Adaptive Cruise Control Device

Abstract

To shorten the time required for a vehicle having a function for following a preceding vehicle to reach the deceleration that satisfies the deceleration request when an automatic brake is applied, as well as, to prevent uncomfortable deceleration due to a fuel supply cut prior to reach the deceleration.SOLUTION: When a target deceleration exceeds a threshold value Ta due to deceleration of a preceding vehicle or the like, a follow-travel controller performs deceleration control (main deceleration control) to make an actual inter-vehicle distance from the preceding vehicle equal to or less than the target inter-vehicle distance. Further, before the main deceleration control and when acceleration becomes unnecessary, the follow-travel controller performs preliminary deceleration control at a deceleration smaller than that of the main deceleration control, and prohibits stoppage of fuel supply. As a result, the wheel cylinders can be pressurized before the main deceleration control, to enable time required until reaching the target deceleration to be shortened. Furthermore, it becomes possible to prevent uncomfortable deceleration caused by cutting off the fuel supply before the main deceleration control.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a following cruise control device that causes a host vehicle to follow a preceding vehicle. [Background technology]

[0002] Recently, vehicles have been equipped with a function that allows the vehicle to travel by following the vehicle ahead, known as an adaptive cruise control (ACC) function.

[0003] During following driving using the ACC function, a target inter-vehicle distance between the host vehicle and the preceding vehicle is set based on the vehicle speed of the host vehicle, and the target inter-vehicle distance is subtracted from the actual inter-vehicle distance to obtain an inter-vehicle distance deviation (= inter-vehicle distance - target inter-vehicle distance). Also, the relative speed between the host vehicle and the preceding vehicle is obtained. Then, a target acceleration / deceleration speed is set according to the inter-vehicle distance deviation and the relative speed, and the output of the host vehicle's engine or the braking force of the friction brake is controlled so that the host vehicle accelerates or decelerates at the target acceleration (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-186097 A Summary of the Invention [Problem to be solved by the invention]

[0005] In a vehicle equipped with an ACC function as in Patent Document 1, for example, when the speed of a preceding vehicle decreases while following, the target acceleration / deceleration (target deceleration) increases, but brake control is not performed immediately. Instead, a deceleration request is made to the brake system at the timing when the target deceleration increases to a predetermined threshold, and automatic brake control toward the target deceleration is performed. However, since there is a time lag between the deceleration request and the brake fluid pressure increasing to a level at which the brakes act, the target deceleration is reached when the inter-vehicle distance is shorter than expected. For this reason, the driver may feel that the timing of the automatic brake is late.

[0006] In addition, the threshold value of the target deceleration is usually set to a value larger than the deceleration equivalent to engine braking so as not to deteriorate the continuity of deceleration. In this case, before the target deceleration reaches the threshold value at which a deceleration request is made and the automatic brake is activated, a large deceleration may occur due to the fuel supply being stopped, and the driver may feel uncomfortable due to a braking force greater than necessary.

[0007] The present invention has been made in consideration of the above-mentioned problems, and aims to shorten the time until a braking force corresponding to a deceleration request is applied when automatic braking is activated in a vehicle having a function of following a preceding vehicle at a specified distance, and to prevent unpleasant deceleration due to a cut in fuel supply before the braking force is activated. [Means for solving the problem]

[0008] In order to achieve the above object, a following cruise control device according to one aspect of the present invention is a following cruise control device that causes the host vehicle to travel following a preceding vehicle by accelerating and decelerating the host vehicle so that an actual inter-vehicle distance between the host vehicle and the preceding vehicle ahead of the host vehicle is maintained at a target inter-vehicle distance, and the following control device includes an acceleration / deceleration control means for controlling the acceleration / deceleration of the host vehicle, and the acceleration / deceleration control means includes a target deceleration determination means for determining a target deceleration of the host vehicle based on a difference distance between the actual inter-vehicle distance and the target inter-vehicle distance and a relative speed between the host vehicle and the preceding vehicle when the actual inter-vehicle distance becomes shorter than the target inter-vehicle distance, and the acceleration / deceleration control means performs a main deceleration control to make the actual inter-vehicle distance the target inter-vehicle distance on condition that the target deceleration determined by the target deceleration determination means exceeds a predetermined threshold value, and performs a main deceleration control to make the actual inter-vehicle distance the target inter-vehicle distance when acceleration is no longer necessary to maintain the actual inter-vehicle distance at the target inter-vehicle distance before the target deceleration exceeds the predetermined threshold value. The above book The pre-deceleration control is performed at a deceleration rate smaller than the deceleration rate at which the deceleration control is performed, and the fuel supply is prohibited from being stopped. Acceleration / Deceleration The pre-deceleration control by the control means is characterized in that it is performed by applying hydraulic pressure to a wheel cylinder (claim 1).

[0009] In addition, the acceleration / deceleration control means may release the prohibition on stopping the fuel supply when a predetermined release condition is met, including the target deceleration determined by the target deceleration determination means exceeding a deceleration equivalent to engine braking determined according to the speed of the host vehicle (claim 2).

[0010] In addition, the specified release condition may be that a specified time has elapsed since the target deceleration determined by the target deceleration determination means exceeded the deceleration equivalent to engine braking, or that the target deceleration has further increased after the target deceleration determined by the target deceleration determination means exceeded the deceleration equivalent to engine braking (claim 3). Effect of the Invention

[0011] According to the invention of claim 1, before performing deceleration control (main control) for making the actual inter-vehicle distance the target inter-vehicle distance, deceleration control is performed at a deceleration rate smaller than the deceleration rate when performing deceleration control for making the actual inter-vehicle distance the target inter-vehicle distance. In this way, the wheel cylinder is decelerated before the main control. Da pressure is pre-pressurized, the time from when a deceleration request to the target deceleration is made in this control until the actual deceleration reaches the target deceleration can be shortened. Also, before the target deceleration exceeds a predetermined threshold, when acceleration is no longer necessary for the actual inter-vehicle distance to maintain the target inter-vehicle distance, deceleration control (pre-control) is performed at a deceleration smaller than that in this control, but the fuel supply cut-off is prohibited at this time. That is, while the fuel supply is generally cut off when this deceleration control is performed, in the present invention, the fuel supply is not cut off when this deceleration control is performed. In this case, it is possible to prevent the occurrence of a temporary large deceleration (overlap between the deceleration due to this deceleration control and the deceleration due to engine braking) caused by the fuel supply cut-off that may be executed when acceleration is no longer necessary, and it is possible to prevent an unpleasant deceleration that occurs when the fuel supply is cut off before this deceleration control.

[0012] According to the invention of claim 2, the temporary large deceleration caused by the fuel supply cutoff is executed during the main control, which is larger than the deceleration in the preliminary control, thereby mitigating the uncomfortable deceleration caused when the fuel supply is cut off. Also, by lifting the prohibition on the fuel supply cutoff, fuel efficiency can be improved.

[0013] According to the invention of claim 3, the effect of mitigating the deceleration shock caused by engine braking is further improved. [Brief description of the drawings]

[0014] [Figure 1] 1 is a block diagram showing a configuration of a main part of a vehicle equipped with a follow-up cruise control device according to an embodiment of the present invention; [Diagram 2] 10 is a flowchart showing a flow of a pre-deceleration control process. [Diagram 3]5 is a flowchart showing a flow of a deceleration control process. [Figure 4] 13 is a flowchart showing a flow of a fuel cut prohibition release process. [Diagram 5] 4 is a time chart showing a flow of conventional deceleration control. [Figure 6] 4 is a time chart showing a flow of deceleration control according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0016] <Vehicle Electrical Configuration> FIG. 1 is a block diagram showing the configuration of a main part of a vehicle 1 equipped with a following cruise control device according to one embodiment of the present invention.

[0017] The vehicle 1 is an automobile that uses an engine as a drive source. The power of the engine is transmitted to left and right drive wheels via a transmission. The transmission may be a continuously variable transmission (CVT), a stepped automatic transmission (AT), or a manual transmission (MT).

[0018] The engine 2 is, for example, a gasoline engine, and is provided with a throttle body 2a, a fuel injector 2b that injects fuel into intake air, etc. The throttle body 2a is a component that takes in fuel and air and sends them to the fuel chamber of the engine 2, and is provided with an electronic throttle valve for adjusting the amount of intake air to the combustion chamber of the engine 2, a throttle position sensor that detects the opening of the electronic throttle valve, a control valve for adjusting the amount of intake air when idling, such as when the vehicle is stopped, etc. The engine 2 is also provided with a starter for starting it.

[0019] An accelerator pedal operated to accelerate or decelerate the vehicle 1, and a brake pedal operated to brake the vehicle 1 are provided under the driver's seat in the cabin of the vehicle 1. The accelerator pedal and the brake pedal are located at positions convenient for the driver sitting in the driver's seat to step on them with his / her right foot.

[0020] The vehicle 1 is also equipped with a hydraulic brake. The hydraulic brake includes a brake booster, a master cylinder, and a brake actuator 3. When the brake pedal is depressed, the depression force input to the brake pedal is transmitted to the brake booster. The depression force transmitted to the brake booster is amplified (doubled) by the negative pressure of the brake booster, and is input from the brake booster to the master cylinder. The master cylinder generates hydraulic pressure according to the force input from the brake booster. The hydraulic pressure generated by the master cylinder is transmitted to the brake actuator 3. Then, by the function of the brake actuator 3, hydraulic pressure (brake fluid pressure) is distributed to the wheel cylinders of the brakes provided on each wheel, and the hydraulic pressure applies braking force from each brake to the wheels including the drive wheels.

[0021] In addition, the brake actuator 3 has an electric pump built therein. When the automatic brake is activated, the electric pump is driven by power from the battery, and the brake fluid pressure generated by the electric pump is supplied to each wheel cylinder.

[0022] The vehicle 1 is equipped with a plurality of ECUs (Electronic Control Units) 4a, 5, 6 each including a microcontroller unit (microcomputer). The microcontroller includes, for example, a CPU, a non-volatile memory such as a flash memory, and a volatile memory such as a dynamic random access memory (DRAM). Although only the ECUs 4a, 5, 6 related to the present invention are illustrated in FIG. 1, the vehicle 1 is equipped with a plurality of ECUs having the same configuration as the ECUs 4a, 5, 6 to control each part. The plurality of ECUs including the ECUs 4a, 5, 6 are connected to enable two-way communication using a controller area network (CAN) communication protocol.

[0023] The forward recognition camera 4 (hereinafter, sometimes referred to as the FR camera 4) is, for example, a stereo camera. The stereo camera is a camera capable of continuously capturing still images at a predetermined frame rate, and is capable of detecting the distance to the position of a target in the captured image from parallax information. The stereo camera is installed, for example, on the windshield surface behind the rear-view mirror in the center of the front part of the vehicle interior so as to be able to capture an image in front of the vehicle 1 at a wide angle. In addition to the stereo camera, the vehicle 1 may be provided with a radar as a unit for recognizing the outside world. The radar is installed in the front of the vehicle 1, and is a sensor for detecting the situation in a predetermined search range in front of the vehicle 1. The radar irradiates a radar wave (millimeter wave, laser) into the search range, receives a reflected wave from an object present in the search range, and outputs a detection signal according to the reflected wave.

[0024] In this embodiment, the FR camera 4 includes a camera ECU 4a. The camera ECU 4a calculates data required to operate the ACC function, such as the relative speed between a target such as a preceding vehicle and the vehicle 1, the target inter-vehicle distance from the preceding vehicle, and the target acceleration / deceleration when following the preceding vehicle, based on an image captured by the FR camera 4.

[0025] Furthermore, when the distance between the preceding vehicle and vehicle 1 becomes wider than the target distance and acceleration becomes necessary, the EFI / transmission control ECU 5 transmits an engine output request signal to the EFI / transmission control ECU 5. When the EFI / transmission control ECU 5 receives an engine output request signal from the camera ECU 4a, it transmits a throttle control signal to the throttle body 2a to control the throttle opening, and transmits a fuel injection control signal to the fuel injector 2b to control the amount of fuel injected, in order to realize acceleration based on the signal.

[0026] Furthermore, when the distance between the preceding vehicle and the vehicle 1 becomes shorter than the target distance and deceleration becomes necessary, the VSC-ECU 6 transmits a deceleration request signal to the VSC-ECU 6. When the VSC-ECU 6 receives a deceleration request signal from the camera ECU 4a, it transmits a valve control signal to the brake actuator 3 to realize the deceleration based on the signal, and adjusts the brake fluid pressure applied to the brake devices (not shown) provided on each of the four wheels by controlling the opening and closing amount of a brake fluid pressure control valve (not shown). The ACC function will be described later.

[0027] The EFI / transmission control ECU 5 normally (when the ACC function is not activated) controls the throttle opening and closing of the engine in order to output a drive torque corresponding to the accelerator operation amount (accelerator opening) detected by an accelerator sensor (not shown). To On the other hand, when the ACC function is operating, as described above, the throttle opening and fuel injection amount are controlled based on the engine output request signal so as to achieve acceleration according to the signal, regardless of the accelerator operation amount.

[0028] The EFI / transmission control ECU 5 also controls the transmission.

[0029] In order to improve the driving stability of the vehicle 1, if the VSC-ECU 6 detects a situation such as skidding based on information from wheel speed sensors provided on each wheel, the VSC-ECU 6 requests the EFI / transmission control ECU 5 to adjust the engine output or controls the brake actuator 3 to prevent the skidding.

[0030] Also, VSC-ECU When the ACC function is activated, the ECU 6 operates the electric pump of the brake actuator 3 based on a deceleration request signal from the camera ECU 4a to apply a predetermined hydraulic pressure (brake fluid pressure that results in deceleration according to the deceleration request signal) to each wheel cylinder (automatic braking).

[0031] Vehicle speed sensor 7 includes, for example, a rotor made of a magnetic material that rotates as vehicle 1 travels, and an electromagnetic pickup that is provided in a non-contact manner with the rotor, and outputs a pulse signal from the electromagnetic pickup every time the rotor rotates a certain angle. The frequency of this pulse signal corresponds to the actual vehicle speed of vehicle 1. VSC-ECU 6 determines the frequency of the signal input from vehicle speed sensor 7, and converts the frequency into vehicle speed.

[0032] Vehicle 1 is equipped with an adaptive cruise control (ACC) function as a driving assistance function.

[0033] The ACC function is a following driving function that causes the vehicle 1 to follow another vehicle ahead of it. For example, the steering wheel is provided with operation switches (not shown) related to the ACC function. The operation switches include an ACC main switch that turns the ACC function on / off, a set switch that sets the current vehicle speed of the vehicle 1 as a set vehicle speed, a set vehicle distance changeover switch that changes the distance between the vehicle 1 and the preceding vehicle, a cancel switch that cancels the operation of the ACC function, and a resume switch that reactivates the ACC function at the previous set vehicle speed.

[0034] When the ACC main switch is pressed, the ACC function is activated. Then, when the set switch is pressed, the current vehicle speed of the vehicle 1 is set to the set vehicle speed. The set vehicle speed can be changed by pressing the resume switch or the set switch. That is, by pressing the resume switch, the set vehicle speed can be increased, and by pressing the set switch, the set vehicle speed can be decreased. In addition, by pressing the set vehicle distance changeover switch, it is possible to switch between setting the vehicle distance longer, shorter, or somewhere in between.

[0035] When the set vehicle speed is set, each ECU 4a, 5, 6 starts ACC control (follow-up driving control) for making the vehicle 1 follow the preceding vehicle ahead of it. In the ACC control, depending on whether there is a preceding vehicle or not, the vehicle 1 automatically switches between following the preceding vehicle with the set vehicle speed set by a switch operation as the upper limit vehicle speed, and constant speed driving at the set vehicle speed. During following-up driving, the vehicle 1 is accelerated or decelerated so that the distance between the vehicle 1 and the preceding vehicle ahead of it is maintained at a target distance.

[0036] Specifically, a target inter-vehicle distance between the vehicle 1 and the preceding vehicle is set based on the vehicle speed of the vehicle 1, and the camera ECU 4a determines the inter-vehicle distance deviation between the target inter-vehicle distance and the actual inter-vehicle distance (=actual inter-vehicle distance-target inter-vehicle distance). The camera ECU 4a also determines the relative speed between the vehicle 1 and the preceding vehicle. The camera ECU 4a then sets a target acceleration of the vehicle 1 according to the inter-vehicle distance deviation and the relative speed. A non-volatile memory built into the microcomputer of the ECU 4a stores the characteristics (relationship) of the target acceleration with respect to the inter-vehicle distance deviation and the relative speed in the form of a map as a target acceleration map. When the target acceleration is set, the engine output or the braking force is controlled so that the vehicle 1 accelerates or decelerates at the target acceleration (automatic acceleration, automatic braking).

[0037] (Conventional deceleration control) Here, a conventional deceleration control in a case where deceleration of the vehicle 1 is required, such as when a preceding vehicle decelerates or stops while the ACC function is operating, will be described with reference to Fig. 5. Note that even if the target acceleration changes from a positive value to a negative value and the target acceleration nominally changes to the target deceleration, deceleration control toward the target deceleration is not immediately performed, but is performed when the target deceleration reaches a predetermined threshold value (Ta). In the following, deceleration control will be described using as an example a case where the target acceleration changes from a positive value to a negative value and the target deceleration (negative acceleration) becomes Tb.

[0038] The camera ECU 4a periodically sets a target acceleration (target acceleration, target deceleration) based on the deviation in the inter-vehicle distance and the relative speed with respect to the preceding vehicle. When the vehicle 1 is following the preceding vehicle at a predetermined target deceleration (target acceleration) (time t1 in FIG. 5) and the preceding vehicle stops or decelerates, causing the target acceleration to decrease, the throttle opening is controlled to decrease accordingly. After that, when the target acceleration set by the camera ECU 4a becomes 0 m / s 2 At this time, the throttle opening is controlled to 0.

[0039] When a predetermined fuel cut operation condition is satisfied from time t2 (time t3), the camera ECU 4a sets the fuel cut operation flag to ON. Information regarding the fuel cut operation flag being set to ON is transmitted to the EFI / transmission control ECU 5 via CAN communication, and the EFI / transmission control ECU 5, upon receiving this information, performs control to stop fuel injection (see FIG. 5(c)). A state in which the predetermined fuel cut operation condition is satisfied is, for example, a state in which the required driving force becomes 0, such as when the vehicle 1 is in a state in which it does not require acceleration and is coasting.

[0040] When the throttle opening is reduced, deceleration based on so-called engine braking occurs in the vehicle 1. At time t3, a temporary large deceleration occurs due to a fuel cut (FIG. 5(d)).

[0041] From time t3, the target deceleration becomes even larger (the negative value of the target acceleration becomes even larger) and when it reaches the target deceleration threshold value Ta (time t4), the camera ECU 4a sets the deceleration request flag to ON (FIG. 5(b)). Information regarding the deceleration request flag being set to ON is transmitted to the VSC-ECU 6 via CAN communication, and the VSC-ECU 6 that receives this information controls the brake actuator 3 so that the target deceleration determined by the camera ECU 4a is achieved (deceleration control).

[0042] At this time, the target deceleration at time t4 is Ta, but if the target deceleration changes thereafter, the VSC-ECU 6 performs deceleration control so that the deceleration becomes the changed deceleration. For example, in Fig. 6(a), since the target deceleration is Tb at time t7, the VSC-ECU 6 performs deceleration control so that the deceleration becomes Tb at time t7.

[0043] There is a time lag (the time it takes to eliminate backlash in FIG. 5(e)) between when the VSC-ECU 6 sends a control signal to the brake actuator 3 and when the brakes actually start to work. The brake device is designed so that the brakes will not work unless the brake fluid pressure is equal to or greater than a predetermined value, and this time lag is the time it takes for the brake fluid pressure to reach that predetermined value.

[0044] Therefore, even if the VSC-ECU 6 starts deceleration control at time t4, it is not until time t6 that the brakes actually start to work, and it is not until time t8 that the actual deceleration reaches the target deceleration Tb set by the camera ECU 4a (Figure 5(f)).

[0045] (Deceleration control of the present invention) The deceleration control of the present invention will be described with reference to Fig. 6. Note that, in the present invention, even if the target acceleration changes from a positive value to a negative value and the target acceleration nominally changes to the target deceleration, the deceleration control toward the target deceleration is not immediately performed, but when the target deceleration reaches a predetermined threshold value (Ta), the deceleration control toward the target deceleration is performed. In the following, the deceleration control will be described using as an example the case where the target acceleration changes from a positive value to a negative value and becomes the target deceleration, and the target deceleration becomes Tb.

[0046] The camera ECU 4a periodically sets a target acceleration (target acceleration, target deceleration) based on the deviation in the inter-vehicle distance and the relative speed with respect to the preceding vehicle. When the vehicle 1 is following the preceding vehicle at a predetermined target deceleration (target acceleration) (time t1 in FIG. 6) and the preceding vehicle stops or decelerates, causing the target acceleration to decrease, the throttle opening is controlled to decrease accordingly. After that, when the target acceleration set by the camera ECU 4a becomes 0 m / s 2 At this time, the throttle opening is controlled to 0.

[0047] In addition, the camera ECU 4a detects that the target acceleration is 0 m / s at time t2. 2 When the target deceleration reaches the threshold value Ta, the deceleration request flag is set to ON (FIG. 6(b)). Information regarding the setting of the deceleration request flag to ON is transmitted to the VSC-ECU 6 via CAN communication, and the VSC-ECU 6 that receives this information controls the brake actuator 3 so that a predetermined deceleration is achieved (pre-deceleration control). The predetermined deceleration is stored in the memory of the camera ECU 4a as a map corresponding to the vehicle speed of the vehicle 1, and a deceleration request is made to the VSC-ECU 6 based on the map. The deceleration at this time is a value smaller than the deceleration requested when a target deceleration, which will be described later, reaches a threshold value Ta, and a deceleration equivalent to engine braking is set in the map.

[0048] Furthermore, at time t2, the camera ECU 4a sets the fuel cut prohibition request flag to ON (FIG. 6(d)). Information regarding the setting of the fuel cut prohibition request flag to ON is transmitted to the EFI / transmission control ECU 5 via CAN communication, and the EFI / transmission control ECU 5, upon receiving this information, prohibits the cut of fuel injection even if the fuel cut activation condition is satisfied after time t2.

[0049] As with the conventional deceleration control described with reference to Fig. 5, there is a time lag (the time it takes to eliminate backlash in Fig. 6(f)) between when the VSC-ECU 6 sends a control signal to the brake actuator 3 and when the brakes actually start to work. The brake device is designed so that the brakes do not work unless the brake fluid pressure is equal to or greater than a predetermined value, and this time lag is the time it takes for the brake fluid pressure to reach that predetermined value.

[0050] Therefore, even if the VSC-ECU 6 starts deceleration control at time t4, it is not until time t3a that the brakes actually start to work, and it is not until time t3b that the actual deceleration reaches a value equivalent to engine braking (Figures 6(f) and 6(g)).

[0051] In addition, since the fuel cut prohibition request flag is set to ON, the target acceleration (target deceleration) is set to 0 m / s at time t2. 2 Even if a predetermined fuel cut operation condition is satisfied after the fuel cut operation is stopped, the EFI / transmission control ECU 5 does not stop the fuel injection. Therefore, a temporary large deceleration caused by the fuel cut does not occur until the deceleration is controlled to a level equivalent to engine braking by the VSC-ECU 6.

[0052] From time t3b, the target deceleration becomes even larger (the negative value of the target acceleration becomes even larger) and when it reaches the target deceleration threshold value Ta (time t4), the camera ECU 4a again requests deceleration. The target deceleration threshold value Ta is set to a value larger than the deceleration equivalent to engine braking (the deceleration equivalent to engine braking requested at time t2) so as not to deteriorate the continuity of deceleration. Information regarding the deceleration request is transmitted to the VSC-ECU 6 via CAN communication, and the VSC-ECU 6 that receives this information controls the brake actuator 3 so as to achieve the target deceleration determined by the camera ECU 4a (main deceleration control).

[0053] At this time, the target deceleration at time t4 is Ta, but if the target deceleration changes thereafter, the VSC-ECU 6 performs deceleration control so that the deceleration becomes the changed deceleration. For example, in Fig. 6(a), since the target deceleration is Tb at time t7, the VSC-ECU 6 performs deceleration control so that the deceleration becomes Tb at time t7.

[0054] Note that the preliminary deceleration control continues until the main deceleration control is performed. That is, the deceleration control equivalent to engine braking continues until the target deceleration reaches Ta. Therefore, the brake fluid pressure is applied before the main deceleration control, and there is no time lag between when the VSC-ECU 6 transmits a control signal to the brake actuator 3 and when the brakes actually start to work, as in the conventional deceleration control.

[0055] Therefore, the timing when the VSC-ECU 6 starts the deceleration control (main deceleration control) and the timing when the brakes actually start to work are substantially the same at time t4, and the actual deceleration becomes the target deceleration Tb set by the camera ECU 4a at time t7 (FIG. 6(g)). That is, in the present invention, the time (time t4 to time t7) taken for the actual deceleration to become the target deceleration after the VSC-ECU 6 starts the deceleration control (main deceleration control) is shorter than the time (time t4 to time t8) taken for the actual deceleration to become the target deceleration after the VSC-ECU 6 starts the deceleration control (main deceleration control) in the conventional deceleration control, since there is no time for the brakes to close up. Therefore, the problem of the target deceleration being reached when the vehicle distance is shorter than expected is unlikely to occur.

[0056] In addition, after time t2, the engine driving force is no longer required and the fuel cut activation condition is met. However, the fuel cut prohibition request flag is set to ON until the fuel cut prohibition release condition is met, so fuel cut is not performed.

[0057] For example, if the fuel cut prohibition release condition is met at time t5, the camera ECU 4a sets the fuel cut prohibition request flag to OFF (FIG. 6(d)), and sets the fuel cut operation flag to ON (FIG. 6(c)).

[0058] The information regarding the OFF setting of the fuel cut prohibition request flag and the information regarding the ON setting of the fuel cut operation flag are transmitted to the EFI / transmission control ECU 5 via CAN communication, and the EFI / transmission control ECU 5 that receives the information stops fuel injection at time t5. Therefore, at time t5, a temporary large deceleration occurs due to the fuel cut (FIG. 6(e)).

[0059] However, the temporary large deceleration does not occur at a timing when the actual deceleration is relatively small as in conventional deceleration control, but occurs during main deceleration control, which is larger than the deceleration equivalent to engine braking (Fig. 6(e) and Fig. 6(f)). Therefore, the discomfort caused by the temporary large deceleration due to the fuel cut occurs during strong deceleration (during main deceleration control), making it difficult to notice.

[0060] The fuel cut prohibition release condition may be, for example, a predetermined time elapses after the target deceleration exceeds the deceleration corresponding to engine braking, or the target deceleration set by the camera ECU 4a becomes a deceleration greater than the deceleration corresponding to engine braking after the target deceleration exceeds the deceleration corresponding to engine braking. The predetermined time is a time for ensuring that the target deceleration becomes sufficiently greater than the value corresponding to engine braking, and is stored in advance in the memory of the camera ECU 4a. The fuel cut prohibition release condition may be, for example, a predetermined time elapses after the target deceleration exceeds the threshold value Ta of the target deceleration, or the target deceleration set by the camera ECU 4a becomes a deceleration greater than the threshold value Ta after the target deceleration reaches the threshold value Ta.

[0061] (Pre-deceleration control process) The flow of the pre-deceleration control process of the present invention will be described with reference to FIG.

[0062] While following the preceding vehicle, the camera ECU 4a periodically (50 ms) determines a target deceleration based on the deviation in the distance between the vehicles and the relative speed. Then, the camera ECU 4a judges whether the preceding vehicle has decelerated or stopped and acceleration is no longer necessary. That is, the camera ECU 4a judges whether the target deceleration, which is periodically determined, has become 0 (step S1).

[0063] The process of step S1 is repeated until it is determined that the target deceleration has become 0 (NO in step S1). If it is determined in step S1 that the target deceleration has become 0, the camera ECU 4a sets a deceleration request flag to ON, and requests the VSC-ECU 6 to achieve deceleration equivalent to engine braking (step S2).

[0064] After making the deceleration request, the camera ECU 4a sets the fuel cut prohibition request flag to ON, requests the EFI / transmission control ECU 5 to prohibit the fuel cut operation (step S3), and ends the process. As a result, even if a predetermined fuel cut operation condition is satisfied after the deceleration request (request for preliminary deceleration), the fuel cut is prohibited.

[0065] (Actual deceleration control process) The flow of the deceleration control process of the present invention will be described with reference to FIG.

[0066] The camera ECU 4a judges whether the periodically determined target deceleration is equal to or greater than the threshold value Ta (step S20). The process of step S20 is repeated until the target deceleration becomes equal to the threshold value Ta (NO in step S20). In other words, even if the distance to the preceding vehicle is decreasing, deceleration control is not performed to make the actual distance equal to the target distance until the target deceleration becomes equal to the threshold value Ta.

[0067] When the periodically determined target deceleration becomes equal to or greater than the threshold value Ta (YES in step S20), the camera ECU 4a again requests the VSC-ECU 6 for deceleration (step S21), and ends the process. Note that the threshold value Ta is set to a value greater than the deceleration equivalent to engine braking, and the deceleration applied to this deceleration control is greater than the deceleration equivalent to engine braking.

[0068] (Fuel cut prohibition release process) The flow of the fuel cut prohibition release process of the present invention will be described with reference to FIG.

[0069] The camera ECU 4a determines (step S31) whether or not the periodically determined target deceleration exceeds a deceleration equivalent to engine braking of the vehicle 1. Note that the deceleration equivalent to engine braking is stored as a map according to the vehicle speed of the vehicle 1.

[0070] Next, if the target deceleration does not exceed the deceleration corresponding to the engine brake (NO in step S31), the camera ECU 4a repeats the process of step S31 until the target deceleration exceeds the deceleration corresponding to the engine brake.

[0071] If the target deceleration exceeds the deceleration corresponding to engine braking (YES in step S31), the camera ECU 4a determines whether a certain time has elapsed or whether the target deceleration has further increased (step S32).

[0072] After the target deceleration exceeds the deceleration corresponding to the engine brake, the process of step S32 is repeated until a certain time has elapsed or the target deceleration further increases (NO in step S32).

[0073] If a certain time has elapsed after the target deceleration exceeded the deceleration corresponding to the engine brake, or if the target deceleration has further increased (YES in step S32), the camera ECU 4a sets the fuel cut prohibition request flag to OFF (step S33) and ends the process. Note that the EFI / transmission control ECU 5, which has received information regarding the setting of the flag to OFF, performs control to stop fuel injection when the fuel cut operation condition is established.

[0074] <Action and effect> Therefore, according to the embodiment described above, before performing deceleration control (main deceleration control) for making the actual inter-vehicle distance from the preceding vehicle into the target inter-vehicle distance, deceleration control is performed at a deceleration rate (deceleration rate equivalent to engine braking) smaller than the deceleration rate of the main deceleration control. In this way, since the wheel cylinders can be pressurized before the main deceleration control, the time from when the camera ECU 4a issues a deceleration request to the VSC-ECU 6 for making the actual deceleration into the target deceleration in the main deceleration control until the actual deceleration becomes the target deceleration can be shortened.

[0075] In addition, in the case of a configuration in which the wheel cylinder is not pressurized before the main deceleration control, no braking force is generated from when the VSC-ECU 6 starts to control the brake actuator 3 until the actual brake hydraulic pressure reaches the hydraulic pressure required to generate the brake. In this case, the time from when the VSC-ECU 6 starts to control the brake actuator 3 until the actual deceleration reaches the target deceleration is longer than expected, so that the target deceleration is reached with the inter-vehicle distance shorter than expected, and the driver may feel that the timing of braking is delayed. On the other hand, in this embodiment, by pressurizing the wheel cylinder before the main deceleration control, it is possible to prevent the target deceleration from being reached with the actual inter-vehicle distance shorter, and therefore it is possible to prevent the driver from feeling uncomfortable that the timing of braking is delayed.

[0076] In addition, in a configuration in which brake fluid pressure is not applied before the deceleration control, one method for shortening the time from when the VSC-ECU 6 starts to control the brake actuator 3 until the actual brake fluid pressure reaches the fluid pressure required to generate the brakes is to increase the motor capacity of the electric pump of the brake actuator 3 to quickly increase the wheel cylinder pressure, but this requires an expensive motor. In this respect, in this embodiment, there is no need to use an expensive motor.

[0077] In addition, since the preliminary deceleration control is performed before the main deceleration control, it is possible to finely adjust the deceleration before the main deceleration control. In particular, in cases where the engine brake before the main deceleration control, which occurs in the case of conventional deceleration control, causes excessive deceleration, it is possible to adjust the deceleration to a smaller deceleration than the deceleration equivalent to the engine brake.

[0078] In addition, before the target deceleration exceeds a predetermined threshold value Ta, when acceleration is no longer required to maintain the actual vehicle distance from the preceding vehicle to the target vehicle distance (target deceleration (target acceleration) = 0 m / s 2), deceleration control (pre-deceleration control) is performed at a deceleration rate equivalent to engine braking, but the fuel supply is prohibited from being stopped at this time. In this case, it is possible to prevent the occurrence of a temporary large deceleration caused by the fuel supply being stopped when acceleration is no longer necessary, and therefore it is possible to reduce the unpleasant deceleration that occurs when the fuel supply is cut off before the main deceleration control.

[0079] Furthermore, the prohibition of the fuel supply cutoff is released when a predetermined time has elapsed since the target deceleration exceeded the deceleration equivalent to engine braking, or when the target deceleration has further increased since exceeding the deceleration equivalent to engine braking. In this way, the temporary large deceleration caused by the fuel supply cutoff can be exerted during the main deceleration control, which is larger than the deceleration in the preliminary deceleration control, and the uncomfortable deceleration caused when the fuel supply is cutoff can be alleviated. Furthermore, by releasing the prohibition of the fuel supply cutoff, fuel efficiency can be improved.

[0080] The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present invention.

[0081] For example, the above-described embodiment is not limited to gasoline-powered vehicles, but can also be applied to electric vehicles, hybrid vehicles, and self-driving vehicles.

[0082] Further, in this embodiment, the configuration in which the camera ECU 4a is provided in the forward recognition camera 4 has been described, but the camera ECU 4a and the forward recognition camera 4 (for example, a stereo camera) may be provided separately. [Explanation of symbols]

[0083] 1: Vehicle (own vehicle) 4a: Camera ECU (acceleration / deceleration control means, target deceleration determination means) 5: EFI / Transmission Control ECU (Acceleration / Deceleration Control Means) 6: VSC-ECU (acceleration / deceleration control means)

Claims

1. A follow-up running control device that causes a host vehicle to run following a preceding vehicle by accelerating or decelerating the host vehicle so that an actual inter-vehicle distance between the host vehicle and a preceding vehicle ahead of the host vehicle is maintained at a target inter-vehicle distance, an acceleration / deceleration control means for controlling acceleration / deceleration of the host vehicle; The acceleration / deceleration control means a target deceleration determining means for determining a target deceleration of the host vehicle based on a difference between the actual inter-vehicle distance and the target inter-vehicle distance and a relative speed between the host vehicle and the preceding vehicle when the actual inter-vehicle distance becomes shorter than the target inter-vehicle distance, The acceleration / deceleration control means performing a main deceleration control for making the actual inter-vehicle distance the target inter-vehicle distance on condition that the target deceleration determined by the target deceleration determination means exceeds a predetermined threshold value; when acceleration is no longer necessary for the actual inter-vehicle distance to be maintained at the target inter-vehicle distance before the target deceleration exceeds the predetermined threshold value, performing a pre-deceleration control at a deceleration rate smaller than a deceleration rate when performing the main deceleration control for making the actual inter-vehicle distance the target inter-vehicle distance, while prohibiting the stop of fuel supply; The pre-deceleration control of the acceleration / deceleration control means is performed by applying hydraulic pressure to a wheel cylinder. A following cruise control device characterized by the above.

2. 2. The following cruise control device according to claim 1, wherein the acceleration / deceleration control means cancels the prohibition on stopping the supply of fuel when a predetermined cancellation condition is satisfied, the cancellation condition including a condition that the target deceleration determined by the target deceleration determination means exceeds a deceleration equivalent to engine braking determined according to a speed of the host vehicle.

3. 3. The following cruise control device according to claim 2, wherein the predetermined release condition is that a predetermined time has elapsed since the target deceleration determined by the target deceleration determination means exceeded the deceleration equivalent to engine braking, or that the target deceleration has further increased after the target deceleration determined by the target deceleration determination means exceeded the deceleration equivalent to engine braking.

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