JP2765292B2 - 4-wheel steering system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel steering system, and more particularly to a four-wheel steering system capable of controlling a steering angle using vehicle behavior such as yaw rate.

[0002]

2. Description of the Related Art As a four-wheel steering device for a vehicle, for example, there is a type in which a rear wheel is steered by feeding back a yaw rate as described in Japanese Patent Application Laid-Open No. 2-85073. The four-wheel steering technology based on the control method in which the vehicle behavior is fed back can contribute to vehicle behavior stability.

[0003]

However, in the above-mentioned system, the steering angle is set so that the yaw rate feedback is activated only in the straight traveling state.
(θ) is compared with a predetermined value, and as a result, if the value is less than the predetermined value, the device executes the steering angle control by the yaw rate feedback control. Considering this, there is room for improvement in order to further improve performance. That is, when the driver turns the steering wheel to the left and right to drive, such as when traveling on a road where the curve is alternately continuous left and right, every time the steering wheel passes near the neutral position (θ = 0),
Yaw rate feedback control is activated. For this reason, for example, a target value of the rear wheel steering angle becomes discontinuous, and as a result, a vehicle behavior that causes discomfort to the occupant may occur. In consideration of such a possibility, if the four-wheel steering control system based on the steering angle control using the vehicle behavior can be realized while avoiding the above-mentioned situation, the effectiveness can be further enhanced.

SUMMARY OF THE INVENTION It is an object of the present invention to set a steering angle control operation region using vehicle behavior in consideration of not only the front wheel steering angle but also the steering angle speed of the front wheels in response to the above-mentioned demands, and thereby to proceed straight ahead by the control. It is an object of the present invention to provide a four-wheel steering device capable of appropriately exhibiting a stability improving function in a state where the function is adapted to vehicle operation by a driver.

[0005]

According to the present invention, as shown in FIG. 1, at least one of a rear wheel of a vehicle and a front and rear wheel are both controlled wheels. In the four-wheel steering device capable of performing auxiliary steering control while the vehicle is traveling in the aspect of the present invention, a front wheel steering angle detecting means for detecting a front wheel steering angle, a front wheel steering angular velocity detecting means for detecting or calculating a front wheel steering angular velocity, and detecting a vehicle behavior Vehicle behavior detecting means, and means for setting a steering angle of a wheel to be controlled based on the output of these means during traveling of the vehicle, wherein the front wheel steering angle is equal to or less than a first predetermined value and the front wheel steering angular velocity is Means for setting a first area equal to or less than a second predetermined value and a second area other than the second area as control areas for executing steering angle control during vehicle running, wherein the first area is larger than the second predetermined value. Front wheel steering angular speed at steering wheel In a turning traveling state in which the vehicle is steered left or right through the neutral position, even if the front wheel steering angle is equal to or smaller than the first predetermined value, a feedback control law using an output of the vehicle behavior detecting means obtained during traveling is used. The first steering angle control is not operated but is prohibited, and the second steering angle control based on the feedforward control law in the second region is performed, and the front wheel steering angle is equal to or less than the first predetermined value and The front wheel steering angular velocity is the second
The first steering angle control is performed in accordance with the first area and the second area so that the first steering angle control is performed in the first area where both the conditions less than or equal to the predetermined value are satisfied. Wheel turning angle setting means including switching means for determining the turning angle target value by the angle control and the second steering angle control, and turning the wheel so that the turning angle is determined by the means. There is provided a four-wheel steering device including a turning means.

[0006]

While the vehicle is running, the wheel steering angle setting means detects the front wheel steering angle, the front wheel steering angular velocity detects or calculates the front wheel steering angular velocity, and the vehicle behavior detecting means detects the vehicle behavior. The steering angle of the wheel to be controlled is set based on the output of the steering wheel, and the turning means steers the wheel to the determined steering angle. Means for setting a control area for executing the steering angle control of the vehicle and a switching means, wherein a first area in which a front wheel steering angle is equal to or less than a first predetermined value and a front wheel steering angular velocity is equal to or less than a second predetermined value; And a second area other than the second area is set as a control area for executing the steering angle control during the running of the vehicle, and in controlling the steering angle during the running of the vehicle, the steering wheel is operated at a front wheel steering angular velocity larger than the second predetermined value. Is steered left or right through the neutral position In the traveling state, even if the front wheel steering angle is equal to or less than the first predetermined value, the first steering angle control based on the feedback control law using the output of the vehicle behavior detection means obtained during traveling is not operated but prohibited. In order to perform the second steering angle control based on the feedforward control law in the second region, the front wheel steering angle is equal to or less than the first predetermined value and the front wheel steering angular speed is equal to or less than the second predetermined value. In order to perform the first steering angle control in the first region where both conditions are satisfied, the first steering angle control and the second steering angle control are performed in accordance with the first region and the second region. The switching control is performed so that the steering angle target value is determined by the steering angle control. This allows
When the driver while the vehicle is traveling on a road where curves are alternately continuous left and right or trying to drive slalom, when the steering wheel is steered left or right through the neutral position, The steering angle control during the running of the vehicle does not switch to the first steering angle control side, and does not frequently switch to the reverse, so that the first
The feedback control law using the output of the vehicle behavior detection means obtained during traveling by the steering angle control of the vehicle is that the vehicle is in a substantially straight traveling state, the front wheel steering angle is equal to or less than the first predetermined value, and the front wheel steering angle speed is equal to the second predetermined value. Is applied only in a region where both of the conditions less than or equal to the predetermined value are satisfied, and during turning, the steering wheel is steered left or right through the neutral position at a front wheel steering angular velocity greater than the second predetermined value. When the vehicle is in a turning traveling state, even if the front wheel steering angle is less than the first predetermined value, the first
The steering angle control of the second steering angle control is inhibited without being operated, and the second steering angle control based on the feedforward control law can be performed. The application of the forward control law can also be ensured, and the function of automatically adjusting the behavior of the vehicle can be provided by setting the steering wheel to the neutral position with the front wheel steering angular velocity larger than the second predetermined value when the vehicle is almost in a straight running state. This method is applied only when the vehicle is not turning to the left or right to improve the straight running stability of the vehicle. In addition, including the case where the steering wheel is steered left or right through the neutral position, fine feedforward control can also improve the basic steering stability of four-wheel steering. Even when traveling on a road where curves are continuous alternately on the left and right, or even when traveling in slalom, vehicle behavior that can avoid discontinuity of the steering angle target value and gives discomfort Can be avoided.

[0007]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 2 shows an embodiment of the four-wheel steering apparatus according to the present invention, in which the front and rear wheels can be steered. In the figure, 1L and 1R denote left and right front wheels, and 2L and 2R denote left and right rear wheels, respectively. The front wheels 1L and 1R transmit the steering input to the steering wheel via the steering gear device 4 to enable main steering as usual, and an actuator (a hydraulic cylinder in this example) 5 in the auxiliary steering system. The front wheel assist steering is enabled by the stroke of the gear case.

The rear wheels 2L, 2R can be steered by a stroke of an actuator 6 in the auxiliary steering system, which also comprises a hydraulic cylinder. For this reason, a cylinder piston rod is interposed between the tie rods connected to the respective knuckle arms, thereby turning the rear wheels.

Actuators 5 and 6 shown are return-type hydraulic cylinders each having a built-in spring, and two chambers thereof are connected to servo valves 7 and 8 for front-wheel auxiliary steering and rear-wheel steering, respectively. The respective servo valves connect them to a hydraulic source 9. Hydraulic source 9 pump 10, unload - Dobarubu 11, accumulator - motor 12, reservoir - shall consisting bus 13 or the like, support the steering system of each - current I _F from servo amplifier 14, _15, Sa according to I _R - The control flow rate of the hydraulic cylinder is varied by the bovalve 7, 8 to control the actuator stroke (displacement), that is, the front wheel auxiliary steering angle and the rear wheel turning angle. Each hydraulic cylinder, front wheel steering angle Sa - Bo system, rear wheel steering angle Sa - displacement sensor as a sensor for detecting use in ball type control steering angle quantity [delta] _f, the [delta] _r (stroke - Kusensa) 16, 17 are provided, and outputs from these are input to a control unit described later as a signal indicating actual steering angle information. In this embodiment, a fail-safe (F / S) valve 18, 1
9 to shut off the hydraulic pressure source at the time of the fail-safe operation, regardless of the operation of the servo valve.
The tabs 5, 6 are kept in a neutral position regulated by their springs.

The driving of the servo valves 7 and 8 of the steering angle servo system is controlled by a control unit 30. In this embodiment, the control unit includes a steering angle sensor for detecting a steering angle θ of a steering wheel. A signal from a vehicle speed sensor 32 for detecting a vehicle speed V, a signal from a yaw rate sensor 33 for detecting a yaw rate (d / dt) φ as a sensor for detecting wheel behavior (output of an amplifier 34) ), The signals from the displacement sensors 16 and 17 and the signal from the engine speed sensor 35 are input. Signals from a neutral switch, a clutch switch, and a STOP lamp switch are also input for fail-safe use. The control unit 30 includes a micro circuit including an input detection circuit, an arithmetic processing circuit, a storage circuit for storing various control programs executed by the arithmetic processing circuit and operation results, an output circuit for transmitting a control signal, and the like. It is configured to include a computer.

The control programs include a control program for a fail-safe, a program for controlling a supply flow rate to an unload valve of a hydraulic power source, and a program for controlling a steering angle. The target steering angle is calculated, and control for driving the actuator is executed so that the actual steering angle matches the target steering angle.

FIG. 3 is a control block diagram of a steering angle servo in the hydraulic system. Here, the bold characters shown to indicate various quantities in the drawing are vector displays, and the vector display δ of the actual steering angle in the steering angle mechanism represents the front and rear wheels as shown in the drawing. Control unit 30
A target value is set by a target rudder angle determining unit included as one of the arithmetic processings in the above. In order to make the actual value follow the target value, the target stroke amount of the actuator corresponding to the target rudder angle is set. The servo amplifier current (i display) is controlled so that the deviation (e display) between the actual stroke amount (x display) obtained by the displacement sensor (x bar display) and the actual stroke amount (x display) obtained by the displacement sensor becomes zero. This constitutes a servo mechanism for varying the control flow rate (Q display) of the hydraulic cylinder. Therefore, in the control unit 30,
For such servo control, a process of calculating, setting and outputting a current value to be supplied to the servo amplifier according to the deviation is also executed.

The control unit 30 further performs the setting of the target value based on a required sensor signal. However, the control unit 30 determines a target value of the turning angle of the wheel to be controlled, and determines the determined turning value. When the corresponding wheel is steered by the aforementioned steering angle servo system so that the steering angle becomes an angle, the control law applied to the determination of the target steering angle is changed in consideration of the steering angle speed of the front wheels in addition to the front wheel steering angle. . Specifically, when such switching is performed in the rear wheel steering angle control, the determination of the steering angle when the rear wheels are steered to the determined steering angle depends on the front wheel steering angle amount and the front wheel steering angular velocity. It is performed only when the value is equal to or less than a predetermined value.

FIG. 4 is a flowchart showing an example of a steering angle control program including a process of selecting a control law according to the front wheel steering angular velocity for determining the target steering angle as described above. This program is an example of the case of controlling the steering angle of the rear wheels, and is executed by the microcomputer in the control unit 30 at regular intervals. In the case of the rear wheel steering angle control, the steering mechanism in FIG. 3 is a rear wheel steering mechanism, and the target stroke amount and the actual stroke of the hydraulic cylinder of the steering angle servo system, and therefore the actual steering angle. Is also about the rear wheel system.

First, in step 100, each of the sensors 31, 32,
Signals from 33 and 17 are input, the steering angle θ, the vehicle speed V, and the yaw rate (d / dt) φ are read, and the displacement (stroke) of the actuator 6 is used to determine the actual rear wheels at that time. Steering angle δ
_{Read r} . In step 101, it is calculated by the following equation front wheel steering angle [delta] _f using the θ value. δ _f = θ / N ----- 1 Here, N is a steering gear ratio.

In the following step 102, the front wheel steering angular velocity is read. Here, the (d / dt) θ value is calculated as the degree of change in the steering angle θ, and this value is used. Next, a check is made as to whether the vehicle is in a straight-ahead state. In this example, whether the rear-wheel steering angle control is based on the yaw rate feedback control aiming at improving the straight-running stability is determined. Whether to use the feedforward control for the purpose of improvement is selectively switched. In this case, the judgment is made based on the front wheel steering angle and the front wheel steering angular velocity.

[0017] That is, the process proceeds to step 103, in this example program, using the theta value and (d / dt) θ values, each per absolute value, | θ | ≦ θ ₀ and | (d / dt) θ | ≦ (d / dt) θ ₁
Are determined at the same time. Where θ ₀ and (d / d
t) theta ₁ is a predetermined decision value. Both conditions are satisfied because θ is small and (d / dt) θ is also small.
This driver steering wheel - means that can be seen to be in a state of trying to keep Le substantially neutral position and, more, even if theta is not more than ± θ ₀ (d / dt) steering transition as theta is more than (d / dt) θ ₁ means that do not. On the other hand, the fact that the above two conditions are not satisfied means that the steering wheel is being turned or the steering wheel is being held in the off state in a state other than the above-mentioned state. Steering period
((d / dt) θ is small, but θ is large). The above determination can appropriately perform such determination, and detects or calculates not only the front wheel steering angle but also the front wheel steering angular velocity ((d / dt) in this example).
When both of them are equal to or less than a predetermined value, it can be determined that the vehicle is in a substantially straight state (a state in which the steering wheel is about to be maintained in a substantially neutral position).

If it is determined in step 103 that the vehicle is in the straight traveling state, the process proceeds to step 104. If not, the process proceeds to step 105. Now, determine that the vehicle is going straight
If you proceed to 104, here, the yaw rate (d / dt) φ
The parameters - Yo comprising a motor - Reitofi - determining the target steering angle [delta] _rm by control law of the rear wheel by Dobakku control.
The target value is determined by the following equation: δ _rm = K ₁ · δ _f + k ₂ · (d / dt) φ ----- 2 Here, K ₁ and k ₂ are constants determined by the vehicle speed V and the vehicle specifications. In this embodiment, in setting the rear wheel target steering angle in this case, the yaw rate
Although the control law of the feedback control is based on the above equation 2,
This may be based on another control law.

When the target steering angle δ _rm is determined in step 104, in step 106, the rear wheel steering is performed so that the obtained target steering angle δ _rm is obtained in order to control the rear wheels so as to have the determined steering angle. A process for supplying a current to the servo amplifier 15 of the square servo system is executed. That is, the processing at step 106, the rear wheel actual steering angle [delta] _r is the target stroke of the hydraulic cylinder corresponding to the ([delta] _rm to match the [delta] _rm - setting the current to click match - the click actual stroke In this case, the servo control is executed with the content of the output, thereby improving the stability of crosswind during straight running and the stability against disturbance from the road surface.

On the other hand, if it is determined in step 103 that the vehicle is not traveling straight, the rear wheel steering angle control is performed by executing steps 105 and 106, and
In this case, even when the vehicle travels on a road where curves are alternately continued to the left and right, or when the vehicle travels in a slalom, occurrence of undesired vehicle behavior is prevented, and It is also possible to improve the steering stability in the feedforward control. That is, at the time of right turn or left turn steering, the process is switched from step 103 to step 105, and the control law of the feedforward control, which is different from that in the case of the straight traveling state, is related to the steering angle control. Is selected. In the present embodiment, the control law in this case is in accordance with the following equation: δ _rm = K · δ _f + τ · (d / dt) δ _f + τ ₁ · (d ² / dt ² ) δ _f ----- 3 The target steering angle δ _rm of the rear wheels is changed to the front wheel steering angle δ
_f, the front wheel is also an element of discrimination at Step 103 the steering angle speed (d / dt) δ _f, even determined based on equation 3 with also the front wheel steering angle acceleration ^{(d 2 / dt 2) δ} f. In Equation 3, K, τ, τ ₁
Is a constant determined by the vehicle speed V and the vehicle specifications. After setting the target steering angle [delta] _rm determined in step 105 the difference in the step 106 - is applied to the servo control, the rear wheels will be the steering angle is the steering angle controlled to be the target value.

Thus, according to the present embodiment, the steering angle of the rear wheels is determined based on the front wheel steering angle, the front wheel steering angular velocity, the yaw rate, the vehicle speed, and the like as in the above two equations, and the determined steering is determined. In the case where the rear wheels are steered so as to form an angle, the steered angle can be determined only when the front wheel steering angle amount and the front wheel steering angular velocity are each equal to or less than a predetermined value. In addition, the front wheel steering angular velocity is also detected or calculated, and when both are below a predetermined value, it is determined that the vehicle is almost in a straight running state, and the control of the yaw rate feedback is operated to improve the straight running stability. it can. This matches well with the actual driver's operation of the vehicle, and the function of the yaw rate feedback control can be appropriately exerted when it is necessary. Therefore, even if the vehicle is traveling on a road where the curve is continuous left and right alternately, the steering wheel can be compared with a system in which the straight traveling state is detected solely based on the fact that the steering angle is near zero. Every time the vehicle passes near neutral, the yaw rate feedback control is activated and the target value δ _rm of the rear wheel steering angle becomes discontinuous,
As a result, it is possible to avoid occurrence of a vehicle behavior that causes discomfort to the occupant. Therefore, even when the feedforward control is being executed as in the program example of the present example, the processing in the above case is performed from the step 105 side.
There is no frequent switching to the 104 side and vice versa, and the control law of the yaw feedback is applied only when the vehicle is almost in a straight-ahead state. The application of the feedforward control law which is easy to make can be secured.

Further, the above points will be supplementarily described as follows. The above-mentioned feed-forward control law is basically obtained theoretically by approximating the vehicle mathematically. However, it is difficult to fit the human feeling as it is, The constants K, τ, τ ₁ are adjusted to various values for that. Furthermore, the control law that determines the rear wheel turning angle can generally be derived from a specific theoretical formula, which is based on the nonlinear characteristics of the vehicle and the parameters that are not taken into account. However, fine adjustment is required, but the above constants K, τ, and τ ₁ perform functions that can meet the demand. According experience of the present inventors, the front wheel steering angle [delta] _f, if we adjusted front steering angular speed (d / dt) δ _f, and the front wheel steering angular acceleration ^{(d 2 / dt 2) δ} f and the vehicle speed as parameters, It has been found that there is a solution that improves the steering stability, which is the fundamental purpose of four-wheel steering, without impairing the driving feeling of the driver, and thus such an approach is effective.

On the other hand, the same
If the operation is to be performed according to the Duback control law, the
The control law in site feedback control has few parameters.
(In this program example, the constant K for the front wheel steering angle
₁And the constant K for the yaw rate _TwoIn some cases,
Then, even if it's okay, there are other effects that affect the driving feeling
This can be difficult. Always while traveling straight or turning
-The method of steering the rear wheel by feeding back the rate
If there are few adjustment parameters, adjust
Has a small effect on the overall properties
It can be said that it is easy.

[0024] scolded if, like the feedforward control law, in addition to the front wheel steering angle [delta] _f, the steering angular velocity (d / dt) δ _f,
Furthermore, _if a parameter for the steering angular acceleration (d ² / dt ² ) δ _f is also added, the result is as described above in the case of selectively switching control between yaw rate feedback and feed forward. Although it is helpful to act in the direction of reducing the discontinuity of control as described above, the control parameter described above includes the term for the yaw rate (d / dt) φ (the second term in the above equation 2). Conversely, the number of parameters is too large compared to the case of feedforward control, which makes it difficult to adjust, and makes it difficult to exhibit the original characteristics of yaw rate feedback control. . The control law of yaw rate feedback is
One of the features is that the number of the parameters is small, and it can be said that it is originally desirable to automatically adjust the vehicle behavior.

In this embodiment, however, the above points are skillfully harmonized, and the function of automatically adjusting the behavior of the vehicle is applied almost only to a straight traveling state to improve the straight traveling stability of the vehicle. Fine feedforward control can improve the basic steering stability of four-wheel steering, and the above function by yaw rate feedback control can be properly exhibited in a state adapted to the driver's vehicle operation. is there. Although the present invention has been described with reference to the above specific embodiment, the present invention is not limited to this embodiment, and can be widely applied to a vehicle in which a steering angle is controlled using a vehicle behavior.

[0026]

According to the present invention, as the control area for executing the steering angle control during the running of the vehicle, the first steering angle control and the feed control based on the feedback control law using the output of the vehicle behavior detecting means obtained during the running are performed. Second by forward control law
It is possible to accurately set the respective steering angle control operation areas with the steering angle control of the vehicle.
When the steering wheel is steered to the left or right through the neutral position during vehicle travel, the steering angle control during vehicle running does not switch to the first steering angle control side, and vice versa. A feedback control law that uses the output of the vehicle behavior detecting means obtained during traveling by the first steering angle control without frequent switching is based on the assumption that the front wheel steering angle is substantially equal to the first steering angle. And the front wheel steering angular velocity is not more than the second predetermined value.
When the steering wheel is steered left or right through the neutral position at a front wheel steering angular velocity greater than the predetermined steering wheel steering speed, the first steering angle control is performed even if the front wheel steering angle is equal to or less than the first predetermined steering wheel steering angle. Can not be operated and can be prohibited to perform the second steering angle control by the feedforward control law, and the feedforward control by the second steering angle control with a large number of adjustment parameters and easy to make the exception rule. The function of automatically adjusting the behavior of the vehicle can be secured by using the function that the driver moves the steering wheel to the left or right through the neutral position at the front wheel steering angular velocity larger than the second predetermined value when the vehicle is almost in a straight running state. Steering, such as running on a road where curves are alternately continued to the left and right while turning, or running in slalom, to improve the straight running stability of the vehicle only when not turning to the right. Including scenes in which the wheel is steered to the left or right through the neutral position, fine feedforward control can also be used to improve the basic steering stability of four-wheel steering, even if the curve continues alternately left and right. Even when traveling on a rough road or in a slalom run, it is possible to avoid the discontinuity of the steering angle target value and also to prevent the occurrence of vehicle behavior that gives discomfort. it can.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of the device of the present invention.

FIG. 2 is a system diagram showing an apparatus according to an embodiment of the present invention.

FIG. 3 is an example of a control block diagram of a steering angle servo in the hydraulic system in the same example.

FIG. 4 is a flowchart showing an example of a control program of a controller in the same example.

[Explanation of symbols]

 1L, 1R Left and right front wheels 2L, 2R Left and right rear wheels 3 Steering wheel 5,6 Actuator 7,8 Servo valve 14,15 Servo amplifier 16,17 Stroke sensor 30 Control unit 31 Steering angle sensor 32 Vehicle speed sensor 33 Yaw rate sensor

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ identification code FI B62D 127: 00 137: 00 (58) Field surveyed (Int.Cl. ⁶ , DB name) B62D 6/00 B62D 7/14

Claims (1)

(57) [Claims] An auxiliary steering control can be performed while the vehicle is running in at least one of a mode in which the rear wheels of the vehicle are controlled wheels and a mode in which both front and rear wheels are controlled wheels.
In a wheel steering device, a front wheel steering angle detecting means for detecting a front wheel steering angle, a front wheel steering angular velocity detecting means for detecting or calculating a front wheel steering angular velocity, a vehicle behavior detecting means for detecting a vehicle behavior , and means for setting the steering angle of the controlled wheel based on the output of the front wheel steering angle is first
And the front wheel steering angular velocity is equal to or less than a second predetermined value.
The vehicle is traveling in the first area and the second area other than the first area
Means for setting as a control area for executing the steering angle control of
At a front wheel steering angular velocity greater than the second predetermined value.
Turning the steering wheel left or right through the neutral position
In the turning state, when the front wheel steering angle is equal to or less than the first predetermined value,
Also uses the output of the vehicle behavior detecting means obtained during running.
The first steering angle control based on the feedback control law is activated
This is forbidden and the feed for
The second steering angle control based on the word control law is performed, and the front wheel steering angle
Is less than or equal to the first predetermined value and the front wheel steering angular velocity is in the second position.
In the first region where both conditions below a fixed value are satisfied,
The first region and the second region are controlled so as to perform a first steering angle control.
, The first steering angle control and the second steering angle
A wheel turning angle setting means including a switching means for determining the turning angle target value by control ; and turning means for turning the wheel so as to have a turning angle determined by the means. Characteristic four-wheel steering system.