Vehicle speed control method and vehicle speed control device

Abstract

This vehicle speed control device (3) comprises a control unit (23) that controls the speed of a vehicle at which the vehicle travels on a curved road. The control unit (23) identifies a curved road on which the vehicle is scheduled to travel, acquires the curvatures and the transverse gradients of the identified curved road, determines a target speed when the vehicle travels on the curved road before the vehicle enters the curved road, on the basis of the acquired curvatures and transverse gradients, and controls the speed of the vehicle such that the speed of the vehicle falls to the target speed when the vehicle travels on the curved road.

Description

Vehicle speed control method and vehicle speed control device

[0001] The present invention relates to a vehicle speed control method and a vehicle speed control device.

[0002] Patent Document 1 discloses a vehicle driving support device that appropriately controls the vehicle speed when driving on a curved road. In this vehicle driving support device, the position of the host vehicle in the lateral direction of the lane is detected by a position sensor, and the lateral gradient of the lane is detected by a lateral gradient sensor. The vehicle driving support device determines the target value of the speed of the host vehicle according to the position of the host vehicle in the lateral direction of the curved road and the lateral gradient of the curved road.

[0003] Japanese Unexamined Patent Application Publication No. 2022-175566

[0004] However, in the above-described vehicle driving support device, since the target value of the speed is determined according to the position of the host vehicle detected by the sensor and the lateral gradient, the target value of the speed is determined while the host vehicle is driving on a curved road. That is, the target value of the speed is determined by feedback control after the host vehicle enters the curved road. Therefore, since a delay occurs in the determined target value of the speed, the host vehicle needs to correct the speed while driving on the curved road, which causes a problem of giving a sense of discomfort to the occupant.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a vehicle speed control method and an apparatus capable of controlling the vehicle speed on a curved road without giving a sense of discomfort to the occupant.

[0006] The vehicle speed control method and its apparatus according to one aspect of the present invention determine the target speed when the vehicle travels on a curved road before the vehicle enters the curved road based on the curvature and the lateral gradient of the curved road on which the vehicle is scheduled to travel, and when the vehicle travels on the curved road, control the speed of the vehicle so that the speed of the vehicle decelerates to the target speed.

[0007] According to the present invention, since the target speed is determined before the vehicle enters the curved road, the vehicle speed can be controlled on the curved road without giving a sense of discomfort to the occupant.

[0008] Figure 1 is a block diagram showing the configuration of a vehicle speed control system equipped with a vehicle speed control device according to one embodiment. Figure 2 is a flowchart showing the processing procedure of the vehicle speed control process by the vehicle speed control device according to one embodiment. Figure 3 is a diagram showing an example of the relationship between vehicle speed and curvature used in the vehicle speed control device according to one embodiment. Figure 4 is a diagram showing an example of the relationship between transverse gradient and curvature used in the vehicle speed control device according to one embodiment. Figure 5 is a diagram showing an example of the vehicle speed control process by the vehicle speed control device according to one embodiment. Figure 6 is a diagram for explaining the effect of the vehicle speed control process by the vehicle speed control device according to one embodiment.

[0009] The vehicle speed control method and vehicle speed control device according to this embodiment will be described below with reference to the drawings. In the drawings, the same parts are denoted by the same reference numerals, and detailed descriptions are omitted.

[0010] Referring to Figure 1, the configuration of the vehicle speed control system equipped with the vehicle speed control device according to this embodiment will be described. The vehicle speed control system 1 is mounted on a vehicle and is a system that controls the speed of the vehicle when it is traveling on a curved road. As shown in Figure 1, the vehicle speed control system 1 includes a driver assistance ECU (electronic control unit) 5 equipped with a vehicle speed control device 3, a navigation device 7, a map database 9, a vehicle speed sensor 11, and a yaw rate sensor 13. The vehicle speed control system 1 also includes an engine control ECU 15, an engine actuator 17, a brake control ECU 19, and a brake actuator 21.

[0011] The vehicle speed control device 3 is a device that controls the speed of the vehicle when it is traveling on a curved road, and is installed in the driver assistance ECU 5. The vehicle speed control device 3 acquires information from the navigation device 7, map database 9, vehicle speed sensor 11 and yaw rate sensor 13 to determine the target speed on the curved road. The vehicle speed control device 3 then outputs deceleration commands to the engine control ECU 15 and brake control ECU 19 so that the vehicle decelerates to the target speed on the curved road.

[0012] In particular, the vehicle speed control device 3 acquires the curvature and transverse gradient of curves along the vehicle's path in advance and determines the target speed before entering the curve. Therefore, since the vehicle speed control device 3 determines the target speed before entering the curve through feedforward control, there is no need to correct the speed while traveling on the curve, and the vehicle can travel stably on the curve.

[0013] The vehicle speed control device 3 comprises a control unit 23 and a storage unit 25. The control unit 23 is a controller that performs processing to control the speed of the vehicle when it is traveling on a curved road. Specifically, the control unit 23 identifies the curved road on which the vehicle is scheduled to travel, obtains the curvature and transverse gradient of the identified curved road, and determines the target speed for the vehicle when it is traveling on the curved road before it enters the curved road, based on the obtained curvature and transverse gradient. Then, when the vehicle is traveling on the curved road, the control unit 23 controls the speed of the vehicle so that the vehicle's speed is reduced to the target speed.

[0014] The storage unit 25 is a memory or database that stores information necessary to perform the process of controlling the speed of the vehicle when it travels on a curved road. Specifically, the storage unit 25 stores map information obtained from the map database 9 and the vehicle's travel route set by the navigation device 7. The storage unit 25 also records the relationship between vehicle speed and curvature when considering the transverse gradient, and the relationship between the transverse gradient and curvature.

[0015] The vehicle speed control device 3 is a computer composed of general-purpose electronic circuits including a microcomputer, microprocessor, and CPU, as well as peripheral devices such as memory, and has a computer program installed to perform the process of controlling the vehicle speed. Each function of the vehicle speed control device 3 can be implemented by one or more processing circuits.

[0016] The driver assistance ECU 5 is an ECU that executes ADAS (Advanced Driver Assistance Systems) and can perform ADAS functions such as ACC (Adaptive Cruise Control System) and FCW (Forward Collision Warning). Therefore, the driver assistance ECU 5 can recognize the surrounding conditions of the vehicle using cameras and radar and control the acceleration and deceleration of the vehicle by controlling the engine control ECU 15 and brake control ECU 19.

[0017] The navigation device 7 is installed in the vehicle's IVI (In-Vehicle Infotainment) and detects the vehicle's current position, outputting it to the vehicle speed control device 3. Furthermore, if a driving route to a destination has been set, the navigation device 7 outputs the set driving route to the vehicle speed control device 3. The navigation device 7 stores map information, which includes the curvature of curved roads.

[0018] Map database 9 stores map information. The map information is high-precision 3D map data such as HD maps, and includes not only location information on the map of three-dimensional objects such as traffic lights and utility poles installed on roads and sidewalks, or lane boundary lines, but also information indicating the road structure, such as the curvature of curved roads and the transverse gradient.

[0019] The vehicle speed sensor 11 detects the vehicle speed and outputs it to the vehicle speed control device 3. The yaw rate sensor 13 detects the vehicle's yaw rate and outputs it to the vehicle speed control device 3.

[0020] The engine control ECU 15 drives the engine actuator 17 to control various engine components such as variable valve timing and ignition timing. In particular, the engine control ECU 15 controls the opening and closing of the throttle to control the acceleration and deceleration of the vehicle in accordance with the deceleration command output from the vehicle speed control device 3.

[0021] The brake control ECU 19 controls the braking state of the vehicle's brakes by driving the brake actuator 21 according to the deceleration command output from the vehicle speed control device 3.

[0022] Next, the vehicle speed control process by the vehicle speed control device 3 according to this embodiment will be described. Figure 2 is a flowchart showing the processing procedure of the vehicle speed control process. The vehicle speed control process shown in Figure 2 starts when the vehicle's power is turned ON.

[0023] As shown in Figure 2, in step S101, the control unit 23 identifies the curved road that the vehicle is scheduled to travel on. If a travel route to the destination is set in the navigation device 7, the control unit 23 identifies the curved road that lies on the set travel route. For example, the control unit 23 identifies the first curved road that the vehicle will reach from among several curved roads on the travel route. If no travel route is set in the navigation device 7, the control unit 23 identifies the first curved road that the vehicle will reach on the road it is currently traveling on.

[0024] In step S103, the control unit 23 determines whether or not high-precision map information for the curved road identified in step S101 can be obtained. The control unit 23 determines that high-precision map information can be obtained if it is stored in the map database 9. Even if it is not stored in the map database 9, the control unit 23 determines that high-precision map information can be obtained if it can be obtained via the Internet. If high-precision map information can be obtained, the process proceeds to step S105; otherwise, the process proceeds to step S109.

[0025] In step S105, the control unit 23 obtains the curvature and transverse gradient of the curved road identified in step S101 from the high-precision map information of the map database 9.

[0026] In step S107, the control unit 23 determines the target speed for the vehicle when it travels along the curved road before it enters the curved road, based on the curvature and transverse gradient acquired in step S105. Since the storage unit 25 stores the relationship between vehicle speed and curvature when transverse gradient is taken into account, the control unit 23 uses this relationship to determine the target speed.

[0027] For example, as shown in Figure 3, the vehicle speed V1 when considering the transverse slope decreases as the curvature increases. Furthermore, the vehicle speed V1 is higher compared to the vehicle speed V0 when the transverse slope is not considered. Generally, the transverse slope increases as the curvature increases, so considering the transverse slope makes it possible to allow higher vehicle speeds. Therefore, the vehicle speed V1 when considering the transverse slope is higher than the vehicle speed V0 when the transverse slope is not considered.

[0028] Since the memory unit 25 stores multiple vehicle speeds V1 according to the transverse gradient, the control unit 23 acquires the V1 data that matches the transverse gradient value acquired in step S105, and uses the V1 data from the curvature acquired in step S105 to determine the target speed.

[0029] In step S109, the control unit 23 cannot obtain high-precision map information of the curved road identified in step S101, so it obtains the curvature of the curved road identified in step S101 from the map information of the navigation device 7.

[0030] In step S111, the control unit 23 estimates the transverse gradient of the curved road identified in step S101 based on the curvature obtained in step S109. Since the relationship between the transverse gradient and curvature is recorded in the storage unit 25, the control unit 23 uses this relationship to estimate the transverse gradient.

[0031] For example, as shown in Figure 4, numerical values ​​of curvature and transverse gradient in actual existing curved roads are collected, a distribution 41 showing the relationship between curvature and transverse gradient is recorded, and the relationship 43 between curvature and transverse gradient is estimated based on the Road Structure Ordinance so that it falls within this distribution 41. Since the relationship 43 between curvature and transverse gradient is recorded in the storage unit 25, the control unit 23 uses the relationship 43 between curvature and transverse gradient to estimate the transverse gradient from the curvature obtained in step S109.

[0032] In step S113, the control unit 23 determines the target speed for the vehicle when it travels along the curved road before it enters the curved road, based on the curvature acquired in step S109 and the transverse gradient estimated in step S111. The storage unit 25 stores the relationship between vehicle speed and curvature when considering the transverse gradient shown in Figure 3, so the control unit 23 uses the relationship shown in Figure 3 to determine the target speed from the curvature acquired in step S109.

[0033] In step S115, the control unit 23 controls the vehicle's speed so that it slows down to the target speed when the vehicle travels along the curved road identified in step S101. The control unit 23 outputs deceleration commands to the engine control ECU 15 and the brake control ECU 19 to slow down the vehicle's speed even before it enters the curved road.

[0034] At this time, the control unit 23 controls the vehicle speed so that the vehicle speed decelerates to the target speed at the point where the curvature of the curved road is greatest. For example, as shown in Figure 5, when the vehicle is traveling on a curved road and the curvature of the curved road reaches its maximum value Rm at time t1, the control unit 23 controls the vehicle speed so that it decelerates to the target speed Vm at time t1. This makes it possible to control the vehicle speed so that it is at its lowest point at the point where it needs to be lowest, and to control the vehicle speed at a deceleration timing similar to that of a human operator.

[0035] In step S117, the control unit 23 determines whether the vehicle's yaw rate is greater than or equal to a predetermined value when the vehicle's speed is decreasing to the target speed. If it is greater than or equal to the predetermined value, the unit proceeds to step S119; otherwise, the unit proceeds to step S121.

[0036] In step S119, the control unit 23 further reduces the vehicle's speed beyond the deceleration control performed in step S115. That is, when the vehicle's speed is decreasing towards the target speed, if the vehicle's yaw rate exceeds a predetermined value, the control unit 23 further reduces the vehicle's speed. This allows the vehicle's speed to be corrected using feedback control based on the yaw rate, even if the target speed determined by the feedforward control is inappropriate, thereby preventing continued overspeeding.

[0037] In step S121, the control unit 23 determines whether the vehicle's speed has decreased to the target speed. If it has decreased to the target speed, the unit proceeds to step S123; otherwise, it returns to step S115.

[0038] In step S123, the control unit 23 determines whether the vehicle's power supply has been turned off. If it has not been turned off, the process returns to step S101. If the power supply has been turned off, the vehicle speed control process according to this embodiment is terminated.

[0039] As described in detail above, the vehicle speed control device 3 according to this embodiment identifies a curved road on which the vehicle is scheduled to travel, acquires the curvature and transverse gradient of the identified curved road, determines a target speed for when the vehicle is traveling on the curved road before it enters the curved road based on the acquired curvature and transverse gradient, and controls the vehicle's speed so that it decelerates to the target speed when the vehicle is traveling on the curved road. As a result, the target speed can be determined by feedforward control before the vehicle enters the curved road, eliminating the need to correct the speed while traveling on the curved road, and allowing the vehicle speed to be controlled on the curved road without causing discomfort to the occupants.

[0040] In particular, in this embodiment, the target speed is determined by considering not only the curvature but also the transverse gradient, so the target speed can be set higher. For example, as shown in Figure 3, the vehicle speed V1 considering the transverse gradient is higher than the vehicle speed V0 that does not consider the transverse gradient.

[0041] Therefore, as shown in FIG. 6, when the curvature of the curved road reaches the maximum value Rm at time t1, if the curvature and the cross slope are obtained by feedforward control as in this embodiment, the vehicle speed 61 is decelerated to the target speed Vm at time t1, and then remains unchanged at Vm. Therefore, the vehicle can stably travel on the curved road without correcting the speed.

[0042] On the other hand, when only the curvature is obtained by feedforward control and the cross slope is obtained by feedback control, the vehicle speed 63 is decelerated to a speed Vn lower than Vm at time t1, and then increased to Vm. Therefore, since the speed of the vehicle is corrected, it cannot travel stably.

[0043] Thus, when comparing the vehicle speed 61 and the vehicle speed 63 in FIG. 6, the vehicle speed control device 3 according to this embodiment does not need to correct the speed while traveling on the curved road, so the vehicle can travel stably on the curved road. As a result, the vehicle speed control device 3 according to this embodiment can control the vehicle speed on the curved road without giving a sense of discomfort to the occupant.

[0044] Further, the vehicle speed control device 3 according to this embodiment obtains the curvature and the cross slope of the specified curved road from the map information. Thereby, the vehicle speed can be controlled using the accurate curvature and cross slope recorded in the map information.

[0045] Furthermore, the vehicle speed control device 3 according to this embodiment obtains the curvature of the specified curved road from the map information, and estimates the cross slope based on the obtained curvature. Thereby, even when the cross slope is not recorded in the map information, the cross slope can be estimated from the curvature and the vehicle speed can be controlled.

[0046] In addition, when the speed of the vehicle is decelerating to the target speed, the vehicle speed control device 3 according to this embodiment decelerates the vehicle speed when the yaw rate of the vehicle becomes a predetermined value or more. Thereby, even when the target speed determined by the feedforward control is not appropriate, the vehicle speed can be corrected by feedback control using the yaw rate, and it is possible to prevent the overspeed from continuing.

[0047] Furthermore, the vehicle speed control device 3 according to the present embodiment controls the vehicle speed so that the vehicle speed decelerates to the target speed at the point where the curvature of the curved road is the largest. Thereby, at the point where it is necessary to make the vehicle speed the lowest, it is possible to control the vehicle speed so that it becomes the lowest, and it is possible to control the vehicle speed at a deceleration timing close to the operation performed by a person.

[0048] As described above, although the embodiments of the present invention have been described, it should not be understood that the arguments and drawings forming part of this disclosure limit this invention. Various alternative embodiments, examples, and operation techniques will be apparent to those skilled in the art from this disclosure.

[0049] 1. Vehicle speed control system 3. Vehicle speed control device 5. Driving support ECU 7. Navigation device 9. Map database 11. Vehicle speed sensor 13. Yaw rate sensor 15. Engine control ECU 17. Engine actuator 19. Brake control ECU 21. Brake actuator 23. Control unit 25. Storage unit 41. Distribution of the relationship between curvature and cross slope 43. Relationship between curvature and cross slope 61, 63. Vehicle speed V0. Vehicle speed when not considering the cross slope V1. Vehicle speed when considering the cross slope

Claims

1. A vehicle speed control method using a controller that controls the speed of a vehicle when it is traveling on a curved road, comprising: identifying a curved road on which the vehicle is scheduled to travel; obtaining the curvature and transverse gradient of the identified curved road; determining a target speed for the vehicle to travel on the curved road before it enters the curved road, based on the obtained curvature and transverse gradient; and controlling the speed of the vehicle so that the speed of the vehicle decreases to the target speed when the vehicle is traveling on the curved road.

2. The vehicle speed control method according to claim 1, wherein the curvature and transverse gradient of the identified curved road are obtained from map information.

3. The vehicle speed control method according to claim 1, wherein the curvature of the identified curved road is obtained from map information, and the transverse gradient is estimated based on the obtained curvature.

4. A vehicle speed control method according to any one of claims 1 to 3, wherein when the speed of the vehicle is decreasing to the target speed, the speed of the vehicle decreases if the yaw rate of the vehicle exceeds a predetermined value.

5. A vehicle speed control method according to any one of claims 1 to 4, wherein the speed of the vehicle is controlled so that the speed of the vehicle decreases to the target speed at the point where the curvature of the curved road is greatest.

6. A vehicle speed control device equipped with a controller for controlling the speed of a vehicle when it is traveling on a curved road, the device identifies a curved road on which the vehicle is scheduled to travel, obtains the curvature and transverse gradient of the identified curved road, determines a target speed for the vehicle when it is traveling on the curved road before it enters the curved road based on the obtained curvature and transverse gradient, and controls the speed of the vehicle when it is traveling on the curved road so that the speed of the vehicle decreases to the target speed.

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