JP5262871B2 - Steering angle control device for vehicle and steering angle control method for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten the time until control is reset to usual four-wheel steering control after abnormality of a front wheel turning actuator 5 is resolved. <P>SOLUTION: When the abnormality of the front wheel turning actuator 5 is detected and abnormality of a rear wheel turning actuator 9 is not detected, a turning angle of a rear wheel is controlled to an angle of a neutral position and driving of the front wheel turning actuator 5 is forbidden, and when the abnormality of the front wheel turning actuator 5 is detected and the abnormality of the rear wheel turning actuator 9 is detected, driving of the front wheel turning actuator 5 and the rear wheel turning actuator 9 is forbidden. Further, the abnormality of the rear wheel turning actuator 9 is not detected after the abnormality of the rear wheel turning actuator 9 is detected, the turning angle of the rear wheel is controlled to the angle of the neutral position. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a vehicle steering angle control technique in which a front wheel and a rear wheel, which are steered wheels, are steered by individual actuators.

In a four-wheel steering vehicle (4WS), the rear wheels are steered in addition to the steering of the front wheels, which are steered wheels, according to the steering angle of the steering wheel (hereinafter simply referred to as the steering angle). For example, in a vehicle such as that described in Non-Patent Document 1, the front wheel turning angle is changed by the front wheel turning actuator for the turning angle corresponding to the steering angle by the correction turning angle corresponding to the vehicle state or the like. . Also, the rear wheels are steered by the rear wheel steering actuator according to the vehicle state and the like. As a result, four-wheel steering is realized.
At this time, when a temporary abnormality such as overheating occurs in the front wheel steering actuator, fail safe control is performed to stop the operations of the front wheel steering actuator and the rear wheel steering actuator.

“SKYLINE V36 series new car manual”, Nissan Motor Co., Ltd., November 2006, p. STC-27

However, when the operations of the front wheel turning actuator and the rear wheel turning actuator are stopped, the corrected turning angle and the turning angle of the rear wheel are held at the angles at the time when the abnormality occurs. For this reason, when the abnormality of the front wheel steering actuator is resolved, a deviation occurs between the front wheel steering angle corresponding to the steering angle and the actual steering angle, which may give the driver a sense of incongruity. In order to prevent this, the next return processing is performed before returning to the normal four-wheel steering control. In the returning process, when the abnormality of the front wheel steering actuator is detected, the returning control is also performed for the corrected turning angle held on the front wheel side after the process of returning the turning angle of the rear wheel to the neutral position. Further, there is a concern that the longer the time required for the operation of the return process at the time of return from the provisional abnormality of the front wheels, the easier it is for the driver to feel uncomfortable.
The present invention has been made paying attention to the above points, and it is an object of the present invention to shorten the time for returning to normal four-wheel steering control after the abnormality of the front wheel steering actuator is resolved.

  In order to solve the above-described problem, the steering angle control for a vehicle according to the present invention detects the abnormality of the front wheel steering actuator and detects the abnormality of the rear wheel steering actuator when the abnormality of the rear wheel steering actuator is not detected. If the front wheel steering actuator is prohibited from being driven and the front wheel steering actuator is detected to be abnormal and the rear wheel steering actuator is detected to be abnormal, the front wheel steering actuator and the rear Prohibit the driving of the wheel steering actuator. Further, after detecting the abnormality of the rear wheel steering actuator, when the abnormality of the rear wheel steering actuator is not detected, the steering angle of the rear wheel is controlled to the neutral position angle.

According to the present invention, if the rear wheel steering actuator is not abnormal while the front wheel steering actuator is abnormal or if the abnormality has been resolved, even before the abnormality of the front wheel steering actuator is resolved. Then, the process of returning the turning angle of the rear wheels to the neutral position is started.
This shortens the time for returning to normal four-wheel steering control after the abnormality of the front wheel steering actuator is resolved. Due to the shortening, it becomes difficult for the driver to feel uncomfortable with respect to the return from the temporary abnormality of the front wheel steering actuator.

It is a lineblock diagram of vehicles concerning an embodiment based on the present invention. It is a figure explaining the steering angle control controller which concerns on embodiment based on this invention. It is a figure explaining the structure of the target value production | generation part which concerns on embodiment based on this invention. It is a figure explaining the structure of the target output value production | generation part which concerns on embodiment based on this invention. It is a figure explaining the structure of the neutral return control calculating part which concerns on embodiment based on this invention. It is a figure explaining the process of the neutral return control calculating part which concerns on embodiment based on this invention. It is a figure which shows the example of a time chart.

Next, embodiments of the present invention will be described with reference to the drawings.
(Constitution)
FIG. 1 shows a configuration diagram of a vehicle according to the present embodiment.
First, the configuration will be described with reference to FIG.
The steering wheel 1 operated by the driver is connected to the front wheels 8 via the front wheel steering mechanism SS. That is, the steering input shaft 2 is connected to the steering wheel 1. A steering output shaft is connected to the steering input shaft 2. The steering output shaft is connected to the rack shaft 7 via a rack and pinion mechanism. That is, the pinion connected to the steering output shaft meshes with the rack of the rack shaft 7. The rack shaft 7 is disposed with its axis directed in the vehicle width direction. The rack shaft 7 is displaced in the axial direction toward the vehicle width direction by rotating the steering output shaft. The left and right ends of the rack shaft 7 are connected to the knuckles of the front wheels 8 through left and right tie rods, respectively.

A front wheel steering actuator 5 is connected to the steering output shaft. The front wheel steering actuator 5 rotates and displaces the steering output shaft based on a command from the front wheel steering controller 6. Specifically, the front wheel steering actuator 5 changes the pinion angle with respect to the steering angle, thereby changing the steering angle of the front wheel 8 that is the steered wheel according to a command from the front wheel steering controller 6. To control. That is, the front wheel 8 is steered by the steered angle corresponding to the steering angle θ of the steering wheel by the front wheel steering mechanism SS, and the ratio of the steering angle to the steered angle (hereinafter referred to as gear) by the front wheel steered actuator 5. The steering angle is changed by adjusting the ratio to be the target front wheel turning angle α ^* . That is, the front wheel turning actuator 5 performs the increase / decrease control by the corrected turning angle that is the difference between the target front wheel turning angle α ^* and the turning angle corresponding to the steering angle θ.

A steering actuator angle sensor (not shown) is provided in the steering motor of the front wheel steering actuator 5. The steering actuator angle sensor detects the rotational angle position of the motor of the front wheel steering actuator 5 and outputs the detection signal to the front wheel steering controller 6 as a feedback control amount.
Here, the steering output shaft may be connected to the steering input shaft 2 via the mechanical backup device 3. In the normal state, the mechanical backup device 3 is in a state in which torque transmission between the steering input shaft 2 and the steering output shaft is cut off. Further, the mechanical backup device connects the steering input shaft 2 and the steering output shaft based on a command from the rudder angle control controller 4 to enable torque transmission. In this case, the front wheel steering actuator 5 drives and rotates the steering output shaft so that the target front wheel steering angle α ^* is obtained.

Reference numeral 9 denotes a rear wheel steering actuator. The rear wheel steering actuator 9 axially displaces the rack shaft 11 in the vehicle width direction in response to a signal from the rear wheel steering controller 10. The left and right end portions of the rack shaft 11 are connected to a knuckle for the rear wheel 12 via left and right tie rods, respectively. A steering actuator angle sensor (not shown) is provided in the steering motor of the rear wheel steering actuator 9. The steered actuator angle sensor detects the rotational angle position of the motor of the rear wheel steered actuator 9 and outputs the detection signal to the rear wheel steered controller 10 as a feedback control amount.
Further, a front wheel turning actuator abnormality detecting means 30 and a rear wheel turning actuator abnormality detecting means 31 are provided.

  The front wheel steering actuator abnormality detection means 30 detects the presence or absence of abnormality of the front wheel steering actuator 5 and outputs the detection result to the steering angle control controller 4. The front wheel steering actuator abnormality detection means 30 detects an abnormality in the electrical system and the mechanical system related to the front wheel steering actuator 5. In the case of a mechanical system, for example, a temperature sensor that measures the temperature of the actuator is provided, and it is determined whether or not the temperature of the actuator is equal to or higher than a predetermined overheat temperature that can be regarded as an overheat state according to the standard of the actuator. That is, when the temperature of the actuator is equal to or higher than the overheat temperature, it is determined that there is an abnormality. In addition, abnormality removal determines with abnormality removal by overheating, when it becomes predetermined temperature a little lower than the said overheating temperature. In the case of an electrical system, for example, a voltage sensor that monitors the voltage supplied to the actuator is provided, and whether or not the voltage supplied to the actuator is below a minimum voltage that cannot be considered sufficient to drive and change the actuator. Determine. That is, when the voltage supplied to the actuator is equal to or lower than the minimum voltage, it is determined that there is an abnormality. It should be noted that the abnormality elimination is determined as the elimination of the abnormality relating to the voltage when the voltage becomes a predetermined voltage slightly higher than the minimum voltage.

The rear wheel steering actuator abnormality detection means 31 detects whether or not the rear wheel steering actuator 9 is abnormal, and outputs the detection result to the steering angle controller 4. The rear wheel steering actuator abnormality detection means 31 detects an abnormality in the electrical system and the mechanical system related to the front wheel steering actuator 5. An example of detection is the same as that of the front wheel steering actuator abnormality detection means 30.
A steering angle sensor 20, a vehicle speed sensor 21, and a mode selection unit 22 are provided.

The steering angle sensor 20 detects the steering angle θ of the steering wheel 1 and outputs the detected steering angle θ signal to the steering angle control controller 4. The steering angle sensor 20 is provided on the steering input shaft 2 or the steering wheel 1. The steering angle sensor 20 includes, for example, a pulse encoder and detects the steering angle θ operated by the driver.
The vehicle body speed sensor 21 detects the vehicle body speed V of the vehicle and outputs the detected vehicle body speed signal to the steering angle controller 4.

  The mode selection unit 22 is a switch that is operated by the driver to select a vehicle characteristic mode. A switch signal corresponding to the vehicle characteristic mode selected by the driver is output to the rudder angle controller 4. In the present embodiment, for example, a comfort mode (mode A) and a sports mode (mode B) are provided as vehicle characteristic modes. There may be three or more types of vehicle characteristic modes.

The front wheel steering controller 6 is a front wheel 8 which is a steered wheel via the front wheel steering actuator 5 so that the actual steering angle of the front wheel 8 coincides with the target front wheel steering angle α ^* calculated by the steering angle control controller 4. The steering is controlled by feedback. That is, the front wheel steering controller 6 determines the target drive current I _ref based on the deviation between the target front wheel steering angle α ^* calculated by the steering angle controller 4 and the rotation angle θ _ACT of the front wheel steering actuator 5 to be controlled. It is calculated, and supplies the current supplied to the steering actuator based on the calculated target drive current I _ref by controlling the PWM method or the like, a drive current I _ACT corresponding to the target drive current I _ref to the steering actuator . Thus, it is controlled so that the rotational angle theta _ACT of the front wheel steering actuator 5 follows the target front wheel steering angle alpha ^*. Here, the front wheel steering actuator 5 rotates and displaces the steering output shaft 3, and the front wheel 88 is steered by the rotational displacement of the front wheel steering actuator 5, so that the target front wheel steering angle α ^* as a control amount and The rotation angle θ _ACT of the front wheel steering actuator 5 is uniquely determined based on the gear ratio between the pinion gear and the rack gear, and thus can be regarded as equivalent.

The rear wheel steering controller 10 performs steering control of the rear wheel 12 that is a steered wheel via the rear wheel steering actuator 9 so that the target rear wheel steering angle δ ^* calculated by the steering angle control controller 4 is obtained.
However, when the front wheel steering controller 6 and the rear wheel steering controller 10 input the drive prohibition command, the driving of the corresponding actuator is stopped.

The steering angle control controller 4 calculates the target front wheel turning angle α ^* and the target rear wheel turning angle δ ^* based on the vehicle speed V, the steering angle θ of the steering wheel 1, and the selected vehicle characteristic mode. Then, the finally selected target front wheel turning angle α ^* and target rear wheel turning angle δ ^* are output to the front wheel turning controller 6 and the rear wheel turning controller 10, respectively.
The rudder angle controller 4 calculates a target yaw rate and a target lateral speed according to the vehicle characteristic mode based on the vehicle state quantity related to the vehicle running state estimated from the vehicle body speed V and the steering angle θ.

Based on the calculated target yaw rate and target lateral speed, the target front wheel turning angles α ^* and δ ^* of the steered wheels are calculated. Here, the vehicle state quantity relating to the vehicle running state estimated from the vehicle body speed V and the steering angle θ is a vehicle state quantity relating to the yaw rate and the lateral acceleration specifying the running state. That is, the target yaw rate and the target lateral velocity are amounts representing the target vehicle behavior as the target vehicle behavior.
As shown in FIG. 2, the rudder angle controller 4 includes a target value generator 41 and a target output value generator 42. As shown in FIG. 3, the target value generation unit 41 includes a vehicle model calculation unit 41A and a front / rear wheel steering target value calculation unit 41B. Further, as shown in FIG. 4, the target output value generation unit 42 includes a front / rear wheel steering control calculation unit 42A, a neutral return control calculation unit 42B, and a target output unit.

(Vehicle model calculation unit 41A)
The vehicle model calculation unit 41A calculates a vehicle state quantity (vehicle parameter) related to the yaw rate and the lateral speed that specify the traveling state of the vehicle according to the current steering angle θ and the vehicle body speed V according to the vehicle model to be applied. The vehicle state quantities to be calculated are gφ (V), ζφ (V), ωφ (V), Tφ (V), and g _v (V), ζ _v (V), ωφ (V), T _v (V). It is. These state quantities can be calculated from the steering angle θ and the vehicle body speed V according to the following expressions (5) and (8).

Here, as described later, the vehicle state quantities related to the yaw rate are gφ (V), ζφ (V), ωφ (V), and Tφ (V). The vehicle state quantities related to the lateral speed are g _v (V), ζ _v (V), ω _v (V), and T _v (V).
Of these, gφ (V) and g _v (V) are basic vehicle state quantities relating to steady-state characteristics. ζφ (V), ωφ (V), ζ _v (V), and ω _v (V) are vehicle state quantities related to transient characteristics.
Here, the vehicle state quantity using the vehicle model will be described.
When a two-wheel model is adopted as the vehicle model, the yaw rate and lateral speed of the vehicle can be expressed by the following equations. That is, the yaw rate and the lateral speed corresponding to the steering angle θ and the vehicle body speed V can be estimated from the state equation of the following expression (1).

here,
φ ′: Yaw rate s: Differential operator θ: Steering angle of driver (equivalent to front wheel turning angle)
δ: Rear wheel turning angle Vx, V: Vehicle speed Vy: Lateral speed Iz: Vehicle inertia moment M: Vehicle weight Lf: Front axle to center of gravity distance Lr: Center of gravity center to rear axle distance N: Gear ratio Kf: Front wheel 8 cornering Power Kr: Rear wheel cornering power

である。
次に、上記状態方程式から、前輪８操舵に対するヨーレート、及び横速度の伝達関数を求めると、下記（３）式及び（４）式となる。

It is.
Next, when the transfer function of the yaw rate and the lateral speed for the front wheel 8 steering is obtained from the above state equation, the following equations (3) and (4) are obtained.

  From the above equation (3), the transfer function of the yaw rate can be expressed by the following equation.

  From the above equation (4), the transfer function of the lateral velocity can be expressed by the following equation.

以上から、操舵角θ及び車体速Ｖに応じた車両の走行状態を、ヨーレート及び横速度で特定することが出来る。
そして、ヨーレートに係る車両状態量（車両パラメータ）が、ｇφ（Ｖ）、ζφ（Ｖ）、ωφ（Ｖ）、Ｔφ（Ｖ）となる。
また、横速度に係る車両状態量（車両パラメータ）は、ｇ_v（Ｖ）、ζ_v（Ｖ）、ω_v（Ｖ）、Ｔ_v（Ｖ）となる。
ここで、ｇφ（Ｖ）、ｇ_v（Ｖ）は、特性モードの基本状態を示す状態量（基本の車両状態量）である。
ζφ（Ｖ）、ζ_v（Ｖ）は、減衰項に係る状態量である。
ωφ（Ｖ）、ω_v（Ｖ）は、バネ系の固有振動数に係わる状態量である。
Ｔφ（Ｖ）、Ｔ_v（Ｖ）は、定常偏差に係わる状態量である。

From the above, the traveling state of the vehicle according to the steering angle θ and the vehicle body speed V can be specified by the yaw rate and the lateral speed.
The vehicle state quantities (vehicle parameters) related to the yaw rate are gφ (V), ζφ (V), ωφ (V), and Tφ (V).
Further, vehicle state quantities (vehicle parameters) relating to the lateral speed are g _v (V), ζ _v (V), ω _v (V), and T _v (V).
Here, gφ (V) and g _v (V) are state quantities (basic vehicle state quantities) indicating the basic state of the characteristic mode.
ζφ (V) and ζ _v (V) are state quantities related to the attenuation term.
ωφ (V) and ω _v (V) are state quantities related to the natural frequency of the spring system.
Tφ (V) and T _v (V) are state quantities related to the steady deviation.

Next, the front / rear wheel steering target value calculation unit 41B will be described.
The front / rear wheel turning target value calculation unit 41B calculates the vehicle target yaw rate φ ′ ^* fr and the target lateral velocity Vy ^* from the driver steering angle θ, the vehicle body speed V, and the vehicle state quantity calculated by the vehicle model calculation unit 41A ^. Find fr.
First, a target characteristic state quantity corresponding to the selected vehicle characteristic mode is calculated.
That is, the vehicle state quantity corresponding to the vehicle model is multiplied by a gain corresponding to each vehicle characteristic mode, as shown in the following equation. Thus, the vehicle state quantity calculated by the vehicle model calculation unit 41A is converted into a target characteristic state quantity corresponding to the vehicle characteristic mode.

Target characteristic state ^{quantity, gφ * (V), ζφ} * (V), ωφ * (V), Tφ * (V), and ^{_{g v * (V), ζ}} v * (V), ω v * (V ), T _v ^* (V).
gφ ^* (V) = gφ (V) xyrate_gain_map1
ζφ ^* (V) = ζφ (V) xyrate_zeta_map1
ωφ ^* (V) = ωφ (V) xyrate_omegn_map1
Tφ ^* (V) = Tφ (V) xyrate_zeta_map1
g _v ^* (V) = g _v (V) × vy_gain_map1
ζ _v ^* (V) = ζ _v (V) × vye_zeta_map1
ω _v ^* (V) = ω _v (V) × vy_zero_mapa1
T _v ^* (V) = Tφ (V) xvy_zeta_map1
However, yrate_gain_map1, yrate_omegn_map1, yrate_zeta_map1, yrate_zero_mapa1, vy_gain_map1, vy_omegn_map1, vye_zeta_map1, and vy_zero_mapa1 are preset tuning parameters that vary depending on the vehicle body speed.

Here, yrate_gain_map1 and vy_gain_map1 have different maps for each vehicle characteristic mode. Then, yrate_gain_map1 and vy_gain_map1 corresponding to the selected vehicle characteristic mode are used.
Next, the front / rear wheel steering target value calculation unit 41B applies a target characteristic state quantity corresponding to the vehicle characteristic mode instead of the vehicle state quantity calculated by the vehicle model calculation unit 41A, based on the following formula: A target yaw rate and a target lateral speed are obtained from the vehicle body speed V, the steering angle θ, and the target characteristic state quantity.
Here, the target yaw rate is expressed by the following equation (9).

  Further, the target lateral speed is expressed by the following equation (10).

Next, the front-rear wheel steering control calculation unit 42A in the target output value generation unit 42 will be described.
The front and rear wheel turning control calculation unit 42A determines the target turning angles α ^* and δ ^* from the target yaw rate φ ′ ^* fr calculated by the target value generation unit 41 and the target lateral velocity Vy ^* fr.
Since the yaw rate and lateral acceleration control are performed at the time of steering using the front and rear wheels as steered wheels, the target front wheel turning angle α ^* and the target rear wheel turning angle δ ^* are obtained from the following equations (12) and (13). .

Then, the front / rear wheel turning control calculation unit 42A outputs the calculated target front wheel turning angle α ^* and the target rear wheel turning angle δ ^* to the target output unit 42C.
Next, the process of the neutral return control calculation unit 42B will be described.
As shown in FIG. 5, the neutral return control calculation unit 42B includes an actuator drive prohibiting means 50, an actuator abnormality return means 51, and a rear wheel neutral return processing means 52.

  The actuator drive prohibiting means 50 makes an abnormality determination based on the detection results of the front wheel steering actuator abnormality detection means 30 and the rear wheel steering actuator abnormality detection means 31. That is, when the actuator drive prohibiting means 50 determines that the front wheel steering actuator 5 is abnormal and determines that the rear wheel steering actuator 9 is not abnormal, the steering angle of the rear wheel is set to the neutral position. The angle is controlled and the driving of the front wheel steering actuator 5 is prohibited. The actuator drive prohibiting means 50 determines that the front wheel steering actuator 5 is abnormal and if the rear wheel steering actuator 9 is abnormal, the front wheel steering actuator 5 and the rear The driving of the wheel steering actuator 9 is prohibited. The actuator drive prohibiting means 50 drives the rear wheel steering actuator 9 when it is determined that the front wheel steering actuator 5 is not abnormal and the rear wheel steering actuator 9 is abnormal. Is prohibited.

As shown in FIG. 5, the actuator abnormality return means 51 includes a rear wheel actuator abnormality return means 51A and a front wheel actuator abnormality return means 51B.
The rear wheel actuator abnormality return means 51A is based on the detection of the rear wheel steering actuator abnormality detection means 31, and after the actuator drive prohibiting means 50 determines that the rear wheel steering actuator 9 is abnormal, the rear wheel steering actuator 9 If it is determined that the abnormality is resolved, the steering angle of the rear wheel is controlled to the neutral position angle.

The processing for controlling the steering angle of the rear wheel to the angle of the neutral position is performed by the rear wheel neutral return processing means 52. That is, the rear wheel neutral return processing means 52 is a processing unit common to the rear wheel actuator abnormality return means 51A and the actuator drive prohibiting means 50.
The front wheel actuator abnormality return means 51B is based on the detection by the front wheel steering actuator abnormality detection means 30, and after the actuator drive prohibiting means 50 determines that the front wheel steering actuator 5 is abnormal, the front wheel steering actuator 5 If it is determined that the abnormality has been resolved, it will operate. When the front wheel actuator abnormality return means 51B is operated, the front wheel 8 is returned when the following conditions are satisfied.
・ No abnormality has occurred in the rear wheel drive actuator.
-The return processing of the rear wheel actuator abnormality return means 51A is not in progress.

The return processing of the front wheels 8 by the front wheel actuator abnormality return means 51B is performed as follows.
First, the target front wheel turning angle α ^* at the time of return is acquired, and the difference between the acquired target front wheel turning angle α ^* and the target front wheel turning angle α ^* (front wheel 8 actual turning angle) at the time of abnormality detection is obtained. Find a certain front wheel turning angle difference.
Next, a front wheel change amount Δθf corresponding to the steering angular velocity θ ′ is obtained. The front wheel change amount Δθf is set to increase as the steering angular velocity θ ′ increases.
Then, correction is performed for each front wheel change amount Δθf for each predetermined control cycle with respect to the target front wheel turning angle α ^* (front wheel 8 actual turning angle) at the time of abnormality detection. The corrected target front wheel turning angle α ^* is output to the target output unit 42C every predetermined control cycle.
Here, when the corrected target front wheel turning angle α ^* is equal to the target front wheel turning angle α ^* at the time of return or when the difference from the target front wheel turning angle α ^* at the time of return becomes small, the return is made. The process ends.

Next, processing of the rear wheel neutral return processing means 52 will be described.
First, a rear wheel change amount Δθr corresponding to the steering angular velocity θ ′ is obtained. The rear wheel change amount Δθr is set so as to increase as the steering angular velocity θ ′ increases. The rear wheel change amount Δθr corresponds to the return speed to the neutral position of the rear wheel. The steering angle detecting means detects the steering angular velocity by differentiating the steering angle θ.
The rear wheel change amount Δθr may be slow when the steering angle is small (near neutral) and fast when the steering angle θ is large. Further, the rear wheel change amount Δθr may be slow when the vehicle speed V is high and fast when the vehicle speed V is low. Further, the rear wheel change amount Δθr may be slow when the estimated lateral acceleration calculated from the vehicle body speed and the steering angle is small, and may be fast when the estimated lateral acceleration is high.

And correction which subtracts rear-wheel change amount (DELTA) (theta) r for every predetermined control cycle with respect to target rear-wheel steering angle (delta) ^* (rear-wheel actual steering angle) at the time of abnormality detection is performed. The corrected target rear wheel turning angle δ ^* is output to the target output unit 42C every predetermined control cycle.
Here, when the corrected target rear wheel turning angle δ ^* is equal to the turning angle of the neutral position (for example, 0 degrees) or the difference from the turning angle of the neutral position becomes small, the return processing is finished. To do.

Next, the processing of the neutral return control calculation unit 42B will be described with reference to the flow shown in FIG.
First, in step S100, it is determined whether either the front wheel steering actuator 5 or the rear wheel steering actuator 9 is abnormal. If it is determined as abnormal, the process proceeds to step S110. If it is determined that neither is abnormal, the process proceeds to step S190 as it is. Here, when the front wheel steering actuator 5 is abnormal, the front wheel provisional abnormality flag FE-FLG is turned ON. When the rear wheel steering actuator 9 is abnormal, the rear wheel temporary abnormality flag RE-FLG is turned ON.

In step S110, a signal prohibiting driving of the front wheel steering actuator 5 and the rear wheel steering actuator 9 is output to the target output unit 42C.
In step S120, it is determined whether or not the rear wheel steering actuator 9 is provisionally abnormal. If the rear wheel steering actuator 9 is abnormal, the process proceeds to step S110. If the rear wheel steering actuator 9 is not abnormal, the process proceeds to step S130.
In step S130, the rear wheel neutral return processing means 52 is operated to perform control for returning the rear wheel turning angle to the neutral position.

In step S140, it is determined whether or not the rear wheel turning angle has reached the turning position at the neutral position. When the rear wheel turning angle becomes the turning angle at the neutral position, the process proceeds to step S150. If the rear wheel turning angle is not the neutral turning angle, the process returns to step S130 to continue the rear wheel return process.
In step S150, it is determined whether or not the front wheel steering actuator 5 is provisionally abnormal. When the provisional abnormality of the front wheel steering actuator 5 is resolved, the process proceeds to step S160.

In step S160, when the return condition is satisfied, the process proceeds to step S170. If the return process is performed when the vehicle body speed is high, the behavior change may become sensitive. Therefore, the case where the vehicle body speed is within a predetermined range is set as the return condition. Step S160 may be omitted.
In step S170, the front wheel actuator abnormality return means 51B is operated to perform control to change the front wheel 8 actual steering angle toward the target front wheel turning angle α ^* when the abnormality of the front wheel 8 is resolved.

In step S180, it is determined whether or not the actual steering angle of the front wheels 8 has reached the target front wheel turning angle α ^* when the abnormality of the front wheels 8 is resolved. If the conditions are satisfied, the process proceeds to step S190.
In step S190, an abnormal recovery process end signal is output to the target output unit 42C. Thereafter, the process returns to step S100. The signal for the completion of the abnormal recovery process is realized by turning off both the front wheel provisional abnormality flag FE-FLG and the rear wheel provisional abnormality flag RE-FLG.
Further, the target output unit 42C normally uses the front wheel steering controller 6 and the rear wheel steering controller 10 to calculate the target front wheel turning angle α ^* and the target rear wheel turning angle δ ^* input from the front and rear wheel turning control calculation unit 42A. Output to.

However, when either the front wheel provisional abnormality flag FE-FLG or the rear wheel provisional abnormality flag RE-FLG is ON, a drive prohibition command is output to the front wheel steering controller 6 and the rear wheel steering controller 10. The target output unit 42C then outputs the target front wheel rotation from the neutral return control calculation unit 42B until a signal indicating completion of the return process (the front wheel provisional abnormality flag FE-FLG and the rear wheel provisional abnormality flag RE-FLG are both OFF) is input. When the steering angle α ^* and the target rear wheel turning angle δ ^* are acquired, the target front wheel turning angle α ^* and the target rear wheel turning angle δ ^* from the neutral return control calculation unit 42B are output with priority.
Here, in the said embodiment, the case where the return process at the time of abnormality is performed by the steering angle control controller 4 is demonstrated. Instead of this, the return processing may be performed by the front wheel steering controller 6 and the rear wheel steering controller 10.

(Operation)
In order to detect the actual traveling state of the vehicle as much as possible, the yaw rate and the lateral speed representing the traveling state of the vehicle are calculated using the vehicle model, and the target yaw rate and the target lateral speed corresponding to the vehicle characteristic mode are obtained. That is, the target vehicle behavior that is the target vehicle behavior is estimated, and the target front wheel turning angle α ^* and the target rear wheel steering for realizing the target yaw rate and the target lateral speed that are the estimated target vehicle behavior are realized. Calculate the angle δ ^* .
Then, the front wheel turning actuator 5 and the rear wheel turning actuator 9 are controlled to change the turning angle of the front wheel 8 and the turning angle of the rear wheel, which are steered wheels, respectively, to the target front wheel turning angle α ^* and the target rear turning angle Adjust the wheel turning angle δ *.

At this time, in order to obtain the target vehicle behavior, the turning angle of the front wheel 8 is determined from the turning angle corresponding to the steering angle of the steering hall by “the target front wheel turning angle α ^* and the turning angle corresponding to the steering angle”. The front wheel turning actuator 5 is driven so as to change only the corrected turning angle, which is “difference from the above”.
In this state, when a provisional abnormality of the front wheel steering actuator 5 is detected, such as the front wheel steering actuator 5 overheating, the driving of the front wheel steering actuator 5 and the rear wheel steering actuator 9 is prohibited (stopped). Thereby, the front wheel steering actuator 5 is protected.

At this time, if the abnormality of the rear wheel steering actuator 9 is not detected, the rear wheel steering angle is adjusted so that the steering angle of the rear wheel becomes the steering angle of the neutral position even if the front wheel steering actuator 5 is abnormal. The wheel turning actuator 9 is driven to return the turning angle of the rear wheel to the turning angle at the neutral position.
Further, when the abnormality of the rear wheel steering actuator 9 is detected, the rear wheel turning angle is corrected so that the rear wheel turning angle becomes the steering angle at the neutral position when the abnormality is resolved. The wheel turning actuator 9 is driven to return the turning angle of the rear wheel to the turning angle at the neutral position.

  In the neutral return control of the rear wheels, the rear wheels are operated at a constant angular velocity from the steering angle to the neutral state when a temporary abnormality occurs. At this time, the return speed to the neutral position of the rear wheel may be slow when the steering angular speed is slow and fast when the steering angular speed is fast. The return speed to the neutral position of the rear wheel may be slow when the steering angle is small (near neutral) and fast when the steering angle is large. Further, the return speed to the neutral position of the rear wheel may be slow when the vehicle body speed is high and may be fast when the vehicle body speed is low. Further, the return speed to the neutral position of the rear wheel may be slow when the estimated lateral acceleration calculated from the vehicle speed and the steering angle is small, and may be fast when the estimated lateral acceleration is high.

When the abnormality of the front-wheel steering actuator 5 determined to be abnormal is resolved, it waits for the rear-wheel steering angle to return to the neutral steering angle, and toward the target front-wheel steering angle α ^* when the abnormality is resolved The steering angle of the front wheel 8 is restored. The neutral return control for the front wheels 8 recognizes the difference between the target front wheel turning angle and the actual front wheel 8 steering angle when returning from the temporary abnormality to the normal state as the neutral deviation amount, and subtracts the neutral deviation amount according to the steering angular velocity. Control to continue. When the neutral deviation amount becomes zero, the normal control is restored.

  When an abnormality is detected only in the front wheel steering actuator 5 by the above processing, the front wheel steering actuator 5 is determined to be abnormal, and when the front wheel steering actuator 5 is stopped driving, the rear wheel steering actuator 9 is A process of driving and returning the turning angle of the rear wheels to the turning angle at the neutral position is performed. Accordingly, the time required for the rear wheel turning angle to return to the turning angle at the neutral position after the front wheel turning actuator 5 is eliminated is shortened. That is, when the front wheel steering actuator 5 becomes temporarily abnormal, the front and rear wheels are in a neutral position as compared with the case where the rear wheel return processing is started after waiting for the abnormality of the front wheel steering actuator 5 to be resolved. Time to return to can be shortened.

  As a result of shortening the time required for the front and rear wheels to return to the neutral position as described above, for example, when the front wheel steering actuator 5 becomes temporarily abnormal when the steering angle of the steering wheel is large, the steering wheel When the wheel is returned to the neutral position, the neutral deviation of the steering wheel is not generated or the neutral deviation that has occurred is quickly eliminated. As a result, it is possible to suppress a sense of discomfort to the driver with respect to the return from the provisional abnormality of the front wheel steering actuator 5.

FIG. 7 shows a time chart example. In this example, only the front wheel steering actuator 5 becomes a temporary abnormality at time t1 to t2. At this time, since the rear wheel steering actuator 9 does not determine that there is an abnormality, the rear wheel steering is returned to the neutral position (0 degree) from time t1. Further, at the time t3, the rear wheel return processing is completed, and the abnormality of the front wheels is also eliminated, so that the actual steering angle of the front wheels is controlled to coincide with the target front wheel turning angle α ^* . Here, the target front wheel turning angle α ^* is an angle corresponding to the steering angle. Then, when the driver returns the steering angle θ of the steering wheel 1 to neutral at this time t3, the target front wheel turning angle α ^* also goes toward zero accordingly, and in the example, at the time t4 Thus, when the return of the steering wheel 1 is completed, the neutral return of the front wheels is completed.
Here, the steering angle control controller 4 constitutes a target turning angle calculation means.

(Effect of this embodiment)
(1) The front wheel steering actuator abnormality detection means 30 detects an abnormality of the front wheel steering actuator 5. The rear wheel steering actuator abnormality detection means 31 detects an abnormality of the rear wheel steering actuator 9.
Then, the actuator drive prohibiting means 50 determines that the front wheel steering actuator 5 is abnormal based on the detection by the front wheel steering actuator abnormality detection means 30 and the rear wheel steering actuator abnormality detection means 31, and the rear wheel steering. When it is determined that the actuator 9 is not abnormal, the steering angle of the rear wheel 12 is controlled to the neutral position angle, and the driving of the front wheel steering actuator 5 is prohibited, and the front wheel steering actuator 5 is abnormal. And when it is determined that the rear wheel steering actuator 9 is abnormal, the driving of the front wheel steering actuator 5 and the rear wheel steering actuator 9 is prohibited.

Further, after the rear wheel actuator abnormality return means 51A determines that the rear wheel steering actuator 9 is abnormal based on the detection of the rear wheel steering actuator abnormality detection means 31, the abnormality of the rear wheel steering actuator 9 is resolved. If it determines with having performed, the turning angle of the said rear wheel will be controlled to the angle of a neutral position.
If the rear wheel steering actuator 9 is not abnormal while the front wheel steering actuator 5 is abnormal, or if the abnormality has been resolved, the rear wheel even before the abnormality of the front wheel steering actuator 5 is resolved. The process which returns the steering angle of to a neutral position is started.
This shortens the time for returning to normal four-wheel steering control after the abnormality of the front wheel steering actuator 5 is resolved. Due to the shortening, it becomes difficult for the driver to feel uncomfortable with respect to the return from the temporary abnormality of the front wheel steering actuator 5.

(2) The front wheel steering mechanism SS steers the front wheels 8 according to the steering angle θ of the steering wheel 1 steered by the driver. The target turning angle calculation means estimates the target vehicle behavior as the target vehicle behavior based on the steering angle θ of the steering wheel 1, and sets the target front wheel turning angle α ^* and the target rear according to the estimated target vehicle behavior. The wheel turning angle δ ^* is calculated. The front wheel turning controller 6 controls the front wheel turning actuator 5 so that the turning angle of the front wheel 8 becomes the target front wheel turning angle α ^* calculated by the target turning angle calculation means. The rear wheel turning controller 10 controls the rear wheel turning actuator 9 so that the turning angle of the rear wheel becomes the target rear wheel turning angle δ ^* calculated by the target turning angle calculation means.
Even if the steering wheel 1 is returned to the neutral position when the front wheel steering actuator 5 is out of order, it does not return to the neutral position by the amount changed by the front wheel steering actuator 5. At this time, by shortening the processing time at the time of return, it is possible to shorten the time of neutral deviation when the steering wheel 1 is returned to neutral.

(3) The return speed at which the turning angle of the rear wheel 12 is turned to the neutral position is made slower when the steering angular speed θ ′ is slow than when the steering angular speed θ ′ is fast.
When the steering angular velocity is low, the driver is more sensitive to changes in vehicle behavior than when the steering angular velocity is high. In view of this, the feeling of discomfort given to the driver is reduced by “lowering the steering angular velocity when compared with the higher steering angular velocity”.

(4) The return speed at which the turning angle of the rear wheel 12 is turned to the neutral position is increased when the steering angle θ is large compared to when the steering angle θ is small.
When the steering angle is large, it can be estimated that the vehicle is turning. In the turning state, the driver's sensitivity to the vehicle behavior is lower than in the straight traveling state in which the steering angle θ is small. In view of this, it is possible to reduce the uncomfortable feeling given to the driver by “increasing the speed when the steering angle is large compared to when the steering angle is small”.

(5) When the vehicle body speed V is high, the return speed at which the steering angle of the rear wheel 12 is turned to the neutral position is made slower than when the vehicle body speed is low.
The higher the vehicle body speed V, the more sensitive the vehicle reacts to changes in vehicle behavior. In view of this, the feeling of discomfort given to the driver is reduced by “lowering the vehicle speed compared to when the vehicle speed is low”.

(6) The return speed at which the turning angle of the rear wheel 12 is turned to the neutral position is made slower when the estimated lateral acceleration is small than when the estimated lateral acceleration is large.
When the lateral acceleration is large, it can be estimated that the vehicle is turning. In the turning state, the driver's sensitivity to the vehicle behavior is lower than in the straight traveling state in which the lateral acceleration is small. In view of this, the feeling of discomfort given to the driver is reduced by “slower when the estimated lateral acceleration is small than when the estimated lateral acceleration is large”.

DESCRIPTION OF SYMBOLS 1 Steering wheel 4 Steering angle control controller 5 Front wheel steering actuator 6 Front wheel steering controller 8 Front wheel 9 Rear wheel steering actuator 10 Rear wheel steering controller 12 Rear wheel 20 Steering angle sensor 21 Car body speed sensor 30 Front wheel steering actuator abnormality detection means 31 Rear wheel steering actuator abnormality detection means 41 Target value generation unit 41A Vehicle model calculation unit 41B Front and rear wheel steering target value calculation unit 42 Target output value generation unit 42A Front and rear wheel steering control calculation unit 42B Neutral return control calculation unit 42C Target output unit 50 Actuator drive prohibiting means 51 Actuator abnormality return means 51A Rear wheel actuator abnormality return means 51B Front wheel actuator abnormality return means 52 Rear wheel neutral return processing means FE Front wheel provisional abnormality flag RE Rear wheel provisional abnormality flag SS Front wheel steering mechanism V Vehicle speed α Target turn Steering angle δ Target rear wheel turning angle Δθf Front wheel change amount Δθr Rear wheel change amount θ Steering angle θ ′ Steering angular velocity φ Target yaw rate

Claims (7)

Front wheels steered at a steered angle corresponding to the steering angle of the steering wheel steered by the driver,
A front wheel steering actuator that changes a steering angle of a front wheel according to a steering angle of the steering wheel, a rear wheel steering actuator that steers a rear wheel, and
Front wheel steering actuator abnormality detection means for detecting abnormality of the front wheel steering actuator; rear wheel steering actuator abnormality detection means for detecting abnormality of the rear wheel steering actuator;
Based on the detection of the front wheel steering actuator abnormality detection means and the detection of the rear wheel steering actuator abnormality detection means, when it is determined that the front wheel steering actuator is abnormal and the rear wheel steering actuator is not abnormal, The steering angle of the rear wheel is controlled to the neutral position angle, and the driving of the front wheel steering actuator is prohibited, and it is determined that the front wheel steering actuator is abnormal and the rear wheel steering actuator is abnormal. An actuator drive prohibiting means for prohibiting the driving of the front wheel steering actuator and the rear wheel steering actuator,
Based on the detection by the rear wheel steering actuator abnormality detection means, after determining that the rear wheel steering actuator is abnormal, if it is determined that the abnormality of the rear wheel steering actuator has been resolved, the steering angle of the rear wheel is neutralized. Rear wheel actuator abnormality return means for controlling the position angle;
A steering angle control device for a vehicle, comprising: A front wheel steering mechanism that steers the front wheels in accordance with the steering angle of the steering wheel that the driver steers,
Target steering angle calculation means for estimating a target vehicle behavior as a target vehicle behavior based on the steering angle of the steering wheel and calculating a target front wheel turning angle and a target rear wheel turning angle according to the estimated target vehicle behavior When,
A front wheel steering controller that controls the front wheel steering actuator so that the steering angle of the front wheel becomes the target front wheel steering angle calculated by the target steering angle calculation means, and the steering angle of the rear wheel is the target steering A rear wheel steering controller that controls the rear wheel steering actuator so as to be the target rear wheel steering angle calculated by the angle calculation means;
The vehicle steering angle control device according to claim 1, comprising:   3. The return speed at which the turning angle of the rear wheel is turned to the neutral position is made slower when the steering angular speed is slow than when the steering angular speed is fast. The steering angle control device for a vehicle described in 1.   4. The return speed at which the turning angle of the rear wheel is turned to the neutral position is made faster when the steering angle is large than when the steering angle is small. The vehicle steering angle control device described in any one of the above.   5. The return speed at which the turning angle of the rear wheel is turned to the neutral position is made slower when the vehicle body speed is high than when the vehicle body speed is low. The vehicle steering angle control device described in any one of the above.   The return speed at which the steering angle of the rear wheel is steered to the neutral position is made slower when the estimated lateral acceleration is small than when the estimated lateral acceleration is large. The vehicle steering angle control device according to any one of Items 1 to 5. Presence or absence of abnormality of the front wheel steering actuator that changes the steering angle of the front wheel that steers at the steering angle according to the steering angle of the steering wheel that the driver steers and the rear wheel steering actuator that steers the rear wheel Detect
When the abnormality of the front wheel steering actuator is detected and the abnormality of the rear wheel steering actuator is not detected, the steering angle of the rear wheel is controlled to the neutral position angle and the front wheel steering actuator is driven. Prohibiting, when detecting an abnormality of the front wheel steering actuator and detecting an abnormality of the rear wheel steering actuator, prohibiting the driving of the front wheel steering actuator and the rear wheel steering actuator;
Further, after detecting the abnormality of the rear wheel steering actuator, when the abnormality of the rear wheel steering actuator is no longer detected, the steering angle of the rear wheel is controlled to the neutral position angle. Angle control method.

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