Automatic speed control device, automatic speed control method and automatic speed control program

Abstract

An automatic speed control device controls the speed of a vehicle so that the lateral acceleration of the vehicle becomes appropriate. The automatic speed control device that automatically controls the speed of a vehicle comprises an upper limit lateral acceleration setting unit that sets the upper limit lateral acceleration, which is the upper limit value of the lateral acceleration allowed during the travel of the vehicle, a road curvature acquisition unit that acquires the value of a curvature parameter related to the curvature of a predetermined road on which the vehicle travels, an upper limit speed setting unit that calculates the speed of the vehicle at which the lateral acceleration of the vehicle becomes the upper limit lateral acceleration when the vehicle travels on the road based on the value of the curvature parameter of the road and sets it as the upper limit speed, and a speed control unit that controls the speed of the vehicle so that it becomes less than the upper limit speed. The upper limit lateral acceleration setting unit sets the upper limit lateral acceleration when the vehicle merges with the main line of a motorway or travels on a connecting road branching from it to be lower than the upper limit lateral acceleration when the vehicle travels on the main line of the motorway.

Description

Technical Field

[0001] The present disclosure relates to an automatic speed control device, an automatic speed control method, and an automatic speed control program. Background Art

[0002] In the past, an automatic speed control device for automatically controlling the speed of a vehicle has been proposed (Patent Documents 1 to 3). In particular, in the device described in Patent Document 1, when the curvature of the road on which the vehicle is to travel is large, the target speed is reduced so that the lateral acceleration applied to the vehicle becomes less than a constant value without the vehicle deviating from the target track.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-203006

[0006] Patent Document 2: Japanese Patent Application Publication No. 2000-293782

[0007] Patent Document 3: International Publication No. 2017 / 145555 Summary of the invention

[0008] Problems to be solved by the invention

[0009] In Patent Document 1, the speed of the vehicle is controlled in such a way that the lateral acceleration is kept below a constant value regardless of the type of road on which the vehicle is traveling. However, for example, the road width of the connecting road of the dedicated road for automobiles (the road between the main lines or the road between the main line and the ordinary road) is generally narrower than the road width of the dedicated road for automobiles. In addition, if the road width is narrow, there is a tendency that the occupants will not feel safe even if the speed of the vehicle is the same. If the upper limit lateral acceleration is set to a constant value that matches the main line (main road), the vehicle may reach a higher speed than necessary when traveling on the connecting road. On the contrary, if the upper limit lateral acceleration is set to a constant value that matches the connecting road (ramp), the speed of the vehicle may be unnecessarily restricted when traveling on the main line.

[0010] In view of the above problems, an object of the present disclosure is to provide an automatic speed control device or the like that can control the speed of a vehicle so that the lateral acceleration of the vehicle becomes appropriate regardless of the type of road on which the vehicle travels.

[0011] Technical solutions to solve problems

[0012] The gist of the present disclosure is as follows.

[0013] (1) An automatic speed control device that automatically controls the speed of a vehicle.

[0014] The automatic speed control device has:

[0015] an upper limit lateral acceleration setting unit for setting an upper limit lateral acceleration which is an upper limit value of lateral acceleration permitted during travel of the vehicle;

[0016] a road curvature acquisition unit that acquires a value of a curvature parameter related to the curvature of a predetermined road on which the vehicle travels;

[0017] an upper limit speed setting unit that calculates a vehicle speed at which the lateral acceleration of the vehicle reaches the upper limit lateral acceleration when the vehicle travels on the road based on the value of the curvature parameter of the road, and sets the calculated speed as the upper limit speed; and

[0018] a speed control unit that controls the speed of the vehicle so as to be below the upper speed limit,

[0019] The upper limit lateral acceleration setting unit sets an upper limit lateral acceleration when the vehicle travels on a link road merging with a main line of the motorway or a link road branching from the main line to be lower than an upper limit lateral acceleration when the vehicle travels on the main line of the motorway.

[0020] (2) The automatic speed control device according to (1) above,

[0021] The upper limit speed setting unit sets the reference upper limit speed as the upper limit speed when the speed of the vehicle, which is such that the upper limit lateral acceleration is reached, is faster than a predetermined reference upper limit speed.

[0022] When the vehicle is decelerated to a speed lower than a predetermined re-acceleration upper limit speed and then accelerated again while traveling on the connecting road, if the vehicle speed reaching the upper limit lateral acceleration is faster than the re-acceleration upper limit speed, the re-acceleration upper limit speed is set as the upper limit speed;

[0023] The reacceleration upper limit speed is lower than the base upper limit speed.

[0024] (3) The automatic speed control device according to (2) above,

[0025] The vehicle is a vehicle whose speed is automatically controlled to stop the vehicle at an exit of a road dedicated to automobiles,

[0026] The upper limit speed setting unit sets a re-acceleration upper limit speed when the vehicle travels on the connecting road to the exit to be lower than a re-acceleration upper limit speed when the vehicle travels on the connecting road merging with a main line.

[0027] (4) The automatic speed control device according to any one of (1) to (3) above,

[0028] The vehicle is a vehicle whose speed is automatically controlled to stop the vehicle at an exit of a road dedicated to automobiles,

[0029] The upper limit lateral acceleration setting unit sets an upper limit lateral acceleration when the vehicle travels on the connecting road to the exit to be lower than an upper limit lateral acceleration when the vehicle travels on the connecting road merging with the main line.

[0030] (5) The automatic speed control device according to any one of (1) to (4) above,

[0031] The upper limit lateral acceleration setting unit sets an upper limit lateral acceleration when traveling on a main line whose distance from a main line exit without the connecting road is less than a predetermined distance to be lower than an upper limit lateral acceleration when traveling on a main line whose distance from the main line exit is greater than the predetermined distance.

[0032] (6) An automatic speed control method for automatically controlling the speed of a vehicle, the automatic speed control method comprising:

[0033] setting an upper limit lateral acceleration which is an upper limit value of lateral acceleration permitted during travel of the vehicle;

[0034] obtaining a value of a curvature parameter related to the curvature of a predetermined road on which the vehicle is traveling;

[0035] calculating a vehicle speed at which the lateral acceleration of the vehicle reaches the upper limit lateral acceleration when the vehicle travels on the road based on the value of the curvature parameter of the road, and setting the calculated speed as the upper limit speed; and

[0036] controlling the speed of the vehicle so as to be below the upper speed limit,

[0037] The upper limit lateral acceleration when the vehicle travels on a link road merging with a main line of the motorway or a link road branching from the main line is lower than the upper limit lateral acceleration when the vehicle travels on the main line of the motorway.

[0038] (7) An automatic speed control program that automatically controls the speed of a vehicle, the automatic speed control program causing a computer to execute the following processing:

[0039] setting an upper limit lateral acceleration which is an upper limit value of lateral acceleration permitted during travel of the vehicle;

[0040] obtaining a value of a curvature parameter related to the curvature of a predetermined road on which the vehicle is traveling;

[0041] calculating a vehicle speed at which the lateral acceleration of the vehicle reaches the upper limit lateral acceleration when the vehicle travels on the road based on the value of the curvature parameter of the road, and setting the calculated speed as the upper limit speed; and

[0042] controlling the speed of the vehicle so as to be below the upper speed limit,

[0043] The upper limit lateral acceleration when the vehicle travels on a link road merging with a main line of the motorway or a link road branching from the main line is lower than the upper limit lateral acceleration when the vehicle travels on the main line of the motorway.

[0044] Effects of the Invention

[0045] According to the present disclosure, an automatic speed control device and the like are provided which can control the speed of a vehicle so that the lateral acceleration of the vehicle becomes appropriate regardless of the type of the road on which the vehicle travels. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 The diagram schematically shows the configuration of a vehicle equipped with an automatic speed control system according to one embodiment.

[0047] Figure 2 This is a hardware configuration diagram of an ECU according to one embodiment.

[0048] Figure 3 It is a functional block diagram of the ECU's processor.

[0049] Figure 4 : is a flowchart showing the flow of the speed control process executed by the speed control unit.

[0050] Figure 5 This is a flowchart schematically showing the flow of the upper limit speed setting process.

[0051] Figure 6 It is shown in Figure 5 Flowchart of the process of calculating the lateral G upper limit speed performed in step S22.

[0052] Figure 7 This is a diagram schematically showing an example of a dedicated road for automobiles in which a link road branches off from a main road.

[0053] Figure 8 It shows that the vehicle is scheduled to Figure 7 A diagram showing the curvature of the road on which the vehicle is scheduled to travel and the lateral G upper limit speed when traveling on a connecting road as shown.

[0054] Fig. 9 It is shown in Figure 5 Flowchart of the process of calculating the re-acceleration upper limit speed performed in step S23.

[0055] Description of Reference Numerals

[0056] 1: Automatic speed control system

[0057] 21: ECU

[0058] 31: Communication interface

[0059] 32: Memory

[0060] 33: Processor

[0061] 100: Vehicles

[0062] 331: Speed ​​control unit

[0063] 332: Upper limit lateral acceleration setting unit

[0064] 333: Road curvature acquisition unit

[0065] 334: Upper speed limit setting unit DETAILED DESCRIPTION

[0066] Hereinafter, the embodiment will be described in detail with reference to the drawings. In the following description, the same reference numerals are given to the same components.

[0067] <Vehicle Configuration>

[0068] Figure 1 1 is a schematic diagram showing a configuration of a vehicle 100 equipped with an automatic speed control system 1 according to an embodiment. The automatic speed control system 1 is mounted on the vehicle 100 and automatically controls the speed of the vehicle 100 under a preset condition. In the present embodiment, the automatic speed control system 1 includes a driving state sensor 11, an exterior camera 12, a distance sensor 13, a positioning sensor 14, a storage device 15, a human-machine interface (hereinafter referred to as "HMI") 16, a vehicle actuator 20, and an electronic control unit (hereinafter referred to as "ECU") 21.

[0069] However, the automatic speed control system 1 does not necessarily have to include all of the above. For example, the automatic speed control system 1 only needs to include the vehicle exterior camera 12 and does not need to include the distance measuring sensor 13.

[0070] The driving state sensor 11, the exterior camera 12, the distance sensor 13, the positioning sensor 14, the storage device 15, the HMI 16, and the ECU 21 are connected in a communicative manner via the in-vehicle network 22. The in-vehicle network 22 is a network that complies with standards such as CAN (Controller Area Network). In addition, the ECU 21 is connected to the vehicle actuator 20 via a signal line.

[0071] The running state sensor 11 is a sensor for detecting the running state of the vehicle 100. The running state sensor 11 is, for example, an inertial measurement sensor, and detects the speed and acceleration of the vehicle 100. The running state sensor 11 outputs the detection result of the running state of the vehicle to the ECU 21 via the in-vehicle network 22.

[0072] The vehicle exterior camera 12 is a device for photographing the surroundings of the vehicle. The vehicle exterior camera 12 has a two-dimensional detector (CCD, C-MOS, etc.) composed of an array of photoelectric conversion elements sensitive to visible light, and an imaging optical system that forms an image of the area to be photographed on the two-dimensional detector. In the present embodiment, the vehicle exterior camera 12 is installed, for example, inside the vehicle 100 in a manner facing the front of the vehicle 100. The vehicle exterior camera 12 photographs the area in front of the vehicle 100 at every predetermined photographing cycle (for example, 1 / 30 second to 1 / 10 second), and generates an image showing the area in front. Whenever the vehicle exterior camera 12 generates an image, it outputs the generated image to the ECU 21 via the in-vehicle network 22. In addition, the vehicle exterior camera 12 can be a monocular camera or a stereo camera. When a stereo camera is used as the vehicle exterior camera 12, the vehicle exterior camera 12 also functions as a distance measuring sensor 13. Multiple vehicle exterior cameras with different photographing directions or focal distances can also be set in the vehicle 100.

[0073] The distance measuring sensor 13 is a sensor that measures the distance to an object existing around the vehicle 100. In the present embodiment, the distance measuring sensor 13 can also measure the orientation of an object existing around the vehicle 100. The distance measuring sensor 13 is, for example, a radar such as a millimeter wave radar, a laser radar (LiDAR), or a sonar. In the present embodiment, the distance measuring sensor 13 measures the distance to an object existing in front of the vehicle. The distance measuring sensor 13 outputs the measurement result of the distance to the surrounding objects to the ECU 21 via the in-vehicle network 22 at every predetermined period.

[0074] The positioning sensor 14 is a sensor for measuring the own position of the vehicle 100. The positioning sensor 14 is, for example, a GNSS (Global Navigation Satellite System) receiver. The GNSS receiver receives signals with time information from a plurality of positioning satellites, and measures the own position of the vehicle 100 based on the received signals. The positioning sensor 14 outputs the own position information of the vehicle 100 to the ECU 21 via the in-vehicle network 22 at every predetermined period.

[0075] The storage device 15 has, for example, a hard disk device or a nonvolatile semiconductor memory. The storage device 15 stores map information. The map information includes information indicating the location of each predetermined section of the road and road markings (for example, lane dividing lines or stop lines). The storage device 15 reads the map information in response to a map information read request from the ECU 21, and sends the map information to the ECU via the in-vehicle network 22.

[0076] HMI16 notifies the driver of the vehicle 100 of the information for notification obtained from ECU21 via the in-vehicle network 22. Therefore, HMI16 functions as a notification device for notifying the driver of information. Specifically, HMI16 has, for example, a display device such as a liquid crystal display, instruments such as a speedometer, a warning light, and a speaker. In addition, HMI16 accepts input from the occupant and sends the accepted input to ECU21 via the in-vehicle network 22. Therefore, HMI16 functions as an input device for accepting input from the occupant or the driver. Specifically, HMI16 has a touch panel, a switch, a button, and a remote control. HMI16 is, for example, disposed on a dashboard.

[0077] The vehicle actuator 20 is an actuator for controlling the operation of the vehicle 100. Specifically, the vehicle actuator 20 includes, for example, a driving actuator for controlling an internal combustion engine or an electric motor for driving the vehicle 100, and a brake actuator for controlling a brake for braking the vehicle 100. The vehicle actuator 20 may also include a steering actuator for controlling the steering of the vehicle 100. The vehicle actuator 20 controls the acceleration and braking of the vehicle 100 according to a control signal sent from the ECU 21 via a signal line, and controls the steering of the vehicle 100 when the vehicle actuator 20 includes a steering actuator.

[0078] Figure 2 1 is a diagram showing a hardware configuration of the ECU 21 according to one embodiment. The ECU 21 includes a communication interface 31, a memory 32, and a processor 33. The communication interface 31, the memory 32, and the processor 33 may be independent circuits or may be configured as one integrated circuit.

[0079] The communication interface 31 includes a communication interface circuit and a device interface circuit. The communication interface circuit is a circuit for connecting the ECU 21 to the in-vehicle network 22. The device interface circuit is a circuit for outputting a control signal to the vehicle actuator 20.

[0080] Whenever the communication interface 31 receives the detection result of the driving state of the vehicle 100 from the driving state sensor 11, the communication interface 31 sends the received detection result to the processor 33. In addition, whenever the communication interface 31 receives an image from the vehicle exterior camera 12, the received image is sent to the processor 33. In addition, whenever the communication interface 31 receives the measurement result of the distance to the surrounding objects of the vehicle from the distance measuring sensor 13, the measurement result is sent to the processor 33. Moreover, whenever the communication interface 31 receives the measurement result of its own position from the positioning sensor 14, the measurement result is sent to the processor 33. In addition, the communication interface 31 sends the high-precision map read from the storage device 15 to the processor 33. In addition, whenever the communication interface 31 receives an input signal from the occupant from the HMI 16, the input signal is sent to the processor 33. Moreover, whenever the communication interface 31 receives information for notification from the ECU 21, the received information is sent to the HMI 16. In addition, whenever the communication interface 31 receives a control signal for the vehicle actuator 20 from the ECU 21, the received control signal is sent to the vehicle actuator 20.

[0081] The memory 32 is a storage device for storing data. The memory 32 includes, for example, a volatile semiconductor memory and a nonvolatile semiconductor memory. The memory 32 stores a program for speed control processing executed by the processor 33 of the ECU 21. In addition, the memory 32 stores images captured by the exterior camera 12, driver's operation information, measurement results of distances to objects around the vehicle, measurement results of the vehicle's own position, passenger input information, and various data used in speed control processing.

[0082] The processor 33 has one or more CPUs (Central Processing Units) and their peripheral circuits. The processor 33 may also have other operation circuits such as a logic operation unit or a numerical operation unit. The processor 33 performs control processing of the vehicle actuator 20 to control the vehicle actuator 20. In the present embodiment, the processor 33 functions as an automatic speed control device that automatically controls the speed of the vehicle 100.

[0083] Figure 3 2 is a functional block diagram of the processor 33 of the ECU 21. Figure 3As shown, the processor 33 includes: a speed control unit 331, which automatically controls the speed of the vehicle 100 based on the upper limit speed; an upper limit lateral acceleration setting unit 332, which sets the upper limit value of the lateral acceleration allowed during the travel of the vehicle 100, that is, the upper limit lateral acceleration; a road curvature acquisition unit 333, which acquires the curvature of the predetermined road on which the vehicle 100 travels; and an upper limit speed setting unit 334, which calculates the speed of the vehicle such that the lateral acceleration of the vehicle 100 becomes the upper limit lateral acceleration when the vehicle 100 travels on the road based on the curvature of the predetermined road on which the vehicle 100 travels, and sets the calculated speed as the upper limit speed. These functional blocks of the processor 33 are, for example, functional modules implemented by a computer program running on the processor 33. Alternatively, these functional blocks of the processor 33 may also be dedicated operation circuits provided in the processor 33. The details of each functional block of the processor 33 of the vehicle 100 will be described later.

[0084] <Overview of speed control>

[0085] Next, the speed control processing of the vehicle 100 based on the speed control device involved in the present embodiment is described. First, when the driver selects automatic speed control via HMI16, the processor 33 of the ECU 21, which functions as the speed control device involved in the present embodiment, automatically controls the speed of the vehicle 100 even without the driver's accelerator operation or brake operation. The automatic speed control here can be a control that requires the driver's monitoring (such as adaptive cruise control (ACC)), or it can be a part of the control that does not require the driver's monitoring. In addition, when the driver selects the automatic speed control, the processor 33 can also automatically control the steering of the vehicle 100 so that the vehicle 100 automatically travels along the lane currently being traveled.

[0086] Furthermore, in the present embodiment, the automatic speed control of the vehicle 100 is performed when the vehicle 100 is traveling on a dedicated road for automobiles (for example, a highway, etc., a road where the main lines are not connected to each other by a signalized intersection but are connected by a connecting road such as an interchange or an overpass). Therefore, when the vehicle 100 passes through the exit of the dedicated road for automobiles, the driving is handed over to the driver with respect to speed control, and the automatic speed control is terminated. Similarly, the automatic steering control of the vehicle 100 may also be performed when the vehicle 100 is traveling on a dedicated road for automobiles. In this case, when the vehicle 100 passes through the exit of the dedicated road for automobiles, the driving is handed over to the driver with respect to steering control, and the automatic steering control is terminated.

[0087] In the automatic speed control, the speed control unit 331 basically sets the target speed of the vehicle 100 to the upper limit speed. However, in the case where there is a preceding vehicle on the driving lane where the vehicle 100 is traveling, the speed control unit 331 controls the target speed of the vehicle 100 in such a manner that the vehicle 100 follows the preceding vehicle. In particular, in the present embodiment, the speed control unit 331 sets the target speed of the vehicle 100 to a speed faster than the speed of the preceding vehicle when the inter-vehicle distance between the vehicle 100 and the preceding vehicle is longer than the target inter-vehicle distance. On the other hand, the speed control unit 331 sets the target speed of the vehicle 100 to a speed slower than the speed of the preceding vehicle when the inter-vehicle distance between the vehicle 100 and the preceding vehicle is shorter than the target inter-vehicle distance. However, in the case where the target speed of the vehicle 100 set in this way is faster than the upper limit speed, the speed control unit 331 sets the target speed of the vehicle 100 to the upper limit speed. Therefore, the speed control unit 331 controls the speed of the vehicle 100 so as to be below the upper limit speed.

[0088] Figure 4 2 is a flowchart showing the flow of the speed control process executed by the speed control unit 331. The process shown in the figure is repeatedly executed at regular time intervals.

[0089] The speed control unit 331 first detects the speed of the preceding vehicle and the distance between the preceding vehicle and the preceding vehicle (step S11). Specifically, the speed control unit 331 first identifies other vehicles traveling around the vehicle 100 based on the image captured by the external camera 12 or the distance information obtained by the ranging sensor 13. The recognition of other vehicles is performed by a well-known pattern recognition method such as a neural network (NN) and a support vector machine (SVM). In addition, the speed control unit 331 calculates the speed of the other identified vehicles and the distance between the other identified vehicles and the vehicle 100 based on the image captured by the external camera 12 or the distance information obtained by the ranging sensor 13.

[0090] Next, the speed control unit 331 determines whether there is a preceding vehicle in the driving lane of the vehicle 100 (step S12). Specifically, the speed control unit 331 recognizes the shape of the lane in which the vehicle 100 is traveling based on the image captured by the vehicle exterior camera 12 or based on the self-position information measured by the positioning sensor 14 and the map information stored in the storage device 15, and determines whether there is a preceding vehicle in the driving lane of the vehicle 100 based on the recognized lane shape and the position information of other vehicles recognized in step S11. If it is determined in step S12 that there is no preceding vehicle in the driving lane of the vehicle 100, the speed control unit 331 sets the target speed of the vehicle 100 to the upper limit speed calculated by the upper limit speed setting unit 334 described later (step S13).

[0091] On the other hand, if it is determined in step S12 that there is a preceding vehicle in the driving lane of the vehicle 100, the speed control unit 331 determines whether the inter-vehicle distance between the vehicle 100 and the preceding vehicle is substantially the same as the target inter-vehicle distance (step S14). The target inter-vehicle distance may be a constant value set in advance or a constant value set in advance by the driver. Alternatively, the target inter-vehicle distance may be a value that varies according to parameters such as the speed of the vehicle 100 (for example, the faster the speed of the vehicle 100, the longer the target inter-vehicle distance).

[0092] When it is determined in step S14 that the inter-vehicle distance between the vehicle 100 and the preceding vehicle is substantially the same as the target inter-vehicle distance, the speed control unit 331 sets the target speed to a speed substantially the same as the speed of the preceding vehicle (step S15 ).

[0093] On the other hand, if it is determined in step S14 that the inter-vehicle distance between the vehicle 100 and the preceding vehicle is different from the target inter-vehicle distance, the speed control unit 331 determines whether the inter-vehicle distance is longer than the target inter-vehicle distance (step S16). If it is determined in step S16 that the inter-vehicle distance is longer than the target inter-vehicle distance, the speed control unit 331 sets the target speed to a speed faster than the speed of the preceding vehicle (step S17). On the other hand, if it is determined in step S16 that the inter-vehicle distance is shorter than the target inter-vehicle distance, the speed control unit 331 sets the target speed to a speed slower than the speed of the preceding vehicle (step S18).

[0094] When the target speed is set based on the speed of the preceding vehicle in steps S15, S17, and S18, the speed control unit 331 determines whether the set target speed is less than the upper limit speed calculated by the upper limit speed setting unit 334 (step S19). If it is determined that the set target speed is less than the upper limit speed, the target speed is maintained unchanged. On the other hand, if it is determined that the set target speed is faster than the upper limit speed in step S19, the speed control unit 331 sets the target speed to the upper limit speed (step S13).

[0095] The ECU 21 of the vehicle 100 controls the vehicle actuator 20 so that the speed of the vehicle 100 becomes the target speed set in this way. Therefore, when the current speed of the vehicle 100 is slower than the target speed, the ECU 21 controls the vehicle actuator 20 so that the vehicle 100 accelerates. In particular, the ECU 21 controls the vehicle actuator 20 so that the vehicle 100 accelerates at an acceleration below a preset upper limit acceleration. On the other hand, when the current speed of the vehicle 100 is faster than the target speed, the ECU 21 controls the vehicle actuator 20 so that the vehicle 100 decelerates. In particular, the ECU 21 controls the vehicle actuator 20 so that the vehicle 100 decelerates at a deceleration below a preset upper limit deceleration.

[0096] <Upper speed limit setting>

[0097] Next, a process of setting the upper limit speed used in the above-described speed control of the vehicle 100 will be described. Figure 5 The flowchart schematically shows the process of setting the upper speed limit. Figure 5 The upper limit speed setting process is shown.

[0098] In the upper limit speed setting process, the upper limit speed setting unit 334 first obtains the reference upper limit speed (step S21). The reference upper limit speed is, for example, a constant speed set in advance by the user via the HMI, and the set reference upper limit speed is stored in the storage device 15. The upper limit speed setting unit 334 obtains the reference upper limit speed from the storage device 15.

[0099] In addition, the reference upper limit speed is not necessarily a constant speed, and may be a speed that varies according to the type of road on which the vehicle 100 is traveling, for example. In this case, the reference upper limit speed is stored for each type of road in the storage device 15. The upper limit speed setting unit 334 determines the type of the road currently being traveled based on the output of the positioning sensor 14 and the map information stored in the storage device 15, and obtains the reference upper limit speed corresponding to the determined type of road from the storage device 15.

[0100] In the upper limit speed setting process, the upper limit speed setting unit 334 then performs a lateral G upper limit speed calculation process to calculate the lateral G upper limit speed (step S22). The lateral G upper limit speed is the speed of the vehicle 100 at which the lateral acceleration of the vehicle 100 reaches the upper limit lateral acceleration (the upper limit value of the lateral acceleration allowed to be applied to the vehicle 100) when the vehicle 100 is traveling on a curved road. The specific steps of the lateral G upper limit speed calculation process will be described later (refer to Figure 6 ).

[0101] Next, in the upper limit speed setting process, the upper limit speed setting unit 334 performs a re-acceleration upper limit speed calculation process (step S23) to calculate the re-acceleration upper limit speed. Here, in the present embodiment, when the vehicle 100 is traveling on a connecting road that merges with the main line of the dedicated road for automobiles or a connecting road that branches from the main line of the dedicated road for automobiles (hereinafter, they are simply collectively referred to as "connecting roads"), after the vehicle 100 temporarily decelerates to a re-acceleration upper limit speed that is lower than the base upper limit speed, the upper limit speed setting unit 334 sets the upper limit speed of the vehicle 100 as the re-acceleration upper limit speed. In step S23, such a re-acceleration upper limit speed is calculated. In addition, when the speed of the vehicle 100 does not temporarily decelerate to a speed lower than the re-acceleration upper limit speed while traveling on the same connecting road, the upper limit speed setting unit 334 does not calculate the re-acceleration upper limit speed as a result of the re-acceleration upper limit speed calculation process. The specific steps of the re-acceleration upper limit speed calculation process will be described later (refer to Fig. 9 ).

[0102] When the reference upper limit speed is obtained, the lateral G upper limit speed is calculated, and the re-acceleration upper limit speed is calculated according to the situation, the upper limit speed setting unit 334 sets the slowest speed among the reference upper limit speed, the lateral G upper limit speed, and the re-acceleration upper limit speed obtained or calculated as the upper limit speed (step S24). As a result, the target speed of the vehicle 100 is not set to a speed faster than the reference upper limit speed, the lateral G upper limit speed, or the re-acceleration upper limit speed.

[0103] In addition, in the present embodiment, the upper limit speed of the vehicle 100 is set to the slowest speed among the reference upper limit speed, the lateral G upper limit speed, and the re-acceleration upper limit speed. However, the upper limit speed of the vehicle 100 may also be set to the slower speed of the reference upper limit speed and the lateral G upper limit speed. In this case, the upper limit speed setting unit 334 does not calculate the re-acceleration upper limit speed. Alternatively, the upper limit speed of the vehicle 100 may also be set to the slower speed of the lateral G upper limit speed and the re-acceleration upper limit speed. In this case, the upper limit speed setting unit 334 does not obtain the reference upper limit speed. In addition, the upper limit speed of the vehicle 100 may also be set to the lateral G upper limit speed. In this case, the upper limit speed setting unit 334 does not obtain the reference upper limit speed and does not calculate the re-acceleration upper limit speed. Therefore, the upper limit speed setting unit 334 basically sets the lateral G upper limit speed as the upper limit speed. In addition, the upper limit speed setting unit 334 may also set the reference upper limit speed or the re-acceleration upper limit speed as the upper limit speed when the lateral G upper limit speed is faster than the reference upper limit speed or the re-acceleration upper limit speed.

[0104] In addition, in this embodiment, the reference upper limit speed is obtained (step S21), the lateral G upper limit speed is calculated (step S22), and the re-acceleration upper limit speed is calculated (step S23). However, the above measures do not necessarily need to be performed in this order, and can be performed in any order or simultaneously.

[0105] <Calculation of lateral G upper limit speed>

[0106] Next, Figure 5 The calculation process of the lateral G upper limit speed performed in step S22 will be described. Figure 6 1 is a flowchart showing the flow of the calculation process of the lateral G upper limit speed. Figure 5 The upper limit speed setting process shown is executed every time step S22 is reached.

[0107] In the calculation process of the lateral G upper limit speed, first, the upper limit lateral acceleration setting unit 332 determines the type of the road on which the vehicle 100 is scheduled to travel (step S31). As described above, in the present embodiment, the automatic speed control is performed when the vehicle 100 is traveling on a road dedicated to automobiles. Therefore, the upper limit lateral acceleration setting unit 332 determines which road of the road dedicated to automobiles the road scheduled to travel (hereinafter referred to as "the road scheduled to travel") is. Specifically, the upper limit lateral acceleration setting unit 332 determines whether the road scheduled to travel is the main line of the road dedicated to automobiles or the connecting road of the road dedicated to automobiles. In addition, when the road scheduled to travel is the main line of the road dedicated to automobiles, the upper limit lateral acceleration setting unit 332 determines whether the road is a road with a distance from the exit that is less than a predetermined distance. In addition, when the road scheduled to travel is the connecting road of the road dedicated to automobiles, the upper limit lateral acceleration setting unit 332 determines whether the connecting road is a connecting road to the exit of the road dedicated to automobiles.

[0108] The upper limit lateral acceleration setting unit 332 determines the type of the road on which the vehicle is scheduled to travel, for example, by comparing the self-position information measured by the positioning sensor 14 with the map information stored in the storage device 15. Alternatively, the upper limit lateral acceleration setting unit 332 may determine the type of the road on which the vehicle is scheduled to travel based on an image generated by the vehicle exterior camera 12 in addition to or instead of the self-position information and the map information. In this case, for example, a dividing line in an image generated by image recognition processing may be identified, and the type of the road on which the vehicle is scheduled to travel may be determined based on the number of lanes grasped from the identified dividing line.

[0109] Next, the upper limit lateral acceleration setting unit 332 sets the upper limit lateral acceleration according to the type of the road on which the vehicle is scheduled to travel (step S32). The upper limit lateral acceleration is the upper limit value of the lateral acceleration allowed to be applied to the vehicle 100 when the vehicle 100 is scheduled to travel on a curved road. When a large lateral acceleration is applied to the vehicle 100, the occupants of the vehicle 100 will feel uneasy, so the upper limit lateral acceleration is basically set to a value that the occupants will not feel uneasy. In this embodiment, the upper limit lateral acceleration is a constant value pre-set for each type of road.

[0110] Specifically, in this embodiment, the upper limit lateral acceleration setting unit 332 sets the upper limit lateral acceleration when the vehicle 100 is traveling on the connecting road of the dedicated road for automobiles to be lower than the upper limit acceleration when the vehicle 100 is traveling on the main line of the dedicated road for automobiles. Specifically, for example, the upper limit lateral acceleration when the vehicle 100 is traveling on the connecting road is set to 0.2G, and the upper limit lateral acceleration when the vehicle 100 is traveling on the main line is set to 0.3G.

[0111] Here, generally, for the same lateral acceleration, the narrower the road width, the more likely the occupants are to feel uneasy. In addition, the road width of the connecting road of the automobile-only road is generally narrower than the road width of the main line. Therefore, when the same lateral acceleration is applied to the vehicle 100, the occupants are more likely to feel uneasy when the vehicle 100 is traveling on the connecting road than when the vehicle 100 is traveling on the main line. In view of this, in the present embodiment, by setting the upper limit lateral acceleration when the vehicle 100 is traveling on the connecting road to be lower than the upper limit acceleration when the vehicle 100 is traveling on the main line, it is possible to suppress the occupants from feeling uneasy when the vehicle 100 is traveling on the connecting road.

[0112] In addition, in the present embodiment, the upper limit lateral acceleration setting unit 332 sets the upper limit lateral acceleration when the vehicle 100 is traveling on the connecting road leading to the exit of the dedicated road for automobiles to be lower than the upper limit lateral acceleration when the vehicle 100 is traveling on the connecting road merging with the main line (i.e., the connecting road not leading to the exit of the dedicated road for automobiles). Specifically, for example, the upper limit lateral acceleration when the vehicle 100 is traveling on the connecting road leading to the exit of the dedicated road for automobiles is set to about 80% or less of the upper limit lateral acceleration when the vehicle 100 is traveling on the connecting road merging with the main line.

[0113] In addition, in the present embodiment, the upper limit lateral acceleration setting unit 332 sets the upper limit lateral acceleration when driving on a main line whose distance from the main line exit without a connecting road is less than a predetermined reference distance (i.e., the main line near the exit) to be lower than the upper limit lateral acceleration when driving on a main line whose distance from the main line exit is longer than the reference distance (i.e., the main line other than the exit). Specifically, the upper limit lateral acceleration when driving on a main line whose distance from the main line exit without a connecting road is less than the reference distance is set to about 80% or less of the upper limit lateral acceleration when driving on a main line whose distance from the main line exit is longer than the reference distance. In addition, the reference distance is a distance at which the driver usually starts to slow down in preparation for the main line exit, for example, 300 meters.

[0114] Here, there is a toll booth at the exit of the dedicated road for automobiles, so the speed of the vehicle 100 needs to be greatly reduced near the exit. In addition, even if there is no toll booth at the exit of the dedicated road for automobiles, the speed of the vehicle 100 needs to be reduced on the normal road connected to the exit of the dedicated road for automobiles. Therefore, the speed of the vehicle 100 needs to be reduced near the exit of the dedicated road for automobiles. In this embodiment, by setting the upper limit lateral acceleration when traveling on the connecting road to the exit of the dedicated road for automobiles to be low, the speed of the vehicle 100 can be reduced without any sense of incongruity in accordance with the road conditions. In addition, when the driver is changed at the exit of the dedicated road for automobiles, the driver can be changed to the driver more safely by reducing the speed of the vehicle 100 near the exit of the dedicated road for automobiles.

[0115] When the upper limit lateral acceleration is set by the upper limit lateral acceleration setting unit 332, the road curvature acquisition unit 333 acquires the curvature of the road on which the vehicle 100 is scheduled to travel (step S33). The road curvature acquisition unit 333 acquires, for example, the curvature of the road on which the vehicle 100 is scheduled to travel from the current location to 300 meters ahead. The scheduled travel road is calculated separately by the ECU 21, for example, and the road curvature acquisition unit 333 acquires the curvature of the scheduled travel road based on the calculated scheduled travel road and map information including curvature information about each road.

[0116] Specifically, the ECU 21 calculates the road on which the vehicle 100 is scheduled to travel based on the destination information input via the HMI 16, the surrounding environment of the vehicle 100, the own position measured by the positioning sensor 14, and the map information stored in the storage device 15. In particular, in the present embodiment, when the road on which the vehicle 100 is scheduled to travel has a plurality of lanes, the information on the road on which the vehicle 100 is scheduled to travel calculated by the ECU 21 may also include information on the lane on which the vehicle 100 is scheduled to travel.

[0117] The map information stored in the storage device 15 includes curvature information for each location of each road. In particular, for a road having multiple lanes, the map information may include curvature information for each location of each lane. In either case, the road curvature acquisition unit 333 acquires the curvature of the road on which the vehicle 100 is scheduled to travel as discrete point group data along the traveling direction of the vehicle 100.

[0118] Figure 7 2 is a diagram schematically showing an example of a dedicated road for automobiles in which a connecting road Rc branches off from a main line Rm. Figure 7 In the example shown, the connecting road Rc has a curved road with a bending angle of 90 degrees after branching from the main line Rm. The curved road has a turnaround region X where the curvature gradually increases, a constant curvature region Y where the curvature is maintained constant, and a turnaround region Z where the curvature gradually decreases. Therefore, in this case, the road curvature acquisition unit 333 discretely acquires a gradually increasing curvature for the turnaround region X, discretely acquires a constant curvature for the constant curvature region Y, and discretely acquires a gradually decreasing curvature for the turnaround region Z.

[0119] Furthermore, in the present embodiment, after the upper limit lateral acceleration is set by the upper limit lateral acceleration setting unit 332, the road curvature acquisition unit 333 acquires the curvature of the road on which the vehicle is scheduled to travel. However, the road curvature acquisition unit 333 may acquire the curvature of the road on which the vehicle is scheduled to travel before the upper limit lateral acceleration is set by the upper limit lateral acceleration setting unit 332 or at the same time as the upper limit lateral acceleration is set. Furthermore, in the present embodiment, the road curvature acquisition unit 333 acquires the curvature of the road on which the vehicle is scheduled to travel. However, the road curvature acquisition unit 333 may acquire other curvature parameters such as the radius of curvature as long as the curvature parameter is related to the curvature of the road on which the vehicle is scheduled to travel. Therefore, in the present embodiment, the lateral G upper limit speed may be said to be calculated based on the value of the curvature parameter of the road on which the vehicle is scheduled to travel.

[0120] When the upper limit lateral acceleration of the vehicle 100 is set and the curvature of the road on which the vehicle 100 is scheduled to travel is obtained, the upper limit speed setting unit 334 calculates the upper limit lateral G speed at each point on the road on which the vehicle 100 is scheduled to travel (step S34). The upper limit lateral G speed at each point on the road on which the vehicle 100 is scheduled to travel is basically calculated based on the curvature of each point on the road on which the vehicle 100 is scheduled to travel so that the lateral acceleration of the vehicle 100 when the vehicle 100 travels at each point on the road becomes the upper limit lateral acceleration. Figure 8 , the method for calculating the lateral G upper limit speed in the upper limit speed setting unit 334 is specifically described.

[0121] Figure 8 is a diagram showing that the vehicle 100 is scheduled to Figure 7 A diagram showing the curvature of the road on which travel is planned and the lateral G upper limit speed when traveling on the connecting road Rc as shown. Figure 8 The horizontal axis of represents the distance from the current location of the vehicle 100. Regarding the curvature in the figure, the solid line represents the change of the actual curvature relative to the current location (the change of the curvature acquired by the road curvature acquisition unit 333). Therefore, the curvature gradually increases in the area X, remains constant in the area Y, and gradually decreases in the area Z.

[0122] In this embodiment, the upper speed limit setting unit 334 corrects the curvature of the road on which the vehicle is scheduled to travel obtained in step S33 when calculating the lateral G upper speed limit. Specifically, the upper speed limit setting unit 334 corrects the curvature of the road on which the vehicle is scheduled to travel so that the area with the maximum curvature in the curved road is enlarged. Figure 8 In the example shown, the curvature of the road to be traveled is corrected so that the area obtained by adding a predetermined distance Δd before and after the area Y with the maximum curvature becomes the area with the maximum curvature in the curved road. As a result, the corrected curvature of the road to be traveled is as follows: Figure 8 The movement is as shown by the dotted line in FIG.

[0123] The upper speed limit setting unit 334 performs calculation based on the calculated corrected curvature of the road to be traveled and the upper lateral acceleration of the road to be traveled. For example, the upper lateral G speed limit Vg at each location is set to the square root of the result obtained by dividing the upper lateral acceleration a at each location by the corrected curvature c at that location (Vg = (a / c) 1 / 2 ). The lateral G limit speed calculated in this way is Figure 8 Indicated by solid line.

[0124] <Calculation of re-acceleration upper limit speed>

[0125] When the vehicle 100 is traveling on a connecting road, the speed control unit 331 sometimes decelerates the speed of the vehicle 100 to less than the reference upper limit speed in order to limit the lateral acceleration of the vehicle 100 when traveling on a sharp curve. In addition, when the vehicle 100 is traveling on a connecting road, the speed control unit 331 sometimes decelerates the speed of the vehicle 100 to less than the reference upper limit speed by causing the vehicle 100 to follow a slow preceding vehicle in front of it. In the present embodiment, in such a case, even if the sharp curve changes to a straight road, or there is no longer a slow preceding vehicle, the speed control unit 331 sets the upper limit speed of the vehicle 100 to be less than the re-acceleration upper limit speed that is lower than the reference upper limit speed. Hereinafter, refer to Fig. 9 , the calculation method of the re-acceleration upper limit speed is explained.

[0126] Fig. 9 It is shown in Figure 5 Flow chart of the calculation process of the re-acceleration upper limit speed performed in step S23. Figure 5The upper limit speed setting process shown is executed every time step S23 is reached.

[0127] In the calculation process of the re-acceleration upper limit speed, first, the upper limit speed setting unit 334 determines the type of road on which the vehicle 100 is currently traveling (step S41). Figure 6 Similarly, step S31 is performed based on the self-position information measured by the positioning sensor 14 and the map information stored in the storage device 15, for example.

[0128] Next, the upper limit speed setting unit 334 determines whether the vehicle 100 is traveling on a connecting road based on the type of the traveling road determined in step S41 (step S42). If it is determined in step S42 that the vehicle 100 is not traveling on a connecting road, that is, traveling on a main line, the upper limit speed setting unit 334 does not calculate but resets the re-acceleration upper limit speed as a result of the calculation process of the re-acceleration upper limit speed (step S43).

[0129] On the other hand, when it is determined in step S42 that the vehicle 100 is traveling on a connecting road, the upper speed limit setting unit 334 calculates the re-acceleration upper speed limit (step S44). The re-acceleration upper speed limit is a pre-set speed lower than the reference upper speed limit. In the present embodiment, the relationship between the type of road and the re-acceleration upper speed limit is pre-stored in the storage device 15. In addition, the upper speed limit setting unit 334 calculates the re-acceleration upper speed limit based on the type of the traveling road determined in step S41 and the relationship stored in the storage device.

[0130] In particular, in the present embodiment, the re-acceleration upper limit speed when the vehicle 100 is traveling on the connecting road leading to the exit of the dedicated road for automobiles is calculated to be lower than the re-acceleration upper limit speed when traveling on the connecting road merging with the main line. Here, as described above, it is necessary to reduce the speed of the vehicle 100 near the exit of the dedicated road for automobiles. According to the present embodiment, by calculating the re-acceleration upper limit speed when traveling on the connecting road leading to the exit of the dedicated road for automobiles to be low, the speed of the vehicle 100 can be reduced without any sense of incongruity in accordance with the road conditions.

[0131] Next, the upper limit speed setting unit 334 determines whether the speed of the vehicle 100 has decelerated to less than the re-acceleration upper limit speed (step S45). The speed of the vehicle 100 is detected by, for example, the driving state sensor 11 of the vehicle 100. In a case where it is determined in step S45 that the speed of the vehicle 100 is above the re-acceleration upper limit speed, that is, when it is determined that the vehicle 100 is not decelerated that much on the connecting road, as a result of the calculation process of the re-acceleration upper limit speed, the upper limit speed setting unit 334 does not calculate but resets the re-acceleration upper limit speed (step S43). Therefore, when the speed of the vehicle 100 is above the re-acceleration upper limit speed, the re-acceleration upper limit speed is not set, and thus, Figure 5 In step S24, the slower speed of the reference upper limit speed and the lateral G upper limit speed is set as the upper limit speed.

[0132] On the other hand, when it is determined in step S45 that the speed of the vehicle 100 is less than the re-acceleration upper limit speed, the upper limit speed setting unit 334 does not reset the re-acceleration upper limit speed but maintains the value calculated in step S44 as it is. Figure 5 In step S24, the slowest speed among the base upper limit speed, the lateral G upper limit speed, and the re-acceleration upper limit speed is set as the upper limit speed. As a result, in the present embodiment, when the vehicle is decelerated to a speed lower than the re-acceleration upper limit speed during driving on the connecting road and then accelerated again, if the lateral G upper limit speed is faster than the re-acceleration upper limit speed, the re-acceleration upper limit speed is set as the upper limit speed.

[0133] Here, usually, when the vehicle 100 enters the connecting road from the main line, the speed of the vehicle 100 is relatively high, and the speed gradually slows down as it travels on the connecting road. Therefore, if the speed of the vehicle 100 temporarily slows down while traveling on the connecting road, the driver will feel uncomfortable when the vehicle 100 accelerates to the original speed afterwards. According to the present embodiment, if the speed of the vehicle 100 temporarily slows down due to some kind of obstacle while traveling on the connecting road, even if the obstacle disappears afterwards, the speed of the vehicle 100 will not return to the original speed while traveling on the connecting road, so the driver can be prevented from feeling uncomfortable.

[0134] In the above embodiment, the upper speed limit setting unit 334 determines in step S45 whether the speed of the vehicle 100 has been decelerated to a speed lower than the re-acceleration upper speed limit. However, the upper speed limit setting unit 334 may determine in step S45 whether the speed of the vehicle 100 has been decelerated to a speed lower than a predetermined speed lower than the re-acceleration upper speed limit. Thus, it is possible to provide hysteresis.

[0135] In addition, the upper limit speed setting unit 334 may determine in step S45 whether the speed of the vehicle 100 has been decelerated to a speed lower than the re-acceleration upper limit speed of multiple stages, and set the re-acceleration upper limit speed in multiple stages when it is determined that the speed of the vehicle 100 has been decelerated to a speed lower than the re-acceleration upper limit speed of multiple stages. For example, the upper limit speed setting unit 334 may set the re-acceleration upper limit speed to the first speed when the speed of the vehicle 100 has been decelerated to a speed lower than the first speed and higher than the second speed, set the re-acceleration upper limit speed to the second speed when the speed of the vehicle 100 has been decelerated to a speed lower than the second speed and higher than the third speed, and set the re-acceleration upper limit speed to the third speed when the speed of the vehicle 100 has been decelerated to a speed lower than the third speed.

[0136] <Function and Effect>

[0137] As described above, for the same lateral acceleration, the narrower the road width, the more likely the occupants will feel uneasy. In addition, the road width of the connecting road of the dedicated road for automobiles is generally narrower than the road width of the main line. In this embodiment, by setting the upper limit lateral acceleration when the vehicle 100 is traveling on the connecting road to be lower than the upper limit acceleration when the vehicle 100 is traveling on the main line, it is possible to suppress the situation where the occupants feel uneasy when the vehicle 100 is traveling on the connecting road. Therefore, according to this embodiment, the speed of the vehicle can be controlled in a manner that makes the lateral acceleration of the vehicle appropriate regardless of the type of road on which the vehicle is traveling.

[0138] As mentioned above, although the preferred embodiment according to the present invention has been described, the present invention is not limited to the above-mentioned embodiment, and various corrections and changes can be made within the scope of the claims.

Claims

1. An automatic speed control device that automatically controls the speed of a vehicle. The automatic speed control device has: an upper limit lateral acceleration setting unit for setting an upper limit lateral acceleration which is an upper limit value of lateral acceleration permitted during travel of the vehicle; a road curvature acquisition unit that acquires a value of a curvature parameter related to the curvature of a predetermined road on which the vehicle travels; an upper limit speed setting unit that calculates a vehicle speed at which the lateral acceleration of the vehicle reaches the upper limit lateral acceleration when the vehicle travels on the road based on the value of the curvature parameter of the road, and sets the calculated speed as the upper limit speed; and a speed control unit that controls the speed of the vehicle so as to be below the upper speed limit, The upper limit lateral acceleration setting unit sets the upper limit lateral acceleration when the vehicle is traveling on a connecting road merging with a main line of the motorway or a connecting road branching from the main line to be lower than the upper limit lateral acceleration when the vehicle is traveling on the main line of the motorway, The upper limit speed setting unit sets the reference upper limit speed as the upper limit speed when the speed of the vehicle, which is such that the upper limit lateral acceleration is reached, is faster than a predetermined reference upper limit speed. When the vehicle is decelerated to a speed lower than a predetermined re-acceleration upper limit speed and then accelerated again while traveling on the connecting road, if the vehicle speed reaching the upper limit lateral acceleration is faster than the re-acceleration upper limit speed, the re-acceleration upper limit speed is set as the upper limit speed; The reacceleration upper limit speed is lower than the base upper limit speed.

2. The automatic speed control device according to claim 1, The vehicle is a vehicle whose speed is automatically controlled to stop the vehicle at an exit of a road dedicated to automobiles, The upper limit speed setting unit sets a re-acceleration upper limit speed when the vehicle travels on the connecting road to the exit to be lower than a re-acceleration upper limit speed when the vehicle travels on the connecting road merging with a main line.

3. The automatic speed control device according to claim 1, The vehicle is a vehicle whose speed is automatically controlled to stop the vehicle at an exit of a road dedicated to automobiles, The upper limit lateral acceleration setting unit sets an upper limit lateral acceleration when the vehicle travels on the connecting road to the exit to be lower than an upper limit lateral acceleration when the vehicle travels on the connecting road merging with the main line.

4. The automatic speed control device according to any one of claims 1 to 3, The upper limit lateral acceleration setting unit sets an upper limit lateral acceleration when traveling on a main line whose distance from a main line exit without the connecting road is less than a predetermined distance to be lower than an upper limit lateral acceleration when traveling on a main line whose distance from the main line exit is greater than the predetermined distance.

5. An automatic speed control method, automatically controlling the speed of a vehicle, The automatic speed control method comprises: setting an upper limit lateral acceleration which is an upper limit value of lateral acceleration permitted during travel of the vehicle; obtaining a value of a curvature parameter related to the curvature of a predetermined road on which the vehicle is traveling; calculating a vehicle speed at which the lateral acceleration of the vehicle reaches the upper limit lateral acceleration when the vehicle travels on the road based on the value of the curvature parameter of the road, and setting the calculated speed as the upper limit speed; as well as controlling the speed of the vehicle so as to be below the upper speed limit, The upper limit lateral acceleration of the vehicle when traveling on a connecting road merging with the main line of the motorway or a connecting road branching from the main line is lower than the upper limit lateral acceleration of the vehicle when traveling on the main line of the motorway, The automatic speed control method further comprises: When the speed of the vehicle that reaches the upper limit lateral acceleration is faster than a predetermined reference upper limit speed, the reference upper limit speed is set as the upper limit speed; When the vehicle is decelerated to a speed lower than a predetermined re-acceleration upper limit speed and then accelerated again while traveling on the connecting road, if the vehicle speed reaching the upper limit lateral acceleration is faster than the re-acceleration upper limit speed, the re-acceleration upper limit speed is set as the upper limit speed; The reacceleration upper limit speed is lower than the base upper limit speed.

6. An automatic speed control program product, comprising an automatic speed control program, the automatic speed control program automatically controlling the speed of a vehicle, The automatic speed control program causes the computer to execute the following processing: setting an upper limit lateral acceleration which is an upper limit value of lateral acceleration permitted during travel of the vehicle; obtaining a value of a curvature parameter related to the curvature of a predetermined road on which the vehicle is traveling; calculating a vehicle speed at which the lateral acceleration of the vehicle reaches the upper limit lateral acceleration when the vehicle travels on the road based on the value of the curvature parameter of the road, and setting the calculated speed as the upper limit speed; as well as controlling the speed of the vehicle so as to be below the upper speed limit, The upper limit lateral acceleration of the vehicle when traveling on a connecting road merging with the main line of the motorway or a connecting road branching from the main line is lower than the upper limit lateral acceleration of the vehicle when traveling on the main line of the motorway, The automatic speed control program also causes the computer to execute the following processing: When the speed of the vehicle that reaches the upper limit lateral acceleration is faster than a predetermined reference upper limit speed, the reference upper limit speed is set as the upper limit speed; When the vehicle is decelerated to a speed lower than a predetermined re-acceleration upper limit speed and then accelerated again while traveling on the connecting road, if the vehicle speed reaching the upper limit lateral acceleration is faster than the re-acceleration upper limit speed, the re-acceleration upper limit speed is set as the upper limit speed; The reacceleration upper limit speed is lower than the base upper limit speed.

Images