JPH09290767A - Four-wheel steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently precisely detect an abnormal condition quickly while setting a dead zone threshold value low even when two steering angle sensors for feedback control of a rear steering angle to a target steering angle are arranged. SOLUTION: Two rear wheel steering angle sensors 38, 39 are arranged coaxially in the position in which a rotation angle of an electric motor 22 in an actuator 1 is detected. A deviation ΔδR1 between an actual rear wheel turning angel δR1 detected by means of one rear steering angle sensor 38 and a target steering angle value δ*R is computed. On the other hand, a deviation ΔδR2 between an actual rear wheel turning angle δR2 detected by means of the other rear wheel steering angle sensor 39 and the target steering angle value δ*R is computed. If either of absolute values of the deviations |ΔδR1 |, |ΔδR2 | is determined to be the dead zone threshold value α1 , which is set at the predetermine value, or more, it is determined that an abnormal condition is caused in a feedback control system including the rear wheel steering angle sensors 38, 39 from the actuator 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a main steering wheel such as a front wheel which is steered by a steering input of a driver.
The present invention belongs to a four-wheel steering system that steers auxiliary steering wheels such as rear wheels in order to improve vehicle motion and vehicle behavior.

[0002]

2. Description of the Related Art As such a four-wheel steering system, there is one disclosed in Japanese Patent Application No. 8-6774 previously proposed by the applicant of the present application. According to this four-wheel steering system, the steering angle of the steering wheel is detected as the steering state of the front wheel, which is the main steering wheel, and the auxiliary angle is detected according to the steering angle, the vehicle speed, or the steering angular speed, which is the steering speed. The target rudder angle of the rear wheel, which is the steered wheel, is set, the actual rudder angle of the rear wheel is detected from the operating state of the actuator, and the deviation between the real rudder angle and the target rudder angle is "0" or in the vicinity thereof. The control unit outputs a control signal to the actuator for steering the auxiliary steering wheel. That is, this actuator is feedback-controlled so as to always follow the target steering angle value set by the control unit while detecting its operating state.

Incidentally, in this four-wheel steering system, the actuator is composed of an electric motor, and a control amount, that is, a so-called robust control, is ensured so that the following response of the actuator to the target steering angle value is secured. The amount of current to the motor is adjusted. Further, this four-wheel steering system is provided with two sensors for detecting the actual steering angle of the auxiliary steering wheel (rear wheel), that is, the operating state of the actuator. One of them is an operating state detecting means of actuator feedback control for tracking the target steering angle value, and the other is detecting an abnormality of the sensor itself or the device for detecting the operating state of the actuator. As a fail safe, it is used to return the steering assist wheels to a neutral state, that is, to initialize (initialize) the wheels.

[0004]

By the way, in the above-mentioned four-wheel steering system, it is conceivable that open loop control such as so-called feed-forward control is performed by using a step motor or the like for the actuator, but in the unlikely event of a problem. If the failsafe does not operate due to an abnormality in the device, and as a result, the steering assist wheel is abnormally steered,
Since it directly affects the steering stability of the vehicle, it is necessary to perform closed loop control such as feedback control.However, if there is only one sensor that detects the operating state of the actuator, the sensor itself and the device However, there is a situation in which it is not possible to detect the above-mentioned abnormality, or a means for surely and promptly detecting the abnormality of the sensor or the device by one sensor is not constructed.

By the way, the target rear wheel steering angle as described above is
For example, when the setting is made by a processing device such as a microcomputer and the robust control is configured by an analog circuit, the command value from the processing device is the command value output from the robust circuit, that is, the drive. This tendency becomes more prominent because it is likely to be different from the signal and therefore not fully aware of the operating state of the actuator within the processor. Therefore, it is necessary to provide two sensors for detecting the operating state of the actuator, which causes the following problems.

Usually, when an abnormality is detected using the detection values of two sensors, for example, the deviation between the detection values of the two sensors may be considered to be a certain predetermined value, that is, a dead zone threshold value. When the value is abnormal, it is generally determined that an abnormality has occurred in either the sensor or the device.

Here, of the two sensors provided in the above-mentioned four-wheel steering system, one sensor detects the actual rear wheel steering angle from the rotation angle of the electric motor, and the other sensor detects the actual rear wheel steering angle from the displacement amount of the steering shaft. It has a structure that detects the rear wheel rudder angle, and the dead zone threshold described above takes into consideration the operating error of the device and the actuator itself, as well as the individual difference between the two sensors and the error in the mounting position of these two sensors. Because I have to
Therefore, the dead zone threshold value becomes large, which may delay the detection of a sensor or device abnormality.

Therefore, if the two sensors are arranged at the same steering angle displacement position of the actuator, for example, at a position where the actual rear wheel steering angle is simultaneously detected from the rotation angle of the electric motor, both detection axes become coaxial. Since the error in the mounting position does not occur and the dead zone threshold becomes small, it is possible to accurately and promptly detect the abnormality of the sensor or the device. However,
Even if abnormalities occur in the sensor levers (detectors) of two sensors at the same time and the detected values are not output from the two sensors,
Since the deviation of the detection values of those sensors is within the dead zone threshold value, it cannot be determined that the sensor abnormality has occurred.

The present invention has been developed in view of these problems. Even if two sensors for detecting the operating state of the actuator are arranged at the same operating position of the actuator, the sensor can be operated more reliably and quickly. It is an object of the present invention to provide a four-wheel steering device capable of detecting an abnormality in a sensor or a device.

[0010]

To achieve the above object, a four-wheel steering system according to claim 1 of the present invention uses at least two detecting means to detect the operating state of an actuator that operates in response to a drive signal. In the feedback control of the actuator according to the operating state of the actuator, so that the actual steering angle value follows the set target steering angle value of the auxiliary steering wheel detected at the same operating position of the actuator, The detection operation state of the actuator detected by one of the two detection means is compared with the target steering angle value, and the detection operation state of the actuator detected by the other detection means and the target steering angle value are compared. The four-wheel steering system detects the abnormality of the feedback control system by comparing the angle value.

According to another aspect of the present invention, there is provided a four-wheel steering system including an actuator for controlling a steering angle of auxiliary steering wheels according to an input drive signal, a detecting means for detecting an operating state of the actuator, and at least a main steering wheel. The target steering angle setting means for setting the target steering angle of the auxiliary steering wheel according to the steering state of the wheels and the motion state of the vehicle, and the actual steering angle of the auxiliary steering wheel based on the detection operating state of the actuator detected by the detection means. And a feedback control that outputs a drive signal to the actuator so that the magnitude of the steering angle deviation between the target steering angle value of the auxiliary steering wheel and the actual steering angle detection value of the auxiliary steering wheel becomes a predetermined value. In a four-wheel steering system including means,
The detection means is at least two detection means for detecting the operating state of the actuator at the same operating position of the actuator, and the feedback control means is detected by one of the two detection means. A first deviation calculating means for calculating a first deviation between the detected operating state of the actuator and the target steering angle value, and the detecting operating state of the actuator detected by the other detecting means of the two detecting means. And a second deviation calculating means for calculating a second deviation between the target steering angle value and one of the magnitude of the first deviation and the magnitude of the second deviation is a predetermined value or more. When it is determined that there is an abnormality in the feedback control system including the detection means, the abnormality detection means is provided.

[0012]

As described above, according to the four-wheel steering system of the first aspect of the present invention, the operating state of the actuator for steering the auxiliary steering wheel is detected by at least two detecting means, that is, by at least two detecting means. Since it is detected by the sensor, the reliability of the device can be improved. Since these sensors are arranged at the same operating position of the actuator, compared to the case where the two sensors are arranged at different operating positions of the actuator, in order to detect the abnormality without considering the mounting error. It is possible to set the dead zone threshold of 1 small. This makes it possible to accurately and promptly detect the abnormality in the feedback control system.

In the four-wheel steering system according to the second aspect of the present invention, the feedback control means can detect the detected operating state detected by one of the two detection means (sensors) and the target steering angle value. A first deviation calculating means for calculating a deviation, a second deviation calculating means for calculating a deviation between the detected operating state detected by the other sensor and the target steering angle value, the first deviation calculating means and the second deviation calculating means. When it is determined that one of the magnitude of the first deviation and the magnitude of the second deviation calculated by is greater than or equal to a predetermined value, there is an abnormality in the feedback control system including the detection means from the actuator. Since it has an abnormality detecting means for detecting the abnormality, even if the two sensors have abnormality at the same time (for example, the detectors of the two sensors have malfunctioned at the same time), the abnormality detection hand Is an abnormality of the sensor can be detected accurately and quickly. Similarly, even when an abnormality occurs in one of the sensors, the abnormality detecting means can accurately and quickly detect the abnormality of the sensor.

Since the two sensors are arranged at the same operating position of the actuator, it is possible to set the dead zone threshold value for detecting the abnormality small without considering the mounting error, and the feedback control system can be set. The abnormality can be detected accurately and promptly.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a four-wheel steering system according to the present invention will be described below with reference to the accompanying drawings. First, FIG. 1 briefly shows the overall configuration of the four-wheel steering system. In the figure, 10FL and 10FR are left and right front wheels that are main steering wheels, and 10RL and 10RR are left and right rear wheels that are auxiliary steering wheels. Among them, the front wheels 10FL and 10FR are connected to a rack shaft of a known rack-and-pinion type steering gear device 14 via tie rods 13, respectively. A pinion (not shown) connected to the steering shaft 16 meshes with the rack shaft, and the front wheel can be mechanically steered by rotating the steering wheel 15.

Reference numeral 2 in FIG. 1 denotes a rear wheel steering device mounted on the vehicle. In the rear wheel steering system 2, the rear wheels 10
The RL and 10RR are connected to each other by a steering shaft 20 for steering the rear wheels via tie rods 18, and the actuator unit 1 moves the steering shaft 20 in the left-right direction of the vehicle to assist the steering of the rear wheels. Is. The actuator unit 1 constitutes a rear wheel steering device 2 with high efficiency and irreversible characteristics, which will be described later, by using the electric motor 22 as a power source.

The actuator unit 1 will be described with reference to FIG. 2. The central portion of the steering shaft 20 is accommodated in a tubular housing 24 so as to be movable in the left-right direction of the vehicle, and the accommodated steering is carried out. A rack 26 is formed on a part of the shaft 20. The shaft 29 of the pinion 28 that meshes with the rack 26 is provided so as to project in the moving direction of the steering shaft 20, that is, the direction orthogonal to the left-right direction of the vehicle, that is, the front-back direction of the vehicle. Further, a hypoid ring gear 30 is coaxially attached to the pinion shaft 29, and a pinion 31 meshing with the ring gear 30 is attached to a rotary shaft 32 of the electric motor 22. Therefore, when the electric motor 22 is rotated, the pinion 31 moves to the ring gear 30, the pinion 28,
Since the power is transmitted to the rack 26, the electric motor 2
When 2 is rotated in both directions, the rack 26, that is, the steering shaft 20
Can be reciprocated in the left-right direction of the vehicle, and therefore the rear wheels 10RL, 10RR that are auxiliary steering wheels can be steered in synchronization in the left-right direction.

The hypoid gear composed of the pinion 31 and the ring gear 30 used here exhibits the above-mentioned high efficiency and irreversible characteristics. That is, as shown in FIG. 4, the rotational driving force from the pinion 31 side is
Since the gear efficiency with 0 is a positive value (about 40%), the ring gear 30 can be rotated in a desired direction. However, even if the ring gear 30 is to be rotated in the opposite direction, the pinion depends on the tooth angle. Only when a force is generated in the axial direction of 31, the gear efficiency is effectively "0" or less, and neither the ring gear 30 nor the pinion 31 is rotated. Therefore, the rear wheel 10
When inputs such as cornering force and road surface irregularities acting on the RL and 10RR are made, the entirety from the pinion 31 to the rack 26 is locked, so that the rear wheels 10RL and 10RR are locked.
The direction of RR, that is, the steering angle cannot be changed.

Here, one end of the sensor shaft 34 is fitted in the shaft center of the ring gear 30, and the outer periphery of the other end of the sensor shaft 34 is circumferentially arranged as shown in FIG. Disc-shaped plate body 3 having a notch 36a
Two 6 are externally fitted at a predetermined interval in the axial direction.
Two rear wheel steering angle sensors 38 and 39, which are rotary potentiometers and the like, are arranged coaxially with the sensor levers 38a and 39a in contact with the cutout portions 36a of the plate bodies 36, respectively.

That is, the two rear wheel steering angle sensors 38, 3
Reference numeral 9 denotes a sensor that detects the rotation angle of the electric motor 22, that is, the actual rear wheel steering angles δ _R1 and δ _R2 of the rear wheels 10RL and 10RR by detecting the rotation angle of the sensor shaft 34. Notch 36 of each plate body 36 according to rotation
The actual rear wheel steering angles δ _R1 and δ _R2 are detected by rotating the sensor levers 38a and 39a that are in contact with a.

Of these, in the present embodiment, the rear wheel steering angle sensor 38 is used as the main sensor, and the actual rear wheel steering angle δ _R1 is used for the rear wheel steering angle control described later. Also, reference numeral 3
The rear wheel steering angle sensor 9 is used as a sub sensor, and the steering shaft 20 and the rear wheels 10RL, 10RR are initialized (initialized) as a comparison target for detecting an abnormality of one of the rear wheel steering angle sensors. Used for. Hereinafter, the rear wheel steering angle sensor 38 is referred to as a main rear wheel steering angle sensor, and the rear wheel steering angle sensor 39 is referred to as a sub rear wheel steering angle sensor.

Returning to FIG. 1, the vehicle is provided with a vehicle speed sensor 6 for detecting the longitudinal speed (vehicle speed) V _C of the vehicle, and if necessary, lateral acceleration (lateral acceleration) of the vehicle (not shown). ) Is also provided to detect the lateral acceleration sensor,
A steering angle sensor 8 for detecting the steering angle θ of the steering wheel 15 is provided on the steering shaft 16. The detection signal of the steering angle θ of the steering angle sensor 8 is composed of a voltage signal which is positive when the steering wheel 15 is turned to the right and negative when the steering wheel 15 is turned to the left, according to the magnitude of the steering angle. The detection signal of the vehicle speed V of the vehicle speed sensor 6 comprises a voltage signal which is positive when the vehicle moves forward and is negative when the vehicle moves backward, and the actual rear wheel steering angle δ of the main rear wheel steering angle sensor 38. The detection signal of _R1 depends on the magnitude of the actual rear wheel steering angle from the middle position of the rear left and right wheels 10RL, 10RR, and when both the rear wheels 10RL, 10RR are right-turned, when left and right-turned. It consists of a voltage signal that is negative.

Further, the vehicle is equipped with the rear wheels 10RL and 10RL.
A control unit 3 for controlling the steering angle of the RR is provided. As shown in FIG. 5, the control unit 3 has an input interface circuit 40a having at least an A / D conversion function, a central processing unit (CPU) 40b, a storage device (ROM, RAM) 40c, and an output having a D / A conversion function. A microcomputer 40 having an interface circuit 40d and the like, and a drive circuit 41 for supplying a drive current I to the electric motor 22 are provided. In the control unit 3, the detection signals from the respective sensors are input and the rear wheels are steered in the same phase as the front wheels are steered by the steering wheel 15, so that the steering characteristic is changed to the weak understeer direction in the medium speed range. The turning performance is improved, and the steering characteristics are changed and controlled in the high speed range so as to be strengthened in the understeer direction to improve the stability of the vehicle at the time of turning and lane change and to improve the cornering convergence. Furthermore, when a fast steering input is given mainly in the medium speed range, the rear wheels are momentarily reversed in phase immediately after the start of steering to improve the yaw rate rise necessary for turning and improve the responsiveness to steering. That is, it is possible to improve the running stability during cornering by improving the turning ability and then performing the in-phase steering of the rear wheels.

The main components of the four-wheel steering system (rear wheel steering system) of this embodiment including the control unit 3 are represented by a hardware circuit as shown in FIG. That is, the target rear wheel steering angle calculation circuit A for calculating the target rear wheel steering angle δ ^* _R from the steering angle θ, the vehicle speed V _C, etc. according to the calculation processing of FIG. 6 described later.
And the output value and the main rear wheel steering angle sensor 3
8 and the actual rear wheel steering angle δ _R and the rear wheel steering angle deviation Δδ _R are calculated by the adder / subtractor B, and based on the rear wheel steering angle deviation Δδ _R , the actuator unit 1 ( A reference control command value calculation circuit C for calculating a reference control command value S _R0 to the electric motor 22) is configured, and for this reference control command value S _R0 , by calculation processing (not shown) or the like, A command value S _R capable of ensuring the responsiveness of the device by configuring the robust computing unit D for performing the so-called robust control as described above is output, and the command value S _R is used as the current value required by the drive circuit 41. It is converted to I and output to the actuator unit 1 (electric motor 22).

Next, in order to configure the target rear wheel steering angle calculation circuit A to the reference control command value calculation circuit C in the hardware circuit of FIG. 6, the microcomputer 40 of the control unit 3 executes The calculation process for outputting the wheel steering control signal will be described based on the flowchart of FIG. 7. This calculation process is performed with a predetermined sampling time ΔT.
It is executed as a timer interrupt process every (for example, 3.3 msec.). In addition, although this arithmetic processing does not include a step for communication in particular, programs and maps stored in the ROM of the storage device 40c or various data stored in the RAM are always stored in the arithmetic processing device 40b. Each calculation result transmitted to the buffer or the like and calculated by the arithmetic processing device 40b is also stored in the storage device 40c as needed.

In this calculation process, first, step S1
Then, it is determined whether the abnormality detection flag F described later is in the reset state of "0", and the abnormality detection flag F is "0".
If it is in the reset state of, the process proceeds to step S2,
If not, the process proceeds to step S3.

In step S3, the rear wheels 10RL, 1
Reference control command value S for steering 0RR_R0As “0”
Then, it outputs this and returns to the main program.
On the other hand, in step S2, the vehicle speed sensor 6
Vehicle speed V which is a detection signal _C, Detection from the steering angle sensor 8
Current value θ of steering angle, which is an output signal_(n)Read.

Next, in step S4, the present value θ _{(n) of} the steering angle read in step S1 and the previous value θ _(n-1) of the steering angle stored in the storage device 40c are set. Then, the steering angular velocity θ ′ is calculated and set according to the following equation (1).

Θ ′ = (θ _(n) −θ _(n−1) ) / ΔT (1) Next, the process proceeds to step S5, and the steering angle θ and the vehicle speed V _C read in step S1 are read. Further, the target rear wheel steering angle δ ^* _R is calculated and set based on the control map of FIG. 8 which will be described in detail later using the steering angular velocity θ ′ calculated in step S4.

Next, in step S6, the actual rear wheel steering angle δ, which is the detection signal of the main rear wheel steering angle sensor 38, is output.
Read _R1 . Next, the process proceeds to step S7, and the following (2)
The rear wheel steering angle deviation Δδ _R between the target rear wheel steering angle δ ^* _R and the actual rear wheel steering angle δ _R1 is calculated according to the formula.

Δδ _R = δ ^* _R −δ _R1 (2) Next, the process proceeds to step S8, and the rear wheel steering angle deviation Δδ _R
From the relational expression determined by the dynamic characteristics of the electric motor 22 considering the responsiveness of the system,
A reference control command value S _R0 is calculated and output to the main program.

Next, the operation of the arithmetic processing of FIG. 6 will be described along with the behavior of the vehicle. However, as described above, since this arithmetic processing is executed collectively by the target rear wheel steering angle calculation circuit A, the adder / subtractor B, and the reference control command value calculation circuit C of the hardware circuit of FIG. The steps corresponding to the circuit of (1) are collectively divided into sections, and the operation of each section will be sequentially described.

First, the sections of step S2, step S4 and step S5 of the arithmetic processing of FIG. 7 correspond to the target rear wheel steering angle calculation circuit A of the hardware circuit of FIG. The target rear wheel steering angle δ ^* _R calculated and set in this section is as described above, but the purpose to be set will be briefly described. The target rear wheel steering angle δ ^* _R is basically set so that a basic yaw rate determined by, for example, the steering angle θ and the vehicle speed V _C is achieved. However, as shown in Fig. 9, the steady-state vehicle characteristics are balanced from neutral steering to weak understeering characteristics in the low speed range and understeering in the medium and high speed ranges to achieve both stability and maneuverability at each vehicle speed. I will try to let you. Further, in a transitional period such as an early turning period, a turning ending period, or a lane change, it is intended to improve the responsiveness and the following capability of the vehicle with respect to the steering of the driver and to obtain a characteristic with less fluctuation.

Therefore, the rear wheel steering angle generation mode shown in FIG.
In the case of slow steering or constant steering like
The rear wheels are steered regardless of the vehicle speed except at extremely low speeds.
In-phase according to the steering angle θ (state of steering in the same direction as the front wheels)
Steering only (running due to understeer characteristics)
Control to increase row stability). On the other hand, during fast steering
Starts steering according to the steering angular velocity θ ', etc.
Immediately after that, steer to the opposite phase side, which increases the yaw rate.
Controllability and followability, and then speed and
By reversing the crab to the same phase side and making a steady steering angle,
Reduces wobbling and enhances stability. Together, like this
The vehicle speed V_CImmediately after starting the steering according to
Of the opposite phase component (A) and the stationary in-phase component (B) of
Change the found. More specifically, the faster
Reduce the weighting factor of the antiphase component (A) and
Manipulation in the medium speed range by increasing the weighting factor in (B)
Compatibility and stability in high speed range. Put this together,
Target rear wheel steering angle δ on the time axis^* _RIs shown in FIG.
It is a control map. However, it is actually used in arithmetic processing.
The steering angle θ is the main variable in the map or table.
Becomes, vehicle speed V_CAnd steering angular velocity θ'are used as parameters
Can be. Further, this embodiment does not employ it in detail.
However, the lateral acceleration is detected or estimated as described above.
The rate of increase in the steering angle of the rear wheels is changed according to the amount of lateral acceleration.
It can also be converted. This makes it possible to enter when turning at high speed.
Turn the vehicle as intended by the driver between
The performance can be obtained.

Next, steps S6 and S7 of the arithmetic processing of FIG. 7 correspond to the adder / subtractor B of the hardware circuit of FIG. 6, and according to the function of the adder / subtractor B, the target rear wheel steering angle δ ^* _R and the actual value are obtained. From the difference value with the rear wheel steering angle δ _R1 , the next reference control command value S
_The rear wheel steering angle deviation Δδ _R necessary for calculating _R0 is calculated.

Next, step S8 of the arithmetic processing of FIG. 7 corresponds to the reference control command value calculation circuit C of the hardware circuit of FIG. In this step S8, the rear wheel steering angle deviation Δδ _R is determined from a relational expression determined by the dynamic characteristics of the electric motor 22 in consideration of the responsiveness of the system as described above, for example, a predetermined value for preventing control hunting, That is, the dead zone threshold α
_{If the} reference control command value S _{R0 that} is sufficient to be within ₁ is output and there is no particularly large input, the actual rear wheel steering angle δ _R1 continues to follow the target rear wheel steering angle δ ^* _R in real time, and As described above, the rear wheel steering is continued so that both the steerability and the stability of the vehicle are compatible. Next, a calculation process for detecting an abnormality in the rear wheel steering system executed by the microcomputer 40 of the control unit 3 will be described with reference to the flowchart of FIG.

This arithmetic processing is performed by a predetermined sampling time ΔT (for example, 3.3 msec.) Equivalent to the arithmetic processing of FIG.
This is executed as a timer interrupt process for each time. Also in this arithmetic processing, the programs and maps stored in the ROM of the storage device 40c and various data stored in the RAM are always transmitted to the buffer and the like of the arithmetic processing device 40b. The calculation results calculated in are also stored in the storage device 40c at any time. The detection signal of the main rear-wheel steering angle sensor 38 used for the above-mentioned rear-wheel steering angle control is referred to as a main actual rear-wheel steering angle δ _R1, and the detection signal of the sub-rear-wheel steering angle sensor 39 is referred to as a sub-real. This is called the rear wheel steering angle δ _R2 .

In this calculation process, first, step S10 is performed.
Then, the main actual rear wheel steering angle δ _R1 which is the detection signal of the main rear wheel steering angle sensor 38 is read. Next, in step S11, the sub actual rear wheel steering angle δ _R2 , which is the detection signal of the sub rear wheel steering angle sensor 39, is read.

Next, in step S12, the main rear wheel steering angle deviation Δδ _R1 between the main actual rear wheel steering angle δ _R1 and the target rear wheel steering angle δ ^* _R is calculated according to the following equation (3). Δδ _R1 = δ _R1 −δ ^* _R (3) Next, the process proceeds to step S13, and the main sub-real rear wheel steering angle δ _R2 and the target rear wheel steering angle δ ^* _R are calculated according to the following equation (4). The rear wheel steering angle deviation Δδ _R2 is calculated.

Δδ _R2 = δ _R2 −δ ^* _R (4) Next, the process proceeds to step S14, and the absolute value | Δδ _R1 | of the main rear wheel steering angle deviation calculated in step S12 is preset. and predetermined determines whether a dead zone threshold alpha ₁ below, the absolute value of the main rear-wheel steering angle deviation | .DELTA..delta _R1 | is proceeds to step S15 if it is dead zone threshold alpha ₁ below, so If not, the process proceeds to step S16.

In step S15, step S13
The absolute value | Δδ _R2 | of the sub rear wheel steering angle deviation calculated in
It is determined whether or not the dead zone threshold value α _{1 is} less than or equal to the above-mentioned dead zone threshold value, and the absolute value of the sub rear wheel steering angle deviation | Δδ _R2 |
If it is ₁ or less, the process proceeds to step S17, and if not, the process proceeds to step S16. In step S16, the abnormality detection flag described in the calculation process of FIG. 6 is set to "1", and then the process returns to the main program.

In step S17, the abnormality detection flag is reset to "0" and then the main program is restored. Before describing the operation of the arithmetic processing of FIG. 11 for detecting the abnormality of the rear wheel steering system, two conventional abnormality detection methods and problems associated therewith will be described with reference to FIGS. 12 and 13.
This will be described with reference to FIG.

First, as one of the conventional abnormality detection methods,
A method of providing two rear wheel steering angle sensors at different positions to detect the actual rear wheel steering angle, that is, a main rear wheel steering angle sensor that detects the actual rear wheel steering angle from the rotation angle of the electric motor 22, and the steering shaft 20.
There is an anomaly detection method equipped with a sub-rear wheel steering angle sensor that detects the actual rear wheel steering angle from the displacement of the vehicle ("New model car description Nissan Skyline (R33 type)" issued in August 1993 C
-101 to C107).

First, the calculation process of FIG.
Target rear wheel steering angle δ as shown in (a) ^* _RIs set
After this, as shown in Fig. 12 (e),
Wheel steering angle δ_RAIs following in real time,
Actual rear wheel steering angle δ from main rear wheel steering angle sensor
_{R (MAIN)}Is a sub rear wheel steering angle sensor as shown in FIG.
Real rear wheel steering angle δ from_{R (SUB)}As shown in FIG. 12 (c)
, True rear wheel steering angle δ_RA, The actuator unit
The operating state of the output 1 (= electric motor 22) accurately or
Accurately detect. Meanwhile, the main rear wheel steering angle sensor, the sub
Actuator including rear wheel steering angle sensor and electric motor 22
In order to detect abnormalities in
Real rear wheel steering angle δ from the wheel steering angle sensor_{R (MAIN)}From after the sub
Real rear wheel steering angle δ from the wheel steering angle sensor_{R (SUB)}Real rear wheel
Steering angle deviation Δδ_{R (MAIN-SUB)}Is calculated from time to time and this real rear wheel
Steering angle deviation Δδ_{R (MAIN-SUB)}Is a preset dead band threshold
Range (-α₁~ + Α₁) To determine whether
(In the case of making a determination by calculation processing, the actual rear wheel steering angle deviation Δ
Absolute value of |_{R (MAIN-SUB)}| Is the dead zone threshold α₁Below
It may be determined whether or not the actual rear wheel steering angle deviation
Difference Δδ_{R (MAIN-SUB)}Is the dead zone threshold range (-α₁~ +
α₁), The main rear wheel rudder angle sensor
A sub-rear wheel steering angle sensor or an electric motor 22
Detects an abnormality in the actuator unit 1. Of course, the above
The actual rear wheel steering angle δ from the main rear wheel steering angle sensor
_{R (MAIN)}Also the actual rear wheel steering angle δ from the sub rear wheel steering angle sensor
_{R (SUB)}Also the true rear wheel steering angle δ_RAState, ie actu
The operating state of the power unit 1 (= electric motor 22) accurately
Or, in the state of detecting almost accurately, the actual rear wheel rudder of both
Angular deviation Δδ_{R (MA IN-SUB)}Is very small and, of course,
Sensitive zone threshold range (-α₀~ + Α₀)
No abnormality is detected.

However, it is assumed that an abnormality has occurred in the main rear wheel steering angle sensor at a certain time t ₀ . Here, a state in which a ground fault occurs due to, for example, a disconnection of a harness to the sensor and the actual rear wheel steering angle δ _{R (MAIN)} from the main rear wheel steering angle sensor is reduced to near “0” is simulated. are doing.
Then, the actual rear wheel steering angle deviation Δδ _{R (MAIN-SUB)} greatly falls below the negative dead zone threshold value −α _1, and the actual rear wheel steering angle deviation Δδ _{R (MAIN-SUB)} falls within the dead zone threshold range ( −α ₀ to + α
₀ ), the abnormality is detected immediately after that, and the abnormality detection flag F is set to "1", for example. Then, for example, in the calculation process of FIG. 7, the process proceeds from step S1 to step S3, and the reference control command value S _R0 is forcibly set to “0”, and therefore the current value I which is the drive signal is basically “0”. "It becomes. Here, as described above, since the rear-wheel steering angle of the actuator unit 1 does not change due to the external force, the true rear-wheel steering angle δ _RA is maintained at the steering angle at that time and the fail-safe operation is performed. It

As described above, in the rear wheel steering system (four-wheel steering system) in which the two rear wheel steering angle sensors are provided at different positions to detect the actual rear wheel steering angle, the sensors and actuators are used to some extent. However, since the dead zone threshold is set to a large value as described above, the detection of the abnormality may be delayed or a disadvantage in terms of layout and cost may occur.

On the other hand, other conventional anomaly detection methods are insensitive.
Main rear wheel rudder angle sensor
Both the sub-rear wheel steering angle sensor and
Real rear wheel steering angle is detected simultaneously from the rotation angle of the electric motor 22.
A method of That is, FIGS. 13B and 13C
At a certain time t₀The main rear wheel steering angle sensor and
And the sub-main rear wheel rudder angle sensor
The actual rear wheel steering angle δ_{R (MA IN)}, Real rear wheel steering angle δ_{R (SUB)}Together
When simulating a state where the value has dropped to near "0",
Inner rear wheel steering angle sensor from rear wheel steering angle δ_{R (MAIN)}From
Actual rear wheel steering angle δ from the sub rear wheel steering angle sensor_{R (SUB)}Reduced
Real rear wheel steering angle deviation Δδ_{R (MAIN-SUB)}Calculate this real rear wheel
Steering angle deviation Δδ_{R (MAIN-SUB)}The dead zone threshold range set in advance
Surrounding (-α ₁~ + Α₁) To determine whether or not
Also, as shown in FIG. 13D, the actual rear wheel steering angle deviation Δδ
_{R (MAIN-SUB)}Is the dead zone threshold range (-α₀~ + Α₀)
Since the main rear wheel steering angle sensor, sub rear wheel steering angle
Unable to detect sensor abnormality.

Thus, two rear wheel steering angle sensors are provided so as to detect the actual rear wheel steering angle of the actuator 1 at the same position, and the actual rear wheel steering angle from the main rear wheel steering angle sensor is changed to the sub rear wheel. Even if the actual rear wheel steering angle deviation calculated by subtracting the actual rear wheel steering angle from the steering angle sensor is calculated and it is judged whether or not the actual rear wheel steering angle deviation falls within a preset dead zone threshold range, If both the rear-wheel steering angle sensor and the sub-rear-wheel steering angle sensor are abnormal at the same time, it may not be possible to reliably detect the abnormality of these sensors.

Therefore, in the present embodiment, the electric motor 22
Even if the main rear-wheel steering angle sensor 38 and the sub-rear-wheel steering angle sensor 39 are coaxially arranged and used as sensors for detecting the rotation angle of the above, in order to detect abnormality of the sensor and the actuator surely and promptly, A calculation process for detecting abnormality in the rear wheel steering system shown in FIG. 11 is performed. An example of the operation of this arithmetic processing will be described with reference to FIG.

Also here, as in the case of FIG.
It is assumed that the target rear wheel steering angle δ ^* _R as shown in FIG. 14 (a) has been set by the calculation processing of, and the true rear wheel steering angle follows this in real time. The actual rear-wheel steering angle δ _R1 from the rear-wheel steering angle sensor 38 is determined by the actuator unit 1 as shown in FIG.
The operating state of (= electric motor 22) is detected accurately or almost accurately. In addition, the normal sub rear wheel steering angle sensor 39
The actual rear wheel steering angle δ _R2 also accurately or almost accurately detects the operating state of the actuator unit 1 (= electric motor 22) as shown in FIG. 14 (c).

In the calculation process of FIG. 11, the main actual rear-wheel steering angle δ _R1 which is the detection signal of the main rear-wheel steering angle sensor 38 is read in step S10, and the sub-rear-wheel steering angle sensor 39 is read in step S11. The sub real rear wheel steering angle δ _R2 , which is a detection signal, is read, and the main rear wheel steering angle deviation Δδ between the main real rear wheel steering angle δ _R1 and the target rear wheel steering angle δ ^* _R is read in step S12.
_R1 is calculated, and in step S13, a main rear wheel steering angle deviation Δδ _R2 between the sub actual rear wheel steering angle δ _R2 and the target rear wheel steering angle δ ^* _R is calculated. Main rear wheel steering angle deviation Δδ _R1
Is very small and, as shown in FIG. 14D, is within the dead zone threshold range (-α ₁ to + α ₁ ), the process proceeds from step S14 to step S15. Further, the sub rear wheel steering angle deviation Δδ _R2 calculated in step S13 is also very small, and as shown in FIG. 14 (e), the dead zone threshold range (−α
_{Since it is within 1} to + α ₁ ), the process proceeds from step S15 to step S17, and the abnormality detection flag F is continuously reset to “0”. Here, the dead zone threshold value α ₁ has the main rear wheel rudder angle sensor 38 and the sub rear wheel rudder angle sensor 39 arranged coaxially as a sensor for detecting the rotation angle of the electric motor 22, so that a mounting error should be considered. Without FIG.
It is set to a value smaller than the conventional dead zone threshold value α ₀ shown in.

By the way, in FIGS. 14 (b) and 14 (c)
Time t₀As shown by the solid line below, the main rear wheel rudder
There is an abnormality in both the angle sensor 38 and the sub rear wheel steering angle sensor 39.
Assume that it has occurred. Here, for example,
Main rear wheel rudder angle sensor 38 and sub rear wheel rudder angle sensor
The sensor levers 38a and 39b of the sensor 39 are fixed
The main actual rear wheel steering angle δ
_R1, Sub actual rear wheel steering angle δ _R2Both decreased to near “0”
Simulates the situation.

In this case, the target rear wheel steering angle δ ^* _R is
Since it is larger than the main actual rear wheel steering angle δ _{R1 that} has decreased to near “0”, the main rear wheel steering angle deviation Δδ _R1 greatly increases beyond the negative dead zone threshold α ₁ and therefore its absolute value | Δδ
_{Since R1} | becomes equal to or larger than the dead zone threshold value α ₁ , in the arithmetic processing of FIG. 11, step S is performed immediately after the sensor abnormality occurrence time t _0.
The routine proceeds from step 14 to step S16, where the abnormality detection flag F is set to "1".

Then, in the above-mentioned arithmetic processing of FIG. 7, the process shifts from step S1 to step S3, and the reference control command value S _R0 is forcibly set to "0". As a result, the current value I, which is the drive signal, also basically becomes "0". here,
As described above, since the rear-wheel steering angle of the actuator unit 1 does not change depending on the external force, the true rear-wheel steering angle is thereafter maintained at the steering angle at that time and the fail-safe operation is performed.

Further, the main actual rear wheel steering angle δ _R1 is shown in FIG.
In the state shown by the alternate long and short dash line after time T ₀ in (b), the sub actual rear wheel steering angle δ _R2 becomes the time T in FIG. 14 (c).
_The state shown by the solid line after ₀ becomes the sub rear wheel steering angle sensor 3
When simulating a state where an abnormality such as a sensor stick occurs only in 9, in this case, the target rear wheel steering angle δ ^* _R is larger than the sub actual rear wheel steering angle δ _R2 which is reduced to near “0”. Therefore, the sub rear wheel steering angle deviation Δδ _R2 greatly increases beyond the negative dead zone threshold α ₁ , and therefore its absolute value | Δδ
_{Since R2} | becomes the dead zone threshold value α ₁ or more, in the arithmetic processing of FIG. 11, step S is performed immediately after the sensor abnormality occurrence time t _0.
The process moves from 15 to step S16, and the abnormality detection flag F is set to "1". As a result, similar to the above-described operation, the true rear wheel steering angle is held at the steering angle at that time, and the fail safe is performed.

Further, the main actual rear wheel steering angle δ_R1Is shown in FIG.
Time T in (b)₀It becomes the state shown by the solid line after that,
Sub actual rear wheel steering angle δ_R2Is time T in FIG.₀Less than
As shown by the rear broken line, the main rear wheel steering angle sensor 3
If only 9 has an abnormality such as a sensor stick,
When emulated, the absolute value of the main rear wheel steering angle deviation | Δδ
_R1| Is the dead zone threshold α₁For the above, the calculation of FIG.
In the processing, the sensor abnormality occurrence time t₀Immediately after step S
14 to step S16, and the abnormality detection flag F
Set to "1", the true rear wheel, as in the previous operation
The rudder angle is maintained at the rudder angle at that time, and the fail safe is realized.
Will be applied.

By the way, the function of this abnormality detection is that, for example, the harness to the main rear wheel rudder angle sensor 38 and the sub rear wheel rudder angle sensor 39 is broken, so that a ground fault occurs and the actual rear wheel rudder angle δ _R1. , Δ _R2 is reduced to around “0”, the actual rear wheel steering angles δ _R1 and δ _R2 are smaller than the target rear wheel steering angle δ ^* _R , and the same is true.

From the above, the electric motor 22 of the actuator unit 1 shown in FIGS. 1 and 2 corresponds to the actuator of the present invention, and the same applies to the rear wheel steering angle sensor 38 of FIGS. 1 and 2 and 5. 39 and steps S10 and S11 of the arithmetic processing of FIG. 11 correspond to the detecting means, the control unit 3 including the arithmetic processing of FIGS. 7 and 11 corresponds to the feedback control means, and steps S2 to S2 of the arithmetic processing of FIG. Step S5 corresponds to the target rudder angle setting means,
The step S12 of the arithmetic processing of FIG. 11 corresponds to the first deviation calculating means, the step S13 of the arithmetic processing of FIG. 11 corresponds to the second deviation calculating means, and the step S1 of the arithmetic processing of FIG.
4 to step S17 correspond to the abnormality detecting means.

In the above embodiment, the main rear wheel rudder angle sensor 38 and the sub rear wheel rudder angle sensor 39 are connected to the electric motor 2.
By detecting the rotation angle of 2, the actual rear wheel steering angles δ _R1 , δ _R2
However, the gist of the present invention is not limited to this. For example, the main rear wheel steering angle sensor 38 and the sub rear wheel steering angle are detected. Even if both of the sensors 39 are arranged at positions where the amount of displacement of the steering shaft 20 is detected, the same operational effect can be obtained.

The positional relationship between the main rear-wheel steering angle sensor 38 and the sub-rear-wheel steering angle sensor 39 arranged coaxially with the sensor shaft 34 is not limited to the above embodiment, and the main rear wheel The structures of the steering angle sensor 38 and the sub rear wheel steering angle sensor 39 are not limited to those in the above embodiment.

Further, in the above embodiment, the operating state of the actuator is directly obtained as the steering angle in order to perform feedback control of the steering angle of the auxiliary steering wheel to the target value, but the operating state of the actuator and the steering angle are not necessarily the same. The rotation angle of the electric motor may be detected or estimated as the operating state of the actuator.

Further, the actuator of the four-wheel steering system is not limited to the electric motor as described above, but may be one which controls the working fluid pressure to the left and right fluid chambers of the fluid pressure cylinder by the pressure control valve. Then, in this case, the operating state of the fluid pressure cylinder, which is the actuator, may be estimated from the drive signal to the pressure control valve that controls the fluid pressure.

Further, in the above embodiment, the case where the microcomputer is applied as the control unit 3 has been described, but instead of this, electronic circuits such as a counter and a comparator may be combined and configured.

[Brief description of drawings]

FIG. 1 shows an example of a vehicle to which a four-wheel steering system according to the present invention is applied, in which (a) is a schematic diagram of the entire vehicle configuration, and (b).
FIG. 3 is a schematic configuration diagram of an actuator.

FIG. 2 is a detailed explanatory view of the actuator of FIG.

3 is a plan view showing a plate body that comes into contact with sensor levers (detectors) of two rear wheel steering angle sensors built in the actuator of FIG. 2. FIG.

FIG. 4 is an explanatory diagram of an irreversible characteristic of the actuator of FIG.

5 is a diagram illustrating the configuration of the control unit shown in FIG.

FIG. 6 is an explanatory diagram in which the four-wheel steering system of FIG. 1 is replaced with a hard circuit.

7 is a flowchart showing an embodiment of arithmetic processing of the four-wheel steering system of the present invention, which is executed by the control unit of FIG.

8 is a control map for calculating and setting a target rear wheel steering angle by the calculation process of FIG. 7.

9 is an explanatory diagram of a steering characteristic of the vehicle according to a target rear wheel steering angle set by the control map of FIG.

10 is an explanatory diagram of a target rear wheel steering angle set by the control map of FIG.

FIG. 11 is a flowchart showing an embodiment of arithmetic processing for detecting an abnormality of two detection means or devices of the present invention.

FIG. 12 is a time chart of rear wheel steering when the arithmetic processing of FIG. 7 is performed in a state where two detecting means are arranged at different positions of the actuator.

FIG. 13 is a diagram showing a calculation process in which two detecting means are arranged at the same position of an actuator, and an abnormality of the detecting means or the device is detected based on a deviation between detected values of steering angles of the detecting means. It is a time chart of rear wheel steering.

14 is a time chart of rear wheel steering based on the arithmetic processing of FIG. 11 of the present invention.

[Explanation of symbols]

1 Actuator Unit 2 Rear Wheel Steering Device 3 Control Unit 10FL to 10RR Front Left Wheel to Rear Right Wheel 20 Steering Axis 22 Electric Motor 38 Main Rear Wheel Steering Angle Sensor 38a Sensor Lever (Detector) 39 Sub Rear Wheel Steering Angle Sensor 39a Sensor Lever (Detector) 40 Microcomputer δ _R1 Real rear wheel steering angle (Detection signal of main rear wheel steering angle sensor) δ _R2 Real rear wheel steering angle (Detection signal of sub rear wheel steering angle sensor) δ ^* _R Target rear wheel rudder Angle Δδ _R1 Main rear wheel steering angle deviation Δδ _R2 Sub rear wheel steering angle deviation α ₁ Dead zone threshold

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B62D 117: 00 137: 00

Claims (2)

[Claims] 1. An operating state of an actuator that operates in response to a drive signal is detected by at least two detecting means at the same operating position of the actuator, and an actual steering angle is set to a target steering angle value of a set auxiliary steering wheel. In feedback controlling the actuator according to the operating state of the actuator so that the angular value follows, the detected operating state of the actuator detected by one of the two detecting means and the target steering angle. The four wheels are characterized by detecting an abnormality of the feedback control system by comparing the detected operating state of the actuator detected by the other detecting means with the target steering angle value while comparing the value with the target steering angle value. Steering device. 2. An actuator for controlling a steering angle of an auxiliary steering wheel according to an input drive signal, a detecting means for detecting an operating state of the actuator, and at least a steering state of a main steering wheel and a motion state of a vehicle. Target rudder angle setting means for setting a target rudder angle of the auxiliary steering wheel, and detecting the actual rudder angle of the auxiliary steering wheel from the detection operating state of the actuator detected by the detecting means, and the target of the auxiliary steering wheel. In a four-wheel steering system including a feedback control means for outputting a drive signal to the actuator so that the magnitude of the steering angle deviation between the steering angle value and the actual steering angle detection value of the auxiliary steering wheel becomes a predetermined value, The detecting means is at least two detecting means for detecting the operating state of the actuator at the same operating position of the actuator, and the feedback control is provided. Means include first deviation calculating means for calculating a first deviation between the detected operating state of the actuator detected by one of the two detecting means and the target steering angle value, and the two detecting means. Second deviation calculation means for calculating a second deviation between the detected operating state of the actuator detected by the other detection means of the means and the target steering angle value, the magnitude of the first deviation and the first deviation. An abnormality detection unit that detects that the feedback control system including the detection unit has an abnormality from the actuator when it is determined that one of the two deviations is greater than or equal to a predetermined value. A four-wheel steering system characterized by.