JP5672226B2 - Rear wheel steering device - Google Patents

Description

  The present invention relates to a rear wheel steering device for steering control of a rear wheel of a vehicle.

  2. Description of the Related Art Conventionally, there is known a rear wheel steering device that detects various state quantities of a vehicle such as a steering angle of a vehicle, a yaw rate, a lateral acceleration, and the like, and controls steering of a rear wheel based on the detected state quantities.

  The rear wheel steering device usually includes a brushless motor as an actuator for steering the rear wheel, and a rotation angle sensor (for example, a resolver) that detects the rotation angle of the brushless motor with high resolution. The rear wheel steering device can control the rear wheel steering angle with high accuracy by controlling the brushless motor based on the detection value of the rotation angle sensor.

  A rotation angle sensor such as a resolver is a sensor that detects a relative rotation angle from a neutral point. Therefore, for example, if the brushless motor is moved by some external force while the ignition switch is off and the motor rotation angle changes, the continuity of the motor rotation angle cannot be maintained, and the motor rotation angle from the neutral point is accurately set after the ignition switch is turned on. Cannot be detected.

  Therefore, in the rear wheel steering device, another sensor for detecting the absolute rotation angle is provided, and after the ignition switch is turned on, the rotation angle sensor is initially set using the detection value of this sensor (for example, Patent Documents). 1). As a sensor for detecting an absolute rotation angle, for example, a stroke sensor for detecting a stroke amount of a shaft connecting the left and right rear wheels is used. The absolute rotation angle of the motor can be obtained from the stroke amount detected by the stroke sensor.

JP-A-5-97046

  However, the resolution of the stroke sensor is not as high as that of the rotation angle sensor. Therefore, even if the rotation angle sensor is initially set based on the detection value of the stroke sensor, the rotation angle sensor may not be able to detect the correct rotation angle. If the detection value of the rotation angle sensor is not accurate, appropriate rear wheel steering control cannot be performed.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a technique capable of detecting an abnormality of the rear wheel steering device in which appropriate steering control cannot be performed.

In order to solve the above-described problems, a rear wheel steering device according to an aspect of the present invention includes a rear wheel steering mechanism that steers a rear wheel, and a rear wheel steering when the ignition switch is turned off when the ignition switch is turned on. A movement determining means for determining whether or not the mechanism has been moved, a neutral control means for returning the rear wheel steering mechanism to a neutral position when the movement determining means determines that the rear wheel steering mechanism has been moved, and the vehicle is in a straight traveling state Vehicle straight-ahead steering angle acquisition means for acquiring a vehicle straight-ahead steering angle that is a steering angle at the time of the vehicle, a vehicle straight-ahead steering angle acquired before the ignition switch is turned off, and after the ignition switch is turned on and the rear wheel And an abnormality determination means for determining an abnormality of the rear wheel steering mechanism by comparing with a straight traveling angle of the vehicle acquired after the steering mechanism is returned to the neutral position.

The rear wheel steering mechanism may include a motor, a first sensor that detects a relative rotation angle of the motor, and a second sensor that detects an absolute rotation angle of the motor. The movement determining means compares the detected value of the first sensor before the ignition switch is turned off with the detected value of the second sensor after the ignition switch is turned on , thereby moving the rear wheel steering mechanism. It may be determined whether or not.

When it is determined that the rear wheel steering mechanism has been moved, initial value setting means for setting the detection value of the second sensor after the ignition switch is turned on as the initial value of the first sensor after the ignition switch is turned on May be further provided.

  The neutral control means may control the rear wheel steering mechanism to the neutral position based on the detection value of the second sensor.

  The vehicle straight steering angle acquisition means may acquire the vehicle straight steering angle from the vehicle brake control device.

  According to the present invention, it is possible to appropriately detect an abnormality in the rear wheel steering device.

It is a figure for demonstrating the rear-wheel steering apparatus which concerns on embodiment of this invention. It is a flowchart for demonstrating control of the rear-wheel steering apparatus which concerns on this embodiment. It is a figure for demonstrating a vehicle straight steering angle.

  The best mode for carrying out the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a view for explaining a rear wheel steering apparatus 10 according to an embodiment of the present invention. A rear wheel steering device 10 shown in FIG. 1 includes a rear wheel steering mechanism 11 that steers rear wheels, and a rear wheel steering ECU 12 that controls the rear wheel steering mechanism 11.

  As shown in FIG. 1, the rear wheel steering mechanism 11 includes side rods 13L and 13R, a shaft 14, a brushless motor 15, a resolver 16, a stroke sensor 17, and the like.

  As shown in FIG. 1, side rods 13L and 13R are connected to both ends of the shaft 14 via ball joints 18L and 18R. The side rods 13L and 13R are connected to left and right rear wheels (not shown) via knuckle arms.

  The rotation of the brushless motor 15 is controlled by a control signal from the rear wheel steering ECU 12. The rotation of the brushless motor 15 moves the shaft 14 in the axial direction (vehicle width direction), and the left and right rear wheels are steered. The turning angle of the left and right rear wheels is proportional to the movement amount of the shaft 14, that is, the rotation angle of the brushless motor 15.

  The resolver 16 detects the rotation angle of the brushless motor 15. The resolver 16 detects a relative rotation angle from a neutral point that is a rotation position of the motor at which the rear wheel steering angle becomes zero. The rotation angle signal (resolver electrical angle) detected by the resolver 16 is sent to the rear wheel steering ECU 12. The rear wheel steering ECU 12 feedback-controls the rotation of the brushless motor 15 based on the rotation angle signal from the resolver 16.

  The stroke sensor 17 detects an absolute movement amount (stroke amount) from the reference point of the shaft 14. As the stroke sensor 17, for example, a potentiometer can be suitably used. The absolute rotation angle from the neutral point of the brushless motor 15 can be obtained from the stroke amount detected by the stroke sensor 17. Hereinafter, an absolute rotation angle obtained from the stroke amount is referred to as a “stroke angle”. The stroke angle signal detected by the stroke sensor 17 is sent to the rear wheel steering ECU 12.

  As shown in FIG. 1, an on / off signal from the ignition switch 20, a vehicle speed signal from the vehicle speed sensor 21, a steering angle signal from the steering angle sensor 22, a yaw rate signal from the yaw rate sensor 23, etc. Is entered. The rear wheel steering ECU 12 controls the amount of rotation of the brushless motor 15 based on these signals, and steers the left and right rear wheels. Since rear wheel steering control using these signals (hereinafter referred to as “normal rear wheel steering control”) is well known, detailed description thereof is omitted here.

  Further, the rear wheel steering ECU 12 can communicate with the brake ECU 30. The brake ECU 30 has a function of monitoring the running state of the vehicle based on signals from various sensors connected to the brake ECU 30 and automatically generating an optimum braking force according to the running state of the vehicle. As an automatic braking control performed by the rear wheel steering ECU 12, there is a vehicle stability control (VSC). VSC stabilizes the vehicle by reducing the side slip that tends to occur when turning a curve. In VSC, a steering wheel steering angle (hereinafter referred to as “vehicle straight steering angle”) when the vehicle is in a straight traveling state is constantly monitored based on information from the steering angle sensor. Even if the steering angle of the steering wheel is 0 degree due to conditions such as the tire pressure, the turning angle of the wheel is not always 0 degree. In the present embodiment, the rear wheel steering ECU 12 acquires information on the vehicle straight steering angle from the brake ECU 30 and uses it in the control described in FIG.

  FIG. 2 is a flowchart for explaining the control of the rear wheel steering apparatus 10 according to the present embodiment. This control is performed when the ignition switch 20 is turned on.

  When an ON signal is input from the ignition switch 20, the rear wheel steering ECU 12 first determines whether or not the rear wheel steering mechanism 11 is moved while the ignition switch is OFF (S10). For example, when some external force is applied to the rear wheel, the shaft 14 is moved by the external force, and thereby the brushless motor 15 is rotated.

  The determination in S10 is performed by comparing the detection value (resolver electrical angle) of the resolver 16 before the ignition switch is turned off with the detection value (stroke angle) of the stroke sensor 17 after the ignition switch is turned off.

  Specifically, the rear wheel steering ECU 12 uses the difference between the stroke angle detected after the ignition switch is turned on and the resolver electrical angle stored before the ignition switch is turned off as the amount to be moved. When the amount of movement is a predetermined amount that is equal to or less than the determination angle, the rear wheel steering ECU 12 determines that the rear wheel steering mechanism 11 is not moved while the ignition switch 20 is off. On the other hand, when the amount is moved and exceeds the determination angle, the rear wheel steering ECU 12 determines that the rear wheel steering mechanism 11 has been moved. In order to perform the process of S10, the rear wheel steering ECU 12 stores the stroke sensor angle when the OFF signal of the ignition switch 20 is input in the nonvolatile memory.

  If it is determined that the rear wheel steering mechanism 11 is not moved (N in S10), the rear wheel steering ECU 12 sets the resolver electrical angle stored before the ignition switch is turned off to the initial value of the electrical angle of the resolver 16 ( S12). This is because it can be determined that the resolver electrical angle before the ignition switch is turned off is maintained because the brushless motor 15 is not moved. In order to perform the process of S12, the rear wheel steering ECU 12 stores the resolver electrical angle when the ignition switch 20 OFF signal is input in the nonvolatile memory. After S12, the rear wheel steering ECU 12 shifts to normal rear wheel steering control (S14).

  On the other hand, when it is determined that the rear wheel steering mechanism 11 has been moved (Y in S10), the rear wheel steering ECU 12 sets the stroke angle detected after the ignition switch is turned on to the initial value of the electrical angle of the resolver 16 (S16). ). When the brushless motor 15 is moved, it is considered that the resolver electrical angle stored before the ignition switch is turned off is not held. Therefore, it is determined that the stroke angle detected after the ignition switch is turned on has higher reliability than the stored resolver electrical angle, and such processing is performed.

  However, the resolution of the stroke sensor 17 is usually lower than that of the resolver 16. Therefore, the stroke angle detected after the ignition switch is turned on does not match the electrical angle of the resolver 16 stored before the ignition switch is turned off, and there is a possibility that a difference has occurred. In this case, since the continuity of the motor rotation angle is not maintained, the resolver 16 cannot accurately detect the rotation angle from the neutral point. Therefore, in the present embodiment, the reliability of the stroke angle detected by the stroke sensor 17 is verified by performing the processing described below.

  First, the rear wheel steering ECU 12 calculates the neutral point of the brushless motor 15 from the stroke angle detected after the ignition switch is turned on. Then, the rear wheel steering ECU 12 returns the rotation angle of the brushless motor 15 to the calculated neutral point (S18).

  Next, the rear wheel steering ECU 12 issues a vehicle straight steering angle detection instruction to the brake ECU 30, and acquires the vehicle straight steering angle from the brake ECU 30 (S20). This vehicle straight steering angle is defined as θsr1.

  Next, the rear-wheel steering ECU 12 compares the vehicle straight-ahead steering angle stored before turning off the ignition switch (referred to as the front trip vehicle straight-ahead steering angle θsr2) and the current vehicle straight-ahead steering angle θsr1 (S22). Specifically, the rear wheel steering ECU 12 determines whether or not the absolute value | θsr2−θsr1 | of the difference between the front trip vehicle straight-ahead steering angle θsr2 and the vehicle straight-ahead steering angle θsr1 is equal to or greater than a predetermined threshold value. In order to perform the process of S22, the rear wheel steering ECU 12 obtains the vehicle straight steering angle θsr2 from the brake ECU 30 when the OFF signal of the ignition switch 20 is input, and this is nonvolatile as the front trip vehicle straight steering angle θsr2. Stored in memory.

  If the absolute value of the difference | θsr2−θsr1 | is equal to or greater than the threshold (Y in S22), the rear wheel steering ECU 12 determines that the abnormality is present (S24). The difference between the front trip vehicle straight steering angle θsr2 and the vehicle straight steering angle θsr1 means that the reliability of the stroke angle detected by the stroke sensor 17 is low. Therefore, in this case, the rotation angle detected by the resolver 16 cannot be determined to be accurate, and an abnormality determination is made assuming that appropriate rear wheel steering control cannot be performed.

  If the absolute value of the difference | θsr2−θsr1 | is less than the threshold (N in S22), the rear wheel steering ECU 12 shifts to normal rear wheel steering control (S14). The fact that there is no difference between the front trip vehicle straight steering angle θsr2 and the vehicle straight steering angle θsr1 or that the difference is small means that the stroke angle detected by the stroke sensor 17 is highly reliable. In this case, since the rotation angle detected by the resolver 16 can be determined to be accurate, the routine shifts to normal rear wheel steering control.

  FIG. 3 is a diagram for explaining the vehicle straight steering angle. In FIG. 3, the vertical axis represents the vehicle straight steering angle, and the horizontal axis represents time. In FIG. 3, a curve 40 represents the vehicle straight-ahead steering angle detected by the brake ECU 30. In addition, although a part of the curve 40 is a dotted line, this represents that the section does not detect the vehicle straight steering angle. The rear wheel steering ECU 12 stores the vehicle straight-ahead steering angle when the ignition switch is turned off as a front-trip vehicle straight-ahead steering angle in a nonvolatile memory (denoted by reference numeral 42).

  As described above, according to the rear wheel steering device 10 according to the present embodiment, after the ignition switch is turned on and the resolver 16 is initially set, the vehicle straight traveling steering angle acquired from the brake ECU 30 is used, The reliability of the initial setting can be verified. By using a system different from the rear wheel steering device, the reliability of the rear wheel steering device 10 can be improved.

  The present invention has been described above based on the embodiment. It should be understood by those skilled in the art that these embodiments are exemplifications, and that various modifications can be made to the combination of each component and each processing process, and such modifications are also within the scope of the present invention.

  DESCRIPTION OF SYMBOLS 10 Rear wheel steering device, 11 Rear wheel steering mechanism, 12 Rear wheel steering ECU, 14 Shaft, 15 Brushless motor, 16 Resolver, 17 Stroke sensor, 20 Ignition switch, 21 Vehicle speed sensor, 23 Yaw rate sensor, 30 Brake ECU

Claims (5)

A rear wheel steering mechanism for steering the rear wheels;
A movement determination means for determining whether or not the rear wheel steering mechanism is moved while the ignition switch is off when the ignition switch is turned on;
When it is determined by the movement determination means that the rear wheel steering mechanism has been moved, neutral control means for returning the rear wheel steering mechanism to a neutral position;
Vehicle straight steering angle acquisition means for acquiring a vehicle straight steering angle that is a steering angle when the vehicle is in a straight traveling state;
Comparing the vehicle straight steering angle acquired before the ignition switch is off with the vehicle straight steering angle acquired after the ignition switch is turned on and after the rear wheel steering mechanism is returned to the neutral position. By means of abnormality determination means for determining abnormality of the rear wheel steering mechanism,
A rear wheel steering apparatus comprising: The rear wheel steering mechanism includes a motor, a first sensor that detects a relative rotation angle of the motor, and a second sensor that detects an absolute rotation angle of the motor,
The movement determination means, by the ignition switch compares the detected value of the first sensor prior between off, the detected value of the second sensor after the ignition switch is turned on, the rear wheel 2. The rear wheel steering apparatus according to claim 1, wherein it is determined whether or not the steering mechanism is moved. When it is determined that the rear wheel steering mechanism has been moved, the detection value of the second sensor after the ignition switch is turned on is set as the initial value of the first sensor after the ignition switch is turned on. The rear wheel steering apparatus according to claim 2, further comprising initial value setting means for performing the operation.   The rear wheel steering apparatus according to claim 2 or 3, wherein the neutral control means controls the rear wheel steering mechanism to a neutral position based on a detection value of the second sensor.   5. The rear wheel steering device according to claim 1, wherein the vehicle straight steering angle acquisition unit acquires the vehicle straight steering angle from a brake control device of a vehicle.

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