JP5192317B2 - Vehicle motion control apparatus and vehicle motion control method - Google Patents

Description

  The present invention relates to a vehicle motion control device and a vehicle motion control method for controlling the motion of a vehicle during turning.

  In general, when the steering wheel is steered by the driver while the vehicle is traveling, the turning angle of the steered wheel (also referred to as “tire cut angle”) is adjusted to an angle corresponding to the steering angle of the steering wheel. And a vehicle turns using the cornering force (force to the direction orthogonal to the advancing direction of a vehicle) according to the turning angle of the steered wheel. The following relationship exists between the cornering force that acts when turning the vehicle and the turning angle of the steered wheels. That is, as shown in FIG. 9, when the turning angle σ of the steered wheels is relatively small, the cornering force F gradually increases as the turning angle σ increases, and the turning angle σ becomes the road surface limit rudder. When the angle σmax is reached, the cornering force F is the largest value. When the turning angle σ is larger than the road surface limit steering angle σmax, the tire slip angle (angle difference between the tire direction and the tire traveling direction) may increase as the turning angle σ increases. The cornering force F gradually decreases.

  By the way, when the vehicle turns while the steering angle of the steering wheel steered by the driver is large, the turning angle σ of the steered wheels may be larger than the road surface limit steering angle σmax. In this case, there is a possibility that the cornering force F becomes small and an understeer state occurs. Therefore, for example, a motion control device described in Patent Document 1 has been proposed as a motion control device for eliminating an understeer state that has occurred during vehicle turning.

  In the motion control device described in Patent Document 1, when the vehicle is in an understeer state during turning, the turning angle σ of the steered wheels is reduced to the road surface limit rudder angle σmax, and then the turning angle σ is reduced to the road surface limit. A steering angle adjustment control for maintaining the steering angle σmax is executed. That is, the turning angle σ of the steered wheels is adjusted so that the cornering force F is maintained at the maximum value. When the cornering force F is increased by executing the turning angle adjustment control, the understeer state is eliminated.

However, particularly when turning on a road surface with a low μ value, the cornering force F cannot be sufficiently increased only by the turning angle adjustment control, and the understeer state may not be eliminated. In such a case, the motion control device executes deceleration control for reducing the vehicle body speed of the vehicle regardless of the driver's will while performing the turning angle adjustment control. When this deceleration control is executed, the centrifugal force applied to the vehicle gradually decreases. Thus, when the centrifugal force applied to the vehicle is reduced, the understeer state is eliminated.
Japanese Patent No. 3175369

  By the way, when the vehicle turns, the frictional resistance between the tire mounted on the steered wheel and the road surface (hereinafter referred to as “road-tire resistance”) is delicate according to the change in the steered wheel turning angle σ. To change. Advanced drivers, who are good at driving, steer the steering wheel while sensing the subtle changes in road-to-tire resistance when turning the vehicle, and adjust the turning angle of the steered wheels appropriately. However, in a vehicle equipped with the motion control device, when it is determined that the vehicle is understeered based on input signals from various sensors mounted on the vehicle, the turning angle is maintained in order to maintain the cornering force F at the maximum value. Adjustment control is executed. Therefore, in an understeer state, the turning angle σ of the steered wheel does not change according to steering of the steering wheel by the driver, and the steered wheel σ does not change following the steering of the steering wheel. There was a risk of discomfort for advanced drivers.

  Further, when the deceleration control is executed to cancel the understeer state of the vehicle, the vehicle body speed immediately after the cancellation of the understeer state becomes slower than when the deceleration control is not executed. As a result, the driver may feel uncomfortable that the recovery of the vehicle body speed is slow after the understeer state is resolved. Furthermore, depending on the condition of the road surface to turn (such as the μ value of the road surface), the cornering force F may be increased or the centrifugal force applied to the vehicle may be decreased even when the above-described turning angle adjustment control or deceleration control is performed. It took a long time to finish, and as a result, it sometimes took time to eliminate the understeer state.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a vehicle that can assist in quickly eliminating an understeer state during turning of the vehicle without causing the driver to feel uncomfortable. A motion control device and a motion control method for a vehicle are provided.

  In order to achieve the above object, the invention according to claim 1 according to a vehicle motion control device is characterized in that a turning angle adjustment capable of adjusting a turning angle (σ) of a turning wheel (FR, FL, RR, RL). A vehicle motion control device (22, 25, 30, 37) for controlling the motion of a vehicle having a mechanism (15) when turning, wherein the steered angle (FR, FL, RR, RL) of the steered wheels (FR, FL, RR, RL) Steering angle calculation means (37, S12) for calculating σ), and the wheel speed of the steered wheels (FR, FL, RR, RL) when the vehicle is turning understeering when the vehicle is turning. The operation determination means (37, S22, S24) for determining whether or not the driver is performing an operation for adjusting (VWF), and the operation determination means (when the turning state of the vehicle is an understeer state) 37, S22, S24) When it is determined that the driver is performing an operation for adjusting the wheel speed (VWF) of the steered wheels (FR, FL, RR, RL), the steered wheels (FR, FL, RR, RL) ) Of the turning angle (σ) is temporarily reduced, and then the turning is performed to adjust the turning angle (σ) of the steered wheels (FR, FL, RR, RL) to the original direction. And a control means (30, 37, S25) for executing grip force recovery control for controlling the angle adjusting mechanism (15).

  According to the above configuration, when the driver is performing an operation for adjusting the wheel speed of the steered wheels in an understeer state during turning of the vehicle, grip force recovery control is executed. Then, during the adjustment of the wheel speed of the steered wheel, the absolute value of the steered angle of the steered wheel temporarily decreases. As a result, when the cornering force is increased, the grip force with respect to the road surface of the tire mounted on the steered wheel is recovered, and the understeer state is eliminated. In this state, the turning angle of the steered wheels is adjusted toward the original angle, and as a result, the vehicle turns in a turning manner corresponding to the steering degree of the driver's steering wheel. In addition, when the understeer state occurs, deceleration control that reduces the centrifugal force applied to the vehicle is not executed. Therefore, the vehicle body speed can be quickly recovered after the understeer state is resolved. Therefore, it is possible to assist in quickly eliminating the understeer state during turning of the vehicle without causing the driver to feel uncomfortable when turning the vehicle.

  According to a second aspect of the present invention, in the vehicle motion control apparatus according to the first aspect of the present invention, the control means (30, 37, S25) is configured such that when the turning state of the vehicle is an understeer state, the steered wheel ( When the wheel speed (VWF) of the steered wheels (FR, FL, RR, RL) starts to change due to the operation by the driver for adjusting the wheel speed (VWF) of FR, FL, RR, RL) The gist is to start the grip force recovery control.

  According to the above configuration, the grip force recovery control is executed when the wheel speed of the steered wheels actually starts to change due to an operation by the driver for adjusting the wheel speed of the steered wheels. Therefore, it becomes possible to quickly eliminate understeer during turning of the vehicle by cooperation of the driver's operation for adjusting the wheel speed of the steered wheels and the grip force recovery control.

  According to a third aspect of the present invention, in the vehicle motion control apparatus according to the first or second aspect, the rotational state estimating means (37) for estimating the rotational state of the steered wheels (FR, FL, RR, RL). , S19), and the operation determining means (37, S22, S24) is in a rotational state of the steered wheels (FR, FL, RR, RL) estimated by the rotational state estimating means (37, S19). The gist is to determine whether the driver is performing a corresponding operation.

  According to the above configuration, the grip force recovery control is executed when the driver performs an appropriate operation corresponding to the rotation state of the steered wheels when the turning state of the vehicle is an understeer state. In other words, it is possible to determine whether or not the vehicle is in a state in which understeer during vehicle turning can be quickly eliminated by the cooperation of the driver's operation for adjusting the wheel speed of the steered wheels and the grip force recovery control. .

  According to a fourth aspect of the present invention, in the vehicle motion control apparatus according to the third aspect, the rotational state estimating means (37, S19) for estimating the rotational state of the steered wheels (FR, FL, RR, RL) is provided. Further, the control means (30, 37, S25) is configured such that the turning state of the vehicle is understeered and the steered wheels (FR, FL, RR, RL) are controlled by the rotation state estimating means (37, S19). When it is estimated that there is a tendency to lock, the driver performs an operation for increasing the wheel speed (VWF) of the steered wheels (FR, FL, RR, RL) by the operation determining means (37, S22, S24). The gist of the present invention is to execute the grip force recovery control when it is determined that the movement is performed.

  According to the above configuration, when the steered wheel tends to lock when an understeer condition occurs, the driver is performing an operation to increase the wheel speed of the steered wheel to eliminate the lock tendency of the steered wheel In addition, the grip force recovery control is executed. As a result, the grip force with respect to the road surface of the tire mounted on the steered wheel is quickly recovered. Therefore, the understeer state caused by the steered wheels tending to be locked is quickly eliminated.

  According to a fifth aspect of the present invention, in the vehicle motion control apparatus according to the third aspect, the rotational state estimating means (37, S19) for estimating the rotational state of the steered wheels (FR, FL, RR, RL) is provided. Further, the control means (30, 37, S25) is configured such that the turning state of the vehicle is understeered and the steered wheels (FR, FL, RR, RL) are controlled by the rotation state estimating means (37, S19). When it is estimated that the vehicle has a tendency to spin, the operation determination means (37, S22, S24) performs an operation for slowing down the wheel speed (VWF) of the steered wheels (FR, FL, RR, RL). The gist of the present invention is to execute the grip force recovery control when it is determined that the movement is performed.

  According to the above configuration, when the steered wheel is in a spin tendency (i.e., idling tendency) when an understeer occurs, an operation is performed to slow down the wheel speed of the steered wheel and eliminate the spin tendency of the steered wheel. Grip force recovery control is executed when the hand is moving. As a result, the grip force with respect to the road surface of the tire mounted on the steered wheel is quickly recovered. Therefore, the understeer state caused by the steered wheels having a spin tendency is quickly eliminated.

  According to a sixth aspect of the present invention, in the vehicle motion control apparatus according to any one of the first to fifth aspects, the turning of the steered wheels (FR, FL, RR, RL) that is a road surface limit. Limit steering angle calculation means (37, S18) for calculating the steering angle (σ) as the road surface limit steering angle (σmax), and the steered wheels (FR, FL, RR, RL) at the end of the grip force recovery control. Estimated turning angle calculation means (37, S41) for calculating the turning angle as an estimated turning angle (σest), and estimated turning angle (σest) calculated by the estimated turning angle calculation means (37, S41) Is equal to or smaller than the absolute value of the road surface limit steering angle (σmax) calculated by the limit steering angle calculation means (37, S18), the estimated turning angle (σest) is set to the turning angle at the end of control. While (σend) is set, the estimated turning angle (σ When the absolute value of est) is larger than the absolute value of the road surface limit steering angle (σmax), the road surface steering angle (σmax) is set as the steering angle at the end of control (σend). Setting means (37, S44, S45), and the control means (30, 37, S25) is configured to turn the steered wheels (FR, FL, RR, RL) at the end of the grip force recovery control. The turning angle adjusting mechanism (15) is such that the turning angle (σ) is equal to or less than the turning angle (σend) at the end of control set by the turning angle setting means (37, S44, S45) at the end of control. ) Is controlled.

  According to the above configuration, the turning angle at the end of control of the steered wheels at the end of the grip force recovery control is adjusted so that the absolute value thereof does not become larger than the absolute value of the road surface limit rudder angle. Therefore, the understeer state is again prevented from turning again after the grip force recovery control is finished.

  A seventh aspect of the present invention is the vehicle motion control apparatus according to any one of the first to fifth aspects, wherein the steered wheels (FR, FL, RR, RL) that are road surface limits are turned. Limit steering angle calculation means (37, S18) for calculating the steering angle (σ) as the road surface limit steering angle (σmax) is further provided, and the control means (30, 37, S25) is configured to execute the grip force recovery control. The turning angle (σ) of the steered wheels (FR, FL, RR, RL) is the road surface limit rudder angle (σmax) whose absolute value is temporarily calculated by the limit rudder angle calculating means (37, S18). ), The turning angle adjusting mechanism (15) is controlled so as to be adjusted in the returning direction. The “road surface limit rudder angle” refers to the steered angle of the steered wheels that maximizes the cornering force.

  According to the above configuration, the grip force recovery control is executed together with the operation for adjusting the wheel speed of the steered wheels by the driver, so that the absolute value of the steered wheel steer angle is temporarily the road surface limit steer angle. It is adjusted to be less than the absolute value of. Therefore, there is a moment when the cornering force increases to the vicinity of the maximum value during turning of the vehicle, and the understeer state is preferably eliminated.

  The invention according to claim 8 is the vehicle motion control apparatus according to claim 7, wherein the turning angle of the steered wheels (FR, FL, RR, RL) at the end of the grip force recovery control is estimated. The absolute value of the estimated turning angle (σest) calculated by the estimated turning angle calculating means (37, S41) calculated as the steering angle (σest) and the estimated turning angle calculating means (37, S41) is the limit. When it is less than the absolute value of the road surface limit steering angle (σmax) calculated by the steering angle calculation means (37, S18), the estimated turning angle (σest) is set as the turning angle at the end of control (σend). On the other hand, when the absolute value of the estimated turning angle (σest) is larger than the absolute value of the road surface limit steering angle (σmax), the road surface limit steering angle (σmax) is set as the turning angle at the end of control (σend). Turning angle setting means at the end of control to be set 37, S44, S45), and the control means (30, 37, S25) includes a turning angle (FR, FL, RR, RL) of the steered wheels (FR, FL, RR, RL) at the end of the grip force recovery control. The turning angle adjusting mechanism (15) is controlled such that σ) is equal to or less than the turning angle (σend) at the end of control set by the turning angle setting means (37, S44, S45) at the end of control. The gist is to do.

  According to the above configuration, the turning angle at the end of control of the steered wheels at the end of the grip force recovery control is adjusted so that the absolute value thereof does not become larger than the absolute value of the road surface limit rudder angle. Therefore, the understeer state is again prevented from turning again after the grip force recovery control is finished.

  According to a ninth aspect of the present invention, in the vehicle motion control apparatus according to any one of the first to fifth, seventh and eighth aspects, the steering amount of the vehicle steering (26) is adjusted. First yaw rate calculating means (37, S15) for calculating the corresponding target yaw rate (Yst), second yaw rate calculating means (37, S14) for calculating the actual yaw rate (Y) of the vehicle, and each yaw rate calculating means Difference calculating means (37, S20) for calculating a yaw rate deviation (Ysub) that is a difference between the yaw rates (Y, Yst) calculated by (37, S15, S14), and the control means (30, S20). 37, S25) is a turning angle of the steered wheels (FR, FL, RR, RL) at the time when the turning state of the vehicle becomes an understeer state when the grip force recovery control is executed. The difference in angle (Δσ) between σ) and the minimum turning angle (σmin) at which the absolute value becomes the smallest during execution of the grip force recovery control is calculated by the yaw rate deviation (37, S20) The gist is to control the turning angle adjusting mechanism (15) so that the larger Ysub) is, the larger it is.

  In general, it is estimated that the greater the yaw rate deviation, which is the difference between the target yaw rate and the actual yaw rate, the greater the difference between the turning angle of the steered wheels and the road surface limit rudder angle. Therefore, in the present invention, the turning angle adjustment mechanism is such that the angle difference between the turning angle at the time of the understeer state and the minimum turning angle when the grip force recovery control is executed becomes larger as the yaw rate deviation increases. Operates. Therefore, the grip force recovery control is executed together with the operation for adjusting the wheel speed of the steered wheels by the driver, thereby creating a moment when the cornering force increases regardless of the magnitude of the yaw rate deviation, and the understeer state Is surely resolved.

  A tenth aspect of the present invention is the vehicle motion control apparatus according to any one of the seventh to ninth aspects, wherein the control means (30, 37, S25) performs the grip force recovery control. As a result, the direction of the steered wheels (FR, FL, RR, RL) is different from the direction of the steered wheels (FR, FL, RR, RL) when the turning state of the vehicle is understeered. The gist of the invention is to control the turning angle adjusting mechanism (15) so as to be regulated.

According to the above configuration, it is avoided that the direction of the steered wheels is opposite to the direction in which the vehicle is desired to turn due to the execution of the grip force recovery control.
An eleventh aspect of the present invention is the vehicle motion control apparatus according to any one of the first to sixth aspects, wherein the control means (30, 37, S25) performs the grip force recovery control. At the time of execution, the turning angle (σ) of the steered wheels (FR, FL, RR, RL) is temporarily reduced until the vehicle has an angle that shows a straight traveling tendency, and then adjusted to the original direction. Therefore, the gist is to control the turning angle adjusting mechanism (15).

  According to the above configuration, the turning angle of the steered wheels is temporarily set to an angle at which the vehicle shows a straight traveling tendency by executing the grip force recovery control. As a result, the grip force with respect to the road surface of the tire mounted on the steered wheels is recovered with good response, and the understeer state is satisfactorily eliminated.

  On the other hand, the invention according to claim 12 according to the vehicle motion control method includes a turning angle calculation step (S12) for calculating a turning angle (σ) of the turning wheels (FR, FL, RR, RL) of the vehicle. An operation for determining whether or not the driver is performing an operation for adjusting the wheel speed (VWF) of the steered wheels (FR, FL, RR, RL) when the turning state of the vehicle is an understeer state. When the determination step (S22, S24) and the turning state of the vehicle are understeered, the wheel speed (VWF) of the steered wheels (FR, FL, RR, RL) in the operation determination step (S22, S24). When it is determined that the driver is performing an operation for adjusting the turning angle (σ) of the steered wheels (FR, FL, RR, RL) temporarily, Steering wheel (FR, FL , RR, RL) and a recovery control step (S25) for executing grip force recovery control for adjusting the turning angle (σ) to the original direction.

  According to the said structure, the effect equivalent to the invention of Claim 1 can be acquired.

(First embodiment)
Hereinafter, a first embodiment of a vehicle motion control device and a vehicle motion control method according to the present invention will be described with reference to FIGS. In the following description of the present specification, the traveling direction (forward direction) of the vehicle is assumed to be the front (front of the vehicle). Unless otherwise specified, the left-right direction in the following description is the same as the left-right direction in the vehicle traveling direction.

  As shown in FIG. 1, the vehicle according to the present embodiment includes a plurality of (four in the present embodiment) wheels (right front wheel FR, left front wheel FL, right rear wheel RR, and left rear wheel RL). This is a so-called front wheel drive vehicle in which FL functions as a drive wheel and rear wheels RR and RL function as driven wheels. In such a vehicle, a driving force generator 13 having an engine 12 capable of generating a driving force corresponding to the amount of depression of the accelerator pedal 11 by the driver, and the driving force generated by the driving force generator 13 are transmitted to the front wheels FR, And a driving force transmission device 14 for transmission to the FL. Further, the vehicle has a front wheel steering device 15 as a turning angle adjusting mechanism for turning the front wheels FR and FL as steered wheels (also referred to as “steering wheels”), and the driver depresses the brake pedal 16. A braking device 17 is provided that can apply a braking force corresponding to the operation amount to each of the wheels FR, FL, RR, and RL.

  As shown in FIGS. 1 and 2, the driving force generator 13 is disposed in the intake pipe 18 extending from the engine 12 to the outside, and the opening cross-sectional area thereof is variable. A throttle valve 19 and a throttle valve actuator 20 (for example, a DC motor) disposed outside the intake pipe 18 and adjusting the opening of the throttle valve 19 are provided. A fuel injection device 21 having an injector for injecting fuel is provided in the vicinity of an intake port (not shown) of the engine 12. Further, the driving force generation device 13 is provided with an engine ECU 22 (also referred to as “engine electronic control device”) having a CPU, a ROM, a RAM, and the like (not shown). The engine ECU 22 is electrically connected to an accelerator opening sensor SE1 that is disposed in the vicinity of the accelerator pedal 11 and that detects the amount of depression of the accelerator pedal 11 by the driver, that is, the accelerator opening. The engine ECU 22 calculates the accelerator opening based on the detection signal from the accelerator opening sensor SE1, and controls the engine 12, the throttle valve actuator 20, and the fuel injection device 21 based on the calculated accelerator opening.

  The driving force transmission device 14 includes a transmission 23 connected to the output shaft of the engine 12 and a front wheel differential gear 24 that appropriately distributes the driving force transmitted from the transmission 23 and transmits it to the front wheels FL and FR. Yes. The driving force transmission device 14 is provided with an AT ECU 25 (also referred to as “AT electronic control device”) having a CPU, a ROM, a RAM, and the like (not shown). The AT ECU 25 controls the transmission 23 and the front wheel differential gear 24 in accordance with the vehicle body speed of the vehicle and the operation status of the accelerator pedal 11 and the brake pedal 16 by the driver.

  The front wheel steering device 15 includes a steering wheel 26 that is steered by a driver, a steering shaft 27 to which the steering wheel 26 is fixed, and a steering actuator 28 that is coupled to the steering shaft 27. Further, the front wheel steering device 15 is provided with a link mechanism unit 29 including a tie rod that is movable in the left-right direction of the vehicle by a steering actuator 28 and a link that steers the front wheels FL and FR by the movement of the tie rod. It has been. Further, the front wheel steering device 15 is provided with a steering ECU 30 (also referred to as “steering electronic control device”) having a CPU, a ROM, a RAM, and the like (not shown), and the steering ECU 30 includes a steering wheel 26. A steering angle sensor SE2 for detecting the steering angle is electrically connected. Then, the steering ECU 30 controls the steering actuator 28 to adjust the turning angle of the front wheels FR and FL to an angle corresponding to the steering angle of the steering wheel 26.

  The braking device 17 includes a hydraulic circuit (not shown), and a braking actuator 31 having a pump and various electromagnetic valves arranged on the hydraulic circuit. Connected to the brake actuator 31 are a plurality of liquid flow paths 33a, 33b, 33c, 33d individually connected to the wheel cylinders 32a, 32b, 32c, 32d provided for the wheels FR, FL, RR, RL. Has been. That is, the brake actuator 31 can individually supply brake fluid into the wheel cylinders 32a to 32d via the liquid flow paths 33a to 33d by operation of the pump and various solenoid valves. Each wheel FR, FL, RR, RL is given a braking force according to the brake fluid pressure generated in each wheel cylinder 32a-32d.

  The braking device 17 is provided with a braking ECU 37 (also referred to as “braking electronic control device”) having a CPU 34, a ROM 35, a RAM 36, and the like. The brake ECU 37 includes a brake switch SW1, a steering angle sensor SE2, wheel speed sensors SE3, SE4, SE5, SE6 for detecting the wheel speeds of the wheels FR, FL, RR, RL, and the traveling direction of the vehicle. A front-rear G sensor SE7 for detecting the front-rear acceleration, which is the acceleration at, is electrically connected. Further, a lateral G sensor SE8 for detecting the lateral acceleration of the vehicle and a yaw rate sensor SE9 for detecting the yaw rate of the vehicle are electrically connected to the braking ECU 37. The steering angle sensor SE2, the lateral G sensor SE8, and the yaw rate sensor SE9 output detection signals corresponding to positive values when turning leftward, and output detection signals corresponding to negative values when turning rightward. . The brake ECU 37 controls the brake actuator 31 based on various detection signals from the brake switch SW1 and the various sensors SE2 to SE9.

  The ECUs 22, 25, 30, and 37 mounted on the driving force generator 13, the driving force transmission device 14, the front wheel steering device 15, and the braking device 17 have various information and various controls as shown in FIG. Each is connected via a bus 38 so that commands can be transmitted and received. The driving force generation device 13, the driving force transmission device 14, the front wheel steering device 15, and the braking device 17 are interlocked with each other so that the vehicle moves appropriately. Therefore, in the present embodiment, the ECUs 22, 25, 30, and 37 mounted on the devices 13, 14, 15, and 17 constitute a motion control device that controls the motion of the vehicle.

Next, the braking ECU 37 that functions as the main ECU among the ECUs 22, 25, 30, and 37 will be described in detail.
In the ROM 35 of the brake ECU 37, various control processes (understeer elimination process described later), various maps (such as the map shown in FIG. 3), various thresholds (such as first threshold and second threshold described later) are stored in advance. . Further, in the RAM 36 of the brake ECU 37, various information that can be appropriately rewritten while an ignition switch (not shown) of the vehicle is “ON” (longitudinal acceleration, lateral acceleration, steering angle, steering angle, actual yaw rate, which will be described later, Each target yaw rate, vehicle body speed, road surface limit steering angle, slip amount, yaw rate deviation, subtraction steering angle amount, minimum turning angle, etc.) are stored.

Next, a map stored in advance in the ROM 35 will be described with reference to FIG.
The map shown in FIG. 3 includes a yaw rate deviation Ysub that is a difference between the first target yaw rate Yst calculated based on the steering angle of the steering wheel 26 and the actual yaw rate of the vehicle (hereinafter referred to as “actual yaw rate”) Y, and the rotation. This shows the relationship with the subtraction rudder angle amount Δσ as an angle difference between the front wheels FR and FL which are steered wheels. As shown in FIG. 3, since the understeer tendency increases as the yaw rate deviation Ysub increases, the subtraction steering angle amount Δσ is set to a large value.

  Next, among various control processes executed by the braking ECU 37 of the present embodiment, an understeer elimination processing routine for eliminating an understeer state that occurs when the vehicle turns is shown in the flowchart shown in FIG. 4, the timing chart shown in FIG. This will be described based on the graph shown in FIG. FIG. 6 is a timing chart in the case where the vehicle is in an understeer state due to the front wheel FR becoming locked when the vehicle turns to the left.

  Now, the braking ECU 37 executes an understeer elimination processing routine at predetermined intervals (in this embodiment, every 10 msec. (Milliseconds)). In this understeer elimination processing routine, the braking ECU 37 calculates the longitudinal acceleration Gx of the vehicle based on the detection signal from the longitudinal G sensor SE7 (step S10), and the lateral acceleration of the vehicle based on the detection signal from the lateral G sensor SE8. Gy is calculated (step S11). Subsequently, the braking ECU 37 calculates the steering angle θ (see FIG. 6) of the steering wheel 26 based on the detection signal from the steering angle sensor SE2, and calculates the turning angle σ of the front wheels FR and FL based on the steering angle θ. (Step S12). When the steering angle θ of the steering wheel 26 is calculated, the steering actuator 28 operates so that the steering angle σ of the front wheels FR and FL becomes an angle corresponding to the steering angle θ by the steering ECU 30. That is, there is a proportional relationship between the steering angle θ and the turning angle σ. Therefore, the braking ECU 37 sets the turning angle σ by multiplying the calculated steering angle θ by a preset gain (a gear ratio n of the steering wheel 26 described later). Therefore, in the present embodiment, the brake ECU 37 functions as a turning angle calculation unit. Step S12 corresponds to a turning angle calculation step.

  Then, the braking ECU 37 calculates the wheel speed of each wheel FR, FL, RR, RL based on each detection signal from each wheel speed sensor SE3 to SE6, and uses at least one wheel speed among the wheel speeds. Then, the vehicle body speed VS (that is, the estimated vehicle body speed) of the vehicle is calculated (step S13). Subsequently, the braking ECU 37 calculates the actual yaw rate Y of the vehicle based on the detection signal from the yaw rate sensor SE9 (step S14). In this regard, in the present embodiment, the brake ECU 37 also functions as a second yaw rate calculation unit. Subsequently, the braking ECU 37 substitutes the steering angle θ of the steering wheel 26 used when calculating the turning angle σ of the front wheels FR and FL in step S12 into the following relational expression (formula 1), A target yaw rate Yst is calculated (step S15). In this regard, in the present embodiment, the brake ECU 37 also functions as the first yaw rate calculation means. Then, the brake ECU 37 substitutes the lateral acceleration Gy calculated in Step S11 into the following relational expression (Expression 2) to calculate the second target yaw rate Ygy (Step S16).

ただし、Ｙｓｔ…第１目標ヨーレート、ＶＳ…車両の車体速度、Ａ…スタビリティファクタ、θ…操舵角、ｎ…ステアリングホイールのギヤ比、Ｌ…車両のホイールベース長、Ｙｇｙ…第２目標ヨーレート、Ｇｙ…横方向加速度
続いて、制動ＥＣＵ３７は、ステップＳ１４にて演算した実ヨーレートＹがステップＳ１５にて演算した第１目標ヨーレートＹｓｔ未満であるか否かを判定する（ステップＳ１７）。なお、実ヨーレートＹが第１目標ヨーレートＹｓｔ未満となる場合とは、車両の旋回状態がアンダーステア状態であることを示す。すなわち、ステップＳ１７では、アンダーステア状態であるか否かが判定される。

However, Yst ... 1st target yaw rate, VS ... Vehicle body speed, A ... Stability factor, θ ... Steering angle, n ... Steering wheel gear ratio, L ... Vehicle wheelbase length, Ygy ... 2nd target yaw rate, Gy ... Lateral acceleration Subsequently, the braking ECU 37 determines whether or not the actual yaw rate Y calculated in step S14 is less than the first target yaw rate Yst calculated in step S15 (step S17). The case where the actual yaw rate Y is less than the first target yaw rate Yst indicates that the turning state of the vehicle is an understeer state. That is, in step S17, it is determined whether or not it is an understeer state.

  If the determination result of step S17 is negative (Y ≧ Yst), the braking ECU 37 once ends the understeer elimination processing routine. That is, as shown in the timing chart of FIG. 6, when the turning of the vehicle is started and the absolute value of the steering angle θ of the steering wheel 26 is relatively small, the turning angle σ of the front wheels FR and FL is small, The slip amount SlpF of the front wheels FR and FL becomes a value close to “0 (zero)”. Therefore, as shown in FIGS. 7A and 7B, the longitudinal frictional force MK between the tire mounted on the front wheels FR and FL and the road surface becomes a relatively large value, and the cornering force F (vehicle The force in the direction perpendicular to the traveling direction is also a relatively large value. As a result, the vehicle turns without the front wheels FR and FL, which are steered wheels, slipping, that is, without being understeered.

  Returning to the flowchart of FIG. 4, when the determination result of step S <b> 17 is affirmative (Y <Yst), the braking ECU 37 determines that the vehicle is understeered, and determines the turning angle at which the cornering force F is maximized as the road limit steering. The angle σmax is calculated (step S18). When the turning angle σ of the front wheels FR and FL becomes the road surface limit steering angle σmax, the respective target yaw rates Yst and Ygy calculated in steps S15 and S16 have the same value. Therefore, using the above relational expressions (Expression 1) and (Expression 2), the steering angle θ when the target yaw rates Yst and Ygy are the same value is calculated, and the turning angle corresponding to the steering angle θ is determined as the road surface limit. The steering angle σmax. Therefore, in this embodiment, the brake ECU 37 also functions as a limit steering angle calculation means.

  Subsequently, the brake ECU 37 calculates the slip amount SlpF of the front wheels FR and FL (step S19). The slip amount SlpF is derived by subtracting the wheel speed VWF (see FIG. 6) of the front wheels FR and FL from the vehicle body speed VS of the vehicle. Therefore, in the present embodiment, the brake ECU 37 also functions as a rotation state estimation unit that calculates the slip amount SlpF as the rotation state of the front wheels FR and FL. Then, the braking ECU 37 calculates a yaw rate deviation Ysub that is a difference between the first target yaw rate Yst calculated in step S15 and the actual yaw rate Y calculated in step S14 (step S20). In this regard, in the present embodiment, the brake ECU 37 also functions as a difference calculation unit.

  Subsequently, the braking ECU 37 determines whether or not the slip amount SlpF calculated in step S19 exceeds a preset first threshold value KSlp1 (step S21). The first threshold value KSlp1 is a determination value for determining whether or not the front wheels FR and FL are in a locking tendency, and is set in advance by experiments or simulations. If the determination result in step S21 is affirmative (SlpF> KSlp1), the braking ECU 37 determines that the front wheels FR and FL are in a locking tendency, and increases the driving force D (see FIG. 6) for the front wheels FR and FL. It is determined whether the driver is performing an accelerator operation for this purpose (step S22). Therefore, in this embodiment, the brake ECU 37 also functions as an operation determination unit. Further, step S22 is an operation determination step for determining whether or not the amount of depression of the accelerator pedal 11 by the driver has increased so as to increase (adjust) the wheel speed VWF (see FIG. 6) of the front wheels FR and FL. It corresponds to.

  When the determination result of step S22 is negative, the brake ECU 37 determines that the accelerator operation for adjusting the wheel speed VWF of the front wheels FR and FL is not performed, and temporarily terminates the understeer elimination processing routine. On the other hand, if the determination result in step S22 is affirmative, the brake ECU 37 determines that an accelerator operation for adjusting the wheel speed VWF of the front wheels FR and FL is being performed, and the process proceeds to step S25 described later. Transition.

  That is, as shown in the timing chart of FIG. 6, even if the turning state of the vehicle is an understeer state and the front wheels FR and FL tend to lock, the accelerator operation that increases the driving force D for the front wheels FR and FL. Is not performed by the driver, grip force recovery control described later is not executed (first timing t1). Thereafter, when the driving force D for the front wheels FR, FL starts to increase due to the accelerator operation by the driver when the turning state of the vehicle is an understeer state, the slip amount SlpF of the front wheels FR, FL starts to decrease (second timing) t2). Then, the locking tendency of the front wheels FR and FL starts to be resolved, and grip force recovery control described later triggered by the accelerator operation by the driver is started (third timing t3).

  On the other hand, returning to the flowchart of FIG. 4, when the determination result of step S21 is negative (SlpF ≦ KSlp1), the braking ECU 37 determines that the slip amount SlpF calculated in step S19 is less than the preset second threshold value KSlp2. It is determined whether or not there is (step S23). The second threshold value KSlp2 is a determination value for determining whether or not the front wheels FR and FL are in a spin tendency, and is set in advance by experiments or simulations. When the front wheels FR and FL show a spin tendency, the slip amount SlpF of the front wheels FR and FL is a value smaller than “0 (zero)”. If the determination result of step S23 is negative (SlpF ≧ KSlp2), the brake ECU 37 once ends the understeer elimination processing routine. On the other hand, if the determination result in step S23 is affirmative (SlpF <KSlp2), the brake ECU 37 determines that the front wheels FR and FL are in a spin tendency, and the accelerator for reducing the driving force D for the front wheels FR and FL. It is determined whether or not the driver is performing the operation (step S24). Therefore, in this embodiment, step S24 is an operation determination step for determining whether or not the amount of depression of the accelerator pedal 11 by the driver has decreased so that the wheel speed VWF of the front wheels FR and FL is slowed (adjusted). It corresponds to.

  If the determination result of step S24 is negative, the braking ECU 37 determines that the accelerator operation for adjusting the wheel speed VWF of the front wheels FR and FL is not performed, and temporarily terminates the understeer elimination processing routine. On the other hand, if the determination result in step S24 is affirmative, the brake ECU 37 determines that an accelerator operation for adjusting the wheel speed VWF of the front wheels FR and FL is being performed, and the process proceeds to step S25 described later. Transition.

  That is, when the turning state of the vehicle is an understeer state and the driver does not perform an accelerator operation that reduces the driving force D on the front wheels FR, FL even if the front wheels FR, FL are in a spin tendency. The grip force recovery control described later is not executed. Thereafter, when the driving state D of the front wheels FR and FL starts to decrease due to the accelerator operation by the driver when the turning state of the vehicle is an understeer state, the slip amount SlpF of the front wheels FR and FL starts to increase. Then, the spin tendency of the front wheels FR and FL begins to be resolved, and grip force recovery control described later triggered by the accelerator operation by the driver is started.

  In step S25, the brake ECU 37 executes a grip force recovery control process (described in detail in FIG. 5) for eliminating the understeer state. The grip force recovery control is a control executed for a predetermined time T (0.5 to 2 sec. (Seconds)) set in advance, and the absolute value of the turning angle σ of the front wheels FR and FL is temporarily set. In this control, the steering angle σ is adjusted to the original angle direction. When such grip force recovery control is executed in response to the accelerator operation by the driver according to the rotation state (lock tendency or spin tendency) of the front wheels FR and FL, the grip force on the road surface of the tire mounted on the front wheels FR and FL. Recovers, the cornering force F increases and the understeer state is eliminated. Therefore, in the present embodiment, the brake ECU 37 and the steering ECU 30 constitute a control means. Step S25 corresponds to a recovery control step. After such grip force recovery control ends, the brake ECU 37 once ends the understeer elimination processing routine.

  Next, the grip force recovery control process (grip force recovery control process routine) in step S25 will be described based on the flowchart shown in FIG. 5 and the timing chart shown in FIG.

  In the grip force recovery control processing routine, the braking ECU 37 sets the subtraction steering angle amount Δσ having a magnitude corresponding to the yaw rate deviation Ysub calculated in step S20 using the map shown in FIG. 3 (step S301). . Then, the braking ECU 37 subtracts the subtraction steering angle amount Δσ set in step S301 from the current steering angle σ of the front wheels FR and FL calculated in step S12, and the subtraction result is set to the minimum steering angle σmin. (Step S302). Subsequently, the brake ECU 37 determines whether or not the absolute value of the minimum turning angle σmin calculated in step S302 is less than the absolute value of the road surface limit steering angle σmax calculated in step S18 (step S31). . That is, as shown in FIG. 7A, unless the absolute value of the turning angle σ of the front wheels FR and FL is reduced, the longitudinal frictional force MK is not increased, and it takes time to eliminate the understeer state. Therefore, when the determination result of step S31 is negative (absolute value of σmin ≧ absolute value of σmax), the brake ECU 37 sets the minimum turning angle σmin to the road surface limit steering angle σmax (step S32), and processing thereof The process proceeds to step S35 described later.

  On the other hand, if the determination result in step S31 is affirmative (absolute value of σmin <absolute value of σmax), the braking ECU 37 determines the current turning angle σ of the front wheels FR and FL calculated in step S12 and step S301. It is determined whether the positive and negative signs are the same as the minimum turning angle σmin calculated in (Step S33). That is, in step S33, the grip force recovery control is executed when turning leftward (or rightward), so that the direction of the front wheels FR and FL becomes the direction for turning rightward (or leftward). It is determined whether there is no timing. If the determination result in step S33 is negative, that is, if the sign of the minimum turning angle σmin is different from the sign of the current turning angle σmin, the braking ECU 37 sets the minimum turning angle σmin to “0 (zero)”. The setting is made (step S34), and the process proceeds to step S35 described later. On the other hand, if the determination result in step S33 is affirmative, that is, if the sign of the minimum turning angle σmin is the same as the sign of the current turning angle σ, the brake ECU 37 proceeds to the next step S35. To do.

  In step S <b> 35, the braking ECU 37 transmits to the steering ECU 30 the steering angle information regarding the set minimum turning angle σmin and a control command for prompting the operation of the turning actuator 28. Then, the steering ECU 30 that has received the steering angle information and the control command controls the steering actuator 28 so as to change the steering angle σ of the front wheels FR and FL as shown in the timing chart of FIG. That is, when the driver performs an accelerator operation for increasing the wheel speed VWF of the front wheels FR and FL and the grip force recovery control is started (third timing t3), the turning angle σ of the front wheels FR and FL is started. Decreases rapidly toward the minimum turning angle σmin. Then, at the fourth timing t4 when the fourth elapsed time ΔT4 (that is, about half of the predetermined time T) has elapsed since the grip force recovery control was started, the driving force D for the front wheels FR and FL becomes the grip force recovery. Compared to before the start of control. As a result, the front wheels FR and FL that have been in a locking tendency have their wheel speeds VWF increased as the driving force D transmitted from the engine 12 increases, and as a result, the locking tendency of the front wheels FR and FL has been eliminated. The That is, the slip amount SlpF of the front wheels FR and FL approaches “0 (zero)”.

  Further, at the fourth timing t4 when the fourth elapsed time ΔT4 has elapsed since the grip force recovery control was started, the turning angle σ of the front wheels FR, FL becomes the minimum turning angle σmin, and the longitudinal frictional force MK is It becomes larger (see FIG. 7A). Therefore, the cornering force F of the vehicle becomes sufficiently large, and the understeer state is eliminated. At this time, information indicating that the turning angle σ of the front wheels FR and FL has reached the minimum turning angle σmin is transmitted from the steering ECU 30 to the braking ECU 37.

  Thereafter, the turning angle σ of the front wheels FR and FL increases toward the turning angle σ at the start of the grip force recovery control. Thus, in the situation where the turning angle σ returns to the original angle, at the fifth timing t5 when the fifth elapsed time ΔT5 (> ΔT4) has elapsed since the grip force recovery control was started, the front wheels FR and FL tend to lock. Therefore, the driving force D for the front wheels FR and FL starts to decrease due to the accelerator operation by the driver. Since the turning angle σ of the front wheels FR and FL is increased again after the understeer state is eliminated in this way, the vehicle turns with the grip force of the front wheels FR and FL sufficiently recovered on the road surface. Therefore, the vehicle turns in a direction according to the steering state of the steering wheel 26 by the driver.

When the grip force recovery control ends, the brake ECU 37 ends the grip force recovery control processing routine.
Although not shown, when the front wheels FR and FL are in a spin tendency, at the second timing t2 after the start of the grip force recovery control, the driving force D for the front wheels FR and FL is determined by the accelerator operation by the driver. Decrease by When the driving force D applied to the front wheels FR and FL is reduced in this way, the wheel speed VWF of the front wheels FR and FL becomes slow, and as a result, the spin tendency of the front wheels FR and FL starts to be eliminated. Since grip force recovery control is executed in this state, the understeer state caused by the front wheels FR and FL having a spin tendency is quickly eliminated.

Therefore, in this embodiment, the following effects can be obtained.
(1) Grip force recovery control is executed when the driver is performing an accelerator operation for adjusting the wheel speed VWF of the front wheels FR and FL, which are steered wheels, when the vehicle is understeered while the vehicle is turning. Is done. Then, during the adjustment of the wheel speed VWF of the front wheels FR and FL, the absolute value of the turning angle σ of the front wheels FR and FL temporarily decreases. As a result, the cornering force F is increased by reducing the absolute value of the turning angle σ, the grip force on the road surface of the tire mounted on the turning wheel is restored, and the understeer state is eliminated. In this state, as a result of adjusting the turning angle σ of the front wheels FR and FL toward the original angle, the vehicle turns in a turning manner corresponding to the steering condition of the driver's steering wheel 26. In addition, when the understeer state occurs, deceleration control that reduces the centrifugal force applied to the vehicle is not executed. Therefore, the vehicle body speed VS can be quickly recovered after the understeer state is resolved. Therefore, it is possible to assist in quickly eliminating the understeer state when the vehicle is turning without causing the vehicle driver to feel uncomfortable with driving.

  (2) Here, a senior driver who is a good driver of the vehicle steers the steering wheel 26 and temporarily turns the steering angle σ of the front wheels FR and FL to “0” when understeering occurs when the vehicle turns. The angle is reduced to an angle in the vicinity of “zero” degree, and then the turning angle σ of the front wheels FR and FL is returned to the original turning angle. Further, the advanced driver performs the depression operation of the accelerator pedal 11 simultaneously with the steering of the steering wheel 26, and adjusts the driving force D for the front wheels FR and FL. That is, the advanced driver can steer the steering wheel 26 corresponding to the grip force recovery control of the present embodiment simultaneously with the accelerator operation. However, very few drivers can perform such operations themselves. Therefore, in this embodiment, when it is detected that the accelerator operation for adjusting the wheel speed VWF of the front wheels FR, FL is detected, the adjustment control of the turning angle σ of the front wheels FR, FL, that is, The grip force recovery control is automatically executed. Therefore, even if it is a driver other than the advanced driver, the vehicle performs a movement substantially equivalent to that of the advanced driver, so that the understeer state can be quickly eliminated.

  (3) At the time when the turning angle σ of the front wheels FR and FL becomes the minimum turning angle σmin during execution of the grip force recovery control (fourth timing t4 in FIG. 6), it depends on the rotation state of the front wheels FR and FL. Adjustment control of the wheel speed VWF is executed. Therefore, as a result of the slip amount SlpF of the front wheels FR and FL approaching “0 (zero)”, the cornering force F can be quickly increased. Accordingly, it is possible to contribute to promptly eliminating the understeer state.

  (4) If the front wheels FR and FL tend to lock when the understeer occurs, the driver performs an accelerator operation to increase the wheel speed VWF of the front wheels FR and FL, so that the front wheels FR and FL The tendency to lock is eliminated. Then, when the locking tendency of the front wheels FR and FL is being eliminated in this way, grip force recovery control is executed. Therefore, if the driver performs an accelerator operation that eliminates the locking tendency of the front wheels FR and FL, the turning angle σ is automatically adjusted according to the accelerator operation. As a result, the front wheels FR and FL are locked. The understeer state caused by the tendency can be easily eliminated.

  (5) On the other hand, if the front wheels FR and FL tend to spin when an understeer condition occurs, the driver performs an accelerator operation to slow down the wheel speed VWF of the front wheels FR and FL, so that the front wheels FR and FL The spin tendency of FL is eliminated. Then, when the spin tendency of the front wheels FR and FL is being eliminated in this way, grip force recovery control is executed. Therefore, if the driver performs an accelerator operation that eliminates the spin tendency of the front wheels FR and FL, the turning angle σ is automatically adjusted according to the accelerator operation. As a result, the front wheels FR and FL are rotated. The understeer state caused by the tendency can be easily eliminated.

  (6) By executing the grip force recovery control, the turning angle of the steered wheels is adjusted so that the absolute value thereof is temporarily less than the absolute value of the road surface limit steering angle σmax. Therefore, the cornering force F can be increased to the vicinity of the maximum value, which can contribute to the elimination of the understeer state.

  (7) It is estimated that the larger the yaw rate deviation Ysub, which is the difference between the first target yaw rate Yst and the actual yaw rate Y, is, the greater the angle difference between the turning angle σ of the front wheels FR and FL and the road surface limit steering angle σmax. Therefore, in the present embodiment, the subtraction steering angle amount Δσ is set to a larger value as the yaw rate deviation Ysub is larger. Therefore, by executing the grip force recovery control, the cornering force F can be increased regardless of the magnitude of the yaw rate deviation Ysub, and the understeer state can be preferably eliminated.

  (8) When the signs of the minimum turning angle σmin calculated in step S302 and the turning angles σ of the front wheels FR and FL before execution of the grip force recovery control are different, the minimum turning angle σmin is “0 (zero). ) ”. Therefore, it is possible to restrict the direction of the front wheels FR and FL from being opposite to the direction in which the vehicle is desired to turn by executing the grip force recovery control. Therefore, the stability of the behavior of the vehicle during turning can be maintained.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIG. Note that the second embodiment is slightly different from the first embodiment in the content of the grip force recovery control process. Therefore, in the following description, parts different from those of the first embodiment will be mainly described, and the same or corresponding member configurations as those of the first embodiment are denoted by the same reference numerals, and redundant description will be omitted. Shall.

  In the grip force recovery control process routine of the present embodiment, when the processes of steps S301 to S35 are executed, the braking ECU 37 sets the turning angle σ of the front wheels FR and FL to the minimum turning angle σmin. It is determined whether information to that effect has been received from the steering ECU 30 (step S40). When this determination result is a negative determination, the brake ECU 37 repeatedly executes the determination process until the determination result of step S40 becomes a positive determination. On the other hand, if the determination result in step S40 is affirmative, the braking ECU 37 determines that the above information has been received, and calculates the current steering angle θ of the steering wheel 26 based on the detection signal from the steering angle sensor SE2. Based on the steering angle θ, the estimated turning angle σest at the end of the grip force recovery control is calculated (step S41). Therefore, in the present embodiment, the brake ECU 37 also functions as an estimated turning angle calculation means.

  Subsequently, the braking ECU 37 calculates the current road surface limit steering angle σmax using the above relational expressions (Expression 1) and (Expression 2) (step S42). Then, the braking ECU 37 determines whether or not the absolute value of the estimated turning angle σest calculated in step S41 is greater than or equal to the absolute value of the road surface limit steering angle σmax calculated in step S42 (step S43). If the determination result is affirmative (absolute value of σest ≧ absolute value of σmax), the braking ECU 37 sets the turning angle σend at the end of control to the road surface limit steering angle σmax calculated in step S42 (step S44). ), The process proceeds to step S46 described later. On the other hand, when the determination result of step S43 is negative (absolute value of σest <absolute value of σmax), the brake ECU 37 sets the turning angle σend at the end of control to the estimated turning angle σest calculated in step S41. (Step S45), the process proceeds to the next Step S46. Therefore, in the present embodiment, the brake ECU 37 also functions as a turning angle setting unit at the end of control.

  In step S <b> 46, the braking ECU 37 transmits the turning angle information related to the turning angle σend at the end of control to the steering ECU 30. The steering ECU 30 that has received the turning angle information controls the turning actuator 28 so that the turning angle σ of the front wheels FR and FL at the end of the grip force recovery control becomes the turning angle σend at the end of the control. To do.

  That is, after the grip force recovery control is finished, the vehicle turns in a state where the absolute value of the turning angle σ of the front wheels FR and FL is maintained at a value equal to or smaller than the absolute value of the road surface limit steering angle σmax. For this reason, even after the grip force recovery control is completed, the vehicle turns with the cornering force F being large. Therefore, after the understeer state is canceled by the execution of the grip force recovery control, the vehicle may be in the understeer state again. It is suppressed. Therefore, the traveling locus of the turning vehicle can be brought close to the traveling locus desired by the driver. When it is determined that the vehicle has finished turning, the turning angle σ of the front wheels FR and FL is set to an angle corresponding to the steering angle θ of the steering wheel 26.

Therefore, in this embodiment, in addition to the effects (1) to (8) of the first embodiment, the following effects can be obtained.
(9) The steering angle σ of the front wheels FR and FL after the end of the grip force recovery control has an absolute value equal to or smaller than the absolute value of the road surface limit steering angle σmax. As a result, the vehicle turns with a sufficiently large cornering force F, so that the behavior stability of the vehicle during turning can be ensured.

Each embodiment may be changed to another embodiment as described below.
In the second embodiment, the turning angle σend at the end of the control is a value whose absolute value is less than the absolute value of the road surface limit steering angle σmax and is larger than the absolute value of the minimum turning angle σmin. If there is, it may be set to an arbitrary value.

  In addition, when the driver operates the steering wheel 26 to reduce the estimated turning angle σest after setting the turning angle σend at the end of control, the front wheels FR, FL at the end of the grip force recovery control Control may be performed such that the turning angle σ is smaller than the turning angle σend at the end of control by an angle corresponding to the amount of operation of the steering wheel 26 by the driver.

  In each embodiment, when the grip force recovery control is executed, the turning angle σ of the front wheels FR and FL is set to an angle at which the vehicle shows a straight traveling tendency regardless of the yaw rate deviation Ysub (that is, “0 (zero)). The turning actuator 28 may be actuated so as to approach the original angle after temporarily reducing it to “degree”). In this case, when the grip force recovery control is executed, there is a moment when the front-rear direction frictional force MK between the tire mounted on the front wheels FR and FL and the road surface has the maximum value, so that the understeer state can be quickly eliminated. it can.

In each embodiment, the determination process in step S33 may be omitted.
In each embodiment, the yaw rate deviation Ysub may be a difference between the second target yaw rate Ygy calculated based on the lateral acceleration Gy and the actual yaw rate Y.

In each embodiment, the subtracted steering angle amount Δσ may be a predetermined constant value regardless of the magnitude of the yaw rate deviation Ysub.
In each embodiment, the determination process in step S31 may be omitted. Even in this configuration, the minimum turning angle σmin becomes closer to the road surface limit steering angle σmax than the turning angle σ immediately before the start of the grip force recovery control, and the cornering force F becomes large. Therefore, it can contribute to the elimination of the understeer state.

  In each embodiment, when the turning state of the vehicle is understeering and the front wheels FR and FL are in a spin tendency, the grip force recovery control is triggered by the detection that the driver depresses the brake pedal 16. It may be executed.

  Further, when a braking force is applied to the wheels FR, FL, RR, and RL while the vehicle is turning, the front wheels FR and FL may tend to be locked when an understeer state occurs. In such a case, the grip force recovery control may be executed in response to a decrease in the amount of depression of the brake pedal 16 by the driver.

  In each embodiment, the grip force recovery control may be such that the turning angle σ of the front wheels FR and FL is maintained at the minimum turning angle σmin for a predetermined time, and then the turning angle σ is returned to the original angle. Good.

  In each embodiment, in the grip force recovery control in a vehicle in which the rear wheels RR and RL are also steered according to the steering of the steering wheel 26 when turning, not only the turning angle σ of the front wheels FR and FL is adjusted, The turning angles of the rear wheels RR and RL may also be adjusted.

  In each embodiment, the slip ratio of the front wheels FR and FL may be calculated in step S19. This slip ratio is a value obtained by dividing the slip amount SlpF by the vehicle body speed VS.

  In each embodiment, the grip force recovery control indicates that the driver is willing to adjust the turning angle σ to an angle for moving the vehicle straight while the grip force recovery control is being executed. The control configuration may be terminated when it is detected from the condition. That is, it is desirable to quickly change the turning angle σ of the front wheels FR and FL to an angle corresponding to the steering angle θ of the steering wheel 26.

  In each embodiment, when the vehicle is provided with a sensor for detecting the depression operation amount of the accelerator pedal 11 by the driver, the change in the depression operation amount of the accelerator pedal 11 by the driver in the understeer state is detected by the sensor. The grip force recovery control may be executed in response to the detection based on the detection signal from. In this case, the start timing of the grip force recovery control can be advanced compared to the case where the grip force recovery control is executed after detecting the change in the wheel speed VWF of the front wheels FR and FL.

  In each embodiment, the grip force recovery control processing routine may be executed by ECUs 22, 25, 30 other than the braking ECU 37. Further, an ECU for comprehensively controlling the ECUs 22, 25, 30, 37 may be separately provided, and the ECU may execute a grip force recovery control processing routine.

1 is a block diagram showing a schematic configuration of a vehicle in a first embodiment. The block diagram which shows typically the electric constitution in 1st Embodiment. The map which shows the relationship between a yaw rate deviation and a subtraction rudder angle amount. The flowchart which shows an understeer cancellation process routine. The flowchart which shows the grip force recovery | restoration control processing routine in 1st Embodiment. The timing chart which shows the change of the steering angle of a steering wheel, the slip amount of a front wheel, the turning angle of a front wheel, the driving force with respect to a front wheel, and the wheel speed of a front wheel. (A) is a graph which shows the relationship between the steering angle of a front wheel, and the front-back direction frictional force of a front wheel, (b) is a graph which shows the relationship between the slip amount of a front wheel, and a cornering force. The flowchart which shows a part of grip force recovery control processing routine in 2nd Embodiment. The graph which shows the relationship between the steering angle of a front wheel, and a cornering force.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 15 ... Front wheel steering apparatus as a turning angle adjustment mechanism, 22, 25, 30, 37 ... Motion control apparatus, turning angle calculation means, control means, rotation state estimation means, limit steering angle calculation means, first yaw rate calculation Means, second yaw rate calculating means, difference calculating means, estimated turning angle calculating means, ECU as turning angle setting means at the end of control, FR, FL: front wheel as steered wheel, RR, RL: rear as steered wheel Wheel, SlpF ... slip amount, Y ... actual yaw rate, Yst ... first target yaw rate, Ysub ... yaw rate deviation, VWF ... wheel speed, θ ... steering angle, σ ... turning angle, σend ... turning angle at the end of control, σest ... Estimated turning angle, σmax ... Road surface limit steering angle, σmin ... Minimum turning angle, Δσ ... Subtraction steering angle amount as an angle difference.

Claims (12)

Vehicle motion control device (22, 25) for controlling the motion of the vehicle having a turning angle adjusting mechanism (15) capable of adjusting the turning angle (σ) of the steered wheels (FR, FL, RR, RL). , 30, 37),
Steered angle computing means (37, S12) for computing the steered angle (σ) of the steered wheels (FR, FL, RR, RL);
Whether the driver is performing an operation for adjusting the wheel speed (VWF) of the steered wheels (FR, FL, RR, RL) when the vehicle is turning understeering when the vehicle is turning Operation determination means (37, S22, S24) for determining
When the turning state of the vehicle is an understeer state, an operation for adjusting the wheel speed (VWF) of the steered wheels (FR, FL, RR, RL) is operated by the operation determination means (37, S22, S24). When it is determined that the hand is performing, the absolute value of the turning angle (σ) of the steered wheels (FR, FL, RR, RL) is temporarily reduced, and then the steered wheels (FR, FL, Control means (30, 37, S25) for performing grip force recovery control for controlling the turning angle adjusting mechanism (15) so as to adjust the turning angle (σ) of RR, RL) to the original direction;
A vehicle motion control apparatus comprising: The control means (30, 37, S25) is operated by a driver for adjusting the wheel speed (VWF) of the steered wheels (FR, FL, RR, RL) when the turning state of the vehicle is an understeer state. The vehicle motion control device according to claim 1, wherein the grip force recovery control is started when a wheel speed (VWF) of the steered wheels (FR, FL, RR, RL) starts to change by an operation. A rotation state estimating means (37, S19) for estimating a rotation state of the steered wheels (FR, FL, RR, RL);
The operation determination means (37, S22, S24) allows the driver to perform an operation corresponding to the rotation state of the steered wheels (FR, FL, RR, RL) estimated by the rotation state estimation means (37, S19). The vehicle motion control device according to claim 1, wherein it is determined whether or not the vehicle is running. In the control means (30, 37, S25), the turning state of the vehicle is understeered, and the steered wheels (FR, FL, RR, RL) tend to be locked by the rotation state estimation means (37, S19). When it is estimated that there is a driver, the operation determination means (37, S22) performs an operation for increasing the wheel speed (VWF) of the steered wheels (FR, FL, RR, RL). The vehicle motion control device according to claim 3, wherein when it is determined, the grip force recovery control is executed. In the control means (30, 37, S25), the turning state of the vehicle is understeered, and the steered wheels (FR, FL, RR, RL) tend to spin by the rotation state estimation means (37, S19). If it is estimated that there is a driver, the operation determination means (37, S24) performs an operation for reducing the wheel speed (VWF) of the steered wheels (FR, FL, RR, RL). The vehicle motion control device according to claim 3, wherein when it is determined, the grip force recovery control is executed. Limit steering angle calculation means (37, S18) for calculating the turning angle (σ) of the steered wheels (FR, FL, RR, RL) that becomes the road surface limit as the road surface limit steering angle (σmax);
Estimated turning angle calculation means (37, S41) for calculating the turning angle of the steered wheels (FR, FL, RR, RL) at the end of the grip force recovery control as an estimated turning angle (σest);
The absolute value of the estimated turning angle (σest) calculated by the estimated turning angle calculation means (37, S41) is the road surface limit steering angle (σmax) calculated by the limit steering angle calculation means (37, S18). When it is less than the absolute value, the estimated turning angle (σest) is set as the turning angle (σend) at the end of control, while the absolute value of the estimated turning angle (σest) is the road surface limit steering angle (σmax). ), The control end turning angle setting means (37, S44, S45) for setting the road surface limit steering angle (σmax) as the control end turning angle (σend). Prepared,
The control means (30, 37, S25) is configured so that the turning angle (σ) of the steered wheels (FR, FL, RR, RL) at the end of the grip force recovery control is the turning angle setting means at the end of the control. Any one of Claims 1-5 which controls the said turning angle adjustment mechanism (15) so that it may become an angle below the turning angle ((sigma) end) at the time of the completion of control set by (37, S44, S45). The motion control device for a vehicle according to one item. Limit steering angle calculation means (37, S18) for calculating the turning angle (σ) of the steered wheels (FR, FL, RR, RL) that become the road surface limit as the road surface limit steering angle (σmax),
When the grip force recovery control is executed, the control means (30, 37, S25) temporarily sets the turning angle (σ) of the steered wheels (FR, FL, RR, RL) in terms of the absolute value. After adjusting so that it may become below the absolute value of the road surface limit steering angle ((sigma) max) calculated by the limit steering angle calculating means (37, S18), the said steering angle adjustment mechanism (15) to adjust in the direction which returns The vehicle motion control apparatus according to any one of claims 1 to 5, which controls the vehicle. Estimated turning angle calculation means (37, S41) for calculating the turning angle of the steered wheels (FR, FL, RR, RL) at the end of the grip force recovery control as an estimated turning angle (σest);
The absolute value of the estimated turning angle (σest) calculated by the estimated turning angle calculation means (37, S41) is the road surface limit steering angle (σmax) calculated by the limit steering angle calculation means (37, S18). When it is less than the absolute value, the estimated turning angle (σest) is set as the turning angle (σend) at the end of control, while the absolute value of the estimated turning angle (σest) is the road surface limit steering angle (σmax). ), The control end turning angle setting means (37, S44, S45) for setting the road surface limit steering angle (σmax) as the control end turning angle (σend). Prepared,
The control means (30, 37, S25) is configured so that the turning angle (σ) of the steered wheels (FR, FL, RR, RL) at the end of the grip force recovery control is the turning angle setting means at the end of the control. The vehicle motion control device according to claim 7, wherein the turning angle adjusting mechanism (15) is controlled so as to be equal to or less than a turning end turning angle (σend) set by (37, S 44, S 45). . First yaw rate calculating means (37, S15) for calculating a target yaw rate (Yst) according to the steering amount of the vehicle steering (26);
Second yaw rate calculating means (37, S14) for calculating the actual yaw rate (Y) of the vehicle;
Difference calculating means (37, S20) for calculating a yaw rate deviation (Ysub) which is a difference between the yaw rates (Y, Yst) calculated by the yaw rate calculating means (37, S15, S14);
When the grip force recovery control is executed, the control means (30, 37, S25) turns the steered angle (FR, FL, RR, RL) of the steered wheels (FR, FL, RR, RL) when the turning state of the vehicle becomes an understeer state. The difference in angle (Δσ) between σ) and the minimum turning angle (σmin) at which the absolute value becomes the smallest during execution of the grip force recovery control is calculated by the yaw rate deviation (37, S20) The vehicle motion control device according to any one of claims 1 to 5, 7, and 8, wherein the turning angle adjusting mechanism (15) is controlled so as to increase as Ysub) increases. . The control means (30, 37, S25) is configured to change the direction of the steered wheels (FR, FL, RR, RL) by executing the grip force recovery control so that the turning state of the vehicle when the turning state of the vehicle is understeered. The steering angle adjustment mechanism (15) is controlled according to any one of claims 7 to 9, wherein the turning angle adjustment mechanism (15) is controlled so as to be restricted from a direction different from the direction of the steered wheels (FR, FL, RR, RL). The vehicle motion control apparatus described. The control means (30, 37, S25) is configured such that when the grip force recovery control is executed, the turning angle (σ) of the steered wheels (FR, FL, RR, RL) is set so that the vehicle tends to go straight. The movement of the vehicle according to any one of claims 1 to 6, wherein the turning angle adjusting mechanism (15) is controlled so as to be adjusted in a direction to return to an original direction after being temporarily reduced to an angle. Control device. A turning angle calculation step (S12) for calculating a turning angle (σ) of the steered wheels (FR, FL, RR, RL) of the vehicle;
Operation determination for determining whether or not the driver is performing an operation for adjusting the wheel speed (VWF) of the steered wheels (FR, FL, RR, RL) when the turning state of the vehicle is an understeer state Steps (S22, S24);
When the turning state of the vehicle is an understeer state, the driver performs an operation for adjusting the wheel speed (VWF) of the steered wheels (FR, FL, RR, RL) in the operation determination step (S22, S24). When it is determined that the turning angle (σ) of the steered wheels (FR, FL, RR, RL) is temporarily reduced, the steered wheels (FR, FL, RR, A recovery control step (S25) for executing grip force recovery control for adjusting the turning angle (σ) of RL) to return to the original direction;
A vehicle motion control method comprising:

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