JP4137086B2 - Vehicle travel control device - Google Patents

Description

  The present invention relates to a travel control device for a vehicle such as an automobile, more specifically, when a travel state of a vehicle becomes unstable, an apparatus that generates at least a yaw moment that stabilizes the travel state, The present invention relates to a control apparatus that performs vehicle steering control as well as behavior stabilization control.

  The running behavior of the vehicle can be stabilized by generating a yaw moment around the center of gravity of the vehicle. In well-known vehicle behavior control (VSC), the vehicle tire force is generated to produce a counter yaw moment, ie, a yaw moment in the opposite direction of oversteer, understeer or other undesirable yaw motion. Thus assisting the driver's steering to suppress undesirable yaw motion.

  Furthermore, in a vehicle equipped with a steering device that enables the steering of wheels independently of the driver's steering, the yaw moment that supports the driver's driving operation to suppress the deterioration of the behavior is It can also be generated by automatic steering of wheels. For example, in the following Patent Document 1-2, in order to generate a counter yaw moment with respect to a braking force imbalance between the left and right wheels of a vehicle, the steering angle of the wheel is controlled, thereby maintaining vehicle linear stability. It is supposed to be. In Patent Document 3, an auxiliary steering device provided on a rear wheel in a four-wheel steering vehicle is controlled by using a proportional term, a differential term and an integral term of deviation from the target value of the actual yaw rate. It has been proposed to improve the responsiveness of the auxiliary steering device against the side slip of the vehicle body caused by sudden steering, side wind disturbance, etc. in the main steering device.

Oversteering tendency, understeering tendency or other tendency of yaw behavior due to tire force imbalance or tire force saturation between the front and rear wheels or the left and right wheels of the vehicle first appears in the yaw rate of the vehicle. Therefore, a conventional device for stabilizing the running behavior of a vehicle such as a VSC device typically has a yaw rate target based on a theoretical equation of motion using parameters such as a steering angle of a wheel or a steering wheel or a vehicle speed. A value (ie, ideal yaw rate) is determined and a counter yaw moment is generated to reduce the deviation of the actual yaw rate from the target yaw rate. By adjusting the actual yaw rate to its target value, further deterioration in yaw behavior is suppressed, thereby preventing vehicle spin, drift out, unintended turning or yaw vibration.
JP-A-5-105055 Patent Publication No. 2540742 JP-A-6-135345

  However, the behavior control or running stabilization control by adjusting the yaw rate in the above-mentioned conventional device completely corrects the deviation between the yaw angle adapted to the traveling direction intended by the driver and the actual yaw angle of the vehicle body. I can't. In the control for adjusting the yaw rate described above, if the actual yaw rate matches the target value, the counter yaw moment can be obtained even if the vehicle body direction (i.e., the vehicle yaw angle) does not match the direction of the course intended by the driver. The generation of is terminated. In this regard, in a normal vehicle that is steered by the driver's steering wheel, it is theoretically difficult to determine the target yaw angle by the control device like the target yaw rate. The target yaw angle is essentially determined by the driver's intention, and the actual direction of travel of the vehicle depends largely on the relationship between the rudder angle (input of the driver's intention) and the driving conditions of the vehicle. Therefore, the driver must adjust the yaw angle through steering while checking the actual course of the vehicle.

  However, for the purpose of vehicle travel stabilization control, that is, for the purpose of assisting the driver's steering, it may be desirable to correct some tendency for the yaw angle to deviate from the driver's intended direction. That is, it is likely that the conventional vehicle behavior control device or steering control device can be improved to operate more appropriately in consideration of the yaw angle deviation caused by the yaw rate deviation.

  According to the present invention, not only the yaw behavior of the vehicle is stabilized by controlling the yaw rate, but also the correction of the yaw angle of the vehicle is performed, so that when the driving state of the new vehicle deteriorates, A vehicle travel control device that supports steering is provided.

  In one aspect of the present invention, the control device according to the present invention includes means (yaw moment applying means) provided on the vehicle to apply a yaw moment around the center of gravity of the vehicle body, such as a braking control device or a steering device. ) To control the running state of the vehicle. In the control by the device according to the present invention, firstly, vehicle running behavior control is performed by generating a stabilized yaw moment to suppress oversteer, understeer or other undesirable yaw behavior trends. . Therefore, this apparatus executes means for determining whether or not the running state of the vehicle has deteriorated, and vehicle running behavior control (running stabilization control) by adjusting the yaw rate of the vehicle, such as normal VSC control. Means.

  Second, in addition to behavior control, the device according to the present invention executes control for correcting the yaw direction of the vehicle body, that is, control for reducing deviation of the yaw angle of the vehicle from the yaw direction intended by the driver. . In order to achieve such correction of the yaw angle, the apparatus according to the present invention generates a yaw moment (orientation correction yaw moment) in a direction that reduces the deviation between the actual yaw rate and its target value based on the integrated value of the yaw rate deviation. Thus, the yaw moment applying means as described above is operated. Accordingly, the apparatus according to the present invention calculates means for detecting the actual yaw rate of the vehicle, means for calculating the target yaw rate of the vehicle based on the driving operation of the driver, and calculates an integral value of the difference between the actual yaw rate and the target yaw rate. Part.

  As can be seen, the change in the yaw angle of the vehicle body is given by the time integration of the yaw rate. Therefore, even if the target yaw angle cannot be determined as described above, the generation of the above-mentioned direction correction yaw moment reduces the yaw angle deviation caused by the yaw rate deviation, and thereby the direction of the vehicle body is driven. In this way, an undesirable tendency that the yaw angle is shifted is suppressed. In this regard, even if the yaw rate deviation is sufficiently canceled or reduced by the behavior control to suppress further yaw behavior deterioration, it is due to the yaw rate deviation during the adjustment of the yaw rate under the behavior control. Yaw angle deviation may remain. Thus, it should be understood that the orientation corrected yaw moment may be generated for correction of the remaining yaw angle deviation after the yaw rate deviation is substantially canceled.

  As described above, for a normal vehicle traveling on a normal road, the traveling direction of the vehicle is essentially determined by the driver, and it is difficult for the control device to estimate the driver's intention. It is difficult to determine the corner. Although the driver's intention is input from the rudder angle, the yaw angle response is second-order lag with respect to the yaw moment change in response to the rudder angle change, so the resulting yaw angle response is the current It is possible that it no longer matches the driver's intention. That is, the change in the yaw angle by the control based on the integral component of the past yaw rate deviation may be excessive or unexpected for the driver.

  In order to avoid such an unexpected change in yaw angle, the apparatus according to the invention described above may first be configured to perform yaw rate deviation integration when behavior control is performed. . In that case, in the normal running state, the direction correction yaw moment is not generated, and it is avoided that the correction control is executed too frequently. The generation of the direction correction yaw moment is started only when the behavior control is started, that is, when the driver's ability to control the vehicle becomes relatively low. Such a configuration in which the integration period is limited also contributes to avoiding an excessive change in yaw angle due to control.

  Furthermore, when the target yaw angle cannot be obtained, it cannot be determined whether the change in the yaw angle caused by the control is sufficient and whether the direction correction control should be terminated. Also, the yaw angle intended by the driver can be changed at any time, but the already calculated time integral value does not decrease arbitrarily. Thus, in order to properly terminate the generation of the orientation-corrected yaw moment, the apparatus according to the present invention calculates the yaw rate deviation every predetermined time, and integrates by reducing the weight of the preceding yaw rate deviation, that is, the past yaw rate deviation. It may be configured to calculate a value. In this configuration, the weight of the yaw rate deviation of the older time may be made smaller. More specifically, the integral value is obtained by multiplying the forgetting factor (constant or decreasing with time) by the integral value calculated for the time before the current time, and the yaw rate at the current time. It may be given by adding the deviation. By multiplying this forgetting factor, the weight of the older yaw rate deviation in the integrated value is reduced.

  According to the method of integration described above, the contribution of each yaw rate deviation to the integrated value is reduced over time, so that even if the yaw angle intended by the driver is changed, it has already been incorporated into the integrated value. The effect of yaw rate deviation is reduced, thus contributing to avoiding excessive or unexpected yaw angle control. After the yaw rate deviation is substantially canceled and the integration process is terminated, the sum of the integrated values, and thus the direction correcting yaw moment, will be gradually reduced. This configuration is desirable in that it can prevent the vehicle behavior from deteriorating when the direction correction yaw moment is suddenly removed.

  As described above, the behavior control and the direction correction control may be executed by operating either the steering device or the braking device. A steering device that allows the front wheels to be steered independently of the driver's steering operation is provided, and the direction correction yaw moment determined based on the integrated value of the yaw rate deviation is generated by the operation of the steering device. Regarding the vehicle, preferably, when the vehicle is in an understeer state, an increase in the direction correction yaw moment is suppressed, and the direction correction control is not executed. This is because the tire force of the front wheels is almost saturated in the understeer state, and therefore further steering that increases the front wheel steering angle deteriorates the running behavior of the vehicle. On the other hand, for a vehicle equipped with a steering device that enables steering of the rear wheels independently of the driver's steering operation, that is, a four-wheel steering vehicle, the direction correction yaw moment determined based on the integration of the yaw rate deviation is However, when the vehicle is in an oversteer state, the tire force of the rear wheels is almost saturated, and in this case, preferably the increase in the direction correction yaw moment is The direction correction control is not executed.

  Both the behavior control and the direction correction control may be executed by the operation of the vehicle brake control device. (Even if the vehicle is equipped with a steering device that enables the steering of the wheels independently of the driver's steering operation, the direction correction control may be executed by the operation of the braking device.) The total target yaw moment generated by the control is the sum of the stabilized yaw moment determined based on the current yaw rate deviation and the direction correction yaw moment determined based on the integral value of the yaw rate deviation. In carrying out the control according to the present invention, preferably, as described above, the target yaw moment will be generated mainly by the wheels whose tire forces are not saturated.

  Therefore, according to the present invention, a novel vehicle travel control device is provided that corrects the yaw angle of the vehicle in the yaw direction intended by the driver, along with vehicle behavior control, by generating or applying the yaw moment.

  Further, according to the present invention, a vehicle travel control device that generates a direction correction yaw moment determined based on an integrated value of a difference or deviation between an actual yaw rate and a target yaw rate by operating a vehicle steering device or a braking device. Is provided.

  Furthermore, according to the present invention, there is provided a vehicle travel control device that continuously generates a yaw moment for correcting a yaw angle of a vehicle even after the yaw rate deviation is canceled by behavior control.

  Furthermore, according to the present invention, there is provided a vehicle travel control device that corrects the yaw angle of a vehicle so that an excessive or unexpected yaw moment is not applied.

  In addition, according to the present invention, there is provided a vehicle travel control device for correcting a yaw angle of a vehicle so that the direction correcting yaw moment disappears smoothly even when the target yaw angle cannot be obtained. Is done.

  Other objects and advantages of the present invention will be in part apparent and pointed out hereinafter.

  FIG. 1 schematically shows a four-wheel rear-wheel drive vehicle having a first preferred embodiment of a vehicle travel control device according to the present invention. In this figure, the vehicle body 12 has left and right front wheels 10FL and 10FR and left and right rear wheels 10RL and 10RR. In an ordinary mode, the engine (in accordance with the throttle valve opening degree responding to depression of the accelerator pedal by the driver) A driving torque or a rotational driving force output from an unillustrated) is transmitted to the rear wheels 10RL and 10RR via a differential gear device or the like (not illustrated).

  In this embodiment, the vehicle is provided with a steering device 16 that enables steering of the front wheels independently of the driver's handling. As shown in the figure, the front wheels 10FL and 10FR are respectively steered by tie rods 20L and R by a rack and pinion type power steering device 16 in response to the rotation of the steering wheel 14 operated by the driver. . The steering device 16 employed here is a semi-steer-by-wire type, and the turning angle varying device 24 is an auxiliary turning device that can change the steering angle of the front wheels independently of the handling of the driver. Is provided.

  The turning angle varying device 24 includes a drive motor 32, which is connected via a housing 24 A operatively connected to the steering wheel 14 via the upper steering shaft 22, a lower steering shaft 26 and a universal joint 28. And a rotor 24B operatively connected to the pinion shaft 30. The drive motor 32 rotates the lower steering shaft 26 with respect to the upper steering shaft 22 under the control of the electronic control unit 34 as described below. In order to control the operation of the turning angle varying device 24, the steering angle of the steering wheel 14, that is, the rotation angle θ of the upper steering shaft 22 and the relative angle θre of the lower steering shaft 26 measured from the upper steering shaft 22 (housing The relative angle between 24A and rotor 24B) is detected by steering angle sensors 50 and 52, respectively.

  The power steering device 16 may be either a hydraulic power steering device or an electric power steering device. However, in order to reduce the reaction torque transmitted from the device 24 to the steering wheel 14 during the automatic steering control, the motor and a ball screw type that converts the rotational torque of the motor into a force in the reciprocating direction of the rack bar 18 are used. A rack coaxial type electric power steering device having such a conversion mechanism is preferably used.

  The braking device 36 that generates braking force on each wheel includes an oil reservoir, an oil pump, various valves (not shown), wheel cylinders 40FL, 40FR, 40RL, 40RR equipped on each wheel, and a driver. The hydraulic circuit 38 includes a master cylinder 44 that is operated in response to depression of the brake pedal 42. In such a braking device, the brake pressure in each wheel cylinder, that is, the braking force in each wheel, is adjusted by the hydraulic circuit 38 in response to the master cylinder pressure. As will be described below, the brake pressure in each wheel cylinder is also controlled by the electronic control unit 34. In order to control the brake pressure, pressure sensors 62 and 64i (i = FL, FR, RL, and RR are the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel, respectively). It may be provided to detect the master cylinder pressure Pm and the pressure Pbi (i = FL, FR, RL, RR) of the wheel cylinders 40FL-40RR.

  The steering angle variable device 24 and the electronic control device 34 for controlling the brake pressure (braking force) of each wheel are a normal type CPU, ROM, RAM and input / output ports connected to each other by a bidirectional common bus. A microcomputer having the device and a drive circuit may be included. As shown in FIG. 1, the control device 34 is connected to the steering angle θ of the steering wheel 14, the relative angle θre of the lower steering shaft, the longitudinal acceleration Gx detected by the longitudinal acceleration sensor 54, and the yaw rate detected by the yaw rate sensor 56. γ, lateral acceleration Gy detected by the lateral acceleration sensor 58, pressure Pbi in the wheel cylinder 40FL-40RR (i = FL, FR, RL, RR) and wheel speed sensor 60i (i = FL, FR, RL, RR) Each signal of the wheel speed Vwi (i = FL, FR, RL, RR) detected by is input.

  As will be described below, the control device 34 performs steering gear ratio control, behavior control, and direction correction control by automatic steering control or control for adjusting the braking force or pressure of each wheel. The parameters in the following expression are defined as positive in the forward direction and the left direction (counterclockwise in FIG. 1).

In the steering gear ratio control, the control device 34 controls the turning angle varying device 24 by rotating the electric motor 32, and the steering gear ratio, that is, the steering angle of the front wheels with respect to the rotation angle of the steering wheel 14. To provide a predetermined steering characteristic. In operation, first, the steering gear ratio Rg for achieving a predetermined steering characteristic is determined based on the vehicle speed V calculated from the wheel speed Vwi using the map shown in FIG. 2A. The target rudder angle δst is expressed by the following formula:
δst = θ / Rg (1)
The steered angle varying device 24 is operated to steer the front wheels and adjust the steered angle of the front wheels to δst. Note that δst may be further determined as a function of the steering speed in order to improve the transient response of the vehicle motion. It should be understood that the steering gear ratio may be determined by other methods known in the art.

  The behavior control for suppressing the understeer or oversteer tendency may be executed in the conventional manner by adjusting the braking force or the brake pressure of each wheel as follows.

First, in order to estimate the vehicle behavior, the spin amount SV and the drift amount DV are determined as follows.
SV = K1 · β + K2 · dVy or = K1 · β + K2 · dβ (2)
DS = γt−γ or = H · (γt−γ) / V (3)
Where β is the slip angle of the vehicle, dVy is the side-slip acceleration of the vehicle, dβ is the time derivative of β, K1 and K2 are appropriate weighting factors, and γt is The target yaw rate estimated from the vehicle speed V and the steering angle δ, γ is the actual yaw rate, and H is the wheelbase. dVy is given by the difference between the product of the lateral acceleration Gy and the yaw rate γ and the vehicle speed V: Gy−γ · V. β is obtained by the ratio of the sideslip velocity to the longitudinal velocity: Vy / Vx. Here, Vx = V, and Vy is given by integrating dVy. γt is obtained by γt = V · δ / {(1 + Kh · V ² ) · H} × (1 / (1 + T · s), where δ is an actual steering angle based on the steering angle θ. , Kh is a stability factor, and T and s are time constants and frequency parameters in the Laplace transform.

Thus, the spin state quantity SS and the drift-out state quantity DS are defined as follows. :
SS = ± SV (4)
DS = ± DV (5)
(+: Turning left;-: turning right. SS and DS are defined as 0 when taking negative values.)
SS and DS indicate the degree of spin and drift out, respectively. (The worse the behavior, the greater one of the values.)

Next, the target braking force for the wheel is calculated as follows using the state quantity. :
Fsfo = Fssfo
Fsfi = 0
Fsro = (Fsall−Fssfo) ・ (1-Ksri)
Fsri = (Fsall−Fssfo) · Ksri (6)
Here, Fsj (j = fo, fi, ro, ri: front wheel outside turning, front wheel inside turning, rear wheel outside turning, rear wheel inside turning) is a target braking force value of each wheel. Fssfo is determined as a function of SS using the map of FIG. 2B. Fsall is determined as a function of DS using the map of FIG. 2C. Ksri is a suitable rear wheel distribution coefficient (typically a positive constant greater than 0.5). When the calculated value of Fsj becomes negative, the value is set to 0. The force distribution determined above results in an anti-spin or anti-drift out-yaw moment, as is known in the art.

Finally, each target braking force value is converted into a target value Pti of the brake pressure of each wheel using a conversion coefficient Kb as follows:
[While turning left]
Ptfl ＝ Fsfi ・ Kb
Ptfr ＝ Fsfo ・ Kb
Ptrl ＝ Fsri ・ Kb
Ptrr = Fsro · Kb (7)
[Turning right]
Ptfl ＝ Fsfo ・ Kb
Ptfr ＝ Fsfi ・ Kb
Ptrl ＝ Fsro ・ Kb
Ptrr = Fsri · Kb (8)
The turning direction can be determined by the sign of the actual yaw rate. If all values of Pti are 0, behavior control is not executed.

  According to the behavior control as exemplified above, the deviation of the actual yaw rate γ from the target yaw rate γt is canceled, but this control is caused by the yaw rate deviation from the yaw direction intended by the driver. The deviation of the yaw angle of the vehicle body 12 is not completely corrected. Therefore, at the end of the behavior control, the yaw angle of the vehicle body may not match the traveling direction intended by the driver.

  However, according to the direction correction control of the control device according to the present invention, the tendency of the yaw angle to be deviated is reduced, thereby making it possible to bring the vehicle direction closer to the direction intended by the driver. In the embodiment illustrated in FIG. 1, the target rudder angle δst is corrected based on the integrated value of the yaw rate deviation during execution of the behavior control, and the steering device 16 is operated based on the corrected target rudder angle. Thus, a yaw moment for correcting the traveling direction (yaw angle) of the vehicle body is generated. In this regard, preferably, after the behavior control is terminated, the orientation correction yaw moment continues to be generated while being gradually reduced to zero in order to cancel or reduce the remaining yaw angle deviation. Further, considering that the traveling direction intended by the driver can be changed during the execution of the direction correction control, the influence of the past traveling state or the old yaw rate deviation on the direction correction yaw moment should be reduced. (If the target rudder angle δst is changed, the past yaw rate deviation becomes useless in the control.)

In order to achieve the application of the direction correction yaw moment as described above, the integral value Δγint of the yaw rate deviation periodically integrates the deviation between the actual yaw rate and the target yaw rate at a predetermined time (or moment), It may be provided by multiplying the forgetting factor set to a value between 0 and 1 by the integral value in the previous cycle. That is,
Δγint = Δγintf · K + Δγ · Kg (9)
Here, Kg is a gain for Δγ having a value of 0 or 1 determined as described later. Since the direction correction yaw moment is given in a direction that reduces the deviation of the actual yaw rate from the target yaw rate, Δγ is given by γt−γ. The target yaw rate γt is given by the following expression similarly to the case of behavior control.
γt = V · δ / (1 + Kh · V ² ) · H · (1 + T · s) (10)
The target yaw rate γt and the yaw rate deviation Δγ may be given from a behavior control routine. (Δγ is equal to the drift amount DV.)

Next, the correction amount Δδft of the target rudder angle of the front wheels is determined using the integrated value Δγint as follows.
Δδft = Δγint · Ksf (11A)
Here, Ksf is a conversion coefficient.

  In equation (9), Δγ is set to 0 after the end of normal state and behavior control. Therefore, the addition of the second term in equation (9) is executed only when behavior control is executed. Further, while repeating the calculation of Equation (9), the contribution of the old yaw rate deviation to the target rudder angle, that is, the direction correction yaw moment, is obtained by periodically multiplying the previously calculated integral value Δγintf by the forgetting factor K. Becomes smaller. Therefore, after the behavior control is finished, the value of Δγint is gradually reduced. The forgetting factor K may be constant, but may be reduced with time or while the cycle repeats.

  The gain Kg is set to 0 when the understeer state of the vehicle reaches a slightly high level. When the front wheel tire force is almost saturated under an understeer condition, increasing the front wheel cornering force causes slippage of the front wheel tire. Therefore, when the understeer state is slightly advanced, no direction correction yaw moment is generated to prevent the front wheel from slipping. On the other hand, Kg is set to 1 in the oversteer state.

  FIG. 3 shows a typical flow chart of the operation of the direction correction control for generating the direction correction yaw moment as described above. This control routine is initiated by closing an ignition switch (not shown in FIG. 1) and may be repeated with a period on the order of milliseconds during operation of the vehicle.

  In this routine, as in the normal mode, first, reading of the above signal is executed (step 10), and it is determined whether or not behavior control is being executed (step 20). When the behavior control is not executed, Δγ and Δγintf are 0 in the equation (9), so the integrated value Δγint is calculated as 0 (step 80).

  On the other hand, when behavior control is started, the difference between the actual yaw rate γ and the target yaw rate γt is acquired (steps 30 and 40), and it is determined whether or not the vehicle is in a slightly advanced understeer state (step 50). ). This determination may be made by determining whether sign γ · Δγ exceeds a positive reference value Δγp. Signγ is a sign of γ. If the answer is yes, Kg is set to 0 (step 70), so yaw rate deviation integration is not performed and no direction correction yaw moment is generated. On the other hand, if the answer to step 50 is no, Kg is set to 1 (step 60). It should be noted that the generation of the direction correction yaw moment may be prohibited whenever the vehicle is understeered. (Δγp is set to a small value.)

  Next, an integral value Δγint and a steering angle correction amount Δδft are calculated in steps 80 and 90 by equations (9) and (11A), respectively, and the steering angle is controlled to be δst + Δδft (δst is (Given by equation (1)). It should be understood that both a stabilizing yaw moment and a direction correction yaw moment are generated during behavior control under oversteer conditions.

  After the end of the behavior control, the integration process in steps 30 to 70 is bypassed. However, since the integral value Δγint is calculated as Δγintf · K, in order to reduce the yaw angle deviation that can remain after the end of the behavior control, A direction correction yaw moment is generated. Δγint, that is, the direction correction yaw moment, is gradually reduced to 0 by repeatedly multiplying the forgetting factor K while repeating the cycle.

  FIG. 4 schematically shows a rear wheel drive vehicle having a second preferred embodiment of the vehicle travel control device according to the present invention. In this vehicle, a steering device 70 for the rear wheels 10RL and RR is provided, and the rear wheels are steered by a hydraulic or electric power steering device 72 via tie rods 74L and R. The The steering angle of the rear wheels is controlled by the control device 34. For the front wheels, the rudder angle may be controlled by driver handling. (A steering device 16 that enables steering of the front wheels independently of the driver's handling as shown in FIG. 1 may be provided.)

  In operation, behavior control (or steering gear ratio control) may be performed as in the first embodiment described above. However, the direction correction control is performed by controlling the steering angle of the rear wheels. That is, the direction correction yaw moment is generated by the rear wheel. In the direction correction control, the yaw rate deviation integration process is the same as in the first embodiment, except that the gain Kg in equation (9) is set to 0 when the vehicle is highly oversteered. It may be. The integration is not performed when the vehicle is slightly oversteered because the rear wheel tire force is almost saturated. On the other hand, when the vehicle is understeered, Kg is set to 1 in equation (9). Thus, in step 50 of the flowchart of FIG. 3, whether or not the vehicle is in an oversteer state is determined by, for example, determining whether or not signγ · Δγ is smaller than a predetermined negative reference value Δγn. To be judged. It should be noted that the generation of the direction correction yaw moment may be prohibited whenever the vehicle is oversteered. (Δγn is set to a small value.)

The target rudder angle Δδrt of the rear wheels is
Δδrt = Δγint · Ksr (11B)
Is set by Here, Ksr is a conversion coefficient. It should be understood that the target steering angle of the rear wheels is controlled only by Δδrt.

  By the way, the direction correction control can be performed through the braking force distribution control by controlling the brake pressure of each wheel together with the behavior control. Therefore, in this case, a steering device for enabling the steering of the wheel independent of the driver's handling is not necessary, and the cost for manufacturing the vehicle can be saved. In the case of the braking force distribution control, the wheel brake pressure for generating the direction correction yaw moment is corrected by an amount determined based on the integrated value of the yaw rate deviation. However, if the tire force on the wheel to generate the orientation correction yaw moment is saturated when the vehicle is slightly understeered or oversteered, the orientation correction yaw moment by that tire is Not generated.

FIG. 5 shows a typical flowchart of the operation of the direction correction control by the braking force control, which is almost the same as the flowchart of FIG. In this flowchart, the integration of the yaw rate deviation is performed in step 150: Δγint = Δγintf · K + Δγ (12)
It is executed by. Therefore, in this equation, the gain Kg in FIG. 3 is not used. Instead, when the vehicle behavior deteriorates, the conversion coefficients Kgf and Kgr from the unit of the integral value to the front wheel and rear wheel brake pressure units are set to 0 for the wheel where the tire force is saturated.

  In operation, as shown in the flowchart of FIG. 3, reading of the above signal is executed (step 10), and it is determined whether behavior control is being executed (step 20). When the behavior control is not executed, Δγintf and Δγ are 0, so that the integral value Δγint is calculated as 0 (step 150).

  On the other hand, when behavior control is executed, an integration process is executed. First, after obtaining the yaw rate deviation, it is determined whether or not the vehicle is understeered (step 50). When the vehicle is understeer, the conversion coefficients Kgf and Kgr for the front wheels and the rear wheels are set to 0 and Kgrs (predetermined values), respectively (step 120). If not, the vehicle is considered oversteered (because the behavior of the vehicle has deteriorated in either direction under behavior control), the conversion for the front and rear wheels The coefficients Kgf and Kgr are set to Kgfs (predetermined value) and 0, respectively (step 130). Thereafter, the integral Δγint is calculated as shown in equation (12) in step 150.

The target brake pressure component Pcti (i = fl, fr, rl, rr) for generating the direction correction yaw moment is determined as follows.
[While turning left]
Pctfl = 0
Pctfr = | Δγint | · Kgf
Pctrl = Δγint · Kgr
Pctrr = 0 (13)
[Turning right]
Ptfl = Δγint · Kgf
Ptfr = 0
Ptrl = 0
Ptrr = | Δγint | · Kgr (14)

Therefore, the total target brake pressure during behavior control is as follows:
[While turning left]
Ptfl = Fsfi · Kb
Ptfr = Fsfo · Kb + | Δγint | · Kgf
Ptrl = Fsri · Kb + Δγint · Kgr
Ptrr = Fsro · Kb (15)
[Turning right]
Ptfl = Fsfo · Kb + Δγint · Kgf
Ptfr = Fsfi · Kb
Ptrl = Fsro · Kb
Ptrr = Fsri · Kb + | Δγint | · Kgr
... (16)
After the behavior control is finished, the total target brake pressure becomes a value represented by the equation (13) or (14).

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

  For example, in the embodiment shown in FIGS. 3 and 5 above, the direction correction control may be terminated together with the behavior control. The direction correction control is executed independently of the driver's handling and has the effect of steering the vehicle. Accordingly, whether or not to continue the direction correction control after the behavior control is ended may be selected according to the driver's preference.

  Furthermore, as will be readily understood by those skilled in the art, in the embodiment of FIGS. 1 and 4, behavior control and orientation correction control may be performed by a steering device and a braking device, respectively.

FIG. 1 is a four-wheel rear-wheel drive vehicle equipped with a semi-steer-by-wire-type steering device that functions as an automatic steering device for front wheels and a first embodiment of a vehicle travel control device according to the present invention. FIG. FIG. 2A shows a map of the relationship between the vehicle speed V and the steering gear ratio Rg used in the steering gear ratio control. 2B and 2C show maps used for calculating the braking force components Fssfo and Fsall based on the spin state quantity SS and the drift-out state quantity DS in behavior control. FIG. 3 is a flowchart of a direction correction control routine executed in a vehicle according to the first and second preferred embodiments of FIGS. 1 and 4 according to the present invention. FIG. 4 is a schematic view of a four-wheel rear wheel drive vehicle equipped with a steering device for rear wheels and another embodiment of the vehicle travel control device according to the present invention. FIG. 5 is a flowchart of a direction correction control routine (third embodiment) according to the present invention executed by the braking force control.

Explanation of symbols

10FR to 10RL Wheel 24 Steering angle variable device 34 Electronic control device 36 Braking device 44 Master cylinder 50 Steering angle sensor 54 Longitudinal acceleration sensor 56 Lateral acceleration sensor 58 Yaw rate sensor 60FL to 60RR Wheel speed sensor 62, 64FL to 64RR Pressure sensor

Claims (8)

When the vehicle running state is determined to be unstable and the vehicle running state is determined to be unstable, at least a first yaw moment applying unit applies a stabilizing yaw moment to the vehicle to control the vehicle running stabilization. A vehicle travel control device having a control means for performing a vehicle yaw rate detection means for detecting an actual yaw rate of the vehicle, a target yaw rate calculation means for calculating a target yaw rate of the vehicle based on a driving operation of the driver, An integral value calculating means for calculating an integral value of the deviation between the yaw rate and the actual yaw rate, and the integral value calculating means calculates the yaw rate deviation at a predetermined time, The yaw rate deviation is reduced by reducing the weight of the yaw rate deviation and integrating the current yaw rate deviation to the integrated value of the past yaw rate deviation. Calculates the minutes value, said control means and performing a vehicle orientation correcting control by applying a yaw moment of the orientation correcting the vehicle by the second yaw moment applying means based on the integral value of the yaw rate deviation vehicle Travel control device.   2. The vehicle travel control apparatus according to claim 1, wherein the integral value calculation means calculates the integral value when the travel stabilization control is being performed. 3. The vehicle travel control apparatus according to claim 1 or 2 , wherein the integral value calculating means calculates a current yaw rate deviation as a sum of a value obtained by multiplying a previously calculated integrated value of the yaw rate deviation by a forgetting factor and a current yaw rate deviation. A device characterized by calculating an integral value of. 3. The vehicle travel control apparatus according to claim 1 , wherein the integral value calculating means calculates an integral value of the yaw rate deviation as a weight sum of yaw rate deviations in which the weight is reduced as the yaw rate deviation becomes older. . A travel control device of a vehicle according to claim 1, wherein the first and second yaw moment applying means yaw moment to the vehicle by controlling the steering angle of the controlled or wheel braking driving force of each wheel The apparatus characterized by providing. 6. The vehicle travel control apparatus according to claim 5 , wherein the second yaw moment applying means applies a yaw moment to the vehicle by controlling a steering angle of a front wheel, and the control means is in an understeer state of the vehicle. An apparatus that suppresses an increase in a control amount of the second yaw moment applying means when it is determined that the second yaw moment is applied. 6. The vehicle travel control apparatus according to claim 5 , wherein the second yaw moment applying means applies a yaw moment to the vehicle by controlling a rudder angle of a rear wheel, and the control means has a vehicle overload. An apparatus that suppresses an increase in a control amount of the second yaw moment applying means when it is determined that the vehicle is in a steering state. A travel control device of a vehicle of claims 1 to 7, wherein said first and second yaw moment applying means is a same means, the sum of the yaw moment of the direction corrected yaw moment of the stabilizing A device characterized by being applied to a vehicle.

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