JP2505234B2 - Rear wheel steering method - Google Patents

Description

The present invention relates to a method of steering a rear wheel of a vehicle.

(Prior Art) As a rear wheel steering technique, as described in Japanese Patent Laid-Open No. 60-229873, a steering angle δ obtained by multiplying a steering angle θ and a steering angular velocity during front wheel steering by a proportional constant K and a differential constant τ, respectively. _r =
There is a technique to steer the rear wheel by K · θ + τ · so that the yaw rate gain characteristic with respect to the steering frequency becomes flat, that is, the yaw rate is generated in proportion to the steering angle θ without phase delay regardless of the steering speed. Are known.

The proportional constant K _s and the differential constant τ
_s is different for each vehicle and according to the vehicle speed. As shown in FIG. 5, a vehicle having a vehicle mass M of 160 kgS ² / m, a yaw moment of inertia I of 252 kgmS ² , and a wheel base 1 of 2.48 m is V = 1.
Case of traveling at _{20km / h, K s, τ} s 0.38 each X ₁ point, -
0.049, and as shown in FIG. 6, M = 125 kgS ² / m, I
= 227kgS ² , l = 2.48m at the same V = 120km / h, K _s and τ _s are X ₂ points of 0.33 and -0.056, respectively.

When the rear wheels are steered by the steering angle δ _r obtained by the above formula from the proportional constant and the differential constant determined in this way, the rear wheel steering angle δ _r is 9
As indicated by the solid line in the figure, the yaw rate and the lateral acceleration G are generated as shown by the solid lines in FIGS. 9 and 10, and the change characteristic of the yaw rate gain / θ with respect to the steering frequency is flat as intended. can do.

(Problems to be Solved by the Invention) However, in this rear wheel steering technique, as shown in FIG. 9, the time ΔT _{1 at} which the rear wheels are initially steered in reverse phase with the front wheels is lengthened, and this reverse phase rotation Since the steering amount −Δδ _r1 becomes large,
As indicated by G ₁ in FIG. 11, the lateral acceleration in the direction opposite to the centripetal direction was increased, and it was generated for a long time, and the rear part of the vehicle body was swung, which was uncomfortable.

(Means for Solving the Problem) The present invention sacrifices the flat yaw rate gain characteristic slightly based on the recognition that the discomfort is a greater problem for the occupant than when the flat yaw rate gain characteristic is not achieved. However, from the viewpoint that the above discomfort should be eliminated, a rear wheel steering method for a vehicle that embodies this idea is proposed.

By the way, the proportional constant K and the differential constant τ are values of the flatness of the yaw rate gain characteristic K = 0.38, τ = −0.04
As shown in Fig. 9, when K = 0.30, τ = -0.015, and further K = 0.25, τ = -0.010, the rear wheel steering angle δ _r is indicated by the one-dot chain line and the dotted line, respectively. The reverse phase steering time can be shortened from ΔT ₁ to ΔT ₂ and ΔT ₃ while the reverse phase steering amount is changed from −Δδ _r1 to −Δδ _r2 , −Δδ _r3.
Can be reduced to.

In this case, the occurrence of yaw rate also changes from the solid line in FIG. 10 to the alternate long and short dash line and the dotted line, and the yaw rate gain characteristic deviates slightly from the flat characteristic, but from the solid line in FIG. 11 to the alternate long and short dash line and the dotted line. As is clear from the state of occurrence of changing lateral acceleration, the lateral acceleration in the direction opposite to the centripetal direction can be reduced to a value that is not a problem.

Further, the proportional constant K and the differential constant τ for making the lateral acceleration in the direction opposite to the centripetal direction such a value differ for each vehicle and according to the vehicle speed. In the case of FIG. 5, such K, τ are The values at Y ₁ are 0.30 and −0.015 or less (values within the shaded area), and in the case of FIG. 6, such K and τ are values at and below 0.26 and −0.017 at Y ₂ (hatched area). It was confirmed that it was a value within.

Here, the ratio of the proportional constant between X ₁ point and Y ₁ point in FIG.
To obtain the ratio τ / τ _S of K / K _S and the differential constant, K / K _S = 0.78
9, τ / τ _S = 0.306, and K / K _S = to find the ratio of proportional constants K / K _S and the ratio of differential constants τ / τ _S between X ₂ point and Y ₂ point in FIG. 0.788 and τ / τ _S = 0.304. As is clear from the comparison of these ratios, the above-mentioned slope region in which lateral acceleration in the direction opposite to the centripetal direction causes almost no problem, the K / K _S <0.78, τ / τ _S <0.30 regardless of the vehicle specifications. It can be integrated by, in other words, it can be displayed as a shaded area in FIG. The point X _{3 in} this figure is K = K _S , τ = τ _S set for the above-mentioned conventional rear wheel steering, and therefore K / K _S = a = 1, τ
/ Τ _s = b = 1, and the shaded area (area where lateral acceleration in the opposite direction to the centripetal direction is of little concern) is displayed as a <0.78, b <0.30, a> b where Y ₃ is the limit can do.

Considering the limit point Y ₃ with respect to the vehicle speed V, a and b at this point do not change with the change of the vehicle speed V as shown in FIG. 8, and a ≦ 0.78, b regardless of the specifications of the vehicle and the vehicle speed. ≤
It was confirmed that K and τ such that 0.30 can reduce the lateral acceleration in the direction opposite to the centripetal direction to such an extent that it does not matter.

The ideal Y ₃ point in Fig. 7 is the reason for this.
This is because, even if a and b are made smaller than the values at the Y ₃ point, the yaw rate gain characteristic deviates from a flat characteristic even while the reverse lateral acceleration is reduced to a level that does not cause a problem. . Further, even if it is not the hatched area in FIG. 7, if it is the area inside the dotted line, it is possible to solve the problem relating to the reverse acceleration of the conventional rear wheel steering system to some extent. Therefore, the regions for achieving the object of the present invention can be defined as 0 <a <1 and 0 <b <1.

In view of such a fact, the present invention makes the yaw rate gain characteristic flat with respect to the steering frequency when steering the rear wheels by the steering angle obtained by multiplying the steering angle and the steering angular velocity by the proportional constant and the differential constant, respectively. A rear wheel steering method for a vehicle, characterized in that the proportional constants and differential constants each having a predetermined ratio less than 1 except for 0 to the proportional constants and differential constants contribute to the calculation of the rear wheel steering angle. Is what you are trying to do.

(Operation) When steering the front wheels, the rear wheels are also steered by the steering angle obtained by multiplying the steering angle and the steering angular velocity by the proportional constant and the differential constant, respectively.

By the way, in the calculation of the rear wheel steering angle, the proportional constant and the differential constant are determined as follows. That is, the proportional constant and the differential constant, which have a ratio to the proportional constant and the differential constant that flatten the yaw rate gain characteristic with respect to the steering frequency, are predetermined values less than 1 excluding 0, respectively, and contribute to the calculation of the rear wheel steering angle.

Therefore, although the flat yaw rate gain characteristic is slightly sacrificed, it is possible to reduce the anti-phase steering amount and the anti-phase steering time of the rear wheels to reduce the discomfort that the lateral acceleration in the centripetal direction and in the opposite direction increases. it can. Therefore, even if the flat yaw rate gain characteristic is slightly sacrificed, the above-mentioned discomfort, which is more important, can be reduced, and the riding comfort can be improved.

(Example) Hereinafter, the Example of this invention is described in detail based on drawing.

FIG. 1 shows a steering system of a vehicle used for carrying out the rear wheel steering method of the present invention. 1L and 1R are front left and right wheels, 2L and 2R are left and right rear wheels, and 3 is a steering wheel. The front wheels 1L and 1R use the steering wheel 3 and the steering gear 4 respectively.
The rear wheels 2L and 2R can be steered by the rear wheel steering actuators 5, respectively.

The actuator 5 is a spring center type hydraulic actuator, and the rear wheels 2L and 2R are each steered to the right by a steering angle proportional to the pressure when the hydraulic pressure is supplied to the chamber 5R, and is proportional to the pressure when the hydraulic pressure is supplied to the chamber 5L. It is assumed that the rear wheels 2L and 2R are steered to the left by the steering angle.

An electromagnetic proportional rear wheel steering control valve 6 for controlling the hydraulic pressure to the actuator chambers 5L, 5R is provided, and the valve 6 is provided with variable throttles 6a, 6b,
6c and 6d are connected in a bridge, and the pump 7, the reservoir 8, and the oil passages 9 and 10 from the actuator chambers 5L and 5R are connected to the bridge circuit, respectively. Valve 6 also has solenoids 6L and 6R
When these solenoids are off, the variable throttles 6a, 6b and 6c, 6d are fully opened to make both actuator chambers 5L, 5R non-pressurized, and the solenoid 6L or 6R is turned on by the current value I _L or I _R.
And supplies the time variable aperture 6c, 6d or 6a, hydraulic pressure corresponding to the current value I _L or I _R 6b to the actuator chamber 5L or 5R Search in opening corresponding to the current value. As described above, the hydraulic pressure steers the rear wheels in the corresponding direction by an angle corresponding to the value, and therefore the relationship between the rear wheel steering angle δ _r and the current values I _L , I _R is shown in FIGS. 3 and 4. It becomes something like.

The controller 11 controls the drive currents I _L and I _R of the solenoids 6L and 6R, and a signal from the steering angle sensor 12 that detects the steering wheel steering angle θ and a signal from the vehicle speed sensor 13 that detects the vehicle speed V are supplied to this controller. Respectively. Based on these input information, the controller 11 functions as shown in FIG. 2 to perform rear wheel steering.

That is, first, the steering angle θ and the vehicle speed V are read, and then the proportional constant K _S and the differential constant τ _S that flatten the yaw rate gain characteristic with respect to the steering frequency are table-looked up from the vehicle speed V. After that, the control constant ratios a and b (0 <a <1,0) determined as described above with reference to FIGS.
From <b <1) and the above K _S and τ _S , the proportional constant K and the differential constant τ that reduce the lateral acceleration in the direction opposite to the centripetal direction are K = a · K _S and τ = b · τ _{S, respectively.} Ask by.

Then, with these proportionality constant K and the differential constant tau, a rear wheel steering angle [delta] _r from the steering angle theta and the steering angular velocity δ _{r =} K · θ
The solenoid drive currents I _R and I _L for obtaining the steered angle after this are calculated by the calculation of + τ ·, and these currents are looked up from the table data corresponding to FIGS. 3 and 4, respectively.
I _R, corresponding to I _L solenoid 6R, steering the rear wheels only [delta] _r is output to 6L.

According to such a rear wheel steering method, since the ratios a and b used in the calculation of the steering angle δ _r are set to a predetermined value less than 1 excluding 0, the yaw rate gain characteristic is slightly deviated from the flat characteristic and the centering direction is Since the lateral acceleration in the opposite direction is reduced, it is possible to reduce the discomfort associated therewith and improve the riding comfort.

As described above, when the differential constant τ is obtained by the product b · τ _S of the predetermined ratio b less than 1 excluding 0 and τ _S for obtaining the flat yaw rate gain, the differential constant τ is shown in FIG. As shown by the solid line, it does not become a large negative value even in the low vehicle speed range. When τ = τ _S as in the conventional case, the differential constant τ becomes a very large negative value in the low vehicle speed range as shown by the dotted line, and the lateral acceleration in the direction opposite to the centripetal direction becomes large, which causes a remarkable discomfort. Since the differential constant τ does not increase significantly in the low vehicle speed range, this discomfort can be eliminated, and the feeling of the rear part of the vehicle body being swung at low vehicle speed can be eliminated.

(Effects of the Invention) Thus, as described above, the method of the present invention uses the proportional constant and the differential constant whose ratios to the proportional constant and the differential constant such that the yaw rate gain characteristic becomes flat are predetermined values less than 1 except 0, respectively. Since the rear wheel steering angle is calculated, the flat yaw rate gain characteristic becomes a little problem, but it is possible to reduce the discomfort that the lateral acceleration in the direction opposite to the centripetal direction becomes large. Therefore, even if the flat yaw rate gain characteristic is slightly sacrificed, the above-mentioned discomfort, which is more important, can be eliminated, and the riding comfort can be improved.

[Brief description of drawings]

FIG. 1 is a system diagram illustrating a vehicle steering apparatus used for carrying out the method of the present invention, FIG. 2 is a flowchart of a rear wheel steering angle control function by the controller of the same example, and FIGS. 3 and 4 are rear wheels respectively. The relationship diagram between the steering angle and the solenoid drive current, and FIGS. 5 and 6 show the combination of control constants for obtaining a flat yaw rate gain characteristic for each vehicle specification and the lateral acceleration in the direction opposite to the centripetal direction. Fig. 7 is a diagram showing a control constant region for reducing the control constant region so that it does not become small, Fig. 7 and Fig. 8 are equivalent diagrams of Fig. 5 and Fig. 6, respectively, and Figs. A time series time chart of the wheel steering angle and the yaw rate lateral acceleration, and FIG. 12 is a characteristic diagram showing how the control constant changes with respect to the vehicle speed in comparison between the conventional method and the present invention. 1L, 1R …… Front wheel, 2L, 2R …… Rear wheel 3 …… Steering wheel 4 …… Steering gear 5 …… Rear wheel steering actuator 6 …… Electromagnetic proportional rear wheel steering control valve 11 …… Controller, 12 …… Steering angle sensor 13 ... Vehicle speed sensor

Claims (1)

(57) [Claims] 1. When steering the front wheels, when steering the rear wheels by a steering angle obtained by multiplying the steering angle and the steering angular velocity by a proportional constant and a differential constant, respectively, a proportional constant and a yaw rate gain characteristic with respect to the steering frequency become flat. A rear wheel steering method for a vehicle, wherein a proportional constant and a differential constant, each having a ratio to a differential constant that is less than 1 except 0, contributes to the calculation of the rear wheel steering angle.