JPH05155350A - Four-wheel steering control device - Google Patents

Abstract

PURPOSE:To carry out the optimum rear wheel steering angle control depending on an accurate yaw rate by correcting a drift of a yaw rate sensor. CONSTITUTION:A front wheel steering angle sensor 1, a yaw rate sensor 2, and a controller 3 to control the rear wheel steering mechanism 10 electrically depending on the output values of the front wheel steering angle sensor 1 and the yaw rate sensor 2, are provided. And a brake lamp switch 5, and wheel speed sensors 6 and 7 to detect the rotation speeds of the rear wheels 13 and 14 are connected to the controller 3. And when the controller 3 detects the condition that the brake lamp switch 5 is OFF, and the difference of the rotation speeds of the rear wheels 13 and 14 is zero for a specific time, a specific average value of the output values of the yaw rate sensor 2 for that period is made as the value of the yaw rate zero, and the correction at the yaw rate zero point is carried out, and furthermore, the yaw rate value is corrected thereafter by making the zero point as the standard.

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 control device for controlling a steering angle of a rear wheel on the basis of a front wheel steering angle and a yaw rate in a four-wheel steering vehicle, that is, a so-called 4WS vehicle.

[0002]

BACKGROUND ART In recent years, the so-called steering wheel in the low vehicle speed range is further improved to improve the small turning performance of the vehicle, and the response of the vehicle to the turning of the steering wheel in the medium / high vehicle speed range is relaxed. A four-wheel steering vehicle that can steer not only the front wheels but also the rear wheels has been put into practical use for the purpose of improving steering stability, and it has become relatively common. In this four-wheel steering vehicle, in addition to the front wheel steering angle and the vehicle speed as the control data of the rear wheel steering angle, the yaw rate of the vehicle body, that is, the rotational angular velocity generated around the vertical axis passing through the center of gravity of the vehicle body as viewed from above ( Yaw angular velocity data may be used. Examples of inventions relating to control of a four-wheel steering vehicle using such a yaw rate include the inventions described in JP-A-60-161258 and JP-A-63-207772.

In a four-wheel steering vehicle, a yaw rate sensor such as a tuning fork type or tuning piece type piezoelectric vibrating gyro shown in FIG. 4 may be used for yaw rate detection. Here, with reference to FIG.
A piezoelectric vibrating gyro will be briefly described. A vibrator 30 having a tuning fork shape as a whole, which is composed of a detecting element 31 and a driving element 32 as shown in the figure, is vibrated by a piezoelectric ceramic as indicated by an arrow A. (Vibration velocity v), and in this state, when a rotational angular velocity (yaw angular velocity) ω as indicated by arrow B about the central axis of the vibrator 30 is applied, a direction deviated by 90 degrees from the original vibration direction. The Coriolis force Fc (= 2 mωv) as shown in FIG. (Here, m is the mass of the oscillator.) Therefore, the yaw angular velocity ω can be detected by electrically detecting the Coriolis force Fc through the detection element 31 by the detection means (not shown). it can.

[0004]

However, when the above-mentioned piezoelectric vibrating gyro is used as a yaw rate sensor to control the rear wheel steering angle of a four-wheel steering vehicle, the piezoelectric vibrating gyro shown in FIG. 3 is used. It has a zero-point drift characteristic and the output voltage (null voltage) at rest does not become zero. Therefore, if the sensor output value is taken as the vehicle body yaw rate, it cannot be ignored from the actual yaw rate. There is an inconvenience that an error may occur and the rear wheel steering angle control may not be performed correctly. On the other hand, the reason why the null voltage does not become zero may be the processing accuracy of the vibrator, the variation of the piezoelectric ceramic, the bonding position, etc., and the cause of the drift may be the instability of the piezoelectric properties of the bonding layer and the piezoelectric ceramic. Furthermore, since it has a two-layer structure, drift is more likely to occur, and it is difficult to completely prevent these.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the problems of the prior art, and an object thereof is to correct the drift of a yaw rate sensor and perform an optimum rear wheel steering angle control based on an accurate yaw rate. An object of the present invention is to provide a four-wheel steering control device that enables it.

[0006]

A four-wheel steering control system according to the present invention comprises a front wheel steering angle sensor for detecting a front wheel steering angle, a yaw rate sensor for detecting a yaw rate of a vehicle body, an output value and a yaw rate of the front wheel steering angle sensor. And a control means for electrically controlling the rear wheel steering mechanism based on the output value of the sensor. Further, the control means is connected to a brake lamp switch which is turned on when the brake is used and a wheel speed detection means for detecting the rotational speeds of the left and right driven wheels. And
When the controller detects that the brake lamp switch is off and the rotational speeds of the left and right driven wheels are not zero and the difference between the two is zero for a certain period of time, the average value of the output values of the yaw rate sensor during that period is determined. Has a yaw rate zero value, and has a yaw rate correction function for correcting the output value of the yaw rate sensor based on the corrected yaw rate zero point. With such a configuration, the above-described object is to be achieved.

[0007]

[Function] If the vehicle is in a straight running state and is in a non-braking state during traveling, the brake lamp switch is turned off and the left and right driven wheels rotate at the same rotational speed (same rotational angular velocity). The yaw rate of can be regarded as zero. In the present invention, the control means detects the state in which the brake lamp switch is off, the rotational speeds of the left and right driven wheels are not zero, and the difference between the two is zero, by the outputs of the brake lamp switch and the wheel speed detecting means. When this state can be detected continuously for a certain period of time, the control means corrects the yaw rate zero point by using a predetermined average value of the output values of the yaw rate sensor during that period as the value of the yaw rate zero, and thereafter, the corrected yaw rate zero point. Is used as a reference to correct the output value of the yaw rate sensor. Moreover, when the vehicle is in a straight running state and is in a non-braking state, the vehicle often visits during traveling, and the yaw rate zero point correction and the yaw rate correction based on the yaw rate zero point correction are performed each time. The yaw rate is corrected at a sufficiently small time interval with respect to the drift period. Therefore, the yaw rate is always corrected to an accurate value that substantially matches the actual yaw rate of the vehicle body.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a simplified diagram showing the overall construction of a four-wheel steering system including a four-wheel steering control device according to an embodiment of the present invention. This embodiment is for a front-wheel drive vehicle (FF vehicle). The left and right front wheels 1 are shown in Fig. 1.
The front wheel steering angle sensor 1 for detecting the steering angles of 1 and 12, the yaw rate sensor 2 for detecting the yaw rate of the vehicle body, and the rear wheel steering mechanism 10 based on the output value of the front wheel steering angle sensor 1 and the output value of the yaw rate sensor 2. The controller 3 is provided as a control means for electrically controlling. Further, the controller 3 includes a brake lamp switch 5, which is turned on when a brake (not shown) is used, and first and first wheel speed detecting means for detecting rotational speeds of the left and right rear wheels 13 and 14, which are left and right driven wheels, respectively. Two wheel speed sensors 6 and 7 are connected. Further, the controller 3 includes the left and right rear wheels 13, 1
Outputs of a rear wheel steering angle sensor 4 for detecting the steering angle of the vehicle 4 and a speedometer 8 as a vehicle speed sensor for detecting the traveling speed of the vehicle are input.

The front wheel steering angle sensor 1 is attached to the tip of the steering shaft 21, and detects the steering angle of the left and right front wheels 11 and 12 by detecting the rotation angle of the steering shaft 21 from the reference point. ing. The left and right front wheels 11 and 12 are attached to both ends of a tie rod 15 having a rack (not shown) formed in the center through knuckle arms 16 and 17, respectively. In addition, a pinion that meshes with the rack formed on the above-mentioned tie rod 15 is equipped in a portion of the steering shaft 21 inside the front wheel gear box 23 to form a rack and pinion mechanism. Then, by rotating (steering) the steering handle 22, the rotational movement of the steering shaft 21 is converted into a reciprocating movement of the tie rod 15 in the direction of the arrow YY 'by the action of the rack and pinion mechanism, whereby the knuckle arm 16 is moved. Left and right front wheel 1 via
1, 12 are steered (turned). Therefore, YY 'of the tie rod 13 is used as a front wheel steering angle sensor.
A device that detects a directional displacement may be used.

The rear wheel steering mechanism 10 includes tie rods 20 provided with left and right rear wheels 13 and 14 on both ends thereof via respective knuckle arms 18 and 19, and the tie rods 20.
A rear wheel gear box 24 in which a rack-and-pinion mechanism including a rack (not shown) formed in the center of the rack and a pinion (not shown) meshing with the rack is housed;
The rear wheel gear box 24 is configured to include a motor 25 and the like, the rotation shaft of which is provided with the pinion. The rotation of the rotary shaft of the motor 25 is controlled by the controller 3 controlling the motor 25.
Tie rod 20 by the action of the rack and pinion mechanism
Is converted into a reciprocating motion in the direction of the arrow Y-Y 'of the left and right rear wheels 13 and 14 via the knuckle arms 18 and 19.
Is being steered. The rear wheel steering angle sensor 4 is
What is attached to the gear box 24 and detects the steering angle of the left and right rear wheels by detecting the displacement of the tie rod 20 in the arrow Y-Y 'direction is used. Besides this,
A device that detects the rotation angle of the rotation axis of the motor 25 from the reference point may be used.

The first and second wheel speed sensors 6 and 7 are sensors that pick up each rotation of the left and right rear wheels 13 and 14 to output a pickup signal having a frequency proportional to the rotation speed of each wheel. .. A piezoelectric vibration gyro is used as the yaw rate sensor.

The controller 3 includes a microcomputer including an interface section (hereinafter referred to as "IF section") for performing analog-digital conversion or waveform shaping of signals from each sensor, a central processing unit (CPU), a memory and the like. The signal from each sensor described above is input to the CPU via the IF unit.

Next, the overall operation of this embodiment thus constructed will be described with a focus on the flowchart of FIG. 2 showing the control program of the controller 3.

When an ignition switch (not shown) is turned on to start the engine, each sensor and the controller 3 are turned on and the control program shown in FIG. 2 is started. When the vehicle starts traveling, an analog signal corresponding to the steering angle of the steering wheel from the front wheel steering angle sensor 1, a rectangular wave signal corresponding to the vehicle speed from the speedometer 8, and a yaw rate of the vehicle body from the yaw rate sensor 2 (a vertical signal passing through the center of gravity of the vehicle body An analog signal corresponding to the rotational angular velocity about the axis) and an analog signal corresponding to the steering angle of the rear wheels from the rear wheel steering angle sensor are sequentially input to the IF unit in the controller 3, and the IF unit digitizes or waveforms. After shaping processing, front wheel steering angle data θf
, Vehicle speed data V according to vehicle speed, yaw rate data γ,
The rear wheel steering angle data θr is sequentially input to the CPU (steps S101, S102, S103, S104). In the next step S105, the process proceeds to a yaw rate correction subroutine to be described later, and after this yaw rate correction processing returns to the main routine, and the CPU in the controller 3 causes the CPU in the controller 3 to input the front wheel steering angle data θf and the vehicle speed. A target rear wheel steering angle θ is calculated based on the data V and a corrected yaw rate value γ ′ described later (step S106). Here, the calculation of the target rear wheel steering angle θ in step S106 is performed based on the following equation.

Θ = K1 · θf + K2 · γ ...
Here, K1 and K2 are predetermined proportional coefficients, of which K1 is a proportional coefficient for steering the left and right rear wheels 13 and 14 in proportion to the front wheel steering angle data θf. Left and right rear wheels 13 and 14 in the low vehicle speed range
In order to improve the small turning performance of the vehicle by steering in the opposite phase (opposite direction) with respect to 1 and 12, in the low vehicle speed range, the vehicle speed V gradually increases from a predetermined negative value to zero as the vehicle speed V increases. It is set to zero in the high-speed vehicle speed range. K2 is the yaw rate data γ for the left and right rear wheels 13 and 14.
Is a proportional coefficient for steering control in proportion to, and steers the left and right rear wheels 13, 14 in the same phase (in the same direction) as the left and right front wheels 11, 12 to mitigate the vehicle response to the turning of the steering wheel 22. In order to do so, it is set to gradually change from zero to a predetermined positive value as the vehicle speed V increases from the low vehicle speed region to the high vehicle speed region.

After calculating the target rear wheel steering angle θ, the controller 3
The CPU therein controls the motor 25 so that the steering angles of the left and right rear wheels 13, 14 match the target rear wheel steering angle θ based on the rear wheel steering angle data θr input in step S105 (step S107). ). Then, returning to step S101, the operations of steps S101 to S107 are repeated. In this way, the steering angles of the left and right rear wheels 13, 14 are controlled.

Next, a yaw rate correction subroutine, which is a main control operation in this embodiment, will be described with reference to the flowchart of FIG.

After shifting to the subroutine of FIG. 3 in step S105 in the control program of the main routine of FIG. 2 described above, in the CPU in the controller 3, the first and second wheel speed sensors 6 and 7 are operated via the IF section. Left and right rear wheels 1
Input the wheel speed data of 3 and 14 (step S20
1), front wheel steering angle data θf input in step S101
Whether the front wheel steering angle is zero, or whether the rear wheel steering angle is zero based on the rear wheel steering angle data θr input in step S104,
Whether or not the brake lamp switch 5 is off, step S2
Based on the wheel speed data of the left and right rear wheels input in 01, it is sequentially determined whether or not the difference between the two is zero (steps S202 to S2).
05). If any of the determination results of steps S202 to S205 is affirmative, the timer value T is updated in the next step S206, and then the timer value T is set to a predetermined time T0 (this time is the front and rear wheels of the vehicle). The steering angle of the vehicle does not coincide with the state when the vehicle is traveling straight as a transient phenomenon during traveling, but it is the time when it can be confirmed that the vehicle is traveling straight. It is determined whether or not the yaw rate is equal to or longer than a predetermined time which is a time sufficient to actually become zero (step S207).

If the determination in step S207 is negative, the CPU proceeds to step S1.
The yaw rate data γ input in 03 and a predetermined average value γa of the yaw rate data up to the previous time (the specific contents of this average value will be described later) are calculated, and this is calculated as a new predetermined average value. γa (step S21
0). Here, since the initial value of γa is zero, the process of γ / 2 → γa is performed in step S210 of the first cycle. Next, the CPU proceeds to the next step S211, and sets the yaw rate zero point to γ0 (the initial value of γ0 is zero), and corrects the yaw rate data γ to γ '. However, until the yaw rate zero point is first corrected, the initial value of γ0 is zero, so that the yaw rate data γ = yaw rate correction value γ ′ input in step S103 results, and the yaw rate is corrected. I can't. Then, in the CPU, after the process of step S211, the process returns to the main routine of FIG. 2 to repeat the control operation described above,
If the determination result in step S207 of FIG. 3 is affirmative at the (n + 1) th cycle, the CPU proceeds to next step S208 to replace the previous predetermined average value γa with a new yaw rate zero point γ0. Correct (change) the zero point. Next, in the CPU, after resetting the timer in the next step S209, step S211
Then, the yaw rate data γ is corrected to γ ′, with the zero point of the yaw rate set as γ0 replaced in step S208. Then, the CPU returns to the main routine and repeats the control operation described above.

The predetermined average value γa, which is the target of the processing in step S210, will be described. As a premise, the yaw rate data in the first cycle is represented by γ1, the data in the second cycle is represented by γ2, and similarly γ3, ..., γn, and γ2 = γ1 + α1, γ3 = γ1 + α2, ...
,, γn = γ1 + αn, n
The predetermined average value γan newly set in step S210 at the cycle is represented by the following equation.

Γan = Σ (γai + γi) / 2 = γ1 (1-1 / ²ⁿ ) + α1 / ^2n-1 + α2 / ^2n-2 + ... + αn-1 / 2 ≈γ1 + αn-3 / 8 + αn -2 / 4 + αn-1 / 2 ………………

What can be understood from this equation is that the predetermined average value γan of the yaw rate data newly set in step S210 at the nth cycle has a great influence on the yaw rate data γ1 at the first cycle and n-2. , N-1,
Yaw rate data for the nth cycle γn-2, γn-1, γn
And γ1 are the differences αn-3, αn-2, and αn-1, which means that if the time T0 is set sufficiently short while taking into consideration the zero-point drift characteristic of the yaw rate sensor 2 shown in FIG.
Is almost equal to the zero point drift amount, and this γan is calculated in step S
Setting the zero point of the new yaw rate value at 207
The zero point drift of the yaw rate sensor 2 can be corrected almost accurately.

On the other hand, in steps S202 to S20
If any one of the determination results of 5 is negative, the CPU proceeds to step S209 and resets the timer, and then in step S211, the yaw rate data γ is set to γ ′ with the previous γ0 as the yaw rate zero point. Correct to. Also in this case, the yaw rate data γ = the yaw rate correction value γ ′ holds, so that the yaw rate is not corrected as a result. Then, the CPU returns to the main routine and repeats the control operation described above.

When the vehicle is in a straight running state and is in a non-braking state during traveling, both the front wheel steering angle and the rear wheel steering angle are zero, the brake lamp switch 5 is off, and the left and right rear wheels 13 and 14 have the same rotational speed (the same rotational angular speed). ), So the left and right rear wheels 13, 14
The difference in the wheel speed of is zero, and if this state continues for a certain time,
Actually, the yaw rate of the car body can be regarded as zero. In this embodiment, if the controller 3 detects the above state for a certain period of time T0 based on the output data from each sensor, the controller 3 determines a predetermined average value γa of the output values of the yaw rate sensor 2 during that period. The yaw rate zero point is corrected with a zero value γ 0, and the output value of the yaw rate sensor 2 is corrected with reference to this corrected yaw rate zero point, so that the rear wheel steering control is always performed based on a substantially accurate yaw rate. .. In addition, when the vehicle is in the straight running state and is in the non-braking state, the vehicle often visits during traveling, and the yaw rate zero point and the yaw rate correction based on the yaw rate zero point are corrected each time the yaw rate sensor 2 operates. The yaw rate is corrected at a sufficiently small time interval with respect to the zero drift period. Therefore, in this embodiment, the yaw rate is always corrected to an accurate value that substantially matches the actual yaw rate of the vehicle body, and optimal rear wheel steering angle control based on the accurate yaw rate becomes possible.

In the above embodiment, the controller 3 is used as a condition for considering the actual yaw rate of the vehicle body as zero.
However, the brake lamp switch 5 is off, the left and right rear wheels 13,
The case where the difference between the wheel speeds of 14 is zero and both the front wheel steering angle and the rear wheel steering angle are confirmed to be zero has been exemplified, but even if there is no condition that both the front wheel steering angle and the rear wheel steering angle are zero, If the former two conditions are satisfied, the actual yaw rate of the vehicle body can be considered to be zero, and therefore the present invention does not necessarily need to determine this condition. Further, in the above-mentioned embodiment, although the slightly special average value described in detail above is used as the predetermined average value of the yaw rate, the present invention is not necessarily limited to this, and a normal arithmetic average and standard deviation are used. Etc. may be used. Further, in the above embodiment, the case where the wheel speed of the rear wheel is obtained from the wheel speed sensor is illustrated.
The configuration may be obtained from the S controller. Furthermore, although the above embodiment describes the FF vehicle, it is needless to say that the present invention can be applied to a rear wheel drive vehicle (FR vehicle). In this case, the wheel speed detecting means is used as a front wheel which is a driven wheel. It is necessary to provide.

[0027]

As described above, according to the present invention,
Even if a piezoelectric vibration gyro that causes a zero-point drift due to manufacturing reasons is used as the yaw rate sensor, the drift of the yaw rate sensor can be corrected almost accurately, and the optimum yaw rate-based optimum It is possible to provide an unprecedented excellent four-wheel steering control device capable of performing excellent rear-wheel steering angle control.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a four-wheel steering system including a four-wheel steering control device according to an embodiment of the present invention.

FIG. 2 is a flowchart showing an overall control operation in the embodiment of FIG.

FIG. 3 is a flowchart showing a yaw rate correction operation in the embodiment of FIG.

FIG. 4 is a diagram for explaining a yaw rate detection principle of a piezoelectric vibration gyro.

FIG. 5 is a diagram showing a zero-point drift characteristic of a piezoelectric vibration gyro.

[Explanation of symbols]

 1 Front Wheel Steering Angle Sensor 2 Yaw Rate Sensors 2 and 3 Controller as Control Means 5 Brake Lamp Switch 6 First Wheel Speed Sensor as Wheel Speed Detection Means 7 Second Wheel Speed Sensor as Wheel Speed Detection Means 10 Rear Wheel Steering Mechanism 11 Left front wheel 12 Right front wheel 13 Left rear wheel as driven wheel 14 Right rear wheel as driven wheel

[Procedure amendment]

[Submission date] November 16, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

Θ = K1θf + K2γ ... where K1 and K2 are predetermined proportional coefficients, of which K
1 is a proportional coefficient for steering control of the left and right rear wheels 13, 14 in proportion to the front wheel steering angle data θf, and the left and right rear wheels 13, 14 are reversed with respect to the left and right front wheels 11, 12 in the low vehicle speed region. In order to improve the small turning performance of the vehicle by steering in the opposite directions, the vehicle gradually changes from a predetermined negative value to zero as the vehicle speed V increases in the low vehicle speed region and reaches zero in the medium and high speed vehicle speed region. Is set to be. Further, K2 is a proportional coefficient for steering control left and right rear wheels 13 and 14 in proportion to the yaw rate data gamma, the left and right rear wheels 13 and 14 drive
Steering in a direction that controls the body's yaw rate to drive the vehicle
In order to improve stability, it is set so as to gradually change from zero to a predetermined positive value as the vehicle speed V increases from the low vehicle speed region to the high vehicle speed region.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

After calculating the target rear wheel steering angle θ, the controller 3
The internal CPU controls the motor 25 so that the steering angles of the left and right rear wheels 13 and 14 match the target rear wheel steering angle θ based on the rear wheel steering angle data θr input in step S104 (step S107). ). Then, returning to step S101, the operations of steps S101 to S107 are repeated. In this way, the steering angles of the left and right rear wheels 13, 14 are controlled.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0022

[Correction method] Change

[Correction content]

Γan = (γai + γi) / 2 = γ1 (1-1 / ²ⁿ ) + α1 / ^2n-1 + α2 / ^2n-2 + ......... + αn ^-1 / 2≈γ1 + ( αn -3 / 8) ) + (Αn−2 / 4) + (αn−1 / 2) ………………

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0024

[Correction method] Change

[Correction content]

On the other hand, in steps S202 to S20
If any one of the determination results of 5 is negative, the CPU proceeds to step S209 to reset the timer, and then in step S211, the yaw rate data γ is set to γ ′ by using the previous γ0 as the yaw rate zero point. Correct to
It Then, the CPU returns to the main routine and repeats the control operation described above.

[Procedure Amendment 5]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

[Fig. 2]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location B62D 109: 00 137: 00

Claims (1)

[Claims] 1. A front wheel steering angle sensor for detecting a front wheel steering angle, a yaw rate sensor for detecting a yaw rate of a vehicle body,
In a four-wheel steering control device including a control means for electrically controlling a rear wheel steering mechanism based on an output value of the front wheel steering angle sensor and an output value of the yaw rate sensor, the control means is turned on when a brake is used. Brake lamp switch and the wheel speed detection means for detecting the rotation speed of the left and right driven wheels are connected, the control means, when the brake lamp switch is off and the rotation speed of the left and right driven wheels are both zero. When the state in which the difference between the two is zero is detected for a certain period of time, the yaw rate zero point is corrected by using the predetermined average value of the output values of the yaw rate sensor during that period as the yaw rate zero value, and thereafter the corrected yaw rate zero point is corrected. A four-wheel steering control device having a yaw rate correction function for correcting the output value of the yaw rate sensor with reference to.