JP2008183689A - Power tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power tool allowing reduction in cost and size of a battery pack. <P>SOLUTION: This battery pack 14 separated from a power tool main body 12 has an overdischarge detection circuit 42 for detecting overdischarge of a battery 40, and battery capacity computing part 46 and overdischarge signal output part 47 for outputting an overdischarge signal when detecting the overdischarge. The power tool main body 12 has a cut-off circuit 38 for cutting off control power supply of a control circuit 34 controlling a brushless DC motor 22 when the overdischarge signal is inputted. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a cordless power tool driven by a battery pack.

  In recent power tools such as impact drivers and grinders, cordless power tools that are driven by attaching a battery pack separate from the power tool main body have become mainstream (see, for example, Patent Document 1).

Recently, a rechargeable battery built in a battery pack has been adopted as a lithium ion battery instead of a nickel metal hydride battery.
JP 2006-315117 A

  As shown in FIG. 4, the conventional power tool 100 includes a power tool body 102 and a separate battery pack 104, and a motor 106 and a drive circuit 108 are built in the power tool body 102. . On the other hand, a lithium ion battery 110 and an overdischarge protection circuit 112 are built in the battery pack 104.

  In the electric power tool 100 having such a configuration, the power supply line must be shut off using the cutoff switch 114 inside the battery pack 104 in order to protect the lithium ion battery 110 from overdischarge. This cut-off switch 114 requires a large current type FET, which is a very expensive circuit including a heat dissipation mechanism, and the size of the battery pack 104 is increased.

  Therefore, in view of the above problems, the present invention provides an electric tool capable of reducing the size and size of a battery pack.

The present invention is separate from the electric power tool main body, which has a motor for driving a tool, an inverter circuit for supplying a driving current to the motor, and a control circuit for controlling the inverter circuit, and the electric power tool main body. A battery pack having a rechargeable battery that supplies power to the inverter circuit and the control circuit, wherein the battery pack includes an overdischarge detection circuit that detects overdischarge of the rechargeable battery, and the overdischarge A signal output circuit that outputs an overdischarge signal when the detection unit detects overdischarge, and the power tool body supplies power from the rechargeable battery to the control circuit when the overdischarge signal is input. Having a shut-off circuit to shut off,
It is a power tool.

  According to another aspect of the present invention, there is provided a power tool body having a motor for driving a tool, an inverter circuit for supplying a drive current to the motor, and a control circuit for controlling the inverter circuit, and the power tool body. And a battery pack having a rechargeable battery for supplying power to the inverter circuit and the control circuit, wherein the battery pack includes a detection circuit for detecting overheating of the rechargeable battery, and the overdischarge detection. A signal output circuit that outputs an overheat signal when the unit detects overheat, and the electric power tool body shuts off power from the rechargeable battery to the control circuit when the overheat signal is input An electric tool having a circuit.

  According to another aspect of the present invention, there is provided a power tool body having a motor for driving a tool, an inverter circuit for supplying a drive current to the motor, and a control circuit for controlling the inverter circuit, and the power tool body. A battery pack having a rechargeable battery for supplying power to the inverter circuit and the control circuit, wherein the battery pack includes a detection circuit for detecting overdischarge and overheating of the rechargeable battery; A signal output circuit that outputs a detection signal when the overdischarge detection unit detects overdischarge or overheat, and the electric power tool body receives the detection signal from the rechargeable battery to the control circuit. It is an electric tool which has the interruption | blocking circuit which interrupts | blocks the power supply of.

  According to the present invention, since the electric tool main body is provided with a cutoff circuit for overdischarge and overheat protection, the battery pack can be inexpensive and reduced in size.

(First embodiment)
Hereinafter, a cordless power tool 10 according to a first embodiment of the present invention will be described with reference to FIGS. In the present embodiment, an impact driver will be described as an example.

(1) Configuration of Electric Tool 10 The electric tool 10 will be described with reference to FIG.

  The electric power tool 10 includes an electric power tool main body 12 and a battery pack 14 that is separate from the electric power tool main body 12.

  The frame 16 of the electric power tool main body 12 is a pistol type, and a tool 20 is attached to the distal end portion of the body portion 18 thereof. In addition, a brushless DC motor (hereinafter simply referred to as a motor) 22 and a gear box 24 for connecting the tool 20 and the output shaft of the motor 22 to rotate at a predetermined rotational speed are provided inside the body portion 18. Yes. A wiring board 23 is disposed below the motor 22.

  A trigger switch 28 is provided on the upper portion of the grip portion 26 of the frame 16. Three terminals 30a, 30b, and 30c are formed at the lower end of the grip portion 26, and a separate battery pack 14 is detachably attached.

(2) Electrical Configuration of Electric Tool 10 Next, the electrical configuration of the electric tool 10 will be described based on the block diagram of FIG.

  On the wiring board 23 in the electric power tool main body 12, an inverter circuit 32 for driving the motor 22, a control circuit 34 for PWM control of the inverter circuit 32, and a control power supply for supplying control power to the control circuit 34 A section 36 and a cutoff circuit 38 are provided.

  The driving power source for driving the inverter circuit 32 is driven by the power source supplied from the two terminals 30a and 30c. The control power supply unit 36 steps down the voltage supplied from the battery pack 14 and supplies the voltage to the control circuit 34 with an optimum voltage (for example, 5 V). The driving power supplied from the control power supply unit 36 is supplied to the cutoff circuit 38 via the trigger switch 28, and is supplied to the control circuit 34 via the cutoff circuit 38. The blocking circuit 38 will be described later.

  The battery pack 14 includes a lithium ion battery (hereinafter simply referred to as a rechargeable battery) 40, an overdischarge detection circuit 42, a current detection circuit 44, a battery capacity calculation unit 46 composed of a microcomputer, an overdischarge signal output unit 47, and a voltage level conversion unit. 48 is built-in.

  The power supplied from the rechargeable battery 40 is supplied to the control power source 36 and the inverter circuit 32 of the electric power tool main body 12 through the terminals 30a and 30c.

(3) Operational state of battery pack 14 As described above, power is supplied from the rechargeable battery 40. At this time, it is detected whether the battery capacity and overdischarge are present. The method will be described below.

  A resistance element 52 is provided on the negative power line 50 of the battery pack 14, and the voltage at both ends of the resistance element 52 is detected by the current detection circuit 44 and converted into a current value. Is detected. The detected current value is output to the battery capacity calculation unit 46. The battery capacity calculator 46 integrates the current values, calculates how much current the rechargeable battery 40 has flowed up to the present, and calculates the remaining battery capacity.

  On the other hand, the overdischarge detection circuit 42 measures the voltage value between the positive terminal and the negative terminal of the rechargeable battery 40 and outputs the voltage value to the battery capacity calculation unit 46. In the battery capacity calculation unit 46, the rechargeable battery 40 is overdischarged if the voltage value output from the overdischarge detection circuit 42 is greater than or equal to a threshold value in the discharge level range where the calculated battery capacity is 0 or more and less than the reference capacity. Judged to be in a state. Similarly, if the current value output from the current detection circuit 44 in the discharge level range is greater than or equal to the threshold value, it is determined that more current than necessary is flowing, and it is determined that overdischarge has occurred.

  When the battery capacity calculation unit 46 determines that overdischarge occurs, the overdischarge signal output unit 47 outputs an overdischarge signal to the voltage level conversion unit 48. For example, the voltage value is increased from level L to H.

  When a level H overdischarge signal is input, the voltage level converter 48 converts the level H into a predetermined voltage (voltage Va), and outputs the overdischarge signal to the power tool body 12.

  When the H level overdischarge signal Va is input to the cutoff circuit 38, the comparator 54 compares the voltage Va with the reference voltage Vd. Since the overdischarge signal Va is equal to or higher than the reference voltage Vd, a trigger signal is output from the comparator 54. The shut-off switch 56 is turned off. As a result, when an overdischarge signal is output, the cutoff switch 56 is turned off, the control power supplied via the control power supply unit 36 and the trigger switch 28 is turned off, and the control circuit 34 is stopped. Therefore, the rotation of the motor 22 is also stopped. The cutoff switch 56 uses a switching element such as a small FET.

(4) Operation Contents of Electric Tool 10 Next, the operation state of the electric tool 10 will be described based on the flowchart of FIG.

  In step 1, when the worker performs work, the trigger switch 28 of the electric tool 10 is turned on.

  In step 2, power is supplied from the battery pack 14, drive power is supplied to the inverter circuit 32, and control power is supplied to the control circuit 34.

  In Step 3, it is determined whether or not the rechargeable battery 40 is overdischarged inside the battery pack 14 as described above.

  If not overdischarge, discharge is permitted in step 4, the cutoff switch 56 is turned on in step 5, and the motor 22 is driven in step 6.

  On the other hand, if it is determined that the battery is in an overdischarged state, the discharge is stopped in step 7, the cutoff switch 56 is turned off in step 8, and the motor 22 is stopped in step 9.

(5) Effect With the electric power tool 10 as described above, the battery pack 14 does not require a large current type FET for preventing overdischarge, and the power tool 10 is small for turning off the control power supplied to the control circuit 34. Since the capacity cutoff switch 56 is simply turned off, the cost is reduced.

  Further, since no interruption circuit is required on the battery pack 14 side, the size can be reduced.

(Second Embodiment)
In the first embodiment, the overdischarge detection circuit 40 is provided in the battery pack 14. However, instead of this, an overheat detection circuit is provided, and when the temperature of the battery pack 14 rises above the reference temperature, the overheat detection signal is electrically driven. The rotation of the motor 22 may be stopped by outputting to the cutoff circuit 38 of the tool body 12.

(Third embodiment)
In the first embodiment, the overdischarge detection circuit 40 is provided in the battery pack 14, but an overheat detection circuit is also provided in addition to this, and when the battery pack 14 is overdischarged, or the temperature of the battery pack 14 is a reference. When the temperature rises above the temperature, a detection signal may be output to the cutoff circuit 38 of the electric power tool body 12 to stop the rotation of the motor 22.

(Example of change)
The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist thereof.

  In the above embodiment, the impact driver has been described. However, other power tools such as a grinder can also be applied.

  Further, a motor that is rotated by an inverter circuit 32 other than the brushless DC motor can be applied.

It is a side view of the electric tool of one embodiment of the present invention. It is a block diagram of an electric tool. It is a flowchart in the case of driving or stopping a motor. It is a block diagram of the conventional electric tool.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electric tool 12 Electric tool main body 14 Battery pack 22 Motor 28 Trigger switch 32 Inverter circuit 34 Control circuit 36 Control power supply part 38 Cutoff circuit 40 Rechargeable battery 42 Overdischarge detection circuit 44 Current detection circuit 46 Battery capacity calculation part 46 Overdischarge signal output 48 Voltage level converter 56 Shut-off switch

Claims (4)

A power tool body having a motor for driving a tool, an inverter circuit for supplying a driving current to the motor, and a control circuit for controlling the inverter circuit;
A battery pack having a rechargeable battery for supplying power to the inverter circuit and the control circuit;
In the electric tool consisting of
The battery pack is
A detection circuit for detecting overdischarge of the rechargeable battery;
A signal output circuit that outputs an overdischarge signal when the overdischarge detection unit detects overdischarge;
The power tool main body has a shut-off circuit that shuts off power from the rechargeable battery to the control circuit when the overdischarge signal is input.
Electric tool. A power tool body having a motor for driving a tool, an inverter circuit for supplying a driving current to the motor, and a control circuit for controlling the inverter circuit;
A battery pack having a rechargeable battery for supplying power to the inverter circuit and the control circuit;
In the electric tool consisting of
The battery pack is
A detection circuit for detecting overheating of the rechargeable battery;
A signal output circuit that outputs an overheat signal when the overdischarge detection unit detects overheating;
The power tool body has a shut-off circuit that shuts off the power supply from the rechargeable battery to the control circuit when the overheat signal is input.
Electric tool. A power tool body having a motor for driving a tool, an inverter circuit for supplying a driving current to the motor, and a control circuit for controlling the inverter circuit;
A battery pack having a rechargeable battery for supplying power to the inverter circuit and the control circuit;
In the electric tool consisting of
The battery pack is
A detection circuit for detecting overdischarge and overheating of the rechargeable battery;
A signal output circuit that outputs a detection signal when the overdischarge detection unit detects overdischarge or overheat;
The power tool main body has a shut-off circuit that shuts off power from the rechargeable battery to the control circuit when the detection signal is input.
Electric tool. The motor is a brushless DC motor;
The power tool according to at least one of claims 1 to 3.

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