JP4042569B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering apparatus configured to assist steering by transmitting a driving force generated by an electric motor to a steering mechanism.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an electric power steering apparatus that assists steering by mechanically transmitting a driving force of an electric motor to a steering mechanism has been used. The electric motor is controlled based on a target current value set in accordance with the steering torque applied to the steering wheel, whereby a steering assist force in accordance with the steering torque is applied to the steering mechanism.
[0003]
The target current value is determined according to the steering torque and the vehicle speed. Basically, the target current value is determined so that steering assistance is performed in the same direction as the direction of the steering torque. The basic characteristics of the target current value with respect to the steering torque and the vehicle speed are called assist characteristics, and are stored in advance in the memory as an assist map (table). Based on the assist map, a basic value of the target current value is determined, and the target current value is determined by correcting the basic value for damping control or the like.
[0004]
In such an electric power steering apparatus, an arithmetic monitoring logic for monitoring the runaway of a microcomputer that controls the electric motor is provided (Patent Document 1 and Patent Document 2 below). The basic operation of this calculation monitoring logic is based on the assist map, and when the excessive target current value or the target current value in the direction opposite to the steering torque is set, it is determined that the microcomputer has runaway. It is to perform fail-safe processing.
[0005]
The above damping control is activated during high-speed driving, and in order to eliminate the influence of the moment of inertia of the electric motor, the target current value is reduced or the target current value is changed to a value opposite to the steering torque direction. Since the control is to be corrected, the direction of the steering torque may not match the direction of the target current value even when there is no abnormality in the microcomputer. Therefore, the actual calculation monitoring logic is based on the condition that the absolute value of the target current value is equal to or greater than a predetermined control abnormality threshold value when the steering torque direction and the steering assist direction corresponding to the target current value do not match. Fail-safe processing is performed.
[0006]
[Patent Document 1]
JP-A-6-270822 [Patent Document 2]
Japanese Patent Application Laid-Open No. 6-270823
[Problems to be solved by the invention]
However, although the damping control is a control that is operated mainly during high-speed traveling, the above-described control abnormality threshold value is a constant value regardless of the vehicle speed range. Therefore, even when a target current value that does not match the direction of the steering torque is set during low-speed traveling or when the vehicle is stopped, fail-safe operation cannot be performed promptly. In particular, when a target current value having an absolute value close to the control abnormality threshold value and corresponding to steering assist in the direction opposite to the steering torque direction is set at the time of stationary, unexpected steering assist or steering (self Steer) may occur, which may cause the driver to feel uncomfortable.
[0008]
SUMMARY OF THE INVENTION An object of the present invention is to provide an electric power steering device that can perform processing when an abnormality occurs without causing a feeling of steering discomfort.
[0009]
[Means for Solving the Problems and Effects of the Invention]
According to the first aspect of the present invention, the electric motor (M) is controlled in accordance with the steering torque applied to the operating member (1), and the driving force generated by the electric motor is controlled by the steering mechanism. An electric power steering device for assisting steering by transmitting to (3), which detects a steering torque applied to the operation member and outputs a torque signal, and this torque detecting means detects Target drive value setting means (11, 13, 14) for setting the target drive value of the electric motor based on the steering torque, and the electric motor based on the target drive value set by the target drive value setting means. Motor driving means (16, 30) for driving, vehicle speed detecting means (7) for detecting the vehicle speed of the vehicle on which the electric power steering device is mounted, and the target drive value setting means When the steering assist direction corresponding to the target drive value set by the step is different from the steering torque direction detected by the torque detection means, the absolute value of the target drive value is equal to or greater than the absolute value of the control abnormality determination threshold value. Determination means (22) for determining whether or not, a threshold value changing means (21) for changing the control abnormality determination threshold value according to the vehicle speed detected by the vehicle speed detection means, and the determination means include the target An electric power steering device comprising: drive prohibiting means (23) for prohibiting driving of the electric motor when it is determined that the absolute value of the drive value is equal to or greater than the absolute value of the control abnormality determination threshold value; It is. The alphanumeric characters in parentheses indicate corresponding components in the embodiments described later. The same applies hereinafter.
[0010]
According to the present invention, the control abnormality determination threshold value, which serves as a reference for control abnormality determination when the steering assist direction corresponding to the target drive value and the direction of the steering torque do not match, is changed according to the vehicle speed. As a result, appropriate control abnormality determination can be performed according to the vehicle speed, and therefore processing at the time of occurrence of abnormality can be appropriately performed without causing a feeling of strange steering.
The target drive value setting means may include means for variably setting the target drive value according to the vehicle speed. For example, the target drive value setting means is a correction means (for example, damping control) that decreases the absolute value of the target drive value or changes the sign of the target drive value (corresponding to the steering assist direction) during a predetermined high-speed travel. Means) may be included.
[0011]
The threshold value changing means preferably sets the control abnormality determination threshold value smaller as the vehicle speed is lower.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram showing an electrical configuration of an electric power steering apparatus according to an embodiment of the present invention. A steering torque applied to the steering wheel 1 as an operation member is transmitted to the steering mechanism 3 via the steering shaft 2. A driving force generated from the electric motor M is mechanically transmitted to the steering mechanism 3 as a steering assist force through a gear mechanism or by a direct drive system.
[0013]
The steering shaft 2 is divided into an input shaft 2A coupled to the steering wheel 1 side and an output shaft 2B coupled to the steering mechanism 3 side. The input shaft 2A and the output shaft 2B are connected to the torsion bar 4. Are connected to each other. The torsion bar 4 is twisted according to the steering torque T applied to the steering wheel 1, and the direction and amount of the twist are detected by the torque sensor 5. The output signal of the torque sensor 5 is input to the first microcomputer 10.
[0014]
In addition to the output signal of the torque sensor 5, the first microcomputer 10 includes an output signal of the vehicle speed sensor 7 that detects the vehicle speed V of the vehicle on which the electric power steering device is mounted, and the terminal of the electric motor M. An output signal of the motor terminal voltage detector 8 that detects the voltage and an output signal of the motor current detector 9 that detects the current (motor current) flowing through the electric motor M are also input.
In this electric power steering apparatus, in addition to the first microcomputer 10, when an abnormality such as a runaway occurs in the first microcomputer 10, this is detected and a fail-safe process is executed. A second microcomputer 20 (or custom IC) is provided.
[0015]
The first microcomputer 10 sets a target current value corresponding to the steering torque T detected by the torque sensor 5 and the vehicle speed V detected by the vehicle speed sensor 7, and controls the motor driver 30 based on the target current value. By doing so, an appropriate drive current is given to the electric motor M. As a result, a steering assist force according to the steering torque T and the vehicle speed V is applied to the steering mechanism 3.
The first microcomputer 10 substantially includes a function processing unit realized by program processing. These function processing units are based on signals from a basic target current value setting unit 11 that sets a basic target current value according to the steering torque T and the vehicle speed V, a motor terminal voltage detection unit 8, and a motor current detection unit 9. A motor angular speed calculation unit 12 that calculates the rotational angular speed ω of the electric motor M, a damping control unit 13 that calculates a damping control correction value based on the vehicle speed V and the motor rotational angular speed ω obtained by the motor angular speed calculation unit 12, and a basic target current A correction processing unit 14 for obtaining a target current value by correcting the basic target current value set by the value setting unit 11 with each correction value generated by the damping control unit 13 and the other correction control unit 17, and the correction processing unit If the deviation calculator 15 calculates the deviation between the target current value generated by the motor 14 and the motor current value detected by the motor current detector A control signal generator 16 that generates a control signal (for example, a PWM (Pulse Width Modulation) control signal) to be given to the motor driver 30 based on the deviation obtained by the deviation calculator 15 is included.
[0016]
The control signal generated by the control signal generation unit 16 is supplied to the motor driver 30 via the opening / closing means 28 including an analog switch or the like. The opening / closing means 28 is normally kept closed, and when an abnormality occurs in the first microcomputer 10, the opening / closing means 28 is switched to the open state under the control of the second microcomputer 20. As a result, when an abnormality occurs in the first microcomputer 10, the supply of the control signal to the motor driver 30 is stopped, and as a result, the power supply to the electric motor M is stopped.
[0017]
The second microcomputer 20 includes a control abnormality threshold setting unit 21 that sets a control abnormality threshold, and a control abnormality threshold and correction processing unit 14 that are set by the control abnormality threshold setting unit 21. An abnormality determination unit 22 that determines whether or not an abnormality has occurred in the first microcomputer 10 by comparing with a target current value to be performed, and an abnormality has occurred in the first microcomputer 10 by the abnormality determination unit 22 And a fail-safe processing unit 23 for executing a fail-safe process for switching the opening / closing means 28 to an open state in response to the determination that the opening / closing means 28 is open.
[0018]
Vehicle speed information detected by the vehicle speed sensor 7 is input to the control abnormality threshold value setting unit 21, and the control abnormality threshold value is variably set according to the vehicle speed V.
FIG. 2 is a diagram for explaining the operation of the basic target current value setting unit 11 and shows the relationship of the basic target current value with respect to the steering torque T (basic assist characteristic curve: a broken line in the example of FIG. 2). . For the steering torque T, for example, the torque for steering in the right direction is a positive value, and the torque for steering in the left direction is a negative value. The basic target current value is a positive value when a steering assist force for rightward steering is to be generated from the electric motor M, and when a steering assist force for leftward steering is to be generated from the electric motor M. Negative value.
[0019]
The basic target current value takes a positive value for a positive value of the steering torque and takes a negative value for a negative value of the steering torque. When the steering torque is a very small value (torque dead zone) in the range of -T1 to T1 (for example, T1 = 0.4 N · m), the basic target current value is set to zero. The absolute value of the basic target current value is set to be smaller as the vehicle speed V detected by the vehicle speed sensor 7 is higher. As a result, a large steering assist force can be generated during low-speed traveling, and the steering assist force can be reduced during high-speed traveling.
[0020]
FIG. 3 is a diagram for explaining the function of the control abnormality threshold value setting unit 21. The control abnormality threshold value setting unit 21 sets a control abnormality threshold curve corresponding to the basic assist characteristic curve set by the basic target current value setting unit 11. In the example of FIG. 3, the control abnormality threshold curve is composed of a pair of broken lines. That is, the control abnormality threshold value setting unit 21 shifts the first control abnormality threshold curve L1 and the second control abnormality, which are shifted from the basic assist characteristic curve L in the positive direction and the negative direction of the coordinate axis of the target current value, respectively. A threshold curve L2 is set.
[0021]
The first control abnormality threshold curve L1 and the second control abnormality threshold curve L2 are determined such that the control abnormality threshold changes according to the steering torque. Specifically, the bending points and end points P11, P12, P13, P14; P21, P22, P23, P24 of the polygonal line are stored in a memory (not shown), and the control abnormality threshold value setting unit 21 The first control abnormality threshold curve L1 and the second control abnormality threshold curve L2 formed by broken lines are set by linear interpolation between the bending points and the end points P11 to P14 and P21 to P24. .
[0022]
Since the basic assist characteristic curve L changes according to the vehicle speed V, the end points P14 and P24 that define the slopes of the inclined line portions in the first and second control abnormality threshold curves L1 and L2 correspond to the vehicle speed V. A variable setting is made according to V.
In the graph of FIG. 3, a region A1 corresponding to a case where the target current value exceeds the first control abnormality threshold curve L1 within the first quadrant is a region where steering assist is excessive. Similarly, a region A2 corresponding to a case where the target current value falls below the second control abnormality threshold curve L2 (exceeds in absolute value) within the third quadrant is a region where steering assist is excessive.
[0023]
On the other hand, in the region A3 corresponding to the case where the target current value falls below the portion located in the fourth quadrant of the second control abnormality threshold curve L2 in the fourth quadrant, the direction of the steering torque and the direction of the steering assist are reversed. It is the area that is. Similarly, the region A4 corresponding to the case where the target current value exceeds the portion located in the second quadrant of the first control abnormality threshold curve L1 in the second quadrant, the steering torque direction and the steering assist direction are This is a reverse area.
Further, a region A5 corresponding to the case where the target current value falls below the portion located in the first quadrant of the second control abnormality threshold curve L2 is that the target current value is abnormally small with respect to the steering torque or This is a region where the steering assist direction is reversed. Similarly, in the region A6 corresponding to the case where the target current value exceeds the portion located in the third quadrant of the first control abnormality threshold curve L1, the absolute value of the target current value is abnormally small with respect to the steering torque. Alternatively, this is a region where the steering torque and the steering assist direction corresponding to the target current value are reversed.
[0024]
Of these areas A1 to A6, the areas where the reverse assist until the fail-safe process is determined during low-speed traveling or stopping are areas A3 and A4. Therefore, the control abnormality threshold value setting unit 21 determines the portions L1A and L2A of the first control abnormality threshold curve L1 and the second control abnormality threshold curve L2 corresponding to the regions A3 and A4 according to the vehicle speed V. Variable setting.
FIG. 4 is a diagram for explaining a setting example of the portions L1A and L2A of the first control abnormality threshold curve L1 and the second control abnormality threshold curve L2. In each of the portions L1A and L2A, the control abnormality threshold value is a constant value k or −k (unit is ampere, where k is a constant and k> 0) regardless of the steering torque. Can be represented by Therefore, the constant values k and -k are variably set according to the vehicle speed V. That is, as the vehicle speed V increases, the constant k is determined to gradually increase (in this embodiment, increase linearly) from a predetermined lower limit value (for example, 2 amperes) to a predetermined upper limit value (for example, 5 amperes). As a result, the constant k is set to a small value when traveling at a low speed or stopped, and the constant k is set to the predetermined upper limit value when traveling at a high speed.
[0025]
As a result, when a target current value that generates a steering assist force in a direction opposite to the direction of the steering torque is set during low speed traveling or when the vehicle is stopped, the abnormality determination unit 22 quickly determines that there is an abnormality. The fail-safe processing is executed by the fail-safe processing unit 23, whereby the electric motor M is quickly stopped. On the other hand, during medium-high speed traveling, the abnormality determination unit 22 does not erroneously determine that there is an abnormality with respect to the target current value in the reverse assist direction set as a result of the damping control. In this way, the damping control can be performed satisfactorily, and the fail-safe process can be performed without causing a sense of incongruity when an abnormality occurs during low-speed traveling or when the vehicle is stopped.
[0026]
As mentioned above, although one Embodiment of this invention was described, this invention can also be implemented with another form. For example, in the above-described embodiment, the portions L1A and L2A of the first and second control abnormality threshold curves L1 and L2 are straight lines that define current values having the same absolute value. The values may be different.
In the above embodiment, the target current value is used as the target drive value for controlling the electric motor M. However, the assist torque target value, which is the target voltage value or the target value of the steering assist force, is used as the target drive value. It may be used.
[0027]
In addition, various design changes can be made within the scope of matters described in the claims.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an electrical configuration of an electric power steering apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining the operation of a basic target current value setting unit, and shows a relationship between a basic target current value and a steering torque.
FIG. 3 is a diagram for explaining the function of a control abnormality threshold value setting unit.
FIG. 4 is a diagram for explaining a setting example of a control abnormality threshold value according to a vehicle speed.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 3 Steering mechanism 4 Torsion bar 5 Torque sensor 7 Vehicle speed sensor 8 Motor terminal voltage detection part 9 Motor current detection part 10 First microcomputer 11 Basic target current value setting part 12 Motor angular speed calculation part 13 Damping control Unit 14 Correction processing unit 15 Deviation calculation unit 16 Control signal generation unit 20 Second microcomputer 21 Control abnormality threshold setting unit 22 Abnormality determination unit 23 Fail-safe processing unit 28 Opening / closing means 30 Motor driver M Electric motor

Claims (1)

An electric power steering device that controls an electric motor in accordance with a steering torque applied to an operation member and transmits a driving force generated by the electric motor to a steering mechanism to assist steering.
Torque detecting means for detecting a steering torque applied to the operation member and outputting a torque signal;
Target drive value setting means for setting a target drive value of the electric motor based on the steering torque detected by the torque detection means;
Motor drive means for driving the electric motor based on the target drive value set by the target drive value setting means;
Vehicle speed detection means for detecting the vehicle speed of a vehicle equipped with the electric power steering device;
When the steering assist direction corresponding to the target drive value set by the target drive value setting means is different from the direction of the steering torque detected by the torque detection means, the absolute value of the target drive value determines that the control is abnormal. A judging means for judging whether or not the absolute value of the threshold value is exceeded;
Threshold change means for changing the control abnormality determination threshold according to the vehicle speed detected by the vehicle speed detection means;
Drive determining means for prohibiting driving of the electric motor when the determining means determines that the absolute value of the target drive value is greater than or equal to the absolute value of the control abnormality determination threshold value. Electric power steering device.

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