JP4687233B2 - Vehicle steering control device and vehicle steering control method - Google Patents

Description

  The present invention relates to vehicle steering control, and more particularly to control of a power steering mechanism that assists and controls steering torque of a driver.

Conventionally, as a technique for assisting a driver's steering torque, for example, a technique described in Patent Document 1 is disclosed. In this publication, when the electric assist amount is calculated by the electric motor of the electric power steering mechanism, the assist amount is determined according to the vehicle speed and the steering speed.
JP 2001-114121 A

  However, as a result of earnest research, the Applicant has, in a vehicle equipped with the technology of Patent Document 1, for example, at high vehicle speed, the driver is mainly driving with steering torque input, and the frequency characteristics of vehicle behavior with respect to steering torque input. We focused on the fact that the better the dumping, the easier it is for the driver to handle. Based on this technical idea, as a result of verifying characteristics when a high-frequency steering torque is input at high vehicle speeds, an area where the damping characteristics of the steering torque and the steering angle deteriorate is found. 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. At this time, it has been found that the steering torque and the steering angle recognized by the driver may have different characteristics depending on the frequency of the steering torque and the vehicle characteristics. This phenomenon may cause an overshoot of the steering angle.

  The present invention has been made paying attention to the above problems, and the object of the present invention is to stabilize the vehicle behavior by optimally assisting the driver's steering torque in accordance with the driving situation. Another object of the present invention is to provide a vehicle steering control device.

To achieve the above object, in vehicular steering control apparatus of the present invention, in the vehicle steering control apparatus provided with a power steering device for applying an assist torque based on steering torque of the driver, the steering angle for steering the steering torque gain characteristic, so that the frequency of the steering torque becomes higher the higher reduced, characterized by comprising a transient assist torque control means to control said assist torque.

  Therefore, since assist torque is applied so that the steering angle characteristic with respect to the steering torque is a favorable characteristic for the driver, it is possible to avoid an overshoot of the steering angle, and to stabilize the vehicle behavior. it can.

  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 the 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 driver's steering torque, steering angular speed, and vehicle speed, 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]
In the vehicle of the first embodiment, when a driver generates a certain steering angle at a certain vehicle speed, it is optimal to achieve such a yaw rate and lateral acceleration as steering feeling and vehicle characteristics. Based on this, a four-wheel active steering system in which auxiliary steering angles are given to the front and rear wheels is mounted. 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.

(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 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 the drive amount of the front wheel side motor 42 with respect to the target steering angle, and a servo that performs feedback control of the control amount of the front wheel side motor 42 based on the detection value of the front wheel side rotation angle sensor 43. A control unit 402 and a front wheel side driver unit 403 that outputs a current value to the front wheel side 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 51, 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 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, a calculation unit 501 that calculates the driving 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 rotation angle sensor 53. A servo control unit 502 that performs feedback control, a rear wheel driver unit 503 that outputs a current value to the rear wheel motor 52, and a target rudder for front and rear wheels based on the steering angle and 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. In addition, when the front wheel actual rudder angle is generated, a 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 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. The transient assist torque control unit 312 includes a reaction torque estimation unit 312a that calculates a steering reaction torque estimation value Trk (s) based on the two-wheel model, and an actual characteristic of the steering angle with respect to the steering torque based on the two-wheel model. An actual characteristic calculation unit 312b for calculating the steering angle and a target characteristic calculation unit 312c for calculating the target characteristic of the steering angle with respect to the steering torque based on the two-wheel model.

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.

  Steering reaction torque estimation unit 312a uses a two-wheel model that considers four-wheel active steering control, estimates the front wheel slip angle by feeding back the steering angle information of the front and rear wheels, and is approximately proportional to the front wheel slip angle Trk (s) can be determined by calculating the steering reaction torque acting on the front wheels.

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

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 arbitrarily set depending on the vehicle, and Gain is represented by the following equation (3) in the actual characteristic calculation unit 312b 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 has no dependence 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 Thus, it may be stored in advance as a map corresponding to the vehicle speed, or each Ratio may be obtained from the rear wheel controller 5 by 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 characteristics and vehicle speed. Therefore, since the gain of equation (3) is configured by a constant or a vehicle speed dependency equation, the gain itself is shown in the actual characteristic calculation unit 312b 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.

  Based on the gain obtained by the actual characteristic calculation unit 312b, the target characteristic calculation unit 312c 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.

[Discussion on the subject of this application]
Here, the phenomenon which the invention of this application makes a subject is demonstrated. FIG. 9 is a diagram illustrating characteristics of the comparative example. In this comparative example, a vehicle equipped with a power steering system that applies assist torque based on the steering torque and vehicle speed of the driver 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 this 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 the steering torque, the steering angle is determined by the balance between the steering torque, the reaction force 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 has a correlation with the reaction force torque acting from the road surface, leading to a decrease in the reaction force torque. 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.

  Here, the vehicle described in the first embodiment is equipped with a four-wheel active steering system, and the front wheel actual steering angle can be physically changed regardless of the steering angle of the driver. Consider using a unit to avoid the overshoot. FIG. 10 shows the front wheel by the four-wheel active steering control when the front wheel actual steering angle by the normal four-wheel active steering control and the control gain of the front wheel actuator 41 are adjusted and the correction to suppress the occurrence of the overshoot is performed. It is a time chart showing the change of an actual turning angle. As shown in FIG. 10, when the above correction is performed, even if a steering angle overshoot occurs, the response gain of the actuator or the like is corrected to be low, so that the overshoot can be suppressed.

  However, as shown in FIG. 11, when normal steering is performed with this correction being performed, the control gain is delayed with respect to the change in the steering angle, and the target actual front wheel turning angle is obtained. I can't. As described above, in the four-wheel active steering system, the optimum yaw rate and lateral acceleration are controlled in accordance with the steering angle of the driver, and this response delay is unacceptable. In addition, it is conceivable to switch control in a specific region, but in the first place, whether quick steering (overshoot) is performed according to the driver's intention, or whether the steering angle overshoot occurs due to insufficient reaction torque. It is difficult to distinguish. In addition, it is difficult to set the switching timing and the return timing for switching the control, which is not necessarily an effective means. That is, it is not possible to suppress the overshoot of the steering angle using the front wheel steering unit.

  From the above verification results, it was decided to introduce transient assist torque control for correcting assist torque by the power steering system. Here, since the transient assist torque control estimates the road surface reaction force from the vehicle model as described above, the front wheel actual turning angle is not used in a vehicle equipped with a four-wheel active steering system in which the vehicle model changes according to the traveling state. And the rear wheel rudder angle must be taken into account. Therefore, the transition assist torque control according to the vehicle system is achieved by feeding back the actual front wheel steering angle and the rear wheel steering angle and reflecting them in the transient assist torque control.

  If the vehicle model is not taken into account by this feedback, the slip angle cannot be estimated accurately, and the road surface reaction force estimation becomes insufficient accordingly. That is, it means that proper control cannot be performed even if transient assist torque control applicable to a vehicle not equipped with an active steering control system is installed.

  FIG. 12 is a time chart showing simulation results of vehicle characteristics of a vehicle equipped with the four-wheel active steering system and transient assist torque control according to the first embodiment and vehicle characteristics without transient assist torque control at high vehicle speeds. The frequency response of the steering angle with respect to the steering torque at that time becomes the solid line characteristic of FIG. 13, 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. 12, when the steering torque is step-inputted, in a vehicle without transient assist torque control, a little assist torque is given, 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. 13 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. Therefore, the amount of assist in the reverse direction is increased with respect to fast 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.

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

  (1) Transient assist control is provided to control the assist torque so that the characteristic of the steering angle with respect to the steering torque becomes smaller as the frequency of the steering torque becomes higher. Therefore, it is possible to avoid an overshoot of the steering angle and the like, and the vehicle behavior can be stabilized. In other words, steering angle control is performed by torque control, and not only the driver's steering torque is assisted by assist torque control, but also vehicle characteristic control is achieved.

  (2) A reaction force torque estimation unit 312a that estimates reaction force torque acting on the steering wheel based on the vehicle model, and an actual characteristic calculation unit that calculates actual characteristics of the steering angle other than the steering torque based on the vehicle model 312b and a target characteristic calculation unit 312c that calculates a target characteristic of the steering angle with respect to the steering torque based on the vehicle model, and the transient assist torque control unit 312 includes the steering torque and the actual torque so that the actual characteristic becomes the target characteristic. The assist torque is controlled based on the reaction force torque.

  That is, by calculating the slip angle from the vehicle model and estimating the reaction torque using the correlation with the slip angle, the assist torque can be controlled in a feed-forward manner. Therefore, there is no response delay or the like, and by making the steering angle an ideal value, it is possible to improve the steering feeling and stabilize the vehicle behavior.

  (3) The vehicle model is a model equipped with a rear wheel steering system that provides a rear wheel assist rudder angle, and the transient assist torque control unit 312 controls the transient assist torque based on the rear wheel rudder angle. Therefore, it becomes possible to always consider the vehicle model that changes according to the running state, and to stabilize the vehicle behavior.

  (4) The reaction force torque estimation unit 312a decreases the transient assist torque as the reaction force torque estimation value decreases. Therefore, it is possible to control according to the steering angle generated in the actual vehicle, and it is possible to control the transient assist torque according to the operating state of the actuator.

  (5) The vehicle model is a model equipped with a front wheel steering system that gives a front wheel auxiliary steering angle, and the transient assist torque control unit 312 controls the transient assist torque based on the actual front wheel steering angle. Therefore, it becomes possible to always consider the vehicle model that changes according to the running state, and to stabilize the vehicle behavior.

  (6) The reaction force torque estimation unit 312a decreases the transient assist torque as the reaction force torque estimation value decreases. Therefore, it is possible to control according to the steering angle generated in the actual vehicle, and it is possible to control the transient assist torque according to the operating state of the actuator.

  Next, Example 2 will be described. FIG. 14 is a system diagram showing the overall configuration of a vehicle equipped with a rear active steering system and a power steering system. Since the basic configuration is the same as that of the first embodiment, only different points will be described.

  In the rear active steering system, the yaw rate or lateral acceleration of the vehicle is controlled by performing in-phase control or reverse-phase control on the steering angle of the front wheels according to the steering angle and vehicle speed of the driver. Here, the control target is the front wheel and the rear wheel in the first embodiment, but only the rear wheel in the second embodiment. Therefore, in calculating the target rear wheel steering angle, the yaw rate-based target is calculated. Value generation control or lateral acceleration based target value generation control logic is installed.

  Specifically, in the low vehicle speed region, the reverse phase control is performed to positively generate the turning ability of the vehicle, that is, the yaw rate. In the middle vehicle speed region, the reverse phase control is performed for a moment to ensure the initial response, and then the in-phase control is appropriately performed, thereby ensuring the vehicle stability while ensuring the turnability. In the high vehicle speed region, the stability of the vehicle, that is, yaw rate is suppressed by performing in-phase control. The system may be a system that controls all of the low speed region, the medium speed region, and the high speed region, or may be a system that performs selective control, and is not particularly limited.

[Configuration of transient assist torque controller]
Next, differences between the transient assist torque control unit and the first embodiment will be described.

  The steering reaction torque estimation unit 312a uses a two-wheel model considering rear active steering control, estimates the front wheel slip angle by feeding back the steering angle information of the rear wheel, and is approximately proportional to the front wheel slip angle. By calculating the steering reaction torque, Trk (s) can be determined.

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

Next, when the target front wheel steering angle characteristic Ref (s) is defined by a general (0th / secondary) transfer function in the control system, it is expressed by the following equation (2-1).
(Formula 2-1)
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 arbitrarily set depending on the vehicle, and Gain is expressed by the following equation (3-1) in the actual characteristic calculation unit 312b based on the vehicle model.
(Formula 3-1)
Gain [rad / Nm] ＝ k [1 / m] / (Gain _{_betaf_4WAS}・ Gain _{_Frk} )
Gain _{_betaf_RAS} : 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 (4-1).
(Formula 4-1)
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_RAS} is expressed by the following equation (5-1).
(Formula 5-1)
Gain _{_betaf_RAS} = {1 / N} −A
A = (Lf / Vx) ・ (Gain _{_yaw_front} + Ratio _{_RAS} × Gain _{_yaw_rear} )
+ (1 / Vx) ・ (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 _{_RAS} : Rear wheel rudder angle per unit steering angle
Lf: Distance between vehicle center of gravity and front axle
Vx: Vehicle speed.

_{Ratio_RAS} is a value determined by the rear active steering control for each vehicle speed, and may be _{stored in} advance as a map corresponding to the vehicle speed, as shown in the map representing the relationship between _{Ratio_RAS} and vehicle speed in FIG. The _{Ratio_RAS} may be obtained from the rear wheel controller 5 by 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 characteristics and vehicle speed. Therefore, since the gain in the equation (3-1) is configured by a constant or a vehicle speed dependence equation, the actual characteristic calculation unit 312b depends on the vehicle speed as shown in the map showing the relationship between the gain and the vehicle speed in FIG. You may keep it as a map.

  Based on the gain obtained by the actual characteristic calculation unit 312b, the target characteristic calculation unit 312c 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.

FIG. 18 shows vehicle characteristics of a vehicle having rear active steering control and transient assist torque control corresponding to Example 2 at high vehicle speeds, and rear active steering control without transient assist torque control as Comparative Example 1. 10 is a time chart showing simulation results of vehicle characteristics of a vehicle and vehicle characteristics of a vehicle that is simply a combination of transient assist torque control and rear active steer control as Comparative Example 2 without correcting the vehicle model. As for the steering torque, it is assumed that a certain torque is step-inputted, and shows the vehicle behavior with respect to the input of the steering torque. In the rear active steering control of Comparative Examples 1 and 2, the characteristics shown in FIG. 17 are used as _{Ratio_RAS} ^* that does not consider the vehicle model.

  As shown in FIG. 18, when the steering torque is step-inputted, in the first comparative example, the assist torque is slightly applied, and the steering angle is exceeded due to the small reaction torque from the road surface. Shoot. In the rear active steering system in which the target rear wheel steering angle is set according to the steering angle by this overshoot, in-phase control is performed on the rear wheel side according to the steering angle. At this time, although the rear wheel steering angle is generated according to the steering angle by the rear active steering control, overshoot occurs in the yaw rate and the lateral acceleration due to the steering angle overshooted on the front wheel side, and the stability of the vehicle is reduced. That's not enough.

  Further, in Comparative Example 2, since the rear active steering control is not considered when performing the transient assist torque control, the generation of the slip angle is actually suppressed by the rear active steering control, but depending on the steering angle. It is mistakenly recognized that a slip angle has occurred, and an excessive reaction force is given as a transient assist torque. Therefore, the generation of the steering angle is excessively suppressed, and conversely, the yaw rate and the lateral acceleration are insufficient, which may cause a vehicle behavior different from the driver's intention.

  On the other hand, in the vehicle of the second embodiment, it is known by calculation that the reaction torque from the road surface is small when the step input of the steering torque is given, and the slip generated due to the influence of the rear active steering control. It can be appropriately estimated that the corner is generated with a small angle. Therefore, reverse assist torque according to the slip angle is applied. That is, it is applied not to the side that assists the driver's steering torque but to the side that provides moderate 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.

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 312 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. It is a time chart showing the relationship of the front-wheel actual turning angle at the time of performing correction which suppresses generation of overshoot. It is a time chart showing the relationship of the front-wheel actual turning angle at the time of performing correction which suppresses generation of overshoot. 6 is a time chart showing simulation results of vehicle characteristics at a high vehicle speed and vehicle characteristics without transient assist torque control according to the first embodiment. 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. It is a system diagram showing the whole structure of the vehicle carrying the rear active steering system and power steering system of Example 2. 10 is a map showing the relationship between _{Ratio_RAS} and vehicle speed in Example 2. 6 is a map showing the relationship between Gain and vehicle speed in Example 2. It is a map showing the relationship between _{Ratio_RAS} ^* of Comparative Examples 1 and 2 and vehicle speed. 6 is a time chart showing simulation results of vehicle characteristics at a high vehicle speed in Example 2, vehicle characteristics in Comparative Example 1, and vehicle characteristics in Comparative Example 2;

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 (7)

In a vehicle steering control device including power steering means for applying assist torque based on a steering torque of a driver,
Gain characteristic of steering rudder angle against the steering torque, so that the smaller the frequency of the steering torque is high, the vehicle steering control apparatus characterized by comprising a transient assist torque control means to control the assist torque . The vehicle steering control device according to claim 1,
Target characteristic setting means for setting a target characteristic of the gain characteristic ;
Have
It said transient assist torque control means, as described above a target characteristic, the steering torque vehicular steering control apparatus characterized by controlling the assist torque based on. The vehicle steering control device according to claim 1 or 2,
A rear wheel auxiliary rudder angle providing means for providing a rear wheel auxiliary rudder angle is provided,
The transient assist control means controls a transient assist torque based on the rear wheel auxiliary steering angle. In the vehicle steering control device according to claim 3,
A reaction torque estimation means for estimating a reaction torque acting on the steered wheel based on the rear wheel auxiliary steering angle is provided;
The vehicle steering control device, wherein the transient assist torque control means reduces the transient assist torque as the estimated reaction force torque is smaller. The vehicle steering control device according to any one of claims 1 to 4,
Provide front wheel auxiliary rudder angle giving means for giving the front wheel auxiliary rudder angle,
The vehicle steering control device, wherein the transient assist control means controls a transient assist torque based on the front wheel auxiliary steering angle. The vehicle steering control device according to claim 5,
A reaction torque estimating means for estimating a reaction torque acting on the steered wheels based on the front wheel auxiliary steering angle is provided;
The vehicle steering control device, wherein the transient assist torque control means reduces the transient assist torque as the estimated reaction force torque is smaller. In a vehicle steering control method including a power steering mechanism that applies assist torque based on a driver's steering torque,
Gain characteristic of steering rudder angle against the steering torque, so as to reduce as the frequency of the steering torque is high, the vehicle steering control method, characterized by controlling the assist torque.

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