JP4807164B2 - Vehicle steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the moving state of a vehicle for an operation of a steering wheel and obtain an excellent steering feeling. <P>SOLUTION: A main ECU100 inputs a steering wheel steering angle &delta; and a vehicle speed V from a steering angle sensor 25 and a vehicle speed sensor 90, and calculates a target motion state amount (a target yaw rate &gamma;* and a vehicle body slip angle &beta;*). In the calculation, the target motion state amount is calculated so as to satisfy the target motion performance of a predetermined vehicle to eliminate a phase difference between the steering wheel steering angle &delta; and lateral forces of front wheels Wfl, Wfr, or to eliminate a phase difference between the steering wheel steering angle &delta; and the turning angle of the front wheel. The main ECU100 calculates a target front wheel turning angle &delta;f* and a target rear wheel turning angle &delta;r* based on the target motion state amount, and a front wheel motor ECU61 and a rear wheel motor ECU71 turning-controls the front wheels Wfl, Wfr and rear wheels Wrl, Wrr to the target front wheel turning angle &delta;f and the target rear wheel turning angle &delta;r. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a vehicle steering apparatus including a front wheel steering actuator that steers front wheels and a rear wheel steering actuator that steers rear wheels.

  2. Description of the Related Art Conventionally, a vehicle steering apparatus that drives and controls a wheel steering actuator so as to improve a vehicle motion state according to a steering operation of a steering wheel is known. For example, in the vehicle steering apparatus disclosed in Patent Document 1 below, the steering angle and the vehicle speed are detected, and the yaw rate and yaw angular acceleration target values as the motion state quantities of the vehicle are detected using these two detection values. Calculate Then, the target rear wheel steering angle at which these yaw rate and yaw angular acceleration become target values is calculated, and the rear wheels are steered to the target rear wheel steering angle using the rear wheel steering actuator.

On the other hand, there is also known a vehicle steering apparatus in which the steering operation of the steering wheel by the driver is matched with the behavior characteristics of the vehicle so that the driver can drive the vehicle without a sense of incongruity. For example, in Patent Document 2 below, a steering angle and a vehicle speed are detected, a target value of a steering reaction force is calculated using these two detection values, and a steering motor is driven and controlled according to the target value. The steering reaction force is appropriately controlled. Further, in the vehicle steering apparatus described in the cited document 2, in order to eliminate the uncomfortable feeling caused by the driver due to the difference between the steering angle of the steering wheel and the turning angle of the front wheels, a steering ratio variable actuator is used. The steering gear ratio representing the ratio of the steering angle of the steering wheel to the front wheel turning angle is also changed according to the steering angle and the vehicle speed.
JP-A-5-155346 JP 2002-370664 A

  However, in the vehicle steering apparatus described in Patent Document 1, the steering sensation by the driver is not taken into consideration, and in particular, a phase shift from the steering reaction force (steering torque) from the front wheels with respect to the driver's steering operation. However, the driver may feel uncomfortable with the steering operation of the steering wheel. In addition, in the vehicle steering device described in Patent Document 2, the vehicle motion performance with respect to the steering operation of the steering handle is not sufficiently considered, and the motion state of the vehicle is not always appropriate for the steering operation of the steering handle. Not controlled. In Patent Document 2, the phase shift between the driver's steering operation and the steering reaction force (steering torque) is not taken into consideration.

  The present invention has been made in order to cope with the above-described problem, and its purpose is to perform steering control of the front wheels and the rear wheels in consideration of both the target motion performance of the vehicle and the target steering feeling of the driver. An object of the present invention is to make it possible to obtain a good vehicle movement state and a good steering feeling with respect to the steering operation of the steering wheel.

  In order to achieve the above object, the structural feature of the present invention includes a front wheel steering actuator that steers a front wheel mechanically connected to a steering handle, and a rear wheel steering actuator that steers a rear wheel. In the vehicle steering apparatus, the steering angle detecting means for detecting the steering angle of the steering handle, the vehicle speed detecting means for detecting the vehicle speed, the detected steering angle of the steering handle and the detected vehicle speed are used in advance. The target motion state quantity calculating means for calculating the target motion state quantity of the vehicle so as to satisfy the determined target motion performance of the vehicle and eliminate the phase difference between the steering angle of the steering wheel and the lateral force of the front wheel; A target turning angle calculation means for calculating a target front wheel turning angle and a target rear wheel turning angle based on the calculated target motion state quantity of the vehicle, and the calculated target front wheel turning angle and target rear wheel turning angle. According to before There is provided a steering control means for driving and controlling the front wheel steering actuator and the rear wheel steering actuator to control the front wheels and the rear wheels to the calculated target front wheel turning angle and target rear wheel turning angle, respectively. There is.

  In this case, the target motion state quantity calculating means calculates, for example, a target value of the motion state quantity of any one or two of the yaw rate generated in the vehicle body, the vehicle body slip angle, and the lateral acceleration generated in the vehicle body. To do. In addition, the motion state quantity of the vehicle is represented by a function of a first-order lag with respect to the steering angle of the steering wheel, for example. Further, eliminating the phase difference between the steering angle of the steering wheel and the lateral force of the front wheels is proportional to the value obtained by multiplying the steering torque of the steering wheel (that is, the steering reaction force) by the steering angle of the steering wheel and the vehicle speed. Means that.

  In the present invention configured as described above, the target motion state quantity of the vehicle satisfies the predetermined target motion performance of the vehicle, and the phase difference between the steering angle of the steering wheel and the lateral force of the front wheels is eliminated. To be determined. Then, based on the target motion state quantity, the target front wheel turning angle and the target rear wheel turning angle are calculated, and the front wheels and the rear wheels are respectively turned to the calculated target front wheel turning angle and target rear wheel turning angle. Is done. Here, since the lateral force of the front wheels is proportional to the steering reaction force applied to the steering wheel as the front wheels are steered, the driver can steer while feeling the steering reaction force in the same phase as the steering operation of the steering wheel. The steering wheel can be steered. Therefore, according to the features of the present invention, a favorable vehicle motion performance is achieved with respect to the steering operation of the steering wheel, and at the same time, the driver can drive the vehicle without feeling uncomfortable, that is, with a good steering feeling. Can do.

  According to another feature of the present invention, the target motion state quantity calculating means uses the detected steering angle of the steering wheel and the detected vehicle speed instead of the above, to determine a predetermined target motion of the vehicle. The target motion state quantity of the vehicle is calculated so as to satisfy the performance and eliminate the phase difference between the steering angle of the steering wheel and the turning angle of the front wheels. In this case, if the vehicle speed is high and the yaw rate and the vehicle body slip angle are small, the turning angle of the front wheels is proportional to the lateral force of the front wheels without a phase difference. Therefore, if the vehicle is traveling at medium speed or high speed and the turning radius is not small, the front wheel turning angle is proportional to the front wheel lateral force without any phase difference. The steering handle can be steered while feeling the steering reaction force in the same phase as the steering operation. The steering feeling of the driver is an important feeling when the vehicle is traveling at medium speed or high speed. In addition, when the vehicle is traveling at a medium speed or a high speed, the turning radius of the vehicle is usually large. Therefore, according to other features of the present invention, the steering operation of the steering wheel is good. At the same time as the movement performance of the vehicle is achieved, the driver can drive the vehicle without feeling uncomfortable, that is, with a good steering feeling.

  The target motion performance of the vehicle is that, for example, the instantaneous center of rotation of the vehicle at the time of turning of the vehicle is always present at any position in a vertical plane extending in the front-rear direction passing through the center of gravity of the vehicle. According to this, since the vehicle always rotates around the substantially central position in the vehicle width direction, the turning of the vehicle is stabilized. In addition, the rotation around the substantially central position in the vehicle width direction feels good for the driver.

  In addition, the instantaneous center of rotation may be a fixed point that is always a predetermined distance away from the center of gravity of the vehicle. For example, the center of rotation instant may be in a vertical plane including the rear wheel axle. According to this, since the vehicle always rotates around the same instantaneous center position, the turning of the vehicle becomes more stable.

  The target motion performance of the vehicle is, for example, that the yaw rate generated in the vehicle body and the vehicle body slip angle are always in a proportional relationship with no phase difference. According to this, since the yaw rate generated in the vehicle body and the vehicle body slip angle always change in the same phase with respect to the steering operation of the steering wheel, the turning of the vehicle is stabilized. Further, the change in the same phase between the yaw rate and the vehicle body slip angle is felt well for the driver.

  Further, the target motion performance of the vehicle is, for example, that the vehicle body slip angle is always “0”. According to this, an ideal turn for the vehicle is performed. This also feels good for the driver.

a. Configuration Example Hereinafter, each embodiment of the present invention will be described. First, a configuration example of a vehicle steering apparatus common to each embodiment will be described with reference to the drawings. FIG. 1 schematically shows the vehicle steering apparatus.

  The steering device 10 includes a front wheel steering unit 20 for steering the left and right front wheels Wfl and Wfr, a rear wheel steering unit 40 for steering the left and right rear wheels Wrl and Wrr, and the front wheel steering unit 20. And a steering control device 50 for controlling the rear wheel steering unit 40. The front wheel steering unit 20 includes a steering handle 21 that is rotated by a driver. The steering handle 21 is connected to upper ends of steering shafts 22a and 22b that are divided into two parts. A pinion gear 23 is provided at the lower ends of the steering shafts 22a and 22b, and a rack bar 24 is engaged with the pinion gear 23. The rack bar 24 is extended to the left and right, and the left and right front wheels Wfl and Wfr are connected to be steerable at both ends thereof, and the left and right front wheels Wfl and Wfr are steered by displacement in the axial direction. Accordingly, the rotation of the steering handle 21 is transmitted to the rack bar 24 via the steering shafts 22a and 22b and the pinion gear 23, and the rack bar 24 is displaced in the axial direction to steer the left and right front wheels Wfl and Wfr.

  The steering shaft 22a is provided with a steering angle sensor 25 that detects the steering angle δ (steering wheel steering angle δ) of the steering handle 21 based on the rotation angle of the steering shaft 22a. Between the steering shafts 22a and 22b, for changing the steering gear ratio which is the ratio of the rotation angle of the steering handle 21 to the turning angle of the left and right front wheels Wfl and Wfr, in other words, the upper steering with respect to the lower steering shaft 22b. A steering gear ratio variable device 30 is provided for making the ratio of the rotation angle of the shaft 22a variable. The steering gear ratio variable device 30 includes a cylindrical casing 31 connected to the lower end portion of the steering shaft 22a so as to rotate integrally. An electric motor 32 constituting a steering gear ratio variable actuator is fixed in the casing 31. An output shaft 32a of the electric motor 32 is rotatably supported by the casing 31, and is connected to the steering shaft 22b at the lower end so as to be integrally rotatable.

  The electric motor 32 includes a speed reduction mechanism 33, and the rotation of the electric motor 32 is decelerated and output to the output shaft 32a. The electric motor 32 is provided with a rotation angle sensor 34 for detecting the rotation speed of the rotor. The rotation angle sensor 34 is configured by a resolver in the present embodiment, detects the rotation angle of the electric motor 32, and outputs a detection signal representing the detected rotation angle to the steering control device 50. Hereinafter, the electric motor 32 is referred to as a front wheel steering angle adjustment motor 32.

  The rear wheel turning unit 40 includes a turning bar 41 that connects the left and right rear wheels Wrl and Wrr so that the left and right rear wheels Wrl and Wrr can be turned, and the left and right rear wheels Wrl and Wrr are turned by the displacement of the turning bar 41 in the axial direction. An electric motor 42 is assembled to the steered bar 41. The electric motor 42 steers the left and right rear wheels Wrl and Wrr by displacing the steered bar 41 in the axial direction via the ball screw mechanism 43 according to the rotation. A rotation angle sensor 44 is assembled to the electric motor 42. The rotation angle sensor 44 is configured by a resolver in the present embodiment, detects the rotation angle of the electric motor 42, and outputs a detection signal representing the detected rotation angle to the steering control device 50. Hereinafter, the electric motor 42 is referred to as a rear wheel steering motor 42.

  The steering control device 50 includes a front wheel motor control device 60 for driving and controlling the front wheel steering angle adjustment motor 32, a rear wheel motor control device 70 for driving and controlling the rear wheel steering motor 42, and steering of the driver's steering wheel. An electronic control unit 100 (hereinafter referred to as a main ECU 100) that calculates a turning control amount according to an operation and outputs a turning control command to the front wheel motor control device 60 and the rear wheel motor control device 70 is provided.

  The front wheel motor control device 60 includes an electronic control device 61 (hereinafter referred to as a front wheel motor ECU 61) that controls energization of the front wheel rudder angle adjustment motor 32, and a front wheel rudder angle adjustment motor 32 according to an energization command from the front wheel motor ECU 61. And a motor drive circuit 62 for driving. The front wheel motor ECU 61 includes a microcomputer including a CPU, a ROM, a RAM, and the like as a main part, and executes a front wheel correction turning program of FIG. 3 according to a front wheel turning control command from the main ECU 100, thereby rotating the rotation angle. Based on the rotation angle detection signal detected by the sensor 34 and the steering angle signal detected by the steering angle sensor 25, the energization of the front wheel steering angle adjustment motor 32 is controlled to control the left and right front wheels Wfl, Wfr.

  The rear wheel motor control device 70 is an electronic control device 71 (hereinafter referred to as a rear wheel motor ECU 71) that controls energization of the rear wheel steering motor 42, and the rear wheel steering motor 42 according to an energization command from the rear wheel motor ECU 71. And a motor drive circuit 72 for driving the motor. The rear wheel motor ECU 71 includes a microcomputer including a CPU, a ROM, a RAM, and the like as a main part, and executes a rear wheel steering program (not shown) according to a rear wheel steering control command from the main ECU 100, thereby rear wheel steering. The energization of the rear wheel steering motor 42 is controlled based on the rotation angle detection signal of the rotation angle sensor 44 that detects the rotation angle of the motor 42 to control the left and right rear wheels Wrl and Wrr.

  The main ECU 100 includes a microcomputer including a CPU, ROM, RAM, and the like as main components. By executing the target front / rear wheel turning angle calculation program shown in FIG. 2, a steering control amount corresponding to the driver's steering operation is obtained. Calculate and output a steering control command to the front wheel motor ECU 61 and the rear wheel motor ECU 71. The main ECU 100 is also connected to a vehicle speed sensor 90 that outputs a vehicle speed signal representing the vehicle speed V.

b. First Embodiment Next, the operation of the first embodiment of the present invention will be described in detail with a mixture of computer processing, but before entering the specific description, the technology employed in the first embodiment will be described. The principle will be explained.

  In the first embodiment, as the target motion performance of the vehicle, the vehicle's instantaneous center of rotation at the time of turning of the vehicle is always present at any position in the vertical plane extending in the front-rear direction passing through the center of gravity of the vehicle. Adopted. Further, as the target steering feeling characteristic of the driver, it is adopted that the phase difference between the steering angle δ (s) and the front wheel lateral force Ff (s) (proportional to the steering reaction force) is “0”.

前記式１，２において、Ｇy，Ｇbは、ハンドル操舵角δ(ｓ)に対するヨーレートγ(ｓ)および車体スリップ角β(ｓ)の制御ゲインをそれぞれ表し、Ｔは時定数を表す。「ｓ」は、ラプラス演算子である。 First, the yaw rate γ (s) and the vehicle body slip angle β (s) as the movement state quantity of the vehicle with respect to the movement of the vehicle body with respect to the steering operation of the steering handle 21, that is, the steering wheel steering angle δ (s) The control law expressed as 2 is adopted. That is, the yaw rate γ (s) and the vehicle body slip angle β (s) are represented by a function of a first-order lag with respect to the steering wheel steering angle δ (s).

In Equations 1 and 2, Gy and Gb represent control gains of the yaw rate γ (s) and the vehicle body slip angle β (s) with respect to the steering angle δ (s), respectively, and T represents a time constant. “S” is a Laplace operator.

なお、Ｖは車速である。 In the first embodiment, as described above, the target motion performance of the vehicle is such that the instantaneous center of rotation of the vehicle at the time of turning of the vehicle is always at any position in the vertical plane extending in the front-rear direction passing through the center of gravity of the vehicle. It exists. As shown in FIG. 7, let this rotation moment center be P, and let the horizontal distance in the front-rear direction of the vehicle from the vehicle center of gravity to the rotation moment center P be X (positive from the center of gravity to the rear). In this case, since the rotation instant center P does not move to the left and right when the vehicle turns, the movement amounts β · V and γ · X in the opposite directions of the rotation instant center P due to the vehicle body slip angle β and the yaw rate γ cancel each other. Equation 3 is established.

V is the vehicle speed.

Then, the following formula 4 is derived from the formulas 1 and 2, and the formula 2 is transformed into the following formula 5 using the formulas 3 and 4.

前記式６，７において、ｍは、車体質量である。Ｌfは、車体重心から前輪車軸までの前後方向の水平距離である。Ｌrは、車体重心から後輪車軸までの前後方向の水平距離である。Ｌは、ホイールベース（Ｌf＋Ｌr）である。Ｋfは、前輪コーナリングパワーである。また、後述するＫrは、後輪コーナリングパワーである。Ｉは、車体重心回りの慣性モーメントである。 On the other hand, the front wheel turning angle δf (s) with respect to the steering wheel steering angle δ (s) is generally expressed as the following equation 6, and the equation 6 is expressed as the following equation 7 using the above equations 1 and 5. Deformed.

In the above formulas 6 and 7, m is the mass of the vehicle body. Lf is the horizontal distance in the front-rear direction from the center of gravity of the vehicle body to the front wheel axle. Lr is a horizontal distance in the front-rear direction from the center of gravity of the vehicle body to the rear wheel axle. L is a wheel base (Lf + Lr). Kf is the front wheel cornering power. Further, Kr to be described later is rear wheel cornering power. I is the moment of inertia around the center of gravity of the vehicle body.

Further, the front wheel lateral force Ff (s) with respect to the steering wheel steering angle δ (s) is generally expressed by the following equation (8). Is done.

Here, in order to improve the steering feeling, it is considered that the steering torque applied to the steering handle 21 by the driver is proportional to the steering angle δ (s) without a phase difference. The steering torque is equal to the steering reaction force applied from the road surface to the steering handle 21, and this steering reaction force is proportional to the steering reaction force applied from the road surface to the front wheels Wfl and Wfr. The steering reaction force is proportional to the front wheel lateral force Ff (s)). Therefore, to make the steering torque proportional to the steering wheel steering angle δ (s) without phase difference, the steering wheel steering angle δ (s) and the front wheel lateral force are proportional to each other. This means eliminating the phase difference from the force Ff (s). Therefore, if the time constant T is Ta and the following equation 10 is established, the term of the temporary delay disappears from the equation 9, and the front wheel lateral force Ff (s) (proportional to the steering torque) becomes the steering angle δ (s). Proportional without phase difference. The elimination of the phase difference between the steering wheel steering angle δ (s) and the front wheel lateral force Ff (s) is, as can be seen from Equation 9, the front wheel lateral force Ff (s) (proportional to the steering torque) This corresponds to proportionality to a value δ · V obtained by multiplying the steering wheel steering angle δ and the vehicle speed V.

Then, by transforming Equation 10 above, the rotation center position X according to the above condition can be expressed as Equation 11 below using the time constant Ta.

これらの目標ヨーレートγ＊(ｓ)および目標車体スリップ角β＊(ｓ)は、前述した車両の目標運動性能と運転者の目標操舵感覚特性を満たすための車両の目標運動状態量である。 Next, the target yaw rate γ * (s) and the target vehicle body slip angle β * (s) are expressed by the following equations 12 and 13 by substituting the time constant Ta and the rotation instantaneous center position X into the equations 1 and 5, respectively. It is expressed as follows.

These target yaw rate γ * (s) and target vehicle body slip angle β * (s) are the target motion state quantities of the vehicle to satisfy the above-described target motion performance of the vehicle and the target steering sense characteristics of the driver.

Next, the target motion state of the vehicle is realized by substituting these target yaw rate γ * (s) and the target vehicle body slip angle β * (s) into the general motion equation of the vehicle of the following equation (14). The target front wheel turning angle δf * (s) and the target rear wheel turning angle δr * (s) are calculated.

  If the left and right front wheels Wf1, Wf2 and the left and right rear wheels Wr1, Wr2 are steered to the target front wheel turning angle δf * (s) and the target rear wheel turning angle δr * (s), respectively, the above-described target motion performance of the vehicle is achieved. And the target steering feeling characteristic of the driver is achieved. That is, when the vehicle turns, the instantaneous center of rotation of the vehicle is always maintained at any position on the vertical plane that passes through the center of gravity of the vehicle and extends in the front-rear direction, and at the same time, the steering angle δ (s) and the front wheel lateral force The phase difference with Ff (s) (proportional to the steering reaction force) is kept at “0”. According to this, since the vehicle always rotates around the substantially central position in the vehicle width direction, the turning of the vehicle is stabilized. In addition, the rotation around the substantially central position in the vehicle width direction feels good for the driver. Further, the driver can steer the steering handle 21 while feeling a steering reaction force having the same phase as the steering operation of the steering handle 21. Therefore, according to this, it is possible to achieve good vehicle motion performance with respect to the steering operation of the steering wheel, and at the same time, the driver can drive the vehicle without feeling uncomfortable, that is, with a good steering feeling.

  Next, the steering control operation of the left and right front wheels Wf1, Wf2 and the left and right rear wheels Wr1, Wr2 based on the theory will be described. After the ignition switch (not shown) is turned on, the main ECU 100 repeatedly executes the target front and rear wheel turning angle calculation program of FIG. 2 consisting of steps S10 to S19 every predetermined short time. In this target front / rear wheel turning angle calculation program, after the start of execution of step S10, the main ECU 100 inputs a detection signal representing the steering angle δ from the steering angle sensor 25 and the vehicle speed V from the vehicle speed sensor 90 in step S11. A vehicle speed signal indicating is input.

  Next, in step S12, the main ECU 100 refers to a yaw rate gain table stored in advance in the ECU 100 and determines a yaw rate gain Gy corresponding to the vehicle speed V. The yaw rate gain Gy increases as the vehicle speed V increases and then decreases as indicated by the solid line in FIG. The characteristic of the yaw rate gain Gy with respect to the vehicle speed V is not limited to this, and may be a characteristic that gradually decreases as the vehicle speed V increases, for example, as indicated by a broken line in FIG. These depend on the mechanical properties of the vehicle and depend on the choice of vehicle motion properties. Further, instead of the yaw rate gain table, a function representing the relationship between the vehicle speed V and the yaw rate gain Gy may be determined in advance, and the yaw rate gain Gy corresponding to the vehicle speed V may be calculated using the function.

  After the process of step S12, the main ECU 100 determines a time constant Ta corresponding to the vehicle speed V with reference to a time constant table stored in advance in the ECU 100 in step S13. For example, as shown by the solid line in FIG. 5, the time constant Ta is a characteristic that gradually decreases as the vehicle speed V increases. Other characteristics may be used in relation to selection. Also in this case, instead of the time constant table, a function representing the relationship between the vehicle speed V and the time constant Ta is determined in advance, and the time constant Ta corresponding to the vehicle speed V is calculated using the function. Also good.

  After the process of step S13, the main ECU 100 calculates the rotation instantaneous center position X by executing the calculation of the equation 11 using the determined time constant Ta and the vehicle speed V in step S14. It should be noted that, instead of the calculation of Equation 11, a rotation moment center position table that defines the relationship between the time constant Ta, the vehicle speed V, and the rotation moment center position X is stored in the main ECU 100 in advance, and the table is referred to. By doing so, you may make it determine the rotation center position X of rotation. In this case, as shown in FIG. 6A, for each of a plurality of different values of the time constant T, a rotation instantaneous center position X that increases as the vehicle speed V increases is prepared. As the time constant T increases, the slope of the straight line of the rotation instantaneous center position X with respect to the vehicle speed V increases.

  Further, in order to add a slight change to the target steering feeling characteristic, it is not necessary to faithfully determine the rotation instantaneous center position X according to the equation 11 using the time constant Ta and the vehicle speed V. That is, as shown in FIG. 6B, in the region R1 located on the upper side of the straight line, the phase of the front wheel lateral force Ff (s) (steering torque) becomes larger than the phase of the steering angle δ (s) as the distance from the straight line (solid line) increases. Proceed greatly. On the other hand, in the region R1 located on the lower side of the straight line, the phase of the front wheel lateral force Ff (s) (steering torque) lags behind the phase of the steering angle δ (s) as the distance from the straight line increases. Therefore, although it is not preferable to deviate greatly from this straight line, as a driving characteristic of the vehicle, when selecting that the phase of the front wheel lateral force Ff (s) (steering torque) slightly advances from the phase of the steering wheel steering angle δ, As indicated by a one-dot chain line in FIG. 6B, a characteristic line indicating the relationship between the vehicle speed V and the rotation center position X may be provided slightly above the straight line. Further, if it is selected as a driving characteristic of the vehicle that the phase of the front wheel lateral force Ff (s) (steering torque) is changed according to the vehicle speed V, the phase of the steering wheel steering angle δ (s) is changed. For example, the relationship between the vehicle speed V and the rotational center position X may be indicated by a broken line. 6B, it is necessary to prepare a plurality of characteristic lines in accordance with the size of the time constant T as in the case of FIG. 6A.

  After the process of step S14, the main ECU 100 calculates the target yaw rate γ (s) * by executing the expression 12 in step S15, and the target vehicle body slip angle by executing the expression 13 in step S16. β (s) * is calculated. Then, using the target yaw rate γ (s) * and the target vehicle body slip angle β (s) *, in step S17, the target front wheel turning angle δf (s) * and target The rear wheel turning angle δr (s) * is calculated. Next, in step S18, the main ECU 100 sends a control command including the calculated target front wheel turning angle δf (s) * and the target rear wheel turning angle δr (s) * to the front wheel motor ECU 61 and the rear wheel motor ECU 71. Output.

  The rear wheel motor ECU 71 receives a control command from the main ECU 100 and outputs a drive signal to the motor drive circuit 72 so that the turning angles of the rear wheels Wrl and Wrr become the target rear wheel turning angle δr *. Steer. In this case, since the steering angles of the rear wheels Wrl and Wrr steered by the rear wheel steering motor 42 are in accordance with the rotation angle of the rotation angle sensor 44, the rear wheel motor ECU 71 is, for example, the rear wheel steering angle. And a map (not shown) for correlating the rotation angle of the rotation angle sensor 44 with each other, and referring to this map, the rear wheel turning angle δr (steering angle with respect to the neutral position) becomes the target rear wheel turning angle δr *. Feedback control.

  On the other hand, the front wheel motor ECU 61 receives a control command from the main ECU 100, and executes a front wheel correction turning program including steps S30 to S35 shown in FIG. In this front wheel correction turning program, the front wheel motor EUC 61, in step S31, the control command including the target front wheel turning angle δf * output from the main ECU 100 and the steering angle representing the steering angle δ of the steering wheel by the steering angle sensor 25. Input the signal.

次に、ステップＳ３３にて、目標ハンドル操舵角δ＊から実際のハンドル操舵角δを減算する下記式１６により、目標補正ハンドル操舵角Δδ＊を計算する。

Next, in step S32, the target steering angle δ * corresponding to the target front wheel turning angle δf * is calculated by the following equation 15 by multiplying the target front wheel turning angle δf * by the steering gear ratio Gg. To do.

Next, in step S33, the target corrected handle steering angle Δδ * is calculated by the following equation 16 that subtracts the actual steering angle δ from the target steering angle δ *.

  In step S34, the front wheel motor ECU 61 controls the rotation of the front wheel steering angle adjustment motor 32 by the target correction handle steering angle Δδ *. In this case, the detection signal of the rotation angle sensor 34 that detects the rotation angle of the front wheel steering angle adjustment motor 32 is read, and feedback control is performed so that the detected rotation angle becomes the target correction handle steering angle Δδ *. By the correction turning of the front wheels Wfl and Wfr by the rotation of the front wheel steering angle adjusting motor 32, the front wheels Wfl and Wfr are steered so as to always coincide with the target front wheel turning angle δf *.

  In the vehicle steering apparatus 10 according to the first embodiment described above, the center of rotation of the vehicle at the time of turning of the vehicle always extends in the front-rear direction passing through the center of gravity of the vehicle by the processing of steps S11 to 16 in FIG. The phase difference between the target motion performance of the vehicle existing at any position in the vertical plane and the steering wheel steering angle δ (s) and the front wheel lateral force Ff (s) (proportional to the steering torque and steering reaction force) is “ A target yaw rate γ * and a target vehicle body slip angle β * as a target motion state quantity of the vehicle corresponding to the steering operation of the steering wheel to satisfy the target steering feeling characteristic of “0” are calculated. In step S17, a target front wheel turning angle δf * and a target rear wheel turning angle δr * for realizing the target motion state quantity of the vehicle are calculated, and the front wheel motor ECU 61 and the rear wheel motor ECU 71 calculate the front wheel. Wfl, Wfr and the rear wheels Wrl, Wrr are steered to the target front wheel turning angle δf * and the target rear wheel turning angle δr *. Therefore, according to the first embodiment, since both the target motion performance of the vehicle and the target steering feeling of the driver are realized at the same time, the driver can drive the vehicle satisfactorily without feeling uncomfortable.

  In the first embodiment, as the target motion performance of the vehicle, the instantaneous center of rotation of the vehicle at the time of turning of the vehicle always exists at any position in the vertical plane extending in the front-rear direction passing through the center of gravity of the vehicle. It was adopted. In other words, if the rotational center of rotation is within the vertical plane, the vehicle can be moved in the front-rear direction as the target motion performance of the vehicle. However, the target motion performance of the vehicle may be further limited to be modified so as to fix the front-rear direction position X of the center of rotation. The fixed position may be any position, but in this modification, the rotation center P is within a vertical plane including the rear wheel axle.

この式１７は、時定数Ｔaが車速Ｖによって規定され、上記第１実施形態のように自由な特性（車速Ｖに応じて自由に変化する特性）に設定され得ないことを意味する。 When this target motion performance of the vehicle is employed, the instantaneous center position X of rotation in the first embodiment is equal to the horizontal distance Lr in the front-rear direction from the center of gravity of the vehicle body to the rear wheel axle. Therefore, the time constant Ta from the above equation 10 is expressed by the following equation 17.

This equation 17 means that the time constant Ta is defined by the vehicle speed V and cannot be set to a free characteristic (a characteristic that changes freely according to the vehicle speed V) as in the first embodiment.

他の点に関しては、上記第１実施形態の場合と同じである。 In order to realize this, the main ECU 100 executes the target front / rear wheel turning angle calculation program of FIG. 8 instead of the target front / rear wheel turning angle calculation program of FIG. In this target front / rear wheel turning angle calculation program, the main ECU 100 executes the calculation of Equation 17 using the vehicle speed V input in Step S21 instead of the processing in Steps S13 and S14 in FIG. Calculate Ta. Also in the calculation of the time constant Ta, the time constant Ta may be calculated using a time constant table representing the relationship between the vehicle speed V and the time constant Ta. Further, in the process of step S22 instead of step S16 of FIG. 2, the target vehicle body slip angle β * is calculated by executing the calculation of the following equation 18 using the distance Lr instead of the rotation instantaneous center position X of the equation 13. .

The other points are the same as those in the first embodiment.

  According to the modification of the first embodiment, the rotation center P is always fixed. Therefore, compared with the first embodiment, although control is added, the uncomfortable feeling when turning the vehicle can be reduced. it can.

c. Second Embodiment In the second embodiment, as the target motion performance of the vehicle, as in the case of the first embodiment, the vehicle rotation center P is always in the front-rear direction passing through the center of gravity of the vehicle when turning the vehicle. It is adopted that it exists at any position in the extended vertical plane. On the other hand, the fact that the phase difference between the steering wheel steering angle δ (s) and the front wheel steering angle δf (s) is “0” is adopted as the target steering feeling characteristic of the driver. As will be described in detail later, this target steering feeling characteristic is obtained by making the steering wheel steering angle δ (s) and the steering torque (that is, the steering reaction force) substantially proportional, as in the case of the first embodiment. means.

Also in this case, Expressions 1 to 7 similar to those in the first embodiment are established. Then, the equation 7 can be modified as the following equation 19.

  Here, in order to achieve the driver's target steering feeling characteristic, it is considered to eliminate the phase difference between the steering wheel steering angle δ (s) and the front wheel turning angle δf (s). If the vehicle speed V is large and the yaw rate γ and the vehicle body slip angle β are small, as can be understood from the equation 8, Lf · γ (s) / {V · δ (s)} and β (s) / The term of δ (s) is ignored, and the front wheel turning angle δf (s) is proportional to the front wheel lateral force Ff (s) without any phase difference. Therefore, if the vehicle is traveling at medium or high speed and the turning radius is not too small, the front wheel turning angle δf (s) is proportional to the lateral force Ff (s) without any phase difference. In addition, the driver can steer the steering handle while feeling a steering reaction force having the same phase as the steering operation of the steering handle 21. The steering sensation of the driver is a particularly important sensation when the vehicle is traveling at medium speed or high speed. In addition, when the vehicle is traveling at medium speed or high speed, the turning radius of the vehicle is usually large, and therefore the position of the steering wheel steering angle δ (s) and the front wheel turning angle δf (s) By achieving the target steering sensation of eliminating the phase difference, the driver can drive the vehicle without a sense of incongruity, that is, with a good steering sensation.

In this case, if the time constant T is Ta and the following equation 20 holds, the term of temporary delay disappears from the equation 19, and the front wheel turning angle δf (s) is proportional to the steering wheel steering angle δ (s) without any phase difference. To do. Then, by transforming the following equation 20, the rotation instantaneous center position X according to the above condition can be expressed as the following equation 21 using the time constant Ta.

  In order to realize this, the main ECU 100 executes a target front / rear wheel turning angle calculation program obtained by modifying a part of the target front / rear wheel turning angle calculation program of FIG. In this modified target front / rear wheel turning angle calculation program, the calculation of the rotational center position X of the rotation in step S14 of FIG. Other processes are the same as those in the first embodiment.

  In this case as well, instead of the calculation of Equation 21, a rotation moment center position table that defines the relationship between the time constant Ta and the vehicle speed V and the rotation moment center position X is stored in the main ECU 100 in advance. The rotational center position X may be determined by referring to the table. In this case, as indicated by the solid line in FIG. 9, as the vehicle speed V increases, the rotation instantaneous center position X decreases after the initial decrease and then increases. Also in this case, as in the case of the first embodiment, the front wheel turning angle δf (s), that is, the phase of the steering reaction force depends on the vehicle steering speed δ (s If it is selected to slightly change the relationship with the phase of), for example, a characteristic indicated by a one-dot chain line or a broken line may be adopted. As for the solid line, the alternate long and short dash line, and the broken line characteristic line in FIG. 9, it is necessary to prepare a plurality of characteristic lines in accordance with the size of the time constant T as in the case of FIG.

  In the vehicle steering apparatus 10 according to the second embodiment as described above, the vertical rotation center P of the vehicle always extends in the front-rear direction passing through the center of gravity of the vehicle by the processing in steps S11 to S16 of FIG. And the target steering performance of the driver that the phase difference between the steering angle δ (s) and the front wheel steering angle δf (s) is “0”. The target yaw rate γ * (s) and the target vehicle body slip angle β * (s) as the target motion state quantity of the vehicle are calculated according to the steering operation for satisfying the above. As in the case of the first embodiment, the target front wheel turning angle δf * (s) and the target rear wheel turning angle δr * (s) are calculated, and the front wheels Wfl and Wfr and the rear wheels Wrl and Wrr are calculated. The vehicle is steered to the target front wheel turning angle δf * (s) and the target rear wheel turning angle δr * (s). Therefore, according to the second embodiment, both the target motion performance of the vehicle and the target steering feeling of the driver are realized at the same time. Therefore, the vehicle can be driven well without a sense of incongruity for the driver. In particular, the steering sensation is the same as that in the first embodiment in the important region of the steering sensation characteristic at medium speed and high speed traveling of the vehicle. This is the same in the case of the fourth and sixth embodiments described later.

  In the second embodiment, the vehicle's target motion performance is such that the vehicle's rotational center P is always present at any position in the vertical plane that passes through the center of gravity of the vehicle and extends in the front-rear direction. . However, in this case as well, the target motion performance of the vehicle may be further limited and may be modified so as to fix the longitudinal position X of the rotation instantaneous center P. In this case as well, any fixed position may be used, but in this modification, the rotation center P is within a vertical plane including the rear wheel axle.

この式２２も、時定数Ｔaが車速Ｖによって規定され、上記第２実施形態のように自由な特性（車速Ｖに応じて自由に変化する特性）に設定され得ないことを意味する。 When this target motion performance of the vehicle is employed, the rotational instant center position X of the second embodiment is equal to the horizontal distance Lr in the front-rear direction from the center of gravity of the vehicle body to the rear axle. From the above equation 20, the time constant Ta is expressed by the following equation 22.

This equation 22 also means that the time constant Ta is defined by the vehicle speed V and cannot be set to a free characteristic (a characteristic that changes freely according to the vehicle speed V) as in the second embodiment.

  In order to realize this, the main ECU 100 executes a target front / rear wheel turning angle calculation program obtained by modifying the target front / rear wheel turning angle calculation program of FIG. In this modified target front / rear wheel turning angle calculation program, the calculation of the time constant Ta in step S21 in FIG. Also in the calculation of the time constant Ta, the time constant Ta may be calculated using a time constant table representing the relationship between the vehicle speed V and the time constant Ta. Other processes are the same as those in the modification of the first embodiment.

  According to the modification of the second embodiment, the rotation center P is always fixed. Therefore, compared with the second embodiment, control is added, but the uncomfortable feeling when turning the vehicle can be reduced. it can.

c. Third Embodiment In the third embodiment, as the target motion performance of the vehicle, it is adopted that the yaw rate γ (s) and the vehicle body slip angle β (s) are always proportional to the steering wheel steering angle δ (s) without a phase difference. To do. On the other hand, as the target steering feeling characteristic of the driver, as in the case of the first embodiment, the phase difference between the steering wheel steering angle δ (s) and the front wheel lateral force Ff (s) (steering torque) is always “0”. Is adopted.

ここで、ＸＸは、ヨーレートγ(ｓ)に対する車体スリップ角β(ｓ)の比例係数である。 Also in this case, the yaw rate γ (s) with respect to the steering wheel steering angle δ (s) is expressed by the following Expression 23, as in the first embodiment. On the other hand, the vehicle body slip angle β (s) with respect to the steering wheel steering angle δ (s) is proportional to the yaw rate γ (s), and is expressed by the following equation 24.

Here, XX is a proportional coefficient of the vehicle body slip angle β (s) with respect to the yaw rate γ (s).

そして、これらの式２３〜２５を用いて、ハンドル操舵角δ(ｓ)に対する前輪横力Ｆf(ｓ)を表す上述した式８を変形すると、同式８は下記式２６のようになる。

By using these formulas 23 and 24 to transform the above-described formula 6 representing the front wheel turning angle δf (s) with respect to the steering wheel steering angle δ (s), the formula 6 becomes the following formula 25.

Then, using these equations 23 to 25 and transforming the above-described equation 8 representing the front wheel lateral force Ff (s) with respect to the steering angle δ (s), the equation 8 becomes the following equation 26.

Here, in order to achieve the driver's target steering feeling characteristic, it is considered to eliminate the phase difference between the steering angle δ (s) and the front wheel lateral force Ff (s). In this case, if the time constant T is Ta and the following equation 27 is satisfied, the term of the temporary delay disappears from the equation 26, and the front wheel lateral force Ff (s) (steering reaction force) becomes the steering wheel steering angle δ (s). Proportional without phase difference. Then, by modifying the following expression 27, the proportionality coefficient XX according to the above condition can be expressed as the following expression 28 using the time constant Ta.

  In order to realize this, the main ECU 100 executes a target front / rear wheel turning angle calculation program obtained by modifying a part of the target front / rear wheel turning angle calculation program of FIG. In the modified target front / rear wheel turning angle calculation program, in step S14 of FIG. 2, instead of calculating the rotation instantaneous center position X, the proportionality coefficient XX is calculated by executing the calculation of Equation 28 above. In step S16, the calculated proportional coefficient XX is substituted into the equation 24 to calculate the target vehicle body slip angle β * (s). Other processes are the same as those in the first embodiment.

  In this case as well, instead of the calculation of Equation 28, a proportional coefficient table that defines the relationship between the time constant Ta, the vehicle speed V, and the proportional coefficient XX is stored in advance in the main ECU 100, and the table is referred to. By doing so, the proportionality coefficient XX may be determined. In this case, the proportionality coefficient XX increases as the vehicle speed V increases as shown by the solid line in FIG. Also in this case, as in the case of the first embodiment, as the driving characteristics of the vehicle, the phase of the front wheel lateral force Ff (s) (steering reaction force) and the steering angle δ ( If it is selected that the relationship between the phase of s) and the phase is slightly changed, for example, a characteristic indicated by a one-dot chain line or a broken line may be employed. Note that it is necessary to prepare a plurality of characteristic lines according to the magnitude of the time constant T as in the case of FIG.

  In such a vehicle steering apparatus 10 according to the third embodiment, the yaw rate γ (s) and the vehicle body slip angle β ( s) always satisfies the target motion performance of the vehicle that is proportional without a phase difference, and the target steering sensory characteristic of the driver that the steering angle δ (s) and the front wheel lateral force Ff (s) are proportional without a phase difference. Therefore, the target yaw rate γ * (s) and the target vehicle body slip angle β * (s) as the target motion state quantity of the vehicle according to the steering wheel steering operation are calculated. As in the case of the first embodiment, the target front wheel turning angle δf * (s) and the target rear wheel turning angle δr * (s) are calculated, and the front wheels Wfl and Wfr and the rear wheels Wrl and Wrr are calculated. The vehicle is steered to the target front wheel turning angle δf * and the target rear wheel turning angle δr *. Therefore, both the target motion performance of the vehicle and the target steering feeling characteristic of the driver are realized at the same time by the third embodiment. Therefore, the vehicle can be driven well without a sense of incongruity for the driver.

e. Fourth Embodiment In the fourth embodiment, the target motion performance of the vehicle includes the yaw rate (s) and the vehicle body slip angle (s) with respect to the steering angle δ (s), as in the third embodiment. Is proportional without phase difference. On the other hand, as the target steering feeling characteristic of the driver, the phase difference between the steering wheel steering angle δ (s) and the front wheel turning angle δf (s) is “0” as in the case of the second embodiment. adopt.

In this case, Expressions 23 to 25 similar to those in the third embodiment are established. Then, the equation 25 is transformed as the following equation 29.

Here, in order to achieve the driver's target steering feeling characteristic, it is considered to eliminate the phase difference between the steering wheel steering angle δ (s) and the front wheel turning angle δf (s). In this case, if the time constant T is Ta and the following equation 30 holds, the term of temporary delay disappears from the equation 29, and the front wheel turning angle δf (s) is proportional to the steering wheel steering angle δ (s) without any phase difference. To do. Then, by modifying the following equation 30, the proportional coefficient XX according to the above condition can be expressed as the following equation 31 using the time constant Ta.

  In order to realize this, the main ECU 100 executes a target front / rear wheel turning angle calculation program obtained by modifying a part of the target front / rear wheel turning angle calculation program of FIG. In this modified target front and rear wheel turning angle calculation program, in step S14 of FIG. 2, instead of calculating the rotation instantaneous center position X, the proportionality coefficient XX is calculated by executing the calculation of Equation 31 above. In step S16, the calculated proportional coefficient XX is substituted into the equation 24 to calculate the target vehicle body slip angle β * (s). Other processes are the same as those in the first embodiment.

  In this case as well, instead of the calculation of Equation 31, a proportional coefficient table that defines the relationship between the time constant Ta, the vehicle speed V, and the proportional coefficient XX is stored in advance in the main ECU 100, and the table is referred to. By doing so, the proportionality coefficient XX may be determined. In this case, as indicated by a solid line in FIG. 11, as the vehicle speed V increases, the proportionality coefficient XX decreases once and then gradually increases. Also in this case, as in the case of the first embodiment, as the driving characteristics of the vehicle, depending on the vehicle speed V, the phase of the front wheel turning angle δf (s) and the phase of the steering wheel steering angle δ (s) If it is selected to slightly change the relationship, for example, a characteristic indicated by a one-dot chain line or a broken line may be adopted. Note that it is necessary to prepare a plurality of characteristic lines according to the size of the time constant T in the same manner as in the case of FIG.

  In the vehicle steering apparatus 10 according to the fourth embodiment, the yaw rate γ (s) and the vehicle body slip angle β ( s) is always proportional without phase difference, and the target steering performance characteristic of the driver that the steering angle δ (s) and the front wheel turning angle δf (s) are proportional without phase difference The target yaw rate γ * (s) and the target vehicle body slip angle β * (s) as the target motion state quantity of the vehicle are calculated according to the steering operation for satisfying the above. As in the case of the first embodiment, the target front wheel turning angle δf * (s) and the target rear wheel turning angle δr * (s) are calculated, and the front wheels Wfl and Wfr and the rear wheels Wrl and Wrr are calculated. The vehicle is steered to the target front wheel turning angle δf * and the target rear wheel turning angle δr *. Therefore, according to the fourth embodiment, both the target motion performance of the vehicle and the target steering feeling characteristic of the driver are realized at the same time. Therefore, the vehicle can be driven well without a sense of incongruity for the driver.

f. Fifth Embodiment In the fifth embodiment, it is adopted that the vehicle body slip angle β is always “0” as the target motion performance of the vehicle. On the other hand, as the target steering feeling characteristic of the driver, the steering angle δ (s) and the front wheel lateral force Ff (s) are proportional to each other without a phase difference, as in the case of the first embodiment.

Also in this case, the yaw rate γ (s) with respect to the steering angle δ (s) is also expressed by the following equation 32 as in the first embodiment. On the other hand, the vehicle body slip angle β (s) is “0” as shown in Equation 33 below.

そして、これらの式３２〜３４を用いて、ハンドル操舵角δ(ｓ)に対する前輪横力Ｆf(ｓ)を表す上述した式８を変形すると、同式８は下記式３５のようになる。

By using these equations 32 and 33 and transforming the above-described equation 6 representing the front wheel turning angle δf (s) with respect to the steering wheel steering angle δ (s), the equation 6 becomes the following equation 34.

Then, using these equations 32 to 34, when the above equation 8 representing the front wheel lateral force Ff (s) with respect to the steering angle δ (s) is modified, the equation 8 becomes the following equation 35.

Here, it is considered that the steering angle δ (s) and the front wheel lateral force Ff (s) (steering reaction force) are proportional to each other without a phase difference in order to achieve the target steering feeling characteristic of the driver. In this case, if the time constant T is Ta and the following equation 36 is established, the term of the temporary delay disappears from the equation 35, and the front wheel lateral force Ff (s) (steering reaction force) becomes the steering wheel steering angle δ (s). Proportional. That is, the time constant Ta may be defined by the following formula 36.

  In order to realize this, the main ECU 100 executes a target front / rear wheel turning angle calculation program of FIG. 12 instead of the target front / rear wheel turning angle calculation program of FIG. 2 according to the first embodiment. In this target front and rear wheel turning angle calculation program, the time constant Ta is calculated by executing the calculation of the expression 36 in step S23 of FIG. Then, using this time constant Ta, the target yaw rate γ * (s) is calculated in step S15 as in the case of the first embodiment. Since the vehicle body slip angle β (s) is “0”, in step S17, the target vehicle body slip angle β * (s) is set to “0”, and the target front wheel turning angle δf * and the target rear wheel turning angle are set. δr * is calculated. Other processes are the same as those in the first embodiment.

  In this case as well, instead of the calculation of Expression 36, a time constant table that defines the relationship between the time constant Ta and the vehicle speed V is stored in the main ECU 100 in advance, and the time constant is referenced by referring to the table. Ta may be determined. In this case, the time constant Ta decreases as the vehicle speed V increases as shown by the solid line in FIG. Also in this case, as in the case of the first embodiment, the driving characteristics of the vehicle include the phase of the front wheel lateral force Ff (s) and the phase of the steering angle δ (s) according to the vehicle speed V. If it is selected to slightly change the relationship, for example, a characteristic indicated by a one-dot chain line or a broken line may be adopted.

  In the vehicle steering apparatus 10 according to the fifth embodiment, the target motion performance of the vehicle in which the vehicle body slip angle β is always “0” by the processing of steps S11, S12, S23, and S15 in FIG. And the target motion state of the vehicle according to the steering operation of the steering wheel in order to satisfy the target steering feeling characteristic of the driver that the steering wheel steering angle δ (s) and the front wheel lateral force Ff (s) are always proportional without phase difference. A target yaw rate γ * as a quantity is calculated. As in the case of the first embodiment, the target front wheel turning angle δf * (s) and the target rear wheel turning angle δr * (s) are calculated, and the front wheels Wfl and Wfr and the rear wheels Wrl and Wrr are calculated. The vehicle is steered to the target front wheel turning angle δf * and the target rear wheel turning angle δr *. Therefore, also in the fifth embodiment, both the target motion performance of the vehicle and the target steering feeling characteristic of the driver are realized at the same time. Therefore, the vehicle can be driven well without a sense of incongruity for the driver.

g. Sixth Embodiment In the sixth embodiment, the vehicle body slip angle β is always “0” as the target motion performance of the vehicle, as in the fifth embodiment. On the other hand, as the target steering feeling characteristic of the driver, the steering wheel steering angle δ (s) and the front wheel turning angle (s) are proportional to each other without a phase difference, as in the second embodiment.

In this case, equations 32 to 34 similar to those in the fifth embodiment are established. The equation 34 is transformed as the following equation 37.

Here, in order to achieve the driver's target steering feeling characteristic, it is considered to eliminate the phase difference between the steering wheel steering angle δ (s) and the front wheel turning angle δf (s). In this case, if the time constant T is Ta and the following equation 38 holds, the term of temporary delay disappears from the equation 37, and the front wheel turning angle δf (s) is proportional to the steering wheel steering angle δ (s) without any phase difference. To do. That is, the time constant Ta may be defined by the following equation 38.

  In order to realize this, the main ECU 100 executes a target front / rear wheel turning angle calculation program obtained by modifying a part of the target front / rear wheel turning angle calculation program of FIG. 12 according to the fifth embodiment. In this modified target front / rear wheel turning angle calculation program, the time constant Ta is calculated by executing the calculation of Equation 38 in step S23 of FIG. Other processes are the same as those in the fifth embodiment.

  In this case as well, instead of the calculation of Equation 38, a time constant table that defines the relationship between the time constant Ta and the vehicle speed V is stored in the main ECU 100 in advance, and the time constant is referenced by referring to the table. Ta may be determined. In this case, the time constant Ta decreases as the vehicle speed V increases as shown by the solid line in FIG. Also in this case, as in the case of the first embodiment, as the driving characteristics of the vehicle, depending on the vehicle speed V, the phase of the front wheel turning angle δf (s) and the phase of the steering wheel steering angle δ (s) If it is selected to slightly change the relationship, for example, a characteristic indicated by a one-dot chain line or a broken line may be adopted.

  In the vehicle steering apparatus 10 according to the sixth embodiment as described above, the vehicle target that the vehicle body slip angle β is always “0” by the modified steps S11, S12, S23, and S15 of FIG. The vehicle target according to the steering operation of the steering wheel for satisfying the motion performance and the target steering feeling characteristic of the driver that the steering wheel steering angle δ (s) and the front wheel steering angle δf (s) are proportional without phase difference. A target yaw rate γ * (s) as a motion state quantity is calculated. As in the case of the first embodiment, the target front wheel turning angle δf * (s) and the target rear wheel turning angle δr * (s) are calculated, and the front wheels Wfl and Wfr and the rear wheels Wrl and Wrr are calculated. The vehicle is steered to the target front wheel turning angle δf * and the target rear wheel turning angle δr *. Therefore, both the target motion performance of the vehicle and the target steering feeling of the driver are realized at the same time in the sixth embodiment. It is possible for the driver to travel well without feeling uncomfortable for the driver.

  The embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the object of the present invention.

For example, in the first to sixth embodiments, the yaw rate γ and the vehicle body slip angle β are used as the target motion state quantity of the vehicle. However, the following equation 39 is established among the yaw rate γ, the vehicle body slip angle β, and the vehicle body lateral acceleration α.

  Therefore, instead of the yaw rate γ or the vehicle body slip angle β, the vehicle body lateral acceleration α may be used to represent the target motion state quantity of the vehicle. That is, the target vehicle body lateral acceleration α * and the target yaw rate γ * are calculated using the steering wheel steering angle δ and the vehicle speed V so as to satisfy the vehicle target motion performance and the driver's target steering feeling characteristic, or the target vehicle body The lateral acceleration α * and the vehicle body slip angle β * are calculated. The target front wheel turning angle δf * and the target rear wheel turning angle δr * are derived in accordance with the target vehicle body lateral acceleration α * and the target yaw rate γ *, or the vehicle body lateral acceleration α * and the vehicle body slip angle β *. You may do it.

1 is an overall schematic diagram of a vehicle steering apparatus according to an embodiment of the present invention. It is a flowchart showing the target front and rear wheel turning angle calculation program executed by the main ECU. It is a flowchart showing the front-wheel correction | amendment steering program performed by front-wheel motor ECU. It is a characteristic view showing the relationship between the vehicle speed V and the yaw rate gain Gy. FIG. 6 is a characteristic diagram showing a relationship between a vehicle speed V and a time constant T. FIG. 6 is a characteristic diagram showing a relationship among a vehicle speed V, a rotational moment center position X, and a time constant T. FIG. 10 is another characteristic diagram showing the relationship between the vehicle speed V and the rotational moment center position X. It is explanatory drawing for demonstrating the autorotation instantaneous center position X. FIG. It is a flowchart showing the other example of the target front and rear wheel turning angle calculation program performed by main ECU. FIG. 10 is another characteristic diagram showing the relationship between the vehicle speed V and the rotational moment center position X. It is a characteristic view showing the relationship between the vehicle speed V and the proportionality coefficient XX. It is another characteristic view showing the relationship between the vehicle speed V and the proportionality coefficient XX. It is a flowchart showing the other example of the target front and rear wheel turning angle calculation program performed by main ECU. FIG. 6 is another characteristic diagram showing the relationship between the vehicle speed V and the time constant T. FIG. 6 is another characteristic diagram showing the relationship between the vehicle speed V and the time constant T.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Steering device, 20 ... Front wheel steering part, 21 ... Steering handle, 25 ... Steering angle sensor, 30 ... Steering gear ratio variable device, 32 ... Front wheel steering angle adjustment motor, 40 ... Rear wheel steering part, 42 ... Rear wheel rolling Steering motor, 50 ... Steering control device, 60 ... Front wheel motor control unit, 61 ... Front wheel motor ECU, 62 ... Motor drive circuit, 70 ... Rear wheel motor control unit, 71 ... Rear wheel motor ECU, 72 ... Motor drive circuit, 90 ... vehicle speed sensor, 100 ... main ECU, Wfl, Wfr ... left and right front wheels, Wrl, Wrr ... left and right rear wheels.

Claims (8)

A front wheel steering actuator that steers the front wheels mechanically connected to the steering handle;
In a vehicle steering apparatus comprising a rear-wheel steering actuator that steers rear wheels,
Steering angle detection means for detecting the steering angle of the steering wheel;
Vehicle speed detection means for detecting the vehicle speed;
By using the detected steering angle of the steering wheel and the detected vehicle speed, a predetermined vehicle target motion performance is satisfied, and a phase difference between the steering angle of the steering wheel and the lateral force of the front wheels is eliminated. A target motion state quantity calculating means for calculating a target motion state quantity of the vehicle,
A target turning angle calculation means for calculating a target front wheel turning angle and a target rear wheel turning angle based on the calculated vehicle target motion state quantity;
The front wheel steering actuator and the rear wheel steering actuator are driven and controlled according to the calculated target front wheel turning angle and target rear wheel turning angle, and the front wheel and the rear wheel are set to the calculated target front wheel turning angle and A vehicle steering apparatus provided with a steering control means for performing steering control on each target rear wheel turning angle. A front wheel steering actuator that steers the front wheels mechanically connected to the steering handle;
In a vehicle steering apparatus comprising a rear-wheel steering actuator that steers rear wheels,
Steering angle detection means for detecting the steering angle of the steering wheel;
Vehicle speed detection means for detecting the vehicle speed;
Using the detected steering angle of the steering wheel and the detected vehicle speed, a predetermined target motion performance of the vehicle is satisfied, and a phase difference between the steering angle of the steering wheel and the turning angle of the front wheels is eliminated. A target motion state quantity calculating means for calculating the target motion state quantity of the vehicle,
A target turning angle calculation means for calculating a target front wheel turning angle and a target rear wheel turning angle based on the calculated vehicle target motion state quantity;
The front wheel steering actuator and the rear wheel steering actuator are driven and controlled according to the calculated target front wheel turning angle and target rear wheel turning angle, and the front wheel and the rear wheel are set to the calculated target front wheel turning angle and A vehicle steering apparatus provided with a steering control means for performing steering control on each target rear wheel turning angle.   The target motion performance of the vehicle according to claim 1 or 2, wherein the instantaneous center of rotation of the vehicle at the time of turning of the vehicle is always present at any position in a vertical plane passing through the center of gravity of the vehicle and extending in the front-rear direction. The vehicle steering device described.   4. The vehicle steering apparatus according to claim 3, wherein the instantaneous center of rotation is a fixed point that is always a predetermined distance away from the center of gravity of the vehicle.   3. The vehicle steering apparatus according to claim 1, wherein the target motion performance of the vehicle is that a yaw rate generated in a vehicle body and a vehicle body slip angle are always in a proportional relationship without a phase difference.   3. The vehicle steering apparatus according to claim 1, wherein the target motion performance of the vehicle is that a vehicle body slip angle is always “0”.   The target motion state quantity calculating means calculates a target value of a motion state quantity of one or two of the yaw rate generated in the vehicle body, the vehicle body slip angle, and the lateral acceleration generated in the vehicle body. Item 7. A vehicle steering apparatus according to any one of Items 1 to 6. The vehicle steering apparatus according to claim 7, wherein the motion state quantity of the vehicle is represented by a function of a first-order lag with respect to a steering angle of a steering wheel.

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