JPH06219298A - Four-wheel steering device - Google Patents

Abstract

PURPOSE:To provide both responsiveness and safety at a high level regardless of a steering speed at the time of turning, in a four-wheel steering device for controlling a rear wheel phase-inverted when a front wheel is steered. CONSTITUTION:In a calculating formula as shown in the following for a rear wheel steering angle target value deltar, primary delay time constants T1, T2 of an in-phase term (Ktheta) and a negative phase term (tautheta'+tau'theta'') are respectively given independently, to set the primary delay time constant T1 of the in-phase term (Ktheta) larger than the primary delay time constant T2 of the negative phase (tautheta'+tau'theta''). deltar=Ktheta/(1+T1.s)+(tautheta'+tau'theta'')/(1+T2.s).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel steering system for controlling phase inversion of rear wheels when steering front wheels.

[0002]

2. Description of the Related Art Conventionally, as a four-wheel steering system for controlling the phase inversion of the rear wheels when steering the front wheels, for example, "MotorFa" is used.
n ”(1987.9), pages 28 and 29.

According to the above-mentioned conventional source, the rear wheel steering angle target value δr is calculated by the following equation using the steering wheel steering angle and the vehicle speed, and the phase inversion control for controlling the rear wheel steering angle so that this target value is obtained. The system is shown.

Δr = (Kθ + τθ ′ + τ′θ ″) / (1 + T ₀ · s) K, τ, τ ′; proportional constant relating to vehicle speed V; steering angle θ ′; steering speed θ ″; steering acceleration T ₀ ; First-order lag time constant s; Laplace operator In this formula, the step steering characteristics of the steering steering angle term Kθ, the steering speed term τθ ′, the steering acceleration term τ′θ ″ and the sum of these (Kθ + τθ ′ + τ′θ ″) are , As shown in FIG.

The phase reversal control is based on the concept of first-order lag control, in which the rear wheels are momentarily reversed in phase to positively add the cornering force to the yaw generation direction.
The yaw rate rise is further improved. And
After sufficient yawing is obtained, the rear wheels are reversed to the in-phase side to suppress an increase in yaw rate and stabilize the vehicle body.

[0006]

However, in the above-described conventional four-wheel steering system, the in-phase term (Kθ) that gives the rear wheel an in-phase steering angle with respect to the steering rudder angle and the steering rudder angle. An anti-phase term (τ that gives the anti-phase steering angle to the rear wheels
θ '+ τ'θ ") is a control that gives a single first-order lag time constant T ₀ , so that it is possible to achieve a compromise between responsiveness and stability. The evaluation is relatively low, and there is a problem that responsiveness and stability cannot be compatible at a high level.

That is, (b) of FIG. 9 is a step response when the first-order lag time constant T ₀ is set to zero, and the reverse phase which gives the turning property at the initial stage of turning is sufficient, but at the same time the in-phase is large. It will be overdamped (overstable).

Therefore, if a large first-order lag time constant T ₀ is given in order to improve the responsiveness, as shown in FIG. 10, the rising of the in-phase is delayed, but at the same time, the anti-phase is decreased and the responsiveness is also slowed down. I will end up. Particularly, when the steering speed by the driver is high, a sufficient amount of reverse phase of the rear wheels cannot be obtained, and the driver's intention to turn is not sufficiently reflected.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a four-wheel steering system for controlling the phase inversion of the rear wheels during steering of the front wheels. And stability at a high level.

[0010]

In order to solve the above-mentioned problems, in the four-wheel steering system of the present invention, the first-order lag time constants of the in-phase term and the anti-phase term are independently set in the rear wheel steering angle target value calculation formula. The first-order lag time constant of the in-phase term is set larger than the first-order lag time constant of the anti-phase term.

That is, as shown in the claim correspondence diagram of FIG. 1, a rear wheel steering angle actuator a for controlling the rear wheel steering angle by an external command, and steering steering angle detection means b for detecting the steering steering angle, The vehicle speed detecting means c for detecting the vehicle speed, the steering angle and the vehicle speed from the detecting means b, c are used, and the first primary delay time constant is set to be larger than the second primary delay time constant. The rear wheel steering angle control means d is provided for calculating a rear wheel steering angle target value by a formula and outputting a control command for obtaining the target value to the rear wheel steering angle actuator a.

Here, the formula for calculating the rear wheel steering angle target value is δr = Kθ / (1 + T ₁ s) + (τθ '+ τ'θ ") /
(1 + T ₂ s) (1) δr; Rear wheel steering angle target value K, τ, τ '; Proportional constant relating to vehicle speed V; Steering angle θ'; Steering speed θ "; Steering acceleration T ₁ ; 1st 1st delay time constant T ₂ ; second 1st delay time constant s; Laplace operator.

[0013]

When the vehicle is turning, the rear wheel steering angle control means d detects the steering rudder angle and the steering rudder angle detection means b is detected.
And the steering angle θ from the vehicle speed detecting means c for detecting the vehicle speed and the vehicle speed V are used, and the first first-order lag time constant T ₁ is set to be larger than the second first-order lag time constant T _2. The rear wheel steering angle target value δr is calculated by the equation), and the rear wheel steering angle is controlled by outputting a control command for obtaining the target value δr to the rear wheel steering angle actuator a.

Therefore, by reducing the second first-order lag time constant T ₂ , the generation of cornering force is positively added in the yaw generation direction while the reverse phase of the rear wheels is sufficiently exerted. By increasing the first-order lag time constant T ₁ , the increase of the yaw rate can be suppressed slowly while delaying the rear wheel in-phase rising.

As a result, in the conventional phase inversion control,
It is possible to improve the responsiveness, which was relatively low compared to the stability, and in particular, when the steering speed is fast, it is possible to obtain a high turning responsiveness according to the driver's intention by the sufficient amount of the reverse phase of the rear wheels. it can.

[0016]

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

First, the structure will be described.

FIG. 2 is an overall system diagram showing a vehicle to which the four-wheel steering system of the embodiment of the present invention is applied, and FIG. 3 is a diagram showing an electric rear wheel steering mechanism of the four-wheel steering system of the embodiment.
FIG. 3 is a system diagram of an electronic control system centering on a 4WS controller of the embodiment apparatus.

In FIG. 2, 1 and 2 are front wheels, 3 and 4 are rear wheels, 5 is a mechanical front wheel steering mechanism, and 6 is an electric rear wheel steering mechanism (corresponding to a rear wheel steering angle actuator a).
Is.

In the mechanical front wheel steering mechanism 5, the steering force input from the steering wheel 7 steered by the driver through the steering shaft 8 is increased by the power steering (not shown), and the increased steering force is increased by the rack shaft 9. Is transmitted via the side rods 10 and 11 and the knuckle arms 12 and 13 to give a steering angle to the front wheels 1 and 2.

The electric rear wheel steering mechanism 6 has four
The rotational force of the high-cass motor 15 controlled by the motor output from the WS controller 14 is decelerated by the worm 16 and the worm wheel 17, and the rotational movement of the worm wheel 17 is divided between the gear portion of the pinion shaft 18 and the gear portion of the rack shaft 19. The mechanism is converted into a linear motion of the rack shaft 19 by meshing and transmitted from the rack shaft 19 through the side rods 20 and 21 and the knuckle arms 22 and 23 to give a steering angle to the rear wheels 3 and 4.

As shown in FIG. 4, the 4WS controller 14 includes a power supply circuit 14a, a sensor power supply circuit 14b, an input interface 14c, a CPU1, a CPU2, a monitoring circuit 14d, D / A conversions 14e, 14f, 14g, 14.
h, 14i, a CPU output monitoring circuit 14j, a relay output driver 14k, a motor output driver 14m, and a power steering solenoid output driver 14n.

The power supply circuit 14a includes a battery power source directly from a battery 24 and an ignition switch 25.
Ignition power from is input.

The input interface 14c has sensor signals from a rear steering angle main sensor 26 and a rear steering angle sub sensor 27 by a potentiometer, a sensor signal from a steering sensor 28 (corresponding to steering steering angle detecting means b), and a vehicle speed. The sensor signal from the sensor 29 (corresponding to the vehicle speed detecting means c) and the stop lamp switch 3
0, brake switch 31 and inhibit switch 3
The switch signal from 2 is input. Here, the rear steering angle main sensor 26 is a sensor that detects the amount of rotation of the pinion shaft 18, and the rear steering angle sub sensor 27.
Is a sensor for detecting the stroke amount of the rack shaft 19.

The relay output driver 14k receives the monitoring output from the monitoring circuit 14d and the warning valve output from the warning valve 33, and receives the high-casing relay 34.
The high-cass relay output is sent to.

The motor output driver 14m is driven by the motor power source via the high-casing relay 34, and C
A rear wheel steering angle command is input from the PU 1 via the D / A conversions 14g and 14h, and a motor output is sent to the high-cass motor 15.

The power steering solenoid output driver 14
n receives a power steering command from the CPU 1 via the D / A conversion 14i, and sends a power steering solenoid output to the power steering solenoid 35.

Next, the operation will be described.

[Rear Wheel Steering Angle Control Operation] FIG. 5 is a flowchart showing the flow of the rear wheel steering angle control operation performed by the 4WS controller 14 at a predetermined control cycle. Each step will be described below (rear wheel steering angle control operation). Equivalent to the control means d).

In step 50, the vehicle speed V, steering steering angle θ, and rear wheel steering angle sensor value δrSEN are read.

In step 51, proportional constants K, τ and τ'are determined by the vehicle speed V.

At step 52, the steering speed θ'is obtained by the differential calculation of the steering angle θ.
Further, the steering acceleration θ ″ is obtained by the differential calculation processing of the steering speed θ ′.

In step 53, the in-phase term Kθ is calculated from the proportional constant K and the steering angle θ.

In step 54, the anti-phase term (τθ '+ τ'θ ") is calculated from the proportional constants τ and τ', the steering speed θ'and the steering acceleration θ".

In step 55, the following in-phase term Kθ, anti-phase term (τθ '+ τ'θ "), first first-order delay time constant T ₁ and second first-order delay time constant T ₂ are used. The rear wheel steering angle target value δr is calculated by the equation, where the first-order lag time constants T ₁ and T ₂ are set so as to obtain optimum responsiveness and stability according to the required performance of the vehicle to which it is applied. Is preset in the relationship of T ₁ > T ₂ .

Δr = Kθ / (1 + T ₁ s) + (τθ '+
τ′θ ″) / (1 + T ₂ · s) In step 56, the rear wheel steering angle deviation δε is calculated from the difference between the rear wheel steering angle target value δr and the rear wheel steering angle sensor value δrSEN.

In step 57, the motor current IM is calculated by the following equation using the rear wheel steering angle deviation δε.

IM = Lδε-md (θM) + Kp L; Proportional constant m; Damping constant d (θM); Motor rotation angular velocity Kp; Friction correction constant In step 58, a command to obtain the motor current IM is output. To be done.

[Turning] During turning, the rear wheel steering angle is controlled according to the steering steering angle θ and the vehicle speed V according to the rear wheel steering angle control differential shown in FIG.

That is, the first first-order lag time constant T _{1 is set} to T ₁
At the time of step steering when = 0, as shown by the solid line characteristic on the right side of FIG. 6, an in-phase term Kθ having a fast rising is given, and when the first first-order lag time constant T ₁ is T ₁ > 0. At the time of step steering, as indicated by the dotted line characteristic on the right side of FIG.
The in-phase term Kθ / (1 + T ₁ · s) having a slow rise is given.

Further, the second first-order lag time constant T _{2 is set} to T ₂ =
At the time of step steering when 0 is set, as shown by the solid line characteristic on the right side of FIG. 7, a reverse-phase term (τθ ′ + τ ′) with a fast rise is obtained.
θ ″) is given and the second first-order lag time constant T _{2 is set} to T ₂ >
At the time of step steering with 0, as shown by the dotted line characteristic on the right side of FIG. 7, the reverse-phase term (τθ '+ τ'
θ ″) / (1 + T ₂ · s) is given.

For this in-phase term and anti-phase term, for example, T ₁
When a first-order lag time constant of> 0, T ₂ = 0 is given, as shown by the solid line characteristic in FIG. 8, in-phase rising can be performed without reducing the reverse phase as compared with the conventional dotted line characteristic. A rear-wheel steering angle characteristic that makes it slower is obtained.

Therefore, at the beginning of turning, the rear wheels 3, 4
As the opposite phase of is sufficiently effective, the generation of cornering force is positively added in the yaw generation direction, and the rise of the yaw rate is secured. Then, after sufficient yawing is obtained, the rear wheels 3 and 4 are slowly reversed to the in-phase side, whereby an increase in yaw rate is suppressed and stability of vehicle body behavior is ensured.

As a result, in the conventional phase inversion control in which only one first-order lag time constant was set, the responsiveness, which was relatively low as compared with the stability, was enhanced, and the stability was improved. And the responsiveness evaluation level can be made substantially equal, and the responsiveness evaluation level can be made higher than the stability depending on the setting of the first-order lag time constants T ₁ and T ₂ .

When the steering speed is slow, the anti-phase term (τ
By decreasing θ ′ + τ′θ ″), the amount of reverse phase of the rear wheels 3 and 4 is suppressed to a small value, as shown by the one-dot chain line characteristic in FIG. 8, and a turning response that matches the steering operation at a slow steering speed. In addition, when the steering speed is high, the anti-phase term (τθ '+ τ'θ ") becomes large, and as shown by the chain double-dashed line characteristic in FIG. Is large and shows a high turning response that matches the steering operation at a high steering speed. In any case, the amount of in-phase depends on the amount of reverse phase, and sufficient stability is secured.

Next, the effect will be described.

In a four-wheel steering system for controlling the phase inversion of the rear wheels 3 and 4 when steering the front wheels 1 and 2, in the rear wheel steering angle target value calculation formula, the first-order lag time constant T _{1 of} the in-phase term and the anti-phase term, Since T ₂ is independently given and the first-order delay time constant T ₁ of the in-phase term is set to be larger than the first-order delay time constant T ₂ of the anti-phase term,
When turning, responsiveness and stability can be achieved at a high level regardless of the steering speed.

Although the embodiments have been described above with reference to the drawings, the specific configuration is not limited to the embodiments, and modifications and additions within the scope of the present invention are included in the present invention. Be done.

For example, in the embodiment, the electric actuator is shown as the rear wheel steering angle actuator, but a hydraulic actuator may be used.

In the embodiment, an example in which the first-order lag time constants T ₁ and T ₂ are set in advance in accordance with the vehicle type and the like has been shown. However, the steering operation by the driver is monitored and the learning control method is used to set 1 The next delay time constants T ₁ and T ₂ may be optimized while maintaining the relationship of T ₁ > T ₂ .

[0051]

As described above, according to the present invention, in the four-wheel steering system for controlling the phase inversion of the rear wheels during the steering of the front wheels, the in-phase term and the anti-phase term are calculated in the rear wheel steering angle target value calculation formula. Since the first-order lag time constants are given independently and the first-order lag time constant of the in-phase term is set larger than the first-order lag time constant of the anti-phase term, responsiveness and stability are improved during turning regardless of the steering speed. The effect that both can be achieved at the level is obtained.

[Brief description of drawings]

FIG. 1 is a claim correspondence diagram showing a four-wheel steering system according to the present invention.

FIG. 2 is an overall system diagram showing a vehicle to which the four-wheel steering system according to the embodiment of the present invention is applied.

FIG. 3 is a diagram showing an electric rear wheel steering mechanism of the four-wheel steering system according to the embodiment.

FIG. 4 is a system diagram of an electronic control system centering on a 4WS controller of the embodiment apparatus.

FIG. 5 is a flowchart showing a flow of rear wheel steering angle control operation performed by the 4WS controller of the embodiment apparatus.

FIG. 6 is a characteristic diagram showing an in-phase term of a rear wheel steering angle target value at the time of step steering in the embodiment apparatus.

FIG. 7 is a characteristic diagram showing an anti-phase term of a rear wheel steering angle target value at the time of step steering in the embodiment apparatus.

FIG. 8 is a characteristic diagram of a rear wheel steering angle target value at the time of step steering in the embodiment apparatus.

FIG. 9 is a characteristic diagram of each term of steering angle, speed, and acceleration, and a rear wheel steering angle target value characteristic diagram during step steering in a conventional device.

FIG. 10 is a characteristic diagram of a rear wheel steering angle target value during step steering when the primary delay time constant is increased in the conventional device.

[Explanation of symbols]

 a rear wheel steering angle actuator b steering rudder angle detection means c vehicle speed detection means d rear wheel rudder angle control means

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location B62D 117: 00 137: 00

Claims (1)

[Claims] 1. A rear wheel steering angle actuator for controlling a rear wheel steering angle according to an external command, a steering steering angle detecting means for detecting a steering steering angle, a vehicle speed detecting means for detecting a vehicle speed, and the detecting means. The steering wheel steering angle and the vehicle speed are used, and the rear wheel steering angle target value is calculated by the following formula in which the first first-order lag time constant is set larger than the second first-order lag time constant, and this target value is obtained. Rear wheel steering angle control means for outputting a control command to the rear wheel steering angle actuator, and δr = Kθ / (1 + T ₁ s) + (τθ ′ + τ′θ ″) /
(1 + T ₂ s) δr; Rear wheel steering angle target value K, τ, τ '; Proportional constant relating to vehicle speed V; Steering steering angle θ'; Steering speed θ "; Steering acceleration T ₁ ; First primary delay A four-wheel steering system comprising: a time constant T ₂ ; a second first-order lag time constant s; a Laplace operator.