JP2006290146A - Control device of electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of an electric power steering device capable of certainly carrying out fail judgement by offsetting output voltage of an electric current detection circuit by varying standard voltage by a microcomputer, etc. by providing the standard voltage in the electric current detection circuit of a motor and setting this offset output voltage by regarding it as the output voltage when a steering wheel is at a neutral position. <P>SOLUTION: This control device of the electric power steering device devised to feedback-control working of the motor in accordance with a motor electric current detected by the electric current detection circuit of the motor is furnished with the electric current detection circuit, a shunt resistor to detect the motor electric current and a voltage detection circuit to detect both end voltage of the shunt resistor, and is devised to offset the output voltage of the electric current detection circuit, to set the standard voltage to recognize the voltage as the steering wheel neutral position and to judge it as failure when the output voltage becomes less than a threshold value. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control device for an electric power steering device (hereinafter referred to as EPS) having a motor that generates a steering assist force for a steering system of a vehicle.

  The EPS mounted on the vehicle is configured to urge the driving force of the motor to assist the steering shaft or the rack shaft by a transmission mechanism such as a gear or a belt via a reduction gear. The EPS controls the assist torque based on detection signals from a torque sensor, a vehicle speed sensor, and the like.

  Here, the general configuration of the EPS will be described with reference to FIG. 7. The column shaft 52 of the steering handle 51 is connected to a tie rod 56 of a steering wheel via a reduction gear 53, universal joints 54 a and 54 b, and a pinion rack mechanism 55. It is connected to. The column shaft 52 is provided with a torque sensor 57 that detects the steering torque of the steering handle 51, and a motor 58 that assists the steering force of the steering handle 51 is connected to the column shaft 52 via the reduction gear 53. ing. The control unit 59 that controls the EPS is supplied with electric power from the battery 60 and receives an ignition signal from the ignition key 61. The control unit 59 calculates the steering assist command value I of the assist command based on the steering torque T detected by the torque sensor 57 and the vehicle speed V detected by the vehicle speed sensor 63, and the calculated steering assist command value I Based on this, the current supplied to the motor 58 is controlled.

As an EPS control device of this type, for example, as shown in Patent Document 1, it is provided with feedback control means for feedback controlling the operation of a motor based on a motor current value detected by a current detection circuit, and a detection signal from a torque sensor. When there is no power, the power supply to the motor drive circuit is stopped, and when the motor current value detected by the current detection circuit is within the predetermined range, the feedback control is prohibited and the motor drive control caused by the offset of the current detection circuit In this example, only the PWM duty value is prevented from increasing.
JP 2003-81110 A

  However, for example, when the handle is in the neutral position, there is no detection signal from the torque sensor and power supply to the motor drive circuit is stopped, so that no current flows through the motor and the output voltage of the current detection circuit becomes 0V. . Therefore, even if the current detection circuit has a ground fault at this time, the output voltage is 0 V, and it cannot be distinguished from the case where the handle is in the neutral position, and the fail determination cannot be performed accurately.

  In addition, when the assist is started, the torque value input by, for example, the reaction force (kickback) of the tire is not constant, and hunting may be caused by the steering wheel. At that time, since the output voltage of the current detection circuit is 0 V at the moment when the torque input returns to the neutral state, it is regarded as normal and the fail determination cannot be performed accurately.

Accordingly, an object of the present invention is to provide a reference voltage in the motor current detection circuit so that the reference voltage can be made variable by a microcomputer or the like. The output voltage of the current detection circuit is offset, and the offset output voltage is It is assumed that the handle is regarded as a value at the neutral position, and the fail determination can be reliably performed when the value is equal to or lower than the offset voltage.

  The object of the present invention is to provide a control device for an electric power steering apparatus in which the operation of the motor is feedback controlled based on the motor current detected by the motor current detection circuit. A shunt resistor for detection and a voltage detection circuit for detecting the voltage across the shunt resistor are provided. The output voltage of the current detection circuit is offset, and a reference voltage is set so that the voltage is recognized as a handle neutral position. In addition, this is achieved by including a control unit that determines that a failure occurs when the output voltage is equal to or lower than a threshold value.

  In addition, the object is achieved by the control unit determining that a failure occurs when the state where the output voltage is lower than the threshold exceeds a preset time.

  Further, the above object is effectively achieved by the control unit changing the reference voltage arbitrarily based on a control signal from the microcomputer.

  As described above, according to the control device for the electric power steering apparatus according to the present invention, the reference voltage of the current detection circuit is arbitrarily set and the output voltage of the current detection circuit is offset and set. As a result, the offset output voltage value is regarded as an initial value (handle neutral position), and assist control is performed. For example, when the reference voltage is set to be offset to 0.5 V and the current detection circuit has a ground fault, the output voltage of the current detection circuit is 0 V (the same potential as GND). The voltage is lower than 0.5V, and the fail determination can be performed accurately.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration when a control device for an electric power steering apparatus according to the present invention is applied to a vehicle. The control unit 10 is based on a microcomputer 11, a motor drive circuit 12 including a plurality of switching elements, a current detection circuit 13 for detecting a current flowing through the motor 30, and a control signal from the microcomputer 11. And a reference voltage control unit 40 for arbitrarily setting the reference voltage.

  The microcomputer 11 includes a CPU 21, an ADC 22 that converts an analog signal into a digital signal, an input interface 23, an output interface 24, and a memory 25 such as a ROM or a RAM.

  The CPU 21 sends an assist signal for the motor 30 to the motor drive circuit 12 via the output interface 24 based on the vehicle speed signal from the vehicle speed sensor 26 via the input interface 23. Here, in the motor drive circuit 12, the rotation direction of the motor 30 is switched by a switching operation of conduction / non-conduction of the switching element formed of the MOSFET based on the assist signal. Further, the ADC 22 receives a torque signal from the torque sensor 28, converts the analog value into a digital value, and sends it to the CPU 21.

  Here, as shown in FIG. 2, the motor drive circuit 12 has a bridge circuit composed of four switching elements 41 to 44 as a main component, and one end of the resistor 31 is connected to a battery 45 mounted on the vehicle. The other end is connected to each drain of the switching elements 41 and 42. The sources of the switching elements 41 and 42 are connected to the drains of the switching elements 43 and 44, respectively, and the ends of the motor 30 are connected between the switching elements 41 and 43 and between the switching elements 42 and 44, respectively. Thus, the rotation direction of the motor 30 is switched. The resistor 31 may be arranged at the lower stage of the motor drive circuit 12 as shown in FIG. 3, or may be arranged at the upper stage as shown in FIG.

  Further, as shown in FIG. 2, the current detection circuit 13 is connected to the motor drive circuit 12 and is connected to a resistor (shunt resistor) 31 for detecting the motor current, and to both ends of the resistor 31 to obtain the motor current. A current detection amplifier 32 for detection, and an operational amplifier 33 that receives an output from the current detection amplifier 32 and a reference voltage generated by the reference voltage control unit 40 are provided. The reference voltage control unit 40 sends a reference voltage that is offset by an arbitrary value to the current detection circuit 13 so that the reference voltage can be changed arbitrarily.

  Moreover, FIG. 4 shows what detected the change of the output voltage supplied to the motor 30 using the conventional control apparatus. When the assist is started, the output voltage increases. However, when the steering wheel returns to the neutral position and the detection signal from the torque sensor disappears, the output voltage becomes 0V. Therefore, even if an abnormality such as a ground fault occurs in the current detection circuit 13 at that time, even if the output voltage decreases to 0 V, it is accurately determined whether it is a failure or the handle is in the neutral position. I couldn't. For example, when assisting a motor, the input torque value does not become constant due to the reaction force of the tire. Therefore, even if hunting occurs, the output voltage of the current detection circuit 13 is 0 V at the moment when the handle returns to the neutral position, so that it is determined to be normal.

  On the other hand, FIG. 5 shows a change detected in the output voltage supplied to the motor 30 using the control device of the present invention. According to this figure, the reference voltage is offset and set to 0.5 V, and this voltage value is recognized as the handle neutral position. As a result, if the output voltage of the current detection circuit 13 becomes smaller than the reference voltage, it can be determined that there is a failure, and the fail determination becomes accurate.

  In addition, the time during which the output voltage of the current detection circuit 13 is lower than the reference voltage (0.5 V) is measured by a timer. Is possible. In other words, the output voltage may be lower than the reference voltage although it is instantaneous in time due to external noise or the back electromotive voltage of the motor. Therefore, in order to accurately discriminate between failure and mere noise, if the time that is below the reference voltage is set in advance as a threshold, it is determined that the failure occurs if the time exceeds the reference voltage and falls below the reference voltage. Can do. Therefore, the fail determination becomes more accurate.

  Next, failure diagnosis operation will be described with reference to FIG.

  First, in step S1, the timer counter is reset (t = 0), in step S2, the output voltage V of the current detection circuit 13 is detected, and in step S3, is the output voltage V larger than a preset reference voltage? It is determined whether or not.

  If the output voltage V is greater than the reference voltage (V ≧ reference voltage) in step S3, it is determined as normal and the process returns to step S1. On the other hand, when the output voltage V is smaller than the reference voltage (V <reference voltage) in step S3, the process proceeds to step S4, and the elapsed time t is counted by a timer.

  Further, in step S5, it is determined whether or not the elapsed time t has passed a predetermined set time (threshold value). If not, the process returns to step S2 and the operations from step S2 to step S5 are repeated. . Then, when the elapsed time t has passed the set time (threshold value) in step S5, it is determined as a failure in step S6.

  Therefore, in the above embodiment, the output voltage of the current detection circuit 13 is offset, and the reference voltage (0.5 V) is set so that the voltage is recognized as the handle neutral position. Then, when the output voltage of the current detection circuit 13 becomes smaller than the reference voltage, it is determined that a failure has occurred. Thus, for example, when the reference voltage is set to 0.5 V, the microcomputer side recognizes this value (0.5 V) as the handle neutral position and diagnoses the failure. Therefore, the output voltage of the current detection circuit 13 does not fall below the reference voltage unless there is a failure, external noise, or motor back electromotive voltage. Therefore, the input voltage to the microcomputer side exceeds the reference voltage over a preset time. When the value is less than, it can be determined that the current detection circuit is out of order. As a result, even when the output voltage of the current detection circuit becomes 0 V as in the prior art, there is no erroneous determination that is regarded as normal in the handle neutral state, and the fail determination becomes accurate.

  In addition, the reference voltage value to be offset is controlled, the reference voltage at the time of normal operation and that at the time of circuit failure diagnosis is changed to a different value, and the failure is determined based on the offset set reference voltage. It may be. For example, in the normal operation state, the reference voltage outputs an offset of 0.5 V of the reference voltage control unit 40, and when used for diagnosis of the current detection circuit 13, the reference voltage is changed to a different voltage such as 2.5 V. Thus, it is possible to determine the failure of the circuit (current detection circuit) by appropriately switching the reference voltage. Also in this case, the same operation and effect as the above-described embodiment are obtained.

  In this embodiment, an H-bridge circuit that is a drive circuit for a motor with a brush is used. However, an inverter circuit that is a drive circuit for a brushless motor may be used, and the same operations and effects as in this embodiment are achieved. .

It is a block diagram which shows schematic structure of the control apparatus of the electric power steering apparatus which concerns on this invention. It is the schematic block diagram which has arranged the motor drive circuit in the lower stage of the current detection circuit. FIG. 3 is a diagram corresponding to FIG. 2, and is a schematic block diagram in which a motor drive circuit is provided in the upper stage of the current detection circuit. It is a figure which shows the change of the output voltage of a current detection circuit using the conventional apparatus. It is a figure which shows the change of the output voltage of a current detection circuit using the apparatus of this invention, and is a figure corresponding to FIG. It is a flowchart explaining the control operation of failure diagnosis. It is a figure showing an example of composition of a general electric power steering device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Microcomputer 12 Motor drive circuit 13 Current detection circuit 30 Motor 31 Resistance 32 Current detection amplifier 33 Operational amplifier 40 Reference voltage control part

Claims (3)

In the control device for the electric power steering device, the operation of the motor is feedback controlled based on the motor current detected by the current detection circuit of the motor.
A shunt resistor for detecting a motor current in the current detection circuit;
A voltage detection circuit for detecting a voltage across the shunt resistor,
A control unit that offsets the output voltage of the current detection circuit, sets a reference voltage so that the voltage is recognized as a handle neutral position, and determines that a failure occurs when the output voltage falls below a threshold value. An electric power steering apparatus control device comprising:   2. The control device for an electric power steering apparatus according to claim 1, wherein when the state where the output voltage is lower than the threshold exceeds a preset time, the control unit determines that a failure has occurred.   The control device for an electric power steering apparatus according to claim 1, wherein the control unit arbitrarily changes the reference voltage based on a control signal from a microcomputer.

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