Motor drive device and motor device

Abstract

To provide a motor drive device, etc. that can start an engine without making the system larger or more complicated.SOLUTION: There is provided a motor drive device that drives a brushless motor that starts an engine, comprising a boost circuit that boosts the voltage of a power supply, a drive circuit that drives the brushless motor, and a control unit that controls the drive circuit and the boost circuit. The control unit operates the boost circuit and starts the brushless motor using the drive circuit to which the voltage boosted by the boost circuit is applied when starting the engine. The boost circuit includes a coil whose one end is connected to the power supply, and a boost switching element connected between the other end of the coil and the ground. The control unit switches the boost switching element to generate an induced electromotive force in the coil.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a motor drive device and a motor device. [Background technology]

[0002] Patent Document 1 discloses a motor drive device that supplies battery voltage to a brushless motor via a drive circuit and starts an engine using the torque of the brushless motor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6019246 Summary of the Invention [Problem to be solved by the invention]

[0004] However, for example, the number and size of electrical components that can be installed in small vehicles such as motorcycles are limited, and the motor used to start the engine must also be made smaller, which creates the problem of making it difficult to obtain the torque required to start the engine using a low-voltage (e.g., 12 V) battery used for control.

[0005] Furthermore, for example, in a four-wheel hybrid vehicle, in addition to a low-voltage (e.g., 12V) battery for control, a high-voltage (e.g., 48V) battery for driving the motor is used, which complicates the system and increases implementation costs.

[0006] The present invention has been made to solve the above problems, and has an object to provide a motor drive device or the like that can start an engine without increasing the size and complexity of the system. [Means for solving the problem]

[0007] In order to solve the above problem, one aspect of the present invention is to A motor drive device that drives a brushless motor that starts an engine, a boost circuit that boosts the voltage of the power supply; a drive circuit for driving the brushless motor; a control unit that controls the drive circuit and the boost circuit; a bypass circuit that connects the power supply and the drive circuit without passing through the boost circuit; Equipped with The boost circuit includes a coil having one end connected to the power supply, and a boost switching element connected between the other end of the coil and ground. a connection switching element connected between the other end of the coil and a drive circuit, and a capacitor connected between the connection switching element and the ground; and The control unit Based on the voltage of the power supply The engine cannot be started using only the voltage of the power supply. It was determined that case to teeth, The output voltage of the boost circuit is set to a predetermined value. The boost switching element is switched to operate the boost circuit, thereby generating an induced electromotive force in the coil, and the brushless motor is started by the drive circuit to which the voltage boosted by the boost circuit is applied. When starting the engine Based on the voltage of the power supply The engine can be started using only the voltage of the power supply. It was determined that In this case, when the bypass circuit is turned on by the control unit, a voltage is supplied from the power supply to a drive circuit via the bypass circuit. [Effects of the Invention]

[0008] According to the present invention, the engine can be started without increasing the size and complexity of the system. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a motor device according to a first embodiment. [Figure 2] 4 is a flowchart showing an operation at the time of starting the engine in the first embodiment. [Figure 3] FIG. 10 is a diagram illustrating the configuration of a motor device according to a second embodiment. [Figure 4] 10 is a flowchart showing an operation at engine start in a second embodiment. [Figure 5] FIG. 10 is a diagram illustrating the configuration of a motor device according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0011] (First Example) FIG. 1 is a diagram showing the configuration of a motor device according to a first embodiment.

[0012] 1, the motor device of this embodiment includes a three-phase (U-phase, V-phase, W-phase) brushless motor M that starts the vehicle engine, and a motor drive device 1 that drives the brushless motor M. Note that the present invention is not limited to any particular type of vehicle, and can be applied to any vehicle, including two-wheeled vehicles and four-wheeled hybrid vehicles.

[0013] The motor drive device 1 includes a control unit 10 configured by an on-board ECU (Electric Control Unit), a drive circuit 20 that drives a brushless motor M, and a boost circuit 30 that boosts the voltage of a battery BT (an example of a power source). The drive circuit 20 and the boost circuit 30 are controlled by the control unit 10. The control unit 10 operates using the battery BT as a power source (control power source). Note that the function of the control unit 10 may be provided in another control device instead of the ECU.

[0014] When starting the engine, the control unit 10 activates the boost circuit 30 and starts the brushless motor M by the drive circuit 20 to which the voltage boosted by the boost circuit 30 is applied.

[0015] 1, the drive circuit 20 includes pairs of switching elements 21u and 22u, switching elements 21v and 22v, and switching elements 21w and 22w, which correspond to the U phase, V phase, and W phase, respectively. The pairs of switching elements 21u and 22u, switching elements 21v and 22v, and switching elements 21w and 22w are connected in series with each other between ground and the boost circuit 30. Furthermore, the midpoints of the pairs of switching elements 21u and 22u, switching elements 21v and 22v, and switching elements 21w and 22w are connected to terminals of the corresponding phases (U phase, V phase, W phase) of the brushless motor M.

[0016] The control unit 10 controls the on / off timing of the switching elements 21u, 22u, 21v, 22v, and 21w, 22w, so that the brushless motor M performs power running and regenerative operations.

[0017] As shown in FIG. 1, the boost circuit 30 includes a coil 31 having one end connected to a battery BT via an ignition switch SW, a boost switching element 32 connected between the other end of the coil 31 and ground, a connection switching element 33 connected between the other end of the coil 31 and the drive circuit 20, and a capacitor 34 connected between the connection switching element 33 and ground.

[0018] 1, the boost switching element 32 and the connection switching element 33 are FETs, the source of the boost switching element 32 is connected to ground, and the drain of the boost switching element 32 and the source of the connection switching element 33 are connected to the other end of the coil 31. The drain of the connection switching element 33 is connected to a capacitor 34 and a drive circuit 20. The gates of the boost switching element 32 and the connection switching element 33 are both connected to a control unit 10, and the on / off of the boost switching element 32 and the connection switching element 33 is controlled by the control unit 10. For example, the control unit 10 controls the on / off of the boost switching element 32 and the connection switching element 33 so that the output voltage V (the voltage between the terminals of the capacitor 34) of the boost circuit 30 shown in FIG. 1 becomes a predetermined voltage.

[0019] The solid arrow in FIG. 1 indicates the direction of current when the engine is started.

[0020] When the engine is started, in the boost circuit 30, a switching operation (repeated ON / OFF operation) is performed by the boost switching element 32 while the connection switching element 33 is turned OFF. As a result, current from the battery BT flows intermittently to the coil 31 via the turned-on ignition switch SW, and an induced electromotive force is generated in the coil 31. When the boost switching element 32 is turned OFF, a voltage obtained by adding the induced electromotive force to the voltage of the battery BT is applied to the source of the connection switching element 33. The connection switching element 33 (parasitic diode of the connection switching element 33) and the capacitor 34 form a rectifier circuit, and a voltage corresponding to the voltage obtained by adding the induced electromotive force to the voltage of the battery BT (the source voltage of the connection switching element 33) is generated across the capacitor 34.

[0021] Therefore, even if the voltage of the battery BT is 12V, for example, by operating the boost circuit 30, it is possible to provide the drive circuit 20 with an output voltage V of a voltage exceeding 12V, such as 24V or 48V.

[0022] The dotted arrows in FIG. 1 indicate the direction of current when the brushless motor M generates power.

[0023] During power generation, control unit 10 controls switching elements 21u, 22u, switching elements 21v, 22v, and switching elements 21w, 22w so that current generated by power generation in brushless motor M flows into boost circuit 30 via drive circuit 20. Furthermore, during power generation, control unit 10 turns on connection switching element 33 of boost circuit 30. This causes current from brushless motor M to flow sequentially through drive circuit 20, connection switching element 33, and coil 31, and further to battery BT via the turned-on ignition switch SW. In this way, the power generated by brushless motor M is recovered by battery BT via the current flowing toward battery BT via a path via coil 31.

[0024] FIG. 2 is a flowchart showing the operation at engine start in the first embodiment.

[0025] In step S102 of FIG. 2, the control unit 10 determines whether or not an instruction to start the engine has been issued based on a predetermined signal, and if the determination is affirmative, the process proceeds to step S104, and if the determination is negative, the process proceeds to step S112.

[0026] In step S104, the control unit 10 switches on the boost switching element 32 and causes the boost circuit 30 to perform a boost operation.

[0027] In step S106, the control unit 10 determines whether the output voltage V of the boost circuit 30 has reached a predetermined voltage, and if the determination is affirmative, the process proceeds to step S108, and if the determination is negative, the process proceeds to step S104.

[0028] In step S108, the control unit 10 controls the switching elements 21u, 22u, 21v, 22v, and 21w, 22w of the drive circuit 20 to rotate the brushless motor M.

[0029] In step S110, the control unit 10 determines whether the engine has started based on a predetermined signal or the like, and if the determination is affirmative, proceeds to step S112, and if the determination is negative, proceeds to step S108.

[0030] In step S112, the control unit 10 turns off the boost switching element 32 to stop the boost operation of the boost circuit 30, and proceeds to step S102.

[0031] As described above, in the first embodiment, the boost circuit 30 is operated when starting the engine, and the brushless motor M is driven at a voltage higher than the voltage of the battery BT. This makes it possible to increase the torque of the brushless motor M and to accommodate engines that cannot be started with the voltage of the battery BT. Furthermore, since there is no need to install a separate high-voltage power supply (battery) for starting the engine in the vehicle, it is possible to avoid an increase in the size and complexity of the system and reduce implementation costs.

[0032] In the first embodiment, the boost circuit 30 may be operated at a timing other than when the engine is started. For example, when the voltage of the battery BT drops, the drop can be compensated for by the operation of the boost circuit 30, thereby obtaining motor characteristics similar to those obtained during normal operation when sufficient voltage is available from the battery BT.

[0033] Furthermore, in the first embodiment, at timings other than when the engine is started, the boost circuit 30 may not be operated and current from the battery BT may be supplied to the drive circuit 20 (brushless motor M). In this case, by turning off the boost switching element 32 and turning on the connection switching element 33, current from the battery BT may be supplied to the drive circuit 20 (brushless motor M) via the coil 31.

[0034] (Second Example) 3 is a diagram showing the configuration of a motor device according to the second embodiment. The differences from the first embodiment will be described below.

[0035] 3, the motor device of the second embodiment is provided with a bypass circuit 40A that connects the battery BT and the drive circuit 20 without passing through the boost circuit 30. A bypass switching element 40 is inserted in the bypass circuit 40A. The bypass switching element 40 is an FET, and the on / off state of the bypass switching element 40 is controlled by the control unit 10 controlling the gate voltage BG of the bypass switching element 40.

[0036] In the second embodiment, when the brushless motor M generates power, the current from the brushless motor M flows into the battery BT via a bypass circuit 40A in which a bypass switching element 40 is inserted.

[0037] The dotted arrows in FIG. 3 indicate the direction of current when the brushless motor M generates power.

[0038] During power generation, control unit 10 controls the on / off of switching elements 21u, 22u, switching elements 21v, 22v, and switching elements 21w, 22w so that the current generated by power generation in brushless motor M is taken in via drive circuit 20. Control unit 10 also controls gate voltage BG to turn on bypass switching element 40. Furthermore, control unit 10 turns off connection switching element 33 of boost circuit 30 to prevent current from brushless motor M from flowing into coil 31. Therefore, current from brushless motor M passes through drive circuit 20 and bypass switching element 40 (bypass circuit 40A) and then flows into battery BT via ignition switch SW, which is turned on. In this way, current from brushless motor M flows toward battery BT via bypass switching element 40 (bypass circuit 40A) rather than via coil 31, thereby charging battery BT.

[0039] In this way, in the second embodiment, during power generation, the battery BT is charged by the current passing through the bypass circuit 40A, thereby avoiding power loss and heat generation due to the current flowing through the boost circuit 30, particularly the coil 31.

[0040] In the second embodiment, depending on the state of charge of battery BT, voltage can be supplied to drive circuit 20 via bypass circuit 40A when the engine is started. The solid arrow in Fig. 3 indicates the direction of current when voltage is supplied to drive circuit 20 via bypass circuit 40A when the engine is started.

[0041] FIG. 4 is a flowchart showing the operation at engine start in the second embodiment.

[0042] In step S102 of FIG. 4, the control unit 10 determines whether or not an instruction to start the engine has been issued based on a predetermined signal, and if the determination is affirmative, the process proceeds to step S103, and if the determination is negative, the process proceeds to step S112.

[0043] In step S103, the control unit 10 determines whether the engine can be started using only the voltage of the battery BT based on the current voltage of the battery BT, and if the determination is affirmative, proceeds to step S122, and if the determination is negative, proceeds to step S104.

[0044] In step S104, the control unit 10 switches on the boost switching element 32 and causes the boost circuit 30 to perform a boost operation.

[0045] In step S106, the control unit 10 determines whether the output voltage V of the boost circuit 30 has reached a predetermined voltage, and if the determination is affirmative, the process proceeds to step S108, and if the determination is negative, the process proceeds to step S104.

[0046] In step S108, the control unit 10 controls the switching elements 21u, 22u, 21v, 22v, and 21w, 22w of the drive circuit 20 to rotate the brushless motor M.

[0047] In step S110, the control unit 10 determines whether the engine has started based on a predetermined signal or the like, and if the determination is affirmative, proceeds to step S112, and if the determination is negative, proceeds to step S108.

[0048] In step S112, the control unit 10 turns off the boost switching element 32 to stop the boost operation of the boost circuit 30, and proceeds to step S102.

[0049] On the other hand, in step S122, the control unit 10 turns off the connection switching element 33 and turns on the bypass switching element 40.

[0050] In step S124, the control unit 10 controls the switching elements 21u, 22u, 21v, 22v, and 21w, 22w of the drive circuit 20 to rotate the brushless motor M.

[0051] In step S126, the control unit 10 determines whether the engine has started based on a predetermined signal or the like, and if the determination is affirmative, the process proceeds to step S102, and if the determination is negative, the process proceeds to step S124.

[0052] As described above, in the second embodiment, when it is necessary to start the engine (when the determination in step S103 is negative), for example, when the voltage of battery BT is low, boost circuit 30 is operated to drive brushless motor M at a voltage higher than the voltage of battery BT. This increases the torque of brushless motor M, and even when the engine cannot be started with the voltage of battery BT alone, boosting the voltage of battery BT makes it possible to start the engine. Furthermore, since there is no need to separately install a high-voltage power supply (battery) for starting the engine on the vehicle, it is possible to avoid an increase in the size and complexity of the system and reduce implementation costs.

[0053] Furthermore, in the second embodiment, when the engine can be started using only the voltage of the battery BT (when the determination in step S103 is affirmative), the engine can be started without operating the boost circuit 30. This makes it possible to suppress unnecessary power consumption. Furthermore, in the second embodiment, not only when starting the engine, but also when not starting the engine, current from the battery BT can be supplied to the drive circuit 20 (brushless motor M) via the bypass circuit 40A without passing through the coil of the boost circuit 30. This makes it possible to avoid power loss and heat generation in the coil 31.

[0054] Furthermore, in the second embodiment, when the brushless motor M generates power, the generated current is supplied to the battery BT via the bypass circuit 40A without passing through the coil 31 of the boost circuit 30, thereby charging the battery BT. This makes it possible to avoid power loss and heat generation in the coil 31.

[0055] In the second embodiment, the boost circuit 30 may be operated at a timing other than when the engine is started. For example, when the voltage of the battery BT drops, the drop can be compensated for by the operation of the boost circuit 30, thereby obtaining motor characteristics similar to those obtained during normal operation when sufficient voltage is available from the battery BT.

[0056] (Third Example) 5 is a diagram showing the configuration of a motor device according to a third embodiment. In the third embodiment, boost circuits corresponding to the boost circuit 30 in the first embodiment are connected in parallel, but similar modifications can also be made to the second embodiment.

[0057] As shown in Fig. 5, in the third embodiment, in a motor drive device 1A, identical boost circuits 30A and 30B, which correspond to the circuit configuration of the boost circuit 30 in the first embodiment, are connected in parallel to each other. For convenience, in the boost circuit 30A in Fig. 5, the same reference numerals are used for corresponding elements in the boost circuit 30. However, the use of the same reference numerals does not mean that the same components as those in the boost circuit 30 are used in the boost circuits 30A and 30B.

[0058] The boost switching element 32 and the connection switching element 33 of the boost circuit 30A are supplied with gate signals G2 and G1 from the control unit 10, and the boost switching element 32 and the connection switching element 33 (not shown in FIG. 4) of the boost circuit 30B are supplied with gate signals G4 and G3 from the control unit 10. The gate signals G2 and G4, and the gate signals G1 and G3 are signals that are 180 degrees out of phase with each other.

[0059] In this way, by connecting the boost circuits 30A and 30B in parallel and alternately switching them, the current can be shared between the boost circuits 30A and 30B. In this case, even if the switching frequencies of the boost circuits 30A and 30B are the same as in the first embodiment, the output capacitor (corresponding to the capacitor formed by connecting two capacitors 34 in parallel) is repeatedly charged at twice the cycle. Therefore, even if the current supplied to the drive circuit 20 is the same as in the first embodiment, the peak current flowing per switching operation is reduced. This reduces the load on the battery BT and reduces EMI (electromagnetic interference). The capacitance of the capacitor 34 can also be reduced. Furthermore, because losses in the coil 31, the boost switching element 32, and the connection switching element 33 are reduced, these elements can be made smaller than in the boost circuit 30 of the first embodiment. That is, although both the boost circuits 30A and 30B are required, the mounting space for each circuit can be reduced compared to the boost circuit 30. Although FIG. 5 shows an example in which the capacitors 34 provided in the booster circuits 30A and 30B are connected in parallel as the output-side capacitors, a single capacitor may also be used.

[0060] The number of boost circuits to be connected in parallel is arbitrary. For example, when three boost circuits are connected in parallel, they can be switched at timings that are 120 degrees out of phase with each other. The circuit size (current capacity) of the boost circuits can also be arbitrary. For example, by connecting the boost circuits 30 of the first embodiment in parallel, the output current capacity can be increased. It is also possible to increase the current capacity of the boost circuit 30 by increasing the switching frequency or the inductance value of the coil 31. However, increasing the output current can cause problems such as increased losses in various parts of the circuit. In particular, increasing the switching frequency increases losses in the boost switching element 32, and increasing the inductance value of the coil 31 increases losses in the coil 31. These problems can be avoided by connecting the boost circuits in parallel.

[0061] As described above, according to the first to third embodiments, when starting the engine, the boost circuit 30 can obtain an output voltage V higher than the voltage of the battery BT. Therefore, the output voltage V can be used to rotate the brushless motor M via the drive circuit 20, so that the torque required to start the engine can be obtained. Furthermore, since the engine can be started without requiring any power source other than the battery BT, the system does not become larger or more complicated.

[0062] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0063] The following additional notes are provided regarding the above-described embodiments of the present invention.

[0064] [Appendix 1] A motor drive device (1) that drives a brushless motor (M) that starts an engine, a boost circuit (30) that boosts the voltage of a power supply (BT); a drive circuit (20) that drives the brushless motor; a control unit (10) that controls the drive circuit and the boost circuit; Equipped with The control unit operates the boost circuit when starting the engine, and starts the brushless motor using the drive circuit to which the voltage boosted by the boost circuit is applied.

[0065] According to the configuration described in Supplementary Note 1, the brushless motor is started by a drive circuit to which a voltage boosted by a boost circuit is applied, so that the torque required to start the engine can be obtained without preparing a separate high-voltage power supply.

[0066] [Appendix 2] In the motor drive device according to Supplementary Note 1, The boost circuit includes a coil (31) having one end connected to the power supply, and a boost switching element (32) connected between the other end of the coil and ground, The control unit switches on and off the boost switching element to generate an induced electromotive force in the coil.

[0067] According to the configuration described in Supplementary Note 2, the voltage of the power supply can be boosted by using the induced electromotive force generated in the coil when the boost switching element is switched.

[0068] [Appendix 3] 3. The motor drive device according to claim 2, wherein, during power generation, current from the brushless motor flows through the coil to the power supply to charge the power supply.

[0069] According to the configuration described in Supplementary Note 3, the coil of the boost circuit can be used as a charging path for flowing current from the brushless motor, thereby charging the power supply.

[0070] [Appendix 4] a bypass circuit (40A) that connects the power supply and the drive circuit without passing through the boost circuit; 3. The motor drive device according to claim 2, wherein, during power generation, current from the brushless motor flows to the power supply via the bypass circuit to charge the power supply.

[0071] According to the configuration described in Supplementary Note 4, the current from the brushless motor can be passed to the power supply via the bypass circuit without passing through the boost circuit, thereby avoiding power loss and heat generation in the boost circuit.

[0072] [Appendix 5] 3. The motor drive device according to claim 2, wherein a plurality of the boost circuits are provided, and the plurality of boost circuits are connected in parallel to one another.

[0073] According to the configuration described in Supplementary Note 5, since a plurality of boost circuits are connected in parallel with each other, the current supplied to the drive circuit can be shared.

[0074] [Appendix 6] The motor drive device according to any one of Supplementary Note 2 to Supplementary Note 5, wherein the boost circuit includes a connection switching element connected between the other end of the coil and the drive circuit and controlled by the control unit.

[0075] According to the configuration described in Supplementary Note 6, by turning off the connection switching element, it is possible to cut off the current flowing from the drive circuit to the coil.

[0076] [Appendix 7] A motor device including a brushless motor that starts an engine and a motor drive device that drives the brushless motor, The motor drive device a boost circuit that boosts the voltage of the power supply; a drive circuit for driving the brushless motor; a control unit that controls the drive circuit and the boost circuit; Equipped with The control unit, when starting an engine, operates the boost circuit and starts the brushless motor by the drive circuit to which the voltage boosted by the boost circuit is applied.

[0077] According to the configuration described in Supplementary Note 7, the brushless motor is started by a drive circuit to which a voltage boosted by a boost circuit is applied, so that the torque required to start the engine can be obtained without preparing a separate high-voltage power supply. [Explanation of symbols]

[0078] 1. Motor drive unit 10 Control Unit 20 Drive circuit 30 Boost circuit 31 Coil 32 Boost switching element 33 Connection switching element 40 Bypass switching element 40A bypass circuit M brushless motor

Claims

1. A motor drive device that drives a brushless motor that starts an engine, a boost circuit that boosts the voltage of the power supply; a drive circuit for driving the brushless motor; a control unit that controls the drive circuit and the boost circuit; a bypass circuit that connects the power supply and the drive circuit without passing through the boost circuit; Equipped with the boost circuit includes a coil having one end connected to the power supply, a boost switching element connected between the other end of the coil and ground, a connection switching element connected between the other end of the coil and a drive circuit, and a capacitor connected between the connection switching element and the ground, When the control unit determines based on the voltage of the power source at the time of starting the engine that the engine cannot be started by the voltage of the power source alone, the control unit switches on and off the boost switching element to operate the boost circuit so that the output voltage of the boost circuit becomes a predetermined value, thereby generating an induced electromotive force in the coil, and starts the brushless motor by the drive circuit to which the voltage boosted by the boost circuit is applied, a motor drive device that supplies voltage from the power supply to a drive circuit via the bypass circuit when it is determined that the engine can be started using only the voltage of the power supply based on the voltage of the power supply at the time of engine start and when the bypass circuit is controlled to be turned on by the control unit.

2. 2. The motor drive device according to claim 1, wherein when the bypass circuit is controlled to be turned on during power generation, current from the brushless motor flows through the bypass circuit to the power supply to charge the power supply.

3. 2. The motor drive device according to claim 1, wherein a plurality of said boost circuits are provided, and the plurality of said boost circuits are connected in parallel with each other.

4. 4. The motor drive device according to claim 1, wherein the boost circuit includes a connection switching element connected between the other end of the coil and the drive circuit and controlled by the control unit.

5. A motor device including a brushless motor that starts an engine and a motor drive device that drives the brushless motor, The motor drive device a boost circuit that boosts the voltage of the power supply; a drive circuit for driving the brushless motor; a control unit that controls the drive circuit and the boost circuit; a bypass circuit that connects the power supply and the drive circuit without passing through the boost circuit; Equipped with the boost circuit includes a coil having one end connected to the power supply, a boost switching element connected between the other end of the coil and ground, a connection switching element connected between the other end of the coil and a drive circuit, and a capacitor connected between the connection switching element and the ground, When the control unit determines based on the voltage of the power source at the time of starting the engine that the engine cannot be started by the voltage of the power source alone, the control unit switches on and off the boost switching element to operate the boost circuit so that the output voltage of the boost circuit becomes a predetermined value, thereby generating an induced electromotive force in the coil, and starts the brushless motor by the drive circuit to which the voltage boosted by the boost circuit is applied, a motor device that supplies voltage from the power supply to a drive circuit via the bypass circuit when it is determined that the engine can be started using only the voltage of the power supply based on the voltage of the power supply at the time of engine start and when the bypass circuit is controlled to be turned on by the control unit.

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