Driving support method and driving support device

Abstract

In this driving support method: a target lateral position that is located forward by a forward gaze distance is determined, and a target slip angle for causing a vehicle body to face the target lateral position is calculated (S3); target braking / driving forces of a front wheel and a rear wheel are calculated in accordance with the target slip angle (S5); at least one of a wheel slip ratio or a wheel speed difference between the front wheel and the rear wheel is calculated as a tire state quantity (S4); an allowable limit of the tire state quantity is set (S6); if the calculated tire state quantity does not exceed the set allowable limit, the target braking / driving forces are generated in the front wheel and the rear wheel (S11); if the calculated tire state quantity exceeds the set allowable limit, a distribution ratio or total of the target braking / driving forces is adjusted such that the tire state quantity is equal to or less than the set allowable limit (S12-S14); the adjusted target braking / driving forces are generated in the front wheel and the rear wheel, and the adjustment of the target braking / driving forces is suppressed if the vehicle is turning (S8).

Description

Driving support method and driving support device

[0001] The present invention relates to a driving assistance method and a driving assistance device.

[0002] Techniques have been proposed for setting the braking / driving forces between the front and rear wheels so that tire state quantities, such as tire slip ratios and front / rear wheel speed differences, do not exceed allowable limits. For example, Patent Document 1 listed below describes a variable transmission torque mechanism that controls the variable transmission torque mechanism so that the relationship between the front wheel slip ratio and the rear wheel slip ratio becomes a set relationship.

[0003] Japanese Patent Application Publication No. 2-227333

[0004] On the other hand, stable handling can be improved by controlling the slip angle (e.g., vehicle body slip angle or tire slip angle) through the distribution of braking / driving force between the front and rear wheels. However, if the distribution of braking / driving force is limited because the tire state variables exceed the allowable limits, as in Patent Document 1, there is a risk that suitable stable handling cannot be achieved. The present invention aims to improve the balance between the slip angle that achieves suitable stable handling and the tire state variables that ensure stability.

[0005] In one aspect of the driving assistance method of the present invention, a target yaw rate is calculated from the vehicle speed and steering angle of the vehicle, a target lateral position a forward gaze distance ahead is determined based on the target yaw rate, a target slip angle for the vehicle body to turn toward the target lateral position is calculated, target braking / driving forces for the front and rear wheels are calculated according to the target slip angle, at least one of the wheel slip rate or the wheel speed difference between the front and rear wheels is calculated as a tire state quantity, and if the calculated tire state quantity does not exceed a predetermined allowable limit, the target braking / driving forces are generated at the front wheels and rear wheels, and if the calculated tire state quantity exceeds the predetermined allowable limit, the target braking / driving forces for the front wheels and / or rear wheels are corrected so that the tire state quantity is equal to or less than the predetermined allowable limit, and the corrected target braking / driving forces are generated at the front wheels and rear wheels, and if the vehicle is turning, the correction of the target braking / driving forces is suppressed.

[0006] According to the present invention, it is possible to improve the balance between the slip angle that realizes favorable handling performance and the tire state quantity that ensures stability.

[0007] 1 is a schematic configuration diagram of an example of a driving assistance device according to an embodiment; (a) to (e) are explanatory diagrams of a driving assistance method according to an embodiment; (a) to (d) are explanatory diagrams of a driving assistance method according to an embodiment; a block diagram of an example of the functional configuration of a chassis controller; an explanatory diagram of an example of a method for setting a target slip angle; an explanatory diagram of an example of a method for calculating a slip ratio correction value; a block diagram of an example of the functional configuration of a drive source controller; a flowchart of an example of a driving assistance method according to a first embodiment; a flowchart of an example of a driving assistance method according to a second embodiment; and a flowchart of an example of a driving assistance method according to a third embodiment.

[0008] First Embodiment Referring to Fig. 1, a driving assistance device 10 includes a steering angle sensor 11, a yaw rate sensor 12, an acceleration sensor 13, a drive mode switch (SW) 14, a brake sensor 15, a wheel speed sensor 16, an accelerator opening sensor 17, a chassis controller 18, a brake controller 19, a drive source controller 20, a braking device 21, and a drive source 22.

[0009] The steering angle sensor 11 detects the steering angle δs of the steering wheel. In this specification, the signs of the steering angle δs and the front wheel steering angle δf when steering left and right are defined as positive and negative, respectively. The yaw rate sensor 12 detects the actual yaw rate γa of the vehicle 1. The acceleration sensor 13 detects the lateral acceleration, which is the acceleration of the vehicle 1 in the vehicle width direction. The drive mode switch (SW) 14 is a switch that accepts a selection input to select the response characteristics of the vehicle 1 in response to driving operations by the driver. For example, the drive mode switch 14 may be a switch that switches between drive modes, which are the driving characteristics of the vehicle 1. For example, the drive modes may include a first mode (sport mode) in which the response characteristics of the vehicle 1 in response to driving operations are high, and a second mode (eco mode) in which the response characteristics of the vehicle 1 in response to driving operations are gentle.

[0010] The brake sensor 15 detects a brake operation amount Br, which is the amount of operation of the brake pedal. The wheel speed sensor 16 detects wheel speeds VwFL, VwFR, VwRL, and VwRR of the left front wheel 2FL, the right front wheel 2FR, the left rear wheel 2RL, and the right rear wheel 2RR, respectively. In the following description, the left front wheel 2FL and the right front wheel 2FR may be referred to as "front wheels 2F," and the left rear wheel 2RL and the right rear wheel 2RR may be referred to as "rear wheels 2R." The accelerator opening sensor 17 detects an accelerator operation amount Ac, which is the amount of operation of the accelerator pedal.

[0011] The chassis controller 18 is an electronic control unit (ECU) that calculates the amount of operation required for chassis control of the vehicle 1. The chassis controller 18 outputs the tire longitudinal forces to be generated on the front wheels 2F and the rear wheels 2R to the drive source controller 20. The chassis controller 18 also outputs the braking forces to be generated on the front wheels 2F and the rear wheels 2R to the brake controller 19. The chassis controller 18 includes a processor 18a and peripheral components such as a storage device 18b. The functions of the chassis controller 18 described below are realized, for example, by the processor 18a executing a computer program stored in the storage device 18b.

[0012] The chassis controller 18 may be formed by dedicated hardware for executing the various information processes described below. For example, the chassis controller 18 may include a functional logic circuit configured in a general-purpose semiconductor integrated circuit. For example, the chassis controller 18 may include a programmable logic device (PLD) such as a field-programmable gate array (FPGA). The same applies to the brake controller 19 and the drive source controller 20.

[0013] The brake controller 19 is an ECU that generates braking forces for the front and rear wheels using braking devices 21 in accordance with information from the chassis controller 18. The brake controller 19 includes a processor 19a and peripheral components such as a storage device 19b. The functions of the brake controller 19 are realized, for example, by the processor 19a executing a computer program stored in the storage device 19b.

[0014] The drive source controller 20 is an ECU that calculates the braking / driving forces to be generated on the front and rear wheels based on the signal from the accelerator opening sensor 17, and generates the braking / driving forces using a drive source 22 such as an engine or a motor. The drive source controller 20 also corrects the distribution ratio of the braking / driving forces to be generated on the front and rear wheels according to information from the chassis controller 18. Note that the drive source controller 20 may change the control amounts for the front and rear wheels respectively. The drive source controller 20 includes a processor 20a and peripheral components such as a storage device 20b. The functions of the drive source controller 20 are realized, for example, by the processor 20a executing a computer program stored in the storage device 20b.

[0015] Next, an outline of the driving assistance method of the first embodiment will be described. The driving assistance device 10 improves handling stability by controlling the vehicle body slip angle β by allocating braking / driving force between the front wheels 2F and the rear wheels 2R, and controls the braking / driving force between the front wheels 2F and the rear wheels 2R so that the slip ratio, which is a "tire state quantity," does not exceed the allowable slip ratio limit. The vehicle body slip angle β is the angle of inclination of the vehicle body in the fore-and-aft direction with respect to the traveling direction of the vehicle 1. For example, if the slip ratio of the front wheels 2F exceeds the allowable slip ratio limit, the drive source controller 20 transfers a portion of the braking / driving force allocated to the front wheels 2F to the rear wheels 2R. If the slip ratio of the rear wheels 2R also exceeds the allowable slip ratio limit, the drive source controller 20 transfers a portion of the braking / driving force allocated to the rear wheels 2R to the front wheels 2F.

[0016] 2A is a diagram showing the change over time in vehicle slip angle β in the early stage (transient state) and the later stage (steady state) of a turn when the vehicle 1 starts turning at time t0. The solid line indicates the vehicle slip angle β at high speed, and the dashed line indicates the vehicle slip angle β at low speed. In this specification, the sign of the vehicle slip angle β when the vehicle 1 is in an "outward facing state" is defined as "positive," and the sign of the vehicle slip angle β when the vehicle 1 is in an "inward facing state" is defined as "negative." The "outward facing state" is a state in which the fore-and-aft direction of the vehicle 1 body is displaced from the direction of travel of the vehicle 1 in the opposite direction to the turning direction of the vehicle 1, and the "inward facing state" is a state in which the fore-and-aft direction of the vehicle 1 body is displaced from the direction of travel of the vehicle 1 in the same direction as the turning direction of the vehicle 1.

[0017] As shown in FIG. 2(a), the vehicle 1 is in an outward-facing state at the beginning of a turn. In the later stages of a turn, if the vehicle speed of the vehicle 1 is high, the vehicle 1 is in an inward-facing state, and if the vehicle speed is low, the vehicle 1 is in an outward-facing state. The chassis controller 18 calculates a target vehicle body slip angle βt so as to reduce the outward and inward-facing state of the vehicle 1, and corrects the target braking / driving force distribution to the front wheels 2F and rear wheels 2R so as to achieve the target vehicle body slip angle βt. FIG. 2(b) shows the vehicle body slip angle when the vehicle speed is high. The dashed-dotted line shows the actual vehicle body slip angle βa, the dashed line shows the target vehicle body slip angle βt, and the solid line shows the slip angle difference, which is the difference between them. FIG. 2(c) shows the corrected target braking / driving force distribution set based on the slip angle difference of FIG. 2(b). In Figure 2(c), the sign of the correction value for transferring the braking / driving force from the front wheels 2F to the rear wheels 2R is defined as "positive," and the sign of the correction value for transferring the braking / driving force from the rear wheels 2R to the front wheels 2F is defined as "negative." The same is true in Figure 3(b).

[0018] At the beginning of the turn, the actual vehicle body slip angle βa becomes larger than the target vehicle body slip angle βt (i.e., the vehicle 1 is in an outward direction). Therefore, in order to increase the lateral force of the tires of the front wheels 2F, the braking / driving force distribution to the front wheels 2F is reduced and the braking / driving force distribution to the rear wheels 2R is increased (i.e., braking / driving force is transferred from the front wheels 2F to the rear wheels 2R). At the later stage of the turn, the actual vehicle body slip angle βa becomes smaller than the target vehicle body slip angle βt (i.e., the vehicle 1 is in an inward direction). Therefore, in order to increase the lateral force of the tires of the rear wheels 2R, the braking / driving force distribution to the rear wheels 2R is reduced and the braking / driving force distribution to the front wheels 2F is increased (i.e., braking / driving force is transferred from the rear wheels 2R to the front wheels 2F).

[0019] On the other hand, as described above, if the slip ratio of the front wheels 2F or the rear wheels 2R exceeds the allowable limit, the drive source controller 20 corrects the braking / driving force distribution. Therefore, when correcting the braking / driving force distribution in accordance with the vehicle slip angle, if the transfer of braking / driving force from the front wheels 2F to the rear wheels 2R causes the slip ratio of the rear wheels 2R to exceed the allowable slip ratio limit, the drive source controller 20 reduces the braking / driving force distribution to the rear wheels 2R. Accordingly, if the braking / driving force distribution to the front wheels 2F is increased, it becomes impossible to increase the lateral force of the front wheels 2F, and there is a risk that the target vehicle slip angle βt cannot be achieved. The same applies when the transfer of braking / driving force from the rear wheels 2R to the front wheels 2F causes the slip ratio of the front wheels 2F to exceed the allowable slip ratio limit.

[0020] Therefore, when the vehicle 1 is turning, the drive source controller 20 suppresses correction of the braking / driving force distribution corrected by the chassis controller 18 to achieve the target vehicle body slip angle βt due to the slip ratio exceeding the allowable slip ratio limit. For example, the drive source controller 20 may correct the allowable slip ratio limit in accordance with the correction value of the target braking / driving force to achieve the target vehicle body slip angle βt, thereby easing the restriction on the slip ratio due to the allowable slip ratio limit. This makes it less likely that the chassis controller 18 will restrict the correction of the braking / driving force distribution, making it easier to achieve the target vehicle body slip angle βt.

[0021] Figures 2(d) and 2(e) show the permissible slip ratio limits for the front and rear wheels when the vehicle speed is high. The solid lines indicate the basic permissible limit determined without considering the braking / driving force distribution between the front wheels 2F and the rear wheels 2R to achieve the target vehicle slip angle βt. For example, the basic permissible limit may be set to a value λ0 that maximizes acceleration / deceleration during straight-line driving, or may be a value obtained by correcting the slip ratio λ0 based on the geometric difference in the front and rear wheel trajectories due to steering or lateral acceleration. The dashed lines indicate the corrected permissible limit corrected according to the corrected target braking / driving force distribution value shown in Figure 2(c). The permissible slip ratio limit is corrected so that it is smaller on the front wheels 2F and larger on the rear wheels 2R at the beginning of a turn compared to before the turn. At the end of a turn, the slip ratio limit is corrected so that it is larger on the front wheels 2F and smaller on the rear wheels 2R compared to before the turn. By correcting the permissible slip ratio limit for the rear wheels 2R to be larger at the beginning of a turn, an increase in the slip ratio of the rear wheels 2R is permitted. This makes it difficult to inhibit an increase in the distribution of braking / driving force to the rear wheels 2R. As a result, the distribution of braking / driving force to the front wheels 2F can be reduced, increasing the lateral force of the front wheels 2F and suppressing an outward turning state at the beginning of a turn.

[0022] FIG. 3(a) shows the vehicle slip angle when the vehicle speed is low. The dashed line shows the actual vehicle slip angle βa, the dashed line shows the target vehicle slip angle βt, and the solid line shows the slip angle difference, which is the difference between them. FIG. 3(b) shows the corrected target braking / driving force distribution value set based on the slip angle difference in FIG. 3(a). FIGS. 3(c) and 3(d) show the permissible slip ratio limits for the front and rear wheels when the vehicle speed is high. The solid line shows the basic permissible limit, and the dashed line shows the corrected permissible limit corrected in accordance with the corrected target braking / driving force distribution value in FIG. 3(b). The permissible slip ratio limit is corrected so that it is smaller on the front wheel 2F side and larger on the rear wheel 2R side at the beginning of the turn compared to before the turn. At the later stage of the turn, the slip ratio is corrected so that it is smaller on the front wheel 2F side and larger on the rear wheel 2R side compared to before the turn. By correcting the allowable slip ratio limit for the rear wheel 2R to be larger at the beginning of a turn, an increase in the slip ratio of the rear wheel 2R is permitted, as in Figure 2(e). This makes it less likely that an increase in the braking / driving force distribution to the rear wheel 2R will be hindered. As a result, the braking / driving force distribution to the front wheel 2F can be reduced, which increases the lateral force of the front wheel 2F and prevents it from turning outward at the beginning of a turn.

[0023] 4 is a block diagram of an example of the functional configuration of the chassis controller 18. The chassis controller 18 includes an input processing unit 30, a target behavior calculation unit 31, and a target braking / driving force correction value calculation unit 32. The input processing unit 30 calculates the vehicle speed Vv based on the wheel speeds VwFL, VwFR, VwRL, and VwRR detected by the wheel speed sensors 16. The input processing unit 30 calculates the front wheel steering angle δf based on the steering angle δs detected by the steering angle sensor 11. The input processing unit 30 calculates the driver-requested deceleration ad1 based on the brake operation amount Br detected by the brake sensor 15. The input processing unit 30 receives from the drive source controller 20 the total target braking / driving force F0 calculated based on the accelerator operation amount Ac detected by the accelerator opening sensor 17, and calculates the driver-requested acceleration ad2 based on the total target braking / driving force F0.

[0024] The target behavior calculation unit 31 calculates a target yaw rate γt from the vehicle speed Vv and the steering angle δs, determines a target lateral position Pt a predetermined forward gaze distance Lg ahead based on the target yaw rate γt, and calculates a target vehicle body slip angle βt for orienting the vehicle body toward the target lateral position Pt. FIG. 5 is an explanatory diagram of an example of a method for setting the target vehicle body slip angle βt. The dashed line Tt indicates the target turning trajectory of the vehicle 1, and the solid line Ta indicates the actual turning trajectory. In the example of FIG. 5, a point on the target turning trajectory Tt a distance ahead of the vehicle 1 by the forward gaze distance Lg is set as the target lateral position Pt. The turning radius Rt of the target turning trajectory Tt is given by Rt = Vv / γt, and the turning radius Ra of the actual turning trajectory Ta is given by Ra = Vv / γa using the actual yaw rate γa. The forward gaze distance Lg is given by the product (T×Vv) of the vehicle speed Vv and a predetermined forward gaze time T. The deviation amount ε of the longitudinal axis ax of the vehicle body from the target turning trajectory Tt at the forward gaze distance Lg is given by ε=(Ra ２ +LG ２ ) １／２ If the angle at which the vehicle's longitudinal axis ax is changed to face the target lateral position Pt is taken as the target vehicle body slip angle βt, the deviation ε is approximated as ε ≈ Lg × sin βt, and therefore the target vehicle body slip angle βt can be calculated using the following equation (1).

[0025]

[0026] The target vehicle body slip angle βt may be calculated by adjusting the adaptation constants a, b, and c in the following equation (2) so as to realize characteristics similar to those of the target vehicle body slip angle βt in the following equation (1): In the following equations (3) to (7), m is the vehicle weight, I is the yaw radius of inertia, l is the wheel base, lf and lr are the distances from the center of gravity P of the vehicle 1 to the front and rear axles, and Kf and Kr are the equivalent cornering powers of the front and rear wheels.

[0027]

[0028] Target driving / braking force correction value calculation unit 32 estimates the current actual vehicle body slip angle βa of vehicle 1. For example, target driving / braking force correction value calculation unit 32 estimates actual vehicle body slip angle βa according to the following equation (8).

[0029]

[0030] Target braking / driving force correction value calculation unit 32 calculates slip angle difference Δβ=(βt-βa), which is the difference between target vehicle body slip angle βt and actual vehicle body slip angle βa, and determines whether actual vehicle body slip angle βa is inward or outward relative to target vehicle body slip angle βt. For example, if the product Δβ×sign(δf) of slip angle difference Δβ and the sign (δf) of front wheel steering angle δf is positive, it determines that actual vehicle body slip angle βa is outward, and if the product Δβ×sign(δf) is negative, it determines that actual vehicle body slip angle βa is inward.

[0031] The target driving / braking force correction value calculation unit 32 calculates target driving / braking force correction values ​​ΔFf and ΔFr, which are correction values ​​for the tire longitudinal forces of the front wheels 2F and the rear wheels 2R, depending on whether the actual vehicle body slip angle βa is inward or outward with respect to the target vehicle body slip angle βt. For example, when the actual vehicle body slip angle βa is outward with respect to the target vehicle body slip angle βt, the calculation unit 32 may calculate a negative target driving / braking force correction value ΔFf that reduces the tire longitudinal force of the front wheels 2F and / or a positive target driving / braking force correction value ΔFr that increases the tire longitudinal force of the rear wheels 2R. Also, when the actual vehicle body slip angle βa is inward with respect to the target vehicle body slip angle βt, the calculation unit 32 may calculate a positive target driving / braking force correction value ΔFf that increases the tire longitudinal force of the front wheels 2F and / or a negative target driving / braking force correction value ΔFr that decreases the tire longitudinal force of the rear wheels 2R.

[0032] In this embodiment, target braking / driving force correction value calculation unit 32 calculates target braking / driving force correction value ΔFr for rear wheels 2R as the product of the difference (βt-βa) between target vehicle body slip angle βt and actual vehicle body slip angle βa, a predetermined proportional gain Pb, the sign (δf) of front wheel steering angle δf, and total target braking / driving force F0, as follows: target braking / driving force correction value ΔFr=(βt-βa)×Pb×sign(δf)×F0. Target braking / driving force correction value ΔFf for front wheels 2F may be calculated as ΔFf=-ΔFr.

[0033] The target braking / driving force correction value calculation unit 32 calculates a slip ratio correction value Δλ. The slip ratio correction value Δλ is a correction value for correcting the permissible slip ratio limit to the slip ratios generated by the target braking / driving forces of the front and rear wheels to achieve the target vehicle slip angle βt. For example, the target braking / driving force correction value calculation unit 32 calculates a slip ratio correction value Δλ that corrects the permissible slip ratio limit of the front wheels 2F from the target braking / driving force correction value ΔFf of the front wheels 2F, and calculates a slip ratio correction value Δλ that corrects the permissible slip ratio limit of the rear wheels 2R from the target braking / driving force correction value ΔFr of the rear wheels 2R. Figure 6 is an explanatory diagram of an example of a method for calculating the slip ratio correction value Δλ. The ideal slip ratio λ0 is the slip ratio at which the longitudinal force generated by the tires becomes the maximum value Fmax. By approximating the relationship between the slip ratio and the tire longitudinal force using an approximate straight line L having a slope obtained by dividing the maximum value Fmax by the ideal slip ratio λ0, the change in slip ratio caused by the target braking / driving force correction values ​​ΔFf and ΔFr can be calculated as the slip ratio correction value Δλ.

[0034] Here, if the coefficient of friction of the road surface is μ and the height of the center of gravity of the vehicle 1 is h, the maximum loads on the front wheels 2F and rear wheels 2R when the vehicle 1 accelerates at an acceleration rate α are m×g×(α-μ×h / l) and m×g×((1-α)+μ×h / l), respectively, and the maximum loads on the front wheels 2F and rear wheels 2R when the vehicle 1 decelerates at a deceleration rate α are m×g×(α+μ×h / l) and m×g×((1-α)-μ×h / l), respectively. The target braking / driving force correction value calculation unit 32 calculates the slip ratio correction values ​​Δλ for the front wheels 2F and rear wheels 2R during acceleration and deceleration, respectively, based on the following equations (9) to (12).

[0035]

[0036] In this way, by adding the term (μ × h / l) corresponding to the load change to equations (9) to (12), the permissible slip ratio limit of the front wheels 2F can be corrected by a slip ratio correction value Δλ that is set smaller when braking than when driving, and the permissible slip ratio limit of the rear wheels 2R can be corrected by a slip ratio correction value Δλ that is set larger when braking than when driving. Target braking / driving force correction value calculation unit 32 outputs target braking / driving force correction values ​​ΔFf and ΔFr and slip ratio correction value Δλ to drive source controller 20.

[0037] 7 is a block diagram of an example of the functional configuration of the drive source controller 20. The drive source controller 20 includes a target drive force calculation unit 40, a front / rear wheel target drive force calculation unit 41, an allowable limit setting unit 42, a state quantity calculation unit 43, and a redistribution unit 44. The target drive force calculation unit 40 calculates a total target braking / driving force F0 based on the accelerator operation amount Ac detected by the accelerator position sensor 17. The front / rear wheel target drive force calculation unit 41 calculates a front wheel basic target braking / driving force Ff0 and a rear wheel basic target braking / driving force Fr0 by distributing the total target target braking / driving force F0 to the front wheels 2F and the rear wheels 2R according to a predetermined distribution method. The front / rear wheel target drive force calculation unit 41 calculates the front wheel target braking / driving force Ff0 and the rear wheel target braking / driving force Fr by correcting the front wheel basic target braking / driving force Ff0 and the rear wheel basic target braking / driving force Fr0 with target braking / driving force correction values ​​ΔFf and ΔFr, respectively.

[0038] The permissible limit setting unit 42 sets a basic permissible limit that is determined without considering the distribution of braking / driving force between the front wheels 2F and rear wheels 2R to achieve the target vehicle body slip angle βt. The basic permissible limit may be set to a value λ0 that maximizes acceleration / deceleration force when traveling straight, or may be a value obtained by correcting the slip ratio λ0 based on the geometric difference in the trajectories of the front and rear wheels due to steering or on the lateral acceleration. The permissible limit setting unit 42 sets the permissible slip ratio limit by correcting the basic permissible limit with a slip ratio correction value Δλ. The state quantity calculation unit 43 calculates the actual slip ratio λa of each wheel. Here, if the wheel speeds VwFL, VwFR, VwRL, and VwRR are collectively referred to as "Vw," the state quantity calculation unit 43 may calculate the actual slip ratio λa using the following equation (13): λa=(Vv-|Vw|) / Vv (13)

[0039] The reallocation unit 44 determines whether the actual slip ratio λa of each wheel exceeds the allowable slip ratio limit. If the actual slip ratio λa does not exceed the allowable slip ratio limit, the reallocation unit 44 controls the drive source 22 so that the front wheel target braking / driving force Ff and the rear wheel target braking / driving force Fr are generated unchanged at the front wheels 2F and the rear wheels 2R. If the actual slip ratio λa exceeds the allowable slip ratio limit, the reallocation unit 44 compares the actual slip ratios λa between the front wheels 2F and the rear wheels 2R. If the slip ratio of the front wheels 2F is greater than the slip ratio of the rear wheels 2R, the reallocation unit 44 determines that the front wheels 2F are slipping and corrects the allocation ratio of the target braking / driving forces Ff and Fr so that a portion of the target driving force allocated to the front wheels 2F is reallocated to the rear wheels 2R (so that the front wheel target braking / driving force Ff decreases and the rear wheel target braking / driving force Fr increases). If the slip ratio of the rear wheels 2R is greater than the slip ratio of the front wheels 2F, it is determined that the rear wheels 2R are slipping, and the allocation ratio of the target braking / driving forces Ff and Fr is corrected so that part of the target driving force allocated to the rear wheels 2R is reallocated to the front wheels 2F (so that the front wheel target braking / driving force Ff increases and the rear wheel target braking / driving force Fr decreases). The reallocation unit 44 controls the drive source 22 so that the corrected target braking / driving forces Ff and Fr are generated at the front wheels 2F and rear wheels 2R.

[0040] 8 is a flowchart of an example of the driving assistance method of the first embodiment. In step S1, the chassis controller 18 and the drive source controller 20 read necessary parameters such as the steering angle δs and the wheel speed Vw. In step S2, the chassis controller 18 determines whether the vehicle 1 is turning. If the vehicle 1 is not turning (step S2: N), the process returns to step S1. If the vehicle 1 is turning (step S2: Y), the process proceeds to step S3. In step S3, the target behavior calculation unit 31 calculates the target vehicle body slip angle βt. In step S4, the target braking / driving force correction value calculation unit 32 estimates the actual vehicle body slip angle βa. In step S5, the target braking / driving force correction value calculation unit 32 calculates the target braking / driving force correction values ​​ΔFf and ΔFr based on the slip angle difference Δβ.

[0041] In step S6, the allowable limit setting unit 42 sets a basic allowable limit. In step S7, the target braking / driving force correction value calculation unit 32 calculates the slip ratio correction value Δλ. In step S8, the allowable limit setting unit 42 corrects the basic allowable limit with the slip ratio correction value Δλ to calculate the allowable slip ratio limit. In step S9, the state quantity calculation unit 43 calculates the actual slip ratio λa of each wheel. In step S10, the reallocation unit 44 determines whether the actual slip ratio λa is less than the allowable slip ratio limit. If the actual slip ratio λa is equal to or greater than the allowable slip ratio limit (step S10: N), the process proceeds to step S12. If the actual slip ratio λa is less than the allowable slip ratio limit (step S10: Y), the process proceeds to step S11.

[0042] In step S11, the front and rear wheel target driving force calculation unit 41 calculates the front wheel target driving force Ff and the rear wheel target driving force Fr by correcting the distribution ratio of the target driving force of the front wheels 2F and the rear wheels 2R using only the target driving force correction values ​​ΔFf and ΔFr. The process then proceeds to step S15. In step S12, the reallocation unit 44 determines whether the actual slip ratio of the rear wheels is greater than the actual slip ratio of the front wheels. If the actual slip ratio of the rear wheels is greater than the actual slip ratio of the front wheels (step S12: Y), the process proceeds to step S13. If the actual slip ratio of the rear wheels is equal to or less than the actual slip ratio of the front wheels (step S12: N), the process proceeds to step S14. In step S13, the reallocation unit 44 corrects the distribution ratio of the target driving force Ff and Fr so that a portion of the target driving force distributed to the rear wheels 2R is reallocated to the front wheels 2F. The process then proceeds to step S15. In step S14, the reallocation unit 44 corrects the allocation ratio of the target braking / driving forces Ff and Fr so that a portion of the target driving force allocated to the front wheels 2F is reallocated to the rear wheels 2R. Then, the process proceeds to step S15. In step S15, the driving source 22 generates the target braking / driving forces Ff and Fr on the front wheels 2F and the rear wheels 2R, respectively.

[0043] (Modifications) (1) In the above embodiment, an example was described in which the vehicle body slip angle was controlled as the slip angle. However, the present invention may also be applied to a case in which the tire slip angle is controlled as the slip angle. Understeer can be suppressed by controlling the tire slip angle of the front wheels 2F, and oversteer can be suppressed by controlling the tire slip angle of the rear wheels 2R. This is similar to the second and third embodiments. (2) In the above embodiment, an example was described in which the present invention is applied to the braking / driving force distribution generated by the drive source 22 to the front wheels 2F and the rear wheels 2R. However, the present invention may also be applied to the braking force distribution generated by the brake device 21 to the front wheels 2F and the rear wheels 2R. This is similar to the second and third embodiments. (3) The magnitude of the slip ratio correction value Δλ may be changed depending on the response characteristics of the vehicle 1 in response to the driver's driving operation. For example, in a sport mode with high response characteristics, handling stability is emphasized over stability, and the magnitude of the slip ratio correction value Δλ may be larger than in an eco mode with gentler response characteristics.

[0044] Second Embodiment In the second embodiment, the braking / driving force between the front wheels 2F and the rear wheels 2R is controlled so that the wheel speed difference between the front wheels 2F and the rear wheels 2R, which is a "tire state quantity," does not exceed the allowable wheel speed difference limit. FIG. 9 is a flowchart of an example of a driving assistance method according to the second embodiment. The processing of steps S21 to S25 is the same as the processing of steps S1 to S5 in FIG. 8. In step S26, the allowable limit setting unit 42 sets a basic allowable limit for the wheel speed difference. For example, the allowable limit setting unit 42 may set the wheel speed difference allowable between the front wheels 2F and the rear wheels 2R as the basic allowable limit based on a geometric linear vehicle model or the lateral acceleration Gy.

[0045] In step S27, the target driving / braking force correction value calculation unit 32 calculates the wheel speed difference correction value ΔWw. For example, the target driving / braking force correction value calculation unit 32 may calculate the wheel speed difference correction value ΔWw by multiplying the slip ratio correction value Δλ of the first embodiment by the vehicle speed Vv. In step S28, the allowable limit setting unit 42 calculates the wheel speed difference allowable limit by correcting the basic allowable limit with the wheel speed difference correction value ΔWw. In step S29, the state quantity calculation unit 43 calculates the actual wheel speed difference between the front wheels 2F and the rear wheels 2R. In step S30, the reallocation unit 44 determines whether the absolute value of the actual wheel speed difference is less than the wheel speed difference allowable limit. If the absolute value of the actual wheel speed difference is not less than the wheel speed difference allowable limit (step S30: N), the process proceeds to step S32. If the absolute value of the actual wheel speed difference is less than the wheel speed difference allowable limit (step S30: Y), the process proceeds to step S31. The process of step S31 is the same as the process of S11 in Fig. 8. Thereafter, the process proceeds to step S37.

[0046] In step S32, the reallocation unit 44 determines whether the vehicle 1 is driving. If the vehicle 1 is braking (step S32: N), the process proceeds to step S34. If the vehicle 1 is driving (step S32: Y), the process proceeds to step S33. In step S33, the reallocation unit 44 determines whether the actual wheel speed difference is greater than the wheel speed difference allowable limit. If the actual wheel speed difference is not greater than the wheel speed difference allowable limit (step S33: N), the process proceeds to step S35. If the actual wheel speed difference is greater than the wheel speed difference allowable limit (step S33: Y), the process proceeds to step S36. In step S34, the reallocation unit 44 determines whether the actual wheel speed difference is smaller than the wheel speed difference allowable limit. If the actual wheel speed difference is not smaller than the wheel speed difference allowable limit (step S34: N), the process proceeds to step S35. If the actual wheel speed difference is smaller than the allowable limit for the wheel speed difference (step S34: Y), the process proceeds to step S36. The processes of steps S35 and S36 are the same as the processes of S13 and S14 in FIG. 8. Thereafter, the process proceeds to step S37. The process of step S37 is the same as the process of S15 in FIG. 8. Note that the reallocation unit 44 may calculate both the actual slip ratio λa of the wheels and the wheel speed difference as tire state quantities. If at least one of the absolute values ​​of the actual slip ratio λa and the actual wheel speed difference exceeds the allowable limit, the target braking / driving forces Ff and Fr may be corrected.

[0047] Third Embodiment In the third embodiment, the reallocation unit 44 determines whether the tire state quantity will be equal to or less than the allowable limit when the allocation ratio of the target braking / driving forces Ff and Fr is corrected. If it is determined that the tire state quantity will not be equal to or less than the allowable limit, the sum of the target braking / driving forces Ff and Fr is reduced. FIG. 10 is a flowchart illustrating an example of a driving assistance method according to the third embodiment. The processing of steps S41 to S54 is the same as the processing of steps S1 to S14 in FIG. 8. In step S55, the reallocation unit 44 determines whether, when the allocation ratio of the target braking / driving forces Ff and Fr is corrected, the actual slip ratio λa of the wheel to which the allocation of braking / driving force is increased as a result of the correction will be equal to or less than the allowable slip ratio limit. For example, the reallocation unit 44 may estimate the actual slip ratio λa after the allocation ratio is corrected by correcting the current actual slip ratio λa with the slip ratio correction value Δλ. If the actual slip ratio λa is equal to or less than the allowable slip ratio limit (step S55: Y), the process proceeds to step S57. If the actual slip ratio λa exceeds the allowable slip ratio limit (step S55: N), the process proceeds to step S56.

[0048] In step S56, the reallocation unit 44 re-corrects the target braking / driving forces Ff and Fr so as to reduce the sum of the target braking / driving forces Ff and Fr while maintaining the allocation ratio of the target braking / driving forces Ff and Fr calculated by the front and rear wheel target driving force calculation unit 41. For example, the reallocation unit 44 uses the target braking / driving forces Ff and Fr calculated by the front and rear wheel target driving force calculation unit 41 and the target braking / driving force correction values ​​ΔFf and ΔFr to calculate corrected target braking / driving forces Ffr when the target braking / driving force of the front wheels 2F is corrected without changing the target braking / driving force of the rear wheels 2R, and corrected target braking / driving forces Frr when the target braking / driving force of the rear wheels 2R is corrected without changing the target braking / driving force of the front wheels 2F, using the target braking / driving forces Ff and Fr calculated by the front and rear wheel target driving force calculation unit 41 and the target braking / driving force correction values ​​ΔFf and ΔFr, according to the following equations (14) and (15): Ffr = Ff × (Fr + ΔFr) / (Ff + ΔFf) (14) Frr = Fr × (Ff + ΔFf) / (Fr + ΔFr) (15) If (Ffr + Fr) is smaller than (Ff + Frr), the reallocation unit 44 corrects the target braking / driving force Ff of the front wheels 2F to the value Ffr. If (Ffr + Fr) is greater than (Ff + Frr), the reallocation unit 44 corrects the target braking / driving force Fr of the rear wheels 2R to the value Frr. This allows the target braking / driving forces to be corrected so that the braking / driving force of one of the front wheels 2F and rear wheels 2R whose slip ratio exceeds the allowable slip ratio limit is reduced while maintaining the distribution ratio of the target braking / driving forces Ff and Fr calculated by the front / rear wheel target driving force calculation unit 41. Then, the process proceeds to step S57. The process of step S57 is the same as the process of S15 in FIG. 8.

[0049] (Modification) In step S55, the reallocation unit 44 may determine whether the resultant force of the longitudinal force and lateral force acting on the vehicle 1 exceeds the tire friction limit. For example, when the variable κ in the following equation (16) is less than 1, the reallocation unit 44 may determine that the resultant force of the longitudinal force and lateral force acting on the vehicle 1 exceeds the tire friction limit. In the following equation (16), Xg and Yg are the longitudinal acceleration and lateral acceleration detected by the acceleration sensor 13, Xoff and Yoff are predetermined margins, Fx is the target longitudinal force (Ff+Fr), and Fy is the target lateral force m×Vv×(γ+dβa / dt). The yaw rate γ may be the value detected by the yaw rate sensor 12, and the differential value dβa / dt may be obtained by differentiating the actual vehicle body slip angle βa.

[0050]

[0051] When the variable κ is less than 1, the reallocation unit 44 may correct the target braking / driving forces Ff and Fr calculated by the front and rear wheel target driving force calculation unit 41 by multiplying the target braking / driving forces Ff and Fr by the variable κ.

[0052] (Effects of the embodiment) (1) In the driving assistance method, a target yaw rate is calculated from the vehicle speed and steering angle of the vehicle, a target lateral position a forward gaze distance ahead is determined based on the target yaw rate, a target slip angle for orienting the vehicle body toward the target lateral position is calculated, target braking / driving forces for the front wheels and rear wheels are calculated according to the target slip angle, at least one of the wheel slip rate or the wheel speed difference between the front wheels and rear wheels is calculated as a tire state quantity, and if the calculated tire state quantity does not exceed a predetermined allowable limit, the target braking / driving forces are generated at the front wheels and rear wheels, and if the calculated tire state quantity exceeds the predetermined allowable limit, the target braking / driving forces for the front wheels and / or rear wheels are corrected so that the tire state quantity is equal to or less than the predetermined allowable limit, and the corrected target braking / driving forces are generated at the front wheels and rear wheels, and if the vehicle is turning, the correction of the target braking / driving forces is suppressed. This makes it possible to prevent the control of the target braking / driving force for achieving the target slip angle from being limited by the tire state quantities, thereby improving the balance between the slip angle that achieves favorable handling performance and the tire state quantities that ensure stability.

[0053] (2) When the vehicle is turning, the predetermined allowable limit may be set to the tire state quantity when the target braking / driving force for achieving the target slip angle is generated, thereby suppressing correction of the target braking / driving force. This makes it possible to prevent control of the target braking / driving force for achieving the target slip angle from being limited by the tire state quantity. (3) The set allowable limit for the slip ratio of the front wheels may be set smaller during braking than during driving, and the set allowable limit for the slip ratio of the rear wheels may be set larger during braking than during driving. This makes it possible to reflect changes in load on the front and rear wheels during acceleration and deceleration.

[0054] (4) Both the wheel slip ratio and the wheel speed difference between the front and rear wheels may be calculated as tire state quantities, and the target braking / driving force may be corrected when at least one of the calculated slip ratio or wheel speed difference exceeds a set allowable limit. This makes it possible to improve stability even in situations where the slip ratio estimation accuracy is reduced. (5) The target slip angle may be a target value for the vehicle body slip angle or a target value for the tire slip angle of the vehicle's wheels. Using the vehicle body slip angle as the target slip angle makes it possible to control the orientation of the vehicle body during cornering, thereby preventing the driver's line of sight from deviating from the target driving line. Using the tire slip angle as the target slip angle makes it possible to suppress oversteer and understeer.

[0055] (6) When a tire state quantity exceeds an allowable limit, the distribution ratio of the target braking / driving forces may be corrected to determine whether the tire state quantity will be equal to or less than the allowable limit. If it is determined that the tire state quantity will not be equal to or less than the allowable limit, the target braking / driving forces may be corrected so that the sum of the target braking / driving forces of the front and rear wheels is reduced while maintaining the distribution ratio of the target braking / driving forces between the front and rear wheels. Also, if it is determined that the tire state quantity will not be equal to or less than the allowable limit, the target braking / driving forces may be corrected so that the braking / driving force of one of the front and rear wheels whose slip ratio exceeds the allowable limit is reduced. This makes it possible to prevent the tire state quantity from exceeding the allowable limit. (7) When a tire state quantity exceeds an allowable limit, it may be determined whether the resultant force of the longitudinal force and the lateral force acting on the vehicle exceeds the friction limit of the tire. If it is determined that the resultant force exceeds the friction limit, the target braking / driving forces may be corrected so that the sum of the target braking / driving forces of the front and rear wheels is reduced while maintaining the distribution ratio of the target braking / driving forces between the front and rear wheels. This makes it possible to prevent the tire state quantity from exceeding the allowable limit even in a situation where the slip ratio estimation accuracy is reduced.

[0056] 1...vehicle, 10...driving assistance device, 11...steering angle sensor, 12...yaw rate sensor, 13...acceleration sensor, 14...drive mode switch, 15...brake sensor, 16...wheel speed sensor, 17...accelerator opening sensor, 18...chassis controller, 19...brake controller, 20...drive source controller, 21...braking device, 22...drive source

Claims

1. Calculate a target yaw rate from the vehicle speed and steering angle of the vehicle, determine a target lateral position ahead by a forward gaze distance based on the target yaw rate, calculate a target slip angle for the vehicle body to face the target lateral position, calculate target driving and braking forces for the front and rear wheels according to the target slip angle, calculate at least one of the slip ratio of the wheels or the wheel speed difference between the front and rear wheels as a tire state quantity, when the calculated tire state quantity does not exceed a predetermined allowable limit, generate the target driving and braking forces for the front and rear wheels, when the calculated tire state quantity exceeds the predetermined allowable limit, correct the target braking force of the front and / or rear wheels so that the tire state quantity becomes equal to or less than the predetermined allowable limit, and generate the corrected target driving and braking forces for the front and rear wheels, and when the vehicle is turning, suppress the correction of the target driving and braking forces. A driving assistance method characterized by the above.

2. When the calculated tire state quantity exceeds the predetermined allowable limit, correct the distribution ratio of the target driving and braking forces between the front and rear wheels or the total of the target driving and braking forces of the front and rear wheels, and generate the corrected target driving and braking forces for the front and rear wheels. The driving assistance method according to claim 1, characterized by the above.

3. When the vehicle is turning, suppress the correction of the target driving and braking forces due to the calculated tire state quantity exceeding the predetermined allowable limit. The driving assistance method according to claim 1 or 2, characterized by the above.

4. When the vehicle is turning, suppress the correction of the target driving and braking forces by setting the predetermined allowable limit to the tire state quantity when the target driving and braking forces for realizing the target slip angle are generated. The driving assistance method according to any one of claims 1 to 3, characterized by the above.

5. Set the predetermined allowable limit of the slip ratio of the front wheels to be smaller during braking than during driving, and set the predetermined allowable limit of the slip ratio of the rear wheels to be larger during braking than during driving. The driving assistance method according to claim 4, characterized by the above.

6. Calculate both the slip ratio of the wheels and the wheel speed difference between the front and rear wheels as the tire state quantity, and correct the target driving and braking forces when at least one of the calculated slip ratio or the wheel speed difference exceeds the predetermined allowable limit. The driving assistance method according to any one of claims 1 to 5, characterized by the above.

7. The driving assistance method according to any one of claims 1 to 6, characterized in that the target slip angle is a target value of the vehicle body slip angle of the vehicle body or a target value of the tire slip angle of the wheels of the vehicle.

8. When the tire state quantity exceeds the allowable limit, by correcting the distribution ratio of the target control driving force, it is determined whether the tire state quantity becomes equal to or less than the allowable limit. When it is determined that the tire state quantity does not become equal to or less than the allowable limit, the target control driving force is corrected so that the total of the target control driving forces of the front wheels and the rear wheels decreases while maintaining the distribution ratio of the target control driving forces between the front wheels and the rear wheels. The driving assistance method according to any one of claims 1 to 7, characterized by this.

9. When the tire state quantity exceeds the allowable limit, by correcting the distribution ratio of the target control driving force, it is determined whether the tire state quantity becomes equal to or less than the allowable limit. When it is determined that the tire state quantity does not become equal to or less than the allowable limit, the target control driving force is corrected so that the control driving force of one of the front and rear wheels whose slip ratio exceeds the allowable limit decreases. The driving assistance method according to any one of claims 1 to 7, characterized by this.

10. When the tire state quantity exceeds the allowable limit, it is determined whether the resultant force of the longitudinal force and the lateral force acting on the vehicle exceeds the friction limit of the tire. When it is determined that the resultant force exceeds the friction limit, the target control driving force is corrected so that the total of the target control driving forces of the front wheels and the rear wheels decreases while maintaining the distribution ratio of the target control driving forces between the front wheels and the rear wheels. The driving assistance method according to any one of claims 1 to 7, characterized by this.

11. A traveling support device comprising: a controller that sets a target driving force; and a driving force source or a braking device that generates the target driving force in the front wheels and the rear wheels, wherein the controller calculates a target yaw rate from the vehicle speed and the steering angle of the vehicle, determines a target lateral position in front by a forward viewing distance based on the target yaw rate, calculates a target slip angle for the vehicle body to face the target lateral position, calculates the target driving force of the front wheels and the rear wheels according to the target slip angle, calculates at least one of the slip ratio of the wheels or the wheel speed difference between the front wheels and the rear wheels as a tire state quantity, generates the target driving force in the driving force source or the braking device when the calculated tire state quantity does not exceed a predetermined allowable limit, corrects the target braking force of the front wheels and / or the rear wheels so that the tire state quantity becomes equal to or less than the predetermined allowable limit when the calculated tire state quantity exceeds the predetermined allowable limit, and generates the corrected target driving force in the driving force source or the braking device, and suppresses the correction of the target driving force when the vehicle is turning.

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