JP3003742B2 - Electric motor driven four-wheel steering system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric motor-driven four-wheel steering system for controlling a rear wheel steering angle by an electric motor, and more particularly to an abnormality detection technique for a rear wheel steering angle sensor.

[0002]

2. Description of the Related Art Conventionally, as a technique for detecting an abnormality of a steering force sensor used for control as feedback information in a power steering control system using an electric motor, for example, a technique disclosed in Japanese Patent Application Laid-Open No. 63-82875 is disclosed. Are known.

[0003] The above-mentioned conventional source uses two steering force sensors and has means for calculating a rate of change for each sensor. When a difference occurs in the rate of change for each sensor, the minimum rate of change is indicated. Abnormality detection technology that makes the sensor abnormal is shown, and when the sensor output from the two steering force sensors exceeds a predetermined range set in advance, abnormality detection that makes the sensor that has exceeded the abnormality occur. The technology is shown.

[0004]

However, in the former prior art described above, since the detection is performed by looking only at the rate of change of the sensor signals from the two steering force sensors,
Although the sensor signal changes in exactly the same way, there is a large offset between the sensor signal output from one side and the sensor signal output from the other, and if one sensor is originally abnormal, only the rate of change is monitored. Is determined to be normal,
Performs false detection of sensor abnormality.

In the latter prior art, since the detection is made based on whether or not a predetermined range is set in advance, the predetermined range has to be set to a wide output range which can be used as a sensor output. Even if the signal output direction or signal output width is abnormal, the sensor cannot be detected as long as the signal is output within the specified range, and in fact, it can only detect the sensor abnormality due to the disconnection or short circuit of the signal line. Absent.

Further, when two sensors are provided to detect a sensor abnormality, a difference between the absolute values of the outputs of the two sensor signals is obtained as a general method, and when the difference is larger than an abnormality determination threshold value, the sensor abnormality is detected. There is a way to do it.

However, in this case, since the output direction of the sensor signal is not taken into consideration, when two sensor signals are output in opposite directions, the sensor abnormality is detected with a considerable delay from the occurrence of the sensor abnormality. become.

In other words, the sensor determination threshold value must be set to a relatively large value in consideration of sensor variations and aging, and one sensor must be set to the abnormality determination threshold value in the plus direction. When a corresponding sensor signal is output and a sensor signal corresponding to the abnormality determination threshold value is output in the negative direction from the other sensor, the absolute value comparison of the sensor signals is zero and it is determined that the sensor is normal. When the two sensor signals are separated from each other by a signal corresponding to the abnormality determination threshold value, the sensor abnormality is finally detected after a considerable time delay from the occurrence of the sensor abnormality.

As a result, the rear wheel steering angle sensor signal is directly used as feedback information for rear wheel steering angle control, and an electric motor-driven four-wheel steering device having a large influence on the vehicle behavior due to the abnormality of the rear wheel steering angle sensor. In this case, if there is a detection delay from the occurrence of the abnormality, the rear-wheel steering angle position at that time is fixed by the fail-safe process after the abnormality is detected, which is not preferable for the subsequent vehicle behavior.

That is, in the electric motor-driven four-wheel steering system, the abnormality detection of the rear wheel steering angle sensor is required at an early stage without erroneous detection. However, the conventional abnormality detection method cannot meet this requirement.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide a four-wheel steering apparatus driven by an electric motor in which a rear wheel steering angle is controlled by an electric motor. That is, an abnormality of a rear wheel steering angle sensor used for control is detected early without erroneous detection including a case where the output is output to the steering wheel.

[0012]

In order to solve the above-mentioned problems, an electric motor-driven four-wheel steering system according to the present invention monitors the direction of increase or decrease in the sensor signal from a sub-rear-wheel steering angle sensor ,
The method of determining the difference between the two sensor signals is defined by the direction of change,
A rear wheel steering angle sensor monitoring means for detecting an abnormality of the main rear wheel steering angle sensor by comparing the signal difference with an abnormality determination threshold value is provided.

That is, as shown in the claim correspondence diagram of FIG. 1, an electric motor a for controlling a rear wheel steering angle by driving by applying a motor control current, and an interposition between the electric motor a and the rear wheel b. A rear wheel steering mechanism c, a main rear wheel steering angle sensor d provided at a movable position of the rear wheel steering mechanism c, and using the sensor value as positioning feedback information for rear wheel steering angle control; A sub-rear wheel steering angle sensor e which is provided in a rear wheel steering mechanism c at a position different from the rear wheel steering angle sensor d and uses the sensor value for monitoring abnormality of the main rear wheel steering angle sensor d; and the sub sensor signal change detection means f for detecting a change direction and amount of the sensor signal from the rear wheel steering angle sensor e, the rear wheels
Considering variations and changes over time of the steering angle sensors d and e,
Anomaly judgment threshold with small value set as anomaly judgment threshold
When the sensor signal from the value setting means g and the sub rear wheel steering angle sensor e is monotonically increasing , the rear wheel steering angle sub sensor value
The value obtained by subtracting the rear wheel steering angle main sensor value from
If it is equal to or greater than the threshold value, the main rear wheel steering angle sensor d is abnormal.
Is detected, and the sensor signal from the sub rear wheel steering angle sensor is
When changing monotonically, the value of the rear wheel steering angle main sensor
The value obtained by subtracting the rear wheel steering angle sub-sensor value is an abnormal judgment threshold.
If the value is greater than or equal to the value, the main rear wheel steering angle sensor d is abnormal.
Rear wheel steering angle sensor monitoring means h for detecting

[0014]

When the abnormality of the main rear wheel steering angle sensor d is detected, the sensor value from the sub rear wheel steering angle sensor e is used by the sub sensor signal change detection means f to monitor the sensor value for abnormality of the main rear wheel steering angle sensor d. The direction and amount of change of the signal are detected, and the abnormality determination threshold value setting means g controls both rear wheel steering.
Minimum considering the variations of the angle sensors d and e and changes over time
The value is set as the abnormality determination threshold. Then, in the rear wheel steering angle sensor monitoring means h, the sub rear wheel steering angle sensor e
When the sensor signal from the motor is monotonically increasing , the rear wheel steering angle
Subtract the rear wheel steering angle main sensor value from the sub sensor value
When the value is equal to or greater than the abnormality determination threshold, the main rear wheel steering angle
Sensor d is detected as abnormal, and the sub rear wheel steering angle sensor
When these sensor signals are monotonically decreasing, the rear wheel steering angle
Value obtained by subtracting the rear wheel steering angle sub-sensor value from the in-sensor value
Is greater than or equal to the abnormality determination threshold, the main rear wheel steering angle
It is detected that the d is abnormal .

Therefore, the criteria for determining the abnormality of the rear wheel steering angle sensor include the direction of change of the sensor signal from the sub-rear wheel steering angle sensor e, and the method of determining the difference by determining the direction of change defines the sensor signal. Is output in the reverse direction.
Error detection due to sensor variation or aging
Is used for control in the shortest time after a sensor
It is possible to detect an abnormality of the wheel steering angle sensor after that.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

First, the configuration will be described.

FIG. 2 is an overall system diagram showing a vehicle to which the electric motor-driven four-wheel steering device according to the embodiment of the present invention is applied, and FIG. 3 is an electric rear wheel steering of the electric motor-driven four-wheel steering device according to the embodiment. FIG. 4 shows the mechanism, and FIG.
FIG. 2 is an electronic control system diagram centered on an S control unit.

In FIG. 2, 1 and 2 are front wheels, 3 and 4 are rear wheels (corresponding to rear wheels b), 5 is a mechanical front wheel steering mechanism, and 6 is an electric rear wheel steering mechanism (rear wheel steering mechanism c). Equivalent).

The mechanical front wheel steering mechanism 5 increases a steering force input from a steering wheel 7 steered by a driver via a steering shaft 8 by a power steering (not shown), and increases the increased steering force to a rack shaft 9. Through the side rods 10 and 11 and the knuckle arms 12 and 13 to provide a steering angle to the front wheels 1 and 2.

The electric rear wheel steering mechanism 6 includes four
The rotational force of the high cas motor 15 (corresponding to the electric motor a) controlled by the motor output from the WS control unit 14 is transmitted to the worm 16 and the worm wheel 17.
And the rotational motion of the worm wheel 17 is converted into linear motion of the rack shaft 19 by meshing the gear portion of the pinion shaft 18 with the gear portion of the rack shaft 19, and the side rods 20, 21 and the knuckle arm are transferred from the rack shaft 19. Via the rear wheels 3,
4 to provide a steering angle.

The 4WS control unit 14 includes:
As shown in FIG. 4, the power supply circuit 14a and the sensor power supply circuit 1
4b, input interface 14c, CPU1, CPU
2, monitoring circuit 14d, D / A conversions 14e, 14f, 14
g, 14h, 14i, a CPU output monitoring circuit 14j, a relay output driver 14k, a motor output driver 14m, and a power steering solenoid output driver 14n.

The power supply circuit 14a has a battery power supply directly from the battery 24 and an ignition switch 25.
The ignition power from is input.

The input interface 14c includes a rear steering angle main sensor 26 (corresponding to a main rear wheel steering angle sensor d) and a rear steering angle sub sensor 2 using a potentiometer.
7 (corresponding to the sub-rear wheel steering angle sensor e), the sensor signal from the steering sensor 28, the sensor signal from the vehicle speed sensor 29, and the stop signal from the stop lamp switch 30, the brake switch 31, and the inhibit switch 32. A switch signal is input. Here, the rear steering angle main sensor 26 is a sensor for detecting the rotation amount of the pinion shaft 18, and its sensor value is used for control as positioning feedback information for rear wheel steering angle control. Further, the rear steering angle sub-sensor 27 is a sensor for detecting a stroke amount of the rack shaft 19,
It is used for monitoring abnormality of the rear steering angle main sensor 26.

The relay output driver 14k receives the monitoring output from the monitoring circuit 14d and the warning valve output from the warning valve 33, and
Sends a high cas relay output to

The motor output driver 14m is driven by a motor power supply via a high cas relay 34,
A rear wheel steering angle command is input from PU1 via D / A converters 14g and 14h, and a motor output is sent to the high cas motor 15.

The power steering solenoid output driver 14
n inputs a power steering command from the CPU 1 via the D / A converter 14i, and sends a power steering solenoid output to the power steering solenoid 35.

Next, the operation will be described.

[Motor control current monitoring operation] FIG.
Each step will be described below with reference to a flowchart showing the flow of the rear steering angle sensor abnormality monitoring operation performed by the monitoring circuit 14d of the control unit 14 (corresponding to the rear wheel steering angle sensor monitoring means h).

In step 50, the rear steering angle main sensor value Vmain and the rear steering angle sub sensor value Vsub are read from the rear steering angle main sensor 26 and the rear steering angle subsensor 27.

In step 51, the rear steering angle main sensor signal change amount Vmain_SUB and the rear steering angle sub sensor signal change amount Vsub_SUB are calculated by the following equations.

Vmain_SUB = Vmain-Vmain5 Vsub_SUB = Vsub-Vsub5 Vmain5; rear steering angle main sensor value before 5 msec Vsub5; rear steering angle sub-sensor value before 5 msec In step 52, the rear steering angle sub-sensor signal is based on the following judgment formula. It is determined whether the direction has changed on the + side or the-side.

Vsub_SUB × Vsub_SUB5> 0 Vsub_SUB5; the change amount of the rear steering angle sub-sensor signal 5 msec earlier In step 53, when it is determined in step 52 that the rear steering angle sub-sensor signal has changed, the rear steering angle main sensor count value CNT_Vmain and the rear steering angle sub-sensor count value CNT_Vsub are calculated by the following equations.

CNT_Vmain + Vmain_SUB → CNT_Vmain CNT_Vsub + Vsub_SUB → CNT_Vsub In step 54, the rear steering angle sub sensor signal change amount Vsu
It is determined whether or not b_SUB is positive (corresponding to the sub sensor signal change detection means f).

In step 55, Vsub_ in step 54
When it is determined that SUB> 0, it is determined whether the rear steering angle main sensor count value CNT_Vmain is 0.1 V or less (corresponding to the main sensor signal change detection means g).

In step 56, CNT_V in step 55
When it is determined that main ≦ 0.1V, it is determined whether the rear steering angle sub-sensor count value CNT_Vsub is 0.4 V or more.

At step 57, Vsub_ at step 54
When it is determined that SUB ≦ 0, it is determined whether or not the rear steering angle main sensor count value CNT_Vmain is equal to or more than −0.1 V (corresponding to the main sensor signal change detection means g).

In step 58, CNT_V in step 57
When it is determined that main ≧ −0.1V, it is determined whether or not the rear steering angle sub sensor count value CNT_Vsub is −0.4V or less.

In step 59, when the condition of step 56 or step 58 is satisfied, a fail flag is set.
1 is added to FAIL_FLG.

In step 60, it is determined whether or not the fail flag FAIL_FLG has become 2 or more by the addition processing in step 59.

In step 61, when the condition of step 60 is satisfied, it is determined that the rear steering angle sensor is abnormal. Based on this abnormality determination, a fail-safe process of prohibiting rear wheel steering angle control and turning on the warning valve 33 is performed.

In step 62, when the condition of step 55 or step 57 is not satisfied, the rear steering angle main sensor count value CNT_Vmain and the rear steering angle sub sensor count value CNT_Vsub are reset to zero.

In step 63, when the condition of step 56 or step 58 is not satisfied, the failure flag FA
IL_FLG is reset to 0.

In step 64, when the condition of step 60 is not satisfied or when the process of step 63 is performed, it is determined that the rear steering angle sensors 26 and 27 are in a normal state. Based on this determination, normal rear wheel steering angle control is performed.

[When the rear steering angle sub-sensor signal changes in the positive direction on the + side] When the rear steering angle sub-sensor signal changes in the positive direction on the + side, the detection of the rear steering angle sensor abnormality is In the flowchart of FIG. 5, steps 50 to 56 → step 59 → step 60 → step 6
It is determined by the flow of 1.

That is, when the condition that the rear steering angle sub-sensor signal in step 52 is changing and the condition that the rear steering angle sub-sensor signal change amount Vsub_SUB in step 54 is positive are satisfied, the CNT_Vmain in step 55 is satisfied. ≤
0.1 V and CNT_Vsub ≧ 0.4 in step 56
When satisfying V is repeated two or more times, it is determined that the rear steering angle sensor is abnormal.

That is, as shown in FIG. 6, even though the rear steering angle main sensor count value CNT_Vmain is in the region of 0.1 V or less, the rear steering angle sub sensor count value CN
When T_Vsub is in the region of 0.4 V or more and its value is increasing in the positive direction, it is determined that the steering angle sensor is abnormal. By this judgment, the rear steering angle main sensor count value
When CNT_Vmain is fixed in a region of 0.1 V or less including a minus region, or when the main sensor signal is changing in the opposite direction to the sub-sensor signal, the rear steering angle main sensor 26 Abnormality can be determined.

Here, in determining the abnormality, if the difference between the rear steering angle main sensor count value CNT_Vmain and the rear steering angle sub sensor count value CNT_Vsub is not more than 0.3 V, it is not determined that there is an abnormality. The threshold value is determined by considering the variation of the rear steering angle sensor and the change with time, and erroneously detecting the abnormality of the rear steering angle sensor if the minimum allowable width of 0.3 V is not provided.

In step 60, the failure flag FAIL
The judgment whether _FLG has been raised more than once is due to the sensor malfunction even if one sensor output becomes momentarily too large or too small to satisfy the abnormality judgment condition even though the sensor is normal. This is to prevent erroneous detection.

[When the rear steering angle sub-sensor signal changes in the negative direction on the negative side] When the rear steering angle sub-sensor signal changes in the negative direction on the negative side, the detection of the rear steering angle sensor abnormality is In the flowchart of FIG. 5, steps 50 to 54 → step 57 → step 58 → step 5
It is determined by the flow of 9 → step 60 → step 61.

That is, when the condition that the rear steering angle sub-sensor signal in step 52 is changed and the condition that the rear steering angle sub-sensor signal change amount Vsub_SUB in step 54 is negative are satisfied, CNT_Vmain in step 57 is satisfied. ≧
−0.1 V and CNT_Vsub ≦ − in step 58
When satisfying 0.4 V is repeated twice or more, it is determined that the rear steering angle sensor is abnormal.

That is, as shown in FIG. 7, even though the rear steering angle main sensor count value CNT_Vmain is in the region of -0.1 V or more, the rear steering angle sub sensor count value
When CNT_Vsub is in the region of -0.4 V or less and its value is increasing in the negative direction, it is determined that the steering angle sensor is abnormal. According to this determination, the rear steering angle main sensor count value CNT_Vmain is in a fixed state in a region of −0.1 V or more including a plus region, or in a state where the main sensor signal is changing in the opposite direction to the sub sensor signal. In some cases, the abnormality of the rear steering angle main sensor 26 can be determined.

Next, the effects will be described.

(1) In an electric motor-driven four-wheel steering system in which the rear wheel steering angle is controlled by the high-cass motor 15,
When the sensor signal from the rear steering angle sub sensor 27 is monotonically increasing or decreasing, the difference between the main sensor signal and the sub sensor signal is determined for each direction based on the determination of the sub sensor signal change direction, and the rear steering angle main sensor count is determined. Value CNT_Vmain and rear steering angle sub sensor count value CNT_V
When the difference from sub is determined to be 0.3 V or more, which is the abnormality determination threshold value, the rear wheel steering angle sensor detects that the rear wheel steering angle sensor is abnormal. It is possible to detect an abnormality of the rear wheel steering angle sensor used for control at an early stage without erroneous detection including the case where the output is performed in the direction.

(2) Since the threshold value for determining abnormality is set to 0.3 V, which is the minimum value in consideration of the variation of the rear steering angle sensor and the change with time, the detection from the occurrence of the sensor abnormality can be performed without erroneous detection due to the change or change with time. An abnormality of the rear steering angle sensor can be detected at the shortest time.

(3) Since the fail-safe processing is performed by judging the sensor abnormality according to whether the fail flag FAIL_FLG has been set twice or more, that is, whether the condition for judging the sensor abnormality has been satisfied twice, it is possible to determine whether the sensor is normal. Regardless, even if one of the sensor outputs momentarily becomes too large or too small to satisfy the abnormality determination condition, erroneous detection of a sensor abnormality can be prevented.

Although the embodiments have been described with reference to the drawings, the specific configuration is not limited to the embodiments, and any changes or additions without departing from the gist of the present invention are included in the present invention. It is.

For example, the abnormality determination threshold value (0.3 V) is not limited to the value of the embodiment, but can be set as appropriate depending on the degree of variation of the sensor or how the sensor changes over time.

The sensor abnormality may be detected immediately after the failure flag FAIL_FLG has risen once, or the sensor abnormality may be detected on condition that the failure flag FAIL_FLG rises three times or more.

[0060]

As described above, according to the present invention, in a four-wheel steering apparatus driven by an electric motor in which a rear wheel steering angle is controlled by an electric motor , variations in both rear wheel steering angle sensors are provided.
The minimum value that takes into account the change in
When the abnormality determination threshold value setting means and the sensor signal from the sub rear wheel steering angle sensor are monotonically increasing ,
Subtract the rear wheel steering angle main sensor value from the rear wheel steering angle sub sensor value.
After the main when the subtracted value is equal to or larger than the abnormality judgment threshold
The wheel steering angle sensor detects that it is abnormal, and
When the sensor signal from the
Subtract the rear wheel steering angle sub sensor value from the angle main sensor value
The main rear wheel steering angle when the
Since the rear wheel steering angle sensor monitoring means that detects that the sensor is abnormal has been provided, erroneous detection due to sensor variation, aging, etc., even when the sensor signal is output in the reverse direction
Unexpectedly, an effect is obtained that an abnormality of the rear wheel steering angle sensor used for control can be detected at the shortest time from the occurrence of a sensor abnormality .

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to a claim showing an electric motor-driven four-wheel steering device of the present invention.

FIG. 2 is an overall system diagram showing a vehicle to which the electric motor-driven four-wheel steering device according to the embodiment of the present invention is applied.

FIG. 3 is a diagram showing an electric rear wheel steering mechanism of the electric motor driven four-wheel steering device of the embodiment.

FIG. 4 is an electronic control system diagram centering on a 4WS control unit of the embodiment apparatus.

FIG. 5 is a flowchart showing a flow of a motor control current monitoring operation performed by a monitoring circuit of a 4WS control unit of the embodiment device.

FIG. 6 is a sensor count value characteristic diagram showing an abnormality determination state when the rear steering angle sub-sensor signal changes in the positive direction on the + side.

FIG. 7 is a sensor count value characteristic diagram showing an abnormality determination state when the rear steering angle sub-sensor signal changes in the negative direction on the negative side.

[Explanation of symbols]

a electric motor b rear wheel c rear wheel steering device d main rear wheel steering angle sensor e sub rear wheel steering angle sensor f sub sensor signal change detecting means g abnormality determination threshold setting means h rear wheel steering angle sensor monitoring means

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ identification code FI B62D 113: 00 (58) Investigated field (Int.Cl. ⁷ , DB name) B62D 6/00 B62D 7/14 B62D 5/04

Claims (1)

(57) [Claims] An electric motor for controlling a rear wheel steering angle by driving by applying a motor control current; a rear wheel steering mechanism interposed between the electric motor and rear wheels; A main rear wheel steering angle sensor which is provided at a movable position and uses the sensor value as positioning feedback information for rear wheel steering angle control; and a rear wheel steering mechanism provided at a position different from the main rear wheel steering angle sensor. A sub-rear wheel steering angle sensor that uses the sensor value for abnormality monitoring of a main rear wheel steering angle sensor; and a sub-sensor signal change detection that detects a direction and an amount of a sensor signal from the sub-rear wheel steering angle sensor. Means and the variation of the two rear wheel steering angle sensors and the change with time.
Is set as the abnormality judgment threshold value.
When the threshold value setting means and the sensor signal from the sub rear wheel steering angle sensor are monotonically increasing , the rear wheel steering angle main sensor is calculated from the rear wheel steering angle sub sensor value.
If the value obtained by subtracting the sensor value is equal to or
When the main rear wheel steering angle sensor detects
The sensor signal from the wheel steering angle sensor is monotonically decreasing
Hour, rear wheel steering angle sub sensor value from rear wheel steering angle main sensor value
If the value obtained by subtracting the
And a rear wheel steering angle sensor monitoring means for detecting that the rear wheel steering angle sensor is abnormal .