JPH0647386B2 - 4-wheel steering system for vehicles - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel steering system for a vehicle, which also steers rear wheels in response to front wheel steering.

(Prior Art) Various types of four-wheel steering devices for vehicles of this type have been conventionally known. For example, in the one disclosed in Japanese Patent Application Laid-Open No. 55-91457, the rear wheel has the opposite phase to the front wheel in the low vehicle speed range, and the same phase in the middle and high vehicle speed ranges. Further, in the one disclosed in JP-A-56-167562, the steering ratio is zero in the low vehicle speed range, and the rear wheels are in phase with the front wheels in the medium and high vehicle speed ranges. That is, in both cases, the rear wheels are in phase with the front wheels in the middle and high vehicle speed ranges so that lane changes and the like can be performed well.

(Problems to be Solved by the Invention) By the way, in the case of performing a lane change in a medium vehicle speed range in which the responsiveness is particularly required in the middle and high vehicle speed ranges, in order to improve the responsiveness, it is usually large. It is necessary to generate lateral acceleration (hereinafter referred to as lateral G). Now, looking at the generation process of the lateral G in detail from the start of the steering operation, first, the steering operation causes a slip angle on the front wheels, and then the lateral force (cornering force) is generated on the front wheels to increase the yaw rate. Occur. Therefore, a slip angle is subsequently generated in the rear wheel, which causes a lateral force in the rear wheel and a lateral G.

However, in the above-mentioned conventional one, since the rear wheels are steered in the same phase at the same time when the front wheels are started to be steered, the amount of yaw rate generated is small, and the yaw rate is generated when the front wheels are steered. A little later. For this reason, at the time of lane change, the front part of the vehicle does not quickly change its direction at the start of the front wheel steering, and there is a drawback that the turning performance of the vehicle is poor.

The present invention has been made in view of such a point, and an object thereof is to steer the rear wheels in the opposite phase to the front wheel steering direction based on the rear wheel steering characteristics at the initial stage of the front wheel steering. And then
By steering the rear wheels in the same phase as the front-wheel steering direction, the yaw rate is increased and the timing is increased to significantly improve the turning performance of the vehicle at the start of front-wheel steering. It is in.

Further, when the rear wheels are steered from the opposite phase to the same phase when steering the front wheels as described above, if the rear wheel steering characteristic from the opposite phase to the same phase is made constant, at the time of lane change, The present invention is further confused that a control slightly different from the rear wheel steering control that exactly matches the steering state of the driver is performed. Therefore, in the present invention, the front wheel steering angle is further increased during the front wheel steering. Of the rear wheel steering characteristics from the opposite phase to the same phase of the rear wheels based on the result of this prediction based on the magnitude of the absolute amount of change in the front wheel steering angle signal, etc. within a predetermined sampling. Accordingly, it is another object of the present invention to further improve the driving operation feeling of the vehicle by performing steering control of the rear wheels that more accurately matches the steering state of the driver during lane change.

(Means for Solving the Problem) In order to achieve the above object, the configuration of the present invention has a steering device that steers front wheels, a rear wheel steering device that steers rear wheels, and a vehicle speed detection device that detects a vehicle speed. Means, a front wheel turning state detecting means for detecting the turning state of the front wheels, and a signal from the vehicle speed detecting means, and in the middle vehicle speed range, the rear wheels are opposite to the front wheel turning direction at the beginning of the front wheel turning start. Steer to phase, then
A control device for controlling the rear wheel steering device based on the rear wheel steering characteristic of steering in the same phase as the front wheel steering direction is provided.
Then, when the front wheels are steered in the medium vehicle speed range, the control device calculates the absolute amount of change in the output signal of the front wheel steering state detecting means within a predetermined sampling time, and the magnitude of the absolute amount of this change. Predict the size of the front wheel steering angle by
The configuration is such that the rear wheel steering device is controlled so as to change the rear wheel steering characteristic according to the prediction result.

(Operation) With the above configuration, in the present invention, when the front wheels are steered to change the lane in the medium vehicle speed range, the rear wheels are steered in the opposite phase to the front wheels based on the rear wheel steering characteristics. After that, the steering wheel is steered to the same phase as the front wheel steering direction as in the conventional case. As a result, the amount of yaw rate generated increases with the steering of the rear wheels to the opposite phase, and the timing of the generation of yaw rate increases, so that when the steering of the front wheels is started, the front part of the vehicle is swung quickly. By turning to the rudder direction, the turning performance of the vehicle improves, and after that, by steering in the same phase as the front wheels of the rear wheels, lateral force acts on the rear wheels and the lane change of the vehicle is improved. Done.

Moreover, the rear wheel steering characteristic from the reverse phase to the same phase of the rear wheels at the time of the lane change is the absolute amount of change in the output signal of the front wheel steering state detection means at the time of the lane change within the predetermined sampling time. Is changed according to the prediction result of the size of the front wheel steering angle determined by the size of the front wheel steering angle, for example, the absolute amount of change in the output signal of the front wheel steering state detection means at a predetermined sampling time is large and the front wheel steering angle is large. When a quick lane change is predicted that the angle is large, if the rear wheel steering characteristics are changed so that the maximum steering angle of the rear wheels to the opposite phase is set to a small value, the rear wheels will be steered to the opposite phase. Since it is possible to generate the lateral force at an early stage while ensuring the generation of a large yaw rate, it is possible to perform a better lane change that is in good agreement with the steering operation of the driver.

(Effects of the Invention) According to the four-wheel steering system for a vehicle of the present invention as described above, the rear wheels are steered in the opposite phase based on the rear wheel steering characteristics at the initial stage of starting the front wheel steering in the medium vehicle speed range. After that, since the rear wheels are steered in the same phase, it is possible to promptly generate a large yaw rate at the start of steering the front wheels, and it is possible to improve the turning ability of the vehicle in the early stage of the lane change. .

Moreover, the rear wheel steering characteristic from the opposite phase to the same phase of the rear wheels is determined by the absolute amount of change in the output signal of the front wheel steering state detection means within a predetermined sampling time. Since the size is changed according to the predicted result, it is possible to perform a better lane change of the vehicle that matches the steering state of the driver.

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

FIG. 1 shows the overall construction of a four-wheel steering system for a vehicle showing a first embodiment of the present invention. Reference numeral 1 denotes a steering system for steering left and right front wheels 2a, 2b. A rack and pinion mechanism 4, left and right tie rods 5, 5, and left and right knuckle arms 6, 6.

Reference numeral 7 denotes a rear wheel steering device that steers the left and right rear wheels 8a and 8b.
Knuckle arms 9 and 9 and tie rods 1 on a and 8b
It is provided with a rod 11 extending in the lateral direction of the vehicle body, which is connected via 0 and 10. The rod 11 is moved in the lateral direction of the vehicle body by the rotational movement of a pinion 13 that meshes with a rack 12 formed on the rod 11. The pinion 13 has a transmission mechanism 15 including a pinion shaft 14 and a pair of bevel gears 15a and 15b. Through the pinion drive pulse motor 16
Is rotatably connected to. In addition, the rod 11
A power cylinder 17 having the rod 11 as an operating rod is connected to the. The power cylinder 17 includes a left-turning hydraulic chamber 17b and a right-turning hydraulic chamber 17c that are partitioned in the lateral direction of the vehicle body by a pinion 17a fixed to the rod 11.
And each hydraulic chamber 17b, 17c communicates with a control valve 18 for controlling the oil supply direction to the power cylinder 17 and the hydraulic pressure via the hydraulic passages 17d, 17e, respectively. A hydraulic pump 21 is connected via an oil supply passage 19 and an oil return passage 20. The control valve 18
Detects the rotation direction of the pinion shaft 14 to detect the rear wheels 8a, 8
When b is turned to the left (turned counterclockwise in the figure), the oil supply passage 19 is connected to the left turning hydraulic chamber 17b and the right turning hydraulic chamber 17c is connected to the oil return passage 20, while the rear wheel 8
When a and 8b are steered to the right (steering in the clockwise direction in the figure), the communication state opposite to the above is established, and at the same time, the hydraulic pressure from the hydraulic pump 21 is reduced to a pressure corresponding to the rotational load of the pinion shaft 14. When the rod 11 laterally moves by the pinion 13, the pressure oil is supplied to the power cylinder 17 to assist the lateral movement of the rod 11.

Further, 22 is a vehicle speed sensor as a vehicle speed detecting means for detecting a vehicle speed, 23 is a front wheel steering angle sensor for detecting a steering amount of the steering wheel 3 to detect the steering angle, and 24 is a rod 11 of the rear wheel steering device 7. Is a rear-wheel steering angle sensor that detects the amount of displacement of the rear-wheel steering angle by detecting the rear-wheel steering angle.
The vehicle speed signal, the front wheel turning angle signal, and the rear wheel turning angle signal from 24 are input to the controller 25, respectively.

The controller 25 constitutes a control device for working control of the motor 26 for driving the hydraulic pump 21 and the pulse motor 16, and changes of the output signal of the front wheel turning angle sensor 23 within a very short predetermined sampling time. It has a function to detect the absolute amount of.

Then, inside the controller 25, the rear wheel steering characteristics that depend on both the front wheel steering angle and the vehicle speed are stored in advance.

The dependence of the rear wheel steering characteristics on the front wheel steering angle will be described with reference to FIG. FIG. 3 shows the dependence of the front wheel turning angle in the high vehicle speed range. As shown by the thin solid line and the thin chain line, the front wheel turning angle tends to gradually increase with time, while the rear wheels 8a, 8
As indicated by the thick solid line and the thick dash-dotted line, the turning angle of b is from the start of the front wheel turning for a predetermined delay time Δt1, Δt2,
Initially, the steering angle is increased to the phase opposite to the steering angle of the front wheels 2a and 2b, and then decreased to a steering angle of zero at the elapse of the predetermined delay times Δt1 and Δt2. The characteristic is that the wheel steering angle gradually increases in the same phase as the front wheel steering angle increases. Furthermore, according to the prediction result that the front wheel turning angle at the time of turning the front wheels is larger or smaller than the set value, in the present embodiment, the front wheel turning angle is predicted to be smaller than the set value. In the case of the front wheel steering angle characteristic shown by the solid line, the predetermined delay time Δt1 until the rear wheels are steered to the same phase is set to be long as in the rear wheel steering angle characteristic shown by the thick solid line in the figure. .
On the other hand, in the case of the front wheel steering angle characteristic shown by the thin chain line in the figure, where the front wheel steering angle is predicted to be larger than the set value, a predetermined delay occurs as in the rear wheel steering characteristic shown by the thick chain line in the figure. Time Δ
t2 is set to be shorter than the predetermined delay time Δt1.

Further, the front wheel turning angle dependency in the middle vehicle speed range of the rear wheel turning characteristics will be described with reference to FIG. In the same figure, as indicated by the thin solid line and the thin dashed-dotted line, the steered angles of the rear wheels 8a and 8b are shown by the thick solid line and the thick-dotted line, while the front-wheel steering angle gradually increases with time. During the predetermined delay time from the start of steering of the front wheels, it is initially increased to the phase opposite to the steering angle of the front wheels 2a and 2b and then decreased, and at the time when the predetermined delay time elapses. The steering angle is set to zero, and thereafter, the characteristic gradually increases from zero rear wheel steering angle in the same phase as the front wheel steering angle increases. Further, according to the prediction result that the turning angle of the front wheels is larger or smaller than the set value, in the present embodiment, the front wheel turning shown by the thin solid line in the figure, in which the front wheel turning angle is predicted to be smaller than the set value, is shown. In the case of the steering angle characteristic, the maximum steering angle a1 for steering the rear wheels 8a and 8b in opposite phases is set to be large, as in the rear wheel steering angle characteristic shown by the thick solid line in the figure. On the other hand, in the case of the front wheel point steering angle characteristic shown by the thin chain line in the figure where the front wheel steering angle is predicted to be larger than the set value, the maximum reverse The phase steering angle a2 is set smaller than the maximum antiphase steering angle a1.

Next, the vehicle speed dependence of the rear wheel steering characteristic will be described with reference to FIG. In the middle and high vehicle speed range in FIG. 2, when the front wheel turning angle tends to gradually increase with time as shown by the thin line, but the front wheel turning angle is predicted to be larger than the set value. In the same manner as in FIGS. 3 and 4 above, the rear wheel 8
The steered angles a and 8b are indicated by a thick solid line and a thick dash-dotted line as shown in FIG.
During that period, the wheel initially increases on the opposite phase side to the front wheels 2a and 2b, and the maximum steering angle on the opposite phase side is required for the vehicle to generate a yaw rate of an appropriate value for each of the middle and high vehicle speed ranges. After matching the set maximum steering angle a, the steering angle of the opposite phase is reduced to a steering angle of zero when the predetermined delay times Δt1 and Δt2 have elapsed, and thereafter, from the rear wheel steering angle of zero. The characteristic is such that it gradually increases in phase with the increase in the steered angle of the front wheels. Further, the predetermined delay time Δt2 of the rear wheel steering angle characteristic in the high vehicle speed range shown by the thick dashed line in the figure is set shorter than the predetermined delay time Δt1 of the rear wheel steering angle characteristic in the medium vehicle speed range shown by the thick solid line. To be done.

Then, the controller 25 controls the vehicle speed sensor 22.
Based on the vehicle speed signal from the front wheel steering angle sensor 23 and the front wheel steering angle signal from the front wheel steering angle sensor 23, the start time of the front wheel steering in the medium and high vehicle speed range is discriminated and detected. Whether the front wheel steering angle is larger or smaller than the set value is calculated by calculating the absolute amount of change in the front wheel steering angle signal within a predetermined sampling time and comparing the magnitude of this absolute amount with a predetermined value. According to the prediction result and the vehicle speed signal from the vehicle speed sensor 22, both the turning angle dependence of the front wheels shown in FIGS. 3 and 4 and the vehicle speed dependence shown in FIG. 2 are determined. By controlling the operation of both motors 16 and 26 while checking the rear wheel steering angle signal from the rear wheel steering angle sensor 24 so as to have the rear wheel steering angle characteristic, a predetermined delay occurs in the medium vehicle speed range and the high speed range. During the time Δt1 (or Δt2), the rear wheels 8a, 8b are at maximum The steering is performed in the opposite phase below the opposite-phase steering angle a1 (or a2), and the predetermined delay time Δt1 (or Δt
After 2), the operation of the rear wheel steering device 7 is controlled on the basis of the rear wheel steering characteristics of steering in the same phase as the front wheels 2a, 2b, and as shown in FIG. Is steered, by changing the maximum steering angle a for steering the rear wheels 8a, 8b in the opposite phase according to the magnitude prediction result of the steering angle of the front wheels, the rear wheels 8a, When the rear wheel steering characteristic from the opposite phase of 8b to the same phase is changed and the steering angle of the front wheels is predicted to be smaller than the set value, the maximum antiphase steering angle a1 is set, and the steering angle of the front wheels is set. Is larger than the set value, the maximum anti-phase steering angle a2 is smaller than the maximum anti-phase steering angle a1, and as shown in FIG.
When the front wheels 2a, 2b are steered in the high speed range, the rear wheels 8a, 8b are selected according to the predicted result of the turning angle of the front wheels.
By changing the predetermined delay time until the vehicle is steered to the same phase as the front wheels, the rear wheel steering characteristic from the opposite phase of the rear wheels 8a and 8b to the same phase is changed, and the steered angle of the front wheels is changed. The rear wheel steering device sets a long predetermined delay time Δt1 when it is predicted to be smaller than the set value and a short predetermined delay time Δt2 when the steered angle of the front wheels is predicted to be larger than the set value. It is configured to control the operation of 7.

Therefore, in the above-described embodiment, when the front wheel steering is started in the medium and high vehicle speed ranges, the initial predetermined delay time Δt1 or Δt.
During 2, the pulse motor 16 and the hydraulic pump drive motor 26 are controlled by the controller 25 based on the rear-wheel steering characteristics (see FIGS. 2, 3, and 4) that depend on the front-wheel steering angle and the vehicle speed. The rear wheels 8a, 8b
Is steered in a phase opposite to that of the front wheels 2a and 2b.
The slip angles of a and 8b have opposite signs to the slip angles of the front wheels 2a and 2b, and the amount of yaw rate generated correspondingly increases and the timing of occurrence increases. As a result, when the steering of the front wheels 2a, 2b is started, the front part of the vehicle is
Since the vehicle turns quickly in the turning direction of 2b, the turning performance of the vehicle is improved.

Then, when the predetermined delay time Δt1 or Δt2 is passed in this state, the pulse motor 16 by the controller 25 is
And by controlling the operation of the hydraulic pump drive motor 26,
Since the rear wheels 8a and 8b are steered from the steering angle of zero to the same phase as the front wheels in accordance with the increase of the front wheel steering angle, the slip angles of the rear wheels 8a and 8b increase as the yaw rate increases. 2b
The slip angle has the same sign. As a result, the rear wheels 8a, 8
Lateral force acts on b to generate lateral G, so that the lane change of the vehicle is favorably performed.

Moreover, when it is predicted that the absolute amount of change in the front wheel turning angle signal of the front wheel turning angle sensor 23 within the predetermined sampling is larger than the predetermined value and the front wheel turning angle is larger than the set value, Although the driver is requesting a quicker lane change, if it is predicted that the steering angle of the front wheels is larger than the set value, the lane change in the medium vehicle speed range is performed as shown in FIG. As described above, the maximum reverse phase steering angle a2 of the rear wheel steering characteristics is set to be smaller than the maximum reverse phase steering angle a1 when the front wheel steering angle is predicted to be smaller than the set value. Since the rudder characteristic is changed, while ensuring the generation of a large yaw rate due to the antiphase steering during the predetermined delay time from the antiphase to the same phase steering,
Since the lateral force toward the vehicle turning center can be greatly generated in the vehicle by the amount that the maximum antiphase steering angle a2 is small, it is possible to perform a good lane change of the vehicle in accordance with a quick steering operation of the driver. .

Further, in the high vehicle speed range, the predetermined delay time Δt of the rear wheel steering characteristic is set to a short predetermined delay time Δt2 when the front wheel steering angle is predicted to be larger than the set value as shown in FIG. When it is predicted that the front wheel turning angle is smaller than the set value, the relatively long predetermined delay time Δt1 is set.
When the driver makes a quick lane change at high vehicle speed, that is, when it is predicted that the front wheel steering angle is larger than the set value, compared to when it is predicted that the front wheel steering angle is smaller than the set value. Therefore, the delay time Δt2 is steered to the same phase earlier because the delay time Δt2 is shorter. As a result, the predetermined delay time Δ
When it is predicted that the front wheel steering angle is larger than the set value while ensuring the generation of a large yaw rate due to the antiphase steering during t2, the front wheel steered angle is predicted to be smaller than the set value. The lateral force can be generated on the rear wheels earlier than in the case, and the lane change corresponding to the steering steering state at high vehicle speed can be more favorably performed.

Further, FIG. 5 shows a second embodiment of the present invention. In the first embodiment, as a drive source of the rear wheel steering system 7, the rotation of the pinion 13 by the pulse motor 16 and the hydraulic pump 21 provided separately. Instead of using the combination with the operation of the power cylinder 17 described above, the hydraulic pressure source of the power steering device provided in advance is used to drive the rear wheel steering device.

That is, in FIG. 5, 30 is a hydraulic pump of the power steering device 31, 32 is a pressure oil distribution device for distributing the pressure oil of the hydraulic pump 30 to the steering device 31 and the rear wheel steering device 7 ', and 33 is a rear wheel steering device. A power cylinder, 34 of the device 7 ′ is a control valve for controlling the pressure oil supply direction and the oil pressure to the power cylinder 33. And
The control 35 prestores therein the rear wheel steering characteristic having both the front wheel steering angle dependency and the vehicle speed dependency described with reference to FIGS. 2, 3, and 4 above. When the front wheels are steered in the middle and high vehicle speed ranges, the control valve 34 is operated and controlled so that the steering characteristics are based on the rear wheel steering characteristics depending on the front wheel steering angle and the vehicle speed. . The above power cylinder 3
3 is provided with return springs 36a and 36b for urging the rod 11 to the neutral position when the hydraulic pressure is not applied.
Other configurations are similar to those of the above-described embodiment, and the same portions are denoted by the same reference numerals and the description thereof is omitted.

Therefore, in the present embodiment, the operation similar to that of the above-described embodiment can be performed by the operation control based on the rear-wheel steering characteristics of the control valve 34 depending on the front-wheel steering angle and the vehicle speed by the controller 35. A large yaw rate can be quickly generated at the start of steering the front wheels in the high vehicle speed range, and the turning performance of the vehicle can be significantly improved. Moreover, in a situation where the driver has to perform a quick steering operation to change the lane of the vehicle more quickly, the rear wheels are steered in the same phase as the front wheels early, so that a lateral force is generated early on the rear wheels. Therefore, the lane change can be performed more favorably.

The set time Δt for turning the rear wheels 8a and 8b in opposite phases
When the steering angle of the front wheels is predicted to be smaller than the set value, is set to be relatively large at both the medium vehicle speed and the high vehicle speed. Further, the maximum steering angle a for steering the rear wheels 8a, 8b in opposite phases is necessary because a yaw rate of an appropriate amount is generated.
It is set variably according to the vehicle speed and the front wheel steering angle (or steering angle), and when the front wheel steering angle is predicted to be smaller than the set value, it is higher in the high vehicle speed range than in the middle vehicle speed. When it is set small and it is predicted that the steered angle of the front wheels is larger than the set value, it is set small in the high vehicle speed range as in the middle vehicle speed.

Further, in the first embodiment described above, the rear wheel steering angle sensor 24 is provided so that the steering angles of the rear wheels 8a and 8b match the proper angle based on the front wheel steering angle and the rear wheel steering characteristics that depend on the vehicle speed. However, in the present invention, the rear wheel steering angle sensor 24 is essentially unnecessary. However, it is more preferable to provide this because steering control of the rear wheels 8a and 8b can be performed with high accuracy.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention, FIG. 1 is an overall schematic configuration view showing the first embodiment, FIG. 2 is an explanatory view of vehicle speed dependence of rear wheel turning angle characteristics, and FIG. 3 is in a high vehicle speed range. FIG. 4 is an explanatory diagram of front wheel steering angle dependency of rear wheel steering angle characteristics, FIG. 4 is an explanatory diagram of front wheel steering angle dependency in the middle vehicle speed range of rear wheel steering angle characteristics, and FIG. It is a schematic block diagram. 1 ... Steering device, 7, 7 '... Rear wheel steering device,
13 ... Pinion, 17, 33 ... Power cylinder, 1
8, 34 ... Control valve, 22 ... Vehicle speed sensor (vehicle speed detecting means), 23 ... Front wheel steering angle sensor, 25,
35 ... Controller (control device).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-58-164477 (JP, A) JP-A-57-15066 (JP, A) 1979 (9th) Road Safety Pollution Research Institute Presentation Lecture Outline, December 18, 1979, Road Safety and Pollution Research Institute, P.P. 16-32

Claims (1)

[Claims] 1. A steering device for steering the front wheels, a rear wheel steering device for steering the rear wheels, a vehicle speed detecting means for detecting a vehicle speed, and a front wheel steering state detecting means for detecting a steering state of the front wheels. In response to the signal from the vehicle speed detection means, the rear wheels are steered in the opposite phase to the front wheel steering direction at the beginning of the front wheel steering in the middle vehicle speed range, and then in the same phase as the front wheel steering direction. A control device for controlling the rear wheel steering device based on the steered rear wheel steering characteristic, wherein the control device, when the front wheel is steered in the medium vehicle speed range, has a predetermined output signal of the front wheel steered state detecting means. Calculate the absolute amount of change within the sampling time,
The magnitude of the absolute amount of this change is used to predict the magnitude of the front wheel steering angle, and the rear wheel steering device is controlled to change the rear wheel steering characteristics according to the prediction result. 4-wheel steering system.