Driving assistance device

Abstract

PURPOSE: To provide a driving support device for supporting a driving operation for starting one's own vehicle, and for temporarily suppressing the acceleration of one's own vehicle in starting according to the request of a driver.SOLUTION: The driving support device 1 includes a processor configured to execute a cruise control for controlling the own vehicle such that the own vehicle follows a preceding vehicle, execute a vehicle stop control for stopping the own vehicle when a predetermined vehicle stop condition is satisfied during execution of the cruise control, and execute a starting control for starting the own vehicle by controlling the own vehicle such that an acceleration of the own vehicle matches a first predetermined value when a predetermined starting operation is executed thereafter. The processor is configured to execute acceleration suppression control for controlling the host vehicle such that the acceleration of the host vehicle matches a second predetermined value smaller than the first predetermined value when the processor detects that a predetermined first accelerator pedal operation indicating suppression of the acceleration of the host vehicle is executed after the start control is executed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a driving assistance device that assists a driver in adjusting the speed of a vehicle. [Background technology]

[0002] A driving assistance device has been proposed that assists in driving operations to adjust the speed of a vehicle (see, for example, Patent Document 1 below). This driving assistance device (hereinafter referred to as the "conventional device") is capable of performing cruise control, which controls the vehicle (drive device, braking device, etc.) so that the vehicle travels at a preset speed when certain conditions are met. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-241872 Summary of the Invention

[0004] This type of conventional device is configured to control the drive system and other components of the host vehicle so that the host vehicle follows the preceding vehicle when there is another vehicle (preceding vehicle) traveling immediately ahead of the host vehicle. When the preceding vehicle stops, the conventional device stops the host vehicle behind the preceding vehicle. If the preceding vehicle then starts moving and the driver of the host vehicle performs a predetermined operation, the conventional device starts the host vehicle so that the host vehicle follows the preceding vehicle. At this time, the conventional device controls the drive system and other components so that the acceleration of the host vehicle matches a preset value. If the driver (passenger) feels that the acceleration of the host vehicle is too high (the acceleration is too sudden) and presses the brake pedal, the cruise control is interrupted. Therefore, the driver must then manually perform driving operations to adjust the speed of the host vehicle.

[0005] One of the objects of the present invention is to provide a driving assistance device that assists in driving operations to start a vehicle, and that can temporarily suppress the acceleration of the vehicle when starting, in accordance with the driver's request.

[0006] To achieve the above object, a driving assistance device (1) of the present invention is capable of executing cruise control to control a host vehicle (V0) so that the host vehicle (V0) follows a preceding vehicle (V1), and includes a processor (10) configured to execute stop control to stop the host vehicle when a predetermined stop condition is met while the cruise control is being executed, and to execute start control to start the host vehicle by controlling the host vehicle so that the acceleration (α) of the host vehicle matches a first predetermined value (αacc) when a predetermined start operation is subsequently executed. After executing the start control, when the processor detects that a predetermined first accelerator pedal operation has been executed, which indicates that acceleration of the host vehicle should be suppressed, it executes acceleration suppression control to control the host vehicle so that the acceleration of the host vehicle matches a second predetermined value (αsup) which is smaller than the first predetermined value.

[0007] The driving assistance device according to the present invention executes start control to automatically start the host vehicle when a start operation is performed while the host vehicle is stopped. That is, the driving operation to start the host vehicle is assisted. If the driver feels that the acceleration of the host vehicle due to the start control is too sudden, the driver can suppress the acceleration of the host vehicle by operating the accelerator pedal in a predetermined manner (performing a first accelerator pedal operation).

[0008] In a driving assistance device according to one aspect of the present invention, the processor When the accelerator pedal depression depth (AD) increases and exceeds a first predetermined value (ADth1) while the host vehicle is stopped, the start control is executed; After the start control is executed, the accelerator pedal depression depth decreases to a second predetermined value (ADth2) or less, and then, if it is detected that the first accelerator pedal is operated, the acceleration suppression control is executed.

[0009] According to this, the driver can request the driving assistance device to start the start control and the acceleration suppression control of the host vehicle by operating a single operating device (accelerator pedal).

[0010] In a driving assistance device according to another aspect of the present invention, the processor executes the start control when a predetermined switch (27) is operated while the vehicle is stopped, and then executes the acceleration suppression control when it detects that the first accelerator pedal has been operated.

[0011] According to this, the driver can request the driving assistance device to start the start control by performing a simple operation (by pressing a switch).

[0012] In another aspect of the driving assistance device of the present invention, when a predetermined second accelerator pedal operation is performed indicating that the acceleration of the vehicle that has started by the start control is to be promoted, the processor performs override control to control the vehicle so that the acceleration of the vehicle matches a third predetermined value (αover) that is greater than the first predetermined value, and when the override control is performed, the execution of the acceleration suppression control is prohibited.

[0013] If the driver is unfamiliar with accelerator pedal operation, there is a risk that the driver may unintentionally operate the first accelerator pedal after override control is initiated. In this case, the host vehicle may shift from a state of rapid acceleration to a state of rapid deceleration, and the driver may feel uncomfortable with the behavior of the host vehicle. The driving assistance device according to this aspect can prevent the above-described behavior of the host vehicle (the operation of shifting from rapid acceleration to rapid deceleration).

[0014] In a driving assistance device according to another aspect of the present invention, the processor determines that the first accelerator pedal operation has been performed when a predetermined condition (A) related to the accelerator pedal depression depth (AD) and its rate of change (ΔAD) is met, which is a predetermined condition for determining that the accelerator pedal is lightly depressed.

[0015] This allows the driver to suppress the acceleration of the vehicle by lightly depressing the accelerator pedal. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a block diagram of a driving assistance device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a graph showing changes in the speed, acceleration, and accelerator pedal depression depth of the vehicle. [Figure 3] FIG. 3 is a flowchart of a first program executed by the CPU to realize the ACC function. [Figure 4] FIG. 4 is a flowchart of a second program executed by the CPU to realize the ACC function. [Figure 5] FIG. 5 is a flowchart of a third program executed by the CPU to realize the ACC function. [Figure 6] FIG. 6 is a flowchart of a fourth program executed by the CPU to realize the ACC function. DETAILED DESCRIPTION OF THE INVENTION

[0017] (Outline) A driving assistance device 1 according to one embodiment of the present invention is applied to, for example, a vehicle V0 (hereinafter referred to as "host vehicle") equipped with an automatic driving function. When a preceding vehicle V1 (a vehicle located immediately in front of the host vehicle) is stopped and the host vehicle is stopped immediately after that, the driving assistance device 1 has a function of controlling the drive device and the like of the host vehicle so that the host vehicle starts following the preceding vehicle V1 when a predetermined condition is met after detecting that the preceding vehicle V1 has started moving.

[0018] (Specific Configuration) As shown in FIG. 1, the driving assistance device 1 includes an ECU 10, an on-vehicle sensor 20, a drive device 30, and a braking device 40.

[0019] The ECU 10 includes a microcomputer equipped with a CPU 10a, a ROM 10b, a RAM 10c, a timer 10d, etc. The ECU 10 is connected to other ECUs provided in the vehicle via a CAN (Controller Area Network).

[0020] The on-board sensor 20 includes a forward sensor that acquires information about the preceding vehicle V1. Specifically, the on-board sensor 20 includes a millimeter wave radar 21, a sonar 22, and a forward camera 23 as forward sensors.

[0021] The millimeter-wave radar 21 includes a transmitter / receiver and a signal processor (not shown). The transmitter / receiver emits millimeter-wave band radio waves (hereinafter referred to as "millimeter waves") ahead of the vehicle and receives millimeter waves (reflected waves) reflected by a three-dimensional object (for example, the preceding vehicle V1) located within the emission range. The signal processor calculates the distance between the vehicle and the three-dimensional object (for example, the preceding vehicle V1), the speed (relative speed) of the three-dimensional object, and the like based on the time from when the transmitter / receiver emits the millimeter waves to when the reflected waves are received, the phase difference between the transmitted millimeter waves and the received reflected waves, the attenuation level of the reflected waves, and the like, and transmits the calculation results to the ECU 10.

[0022] The sonar 22 intermittently emits ultrasonic waves into the area surrounding the vehicle and receives the ultrasonic waves (reflected waves) reflected by a three-dimensional object. Based on the time from when the ultrasonic waves are transmitted until when the reflected waves are received, the sonar 22 calculates the distance between the vehicle and the three-dimensional object, the position (direction) of the three-dimensional object relative to the vehicle, and the like, and transmits the calculation results to the ECU 10.

[0023] The forward camera 23 includes an imaging device and an image analysis device. The imaging device incorporates a lens and an imaging element such as a charge coupled device (CCD) or a CMOS image sensor (CIS). The imaging device is located above the front windshield glass and faces forward. The imaging device captures images of the front view of the vehicle at a predetermined frame rate to acquire image data. The imaging device transmits the image data to the image analysis device. The image analysis device analyzes the acquired image data and acquires information about objects located in front of the vehicle from the images. For example, the image analysis device identifies (recognizes) the type of object located in front of the vehicle (e.g., another vehicle, lane mark, etc.) and transmits the identification result to the ECU 10.

[0024] Additionally, the on-board sensor 20 includes a vehicle sensor that acquires information about the behavior (speed and acceleration) of the vehicle itself. Specifically, the on-board sensor 20 includes a speed sensor 24 and an acceleration sensor 25 as vehicle sensors.

[0025] The speed sensor 24 detects the rotation speed (wheel speed) of each wheel, calculates the speed sp0 (measured value) of the host vehicle based on the wheel speeds, and transmits the calculation result to the ECU 10.

[0026] The acceleration sensor 25 detects the acceleration α of the host vehicle in the longitudinal direction and transmits the detection result to the ECU 10.

[0027] Furthermore, the on-vehicle sensors 20 include an accelerator pedal sensor 26 as an operation sensor. The accelerator pedal sensor 26 detects the depression depth AD of the accelerator pedal AP and transmits the detection result to the ECU 10.

[0028] The drive unit 30 applies driving force to the drive wheels. The drive unit 30 includes an engine ECU, an internal combustion engine, a transmission, a driving force transmission mechanism that transmits the driving force to the wheels, and the like. The engine ECU acquires information (target value) that indicates a target driving force from another ECU (ECU 10). The engine ECU drives the throttle valve of the internal combustion engine to make the driving force applied to the drive wheels match the target value. The output (driving force) of the internal combustion engine is transmitted to the drive wheels via the transmission and the driving force transmission mechanism.

[0029] If the vehicle to which the driving assistance device 1 is applied is a hybrid vehicle (HEV), the engine ECU can adjust the output (driving force) of either or both of the "internal combustion engine and electric motor" as the vehicle drive source. Also, if the vehicle to which the driving assistance device 1 is applied is an electric vehicle (BEV), an electric motor ECU is used instead of the engine ECU to adjust the output (driving force) of the "electric motor" as the vehicle drive source.

[0030] The braking device 40 applies braking force to the wheels (brake discs). The braking device 40 includes a brake ECU, a brake caliper, etc. The brake caliper includes an actuator that presses brake pads against the brake discs. The brake ECU acquires information (target value) indicating a target braking force from another ECU. The brake ECU drives the actuator of the brake caliper to make the braking force applied to the wheels (brake discs) match the target value.

[0031] (Operation) When an ACC switch (not shown) mounted on the host vehicle is in the on state, the ECU 10 determines whether or not a preceding vehicle V1 is present, as will be described below, and controls the drive unit 30 and braking unit 40 (hereinafter referred to as "drive unit, etc.") of the host vehicle based on the determination result. This control is sometimes referred to as adaptive cruise control (ACC). ACC includes constant speed control and following distance maintenance control.

[0032] [Constant-Speed ​​Cruise Control] The ECU 10 determines whether or not a preceding vehicle V1 is present based on information acquired from the forward sensors (millimeter-wave radar 21, sonar 22, and forward camera 23). If a preceding vehicle V1 is not present, the ECU 10 executes constant-speed cruise control. Specifically, the ECU 10 controls the drive system and the like so that the speed sp0 of the host vehicle matches a predetermined target value spt (for example, a speed value set by the driver or a speed value that minimizes fuel consumption). Note that even if a preceding vehicle V1 is present, if its speed sp1 is greater than the target value spt, the ECU 10 executes constant-speed cruise control.

[0033] [Inter-vehicle distance maintenance control] On the other hand, when the ECU 10 determines that a preceding vehicle V1 is present and the speed sp1 of the preceding vehicle SP1 is smaller than the target value spt, the ECU 10 executes inter-vehicle distance maintenance control. Specifically, the ECU 10 acquires the speed sp0 of the host vehicle from the speed sensor 24. Furthermore, the ECU 10 acquires the inter-vehicle distance D between the preceding vehicle V1 and the host vehicle and the speed sp1 of the preceding vehicle V1 based on information acquired from the forward sensor and the vehicle sensor. The ECU 10 calculates the target value Dt of the inter-vehicle distance D based on the speed sp0 of the host vehicle and the speed sp1 of the preceding vehicle V1, etc.

[0034] When the speed sp1 of the preceding vehicle V1 relative to the speed sp0 of the host vehicle (relative speed spr = sp1 - sp0) is greater than "0", the inter-vehicle distance D increases. When the inter-vehicle distance D is greater than the target value Dt, the ECU 10 assigns a predetermined value αacc (>0) to the target value αt of the host vehicle's acceleration α so that the host vehicle's speed sp0 is greater than the speed sp1 of the preceding vehicle V1. Then, the ECU 10 controls the drive system and the like so that the host vehicle's acceleration α (actual measured value) matches the predetermined value αacc (acceleration control). As a result, the inter-vehicle distance D decreases and approaches the target value Dt. Then, when the inter-vehicle distance D matches the target value Dt, the ECU 10 assigns "0" to the target value αt of the host vehicle's acceleration α. ​​In other words, the ECU 10 controls the drive system and the like so that the host vehicle travels at the same speed as the preceding vehicle V1.

[0035] On the other hand, when the relative speed spr is smaller than "0", the inter-vehicle distance D decreases. When the inter-vehicle distance D is smaller than the target value Dt, the ECU 10 assigns a predetermined value αdec (<0) to the target value αt of the acceleration α so that the speed sp0 of the host vehicle becomes smaller than the speed sp1 of the preceding vehicle V1. Then, the ECU 10 controls the drive device, etc. so that the acceleration α (actual measured value) of the host vehicle matches the predetermined value αdec (deceleration control). As a result, the inter-vehicle distance D increases and approaches the target value Dt. Then, when the inter-vehicle distance D matches the target value Dt, the ECU 10 assigns "0" to the target value αt of the acceleration α of the host vehicle.

[0036] The target distance Dt is correlated with the speed sp0 of the host vehicle and the speed sp1 of the preceding vehicle V1. For example, the target value Dta when the speeds sp0 and sp1 are relatively small is smaller than the target value Dtb when the speeds sp0 and sp1 are relatively large. A database (table) showing the relationship between the speeds sp0 and sp1 and the target value Dt or an arithmetic expression for calculating the target value Dt is stored in the ROM 10b. The ECU 10 determines the target value Dt based on the database or the arithmetic expression.

[0037] The predetermined values ​​αacc and αdec assigned to the target value αt of the acceleration α are fixed values ​​determined in advance. However, these predetermined values ​​αacc and αdec may be determined according to the inter-vehicle distance D (actually measured value). For example, the absolute values ​​of the predetermined values ​​αacc and αdec may be set to be larger as the inter-vehicle distance D increases.

[0038] If the preceding vehicle V1 stops while the vehicle distance maintenance control is being executed (sp1=0 km / h (when the stopping condition of the host vehicle is met)), the vehicle distance maintenance control is executed, and the host vehicle stops behind the preceding vehicle V1 (sp0=0 km / h (stopping control)). If the preceding vehicle V1 then starts moving, the ECU 10 does not immediately start the host vehicle to follow the preceding vehicle V1, but keeps the host vehicle stopped until a predetermined starting operation is performed. Then, when the starting operation is performed, the ECU 10 executes starting control to control the drive system and the like so that the host vehicle starts moving following the preceding vehicle V1.

[0039] [Start Control] The ECU 10 starts monitoring the behavior of the preceding vehicle V1 from the point when the host vehicle stops behind the stopped preceding vehicle V1. That is, the ECU 10 acquires various information from the forward sensors and sequentially determines whether the preceding vehicle V1 has started moving based on the acquired information. For example, the ECU 10 determines that the preceding vehicle V1 has started moving when the speed sp1 of the preceding vehicle V1 acquired from the millimeter-wave radar 21 exceeds a predetermined threshold sp1th. Alternatively, for example, the ECU 10 may determine that the preceding vehicle V1 has started moving when the distance between the preceding vehicle V1 and the host vehicle (inter-vehicle distance D) exceeds a threshold Dth.

[0040] After determining that the preceding vehicle V1 has started, if the ECU 10 detects that the driver of the host vehicle has performed a predetermined start operation (an operation indicating that the driver intends to start the host vehicle), the ECU 10 starts the host vehicle. Specifically, the ECU 10 determines that the conditions for starting the host vehicle are met when the accelerator pedal AP is depressed from a released state (AD = "0%), causing the accelerator pedal depression depth AD to increase and exceed a predetermined value ADth1 (="X%"). In this case, the ECU 10 controls the drive system, etc., so that the acceleration α of the host vehicle coincides with a predetermined value αacc (see FIG. 2). Note that, as indicated by the dashed lines in FIGS. 2(A) to 2(C), even if the driver releases the accelerator pedal AP after the host vehicle has started, the ECU 10 continues the start control.

[0041] [Override Control] The driver of the host vehicle may feel that the acceleration α (predetermined value αacc) when the host vehicle starts due to the start control is too small. If the driver depresses the accelerator pedal AP to promote the acceleration of the host vehicle, override control is executed to rapidly accelerate the host vehicle. Specifically, when the depression depth AD exceeds a predetermined value ADth2 (= Y% > X%), the ECU 10 controls the drive device, etc. so that the acceleration α of the host vehicle coincides with the value αover determined based on the depression depth AD.

[0042] [Acceleration Suppression Control] On the other hand, the driver of the host vehicle may feel that the acceleration α (predetermined value αacc) when the host vehicle starts due to the start control is too large. If the driver depresses the brake pedal to suppress a sudden start of the host vehicle, the ECU 10 suspends the ACC. That is, the ECU 10 transitions the ACC switch to the OFF state. Therefore, the driver must then manually perform a driving operation to adjust the speed of the host vehicle. To resume the ACC, the driver must press the ACC switch. To eliminate such complicated operations, the driving assistance device 1 has a function of executing acceleration suppression control that controls the drive device, etc. so that the acceleration α when the host vehicle starts is smaller than the value (αacc) set by normal start control. Note that the ECU 10 does not transition the ACC switch to the OFF state even when the acceleration suppression control is started.

[0043] As will be described below, after detecting a start operation, the ECU 10 executes acceleration suppression control when a condition for determining that the driver is requesting suppression of acceleration of the vehicle is met.

[0044] Specifically, when it is determined that a start operation has been executed, the ECU 10 monitors the depression depth AD of the accelerator pedal AP and sequentially determines whether a predetermined return operation (release operation) has been executed. As shown by the solid line in FIG. 2(C), when the ECU 10 detects that the depression depth AD has decreased and become equal to or less than a predetermined value ADth3 (= Z% < X%), it determines that a return operation has been executed. When the ECU 10 determines that a return operation has been executed, it continues to monitor the depression depth AD and sequentially determines whether a predetermined acceleration suppression operation has been executed. When the following condition A (a condition for determining that the accelerator pedal AP is lightly depressed) is satisfied, the ECU 10 determines that an acceleration suppression operation has been executed. Condition A... In a Cartesian coordinate system (FIG. 2(D)) with the change rate (increase rate) ΔAD of the depression depth AD on the horizontal axis and the depression depth AD on the vertical axis, the point P[ΔAD, AD] indicating the current values of both parameters is included in a predetermined range R. Here, as shown in FIG. 2(D), the range R is located to the left (inside) of the average locus T of the point P when it is required to promote the acceleration of the host vehicle at the start. That is, the lower end in the vertical axis direction (depression depth AD) of the range R is greater than "Z%". Also, the upper end in the vertical axis direction (depression depth AD) of the range R is less than "Y%". Also, the right end in the horizontal axis direction (change rate ΔAD) of the range R is smaller than the maximum value (ΔADmax) of the locus T. Also, the left end in the horizontal axis direction (change rate ΔAD) of the range R is infinitesimal.

[0045] When the ECU 10 determines that an acceleration suppression operation has been executed, as shown by the solid line in FIG. 2(A), it controls the drive device of the host vehicle so that the acceleration α of the host vehicle matches a predetermined value αsup. Here, the predetermined value αsup is smaller than the predetermined value αacc and is, for example, about 1 / 4 of the predetermined value αacc.

[0046] Note that the driving support device 1 prohibits the execution of acceleration suppression control after the execution of override control. Thereafter, when the host vehicle stops again during the execution of ACC, the driving support device 1 makes the acceleration suppression control executable again.

[0047] After starting the host vehicle by the start control, the ECU 10 executes constant speed traveling control or inter-vehicle distance maintenance control according to the inter-vehicle distance D. For example, as shown in FIG. 2B, the ECU 10 sets the target value αt of the acceleration α to "0" (constant speed traveling control) when the speed sp0 of the host vehicle reaches a predetermined target value spt.

[0048] Next, with reference to FIGS. 3 to 6, the programs PR1, PR2, PR3, and PR4 executed by the CPU 10a (hereinafter simply referred to as "CPU") to realize the above functions of the driving assistance device 1 (functions of executing start control, override control, and acceleration suppression control) will be described. Note that various flags are used in these programs. Flag Fs indicates whether the host vehicle has started (whether a start operation has been performed). Flag Frel indicates whether a return operation has been performed. Furthermore, flag Fdis indicates whether the acceleration suppression control is prohibited. The CPU initializes various flags when the host vehicle is stopped behind the preceding vehicle V1. Specifically, the CPU sets flag Fs to "0" indicating that the host vehicle has not started. Furthermore, the CPU sets flag Frel to "0" indicating that a return operation has not been performed. Furthermore, the CPU sets flag Fdis to "0" indicating that the execution of acceleration suppression control is not prohibited.

[0049] When the ACC switch is in the on state, the CPU executes the programs PR1, PR2, PR3, and PR4 at predetermined intervals.

[0050] (Program PR1) The CPU starts execution of program PR1 from step 100 and proceeds to step 101.

[0051] In step 101, the CPU determines whether the preceding vehicle V1 has started moving from a state in which the host vehicle and the preceding vehicle V1 are stopped. The CPU determines that the preceding vehicle V1 has started moving if the inter-vehicle distance ΔD exceeds a threshold ΔDth. If the CPU determines that the preceding vehicle V1 has started moving (101: Yes), the CPU proceeds to step 102. On the other hand, if the CPU does not determine that the preceding vehicle V1 has started moving (101: No), the CPU proceeds to step 105, where it ends execution of the program PR1.

[0052] In step 102, the CPU determines whether or not a starting operation has been performed. If the depression depth AD exceeds a predetermined value ADth1 (X%), the CPU determines that a starting operation has been performed. If the CPU determines that a starting operation has been performed (102: Yes), the CPU proceeds to step 103. On the other hand, if the CPU does not determine that a starting operation has been performed (102: No), the CPU proceeds to step 105, where it ends the execution of program PR1.

[0053] In step 103, the CPU sets the flag Fs to “1” (a value indicating that a start operation has been performed).

[0054] In step 104, the CPU sets the target value αt of the acceleration α of the host vehicle to a predetermined value αacc. That is, the CPU controls the drive device and the like so that the host vehicle starts moving. Next, the CPU proceeds to step 105, where it ends execution of the program PR1.

[0055] (Program PR2) The CPU starts execution of program PR2 from step 200 and proceeds to step 201.

[0056] In step 201, the CPU determines whether or not the driver is requesting that the acceleration of the vehicle be accelerated. If the depression depth AD exceeds a predetermined value ADth2 (Y%), the CPU determines that the driver is requesting that the acceleration of the vehicle be accelerated (an acceleration acceleration operation is being performed). If the CPU determines that an acceleration acceleration operation is being performed (201: Yes), the CPU proceeds to step 202. On the other hand, if the CPU does not determine that an acceleration acceleration operation is being performed (201: No), the CPU proceeds to step 204, where it ends execution of program PR2.

[0057] In step 202, the CPU sets the target value αt of the acceleration α to a predetermined value αover.

[0058] The CPU sets the flag Fdis to "1" (a value indicating that the execution of acceleration suppression control is prohibited) in step 203. Next, the CPU proceeds to step 204, where it ends the execution of the program PR2.

[0059] (Program PR3) The CPU starts execution of program PR3 from step 300 and proceeds to step 301.

[0060] In step 301, the CPU determines whether the host vehicle has started moving. If flag Fs is "1," the CPU determines that the host vehicle has started moving. If the CPU determines that the host vehicle has started moving (301: Yes), the CPU proceeds to step 302. On the other hand, if the CPU does not determine that the host vehicle has started moving (301: No), the CPU proceeds to step 304, where it ends execution of program PR3.

[0061] In step 302, the CPU determines whether a releasing operation of the accelerator pedal AP has been performed. The CPU determines that a releasing operation has been performed when the depression depth AD is equal to or less than a predetermined value ADth3 (Z%). If the CPU determines that a releasing operation has been performed (302: Yes), the CPU proceeds to step 303. On the other hand, if the CPU does not determine that a releasing operation has been performed (302: No), the CPU proceeds to step 304, where it ends execution of the program PR3.

[0062] The CPU sets the flag Frel to "1" (a value indicating that a return operation has been executed) in step 303. Next, the CPU proceeds to step 304, where it ends the execution of the program PR3.

[0063] (Program PR4) The CPU starts execution of program PR4 from step 400 and proceeds to step 401.

[0064] In step 401, the CPU determines whether or not the execution of acceleration suppression control is permitted. If the flag Fdis is "0", the CPU determines that the execution of acceleration suppression control is permitted. If the CPU determines that the execution of acceleration suppression control is permitted (401: Yes), the CPU proceeds to step 402. On the other hand, if the CPU does not determine that the execution of acceleration suppression control is permitted (401: No), the CPU proceeds to step 405, which will be described later.

[0065] In step 402, the CPU determines whether or not the driver has already performed the return operation. If the flag Frel is "1", the CPU determines that the driver has already performed the return operation. If the CPU determines that the driver has already performed the return operation (402: Yes), the CPU proceeds to step 403. On the other hand, if the CPU does not determine that the driver has already performed the return operation (402: No), the CPU proceeds to step 405.

[0066] In step 403, the CPU determines whether or not the driver has requested the execution of acceleration suppression control. When point P[ΔAD, AD] is included in range R in the orthogonal coordinate system shown in FIG. 2(D), the CPU determines that the driver has requested the execution of acceleration suppression control (that is, that an acceleration suppression operation is being performed). When the CPU determines that an acceleration suppression operation is being performed (403: Yes), the CPU proceeds to step 404. On the other hand, when the CPU does not determine that an acceleration suppression operation is being performed (403: No), the CPU proceeds to step 405.

[0067] The CPU sets the target value αt of the acceleration α to a predetermined value αsup (<αacc) in step 404. Next, the CPU proceeds to step 407, where it ends the execution of the program PR4.

[0068] In step 405, the CPU determines whether the depression depth AD is equal to or less than a predetermined value ADth2. If the CPU determines that the depression depth AD is equal to or less than the predetermined value ADth2 (405: Yes), the CPU proceeds to step 406. On the other hand, if the CPU does not determine that the depression depth AD is equal to or less than the predetermined value ADth2 (405: No), the CPU proceeds to step 407, where it ends execution of program PR4. In this case, override control is performed by executing program PR2.

[0069] The CPU sets the target value αt of the acceleration α to a predetermined value αacc in step 406. Next, the CPU proceeds to step 407, where it ends the execution of the program PR4.

[0070] (Effect) When a start operation is performed while the host vehicle is stopped, the driving assistance device 1 executes start control to automatically start the host vehicle. That is, the driving operation to start the host vehicle is assisted. When the driver feels that the acceleration of the host vehicle due to the start control is too sudden, the driver can suppress the acceleration of the host vehicle by operating the accelerator pedal AP in a predetermined manner (performing an acceleration suppression operation).

[0071] (Variation 1) In the above embodiment, the ECU 10 determines that a start operation has been performed when the depression depth AD of the accelerator pedal AP increases and exceeds "X%." Alternatively, the ECU 10 may determine that a start operation has been performed when a predetermined resume switch 27 is pressed. In this example, the ECU 10 executes acceleration suppression control when condition A is satisfied after the start operation has been performed.

[0072] (Modification 2) In the above embodiment, the value assigned to the target value αt of the acceleration α in the acceleration suppression control is set in advance, but the value assigned to the target value αt may be changeable by the driver.

[0073] (Variation 3) In the acceleration suppression control, the ECU 10 may continue the acceleration suppression control if the accelerator pedal AP is released after the time during which the acceleration suppression operation has continued to be performed exceeds a threshold value (for example, 3 seconds).

[0074] (Variation 4) The present invention may be applied to a situation where the host vehicle starts from a state where the host vehicle is stopped alone (or at the head of a convoy of vehicles) (a state where the preceding vehicle V1 is not present). That is, the ECU 10 may be configured to start the host vehicle when a start operation is performed when there are no obstacles ahead, and to subsequently suppress the acceleration of the host vehicle when an operation requesting suppression of the acceleration (reducing the acceleration) is performed while the host vehicle is accelerating. [Explanation of symbols]

[0075] 1... driving assistance device, 10... ECU, 20... on-vehicle sensor, 30... drive device, 40... braking device

Claims

1. A driving assistance device including a processor configured to execute cruise control for controlling a host vehicle so that the host vehicle follows a preceding vehicle, execute stop control for stopping the host vehicle when a predetermined stop condition is met while the cruise control is being executed, and execute start control for starting the host vehicle by controlling the host vehicle so that an acceleration of the host vehicle coincides with a first predetermined value when a predetermined start operation is subsequently executed, The driving assistance device is configured such that, when the processor detects that a predetermined first accelerator pedal operation indicating that acceleration of the vehicle is to be suppressed has been performed after the start control has been performed, the processor executes acceleration suppression control to control the vehicle so that the acceleration of the vehicle matches a second predetermined value that is smaller than the first predetermined value.

2. The driving assistance device according to claim 1, The processor: When the depression depth of the accelerator pedal increases and exceeds a first predetermined value while the host vehicle is stopped, the start control is executed; and executing the acceleration suppression control when it is detected that the depression depth of the accelerator pedal decreases to a second predetermined value or less after the execution of the start control and that the first accelerator pedal operation is then performed. A driving assistance device configured as follows.

3. The driving assistance device according to claim 1, The processor executes the start control when a predetermined switch is operated while the host vehicle is stopped, and then executes the acceleration suppression control when it detects that the first accelerator pedal has been operated.

4. The driving assistance device according to claim 1, The driving assistance device is configured such that, when a predetermined second accelerator pedal operation is performed indicating that the acceleration of the vehicle that has started by the start control is to be promoted, the processor executes override control to control the vehicle so that the acceleration of the vehicle matches a third predetermined value that is greater than the first predetermined value, and when the override control is executed, execution of the acceleration suppression control is prohibited.

5. 5. The driving assistance device according to claim 1, The processor is configured to determine that the first accelerator pedal operation has been performed when predetermined conditions for determining that the accelerator pedal is lightly depressed, which conditions relate to the depression depth of the accelerator pedal and its rate of change, are met.

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