JPH0310972A - Rear wheel control method for four-wheel steering vehicle - Google Patents

Abstract

PURPOSE:To obtain overall flat gain characteristics, increase a natural frequency and a convergent level and improve maneuverability by detecting lateral acceleration at a position aft of the center of gravity of a vehicle, for example, on a rear wheel, and controlling the rear wheel with the proportional and differential signals from the detected acceleration. CONSTITUTION:In a four-wheel steering vehicle, a rear wheel steering angle deltar is so controlled as to be proportional to lateral acceleration yr at a position aft of the center of gravity of the vehicle. Also, when a differential transfer function including proportional terms is G(S), a proportional gain is alpha, a time constant is T and a steering factor is kr, respectively expressed by an equation G(S)=1+alphaTs/(1+Ts) is G(S), the rear wheel is controlled on the basis of an equation deltar=G(S)kr.yr. According to the aforesaid construction, a peak value of frequency characteristics giving a high yaw rate pertaining to a four-wheel steering vehicle with the center of gravity proportional to lateral G, is eliminated together with a large yaw rate drop in a high frequency range. Overall flat gain characteristics are thereby obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for controlling rear wheels in a four-wheel steering vehicle.

Conventional Technology Many four-wheel steering techniques for steering front and rear wheels for the purpose of improving steering stability have been developed and published since Japanese Patent Publication No. 10728/1973.

Rear wheel control methods can be roughly divided into steering angle proportional type and steering force proportional type. Among the latter type, there is a technology that controls the rear wheels according to the lateral acceleration acting on the center of gravity of the vehicle (hereinafter referred to as There are several examples of the gravity center point lateral G proportional type) such as Japanese Patent Application Laid-Open No. 57-44568 and Japanese Patent Application Laid-Open No. 60-161256.

WIWJ to be solved by the invention Control of rear wheel steering angle δr proportional to front wheel steering angle δf (δr ”
4δf), the natural frequency for steering is the same as the conventional two-wheel steering in which only the front wheels are steered. In comparison, the steering force proportional type (including the center of gravity lateral G proportional type) can have a higher natural frequency than the above two-wheel steering due to rear wheel in-phase steering (steering the rear wheels in the same phase as the front wheels). Although it has the advantage of reducing phase lag, it also has the disadvantage that the attenuation deteriorates and the frequency characteristics of the yaw rate gain have a larger peak than in two-wheel steering.

The present invention improves the attenuation of the vehicle response, which is a drawback of the center-of-gravity stipple G proportional type, which controls the rear wheels according to the lateral acceleration acting on the center of gravity, thereby providing a flatter frequency characteristic. It is an object of the present invention to provide a rear wheel control method that takes advantage of the small phase delay, which is an advantage of the center-of-gravity pointillist G proportional type.

Means for Solving the Problems The present invention controls the rear wheel steering angle δ' in proportion to the lateral acceleration Sr behind the center of gravity of the vehicle, and also controls the differential transfer function G(S)=1+x including a proportional term. /+TS δr = G(S) 4r yr (However, F is the steering coefficient and T is the time constant.

α is proportional gain) The system is designed to control the rear wheels.

As a result of the above, the larger peak of the yaw rate gain in the frequency characteristic that occurs in conventional vehicles with G-proportional four-wheel steering vehicles that control the rear wheels according to the lateral acceleration acting on the center of gravity is eliminated. The drop in yaw rate gain in the high frequency range is also reduced, making it possible to obtain flatter gain characteristics as a whole, with less phase lag, and improving the natural frequency and convergence, making it a four-wheel steering vehicle that is easy to drive. It is something that can be done.

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

In a two-wheel model of a four-wheel steering vehicle as shown in Figure 1,
The front wheel steering angle is δf, and the rear wheel steering angle is δ.

The distance from the front wheels to the vehicle center of gravity is f, the distance from the rear wheels to the vehicle center of gravity is lr, and the yaw angular velocity is ψ.

Center of gravity inspection If the slip angle is β and the vehicle speed is V, then center of gravity inspection G
Rear wheel control in a proportional 4-wheel steering vehicle is 8r = 4y = = 4V
C/"ri...group-(1), however, for the silkworm, it is the steering coefficient, and S is the acceleration in the direction of the center of gravity.

In a four-wheel steered vehicle whose rear wheels are controlled by equation (1) above, the frequency response characteristics of yaw rate to steering and the frequency response characteristics of lateral acceleration to steering are shown in Figures 2 and 3.
As shown in ■ in the figure.

In other words, in the center-of-gravity stippled G proportional type controlled by the above equation (1), the natural frequency is the same as that of a two-wheel steering vehicle in which the rear wheels are not steered, as shown by the curve indicated by the symbol ■ in Figures 2 and 3. (2WS) and can reduce the phase delay, but this has the disadvantage that the attenuation deteriorates and the frequency-responsive yaw rate gain has a larger peak.

Therefore, in the present invention, the lateral acceleration behind the center of gravity of the vehicle, for example, on the rear wheels, is detected, and the rear wheels are controlled using the proportional + differential signals. That is, if the lateral acceleration on the rear wheels is νr, and the ratio is taken as the ratio, then the rear wheel steering angle δr in the present invention is
The control method is as follows: δr ”G(S) 4r 5'r= (t +T
V) 4r (j-ur tj)...(3). However, α is the proportional gain, T is the time constant, and S
is the Laplace operator, an element, a number, is the acceleration in the direction of the center of gravity, or is the distance from the rear wheels to the center of gravity of the vehicle, ψ is the yaw angular acceleration, m is the mass of the vehicle, and the yaw moment of inertia of the car h
, Kr is the cornering power of the rear wheels.

By performing the rear wheel control expressed by equation (3) in this way, as shown in the curve shown by the symbol ■ in Figs. 2 and 3, the center of gravity point-pointed G Compared to proportional type (■) which has a peak, it is possible to obtain a flatter gain characteristic as a whole, and in terms of lateral acceleration characteristics, there is less phase delay in the high frequency range compared to center of gravity stippled G proportional type (■). This makes it extremely easy to drive.

The explanation will be given below.

In a four-wheel steered vehicle, the equations of motion for the lateral M motion (in the y-axis direction) and the yaw moment direction motion around the center of gravity (around the Z-axis) are expressed by the following equations (4) and (5), respectively.

Expanding the formula, = Toshi Samurai + 21F: rir ... (4) (However, the above (
(For each symbol in equations 4) and (5), refer to the symbol explanation table in FIG. 1.) First, the natural frequency and low normal yaw rate gain are determined for the center-of-gravity pointillist G proportional type four-wheel steering vehicle. Substituting the rear wheel steering angle δ, expressed by equation (1), into (0°) into equation (5) and converting it to Laplace, however, the natural frequency is:・(9) ・・・・・・・・・(10) Taking the damping ratio into consideration, ζω is From equation (8), the characteristic equation is: ・・・(11) However, θ is the steering wheel turning angle, G is the steering gear ratio and is expressed as θ=G−δf.

Next, the natural frequency and steady yaw rate gain are determined for the rear wheel inspection G-proportional four-wheel steering vehicle. In the rear wheel inspection G proportional type, the rear wheel steering angle is expressed as δ:44r=h(y-14)=/erfV(Ink(pl=-(13)).

Rear wheel steering angle δr expressed by equation (13) is expressed as (4), (5)
Substituting into the equation and applying the Laplace transform, and expanding equation (15), the natural frequency is therefore... (18) If the damping ratio is ζr, ζ' (From equation 10, the characteristic equation is:・・・・・・・・・(13) J envelope 6 Steady yaw rate gain θ Next, compare the characteristics of the above-mentioned center of gravity inspection G proportional type and rear wheel stippled G proportional type under the condition that the steady yaw rate gain is equal. To do this, first, equation (12) expressing the steady yaw rate gain and (
20) Assuming that the formulas are equal, then 4 = 4 r...
・(21) Here, equation (10) representing the natural frequency and (1
8) Comparing the equations, we find that in the above, ω, −ω, which indicates the stability factor
0 that is ω, 〉ω ・・・・・・・・・
...(22) Therefore, when in-phase steering (4>0) is performed, the natural frequency of the rear wheel stipple G proportional type is higher than that of the center of gravity inspection G proportional type.

Next, ζω, ζr related to the settling time, which is a guideline for convergence.
Comparing Equation (11) and Equation (19), which express ωr, we find that ζr ω'' 〉ζω Therefore, when performing in-phase steering (4>O), the rear wheel stippled G proportional type has a lower center of gravity inspection G proportional type than the center of gravity inspection G proportional type. Since this becomes larger, the settling time (settling time oc 70,000) becomes shorter, the vibration subsides more quickly, and characteristics that are extremely easy to drive can be obtained.

Next, the transfer function G (S) expressed by the above equation (2) will be explained.

When α>0, the Bode diagram becomes as shown in FIG.

The normal gain is set equal to 61 = 4r'Yr, and the rear wheel steering angle δ in the peak in-phase direction is compared with the conventional one.
dB], since IG(S) is 1, the rear wheel steering angle is δ
r = 4r Yr.

Therefore, the rear wheel steering angle δ is.

! r% (J, ≦r 4.” Tonal.

,2/r Therefore, the rear wheel steering angle δ is δ,≠(l+α)4rY+-.

In other words, the center of gravity inspection G proportional type that does not perform differential control has a large peak due to the yaw rate gain, as shown in ■ in Figure 2, whereas the above equation (2) using the lateral acceleration νr on the rear wheels In order to control the rear wheels using the transfer function G (S), δ and Φ(1+α)4rν1 are maintained, and the amount of rear wheel steering in the in-phase direction is kept constant to prevent a decrease in gain.
It is possible to obtain a preferable frequency response as shown by the symbol ■ in FIG. 2, and also to improve the natural frequency and convergence.

In the above embodiment, an example was shown in which rear wheel control is performed by detecting the lateral acceleration on the rear wheels, but it does not necessarily have to be on the rear wheels, but can be applied at any point between the vehicle center of gravity and the rear wheels. Needless to say, it is possible to adopt

Effect of the invention As described above, according to the present invention, the rear wheel steering angle δ.

is controlled in proportion to the lateral acceleration Yr behind the vehicle's center of gravity, and the differential transmission interval T5 including the proportional term is controlled at the number G (St) = 1 + / + 75 δr = G (S) 4 r Y r ( However, 4
r is the steering coefficient and T is the time constant.

α is the proportional gain) By performing rear wheel control, the frequency that was used in conventional vehicles with 4-wheel steering proportional to the center of gravity, which controls the rear wheels according to the lateral acceleration acting on the center of gravity. The large peak of the characteristic yaw rate gain is eliminated, and the large drop in yaw rate gain in the high frequency range is also reduced, making it possible to obtain an overall flatter gain characteristic, less phase lag, and improved natural frequency and convergence. As a result, it is possible to create a four-wheel steering vehicle that is easy to drive, and can bring about great practical effects.

[Brief explanation of the drawings] Figure 1 is a two-wheel model diagram of a four-wheel steering vehicle, Figure 2 is a frequency response characteristic diagram of yaw rate to steering, Figure 3 is a frequency response characteristic diagram of lateral acceleration to steering, FIG. 4 is a Bode diagram of the transfer function in the present invention. Jkt + - 1 Kott me late, /Niheenhan brother answering the helmsman, Puska Mukikano Shidosu Uchiwatani

Claims (1)

[Claims] The rear wheel steering angle δ_r is the lateral acceleration behind the vehicle center of gravity ■_r
δ_r with the differential transfer function G(S)=1+[αTs]/[1+Ts] including the proportional term.
=G(S)k_r■_r (where k_r is a steering coefficient, T is a time constant, and α is a proportional gain).