JP5194430B2 - Four-wheel steering control device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a four-wheel steering controller capable of preventing a yaw moment for increasing stability produced by "front wheel steering angle correction control" from being canceled by "rear wheel steering control". <P>SOLUTION: In a "front wheel steering control", a front wheel reference steering angle (equivalent to &theta;rel1t) is determined according to a vehicle body speed Vx and the rotational angle &theta;sw of a steering wheel, and a front wheel correction steering angle (equivalent to &theta;rel2t) is determined according to the state of the vehicle (a difference &Delta;FX between the front and rear forces of left and right wheels and the deviation of the quantity of the state of the motion &Delta;Vm_os, &Delta;vm_us). The front wheel steering angle is controlled to the value obtained by correcting the front wheel reference steering angle by the amount of the front wheel correction steering angle. Namely, the "front wheel steering angle correction control" is performed. In the (same phase control) of the "rear wheel steering control", a rear wheel reference steering angle (&delta;rt) is determined according to an actual front wheel steering angle &delta;fa and the vehicle body speed Vx. The rear wheel steering angle is so controlled as to be generally aligned with the rear wheel reference steering angle. When the "front wheel steering angle correction control" is started, the rear wheel steering angle is held at a value at the start time or gradually moved toward "zero". <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a four-wheel steering control device for a vehicle.

  While the vehicle is traveling on a road surface having a different friction coefficient between the left and right road surfaces (hereinafter referred to as “μ split road surface”), wheel slip such as so-called anti-skid control (ABS control), so-called traction control (TCS control), etc. When the slip suppression control is performed (hereinafter referred to as “μ split control”), the front / rear force of the left and right wheels (the friction force in the acceleration / deceleration direction generated between the road surface and the tire). This is also called braking / driving force. A yaw moment that deflects the vehicle due to the difference between the longitudinal forces (hereinafter referred to as “the longitudinal force difference-induced yaw moment”) is generated.

  In order to suppress the deflection of the vehicle due to the longitudinal force difference-induced yaw moment, the steering angle of the front wheels is corrected in the direction opposite to the vehicle deflection direction to reduce (cancel) this longitudinal force difference-induced yaw moment. It is necessary to generate the yaw moment. The operation of correcting the steering angle of the front wheels in the direction opposite to the vehicle deflection direction is called a counter steer operation.

  In the apparatus described in Patent Document 1 below, the counter steer operation is automatically executed without the driver's steering wheel operation. More specifically, the corrected steering angle of the front wheels is determined based on the difference between the front and rear forces of the left and right wheels. Then, the rudder angle of the front wheels is automatically corrected by the corrected rudder angle from the reference rudder angle determined based on the rotation angle of the steering wheel.

  Further, in the device described in Patent Document 2 below, when the turning state of the vehicle is different from the target state (neutral steer state or understeer state) (oversteer state), the yaw in the direction in which the turning state approaches the target state The corrected steering angle of the front wheels for generating the moment is determined. Then, the rudder angle of the front wheels is automatically corrected by the corrected rudder angle from the reference rudder angle.

  Hereinafter, the yaw moment generated for improving vehicle stability is referred to as “stability improving yaw moment”, and the steering angle of the front wheels is automatically set to generate the stability improving yaw moment. The control to be corrected is referred to as “front wheel steering angle correction control”.

  On the other hand, in recent years, devices for performing “rear wheel steering control” for controlling the steering angle of the rear wheels in accordance with the steering angle of the front wheels and the traveling state (vehicle speed, etc.) of the vehicle have been known. For example, in the device described in Patent Document 3 below, the rear wheel rudder angle is controlled in accordance with the front wheel rudder angle in the opposite direction to the front wheel rudder angle (reverse phase control) at low vehicle speeds, and the rear wheel rudder angle at high vehicle speeds. Is controlled according to the front wheel steering angle in the same direction as the front wheel steering angle (in-phase control).

By the way, consider a case where the above-described front wheel steering angle correction control is performed in an apparatus in which the above-described rear wheel steering control (particularly, in-phase control) is performed. In this case, when the front wheel steering angle is corrected by the front wheel steering angle correction control (when the front wheel is steered), the rear wheel is steered in the same direction as the correction direction of the front wheel steering angle by the rear wheel steering control. Such a change in the rear wheel steering angle generates a yaw moment in the opposite direction to the stability improving yaw moment generated by the correction of the front wheel steering angle. That is, there may be a problem that the stability improving yaw moment generated by the front wheel steering angle correction control is canceled by the rear wheel steering control (see FIGS. 9A and 10A described later).
JP 2005-255035 A Japanese National Patent Publication No. 4-500341 Japanese Examined Patent Publication No. 6-49465

  Accordingly, an object of the present invention is to provide a four-wheel steering control device capable of suppressing the stability improving yaw moment generated by the front wheel steering angle correction control from being canceled by the rear wheel steering control.

  The four-wheel steering control device for a vehicle according to the present invention is applied to a vehicle that performs both the front wheel steering angle correction control and the rear wheel steering control, and based on the operation of the steering operation member by the driver of the vehicle. A reference value determining means for determining a reference value of a value corresponding to the steering angle; a correction value determining means for determining a correction value of the front wheel steering angle equivalent value based on a value representing a motion state in the yaw direction of the vehicle; Target value determining means for determining the target value of the front wheel steering angle equivalent value by correcting the reference value by the correction value, and the front wheel so that the actual value of the front wheel steering angle equivalent value matches the target value. First control means for controlling the steering angle.

  Here, the “value corresponding to the rudder angle of the front wheels” means, for example, a steering gear that automatically adjusts the ratio of the rudder angle of the front wheels to the rotation angle of the steering wheel itself using an electric motor. (Absolute) rotation angle of the same electric motor when a variable ratio mechanism (hereinafter referred to as “VGRS”) is used, upper steering shaft and lower steering shaft interposing VGRS when VGRS is used Relative rotation angle, etc.

  The “reference value” of the front wheel steering angle equivalent value is determined based on, for example, the operation (amount) of the steering operation member, the vehicle speed, and the like. In addition, the “value representing the motion state of the vehicle in the yaw direction” is a value calculated using the yaw rate, lateral acceleration, etc. that appear as a result of the yaw motion of the vehicle, and the steering operation member that causes the yaw motion of the vehicle The value calculated using the operation (amount), the longitudinal force of the wheel, the lateral force, etc., for example, the longitudinal force difference between the left and right wheels (during the above μ split control), the target motion state amount and the actual motion state amount Difference (degree of understeer / oversteer). By providing these means, the front wheel steering angle correction control can be achieved according to the movement state of the vehicle in the yaw direction, and the above-described stability improving yaw moment can be generated.

  In addition, the four-wheel steering control device for a vehicle according to the present invention includes a target rear wheel steering angle determination unit that determines a target rear wheel steering angle (in the same direction as the front wheel steering angle) based on the steering angle of the front wheel, Second control means for controlling the steering angle of the rear wheel so that the actual value of the steering angle of the rear wheel coincides with the target rear wheel steering angle. By providing these means, the rear wheel steering control is achieved.

  The four-wheel steering control device according to the present invention is characterized in that it includes a determination unit that determines whether or not the steering angle of the front wheel is corrected using the correction value, and the target When the rear wheel rudder angle determining means is determined to be in the corrected state, a control stop process is performed to hold the target rear wheel rudder angle constant or to gradually return it toward zero (neutral position). It is in providing a means. Hereinafter, “when determined to be in the corrected state” may be referred to as “in front wheel steering angle correction control being executed”.

  Here, the determination means, for example, when the period during which the correction value is maintained within the predetermined range has reached a predetermined period from when the correction value has changed from zero to a value outside the predetermined range including zero. May be configured to determine that the correction state exists. Alternatively, the determination unit may be configured to determine that the correction value is in the correction state when the correction value is outside a predetermined range including zero.

  According to this, when “front wheel steering angle correction control is being executed”, the “control stop process” is performed on the target rear wheel steering angle. Accordingly, when the front wheel rudder angle is corrected by the front wheel rudder angle correction control, that is, when “front wheel rudder angle correction control is being executed”, the rear wheels are steered in the same direction as the correction direction of the front wheel rudder angle by the rear wheel steering control. Is suppressed. As a result, the problem that the stability improving yaw moment generated by the front wheel steering angle correction control is canceled by the rear wheel steering control can be suppressed (see FIGS. 9B and 10B described later).

  In the four-wheel steering control device according to the present invention, the target rear wheel rudder angle determining means includes, for example, reference rudder angle determining means for determining a reference rudder angle of the rear wheel based on the rudder angle of the front wheel. The target rear wheel steering angle before the control stop process is performed is determined to be equal to the reference steering angle. The “rear wheel reference rudder angle” is determined based on, for example, the rudder angle of the front wheel and the vehicle speed.

  The target rear wheel rudder angle determining unit includes the reference rudder angle determining unit, and a corrected rudder angle determining unit that determines a corrected rudder angle of the rear wheel based on a value representing a motion state of the vehicle in the yaw direction. The target rear wheel steering angle before the control stop processing is performed is determined to be equal to the reference steering angle, and the target rear wheel steering angle after the control stop processing is corrected is corrected. The target rear wheel rudder angle may be determined by correcting (finally) the rudder angle.

  In this case, the “value indicating the motion state of the vehicle in the yaw direction” is also a value calculated using the yaw rate, the lateral acceleration, etc. that appear as a result of the yaw motion of the vehicle, and causes the yaw motion of the vehicle. This is a value calculated using the operation (amount) of the steering operation member, the longitudinal force of the wheel, the lateral force, etc., for example, the longitudinal force difference between the left and right wheels (during the above-mentioned μ split control), This is the difference in the amount of actual motion. By determining the target rear wheel rudder angle in this way, the rear wheel rudder angle is automatically corrected by the corrected rudder angle from the reference rudder angle, and the stability according to the movement state of the vehicle in the yaw direction is improved. An improvement yaw moment may be generated. Hereinafter, the control for automatically correcting the steering angle of the rear wheel in order to generate the stability improving yaw moment is referred to as “rear wheel steering angle correction control”. That is, in this case, in addition to the stability improving yaw moment by the front wheel rudder angle correction control, the stability improving yaw moment by the rear wheel rudder angle correction control can be generated, and the stability of the vehicle in the yaw motion is further improved. obtain.

  The correction direction of the rear wheel steering angle by the rear wheel steering angle correction control is usually opposite to the correction direction of the front wheel steering angle by the front wheel steering angle correction control. On the other hand, when “front wheel steering angle correction control is being executed”, the above-mentioned “control stop processing” is performed on the target rear wheel steering angle, so that the target rear wheel steering angle is corrected by the rear wheel steering control. Is prevented from changing in the same direction. As described above, in the above configuration, the direction of change of the target rear wheel steering angle when the front wheel steering angle is corrected by the front wheel steering angle correction control and the direction of correction of the rear wheel steering angle by the rear wheel steering angle correction control do not conflict ( Hard to do). As a result, the vehicle stability improvement effect by the front wheel steering angle correction control can be maintained, and the vehicle stability improvement effect by the rear wheel steering angle correction control can be sufficiently exhibited.

  Embodiments of a four-wheel steering control device for a vehicle according to the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 shows a schematic configuration of a vehicle equipped with a four-wheel steering control device (hereinafter referred to as “this device”) according to a first embodiment of the present invention. The present apparatus includes a front wheel steering control mechanism 20, a rear wheel steering control mechanism 30, and a hydraulic unit 40.

  In the front wheel steering control mechanism 20, a steering wheel 21 operated by a driver is connected to an electric power steering mechanism (EPS) via an upper steering shaft 22, a steering gear ratio variable mechanism VGRS (STRf), and a lower steering shaft 23. ing. Thereby, the rotation of the steering wheel 21 is transmitted to the EPS.

  The EPS is constituted by one of well-known configurations, and converts the rotational motion of the lower steering shaft 23 into the translational motion of the rod 24 in the left-right direction of the vehicle body and in a direction to assist the rotational torque received from the lower steering shaft 23. An assist force for driving the rod 24 is generated by an electric motor (not shown). As described above, when the steering wheel 21 is rotated by the driver, the front wheels FL and FR are steered while the driver's steering torque is assisted by the assist force.

  The STRf is composed of a motor MTf and a gear mechanism (not shown). By controlling the (absolute) rotation angle of the motor MTf, the relative rotation angle of the lower steering shaft 23 with respect to the upper steering shaft 22 (hereinafter, simply referred to as STRf). It is also called “relative angle”). Thereby, by controlling the relative angle, the ratio of the rotation angle of the steering wheel 21 to the steering angle of the front wheels FL and FR (steering gear ratio) can be changed.

  The rear wheel steering control mechanism 30 has a rear wheel steering mechanism STRr. The STRr includes a motor MTr and a gear mechanism (not shown), and the position of the rod 31 in the left-right direction of the vehicle body can be adjusted by controlling the (absolute) rotation angle of the motor MTr. Thus, the steering angle of the rear wheels RL and RR can be changed by controlling the rotation angle of the motor MTr.

  The hydraulic unit (HU) 40 has a known configuration including a plurality of solenoid valves, a hydraulic pump, a motor, and the like. The HU 40 supplies the brake fluid pressure corresponding to the operation of the brake pedal BP by the driver to the wheel cylinders W ** at the time of non-control, and independently of the operation of the brake pedal BP at the time of control. The brake fluid pressure in the wheel cylinder W ** can be adjusted for each wheel.

In addition, “**” added to the end of various symbols, etc., indicates “fl”, “fr” added to the end of the various symbols, etc. to indicate which wheel the various symbols, etc. relate to. "Fl" indicates the left front wheel, "fr" indicates the right front wheel, "rl" indicates the left rear wheel, and "rr" indicates the right rear wheel. For example, the wheel cylinder W ** is the left front wheel wheel cylinder Wfl,
A right front wheel wheel cylinder Wfr, a left rear wheel wheel cylinder Wrl, and a right rear wheel wheel cylinder Wrr are comprehensively shown.

  This apparatus includes a wheel speed sensor 51 ** that detects a wheel speed Vw **, a steering wheel rotation angle sensor 52 that detects a rotation angle θsw (from a neutral position) of the steering wheel 21, and a driver's steering wheel 21. A steering torque sensor 53 for detecting the steering torque Tsw of the vehicle body, a yaw rate sensor 54 for detecting the yaw rate Yr of the vehicle body, a longitudinal acceleration sensor 55 for detecting the longitudinal acceleration Gx in the longitudinal direction of the vehicle body, and a lateral acceleration Gy in the lateral direction of the vehicle body. A lateral acceleration sensor 56 that detects the actual relative rotational angle (actual relative angle θrela) of the lower steering shaft 23 with respect to the upper steering shaft 22, and the actual steering angle (rear) of the rear wheels RL and RR. A rear wheel steering angle sensor 58 for detecting the wheel steering angle δra) and a wheel cylinder for detecting the wheel cylinder pressure Pw **. It includes a force sensor 59 **, and an electronic control unit (ECU) 60.

  The ECU 60 is a microcomputer composed of a plurality of ECUs (ECUs 0 to 4) connected to each other via a communication bus CB. The ECU 60 is electrically connected to the HU 40 and the sensors 51 to 59. The ECUs 0 to 4 in the ECU 60 execute dedicated controls.

  Specifically, the ECU 0 controls slip suppression control (front / rear force) such as anti-skid control (ABS control) and traction control (TCS control) well-known based on signals from the wheel speed sensor 51 **, the longitudinal acceleration sensor 55, and the like. Control). The ECU 1 performs front wheel steering control, which will be described in detail later, based on signals from the steering wheel rotation angle sensor 52, the wheel speed sensor 51 **, and the like. The ECU 2 executes rear wheel steering control, which will be described in detail later, based on signals from the relative angle sensor 57, the wheel speed sensor 51 **, and the like. The ECU 3 executes well-known electric power steering control based on a signal from the steering torque sensor 53. The ECU 4 executes control of a power train system such as an engine (not shown) and an automatic transmission.

(Front wheel steering control)
Next, front wheel steering control by the present apparatus (specifically, ECU 1) will be described in detail with reference to FIG. 2 (upper part) which is a functional block diagram thereof. This apparatus is configured to include functional blocks A1 to A4 related to front wheel steering control.

  The target reference front wheel rudder angle calculating means A1 is a means for calculating a target reference relative angle θrel1t (corresponding to the “reference value of the front wheel rudder angle equivalent value”) relating to the relative angle (corresponding to the front wheel rudder angle equivalent value). And functional blocks A11 and A12.

  The steering gear ratio calculation unit A11 calculates the first steering gear ratio SGf1 based on the vehicle body speed Vx calculated based on the wheel speed Vw ** obtained from the wheel speed sensor 51 ** and the table shown in FIG. The second steering gear ratio SGf2 is determined based on the rotation angle θsw of the steering wheel 21 obtained from the steering wheel rotation angle sensor 52 and the table shown in FIG. 4, and based on the following equation (1): A steering gear ratio SGf, which is the ratio of the rotation angle of the steering wheel 21 to the front wheel steering angle, is obtained.

SGf = SGf1 + SGf2 (1)

  Thus, the steering gear ratio SGf is determined based on the vehicle body speed Vx and the rotation angle θsw of the steering wheel 21, and is determined to be a larger value as the vehicle body speed Vx is larger, and the rotation angle θsw (absolute value) is smaller. A larger value is determined.

  The target reference relative angle calculation unit A12 is based on the steering gear ratio SGf obtained by the steering gear ratio calculation unit A11 and the rotation angle θsw of the steering wheel 21, and the above-described relative necessary for achieving the steering gear ratio SGf. A target reference relative angle θrel1t that is an angle is obtained. As described above, the target reference front wheel steering angle calculating means A1 for obtaining the target reference relative angle θrel1t corresponds to the reference value determining means.

  The target correction front wheel steering angle calculation means A2 is a means for calculating the target correction relative angle θrel2t (corresponding to the “correction value of the front wheel steering angle equivalent value”) relating to the relative angle, and is composed of functional blocks A21 to A26. Yes.

  The target motion state quantity calculation unit A21 is configured to output the vehicle body speed Vx, the rotation angle θsw of the steering wheel 21, the steering gear ratio SGf, and the actual steering angles δra of the rear wheels RL and RR obtained from the rear wheel steering angle sensor 58. And a target motion state quantity Vmt, which is a target value of a parameter representing the turning state of the vehicle, based on one of known methods. Here, the parameter representing the turning state (movement state in the yaw direction) of the vehicle is a value calculated using at least one of yaw rate, lateral acceleration, vehicle body slip angle, and vehicle body slip angular velocity, for example.

  Based on the vehicle speed Vx, the lateral acceleration Gy obtained from the lateral acceleration sensor 56, the yaw rate Yr obtained from the yaw rate sensor 54, and one of the well-known methods, the actual motion state amount calculation unit A22 The actual motion state quantity Vma, which is an actual value, is obtained.

  The motion state quantity deviation computing unit A23 subtracts the actual motion state quantity Vma obtained by the actual motion state quantity computing unit A22 from the target motion state quantity Vmt obtained by the target motion state quantity computing unit A21, thereby preventing oversteering. The motion state quantity deviation ΔVm_os which is a parameter representing the degree and the motion state quantity deviation ΔVm_us which is a parameter representing the degree of understeer are obtained.

  The longitudinal force calculation unit A24 calculates the wheel cylinder pressure Pw ** obtained from the wheel cylinder pressure sensor 59 **, the wheel speed Vw **, etc., and the longitudinal force FX ** of the wheel ** according to one of known methods. calculate. The longitudinal force FX ** is, for example, the braking torque for the wheel ** obtained from the wheel cylinder pressure Pw **, the driving torque of the wheel ** obtained from the driving torque of the engine (not shown), and the differential value of the wheel speed Vw **. Can be calculated from the angular acceleration of the wheel ** and the rotational motion equation of the wheel **. Also, the wheel cylinder pressure sensor 59 ** can be omitted. In this case, the longitudinal force FX ** can be estimated based on the operating state of the hydraulic pump, the motor, the electromagnetic valve, etc. constituting the HU 40.

  The longitudinal force difference calculation unit A25 calculates a longitudinal force difference ΔFX between the left and right wheels. The longitudinal force difference ΔFX can be obtained, for example, according to the following equation (2).

ΔFX = (FXfr + FXrr) − (FXfl + FXrl) (2)

  The target correction relative angle calculation unit A26 determines the first correction relative angle θrel2t_fx based on the longitudinal force difference ΔFX obtained by the longitudinal force difference calculation unit A25 and the table shown in FIG. The second modified relative angle θrel2t_vmos is determined based on the motion state quantity deviation ΔVm_os obtained by the part A23 and the table shown in FIG. 6, and the motion state quantity deviation ΔVm_us obtained by the motion state quantity deviation computing unit A23 is determined. The third corrected relative angle θrel2t_vmus is determined based on the table shown in FIG. 7, and is the relative angle corresponding to the correction amount (the amount to be corrected) of the front wheel steering angle based on the following equation (3). The target correction relative angle θrel2t is obtained. As described above, the pre-target correction wheel steering angle calculation means A2 for obtaining the target correction relative angle θrel2t corresponds to the correction value determination means.

θrel2t = θrel2t_fx + θrel2t_vmos + θrel2t_vmus (3)

  Thus, the target correction relative angle θrel2t is determined based on at least one of the longitudinal force difference ΔFX, the motion state amount deviation ΔVm_os, and the motion state amount deviation ΔVm_us, and the front / rear force difference ΔFX, the motion state amount The larger the deviation ΔVm_os and the movement state quantity deviation ΔVm_us (the absolute value thereof) are, the larger the absolute value is determined. The first modified relative angle θrel2t_fx is determined based on the table shown in FIG. 5 as described above only when the ABS control or the TCS control is being executed (and the μ split road surface is running). In this case, it may be set to “0”.

  The target relative angle calculation unit A3 corrects the target reference relative angle θrel1t by the target correction relative angle θrel2t according to the following equation (4), and sets the target relative angle θrelt (the “front wheel rudder” as a control target value related to the relative angle). Corresponding to the target value of the angle equivalent value). The target relative angle calculation unit A3 corresponds to the target value determining means.

θrelt ＝ θrel1t ＋ θrel2t (4)

  The motor drive instruction unit A4 controls the motor MTf in the STRf so that the actual relative angle θrela obtained from the relative angle sensor 57 matches the target relative angle θrelt obtained by the target relative angle calculation unit A3.

  Thus, the front wheel steering angle is a value determined from the rotation angle θsw of the steering wheel 21 and the steering gear ratio SGf obtained by the steering gear ratio calculation unit A11 (= θsw / SGf, hereinafter referred to as “front wheel reference steering angle”). Is also controlled to a value corrected by an amount corresponding to the target corrected relative angle θrel2t (hereinafter also referred to as “front wheel corrected steering angle”).

  Thus, when the target correction relative angle θrel2t is maintained at “0”, the front wheel steering angle is controlled to coincide with the front wheel reference steering angle. On the other hand, in this state, when the target correction relative angle θrel2t is other than “0”, the front wheel steering angle is automatically corrected from the front wheel reference steering angle by the front wheel correction steering angle.

  As a result, the above-described stability improving yaw moment is generated, and the vehicle stability is improved. Specifically, the deflection of the vehicle due to the aforementioned longitudinal force difference-induced yaw moment is suppressed, and the turning state of the vehicle approaches the target state. In other words, the present apparatus executes the above-described “front wheel steering angle correction control”. The motor drive instruction unit A4 corresponds to the first control unit.

  Further, the target correction relative angle calculation unit A26 determines whether or not the "front wheel steering angle is being corrected using the target correction relative angle θrel2t", that is, "front wheel steering angle correction control is being executed". It is determined whether or not there is. Specifically, when the target correction relative angle θrel2t is changed from zero to a value outside the minute range including zero, the target correction relative angle θrel2t is changed from zero to a value outside the minute range. It is determined that “the front wheel steering angle correction control is being executed” from the time of change until the time when the target correction relative angle θrel2t is maintained within the minute range reaches the predetermined period.

  As a result, when the target correction relative angle θrel2t is transiently set to a value within the above minute range for a very short period (for example, when the target correction relative angle θrel2t changes across “0”), the “front wheel steering It may continue to be determined that “the angle correction control is being executed”. In other words, from the state in which it is determined that “front wheel rudder angle correction control is being executed”, it is once determined that “front wheel rudder angle correction control is not being executed”, and after a very short period of time, “front wheel rudder angle correction control is currently being executed”. It is possible to prevent a situation in which the determination result is unnecessarily reversed at a short time interval such that it is determined that

  The target correction relative angle calculation unit A26 may determine that “front wheel steering angle correction control is being executed” when the target correction relative angle θrel2t is a value outside the minute range. That is, the target correction relative angle calculation unit A26 may always determine that the “front wheel steering angle correction control is not being executed” when the target correction relative angle θrel2t is within the minute range. However, in this case, as described above, when the target correction relative angle θrel2t transiently becomes a value within the above minute range for a very short period, a situation occurs in which the determination result is unnecessarily reversed at a short time interval. obtain.

  Then, the target correction front wheel steering angle calculation means A26 determines that the value of the flag Flg is “1” when it is determined that “the front wheel steering angle correction control is being executed” and is not “the front wheel steering angle correction control is being executed”. The value of the case flag Flg is set to “0”. As described above, the target-corrected pre-correction wheel steering angle calculation means A26 corresponds to the determination means.

(Rear wheel steering control)
Next, the rear wheel steering control by this device (specifically, the ECU 2) will be described in detail with reference to FIG. 2 (lower part) which is a functional block diagram thereof. This device includes functional blocks A5 to A8 related to rear wheel steering control.

  The actual front wheel steering angle calculation unit A5 obtains the actual front wheel steering angle δfa used for determining the target rear wheel steering angle in the rear wheel steering control based on the following equation (5). Here, the value K is the ratio of the front wheel steering angle to the rotation angle (from the neutral position) of the lower steering shaft 23 (see FIG. 1).

δfa ＝ K ・ (θsw ＋ θrela) (5)

  The target rear wheel steering angle calculation means A6 is a means for calculating a target rear wheel steering angle δrt, which is a control target value related to the rear wheel steering angle, and is composed of functional blocks A61 and A62.

  The front and rear wheel steering ratio calculation unit A61 obtains a front and rear wheel steering ratio SGr that is a ratio of the rear wheel steering angle to the front wheel steering angle based on the vehicle body speed Vx and the table shown in FIG. Thus, the front / rear wheel steering ratio SGr is determined to be a larger value (≧ 0) as the vehicle body speed Vx increases.

  The target rear wheel rudder angle calculation unit A62 calculates the target rear wheel rudder angle δrt based on the following equation (6). The target rear wheel rudder angle calculating means A6 corresponds to the target rear wheel rudder angle determining means and the reference rudder angle determining means.

δrt = δfa · SGr (6)

  When the value of the flag Flg transmitted from the target correction front wheel steering angle calculation means A26 is “0” (that is, when “front wheel steering angle correction control is not being executed”), the control stop unit A7 sets the target rear wheel steering angle δrts. Is set to a value equal to the target rear wheel steering angle δrt determined by the target rear wheel steering angle calculating means A6.

  On the other hand, when the value of the flag Flg transmitted from the target correction front wheel steering angle calculation means A26 is “1” (that is, when “front wheel steering angle correction control is being executed”), the control stop unit A7 performs the target rear wheel. The target rear wheel rudder angle δrt obtained by the target rear wheel rudder angle calculation means A6 when the value of the flag Flg changes from “0” to “1” (front wheel rudder angle correction control start time). Is held (maintained) at a value equal to. Alternatively, the control stop unit A7 calculates the target rear wheel steering angle δrts from the value of the target rear wheel steering angle δrt obtained by the target rear wheel steering angle calculation means A6 at the same time after the start of the front wheel steering angle correction control. Gradually approach (for example, with a predetermined change speed) toward “0” (neutral position).

  Hereinafter, such processing is also referred to as “control stop processing”. Here, the target rear wheel steering angle δrt corresponds to the “target rear wheel steering angle before the control stop process is performed”, and the target rear wheel steering angle δrts is the target target after the control stop process is performed. It corresponds to "Rear Wheel Rudder Angle". The control stop unit A7 corresponds to the control stop unit.

  Note that when the value of the flag Flg changes from “1” to “0” (when the front wheel steering angle correction control ends), the control stop unit A7 sets the target rear wheel steering angle δrts after the front wheel steering angle correction control ends. Then, it gradually approaches (for example, with a predetermined change speed) toward the target rear wheel steering angle δrt obtained by the target rear wheel steering angle calculation means A6, and a predetermined time has elapsed since the end of the front wheel steering angle correction control. After that, the target rear wheel steering angle δrts is set to a value equal to the target rear wheel steering angle δrt obtained by the target rear wheel steering angle calculation means A6.

  The motor drive instruction unit A8 controls the motor MTr in the STRr so that the actual rear wheel steering angle δra obtained from the rear wheel steering angle sensor 58 matches the target rear wheel steering angle δrts obtained by the control stop unit A7. .

  Thus, the rear wheel steering angle is obtained by the actual front wheel steering angle δfa obtained by the actual front wheel steering angle computing unit A5 and the front and rear wheel steering ratio computing unit A61 when the "front wheel steering angle correction control is not being executed". Control is performed so as to coincide with a value determined from the front-rear wheel steering ratio SGr (= δfa · SGr, hereinafter also referred to as “rear wheel reference rudder angle”).

  As a result, the rear wheel rudder angle is controlled to a larger value in the same phase direction as the front wheel rudder angle (more specifically, the actual front wheel rudder angle δfa) is larger and the vehicle body speed Vx is larger. That is, in this example, the above-described in-phase control is performed. The motor drive instruction unit A8 corresponds to the second control unit.

(Function)
Next, the rear wheel steering control is performed using the target rear wheel steering angle δrts instead of the target rear wheel steering angle δrt, that is, the “control stop process” is performed in the “running front wheel steering angle correction control”. The effect of this will be described with reference to FIGS. 9A and 9B and FIGS. 10A and 10B. First, with reference to FIGS. 9A and 9B, a description will be given of a case where a brake operation is performed while traveling on the μ split road surface while the steering wheel 21 is maintained at the neutral position. FIG. 9A shows a case where the rear wheel steering control is performed using the target rear wheel steering angle δrt (before the control stop process is performed), and FIG. This shows the case where the rear wheel steering control is performed using the target rear wheel steering angle δrts (after being applied).

  As shown in FIGS. 9A and 9B, in this example, the left side of the vehicle body corresponds to the high friction road surface, and the right side of the vehicle body corresponds to the low friction road surface. Therefore, when the brake operation is performed, the above-described difference in the longitudinal force (braking force difference) between the left and right wheels is generated, and the vehicle body is deflected counterclockwise (counterclockwise as viewed from above the vehicle). Yaw moment "occurs.

  In this case, the first corrected relative angle θrel2t_fx (absolute value) determined according to the table shown in FIG. 5 is a large value, and the target corrected relative angle θrel2t (absolute value) is a large value (greater than zero). Value). As a result, the “front wheel rudder angle correction control” described above automatically corrects the front wheel rudder angle in the right direction from the front wheel reference rudder angle (= 0, see the broken line in the figure). That is, a counter steer operation is performed. As a result, a “stability improving yaw moment” is generated in the clockwise direction (clockwise as viewed from above the vehicle) (see the arc-shaped arrow in the figure), and this is caused by the “front-rear force difference yaw moment”. The deflection of the vehicle to the left can be suppressed.

  In this way, when the front wheel steering angle is corrected from “0” to the right by the “front wheel steering angle correction control”, the rear wheel steering control is performed using the target rear wheel steering angle δrt. As shown, the rear wheels are steered in the same direction as the correction direction of the front wheel steering angle, that is, in the right direction by the same phase control of “rear wheel steering control”. Such a change in the rear wheel steering angle generates a counterclockwise yaw moment. As a result, the “stability improving yaw moment” generated by the “front wheel steering angle correction control” is canceled by the “rear wheel steering control”, and the above-described leftward deflection of the vehicle cannot be effectively suppressed. Problems can arise.

  On the other hand, when the front wheel steering angle is corrected in the right direction from “0” by “front wheel steering angle correction control” as described above, when the rear wheel steering control is performed using the target rear wheel steering angle δrts (control) When the stop process is performed), as shown in FIG. 9B, the rear wheels are steered in the same direction as the correction direction of the front wheel steering angle (ie, in the right direction) by the same phase control of “rear wheel steering control”. The situation is suppressed. As a result, the situation where the “stability improving yaw moment” generated by the “front wheel steering angle correction control” is canceled by the “rear wheel steering control” can be suppressed, and the above-described leftward deflection of the vehicle is effectively prevented. Can be suppressed. That is, the effect of improving the vehicle stability by the “front wheel steering angle correction control” can be effectively exhibited.

  Next, a case where the turning state is oversteered while turning right will be described with reference to FIGS. 10A and 10B. FIG. 10A shows the case where the rear wheel steering control is performed using the target rear wheel steering angle δrt (before the control stop process is performed), and FIG. This shows the case where the rear wheel steering control is performed using the target rear wheel steering angle δrts (after being applied).

  In this case, the second corrected relative angle θrel2t_vmos (absolute value) determined according to the table shown in FIG. 6 becomes a large value, and the target corrected relative angle θrel2t (absolute value) is a large value (greater than zero). Value). As a result, the above-mentioned “front wheel rudder angle correction control” automatically corrects the front wheel rudder angle from the front wheel reference rudder angle (right rudder angle, see broken line in the figure) to the left. As a result, a “stability improving yaw moment” in the counterclockwise direction is generated (see the arc-shaped arrow in the figure), and the degree of oversteering can be suppressed.

  In this way, when the front wheel steering angle is corrected from a certain steering angle in the right direction to the left by the “front wheel steering angle correction control”, the rear wheel steering control is performed using the target rear wheel steering angle δrt. As shown in FIG. 10A, the rear wheels are steered in the same direction as the correction direction of the front wheel steering angle, that is, in the left direction by the same phase control of “rear wheel steering control”. Such a change in the rear wheel steering angle generates a yaw moment in the clockwise direction. As a result, the “stability improving yaw moment” generated by the “front wheel steering angle correction control” is canceled by the “rear wheel steering control”, and the degree of oversteer cannot be effectively suppressed.

  On the other hand, when the front wheel steering angle is corrected from a certain steering angle in the right direction to the left by the "front wheel steering angle correction control", the rear wheel steering control is performed using the target rear wheel steering angle δrts. 10B (when the control stop process is performed), as shown in FIG. 10B, the rear wheels are moved in the same direction as the correction direction of the front wheel steering angle (ie, leftward) by the same phase control of “rear wheel steering control”. The situation of being steered is suppressed. As a result, the situation where the “stability improving yaw moment” generated by the “front wheel steering angle correction control” is canceled by the “rear wheel steering control” can be suppressed, and the degree of oversteer can be effectively suppressed. That is, the effect of improving the vehicle stability by the “front wheel steering angle correction control” can be effectively exhibited.

  As described above, according to the four-wheel steering control device according to the first embodiment of the present invention, the front wheel reference steering angle is determined based on the vehicle body speed Vx and the rotation angle θsw of the steering wheel 21 in the front wheel steering control. (Corresponding to θrel1t) is determined, and the front wheel corrected steering angle (at least one of the longitudinal force difference ΔFX and the movement state quantity deviation ΔVm_os, ΔVm_us) of the vehicle in the yaw direction of the vehicle ( is equivalent to θrel2t). The front wheel rudder angle is controlled to a value obtained by correcting the front wheel reference rudder angle by the front wheel correction rudder angle. That is, “front wheel steering angle correction control” is executed.

  On the other hand, in the rear wheel steering control (in-phase control), the rear wheel reference steering angle (δrt) is determined based on the actual front wheel steering angle δfa and the vehicle body speed Vx. Control is performed so as to coincide with the wheel reference steering angle δst. Further, when “front wheel rudder angle correction control” is started, “control stop processing” is executed, and the rear wheel rudder angle is held at the value at the start of front wheel rudder angle correction control, or “0”. Gradually approach toward (neutral position).

  In this way, when the “control stop process” is executed during “running front wheel steering angle correction control”, the rear wheels are rotated in the same direction as the correction direction of the front wheel steering angle by the same phase control of “rear wheel steering control”. The situation of being steered is suppressed. As a result, the situation where the “stability improvement yaw moment” generated by the “front wheel steering angle correction control” is canceled by the “rear wheel steering control” can be suppressed, and the vehicle stability improvement effect by the “front wheel steering angle correction control” can be suppressed. Can be effectively exhibited.

(Second Embodiment)
Next, a four-wheel steering control device according to a second embodiment of the present invention will be described. In the second embodiment, the “rear wheel steering control” is performed only in the “rear wheel steering angle correction control” similar to the “front wheel steering angle correction control” in the “front wheel steering control”. This is different from the first embodiment in which “correction control” is not performed.

  Hereinafter, only the difference will be described with reference to FIG. In addition, in 2nd Embodiment, the same code | symbol as the code | symbol in 1st Embodiment is attached | subjected about the same thing as the member in 1st Embodiment, a functional block, etc.

  As shown in FIG. 11, in the second embodiment, the target rear wheel steering angle δrts obtained by the control stop unit A7 (that is, the value obtained by performing the “control stop processing” on the rear wheel reference steering angle δrt) The target rear wheel steering angle δrts is determined by adding the target corrected rear wheel steering angle (hereinafter also referred to as “rear wheel correction steering angle”) δst determined by the target corrected wheel steering angle calculation unit A9.

  The post-target correction wheel steering angle calculation unit A9 is very similar to the above-described pre-target correction wheel steering angle calculation unit A2, and corresponds to FIGS. 12, 13, and 14 corresponding to FIGS. 5, 6, and 7, respectively. Based on the table shown, the first corrected rear wheel steering angle δst_fx, the second corrected rear wheel steering angle δst_vmos, and the third corrected rear wheel steering angle δst_vmus are determined. Based on the following equation (7), the target corrected rear wheel Obtain the steering angle δst. As described above, the target corrected wheel steering angle calculation means A9 for obtaining the target corrected wheel steering angle δst corresponds to the corrected steering angle determination means.

δst = δst_fx + δst_vmos + δst_vmus (7)

  Accordingly, the target corrected rear wheel steering angle (rear wheel corrected steering angle) δst is determined based on at least one of the longitudinal force difference ΔFX, the motion state amount deviation ΔVm_os, and the motion state amount deviation ΔVm_us. The larger the (absolute value) of the longitudinal force difference ΔFX, the motion state quantity deviation ΔVm_os, and the dynamic state quantity deviation ΔVm_us, the larger the (absolute value) is determined. The first corrected post-steering wheel angle δst_fx is determined based on the table shown in FIG. 12 as described above only when the ABS control or the TCS control is being executed (and during the μ split road surface traveling). Otherwise, it may be set to “0”.

  In the motor drive instruction section A8, the actual rear wheel steering angle δra is the target rear wheel steering angle δrts (the value obtained by performing the “control stop process” on the rear wheel reference steering angle δrt + the rear wheel corrected steering angle δst). The motor MTr in the STRr is controlled so as to match. As a result, the rear wheel steering angle is controlled to a value obtained by correcting the value obtained by performing the “control stop process” on the rear wheel reference steering angle δrt by the rear wheel correction steering angle δst.

  As a result, when the rear wheel correction rudder angle δst is maintained at “0”, the rear wheel rudder angle is controlled to coincide with the value obtained by performing the “control stop process” on the rear wheel reference rudder angle δrt. . On the other hand, if the rear wheel correction rudder angle δst is other than “0” in this state, the rear wheel rudder angle is corrected from the value obtained by performing “control stop processing” on the rear wheel reference rudder angle δrt. It is automatically corrected by the steering angle δst. That is, “rear wheel steering angle correction control” is executed.

  As described above, according to the four-wheel steering control device according to the second embodiment of the present invention, the “stability improving yaw moment” is generated by the “rear wheel steering angle correction control”, and the vehicle stability is improved. improves. That is, in addition to the stability improving yaw moment by the “front wheel rudder angle correction control”, the stability improving yaw moment by the “rear wheel rudder angle correction control” can also be generated. Compared to the first embodiment, the vehicle Stability can be further improved.

  Hereinafter, the “rear wheel steering angle correction control” will be additionally described. Generally, the correction direction of the rear wheel steering angle by the “rear wheel steering angle correction control” is opposite to the correction direction of the front wheel steering angle by the “front wheel steering angle correction control”. For example, in the case shown in FIGS. 9A and 9B, the correction direction of the front wheel rudder angle by the “front wheel rudder angle correction control” is the right direction, whereas the rear wheel rudder angle by the “rear wheel rudder angle correction control” is changed. The correction direction is the left direction.

  On the other hand, in the second embodiment, as in the first embodiment, the “control stop process” is performed on the target rear wheel steering angle when “front wheel steering angle correction control is being executed”. The control prevents the target rear wheel steering angle δrts from changing in the same direction as the correction direction of the front wheel steering angle. That is, in the second embodiment, the change direction of the target rear wheel steering angle δrts and the rear wheel steering angle by the “rear wheel steering angle correction control” when the front wheel steering angle is corrected by the “front wheel steering angle correction control”. The correction direction is not contradictory (difficult to do). As a result, the vehicle stability improvement effect by the “front wheel rudder angle correction control” can be maintained, and the vehicle stability improvement effect by the “rear wheel rudder angle correction control” can be sufficiently exhibited.

  The present invention is not limited to the first and second embodiments, and various modifications can be employed within the scope of the present invention. For example, in the first and second embodiments, the steering gear ratio calculation unit A11 is based on the first steering gear ratio SGf1, the second steering gear ratio SGf2, and the formula (1) (SGf = SGf1 + SGf2). The steering gear ratio SGf is obtained, and the third steering gear ratio SGf3 is further determined based on the motion state quantity deviation ΔVm_us obtained by the motion state quantity deviation computing unit A23 and the table shown in FIG. The steering gear ratio SGf may be obtained based on the equation (8).

SGf = SGf1 + SGf2 + SGf3 (8)

  This is a case where the turning state is understeer, and while the “front wheel steering angle correction control” is being executed, the turning direction of the front wheels coincides with the direction corresponding to the rotational direction from the neutral position of the steering wheel 21. Based on continuing. As a result, the steering gear ratio SGf is corrected in a direction in which the turning angle (absolute value) of the front wheels decreases. In this case, the target corrected relative angle θrel2t can be obtained based on an equation obtained by omitting the third corrected relative angle θrel2t_vmus in the above equation (3).

  In the first and second embodiments, regarding the same phase control of the “rear wheel steering control”, the start of turning the rear wheels is intentionally delayed for a very short period with respect to the start of turning the front wheels. The “turning control” may be executed to improve the turning characteristics of the vehicle at the beginning of turning.

  In this case, as shown in FIG. 16, functional blocks A10 to A12 are added. Hereinafter, the function blocks A10 to A12 will be described with reference to FIG. The time change rate calculation unit A10 obtains a time change rate (time differential value) dδfa of the actual front wheel steering angle δfa at the steering start time of the front wheels (immediately after time t1 in FIG. 17).

  The phase delay time calculation unit A11 obtains the phase delay time τph (see FIG. 17) based on the time change rate dδfa. For example, the phase delay time τph is set to a larger value as the time change rate dδfa is larger.

  The phase delay processing calculation unit A12 performs the target rear wheel steering angle (before the “control stop processing” is performed) (rear wheel reference steering angle) after the steering start time of the front wheels (immediately after time t1 in FIG. 17). ) Δrt is set to a value obtained by subjecting the target rear wheel rudder angle (rear wheel reference rudder angle) δrs obtained by the target rear wheel rudder angle calculation unit A62 to the dead time processing of the phase delay time τph.

  As a result, the start of turning of the rear wheels in the same phase direction is delayed by the phase delay time τph with respect to the start of turning of the front wheels.

  Further, as the turning ability control, control for turning the rear wheels in the opposite phase direction only for the first extremely short period with respect to the start of turning of the front wheels may be executed. In this case, as shown in FIG. 18, functional blocks A10, A13, A14 are added. This functional block A10 is the same as that in FIG.

  Hereinafter, the functional blocks A13 and A14 will be described with reference to FIG. The instantaneous reverse phase rudder angle calculation unit A13 calculates the instantaneous reverse phase rudder angle δrg based on the time change rate dδfa of the control front wheel rudder angle δfh at the front wheel turning start time (immediately after time t11 in FIG. 19). A phase delay time τrg (see FIG. 19) is obtained. For example, the instantaneous reverse phase steering angle δrg and the phase delay time τrg are set to larger values as the time change rate dδfa is larger.

  The instantaneous reverse phase processing calculation unit A14 performs the target rear wheel steering angle (before the “control stop processing” is performed) (the rear wheel reference rudder) after the steering start time of the front wheels (immediately after time t11 in FIG. 19). (Angle) δrt is set to a value obtained by subjecting the target rear wheel rudder angle (rear wheel reference rudder angle) δrs obtained by the target rear wheel rudder angle calculation unit A62 to the dead time processing of the phase delay time τrg. In addition, it is set to a value in the reverse phase direction with the instantaneous reverse phase steering angle δrg as a peak only during the phase delay time τrg from the steering start time of the front wheels (immediately after time t11 in FIG. 19).

  As a result, the steering start of the rear wheels in the same phase direction is delayed by the phase delay time τrg with respect to the start of the steering of the front wheels, and the rear wheels are reversed by the initial phase delay time τrg with respect to the steering start of the front wheels. Since the vehicle is steered in the phase direction, the turning characteristics of the vehicle at the beginning of turning are further improved.

  The following is a supplementary explanation of “turning control”. In order to accurately perform such turning control, the value of the “front wheel steering angle” used to determine the target rear wheel steering angle (rear wheel reference steering angle) δrt is a value very close to the actual value of the front wheel steering angle. It is required to be.

  Here, a response delay inevitably exists in the motor MTf used for the “front wheel steering angle correction control”. That is, for example, when the control target value of the front wheel rudder angle (specifically, K · (θsw + θrelt)) suddenly changes, the actual value of the front wheel rudder angle deviates greatly (delays) from the control target value of the front wheel rudder angle. Can occur. Therefore, when the control target value of the front wheel steering angle (= K · (θsw + θrelt)) is used as the “front wheel steering angle” used to determine the target rear wheel steering angle δrt, the steering of the rear wheels starts earlier. In some cases, the turning control is not accurately performed.

  On the other hand, in the first and second embodiments, the actual front wheel steering angle δfa based on the detected value θrela of the relative angle sensor 57 is used as the “front wheel steering angle” used for determining the target rear wheel steering angle δrt (described above). (See equation (5)). That is, since a value that can be maintained at a value very close to the actual value of the front wheel steering angle is used, the turning ability control can be performed accurately.

  In the first and second embodiments, when calculating the target rear wheel steering angle (rear wheel reference steering angle) δrt, the actual front wheel steering angle expressed by the above formula (5) as the “front wheel steering angle”. Although δfa (= K · (θsw + θrela)) is used, a value δft represented by the following equation (9) may be used as the “front wheel steering angle”. The front wheel reference rudder angle (= θsw / SGf) may be used as the “front wheel rudder angle”. Further, values Δfa1 and Δfa2 excluding correction components by “front wheel steering angle correction control” represented by the following formulas (10) and (11) may be used as the “front wheel steering angle”.

δft = K · (θsw + θrelt) (9)
δfa1 = K ・ (θsw + θrela−θrel2t) (10)
δfa2 = K ・ (θsw + θrelt−θrel2t) (11)

  In the first and second embodiments, the actual front wheel steering angle δfa is obtained using the detected value θrela of the relative angle sensor 57 according to the above equation (5), but the front wheel steering angle is directly detected. The actual front wheel steering angle δfa may be obtained by using the detected value of the sensor.

  In the first and second embodiments, the absolute value of the front wheel correction rudder angle (specifically, the target correction relative angle θrel2t) may be limited. As a result, it is possible to leave room for overriding the counter steering operation by the driver's aggressive steering wheel operation.

  In the first and second embodiments, the longitudinal force difference ΔFX between the left and right wheels is calculated by adding the longitudinal forces FXfl and FXrl of the left front and rear wheels FL and RL from the sum of the longitudinal forces FXfr and FXrr of the right and left front wheels FR and RR. The value obtained by subtracting the sum is used (see equation (2) above), but the front / rear force difference FX of the left and right wheels is reduced by subtracting the front / rear force FXfl of the left front wheel FL from the front / rear force FXfr of the right front wheel FR. The resulting value may be used. When the longitudinal force difference is a braking force difference, a value obtained by subtracting the braking force of the left front wheel FL from the braking force of the right front wheel FR can be used as the longitudinal force difference ΔFX of the left and right wheels. When the longitudinal force difference is a driving force difference, a value obtained by subtracting the driving force of the left driving wheel from the driving force of the right driving wheel can be used as the longitudinal force difference ΔFX of the left and right wheels.

  In the first and second embodiments, the steering wheel 21 and the steering wheels FL and FR are mechanically connected in the front wheel steering control mechanism 20, but the steering wheel 21 and the steering wheels FL and FR are For a vehicle equipped with a so-called steer-by-wire front wheel steering control mechanism (that is, a mechanism that performs front wheel steering control based on an electrical signal indicating the rotation angle θsw of the steering wheel 21) that is not mechanically connected However, the present invention is applicable. In this case, a rod-like member (so-called joystick) may be used as the steering operation member instead of the steering wheel 21.

1 is a schematic configuration diagram of a vehicle equipped with a four-wheel steering control device according to a first embodiment of the present invention. FIG. 2 is a functional block diagram when the four-wheel steering control device shown in FIG. 1 performs front wheel steering angle control and rear wheel steering control. It is the graph which showed the table which prescribes | regulates the relationship between vehicle body speed and a 1st steering gear ratio. It is the graph which showed the table which prescribes | regulates the relationship between the rotation angle of a steering wheel, and a 2nd steering gear ratio. It is the graph which showed the table which prescribes | regulates the relationship between a longitudinal force difference and a 1st correction relative angle. It is the graph which showed the table which prescribes | regulates the relationship between an exercise | movement state-quantity deviation and a 2nd correction relative angle. It is the graph which showed the table which prescribes | regulates the relationship between an exercise | movement state-quantity deviation and a 3rd correction relative angle. It is the graph which showed the table which prescribes | regulates the relationship between vehicle body speed and front-and-rear wheel steering ratio. The rear wheel steering control is performed using the target rear wheel steering angle before the control stop process is performed when the brake operation is performed while the μ-split road surface is running while the steering wheel is maintained at the neutral position. It is the figure which showed the steering state of the wheel in the case of being performed. The rear wheel steering control is performed using the target rear wheel steering angle after the control stop process is performed when the braking operation is performed while the μ split road surface is running with the steering wheel maintained at the neutral position. It is the figure which showed the steering state of the wheel in the case of being performed. Steering state of the wheel when the turning state is oversteering during a right turn and the rear wheel steering control is performed using the target rear wheel steering angle before the control stop process is performed FIG. Steering state of the wheel when the turning state becomes oversteer during a right turn and the rear wheel steering control is performed using the target rear wheel steering angle after the control stop process is performed FIG. It is a part of functional block diagram when the four-wheel steering control apparatus which concerns on 2nd Embodiment of this invention performs rear-wheel steering control. It is the graph which showed the table which prescribes | regulates the relationship between a longitudinal force difference and the 1st correction rear wheel steering angle. It is the graph which showed the table which prescribes | regulates the relationship between an exercise | movement state-quantity deviation and a 2nd corrected post-steer angle. It is the graph which showed the table which prescribes | regulates the relationship between an exercise | movement state-quantity deviation and a 3rd corrected wheel steering angle. It is the graph which showed the table which prescribes | regulates the relationship between a movement state amount deviation and a 3rd steering gear ratio. It is a part of functional block diagram when the four-wheel steering control device which concerns on the modification of embodiment of this invention performs turnability control in rear-wheel steering control. FIG. 17 is a time chart showing an example of a change in the target rear wheel steering angle when performing the turning control shown in FIG. 16. FIG. FIG. 9 is a part of a functional block diagram when a four-wheel steering control device according to another modification of the embodiment of the present invention performs other turning control in rear wheel steering control. FIG. 19 is a time chart showing an example of a change in the target rear wheel steering angle when performing the turnability control shown in FIG. 18. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Four-wheel steering control apparatus of a vehicle, 20 ... Front-wheel steering control mechanism, 21 ... Steering wheel, 22 ... Upper steering shaft, 23 ... Lower steering shaft, 30 ... Rear-wheel steering control mechanism, 40 ... Hydraulic unit, 51 * * ... Wheel speed sensor, 52 ... Steering wheel rotation angle sensor, 57 ... Relative angle sensor, 58 ... Rear wheel steering angle sensor, 60 ... Electronic control unit (ECU), STRf ... Steering gear ratio variable mechanism, STRr ... Rear wheel steering Mechanism, MTf, MTr ... Motor

Claims (5)

A four-wheel steering control device for a vehicle applied to a vehicle capable of adjusting a steering angle of a front wheel independently of an operation of a steering operation member by a driver and capable of adjusting a steering angle of a rear wheel,
Reference value determining means for determining a reference value of a value corresponding to a steering angle of the front wheel based on an operation of a steering operation member by a driver of the vehicle;
Correction value determining means for determining a correction value of the front wheel steering angle equivalent value based on a value representing a motion state of the vehicle in the yaw direction;
Target value determining means for correcting the reference value by the correction value and determining a target value of the front wheel steering angle equivalent value;
First control means for controlling the steering angle of the front wheels so that the actual value of the front wheel steering angle equivalent value matches the target value;
Target rear wheel rudder angle determining means for determining a target rear wheel rudder angle based on the rudder angle of the front wheel;
Second control means for controlling the steering angle of the rear wheel so that the actual value of the steering angle of the rear wheel coincides with the target rear wheel steering angle;
A four-wheel steering control device for a vehicle comprising:
Using a change in the correction value, comprising determination means for determining whether or not the steering angle of the front wheel is in a correction state corrected using the correction value;
The target rear wheel rudder angle determining means is
A vehicle four-wheel steering control device comprising control stop means for performing control stop processing for holding the target rear wheel steering angle constant or gradually returning it to zero when the correction state is determined. The four-wheel steering control device for a vehicle according to claim 1,
The determination means includes
When the correction value is in the correction state from the time when the correction value changes to a value outside the predetermined range including zero until the time when the period during which the correction value is maintained within the predetermined range reaches the predetermined period. A four-wheel steering control device for a vehicle configured to determine. The four-wheel steering control device for a vehicle according to claim 1,
The determination means includes
A four-wheel steering control device for a vehicle configured to determine that the vehicle is in the correction state when the correction value is outside a predetermined range including zero. The four-wheel steering control device for a vehicle according to any one of claims 1 to 3,
The target rear wheel rudder angle determining means is
A reference rudder angle determining means for determining a reference rudder angle of the rear wheel based on the rudder angle of the front wheel;
A four-wheel steering control device for a vehicle configured to determine the target rear wheel steering angle before the control stop process to a value equal to the reference steering angle. The four-wheel steering control device for a vehicle according to any one of claims 1 to 3,
The target rear wheel rudder angle determining means is
Reference rudder angle determining means for determining a reference rudder angle of the rear wheel based on the rudder angle of the front wheel;
Correction steering angle determination means for determining a corrected steering angle of the rear wheel based on a value representing a motion state of the vehicle in the yaw direction, and
The target rear wheel rudder angle before the control stop process is performed is determined to be equal to the reference rudder angle,
A four-wheel steering control device for a vehicle configured to determine the target rear wheel steering angle by correcting the target rear wheel steering angle after the control stop processing is performed by the corrected steering angle.

Images