JP4692403B2 - Vehicle steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To set an appropriate steering controlled variable in a case of controlling the steering using the both of a vehicle motion target value according to the steering operation of a driver and a vehicle motion target value by an automatic steering. <P>SOLUTION: This steering device calculates a first target value (&gamma;auto* and &beta;auto*) of the vehicle motion for automatically steering the vehicle (S27 and S28) and calculates a virtual steering angle of a steering wheel by a driver necessary for obtaining the first target value (S29). Secondly, this device calculates a second target value (&gamma;driv* and &beta;driv*) of the vehicle motion by the steering operation of the driver corresponding to a difference between the actual steering angle of the steering wheel and the calculated virtual steering angle (S32 and S33). Then, this device calculates a final target value of the vehicle motion based on the sum of the first target value and the second target value (S34 and S35), calculates the target steering angle of the wheels necessary for obtaining the final target value (S36) and drivingly controls the steering motor of the front/rear wheels (S37). <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a vehicle steering apparatus that includes a steering actuator that steers a wheel and obtains a desired turning angle by driving and controlling the steering actuator.

2. Description of the Related Art Conventionally, there is known a vehicle steering apparatus that calculates a target value of vehicle motion according to a steering operation of a steering wheel and drives and controls a steering actuator for front and rear wheels so as to obtain the vehicle motion target value. .
For example, in Patent Document 1, a steering angle and a vehicle speed are detected, and a target yaw rate and a target lateral velocity are calculated as vehicle motion target values based on these two detection values. Then, a target front wheel steering angle and a target rear wheel steering angle at which the target yaw rate and target lateral velocity are obtained are calculated, and the front wheel steering actuator and the rear wheel steering actuator are driven and controlled to the target steering angle.
JP 2004-182197 A

However, in an apparatus that controls the turning angle of the front and rear wheels so that a vehicle movement target value corresponding to the steering wheel operation can be obtained, if an automatic steering function such as a lane keeping support function is added, abnormal vehicle behavior occurs. End up.
For example, an image of a road ahead of the vehicle is captured by a camera, a lane is recognized from the captured image, a motion target value of the vehicle that travels along the lane is calculated, and the vehicle motion target value is obtained. Let us consider a case in which an autopilot function for controlling the turning angle of a wheel is provided. In this case, the steering actuator is driven according to the lane shape, and the steering handle is also rotated accordingly.

  On the other hand, if the driver operates the steering wheel during automatic steering, it is necessary to calculate the vehicle motion target value including the amount of steering by the steering wheel operation and perform the steering control. However, when calculating the vehicle motion target value according to the driver's steering wheel operation, the steering handle by the automatic steering control is misrecognized as being rotated by the driver's turning operation, and is added accordingly. The vehicle motion target value that is more than necessary is calculated. As a result, the final vehicle motion target value deviates from the original vehicle motion target value.

  The present invention was made to cope with such problems, and even when steering control is performed using both the vehicle motion target value according to the driver's steering operation and the vehicle motion target value by automatic steering, The purpose is to set an appropriate steering control amount.

  In order to achieve the above object, the structural features of the present invention include a steering handle that is operated by a driver to steer a wheel to a rudder angle corresponding to an operation amount, and a steering wheel that steers the wheel. In a vehicle steering apparatus including a rudder actuator, a steering angle detection unit that detects a steering angle of the steering handle and a vehicle steering state in order to automatically steer the vehicle, regardless of the operation of the steering handle. A first vehicle motion target value calculating means for calculating a first target value of the vehicle motion and a virtual for calculating a virtual steering angle of the steering wheel by a driver necessary for obtaining the first target value of the motion of the vehicle. A vehicle by a steering operation of a driver corresponding to a difference between a steering angle calculating unit and a steering angle of a steering wheel detected by the steering angle detecting unit and a virtual steering angle calculated by the virtual steering angle calculating unit. luck Second vehicle motion target value calculation means for calculating the second target value of the vehicle, and final vehicle motion target value calculation for calculating a final target value of the vehicle motion based on the sum of the first target value and the second target value Means, a turning angle calculation means for calculating a target turning angle of a wheel necessary for obtaining the final target value, and the turning actuator based on the target turning angle calculated by the turning angle calculation means And an actuator control means for realizing the calculated target turning angle.

According to this, the first vehicle motion target value calculation means calculates the first target value of the vehicle motion. The first target value of the vehicle is calculated in accordance with the traveling state of the vehicle regardless of the operation of the steering handle in order to automatically steer the vehicle.
On the other hand, the virtual rudder angle calculating means calculates the virtual rudder angle of the steering wheel by the driver necessary for obtaining the first target value of the vehicle motion. That is, in order to obtain the first target value of the vehicle motion, it is calculated how much steering angle is necessary in terms of the driver's steering wheel operation.

  Then, the second vehicle motion target value calculation means obtains a difference between the steering angle of the steering wheel detected by the steering angle detection means and the virtual steering angle. This difference is the amount of steering added by the driver with respect to steering by autopilot. Further, the second vehicle motion target value calculation means calculates a second target value of vehicle motion by the driver's steering operation corresponding to this difference. That is, the target value of the vehicle motion when the driver steers the steering angle difference is calculated as the second target value.

When the first target value and the second target value of the vehicle motion are calculated, the final vehicle motion target value calculation means calculates the sum of the two first target values and the second target value as the final target value of the vehicle motion. To do.
Then, the turning angle calculation means calculates the target turning angle of the wheel necessary to obtain this final target value, and the turning actuator control means controls driving of the turning actuator based on this target turning angle. To do.
Thus, the final vehicle motion target value is obtained by controlling the wheel to the target turning angle.

The vehicle steering apparatus according to the present invention thus calculates the steering angle for which the driver steered the steering with respect to the automatic steering, and sets the second target value corresponding to the steering angle to the first target by the automatic steering. By adding to the value, an appropriate final vehicle motion target value can be obtained.
For example, when the driver does not handle the steering wheel automatically, the difference between the steering angle of the steering wheel and the virtual steering angle is zero, and the second target value is zero. For this reason, since the target value of the vehicle motion is not added to the autopilot, the final vehicle motion target value is an appropriate value. Further, when the driver applies an operation to the autopilot, the operation amount is set as the second target value of the vehicle motion, so that the steering state intended by the driver can be obtained.
Therefore, even when steering control is performed using both the vehicle motion target value corresponding to the driver's steering operation and the vehicle motion target value by automatic steering, an appropriate steering control amount can be set.

Another feature of the present invention is that the first target value, the second target value, and the final target value of the vehicle motion include at least a yaw rate of the vehicle.
Further, the first target value, the second target value, and the final target value of the vehicle motion include at least a vehicle body slip angle.

  According to this, since the target turning angle is calculated using at least the yaw rate of the vehicle or the vehicle body slip angle as a target value, appropriate steering angle control of the wheel is possible.

  Hereinafter, an embodiment of a vehicle steering apparatus of the present invention will be described. FIG. 1 schematically shows a vehicle steering apparatus according to the embodiment.

  This steering device 10 includes a front wheel steering unit 20 for steering the left and right front wheels Wfl, Wfr, a steering assist unit 30 that generates assist torque in response to a driver's steering operation, and left and right rear wheels Wrl, Wrr. A rear wheel turning unit 40 for turning, and a front wheel turning unit 20, a steering assist unit 30, and a turning control device 50 for controlling the rear wheel turning unit 40 are provided.

  The front wheel steering unit 20 includes a steering handle 21 that is rotated by a driver. The steering handle 21 is connected to the upper end of the steering shaft 22. A pinion gear 23 is provided at the lower end portion of the steering shaft 22, and a rack bar 24 is engaged with the pinion gear 23. The rack bar 24 is extended to the left and right, and the left and right front wheels Wfl and Wfr are connected to each other so that the left and right front wheels Wfl and Wfr can be steered, and the left and right front wheels Wfl and Wfr are steered by axial displacement. Therefore, the rotation of the steering handle 21 is transmitted to the rack bar 24 via the steering shaft 22 and the pinion gear 23, and the rack bar 24 is displaced in the axial direction to steer the left and right front wheels Wfl, Wfr.

  The steering shaft 22 has a steering angle sensor 25 that detects a steering angle δh of the steering handle 21 based on the rotation angle of the steering shaft 22, and an input torque that is input when the driver operates the steering handle 21. A torque sensor 26 that detects Th is provided.

An electric motor 27 is assembled to the rack bar 24. The electric motor 27 applies a steering force to the left and right front wheels Wfl and Wfr by driving the rack bar 24 in the axial direction via the ball screw mechanism 28 according to the rotation. A rotation angle sensor 29 is assembled to the electric motor 27.
The rotation angle sensor 29 is constituted by a resolver in the present embodiment, detects the rotation angle of the electric motor 27, and outputs a detection signal indicating the detected rotation angle to a front wheel steering ECU 61 described later of the steering control device 50. To do. This rotation angle is not only used as a signal for motor phase control, but can also be converted into the turning angle of the left and right front wheels Wfl, Wfr to be steered by the electric motor 27, so that it is also used as a turning angle sensor. .
Hereinafter, this electric motor is referred to as a front wheel steering motor 27.

The rack bar 24 is assembled with an electric motor 31 as a steering assist unit 30 along with the front wheel steering motor 27. Similar to the front wheel steering motor 27, the electric motor 31 drives the rack bar 24 in the axial direction through the ball screw mechanism 32 according to the rotation thereof, thereby giving assist torque to the driver's handle operation. To do. A rotation angle sensor 33 is assembled to the electric motor 31.
The rotation angle sensor 33 is configured by a resolver in the present embodiment, detects the rotation angle of the electric motor 31, and outputs a detection signal representing the detected rotation angle to an assist ECU 71 described later of the steering control device 50. This rotation angle is used as a signal for motor phase control.
Hereinafter, this electric motor is referred to as an assist motor 31.

The rear wheel steering unit 40 includes a steering bar 41 that connects the left and right rear wheels Wrl and Wrr so as to be steerable, and steers the left and right rear wheels Wrl and Wrr by displacement in the axial direction of the steering bar 41. An electric motor 42 is assembled to the steered bar 41. The electric motor 42 applies a turning force to the left and right rear wheels Wrl and Wrr by driving the turning bar 41 in the axial direction via the ball screw mechanism 43 according to the rotation. A rotation angle sensor 44 is assembled to the electric motor 42.
The rotation angle sensor 44 is constituted by a resolver in the present embodiment, detects the rotation angle of the electric motor 42, and outputs a detection signal representing the detected rotation angle to a rear wheel steering ECU 81 described later of the steering control device 50. To do. This rotation angle is used not only as a signal for motor phase control but also as a turning angle sensor because it can be converted into the turning angle of the left and right front wheels Wfl and Wfr to be turned by the electric motor 42.
Hereinafter, this electric motor is referred to as a rear wheel steering motor 42.

  The steering control device 50 drives and controls the front wheel steering control device 60 for driving and controlling the front wheel steering motor 27, the assist control device 70 for driving and controlling the assist motor 31, and the rear wheel steering motor 42. A rear wheel steering control device 80, a lane detection device 90 that captures the front of the vehicle and obtains lane information, a steering control amount based on lane information and driver steering information from the lane detection device 90, and An electronic control unit 100 (hereinafter referred to as a main ECU 100) that calculates an assist correction control amount and outputs a control command to the front wheel steering control device 60, the assist control device 70, and the rear wheel steering control device 80 is provided.

  The front wheel steering control device 60 is an electronic control device 61 (hereinafter referred to as a front wheel steering ECU 61) that controls energization of the front wheel steering motor 27, and the front wheel steering motor 27 in accordance with an energization command from the front wheel steering ECU 61. And a motor drive circuit 62 for driving the motor. The front wheel steering ECU 61 includes a microcomputer including a CPU, a ROM, a RAM, and the like as a main part, and rotates a rotation angle sensor 29 that detects a front wheel steering control command from the main ECU 100 and a rotation angle of the front wheel steering motor 27. Energization of the front wheel steering motor 27 is controlled based on the angle detection signal.

The assist control device 70 includes an electronic control device 71 (hereinafter referred to as an assist ECU 71) that controls energization of the assist motor 31, and a motor drive circuit 72 that drives the assist motor 71 in response to an energization command from the assist ECU 71. . The motor drive circuit 72 is provided with a current sensor 73 that detects the amount of current flowing through the assist motor 31, and outputs a detected current value i detected by the current sensor 73 to the assist ECU 71.
The assist ECU 71 includes a microcomputer including a CPU, a ROM, a RAM, and the like as a main part. The assist ECU 71 calculates a target assist torque corresponding to the steering state, and based on the current value i detected by the current sensor 73, the target assist torque. The motor drive voltage 72 is controlled to adjust the motor applied voltage so that the target assist current corresponding to the? For example, when a three-phase brushless motor is used as the assist motor 31 and the motor drive control is performed by the motor drive circuit 72 configured by a three-phase inverter, the voltage is adjusted by PWM control of the duty ratio of the switching element of the three-phase inverter. To do.

  The rear wheel steering control device 80 is an electronic control device 81 (hereinafter referred to as a rear wheel steering ECU 81) that controls energization of the rear wheel steering motor 42, and the rear wheel steering motor 42 according to an energization command from the rear wheel steering ECU 81. And a motor drive circuit 82 for driving the motor. The rear wheel steering ECU 81 includes a microcomputer including a CPU, a ROM, a RAM, and the like as a main part, and rotates a rotation angle sensor 44 that detects a rear wheel steering control command from the main ECU 100 and a rotation angle of the rear wheel steering motor 42. The energization of the rear wheel steering motor 42 is controlled based on the angle detection signal.

  The lane detection device 90 includes a stereo camera 91 that captures the front of the host vehicle, and an image processing device 92 that performs various types of image processing on an image signal output from the stereo camera 91 (hereinafter referred to as an image ECU 92). With.

  The stereo camera 91 is a compound-eye camera in which two cameras 91a and 91b whose optical axes are parallel to each other are arranged on the left and right, and images the road condition ahead from two viewpoints by the two cameras 91a and 91b. The stereo camera 91 is fixed to the vehicle body, images a road in a range ahead of the vehicle (for example, a range of 17 to 20 meters ahead) as a gaze area, and the left and right image signals are sent to the image ECU 92 at a predetermined cycle. Output.

  The image ECU 92 includes a microcomputer including a CPU, a ROM, a RAM, and the like as a main part. The image ECU 92 inputs a pair of left and right image signals obtained by imaging with the stereo camera 91, and outputs each image signal. By performing image processing (edge extraction processing or the like) to extract feature points, the formation state of a lane marker (hereinafter simply referred to as a white line) such as a white line on the road ahead is detected. In this case, the corresponding points p1 (x1, y1) and p2 (x2, y2) on the left and right images captured by the stereo camera 91 are collated, and based on the correlation, the object to be imaged is obtained by triangulation. Three-dimensional distance data (x, y, z) is generated. Therefore, the formation state of the white line formed on the road can be recognized together with the distance from the own vehicle.

The image ECU 92 processes an image signal obtained by imaging with the stereo camera 91 to detect a front lane situation and a vehicle state in the lane.
Here, the lane vehicle state detection process executed by the image ECU 92 will be described. FIG. 2 shows a lane vehicle state detection control routine executed by the image ECU 92, and this lane vehicle state detection control routine is stored in the ROM of the image ECU 92 as a control program.
This lane vehicle state detection control routine is started by turning on an ignition switch (not shown), and is repeatedly executed at a predetermined short cycle.

When this control routine is activated, the image ECU 92 inputs an image signal from the stereo camera 91 in step S11. Subsequently, in step S12, image processing such as edge extraction processing is performed on the input image signal to recognize the formation state of the left and right white lines on the road ahead of the vehicle.
Next, in step S13, as shown in FIG. 3, the position of the road center line LC serving as the target track of the vehicle C is calculated from the left and right white lines LL and LR.

In this example, a single lane road without an oncoming lane is shown, but in the case of a road with multiple lanes, the white line closest to the vehicle formed on the right side and the white line closest to the vehicle formed on the left side are shown. And the area surrounded by the left and right white lines is recognized as a travel lane, and the center line in the travel lane may be obtained as the road center line.
In this case, the image ECU 92 three-dimensionally recognizes the formation state of the road center line LC on the image data by obtaining the three-dimensional distance data of the road center line LC from the three-dimensional distance data of the left and right white lines LL and LR. can do.

Subsequently, the image ECU 92 advances the processing to step S14, and calculates the curvature radius R (see FIG. 3) of the road center line LC at the current vehicle position. In the present embodiment, an intersection A of a road center line LC and a line drawn from the vehicle center of gravity position G toward the right side (a direction orthogonal to the vehicle longitudinal axis) is obtained, and the road center line LC at the intersection A portion is obtained. The radius of curvature R (the radius R of the curve) is calculated.
In this calculation, since the stereo camera 91 images the front of the vehicle C (for example, 17 to 20 meters ahead of the vehicle), an image captured when the vehicle is traveling a predetermined distance behind the current vehicle position. Based on the above. Further, since the shape of the road center line LC is grasped from the three-dimensional distance data, a curve in the vicinity of the intersection A may be approximated to an arc, and the radius of the arc may be a curvature radius R.

Subsequently, in step S15, a lateral shift between the position of the road center line LC and the position of the vehicle C is calculated as a lateral displacement amount D. In the present embodiment, the distance between the intersection point A and the vehicle gravity center position G is defined as the lateral displacement amount D.
Next, in step S16, the angle formed by the formation direction of the road center line LC (the tangential direction of the road center line at the current position of the vehicle) and the direction of the vehicle C (the longitudinal axis direction of the vehicle) is calculated as the vehicle attitude angle θ. To do. In the present embodiment, the vehicle attitude angle θ is the direction of the vehicle C with respect to the tangential direction at the intersection A.
Note that in steps S15 and S16, the lateral displacement amount D and posture angle θ of the vehicle with respect to the road center line LC at the present time may be calculated from the coordinate position of the road center line LC on the captured image and the transition of the coordinate position.

  When the calculation processing of the curvature radius R, the lateral displacement D, and the vehicle attitude angle θ is completed in steps S14 to S16, the image ECU 92 outputs these calculated values R, D, and θ to the main ECU 100 (S17). This control routine is once terminated. Since this control routine is repeated at a predetermined cycle, the traveling state information of the vehicle with respect to the road is always output from the image ECU 92 to the main ECU 100.

  The main ECU 100 includes a microcomputer including a CPU, ROM, RAM, and the like as main components, and performs automatic driving (automatic steering) in which a vehicle travels along a road center line by executing a front and rear wheel steering control program described later. The steering control amount obtained by adding the steering amount of the driver is calculated, and a steering control command is output to the front wheel steering ECU 61 and the rear wheel steering ECU 81. Further, the main ECU 100 connects the vehicle speed sensor 110 and inputs the vehicle speed signal V in order to execute the front and rear wheel steering control program.

Next, front and rear wheel turning control processing will be described. FIG. 4 shows a front / rear wheel steering control routine executed by the main ECU 100, and this front / rear wheel steering control routine is stored in the ROM of the main ECU 100 as a control program.
This front / rear wheel steering control routine is started by turning on an ignition switch (not shown), and is repeatedly executed at a predetermined short cycle. In parallel with this control routine, the lane vehicle state detection process described above by the lane detection device 90 is performed.

This front / rear wheel steering control routine basically includes a target value for vehicle motion for performing autopilot to drive the vehicle along the road center line, and a target for vehicle motion as much as the driver steers the steering wheel. And the sum of these target values is set as a target value for the final vehicle motion, and the front and rear wheels Wfl, Wfr, Wrl, Wrr are steered at a steering angle that provides the final vehicle motion target value. To do. In this embodiment, the yaw rate γ and the vehicle body slip angle β are used as target values for the vehicle motion.
Hereinafter, specific control processing will be described in detail.

  When this control routine is started, first, in step S21, the vehicle speed signal V is read from the vehicle speed sensor 110 and the steering angle signal δh is read from the steering angle sensor 25. Subsequently, in step S22, a yaw rate gain Kyh (γ / δh) with respect to the steering angle δh is calculated. The yaw rate gain Kyh is an instantaneous yaw rate gain for generating a vehicle motion target value (target yaw rate) from the driver's steering operation, and is calculated with reference to the yaw rate gain calculation map MPyh shown in FIG. The yaw rate gain Kyh with respect to the steering angle δh is set to a value corresponding to the vehicle speed V as shown in the calculation map MPyh. If the range is less than the predetermined speed, the yaw rate gain Kyh increases as the vehicle speed V increases and becomes equal to or higher than the predetermined speed. The range is set so as to decrease as the vehicle speed V increases.

Subsequently, in step S23, a vehicle body slip angle gain Kbh (β / δh) with respect to the steering angle δh is calculated. The vehicle body slip angle gain Kbh is an instantaneous vehicle body slip angle gain for generating a vehicle movement target value (target vehicle body slip angle) from the driver's steering operation, and is a vehicle body slip angle gain calculation map MPbh shown in FIG. To calculate. The vehicle body slip angle gain Kbh with respect to the steering angle δh is set to a value corresponding to the vehicle speed V as shown in the calculation map MPbh. If the range is less than the predetermined speed, the vehicle body slip angle gain Kbh takes a positive value. Set to take a negative value.
The yaw rate gain calculation map MPyh and the vehicle body slip angle gain calculation map MPbh are stored in the ROM of the main ECU 100.

  Next, in step S24, lane information (θ, D, R) is read from the image ECU 92. As described above, the image ECU 92 includes the lateral displacement amount D information between the current vehicle position and the road center line, the vehicle attitude angle θ information indicating the vehicle orientation with respect to the formation direction of the road center line, and the road center line at the vehicle position. Therefore, the main ECU 100 reads the latest output information from the image ECU 92.

Subsequently, in step S25, a target yaw rate Δγauto * for performing trajectory correction by autopilot is calculated as follows.
Δγauto * ＝ Kyauto ・ θ
Kyauto: Yaw rate control gain for autopilot Next, in step S26, a target vehicle body slip angle Δβauto * for correcting a track by autopilot is calculated as follows.
Δβ * = θ + Kbauto · D
Kbauto: Auto body steering slip angle control gain

Here, the calculation formula in steps S25 and S26 will be described.
At the time of automatic steering in the present embodiment, the road center line is set as the target track of the vehicle, and the turning angles of the front and rear wheels Wfl, Wfr, Wrl, Wrr are controlled so that the vehicle travels along the road center line. . In controlling the turning angles of the front and rear wheels Wfl, Wfr, Wrl, Wrr, the turning angles are controlled so that a predetermined yaw rate and vehicle body slip angle are generated in the vehicle. Therefore, the trajectory correction yaw rate and the vehicle slip angle target values Δγauto * and Δβauto * corresponding to the lateral displacement D and the vehicle attitude angle θ are set.

従って、次式（３）が得られる。

ここで

としたフィードバック制御を考えると（Ｋ１〜Ｋ４は制御ゲイン）、次式のように表すことができる。

そして、車両姿勢角θおよび横方向変位量Ｄを独立して制御するために、
Ｋ２＝０，Ｋ３＝１
とすると、車両の運動方程式を次式（８）のように表すことができる。

従って、車両の運動方程式は、

となり、式（１）、（２）から最終的に、

という関係式が得られる。 Now, consider the vehicle state shown in FIG. FIG. 7 shows the relationship between the traveling vehicle C and the road center line LC. This vehicle C is displaced from the road center line LC by a lateral displacement amount D and a vehicle attitude angle θ. Further, the traveling direction of the vehicle is shifted by an angle β with respect to the direction of the vehicle body. This angle β is the vehicle body slip angle.
In this state, the equation of motion of the vehicle can be expressed as the following equations (1) and (2) using the yaw rate γ, the vehicle body slip angle β, the vehicle speed V, the lateral displacement D, and the vehicle attitude angle θ. it can.

Therefore, the following expression (3) is obtained.

here

When the feedback control is considered (K1 to K4 are control gains), it can be expressed as the following equation.

In order to independently control the vehicle attitude angle θ and the lateral displacement D,
K2 = 0, K3 = 1
Then, the equation of motion of the vehicle can be expressed as the following equation (8).

Therefore, the equation of motion of the vehicle is

And finally from equations (1) and (2),

Is obtained.

ｓ…ラプラス演算子
従って、式（１３）におけるＶ・Ｋ４の項から横方向変位量Ｄに対する応答性が車速Ｖに依存することがわかる。
そこで、ステップＳ２６の算出式で用いる自動操縦用車体スリップ角制御ゲインＫｂautoは、この制御ゲインＫ４を車速Ｖで除算した値（Ｋ４／Ｖ）に設定する。また、ステップＳ２５の算出式で用いる自動操縦用ヨーレート制御ゲインＫｙautoについては制御ゲインＫ１と同様のものでよい。 Thus, the yaw rate γ and the vehicle body slip angle β can be expressed using the lateral displacement D and the vehicle attitude angle θ, respectively.
Therefore, the target yaw rate Δγauto * and the target vehicle body slip angle Δβauto * for correcting the trajectory calculated in steps S25 and S26 may use these equations (11) and (12). Responsiveness to the lateral displacement amount D depends on the vehicle speed V.
Here, the response to the vehicle attitude angle initial value θ (0) and the lateral displacement initial value D (0) is expressed by the following equation (13).

s... Laplace operator Therefore, it can be seen from the term V · K4 in the equation (13) that the response to the lateral displacement D depends on the vehicle speed V.
Therefore, the autopilot vehicle body slip angle control gain Kbauto used in the calculation formula of step S26 is set to a value (K4 / V) obtained by dividing the control gain K4 by the vehicle speed V. Further, the yaw rate control gain Kyauto for automatic steering used in the calculation formula in step S25 may be the same as the control gain K1.

Further, the automatic steering yaw rate control gain Kyauto and the automatic steering vehicle body slip angle control gain Kbauto used in steps S25 and S26 are set so as to change according to the vehicle speed V and the curvature radius R of the road center line.
FIG. 8 shows an automatic pilot yaw rate control gain calculation map MPyauto, and FIG. 9 shows an automatic pilot vehicle body slip angle control gain calculation map MPbauto.
The control gains Kyauto and Kbauto are set to larger values as the vehicle speed V is higher as shown in the calculation maps MPyauto and MPbauto. Therefore, the turning radius and the correction distance of the vehicle when correcting the vehicle posture and the vehicle lateral position can be made constant regardless of the vehicle speed V. For this reason, the feeling given to the occupant does not change according to the vehicle speed during autopilot, so the occupant does not feel uncomfortable.
Furthermore, the control gains Kyauto and Kbauto are set to larger values as the curvature radius R of the road center line is smaller. Therefore, quick response on the curved road surface is ensured, and for example, it is possible to follow the road center line without the driver's steering operation. In addition, the vehicle posture and vehicle position correction operation on the straight road surface is suppressed, and a natural feeling of straight running is possible, so that the driver does not feel uncomfortable.

  Each of these calculation maps MPyauto and MPbauto is stored in the ROM of the main ECU 100, and is referred to when calculating the target yaw rate Δγauto * and the target vehicle body slip angle Δβauto * for trajectory correction in steps S25 and S26.

Subsequently, the main ECU 100, based on the target yaw rate Δγauto * and the target vehicle body slip angle Δβauto * for trajectory correction calculated in this way, in step S27 and step S28, the target yaw rate γauto * and the target vehicle body by autopilot. The slip angle βauto * is calculated.
That is, the trajectory correction target yaw rate Δγauto * and target vehicle body slip angle Δβauto * calculated in step S25 and step S26 are vehicle motion target values for correcting the deviation of the position and posture angle of the vehicle with respect to the road center line. Thus, it is not the vehicle motion target value corresponding to the steered state with respect to the wheel neutral position.

Therefore, in step S27, the integral value of the target yaw rate Δγauto * for trajectory correction is calculated, and this calculated value is used as the target yaw rate for automatic steering in the current steered state γauto *. Since this control routine is repeatedly executed at a predetermined cycle, the integrated value of Δγauto * can be set to the target yaw rate γauto * by setting the initial value of Δγauto * to the value “0”.
Similarly, in step S28, the initial value of the target vehicle body slip angle Δβauto * for correcting the track is set to the value “0” and integrated so that this integrated value corresponds to the steered state with respect to the wheel neutral position. The target body slip angle βauto * for autopilot is set.

  The target yaw rate for autopilot γauto * and the target vehicle body slip angle βauto * calculated in steps S27 and S28 correspond to the first target value for vehicle motion in the present invention.

When the target yaw rate γauto * and the target vehicle body slip angle βauto *, which are instantaneous vehicle motion target values by autopilot, are calculated in this way, it is necessary to obtain the vehicle motion target value (target yaw rate γauto *) in step S29. A steering angle of the steering wheel 21 by a driver is calculated as a virtual steering angle δhauto. That is, in order to obtain this vehicle motion target value, it is calculated how much steering angle is required in terms of the driver's steering operation.
Therefore, in this step S29, the virtual steering angle δhauto is calculated as follows.
δhauto = γauto * / Kyh
Here, Kyh is an instantaneous yaw rate gain for generating a target value of vehicle motion from the driver's steering wheel operation calculated in step S22.

  Subsequently, the main ECU 100 advances the process to step S30, and outputs data representing the virtual steering angle δhauto to the assist ECU 71. The assist ECU 71 calculates the correction assist torque based on the virtual steering angle δhauto when executing the assist control routine. This process will be described later.

Next, in step S31, the steering wheel steering angle δhdriv operated by the driver is calculated by the following equation.
δhdriv = δh−δhauto
That is, the difference between the actual steering angle δh detected by the steering angle sensor 25 and the virtual steering angle δhauto by automatic steering is estimated as the steering angle δhdriv operated by the driver.

Subsequently, in step S32, a target yaw rate γdriv * for steering the steering wheel operated by the driver is calculated as follows.
γdriv * = Kyh ・ δhdriv
That is, by multiplying the steering angle δhdriv estimated that the driver has operated the steering wheel by the instantaneous yaw rate gain Kyh (calculated in step S22) for generating the target value of the vehicle motion from the driver's steering operation, the driver The target yaw rate γdriv * for steering the steering wheel operated is calculated.

Similarly, in step S33, a target vehicle body slip angle βdriv * for steering the steering wheel operated by the driver is calculated as follows.
βdriv * = Kbh ・ δhdriv
That is, by multiplying the steering angle δhdriv estimated that the driver has operated the steering wheel by the instantaneous vehicle body slip angle gain Kbh (calculated in step S23) for generating the target value of the vehicle motion from the driver's steering operation, A target vehicle body slip angle βdriv * for steering the steering wheel operated by the driver is calculated.

  The target yaw rate γdriv * and the target vehicle body slip angle βdriv * calculated in steps S33 and S33 correspond to the second target value of the vehicle motion in the present invention.

Subsequently, the main ECU 100 advances the process to step S34, and calculates the final target yaw rate γ * as the following equation.
γ * = γauto * + γdriv *
In other words, the sum of the target yaw rate γauto * by automatic steering calculated in step S27 and the target yaw rate γdriv * for steering the steering wheel operated by the driver in step S32 is calculated as the final target yaw rate γ *.

Similarly, in step S35, the main ECU 100 calculates the final target vehicle body slip angle β * as follows: β * = βauto * + βdriv *
In other words, the final target vehicle body slip angle β is calculated by adding the sum of the target vehicle body slip angle βauto * calculated by step S28 and the target vehicle body slip angle βdriv * for the steering wheel operated by the driver calculated in step S33. * Calculated as

  The final target yaw rate γ * and the final target vehicle body slip angle β * calculated in steps S34 and S35 correspond to the final target value of the vehicle motion of the present invention.

Ｃｆ：前輪コーナリングパワー
Ｃｒ：後輪コーナリングパワー
Ｉ：車体重心回りの慣性モーメント
ｍ：車体質量
Ｖ：車速
Ｌｆ：車体重心から前輪車軸までの前後方向の水平距離
Ｌｒ：車体重心から後輪車軸までの前後方向の水平距離
この式は、前後輪操舵２輪モデルにおける前後輪目標舵角の演算式である。 When the final target values (γ *, β *) of the vehicle motion are calculated in this way, subsequently, in step S36, the target front wheel turning angle δf * and the target rear wheel turning angle δr * are calculated by the following equations.

Cf: Front wheel cornering power
Cr: Rear wheel cornering power
I: Moment of inertia around the center of gravity
m: Body mass
V: Vehicle speed
Lf: Horizontal distance in the front-rear direction from the center of gravity of the vehicle body to the front axle
Lr: Horizontal distance in the front-rear direction from the center of gravity of the vehicle body to the rear axle. This equation is an arithmetic expression for the front-rear wheel target rudder angle in the front-rear wheel steering two-wheel model.

Subsequently, in step S37, the main ECU 100 outputs a control command corresponding to the target front wheel turning angle δf * and the target rear wheel turning angle δr * calculated in the previous step S36 to the front wheel turning ECU 61 and the rear wheel turning ECU 81. To do.
The front wheel steering ECU 61 receives a control command from the main ECU 100 and outputs a drive signal to the motor drive circuit 62 to steer the front wheels Wfl and Wfr so that the target front wheel steering angle δf * is obtained. That is, a signal of the rotation angle sensor 29 that detects the rotation angle of the front wheel steering motor 27 is input to detect the turning angle δf (steering angle with respect to the neutral position), and the detected turning angle δf is the target front wheel turning angle. The front wheel steering motor 27 is feedback-controlled so as to coincide with δf *.

  Further, the rear wheel steering ECU 81 receives a control command from the main ECU 100 and outputs a drive signal to the motor drive circuit 82 to steer the rear wheels Wrl and Wrr so that the target rear wheel steering angle δr * is obtained. . That is, a signal of the rotation angle sensor 44 that detects the rotation angle of the rear wheel steering motor 42 is input to detect the steering angle δr (steering angle with respect to the neutral position), and the detected steering angle δr is the target rear wheel steering angle. The rear wheel steering motor 42 is feedback-controlled so as to coincide with δr *.

When the main ECU 100 outputs a control command to the front wheel steering ECU 61 and the rear wheel steering ECU 81, the control routine is temporarily terminated. Then, this control routine is repeatedly executed at a predetermined cycle.
Therefore, while the vehicle is traveling, the front and rear wheels Wfl, are always based on the sum of the vehicle motion target value by autopilot with the road center line as the target track and the vehicle motion target value by the steering by the driver. Wfr, Wrl, and Wrr are driven and controlled.

Next, an assist control process executed by the assist ECU 71 will be described. FIG. 10 shows an assist control routine executed by the assist ECU 71. This assist control routine is stored in the ROM of the assist ECU 71 as a control program.
This assist control routine is started by turning on an ignition switch (not shown), and is repeatedly executed at a predetermined short period in parallel with the above-described front and rear wheel steering control routine.

When the assist control routine is started, first, in step S51, a detection signal from the torque sensor 26 is read to acquire the steering torque Th information indicating the torque value applied to the steering handle 21 by the driver, and the vehicle speed sensor 110 is obtained. The vehicle speed V information is acquired by reading the detection signal from the vehicle.
Subsequently, in step S52, the basic assist torque Ta1 is calculated from the steering torque Th and the vehicle speed V with reference to the basic assist map MPa1 shown in FIG. The basic assist map MPa1 is stored in the ROM of the assist ECU 71, and a plurality of basic assist torques Ta1 are determined depending on the steering torque Th for each of a plurality of representative vehicle speed values. The basic assist torque Ta1 is for giving an assisting force to the operation of the steering handle 21 performed by the driver. The basic assist torque Ta1 increases nonlinearly as the steering torque Th increases, and is set to a larger value as the vehicle speed V is lower. The

Next, the process proceeds to step S53, and the virtual rudder angle δhauto information by automatic steering is acquired. As described above, the main ECU 100 outputs the virtual steering angle δhauto information to the assist ECU 71 at a predetermined cycle during the execution of the front and rear wheel steering control routine (S30).
Therefore, in step S53, the assist ECU 71 obtains the latest one of the virtual steering angle δhauto information output from the assist ECU 71 as the virtual steering angle δhauto.

  Subsequently, in step S54, when the front wheels Wfl and Wfr are steered at the turning angle corresponding to the virtual steering angle δhauto, the reaction force acting on the front wheels Wfl and Wfr (force to return the wheels to the neutral position side) is applied. A corresponding assist assist torque Ta2 is calculated. The auxiliary assist torque Ta2 may be calculated, for example, by multiplying the front wheel cornering force obtained by multiplying the virtual steering angle δhauto by the reciprocal of the steering gear ratio and the cornering power by a predetermined coefficient. That is, the torque that opposes the cornering force acting on the front wheels Wfl, Wfr is calculated as the auxiliary assist torque Ta2.

When the basic assist torque Ta1 and the assist assist torque Ta2 are calculated in this way, the final target assist torque Ta * is then calculated as the sum of them in step S55.
Ta * = Ta1 + Ta2
Subsequently, in step S56, the assist ECU 71 outputs a control command to the motor drive circuit 72 so as to energize the assist motor 31 with an assist current corresponding to the target assist torque Ta *. Accordingly, a target assist current corresponding to the target assist torque flows from the motor drive circuit 72 to the assist motor 31, and assist torque is generated in the steering direction of the steering handle 21.

When the assist ECU 71 outputs a control command to the motor drive circuit 72, the control routine is temporarily terminated. Then, this control routine is repeated at a predetermined cycle.
Therefore, not only the basic assist torque Ta1 for the driver's steering wheel operation, but also the assist assist torque Ta2 for the steering by automatic steering is always applied.

  According to the vehicle steering device of the present embodiment described above, the main ECU 100 executes the front-rear wheel steering control routine, thereby performing the vehicle motion for performing the autopilot that causes the vehicle to travel along the road center line. One target value (γauto *, βauto *) is calculated, and a virtual steering angle δhauto converted to a steering wheel steering angle by the driver for obtaining the target value of the vehicle motion is obtained. Then, the difference in steering angle between the actual steering angle δh and the virtual steering angle δhauto is estimated as the steering amount operated by the driver, and the second target value (γdriv *, βdriv *) is calculated. Subsequently, the sum of the first target value (γauto *, βauto *) and the second target value (γdriv *, βdriv *) of the vehicle motion is calculated as the final target value (γ *, β *) of the vehicle motion, The target turning angles (δf *, δr *) of the front wheels Wfl, Wfr and the rear wheels Wrl, Wrr necessary for obtaining the final target values (γ *, β *) are calculated to calculate the front wheel steering ECU and the rear wheel rotation. A control command is output to the rudder ECU.

As a result, even when steering control is performed using both the vehicle motion target value according to the driver's steering operation and the vehicle motion target value by autopilot, the steering wheel operation of the driver is appropriately added to the autopilot. Since the final target value of the vehicle movement is obtained, the wheel can be steered optimally. Therefore, the steering state intended by the driver is obtained, and the steering feeling and the turning motion feeling are very good.
Even when the driver does not operate the steering wheel, the vehicle is automatically operated in accordance with an appropriate exercise target value, which is safe and does not cause the driver to feel uneasy.

  In addition, when driving automatically, the vehicle is driven along the lane so as to obtain the optimum yaw rate and vehicle body slip angle according to the driving state of the vehicle. Does not give a sense of incongruity. That is, if it is attempted to correct the lateral deviation and the vehicle attitude angle deviation only by the turning motion of the vehicle, an excessive turning motion may be performed, but in the present embodiment, the optimum according to the traveling state of the vehicle. Such a problem does not occur because the steering angle is controlled so as to obtain a stable yaw rate and vehicle body slip angle.

Further, since the vehicle attitude angle θ and the lateral displacement D can be controlled independently, the vehicle can be efficiently traveled along the target track.
For example, the vehicle is likely to be displaced laterally with respect to the road when traveling on a crosswind or traveling on an inclined road surface (a road surface inclined in the vehicle body width direction). However, even in such a case, according to the steering device 10 of the present embodiment, the lateral position can be corrected without turning the vehicle. That is, when the vehicle is displaced only laterally with respect to the road center line (vehicle attitude angle θ = 0), the target yaw rate Δγauto * for trajectory correction is set to zero and the target vehicle body slip angle Δβauto * Is set to a value corresponding to the lateral displacement amount D, so that only the lateral position can be corrected without turning the vehicle.
Therefore, there is no problem of excessive turning motion (meandering operation), and stable running is possible. In addition, the passengers in the following vehicles are not worried.

Further, when the vehicle is not shifted laterally with respect to the road center line but only the direction is shifted, only the direction can be corrected without moving the vehicle laterally. In this case, the lateral displacement amount D is D = 0, and the target yaw rate Δγauto * for trajectory correction and the target vehicle body slip angle Δβauto * are set to values corresponding to the vehicle attitude angle θ. The orientation can be corrected without any change.
As a result, the vehicle can be efficiently traveled along the target track, and excessive yaw moment and lateral acceleration can be suppressed.

Furthermore, the control responsiveness of the lateral displacement amount D and the vehicle attitude angle θ can be made variable.
For example, the control responsiveness can be individually adjusted such that the responsiveness of the lateral displacement amount D is slow and the responsiveness of the vehicle attitude angle θ is fastened.
The response of the vehicle attitude angle θ is expressed as dθ / dt = K1 · θ + K2D. In this case, in the calculation example described above, K2 = 0, but by giving a predetermined value (≠ 0) to K2, a change in the lateral displacement amount D appears in the response of the vehicle attitude angle θ.
Further, the response of the lateral displacement D is expressed as dD / dt = V (K3-1) θ + K4 · V · D. In this case, in the above calculation example, K3 = 1, but by giving a predetermined value (≠ 1) to K3, a change in the vehicle attitude angle θ appears in the response of the lateral displacement D.
Therefore, by adjusting the control gains K2 and K3, the control responsiveness of the lateral displacement amount D and the vehicle attitude angle θ can be freely set.

  Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the object of the present invention.

For example, in this embodiment, the steering angles of the front wheels Wfl and Wfr are adjusted by the front wheel steering motor 27 provided on the rack bar 24. However, the steering angle control may be performed using a steering-by-wire type steering device. Good. Further, the turning angle control may be performed using a gear ratio variable device (VGRS) that changes the steering gear ratio by an electric motor.
Further, in the present embodiment, in order to perform the autopilot operation, a configuration is adopted in which the road ahead is imaged and the lane state is detected. For example, lane information is acquired from the navigation system and a GPS signal is input. Then, the vehicle state (lateral displacement amount and vehicle attitude angle) on the lane may be calculated to control the steering angle of the front and rear wheels.
In the present embodiment, the front wheel Wfl, Wfr and the rear wheels Wrl, Wrr are independently steered by the front wheel steering actuator and the rear wheel steering actuator. However, only the front wheels Wfl, Wfr are configured. The structure which provided the steering actuator may be sufficient.

  The front wheel steering motor 27 and the rear wheel steering motor 42 in the present embodiment correspond to the steering actuator of the present invention, and the steering angle sensor 25 in the present embodiment corresponds to the steering angle detection means of the present invention. Further, the processing of steps S27 and S28 performed in the main ECU 100 in the present embodiment corresponds to the first vehicle motion target value calculation means of the present invention, and the processing of step S29 performed in the main ECU 100 in the present embodiment is the present invention. The process corresponds to the virtual rudder angle calculation means, and the processing of steps S31 to S33 performed in the main ECU 100 in the present embodiment corresponds to the second vehicle motion target value calculation means of the present invention. Further, the processing of steps S34 and S35 performed in the main ECU 100 in the present embodiment corresponds to the final vehicle motion target value calculation means of the present invention, and the processing of step S36 performed in the main ECU 100 in the present embodiment is the conversion of the present invention. This corresponds to the rudder angle calculation means. Further, the front wheel steering control device 60 and the rear wheel steering control device 80 in the present embodiment correspond to the actuator control means of the present invention.

1 is an overall schematic diagram of a vehicle steering apparatus according to an embodiment of the present invention. It is a flowchart showing the lane vehicle state detection control routine which image ECU performs. It is explanatory drawing explaining the vehicle state on a road. It is a flowchart of the front and rear wheel steering control routine performed by the main ECU. It is a calculation map for calculating the yaw rate gain Kyh. 5 is a calculation map for calculating a vehicle body slip angle gain Kbh. It is explanatory drawing showing lateral direction displacement amount D, vehicle attitude angle (theta), and vehicle body slip angle (beta). It is a calculation map in order to calculate the yaw rate control gain Kyauto. 7 is a calculation map for calculating a vehicle body slip angle control gain Kbauto. It is a flowchart showing the assist control routine which assist ECU performs. It is a calculation map for calculating basic assist torque Ta1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Steering device, 20 ... Front wheel steering part, 21 ... Steering handle, 25 ... Steering angle sensor, 27 ... Front wheel steering motor, 29 ... Rotation angle sensor, 30 ... Steering assist part, 31 ... Assist motor, 40 ... Rear Wheel steering section, 42 ... rear wheel steering motor, 44 ... rotation angle sensor, 50 ... steering control device, 60 ... front wheel steering control device, 61 ... front wheel steering ECU, 62 ... motor drive circuit, 70 ... assist control device 71 ... Assist ECU, 72 ... Motor drive circuit, 80 ... Rear wheel steering control device, 81 ... Rear wheel steering ECU, 82 ... Motor drive circuit, 90 ... Lane detection device, 91 ... Stereo camera, 92 ... Image processing device, DESCRIPTION OF SYMBOLS 100 ... Main ECU, 110 ... Vehicle speed sensor, Wfl, Wfr ... Left and right front wheel, Wrl, Wrr ... Left and right rear wheel

Claims (3)

A steering handle that is operated by the driver to steer the wheel to a steering angle according to the operation amount;
In a vehicle steering apparatus comprising a steering actuator that steers the wheel,
Steering angle detection means for detecting a steering angle of the steering wheel;
First vehicle motion target value calculating means for calculating a first target value of vehicle motion in accordance with a traveling state of the vehicle irrespective of operation of the steering handle in order to automatically steer the vehicle;
Virtual steering angle calculation means for calculating a virtual steering angle of the steering wheel by a driver necessary for obtaining a first target value of the vehicle motion;
From the difference between the steering angle of the steering wheel detected by the steering angle detection means and the virtual steering angle calculated by the virtual steering angle calculation means, the second target value of the vehicle motion by the driver's steering operation corresponding to the difference Second vehicle motion target value calculating means for calculating
Final vehicle motion target value calculation means for calculating a final target value of vehicle motion based on the sum of the first target value and the second target value;
A turning angle calculation means for calculating a target turning angle of a wheel necessary for obtaining the final target value;
Actuator control means for driving the steering actuator based on the target turning angle calculated by the turning angle calculation means to realize the calculated target turning angle. Vehicle steering device.   2. The vehicle steering apparatus according to claim 1, wherein the first target value, the second target value, and the final target value of the vehicle motion include at least a yaw rate of the vehicle. The vehicle steering apparatus according to claim 1 or 2, wherein the first target value, the second target value, and the final target value of the vehicle motion include at least a vehicle body slip angle.

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