JP3320833B2 - 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) of a vehicle such as an automobile, and more particularly to a vibration gyro type yaw rate sensor. On measures to be taken when output is unstable.

[0002]

2. Description of the Related Art Generally, rear wheel steering control is of a vehicle speed sensitive type. In a low speed range, the rear wheels are steered in reverse phase to improve small turning performance. Basically, the steering ratio is variably controlled in accordance with the stability of the vehicle. By the way, the vehicle generates a yawing motion (rotational motion) about a vertical axis of the vehicle body due to disturbances such as a road surface condition, a difference in driving force and grip force between left and right rear wheels, and a cross wind. It is known that these disturbances change the behavior of the vehicle irrespective of the skill of the driver and impair stability.

Recently, a yaw rate sensor has been developed which directly detects the yaw rate (rotational angular velocity) of a yawing motion of a vehicle with high accuracy. According to the yaw rate sensor, not only the front wheel steering, but also the road surface condition,
A change in the behavior of the vehicle due to disturbance such as a cross wind can be detected quickly. For this reason, actively use the yaw rate,
A control method of rear-wheel steering has been proposed so as to ensure the stability of the vehicle even for various disturbances.

Here, for example, a vibrating gyro-type yaw rate sensor has a piezoelectric element mounted orthogonally above and below a metal diaphragm of a tuning fork vibrator, and a rated voltage is applied to a lower piezoelectric element so that the upper piezoelectric element vibrates. The element outputs a voltage corresponding to the rotational angular velocity. In the neutral position, the upper piezoelectric element also oscillates synchronously and outputs a reference voltage of, for example, 2.5 V. When the vehicle turns left or right, it outputs a voltage higher than the reference voltage, and when it turns to the other side, it outputs a lower voltage than the reference voltage. It is configured to output a voltage. Therefore, when the ignition switch is turned on during engine operation, it becomes possible to apply a voltage to the yaw rate sensor and detect the yaw rate.

In this case, immediately after the engine is started, the voltage is rapidly applied by the yaw rate sensor to vibrate the piezoelectric element, and unstable engine vibration and the like are transmitted. Therefore, during the initial few 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, in the state where 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, it is necessary to prevent a malfunction of the rear wheel steering due to an unstable output signal until the output signal of the yaw rate sensor becomes neutral. In this case, by calculating the differential value of the yaw rate, the unstable state of the sensor output signal can be determined. However, when the vehicle starts to move, the actual yaw rate is added to the differential value of the yaw rate, and it is difficult to make an accurate determination. Become. Therefore, it is desired to deal with an unstable state of the sensor output signal without using the differential value of the yaw rate.

Conventionally, correction of an inaccurate sensor signal of the yaw rate sensor is disclosed in, for example,
There is a prior art of 49765. In this prior art, when the zero value of the sensor changes due to an environmental change, a change over time, or the like, the zero estimated value of the sensor is updated, and the yaw rate is accurately detected based on the updated zero estimated value. ing.

[0007]

In the above-mentioned prior art, the value of the yaw rate sensor at the time when the time required for stabilizing the sensor output elapses after the ignition switch is turned on is set to a zero estimated value. And Therefore, there is a problem that control cannot be performed in a state where the sensor output is unstable immediately after the switch is turned on.

In view of the foregoing, the present invention has been made to optimize the rear wheel steering in the rear wheel steering control using the yaw rate, particularly when the vehicle is running in a state where the output signal of the yaw rate sensor is unstable. With the goal.

[0009]

SUMMARY OF THE INVENTION In order to achieve this object, the present invention firstly provides a method for detecting a detected yaw rate, a yaw rate coefficient set in the in-phase direction by a function of vehicle speed, and a detected steering wheel angle. A target rear wheel steering angle is calculated from a steering wheel angle coefficient set in a reverse phase direction by a function of a vehicle speed, and the yaw rate is calculated by a rear wheel steering device that automatically steers rear wheels based on the target rear wheel steering angle. Immediately after the operation of the yaw rate sensor to be detected, the yaw rate coefficient is set to substantially zero, and the steering wheel angle coefficient is set to the first mode in which the anti-phase direction is small and the in-phase direction is large. The mode is switched so that the steering angle coefficient has a large value and the phase in the opposite phase is increased, and the mode is switched to the normal mode when the vehicle is in neutral neutral state. Secondly, in the rear wheel steering device, the yaw rate coefficient is set by a plurality of characteristics in which a value in the in-phase direction is increased from zero in advance in a yaw rate gain map, and the steering wheel angle coefficient is a steering angle gain. The mode switching is performed by setting a plurality of characteristics in which values and ratios in the opposite phase direction and the same phase direction are changed in advance on a map, and selecting the characteristics of the yaw rate coefficient and the steering wheel angle coefficient with the passage of time. I do.

[0010]

According to the present invention, the target rear wheel steering angle is calculated from the yaw rate, the yaw rate coefficient, the steering wheel angle, and the steering wheel angle coefficient when the vehicle is running, and the rear wheel steering device is operated based on the target rear wheel steering angle. . Therefore, the rear wheels are automatically steered in phase or in opposite phases to obtain a desired steering angle or the like by the yaw rate when the behavior of the vehicle changes due to disturbances such as the vehicle speed, steering wheel angle, or side wind, and at low speeds. The turning property and the 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 mode is forcibly changed after a lapse of time corresponding to the stabilization pattern of the sensor output signal. Therefore, in the case of the initial unstable state, for example, the rear wheels are steered only by the steering wheel angle and its coefficient, and even if the vehicle runs immediately, a malfunction due to the unstable yaw rate is avoided. Further, as the stability of the neutral position of the sensor output signal increases, the feedback control is performed by increasing the in-phase steering angle and the in-phase yaw rate so that the rear wheels are steered to a stable side even when the vehicle behavior changes. And when it is stable neutral,
A smooth transition is made to the normal mode based on the inverse 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, the outline of the drive system and the four-wheel steering system of the vehicle will be described. First, in a vehicle 1, an engine 2 is connected to a clutch 3 and a transmission 4, and an output side of the transmission 4 is transmitted to a front wheel 7 via a front differential 5, an axle 6, and the like. The output side of the transmission 4 is also configured to transmit power to the rear wheel 11 via a propeller shaft 8, a rear differential 9, an axle 10, and the like.
The vehicle is driven by four wheels. The four-wheel steering system includes a front wheel steering device 20 and a rear wheel steering device 30.

The front wheel steering device 20 includes a steering shaft 22 having a handle 21 and a hydraulic control valve 2.
3, and is connected to the front wheel 7 via a power cylinder 24, a rod 25, and a knuckle arm 26, and is configured to manually steer the front wheel 7 by operating a 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 deceleration, and from the eccentric shaft 33 via a link 34, a lever 35, a knuckle arm 36 and the like. The rear wheel 11 is connected to the wheel 11 and is configured to automatically steer the rear wheel 11 by driving a motor. If the motor power is turned off at the time of abnormality, the worm gear 32
Keeps the rear wheel 11 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 speed sensor 41 for detecting a steering wheel angular speed dθ, a rear wheel steering angle sensor 42 for detecting a rear wheel steering angle Er, and a rear wheel steering angular speed ωr are provided. It has a rear wheel steering angular velocity sensor 43 for detecting. The vehicle also has a yaw rate sensor 44 that detects a yaw rate γ of the rotational angular velocity according to the turning state of the vehicle. Further, the control unit 50 has a front left wheel speed sensor 45 for detecting a front left wheel speed Nfr and a rear right wheel speed sensor 46 for detecting a rear right wheel speed Nrl in order to calculate the control vehicle speed V. And outputs a motor signal to the motor 31 in accordance with the steering direction, the steering angle, and the steering angular velocity of the rear wheels.

The yaw rate sensor 44 is of a vibrating gyroscope type, and is constituted by vertically attaching piezoelectric elements to a metal diaphragm of a tuning fork vibrator. Then, when the ignition switch is turned on at the time of starting the engine, it operates by applying voltage and the output signal at the neutral position becomes unstable at the beginning,
When stable and 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 calculator 51 to which the front left wheel speed Nfr and the rear right wheel speed Nrl are input, 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, and the steering wheel angle coefficient Kθ is set by a function of the vehicle speed V. At the same time, the vehicle speed V is input to the yaw rate coefficient setting unit 53, and the yaw rate coefficient Kγ is similarly set by the function of the vehicle speed V I do. Here, the normal mode in which the yaw rate sensor 44 is stable and neutral will be described. The steering angle coefficient Kθ is opposite in phase across the entire vehicle speed as indicated by Kθ1 in the steering angle gain map in FIG. Is a characteristic in which the absolute value of the value decreases and changes as the value is lower. The yaw rate coefficient Kγ has the same phase over the entire range of the vehicle speed as Kγ1 in the yaw rate gain map of FIG. 3B, and has a characteristic that gradually increases and changes as the vehicle speed V increases. Therefore, referring to this map, both coefficients Kθ, Kγ
Set.

The handle angle θ and the handle angle coefficient Kθ are input to a multiplier 54 to calculate a product value Kθ · θ of the two, and the yaw rate γ and the yaw rate coefficient Kγ are also input to the multiplier 55 to calculate the product value Kγ · 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 Kγ · γ is a stable element that keeps the vehicle on a stable side, and the term 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. Since this coefficient Kγ is a characteristic of the increasing function of the vehicle speed V, the value of Kγ · γ increases as the vehicle speed V increases. growing. In general, the steering wheel angle θ is very small in a middle to high speed range. Therefore, even if the coefficient Kθ is small in the opposite phase direction, the value of Kθ · θ is close to zero. Therefore, when the yaw rate γ occurs in the middle and high speed range, the target rear wheel steering angle ET becomes in the same phase direction by the value of Kγ · γ, and is controlled with emphasis on stability. In a low-speed range where the steering wheel angle θ is large, turning is emphasized by 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 same phase direction.

The target rear wheel steering angle ET and the rear wheel steering angle Er are input to a deviation calculator 57, and the deviation ED is calculated by ED = ET−Er. This deviation ED is determined by the target rear wheel turning speed setting unit 5.
8 to set a target rear wheel turning speed ωo according to the deviation ED according to the map of FIG. Further, the target rear wheel turning speed ωo and the rear wheel steering angular speed ωr are input to the speed difference calculating section 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,
A control amount Kp of a proportional component according to the speed difference ωd is set, and the drive unit 61 supplies a forward or reverse rotation motor current I to the motor 31 according to the control amount Kp.

In the above control system, the yaw rate sensor 4
The correction control when the output signal of No. 4 is unstable neutral will be described. First, the yaw rate sensor 4 immediately after starting the engine
In the case where the output signal of No. 4 is unstable, the yaw rate feedback control may be suppressed in accordance with the unstable state, and the steering angle feedback control may be modified to be stronger. Further, since the pattern in which the yaw rate sensor 44 is stable and neutral is known in advance as a function of time, in consideration of running of the vehicle, the control mode is forcibly switched over time to stabilize the steering performance. Therefore, in the steering angle coefficient setting unit 52, as an unstable neutral case, for example, three steering wheel angle coefficients Kθ2, Kθ3, and Kθ4 are sequentially reduced as shown by a broken line in FIG. It is set with the characteristics that have been set. Also in the yaw rate coefficient setting unit 53, three yaw rate coefficients Kγ2 and Kγ
γ3 and Kγ4 are set with characteristics in which the values are sequentially reduced as shown by the broken line in FIG.

On the other hand, a mode switching unit 62 for inputting the yaw rate γ is provided.
Is set. Then, after the elapse of time T, the mode switching signal is input to both setting units 52 and 53, and each coefficient is selected to switch the control mode. That is, when the initial output signal is most unstable, the mode d is only the steering angle feedback control using the coefficients Kθ4 and Kγ4, and then the mode c and the coefficient c are the coefficients Kθ3 and Kγ3 in which the antiphase steering angle and the in-phase yaw rate are sequentially strengthened The mode is switched to the mode b by Kθ2 and Kγ2, and is switched to the normal mode a by the coefficients Kθ1 and Kγ1 when the stability becomes neutral.

Next, the operation of this embodiment will be described. First, the engine 1 is operated, and the shifting power of the transmission 4 is transmitted to the front wheels 7 and the rear wheels 11 by the driving system, so that the vehicle 1
It runs with wheel drive. When the driver operates the steering wheel 21 at this time, the front wheels 7 are steered by the front wheel steering device 20 to be manually steered. The flowcharts of FIGS. 4A and 4B are executed at predetermined time intervals, and the rear wheel steering is controlled according to the running, steering operation, turning of the vehicle, and the like.

That is, when the operation of the yaw rate sensor at the time of starting the engine is determined in step S1 of the control mode switching routine (a), a timer time T is set in step S2. Thereafter, in steps S3, S4, and S5, the timer time T is compared with three types of set times t1, t2, and t3 (t3>t2> t1). Therefore, at the initial rising when the neutral position of the sensor output signal is most unstable, steps S3 to S
Then, as shown in FIG. 6, a mode d of the steering angle feedback control based on the coefficients Kθ4 and Kγ4 is determined.

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 is executed.
2, the vehicle speed V is calculated. In step S13, the control mode is checked. In the mode d, the coefficients Kθ4 and Kγ4 are set as the handle angle coefficient Kθ and the yaw rate coefficient Kγ 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 ED between the target rear wheel steering angle ET and the rear wheel steering angle Er.
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 the speed difference ωd is calculated in step S18. The control amount Kp is determined, and step S19 is performed.
Output the motor current I of the control amount Kp to drive the motor 31.

For this reason, in the rear wheel steering device 30, the motor 3
1, the worm gear 32 and the eccentric shaft 33 rotate, the link 34 and the lever 35 swing right and left, and the rear wheel 11 is automatically steered. In this case, the rear wheels 11 are controlled so as to obtain a desired steering angle or steering angular velocity in the same phase or the opposite phase.

Therefore, in the most unstable initial stage, Kγ
4 = 0, the target rear wheel steering angle ET is calculated only by the steering wheel angle θ and the coefficient Kθ4, and the steering angle feedback control is performed. For this reason, even if the vehicle runs immediately while operating the steering wheel, erroneous rear wheel steering due to an unstable yaw rate is avoided. Then, by the characteristic of the coefficient Kθ4, the rear wheels 11 are steered in the opposite phase or the same phase, and the turning performance at low speed and the stability at high speed are ensured.

Next, when time t1 has elapsed, step S
4 to step S8, the mode is switched to the mode c of the coefficients Kθ3 and Kγ3, and after the lapse of time t2, the process proceeds from step S5 to step S9 and the mode b of the coefficients Kθ2 and Kγ2
Switch to. Therefore, as the neutral position of the sensor output gradually becomes stable with the passage of time, feedback control is performed by increasing the in-phase steering angle and the in-phase yaw rate, so that the rear wheels 11 are stable even with changes in vehicle behavior. Steered to the side. Then, when the sensor output signal reaches a point at which the sensor output signal becomes substantially stable neutral after elapse of the longest time t3, the process proceeds from step S5 to step S6, and smoothly shifts to the normal mode a with little change in the vehicle behavior as shown in FIG. I do.

Therefore, in the normal mode a, when the steering wheel 21 is turned greatly at a low speed such as when starting, the target rear wheel steering angle ET becomes K
Becomes negative depending on the values of θ and θ, and the rear wheel 11 is turned in the opposite direction to make a small turn. At this time, if the vehicle turns sharply or the vehicle turns around due to the road surface μ to increase the yaw rate γ, Kγ · γ
Is corrected to decrease the reverse-phase steering of the rear wheels 11, and the behavior of the vehicle is stabilized. When turning at middle and high speeds, the target rear wheel steering angle ET becomes positive mainly due to the value of Kγ · γ, and the rear wheel 11
Are steered in-phase, so that the stability of the vehicle during turning is improved. FIG. 5 shows the relationship among the steering wheel angle θ, the yaw rate γ, both coefficients Kθ, Kγ, and the target rear wheel steering angle ET in this case. When the vehicle suddenly turns left and right due to a disturbance such as a cross wind, the yaw rate γ changes greatly, and the change in behavior of the vehicle 1 is quickly detected. Then, the rear wheels 11 are steered so as to maintain the in-phase state regardless of the turning of the vehicle 1 by the values of Kγ · γ. For this reason, the vehicle 1 is stably opposed so as not to be swept away by the crosswind,
And return to the original course smoothly. In this way, the reverse phase control and the yaw rate feedback control are performed.

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

[0029]

As described above, according to the present invention,
In a rear-wheel steering device that automatically steers the rear wheels by anti-phase steering angle proportional control and yaw rate feedback control, when the output signal of the yaw rate sensor changes from an unstable state to a stable neutral state, the steering wheel angle coefficient is calculated as a function of time. Since the control is forcibly switched to the control mode by changing the characteristics of the yaw rate coefficient, especially when the vehicle is running immediately after the engine is started, malfunction due to unstable yaw rate is prevented, and the rear wheels are always properly steered. And steerability of the vehicle is stabilized. Since the control method switches the control mode as a function of time, the switching control can be accurately performed without being affected by the behavior of the vehicle, and the control becomes easy. Since the steering angle feedback control is gradually switched to the reverse phase steering angle proportional control and the yaw rate feedback control, the rear wheels are smoothly steered, and the behavior change of the vehicle is extremely reduced.

[Brief description of the drawings]

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

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

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 at the time of turning left and right.

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

[Explanation of symbols]

 Reference Signs List 30 rear wheel steering device 31 electric motor 40 handle angle sensor 44 yaw rate sensor 50 control unit 52 handle angle coefficient setting unit 53 yaw rate coefficient setting unit 56 target rear wheel steering angle calculation unit 62 mode switching unit 63 timer

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ identification code FI B62D 117: 00 B62D 117: 00 137: 00 137: 00 (58) Field surveyed (Int.Cl. ⁷ , DB name) B62D 6 / 00-6/06

Claims (2)

(57) [Claims] 1. A target afterward based on a detected yaw rate, a yaw rate coefficient set in an in-phase direction by a function of vehicle speed, a detected steering wheel angle, and a steering wheel angle coefficient set in a reverse phase direction by a function of vehicle speed. In a rear wheel steering device that calculates a wheel steering angle and automatically steers a rear wheel based on the target rear wheel steering angle, immediately after an operation of a yaw rate sensor that detects the yaw rate, the yaw rate coefficient is set to substantially zero and the steering wheel angle is set. The mode is changed to a first mode in which the coefficient has a small number of opposite phases and a large number of in-phase directions, and thereafter, as time elapses, the mode is switched such that the value of the yaw rate coefficient increases in the same direction and the steering angle coefficient increases in the opposite phase. And switching to a normal mode when the vehicle is in a stable neutral state. 2. The yaw rate coefficient is set by a plurality of characteristics in which a value in the in-phase direction is increased from zero in advance in a yaw rate gain map. 2. The rear wheel steering device according to claim 1, wherein the mode switching is performed by selecting a characteristic of the yaw rate coefficient and a characteristic of the steering wheel angle coefficient with a lapse of time. Control method.