JPS60229873A - Method of controlling steering of rear wheel in four wheel steering vehicle - Google Patents

Abstract

PURPOSE:To make a phase lag in the yaw rate completely zero over all angle range of operation of a steering wheel, by controlling the steering angle betar of rear wheels, corresponding to the sum of a value which is obtained by multiplying the steering angle betaf of front wheels by (K) and a value which is obtained by multiplying the steering speed beta'f of the front wheel by (a). CONSTITUTION:A sensor 7 for detecting the steering angle betaf and speed beta'f of front wheels is attached to a shaft 2, and issues a signal to a rear wheel steering angle computer 9 which also receives a vehicle speed (u) signal from a vehicle speed sensor 8. A computer 9 computes the steering angle betar of rear wheels in accordance with betaf, beta'f and u, and delivers the thus obtained result to a differential amplifier 10 which delivers a voltage corresponding to an actual rear wheel steering angle betar0 and a voltage difference (betar-betar0) corresponding to the beta'r to an amplifier 12. The amplified values are delivered, as control signals, to control an electrohydraulic servo-valve 13 for controlling the feed and discharge of hydraulic pressure into and from a hydraulic cylinder 13, thereby the steering angle of rear tires 17 is controlled by means of rear wheel nuckles 16.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a rear wheel steering control method for a four-wheel steering vehicle in which the front wheels are steered by a steering wheel.

[Prior art]

As a method to improve the steering stability of a vehicle, it has been proposed to reduce the response phase delay of the yaw rate to the steering wheel operating angle. A proposal to realize this was made in Japanese Patent Laid-Open No. 15066/1983. Here, by steering the rear wheels in proportion to the front wheel steering angular velocity, the phase lag near the natural frequency ωn of the yaw rate is made zero, but the phase lag is reduced for steering wheel operation angles that deviate from ωn. The problem is that it cannot be reduced to zero.

[Purpose of the invention]

The present invention solves this problem! The purpose was to reduce the phase delay of the yaw rate to zero over the entire frequency range, not just around ωn, and to further improve the steering stability of the vehicle. An object of the present invention is to provide a wheel steering control method.

[Structure of the invention]

In order to achieve this object, in the present invention, in a rear wheel steering control method of a four-wheel steering vehicle in which the front wheels are steered by a steering wheel, a value obtained by multiplying the front wheel steering angle βr by 3 times the front wheel steering angular velocity βf is provided. The rear wheel steering angle β is
In particular, the coefficients a and k are changed according to the vehicle speed U (where A, B, C, D, and E are constants).

[Action/effect of the invention]

As a result, in the present invention, as is clear from the embodiments detailed below, it is possible to completely eliminate the phase delay of the yaw rate for all steering wheel operation angles, greatly improving the steering stability of the vehicle. can be improved.

Furthermore, at low vehicle speeds, it is possible to turn with a smaller radius than the vehicle disclosed in JP-A-57-15066, thereby improving maneuverability and stability.

〔Example〕

The present invention will be explained below based on the drawings. FIG. 1 is a diagram schematically showing a steering system of a four-wheel steering vehicle. In the steering system, by operating a handle l, a shaft 2. Binion 3. Rank par 4. The front tires 6 are steered via the front wheel knuckles 5 in the same manner as in the conventional system. A sensor 7 that detects the front wheel steering angle βf and the front wheel steering angular velocity βf is attached to the shaft 2, and the signal from the sensor 7 is sent to the rear wheel steering angle calculator 9 along with the signal from the sensor 8 that detects the vehicle speed U. is input. In the calculator 9, the front wheel steering angle βf
, a rear wheel steering angle βr is calculated based on the front wheel steering angular velocity βf and the vehicle speed U, and this is output to the differential amplifier 10. The differential amplifier 10 uses a voltage corresponding to the rear wheel actual steering angle βro detected by the rear wheel steering angle detector 11 and a rear wheel calculated steering angle β.
The difference (βr−βro) between the voltage corresponding to r and the voltage corresponding to
The electro-hydraulic servo valve 13 is controlled using the amplified (β "-βro) as a control signal. The servo valve 13 supplies hydraulic pressure generated by a hydraulic pump 14 driven by an engine or the like to an oil cylinder 15. The steering angle of the rear tire 17 is controlled via the rear wheel knuckle 16.

As mentioned above, the rear wheel actual steering angle βrO is the front wheel steering angle βf
, the front wheel steering angular velocity βf and the vehicle speed U are feedback-controlled, and as will be described later, it is possible to move the vehicle without causing a phase lag in the yaw rate with respect to the steering angle.

As is well known, the response of the vehicle's yaw rate to the steering angle can be written in the form of a transfer function as follows.

The above formula fl+ has a first-order lead system in the numerator and a second-order lag system in the 7th denominator, so the overall form corresponds to a first-order lag system, resulting in a phase lag in the high frequency range. .

If we can devise so that S2+2ζrωrs+ωr2 ++・+ (2) and also satisfy the following two conditions: ζr=ζn...(3) ωr=ωn...(4), the transfer function G
'5f, (S) can be made into a simple proportional element as shown in equation (5) below, and the phase delay can be made completely zero.

(αl, ζr, ωr are constants determined by the vehicle) In the present invention, in order to realize the above, the arithmetic unit 9 shown in FIG. 1 performs the calculation of the following equation (6).

βr=a′βf+βf (6) The conditions required for the coefficients a and k in the above equation (6) will be explained below.

In the vehicle model shown in Figure 4, which ignores the effects of roll on the vehicle, the vehicle speed is , and the vehicle lateral speed is .

Yaw rate is r, front wheel steering angle is βf, rear wheel steering angle is βr
, the wheel height is E, and the distance between the front wheels and the center of gravity of the vehicle is ef.
, the distance between the rear wheels and the center of gravity of the vehicle is expressed as l'', the cornering power per wheel of the front tires is Cf, the cornering power per wheel of the rear tires is Cr, the moment of inertia around the center of gravity of the vehicle is lx, and the vehicle mass When M is the equation of motion in the lateral direction and the yawing direction, the equations of motion in the lateral direction and the yawing direction are subjected to Laplace transform and expressed in the form of a matrix, resulting in the following equation (7).

By setting the coefficient matrix of (V (s) ·R (S)) in the above equation (7) to 8, we can solve for (V (s) ·R (s)).

Therefore, the front wheel steering angle β at vehicle lateral speed V, yaw rate “
The transfer function for f is as follows. Here, the transfer function GHf(s) of yaw rate r
Specifically, (!1 = -2aCrlrM/fMI4)2(rωr
= (M(Cflf −kcrlr) −−a−Cf
CrL)/(-acr9.rM)ωr2=-' (J
CrL(1-k) / (-acrlrM)2 2(nωn = -((cf+Cr)Iz + u(c
fir2+Crt! , r2))/(M engineering ωn' =
(-!-12cfcr -2M(Cflf -Cr1r
))/(M-Z)2, and both the denominator and 9 numerators of the transfer function can be composed of quadratic expressions of S. Here, the above formula +31. (By applying the conditions in 41, a simultaneous equation regarding the coefficients a and k is obtained, and by solving this, it is possible to find the coefficients a and k that make the phase delay completely zero. When solved, the following formula (9
1, +II.

That is, when each coefficient a is expressed in a simplified form using the vehicle speed U as a parameter, it is expressed as the following equation (9)'', OI''.

(A, B, C, D, and E are constants) Of course, since the above formulas f01' and Ql' were calculated using a simplified vehicle model,
The parameter values of A, B, C, D, and E are not exact values calculated from various vehicle parameters, but values modified through experiments, etc., but each coefficient with respect to the vehicle speed U is used. The form of the function of change in a is given by the above equation (91', QO1
' remains the same.

Therefore, the rear wheel steering angle βr is controlled in accordance with the sum of the front wheel steering angle βf multiplied by 8 and the front wheel steering angular velocity βr multiplied by 8, and in particular, the coefficients a and k are adjusted according to the vehicle speed U. By changing the yaw rate as follows, it is possible to completely eliminate the phase delay of the yaw rate for all steering angles, and it is possible to greatly improve the steering stability of the vehicle.

In addition, FIGS. 2 and 3 show each coefficient a.

The value of k with respect to vehicle speed U is calculated and shown using a certain vehicle as an example. As is clear from Fig. 3, the value of the coefficient is negative in the low vehicle speed range, so it is possible to turn with a small radius at low vehicle speeds, and the ? lil verticality and stability can be improved.

Note that, as is clear from FIGS. 2 and 3, each coefficient a has a very large value in a low vehicle speed range, so there is a strong possibility that this will cause a problem in practical use. Therefore, in a low vehicle speed range, a modification method such as fixing the coefficients a and k to a small value instead of taking the functional form of the above equations +91' and 01' can also be considered.

[Brief explanation of the drawing]

FIG. 1 is a block diagram schematically showing the steering system of a four-wheel steering vehicle used to carry out the present invention, and FIGS. 2 and 3 are graphs showing specific numerical examples of each coefficient a. FIG. 4 is a vehicle model diagram used to calculate each coefficient a, k. Explanation of symbols 1... Handle, 6... Front tire, 7, 8...
Sensor, 9... Rear wheel steering angle calculator, lO... Differential amplifier, 11... Rear wheel steering angle detector, 12... Amplifier, 1
3...Electro-hydraulic servo valve, 14...Hydraulic pump, 1
5...Oil cylinder, 17...Rear tire, βr
...Front wheel steering angle, β "...Rear wheel steering angle, U...Vehicle speed, a. k...Coefficient. 1IjA Figure 4 Figure 2 Figure 3

Claims (1)

[Claims] +11 In a rear wheel steering control method for a four-wheel steering vehicle in which the front wheels are steered by a steering wheel, the sum of the front wheel steering angle βf multiplied by 3 and the front wheel steering angular velocity βf multiplied by 3 A rear wheel steering control method for a four-wheel steering vehicle, characterized in that a rear wheel steering angle βr is controlled in a corresponding manner. (2) The coefficients a and k are set according to the vehicle speed U (however, A,
2. The rear wheel steering control method for a four-wheel steering vehicle according to claim 1, wherein B, C, D, and E are constants.