JPH01266074A - Method for controlling rear wheel of four-wheel steering vehicle - Google Patents

Abstract

PURPOSE:To improve driving stability in the captioned method in which rear-wheel steering angle control proportionate to rear-wheel slide-slip angle is performed by carrying out rear-wheel steering angle control based on a steering coefficient which is operated according to a defined formula at the time of hauling a trailer. CONSTITUTION:At the the of traveling of a four-wheel steering vehicle which can haul a trailer T, a rear wheel steering angle deltar is operated based on a rear-wheel slide-slip angle betar and a defined steering coefficient kr to carry out the steering control of rear wheels 12 according to the operated value. When the traction of the trailer T is detected by a traction sensor 7, a trailer-hauling-time steering coefficient krt is operated from the formula I to carry out rear-wheel steering angle control using this steering coefficient krt. In the formula, in the hauling vehicle, m1= vehicle mass, l= wheel base, l1= distance from front wheels to center of gravity of vehicle, l2= distance from rear wheels to center of gravity of vehicle, lh= distance from center of gravity of vehicle to trailer linking point, K1= front wheel cornering power, and K2= rear wheel cornering power. In the trailer, m2= vehicle mass, lt= wheel base, l3= distance from trailer linking point to center of gravity of vehicle, and l4= distance from center of gravity of vehicle to trailer wheels.

Description

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

Conventional technology Four-wheel steering technology, which enables steering of the front and rear wheels and improves vehicle steering by steering the rear wheels in the same phase as the front wheels when traveling at high speeds, has been published numerous times since Japanese Patent Laid-Open No. 55-91457. has been done.

Problems to be Solved by the Invention In recent years, there has been an increasing number of cases in which a trailer such as a camper car is connected to the rear of a vehicle, for example, a passenger car, for leisure purposes.

In general, the steering characteristics of the vehicle itself are normally set to understeer in order to improve handling stability, but in vehicles, especially passenger cars, where the trailer connection point must be placed behind the center of the rear wheels. Since the stability factor when towing a trailer is smaller than when towing a trailer, the steering characteristics change to the side of oversteer, and as a result, vehicles towing trailers have a problem in that the steering stability at high speeds decreases. .

The present invention provides a rear wheel steering control method when towing a trailer in the four-wheel steering vehicle as described above, and the conventional problem of reduced steering stability when towing a trailer is solved by the rear wheel steering control method. This is what we are trying to solve.

Means for Solving the Problems The present invention provides a four-wheel steering vehicle in which the steering coefficient is kr and rear wheel steering angle control is performed in proportion to the rear wheel sideslip angle. For the symbols, refer to the symbol explanation table in Figure 2).When towing a trailer, the steering coefficient krt is used to control the rear wheel steering angle in proportion to the rear wheel sideslip angle. It is something.

As mentioned above, when towing a trailer, the steering characteristics change to oversteer and the understeer tendency weakens compared to when not towing, so if you try to steer the same way when towing a trailer as when not towing, the steering will be turned too far and the vehicle will spin. However, by controlling the steering coefficient of the rear wheels when towing a trailer as described above, the steering characteristics when towing a trailer are the same as those when not towing, and the steering characteristics when towing a trailer are It is easy to operate and can improve safety.

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

FIG. 1 is a diagram showing an example of a four-wheel steering mechanism in a trailer towing vehicle, where 1 is a steering handle, 2 is a conventionally known front wheel steering mechanism such as a rack and pinion type, and 3 is a front wheel.

4 is the lateral force (cornering force) generated on the rear wheel 12
The signal of the rear wheel lateral force CF2 detected by the lateral force sensor 4 and the signal of the vehicle speed V detected by the vehicle speed sensor 5 are both input to the control unit 6.

7 is a trailer traction sensor that detects whether or not the trailer is being towed and inputs the detection signal to the control unit 6; the trailer traction sensor 7 is a stop lamp connector that is always connected when the trailer is connected as shown in the figure; It is most reliable and simple to use a manual switch, but a manual switch that is manually operated by the driver may also be used.

The control unit 6 determines the rear wheel sideslip angle βT from the signal of the rear wheel lateral force CF2 from the lateral force sensor 4 (β
2 can be easily obtained using the formula: , = C-F2. (2 is the cornering power of the rear wheels), and δr = -kr・δr (where kr is the steering coefficient, and the steering coefficient kr is set as a function of the vehicle speed V). The steering angle δr is calculated, and an output signal is issued to the rear wheel steering actuator, such as the electric motor 8, to operate it, and the electromagnetic clutch 9. Reduction mechanism 10. The rear wheels 12 are steered through a rear wheel steering mechanism 11 consisting of a link mechanism, etc., and the rear wheel steering angle sensor 13 detects the rear wheel steering angle, and the motor rotation detects the rear wheel steering angle signal and motor rotation speed. The steering angle 81 of the rear wheel 12 determined by the control unit is determined by feedback control based on the rotational speed signal of the speed sensor 14.
It is designed to be steered onto the street.

As the lateral force sensor 4 for detecting the lateral force on the rear wheels, an electric motor 8 is used as an actuator for steering the rear wheels, as shown in the figure.
For example, it is convenient to use a torque sensor that detects the torque of the output shaft of the reduction mechanism IO and detect the rear wheel lateral force from this torque, but it is also convenient to use a hydraulic cylinder as the rear wheel steering actuator. When used, various means can be adopted depending on the specific structure of the rear wheel steering bag, such as detecting the rear wheel lateral force using a hydraulic pressure difference detection means for detecting the hydraulic pressure difference between the left and right hydraulic chambers of the hydraulic cylinder.

As mentioned above, the rear wheel steering angle δ is proportional to the rear wheel steering angle βr.
In a four-wheel steering vehicle that performs rear wheel steering control with r, the stability factor kr when the trailer is not towed is calculated as follows, where A is the stability factor of a two-wheel steering vehicle with only front wheels, kr=A+kr-''mu=72, etc. to 0+, yntlr
−−−−−−(.

zkxL' zK+ K71' 2
K2p, and the stability factor krt when towing a trailer is the steering coefficient krt.

(Each symbol in the above formulas (1) and (2) is the second
(Please refer to the two-wheel model diagram and symbol explanation table of the trailer towing vehicle in the figure).

From the above equations (1) and (2), in the case of a vehicle where the trailer connection point must be located behind the rear wheels (for example, Toyo East, etc.), if At = krt, then kr > krt. Therefore, when towing a trailer, the steering characteristics change in a direction approaching oversteer compared to when not towing, and if the steering is performed when towing a trailer in the same way as when not towing a trailer, the steering may be turned too much and cause the vehicle to spin.

Therefore, in the present invention, in a four-wheel steering vehicle that performs rear wheel steering angle control proportional to the rear wheel tank slip angle, the steering coefficient 1a of the rear wheels when towing a trailer is
krt is calculated using the formula shown below, and by controlling the rear wheel steering angle δ' when the trailer is pulled by δr--krt・δf, the steady steering characteristics are the same when towing the trailer and when not towing the trailer. This makes it easier to turn around when towing a trailer and improves safety.

That is, in a four-wheel steering vehicle that performs rear wheel steering control with a rear wheel steering angle δ which is proportional to the rear wheel tank slip angle βr, the steering characteristic when not towing a trailer is (where δf is the front wheel steering angle and δfo is V
:Initial front wheel steering angle when the vehicle is O) The steering characteristic when towing a trailer is expressed as (where δft is the front wheel steering angle when towing a trailer).

Here, in order to keep the steering characteristics unchanged between when the trailer is not towed and when the trailer is towed, it is necessary to make equation (3) and equation (0 equal) kr = Alt 〜−−−−−−−−−−−−−−−
-1 σ), and by solving equation (5) using equations (1) and (2) above, we can find krt using equation (6) when towing a trailer, and use this steering coefficient fjLrt to calculate the steering coefficient fjLrt. By controlling the rear wheel steering angle in proportion to the wheel tank slip angle, steady steering characteristics can be achieved even when a trailer is being towed, which is the same as when not towing.

In the above formula (6), each symbol is a numerical value determined as each vehicle specification of the towing vehicle and trailer, as described in the symbol explanation table in FIG. This can be easily calculated by providing a steering coefficient calculation device, also known as a memory bag.

That is, as shown in FIG. 3, by inputting the vehicle specifications of the towing vehicle and the towed vehicle through the input bag Ha and storing them in the storage device b+c, the towing/non-towing switching device f, i.e. When a trailer traction signal is input from the trailer traction sensor 7, the steering coefficient calculation bag fid calculates the steering coefficient when the trailer is not towed, which is determined from the information on the vehicle speed V input from the vehicle speed detection device δe, that is, the vehicle speed sensor 5. kr and memory bag δ(b)
, and the vehicle specifications stored in (C).
) to find the steering coefficient krt when towing a trailer, and when the rear wheel tank slip angle βr occurs, the rear wheel steering means control system! ! 1g is β from the steering coefficient krt obtained by the above calculation and the above βr.
By determining the rear wheel steering angle δr proportional to r and issuing an output signal to operate the actuator of the rear wheel steering bag ηh, that is, for example, the electric motor 8, to control the rear wheel steering angle, even when towing a trailer, as described above. It is possible to achieve steady steering characteristics that are the same as when the vehicle is not being towed, and it is possible to significantly improve maneuverability when towing a trailer.

The present invention is not limited to the rear wheel steering device shown in FIG. 1, but can be applied to any rear wheel steering device that controls the rear wheel steering angle δr proportionally to the rear axle side slip angle βr.

As a supplementary explanation, the equations (1) and (2) (stability factors kr, krt) in a coupled vehicle (four-wheel steered vehicle + trailer) that performs rear wheel steering angle control in proportion to the rear axle sideslip angle will be explained below. Guidance will be explained with reference to the two-wheeled model shown in Fig. 752.

Of course, there is only one trailer connection point.

In FIG. 2, for ease of explanation, the connection point at the rear of the towing vehicle and the connection point at the front of the trailer are shown separately in the front and rear on the X-axis.

First, consider the following model. It is assumed that there is no moment transmission at the trailer connection point, and that only cornering force acts on each wheel. In addition, the front and rear wheel steering angles δf, δr, center of gravity inspection slip angles β, β', sideslip angles βr, βr, βt of each wheel, and bending angle φ at the connection point are all assumed to be small, and are calculated as follows: cos O medium 1, 5ino medium θ, tanO Set to 0.

Further, it is assumed that steady running 9=0.

Here, we can ignore the motion in the x and x' axis directions, so we will consider the balance in the lateral direction and yawing direction of the vehicle, respectively.

In the towing vehicle section.

What is the balance of forces in the y-axis direction? yIIV(βC7J) = 2 CF120Fz
What is the balance of moments around (ll) z@b?

I, φ ”'21tCE+ 21zCFz-ノ4F
−−−−−−=<tz) In the trailer section, the balance of forces in the y′ axis direction is m2V = 7 + ψ′ = 2C7: s−F′−−−−1−−
-----(15) The balance of moments around the Z' axis is IA"=-;yノ4c/:B-ノ:iF'----
−−−−−−−64) The following constraint condition holds at the connection point.

v'=v+muφφ→V −−−−=−os>V泗′
15Φ'-V (β10q-noAφ ----------
−−−(l(1)φ=φ−ψ′−−1−−1−−−−1−−−11−−−・−(/7) F′ groanF −−−〜−−
−−−−−−−−−−−−−−−−−−−(18) Front axle sideslip angle Rear axis sideslip angle Trailer axis sideslip angle In addition, the cornering forces CFl and CF2°CF3 are the cornering power Kl, respectively. Assuming 2°F3.

ノ、φ C"F+= K+β,=-に啄（β1000−7−4)−−
−−−−−−−−−−<n)ノ, φ CF2= Kzβ, =−to 2(β−7−Σpiece−−
−−−−−・(23) 7!4ψ′−m− CF5=− to 9β4= Ky(β−vra −−−−
-----(J4) When F and F' are eliminated from equations (11), (13), and (18).

771.
((Fl + CFx i CFs) = 0 In the above formula, (2
2) Substituting equations (24) to obtain the bay rv(βsψ)V
? β'sφ = zK, , S = 2, μ Further, substituting equations (15) to (17) and rearranging, we get
+711. /, φ meridian φ+2, ψ−2kt54+2k
Jr −−=−(y) By eliminating F and F′ from equations (11), (14), and (18), I2φ′+mzlav(p
+tjsu+2-k(Fi-2b(CFttCFz)=
0Substituting equations (22) to (24) into the above equation, ■2φ'17
yl+I to V(β+ψ)-2, no. (ρ′-J addition)+z13/(K,-1-y,)p+$,, 1
=21aK+s5 +213 to 2& Furthermore, substituting equations (15) to (17) and rearranging, we get
−1, Vρ+2((K+”KJ)Iy− to box Ip錡φ−
1,'P--;-ψ-2<, ノ. Ya;27JkLLS+
↑2ノ3kJr ---Cz6) (12), (13),
If F and F' are eliminated from equation (18).

I, ←77721kV'(S" ψtsu-24(Ftsu2
Tsuyu cr, su2 so-CF yaw 0 in the above formula (21) ~ (20
Substituting the formula, 11φ−m−JJ,V′(/3′+φ+2(K+
Il-KxlJβ+2'"0φ-2kddp Lsu V V'=2, ]ts
4 2kzllSr Furthermore, by substituting and rearranging equations (15) to (17), we get
m2 no kVp +2 (-+1++ to 2A+ks!')
73-IL”=xl/U C nori stop+19.-Kamobaku Ichikuヰ1φ 10m, 1.7.t+”t 14 Zt≠←z＊yh
ttp −−2+ノJ4+2kylz5Y or more, (2
Equations 5), (2G), and (27) are interlocking equations for the connected vehicle (towing vehicle + trailer) in the vehicle body coordinate system.

Next, consider steady circular turning and steering characteristics.

In steady circular turning, β=0...Constant sideslip angle of center of gravity ψ; 0
... Yaw angular velocity constant d, indicated = 0 ... Relative angle constant. Substituting into equations (25) to (27) and expressing it in a matrix gives the following.

If the turning radius is R, then ■(Grade resistance-------(3o)) Here, in steady circular turning, 4=O, so ψ" R----=-- ------- (31) Next, assuming the steering coefficient kr of the rear wheels of the towing vehicle, 5y=Igr-ρr
=-h, (β-sφ-tar)-(32) However, if it is assumed to be controlled by Okurku1 (in-phase steering), equation (29) becomes---(3F) where (33 ) equation as Δ・γ='f5s.

−−−(3+) Solving equation (33) for silkworms, substituting equations (31) and (34) and rearranging for δf, ・−−−Qf) However, Sea = ′L (in y O).

From equation (35), the stability factor krt of the 6Q four-wheel steering vehicle with a proportional angle of rear wheel tank when towing a trailer is obtained.

---=-C36) Let krt be the steering coefficient when towing a trailer.

Equation (35) becomes equation (4) above, and equation (3B) becomes equation (2) above.

In the case of a four-wheel steering vehicle with rear wheel sideslip color proportional type (without trailer being towed), it is also possible to delete the term related to the trailer and set m2 = 0 in equations (35) and (3G) using the same method. ), the stability factor kr is.

Equation (37) becomes equation (3) above, and equation (38) becomes equation (
1) Equation becomes.

Stability factors kr and krt are determined as described above.
can lead to.

Effects of the Invention As described above, according to the present invention, in a four-wheel steering vehicle that performs rear wheel steering angle control proportional to the rear wheel sideslip angle, when towing a trailer, the steady steering characteristic when towing is different from the steady steering characteristic when not being towed. By controlling the rear wheel steering angle so that the vehicle has a steady steering characteristic, it is possible to drive safely even when towing a trailer with the same steering wheel operation as when not towing, thereby significantly improving steering stability. This is something that can bring about great practical effects.

[Brief explanation of the drawing]

: Figure 51 is a top explanatory view showing an example of a rear wheel steering device of a four-wheel steering vehicle to which the method of the present invention is applied, Figure 2 is a two-wheel model diagram of a four-wheel steering vehicle towing a trailer, and Figure 3 is a main It is a block diagram showing an example of a rear wheel steering angle control circuit in the invention. l...Steering handle, 3...Front wheel, 4...
・Rear wheel lateral force sensor, 5... Vehicle speed sensor, 6... Control unit, 7... Trailer traction sensor, 8...
...Electric motor, 11...Rear wheel steering mechanism, 12...
Rear wheel, 13... Rear wheel steering angle sensor. that's all

Claims (1)

[Scope of Claims] In a four-wheel steering vehicle in which the steering coefficient is set to kr and rear wheel steering is controlled using a rear wheel steering angle proportional to the rear wheel sideslip angle, the steering coefficient when towing a trailer is determined based on the steering coefficient kr. The coefficient krt is calculated using the following formula, and when towing a trailer, the rear wheel steering coefficient k
1. A rear wheel control method for a four-wheel steering vehicle, comprising performing rear wheel steering angle control proportional to a rear wheel sideslip angle at rt. krt=(m_1l_1ltkr+m_2l_4(l_
1+lh)+m_2l_4(lh-l_2)(K_2/
K_1)/m_1l_1lt+m_2l_4(l_1+
lh)) However, for the towing vehicle, m_1 is the vehicle mass, l is the wheelbase, l_1 is the distance from the front wheels to the vehicle center of gravity, l_2 is the distance from the rear wheels to the vehicle center of gravity, and lh is the distance from the vehicle center of gravity to the trailer attachment point. distance, K_1 is front wheel cornering power, K_2 is rear wheel cornering power. For the trailer, m_2 is the vehicle mass, lt is the wheelbase, l_3 is the distance from the trailer connection point to the vehicle center of gravity, and l_4 is the distance from the vehicle center of gravity to the trailer wheels.