JP2010188854A - Lane maintenance assisting device and lane maintenance assisting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lane maintenance assisting device capable of performing lane maintenance control not giving a sense of incongruity to a driver by taking into consideration a lane following property and driver cooperation property. <P>SOLUTION: When steering intention of the driver is not detected, first steering angle control is performed mainly taking into consideration to the lane following property, and when the steering intention of the driver is detected, second steering angle control that steering operation of the driver is easily reflected. When steering torque Th is a steering torque threshold value T0 or less and steering angle deviation Δθ(=θr-θs) is not more than a steering angle threshold value Δθ0, it is determined that the steering intention of the driver is not present and it is transferred from the second steering angle control to the first steering angle control. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a lane keeping assist device for keeping a host vehicle in a traveling lane.

A conventional lane keeping assist device controls an additional torque applied to a steering system so as to travel along a traveling lane (see, for example, Patent Document 1).
Here, when the driver's intention to steer is not detected, the additional torque is controlled so that the host vehicle travels in a predetermined position on the travel lane (first additional torque control). Further, when the driver's steering intention is detected, the additional torque is controlled so that the steering operation by the driver is easily reflected (second additional torque control). This allows the driver to travel with a sense of incongruity in consideration of lane tracking and driver cooperation.

JP-A-2005-306283

However, the conventional lane keeping assist device is configured to switch between the first additional torque control and the second additional torque control according to the steering torque by the driver. Therefore, for example, when the steering torque by the driver falls below the threshold value and the second additional torque control is switched to the first additional torque control, the additional torque suddenly changes, and accordingly, the steering torque by the driver increases. Then, the driver erroneously determines that the steering intervention has occurred again. Such hunting of the steering intervention determination results in an unpleasant behavior for the driver.
In view of the above, an object of the present invention is to provide a lane keeping support device that can perform lane keeping control without causing the driver to feel uncomfortable in consideration of lane following ability and driver cooperation.

  In order to solve the above-described problem, the lane keeping assist device according to the present invention provides a steering angle deviation that is a difference value between a target steering angle and an actual steering angle necessary for the host vehicle to travel a predetermined position in the traveling lane. calculate. When the steering intention detection means does not detect the steering intention by the driver, the first steering angle control means drives the host vehicle at a predetermined position on the travel lane with a predetermined calculation gain according to the steering angle deviation. The first steering angle control is performed to add the first additional torque necessary for this to the steering system. When the steering intention detection means detects the steering intention by the driver, the second steering angle control means has a calculated gain smaller than the first additional torque calculated gain according to the steering angle deviation, Second steering angle control is performed in which a second additional torque that is more easily reflected by the driver than the first additional torque is applied to the steering system. The steering intention detection means detects the steering intention by the driver when the steering torque is equal to or less than a predetermined torque threshold and the calculated steering angle deviation is equal to or less than a predetermined steering angle deviation threshold that is zero or substantially zero. From state to non-detection state.

  According to the present invention, since the additional torque is controlled by a different control method according to the driver's steering intention, it is possible to perform appropriate lane keeping control in consideration of the lane following ability and the cooperation with the driver steering operation. it can. Further, when the driver's steering torque is equal to or less than a predetermined torque threshold and the calculated steering angle deviation is equal to or less than a predetermined steering angle deviation threshold which is zero or substantially zero, the steering intervention by the driver is ended. Determination is made and the additional torque applied to the steering system is changed from the second additional torque to the first additional torque. As a result, a change in the additional torque when the additional torque applied to the steering system is changed from the second additional torque to the first applied torque is suppressed, and steering intervention due to the change in the additional torque added to the steering system Judgment hunting can be prevented. Therefore, it is possible to perform lane keeping control that does not give the driver a sense of incongruity.

1 is a schematic configuration diagram of a vehicle to which a lane keeping assist device according to the present invention is applied. It is a figure explaining the vehicle state quantity measured with a camera. It is a block diagram which shows the structure of a control unit. It is a control block diagram which shows the specific structure of a friction compensation calculating part. It is a flowchart which shows the lane maintenance control processing procedure performed with the control unit in 1st Embodiment. It is a figure for demonstrating the calculation method of a target steering angle. It is a timing chart for explaining operation. It is a figure which shows a control transition state. It is a timing chart for demonstrating operation | movement in a common lane maintenance assistance apparatus. It is a flowchart which shows the lane maintenance control processing procedure performed with the control unit in 2nd Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<< First Embodiment >>
"Constitution"
FIG. 1 is a schematic configuration diagram of a vehicle to which a lane keeping assist device according to the present invention is applied.
In the figure, 1FL is the front left wheel, and 1FR is the front right wheel. The steering gear 2, the steering wheel 3, and the steering shaft 4 constitute a steering system. The steering gear 2 generates a turning angle for the front left and right wheels 1FL and 1FR. The steering wheel 3 is operated by a driver to steer the vehicle. The steering shaft 4 mechanically connects the steering wheel 3 and the steering gear 2. The steering shaft 4 transmits the rotation of the steering wheel 3 as steering angles of the front left and right wheels 1FL and 1FR as steering wheels.

  Further, the vehicle is provided with a steering torque sensor 5 that detects a steering torque Th applied to the steering system by the driver via the steering wheel 3 from the amount of twist of the steering shaft 4. Further, the vehicle is provided with a steering angle sensor 6 that detects an angle (steering angle) θs of the steering wheel 3 steered by the driver. Detection signals from the steering torque sensor 5 and the steering angle sensor 6 are output to a control unit 10 described later.

The steering shaft 4 is provided with a steering actuator 7 for adding a steering assist force (additional torque). The steering actuator 7 is driven and controlled in accordance with a control current command value from the control unit 10.
Further, this vehicle is provided with a CCD camera 8a and a camera controller 8b as a traveling position detection sensor for detecting a relative position between the traveling lane shape in front of the vehicle and the host vehicle. The camera controller 8b detects a lane marker by detecting a lane marker such as a road marking line from a captured image in front of the host vehicle captured by the CCD camera 8a. Then, the yaw angle Φ of the host vehicle with respect to the travel lane, the lateral displacement y from the center of the travel lane, the curvature ρ of the travel lane, and the like are calculated (FIG. 2). These detection signals are output to the control unit 10.

Further, the vehicle is provided with a wheel speed sensor 9 for detecting the wheel speed Vw _i (i = FL to RR) of each wheel 1FL to 1RR. The wheel speed Vw _i also outputs to the control unit 10.
The control unit 10 calculates a control current command value for the steering actuator 7 based on various input detection signals, and outputs this to the steering actuator 7. The steering actuator 7 generates a torque proportional to the control current command value and adds a steering assist force.

(Configuration of control unit)
FIG. 3 is a control block diagram showing the configuration of the control unit 10.
The control unit 10 includes a steering intervention determination unit 21, a lane keeping control unit 22, a steering angle control unit 23, a friction compensation calculation unit 24, and a current control unit 25.
The steering intervention determination unit 21 inputs the steering torque Th detected by the steering torque sensor 5, the steering angle θs detected by the steering angle sensor 6, and the target steering angle θr calculated by the lane keeping control unit 22 described later. Next, a steering angle deviation Δθ (= θr−θs), which is a difference value between the target steering angle θr and the steering angle θs, is calculated. When the steering torque Th is larger than a predetermined steering torque threshold value or the steering angle deviation Δθ is larger than a predetermined steering angle deviation threshold value (zero or substantially zero), it is determined that there is a steering intention by the driver.

Lane keeping control section 22 inputs the driving lane information detected by the camera controller 8b, and a vehicle speed V calculated from the wheel speed Vw _i detected by the wheel speed sensor 9. Then, the target steering angle θr necessary for the host vehicle to travel in the center position of the travel lane is calculated. The calculated target steering angle θr is output to the steering angle control unit 23.
The steering angle control unit 23 inputs the target steering angle θr calculated by the lane keeping control unit 22 and the steering angle θs detected by the steering angle sensor 6. The steering angle control unit 23 also inputs the steering intervention determination result of the steering intervention determination unit 21. The steering angle control unit 23 calculates a control current command value Ir for the steering actuator 7. The calculated control current command value Ir is output to the current control unit 25.

  The steering angle control unit 23 includes a first steering angle control unit 23a and a second steering angle control unit 23b. The first steering angle control unit 23a calculates a control current command value Ir for performing lane keeping control (first steering angle control) such that the host vehicle is kept at the center of the traveling lane. Further, the second steering angle control unit 23b calculates a control current command value Ir for performing lane keeping control (second steering angle control) in which a steering operation by the driver is easily reflected.

The first steering angle control unit 23a and the second steering angle control unit 23b both calculate a control current command value Ir according to a steering angle deviation Δθ that is a difference value between the target steering angle θr and the actual steering angle θs. . Here, the second steering angle control unit 23b calculates the control current command value Ir in the second steering angle control with a gain smaller than the calculation gain of the control current command value Ir in the first steering angle control.
In the present embodiment, when the steering intervention determination unit 21 does not detect the driver's steering intention, the control current command value Ir calculated by the first steering angle control unit 23 a is output to the current control unit 25. When the steering intervention determination unit 21 detects the driver's steering intention, the control current command value Ir calculated by the second steering angle control unit 23 b is output to the current control unit 25.

The friction compensation calculation unit 24 inputs the steering torque Th detected by the driver detected by the steering torque sensor 5 and the steering angle θs detected by the steering angle sensor 6. Then, a friction compensation current Id for removing disturbance torque such as input from the tire to the steering system and friction of the steering device is calculated. The calculated friction compensation current Id is output to the current control unit 25.
The current control unit 25 subtracts the friction compensation current Id output from the friction compensation calculation unit 24 from the control current command value Ir output from the steering angle control unit 23. Then, the result is output to the steering actuator 7 as a control current command value I to be finally applied to the steering actuator 7.
I = Ir-Id (1)

(Configuration of friction compensation calculation unit)
Next, the calculation process in the friction compensation calculation unit 24 will be described more specifically.
FIG. 4 is a control block diagram showing a specific configuration of the friction compensation calculation unit 24.
The Laplace transform of the steering equation of motion is as follows.
ω (s) = P (s) (I (s) + (Td (s) + Th (s) / Kt)) (2)
However,
P (s) = Kt / (J _s s + D _s ) (3)
It is. This is a model for the rotational motion of the steering system from the rotational operating force to the steering system.
Each symbol represents the following parameter.
J _s : Moment of inertia of steering system,
D _s: viscosity coefficient of the steering system,
Kt: torque constant of the steering actuator,
ω: Steering shaft rotation angular velocity

Therefore, the disturbance torque Td can be obtained by the following equation using the inverse characteristic of the steering system model of the above equation (3).
Td (s) = Kt (ω (s) / P (s) −I (s)) − Th (s) (4)
However, there are cases where appropriate disturbance estimation cannot be performed due to noise generated in the differential term. Therefore, a low-pass filter having a disturbance elimination frequency band ωc L (s) = ωc / (s + ωc) (5)
And all disturbance torques Td to the steering system including friction and tire input are estimated based on the following equation.
Td (s) = Kt · L (s) / P (s) · ω (s) −L (s) (Th (s) + KtI (s)) (6)

Then, the friction compensation current Id is calculated based on the following equation.
Id (s) = Td (s) / Kt
= L (s) / P (s) .omega. (S) -L (s) (Th (s) / Kt + I (s)) (7)

Here, the role of the friction compensation current Id will be described.
When the transfer function of the steering system is obtained from the above equations (1), (2), and (7),
ω (s) = P (s) (KtIr + Th (s) + H (s) Td (s)) (8)
here,
H (s) = 1−L (s) = s / (s + ωc) (9)
It is.

Thus, it can be seen that the influence of the disturbance torque Td (s) on the motion of the steering actuator is removed in a frequency range lower than the frequency band ωc where the disturbance is desired to be removed.
That is, the friction compensation calculation unit 24 has a model P (s) driven by a control input and a driver operation force. Then, from the difference between the estimated value of the sum of the control input and the operation input obtained when the steering angular velocity ω is passed through the inverse characteristic of the model P (s) and the total value of the actual control input and the operation input, The force input as a disturbance is used as an estimated friction value. Therefore, a reasonable friction estimation configuration can be provided, and only the operation reaction force by the steering angle control unit 23 is transmitted to the driver as information.

(Lane maintenance control procedure)
Next, a lane keeping control processing procedure executed by the control unit 10 will be described.
FIG. 5 is a flowchart showing a lane keeping control processing procedure executed by the control unit 10. This lane keeping control process is executed as a timer interrupt process for every predetermined time (for example, 10 msec). First, in step S1, the control unit 10 reads signals from various sensors.
Specifically, the steering torque Th, the steering angle θs, the wheel speed Vw _i (i = FL to RR), the yaw angle Φ of the host vehicle with respect to the traveling lane, the lateral displacement y from the center of the traveling lane, and the curvature ρ of the traveling lane Read.

Next, in step S2, the control unit 10 calculates the vehicle speed V. The vehicle speed V, of the wheel speed Vw _i detected by the wheel speed sensors 9FL～9RR, for example, wheel speed Vw _FL of the front wheels as non-driven wheels, the average value of Vw _FR, is calculated based on the following equation .
V = (Vw _FL + Vw _FR ) / 2 (10)
For example, when an ABS control device that performs known anti-skid control is mounted on the vehicle, and the anti-skid control is performed by this ABS control device, it is estimated in the process of the anti-skid control. The estimated vehicle speed can be used as the vehicle speed V.
Further, when the present invention is applied to a front wheel drive vehicle, among the wheel speeds Vw _FL ~Vw _RR, the wheel speed Vw _RL of the rear wheels are non-drive wheels, Vw speed from the average value of the vehicle of _RR V May be calculated.
Next, in step S3, the control unit 10 calculates the target steering angle θr. As a method of calculating the target steering angle θr, for example, a method of calculating from the target yaw rate γr is used.

FIG. 6 is a diagram illustrating a method for calculating the target steering angle θr.
First, as shown in FIG. 6, a target point P on the target route Mp is set based on various signals read from the camera controller 8b. The target point P is obtained as an intersection point on the target route Mp and a line extending in the lateral direction with respect to the vehicle body axis at the front gazing point.
The distance Ls from the vehicle to the forward gazing point is corrected to a small value at low speeds where small R is important so that appropriate control is performed on the road on which the vehicle actually travels.

The lateral deviation ys between the target point P and the vehicle body axis is based on the following equation using the lateral displacement y with respect to the target path of the host vehicle, the yaw angle Φ, and the curvature ρ of the target path read from the camera controller 8b. To calculate.
ys = 0.5Ls ² ρ− (y + LsΦ) (11)
Next, the yaw rate γr when the vehicle travels along the route Sp that reaches the target point P is calculated based on the following equation.
γr = 2Vys / Ls ² (12)
Therefore, from the above equations (11) and (12), when the vehicle is traveling on the target route Mp,
γr = Vρ (13)
It becomes.

On the other hand, when the actual route of the vehicle greatly deviates to the inside of the turn, the yaw rate for traveling on the target route is moved to the outside of the turn by the correction value γr0 expressed by the following equation according to the amount of deviation. The corrected value is calculated as the target yaw rate γr.
γr0 = 2V (y + LsΦ) / Ls 2 ......... (14)
When the yaw rate of the vehicle is controlled and the lateral displacement y and the yaw angle Φ of the vehicle become small, the correction value γr0 of the above equation (14) becomes small. Therefore, the target yaw rate γr approaches the yaw rate when traveling on the target route Mp, and finally travels on the target route Mp.

Next, the target steering angle θr of the front wheels necessary for realizing the target yaw rate γr calculated based on the equation (12) is calculated based on the following equation (15).
θr = 1 / (1 + AV ² ) · L / V · γr (15)
Here, L is the wheelbase of the host vehicle, and A is the stability factor of the steering characteristics.

In this way, the target steering angle θr that guides the host vehicle toward the center of the traveling lane is calculated based on the state of the front lane and the driving state of the vehicle.
The target steering angle θr can also be calculated based on the following equation (16).
θr = θs + Δθr = θs + 1 / (1 + AV ² ) · L / V · Δγr (16)
Here, Δθr is a steering angle correction amount (θr−θs) from the current steering angle θs to the target steering angle θr. Δγr is a yaw rate correction amount (γr−γ) from the current yaw rate γ to the target yaw rate γr. Thereby, it is possible to cope with a change in turning characteristics due to a road surface cant or a tire difference.

Next, in step S4, the control unit 10 calculates the friction compensation current Id. First, the disturbance torque Td is calculated (estimated) based on the above equation (6). Next, the friction compensation current Id necessary for canceling the estimated disturbance torque Td is calculated based on the equation (7).
Next, in step S5, the control unit 10 determines whether or not the steering intervention determination flag flag is “1”. The steering intervention determination flag flag is set to flag = 1 when it is determined that the driver is intentionally steering input. The steering intervention determination flag flag is reset to flag = 0 when it is determined that the driver is not intentionally steering.

When it is determined in this step S5 that flag = 0, the process proceeds to step S6. When it is determined that flag = 1, the process proceeds to step S12 described later.
In step S6, the control unit 10 calculates a deviation Δθ (= θr−θs) between the steering angle θs read in step S1 and the target steering angle θr calculated in step S3.

Next, in step S7, the control unit 10 calculates a control current command value Ir for performing the first steering angle control. Here, it calculates the control current command value Ir multiplied by the feedback gain K ₁ to the steering angle deviation Δθ calculated in step S6. The feedback control of the steering angle deviation performed here is for the main purpose of maintaining the lane, and it is difficult to allow the driver to intervene in steering. A predetermined upper limit value is provided for the control current command value Ir.

Next, in step S8, the control unit 10 determines whether or not the absolute value | Th | of the steering torque Th read in step S1 exceeds a preset steering torque threshold value T0. When | Th | ≦ T0, the process proceeds to step S9. When | Th |> T0, the process proceeds to step S10 described later.
In step S9, the control unit 10 determines whether or not the absolute value | Δθ | of the steering angle deviation Δθ calculated in step S6 exceeds a preset steering angle deviation threshold value Δθ0. Here, the steering angle deviation threshold Δθ0 is set to zero or substantially zero. When | Δθ |> Δθ0, the process proceeds to step S10, and when | Δθ | ≦ Δθ0, the process proceeds to step S11 described later.

In step S10, the control unit 10 sets the steering intervention determination flag flag to “1”, and proceeds to step S11.
In step S11, the control unit 10 calculates a control current command value I to be applied to the steering actuator 7 based on the following equation, and then ends the timer interrupt process.
I = Ir-Id (17)
In step S12, the control unit 10 calculates a deviation Δθ (= θr−θs) between the steering angle θs read in step S1 and the target steering angle θr calculated in step S3.

Next, in step S13, the control unit 10 calculates a control current command value Ir for performing the second steering angle control. Here, the control current command value Ir is calculated by multiplying the steering angle deviation Δθ calculated in step S12 by the feedback gain K ₂ (<K ₁ ). The feedback control of the steering angle deviation performed here is strong enough to allow the driver to easily perform steering intervention. That is, when the driver intervenes in steering, a steering assist force felt by the driver is generated according to the magnitude of the steering angle deviation, and the driver's steering operation is encouraged so that the vehicle is directed in an appropriate direction. ing.

Further, the control current command value Ir is provided with a predetermined upper limit value as in step S8. The increase rate of the control current command value Ir with respect to the steering angle deviation Δθ can be set smaller as the steering angle deviation Δθ is larger.
Next, in step S14, the control unit 10 determines whether or not the absolute value | Th | of the steering torque Th read in step S1 is equal to or less than the steering torque threshold value T0. When | Th | ≦ T0, the process proceeds to step S15, and when | Th | <T0, the process proceeds to step S11.

In step S15, the control unit 10 determines whether or not the absolute value | Δθ | of the steering angle deviation Δθ calculated in step S12 is equal to or smaller than the steering angle deviation threshold value Δθ0. If | Δθ | ≦ Δθ0, the process proceeds to step S16. If | Δθ |> Δθ0, the process proceeds to step S11.
In step S16, the control unit 10 resets the steering intervention determination flag flag to “0”, and then proceeds to step S11.
Thus, when | Th |> T0 or | Δθ |> Δθ0, it is determined that the driver has performed steering intervention, and second steering angle control is performed. When | Th | ≦ T0 and | Δθ | ≦ Δθ0, it is determined that the driver is not performing steering intervention, and the first steering angle control is performed.

<Operation>
Next, the operation of the first embodiment will be described.
FIG. 7 is a timing chart for explaining the operation of the present embodiment.
It is assumed that the driver has finished the steering operation during the second steering angle control. Then, the steering torque Th gradually decreases, and | Th | ≦ T0 at time t0 in FIG. At this time, Yes is determined in step 14 of FIG. 5, but since | Δθ |> Δθ0, it is determined No in step S15. Therefore, the control unit 10 determines that the driver is continuing the steering intervention, and continues the second steering angle control.

  Thereafter, the second steering angle control is continued even when the steering torque Th = 0. In the present embodiment, a friction compensation calculation unit 24 is provided. Therefore, even if the second steering angle control is continued, if the driver's steering torque Th is sufficiently small, the actual steering angle θs gradually approaches the target steering angle θr by the action of the friction compensation current Id (steering). The angular deviation Δθ asymptotically approaches zero).

When the steering angle deviation | Δθ | becomes equal to or smaller than the sufficiently small steering angle deviation threshold value Δθ0 at time t1, the control unit 10 determines that the driver's steering intervention has ended. At this time, it is determined Yes in step S15, the process proceeds to step S16, and the steering intervention determination flag flag = 0 is reset. Thereby, it shifts to the first steering angle control from the next control cycle.
FIG. 8 is a diagram showing a control transition state in the present embodiment.

  As indicated by the arrow a in FIG. 8, when the second steering angle control is performed, when the steering angle deviation Δθ becomes sufficiently small, the lane maintenance control by the first steering angle control is performed. After that, the first steering angle control is stably performed, and the actual steering angle θs follows the target steering angle θr with good responsiveness. That is, at the stage of transition from the second steering angle control to the first steering angle control, there is no steering behavior against the driver's intention and there is a smooth transition.

By the way, in the general lane keeping assist device, when the absolute value of the steering torque of the driver becomes smaller than a threshold value for judging the end of the steering intervention, the shift to the first steering angle control mainly for the lane keeping performance is made. .
FIG. 9 is a timing chart for explaining operations in a general lane keeping assist device. In the example shown in FIG. 9, a hysteresis characteristic is provided for a steering torque threshold value for determining steering intervention.

  During the second steering angle control, if the steering torque | Th | ≦ T0 at time t10, it is determined that the driver's steering intervention has ended. Then, at a time t11 when a predetermined determination time has elapsed, the second steering angle control is shifted to the first steering angle control whose main purpose is lane keeping performance. At this time, the steering angle deviation is a relatively large value as shown in FIG. Therefore, in the first steering angle control, a large control current command value is calculated to make the steering angle deviation asymptotic to zero. Therefore, the generated steering assist force also increases, and as a result, the steering torque detected by the steering torque sensor also increases.

  Then, at time t12, the steering torque | Th |> T0, and it is determined that the driver has performed the steering intervention, and the first steering angle control is shifted to the second steering angle control. At this time, since the driver does not actually perform the steering intervention operation, the steering torque Th gradually decreases. At time t13, | Th | ≦ T0. Thereby, at the time t14, the second steering angle control is shifted to the first steering angle control.

However, since the steering angle deviation is a relatively large value in this case as well, when shifting to the first steering angle control, the steering torque Th increases again, and the steering intervention determination is made at time t15.
In this way, the steering torque Th varies and hunting for steering intervention determination occurs. Even if a hysteresis characteristic is provided in the steering intervention determination threshold as described above, only the timing at which a behavior undesirable for the driver occurs changes, and it does not constitute a fundamental solution. Therefore, conventionally, there has been a situation where the lane keeping performance has to be lowered so that the fluctuation of the steering torque is allowed to the extent allowed by the driver.

  On the other hand, in this embodiment, when the steering torque Th is equal to or less than the steering torque threshold value T0 and the steering angle deviation Δθ is equal to or less than the steering angle deviation threshold value Δθ0, it is determined that the driver's steering intervention is completed. . Thereby, the fluctuation | variation of the steering torque accompanying the change of steering assist force as mentioned above can be prevented. As a result, it is possible to achieve both a feeling of steering with less discomfort and good lane keeping performance.

  Further, in the present embodiment, by performing friction compensation, when the steering torque Th is sufficiently small, the steering angle deviation Δθ gradually approaches zero. For this reason, it is only necessary to return to the first steering angle control when the steering angle deviation Δθ is equal to or smaller than the sufficiently small threshold Δθ0, without specially determining whether the steering intervention is completed. Thereby, it is possible to shift to the steering control mainly for maintaining the lane without accompanying the behavior of the steering wheel due to the change of the steering assist force.

At this time, if the driver again applies the steering torque Th to the steering wheel before shifting to the first steering angle control, the steering angle deviation Δθ does not gradually approach zero. As a result, the second steering angle control in which the steering reaction force characteristic is appropriately set is maintained. Therefore, a change in the steering assist force unintended by the driver is eliminated, and a steering system without a sense of incongruity can be achieved.
In FIG. 1, a CCD camera 8a, a camera controller 8b, and a wheel speed sensor 9 constitute a running state detecting means. Further, the steering torque sensor 5 constitutes a steering torque detection means, and the steering angle sensor 6 constitutes a steering angle detection means.
In the processing of FIG. 5, step S3 constitutes a target steering angle calculation means, steps S8 to 10 and S14 to S16 constitute steering intention detection means, and steps S6 and S12 constitute steering angle deviation calculation means. ing. Further, step S7 constitutes a first steering angle control means, and step S13 constitutes a second steering angle control means.

"effect"
(1) The target steering angle calculation means calculates a target steering angle necessary for the host vehicle to travel in a predetermined position on the travel lane based on the travel state detected by the travel state detection means. The steering angle deviation calculating means calculates a steering angle deviation which is a difference value between the target steering angle calculated by the target steering angle calculating means and the steering angle detected by the steering angle detecting means. The first steering angle control means has a predetermined calculation gain according to the steering angle deviation calculated by the steering angle deviation calculation means when the driver's steering intention is not detected by the steering intention detection means. A first additional torque necessary for traveling in a predetermined position of the travel lane is calculated, and first steering angle control for adding the first additional torque to the steering system is performed. The second steering angle control means calculates smaller than the calculated gain of the first additional torque according to the steering angle deviation calculated by the steering angle deviation calculating means when the steering intention detecting means detects the steering intention by the driver. Based on the gain, a second additional torque that easily reflects the steering operation by the driver is calculated from the first additional torque, and second steering angle control is performed to apply the second additional torque to the steering system.

The steering intention detection means is a predetermined steering angle deviation threshold value in which the steering torque detected by the steering torque detection means is equal to or less than a predetermined torque threshold value and the steering angle deviation calculated by the steering angle deviation calculation means is zero or substantially zero. In the following cases, the steering intention by the driver is not detected.
In this way, the steering intention of the driver is detected, and the control method of the lane keeping control is changed according to the driver's steering intention. In the first steering angle control, a sufficient lane following performance can be realized and stable running can be performed. Further, in the second steering angle control, it is possible to perform the traveling control in which the steering operation by the driver is easily reflected, and it is possible to perform the steering angle control without causing the driver to feel uncomfortable.

  Furthermore, when the driver's steering intention becomes zero, the vehicle can return to the lane keeping control (first steering angle control). By using the steering angle deviation for the steering intention determination, it is possible to prevent the hunting of the steering intervention determination due to the fluctuation of the additional torque accompanying the switching of the steering angle control. Therefore, an operation mode faithful to the driver's intention can be realized.

  (2) The target steering angle calculation means calculates a target yaw rate based on the traveling state detected by the traveling state detection means, and calculates a target steering angle that realizes the target yaw rate. Thereby, an appropriate target steering angle can be calculated.

(3) The second steering angle control means calculates the second additional torque to be larger as the steering angle deviation calculated by the steering angle deviation calculation means is larger, and the second additional torque with respect to the increase amount of the steering angle deviation. Is increased as the steering angle deviation increases.
Thereby, when the steering angle deviation is small, a large additional torque can be generated even with a slight increase in the steering angle deviation. For this reason, the driver receives the steering assist force sensitively. Therefore, when there is an actual intention to steer, information that informs the center position of the traveling lane can be transmitted to the driver. Further, when there is no actual intention to steer, the course can be corrected in a direction to avoid lane departure by an additional torque generated as a steering assist force.
Further, when the steering angle deviation is large, it can be clearly judged that the driver has intentionally deviated from the lane, and the steering torque exceeding a certain value can be prevented from being generated. Therefore, the driver's steering operation can be appropriately reflected, and the driver can change lanes and the like without feeling uncomfortable.

(4) Based on the traveling state of the host vehicle, the target steering angle required for the host vehicle to travel a predetermined position in the traveling lane is calculated, and is a difference value between the calculated target steering angle and the actual steering angle. The actual steering angle deviation is calculated. When the steering torque by the driver is greater than a predetermined torque threshold or when the calculated steering angle deviation is greater than a predetermined steering angle deviation threshold that is zero or substantially zero, a steering operation by the driver is performed according to the calculated steering angle deviation. Is calculated, and second steering angle control is performed to add the second additional torque to the steering system. When the driver's steering torque is less than or equal to the torque threshold value and the calculated steering angle deviation is less than or equal to the steering angle deviation threshold value, the host vehicle travels in a predetermined position on the traveling lane according to the calculated steering angle deviation. The first additional torque necessary for the calculation is calculated, and the first steering angle control for adding the first additional torque to the steering system is performed.
Thereby, at the time of control transition, torque fluctuation that is unpleasant for the driver can be prevented regardless of the steering operation state of the driver. As a result, it is possible to perform the lane keeping control without causing the driver to feel uncomfortable.

<< Second Embodiment >>
Next, a second embodiment of the present invention will be described.
In the second embodiment, a dynamic compensator that arbitrarily sets the dynamic characteristic from the steering torque Th to the steering angle deviation Δθ is used in the first and second steering angle controls. is there.
"Constitution"
The configuration of the control unit 10 in the second embodiment is the same as the configuration of the control unit 10 in the first embodiment described above shown in FIG.
First, a dynamic compensator that arbitrarily sets dynamic characteristics from the steering torque Th to the steering angle deviation Δθ will be described.

The dynamic compensator used for the first steering angle control unit can be written as follows in a general format of a discrete value system.
x ₁ (k + 1) = A ₁ x ₁ (k) + B ₁ Δθ (k),
Ir (k) = C ₁ x ₁ (k) + D ₁ Δθ (k) (18)
Further, a dynamic compensator used for the second steering angle control unit can be written as follows in a general format of a discrete value system.
x ₂ (k + 1) = A ₂ x ₂ (k) + B ₂ Δθ (k),
Ir (k) = C ₂ x ₂ (k) + D ₂ Δθ (k) (19)

Here, x ₁ and x ₂ are state variables inside the compensator that performs the first or second steering angle control, respectively. A _{1 to} D ₁ and A _{2 to} D ₂ arbitrarily set the response of the steering angle deviation Δθ from the steering torque Th when the first or second steering angle control is performed to form a closed loop system. It is a parameter. A _{1 to} D ₁ and A _{2 to} D ₂ are scalar or matrix variables or constants. Furthermore, k represents a calculation step, and is a variable that satisfies t = k × dt, where dt is the calculation cycle and time t.

(Lane maintenance control procedure)
Next, a lane keeping control process procedure executed by the control unit 10 of the second embodiment will be described.
FIG. 10 is a flowchart showing a lane keeping control processing procedure executed by the control unit 10 of the second embodiment. This lane keeping control process is the same as FIG. 5 except that steps S7 and S13 are replaced with steps S21 and S22 in the lane keeping control process shown in FIG. Accordingly, parts corresponding to those in FIG.

In step S21, the control unit 10, based on the following equation, it calculates the control current command value Ir and the first steering angle control compensator state variables x _1.
Ir = C ₁ x ₁ + D ₁ Δθ,
x ₁ = A ₁ x ₁ + B ₁ Δθ (20)
In step S22, the control unit 10, based on the following equation, calculates the control current command value Ir and a second steering angle control compensator state variable x _2.
Ir = C ₂ x ₂ + D ₂ Δθ,
x ₂ = A ₂ x ₂ + B ₂ Δθ (21)

  Here, in the second steering angle control, the steering reaction force felt by the driver is generated according to the steering angle deviation or the steering angle deviation speed when the driver performs steering intervention, or the steering wheel movement is smoothly performed. Such a current command value is calculated. The magnitude of the steering reaction force (steering torque) is limited to a strength that allows the driver to easily perform steering intervention. Therefore, as in the first embodiment, the driver's steering operation is urged so that the vehicle heads in an appropriate direction.

"effect"
(5) By the model matching control or the like, the second steering angle control can be designed so that the dynamic characteristic of the steering system matches the ideal dynamic characteristic. Therefore, in consideration of the lane following ability and the driver cooperation, the lane keeping assist device that performs the lane keeping control without causing the driver to feel strange is more preferable.
<Modification>
(1) In each of the embodiments described above, the case where the friction estimated value is calculated using the steering angular velocity has been described. However, a configuration in which the steering angle and the secondary low-pass filter are combined may be employed. Further, when the steering torque sensor drifts, a dead zone can be set so that the friction compensation does not operate sensitively in a range where the steering torque is close to zero.

(2) In each of the above-described embodiments, the case has been described in which control is performed such that the vehicle travels along the lane target route (traveling lane center position) as lane keeping control. However, the vehicle does not protrude from the lane. It is also possible to apply a control so that the vehicle travels.
(3) In each of the above embodiments, the second steering angle control can have a plurality of calculation gains for the control current command value Ir. Then, the control current command value Ir may be calculated by changing the calculation gain according to the traveling state of the vehicle (the presence or absence of an obstacle, the presence or absence of a vehicle in an adjacent lane, etc.). As a result, it is possible to perform travel control that more matches the driver's feeling.

  (4) In each of the above embodiments, differential control for feeding back the steering speed of the steering angle θs can be added by the first and second steering angle control. Thereby, the steering reaction force characteristic with respect to the steering angle deviation can be adjusted. For example, even when the driver suddenly releases his / her hand from the steering wheel, the movement of the steering wheel can be adjusted to be gentle. Therefore, it is possible to obtain a steering characteristic with less driver discomfort.

1FL, 1FR Front wheel 2 Steering gear 3 Steering wheel 4 Steering shaft 5 Steering torque sensor 6 Steering angle sensor 7 Steering actuator 8a CCD camera 8b Camera controller 9 Wheel speed sensor 10 Control unit

Claims (4)

In a lane keeping assist device that controls an additional torque that is a torque added to a steering system that is steered by a driver so that the host vehicle travels along a traveling lane,
Traveling state detection means for detecting the traveling state of the host vehicle;
Target steering angle calculating means for calculating a target steering angle required for the host vehicle to travel a predetermined position in the traveling lane based on the traveling state detected by the traveling state detecting means;
Steering angle detection means for detecting the steering angle;
Steering angle deviation calculating means for calculating a steering angle deviation which is a difference value between the target steering angle calculated by the target steering angle calculating means and the steering angle detected by the steering angle detecting means;
Steering intention detection means for detecting the steering intention by the driver;
When the steering intention detection means does not detect the driver's steering intention, the host vehicle travels in a predetermined position on the travel lane with a predetermined calculation gain according to the steering angle deviation calculated by the steering angle deviation calculation means. A first steering angle control means for calculating a first additional torque necessary for performing the first steering angle control for calculating the first additional torque and adding the first additional torque to the steering system;
When the steering intention detecting means detects the steering intention by the driver, the first gain is calculated with a smaller gain than the first additional torque according to the steering angle deviation calculated by the steering angle deviation calculating means. A second steering angle control means for calculating a second additional torque in which the steering operation by the driver is easily reflected from the additional torque of the second steering angle, and for performing a second steering angle control for applying the second additional torque to the steering system; ,
Steering torque detection means for detecting a steering torque applied to the steering system by a driver,
The steering intention detection means has a predetermined steering angle deviation in which the steering torque detected by the steering torque detection means is equal to or less than a predetermined torque threshold and the steering angle deviation calculated by the steering angle deviation calculation means is zero or substantially zero. A lane keeping assist device characterized in that the driver's intention to steer is not detected when the value is equal to or less than a threshold value. The traveling state detection means detects a traveling lane state, a position state of the host vehicle with respect to the traveling lane, and a vehicle speed of the host vehicle,
2. The target steering angle calculation unit calculates a target yaw rate based on the traveling state detected by the traveling state detection unit, and calculates a target steering angle that realizes the target yaw rate. The lane keeping assist device described.   The second steering angle control means calculates the second additional torque to be larger as the steering angle deviation calculated by the steering angle deviation calculation means is larger, and the second steering angle control means calculates the second additional torque with respect to the increase amount of the steering angle deviation. The lane keeping assist device according to claim 1 or 2, wherein the increase amount of the additional torque is set to be smaller as the steering angle deviation is larger. In a lane keeping assist method for controlling an additional torque, which is a torque added to a steering system that is steered by a driver, so that the host vehicle travels along a traveling lane,
Based on the traveling state of the host vehicle, a target steering angle required for the host vehicle to travel a predetermined position in the traveling lane is calculated, and actual steering that is a difference value between the calculated target steering angle and the actual steering angle is calculated. When the angle deviation is calculated and the steering torque by the driver is greater than a predetermined torque threshold value or when the calculated steering angle deviation is greater than a predetermined steering angle deviation threshold value that is zero or substantially zero, The second additional torque that easily reflects the steering operation by the driver is calculated, the second steering angle control is performed to add the second additional torque to the steering system, and the steering torque by the driver is equal to or less than the torque threshold value. When the calculated steering angle deviation is equal to or less than the steering angle deviation threshold, the first additional torque necessary for the host vehicle to travel a predetermined position in the traveling lane is calculated according to the calculated steering angle deviation. And the first appendix Lane keeping assist method characterized by performing the first steering angle control for adding torque to the steering system.

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