain gauge, or, alternatively, the steering torque may be estimated from the value of the electric current flowing through the electric motor of the reaction force actuator13.

The steering system1further includes a first rotational angle sensor23that detects the rotational angle θ of the reaction force actuator13. The first rotational angle sensor23may be a per se known resolver or rotary encoder.

The steering mechanism11has a rack26extending in the vehicle lateral direction. The rack26is supported by a gear housing27so as to be movable in the vehicle lateral direction. The left and right ends of the rack26are respectively connected to knuckles7that support the left and right front wheels3via respective tie rods30. As the rack26moves in the vehicle lateral direction, the steered angle α of the front wheels3changes. The steering mechanism11is mechanically separated from the steering member10.

The steering actuator12consists of an electric motor. The steering actuator12moves the rack26in the vehicle lateral direction according to the signal from the control unit15, and changes the steered angle α of the left and right front wheels3accordingly.

The steering system1is further provided with a second rotational angle sensor31that detects the rotational angle θ of the steering actuator12. The second rotational angle sensor31may be a per se known resolver or rotary encoder. Further, the steering system1has a steered angle sensor32that detects the steered angle α of the front wheels3. In the present embodiment, the steered angle sensor32consists of a rack stroke sensor that detects the rack position (the position of the rack26along the lateral direction of the vehicle), and the steered angle α of the front wheels3is determined from the rack position.

The control unit15consists of an electronic control unit including a CPU, memory, a storage device for storing a program, and the like. The steering angle sensor21, the torque sensor22, the first rotational angle sensor23, the second rotational angle sensor31, and the steered angle sensor32are connected to the control unit15. Based on the signals from these sensors, the control unit15acquires signals corresponding to the steering angle β, the steering torque Ts, the rotational angle θ of the reaction force actuator13, the rotational angle θ of the steering actuator12, and the steered angle α. Further, the control unit15is connected to a vehicle speed sensor33, and a shift position sensor34, and acquires signals corresponding to the vehicle speed V and the transmission shift position SP of a transmission device35.

The transmission device35is a device that changes the mode of power transmission from the drive source mounted on the vehicle2to the wheels. For example, when the vehicle2is equipped with an internal combustion engine as a propelling drive source, the transmission device35is a device that changes the mode of driving force transmission from the internal combustion engine to the driven wheels. Further, when the vehicle2is equipped with an electric motor as a propelling drive source, the transmission device35is a power unit that changes the mode of driving force transmission from the electric motor to the driven wheels.

In the case of an automatic transmission device, the transmission device35includes a park position “P”, a neutral position “N”, a drive position “D”, and a reverse position “R” as transmission shift positions SP representing different driving force transmission modes. The drive position “D” may have one range, or may have a plurality of ranges including the first speed, the second speed, and the like. When the transmission device35is a manual transmission device, the transmission device35has a neutral position “N”, a drive position “D”, and a reverse position “R”. The drive position “D” may have a plurality of ranges such as 1st speed to 5th speed. Hereinafter, the drive position “D” and the reverse position “R” are collectively referred to as the travel position.

The transmission shift position SP of the transmission device35is switched by the driver's switching operation performed to a switching member such as a shift lever or a shift button. The shift button may be a function button displayed on a touch panel display. The shift position sensor34acquires a signal corresponding to the transmission shift position SP of the transmission device35switched by the driver. The vehicle system provided with the control unit15is configured to be turned on and off only when the transmission device35is in the park position “P” or the neutral position “N”.

The control unit15is connected to the reaction force actuator13and the steering actuator12, and controls the reaction force actuator13and the steering actuator12. The control unit15controls the steering actuator12according to the steering angle β, and controls the reaction force actuator13according to the steered angle α.

The control action of the control unit15in the SBW mode is specifically described in the following. The control unit15computes a target steered angle at having a prescribed relationship with the steering angle β according to the actual steering angle β detected by the steering angle sensor21. The control unit15may compute the target steered angle αt by, for example, multiplying the steering angle β by a predetermined gear ratio K(αt=R×K). The gear ratio K may be, for example, 0.01 to 0.5, and is preferably 0.125. Then, the control unit15computes a first current value A1 to be supplied the steering actuator12according to the deviation Δα(=αt−α) between the target steered angle αt and the actual steered angle α so that the steered angle α coincides with the target steered angle αt. In other words, the control unit15performs a feedback control of the steering actuator12according to the deviation Δα. With an increase in the deviation Δα, the first current value A1 supplied to the steering actuator12becomes greater, and the output of the steering actuator12is increased with the result that the amount of change in the steered angle α increases.

The control unit15computes the target reaction torque Tt to be generated by the reaction force actuator13according to the steering state of the front wheels3, in particular according to the deviation Δα. The target reaction torque Tt may be computed by multiplying Δα by a predetermined coefficient. Then, the control unit15computes a second current value A2 to be supplied to the reaction force actuator13according to the computed target reaction torque Tt. The second current value A2 to be supplied to the reaction force actuator13may be determined by referring to a predetermined map according to the target reaction torque Tt. Alternatively, the control unit15may determine the second current value A2 by referring to a predetermined map according to the deviation Δα. The target reaction torque Tt and the second current value A2 become greater in value as the deviation Δα of the steered angle α increases.

The control unit15supplies the second current value A2 to the reaction force actuator13and generates a driving force in the reaction force actuator13. The driving force generated by the reaction force actuator13is applied to the steering shaft18as a reaction torque T that opposes the operation input of the driver. As a result, the driver can receive a reaction force (resistance force) against the steering operation from the steering wheel19.

The control unit15is activated when the ignition switch of the vehicle2is turned on, and is deactivated when the ignition switch is turned off. Therefore, with the ignition switch turned off, even if the steering member10is turned and the steering angle β changes, the steered angle α of the front wheels3does not change, and no reaction torque T is produced. Therefore, while the ignition switch is turned off, the steering angle β of the steering member10and the steered angle α of the front wheels3may deviate from the above-mentioned prescribed gear ratio relationship. In the following disclosure, the two angles which are normalized by taking into account the gear ratio are referred to as phases, and the angular deviation from the prescribed relationship between the steered angle α and the steering angle β is referred to as the phase difference. The phase difference can be created in a plurality of different types.

FIG.2is a diagram showing a phase relationship between the steering angle β of the steering member10and the steered angle α of the front wheels3. As shown inFIG.2, the phases of the steering angle β and the steered angle α may deviate from each other in two different types; type A or an opposite phase relationship where the phases of the steering angle β and the steered angle α are opposite to each other, and type B or a same phase relationship where the phases of the steering angle β and the steered angle α agree with each other. When only one of the phases of the steering angle β and the steered angle α is 0, or within a prescribe small angular range around zero, the two phases are regarded as the same. Thus, type B can be further classified into four types; type β1 where the steering angle β is 0 and the steered angle α is not 0, type β2 where the phase of the steered angle α is greater than the phase of the steering angle β, type β3 where the phase of the steered angle α is smaller than the phase of the steering angle β, and type β4 where the steering angle β is greater than 0 in either direction andFIG.3is a graph showing the relationship between the steering angle β of the steering member10and the steered angle α of the front wheels3which includes the single opposite phase type, and the four same phase types.

Since the phase relationship between the steering angle θ and the steered angle α may be disturbed while the ignition switch is off, the control unit15performs a phase matching control process as shown inFIG.4when the ignition switch is turned on and the control unit15is activated.

FIG.4shows a flowchart of the phase matching control process executed by the control unit15at startup. As shown inFIG.4, upon activation, the control unit15acquires the steering angle β and the steered angle α (step ST1), and determines if there is any deviation between the phases of the steering angle β and the steered angle α (Step ST2). In step ST2, it is determined if the phase relationship between the steering angle β and the steered angle α deviates from the predetermined gear ratio relationship (if the phase relationship deviates from the oblique gear ratio line K shown inFIG.3). If the phases of the steering angle β and the steered angle α coincide with each other (ST2: No), the control unit15concludes this process.

If the phases of the steering angle β and the steered angle α deviate from each other (ST2: Yes), the control unit15acquires the vehicle speed V (step ST3), and determines if the vehicle2is traveling (Step ST4). More specifically, the control unit15determines that the vehicle2is traveling when the vehicle speed V is higher than a predetermined threshold value Vth, and otherwise determines that the vehicle2is stationary. When it is determined that the vehicle2is stationary (ST4: No), the control unit15determines the type of phase deviation according to the steering angle R and the steered angle α (step ST5) to determine if it is the case of the opposite phase relationship (type A) (step ST6).

In the case of the opposite phase relationship (ST6: Yes), the control unit15acquires the transmission shift position SP (step ST7), and determines if the transmission shift position SP is either the drive position “D” or the reverse position “R” (step ST8). If the driver has not yet operated the shift lever, and the transmission shift position SP is still in the park position “P” or the neural position “N” (ST8: No), or if the determination result of step ST6is No, the control unit15acquires the steering angular velocity βdot (Step ST9). The control unit15determines if the steering angular velocity βdot is 0 (deg/sec) or is within a predetermined small velocity range that can be regarded as 0 (deg/sec) (step ST10). The latter case will be simply referred to as the case of “βdot=0” in the following disclosure for the convenience of description.

When the steering angular velocity βdot is 0 (ST10: Yes), the control unit15repeats the above process. When the steering member10is operated or steered by the driver and the steering angular velocity βdot is not 0 (ST10: No), the control unit15executes a passive phase matching (step ST11). In the passive phase matching in step ST11, at least one of the steering actuator12and the reaction force actuator13is driven so that the phases of the steering angle β and the steered angle α are brought closer to each other while the steering member10is being steered (ST10: No). Here, “bringing the phases of the steering angle β and the steered angle α closer to each other” means that the steering angle β and the steered angle α are brought closer to a prescribed relationship (the gear ratio relationship mentioned above). This phase matching is characterized as “passive” because the phase matching takes place only during a certain action such as a steering operation is being performed. In the present embodiment, the control unit15drives the steering actuator12in order to match the phases of the steering angle β and the steered angle α.

In the passive phase matching in step ST11, the control unit15causes the steering actuator12to bring the phases of the steering angle θ and the steered angle α closer to each other using the event of operating the steering member10as a trigger (ST10: No). In this way, since the steered angle α is brought closer to the steering angle β in phase by using the operation of the steering member10as a trigger, the front wheels3is prevented from being steered without the driver anticipating it.

FIG.5is a time chart showing changes in the steered angle α in the passive phase matching. As shown inFIG.5, in the passive phase matching, the control unit15drives the steering actuator12so as to gradually reduce the deviation Δα(=αt−α) between the target steered angle αt which is set according to the steering angle β and the actual steered angle α. Even when the steering member10is steered in a direction to come closer to the phase of the steered angle α, if the steering speed of the steering member10is equal to or higher than a predetermined steering speed, the control unit15drives the steering actuator12so that the front wheels3are steered in the same direction as the steering direction of the steering member10.

Referring toFIG.4once again, in the passive phase matching in step ST11, the control unit15repeats the above process, or ceases driving the steering actuator12using the event of ceasing the operation of the steering member10as a trigger (ST10: Yes). As a result, the steered angle α is kept constant while the steering member10is not operated so that the driver is prevented from experiencing any discomfort.

When the driver performs a transmission shift operation to change the transmission shift position SP to the drive position “D” or the reverse position “R”, the determination result in step ST8becomes Yes, and the control unit15performs an opposite phase matching (step ST12). The opposite phase matching is a control process in which at least one of the steering actuator12and the reaction force actuator13is driven so that the phases of the steering angle β and the steered angle α are brought closer to each other, and into the same phase regardless if the steering member10is steered or not.

The opposite phase matching in step ST12is triggered by the occurrence of the event that the transmission shift position SP is changed from the park position “P” or the neutral position “N” to the drive position “D” or the reverse position “R” in the determination process of step ST8. In other words, the control unit15starts the opposite phase matching on condition that the transmission shift position SP has been changed from the park position “P” or the neutral position “N” to a travel position. The opposite phase matching may be started immediately after this condition is met, possibly with a certain time delay.

In this way, triggered by the driver's to change the transmission shift position SP from the park position “P” or the neutral position “R” to the travel position, the control unit15performs the opposite phase matching in step ST12, and brings the phases of the steered angle α and the steering angle β closer to each other. Therefore, only when the driver intends to start the vehicle, the phases of the steered angle α and the steering angle β are brought closer to each other.

In the present embodiment, the control unit15drives the steering actuator12in order to bring the steering angle β and the steered angle α into the same phase. In the opposite phase matching (ST12) of the present embodiment, the control unit15drives the steering actuator12with the target steered angle α t set at 0° (neutral position), and once the steered angle α coincides with the target steered angle α t, and once the phase of the steered angle α becomes the same as the phase of the steering angle β, ceases driving the steering actuator12. Here, the target steered angle α t may be set to any value as long as it is within a certain range of 0° in the same phase relationship with steering angle β.

The steering actuator12ceases to be driven when the control unit15has determined that the direction of the steering angle β and the direction of the steered angle α coincide with each other (ST6: No). As a result, even when the steering member10is not operated (ST10: Yes), the steered angle α and/or the steering angle β are prevented from unnecessarily changing, and the vehicle2is prevented from traveling in a direction which the driver does not expect.

The opposite phase matching in step ST12is performed regardless of whether the steering member10has been operated or not, unlike in the case of the passive phase matching in step ST11. Therefore, when the direction of the steering angle β and the direction of the steered angle α are opposite to each other (ST6: Yes), the phases of the steered angle α and the steering angle β can be brought close to each other immediately after the transmission shift position SP is changed from the park position “P” or the neutral position “N” to the travel position regardless of the operation of the steering member10.

When the control unit15executed the opposite phase matching in step ST12, the type of phase deviation is subsequently determined to be the opposite phase type in step ST6(ST6: No). In this case, the control process executed by the control unit15advances the step ST9, and executes the passive phase matching (ST11) for matching the phases of the steering angle β and the steered angle α with each other while the steering member10is not steered (ST10: No).

Further, when the direction of the steering angle β and the direction of the steered angle α are opposite to each other (ST6: Yes), the passive phase matching in step ST11is executed by using the operation of the steering member10(ST10: No) while the transmission shift position SP is the park position “P” or the neutral position “N” (ST8: No) as a trigger. In this way, when the direction of the steering angle β and the direction of the steered angle α are opposite to each other, by using the operation of the steering member10as a trigger, the phases of a and the steering angle β can be brought close to each other without causing any discomfort to the driver.

If the vehicle2starts traveling without completing the phase matching of the steering angle β and the steered angle α by the passive phase matching in step ST11, it is determined in step ST4that the vehicle2is traveling (ST4: Yes). In this case, the control unit15limits the vehicle speed by setting an upper limit value for the vehicle speed V (step ST13). For example, the control unit15sets the upper limit value of the vehicle speed V to 10 km/h. Once the phase matching control process is completed, the control unit15releases the upper limit value of the vehicle speed V. Therefore, the vehicle2is prevented from traveling at a vehicle speed V higher than the upper limit value until the phases of the steering angle β and the steered angle α are matched with each other, and the determination result in step ST2becomes No or, in other words, until the phase matching control shown inFIG.4is completed.

In this way, if the vehicle2starts traveling (ST4: Yes) with the phases of the steering angle β and the steered angle α deviated from each other, the steering angle β and the steered angle α, the control unit15sets an upper limit value for the vehicle speed V until the phase matching is completed (ST13). As a result, the vehicle2is prevented from traveling at high speed in a direction which is not intended by the driver.

Thereafter, the control unit15acquires the steering angular velocity βdot (step ST14), and determines whether the steering angular velocity βdot is 0 (step ST15) or not. When the steering angular velocity βdot is 0 (ST15: Yes), the control unit15executes an active phase matching (step ST16). The active phase matching is a control action by which at least one of the steering actuator12and the reaction force actuator13is driven so that the phases of the steering angle β and the steered angle α are gradually brought into agreement after the vehicle2has started traveling (ST4: Yes) even when the driver does not steer the steering member10(ST15: Yes). In the present embodiment, the control unit15drives the steering actuator12in order to match the phases of the steering angle β and the steered angle α.

In this way, regardless of whether the steering member10is operated or not, the control unit15executes the active phase matching in step ST16so that the vehicle2is prevented from traveling at high speed in a direction which is not indented by the driver even when the steering member10is not operated. By executing the active phase matching, the phases of the steering angle β and the steered angle α are always brought into agreement after the vehicle2has started traveling. The phase matching control is concluded once the determination result in step ST2becomes No. Thereby, the upper limit of the vehicle speed V is released.

FIG.6is a time chart showing changes in the steered angle α due to the active phase matching. As shown inFIG.6, once the vehicle speed V becomes higher than a predetermined threshold value Vth, the control unit15initiates the active phase matching, and drives the steering actuator12so that the phase deviation between the steering angle β and the steered angle α is decreased.

At this time, in driving the steering actuator12, the control unit15multiplies a deceleration gain G to the first current value A1 computed from to the deviation Δα between the target steered angle αt and the actual steered angle α in order to reduce the changing speed of the steered angle α as compared to the case of the normal steering angle control. As a result, the rate of change of the steered angle α becomes slower than in the normal state, and the vehicle2is prevented from behaving in a manner not anticipated by the driver.

The deceleration gain G may be selected so as to change with the vehicle speed V. More specifically, the deceleration gain G may be selected as a relatively large value when the vehicle speed V is low, and may be selected as a smaller value so that the change speed of the steered angle α is made slower with an increase in the vehicle speed V. As a result, when the vehicle speed V is low, and the change in the steered angle α has a small effect on the vehicle behavior, the steered angle α is changed at a relatively high speed. Conversely, when the vehicle speed V is high, and the change in the steered angle α has a large effect on the vehicle behavior, the steered angle α is changed at a relative low speed. Thereby, the vehicle2is prevented from behaving in an unexpected manner.

Referring toFIG.4once again, when the steering member10is steered by the driver while the vehicle2is traveling (ST4: Yes), and the steering angular velocity βdot is not 0 (ST15: No), the control unit15executes the passive phase matching (Step ST17). In the passive phase matching in step ST17, at least one of the steering actuator12and the reaction force actuator13is driven so that the phases of the steering angle β and the steered angle α are matched while the steering member10is not steered (ST15: No). In the present embodiment, the control unit15drives the steering actuator12in order to match the phases of the steering angle β and the steered angle α.

In the passive phase matching in step ST17, the control unit15drives the steering actuator12in such a manner that the change speed of the steered angle α is faster as compared to the case of the active phase matching (ST16) which is executed when the steering member10is operated. As a result, the steered angle α is caused to change at a high speed during the steering operation because the driver can easily predict the behavior of the vehicle2in such a situation, with the result that the phases of the steering angle β and the steered angle α can be matched at an early stage.

When the phases of the steering angle β and the steered angle α are matched by the passive phase matching in step ST11, the active phase matching in step ST16, or the passive phase matching in step ST17, and the determination result in step ST2becomes No, the phase matching control is concluded.

Next, examples of vehicle behavior during the phase matching control ofFIG.4will be described in the following with reference toFIGS.7to9.

In the example shown inFIG.7, at time point t1, the ignition switch is turned on, and the control unit15is activated. At this time, the phases of the steering angle β of the steering member10and the steered angle α of the front wheels3are opposite to each other because the steering member is turned left and the front wheels are steered to the right. When the transmission shift position SP is changed from the park position “P” or the neutral position “N” to the travel position at time point t2, the control unit15starts the opposite phase matching (ST12) using the shift change as a trigger.

Owing to the control action of the opposite phase matching, the target steered angle α t is set to 0°, the steering actuator12is commanded to steer to the left, and the front wheels3are steered to the left. At time point t3, the steered angle α becomes 0°, and the opposite phase matching is completed. The vehicle speed V is maintained at 0 km/h from time point t2to time point t3.

During the time interval between time point t2and time point t3where the opposite phase matching is executed, the control unit15notifies the driver by visual display or sound that the phase synchronization is in progress (phase matching is being executed).

In the example shown inFIG.8, at time point t11, the ignition switch is turned on and the control unit15is activated. At this time, the phases of the steering angle β of the steering member10and the steered angle α of the front wheels3are in the same phase because the former has a small value to the right and the latter has a large value to the right. At time t12, the transmission shift position SP is changed from the park position “P” or the neutral position “N” to the travel position. As this is a case of the same phase, the opposite phase matching is not performed.

When it is determined that the vehicle2has started traveling at time point t13, and the vehicle speed V becomes higher than the predetermined threshold value Vth at time point t14, using this as a trigger, the control unit15sets an upper limit value for the vehicle speed V. Since the steering member10is not steered at time point t14, the control unit15starts the active phase matching (ST16).

Owing to the control action of the active phase matching, the target steered angle αt is set to a value corresponding to the steering angle β, and the steering actuator12is commanded to steer to the left so that the front wheels3are steered to the left. At time point t15, the actual steered angle α becomes equal to the target steered angle αt corresponding to the steering angle β, and the active phase matching is concluded. During the time interval between time point t14and time point t15, the control unit15notifies the driver by visual display or sound that the phase matching is in progress (phase matching is being executed).

In the example shown inFIG.9, at time point t21, the ignition switch is turned on and the control unit15is activated. At this time, the steering angle β of the steering member10and the steered angle α of the front wheels3are in the same phase because the former is 0° and the latter is a large value to the right. At time t22, the transmission shift position SP is changed from the park position “P” or the neutral position “N” to the travel position. Since they are in the same phase, the opposite phase matching is not performed.

When it is determined that the vehicle2starts traveling at time point t23and the vehicle speed V becomes larger than the predetermined threshold value Vth at time point t24, the control unit15sets an upper limit value for the vehicle speed V using this as a trigger. Since the steering member10is not steered at time point t24, the control unit15initiates the active phase matching (ST16).

Owing to the control action of the active phase matching, the target steered angle α t is set to a value (0°) corresponding to the steering angle β, the steering actuator12is commanded to steer to the left, and the front wheels3are steered to the left. When the steering member10starts to be turned to the right at time t25, the control unit15switches from the active phase matching to the passive phase matching (ST17). In the passive phase matching, the control unit15steers the front wheels3in the same direction as the steering member10so that the steered angle α of the front wheels3increases to the right, but the phase deviation of between the steered angle α and the steering angle β (or the deviation Δα between the actual steered angle α and the target steered angle αt which is set in accordance with the steering angle β) becomes smaller.

When the turning of the steering member10is stopped at time point t26, and the steering angle β starts to be maintained at a constant value without any steering operation, the control unit15initiates the active phase matching once again. A leftward steering command is given to the steering actuator12, and the front wheels3are steered to the left. When the steering member10starts to be turned to the left at time point t27, the control unit15switches from the active phase matching to the passive phase matching again. In the passive phase matching, the control unit15steers the front wheels3in the same direction as the steering direction of the steering member10so that the deviation Δα between the target steered angle αt and the actual steered angle α gradually decreases. The front wheels3are thus steered to the left, and at time point t28, the steered angle α comes to correspond to the target steered angle α t, or the value corresponding to the steering angle β. As a result, the phases of the steering angle β and the steered angle α are matched, and the phase matching control is completed.

During the time interval between time point t24and time point28or during the time the active phase matching or the passive phase matching are being executed, the control unit15notifies the driver by visual display or sound that the phase matching is in progress (phase matching is being executed).

As described above, according to the present embodiment, as shown inFIG.4, if the steered angle α deviates from the prescribed relationship with respect to the steering angle β at the time of activation (ST2: Yes), using the shifting of the transmission shift position SP from the park position “P” or the neutral position “N” to the travel position (ST8: Yes), the control unit15drives at least one of the steering actuator12and the reaction force actuator13(ST12) so as to bring the steered angle α closer to the prescribed relationship with the steering angle β. Therefore, only when the driver has an intention to start the vehicle, the steered angle α and the steering angle β can be brought closer to the prescribed relationship.

The present invention has been described in terms of a specific embodiment, but is not limited by such an embodiment, and can be modified in various ways without departing from the scope of the present invention. In the foregoing embodiment, it was arranged such that the control unit15drives the steering actuator12in the opposite phase matching in step ST12, but the control unit15drive the reaction force actuator13instead of or in addition to the steering actuator12. Also, the specific configuration, arrangement, quantity, angle, procedure, and the like of each member and part can be appropriately changed without deviating from the gist of the present invention. Further, all of the components shown in the above embodiments are not necessarily essential to the present invention, and can be appropriately selected and omitted without departing from the gist of the present invention.

[Reference Signs List]1: steering device2: vehicle3: front wheel10: steering member11: steering mechanism12: steering actuator13: reaction force actuator15: control unit21: steering angle sensor32: steered angle sensor35: transmission deviceα: steered angleβ: steering angleSP: transmission shift position