Vehicle speed control device, vehicle speed control method, and computer program for vehicle speed control

Abstract

To provide a vehicle speed control device capable of appropriately controlling a vehicle speed when a vehicle travels through a curve while suppressing a sense of discomfort felt by a driver about the behavior of the vehicle.SOLUTION: A vehicle speed control device includes: a lane detection section 31 for detecting an own lane in which a vehicle 10 is traveling; a curvature estimation section 32 for detecting a start point at which a curved road section starts within a prescribed distance ahead of the vehicle 10, and estimating the curvature of the own lane in the road section; a determination section 33 for determining whether the own lane is a high-speed lane or a low-speed lane; a reference speed setting section 34 for setting a reference speed so that the reference speed of the vehicle 10 decreases as the curvature of the own lane increases, and so that the reference speed when the own lane is the high-speed lane is higher than the reference speed when the own lane is the low-speed lane; and a control section 35 for controlling the speed of the vehicle 10 so that the speed of the vehicle 10 when the vehicle 10 reaches the start point of the road section is equal to or lower than the reference speed.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a vehicle speed control device, a vehicle speed control method, and a computer program for vehicle speed control. [Background technology]

[0002] In automatic vehicle driving control, the speed of a vehicle is controlled so that the vehicle can travel safely around curves (see Patent Document 1).

[0003] The vehicle speed control device disclosed in Patent Document 1 detects the presence of a curve on the road ahead of the vehicle based on road map information and the current position of the vehicle, and detects the radius of curvature of the detected curve. The vehicle speed control device then calculates the curve entry speed of the vehicle that can trace the curve based on the radius of curvature of the curve. The vehicle speed control device also detects the driving state of the driver. Furthermore, the vehicle speed control device sets a deceleration start distance at which the vehicle should start decelerating based on the driving state of the driver, the curve entry speed, and the vehicle speed. The vehicle speed control device then reduces the vehicle speed toward the curve entry speed when the distance from the start point of the curve to the vehicle falls within the range of the deceleration start distance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-269498 Summary of the Invention [Problem to be solved by the invention]

[0005] In a road section that is a curve including multiple lanes, the curvature of the curve differs for each lane. Therefore, in some cases, the degree of suppression of the vehicle speed for the vehicle to travel safely may differ depending on the lane in which the vehicle is traveling. In particular, depending on the direction of the curve, the degree of suppression of the vehicle speed when the vehicle is traveling in the overtaking lane may be greater than the degree of suppression of the vehicle speed when the vehicle is traveling in the driving lane. In such a case, if the vehicle speed is reduced to the curve entry speed, the driver may feel uncomfortable.

[0006] Therefore, an object of the present invention is to provide a vehicle speed control device that can appropriately control the vehicle speed when the vehicle is traveling around a curve while suppressing the driver from feeling uncomfortable about the vehicle's behavior. [Means for solving the problem]

[0007] According to one embodiment, there is provided a vehicle speed control device, which includes a lane detection unit that detects the lane in which the vehicle is traveling, a curvature estimation unit that detects a start point of a curved road section within a predetermined distance ahead of the vehicle and estimates a curvature of the lane in the road section based on map information or a sensor signal obtained by a sensor provided on the vehicle that detects the conditions around the vehicle, a determination unit that determines whether the lane in question is a high-speed lane in which the vehicle is permitted to travel at a relatively high speed in the road section or a low-speed lane in which the vehicle is required to travel at a relatively low speed in the road section by referring to the map information, a reference speed setting unit that sets a reference speed such that the reference speed of the vehicle decreases as the curvature of the lane in question increases and that the reference speed when the lane in question is a high-speed lane is higher than the reference speed when the lane in question is a low-speed lane, and a control unit that controls the speed of the vehicle so that the speed of the vehicle when the vehicle reaches the start point of the road section is equal to or lower than the reference speed.

[0008] In this vehicle speed control device, it is preferable that the reference speed setting unit sets one of a plurality of lanes included in the road section as the reference lane, and sets the reference speed based on the curvature of the reference lane.

[0009] In this case, it is preferable that the reference speed setting unit sets a low-speed lane among a plurality of lanes included in the road section as the reference lane.

[0010] Alternatively, it is preferable that the reference speed setting unit sets the innermost lane in a curve in the road section as the reference lane.

[0011] Alternatively, it is preferable that the reference speed setting unit sets the high-speed lane as the reference lane when the direction of the curve in the road section is a direction toward the high-speed lane, and sets the own lane as the reference lane when the direction of the curve in the road section is a direction toward the low-speed lane.

[0012] Furthermore, when the reference lane and the own lane are different, it is preferable that the reference speed setting unit calculates the curvature of the reference lane by determining the number of lanes from the reference lane to the own lane and the width of each lane in the road section based on map information, and correcting the curvature of the own lane based on the distance obtained by multiplying the number of lanes by the lane width.

[0013] According to another embodiment, there is provided a vehicle speed control method, which includes detecting a lane in which a vehicle is traveling, detecting a start point of a curved road section within a predetermined distance ahead of the vehicle based on a sensor signal obtained by a sensor provided on the vehicle that detects the conditions around the vehicle or map information, determining whether the vehicle's lane is a high-speed lane in which travel is permitted at a relatively high speed in the road section or a low-speed lane in which travel is required at a relatively low speed in the road section by referring to the map information, setting a reference speed such that the reference speed of the vehicle is lower the greater the curvature of the lane and that the reference speed when the lane is a high-speed lane is higher than the reference speed when the lane is a low-speed lane, and controlling the speed of the vehicle such that the speed of the vehicle when the vehicle reaches the start point of the road section is equal to or lower than the reference speed.

[0014] According to yet another embodiment, there is provided a computer program for controlling a vehicle speed, the computer program for controlling a vehicle speed including instructions to cause a processor mounted on the vehicle to execute the following operations: detect a lane in which the vehicle is traveling, detect a start point of a curved road section within a predetermined distance ahead of the vehicle based on a sensor signal obtained by a sensor provided on the vehicle that detects the conditions around the vehicle or map information, determine whether the lane is a high-speed lane in which the vehicle is permitted to travel at a relatively high speed in the road section or a low-speed lane in which the vehicle is required to travel at a relatively low speed in the road section, set a reference speed such that the reference speed of the vehicle is lower the greater the curvature of the lane and that the reference speed when the lane is a high-speed lane is higher than the reference speed when the lane is a low-speed lane, and control the speed of the vehicle so that the speed of the vehicle when the vehicle reaches the start point of the road section is equal to or lower than the reference speed. Effect of the Invention

[0015] The vehicle speed control device according to the present disclosure has the effect of being able to appropriately control the vehicle speed when the vehicle is traveling around a curve, while suppressing the driver from feeling uncomfortable about the vehicle's behavior. [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic configuration diagram of a vehicle control system in which a vehicle speed control device is implemented. [Diagram 2] 1 is a hardware configuration diagram of an electronic control device that is one embodiment of a vehicle speed control device. [Diagram 3] FIG. 2 is a functional block diagram of a processor of the electronic control unit, which is related to a vehicle speed control process. [Figure 4] FIG. 2 is a diagram showing an example of a low speed lane and a high speed lane. [Diagram 5] FIG. 4 is a diagram illustrating an example of deceleration control. [Figure 6] 4 is an operation flowchart of a vehicle speed control process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, a vehicle speed control device, a vehicle speed control method executed on the vehicle speed control device, and a computer program for vehicle speed control will be described with reference to the drawings. When the vehicle enters a curve, the vehicle speed control device automatically controls the vehicle speed so that the vehicle can travel around the curve safely.

[0018] For this purpose, the vehicle speed control device detects the lane in which the vehicle is traveling (hereinafter, sometimes referred to as the vehicle's own lane). The vehicle speed control device then determines whether the detected vehicle's own lane is a high-speed lane in which the vehicle is permitted to travel at a relatively high speed in the road section that curves ahead of the vehicle, or a low-speed lane in which the vehicle is required to travel at a relatively low speed. Furthermore, the vehicle speed control device sets a reference speed such that the vehicle's reference speed decreases as the curvature of the vehicle's own lane increases, and the reference speed when the vehicle's own lane is a high-speed lane is equal to or greater than the reference speed when the vehicle's own lane is a low-speed lane. The vehicle speed control device then controls the vehicle's speed so that the vehicle's speed when the vehicle reaches the start point of the road section that curves is equal to or less than the reference speed. Note that, hereinafter, the road section that curves may simply be referred to as a curve section.

[0019] FIG. 1 is a schematic diagram of a vehicle control system in which a vehicle speed control device is implemented. FIG. 2 is a hardware configuration diagram of an electronic control device which is an embodiment of the vehicle speed control device. In this embodiment, a vehicle control system 1 which is mounted on a vehicle 10 and controls the vehicle 10 includes a camera 2, a GPS receiver 3, a storage device 4, and an electronic control unit (ECU) 5 which is an example of a vehicle speed control device. The camera 2, the GPS receiver 3, the storage device 4, and the ECU 5 are communicatively connected via an in-vehicle network conforming to a standard such as a controller area network. The vehicle control system 1 may further include a distance measuring sensor (not shown) such as a LiDAR or a radar for measuring the distance from the vehicle 10 to an object present around the vehicle 10. The vehicle control system 1 may further include a wireless communication terminal (not shown) for communicating with other devices. The vehicle control system 1 may further include a navigation device (not shown) for setting a planned driving route of the vehicle 10.

[0020] Camera 2 is an example of a sensor that detects the situation around vehicle 10, and has a two-dimensional detector configured with an array of photoelectric conversion elements sensitive to visible light, such as a CCD or C-MOS, and an imaging optical system that forms an image of the area to be photographed on the two-dimensional detector. Camera 2 is attached, for example, inside the passenger compartment of vehicle 10 so as to face the front of vehicle 10. Camera 2 photographs the area in front of vehicle 10 at a predetermined photographing period (for example, 1 / 30 to 1 / 10 seconds) and generates an image showing the area in front of vehicle 10. The image obtained by camera 2 is an example of a sensor signal. Note that vehicle 10 may be provided with multiple cameras with different photographing directions or focal lengths.

[0021] Every time the camera 2 generates an image, it outputs the generated image to the ECU 5 via the in-vehicle network.

[0022] The GPS receiver 3 receives GPS signals from GPS satellites at predetermined intervals and measures the own position of the vehicle 10 based on the received GPS signals. Then, the GPS receiver 3 outputs positioning information representing the positioning result of the own position of the vehicle 10 based on the GPS signals to the ECU 5 via the in-vehicle network at predetermined intervals. Note that the vehicle 10 may have a receiver that receives positioning signals from satellites of other satellite positioning systems and measures the own position of the vehicle 10, instead of the GPS receiver.

[0023] The storage device 4 is an example of a storage unit, and includes, for example, a hard disk device, a non-volatile semiconductor memory, or an optical recording medium and an access device therefor. The storage device 4 stores a high-precision map. The high-precision map is an example of map information. The high-precision map includes information representing road markings such as the number of lanes, lane widths, lane dividing lines, and stop lines in each road section included in a predetermined area shown on the high-precision map, information representing road signs provided in each road section, and information representing vehicle speed limits in each road section. Furthermore, the high-precision map includes information representing the positions of both ends of each curve section in each road section. Furthermore, the high-precision map may include information representing the curvature of each curve section.

[0024] Furthermore, the storage device 4 may have a processor for executing an update process of the high-precision map, and a process related to a read request of the high-precision map from the ECU 5. The storage device 4 may transmit a request to acquire a high-precision map together with the current position of the vehicle 10 to a map server via a wireless communication terminal (not shown), for example, every time the vehicle 10 moves a predetermined distance. The storage device 4 may also receive a high-precision map of a predetermined area around the current position of the vehicle 10 from the map server via the wireless communication terminal. When the storage device 4 receives a read request of the high-precision map from the ECU 5, the storage device 4 extracts an area that includes the current position of the vehicle 10 and is relatively narrower than the above-mentioned predetermined area from the stored high-precision map, and outputs the area to the ECU 5 via the in-vehicle network.

[0025] The ECU 5 automatically controls the speed of the vehicle 10. In particular, the ECU 5 controls the speed of the vehicle 10 so that the vehicle 10 can safely travel through curved sections.

[0026] 2, the ECU 5 has a communication interface 21, a memory 22, and a processor 23. The communication interface 21, the memory 22, and the processor 23 may each be configured as a separate circuit, or may be integrated into a single integrated circuit.

[0027] The communication interface 21 has an interface circuit for connecting the ECU 5 to an in-vehicle network. Every time the communication interface 21 receives an image from the camera 2, it passes the received image to the processor 23. Every time the communication interface 21 receives positioning information from the GPS receiver 3, it passes the positioning information to the processor 23. Furthermore, the communication interface 21 passes the high-precision map read from the storage device 4 to the processor 23.

[0028] The memory 22 is another example of a storage unit, and includes, for example, a volatile semiconductor memory and a non-volatile semiconductor memory. The memory 22 stores various data used in the vehicle speed control process executed by the processor 23. For example, the memory 22 stores parameters such as the focal length, shooting direction, and mounting position of the camera 2, and various parameters for identifying a classifier used to detect objects around the vehicle 10. The memory 22 also stores a pre-deceleration table representing the relationship between the curvature and the reference speed, and a curve traveling speed table representing the relationship between the curvature and the traveling speed in the curve section. The memory 22 also stores positioning information of the vehicle 10, an image of the surroundings of the vehicle 10, and a high-precision map. The memory 22 also temporarily stores various data generated during the vehicle speed control process.

[0029] The processor 23 has one or more central processing units (CPUs) and their peripheral circuits. The processor 23 may further have other arithmetic circuits such as a logic arithmetic unit, a numerical arithmetic unit, or a graphic processing unit. The processor 23 executes a vehicle speed control process for the vehicle 10 at predetermined intervals.

[0030] 3 is a functional block diagram of the processor 23 related to the vehicle speed control process. The processor 23 has a lane detection unit 31, a curvature estimation unit 32, a determination unit 33, a reference speed setting unit 34, and a control unit 35. Each of these units in the processor 23 is, for example, a functional module realized by a computer program running on the processor 23. Alternatively, each of these units in the processor 23 may be a dedicated arithmetic circuit provided in the processor 23.

[0031] The lane detection unit 31 detects the lane in which the vehicle 10 is traveling. In this embodiment, the lane detection unit 31 detects the lane by comparing an image (hereinafter, sometimes simply referred to as an image) generated by the camera 2 with a high-precision map. To this end, the lane detection unit 31 detects features on or around the road, such as road markings such as lane dividing lines, curbs, or road signs, from the image. For example, the lane detection unit 31 detects features shown in the image by inputting the image to a classifier. As such a classifier, the lane detection unit 31 can use a deep neural network (DNN) having a convolutional neural network (CNN) type architecture, such as Single Shot MultiBox Detector (SSD) or Faster R-CNN. Alternatively, the lane detection unit 31 can use a DNN having a self attention network (SAN) type architecture, such as Vision Transformer, as such a classifier. Such a classifier is trained in advance to detect features to be detected from an image. The classifier outputs information that identifies an object region that includes a feature detected on the input image and information that indicates the type of the detected feature.

[0032] When the features are detected, the lane detection unit 31 assumes the position and attitude of the vehicle 10 and projects each feature detected from the image onto the high-precision map, or projects each feature on or around the road around the vehicle 10 shown on the high-precision map onto the image. The lane detection unit 31 then estimates the position and attitude of the vehicle 10 when each feature detected from the image most closely matches the corresponding feature shown on the high-precision map, as the self-position of the vehicle 10. The lane detection unit 31 then refers to the high-precision map and identifies the lane that includes the self-position of the vehicle 10 as the own lane in which the vehicle 10 is traveling.

[0033] The lane detection unit 31 may determine the position where the feature is projected on the high-precision map or image by using the assumed initial values ​​of the position and attitude of the vehicle 10 and the parameters of the camera 2, such as the focal length, the installation height, and the shooting direction. As the initial values ​​of the position and attitude of the vehicle 10, the position of the vehicle 10 measured by the GPS receiver 3, or the position and attitude of the vehicle 10 estimated at the time of the previous own lane detection, corrected by using the odometry information, is used. Then, the lane detection unit 31 calculates the degree of match between the features on or around the road detected from the image and the features on or around the road shown on the high-precision map (for example, the reciprocal of the squared sum of the distance between each detected feature and the corresponding feature).

[0034] The lane detection unit 31 repeats the above process while changing the assumed position and attitude of the vehicle 10. Then, the lane detection unit 31 determines the assumed position and attitude when the degree of agreement is maximized as the actual self-position of the vehicle 10.

[0035] When the positioning accuracy of the vehicle 10 by the GPS receiver 3 is sufficient, the lane detection unit 31 may take the position of the vehicle 10 represented in the latest positioning information received from the GPS receiver 3 as the actual own position of the vehicle 10. Then, similarly to the above embodiment, the lane detection unit 31 may refer to the high-precision map and identify the lane including the own position of the vehicle 10 as the own lane in which the vehicle 10 is traveling.

[0036] Furthermore, the lane detection unit 31 identifies the lane markings that define the own vehicle lane among the lane markings detected from the image. For example, the lane detection unit 31 can identify the lane markings that are closest to the center of the image, which is to the right of the center in the horizontal direction of the image and closest to the bottom edge of the image, i.e., the position closest to the vehicle 10, as the lane markings that define the right side of the own vehicle lane. Similarly, the lane detection unit 31 can identify the lane markings that are closest to the center of the image, which is to the left of the center in the horizontal direction of the image and closest to the bottom edge of the image, as the lane markings that define the left side of the own vehicle lane.

[0037] The lane detection unit 31 notifies the curvature estimation unit 32, the determination unit 33, and the control unit 35 of information representing the detected own lane and information representing the own position. Furthermore, the lane detection unit 31 notifies the curvature estimation unit 32 of the position of each pixel representing either the left or right lane marking that divides the own lane detected from the image.

[0038] The curvature estimation unit 32 refers to the vehicle 10's own position and the high-precision map, and determines whether or not the start point of the curve section is within a predetermined distance ahead of the vehicle 10 in the traveling direction of the vehicle 10. When the curvature estimation unit 32 detects a curve section whose start point is within the predetermined distance, it estimates the curvature of the own lane in the curve section. Note that, hereinafter, a curve section that starts at a start point that is within a predetermined distance ahead of the vehicle 10 in the traveling direction of the vehicle 10 may be simply referred to as a curve section or a detected curve section.

[0039] For example, the curvature estimation unit 32 selects three or more points located farther away from the start point of the detected curve section on the lane markings on either the left or right side of the vehicle's own lane. The position of each pixel on the image corresponds one-to-one to the orientation as seen from the camera 2. The parameters of the camera 2, such as the shooting direction, installation height, and focal length of the camera 2, are known, and the lane markings are located on the road surface. Therefore, the curvature estimation unit 32 can obtain the position in real space of the point on the lane markings represented by each pixel on the image, with the camera 2 as the reference, for each pixel on the image on which the lane markings are represented. Therefore, the curvature estimation unit 32 reads from the memory 22 an image generated after the detected curve section is included in the shooting range of the camera 2. Then, the curvature estimation unit 32 may select three or more points located farther away from the start point of the detected curve section from among the points represented by each pixel on the image on which the lane markings are represented. Then, the curvature estimation unit 32 obtains an approximation curve passing through each point, and sets the curvature of the approximation curve as the curvature of the own lane in the detected curve section.

[0040] The curvature estimation unit 32 may perform the above process on each of the lane markings on the left side and the right side of the own lane to calculate the curvature of each, and may use the average of the calculated curvatures as the curvature of the own lane in the detected curve section. The curvature estimation unit 32 may also use the curvature of the curve section shown on the high-precision map as the curvature of the own lane in that curve section.

[0041] The curvature estimation unit 32 notifies the reference speed setting unit 34 of the curvature of the own lane in the detected curve section. Furthermore, the curvature estimation unit 32 notifies the determination unit 33 of information indicating the detected curve section.

[0042] The judgment unit 33 judges whether the vehicle's lane in the detected curve section is a high-speed lane in which driving at a relatively high speed is permitted in the curve section, or a low-speed lane in which driving at a relatively low speed is required in the curve section.

[0043] The determination unit 33 refers to the high-precision map to determine whether the lane in the curve section is a driving lane or an overtaking lane. If the lane is a driving lane, the determination unit 33 determines the lane as a low-speed lane. On the other hand, if the lane is an overtaking lane, the determination unit 33 determines the lane as a high-speed lane.

[0044] Fig. 4 is a diagram showing an example of a low-speed lane and a high-speed lane. In the example shown in Fig. 4, it is assumed that a lane 401 on the right side in the traveling direction of the vehicle 10 is an overtaking lane, and a lane 402 on the left side is a driving lane. In this case, since the vehicle 10 is traveling in the driving lane 402 on the left side, the own lane is determined to be a low-speed lane.

[0045] The determination unit 33 may determine whether the own lane corresponds to a driving lane or an overtaking lane in a curve section based on the position of the own lane on the image. For example, in an area where driving on the left side is applied, such as Japan, if there is no lane on the right side of the own lane on the image that faces the same direction as the traveling direction of the vehicle 10, the determination unit 33 determines that the own lane is an overtaking lane, i.e., a high-speed lane. On the other hand, if there is a lane on the right side of the own lane on the image that faces the same direction as the traveling direction of the vehicle 10, the determination unit 33 determines that the own lane is a driving lane, i.e., a low-speed lane. If only one or less lane markings are detected on the right side of the own lane, or if a median strip is detected to the right of the own lane, the determination unit 33 may determine that there is no lane on the right side of the own lane that faces the same direction as the traveling direction of the vehicle 10.

[0046] In addition, there are cases where a so-called yield lane, such as an uphill lane, is provided in a curved section. In such a case, if the own lane is a yield lane, the determination unit 33 may determine the own lane as a low-speed lane. In addition, if the own lane is a lane other than a yield lane, the determination unit 33 may determine the own lane as a high-speed lane.

[0047] The determination unit 33 notifies the reference speed setting unit 34 of the result of the determination as to whether the own lane is a high-speed lane or a low-speed lane.

[0048] The reference speed setting unit 34 sets the reference speed so that the reference speed of the vehicle 10 decreases as the curvature of the own lane increases, and the reference speed when the own lane is a high-speed lane is equal to or greater than the reference speed when the own lane is a low-speed lane. The reference speed is a target upper limit speed when the vehicle 10 enters a curved section, and is set to a speed at which the vehicle 10 can travel through the curved section without suddenly decelerating.

[0049] When setting the reference speed, the reference speed setting unit 34 sets one of a plurality of lanes in the curve section as a lane that is a reference for setting the reference speed (hereinafter, may be referred to as a reference lane). The reference speed setting unit 34 sets the reference speed based on the curvature of the reference lane. For example, the reference speed setting unit 34 sets a low-speed lane as the reference lane. In addition, when the number of lanes in the curve section is three or more, the reference speed setting unit 34 sets the lane farthest from the high-speed lane (for example, the leftmost lane in Japan) as the reference lane. Alternatively, the reference speed setting unit 34 may set the innermost lane in the curve section as the reference lane. This prevents a situation in which the vehicle 10 decelerates when traveling in the high-speed lane when entering the curve section, but does not decelerate when traveling in the low-speed lane.

[0050] When the own lane and the reference lane are different and the curvature of the reference lane is not indicated in the high-precision map, the reference speed setting unit 34 calculates the distance obtained by multiplying the number of lanes from the own lane to the reference lane by the width of each lane as the correction radius. The reference speed setting unit 34 estimates the curvature of the reference lane by setting the value obtained by subtracting the correction radius from the curvature radius corresponding to the curvature of the own lane as the curvature radius of the reference lane. The reference speed setting unit 34 may refer to the high-precision map to determine the number of lanes from the own lane to the reference lane and the width of each lane.

[0051] In addition, it is preferable that the reference speed setting unit 34 corrects the curvature of the reference lane so that the curvature of the reference lane is equal to or greater than the curvature of the express lane, thereby preventing the reference speed from becoming too high when the vehicle 10 is traveling on the express lane.

[0052] The reference speed setting unit 34 refers to the high-precision map to determine whether the current position of the vehicle 10 belongs to an area where the high-speed lane is located to the right of the low-speed lane, as in Japan, or conversely, to an area where the high-speed lane is located to the left of the low-speed lane. Furthermore, the reference speed setting unit 34 refers to the high-precision map to determine whether the curve section is a right curve or a left curve in the traveling direction of the vehicle 10. If the curve section is a section that turns toward the high-speed lane, for example, if the current position of the vehicle 10 is in Japan and the curve section is a right curve, the reference speed setting unit 34 corrects the curvature of the reference lane to the curvature of the overtaking lane, i.e., the high-speed lane. Furthermore, if the current position of the vehicle 10 is in Japan and the curve section is a left curve, the reference speed setting unit 34 corrects the curvature of the reference lane to the curvature of the leftmost driving lane or the yield lane. In the above case, if the reference lane is set as the leftmost driving lane or the yield lane, the reference speed setting unit 34 does not need to correct the curvature of the reference lane.

[0053] Referring again to FIG. 4, the left driving lane (i.e., low speed lane) 402 is set as the reference lane. However, the curve section 410 located ahead of the vehicle 10 is a right curve. Therefore, the curvature of the overtaking lane (i.e., high speed lane) 401 on the right is greater than the curvature of the reference lane, which is the low speed lane 402. Therefore, the curvature of the reference lane is corrected to the curvature of the high speed lane 401. If the curve section 410 were a left curve, the curvature of the low speed lane 402 would be greater than the curvature of the high speed lane 401. Therefore, in this case, the curvature of the low speed lane 402 is set as it is as the curvature of the reference lane.

[0054] Once the curvature of the reference lane is determined, the reference speed setting unit 34 identifies a reference speed corresponding to the curvature of the reference lane by referring to a pre-deceleration table that indicates the relationship between the curvature and the reference speed. In the pre-deceleration table, the reference speed is set so that the reference speed is lower as the curvature is larger. The reference speed setting unit 34 then sets the identified reference speed as the reference speed to be applied to the curve section. Therefore, the larger the curvature of the own lane or the reference lane, the lower the reference speed to be applied. The reference speed setting unit 34 notifies the control unit 35 of the set reference speed.

[0055] According to the modified example, the reference speed setting unit 34 may set the reference lane to the high-speed lane when the curve direction in the curve section is a direction bending toward the high-speed lane side, regardless of whether the own lane is a low-speed lane or a high-speed lane. On the other hand, the reference speed setting unit 34 may set the own lane to the reference lane when the curve direction in the curve section is a direction bending toward the low-speed lane side. Thereby, when the curvature of the low-speed lane is smaller than that of the high-speed lane in the curve section, the same reference speed is set regardless of whether the vehicle 10 is traveling in the low-speed lane or the high-speed lane. Therefore, a situation in which the vehicle 10 is decelerated only when traveling in the high-speed lane is prevented. On the other hand, when the curvature of the high-speed lane is smaller than that of the low-speed lane in the curve section, the reference speed when the own lane is a low-speed lane is lower than the reference speed when the own lane is a high-speed lane. Therefore, the processor 23 can reduce the degree of deceleration of the vehicle 10 when the vehicle 10 is traveling in a high-speed lane with a relatively small curvature.

[0056] The control unit 35 controls the speed of the vehicle 10 so that the speed of the vehicle 10 when the vehicle 10 reaches the start point of the curve section is equal to or lower than a reference speed. To this end, the control unit 35 compares the current vehicle speed of the vehicle 10 measured by a vehicle speed sensor (not shown) provided in the vehicle 10 with the reference speed. If the current vehicle speed is equal to or lower than the reference speed, the control unit 35 controls the vehicle 10 so that the current vehicle speed is maintained until the start point of the curve section. On the other hand, if the current vehicle speed is faster than the reference speed, the control unit 35 calculates a travel distance (hereinafter, sometimes referred to as a deceleration distance) required to decelerate the speed of the vehicle 10 from the current vehicle speed to the reference speed at a predetermined pre-deceleration. Then, when the current position of the vehicle 10 indicated by the positioning information reaches a position (hereinafter, referred to as a deceleration start position) that is a deceleration distance before the start point of the curve section, the control unit 35 controls the vehicle 10 to decelerate at the pre-deceleration. That is, when the vehicle 10 reaches the deceleration start position, the control unit 35 sets the accelerator opening so that the deceleration of the vehicle 10 becomes equal to the pre-deceleration. Then, the control unit 35 determines the amount of fuel injection according to the set accelerator opening, and outputs a control signal corresponding to the amount of fuel injection to a fuel injection device of the engine of the vehicle 10. Alternatively, the control unit 35 determines the amount of power to be supplied to the motor according to the set accelerator opening, and controls a drive circuit of the motor so that the amount of power is supplied to the motor. Furthermore, the control unit 35 sets a braking amount as necessary, and outputs a control signal corresponding to the set braking amount to the brake of the vehicle 10. Note that the preliminary deceleration is set to a deceleration at which the driver does not feel strange or uncomfortable with the deceleration of the vehicle 10 before the curve section, for example, the deceleration when the accelerator opening is minimized or 0.05G to 0.15G.

[0057] Further, the control unit 35 controls the speed of the vehicle 10 while the vehicle 10 is traveling through the curve section so that the vehicle 10 can travel through the curve section safely. That is, the control unit 35 sets a target speed during traveling through the curve section (hereinafter, sometimes referred to as curve traveling speed) based on the curvature of the own lane in the curve section. At this time, the control unit 35 specifies the traveling speed corresponding to the curvature of the own lane by referring to a curve traveling speed table that indicates the relationship between the curvature and the traveling speed in the curve section, and sets the specified traveling speed as the curve traveling speed. Then, the control unit 35 controls the speed of the vehicle 10 so that the speed of the vehicle 10 is decelerated to the curve traveling speed. At this time, the control unit 35 decelerates the vehicle 10 at a deceleration that is preset for traveling through the curve section. The absolute value of this deceleration is set to a value (for example, 0.15G to 0.3G) larger than the absolute value of the above-mentioned preliminary deceleration. The control unit 35 may decelerate the vehicle 10 by the same control as the deceleration before the start point of the curve section.

[0058] Furthermore, the control unit 35 starts accelerating the vehicle 10 in the middle of the curve section so that the speed of the vehicle 10 when the vehicle 10 reaches the end of the curve section will be a preset speed (hereinafter, sometimes simply referred to as the set speed). Then, the control unit 35 controls the speed of the vehicle 10 so that it accelerates at a predetermined acceleration. The control unit 35 may set the position at which acceleration starts to the front of the end of the curve section by a travel distance (hereinafter, sometimes referred to as the acceleration distance) required to reach the set speed at a predetermined acceleration from the curve traveling speed. Also, the control unit 35 sets the accelerator opening so that the acceleration of the vehicle 10 becomes a predetermined acceleration, similar to when decelerating the vehicle 10. Then, the control unit 35 calculates the fuel injection amount according to the set accelerator opening, and outputs a control signal according to the fuel injection amount to the fuel injection device of the engine of the vehicle 10. Alternatively, the control unit 35 calculates the amount of power supplied to the motor according to the set accelerator opening, and controls the drive circuit of the motor so that the amount of power is supplied to the motor.

[0059] The control unit 35 may set the acceleration start position when the own lane is a high-speed lane closer to the start position of the curve section than the acceleration start position when the own lane is a low-speed lane.

[0060] Fig. 5 is a diagram showing an example of deceleration control when the vehicle 10 is traveling through a curve section. In Fig. 5, the vertical axis represents the vehicle speed, and the horizontal axis represents the position of the vehicle 10. A graph 501 represents the relationship between the position of the vehicle 10 and the vehicle speed.

[0061] As shown in graph 501, the vehicle speed of the vehicle 10 is maintained at the set speed until the vehicle 10 reaches the deceleration start position P1. When the vehicle 10 reaches the deceleration start position P1, deceleration of the vehicle 10 begins at the preliminary deceleration. Then, when the vehicle 10 reaches the start position P2 of the curve section C, the speed of the vehicle 10 decreases to the reference speed. Thereafter, the vehicle speed of the vehicle 10 is controlled to further decrease to the curve driving speed in the curve section C, and thereafter, the vehicle 10 is accelerated until it reaches the end position P3 of the curve section. Then, when the vehicle 10 reaches the end position P3 of the curve section, the vehicle speed of the vehicle 10 returns to the set speed.

[0062] 6 is an operational flowchart of the vehicle speed control process executed by the processor 23. The processor 23 may execute the vehicle speed control process in accordance with the following operational flowchart at predetermined intervals.

[0063] The lane detection unit 31 of the processor 23 detects the lane in which the vehicle 10 is traveling (step S101). The curvature estimation unit 32 of the processor 23 determines whether or not the start point of a curve section is within a predetermined distance ahead of the vehicle 10 (step S102). If the start point of a curve section is not within the predetermined distance (step S102-No), the control unit 35 of the processor 23 controls the vehicle 10 to maintain the current vehicle speed of the vehicle 10 (step S103). Then, the processor 23 ends the vehicle speed control process.

[0064] On the other hand, if the start point of the curve section is within the predetermined distance (step S103-Yes), the curvature estimation unit 32 estimates the curvature of the own lane in the curve section (step S104). Then, the determination unit 33 of the processor 23 determines whether the own lane is a low-speed lane or a high-speed lane in the curve section (step S105).

[0065] The reference speed setting unit 34 of the processor 23 sets the reference speed so that the reference speed of the vehicle 10 is lower as the curvature of the own lane increases, and the reference speed when the own lane is a high-speed lane is equal to or higher than the reference speed when the own lane is a low-speed lane (step S106). Then, the control unit 35 of the processor 23 controls the speed of the vehicle 10 so that the speed of the vehicle 10 when the vehicle 10 reaches the start point of the curve section is equal to or lower than the reference speed (step S107). Then, the control unit 35 decelerates the speed of the vehicle 10 while the vehicle 10 is traveling in the curve section to the curve traveling speed, and then accelerates the vehicle 10 so that the speed of the vehicle 10 reaches the set speed when the vehicle 10 reaches the end of the curve section (step S108). Then, the processor 23 ends the vehicle speed control process.

[0066] As described above, the vehicle speed control device determines whether the lane in which the vehicle is traveling is a high-speed lane or a low-speed lane in the curved section ahead of the vehicle. Furthermore, the vehicle speed control device sets a reference speed such that the reference speed of the vehicle is lower as the curvature of the lane in question is greater, and the reference speed when the lane in question is a high-speed lane is equal to or greater than the reference speed when the lane in question is a low-speed lane. The vehicle speed control device controls the speed of the vehicle so that the speed of the vehicle when the vehicle reaches the start point of the curved section is equal to or less than the reference speed. By controlling the speed of the vehicle in this manner, the vehicle speed control device can prevent the vehicle from departing from the lane in the curved section. Furthermore, the vehicle speed control device can prevent a situation in which the vehicle decelerates when traveling in the high-speed lane but does not decelerate when traveling in the low-speed lane when entering a curved section, and can decelerate the vehicle without giving a sense of discomfort to the driver.

[0067] In addition, a computer program for realizing the functions of the processor 23 of the ECU 5 according to the above embodiment or modified example may be provided in a form recorded on a computer-readable portable recording medium, such as a semiconductor memory, a magnetic recording medium, or an optical recording medium.

[0068] As described above, those skilled in the art can make various modifications to the embodiments within the scope of the present invention. [Explanation of symbols]

[0069] 1 Vehicle Control System 10 Vehicles 2 Camera 3 GPS receiver 4. Storage Devices 5 Electronic Control Unit (ECU) 21 Communication Interface 22 Memory 23 Processors 31 Lane detection unit 32 Curvature estimation part 33 Judgment section 34 Reference speed setting section 35 Control section

Claims

1. A lane detection unit that detects the lane in which the vehicle is traveling; a curvature estimation unit that detects a start point of a curved road section within a predetermined distance ahead of the vehicle based on map information or a sensor signal obtained by a sensor that detects a situation around the vehicle and that is provided on the vehicle, and estimates a curvature of the host lane in the road section; a determination unit that determines, with reference to the map information, whether the vehicle's lane is a high-speed lane in which the vehicle is permitted to travel at a relatively high speed in the road section, or a low-speed lane in which the vehicle is required to travel at a relatively low speed in the road section; a reference speed setting unit that sets one of a plurality of lanes included in the road section as a reference lane, and sets the reference speed based on a curvature of the reference lane such that the reference speed set for the vehicle is lower as the curvature of the own lane is larger, and the reference speed when the own lane is the high-speed lane is equal to or higher than the reference speed when the own lane is the low-speed lane; a control unit that controls a speed of the vehicle so that the speed of the vehicle when the vehicle reaches the start point of the road section is equal to or less than the reference speed; A vehicle speed control device having the same.

2. The vehicle speed control device according to claim 1 , wherein the reference speed setting unit sets the low speed lane among the plurality of lanes included in the road section as the reference lane.

3. The vehicle speed control device according to claim 1 , wherein the reference speed setting unit sets the reference lane to an innermost lane in a curve in the road section.

4. 2. The vehicle speed control device according to claim 1, wherein the reference speed setting unit sets the high-speed lane as the reference lane when the direction of the curve in the road section is a direction curving toward the high-speed lane, and sets the own lane as the reference lane when the direction of the curve in the road section is a direction curving toward the low-speed lane.

5. 2. The vehicle speed control device according to claim 1, wherein, when the reference lane and the own lane are different, the reference speed setting unit calculates the curvature of the reference lane by determining the number of lanes from the reference lane to the own lane and the width of each lane in the road section based on the map information, and correcting the curvature of the own lane based on a distance obtained by multiplying the number of lanes by the width.

6. Detects the lane the vehicle is traveling in, detecting a start point of a curved road section within a predetermined distance ahead of the vehicle based on map information or a sensor signal obtained by a sensor provided on the vehicle that detects the conditions around the vehicle, and estimating a curvature of the vehicle's lane in the road section; With reference to the map information, determine whether the vehicle lane is a high-speed lane in which a relatively high speed is permitted to be traveled in the road section, or a low-speed lane in which a relatively low speed is required to be traveled in the road section; setting one of a plurality of lanes included in the road section as a reference lane, and setting the reference speed based on a curvature of the reference lane such that the larger the curvature of the own lane, the lower the reference speed set for the vehicle, and the reference speed when the own lane is the high-speed lane is equal to or higher than the reference speed when the own lane is the low-speed lane; controlling a speed of the vehicle so that the speed of the vehicle when the vehicle reaches the start point of the road section is equal to or lower than the reference speed; A vehicle speed control method comprising the steps of:

7. Detects the lane the vehicle is traveling in, detecting a start point of a curved road section within a predetermined distance ahead of the vehicle based on map information or a sensor signal obtained by a sensor provided on the vehicle that detects the conditions around the vehicle, and estimating a curvature of the vehicle's lane in the road section; With reference to the map information, determine whether the vehicle lane is a high-speed lane in which a relatively high speed is permitted to be traveled in the road section, or a low-speed lane in which a relatively low speed is required to be traveled in the road section; setting one of a plurality of lanes included in the road section as a reference lane, and setting the reference speed based on a curvature of the reference lane such that the larger the curvature of the own lane, the lower the reference speed set for the vehicle, and the reference speed when the own lane is the high-speed lane is equal to or higher than the reference speed when the own lane is the low-speed lane; controlling a speed of the vehicle so that the speed of the vehicle when the vehicle reaches the start point of the road section is equal to or lower than the reference speed; A computer program for vehicle speed control that causes a processor mounted on the vehicle to execute the above steps.

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