Lane Departure Prevention Device

Abstract

To speed up starting of a traffic lane deviation preventing control and improve a traffic lane deviation preventing effect even in a situation where a driver is in a state of low arousal and hands-free driving.SOLUTION: In a traffic lane deviation preventing device in which when a control unit determines that a driver has let go of his / her hand (S50), the control unit executes a traffic lane deviation preventing control earlier than when the control unit determines that the driver has not let go of his / her hand (S70), the control unit being configured to execute the traffic lane deviation preventing control of at least one of automatic steering of steerable wheels and issuing of a warning (S90) when the control unit determines that there is a risk of a vehicle deviating from a traffic lane (S80). When the control unit determines that the driver is not awake (S20), the control unit makes it easier to determine that the driver is letting go of his / her hand by relaxing a condition for determining whether the driver is letting go of his / her hand (S40).SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a lane departure prevention device for a vehicle such as an automobile. [Background technology]

[0002] The lane departure prevention device detects the vehicle's position relative to the lane using a vehicle position detection device, and when it determines that there is a risk of the vehicle deviating from the lane based on the detected vehicle position, it executes lane departure prevention control, such as at least one of automatic steering of the steered wheels and issuing an alarm.

[0003] When a vehicle is traveling, the driver may let go of the steering wheel while driving. When the driver lets go of the steering wheel while driving, the vehicle is more likely to deviate from the lane, and the time required for the driver to perform a steering operation to prevent the vehicle from deviating from the lane increases. Therefore, when the driver lets go of the steering wheel, it is preferable that the lane departure prevention control be started earlier than when the driver does not let go of the steering wheel.

[0004] For example, the following Patent Document 1 describes a lane departure prevention device that estimates a return time until the driver returns to gripping the steering wheel based on the duration of hands-off and determines the timing of the warning based on the return time so that the timing of the warning is earlier the longer the estimated return time is. This type of lane departure prevention device can speed up the timing of the warning in situations where the hands-off duration is long, improving the effectiveness of preventing lane departure, compared to when the timing of the warning is not determined based on the return time based on the duration of hands-off. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-193683 A Summary of the Invention

[0006] [Problem to be solved by the invention] While a vehicle is traveling, the driver may be in a state of low alertness due to driving fatigue, etc. If the driver drives with his / her hands off the steering wheel while in a low alertness state, it takes longer for the driver to perform steering operation to prevent the vehicle from leaving the lane compared to when the driver drives with his / her hands off the steering wheel while in an alert state.

[0007] However, conventional lane departure prevention devices such as the lane departure prevention device described in Patent Document 1 above do not take into account the driver's state of alertness, and therefore cannot advance the timing of the warning in situations where the driver is in a low state of alertness and drives with his / her hands off the wheel, and therefore cannot improve the effectiveness of preventing lane departure.

[0008] A primary object of the present invention is to provide an improved lane departure prevention device that can speed up the initiation of lane departure prevention control and improve the effectiveness of preventing lane departure, even in situations where the driver is in a low-wakefulness state and driving with his / her hands off the wheel.

[0009] [Means for solving the problems and effects of the invention] According to the present invention, there is provided a lane departure prevention device (100) including a vehicle position detection device (exterior camera sensor 11) that detects the position of a vehicle (50) relative to a lane (54), a gripping condition detection device (torque sensor 32) that detects the driver's gripping condition with respect to a steering input device (steering wheel 28), and a control unit (LDA·ECU10) configured to execute lane departure prevention control of at least one of automatic steering of steered wheels (24) and issuing an alarm (S90) when it is determined that the vehicle is at risk of deviating from the lane based on the position of the vehicle detected by the vehicle position detection device (S80), wherein the control unit is configured to execute lane departure prevention control earlier (S70) when it is determined that the driver has let go of the steering wheel based on the gripping condition detected by the gripping condition detection device (S50) than when it is determined that the driver has not let go of the steering wheel.

[0010] The control unit is configured to determine that the driver has let go of the steering wheel (S56) when it is determined that the time (Tn) during which the absolute value of the steering torque (Ts) detected by the gripping condition detection device (torque sensor 32) is less than the reference torque (Tsc) exceeds the reference time (Tnc) (S51, S54).The lane departure prevention device (100) further includes an awakening state detection device (in-vehicle camera sensor 13) that detects the awakening state of the driver, and the control unit The reference torque and the reference time are variably set according to the vehicle speed (S30, S40) so that the higher the vehicle speed (V), the smaller the reference torque and the reference time. When it is determined that the driver is not awake based on the driver's awake state detected by the awake state detection device (S20), Increase the reference torque and decrease the reference time. The system is configured to ease the conditions for determining whether the driver has let go of the handlebars, thereby making it easier to determine that the driver has let go of the handlebars (S40).

[0011] According to the above configuration, when it is determined that the driver has released the steering wheel, the lane departure prevention system is executed earlier than when it is determined that the driver has not released the steering wheel. difference Furthermore, when it is determined that the driver is not awake, the conditions for determining whether the driver should let go of the hands are set. but relief Therefore, when it is determined that the driver is not awake, This makes it easier to determine when the driver has let go of the steering wheel.

[0012] Therefore, when the driver is not awake, it is more likely that the driver has let go of the steering wheel, and therefore when the driver is not awake, it is determined that the driver has let go of the steering wheel earlier than when the driver is awake. Therefore, when the driver is not awake and has let go of the steering wheel, lane departure prevention control is started earlier than when the driver's awareness is not taken into consideration, and the risk of the vehicle leaving the lane can be effectively reduced. In particular, according to the above configuration, when it is determined that the time during which the absolute value of the steering torque is less than the reference torque exceeds the reference time, it is determined that the driver has let go of the steering wheel. Furthermore, when it is determined that the driver is not awake, the reference torque is increased and the reference time is decreased. Therefore, when it is determined that the driver is not awake, the conditions for determining that the driver has let go of the steering wheel can be relaxed reliably. Furthermore, according to the above configuration, the reference torque and the reference time are variably set according to the vehicle speed so that the reference torque and the reference time are smaller as the vehicle speed increases, so that it is possible to more appropriately determine whether the driver has released the hands of the vehicle compared to a case in which the reference torque and the reference time are constant regardless of the vehicle speed.

[0013] In the above description, in order to facilitate understanding of the present invention, the names and / or symbols used in the embodiments described below are added in parentheses to the configurations of the invention corresponding to those embodiments. However, each component of the present invention is not limited to the components of the embodiments corresponding to the names and / or symbols added in parentheses. Other objects, other features, and associated advantages of the present invention will be easily understood from the description of the embodiments of the present invention described below with reference to the drawings. [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic diagram showing an embodiment of a lane departure prevention device according to the present invention; [Diagram 2] 4 is a flowchart showing a lane departure prevention control routine in the embodiment. [Diagram 3] 3 is a flowchart showing a driver's hands-off determination routine executed in step S50 of the flowchart shown in FIG. 2. [Figure 4] FIG. 1 is a diagram showing a situation in which a vehicle is traveling at an angle relative to the longitudinal direction of a lane. [Diagram 5] 2 is a map for calculating a standard value Tscn and a relaxation value Tsch of the reference value Tsc of the steering torque Ts based on the vehicle speed V. [Figure 6] 11 is a map for calculating a standard value Tncn and a relaxed value Tncr of a reference value Tnc for an elapsed time based on a vehicle speed V. [Figure 7] FIG. 13 is a diagram for explaining that when the reference value Tnc is the relaxed value Tncr, it is determined that the hand is released earlier than when the reference value Tnc is the standard value Tncn. [Figure 8] FIG. 13 is a diagram for explaining that lane departure prevention control is started earlier when the reference value Dyc is the relaxed value Dych than when the reference value Dyc is the standard value Dycn. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A lane departure prevention device according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

[0016] <Configuration> 1, a lane departure prevention device 100 according to an embodiment is applied to a vehicle 50, and includes a lane departure prevention ECU 10 and an electric power steering ECU 20. In this specification, lane departure prevention is referred to as LDA (abbreviation of Lane Departure Alert with Control) as necessary, and electric power steering is referred to as EPS (abbreviation of Electric Power Steering) as necessary.

[0017] These ECUs are electronic control units that include a microcomputer as a main component, and are connected to each other via a CAN (Controller Area Network) 52 so that they can transmit and receive information to each other. Each microcomputer includes a CPU, ROM, RAM, non-volatile memory, an interface, etc. The CPU is adapted to realize various functions by executing instructions (programs, routines) stored in the ROM. These ECUs may be integrated into one ECU.

[0018] As will be described in detail later, the ROM of the LDA·ECU 10 stores a program for lane departure prevention control corresponding to the flowcharts shown in FIGS. 2 and 3, and the CPU executes the lane departure prevention control in accordance with the program.

[0019] To the LDA·ECU 10, an exterior camera sensor 11, a radar sensor 12, an interior camera sensor 13, a vehicle speed sensor 14, an LDA switch 15, and an alarm device 16 are connected.

[0020] The exterior camera sensor 11 includes a camera unit and a recognition unit that recognizes white lines and obstacles on the road by analyzing image data captured by the camera unit. The camera sensor 11 (camera unit) captures images of the scenery ahead of the vehicle 50. The camera sensor 11 (recognition unit) repeatedly supplies information about the recognized white lines and obstacles to the LDA·ECU 10 at every predetermined calculation period.

[0021] As shown in Fig. 4, the camera sensor 11 is capable of recognizing white lines 56L and 56R, which are boundaries of a lane 54 (called lane boundaries), and detecting the relative positional relationship of the vehicle with respect to the lane 54 based on the relationship between the white lines and the position of the vehicle 50. Here, the position of the vehicle 50 refers to the position of the center of gravity 50A of the vehicle, but may also be the center position of the vehicle in a plan view. The lateral position of the vehicle, which will be described later, refers to the position of the center of gravity of the vehicle in the lane width direction, and the lateral speed of the vehicle refers to the speed of the center of gravity of the vehicle in the lane width direction. These are found based on the relative positional relationship between the white lines detected by the camera sensor 11 and the vehicle.

[0022] The radar sensor 12 includes a radar transmitting / receiving unit and a signal processing unit (not shown), and the radar transmitting / receiving unit emits millimeter-wave band radio waves (hereinafter referred to as "millimeter waves") and receives millimeter waves (i.e., reflected waves) reflected by three-dimensional objects (e.g., other vehicles, bicycles, guardrails, roadside structures, etc.) within the emission range. The signal processing unit acquires information (hereinafter referred to as peripheral information) indicating the distance between the vehicle and the three-dimensional object, the relative speed between the vehicle and the three-dimensional object, the relative position (direction) of the three-dimensional object with respect to the vehicle, etc., based on the phase difference between the transmitted millimeter waves and the received reflected waves, the attenuation level of the reflected waves, and the time from transmitting the millimeter waves to receiving the reflected waves, and supplies the information to the LDA·ECU 10 at predetermined time intervals.

[0023] The in-vehicle camera sensor 13 is installed in front of the driver's seat and captures the face of the driver. A plurality of camera sensors 13 may be provided so as to capture the driver from a plurality of directions. The vehicle includes a camera unit and a determination unit that determines the degree of eye opening, the direction of gaze, the speed of blinking, etc. of the driver by a recognition process of the face image captured by the camera unit. The image recognition process may be a known pattern recognition method such as a neural network or a support vector machine. In this embodiment, the determination unit determines that the driver's level of awakening is higher when the driver's level of eye opening is larger, the speed of movement in the direction of gaze is faster, and the driver blinks faster. The camera sensor 13 functions as an awakening state detection device that detects the awakening state of the driver as described later.

[0024] The vehicle speed sensor 14 detects the vehicle speed V of the vehicle 50, and repeatedly supplies a signal indicating the vehicle speed V to the LDA·ECU 10 at a predetermined control period. The LDA switch 15 is operated by the driver, and supplies a signal indicating whether it is on or off to the LDA·ECU 10. The fact that the LDA switch 15 is on means that lane departure prevention control is being executed according to the flowchart shown in FIG.

[0025] The warning device 16 is activated when the LDA·ECU 10 determines that the vehicle 50 is at risk of deviating from the lane 54, and issues a warning as one of the lane departure prevention controls, i.e., issues a warning that the vehicle 50 is at risk of deviating from the lane. The warning device 16 may be any of a warning device that issues a visual warning such as a warning lamp, a warning device that issues an auditory warning such as a warning buzzer, a warning device that issues a tactile warning such as seat vibration, or any combination thereof.

[0026] The EPS·ECU 20 can steer the steered wheels 24 as necessary by controlling the EPS device 22. Thus, the EPS·ECU 20 and the EPS device 22 constitute a steering device 26 that automatically steers the steered wheels 24 as necessary. When the LDA·ECU 10 determines that the vehicle 50 is at risk of deviating from its lane, the EPS·ECU 20 performs automatic steering of the steered wheels 24 to prevent the vehicle from deviating from its lane, as another type of lane departure prevention control.

[0027] 1, a steering shaft 30 to which a steering wheel 28 operated by a driver is integrally connected is provided with a torque sensor 32 for detecting a steering torque Ts and a steering angle sensor 34 for detecting a steering angle θ. A signal indicative of the steering torque Ts detected by the torque sensor 32 and a signal indicative of the steering angle θ detected by the steering angle sensor 34 are input to the EPS·ECU 20. The steering wheel 28 is a steering input device, and the torque sensor 32 functions as a gripping condition detection device for detecting the gripping condition of the steering wheel 28 by the driver, as described later. In this embodiment, the steering torque Ts and the steering angle θ are positive values ​​when the vehicle 50 turns left, and negative values ​​when the vehicle turns right.

[0028] The EPS·ECU 22 controls the steering assist torque and reduces the steering burden on the driver by controlling the EPS device 22 in a manner known in the art based on the steering torque Ts and the vehicle speed V detected by the vehicle speed sensor 14. A signal indicating the steering torque Ts is input from the EPS·ECU 20 to the LDA·ECU 10 via the CAN 52.

[0029] <Lane Departure Prevention Control Routine> Next, a lane departure prevention control routine in this embodiment will be described with reference to the flowchart shown in Fig. 2. The lane departure prevention control according to the flowchart shown in Fig. 2 is repeatedly executed by the CPU of the LDA·ECU 10 at a predetermined control period when the LDA switch 15 is on. In the following description, the lane departure prevention control will simply be referred to as "control".

[0030] First, in step S10, the CPU determines whether or not there is a possibility that the vehicle will deviate from the lane, based on the relative positional relationship of the vehicle 50 with respect to the lane 54 detected by the exterior image capturing camera sensor 11. If the CPU determines that the vehicle is likely to deviate from the lane, it temporarily ends the control, and if the CPU determines that the vehicle is likely to deviate from the lane, it advances the control to step S20.

[0031] In this case, the determination of whether or not there is a possibility that the vehicle 50 will deviate from the lane may be performed, for example, in the following manner. First, as shown in Fig. 4, an angle (inclination angle) θy between the longitudinal direction 60 of the lane 54 and the vehicle's traveling direction 62 is estimated based on image information of the front of the vehicle 50. A moving speed Vy of the vehicle 50 in a direction perpendicular to the longitudinal direction 60 of the lane 54 is estimated as Vsinθy based on the angle θy and the vehicle speed V. Note that the angle θy is the same as the inclination angle with respect to the white lines 56L and 56R, and is therefore also the skew angle of the vehicle 50.

[0032] Also, a distance Dy (not shown) in the lane width direction between the white line 56L (lane boundary) on the side where the vehicle 50 is approaching and the center of gravity 50A of the vehicle is estimated. Furthermore, when the judgment distance ΔDy (=Dy-VyΔt) is equal to or less than a preset reference value Dycp (a positive constant), where Δt is a preset time, it is determined that the vehicle 50 may deviate from the lane.

[0033] In step S20, the CPU determines whether the driver's wakefulness determined by the in-vehicle camera 13 is equal to or higher than a reference value, that is, whether the driver is wakeful. If the CPU makes a positive determination, the control proceeds to step S30, and if the CPU makes a negative determination, that is, if the CPU determines that the driver is not wakeful, the control proceeds to step S40.

[0034] In step S30, the CPU sets the reference values ​​Tsc and Tnc for the hands-off determination performed in step S50 described later to standard values ​​Tscn and Tncn, respectively, by referring to the maps shown by solid lines in Figures 5 and 6 based on the vehicle speed V.

[0035] In step S40, the CPU refers to the maps shown by dashed lines in Figures 5 and 6 based on the vehicle speed V, and sets the reference value Tsc for the hands-off determination performed in step S50 described later to a relaxed value Tsch that is greater than the standard value Tscn, and sets the reference value Tnc to a relaxed value Tncr that is smaller than the standard value Tncn.

[0036] The standard value Tscn and the relaxation value Tsch may be positive constants. However, the steering resistance when the steered wheels are turned by the steering operation of the driver becomes smaller as the vehicle speed V increases. Therefore, as shown in Fig. 5, the standard value Tscn and the relaxation value Tsch are variably set according to the vehicle speed so that the standard value Tscn and the relaxation value Tsch become smaller as the vehicle speed V increases.

[0037] The standard value Tncn and the relaxation value Tncr may be positive constants. However, the higher the vehicle speed V, the earlier the risk of the vehicle 50 deviating from the lane due to the driver's hands being off the handlebars increases, so it is preferable that the driver's hands being off the handlebars be detected earlier as the vehicle speed V is higher. Therefore, as shown in Fig. 6, the standard value Tncn and the relaxation value Tncr are variably set according to the vehicle speed so as to become smaller as the vehicle speed V is higher.

[0038] In step S50, the CPU determines whether or not the driver has let go of the handlebars in accordance with the hands-off determination routine shown in the flowchart of Fig. 3. If the CPU makes a positive determination, the control proceeds to step S70, and if the CPU makes a negative determination, the control proceeds to step S60.

[0039] In step S60, the CPU sets a reference value Dyc for determining whether or not there is a risk of lane departure, which is performed in step S80 described below, to a standard value Dycn. The standard value Dycn is a positive constant smaller than the reference value Dycp in step S10.

[0040] In step S70, the CPU sets the reference value Dyc for determining whether or not there is a risk of lane departure, which is performed in step S80 described below, to a relaxation value Dych, which is a positive constant that is greater than the standard value Dycn and smaller than the reference value Dycp.

[0041] In step S80, the CPU determines whether or not there is a risk that the vehicle 50 will deviate from the lane by determining whether or not the determination distance ΔDy (=Dy-VyΔt) is equal to or less than the reference value Dyc. If the CPU makes a negative determination, it temporarily terminates control, and if the CPU makes a positive determination, it proceeds to step S90. Note that if the CPU makes a negative determination while the lane departure prevention control described below is being executed, it terminates lane departure prevention control.

[0042] In step S90, the CPU executes lane departure prevention control. That is, the CPU activates the warning device 16 to issue a warning that the vehicle 50 is at risk of departing from the lane. The CPU also outputs an automatic steering command signal to the EPS·ECU 22, causing the EPS device 22 to automatically steer the steered wheels 24 so that the vehicle 50 does not deviate from the lane.

[0043] <Hands-off Judgment Routine> Next, a hands-off determination routine in this embodiment will be described with reference to the flowchart shown in FIG.

[0044] In step S51, the CPU determines whether the absolute value of the steering torque Ts is less than the reference value Tsc set in step S30 or S40. When the CPU makes a negative determination, it resets the release continuation time Tn to 0 in step S51. On the other hand, when the CPU makes an affirmative determination, it sets the previous value of the release continuation time Tn as Tnf, sets the cycle time of the release determination routine shown in FIG. 2 as ΔT, and increments the release continuation time Tn to Tnf + ΔT in step S52.

[0045] In step S54, the CPU determines whether the release continuation time Tn exceeds the reference value Tnc set in step S30 or S40. When the CPU makes a negative determination, it determines in step S55 that the driver has not released the steering wheel, and when it makes an affirmative determination, it determines in step S56 that the driver has released the steering wheel.

[0046] <Operation of the Embodiment> The operation of the embodiment will be described for various cases where the vehicle may deviate from the lane and an affirmative determination is made in step S10, and where the driver's arousal level and whether the driver has released the steering wheel are different.

[0047] <C1. When the driver is awake and has not released the steering wheel> In step S20, since an affirmative determination is made, in step S30, the reference values Tsc and Tnc for release determination are set to the standard values Tscn and Tncn, respectively. In step S50, since a negative determination is made, in step S60, the reference value Dyc for the determination of the risk of lane departure is set to the standard value Dycn. Note that if it is determined in step S80 that the determination distance ΔDy is less than or equal to the reference value Dyc (= Dycn), lane departure prevention control is executed in step S90.

[0048] <C2. When the driver is awake but has released the steering wheel> Similar to the case of C1 above, in step S20, since an affirmative determination is made, in step S30, the release determination reference values Tsc and Tnc are set to the standard values Tscn and Tncn, respectively. However, since an affirmative determination is made in step S50, in step S70, the lane departure risk determination reference value Dyc is set to a relaxation value Dych that is a positive constant greater than the standard value Dycn. Therefore, since it becomes easier to determine that the determination distance ΔDy is less than or equal to the reference value Dyc (= Dych), lane departure prevention control is started earlier in step S90 compared to the case of C1 above.

[0049] <C3. When the driver is not awake and has not released the steering wheel> In step S20, a negative determination is made, and in step S40, the release determination reference value Tsc is set to a relaxation value Tsch that is greater than the standard value Tscn, and the reference value Tnc is set to a relaxation value Tncr that is less than the standard value Tncn. Therefore, it becomes easier to make an affirmative determination in steps S51 and S54, but in step S50, it is determined that the driver has not released the steering wheel.

[0050] Similar to the case of C1 above, in step S60, the lane departure risk determination reference value Dyc is set to the standard value Dycn. Note that if it is determined in step S80 that the determination distance ΔDy is less than or equal to the reference value Dyc (= Dycn), lane departure prevention control is executed in step S90.

[0051] <C4. When the driver is not awake and has released the steering wheel> Similar to the case of C3 above, in step S20, a negative determination is made, and in step S40, the release determination reference value Tsc is set to a relaxation value Tsch that is greater than the standard value Tscn, and the reference value Tnc is set to a relaxation value Tncr that is less than the standard value Tncn. Therefore, since it becomes easier to make an affirmative determination in steps S51 and S54, it is determined earlier in step S50 that the driver has released the steering wheel compared to the case of C1 above.

[0052] Furthermore, in step S70, the reference value Dyc for determining the risk of lane departure is set to a relaxation value Dych, which is a positive constant greater than the standard value Dycn. Therefore, it becomes easier to determine that the determination distance ΔDy is equal to or smaller than the reference value Dyc (=Dych), and therefore lane departure prevention control is started earlier than in the above cases C1 to C3.

[0053] 7 shows a situation in which the hands-off duration Tn increases continuously and becomes gradually larger than the relaxed value Tncr and the standard value Tncn as the reference value Tnc. When the reference value Tnc is the standard value Tncn, the determination in step S54 becomes positive at the time t2 when the hands-off duration Tn exceeds the standard value Tncn, and it is determined that the driver has let go of the hands.

[0054] On the other hand, when the reference value Tnc is the relaxation value Tncr, the determination in step S54 becomes positive at time t1 when the hands-off duration Tn exceeds the relaxation value Tncr, and it is determined that the driver has let go of the hands. Since the relaxation value Tncr is smaller than the standard value Tncn, time t1 is earlier than time t2. In other words, when the reference value Tnc is the relaxation value Tncr, it can be determined that the driver has let go of the hands earlier than when the reference value Tnc is the standard value Tncn.

[0055] 8 shows a situation in which the judgment distance Dy is continuously decreased and successively becomes smaller than the reference value Dycp, the mitigation value Dych, and the standard value Dycn. If the reference value Dyc is the mitigation value Dych after time t3 when the judgment distance Dy becomes smaller than the reference value Dycp, the judgment in step S80 becomes positive at time t4 when the judgment distance Dy becomes equal to or smaller than the mitigation value Dych, and lane departure prevention control is started.

[0056] In contrast, when the reference value Dyc is the standard value Dycn, the determination in step S80 becomes positive at time t5 when the reference value Dyc becomes equal to or less than the standard value Dycn, and lane departure prevention control is started. Since the mitigation value Dych is greater than the standard value Dycn, time t4 is earlier than time t5. In other words, when the reference value Dyc is the mitigation value Dych, lane departure prevention control can be started earlier than when the reference value Dyc is the standard value Dycn.

[0057] As can be seen from the above explanation, when it is determined that the driver has let go of the steering wheel (S50), the conditions for determining the risk of lane departure are relaxed (S70) compared to when it is determined that the driver has not let go of the steering wheel, and lane departure prevention control is executed earlier (S80, S90). Furthermore, when it is determined that the driver is not awake (S20), the conditions for determining that the driver has let go of the steering wheel are relaxed (S40), making it easier to determine that the driver has let go of the steering wheel.

[0058] Therefore, when the driver is not awake, it is more likely that the driver has let go of the handlebars, and therefore, when the driver is not awake, it is determined that the driver has let go of the handlebars earlier than when the driver is awake. Therefore, when the driver is not awake and has let go of the handlebars, lane departure prevention control is started earlier than when the driver's awareness is not taken into consideration, and the risk of the vehicle 50 leaving the lane can be effectively reduced.

[0059] 5, the standard value Tscn and the relaxation value Tsch are variably set according to the vehicle speed so as to become smaller as the vehicle speed V increases. Therefore, it is possible to more appropriately determine whether the driver has released the hands, compared to a case in which the standard value Tscn and the relaxation value Tsch are constant regardless of the vehicle speed.

[0060] 6, the standard value Tncn and the relaxation value Tncr are variably set according to the vehicle speed so as to be smaller as the vehicle speed V increases. Therefore, it is possible to more appropriately determine whether the driver has released the hands, compared to a case in which the standard value Tncn and the relaxation value Tncr are constant regardless of the vehicle speed.

[0061] Although the present invention has been described in detail above with reference to specific embodiments, it will be apparent to those skilled in the art that the present invention is not limited to the above-described embodiments, and that various other embodiments are possible within the scope of the present invention.

[0062] For example, in the above-described embodiment, lane departure prevention control involves issuance of a warning by activation of the warning device 16 and automatic steering of the steered wheels 24 by the EPS device 22. However, one of the issuance of a warning and the automatic steering of the steered wheels 24 may be omitted.

[0063] Furthermore, in the above-described embodiment, when a positive determination is made in step S80, issuance of a warning and automatic steering of the steered wheels 24 are started simultaneously. However, the above may be modified so that issuance of a warning is started when it is determined that the determination distance ΔDy is equal to or less than a warning reference value, and automatic steering of the steered wheels 24 is started when it is determined that the determination distance ΔDy is equal to or less than a reference value for automatic steering that is smaller than the warning reference value.

[0064] In the above embodiment, the standard value Tscn and the relaxation value Tsch are variably set according to the vehicle speed so as to be smaller as the vehicle speed V increases. However, at least one of the standard value Tscn and the relaxation value Tsch may be constant regardless of the vehicle speed.

[0065] In the above embodiment, the standard value Tncn and the relaxation value Tncr are variably set according to the vehicle speed so as to be smaller as the vehicle speed V increases. However, at least one of the standard value Tncn and the relaxation value Tncr may be constant regardless of the vehicle speed.

[0066] In the above embodiment, the determination of whether the driver has let go of the steering wheel in step S50 is based on the duration Tn of the state in which the absolute value of the steering torque Ts is less than the reference value Tsc. However, the determination of whether the driver has let go of the steering wheel may be performed by determining whether the moving average value of the absolute value of the steering torque Ts over a predetermined time is less than the reference value. In that case, when it is determined that the driver is not awake, the conditions for determining whether the driver has let go of the steering wheel may be relaxed by at least one of shortening the predetermined time and increasing the reference value so that it is easier to determine that the driver has let go of the steering wheel.

[0067] Furthermore, the grip force of the steering wheel 28 by the driver may be detected by a grip sensor, and the determination of whether the driver has let go may be made by determining whether the moving average value of the grip force over a predetermined time is less than a reference value. In this case, when it is determined that the driver is not awake, the conditions for determining whether the driver has let go may be relaxed by at least one of shortening the predetermined time and increasing the reference value so that it is easier to determine that the driver has let go. [Explanation of symbols]

[0068] 10...Lane departure prevention ECU (LDA·ECU), 11...Exterior camera sensor, 12...Radar sensor, 13...Interior camera sensor, 14...Vehicle speed sensor, 16...Alarm device, 20...Electric power steering ECU (EPS·ECU), 22...EPS device, 24...Steering wheel, 28...Steering wheel, 32...Torque sensor, 34...Steering angle sensor, 50...Vehicle, 54...Lane, 56L, 56R...White line, 100...Lane departure prevention device

Claims

[Claim 1] a vehicle position detection device that detects a position of a vehicle relative to a lane; a gripping condition detection device that detects a driver's gripping condition with respect to a steering input device; and a control unit configured to execute at least one of lane departure prevention control of automatic steering of steered wheels and issuance of an alarm when it is determined that the vehicle is at risk of deviating from the lane based on the position of the vehicle detected by the vehicle position detection device, wherein the control unit is configured to execute the lane departure prevention control earlier when it is determined that the driver has let go of the steering wheel based on the gripping condition detected by the gripping condition detection device than when it is determined that the driver has not let go of the steering wheel, the control unit is configured to determine that the driver has let go of the steering wheel when it is determined that a time during which an absolute value of the steering torque detected by the gripping state detection device is less than a reference torque exceeds a reference time, The lane departure prevention device further includes an awakening state detection device that detects the driver's awakening state, and the control unit variably sets the reference torque and the reference time according to the vehicle speed so that the higher the vehicle speed, the smaller the reference torque and the reference time.When it is determined that the driver is not awake based on the driver's awakening state detected by the awakening state detection device, the control unit increases the reference torque and decreases the reference time to relax the conditions for determining whether the driver has let go of the hands, thereby making it easier to determine that the driver has let go of the hands of the vehicle.

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