JP2011161545A - Power tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive cordless power tool with excellent safety and long service life. <P>SOLUTION: This small power tool has a lithium ion battery of one cell as a power source. The power tool detects overdischarge/overcurrent and controls current flowing in a motor to be shut off by turning OFF a switching element when detecting the overdischarge/overcurrent. The switching element is driven by voltage obtained by boosting battery voltage to stably monitor and protect overdischarge/overcurrent, even in a state in which battery voltage is low. Whether or not the battery voltage is boosted is determined based on the voltage impressed on the motor. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a cordless power tool driven by a battery pack such as a lithium ion secondary battery.

  In recent years, lithium-ion batteries that can be increased in capacity and weight have been used as batteries for driving cordless power tools. In general, a battery pack including a battery set formed by connecting a plurality of lithium ion battery cells in series is mounted on an electric tool for use. Lithium-ion batteries may be deteriorated or ignited if overdischarge or overcurrent discharge occurs. Monitor overdischarge and overcurrent discharge with a dedicated protection IC or microcomputer (hereinafter referred to as “microcomputer”). is doing. Protection ICs and microcomputers operate to shut off switching elements (FETs) provided in the discharge path when overdischarge / overcurrent discharge is detected, ensuring safe use of lithium ion batteries (Patent Literature) 1).

  On the other hand, some cordless electric tools use a lithium ion battery having only one cell for light work. Many of these types of power tools do not have a protective IC for monitoring overdischarge / overcurrent.

JP 2002-76340 A

  There is a need to further increase the safety of an electric tool using a lithium ion battery having only one cell and to prevent the battery from being shortened due to overdischarge and overcurrent. However, if a power IC driven by a single-cell lithium-ion battery is also provided with a protection IC to monitor overdischarge and overcurrent, a switching element (FET) that should operate in response to detection of overdischarge or overcurrent ) May not work properly. This is because the battery voltage of a 1-cell lithium ion battery is about 3.6 V, so when the remaining battery capacity decreases and the battery voltage decreases, the voltage applied to the switching element (FET) also decreases. It is because it ends up.

  An object of the present invention is to provide an inexpensive cordless electric tool that solves the above-described problems and is excellent in safety and long life.

  In order to achieve the above object, a power tool according to claim 1 includes a battery, a motor, a switching element for switching a current flowing through the motor, and a motor voltage detecting means for detecting a voltage applied to the motor. And based on the voltage detected by the motor voltage detecting means, and the switching element is driven by the output voltage from the drive voltage generating means.

  In the electric tool configured as described above, the drive voltage generation unit generates the drive voltage of the switching element, and the generation of the drive voltage is performed based on the voltage detected by the motor voltage detection unit. Therefore, for example, when the motor is stopped, the driving voltage of the switching element is not generated, and the driving voltage of the switching element can be generated only when the motor is rotating, thereby suppressing current consumption when not in use. be able to.

  The power tool according to claim 2 is characterized in that the drive voltage generating means is a boosting means for boosting the battery voltage.

  In the electric power tool configured as described above, since the switching element that switches the current flowing through the motor is driven by the voltage obtained by boosting the battery voltage, stable operation of the switching element is expected even when the battery voltage is low. Can do.

  The electric power tool according to claim 3 further includes filter means for shaping the detection signal output from the motor voltage detection means, and the filter means includes two of the first stage integration circuit and the second stage integration circuit. The time constant of the second stage integration circuit is larger than the time constant of the first stage integration circuit, and the boosting means boosts the voltage according to the detection signal shaped by the filter means. It is characterized in that the output voltage is output.

  In the electric tool configured as described above, the filter means for shaping the motor voltage signal includes two integration circuits, and the time constant of the second stage integration circuit is set to be greater than the time constant of the first stage integration circuit. The first stage integration circuit is relatively high in voltage, and the circuit is protected from surge noise with a high frequency. The second stage integration circuit generates a relatively high frequency due to the back electromotive force of the motor. The circuit can be protected from a low voltage rise.

  According to a fourth aspect of the present invention, the power tool further includes an illuminating unit, and the illuminating unit is turned on when supplied from the boosting unit.

  In the electric tool configured as described above, since the lighting unit is driven by the boosted voltage, it is possible to drive the lighting tool even when the driving voltage of the white LED or the like is higher than the battery voltage.

  According to a fifth aspect of the present invention, when the battery voltage is equal to or lower than a predetermined value, the battery overdischarge detection means for turning off the switching element as being in an overdischarge state, and the current flowing through the motor are detected and the electric tool flows When the current value is greater than or equal to a predetermined value, the battery overcurrent detection means is further provided for turning off the switching element because it is in an overcurrent state.

  In the electric power tool configured in this way, the operation of the switching element is stable even when the battery voltage is low, so that overdischarge / overcurrent can be reliably monitored and protected.

  The electric tool according to claim 6 further includes a forward / reverse switch for switching ON / OFF of the motor and a rotation direction, and the motor voltage detecting means detects both positive and negative voltages of the motor.

  In the electric tool configured as described above, the motor voltage detecting means detects both positive and negative voltages of the motor, and therefore can correspond to a forward / reverse switch.

  According to the present invention, current consumption can be suppressed, and overcurrent / overdischarge can be monitored stably even when the battery voltage decreases.

The circuit diagram which showed the electric constitution of the cordless electric tool which concerns on one Embodiment of this invention. The lineblock diagram of the cordless electric tool concerning one embodiment of the present invention.

  Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 2 is a configuration diagram showing an embodiment of the cordless power tool. In FIG. 2, 101 is an overdischarge / overcurrent monitoring circuit, 102 is a battery pack, 103 is a forward / reverse switch, 104 is a motor, and 105 is an LED for illumination. When the forward / reverse switch 103 is pushed to the R side, the motor 104 rotates clockwise, and when the forward / reverse switch 103 is pushed to the L side, the tip bit rotates accordingly, and screw tightening and drilling operations can be performed. When the forward / reverse switch 103 is in an intermediate position between the R side and the L side, as can be seen from FIG. 1, the electrical connection between the motor 104 and the battery pack 102 is interrupted, and the rotation of the motor 4 stops.

  Next, overdischarge / overcurrent monitoring according to the present embodiment will be described with reference to FIG. FIG. 1 is a circuit diagram showing an electrical configuration of a cordless power tool according to an embodiment of the present invention. The cordless electric tool includes a motor 104 and a battery pack 102 as a driving source of the motor 104, and a forward / reverse switch 103 that switches the rotation direction of the tip bit by switching the direction of the current flowing through the motor 104 is provided with the motor 10 and the battery pack. 102 is interposed.

  An overdischarge / overcurrent monitoring circuit 101 detects a voltage signal applied to the motor 104, a voltage detection / filter circuit 106 having a filter function for shaping the detected voltage signal, a booster circuit 107 that boosts the battery voltage, FET 108 for switching the current flowing through the motor 104, a current detecting shunt resistor 109 for detecting the current flowing through the motor 104, a protection IC 110 for monitoring the battery voltage and the current flowing through the motor 104, and resistors 111, 112, 115 , 128 and FETs 113 and 114.

  First, when the battery pack 102 is attached to the power tool body, the battery voltage is supplied to the protection IC 110 and the booster circuit 107. Next, when the forward / reverse switch 103 is pushed to either the L side or the R side, the battery voltage is supplied to the motor 104, and the voltage applied to the motor 104 is also input to the voltage detection / filter circuit 106. The voltage detection / filter circuit 106 includes resistors 116, 117, 121, capacitors 118, 122, and diodes 119, 120. The motor voltage is input to the resistor 116 if the forward / reverse switch 103 is pressed to the R side, and to the resistor 117 if the forward / reverse switch 103 is pressed to the L side. The input motor voltage removes surge noise by a first-stage integrating circuit composed of resistors 116 and 117 and a capacitor 118, passes through diodes 119 and 120, and is composed of a resistor 121 and a capacitor 122. The signals are averaged by the second-stage integrating circuit and input to the enable terminal (EN) of the boosting IC 124.

  The voltage detection / filter circuit 106 has two integration circuits, but the first-stage integration circuit has a relatively high voltage generated from chattering of the forward / reverse switch 103 and the brush of the motor 103, and a high frequency surge noise. Therefore, the diodes 119 and 120 and the boosting IC 124 are protected. Specifically, the peak voltage of surge noise is about 40V, and the withstand voltages of the diodes 119 and 120 are 30V. Therefore, the diodes 119 and 120 are protected by the first stage integration circuit.

  The second-stage integrating circuit plays a role of protecting the boosting IC 124 from a voltage increase (peak voltage is about 10 V) having a relatively low frequency generated by the counter electromotive voltage of the motor 103. That is, as the time constant of the integration circuit, the second stage is set to a larger value than the first stage. The resistor 128 connected in parallel with the capacitor 122 has a discharge path for discharging the electric charge stored in the capacitor 122 when the forward / reverse switch 103 is in an intermediate position between the R side and the L side, that is, when it is off. Is configured.

  As described above, the voltage detection / filter circuit 106 is a circuit for detecting the voltage applied to the motor 104, and at the same time, has a filter function for removing the noise component superimposed on the detection voltage and shaping the detection voltage. Have.

  Next, the booster circuit 107 will be described. The booster circuit 107 includes a booster IC 124, capacitors 123, 126, 127, and a diode 125. The booster circuit 107 is a booster system generally called a capacitor charge pump system, which superimposes the input voltage and the voltage charged in the capacitor 127 to boost the input voltage by a factor of 2 and output it. In this embodiment, “LM2766” sold by National Semiconductor is used as the boosting IC 124. The boosting IC 124 is a capacitor charge pump type IC, and includes an oscillator and an analog switch inside the IC. The connection of the capacitor 127 is switched by the analog switch, and the output voltage is doubled. Further, the boosting IC 124 has an enable terminal, and has a function of starting a boosting operation when a predetermined voltage is inputted to the enable terminal and stopping the boosting operation when no voltage is inputted to the enable terminal. ing. That is, when the forward / reverse switch 103 is pushed to either the L side or the R side, the motor voltage is input to the enable terminal (EN) of the boosting IC 124 through the voltage detection / filter circuit 106 and the booster circuit 107 is The boosting operation is started and a voltage twice the battery voltage is output.

  Next, the protection IC 110 will be described. The protection IC 110 is a battery protection IC for one cell, and monitors battery overdischarge and overcurrent. When the voltage input to the battery voltage detection terminal V is a predetermined value set in advance, for example, when it is 2.3 V or more, it is determined to be normal, and when it is 2.3 V or less, it is determined that the battery is overdischarged. The voltage input to the battery voltage detection terminal V is output at the time, and 0 V is output at the overdischarge. In addition, the protection IC 110 monitors overcurrent through the current detection terminal I. A voltage generated by the ON resistance of the FET 108 and the resistance value of the shunt resistor 109 for current detection is input to the current detection terminal I of the protection IC 110 and current is measured. The protection IC 110 assumes that it is in an overcurrent state when the voltage input to the current detection terminal I is a predetermined value that is set in advance, for example, 150 mV or more. When the voltage input to the voltage detection terminal V is overcurrent, 0V is output.

  Next, the voltage output from the protection IC 110 is input to the gate terminal of the FET 113. The FET 113 is normally turned on, and is turned off during overdischarge / overcurrent. Next, the drain terminal of the FET 113 is connected to the gate terminal of the FET 114 through the resistor 121. The FET 113 is normally turned on in conjunction with the operation of the FET 113, and the boosted voltage output from the booster circuit 107 is converted to the gate of the FET 108. Supply to the terminal. Further, when the protection IC 110 detects overdischarge / overcurrent, the FET 114 is turned off, so that the voltage to the gate terminal of the FET 108 is cut off. Therefore, the FET 108 is turned off, the discharge path of the battery pack 102 is interrupted, and overdischarge / overcurrent of the battery pack 102 can be prevented.

  The voltage boosted by the booster circuit 107 is also supplied to the LED 105 through the resistor 115. Therefore, the LED 105 can sufficiently emit light even if it is a white LED whose driving voltage is higher than the battery voltage, for example.

  In this embodiment, the capacitor charge pump system is used for the booster circuit, but the present invention is not limited to this. Although the cost increases, there is no particular problem even if the battery voltage is boosted by a generally used DC / DC converter.

103: Forward / reverse switch 104: Motor 105: LED
106: Voltage detection / filter circuit 107: Booster circuits 108, 113, 114: FET
109: Current detection shunt resistor 110: Battery protection IC
111, 112, 115, 116, 117, 121: Resistors 118, 122, 123, 126, 127: Capacitors 119, 120, 125: Diode 101: Overdischarge / overcurrent monitoring circuit 102: Battery pack

Claims (6)

Battery,
A motor,
A switching element for switching a current flowing through the motor;
Motor voltage detecting means for detecting a voltage applied to the motor;
Drive voltage generation means for generating a drive voltage for the switching element based on the voltage detected by the motor voltage detection means, and the switching element is driven by an output voltage from the drive voltage generation means. A featured electric tool.   2. The electric tool according to claim 1, wherein the drive voltage generating means is a boosting means for boosting a battery voltage. Filter means for shaping a detection signal output from the motor voltage detection means, the filter means having two integration circuits, a first stage integration circuit and a second stage integration circuit, The time constant of the second stage integration circuit is greater than the time constant of the first stage integration circuit,
3. The electric tool according to claim 2, wherein the boosting unit outputs a voltage boosted according to the detection signal shaped by the filter unit.   4. The electric tool according to claim 2, further comprising an illuminating unit, wherein the illuminating unit is turned on by supply from the boosting unit.   When the battery voltage is below a predetermined value, the battery overdischarge detection means for turning off the switching element as being overdischarged, and the current flowing through the motor are detected, and the current value flowing through the motor is above the predetermined value 5 further comprises battery overcurrent detection means for turning off the switching element as being in an overcurrent state.   6. The motor according to claim 1, further comprising a forward / reverse switch for switching ON / OFF of the motor and a rotation direction, wherein the motor voltage detection unit detects both positive and negative voltages of the motor. The electric tool described.

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