JP4032724B2 - 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. 3. 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. 4 shows general functions executed by a program inside 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. 5. 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 a steering mechanism based on a current control value calculated from a steering assist command value calculated by a calculation means based on a steering torque and a vehicle speed and a motor current value detected by a motor current detection means. Control means for controlling the motor for supplying the motor with the H bridge circuit comprising four semiconductor elements based on the current control value, and supplying power to the H bridge circuit via the first switch. The motor is connected to the H bridge circuit via a second switch, and the motor current detection means is connected to the current detection element of the H bridge circuit, and the output of the motor current detection means The electric power step comprises an abnormality detecting means for detecting an abnormality of the motor current detecting means by means of a third switch connected in parallel with the current detecting element. The object of the present invention is to provide an abnormality of the output value based on the output of the motor current detection means when the current control value is 0 and the third switch is turned on. This is achieved by providing a check function for detecting.
[0013]
Further, the object of the present invention is to provide the motor current detecting means when the check function is operated every time an ignition key is turned on, or when the third switch is ON and the current control value is 0. This is achieved more effectively by adding the detected value as a correction value to the actual detected current value.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a switch SW3 that is ON / OFF controlled is connected in parallel to the current detection resistor R, and the switch SW3 is turned ON during failure diagnosis. When the switch SW3 is turned ON, the value of the current detection resistor for detecting the motor current becomes almost zero, and even if disturbance noise enters, the influence does not appear in the output of the motor current detection means. In this way, hardware can be handled by simply connecting the switch SW3, so that the others can be handled by software, so that the cost increase can be reduced and the erroneous determination of failure due to disturbance noise can be reduced.
[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. 5, SW3 (for example, an electronic switch made of a transistor) which is ON / OFF controlled and normally turned off is connected in parallel to the resistor R.
[0017]
In such a configuration, the operation will be described with reference to FIG.
[0018]
When the ignition key is turned on (step S1), the switch SW3 is turned on (step S2). In this state, the motor current detection means 38 detects the motor current i (step S3), and the abnormality detection means 33 detects the motor current. It is determined whether i is abnormal (step S4). If not abnormal, the motor current i at this time is stored in the memory (step S5) and added to the actual motor current during actual motor control (step S6). This added and corrected current value is added to the steering assist command value. If it is determined in step S4 that there is an abnormality, the system operation is stopped.
[0019]
In the above description, the check function is operated when the ignition key is turned on, but it may be operated by other means.
[0020]
【The invention's effect】
As described above, in the present invention, the switch SW3 is turned on or off as necessary, and the abnormality is checked by the output of the motor current detecting means at the time of turning on. In terms of hardware, only the switch SW3 is connected, and the others can be handled in software, so that the cost increase is small and the erroneous determination of failure due to disturbance noise is remarkably improved.
[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 illustrating an example of an electric power steering apparatus.
FIG. 4 is a block diagram showing a general internal configuration of a control unit.
FIG. 5 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 assistance command value calculator 33 Abnormality detection means 37 Motor drive circuit 38 Motor current detection means

Claims (3)

A motor that gives steering assist force to the steering mechanism based on a current control value calculated from a steering assist command value calculated by the calculating means based on the steering torque and the vehicle speed and a motor current value detected by the motor current detecting 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 a circuit via a second switch, and the motor current detection means is connected to a current detection element of the H bridge circuit, and the motor current is detected by the output of the motor current detection means. An abnormality detection means for detecting an abnormality of the detection means; and a third switch connected in parallel with the current detection element, wherein the current control value is 0, An electric power steering apparatus, wherein the abnormality detecting means based on an output of said motor current detecting means in a state of ON the third switch is provided with a check function for detecting an abnormality of the output values. The electric power steering apparatus according to claim 1, wherein the check function is operated each time an ignition key is turned on. The detection value of the motor current detection means when the third switch is ON and the current control value is 0 is added to the actual current detection value as a correction value. Electric power steering device.

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