JP2006282067A - Steering control device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steering control device for a vehicle avoiding deterioration of vehicle behavior due to displacement of a neutral position of the steering system. <P>SOLUTION: The steering control device is equipped with a steering angle detection means detecting the steering angle of a steering wheel of a driver, and a first vehicle behavior control means setting a front and rear wheel auxiliary steering angle based on the steering angle to be detected. The steering control device is equipped with a neutral displacement detection means detecting the neutral displacement relative to the front wheel steered angle, and a second vehicle behavior control means which calculates a virtual steering angle based on the front wheel steered angle, and sets the rear wheel auxiliary steered angle based on the virtual steering angle when the neutral displacement is detected. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a vehicle steering control device that controls the steering angle of front and rear wheels to obtain desired vehicle characteristics.

Conventionally, as a vehicle steering control device, when an auxiliary steering angle is given to front and rear wheels at the time of steering input, there is a device that calculates an auxiliary steering angle by feedforward control based on the steering angle and feedback control based on the actual yaw rate (for example, , See Patent Document 1). In addition, the absolute steering angle is calculated from the relative steering angle by detecting the neutral position of the steering wheel.If the neutral position detection is not completed, the rear wheel auxiliary steering angle is calculated from the vehicle speed and the actual yaw rate. Some have a stable vehicle behavior (see, for example, Patent Document 2).
JP-A-5-105102 JP-A-5-310141

  However, in the technique of Patent Document 1, feedforward control based on the steering angle is mainly used in order to obtain a good steering response. However, when a neutral deviation occurs in the front wheel steering angle, this deviation is fed forward based on the steering angle. There is a problem in that the desired auxiliary steering angle cannot be obtained because the control is affected. Also in the technique of Patent Document 2, since the yaw rate is generated after the steering is performed, an accurate front wheel turning amount is calculated even if the rear wheel turning amount is calculated when a deviation occurs in the front wheel turning angle. This is difficult and the vehicle behavior may not be stable.

  The present invention has been made paying attention to the above problems, and an object of the present invention is to provide a vehicle steering control device that avoids deterioration of vehicle behavior due to neutral deviation of the steering system.

  In order to achieve the above object, in the present invention, steering angle detection means for detecting a steering wheel steering angle of a driver, and first vehicle behavior control means for setting front and rear wheel auxiliary steering angles based on the detected steering angle. And a neutral deviation detecting means for detecting a neutral deviation between the steering angle and the front wheel turning angle, and when a neutral deviation is detected, based on the front wheel turning angle. And a second vehicle behavior control means for calculating a virtual steering angle and setting a rear wheel auxiliary steering angle based on the virtual steering angle.

  Therefore, by using the virtual steering angle instead of the steering angle, the deterioration of the vehicle behavior due to the neutral deviation of the steering system can be avoided.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS The best mode for realizing a vehicle steering control apparatus according to the present invention will be described below based on an embodiment shown in the drawings.

[System configuration of vehicle steering control device]
FIG. 1 is a system configuration diagram of the vehicle steering control apparatus according to the first embodiment. A steering wheel 2 that is rotatably supported on the vehicle body side and connected to the steering wheel 1 is connected to the steering wheel 1 that is steered by the driver.

  The steering shaft 2 is provided with a steering angle sensor 8 that detects the steering angle θd of the driver, and outputs the steering angle θd to the control unit 100. A variable steering angle actuator 3 that changes the steering angle ratio (ratio of the actual front wheel turning angle to the steering angle θd of the driver) is provided on the front wheel 20 side of the steering angle sensor 8. The variable steering angle actuator 3 is provided with a front wheel motor 3a, and the steering angle ratio is changed by adding or subtracting the front wheel motor rotation angle θmf with respect to the steering angle θd.

  The front wheel motor 3 a is provided with an encoder 10, and the rotation angle θmf of the front wheel motor 3 a is output to the control unit 100. A pinion 4 is provided on the front wheel 20 side of the variable rudder angle actuator 3, and the rack shaft 5 is moved left and right in the axial direction by a so-called rack and pinion mechanism to steer the front wheel 20.

  The rear wheel 30 is provided with a rear wheel steering actuator 6 for providing a rear wheel steering angle. The rear wheel steering actuator 6 is provided with a rear wheel motor 6 a that gives a steering angle to the rear wheel 30. The rear wheel motor 6 a is provided with an encoder 11 that detects a rear wheel motor rotation angle θmr corresponding to the rear wheel steering angle, and the rotation angle θmr of the rear wheel motor 6 a is output to the control unit 100. A vehicle speed sensor 7 is provided, and the detected vehicle speed VSP is output to the control unit 100.

[Control unit control configuration]
FIG. 2 is a block diagram showing the configuration of the control unit 100. The control unit 100 includes a main controller 100a, a front wheel steering controller 100b, and a rear wheel steering controller 100c.

  In the main controller 100a, a target value generation unit 110 that generates a target front wheel steering angle θ * p_ref and a target rear wheel steering angle δ * ref based on the detected values θd and VSP of the steering angle sensor 8 and the vehicle speed sensor 7, Each target value is corrected based on the front wheel motor rotation angle θmf fed back from the encoder 10, and includes a target value correction unit 120 that outputs a corrected target front wheel steering angle θ * p and a corrected target rear wheel steering angle δ *. Has been.

  The front wheel steering controller 100b outputs a steering angle command value to the front wheel motor 3a as a front wheel steering actuator based on the corrected target front wheel steering angle θ * p output from the target value correction unit 120, and between the front wheel motor 3a. Execute servo control with.

  The rear wheel steering controller 100c outputs a steering angle command value to the rear wheel motor 6a as a rear wheel steering actuator based on the corrected target rear wheel steering angle δ * output from the target value correction unit 120, and the rear wheel motor. Servo control is executed with 6a.

[Control contents of target value generator]
Next, the control content of the target value generation unit 110 will be described.
(Front wheel control)
First, the target value of the proportional component is obtained from the steering angle θd of the driver and the front wheel proportional gain KPf (VSP) depending on the vehicle speed VSP shown in FIG. Here, when the vehicle speed VSP is low, the steering angle ratio is set large (quickly) so that a large steering angle can be obtained with a small steering angle θd of the driver. On the other hand, when the vehicle speed VSP is high, the steering angle ratio is set to be small (slow) in consideration of stability.

  Next, the target value of the differential component is obtained from the steering angular velocity dθd / dt obtained by differentiating the steering angle θd and the front wheel differential gain KDf depending on the vehicle speed VSP shown in FIG. This differential steering can generally improve the yaw rate response of the vehicle.

These proportional and differential components are added, and the front wheel target steering angle θ * p_ref is calculated by the following formula θ * p_ref = KPf × θd + KDf × dθd / dt
It is represented by In this case, the front wheel motor rotation angle command value θmf * is expressed by the following equation: θ * mf = θ * p_ref−θd
It is represented by

(Rear wheel control)
Similar to the front wheel control, the rear wheel steering angle target value is obtained using the rear wheel proportional gain KPr (VSP) depending on the vehicle speed VSP shown in FIG. 5 and the rear wheel differential gain KDr depending on the vehicle speed VSP shown in FIG. δ * ref is the following formula δ * ref = KPr × θd + KDr × dθd / dt
It is represented by

(Servo control)
The deviation e between the actual steering angle θ of the front wheels and the corrected target front wheel steering angle θ * is
e = θ-θ *
Is required.
The front wheel control command value I _theta, and the deviation e, a proportional gain P and, derivative gain D and the following formula I and a integral gain _{I θ = P × e + D} × de / dt + I × ∫edt
Is required. The proportional gain P, differential gain D, and integral gain I are tuning constants. Similar servo control is executed for the rear wheels.

[Details of target value correction unit]
FIG. 3 is a block diagram showing a control configuration of the target value correction unit 120. The target value correction unit 120 includes an abnormal state determination unit 121, a driver steering angle equivalent value calculation unit 122, a target front wheel turning angle correction unit 123, and a target rear wheel steering angle correction unit 124.

  The abnormal state determination unit 121 determines whether there is an abnormality in the front wheel motor 3a based on the target front wheel steering angle θ * p_ref, the steering angle θd, and the front wheel motor rotation angle θmf. 1 is output to the target front wheel turning angle correction unit 123 and the target rear wheel turning angle correction unit 124.

  The driver steering angle equivalent value calculation unit 122 calculates a driver steering angle equivalent value θh (corresponding to the virtual steering angle described in the claims) based on the steering angle θd, the front wheel motor rotation angle θmf, and the vehicle speed VSP. And output to the target rear wheel rudder angle correction unit 124.

  Here, the driver steering angle equivalent value θh means that the front wheel control system operates normally in a state where the target front wheel steering angle θ * p_ref corresponding to the driver steering angle θd is not obtained as the current front wheel steering angle. Assuming that it is the driver steering angle equivalent value θh (virtual steering angle) that is the current front wheel steering angle.

[Abnormalities in the abnormal state determination unit]
In the abnormal state determination unit 121, when the normal front / rear wheel steering angle control (corresponding to the first vehicle behavior control means described in the claims) is being performed, an error is detected when a neutral shift occurs on the front wheel side. Judge as the state.

  That is, at the normal time, the front wheel motor 3a is driven and controlled by calculating the front wheel steering angle target value θ * p_ref from the driver steering angle θd, the vehicle speed VSP, and the set control gain. At this time, the actual front wheel turning angle is equal to the sum of the driver steering angle θd and the front wheel motor rotation angle θmf.

  However, there may be a temporary difference between the neutral position of the steering angle θd and the neutral position of the actual front wheel turning angle. For example, when the steering wheel 1 is steered when the ignition OFF control is stopped, or when some tentative abnormality occurs in the control system and then recovers. In that case, it is conceivable to continue the control while maintaining the neutral deviation angle. Then, the neutral deviation angle is calculated as an offset angle, and control or the like for gradually reducing the offset angle to zero is performed.

  That is, the correction command value is obtained by adding the offset angle to the above-described front wheel motor rotation angle command value, and control is performed so that the front wheel motor has the correction command value. At the same time, the control for gradually reducing the offset angle included in the correction command value to zero is also executed in parallel.

  The control for gradually reducing the offset angle to zero is not described in detail, but a known control method can be applied. For example, it is described in a method of driving the front wheel motor 3a so that the offset angle is reduced at a constant rate only while the steering angular velocity exceeds a predetermined speed, or disclosed in JP 2000-344121A. Is omitted.

  Thus, when the actual front wheel turning angle differs between the driver steering angle θd and the front wheel steering angle target value θ * p_ref determined from the set steering angle ratio, the rear wheel steering angle target value calculation is performed. When the driver steering angle θd is used as it is, the rear wheel turning angle does not match the actual front wheel turning angle, and desired vehicle characteristics cannot be obtained.

  Therefore, when the offset angle is generated, the calculation method of the rear wheel steering angle target value δ * ref is changed to control the vehicle so as to be close to desired vehicle characteristics. Here, the premise of the first embodiment will be described.

  Assumption 1) When performing the steering operation, the driver first visually recognizes the angular relationship of the front traveling road, converts the recognized angle into torque by muscles, and steers. In other words, since the steering wheel is not visually observed for steering, even if a neutral shift occurs on the front wheel side, steering based on the forward angular relationship is executed in consideration of the neutral shift unconsciously.

  Assumption 2) In the vehicle steering control device of the first embodiment, when a driver generates a certain steering angle at a certain vehicle speed, this degree of yaw rate and lateral acceleration are achieved as steering feeling and vehicle characteristics. Based on the theory that is optimal, the auxiliary steering angle is given to the front and rear wheels. In other words, the feedback control system using a yaw rate sensor, a lateral acceleration sensor, or the like does not reflect the driver's steering intention, but starts control based on the actually generated vehicle behavior. The optimal vehicle characteristics in line with the steering intention of the vehicle cannot be obtained. Therefore, before and after the vehicle behavior is generated by feedforward control with respect to the steering angle and the vehicle speed, the front and rear wheel auxiliary steering angles are set to ensure a quick response.

  Here, assuming that the vehicle behavior is always estimated from the actual front wheel steering angle and the front and rear wheel auxiliary steering angles are given to obtain the desired behavior, before the front wheels are steered from the driver's steering operation, Since a delay occurs, the driver's steering intention cannot be reflected, and the vehicle control characteristics aimed at cannot be obtained in the first place.

  Therefore, during normal control, the front and rear wheel auxiliary steering angles are given based on the driver's steering angle and vehicle speed, and the driver steering angle equivalent value θh estimated from the actual front wheel steering angle only when neutral deviation occurs on the front wheel side. The front and rear wheel auxiliary rudder angles are given based on the vehicle speed.

(Rear wheel rudder angle target value correction method)
Next, a specific correction method will be described. The current front wheel steering angle (θd + θmf) is obtained from the steering angle θd and the front wheel motor rotation angle θmf. Further, since the steering angular velocity dθd / dt is a steering angle per unit time, it is not affected by neutral deviation. Therefore, the differential component KDf × dθd / dt is subtracted from the current front wheel rudder angle (θd + θmf), and the current wheel steer angle (θd + θmf) is calculated in consideration of the neutral deviation. Therefore, the driver steering angle equivalent value θh is expressed by the following formula θh = {(θd + θmf) −KDf × dθd / dt} / KPf
It is represented by

  That is, the current front wheel steering angle (θd + θmf) including the amount of neutral deviation with respect to this driver steering angle equivalent value θh is equivalent to that during normal control, and the rear wheel steering angle target value δ * By calculating ref, a desired characteristic can be obtained using the conventional control gain as it is even if neutral deviation occurs.

With respect to the driver steering angle θd, the actual front wheel turning angle is delayed due to a follow-up delay of the front wheel motor 3a, a twist of a coupling or the like disposed in the column portion, and the like. Therefore, when the rear wheel steering angle target value is corrected using the driver steering angle equivalent value θh, the proportional component is calculated using θh, while the differential component is the steering angular velocity dθd / dt that is not affected by the neutral deviation. It was decided to calculate using as is.
When the abnormal state flag Fi is set to 1, the corrected target rear wheel steering angle δ * is expressed by the following formula δ * = KPr × θh + KDr × dθd / dt
It is represented by Thereby, it is possible to obtain a target value in which the influence of the delay is very small while taking the neutral deviation into consideration.

[Target value correction control processing]
FIG. 8 is a flowchart showing the flow of the target value correction control process. Hereinafter, each step will be described.
In step 101, the vehicle speed VSP and the steering angle θd are read, and the routine proceeds to step 102.
In step 102, the target front wheel steering angle θ * p_ref and the target rear wheel steering angle δ * ref are calculated, and the routine proceeds to step 103.
In step 103, the front wheel rudder angle abnormality determination is performed. If normal, the process proceeds to step 108, and if abnormal, the process proceeds to step 104.

In step 104, the target front wheel steering angle is corrected, and the corrected target front wheel steering angle θ * p is calculated.
In step 105, it is determined whether or not the offset steering angle, which is a neutral deviation generated in the front wheel steering angle, is within a permissible range, that is, a value that does not affect the vehicle behavior. Otherwise, go to step 106.
In step 106, the actual front wheel turning angle (θd + θmf) is calculated from the steering angle θd and the front wheel motor rotation angle θmf.
In step 107, a driver steering angle equivalent value θh is calculated.
In step 108, the corrected target rear wheel steering angle δ * is calculated.
In step 109, the front wheel motor 3a and the rear wheel motor 6a, which are front and rear wheel actuators, are driven and controlled.

  The effect of the target value correction control based on the flowchart will be described based on the time charts of FIGS. FIG. 9 is a diagram illustrating the angular relationship when the neutral displacement occurs during the slalom running of the first to third pylons arranged at substantially equal intervals. In this time chart, the traveling speed of the vehicle is traveling in a relatively low speed region, and as the steering angle control on the front wheel side, the front wheel motor rotation angle θmf is added to the steering angle θd to control the steering angle on the rear wheel side. Assuming that reverse phase control is performed.

  When the driver visually observes the pylon and avoids the pylon by slalom traveling, the driver does not steer by looking at the steering wheel 1 but operates the steering wheel 1 by visually observing the pylon. At this time, at time t1, a temporary failure that can be restored occurs due to an increase in the temperature of the actuator or the like, and the control gain begins to decrease. At this time, the control is performed so that only the control amount decreases while maintaining the phase so that the direction steered by the driver does not coincide with the control direction. When the steering wheel 1 is turned back after clearing the first pylon in this state, the actual front wheel motor rotation angle θmf starts to be delayed with respect to the front wheel motor rotation angle command value, and a neutral deviation occurs (A region in FIG. 9). When the steering wheel 1 is turned back to the right side to clear the second pylon in a state where this neutral deviation has occurred, the front wheel motor rotation angle command value is calculated without the neutral deviation being eliminated. Therefore, since the actual front wheel steering angle θ is generated with the neutral deviation added, the driver clears the second pylon without steering the steering wheel 1 to the right side (the value of the steering angle sensor 8 is small). (B area in FIG. 9).

  Next, when the driver steers the steering wheel 1 to the left in order to clear the second pylon and clear the third pylon, the steering wheel 1 is steered in a state where the neutral deviation is added. Therefore, the value of the steering angle sensor 8 is steered to the left larger than the actual front wheel turning angle θ (C region in FIG. 9), and this makes it possible to obtain a desired actual front wheel turning angle θ for the first time. . Since the front wheel motor rotation angle command value is set based on the value of the steering angle sensor 8, a larger value is output, but a neutral shift is detected.

  That is, the relationship between the front wheel motor rotation angle θmf and the front wheel motor rotation angle command value cannot eliminate the offset angle as shown in FIG. 10, and the front wheel turning angle command value and the actual front wheel turning angle θ The relationship is deviated as shown in FIG.

  At this time, in the rear wheel steering angle control, the control is basically performed based on the steering angle θd. When the rear wheel control is executed without performing the target value correction control, the rear wheel steering angle is controlled in reverse phase as shown by the dotted line in FIG. 12, and the steering angle is given to the right side. Therefore, yaw rate cannot be generated sufficiently and smooth pylon clearing may not be possible.

  On the other hand, when the rear wheel control is executed in a state where the target value correction control is performed, the rear wheel steering angle is controlled according to the driver steering angle equivalent value θh, and therefore, as shown by the solid line in FIG. The rear wheel rudder angle is given according to the state in which the driver has visually cleared the pylon. Therefore, it becomes possible to always obtain an appropriate reverse phase steering angle and obtain a desired yaw rate.

1 is a system configuration diagram illustrating a vehicle steering control device in Embodiment 1. FIG. 2 is a block diagram illustrating a configuration of a control unit in Embodiment 1. FIG. 3 is a map showing a relationship between a front wheel proportional gain and a vehicle speed in the first embodiment. 3 is a map showing a relationship between a rear wheel proportional gain and a vehicle speed in the first embodiment. 3 is a map showing the relationship between front wheel differential gain and vehicle speed in the first embodiment. 3 is a map showing a relationship between a rear wheel differential gain and a vehicle speed in the first embodiment. FIG. 3 is a block diagram illustrating a configuration of a target value correction unit according to the first embodiment. 3 is a flowchart illustrating target value correction control in the first embodiment. 6 is a time chart showing an angular relationship during slalom traveling in the first embodiment. 3 is a time chart showing a relationship between a front wheel motor rotation angle command value and an actual front wheel motor rotation angle in the first embodiment. 3 is a time chart showing a relationship between a front wheel turning angle command value and an actual front wheel turning angle in the first embodiment. 3 is a time chart showing a relationship between a rear wheel steering angle with correction control and a rear wheel steering angle without correction control in the first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 3 Front wheel steering angle actuator 3a Front wheel motor 6 Rear wheel steering angle actuator 6a Rear wheel motor 7 Vehicle speed sensor 8 Steering angle sensor
100 control unit

Claims (3)

Steering angle detection means for detecting the steering wheel steering angle of the driver;
First vehicle behavior control means for controlling the front and rear wheel steering angles based on the detected steering angle;
In a vehicle steering control device comprising:
A neutral deviation detecting means for detecting a neutral deviation between the steering angle and the front wheel steering angle;
A second vehicle behavior control means for calculating a virtual steering angle based on the front wheel steering angle and controlling the rear wheel steering angle based on the virtual steering angle when a neutral shift is detected;
A vehicle steering control device comprising: The vehicle steering control device according to claim 1,
The vehicle steering control device, wherein the second vehicle behavior control means calculates a rear wheel steering angle from a proportional component of the virtual steering angle and a differential component of the detected steering angle. In the vehicle steering control method for controlling the turning angle of the front and rear wheels in accordance with the operation of the steering wheel (actual steering angle),
When a deviation is detected between the neutral position of the steering wheel and the neutral position of the front wheel that is steered according to the steering wheel operation,
A steering control method for a vehicle, characterized in that a turning angle of a rear wheel is controlled in accordance with a turning state of a front wheel.

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