JP2008189058A - Steering system for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steering system for a vehicle capable of improving precision of automatic steering control. <P>SOLUTION: This steering system for the vehicle has an EPS device 2 to control steering angles of steered wheels 11FL, 11FR by driving the steered wheels 11FL, 11FR of the vehicle 10 by an electric motor 24, and steering operation of a driver is supported as the EPS device 2 automatically steers the steered wheels 11FL, 11FR of the vehicle 10 when the vehicle 10 travels. The EPS device 2 carries out torque control to generate assist torque with reaction torque of a steering wheel 12 as a target. Further, the EPS device 2 carries out angular control with the steering angles of the steered wheels 11FL, 11FR as controlling objects in automatic steering. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a vehicle steering system, and more particularly to a vehicle steering system that can improve the accuracy of automatic steering control.

  In recent vehicle steering systems, automatic steering control such as LKA (Lane Keeping Assist) control is being adopted. In such automatic steering control, for example, a lane of a traveling road is recognized by a CCD camera, and various information such as a curvature radius of the traveling road, a yaw angle of the vehicle with respect to the traveling lane on the traveling road, an offset amount, and a traveling speed are acquired. The Then, the electric power steering of the vehicle is driven based on these pieces of information, and the steering angle of the steered wheels is controlled so that the vehicle travels along the target line in the lane. This reduces the driver's steering burden.

  As a conventional vehicle steering system that employs such automatic steering control, a technique described in Patent Document 1 is known.

JP 2006-44563 A

  Here, in the vehicle steering system having the above-described configuration, there is a demand for improving the accuracy of the automatic steering control.

  Therefore, the present invention has been made in view of the above, and an object thereof is to provide a vehicle steering system that can improve the accuracy of automatic steering control.

  In order to achieve the above object, a vehicle steering system according to the present invention includes an EPS device that controls a steering angle of a steering wheel by driving a steering wheel of the vehicle with an electric motor. A steering system for a vehicle in which a steering operation of a driver is supported by automatically steering a steering wheel of a vehicle, and the EPS device applies an assist torque with a reaction force torque of a steering wheel as a control target during normal steering. In addition to performing torque control to be generated, the EPS device performs angle control in which the steering angle of the steered wheels is controlled during automatic steering.

  In this vehicle steering system, the EPS device performs angle control in which the steering angle of the steered wheels is controlled during automatic steering, so that the EPS device drives the steered wheels of the vehicle only by torque control. , Robustness against disturbance (road gamble) and preload friction of EPS gear is improved. Thereby, there is an advantage that the accuracy of the control of the steering angle is improved and the automatic steering of the steered wheels is appropriately performed.

In the vehicle steering system according to the present invention, the EPS device is driven by a predetermined control instruction (for example, a target instruction current I ^* , an assist torque AT, etc.) to perform the torque control and the angle control. The control instruction at the time is calculated based on a control instruction for torque control (for example, a target current for torque control It), and the control instruction at the time of angle control is calculated as the control instruction for angle control (for example, the target current for angle control Ia ^* ), and when the steering mode is switched between normal steering and automatic steering, the command value difference between the torque control control command and the angle control target command (for example, current value difference ΔI). When the control instruction is changed by the above, the change control for changing the control instruction is performed.

  This vehicle steering system has an advantage of reducing the uncomfortable feeling that the driver feels over the steering wheel because the fluctuation of the reaction torque is reduced when the steering mode is switched.

Further, in the vehicle steering system according to the present invention, the command value difference between the torque control control command and the angle control target command is greater than a predetermined threshold value (for example, threshold value ΔI _MAX ) during the change-over control. When the value is larger, the control instruction is calculated based on the sum of the torque control control instruction and a predetermined change control value (for example, change current ΔI ′).

  In this vehicle steering system, the instruction value difference between the control instruction for torque control and the target instruction for angle control is reduced by the change control value. Therefore, the fluctuation ΔMT of the reaction force torque MT caused by this instruction value difference is effective. Alleviated. Thereby, there is an advantage that the uncomfortable feeling that the driver feels through the steering wheel is effectively reduced.

  In the vehicle steering system according to the present invention, a VGRS device that is disposed in a steering system between the steering wheel and the steering wheel and assists the steering wheel relative to the steering wheel automatically and automatically is provided. In addition, the VGRS device performs motion performance compensation control for compensating for the delay in motion performance of the steered wheels caused by the change control when the steering mode is switched between normal steering and automatic steering.

  In this vehicle steering system, the VGRS device controls the steering angle of the steered wheels, thereby compensating for the delay in the motion performance of the steered wheels. Thereby, the steering angle of the steering wheel required for LKA control is ensured, and automatic steering control is performed appropriately.

In the vehicle steering system according to the present invention, the motion performance compensation control is performed with the target rudder angle δ ^* of the steered wheel as a control target, and the target rudder angle δ ^* It is calculated based on the difference from the value.

In this vehicle steering system, the torque control control instruction and the instruction value difference between the angle control target instructions that are generated when the control mode is switched, and the change control value added to the control instruction in the change control are taken into account. Thus, the target rudder angle δ ^* is calculated, and motion performance compensation control is performed based on the target rudder angle δ ^* . As a result, there is an advantage that the steering angle deficiency due to the displacement change control is appropriately compensated, and the automatic steering of the vehicle 10 is suitably performed.

  In the vehicle steering system according to the present invention, the EPS device performs reaction force compensation control for maintaining the reaction force torque of the steering wheel resulting from the motion performance compensation control substantially constant.

  In this vehicle steering system, for example, when reaction force torque is generated in the steering wheel due to the motion performance compensation control, the EPS device generates assist torque and maintains the reaction force torque MT substantially constant. . Thereby, there is an advantage that the uncomfortable feeling that the driver feels through the steering wheel is reduced.

  In the vehicle steering system according to the present invention, since the EPS device performs angle control in which the steering angle of the steering wheel is controlled during automatic steering, the EPS device drives the vehicle steering wheel only by torque control. In comparison, robustness against disturbance (load gamble) and preload friction of the EPS gear is improved. Thereby, there is an advantage that the accuracy of the control of the steering angle is improved and the automatic steering of the steered wheels is appropriately performed.

  Hereinafter, the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. The constituent elements of this embodiment include those that can be easily replaced by those skilled in the art or those that are substantially the same. In addition, a plurality of modifications described in this embodiment can be arbitrarily combined within a range obvious to those skilled in the art.

  FIG. 1 is a configuration diagram showing a vehicle steering system according to an embodiment of the present invention. 2 to 6 are a flowchart (FIGS. 2 and 3) and an explanatory diagram (FIGS. 4 to 6) showing an operation of the vehicle steering system shown in FIG. FIG. 7 is a flowchart showing a modification of the vehicle steering system shown in FIG.

[Vehicle steering system]
The vehicle steering system 1 has a function of reducing the steering burden on the driver by automatically controlling the steering wheel without depending on the steering operation of the driver. As such automatic steering control, for example, LKA (Lane Keeping Assist) control is known. In the LKA control, the steering wheel is automatically steered so that the vehicle travels in the lane when the vehicle travels, and the driver's steering operation is supported (lane keeping support function).

  The vehicle steering system 1 includes an electric power steering device (hereinafter referred to as an EPS (electronic power steering) device) 2 and a gear ratio variable steering device (hereinafter referred to as a VGRS (variable gear ratio steering) device) 3. And various sensors 41 to 45, a steering control device 5, and an LKA switch 6 (see FIG. 1). In this embodiment, the left rear wheel 11RL and the right rear wheel 11RR of the vehicle 10 are drive wheels of the vehicle 10, and the left front wheel 11FL and the right front wheel 11FR are steering wheels of the vehicle 10.

  The EPS device 2 is a device that generates power (auxiliary steering force) in conjunction with turning of the steering wheel 12 and assists the steering of the left and right steered wheels 11FL and 11FR. The EPS device 2 is, for example, a rack and pinion type steering device, and includes a pinion shaft 21, a rack bar 22, a pair of tie rods 23L and 23R, an electric motor 24, a conversion mechanism 25, and an EPS control device. 26.

  The pinion shaft 21 is connected to the steering wheel 12 of the vehicle 10 via the VGRS device 3 and is rotated by the operation of the steering wheel 12. The rack bar 22 is connected to the pinion shaft 21 and is slid in the axial direction by the rotation of the pinion shaft 21. The tie rod 23L (23R) connects the rack bar 22 and the left steering wheel 11FL (right steering wheel 11FR), transmits the displacement of the rack bar 22 to the left steering wheel 11FL (right steering wheel 11FR), and the left steering wheel. The steering angle of 11FL (right steering wheel 11FR) is changed. The electric motor 24 slides and displaces the rack bar 22 in the axial direction via the conversion mechanism 25. As the conversion mechanism 25, for example, a ball screw type is adopted. The EPS control device 26 drives and controls the electric motor 24 to slide the rack bar 22 to change the steering angles of the left and right steering wheels 11FL and 11FR.

  In the EPS device 2, when the driver turns the steering wheel 12, the pinion shaft 21 rotates and the rack bar 22 slides in the axial direction (the turning direction of the steering wheel 12). Then, the tie rods 23L and 23R are displaced in conjunction with the rack bar 22, and the steering angles of the left and right steering wheels 11FL and 11FR are changed. At this time, the EPS control device 26 drives and controls the electric motor 24, and the rotational torque of the electric motor 24 is transmitted to the rack bar 22 via the conversion mechanism 25. Specifically, the electric motor 33 is driven and controlled on the basis of the traveling speed V of the vehicle and the steering angle (rotation angle φs of the upper / steering shaft 31 described later). As a result, the steering of the left and right steering wheels 11FL and 11FR is assisted, and the driver's steering burden is reduced.

  Further, the EPS device 2 generates an assist torque AT for maintaining the reaction force torque MT substantially constant when the reaction force torque MT is generated in the steering wheel 12 by steering the steering wheels 11FL and 11FR. Specifically, the generated reaction force torque MT is detected, and a necessary assist torque AT is calculated based on the reaction force torque MT. Then, the EPS control device 26 drives and controls the electric motor 24 based on the assist torque AT, so that the reaction force torque MT transmitted to the steering wheel 12 is maintained constant. Thereby, the uncomfortable feeling that the driver feels through the steering wheel 12 during steering is reduced.

  The VGRS device 3 is disposed in a steering system between the steering wheel 12 and the steered wheels 11FL and 11FR, and assists the steered wheels 11FL and 11FR in an auxiliary manner automatically and relative to the steering of the steering wheel 12. It is. The VGRS device 3 includes an upper steering shaft 31 and a lower steering shaft 32, an electric motor 33, and a turning angle variable control device 34. The upper steering shaft 31 is connected to the steering wheel 12. The lower steering shaft 32 is connected to the pinion shaft 21 of the EPS device 2 via the universal joint 35. The upper steering shaft 31 and the lower steering shaft 32 are connected to each other via an electric motor 33. Specifically, the upper steering shaft 31 is connected to the electric motor 33, and the lower steering shaft 32 is connected to the rotor 332 side of the electric motor 33. The turning angle variable control device 34 drives and controls the electric motor 33 to rotate the lower steering shaft 32.

  In the VGRS device 3, when the driver turns the steering wheel 12, the upper steering shaft 31 rotates together with the steering wheel 12. Then, the electric motor 33 is driven in conjunction with the rotation of the upper steering shaft 31, the lower steering shaft 32 rotates, and the power is transmitted to the pinion shaft 21 of the EPS device 2. As a result, the EPS device 2 is driven and the left and right steering wheels 11FL and 11FR are steered.

  Further, at this time, the turning angle variable control device 34 drives and controls the electric motor 33, so that the difference between the rotation angle φs of the upper steering shaft 31 and the rotation angle φa of the lower steering shaft 32 (relative rotation angle φa− φs) is controlled. Specifically, the electric motor 33 is driven and controlled on the basis of the traveling speed V of the vehicle and the rotation angles φs and φa of each steering shaft, and the rotation angle φs of the upper steering shaft 31 and the rotation angle φa of the lower steering shaft 32 The relative rotation angle φa−φs is controlled. Thereby, the steering of the steering wheel 12 is assisted, and the driver's steering burden is reduced.

  For example, during normal steering of the vehicle 10, a steering operation is performed by the driver to steer the steered wheels 11FR and 11FL. At this time, in the VGRS device 3, the turning angle variable control device 34 drives and controls the electric motor 33 so that the rotation angle φs of the upper steering shaft 31 and the rotation angle φa of the lower steering shaft 32 are φs = φa ( (Neutral position) is maintained (holding state). Specifically, such control is performed when LKA control is OFF, when turning left or right at an intersection, or when entering a garage. As a result, the steering angle of the steered wheels 11FL and 11FR changes quickly with respect to the steering operation, so that the steering performance of the vehicle 10 is improved.

  On the other hand, at the time of automatic steering of the vehicle 10, the turning angle variable control device 34 controls the drive of the electric motor 33 and the relative rotation angle φa between the rotation angle φs of the upper steering shaft 31 and the rotation angle φa of the lower steering shaft 32. −φs is positively provided. For example, in the LKA control, the steered wheels are automatically steered so that the traveling of the vehicle 10 in the lane during traveling is maintained. As a result, the steering wheel is appropriately operated without depending on the driver's steering operation, which has the advantage of reducing the driver's steering burden. Further, for example, during high speed running, the rotation angle φa of the lower steering shaft 32 is set smaller than the rotation angle φs of the upper steering shaft 31 (φa <φs). As a result, the steering angle of the steered wheels 11FL and 11FR changes gradually with respect to the steering operation, and a gentle and stable handling is realized, thereby improving the running stability during high speed running.

  The various sensors 41 to 45 include a vehicle speed sensor 41, a yaw rate sensor 42, an upper rotation angle sensor 43, a lower rotation angle sensor 44, and a torque sensor 45. The vehicle speed sensor 41 is a sensor that detects the traveling speed V of the vehicle 10. The yaw rate sensor 42 is a sensor that detects the yaw rate θ of the vehicle 10 (see FIG. 4). The upper rotation angle sensor 43 is a sensor that detects the rotation angle φs of the upper steering shaft 31. The lower rotation angle sensor 44 is a sensor that detects the rotation angle φa of the lower steering shaft 32. The rotation angle φs of the upper steering shaft 31 is equal to the steering angle of the steering. Further, the actual steering angle of the left and right steering wheels 11FL, 11FR is calculated based on the rotation angle φa of the lower steering shaft 32. The torque sensor 45 is a sensor that detects the steering torque Ts of the lower steering shaft 32.

  The steering control device 5 is a device that controls driving of the EPS device 2 and the VGRS device 3 during normal steering and automatic steering of the vehicle 10. Specifically, the EPS device 2 and the VGRS are based on the traveling speed V, yaw rate θ, rotation angle φs of the upper steering shaft 31 and rotation angle φa of the lower steering shaft 32 detected by the various sensors 41 to 45. The device 3 is driven and controlled. The control during the normal steering and the automatic steering will be described in detail with reference to a flowchart described later.

  The LKA switch 6 is a switch for selecting ON / OFF of LKA control, and is connected to the steering control device 5. The LKA switch 6 is installed in the driver's seat of the vehicle 10. By switching the LKA switch 6 on and off, the steering mode (normal steering or automatic steering) of the vehicle 10 is switched.

[Vehicle steering control]
In the vehicle steering system 1, steering control of the vehicle 10 is performed as follows (see FIGS. 2 and 3). First, when the vehicle 10 travels, the radius of curvature R of the travel path 100, the offset amount D of the vehicle 10 on the travel path 100, the yaw rate θ, and the travel speed V are acquired (ST101) (see FIG. 2). For example, the yaw rate sensor 42 is configured by a CCD (Charge Coupled Device) camera, and the CCD camera captures an image of the condition of the travel path 100 (for example, the center line of the travel path 100) in front of the vehicle 10. The steering control device 5 performs image processing based on the image information from the CCD camera, the radius of curvature R of the traveling road 100, the offset amount D of the vehicle 10 (the amount of deviation of the vehicle 10 in the vehicle width direction with respect to the target traveling road 101). And the yaw rate θ is calculated. Further, the traveling speed V of the vehicle 10 is detected by the vehicle speed sensor 41.

During normal steering of the vehicle 10 (when the LKA switch 6 is in the OFF state), normal power steering control is performed (ST102, ST103). Specifically, first, when the vehicle 10 is traveling, the torque sensor 45 detects the steering torque Ts of the lower steering shaft 32. Then, the steering control device 5 calculates the reaction force torque MT based on the steering torque Ts. The reaction torque MT is transmitted to the steering wheel 12 via the upper steering shaft 31 when the steering wheels 11FL and 11FR are steered. Next, the steering control device 5 calculates an assist torque AT for maintaining the reaction force torque MT substantially constant, and calculates a torque control target current It (torque control control instruction) based on the assist torque AT. . Next, the steering control device 5 inputs the torque control target current It as the target command current I ^* (control command) to the EPS device 3 (EPS control device 26) (ST104), and based on the target command current I ^*. The EPS control device 26 controls the drive of the electric motor 24 (ST105). As a result, the assist torque AT is generated and the reaction force torque MT of the steering wheel 12 is maintained substantially constant, and the uncomfortable feeling that the driver feels over the steering wheel 12 during steering is reduced.

なお、この算出式（１）では、Ｌが車両のホイールベース、Ｋｈがスタビリティファクター、Ｋ１、Ｋ２およびＫ３が定数である。 On the other hand, when the vehicle 10 is automatically steered (during LKA control), the following control is performed. First, when the driver turns on the LKA switch 6 (ST102), the steering control device 5 calculates the target steering angle (clearance angle) δ ^* of the left and right steering wheels 11FL, 11FR (ST106). The target rudder angle δ ^* is a steering angle necessary for causing the vehicle 10 to travel along the target travel path 101. The target rudder angle δ ^* is calculated by the following calculation formula (1) based on the curvature radius R, the offset amount D, the travel speed V, and the yaw rate θ of the travel path 100.

In the calculation formula (1), L is a wheel base of the vehicle, Kh is a stability factor, and K1, K2, and K3 are constants.

Next, the angle control target current Ia ^* (angle control control instruction) used for the LKA control is calculated based on the target steering angle δ ^* and the actual steering angle δ of the steered wheels 11FL and 11FR (2) ).
Ia ^* = K · (δ ^* −δ) (2)
In this calculation formula (2), K is a constant. The actual steering angle δ is calculated based on the rotation angle φa of the lower steering shaft 32.

Here, the angle control target current Ia ^* and the torque control target current It during normal steering have a current value difference ΔI (indicated value difference) (see FIG. 5). That is, during normal steering, the EPS device 2 generates the assist torque AT by torque control, so that the target command current I ^* to the EPS device 2 is calculated based on the torque control target current It. However, the torque control target current It and the angle control target current Ia ^* generally have different current values. For this reason, when the LKA switch 6 is turned on and the steering mode is switched from normal steering to automatic steering (t = tc), the torque control target current It is directly input to the EPS device 2 as the target command current I ^*. Then, a large discontinuity occurs in the reaction force torque MT to be controlled, and the driver may feel uncomfortable over the steering wheel 12 (see FIG. 6). Therefore, the following processing is performed in order to reduce the uncomfortable feeling of the driver by changing the target command current I ^* .

First, a current value difference ΔI between the torque control target current It and the angle control target current Ia ^* is calculated (ST107). Next, the current value difference ΔI is compared with a predetermined threshold (safety factor guard) ΔI _MAX (ST108). When the current value difference ΔI is smaller than the predetermined threshold value ΔI _MAX , FlagG for performing change control is maintained in the OFF state, and the angle control target current Ia ^* is set as the target command current I ^* in the EPS device. 2 (ST109). Then, the EPS control device 26 drives and controls the electric motor 24 based on the target instruction current I ^* (ST105). As a result, the steering angles of the steered wheels 11FL and 11FR are controlled, and the driver's steering burden for causing the vehicle 10 to travel along the target travel path 101 is reduced.

On the other hand, when the current value difference ΔI is larger than the predetermined threshold value ΔI _MAX , FlagG for performing change control is turned on (ST110). Then, the sum of the target current It for torque control during normal steering and a predetermined change / change current ΔI ′ (change / change control value) is calculated as the target command current I ^* (ST111). This removal / change current ΔI ′ is an addition for keeping the target command current I ^* within the threshold value ΔI _MAX . Then, the target command current I ^* is input to the EPS device 2, and the EPS control device 26 drives and controls the motor 24 based on the target command current I ^* (ST105).

In such a configuration, the torque control target current It and the angle control target current Ia ^* are added by adding the variable current ΔI ′ to the target command current I ^* when the steering mode is switched between normal steering and automatic steering ^. The change in the current value difference ΔI is relaxed (variation control). As a result, the fluctuation ΔMT of the reaction torque MT when the steering mode is switched is alleviated, and the uncomfortable feeling that the driver feels over the steering wheel 12 is reduced.

The variable current ΔI ′ can be appropriately defined according to the threshold value ΔI _MAX . Further, the variable current ΔI ′ may have a constant current value, or may have a current value that varies depending on the current value difference ΔI or time t.

[effect]
As described above, in this vehicle steering system 1, the EPS device 2 performs angle control with the steering angle of the steered wheels 11FL and 11FR as a control target during automatic steering (see FIGS. 1 and 2). Compared with the configuration in which the EPS device drives the steering wheel of the vehicle only by torque control, the robustness against disturbance (load gamble) and preload friction of the EPS gear is improved. Thereby, there is an advantage that the accuracy of the control of the steering angle is improved and the automatic steering of the steered wheels is appropriately performed. For example, during steering, the reaction force that the steered wheel receives from the road surface changes depending on the road surface condition of the traveling road. In the EPS apparatus, there is a gear friction due to the rack and pinion structure, and this gear friction is different in each EPS apparatus due to variations in the manufacturing process. For this reason, in the configuration in which the steering angle of the steered wheels is driven and controlled by torque control, the influence of road surface conditions and gear friction cannot be ignored, and the accuracy of control of the steering angle is likely to decrease.

Further, in the vehicle steering system 1, the current value difference ΔI (= It−Ia ^* ) between the torque control target current It and the angle control target current Ia ^* when the steering mode is switched between normal steering and automatic steering ^. when the target command current I ^* changes due), removal change control for varying dividing the target command current I ^* is performed (see FIGS. 2 and 5). As a result, the variation ΔMT of the reaction torque MT is mitigated when the steering mode is switched, and there is an advantage that the uncomfortable feeling that the driver feels over the steering wheel 12 is reduced.

Specifically, as described above, when the current value difference ΔI between the torque control target current It and the angle control target current Ia ^* is larger than the predetermined threshold value ΔI _MAX during the change control, the target instruction The current I ^* is preferably calculated based on the sum of the torque control target current It and a predetermined variable current ΔI ′ (see FIG. 2). In such a configuration, since the current value difference ΔI between the torque control target current It and the angle control target current Ia ^* is reduced by the variable current ΔI ′, the fluctuation of the reaction force torque MT caused by the current value difference ΔI. ΔMT is effectively mitigated. Thereby, there is an advantage that the uncomfortable feeling that the driver feels through the steering wheel 12 is effectively reduced.

[Exercise performance compensation control]
On the other hand, as described above, when the steering mode is switched, the target command current I ^* is changed and the fluctuation ΔMT of the reaction torque MT is relaxed (variation control), so that automatic steering may not be performed properly. There is. That is, if the change control is performed at the time of switching the steering mode, the target command current I ^* is not immediately switched from the torque control target current It to the angle control target current Ia ^* , so the steering angles of the steered wheels 11FL and 11FR Is lacking. Then, a delay occurs in the exercise performance as the LKA control, and there is a possibility that automatic steering is not properly performed.

  Therefore, in this vehicle steering system 1, control (motion performance) for compensating for a delay in the motion performance of the steered wheels 11FL and 11FR caused by the displacement control when the steering mode is switched between normal steering and automatic steering. Compensation control) is performed by the VGRS device 3 (see FIGS. 3 and 5). Specifically, the VGRS device 3 controls the steering angles of the steered wheels 11FL and 11FR to compensate for the delay in the motion performance of the steered wheels 11FL and 11FR. Thereby, the steering angles of the steered wheels 11FL and 11FR necessary for the LKA control are ensured, and the vehicle 10 is automatically steered appropriately.

  In particular, in the above configuration, (1) removal control by the EPS device 2 and (2) motion performance compensation control by the VGRS device 3 are performed in conjunction with switching of the steering mode between normal steering and automatic steering. . That is, (1) By the change control of the EPS device 2, the fluctuation ΔMT of the reaction torque MT of the steering wheel 12 is relaxed, and the uncomfortable feeling that the driver feels over the steering wheel 12 is reduced. In addition, (2) the motion performance compensation control of the VGRS device 3 compensates for the shortage of the steering angle of the steered wheels 11FL and 11FR due to the displacement control, and the automatic steering is appropriately performed. Therefore, these synergistic effects have the advantage that the accuracy and practicality of automatic steering can be dramatically improved.

For example, in this embodiment, at the time of switching the steering mode, the motion performance compensation control is performed as follows (see FIG. 3). First, the ON / OFF state of the LKA switch 6 and the ON / OFF state of FlagG for change control are confirmed (ST201 and ST202). When the LKA switch 6 is in the ON state and the flag G for change control is in the ON state, the steering control device 5 calculates the target steering angle δ ^* of the left and right steering wheels 11FL and 11FR (ST203). ). Then, this target rudder angle δ ^* is output to the VGRS device 3, and the steering angles of the steered wheels 11FL and 11FR are controlled based on the target rudder angle δ ^* (ST204). At this time, the steering angles of the steering wheels 11FL and 11FR are feedback-controlled based on the rotation angle φa of the lower steering shaft 32 (the actual steering angle of the steering wheels 11FL and 11FR). Thereby, the steering angles of the steered wheels 11FL and 11FR necessary for the LKA control are ensured, and the vehicle 10 is automatically steered appropriately.

In the above configuration, the target rudder angle δ ^* is calculated based on the difference (ΔI−ΔI ^′ ) between the current value difference ΔI used for the change control and the change current ΔI ^′ (see FIG. 5). . That is, the current value difference ΔI between the torque control target current It and the angle control target current Ia ^* generated when the control mode is switched, and the removal current ΔI ^′ added to the target command current I ^* in the removal control. There is calculated is in the target steering angle [delta] ^* enjoined, exercise performance compensation control is performed based on the target steering angle [delta] ^*. As a result, there is an advantage that the steering angle deficiency due to the displacement control is appropriately compensated, and the automatic steering of the vehicle 10 is suitably performed.

[Reaction force compensation control]
Further, as described above, in the configuration in which the VGRS device 3 is driven and exercise performance compensation control is performed, the reaction force torque MT is generated by the steering of the steered wheels 11FL and 11FR.

  Therefore, in the vehicle steering system 1, it is preferable that the EPS device 2 performs the reaction force compensation control for maintaining the reaction force torque MT of the steering wheel 12 resulting from the motion performance compensation control substantially constant. For example, when the reaction force torque MT is generated in the steering wheel 12 due to the motion performance compensation control, the EPS device 2 generates the assist torque AT and keeps the reaction torque MT substantially constant (reaction force). Compensation control). Thereby, there is an advantage that the uncomfortable feeling that the driver feels through the steering wheel 12 is reduced.

For example, in this embodiment, the target command current I ^* is calculated by adding the reaction torque generated by driving the VGRS device 3 when calculating the target command current I ^* in the change-over control (ST111) (FIG. 7). Specifically, the target command current I ^* is calculated by the following calculation formula based on the torque control target current It, the variable current ΔI ^′, and the steering angle _δVGRS ^* of the steered wheels 11FL and 11FR by the VGRS device 3. The
I ^* = It + ΔI ^′ + K _V · δ _VGRS ^* (3)
In this calculation formula (3), K _V is a constant. Thereby, the variation ΔMT of the reaction torque MT due to the driving of the VGRS device 3 is reduced.

  As described above, the vehicle steering system according to the present invention is useful in that the accuracy of automatic steering control can be improved.

1 is a configuration diagram showing a vehicle steering system according to an embodiment of the present invention. It is a flowchart which shows the effect | action of the vehicle steering system described in FIG. It is a flowchart which shows the effect | action of the vehicle steering system described in FIG. It is explanatory drawing which shows the effect | action of the vehicle steering system described in FIG. It is explanatory drawing which shows the effect | action of the vehicle steering system described in FIG. It is explanatory drawing which shows the effect | action of the vehicle steering system described in FIG. It is a flowchart which shows the modification of the steering system for vehicles described in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vehicle steering system 2 EPS apparatus 21 Pinion shaft 22 Rack bar 23 Tie rod 24 Electric motor 25 Conversion mechanism 26 EPS control apparatus 3 VGRS apparatus 31 Upper steering shaft 32 Lower steering shaft 33 Electric motor 332 Rotor 34 Steering angle variable control apparatus 35 Universal joint 41 Vehicle speed sensor 42 Yaw rate sensor 43 Upper rotation angle sensor 44 Lower rotation angle sensor 45 Torque sensor 5 Steering control device 6 LKA switch 10 Vehicle 11FR, 11FL Steering wheel 11RR, 11RL Driving wheel 12 Steering wheel

Claims (6)

An EPS device that drives a steering wheel of a vehicle with an electric motor to control the steering angle of the steering wheel, and when the vehicle travels, the EPS device automatically steers the steering wheel of the vehicle so that the driver can perform a steering operation. A supported vehicle steering system,
During normal steering, the EPS device performs torque control for generating assist torque using the reaction force torque of the steering wheel as a control target, and at the time of automatic steering, the EPS device uses the steering angle of the steered wheel as a control target. A vehicle steering system characterized by performing control. The EPS device is driven by a predetermined control instruction to perform the torque control and the angle control, the control instruction at the time of torque control is calculated based on the control instruction for torque control, and the control instruction at the time of angle control is Calculated based on the control instruction for angle control, and
When switching the steering mode between normal steering and automatic steering, when the control instruction changes due to an instruction value difference between the torque control control instruction and the angle control target instruction, the control instruction is changed. The vehicle steering system according to claim 1, wherein change control is performed.   When the difference control between the torque control control instruction and the angle control target instruction is greater than a predetermined threshold value during the change control, the control instruction is changed from the torque control control instruction to a predetermined change control. The vehicle steering system according to claim 2, wherein the vehicle steering system is calculated based on a sum with a control value. A VGRS device that is disposed in a steering system between the steering wheel and the steering wheel and that assists the steering wheel in a relative and automatic manner relative to steering of the steering wheel; and
4. The VGRS device performs motion performance compensation control for compensating for a delay in motion performance of a steered wheel caused by the displacement control when the steering mode is switched between normal steering and automatic steering. The vehicle steering system described in 1. The motion performance compensation control is performed with a target steering angle δ ^* of a steered wheel as a control target, and the target steering angle δ ^* is calculated based on a difference between the indicated value difference and the change control value. 5. The vehicle steering system according to 4.   The vehicle steering system according to claim 4 or 5, wherein the EPS device performs reaction force compensation control for maintaining a reaction force torque of a steering wheel caused by the motion performance compensation control substantially constant.

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