JP4021186B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering apparatus that applies a steering assist force by a motor to a steering system of an automobile or a vehicle, and in particular, reliably distinguishes between offset and disturbance noise due to failure of the motor current detection means or aging. The present invention relates to an electric power steering apparatus.
[0002]
[Prior art]
An electric power steering device for energizing an automobile or vehicle steering device with an auxiliary load by the rotational force of a motor is an auxiliary load applied to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a speed reducer. It comes to be energized. Such a conventional electric power steering apparatus performs feedback control of motor current in order to accurately generate assist torque (steering assist torque). The feedback control adjusts the motor applied voltage so that the difference between the current control value and the motor current detection value becomes small. The adjustment of the motor applied voltage is generally performed by a PWM (pulse width modulation) control duty. This is done by adjusting the tee ratio.
[0003]
Here, the general configuration of the electric power steering apparatus will be described with reference to FIG. 5. The shaft 2 of the steering handle 1 is coupled to the tie rod 6 of the steering wheel via the universal joints 4 a and 4 b and the pinion rack mechanism 5. ing. The shaft 2 is provided with a torque sensor 10 that detects the steering torque of the steering handle 1, and a motor 20 that assists the steering force of the steering handle 1 is coupled to the shaft 2 via the reduction gear 3. . The control unit 30 that controls the power steering device is supplied with electric power from the battery 14 via the ignition key 11 and the relay 13, and the control unit 30 is detected by the steering torque T detected by the torque sensor 10 and the vehicle speed sensor 12. The steering assist command value I of the assist command is calculated based on the vehicle speed V, and the current supplied to the motor 20 is controlled based on the calculated steering assist command value I.
[0004]
The control unit 30 is mainly composed of a CPU, and FIG. 6 shows general functions executed by programs in the CPU. For example, the phase compensator 31 does not indicate a phase compensator as independent hardware, but indicates a phase compensation function executed by the CPU.
[0005]
The function and operation of the control unit 30 will be described. The steering torque T detected and input by the torque sensor 10 is phase-compensated by the phase compensator 31 in order to improve the stability of the steering system, and the phase-compensated steering torque. TA is input to the steering assist command value calculator 32. The vehicle speed V detected by the vehicle speed sensor 12 is also input to the steering assist command value calculator 32. The steering assist command value calculator 32 determines a steering assist command value I that is a control target value of the current supplied to the motor 20 based on the input steering torque TA and vehicle speed V. The steering assist command value I is input to the subtractor 30A, and is also input to the feedforward differential compensator 34 for increasing the response speed. The deviation (Ii) of the subtractor 30A is input to the proportional calculator 35. The proportional output is input to the adder 30B and also input to the integration calculator 36 for improving the characteristics of the feedback system. The outputs of the differential compensator 34 and the integral compensator 36 are also added to the adder 30B, and the current control value E, which is the addition result of the adder 30B, is input to the motor drive circuit 37 as a motor drive signal. The motor current value i of the motor 20 is detected by the motor current detection means 38, and the detected motor current value i is input to the subtractor 30 </ b> A and fed back, and is input to the abnormality detection means 33.
[0006]
The abnormality detection means 33 detects an offset abnormality due to a failure of the motor current detection means 38 or a secular change and outputs an alarm when the abnormality is detected to stop the steering control. The motor drive circuit 37 is supplied with electric power from the battery 14 via a switch SW1 (for example, an electronic switch composed of a transistor or the like) that is ON / OFF controlled.
[0007]
Further, the configuration example of the motor drive circuit 37 will be described with reference to FIG. 7. The motor drive circuit 37 drives the gates of the field effect transistors (FETs) FET1 to FET4 based on the current control value E from the adder 30B. An FET gate drive circuit 372, an H bridge circuit composed of FET1 to FET4, a boost power supply 371 for driving the high side of FET1 and FET2, and the like. The FET1 and FET2 are turned on / off by a PWM (pulse width modulation) signal having a duty ratio D1 determined based on the current control value E, and the magnitude of the current Ir that actually flows through the motor 20 is controlled. FET3 and FET4 are driven by a PWM signal having a duty ratio D2 defined by a predetermined linear function equation (D2 = a · D1 + b, where a and b are constants) in a region where the duty ratio D1 is small, and the duty ratio D2 is also 100%. After reaching the value, it is turned ON / OFF according to the rotation direction of the motor 20 determined by the sign of the PWM signal.
[0008]
The motor 20 is connected to a switch SW2 (for example, an electronic switch composed of a transistor or the like) that is ON / OFF controlled in order to cut off the inflow of current to the motor 20. A resistor R having an extremely small resistance value for current detection is grounded to the H bridge circuit, and a motor current detecting means (for example, a high gain differential amplifier) 38 is connected to the resistor R.
[0009]
In such an electric power steering apparatus, there is a possibility that the steering feeling is lowered due to an offset due to a failure of the motor current detecting means 38 or a secular change. Therefore, conventionally, in the initial diagnosis (electrical system failure check) when the ignition key 11 is ON, the output current of the motor current detecting means 38 when the motor current is set to 0 is detected, and the detected value is used as a correction value in advance. By storing the correction value and adding the correction value to the actual current detection value, a highly accurate steering feeling has been realized.
[0010]
[Problems to be solved by the invention]
However, when an inherent failure or a certain offset or more occurs, the abnormality detection means 33 detects it as a failure and it is necessary to stop the system. For this reason, when the conventional abnormality detection means 33 detects an offset value greater than a certain value, it detects it as a failure and stops the system. In this case, for example, when disturbance noise intrudes in front of the motor current detecting means 38 when the ignition key 11 is turned on, the motor current detecting means 38 uses an amplifier (differential amplifier) having a high gain, and therefore its output In this case, noise appears as an offset value, and there is a possibility of erroneous determination as a failure due to the influence of noise even though no failure has occurred. That is, conventionally, even disturbance noise is determined as a failure of the motor current detection means 38 or an abnormality of the offset, and the system is stopped.
[0011]
The present invention has been made under the circumstances as described above, and the object of the present invention is to reliably distinguish between offset and disturbance noise due to failure of the motor current detection means, aging, etc. It is another object of the present invention to provide an electric power steering device that does not stop the system.
[0012]
[Means for Solving the Problems]
The present invention provides a steering assist force to the steering mechanism based on the current control value calculated from the steering assist command value calculated by the calculating means based on the steering torque vehicle speed and the motor current value detected by the motor current detecting means. Control means for controlling the motor to be applied, driving the motor with an H bridge circuit composed of four semiconductor elements based on the current control value, and supplying power to the H bridge circuit via a first switch; The present invention relates to an electric power steering apparatus having an abnormality detection means for detecting an abnormality of the motor current detection means, wherein the motor is connected to the H bridge circuit via a second switch. The purpose is that the current control value is 0, the ON / OFF combination of the first switch, the second switch, and the four semiconductor elements is Stores the detected combination of impedance to ground of the motor current detecting means becomes a minimum in the memory, the abnormality the said detection combinations during operation of the detecting means reads from the memory the first switch and the second switch and the four This is accomplished by providing a check function for detecting an abnormality of the motor current detecting means by turning on / off the semiconductor element.
[0013]
Further, the above object of the present invention is to operate the check function every time the ignition key is turned on, or the check function stores the detected combination in the memory in advance and the ignition key is turned on. Each time the detection combination is read out from the memory , or the detection combination with the lowest grounding impedance and the current control value is 0, the detection value of the motor current detection means is used as the correction value. This is achieved more effectively by adding to the actual current detection value.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the switches SW1 and SW2 and the FET1 to FET4 of the H bridge circuit are turned on or off as necessary, and the combination of ON / OFF that minimizes the resistance to ground of the motor current detection means is detected. A function of adding the motor current at the time of the combination to the actual motor current is provided. For this reason, it is possible to reduce an erroneous determination of failure due to disturbance noise without increasing the cost by a software method. This utilizes the fact that the influence of disturbance noise is minimized as a voltage when the resistance to ground of the motor current detection means is minimum.
[0015]
Embodiments of the present invention will be described below with reference to the drawings.
[0016]
In the present invention, as shown in FIG. 1 corresponding to FIG. 7, an impedance measuring device 40 for measuring the impedance to ground is connected to the resistor R, and the switches SW1 and SW2 and the FET1 to FET4 are ON / OFF controlled. / OFF control unit 373 is provided. In FIG. 1, for example, signal SG1 turns on / off switch SW1, signal SG2 turns on / off switch SW2, signal ST1 turns on / off FET1, signal ST2 turns on / off FET2, and signal ST3 The FET 3 is turned ON / OFF, and the signal ST4 turns the FET 4 ON / OFF. In addition, a memory 41 for storing the ON / OFF states of the switches SW1 and SW2 and the FET1 to FET4 by the ON / OFF control unit 373 and the impedance value from the impedance measuring device 40 is provided.
[0017]
In such a configuration, the operation will be described with reference to FIG.
[0018]
First, the ON / OFF control unit 373 sequentially controls ON / OFF of the switches SW1 and SW2 and the FET1 to FET4 of the bridge circuit (step S1). The ON / OFF control of the switches SW1 and SW2 and FET1 to FET4 is performed for all ON / OFF combinations as shown in FIG. 3, and the impedance measurement instrument 40 measures the impedance to ground [mΩ] for each state at that time. At the same time, the impedance and the ON / OFF state are stored in the memory 41 (step S3). Such ON / OFF control is executed for all combinations (step S4), and after all combinations are executed, the memory 41 is searched and the minimum impedance is detected from the stored impedance values (step S5). The ON / OFF state at the minimum impedance is stored as a detection combination in the memory 41 as shown in FIG. 4 (step S6).
[0019]
For example, when the ignition key is turned on (step S10), the ON / OFF states (detection combinations) of SW1 and SW2 and FET1 to FET4 that are the minimum impedance stored in advance are read from the memory 41 (step S11). According to the ON / OFF state of this detection combination, the ON / OFF control unit 373 performs ON / OFF control of the switches SW1, SW2 and FET1 to FET4 (step S12). In this state, the motor current detection means 38 detects the motor current i (step S13), and the abnormality detection means 33 determines whether or not the motor current i is abnormal (step S14). If not abnormal, the motor current i at this time is stored in the memory 41 (step S15), and added to the actual motor current during actual motor control (step S16). This added and corrected current value is added to the steering assist command value. If it is determined in step S14 that there is an abnormality, the system operation is stopped.
[0020]
In the above description, the detected combination is stored in the memory in advance, and when the ignition key is turned on, the detected combination is read from the memory to detect the motor current. However, each time the ignition key is turned on, the detected combination is obtained. You may do it.
[0021]
Further, it may be programmed so that the lowest combination is inspected in advance and the combination is checked. Furthermore, it goes without saying that a circuit configuration having no second switch may be realized by a combination of other switch elements.
[0022]
【The invention's effect】
As described above, in the present invention, the switches SW1, SW2, and FET1 to FET4 are turned on or off as necessary, and ON / OFF that minimizes the resistance between the grounds in front of the motor current detection means that can be realized in the combination. It has a function to detect and check the OFF state. For this reason, all can be configured in a software manner, and erroneous determination of failure due to disturbance noise can be remarkably improved without an increase in cost.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a configuration example of the present invention.
FIG. 2 is a flowchart showing an operation example of the present invention.
FIG. 3 is a diagram for explaining the present invention.
FIG. 4 is a diagram for explaining the present invention.
FIG. 5 is a diagram illustrating an example of an electric power steering apparatus.
FIG. 6 is a block diagram showing a general internal configuration of a control unit.
FIG. 7 is a connection diagram illustrating an example of a motor drive circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Steering handle 5 Pinion rack mechanism 10 Torque sensor 12 Vehicle speed sensor 20 Motor 30 Control unit 31 Phase compensation part 32 Steering auxiliary command value calculator 33 Abnormality detection means 37 Motor drive circuit 38 Motor current detection means 40 Impedance measurement instrument 41 Memory 373 ON / OFF control unit

Claims (5)

A motor for giving a steering assist force to the steering mechanism based on a current control value calculated from a steering assist command value calculated by the calculation means based on the steering torque and the vehicle speed and a motor current value detected by the motor current detection means. Control means for controlling, driving the motor by an H bridge circuit comprising four semiconductor elements based on the current control value, supplying power to the H bridge circuit via a first switch, and The motor is connected to the circuit via a second switch, and in the electric power steering apparatus having an abnormality detection means for detecting an abnormality of the motor current detection means, the current control value is 0, for the combination of ON / OFF of the first switch and the second switch and the four semiconductor elements, the isolation in the motor current detecting means -Impedance is stores the detected combination of the lowest in the memory, the abnormality the said detection combinations during operation of the detecting means reads from the memory the first switch and the second switch and the four an ON / OFF the semiconductor element An electric power steering apparatus comprising a check function for detecting an abnormality of the motor current detecting means. 2. The electric power steering apparatus according to claim 1, wherein the check function is operated every time an ignition key is turned on. 2. The electric power steering apparatus according to claim 1, wherein the check function stores the detected combination in the memory in advance, and reads the detected combination from the memory every time an ignition key is turned on. . A detection value of the motor current detection means in the case of the detection combination having the lowest ground impedance and a current control value of 0 is added as a correction value to an actual current detection value. The electric power steering apparatus according to 2 or 3. A motor for giving a steering assist force to the steering mechanism based on a current control value calculated from a steering assist command value calculated by the calculation means based on the steering torque and the vehicle speed and a motor current value detected by the motor current detection means. A control means for controlling, driving the motor by an H bridge circuit comprising four semiconductor elements based on the current control value, supplying power to the H bridge circuit via a switch, and supplying the H bridge circuit to the H bridge circuit; In the electric power steering apparatus having an abnormality detecting means for detecting an abnormality of the motor current detecting means, wherein the current control value is 0, the switch and the four semiconductor elements are connected to the motor. impedance to ground of previously said motor current detecting means for a combination of the ON / OFF is advance checks the combination of the lowest, Serial abnormality detecting means electric power steering apparatus characterized by comprising a check function for detecting an abnormality of the motor current detecting means by the combination during operation of.

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