JP2502761B2 - Four-wheel steering system for vehicles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a four-wheel vehicle for controlling the rear wheels so that the yaw rate generation characteristic of the vehicle with respect to the front wheel steering angle becomes an output with a first-order lag. The present invention relates to a steering device.

(Prior Art) Conventionally, as a four-wheel steering device for a vehicle provided with a rear wheel turning angle control means, for example, one described in JP-A-59-186773 is known.

In this conventional publication, the vehicle speed and the front wheel turning angle are used as input information, and in the middle and high speed regions, the rear wheels are steered in the opposite phase for a set time from the start of the front wheel turning, and after the set time has elapsed, Rear wheel steering angle control means for steering the rear wheels in the same phase is shown.

(Problems to be Solved by the Invention) However, in such a conventional device, the rear wheel steering angle is controlled by a function of only the vehicle speed and the front wheel steering angle. However, there was a problem that the control could not be performed according to the vehicle characteristics described above and that the transient response and stability of the steering could not be significantly improved.

 Specifically, the following characteristics cannot be expected.

Regarding the yaw rate frequency response, set a target such as flattening the yaw rate gain to a high frequency range or reducing the phase delay, and realize the set target well.

When step steering in lane change etc.,
Minimize the yaw rate overshoot when turning the steering wheel.

Therefore, the present applicant solves the above-mentioned problems by applying Japanese Patent Application No. 63-25223 to control the rear wheels so that the yaw rate generation characteristic of the vehicle with respect to the front wheel steering angle becomes a first-order output. A method was proposed.

For example, in this prior application, when the Laplace conversion value of the front wheel steering angle is δ _{f (s)} and the Laplace conversion value of the rear wheel steering angle is δ _{r (s)} , However, s; Laplace operator K; Steady-state yaw rate gain τ ₁ , τ ₂ , T ₁ , T ₂ ; A means for giving the rear wheel steering angle by a control system transfer function that is a constant determined by vehicle specifications and vehicle speed is shown. ing.

However, the arithmetic control transfer function represented by the equation (1) includes a quadratic term in the denominator, and the constant T ₁ of the primary term and the constant T ₂ of the secondary term must be variable depending on the vehicle speed. Therefore, it is necessary to speed up the calculation, and for example, the capacity of an 8-bit microcomputer becomes insufficient.

In addition, an actuator with extremely high responsiveness is required in order to accurately perform control by the second-order / second-order control transfer function.

The present invention has been made in view of the above problems, and four-wheeled vehicles for steering the rear wheels such that the yaw rate generation characteristic of the vehicle with respect to the steered angle of the front wheels has a first-order lag output. An object of the steering device is to simplify the system and the calculation while making the yaw rate characteristic of the vehicle approximate to the target yaw rate performance.

(Means for Solving the Problems) In order to solve the above problems, in the vehicle four-wheel steering system of the present invention, the actuator system is provided with a first-order lag, and
The control transfer function of the arithmetic system is a quadratic / first-order equation by deleting the quadratic term, which has a small effect in the normal steering input frequency range.

That is, in a four-wheel steering operation for wheels equipped with rear wheel steering angle control means for controlling the steering angle of the rear wheels in accordance with the running state of the vehicle, the rear wheel steering angle control means is a Laplace of the front wheel steering angle. When the conversion value is δ _{f (s)} and the Laplace conversion value of the rear wheel steering angle is δ _{r (s)} , However, s; Laplace operator K; Steady-state gain of yaw rate τ ₁ , τ ₂ ; Constant determined by vehicle specifications and vehicle speed T ₀ ; First-order delay constant of calculation system T; First-order delay constant of actuator system It is characterized in that it is a means for performing control so that the yaw rate generation characteristic of the vehicle with respect to the front wheel turning angle is output with a first-order lag, given the rear wheel turning angle.

(Operation) When steering the steering wheel, the rear wheel steering angle control means
The constants τ ₁ , τ ₂ , T ₀ , T are obtained from the vehicle specifications and vehicle speeds, and based on these and the yaw rate steady-state gain K, the rear wheel steering angle δ _r given by the control transfer function of the above equation (2). The control for steering the rear wheels is performed so that

In this control, the first-order delay constant T ₀ of the operation system is set to T ₀ = T ₁
-T If the first-order delay constant T of the actuator system is small to some extent, Becomes

That is, in determining the steering angle of the rear wheels, the denominator and numerator of the control transfer function (2 ') in the total system of the arithmetic system and the actuator system are both quadratic terms (s ² ) with respect to the Laplace operator s. Since the first term (s) and the constant term are included, the rear wheels are controlled not only according to the front wheel turning angle δ _f but also according to the turning angular velocity and the turning angular acceleration.

Therefore, the gain flattening of the yaw rate characteristic, the reduction of the phase delay, the prevention of the overshoot at the time of step steering, etc. are achieved, and the yaw rate steady-state characteristic and the yaw rate transient characteristic which are almost similar to the set target yaw rate performance can be obtained.

Also, the transfer function of the actuator system Since there is a first-order delay, the actuator having a very high response is not required, and the system can be simplified.

Also, the transfer function of the arithmetic system Since it is a quadratic / first-order arithmetic expression, there is no need to speed up the calculation as in the case of the quadratic / secondary arithmetic expression.
Even a microcomputer having a bit capacity can sufficiently perform the operation.

(Example) Hereinafter, the Example of this invention is described based on drawing.

 First, the configuration will be described.

FIG. 1 shows a vehicle four-wheel steering system according to an embodiment, in which the left and right front wheels 1L, 1R can be steered by a steering wheel 3 via a steering gear 4. The front wheel turning angle δ _f is represented by δ _f = θ / N where θ is the steering wheel steering angle and N is the steering gear ratio.

The left and right rear wheels 2L, 2R are suspended on a rear suspension member 7 of the vehicle body by a rear suspension device including transverse links 5L, 5R and upper arms 6L, 6R, and left and right knuckle arms for the purpose of steering the rear wheels. 8L, 8R
Between the actuator 9 and the side rods 10L on both ends,
They are connected to each other by 10R.

The actuator 9 is a spring center type return hydraulic cylinder, and its two chambers are connected to an electromagnetic proportional pressure control valve 12 by lines 11L and 11R, respectively. This control valve 12
Further, a hydraulic pressure line 15 and a drain line 16 of a hydraulic pressure source including a pump 13 and a reservoir tank 14 are connected to each.

The electromagnetic proportional pressure control valve 12 is a spring center type three-position valve, and both solenoids 12L and 12R have a pipeline 11L,
The pressure is proportional to the energization amount when the solenoid 12 is ON, the pressure is proportional to the energization amount when the solenoid 12 is ON, and the pressure is proportional to the energization amount when the solenoid 12R is ON. You.

It should be noted that the actuator 9 and the electromagnetic proportional pressure control valve 12 constitute an actuator system of a rear wheel steering control system. The actuator system includes a Laplace conversion value of the front wheel steering angle δ _{f (s)} and a rear wheel rolling system. The Laplace conversion value of the steering angle is δ _{r (s)}
When 1 has a first-order lag characteristic represented by the control transfer function equation.

However, T is the first-order delay constant of the actuator system,
s is a Laplace operator.

A controller 17 electronically controls ON / OFF and energization amount of the solenoids 12L and 12R, and the controller 17 has a digital operation circuit 17a, a digital input detection circuit 17b, a storage circuit 17c, and a D circuit as shown in FIG. It is composed of an / A converter 17d and a drive circuit 17e.

In the controller 17, the signal from the steering angle sensor 18 for detecting the steering angle θ of the steering wheel 3 and the signal from the vehicle speed sensor 19 for detecting the vehicle speed V are respectively inputted through the digital input detection circuit 17b, and the digital arithmetic circuit is inputted. In 17a, the following arithmetic expression is calculated based on these input information and the constants stored in the ROM of the storage circuit 17c and the information temporarily stored in the RAM of the storage circuit 17c, and the rear wheel rotation corresponding to the calculation result is performed. D / A converter 17d converts digital signals related to steering angle δ _r
To convert it to an analog signal. This analog signal is converted into a current i corresponding to the rear wheel turning angle δ _r by the drive circuit 17e and supplied to the control valve 12.

At this time, the controller 17 determines from the steering angle θ which solenoid 12L, 12R of the control valve 12 should be supplied with the current i, and the current i (rear wheel turning angle δ _r ) is supplied to the corresponding pipeline 11L or 11R. To generate a hydraulic pressure corresponding to. Actuator 9
Stroke in the direction corresponding to this hydraulic pressure or by the distance corresponding to this hydraulic pressure, and steer the rear wheels 2L and 2R through the side rods 10L and 10R in the corresponding direction by the angle corresponding to the calculation result. You can

The formula calculated by the digital calculation circuit 17a is, when the Laplace conversion value of the front wheel turning angle is δ _{f (s)} and the Laplace conversion value of the rear wheel turning angle is δ _{r (s)} , However, K: Yaw rate steady-state gain τ ₁ , τ ₂ ; Constant determined by vehicle specifications and vehicle speed T ₀ ; Control transfer function expressed by the first-order delay constant of the calculation system.

Then, the rear wheel steering angle is given to the rear wheels 2L and 2R, and the yaw rate generation characteristic of the vehicle with respect to the front wheel steering angle δ _f is 1
The device is designed to control so that the output of the next delay occurs.

 Next, the operation will be described.

First, the target performance of the vehicle is set so that the yaw rate characteristic of the vehicle with respect to the front wheel turning angle δ _f is obtained by the following transfer function, which is an output with a first-order delay.

However, ₀ ; Steady yaw rate of base vehicle K, τ; Constant s; Laplace operator On the other hand, the equation of motion of the vehicle is known to be expressed by the following equation (see Fig. 3).

The mass of the vehicle is M, the lateral displacement acceleration of the vehicle is V, the vehicle speed is V,
If the yaw rate is F ₁ for the front wheel side force and F ₂ for the rear wheel side, then M (+ V ·) = F ₁ + F ₂ is obtained, the yaw moment of inertia of the vehicle is I, the yaw angular acceleration is the center of gravity of the vehicle. Is the distance from the front axle to the front axle and b is the distance from the center of gravity of the vehicle to the rear axle, I · = a · F ₁ −b · F ₂ is obtained, and the equivalent cornering powers of the front and rear wheels are C ₁ and C, respectively.
₂ , the front wheel steering angle is δ _f , the rear wheel steering angle is δ _r , and the lateral displacement acceleration of the vehicle is Is found.

Then, the four types of equations of motion are Laplace transformed, and in order to obtain the target vehicle characteristics of the above equation (3), both the denominator and the numerator are put together in the form of a quadratic / quadratic control transfer function with respect to the Laplace operator s. Becomes

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

Then, if the theoretical formula of (4) above is simplified, However, s; Laplace operator K; Yaw rate steady-state gain τ ₁ , τ ₂ , T ₁ , T ₂ ; Constants determined by vehicle specifications and vehicle speed.

In this equation (1), the value of T ₂ in the term of T ₂ · s ² is smaller than the other values, and it is noted that the influence is extremely small at the normal steering frequency of 1 Hz to 2 Hz. , The one obtained by deleting the term of T ₂ · s ² is the control transfer function (2 ′) of the following operation system, and the setting of the term of T ₂ · s ² was made following the deletion. 2 is a control transfer function (2 ″) of the actuator system of FIG.

Here, the yaw rate characteristic first-order delay system (yaw rate 1
A specific example for realizing the next delay time constant 50 msec) will be described.

* Vehicle specifications Wheelbase 2.55m Distance between front wheel and center of gravity 1.07m Mass 146kg ・ s ² / m Yaw inertia 205kg ・ s ²・ m Front wheel equivalent cornering power 6900kg / rad Rear wheel equivalent cornering power 9200kg / rad ＊ Theoretical control vehicle speed 120km At / h, if the yaw rate steady gain K is 2WS and K = 0, * When delay constant T = 0.08 Example control actuator system _{T 0 = T 1 -T = 0.4594-0.08} = 0.3794 T 0 · T = 0.3794 × 0.08 = 0.0304 , and the transfer function in the example control, Becomes

That is, when comparing equations (1a) and (2a), s ²
The constants of are only slightly different, such as 0.0205 and 0.0304.

As described above, the embodiment apparatus also has the features listed below.

The control transfer function (2) in the total system of the arithmetic system and the actuator system, the denominator and numerator of the Laplace operator s are both the quadratic term (s ² ), the primary term (s) and the constant term. Therefore, the rear wheels 2L and 2R are controlled not only according to the turning angle of the front wheels but also according to the turning angular velocity and the turning angular acceleration, and it is clear from the comparison between the equations (1a) and (2a). As described above, the control of the embodiment is a control that substantially matches the theoretical control, and it is possible to obtain the steady yaw rate characteristic and the transient yaw rate characteristic that are approximately similar to the set target yaw rate performance. In particular, the following characteristics can be realized.

・ As the yaw rate frequency characteristic, it is possible to realize a flat yaw rate gain up to a high frequency range (Fig. 4).

・ Reduction of yaw rate phase delay can be realized (5th
Figure).

・ It is possible to reduce the overshoot of the yaw rate at the beginning of turning the steering wheel during step steering such as lane change (Fig. 6).

Incidentally, FIG. 7 shows steering wheel steering angle characteristics during step steering, and FIG. 8 shows rear wheel steering angle characteristics capable of realizing reduction of the overshoot of the yaw rate at that time.
At the beginning of turning the steering wheel, the rear wheels 2L and 2R are temporarily the front wheels 1
The phase shifts to the opposite phase to L, 1R, then shifts to the same phase, and the rear wheel steering angle δ _r converges to zero with a predetermined time constant.

Transfer function of actuator system Since there is a first-order delay, the actuator system including the actuator 9 and the electromagnetic proportional pressure control valve 12 does not need to have a high response, and the system can be simplified.

Transfer function of arithmetic system Since it is a quadratic / first-order arithmetic expression, there is no need to speed up the calculation as in the case of the quadratic / secondary arithmetic expression.
Even a microcomputer having a bit capacity can sufficiently perform the operation.

Although the embodiment has been described above with reference to the drawings, the specific configuration is not limited to this embodiment.

(Effects of the Invention) As described above, according to the present invention, the vehicle four-wheel steering control that controls the rear wheels so that the yaw rate generation characteristic of the vehicle with respect to the front wheel steering angle becomes an output with a first-order lag. In a wheel steering system, the actuator system has a first-order delay, and the control transfer function of the arithmetic system is controlled as a quadratic / first-order equation by deleting quadratic terms that have a small effect in the normal steering input frequency range. Since the configuration is performed, it is possible to obtain an effect that the system and the calculation can be simplified while the yaw rate performance of the vehicle is approximated to the target yaw rate performance.

[Brief description of drawings]

FIG. 1 is an overall view showing a vehicle four-wheel steering system 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 apparatus, and FIG. 3 is a motion model during turning of the vehicle. Figure,
FIG. 4 is a yaw rate gain characteristic diagram with respect to steering wheel steering frequency, FIG. 5 is a yaw rate phase delay characteristic diagram with respect to steering wheel steering frequency, FIG. 6 is a yaw rate time chart diagram during step steering, and FIG. 7 is steering wheel steering during step steering. FIG. 8 is a time chart of the rear wheel turning angle during step steering. 1L, 1R …… front wheel 2L, 2R …… rear wheel 3 …… steering wheel 4 …… steering gear 5L, 5R …… 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)

(57) [Claims] 1. A four-wheel steering system for a vehicle comprising rear wheel steering angle control means for controlling a steering angle of rear wheels according to a running state of a vehicle, wherein the rear wheel steering angle control means comprises front wheel steering. When the Laplace transform value of the angle is δ _{f (s)} and the Laplace transform value of the rear wheel steering angle is δ _{r (s)} , However, s; Laplace operator K; Steady-state gain of yaw rate τ ₁ , τ ₂ ; Constant determined by vehicle specifications and vehicle speed T ₀ ; First-order delay constant of calculation system T; First-order delay constant of actuator system A four-wheel steering system for a vehicle, which is a means for performing control such that a rear wheel steering angle is given and a yaw rate generation characteristic of the vehicle with respect to a front wheel steering angle becomes an output with a first-order lag.