JP2007008242A - Steering control device for vehicle, and steering control method for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steering control device for a vehicle capable of controlling vehicle behaviors without giving a sense of incongruity to a driver. <P>SOLUTION: This steering control device comprises a power steering means giving an assist torque based on a steering torque of a driver comprises an ideal steering angle estimation value calculation means for calculating an ideal steering angle according to the steering torque, a target characteristic setting means for setting a target characteristic to make the characteristic of the vehicle behavior or the steering angle relative to the steering torque of the driver smaller as the frequency of the steering torque becomes high, a transition assist torque control means for controlling the assist torque so that the characteristic of the vehicle behavior or the steering angle relative to the steering torque becomes the target characteristic based on the steering torque and the ideal steering angle, and an ideal steering angle changing means for changing the ideal steering angle based on the vehicle behavior characteristic relative to the steering angle of the vehicle. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a vehicle steering control, and more particularly to a vehicle steering control device that controls vehicle behavior based on a steering state of a driver and a traveling state of the vehicle.

Conventionally, as a vehicle steering control device that gives an auxiliary steering angle to a front wheel or a rear wheel, a technique described in Patent Document 1 has been disclosed. In this publication, in a vehicle that gives an auxiliary rudder angle to a rear wheel, when a failure is detected in the rear wheel rudder angle control system, control is performed so that the rear wheel auxiliary rudder angle is returned to neutral. Ensures stability.
Japanese Patent Laid-Open No. 62-152977

  However, in the above prior art, since the vehicle characteristics are different between when the rear wheel steering angle control system is normal and when it fails, there is a concern that the driver may feel uncomfortable. That is, when the driver steers the vehicle, he visually recognizes the forward angular relationship, converts the angular relationship into muscle strength, that is, torque based on the experience value during normal driving, and steers the steering wheel. This is because the yaw rate generated by the vehicle is different even if the steering is performed with the torque intended by the driver.

  The present invention has been made paying attention to the above-described problem, and the object of the present invention is to control the vehicle behavior without giving the driver a sense of incongruity even if the vehicle behavior characteristics with respect to the steering angle of the vehicle change. An object of the present invention is to provide a vehicle steering control device and a vehicle steering control method.

  In order to achieve the above object, according to the present invention, an ideal steering for calculating an ideal steering angle according to a steering torque in a vehicle steering control device including a power steering means for applying an assist torque based on a steering torque of a driver. An angle estimation value calculating means; a target characteristic setting means for setting a target characteristic that the vehicle behavior or the steering angle characteristic with respect to the steering torque of the driver becomes smaller as the frequency of the steering torque becomes higher; and the steering torque and the ideal steering angle Based on the above, based on the vehicle behavior characteristic with respect to the steering angle of the vehicle, the transient assist torque control means for controlling the assist torque so that the characteristic of the vehicle behavior or the steering angle with respect to the steering torque becomes the target characteristic, And an ideal steering angle changing means for changing the ideal steering angle.

  Therefore, even when the vehicle behavior characteristic with respect to the steering angle of the vehicle changes, it is possible to obtain the same vehicle behavior or steering angle characteristic, and to stabilize the vehicle behavior without giving the driver a sense of incongruity. .

  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.

[Configuration of vehicle control system]
FIG. 1 is a system configuration diagram illustrating a vehicle control system according to a first embodiment. The vehicle of the first embodiment is provided with a vehicle speed sensor 1 that detects the vehicle speed, a torque sensor 2 that detects the steering torque of the driver, and a steering angle sensor 7 that detects the steering angle of the driver.

  Further, the power steering unit 30 that assists the driver's steering torque by the power motor 31, the front wheel steering unit 40 that can control the addition and subtraction of the steering angle of the front wheel 4a with respect to the steering angle of the driver, and the rear wheel 5a. A rear wheel steering unit 50 capable of controlling the steering angle is mounted.

  The power steering unit 30 includes an assist controller 3 and a power motor 31 that operates based on a command from the assist controller 3, and is disposed in front of the vehicle. The front wheel steering unit 40 includes a front wheel controller 4 and a front wheel actuator 41 that operates based on a command from the front wheel controller 4, and is disposed below an instrument panel in front of the vehicle. The rear wheel steering unit 50 includes a rear wheel controller 5 and a rear wheel actuator 51 that operates based on a command from the rear wheel controller 5, and is disposed in the vicinity of the rear wheel behind the vehicle.

  The vehicle speed sensor 1, the torque sensor 2, the assist controller 3, the steering angle sensor 7, and the rear wheel controller 5 are provided with communication control ports and are connected by a CAN communication line 100. The communication speed of the CAN communication line 100 is configured such that data output from each controller can be transmitted and received every 10 msec.

  In the CAN communication line, sensor signals and the like output from each controller are output at regular intervals or every event occurrence, and only a necessary controller receives necessary information.

  The front wheel controller 4 and the rear wheel controller 5 are provided with a communication control port and are connected by a CAN communication line 200. The communication speed of the CAN communication line 200 is configured so that data output from each controller can be transmitted and received every 1 msec. As described above, the rear wheel controller 5 is provided with two communication control ports and is connected to both the CAN communication line 200 and the CAN communication line 100.

[Power steering system]
The vehicle of the first embodiment is equipped with a power steering system that applies a steady assist torque to the second steering shaft based on the steering torque, steering angular velocity, and vehicle speed of the driver, and also applies a transient assist torque described later. . This power steering system is connected to a low-speed CAN communication line 100 and transmits and receives various signals from the vehicle speed sensor 1, the steering angle sensor 7, the front wheel controller 4 and the rear wheel controller 5.

  The power motor 31 is connected via a worm wheel and a worm wheel fixed to the outer periphery of the second steering shaft connected to the pinion. By driving the power motor 31, assist torque is applied so that the steering torque of the driver becomes a desired value set by calculation.

  The power motor 31 is provided with a rotation angle sensor that detects the rotation angle of the power motor 31 and is output to the assist controller 3. In the assist controller 3, an assist torque calculation unit 301 that calculates a target assist torque calculated based on various sensor values, and a torque control unit that controls a control amount of the power motor 31 based on a detection value of the rotation angle sensor. 302 and a driver unit 303 that outputs a current value to the power motor 31 are provided.

[4-wheel active steering system]
The theory that the vehicle of the first embodiment is optimal to achieve such yaw rate and lateral acceleration as steering feeling and vehicle behavior characteristics when a driver generates a certain steering angle at a certain vehicle speed. Based on this, a four-wheel active steering system is provided in which auxiliary steering angles are 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. It is not possible to obtain the optimal vehicle behavior characteristics according to the steering intention. 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.

(Configuration of front wheel steering unit)
The front wheel actuator 41 is provided on a steering shaft between the steering wheel and the rack and pinion mechanism. The steering shaft is composed of a first steering shaft connected to the steering wheel and a second steering shaft connected to the pinion, and the rotation of the second steering shaft with respect to the rotation angle of the first steering shaft is driven by the front wheel side motor 42. The angle is controlled so that it can be added or subtracted. The front wheel actuator is a well-known technique and will not be described.

  The front wheel side motor 42 is provided with a front wheel side motor rotation angle sensor 43 that detects the rotation angle of the front wheel side motor 42 and is output to the front wheel controller 4. In the front wheel controller 4, a calculation unit 401 that calculates a driving amount of the front wheel side motor 42 with respect to the target steering angle, and a control amount of the front wheel side motor 42 are feedback-controlled based on a detection value of the front wheel side motor rotation angle sensor 43. A servo control unit 402 and a front wheel driver 403 that outputs a current value to the front wheel motor 42 are provided.

(Configuration of rear wheel steering unit)
The rear wheel actuator 51 is provided between the left and right rear wheels 5a. The left and right rear wheels 5a are connected by a parallel link. When one side of this link is moved in the vehicle width direction by the rear wheel side motor 52, a steering angle is generated in the rear wheel 5a due to elastic deformation of the parallel link. Since this rear wheel actuator is a well-known technique, description thereof is omitted.

  The rear wheel side motor 52 is provided with a rear wheel side motor rotation angle sensor 53 that detects the rotation angle of the rear wheel side motor 52 and is output to the rear wheel controller 5. In the rear wheel controller 5, the calculation unit 501 that calculates the drive amount of the rear wheel side motor 52 with respect to the target steering angle, and the control amount of the rear wheel side motor 52 are based on the detection value of the rear wheel side motor rotation angle sensor 53. A servo control unit 502 that performs feedback control, a rear wheel driver 503 that outputs a current value to the rear wheel motor 52, and a target steering for the front and rear wheels based on the steering angle and the vehicle speed detected by the steering angle sensor 7. A target value calculation unit 504 that calculates a corner is provided. The front wheel controller 4 controls the front wheel side motor 42 based on the target steering angle of the front wheels.

(4-wheel active steering control configuration)
The rear wheel controller 5 connected to the CAN communication line 100 receives the steering angle information from the steering angle sensor 7 connected to the CAN communication line 100 and the vehicle speed information from the vehicle speed sensor 1 connected to the CAN communication line 100. Then, the target value calculation unit 504 calculates the target front wheel steering angle and the target rear wheel steering angle based on these two values. The target front wheel steering angle is output from the rear wheel controller 5 to the front wheel controller 4 via the CAN communication line 200.

  The front wheel controller 4 drives the front wheel side motor 42 so that the received target front wheel steering angle is obtained. At this time, the servo control unit 402 and the front wheel side driver 403 calculate the control amount every 1 msec based on the detected value of the front wheel side motor rotation angle sensor 43 and the value of the current sensor, etc. Output. Such processing is executed by multitask processing or the like, and is appropriately assigned according to the processing capability of the CPU.

  The rear wheel controller 5 drives the rear wheel motor 52 so as to achieve the calculated target rear wheel steering angle. At this time, the servo control unit 502 and the rear wheel side driver 503 calculate the control amount every 1 msec based on the detection value of the rear wheel side motor rotation angle sensor 53 and the value of the current sensor, etc. Output to the motor 52.

  Further, the auxiliary steering angles of the front wheels 4a and the rear wheels 5a are controls for directly changing the direction of the tire, in other words, the lateral force mainly of the tire force generated between the tire and the road surface is directly controlled by the actuator. It will be. At this time, if a failure or the like occurs in each actuator, there is a risk of directly affecting the behavior of the vehicle (particularly the turning state), so it is necessary to always perform a fail check. Therefore, the front wheel controller 4 transmits / receives rear wheel-side fail-related information (for example, an actuator signal, etc.) a plurality of times via the CAN communication line 200 until a new target value is calculated by the target value calculation unit 504. Always monitor. Similarly, the rear wheel controller 5 transmits / receives fail related information (for example, an actuator signal) on the front wheel side a plurality of times via the CAN communication line 200 until the target value calculation unit 504 calculates a new target value. Always monitor while.

  FIG. 2 is a vehicle model representing the vehicle system. When the driver inputs the steering torque, the steering wheel performs a rotational motion. The steering angle generated by the rotational motion is input to the target value calculation unit 504, and the target front and rear wheel steering angles are calculated based on the steering angle, the vehicle speed, and the like. Based on the target front and rear wheel steering angles, the front wheel steering unit (401, 402, 403) and the rear wheel steering unit (501, 502, 503) output drive commands to the front wheel side motor 42 and the rear wheel side motor 52. .

  A torque value obtained by adding the steering torque of the driver and the motor torque of the front wheel side motor 42 is input to the assist torque calculating unit 301, and the total torque obtained by adding the assist torque calculated by the assist torque calculating unit 301 is the rack. & Is transmitted to the pinion mechanism. This total torque undergoes thrust conversion by moving the rack shaft in the axial direction from the rotational torque by the rack and pinion mechanism (k in FIG. 2 indicates a thrust conversion coefficient), and the front wheels are steered by the translational motion of the rack shaft. As a result, the actual steering angle of the front wheels is generated. When the front wheel actual rudder angle is generated, a steering reaction torque that changes in accordance with the slip angle is applied from the road surface. This steering reaction torque will be described later.

  FIG. 3 is a control block diagram showing the configuration of the assist torque calculation unit 301. The assist torque calculation unit 301 includes a steady assist torque control unit 311 that calculates a steady assist torque based on the steering torque, the vehicle speed, the steering angular velocity, and the like detected by the torque sensor 2, and a torque − that will be described later according to the traveling state of the vehicle. The transition assist torque control unit 312 controls the assist torque based on the steering torque and the steering reaction torque so that the steering angle characteristic becomes the target characteristic.

  FIG. 4 is a control block diagram showing the configuration of the transient assist torque control unit 312. In the transient assist torque control unit 312, an ideal steering angle estimation value calculation unit 312 a that calculates an ideal steering angle estimation value and a virtual auxiliary steering angle estimation value that estimates a virtual auxiliary steering angle based on the ideal steering angle estimation value The calculation unit 312b, the steering reaction force torque estimation value calculation unit 312c that calculates the steering reaction torque estimation value Trk (s) based on the two-wheel model, and the actual characteristics of the steering angle with respect to the steering torque are calculated based on the two-wheel model An actual characteristic calculation unit 312d that performs a target characteristic calculation unit 312e that calculates a target characteristic of a steering angle with respect to a steering torque based on a two-wheel model, and a failure time control unit 312f that changes a vehicle model when a failure occurs (claims) It corresponds to the ideal steering angle estimated value changing means described in the range).

Hereinafter, the transient assist torque calculation is shown in the following formula (1).
(Formula 1)
Tassist (s) = Tdr (s) ・ [{Ref (s) / (k × Strg (s))} − 1] + Trk (s)
Tassist (s): Transient assist torque
Tdr (s): Steering torque of driver with steady assist
Trk (s): Steering reaction torque
Ref (s): Target transfer function from steering torque to steering angle
Strg (s): Transfer function of steering angle from rack shaft thrust
k: Conversion coefficient from torque to rack axial force.

  Driver input torque Tdr (s) can be detected by using the torque sensor 2 of the power steering system, and k × Strg (s) can be calculated based on various factors such as inertia and mass damping of each part of the steering system. It is.

FIG. 5 is a diagram showing a correspondence relationship in which the period from the position where the steady assist torque is applied until the actual front wheel turning angle is generated is replaced with the target front wheel steering angle characteristic Ref (s). Here, when the target front wheel rudder angle characteristic Ref (s) is defined by a general (0-order / second-order) transfer function in the control system, it is expressed by the following equation (2).
(Formula 2)
Ref (s) = (Gain × ω _n ² ) / (s ² + 2ζω _n s + ω _n ² )
ζ: target damping coefficient ω _n : target natural frequency
Gain: Steering torque minus actual characteristic steady gain of front wheel actual steering angle.

ζ · ωn can be set to an arbitrarily suitable value depending on the vehicle, and Gain is expressed by the following equation (3) in the actual characteristic calculation unit 312d based on the vehicle model.
(Formula 3)
Gain [rad / Nm] ＝ k [1 / m] / (Gain _{_betaf_4WAS}・ Gain _{_Frk} )
Gain _{_betaf_4WAS} : Front wheel slip angle gain per unit steering angle
Gain _{_Frk} : Rack reaction force gain per unit front wheel slip angle [N / rad]
It is.

_{Gain_Frk} is not dependent on the vehicle speed and is determined by vehicle specifications and is expressed by the following equation (4).
(Formula 4)
Gain _{_Frk} = ((CP1 [N / rad] x CT [m]) / (NAL [m] x NAL efficiency)) x 2 (for 2 wheels) x SAT coefficient
CP1: Cornering power for one front wheel
CT: Caster rail
NAL: Knuckle arm length
NAL efficiency: knuckle arm link efficiency
SAT coefficient: Self-aligning torque coefficient.

_{Gain_betaf_4WAS} is expressed by the following equation (5).
(Formula 5)
Gain _{_betaf_4WAS} = {(Ratio _{_AFS} ) / N} −A
A = (Lf / Vx) ・ (Ratio _{_AFS} × Gain _{_yaw_front} + Ratio _{_RAS} × Gain _{_yaw_rear} )
+ (1 / Vx) ・ (Ratio _{_AFS} × Gain _{_Vy_front} + Ratio _{_RAS} × Gain _{_Vy_rear} )
Gain _{_yaw_front} : Unit steering angle yaw rate gain
Gain _{_yaw_rear} : Unit rear wheel rudder angle yaw rate gain
Gain _{_Vy_front} : Unit steering angle lateral speed gain
Gain _{_Vy_rear} : Unit rear wheel rudder angle lateral speed gain
Ratio _{_AFS} : Front wheel steering angle per unit steering angle
Ratio _{_RAS} : Rear wheel rudder angle per unit steering angle
Lf: Distance between vehicle center of gravity and front axle
Vx: Vehicle speed.

Ratio _{_AFS} and Ratio _{_RAS} is a value determined by the four-wheel active steering control for each vehicle speed, shown in the map representing map, and Ratio _{_RAS} and speed relationship of FIG. 7 showing the relationship Ratio _{_AFS} and the vehicle speed in FIG. 6 As described above, a map corresponding to the vehicle speed may be stored in advance, or each Ratio may be obtained from the rear wheel controller 5 through communication, and is not particularly limited. Further, the yaw rate gain and the lateral speed gain with respect to the front and rear wheel steering angles are characteristics determined using a two-wheel model based on vehicle behavior characteristics and vehicle speed. Therefore, since the gain in equation (3) is configured by a constant or a vehicle speed dependency equation, the gain itself is shown in the actual characteristic calculation unit 312d as a vehicle speed dependency map as shown in the map showing the relationship between the gain and the vehicle speed shown in FIG. You may keep it.

  As described above, the target front wheel steering angle characteristic Ref (s) represents an ideal steering angle with respect to the input steering torque. Therefore, the ideal steering angle estimated value calculation unit 312a calculates the ideal steering angle based on the target front wheel steering angle characteristic Ref (s) based on the input steering torque.

  The virtual auxiliary rudder angle estimated value calculation unit 312b calculates a virtual auxiliary rudder angle estimated value based on the ideal steering angle using the control logic of the above-described four-wheel active steering system.

  The steering reaction force torque estimated value calculation unit 312c uses a front and rear wheel auxiliary steering angle calculated by the virtual auxiliary steering angle estimated value calculation unit 312b in a two-wheel model that considers performing four-wheel active steering control. The front wheel slip angle is estimated, and the steering reaction force torque estimated value Trk (s) is calculated because the front wheel slip angle and the steering reaction torque are in a substantially proportional relationship.

  Based on the gain obtained by the actual characteristic calculation unit 312d, the target characteristic calculation unit 312e can calculate the equation (1) to obtain the necessary transient assist torque. A torque obtained by adding a normal steady torque to the obtained transient assist torque is a torque to be compensated by the power steering system.

  When the failure control unit 312f receives a fail signal from the four-wheel active steering system, it outputs Ratio_AFS, Ratio_RAS for failure to the steering reaction force torque estimated value calculation unit 312c.

(Logical configuration)
That is, the transient assist torque control unit 312 is set based on the following logical configuration.
(Step 1) When the steering torque of the driver is detected, transient assist torque control is performed so that an ideal steering angle corresponding to the steering torque is obtained. Therefore, it can be assumed that the actual steering angle obtained as a result is an ideal steering angle (or a value close thereto).
(Step 2) Next, when the actual steering angle becomes the ideal steering angle, how much auxiliary steering angle is given by referring to the four-wheel active steering control logic (virtual auxiliary steering angle estimation value) I understand.
(Step 3) By using this virtual auxiliary rudder angle estimated value, it is possible to calculate the slip angle and the steering reaction torque that will occur in the vehicle.

  In other words, in each of the above steps, the transient assist torque control unit 312 estimates all phenomena occurring in the vehicle based only on the steering torque, and determines the assist torque according to the estimated vehicle state. A closed loop system related to the vehicle state (for example, a system that feeds back and refers to a steering angle sensor, various actuator driving amounts, etc.) is not configured. Therefore, even if there is a deviation in the vehicle model, since the control target is controlled using the steering torque as the torque, a stable steering torque-steering angle characteristic can be obtained without affecting the steering angle. I understand.

  Here, the transient assist torque control will be described. FIG. 9 is a diagram illustrating the characteristics of the first comparative example. In Comparative Example 1, a vehicle equipped with a power steering system that applies assist torque based on the driver's steering torque and vehicle speed was used. FIG. 9 shows the gain characteristic of the steering angle / steering torque with respect to the steering torque frequency of the vehicle in the first comparative example. As shown in FIG. 9, in the specific region of the steering torque frequency, the steering angle increases rapidly with respect to the steering torque as the vehicle speed increases. Improving the damping of the vehicle behavior with respect to the steering torque input is equivalent to improving the damping of the steering angle with respect to the steering torque input. This is because the vehicle behavior is generated from the steering angle (the equation of motion of the vehicle two-wheel model), and the steering torque is determined from the vehicle behavior (the equation of motion of the steering system).

  When the driver applies steering torque, the steering angle is determined by a balance relationship between the steering torque, the steering reaction torque acting on the steered wheel from the road surface, the friction acting on the steering system, and the like. At this time, if the slip angle characteristic acting on the steered wheels changes as the vehicle speed increases, the slip angle characteristic correlates with the steering reaction force torque acting from the road surface, and the steering reaction force torque is reduced. Therefore, there is a risk of causing an overshoot of the steering angle.

  Therefore, the road surface reaction force is estimated using a vehicle model, and the assist torque is controlled so that the ideal steering torque-steering angle correlation can be obtained based on this value. It was decided to get the vehicle behavior.

  Since the transient assist torque control estimates the road surface reaction force from the vehicle model as described above, the front wheel actual steering angle and the rear wheel are not used in a vehicle equipped with a four-wheel active steer system in which the vehicle model changes depending on the driving situation. It is necessary to consider the rudder angle. Therefore, the vehicle system is considered by considering these actual front wheel turning angle and rear wheel steering angle (ideal steering angle estimated value calculation unit 312a, virtual auxiliary steering angle estimated value calculation unit 312b, etc.) and reflecting them in the transient assist torque control. The transient assist torque control according to is achieved.

  In addition, when this vehicle model is not taken into account, the slip angle cannot be estimated accurately, and accordingly, the road surface reaction force estimation becomes insufficient. In other words, even if the transient assist torque control that is simply applied to a conventional vehicle is applied to a vehicle equipped with a four-wheel active steering system, it means that proper control cannot be performed.

  FIG. 11 is a time chart showing simulation results of the vehicle behavior characteristics of the vehicle having the four-wheel active steering system of Example 1 and the transient assist torque control and the vehicle behavior characteristics without the transient assist torque control at the high vehicle speed. is there. The frequency response of the steering angle with respect to the steering torque at that time becomes the solid line characteristic of FIG. 10, and it can be seen that damping is improved. As the steering torque, a certain constant torque is step-inputted, and the vehicle behavior with respect to the input of the steering torque is shown.

  As shown in FIG. 11, when the steering torque is step-inputted, in a vehicle without transient assist torque control, the assist torque is slightly applied, and the reaction torque from the road surface is small. Steering angle overshoots. In this four-wheel active steering system that sets the target front and rear wheel steering angles according to the steering angle, subtraction control is performed according to the steering angle on the front wheel side, and in-phase control is performed according to the steering angle on the rear wheel side. Is done. At this time, overshoot occurs in the yaw rate and lateral acceleration, and it cannot be said that the stability of the vehicle is sufficient.

  On the other hand, in a vehicle equipped with transient assist torque control, it is known by calculation that the reaction torque from the road surface is small when step input of steering torque is given, and reverse assist torque is applied. That is, it is applied not to the side that assists the driver's steering torque but to the side that provides resistance. Thereby, it can be seen that the overshoot of the steering angle is suppressed and the desired yaw rate and lateral acceleration are obtained.

  The present invention aims to realize an ideal form of vehicle behavior with respect to steering torque input. In other words, in consideration of the human-automobile system, it is said that the driver mainly controls the vehicle motion by inputting the steering torque during high-speed driving, and the gain of the vehicle behavior (lateral acceleration and yaw rate) with respect to the steering torque. By keeping the force constant regardless of the frequency, the vehicle should be easy to handle for humans.

  Therefore, looking at the vehicle behavior with respect to the actual steering torque, the frequency characteristic of the vehicle behavior with respect to the steering torque input of the vehicle has a problem that the damping at a predetermined frequency deteriorates at a high speed as shown in FIG.

  Therefore, in the first embodiment, when a transient steering torque is detected, for example, when the lane change is performed and the steering torque is changed, in the turning process (steering torque is increased), the direction of change of the steering torque is substantially opposite. When the assist torque is generated, the steering torque increases, and even in the returning process (the steering torque decreases), the assist torque is generated substantially in the opposite direction of the change direction of the steering torque so that the steering torque decreases. Therefore, even if the same vehicle behavior occurs, the change in the steering torque increases, and the gain of the vehicle behavior with respect to the steering torque is reduced. As a result, the damping shown in FIG. 10 is improved, and a good steering feeling can be obtained without causing the driver to feel uncomfortable.

  Further, when the input frequency of the steering torque is increased, the output of the reverse assist torque is increased, so that the amount of assist in the reverse direction is increased with respect to quick steering such as lane change during high speed traveling, and the steering wheel becomes heavy. Therefore, the driver's sudden steering can be prevented, and the vehicle behavior with respect to the vehicle steering amount, that is, the steering characteristic can be made understeer, so that the running stability of the vehicle can be improved.

  With such a configuration, damping of the steering angle and vehicle behavior with respect to the steering torque input is improved, and an increase in gain can be prevented regardless of the frequency.

(Transient assist torque control when the four-wheel active steering system fails)
Next, processing in the case where the four-wheel active steering system fails in the above control configuration and this system is stopped will be described based on the flowchart of FIG.
In step 101, steering torque and vehicle speed information are read.

[4-wheel active steering system abnormality detection processing]
In step 102, it is determined whether or not an abnormality is detected in the four-wheel active steering system. If an abnormality is detected, the process proceeds to step 107. Otherwise, the process proceeds to step 103. In the case of an abnormality in the four-wheel active steering system, a fail signal is supplied to the failure control unit 312f from a fail check process or the like performed in the front wheel controller 4 and / or the rear wheel controller 5. As specific fail check processing, for example, temperature rise monitoring processing of the front wheel side motor 42 and rear wheel side motor 52, current value monitoring processing, and monitoring processing of various sensors are performed. As a result of each of these monitoring processes, when it is determined that a failure has occurred in the four-wheel active steering system, a fail signal is supplied to the power steering system, and after a predetermined active steering stop process is executed, The steering system is stopped. At this time, if a failure occurs in a state where auxiliary steering angles are given to the front and rear wheels, the system is shut off after returning to neutral. However, in the case of an emergency stop, it may stop at a position deviated from neutral (with an offset angle), and is not particularly limited.

[4-wheel active steering system normal processing]
In step 103, the actual characteristic of the actual front wheel steering angle with respect to the steering torque is calculated from the vehicle speed information. At this time, a gain corresponding to vehicle speed information is set from the map representing the relationship between _{Ratio_AFS} and vehicle speed in FIG. 6 and the map representing the relationship between _{Ratio_RAS} and vehicle speed in FIG.
In step 104, a target torque characteristic is calculated based on the vehicle speed information and the steering torque information.
In step 105, an ideal steering angle is calculated based on the steering torque information.
In step 106, a virtual front and rear wheel steering angle is calculated from the ideal steering angle.

[Treatment for failure of 4-wheel active steering system]
In step 107, the actual characteristic of the front wheel actual steering angle with respect to the steering torque is calculated from the vehicle speed information. At this time, Ratio_AFS = 1 and Ratio_RAS = 0 are output from the failure time control unit 312f to the steering reaction force torque estimated value calculation unit 312c.
In step 108, a target torque characteristic is calculated based on the vehicle speed information and the steering torque information.
In step 109, an ideal steering angle is calculated based on the steering torque information.
In step 110, a virtual front and rear wheel steering angle is calculated from the ideal steering angle.

[Steering reaction force torque estimated value calculation processing]
In step 111, a steering reaction torque estimation value is calculated from the target front and rear wheel steering angles.

[Transient assist torque calculation processing]
In step 112, the estimated steering reaction force torque and the target torque characteristic are added to calculate a transient assist torque.

(Operation of transient assist torque control when a 4-wheel active steering system fails)
Next, the operation based on the flowchart will be described. FIG. 13 shows vehicle characteristics of a vehicle equipped with the four-wheel active steering system and the transient assist torque control according to the first embodiment at a high vehicle speed, and when the four-wheel active steering system is normal in a state where the four-wheel active steering system has failed. It is a time chart showing the simulation result with the vehicle behavior characteristic which performed the same transient assist torque control.

  As shown in FIG. 13, when the steering torque is step-inputted, as described with reference to FIG. 12, it is found by calculation that the reaction torque from the road surface is small when the steering torque step input is given in the normal state. The reverse assist torque is applied. That is, it is applied not to the side that assists the driver's steering torque but to the side that provides resistance. Thereby, it can be seen that the overshoot of the steering angle is suppressed and the desired yaw rate and lateral acceleration are obtained. At this time, in the four-wheel active steering control, subtraction control is performed according to the steering angle of the driver, and in-phase control is performed according to the steering angle on the rear wheel side. Therefore, since the subtraction control is performed such that the steering angle is smaller than the steering angle, the actual steering angle is smaller than the steering angle (solid line) in FIG.

  On the other hand, in a vehicle without four-wheel active steering control (at the time of failure), since the driver's steering angle and the turning angle have a one-to-one relationship, the vehicle behavior characteristics with respect to the vehicle steering angle change. However, the turning angle is larger than that during subtraction control. At this time, since the transient assist torque is calculated on the transient assist torque control side on the assumption of a small turning angle, it is estimated that the reaction force torque from the road surface is small. Actually, the steering angle has a one-to-one correspondence with the steering angle. As a result, the steering angle overshoots. Due to this overshoot, overshoot occurs in the yaw rate and lateral acceleration, and the stability of the vehicle cannot be said to be sufficient.

  FIG. 14 shows vehicle characteristics of the vehicle equipped with the four-wheel active steering system and the transient assist torque control according to the first embodiment at the time of high vehicle speed, and when the four-wheel active steering system fails when the four-wheel active steering system fails. It is a time chart showing the simulation result with the vehicle behavior characteristic which performed transient assist torque control for the purpose.

  As shown by the dotted line in FIG. 14, when the steering torque is step-inputted, in a vehicle without four-wheel active steering control (at the time of failure), there is a one-to-one relationship between the driver's steering angle and the turning angle. Therefore, the turning angle is larger than that during subtraction control. At this time, the transient assist torque control side assumes that the steering angle and the steering angle have a one-to-one correspondence (that is, the vehicle behavior characteristic with respect to the steering angle of the vehicle has changed). (Ratio_AFS = 1, Ratio_RAS = 0), the reaction torque from the road surface can be estimated appropriately. Therefore, since the ideal steering angle that provides the desired vehicle behavior characteristics is known, the assist torque in the reverse direction is output to a larger value so that the ideal steering angle is obtained. As a result, the steering angle becomes small, and it can be seen that the vehicle behavior characteristic close to that when the four-wheel active steering control is normal is obtained.

  Although the case where the steering torque is step-inputted at the high vehicle speed has been described, for example, the same effect can be obtained even at the low vehicle speed. Specifically, addition control is performed on the steering angle when the four-wheel active steering system is normal. Therefore, when the four-wheel active steering system fails and the vehicle speed is low, the assist torque may be increased so that the steering angle with respect to the steering torque of the driver is increased.

  As a result, even when the four-wheel active steering system fails, it is possible to obtain vehicle behavior characteristics that approach normal times. However, simply controlling the steering angle on the front wheel side does not provide the characteristics obtained by, for example, rear wheel steering angle control. Even if the assist torque control is performed, the vehicle behavior characteristics can only be brought close to each other, and the same behavior is not achieved.

  Further, even when an offset angle exists when the four-wheel active steering system fails, in the first embodiment, the steering angle is not used for control, and thus there is no particular influence on the transient assist torque control.

  As described above, in the vehicle steering control apparatus according to the first embodiment, the following effects can be obtained.

  (1) As the ideal steering angle changing means that changes the ideal steering angle based on the actual characteristics of the vehicle, the controller at the time of failure 312f is provided, and the ideal steering of the transient assist torque control unit 312 at the time of failure of the 4-wheel active steering system It was decided to change the corner. Therefore, even if the vehicle behavior characteristic with respect to the steering angle of the vehicle changes, the vehicle behavior can be stabilized without causing the driver to feel uncomfortable.

  (2) When an abnormality (failure) of the four-wheel active steering system is detected, the four-wheel active steering system is stopped, and the ideal steering angle estimated value calculation unit 312a performs vehicle characteristics achieved by the four-wheel active steering system. The ideal steering angle was changed to approach Specifically, Ratio_AFS = 1 was set, and Ratio_RAS = 0 was set. Therefore, even when the four-wheel active steering system fails, the vehicle behavior characteristics can be controlled so that the transient assist torque control approaches the normal time.

  Next, Example 2 will be described. Since the basic configuration is the same as that of the first embodiment, only different points will be described. FIG. 15 is a control block diagram illustrating the configuration of the transient assist torque control unit according to the second embodiment. In the first embodiment, the ideal steering angle is calculated from the steering torque, and the virtual steering angle estimated value is calculated from the ideal steering angle using the 4WAS control logic. Instead, the actual steering angle of the front wheels is used in the second embodiment. The point is different.

  The failure time control unit 312f is provided with a storage unit that stores the front wheel actual steering angle and the steering angle sensor value when the four-wheel active steering system fails. When the fail signal is received, an offset value is calculated from the value stored in the storage unit, and Ratio_AFS = 1, Ratio_RAS = 0 and the offset value are output to the steering reaction force torque estimated value calculation unit 312a.

  As described in the first embodiment, in the present application, the expression (2) in which the period from the position where the steady assist torque is applied until the actual front wheel turning angle is generated is replaced with the target front wheel steering angle characteristic Ref (s). The transient assist torque Tassist (s) is calculated by equation (1) including: At this time, based on the Gain obtained by the actual characteristic calculation unit 312d, the target characteristic calculation unit 312e performs the calculation of Equation (1), so changing the Ratio_AFS and Ratio_RAS means changing the Gain. This change in Gain represents that the target characteristic is changed in the target characteristic calculation unit 312e. As described above, when the vehicle behavior characteristic with respect to the steering angle of the vehicle changes, the target characteristic is changed according to the change, thereby stabilizing the vehicle.

  Further, in the transient assist torque control of the second embodiment, since the front wheel actual steering angle is fed back, if the front wheel actual steering angle has an offset angle when the four-wheel active steering system fails, an incorrect front wheel actual steering angle is obtained. Since transient assist torque control is performed based on the information, appropriate characteristics cannot be obtained.

  Therefore, the offset value is calculated by storing the front wheel actual steering angle and the steering angle sensor value when the system fails. Therefore, the offset of the front wheels can be corrected by adding or subtracting the calculated offset value to the value of the steering angle sensor, and the transient assist control can be performed appropriately.

  As described above, in the vehicle steering control device according to the second embodiment, the following effects can be obtained.

  (3) As a target characteristic changing means for changing the target characteristic based on the vehicle behavior characteristic with respect to the steering angle of the vehicle, a failure time control unit 312f is provided, and when the four-wheel active steering system fails, the transient assist torque control unit 312 The characteristic of the target characteristic calculation unit 312e is changed. Therefore, even if the vehicle behavior characteristic with respect to the steering angle of the vehicle changes, the vehicle behavior can be stabilized without causing the driver to feel uncomfortable.

  (4) When an abnormality (failure) of the four-wheel active steering system is detected, the four-wheel active steering system is stopped, and the target characteristic calculation unit 312e approaches the vehicle characteristics achieved by the four-wheel active steering system. It was decided to change the target characteristics. Specifically, Ratio_AFS = 1 was set, and Ratio_RAS = 0 was set. Therefore, even when the four-wheel active steering system fails, the vehicle behavior characteristics can be controlled so that the transient assist torque control approaches the normal time.

  As described above, in the vehicle steering control device described in the first and second embodiments, even if the four-wheel active steering system fails, the vehicle is controlled by performing the transient assist torque control by the power steering mechanism. It is possible to control the behavior characteristics so that they are close to normal, and the stability of the vehicle can be improved without causing the driver to feel uncomfortable. In Examples 1 and 2, the four-wheel active steering system has been described. However, a front active steering system that provides an auxiliary steering angle only on the front wheel side and a rear active steering system that provides an auxiliary steering angle only on the rear wheel side are installed. It can be applied to the same vehicle.

1 is a system configuration diagram illustrating a vehicle control system according to a first embodiment. 1 is a vehicle model representing a vehicle system according to a first embodiment. FIG. 3 is a control block diagram illustrating a configuration of an assist torque calculation unit according to the first embodiment. FIG. 3 is a control block diagram illustrating a configuration of a transient assist torque control unit according to the first embodiment. It is a figure showing the correspondence which replaced the assist torque calculation part of Example 1 with the target front wheel steering angle characteristic. 6 is a map showing the relationship between _{Ratio_AFS} and vehicle speed in the first embodiment. 6 is a map showing the relationship between _{Ratio_RAS} and vehicle speed in Example 1; 2 is a map showing the relationship between Gain and vehicle speed in Example 1; It is a figure showing the gain characteristic of the steering angle / steering torque with respect to the steering torque frequency of the vehicle in a comparative example. FIG. 6 is a characteristic diagram illustrating a frequency response of a steering angle with respect to a steering torque of Example 1 and a frequency response of a steering angle with respect to a steering torque of a conventional example. 6 is a time chart showing simulation results of vehicle behavior characteristics at high vehicle speed and vehicle characteristics without transient assist torque control in Example 1. It is a flowchart showing the process when the four-wheel active steering system of Example 1 fails and this system is stopped. The vehicle behavior characteristics of the vehicle having the four-wheel active steering system and the transient assist torque control according to the first embodiment, and the same transient assist torque control as in the normal operation of the four-wheel active steering system in a state where the four-wheel active steering system has failed. 6 is a time chart showing a simulation result with the vehicle behavior characteristics. Vehicle behavior characteristics of a vehicle equipped with the four-wheel active steering system and the transient assist torque control according to the first embodiment, and the transient assist torque control for failure of the four-wheel active steering system in a state where the four-wheel active steering system has failed. It is a time chart showing the simulation result with the vehicle behavior characteristic performed. FIG. 5 is a control block diagram illustrating a configuration of a transient assist torque control unit according to a second embodiment.

Explanation of symbols

1 Vehicle speed sensor 2 Torque sensor 3 Assist controller 4 Front wheel controller 5 Rear wheel controller 7 Steering angle sensor 30 Power steering unit 31 Power motor 40 Front wheel steering unit 50 Rear wheel steering unit

Claims (8)

In a vehicle steering control device including power steering means for applying assist torque based on a steering torque of a driver,
An ideal steering angle estimated value calculating means for calculating an ideal steering angle according to the steering torque;
A target characteristic setting means for setting a target characteristic in which the characteristic of the vehicle behavior or the steering angle with respect to the driver's steering torque becomes smaller as the frequency of the steering torque becomes higher;
Based on the steering torque and the ideal steering angle, transient assist torque control means for controlling the assist torque so that a vehicle behavior or a characteristic of the steering angle with respect to the steering torque becomes the target characteristic;
Ideal steering angle changing means for changing the ideal steering angle based on vehicle behavior characteristics with respect to the steering angle of the vehicle;
A vehicle steering control device comprising: The vehicle steering control device according to claim 1,
A front wheel auxiliary rudder angle giving means for giving an auxiliary rudder angle to the front wheel and achieving a desired vehicle behavior characteristic;
An abnormality detecting means for detecting an abnormality of the auxiliary rudder angle providing means;
When an abnormality is detected by the abnormality detecting means, a stopping means for stopping the front wheel auxiliary steering angle providing means,
Provided,
The ideal steering angle changing means changes the ideal steering angle so as to approach the vehicle behavior characteristic achieved by the front wheel auxiliary steering angle providing means when an abnormality of the front wheel auxiliary steering angle providing means is detected. A vehicle steering control device. The vehicle steering control device according to claim 1 or 2,
A rear wheel auxiliary rudder angle providing means for providing an auxiliary rudder angle to the rear wheel to achieve a desired vehicle behavior characteristic;
An abnormality detecting means for detecting an abnormality of the auxiliary rudder angle providing means;
When an abnormality is detected by the abnormality detecting means, a stopping means for stopping the auxiliary steering angle providing means,
Provided,
The ideal steering angle changing means changes the ideal steering angle so as to approach the vehicle behavior characteristic achieved by the rear wheel auxiliary steering angle applying means when an abnormality of the rear wheel auxiliary steering angle applying means is detected. A vehicle steering control device. In a vehicle steering control device including a power steering mechanism that applies assist torque based on a steering torque of a driver,
A target characteristic setting means for setting a target characteristic in which the characteristic of the vehicle behavior or the steering angle with respect to the steering torque decreases as the frequency of the steering torque increases;
A transient assist control means for controlling the assist torque so that a vehicle behavior or a steering angle characteristic with respect to the steering torque becomes the target characteristic;
Target characteristic changing means for changing the target characteristic based on a vehicle behavior characteristic with respect to a steering angle of the vehicle;
A vehicle steering control device comprising: The vehicle steering control device according to claim 4,
A front wheel auxiliary rudder angle giving means for giving an auxiliary rudder angle to the front wheel and achieving a desired vehicle behavior characteristic;
An abnormality detecting means for detecting an abnormality of the auxiliary rudder angle providing means;
When an abnormality is detected by the abnormality detecting means, a stopping means for stopping the front wheel auxiliary steering angle providing means,
Provided,
The target characteristic changing means changes the target characteristic so as to approach the vehicle behavior characteristic achieved by the front wheel auxiliary rudder angle giving means when an abnormality of the front wheel auxiliary rudder angle giving means is detected. A vehicle steering control device. In the vehicle steering control device according to claim 4 or 5,
A rear wheel auxiliary rudder angle providing means for providing an auxiliary rudder angle to the rear wheel to achieve a desired vehicle behavior characteristic;
An abnormality detecting means for detecting an abnormality of the auxiliary rudder angle providing means;
When an abnormality is detected by the abnormality detecting means, a stopping means for stopping the auxiliary steering angle providing means,
Provided,
The target characteristic changing means changes the target characteristic so as to approach the vehicle behavior characteristic achieved by the rear wheel auxiliary rudder angle providing means when an abnormality of the rear wheel auxiliary rudder angle giving means is detected. A vehicle steering control device. In a vehicle steering control method including power steering means for applying an assist torque based on a driver's steering torque,
An ideal steering angle corresponding to the steering torque is calculated, a target characteristic is set such that the vehicle behavior or the steering angle characteristic with respect to the driver's steering torque becomes smaller as the steering torque frequency increases, and the steering torque and the ideal steering angle are set. Based on the above, transient assist torque control for controlling the assist torque is performed so that the vehicle behavior or the steering angle characteristic with respect to the steering torque becomes the target characteristic, and the ideal steering is performed based on the vehicle behavior characteristic with respect to the vehicle steering angle. A vehicle steering control method characterized by changing a corner. In a vehicle steering control device including a power steering mechanism that applies assist torque based on a steering torque of a driver,
The assist torque is set such that the vehicle behavior or the steering angle characteristic with respect to the steering torque becomes smaller as the steering torque frequency becomes higher, and the vehicle behavior or the steering angle characteristic with respect to the steering torque becomes the target characteristic. A vehicle steering control method, wherein transient assist control for controlling the vehicle is performed, and the target characteristic is changed based on a vehicle behavior characteristic with respect to a steering angle of the vehicle.

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