Driving assistance apparatus for vehicle

Abstract

To provide a driving support device improved so that a ratio of power train deceleration force to target deceleration force can be changed according to tolerance of a driver.SOLUTION: The driving support ECU is configured to calculate a target deceleration force for setting the vehicle speed to the set vehicle speed when the vehicle speed exceeds the set vehicle speed, and control the deceleration force such that the sum of the power train deceleration force and the service brake deceleration force becomes the target deceleration force. The driving support ECU determines the tolerance of the driver to the increase of the engine speed by the shift-down when the vehicle travels on a downhill (S20-S60), and controls the ratio according to the tolerance so that the ratio of the power train deceleration force to the target deceleration force becomes higher as the tolerance becomes higher (S70).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a driving assistance device for a vehicle such as an automobile, and more particularly to a driving assistance device that performs constant speed cruise control. [Background technology]

[0002] In constant speed cruise control, when it is necessary to decelerate the vehicle to bring the vehicle speed to a set speed, a target deceleration force is calculated, and control is performed so that the sum of the power train deceleration force and the service brake deceleration force becomes the target deceleration force. If the target deceleration force cannot be achieved by the power train deceleration force, the deceleration force is increased by shifting down or by generating a service brake deceleration force.

[0003] When a downshift is performed, the engine speed increases, which increases vibration and noise. For this reason, a technique is known that suppresses downshifts in situations where the target deceleration force cannot be achieved by the power train deceleration force. For example, Patent Document 1 listed below describes a technique that, when a vehicle is traveling downhill and the vehicle speed is increasing, does not perform a downshift until a predetermined time has elapsed since a downshift request was made, and instead generates a service brake deceleration force (paragraph 0006). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-47151 Summary of the Invention

[0005] [Problem to be solved by the invention] In conventional technologies such as the technology described in Patent Document 1, when the vehicle is traveling downhill for a long distance, a downshift is automatically performed after a certain time has passed since a request for a downshift was made, which inevitably increases the engine speed. This inevitably causes discomfort to users who cannot tolerate the increased vibration and noise that accompanies the increased engine speed.

[0006] The present invention focuses on the fact that tolerance for increased vibration and noise due to increased engine speed varies from person to person, and provides an improved driving assistance device that can change the ratio of power train deceleration force to target deceleration force according to the driver's tolerance.

[0007] [Means for solving the problems and effects of the invention] According to the present invention, there is provided a vehicle driving assistance device (100) that includes a control unit (driving assistance ECU 10) that executes constant speed control to control the vehicle speed (V) so that it becomes a set vehicle speed (Vset), and the control unit is configured to calculate a target deceleration force (S230, S250) to bring the vehicle speed to the set vehicle speed when the vehicle speed exceeds the set vehicle speed, and to control the deceleration force so that the sum of the power train deceleration force and the service brake deceleration force becomes the target deceleration force (S260 to S320).

[0008] The control unit (driving assistance ECU10) is configured to determine the driver's tolerance for an increase in engine speed due to downshifting when the vehicle is traveling downhill (S20 to S60), and to control the ratio according to the tolerance so that the ratio of the power train deceleration force to the target deceleration force becomes higher as the tolerance increases (S70).

[0009] According to the above configuration, when the vehicle is traveling downhill, the driver's tolerance for an increase in engine speed due to a downshift is determined, and the ratio is controlled in accordance with the tolerance so that the higher the tolerance, the higher the ratio of the power train deceleration force to the target deceleration force. Thus, it is possible to increase the ratio of the power train deceleration force to the target deceleration force in situations where a driver with a high tolerance is driving, while reducing the risk that a driver with a low tolerance will feel uncomfortable due to increased vibration and noise associated with an increase in engine speed.

[0010] [Mode of the Invention] In one aspect of the present invention, the control unit (driving assistance ECU10) is configured to determine the frequency (ratio N / T) of downshifts by the driver when the vehicle is traveling downhill without constant speed control being executed, and to determine that the tolerance is high when the frequency of downshifts is equal to or greater than a reference value (α) (S20 to S60).

[0011] The higher the driver's tolerance for an increase in engine speed due to a downshift, the more frequently the driver will downshift when the vehicle is traveling downhill without constant speed control being executed. Therefore, according to the above aspect, the driver's tolerance for an increase in engine speed due to a downshift can be determined based on the frequency of downshifts.

[0012] In another aspect of the present invention, the control mode of the power train deceleration force includes a plurality of control modes with different ratios of the power train deceleration force to the target deceleration force, and the control unit (driving assistance ECU10) is configured to set the control mode with a higher ratio as the basic control mode when the vehicle is traveling downhill (S70, S65) the more frequently downshifts are performed.

[0013] According to the above aspect, the basic control mode when the vehicle is traveling downhill can be set to a control mode in which the ratio of the power train deceleration force to the target deceleration force increases as the frequency of downshifts increases.

[0014] Furthermore, in another aspect of the present invention, the control unit (driving assistance ECU10) is configured to control the power train deceleration force in a plurality of control modes with different ratios of the power train deceleration force to the target deceleration force, and further, when the basic control mode when the vehicle is traveling downhill is not the control mode with the highest ratio among the plurality of control modes (S80, S90), it is configured to determine whether the driver will allow a downshift (S120, S130), and when it is determined that the driver will allow a downshift, change the basic control mode to a control mode with a higher ratio than the basic control mode (S170).

[0015] According to the above aspect, when the basic control mode for the vehicle traveling downhill is not the control mode with the highest ratio among the plurality of control modes, it is possible to determine whether the driver will allow a downshift, and when it is determined that the driver will allow a downshift, it is possible to change the basic control mode to a control mode with a higher ratio than the basic control mode.

[0016] Furthermore, in another aspect of the present invention, the control unit (driving assistance ECU10) is configured to determine whether the driver allows a downshift (S120, S130) when supplemental service brake deceleration force is required (S100) and when changing the basic control mode to a control mode having a higher ratio than the basic control mode is permitted (S110).

[0017] According to the above aspect, it is possible to prevent a determination from being made as to whether the driver will allow a downshift when supplementing the service brake deceleration force is not necessary or when changing the basic control mode to a control mode with a higher ratio than the basic control mode is not permitted.

[0018] In the above description, to facilitate understanding of the present invention, the names and / or symbols used in the embodiments described below are enclosed in parentheses for the configurations of the invention corresponding to those embodiments. However, each component of the present invention is not limited to the components of the embodiments corresponding to the names and / or symbols enclosed in parentheses. Other objects, features, and attendant advantages of the present invention will be easily understood from the following description of the embodiments of the present invention, which will be given with reference to the drawings. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a schematic diagram illustrating an embodiment of a vehicle driving assistance device according to the present invention; [Figure 2] 4 is a flowchart showing a power train deceleration force upper limit map setting routine in the embodiment. [Figure 3] 4 is a flowchart illustrating an ACC routine in the embodiment. [Figure 4] 4 is a diagram showing power train deceleration force upper limit maps A to C which show the relationship between vehicle speed V and the upper limit value of power train deceleration force. FIG. [Figure 5] FIG. 10 is a diagram showing an example of the relationship between the gradient of a downhill road and the deceleration force required to maintain a constant vehicle speed. [Figure 6] 10 is a flowchart showing a main part of a power train deceleration force upper limit map setting routine in a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A driving assistance device according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

[0021] [Embodiment] As shown in Fig. 1, a driving assistance device 100 according to an embodiment of the present invention is applied to a vehicle 102 and includes a driving assistance ECU 10. The vehicle 102 is capable of autonomous driving and includes a drive ECU 20, a brake ECU 30, and a meter ECU 40. The ECU stands for an electronic control unit that includes a microcomputer as its main component. The vehicle 102 will be referred to as the host vehicle 102 as necessary to distinguish it from other vehicles.

[0022] The microcomputer of each ECU includes a CPU, ROM, RAM, read / write non-volatile memory (N / M), and an interface (I / F). The CPU performs various functions by executing instructions (programs, routines) stored in the ROM. Furthermore, these ECUs are interconnected via a Controller Area Network (CAN) 104 to enable data exchange (communication). Therefore, the detected values ​​of sensors (including switches) connected to a specific ECU are transmitted to other ECUs.

[0023] The driving assistance ECU 10 is a central control device that performs driving assistance control such as adaptive cruise control and collision avoidance assistance control. Adaptive cruise control is sometimes called adaptive cruise control, and is abbreviated as "ACC" in this application. In this embodiment, the driving assistance ECU 10 executes adaptive cruise control in cooperation with other ECUs, as will be described in detail later.

[0024] ACC includes two types of control: constant speed cruise control and adaptive cruise control. Constant speed cruise control adjusts the acceleration / deceleration of the vehicle so that the vehicle speed matches a set vehicle speed (target vehicle speed) Vset without requiring the driver to perform braking or driving operations. Adaptive cruise control causes the host vehicle to follow a preceding vehicle traveling immediately ahead of the host vehicle while maintaining the inter-vehicle distance between the host vehicle and the preceding vehicle at a target inter-vehicle distance Dset.

[0025] The driving assistance ECU 10 is connected to a camera sensor 12, a radar sensor 14, and a setting operation device 16. The camera sensor 12 and the radar sensor 14 each include a plurality of camera devices and a plurality of radar devices. The camera sensor 12 and the radar sensor 14 function as a target information acquisition device 18 that acquires target information around the vehicle 102.

[0026] Although not shown in the figure, each camera device of the camera sensor 12 includes a camera unit that captures images of the surroundings of the vehicle 102 and a recognition unit that analyzes image data captured by the camera unit to recognize targets such as white lines on the road and other vehicles. The recognition unit supplies information about the recognized targets to the driving assistance ECU 10 at predetermined time intervals.

[0027] Each radar device of the radar sensor 14 uses millimeter wave radio waves to detect the distance between the vehicle and a three-dimensional object, the relative speed between the vehicle and the three-dimensional object, the relative position (direction) of the three-dimensional object with respect to the vehicle, etc., and supplies information representing these at predetermined time intervals to the driving assistance ECU 10. Note that instead of or in addition to the radar sensor 14, a LiDAR (Light Detection And Ranging) may be used.

[0028] The setting operator 16 is provided in a position operable by the driver, such as a steering wheel (not shown in Fig. 1), and is operated by the driver. Although not shown in Fig. 1, the setting operator 16 includes an ACC switch 16A. As will be described in detail later, the driving assistance ECU 10 executes ACC when the ACC switch is on. Note that the setting operator 16 may also include operators for setting the set vehicle speed Vset and the target inter-vehicle distance Dset.

[0029] The drive ECU 20 is connected to a drive unit 22 that accelerates the vehicle 102 by applying drive force to drive wheels 24. The drive ECU 20 normally controls the drive unit 22 so that the drive force generated by the drive unit 22 changes in response to the driving operation by the driver, and when it receives a command signal from the driving assistance ECU 10, it controls the drive unit 22 based on the command signal. Thus, the drive ECU 20 and the drive unit 22 work together to function as a drive control device 26.

[0030] In this embodiment, the drive device 22 includes an engine 28 and a gear-type automatic transmission 29 that constitute a powertrain 27. When the drive device 22 is not generating driving force, the powertrain generates a deceleration force due to the inertia, friction, and the like of its components. In this application, this deceleration force is referred to as a "powertrain deceleration force." Note that the drive device 22 may be a so-called hybrid system that combines an engine and a continuously variable transmission, an engine and a motor, a so-called plug-in hybrid system, or the like, as long as it is capable of generating a powertrain deceleration force.

[0031] The braking ECU 30 is connected to a braking device 32 that applies a braking force due to friction to the wheels 34, thereby applying a braking deceleration force (referred to in this application as a "service brake deceleration force") to the vehicle 102. The braking ECU 30 normally controls the braking device so that the braking force generated by the braking device 32 changes in response to the braking operation by the driver, and when it receives a command signal from the driving assistance ECU 10, it controls the braking device 32 based on the command signal to perform automatic braking.

[0032] Therefore, the brake ECU 30 and the brake device 32 work together to function as an automatic braking device 36. When braking force is applied to the wheels by cruise control or the like, a brake lamp (not shown in FIG. 1) is turned on.

[0033] A touch panel display 42 that displays the status of control by the driving assistance ECU 10 is connected to the meter ECU 40. The display 42 may be, for example, a multi-information display that displays meters and various information, or may be a display of a navigation device 70 described below. As described below, the display 42 displays the status of the ACC when it receives a signal from the driving assistance ECU 10.

[0034] The driving operation sensor 50 and the vehicle condition sensor 60 are also connected to the CAN 104. Information detected by the driving operation sensor 50 and the vehicle condition sensor 60 (referred to as sensor information) is transmitted to the CAN 104. The sensor information transmitted to the CAN 104 can be used appropriately in each ECU. Note that the sensor information may be information from a sensor connected to a specific ECU and transmitted to the CAN 104 from that specific ECU.

[0035] The driving operation sensor 50 includes a driving operation amount sensor that detects the amount of accelerator pedal operation, a braking operation amount sensor that detects the master cylinder pressure or the force applied to the brake pedal, a brake switch that detects whether the brake pedal is operated, a shift position sensor that detects the shift position of the automatic transmission 29, a steering angle sensor that detects the steering angle, a steering torque sensor that detects the steering torque, etc.

[0036] The vehicle state sensor 60 includes a vehicle speed sensor that detects the vehicle speed V of the vehicle 102, a longitudinal acceleration sensor that detects the longitudinal acceleration of the vehicle, a lateral acceleration sensor that detects the lateral acceleration of the vehicle, and a yaw rate sensor that detects the yaw rate of the vehicle.

[0037] Furthermore, the navigation device 70 is also connected to the CAN 104. The navigation device 70 includes a GPS receiver that detects the position of the vehicle 102, a storage device that stores map information and road information, and a communication device that acquires the latest map information and road information from an external device. In particular, the road information includes information on the position, range, and gradient of downhill roads.

[0038] In this embodiment, the ROM of the driving assist ECU 10 stores a power train deceleration force upper limit map setting program corresponding to the flowchart shown in Fig. 2 and an ACC program corresponding to the flowchart shown in Fig. 3. Furthermore, the ROM of the driving assist ECU 10 stores power train deceleration force upper limit maps A to C shown in Fig. 4. As shown in Fig. 4, maps A to C are set in this order so that the upper limit of the power train deceleration force increases in this order, and the upper limit of the power train deceleration force in each map increases as the vehicle speed V increases. Note that map A, which has the smallest upper limit of the power train deceleration force, is set as the standard power train deceleration force upper limit map.

[0039] In the present application, the power train deceleration force control modes that are performed when the power train deceleration force upper limit map is A to C are referred to as first to third control modes, respectively. When the vehicle 102 starts traveling, the power train deceleration force control mode is set to the first control mode as the basic control mode.

[0040] <Powertrain deceleration force upper limit map setting routine (Fig. 2)> Next, a power train deceleration force upper limit map setting routine in this embodiment will be described with reference to the flowchart shown in Figure 2. Setting of the power train deceleration force upper limit map according to the flowchart shown in Figure 2 is repeatedly executed at predetermined time intervals by the CPU of the driving assistance ECU 10 while the ACC switch 16A is on.

[0041] First, in step S10, the CPU determines whether or not ACC is being executed. If a positive determination is made, the control proceeds to step S30, and if a negative determination is made, the control proceeds to step S20.

[0042] In step S20, the CPU determines whether the vehicle 102 is traveling on a downhill road and whether the gradient of the downhill road (inclination angle φ) is equal to or greater than a reference value φc (positive constant). If a negative determination is made, the control temporarily ends, and if a positive determination is made, the control proceeds to step S30.

[0043] In step S30, the CPU increments the time T that the vehicle 102 travels on a downhill road by ΔT, where ΔT is the cycle time (positive constant) of the power train deceleration force upper limit map setting routine according to the flowchart shown in FIG.

[0044] In step S40, the CPU determines whether or not a downshift operation has been performed by the driver based on the shift position of the automatic transmission 29 detected by the shift position sensor of the driving operation sensor 50. If a negative determination is made, this control is temporarily terminated, and if a positive determination is made, this control proceeds to step S50.

[0045] In step S50, the CPU increments the number of downshift operations N by 1. In this embodiment, the time T that the vehicle travels downhill and the number of downshift operations N are cleared when an ignition switch (not shown) is turned off. However, these may be stored in a nonvolatile readable and writable storage device and updated each time the vehicle travels downhill.

[0046] In step S60, the CPU determines whether the ratio N / T of the number of downshift operations N to the time T that the vehicle 102 travels downhill is equal to or greater than a reference value α (a positive constant). If a negative determination is made, the control temporarily ends, and if a positive determination is made, the control proceeds to step S70. The ratio N / T is the frequency of downshift operations when the vehicle is traveling downhill, and is calculated as an index of the driver's tolerance for an increase in engine speed due to downshifts when the vehicle is traveling downhill.

[0047] In step S70, the CPU changes the power train deceleration force upper limit map so that the upper limit of the power train deceleration force is raised by one level. For example, if the current map is A, the map is changed to B, and if the current map is B, the map is changed to C. Thus, the basic control mode of the power train deceleration force is set to one of the first to third control modes depending on the frequency of downshifting operations. Note that if a negative determination is made in step S20, S40, or S60, the power train deceleration force upper limit map is not changed and remains the current map.

[0048] In step S80, similar to step S20, the CPU determines whether the vehicle 102 is traveling on a downhill road and the gradient of the downhill road is equal to or greater than the reference value φc. If a negative determination is made, the control temporarily ends, and if a positive determination is made, the control proceeds to step S90. The reference value used in the determination in step S80 may be different from the reference value used in the determination in step S20.

[0049] In step S90, the CPU determines whether the current map is A or B, i.e., whether it is possible to change the power train deceleration force upper limit map so that the upper limit of the power train deceleration force is increased by one level. If a negative determination is made, this control is temporarily terminated, and if a positive determination is made, this control proceeds to step S100.

[0050] In step S100, the CPU determines whether or not the service brake deceleration force needs to be replenished. If a negative determination is made, the control temporarily ends, and if a positive determination is made, the control proceeds to step S110. Note that if the target deceleration force Fdt is greater than the maximum power train deceleration force Fdpmax in the ACC routine described below and the determination in step S270 is positive, it may be determined that the service brake deceleration force needs to be replenished.

[0051] FIG. 5 is a diagram showing an example of the relationship between the gradient (horizontal axis) of a downhill road and the deceleration force (vertical axis) required to maintain a constant vehicle speed. In FIG. 5, the dashed-dotted line indicates the deceleration force Fd required to maintain a constant vehicle speed, the solid line indicates the sum of the power train deceleration force Fdp and the service brake deceleration force Fds, and the dashed line indicates the power train deceleration force upper limit, which is the upper limit of the power train deceleration force. The deceleration force between the dashed-dotted line and the solid line is the deceleration force due to the running resistance of the vehicle 102. The dashed line moves downward in FIG. 5 when the power train deceleration force upper limit map is changed so that the upper limit of the power train deceleration force is increased. The determination in step S100 is whether the inclination angle φ of the downhill road is greater than the inclination angle of the downhill road at the intersection of the solid line and the dashed line in FIG. 5.

[0052] In step S110, the CPU determines whether a change to the power-train deceleration force upper limit map that increases the upper limit of the power-train deceleration force by one step is permitted. This determination is made to determine whether the upper limit of the power-train deceleration force will not exceed the deceleration force (solid line) required for the current gradient even if the power-train deceleration force upper limit map is changed so that the upper limit of the power-train deceleration force is increased by one step. If a negative determination is made, the control temporarily ends, and if a positive determination is made, the control proceeds to step S120. Note that if the map is changed so that the upper limit of the power-train deceleration force is increased by one step but the upper limit of the power-train deceleration force does not exceed the target deceleration force Fdt, it may be determined that a change to the power-train deceleration force upper limit map that increases the upper limit of the power-train deceleration force by one step is permitted.

[0053] In step S120, the CPU sends a command signal to the meter ECU 40 to cause the display 42 to display, for example, "Allow automatic downshift?", "Yes" or "No," and suggest allowing downshifting.

[0054] In step S130, the CPU determines whether the driver has approved the automatic downshift, for example, by determining whether the driver has touched "Yes" on the display 42. When a negative determination is made, this control ends once. When an affirmative determination is made, this control proceeds to step S140. Note that a negative determination may be made if "Yes" is not touched within a reference time (a positive constant) after the display of the downshift approval proposal is started on the display 42.

[0055] In step S140, the CPU changes the power train deceleration force upper limit map so that the upper limit of the power train deceleration force increases by one step, similar to step S70. As a result, the basic control mode of the power train deceleration force is changed according to the change of the map. Note that when a negative determination is made in step S80, S90, S100, S110, or S130, the power train deceleration force upper limit map is not changed and is maintained at the current map.

[0056] <ACC routine (Figure 3)> Next, the ACC routine in the embodiment will be described with reference to the flowchart shown in FIG. 3. The ACC according to the flowchart shown in FIG. 3 is repeatedly executed by the CPU of the driving support ECU 10 at predetermined time intervals in a situation where the ACC switch 16A is on.

[0057] First, in step S210, the CPU determines whether there is a preceding vehicle in front of the vehicle 102. When a negative determination is made, this control proceeds to step S230. When an affirmative determination is made, this control proceeds to step S220.

[0058] In step S220, the CPU executes the following-distance control of ACC. That is, the CPU controls the running of the vehicle 102 with respect to the preceding vehicle so that the following distance D between the vehicle 102 and the preceding vehicle acquired by the target information acquisition device 18 becomes the set target following distance Dset.

[0059] In step S230, the CPU determines whether the vehicle speed V exceeds the set vehicle speed Vset of the ACC constant speed cruise control. If a positive determination is made, the control proceeds to step S250, and if a negative determination is made, the control proceeds to step S240.

[0060] In step S240, the CPU sends a command signal to the drive ECU 20 to execute drive force control, which controls the drive force of the drive unit 22 so that the vehicle speed V becomes the set vehicle speed Vset.

[0061] In step S250, the CPU calculates a target deceleration force Fdt for bringing the vehicle speed V to the set vehicle speed Vset based on the difference between the vehicle speed V and the set vehicle speed Vset, in a manner known in the art.

[0062] In step S260, the CPU calculates the maximum power train deceleration force Fdpmax, which is the upper limit of the power train deceleration force, based on the vehicle speed V and from the currently set power train deceleration force upper limit map (FIG. 4).

[0063] In step S270, the CPU determines whether the target deceleration force Fdt is greater than the maximum power train deceleration force Fdpmax, i.e., whether supplemental deceleration force by the service brake deceleration force Fds is required. If a negative determination is made, the control proceeds to step S300, and if a positive determination is made, the control proceeds to step S280.

[0064] In step S280, the CPU sets the target power train deceleration force Fdpt to the maximum power train deceleration force Fdpmax.

[0065] In step S290, the CPU sets the target service brake deceleration force Fdst to the difference Fdt-Fdpt between the target deceleration force Fdt and the target power train deceleration force Fdpt.

[0066] In step S300, the CPU sets the target power train deceleration force Fdpt to the target deceleration force Fdt, and in step S310, the CPU sets the target service brake deceleration force Fdst to zero.

[0067] In step S320, the CPU sends a signal indicating the target power train deceleration force Fdpt to drive ECU 20. Drive ECU 20 controls powertrain 27 so that power train deceleration force Fdp becomes the target power train deceleration force Fdpt. In this case, if the target power train deceleration force Fdpt is large and power train deceleration force Fdp cannot be made equal to the target power train deceleration force Fdpt, an automatic downshift is performed.

[0068] Furthermore, in step S320, the CPU transmits a signal indicating the target service brake deceleration force Fdst to the brake ECU 30. The brake ECU 30 controls the braking device 32 so that the service brake deceleration force Fds becomes the target deceleration force Fdst. Thus, the sum of the power train deceleration force Fdp and the service brake deceleration force Fds becomes the target deceleration force Fdst.

[0069] [Variations] 6 is a flowchart showing the main parts of the power train deceleration force upper limit map setting routine in the modified example. As shown in FIG. 6, in the modified example, step S65 is executed instead of steps S60 and S70. The other steps of the power train deceleration force upper limit map setting routine and the steps of the ACC routine are executed in the same manner as in the embodiment.

[0070] In step S65, similar to step S60, the ratio N / T, which is the frequency of downshift operations when the vehicle is traveling downhill, is calculated. Furthermore, when the ratio N / T is less than a first reference value β1 (a positive constant), the power train deceleration force upper limit map is set to map A. When the ratio N / T is equal to or greater than the first reference value β1 and less than a second reference value β2 (a positive constant greater than the first reference value β1), the power train deceleration force upper limit map is set to map B. Furthermore, when the ratio N / T is equal to or greater than the second reference value β2, the power train deceleration force upper limit map is set to map C.

[0071] As can be seen from the above explanation, according to the embodiment and the modified example, the ratio N / T is calculated as the frequency of downshift operations when the vehicle 102 is traveling downhill (S20 to S60). Then, in the embodiment, when the ratio N / T is equal to or greater than the reference value α (a positive constant), the power train deceleration force upper limit map is changed so that the upper limit of the power train deceleration force is increased by one level (S70). In the modified example, the power train deceleration force upper limit map is set in accordance with the ratio N / T so that the upper limit of the power train deceleration force increases as the ratio N / T increases (S65).

[0072] The ratio N / T indicates the driver's tolerance for an increase in engine speed due to a downshift when the vehicle is traveling downhill. Therefore, the ratio is controlled according to the tolerance so that the ratio of the powertrain deceleration force to the target deceleration force increases as the tolerance increases. This reduces the possibility that a driver with low tolerance will feel uncomfortable due to increased vibration and noise caused by an increase in engine speed, while making it possible to increase the ratio of the powertrain deceleration force to the target deceleration force in situations where a driver with high tolerance is driving.

[0073] Furthermore, according to this embodiment, the ratio N / T is calculated as the frequency of downshifts by the driver when the vehicle is traveling downhill without constant speed control being executed, and when the ratio N / T is equal to or greater than the reference value α, it is determined that tolerance is high (S20 to S60). Furthermore, according to this modification, the power train deceleration force upper limit map is set so that the higher the ratio N / T, the larger the power train deceleration force upper limit value. Therefore, it is possible to determine the driver's tolerance for an increase in engine speed due to downshifts based on the ratio N / T as the frequency of downshifts.

[0074] Furthermore, according to the embodiment and the modified example, when it is determined that the current map when the vehicle is traveling downhill is A or B (S80, S90), permission of a downshift is suggested (S120), and it is determined whether the driver has consented to the automatic downshift (S130). If it is determined that the driver has consented to the automatic downshift, the power train deceleration force upper limit map is changed so that the upper limit of the power train deceleration force is increased by one level (S140).

[0075] In other words, when the basic control mode for the vehicle traveling downhill is not the control mode with the highest ratio among the plurality of control modes, it is determined whether the driver allows a downshift, and when it is determined that the driver allows a downshift, the basic control mode is changed to a control mode with a higher ratio than the basic control mode.

[0076] Therefore, when the basic control mode when the vehicle is traveling downhill is not the control mode with the highest ratio among the plurality of control modes, it is possible to determine whether the driver will allow a downshift. Furthermore, when it is determined that the driver will allow a downshift, the basic control mode can be changed to a control mode with a higher ratio than the basic control mode.

[0077] Furthermore, according to the embodiment and modified examples, when it is determined that the service brake deceleration force needs to be replenished (S100) and it is determined that a change to the power train deceleration force upper limit map that would increase the upper limit of the power train deceleration force by one level is permissible (S110), a suggestion is made to allow a downshift (S120).

[0078] This prevents the driver from determining whether to allow a downshift when supplementing the service brake deceleration force is not required or when changing the basic control mode to a control mode with a higher ratio than the basic control mode is not permitted.

[0079] Although the present invention has been described in detail above with reference to specific embodiments, it will be apparent to those skilled in the art that the present invention is not limited to the above-described embodiments and modifications, and that various other embodiments are possible within the scope of the present invention.

[0080] For example, in the above-described embodiment and modified examples, the index of the driver's tolerance for an increase in engine speed due to a downshift when the vehicle is traveling downhill is the ratio N / T, which is the frequency of downshift operations when the vehicle is traveling downhill. However, the index of tolerance may also be the ratio N / M, which is the number of downshift operations N to the number of times the vehicle travels downhill M.

[0081] Furthermore, in the above-described embodiment and modified examples, if it is determined that the current map when the vehicle is traveling downhill is A or B (S80, S90), permission for a downshift is suggested (S120), and it is determined whether the driver has consented to the automatic downshift (S130). If it is determined that the driver has consented to the automatic downshift, the power train deceleration force upper limit map is changed so that the upper limit of the power train deceleration force is increased by one level (S140). However, steps S80 to S140 may be omitted.

[0082] In the above-described embodiment and modified examples, a control mode setter for allowing the driver to set the control mode is not provided, but a control mode setter may be provided so that the driver can set a basic control mode by operating the control mode setter. In this case, the set basic control mode may be regarded as one of the indicators of the driver's tolerance for an increase in engine speed due to downshifting when the vehicle is traveling downhill.

[0083] In the above-described embodiment and modified examples, the power train deceleration force upper limit maps are A to C, and the power train deceleration force control modes are first to third control modes. However, the number of power train deceleration force upper limit maps and power train deceleration force control modes may be other than three.

[0084] Furthermore, in the above-described embodiment and modified examples, the constant speed control is ACC, but the constant speed control may be any control that controls the vehicle speed to a target vehicle speed. [Explanation of symbols]

[0085] 10... driving assistance ECU, 12... camera sensor, 14... radar sensor, 18... target information acquisition device, 22... drive device, 27... power train, 32... braking device, 50... meter ECU, 100... driving assistance device, 102... vehicle

Claims

1. A vehicle driving assistance device including a control unit that executes constant speed control to control a vehicle speed so that the vehicle speed becomes a set vehicle speed, wherein when the vehicle speed exceeds the set vehicle speed, the control unit calculates a target deceleration force for bringing the vehicle speed to the set vehicle speed, and controls the deceleration force so that the sum of a power train deceleration force and a service brake deceleration force becomes the target deceleration force, The control unit is configured to determine a driver's tolerance for an increase in engine speed due to a downshift when the vehicle is traveling downhill, and to control the ratio in accordance with the tolerance so that the ratio of the power train deceleration force to the target deceleration force becomes higher as the tolerance becomes higher.

2. 2. The vehicle driving assistance device according to claim 1, wherein the control unit is configured to determine a frequency of downshifts by the driver when the vehicle is traveling downhill without constant speed control being executed, and to determine that the tolerance is high when the frequency of downshifts is equal to or greater than a reference value.

3. 2. The vehicle driving assistance device according to claim 1, wherein the control unit has a plurality of control modes with different ratios of the power train deceleration force to the target deceleration force, and is configured to set a control mode with a higher ratio as the frequency of downshifting increases as a basic control mode when the vehicle is traveling downhill.

4. 4. The vehicle driving assistance device according to claim 3, wherein the control unit is configured to control the power train deceleration force in a plurality of control modes having different ratios of the power train deceleration force to the target deceleration force, and further configured to determine whether the driver will allow a downshift when the basic control mode when the vehicle is traveling downhill is not a control mode among the plurality of control modes having the highest ratio, and to change the basic control mode to a control mode having a higher ratio than the basic control mode when it is determined that the driver will allow a downshift.

5. 5. The vehicle driving assistance device according to claim 4, wherein the control unit is configured to determine whether the driver allows a downshift when supplemental service brake deceleration force is required and changing the basic control mode to a control mode in which the ratio is higher than that of the basic control mode is permitted.

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