JP2003112651A - Steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the stability of a vehicle in lateral motion. SOLUTION: This steering device is constituted capable of independently steering each of left and right wheels and is provided with an actual steering angle control part 31 for controlling actual steering angles of the left and right wheels based on a steering angle and an estimation calculating part 35 for estimating a wheel load of an inner wheel and a slip angle of an outer wheel during the lateral motion of the vehicle. The actual steering angle control part 31 controls an actual steering angle of the outer wheel so that the slip angle of the outer wheel estimated by the estimation calculating part 35 is held to the slip angle of the outer wheel when the wheel load becomes zero, when the wheel load estimated by the estimation calculating part 35 is zero, that is, in an inner wheel floating state.

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 exercises while the tire is sufficiently in contact with the ground, the exercise performance can be improved by making full use of the degree of freedom in setting the actions of the left and right wheels. However, there is a problem that it is difficult to improve the stability of the vehicle when the wheel load of the inner wheel is significantly reduced or becomes zero in the limit range of the turning motion of the vehicle.

For example, the inner ring is
When the ground contact begins to be lost, the inner and outer wheels are almost the same.
The same slip angle occurs, but in (A) and
As shown in (B), one inner ring 10_INIs completely grounded
In the lost state, the outer ring 10 _OUT, 10_OUTOnly freight
It is difficult to improve the stability of the vehicle due to the heavy weight.
Especially both inner rings 10_IN, 10_INLoses contact with the ground and floats
Vehicle stability is further improved under
It's hard to do.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a steering system capable of improving the stability of a vehicle during lateral movement.

[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 apparatus 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 outer wheel slip angle estimating means for estimating a slip angle of an outer wheel. And the actual steering angle control means, when the wheel load of the inner wheel estimated by the wheel load estimating means is less than a set value, the slip angle of the outer wheel estimated by the outer wheel slip angle estimating means is a predetermined angle. Alternatively, it is characterized in that the actual steering angle of the outer wheel is controlled so as to be equal to or less than a predetermined angle.

According to a second aspect of the present invention, in the steering system according to the first aspect, the predetermined angle is a slip angle of the outer wheel when the wheel load of the inner wheel reaches a set value. It has a feature. The steering apparatus according to claim 3 is configured such that the left and right wheels can be independently steered, and the steering apparatus includes an actual steering angle control means for controlling the actual steering angles of the left and right wheels based on the steering angle. The apparatus includes a wheel load estimating means for estimating a wheel load of an inner wheel during a lateral motion of a vehicle, and an outer wheel slip angle estimating means for estimating a slip angle of an outer wheel, and the actual steering angle control means includes the wheel When the wheel load of the inner wheel estimated by the load estimating means is less than or equal to a set value, the slip angle of the outer wheel estimated by the outer wheel slip angle estimating means causes the yaw generated on the vehicle by each lateral force due to the slip angles of the front and rear outer wheels. It is characterized in that the actual steering angle of the outer wheel is controlled so that the turning moment of the direction becomes 0 or an angle that makes it equal to or less than a predetermined value.

According to a fourth aspect of the present invention, in the steering system according to the first to third aspects, the set value is 0.
It is characterized by being. According to a fifth aspect of the present invention, in the steering system according to the first to fourth aspects, the actual steering angle control means resets the wheel load of the inner wheel from the set value again after the wheel load of the inner wheel falls below the set value. When it becomes larger, the control is returned to the control of the actual steering angle based on the steering angle.

According to a sixth aspect of the present invention, in the steering system according to the first to fifth 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. The steering apparatus according to claim 7 is the steering apparatus according to any one of claims 1 to 5, 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 first aspect of the present invention, the estimated slip angle of the outer wheel becomes a predetermined angle or a predetermined angle when the wheel load of the inner wheel is equal to or less than a set value during the lateral movement of the vehicle. Thus, the actual steering angle of the outer wheel is controlled. As a result, when the vehicle tilts to some extent during lateral movement and the wheel load on the inner wheels decreases to some extent during the lateral movement, the steering device sets the slip angle of the outer wheel to a predetermined angle or a predetermined angle or less, thereby performing lateral movement. It prevents the slip angle of the outer ring from becoming too large. As a result, it is possible to prevent the lateral force of the outer wheel from changing significantly and to improve the stability of the vehicle during lateral movement.

Further, in the steering apparatus according to the present invention, since the predetermined angle is a slip angle of the outer wheel when the wheel load of the inner wheel reaches the set value, at least the wheel load of the inner wheel reaches the set value. It is kept below the slip angle of the outer ring. As a result, it is possible to prevent the lateral force of the outer wheel from changing significantly and to improve the stability of the vehicle during lateral movement.

Further, in the steering apparatus according to a third aspect of the present invention, when the wheel load of the inner wheel is equal to or less than a set value during the lateral movement of the vehicle during the lateral movement of the vehicle, the estimated slip angle of the outer wheel is The actual steering angle of the outer wheel is controlled so that the turning moment in the yaw direction generated in the vehicle by each lateral force due to the slip angle of the outer wheel becomes 0 or an angle that makes it equal to or less than a predetermined value. As a result, when the vehicle tilts to some extent during lateral movement and the wheel load on the inner wheels decreases to a certain extent, the steering device sets the slip angle of the outer wheels to an angle that makes the yaw direction turning moment 0 or a predetermined value or less. By doing so, it is possible to eliminate the influence of the turning moment in the yaw direction on the vehicle during lateral movement, and improve the stability of the vehicle during lateral movement.

According to a fourth aspect of the present invention, when the wheel load of the inner wheel is 0, the steering wheel has a slip angle of the outer wheel set to a predetermined angle, or a slip of the outer wheel. The turning moment in the yaw direction is 0
Alternatively, by setting the angle to a predetermined value or less, the effect of controlling the slip angle of the outer wheel can be more effectively exerted.

Further, in the steering apparatus according to the present invention, when the wheel load of the inner wheel becomes smaller than the set value and then becomes larger than the set value again, the actual steering angle is controlled based on the steering angle. By returning, it is possible to achieve the effect of improving the stability of the vehicle during lateral movement without impairing the driving performance of the vehicle by controlling the actual steering angle based on the steering angle.

Further, in the steering apparatus according to the sixth aspect, the wheel load of the inner wheel can be estimated based on the roll angle of the vehicle, so that the wheel load of the inner wheel can be estimated without using a dedicated sensor or the like. Further, in the steering apparatus according to the seventh aspect, the wheel load of the inner wheel can be estimated 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.

[0016]

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.
As shown in FIG. 1, the steering system according to the first embodiment has 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. 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 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 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. In addition, the steering device, as various sensors, from the rotation angle of the nut 23 of the ball screw, that is, the rotor 20R of the motor 20,
A steering angle sensor 27 for detecting the steering angles δ _fL , δ _fR of the front left and right wheels 10FL, 10FR, a steering torque sensor 18 for detecting the steering torque, and a steering angle sensor 19 for detecting the steering angle are provided. Further, the vehicle is equipped with a vehicle speed sensor 4 that detects a vehicle speed, a yaw rate sensor 41 that detects a yaw rate, and a lateral acceleration sensor 42 that detects a lateral acceleration that occurs during lateral movement. 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 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 and roll angular velocity estimation unit 37.
And an outer wheel slip angle estimating section 39.

The wheel load estimating section 36 constitutes a wheel load estimating means for estimating the wheel load of the inner wheel during the lateral motion of the vehicle, and the outer wheel slip angle estimating section 39 estimates the slip angle of the outer 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 control of the actual steering angle of the outer wheel that maintains the slip angle (tire slip angle) of the front outer wheel at a constant angle (hereinafter, referred to as slip angle holding control), and when the inner wheel subsequently recovers from the ground. The normal steering control is restored. Hereinafter, (1) normal steering control and (2) slip angle holding control will be described.

(1) Normal Steering Control FIG. 5 shows a flowchart of the calculation processing of the steering angle difference calculation unit 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 front wheel rudder
Angle δ_f ^*To front left wheel steering angle δ_fLThe value obtained by subtracting the
δ_fRIs the target front 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 difference calculation unit 32 executes such calculation processing as timer interrupt processing for each predetermined control time ΔT (for example, 10 msec). Through the processing during the normal steering control by the control unit 3 as described above, the steering device provides the front right steering actuator 14FR and the front left steering actuator 14FL with the front left and right wheel steering angle differences Δδ _fL and Δ, respectively.
A current value control signal corresponding to δ _fR is output to output the front right steering actuator 14FR and the front left steering actuator 14FL.
Drive the left and right wheels 10FL and 10FL independently.
The FRs are individually steered 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. (2) Slip Angle Holding Control FIG. 6 shows a flowchart of the calculation processing by the estimation calculating section 35 for executing the slip angle holding 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 from the lateral acceleration Gy obtained from the lateral acceleration sensor 42.

As shown in FIG. 17A, when the vehicle is making a turning motion, a roll angle φ is generated in the vehicle, and when the vehicle is tilting, the roll angular velocity (d
φ / dt) occurs, and the roll angle φ is estimated based on the lateral acceleration Gy generated during the turning motion. Specifically, the roll angle φ is obtained based on the following relationship.

(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. (2-1-1) When the tire lateral force that causes centripetal acceleration acts on the vehicle at the time of wheel load movement turning of the wheel load moment through the suspension link due to the roll center height, the center of gravity and lateral force of the vehicle The distance between them (the height of the center of gravity) becomes the moment lever, and the vehicle 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.

Further, in steady turning, 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).

[0033]

[Equation 1]

[0034]

[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 gravity 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 link stretching. 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).

[0036]

[Equation 3]

[0037]

[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. (2-1-2) Wheel load movement due to roll rigidity On the other hand, the roll center at the center of gravity is the line connecting the roll center of the previous section and the roll center of the rear wheel, and the perpendicular line drawn vertically from the center of gravity. It is located at the intersection. Roll moment due to lateral acceleration Gy acting on the center of gravity and vehicle 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.

[0039]

[Equation 5]

[0040]

[Equation 6]

[0041]

[Equation 7]

[0042]

[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.

(2-1-3) Total wheel load movement amount of four wheels From the above, the wheel load movement amount of each of the four wheels accompanying the turning motion
The sum of can be calculated in the item (2-1-1) above.
Wheel load movement amount and the value obtained in item (2-1-2) above.
Is the sum of the wheel load movement that can
Heavy movement amount ΔFz _FR(Gy) is the front left according to the following equation (9)
Wheel load movement ΔFz_FL(Gy) is given by the following equation (10).
Therefore, the wheel load movement amount ΔFz of the rear right wheel_RR(Gy) is the following
From equation (11), the wheel load movement amount ΔFz of the front left wheel_RL(G
y) can be calculated by the following equation (12).
Furthermore, each equation is given as a function of the lateral acceleration Gy.
Be done.

[0045]

[Equation 9]

[0046]

[Equation 10]

[0047]

[Equation 11]

[0048]

[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 on the outer wheel turning 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.

Next, step S13 and subsequent step S
At 14, 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. Specifically, using the equations (9) to (12), the lateral acceleration Gy and the like required by the equations are calculated.
The wheel load movement amount of the four wheels is estimated from 2 and the like, and the wheel load of each of the four wheels is estimated from 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 outer wheel slip angle estimating section 39 determines the slip angles β of the front and rear outer wheels.
Estimate _f and β _r . Slip angles β _f and β _{r of} front and rear outer _wheels
Will be described using a vehicle model including front and rear wheels 10F and 10R shown in FIG. The linear equation of motion 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 equation (13), and the equation of motion in the yaw rotation direction can be expressed as the following equation (14). .

[0052]

[Equation 13]

[0053]

[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 the front and rear outer wheels. It is a cornering force. Here, the vehicle body slip angle β can be expressed as the following expression (15) using the relationship of the expression (13).

[0055]

[Equation 15]

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

[0057]

[Equation 16]

[0058]

[Equation 17]

Here, δ (rad) is the actual steering angle of the front outer 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.

[0060]

[Equation 18]

The slip angles β _f and β _r of the front and rear outer wheels can be derived from the above relationship. Specifically, the slip angle β of the vehicle 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. This vehicle's slip angle β, rudder angle sensor 2
Based on the actual steering angle δ of the front wheels from 7, the yaw rate γ from the yaw rate sensor 41, and the vehicle speed V from the vehicle speed sensor 4, the slip angles β _f of the front and rear outer wheels are expressed by the equations (16) and (17). Estimate β _r .

Next, at step S16, the slip angle holding control executed at step S18 described later is turned on.
It is determined whether or not the state (execution state) is set, and if the slip angle holding control is in the ON state, the process proceeds to step S17, and if the slip angle holding control is not in the ON state, the step is performed. Proceed to S21. Step S1
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 S14. This determination is a determination as to whether or not the inner wheel has lost contact with the road surface.

Here, FIG. 9 shows the relationship between the lateral acceleration Gy and the wheel load Fz estimated in step S15.
This characteristic diagram is for the case where the vehicle weight is biased to either the front or the rear. In the figure, the two dotted lines show the changes of the front and rear wheels of the turning outer wheel, respectively. Indicate changes in the front and rear wheels of the inner ring, respectively. 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, it can be seen that the wheel load Fz becomes 0 at a certain lateral acceleration Gy and the ground contact of the inner wheel is lost.

Incidentally, while FIG. 9 shows the relationship when the vehicle speed V is fixed, FIG. 10 shows the change of the ground contact state of the inner wheel when the vehicle speed V is changed. Figure 1
By indicating as 0, 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, on the upper side of the boundary line (two solid lines in the figure) of the front and rear theory. It indicates that the tire has completely lost contact with the ground. From FIG. 10, it can be seen that even if the vehicle speed V is slow, the ground contact is lost if the lateral acceleration Gy is large, while if the lateral acceleration Gy is small, the ground contact is not lost even if the vehicle speed V is fast. I understand.

In step S17, if the wheel load of the inner ring is 0, that is, if the inner ring has lost contact with the ground, step S18 follows. If the wheel load of the inner ring is not 0, that is, the inner ring is grounded. If step S
Proceed to 19. In step S18, the outer wheel steering angle calculation unit 34 executes slip angle holding control. The slip angle holding control controls the actual steering angle so that the slip angle of the outer wheel is held at the set value, and the set value here is
It is the slip angle of the outer ring when the wheel load of the inner ring becomes zero.

Specifically, as slip angle holding control,
The actual steering angle of the outer wheels is controlled so that the target actual steering angle corresponds to the slip angle β _f0 of the outer wheels when the wheel load on the inner wheels becomes zero. Here, the target actual steering angle can be obtained as the following formula (19) by modifying the formula (16).

[0067]

[Formula 19]

FIG. 10 shows a flowchart of the processing for the slip angle holding control by the outer wheel steering angle calculation unit 34. First, in step S31, the vehicle slip angle β estimated in step S15 of FIG. 6, the yaw rate γ from the yaw rate sensor 41, and the vehicle speed V from the vehicle speed sensor 4 are read. Next, in step S32, each read value and the held slip angle β
_The target steering angle δ _f ^* is calculated by substituting _f0 and the equation (19) into the target steering angle δ _f ^* and the current actual steering angle of the outer wheel from the steering angle sensor 27 in step S33. The steering angle difference Δδ _f is calculated from δ. Then, this value is output to the actual steering angle control unit 31, and the actual steering angle control unit 31 outputs a current value control signal corresponding to the input steering angle difference Δδ _f to the corresponding outer wheel steering. Output to actuator.

By the slip angle holding control in step S18, the current slip angle of the outer wheel is
The actual rudder angle of the outer wheel is controlled so that the slip angle of the outer wheel when the wheel load of the inner wheel becomes 0 is obtained. In this slip angle holding control, the actual steering angle control unit 31 and the outer wheel actual steering angle calculation unit 34 determine that the current slip angle of the outer wheel is 0 when the wheel load of the inner wheel is 0 when the wheel load of the inner wheel loses contact with the ground. The actual rudder angle control means for controlling the actual rudder angle of the outer wheel is configured so that the slip angle of the outer wheel becomes the same.

On the other hand, in step S19, the slip angle holding control is stopped, and in the subsequent step S20, the actual steering angle is controlled by the normal steering control, that is, the actual steering angle control section 31 and the steering angle difference calculation section 32. The actual steering angle of the left and right wheels is controlled based on the steering angle, and the process ends. In step S21, 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, step S22 is performed.
If the wheel load of the inner ring is not 0, proceed to step S2.
3, the normal steering control is executed, and the process ends.

In step S22, 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 S18, and the slip angle holding control is executed. The estimation calculation unit 35 uses the above step S11.
~ The process of step S23 is repeated.

With the above-described processing, the actual steering angle of the outer wheel is maintained so that the slip angle of the outer wheel is maintained when the inner wheel loses the ground by the slip angle holding control while the inner wheel loses the ground. When the inner wheel is grounded, the actual steering angle is controlled by the normal steering control. Here, for example, the ground contact state of the inner wheel can be indicated not only as the wheel load of the inner wheel but also as the roll angle φ of the vehicle. For this reason, as shown in FIG. 11, 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 predetermined slip angle φ is taken as the boundary to hold the slip angle. It can be divided into a control range and the normal steering control range.

Here, as shown in FIG. 17, the roll angle φ and the roll angular velocity (dφ / dt) serve as information indicating the state of the vehicle when the vehicle makes a lateral motion. Also,
The predetermined roll angle φ has a value at which the inner ring loses ground contact.
The sign of the roll angle φ also indicates the inclination direction of the vehicle, and therefore, for example, in the present embodiment, the vehicle in which the right wheel forms the inner ring on the first and fourth quadrant sides. In this case, the left wheel is the control target of the actual steering angle by the slip angle holding control, while the second and third quadrant sides are the wheel tilt directions in which the left wheel is the inner wheel. In this case, the right wheel becomes the control target of the actual steering angle by the slip angle holding control.

The roll angular velocity on the vertical axis (dφ / d
t) is an index of the speed at which the vehicle leans during lateral movement,
That is, in the present embodiment, the third quadrant represents the speed of tilting to the left, the second quadrant represents the speed of recovering from the left tilt to the normal posture, and The original represents the speed of leaning to the right, and the fourth quadrant represents the speed of recovery from the tilt to the right to the normal posture. The slip angle holding control and the normal steering control are
As shown in FIG. 11, the switching is performed at a timing with the roll angle φ as a variable.

As described above, the steering device performs the above-described slip angle holding control when the inner wheel loses contact with the ground,
The actual steering angle of the outer wheel is controlled so that the slip angle of the outer wheel when the inner wheel loses contact with the ground is maintained.
It is possible to prevent the slip angle of the outer wheel from increasing during lateral movement, prevent the lateral force of the outer wheel from changing significantly, and improve the stability of the vehicle.

Here, the effect will be described with reference to examples. In FIG. 12, (A) shows the change over time of the steering angle,
12B shows the time-dependent change of the outer wheel actual steering angle at that time, and FIG. 12C shows the time-dependent change of the outer wheel slip angle 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. Also, FIG. 13 and FIG.
Shows the vehicle behavior when the characteristics shown in FIG. 12 are obtained. In addition, the arrow A in the figure is the time when the inner ring has lost contact with the ground, which is around 0.75 seconds due to a change over time.

In the case of the normal steering control, the actual steering angle of the outer wheel is controlled as shown in (B) of FIG. 12 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 performed, the actual steering angle of the outer wheel is controlled from the vicinity of the arrow A where the inner wheel has lost contact with the ground, as shown in (B) of FIG. ),
The slip angle of the outer ring shown in the vicinity of arrow A is maintained thereafter.

As a result, the behavior of the vehicle under the normal steering control even when the inner wheels have lost contact with the ground is shown in FIG.
As shown in (B) and (B), the vehicle enters in the oversteer direction while the inner ring 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) Yaw Moment Zero Control (Second Embodiment) Next, a steering system according to a second embodiment will be described. The steering system according to the second embodiment is configured such that when the inner wheel loses contact with the ground, the actual steering angle of the outer wheel is adjusted so that the yaw moment, which is the turning moment in the yaw direction acting on the vehicle, becomes zero. Are in control. Here, the yaw moment in this case is a force acting on the vehicle by the lateral force due to the slip angles of the front and rear outer wheels. 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 according to the second embodiment is as shown in FIG.

First, in the processing from step S41 to step S45, the steering apparatus of the first embodiment shown in FIG.
The same processing as the processing in steps S11 to S15 shown in FIG. After such processing, step S
At 46, it is judged whether or not the control for setting the yaw moment to 0 (hereinafter referred to as yaw moment zero control) executed in step S48 described later is in the ON state (execution state), and the yaw moment zero control is performed. Is ON, the process proceeds to step S47, and if the yaw moment zero control is not ON, the process proceeds to step S51.

At step S47, the step S44 is executed.
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 S48, and the wheel load of the inner ring is greater than 0. If so, the process proceeds to step S49. Step S4
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 (20).
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 (21) as shown in the following equation (21). 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.

[0083]

[Equation 20]

[0084]

[Equation 21]

When both inner wheels are floating, the wheel load TFz _F applied to the front outer wheel is approximately the same 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. The slip angles β _f and β _r of the front and rear outer wheels are values that can be obtained by the above 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 (22) below.

[0087]

[Equation 22]

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 (23).

[0089]

[Equation 23]

Then, based on the function g of the equation (20), a function g ′ shown in the following (24) which gives the slip angle with the wheel load and the lateral force as variables is obtained, and the equation (24) is obtained by the above. Lateral force TFy of the front outer wheel obtained by the equation (23)
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 at this time is the slip angle of the yaw moment to zero.

[0091]

[Equation 24]

The function g (lateral force T
As shown in FIG. 16, 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, a numerical solution method such as Newton's method is used to obtain the function g ′ of the equation (24) that gives the slip angle β _t from the function g of the equation (20). . Note that, for the sake of simplicity, if the function g ′ of the equation (24) 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 equation (19) for substitution, the target actual steering angle δ 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 34
However, in step S32, for example, the slip angle β _f0
To the slip angle β _f1 to calculate the target steering angle δ _f ^*, and in the subsequent step S33, the target steering angle δ _f ^* and the current actual steering angle δ of the outer wheel from the steering angle sensor 27 are calculated. The steering angle difference Δδ _f is calculated.

Then, 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. In this zero yaw moment control, the actual steering angle control unit 31 and the outer wheel actual steering angle calculation unit 34 determine the angle at which the yaw moment is 0 when the wheel load of the inner wheel loses contact with the slip angle of the outer wheel. The actual rudder angle control means for controlling the actual rudder angle of the outer wheel is configured as described above.

On the other hand, in step S49, the yaw moment zero control is stopped, and in the subsequent step S50, the actual steering angle is controlled by the normal steering control, and the process ends. In step S51, 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 S48, the yaw moment zero control is executed, and the wheel load of the inner ring is not 0. In this case, the process proceeds to step S52, the normal steering control is executed, and the process ends.

The estimation calculation section 35 repeats the above-described steps S41 to S52. With the above-described 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, and the yaw moment acting on the vehicle is maintained at 0. Is grounded, the normal steering control is performed together with the actual steering angle of the inner wheel.

As shown in FIG. 17B, 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. Secondly, the steering system according to the second embodiment aims to improve the stability of the vehicle by eliminating the yaw moment during the turning motion to prevent the lateral force of the vehicle from being greatly changed. There is.

(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 steering device includes the lateral acceleration sensor 42 as a specific example of the wheel load estimating means for estimating the wheel load of the inner wheel during the lateral movement.
The wheel load movement is obtained from the detected value of and the ground contact state of the inner ring is estimated by the value, but the present invention 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 suspension stroke amount of the wheel. 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 wheel based on the roll angle of the vehicle, the wheel load is obtained by using the roll angle generated in the vehicle during lateral movement. By determining the wheel load of the inner wheel based on the stroke, the wheel load can be determined by using the stroke of the suspension which naturally changes during the lateral movement. As a result, it is not necessary to directly measure the ground contact state between the wheels and the road surface, and the existing means can be 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 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 is possible to improve the stability of the vehicle by preventing the lateral force of the vehicle from being significantly changed even in the limit posture in which the vehicle does not reach the ground contact but loses the ground contact. Further, 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.

Here, in the above-described first embodiment, the actual steering angle of the outer wheel is set so as to maintain the slip angle when the outer wheel loses contact with the ground. However, even when the turning limit posture is reached, that is, even when the predetermined wheel load is applied in the contact area, the slip angle of the outer wheel at this time may be held in the turning limit posture. As a result, it is possible to prevent the slip angle of the outer wheel from increasing during the limit posture, prevent the lateral force of the outer wheel from significantly changing, and improve the stability of the vehicle.

However, when the inner wheel loses contact with the ground, the vehicle behavior is dominated by the outer wheel behavior. Therefore, particularly when the inner ring has lost contact with the ground as in the above-described embodiment, maintaining the slip angle constant or reducing the yaw moment to zero is more effective in improving stability. It can be said to work. Further, in the above-described first embodiment, the held slip angle is the slip angle when the predetermined wheel load is applied. However, the present invention is not limited to this, and may be an arbitrary predetermined angle or a predetermined predetermined angle or less. As a result, it is possible to prevent the lateral force of the outer wheel from changing significantly due to a large change in the slip angle of the outer wheel during the turning motion, and it is possible to improve the stability of the vehicle.

Further, in the above-described second embodiment, the yaw moment is controlled to be 0, but the present invention is not limited to this. Although it is preferable to set the yaw moment to 0, the yaw rate may be set to a predetermined angle in the vicinity of 0 or less in consideration of the control characteristics of the actual steering angle of the outer wheel and the errors of various estimated values. Also in this case, the steering system
The same effect as when the yaw moment is set to 0 can be obtained.

Further, in the above-mentioned embodiment, various equations have been concretely described for 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 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 may be a sudden or transient lateral movement generated by, for example, turning the steering wheel suddenly.

Further, in the above-mentioned embodiment, the steering device has a structure in which the left and right wheels can be independently steered in FIGS. 1 to 3, but the present invention is not limited to this, and the left and right wheels are independent. 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 control procedure during normal steering control of the control unit.

FIG. 6 is a flowchart showing a control procedure executed by a control unit of the steering system according to the first embodiment.

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 flowchart showing a processing procedure of slip angle holding control.

FIG. 11 is a diagram used for explaining a control timing of the slip angle holding control.

FIG. 12 is a view showing a state of the steering device during turning motion shown as an example, (A) shows a change with time of a steering angle, (B) shows a change with time 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.

13A and 13B show a behavior of a vehicle during a turning motion by the normal steering control in the above-described embodiment, FIG. 13A shows a temporal change of the behavior, and FIG. FIG.

14A and 14B show a behavior of a vehicle during a turning motion by a slip angle holding control in the above-described embodiment, FIG. 14A shows a temporal change of the behavior, and FIG. It is a figure which shows one posture.

FIG. 15 is a flowchart showing a control procedure executed by a control unit of the steering system according to the second embodiment.

FIG. 16 is a characteristic diagram showing a relationship between a tire slip angle β _t and a lateral force TFy as a general tire characteristic.

FIG. 17 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 39 Outer wheel slip angle estimation unit 41 Yaw rate sensor 42 Lateral acceleration sensor 43 Wheel speed sensor

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Keijiro Iwa             Nissan, Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan             Inside the automobile corporation (72) Inventor Michito Hirahara             Nissan, Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan             Inside the automobile corporation F term (reference) 3D032 CC02 CC14 DA02 DA03 DA24                       DA29 DA33 DA36 DD02 EB04                       EB16 EB17 GG01

Claims (7)

[Claims] 1. A steering apparatus comprising left and right wheels that can be independently steered, and comprising 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 outer wheel slip angle estimating means for estimating the slip angle of the outer wheel are provided, and the actual steering angle control means is
When the wheel load of the inner wheel estimated by the wheel load estimating means is equal to or less than a set value, the outer wheel slip angle estimated by the outer wheel slip angle estimating means is set to a predetermined angle or a predetermined angle or less A steering device characterized by controlling a corner. 2. The steering apparatus according to claim 1, wherein the predetermined angle is a slip angle of the outer wheel when the wheel load of the inner wheel reaches a set value. 3. A steering system comprising left and right wheels that can be steered independently of each other and provided with an 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 outer wheel slip angle estimating means for estimating the slip angle of the outer wheel are provided, and the actual steering angle control means is
When the wheel load of the inner wheel estimated by the wheel load estimating means is equal to or less than a set value, the slip angle of the outer wheel estimated by the outer wheel slip angle estimating means is generated in the vehicle by each lateral force due to the slip angles of the front and rear outer wheels. A steering apparatus for controlling the actual steering angle of the outer wheel so that the turning moment in the yaw direction becomes 0 or an angle that makes it equal to or less than a predetermined value. 4. The steering apparatus according to claim 1, wherein the set value is 0. 5. The actual steering angle control means returns to the control of the actual steering angle based on the steering angle when the wheel load of the inner wheel becomes smaller than the set value and then becomes larger than the set value again. The steering apparatus according to any one of claims 1 to 4, wherein: 6. 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. 7. 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.