JP3366685B2 - Control method of rear wheel steering device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a rear wheel steering device for electronically steering a rear wheel in a four-wheel steering system (4WS) for a vehicle such as an automobile, and more particularly, a vibration gyro type yaw rate sensor. Measures against unstable output.

[0002]

2. Description of the Related Art Generally, rear wheel steering control is a vehicle speed sensitive type, in which a rear wheel is reverse-phase steered in a low speed range to improve a small turning performance, and a rear wheel is in-phase steered in a medium and high speed range to obtain a vehicle speed. Accordingly, it is fundamental to variably control the steering ratio to achieve vehicle stability. By the way, the vehicle causes a yawing motion (rotational motion) around the vertical axis of the vehicle body due to a road surface condition, a difference in driving force between left and right rear wheels and a grip force, and a disturbance such as a side wind. It is known that these disturbances change the behavior of the vehicle regardless of the driver's skill and impair the stability.

By the way, in recent years, a yaw rate sensor for directly detecting the yaw rate (rotational angular velocity) of the yawing motion of the vehicle with high accuracy has been developed. According to this yaw rate sensor, not only in the case of front wheel steering,
Changes in the behavior of the vehicle due to disturbances such as cross winds can also be detected quickly. Therefore, the yaw rate is actively used,
A control method has been proposed in which the rear wheels are steered so as to ensure the stability of the vehicle against various disturbances.

Here, for example, in a vibration gyro type yaw rate sensor, piezoelectric elements are mounted vertically above and below a metal diaphragm of a tuning fork vibrator, and a piezoelectric element above the piezoelectric element is vibrated by applying a rated voltage to the piezoelectric element below. The element outputs a voltage according to the angular velocity of rotation. At the neutral position, the upper piezoelectric element also oscillates synchronously to output a reference voltage of, for example, 2.5V. When the vehicle turns to the left or right, it outputs a voltage higher than the reference voltage, and when it turns to the other, it is lower than the reference voltage. It is configured to output a voltage. Therefore, when the ignition switch is turned on during engine operation, the yaw rate can be detected by applying a voltage to the yaw rate sensor.

In this case, immediately after the engine is started, the yaw rate sensor suddenly applies a voltage to vibrate the piezoelectric element, and an unstable engine vibration or the like is also transmitted. Therefore, during the initial seconds or minutes, the reference voltage at the neutral position fluctuates up and down as shown in FIG. 6 due to poor synchronization of the piezoelectric element. Therefore, when the output voltage of the yaw rate sensor is unstable, the rear wheel steering control by the yaw rate feedback control cannot necessarily be performed accurately. Therefore, until the output signal of the yaw rate sensor becomes stable and neutral, it is desirable to take measures to prevent erroneous operation of the rear wheel steering due to an unstable output signal.

Conventionally, regarding the correction of the inaccurate sensor signal of the yaw rate sensor, for example, Japanese Patent Laid-Open No. 2-2
There is a prior art of Japanese Patent No. 49765. In this prior art, it is shown that when the zero value of the sensor changes due to environmental changes, changes over time, etc., the zero estimated value of the sensor is updated, and the yaw rate is accurately detected based on this updated zero estimated value. ing.

[0007]

By the way, in the above-mentioned prior art, the value of the yaw rate sensor at the time when the time necessary for stabilizing the sensor output has passed after the ignition switch was turned on is the zero estimated value. And Therefore, there is a problem that it cannot be applied to the control when the sensor output immediately after the switch is turned on is unstable.

In view of the above, the present invention has an object of optimizing the rear wheel steering when the output signal of the yaw rate sensor is unstable in the rear wheel steering control using the yaw rate.

[0009]

In order to achieve this object, the present invention calculates a target rear-wheel snake angle in accordance with at least a yaw rate and a control coefficient for the yaw rate, and determines the rear wheel based on the target rear-wheel snake angle. In a rear-wheel steering device that steers automatically, the stable state of the output signal of the yaw rate sensor is determined when the vehicle behavior is stable, and the control coefficient for the yaw rate has a smaller value as it becomes unstable. To do. Further, according to the present invention, the target rear wheel snake angle is calculated based on the in-phase directional component set by the yaw rate and the yaw rate coefficient and the anti-phase directional component set by the steering wheel angle and the steering wheel angle coefficient, and the target rear wheel snake angle is calculated. in rear wheel steering apparatus for automatically steering the rear wheels based on the steering angle, to determine the steady state of the output signal of the yaw rate sensor in a stable state of the vehicle behavior, the more unstable the yaw rate coefficient and the steering wheel angle coefficient It is characterized by having a characteristic with a small value .

[0010]

In the present invention based on the above control method, the target rear wheel steering angle is calculated by the yaw rate, the yaw rate coefficient, the steering wheel angle, and the steering wheel angle coefficient when the vehicle is traveling, and the rear wheel steering device is operated based on this target rear wheel steering angle. . Therefore, the yaw rate when the vehicle behavior changes due to disturbances such as vehicle speed, steering wheel angle, or crosswind, the rear wheels are automatically steered in-phase or in anti-phase to obtain the desired steering angle, etc. Turnability and stability at high speed and against disturbance are improved. on the other hand,
When the yaw rate sensor operates when the engine is started, the stable state at the neutral position of the output signal is judged, and when it is the most unstable, for example, the steering wheel and the coefficient are used to steer the rear wheels to immediately drive the vehicle. Also, malfunction due to unstable yaw rate is avoided. Further, as the stability of the neutral position increases, the anti-phase steering angle and the in-phase yaw rate are strengthened to perform feedback control, and the rear wheels are steered to the stable side even when the vehicle behavior changes. Then, when it becomes stable neutral, it smoothly shifts to the normal mode by the antiphase steering angle proportional control and the yaw rate feedback control.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 2, an outline of the vehicle drive system and the four-wheel steering system will be described. First, in the vehicle 1, the engine 2 is connected to the clutch 3 and the transmission 4, and the output side of the transmission 4 is configured to be transmitted to the front wheels 7 via the front differential 5, the axle 6, and the like. The output side of the transmission 4 is also configured to be transmitted to the rear wheel 11 via the propeller shaft 8, the rear differential 9, the axle 10, and the like.
Four-wheel drive runs. Further, it has a front wheel steering device 20 and a rear wheel steering device 30 as a four-wheel steering system.

In the front wheel steering system 20, a steering shaft 22 having a steering wheel 21 has a hydraulic control valve 2.
3 is connected to the front wheels 7 via the power cylinder 24, the rod 25, and the knuckle arm 26, and the front wheels 7 are manually steered by operating the steering wheel. Rear wheel steering device 3
Reference numeral 0 denotes an electric motor 31, which is connected to an eccentric shaft 33 via a worm gear 32 for reduction, and which is connected to the eccentric shaft 33 via a link 34, a lever 35, a knuckle arm 36, and the like. It is connected to the wheels 11 and is configured to automatically steer the rear wheels 11 by driving a motor. In addition, when the motor power is turned off during an abnormality, the worm gear 32
Due to the non-reciprocity, the rear wheel 11 is maintained in a predetermined steering angle state with respect to the road surface external force.

As a control system, a steering wheel angle sensor 40 for detecting a steering wheel angle θ, a steering wheel angular velocity sensor 41 for detecting a steering wheel angular velocity dθ, a rear wheel steering angle sensor 42 for detecting a rear wheel steering angle Er, and a rear wheel steering angular velocity ωr. It has a rear wheel steering angular velocity sensor 43 for detecting. Further, it has a yaw rate sensor 44 for detecting a yaw rate γ of a rotational angular velocity according to the turning state of the vehicle. Further, in order to calculate the control vehicle speed V, a front left wheel speed sensor 45 for detecting the front left wheel speed Nfr and a rear right wheel speed sensor 46 for detecting the rear right wheel speed Nrl are provided, and these sensor signals are used as the control unit 50. Is input to the motor 31 to be electrically processed, and a motor signal corresponding to the steering direction of the rear wheels, the steering angle, and the steering angular velocity is output to the motor 31.

The yaw rate sensor 44 is a vibrating gyro type, and is constructed by mounting piezoelectric elements orthogonally above and below a metal vibrating plate of a tuning fork vibrator. Then, when the ignition switch is turned on when the engine is started, a voltage is applied to operate, and the output signal at the neutral position becomes unstable initially,
When stable neutral, the yaw rate γ according to the turning state of the vehicle,
That is, the rotational angular velocity (deg / s) is detected and the signal is output.

The control unit 50 has a vehicle speed calculating section 51 to which the front left wheel speed Nfr and the rear right wheel speed Nrl are inputted, and calculates the control vehicle speed V by V = (Nfr + Nrl) / 2. The vehicle speed V is input to the steering wheel angle coefficient setting unit 52, the steering wheel angle coefficient Kθ is set as a function of the vehicle speed V, and simultaneously input to the yaw rate coefficient setting unit 53, and the yaw rate coefficient Kγ is similarly set as a function of the vehicle speed V. To do. Here, the normal mode in which the yaw rate sensor 44 is stable and neutral will be described. The steering wheel angle coefficient Kθ is in the opposite phase throughout the vehicle speed like Kθ1 in the steering angle gain map of FIG. It is a characteristic that the absolute value of the value decreases and decreases as is lower. The yaw rate coefficient Kγ is in-phase throughout the vehicle speed like Kγ1 in the yaw rate gain map of FIG. 7B, and has a characteristic of gradually increasing as the vehicle speed V increases. Therefore, referring to this map, both coefficients Kθ and Kγ
To set.

The steering wheel angle θ and the steering wheel angle coefficient Kθ are input to the multiplication unit 54 to calculate a multiplication value Kθ · θ of both, and the yaw rate γ and the yaw rate coefficient Kγ are also input to the multiplication unit 55 to calculate both multiplication values Kγ · θ. Calculate γ. These two multiplication values Kθ · θ and Kγ · γ are input to the target rear wheel steering angle calculation unit 56, and the target rear wheel steering angle ET is calculated by ET = Kγ · γ + Kθ · θ. Therefore, the term of Kγ · γ is a stabilizing element that keeps the vehicle on the stable side, and the term of Kθ · θ is a turning element that promotes turning.

Here, the yaw rate γ is generated according to the turning state of the vehicle due to turning or disturbance over the entire vehicle speed, and this coefficient Kγ is a characteristic of an increasing function of the vehicle speed V. Therefore, the value of Kγ · γ increases as the vehicle speed V increases. growing. The steering wheel angle θ is generally very small in the medium-high speed range, and therefore the value of Kθ · θ becomes close to zero even if the coefficient Kθ is small in the opposite phase direction. Therefore, when the yaw rate γ is generated in the medium-high speed range, the target rear wheel steering angle ET is in the in-phase direction due to the value of Kγ · γ, and stability is emphasized in the control. In the low speed range where the steering wheel angle θ is large, the turning property is controlled with emphasis on the value of Kθ · θ in the opposite phase direction, and at this time, the yaw rate γ is corrected to the stable side by the value of Kγ · γ in the in-phase direction.

The target rear wheel steering angle ET and the rear wheel steering angle Er are input to the deviation calculating section 57 to calculate the deviation ED by ED = ET-Er. This deviation ED is the target rear wheel turning speed setting unit 5
8, and the target rear wheel turning speed ωo corresponding to the deviation ED is set by the map of FIG. 3 (c). Further, the target rear wheel turning speed ωo and the rear wheel steering angular speed ωr are input to the speed difference calculation unit 59, and the speed difference ωd is calculated by ωd = ωo−ωr. Then, the speed difference ωd is input to the control amount setting unit 60,
The control amount Kp of the proportional component is set according to the speed difference ωd, and the driving unit 61 supplies the forward or reverse motor current I according to the control amount Kp to the motor 31.

In the above control system, the yaw rate sensor 4
The correction control when the output signal of 4 is unstable neutral will be described. First, the yaw rate sensor 4 immediately after the engine is started
If the output signal of 4 is unstable, the yaw rate feedback control may be suppressed according to the unstable state, and the steering angle feedback control may be strengthened. Therefore, in the case of unstable neutral, the steering wheel angle coefficient setting unit 52 has, for example, three steering wheel angle coefficients Kθ2, Kθ3, Kθ4.
However, as shown by the broken line in FIG. 3A, the reverse phase side is gradually decreased and the in-phase side is increased. The yaw rate coefficient setting unit 53 also sets the three yaw rate coefficients Kγ2, Kγ3, and Kγ4 in the case of unstable neutrality with the characteristic that the values are successively reduced as shown by the broken line in FIG.

On the other hand, it has a stable neutrality determining unit 62 for inputting the yaw rate γ, the vehicle speed V, and the steering wheel angle θ, and differentiates the yaw rate γ with time when the vehicle is stationary or the vehicle is in a stable state. Absolute value of the slope according to the state of | dγ / d
Calculate t | Then, the tilt signal is output to both setting units 52 and 53.
And the control mode is selected together with each coefficient according to the amount of inclination. That is, when the inclination is the largest and the output signal is unstable, the mode d of only the steering angle feedback control by the coefficients Kθ4 and Kγ4 is selected, and as the inclination becomes smaller, the antiphase steering with the coefficients Kθ3 and Kγ3 and the coefficients Kθ2 and Kγ2. It is configured such that modes c and b having a strong angle and in-phase yaw rate are selected, and when stable neutral is achieved, the normal mode a based on the coefficients Kθ1 and Kγ1 is selected.

Next, the operation of this embodiment will be described. First, the engine 2 is operated, and the transmission power of the transmission 4 is transmitted to the front wheels 7 and the rear wheels 11 by the drive system, so that the vehicle 1 moves
Drive with wheel drive. At this time, when the driver operates the steering wheel 21, the front wheels 7 are steered and manually steered by the front wheel steering device 20. The flowcharts of FIGS. 4 (a) and 4 (b) are executed at predetermined time intervals, and the rear wheel steering control is performed according to the conditions such as traveling, steering wheel operation, and vehicle turning.

That is, the vehicle speed V after the engine is started is checked in step S1 of the control mode selection routine (a), and when the vehicle is stopped at the set value Vs (5 km / h) or less, the process proceeds to step S3. When the vehicle is traveling, the steering wheel angle θ is checked in step S2, and if | θ | is equal to or less than the set value θs (10 degrees), the process similarly proceeds to step S3. In this way, in a state where the vehicle behavior is stable after the engine is started or when the vehicle is running, the absolute value | dγ / dt | of the inclination according to the stable state of the neutral position of the yaw rate output signal is calculated in step S3,
Three kinds of set values A, B, C (A
>B> C). Therefore, when the engine is started, the yaw rate sensor 44 is also actuated by applying a voltage, and the absolute value of the inclination | dγ / dt |
When stable neutrality smaller than C is reached, the coefficient K is calculated in step S7.
The normal mode a depending on θ1 and Kγ1 is selected.

In the rear wheel steering control routine (b), the steering wheel angle θ, the yaw rate γ, the rear wheel steering angle Er and the rear wheel steering angular velocity ωr are read in step S11, and step S1
The vehicle speed V is calculated at 2. Then, in step S13, the control mode is checked, and in the above-described normal mode, the steering wheel angle coefficient Kθ and the yaw rate coefficient Kγ are set as the coefficients Kθ1 and Kγ1 according to the vehicle speed V. In step S14, the target rear wheel steering angle ET is calculated from the steering wheel angle θ and its coefficient Kθ, and the yaw rate γ and its coefficient Kγ. Thereafter, in step S15, the deviation E between the target rear wheel steering angle ET and the rear wheel steering angle Er
D is calculated, the target rear wheel turning speed ωo is set in step S16, the speed difference ωd between the target rear wheel turning speed ωo and the rear wheel steering angular speed ωr is calculated in step S17, and step S18
The control amount Kp according to the speed difference ωd is determined by
At 9, the motor current I of the controlled variable Kp is output to drive the motor 31.

Therefore, in the rear wheel steering system 30, the motor 3
1, the worm gear 32 and the eccentric shaft 33 rotate, the link 34 and the lever 35 swing left and right, and the rear wheel 11 is automatically steered. In this case, the rear wheels 11 are in-phase or anti-phase, and are subjected to anti-phase steering angle proportional control and yaw rate feedback control so as to obtain a desired steering angle or steering angular velocity.

Therefore, when the steering wheel 21 is greatly turned at a low speed such as starting, the target rear wheel steering angle ET becomes negative due to the value of Kθ · θ, and the rear wheel 11 is steered in a small turn by reverse-phase steering.
At this time, if the vehicle makes a sharp turn or the yaw rate γ increases due to the vehicle turning due to the road surface μ, the value of Kγ · γ causes the rear wheel 1
The reverse-phase steering of 1 is reduced and corrected, and the behavior of the vehicle is stabilized. When turning at medium and high speeds, the target rear wheel steering angle ET is mainly K
The value of γ · γ becomes positive and the rear wheels 11 are steered in phase,
Therefore, the stability of the vehicle when turning is improved. The relationship among the steering wheel angle θ, the yaw rate γ, the coefficients Kθ and Kγ, and the target rear wheel steering angle ET in this case is shown in FIG. Further, when the vehicle rapidly turns to the left or right due to a disturbance such as a side wind, the yaw rate γ changes greatly, and this behavior change of the vehicle 1 is quickly detected. Then, the rear wheel 11 is steered so as to maintain the in-phase state regardless of the turning of the vehicle 1 by the value of Kγ · γ. For this reason, the vehicle 1 stably assumes an opposite posture so as not to be swept away by a side wind, and smoothly returns to the original course.

On the other hand, when the output signal of the yaw rate sensor 44 is unstable immediately after the engine is started, the absolute value of the inclination | dγ / dt |
In the control mode selection routine of (a), the process proceeds from step S4 to step S8, and the coefficients Kθ4 and Kγ4 are set as shown in FIG.
The mode d is selected. Therefore, when the neutral position of this sensor output signal is the most unstable, Kγ4 = 0, and the target rear wheel steering angle ET is calculated only by the steering wheel angle θ and its coefficient Kθ4 to perform feedback control. Therefore, even if the vehicle runs immediately while operating the steering wheel, erroneous rear wheel steering due to an unstable yaw rate is avoided, and the turning characteristic at low speed and the stability at high speed are secured by the characteristic of the coefficient Kθ4.

Next, when the inclination of the sensor output signal decreases a little, the process proceeds from step S5 to step S9 and the coefficient Kθ3
And the mode c of Kγ3 are selected, and when the stability of the neutral position further increases, the process proceeds from step S6 to step S10 to select the mode b of the coefficients Kθ2 and Kγ2. Therefore, in response to the stabilization of the neutral position of the sensor output, the anti-phase steering angle and the in-phase yaw rate are strengthened and feedback control is performed, and thus, stabilization is also performed against changes in vehicle behavior. When the sensor output signal is stable and neutral, the mode smoothly shifts to the normal mode a with little change in vehicle behavior.

The embodiment of the present invention has been described above, but the present invention is not limited to this.

[0029]

As described above, according to the present invention,
In a rear wheel steering system that automatically steers the rear wheels by anti-phase steering angle proportional control and yaw rate feedback control, the stable neutral state of the output signal of the yaw rate sensor is determined, and if unstable, the steering wheel angle coefficient and yaw rate coefficient Since the characteristic is corrected, it is possible to avoid malfunction due to an unstable yaw rate, and the steering performance of the vehicle is stabilized. Since the unstable state is determined based on the differential value of the yaw rate and the mode is switched to a mode suitable for the unstable state, the rear wheels can be appropriately steered even when any unstable state continues for a long time. Since the steering angle feedback control is gradually switched to the anti-phase steering angle proportional control and the yaw rate feedback control, the rear wheels are smoothly steered, and the behavior of the vehicle is greatly reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a control system suitable for a control method for a rear wheel steering system according to the present invention.

FIG. 2 is a configuration diagram showing an outline of a vehicle drive system and a four-wheel steering system.

FIG. 3 is a diagram showing a map of a steering wheel angle coefficient, a yaw rate coefficient, and a target rear wheel turning speed.

FIG. 4 is a flowchart showing mode selection control and rear wheel steering control.

FIG. 5 is a diagram showing a state of rear wheel steering when turning left and right.

FIG. 6 is a diagram showing an output signal of a yaw rate sensor and a mode selection state.

[Explanation of symbols]

30 Rear wheel steering system 31 Electric motor 40 steering wheel angle sensor 44 Yaw rate sensor 50 control unit 52 Handle angle coefficient setting section 53 Yaw rate coefficient setting section 56 Target rear wheel steering angle calculation unit 62 Stable neutrality determination unit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI B62D 117: 00 B62D 117: 00 137: 00 137: 00 (56) References JP-A-5-8746 (JP, A) JP Flat 4-293674 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) B62D 6 / 00,6 / 06 B62D 7/14

Claims (3)

(57) [Claims] 1. A rear wheel steering system for calculating a target rear wheel snake angle according to at least a yaw rate and a control coefficient for the yaw rate, and automatically steering the rear wheels based on the target rear wheel snake angle. A control method for a rear wheel steering system, characterized in that a stable state of an output signal of a yaw rate sensor in a stable state is judged, and a control coefficient for the yaw rate is set to have a smaller value as it becomes unstable . 2. A target rear wheel snake angle is calculated based on an in-phase directional component set by a yaw rate and a yaw rate coefficient and an anti-phase directional component set by a steering wheel angle and a steering wheel angle coefficient, and the target rear wheel snake angle is calculated. in rear wheel steering apparatus for automatically steering the rear wheels based on the angle, to determine the steady state of the output signal of the yaw rate sensor in a stable state of the vehicle behavior, unstable as the value of the yaw rate coefficient and the steering wheel angle coefficient A method for controlling a rear wheel steering device, characterized in that: 3. The control method for the rear wheel steering system according to claim 1, wherein the stable state of the output signal of the yaw rate sensor is judged by the magnitude of the yaw rate differential value.