Driving assistance device for vehicle

Abstract

A vehicle driving assistance device (100) includes a driving assistance ECU (10) that is a control unit that executes constant speed control for controlling a vehicle speed (V) so that the vehicle speed (V) reaches a set vehicle speed (Vset), and is configured to calculate a target deceleration force (S230, S250) for setting the vehicle speed to the set vehicle speed when the vehicle speed exceeds the set vehicle speed, and to execute constant speed control for controlling the vehicle speed (V) to the set vehicle speed (Vset) when the vehicle speed exceeds the set vehicle speed (Vset). In the present invention, a driving assistance ECU (10) determines the permissibility of a driver for an increase in the engine speed due to a downshift during downhill travel of a vehicle (S20-S60), and controls a deceleration force so that the sum of a power train deceleration force and a service brake deceleration force becomes a target deceleration force (S260-S320). The ratio is controlled on the basis of the permissibility such that the ratio of the power train deceleration force to the target deceleration force is higher as the permissibility is higher (S70).

Description

Technical Field

[0001] This invention relates to a driving assistance device for automobiles and other vehicles, and more specifically, to a driving assistance device for constant speed driving control. Background Technology

[0002] In constant speed driving control, when it is necessary to decelerate the vehicle to reach the set speed, the target deceleration force is calculated, and control is performed so that the sum of the powertrain deceleration force and the service brake deceleration force equals the target deceleration force. If the target deceleration force cannot be achieved due to the powertrain deceleration force, the deceleration force is increased by downshifting (shifting down) or by generating the service brake deceleration force.

[0003] When downshifting, the engine speed increases, leading to increased vibration and noise. Therefore, a technique for suppressing downshifting is known when the target deceleration force cannot be achieved due to the deceleration force of the powertrain. For example, Patent Document 1 describes a technique (paragraph 0006) in which, when a vehicle is traveling downhill and its speed is increasing, a service braking deceleration force is generated from the time a downshift request is made until a predetermined time has elapsed, without downshifting.

[0004] Existing technical documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2023-47151 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] In the prior art described in Patent Document 1, when the downhill distance is long, a downshift is performed unconditionally after a predetermined time has elapsed since the downshift request was issued, and the engine speed inevitably increases. Therefore, users who cannot tolerate the increased vibration and noise caused by the increased engine speed will inevitably feel uncomfortable (unpleasant).

[0008] This invention addresses the fact that the tolerance for increased vibration and noise caused by increased engine speed varies from person to person, and provides an improved driving assistance device that can change the ratio of the powertrain deceleration force to the target deceleration force according to the driver's tolerance.

[0009] Technical solutions used to solve problems and the effects of inventions

[0010] According to the present invention, a driving assistance device (100) for a vehicle is provided, which includes a control unit (driving assistance ECU 10). The control unit performs constant speed control to control the vehicle speed so that the vehicle speed (V) becomes a set vehicle speed (Vset). The control unit is configured to calculate a target deceleration force (S230, S250) to make the vehicle speed become the set vehicle speed when the vehicle speed exceeds the set vehicle speed, and control the deceleration force in such a way that the sum of the power transmission deceleration force and the service brake deceleration force becomes the target deceleration force (S260 to S320).

[0011] The control unit (driving assistance ECU10) is configured to determine the driver's tolerance for the increase in engine speed caused by downshifting when the vehicle is driving downhill (S20 to S60), and control the ratio based on the tolerance in a way that the higher the tolerance, the higher the ratio of the powertrain deceleration force to the target deceleration force (S70).

[0012] Based on the above structure, the driver's tolerance for the increase in engine speed caused by downshifting when driving downhill is determined. The ratio is controlled based on the tolerance, where a higher tolerance results in a higher ratio of powertrain deceleration force to target deceleration force. This reduces the likelihood of discomfort experienced by drivers with low tolerance due to increased vibration and noise from the increased engine speed, while simultaneously increasing the ratio of powertrain deceleration force to target deceleration force when driven by drivers with high tolerance.

[0013] Invention methods

[0014] In one embodiment of the present invention, the control unit (driving assistance ECU 10) is configured to determine the frequency (ratio N / T) of downshifting by the driver when the vehicle is driving downhill without constant speed control, and to determine that the tolerance is high when the frequency of downshifting is above a reference value (α) (S20 to S60).

[0015] The higher the driver's tolerance for the increase in engine speed caused by downshifting, the more frequently the driver will downshift when the vehicle is going downhill without constant speed control. Therefore, based on the above method, the driver's tolerance for the increase in engine speed caused by downshifting can be determined based on the frequency of downshifting.

[0016] In another aspect of the invention, the control mode of the powertrain deceleration force includes multiple control modes with different ratios of the powertrain deceleration force to the target deceleration force. The control unit (driving assistance ECU 10) is configured such that the higher the frequency of downshifting, the higher the control mode with the higher ratio is set as the basic control mode when the vehicle is driving downhill (S70, S65).

[0017] Based on the above method, the higher the frequency of downshifting, the higher the ratio of the powertrain deceleration force to the target deceleration force can be set when the vehicle is driving downhill.

[0018] Furthermore, in another embodiment of the present invention, the control unit (driving assistance ECU 10) is configured to control the deceleration force of the powertrain under multiple control modes with different ratios of the deceleration force of the powertrain to the target deceleration force. Moreover, when the basic control mode is not the control mode with the highest ratio among the multiple control modes when the vehicle is driving downhill (S80, S90), it determines whether the driver is allowed to downshift (S120, S130). When it is determined that the driver is allowed to downshift, the basic control mode is changed to a control mode with a higher ratio than the basic control mode (S170).

[0019] Based on the above method, it is possible to determine whether the driver is permitted to downshift when the basic control mode is not the control mode with the highest ratio among multiple control modes while the vehicle is driving downhill. Moreover, when it is determined that the driver is permitted to downshift, the basic control mode can be changed to a control mode with a higher ratio than the basic control mode.

[0020] Furthermore, in another embodiment of the present invention, the control unit (driving assistance ECU 10) is configured to determine whether the driver is permitted to downshift when additional braking force is required (S100) and it is permissible to change the basic control mode to a control mode with a higher ratio than the basic control mode (S110) (S120, S130).

[0021] Based on the above method, it is possible to prevent the determination of whether the driver is allowed to downshift when there is no need to supplement the vehicle braking deceleration force or when it is not permissible to change from the basic control mode to a control mode with a higher ratio than the basic control mode.

[0022] In the foregoing description, to aid in understanding the invention, the names and / or reference numerals used in the embodiments corresponding to the following description of the invention are enclosed in parentheses. However, the constituent elements of the invention are not limited to the constituent elements of the embodiments corresponding to the enclosed names and / or reference numerals. Other objects, features, and incidental advantages of the invention can be readily understood from the following description of embodiments of the invention with reference to the accompanying drawings. Attached Figure Description

[0023] Figure 1 This is a schematic structural diagram illustrating an embodiment of the vehicle driving assistance device of the present invention.

[0024] Figure 2 This is a flowchart illustrating the routine for setting the upper limit of the deceleration force of the powertrain in the implementation method.

[0025] Figure 3 This is a flowchart illustrating the ACC routine in the implementation method.

[0026] Figure 4 This is a diagram showing the upper limit mapping A to C of the powertrain deceleration force, which represents the relationship between vehicle speed V and the upper limit of the powertrain deceleration force.

[0027] Figure 5 This is a diagram illustrating the relationship between the gradient of a downhill road required to maintain a constant vehicle speed and the deceleration force.

[0028] Figure 6 This is a flowchart showing the main part of the routine for setting the upper limit of the deceleration force in the power transmission system in the modified example.

[0029] Explanation of reference numerals in the attached figures

[0030] 10 Driving assistance ECU; 12 Camera sensor; 14 Radar sensor; 18 Target information acquisition device; 22 Drive unit; 27 Powertrain; 32 Braking device; 40 Instrument ECU; 100 Driving assistance device; 102 Vehicle. Detailed Implementation

[0031] Hereinafter, the driving assistance device according to the embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0032] [Implementation Method]

[0033] like Figure 1 As shown, the driving assistance device 100 according to the embodiments of the present invention is applied to a vehicle 102 and includes a driving assistance ECU 10. The vehicle 102 is a vehicle capable of autonomous driving and includes a drive ECU 20, a brake ECU 30, and an instrument ECU 40. An ECU refers to an Electronic Control Unit (ECU) with a microcomputer as its main component. The vehicle 102 is referred to as "this vehicle 102" as needed to distinguish it from other vehicles.

[0034] Each ECU's microcomputer includes a CPU, ROM, RAM, read / write non-volatile memory (N / M), and interfaces (I / F). The CPU executes instructions (programs, routines) stored in the ROM to perform various functions. Furthermore, these ECUs are interconnected via CAN (Controller Area Network) 104 to exchange data (communicate). Therefore, the detection values ​​of sensors (including switches) connected to a specific ECU will also be sent to other ECUs.

[0035] The driver assistance ECU 10 is the central control device for performing driver assistance controls such as following distance control and collision avoidance assist control. Following distance control is sometimes referred to as Adaptive Cruise Control (ACC) in this application. In the implementation, as detailed later, the driver assistance ECU 10 cooperates with other ECUs to perform following distance control.

[0036] ACC includes two controls: constant speed control and follow-the-car control. Constant speed control adjusts the vehicle's acceleration and deceleration to keep the vehicle speed consistent with the set speed (target speed) Vset without requiring driver braking. Follow-the-car control keeps the vehicle following the leading vehicle (the vehicle in front) while maintaining a target distance Dset between the two vehicles.

[0037] A camera sensor 12, a radar sensor 14, and a setting operator 16 are connected to the driver assistance ECU 10. The camera sensor 12 and the radar sensor 14 each include multiple camera devices and multiple radar devices. The camera sensor 12 and the radar sensor 14 function as a target information acquisition device 18 for acquiring target information about the surrounding objects of the vehicle 102.

[0038] Although not illustrated, each camera device of the camera sensor 12 includes a camera unit and a recognition unit. The camera unit captures images of the area around the vehicle 102, and the recognition unit analyzes the image data captured by the camera unit to identify targets such as white lines on the road and other vehicles. The recognition unit provides information about the identified targets to the driver assistance ECU 10 at predetermined intervals.

[0039] Each radar unit of 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, and the relative position (direction) of the three-dimensional object relative to the vehicle, and supplies this information to the driver assistance ECU 10 at predetermined intervals. Alternatively, LiDAR (Light Detection and Ranging) can be used instead of radar sensor 14, or based on radar sensor 14.

[0040] Setting the operator 16, for example Figure 1 The steering wheel, not shown, is positioned in a way that allows the driver to operate it. Although Figure 1Not shown, but the setting operator 16 includes an ACC switch 16A. As described in detail later, the driver assistance ECU 10 performs ACC when the ACC switch is ON. Furthermore, the setting operator 16 may also include operators for setting the set vehicle speed Vset and the target inter-vehicle distance Dset.

[0041] A drive unit 22 is connected to the drive ECU 20, which accelerates the vehicle 102 by applying driving force to the drive wheels 24. Normally, the drive ECU 20 controls the drive unit 22 in a manner that varies the driving force generated by the drive unit 22 according to the driving operation performed by the driver. If a command signal is received from the driver assistance ECU 10, the drive unit 22 is controlled based on the command signal. Thus, the drive ECU 20 and the drive unit 22 cooperate to function as a drive control device 26.

[0042] In this embodiment, the drive unit 22 includes an engine 28 and a gear-type automatic transmission 29 constituting the powertrain 27. When the drive unit 22 does not generate driving force, the powertrain generates a deceleration force caused by the inertia, friction, etc., of its components. In this application, this deceleration force is referred to as "powertrain deceleration force". Furthermore, as long as a powertrain deceleration force can be generated, the drive unit 22 can also be a combination of an engine and a continuously variable transmission (CVT), an engine and a motor, i.e., a so-called hybrid system, a so-called plug-in hybrid system, etc.

[0043] A braking device 32 is connected to the braking ECU 30, which applies a deceleration force (referred to in this application as "service braking deceleration force") to the vehicle 102 by applying a braking force generated by friction to the wheels 34. Under normal circumstances, the braking ECU 30 controls the braking device 32 in a manner that varies according to the braking operation performed by the driver. If a command signal is received from the driver assistance ECU 10, automatic braking is performed by controlling the braking device 32 based on the command signal.

[0044] Therefore, the braking ECU 30 and the braking device 32 cooperate to function as the automatic braking device 36. Furthermore, when applying braking force to the wheels through driving control or other means, Figure 1 The brake light (not shown) is illuminated.

[0045] A touch panel-type display 42 is connected to the instrument cluster ECU 40 to display the status of controls performed by the driver assistance ECU 10. The display 42 can be, for example, an instrument cluster display or a multi-function information display showing various information, or it can be the display of the navigation device 70 described later. As will be described later, when a signal is received from the driver assistance ECU 10, the display 42 displays the ACC status.

[0046] The driving operation sensor 50 and the vehicle status sensor 60 are also connected to the CAN 104. Information detected by the driving operation sensor 50 and the vehicle status sensor 60 (referred to as sensor information) is sent to the CAN 104. The sensor information sent to the CAN 104 can be appropriately utilized by each ECU. Furthermore, the sensor information can also be information from sensors connected to a specific ECU, sent from that specific ECU to the CAN 104.

[0047] The driving operation sensor 50 includes a drive operation sensor that detects the amount of accelerator pedal operation, a brake operation sensor that detects master cylinder pressure or the force applied to the brake pedal, and a brake switch that detects the presence or absence of brake pedal operation. Additionally, the driving operation sensor 50 includes a gear position sensor that detects the gear position of the automatic transmission 29, a steering angle sensor that detects the steering angle, and a steering torque sensor that detects the steering torque.

[0048] The vehicle status sensor 60 includes a vehicle speed sensor for detecting the vehicle speed V of the vehicle 102, a front-rear acceleration sensor for detecting the vehicle's front-to-back acceleration, a lateral acceleration sensor for detecting the vehicle's lateral acceleration, and a yaw rate sensor for detecting the vehicle's yaw rate.

[0049] Furthermore, the navigation device 70 is also connected to the CAN 104. The navigation device 70 includes a GPS receiver for detecting the position of the vehicle 102, a storage device for storing map information and road information, and a communication device for obtaining the latest map information and road information from external sources. In particular, the road information includes information on the location, extent, and gradient of downhill roads.

[0050] In the implementation, the ROM of the driving assistance ECU 10 stores information related to... Figure 2 The flowchart shown corresponds to the powertrain deceleration force upper limit mapping setting program and is related to... Figure 3 The flowchart shown corresponds to the ACC program. Furthermore, the ROM of the driver assistance ECU10 stores... Figure 4 The diagram shows the upper limit mapping of the deceleration force of the powertrain from A to C. For example... Figure 4 As shown, mappings A through C are set as the upper limits of the powertrain deceleration force, increasing in that order. The higher the vehicle speed V, the greater the upper limit of the powertrain deceleration force in each mapping. Furthermore, mapping A, which has the smallest upper limit of the powertrain deceleration force, is set as the standard upper limit mapping for the powertrain deceleration force.

[0051] In this application, the powertrain deceleration force control modes, where the upper limit of the powertrain deceleration force is mapped as A to C, are referred to as the first to third control modes, respectively. When the vehicle 102 starts moving, the powertrain deceleration force control mode is set to the first control mode as the basic control mode.

[0052] Example of setting the upper limit of deceleration force in the powertrain ( Figure 2 )>

[0053] Next, refer to Figure 2 The flowchart shown illustrates the powertrain deceleration force upper limit mapping setting routine in the embodiment. With ACC switch 16A on, the CPU of the driver assistance ECU 10 repeatedly executes the following routine at predetermined intervals: Figure 2 The flowchart shown illustrates the setting of the upper limit mapping for the deceleration force of the powertrain.

[0054] First, in step S10, the CPU determines whether ACC is being executed. If a positive determination is made, the control proceeds to step S80; if a negative determination is made, the control proceeds to step S20.

[0055] In step S20, the CPU determines whether vehicle 102 is traveling downhill and whether the slope (inclination angle φ) of the downhill road is greater than or equal to the reference value φc (a positive constant). If a negative determination is made, the control temporarily ends; if a positive determination is made, the control proceeds to step S30.

[0056] In step S30, the CPU increases the time T that the vehicle 102 travels on the downhill road by ΔT. Furthermore, ΔT is based on... Figure 2 The flowchart shown maps the upper limit of the powertrain deceleration force to the cycle time of the set routine (a positive constant).

[0057] In step S40, the CPU determines whether the driver has downshifted based on the gear position of the automatic transmission 29 detected by the gear position sensor of the driving operation sensor 50. If a negative determination is made, the control temporarily ends; if a positive determination is made, the control proceeds to step S50.

[0058] In step S50, the CPU increments the number of downshift operations N by 1. Furthermore, in this embodiment, if the ignition switch (not shown) is turned off, the vehicle's downhill travel time T and the number of downshift operations N are reset to zero. However, they can also be stored in a non-volatile read / write memory and updated each time the vehicle travels downhill.

[0059] In step S60, the CPU determines whether the ratio N / T, which is the number of downshifting operations N, to the time T the vehicle 102 travels on the downhill road, is greater than or equal to a reference value α (a positive constant). If a negative determination is made, the control temporarily terminates; if a positive determination is made, the control proceeds to step S70. Furthermore, the ratio N / T, representing the frequency of downshifting operations while the vehicle is traveling downhill, is calculated as an indicator of the driver's tolerance for the increase in engine speed caused by downshifting during downhill driving.

[0060] In step S70, the CPU changes the upper limit mapping of the powertrain deceleration force to increase the upper limit of the powertrain deceleration force by one level. For example, if the current mapping is A, the mapping is changed to B; if the current mapping is B, the mapping is changed to C. Thus, the basic control mode of the powertrain deceleration force is set to any one of the first to third control modes based on the frequency of downshifting operations. Furthermore, if a negative determination is made in steps S20, S40, or S60, the upper limit mapping of the powertrain deceleration force remains unchanged and is maintained at the current mapping.

[0061] In step S80, similar to step S20, the CPU determines whether vehicle 102 is traveling downhill and whether the slope of the downhill road is above the reference value φc. If a negative determination is made, the control temporarily terminates; if a positive determination is made, the control proceeds to step S90. The reference value in step S80 may also be different from the reference value in step S20.

[0062] In step S90, the CPU determines whether the current mapping is A or B, that is, whether it is possible to change the upper limit mapping of the powertrain deceleration force by increasing the upper limit of the powertrain deceleration force by one level. If a negative determination is made, this control temporarily ends; if a positive determination is made, this control proceeds to step S100.

[0063] In step S100, the CPU determines whether additional service braking deceleration force is needed. If a negative determination is made, the control temporarily terminates; if a positive determination is made, the control proceeds to step S110. Furthermore, in the ACC routine described later, if the target deceleration force Fdt is greater than the maximum powertrain deceleration force Fdpmax, and the determination in S270 is positive, it is determined that additional service braking deceleration force is needed.

[0064] Figure 5 This is a graph illustrating an example of the relationship between the slope (horizontal axis) of a downhill road required to maintain a constant vehicle speed and the deceleration force (vertical axis). Figure 5In this figure, the single-dashed line indicates the deceleration force Fd required to maintain a constant vehicle speed, the solid line indicates the sum of the powertrain deceleration force Fdp and the service brake deceleration force Fds, and the dashed line indicates the upper limit of the powertrain deceleration force, which is the upper limit value of the powertrain deceleration force. The deceleration force between the single-dashed line and the solid line is the deceleration force generated by the driving resistance of the vehicle 102. When the upper limit of the powertrain deceleration force mapping is changed such that the upper limit of the powertrain deceleration force becomes larger, the dashed line moves downward in Figure 5 The determination in step S100 is a determination of whether the inclination angle φ of the downhill road is larger than the inclination angle of the downhill road at the intersection of the solid line and the dashed line in Figure 5 .

[0065] In step S110, the CPU determines whether to permit the change of the powertrain deceleration force upper limit mapping that increases the upper limit of the powertrain deceleration force by one level. This determination is as follows: Even if the powertrain deceleration force upper limit mapping is changed to increase the upper limit of the powertrain deceleration force by one level, whether the upper limit of the powertrain deceleration force does not exceed the deceleration force (solid line) required for the current slope. When a negative determination is made, this control temporarily ends. When a positive determination is made, this control proceeds to step S120. It can be determined that the change of the powertrain deceleration force upper limit mapping that increases the upper limit of the powertrain deceleration force by one level is permitted when, even if the mapping change that increases the upper limit of the powertrain deceleration force by one level is made, the upper limit of the powertrain deceleration force does not exceed the target deceleration Fdt.

[0066] In step S120, the CPU recommends permitting downshifting by sending a command signal to the meter ECU40 to display, for example, "Is downshifting permitted?", "Yes", and "No" on the display 42.

[0067] In step S130, the CPU determines whether the driver agrees to automatic downshifting, for example, by determining whether the driver touches "Yes" on the display 42. When a negative determination is made, this control temporarily ends. When a positive determination is made, this control proceeds to step S!40. In addition, a negative determination can be made when "Yes" is not touched within the reference time (a positive constant) since the display of the downshifting permission recommendation starts on the display 42.

[0068] In step S140, similar to step S70, the CPU changes the powertrain deceleration force upper limit mapping to increase the upper limit of the powertrain deceleration force by one level. Thus, the basic control mode of the powertrain deceleration force changes according to the change of the mapping. In addition, when a negative determination is made in step S80, S90, S100, S110, or S130, the powertrain deceleration force upper limit mapping is not changed and remains the current mapping.

[0069] <ACC routine( Figure 3 )>

[0070] Next, refer to Figure 3 The flowchart shown illustrates the ACC routine in the implementation method. With ACC switch 16A on, the CPU of the driver assistance ECU 10 repeatedly executes the ACC routine at predetermined intervals. Figure 3 The flowchart shown is for ACC.

[0071] First, in step S210, the CPU determines whether there is a leading vehicle ahead of vehicle 102. If a negative determination is made, the control proceeds to step S230; if a positive determination is made, the control proceeds to step S220.

[0072] In step S220, the CPU performs ACC following vehicle distance control. That is, the CPU controls the movement of vehicle 102 for the leading vehicle so that the vehicle distance D between vehicle 102 and the leading vehicle obtained by the target information acquisition device 18 becomes the set target vehicle distance Dset.

[0073] In step S230, the CPU determines whether the vehicle speed V exceeds the set vehicle speed Vset of the ACC constant speed driving control. If a positive determination is made, the control proceeds to step S250; if a negative determination is made, the control proceeds to step S240.

[0074] In step S240, the CPU performs drive force control: by sending a command signal to the drive ECU 20, the drive device 22 controls the drive force to make the vehicle speed V become the set vehicle speed Vset.

[0075] In step S250, the CPU calculates the target deceleration force Fdt for making the vehicle speed V become the set vehicle speed Vset, based on the difference between the vehicle speed V and the set vehicle speed Vset, using methods known in the art.

[0076] In step S260, the CPU maps the current set upper limit of the powertrain deceleration force based on the vehicle speed V. Figure 4 The maximum power transmission deceleration force Fdpmax is calculated as the upper limit of the power transmission deceleration force.

[0077] In step S270, the CPU determines whether the target deceleration force Fdt is greater than the maximum powertrain deceleration force Fdpmax, i.e., whether supplementary deceleration force based on the service braking deceleration force Fds is needed. If a negative determination is made, the control proceeds to step S300; if a positive determination is made, the control proceeds to step S280.

[0078] In step S280, the CPU sets the target powertrain deceleration force Fdpt to the maximum powertrain deceleration force Fdpmax.

[0079] In step S290, the CPU sets the target vehicle braking deceleration force Fdst to the difference between the target deceleration force Fdt and the target power transmission deceleration force Fdpt, which is Fdt-Fdpt.

[0080] In step S300, the CPU sets the target power transmission deceleration force Fdpt to the target deceleration force Fdt. In step S310, the CPU sets the target service brake deceleration force Fdst to 0.

[0081] In step S320, the CPU sends a signal representing the target powertrain deceleration force Fdpt to the drive ECU 20. The drive ECU 20 controls the powertrain 27 to make the powertrain deceleration force Fdp become the target powertrain deceleration force Fdpt. In this case, if the target powertrain deceleration force Fdpt is too large to make the powertrain deceleration force Fdp become the target powertrain deceleration force Fdpt, automatic downshifting is performed.

[0082] Additionally, in step S320, the CPU sends a signal representing the target service braking deceleration force Fdst to the braking ECU 30. The braking ECU 30 controls the braking device 32 to make the service braking deceleration force Fds the target deceleration force Fdst. Thus, the control is performed in a manner that makes the sum of the powertrain deceleration force Fdp and the service braking deceleration force Fds the target deceleration force Fdst.

[0083] [Variation Example]

[0084] Figure 6 This is a flowchart illustrating the main part of the routine for setting the upper limit of the deceleration force in the powertrain in a modified example. For example... Figure 6 As shown, in the modified example, step S65 is performed instead of steps S60 and S70. The other steps of the powertrain deceleration force upper limit mapping setting routine and the steps of the ACC routine are performed in the same way as in the implementation method.

[0085] In step S65, similarly to step S60, the frequency of downshifting operations when the vehicle is traveling downhill, i.e., the N / T ratio, is calculated. Furthermore, when the N / T ratio is less than a first reference value β1 (a positive constant), the upper limit mapping of the powertrain deceleration force is set to mapping A. When the N / T ratio is greater than or equal to the first reference value β1 and less than a second reference value β2 (a positive constant greater than the first reference value β1), the upper limit mapping of the powertrain deceleration force is set to mapping B. Moreover, when the N / T ratio is greater than or equal to the second reference value β2, the upper limit mapping of the powertrain deceleration force is set to mapping C.

[0086] As can be seen from the above description, according to the implementation method and its variations, the calculation ratio N / T is used as the frequency of downshifting operations when the vehicle 102 is traveling downhill (S20 to S60). Furthermore, in the implementation method, when the ratio N / T is above a reference value α (a positive constant), the upper limit mapping of the powertrain deceleration force is changed to increase the upper limit of the powertrain deceleration force by one level (S70). In the variations, the upper limit mapping of the powertrain deceleration force is set according to the ratio N / T, so that the larger the ratio N / T, the larger the upper limit of the powertrain deceleration force (S65).

[0087] The N / T ratio represents the driver's tolerance for the increase in engine speed caused by downshifting when driving downhill. Therefore, the ratio of the powertrain's deceleration force to the target deceleration force is controlled based on this tolerance, so that the higher the tolerance, the higher this ratio. This reduces the likelihood of discomfort experienced by drivers with low tolerance due to increased vibration and noise from the increased engine speed, while simultaneously increasing the ratio of the powertrain's deceleration force to the target deceleration force when driven by a driver with high tolerance.

[0088] Furthermore, according to the implementation method, the ratio N / T is determined as the frequency at which the driver downshifts when the vehicle is traveling downhill without constant speed control. When the ratio N / T is above a reference value α, it is considered to have high tolerance (S20~S60). Additionally, according to a modified example, a powertrain deceleration force upper limit mapping is set such that the higher the ratio N / T, the larger the upper limit of the powertrain deceleration force. Therefore, based on the ratio N / T, which is the frequency of downshifting, it is possible to determine the driver's tolerance for the increase in engine speed caused by downshifting.

[0089] Furthermore, according to the implementation method and its variations, if it is determined that the current mapping when the vehicle is driving downhill is A or B (S80, S90), it is suggested to allow downshifting (S120), and it is determined whether the driver agrees to automatic downshifting (S130). When it is determined that the driver agrees to automatic downshifting, the upper limit mapping of the powertrain deceleration force is changed so that the upper limit of the powertrain deceleration force is increased by one level (S140).

[0090] In other words, when the basic control mode is not the control mode with the highest ratio among multiple control modes when the vehicle is driving downhill, it is determined whether the driver can allow downshifting. Moreover, if it is determined that the driver can allow downshifting, the basic control mode is changed to a control mode with a higher ratio than the basic control mode.

[0091] Therefore, when the basic control mode is not the control mode with the highest ratio among multiple control modes when the vehicle is driving downhill, it can determine whether the driver allows downshifting. Furthermore, when it is determined that the driver allows downshifting, the basic control mode can be changed to a control mode with a higher ratio than the basic control mode.

[0092] Furthermore, according to the implementation method and its variations, when it is determined that additional service braking deceleration force is needed (S100), and when it is determined that a change in the upper limit mapping of the powertrain deceleration force is allowed to increase the upper limit of the powertrain deceleration force by one level (S110), it is recommended to allow downshifting (S120).

[0093] Therefore, it can prevent the determination of whether the driver is allowed to downshift when there is no need to supplement the vehicle braking deceleration force or when it is not permissible to change from the basic control mode to a control mode with a higher ratio than the basic control mode.

[0094] The present invention has been described in detail above with respect to specific embodiments, but the present invention is not limited to the above embodiments and variations. Various other embodiments can be implemented within the scope of the present invention, which will be obvious to those skilled in the art.

[0095] For example, in the above-described embodiments and variations, the driver's tolerance for the increase in engine speed caused by downshifting when driving downhill is indicated by the frequency of downshifting operations, i.e., the ratio N / T. However, the tolerance indicator could also be the ratio N / M of the number of downshifting operations to the number of times the vehicle travels downhill.

[0096] Furthermore, in the above-described implementation and its variations, if the current mapping for the vehicle traveling downhill is determined to be A or B (S80, S90), downshifting is recommended (S120), and it is determined whether the driver agrees to automatic downshifting (S130). Moreover, when it is determined that the driver agrees to automatic downshifting, the upper limit mapping of the powertrain deceleration force is changed to increase the upper limit of the powertrain deceleration force by one level (S140). However, steps S80 to S140 may be omitted.

[0097] Furthermore, in the above-described embodiments and variations, a control mode setter is not provided for the driver to set the control mode. However, a control mode setter may be provided, allowing the driver to set the basic control mode by operating the control mode setter. In this case, the set basic control mode can also be regarded as one of the indicators of the driver's tolerance for the increase in engine speed caused by downshifting when the vehicle is driving downhill.

[0098] Furthermore, in the above-described embodiments and variations, the upper limit of the powertrain deceleration force is mapped as A to C, and the control mode of the powertrain deceleration force is the first to the third control mode. However, the upper limit mapping of the powertrain deceleration force and the number of control modes of the powertrain deceleration force may not be three.

[0099] Furthermore, in the above-described implementation methods and variations, constant speed control is ACC, but constant speed control can also be any control that uses the vehicle speed as the target vehicle speed.

Claims

1. A driving assistance device for a vehicle, comprising a control unit, the control unit performing constant speed control to control the vehicle speed to a set vehicle speed, the control unit being configured to, when the vehicle speed exceeds the set vehicle speed, calculate a target deceleration force to make the vehicle speed reach the set vehicle speed, and control the deceleration force in such a manner that the sum of the powertrain deceleration force and the service brake deceleration force becomes the target deceleration force. The control unit is configured to determine the driver's tolerance for the increase in engine speed caused by downshifting when the vehicle is driving downhill, and to control the ratio based on the tolerance, such that the higher the tolerance, the higher the ratio of the powertrain deceleration force to the target deceleration force.

2. The vehicle driving assistance device according to claim 1, The control unit is configured to determine the frequency at which the driver downshifts when the vehicle is traveling downhill without constant speed control, and to determine that the tolerance is high when the frequency of downshifting is above a reference value.

3. The vehicle driving assistance device according to claim 1, The control unit is configured to have multiple control modes with different ratios of the deceleration force of the powertrain to the target deceleration force. The higher the frequency of downshifting, the higher the ratio of the control mode is set as the basic control mode when the vehicle is driving downhill.

4. The vehicle driving assistance device according to claim 3, The control unit is configured to control the deceleration force of the powertrain in multiple control modes with different ratios of the deceleration force to the target deceleration force. Furthermore, when the basic control mode is not the control mode with the highest ratio among the multiple control modes when the vehicle is driving downhill, it determines whether the driver is allowed to downshift. If it is determined that the driver is allowed to downshift, the basic control mode is changed to a control mode with a higher ratio than the basic control mode.

5. The vehicle driving assistance device according to claim 4, The control unit is configured to determine whether the driver allows downshifting when additional braking force is required and it is permissible to change the basic control mode to a control mode with a higher ratio than the basic control mode.

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