JP2003112650A - Steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of abrupt lateral force in an inner wheel when recovering from lateral movement. SOLUTION: A steering device can steer right and left wheels independently, and an actual steering angle control part 31 controls actual steering angles of the right and left wheels based on a steering angle in this steering device. It is provided with a wheel load estimation part 36 for estimating wheel load of the inner wheel during lateral movement of the vehicle and an inner wheel slip angle estimation part 38 for estimating a slip angle for a road surface of the inner wheel. The actual steering angle control part 31 controls an actual steering angle of the inner wheel so that a slip angle βf ,r of the inner wheel estimated by the inner wheel slip angle estimation part 38 becomes a zero degree or below a predetermined angle when a roll angle and a roll angle ϕobtained by a roll angle speed estimation part 37 are above a first set value ϕ1 .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steering device for individually steering left and right wheels according to a steering state of a driver.

[0002]

2. Description of the Related Art As a conventional steering device for individually steering the left and right wheels according to the steering state of the driver, for example, Japanese Patent Laid-Open No. 8-3
There is one disclosed in Japanese Patent No. 37106.
In this conventional steering device, instead of steering using a normal steering rack and a tie rod, actuators are arranged in series on the links of the left and right suspensions, and the length of the link is operated by this actuator, so that A similar steering is realized.

[0003]

By the way, the steering device for independently operating the left and right wheels as described above to steer is as follows.
When the vehicle is moving while ensuring a sufficient ground contact state of the tire, the exercise performance can be improved by making full use of the degree of freedom in setting the operation of each of the left and right wheels. However, when the load on the inner wheel is significantly reduced or becomes zero in the limit range of the turning motion of the vehicle, the steering angle itself of the tire maintained by the steering device loses its meaning. Will end up.

For example, in the situation where the load on the inner ring becomes 0 in the limit region of the turning motion of the vehicle, (A) in FIG.
As shown in (B) and (B), one inner ring 10 _IN completely loses contact with the ground, and the wheel load is applied only to the outer rings 10 _OUT , 10 _OUT . However, eventually, when the vehicle motion recovers from the turning, the inner wheel that has lost contact with the ground again starts to generate lateral force on the inner ring, but if recovery from the turning motion suddenly occurs, However, if the rudder angle given to the inner wheel that has lost contact with the ground is in a state of increasing the slip angle with respect to the road surface, there is a problem that a sudden lateral force is generated due to the ground contact recovery of the inner wheel.

Therefore, the present invention has been made in view of the above problems, and it is possible to prevent a sudden lateral force from being generated in the inner wheels when the vehicle recovers from a required lateral movement. The purpose is to provide the device.

[0006]

In order to solve the above problems, a steering apparatus according to claim 1 is configured such that the left and right wheels can be independently steered, and the left and right wheels can be steered based on a steering angle. In a steering device including an actual steering angle control means for controlling an actual steering angle, a wheel load estimating means for estimating a wheel load of an inner wheel during a lateral movement of a vehicle, and an inner wheel slip angle estimating means for estimating a slip angle of the inner wheel. And the actual steering angle control means determines the slip angle of the inner wheel estimated by the inner wheel slip angle estimating means when the wheel load of the inner wheel obtained by the wheel load estimating means is equal to or less than a first set value. 0 °
Alternatively, the actual steering angle of the inner wheel is controlled so as to be equal to or less than a predetermined angle.

The steering device according to a second aspect is the steering device according to the first aspect, wherein the first set value is a distance at which the inner wheel is not grounded with respect to a road surface. There is. Further, a steering device according to a third aspect is the steering device according to the first or second aspect, wherein the actual steering angle control means again causes the wheel load of the inner wheel to become equal to or less than the first set value. When it becomes larger than the first set value, the control is returned to the actual steering angle control based on the steering angle.

According to a fourth aspect of the present invention, in the steering system according to the first or second aspect, the actual steering angle control means determines that the wheel load of the inner wheel is equal to or less than the first set value. When it becomes larger than the first set value again,
Until the second set value, which is a value larger than the first set value, is obtained, the actual steering angle of the inner wheel is directed toward the angle based on the steering angle according to the wheel load of the inner wheel that is sequentially obtained. It is characterized by continuously changing.

According to a fifth aspect of the present invention, in the steering system according to the first to fourth aspects, the wheel load estimating means estimates the wheel load of the inner wheel based on the roll angle of the vehicle. I am trying. A steering device according to a sixth aspect is the steering device according to the first to fourth aspects, wherein the wheel load estimating means estimates the wheel load of the inner wheel based on a suspension stroke of the wheel.

[0010]

According to the steering device of the present invention, when the wheel load of the inner ring between the center of the inner ring and the road surface is equal to or less than the first set value during the lateral movement of the vehicle, the estimated slip angle of the inner ring is 0 °
Alternatively, the actual steering angle of the inner wheel is controlled so as to be equal to or less than the predetermined angle. As a result, when the vehicle tilts to some extent during lateral motion and the wheel load on the inner wheel decreases to some extent during the lateral movement, the steering device sets the slip angle of the inner wheel to 0 ° or a predetermined angle or less, thereby When the posture is restored, unnecessary lateral force is not generated on the inner ring. As a result, the vehicle is stably returned from the small posture state in which the wheel load of the inner ring is present to the normal posture.

Further, in the steering apparatus according to the second aspect, when the inner wheel is not in contact with the road surface, the slip angle of the inner wheel is set to 0 ° or less than a predetermined angle, so that the inner wheel is Since the lateral force is not generated in the inner ring when the ground contact is restored to the road surface, it is possible to eliminate the sudden generation of the lateral force due to the ground contact recovery. Further, in the steering apparatus according to claim 3, the actual steering angle based on the steering angle is changed when the wheel load of the inner wheel becomes larger than the first set value again after the wheel load becomes less than or equal to the first set value. By returning to the control, the lateral force can be prevented from being generated without impairing the driving performance of the vehicle due to the control of the actual steering angle based on the steering angle.

Further, in the steering apparatus according to the present invention, when the steering system becomes larger than the first set value again, until the second set value set larger than the first set value is obtained. The actual steering angle according to the steering angle is changed by continuously changing the actual steering angle of the inner wheel toward an angle based on the steering angle according to the wheel load of the inner wheel sequentially obtained from the distance measuring means. The transition of can be gradual.

The steering apparatus according to the fifth aspect of the present invention estimates the wheel load of the inner wheel based on the roll angle of the vehicle,
It is possible to estimate the wheel load of the inner ring without using a dedicated sensor or the like. The steering apparatus according to the sixth aspect can estimate the wheel load of the inner wheel based on the suspension stroke of the wheel, thereby estimating the wheel load of the inner wheel without using a dedicated sensor or the like.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A plurality of embodiments to which the present invention is applied will be described in detail below with reference to the drawings. This embodiment is applied to a steering device capable of individually steering the front left and right wheels by a steering actuator. (1) First Embodiment As shown in FIG. 1, the steering system according to the first embodiment includes left and right front wheels 10FL and 10FR that are steered wheels, and left and right rear wheels 10RL and 10RR that are not individually steered. Among these, the front wheels 10FL and 10FR are supported by the axles 11FL and 11FR so as to be rotatable about the steering axis with respect to the vehicle body. This front wheel 10FL, 10
The FR is not mechanically connected to the steering wheel 15 unlike a general vehicle.

As shown in FIG. 2, one end of a tie rod 13 is swingably connected to the front end of the vehicle to the axle 11FR of the front right wheel 10FR, and the front side of the vehicle is connected to the axle 11FL of the front left wheel 10FL. One end of the tie rod 13 is swingably connected to the end. And tie rod 1
The other end of 3 is an actuator 14FR mounted on the vehicle rear side of the front axle of the suspension member 12,
It is swingably connected to a 14 FL drive rod 16.

The actuators 14FR and 14FL have the same structure, and as shown in FIG. 3, rotate the motor 20 to move the drive rod 16 in the vehicle width direction, that is, in the lateral direction in FIG. In particular,
The motor 20 includes a brush 20B, a stator 20S and a rotor 2
The rotary shaft 21 of the rotor 20 is a hollow cylindrical tube, and the drive rod 16 is
Has been inserted.

The drive rod 16 is rotatably supported by a bearing 26, and the rotary shaft 21 of the motor 20 is rotatably supported by a bearing 22. The expanded diameter portion of the rotary shaft 21 has a ball screw nut 23. Is formed, drive rod 1
A male screw portion 24 of the ball screw is formed on the outer peripheral portion of 6,
A ball 25 is interposed between the two. In such actuators 14FR and 14FL, the motor 20
When power is supplied to the rotor 20R from the brush 20B, the rotary shaft 21 and the nut 23 of the ball screw rotate together with the rotor 20R, and the thrust of the screw is transmitted to the male screw portion 24 of the ball screw via the ball 25. 16 is the axial direction, that is, the left-right direction in FIG. 3, and is moved in the vehicle width direction.

When the front right wheel actuator 14FR is extended, the front right wheel 10FR is steered to the left, and when it is contracted, it is steered to the right. In addition, the front left wheel actuator 14FL
When the vehicle is extended, the front left wheel 10FL is steered to the right, and when it is contracted, the vehicle is steered to the left. In the following description, the front right steering actuator 14FR and the front left steering actuator 14FL are also simply referred to.

A steering reaction force motor 9 that applies a steering reaction force from the steering shaft 17 to the steering wheel 15 is attached to the steering shaft 17 that supports the steering wheel 15. Further, the steering device uses various sensors as steering angles for detecting steering angles δ _fL and δ _fR of the front left and right wheels 10FL and 10FR from the rotation angle of the ball screw nut 23, that is, the rotor 20R of the motor 20. Sensor 27, steering torque sensor 18 for detecting steering torque, steering angle sensor 1 for detecting steering angle
9 is equipped. Further, the vehicle includes a vehicle speed sensor 4 for detecting a vehicle speed, a yaw rate sensor 41 for detecting a yaw rate,
A lateral acceleration sensor 42 that detects a lateral acceleration generated during lateral motion or the like is mounted. Instead of the vehicle speed sensor 4, a wheel speed sensor 43 for detecting the vehicle speed from the wheel speed of each of the four wheels may be provided. The values detected by these sensors are output to the control unit 3.

The control unit 3 is provided in the vehicle as a unit for performing various calculations for controlling each part of the steering device such as the actuators 14FR and 14FL. The control unit 3 includes an input interface circuit having an A / D conversion function and a central processing unit (CP).
U), a storage device (ROM, RAM), a microcomputer having an output interface circuit having a D / A conversion function and the like, a drive circuit for converting an output signal from the microcomputer into a drive signal for driving each actuator, and the like. It is configured with. Specifically, as shown in FIG. 4, the control unit 3 includes an actual steering angle control unit 31,
The steering angle difference calculation unit 32, the inner wheel actual steering angle calculation unit 33, the outer wheel actual steering angle calculation unit 34, and the estimation calculation unit 35 are provided. Furthermore, the estimation calculation unit 35 includes a wheel load estimation unit 36, a roll angle / roll angular velocity estimation unit 37, and an inner wheel slip angle estimation unit 38.
And an outer wheel slip angle estimating section 39.

Here, the wheel load estimating section 36 constitutes a wheel load estimating means for estimating the wheel load of the inner wheel during the lateral movement of the vehicle, and the inner wheel slip angle estimating section 38 estimates the slip angle of the inner wheel. It constitutes a slip angle estimating means. The control unit 3 having such a configuration performs the following front wheel steering control.

Here, the steering device, as a series of processing,
When the inner wheel loses contact with the ground, control of the actual steering angle of the wheel based on the steering angle (hereinafter referred to as normal steering control).
To the slip angle control (hereinafter, referred to as slip angle zero control) for setting the slip angle (tire slip angle) of the inner wheel to 0 °, and after that, when the inner wheel is restored to the ground, the normal steering control is performed. The normal steering control (1-1) and the slip angle zero control (1-2) will be described below.

Note that the control described here is performed on the basis of the slip angle of the inner wheel, which is in a state where the ground has been lost, as if it were virtually grounded. The definition of the slip angle (tire slip angle) of the inner ring in 1) includes not only the state in which the inner ring is in contact with the road surface but also the concept in the state in which the inner ring has lost contact with the road surface.

(1-1) Normal Steering Control FIG. 5 shows a flowchart of the processing of the steering angle difference calculating section 32 in the normal steering control based on the steering angle. Here, the arithmetic processing does not have a step for communication in particular, but the programs and maps stored in the ROM of the storage device or various data stored in the RAM are always stored in the buffer of the arithmetic processing device. Each calculation result transmitted to the computer and calculated by the calculation processing device is also stored in the storage device as needed.

First, in step S1, the steering angle is calculated.
From the steering angle θ from the sensor 19 and the steering angle sensor 27
Front left wheel actual steering angle δ_fL, Front right wheel actual steering angle δ_fRRead in. Next
Then, in step S2,
According to another calculation process, the operation read in step S1 is performed.
Target front wheel steering angle δ according to steering angle θ_f ^*Is calculated and the next step
In step S3, individual calculation processing performed in the same step
According to the reason, the front and rear wheel steering angle difference Δδ_fL, Δδ_fRCalculate
It Specifically, the front left wheel steering angle difference Δδ_fLIs the target rear wheel rudder
Angle δ_f ^*To front left wheel steering angle δ_fLThe value obtained by subtracting the
δ_fRIs the target rear wheel steering angle δ_f ^*To front right wheel steering angle δ_fRReduced
Value. Then, this value is used as the actual steering angle control unit 31.
The actual steering angle control unit 31 outputs the input to the front left and right.
Wheel steering angle difference Δδ _fL, Δδ_fRDepending on the current value control signal
To the steering actuators 14FL and 14FR.

The steering angle difference calculation unit 32 performs the calculation processing in the above-described procedure in the normal steering control.
For example, the steering angle calculation unit 32 executes such calculation processing as timer interrupt processing for each predetermined control time ΔT (for example, 10 msec). The steering device, by the processing during the normal steering control by the control unit 3 as described above,
The front right steering actuator 14FR and the front left steering actuator 14FL have front left and right wheel steering angle differences Δδ _fL and Δδ _{fR, respectively.}
The front right steering actuator 14FR and the front left steering actuator 14FL are independently driven by outputting a current value control signal corresponding to the left and right wheels 10FL and 10FR.
Are steered independently according to the steering angle.

In this normal steering process, the actual steering angle control section 31 and the steering angle difference calculation section 32 constitute an actual steering angle control means for controlling the actual steering angles of the left and right wheels based on the steering angle. Has become. (1-2) Slip Angle Zero Control FIG. 6 shows a flowchart of the calculation processing by the estimation calculation section 35 for executing the slip angle zero control.

First, in step S11, the vehicle speed V is detected from the detection value of the vehicle speed sensor 4. As shown in FIG. 4, a wheel speed sensor 43 installed on each wheel may be provided to estimate the vehicle speed V based on the detected value of the wheel speed sensor 43. Next, in step S12, the roll angle and roll angular velocity estimation unit 37 estimates the roll angle φ of the vehicle body from the lateral acceleration Gy obtained from the lateral acceleration sensor 42, and in subsequent step S13, the displacement velocity of the vehicle body in the roll direction. Roll angular velocity (dφ / d
Estimate t).

As shown in FIG. 24, when the vehicle makes a turning motion, a roll angle φ occurs in the vehicle body, and
Roll angular velocity (dφ / dt) while the vehicle is tilting
Occurs, and these values are estimated based on the lateral acceleration Gy generated during the turning motion. Specifically, the roll angle φ is obtained based on the following relationship. (1-2-1) Wheel Load Movement Amount of Four Wheels Here, the wheel load movement amount of the four wheels obtained by using the roll angle φ as a variable will be described.

(1-2-1-1) When the wheel lateral movement force that causes centripetal acceleration acts on the vehicle body at the time of wheel load movement turning of a moment corresponding to the wheel load through the suspension link due to the roll center height, The distance between the center of gravity and the lateral force (height of center of gravity) becomes the moment lever, and the vehicle body receives the moment. In the equilibrium state, load movement that cancels the moment occurs between the four wheels, and the equilibrium state is established by the moment due to the load movement.

Furthermore, in the steady turn, the moments generated by the lateral forces of the front and rear wheels are balanced around the center of gravity. At this time,
The yaw angular velocity (yaw rate) is constant, that is, the angular acceleration is 0.
Therefore, the tire lateral force TFy _{F for} the front wheels and the tire lateral force TFy _R for the front wheels of the front and rear wheels (all of the inside and outside wheels respectively for turning) are the distance L _F (m) from the front wheel to the center of gravity and the rear wheels. To the center of gravity L _R (m). This relationship can be considered as a condition that the lateral force moments around the center of gravity due to the lateral forces acting on the front wheels and the rear wheels are balanced. Such a relationship is derived as the following equations (1) and (2).

[0032]

[Equation 1]

[0033]

[Equation 2]

Here, m (kg) is the mass of the car, and Gy
(M / sec ² ) is lateral acceleration. Also, for both front and rear wheels,
Of the roll moment around the center of weight of the vehicle due to the total lateral force of the inner and outer wheels, the height of the roll center is borne by the suspension links. This moment is balanced by the moment generated by the wheel load movement between the turning inner and outer wheels, so the wheel load movement amount between the inner and outer wheels has the opposite sign but the same magnitude. Such a relationship is derived as the following expressions (3) and (4).

[0035]

[Equation 3]

[0036]

[Equation 4]

Here, ΔFzRC _F is the amount of wheel load movement through the suspension link of the front wheels, and ΔFzR
C _R is the wheel load movement amount of minute through suspension link of the rear wheel, HR _F is the front of the roll center height,
HR _R is the roll center height of the rear wheel, T _F is the tread of the front wheel, and T _R is the tread of the rear wheel. (1-2-1-2) Wheel load movement due to roll rigidity On the other hand, the roll center at the center of gravity position was perpendicular to the line connecting the roll center of the previous section and the roll center of the rear wheel, and from the center of gravity position. It is located at the intersection of the vertical lines. Roll moment due to lateral acceleration Gy acting on the center of gravity and vehicle body roll angle φ
The roll angle φ is obtained under the condition that the moments of the roll rigidity due to the occurrence of are balanced. The moment of the roll rigidity due to the generation of the roll angle φ is balanced by the moment generated by the wheel load movement during the turning internal / external theory. Such relationships are expressed by the following equations (5) to (8).
It is introduced as an expression.

[0038]

[Equation 5]

[0039]

[Equation 6]

[0040]

[Equation 7]

[0041]

[Equation 8]

Here, HG is the height up to the center of gravity of the vehicle, HR is the roll center height at the center of gravity, and φ
Is the roll angle when the centripetal acceleration Gy occurs, and Δ
FzNR _F is a wheel load movement amount due to roll rigidity of the front wheel suspension, ΔFzNR _R is a wheel load movement amount due to roll rigidity of the front wheel suspension, NR _F is roll rigidity on the front wheel side, and NR _R is a rear wheel side. Roll rigidity.

(1-2-1-3) The total of the wheel load movement amounts of the four wheels is equal to or more than the total of the wheel load movement amounts of the four wheels due to the turning motion. ) Is the sum of the wheel load movement amount that can be obtained in () and the wheel load movement amount that can be obtained in the above item (1-2-1-2), and is the wheel load movement amount ΔFz _FR (Gy of the front right wheel. ) Is based on the following formula (9), and the wheel load movement amount ΔFz _FL (Gy) of the front left wheel is (1)
0) Equation, the wheel load movement amount of the rear right wheel ΔFz _RR (Gy)
Is the wheel load movement amount ΔFz of the front left wheel according to the following equation (11).
_RL (Gy) can be calculated by the following equation (12), and each equation is given as a function of the lateral acceleration Gy.

[0044]

[Equation 9]

[0045]

[Equation 10]

[0046]

[Equation 11]

[0047]

[Equation 12]

From the above relationship, the wheel load movement of the four wheels can be estimated, that is, the load can be estimated to decrease on the inner wheel side and increase correspondingly on the turning outer wheel side. The roll angle φ can be estimated by the equation (6). Specifically, the lateral acceleration Gy by the lateral acceleration sensor 42 is substituted into the equation (6) to obtain the roll angle φ. Further, by differentiating the roll angle φ with time, the roll angular velocity (dφ / dt)
Are seeking.

Next, step S14 and subsequent step S
At 15, the wheel load movement amount of the four wheels is estimated, and the wheel load of the four wheels is estimated based on this wheel load movement amount. Note that this estimation is performed by the wheel load estimating unit 36 that estimates the ground contact state of the inner ring with respect to the road surface by obtaining the wheel load of the inner ring. Next, in step S16, the inner wheel slip angle estimating unit 38 estimates the slip angles β _f and β _r of the front and rear inner wheels. Front and rear wheels 10F, 10R shown in FIG.
The estimation of each slip angle β _f , β _r of the front and rear inner wheels will be explained using the vehicle model consisting of.

The linear motion equation of the front and rear two-wheel model of the vehicle having two planes viewed from the vehicle coordinate system can be expressed as the following formula (13), and the motion equation in the yaw rotation direction is expressed as the following formula (14). be able to.

[0051]

[Equation 13]

[0052]

[Equation 14]

Here, V (m / sec) is the vehicle speed, and II
(Kg · m ² ) is the moment of inertia, β (rad) is the vehicle body slip angle, γ (deg / sec) is the yaw rate, and C _f and C _r (N) are each cornering acting on the front and rear inner wheels. It is the force. Here, the vehicle body slip angle β can be expressed as the following expression (15) using the relationship of the expression (13).

[0054]

[Equation 15]

Further, the slip angles β _f and β _{r of the} front and rear inner wheels
(Rad) can be expressed by the following equations (16) and (17).

[0056]

[Equation 16]

[0057]

[Equation 17]

Here, δ (rad) is the actual steering angle of the front inner wheel 10F. The lateral acceleration Gy can be calculated by using the yaw rate γ, the vehicle body slip angle β, and the vehicle speed V as shown in (18) below.
It can also be obtained as a formula.

[0059]

[Equation 18]

With the above relationships, the slip angles β _f and β _r of the front and rear inner wheels can be derived. Specifically, the slip angle β of the vehicle body is estimated by the equation (15) based on the lateral acceleration Gy from the lateral acceleration sensor 42, the yaw rate γ from the yaw rate sensor 41, and the vehicle speed V from the vehicle speed sensor 4. Then, based on the slip angle β of the vehicle body, the actual steering angle δ of the front wheels from the steering angle sensor 27, the yaw rate γ from the yaw rate sensor 41, and the vehicle speed V from the vehicle speed sensor 4, the equations (16) and (17) are given. The slip angles β _f and β _r of the front and rear inner wheels are calculated by the equation).

Next, in step S17, it is determined whether the wheel load of the inner ring is 0 or less based on the wheel load movement amount obtained in step S15. This determination is a determination as to whether or not the inner wheel has lost contact with the road surface. FIG. 8 shows the relationship between the lateral acceleration Gy and the wheel load Fz obtained in step S15. In addition, this characteristic diagram is
When the vehicle weight is biased to either the front or the rear, the two dotted lines in the figure show changes in the front and rear wheels of the turning outer wheel, and the two solid lines indicate the front and rear wheels of the inner wheel, respectively. It shows the change in the ring. As shown in this characteristic diagram, it can be seen that the decrease of the wheel load of the inner wheel appears as the increase of the wheel load of the turning outer wheel. Then, in this characteristic diagram, the wheel load Fz becomes 0 at a certain lateral acceleration Gy,
It can be seen that the ground contact of the inner ring is lost.

Although FIG. 8 shows the relationship when the vehicle speed V is fixed, FIG. 9 shows the change in the ground contact state of the inner wheel when the vehicle speed V is changed. As shown in FIG. 9, the ground contact state of the inner wheels of the front and rear wheels is mapped in the relationship between the speed V and the lateral acceleration Gy, that is, for example, the upper side of the boundary line (two solid lines in the figure) of the front and rear theory. Indicates that the tire has completely lost contact with the ground. From FIG. 9, even if the vehicle speed V is slow, the lateral acceleration G
It can be seen that the ground contact is lost when y is large, while the ground contact is not lost even when the vehicle speed V is high when the lateral acceleration Gy is small.

In step S17, the wheel load is zero.
If it is the following, that is, if the inner ring has lost contact with the ground, proceed to step S18. If the wheel load is greater than 0, that is, if the inner ring is on the ground, step S2.
Go to 0. In step S18, the behavior of the vehicle is estimated by the sign determination of the roll angle φ and the roll angular velocity (dφ / dt). FIG. 10 shows the roll angle φ and the roll angular velocity (dφ / d
The relationship with t) is shown.

The roll angle φ is information indicating the inclination of the vehicle body and also information indicating the ground contact state of the inner ring. When the roll angle φ is positive, that is, when the roll angle φ is located in the first quadrant or the fourth quadrant, it indicates that the vehicle body is performing lateral movement to the right or left, while When it is located in the second quadrant or the third quadrant, it indicates that the lateral movement is in the direction opposite to the direction of the first quadrant or the fourth quadrant.

Then, as shown in FIG.
In the second and fourth elements, a set value (absolute value) φ ₁ as a ground contact limit at which the inner wheel is in contact with the road surface is provided as a boundary for switching between the slip angle control and the normal steering control. When the roll angle φ is above this set value φ ₁ , the inner ring is in the state of losing contact with the ground, and when the roll angle φ is less than this set value φ ₁ , the inner ring is in the state of touching the ground. It will be.

On the other hand, the roll angular velocity (dφ / dt) serves as an index of the speed at which the vehicle body tilts during lateral movement, and indicates the speed in the direction in which the third element tilts in one tilt direction, Two quadrants indicate the speed in the direction in which the vehicle tilts back to the normal posture, in the other tilting direction, the first quadrant represents the speed in the direction in which the vehicle leans, and the fourth quadrant represents the vehicle's speed. It indicates the speed in the direction in which the inclination recovers to the normal posture. Therefore, the reversal of the sign of the roll angular velocity (dφ / dt) indicates that the posture of the vehicle has changed from the tilting direction to the normal posture during the turning motion, that is, the roll angular velocity (dφ / dt). When dt) is 0, it becomes the switching point.

In addition, the roll angular velocity (dφ / d
If the sign of t) is reversed, it indicates that the posture of the vehicle is switched rapidly, that is, the roll motion is transient, while the roll angular velocity (dφ / d) is relatively long.
If the sign of t) is reversed, it means that the posture of the vehicle switches slowly and the roll motion is gentle. As described above, while the roll angle φ shows static information, the roll angular velocity (dφ / dt) carries information showing the degree of recovery from the turning motion of the vehicle to the normal posture. .

The behavior of the vehicle during lateral movement is estimated by setting the roll angular velocity (dφ / dt) and the roll angle φ as coordinates in the coordinates. That is, when the roll angle φ and the roll angular velocity (dφ / dt) in the map shown in FIG. 10 are located within the first quadrant and the third quadrant, the vehicle is leaning. , Indicates that the lateral movement has started, and the roll angle φ and the roll angular velocity (dφ / d
If the vehicle is located in the second quadrant or the fourth quadrant where t) is opposite, it means that the vehicle is returning (restoring) to its original posture, and that the lateral movement is ending. Shows. As described above, the set value (absolute value) φ ₁ is such that the roll angle φ and the roll angular velocity (dφ / dt) have different signs.
It is set to the quadrant or the fourth quadrant, that is, the region where the vehicle recovers its original posture.

In step S18, the state of the vehicle behavior is identified with reference to the relationship shown in FIG. 10, which is such a so-called control timing determination map. In the present embodiment, specifically, if the vehicle is in the first quadrant or the third quadrant (in the case of the same sign), it is determined that the vehicle is still tilting, and the process proceeds to step S20. Also, the second elephant and the fourth
If it is in the quadrant (if it has the different sign), roll angle φ
Is equal to or greater than the set value φ ₁ and it is determined that the posture of the vehicle has returned to the normal posture, and the process proceeds to step S19.

Even if the wheel load is determined to be greater than 0 in step S17, in step S20 to proceed,
The actual steering angle is controlled by the normal steering control, that is, the actual steering angles of the left and right wheels are controlled by the actual steering angle control unit 31 and the steering angle difference calculation unit 32 based on the steering angle. On the other hand, in step S19, the slip angle zero control is executed by the inner wheel actual steering angle calculation unit 33. That is, the slip angle of the wheel is 0
The steering angle correction amount is determined so that the steering angle becomes 0 °, and the steering is performed in consideration of the steering angle correction amount. FIG. 11 shows a flowchart of processing of the inner wheel actual steering angle calculation unit 33 for the slip angle zero control.

First, in step S21, the step
Slip angle β of the inner ring estimated in step S16_fIs 0 °
It is determined whether or not the slip angle β of the inner ring_fIf is 0 °,
The processing is terminated without correcting the actual steering angle of the inner wheel,
Inner ring slip angle β_fIf is not 0 °, step S22
Proceed to. In step S22, the slip angle β_fTo 0 °
Target steering angle δ of the inner wheel_f ^*To calculate. For example,
The target steering angle δ is calculated back from the equation (16)._f ^*Calculate
It Next, the target steering angle δ_f ^*And the actual steering angle δ of the inner ring
Steering angle correction amount and steering angle difference Δδ_fTo calculate. That
Then, this value is output to the actual steering angle control unit 31, and the actual steering angle control is performed.
The control unit 31 receives the input steering angle difference Δδ._fCurrent according to
Value control signal to the corresponding inner wheel steering actuator
Output.

By the slip angle zero holding control in step S19 as described above, the slip angle of the inner ring becomes 0 °.
The actual steering angle of the inner wheel is controlled so that In this slip angle zero control, the actual steering angle control unit 31 and the inner wheel actual steering angle calculation unit 33 adjust the inner wheel slip angle to 0 ° when the wheel load of the inner wheel loses ground contact. The actual steering angle control means for controlling the actual steering angle is constructed.

The estimation calculation section 35 repeats the processing of steps S11 to S20 as described above. As described above, the steering device has the roll angle φ of the second quadrant or the fourth quadrant.
An elephant source, in the case of the set value phi ₁ or more, the inner ring of the slip angle do slip angle null control to 0 °, while maintaining the control until the roll angle phi becomes the set value phi ₁ , When the roll angle φ returns to the set value φ ₁ or less, the normal steering control is resumed.

With such control, the actual steering angle of the inner wheel is controlled based on the normal steering control as in the case where the ground is not lost while the ground is lost and the vehicle is leaning. Then, after that, the vehicle turns to a direction in which the posture is restored, and until the inner wheel comes into contact with the ground again, the slip angle control keeps the inner wheel at the actual steering angle such that the slip angle becomes 0 °. Then, after the touchdown, the actual steering angle of the inner wheels is controlled based on the steering angle by returning to the normal steering control again.

That is, as shown in FIG.
As the inner ring floats initially, the inner ring 10
_INWhen the vehicle starts to lose contact with the ground, the inner and outer rings 10_IN, 10
_OUTBoth have almost the same slip angle β_IN, Β_OUTHas occurred
There is. Then, for example, in the turning maintaining state, the inner ring 10_IN
Is completely in the state where it loses grounding, it is shown in Fig. 12 (B).
So that the outer ring 10 is grounded_OUTSlip angle β_{O UT}
Is increasing. Here, the outer ring 10_OUTSlip angle
The increase in the
This is done to maintain stable times. In addition, after
The slip angle control of the outer ring performed during the lateral movement described above
The slip angle of the outer ring in the turning maintaining state such as
Is controlled to be kept constant.

Further, immediately before the ground contact recovery, when the attitude of the vehicle shows the behavior toward the recovery side from the turning maintaining state, as shown in FIG. 12C, the slip angle generated on the inner wheel 10 _IN thereof. The actual steering angle of the inner wheel 10 _IN is held at an angle such that β _IN becomes 0 °, and further, the actual steering angle of the inner wheel 10 _IN is returned to an angle according to the steering angle in accordance with the ground contact recovery.

[0077] Therefore, in the state shown in FIG. 12 (B), again ground inner ring wheel load of the inner ring 10 _IN is from the state of 0 (i.e., the wheel load is generated) until its inner ring 10 _IN Since the slip angle of the inner ring 10 _IN is maintained at 0 °, the slip angle of the inner ring 10 _IN becomes 0 ° when the inner ring 10 _IN touches down.
The inner ring 10 that has lost contact with the ground
_{When IN} is restored to the grounded state, a sudden increase in lateral force due to the inner ring 10 _IN is prevented. That is, when the vehicle motion recovers from turning and the tire that has lost contact with the ground regains contact with the ground and a lateral force begins to act, the steering device keeps the slip angle at 0 ° to make a sudden lateral movement. Force generation can be prevented and the behavior of the vehicle can be kept stable.

Here, the characteristics of the tire lateral force will be described with respect to the case where the slip angle and the camber angle of the tire change. As shown by the solid line in FIG. 13, the lateral force characteristic with respect to the slip angle has substantially symmetrical characteristics with respect to the slip angle of 0 ° near the camber angle of 0 ° obtained in the normal motion region. There is. However, as shown by a broken line in FIG. 13, the lateral force characteristic loses its symmetry due to an increase in the camber angle of the tire under conditions such as the limit turning of the vehicle in which the tire loses ground contact.
The turning outer wheel of a normal automobile tire leads to a decrease in lateral force because the camber angle is in the additional direction. Therefore, during the turning motion, it is necessary to increase the slip angle in order to ensure a sufficient tire lateral force at the contact wheel. For this reason, as described above, generally, the actual steering angle of the outer wheel 10 _OUT during the turning motion is controlled in the direction in which the slip angle increases.

As described above, the steering apparatus of the first embodiment utilizes the fact that the front inner wheels are independently steerable, so that the inner wheels lose contact with the ground during the turning motion and then contact again. By steering the inner wheel so that the slip angle becomes 0 °, a sudden lateral force is prevented from being generated when the vehicle motion is recovered from turning, and the vehicle behavior is kept stable. (2) Second Embodiment Next, a steering system according to a second embodiment will be described. The steering system according to the first embodiment starts the normal steering control immediately after the inner wheel comes into contact with the ground, whereas the steering system according to the second embodiment has a predetermined condition even after the inner wheel comes into contact with the ground. Slip angle control is implemented. The configuration and control of the steering device of the second embodiment are the same as those of the steering device of the first embodiment unless otherwise stated.

The processing procedure performed by the estimation calculation section 35 of the steering system of the second embodiment is as shown in FIG. First,
In the processing from step S31 to step S36, the step S shown in FIG. 6 of the steering system according to the first embodiment is performed.
The same processing as the processing in 11 to step S16 is performed.
After such processing, in step S37, it is determined whether the load of the inner ring is 0 or less. If the load of the inner ring is 0 or less, the process proceeds to step S38, and the load of the inner ring is less than 0. If so, the process proceeds to step S41.

In step S38, a flag is set to indicate that the inner race has lost contact with the ground, and in step S39, the roll angle φ and roll angular velocity (dφ / d) are set.
The behavior of the vehicle is estimated by the sign determination of t). Further, in this step S39, it is determined whether or not it is the area A.
When coordinates are taken with the roll angle φ and the roll angular velocity (dφ / dt) as axes, as shown in FIG.
Although it can be divided into quadrants, here, as shown in FIG. 15, the first quadrant and the third quadrant, which have the same sign of the roll angle φ and the roll angular velocity (dφ / dt). Area A is provided.

Region A is a region in which the roll angle φ as an absolute value is equal to or more than the set value φ ₁ in the first quadrant and the third quadrant, and the roll angular velocity (dφ / dt) is near 0. Is. That is, in the area A, the inner ring is not grounded,
This is a region in which the vehicle still behaves in a tilting direction, but the tilting behavior is becoming gradual or the posture is about to be reversed.

In step S39, if the roll angle φ and the roll angular velocity (dφ / dt) have different signs, or even if the signs have the same sign, but within the area A, the process proceeds to step S40, and the roll angle φ And roll angular velocity (dφ / dt)
If and are the same sign and are outside the area A, the process proceeds to step S45. In step S40, similar to the process in step S19, the inner wheel actual steering angle calculation unit 3
The zero slip angle control by 3 is executed, the steering angle correction amount is determined so that the slip angle of the inner wheel becomes 0 °, and the steering is performed in consideration of the steering angle correction amount.

On the other hand, in step S41, when it is determined that the load of the inner ring is larger than 0 in step S37, the state of the flag indicating the inner ring ground contact state is determined. here,
When the flag is ON (when standing), that is, when the wheel load of the inner wheel is 0 or less until immediately before, the process proceeds to step S42, and when the flag is OFF, the step S45. Proceed to.

In step S42, it is determined whether or not the roll angle φ is within the threshold value. The threshold is defined as follows. As shown in FIG. 15, it is the second quadrant and the third quadrant, and the absolute value from the set value (hereinafter referred to as the first set value) φ ₁ indicating the ground contact limit at which the inner ring is grounded on the road surface. The second set value φ ₀ is set to the first set value φ _{1 in the} normal steering control range in FIG.
And the second set value φ ₂ is set as the threshold value.

Based on such a threshold value, step S42
Then, if the roll angle φ is within the threshold (φ ₀ <| φ | <
φ ₁ ), the process proceeds to step S 43, and when the absolute value of the roll angle φ is equal to or larger than the _first set value φ ₁ (| φ | ≧ φ ₁ ), the process proceeds to step S 40 and the absolute value of the roll angle φ is If the second set value φ ₀ or less (| φ | ≦ φ ₀ ), the above step S
Proceed to 44.

In the step S43, the inner wheel actual steering angle calculation unit 33 adjusts the actual value so that the slip angle of the inner wheel takes a value corresponding to the roll angle φ between 0 ° and the slip angle of the current tire (inner wheel) position. Processing for correcting the steering angle is performed. That is, the inner wheel actual steering angle calculation unit 33 determines the actual steering angle of the inner wheel between the angle at which the slip angle of the inner wheel becomes 0 ° and the angle based on the steering angle as a measured value of the roll angle φ.
According to.

Specifically, the inner wheel actual steering angle calculation unit 33 corrects the actual steering angle of the inner wheel so that the slip angle (slip angle of the control target) β _f 'as shown in the following equation (19). According to the roll angle φ obtained by the estimation calculation unit 35, it is determined between an angle based on the steering angle and an angle at which the slip angle of the inner wheel becomes 0 °.

[0089]

[Formula 19]

The inner wheel actual steering angle calculation unit 33 outputs the steering angle thus determined to the actual steering angle control unit 31 as a correction value of the current steering angle (steering angle difference Δδ _f ). The control unit 31
A current value control signal corresponding to the correction amount is output to the steering actuator on the inner wheel side, whereby the actual steering angle of the inner wheel is corrected. Note that in such control, the actual steering angle control unit 31 and the inner wheel actual steering angle calculation unit 33 obtain the second set value φ ₀ when the value becomes less than the first set value φ _1. Up to the angle based on the steering angle, the actual steering angle control means for continuously changing the actual steering angle of the inner wheel corresponding to the roll angle φ equivalent to the wheel load of the inner wheel that is sequentially obtained. It has become.

On the other hand, in step S44, it is determined that the inner ring has reached the ground contact state to some extent, the flag representing the inner wheel ground contact state is turned off, and the process proceeds to step S45. In step S45, when the flag is OFF in step S41 or when the roll angle φ and the roll angular velocity (dφ / dt) have the same sign in step S39 and are outside the area A. In this step S45, the normal steering control is performed in the same manner as the processing in step S20. Then, the calculation and estimation unit 35 performs the steps S31 to S as described above.
The processing of 45 is repeated.

In the steering apparatus of the second embodiment, the roll angle φ is controlled from the area A of the third quadrant to the first set value φ _{1 of} the second quadrant by the control of the actual steering angle as described above. Until the roll angle φ reaches the roll angle φ from the area A of the fourth quadrant to the first set value φ ₁ of the first quadrant, the slip angle of the inner ring becomes 0 °.
To maintain the control of the
Up to the set value φ ₀ of the inner wheel, the angle is based on the steering angle between the angle at which the slip angle of the inner wheel is 0 ° and the angle based on the steering angle. The actual steering angle of is controlled so as to continuously change.

As a result, the vehicle still behaves in the direction in which the vehicle is leaning in the state where the ground contact is lost, but the slip angle zero control is performed to make the slip angle of the inner wheel be 0 ° at the timing when the leaning behavior becomes gentle. After the start, and even after the inner ring touches down, the slip angle becomes 0 until the predetermined timing.
The actual steering angle of the inner wheel is controlled within a range from the angle set to ° to the angle based on the steering angle.

Therefore, after the inner wheel comes into contact with the ground, it smoothly connects to the slip angle generated at the actual steering angle according to the steering angle. Therefore, the steering system smoothly connects to the vehicle behavior by the normal steering control, and the sudden change when the inner wheel comes into contact with the ground is achieved. It is possible to realize slip angle control that prevents the generation of various lateral forces without impairing driving performance. As a result, for example, it is possible to suppress the stepwise change in slip angle that may occur when the transition is fast and to ensure the stability of the control end.

Further, the steering system of the second embodiment is provided with the area A, so that when the vehicle still behaves in the direction in which the vehicle tilts after non-grounding, that is, immediately after the inner wheel loses grounding. , It becomes possible to start the control for setting the slip angle of the inner ring to 0 °. For example, it is a transitional lateral motion in which the behavior from the loss of contact to the contact of the ground again is made in a short time. Even if the slip angle of the inner ring is 0 °
The responsiveness of the control to be performed is made faster, and more accurate implementation is realized.

(3) Slip angle control of outer ring For example, the inner wheel may lose contact with the ground in the limit range of the turning motion of the vehicle.
When slipping, both the inner and outer rings have almost the same slip angle.
Is occurring, as shown in (A) and (B) in FIG.
Sea urchin one inner ring 10_INHas completely lost ground
Then, the outer ring 10 _OUT, 10_OUTWheel load is only on
Therefore, it is difficult to improve the stability of the vehicle. Especially both inner rings 10
_IN, 10_INHas lost contact with the ground and is floating.
However, it is difficult to further improve the stability of the vehicle.

Therefore, the steering system of the present embodiment improves the stability of the vehicle by appropriately controlling the outer wheels also during the lateral movement. Specifically, the steering device is designed to maintain the slip angle of the front outer wheel at a constant angle when the vehicle loses contact with the ground during a lateral motion such as a turning motion. It is designed to steer independently.

(3-1) Slip Angle Holding Control FIG. 16 shows a flowchart of the calculation processing by the estimation calculating section 35 for executing the slip angle holding control. First, in step S51, the vehicle speed V is detected from the detection value of the vehicle speed sensor 4, as in step S11 of FIG. Next, in step S52,
Similar to step S12, the lateral acceleration Gy by the lateral acceleration sensor 42 is substituted into the equation (6) to estimate the roll angle φ.

Next, step S53 and the following step S
54, the steps S14 and S15
Similarly to the above, by using the equations (9) to (12), the lateral acceleration Gy and the like required by the equations are calculated.
And the like, the wheel load movement amount of the four wheels is estimated, and the wheel load of each of the four wheels is estimated from the movement amount of the wheel load. next,
In step S55, the outer wheel slip angle estimating section 39 estimates the slip angles β _F and β _R of the front and rear outer wheels.
The slip angles β _F and β _R of the front and rear outer wheels can be estimated using the vehicle model including the front and rear wheels 10F and 10R shown in FIG. That is, in the inner ring of the slip angle zero control described above, the inner ring of the slip angle beta _f, but to estimate the beta _r, in the same manner, the slip angle beta _F of the outer ring, said beta _R (16) and equation It can be expressed as in equation (17).

Specifically, as in the case of the inner ring,
Based on the lateral acceleration Gy from the lateral acceleration sensor 42, the yaw rate γ from the yaw rate sensor 41, and the vehicle speed V from the vehicle speed sensor 4, the slip angle β of the vehicle body is estimated by the equation (15). This slip angle β, the steering angle sensor 27
Actual steering angle δ _OUT of the front outer wheel and the yaw rate sensor 4
Based on the yaw rate γ from 1 and the vehicle speed V from the vehicle speed sensor 4, the slip angles β _F and β _R of the front and rear outer wheels can be estimated.

Next, in step S56, the slip angle holding control executed in step S58 described later is turned on.
If it is determined that the slip angle holding control is in the ON state, the process proceeds to step S57, and if the slip angle holding control is not in the ON state, the step proceeds to step S57. Proceed to S61. Step S5
In step 7, it is determined whether or not the wheel load of the inner ring is 0 based on the wheel load movement amount obtained in step S54. This determination is a determination as to whether or not the inner wheel has lost contact with the road surface. Here, if the wheel load of the inner ring is 0, that is, if the inner ring has lost contact with the ground, proceed to step S58. If the wheel load of the inner ring is not 0, that is, if the inner ring is grounded, step S59. Proceed to.

In step S58, the outer wheel steering angle calculation unit 3
4, the slip angle holding control is executed. The slip angle holding control controls the actual steering angle so that the slip angle of the outer wheel is held at a set value. The set value here is the slip angle of the outer wheel when the wheel load of the inner wheel becomes zero. Is. Specifically, as the slip angle holding control, the actual steering angle of the outer wheel is controlled so that the target actual steering angle corresponds to the slip angle β _F0 of the outer wheel when the wheel load of the inner wheel becomes zero. . Here, the target actual steering angle can be obtained by modifying the equation (16).
It can be obtained as the following formula (20).

[0103]

[Equation 20]

FIG. 17 is a block diagram of the outer wheel steering angle calculation unit 34.
The flowchart of the process for lip angle maintenance control is shown.
ing. First, in step S71, as shown in FIG.
The slip angle β of the vehicle body estimated in step S55,
The yaw rate γ from the yaw rate sensor 41 and the vehicle speed
The vehicle speed V from the sensor 4 is read. Then, in step S72
In addition, each value read and the slip angle held
β_F0Substituting and into the equation (20), the target steering angle δ _F ^*Calculate
Then, in the subsequent step S73, the target steering angle δ_F ^*
And the current actual steering angle δ of the outer wheel from the steering angle sensor 27._OUT
And the steering angle difference Δδ_FTo calculate. And this value
The actual steering angle control unit 31 outputs to the actual steering angle control unit 31.
The applied steering angle difference Δδ_FCorresponding to the current value control signal
It outputs to the steering actuator on the outer wheel side.

By the slip angle holding control in step S58, the actual steering angle of the outer wheel is controlled so that the current slip angle of the outer wheel becomes the slip angle of the outer wheel when the wheel load of the inner wheel becomes zero. To be done. On the other hand, in step S59, the slip angle holding control is stopped, and in the subsequent step S60, the actual steering angle is controlled by the normal steering control, and the process ends.

In step S61, it is determined whether or not the wheel load of the inner ring is 0. If the wheel load of the inner ring is 0, the process proceeds to step S62, and if the wheel load of the inner ring is not 0, step S23. To execute the normal steering control,
The process ends. In step S62, the current set value of the slip angle is set. The set value here is the slip angle of the outer wheel when the wheel load of the inner wheel becomes zero. Then, the process proceeds to step S58, and the slip angle holding control is executed.

The estimation calculation section 35 repeats the above-described steps S51 to S63. Through the above processing, the actual steering angle of the outer wheel is controlled by the slip angle holding control so that the slip angle of the outer wheel when the inner wheel loses the ground is held while the inner wheel loses the ground. When the inner wheel is grounded, the actual steering angle is controlled by the normal steering control.

As shown in FIG. 18, when the roll angle φ is taken as the horizontal axis and the roll angular velocity (dφ / dt) is taken as the vertical axis, the slip angle holding control is performed with the predetermined roll angle φ as the boundary. It can be divided into a range and the normal steering control range. As described above, the steering device performs the slip angle holding control described above when the inner wheel loses contact with the ground so that the slip angle of the outer wheel is maintained when the inner wheel loses contact with the ground. The steering angle is controlled, which prevents the slip angle of the outer wheel from increasing during lateral movement, and prevents the lateral force of the outer wheel from changing significantly, thus improving vehicle stability. Can be improved.

Here, the effect will be described with reference to examples. In FIG. 19, (A) shows the change over time of the steering angle,
19B shows a temporal change of the outer wheel actual steering angle at that time, and FIG. 19C shows a temporal change of the slip angle of the outer wheel at that time. Further, the solid lines in FIGS. 6B and 6C show the case of the normal steering control, and the broken line shows the case of the slip angle holding control. 20 and 21.
Shows the vehicle behavior when the characteristics shown in FIG. 19 are obtained. Further, in this example, a case is shown in which the inner ring has lost contact with the ground in the vicinity of about 0.75 seconds of aging.

In the case of the normal steering control, the actual steering angle of the outer wheel is controlled as shown in (B) of FIG. 19 according to the steering angle shown in (A) of FIG. The slip angle also changes as shown in (). On the other hand, when the slip angle holding control is executed, the actual steering angle of the outer wheel is controlled as shown in (B) in FIG. As shown in (), the slip angle of the outer ring shown in the vicinity of 0.75 seconds is maintained after that.

As a result, the behavior of the vehicle under the normal steering control even when the inner wheel loses the ground contact is shown in FIG.
As shown in (B) and (B), the vehicle enters in the oversteer direction while the inner wheel floats, but the behavior of the vehicle in which the slip angle holding control is performed is shown in (A) and (B) of FIG. ), It exhibits a turning motion with improved stability.

(3-2) Yaw Moment Zero Control Next, another example of appropriately controlling the outer wheel during lateral movement will be described. The steering apparatus described here controls the actual steering angle of the outer wheels so that the slip angle is such that the yaw moment, which is the turning moment in the yaw direction acting on the vehicle, becomes 0 when the inner wheels lose contact with the ground. There is. Hereinafter, this control is called yaw moment zero control. Further, the yaw moment in this case is a force acting on the vehicle by a lateral force due to the slip angles of the front and rear outer wheels. FIG. 22 shows a processing procedure performed by the outer wheel actual steering angle calculation unit 34 of the steering system.

First, in the processing from step S81 to step S85, the same processing as the processing in step S51 to step S55 shown in FIG. 16 is performed. After such processing, in step S86, it is determined whether or not the yaw moment zero control executed in step S88 described later is in the ON state (execution state),
If the yaw moment zero control is in the ON state, the process proceeds to step S87, and the yaw moment zero control is O.
If it is not in the N state, the process proceeds to step S91.

At step S87, step S84 is performed.
It is determined whether or not the wheel load of the inner ring is 0 based on the wheel load movement amount obtained by. If the wheel load of the inner ring is 0 or less, the process proceeds to step S88, and the wheel load of the inner ring is greater than 0. If so, the process proceeds to step S89. Step S8
At 8, the yaw moment zero control is executed. The actual steering angle of the outer wheel that reduces the yaw moment to 0 is derived from the following relationship.

The lateral force TFy _F acting on the front outer wheel is the wheel load T applied to the front outer wheel as shown in the following equation (21).
Fz _F and the slip angle β _{f of the} front outer wheel can be expressed as a function g. Similarly, the lateral force TFy _R acting on the rear outer wheel can be expressed by the following formula (22). Wheel load TFz _R applied to the outer ring and slip angle β _{r of the} rear outer wheel
It can be expressed as a function h having variables and. For example, an appropriate tire model is used to identify these functions g and h.

[0116]

[Equation 21]

[0117]

[Equation 22]

When both inner wheels are floating, the wheel load TFz _F applied to the front outer wheel is approximately the same value as the sum of the front outer wheel and the front inner wheel at rest, and the wheel applied to the rear outer wheel. The load TFz _R has substantially the same value as the sum of the rear outer wheel and the rear inner wheel when stationary. Further, the slip angles β _F and β _R of the front and rear outer wheels are values that can be obtained by the equations (16) and (17).

Using the lateral forces TFy _F and TFy _R of the front and rear wheels obtained as such a relationship, the yaw moment Mz generated around the center of gravity can be expressed as (23) below.

[0120]

[Equation 23]

Here, assuming that the yaw moment Mz is 0,
If the above (22) is transformed, the lateral force TFy _F of the front outer ring becomes
It is obtained as the following formula (24).

[0122]

[Equation 24]

Then, based on the function g of the equation (21), a function g'shown in the following (25) which gives a slip angle using the wheel load and the lateral force as variables is obtained, and the equation g is given in the equation (25). Lateral force TFy of the front outer wheel obtained by the equation (24)
And _F, before the slip angle beta _F1 is obtained by giving the wheel load TFZ _F of the outer ring, the slip angle beta _F1 in this case is a slip angle of the yaw moment to zero.

[0124]

[Equation 25]

The function g (lateral force T
As shown in FIG. 23, Fy) usually has a relationship that the characteristic deteriorates in a region where the tire slip angle β _t is large. Simply find the tire slip angle β _t based on the lateral force TFy. Then, since the lateral force TFy itself is also the tire slip angle β _t , the finally calculated tire slip angle β _t has a binary value and cannot be expressed as a constant function.

Therefore, the numerical solution root finding method such as Newton's method is used to obtain the function g ′ of the equation (25) that gives the slip angle β _t from the function g of the equation (21). . For the sake of simplicity, if the function g ′ of the equation (25) is limited to only the region before the peak of the function g,
It can also be obtained as the inverse function of the function g. The slip angle β _F1 when the yaw moment thus obtained is 0 is
By substituting the slip angle β _F0 in the expression (20) for substitution, the target actual steering angle δ _OUT that makes the yaw moment 0 can be obtained. Specifically, it can be obtained by the procedure according to FIG. That is, the outer wheel actual steering angle calculation unit 3
4 indicates, for example, the slip angle β in step S72.
Calculate the target rudder angle δ _F ^* by _{replacing F0} with the slip angle β _F1 ,
In the subsequent step S73, the steering angle difference Δδ _F is calculated from the target steering angle δ _F ^* and the current actual steering angle δ _OUT of the outer wheel from the steering angle sensor 27.

The actual steering angle control unit 31 outputs a current value control signal corresponding to the steering angle difference Δδ _f obtained by the outer wheel actual steering angle calculation unit 34 to the corresponding steering actuator on the outer wheel side. Then, the actual steering angle of the outer wheel is controlled to an angle that makes the yaw moment zero. On the other hand, in step S89, the yaw moment zero control is stopped,
In subsequent step S90, the actual steering angle is controlled by the normal steering control, and the process ends.

In step S91, it is determined whether the wheel load of the inner ring is 0. If the wheel load of the inner ring is 0, the process proceeds to step S88, the yaw moment zero control is executed, and the wheel load of the inner ring is determined. If is not 0, step S92
Then, the normal steering control is executed, and the process ends. The estimation calculation unit 35 performs the above steps S81-
The process of step S92 is repeated.

With the above processing, the actual steering angle of the outer wheel is controlled by the yaw moment zero control when the inner wheel loses contact with the ground, so that the yaw moment acting on the vehicle is maintained at zero. If the inner wheel is grounded, the normal steering control is performed together with the actual steering angle of the inner wheel. As shown in FIG. _24B , a lateral force is generated during the turning motion due to the front and rear outer wheels 10 _OUT having a slip angle β _t . A yaw moment is generated by this lateral force. In the zero yaw moment control, by controlling the slip angle of the front outer wheel to control the lateral force, the yaw moment due to the lateral force and the yaw moment due to the lateral force of the rear outer wheel are canceled to act on the vehicle. The yaw moment is set to 0. The steering device eliminates the yaw moment during the turning motion as described above to prevent the lateral force of the vehicle from being greatly changed, thereby improving the stability of the vehicle.

(4) Other Embodiments Needless to say, the present invention is not limited to being applied to the above-described embodiments. In the above-described embodiment, the slip angle is controlled to be 0 °, but the present invention is not limited to this. It is preferable that the slip angle of the inner wheels be set to 0 ° by the slip angle control. The angle may be set to a predetermined angle in the vicinity of 0 ° or less. The point is that when the tire that has lost contact with the ground returns to the contact state again and lateral force begins to be generated, the actual steering angle should be such that the slip angle of the inner wheel becomes such that a sudden lateral force is prevented. .

Further, in the above-described embodiment, the steering device obtains the wheel load movement from the detection value of the lateral acceleration sensor 32 as a specific example of the wheel load estimating means for estimating the wheel load of the inner wheel during the lateral movement. , The ground contact state of the inner ring is estimated by the value, but the value is not limited to this. For example,
The ground contact state between the inner wheel and the road surface may be estimated from the roll angle or the stroke amount of the wheel suspension. For example, when the suspension is in a full stroke state, it is determined that the inner ring has lost contact with the ground. Thus, by obtaining the wheel load of the inner ring based on the roll angle of the vehicle, the wheel load of the inner ring is obtained by using the roll angle generated in the vehicle during the lateral movement. By determining the wheel load of the inner ring based on the stroke of the suspension, the wheel load of the inner ring can be obtained by using the stroke of the suspension that naturally changes during the lateral movement. As a result, it is not necessary to directly measure the ground contact state between the wheel and the road surface, and the existing means is used. Needless to say, the wheel load may be directly measured using a load sensor or the like.

Further, in the above-described embodiment, the state in which the inner ring loses contact with the ground is determined by whether or not the load amount, which is the estimated value obtained by the calculation, is zero. However, the present invention is not limited to this, and such an estimated value may be compared with a set value of a value near 0 (for example, a width may be provided in such a set value). In this case, it becomes possible to absorb the estimation error amount due to the use of the sensor or the calculation, and to judge the state where the inner ring loses the ground contact based on the estimated value.

Further, in the above-described embodiment, the roll angle φ is used as a variable in FIGS. 11 and 16, and the ground state is compared with the _first set value φ ₁ which is the boundary value at which the ground is lost. Is determined. However, the present invention is not limited to this, and the distance between the center of the inner ring and the road surface, which is a value capable of determining the ground contact state, may be estimated, and the estimated distance may be used as a variable for determination.

Further, in the above-described embodiment, various equations have been concretely described in obtaining the slip angle and the wheel load movement. However, the present invention is not limited to this, and the slip angle and wheel load movement may be obtained by another theory or means. Further, in the above-described embodiment, the actual steering angle of the inner wheel is controlled according to the roll angle based on the relationship in which the linear interpolation is performed as shown in the equation (19). However, the present invention is not limited to this. For example, the actual steering angle of the inner wheel may be controlled by interpolating with a multi-order function and having a relationship determined by this. Further, in this case, the roll angle is not limited to determining the actual steering angle of the inner wheel, but the value indicating the distance between the center of the inner wheel and the road surface is used as a variable to determine the actual steering angle of the inner wheel. May be.

Further, in the above-described embodiment, the turning motion, which is a relatively gentle vehicle motion, has been described as an example of the lateral motion of the vehicle. However, the present invention is not limited to this, and for example, a sudden or transient lateral movement that occurs when the steering wheel is suddenly turned may be used.
The steering device can prevent the sudden lateral force from being generated at the time of touchdown by setting the slip angle of the inner wheel to 0 °.

In the above-described embodiment, the steering device has been described in FIGS. 1 to 3 as a structure in which the left and right wheels can be independently steered. However, the invention is not limited to this, and the left and right wheels can be independently operated. It goes without saying that the present invention can be applied to any steering device having a structure capable of steering.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a steering device according to an embodiment of the present invention.

FIG. 2 is a perspective view of main components of the steering device.

FIG. 3 is a sectional view of a steering actuator of the steering device.

FIG. 4 is a block diagram showing a specific configuration of a control unit of the steering device.

FIG. 5 is a flowchart showing a process during normal steering control of a control unit of the steering device.

FIG. 6 is a flowchart showing a control procedure for making the slip angle of the control unit of the steering system of the first embodiment 0 °.

FIG. 7 is a diagram showing front and rear wheels modeled for estimating a slip angle.

FIG. 8 is a characteristic diagram showing a relationship between lateral acceleration and wheel load.

FIG. 9 is a characteristic diagram showing the ground contact state of the inner wheel from the relationship between vehicle speed and lateral acceleration.

FIG. 10 is a diagram used for explaining a control timing at which the control unit of the steering system according to the first embodiment sets the slip angle to 0 °.

FIG. 11 is a flowchart showing a process in slip angle control of the control unit 3.

FIG. 12 is a diagram showing the behavior of the inner wheel due to lateral movement of the vehicle and slip angle control.

FIG. 13 is a characteristic diagram showing a relationship between a slip angle and a tire lateral force with different camber angles.

FIG. 14 is a flowchart showing a procedure of control for making the slip angle 0 ° by the control unit of the steering system of the second embodiment.

FIG. 15 is a diagram used for explaining a control timing for making the slip angle zero by the control unit of the steering system according to the second embodiment.

FIG. 16 is a flowchart showing a processing procedure for slip angle holding control.

FIG. 17 is a flowchart showing a processing procedure of slip angle holding control.

FIG. 18 is a diagram used for explaining the control timing of the slip angle holding control.

FIG. 19 is a diagram showing a state of the steering device during a turning motion shown as an example, (A) shows a temporal change of a steering angle, (B) shows a temporal change of an outer wheel actual steering angle, and (C). [Fig. 4] is a characteristic diagram showing a change over time in a slip angle of an outer ring.

20A and 20B show the behavior of the vehicle during a turning motion by the normal steering control in the above-described embodiment, where FIG. 20A shows a temporal change of the behavior, and FIG. FIG.

21A and 21B show the behavior of a vehicle during a turning motion by the slip angle holding control in the above embodiment, where FIG. 21A shows a temporal change of the behavior, and FIG. It is a figure which shows one posture.

FIG. 22 is a flowchart showing a processing procedure for zero yaw moment control.

FIG. 23 is a characteristic diagram showing the relationship between the tire slip angle β _t and the lateral force TFy as a general tire characteristic.

FIG. 24 is a view showing a state of the vehicle when the inner wheel has lost contact with the ground, where (A) is a view as seen from the front of the vehicle and (B) is a view as seen from the lower side of the vehicle. .

[Explanation of symbols]

3 control unit 4 speed sensor 10FL-10RR Front left wheel-Rear right wheel 14FL, 14FR actuator 19 Steering angle sensor 27 Rudder angle sensor 31 Actual steering angle control unit 32 Steering angle difference calculation unit 33 Inner wheel actual steering angle calculator 34 Outer wheel actual steering angle calculation unit 35 Estimating calculator 36-wheel load estimation section 37 Roll angle and roll angular velocity estimation unit 38 Inner wheel slip angle estimation unit 39 Outer wheel slip angle estimation unit 41 Yaw rate sensor 42 Lateral acceleration sensor 43 Wheel speed sensor

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Michito Hirahara             Nissan, Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan             Inside the automobile corporation (72) Inventor Kenji Suma             Nissan, Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan             Inside the automobile corporation F term (reference) 3D032 CC15 DA02 DA03 DA23 DA24                       DA29 DA33 DD02 EB04 EB16                       EB17 GG01

Claims (6)

[Claims] 1. A steering system comprising left and right wheels that are independently steerable and provided with actual steering angle control means for controlling the actual steering angles of the left and right wheels based on the steering angle. A wheel load estimating means for estimating the wheel load of the inner wheel during the directional movement, and an inner wheel slip angle estimating means for estimating the slip angle of the inner wheel are provided, and the actual steering angle control means is
When the wheel load of the inner ring obtained by the wheel load estimating means is less than or equal to a first set value, the inner wheel slip angle estimated by the inner wheel slip angle estimating means is 0 ° or a predetermined angle or less. A steering device for controlling the actual steering angle of the vehicle. 2. The steering system according to claim 1, wherein the first set value is 0. 3. The actual steering angle control means, based on the steering angle, when the wheel load of the inner wheel becomes equal to or lower than the first set value and then becomes larger than the first set value again. The control is returned to the control of the steering angle.
The steering device according to. 4. The actual steering angle control means sets the first set value when the wheel load of the inner wheel becomes larger than the first set value again after the wheel load becomes less than or equal to the first set value. Until the second set value, which is a larger value, is obtained, the actual steering angle of the inner wheel is continuously changed toward the angle based on the steering angle according to the wheel load of the inner wheel that is sequentially obtained. The steering apparatus according to claim 1 or 2, characterized in that. 5. The steering apparatus according to claim 1, wherein the wheel load estimating means estimates the wheel load of the inner wheel based on the roll angle of the vehicle. 6. The steering apparatus according to claim 1, wherein the wheel load estimating means estimates the wheel load of the inner wheel based on a suspension stroke of the wheel.