JP4019879B2 - Vehicle behavior control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vehicle behavior control device that controls a vehicle behavior by controlling a braking force applied to each wheel based on a turning state amount generated in a vehicle.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as this type of vehicle behavior control device, a device that controls a braking force to each wheel so that a yaw rate generated in a vehicle matches a target value is known. In such a vehicle behavior control device, usually, when the vehicle has an oversteer tendency, a braking force is applied to the front wheels on the outside of the turn so as to suppress the oversteer tendency.
[0003]
Therefore, when the conventional vehicle behavior control device is used in a four-wheel drive vehicle in which the differential between the front axle and the rear axle is limited by a center differential lock or the like, the vehicle becomes an oversteer tendency and the oversteer tendency is suppressed. Thus, when a braking force is applied to the front wheel outside the turn, the braking force also acts on the rear wheel via a propeller shaft or the like, and the lateral grip limit of the rear wheel is reduced, conversely promoting an oversteer tendency. There was a fear. Similarly, when the vehicle is understeered and braking force is applied to the rear wheels inside the turn so as to suppress the understeering tendency, the braking force also acts on the front wheels via the propeller shaft, etc. There was a risk that the lateral grip limit of the front wheel would become smaller and conversely promote an understeer tendency.
[0004]
Therefore, in the conventional vehicle behavior control device, when the vehicle behavior control device is used for a four-wheel drive vehicle in which the differential between the front axle and the rear axle is limited by a center differential lock or the like, an oversteer tendency or an understeer tendency is suppressed. So that the braking force applied to either one of the front and rear wheels is corrected to be small, and the braking force that acts on any one of the other wheels via the propeller shaft is reduced. The lateral grip of one of the other wheels is secured, and the promotion of oversteer tendency and understeer tendency is suppressed (Patent Document 1).
[0005]
[Patent Document 1]
JP 2000-344077 A
[0006]
[Problems to be solved by the invention]
However, in the conventional vehicle behavior control device described above, the braking operation is performed by the driver when the braking force is applied to one of the front and rear wheels so as to suppress the oversteer tendency and the understeer tendency. Then, the braking force acts on the other wheel via the propeller shaft from the one wheel and also the braking force by the braking operation, and the total braking force of the other wheel is As a result, the lateral grip limit of one of the other wheels is reduced, which may promote an oversteer tendency or an understeer tendency.
[0007]
The present invention has been developed in view of these problems, and an object thereof is to provide a vehicle behavior control device that can suppress the promotion of an oversteer tendency and an understeer tendency even when a braking operation is performed by a driver. Is.
[0008]
[Means for Solving the Problems]
  For the above purpose, the vehicle behavior control device of the present invention is a vehicle behavior control device for a four-wheel drive vehicle capable of limiting the differential between the front axle and the rear axle,When the braking force to each wheel is controlled so that the oversteer tendency is suppressed, the braking force applied to both rear wheels by the braking means is corrected to a small value.It is characterized by this.
  Further, in the vehicle behavior control device of a four-wheel drive vehicle capable of limiting the differential between the front axle and the rear axle, when the braking force to each wheel is controlled so that the understeer tendency is suppressed, The braking force applied to both rear wheels by the braking means is corrected to a small value.
[0009]
【The invention's effect】
  Therefore, according to the vehicle behavior control device of the present invention,, ExampleFor example,Oversteer and understeerButSuppressionIsAs described above, when a braking force is applied to one of the front and rear wheels, the braking force applied to any one of the wheels acts on the other wheel via the propeller shaft. When a braking operation is performed by the driver, the braking force applied to the other wheel is corrected to be small by the braking operation, and an increase in the total braking force acting on the other wheel can be suppressed. The other wheel can be secured with a lateral grip to suppress oversteering and understeering.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a first embodiment of a vehicle behavior control device of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic vehicle configuration diagram showing an outline of a braking fluid pressure control device as a vehicle behavior control device (VDC) of the present embodiment. Reference numerals 1FL and 1FR in the figure indicate the front left wheel and the front right wheel, respectively, and 1RL and 1RR indicate the rear left wheel and the rear right wheel, respectively. The vehicle of this embodiment is a four-wheel drive vehicle, and the differential between the front axle and the rear axle is limited (a state corresponding to direct connection by 4WD transfer or the like).
[0011]
Further, wheel cylinders 2FL to 2RR are attached to the respective wheels 1FL to 1RR as brake cylinders. Each of the wheel cylinders 2FL to 2RR is a so-called disc brake that presses a pad against the disc rotor for braking (a drum brake may be used). The brake fluid pressure to each of the wheel cylinders 2FL to 2RR can be controlled by the brake fluid pressure unit 3. The brake fluid pressure unit 3 includes an electric pump, like the brake fluid pressure unit used in the conventional vehicle behavior control device, and can increase or decrease the brake fluid pressure separately from the depression of the brake pedal 13. Yes, the brake fluid pressure to each of the wheel cylinders 2FL to 2RR can be individually controlled to increase and decrease.
[0012]
The brake fluid pressure applied to the wheel cylinders 2FL to 2RR by the brake fluid pressure unit 3 is controlled to increase or decrease by a command signal from the control unit 4. In the control unit 4, for example, the wheel speeds Vwj (j = FL to RR) detected by the wheel speed sensors 5 FL to 5 RR, the steering angle θ detected by the steering angle sensor 6, and the travel detected by the travel speed sensor 7. Speed Vsp, yaw rate ψ ′ detected by the yaw rate sensor 8, longitudinal acceleration αv detected by the acceleration sensor 9, brake pedal operation state detected by the brake switch 10, master cylinder pressure Pm detected by the master cylinder pressure sensor 11 The value detected by the VDC off switch 12 is read, for example, the target yaw rate ψ ′ set in accordance with the traveling speed Vsp and the steering angle θ.^*A braking force for making the detected yaw rate ψ ′ coincide with each other is determined, and the braking fluid pressure Pj of each wheel is directed toward the braking fluid pressure unit 3 so that the braking force is achieved.^*Or command.
[0013]
The control unit 4 receives a detection signal from each of the sensors and switches described above, outputs a control signal to the brake fluid pressure unit 3, and outputs a control signal output from the microcomputer. And a drive circuit for converting into a drive signal to each control valve solenoid including an electromagnetic switching valve or the like in the brake fluid pressure unit 3. The microcomputer includes an input interface circuit having an A / D conversion function, an output interface circuit having a D / A conversion function, an arithmetic processing unit including a microprocessor unit MPU, a ROM, a RAM, and the like. A storage device is provided. In the microcomputer, not only the generation output of the main control signals necessary for various controls, but also the drive control signal of the pump necessary for the pressure increase / decrease control in the vehicle behavior control and the power supply to the actuator itself, for example. Needless to say, the control signals to the switching elements of the actuator relay that it controls are also generated and output in parallel.
[0014]
Next, a calculation process of the braking fluid pressure control executed by the microcomputer in the control unit 4 in order to control the yawing momentum of the vehicle will be described based on each flowchart in the attached drawings. In this arithmetic processing, there is no particular communication step. However, the program stored in the ROM of the storage device in the microcomputer, the map, various data stored in the RAM, etc. are constantly processed. Each calculation result transmitted to the buffer of the apparatus and calculated by the arithmetic processing unit is also stored in the storage device as needed.
[0015]
In FIG. 2, the target yaw rate ψ ′^*The yaw moment control amount ΔM for matching the actual yaw rate ψ ′ is obtained, and the braking fluid pressure Pj of each wheel is commanded to the braking fluid pressure unit 3 so that the yaw moment control amount ΔM is achieved. The flow of a brake fluid pressure calculation process is shown. This calculation process is executed as a timer interrupt every predetermined sampling period ΔT, for example, 10 msec. First, in step S 101, the steering angle θ detected by the steering angle sensor 6, and the traveling speed Vsp detected by the traveling speed sensor 7. The longitudinal acceleration αv detected by the acceleration sensor 9 and the yaw rate ψ ′ detected by the yaw rate sensor 8 are read.
[0016]
Next, the process proceeds to step S102, where the steering angular velocity dθ and the steering angular acceleration d (dθ) are calculated based on the steering angle θ read in step S101. Specifically, the steering angular velocity dθ and the steering angular acceleration d (dθ) are calculated by differentiating the steering angle θ using a high-pass filter or the like, or performing a secondary differentiation.
Next, the process proceeds to step S103, and the control gain τ is added to the steering angular velocity dθ calculated in step S102.¹Is multiplied by the steering angular acceleration d (dθ) calculated in step S102 and the control gain τ.²Yaw moment control amount ΔM by feedforward control by adding the value multiplied by_{F / F}Is calculated.
[0017]
Next, the process proceeds to step S104, and the target yaw rate ψ ′ set according to the traveling speed Vsp and the steering angle θ.^*From the yaw rate ψ ′ read in step S101, and the yaw moment control amount ΔM by feedback control is reduced._{F / B}Is calculated.
Next, the process proceeds to step S105, where the yaw moment control amount ΔM by the feedforward control calculated in step S103 is calculated._{F / F}Yaw moment control amount ΔM by feedback control calculated in step S104_{F / B}And the target yaw rate ψ ′^*The yaw moment control amount ΔM for making the actual yaw rate ψ ′ coincide with is calculated.
[0018]
Next, the process proceeds to step S106, and the braking fluid pressure Pj of one of the front and rear wheels is directed toward the braking fluid pressure unit 3 so that the yaw moment control amount ΔM calculated in step S105 is achieved. A command is executed, and a brake fluid pressure correction calculation process (described later) for correcting the brake fluid pressure Pj applied to one of the other wheels to a small value by the depression of the brake pedal is executed, and then the process proceeds to the main program.
[0019]
FIG. 3 shows a flow of the brake fluid pressure correction calculation process executed in step S106 of the brake fluid pressure calculation process. In this calculation process, first in step S201, it is determined whether or not there is a yaw rate control request from the calculation result of the brake fluid pressure calculation process. If there is a yaw rate control request, the process proceeds to step S202. Returns to the main program. Specifically, it is determined that there is a yaw rate control request when | ΔM |> 0 or when the VDC off switch 12 is not operated.
[0020]
In step S202, a braking force to be applied to each wheel in order to realize the yaw moment control amount ΔM calculated in the braking fluid pressure calculation process is calculated, and a braking fluid pressure command value Pj for generating the braking force is calculated.^*Is calculated. For example, when suppressing the oversteer tendency, a braking force is applied to the front wheel on the turning outer wheel side, and when suppressing the understeer tendency, a braking force is applied to the rear wheel on the turning inner wheel side.
[0021]
Next, the process proceeds to step S203, where it is determined whether or not the brake pedal is operated by the driver. If it is operated, the process proceeds to step S204, and if not, the process returns to the main program. Specifically, it is determined that the brake pedal is operated when the brake switch 10 is in the ON state or when the detected value of the master cylinder pressure sensor 11 is greater than a predetermined value.
[0022]
Next, the process proceeds to step S204, where oversteer suppression control or understeer suppression control is to be performed based on the yaw moment control amount ΔM calculated in the brake fluid pressure calculation process (depending on whether the direction is + or-). If it is oversteer suppression control, the process proceeds to step S205. If it is understeer suppression control, the process proceeds to step S206.
[0023]
In step S205, the brake fluid pressure command value Pro is obtained by subtracting the brake fluid pressure correction amount ΔPv from the rear wheel brake fluid pressure (estimated from the master cylinder pressure) according to the brake pedal operation.^*, Pri^*And The braking fluid pressure correction amount ΔPv is, for example, the braking fluid pressure command value Pj for the front wheel outside the turn calculated in step S202.^*Of 15%.
[0024]
On the other hand, in step S206, the brake fluid pressure command value Pfo is obtained by subtracting the brake fluid pressure correction amount ΔPv from the brake fluid pressure of the front wheels (estimated from the master cylinder pressure) according to the brake pedal operation.^*, Pfi^*And The braking fluid pressure correction amount ΔPv is, for example, the braking fluid pressure command value Pj for the rear wheel inside the turn calculated in step S202.^*Of 35%.
[0025]
Next, the process proceeds to step S207, and the target yaw rate ψ ′ set according to the traveling speed Vsp and the steering angle θ.^*And the actual difference in yaw rate ψ ′ (hereinafter referred to as yaw rate deviation Δφn) is calculated.
Next, the process proceeds to step S208, where it is determined whether or not the margin has returned to the side grip based on the change state of the yaw rate deviation Δφn calculated in step S207. The process proceeds to step S209. If not, the process returns to the main program. Specifically, the yaw rate deviation Δφn calculated in step S207 is smaller than a predetermined value α, and this time calculation is performed from the yaw rate deviation Δφn-1 calculated when the braking fluid pressure correction calculation process was executed last time. When the yaw rate deviation Δφn is small, that is, when the yaw rate deviation Δφn is sufficiently small and tends to decrease, it is determined that the margin has returned to the lateral grip.
[0026]
If it is determined in step S209 that oversteer suppression control is being performed, the rear-wheel braking fluid pressure command value Pro calculated in step S205 is used.^*, Pri^*A value obtained by adding the braking fluid pressure reduction release amount ΔPdec to the new braking fluid pressure command value Pro^*, Pri^*And If understeer suppression control is being performed, the braking fluid pressure command value Pfo for the front wheels calculated in step S206 is used.^*, Pfi^*Is set to a new braking fluid pressure command value Pfo.^*, Pfi^*And As shown in FIG. 4, the braking fluid pressure decompression release amount ΔPdec is obtained by subtracting the yaw rate deviation Δφn calculated this time from the yaw rate deviation Δφn−1 calculated when the braking fluid pressure correction calculation process was executed last time. The value is set to be larger as the decrease value (φn−1−φn) of the yaw rate deviation is larger. That is, the reduction amount of the correction amount Pv is set according to the return state of the margin of the lateral grip.
[0027]
Next, the operation of the vehicle behavior control device of this embodiment will be specifically described.
First, as shown at time t1 in FIGS. 5 (a) and 5 (b), when the driver is turning right while operating the brake pedal, the yaw rate control is performed so as to suppress the understeer tendency in the brake fluid pressure calculation process. And the yaw moment control amount ΔM for turning the vehicle to the right is calculated. Then, as shown in FIG. 3, the determination in step S201 of the braking fluid pressure correction calculation process is “YES”, and the braking force applied to the rear right wheel 1RR in order to realize the yaw moment control amount ΔM in step S202. Is calculated and the braking fluid pressure command value Pj for generating the braking force is calculated.^*Further, the determination in step S203 is “YES”, the determination in step S204 is “NO”, and a value obtained by subtracting the braking fluid pressure correction amount ΔPv from the braking fluid pressure of the front wheel according to the brake pedal operation in step S206. Is the brake fluid pressure command value Pfo^*, Pfi^*Thus, as shown in FIG. 5B, the braking fluid pressures Pfo and Pfi of the front wheels are corrected to be reduced.
[0028]
Thus, according to the present embodiment, when the braking force is applied to the rear right wheel 1RR so as to suppress the understeer tendency, the braking force of the rear right wheel 1RR is transmitted through the propeller shaft as shown in FIG. Although acting on 1FL, 1FR, the braking fluid pressure command values Pfo, Pfi for the front wheels are reduced and corrected to reduce pressure, so that an increase in the total braking force acting on the front wheels 1FL, 1FR is suppressed, and the front wheels 1FL, 1FR A lateral grip is secured, and as shown by a solid line in FIG. Incidentally, when applying the braking force to the rear right wheel 1RR so as to suppress the understeer tendency, the conventional method of applying the normal braking force to the front wheels 1FL, 1FR, as shown in FIG. A braking force is applied to 1FR from the rear right wheel 1RR via the propeller shaft, and a braking force by the operation of the brake pedal is also applied. The total braking force of the front wheels 1FL, 1FR increases, and the front wheels 1FL, 1FR The lateral grip limit is lowered, and as shown by a broken line in FIG. 5A, an understeer tendency may be promoted.
[0029]
As the above flow is repeated, as shown at time t2 in FIG. 5A, the understeer tendency is suppressed, and the yaw rate deviation Δφn calculated in step S207 is smaller than the predetermined value α and tends to decrease. Suppose. Then, as shown in FIG. 3, through steps S201 to S207 of the calculation process for braking fluid pressure correction, the determination in step S208 becomes “YES”. In step S209, the braking of the front wheels calculated in step S206 is performed. Fluid pressure command value Pfo^*, Pfi^*The value obtained by adding the brake fluid pressure reduction release amount ΔPdec to the new brake fluid pressure command value Pfo^*, Pfi^*Thus, as shown in FIG. 5B, the pressure reduction correction to the braking fluid pressures Pfo and Pfi of the front wheels is released.
[0030]
Then, as the above flow is further repeated, it is assumed that the yaw rate deviation Δφn is accelerated and the vertical grip limit of the front wheels 1FL and 1FR is increased as shown at time t3 in FIG. Then, as shown in FIG. 3, the amount of decrease in the yaw rate deviation (Δφn−1−Δφn) is largely calculated through steps S201 to S208 of the braking fluid pressure correction calculation process. In step S209, the braking fluid is calculated. The pressure reduction release amount ΔPdec is calculated to be large in terms of acceleration, and the front wheel braking fluid pressure command value Pfo is calculated.^*, Pfi^*As shown in FIG. 5B, the hydraulic pressure in the front wheel cylinder returns to the braking fluid pressures Pfo and Pfi corresponding to the operation of the brake pedal.
[0031]
Thus, according to the present embodiment, when the yaw rate deviation Δφn is smaller than the predetermined value α and tends to decrease, that is, when the understeer tendency is suppressed and the vertical grip limit of the front wheels 1FL and 1FR becomes large, In order to cancel the decompression correction to the front wheels 1FL and 1FR, without increasing the understeer tendency, the braking force according to the driver's brake pedal operation is returned to the braking force according to the return state of the margin of the side grip. You can maximize your grip.
[0032]
On the other hand, as shown at time t1 in FIGS. 5 (a) and 5 (b), when the driver is turning right while operating the brake pedal, the yaw rate control is performed so as to suppress the oversteer tendency by the brake fluid pressure calculation process. And the yaw moment control amount ΔM for turning the vehicle to the left is calculated. Then, as shown in FIG. 3, the determination in step S201 of the calculation process for correcting the braking fluid pressure is “YES”, and the braking force applied to the front left wheel 1FL in order to realize the yaw moment control amount ΔM in step S202. Brake fluid pressure command value Pj for calculating and generating the braking force^*Further, the determination in steps S203 and S204 is “YES”, and a value obtained by subtracting the braking fluid pressure correction amount ΔPv from the braking fluid pressure of the rear wheel corresponding to the brake pedal operation in step S205 is the braking fluid pressure command value Pro.^*, Pri^*Thus, as shown in FIG. 5B, the braking fluid pressures Pro, Pri of the rear wheels are corrected to be reduced.
[0033]
Thus, according to the present embodiment, when a braking force is applied to the front left wheel 1FL in order to suppress the oversteer tendency, the braking force of the front left wheel 1FL is applied to the rear wheel 1RL via the propeller shaft as shown in FIG. , 1RR, but the rear wheel braking fluid pressure command value Pro^*, Pri^*Is reduced and the pressure reduction is corrected, so that an increase in the total braking force acting on the rear wheels 1RL and 1RR is suppressed, and a lateral grip of the rear wheels 1RL and 1RR is secured, as shown in FIG. The promotion of oversteer tendency is suppressed. Incidentally, when a braking force is applied to the front left wheel 1FL so as to suppress an oversteer tendency, the conventional method of applying a normal braking force to the rear wheels 1RL and 1RR, as shown in FIG. A braking force is applied to the 1RL and 1RR from the front left wheel 1FL via the propeller shaft, and a braking force by the operation of the brake pedal is also applied to increase the total braking force of the rear wheels 1RL and 1RR, thereby increasing the rear wheels 1RL and 1RR. The lateral grip limit of 1RR is lowered, and there is a possibility that an oversteer tendency is promoted as shown by a broken line in FIG.
[0034]
Next, a second embodiment of the vehicle behavior control device of the present invention will be described. In this embodiment, the flowchart of FIG. 8 is used instead of the flowchart of the braking fluid pressure correction calculation process shown in FIG. In this flowchart, first, in step S301, it is determined whether or not the brake pedal is operated by the driver. If it is operated, the process proceeds to step S302, and if not, the process returns to the main program. Specifically, it is determined that the brake pedal is operated when the brake switch 10 is in the ON state or when the detected value of the master cylinder pressure sensor 11 is greater than a predetermined value.
[0035]
In step S302, it is determined whether or not there is a yaw rate control request from the calculation result of the braking fluid pressure calculation process. If there is a yaw rate control request, the process proceeds to step S303, and if not, the process returns to the main program. To do. Specifically, it is determined that there is a yaw rate control request when | ΔM |> 0 or when the VDC off switch 12 is not operated.
[0036]
In step S303, a braking force to be applied to each wheel in order to realize the yaw moment control amount ΔM calculated in the braking fluid pressure calculation process is calculated, and a braking fluid pressure command value Pj for generating the braking force is calculated.^*Is calculated. For example, when suppressing the oversteer tendency, a braking force is applied to the front wheel on the turning outer wheel side, and when suppressing the understeer tendency, a braking force is applied to the rear wheel on the turning inner wheel side.
[0037]
Next, the process proceeds to step S304, where oversteer suppression control or understeer suppression control is to be performed based on the yaw moment control amount ΔM calculated in the brake fluid pressure calculation process (depending on whether the direction is + or-). If it is oversteer suppression control, the process proceeds to step S305. If it is understeer suppression control, the process proceeds to step S310.
[0038]
In step S305, a value obtained by subtracting the wheel speeds Vwro and Vwri detected by the wheel speed sensors 5RL and 5RR of the rear wheels 1RL and 1RR from the travel speed Vsp detected by the travel speed sensor 7 is divided by the travel speed Vsp. To calculate the slip ratios Sro and Sri of the rear wheels.
Next, the process proceeds to step S306, where the lateral grip limit Fn of the rear wheel is calculated based on the slip ratios Sro and Sri of the rear wheel calculated in step S305, and the detected value of the lateral G sensor or the vehicle speed and the rudder are calculated. The margin Fn ′ of the side grip is calculated from the corner. Here, the lateral grip limit Fn of the rear wheel is a lateral grip force at which the rear wheels 1RL and 1RR become the grip limit, and can be estimated from a well-known tire characteristic map, for example, as shown in FIG. Further, the lateral grip limit Fn may be obtained from the wheel load and braking / driving force.
[0039]
Next, the process proceeds to step S307, where the lateral grip margin allowance Fn-1 ′ of the rear wheel calculated when this braking fluid pressure correction calculation process was executed last time is calculated from the lateral grip margin allowance Fn ′ calculated this time. By subtracting, an increase amount of the rear wheel lateral grip margin Fn ′ (hereinafter referred to as a margin degree increase amount ΔF) is calculated.
Next, the process proceeds to step S308, and the braking fluid pressure reduction correction amount P ′ for the rear wheel is calculated by multiplying the margin degree increase ΔF calculated in step S307 by the coefficient Kr. This coefficient Kr is set based on the wheel cylinder pressure receiving area, the pad pressure receiving area, etc. of the rear wheel.
[0040]
In step S309, the brake fluid pressure command value Pro is obtained by subtracting the brake fluid pressure correction amount ΔPv from the brake fluid pressure of the rear wheel by the brake pedal operation.^*, Pri^*And This braking fluid pressure correction amount ΔPv is a value obtained by subtracting the braking fluid pressure reduction correction amount P ′ calculated in step S308 from the braking fluid pressure correction amount ΔPvn−1 calculated when this calculation process was executed last time. In the initial state, the brake fluid pressure of the rear wheel is set by operating the brake pedal.
[0041]
On the other hand, in step S310, a value obtained by subtracting the wheel speeds Vwfo and Vwfi detected by the wheel speed sensors 5FL and 5FR of the front wheels 1FL and 1FR from the travel speed Vsp detected by the travel speed sensor 7 is divided by the travel speed Vsp. Thus, the slip ratios Sfo and Sfi of the front wheels are calculated.
Next, the process proceeds to step S311, where the lateral grip limit Fn of the front wheel is calculated based on the slip ratios Sfo and Sfi of the front wheel calculated in step S310, and the actual lateral grip force is estimated from the vehicle speed and the steering angle. Then, a margin Fn ′ for the lateral grip limit Fn is calculated. Here, the lateral grip limit Fn of the front wheel is a lateral grip force at which the front wheels 1FL and 1FR become the grip limit, and can be estimated from a well-known tire characteristic map, for example, as shown in FIG.
[0042]
Next, the process proceeds to step S312, and the front wheel lateral grip margin Fn-1 ′ calculated when the braking fluid pressure correction calculation process was executed last time is subtracted from the currently calculated lateral grip margin Fn ′. Thus, an increase amount of the lateral grip margin Fn ′ of the front wheel (hereinafter referred to as a margin degree increase amount ΔF) is calculated.
Next, the process proceeds to step S313, where the braking fluid pressure reduction correction amount P ′ for the front wheels is calculated by multiplying the margin degree increase ΔF calculated in step S312 by the coefficient Kf. The coefficient Kf is set based on the wheel cylinder pressure receiving area, the pad pressure receiving area, and the like of the front wheels.
[0043]
Next, the process proceeds to step S314, where a value obtained by subtracting the braking fluid pressure correction amount ΔPv from the braking fluid pressure of the front wheels by operating the brake pedal is used as the braking fluid pressure command value Pfo.^*, Pfi^*And This braking fluid pressure correction amount ΔPv is a value obtained by subtracting the braking fluid pressure reduction correction amount P ′ calculated in step S313 from the braking fluid pressure correction amount ΔPvn−1 calculated when this calculation process was executed last time. In the initial state, the brake fluid pressure of the rear wheel is set by operating the brake pedal.
[0044]
Next, the operation of the vehicle behavior control device of this embodiment will be specifically described.
First, as shown at time t1 in FIG. 10, when the driver is turning right while operating the brake pedal, the yaw rate control is performed so as to suppress the understeer tendency in the brake fluid pressure calculation process, and the vehicle Suppose that a yaw moment control amount ΔM that turns the right is calculated. Then, as shown in FIG. 8, the determinations in steps S301 and S302 of the calculation process for correcting the braking fluid pressure are “YES”. In step S303, the control is applied to the rear right wheel 1RR in order to realize the yaw moment control amount ΔM. The braking fluid pressure command value Pj for calculating the braking force to be generated and generating the braking force^*Is determined, the determination in step S304 is “NO”, and the slip ratios Sfo and Sfi of the front wheels are calculated in step S310. Here, it is assumed that the lateral grip force acting on the front wheels 1FL and 1FR is increased and the slip ratios Sfo and Sfi of the front wheels are calculated to be large. Then, in step S311, the front wheel lateral grip margin Fn ′ is calculated to be small according to the slip ratios Sfo and Sfi of the front wheel, and in step S312, the margin degree increase amount ΔF is set to a negative value. In step S313, the front wheel The brake fluid pressure reduction correction amount P ′ is set to a negative value, and in step S314, the brake fluid pressure command value Pfo for the front wheels is set.^*, Pfi^*Is a negative value, and as shown in FIG. 10C, the braking fluid pressures Pfo and Pfi of the front wheels are reduced and corrected for acceleration.
[0045]
As described above, according to the present embodiment, when the braking force is applied to the rear right wheel 1RR so as to suppress the understeer tendency, the front wheel side grip margin Fn ′ tends to decrease. In order to increase the depressurization amount of the braking fluid pressures Pfo and Pfi, the margin of the lateral grip of the front wheel is increased, and the promotion of the understeer tendency is effectively suppressed.
[0046]
Further, as the above flow is repeated, as shown at time t2 in FIGS. 10A and 10B, it is assumed that the understeer tendency is suppressed and the increase amount ΔF of the lateral grip force margin of the front wheels tends to increase. Then, as shown in FIG. 8, through steps S301 to S311 of the above-described braking fluid pressure correction calculation processing, the margin degree increase amount ΔF is set to a positive value in step S312. In step S313, the braking fluid pressure reduction of the front wheels is performed. The correction amount P ′ is set to a positive value, and in step S314, the braking fluid pressure command value Pj for the front wheels is set.^*Is gradually set to a positive value, and as shown in FIG. 10 (c), the pressure reduction amounts of the brake fluid pressures Pfo and Pfi of the front wheels are gradually reduced.
[0047]
As the above flow is further repeated, as shown at time t3 in FIGS. 10 (a) and 10 (b), the yaw rate deviation Δφn is accelerated and the front wheel lateral grip margin Fn ′ is increased. To do. Then, as shown in FIG. 8, through steps S301 to S311 of the brake fluid pressure correction calculation process, the margin degree increase amount ΔF is calculated to be large in step S312. In step S313, the brake fluid pressure reduction correction for the front wheels is performed. The amount P ′ is greatly calculated, and in step S314, the braking fluid pressure command value Pfo for the front wheels is calculated.^*, Pfi^*As shown in FIG. 10C, the wheel cylinder hydraulic pressure of the front wheels returns to the braking fluid pressures Pfo and Pfi corresponding to the brake pedal operation.
[0048]
Thus, according to the present embodiment, when the braking force is applied to the rear right wheel 1RR so as to suppress the understeer tendency, the front wheel's lateral grip margin Fn ′ tends to increase. In order to increase the amount of brake fluid pressure Pfo, Pfi, the tire grip is restored by returning to the braking force according to the driver's brake pedal operation according to the margin of the side grip without promoting the understeer tendency. Can be maximized.
[0049]
In the above embodiment, the yaw rate sensor 8 corresponds to the turning state amount detection means, the control unit 4 corresponds to the control means and the braking means, and steps S204 to S209 and S304 to S314 correspond to the braking force correction means. Steps S305 and S310 correspond to slip state detection means, Steps S306 and S311 correspond to side grip margin calculation means, and Steps S307 to S309 and S312 to S314 correspond to correction amount setting means.
[0050]
Moreover, the said embodiment showed an example of the vehicle behavior control apparatus of this invention, and does not limit the structure of an apparatus.
For example, in the above embodiment, an example in which the vehicle behavior control device of the present invention is applied to a so-called rigid four-wheel drive vehicle has been described. However, the present invention is not limited to this, and is not limited to this. On-demand 4WD that can adjust the driving force distribution of the front and rear wheels from the two-wheel drive state to the rigid four-wheel drive state by adjusting the clutch engagement force according to the thing that can be in the wheel drive state or the slip ratio during acceleration As long as the braking force is applied to the other wheel via the propeller shaft when the braking force is applied to one of the front and rear wheels, the invention can be applied to any four-wheel drive vehicle. In other words, the present invention acts on two types of braking force acting on each wheel (the braking force applied to suppress the oversteer tendency and the understeer tendency via the propeller shaft, and the driver's pedal operation. Is adjusted so that the wheel does not exceed the grip limit, and the promotion of oversteering tendency and understeering tendency is suppressed. Absent.
[0051]
In the first embodiment, the braking fluid pressure command value Pj to which the braking fluid pressure correction amount ΔPv is given by the yaw rate control.^*However, the present invention is not limited to this. For example, the braking fluid pressure command value Pj given by the yaw rate control is shown.^*It is good also as 50% of.
Further, the brake fluid pressure command value Pj given by the yaw rate control^*However, the present invention is not limited to this. For example, the brake fluid pressure command value Pj for a predetermined wheel is not limited to this.^*The pressure may be reduced so as to be maintained below a predetermined value, or the pressure may be reduced so that the lateral grip can be secured and the vertical grip force is maximized (for example, the slip ratio is 10 to 20%). In other words, if the pressure is reduced so that the horizontal grip can be secured and the vertical grip force is maximized, it is possible to respond to the driver's braking operation with a predetermined braking performance. That is, by setting the braking fluid pressure correction amount ΔPv so as to reduce the excessive braking force exceeding the grip limit, the braking force does not become insufficient with respect to the driver's braking request.
[0052]
Further, the brake fluid pressure command value Pj until the yaw rate deviation Δφn becomes sufficiently small and tends to decrease.^*However, the present invention is not limited to this. For example, the pressure reduction correction may be performed until the wheel slip ratio Sj becomes smaller than the predetermined value α.
Further, in the above embodiment, an example in which the braking force is applied only to the front wheel outside the turn when suppressing the oversteer tendency is not limited to this. For example, the braking force is applied to the front and rear wheels outside the turn. It may be given. When applying a braking force to the front and rear wheels on the turning outer wheel side, the braking fluid pressure correction amount ΔPv may be subtracted from only the braking fluid pressure command value Pri of the rear wheel inside the turning. In addition, when suppressing the understeer tendency, an example in which braking force is applied only to the rear wheel on the inner side of the turning wheel is not limited to this. For example, the front and rear wheels on the inner side of the turning and the rear wheel on the outer side of the turning are shown. A braking force may be applied. When applying a braking force to the front and rear wheels on the inside of the turn and the rear wheel on the outside of the turn, the brake fluid pressure correction amount ΔPv may be subtracted from only the brake fluid pressure command value Pfo of the front wheels on the outside of the turn.
[0053]
In addition, an example has been described in which the normal brake applies hydraulic pressure to the wheel cylinder by the master cylinder hydraulic pressure connected to the brake pedal. However, like a brake-by-wire, the hydraulic source is changed from the hydraulic source to the wheel cylinder according to the operation amount of the brake pedal. The hydraulic pressure supplied may be controlled. Further, an electric brake (electric caliper) may be used instead of the hydraulic brake.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an embodiment of a vehicle behavior control device of the present invention.
FIG. 2 is a flowchart showing a brake fluid pressure calculation process executed in the control unit of FIG. 1;
FIG. 3 is a flowchart showing a braking fluid pressure correction calculation process executed in the control unit of FIG. 1;
4 is a control map used in the arithmetic processing of FIG.
FIG. 5 is a timing chart for explaining the operation of the present invention.
FIG. 6 is an explanatory diagram for explaining the operation of the present invention.
FIG. 7 is an explanatory diagram for explaining the operation of the present invention.
FIG. 8 is a flowchart showing a braking fluid pressure correction calculation process executed in the control unit of FIG. 1 in the second embodiment of the vehicle behavior control apparatus of the present invention.
9 is a control map used in the arithmetic processing of FIG.
FIG. 10 is a timing chart for explaining the operation of the second embodiment.
[Explanation of symbols]
1FL to 1RR are wheels
2FL to 2RR are wheel cylinders
3 is a brake fluid pressure unit
4 is the control unit
5FL-5RR is a wheel speed sensor
6 is a steering angle sensor
7 is a running speed sensor
8 is the yaw rate sensor
9 is an acceleration sensor
10 is a brake switch
11 is a master cylinder pressure sensor
12 is a VDC off switch
13 is a brake pedal

Claims (4)

A vehicle behavior control device for a four-wheel drive vehicle capable of limiting a differential between a front axle and a rear axle,
Based on the turning state amount detecting means for detecting the turning state amount generated in the vehicle and the turning state amount detected by the turning state amount detecting means, the braking force to each wheel is controlled so that the oversteer tendency is suppressed. Control means for controlling, braking means for applying a braking force to each wheel based on the driver's braking operation, and when the control means is controlling the braking force to each wheel so that the oversteer tendency is suppressed, A vehicle behavior control device comprising braking force correcting means for correcting the braking force applied to both rear wheels by the braking means to a small value . A vehicle behavior control device for a four-wheel drive vehicle capable of limiting a differential between a front axle and a rear axle,
Based on the turning state amount detecting means for detecting the turning state amount generated in the vehicle and the turning state amount detected by the turning state amount detecting means, the braking force to each wheel is controlled so that the understeer tendency is suppressed. Control means for controlling, braking means for applying a braking force to each wheel based on a driver's braking operation, and when the control means controls the braking force to each wheel so that an undertea tendency is suppressed. A vehicle behavior control device comprising: braking force correcting means for correcting the braking force applied to both front wheels by the braking means to a small value. The braking force correcting means includes a slip state detecting means for detecting a slip state of the predetermined wheel, and a side grip margin for calculating a side grip margin for the predetermined wheel based on the slip state detected by the slip state detecting means. a cash calculation means, the vehicle according to claim 1 or 2, characterized in that a correction amount setting means for setting a correction amount based on the lateral grip margin calculated in the lateral grip margin calculation means Behavior control device. The braking force correcting means cancels the correction when the difference between the turning state quantity detected by the turning state quantity detecting means and the target value is decreasing and the difference is not more than a predetermined value. The vehicle behavior control device according to any one of claims 1 to 3 .

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