Steering device

A steering device includes a steering member, a steering operation mechanism, a reactive force motor, a steering motor that drives the steering operation mechanism, a steering torque sensor, and an electronic control unit. The electronic control unit sets a manual steering angle command value. The electronic control unit computes a reactive-force-related composite angle command value. The electronic control unit computes a steering-related composite angle command value based on a steering-related automatic steering angle command value and the manual steering angle command value. The electronic control unit causes a rotational angle of the reactive force motor to follow the reactive-force-related composite angle command value. The electronic control unit causes a rotational angle of the steering motor to follow the steering-related composite angle command value. The electronic control unit estimates a first disturbance torque.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2020-120594 filed on Jul. 14, 2020, incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The disclosure relates to a steering device in which a steering operation mechanism is driven by a steering motor, in a state in which a steering member operated for steering and the steering operation mechanism are not mechanically linked.

2. Description of Related Art

Japanese Unexamined Patent Application Publication No. 2004-224238 (JP 2004-224238 A) discloses a steer-by-wire system in which a steering operation mechanism is driven by a steering motor, in a state in which a steering member operated for steering and the steering operation mechanism are not mechanically linked. The steer-by-wire system described in JP 2004-224238 A is provided with an operating unit that has an operating reactive force motor, a steering unit that has a steering motor, an operation reactive force control unit that controls the operating unit, a turning control unit that controls the steering unit, and an automatic following system. The turning control unit controls the steering motor based on a final target steered angle.

In the automatic following system in JP 2004-224238 A, the final target steered angle is set as follows. When the automatic following system is not operating, a target steered angle computed based on an operating angle of an operating wheel is set as the final target steered angle. When the automatic following system is operating and steering torque is no lower than a first threshold value, or when the automatic following system is operating and the operating angle is no lower than a second threshold value, a value obtained by multiplying the target steered angle computed based on the operating angle of the operating wheel by a predetermined value that is larger than 1 is set as the final target steered angle. When the automatic following system is operating and the steering torque is lower than the first threshold value and also the operating angle is lower than the second threshold value, a target steered angle set by the automatic following system is set as the final target steered angle.

SUMMARY

In the steer-by-wire system described in the aforementioned JP 2004-224238 A, during automatic steering control in which the automatic following system is operating, intent of a driver is not reflected in the target steered angle until the steering torque reaches the first threshold value or higher, or the operating angle reaches the second threshold value or higher. It is an object of the disclosure to provide a steering device capable of promptly reflecting intent of the driver with regard to the steering motor and the reactive force motor during automatic steering control.

An aspect of the disclosure is a steering device. The steering device includes a steering member, a steering operation mechanism mechanically separated from the steering member, a reactive force motor configured to impart reactive force torque to the steering member, a steering motor configured to drive the steering operation mechanism; a steering torque sensor configured to detect steering torque imparted to the steering member; and an electronic control unit. The electronic control unit is configured to set a manual steering angle command value based on the steering torque. The electronic control unit is configured to compute a reactive-force-related composite angle command value based on a reactive-force-related automatic steering angle command value and the manual steering angle command value. The electronic control unit is configured to compute a steering-related composite angle command value based on a steering-related automatic steering angle command value and the manual steering angle command value. The electronic control unit is configured to cause a rotational angle of the reactive force motor to follow the reactive-force-related composite angle command value. The electronic control unit is configured to cause a rotational angle of the steering motor to follow the steering-related composite angle command value. The electronic control unit is configured to estimate first disturbance torque. The first disturbance torque is disturbance torque other than motor torque of the steering motor acting on an object of driving by the steering motor.

According to the above configuration, intent of the driver can be promptly reflected with regard to the steering motor and the reactive force motor during automatic steering control.

In the steering device, the electronic control unit may be configured to compute a first basic command value based on the steering-related composite angle command value, and may be configured to compensate the first basic command value by the first disturbance torque. According to the above configuration, the first basic command value is compensated by the first disturbance torque, and accordingly the effects of disturbance on the angle control capabilities of the electronic control unit can be suppressed. Thus, highly precise angle control of the steering motor can be realized.

In the steering device, the electronic control unit may be configured to compute a second basic command value based on the reactive-force-related composite angle command value. The electronic control unit may be configured to estimate second disturbance torque. The second disturbance torque may be a disturbance torque other than motor torque of the reactive force motor acting on an object of driving by the reactive force motor. The electronic control unit may be configured to compensate the second basic command value by the second disturbance torque.

In the steering device, the electronic control unit may be configured to use estimated torque calculated based on the first disturbance torque to generate the manual steering angle command value.

DETAILED DESCRIPTION OF EMBODIMENTS

An embodiment of the disclosure will be described below in detail with reference to the attached drawings.

1. Schematic Configuration of Steering Device1

A steering device1includes a steering wheel2serving as a steering member by which a vehicle is steered, a steering operation mechanism4for steering steered wheels3, and a steering shaft5linked to the steering wheel2, as illustrated inFIG.1. Note, however, that there is no mechanical linkage between the steering shaft5and the steering operation mechanism4whereby torque, motion such as rotations, and so forth, would be transmitted.

The steering shaft5includes a first shaft7of which one end is linked to the steering wheel2, a torsion bar8of which one end is linked to the other end of the first shaft7, and a second shaft9of which one end is linked to the other end of the torsion bar8. A torque sensor11is disposed in the proximity of the torsion bar8. The torque sensor11detects steering torque Tdapplied to the steering wheel2based on relative rotational displacement amount of the first shaft7and the second shaft9. In this embodiment, the steering torque Tddetected by the torque sensor11is detected as follows, for example. That is to say, torque for steering toward the left direction is detected as a positive value, and torque for steering toward the right direction is detected as a negative value. The greater the absolute value thereof is, the greater the magnitude of the steering torque Tdis.

A reactive force motor13for controlling the rotational angle of the second shaft9(hereinafter may be referred to as “steering wheel angle”) is linked to the second shaft9via reduction gear12. The reactive force motor13is an electric motor to impart reactive torque to the second shaft9. The reduction gear12is made up of a worm gear mechanism that includes a worm gear (omitted from illustration) that is linked to an output shaft of the reactive force motor13so as to be integrally rotatable therewith, and a worm wheel (omitted from illustration) that is meshed with this worm gear and that is linked to the second shaft9so as to be integrally rotatable therewith. A rotational angle sensor14that detects the rotational angle of the reactive force motor13is provided to the reactive force motor13.

The steering operation mechanism4is made up of a rack-and-pinion mechanism that includes a pinion shaft15and a rack shaft16. The steered wheel3is linked to each end portion of the rack shaft16via a tie rod17and a knuckle arm (omitted from illustration). The pinion shaft15is linked to an output shaft of a steering motor19via reduction gear18. The reduction gear18is made up of a worm gear mechanism that includes a worm gear (omitted from illustration) that is linked to an output shaft of the steering motor19so as to be integrally rotatable therewith, and a worm wheel (omitted from illustration) that is meshed with this worm gear and that is linked to the pinion shaft15so as to be integrally rotatable therewith. A pinion15A is linked to a distal end of the pinion shaft15. A rotational angle sensor20that detects the rotational angle of the steering motor19is provided to the steering motor19.

In the following, the reduction gear ratio (gear ratio) of the reduction gear12is represented by Nr, and the reduction gear ratio of the reduction gear18is represented by Ns. The reduction gear ratio is defined as the ratio of the rotation speed of the worm gear as to the rotation speed of the worm wheel. The rack shaft16extends linearly following the right-left direction of the vehicle. A rack16A that meshes with the pinion15A is formed on the rack shaft16. When the steering motor19rotates, the rotational force thereof is transmitted to the pinion shaft15via the reduction gear18. The rotation of the pinion shaft15is then converted into axial-direction movement of the rack shaft16by the rack-and-pinion mechanism. Thus, the steered wheels3are steered.

A charge-coupled device (CCD) camera25that takes images of the road ahead of the vehicle in the direction of travel, a Global Positioning System (GPS) receiver26for detecting own-vehicle position, a radar system27for detecting road features and obstructions, and map information memory28storing map information, are installed in the vehicle. The CCD camera25, the GPS receiver26, the radar system27, and the map information memory28are connected to a higher-order electronic control unit (ECU)201performing driving assistance control and automatic driving control. The higher-order ECU201performs surrounding-environment recognition, vehicle position estimation, route planning, and so forth, based on information obtained from the CCD camera25, the GPS receiver26, and the radar system27, and the map information obtained from the map information memory28, and decides control target values for steering and drive actuators.

In this embodiment, the higher-order ECU201sets a steering-related automatic steering angle command value for automatic steering as an automatic steering angle command value θad. In this embodiment, automatic steering control is control for causing the vehicle to travel along a target path, for example. The automatic steering angle command value θadis a target value for the steering angle, to cause the vehicle to automatically travel along the target path. Processing of setting such an automatic steering angle command value θadis known, and accordingly detailed description thereof will be omitted here. The automatic steering angle command value θadis an example of a “steering-related automatic steering angle command value” of the disclosure, and also is an example of a “reactive-force-related automatic steering angle command value”.

In this embodiment, the automatic steering angle command value θad, and a later-described assist torque command value Tacand a later-described manual steering angle command value θmd, are set to positive values when rotating the second shaft9in the left-steering direction by the reactive force motor13, or steering the steered wheels3in the left-steering direction by the steering motor19. On the other hand, these command values θad, Tac, and θmdare set to negative values when rotating the second shaft9in the right-steering direction by the reactive force motor13, or steering the steered wheels3in the right-steering direction by the steering motor19. Note that in this embodiment, the automatic steering angle command value θadis set as the rotational angle of the pinion shaft15, and the manual steering angle command value θmdis set as the rotational angle of the second shaft9.

The automatic steering angle command value θadset by the higher-order ECU201is given to a reactive force ECU202and to a steering ECU203via an in-vehicle network. The reactive force ECU202is an ECU for controlling the reactive force motor13, and the steering ECU203is an ECU for controlling the steering motor19. The steering torque Tddetected by the torque sensor11and the output signals of the rotational angle sensor14are input to the reactive force ECU202. The reactive force ECU202controls the reactive force motor13based on these input signals and information given from the higher-order ECU201.

Output signals of the rotational angle sensor20are input to the steering ECU203. The steering ECU203controls the steering motor19based on the output signals of the rotational angle sensor20, information given from the reactive force ECU202, and information given from the higher-order ECU201.

2. Electrical Configuration of Reactive Force ECU202and Steering ECU203

The reactive force ECU202is provided with a microcomputer40, a drive circuit (inverter circuit)31that is controlled by the microcomputer40and that supplies electric power to the reactive force motor13, and a current detecting circuit32for detecting an electrical current flowing to the reactive force motor13(hereinafter referred to as “motor current Irm”), as illustrated inFIG.2.

The microcomputer40is provided with a central processing unit (CPU) and memory (read-only memory (ROM), random access memory (RAM), or the like), and is arranged to function as a plurality of function processing units by executing a predetermined program. The function processing units include a manual steering angle command value setting unit41, a hands-on/off determining unit42, a switchover unit43, a reactive-force-related composite angle command value computing unit44, and a reactive-force-related angle control unit45.

The manual steering angle command value setting unit41is provided so that when the driver operates the steering wheel2, a steering angle corresponding to this steering wheel operation (more accurately, the rotational angle of the second shaft9) is set as the manual steering angle command value θmd. The manual steering angle command value setting unit41sets the manual steering angle command value θmdby using the steering torque Tddetected by the torque sensor11. Details of the manual steering angle command value setting unit41will be described later. The manual steering angle command value θmdset by the manual steering angle command value setting unit41is given to the reactive-force-related composite angle command value computing unit44.

The hands-on/off determining unit42determines whether the driver is gripping the steering wheel2(hands-on) or not gripping the steering wheel2(hands-off). Examples of arrangements that can be used as the hands-on/off determining unit42include an arrangement that determines hands-on/off based on output signals of a touch sensor provided to the steering wheel2, an arrangement that determines hands-on/off based on images taken by a camera provided in the cabin, and so forth. Note that arrangements other than the above-described configurations may be used for the hands-on/off determining unit42, as long as hands-on/off can be determined. A hands-on/off determination signal output from the hands-on/off determining unit42is given to the switchover unit43.

When determination is made by the hands-on/off determining unit42that the driver is gripping the steering wheel2, the switchover unit43gives the automatic steering angle command value θadset by the higher-order ECU201to the reactive-force-related composite angle command value computing unit44as a reactive-force-related automatic steering angle command value θrf. On the other hand, when determination is made by the hands-on/off determining unit42that the driver is not gripping the steering wheel2, the switchover unit43gives zero to the reactive-force-related composite angle command value computing unit44as the reactive-force-related automatic steering angle command value θrf.

The reactive-force-related composite angle command value computing unit44adds the manual steering angle command value θmdset by the manual steering angle command value setting unit41to the reactive-force-related automatic steering angle command value θrfgiven by the switchover unit43, and computes a reactive-force-related composite angle command value θrcmd. The reactive-force-related angle control unit45performs angle control of the reactive force motor13based on the reactive-force-related composite angle command value θrcmd. In this embodiment, the reactive-force-related angle control unit45performs drive control of the drive circuit31so that an estimation value {circumflex over ( )}θrt(seeFIG.6) of a steering angle θrt(rotational angle of the second shaft9) approximates the reactive-force-related composite angle command value θrcmd. The reactive-force-related angle control unit45may perform drive control of the drive circuit31so that the steering angle θrtapproximates the reactive-force-related composite angle command value θrcmd. Details of the reactive-force-related angle control unit45will be described later.

The steering ECU203is provided with a microcomputer80, a drive circuit (inverter circuit)33that is controlled by the microcomputer80and that supplies electric power to the steering motor19, and a current detecting circuit34for detecting an electrical current flowing to the steering motor19(hereinafter referred to as “motor current Ism”).

The microcomputer80is provided with a CPU and memory (ROM, RAM, or the like), and is arranged to function as a plurality of function processing units by executing a predetermined program. The function processing units include a steering-related composite angle command value computing unit81and a steering-related angle control unit82.

The steering-related composite angle command value computing unit81adds the manual steering angle command value θmdset by the manual steering angle command value setting unit41within the reactive force ECU202to the automatic steering angle command value (steering-related steering angle command value) θadset by the higher-order ECU201, and computes a steering-related composite angle command value θscmd. The steering-related angle control unit82performs angle control of the steering motor19based on the steering-related composite angle command value θscmd. In this embodiment, the steering-related angle control unit82performs drive control of the drive circuit33so that an estimation value {circumflex over ( )}θspof a steered angle θsp(rotational angle of the pinion shaft15) (seeFIG.9) approximates the steering-related composite angle command value θscmd. The steering-related angle control unit82may perform drive control of the drive circuit33so that the steered angle θspapproximates the steering-related composite angle command value θscmd. Details of the steering-related angle control unit82will be described later.

3. Configuration of Manual Steering Angle Command Value Setting Unit41

The manual steering angle command value setting unit41includes an assist torque command value setting unit51and a command value setting unit52, as illustrated inFIG.3.

The assist torque command value setting unit51sets the assist torque command value Tacthat is a target value for assist torque necessary for manual operations. The assist torque command value setting unit51sets the assist torque command value Tacbased on the steering torque Tddetected by the torque sensor11.FIG.4shows a setting example of the assist torque command value Tacas to the steering torque Td.

The assist torque command value Tacassumes a positive value as to a positive value for the steering torque Td, and assumes a negative value as to a negative value for the steering torque Td. The assist torque command value Tacis set so as to have a larger absolute value the greater the absolute value of the steering torque Tdis. Note that the assist torque command value setting unit51may compute the assist torque command value Tacby multiplying the steering torque Tdby a constant that is set in advance.

In this embodiment, the command value setting unit52sets a manual steering command value θmdacusing a reference electric power steering (EPS) model.FIG.5is a schematic diagram illustrating an example of the reference EPS model used by the command value setting unit52. This reference EPS model is a single inertia model that includes a lower column. InFIG.5, Jcrepresent inertia of the lower column, θcrepresents the rotational angle of the lower column, and Tdrepresent the steering torque. The steering torque Td, torque Nc·Tmfrom the electric motor (assist motor), and road surface load torque Trlare applied to the lower column. Ncis the reduction gear ratio of the reduction gear provided on a transmission path between the assist motor and the lower column, and Tmis motor torque generated by the assist motor. The road surface load torque Trlis expressed by the following Expression (1), using a spring constant k and a viscous damping coefficient c.
Trl=−kθc−c{dot over (θ)}c(1)

In this embodiment, predetermined values found in advance through experimentation, analysis, and so forth, are set as the spring constant k and the viscous damping coefficient c. Accordingly, the Tri computed by Expression (1) is a virtual road surface load torque. The equation of motion of the reference EPS model is expressed by the following Expression (2).
Jc{umlaut over (θ)}c=Td·Nc·Tm−kθc−c{dot over (θ)}c(2)

The command value setting unit52computes the rotational angle θcof the lower column by substituting the steering torque Tddetected by the torque sensor11into Td, and substituting the assist torque command value Tacset by the assist torque command value setting unit51into Nc·Tm, and solving the differential equation of Expression (2). The command value setting unit52then sets the obtained rotational angle θcof the lower column as the manual steering angle command value θmd.

4. Configuration of Reactive-Force-Related Angle Control Unit45

The reactive-force-related angle control unit45controls the drive circuit31of the reactive force motor13based on the reactive-force-related composite angle command value θrcmd, the motor current Irmdetected by the current detecting circuit32, and output signals of the rotational angle sensor14, as illustrated inFIG.6. The reactive-force-related angle control unit45includes an angle deviation computing unit61, a proportional-derivative (PD) control unit62, a disturbance torque estimating unit63, a disturbance torque compensating unit64, a first reduction gear ratio dividing unit65, a reduction gear ratio multiplying unit66, a current command value computing unit67, a current deviation computing unit68, a proportional-integral-derivative (PID) control unit69, a pulse-width modulation (PWM) control unit70, a rotational angle computing unit71, and a second reduction gear ratio dividing unit72.

The rotational angle computing unit71computes a rotor rotational angle θrmof the reactive force motor13based on output signals of the rotational angle sensor14. The second reduction gear ratio dividing unit72converts the rotor rotational angle θrminto the rotational angle (actual steering angle) θrtof the second shaft9, by dividing the rotor rotational angle θrm, computed by the rotational angle computing unit71, by the reduction gear ratio Nrof the reduction gear12. The disturbance torque estimating unit63is provided to estimate nonlinear torque generated as disturbance (disturbance torque, i.e., torque other than reactive force motor torque) at a control object of the reactive force motor13(hereinafter referred to as “first plant”). The disturbance torque estimating unit63estimates disturbance torque (disturbance load) Trtd, steering angle θrt, and steering angle derivative value (angular velocity) dθrt/dt, based on a torque command value Nr·Trcmdthat is an input value of the first plant, and the actual steering angle θrtthat is output of the first plant. Estimation values of the disturbance torque Trtd, steering angle θrt, and steering angle derivative value dθrt/dt, will respectively be written as {circumflex over ( )}Trtd, {circumflex over ( )}θrt, and d{circumflex over ( )}θrt/dt. Details of the disturbance torque estimating unit63will be described later.

The disturbance torque estimation value {circumflex over ( )}Trta computed by the disturbance torque estimating unit63is given to the disturbance torque compensating unit64as a disturbance torque compensation value. The steering angle estimation value {circumflex over ( )}θrtcomputed by the disturbance torque estimating unit63is given to the angle deviation computing unit61. The angle deviation computing unit61computes the deviation Δθrbetween the reactive-force-related composite angle command value θrcmdand the steering angle estimation value {circumflex over ( )}θrt(i.e., θrcmd−{circumflex over ( )}θrt). Note that the angle deviation computing unit61may compute the deviation between the reactive-force-related composite angle command value θrcmdand the actual steering angle θrtcomputed by the second reduction gear ratio dividing unit72(θrcmd−θrt) as the angular deviation Δθr.

The PD control unit62performs PD computation with regard to the angular deviation Δθrcomputed by the angle deviation computing unit61, thereby computing a basic torque command value Trcmda(basic torque command value as to the second shaft9). The disturbance torque compensating unit64subtracts the disturbance torque estimation value {circumflex over ( )}Trtdfrom the basic torque command value Trcmda, thereby computing a torque command value Trcmdb(i.e., Trcmda−{circumflex over ( )}Trtd). This yields a disturbance-torque-compensated torque command value Trcmdb(torque command value as to the second shaft9).

The first reduction gear ratio dividing unit65divides the torque command value Trcmdbby the reduction gear ratio Nr, thereby computing a motor torque command value Trcmdwith regard to the reactive force motor13. This motor torque command value Trcmdis given to the current command value computing unit67, and also to the reduction gear ratio multiplying unit66. The reduction gear ratio multiplying unit66multiplies the motor torque command value Trcmdby the reduction gear ratio Nrto convert the motor torque command value Trcmdinto the torque command value Nr·Trcmdfor the second shaft9. This torque command value Nr·Trcmdis given to the disturbance torque estimating unit63.

The current command value computing unit67divides the motor torque command value Trcmdcomputed by the first reduction gear ratio dividing unit65by a torque constant Krof the reactive force motor13, thereby computing a current command value Ircmd. The current deviation computing unit68computes the deviation ΔIrbetween the current command value Ircmdobtained by the current command value computing unit67and the motor current Irmdetected by the current detecting circuit32(i.e., Ircmd−Irm).

The PID control unit69performs PID computation with regard to the current deviation ΔIrcomputed by the current deviation computing unit68, thereby generating a drive command value for transitioning the motor current Irmflowing to the reactive force motor13to the current command value Ircmd. The PWM control unit70generates PWM control signals of a duty ratio corresponding to the drive command value, which are supplied to the drive circuit31. Accordingly, electric power corresponding to the drive command value is supplied to the reactive force motor13.

4.1 Detailed Description of Disturbance Torque Estimating Unit63

The disturbance torque estimating unit63is configured of a disturbance observer that estimates disturbance torque Trta, steering angle θrt, and angular velocity dθrt/dt, using a physical model301of a reactive-force-motor-side mechanism illustrated inFIG.7A, for example. InFIG.7A, the worm wheel of the reduction gear12inFIG.1is denoted by12ww, and the worm gear of the reduction gear12is denoted by12wg.

This physical model301includes a first plant302including the second shaft9and the worm wheel12wwfixed to the second shaft9. The first plant302is given motor torque Nr·Trcomfrom the reactive force motor13and disturbance torque Trtd. The disturbance torque Trtdincludes the steering torque Tdgiven to the first plant302from the steering wheel2via the torsion bar8, and disturbance torque Trotherother than the steering torque Td. The disturbance torque Trotherother than the steering torque Tdincludes frictional torque due to friction between the worm wheel12wwand the worm gear12wg.

The equation of motion for inertia of the physical model301is as expressed in the following Expression (3)
Jrθrt=Nr·Trcmd+Trtd
Trtd=Td+Trother(3)
where Jrrepresents the inertia of the first plant302.

Here, d2θ/dt2is the angular acceleration of the first plant302. Trtdrepresents the disturbance torque given to the first plant302. In this embodiment, the disturbance torque estimating unit63estimates the disturbance torque Trtd, the steering angle θrt, and the angular velocity dθrt/dt, based on the disturbance observer constructed from the equation of motion for inertia of the physical model301(extended state observer). This will be described in detail below.

The equation of state for the physical model301inFIG.7Ais as expressed in the following Expression (4).

Here, x is a state variable vector, u1is a known input vector, u2is an unknown input vector, and y is an output vector (measured value). Also, A is a system matrix, B1is a first input matrix, B2is a second input matrix, C is an output matrix, and D is a direct matrix. The above equation of state is extended to a system including the unknown input vector u2as one state. The equation of state of the extended system (extended equation of state) is expressed by the following Expression (5).

Aeis a system matrix of the extended system, Beis a known input matrix of the extended system, and Ceis an output matrix of the extended system. Also, xeis a state variable vector of the extended system, and is expressed as in the following Expression (6).

From the extended equation of state in the above Expression (5), a disturbance observer expressed by the equation of the following Expression (7) (extended state observer) is constructed.

Here, {circumflex over ( )}xerepresents an estimation value of xe. L is an observer gain. Also, {circumflex over ( )}y represents an estimation value of y. Further, {circumflex over ( )}xeis as expressed by the following Expression (8).

Here, {circumflex over ( )}θrtis an estimation value of θrt, and {circumflex over ( )}Trtdis an estimation value of Trtd. The disturbance torque estimating unit63computes a state variable vector {circumflex over ( )}xebased on the equation of Expression (7) above. The disturbance torque estimating unit63includes an input vector input unit91, an output matrix multiplying unit92, a first adding unit93, a gain multiplying unit94, an input matrix multiplying unit95, a system matrix multiplying unit96, a second adding unit97, an integrating unit98, and a state variable vector output unit99, as illustrated inFIG.8.

The torque command value Nr·Trcmdcomputed by the reduction gear ratio multiplying unit66(seeFIG.6) is given to the input vector input unit91. The input vector input unit91outputs an input vector u1. The output of the integrating unit98is the state variable vector {circumflex over ( )}xe(see Expression (8) above). When starting computation, an initial value is given as the state variable vector {circumflex over ( )}xe. The initial value of the state variable vector {circumflex over ( )}xeis 0, for example.

The system matrix multiplying unit96multiples the state variable vector {circumflex over ( )}xeby a system matrix Ae. The output matrix multiplying unit92multiples the state variable vector {circumflex over ( )}xeby the output matrix Ce. The first adding unit93subtracts the output (Ce·{circumflex over ( )}xe) of the output matrix multiplying unit92from the output vector (measured value) y that is the actual steering angle θrtcomputed by the second reduction gear ratio dividing unit72(seeFIG.6). That is to say, the first adding unit93computes the difference (y−{circumflex over ( )}y) between the output vector y and the output vector estimation value {circumflex over ( )}y (i.e., Ce·{circumflex over ( )}xe). The gain multiplying unit94multiples the output (y−{circumflex over ( )}y) of the first adding unit93by the observer gain L (see Expression (7) above).

The input matrix multiplying unit95multiples the input vector u1output from the input vector input unit91by the input matrix Be. The second adding unit97adds the output of the input matrix multiplying unit95(Be·u1), the output of the system matrix multiplying unit96(Ae·{circumflex over ( )}xe), and the output of the gain multiplying unit94(L(y−{circumflex over ( )}y)), thereby computing a derivative value d{circumflex over ( )}xe/dt of the state variable vector. The integrating unit98integrates the output (d{circumflex over ( )}xe/dt) of the second adding unit97, thereby computing the state variable vector {circumflex over ( )}xe. The state variable vector output unit99computes the disturbance torque estimation value {circumflex over ( )}Trtd, the steering angle estimation value {circumflex over ( )}θrt, and angular velocity estimation value d{circumflex over ( )}θrt/dt, based on the state variable vector {circumflex over ( )}xe.

5. Configuration of Steering-Related Angle Control Unit82

The steering-related angle control unit82controls the drive circuit33of the steering motor19based on the steering-related composite angle command value θscmd, and the motor current Ismdetected by the current detecting circuit34and the output signals of the rotational angle sensor20, as illustrated inFIG.9. The steering-related angle control unit82includes an angle deviation computing unit101, a PD control unit102, a disturbance torque estimating unit103, a disturbance torque compensating unit104, a third reduction gear ratio dividing unit105, a reduction gear ratio multiplying unit106, a current command value computing unit107, a current deviation computing unit108, a PID control unit109, a PWM control unit110, a rotational angle computing unit111, and a fourth reduction gear ratio dividing unit112.

The rotational angle computing unit111computes a rotor rotational angle θsmof the steering motor19based on output signals of the rotational angle sensor20. The fourth reduction gear ratio dividing unit112converts the rotor rotational angle θsmcomputed by the rotational angle computing unit111into the rotational angle (actual steered angle) θspof the pinion shaft15by dividing the rotor rotational angle θsmby a reduction gear ratio Nsof the reduction gear18. The disturbance torque estimating unit103is provided to estimate nonlinear torque generated as disturbance (disturbance torque, i.e., torque other than steering motor torque) at a control object of the steering motor19(hereinafter referred to as “second plant”). The disturbance torque estimating unit103estimates disturbance torque (disturbance load) Tstd, steered angle θsp, and steered angle derivative value (angular velocity) dθsp/dt, based on a torque command value Ns·Tscmdthat is an input value of the second plant, and the actual steered angle θspthat is output of the second plant. Estimation values of the disturbance torque Tstd, the steered angle θsp, and the steered angle derivative value dθsp/dt, will respectively be written as {circumflex over ( )}Tstd, {circumflex over ( )}θsp, and d{circumflex over ( )}θsp/dt. Details of the disturbance torque estimating unit103will be described later.

The disturbance torque estimation value {circumflex over ( )}Tstdcomputed by the disturbance torque estimating unit103is given to the disturbance torque compensating unit104as a disturbance torque compensation value. The steered angle estimation value {circumflex over ( )}θspcomputed by the disturbance torque estimating unit103is given to the angle deviation computing unit101. The angle deviation computing unit101computes the deviation Δθspbetween the steering-related composite angle command value θscmdand the steered angle estimation value {circumflex over ( )}θp(i.e., θscmd−{circumflex over ( )}θsp). Note that the angle deviation computing unit101may compute the deviation between the steering-related composite angle command value θscmdand the actual steered angle θspcomputed by the fourth reduction gear ratio dividing unit112(θscmd−θsp) as the angular deviation Δθs.

The PD control unit102performs PD computation with regard to the angular deviation Δθscomputed by the angle deviation computing unit101, thereby computing a basic torque command value Tscmda(basic torque command value as to the pinion shaft15). The disturbance torque compensating unit104subtracts the disturbance torque estimation value {circumflex over ( )}Tstdfrom the basic torque command value Tscmda, thereby computing a torque command value Tscmdb(i.e., Tscmda−{circumflex over ( )}Tstd). This yields a disturbance-torque-compensated torque command value Trcmdb(torque command value as to the pinion shaft15).

The third reduction gear ratio dividing unit105divides the torque command value Tscmdbby the reduction gear ratio Ns, thereby computing a motor torque command value Tscmdwith regard to the steering motor19. This motor torque command value Tscmdis given to the current command value computing unit107, and also to the reduction gear ratio multiplying unit106. The reduction gear ratio multiplying unit106multiples the motor torque command value Tscmdby the reduction gear ratio Nsto convert the motor torque command value Tscmdinto the torque command value Ns·Tscmdfor the pinion shaft15. This torque command value Ns·Tscmdis given to the disturbance torque estimating unit103.

The current command value computing unit107divides the motor torque command value Tscmdcomputed by the third reduction gear ratio dividing unit105by a torque constant Ks of the steering motor19, thereby computing a current command value Iscmd. The current deviation computing unit108computes the deviation ΔIsbetween the current command value Iscmdobtained by the current command value computing unit107and the motor current Ismdetected by the current detecting circuit34(i.e., Iscmd−Ism).

The PID control unit109performs PID computation with regard to the current deviation ΔIscomputed by the current deviation computing unit108, thereby generating a drive command value for transitioning the motor current Ismflowing to the steering motor19to the current command value Iscmd. The PWM control unit110generates PWM control signals of a duty ratio corresponding to the drive command value, which are supplied to the drive circuit33. Accordingly, electric power corresponding to the drive command value is supplied to the steering motor19.

5.1 Detailed Description of Disturbance Torque Estimating Unit103

The disturbance torque estimating unit103is configured of a disturbance observer that estimates disturbance torque Tstd, steered angle θsp, and angular velocity dθsp/dt, using a physical model303of a steering-motor-side mechanism illustrated inFIG.7B, for example. InFIG.7B, the worm wheel of the reduction gear18inFIG.1is denoted by18ww, and the worm gear of the reduction gear18is denoted by18wg.

This physical model303includes a second plant304(object of driving by steering motor19) including the pinion shaft15and the worm wheel18wwfixed to the pinion shaft15. The second plant304is given motor torque Ns·Tscomfrom the steering motor19and disturbance torque Tstd. The disturbance torque Tstdincludes road surface load torque Trl, and disturbance torque Tsotherother than the road surface load torque Trl. The disturbance torque Tsotherother than the road surface load torque Tri includes frictional torque due to friction between the worm wheel18wwand the worm gear18wg.

The equation of motion for inertia of the physical model303is as expressed in the following Expression (9)
Js{umlaut over (θ)}so=Ns·Tscomd+Tstd
Tstd=Trl+Tsother(9)
where Jsrepresents the inertia of the second plant304.

Here, d2θ/dt2is the angular acceleration of the second plant304. Tstdrepresents the disturbance torque given to the second plant304. The disturbance torque estimating unit103estimates the disturbance torque Tstd, the steered angle θsp, and the angular velocity dθsp/dt, by a method similar to that of the disturbance torque estimating unit63described above, based on the equation of motion in Expression (9). That is to say, the disturbance torque Tstd, the steered angle θspand the angular velocity dθsp/dt are estimated by the disturbance torque estimating unit103based on an extended state observer constructed from the equation of motion in the Expression (9) (corresponding to Expression (7) above).

6. Description of Operations and Effects of Reactive Force ECU202and Steering ECU203

With reference toFIG.2, when the hands-on/off determining unit42determines that the driver is gripping the steering wheel2, the automatic steering angle command value θadset by the higher-order ECU201is set as the reactive-force-related automatic steering angle command value θrf, to which the manual steering angle command value θmdis added, and the reactive-force-related composite angle command value θrcmdis computed. The reactive force motor13is controlled based on this reactive-force-related composite angle command value θrcmd. Also, the manual steering angle command value θmdis added to the automatic steering angle command value θad, thereby computing the steering-related composite angle command value θscmd. The steering motor19is controlled based on this steering-related composite angle command value θscmd.

Accordingly, the intent of the driver can be promptly reflected at the steering motor19and the reactive force motor13during automatic steering control. Thus, collaborative control in which manual operations can be performed while performing steering control (turning control and reactive force control (steering wheel angle control)) under automatic steering control, without switching between manual steering control and automatic steering control, can be realized. Also, transitioning between manual steering control and automatic steering control can be performed seamlessly, and accordingly, the driver is not presented with an unnatural sensation when performing manual operations.

When determination is made by the hands-on/off determining unit42that the driver is not gripping the steering wheel2, the reactive-force-related composite angle command value computing unit44is given zero as the reactive-force-related automatic steering angle command value θrf. Accordingly, in this case, the steering motor19is controlled based on the steering-related composite angle command value θscmdthat is obtained by adding the manual steering angle command value θmdto the automatic steering angle command value θad, but the reactive force motor13is controlled based on the reactive-force-related composite angle command value θrcmdthat is made up of the manual steering angle command value θmdalone. In this case, the manual steering angle command value θmdis approximately zero, so the steering wheel2is fixed at a neutral position during automatic steering. Accordingly, a situation can be avoided in which the steering wheel2rotates due to automatic steering in a state in which the driver is not gripping the steering wheel2, resulting in the driver being caught in the steering wheel2.

Also, in the present embodiment, the basic torque command value Trcmdais computed based on the reactive-force-related composite angle command value θrcmd, and the basic torque command value Trcmdais corrected in accordance with the disturbance torque estimation value {circumflex over ( )}Trtdcomputed by the disturbance torque estimating unit63, and accordingly the effects of disturbance on the angle control capabilities of the reactive-force-related angle control unit45can be suppressed, as illustrated inFIG.6. Thus, highly precise angle control of the reactive force motor13can be realized.

In the same way, the basic torque command value Tscmdais computed based on the steering-related composite angle command value θscmd, and the basic torque command value Tscmdais corrected in accordance with the disturbance torque estimation value {circumflex over ( )}Tstdcomputed by the disturbance torque estimating unit103, and accordingly the effects of disturbance on the angle control capabilities of the steering-related angle control unit82can be suppressed, as illustrated inFIG.9. Thus, highly precise angle control of the steering motor19can be realized.

7. Description of Modification of Manual Steering Angle Command Value Setting Unit41

In the above-described embodiment, the command value setting unit52(seeFIG.3) within the manual steering angle command value setting unit41computes the rotational angle θcof the lower column based on Expression (2).

However, an arrangement may be made in which the command value setting unit52computes the rotational angle θcof the lower column taking into consideration the disturbance torque {circumflex over ( )}Tstdestimated by the disturbance torque estimating unit103(seeFIG.9) within the steering-related angle control unit82, as indicated by the long dashed double-short dashed line inFIG.3. Specifically, the command value setting unit52may compute the rotational angle θcof the lower column based on any of the following Expressions (10) through (12).
Jc{umlaut over (θ)}c=Td+Nc·Tm+(−kθc−c{circumflex over (θ)}c)+{circumflex over (T)}std, HPF(10)

Here, {circumflex over ( )}Tstd, HPFrepresents disturbance torque following the disturbance torque {circumflex over ( )}Tstdestimated by the disturbance torque estimating unit103being subjected to high-pass filter processing. The command value setting unit52substitutes the steering torque Tddetected by the torque sensor11into Tdin Expression (10), substitutes the assist torque command value Tacset by the assist torque command value setting unit51into Nc·Tm, and solves the differential equation of Expression (10), thereby computing the rotational angle θcof the lower column. The command value setting unit52then sets the obtained rotational angle θcof the lower column as the manual steering angle command value θmd. The disturbance torque Tstdprimarily includes road surface load torque Trl.
Jc{umlaut over (θ)}c=Td+Nc·Tm+(−kθc−c{dot over (θ)}c+α{circumflex over (T)}std(11)

Here, α is a predetermined coefficient, and {circumflex over ( )}Tstdis the disturbance torque {circumflex over ( )}Tstdestimated by the disturbance torque estimating unit103. The command value setting unit52computes the rotational angle θcof the lower column by solving the differential equation of Expression (11), and sets the obtained rotational angle θcas the manual steering angle command value θmd.
Jc{umlaut over (θ)}c=Td·Nc·Tm+β{circumflex over (T)}std(12)

Here, β is a predetermined coefficient, and {circumflex over ( )}Tstdis the disturbance torque {circumflex over ( )}Tstdestimated by the disturbance torque estimating unit103. The command value setting unit52computes the rotational angle θcof the lower column by solving the differential equation of Expression (12), and sets the obtained rotational angle θcas the manual steering angle command value θmd. When setting the manual steering angle command value θmdin this way, the driver will be able to feel road surface information, such as irregularities on the road surface and so forth, through the steering wheel2.

Although an embodiment of this disclosure has been described above, this disclosure can be carried out further by other embodiments as well. For example, the same automatic steering angle command value θadis given by the higher-order ECU201to the reactive force ECU202and the steering ECU203in the above-described embodiment. However, an automatic steering angle command value for the reactive force motor13and an automatic steering angle command value for the steering motor19may be separately set, and given to the respective ECUs202,203by the higher-order ECU201.

The disturbance torque estimating units63,103are provided to the reactive-force-related angle control unit45and the steering-related angle control unit82respectively in the above-described embodiment. However, the disturbance torque estimating unit63does not have to be provided to the reactive-force-related angle control unit45. Also, the disturbance torque compensating units64,104are not indispensable configurations for the disclosure. The disturbance torque {circumflex over ( )}Tstdestimated by the disturbance torque estimating unit103may be used for settings of the manual steering angle command value θmdalone, without being used for compensation of the disturbance torque.

This disclosure can be applied to a steer-by-wire system, in which a right-left independent steering system, with a right steered wheel and a left steered wheel each being independently steered, is employed. In this case, a steering ECU is provided for each of the right steered wheel and the left steered wheel. This disclosure can also be applied to a steer-by-wire system in which a four-wheel steering system, with the front wheels and the rear wheels being independently steered, for example, is employed. In this case, a steering ECU is provided for the front wheels and another steering ECU is provided for the rear wheels. This disclosure can also be applied to a steer-by-wire system in which a four-wheel independent steering system, with each of the four wheels being independently steered, is employed. In this case, a steering ECU is provided for each wheel.

Various design modifications of the disclosure may be made within the scope of matters set forth in the Claims.