Preceding vehicle travel state estimation method and preceding vehicle travel state estimation device

Abstract

A traveling state estimation method of a preceding vehicle includes: acquiring behavior of the preceding vehicle before the preceding vehicle cannot be detected from an own vehicle; determining whether or not the preceding vehicle entering a curved road can be detected; and estimating an inter-vehicle distance of the preceding vehicle with respect to the own vehicle on the basis of the behavior of the preceding vehicle before the preceding vehicle cannot be detected and navigation information when the preceding vehicle entering the curved road cannot be detected.

Description

Method for Estimating Driving State of Leading Vehicle and Device for Estimating Driving State of Leading Vehicle

[0001] The present invention relates to a method for estimating the driving state of a leading vehicle and a device for estimating the driving state of a leading vehicle.

[0002] A method for measuring the driving state of a leading vehicle ahead of the host vehicle is known (see, for example, Patent Document 1).

[0003] Japanese Unexamined Patent Application Publication No. 2021-118002

[0004] In the method for measuring the inter-vehicle distance (driving state estimation method) described in Patent Document 1, the target vehicle (leading vehicle) is detected from an image obtained by imaging the target vehicle, and the inter-vehicle distance between the target vehicle and the host vehicle is measured. However, when the target vehicle enters a curved road and cannot be detected, the inter-vehicle distance cannot be measured.

[0005] An object of the present invention is to provide a method for estimating the driving state of a leading vehicle and a device for estimating the driving state of a leading vehicle that can estimate the driving state of the leading vehicle when the leading vehicle cannot be detected.

[0006] One aspect of the present invention estimates the inter-vehicle distance between the leading vehicle and the host vehicle based on the behavior of the leading vehicle before it becomes undetectable and navigation information when the leading vehicle entering a curved road cannot be detected.

[0007] It is a schematic diagram showing a schematic configuration of a vehicle according to an embodiment. It is a control block diagram of a controller. It is a diagram showing a pattern in which a leading vehicle enters a curved road and the leading vehicle cannot be detected. It is a diagram showing a pattern in which a leading vehicle enters a curved road and the leading vehicle cannot be detected. It is a diagram showing a pattern in which a leading vehicle enters a curved road and the leading vehicle cannot be detected. It is a flowchart of a method for estimating the driving state of a leading vehicle and a method for controlling the host vehicle. It is a diagram showing the driving tendency of the driver of the leading vehicle. It is a diagram showing the estimated speed of the leading vehicle when the leading vehicle cannot be detected in the first section of the curved road. It is a flowchart showing a drive force setting process.

[0008] Embodiments of the present invention will be described below with reference to the drawings. In the following, the driver's operation to request braking force using a braking force requesting means such as an accelerator pedal will be referred to as "accelerator operation," and the amount of this operation will be referred to as "accelerator operation amount." Acceleration refers to the value in the acceleration direction, where the speed increases, and the value in the deceleration direction, where the speed decreases. It is a positive value in the acceleration direction and a negative value in the deceleration direction. Braking force refers to the driving force and braking force.

[0009] Figure 1 is a schematic diagram showing the general configuration of an electric vehicle (hereinafter referred to as "vehicle") 1. Vehicle 1 is an electric vehicle that generates its driving force and regenerative braking force (hereinafter also referred to as braking force) using an electric drive source. Vehicle 1 is equipped with a braking force generating device 2 and a control device 3.

[0010] The braking and driving force generating device 2 comprises an inverter 21, a battery 22, an electric motor 23, a reduction gear 24, and wheels 25. The inverter 21 converts the DC current input from the battery 22 into AC current and outputs it to the electric motor 23 based on commands input from the control device 3. The inverter 21 also converts the AC current input from the electric motor 23 into DC current and inputs it to the battery 22 based on commands input from the control device 3. The reduction gear 24 comprises a transmission 24A and a differential gear 24B, and reduces the output of the electric motor 23 at a predetermined gear ratio based on the control of the control device 3 and transmits it to the wheels 25.

[0011] The control device 3 estimates the driving state of the preceding vehicle ahead of vehicle 1 and uses this to control the braking and driving force of vehicle 1. The control device 3 is a device for estimating the driving state of the preceding vehicle and is a control device for vehicle 1.

[0012] The control device 3 includes a navigation device 4, an accelerator position sensor 5 as an accelerator operation amount sensor, a steering angle sensor 6, a vehicle speed sensor 7, a vehicle distance sensor 8, and a controller 9.

[0013] The navigation device 4 is equipped with a position detection sensor 41 such as a GNSS (Global Navigation Satellite System). The navigation device 4 acquires map information and driving environment information within a predetermined distance around the vehicle 1 from a cloud 42 such as a server or database, and displays the map information and driving environment information on a display (not shown) installed inside the vehicle, or outputs it as voice. For example, the navigation device 4 displays the current position of the vehicle 1 and the driving route to the destination or waypoint on the map displayed on the display, or provides guidance as voice output. The navigation device 4 outputs map information, driving environment information, and the driving route to the destination or waypoint as navigation information. Map information includes, for example, information on intersection locations, traffic light locations, railway crossing locations, pedestrian crossing locations, stop locations, whether right or left turns are permitted at intersections, the degree of road gradient, the number of lanes on the road, and the possible directions of travel for the vehicle 1 in each lane. Driving environment information includes, for example, the speed of vehicle 1, the road speed limit, the statistical average speed and statistical average acceleration of a given section, the traffic volume of a given section, congestion information, construction information, road surface conditions, outside temperature, weather conditions, and information on changes in road surface conditions due to weather.

[0014] The accelerator position sensor 5 detects the amount of accelerator operation of the vehicle 1. The accelerator position sensor 5 is composed of, for example, a pedal stroke sensor and detects the amount of operation of the accelerator pedal 51, which is a means for requesting braking and driving force, as the amount of accelerator operation.

[0015] The steering angle sensor 6 is composed of, for example, an encoder or a potentiometer, and detects the steering angle of the vehicle 1.

[0016] The vehicle speed sensor 7 is composed of, for example, a rotation speed sensor for the wheel 25, and detects the speed of the vehicle 1.

[0017] The inter-vehicle distance sensor 8 is mounted on the vehicle 1 and detects the distance and relative speed of the vehicle ahead of the vehicle 1. In this embodiment, the inter-vehicle distance sensor 8 includes a camera 81 and a radar 82, and the radar 82 detects the distance to the vehicle ahead recognized by the camera 81. As the radar 82, a laser radar, millimeter-wave radar, LiDAR (Light Detection And Ranging), etc., can be used.

[0018] When the controller 9 cannot detect the preceding vehicle, it estimates the speed of the preceding vehicle and the distance between the preceding vehicle and vehicle 1 as the driving state of the preceding vehicle. The controller 9 also controls the braking and driving force generated by the electric motor 23 based on the speed of vehicle 1 and the amount of accelerator operation. The controller 9 is implemented by a microcomputer equipped with, for example, a processing unit such as a CPU or GPU, a storage unit 91 such as ROM and RAM, and an input / output unit such as an input / output interface. The navigation device 4, accelerator position sensor 5, steering angle sensor 6, vehicle speed sensor 7, following distance sensor 8, and inverter 21 are electrically or communicatively connected to the controller 9.

[0019] Figure 2 is a control block diagram of the controller 9. As shown in Figure 2, the controller 9 includes a memory unit 91, a basic braking force setting unit 92, a preceding vehicle detection and determination unit 93, a preceding vehicle behavior acquisition unit 94, a preceding vehicle driving tendency determination unit 95, a curved road driving determination unit 96, a preceding vehicle driving state estimation unit 97, and a braking force setting unit 98.

[0020] The memory unit 91 stores computer programs for operating the controller 9, various maps used for control, and various parameter values. Maps stored in the memory unit 91 include, for example, a map that defines the relationship between the vehicle 1's speed, accelerator operation amount, and basic braking force, and a map for setting correction amounts. Parameter values ​​stored in the memory unit 91 include, for example, various thresholds such as the speed threshold of other vehicles on a curved road.

[0021] The basic braking force setting unit 92 sets the basic braking force based on the vehicle speed and accelerator operation amount. The basic braking force is the braking force when no correction is made.

[0022] The preceding vehicle detection and determination unit 93 detects the presence or absence of a preceding vehicle based on the output of the inter-vehicle distance sensor 8. The preceding vehicle detection and determination unit 93 also determines whether or not it can detect a preceding vehicle that has entered a curved road.

[0023] The preceding vehicle behavior acquisition unit 94 calculates the actual acceleration of the preceding vehicle, which is the behavior of the preceding vehicle before it can no longer be detected, based on the speed of vehicle 1 and the relative speed with the preceding vehicle. The preceding vehicle behavior acquisition unit 94 determines the actual speed of the preceding vehicle, which is the behavior of the preceding vehicle before it can no longer be detected, from the speed of vehicle 1 and the relative speed, and calculates the acceleration of the preceding vehicle from the change in the speed of the preceding vehicle.

[0024] The preceding vehicle driving tendency determination unit 95 determines the driving tendency of the driver of the preceding vehicle based on the behavior of the preceding vehicle before it could no longer be detected.

[0025] The curved road driving determination unit 96 determines whether or not the vehicle 1 has exited the curved road based on the position of the vehicle 1 and map information.

[0026] The preceding vehicle driving state estimation unit 97 estimates the speed of the preceding vehicle, which is the driving state of the preceding vehicle, based on the behavior of the preceding vehicle before it could no longer be detected and the navigation information. The preceding vehicle driving state estimation unit 97 also estimates the distance between the preceding vehicle and vehicle 1 as the driving state of the preceding vehicle, based on the estimated speed of the preceding vehicle, the speed of vehicle 1, and the stored value of the distance between vehicles when the preceding vehicle could no longer be detected.

[0027] The braking force setting unit 98 sets the braking force to be generated by the electric motor 23 based on the basic braking force and a correction amount for the basic braking force. The braking force setting unit 98 outputs a command to the inverter 21 such that the set braking force is output, and drives or regenerates the electric motor 23 according to the command. If the set braking force is positive, a positive torque is output from the electric motor 23 and becomes the driving force; if it is negative, regeneration is performed by the electric motor 23 and becomes the braking force.

[0028] In this embodiment, the braking and driving force setting unit 98 calculates THW (Time Headway), which is the time between vehicle 1 and the preceding vehicle, based on the distance to the preceding vehicle and the speed of vehicle 1, and calculates TTC (Time to Collision), which is the time to reach the preceding vehicle, based on the distance to the preceding vehicle and the relative speed. The braking and driving force setting unit 98 sets a correction amount for the basic braking and driving force based on THW, TTC, the speed of vehicle 1, and the accelerator operation amount. This correction amount increases or decreases the amount of regeneration of the electric motor 23, and adjusts the acceleration of vehicle 1 in the deceleration direction.

[0029] Figures 3 to 5 show patterns in which the preceding vehicle FC enters the curved road CR and the preceding vehicle FC cannot be detected. Patterns in which the preceding vehicle FC enters the curved road CR and cannot be detected include, as shown in Figure 3, a pattern in which the preceding vehicle FC cannot be detected in the first section SC1 including the entrance position CR1 of the curved road CR; as shown in Figure 4, a pattern in which the preceding vehicle FC cannot be detected in the second section SC2 including the position where the curvature of the curved road CR is maximum; and as shown in Figure 5, a pattern in which the preceding vehicle FC cannot be detected in the third section SC3 including the exit position CR2 of the curved road CR. For example, the first section SC1 includes the entrance position CR1 of the curved road CR and is the section in which the increase in the curvature of the curved road CR is greater than or equal to a threshold; the second section SC2 includes the position where the curvature of the curved road CR is maximum and is the section in which the change in the curvature of the curved road CR is less than a threshold; and the third section SC3 includes the exit position CR2 of the curved road CR and is the section in which the decrease in the curvature of the curved road CR is greater than or equal to a threshold.

[0030] Figure 6 is a flowchart of the method for estimating the driving state of the preceding vehicle and controlling vehicle 1, as executed by controller 9. The control routine shown in the flowchart is pre-programmed and installed in controller 9. Controller 9 repeatedly executes the following control routine according to the program, for example, in calculation cycles of about 10 milliseconds.

[0031] In step S1 of Figure 6, the controller 9 acquires the outputs of the navigation device 4 and sensors 5, 6, 7, and 8, namely navigation information including map information and driving environment information, the accelerator operation amount of vehicle 1, steering angle and speed, the distance to the preceding vehicle and relative speed.

[0032] In step S2, the basic braking force setting unit 92 refers to a map that defines the relationship between the vehicle speed 1, the accelerator operation amount, and the basic braking force, and sets the basic braking force based on the vehicle speed 1 and the accelerator operation amount.

[0033] In step S3, the preceding vehicle detection determination unit 93 determines whether or not a preceding vehicle has been detected based on the output of the inter-vehicle distance sensor 8. If it is determined in step S3 that a preceding vehicle has been detected, the preceding vehicle detection determination unit 93 sets the preceding vehicle detection flag in step S4.

[0034] In the subsequent step S5, the preceding vehicle behavior acquisition unit 94 calculates the actual acceleration of the preceding vehicle from the actual change in speed of the preceding vehicle before it could no longer be detected.

[0035] In the subsequent step S6, the preceding vehicle driving tendency determination unit 95 determines the driving tendency of the driver of the preceding vehicle. In this embodiment, the preceding vehicle driving tendency determination unit 95 determines the driving tendency of the driver of the preceding vehicle from the acceleration fluctuations of the preceding vehicle before it could no longer be detected and the speed of the preceding vehicle before it could no longer be detected.

[0036] For example, as shown in Figure 7, the preceding vehicle driving tendency determination unit 95 determines that if the acceleration of the preceding vehicle before detection becomes impossible exceeds thresholds TH1 and TH2, the driver of the preceding vehicle tends to drive with large acceleration changes; otherwise, it determines that the driver tends to drive with small acceleration changes. In the case of the driver shown in Figure 7, since the positive acceleration is below threshold TH1, it is determined that the driver tends to drive with small acceleration changes in the acceleration direction, while the negative acceleration exceeds threshold TH2, it is determined that the driver tends to drive with large acceleration changes in the deceleration direction. Also, since the speed of the preceding vehicle is fluctuating near the statistical average speed, it is determined that the driver tends to drive at a speed close to the statistical average speed. The thresholds TH1 and TH2 are set according to the statistical average acceleration of the relevant section. Statistical average acceleration is the statistical value of the average acceleration of any group of vehicles traveling in the relevant section, such as a curved road. Statistical average speed is the statistical value of the average speed of any group of vehicles traveling in the relevant section, such as a curved road. Statistical average acceleration and statistical average speed can be obtained from the cloud 42 via the navigation device 4.

[0037] Returning to Figure 6, in step S7, the braking force setting unit 98 uses the value of the distance between vehicles detected by the distance sensor 8 as the distance between vehicles to be used for setting the braking force, and in the following step S8, it performs the braking force setting process. The braking force setting process will be described later.

[0038] On the other hand, if it is not determined in step S3 that a preceding vehicle has been detected, the preceding vehicle detection determination unit 93 determines in step S9 whether or not the preceding vehicle detection flag is set. If it is determined in step S9 that the preceding vehicle detection flag is not set, the process proceeds to step S8; if it is determined that the preceding vehicle detection flag is set, the process proceeds to step S10.

[0039] In step S10, the preceding vehicle detection determination unit 93 determines whether the preceding vehicle has entered a curved road and can no longer be detected. Based on the position of vehicle 1, the distance to the preceding vehicle, and map information, the preceding vehicle detection determination unit 93 recognizes that the preceding vehicle has entered a curved road, and if it subsequently becomes impossible to detect the preceding vehicle, it determines that the preceding vehicle has entered a curved road and can no longer be detected. At this time, the preceding vehicle detection determination unit 93 stores the distance to the preceding vehicle at the time it could no longer be detected in the storage unit 91. If it is not determined in step S10 that the preceding vehicle has entered a curved road and can no longer be detected, it is considered that the preceding vehicle has not entered a curved road and can no longer be detected, but rather, for example, has deviated from the driving route of vehicle 1, or has moved far away from vehicle 1 and disappeared. In this case, the preceding vehicle detection determination unit 93 resets the preceding vehicle detection flag in step S14 and then proceeds to step S8. On the other hand, if it is determined in step S10 that the preceding vehicle has entered a curved road and can no longer be detected, the process proceeds to step S11.

[0040] In step S11, the curved road driving determination unit 96 determines whether or not vehicle 1, which is the vehicle itself, has exited the curved road. Based on the position of vehicle 1 and map information, if the curved road driving determination unit 96 recognizes that vehicle 1 has traveled along the curved road that a preceding vehicle entered and that vehicle 1 has passed the exit of the curved road, it determines that vehicle 1 has exited the curved road. If it is determined in step S11 that vehicle 1 has exited the curved road, the process proceeds to step S14 and then to step S8. If it is not determined that vehicle 1 has exited the curved road, the process proceeds to step S12. If it is not determined in step S11 that vehicle 1 has exited the curved road, it means that the preceding vehicle that was detected before entering the curved road was not detected in step S3, and that even if vehicle 1 exits the curved road, the preceding vehicle will not be detected. In this case, the preceding vehicle detection determination unit 93 determines that the preceding vehicle has disappeared.

[0041] In step S12, the preceding vehicle running state estimation unit 97 estimates the speed of the preceding vehicle that has entered the curved road and cannot be detected. When the preceding vehicle cannot be detected in the first section of the curved road, the preceding vehicle running state estimation unit 97 estimates the speed of the preceding vehicle based on the behavior of the preceding vehicle before entering the first section. When the preceding vehicle cannot be detected in the second section, it estimates the speed of the preceding vehicle based on the behavior of the preceding vehicle before entering the second section. When the preceding vehicle cannot be detected in the third section, it estimates the speed of the preceding vehicle based on the behavior of the preceding vehicle before entering the third section.

[0042] In the case of this embodiment, the preceding vehicle running state estimation unit 97 estimates the speed of the preceding vehicle in each section of the curved road in consideration of the actual acceleration and actual speed of the preceding vehicle, which are the behaviors of the preceding vehicle before it becomes undetectable, the driving tendency of the driver of the preceding vehicle, the curvature of the curved road included in the navigation information, the statistical average speed, and the statistical average acceleration.

[0043] As shown in FIG. 3, FIG. 8 is a diagram showing the estimated speed of the preceding vehicle when the preceding vehicle cannot be detected in the first section SC1 of the curved road CR. In FIG. 8, the actual speed of the preceding vehicle is shown by a solid line, and the estimated speed is shown by a broken line. In FIG. 8, the preceding vehicle enters the curved road while decelerating at the speed shown by the solid line and becomes undetectable in the first section SC at time t0. Until time t0, the preceding vehicle behavior acquisition unit 94 calculates the actual acceleration of the preceding vehicle before it is detected. Therefore, the preceding vehicle running state estimation unit 97 estimates the speed of the preceding vehicle in the first section SC1 based on this acceleration, taking into account the driving tendency of the driver of the preceding vehicle and information such as the curvature of the curved road. Here, since the driver of the preceding vehicle tends to drive at a speed close to the statistical average speed and tends to drive with a large acceleration change in the deceleration direction (see FIG. 7), the preceding vehicle running state estimation unit 97 estimates the speed of the preceding vehicle so that the acceleration of the preceding vehicle becomes larger in the deceleration direction after time t0 than before.

[0044] Regarding the second section SC2, the preceding vehicle running state estimation unit 97 estimates the speed of the preceding vehicle to be a constant speed because the second section SC2 includes the position of the maximum curvature and it is considered that the curvature of the second section SC2 is substantially constant.

[0045] Regarding the third section SC3, the leading vehicle running state estimation unit 97 maintains the speed of the leading vehicle in the second section SC2 in the third section SC3 as well. This is because it is considered that the driver of the leading vehicle tends to drive with a small acceleration change in the acceleration direction (see FIG. 7).

[0046] When the leading vehicle is detected at time t1, the estimation of the speed of the leading vehicle ends, and thereafter, the speed obtained from the detection values of the sensors 7 and 8 is used.

[0047] In FIG. 8, the estimation of the speed of the leading vehicle when the leading vehicle cannot be detected in the first section SC1 of the curved road has been described. However, as shown in FIG. 4, when the leading vehicle cannot be detected in the second section SC2, based on the acceleration of the leading vehicle before entering the second section SC2, and as shown in FIG. 5, when the leading vehicle cannot be detected in the third section SC3, based on the acceleration of the leading vehicle before entering the third section SC3, considering the driving tendency of the driver of the leading vehicle, information such as the curvature of the curved road, etc., the speed of the leading vehicle in the sections SC2 and SC3 is estimated.

[0048] Returning to FIG. 6, in step S12, the leading vehicle running state estimation unit 97 calculates the relative moving distance of the leading vehicle with respect to the vehicle 1 from the difference between the estimated speed of the leading vehicle and the speed of the vehicle 1, and adds it to the stored value of the inter-vehicle distance when the leading vehicle cannot be detected, thereby estimating the inter-vehicle distance.

[0049] In step S13, the drive force control setting unit 98 uses the estimated inter-vehicle distance value as the inter-vehicle distance for setting the drive force control, and performs the drive force control setting process in the subsequent step S8.

[0050] Thereafter, when the vehicle 离开 the curved road and the leading vehicle is re-detected in step S3, the drive force control setting unit 98 ends the estimation of the speed and the inter-vehicle distance, and in steps S4 and S5, performs the drive force control setting process using the detection value of the inter-vehicle distance sensor 8 as the inter-vehicle distance for setting the drive force control.

[0051] Figure 9 is a flowchart showing the braking force setting process. In step S81 of Figure 9, the preceding vehicle detection determination unit 93 determines whether or not the preceding vehicle detection flag is set. If it is determined in step S81 that the preceding vehicle detection flag is not set, the braking force setting unit 98 sets the basic braking force to the final braking force in step S82.

[0052] On the other hand, if it is determined in step S82 that the preceding vehicle detection flag is set, the braking force setting unit 98, in step S83, obtains the speed of other vehicles on the curved road from the cloud 42 via the navigation device 4 and determines whether the speed of other vehicles on the curved road is fluctuating by more than a threshold. If it is determined in step S83 that the speed of other vehicles on the curved road is fluctuating by more than a threshold, the system proceeds to step S82; otherwise, it proceeds to step S84.

[0053] In step S84, the braking force setting unit 98 determines whether the road surface of the curved road is slippery based on the image captured by the camera 81, the road surface conditions of the driving route included in the navigation information, the outside temperature, and the weather conditions. For example, the braking force setting unit 98 determines that the road surface of the curved road is slippery if it determines from the image that there is snow on the road surface of the curved road, or if it determines from the navigation information that the weather on the curved road is snowy. If it is determined in step S84 that the road surface of the curved road is slippery, the process proceeds to step S82; otherwise, the process proceeds to step S85.

[0054] In step S85, the braking force setting unit 98 determines whether there are speed restriction points such as traffic lights, railway crossings, pedestrian crossings, or stop signs on the curved road, based on the image captured by the camera 81 and map information included in the navigation information. If it is determined in step S85 that there are speed restriction points on the curved road, the process proceeds to step S82; otherwise, the process proceeds to step S86.

[0055] In step S86, the braking and driving force setting unit 98 calculates THW, which is the time from the vehicle 1 to the preceding vehicle, and TTC, which is the time to reach the preceding vehicle, using the following equations (1) and (2): THW = distance between vehicles ÷ vehicle speed ... (1) TTC = distance between vehicles ÷ relative speed ... (2)

[0056] In the following step S87, the braking force setting unit 98, for example, refers to a map and sets a first correction amount based on TWH and the speed of vehicle 1, and sets a second correction amount based on TTC and the speed of vehicle 1. The braking force setting unit 98 also sets a first coefficient based on the accelerator operation amount and sets a second coefficient based on the speed of vehicle 1. The first coefficient is a value in the range of 0 to 1, and for example, it is set to be smaller as the accelerator operation amount increases. The second coefficient is a value in the range of 0 to 1, and for example, it is set to be small when the speed of vehicle 1 is low or high, and large when the speed is between low and high. The braking force setting unit 98 then sets the correction amount of the braking force according to the following formula (3): Correction amount = (First correction amount + Second correction amount) × First coefficient × Second coefficient ... (3)

[0057] In the following step S88, the braking force setting unit 98 sets the value obtained by adding a correction amount to the basic braking force to set the final braking force, and outputs a command to the electric motor 23 such that the set braking force is output.

[0058] According to the above embodiment, if a preceding vehicle entering a curved road cannot be detected, the following distance to the vehicle is estimated based on the behavior of the preceding vehicle before detection was lost and the navigation information. Therefore, when the preceding vehicle can no longer be detected, the driving state of the preceding vehicle can be estimated. Furthermore, since the following distance can be used for controlling vehicle 1, interruption of vehicle 1 control can be prevented.

[0059] According to the embodiment, if the preceding vehicle can no longer be detected in the first section of the curved road, the speed of the preceding vehicle is estimated based on the behavior of the preceding vehicle before entering the first section. If the preceding vehicle can no longer be detected in the second section of the curved road, the speed of the preceding vehicle is estimated based on the behavior of the preceding vehicle before entering the second section. If the preceding vehicle can no longer be detected in the third section of the curved road, the speed of the preceding vehicle is estimated based on the behavior of the preceding vehicle before entering the third section. In all cases, since the speed of the preceding vehicle is estimated based on the behavior of the preceding vehicle most recently before entering each section, the accuracy of estimating the speed of the preceding vehicle can be improved.

[0060] According to this embodiment, the speed of the preceding vehicle is estimated based on the behavior of the preceding vehicle before it becomes undetectable and the driving tendencies of the driver of the preceding vehicle. Therefore, the speed of the preceding vehicle can be estimated while taking into account the driving tendencies of the driver of the preceding vehicle.

[0061] According to the embodiment, the speed of the preceding vehicle is estimated based on the acceleration and driving tendencies of the preceding vehicle, so the speed of the preceding vehicle can be estimated by taking into account the acceleration of the preceding vehicle before entering each section of a curved road.

[0062] According to the embodiment, the speed of the preceding vehicle is estimated based on information about the acceleration of the preceding vehicle and the curvature of the curved road. Therefore, the speed of the preceding vehicle can be estimated while taking into account the curvature of the curved road, which has a significant impact on the speed of the preceding vehicle.

[0063] According to the embodiment, the speed of the preceding vehicle is estimated based on the acceleration of the preceding vehicle and the statistically average acceleration of the curved road, so that the speed of the preceding vehicle can be estimated by taking objective statistical data into consideration.

[0064] As described above, the best configurations, methods, etc., for carrying out the present invention are disclosed in the above description, but the present invention is not limited thereto. That is, although the present invention is mainly illustrated and described in part with respect to specific embodiments, those skilled in the art can make various modifications to the embodiments described above in terms of shape, material, quantity, and other detailed configurations without departing from the scope of the technical idea and objectives of the present invention. Furthermore, the descriptions of shapes, materials, etc. disclosed above are illustrative to facilitate understanding of the present invention and do not limit the present invention; therefore, descriptions of components with some or all of those limitations on shape, material, etc. removed are included in the present invention.

[0065] The braking and driving force generating device 2 may be equipped with an engine and drive a generator with the engine to supply power to the electric motor 23, thereby driving the wheels 25 with the electric motor 23, or the wheels 25 may be driven by the electric motor 23 and the engine. In other words, the vehicle 1 may be a so-called series hybrid vehicle or a parallel hybrid vehicle. The braking and driving force generating device 2 may be equipped with an engine instead of the inverter 21 and electric motor 23, and the wheels 25 may be driven by the engine. In other words, the vehicle 1 may be an engine-driven vehicle that runs using the engine as the sole power source. In this case, a command may be output to the engine and transmission 24A such that a set braking and driving force is output, and the engine and transmission 24A may be operated according to the command.

[0066] The transmission 24A may be configured to allow stepwise switching between multiple gear ratios, or it may be configured to allow continuous switching of gear ratios, such as a CVT (Continuously Variable Transmission).

[0067] In the control device 3, the driving force request operation means was configured as an accelerator pedal 51, and the accelerator operation amount sensor was configured as an accelerator position sensor 5, but other configurations are also possible. For example, the driving force request operation means may be configured as an operation lever or operation dial, and the accelerator operation amount sensor may be configured as a sensor such as a stroke sensor or potentiometer that detects the amount of operation of these.

[0068] The vehicle speed sensor 7 is not particularly limited and may, for example, be a ground speed sensor.

[0069] The controller 9 may be divided into a controller for estimating the driving state of a preceding vehicle, which includes a memory unit 91, a preceding vehicle detection and determination unit 93, a preceding vehicle behavior acquisition unit 94, a preceding vehicle driving tendency determination unit 95, a curved road driving determination unit 96, and a preceding vehicle driving state estimation unit 97; and a controller for setting the braking force, which includes a memory unit 91, a basic braking force setting unit 92, and a braking force setting unit 98.

[0070] The preceding vehicle driving tendency determination unit 95 may, for example, detect the frequency and duration of the preceding vehicle's brake lights from the image captured by the camera 81 as the behavior of the preceding vehicle before it can no longer be detected, and from the frequency and duration of the brake lights, determine whether the driver of the preceding vehicle tends to decelerate repeatedly, or whether they tend to drive in a way that results in long or short periods of deceleration.

[0071] The preceding vehicle driving state estimation unit 97 may estimate the speed and distance of the preceding vehicle in each section of the curved road before vehicle 1 enters the section, or after vehicle 1 enters the section. If the estimation is done after vehicle 1 enters the section, the preceding vehicle driving state estimation unit 97 may also take into consideration information such as the speed, acceleration, and steering angle of vehicle 1 in the section when estimating the speed and distance of the preceding vehicle in that section.

[0072] The braking force setting unit 98 may determine that vehicle 1 has started driving in a straight line when it is determined in step S11 of Figure 6 that vehicle 1 has exited a curved road and the steering angle of vehicle 1 falls below a threshold, and then gradually reduce the correction amount to zero. The braking force setting unit 98 may set a target acceleration for vehicle 1, convert the target acceleration into the braking force of vehicle 1, and set the correction amount. The braking force setting unit 98 may, for example, set an allowable upper limit and an allowable lower limit for the correction amount of the braking force based on the speed of vehicle 1. The braking force setting unit 98 may also perform so-called rate of change limiting, which limits the amount of change of the correction amount over time. If vehicle 1 is an engine-driven vehicle, the braking force setting unit 98 may output a command to the engine and transmission 24A that outputs the set braking force, and operate the engine and transmission 24A according to the command.

[0073] The curved section may be divided according to the amount of change in steering angle. For example, the first section may include the entrance position of the curved section and be the section in which the increase in steering angle is greater than or equal to a threshold; the second section may include the position where the curvature of the curved section is greatest and be the section in which the change in steering angle is less than a threshold; and the third section may include the exit position of the curved section and be the section in which the decrease in steering angle is greater than or equal to a threshold. The curved section may also have other sections with different curvature between the first and second sections, or between the second and third sections.

[0074] 1...Vehicle (own vehicle), 7...Vehicle speed sensor (sensor), 8...Distance sensor (sensor), 9...Controller

Claims

1. A method for estimating the driving state of a vehicle preceding another vehicle, comprising: acquiring the behavior of the preceding vehicle before it becomes undetectable from the vehicle; determining whether the preceding vehicle can be detected when it enters a curved road; and, if the preceding vehicle cannot be detected when it enters a curved road, estimating the distance between the vehicle and the preceding vehicle based on the behavior of the preceding vehicle before it became undetectable and navigation information.

2. A method for estimating the driving state of a preceding vehicle according to claim 1, wherein if the preceding vehicle can no longer be detected in a first section including the entrance position of the curved road, the method for estimating the speed of the preceding vehicle based on the behavior of the preceding vehicle before it entered the first section.

3. A method for estimating the driving state of a preceding vehicle according to claim 1, wherein if the preceding vehicle can no longer be detected in a second section including the position where the curvature of the curved road is maximum, the method for estimating the speed of the preceding vehicle based on the behavior of the preceding vehicle before entering the second section.

4. A method for estimating the driving state of a preceding vehicle according to claim 1, wherein if the preceding vehicle can no longer be detected in a third section including the exit position of the curved road, the method for estimating the speed of the preceding vehicle based on the behavior of the preceding vehicle before entering the third section.

5. A method for estimating the driving state of a preceding vehicle according to any one of claims 1 to 4, wherein the method involves determining the driving tendencies of the driver of the preceding vehicle based on the behavior of the preceding vehicle, and estimating the speed of the preceding vehicle based on the behavior of the preceding vehicle and the driving tendencies of the preceding vehicle.

6. A method for estimating the driving state of a preceding vehicle according to claim 5, wherein the behavior of the preceding vehicle includes the acceleration of the preceding vehicle before it becomes undetectable, and the method for estimating the speed of the preceding vehicle based on the acceleration of the preceding vehicle and the driving tendency of the preceding vehicle.

7. A method for estimating the driving state of a preceding vehicle according to any one of claims 1 to 4, wherein the behavior of the preceding vehicle includes the acceleration of the preceding vehicle before it becomes undetectable, the navigation information includes information on the curvature of the curved road, and the method for estimating the speed of the preceding vehicle based on the acceleration of the preceding vehicle and the information on the curvature of the curved road.

8. A method for estimating the driving state of a preceding vehicle according to any one of claims 1 to 4, wherein the behavior of the preceding vehicle includes the acceleration of the preceding vehicle before it becomes undetectable, the navigation information includes a statistically average acceleration which is the average acceleration of the group of vehicles that traveled the curved road on the curved road, and the method for estimating the speed of the preceding vehicle based on the acceleration of the preceding vehicle and the statistically average acceleration.

9. A driving state estimation device for a vehicle preceding another vehicle, comprising a controller that acquires the behavior of the preceding vehicle before it becomes undetectable from the vehicle, determines whether or not the preceding vehicle can be detected as it enters a curved road, and, if the preceding vehicle cannot be detected as it enters the curved road, estimates the distance between the vehicle and the preceding vehicle based on the behavior of the preceding vehicle before it became undetectable and navigation information.

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