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

Abstract

A vehicle speed control device, a vehicle speed control method, and a computer program for vehicle speed control are provided. The vehicle speed control device includes: a lane detection unit (31) that detects the vehicle's own lane while the vehicle (10) is traveling; a curvature estimation unit (32) that detects the starting point of a road section within a predetermined distance ahead of the vehicle (10) that is a curve, and estimates the curvature of the vehicle's own lane in the road section; a determination unit (33) that determines whether the vehicle's own lane is a high-speed lane or a low-speed lane; a reference speed setting unit (34) that sets a reference speed in such a way that the greater the curvature of the vehicle's own lane, the lower the reference speed of the vehicle (10), and the reference speed when the vehicle's own lane is a high-speed lane is higher than the reference speed when the vehicle's own lane is a low-speed lane; and a control unit (35) that controls the vehicle's speed so that the vehicle's speed when the vehicle reaches the starting point of the aforementioned road section is below the reference speed.

Description

Technical Field

[0001] This 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 the automatic driving control of vehicles, the speed of the vehicle is controlled so that the vehicle can drive safely on curves (see Japanese Patent Application Publication No. 10-269498).

[0003] The vehicle speed control device disclosed in Japanese Patent Application Publication No. 10-269498 detects the presence of curves in the road ahead of the vehicle based on road map information and the vehicle's current position, and detects the radius of curvature of the detected curves. Furthermore, based on the radius of curvature of the curves, the speed control device calculates the curve entry speed of the vehicle capable of tracking the curve. Additionally, the speed control device detects the driver's driving state. Further, based on the driver's driving state, the curve entry speed, and the vehicle speed, the speed control device sets a deceleration initiation distance at which the vehicle should begin to decelerate. Moreover, when the distance from the start point of the curve to the vehicle falls within this deceleration initiation distance, the speed control device reduces the vehicle speed towards the curve entry speed. Summary of the Invention

[0004] In road sections with multiple lanes forming a curve, the curvature of the curve varies from lane to lane. Therefore, depending on the situation, the degree of speed reduction for safe driving may sometimes differ depending on the lane the vehicle is traveling in. In particular, depending on the direction of the curve, sometimes the speed reduction for a vehicle traveling in the overtaking lane may be greater than that for a vehicle traveling in the driving lane. In such cases, the decrease in speed as the vehicle approaches the curve may feel unnatural to the driver.

[0005] Therefore, the object of the present invention is to provide a vehicle speed control device that can appropriately control the vehicle speed when driving on a curve while suppressing the driver's sense of unease about the vehicle's behavior.

[0006] According to one embodiment, a vehicle speed control device is provided. This vehicle speed control device includes: a lane detection unit that detects the vehicle's own lane while it is traveling; a curvature estimation unit that, based on sensor signals obtained by sensors installed on the vehicle to detect the conditions around the vehicle or map information, detects the starting point of a road section within a predetermined distance ahead of the vehicle that is a curve, and estimates the curvature of its own lane within that road section; a determination unit that, with reference to map information, determines whether its own lane is a high-speed lane where relatively high speeds are permitted in the road section, or a low-speed lane where relatively low speeds are required in the road section; a reference speed setting unit that sets a reference speed such that the greater the curvature of its own lane, the lower the reference speed of the vehicle, and the reference speed when its own lane is a high-speed lane is higher than the reference speed when its own lane is a low-speed lane; and a control unit that controls the vehicle's speed so that the vehicle's speed when it reaches the starting point of the road section is below the reference speed.

[0007] In this vehicle speed control device, it is preferable that the reference speed setting unit sets any one of the multiple lanes included in the road section as the reference lane, and sets the reference speed based on the curvature of the reference lane.

[0008] In this case, it is preferable that the reference speed setting unit sets the low-speed lane among the multiple lanes included in the road section as the reference lane.

[0009] Alternatively, the preferred reference speed setting unit may set the innermost lane in the curves of the road section as the reference lane.

[0010] Alternatively, the preferred method is to set the high-speed lane as the reference lane when the curve in the road section curves towards the high-speed lane, and to set its own lane as the reference lane when the curve in the road section curves towards the low-speed lane.

[0011] Furthermore, when the reference lane and its own lane are different, the preferred reference speed setting unit calculates the number of lanes from the reference lane to its own lane and the width of each lane in the road section based on map information. Based on the distance obtained by multiplying the number of lanes by the width of the lane, the curvature of its own lane is corrected, thereby calculating the curvature of the reference lane.

[0012] According to other embodiments, a vehicle speed control method is provided. The vehicle speed control method includes: detecting the vehicle's own lane while it is traveling; detecting the starting point of a road section within a predetermined distance ahead of the vehicle, which is a curve, based on sensor signals or map information obtained by sensors installed on the vehicle to detect the conditions around the vehicle; estimating the curvature of the vehicle's own lane within the road section; determining, with reference to map information, whether the vehicle's own lane is a high-speed lane where relatively high speeds are permitted or a low-speed lane where relatively low speeds are required; setting a reference speed such that a greater curvature of the vehicle's own lane results in a lower reference speed, and that the reference speed when the vehicle's own lane is a high-speed lane is higher than the reference speed when the vehicle's own lane is a low-speed lane; and controlling the vehicle's speed so that when the vehicle reaches the starting point of the road section, the vehicle's speed is below the reference speed.

[0013] Furthermore, according to other embodiments, a computer program for vehicle speed control is provided. This computer program includes commands for causing a processor mounted on a vehicle to perform the following processing: detecting the vehicle's own lane while it is traveling; based on sensor signals or map information obtained by sensors installed on the vehicle to detect the conditions around the vehicle, detecting the starting point of a road section within a predetermined distance ahead of the vehicle that is a curve, and estimating the curvature of the vehicle's own lane within that road section; referring to map information, determining whether the vehicle's own lane is a high-speed lane where relatively high speeds are permitted in the aforementioned road section or a low-speed lane where relatively low speeds are required in the aforementioned road section; setting a reference speed such that a greater curvature of the vehicle's own lane results in a lower reference speed, and that the reference speed when the vehicle's own lane is a high-speed lane is higher than the reference speed when the vehicle's own lane is a low-speed lane; and controlling the vehicle's speed so that when the vehicle reaches the starting point of the aforementioned road section, the vehicle's speed is below the reference speed.

[0014] According to the vehicle speed control device disclosed herein, the following effect is achieved: while suppressing the driver's sense of unease about the vehicle's behavior, the vehicle speed can be appropriately controlled when driving in a curve. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a vehicle control system equipped with a speed control device.

[0016] Figure 2 This is a hardware structure diagram of an electronic control device as one embodiment of a vehicle speed control device.

[0017] Figure 3This is a functional block diagram of the processor of the electronic control device related to vehicle speed control processing.

[0018] Figure 4 This is a diagram illustrating an example of low-speed lanes and high-speed lanes.

[0019] Figure 5 This is a diagram illustrating an example of deceleration control.

[0020] Figure 6 This is a flowchart of the vehicle speed control process. Detailed Implementation

[0021] The following description, with reference to the accompanying drawings, describes the vehicle speed control device, the vehicle speed control method executed on the vehicle speed control device, and the computer program for vehicle speed control. This vehicle speed control device automatically controls the vehicle speed when the vehicle enters a curve, so that the vehicle can travel safely on the curve.

[0022] To this end, the speed control device detects the lane in which the vehicle is traveling (hereinafter sometimes referred to as its own lane). Furthermore, the speed control device determines whether the detected own lane is a high-speed lane, where relatively high speeds are permitted, or a low-speed lane, where relatively low speeds are required, within a road section that becomes a curve ahead of the vehicle. Further, the speed control device sets a reference speed such that the greater the curvature of the own lane, the lower the vehicle's reference speed, and the reference speed when the own lane is a high-speed lane is higher than the reference speed when the own lane is a low-speed lane. The speed control device then controls the vehicle's speed so that when the vehicle reaches the beginning of the road section that becomes a curve, the vehicle's speed is below the reference speed. In the following, the road section that becomes a curve is sometimes simply referred to as a curve section.

[0023] Figure 1 This is a schematic diagram of a vehicle control system equipped with a speed control device. Additionally, Figure 2This is a hardware structure diagram of an electronic control device as one embodiment of a vehicle speed control device. In this embodiment, the vehicle control system 1, mounted on and controlling 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, GPS receiver 3, and storage device 4 are connected to the ECU 5 in a communicable manner via an in-vehicle network following a standard controller area network. Furthermore, the vehicle control system 1 may also include a distance-measuring sensor (not shown) such as LiDAR (Light Detection and Ranging) or radar to detect the distance from the vehicle 10 to objects present around the vehicle 10. Additionally, the vehicle control system 1 may also include a wireless communication terminal (not shown) for communicating with other devices. Furthermore, the vehicle control system 1 may also include a navigation device (not shown) for setting a predetermined driving route for the vehicle 10.

[0024] Camera 2 is an example of a sensor that detects the conditions around vehicle 10. It has a two-dimensional detector composed of an array of photoelectric conversion elements sensitive to visible light, such as CCD or C-MOS, and an imaging optical system that images the area to be photographed onto the two-dimensional detector. Furthermore, camera 2 is mounted, for example, in the interior of vehicle 10, facing forward of vehicle 10. Camera 2 captures images of the area in front of vehicle 10 at predetermined shooting intervals (e.g., 1 / 30 to 1 / 10 of a second), generating an image reflecting that area. The image obtained by camera 2 is an example of a sensor signal. Alternatively, multiple cameras with different shooting directions or focal lengths may be provided in vehicle 10.

[0025] Whenever an image is generated, camera 2 outputs the generated image to ECU 5 via the in-vehicle network.

[0026] The GPS receiver 3 receives GPS signals from GPS satellites at predetermined intervals and measures the vehicle 10's own position based on the received GPS signals. Furthermore, the GPS receiver 3 outputs positioning information, representing the vehicle 10's own position based on GPS signals, to the ECU 5 via the in-vehicle network at predetermined intervals. Alternatively, the vehicle 10 may have a receiver that measures its own position by receiving positioning signals from satellites based on other satellite positioning systems, instead of a GPS receiver.

[0027] Storage device 4 is an example of a storage unit, such as a hard disk drive, a non-volatile semiconductor memory, or an optical recording medium and its access device. Storage device 4 stores a high-precision map. Furthermore, the high-precision map is an example of map information. The high-precision map includes information representing the number of lanes, lane widths, lane markings, or stop lines in each road section within a predetermined area of ​​the high-precision map; information representing road signs installed in each road section; and information representing speed limits in each road section. Further, the high-precision map includes information representing the positions of the two ends of each curve section in each road section. Additionally, the high-precision map may also include information representing the curvature of each curve section.

[0028] Furthermore, the storage device 4 may also include a processor for performing high-precision map update processing and processing related to high-precision map readout requests from the ECU 5. Additionally, the storage device 4 may, for example, send a high-precision map acquisition request along with the vehicle 10's current position to a map server via a wireless communication terminal (not shown) whenever the vehicle 10 moves a predetermined distance. Furthermore, the storage device 4 may also receive a high-precision map of a predetermined area surrounding the vehicle 10's current position from the map server via the wireless communication terminal. Moreover, when the storage device 4 receives a high-precision map readout request from the ECU 5, it extracts a relatively small area from the stored high-precision map, including the vehicle 10's current position, and outputs it to the ECU 5 via the in-vehicle network.

[0029] ECU5 automatically controls the speed of vehicle 10. In particular, ECU5 controls the speed of vehicle 10 to ensure that vehicle 10 can drive safely in curved sections.

[0030] like Figure 2 As shown, ECU5 has a communication interface 21, a memory 22, and a processor 23. The communication interface 21, the memory 22, and the processor 23 can be configured as separate circuits, or they can be configured as a single integrated circuit.

[0031] The communication interface 21 has an interface circuit for connecting the ECU 5 to the vehicle network. Furthermore, whenever the communication interface 21 receives an image from the camera 2, it delivers the received image to the processor 23. Additionally, whenever the communication interface 21 receives location information from the GPS receiver 3, it delivers that location information to the processor 23. Further, the communication interface 21 delivers a high-precision map read from the storage device 4 to the processor 23.

[0032] Memory 22 is another example of a storage unit, such as a volatile semiconductor memory and a non-volatile semiconductor memory. Furthermore, memory 22 stores various data used in the vehicle speed control processing executed by processor 23. For example, memory 22 stores parameters such as the focal length, shooting direction, and mounting position of camera 2, as well as various parameters of the detector used to determine objects around vehicle 10. Further, memory 22 stores a pre-deceleration table representing the relationship between curvature and reference speed, and a cornering speed table representing the relationship between curvature and driving speed in the cornering section. Additionally, memory 22 also stores vehicle 10 positioning information, images of the area around vehicle 10, and a high-precision map. Furthermore, memory 22 also temporarily stores various data generated during the vehicle speed control processing.

[0033] The processor 23 has one or more CPUs (Central Processing Units) and their peripheral circuits. The processor 23 may also have other arithmetic circuits such as logic units, numerical processing units, or graphics processing units. Furthermore, the processor 23 executes speed control processing for the vehicle 10 according to a predetermined cycle.

[0034] Figure 3 This is a functional block diagram of the processor 23 related to vehicle speed control processing. The processor 23 includes 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. These units of the processor 23 are, for example, functional modules implemented by a computer program operating on the processor 23. Alternatively, these units of the processor 23 may also be dedicated arithmetic circuits provided on the processor 23.

[0035] The lane detection unit 31 detects its own lane while the vehicle 10 is traveling. In this embodiment, the lane detection unit 31 detects its own lane by comparing an image (hereinafter referred to as an image) generated by the camera 2 with a high-precision map. Therefore, the lane detection unit 31 detects road markings such as lane lines, curbs, or road signs, as well as other features on or around the road, from the image. For example, the lane detection unit 31 detects features represented in the image by inputting the image to the recognizer. As such a recognizer, the lane detection unit 31 can, for example, use a SingleShot MultiBox Detector (SSD) or a deep neural network (DNN) with a convolutional neural network (CNN) architecture, such as Faster R-CNN. Alternatively, the lane detection unit 31 can also use a DNN with a self-attention network (SAN) architecture, such as a VisionTransformer. Such a recognizer is pre-learned in a way that allows the detection of features from the image to be detected. The recognizer outputs information identifying the object region containing the ground feature and information indicating the type of ground feature detected on the input image.

[0036] When a feature is detected, the lane detection unit 31 assumes the position and orientation of the vehicle 10 and projects each feature detected from the image onto a high-precision map, or projects each feature on the road or around the road represented on the high-precision map onto the image. Furthermore, the lane detection unit 31 estimates the vehicle 10's own position as the position and orientation of the vehicle 10 when the detected features most closely match the corresponding features represented on the high-precision map. Then, referring to the high-precision map, the lane detection unit 31 determines the lane containing the vehicle 10's own position as the vehicle 10's own lane.

[0037] The lane detection unit 31 uses the initial values ​​of the assumed position and posture of the vehicle 10, along with parameters of the camera 2 such as focal length, setting height, and shooting direction, to determine the position of the ground features projected onto the high-precision map or image. Furthermore, the initial values ​​of the vehicle 10's position and posture are obtained by correcting the position of the vehicle 10 measured by the GPS receiver 3 using odometer information, or the position and posture of the vehicle 10 estimated during the previous lane detection. The lane detection unit 31 also calculates the degree of similarity between the ground features detected from the image on the road or around the road and the ground features represented on the high-precision map (e.g., the reciprocal of the sum of the squares of the distances between each detected ground feature and the ground features around the road).

[0038] The lane detection unit 31 repeatedly performs the above process while changing the assumed position and posture of the vehicle 10. Furthermore, the lane detection unit 31 takes the assumed position and posture at which the consistency is maximized as the actual self-position of the vehicle 10.

[0039] Furthermore, if the positioning accuracy of the vehicle 10 based on the GPS receiver 3 is sufficient, the lane detection unit 31 can also use the position of the vehicle 10 represented by the latest positioning information received from the GPS receiver 3 as the actual self-position of the vehicle 10. And, similarly to the above embodiment, the lane detection unit 31 refers to a high-precision map to determine the lane containing the self-position of the vehicle 10 as the lane in which the vehicle 10 is traveling.

[0040] Furthermore, the lane detection unit 31 determines the lane markings that define its own lane from the lane markings detected from the image. For example, the lane detection unit 31 can determine the lane marking closest to the center of the image at a position that is to the right of the horizontal center and closest to the bottom of the image, i.e., closest to the vehicle 10, as the lane marking that defines the right side of its own lane. Similarly, the lane detection unit 31 can determine the lane marking closest to the center of the image at a position to the left of the horizontal center and closest to the bottom of the image as the lane marking that defines the left side of its own lane.

[0041] The lane detection unit 31 notifies the curvature estimation unit 32, the determination unit 33, and the control unit 35 of information indicating its own detected lane and information indicating its own position. Furthermore, the lane detection unit 31 notifies the curvature estimation unit 32 of the position of each pixel indicating the position of either the left or right lane dividing line detected from the image that divides its own lane.

[0042] The curvature estimation unit 32, referring to the vehicle 10's own position and a high-precision map, determines whether the starting point of a curve section is within a predetermined distance in front of the vehicle 10 in its direction of travel. Furthermore, when the curvature estimation unit 32 detects a curve section with a starting point within the predetermined distance, it estimates the curvature of its own lane within that curve section. Additionally, in the following text, a curve section starting at a location within a predetermined distance in front of the vehicle 10 in its direction of travel will sometimes be referred to simply as a curve section or a detected curve section.

[0043] For example, the curvature estimation unit 32 selects at least three locations that are farther away from the start point of the detected curve section on either the left or right lane marking line that divides its own lane. Furthermore, the position of each pixel in the image corresponds one-to-one with the orientation seen from the camera 2. Additionally, the parameters of the camera 2, such as its shooting direction, setting height, and focal length, are known, and the lane marking lines are located on the road surface. Therefore, based on the parameters of the camera 2, the curvature estimation unit 32 can calculate the position in actual space of the location on the lane marking line represented by that pixel, with the camera 2 as a reference, for each pixel representing the lane marking line in the image. Thus, the curvature estimation unit 32 reads an image generated from the memory 22 containing the curve section detected within the shooting range of the camera 2. The curvature estimation unit 32 then selects at least three locations that are farther away from the start point of the detected curve section from the locations represented by the pixels representing the lane marking lines in the image. Furthermore, the curvature estimation unit 32 calculates the approximate curve passing through each location, and uses the curvature of the approximate curve as the curvature of its own lane in the detected curve section.

[0044] Furthermore, the curvature estimation unit 32 can also perform the above processing on the lane markings on the left and right sides of its own lane respectively, calculate the curvature for each, and use the average of the calculated curvatures as the curvature of its own lane in the detected curve section. Alternatively, the curvature estimation unit 32 can also use the curvature of the curve section represented on the high-precision map as the curvature of its own lane in that curve section.

[0045] The curvature estimation unit 32 notifies the reference speed setting unit 34 of the curvature of its own lane in the detected curve section. Furthermore, the curvature estimation unit 32 notifies the determination unit 33 of information representing the detected curve section.

[0046] The determination unit 33 determines whether the lane it is in the detected curve section is a high-speed lane that allows relatively high speeds in the curve section or a low-speed lane that requires relatively low speeds in the curve section.

[0047] The determination unit 33 refers to a high-precision map to determine whether its own lane is a driving lane or an overtaking lane in the curve section. If its own lane is a driving lane, the determination unit 33 classifies it as a low-speed lane. On the other hand, if its own lane is an overtaking lane, the determination unit 33 classifies it as a high-speed lane.

[0048] Figure 4 This is a diagram illustrating an example of low-speed and high-speed lanes. Figure 4In the example shown, lane 401 on the right side of the direction of travel of vehicle 10 is designated as the overtaking lane, and lane 402 on the left side is designated as the driving lane. In this case, vehicle 10 is traveling in the driving lane 402 on the left side, therefore, its own lane is determined to be a low-speed lane.

[0049] Furthermore, the determination unit 33 can also determine whether its own lane belongs to the driving lane or the overtaking lane in a curve section based on the position of its own lane on the image. For example, in areas where left-hand traffic is used, such as Japan, if there is no lane on the right side of its own lane with the same direction of travel as vehicle 10 on the image, the determination unit 33 determines that its 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 its own lane with the same direction of travel as vehicle 10 on the image, the determination unit 33 determines that its own lane is a driving lane, i.e., a low-speed lane. In addition, if the determination unit 33 detects only one or less lane markings on the right side of its own lane, or detects a central divider on the right side of its own lane, it determines that there is no lane on the right side of its own lane with the same direction of travel as vehicle 10.

[0050] Additionally, sometimes there are yield lanes, such as uphill lanes, in curved sections. In such cases, when its own lane is a yield lane, the determination unit 33 can also determine its own lane as a low-speed lane. Conversely, when its own lane is a lane other than a yield lane, the determination unit 33 can also determine its own lane as a high-speed lane.

[0051] The determination unit 33 notifies the reference speed setting unit 34 of the determination result of whether its own lane is a high-speed lane or a low-speed lane.

[0052] The reference speed setting unit 34 sets the reference speed in such a way that the greater the curvature of its own lane, the lower the reference speed of the vehicle 10, and the reference speed when its own lane is a high-speed lane becomes higher than the reference speed when its own lane is a low-speed lane. The reference speed is the target upper limit speed when the vehicle 10 enters the curve section, and is set to the speed at which the vehicle 10 can travel in the curve section without decelerating suddenly.

[0053] When setting the reference speed, the reference speed setting unit 34 sets any one of the multiple lanes in the curve section as the reference lane (hereinafter sometimes referred to as the reference lane) for setting the reference speed. Furthermore, 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 the low-speed lane as the reference lane. Additionally, when there are three or more lanes in the curve section, the reference speed setting unit 34 sets the lane furthest 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 situations where, when the vehicle 10 enters the curve section, it decelerates while traveling in the high-speed lane, but does not decelerate while traveling in the low-speed lane.

[0054] When the current lane and the reference lane are different, and the curvature of the reference lane is not shown in the high-precision map, the reference speed setting unit 34 calculates the distance obtained by multiplying the number of lanes from the current lane to the reference lane by the width of each lane as the correction radius. Furthermore, the reference speed setting unit 34 estimates the curvature of the reference lane by subtracting the correction radius from the curvature radius corresponding to the curvature of the current lane. In addition, the reference speed setting unit 34 refers to the high-precision map to determine the number of lanes from the current lane to the reference lane and the width of each lane.

[0055] Furthermore, the reference speed setting unit 34 preferably corrects the curvature of the reference lane so that the curvature of the reference lane is greater than or equal to that of the high-speed lane. This prevents the reference speed from being too high when the vehicle 10 is traveling in the high-speed lane.

[0056] The reference speed setting unit 34 refers to a high-precision map to determine whether the current position of vehicle 10 is in an area where the high-speed lane is located to the right of the low-speed lane (as in Japan), or conversely, 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 is a right or left curve in the direction of vehicle 10's travel. If the curve curves towards the high-speed lane, for example, if vehicle 10's current position is in Japan and the curve is a right curve, the reference speed setting unit 34 corrects the curvature of the reference lane to that of the overtaking lane, i.e., the high-speed lane. Conversely, if vehicle 10's current position is in Japan and the curve is a left curve, the reference speed setting unit 34 corrects the curvature of the reference lane to that of the leftmost driving lane or yielding lane. Furthermore, in the above cases, if the reference lane is set to the leftmost driving lane or yielding lane, the reference speed setting unit 34 does not need to correct the curvature of the reference lane.

[0057] When referring again Figure 4 At this time, the left-hand driving lane (i.e., the low-speed lane) 402 is set as the reference lane. However, the curve section 410 in front of vehicle 10 is a right curve. Therefore, the curvature of the right-hand overtaking lane (i.e., the high-speed lane) 401 is greater than the curvature of the low-speed lane 402, which serves as the reference lane. Therefore, the curvature of the reference lane is adjusted to the curvature of the high-speed lane 401. If the curve section 410 is a left curve, the curvature of the low-speed lane 402 becomes greater than the curvature of the high-speed lane 401. Therefore, in this case, the curvature of the low-speed lane 402 is directly set to the curvature of the reference lane.

[0058] When the curvature of the reference lane is determined, the reference speed setting unit 34 determines the reference speed corresponding to the curvature of the reference lane by referring to a pre-set deceleration table that shows the relationship between curvature and reference speed. In the pre-set deceleration table, the reference speed is set such that the greater the curvature, the lower the reference speed. Furthermore, the reference speed setting unit 34 sets the determined reference speed as the reference speed applied to the curve section. Therefore, the greater the curvature of its own lane or the reference lane, the lower the applied reference speed becomes. The reference speed setting unit 34 notifies the control unit 35 of the set reference speed.

[0059] According to a modified example, the reference speed setting unit 34 can also set the reference lane to a high-speed lane regardless of whether its own lane is a low-speed lane or a high-speed lane when the curve direction in the curve section is towards the high-speed lane. On the other hand, the reference speed setting unit 34 can also set its own lane as the reference lane when the curve direction in the curve section is towards the low-speed lane. Thus, when the curvature of the low-speed lane in the curve section is smaller than that of the high-speed lane, 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, it is possible to prevent the situation where the vehicle 10 decelerates only when it is traveling in the high-speed lane. On the other hand, when the curvature of the high-speed lane in the curve section is smaller than that of the low-speed lane, the reference speed when its own lane is a low-speed lane becomes lower than the reference speed when its own lane is a high-speed lane. Therefore, the processor 23 can reduce the degree of deceleration of the vehicle 10 when it is traveling in a high-speed lane with relatively small curvature.

[0060] The control unit 35 controls the speed of the vehicle 10 so that when the vehicle 10 reaches the beginning of the curve section, its speed is below a reference speed. To do this, the control unit 35 compares the current speed of the vehicle 10, measured by a speed sensor (not shown) installed on the vehicle 10, with a reference speed. If the current speed is below the reference speed, the control unit 35 controls the vehicle 10 to maintain the current speed until the beginning of the curve section. On the other hand, if the current speed is higher than the reference speed, the control unit 35 calculates the distance (hereinafter sometimes referred to as deceleration distance) required to decelerate the vehicle 10 from the current speed to the reference speed at a predetermined pre-deceleration rate. Furthermore, when the current position of the vehicle 10, as indicated by the positioning information, is a position before the deceleration distance to the beginning of the curve section (hereinafter referred to as the deceleration start position), the control unit 35 controls the vehicle 10 to decelerate it in advance. 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 is the predetermined deceleration rate. Furthermore, the control unit 35 calculates the fuel injection quantity according to the set accelerator opening and outputs a control signal corresponding to the fuel injection quantity to the fuel injection device of the engine of the vehicle 10. Alternatively, the control unit 35 calculates the electrical force supplied to the motor according to the set accelerator opening and controls the motor drive circuit to supply the electrical force to the motor. Further, the control unit 35 sets the braking amount as needed and outputs a control signal corresponding to the set braking amount to the brakes of the vehicle 10. In addition, the deceleration is preset to a level that will not cause the driver to feel any discomfort or discomfort when the vehicle 10 decelerates in front of the curve, for example, the deceleration at the minimum accelerator opening or 0.05G to 0.15G.

[0061] Furthermore, the control unit 35 also controls the speed of vehicle 10 while it is traveling in the curve section to ensure its safe operation. Specifically, the control unit 35 sets a target speed (hereinafter sometimes referred to as the curve speed) based on the curvature of its own lane within the curve section. At this time, the control unit 35 determines the speed corresponding to the curvature of its own lane by referring to a curve speed table that shows the relationship between curvature and travel speed in the curve section, and sets this determined speed as the curve speed. The control unit 35 then controls the speed of vehicle 10 to decelerate it to the curve speed. At this time, the control unit 35 decelerates vehicle 10 using a pre-set deceleration rate for travel in the curve section. The absolute value of this deceleration rate is set to a value larger than the absolute value of the pre-set deceleration rate (e.g., 0.15G to 0.3G). The control unit 35 decelerates vehicle 10 using the same control as before the deceleration at the beginning of the curve section.

[0062] Furthermore, the control unit 35 begins accelerating the vehicle 10 during the curve section, so that the vehicle 10's speed at the end of the curve section reaches a preset speed (hereinafter sometimes referred to as the set speed). The control unit 35 also controls the speed of the vehicle 10 to accelerate at a predetermined acceleration. Additionally, the control unit 35 sets the acceleration start position before the end of the curve section at a distance (hereinafter sometimes referred to as the acceleration distance) required to reach the set speed from the curve speed with the predetermined acceleration. Similarly, the control unit 35 sets the accelerator opening to achieve the predetermined acceleration of the vehicle 10, just as it does when decelerating the vehicle 10. The control unit 35 then calculates the fuel injection quantity according to the set accelerator opening and outputs a control signal corresponding to that fuel injection quantity to the fuel injection device of the vehicle 10's engine. Alternatively, the control unit 35 calculates the electrical force supplied to the motor according to the set accelerator opening and controls the motor's drive circuit to supply that electrical force to the motor.

[0063] In addition, the control unit 35 can also set the acceleration start position when its own lane is a high-speed lane to be closer to the start position of the curve section than the acceleration start position when its own lane is a low-speed lane.

[0064] Figure 5 This diagram illustrates an example of deceleration control for vehicle 10 while it is traveling in a curved section. Figure 5 In the diagram, the vertical axis represents vehicle speed, and the horizontal axis represents the position of vehicle 10. Furthermore, curve 501 illustrates the relationship between the position of vehicle 10 and its speed.

[0065] As shown in curve 501, the vehicle speed of vehicle 10 is maintained at a set speed before it reaches the deceleration start position P1. When vehicle 10 reaches the deceleration start position P1, it begins to decelerate at the pre-decelerated speed. Furthermore, at the point when vehicle 10 reaches the start position P2 of the curve section C, the speed of vehicle 10 decreases to the base speed. Then, the speed of vehicle 10 is controlled to further reduce its speed within the curve section C, and then vehicle 10 accelerates before reaching the end position P3 of the curve section. Finally, at the point when vehicle 10 reaches the end position P3 of the curve section, the speed of vehicle 10 returns to the set speed.

[0066] Figure 6 This is a flowchart of the vehicle speed control process executed by processor 23. Processor 23 executes the vehicle speed control process according to the following flowchart at predetermined cycles.

[0067] The lane detection unit 31 of the processor 23 detects the vehicle 10's own lane while it is traveling (step S101). Additionally, the curvature estimation unit 32 of the processor 23 determines whether there is a starting point of a curve section within a predetermined distance in front of the vehicle 10 (step S102). If there is no starting point of a curve section within the predetermined distance (step S102 – No), the control unit 35 of the processor 23 controls the vehicle 10 to maintain its current speed (step S103). Then, the processor 23 terminates the speed control process.

[0068] On the other hand, if there is a starting point of a curve section within a predetermined distance (step S102 - Yes), the curvature estimation unit 32 estimates the curvature of its own lane in that curve section (step S104). Then, the determination unit 33 of the processor 23 determines whether its own lane is a low-speed lane or a high-speed lane in that curve section (step S105).

[0069] The reference speed setting unit 34 of processor 23 sets a reference speed such that the greater the curvature of its own lane, the lower the reference speed of vehicle 10, and the reference speed when its own lane is a high-speed lane becomes higher than the reference speed when its own lane is a low-speed lane (step S106). Furthermore, the control unit 35 of processor 23 controls the speed of vehicle 10 so that the speed of vehicle 10 when it reaches the beginning of the curve section is lower than the reference speed (step S107). Then, the control unit 35 decelerates the speed of vehicle 10 during its travel in the curve section to the curve travel speed, and then accelerates vehicle 10 so that the speed of vehicle 10 reaches the set speed at the end of the curve section (step S108). Finally, processor 23 ends the vehicle speed control process.

[0070] As explained above, the speed control device determines whether the vehicle's lane is a high-speed lane or a low-speed lane in the curve section ahead. Furthermore, the speed control device sets a reference speed such that the greater the curvature of the lane, the lower the vehicle's reference speed, and 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. Moreover, the speed control device controls the vehicle's speed so that when the vehicle reaches the beginning of the curve section, its speed is below the reference speed. By controlling the vehicle's speed in this way, the speed control device can prevent the vehicle from leaving its lane in the curve section. Furthermore, the speed control device can prevent situations where the vehicle decelerates when entering a curve section while traveling in a high-speed lane but does not decelerate when traveling in a low-speed lane, thus slowing the vehicle down without causing discomfort to the driver.

[0071] In addition, the computer program that implements the function of the processor 23 of the ECU5 according to the above embodiments or variations may also be provided in the form of a computer-readable portable recording medium such as a semiconductor memory, a magnetic recording medium or an optical recording medium.

[0072] As described above, those skilled in the art can make various modifications within the scope of this invention according to the implemented form.

Claims

1. A vehicle speed control device, comprising: The lane detection unit detects vehicles traveling in their own lanes. The curvature estimation unit detects the starting point of a road section within a predetermined distance in front of the vehicle that becomes a curve, based on sensor signals or map information obtained by sensors installed on the vehicle to detect the conditions around the vehicle, and estimates the curvature of its own lane in the road section. The determination unit, referring to the map information, determines whether its own lane is a high-speed lane in the road section where relatively high speeds are permitted, or a low-speed lane in the road section where relatively low speeds are required. The reference speed setting unit sets the reference speed in such a way that the greater the curvature of its own lane, the lower the reference speed of the vehicle, and the reference speed when its own lane is a high-speed lane becomes a reference speed or higher when its own lane is a low-speed lane; and The control unit controls the speed of the vehicle so that when the vehicle reaches the starting point of the road section, its speed is below the reference speed. The reference speed setting unit sets any one of the multiple lanes included in the road section as the reference lane, and sets the reference speed based on the curvature of the reference lane. When the reference speed setting unit is different from the reference lane and its own lane, it calculates the number of lanes from the reference lane to its own lane and the width of each lane in the road section based on the map information. It then corrects the curvature of its own lane based on the distance obtained by multiplying the number of lanes by the width, thereby calculating the curvature of the reference lane.

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

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

4. The vehicle speed control device according to claim 1, When the direction of the curve in the road section is towards the high-speed lane, 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 towards the low-speed lane, it sets its own lane as the reference lane.

5. A vehicle speed control method, comprising: Detects the vehicle's own lane while it is traveling; Based on sensor signals or map information obtained by sensors installed on the vehicle to detect the conditions around the vehicle, the starting point of a road section within a predetermined distance in front of the vehicle that becomes a curve is detected, and the curvature of the lane itself in the road section is estimated. Referring to the map information, determine whether the lane itself is a high-speed lane that allows relatively high speeds in the road section, or a low-speed lane that requires relatively low speeds in the road section; The reference speed is set in such a way that the greater the curvature of its own lane, the lower the reference speed of the vehicle, and the reference speed when its own lane is a high-speed lane becomes higher than the reference speed when its own lane is a low-speed lane. The speed of the vehicle is controlled such that when the vehicle reaches the starting point of the road section, the speed of the vehicle is below the reference speed. Any one of the multiple lanes contained in the road section is set as the reference lane, and the reference speed is set based on the curvature of the reference lane; as well as When the reference lane and the current lane are different, based on the map information, the number of lanes from the reference lane to the current lane and the width of each lane in the road section are calculated. The curvature of the current lane is corrected based on the distance obtained by multiplying the number of lanes by the width, thereby calculating the curvature of the reference lane.

6. A computer program product comprising a vehicle speed control computer program that causes a processor mounted in a vehicle to execute: Detect the vehicle's own lane while it is traveling; Based on sensor signals or map information obtained by sensors installed on the vehicle to detect the conditions around the vehicle, the starting point of a road section within a predetermined distance in front of the vehicle that becomes a curve is detected, and the curvature of the lane itself in the road section is estimated. Referring to the map information, determine whether the lane itself is a high-speed lane that allows relatively high speeds in the road section, or a low-speed lane that requires relatively low speeds in the road section; The reference speed is set in such a way that the greater the curvature of its own lane, the lower the reference speed of the vehicle, and the reference speed when its own lane is a high-speed lane becomes higher than the reference speed when its own lane is a low-speed lane. The speed of the vehicle is controlled such that when the vehicle reaches the starting point of the road section, the speed of the vehicle is below the reference speed. Any one of the multiple lanes contained in the road section is set as the reference lane, and the reference speed is set based on the curvature of the reference lane; as well as When the reference lane and the current lane are different, based on the map information, the number of lanes from the reference lane to the current lane and the width of each lane in the road section are calculated. The curvature of the current lane is corrected based on the distance obtained by multiplying the number of lanes by the width, thereby calculating the curvature of the reference lane.

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