JP2019162918A - Vehicle steering assist device - Google Patents

Abstract

An object of the present invention is to perform steering assist control on the assumption that a driver holds a steering wheel, to eliminate the influence of the shape of a traveling path and disturbances, and to ensure the accuracy of a steering wheel release determination. A target output change rate calculation unit calculates a target output change rate from a target output of steering assist control in a steering assist control unit. If the target output is less than the output threshold and the target output change rate is less than the change rate threshold, the release threshold determination unit 53 sends the handle release determination threshold to the handle release determination unit 54 with a normal value, and sends the target release If the output is greater than the output threshold, or if the target output change rate is greater than the change rate threshold, the threshold value for the steering wheel release determination should be made larger than normal and corrected in a direction that makes it easier to determine that the steering wheel is released. In this way, the influence of the shape of the traveling path and disturbances is eliminated, and the accuracy of the judgment of releasing the steering wheel is ensured. [Selection] Figure 2

Description

  The present invention relates to a steering assist device for a vehicle that performs steering assist control via a steering device on the assumption that a driver's handle is held.

  A vehicle such as an automobile is provided with a steering device such as an electric power steering device capable of controlling a steering angle via an electric motor, and is controlled via a steering device based on an external environment around the vehicle recognized by a camera, a radar device, or the like. Steering support control for assisting a driver's steering operation is known.

  Such steering assist control is often executed on the assumption that the driver holds the steering wheel. When the driver releases his / her hand from the steering wheel, it is determined that the steering wheel is released and a warning is issued. It has become.

  For this reason, it is necessary to accurately determine the handle release state. For example, in Patent Document 1, when a straight path is detected, it is difficult to determine that the handle is released as compared to a case where a straight path is not detected. A technique for determining a determination threshold is disclosed.

Japanese Patent No. 5800971

  However, in the conventional handle release determination as disclosed in Patent Document 1, sufficient determination accuracy may not be obtained depending on the shape of the curve of the traveling road, and it may be affected by disturbances such as crosswinds and road crossing gradients. On the other hand, it is difficult to ensure the determination accuracy.

  The present invention has been made in view of the above circumstances, and when performing steering assist control on the assumption that the driver's handle is held, the accuracy of the handle release determination is ensured by eliminating the influence of the shape of the travel path and disturbance. An object of the present invention is to provide a steering assist device for a vehicle capable of performing the above.

  A vehicle steering assistance device according to an aspect of the present invention is a vehicle steering assistance device that performs steering assistance control via a steering device on the premise that a driver's steering wheel is held, and in the steering assistance control via the steering device. Based on the target output change rate calculation unit for calculating the target output change rate, and the target output or the change rate of the target output, a threshold value for determining a handle release state in which the driver does not hold the handle. And a hand release determination threshold value correction unit for correcting in a direction in which it is easily determined that the handle is released.

  According to the present invention, when steering assist control is executed on the premise that the driver holds the steering wheel, the influence of the shape of the traveling path and disturbance can be eliminated to ensure the accuracy of the handle release determination.

Configuration diagram of vehicle steering system Block diagram showing functions of steering control system Flowchart of handle release determination processing

  Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes an electric power steering (EPS) device as a steering device capable of controlling a steering angle via an actuator independently of a steering operation by a driver. In the EPS apparatus 1, a steering shaft 2 is rotatably supported via a steering column 3 on a body frame of a vehicle such as an automobile (not shown).

  One end of the steering shaft 2 extends toward the driver's seat, and the other end extends toward the engine room. A steering wheel (handle) 4 is fixed to the driver seat side end of the steering shaft 2, and a steering angle sensor 21 is disposed on the outer peripheral side of the steering shaft 2 to which the handle 4 is coupled.

  The rudder angle sensor 21 includes, for example, two sets of magnetoresistive elements that detect rotation of a magnet built in a detection gear. The rudder angle sensor 21 sets in advance a rotation position that serves as a reference for the handle 4 (for example, a rotation position of the upper portion of the handle 4 in a straight traveling state of the vehicle), and based on a magnetic change caused by rotation of the detection gear, A rotation angle (steering angle) and a rotation direction (steering direction) from a preset fixed reference position are detected.

  Further, a torsion bar 2 a is interposed in the middle of the steering shaft 2, and a pinion shaft 5 is connected to an end extending to the engine room side. A torque sensor 22 is disposed on the outer peripheral side of the torsion bar 2a. The torque sensor 22 detects the steering torque by the driver's operation by detecting the displacement between the handle 4 side and the pinion shaft 5 side that occurs around the steering shaft 2 due to the twist of the torsion bar 2a.

  On the other hand, a steering gear box 6 extending in the vehicle width direction is disposed in the engine room, and a rack shaft 7 is inserted into and supported by the steering gear box 6 so as to be reciprocally movable. A rack (not shown) formed on the rack shaft 7 is engaged with a pinion formed on the pinion shaft 5 to form a rack and pinion type steering mechanism.

  The left and right ends of the rack shaft 7 protrude from the end of the steering gear box 6, and a front knuckle 9 is connected to the end via a tie rod 8. The front knuckle 9 rotatably supports left and right wheels 10L and 10R as steering wheels and is supported by a vehicle body frame so as to be steerable. When the steering shaft 4 and the pinion shaft 5 are rotated by operating the handle 4, the rack shaft 7 moves in the left-right direction by the rotation of the pinion shaft 5, and the front knuckle 9 moves the kingpin shaft (not shown) by the movement. By turning to the center, the left and right wheels 10L, 10R are steered in the left-right direction.

  In addition, an electric power steering motor (EPS motor) 12 as an actuator that enables assisting and automatic steering for a driver's steering operation is connected to the pinion shaft 5 via an assist transmission mechanism 11 including a reduction gear mechanism such as a worm gear. It is installed. The EPS motor 12 is an electric motor composed of, for example, a DC brushless motor having a stator fixed to a case and a rotor that rotates inside the stator. The rotation of the rotor of the electric motor is supported by a rack shaft via the assist transmission mechanism 11. 7 is converted into an axial movement.

  The EPS motor 12 is driven and controlled by the steering control device 50. The steering control device 50 is a control unit configured mainly with a microcomputer, and drives and controls the EPS motor 12 via the motor drive unit 20. The steering control device 50 includes a steering angle sensor 21, a torque sensor 22, other sensors such as a vehicle speed sensor 24 for detecting the vehicle speed, a yaw rate sensor 25 for detecting a rotational speed around the vertical axis of the vehicle, that is, a yaw rate, and a switch not shown A signal from a class is input.

  The steering control device 50 is connected to a communication bus 200 that forms an in-vehicle network. The communication bus 200 includes an external environment recognition device 150 that recognizes the external environment of the vehicle and acquires travel environment information, and other controls such as an engine control device, a transmission control device, and a brake control device (not shown). Devices are connected, and each control device can exchange control information with each other via the communication bus 200.

  The external environment recognition device 150 includes detection information of objects around the vehicle by various devices such as a front recognition camera and millimeter wave radar, a side recognition side camera and a side radar, road-to-vehicle communication, vehicle-to-vehicle communication, etc. Traffic information acquired by infrastructure communication, positioning information of own vehicle position based on signals from GPS satellites, road shape data such as road curvature, lane width, shoulder width, road azimuth, lane line type, The external environment around the vehicle is recognized based on high-definition map information including travel control data such as the number of lanes.

  In the present embodiment, the external environment recognition device 150 mainly recognizes the front environment of the host vehicle using an in-vehicle camera and an image recognition device, and the same object is imaged from different viewpoints as a front recognition camera. A stereo camera composed of two cameras is used. The two cameras constituting this stereo camera are shutter-synchronized cameras having an image sensor such as a CCD or a CMOS, and are, for example, arranged with a predetermined baseline length in the vicinity of a room mirror inside the front window in the upper part of the vehicle interior. Yes.

  Processing of image data from the stereo camera is performed as follows, for example. First, a distance image having distance information is generated from a corresponding positional deviation amount for a pair of stereo images in the traveling direction of the host vehicle captured by a stereo camera, and a white line is generated using the distance information of the distance image. And the like, and recognition processing of three-dimensional objects such as preceding vehicles and oncoming vehicles.

  In recognition of lane markings such as white lines, the lane markings are brighter than the road surface, and the change in the brightness in the width direction of the road is evaluated. The position is specified on the image plane. The position (x, y, z) of the lane marking in the real space is based on the position (i, j) on the image plane and the parallax calculated with respect to this position, that is, based on the distance information. It is calculated from a known coordinate conversion formula.

  The recognition result of the external environment by the external environment recognition device 150 is transmitted to the steering control device 50 and other control devices. The steering control device 50 executes steering support control that supports automatic driving of the host vehicle and steering operation of the driver. Examples of the steering assist control include lane keeping control for keeping the host vehicle at the center position of the lane, leading vehicle follow-up control for traveling following the preceding vehicle, lane departure preventing control for preventing the own vehicle from departing from the lane, and the like. is there.

  The target route may be set not by the steering control device 50 but by another control device such as the external environment recognition device 150.

  Such steering assist control is executed on the assumption that the driver is gripping the handle 4 and applying a predetermined steering holding force (handle holding state). When the driver releases his / her hand from the handle 4 during steering assist control and the steering force is reduced, it is determined that the steering wheel is released and the steering assist control is released.

  The magnitude of the holding force is determined by comparing the torque value (torque sensor value) detected by the torque sensor 22 with a threshold value. When the torque sensor value of the torque sensor 22 is equal to or greater than the threshold value, it is determined as “handle holding state”, and when the torque sensor value is less than the threshold value for a predetermined time or longer, it is determined as “handle release state”.

  In this case, since the steering assist control is executed under various driving environments, a target output (to be described later) changes suddenly or is larger than a predetermined value due to road curvature or disturbance (crosswind, road crossing gradient, etc.). May be output. In such a case, the torsion bar 2a is twisted by an external force transmitted from the road surface side, and even if the driver does not grip the handle 4, the torque sensor value fluctuates and exceeds the threshold value. May not be determined correctly.

  Therefore, as shown in FIG. 2, the steering control device 50 correctly determines the state of releasing the steering wheel by eliminating the influence of the external force from the road surface side with respect to the steering assistance control unit 51 that executes the steering assistance control. As the functional units, a target output change rate calculation unit 52, a hand release determination threshold value correction unit 53, and a handle release determination unit 54 are provided.

  The steering assist control unit 51, based on information from the external environment recognition device 150 and detection information from each sensor (steering angle sensor 21, vehicle speed sensor 24, yaw rate sensor 25), lane keeping control, preceding vehicle following control, Steering support control such as lane departure prevention control is executed. This steering assist control is executed when the driver grips the handle 4 and the torque sensor value of the torque sensor 22 is determined to be in the “handle state” that is equal to or greater than the threshold, and the “handle release state” in which the torque sensor value is less than the threshold. Is determined to be released.

  In the steering assist control by the steering assist control unit 51, the lane keeping control and the preceding vehicle follow-up control are basically the same control, and the target route from the trajectory of the target point to be followed according to the recognition result of the external environment. Is executed as control to follow this target route. For example, in lane keeping control, the target point to be followed is set at the center position in the road width direction of the left and right white lines as lane markings, and in the preceding vehicle follow-up control, it is set at the center position in the vehicle width direction of the preceding vehicle. Then, the trajectory of such a target point is calculated as a target route.

  The steering assist control unit 51 calculates a target steering angle for following the target route, and outputs an instruction torque corresponding to the target steering angle to the EPS device 1. The EPS device 1 controls the drive current of the EPS motor 12 via the motor drive unit 20 so that a steering torque corresponding to the command torque can be obtained. As a result, the actual steering angle of the host vehicle is controlled to converge to the target steering angle, and steering assist control for traveling following the target route is realized.

  In the lane departure prevention control, the steering assist control unit 51 estimates the time until the host vehicle crosses the lane in the departure direction with respect to the lane in which the traveling direction of the host vehicle faces the departure direction. If the set time is less than or equal to the set value, lane departure prevention control is executed. Specifically, the steering assist control unit 51 calculates a target yaw rate as a target turning amount for preventing deviation from the lane, and outputs a target steering torque corresponding to the target yaw rate as an instruction torque for the EPS device 1. To do.

  The EPS device 1 controls the drive current of the EPS motor 12 so that the steering torque becomes the target steering torque, and controls the yaw rate of the host vehicle to become the target yaw rate. As a result, turning behavior corresponding to the target yaw rate occurs in the host vehicle, and lane departure prevention control for preventing departure from the lane is realized.

  The target output change rate calculation unit 52 reads the target output TGT of the steering support control by the steering support control unit 51, calculates the change rate (target output change rate) ΔTGT per predetermined time of the target output TGT, and sets the release determination threshold value. The data is sent to the correction unit 53. As the target output TGT for the steering assist control, at least one of the above-described target steering angle, target yaw rate, and instruction torque to the EPS device 1 is used.

  The hand release determination threshold value correcting unit 53 determines the handle release state during the steering support control based on the target output TGT of the steering support control unit 51 or the target output change rate ΔTGT calculated by the target output change rate calculation unit 52. The threshold value Dth is corrected. Specifically, the threshold value Dth for determining whether to release the steering wheel during normal driving is set in advance as a fixed value, and a comparison between the target output TGT and the output threshold value TGTth, and a comparison between the target output change rate ΔTGT and the change rate threshold value ΔTGTth, The normal threshold value Dth is corrected.

  In this case, for example, when the target output TGT is set as the command torque to the EPS device 1, the output threshold value TGTth is set as a torque having a predetermined magnification with respect to the reference value with reference to the command torque when traveling on a normal straight road. The The magnification with respect to the reference instruction torque is a factor of the magnitude of the external force from the road surface side that causes torsion in the torsion bar 2a where the torque sensor 22 is disposed, for example, the magnitude of the curvature of the traveling road, the crosswind and the road It is set according to the vehicle weight, the tire size, and the characteristics of the steering mechanism in consideration of the required steering wheel holding force with respect to the magnitude of disturbance such as a cross gradient.

  The change rate threshold value ΔTGTth is a predetermined value relative to a reference value, for example, when the target output angle TGT is set as a target steering angle for following the target route, with the change speed of the steering angle when traveling on a normal straight road as a reference. Set as the rate of change of magnification. The magnification with respect to the reference change speed is a change speed of external force from the road surface side that causes torsion of the torsion bar 2a in which the torque sensor 22 is disposed, for example, a change in curvature of a traveling road, a cross wind, a cross slope of a road, etc. It is set according to the vehicle weight, the tire size, and the characteristics of the steering mechanism in consideration of the steering wheel holding force required for the changing speed of the disturbance.

  When the target output TGT is less than the output threshold value TGTth and the target output change rate ΔTGT is less than the change rate threshold value ΔTGTth, the normal value threshold value Dth is sent to the handle release determination unit 54. On the other hand, when the target output TGT is greater than the output threshold value TGTth, or when the target output change rate ΔTGT is greater than the change rate threshold value ΔTGTth, the threshold value Dth is set to be larger than the normal value, and it is easily determined that the steering wheel is released. Correct in the direction.

  The correction to the threshold value Dth may be a correction that is larger than a normal value by a preset constant value, or may be a correction according to the curvature of the traveling path, the crossing gradient, and the estimated crosswind intensity. For example, the greater the curvature of the travel path obtained from the external environment recognition device 150 or the map information, the larger the steering wheel release determination threshold Dth than the normal value, and the greater the crossing gradient, the normal threshold Dth. Larger than. Further, the strength of the cross wind is estimated from, for example, the magnitude of the local change in the target output, and the threshold Dth is set larger than the normal value as the cross wind increases.

  The handle release determination unit 54 compares the torque sensor value Tsen from the torque sensor 22 with the threshold value Tth from the release determination threshold value correction unit 53, and determines whether the gripping state of the handle 4 by the driver is “handle holding state” or “handle release state”. Is determined. When the torque sensor value Tsen is equal to or greater than the threshold value Tth, it is determined as “handle holding state”, and when the torque sensor value Tsen is less than the threshold value Tth continues for a certain period of time, it is determined as “handle release state”.

  The determination result of the handle release determination unit 54 is sent to the steering assist control unit 51. When the steering assist control unit 51 determines that the steering wheel is released, the steering assist control unit 51 cancels the steering assist control and warns the driver with a display, an alarm sound, or the like so as to reliably hold the steering wheel 4.

  Next, the handle release determination process in the above steering control device 50 will be described with reference to the flowchart of FIG.

  In the first step S1, the steering control device 50 acquires a target output TGT in the steering assist control. Next, the process proceeds to step S2, and the change rate per control cycle (processing cycle) of the target output TGT is calculated as the target output change rate ΔTGT.

  Thereafter, the process proceeds to step S3, where the target output TGT is compared with the output threshold value TGTth to check whether the target output TGT has become larger than the threshold value. When the target output TGT is equal to or greater than the output threshold value TGTth, the process proceeds from step S3 to step S5, the handle release determination threshold value Dth is set larger than the normal value, and the process proceeds to step S6.

  On the other hand, when the target output TGT is less than the output threshold value TGTth in step S3, the process proceeds from step S3 to step S4, and the target output change rate ΔTGT is compared with the change rate threshold value ΔTGTth. As a result, when the target output change rate ΔTGT becomes equal to or greater than the change rate threshold value ΔTGTth, the process proceeds from step S4 to step S6 through the above-described step S5. If the target output change rate ΔTGT is less than the change rate threshold value ΔTGTth, the handle The threshold Dth for hand release determination is set to a normal value, and the process proceeds to step S6.

  In step S6, the torque (torque sensor value) Tsen detected by the torque sensor 22 is compared with a threshold value Tth, and a handle release determination is performed. When the torque sensor value Tsen is equal to or greater than the threshold value Tth, it is determined that the steering wheel is held and the execution of the steering assist control is permitted, and when the torque sensor value Tsen is less than the threshold value Tth for a certain period of time, It is determined that the steering wheel is released and the driver is warned to hold the steering wheel securely.

  As described above, in the present embodiment, when it is determined that the disturbance such as the curvature of the traveling road, the crosswind and the crossing slope of the road is large, the threshold value Tth for the handle release determination is made larger than the normal value. Even if the torsion bar 2a is twisted due to an external force from the road surface side, it is possible to prevent erroneous determination and accurately determine the state of releasing the handle.

DESCRIPTION OF SYMBOLS 1 Electric power steering (EPS) apparatus 2a Torsion bar 4 Handle 12 EPS motor 15 Steering assistance control apparatus 20 Motor drive part 21 Steering angle sensor 22 Torque sensor 24 Vehicle speed sensor 25 Yaw rate sensor 50 Steering control apparatus 51 Steering assistance control part 52 Target output Change rate calculation unit 53 Hand release determination threshold correction unit 54 Handle release determination unit 150 External environment recognition device

Claims (4)

A vehicle steering assist device that performs steering assist control via a steering device on the premise of holding the steering wheel of a driver,
A target output change rate calculation unit for calculating a change rate of a target output in the steering assist control via the steering device;
Based on the target output or the rate of change of the target output, a threshold for determining a handle release state in which the driver does not hold the handle is corrected to a direction in which it is easy to determine a handle release state. A vehicle steering assist device comprising: a correction unit.   The let-off determination threshold value correction unit is configured such that the target output is larger than a threshold value set in consideration of the magnitude of external force transmitted from the road surface side to the steering device, or the change rate of the target output is from the road surface side. The threshold for determining the state of releasing the steering wheel is set to be larger than a value during normal driving when the threshold is larger than a threshold set in consideration of a change speed of an external force transmitted to the steering device. The vehicle steering assist device according to claim 1.   The vehicle steering assist device according to claim 1, wherein the target output is a target steering angle for traveling following a target route along which the host vehicle travels.   The vehicle steering assist device according to claim 1, wherein the target output is an instruction torque with respect to a steering torque of the steering device.

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