JPH0325078A - Vehicular steering angle control device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a vehicle steering angle control device that performs auxiliary steering of at least one of front wheels or rear wheels in order to obtain optimal vehicle dynamic characteristics during steering.

(Prior art) Conventionally, rear wheel steering angle control for vehicles has been described, for example, in ``Proceedings of the Society of Instrument and Control Engineers, Vol. 23, No. 8J.
The method described on pages 48 to 54 of (Published August 1986) is known.

In the above conventional source, there are three rear wheel steering angle control methods: when the controlled variable is yaw rate, when it is lateral acceleration, and when it is D* defined as a linear combination of yaw rate and lateral acceleration. However, the yaw rate control system will be explained below as an example.

FIG. 10 is a block diagram when a generally well-known integral type servo system is used as an actuator control system, and is often used in systems having a motor as an actuator.

In this rear wheel steering angle calculation section, as shown in the conventional source,
The rear steering angle target value δ8 is output so that the actual vehicle response matches the output of the reference model having the desired yaw rate response characteristic. Then, in the actuator control unit, the rear wheel actual steering angle 6R and the state variable x2=[δ8. [delta]Il] is used to drive the actuator so that the actual rear wheel steering angle 8 approaches the rear wheel steering angle target value 6R.

Incidentally, in FIG. 10, the integral gain Kj and the proportional gain Kp are generally set according to the optimal control theory.

(Problem to be solved by the invention) However, in such a trailing steering angle control method,
The actuator control is performed only by feedback control that takes in the rear wheel actual steering angle 6R and the state variable XP as feedback information and makes the detected value of the rear wheel actual steering angle δ8 match the rear wheel steering angle target value δ8. Therefore, even if the integral gain K1 and proportional gain Kp are set to obtain the best performance within a practical range, during step steering, the ideal rear wheel steering angle value (dotted line characteristic) As shown in Fig. 12, the response of the rear wheel actual steering angle (solid line characteristic) to The problem remained that vibration-like fluctuations occurred due to deviation from the set target value and overshoot.

In particular, in the case of high-response type actuators such as hydraulic servos, sufficient response performance can be obtained, but in the case of motor actuators, which have large inertia and whose dynamic characteristics cannot be ignored. If this is used, the vibrational fluctuation mentioned above will be significant.

Therefore, in the application of Japanese Patent Application No. 107311/1982, the present applicant constructed a rear wheel actual steering angle control system by adding feedforward compensation to the feedback control to predict and cancel the change in the control amount by the actuator. By doing so, we have proposed a device that prevents fluctuations in the actual rear wheel steering angle and vehicle behavior during steering, regardless of the response performance of the rear wheel drive actuator.

However, in this earlier application, the control system is configured with a continuous optimum regulator, so in order to make the rear steering angle follow the target value, the reference model is
The form of the normative model cannot be freely determined because it must take the following form.

As a result, the dynamics of the actuator may not be fully taken into account. Furthermore, since the order of the reference model is high, calculations are complicated and a microcomputer with high calculation capacity is required.

The present invention has been made in view of the above-mentioned problems, and is a vehicle steering angle control device for auxiliary steering of at least one of the front and rear wheels during steering. An object of the present invention is to provide a device that can perform fine control to obtain a desired response regardless of response performance.

(Means for Solving the Problems) In order to solve the above problems, in the vehicle steering angle control device of the present invention, the control system is a digital control system, and by approximately performing differentiation; This is a means of total control using the dynamic characteristics of the actuator, the reference model, and the vehicle dynamic characteristics.

That is, as shown in the diagram corresponding to the claims in FIG. An actual steering angle detection step C detects the steering angle, an actuator d performs auxiliary steering of at least one of the front wheels or the rear wheels, and a steering angle signal and a vehicle speed signal are inputted to the actual steering angle detection stage C, which is a constant or a function of the vehicle speed. 1 filter e, the actual steering angle signal and the vehicle speed signal are inputted, and the second filter f whose constant is a function of the vehicle speed performs subtraction of the first filter output signal and the second filter output signal to send the signal to the actuator d. The present invention is characterized in that it includes a digital auxiliary steering control signal calculation means h consisting of a subtractor 9 for calculating a control signal.

(Function) During steering, a steering angle signal and a vehicle speed signal are input to the digital auxiliary steering control signal calculating means h, and the first filter output signal whose constant is a function of the vehicle speed is sent to the first filter e.
A second filter output signal whose constant is a function of the vehicle speed is output from the second filter f, which inputs the actual steering angle signal and the vehicle speed signal, and outputs the second filter output signal from the second filter f, which inputs the actual steering angle signal and the vehicle speed signal. The auxiliary steering control signal is calculated by subtracting the output signal.

Based on this auxiliary steering control signal, a command to obtain a desired auxiliary steering angle is output to actuator d.

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

First, the configuration will be explained.

FIG. 2 is a block diagram showing the vehicle steering angle control device of the first embodiment, which is a system for auxiliary steering of the rear wheels using a motor actuator when steering the front wheels.

The vehicle steering angle control device of the first embodiment includes a steering angle sensor 1 for detecting a front wheel steering angle O, a vehicle speed sensor 2 for detecting a vehicle speed V, and a motor rotation angle Φ corresponding to an actual rear wheel steering angle. a motor rotation angle sensor 8 for steering the rear wheels, a motor actuator 6 for auxiliary steering of the rear wheels, a rear wheel steering mechanism 7 for converting the drive of the motor actuator 6 into a steering drive for the rear wheels, and a steering angle signal (0). Input the vehicle speed signal (V), and the constant is the vehicle speed V
A first signal calculation unit 3 (first filter) outputs a first signal that is a function of the motor rotation angle signal (Φ) and a vehicle speed signal (
V) and outputs a second signal whose constant is a function of the vehicle speed V;
Motor torque command value T. ．． A digital controller 10 (
(auxiliary steering control signal calculation means) and a motor driver 5 that converts a current command value I from a digital controller 10 into a current I.

As shown in FIG. 3, the rear wheel steering mechanism 7 includes a worm gear 71 driven by a motor actuator 6;
A worm wheel 72 that meshes with the worm gear 71, a pinion gear 73 provided at the rotating shaft position of the worm wheel 72, a rack gear 74 that meshes with the pinion gear 73, a tie rod 75 on which the rack gear 74 is formed, and the tie rod 75. The rear wheels are steered according to the stroke of the tie rod 75.

Next, the effect will be explained.

FIG. 4 is a control block diagram showing the device of the first embodiment as a continuous value control system.

First, modeling of the motor driver 5, actuator motor 6, and rear wheel steering mechanism 7 to be controlled in a continuous time system can be performed as follows.

The motor driver 5 sends a current to the current command value air actuator motor 6, and in a practical range, the transfer characteristic can be considered as: (1) 2=1 (1) (1).

Next, if the motor 6 and the steering gear side 7 are configured as shown in Fig. 3, the equation of motion is approximately as follows: 0: actuator viscosity converted to motor shaft (D≧0) K: actuator converted to motor shaft Rigidity (K≧O)T, ,: Motor torque (T.
=Ky"I, Kt: l' Luk constant 0Td: Disturbance from the road surface Φ: Motor rotation angle NR: Gear ratio. Now, if we ignore the disturbance T, the motor rotation angle with respect to the motor torque Transfer function G of Φ
(S) becomes as follows.

The attainment characteristics are given as follows. (Φ=6,・NR) The transfer characteristic (normative model) of the motion of the vehicle's yaw rate ψ with respect to the steering angle e is, where T: time constant G (V): gain that changes depending on the vehicle speed V, then the vehicle's yaw rate transmission The characteristics are A, (V
)ψ=8, (V)・e182(V)・δ8...
However, A+(V)"S2+A++(V)・S+A+2(
V)B+(V)”8++・S+8+2(V)B2 (V
) =82+ -s+822 (V)? eKF: Front wheel equivalent cornering power KR: Rear wheel cornering power L, L■: Distance between front and rear axle center of gravity IJ Two vehicle mass I2 Two vehicle yaw inertia NO = Steering gear ratio L: Wheel base length (5 ), so in equation (5), the yaw rate ψ is (4)
To match the formula, find the target transfer characteristic (δR/e)' of the rear wheel steering angle δ8 with respect to the steering angle O from the formula (6). However, next, in the control system of Fig. 4, the steering angle f. so that the transfer characteristic of the actual rear wheel steering angle is as close as possible to the transfer characteristic of equation (7). ,f,,β1β2. Determine the value of β3.

In Fig. 4, the transfer function GxδR(S) from X to 6Fl is calculated by making the denominator of equation (8) and equation (7) the same.
'． f,=A,,・J−D
...(9)fo=Ar2・JK
−(10) However, (8
) is J times larger than the denominator of equation (7), so
By multiplying that amount by β, , βr2rBr3, (
Model matching between equation 7) and the control system shown in FIG. 4 is achieved.

．．゜． β,=Jx ll, ,
...(11) β2"JX B,2- (+2) a3=Jxill,3...
- (13) Although the gain of the continuous value control system has been found above, the gain when configuring an actual digital controller can be found, for example, as follows.

As shown in FIG. 5, the Laplace transform of the signal before the sampler is converted to X. (S), and when it is sampled at the sub-ring period T, the following is obtained.

Therefore, if GT (S) =f, +f, 8, then? (
x+' (Z)J ■: eTS Therefore, the output X3(S) of the ○th hold is... (14) -... (20) When 0S is expanded by Maclaurin in the vicinity of S=0, 1.゜． Δ = - (1-e Ding TS) On the other hand, sampling period! When 4#T is sufficiently short, in the vicinity of S;O, the approximation of equation (20) holds well.

Therefore, X3(S) in equation (15) is approximated as follows, and in the end, the sample (!!) is the approximate transfer function of the control device.
'． f. ”=f.-A,,・J-K Gll (s) =a3+82s〇 52 similarly, ...(24) (J(S):Il3+β2S+β,S2β3=a3ゝ1 β2=02'- Tel3 ” 2 1 β1: β, book - T - 1lz book + 72・β3I6 .゜.β3●=β3”J・=0,3 1l β, car: 11, +T(β2+− Tlh)−12・β
,26 1 Eβl+Tβ2+-β,72 3 1 =Jβ,++TJfl,2+ [l37'3 Therefore, Gf"(A)=fo#+f,'-4 ?ill (Δ)=83 lines+82'・Δ181 Thing/Δ2
+-Z Δ=■ From T ~car ~car ~rate car
$ 1-ZOf(Z)=f, +f1Z-
'=f. +fl-,~Ningne 1. '． f0=f. +-fI car T ~car 1 f =-1・f,ne・2 T ~umbrella ~rate ~thing Gtl (Z) =Bv+82−z ~car ne ne umbrella'+4+・Z−
'=L"j2Δ+muΔ2...(39)...(27)...(28)...(29)...(30)...(32)...(33) ...(34) ...(35) ...(36) ...(37) ...(38) ?The control block diagram of the discrete value control system used is as shown in FIG.

As explained above, in the vehicle steering angle control device of the first embodiment, the control system is a digital control system, and the differential calculation is approximately performed by this digital control system when the rear wheels are assisted during steering. As a result, we have created a device that performs total control using the dynamic characteristics of the motor 6, which is the actuator, a reference model, and the vehicle dynamic characteristics.The calculation for control is simplified, and the motor 6, whose inertia cannot be ignored, can be used as an actuator. Even though it takes a lot of effort, the actual rear wheel steering angle of 6cm can be obtained by the desired response.

Incidentally, Fig. γ shows the simulation results of the rear wheel actual steering angle 8 and the rear wheel steering angle target value δ8* with respect to the front wheel steering angle e, and very similar results were obtained.

FIG. 8 shows a control block diagram of the discrete value control system of the vehicle steering angle control device of the second embodiment.

In this second embodiment, a robust compensator is added to the device of the first embodiment, so that the influence on the actual rear wheel steering angle 6R due to external disturbances and actuator parameter fluctuations is reduced.

In Figure 8, H (Z) is a low-pass filter, Gm (Z)
is the actuator model.

However, Gm(Z) is GP(S) = 1/(JS2+OS
+K) is discretized using a zero-order holder.

Fig. 9 shows the simulation results when a disturbance is applied, and the actual rear wheel steering angle δ with respect to the disturbance is determined by robust compensation.

It can be seen that the impact on is kept small.

Although the embodiment has been described above based on the drawings, the specific configuration is not limited to this embodiment. include.

(Effects of the Invention) As explained above, in the vehicle steering angle control device of the present invention, the control system is a digital control system, and by approximately performing differential calculation in this digital control system, the control system of the actuator is controlled. Since this is a means of total control using dynamic characteristics, a reference model, and vehicle dynamic characteristics, calculations for control are performed in a vehicle steering angle control system that assists in steering at least one of the front and rear wheels during steering. This has the effect of simplifying the process and enabling fine-grained control to obtain a desired response regardless of the response performance of the actuator.

[Brief explanation of drawings]

FIG. 1 is a claim correspondence diagram showing a vehicle steering angle control device according to the present invention, FIG. 2 is a system block diagram showing a vehicle steering angle control device according to a first embodiment of the present invention, and FIG. A diagram showing a specific example of the wheel steering mechanism, FIG. 4 is a control block diagram of the continuous value control system of the first embodiment device, FIG. 5 is a sampling block diagram of the discrete value control system, and FIG. 6 is the control block diagram of the first embodiment device. Fig. 7 is a control flow diagram of the discrete value control system of the example device; Fig. 7 is a simulation result characteristic diagram of the first example device;
The figure is a control block diagram of a discrete value control system in the second embodiment device, FIG. 9 is a simulation result characteristic diagram in the second embodiment device, and FIG. 10 is a block diagram showing a conventional vehicle steering angle control device. FIGS. 11 and 12 are characteristic diagrams of rear wheel actual steering angle and yaw rate during step steering in a vehicle that uses a motor actuator and applies conventional model-adapted control of yaw rate. a...Steering angle detection means b...Vehicle speed detection means C...Actual steering angle detection means d...Actuator e...First filter f...Second filter 9...Subtractor h...Auxiliary steering control signal calculation means

Claims (1)

[Scope of Claims] 1) Steering angle detection means for detecting a steering angle by driver steering, vehicle speed detection means for detecting vehicle speed, and actual steering for detecting the actual turning angle of a wheel on which auxiliary steering is performed. An actuator for auxiliary steering of at least one of the front wheels or the rear wheels; A first filter to which the steering angle signal and the vehicle speed signal are input and whose constant is a function of the vehicle speed; and the actual steering angle signal and the vehicle speed signal. Enter
A digital auxiliary steering control signal calculation comprising a second filter whose constant is a function of vehicle speed, and a subtracter that calculates a control signal to the actuator by subtracting the first filter output signal and the second filter output signal. A vehicle steering angle control device comprising: means; 2) The transfer characteristic of the actuator is (B_P)/(A_P
) and the transfer characteristic of the set actual steering angle δ to the steering angle θ is (B_C)/(A_C), then the transfer characteristic F_1 of the first filter and the transfer characteristic F_2 of the second filter have the following relationship. F_1=(B_C)/(B_P)F_2=(A_C-A
2. The vehicle steering angle control device according to claim 1, wherein the vehicle steering angle control device satisfies the expression _P)/(B_P). 3) The vehicle steering angle control device according to claim 2, wherein the transfer characteristic (B_C)/(A_C) is set from vehicle specifications or vehicle dynamic characteristics and vehicle speed. 4) The vehicle steering angle control device according to claim 2, wherein the transfer characteristic (B_C)/(A_C) is arbitrarily set by a designer based on vehicle speed and steering angle.