JP2009261090A - Motor controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost motor controller which detects the motor current with high accuracy. <P>SOLUTION: A motor controller controls the motor current in an H bridge circuit which switches the rotational direction of a motor, between the forward direction and reverse direction by any one of vertical drives, where PWM control is performed for both upper switching element and lower switching element, or bottom drive where PWM control is performed for only the lower switching element, by turning the upper switching element on. When the bottom drive characteristics 200, where the motor current increases for the duty ratio of PWM control is compared with the vertical drive characteristics 210, duty ratio of vertical drive is higher for the same motor current. The motor controller performs PWM control by vertical drive, when the motor current is smaller than a predetermined current value 230, and performs PWM control by bottom drive, when the motor current is larger than the predetermined current value 230. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a motor control device that switches the rotation direction of a motor with an H-bridge circuit.

  2. Description of the Related Art Conventionally, a motor control device that switches the direction of a motor current flowing through a motor by an H bridge circuit and switches the rotation direction of the motor to a normal rotation direction or a reverse rotation direction is known (see, for example, Patent Document 1).

In Patent Document 1, in the H-bridge circuit, the upper switching element installed between the motor and the power supply side is turned on, and the lower switching element installed between the motor and the ground side is PWM (Pulse Width Modulation). The current value of the motor current is controlled by the lower drive to be controlled. The motor current increases as the PWM control duty ratio increases, and the motor current decreases as the PWM control duty ratio decreases. In Patent Document 1, the motor current is detected by a current detection circuit in order to control the current value of the motor current flowing from the H bridge circuit to the motor.
JP 2002-238290 A

  Here, when the lower switching element is PWN controlled with the upper switching element turned on, the motor current detection waveform is detected by the current detection circuit when the motor current flows when the lower switching element is turned on from the off state. Noise occurs. When the duty ratio of the PWM signal is high as shown in FIG. 5A, the pulse width for turning on the lower switching element is smaller than when the duty ratio is low as shown in FIG. Since it is long, noise in the detected waveform of the motor current is attenuated while the motor current is flowing, and the detected waveform is stabilized. As a result, the motor current can be detected with high accuracy.

  On the other hand, as shown in FIG. 5B, when the duty ratio of the PWM signal is low, the pulse width for turning on the lower switching element is short. Noise may remain unattenuated. As a result, when the duty ratio of the PWM signal is low, there is a possibility that the motor current cannot be detected with high accuracy by the lower drive.

  If a circuit that quickly attenuates noise is used as the current detection circuit that detects the motor current, even when the duty ratio of the PWM signal is low, the noise is attenuated while the motor current is flowing to stabilize the detection waveform. I can. However, since such a current detection circuit is expensive, the manufacturing cost increases.

  The present invention has been made to solve the above problems, and an object thereof is to provide an inexpensive motor control device that detects motor current with high accuracy.

  According to the first to third aspects of the present invention, both the upper switching element installed between the motor and the power supply side and the lower switching element installed between the motor and the ground side are PWM-controlled. The motor current is PWM controlled by either the vertical drive or the lower drive that turns on the upper switching element and PWM controls the lower switching, and when the motor current is smaller than a predetermined current value, the vertical drive is performed. When the motor current is larger than the predetermined current value, the lower drive is performed.

  Here, as the duty ratio of PWM control increases, the motor current increases. When a motor current having the same current value is supplied, the duty ratio of the PWM signal applied to the switching element in the case of vertical driving is larger than the duty ratio of the PWM signal applied to the switching element in the case of lower side driving. There is. Therefore, when the motor current is smaller than the predetermined current value, the PWM control by the vertical drive is performed, thereby increasing the duty ratio of the PWM signal as much as possible and making the switching element on time as long as possible. Can flow. As a result, noise in the detected waveform of the motor current detected by the current detection circuit while the motor current is flowing is attenuated. As a result, when the motor current is smaller than the predetermined current value, the motor current value can be detected with high accuracy by the current detection circuit.

  On the other hand, when the motor current is larger than the predetermined current value and the duty ratio of the PWM signal is high, the motor current detected by the current detection circuit while the motor current is flowing even if the PWM control by the lower drive is performed. The detected waveform noise is attenuated. In the PWM control by the lower drive, only the lower switching element is PWM controlled with the upper switching element turned on, so that the power loss due to the switching is smaller than the PWM control by the upper and lower drive.

  Therefore, when the motor current is larger than the predetermined current value and the duty ratio of the PWM signal is high, the PWM control by the lower drive is performed. As a result, the motor current value can be detected with high accuracy by the current detection circuit, and the power loss can be reduced.

  In addition, since a simple method of switching between PWM control by vertical drive and lower drive is adopted, the motor current is smaller than a predetermined current value without using an expensive current detection circuit that quickly attenuates noise. In addition, the motor current can be detected with high accuracy by an inexpensive motor control device.

  According to the second aspect of the present invention, the motor current increases with respect to the duty ratio of the PWM control with respect to the lower drive characteristic in which the motor current increases at a substantially constant increase rate with respect to the duty ratio of the PWM control. The increase rate of vertical drive is lower than the increase rate of lower drive when the duty ratio of PWM control by vertical drive is lower than the predetermined duty ratio, and the duty ratio of PWM control by vertical drive is higher than the predetermined duty ratio Has a higher characteristic than the increase rate of the lower drive, and the predetermined current value for switching between the vertical drive and the lower drive is the range of the motor current when the duty ratio of the PWM control by the vertical drive is larger than the predetermined duty ratio Set in.

  In the range where the duty ratio of the PWM control by the vertical drive is lower than the predetermined duty ratio, the increase rate of the vertical drive is lower than the increase rate of the lower drive. In other words, in the vertical drive, in the range where the duty ratio of PWM control is lower than the predetermined duty ratio, the increase rate of the motor current is low even if the duty ratio of PWM control is increased. Therefore, the motor current is small in the range where the duty ratio of the PWM control by the vertical drive is lower than the predetermined duty ratio. As described above, even if the PWM control is performed by switching the vertical driving and the lower driving in a range where the motor current is small, it is difficult to control the motor current with high accuracy based on the detected motor current value.

  Therefore, as in the second aspect of the invention, the predetermined current value for switching between the vertical drive and the lower drive is set in a range where the duty ratio of the PWM control by the vertical drive is larger than the predetermined duty ratio. The motor current can be controlled by switching between the upper and lower drive and the lower drive within a large current range. Thereby, the motor current can be controlled with high accuracy based on the detected motor current value.

According to the third aspect of the present invention, the motor control device controls the current flowing through the motor for retracting the seat belt and for canceling the retract.
Thereby, the motor current value can be detected with high accuracy, and the restraining force of the seat belt that restrains the passenger can be controlled appropriately.

  The functions of the means provided in the present invention are realized by hardware resources whose functions are specified by the configuration itself, hardware resources whose functions are specified by a program, or a combination thereof.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
A motor control device according to an embodiment of the present invention is shown in FIG.
(Motor control device 10)
The motor control device 10 controls the current flowing in the motor 2 for retracting the seat belt and for retracting the seat belt. The motor 2 is a DC motor.

  The switching elements 20, 22, 30, and 32 are formed of, for example, a MOSFET (metal-oxide-semiconductor field-effect transistor), and constitute an H-bridge circuit as a current control circuit. The switching elements 20 and 30 installed between the power supply and the motor 2 correspond to the upper switching elements described in the claims, and the switching elements 22 and 32 installed between the motor 2 and the ground side are This corresponds to the lower switching element recited in the claims.

  The switching elements 20, 22, 30, and 32 constitute an H bridge circuit. In the H-bridge circuit, the switching element 20 and the switching element 32 are connected in series, and the switching element 30 and the switching element 22 are connected in series. The motor 2 is connected between a connection point where the switching element 20 and the switching element 32 are connected and a connection point where the switching element 30 and the switching element 22 are connected.

  The switching elements 20, 22, 30, and 32 are PWM-controlled by the MPU 50, thereby controlling the magnitude of the motor current flowing through the motor 2 and switching the current direction. When the direction of the current flowing through the motor 2 is switched, the motor 2 rotates in the forward direction or the reverse direction. When the duty ratio of PWM control is 0, the switching state of the switching elements 20, 22, 30, 32 is always off, and when the duty ratio of PWM control is 100, the switching elements 20, 22, 30, 32 The switching state is always on. The PWM control by the MPU 50 for the switching elements 20, 22, 30, 32 will be described later.

  A seat belt retractor (not shown) that transmits the rotational driving force of the motor 2 to the seat belt has a one-way clutch that is fastened when the motor 2 rotates forward and is released when the motor 2 rotates backward.

  When current flows through the switching elements 20 and 22 and the switching elements 30 and 32 are turned off, the motor 2 rotates in the forward rotation direction. When the motor 2 rotates in the forward direction, the seat belt is retracted by engaging the one-way clutch of the seat belt retractor.

  On the other hand, when the switching elements 20 and 22 are turned off and a current flows through the switching elements 30 and 32, the motor 2 rotates in the reverse direction with respect to the normal direction. When the motor 2 rotates in the reverse direction, the seat belt is pulled out once, and the one-way clutch of the seat belt retractor is released, thereby releasing the seat belt.

When all of the switching elements 20, 22, 30, 32 are turned off, the motor 2 does not rotate in either the forward rotation direction or the reverse rotation direction, and the seat belt is held.
The current detection circuit 40 includes a detection resistor 42 and an amplifier 44, and is installed between the switching elements 22 and 32 and the ground side. When a current flows through the motor 2, a potential difference is generated between both ends of the detection resistor 42, and this potential difference is amplified by the amplifier 44.

In the present embodiment, since the current flowing through the motor 2 is detected by the detection resistor 42 in the current detection circuit 40, the current detection circuit 40 can be realized with a simple configuration.
The MPU (Micro Processing Unit) 50 includes a microcomputer having a CPU, ROM, RAM, A / D converter, I / O port, communication interface, and the like. The MPU 50 functions as drive control means described below by a control program stored in the ROM.

(Drive control means)
The MPU 50 calculates the duty ratio of the PWM signal commanded to the switching elements 20, 22, 30, and 32 based on the rotation direction commanded to the motor 2 and the command current value passed to the motor 2.

  For example, when the MPU 50 receives an instruction from a detection device that detects that the distance to the vehicle ahead is closer than a predetermined distance via a communication line such as an in-vehicle LAN, the MPU 50 alerts the vehicle driver and In order to ensure safety, the drive circuit 52 is commanded to rotate the motor 2 in the forward direction, and the seat belt is retracted. When the distance from the preceding vehicle is greater than the predetermined distance, the MPU 50 instructs the drive circuit 52 to reverse the motor 2 and releases the seat belt.

  The MPU 50 detects the value of the current flowing through the motor 2 based on the detection signal of the current detection circuit 40 while the motor 2 is being driven. Then, based on the difference between the detected current value detected by the current detection circuit 40 and the command current value of the motor current passed through the motor 2 commanded to the H-bridge circuit, the MPU 50 applies the switching elements 20, 22, 30, 32 to each other. The duty ratio of the commanded PWM signal is feedback controlled.

  Here, the MPU 50 performs two types of PWM control on the switching elements 20, 22, 30, and 32, (1) vertical drive and (2) lower drive. 2A shows the switching state of the switching element in the vertical drive, and FIG. 2B shows the switching state of the switching element in the lower side drive.

(1) Vertical drive As shown in FIG. 2A, the upper switching element and the lower switching element, such as the switching elements 20 and 22 in the forward direction and the switching elements 30 and 32 in the reverse direction. PWM control is performed for both of these.

(2) Lower side drive As shown in FIG. 2B, the switching element 20 is always turned on in the forward rotation direction to perform PWM control of the switching element 22, and the switching element 30 is always turned on in the reverse direction. As described above, the switching element 32 is PWM-controlled so that the upper switching element is always turned on and the PWM control is performed only on the lower switching element.

  Here, when the motor 2 is rotated in the forward rotation direction, the motor current flowing in the motor 2 in the case of vertical driving with respect to the same duty ratio of PWM control is shown in FIG. The motor current flowing through the motor 2 is shown in FIG. It can be seen that when the duty ratio is the same, a larger current flows in the lower drive. Note that the motor current shown in FIG. 3 indicates not the output signal of the current detection circuit 40 but the current flowing in the motor 2.

FIG. 4 shows the relationship between the duty ratio and the motor current in the vertical drive and the lower drive. The motor current shown in FIG. 4 is an average value of the motor current.
The lower drive characteristic 200 has an increase rate at which the motor current increases at a substantially constant rate with respect to the duty ratio of the PWM control. On the other hand, the vertical drive increase rate characteristic 210 is lower than the lower drive increase rate when the PWM control duty ratio is lower than the predetermined duty ratio 220, and the PWM control duty ratio is higher than the predetermined duty ratio 220. Is higher than the increase rate of the lower drive. However, as described above, if the duty ratio is the same, the motor current in the lower drive is larger than that in the vertical drive. In other words, if the motor current is the same, the vertical drive has a higher duty ratio than the lower drive.

  Here, when the motor current is low and the duty ratio is low, when the PWM control of the motor current is performed by the lower drive, the pulse width for turning on the PWM controlled switching element is larger than when the motor current is PWM controlled by the vertical drive. short. As a result, as shown in FIG. 5B, before the PWM signal is turned on from off, the noise generated in the detection waveform for detecting the motor current by the current detection circuit 40 is attenuated, and the detection waveform is stabilized. The PWM signal is turned off from on. As a result, the MPU 50 cannot detect the motor current with high accuracy based on the output signal of the current detection circuit 40.

  Therefore, when the command current value of the motor current commanded to the H bridge circuit by the PWM control is smaller than the predetermined current value 230, the MPU 50 performs the PWM control by the vertical drive. The predetermined current value 230 is set in a range in which the duty ratio of PWM control is higher than the predetermined duty ratio 220 in the vertical drive characteristic 210.

  Since the up / down driving has a higher duty ratio than the lower driving for the same motor current value, the pulse width for turning on the PWM controlled switching element becomes longer. As a result, as shown in FIG. 5A, the PWM signal is turned on from off, and the noise generated in the detection waveform that rises when the motor current is detected by the current detection circuit 40 is detected while the PWM signal is on. As a result, the detected waveform becomes stable. As a result, based on the stable output signal of the current detection circuit 40, the MPU 50 can detect the motor current with high accuracy.

  On the other hand, when the command current value of the motor current is larger than the predetermined current value 230, the PWM control is performed by the lower drive instead of the vertical drive. When the command current value of the motor current is larger than the predetermined current value 230, the duty ratio in the lower drive is also increased, so that the PWM signal is turned on from off, and the current detection circuit 40 generates a detection waveform for detecting the motor current. Since the noise is attenuated while the PWM signal is on, the detected waveform is stabilized. Thereby, based on the output signal of the stable current detection circuit 40, the MPU 50 can detect the motor current with high accuracy.

  In the lower drive, since the upper switching element is always on, power loss due to switching is smaller than in the vertical drive. Therefore, when the command current value of the motor current is larger than the predetermined current value 230, the motor current can be detected with high accuracy and the power loss can be reduced by performing the PWM control by the lower drive.

When the command current value of the motor current is the predetermined current value 230, either the vertical drive or the lower drive PWM control may be performed.
According to the embodiment described above, when the command current value of the motor current is smaller than the predetermined current value 230, the PWM control is performed by the vertical drive in which the duty ratio of the PWM signal is larger than the lower drive. Thereby, the motor current can be detected with high accuracy by the current detection circuit 40 in a state where the detection waveform is stable.

  On the other hand, when the command current value of the motor current is larger than the predetermined current value 230, the duty ratio of the PWM signal is increased even in the lower drive, so the PWM control is performed in the lower drive. As a result, the motor current can be detected with high accuracy by the current detection circuit 40 in a state where the detection waveform is stable, and power loss due to switching can be reduced as compared with vertical driving.

  Moreover, since a simple method of switching the PWM control by the vertical drive and the lower drive based on whether the motor current is smaller or larger than the predetermined current value is adopted, it is expensive to quickly attenuate the noise. Even when the motor current is smaller than the predetermined current value without using the current detection circuit, the motor current can be detected with high accuracy by the inexpensive motor control device 10.

[Other Embodiments]
In the above embodiment, in the vertical drive characteristic 210, the predetermined current value 230 is set in a range where the duty ratio of PWM control is higher than the predetermined duty ratio 220, and the vertical drive and the lower drive are switched at the predetermined current value 230. It was. On the other hand, when there is a request for switching between vertical driving and lower driving on the low current side of the motor current, the duty ratio of PWM control is within a range lower than the predetermined duty ratio 220 in the vertical driving characteristic 210. A predetermined current value may be set.

  In the above embodiment, when the motor 2 rotates in the reverse direction, the one-way clutch of the seat belt retractor is released and the seat belt retracting is released. On the other hand, when the motor 2 rotates in the reverse direction, the seat belt may be pulled out according to the rotation amount of the motor 2 to release the seat belt.

  Moreover, in the said embodiment, the control apparatus of the motor 2 used for drawing in of a seatbelt and cancellation of drawing-in was demonstrated. On the other hand, as long as the forward rotation control and the reverse rotation control for the motor are performed by the H-bridge circuit, the present invention is applied to any use, not limited to seat belt retracting and retracting release. Thus, the motor current can be detected with high accuracy.

  In the above embodiment, the function of the drive control means is realized by the MPU 50 whose function is specified by the control program. On the other hand, at least a part of the functions of the above means may be realized by hardware whose function is specified by the circuit configuration itself.

  As described above, the present invention is not limited to the above-described embodiment, and can be applied to various embodiments without departing from the gist thereof.

The circuit block diagram which shows the motor control apparatus by this embodiment. (A) is up-down drive, (B) is explanatory drawing which shows the switching state of the switching element by a lower side drive. (A) is a time chart which shows the switching state and motor current of the switching element by a vertical drive, (B) by a lower side drive. The characteristic view which shows the relationship between the duty ratio in a vertical drive and a lower side drive, and a motor current. (A) is an explanatory view showing a detection waveform and a PWM signal when the duty ratio is high, and (B) is a detection waveform when the duty ratio is low.

Explanation of symbols

2: motor, 10: motor control device, 20, 30: switching element (upper switching element, H bridge circuit), 22, 32: switching element (lower switching element, H bridge circuit), 40: current detection circuit, 42 : Detection resistor, 44: amplifier, 50: MPU (drive control means), 220: predetermined duty ratio, 230: predetermined current value

Claims (3)

In the motor control device that controls the current flowing through the motor,
An upper switching element installed between the motor and the power supply side; and a lower switching element installed between the motor and the ground side, the motor being driven by the upper switching element and the lower switching element. An H bridge circuit that controls the motor current flowing through the motor and switches the rotation direction of the motor to the normal rotation direction or the reverse rotation direction;
A current detection circuit for detecting the motor current;
The motor current is PWMed by either a vertical drive that PWM-controls both the upper switching element and the lower switching element or a lower drive that turns on the upper switching element and PWM-controls the lower switching element. Control, and when the motor current is smaller than a predetermined current value, the vertical drive is performed, and when the motor current is larger than the predetermined current value, the drive control means for performing the lower drive,
A motor control device comprising: In contrast to the characteristic of the lower drive in which the motor current increases at a substantially constant increase rate with respect to the duty ratio of the PWM control, the increase in the vertical drive in which the motor current increases with respect to the duty ratio of the PWM control The rate is lower than the increase rate of the lower drive when the duty ratio of the PWM control by the vertical drive is lower than a predetermined duty ratio, and the duty ratio of the PWM control by the vertical drive is lower than the predetermined duty ratio. Is higher than the increase rate of the lower drive,
2. The motor control device according to claim 1, wherein the predetermined current value is set within a range of the motor current when a duty ratio of the PWM control by the vertical drive is larger than the predetermined duty ratio. .   The motor control device according to claim 1, wherein a current flowing through the motor for retracting the seat belt and the motor for canceling the retract is controlled.

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