JP2515880B2 - Rear wheel steering system - Google Patents

Description

The present invention relates to a rear wheel steering system for a vehicle.

(Prior Art) A rear wheel steering system steers rear wheels in order to improve low-speed small turning performance and high-speed turning stability of a vehicle when steering front wheels. Various devices have been proposed as this type of device, and the applicant of the present application has previously disclosed, in Japanese Patent Application No. 62-330283, that the rear wheel steering angle δ _r is compared with the following transfer function with _respect to the front wheel steering angle δ _f. Is satisfied so that in the rear-wheel non-steering vehicle, the sixth
A rear wheel steering system has been proposed which keeps the side-slip angle of the center of gravity of the vehicle, which has changed as indicated by a1 in the figure, at 0 as indicated by a2 in the figure.

And in this case, the proportional constant K, the differential constant τ and the time constant T are respectively expressed by the following equations. (Problems to be Solved by the Invention) However, in this rear wheel steering system, even when the front wheel steering angle is kept constant (S = 0), the center of gravity side slip angle of the vehicle is kept at 0, and Normal yaw rate gain (rear wheel steering angle), that is, steady-state yaw rate gain The proportionality constant K that determines is determined by the vehicle speed V and vehicle specifications as shown in equation (2). Therefore, the steady-state yaw rate gain for each vehicle speed is a constant value determined by the vehicle specifications, and depending on the vehicle specifications, the rear one-wheel equivalent cornering power C _pr is 7692.
As an example of a vehicle having 2 kg / rad and a front one-wheel equivalent cornering power C _pf of C _pf1 , the steady-state yaw rate gain is 3.2 dB lower than that of the rear-wheel non-steering vehicle (b1) to be b2. In this case, the steady-state yaw rate gain corresponding to the appropriate steer characteristic On the other hand, the steady-state yaw rate gain is largely insufficient, and the vehicle tends to have a strong understeer tendency.

In order to solve the above-mentioned problem while keeping the control for keeping the sideslip angle of the center of gravity of the vehicle at 0, the front one-wheel equivalent cornering power is changed to ΔC _pf by changing the front tires in Fig. 7.
It is possible to increase it only. However, the characteristic b2 has a _gentle inclination with respect to the characteristic b1, and ΔC _pf1 has a considerable magnitude, which is much larger than the maximum increase amount ΔC _{pf2 of the} front single-wheel equivalent cornering power achieved by changing the front tires.
Changing the front tires cannot solve the above problems.

According to the present invention, since the steady-state yaw rate gain depends on the proportional constant K, the proportional constant is first corrected to a value such that a suitable steady-state yaw rate gain can be obtained. However, this correction corrects the rear wheel rudder angle to a value outside the theoretical formula for the center of gravity side slip angle of 0 while the front wheel rudder angular velocity is generated, and the steering frequency-rear wheel rudder is set in the high steering frequency region. The gradient of the angular gain characteristic is different from the gradient when the center of gravity side slip angle is controlled to 0, or the phase delay is different, which gives the occupant a feeling of strangeness.

Therefore, the present invention corrects the differential constant to make the steering frequency-rear wheel steering angle gain characteristic similar to that at the time of control of the center-of-gravity point side slip angle, so that the steady-state yaw rate gain is set to a suitable value without the above-mentioned discomfort. The purpose is to obtain the steer characteristics of.

(Means for Solving the Problem) For this purpose, the present invention is based on the concept shown in FIG. 1. When steering the front wheels, the rear wheel steering angle δ _r is _converted into the following transfer function with _respect to the front wheel steering angle δ _f. Is satisfied so that the side slip angle of the center of gravity of the vehicle is 0
In the rear wheel steering device which maintains the proportional constant K, the proportional constant K is modified so that the steady-state yaw rate gain becomes a suitable value, and the steering frequency-rear wheel steering angle gain characteristic after the correction of the proportional constant is the transfer function. And a differential constant correcting means for correcting the differential constant so as to be similar to the steering frequency-rear wheel steering angle gain characteristic.

(Operation) The rear wheel steering system transfers the rear wheel steering angle δ _r to the front wheel steering angle δ _f when the front wheels are steered. Is satisfied so that the rear wheels are steered. At this time, the proportional constant correcting means corrects the proportional constant K so that the steady-state yaw rate gain becomes a suitable value, and the differential constant correcting means changes the differential constant τ by proportionally. The steering frequency-rear wheel steering angle gain characteristic due to the correction of the constant is corrected so as to be similar to the steering frequency-rear wheel steering angle gain characteristic by the transfer function.

Therefore, the steady-state yaw rate gain becomes appropriate by modifying the proportional constant K, and the steer characteristic during steady-state circular turning can be achieved as desired regardless of the vehicle specifications. The gradient change in the steering frequency-rear wheel steering angle gain characteristic due to this modification can be corrected by modifying the differential constant, and the modification of the proportional constant also causes the vehicle's motion performance to be uncomfortable during the transitional period during the change of the front wheel steering angle. It is possible to prevent it from becoming a thing with.

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

FIG. 2 shows a system of the rear wheel steering device according to the present invention.
1L and 1R are left and right front wheels respectively, and 2L and 2R are left and right rear wheels respectively. The front wheels 1L, 1R can be steered by the steering wheel 3 via the steering gear 4, and the rear wheels suspended by the rear suspension member 7 of the vehicle body by the rear suspension device including the transverse links 5L, 5R and the upper arms 6L, 6R. Since the 2L and 2R can also be steered, the knuckle arms 8L and 8R of the rear wheels are interconnected by the actuator 9 and side rods 10L and 10R at both ends thereof.

The actuator 9 is a spring-centered backward hydraulic cylinder, and its two chambers are connected to the electromagnetic proportional pressure control valve 12 by pipe lines 11L and 11R, respectively. The control valve 12 is further connected to a hydraulic line 15 and a drain line 16 of a hydraulic source including a pump 13 and a reservoir tank 14, respectively. The control valve 12 is a spring-centered three-position valve. When both solenoids 12L and 12R are OFF, the lines 11L and 11R are in a non-pressure state, and when the solenoid 12L is ON, the amount of electricity is ON.
The pressure proportional to i _L supplied to the conduit 11L, the solenoid 12R
The pressure proportional to the energization amount i _R ON and supplies the pipe 11R. The pressure from the pipeline 11L turns the rear wheel to the left by the actuator 9 by the steering angle corresponding to the value, and the pressure from the pipeline 11R turns the rear wheel to the right by the actuator 9 at the steering angle corresponding to the value. To do.

The ON / OFF and energizing amounts of the solenoids 12L and 12R are electronically controlled by a controller 17, and the controller 17 includes a digital operation circuit 17a, a digital input detection circuit 17b, a storage circuit 17c, and a D / A as shown in FIG. Converter 17d and drive circuit 17
and e. A signal from a steering angle sensor 18 for detecting the steering angle θ of the steering wheel 3 and a signal from a vehicle speed sensor 19 for detecting the vehicle speed V are input to the controller 17 via a digital input detection circuit 17b. The digital operation circuit 17a of the controller 17 executes the control program shown in FIG. 4 from the input information and the information stored in the storage circuit 17c to steer the rear wheels.

In Figure 4 in step 31, the steering angle θ and the vehicle speed V read, a front wheel steering angle [delta] _f in the next step 32 from the steering wheel steering angle θ and the steering gear ratio N Calculated by Then, in steps 33 and 34, the proportional constant K obtained from the vehicle speed V by the equations (2) and (3), respectively.
And calculate or look up the differential constant τ. The proportionality constant K is a positive value, the in-phase rear wheel steering angle amount corresponding to the front wheel steering angle δ _f is determined, and the differential constant τ is a negative value, as is clear from the above equation (1). ), The anti-phase rear wheel steering angle amount corresponding to the front wheel steering angular velocity δ _f is determined.

In step 35, the proportional constant K relating to the steady-state yaw rate gain is set to the steady-state yaw rate gain corresponding to the required steer characteristic during steady circle turning (in the vehicle described above with reference to FIG. 7, Is decreased by ΔK so that the steady yaw rate gain characteristic shown by b2 in FIG. 7 is increased to b3. In this case, the rear wheel steering angle gain and the phase delay with respect to the steering frequency (steering speed) f have the characteristics shown by C3 in FIG. 5, respectively, and the rear wheel steering angle gain characteristic and the phase angle characteristic C2 by the center of gravity side slip angle O control become On the other hand, the gain change rate per steering frequency is made different and the phase delay is increased. Therefore, during high-speed steering with a high steering frequency, the vehicle behavior is different from that in the case of the center-of-gravity point side slip angle O control, which gives an occupant an uncomfortable feeling. Therefore, in step 36, the differential constant τ related to the rear wheel steering angle gain and the phase angle characteristic is also reduced by Δτ so that the characteristic becomes C4 which is similar to C2. Here, since the differential constant τ is a negative value, the positive correction amount Δτ is added to correct the differential constant τ so that its absolute value becomes small.

In step 37, based on K and τ corrected in steps 35 and 36, the same as (1) above The rear wheel steering angle δ _r is calculated by calculating Then step 38
Then, the current i _L or i _R corresponding to the calculated steering angle δ _r is output to the valve 12 in FIG. 2 to steer the rear wheels as calculated.

By modifying the proportional constant K as described above, the steady-state yaw rate gain becomes the target value, and the steer characteristic during steady-state circular turning can be made suitable regardless of the vehicle specifications. Despite the correction of the proportional constant K, the rear wheel steering angle gain characteristic with respect to the steering frequency resembles the characteristic at the time of performing the center-of-gravity point side slip angle O control by modifying the differential constant τ as described above. Therefore, the change of the rear wheel steering angle gain with respect to the steering frequency is the same as that of the center-of-gravity point side slip angle O control, and the occupant does not feel uncomfortable.

The action and effect will be additionally described with respect to a time-series change of the sideslip angle of the center of gravity shown in FIG. This side slip angle sharply increases in the transition period as shown by a3 when only the proportional constant K is decreased, and then gradually decreases and then gradually increases, but by decreasing the differential constant τ at the same time, as shown by a4, the barycenter side slip angle Will be gradually increased throughout, and the discomfort of the passengers can be eliminated.

(Advantages of the Invention) As described above, the rear wheel steering system of the present invention is configured to correct the proportional constant K so that the steady-state yaw rate gain becomes a suitable value regardless of vehicle specifications. Can be exactly what you want. At the same time, the differential constant τ is also corrected to correct the gradient change of the steering frequency-rear wheel steering angle gain characteristic due to the correction of the proportional constant. It is possible to prevent the behavior change of the vehicle from becoming uncomfortable.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a rear wheel steering device of the present invention, FIG. 2 is a steering system diagram of a four-wheel steering vehicle showing an embodiment of the present invention device, and FIG. 3 is a block diagram of a controller in the system. FIG. 4 is a flow chart showing a control program of the controller, FIG. 5 is a characteristic diagram of a rear wheel steering angle gain and a phase angle with respect to a steering frequency, FIG. 6 is a time chart showing how the center of gravity side slip angle changes, and FIG. The figure is a steady-state yaw rate gain characteristic diagram. 1L, 1R front wheel, 2L, 2R rear wheel 3 steering wheel 4 steering gear 5L, 5R transverse link 6L, 6R upper arm 7 rear suspension member 9 actuator 12 … Electromagnetic proportional pressure control valve 17 …… Controller, 18 …… Steering angle sensor 19 …… Vehicle speed sensor

Claims (1)

(57) [Claims] 1. When steering front wheels, the rear wheel steering angle δ _r is _expressed by the following transfer function with _respect to the front wheel steering angle δ _f. Is satisfied so that the side slip angle of the center of gravity of the vehicle is 0
In the rear wheel steering device which maintains the proportional constant K, the proportional constant K is modified so that the steady-state yaw rate gain becomes a suitable value, and the steering frequency-rear wheel steering angle gain characteristic after the correction of the proportional constant is the transfer function. A rear wheel steering device, comprising: a steering frequency-rear wheel steering angle gain characteristic according to 1.