JP2699082B2 - Rear wheel control method for four-wheel steering vehicle - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for controlling rear wheels of a four-wheel steering vehicle.

2. Description of the Related Art A number of four-wheel steering technologies have been disclosed since JP-A-55-91457, in which the front and rear wheels are steerable and the rear wheels are steered in phase with the front wheels during high-speed driving to improve the vehicle's steerability. ing.

Problems to be Solved by the Invention In recent years, cases for leisure use have been increasing in which a vehicle, for example, a trailer such as a camper is connected to a rear part of a passenger car to travel.

Generally, as a vehicle itself, it is usual that the steering characteristic is set to understeer in order to improve stability, but for vehicles that have to arrange the trailer connection point behind the center of the rear wheel, especially for passenger vehicles, However, since the stability factor at the time of trailer pulling is smaller than when the trailer is not towed, the steer characteristics change to the oversteer side, and therefore, there is a problem that the steerability at the time of high-speed running is reduced in a trailer-towed vehicle.

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

Means for Solving the Problems When the trailer is not towed, the present invention provides kf = −δ at a rear wheel steering angle δr that is proportional to the front wheel side slip angle βf, with the steering coefficient being kf.
In a four-wheel steering vehicle that performs rear wheel steering angle control based on the equation of r / βf, the steering coefficient kft when the trailer is towed is compared with the steering coefficient kf when the trailer is not towed, (However, refer to the symbol explanation table in Fig. 2 for the symbols of the formula.) The following formula is used. When the trailer is towed, the rear wheel steering angle is controlled by this turning coefficient kft in proportion to the front wheel side slip angle. It is assumed that.

Operation As described above, when the trailer is towed, the steer characteristics change in the oversteer direction and the understeer tendency is weakened compared to when the trailer is not towed. However, by performing the steering coefficient control of the rear wheels at the time of trailing as described above, the steering characteristic at the time of trailing becomes the same as the steering characteristic at the time of non-towing, and at the time of trailing, The driving operation can be facilitated and safety can be improved.

Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawings.

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

Reference numeral 4 denotes a lateral force sensor for detecting a lateral force (corner force) generated at the front wheel 3. A signal of the front wheel lateral force CF ₁ detected by the lateral force sensor 4 and a signal of the vehicle speed V detected by the vehicle speed sensor 5 are provided. Both are input to the control unit 6.

Reference numeral 7 denotes a trailer traction sensor for detecting whether or not the vehicle is in a trailer traction state and inputting a detection signal to the control unit 6. The trailer traction sensor 7 is a stop lamp connector which is always connected when a trailer is connected as shown in the figure. Is the most reliable and simple to use, but a manual switch manually operated by the driver may be used.

The control unit 6 calculates the front wheel side slip angle βf from the signal of the front wheel side force CF ₁ from the side force sensor 4. It is easily obtained by the following formula. However, K1 is the cornering power of the front wheels), δr = −kf · βf (where kf is a turning coefficient, and the turning coefficient kf is set as a function of the vehicle speed V), and the rear wheel steering angle is obtained. δr is calculated, and an output signal is issued to a rear-wheel steering actuator, for example, an electric motor 8 to operate the same, and the rear wheel 12 is driven through a rear-wheel steering mechanism 11 including an electromagnetic clutch 9, a speed reduction mechanism 10, and a link mechanism. Steering operation,
The control unit determines the rear wheels 12 by feedback control based on a rear wheel steering angle sensor 13 for detecting a rear wheel steering angle and a feedback control by a rotation speed signal of a motor rotation speed sensor 14 for detecting a motor rotation speed. The steering is performed according to the angle δr.

As the lateral force sensor 4 for detecting the lateral force of the front wheels, for example, in a vehicle equipped with a known hydraulic power steering device in the front wheel steering system, the hydraulic pressure difference between the left and right hydraulic chambers of the power cylinder of the hydraulic power steering device is used. It is easy to detect the front wheel lateral force from the hydraulic pressure difference by using the hydraulic pressure difference detecting means for detecting the front wheel lateral force. However, the known front wheel force detecting means for detecting the steering torque of the steering wheel 1 is used to detect the front wheel lateral force therefrom. For example, any means can be adopted.

As described above, in a four-wheel steering vehicle that performs rear wheel steering control at a rear wheel steering angle δr proportional to the front wheel side slip angle βf, the stability factor Af when the trailer is not towed is the stability of a two-wheel steering vehicle having only front wheels. Assuming the factor is A, And the stability factor Aft for trailer towing.
Is the steering coefficient kft, (Each symbol in the above equations (1) and (2) is
(Refer to the two-wheel model diagram and the symbol explanation table of the trailer towing vehicle in the figure).

From the above equations (1) and (2), generally, when kf = kft, Aft <Af, and the steer characteristics change in the direction approaching oversteer when the trailer is towed compared to when the tow is not towed,
When the trailer is towed in the same manner as when the vehicle is not towed, the rudder may be overturned and the vehicle may spin.

Therefore, in the present invention, in a four-wheel steering vehicle that performs rear wheel steering angle control in proportion to the front wheel side slip angle, the steering coefficient kf of the rear wheel when the trailer is towed is compared with the steering coefficient kf when the trailer is not towed.
t is calculated by the formula shown below, and the trailing rear wheel steering angle δr is controlled by δr = −kft · βf at the time of trailer pulling, so that the steady steering characteristics at the time of trailer pulling and at the time of non-traction are equalized. As a result, the driving operation at the time of towing the trailer is facilitated and the safety is improved.

That is, in a four-wheel steering vehicle that performs rear wheel steering control at a rear wheel steering angle δr proportional to the front wheel side slip angle βf, the steering characteristic when the trailer is not towed is (Where δf is the front wheel steering angle and δf ₀ is the initial front wheel steering angle when V ≒ 0). (However, δft is the steering angle of the front wheels when the trailer is being pulled.)

Here, in order that the steer characteristics do not change when the trailer is not towed and when the trailer is towed, the equations (3) and (4) may be used as equals as long as Af = Aft (5). By solving equation (5) using equation (2), Therefore, when the trailer is towed, kft is calculated by equation (6), and the rear wheel steering angle is controlled in proportion to the front wheel side slip angle by using the turning coefficient kft. It can be.

In the above equation (6), each symbol is a numerical value determined as each vehicle specification of the towing vehicle amount and the trailer as described in the description table of symbols in FIG. The calculation can be easily performed by providing the original storage device and the turning coefficient calculation device.

That is, as shown in FIG. 3, by inputting the vehicle specifications of the towing vehicle and the towed vehicle from the input device a and storing them in the storage devices b and c, the towing / non-towing switching device f, namely, When a trailer traction signal is input from the trailer traction sensor 7, the steering coefficient calculation device d determines the steering coefficient when the trailer is not towed, which is determined from the vehicle speed detection device e, that is, the vehicle speed V input from the vehicle speed sensor 5. kf and storage devices (b) and (c)
The steering coefficient kft when the trailer is towed is calculated by the above equation (6) based on the vehicle specifications stored in the vehicle, and the front wheel side slip angle β
When f occurs, the rear wheel steering means control device g obtains a rear wheel steering angle δr proportional to βf from the turning coefficient kft obtained by the above calculation and βf to obtain an actuator of the rear wheel steering device h, for example, an electric motor. 8 to control the rear wheel steering angle by issuing an output signal to operate the steering wheel 8 as described above, it is possible to obtain a steady steering characteristic that is the same as non-traction when the trailer is towed. Significant improvements can be made.

The present invention is not limited to the rear wheel steering device shown in FIG. 1, but can be applied to a rear wheel steering device having an arbitrary configuration for controlling the rear wheel steering angle δr proportionally to the front wheel side slip angle βf.

As a supplementary explanation, the induction of the equations (1) and (2) (stability factors Af, Aft) in a connected vehicle (4-wheel steering vehicle + trailer) that performs rear wheel steering angle control in proportion to the front wheel side slip angle. Will be described with reference to the two-wheel model in FIG.

Although there is naturally one trailer connection point, in FIG. 2, the connection point at the rear of the towing vehicle and the connection point at the front of the trailer are separately shown on the x-axis for ease of explanation.

First, consider the following model. It is assumed that there is no moment transmission at the trailer connection point, and that only the cornering force acts on each wheel. Further, the front and rear wheel turning angles δf, δr, the center-of-gravity point side slip angles β, β ′, the side slip angles βf, βr, βt of each wheel, and the bend angle φ of the connection point are all small cos θ ≒ 1, sin θ ≒ θ, tan θ ≒ θ. It is also assumed that steady running = 0.

Here, since the movements in the x and x'-axis directions can be ignored, a balance is considered in each of the lateral direction and the yawing direction of the vehicle.

In the towing vehicle, the balance of the force in the y-axis direction is m ₁ V (+) = 2CF ₁ + 2CF ₂ + F (11) The balance of the moment about the z-axis is I ₁ = 2l ₁ CF ₁ −2l ₂ CF ₂ −lhf (12) In the trailer section, the force and balance in the y′-axis direction are: m ₂ V ′ (′ + ′) = 2CF ₃ −F ′ (13) The moment around the z′-axis The balance is I ₂ ′ = −2l ₄ CF ₃ −l ₃ F ′ (14) At the connection point, the following constraint condition is satisfied.

V '= V + lhφ ≒ V ...... (15) V'β' + l 3 '= V (β + φ) -lh ...... (16) = -' ...... (17) F '≒ F ...... (18) the front wheel side slip angle Rear wheel side slip angle Trailer wheel side slip angle Further, assuming that the cornering forces CF ₁ , CF ₂ and CF ₃ are K ₁ , K ₂ and K ₃ respectively, Eliminating F and F 'from equations (11), (13) and (18) gives m ₁ V (+) + m ₂ V'('+') -2 (CF ₁ + CF ₂ + CF ₃ ) = 0 Substituting equations (22)-(24) into Furthermore, rearranging by substituting equations (15) to (17), Eliminating F and F 'from equations (11), (14) and (18) gives: I ₂ ′ + m ₁ l ₃ V (+) + 2l ₄ CF ₃ −2l ₃ (CF ₁ + CF ₂ ) = 0 Substituting equations (22)-(24) Furthermore, rearranging by substituting equations (15) to (17), Eliminating F and F 'from equations (12), (13), and (18) yields: I ₁ −m ₂ lhV ′ (′ + ′) − 2l ₁ CF ₁ + 2l ₂ CF ₂ + 2lhCF ₃ = 0 Substituting equations 22) to (24) Furthermore, rearranging by substituting equations (15) to (17), As described above, equations (25), (26), and (27) are equations of motion of the connected vehicle (towing vehicle + trailer) in the vehicle body coordinate system.

 Next, steady circular turning and steer characteristics will be considered.

In the steady circular turning, = 0... Constant side slip angle at the center of gravity point = 0... Constant yaw angular velocity, = 0... Relative angle constant. Substituting into equations (25) to (27) and expressing in a matrix gives:

If the turning radius is R, Here, since it is = 0 in the steady circular turning, Next, the rear wheel of the towing vehicle is used as the steering coefficient kf, However, assuming that the control is performed with kf> 0 (in-phase steering), the equation (29) becomes Here, when equation (33) is set as Δ · x = y · δf, Solving equation (33) gives Here, by substituting the equations (31) and (34) and organizing δf, From equation (35), the stability factor Aft of the front-wheel sideslip angle proportional four-wheel steering vehicle when the trailer is towed is If the turning coefficient at the time of trailer towing is kft, equation (35) becomes equation (4), and equation (36) becomes equation (2).

For a front-wheel side-slip angle proportional four-wheel steering vehicle alone (trailer non-traction state), the term relating to the trailer may be deleted, and m ₂ = 0 may be set in the equations (35) and (36). ), The stability factor Af is Equation (37) is the above equation (3), and equation (38) is the above equation (1).
It becomes an expression.

The stability factors Af and Aft can be derived as described above.

Advantageous Effects of the Invention As described above, according to the present invention, in a four-wheel steering vehicle that refers to rear wheel steering angle control proportional to the front wheel side slip angle, when the trailer is towed, the steady steering characteristic during towing is reduced during non-traction. By performing rear wheel steering angle control so as to have a steady steering characteristic, it is possible to perform sufficiently safe driving with the same steering wheel operation as when the trailer is not towed even when towing the trailer, and it is possible to significantly improve steering stability It can bring a great effect practically.

[Brief description of the drawings]

FIG. 1 is an explanatory plan view showing an example of a rear wheel steering device to which the method of the present invention is applied, FIG. 2 is a two-wheel model diagram of a trailer-truck four-wheel steering vehicle, and FIG. FIG. 3 is a block diagram showing an example of a rear wheel steering angle control circuit in FIG. 1 ... steering wheel, 3 ... front wheel, 4 ... front 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.

Claims (1)

(57) [Claims] When the trailer is not towed, the steering coefficient is kf, and at a rear wheel steering angle δr proportional to the front wheel side slip angle βf, kf = −δ.
In a four-wheel steering vehicle that performs rear wheel steering control based on the equation of r / βf, a steering coefficient kft when trailer is towed is calculated by the following equation with respect to a steering coefficient kf when the trailer is not towed. At the steering coefficient kft, the front wheel sideslip angle βf
A method of controlling rear wheels of a four-wheel steering vehicle, comprising performing rear wheel steering angle control in proportion to the following. In the towing vehicle, m ₁ is the vehicle mass, l is the wheelbase, l ₁ is the distance from the front wheel to the vehicle center of gravity, l ₂ is the distance from the rear wheel to the vehicle center of gravity, lh
Distance from the center of gravity of the vehicle to the trailer coupling point, K ₁ is a front wheel cornering power, K ₂ is the rear wheel cornering power. In the trailer, the distance m ₂ is vehicle mass, lt is wheel base, the distance l ₃ from the coupling point of the trailer to the vehicle center of gravity, l ₄ from the center of gravity of the vehicle to the trailer wheels.