JP4639985B2 - Vehicle steering control device - Google Patents

Description

  The present invention relates to a steering control device for a vehicle.

  2. Description of the Related Art Conventionally, a vehicle steering control device that can independently control the steering angle of a front wheel and a rear wheel is known. For example, Patent Literature 1 describes a technique for controlling the front / rear steering angle ratio so that the turning radius of the vehicle is always smaller than the distance between the turning center and the side wall. Patent Document 2 describes a technique for performing steering control so that a side slip angle (slip angle) becomes “0” at a predetermined position of a vehicle. Further, Patent Document 3 describes a technique for performing steering control so that the yaw rate and the skid angle are along the target locus.

Japanese Examined Patent Publication No. 7-74004 JP-A-1-215672 JP-A-4-334660

  However, the techniques described in Patent Documents 1 to 3 described above sometimes lack ride comfort and running stability during turning.

  The present invention has been made to solve such problems. The object of the present invention is to perform the steering control taking into consideration the instantaneous center of yawing, thereby improving the running stability and riding during turning. An object of the present invention is to provide a vehicle steering control device capable of improving comfort.

In one aspect of the present invention, a vehicle steering control device includes: an instantaneous center selecting unit that selects a position that should be an instantaneous center of yawing based on a running state of the vehicle; and the selected position is an instantaneous center of yawing. The target vehicle body slip angle calculating means for calculating the target vehicle body slip angle and the steering angle calculation for calculating each of the steering angle of the front wheels and the steering angle of the rear wheels based on the calculated target vehicle body slip angle And a turning state determination means for determining whether the turning state is a steady turning state or a transient state based on a steering angle and a steering angular velocity of the vehicle, and the instantaneous center selecting means includes the turning state of the vehicle used as a running state, when the turning state determination means determines that the a steady turning state, the turning state-determining means determines that said a transient state situ Than even with selecting the location of the instantaneous center in the rear, to select the position of the instantaneous center on the rear side of the vehicle center of gravity of the vehicle.

The above-described vehicle steering control device is suitably used for independently steering-controlling the front wheels and the rear wheels of the vehicle. The instantaneous center selection means selects a position that should be the instantaneous center of yawing, that is, a position on a plane that includes a vehicle whose lateral speed should be “0” when turning. The target vehicle body slip angle calculating means calculates the target vehicle body slip angle so that the position selected by the instantaneous center selecting means is the instantaneous center of yawing. The steering angle calculation means calculates a front wheel steering angle and a rear wheel steering angle based on the calculated target vehicle body slip angle. In this manner, the vehicle steering control device calculates the steering angle set for each of the front wheels and the rear wheels so that the selected position is the instantaneous center when the vehicle is turning. As a result, according to the vehicle steering control apparatus described above, the instantaneous center does not move due to changes in the vehicle speed or the like when turning, that is, the instantaneous center is fixed at the same position. Comfort is improved.
More specifically, in the vehicle steering control device, the turning state determination means determines whether the turning state is a steady turning state or a transient state based on the steering angle and the steering angular velocity of the vehicle. The instantaneous center selection means uses the turning state of the vehicle as the running state, and when the turning state determination means determines that the turning state is a steady turning state , the instantaneous center selection means The center position is selected rearward, and the instantaneous center position is selected rearward of the vehicle from the center of gravity of the vehicle. Thus, based on the turning state determined by the turning state determination unit, the instantaneous center selection unit selects a position that should be the instantaneous center of yawing. This makes it possible to obtain appropriate maneuverability and stability with respect to the turning state.

In a preferred embodiment, the instantaneous center selecting means selects a position to be the instantaneous center based on the speed and steering angle of the vehicle.

  In another aspect of the vehicle steering control apparatus, the vehicle further includes target yaw rate calculating means for calculating a target yaw rate at the time of turning, and the steering angle calculating means is based on the target yaw rate and the target vehicle body slip angle. The steering angle of the front wheel and the steering angle of the rear wheel are calculated.

  In this aspect, the target yaw rate calculation means calculates the target yaw rate based on the traveling state of the vehicle. Then, the steering angle calculation means calculates the steering angle of the front wheels and the steering angle of the rear wheels based on the calculated target yaw rate and target vehicle body slip angle. As a result, the vehicle can turn appropriately in a state where the instantaneous center of yawing is set at a desired position.

  Preferably, in the above vehicle steering control device, the target vehicle body slip angle calculating means is configured such that, at the selected position, the lateral component of the speed due to turning is equal to the speed due to rotation around the center of gravity, and the reverse direction. The target vehicle slip angle can be calculated such that

  Preferred embodiments of the present invention will be described below with reference to the drawings.

[Vehicle configuration]
First, an overall configuration of a vehicle to which a steering control device according to an embodiment of the present invention is applied will be described with reference to FIG.

  FIG. 1 is a schematic diagram showing a schematic configuration of a vehicle. FIG. 1 is a view of the vehicle observed from above, with the left showing the front of the vehicle and the right showing the rear of the vehicle.

  The vehicle mainly includes an engine 1, front wheels 2fR, 2fL, rear wheels 2rR, 2rL, a front wheel steering shaft 3f, a rear wheel steering shaft 3r, a handle 4, a handle angle sensor 5, and a vehicle speed sensor. 6, a front wheel actuator 7 f, a rear wheel actuator 7 r, and a system controller 10. In the following description, regarding the components arranged symmetrically, “L” and “R” are added to the reference signs when left and right distinction is necessary, and “L” when right and left distinction is not necessary. , “R” is omitted.

  The engine 1 is an internal combustion engine that generates power by exploding an air-fuel mixture in a combustion chamber. The power generated by the engine 1 is transmitted to at least one of the front wheels 2f and the rear wheels 2r via a torque converter, a transmission, a drive shaft, and the like (not shown).

  The steering angle of the front wheel 2f is controlled by the front wheel actuator 7f via the front wheel steering shaft 3f. The steering angle of the rear wheel 2r is controlled by the rear wheel actuator 7r via the rear wheel steering shaft 3r. That is, the steering angles of the front wheels 2f and the rear wheels 2r are independently controlled (that is, individually steered).

  The handle 4 is operated in order for the driver to turn the vehicle, and the steering force by the driver is transmitted to the front wheel actuator 7f via the steering shaft. An angle (handle angle) by which the driver rotates the handle 4 is detected by a handle angle sensor 5. The handle angle detected by the handle angle sensor 5 is output to the system controller 10 as a detection signal S1. The vehicle speed sensor 6 detects the vehicle speed and outputs the detected vehicle speed to the system controller 10 as a detection signal S2.

  The front wheel actuator 7f and the rear wheel actuator 7r acquire the steering angle determined by the system controller 10 as control signals S3f and S3r. The front wheel actuator 7f and the rear wheel actuator 7r respectively steer the front wheel 2f and the rear wheel 2r with the acquired steering angle via the front wheel steering shaft 3f and the rear wheel steering shaft 3r.

  The system controller 10 is configured by a so-called ECU (Electric Control Unit) or the like, and includes a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like. The system controller 10 performs a process of determining the steering angles of the front wheels 2f and the rear wheels 2r based on the steering wheel angle acquired from the steering wheel angle sensor 5 and the vehicle speed acquired from the vehicle speed sensor 6. Specifically, the system controller 10 is based on the instantaneous center selection means for selecting the position that should be the instantaneous center of yawing, the target yaw rate calculation means for calculating the target yaw rate during steering, and the position selected by the instantaneous center selection means. The vehicle body slip angle calculating means for calculating the target vehicle body slip angle and the steering angle calculating means for calculating the steering angle of the front wheel 2f and the steering angle of the rear wheel 2r. That is, the system controller 10 functions as a steering control device.

  In the present specification, the position on the plane including the vehicle where the lateral speed when turning is “0” is referred to as “instantaneous center”.

[System controller configuration]
Here, a specific configuration of the system controller 10 described above will be described with reference to FIG.

  FIG. 2 is a block diagram illustrating a schematic configuration of the system controller 10. The system controller 10 includes a target yaw rate calculation unit 11, a target vehicle body slip angle calculation unit 12, a steering angle calculation unit 13, a front wheel steering angle command value transmission unit 14f, a rear wheel steering angle command value transmission unit 14r, A center selection unit 15.

  The handle angle sensor 5 supplies a detection signal S 1 corresponding to the detected handle angle to the target yaw rate calculation unit 11 and the instantaneous center selection unit 15. The vehicle speed sensor 6 supplies a detection signal S2 corresponding to the detected vehicle speed to the target yaw rate calculation unit 11, the target vehicle body slip angle calculation unit 12, the steering angle calculation unit 13, and the instantaneous center selection unit 15.

  The target yaw rate calculation unit 11 calculates a target yaw rate based on the acquired steering wheel angle and vehicle speed. Then, the yaw rate calculation unit 11 supplies the calculated target yaw rate as a signal S11 to the target vehicle body slip angle calculation unit 12 and the steering angle calculation unit 13.

  The instantaneous center selection unit 15 selects a position that should be the instantaneous center in the vehicle based on the acquired steering wheel angle and vehicle speed (hereinafter, the selected position is referred to as “selected position”). That is, the instantaneous center selection unit 15 selects a position on a plane including the vehicle where the lateral speed when turning should be “0” based on the traveling state. The instantaneous center selection unit 15 supplies the selected position to the target vehicle body slip angle calculation unit 12 as a signal S15. Note that the instantaneous center selection unit 15 may output a predetermined position or a position selected by the driver as a selected position instead of the position selected based on the traveling state.

  The target vehicle body slip angle calculation unit 12 calculates a target vehicle body slip angle based on the acquired target yaw rate, vehicle speed, and selected position. More specifically, the target vehicle body slip angle calculation unit 12 calculates the target vehicle body slip angle so that the selection position selected by the instantaneous center selection unit 15 becomes the instantaneous center of yawing. That is, the target vehicle body slip angle calculation unit 12 calculates the target vehicle body slip angle so that the lateral speed at the time of turning at the selected position becomes “0”. Then, the target vehicle body slip angle calculation unit 12 supplies the calculated target vehicle body slip angle to the steering angle calculation unit 13 as a signal S12.

  The steering angle calculation unit 13 sets the steering angle to be set for the front wheels 2f (hereinafter referred to as “front wheel steering angle”) and the rear wheels 2r based on the acquired target vehicle body slip angle, target yaw rate, and vehicle speed. On the other hand, a steering angle to be set (hereinafter referred to as “rear wheel steering angle”) is calculated. The steering angle calculation unit 13 supplies the calculated front wheel steering angle as a signal S13f to the front wheel steering angle command value transmission unit 14f, and uses the calculated rear wheel steering angle as a signal S13r as a rear wheel steering angle command value transmission unit 14r. To supply.

  The front wheel steering angle command value transmission unit 14f supplies a command value S3f corresponding to the acquired front wheel steering angle to the front wheel actuator 7f. Further, the rear wheel steering angle command value transmission unit 14r supplies a command value S3r corresponding to the acquired rear wheel steering angle to the rear wheel actuator 7r. The front wheel actuator 7f steers the front wheel 2f with the acquired front wheel steering angle, and the rear wheel actuator 7r steers the rear wheel 2r with the acquired rear wheel steering angle.

  As described above, in the steering control device according to the present embodiment, the front wheel steering angle and the rear wheel steering angle are calculated so that the selected position becomes the instantaneous center when the vehicle turns. Therefore, according to the steering control device according to the present embodiment, the instantaneous center does not move due to a change in the vehicle speed or the like at the time of turning, that is, the instantaneous center is fixed at the same position. improves.

[Calculation method of target body slip angle]
Next, a target vehicle body slip angle calculation method performed by the above-described target vehicle body slip angle calculation unit will be described.

(First embodiment)
First, the target vehicle body slip angle calculation method according to the first embodiment will be described with reference to FIG. FIG. 3 is a schematic diagram showing the state of the vehicle during a turn.

  For example, the vehicle is turning on the circumference of a turning radius R (distance from the turning center RC to the center of gravity G of the vehicle) around the turning center RC at a vehicle speed V, a yaw rate γ, and a vehicle body slip angle β. . In this case, the longitudinal distance of the vehicle from the turning center RC to the center of gravity G is “X”. The following formula (1) is established between the longitudinal distance X from the turning center RC to the center of gravity G and the turning radius R. Further, the following equation (2) is established for the yaw rate γ and the vehicle speed V.

X = R × sin (β) Equation (1)
V = γ × R Formula (2)
Here, a method of calculating the target yaw rate γ_ta will be described. The target yaw rate γ_ta is calculated by the target yaw rate calculation unit 11 in the system controller 10 based on the steering wheel angle MA and the vehicle speed V. Specifically, the target yaw rate calculation unit 11 calculates the target yaw rate γ_ta using a map showing the relationship between the steering wheel angle MA and the vehicle speed V and the target yaw rate γ.

  FIG. 4 shows an example of a map used for calculating the target yaw rate γ_ta. FIG. 4 shows the vehicle speed V on the horizontal axis and the yaw rate gain Gγ on the vertical axis. The yaw rate gain Gγ is expressed by the following equation (3).

Gγ = γ / MA Formula (3)
The target yaw rate calculation unit 11 determines the yaw rate gain Gγ corresponding to the vehicle speed V using the map, and calculates the target yaw rate γ_ta using the steering angle MA from the determined yaw rate gain Gγ. Specifically, the target yaw rate γ_ta is “γ_ta = Gγ × MA” by using Expression (3).

Next, returning to FIG. 3, a method of calculating the target vehicle body slip angle β_ta will be described. Here, a case will be described in which the instantaneous center selection unit 15 selects the position indicated by the symbol A as the position that should be the instantaneous center. In this case, a lateral velocity Vay is generated due to rotation around the center of gravity as shown in Equation (5). “Xa” indicates the distance from the center of gravity G to the selected position A.

Vay = γ × Xa Formula (5)

In order for the selected position A to be the instantaneous center, that is, in order for the lateral speed at the selected position A to be “0”, the magnitudes of the lateral speed Vay due to rotation around the center of gravity and the lateral component of the speed V are It must be equal and reverse. That is, at the selected position A, the following conditional expression (7) needs to be satisfied.

Vay = V × sin (β) Equation (7)
At this time, when Expression (5) is substituted into Conditional Expression (7), that is, when the lateral velocity Vay in Conditional Expression (7) is deleted using Expression (5), Conditional Expression (7) becomes Conditional Expression (8). Transformed into

sin (β) = γ · Xa / V equation (8)

  Therefore, the target vehicle body slip angle β can be expressed by the following equation (10).

β = sin ⁻¹ (Xa × γ / V) Formula (10)
Therefore, when the target yaw rate γ_ta calculated earlier is used, the target vehicle body slip angle β_ta can be expressed by the following equation (11).

β_ta = sin ⁻¹ ( Xa × γ_ta / V) Equation (11)
The target vehicle body slip angle calculation unit 12 obtains the target vehicle body slip angle β_ta by substituting the distance Xa from the center of gravity G to the selected position A, the target yaw rate γ_ta, and the vehicle speed V into Expression (11). Then, the target vehicle body slip angle calculation unit 12 supplies the calculated target vehicle body slip angle β_ta to the steering angle calculation unit 13.

  The steering angle calculator 13 calculates the front wheel steering angle δf and the rear wheel steering angle δr based on the theory of front and rear wheel active steering. Specifically, the steering angle calculation unit 13 calculates the front wheel steering angle δf and the rear wheel steering angle δr using the target yaw rate γ_ta, the target vehicle body slip angle β_ta and the vehicle speed V calculated as described above. More specifically, the steering angle calculation unit 13 calculates the front wheel steering angle δf using the following equation (12), and calculates the rear wheel steering angle δr using the following equation (13).

なお、式（１２）と式（１３）中において、「ζ」はラプラス演算子を示し、「ｍ」は車両の質量を示し、「Ｌ」は車両のホイールベースを示し、「Ｌｆ」は車両の重心Ｇから前輪２ｆのドライブシャフトまでの距離を示し、「Ｌｒ」は重心Ｇから後輪２ｒのドライブシャフトまでの距離を示し、「Ｋｆ」は前輪２ｆのコーナリングパワーを示し、「Ｋｒ」は後輪２ｒのコーナリングパワーを示し、「Ｉ」はヨー方向の慣性モーメントを示し、「δ」はハンドル角を示している（「δ」は、前述した「ＭＡ」に対応する）。

In Expressions (12) and (13), “ζ” represents a Laplace operator, “m” represents a vehicle mass, “L” represents a vehicle wheelbase, and “Lf” represents a vehicle. Indicates the distance from the center of gravity G to the drive shaft of the front wheel 2f, "Lr" indicates the distance from the center of gravity G to the drive shaft of the rear wheel 2r, "Kf" indicates the cornering power of the front wheel 2f, and "Kr" The cornering power of the rear wheel 2r is indicated, “I” indicates the moment of inertia in the yaw direction, and “δ” indicates the handle angle (“δ” corresponds to “MA” described above).

  Next, a specific example of the position selected as the position to be the instantaneous center of yawing will be described with reference to FIG. Here, the case where the selected position is fixed at a predetermined position, instead of changing the selected position according to the traveling state, will be described.

  FIG. 5 is a schematic view of the vehicle observed from above, with the top showing the front of the vehicle and the bottom showing the rear of the vehicle. FIG. 5A shows an example in which the selected position D1 is set to the center position of the axle of the rear wheel 2r. In this case, the grip feeling at the rear wheel 2r is improved by performing steering control so that the selected position D1 becomes the instantaneous center during turning. In addition, when the vehicle is traveling substantially straight, maintaining the selected position D1 at the instantaneous center improves the sense of stability against small steering (for example, lane change, etc.) when traveling straight.

  FIG. 5B shows an example in which the selected position D2 is set between the front seats 9R and 9L, that is, next to the driver (side). In this case, by performing steering control so that the selected position D2 becomes the instantaneous center at the time of turning, the driver feels a sense of being located at the center of the turning. Therefore, the smooth feeling that the driver learns in turning is improved.

(Second Embodiment)
Next, a target vehicle body slip angle calculation method according to the second embodiment will be described.

  Also in the second embodiment, the target vehicle body slip angle is calculated in consideration of the instantaneous center. However, in the first embodiment described above, the selected position selected as the position to be the instantaneous center is fixed, but in the second embodiment, the selected position is moved according to the turning of the vehicle. Specifically, in the second embodiment, the selected position is moved based on the turning state, and the target vehicle body slip angle is calculated based on the moved selected position. The target vehicle body slip angle calculation method according to the second embodiment is also executed by the controller 10 described above.

  The basic concept of the second embodiment will be described with reference to FIG.

  FIG. 6A and FIG. 6B are schematic views showing the state of the vehicle when turning. Specifically, FIG. 6A shows a view when the position indicated by the reference symbol P is the selected position, and FIG. 6B shows a view when the position indicated by the reference symbol Q is the selected position. Here, a case where the selected position is moved from the selected position P to the selected position Q will be described. Note that the selected position P is an initial position in movement, and the selected position Q is a final position in movement. The selection position P and the selection position Q are selected by the instantaneous center selection unit 15.

  First, as described above, the target yaw rate calculation unit 11 determines the yaw rate gain Gγ corresponding to the vehicle speed V using the map, and calculates the target yaw rate γ_ta using the steering angle MA from the determined yaw rate gain Gγ. Specifically, the target yaw rate γ_ta is “γ_ta = Gγ × MA” by using Expression (3). In this case, the vehicle speed V is “V = γ_ta × R” when the target yaw rate γ_ta and the turning radius R are used.

  Here, the target vehicle body slip angle βvp at the selected position P and the target vehicle body slip angle βvq at the selected position Q are expressed by the following equations (14) and (15) by using the above-described equation (11). The

βvp = sin ⁻¹ ( Lp × γ_ta / V) Equation (14)
βvq = sin ⁻¹ ( Lq × γ_ta / V) Equation (15)
In Expressions (14) and (15), “Lp” represents the distance in the front-rear direction from the selected position P to the center of gravity G in the case of the selected position P , and “Lq” represents the selected position Q in the case of the selected position Q. The distance in the front-rear direction from the center of gravity to the center of gravity G is shown.

  Furthermore, the target vehicle body slip angles βvp and βvq can be expressed using approximate expressions shown in Expressions (16) and (17).

βvp ≒ Lp × γ_ta / V Equation (16)
βvq ≒ Lq × γ_ta / V Equation (17)
Here, the target vehicle body slip angle at the initial position (hereinafter also simply referred to as “initial value”) is “βstart”, and the target vehicle body slip angle at the final position (hereinafter also simply referred to as “final value”) is “βend”. In the above example, “βstart = βvp” and “βend = βvq”. When these initial value βstart and final value βend are used, the movement amount βm of the target vehicle body slip angle is expressed by the following equation (18).

βm = βend−βstart equation (18)
In this case, the process from reaching βstart to βend can be expressed by the following equation (19).

β_ta (t) = βm (t) + βstart Equation (19)
In Expression (19), “β_ta (t)” represents the target vehicle body slip angle at time t. “Βm (t)” indicates a value to be added to βstart at time t. Therefore, when βm (t) reaches βm, β_ta (t) becomes βend.

  FIG. 7 is a diagram for explaining a specific example of a method for determining “βm (t)” in Equation (19). FIG. 7 shows time on the horizontal axis and βm (t) on the vertical axis. The curves and line segments indicated by reference numerals 31, 32, and 33 indicate specific examples of the time change of βm (t). According to the line segment indicated by reference numeral 31, βm (t) rises in proportion to the time, and according to the curve indicated by reference numeral 32, βm (t) immediately reaches βm, and according to the curve indicated by reference numeral 33. For example, βm (t) gradually reaches βm. In the above example, βm (t) gradually changes with time. However, βm (t) may be changed in a step function from “0” to “βm”.

  Note that the initial value βstart and final value βend of the target vehicle body slip angle and the target vehicle body slip angle β_ta (t) at time t are calculated by the target vehicle body slip angle calculation unit 12 described above.

  In this way, the front wheel steering angle δf and the rear wheel steering angle δr are obtained by substituting β_ta (t) calculated using the equation (19) into the equations (12) and (13). Specifically, the front wheel steering angle δf is obtained by substituting β_ta (t) into “β_ta” in equation (12), and β_ta (t) is substituted into “β_ta” in equation (13). Thus, the rear wheel steering angle δr is obtained. The front wheel steering angle δf and the rear wheel steering angle δr are calculated by the steering angle calculation unit 13.

  Here, a specific example of the method of moving the selected center in accordance with the turning state will be described with reference to FIG.

  FIG. 8 is a schematic view of the vehicle observed from above, with the top showing the front of the vehicle and the bottom showing the rear of the vehicle. In this case, the position indicated by reference numeral E1 is the initial position of the selected position, and the position indicated by reference numeral E2 is the final position of the selected position. Specifically, the middle of the front seats 9R and 9L, that is, the side (side) of the driver is selected as the initial position, and the center position of the axle of the rear wheel 2r is selected as the final position.

  In the above case, the target vehicle body slip angle calculation unit 12 is in the initial stage of turning, that is, while the driver is turning the steering wheel 4 (hereinafter, this state is also referred to as “transient state”). The target yaw rate is calculated according to the steering wheel operation. Specifically, the target vehicle body slip angle calculation unit 12 calculates the target vehicle body slip angle β_ta so that the instantaneous center is next to the driver (initial position E1) when the vehicle is in a transient state. Specifically, the target vehicle body slip angle calculation unit 12 uses the initial value βstart of the target vehicle body slip angle as the target vehicle body slip angle β_ta when the turning state is a transient state.

Then, the target vehicle body slip angle calculating unit 12 finishes the operation of turning the steering wheel 4 by the driver, that is, when the steering wheel angular velocity becomes “0” (hereinafter, this state is also referred to as “steady turning state”). Then, the target vehicle body slip angle β_ta is calculated so that the instantaneous center moves to the center position (final position E2) of the axle of the rear wheel 2r. In this case, the target vehicle body slip angle β_ta set when the instantaneous center is moved from the initial position E1 to the final position E2 can be expressed by the following equation (20). Note that “T _β ” in the equation (20) indicates a time constant of the vehicle body slip angle.

上記の式（２０）を、重心Ｇから初期位置Ｅ１までの距離Ｌ１、及び重心Ｇから最終位置Ｅ２までの距離Ｌ２を用いて変形すると、式（２１）が得られる。なお、式（２１）中の「Ｔ_γ」はヨーレートの時定数を示している。

When the above equation (20) is transformed using the distance L1 from the center of gravity G to the initial position E1 and the distance L2 from the center of gravity G to the final position E2, equation (21) is obtained. Note that “T _γ ” in the equation (21) indicates the time constant of the yaw rate.

目標車体スリップ角算出部１２は、旋回状態が定常旋回状態であるときには、上記の式（２０）又は式（２１）を用いて目標車体スリップ角β_taを算出する。このようにして算出された目標車体スリップ角β_taに基づいて操舵制御することにより、瞬間中心は運転者の隣から後輪２ｒにおける車軸の中心位置へと移動する。以上により、旋回状態が過渡状態であるときには、運転者の隣に瞬間中心があるため、旋回におけるスムーズさ（回頭性）が向上する。そして、旋回状態が定常旋回状態にあるときには、後輪２ｒの車軸の中心位置に瞬間中心があるため、後輪２ｒのグリップ感が向上し、安定した走行が可能となる。

The target vehicle body slip angle calculation unit 12 calculates the target vehicle body slip angle β_ta using the above equation (20) or equation (21) when the turning state is the steady turning state. By performing steering control based on the target vehicle body slip angle β_ta calculated in this manner, the instantaneous center moves from the side of the driver to the center position of the axle of the rear wheel 2r. As described above, when the turning state is a transient state, since the instantaneous center is next to the driver, smoothness (turning performance) in turning is improved. When the turning state is a steady turning state, the center of the axle of the rear wheel 2r has an instantaneous center, so that the grip feeling of the rear wheel 2r is improved and stable running is possible.

  The instantaneous center selection unit 15 can determine whether the turning state is a transient state or a steady turning state. In this case, the instantaneous center selection unit 15 determines the turning state based on the vehicle speed V supplied from the vehicle speed sensor 6 and the handle angle δ supplied from the handle angle sensor 5. And the instantaneous center selection part 15 selects the position which should become an instantaneous center in a vehicle based on the determination result of a turning state. As described above, the instantaneous center selection unit 15 functions as an instantaneous center selection unit and a turning state determination unit.

  Next, processing executed when the selected position is moved from the initial position E1 to the final position E2 as described above will be described with reference to FIG. FIG. 9 is a flowchart showing a process performed when the front wheel steering angle δf and the rear wheel steering angle δr are calculated. This process is repeatedly executed by the system controller 10 at a predetermined cycle. In brief, the system controller 10 calculates the target vehicle body slip angle β_ta based on the turning state of the vehicle, and calculates the front wheel steering angle δf and the rear wheel steering angle δr based on the calculated target vehicle body slip angle β_ta. .

  First, in step S101, the instantaneous center selection unit 15 of the system controller 10 determines whether or not the handle angle δ is “0”. In other words, in step S101, it is determined whether or not the vehicle is turning. The instantaneous center selection unit 15 makes a determination based on the handle angle δ supplied from the handle angle sensor 5. If the steering wheel angle δ is “0” (step S101; Yes), the process exits the flow because it is not turning. On the other hand, when the steering wheel angle δ is not “0” (step S101; No), since the vehicle is turning, the process proceeds to step S102. In this case, the turning state is in a transient state.

  In step S102, the target yaw rate calculation unit 11 in the system controller 10 calculates the target yaw rate γ_ta based on the vehicle speed V and the steering wheel angle δ, and the target vehicle body slip angle calculation unit 12 calculates based on the vehicle speed V and the steering wheel angle δ. The initial value βstart and final value βend of the target vehicle body slip angle are calculated. Specifically, the target vehicle body slip angle calculation unit 12 calculates the initial value βstart and the final value βend by obtaining the initial position and the final position of the selected position from the instantaneous center selection unit 15. When the above process ends, the process proceeds to step S103.

  In step S103, the steering angle calculation unit 13 calculates the front wheel steering angle δf and the rear wheel steering angle δr based on the initial value βstart of the target vehicle body slip angle and the target yaw rate γ_ta. In this case, since the turning state is in a transient state, the steering angle calculation unit 13 uses the initial value βstart of the target vehicle body slip angle to steer the front wheel steering angle δf and the rear wheel steering so that the initial position becomes the instantaneous center. The angle δr is calculated. Specifically, the steering angle calculation unit 13 calculates the front wheel steering angle δf and the rear wheel steering angle δr by substituting βstart into “β_ta” in the equations (12) and (13). When the above process ends, the process proceeds to step S104.

  In step S104, the instantaneous center selection unit 15 determines whether or not the steering wheel angular velocity (dδ / dt) is “0”. That is, in step S104, it is determined whether the current turning state is a transient state or a steady turning state. If the steering wheel angular velocity (dδ / dt) is “0” (step S104; Yes), the process proceeds to step S105 because the steering wheel is in a steady turning state. In this case, processing for moving the instantaneous center is performed in the processing after step S105.

  On the other hand, when the steering wheel angular velocity (dδ / dt) is not “0” (step S104; No), the turning state is still in a transient state, and thus the process exits the flow. In this case, the steering control is performed so that the initial position becomes the instantaneous center until the turning state becomes the steady turning state. That is, the steering control based on the front wheel steering angle δf and the rear wheel steering angle δr calculated using the initial value βstart of the target vehicle body slip angle is continued.

  In step S105, the target vehicle body slip angle calculation unit 12 calculates the target vehicle body slip angle β_ta using the initial value βstart and the final value βend of the target vehicle body slip angle. For example, the target vehicle body slip angle calculation unit 12 calculates the target vehicle body slip angle β_ta by substituting the initial value βstart and the final value βend calculated in step S102 into the equation (20). Then, the process proceeds to step S106.

  In step S106, the steering angle calculation unit 13 calculates the front wheel steering angle δf and the rear wheel steering angle δr based on the target vehicle body slip angle β_ta and the target yaw rate γ_ta. Specifically, the steering angle calculation unit 13 substitutes the target yaw rate γ_ta calculated in step S102 and the target vehicle body slip angle β_ta calculated in step S105 into the above-described equations (12) and (13). Thus, the front wheel steering angle δf and the rear wheel steering angle δr are calculated. By controlling the steering by the front wheel steering angle δf and the rear wheel steering angle δr thus calculated, the instantaneous center moves from the initial position to the final position. Then, the process proceeds to step S107.

  In step S107, the system controller 10 determines whether the steering wheel angular velocity (dδ / dt) is “0”. That is, in step S107, it is determined whether or not the driver further turns the handle 4. When the steering wheel angular velocity (dδ / dt) is “0” (step S107; Yes), the determination in step S107 is performed again. That is, the determination in step S107 is performed until the handle 4 is operated by the driver.

  On the other hand, when the steering wheel angular velocity (dδ / dt) is not “0”, since the driver is turning the steering wheel 4, the process exits the flow. For example, the steering wheel angular velocity (dδ / dt) is not “0” because the driver turns the steering wheel 4 when changing from turning to straight traveling or turning a curve having a different curvature. In this case, the front wheel steering angle δf and the rear wheel steering angle δr are calculated based on the newly calculated initial value βstart and final value βend of the target vehicle body slip angle.

  By executing the above processing, when the turning state is a transient state, a vehicle posture suitable for the steering operation by the driver can be obtained, and when the turning state is a steady turning state, the grip of the rear wheel 2r is obtained. A feeling improves and the stable run is attained. Thereby, it becomes possible to further improve the maneuverability and stability of the vehicle in a series of processes in turning.

1 is a schematic diagram illustrating a schematic configuration of a vehicle to which a steering control device according to an embodiment of the present invention is applied. It is a block diagram which shows schematic structure of a system controller. It is a figure for demonstrating the basic concept of 1st Embodiment. It is a figure which shows an example of the map used in order to calculate a target yaw rate. It is a figure which shows the specific example of the position selected as an instantaneous center. It is a figure for demonstrating the basic concept of 2nd Embodiment. It is a figure for demonstrating the value used in order to calculate a target vehicle body slip angle. It is a figure which shows the specific example of the method of moving a selection center. It is a flowchart which shows the calculation process of a steering angle when a selection position is moved.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2f Front wheel 2r Rear wheel 4 Handle 5 Handle angle sensor 6 Vehicle speed sensor 7f Front wheel actuator 7r Rear wheel actuator 10 System controller 11 Target yaw rate calculation part 12 Target vehicle body slip angle calculation part 13 Steering angle calculation part

Claims (4)

Instantaneous center selection means for selecting a position that should be the instantaneous center of yawing based on the running state of the vehicle;
Target vehicle body slip angle calculating means for calculating a target vehicle body slip angle so that the selected position is the instantaneous center of yawing;
Steering angle calculating means for calculating each of the steering angle of the front wheels and the steering angle of the rear wheels based on the calculated target vehicle body slip angle;
A turning state determining means for determining whether the turning state is a steady turning state or a transient state based on a steering angle and a steering angular velocity of the vehicle,
The instantaneous center selection means uses the turning state of the vehicle as the running state, and determines that the turning state determination means is in the transient state when the turning state determination means determines that the turning state is the steady turning state. The vehicle steering control device is characterized in that the position of the instantaneous center is selected rearward than the case, and the position of the instantaneous center is selected rearward of the vehicle from the center of gravity of the vehicle.   2. The vehicle steering control device according to claim 1, wherein the instantaneous center selection unit selects a position to be the instantaneous center based on a speed and a steering angle of the vehicle. A target yaw rate calculating means for calculating a target yaw rate at the time of turning;
3. The vehicle according to claim 1, wherein the steering angle calculation unit calculates a steering angle of the front wheel and a steering angle of the rear wheel based on the target yaw rate and the target vehicle body slip angle. Steering control device.   The target vehicle body slip angle calculating means calculates the target vehicle slip angle so that, at the selected position, the lateral component of the speed due to the turn and the speed due to the rotation around the center of gravity are equal and opposite to each other. The vehicle steering control device according to any one of claims 1 to 3, wherein the vehicle steering control device is a vehicle steering control device.

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