JP2021010222A - Current direction determination apparatus - Google Patents

Abstract

To provide a current direction determination apparatus capable of correctly determining a direction of a current flowing in an electric motor.SOLUTION: In a current direction determination process, it is determined that a direction of a current flowing in an electric motor M is a direction of right driving until a lapsed time exceeds a threshold value after an output of a control pulse signal to a switch SW1 was detected. In addition, it is determined that the direction of the current flowing in the electric motor M is a direction of left driving until the lapsed time exceeds the threshold value after ON of a switch SW due to an output of the control pulse signal to the switch SW2 was detected. When the control pulse signal is being output to neither the switch SW1 or switch SW2, it is determined that the direction of the current flowing in the electric motor M is the same as the last direction that was determined.SELECTED DRAWING: Figure 5

Description

The present invention relates to a current direction determination device.

Conventionally, an electric power steering device (EPS: Electric Power Steering), which is mounted on a vehicle and assists steering of a steering mechanism by the power of an electric motor, is known.

In the control of the electric power steering device, the direction and magnitude of the steering torque applied to the steering wheel (steering wheel) and the target current value according to the vehicle speed are set. Then, the electric motor is feedback-controlled based on the target current value. As a result, power according to the steering state is output from the electric motor, and the power is given to the steering mechanism as steering assist force.

On the other hand, a sub CPU other than the main CPU (Central Processing Unit) that executes such control monitors whether or not abnormal control that is an illegal assist is performed. In this fraudulent assist monitoring, the sub CPU determines the driving direction of the electric motor by the main CPU. In addition, the current flowing through the electric motor is detected. Then, from the drive direction and the current value of the electric motor, it is determined whether or not the abnormality control that is an illegal assist is performed.

For example, when the electric motor is a brushed DC motor, the H-bridge circuit 101 shown in FIG. 5 can be used as the drive circuit of the electric motor. The H-bridge circuit 101 is a circuit having a configuration in which a series circuit of the switches SW1 and SW2 and a series circuit of the switches SW3 and SW4 are provided in parallel. A DC power supply is connected to switches SW1 and SW3, and switches SW2 and SW4 are connected to ground via a resistor R. The electric motor M is connected to the connection points of the switches SW1 and SW2 and the connection points of the switches SW3 and SW4.

When the switches SW1 and SW4 are turned on and the switches SW2 and SW3 are turned off, a rightward current (right current) that rotates the electric motor M to the right flows through the electric motor M. On the other hand, when the switches SW2 and SW3 are turned on and the switches SW1 and SW4 are turned off, a leftward current (left current) that rotates the electric motor M to the left flows through the electric motor M.

Therefore, when the control pulse signal is output from the main CPU to the switch SW1, the drive direction of the electric motor M by the main CPU is to the right, and when the control pulse signal is not output from the main CPU to the switch SW1, The drive direction of the electric motor M by the main CPU is to the left. From this, the sub CPU detects the edge of the control pulse signal output from the main CPU to the switch SW1, and when the edge is detected, it is determined that the drive direction of the electric motor M is the right direction. When the edge is not detected, it is determined that the drive direction of the electric motor M is the left direction.

Further, the sub CPU detects the current flowing through the resistor R. However, the value of the detected current is not marked according to the direction of the current flowing through the electric motor M. Therefore, for example, when the sub CPU determines that the drive direction of the electric motor M is in the right direction, a positive sign is given to the current value, and when it is determined that the drive direction is in the left direction, the sub CPU gives a positive sign. The current value is marked with a negative sign. Then, if the current value with the sign is a normal value, it is determined that the abnormal control that becomes the illegal assist is not performed, and if the current value with the sign is an abnormal value, the abnormal assist is performed. It is determined that abnormal control is being performed.

JP-A-2016-208595

However, immediately after the output of the control pulse signal from the main CPU to the switch SW1 is stopped, a right current is flowing through the electric motor M. At this time, if the drive direction of the electric motor M is determined and the current value is detected, the sub CPU does not detect the edge of the control pulse signal to the switch SW1, so that the drive direction of the electric motor M is determined to be the left direction. Then, according to this determination, the current value is given a negative sign even though the current value is the right current value. Even if the current value is a normal value as the right current value, it may show an abnormal value as the current value with a negative sign. In this case, it is erroneously determined that abnormal control that is an illegal assist is being performed.

An object of the present invention is to provide a current direction determining device capable of accurately determining the direction of a current flowing through an electric motor.

In order to achieve the above object, the current direction determination device according to the present invention has a first switch that is turned on when the electric motor is driven to the right and turned off when the electric motor is not driven, and a first switch that is turned on when the electric motor is driven to the left. A current is supplied to the electric motor from a drive circuit including a second switch that is turned off when not driven, and the first switch is turned on, the first switch and the second switch are turned off, and the second switch is turned on at a predetermined cycle. A device that determines the direction of the current flowing through the electric motor, the first timer that measures the elapsed time from the on of the first switch, and the second that measures the elapsed time from the on of the second switch. When both the timer and the measurement time by the first timer and the measurement time by the second timer are 0, it is determined that the electric motor is in the non-driving state, and the measurement time by the first timer is set to a predetermined cycle or longer. When it is below the threshold value, it is determined that the electric motor is in the right drive state, and when the measurement time by the second timer is below the threshold value, the first determination means and the first determination means that determine that the electric motor is in the left drive state. When the determination means determines that the electric motor is in the right drive state, the direction of the current flowing through the electric motor is determined to be the right drive direction, and the first determination means determines that the electric motor is in the left drive state. In this case, the direction of the current flowing through the electric motor is determined to be the left drive direction, and when the first determination means determines that the electric motor is in the non-drive state, the direction of the current flowing through the electric motor is the previous direction. A second determination means for determining the same direction as the determination direction is included.

According to this configuration, it is determined that the direction of the current flowing through the electric motor is the right drive direction until the elapsed time from the on of the first switch exceeds the threshold value. Further, it is determined that the direction of the current flowing through the electric motor is the left drive direction until the elapsed time from the on of the second switch exceeds the threshold value. When both the first switch and the second switch are off, it is determined that the direction of the current flowing through the electric motor is the same as the direction previously determined. As a result, it is possible to prevent the direction of the current flowing through the electric motor from being erroneously determined immediately after each of the first switch and the second switch is turned off, and it is possible to accurately determine the direction of the current flowing through the electric motor.

According to the present invention, the direction of the current flowing through the electric motor can be accurately determined.

It is a figure which shows the structure of the motor control device to which the current direction determination device which concerns on one Embodiment of this invention is applied. It is a flowchart which shows the flow of the current direction determination processing. It is a truth table A used in the current direction determination process. It is a truth table B used in the current direction determination process. It is a circuit diagram which shows the structure of an H bridge.

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

<Motor control device>
FIG. 1 is a diagram showing a configuration of a motor control device 1 to which the current direction determination device according to the embodiment of the present invention is applied.

The motor control device 1 controls, for example, the electric motor M, which is mounted on a vehicle and is a power source of a steering assist force of the electric power steering device that assists the steering of the steering mechanism.

The motor control device 1 includes a drive circuit (motor driver) 2 for driving the electric motor M. The electric motor M is a DC motor with a brush, and the drive circuit 2 includes an H-bridge circuit. The configuration of the H-bridge circuit is the configuration shown in FIG. 5, and is as described above. Therefore, the description thereof will be omitted here. Further, in the following description, it is assumed that the configuration shown in FIG. 5 is the configuration of the drive circuit 2, and the reference reference numerals shown in FIG. 5 are used as they are.

The motor control device 1 includes a main CPU 3 and a sub CPU 4. The main CPU 3 and the sub CPU 4 are built in, for example, individual microcomputers (microcontroller units). The microcomputer further incorporates a non-volatile memory such as a flash memory and a volatile memory such as a DRAM (Dynamic Random Access Memory).

The main CPU 3 controls the electric motor M. Specifically, the main CPU 3 sets the direction and magnitude of the steering torque applied to the steering wheel of the vehicle, and the target current value according to the vehicle speed. Then, a control pulse signal having a duty corresponding to the target current value is output to the drive circuit 2 so that the current of the target current value is supplied to the electric motor M. When the electric motor M is driven in the right direction (the direction in which the steering assist force in the right direction is applied to the steering mechanism), the main CPU 3 outputs a control pulse signal to the switches SW1 and SW4. On the other hand, when the electric motor M is driven in the left direction (the direction in which the steering assist force in the left direction is applied to the steering mechanism), the main CPU 3 outputs a control pulse signal to the switches SW2 and SW3. As a result, power according to the steering state is output from the electric motor M, and the power is given to the steering mechanism as a steering assist force.

Therefore, if an abnormality occurs in the control of the electric motor M due to a runaway of the main CPU 3, a steering assist force contrary to the operation of the steering wheel may be applied to the steering mechanism. Therefore, the sub CPU 4 monitors whether or not abnormal control that is an illegal assist is performed. For fraudulent assist monitoring, the sub CPU 4 samples signals given from the main CPU 3 to the switches SW1 and SW2 of the drive circuit 2. Further, the sub CPU 4 detects the value of the current flowing through the resistor R of the drive circuit 2, that is, the value of the current flowing through the electric motor M (hereinafter, referred to as “motor current value”).

Further, the sub CPU 4 determines the direction of the current flowing through the electric motor M by the current direction determination process described below. When it is determined that the direction of the current is the right direction for rotating the electric motor M to the right, the motor current value is given a positive sign and the direction of the current is the right direction for rotating the electric motor M to the right. If it is determined that the motor current value is, a negative sign is added to the motor current value. If the coded current value is a normal value, the sub CPU 4 determines that the abnormal control for illegal assist is not performed, and if the signed current value is an abnormal value, the sub CPU 4 is illegal assist. It is determined that abnormal control is being performed.

When the switches SW1 to SW4 of the drive circuit 2 are composed of semiconductor devices, for example, a P-channel MOSFET is adopted for the switches SW1 and SW3, and an N-channel MOSFET is used for the switches SW2 and SW4. Will be adopted.

<Current direction determination processing>
FIG. 2 is a flowchart showing the flow of the current direction determination process executed by the sub CPU 4. FIG. 3 is a truth table A used in the current direction determination process. FIG. 4 is a truth table B used in the current direction determination process.

When the interrupt timing at a fixed cycle or the timing immediately before the A / D conversion arrives, the sub CPU 4 executes the current direction determination process shown in FIG. The constant cycle is, for example, a sampling cycle in which the sub CPU 4 samples signals given to the switches SW1 and SW2 of the drive circuit 2. The main CPU 3 has a right drive state in which the control pulse signal is output to the switches SW1 and SW4, a left drive state in which the control pulse signal is output to the switches SW2 and SW3, and a control pulse signal in a constant drive switching cycle (predetermined cycle). Switch to the non-driving state that does not output. The sampling cycle is set to less than 1/2 of the drive switching cycle. The A / D conversion is conversion of the current flowing through the resistor R of the drive circuit 2 into a digital value (detection of the motor current value) by the sub CPU 4, and is executed at a constant detection cycle.

In the current direction determination process, first, the signals given to the switches SW1 and SW2 of the drive circuit 2 are sampled. Then, the rising or falling edge of the signal is detected. When an edge is detected in the signal given to the switch SW1, the control pulse signal is output from the main CPU 3 to the switch SW1 in the right drive state, and the drive direction of the electric motor M is the right direction (right drive direction). Can be determined. When an edge is detected in the signal given to the switch SW2, the control pulse signal is output from the main CPU 3 to the switch SW2 in the left drive state, and the drive direction of the electric motor M is the left direction (left drive direction). Can be determined to be. When the edge is not detected in the signals given to the switches SW1 and SW2, it can be determined that the control pulse signal is not output from the main CPU 3 and the state is not driven. For control purposes, the control pulse signals are not given to the switches SW1 and SW2 at the same time, so that no edge is detected in both of the signals given to the switches SW1 and SW2.

As shown in FIG. 1, a right timer 5 and a left timer 6 are connected to the sub CPU 4. When an edge is detected in the signal given to the switch SW1, the right timer 5 is started, and the measurement of the elapsed time by the right timer 5 is started. When an edge is detected in the signal given to the switch SW2, the left timer 6 is started, and the measurement of the elapsed time by the left timer 6 is started.

After that, the measured value of the right timer 5 (hereinafter referred to as “right timer value”) and the measured value of the left timer 6 (hereinafter referred to as “left timer value”) are acquired. Then, with reference to the truth table A shown in FIG. 3, the drive direction of the electric motor M is determined from the right timer value and the left timer value (step S1).

The content of the truth table A shown in FIG. 3 is an example in the case where a predetermined cycle, that is, a drive switching cycle is 50 μs. According to the contents of the truth table A, for example, when the right timer value is in the range of 0 to 55 μs and the left timer value is 0 μs, it is determined that the drive direction of the electric motor M is the right drive direction. When the right timer value is 0 μs and the left timer value is in the range of 0 to 55 μs, it is determined that the drive direction of the electric motor M is the left drive direction. When both the left timer value and the right timer value are 0 μs, it is determined that the electric motor M is in the non-driving state. Other combinations of the right timer value and the left timer value do not exist unless some abnormality has occurred, but the drive direction is determined according to the combination of the right timer value and the left timer value according to the truth table A. Will be done. When the electric motor M is in the non-driving state, the driving direction thereof is defined as the “non-driving direction”.

After the drive direction is determined, it is determined whether or not the timing is immediately before the A / D conversion (step S2).

Then, when the current current direction determination process is started at the timing immediately before the A / D conversion (YES in step S2), the truth table B shown in FIG. 4 is referred to and the determination is made in the previous current direction determination process. The direction of the current flowing through the electric motor M is determined from the driven direction (hereinafter referred to as "previous drive direction") and the drive direction determined by the current direction determination process (hereinafter referred to as "current drive direction"). It is determined (step S3).

For example, when the previous drive direction is the right drive direction and the current drive direction is the right drive direction, it is determined that the direction of the current flowing through the electric motor M is the right direction (right current). When the previous drive direction is the right drive direction and the current drive direction is the non-drive direction, it is determined that the direction of the current flowing through the electric motor M is the right direction (right current). When the previous drive direction is the right drive direction and the current drive direction is the left drive direction, it is determined that the direction of the current flowing through the electric motor M is the left direction (left current). Further, when the previous drive direction is the left drive direction and the current drive direction is the right drive direction, it is determined that the direction of the current flowing through the electric motor M is the right direction (right current). When the previous drive direction is the left-right drive direction and the current drive direction is the non-drive direction, it is determined that the direction of the current flowing through the electric motor M is the left direction (left current). When the previous drive direction is the left drive direction and the current drive direction is the left drive direction, it is determined that the direction of the current flowing through the electric motor M is the left direction (left current).

On the other hand, when the timing is not immediately before the A / D conversion, that is, when the current direction determination process is started at the interrupt timing (NO in step S2), the process of determining the direction of the current flowing through the electric motor M (step S3). Is skipped. If the current current direction determination process is not started at the timing immediately before the A / D conversion, the motor current value is newly added until the current direction determination process is executed at the timing immediately before the next A / D conversion. It will not be detected. Therefore, by skipping the process of determining the current direction, it is possible to prevent the process from being unnecessarily executed, and it is possible to reduce the load on the sub CPU 4.

After that, it is determined whether or not the drive direction is the non-drive direction this time (step S4). When the drive direction is the non-drive direction this time (YES in step S4), the previous drive direction continues as it is and is held as the previous drive direction (step S5). If the drive direction this time is not the non-drive direction (NO in step S4), the drive direction this time is held as the previous drive direction (step S6). Then, the current direction determination process is completed.

<Effect>
According to this current direction determination process, it is an example of a threshold value in which the elapsed time from the detection of the on of the switch SW1 due to the output of the control pulse signal from the main CPU 3 to the switch SW1 is set to be equal to or longer than the drive switching cycle. Until it exceeds 55 μs, it is determined that the direction of the current flowing through the electric motor M is the right drive direction. Further, until the elapsed time from the detection of the on of the switch SW2 due to the output of the control pulse signal from the main CPU 3 to the switch SW2 exceeds 55 μs, the direction of the current flowing through the electric motor M is the left drive direction. It is determined that there is. When no control pulse signal is output to both switches SW1 and SW2 and both switch SW1 and switch SW2 are off, it is determined that the direction of the current flowing through the electric motor M is the same as the direction previously determined. Will be done. As a result, it is possible to prevent the direction of the current flowing through the electric motor M from being erroneously determined immediately after each of the switch SW1 and the switch SW2 is turned off, and it is possible to accurately determine the direction of the current flowing through the electric motor M. As a result, it is possible to accurately determine whether or not abnormal control that is an illegal assist is performed.

<Modification example>
Although one embodiment of the present invention has been described above, the present invention can also be implemented in other embodiments.

For example, it is assumed that the signals given to the switches SW1 and SW2 of the drive circuit 2 are sampled, but instead of the signal given to the switch SW1, the signal given to the switch SW4 is sampled and replaced with the signal given to the switch SW2. Then, the signal given to the switch SW3 may be sampled and the same processing as described above may be executed.

In the above-described embodiment, the motor control device 1 controls the electric motor M of the electric power steering device. However, the motor control device 1 may control an electric motor provided in a device other than the electric power steering device.

In addition, various design changes can be made to the above-mentioned configuration within the scope of the matters described in the claims.

2: Drive circuit 4: Sub CPU (current direction determination device)
5: Right timer (1st timer)
6: Left timer (second timer)
M: Electric motor SW1: Switch (1st switch)
SW2: Switch (second switch)

Claims (1)

From a drive circuit including a first switch that is turned on when the electric motor is driven to the right and turned off when the electric motor is not driven, and a second switch that is turned on when the electric motor is driven to the left and turned off when the electric motor is not driven. The direction of the current flowing through the electric motor in a configuration in which a current is supplied to the electric motor and the first switch is turned on, the first switch and the second switch are turned off, and the second switch is turned on at a predetermined cycle. It is a device to judge
A first timer that measures the elapsed time from the on of the first switch, and
A second timer that measures the elapsed time from the on of the second switch, and
When both the measurement time by the first timer and the measurement time by the second timer are 0, it is determined that the electric motor is in the non-driving state, and the measurement time by the first timer is set to the predetermined cycle or more. When it is equal to or less than the threshold value, it is determined that the electric motor is in the right drive state, and when the measurement time by the second timer is equal to or less than the threshold value, it is determined that the electric motor is in the left drive state. Judgment means and
When the first determination means determines that the electric motor is in the right drive state, the direction of the current flowing through the electric motor is determined to be the right drive direction, and the first determination means causes the electric motor to move to the left. When it is determined that the electric motor is in the driving state, the direction of the current flowing through the electric motor is determined to be the left driving direction, and when the first determining means determines that the electric motor is in the non-driving state, A current direction determination device including a second determination means for determining the direction of the current flowing through the electric motor in the same direction as the previous determination direction.

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