JP2014024448A - Steering support device of vehicle - Google Patents

Abstract

Sufficient gain characteristics and phase characteristics are obtained even in a situation where responsiveness is required while preventing interference with driver steering.
When there is no change in the sign of the disturbance value and no change in the curvature, the steering angle control distribution ratio Nctrl is set to 0 (S8). When there is a change in the sign of the disturbance value or when there is a change in the curvature, the steering angle The control distribution ratio Nctrl is set to 1 (S9). Then, the final target steering torque Tcmd is calculated using the steering angle control distribution ratio Nctrl (S10). As a result, when Nctrl = 0, the final target steering torque Tcmd is set as the target steering torque Ttrqd for torque control, and steering assistance is performed without interfering with the steering of the driver. On the other hand, when Nctrl = 1, the final target steering torque Tcmd is a steering torque obtained by adding the target steering torque Tstrd of the steering angle feedback control to the target steering torque Ttrqd of the torque control, and converges to the target steering angle with good followability. Assist steering.
[Selection] Figure 7

Description

  The present invention relates to a steering assist device for a vehicle that applies steering torque to a steering system so as to travel along a lane to provide steering assistance to a driver.

  Conventionally, in vehicles such as automobiles, various support devices have been developed that reduce the burden of driving operations of drivers. In particular, the steering assist device that assists the driver's steering can reduce the burden on the driver while preventing the vehicle from departing from the lane.

  In such a steering assist device, as disclosed in Patent Document 1, it is common to take a control form in consideration of prevention of interference with the steering of the driver, and assist the steering torque rather than the steering angle. In many cases, torque control is employed.

Japanese Patent Laid-Open No. 11-78953

  However, the torque control that assists the steering torque rather than the steering angle has a control characteristic that depends on the characteristic of the steering system. In situations where responsiveness to the target value is required, such as situations, sufficient gain / phase characteristics may not be obtained.

  The present invention has been made in view of the above circumstances, and is a vehicle steering assist device capable of obtaining sufficient gain characteristics and phase characteristics even in a situation where responsiveness is required while preventing interference with steering of a driver. The purpose is to provide.

  The vehicle steering assist device according to the present invention is a vehicle steering assist device that applies steering torque to the steering system to assist the driver so that the host vehicle travels along the lane, and generates a steering assist target value. Determining a magnitude of a request for responsiveness to the target value, a torque support control unit that performs steering support with a torque that compensates for the external force torque, a feedback support control unit that performs steering support by feedback control with respect to the target value, A control distribution setting unit that sets a control distribution ratio of the feedback support control unit that is added to the torque support control unit according to the level of the request for responsiveness.

  According to the present invention, sufficient gain characteristics and phase characteristics can be obtained even in a situation where responsiveness is required while preventing interference with the steering of the driver.

Configuration diagram of steering assist device Functional block diagram of steering control system Explanatory diagram showing the response of the actual steering angle to the target phase steering angle Explanatory drawing showing the driving lane in the vehicle coordinate system Explanatory drawing showing switching of control system based on disturbance value Explanatory drawing showing switching of control system based on curvature value Flowchart of steering assist control processing

Embodiments of the present invention will be described below with reference to the drawings.
The steering assist device according to the present embodiment calculates a target steering torque for causing the vehicle to travel following the target course, and achieves the control target by turning the steered wheels based on the target steering torque. In FIG. 1, it is assumed that the left and right front wheels FL and FR of the vehicle 1 are steering-assisted through an electric power steering device (EPS) 2.

  The EPS 2 steering system is connected to a steering wheel 3 steered by a driver via a steering shaft 4 and is connected to front wheels FL and FR via left and right tie rods 5 that can extend and contract in the axial direction. Has been. The tie rod 5 is disposed on the left and right as a ball screw type linear actuator driven by a motor 6 provided in the EPS 2.

  The EPS 2 motor 6 is driven and controlled by an EPS control unit (EPS_ECU) 20. The EPS control unit 20 supports the steering operation of the driver by adding the driving torque of the motor 6 to the steering torque of the driver. The EPS control unit 20 is connected to the control unit (ECU) 30 via, for example, an in-vehicle network via a CAN (Controller Area Network) bus and the like, and the lane maintenance is performed by a control command transmitted from the control unit 30. For this purpose, the steering support is shared and controlled.

  In addition, a plurality of control units that share vehicle control such as an engine control unit, a transmission control unit, and a brake control unit are connected to the in-vehicle network to which the EPS control unit 20 and the control unit 30 are connected. Each control unit transmits / receives data to / from each other and exchanges various types of information.

  In the present embodiment, a stereo camera 7 is provided as a sensor for recognizing the traveling environment of the host vehicle in steering assistance. The stereo camera 7 is formed by unitizing two cameras arranged with a predetermined baseline length and an image processing engine that processes a pair of stereo images captured by the two cameras. The surrounding situation in a predetermined area ahead is photographed through the front window. Three-dimensional information about the environment outside the vehicle is obtained from the image captured by the stereo camera 7, and the travel lane of the vehicle 1 is recognized based on the three-dimensional information.

  The control unit 30 receives signals from the steering angle sensor 8, the wheel speed sensor 9, the yaw rate sensor 10, the lateral acceleration sensor 11, and other various sensors (not shown). The steering angle sensor 8 is attached to the steering shaft 4 and detects the steering angle of the steering wheel 3. The detected steering angle is transmitted to the control unit 30 via the EPS control unit 20. The wheel speed sensor 9 is attached to each of the left and right front wheels FL and FR and the left and right rear wheels RL and RR of the vehicle 1 and generates a pulse signal having a cycle corresponding to the wheel speed of each wheel. Output to 30. The yaw rate sensor 10 and the lateral acceleration sensor 11 are configured as MEMS (Micro Electro Mechanical Systems) sensors, detect the rotational speed around the vertical axis of the vehicle body and the lateral acceleration, and output them to the control unit 30.

  The control unit 30 recognizes the travel environment recognition information based on the image captured by the stereo camera 7 and the vehicle state quantity detected based on signals from the steering angle sensor 8, the wheel speed sensor 9, the yaw rate sensor 10, the lateral acceleration sensor 11, and the like. Based on this, a target steering torque for lane keeping steering assist control is calculated. The calculated target steering torque is transmitted from the control unit 30 to the EPS control unit 20, and the EPS control unit 20 achieves the control target by drivingly controlling the motor 6 based on the target steering torque.

  As shown in the block diagram of FIG. 2, the steering control system using the target steering torque as an operation output includes a lane recognition unit 41, a target steering angle setting unit 42, a torque support control unit 43, and feedback (F / B). A support control unit 44, a control distribution setting unit 45, and a steering system 46 by EPS2 are provided. The steering control system shown in FIG. 2 is based on torque control that compensates for the road reaction force that is expected to occur at the target steering angle in consideration of interference with the driver's steering. In situations where responsiveness is required, steering angle feedback control by PID control of the actual steering angle is used together.

  This is because when the follow-up performance with respect to the target steering angle is taken into consideration, torque control may not be able to obtain sufficient gain / phase characteristics depending on the characteristics of the steering system. In other words, in torque control, the gain of the lane following feedback system is set in consideration of the phase margin, but when a disturbance is input due to changes in crosswind or road surface cant (crossing gradient), a straight road such as a sharp curve is changed to a curved road. As shown in FIG. 3, when the control system frequency response is compared, the torque control has a remarkable gain and phase delay compared to the steering angle feedback control. Therefore, in the present embodiment, the magnitude of the request for responsiveness with respect to the target steering angle is determined, and when it is determined that the request for responsiveness is large, the steering angle feedback control is introduced, thereby Compensates for gain and phase characteristics.

  The lane recognition unit 41 is formed as a function of the stereo camera 7 or the control unit 30. The target steering angle setting unit 42, the torque support control unit 43, the feedback support control unit 44, and the control distribution setting unit 45 are included in the control unit 30. It is formed as a function.

  Specifically, the lane recognition unit 41 detects, for example, a white line on a road on which the host vehicle travels from an image captured by the stereo camera 7 by edge detection or the like, and recognizes a travel lane of the host vehicle formed by the white line. To do. Specifically, in the vehicle coordinate system of FIG. 4 where the center of gravity of the host vehicle 1 is the origin, the vehicle width direction is the X axis, and the front side of the vehicle body is the Z axis, the front gazing point L (for example, about 1 second later). Then, the center position Xc of the driving lane at the gazing point L is obtained, and the lane (the lane indicated by the broken line in FIG. 4) having the center position Xc as a locus is set as the target course (target lane) that the host vehicle 1 should follow. Then, the curvature K of the target course based on the curve radius of the traveling lane is obtained.

  Then, based on the state quantity of the vehicle, the traveling locus of the own vehicle (vehicle locus indicated by a two-dot chain line in FIG. 4) is estimated, and the vehicle yaw angle θyaw formed by the own vehicle with respect to the target course, The estimated lateral position of the vehicle (own vehicle position with respect to the lane center position) Xe is obtained. The estimated lateral position Xe of the vehicle at the gazing point L can be estimated using vehicle specifications, vehicle-specific stability factors, or the like, or can be estimated using vehicle speed or yaw rate.

  In the present embodiment, the curve radius (curvature), the lateral position of the vehicle, and the yaw angle are expressed by positive values on the left side of the central axis in the front-rear direction of the vehicle 1. The right side is represented by a negative value.

The lateral position Xe of the vehicle can be obtained based on the following equation (1) when using vehicle specifications, vehicle-specific stability factors, and the like. Further, when the vehicle speed or the yaw rate is used, the lateral position Xe can be obtained based on the following equation (2).
Xe = α · Lz ² / (2 (1 + A · V ² ) · Lw · Nsgr) (1)
Xe = γ · Lz ² / 2V (2)
Where α: Steering angle
Lz: Gaze distance (distance to the gaze point)
A: Stability factor
V: Vehicle speed
Lw: Wheel base Nsgr: Steering gear ratio
γ: Yaw rate

The target steering angle setting unit 42 uses the target steering angle αd for following the target course (target lane) as shown in the following formula (3), and the curvature K of the lane for feedforward control with respect to the turning of the curve. Based on the steering angle, the deviation (Xc−Xe) between the lane center position Xc and the estimated lateral position Xe to the target value in the closed loop, and the steering to converge the vehicle yaw angle θyaw to the target value in the closed loop Calculate from the corners.
αd = Gff · K + Gl · (Xc−Xe) + Gy · θyaw (3)
Gff: Feed forward gain
Gl: Feedback gain for the lateral position of the vehicle
Gy: Feedback gain for the yaw angle of the vehicle

  The steering torque for realizing the target steering angle αd is calculated by the torque support control unit 43 and the feedback support control unit 44, respectively. Then, the steering torque calculated by the feedback support control unit 44 is added at a ratio corresponding to the distribution ratio set by the control distribution setting unit 45 and output to the steering system. The distribution ratio of the steering torque from the feedback support control unit 44 is set according to the disturbance and the state of the traveling road, and the steering angle feedback control is introduced when the demand for responsiveness with respect to the target steering angle αd is large. Compensates the gain / phase characteristics of the control.

Specifically, the torque support control unit 43 calculates a steering torque that compensates for external force torque such as self-aligning torque generated by control to the target steering angle as the target steering torque Ttrqd that achieves the target steering angle. This target steering torque Ttrqd can be calculated from a self-aligning torque expressed by using a steady circle turning type of a two-wheel model as shown in the following equation (4).
Ttrqd = 2ξ · Kf · (Lw · A + Lf · M / Lw · Kr) · V ² · αd / (Nsgr · Lw · (1 + A · V ² )) (4)
Where ξ: Trail
Kf: Front wheel cornering power
Kr: Rear wheel cornering power
Lf: Center-of-gravity point-front wheel distance
Lr: Center-of-gravity point-rear wheel distance
M: Vehicle mass

The feedback support control unit 44 calculates a steering torque (target steering torque) for achieving the target steering angle by feedback control of the actual steering angle with respect to the target steering angle. The target steering torque Tstrd for this feedback control is calculated by PID control of the actual steering angle with respect to the target steering angle, as shown in the following equation (5).
Tstrd = Gp · (αd−α) + Gd · d (αd−α) / dt + Gi · ∫ (αd−α) dt (5)
Where α is the actual steering angle
Gp: Proportional gain
Gd: Differential gain
Gi: integral gain

The control distribution setting unit 45 determines the level of the request for responsiveness with respect to the target steering angle, and according to the determination result, the distribution ratio between the control by the torque support control unit 43 and the control by the feedback support control unit 44 (steering angle control). Distribution ratio) Nctrl is set. Then, a target steering torque (final target steering torque) Tcmd finally instructed to the steering system actuator (motor 6 of EPS 2) is calculated by the following equation (6) using the steering angle control distribution ratio Nctrl.
Tcmd = Ttrqd + Nctrl · Tstrd (6)

  In the present embodiment, the steering angle control distribution ratio Nctrl assumes the following situations (a) and (b) as the situation for determining the magnitude of the request for responsiveness to the target steering angle. , Nctrl = 1 and Nctrl = 0. When Nctrl = 0, the basic control state includes only torque control. When Nctrl = 1, feedback control is added to the torque control to improve the response to the target steering angle.

(A) Disturbances such as road surface gradient changes and crosswinds Disturbance values input to the control system are estimated, and as shown in FIG. 5, when the rate of change of the disturbance values exceeds a threshold, or the sign of the disturbance value When there is a switch, it is determined that there is a large demand for responsiveness to the target steering angle, and the steering angle control distribution ratio Nctrl is changed from 0 to 1 for a certain time Tstr. As a result, the entire steering control system is switched from a control system having only torque control to a control system in which feedback control is added to torque control.

  The disturbance value is estimated as a lateral force acting on the vehicle based on a sensor measurement value, a vehicle model, a steering model, or the like. For example, by inputting the yaw rate by the yaw rate sensor 10 and the steering angle measured by the steering angle sensor 8 to the vehicle model and comparing the yaw rate calculated by the model, an external force acting on the host vehicle 1 due to a road surface cant or the like is obtained. Estimated as lateral force disturbance value. The disturbance value may be calculated by directly measuring the gradient of the road surface cant, for example, using an inclination sensor.

(B) Transition from straight road to curved road When the rate of change in curvature of the driving lane detected by the stereo camera 7 exceeds the threshold value, it is determined that the demand for responsiveness to the target steering angle is large, as shown in FIG. In addition, the steering angle control distribution ratio Nctrl is changed from 0 to 1 for a certain time Tstr. Even in this case, the entire steering control system is switched from a control system with only torque control to a control system in which feedback control is added to torque control.

  Specifically, the above-described processing in the steering control system is executed by software processing executed by the control unit 30. Hereinafter, the steering assist control of the steering control system will be described with reference to the flowchart of FIG.

  The flowchart of FIG. 7 is a steering assist control process that is repeatedly executed in the control unit 30 at a predetermined time period. In this steering assist control process, first, in first step S1, lane information such as curvature and width of the traveling lane in which the host vehicle is traveling is acquired, and in step S2, the lateral position and yaw of the host vehicle with respect to the target lane are obtained. Get vehicle state quantities such as corners.

  Next, the process proceeds to step S3, where the target steering torque Ttrqd in torque control is calculated based on the above-described equation (4), and in step S4, the target steering torque Tstrd in steering angle feedback control is calculated according to the above-described equation (5). Calculate based on In step S5, the disturbance value is estimated. In step S6, it is determined whether or not the sign of the disturbance value has changed from the + side to the-side or from the-side to the + side. Here, the change of the sign of the disturbance value is determined, but it may be determined whether or not the rate of change of the disturbance value exceeds a threshold value.

  As a result, when the disturbance value changes in sign, the process proceeds from step S6 to step S7, and it is checked whether or not the curvature of the traveling lane has changed. If there is no change in curvature, the process proceeds from step S7 to step S8, the steering angle control distribution ratio Nctrl is set to Nctrl = 0, and the process proceeds to step S10. On the other hand, in step 6, there is a sign change in the disturbance value. Alternatively, if there is a change in curvature in step S7, the steering angle control distribution ratio Nctrl is set to Nctrl = 1 for a fixed time Tstr in step S9, and the process proceeds to step S10.

  In step S10, the final target steering torque Tcmd is calculated by the aforementioned equation (6) using the steering angle control distribution ratio Nctrl. When the sign of the disturbance value does not change and the curvature of the driving lane does not change, Nctrl = 0 causes the final target steering torque Tcmd to be the target steering torque Ttrqd for torque control, which interferes with the driver's steering. Without steering assistance. On the other hand, when there is a change in sign of the disturbance value or a change in curvature, Nctrl = 1 causes the final target steering torque Tcmd to add the target steering torque Tstrd for steering angle feedback control to the target steering torque Ttrqd for torque control. The steering assist is performed so that the steering torque converges to the target steering angle with good followability.

  Thus, in the present embodiment, the steering control system includes a torque support control unit 43 that compensates for external force torque generated at the target steering angle, and a feedback support control unit 44 that performs feedback control of the actual steering angle with respect to the target steering angle. The two control systems are configured to function in accordance with the level of demand for responsiveness to the target steering angle. In other words, in normal situations where the demand for responsiveness to the target steering angle is relatively small, interference with the driver's steering can be prevented by torque control, and when a disturbance is input due to changes in the crosswind or road surface cant, a sharp curve, etc. In situations where responsiveness is required, such as when transitioning from a straight road to a curved road, the feedback control of the steering angle is introduced to compensate for the gain and phase characteristics of torque control and improve responsiveness. And good support performance can be obtained.

1 Vehicle 2 Electric power steering system (EPS)
20 EPS control unit 30 Control unit 41 Lane recognition unit 42 Target steering angle setting unit 43 Torque support control unit 44 Feedback support control unit 45 Control distribution setting unit

Claims (4)

In a steering assist device for a vehicle that applies steering torque to a steering system so that the host vehicle travels along a lane and performs steering support for a driver.
A torque support control unit that performs steering support with torque that compensates for external force torque generated at a target value of steering support;
A feedback support control unit that performs steering support by feedback control with respect to the target value;
A control distribution setting unit that determines the magnitude of a request for responsiveness to the target value, and sets a control distribution ratio of the feedback support control unit to be added to the torque support control unit according to the size of the request for responsiveness; A vehicle steering assist device.   The vehicle steering assist device according to claim 1, wherein the control distribution setting unit determines the magnitude of the request for responsiveness to the target value based on a disturbance value.   The vehicle steering assist device according to claim 1, wherein the control distribution setting unit determines whether the request for responsiveness to the target value is large or small based on a curvature of a traveling road.   2. The vehicle steering assist according to claim 1, wherein the control distribution setting unit sets a control distribution ratio of the feedback support control unit to zero when it is determined that a request for responsiveness to the target value is small. apparatus.

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