Driving support apparatus for vehicle

Abstract

To properly degenerate assist torque.SOLUTION: Assist torque for maintaining a vehicle in a traveling lane or bringing the vehicle close to the center of the traveling lane is set to support steering performed by a driver, and assist torque degeneration processing for bringing the assist torque close to 0 with the lapse of time is performed. Curvatures of a road on which a vehicle is traveling or road shape parameters which are indexes related to the curvatures are detected (road shape detection part B117), and degeneration characteristics which are characteristics of changes drawn by assist torque when assist torque degeneration processing is performed are made different according to the road shape parameters (assist torque degeneration processing part B113).SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a driving assistance device for a vehicle. [Background technology]

[0002] There is a technology that applies an assist torque generated by an electric motor to the steering wheel (also called the steering wheel) located at the driver's seat to keep the vehicle near the center of the lane it is traveling in or prevent the vehicle from deviating from the lane it is traveling in. If the driver applies torque in the opposite direction to the assist torque while it is being generated, a degeneration process is performed to reduce the assist torque. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-072021 Summary of the Invention [Problem to be solved by the invention]

[0004] When the reduction of the assist torque by the reduction process (hereinafter referred to as "reducing the assist torque") is performed uniformly, the following problem occurs.

[0005] If the reduction in assist torque is sudden and the amount of reduction in assist torque is large, the sudden loss of assist torque is likely to cause excessive steering, resulting in a sudden change in vehicle behavior.

[0006] On the other hand, if the reduction of the assist torque is slow and the amount of reduction of the assist torque is small, resistance to the driver's steering (hereinafter referred to as a "wall feeling") is likely to remain, resulting in a deterioration in the steering feel.

[0007] Therefore, an object of the present invention is to provide a driving assistance device for a vehicle that can appropriately perform the reduction of the assist torque. [Means for solving the problem]

[0008] In order to solve the above problems, a driving assistance device for a vehicle according to one aspect of the present invention includes an assist torque setting means for setting an assist torque that keeps the vehicle in a current lane or moves the vehicle closer to the center of the lane, and a road shape detection means for detecting the curvature of the road on which the vehicle is traveling or a road shape parameter that is an index related thereto. The assist torque setting means performs an assist torque reduction process that reduces the assist torque to zero over time, and varies a reduction characteristic, which is a characteristic of the change in the assist torque when the assist torque reduction process is performed, depending on the road shape parameter detected by the road shape detection means. [Effects of the Invention]

[0009] According to one aspect of the present invention, by detecting road shape parameters and varying the characteristics of the change in the assist torque (i.e., the degeneration characteristics) when performing the assist torque degeneration process depending on the driving shape parameters, it is possible to appropriately degenerate the assist torque and prevent situations in which a sudden degeneration of the assist torque causes a sudden change in the vehicle behavior or a slow degeneration of the assist torque causes a deterioration in the steering feel. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing the configuration of a vehicle driving assistance device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a schematic diagram illustrating an internal configuration of a controller according to the embodiment. [Figure 3] 3 is a flowchart showing a basic flow of driving assistance control according to the embodiment; [Figure 4] 6 is a flowchart showing specific content of an assist torque reduction process according to the embodiment; [Figure 5] 10A and 10B are explanatory diagrams showing changes in assist torque due to the assist torque reduction process in (a) normal operation, (b) when traveling on a curved road, and (c) when traveling on a straight road. [Figure 6] 10 is an explanatory diagram showing an example of the behavior of a vehicle when an assist torque degeneration process is performed, when the vehicle is traveling on a straight road. FIG. [Figure 7] 10A and 10B are explanatory diagrams showing an example of the behavior of a vehicle when an assist torque reduction process is performed, when the vehicle is traveling on a curved road. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0012] (Overall configuration of driving assistance system) FIG. 1 is a schematic diagram showing the configuration of a vehicle driving assistance device 1 according to one embodiment of the present invention.

[0013] The vehicle driving assistance device 1 includes, as main elements related to this embodiment, a controller 101, a front camera 111, a rear camera 112, a steering angle sensor 113, a steering sensor 114, an acceleration sensor 115, a turn signal switch 116, and a system start switch 117, as well as a steering assist motor 201 and an HMI device 301.

[0014] The controller 101 constitutes the calculation unit of the driving assistance device 1. The controller 101 is configured by a microcomputer equipped with a central processing unit (CPU), an input / output interface, and storage devices such as ROM and RAM, and performs predetermined calculations related to driving assistance control based on predetermined control information acquired via various sensors 111 to 115 and a switch 116, and generates a command signal according to the result of the calculation. The controller 101 then outputs the command signal to a steering assist motor 201 and an HMI (human-machine interface) device 301, which will be described later.

[0015] The front camera 111, together with the rear camera 112 and various other sensors 112 to 115 and a switch 116, constitutes the detection unit of the driving assistance device 1. The front camera 111 has a field of view set in front of the vehicle, and analyzes the captured image to detect the presence of obstacles and the like ahead. In addition, the front camera 111 calculates the curvature of the road on which the vehicle is traveling by analyzing the image, and outputs the calculated curvature as control information. The curvature of the road can be determined not only by the front camera 111 but also from road map information stored in an in-vehicle navigation system (not shown).

[0016] The rear camera 112 has a field of view behind and diagonally behind the vehicle, and monitors the blind spots of the vehicle in the lane in which the vehicle is traveling and in adjacent lanes. Based on the images captured by the rear camera 112, it is possible to detect the presence of another vehicle in the blind spot of the vehicle. Furthermore, the rear camera 112 can also detect the presence of another vehicle approaching the vehicle in an attempt to overtake it or traveling alongside the vehicle. The rear camera 112 can also be replaced by an external sensor included in a blind spot monitor, specifically, an ultrasonic sensor or millimeter-wave radar sensor installed facing the rear or diagonally rear of the vehicle.

[0017] The steering angle sensor 113 detects the steering angle of the vehicle. Here, the steering angle refers to the actual direction of the wheels relative to the longitudinal direction of the vehicle body.

[0018] The steering sensor 114 detects the torque applied to the steering wheel by the driver (the torque applied to the steering wheel by the driver when steering is hereinafter referred to as "steering torque"). In this embodiment, based on the steering torque, the steering wheel operation status by the driver, specifically, whether the driver is gripping the steering wheel firmly and operating it proactively, or gripping it loosely and operating it passively, is determined.

[0019] The acceleration sensor 115 detects acceleration acting on the vehicle body around each of the front-rear, left-right, and up-down axes of the vehicle. In this embodiment, the acceleration sensor 115 detects the orientation of the vehicle relative to the straight-ahead direction.

[0020] The blinker switch 116 outputs a signal according to the operating status of a turn signal (hereinafter referred to as "blinker") provided on the vehicle. When the driver operates the blinker to issue a right or left direction instruction, the blinker switch 116 outputs a signal indicating that the blinker is operating. In this embodiment, the output signal from the blinker switch 116 is used as an indicator of the driver's intention to change lanes.

[0021] The system activation switch 117 outputs a signal instructing the controller 101 to perform and stop driving assistance control. The controller 101 performs and stops driving assistance control in response to the output signal from the system activation switch 117.

[0022] In addition to the above, the driving assistance device 1 includes a steering assist motor 201 and an HMI device 301 as output units.

[0023] The steering assist motor 201 operates in response to a command signal from the controller 101, and outputs a motor torque corresponding to the assist torque. In this embodiment, for ease of explanation, it is assumed that the assist torque applied to the steering wheel is equal to the motor torque that should be output from the steering assist motor 201 to generate the assist torque. The steering assist motor 201 is composed of an electric motor and its drive circuit.

[0024] The HMI device 301 has various buttons that can be operated by the driver, and a display unit that displays indicators to prompt the driver to recognize the situation, to pay attention, and to take action. The display unit of the HMI device 301 includes indicator lights that display the operating status of various controls such as traction control and vehicle stability control, and various devices such as the immobilizer, as well as warning lights that warn the driver when the seat belt is not fastened or when the fuel level is low. The HMI device 301 may also include an alarm that works in conjunction with the warning lights to prompt the driver to recognize the warning by providing auditory information.

[0025] In addition to the above, the HMI device 301 displays an indicator indicating that driving assist control is being performed and an indicator indicating that assist torque reduction processing is being performed. These indicators allow the driver to recognize that assist torque is being applied to the steering wheel and that the assist torque is being reduced due to reduction.

[0026] (Internal structure of the controller) FIG. 2 is a schematic diagram showing the internal configuration of the controller 101 according to this embodiment.

[0027] The controller 101 includes a lane change intention detection unit B111, a degeneration condition determination unit B112, a basic assist torque calculation unit B113, an assist torque degeneration processing unit B114, an assist motor drive unit B115, a required steering torque setting unit B116, a steering torque detection unit B117, a road shape detection unit B118, and a blind spot monitoring unit B119. The controller 101 reads out a control computer program stored in a storage device and executes instructions indicated by this program using a central processing unit, thereby realizing the functions of each of these units in software.

[0028] The lane change intention detection unit B111 determines, based on the output signal from the blinker switch 116, whether or not the driver has an intention to change lanes (hereinafter referred to as "lane change intention").

[0029] The degeneration condition determination unit B112 determines whether or not a condition for performing the assist torque degeneration process (hereinafter referred to as a "degeneration implementation condition") is met, based on the output from the lane change intention detection unit B111 and the output signal from the system activation switch 117. In this embodiment, the degeneration implementation condition includes the driver having the intention to change lanes and the system activation switch 117 being switched from an on state to an off state. In other words, the driving assistance device 1 not only performs the assist torque degeneration process when the vehicle changes lanes, but also when halting the implementation of driving assistance control.

[0030] The basic assist torque calculation unit B113 sets a basic value (hereinafter referred to as "basic assist torque") ASSb of the assist torque ASS based on the output signal from the steering angle sensor 113, the outputs from the required steering torque setting unit B116 and the steering torque detection unit B117. The basic assist torque calculation unit B113 sets the basic assist torque ASS as the difference between the required steering torque Tstr and the steering torque STR, which will be described later. That is, according to the following equation (1): ASSb = Tstr - STR … (1)

[0031] The assist torque degradation processing unit B114 performs the assist torque degradation processing in accordance with the output from the degradation condition determination unit B112. Specifically, when the degradation condition determination unit B112 detects that the degradation condition is met, for example, when the driver indicates his / her intention to change lanes by operating a turn signal and the lane change intention detection unit B111 detects this intention, or when the driver switches the system activation switch 117 to the OFF state, the assist torque degradation processing unit B114 performs the assist torque degradation processing. On the other hand, when the driver keeps the system activation switch 117 in the ON state and the turn signal is not activated, the execution of the assist torque degradation processing is suspended. In this embodiment, the specific content of the assist torque degradation processing is based on the outputs from the required steering torque setting unit B116, the steering torque detection unit B117, and the road shape detection unit B118. The details of the assist torque degradation processing will be described later with reference to the flowchart shown in FIG. 4.

[0032] The assist motor drive unit B115 sets the assist torque ASSd after the processing by the assist torque reduction processing, i.e., after reduction, as the final assist torque ASS, and generates and outputs a command signal to the steering assist motor 201 according to the assist torque ASS. The command signal from the assist motor drive unit B115 is received as an input signal by the drive circuit of the steering assist motor 201.

[0033] The required steering torque setting unit B116 sets the required steering torque Tstr based on output signals from the front camera 111, the steering angle sensor 113, and the acceleration sensor 115. The required steering torque Tstr is the torque that should be applied to the steering wheel to bring the vehicle closer to the center of the lane when the vehicle deviates to the left or right from the center of the lane in which it is traveling. When the front camera 111 detects that the vehicle has deviated from the center of the lane, the required steering torque setting unit B116 calculates and sets the required steering torque Tstr based on the direction of the vehicle and the steering angle θstr. The direction of the vehicle refers to the direction of the vehicle relative to the straight-ahead direction, and is detected by the acceleration sensor 115 as the rotation angle of the vehicle relative to the center line of the lane.

[0034] The steering torque detection unit B117 detects the steering torque STR based on the output signal from the steering sensor 114.

[0035] The road shape detection unit B118 detects the road type, i.e., whether the road on which the vehicle is traveling is a straight road or a curved road, based on the output signal from the front camera 111. Specifically, the road curvature, for example, the curvature of the road center line, is detected from the image captured by the front camera 111. If the road curvature is small, the road on which the vehicle is traveling is determined to be a straight road, and if the road curvature is large, the road on which the vehicle is traveling is determined to be a curved road. Here, the road type is an index related to the curvature of the road, that is, an example of a road shape parameter.

[0036] When the driver indicates an intention to change lanes, the blind spot monitoring unit B119 monitors the blind spot diagonally behind the vehicle, specifically, the blind spot of the host vehicle in the lane after the lane change or in an adjacent lane between the current lane and the lane after the lane change, based on the output signal from the rear camera 112. When the blind spot monitoring unit B119 detects the presence of another vehicle approaching the host vehicle or traveling alongside the host vehicle in this blind spot, it generates a signal indicating the presence of the other vehicle in the blind spot. The blind spot monitoring unit B119 then outputs the generated signal to the HMI device 301 and to the assist torque degeneration processing unit B114.

[0037] The HMI device 301 operates in response to output signals from the assist torque reduction processing unit B114 and the blind spot monitoring unit B119, displays an indicator indicating that the assist torque reduction processing is being performed, and stops displaying the indicator when the assist torque reduction processing is terminated or its execution is stopped.

[0038] (Driving assistance control details) Fig. 3 is a flowchart showing the basic flow of driving assist control according to this embodiment, and Fig. 4 is a flowchart showing the specific contents of the assist torque degeneration process in the driving assist control. The controller 101 repeatedly executes the driving assist control at predetermined time intervals after the system is started by turning on the system start switch 117.

[0039] As driving assistance control, the controller 101 sets an assist torque for keeping the vehicle near the center of the lane in which the vehicle is traveling, applies this to the steering wheel provided at the driver's seat, and also controls the reduction of the assist torque performed when changing lanes to be coordinated with the actual steering operation by the driver. Specifically, the time taken for the reduction of the assist torque is varied depending on the effect that the reduction of the assist torque has on the behavior of the vehicle, and the reduction of the assist torque is performed quickly in a short time in situations where the effect is estimated to be small, while the reduction is performed gradually over a long time in situations where the effect is estimated to be large.

[0040] In the flowchart shown in FIG. 3, in S111, various control information used for the driving assist control according to this embodiment, such as the steering angle θstr and steering torque STR of the vehicle, is read.

[0041] In S112, a target steering angle θtrg is set to move the vehicle closer to the center of the lane. The setting of the target steering angle θtrg is based on the direction of the vehicle's departure from the center of the lane and the orientation of the vehicle relative to the straight-ahead direction. The direction of the vehicle's departure can be detected by the front camera 111, and the orientation of the vehicle can be detected by the acceleration sensor 115.

[0042] In S113, the required steering torque Tstr is calculated. The calculation of the required steering torque Tstr is based on the target steering angle θtrg and the actual steering angle θstr of the vehicle. The steering angle θstr of the vehicle can be detected by the steering angle sensor 113.

[0043] In step S114, the basic assist torque ASSb is calculated by subtracting the steering torque STR from the required steering torque Tstr using the above equation (1).

[0044] In S115, it is determined whether the degeneration implementation condition is satisfied. If it is determined that the degeneration implementation condition is satisfied, for example, if the blinker is activated and the driver intends to change lanes, the process proceeds to S116, and if it is determined that the degeneration implementation condition is not satisfied, the process proceeds to S117. As described above, the degeneration implementation condition is satisfied when the driver intends to change lanes or when the system activation switch 117 is switched from the on state to the off state.

[0045] In step S116, the assist torque reduction process is carried out in accordance with the procedure shown in the flowchart of FIG.

[0046] In S117, the basic assist torque ASSb is set to the final assist torque ASS.

[0047] In S118, a command signal according to the assist torque ASS is output to the drive circuit of the steering assist motor 201, causing the steering assist motor 201 to generate the assist torque ASS, which is applied to the steering wheel.

[0048] In the flowchart shown in Fig. 4, in S211, it is determined whether the blinkers are on. In other words, it is determined whether the degeneration implementation condition in the previous S115 is met because the driver has an intention to change lanes. If the blinkers are on, it is determined that the degeneration implementation condition is met because the driver has an intention to change lanes, and the process proceeds to S212. If the blinkers are not on, it is determined that another degeneration implementation condition is met, specifically, because the system activation switch 117 has been switched off, and the process proceeds to S214.

[0049] In S212, it is determined whether or not another vehicle is present in the blind spot diagonally rearward of the vehicle. Detection of another vehicle in the blind spot is possible based on the output signal from the rear sensor 112. If the presence of another vehicle in the blind spot is not detected, the process proceeds to S213, where assist torque reduction processing is performed using early reduction characteristics according to the road type. On the other hand, if the presence of another vehicle in the blind spot is detected, the process proceeds to S214, where assist torque reduction processing is performed using standard reduction characteristics. In this embodiment, the assist torque reduction processing is a process that reduces the assist torque to 0 over time, and is started when a reduction execution condition is met while the assist torque is being generated.

[0050] In S213, it is determined whether the road on which the vehicle is traveling is a straight road. Whether the road on which the vehicle is traveling is a straight road can be determined by analyzing an image captured by the forward sensor 111. In this embodiment, the curvature of the road on which the vehicle is traveling is detected, and if the curvature of the road is equal to or less than a predetermined first threshold (in other words, if the radius of curvature of the road is equal to or greater than a predetermined second threshold), it is determined that the road on which the vehicle is traveling is a straight road. On the other hand, if the curvature of the road is greater than the predetermined first threshold (in other words, if the radius of curvature of the road is smaller than the predetermined second threshold), it is determined that the road on which the vehicle is traveling is a curved road. If it is determined that the road on which the vehicle is traveling is a straight road, the process proceeds to S215, and if it is determined that the road is a curved road, the process proceeds to S216.

[0051] In S214, the normal assist torque degeneration diagram is selected as a diagram that defines the characteristics of the change that the assist torque makes when it is degenerated (that is, the degeneration characteristics).

[0052] In S215, the assist torque degeneration diagram for straight road running is selected as the diagram that determines the degeneration characteristics of the assist torque.

[0053] In S216, the assist torque degeneration diagram for traveling on a curved road is selected as the diagram that determines the degeneration characteristics of the assist torque.

[0054] Here, the assist torque degeneration diagram and the difference in degeneration characteristics depending on the road type will be described.

[0055] Fig. 5 is an explanatory diagram showing assist torque degeneration diagrams for (a) normal use, (b) curved road running, and (c) straight road running, respectively. That is, Fig. 5(a) shows the assist torque degeneration diagram for normal use, Fig. 5(b) shows the assist torque degeneration diagram for curved road running, and Fig. 5(c) shows the assist torque degeneration diagram for straight road running.

[0056] In each of Figures 5(b) and 5(c), the basic degenerate line diagram for each road type is shown by a solid line. The dashed lines show the shortened degenerate line diagram according to the driver's steering operation status. The shortened degenerate line diagram will be explained in detail later.

[0057] As described above, in this embodiment, the assist torque reduction process reduces the assist torque from the assist torque at the start of the process to 0 over time. That is, the assist torque reduction process ends when the assist torque reduces and reaches 0 (times T31, T32, T33) after the reduction implementation condition is met (time T0). Figure 5 shows the time ΔTdgn1 spent on reducing the assist torque under normal conditions (i.e., reduction time), as well as the time ΔTdgn21 spent on reducing the assist torque when traveling on a curved road and the time ΔTdgn22 spent on reducing the assist torque when traveling on a straight road.

[0058] The degeneration characteristic is given to the assist torque by setting a degeneration coefficient Kdgn and multiplying this by the assist torque ASS0 at the start of the assist torque degeneration process, in other words, according to the following equation (2). The degeneration coefficient Kdgn is set as a coefficient that decreases from 1 to 0 over time for each of normal use, curved road travel, and straight road travel, within the range of 0 to 1. ASS = ASS0 × Kdgn … (2)

[0059] Here, when comparing the degeneration coefficient Kdgn for normal use (hereinafter referred to as the "standard degeneration coefficient Kdgn1"), the degeneration coefficient Kdgn for driving on a curved road (hereinafter referred to as the "first early degeneration coefficient Kdgn21"), and the degeneration coefficient Kdgn for driving on a straight road (hereinafter referred to as the "second early degeneration coefficient Kdgn22"), it is found that the standard degeneration coefficient Kdgn1 decreases over a longer period of time than the first early degeneration coefficient Kdgn21, and the first early degeneration coefficient Kdgn21 decreases over a longer period of time than the second early degeneration coefficient Kdgn22. In other words, assuming that the assist torque degeneration process is started simultaneously (time T0), the time at which the coefficients Kdgn1, Kdgn21, and Kdgn22 reach 0 is later for the standard degeneration coefficient Kdgn1 (time T31) than for the first early degeneration coefficient Kdgn21 (time T32), and later for the first early degeneration coefficient Kdgn21 than for the second early degeneration coefficient Kdgn22 (time T33).

[0060] Furthermore, after the assist torque degeneration process starts (time T0), the time at which the coefficients Kdgn1, Kdgn21, and Kdgn22 start to decrease from 1 is later for the standard degeneration coefficient Kdgn1 (time T11) than for the first early degeneration coefficient Kdgn21 (time T12), and later for the first early degeneration coefficient Kdgn21 than for the second early degeneration coefficient Kdgn22 (time T13).

[0061] In this embodiment, after the process starts, the first early shrinkage coefficient Kdgn21 is maintained at or near 1 for a certain period of time and then decreased. In contrast, the second early shrinkage coefficient Kdgn22 is decreased immediately after the process starts.

[0062] The slope at which the coefficients Kdgn21 and Kdgn22 are decreased also differs between when traveling on a curved road and when traveling on a straight road. Specifically, the first early degeneration coefficient Kdgn21 decreases at a relatively gradual slope after starting to decrease at time T12, and then the slope increases and transitions to a steep decrease. In contrast, the second early degeneration coefficient Kdgn22 decreases at a relatively steep slope after starting to decrease at time T13, and then the slope decreases and transitions to a gradual decrease. The change in the slope of the coefficients Kdgn21 and Kdgn22 may be gradual or smooth.

[0063] Returning to the explanation of the flowchart, the steering torque ratio Rtrq is calculated in S217. The steering torque ratio Rtrq is the ratio of the steering torque STR to the required steering torque Tstr, and is calculated by the following equation (3). Rtrq=STR / Tstr …(3)

[0064] In S218, it is determined whether the steering torque ratio Rtrq is equal to or greater than a predetermined threshold value Rth1. If it is determined that the steering torque ratio Rtrq is equal to or greater than the threshold value Rth1, it is determined that the driver is gripping the steering wheel firmly and operating it proactively, and the process proceeds to S219. On the other hand, if it is determined that the steering torque ratio Rtrq is less than the threshold value Rth1, it is determined that the driver is gripping the steering wheel loosely and operating it passively, and the process bypasses S219 and proceeds to S220.

[0065] In S219, the assist torque degeneration diagram is corrected. Specifically, the assist torque degeneration diagram is changed from the basic degeneration diagram indicated by the solid line to a shortened degeneration diagram for each of the curved road and straight road driving, thereby shortening the times ΔTdgn21 and ΔTdgn22 spent on the assist torque degeneration process. In this embodiment, this is done by changing the first early degeneration coefficient Kdgn21 and the second early degeneration coefficient Kdgn22 to have a steeper slope while maintaining the aforementioned change tendency. Figures 5(b) and 5(c) show the coefficients Kdgn21 and Kdgn22 in the case of the shortened degeneration diagram using dashed lines.

[0066] In S220, the assist torque after degeneration (hereinafter referred to as "degenerate assist torque") ASSd is calculated. The calculation of the shortened assist torque ASSd is performed by multiplying the assist torque ASS0 at the start of the assist torque degeneration process by the degeneration coefficients Kdgn (standard degeneration coefficient Kdgn1, first early degeneration coefficient Kdgn21, second early degeneration coefficient Kdgn22) according to the above equation (2).

[0067] In step S221, the degenerate assist torque ASSd is set to the final assist torque ASS.

[0068] (Explanation of action and effect) The actions and effects obtained by this embodiment will be described below.

[0069] First, by detecting the road curvature or a road shape parameter which is an index related to the curvature, and by using the assist torque reduction process to bring the assist torque ASS closer to 0, the characteristics of the change in the assist torque ASS (i.e., the reduction characteristics) can be varied depending on the driving shape parameter, thereby making it possible to appropriately reduce the assist torque ASS.

[0070] Specifically, it is possible to prevent situations in which a sudden reduction in assist torque ASS causes the driver to operate the steering wheel excessively, resulting in a sudden change in vehicle behavior, and a gradual reduction in assist torque ASS causes the driver to feel a sense of barriers in steering wheel operation.

[0071] 6 and 7 are explanatory diagrams illustrating the behavior of a vehicle when the assist torque reduction process is performed, with Fig. 6 showing the behavior of a vehicle V1 when changing lanes on a straight road, and Fig. 7 showing the behavior of a vehicle V2 when changing lanes on a curved road. In this embodiment, the assist torque reduction process is performed when changing lanes.

[0072] 6 and 7 show the routes or trajectories TR1, TR2, and TR3 taken by vehicles V1 and V2 when changing lanes from LN1 to LN2, respectively. Route TR1 shows, for reference, the route when assist torque reduction processing is not performed or when assist torque reduction processing is performed using the standard degeneration diagram. As described above, when using the standard degeneration diagram, the assist torque ASS is maintained at the assist torque ASS0 at the start of the assist torque reduction processing for a relatively long time after detecting a lane change intention. Route TR2 shows the route when using the basic degeneration diagram shown by the solid lines in FIGS. 5(b) and 5(c) in a situation where the driver's grip on the steering wheel is loose and the steering wheel is operated passively. Route TR3 shows the route when using the shortened degeneration diagram shown by the dashed lines in FIGS. 5(b) and 5(c) in a situation where the driver grips the steering wheel firmly and operates the steering wheel proactively.

[0073] When driving on a straight road, as shown in Fig. 5(c), after detecting the intention to change lanes, the assist torque ASS is immediately reduced by degeneration, and the slope of the change after the reduction starts is set large immediately after the reduction starts and is reduced over time. This quickly eliminates the sense of a wall in the driver's steering and enables light steering, ensuring a good steering feel and making it possible to quickly complete the lane change, as shown by the routes TR2 and TR3 leading to vehicles V12 and V13 after the lane change in Fig. 6.

[0074] In contrast, when traveling on a curved road, as shown in Fig. 5(b), the assist torque ASS is decreased after a certain time has elapsed after detecting the intention to change lanes, and the slope of the change after the decrease starts is set small immediately after the decrease starts and increases over time. This makes it possible to prevent a sudden change in vehicle behavior due to the driver operating the steering wheel excessively due to a sudden drop in assist torque ASS, and therefore, as shown in Fig. 7 by the routes TR2 and TR3 leading to vehicles V22 and V23 after changing lanes, it is possible to avoid a situation in which vehicles V22 and V23 are significantly swung outward from lane LN2 due to a decrease in assist torque ASS, and ensure safety when changing lanes while traveling on a curved road.

[0075] Secondly, as a road shape parameter, the road type of the road being traveled on, whether it is a straight road or a curved road, is detected, and the degeneration characteristics are made different depending on whether the road being traveled on is a straight road or a curved road. This makes it possible to take into account the effect of the road shape (straight or curved) on the behavior of the vehicle when the assist torque degeneration process is performed, and to perform the assist torque degeneration process with appropriate characteristics for both straight roads and curved roads.

[0076] Third, when the road being traveled is a straight road, the time from the start to the end of the assist torque reduction process (i.e., reduction times ΔTdgn21, ΔTdgn22) is shortened compared to when the road is a curved road. This allows the assist torque ASS to be added for a relatively long time after the start of the assist torque reduction process when traveling on a curved road, thereby more reliably preventing situations in which a sudden change occurs in the vehicle's behavior after the reduction begins.

[0077] Fourth, by detecting the steering torque STR applied by the driver and changing the time taken to reduce the assist torque ASS (i.e., reduction time ΔTdgn21, ΔTdgn22) according to the steering torque STR at the start of the assist torque reduction process, it is possible to optimize the reduction time according to the steering wheel operation status by the driver, thereby improving the steering feel while further suppressing changes in the vehicle behavior.

[0078] Specifically, the system determines whether the driver is gripping the steering wheel firmly and operating it proactively or actively, or whether the driver is gripping the steering wheel loosely and operating it passively or proactively, based on the steering torque STR. If the driver is operating the steering wheel proactively, the degeneration time is shortened (using the shortened degeneration diagram) to quickly eliminate the wall feeling and improve the steering feel. This prioritizes the driver's proactive operation, allowing the lane change to be completed quickly, as shown by route TR3 in Figures 6 and 7. On the other hand, if the driver is operating the steering wheel passively, the degeneration time is maintained long (using the basic degeneration diagram) to suppress changes in vehicle behavior. In this way, it is possible to perform assist torque degeneration processing with an appropriate degeneration time according to the steering wheel operation situation.

[0079] Here, the assist torque ASS is set as the difference between the required steering torque Tstr and the steering torque STR, and when the steering torque reduction process is performed, the greater the ratio of the steering torque STR to the required steering torque Tstr (=STR / Tstr), the shorter the reduction time is, which makes it possible to more appropriately grasp the steering wheel operation status by the driver, and by further optimizing the reduction time, it becomes possible to further suppress changes that occur in the vehicle behavior.

[0080] Fifth, by detecting the driver's intention to change lanes and performing assist torque reduction processing in response to the detection of the lane change intention, it is possible to easily and appropriately detect situations in which the addition of assist torque ASS is unnecessary and perform assist torque reduction processing at the appropriate timing.

[0081] Sixth, by monitoring the blind spot of the vehicle in the lane after the lane change or in the adjacent lane on the side of the lane change, and detecting the presence of another vehicle in this blind spot, the assist torque reduction process is stopped or the assist torque reduction process is performed according to the standard reduction diagram, and by leaving a sense of barrier to the driver's steering, it is possible to prevent the vehicle from approaching other vehicles and promote traffic safety when changing lanes.

[0082] In the above description, when the presence of another vehicle in the blind spot of the host vehicle is detected, the execution of the assist torque degradation process itself is prohibited or the assist torque degradation process is performed according to the standard degeneration diagram. Measures taken in similar situations are not limited to this. The execution of the assist torque degradation process itself may be continued while delaying the change in the assist torque ASS due to the degeneration. For example, the time taken for the degeneration is extended within a range shorter than the degeneration time ΔTdgn1 according to the standard degeneration diagram, compared to when the presence of another vehicle in the blind spot is not detected. This eliminates the sense of impasse in the driver's steering operation, thereby avoiding excessive deterioration of the steering feel. Furthermore, by maintaining the sense of impasse for a relatively long period of time, it is possible to prevent the driver from inadvertently changing lanes after operating the turn signal, causing the host vehicle to approach or even contact another vehicle.

[0083] Furthermore, the driving assistance control is not limited to control for keeping the vehicle near the center of the lane in which the vehicle is traveling (i.e., lane keeping control), but may also be control for suppressing departure of the vehicle from the lane in which the vehicle is traveling (i.e., lane departure prevention control). In the case of lane departure prevention control, the specific content of the control may be different from that of lane keeping control, and when the vehicle is about to deviate from the lane in which the vehicle is traveling, vibration may be added to the steering wheel in addition to the application of assist torque to prompt the driver to recognize that the vehicle is in a situation where it is about to deviate from the lane. [Explanation of symbols]

[0084] 1...vehicle driving assistance device, 101...controller, 111...front camera, 112...rear camera, 113...steering angle sensor, 114...steering sensor, 115...acceleration sensor, 116...turn signal switch, 117...system start switch, 201...steering assist motor, 301...HMI device, R1...straight road, R2...curved road, LN1...driving lane, LN2...adjacent lane, V1, V2...vehicle, CTR...road centerline.

Claims

1. an assist torque setting means for setting an assist torque that keeps the vehicle in the lane in which the vehicle is traveling or moves the vehicle closer to the center of the lane in which the vehicle is traveling; a road shape detection means for detecting a curvature of a road on which the vehicle is traveling or a road shape parameter which is an index related thereto; The assist torque setting means Execute an assist torque reduction process to bring the assist torque closer to 0 over time; A driving assistance device for a vehicle that varies a degeneration characteristic, which is a characteristic of the change in the assist torque when the assist torque degeneration process is performed, depending on the road shape parameters detected by the road shape detection means.

2. the road shape detection means detects, as the road shape parameter, a road type, i.e., whether the road on which the vehicle is traveling is a straight road or a curved road; 2. The vehicle driving assistance device according to claim 1, wherein the assist torque setting means sets the degeneration characteristic to be different depending on whether the road on which the vehicle is traveling is a straight road or a curved road.

3. The assist torque setting means After the assist torque reduction process is started, when the assist torque decreases from a start torque, which is a torque at the start of the process, and reaches 0 or reaches a target end torque that is closer to 0 than the start torque, the assist torque reduction process is terminated.

3. The vehicle driving assistance device according to claim 2, wherein a reduction time, which is a time from start to end of the assist torque reduction process, is made shorter when the road on which the vehicle is traveling is a straight road than when the road is a curved road.

4. The vehicle further includes a steering torque detection means for detecting a steering torque applied to the steering wheel by a driver, 4. The vehicle driving assistance device according to claim 3, wherein the assist torque setting means further changes the reduction time in accordance with the steering torque detected by the steering torque detection means at the start of the assist torque reduction process.

5. The steering system further includes a required steering torque setting means for setting a required steering torque according to a steering angle of the vehicle, The steering torque setting means The assist torque is set as a difference between the required steering torque set by the required steering torque setting means and the steering torque, The vehicle driving assistance device according to claim 4 , wherein, when the assist torque reduction process is performed, the reduction time is shortened as the ratio of the steering torque to the required steering torque increases.

6. The vehicle further includes a lane change intention detection means for detecting a driver's intention to change lanes, 6. The driving assistance device for a vehicle according to claim 1, wherein the assist torque setting means performs the assist torque reduction process in response to the detection of the lane change intention by the lane change intention detection means.

7. a reduction condition determination means for determining whether a predetermined condition for performing the assist torque reduction process is satisfied; Further, the vehicle is provided with a lane change intention detection means for detecting a driver's intention to change lanes, The degeneration condition determination means determines that the predetermined conditions include the lane change intention detection means detecting the lane change intention, The assist torque setting means When the degeneration condition determination means determines that the predetermined condition is satisfied, the assist torque degeneration process is performed, and the degeneration characteristics are switched between a first degeneration process performed when the intention to change lanes is detected and a second degeneration process performed when another predetermined condition is satisfied, When the first degeneration is performed, the assist torque degeneration process is performed using the degeneration characteristics that vary depending on the road shape parameter; The driving assistance device for a vehicle according to claim 1 , wherein, when the second degeneration is performed, the assist torque degeneration process is performed according to a predetermined standard degeneration characteristic, regardless of the road shape parameter.

8. a blind spot monitoring means for monitoring a blind spot of the vehicle in the lane after the change or in an adjacent lane between the lane currently being traveled and the lane after the change, and detecting the presence of another vehicle in the blind spot; 8. The vehicle driving assistance device according to claim 7, wherein when the blind spot monitoring means detects the presence of the other vehicle during the first degeneration, the assist torque setting means stops the execution of the assist torque degeneration process or executes the assist torque degeneration process according to the standard degeneration characteristics.

9. a lane change intention detection means for detecting a driver's intention to change lanes; a blind spot monitoring means for monitoring a blind spot of the vehicle in the lane after the change or in an adjacent lane between the lane currently being traveled and the lane after the change, and detecting the presence of another vehicle in the blind spot; The assist torque setting means In response to the detection of the lane change intention by the lane change intention detection means, the assist torque reduction process is performed; 6. The vehicle driving assistance device according to claim 1, wherein when the blind spot monitoring means detects the presence of the other vehicle, the change in the assist torque due to the assist torque reduction process is delayed compared to other cases.

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