JPH06171538A - Car steering device - Google Patents

Abstract

PURPOSE:To enhance the maneuvering stability by controlling the rear wheel steering angle using the yawrate. CONSTITUTION:When the rear wheel steering angle is to be controlled in accordance with the turning angle of a steering wheel, the actual yawrate sensed is used as parameter. Therein an actual yaw acceleration calculating means 31 calculates the actual yaw acceleration from the actual yawrate which is sensed by a yawrate sensor 28, and a presumed yawrate calculating means 32 calculates the presumed yawrate from the output of a wheel speed sensor 27, and a presumed yaw acceleration calculating means 34 calculates the presumed yaw acceleration from the fore-foregoing presumed yawrate and the foregoing presumed yawrate. An allowable value setting means 35 cumulatively adds the specified allowable value to the presumed yaw acceleration at each calculation of the actual yaw acceleration and sets the updated yaw acceleration allowable value. An actual yawrate restricting means 36 admits the use of the updated actual yawrate if the updated actual yaw acceleration lies within the actual yaw acceleration allowable value and prohibits the use if lies outside of the region. This ensures an enhanced maneuvering stability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle steering system for controlling a turning angle of rear wheels by using a yaw rate detected by a yaw rate sensor.

[0002]

2. Description of the Related Art Conventionally, there has been known a vehicle steering system configured to variably set a steering ratio of a rear wheel with respect to a steering angle of a front wheel according to a vehicle speed, a steering angle of a steering wheel, a yaw rate, etc. (See Japanese Patent Publication No. 57-44568). The yaw rate sensor is used for steering control of these vehicles, for example, under predetermined traveling conditions, the rear wheels are first steered in reverse phase with the front wheels in accordance with steering wheel operation, and the vertical axis passing through the center of gravity of the vehicle is used. It is necessary to detect the yaw rate (yaw angular velocity) when steering control is performed in the same phase as the front wheels when the turning motion (yawing) of the steering wheel occurs and the steering wheel operation is controlled properly. .

The yaw rate sensor used for these steering controls is expensive, and the yaw rate detected by the yaw rate sensor is judged to be reliable or not. Comparing the estimated yaw rate with the actual yaw rate detected by the yaw rate sensor, the estimated yaw rate is calculated based on the wheel speed difference between the left and right driven wheels, which is more reliable in detecting vehicle speed than the unreliable driving wheel. Then, a steering apparatus for a vehicle having a function of determining a failure (failure) of the yaw rate sensor has also been proposed (see Japanese Patent Laid-Open No. 2-249765, etc.).
In this type of vehicle steering system, when the yaw rate sensor fails, a steering control mode is immediately switched to another running state detection sensor, for example, a vehicle speed sensor or a steering angle sensor.

[0004]

In the vehicle steering system with the fail determination function, the yaw rate sensor is attached to the vehicle body, and the yaw rate is detected in accordance with the actual behavior (yawing) of the vehicle body. The yaw rate is detected in a relatively short cycle, and the steering angle control of the rear wheels is performed using this yaw rate. In accordance with this, the determination as to whether or not to use the latest actual yaw rate detected by the yaw rate sensor is also made in a short cycle. On the other hand, the estimated yaw rate is calculated from the wheel speed difference between the left and right driven wheels, and this wheel speed data is also used as a control parameter for the antilock braking device. Therefore, if the wheel speed sampling cycle is set to be short, the antilock braking device operates at a relatively short cycle due to the fluctuation of the wheel speed difference between the left and right wheels, which causes a problem in steering stability. Therefore, in order to improve the operating performance of the anti-lock braking device, the wheel speed sampling period is generally set longer than the yaw rate sampling period from the yaw rate sensor.

Based on the actual yaw rate sampled at such a different cycle and the estimated yaw rate, whether or not to use the actual yaw rate detected by the yaw rate sensor is determined by the sampling cycle of the actual yaw rate for the above reason. It is done according to. In this case, since the actual yaw rate changes momentarily from the time when the previous estimated yaw rate was sampled to the time when this sampling was performed, the allowable value was calculated when the previous estimated yaw rate was calculated in accordance with the expected change range of the actual yaw rate. If the difference between the detected actual yaw rate and the estimated yaw rate is within this tolerance when the actual yaw rate is set to a large value, the rear wheel steering control using the latest detected actual yaw rate will be performed. Done.

However, among the detected actual yaw rates, even if the difference from the estimated yaw rate is within the allowable value,
The actual yaw rate that has changed abruptly due to the slight vibration (rolling) of the vehicle body is also included. If the steering control of the rear wheels is performed using the yaw rate based on this slight vibration of the vehicle body, the steering stability is extremely poor. There is a problem such as.

An object of the present invention is to provide a vehicle steering system capable of improving steering stability by restricting steering control using an abruptly changed actual yaw rate.

[0008]

A vehicle steering system according to a first aspect of the present invention includes a yaw rate sensor for detecting a yaw rate,
The yaw rate sensor is provided with a rear wheel steering means for controlling the steering angle of the rear wheels by using the yaw rate detected by the yaw rate sensor, and a yaw rate sensor for detecting a running state of the vehicle. An actual yaw acceleration calculating means for calculating an actual yaw acceleration from the output of the driving method, and an estimated yaw rate calculating means for calculating an estimated yaw rate at a cycle longer than a calculation cycle by the actual yaw acceleration calculating means based on the output of the running state detecting means. , The estimated yaw rate calculation means receives the output of the estimated yaw rate calculation means, and the estimated yaw acceleration calculation means calculates the estimated yaw acceleration this time from the estimated yaw rate two times before and the estimated yaw rate last time , By accumulating a predetermined allowable value for each calculation of the actual yaw acceleration, the latest actual yaw acceleration It is determined whether the latest actual yaw acceleration calculated by the allowable value setting means for setting a value and the actual yaw acceleration calculating means is within the range of the actual yaw acceleration allowable value set by the allowable value setting means. When it is inside the range, the latest actual yaw rate is allowed to be used, and when it is out of the range, the latest actual yaw rate is prohibited and the actual yaw rate limiting means is provided.

Then, the actual yaw rate limiting means is configured to maintain the latest actual yaw rate immediately before the use of the latest actual yaw rate is prohibited (claim 2). Further, the traveling state detecting means is composed of a wheel speed sensor (claim 3) for detecting the wheel speed of the left and right driven wheels or a steering angle sensor (claim 4) for detecting the steering angle of the steering wheel.

[0010]

In the vehicle steering system according to the first aspect of the present invention, the detected actual yaw rate is used as a parameter when the steering angle of the rear wheels is controlled according to the steering angle of the steering wheel. In this case, in order to judge the reliability of the yaw rate sensor, the actual yaw acceleration calculation means calculates the actual yaw acceleration from the actual yaw rate detected by the yaw rate sensor, while the estimated yaw rate calculation means outputs the output of the running state detection means. Based on the estimated yaw rate,
The estimated yaw acceleration calculating means calculates the estimated yaw acceleration from the estimated yaw rate two times before and the previous estimated yaw rate.

Since the calculation cycle of the estimated yaw acceleration is longer than the calculation cycle of the actual yaw acceleration, the allowable value setting means accumulates a predetermined allowable value in the estimated yaw acceleration for each calculation of the actual yaw acceleration. To set the latest actual yaw acceleration allowable value. The actual yaw rate limiting means determines whether the latest actual yaw acceleration calculated by the actual yaw acceleration calculating means is within the range of the actual yaw acceleration allowable value, and when it is within the range, the latest actual yaw rate is allowed to be used. , Also, when it is out of the range, the latest real yaw rate is prohibited.

As described above, the determination as to whether or not to use the latest actual yaw rate detected by the yaw rate sensor is made based on the yaw acceleration (rate of change in yaw rate).
The determination can be made early, and the actual yaw acceleration allowable value is cumulatively added to the estimated yaw acceleration each time the actual yaw acceleration is calculated, so the setting range is the actual yaw rate detection period. Can be set to a small value, and for yaw rate with an abnormal rate of change due to slight vibration of the vehicle body, the steering control of the rear wheels using that yaw rate can be restricted, and control with excellent steering stability is possible. Can be realized.

In the vehicle steering system according to the second aspect of the present invention, when the latest actual yaw rate is prohibited to be used, the latest actual yaw rate is maintained so that the steering stability is improved. In the vehicle steering system according to claim 3, the estimated yaw rate is calculated from the wheel speed difference between the left and right driven wheels by the output from the wheel speed sensor, and in the vehicle steering system according to claim 4, the steering angle sensor outputs the yaw rate. The steering wheel steering angle signal is received, and the estimated yaw rate is calculated from the steering wheel steering angle.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. The present embodiment is a case where the vehicle steering system according to the present invention is applied to a four-wheel steering system, and FIG. 1 is a schematic overall configuration diagram showing the four-wheel steering system. In FIG.
The vehicle 1 includes left and right front wheels 3FL and 3FR which are drive wheels connected by a front wheel steering mechanism 2 and left and right rear wheels 5RL and 5RR which are driven wheels connected by a rear wheel steering mechanism 4.

The front wheel steering mechanism 2 includes a pair of knuckle arms 6FL and 6FR and tie rods 7FL and 7FR, and a relay rod 8F which connects these tie rods 7FL and 7FR to each other.
It has and. A rack-and-pinion type steering mechanism 11 including a rack (not shown) connected to a relay rod 8F and a pinion 10 connected to a steering shaft 9 is connected to the front wheel steering mechanism 2. The mechanism 2 is the operation amount of the handle 12, that is,
The relay rod 8F is displaced leftward and rightward according to the steering angle of the handle 12 to steer the left and right front wheels 3FL, 3FR.

The rear wheel steering mechanism 4 includes a pair of knuckle arms 6RL, 6RR and tie rods 7RL, 7RR, and a relay rod 8R connecting these tie rods 7RL, 7RR to each other.
And a steering ratio variable unit 14 including a motor 13 that acts as a drive source for steering the left and right rear wheels 5RL, 5RR.
And a transmission mechanism 15 for transmitting the driving force of the motor 13 to the relay rod 8R. Then, the rear wheel steering mechanism 4 causes the motor 13 to rotate normally or reversely,
The relay rod 8R is displaced to the left and right via the transmission mechanism 15 to steer the left and right rear wheels 5RL and 5RR.

Further, the steering amounts of the front wheels 3FL, 3FR are mechanically transmitted to the steering ratio variable unit 14 of the rear wheel steering mechanism 4 via the pinion 16 and the shaft 17. Further, the rear wheel steering mechanism 4 is provided with a fail-safe mechanism 19. The fail-safe mechanism 19 is provided between the transmission mechanism 15 and the clutch 20 capable of releasing the connection between the motor 13 and the relay rod 8R, and between the relay rod 8R and the vehicle body. Spring 21 biasing in the neutral direction
neutral holding means 21 having a. And
When a failure occurs and the steering angle control of the rear wheels 5RL and 5RR should be stopped, the fail-safe mechanism 19 releases the clutch 20 and the neutral holding means 21 forcibly brings the relay rod 8R to the neutral position. It is configured so that it can be held and operated as a two-wheel steering vehicle.

In the vehicle 1, a steering wheel angle sensor 25 for detecting the steering angle θh and a steering ratio sensor 2 for detecting the steering ratio of the rear wheels 5RL, 5RR to the front wheels 3FL, 3FR.
6, a wheel speed sensor 27 that detects the wheel speed of the left and right front wheels 3FL and 3FR and rear wheels 5RL and 5RR, and a yaw rate sensor 28 that detects the yaw rate of the vehicle body. In particular,
The wheel speed sensor 27 is a main constituent element of the running state detecting means 29 for detecting the running state of the vehicle, and when calculating the estimated yaw acceleration from the wheel speed difference between the left and right rear wheels 5RL and 5RR which are driven wheels. Besides, it is also used for calculating the vehicle speed from the average value of the wheel speeds of the left and right rear wheels 5RL, 5RR, and for controlling the operation of the antilock braking device.

Detection signals are respectively input from the steering wheel steering angle sensor 25, the steering ratio sensor 26, the wheel speed sensor 27, and the yaw rate sensor 28, and the rotation of the motor 13 is controlled based on these detection signals. With
A control unit 30 that connects or disconnects the clutch 20 is provided.

FIG. 2 is a block diagram of the vehicle steering system of this embodiment. The control unit 30 of the vehicle steering system according to the present embodiment includes the actual yaw acceleration calculation means 3
1, estimated yaw rate calculation means 32, estimated yaw rate storage means 33, estimated yaw acceleration calculation means 34, allowable value setting means 35, actual yaw rate limiting means 36, sensor failure determination means 37, and control mode selection means. 38
And rear wheel steering angle control means 39.

The actual yaw acceleration calculating means 31 receives the output from the yaw rate sensor 28 and receives the output from the yaw rate sensor 2.
The actual yaw rate is calculated from the actual yaw rate detected in 8 at a relatively short cycle (10 ms in this embodiment), and the actual yaw acceleration signal is output to the actual yaw rate limiting means 36.

The estimated yaw rate calculation means 32 receives the output from the wheel speed sensor 27, and based on the wheel speed difference between the left and right rear wheels 5RL and 5RR which are the driven wheels detected by the wheel speed sensor 27, the actual yaw rate is calculated. The estimated yaw rate Yp is estimated and calculated at a cycle (100 ms in this embodiment) that is relatively longer than the calculation cycle of the acceleration calculation means 31, and the estimated yaw rate signal is output to the estimated yaw rate storage means 33. In this estimated yaw rate calculation means 32, the estimated yaw acceleration Yp is calculated as in the mathematical expression, where the wheel speeds of the left and right rear wheels are VL and VR, the tread width is Tb, and a constant K1.

[0023]

## EQU1 ## Absolute value of Yp = K1 × (VR-VL) / Tb

The estimated yaw rate storage means 33 receives the output from the estimated yaw rate calculation means 32, stores the estimated yaw rate calculated two times before and the estimated yaw rate calculated last time, and outputs the estimated yaw rate signal to the yaw acceleration calculation means 34. Configured to output to.

The estimated yaw acceleration calculation means 34 calculates the estimated yaw acceleration dYP of this time from the estimated yaw rate of the previous two times output from the estimated yaw acceleration storage means 33 and the estimated yaw rate of the previous time, and outputs the estimated yaw acceleration signal. It is configured to output to the allowable value setting means 35.

The allowable value setting means 35 outputs the current estimated yaw acceleration d output from the estimated yaw acceleration calculation means 34.
By accumulating a predetermined allowable value α for each calculation of the actual yaw acceleration to Yp, the latest actual yaw acceleration allowable value dYp + nα (n = 1, 2, 3 ... 10) of the actual yaw acceleration is obtained. The actual yaw acceleration allowable value dYp + nα is set and output to the actual yaw rate limiting means 36.

The actual yaw rate limiting means 36 stores the actual yaw rate output from the yaw rate sensor 28, and based on the outputs from the actual yaw acceleration calculating means 31 and the allowable value setting means 35, the actual yaw acceleration calculating means. In accordance with the calculation cycle output from 31, the absolute value of the actual yaw acceleration dYa is the absolute value of the actual yaw acceleration allowable value dYp +
It is determined whether or not it is within the range of nα, and when it is within the range, use of the latest actual yaw rate Ya is permitted, and a signal of the latest actual yaw rate Ya is output to the rear wheel steering angle control means 39,
Further, when it is out of the range, the use of the latest actual yaw rate is prohibited, and the latest signal of the actual yaw rate Yn-1 is output to the rear wheel turning angle control means 39.

Now, the setting of the actual yaw acceleration allowable value dYp + nα in the allowable value setting means 35 will be described with reference to FIGS. FIG. 4 is a diagram showing a temporal change of the yaw rate, in which the vertical axis represents the yaw rate Y and the horizontal axis represents the time t. In FIG. 4, Ya is the actual yaw rate, Ypn
-1 is the estimated yaw rate calculated at the time point B (100 ms) two times before, Ypn is the estimated yaw rate calculated at the time point A (200 ms) at the previous time, and a1 to a10 are the estimated values at the time of the previous estimated yaw rate calculation (A). The determination time is shown when the actual yaw rate limiting means 36 makes 10 determinations based on the actual yaw acceleration dYa up to time C (300 ms), which is the time when the yaw rate is calculated.

In this embodiment, as shown in FIG. 4, the amount of change ΔYp is calculated from the estimated yaw rate Ypn−1 of the last two times (time B) and the estimated yaw rate Ypn of the previous time (time A).
Based on this change amount ΔYp, the allowable range Δ of the change amount (actual yaw acceleration) of the actual yaw rate for each determination of a1 to a10
Yp + K is set. That is, the allowable width ΔYp + K
Is a shaded portion in FIG. 4, and is set to gradually spread from a1 to a10.

In FIG. 4, the allowable width ΔYp + K
In order to make the description easy to understand, is shown in analog form, but is actually represented digitally as shown in FIG. That is, in FIG. 5, the vertical axis represents the absolute value of the amount of change in yaw rate (yaw acceleration), and the horizontal axis represents time t.
It is a figure showing the relationship between the actual yaw acceleration dYa and the estimated yaw acceleration dYp. In FIG. 5, a broken line D is an absolute value of the estimated yaw acceleration dYp, a solid line E is an absolute value of the actual yaw acceleration dYa, and a chain line F is an absolute value of the estimated yaw acceleration dYp. Shows a value obtained by adding a permissible value (permissible error) nα added to.

In FIG. 5, the sampling cycle of the actual yaw rate, that is, the calculation cycle of the actual yaw acceleration dYa is 10 m.
s, the sampling cycle of the wheel speed, that is, the sampling cycle of the estimated yaw rate is 100 ms. Therefore, the actual yaw acceleration allowable value is set to the absolute value of the estimated yaw acceleration dYp at this time in accordance with the calculation cycle of the actual yaw acceleration dYa. The allowable value α is cumulatively added, which tends to increase on the stairs. Then, in the actual yaw rate limiting means 36,
When the absolute value of the actual yaw acceleration dYa is smaller than the actual yaw acceleration allowable value obtained by adding the actual yaw acceleration allowable value nα added for each determination to the absolute value of the estimated yaw acceleration dYp,
That is, in the figure, the use of the latest actual yaw rate Ya is permitted only when the absolute value of the actual yaw acceleration dYa exists in the shaded area.

The sensor failure determination means 37 receives the detection signals from the yaw rate sensor 28, the wheel speed sensor 27, and the steering angle sensor 25, respectively, and determines the failure of these sensors through a predetermined calculation process. Although the determination is made, the calculation process of the fail determination is not directly related to the present invention, and therefore its detailed description is omitted.

The control mode selection means 38 receives the sensor status signal from the sensor failure determination means 37 and selects one of the following first to fifth modes according to the failure status of the sensors. Is configured to. First control mode: When all of the sensors 25, 27, 28 are normal, the detected vehicle speed V and steering angle θh, respectively.
The rear wheel steering control mode based on the yaw rate Ya and the yaw rate Ya. Second control mode: a mode in which rear wheel steering control is performed based on the vehicle speed V and the steering angle θh respectively detected when the yaw rate sensor 28 fails. Third control mode: a mode in which the rear wheel steering control is performed based on the vehicle speed V and the yaw rate Ya detected when the steering angle sensor 25 fails. Fourth control mode ... When the wheel speed sensor 27 fails
A mode in which rear wheel steering is stopped and only the two front wheels are steered. Fifth control mode ... A mode in which rear wheel steering control is performed based on only the vehicle speed V when the steering angle sensor 25 and the yaw rate sensor 28 fail.

The rear wheel turning angle control means 39 has a wheel speed sensor 27, a steering angle sensor 25, an angle detection signal from the turning ratio sensor 26, a yaw rate signal from the actual yaw rate limiting means 36, and a control mode selection. The steering ratio of the rear wheels to the front wheels is calculated by receiving each of the mode selection signals from the means 38, and the calculated steering ratio is compared with the detected steering ratio to perform feedback control while performing the calculation. The steering angle of the rear wheels is calculated based on the calculated steering ratio and the detection signals from the sensors 25, 27, 28, and a control signal corresponding to the steering angle of the rear wheels is output to the motor drive circuit 40. Is configured to. Further, the rear wheel turning angle control means 39, when the fourth control mode signal is input from the control mode selection means 38,
The clutch 20 is released, and the neutral holding means 21 forcibly holds the relay rod 8R at the neutral position. Note that the processing for calculating the turning ratio and the turning angle in each control mode is not directly related to the present invention, and therefore a detailed description thereof will be omitted.

The motor drive circuit 40 is configured to set a motor drive current based on a control signal from the rear wheel turning angle control means 39 and to supply the motor drive current to the motor 13. .

FIG. 3 is a flow chart showing the routine of the actual yaw rate limiting control. This actual yaw rate limiting control is control for determining whether or not the latest actual yaw rate is used when the yaw rate sensor 28 is normal.
The control using the other sensors 25 and 27 when the yaw rate sensor 28 fails is not directly related to the present invention, so the description thereof will be omitted. In the figure, S
i (i = 1, 2, 3 ...) Shows each step. The actual yaw rate limiting control of this embodiment is started by turning on the ignition switch, and first, various signals from the steering wheel steering angle sensor 25 and the wheel speed sensor 27, for example,
Reading of wheel speed, steering wheel steering angle signal, etc. is executed (S
1). In the present embodiment, of these signals, the estimated yaw rate Yp is calculated from the difference between the wheel speeds of the left and right driven wheels by the wheel speed signal (S2).

Next, the estimated yaw rate Ypn-1 of the previous two times.
And the previous estimated yaw rate Ypn from the estimated yaw acceleration d
Yp is calculated (S3), and at the time of this determination, that is, 10 ms
At the time of each determination, the actual yaw rate Ya is read from the yaw rate sensor 28 (S4).
The actual yaw acceleration dYa is calculated from a (S5), and the actual yaw acceleration allowable value nα (n = 1, 2, 3 ... 10) is set (S6). Then, the absolute value of the calculated actual yaw acceleration dYa is the absolute value of the actual yaw acceleration allowable value dYp + nα obtained by cumulatively adding the allowable value α to the absolute value of the estimated yaw acceleration dYp.
It is determined whether or not (n = 1, 2, 3 ... 10) or less (S
7) As a result of the determination, when the absolute value of the actual yaw acceleration dYa is equal to or less than the actual yaw acceleration allowable value (S7: Yes), the latest actual yaw rate detected by the yaw rate sensor 28 is normal, and thus the latest actual yaw rate is detected. Control using the actual yaw rate Ya is executed (S8).

When the absolute value of the actual yaw acceleration dYa is larger than the absolute value + nα of the actual yaw acceleration allowable value dYp in S7 (S7: No), the use of the latest actual yaw rate Ya is prohibited and the latest latest yaw rate Ya is prohibited. The control using the actual yaw rate is executed (S9). Then, it is determined whether or not the above determination (S7) is a predetermined number of times (N = 10) or more since the calculation of the estimated yaw rate (S10). This is because the estimated yaw rate calculation cycle is 100 ms and the actual yaw acceleration calculation cycle is 10 ms, so that it is determined how many times the determination is made.

If the result of this determination is that the predetermined number of times has not been reached (S10: No), the counter is incremented (S11), the process returns to S4, and the above determination is repeated. That is, the absolute value + nα of the actual yaw acceleration allowable value dYp is set for each calculation of the actual yaw acceleration dYa (S6). And
If the predetermined number of times (10 times) is reached (S10: Ye
s), clear the counter (S12), return to S1,
Various signals are read, the estimated yaw rate is newly calculated (S2), the estimated yaw acceleration dYp at the time of this determination is calculated (S3), and the determination as to whether or not the latest actual yaw rate can be used is repeated.

As described above, since the judgment as to whether or not to use the actual yaw rate detected by the yaw rate sensor is made based on the yaw acceleration (rate of change in yaw rate), the judgment can be made early. , The actual yaw acceleration allowable value is cumulatively added to the estimated yaw acceleration for each calculation of the actual yaw acceleration, so the setting range can be set small according to the actual yaw rate detection cycle, and For yaw rate with an abnormal rate of change based on vibration or the like, steering control of the rear wheels using the yaw rate can be restricted, and control with extremely good steering stability can be realized.

The present invention is not limited to the above embodiments, and it goes without saying that many modifications and changes can be made within the scope of the present invention. For example, in the above-described embodiment, the present invention is applied to the rear wheel steering mechanism in which the steering amount of the front wheels is mechanically transmitted to the rear wheels, but the invention is not limited to this, and the steering amount of the front wheels uses hydraulic pressure or the like. The present invention may be applied to a system in which the steering amount of the rear wheels is controlled by transmitting the rear wheels to the rear wheels. Further, in the above embodiment, the traveling state detecting means is composed of the wheel speed sensor, but it goes without saying that it may be composed of the steering wheel steering angle sensor (claim 4).

[Brief description of drawings]

FIG. 1 is a schematic overall configuration diagram showing a vehicle steering system according to an embodiment of the invention.

2 is a block diagram of the vehicle steering system of FIG. 1. FIG.

3 is a flowchart showing a routine of an actual yaw rate limiting control in the steering control of the vehicle of FIG.

FIG. 4 is a diagram showing a temporal change of a yaw rate for calculating an estimated yaw acceleration.

FIG. 5 is a diagram illustrating a setting state of a permissible value at the time of comparing and determining an actual yaw acceleration and an estimated yaw acceleration.

[Explanation of symbols]

 1 Vehicle 2 Front Wheel Steering Mechanism 4 Rear Wheel Steering Mechanism 5RL, 5RR Rear Wheel 6RL, 6RR Knuckle Arm 7RL, 7RR Tie Rod 8R Relay Rod 13 Motor 14 Steering Ratio Variable Unit 15 Transmission Mechanism 16 Pinion 17 Shaft 19 Fail Safe Mechanism 20 Clutch 21 Neutral Holding means 25 Steering angle sensor 26 Steering ratio sensor 27 Wheel speed sensor 28 Yaw rate sensor 29 Running state detection means 30 Control unit 31 Actual yaw acceleration calculation means 32 Estimated yaw rate calculation means 33 Estimated yaw rate storage means 34 Estimated yaw acceleration calculation means 35 Allowable value setting means 36 Actual yaw rate limiting means 37 Sensor failure determination means 38 Control mode selection means 39 Rear wheel steering angle control means

Claims (4)

[Claims] 1. A steering apparatus for a vehicle, comprising: a yaw rate sensor for detecting a yaw rate; and a rear wheel steering means for controlling a steering angle of a rear wheel by using the yaw rate detected by the yaw rate sensor. A running state detecting means for detecting a running state, an actual yaw acceleration calculating means for calculating an actual yaw acceleration from the output of the yaw rate sensor, and an output cycle of the actual yaw acceleration calculating means based on the output of the running state detecting means. And an estimated yaw rate calculation means for calculating an estimated yaw rate in a long cycle, and an output of the estimated yaw rate calculation means, and an estimated yaw acceleration calculation for calculating the estimated yaw acceleration this time from the estimated yaw rate two times before and the estimated yaw rate last time. Means and the current estimated yaw acceleration received from the estimated yaw acceleration calculation means for each calculation of the actual yaw acceleration. Tolerance value setting means for setting the latest actual yaw acceleration allowable value of the actual yaw acceleration by cumulatively adding the predetermined allowable values, and the latest actual yaw acceleration calculated by the actual yaw acceleration calculating means. Is within the range of the actual yaw acceleration allowable value set by the allowable value setting means.If it is within the range, the latest actual yaw rate is allowed to be used, and if it is out of the range, the latest actual yaw rate is allowed. A steering device for a vehicle, comprising: an actual yaw rate limiting means for prohibiting the use of the yaw rate. 2. The actual yaw rate limiting means is configured to maintain the latest actual yaw rate immediately before when prohibiting the use of the latest actual yaw rate. Vehicle steering system. 3. The vehicle steering system according to claim 1, wherein the traveling state detecting means is composed of a wheel speed sensor that detects wheel speeds of the left and right driven wheels. 4. The steering apparatus for a vehicle according to claim 1, wherein the traveling state detecting means is a steering angle sensor for detecting a steering angle of the steering wheel.