JP2018182797A - Electronic control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect elements composing a circuit from a current flowing due to induction voltage.SOLUTION: A motor driver device 1 includes an H bridge circuit 3 for driving a motor 2 equipped on a vehicle, a drive control unit 4, current limiting resistors R3 and R4, and a switching unit 10. The drive control unit 4 controls electric conduction from a power line Lb to the motor 2 by controlling the operation of the H bridge circuit 3. The current limiting resistors R3 and R4 are provided for limiting a current flowing the motor 2 during a non-energized period which is a period when electric conduction from the power line Lb to the motor 2 is halted. The switching unit 10 switches state between a limit state in which the current limiting resistors R3 and R4 are included in the current path of the current and a normal state in which the current limiting resistors R3 and R4 are not included in the current path.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electronic control unit provided with an H bridge circuit for driving a motor mounted on a vehicle.

  In general, a motor is known to generate an induced voltage that is proportional to its rotation speed and reverse to the direction of energization. For example, a valve for an internal combustion engine (for example, a valve for supplying and discharging air and the like) mounted on a vehicle is opened and closed using a motor that is a direct current motor as a power source. As a drive circuit for driving a direct current motor, an H bridge circuit composed of four switching elements is generally used (see, for example, Patent Document 1).

JP, 2013-162701, A

  In a configuration in which a motor is used as a power source to open the valve for an internal combustion engine, power supply to the motor is often PWM controlled. In the above configuration, when the valve opening / closing operation is performed, a high duty (on-duty) is set so that the energization period to the motor becomes long immediately after the start of the operation, whereby the valve body operates at high speed. Then, as the target opening degree is approached, the duty is gradually reduced such that the energization period to the motor is gradually shortened.

  Here, during the off-duty period in which energization of the motor is stopped, that is, in the non-energization period, a current in the reverse direction to the controlled energization direction flows due to the action of the induced voltage generated in the motor. The magnitude of the induced voltage varies depending on the specification of the motor etc. In the case of a motor with a large induced voltage, a circuit (for example, a current detection circuit for detecting the current of the motor, an H bridge circuit) Etc.), and there is a risk that a circuit element may be damaged.

  The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to provide an electronic control device capable of protecting elements constituting a circuit from a current flowing by the action of an induced voltage.

  The electronic control unit (1, 21, 31) according to claim 1 comprises an H bridge circuit (3) for driving a motor (2) mounted on a vehicle, a drive control unit (4), a current limiting resistor (R3, R4, R31) and a switching unit (10, 23, 33) are provided. The drive control unit controls the energization of the motor from the DC power supply by controlling the operation of the H bridge circuit. The current limiting resistor is for limiting the current flowing through the motor during the non-energization period, which is a period during which energization of the motor from the DC power supply is stopped. The switching unit switches between a limited state in which the current limiting resistor is interposed in the current path through which the current flows, and a normal state in which the current limiting resistor is not interposed in the current path.

  As described above, in the non-energization period in which the energization of the motor is stopped, a current in the opposite direction to the energization direction controlled by the action of the induced voltage generated in the motor flows. Such a reverse current can be an excessive current depending on the specification of the motor. Therefore, in the above configuration, when the switching unit switches to the limit state, the reverse current is limited by flowing through the current limiting resistor provided separately from the H bridge circuit. Therefore, in the above configuration, an excessive current exceeding the current rating does not flow to each circuit element constituting the circuit such as the H bridge circuit. Therefore, according to the above configuration, an excellent effect can be obtained that the elements constituting the circuit can be protected from the current flowing by the action of the induced voltage.

  Further, the magnitude of the current flowing by the action of the induced voltage varies depending on the specification of the motor and the like. Therefore, when the magnitude of the current can be suppressed to less than the current rating of the circuit element, the switching unit may switch to the normal state in which the current limiting resistor is not interposed in the current path. In this way, the operation of current limiting by the current limiting resistor is not performed blindly, and as a result, the effect of improving the life of the current limiting resistor, the switches constituting the switching unit, and the like can be obtained.

A diagram schematically showing a configuration of a motor drive device according to a first embodiment Diagram for explaining the circuit operation of the H bridge circuit and the current limiting circuit according to the first embodiment Diagram summarizing the circuit operation of the H bridge circuit and the current limiting circuit according to the first embodiment Timing chart for explaining the operation state of each part when rotating the motor according to the first embodiment in the forward direction Timing chart for explaining the operation state of each part when rotating the motor according to the first embodiment in the reverse direction A diagram schematically showing a configuration of a motor drive device according to a second embodiment A diagram schematically showing a configuration of a motor drive device according to a third embodiment Diagram summarizing the circuit operation of the H bridge circuit and the current limiting circuit according to the third embodiment

Hereinafter, a plurality of embodiments of the present invention will be described with reference to the drawings. The same reference numerals are given to substantially the same configuration in each embodiment and the description will be omitted.
First Embodiment
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. 1 to 5.

  The motor drive device 1 shown in FIG. 1 is provided in an electronic control unit (ECU) mounted on a vehicle. The motor drive device 1 drives a motor 2 mounted on a vehicle, and includes an H bridge circuit 3, a drive control unit 4, and a current limiting circuit 5. In the present embodiment, the motor 2 is a direct current motor, and drives, for example, a valve for an internal combustion engine such as a throttle valve. The motor drive device 1 is supplied with a battery voltage VB output from an on-vehicle battery (not shown). The on-board battery corresponds to a DC power supply.

  The drive control unit 4 controls the operation of the H bridge circuit 3 to control the energization of the motor 2 from the DC power supply. The drive control unit 4 includes a microcomputer 6, a driver 7 and current detection circuits 8 and 9. The microcomputer 6 controls the overall operation of the device. The opening degree detection signal Sa and the current detection signal Sb are input to the microcomputer 6.

  The opening degree detection signal Sa is output from an opening degree sensor that detects the opening degree of a valve (not shown), and is a voltage signal corresponding to the opening degree of the valve driven by the motor 2. The current detection signal Sb is output from the current detection circuit 8 and is a voltage signal corresponding to the current flowing through the motor 2.

  The microcomputer 6 performs PWM control (DUTY control) on energization of the motor 2 based on the detection signals Sa, Sb, etc., so that the opening degree of a valve (not shown) becomes a desired opening degree. The microcomputer 6 generates a drive command so that energization of the motor 2 is desired, and outputs the drive command to the driver 7. The driver 7 controls the operation of the H bridge circuit 3 and the current limiting circuit 5 in accordance with a drive command given from the microcomputer 6.

  The H bridge circuit 3 is a motor drive circuit for driving the motor 2 which is a direct current motor, and has a general configuration including four transistors Tr1 to Tr4. In the present embodiment, the transistors Tr1 to Tr4 are all N-channel type MOS transistors, and a body diode whose source side is an anode is connected between the source and drain thereof.

  The drains of the transistors Tr1 and Tr2 are connected to the power supply line Lb to which the battery voltage VB is applied. The sources of the transistors Tr1 and Tr2 are connected to the drains of the transistors Tr3 and Tr4, respectively. The sources of the transistors Tr3 and Tr4 are connected to a ground line Lg to which a ground potential GND (= 0 V), which is a reference potential of the circuit, is applied.

  An interconnection node N1 between the transistors Tr1 and Tr3 is connected to one terminal M1 of the motor 2 via a detection resistor R1 for detecting the current flowing through the motor 2. An interconnection node N2 between the transistors Tr2 and Tr4 is connected to the other terminal M2 of the motor 2. The motor 2 rotates in the forward direction when current flows from the terminal M1 to the terminal M2, and rotates in the reverse direction when current flows from the terminal M2 to the terminal M1. The drive signal output from the driver 7 is given to each gate of the transistors Tr1 to Tr4.

  In the above configuration, the transistors Tr1 and Tr2 correspond to an upstream switching element which is a switching element provided on the upstream side of the H bridge circuit 3. The transistors Tr3 and Tr4 correspond to downstream switching elements, which are switching elements provided on the downstream side of the H bridge circuit 3.

  The current detection circuit 8 detects a current flowing through the motor 2 and outputs a current detection signal Sb corresponding to the current. In this case, the current detection circuit 8 outputs, as a current detection signal Sb, a voltage signal obtained by amplifying the voltage between the terminals of the detection resistor R1 provided between the node N1 and the terminal M1 of the motor 2.

  The current limiting circuit 5 includes current limiting resistors R3 and R4 and transistors Tr5 and Tr6. The current limiting resistors R3 and R4 are resistors for limiting the current flowing through the motor 2 (hereinafter also referred to as return current) during the non-energization period in which the energization of the motor 2 is stopped. The transistors Tr5 and Tr6 are both N-channel type MOS transistors, and a body diode whose source side is an anode is connected between the source and drain thereof.

  The current limiting resistor R3 is connected between the node N1 and the drain of the transistor Tr5. The source of the transistor Tr5 is connected to the ground line Lg. That is, the series circuit of the current limiting resistor R3 and the transistor Tr5 is connected in parallel to the transistor Tr3 of the H bridge circuit 3.

  The current limiting resistor R4 is connected between the node N2 and the drain of the transistor Tr6. The source of the transistor Tr6 is connected to the ground line Lg. That is, the series circuit of the current limiting resistor R4 and the transistor Tr6 is connected in parallel to the transistor Tr4 of the H bridge circuit 3.

  The drive signal output from the driver 7 is given to each gate of the transistors Tr5 and Tr6. The driver 7 drives the transistors Tr5 and Tr6 based on the drive command given from the microcomputer 6. Therefore, the driving of the transistors Tr5 and Tr6 is controlled by the microcomputer 6.

  In the above configuration, the transistor Tr5 corresponds to a switch connected in series to the current limiting resistor R3. The transistor Tr6 corresponds to a switch connected in series to the current limiting resistor R4. The transistors Tr5 and Tr6, the microcomputer 6, and the driver 7 constitute a switching unit 10.

  The switching unit 10 switches between a limiting state in which the current limiting resistors R3 and R4 are interposed in a path through which the return current flows, and a normal state in which the current limiting resistors R3 and R4 are not intervened in a path through which the return current flows. In this case, the transistors Tr5 and Tr6 are turned on to switch to the restricted state, and the transistors Tr5 and Tr6 are turned off to switch to the normal state. Such switching operation is controlled by the microcomputer 6.

  In the present embodiment, when the transistor Tr1 of the H bridge circuit 3 transitions from on to off, the switching unit 10 switches to the restricted state by turning on the transistor Tr5. Further, when the transistor Tr2 of the H bridge circuit 3 transitions from on to off, the switching unit 10 switches to the restricted state by turning on the transistor Tr6.

  However, the switching unit 10 is configured to switch to the restricted state on condition that the number of rotations of the motor 2 is equal to or more than a predetermined threshold number of rotations. The rotational speed of the motor 2 can be estimated from the inclination (differential value) of the opening degree detection signal Sa. The threshold rotational speed may be set to a value such that the effects of the present embodiment described later can be reliably obtained based on the specifications of the motor 2 and the ratings of the circuit elements that constitute each circuit. In the present embodiment, for example, the threshold rotational speed is a predetermined margin with respect to the rotational speed of the motor 2 when the return current having the same magnitude as the current rating of the circuit element provided in the path through which the return current flows. It is set to a low value only.

Next, the operation of the above configuration will be described.
In the motor drive device 1, an energizing period (hereinafter also referred to as an ON DUTY period) in which energization of the motor 2 is performed from the DC power supply Is repeated alternately. Further, a penetration suppression period is provided between the conduction period and the non-conduction period to suppress the generation of the through current.

  Hereinafter, the circuit operation in each of these periods will be described with reference to FIG. In this case, it is assumed that the motor 2 is rotated in the forward direction. Further, in FIG. 2, the transistors Tr1 to Tr4 are represented by simple switch symbols so that their ON / OFF (ON / OFF) becomes clear. Furthermore, in FIG. 2, the motor 2 is equivalently represented as a resistance Ra, an inductance La and an induced voltage Ec.

[1] ON DUTY Period As shown in FIG. 2A, in the ON DUTY period, the transistors Tr1 and Tr4 are turned ON, and the transistors Tr2, Tr3, Tr5 and Tr6 are turned OFF. As a result, current flows in the path shown by the solid arrow in FIG. 2A, that is, the path “power supply line Lb → Tr1 → terminal M1 → terminal M2 → Tr4 → ground line Lg”, and the motor 2 rotates in the forward direction. Do.

[2] Penetration suppression period (during transition from ON to OFF)
As shown in FIG. 2B, in the penetration suppression period provided in the transition period from the ON DUTY period to the OFF DUTY period, the transistors Tr1 to Tr3, Tr5, and Tr6 are turned off and the transistor Tr4 is turned on. As a result, current flows along a path shown by a solid arrow in FIG. 2B, that is, a path of “ground line Lg → Tr3 body diode → terminal M1 → terminal M2 → Tr4 → ground line Lg”.

[3] OFF DUTY period (normal state)
When the condition for switching to the limited state is not satisfied, that is, when the number of revolutions of the motor 2 is less than the threshold number of revolutions, the circuit operation as shown in FIG. 2C is performed. That is, in this case, the transistors Tr1, Tr2, Tr5, and Tr6 are turned off, and the transistors Tr3 and Tr4 are turned on.

  Thus, at the beginning of the switching to the period, a current flows through a route of “ground line Lg → Tr3 → terminal M1 → terminal M2 → Tr4 → ground line Lg”. However, after that, due to the action of the induced voltage Ec, the current starts to flow in the path opposite to the above path. That is, as indicated by solid arrows in FIG. 2C, current flows in a route of “ground line Lg → Tr4 → terminal M2 → terminal M1 → Tr3 → ground line Lg”. As described above, in the present embodiment, a so-called low-side reflux system is employed in which reflux is performed by turning on the downstream side transistor forming the H bridge circuit 3.

[4] OFF DUTY period (limited state)
When the conditions for switching to the limited state are satisfied, that is, when the number of revolutions of the motor 2 is equal to or more than the threshold number of revolutions, the circuit operation as shown in FIG. 2D is performed. That is, in this case, the transistors Tr1 to Tr3 and Tr6 are turned off, and the transistors Tr4 and Tr5 are turned on.

  Thus, at the beginning of switching to the relevant period, a current flows through a route of “ground line Lg → Tr5 → current limiting resistor R3 → terminal M1 → terminal M2 → Tr4 → ground line Lg”. However, after that, due to the action of the induced voltage Ec, the current starts to flow in the path opposite to the above path. That is, as shown by a solid arrow in FIG. 2D, a current flows through a route of “ground line Lg → Tr4 → terminal M2 → terminal M1 → current limiting resistor R3 → Tr5 → ground line Lg”. During this period, the current flowing through the motor 2 is limited by flowing through the current limiting resistor R3.

[5] penetration suppression period (during transition from OFF to ON)
As shown in FIG. 2B, in the penetration suppression period provided in the transition period from the off duty period to the on duty period, the transistors Tr1 to Tr3, Tr5, and Tr6 are turned off and the transistor Tr4 is turned on. As a result, current flows along a path shown by a broken arrow in FIG. 2B, that is, a path of “ground line Lg → Tr4 → terminal M2 → terminal M1 → body diode of transistor M1 → power line Lb”.

  FIG. 3 is a table summarizing such circuit operation. The items on the top of FIG. 3 represent the respective periods, “ON” represents the ON DUTY period, “→” represents the penetration suppression period, and “OFF” represents the OFF DUTY period. Further, the item at the bottom of FIG. 3 is an item indicating whether or not the condition for switching to the restricted state is satisfied, and when the condition is satisfied, “1” is described, and the condition is If not satisfied, it is described as "0".

  As shown in FIG. 3, in the motor control device 1, the ON DUTY period and the OFF DUTY period are alternately repeated, thereby controlling the current flowing through the motor 2, and hence the opening degree of the valve. In addition, in the OFF DUTY period in the case of satisfying the switching condition to the limiting state, the transistor Tr5 is turned on, and the current limiting operation by the current limiting resistor R3 is enabled.

  Subsequently, an operation waveform of each portion when the motor 2 is rotated in the forward direction will be described with reference to FIG. In FIG. 4 and FIG. 5 described later, the direction of the current flowing from the terminal M1 to the terminal M2 is positive (+) and the direction of the current flowing from the terminal M2 to the terminal M1 is negative (-) And Further, when the opening detection signal Sa is 0 [V], the opening is at the minimum value, that is, the valve is closed, and when the opening detection signal Sa is 5 [V], the opening is maximum. It is a value state, that is, a state in which the valve is open.

  A period before time t1 is a period in which the motor 2 is not energized. At time t1, there is an instruction to perform normal rotation, and energization of the motor 2 is started. As described in the prior art, immediately after the start of operation, the valve body is operated quickly so that the ON DUTY period becomes long, and the ON DUTY period is gradually reduced as the target opening is approached.

  A period of time t1 to t2 is an ON DUTY period. In the ON DUTY period, the current of the motor 2 increases rapidly in the positive direction at first, but then gradually decreases in proportion to the increase of the rotational speed of the motor 2 due to the action of the induced voltage. A period from time t2 to t3 is an OFF DUTY period. During this OFF DUTY period, the current of the motor 2 increases in the negative direction due to the action of the induced voltage, that is, a current (-) flows in the direction opposite to the controlled conduction direction (+). The subsequent period of time t3 to t4 is an ON DUTY period. In the ON DUTY period, the current of the motor 2 increases in the positive direction.

  From time t4 to t12, the same operation as that from time t2 to t4 is repeated. In this case, as the process proceeds to the second half, the ratio of the OFF DUTY period increases. Therefore, the current of the motor 2 increases in the negative direction as it progresses to the second half, and becomes the maximum negative current at time t11 when the target opening is approached.

  Time t12 to t13 is an OFF DUTY period. However, at this time, since the number of revolutions of the motor 2 is reduced, the induced voltage is also reduced, so the current of the motor 2 increases in the positive direction, that is, the negative current decreases. Time t13 to t14 is an ON DUTY period, and the current of the motor 2 increases in the positive direction. Then, at time t14, there is an instruction to stop energization, and energization of the motor 2 is stopped.

  Subsequently, an operation waveform of each part when the motor 2 is rotated in the reverse direction will be described with reference to FIG. A period before time t1 is a period in which the motor 2 is not energized. At time t1, there is an instruction to perform reverse rotation, and energization of the motor 2 is started. A period of time t1 to t2 is an ON DUTY period. In this ON DUTY period, the current of the motor 2 initially increases in the negative direction rapidly, but then gradually decreases in proportion to the increase in the number of rotations of the motor 2 due to the action of the induced voltage. A period from time t2 to t3 is an OFF DUTY period. In the OFF DUTY period, the current of the motor 2 increases in the positive direction, that is, a current (+) in the direction opposite to the controlled conduction direction (−) flows due to the action of the induced voltage. The subsequent period of time t3 to t4 is an ON DUTY period. In this ON DUTY period, the current of the motor 2 increases in the negative direction.

  From time t4 to t12, the same operation as that from time t2 to t4 is repeated. In this case, as the process proceeds to the second half, the ratio of the OFF DUTY period increases. Therefore, the current of the motor 2 increases in the positive direction as it progresses to the second half, and becomes the maximum positive current at time t11 when the target opening is approached.

  Time t12 to t13 is an OFF DUTY period. However, at this time, since the rotation speed of the motor 2 is decreased, the induced voltage is also decreased, and thus the current of the motor 2 is increased in the negative direction, that is, the positive current is decreased. Time t13 to t14 is an ON DUTY period, and the current of the motor 2 increases in the negative direction. Then, at time t14, there is an instruction to stop energization, and energization of the motor 2 is stopped.

According to the present embodiment described above, the following effects can be obtained.
As in the motor drive device 1 of the present embodiment, in the configuration in which the motor 2 is driven using the H bridge circuit 3, during the OFF DUTY period in which the energization of the motor 2 is stopped, the induced voltage generated by the motor 2 acts. A current flows in the opposite direction to the controlled current flow direction. Such a reverse current may be an excessive current depending on the specification of the motor 2.

  Therefore, in the above configuration, when the switching unit 10 switches to the limiting state, the reverse current is limited by flowing through the current limiting resistors R3 and R4 provided separately from the H bridge circuit 3. . Therefore, in the above configuration, an excessive current exceeding the current rating does not flow to each circuit element constituting the circuit provided in the path through which the reverse current flows. Therefore, according to the above configuration, an excellent effect can be obtained that the elements constituting the circuit can be protected from the current flowing by the action of the induced voltage.

  In the above configuration, the current detection circuit 8, the H bridge circuit 3, and the like can be considered as circuits that may fail when the reverse current becomes an excessive current. In particular, the current detection circuit 8 includes an amplifier for inputting the voltage between the terminals of the detection resistor R1 provided in series in a path through which the current of the motor 2 flows, and when an excessive current flows, the amplifier There is a risk of malfunction or failure.

  Further, when the voltage value of the induced voltage is significantly higher than the voltage value of the battery voltage VB, the reverse current flowing by the action of the induced voltage is the current of the transistors Tr3 and Tr4 constituting the H bridge circuit 3. There is also a possibility that the rated current may be exceeded, which may cause the H bridge circuit 3 to break down. According to the present embodiment, as described above, since the reverse current is suppressed from being excessive, it is possible to prevent such a failure from occurring.

  Further, the magnitude of the current flowing by the action of the induced voltage differs depending on the specification of the motor 2, the number of rotations, and the like. Therefore, when the magnitude of the current can be suppressed to less than the current rating of the circuit element, the switching unit 10 may switch to a normal state in which the current limiting resistors R3 and R4 are not interposed in the current path. Specifically, in the present embodiment, the switching unit 10 performs switching to the restricted state on condition that the number of rotations of the motor 2 is equal to or higher than the threshold number of rotations, in other words, the number of rotations of the motor 2 is equal to the threshold rotation When it is less than the number, switching to the normal state is performed. In this way, the current limiting operation by the current limiting resistors R3 and R4 is not performed indiscriminately, and as a result, the current limiting resistors R3 and R4 and the switches (transistors Tr5 and Tr6) constituting the switching unit 10, etc. The effect of improving the life of the

  The magnitude of the current flowing due to the action of the induced voltage becomes maximum when the valve opening approaches the target opening, as shown in FIG. 4 and FIG. Therefore, the switching period to the above-described restricted state may be set at least to a period including the timing at which the opening degree of the valve approaches the target opening degree (time t11 in FIGS. 4 and 5). In this way, the effect of the above-described life improvement can be further enhanced. The timing described above can be detected based on the opening degree detection signal Sa.

  The series circuit of current limiting resistor R3 and transistor Tr5 constituting current limiting circuit 5 and the series circuit of current limiting resistor R4 and transistor Tr6 are connected in parallel to transistors Tr3 and Tr4 of H bridge circuit 3, respectively. . According to such a configuration, by turning off the transistors Tr5 and Tr6, each circuit element of the current limiting circuit 5 can be completely disconnected from the conduction path of the motor 2. Therefore, the current limiting circuit 5 configured as described above can exert the function of limiting the return current without affecting normal motor control.

Second Embodiment
Hereinafter, the second embodiment will be described with reference to FIG.
As shown in FIG. 6, the motor drive device 21 of the present embodiment is different from the motor drive device 1 of the first embodiment in that a current limit circuit 22 is provided instead of the current limit circuit 5. Further, the motor drive device 21 adopts a so-called high side reflux system in which reflux is performed by turning on the upstream side transistor that constitutes the H bridge circuit 3.

  The current limiting circuit 22 includes circuit elements similar to the current limiting circuit 5. However, in this case, the connection form of each circuit element is different. That is, the current limiting resistor R3 is connected between the power supply line Lb and the drain of the transistor Tr5. The source of the transistor Tr5 is connected to the node N1. That is, the series circuit of the current limiting resistor R3 and the transistor Tr5 is connected in parallel to the transistor Tr1 of the H bridge circuit 3.

  The current limiting resistor R4 is connected between the power supply line Lb and the drain of the transistor Tr6. The source of the transistor Tr6 is connected to the node N2. That is, the series circuit of the current limiting resistor R4 and the transistor Tr6 is connected in parallel to the transistor Tr2 of the H bridge circuit 3.

  In the above configuration, the switching unit 23 is configured by the transistors Tr5 and Tr6, the microcomputer 6, and the driver 7. In this case, when the transistor Tr4 of the H bridge circuit 3 transitions from on to off, the switching unit 23 switches to the restricted state by turning on the transistor Tr5. Further, when the transistor Tr3 of the H bridge circuit 3 transitions from on to off, the switching unit 23 switches to the restricted state by turning on the transistor Tr6.

  Even in the motor drive device 21 adopting the high side reflux system as in the embodiment described above, the switching unit 23 performs switching to the restricted state as in the motor drive device 1 of the first embodiment. Thus, the reverse current generated by the action of the induced voltage during the OFF DUTY period is limited by flowing through the current limiting resistors R3 and R4. Therefore, the same effect as that of the first embodiment can be obtained also by the present embodiment.

Third Embodiment
The third embodiment will be described below with reference to FIGS. 7 and 8.
As shown in FIG. 7, the motor drive device 31 of the present embodiment differs from the motor drive device 1 of the first embodiment in that a current limit circuit 32 is provided instead of the current limit circuit 5. The current limiting circuit 32 includes a current limiting resistor R31 which is a resistor for limiting the return current, and a switch SW31.

  The current limiting resistor R31 is connected in series between the node N1 which is one output terminal of the H bridge circuit 3 and the terminal M1 of the motor 2, together with the detection resistor R1. The switch SW31 is formed of, for example, a semiconductor switching element such as a MOS transistor, and is connected in parallel to the current limiting resistor R31. The on / off of the switch SW31 is switched by a switching signal supplied from the driver 7. The driver 7 turns on / off the switch SW 31 based on the switching command given from the microcomputer 6. Therefore, the on / off of the switch SW31 is controlled by the microcomputer 6.

  In the above configuration, the switch SW 33, the microcomputer 6, and the driver 7 constitute a switching unit 33. In this case, the switch SW31 is turned off to switch to the restricted state, and the switch SW31 is turned on to switch to the normal state. Such switching operation is controlled by the microcomputer 6.

  The circuit operation in each period of the motor drive device 31 of the present embodiment is as shown in FIG. In this case, as in the first embodiment, it is assumed that the low side reflux is performed and the motor 2 is rotated in the forward direction.

  As described above, in the motor drive device 31 of the present embodiment, as in the motor drive device 1 of the first embodiment, the action of the induced voltage in the OFF DUTY period is performed by the switching unit 33 switching to the restricted state. The reverse current caused by the current is limited by flowing through the current limiting resistor R31. Therefore, the same effect as that of the first embodiment can be obtained also by the present embodiment.

  Furthermore, according to the configuration of the present embodiment, it is possible to cope with not only the low side reflux system but also the high side reflux system as the reflux system, so that an effect of increasing versatility can be obtained. Further, the current limiting circuit 32 is configured by two circuit elements, that is, a current limiting resistor R31 and a switch SW31. Therefore, according to the present embodiment, it is possible to obtain an effect that the number of additional circuit elements for limiting the reflux current can be reduced as compared with the above-described embodiments.

(Other embodiments)
The present invention is not limited to the embodiments described above and described in the drawings, and can be arbitrarily modified, combined, or expanded without departing from the scope of the invention.
The motor driven by the H-bridge circuit 3 is not limited to the motor 2 driving a valve for an internal combustion engine, and all motors mounted on a vehicle can be used.
The switching elements constituting H bridge circuit 3 and current limiting circuit 5 are not limited to N channel type MOS transistors, and various switching elements such as P channel type MOS transistors, bipolar transistors, IGBTs, etc. may be used. Can.

  The conditions for switching to the restricted state can be appropriately changed as long as the reverse current flowing by the action of the induced voltage can not exceed the rated current of the circuit element. For example, the condition may be that the slope (differential value) of the opening degree detection signal Sa output from the opening degree sensor is equal to or greater than a predetermined threshold slope. Alternatively, a sensor (rotational speed detection unit) such as an encoder for detecting the rotational speed of the motor 2 may be provided, and the rotational speed detected thereby may be equal to or higher than the threshold rotational speed. Alternatively, a voltage detection unit may be provided to detect an induced voltage from the voltage at each of the terminals M1 and M2 of the motor 2, and the induced voltage detected thereby may be equal to or higher than a predetermined threshold voltage.

  In the above embodiments, the resistance values of the current limiting resistors R3, R4, and R31 are fixed, but may be variable. In this way, the effect of limiting the reverse current generated by the action of the induced voltage can be adjusted to the optimum one according to the specification of the motor 2 and the like.

  Although the present disclosure has been described based on the examples, it is understood that the present disclosure is not limited to the examples and structures. The present disclosure also includes various modifications and variations within the equivalent range. In addition, various combinations and forms, and further, other combinations and forms including only one element, or more or less than these elements are also within the scope and the scope of the present disclosure.

  1, 21, 31 ... motor drive device, 2 ... motor, 3 ... H bridge circuit, 4 ... drive control unit, 10, 23, 33 ... switching unit, R3, R4, R31 ... current limiting resistance, Tr1 to Tr6 ... transistor .

Claims (12)

An H bridge circuit (3) for driving a motor mounted on a vehicle;
A drive control unit (4) that controls energization of the motor (2) from the DC power supply by controlling the operation of the H bridge circuit;
Current limiting resistors (R3, R4, R31) for limiting the current flowing through the motor during the non-energization period in which the energization of the motor from the DC power source is stopped;
A switching unit (10, 23, 33) that switches between a limiting state in which the current limiting resistor is interposed in a current path through which the current flows, and a normal state in which the current limiting resistor is not intervening in the current path;
An electronic control unit comprising: The switching unit (10)
A switch (Tr5, Tr6) connected in series to the current limiting resistor;
The series circuit of the current limiting resistor and the switch is connected in parallel to a downstream switching element (Tr3, Tr4) which is a switching element provided on the downstream side of the H bridge circuit. Electronic control unit.   When the upstream switching elements (Tr1 and Tr2), which are switching elements provided on the upstream side of the H bridge circuit, transition from on to off, the switching unit turns on the switch to switch to the restricted state. The electronic control unit according to claim 2, wherein switching of The switching unit (23)
A switch (Tr5, Tr6) connected in series to the current limiting resistor;
The series circuit of the current limiting resistor and the switch is connected in parallel to an upstream switching element (Tr1, Tr2) which is a switching element provided on the upstream side of the H bridge circuit. Electronic control unit.   The switching unit turns on the switch when the downstream switching elements (Tr3 and Tr4), which are switching elements provided on the downstream side of the H bridge circuit, transition from on to off, the switching state is brought about to the restricted state. The electronic control unit according to claim 4, wherein switching of The current limiting resistor (R31) is connected in series between the output terminal of the H bridge circuit and the terminal of the motor,
The electronic control unit according to claim 1, wherein the switching unit (33) includes a switch (SW 31) connected in parallel to the current limiting resistor.   The electronic control unit according to claim 6, wherein the switching unit switches to the restricted state by turning off the switch.   The electronic control device according to any one of claims 1 to 7, wherein the switching unit performs switching to the restricted state on condition that a rotation number of the motor is equal to or more than a predetermined threshold rotation number.   The electronic control unit according to any one of claims 1 to 7, wherein the switching unit switches to the restricted state on condition that an induced voltage of the motor is equal to or higher than a predetermined threshold voltage.   The electronic control device according to any one of claims 1 to 9, wherein the motor drives a valve for an internal combustion engine mounted on a vehicle.   The switching unit performs switching to the restricted state on the condition that the inclination of the opening detection signal output from the opening sensor that detects the opening of the valve is equal to or greater than a predetermined threshold inclination. Electronic control unit as described.   The electronic control device according to any one of claims 1 to 11, wherein the resistance value of the current limiting resistor is variable.

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