阅读说明：本技术 电气机器 (Electrical machine ) 是由 豊田慎也 于 2020-03-27 设计创作，主要内容包括：本发明提供一种可抑制故障风险的电气机器。电气机器包括：马达(32)；逆变电路(30),具有开关元件(S1～S6)且驱动所述马达(32)；以及电荷泵电路(22),生成所述开关元件(S1～S6)的驱动电压。在供给所述马达(32)的驱动电压(VM)的电源线与所述电荷泵电路(22)的输出端子(VGT端子)之间设有放电电路(放电电阻R及电容器C1)。开关元件(S4～S6)关断时在寄生电感(Ls)产生的浪涌电压(Vs)的能量由放电电路(放电电阻R及电容器C1)吸收。(The invention provides an electric machine capable of suppressing failure risk. The electric machine includes: a motor (32); an inverter circuit (30) that has switching elements (S1-S6) and drives the motor (32); and a charge pump circuit (22) that generates drive voltages for the switching elements (S1-S6). A discharge circuit (discharge resistor R and capacitor C1) is provided between a power supply line for supplying a drive Voltage (VM) of the motor (32) and an output terminal (VGT terminal) of the charge pump circuit (22). The energy of the surge voltage (Vs) generated in the parasitic inductance (Ls) when the switching elements (S4 to S6) are turned off is absorbed by the discharge circuit (the discharge resistor R and the capacitor C1).)

1. An electrical machine comprising:

a motor;

an inverter circuit having a switching element for driving the motor; and

a charge pump circuit for generating a drive voltage for the switching element

A discharge circuit is provided between a power supply line for supplying a drive voltage to the motor and an output terminal of the charge pump circuit.

2. The electrical machine of claim 1,

a discharge element is provided between the power supply line and an output terminal of the charge pump circuit.

3. An electrical machine comprising:

a motor;

an inverter circuit having a switching element for driving the motor; and

a charge pump circuit for generating a drive voltage for the switching element

A discharge element is provided between a power supply line that supplies a drive voltage of the motor and an output terminal of the charge pump circuit.

4. The electric machine of any one of claims 1 to 3,

an output terminal of the charge pump circuit is at a high potential with respect to the power supply line.

5. The electric machine of claim 2 or 3,

the switching element includes: a high-voltage side switching element connected to the power supply line; and a low-voltage side switching element connected to the ground,

the charge pump circuit has: a high-voltage side part connected to a control terminal of the high-voltage side switching element; and a low-voltage side portion connected to the low-voltage side switching element,

the discharge element is provided between the power supply line and the high voltage side portion.

6. The electrical machine of claim 5, comprising:

and a diode connecting a connection portion of the high-voltage-side switching element and the low-voltage-side switching element to the high-voltage side portion of the charge pump circuit, wherein a cathode of the diode is connected to the high-voltage side portion.

7. The electric machine of any one of claims 2, 3, 5, 6,

the discharge element is a resistor.

8. The electric machine of any one of claims 2, 3, 5, 6,

the discharge element is a zener diode.

Technical Field

The present invention relates to an electric machine which generates a drive voltage of an inverter circuit for driving a motor by using a charge pump (charge pump) circuit.

Background

Patent document 1 listed below discloses an electric apparatus in which a motor is driven by an inverter circuit. The electric machine is driven by alternating current, and includes an electrolytic capacitor for absorbing surge (surge) between output terminals of a diode bridge (diode bridge) for supplying direct current to an inverter circuit.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2018-057178

Disclosure of Invention

Problems to be solved by the invention

At a timing when a part of the switching elements of the inverter circuit is turned off, a surge voltage (large voltage) is generated in a parasitic inductance of the wiring. The surge voltage may cause a voltage at the output terminal of the charge pump circuit to rise and exceed a set value of the output voltage of the charge pump circuit. If the voltage of the output terminal of the charge pump circuit exceeds the withstand voltage of the circuit element, the risk of malfunction increases.

The present invention has been made in view of such a situation, and an object thereof is to provide an electric machine capable of suppressing a risk of failure.

Means for solving the problems

An embodiment of the present invention is an electric machine. The electric machine includes:

a motor;

an inverter circuit having a switching element for driving the motor; and

a charge pump circuit for generating a drive voltage for the switching element

A discharge circuit is provided between a power supply line for supplying a drive voltage to the motor and an output terminal of the charge pump circuit.

Here, a discharge element may be provided between the power supply line and the output terminal of the charge pump circuit.

The present invention in one aspect is an electrical machine. The electric machine includes:

a motor;

an inverter circuit having a switching element for driving the motor; and

a charge pump circuit for generating a drive voltage for the switching element

A discharge element is provided between a power supply line that supplies a drive voltage of the motor and an output terminal of the charge pump circuit.

Here, the output terminal of the charge pump circuit may be at a high potential with respect to the power supply line.

The switching element may also include: a high-voltage side switching element connected to the power supply line; and a low-voltage side switching element connected to the ground,

the charge pump circuit has: a high-voltage side part connected to a control terminal of the high-voltage side switching element; and a low-voltage side portion connected to the low-voltage side switching element,

the discharge element is provided between the power supply line and the high voltage side portion.

May also include: and a diode connecting a connection portion of the high-voltage-side switching element and the low-voltage-side switching element to the high-voltage side portion of the charge pump circuit, wherein a cathode of the diode is connected to the high-voltage side portion.

The discharge element may also be a resistor.

The discharge element may also be a Zener diode (Zener diode).

In addition, any combination of the above-described components and a form obtained by converting the expression of the present invention between a method, a system, or the like is also effective as a form of the present invention.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, an electric machine capable of suppressing the risk of failure can be provided.

Drawings

Fig. 1 is a perspective view of an electric power tool 1 according to an embodiment of the present invention.

Fig. 2 is a block circuit diagram of the electric power tool 1.

Fig. 3 is a circuit block diagram of the control unit 20 of fig. 2.

Fig. 4 is a time chart showing on/off (on-off) of the switching elements S1 to S6 in fig. 2.

Fig. 5 is a block diagram of a main circuit of the electric power tool 1 in a case where the discharge element 14 of fig. 2 is the zener diode ZD.

Fig. 6 is a block diagram of a main circuit of the electric power tool 1 in a case where the discharge element 14 of fig. 2 is the resistor R.

Fig. 7 is a main circuit block diagram of a comparative example with the discharge element 14 of fig. 2 removed.

Fig. 8 is a timing chart showing the on/off states of the switching elements S1, S2, S4, and S5, and the waveforms of the high-side charge pump voltage VGT, the drain-source voltage Vu of the switching element S4, and the low-side charge pump voltage VGB in the circuit of fig. 6.

Fig. 9 is a graph showing waveforms of the voltage Vu and VGT in the vicinity of 60 degrees when the electrical angle θ in fig. 8 is enlarged.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The same or equivalent components and members shown in the respective drawings are denoted by the same reference numerals, and redundant description thereof will be omitted as appropriate. The embodiments are illustrative and do not limit the invention, and all the features or combinations thereof described in the embodiments are not necessarily essential to the invention.

The present embodiment relates to an electric power tool 1. The electric power tool 1 is an example of an electric machine. As shown in fig. 1, the electric power tool 1 includes an electric power tool body 10 and a battery pack 5. The battery pack 5 is detachably connected to the electric tool body 10. When the operator pulls a trigger (trigger)11 of the electric power tool body 10, electric power is supplied from the battery pack 5 to the electric power tool body 10. The mechanical structure of the power tool 1 is well known, and therefore, the description thereof is omitted here. The circuit configuration of the electric power tool 1 will be described below. As shown in fig. 2, the electric power tool 1 includes a motor 31, an inverter circuit 30, and a control unit 20. Here, the motor 31 is a brushless motor (brushless motor) of an inner rotor type, and includes a stator 32 and a rotor 33. The stator 32 has U-phase, V-phase, and W-phase stator windings connected in star (Y-connection).

The inverter circuit 30 converts the dc output from the battery pack 5 into ac, supplies the ac to each stator winding of the stator 32, and drives the motor 31. A parasitic inductance (wiring inductance) Ls exists in a wiring path between the battery pack 5 and the inverter circuit 30. A surge absorbing capacitor (electrolytic capacitor) is not provided between the output terminals of the battery pack 5. The inverter circuit 30 includes switching elements S1 to S6 such as a Field Effect Transistor (FET) or an Insulated Gate Bipolar Transistor (IGBT) connected in a three-phase bridge. The drains or sources of the switching elements S1 to S6 are connected to the star-connected stator winding U, V, W. The switching elements S1 to S6 are turned on when the input voltage to their own gate (control terminal) is at a high level (high level), and are turned off when the input voltage is at a low level (low level). The on/off of the switching elements S1 to S6 is controlled by the control unit 20.

The gates of the switching elements S1 to S6 are connected to the inverter driving unit 25 of the control unit 20, and the switching elements S1 to S6 perform switching operations in accordance with the switching element driving signals H1 to H6 input from the inverter driving unit 25. Thus, the dc voltage from the battery pack 5 applied to the inverter circuit 30 is supplied as three-phase (U-phase, V-phase, and W-phase) voltages Vu, Vv, and Vw to the U-phase, V-phase, and W-phase stator windings. The counter voltage signals Hu, Hv, and Hw generated in the respective stator windings are input to the control unit 20.

A resistor R1 is provided on a path through which the reverse voltage signal Hu reaches the control unit 20. One end of the resistor R1 is connected to the interconnection of the switching elements S1 and S4. The other end of the resistor R1 is connected to the cathode of the diode D4 and the controller 20. The anode of diode D4 is connected to ground. A resistor R2 is provided on a path through which the counter voltage signal Hv reaches the control unit 20. One end of the resistor R2 is connected to the interconnection of the switching elements S2 and S5. The other end of the resistor R2 is connected to the cathode of the diode D5 and the controller 20. The anode of diode D5 is connected to ground. A resistor R3 is provided on a path through which the counter voltage signal Hw reaches the control unit 20. One end of the resistor R3 is connected to the interconnection of the switching elements S3 and S6. The other end of the resistor R3 is connected to the cathode of the diode D6 and the controller 20. The anode of diode D6 is connected to ground. The resistors R1 to R3 and the diodes D4 to D6 are protection elements for absorbing a negative component of the surge voltage Vs generated in the parasitic inductance Ls.

As shown in fig. 4, the high-side (high-voltage side) switching elements S1 to S3 are turned on at 120 degrees per 360 degrees of the cycle, and the low-side (low-voltage side) switching elements S4 to S6 are also turned on at 120 degrees per 360 degrees of the cycle, by 120 degrees of energization (rectangular wave drive) in which the energization method of the inverter circuit 30 is well known. In fig. 4, the on periods of the switching elements S1 to S6 are shown in black. During the on period, at least one of the high-side switching elements S1 to S3 and the low-side switching elements S4 to S6 may be controlled by Pulse Width Modulation (PWM).

The current detection circuit 12 detects the drive current of the motor 31 from the voltage of the resistor Rs in the path of the drive current of the motor 31 (the current flowing through each stator winding of the stator 32), and sends the drive current to the control unit 20. The voltage detection circuit 13 detects an output voltage of the battery pack 5 (an input voltage to the inverter circuit 30), and transmits the detected voltage to the control unit 20. The output voltage of the battery pack 5 is input to the VM terminal of the control section 20. The discharge element (power consumption element) 14 and the second discharge element (capacitor C1) are connected in series between the VM terminal and the VGT terminal of the control unit 20. The capacitor C2 is connected between the VGB terminal of the control unit 20 and ground. That is, the discharge element 14, the capacitor C1, and the capacitor C2 are provided separately from the control unit 20.

The temperature detection element 15 is, for example, a thermistor (thermistor), and is provided in the vicinity of the motor 31 or the inverter circuit 30. The temperature detection circuit 16 detects the temperature of the motor 31 or the inverter circuit 30 from the output voltage of the temperature detection element 15, and transmits the detected temperature to the control unit 20. The hall ICs (ICs) 19 are exemplified as magnetic detection elements, and three, for example, are provided near the motor 31. The rotor position detection circuit 17 is a filter circuit that removes noise from the output signal of the hall IC 19. The three output signals of the rotor position detection circuit 17 are input to the UH terminal, VH terminal, and WH terminal of the controller 20, respectively. The switch structure 18 switches on and off in conjunction with the operation of the trigger 11 in fig. 1, and transmits a switch operation detection signal to the control unit 20.

Fig. 3 shows a specific configuration example of the control unit 20. The control unit 20 may use a general motor control ic (integrated circuit) adapted to control a three-phase Direct Current (DC) brushless motor. The control unit 20 includes a plurality of external terminals as a means for establishing electrical connection with the outside. The UH terminal, the VH terminal, and the WH terminal are input terminals to which signals from three hall ICs 19 are input. The UHOUT terminal, the ULOUT terminal, the VHOUT terminal, the VLOUT terminal, the WHOUT terminal, and the WLOUT terminal are output terminals from which driving signals (switching element driving signals H1 to H6 in fig. 2) of the inverter circuit 30 are output. The U terminal, the V terminal, and the W terminal are input terminals for detecting the counter voltages (counter voltage signals Hu, Hv, and Hw in fig. 2) generated in the stator winding. The VGT terminal is a terminal through which a high-side gate driving voltage (high-side charge pump voltage) VGT outputted from the charge pump circuit 22 appears. The VGB terminal is a terminal through which a low-side gate drive voltage (low-side charge pump voltage) VGB output from the charge pump circuit 22 appears. The VM terminal is a power supply terminal for receiving supply of the power supply voltage VM from the battery pack 5. As described above, in the present embodiment, the discharge element 14 is externally connected in series with the capacitor C1 between the VM terminal and the VGT terminal of the control unit 20. The reason for this will be described later. Although not shown, the control unit 20 is also provided with terminals to which the output signals of the current detection circuit 12, the voltage detection circuit 13, the temperature detection circuit 16, and the switch structure 18 are input, and the terminals are connected to the operation unit 21.

The control unit 20 includes an arithmetic unit 21, a charge pump circuit 22, a rotor position detection circuit 23, a constant voltage generation circuit 24, and an inverter drive unit (pre-drive circuit) 25. The constant voltage generating circuit 24 includes a constant voltage generating circuit 24a that outputs 3.3V and a constant voltage generating circuit 24b that outputs 5.0V. The operating voltage of 3.3V is supplied to the computing unit 21. 5.0V is supplied to the inverter driving unit 25. The charge pump circuit 22 operates under the control of the arithmetic unit 21, generates a high-side gate drive voltage (31V in this case) and a low-side gate drive voltage (13V in this case) higher than the output voltage (18V in this case) of the battery pack 5, and supplies the voltages to the inverter drive unit 25. The charge pump circuit 22 includes a high-voltage side portion (high-side charge pump) and a low-voltage side portion (low-side charge pump), and generates a high-side gate drive voltage from the high-voltage side portion and a low-side gate drive voltage from the low-voltage side portion. The rotor position detection circuit 23 detects the rotational position of the motor 31 based on signals input from the UH terminal, the VH terminal, and the WH terminal, and transmits the detected rotational position to the arithmetic unit 21. The arithmetic unit 21 generates a gate control signal based on a signal from the rotor position detection circuit 23, and outputs the gate control signal to the inverter driving unit 25. The gate control signals are binary signals corresponding to 6 switching elements S1 to S6 of the inverter circuit 30, and are set to a high level when the switching elements S1 to S6 are turned on and set to a low level when the switching elements are turned off. The inverter driving unit 25 generates gate voltages (switching element driving signals H1 to H6) having improved current capacities of the gate control signals, and outputs the gate voltages to gates (control terminals) of the switching elements S1 to S6 of the inverter circuit 30. Each gate voltage is set to a high level when the corresponding gate control signal is at a high level, and is set to a low level when the gate control signal is at a low level.

Fig. 5 is a block diagram of a main circuit of the electric power tool 1 in a case where the discharge element 14 of fig. 2 is the zener diode ZD. Fig. 6 is a block diagram of a main circuit of the electric power tool 1 in a case where the discharge element 14 of fig. 2 is the resistor R. The resistor R is a fixed resistor. Fig. 7 is a main circuit block diagram of a comparative example with the discharge element 14 of fig. 2 removed. Fig. 5 to 7 show portions related to driving of the switching elements S1 and S4 in the internal circuit of the inverter driving unit 25. Although not shown, in the internal circuit of the inverter driving unit 25, the portions related to the driving of the switching elements S2 and S5 and the portions related to the driving of the switching elements S3 and S6 are configured in the same manner as the portions related to the driving of the switching elements S1 and S4, and operate in the same manner.

The inverter driving unit 25 includes switching elements Q1 to Q12 such as FETs. The switching elements Q1, Q3, Q5, Q7, Q9, and Q11 are P-channel type, and the switching elements Q2, Q4, Q6, Q8, Q10, and Q12 are N-channel type. A diode D1 is provided between the U terminal (interconnection portion of the switching elements S1 and S4) and the VGT terminal. The diode D1 has an anode connected to the U terminal and a cathode connected to the VGT terminal. Diodes D2, D3 are provided between the U terminal and ground. The anode of the diode D2 is connected to the U terminal. The cathodes of the diodes D2, D3 are connected to each other. The anode of diode D3 is connected to ground.

The arithmetic unit 21 inputs a gate control signal for outputting the gate voltage of the switching element S1 to the gates (control terminals) of the switching elements Q5 to Q8. When the gate control signals to the switching elements Q5 to Q8 are at a high level, the switching elements Q5 and Q7 are turned off, the switching elements Q6 and Q8 are turned on, the switching element Q1 is turned on, the switching element Q2 is turned off, and the switching element S1 is turned on. When the gate control signals to the switching elements Q5 to Q8 are at a low level, the switching elements Q5 and Q7 are turned on, the switching elements Q6 and Q8 are turned off, the switching element Q1 is turned off, the switching element Q2 is turned on, and the switching element S1 is turned off. Similarly, the switching element S4 is turned on when the gate control signal supplied from the arithmetic unit 21 to the switching elements Q9 to Q12 is at a high level, and the switching element S4 is turned off when the gate control signal is at a low level.

Fig. 8 is a timing chart showing the on/off states of the switching elements S1, S2, S4, and S5, and the waveforms of the high-side charge pump voltage VGT, the drain-source voltage Vu of the switching element S4, and the low-side charge pump voltage VGB in the circuit of fig. 6. As an example, the operation when the electrical angle θ is 0 to 60 degrees will be described with reference to fig. 5, 6, and 8. In the range of the electrical angle θ from 0 degree to 60 degrees, the switching element S1 and the switching element S5 are turned ON (ON), and the other switching elements are turned OFF (OFF). At this time, the drain-source voltage Vu of the switching element S4 becomes Vu ═ VM.

When the electrical angle θ is 60 degrees, the switching element S5 is turned from ON (ON) to OFF (OFF). Fig. 5 and 6 show a state immediately after the switching element S5 is turned off and before the switching element 6 is turned on when the electrical angle θ is 60 degrees, and a surge voltage Vs is generated in the parasitic inductance Ls. At this time, the energy stored in the parasitic inductance Ls is applied as a surge voltage Vs between the drain and the source of the switching element S4 via the switching element S1, and the drain-source voltage Vu of the switching element S4 becomes Vu ═ VM + Vs. When the drain-source voltage Vu of the switching element S4 becomes greater than the high-side charge pump voltage VGT due to the surge voltage Vs, a charge current flows to the VGT terminal via the diode D1.

In the circuit of fig. 5, the charging current is consumed by the zener diode ZD connected between the VGT terminal and the VM terminal, and thus the high-side charge pump voltage VGT is always substantially constant. That is, a discharge circuit including the zener diode ZD is formed between the VGT terminal and the VM terminal. The VGT terminal is at a high potential with respect to the VM terminal. The discharge circuit is formed by, for example, a zener diode ZD, a parasitic inductance Ls, a switching element S1, a diode D1, and a capacitor C1. In this way, when the zener diode ZD is used as the protection element, the energy having Vu > VGT due to the surge voltage Vs generated in the parasitic inductance when the low-side (lower arm side) switching elements S4 to S6 are turned off is consumed by the instantaneous large current flowing through the zener diode ZD forming the discharge circuit. Therefore, the zener diode ZD needs to have a large allowable loss, and the external size of the zener diode ZD increases, and the component cost also increases. Further, the capacitor C1 may not be provided in series with the zener diode ZD, and in this case, the surge voltage Vs may be consumed by a momentary large current flowing through the zener diode ZD.

In the circuit of fig. 6, the charging current is consumed as heat by the resistor R connected between the VGT terminal and the VM terminal. Similarly to the circuit of fig. 5, a discharge circuit including a resistor R is formed between the VGT terminal and the VM terminal. At this time, the VGT terminal is also at a high potential with respect to the VM terminal. The discharge circuit is formed by a resistor R, a parasitic inductor Ls, a switching element S1, a diode D1, and a capacitor C1, for example. Unlike the case where the protection element is the zener diode ZD, the charging current at this time is relatively small according to Ohm's law, and the flow is relatively time-consuming. The high-side charge pump voltage VGT is higher in a period in which a current flows through the resistor R forming the discharge circuit than in other periods. By appropriately selecting the resistance value of the resistor R, the increase of the high-side charge pump voltage VGT can be suppressed within the allowable range. The risk of short-circuit failure of the zener diode ZD is relatively high, but the risk of short-circuit failure of the resistor R as a passive element is low, and thus reliability is improved. In addition, the capacitor C1 may not be provided in series with the resistor R, and in this case, the surge voltage Vs may be consumed by the current flowing through the resistor R.

In the circuit of the comparative example of fig. 7, only the capacitor C1 serving as the second discharge element is present between the VGT terminal and the VM terminal, and there is no element consuming power, so the high-side charge pump voltage VGT greatly increases. In the charge pump circuit 22, the maximum rating of the high-side charge pump voltage VGT is, for example, 48V. In the circuit of the comparative example in fig. 7, the high-side charge pump voltage VGT is likely to exceed the maximum rating due to the surge voltage Vs, and the risk of failure of the high-side charge pump is high. However, if the surge voltage Vs is small, the surge voltage Vs can be absorbed only by the capacitor C1 serving as the second discharge element without providing the discharge element 14 as shown in fig. 5 or 6. At this time, a discharge circuit including the capacitor C1 is also formed between the VGT terminal and the VM terminal. The discharge circuit is formed by, for example, a capacitor C1, a parasitic inductance Ls, a switching element S1, and a diode D1.

Fig. 9 is a graph showing waveforms of the voltages Vu and VGT in the vicinity of 60 degrees when the electrical angle θ in fig. 8 is enlarged. As shown in fig. 9, the voltage VGT rises from a point a at which Vu > VGT, and then the voltage VGT gradually falls from a point B at which Vu < VGT. The delay of the rise of the voltage VGT with respect to the rise of the voltage Vu and the temporal deviation of the voltage Vu from the top of the voltage VGT are caused by the resistor R1. The voltage fluctuation shown in fig. 9 is caused by the surge voltage Vs of the parasitic inductance Ls due to the turn-off of the switching element S5 when the electrical angle θ is 60 degrees, but the same surge voltage Vs is generated in the parasitic inductance Ls also by the turn-off of the switching element S6 when the electrical angle θ is 180 degrees and the turn-off of the switching element S4 when the electrical angle θ is 300 degrees, and the same voltage fluctuation as shown in fig. 9 is caused.

According to the present embodiment, the following effects can be exhibited.

(1) Since the discharge circuit is configured between the VGT terminal at which the high-side charge pump voltage VGT generated by the charge pump circuit 22 appears and the VM terminal at which the output voltage VM of the battery pack 5 is inputted, the energy of the surge voltage Vs generated in the parasitic inductance Ls by turning off the low-side switching elements S4 to S6 can be consumed by the discharge circuit. Therefore, the risk of malfunction of the circuit elements (the charge pump 22, particularly the high-side (high-voltage side) charge pump) due to sudden increase in the high-side charge pump voltage VGT can be suppressed.

Since the discharge element 14 is provided between the VGT terminal and the VM terminal, energy of the surge voltage Vs generated in the parasitic inductance Ls by turning off the low-side switching elements S4 to S6 can be consumed by the discharge element 14. Therefore, the risk of malfunction of the circuit elements (the charge pump 22, particularly the high-side (high-voltage side) charge pump) due to sudden increase in the high-side charge pump voltage VGT can be suppressed. Further, since the second discharge element (the capacitor C1) is provided between the VGT terminal and the VM terminal, the energy of the relatively small surge voltage Vs generated in the parasitic inductance Ls by turning off the low-side switching elements S4 to S6 can be consumed by the second discharge element.

(2) When the discharge element 14 is the zener diode ZD as shown in fig. 5, the high-side charge pump voltage VGT can be always substantially constant.

(3) When the discharge element 14 is the resistor R as shown in fig. 6, the high-side charge pump voltage VGT varies to some extent, but the risk of short-circuit failure is low, so that the reliability is high, and the component cost can be suppressed.

(4) By providing the discharge element 14 as described above, it is possible to suppress the influence of the disadvantage, that is, the large variation in the high-side charge pump voltage VGT, while enjoying the advantage of the charge pump system described later. This point will be explained below. As a method of driving the high-side (upper arm side) switching elements S1 to S3, there is a bootstrap (bootstrap) method in addition to the charge pump method. The bootstrap mode has the following disadvantages: a period during which the bootstrap capacitor needs to be charged in the motor drive; or the occupancy (Duty) of 100% cannot be maintained for a long period. In contrast, the charge pump system of the present embodiment has the following advantages: there is no need to charge the bootstrap capacitor in driving of the motor 31; or may maintain the occupancy (Duty) at 100% for a long period of time, etc. On the other hand, the bootstrap method is a floating power supply (floating power) and thus allows voltage variation, and voltage variation due to a surge voltage Vs generated in the parasitic inductance Ls is not a big problem. In contrast, the charge pump system of the present embodiment is based on the idea that a constant voltage is always maintained with respect to the ground (the charge pump system is a ground power supply), and thus variation of the high-side charge pump voltage VGT due to the surge voltage Vs becomes a problem. In the present embodiment, the influence of the disadvantages of the charge pump system can be suppressed by suppressing the variation of the high-side charge pump voltage VGT due to the surge voltage Vs by the discharge element 14.

(5) Since the energy of the surge voltage Vs of the parasitic inductance Ls is consumed by the discharge element 14, it is not necessary to provide an electrolytic capacitor for surge absorption between the output terminals of the battery pack 5, and the cost is low.

(6) By providing the discharge element 14 externally separately from the control unit 20, only the discharge element can be selected according to the product specification as compared with a structure integrally encapsulated (one package) with the control unit 20, so that the degree of freedom in design is improved, and the risk of failure of the circuit element due to sudden increase in the high-side charge pump voltage can be easily suppressed.

(7) Since the discharge element 14 and the capacitor C1 are connected in series between the VGT terminal at which the high-side charge pump voltage VGT generated by the charge pump circuit 22 appears and the VM terminal to which the output voltage VM of the battery pack 5 is inputted, the withstand voltage of the discharge element serving as a protection element can be reduced as compared with the case where the discharge element is connected between the VGT terminal and the ground. Further, when the voltage is connected between the VGT terminal and the ground, a voltage obtained by adding a surge voltage to a power supply voltage (battery voltage) is applied to the discharge element, and therefore, it is necessary to increase the withstand voltage.

While the present invention has been described above by way of examples of the embodiments, those skilled in the art will appreciate that various modifications may be made to the components and processes of the embodiments within the scope of the claims. The following describes modifications.

The electric machine of the present invention is not limited to DC drive (cordless type), and may be AC drive (corded type), and may be an electric working machine or a power tool other than an electric tool, and may be another electric machine. The specific voltage values and the like described in the embodiments are examples, and may be changed as appropriate.

Description of the symbols

1: electric tool

5: battery pack

10: electric tool body

11: trigger

12: current detection circuit

13: voltage detection circuit

14: discharge element (Power consumption element)

15: temperature detecting element

16: temperature detection circuit

17: rotor position detection circuit

18: switch structure

19: hall IC

20: control unit

21: arithmetic unit

22: charge pump circuit

23: rotor position detection circuit

24: constant voltage generating circuit

24 a: constant voltage generating circuit (3.3V)

24 b: constant voltage generating circuit (5.0V)

25: contravariant driving part (predrive circuit)

30: inverter circuit

31: motor (brushless motor)

32: stator

33: rotor