JPH01202579A - Four-wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To contrive the gain flatness and the decrease of phase delay of the yaw rate characteristic by controlling a rear wheel in accordance with not only a front wheel steered angle but also a speed of the steered angle and its acceleration. CONSTITUTION:On and off action of solenoids 12L, 12R and their electrification quantity are electronically controlled by a controller 17. The controller 17 inputs a signal from a steering angle sensor 18 detecting a steering angle theta of a steering wheel 3 and a signal from a car speed sensor 19 detecting a car speed V. The controller 17 determines an electric current (i) for whether or not it must be supplied to either the solenoid 12L or 12R, generating a fluid pressure in accordance with a rear wheel steering angle in corresponding pipe line 11L or 11R. An actuator 9 moves by a stroke of predetermined distance in a direction in accordance with a fluid pressure of the actuator, steering a rear wheel by an angle in accordance with an arithmetic result.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a four-wheel steering system for a vehicle that steers rear wheels so as to obtain target vehicle characteristics depending on the driving condition.

(Prior Art) Conventionally, as a four-wheel steering system for a vehicle equipped with a rear wheel steering angle control means, for example, one described in Japanese Patent Application Laid-open No. 186773/1983 is known.

This conventional publication uses vehicle speed and front wheel steering angle as input information, and in medium and high speed ranges, the rear wheels are steered in the opposite phase for a set time from the start of front wheel steering, and after the set time has elapsed. Rear wheel steering angle control means for steering the rear wheels in the same phase is shown.

(Problem to be Solved by the Invention) However, in such conventional devices, the rear wheel steering angle is controlled by a function of only the vehicle speed and the front wheel steering angle, so it is difficult to set it as a target in advance. However, there were problems in that it was not possible to perform control according to the vehicle characteristics, and it was not possible to significantly improve transient steering response and stability.

Specifically, the following characteristics cannot be expected.

■ Concerning yaw rate frequency response, set goals such as flattening the yaw rate gain to high frequency ranges or reducing phase delay, and successfully achieve the set goals.

■ When performing step steering during lane changes, etc.
Reduce the overshoot of the yaw rate at the beginning of the steering wheel turn.

(Means for Solving the Problems) The present invention has been made for the purpose of solving the above-mentioned problems, and in order to achieve this purpose, the present invention includes the following:
In a four-wheel steering system for a vehicle, the rear wheel steering angle control means controls a Laplace transform value of a front wheel steering angle. δfls) + retransmit, S nila plus operator a i a +, a 2. a3. a a, a
s: Vehicle target performance It is characterized by being a means for performing control to obtain a rear wheel turning angle given by a constant control transfer function determined by vehicle specifications and vehicle speed.

(Function) When steering the steering wheel, the rear wheel steering angle control means sets constants a0 and a+ according to vehicle target performance, vehicle specifications, and vehicle speed.
+a2+a3-am, a5 are determined, and based on these, control is performed to steer the rear wheels so that the rear wheel steering angle δ2 is given by the control transfer function of equation (1) above. .

In determining the rear wheel steering angle, the denominator and numerator of the control transfer function both include a quadratic term (S2), a linear term (S), and a constant term with respect to the Laplace operator S. is controlled not only according to the front wheel turning angle δ, but also the turning angular velocity and the turning angular acceleration.

Therefore, it is possible to obtain vehicle characteristics that match the set target performance, making it easier to tune vehicle characteristics in terms of design, and
Steering responsiveness and stability are greatly improved as it is possible to change the gain angle of the yaw rate characteristic, reduce phase lag, and prevent overshoot during step steering.

(Example) Embodiments of the present invention will be described below based on the drawings.

First, the configuration will be explained.

FIG. 1 shows a four-wheel steering system for a vehicle according to an embodiment, in which left and right front wheels IL and IR can be steered by a steering wheel 3 via a steering gear 4. FIG. Incidentally, the front wheel turning angle δ is expressed as θ=θ/N, where θ is the steering wheel steering angle and N is the steering gear ratio.

The left and right rear wheels 2L and 2R are transverse links 5L,
It is suspended on the rear suspension member 7 of the vehicle body by a rear suspension device including 5R and upper arms 6L and 6R, and for the purpose of steering the rear wheels, an actuator 9 and side rods 10m at both ends are connected between the left and right knuckle arms 8L and 8R. , are interconnected by IOR.

The actuator 9 is a spring center type double-acting hydraulic cylinder, and its two chambers are each connected to an electromagnetic proportional pressure control valve 12 through a conduit 11LIIR. Note that this control valve 12 is further connected to a hydraulic pressure line 15 and a drain line 16 of a hydraulic pressure source including a pump 13 and a reservoir tank 14, respectively.

The electromagnetic proportional pressure control valve 12 is a spring center type 3-position valve with a single solenoid 12L.

When 12R is OFF, pipes 11L and 11R are in a pressure-free state, and when solenoid 12L is ON, a pressure proportional to the amount of energization is supplied to pipe 11L, and when solenoid 12R is ON, a pressure proportional to the amount of energization is supplied to pipe 11R. It is intended to supply

The ON/OFF and energization amounts of the solenoids 12L and 12R are electronically controlled by a controller 1, and this controller 17 has a digital arithmetic circuit 17a as shown in FIG.
, digital input detection circuit +7b, -storage circuit 17c
, a D/A converter 17d, and a drive circuit 17e.

A signal from a steering angle sensor 18 that detects the steering angle θ of the steering wheel 3 and a signal from a vehicle speed sensor 19 that detects the vehicle speed V are respectively input to the controller 17 via a digital input detection circuit 17b.

The digital arithmetic circuit 17a of the controller 17 calculates the above a from these input information and the constants stored in the ROM of the storage circuit 17c. + a l + a 2r a3+
84+ a S and store them in R of the storage circuit 17c.
Temporarily store in AM. After that, the digital arithmetic circuit 17
a temporarily stored in a. +a l+a2
Equation (1) is calculated based on + a3 + a 41 a 5, and a digital signal related to the rear wheel turning angle δ corresponding to the calculation result is converted into an analog signal by the D/A converter 17d. This analog signal is converted by the drive circuit 17e into a current i corresponding to the rear wheel turning angle δ, and is supplied to the control valve 12.

At this time, the controller 17 determines which of the solenoids 12L and 12R of the control valve 12 the current i should be supplied with from the steering angle θ, and supplies the current i (rear wheel steering angle δ,) to the corresponding conduit 11L or 11R. Generates hydraulic pressure according to. The actuator 9 strokes in a direction corresponding to this hydraulic pressure and by a distance corresponding to this hydraulic pressure, and rotates the rear wheels 2L and 2 via the side rods IOL and IOR in the corresponding direction by an angle according to the calculation result. I can steer it.

Next, the effect will be explained.

First, it is known that the equation of motion of a vehicle is expressed by the following equation (see Figure 3).

If the vehicle mass is M, the vehicle's lateral displacement acceleration is S, the vehicle speed is V, the yaw rate is ψ, the side force of the front wheels is Fl, and the side force of the rear wheels is F2, then M (ψ 1 ■ ψ) = FI
+F2 is calculated, and if the vehicle's yaw moment of inertia is I, the yaw angular acceleration is ψ, the distance from the vehicle center of gravity to the front axle is a, and the distance from the vehicle center of gravity to the rear axle is b, then ■-φ=a-F, -b-F2 is calculated, and the equivalent cornering power of the front and rear wheels is C,
,C,, assuming that the front wheel steering angle is 61, the rear wheel steering angle is 67, and the lateral displacement acceleration of the vehicle is 9, is found.

Then, the target performance of the vehicle is expressed as a transfer function as the vehicle's yaw rate characteristic (yaw rate steering characteristic) with respect to the steering wheel operation amount θ, where ψ. ; Set the steady yaw rate of the base vehicle as T: constant S; Laplace operator, apply the Laplace transform to the above 24 equations of motion, and form a quadratic control transfer function with respect to the Laplace operator S for both the denominator and numerator. In summary, a 3 =C2bllJT.

However, β is the wheel base length, and β=a+b.

Therefore, ψ151/θ1 determines the target vehicle characteristics.
81, for example, with a first-order lag as in the example,
Using the set values, each coefficient 81 of the control transfer function described above is
(0≦i≦5), and based on the control transfer function, the steering angle δ of the rear wheels 2L and 2nd day is determined.

By controlling this, the vehicle characteristics as desired can be obtained.

In other words, the target characteristics are obtained when the denominator 2 of the control transfer function
Since both the numerators include a quadratic term (s2), a linear term (s), and a constant term with respect to the Laplace operator S, the rear wheels 2L and 2R determine not only the steering angle of the front wheels but also the steering angular velocity and steering. By being controlled according to angular acceleration.

In particular, the following characteristics can be realized.

- As for the yaw rate frequency characteristic, flattening of the yaw rate gain up to the high frequency range can be achieved (Figure 4).

- It is possible to reduce the yaw rate phase delay (Figure 5).

- Reduces yaw rate overshoot when starting to turn the steering wheel during step steering such as when changing lanes (Figure 6).

In addition, Fig. 7 shows the steering angle characteristics of the steering wheel during step steering, and Fig. 8 shows the rear wheel turning angle characteristics that can reduce the overshoot of the yaw rate at that time. At this time, the rear wheels 2L and 2R temporarily go out of phase with the front wheels IL and IR, and then change to the same phase.
Furthermore, the rear wheel turning angle 61 converges to zero with a predetermined time constant.

Although the embodiment has been described above based on the drawings, the specific configuration is not limited to this embodiment, and even if there is a design change within the scope of the gist of the present invention, it is included in the present invention. .

For example, as φ/θ for determining the target vehicle characteristics, the above equation (2) is shown in the embodiment, but it is not limited to this equation, and may be expressed as (primary/secondary) etc. Furthermore, the target vehicle characteristics may be approximated by a higher-order equation.

(Effects of the Invention) As explained above, in the four-wheel steering system for a vehicle of the present invention, the rear wheel steering angle control means controls the rear wheel steering angle given by the control transfer function of equation (1) above. Since this is a means for performing such control, the following effects can be obtained.

■ It is easy to tune the vehicle characteristics in terms of design since the characteristics can be obtained in accordance with the vehicle target performance set in advance.

■ Gain flattening of yaw rate characteristics, reduction of phase lag, and prevention of overshoot during step steering can be achieved, significantly improving steering response and stability.

[Brief explanation of the drawing]

FIG. 1 is an overall diagram showing a four-wheel steering system for a vehicle according to an embodiment of the present invention, FIG. 2 is a block diagram showing a rear wheel steering angle control system of the embodiment, and FIG. 3 is a motion model when the vehicle turns. figure,
Figure 4 is a yaw rate gain characteristic diagram with respect to steering wheel steering frequency, Figure 5 is a yaw rate phase delay characteristic diagram with respect to steering wheel steering frequency, Figure 6 is a yaw rate time chart diagram during step steering, and Figure 7 is a diagram showing steering wheel steering during step steering. The angle characteristic diagram, FIG. 8, is a time chart of the rear wheel turning angle during step steering. IL, IR...Front wheel 2L, 2R...Rear wheel 3...Steering wheel 4...Steering gear 5L, 5th...Transverse link 6L, 6R...
- Upper arm 7... Rear suspension member 9... Actuator 12... Electromagnetic proportional pressure control valve 17... Controller 18... Steering angle sensor 19... Vehicle speed sensor

Claims (1)

[Scope of Claims] 1) A four-wheel steering system for a vehicle including a rear wheel steering angle control means for controlling a rear wheel steering angle according to a running state of the vehicle, wherein the rear wheel steering angle control means comprises: When the Laplace transform value of the front wheel steering angle is δ_f_(_S_) and the Laplace transform value of the rear wheel steering angle is δ_r_(_S_), δ_r_(_S_)/δ_f_(_S_) = (a_0・
s^2+a_1・s+a_2)/(a_3・s^2+a
_4・s+a_5) However, s: Laplace operator a_0, a_1, a_2, a_3, a_4, a_5; Vehicle target performance The rear wheel turning angle given by the constant control transfer function determined by vehicle specifications and vehicle speed is obtained. A four-wheel steering system for a vehicle, characterized in that it is a means for performing control.