JP4175293B2 - Vehicle steering assist device - Google Patents

Description

  The present invention relates to a vehicle steering assist device that applies an appropriate steering assist torque to assist travel along a travel lane.

  There has been proposed a vehicle steering assist device that supports traveling of a vehicle along a travel lane (see, for example, Patent Document 1). In this support apparatus, first, an image of a lane in which the host vehicle travels is acquired using a CCD camera or the like. By detecting a road marking line (white line) that divides the travel lane by image recognition processing from the acquired image, travel lane information that the host vehicle should travel is acquired. Based on the acquired travel lane information, a steering torque necessary for steering is obtained and an appropriate steering assist torque is applied to assist the driver in steering.

In the technique of Patent Document 1, the curvature of the traveling lane, the lane offset that is the lateral deviation amount between the vehicle center line and the traveling path center line, and the differential value of the deflection angle that is the angle formed by the traveling path center line and the vehicle center line are used. It is described that an appropriate assist torque can be calculated by calculating the steering assist torque.
JP 2001-10518 A

  In a curve section such as an expressway, the road surface is arranged to be inclined toward the center of the curve. Under the influence of the slope of the curved road surface (road surface cant), a force (lateral acceleration) directed toward the center of the curve acts on the vehicle. However, since the technique of Patent Document 1 does not consider the influence of such disturbances, excessive lateral acceleration may occur, and the stability of the vehicle during curve traveling may be reduced.

  Accordingly, an object of the present invention is to provide a vehicle steering assist device that suppresses the influence of lateral acceleration caused by a road surface cant and improves the lateral steering stability of the vehicle.

  In order to solve the above-described problem, a vehicle steering assist device according to the present invention includes a unit that acquires an image of a course direction of a host vehicle, a unit that recognizes a travel lane from the acquired image, and a target position in the travel lane. A means for calculating a lane offset that is a deviation amount of the vehicle, a means for obtaining an integral term of the lane offset, a means for computing an assist torque to be applied to the steering system using the obtained lane offset and the integral term, and In a vehicle steering assist device including means for applying assist torque to a steering system, a curve state of a traveling lane has changed from a curve state having a curvature larger than the first curvature to a curve state having a curvature smaller than the first curvature. And a means for resetting the integral term of the lane offset when the determination is made.

  Alternatively, when it is determined that the curve state of the traveling lane has changed from a curve state having a curvature larger than the second curvature to a curve state having a curvature smaller than the first curvature, the integral term of this lane offset is set. It may be reset. At this time, the second curvature is set larger than the first curvature.

  When calculating the assist torque, by using the integrated value of the lane offset in addition to the current lane offset amount, the influence of the lateral acceleration due to the road surface cant is suppressed. On the other hand, the road surface cant disappears at the exit of the curve, but the value of the integral term of the lane offset remains, which may cause excessive target lateral acceleration and steering torque based on this, generating a low-frequency vibration response There is. Therefore, in the present invention, by reducing the integral term in the vicinity of the curve exit where the curve state shifts to a curve state having a curvature smaller than the first curvature, a decrease in lane following performance due to the remaining integral term is suppressed. To do. The transition to the curve state having a curvature smaller than the first curvature is not only the transition from the curve state to the linear state, but also the switching from the turning state in the right direction to the turning state in the left direction. The reverse (and vice versa) is also included.

  The reset means transitions to a curve state having a curvature smaller than the first curvature when the condition that the curve state of the driving lane becomes a curve state having a curvature smaller than the first curvature continues for a predetermined time or longer. It is good to judge.

  The determination of the curve state is performed based on the image recognition result, and an error may be included in the shape parameter (curve curvature) of the traveling lane itself. For this reason, even when a transition is made to a curve state having a curvature smaller than the first curvature at a certain time, this may be due to erroneous detection of the shape parameter. In this case, if a reset operation or the like is performed, there is a possibility that the lane following capability is rather deteriorated. Therefore, the reset operation is performed on the condition that continuation for a certain period of time is a condition. Similarly, even when the curve curvature shifts to a curve state having a curvature larger than the first curvature at a certain time, it may be caused by a false detection of the shape parameter. The stability of the vehicle behavior is improved by resetting the integral term only when the curve state having the curvature of 2 is changed to the curve state having the curvature lower than the first curvature.

  Whether the vehicle is in a curved state having a predetermined curvature can be determined not only by the road curvature but also by the road radius, the amount of lateral deviation of the road center at a position away from the target, and the like. .

  According to the present invention, it is possible to suppress the influence of the lateral acceleration caused by the road surface cant during the curve traveling, and it is also possible to suppress the occurrence of unnecessary lateral acceleration due to the integral term of the lane offset at the curve exit transition. The vibrational response of the frequency can be suppressed and the vehicle behavior can be stably controlled.

  In addition, by determining the curve state as described above, when the lane offset value changes in vibration, the integrated value of the lane offset is not frequently reset, resulting in stable vehicle behavior. Can be controlled.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. In order to facilitate the understanding of the description, the same reference numerals are given to the same components in the drawings as much as possible, and duplicate descriptions are omitted.

  An embodiment of a vehicle steering assist device according to the present invention will be described below. FIG. 1 shows a configuration diagram of a vehicle 1 provided with the vehicle steering assist device of the present embodiment. The vehicle 1 includes an electronic control unit (ECU) 2, and vehicle behavior control (lane keeping control) is executed by the ECU 2. As shown in FIG. 1, the vehicle 1 includes a steering wheel 3. The steering wheel 3 is disposed in the vehicle interior of the vehicle 1 and steers steered wheels (here, left and right front wheels FR, FL) when operated by a driver. The steering wheel 3 is fixed to one end of the steering shaft 4. The steering shaft 4 rotates as the steering wheel 3 rotates.

  A rack bar 6 is connected to the other end of the steering shaft 4 via a steering gear box 5. The steering gear box 5 has a function of converting the rotational movement of the steering shaft 4 into the linear movement of the rack bar 6 in the axial direction. Both ends of the rack bar 6 are connected to the hub carriers of the wheels FL and FR via the knuckle arm 7. Because of this configuration, the wheels FL and FR are steered via the steering shaft 4 and the steering gear box 5 (rack bar 6) when the steering wheel 3 is rotated.

  Further, a CCD camera 8 for imaging the front is built in the rearview mirror (see FIG. 2). The CCD camera 8 photographs the surrounding situation in a predetermined area ahead through the front window 30 of the vehicle 1. Specifically, a moving image of the situation around the traveling lane 51 where the vehicle 1 on the road 50 is traveling is taken. An image processing unit 9 is connected to the CCD camera 8. The image data of the surrounding situation photographed by the CCD camera 8 is supplied to the image processing unit 9. The image processing unit 9 performs image processing on image data from the CCD camera 8 and travel lanes (travel route = lane) based on road marking lines (hereinafter referred to as white lines) drawn on the road on which the vehicle 1 travels. ) Is detected. In the captured image or video, the brightness difference between the road surface and the white line drawn on it is large, so the white line that divides the driving lane is relatively easy to detect by edge detection etc. and detects the lane ahead of the vehicle Convenient for

  The image processing unit 9 is connected to the ECU 2 described above. Based on the detected lane, the image processing unit 9 calculates the curve curvature (χ = 1 / R) of the forward travel route, the offset D of the vehicle 1 with respect to the lane (the center in the longitudinal direction of the vehicle), as shown in FIG. This corresponds to the amount of lateral deviation between the axis 1a and the tangent line 51a at the vehicle center of gravity position of the center line 51c of the travel lane 51.) and the yaw angle θ (vehicle center of gravity of the center axis 1a in the vehicle longitudinal direction and the center line 51c of the travel lane 51) This corresponds to the angle formed by the tangent line 51a at the position.) And the result is sent to the ECU 2. Note that the curve curvature, the offset D, and the yaw angle θ may all be positive and negative, and the sign indicates the direction and direction. As a method for detecting various information amounts (curve curvature χ, vehicle offset D / yaw angle θ) of the forward travel route based on the image, a known method can be used.

  A steering angle sensor 10 and a vehicle speed sensor 11 are also connected to the ECU 2. The steering angle sensor 10 outputs a signal corresponding to the steering angle of the steering wheel 3. The vehicle speed sensor 11 is a wheel speed sensor attached to each wheel, and generates a pulse signal at a cycle corresponding to the speed of the vehicle 1. The vehicle speed sensor 11 functions as vehicle speed detection means. It is also possible to obtain a vehicle speed by attaching a sensor for detecting the longitudinal acceleration of the vehicle body as the vehicle speed detection means and integrating the output over time. The output signal of the steering angle sensor 10 and the output signal of the vehicle speed sensor 11 are respectively supplied to the ECU 2. The ECU 2 detects the steering angle based on the output signal of the steering angle sensor 10 and detects the vehicle speed based on the output signal of the vehicle speed sensor 11.

  In addition, a yaw rate sensor 12 and a navigation system 13 are also connected to the ECU 2. The yaw rate sensor 12 is disposed near the center of gravity of the vehicle 1, detects the yaw rate around the center of gravity vertical axis, and sends the detection result to the ECU 2. The navigation system 13 is a device for detecting the position of the vehicle 1 using GPS or the like. The navigation system 13 also has a function of detecting a situation such as a curve curvature (χ) and a gradient in front of the vehicle 1. The ECU 2 uses the navigation system 13 to grasp the position of the vehicle 1 and the road situation expected to travel.

  Further, a motor driver 14 is also connected to the ECU 2. The motor driver 14 is connected to a motor (actuator) 15 disposed in the steering gear box 5 described above. Although not shown, a ball screw groove is formed on a part of the outer peripheral surface of the rack bar 6, and a ball nut having a ball screw groove corresponding to the ball screw groove on the inner peripheral surface of the rotor of the motor 15. Is fixed. A plurality of bearing balls are accommodated between the pair of ball screw grooves, and when the motor 15 is driven, the rotor rotates to assist the axial movement of the rack bar 6, that is, the steering.

  The motor driver 14 supplies a drive current to the motor 15 in accordance with a command signal from the ECU 2. The motor 15 applies a steering torque corresponding to the drive current supplied from the motor driver 14 to the rack bar 6. The ECU 2 supplies a command signal to the motor driver 14 according to the logic described later and drives the motor 15 to displace the rack bar 6 and steer the wheels FL and FR.

  Further, a warning lamp 16 and a warning buzzer 17 are connected to the ECU 2. The warning lamp 16 is arranged at a position where a passenger in the passenger compartment can visually recognize and lights up according to a command signal from the ECU 2. Further, the alarm buzzer 17 emits a sound into the vehicle interior according to a command signal from the ECU 2. The ECU 2 drives the warning lamp 16 and the alarm buzzer 17 according to the logic described later, and alerts the occupant.

  Next, steering assist control in this embodiment will be described. FIG. 4 is a block diagram showing the operation of the steering assist control, and FIG. 5 is a flowchart showing the processing of the lane offset information.

  First, the front situation of the vehicle 1 is imaged by the CCD camera 8 (lower right in FIG. 2), and the situation (curve curvature χ) of the traveling lane 51 and the vehicle 1 are detected by the image processing unit 9 based on the captured image. An offset D and a yaw angle θ are calculated. The curve curvature χ is obtained by geometrically obtaining the curvature R of the forward curve from the captured image and taking the reciprocal (1 / R). As a geometrical calculation method, it may be performed with reference to the lateral displacement amount of the white line in front of the host vehicle 1 at a predetermined distance and the inclination of the tangent line of the white line in front of the host vehicle 1 at a predetermined distance.

Further, the target offset and yaw angle with respect to the travel route are determined in advance as the target offset D ₀ and the target yaw angle θ ₀ .

In calculating the control amount to the motor driver 14, it is necessary to calculate the yaw rate ω as the control amount. The yaw rate omega is obtained as the sum of the yaw rate omega _theta compensating the yaw rate omega _d and the yaw angle theta for compensating the offset D in the yaw rate omega _r based on the curve curvature chi.

First, based on the curve curvature χ in front of the vehicle 1, a yaw rate ω _r necessary for causing the vehicle 1 to travel along this curve is obtained. The yaw rate ω _r is calculated by a feed forward controller (F / F controller) 21 based on a predetermined characteristic from the input curve curvature χ. The predetermined characteristic may, for example, may be stored in a map form in ECU 2, it may determine a format for reading the required yaw rate omega _r based on the curve curvature chi. Alternatively, leave written in functional form in a program stored in the ECU 2, may be calculated required yaw rate omega _r based on the curve curvature chi.

The yaw rate ω _θ necessary for compensating the yaw angle θ (converging to the target) is calculated by multiplying the deviation (θ ₀ −θ) between the yaw angle θ and the target yaw angle θ ₀ by a coefficient K _θ. .

On the other hand, the yaw rate ω _d required to compensate the offset D (converge to the target value) is calculated as follows. First, a deviation (D ₀ -D) between the offset D and the target offset D ₀ is obtained, and this is input to the integrating means 23 as an offset deviation D ′. In the integrating means 23, the processing shown in FIG. 5 is executed. This process is repeatedly executed at a predetermined timing (time step) during support control. This integrating means includes means for resetting the integral term.

  First, the curve radius R and the obtained offset deviation D ′ are read (step S1). Next, the absolute value of the curve radius | R | is compared with a threshold value Ra (curve state having the second curvature 1 / Ra), and the value of flagLCM indicating the determination result of the curve state at the previous time step is set. Determine (step S2). This flagLCM is set to ON when it is determined that the vehicle is traveling on a curve at the previous time step.

  When it is determined that | R | is smaller than Ra and flagLCM is off, that is, the curve state is steeper than the second curve state (the curve radius | R | is smaller than the second curve radius Ra = curve (Curvature | 1 / R | is greater than the second curve curvature 1 / Ra) If it is determined that the vehicle is traveling in a curved state and is not traveling in a curve at the previous time step, 1 is added to the value of tmrLCon. (Step S3). When it is determined that | R | is equal to or greater than Ra or flagLCM is on, that is, the curve state is looser than the second curve state (the curve radius | R | is greater than the second curve radius Ra = curve curvature | 1 / R | is less than the second curve curvature 1 / Ra) If you are driving on a road (including straight roads) or if you are already driving on a curve in the previous time step, set the value of tmrLCon to Reset to 0 (step S4).

  After completion of steps S3 and S4, the process proceeds to step S5, where the absolute value | R | of the curve radius is compared with a threshold value Rb (curve state having the first curvature 1 / Rb) and the previous time step. The flagLCM value indicating the determination result of the curve state at is determined. This Rb is set to a value larger than Ra. That is, the road in the first curve state (curve radius is Rb) is more gradual than the road in the second curve state (curve radius is Ra).

  When it is determined that | R | is larger than Rb and flagLCM is on, that is, the curve state is looser than the first curve state (the curve radius | R | is larger than the first curve radius Rb = curve curvature) If it is determined that | 1 / R | is less than the first curve curvature 1 / Rb) road (including straight roads) and the vehicle is traveling in a curve at the previous time step, the value of tmrLCoff 1 is added to (step S6). When it is determined that | R | is smaller than Rb or flagLCM is off, that is, the curve state is steeper than the first curve state (the curve radius | R | is smaller than the first curve radius Rb = curve curvature) | 1 / R | is greater than the first curve curvature 1 / Rb), or if it is determined that the vehicle is not already driving in the previous time step, the value of tmrLCoff is reset to 0 (Step S7).

  After steps S6 and S7 are completed, the process proceeds to step S8, and the value of flagLC indicating the determination result of the curve state is determined. Here, flagLC has a value equal to flagLCM. If flagLC is off, that is, it is set that the vehicle is not running on a curve, the process proceeds to step S9, and the value of tmrLCon is further compared with the threshold value T1. Only when tmrLCon is equal to or greater than T1, flagLC is switched on (step S10). In other cases, flagLC is kept off. On the other hand, if flagLC is set to on, that is, the vehicle is running on a curve, the process proceeds to step S11, and the value of tmrLCoff is compared with the threshold value T2. This threshold value T2 may be the same as or different from T1. Only when tmrLCoff is equal to or greater than T2, flagLC is switched off (step S12). In other cases, flagLC remains on.

  As a result, if it is determined that the vehicle is not traveling on a curve until the previous time step, and if it is determined that the vehicle has traveled continuously for a time step of T1 times on a road having a curve radius smaller than Ra, the vehicle is traveling on a curve. And switch flagLC to ON. On the other hand, if it is determined that the vehicle is traveling on a curve until the previous time step, and if it is determined that the vehicle has traveled T2 time steps continuously on a road having a radius greater than Rb, the vehicle has passed the curve. Determine and switch flagLC to OFF. Since the curve radius R is obtained by the image processing unit 9 based on the image acquired from the CCD camera 8, the curve radius R deviates from the actual value depending on the resolution of the acquired image, the shooting situation, and the positional relationship between the road and the vehicle. Can occur. Therefore, in this way, by performing switching determination when the comparison result with the threshold value is not satisfied once, but is continuously satisfied T1 times or T2 times, the curve and the straight path are Switching can be performed with high accuracy. In addition, by changing the judgment threshold for transition from curve to straight path and transition from straight path to curve, frequent switching between curve and straight path is suppressed, and control based on this is controlled. It can be performed stably.

  After setting flagLC, the process proceeds to step S13 to determine the value of flagLCM and the value of flagLC. If flagLCM is on and flagLC is off, that is, it is determined that the vehicle is running on the curve until the previous time step, but if it is determined that the vehicle has left the curve at the current time step, the process proceeds to step S14. Then, the integral value IntD is reset. In other cases, the process proceeds to step S15, where D '× dt (dt is a time step interval) is added to the integral value IntD, and the offset deviation D' is integrated. When the integral value IntD is obtained, the value of flagLC is stored in flagLCM (step S16), the integral value IntD is output, and the process is terminated (step S17).

'Multiplied by which the deviation D of the offset' coefficient Kd to the integral value IntD obtained by integrating means 23 yaw rate omega _d to compensate for the offset D by adding the value obtained by multiplying the coefficient Kd in is calculated.

  The target yaw rate ω is calculated by adding the three yaw rates calculated in this way. This target yaw rate ω is converted into the target lateral acceleration G using the vehicle speed Vn detected by the vehicle speed sensor 11, and the turning amount = motor required to generate the target lateral acceleration G by the torque calculator 22. A driving torque T of 15 is calculated.

  The ECU 2 instructs the motor driver 14 to drive the motor 15 according to the obtained drive torque T. As a result, the left and right front wheels FR and FL are steered, and the vehicle 1 is turned to maintain the lane. When the vehicle 1 turns, the CCD camera 8 captures the front situation again, and the above is repeated.

In the present embodiment, when calculating the yaw rate ω _d for compensating for the offset D, the integral term is used in addition to the deviation (D ₀ -D) between the offset D and the target offset D _0. It is possible to cancel the excess lateral acceleration caused by the cant, and to effectively suppress the entanglement in the inner direction of the curve. For example, in the relationship between the road and the travel locus shown in FIG. 6, this integral term corresponds to the area of the hatched portion defined by the travel lane center line 51c and the vehicle locus P, and is accumulated up to the exit of the curve. Go. Therefore, in the curve exit, according to the yaw rate omega _d which is directly calculated, it will act in the direction to push toward the vehicle 1 to the outside of the curve. This generates a vibration steering torque in the vicinity of the curve exit, which may make the behavior of the vehicle unstable.

  Therefore, in the present invention, by resetting the integral term before the curve exit, it is possible to suppress the occurrence of excessive lateral acceleration (steering torque) in the vehicle near the curve exit and to perform stable control. Yes. As a result, the behavior of the vehicle is stabilized, and the lateral steering stability is improved.

  In the above description, the transition of the curve state is determined based on the curve radius, but of course, the determination may be performed based on the curvature. In that case, the magnitude relationship with the threshold is reversed. The number of time steps (or duration) until the switching determination is performed may be set to an appropriate value in accordance with the estimation accuracy of the road shape parameter (curve radius or curvature) and the value of the shape parameter for performing the switching determination. Further, as a determination criterion for the transition of the curve state, a lateral deviation width of the center of the road at a predetermined distance may be used as a reference.

  In the above description, the means for resetting the integral term and the means for integrating are integrated. However, a means for resetting the integral term based on road parameters may be provided separately from the means for integrating.

It is a lineblock diagram of vehicles 1 provided with a steering assistance device for vehicles of this embodiment. It is a figure explaining the acquisition condition of the driving lane by the CCD camera of this embodiment. It is a figure explaining a road parameter. It is a block diagram which shows operation | movement of steering assistance control. It is a flowchart which shows the process of lane offset information. It is a figure which shows the relationship between the road under control, and a driving locus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Vehicle, 2 ... ECU, 3 ... Steering wheel, 4 ... Steering shaft, 5 ... Steering gear box, 6 ... Rack bar, 7 ... Knuckle arm, 8 ... Camera, 9 ... Image processing part, 10 ... Steering angle sensor, DESCRIPTION OF SYMBOLS 11 ... Vehicle speed sensor, 12 ... Yaw rate sensor, 13 ... Navigation system, 14 ... Motor driver, 15 ... Motor, 16 ... Warning lamp, 17 ... Alarm buzzer, 21 ... Feed forward controller, 22 ... Torque calculator, 23 ... Integration means 30 ... front window, 50 ... road, 51 ... travel lane, D ... offset, G ... target lateral acceleration, R ... curve radius, T ... drive torque, Vn ... vehicle speed, θ ... yaw angle, χ ... curve curvature, ω ... Yaw rate.

Claims (3)

Means for acquiring an image in the course direction of the host vehicle, means for recognizing a travel lane from the acquired image, means for calculating a lane offset that is a deviation from a target position in the travel lane, and integration of the lane offset In a vehicle steering assist device, comprising: means for obtaining a term; means for computing an assist torque to be applied to the steering system using the obtained lane offset and its integral term; and means for imparting the calculated assist torque to the steering system ,
And a means for resetting the integral term of the lane offset when it is determined that the curve state of the traveling lane has transitioned from a curve state having a curvature larger than the first curvature to a curve state having a curvature smaller than the first curvature. A vehicle steering assist device. Means for acquiring an image in the course direction of the host vehicle, means for recognizing a travel lane from the acquired image, means for calculating a lane offset that is a deviation from a target position in the travel lane, and integration of the lane offset In a vehicle steering assist device, comprising: means for obtaining a term; means for computing an assist torque to be applied to the steering system using the obtained lane offset and its integral term; and means for imparting the calculated assist torque to the steering system ,
When it is determined that the curve state of the traveling lane has transitioned from a curve state having a curvature larger than the second curvature to a curve state having a curvature smaller than the first curvature, the integral term of the lane offset is reset. The vehicle steering assist device further includes means, wherein the second curvature is larger than the first curvature.   The reset means transitions to a curve state having a curvature smaller than the first curvature when the condition that the curve state of the traveling lane becomes a curve state having a curvature smaller than the first curvature continues for a predetermined time or longer. The vehicle steering assist device according to claim 1, wherein the vehicle steering assist device is determined.

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