WO2014038165A1 - Power tool - Google Patents

Power tool Download PDF

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Publication number
WO2014038165A1
WO2014038165A1 PCT/JP2013/005129 JP2013005129W WO2014038165A1 WO 2014038165 A1 WO2014038165 A1 WO 2014038165A1 JP 2013005129 W JP2013005129 W JP 2013005129W WO 2014038165 A1 WO2014038165 A1 WO 2014038165A1
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WO
WIPO (PCT)
Prior art keywords
over
battery
discharge
detection unit
temperature
Prior art date
Application number
PCT/JP2013/005129
Other languages
French (fr)
Inventor
Yuki Horie
Yukihiro Shima
Kazuhiko Funabashi
Original Assignee
Hitachi Koki Co., Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hitachi Koki Co., Ltd. filed Critical Hitachi Koki Co., Ltd.
Publication of WO2014038165A1 publication Critical patent/WO2014038165A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25F—COMBINATION OR MULTI-PURPOSE TOOLS NOT OTHERWISE PROVIDED FOR; DETAILS OR COMPONENTS OF PORTABLE POWER-DRIVEN TOOLS NOT PARTICULARLY RELATED TO THE OPERATIONS PERFORMED AND NOT OTHERWISE PROVIDED FOR
    • B25F5/00—Details or components of portable power-driven tools not particularly related to the operations performed and not otherwise provided for
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/18—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for batteries; for accumulators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/24—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to undervoltage or no-voltage

Definitions

  • the present invention relates to a power tool that is powered by a secondary battery, such as a lithium-ion battery.
  • cordless power tools are that they can be used anywhere since they do not need to be connected to a commercial power source with a power cord, and the power tool is easier to operate without the cord getting in the way. For this reason, cordless power tools have become widely popular.
  • Recently battery packs housing lithium-ion secondary battery have become more widely used as the power supply for cordless power tools.
  • These battery packs have a built-in protection circuit to prevent battery degradation and to ensure safety for the user. When the battery is in an over-discharge condition, the protection circuit outputs an over-discharge signal for cutting off the power supplied to the power tool on which the battery pack is mounted (For example, refer to Japanese Patent Application Publication No. 2009-95162).
  • the battery temperature may be low at times due to the effects of ambient temperature and the like.
  • the internal resistance of the battery packs is high when the battery temperature is low. Therefore, if operating the power tool when the battery temperature is low, a phenomenon may occur in which the output voltage temporarily drops in the initial drive stage, even though the charge capacity of the battery is sufficiently high. Consequently, when the power tool is used in a cold environment, the protection circuit built into the battery pack may wrongly determine that this temporary drop in voltage at the beginning of operations is an over-discharge condition, leading the protection circuit to cut off the power supply to the power tool. Thus, when the operator attempts to use the power tool initially, the tool may stop operating temporarily, preventing the operator from using the tool until the battery temperature rises to its operable temperature range.
  • the present invention features a power tool.
  • the power tool includes a secondary battery, a drive unit, a battery temperature detection unit, an over-discharge detection unit, and a control unit.
  • the battery voltage detection unit is configured to detect a battery voltage of the secondary battery.
  • the battery temperature detection unit is configured to detect a temperature of the secondary battery.
  • the over-discharge detection unit is configured to detect that a charge capacity of the secondary battery is less than a prescribed value and output an over-discharge signal indicating that the secondary battery is in an over-discharge state.
  • the power tool is characterized in that the control unit is configured to control the over-discharge signal outputted from the over-discharge detection unit based on the temperature detected by the battery temperature detection unit.
  • control unit is further configured to interrupt power supply from the secondary battery to the drive unit in response to the over-discharge signal, and delay the interruption in the power supply by controlling the over-discharge signal.
  • the supply of power from the secondary battery to the drive unit is interrupted when the over-discharge signal is outputted.
  • the power tool can continue operating without an interruption in the power supply when internal battery resistance temporarily rises due to a low temperature of the secondary battery.
  • control unit has a dead interval not to respond to the over-discharge signal or a reset interval to output a reset signal to reset the over-discharge signal, if the temperature detected by the battery temperature detection unit is lower than or equal to a temperature threshold and the over-discharge detection unit outputs the over-discharge signal.
  • the power tool does not respond the over-discharge signal or resets the over-discharge signal during the dead interval or the reset interval, even when the temperature detected by the battery temperature detection unit is lower than or equal to the temperature threshold and the over-discharge signal is outputted. Accordingly, the power tool hardly determines a voltage drop in the initial stage of discharge accompanying a rise in internal battery resistance mistakenly as over-discharge when the temperature of the secondary battery is low.
  • an interval for delaying the interruption in the power supply begins at a timing in a duration between timing of initial output from the secondary battery and timing of detection of the temperature lower than or equal to the temperature threshold by the battery temperature detection unit, and ends when or after the battery temperature detection unit detects the temperature higher than the temperature threshold and the over-discharge detection unit stops the output of the over-discharge signal.
  • the power tool delays the interruption in power supply to the drive unit between the timing of detection of a low temperature state of the secondary battery and the timing when the temperature of the secondary battery exceeds the temperature threshold. Accordingly, the power tool can continue operating without an interruption in the power supply even when the temperature of the secondary battery is low. Further, after the temperature of the secondary battery becomes normal, the power is supplied to the drive unit as per normal. Therefore, the power tool can continue operating without any interruption even in a cold environment, as described above.
  • control unit is further configured to set the dead interval and the reset interval based on the temperature detected by the battery temperature detection unit.
  • the dead interval and the reset interval are set longer as the temperature is lower.
  • the dead interval and the reset interval can be set based on the temperature of the secondary battery.
  • the present invention further features a power tool.
  • the power tool includes a secondary battery, a drive unit, a battery voltage detection unit, a battery temperature detection unit, an over-discharge detection unit, and a reset unit.
  • the battery voltage detection unit is configured to detect a battery voltage of the secondary battery.
  • the battery temperature detection unit is configured to detect a temperature of the secondary battery.
  • the over-discharge detection unit is configured to detect that charge capacity of the secondary battery is less than a prescribed value and output an over-discharge signal indicating that the secondary battery is in an over-discharge state.
  • the power tool is characterized in that the reset unit is configured to reset the over-discharge signal outputted from the over-discharge detection unit based on the temperature detected by the battery temperature detection unit.
  • power supply from the secondary battery to the drive unit is interrupted in response to the over-discharge signal, and the reset unit is further configured to delay the interruption in the power supply by resetting the over-discharge signal.
  • the reset unit temporarily resets the over-discharge signal when the over-discharge detecting unit determines that a voltage drop in the initial stage of discharge is over-discharge and outputs the over-discharge signal, provided that the temperature of the secondary battery is low due to cold ambient temperature, for example. Accordingly, the power tool can continue operating without an interruption in the power supply to the drive unit.
  • every well-known battery can be included in the secondary battery, and the developed secondary battery is also applicable in future. However, it is preferable to use a lithium-ion battery at the time of the present application.
  • the power tool according to the present invention does not perform an over-discharge determination during the initial stage of discharge upon determining that the battery temperature is low. Accordingly, the power tool can continue operating without an interruption in the supply of power to the drive unit, as occurs in the conventional technology, even when the over-discharge detecting unit determines that a voltage drop in the initial stage of discharge accompanying a rise in internal battery resistance is over-discharge, provided that the temperature of the secondary battery is low due to cold ambient temperature, for example.
  • Fig. 1 is a circuit diagram of a power tool (a tool body and a battery pack) according to a first embodiment of the present invention.
  • Fig. 2 is a flowchart for explaining operations of the power tool shown in Fig. 1.
  • Fig. 3 is a circuit diagram of a power tool (a tool body and a battery pack) according to a second embodiment of the present invention.
  • Fig. 4 is a flowchart for explaining operations of the power tool shown in Fig. 3.
  • Fig. 5 is a graph for explaining operations, in which time variations of a battery voltage and a battery temperature are illustrated.
  • FIG. 1 shows the circuit diagram of a battery pack 2 when the battery pack 2 is mounted on a tool body 1.
  • the integrated formed of the battery pack 2 mounted on the tool body 1 will be referred to as the "power tool.”
  • a power drill is used as an example of the power tool, but the power tool may be any type of tool that is powered by a secondary battery and is not limited to this example.
  • the tool body 1 has a positive (+) terminal and a negative (-) terminal that connect to the corresponding positive and negative terminals of the battery pack 2. Both the tool body 1 and battery pack 2 possess a battery shutdown terminal 9 that connect to each other when the battery pack 2 is mounted on the tool body 1.
  • the battery pack 2 is mounted on the tool body 1 of a power drill, the battery pack 2 is inserted into space formed inside a handle part of the power drill and is locked so as not to fall out of the handle part.
  • the tool body 1 has a DC motor 3 that operates on direct current, a trigger switch 4, and a motor control field-effect transistor (FET) 5 (a switching element) that are connected in series between the positive and negative terminals of the tool body 1.
  • FET motor control field-effect transistor
  • a lithium-ion battery 6 supplies power to the motor 3 for driving the motor 3 to rotate.
  • the rotation of the motor 3 rotates the drill bit through a speed reduction mechanism (not shown).
  • Resistors Ra and Rb are connected in series between the positive terminal of the motor 3 and the source of the motor control FET 5. The connection point between the resistors Ra and Rb is further connected to the gate of the motor control FET 5 and the battery shutdown terminal 9. As will be described later, the motor control FET 5 is on when an over-discharge signal applied to the battery shutdown terminal 9 is low level, and off when the over-discharge signal is high level.
  • the battery pack 2 houses an over-discharge detection unit 7, and a temperature detection unit 8.
  • the over-discharge detection unit 7 is configured of a lithium-ion battery (hereinafter referred to as a "secondary battery") 6, and a protection circuit 7a.
  • the secondary battery 6 is configured of a plurality of battery cells connected in series. In the preferred embodiment, the secondary battery 6 has five lithium-ion battery cells connected in series. Each of the lithium-ion battery cells has a rated voltage of 3.6 V in this example. Therefore, the secondary battery 6 outputs a battery voltage of 18 V to be applied to the motor 3.
  • the rated voltage of the motor 3 built into the tool body 1 is 18 V.
  • the battery pack 2 is removed from the tool body 1 and recharged with a charging device. Specifically, the protection circuit 7a determines that the secondary battery 6 is depleted when the battery voltage of any of the lithium-ion battery cells drops below a prescribed threshold (2.0 V, for example), at which time the user is prompted to recharge the battery pack 2.
  • a prescribed threshold 2.0 V, for example
  • the protection circuit 7a is connected to the secondary battery 6. More specifically, the protection circuit 7a is connected to the positive and negative terminals of each cell in the secondary battery 6 and functions to detect the battery voltage of each cell. The protection circuit 7a also monitors the discharge current of the secondary battery 6. When the battery voltage of any cell drops below the prescribed threshold, the protection circuit 7a determines that the secondary battery 6 is in an over-discharge condition and outputs an over-discharge signal to a microcomputer 11 described later. As described above, the rated voltage of each lithium-ion battery cell is 3.6 V, and the threshold for determining an over-discharge condition is 2.0 V in the preferred embodiment.
  • the protection circuit 7a determines that an over-current condition has occurred and outputs an over-current signal to the microcomputer 11.
  • the protection circuit 7a also detects an over-charge condition and the like when the secondary battery 6 is being charged and outputs an over-charge signal to the charging device for halting the charging operation.
  • the temperature detection unit 8 is configured of a thermistor TSR, and a resistor R1.
  • the thermistor TSR is a temperature sensor disposed near to or in contact with the secondary battery 6.
  • the temperature detection unit 8 functions to detect the temperature of the secondary battery 6. More specifically, the resistor R1 and thermistor TSR are connected in series between the supply voltage (5 V) and ground.
  • the resistance value of the thermistor TSR fluctuates in response to changes in temperature, and the voltage of the thermistor TSR is inputted into the microcomputer 11 (described later).
  • the battery pack 2 has a three-terminal regulator 10 for producing the supply voltage (5V).
  • the three-terminal regulator 10 is provided in the battery pack 2 for outputting a 5-V constant voltage based on the battery voltage supplied from the secondary battery 6.
  • the 5-V constant voltage is used to power a microcomputer 11, the temperature detection unit 8 described above, and a tool-insertion detection unit 12 described later.
  • Capacitors C1 and C2 are connected to the three-terminal regulator 10 for preventing circuit oscillation.
  • the battery pack 2 includes a built-in microcomputer 11.
  • the output terminal of the three-terminal regulator 10 is connected to the VDD terminal of the microcomputer 11 across which a voltage of 5 V is applied.
  • the microcomputer 11 is in an operating state when the 5-V voltage is applied to the VDD terminal.
  • the protection circuit 7a inputs an over-discharge signal into the microcomputer 11, while the temperature detection unit 8 inputs a battery temperature signal into the microcomputer 11.
  • the microcomputer 11 is also connected to a battery voltage detection unit 13, a current detection unit 14, and an over-discharge output unit 15.
  • the battery voltage detection unit 13 is configured of a battery voltage detection command unit, and a battery voltage detection unit for detecting the battery voltage in response to output from the battery voltage detection command unit.
  • the battery voltage detection command unit of the battery voltage detection unit 13 is configured of an FET 13a, resistors R2 and R3, and zener diode ZD1.
  • a parallel circuit configured of the resistor R2 and the zener diode ZD1 is connected between the gate and source of the FET 13a.
  • the resistor R3 is connected between the output terminal of the microcomputer 11 and the gate of the FET 13a.
  • the battery voltage detection unit of the battery voltage detection unit 13 is configured of an FET 13b, resistors R4 and R5, and a zener diode ZD2.
  • a parallel circuit configured of the resistor R4 and zener diode ZD2 is connected between the positive terminal of the battery pack 2 and the gate of the FET 13a.
  • the resistor R5 is connected between the drain of the FET 13a and the gate of the FET 13b.
  • the microcomputer 11 When the microcomputer 11 outputs a high-level command signal representing a command to detect battery voltage, the voltage divided by the resistors R3 and R2 is inputted into the gate of the FET 13a, turning the FET 13a on.
  • Resistors R6 and R7 form a series current with the FET 13b that is connected in parallel to the secondary battery 6.
  • the battery voltage of the secondary battery 6 is divided by the resistors R6 and R7 connected in series with the divided voltage corresponding to the battery voltage of the secondary battery 6 being inputted into the microcomputer 11.
  • the battery voltage detection unit 13 is configured to detect the battery voltage of the secondary battery 6 only when detections are desired.
  • the battery voltage detection unit 13 can detect the battery voltage of the secondary battery 6 when the microcomputer 11 detects that the battery pack 2 has been mounted on the tool body 1. Since the battery voltage detection unit 13 according to the preferred embodiment is provided with the battery voltage detection command unit, the series circuit including the resistors R6 and R7 connected in parallel to the secondary battery 6 consumes less power from the secondary battery 6 than a structure that continuously detects battery voltage from the voltage dividing resistors.
  • the current detection unit 14 is connected to the microcomputer 11 for detecting current flowing to the motor 3 and for inputting the detected current value into the microcomputer 11.
  • the current detection unit 14 is configured of a resistor.
  • the over-discharge output unit 15 is connected to an output terminal of the microcomputer 11.
  • the output of the over-discharge output unit 15 is connected to the battery shutdown terminal 9 on the battery pack 2 side through a resistor R12.
  • the over-discharge output unit 15 is configured of an FET 15a, and resistors R10 and R11.
  • the resistor R10 is connected between an over-discharge signal output terminal of the microcomputer 11 and the gate of the FET 15a, and the resistor R11 is connected between the gate and source of the FET 15a.
  • the microcomputer 11 when the microcomputer 11 is not outputting an over-discharge signal, i.e., when a low-level signal is outputted from the over-discharge signal output terminal of the microcomputer 11, the FET 15a of the over-discharge output unit 15 is off and current flows through the resistors Ra and Rb on the tool body 1 side. Since the resistance value of the resistor Rb is set greater than that of the resistor R12, the motor control FET 5 is on and the motor 3 is driven to rotate when the trigger switch 4 is on.
  • the tool-insertion detection unit 12 is connected between an input terminal of the microcomputer 11 and the battery shutdown terminal 9 on the battery pack 2 side.
  • the tool-insertion detection unit 12 is configured of an FET 12a and resistors R8 and R9.
  • the resistor R8 is connected between the gate and source of the FET 12a, while the resistor R9 is connected between the gate of the FET 12a and the battery shutdown terminal 9.
  • the battery pack 2 is not mounted in the tool body 1 if an over-discharge signal is not being outputted from the protection circuit 7a and the battery shutdown terminal 9 is open on the battery pack 2 side. When the battery shutdown terminal 9 on the battery pack 2 side is in an open state, the FET 12a is off.
  • a 5-V supply voltage supplied from the three-terminal regulator 10 to the tool-insertion detection unit 12 (i.e., a high-level signal) is inputted into a tool-insertion detection input terminal of the microcomputer 11.
  • the microcomputer 11 recognizes that the battery pack 2 is in a non-mounted state relative to the tool body 1 when the signal inputted into the tool-insertion detection input terminal of the microcomputer 11 is a high-level signal.
  • the microcomputer 11 recognizes that the battery pack 2 is connected into the tool body 1.
  • the FET 12a is on and the signal at the tool-insertion detection input terminal of the microcomputer 11 is at low level for grounding the terminal via the FET 12a.
  • the microcomputer 11 recognizes that the battery pack 2 is connected into the tool body 1.
  • the three-terminal regulator 10 applies a 5-V supply voltage to the microcomputer 11 based on the battery voltage supplied from the secondary battery 6.
  • the microcomputer 11 enters an operable state. Upon entering this state, in S101 the microcomputer 11 detects the battery voltage by outputting a high-level command signal to the battery voltage detection unit 13 representing a command to detect the battery voltage.
  • the microcomputer 11 determines whether the battery pack 2 is connected into the tool body 1. The microcomputer 11 makes this determination by detecting whether the signal level at the tool-insertion detection input terminal is high or low.
  • the microcomputer 11 continues to wait until the battery pack 2 has been connected.
  • the microcomputer 11 determines whether the battery voltage detected in S101 can be discharged. If the detected voltage is lower than the prescribed threshold, the microcomputer 11 determines that the charge capacity of the secondary battery 6 is insufficient and that the battery pack 2 currently connected into the tool body 1 cannot be used, i.e., cannot be discharged (S103: NO).
  • Determining the remaining charge capacity of the battery using the battery voltage in S101 is just one method.
  • the microcomputer 11 may also detect the electric current during charging and discharging operations and calculate the charge capacity based on the integrated current value, or may employ a combination of both methods.
  • the microcomputer 11 determines that discharge is possible (S103: YES) and advances to S104. However, if the detected battery voltage is less than the threshold, the microcomputer 11 determines that discharge is not possible (S103: NO) and in S108 halts discharge of the battery.
  • the microcomputer 11 In order to halt discharge in S108, the microcomputer 11 outputs a high-level over-discharge signal from its over-discharge signal output terminal to the over-discharge output unit 15.
  • the FET 15a of the over-discharge output unit 15 is turned on in response to this over-discharge signal. Consequently, a value divided by the resistors Ra and R12 is inputted into the battery shutdown terminal 9.
  • the motor control FET 5 of the tool body 1 is turned off.
  • the microcomputer 11 determines in S103 that the secondary battery 6 can be used (S103: YES), in S104 the microcomputer 11 allows discharge. Specifically, the microcomputer 11 does not output an over-discharge signal from its over-discharge signal output terminal to the over-discharge output unit 15, thereby turning on the motor control FET 5 of the battery pack 2.
  • the microcomputer 11 determines whether the secondary battery 6 is in an over-discharge state.
  • the microcomputer 11 determines that the secondary battery 6 is in an over-discharge state when the over-discharge detection unit 7 inputs an over-discharge signal into the microcomputer 11 after discharging has begun. If an over-discharge signal is not inputted into the microcomputer 11 (i.e., the secondary battery 6 is not in an over-discharge state), the microcomputer 11 determines that discharge can continue (S105: NO) and loops back to S104, while continuing to monitor the secondary battery 6 for an over-discharge state. As illustrated in Fig.
  • the battery voltage of the secondary battery 6 is sufficiently larger than the threshold of 3.6 V per cell, for example.
  • the microcomputer 11 determines in S103 that discharge is possible based on the detected battery voltage, the battery voltage will drop abruptly immediately following the start of discharge due to high internal resistance if the battery temperature at the beginning of discharge is low, such as -10 degrees C. Since the threshold for determining an over-discharge state is 2.0 V per cell in this example, the over-discharge detection unit 7 will determine that the secondary battery 6 is in an over-discharge state when the battery voltage immediately following the start of discharge falls below 2.0 V per cell and consequently will output an over-discharge signal to the microcomputer 11. Upon receiving this over-discharge signal, the microcomputer 11 will determine that the secondary battery 6 has entered an over-discharge state (S105: YES) and advance to S106.
  • S105 over-discharge state
  • the microcomputer 11 determines whether the temperature of the battery was low when the over-discharge signal was inputted into the microcomputer 11.
  • the threshold for determining whether the battery temperature is low is -10 degrees C. If the detected battery temperature is lower than or equal to -10 degrees C, the microcomputer 11 determines that the secondary battery 6 is in a low-temperature state (S106: YES). However, if the detected battery temperature is higher than -10 degrees C, the microcomputer 11 determines that the battery temperature is normal (S106: NO). If the battery temperature is found to be normal, the microcomputer 11 advances to S108 and halts discharge since the secondary battery 6 was determined to be in an over-discharge state in S105.
  • the microcomputer 11 determines that an over-discharge signal was detected and the secondary battery 6 is at a low temperature at timing T1 in the graph of Fig. 5. In this case, the microcomputer 11 cancels the over-discharge signal in S107.
  • "canceling the over-discharge signal” simply means not responding to the over-discharge signal inputted from the over-discharge detection unit 7 for a prescribed time interval. Specifically, the interval from timing T1 to timing T2 shown in Fig. 5 is a dead interval in which the microcomputer 11 does not respond to an over-discharge signal inputted from the over-discharge detection unit 7.
  • the microcomputer 11 Since the microcomputer 11 does not output an over-discharge signal to the over-discharge output unit 15 from its over-discharge signal output terminal during the dead interval, the signal at the over-discharge signal output terminal is maintained at the low level. Consequently, the motor control FET 5 of the tool body 1 is not interrupted but is maintained in an ON state during the dead interval.
  • the microcomputer 11 determines in S105 that the secondary battery 6 is in an over-discharge state and further determines in S106 that the battery temperature is low (-10 degrees C or lower, for example), in most cases the secondary battery 6 is not actually in an over-discharge state, but rather a temporary voltage drop due to the low temperature environment has been incorrectly detected as over-discharge.
  • the method of the preferred embodiment prevents the microcomputer 11 from outputting an over-discharge signal to the over-discharge output unit 15 from its over-discharge signal output terminal during this dead interval.
  • the battery temperature will have risen because the process of steps S104 through S107 will have been repeated once or a plurality of times. In this case, the microcomputer 11 will advance to S108 to halt further discharge.
  • the battery voltage drops temporarily immediately after the start of discharge from secondary battery cells in a low-temperature state, but begins to recover as the battery temperature rises, i.e., as current flows through the secondary battery cells, and the voltage per cell surpasses 2.0 V at timing T2.
  • the over-discharge detection unit 7 no longer outputs an over-discharge signal to the microcomputer 11 and, hence, the microcomputer 11 determines in S105 that the secondary battery 6 is not in an over-discharge state (S105: NO).
  • the microcomputer 11 After determining that the secondary battery 6 is not in an over-discharge state, the microcomputer 11 returns to S104 and continues to allow the secondary battery 6 to discharge while monitoring the secondary battery 6 for over-discharge.
  • timing T2 The timing at which the microcomputer 11 first determines in S105 that the secondary battery 6 is not in an over-discharge state because the battery temperature of the secondary battery 6 has returned to normal is timing T2 in Fig. 5.
  • the interval between timings T1 and T2 constitutes a dead interval during which the microcomputer 11 does not respond to an over-discharge signal outputted from the over-discharge detection unit 7.
  • the microcomputer 11 determines that a drop in battery voltage is caused by a low battery temperature and does not interrupt the supply of power from the battery pack 2 to the tool body 1 when the battery temperature is low, even when determining that the secondary battery 6 is in an over-discharge state.
  • the user of the tool body 1 can operate a battery pack having sufficient charge capacity, even when the battery pack is at a low temperature, without the unpleasant experience of receiving an over-discharge warning and having the drive of the tool body 1 halted, for example.
  • the initial timing of the interval for delaying an interruption in the power supply may be between timing T0 and timing T1 and is not limited to timing T1 specified in the above example.
  • Fig. 3 The structure of the circuit shown in Fig. 3 is identical to that shown in Fig. 1, except for the following points, and like components with those in Fig. 1 are designated using the same reference numerals to avoid duplicating description.
  • the battery pack 2 according to the second embodiment shown in Fig. 3 further includes an over-discharge signal cancellation unit 16 provided between the over-discharge detection unit 7 and over-discharge output unit 15.
  • the over-discharge signal cancellation unit 16 is configured of an FET 16a, and two resistors R14 and R15.
  • the drain of the FET 16a is connected to the output terminal of the over-discharge detection unit 7 and is also connected to the over-discharge output unit 15 via the resistor R10.
  • the gate of the FET 16a is connected to the over-discharge signal output terminal of the microcomputer 11 via the resistor R14.
  • the resistor R15 is connected between the gate and source of the FET 16a.
  • an over-discharge signal outputted from the over-discharge detection unit 7 is inputted into the microcomputer 11.
  • this over-discharge signal is inputted into the over-discharge signal cancellation unit 16 rather than the microcomputer 11.
  • the circuit structure in Fig. 3 for determining when the battery pack 2 is connected into the tool body 1 differs from the circuit structure in Fig. 1.
  • the battery pack 2 in Fig. 3 has an insertion detection unit configured of resistors R16 and R17.
  • the resistors R16 and R17 divide the voltage at the battery shutdown terminal 9, and the divided voltage is inputted into the microcomputer 11.
  • the microcomputer 11 determines whether the battery pack 2 has been connected into the tool body 1 based on the level of the inputted voltage.
  • the battery shutdown terminal 9 has a high potential when the battery pack 2 is connected into the tool body 1 and a low potential when the battery pack 2 is not connected into the tool body 1.
  • the microcomputer 11 determines that the tool body 1 has been connected into the battery pack 2 when a high level signal has been inputted into the tool-insertion detection input terminal of the microcomputer 11, and conversely determines that the tool body 1 is not connected into the battery pack 2 when a low level signal has been inputted into the terminal.
  • a dead interval is set in the first embodiment described above to a period from the point that the over-discharge signal was detected until the battery temperature reaches a level at which the internal resistance is sufficiently low. During this dead interval, the microcomputer 11 and the tool body 1 do not react to an over-discharge signal inputted from the over-discharge detection unit 7 into the microcomputer 11.
  • the microcomputer 11 determines that the secondary battery 6 is in a low-temperature state after the over-discharge detection unit 7 has determined the secondary battery 6 is in an over-discharge state and has outputted an over-discharge signal, the microcomputer 11 outputs a reset signal from its reset output terminal to the over-discharge signal cancellation unit 16, preventing the over-discharge signal from being inputted into the tool body 1 via the over-discharge output unit 15.
  • the over-discharge detection unit 7 when an over-discharge state is detected in the protection circuit 7a, the over-discharge detection unit 7 outputs a high-level over-discharge signal. However, when the secondary battery 6 is in a low-temperature state, the microcomputer 11 outputs a reset signal from its reset output terminal to the over-discharge signal cancellation unit 16 in response to the over-discharge signal. The reset signal turns on the FET 16a of the over-discharge signal cancellation unit 16. If the over-discharge signal cancellation unit 16 were not interposed between the over-discharge detection unit 7 and the over-discharge output unit 15, the high-level over-discharge signal would be applied directly to the gate of the FET 15a of the over-discharge output unit 15.
  • the over-discharge signal cancellation unit 16 interposed between the over-discharge detection unit 7 and over-discharge output unit 15 inverts the high-level over-discharge signal, so that a low-level signal is applied to the FET 15a in the over-discharge output unit 15. Consequently, the FET 15a is turned off, maintaining the motor control FET 5 on the tool body 1 side in an ON state.
  • the operations of the power tool according to the second embodiment shown in Fig. 4 are identical to the operations of the first embodiment shown in Fig. 2 for the initial steps from S101 to S104, but are different in subsequent steps.
  • the microcomputer 11 determines whether the secondary battery 6 is in a low-temperature state (-10 degrees C or lower). If the microcomputer 11 determines that the temperature of the secondary battery 6 is low (S205: YES), in S206a the microcomputer 11 outputs a reset signal from its reset output terminal to the over-discharge signal cancellation unit 16.
  • the microcomputer 11 determines whether the secondary battery 6 is in an over-discharge state. This step is equivalent to S105 in the flowchart of Fig. 2. If the microcomputer 11 determines that the secondary battery 6 is not in an over-discharge state (S207: NO), the microcomputer 11 returns to S102 and continues monitoring the secondary battery 6 to determine whether the secondary battery 6 is in an over-discharge state.
  • microcomputer 11 determines in S207 that the secondary battery 6 is in an over-discharge state (S207: YES), then in S208 the microcomputer 11 halts discharge from the secondary battery 6.
  • This step is equivalent to S108 in the flowchart of Fig. 2. Since the microcomputer 11 switches output of the reset signal on and off in steps S206a and S206b in the second embodiment, a step equivalent to S107 of Fig. 2 in which the microcomputer 11 sets a dead interval is no longer necessary.
  • the microcomputer 11 predicts that a drop in battery voltage will occur immediately after discharge begins if the battery temperature is low and predicts that the over-discharge detection unit 7 will output an over-discharge signal due to this drop in voltage. Therefore, the microcomputer 11 resets the over-discharge signal in order to prevent the over-discharge output unit 15 from outputting this over-discharge signal to the tool body 1 side.
  • This method prevents power supplied from the battery pack 2 to the tool body 1 from being interrupted because the battery temperature is low and, hence, the operator of the tool body 1 does not experience the unpleasant sensation of the tool body 1 stopping abruptly during operations.
  • steps S105 and S106 in the flowchart of Fig. 2 according to the first embodiment may be switched.
  • a temperature threshold of -10 degrees C is used as an example in the first embodiment for determining whether the temperature of the secondary battery 6 is low, a different threshold may be employed.
  • a dead interval is configured to last until the battery temperature reaches a normal temperature.
  • the dead interval may instead be set to a predetermined fixed time interval from the start of discharge (60 seconds, for example) when the battery temperature is found to be below the temperature threshold.
  • the length of the dead interval is not limited to a single predetermined fixed time interval but may be freely set according to the temperature threshold.
  • a plurality of dead intervals may be set based on a plurality of temperature thresholds, or the length of the dead interval may be modified as a function of temperature so as to last 60 seconds from the start of discharge when the temperature threshold is -10 degrees C and 30 seconds from the start of discharge when the temperature threshold is 0 degrees C.
  • the current detection unit 14 may detect the current flowing to the motor 3, and the microcomputer 11 may be set the dead interval based on the battery voltage detected by the battery voltage detection unit 13 or the battery's charge capacity. In the latter case, the microcomputer 11 may reference the charge capacity of the battery and set the dead interval to 120 seconds when the capacity is at least 80%, 60 seconds when the capacity is at least 60%, 40 seconds when the capacity is less than 30%, and the like.
  • the battery voltage detection unit 13 shown in Figs. 1 and 3 detects the battery voltage of the secondary battery 6 through an actual measurement.
  • the microcomputer 11 can determine the battery voltage by reading this ID data.
  • the battery voltage detection unit 13 provided in the embodiments may be omitted, thereby eliminating power dissipation of the secondary battery 6 caused by the battery voltage detection unit 13.
  • the identification data described above includes the type of battery (e.g., lithium-ion battery cells or the like), and the number of cells.
  • the microcomputer 11 various units for inputting signals into the microcomputer 11, and various units for receiving output from the microcomputer 11 are provided in the battery pack 2.
  • the microcomputer 11 and its related units may be provided in the tool body 1 instead, while the battery pack is only provided with the over-discharge detection unit 7 (including the secondary battery 6), and the thermistor TSR.
  • the present invention may be applied to a power tool having a drive unit that employs an FET for driving the motor such as a brushless DC motor or the like. Further, the present invention is not limited to a power tool employing a motor.
  • a power tool employing a motor One suitable example is a work light or lantern that employs a secondary battery designed for a power tool as its power supply. In this case, the effects of the present invention can be obtained by performing the same control described in the embodiments.

Abstract

A power tool includes: a secondary battery; a drive unit; a battery voltage detection unit configured to detect a battery voltage of the secondary battery; a battery temperature detection unit configured to detect a temperature of the secondary battery; an over-discharge detection unit configured to detect that a charge capacity of the secondary battery is less than a prescribed value and output an over-discharge signal indicating that the secondary battery is in an over-discharge state; and a control unit configured to control the over-discharge signal outputted from the over-discharge detection unit based on the temperature detected by the battery temperature detection unit.

Description

POWER TOOL
The present invention relates to a power tool that is powered by a secondary battery, such as a lithium-ion battery.
The advantage of cordless power tools is that they can be used anywhere since they do not need to be connected to a commercial power source with a power cord, and the power tool is easier to operate without the cord getting in the way. For this reason, cordless power tools have become widely popular. Recently battery packs housing lithium-ion secondary battery have become more widely used as the power supply for cordless power tools. These battery packs have a built-in protection circuit to prevent battery degradation and to ensure safety for the user. When the battery is in an over-discharge condition, the protection circuit outputs an over-discharge signal for cutting off the power supplied to the power tool on which the battery pack is mounted (For example, refer to Japanese Patent Application Publication No. 2009-95162).
Japanese Patent Application Publication No. 2009-95162
However, the battery temperature may be low at times due to the effects of ambient temperature and the like. Generally, the internal resistance of the battery packs is high when the battery temperature is low. Therefore, if operating the power tool when the battery temperature is low, a phenomenon may occur in which the output voltage temporarily drops in the initial drive stage, even though the charge capacity of the battery is sufficiently high. Consequently, when the power tool is used in a cold environment, the protection circuit built into the battery pack may wrongly determine that this temporary drop in voltage at the beginning of operations is an over-discharge condition, leading the protection circuit to cut off the power supply to the power tool. Thus, when the operator attempts to use the power tool initially, the tool may stop operating temporarily, preventing the operator from using the tool until the battery temperature rises to its operable temperature range.
In view of the foregoing, it is an object of the present invention to provide a more user-friendly power tool that does not stop operating temporarily when the battery is in a low-temperature state.
The present invention features a power tool. The power tool includes a secondary battery, a drive unit, a battery temperature detection unit, an over-discharge detection unit, and a control unit. The battery voltage detection unit is configured to detect a battery voltage of the secondary battery. The battery temperature detection unit is configured to detect a temperature of the secondary battery. The over-discharge detection unit is configured to detect that a charge capacity of the secondary battery is less than a prescribed value and output an over-discharge signal indicating that the secondary battery is in an over-discharge state. The power tool is characterized in that the control unit is configured to control the over-discharge signal outputted from the over-discharge detection unit based on the temperature detected by the battery temperature detection unit. With this construction, the power tool does not misread a voltage drop in the initial stage of discharge accompanying a rise in internal battery resistance as over-discharge, provided that the temperature of the secondary battery is low due to cold ambient temperature, for example.
Preferably, the control unit is further configured to interrupt power supply from the secondary battery to the drive unit in response to the over-discharge signal, and delay the interruption in the power supply by controlling the over-discharge signal.
In the conventional technology, the supply of power from the secondary battery to the drive unit is interrupted when the over-discharge signal is outputted. However, with this construction, the power tool can continue operating without an interruption in the power supply when internal battery resistance temporarily rises due to a low temperature of the secondary battery.
Preferably, the control unit has a dead interval not to respond to the over-discharge signal or a reset interval to output a reset signal to reset the over-discharge signal, if the temperature detected by the battery temperature detection unit is lower than or equal to a temperature threshold and the over-discharge detection unit outputs the over-discharge signal.
With this construction, the power tool does not respond the over-discharge signal or resets the over-discharge signal during the dead interval or the reset interval, even when the temperature detected by the battery temperature detection unit is lower than or equal to the temperature threshold and the over-discharge signal is outputted. Accordingly, the power tool hardly determines a voltage drop in the initial stage of discharge accompanying a rise in internal battery resistance mistakenly as over-discharge when the temperature of the secondary battery is low.
Preferably, an interval for delaying the interruption in the power supply begins at a timing in a duration between timing of initial output from the secondary battery and timing of detection of the temperature lower than or equal to the temperature threshold by the battery temperature detection unit, and ends when or after the battery temperature detection unit detects the temperature higher than the temperature threshold and the over-discharge detection unit stops the output of the over-discharge signal.
With this construction, the power tool delays the interruption in power supply to the drive unit between the timing of detection of a low temperature state of the secondary battery and the timing when the temperature of the secondary battery exceeds the temperature threshold. Accordingly, the power tool can continue operating without an interruption in the power supply even when the temperature of the secondary battery is low. Further, after the temperature of the secondary battery becomes normal, the power is supplied to the drive unit as per normal. Therefore, the power tool can continue operating without any interruption even in a cold environment, as described above.
Preferably, the control unit is further configured to set the dead interval and the reset interval based on the temperature detected by the battery temperature detection unit.
Preferably, the dead interval and the reset interval are set longer as the temperature is lower.
As described above, the dead interval and the reset interval can be set based on the temperature of the secondary battery. Preferably, the lower the temperature is, the longer the dead interval and the reset interval are set.
The present invention further features a power tool. The power tool includes a secondary battery, a drive unit, a battery voltage detection unit, a battery temperature detection unit, an over-discharge detection unit, and a reset unit. The battery voltage detection unit is configured to detect a battery voltage of the secondary battery. The battery temperature detection unit is configured to detect a temperature of the secondary battery. The over-discharge detection unit is configured to detect that charge capacity of the secondary battery is less than a prescribed value and output an over-discharge signal indicating that the secondary battery is in an over-discharge state. The power tool is characterized in that the reset unit is configured to reset the over-discharge signal outputted from the over-discharge detection unit based on the temperature detected by the battery temperature detection unit.
Preferably, power supply from the secondary battery to the drive unit is interrupted in response to the over-discharge signal, and the reset unit is further configured to delay the interruption in the power supply by resetting the over-discharge signal.
With this construction, the reset unit temporarily resets the over-discharge signal when the over-discharge detecting unit determines that a voltage drop in the initial stage of discharge is over-discharge and outputs the over-discharge signal, provided that the temperature of the secondary battery is low due to cold ambient temperature, for example. Accordingly, the power tool can continue operating without an interruption in the power supply to the drive unit.
Specifically, every well-known battery can be included in the secondary battery, and the developed secondary battery is also applicable in future. However, it is preferable to use a lithium-ion battery at the time of the present application.
The power tool according to the present invention does not perform an over-discharge determination during the initial stage of discharge upon determining that the battery temperature is low. Accordingly, the power tool can continue operating without an interruption in the supply of power to the drive unit, as occurs in the conventional technology, even when the over-discharge detecting unit determines that a voltage drop in the initial stage of discharge accompanying a rise in internal battery resistance is over-discharge, provided that the temperature of the secondary battery is low due to cold ambient temperature, for example.
Fig. 1 is a circuit diagram of a power tool (a tool body and a battery pack) according to a first embodiment of the present invention. Fig. 2 is a flowchart for explaining operations of the power tool shown in Fig. 1. Fig. 3 is a circuit diagram of a power tool (a tool body and a battery pack) according to a second embodiment of the present invention. Fig. 4 is a flowchart for explaining operations of the power tool shown in Fig. 3. Fig. 5 is a graph for explaining operations, in which time variations of a battery voltage and a battery temperature are illustrated.
Next, a power tool according to a first embodiment of the present invention will be described while referring to the accompanying drawings. Fig. 1 shows the circuit diagram of a battery pack 2 when the battery pack 2 is mounted on a tool body 1. In the following description, the integrated formed of the battery pack 2 mounted on the tool body 1 will be referred to as the "power tool."
In the preferred embodiment described below, a power drill is used as an example of the power tool, but the power tool may be any type of tool that is powered by a secondary battery and is not limited to this example.
The tool body 1 has a positive (+) terminal and a negative (-) terminal that connect to the corresponding positive and negative terminals of the battery pack 2. Both the tool body 1 and battery pack 2 possess a battery shutdown terminal 9 that connect to each other when the battery pack 2 is mounted on the tool body 1. When the battery pack 2 is mounted on the tool body 1 of a power drill, the battery pack 2 is inserted into space formed inside a handle part of the power drill and is locked so as not to fall out of the handle part.
The tool body 1 has a DC motor 3 that operates on direct current, a trigger switch 4, and a motor control field-effect transistor (FET) 5 (a switching element) that are connected in series between the positive and negative terminals of the tool body 1. When the battery pack 2 is mounted on the tool body 1 and both the trigger switch 4 and motor control FET 5 are on, a lithium-ion battery 6 supplies power to the motor 3 for driving the motor 3 to rotate. The rotation of the motor 3 rotates the drill bit through a speed reduction mechanism (not shown).
Resistors Ra and Rb are connected in series between the positive terminal of the motor 3 and the source of the motor control FET 5. The connection point between the resistors Ra and Rb is further connected to the gate of the motor control FET 5 and the battery shutdown terminal 9. As will be described later, the motor control FET 5 is on when an over-discharge signal applied to the battery shutdown terminal 9 is low level, and off when the over-discharge signal is high level.
Next, the electrical structure of the battery pack 2 will be described.
The battery pack 2 houses an over-discharge detection unit 7, and a temperature detection unit 8. The over-discharge detection unit 7 is configured of a lithium-ion battery (hereinafter referred to as a "secondary battery") 6, and a protection circuit 7a. The secondary battery 6 is configured of a plurality of battery cells connected in series. In the preferred embodiment, the secondary battery 6 has five lithium-ion battery cells connected in series. Each of the lithium-ion battery cells has a rated voltage of 3.6 V in this example. Therefore, the secondary battery 6 outputs a battery voltage of 18 V to be applied to the motor 3. The rated voltage of the motor 3 built into the tool body 1 is 18 V. When the capacity of the secondary battery 6 drops, the battery pack 2 is removed from the tool body 1 and recharged with a charging device. Specifically, the protection circuit 7a determines that the secondary battery 6 is depleted when the battery voltage of any of the lithium-ion battery cells drops below a prescribed threshold (2.0 V, for example), at which time the user is prompted to recharge the battery pack 2.
The protection circuit 7a is connected to the secondary battery 6. More specifically, the protection circuit 7a is connected to the positive and negative terminals of each cell in the secondary battery 6 and functions to detect the battery voltage of each cell. The protection circuit 7a also monitors the discharge current of the secondary battery 6. When the battery voltage of any cell drops below the prescribed threshold, the protection circuit 7a determines that the secondary battery 6 is in an over-discharge condition and outputs an over-discharge signal to a microcomputer 11 described later. As described above, the rated voltage of each lithium-ion battery cell is 3.6 V, and the threshold for determining an over-discharge condition is 2.0 V in the preferred embodiment. Similarly, when the discharge current exceeds a prescribed value, the protection circuit 7a determines that an over-current condition has occurred and outputs an over-current signal to the microcomputer 11. The protection circuit 7a also detects an over-charge condition and the like when the secondary battery 6 is being charged and outputs an over-charge signal to the charging device for halting the charging operation.
The temperature detection unit 8 is configured of a thermistor TSR, and a resistor R1. The thermistor TSR is a temperature sensor disposed near to or in contact with the secondary battery 6. The temperature detection unit 8 functions to detect the temperature of the secondary battery 6. More specifically, the resistor R1 and thermistor TSR are connected in series between the supply voltage (5 V) and ground. The resistance value of the thermistor TSR fluctuates in response to changes in temperature, and the voltage of the thermistor TSR is inputted into the microcomputer 11 (described later). The battery pack 2 has a three-terminal regulator 10 for producing the supply voltage (5V).
The three-terminal regulator 10 is provided in the battery pack 2 for outputting a 5-V constant voltage based on the battery voltage supplied from the secondary battery 6. The 5-V constant voltage is used to power a microcomputer 11, the temperature detection unit 8 described above, and a tool-insertion detection unit 12 described later. Capacitors C1 and C2 are connected to the three-terminal regulator 10 for preventing circuit oscillation.
The battery pack 2 includes a built-in microcomputer 11. The output terminal of the three-terminal regulator 10 is connected to the VDD terminal of the microcomputer 11 across which a voltage of 5 V is applied. The microcomputer 11 is in an operating state when the 5-V voltage is applied to the VDD terminal.
As described above, the protection circuit 7a inputs an over-discharge signal into the microcomputer 11, while the temperature detection unit 8 inputs a battery temperature signal into the microcomputer 11. The microcomputer 11 is also connected to a battery voltage detection unit 13, a current detection unit 14, and an over-discharge output unit 15. The battery voltage detection unit 13 is configured of a battery voltage detection command unit, and a battery voltage detection unit for detecting the battery voltage in response to output from the battery voltage detection command unit.
The battery voltage detection command unit of the battery voltage detection unit 13 is configured of an FET 13a, resistors R2 and R3, and zener diode ZD1. A parallel circuit configured of the resistor R2 and the zener diode ZD1 is connected between the gate and source of the FET 13a. The resistor R3 is connected between the output terminal of the microcomputer 11 and the gate of the FET 13a. The battery voltage detection unit of the battery voltage detection unit 13 is configured of an FET 13b, resistors R4 and R5, and a zener diode ZD2. A parallel circuit configured of the resistor R4 and zener diode ZD2 is connected between the positive terminal of the battery pack 2 and the gate of the FET 13a. The resistor R5 is connected between the drain of the FET 13a and the gate of the FET 13b. When the microcomputer 11 outputs a high-level command signal representing a command to detect battery voltage, the voltage divided by the resistors R3 and R2 is inputted into the gate of the FET 13a, turning the FET 13a on.
When the FET 13a turns on, the voltage from the secondary battery 6 divided by resistors R4 and R5 produces a potential difference between the gate and source of the FET 13b, turning the FET 13b on. Resistors R6 and R7 form a series current with the FET 13b that is connected in parallel to the secondary battery 6. The battery voltage of the secondary battery 6 is divided by the resistors R6 and R7 connected in series with the divided voltage corresponding to the battery voltage of the secondary battery 6 being inputted into the microcomputer 11.
With this configuration, the battery voltage detection unit 13 is configured to detect the battery voltage of the secondary battery 6 only when detections are desired. For example, the battery voltage detection unit 13 can detect the battery voltage of the secondary battery 6 when the microcomputer 11 detects that the battery pack 2 has been mounted on the tool body 1. Since the battery voltage detection unit 13 according to the preferred embodiment is provided with the battery voltage detection command unit, the series circuit including the resistors R6 and R7 connected in parallel to the secondary battery 6 consumes less power from the secondary battery 6 than a structure that continuously detects battery voltage from the voltage dividing resistors.
The current detection unit 14 is connected to the microcomputer 11 for detecting current flowing to the motor 3 and for inputting the detected current value into the microcomputer 11. The current detection unit 14 is configured of a resistor.
The over-discharge output unit 15 is connected to an output terminal of the microcomputer 11. The output of the over-discharge output unit 15 is connected to the battery shutdown terminal 9 on the battery pack 2 side through a resistor R12. The over-discharge output unit 15 is configured of an FET 15a, and resistors R10 and R11. The resistor R10 is connected between an over-discharge signal output terminal of the microcomputer 11 and the gate of the FET 15a, and the resistor R11 is connected between the gate and source of the FET 15a.
When a high-level over-discharge signal indicating an over-discharge condition is inputted from the over-discharge signal output terminal of the microcomputer 11 into the over-discharge output unit 15, the FET 15a turns on, and a current flows from the resistor Ra on the tool body 1 side to the resistor R12 on the battery pack 2 side. Consequently, the motor control FET 5 is turned off, cutting off the current flow to the motor 3, regardless of whether the trigger switch 4 is on or off. On the other hand, when the microcomputer 11 is not outputting an over-discharge signal, i.e., when a low-level signal is outputted from the over-discharge signal output terminal of the microcomputer 11, the FET 15a of the over-discharge output unit 15 is off and current flows through the resistors Ra and Rb on the tool body 1 side. Since the resistance value of the resistor Rb is set greater than that of the resistor R12, the motor control FET 5 is on and the motor 3 is driven to rotate when the trigger switch 4 is on.
The tool-insertion detection unit 12 is connected between an input terminal of the microcomputer 11 and the battery shutdown terminal 9 on the battery pack 2 side. The tool-insertion detection unit 12 is configured of an FET 12a and resistors R8 and R9. The resistor R8 is connected between the gate and source of the FET 12a, while the resistor R9 is connected between the gate of the FET 12a and the battery shutdown terminal 9. The battery pack 2 is not mounted in the tool body 1 if an over-discharge signal is not being outputted from the protection circuit 7a and the battery shutdown terminal 9 is open on the battery pack 2 side. When the battery shutdown terminal 9 on the battery pack 2 side is in an open state, the FET 12a is off. A 5-V supply voltage supplied from the three-terminal regulator 10 to the tool-insertion detection unit 12 (i.e., a high-level signal) is inputted into a tool-insertion detection input terminal of the microcomputer 11. The microcomputer 11 recognizes that the battery pack 2 is in a non-mounted state relative to the tool body 1 when the signal inputted into the tool-insertion detection input terminal of the microcomputer 11 is a high-level signal. However, when the battery shutdown terminal 9 on the battery pack 2 side is in a high-level state, the microcomputer 11 recognizes that the battery pack 2 is connected into the tool body 1. In this state, the FET 12a is on and the signal at the tool-insertion detection input terminal of the microcomputer 11 is at low level for grounding the terminal via the FET 12a. At this time, the microcomputer 11 recognizes that the battery pack 2 is connected into the tool body 1.
Next, the operations of the tool body 1 and battery pack 2 having the above configuration will be described while referring to the flowchart in Fig. 2 and the graph in Fig. 5.
When the battery pack 2 is mounted on the tool body 1 and a power switch on the tool body 1 is turned on, the three-terminal regulator 10 applies a 5-V supply voltage to the microcomputer 11 based on the battery voltage supplied from the secondary battery 6. When the three-terminal regulator 10 applies this voltage, the microcomputer 11 enters an operable state. Upon entering this state, in S101 the microcomputer 11 detects the battery voltage by outputting a high-level command signal to the battery voltage detection unit 13 representing a command to detect the battery voltage.
In S102 the microcomputer 11 determines whether the battery pack 2 is connected into the tool body 1. The microcomputer 11 makes this determination by detecting whether the signal level at the tool-insertion detection input terminal is high or low.
If the battery pack 2 is not connected into the tool body 1 (S102: NO), the microcomputer 11 continues to wait until the battery pack 2 has been connected.
When the microcomputer 11 determines that the battery pack 2 has been connected into the tool body 1 (S102: YES), in S103 the microcomputer 11 determines whether the battery voltage detected in S101 can be discharged. If the detected voltage is lower than the prescribed threshold, the microcomputer 11 determines that the charge capacity of the secondary battery 6 is insufficient and that the battery pack 2 currently connected into the tool body 1 cannot be used, i.e., cannot be discharged (S103: NO).
Determining the remaining charge capacity of the battery using the battery voltage in S101 is just one method. The microcomputer 11 may also detect the electric current during charging and discharging operations and calculate the charge capacity based on the integrated current value, or may employ a combination of both methods.
If the battery voltage detected by the battery voltage detection unit 13 is greater than or equal to the prescribed threshold, the microcomputer 11 determines that discharge is possible (S103: YES) and advances to S104. However, if the detected battery voltage is less than the threshold, the microcomputer 11 determines that discharge is not possible (S103: NO) and in S108 halts discharge of the battery.
In order to halt discharge in S108, the microcomputer 11 outputs a high-level over-discharge signal from its over-discharge signal output terminal to the over-discharge output unit 15. The FET 15a of the over-discharge output unit 15 is turned on in response to this over-discharge signal. Consequently, a value divided by the resistors Ra and R12 is inputted into the battery shutdown terminal 9. By setting the resistor R12 so that the resulting divided voltage value is sufficiently lower than the ON voltage of the over-discharge output unit 15, the motor control FET 5 of the tool body 1 is turned off.
If the microcomputer 11 determines in S103 that the secondary battery 6 can be used (S103: YES), in S104 the microcomputer 11 allows discharge. Specifically, the microcomputer 11 does not output an over-discharge signal from its over-discharge signal output terminal to the over-discharge output unit 15, thereby turning on the motor control FET 5 of the battery pack 2.
In S105 the microcomputer 11 determines whether the secondary battery 6 is in an over-discharge state. The microcomputer 11 determines that the secondary battery 6 is in an over-discharge state when the over-discharge detection unit 7 inputs an over-discharge signal into the microcomputer 11 after discharging has begun. If an over-discharge signal is not inputted into the microcomputer 11 (i.e., the secondary battery 6 is not in an over-discharge state), the microcomputer 11 determines that discharge can continue (S105: NO) and loops back to S104, while continuing to monitor the secondary battery 6 for an over-discharge state. As illustrated in Fig. 5, if discharge begins while the secondary battery 6 is in a fully charged state, the battery voltage of the secondary battery 6 is sufficiently larger than the threshold of 3.6 V per cell, for example. However, even though the microcomputer 11 determines in S103 that discharge is possible based on the detected battery voltage, the battery voltage will drop abruptly immediately following the start of discharge due to high internal resistance if the battery temperature at the beginning of discharge is low, such as -10 degrees C. Since the threshold for determining an over-discharge state is 2.0 V per cell in this example, the over-discharge detection unit 7 will determine that the secondary battery 6 is in an over-discharge state when the battery voltage immediately following the start of discharge falls below 2.0 V per cell and consequently will output an over-discharge signal to the microcomputer 11. Upon receiving this over-discharge signal, the microcomputer 11 will determine that the secondary battery 6 has entered an over-discharge state (S105: YES) and advance to S106.
In S106 the microcomputer 11 determines whether the temperature of the battery was low when the over-discharge signal was inputted into the microcomputer 11. In the preferred embodiment, the threshold for determining whether the battery temperature is low is -10 degrees C. If the detected battery temperature is lower than or equal to -10 degrees C, the microcomputer 11 determines that the secondary battery 6 is in a low-temperature state (S106: YES). However, if the detected battery temperature is higher than -10 degrees C, the microcomputer 11 determines that the battery temperature is normal (S106: NO). If the battery temperature is found to be normal, the microcomputer 11 advances to S108 and halts discharge since the secondary battery 6 was determined to be in an over-discharge state in S105.
If the battery temperature is low (S106: YES), then the microcomputer 11 determines that an over-discharge signal was detected and the secondary battery 6 is at a low temperature at timing T1 in the graph of Fig. 5. In this case, the microcomputer 11 cancels the over-discharge signal in S107. Here, "canceling the over-discharge signal" simply means not responding to the over-discharge signal inputted from the over-discharge detection unit 7 for a prescribed time interval. Specifically, the interval from timing T1 to timing T2 shown in Fig. 5 is a dead interval in which the microcomputer 11 does not respond to an over-discharge signal inputted from the over-discharge detection unit 7. Since the microcomputer 11 does not output an over-discharge signal to the over-discharge output unit 15 from its over-discharge signal output terminal during the dead interval, the signal at the over-discharge signal output terminal is maintained at the low level. Consequently, the motor control FET 5 of the tool body 1 is not interrupted but is maintained in an ON state during the dead interval.
When the microcomputer 11 determines in S105 that the secondary battery 6 is in an over-discharge state and further determines in S106 that the battery temperature is low (-10 degrees C or lower, for example), in most cases the secondary battery 6 is not actually in an over-discharge state, but rather a temporary voltage drop due to the low temperature environment has been incorrectly detected as over-discharge. Therefore, by recognizing that a temporary drop in battery voltage can occur in the initial stage of discharge due to a low battery temperature and by providing a dead interval in which the microcomputer 11 does not respond to an over-discharge signal inputted from the over-discharge detection unit 7, the method of the preferred embodiment prevents the microcomputer 11 from outputting an over-discharge signal to the over-discharge output unit 15 from its over-discharge signal output terminal during this dead interval. Note that when the secondary battery 6 is actually in an over-discharge state, the battery temperature will have risen because the process of steps S104 through S107 will have been repeated once or a plurality of times. In this case, the microcomputer 11 will advance to S108 to halt further discharge.
As illustrated in Fig. 5, the battery voltage drops temporarily immediately after the start of discharge from secondary battery cells in a low-temperature state, but begins to recover as the battery temperature rises, i.e., as current flows through the secondary battery cells, and the voltage per cell surpasses 2.0 V at timing T2. At this point, the over-discharge detection unit 7 no longer outputs an over-discharge signal to the microcomputer 11 and, hence, the microcomputer 11 determines in S105 that the secondary battery 6 is not in an over-discharge state (S105: NO). After determining that the secondary battery 6 is not in an over-discharge state, the microcomputer 11 returns to S104 and continues to allow the secondary battery 6 to discharge while monitoring the secondary battery 6 for over-discharge. The timing at which the microcomputer 11 first determines in S105 that the secondary battery 6 is not in an over-discharge state because the battery temperature of the secondary battery 6 has returned to normal is timing T2 in Fig. 5. As described above, the interval between timings T1 and T2 constitutes a dead interval during which the microcomputer 11 does not respond to an over-discharge signal outputted from the over-discharge detection unit 7.
According to the first embodiment described above, the microcomputer 11 determines that a drop in battery voltage is caused by a low battery temperature and does not interrupt the supply of power from the battery pack 2 to the tool body 1 when the battery temperature is low, even when determining that the secondary battery 6 is in an over-discharge state. Hence, the user of the tool body 1 can operate a battery pack having sufficient charge capacity, even when the battery pack is at a low temperature, without the unpleasant experience of receiving an over-discharge warning and having the drive of the tool body 1 halted, for example. If initial output from the secondary battery cells being at timing T0, the interval from the timing T0 to the timing T1 in the graph of Fig. 5 is extremely short. Therefore, the initial timing of the interval for delaying an interruption in the power supply may be between timing T0 and timing T1 and is not limited to timing T1 specified in the above example.
Next, a second embodiment of the present invention will be described while referring to Figs. 3 and 4.
The structure of the circuit shown in Fig. 3 is identical to that shown in Fig. 1, except for the following points, and like components with those in Fig. 1 are designated using the same reference numerals to avoid duplicating description.
The battery pack 2 according to the second embodiment shown in Fig. 3 further includes an over-discharge signal cancellation unit 16 provided between the over-discharge detection unit 7 and over-discharge output unit 15. The over-discharge signal cancellation unit 16 is configured of an FET 16a, and two resistors R14 and R15. The drain of the FET 16a is connected to the output terminal of the over-discharge detection unit 7 and is also connected to the over-discharge output unit 15 via the resistor R10. The gate of the FET 16a is connected to the over-discharge signal output terminal of the microcomputer 11 via the resistor R14. The resistor R15 is connected between the gate and source of the FET 16a.
In the first embodiment shown in Fig. 1, an over-discharge signal outputted from the over-discharge detection unit 7 is inputted into the microcomputer 11. However, in the circuit structure of the second embodiment shown in Fig. 3, this over-discharge signal is inputted into the over-discharge signal cancellation unit 16 rather than the microcomputer 11.
Further, the circuit structure in Fig. 3 for determining when the battery pack 2 is connected into the tool body 1 differs from the circuit structure in Fig. 1. The battery pack 2 in Fig. 3 has an insertion detection unit configured of resistors R16 and R17. The resistors R16 and R17 divide the voltage at the battery shutdown terminal 9, and the divided voltage is inputted into the microcomputer 11. The microcomputer 11 determines whether the battery pack 2 has been connected into the tool body 1 based on the level of the inputted voltage.
Specifically, the battery shutdown terminal 9 has a high potential when the battery pack 2 is connected into the tool body 1 and a low potential when the battery pack 2 is not connected into the tool body 1. Hence, the microcomputer 11 determines that the tool body 1 has been connected into the battery pack 2 when a high level signal has been inputted into the tool-insertion detection input terminal of the microcomputer 11, and conversely determines that the tool body 1 is not connected into the battery pack 2 when a low level signal has been inputted into the terminal.
When the microcomputer 11 determines that secondary battery cells generating an over-discharge signal are in a low-temperature state, a dead interval is set in the first embodiment described above to a period from the point that the over-discharge signal was detected until the battery temperature reaches a level at which the internal resistance is sufficiently low. During this dead interval, the microcomputer 11 and the tool body 1 do not react to an over-discharge signal inputted from the over-discharge detection unit 7 into the microcomputer 11. In the second embodiment, if the microcomputer 11 determines that the secondary battery 6 is in a low-temperature state after the over-discharge detection unit 7 has determined the secondary battery 6 is in an over-discharge state and has outputted an over-discharge signal, the microcomputer 11 outputs a reset signal from its reset output terminal to the over-discharge signal cancellation unit 16, preventing the over-discharge signal from being inputted into the tool body 1 via the over-discharge output unit 15.
As an example, when an over-discharge state is detected in the protection circuit 7a, the over-discharge detection unit 7 outputs a high-level over-discharge signal. However, when the secondary battery 6 is in a low-temperature state, the microcomputer 11 outputs a reset signal from its reset output terminal to the over-discharge signal cancellation unit 16 in response to the over-discharge signal. The reset signal turns on the FET 16a of the over-discharge signal cancellation unit 16. If the over-discharge signal cancellation unit 16 were not interposed between the over-discharge detection unit 7 and the over-discharge output unit 15, the high-level over-discharge signal would be applied directly to the gate of the FET 15a of the over-discharge output unit 15. However, the over-discharge signal cancellation unit 16 interposed between the over-discharge detection unit 7 and over-discharge output unit 15 inverts the high-level over-discharge signal, so that a low-level signal is applied to the FET 15a in the over-discharge output unit 15. Consequently, the FET 15a is turned off, maintaining the motor control FET 5 on the tool body 1 side in an ON state.
Next, the operations of the tool body 1 and battery pack 2 according to the second embodiment will be described with reference to the flowchart in Fig. 4.
The operations of the power tool according to the second embodiment shown in Fig. 4 are identical to the operations of the first embodiment shown in Fig. 2 for the initial steps from S101 to S104, but are different in subsequent steps. In S205 following S104 of Fig. 4, the microcomputer 11 determines whether the secondary battery 6 is in a low-temperature state (-10 degrees C or lower). If the microcomputer 11 determines that the temperature of the secondary battery 6 is low (S205: YES), in S206a the microcomputer 11 outputs a reset signal from its reset output terminal to the over-discharge signal cancellation unit 16. However, if the microcomputer determines in S205 that the secondary battery is not at a low temperature, i.e., is in a normal temperature state, then in S206b the microcomputer 11 halts output of the reset signal, or does nothing if a reset signal is not being outputted, and advances to S207. In S207 the microcomputer 11 determines whether the secondary battery 6 is in an over-discharge state. This step is equivalent to S105 in the flowchart of Fig. 2. If the microcomputer 11 determines that the secondary battery 6 is not in an over-discharge state (S207: NO), the microcomputer 11 returns to S102 and continues monitoring the secondary battery 6 to determine whether the secondary battery 6 is in an over-discharge state. If the microcomputer 11 determines in S207 that the secondary battery 6 is in an over-discharge state (S207: YES), then in S208 the microcomputer 11 halts discharge from the secondary battery 6. This step is equivalent to S108 in the flowchart of Fig. 2. Since the microcomputer 11 switches output of the reset signal on and off in steps S206a and S206b in the second embodiment, a step equivalent to S107 of Fig. 2 in which the microcomputer 11 sets a dead interval is no longer necessary.
In the second embodiment described above, the microcomputer 11 predicts that a drop in battery voltage will occur immediately after discharge begins if the battery temperature is low and predicts that the over-discharge detection unit 7 will output an over-discharge signal due to this drop in voltage. Therefore, the microcomputer 11 resets the over-discharge signal in order to prevent the over-discharge output unit 15 from outputting this over-discharge signal to the tool body 1 side. This method prevents power supplied from the battery pack 2 to the tool body 1 from being interrupted because the battery temperature is low and, hence, the operator of the tool body 1 does not experience the unpleasant sensation of the tool body 1 stopping abruptly during operations.
While the tool body 1 according to the present invention has been described in detail with reference to specific embodiments thereof, it would be apparent to those skilled in the art that many modifications and variations may be made therein without departing from the spirit of the invention, the scope of which is defined by the attached claims.
For example, the order of steps S105 and S106 in the flowchart of Fig. 2 according to the first embodiment may be switched. Further, while a temperature threshold of -10 degrees C is used as an example in the first embodiment for determining whether the temperature of the secondary battery 6 is low, a different threshold may be employed.
Further, when the temperature of the battery is determined to be lower than the prescribed temperature threshold in the first embodiment, a dead interval is configured to last until the battery temperature reaches a normal temperature. However, the dead interval may instead be set to a predetermined fixed time interval from the start of discharge (60 seconds, for example) when the battery temperature is found to be below the temperature threshold. Also, the length of the dead interval is not limited to a single predetermined fixed time interval but may be freely set according to the temperature threshold. For example, a plurality of dead intervals may be set based on a plurality of temperature thresholds, or the length of the dead interval may be modified as a function of temperature so as to last 60 seconds from the start of discharge when the temperature threshold is -10 degrees C and 30 seconds from the start of discharge when the temperature threshold is 0 degrees C. Further, the current detection unit 14 may detect the current flowing to the motor 3, and the microcomputer 11 may be set the dead interval based on the battery voltage detected by the battery voltage detection unit 13 or the battery's charge capacity. In the latter case, the microcomputer 11 may reference the charge capacity of the battery and set the dead interval to 120 seconds when the capacity is at least 80%, 60 seconds when the capacity is at least 60%, 40 seconds when the capacity is less than 30%, and the like.
In the first and second embodiments, the battery voltage detection unit 13 shown in Figs. 1 and 3 detects the battery voltage of the secondary battery 6 through an actual measurement. However, if the battery pack 2 has a built-in identification resistor representing ID data for its internal battery cells, the microcomputer 11 can determine the battery voltage by reading this ID data. With this configuration, the battery voltage detection unit 13 provided in the embodiments may be omitted, thereby eliminating power dissipation of the secondary battery 6 caused by the battery voltage detection unit 13. The identification data described above includes the type of battery (e.g., lithium-ion battery cells or the like), and the number of cells.
In the first and second embodiments described above, the microcomputer 11, various units for inputting signals into the microcomputer 11, and various units for receiving output from the microcomputer 11 are provided in the battery pack 2. However, the microcomputer 11 and its related units may be provided in the tool body 1 instead, while the battery pack is only provided with the over-discharge detection unit 7 (including the secondary battery 6), and the thermistor TSR.
Further, the present invention may be applied to a power tool having a drive unit that employs an FET for driving the motor such as a brushless DC motor or the like. Further, the present invention is not limited to a power tool employing a motor. One suitable example is a work light or lantern that employs a secondary battery designed for a power tool as its power supply. In this case, the effects of the present invention can be obtained by performing the same control described in the embodiments.
1 tool body
2 battery pack
3 motor
4 trigger switch
5 motor control FET
6 lithium-ion battery (secondary battery)
7 over-discharge detection unit
7a protection circuit
8 temperature detection unit
9 battery shutdown terminal
10 three-terminal regulator
11 microcomputer
12 tool-insertion detection unit
13 battery voltage detection unit
14 current detection unit
15 over-discharge output unit
16 over-discharge signal cancellation unit
R1-R12 resistors
C1, C2 capacitors for preventing circuit oscillation
TSR thermistor

Claims (12)

  1. A power tool comprising:
    a secondary battery;
    a drive unit;
    a battery voltage detection unit configured to detect a battery voltage of the secondary battery;
    a battery temperature detection unit configured to detect a temperature of the secondary battery; and
    an over-discharge detection unit configured to detect that a charge capacity of the secondary battery is less than a prescribed value and output an over-discharge signal indicating that the secondary battery is in an over-discharge state;
    characterized in that the power tool further comprises:
    a control unit configured to control the over-discharge signal outputted from the over-discharge detection unit based on the temperature detected by the battery temperature detection unit.
  2. The power tool according to claim 1, wherein the control unit is further configured to interrupt power supply from the secondary battery to the drive unit in response to the over-discharge signal, and delay the interruption in the power supply by controlling the over-discharge signal.
  3. The power tool according to claim 1, wherein the control unit has a dead interval not to respond to the over-discharge signal, if the temperature detected by the battery temperature detection unit is lower than or equal to a temperature threshold and the over-discharge detection unit outputs the over-discharge signal.
  4. The power tool according to claim 1, wherein the control unit has a reset interval to output a reset signal to reset the over-discharge signal, if the temperature detected by the battery temperature detection unit is lower than or equal to a temperature threshold and the over-discharge detection unit outputs the over-discharge signal.
  5. The power tool according to claim 2, wherein an interval for delaying the interruption in the power supply begins at a timing in a duration between timing of initial output from the secondary battery and timing of detection of the temperature lower than or equal to the temperature threshold by the battery temperature detection unit, and ends when or after the battery temperature detection unit detects the temperature higher than the temperature threshold and the over-discharge detection unit stops the output of the over-discharge signal.
  6. The power tool according to claim 3, wherein the control unit is further configured to set the dead interval based on the temperature detected by the battery temperature detection unit.
  7. The power tool according to claim 6, wherein the dead interval is set longer as the temperature is lower.
  8. The power tool according to claim 4, wherein the control unit is further configured to set the reset interval based on the temperature detected by the battery temperature detection unit.
  9. The power tool according to claim 8, wherein the reset interval is set longer as the temperature is lower.
  10. A power tool comprising:
    a secondary battery;
    a drive unit;
    a battery voltage detection unit configured to detect a battery voltage of the secondary battery;
    a battery temperature detection unit configured to detect a temperature of the secondary battery; and
    an over-discharge detection unit configured to detect that charge capacity of the secondary battery is less than a prescribed value and output an over-discharge signal indicating that the secondary battery is in an over-discharge state;
    characterized in that the power tool further comprises:
    a reset unit configured to reset the over-discharge signal outputted from the over-discharge detection unit based on the temperature detected by the battery temperature detection unit.
  11. The power tool according to claim 10, wherein power supply from the secondary battery to the drive unit is interrupted in response to the over-discharge signal, and the reset unit is further configured to delay the interruption in the power supply by resetting the over-discharge signal.
  12. The power tool according to any one of claims 1 to 11, wherein the secondary battery comprises a lithium-ion battery cell.
PCT/JP2013/005129 2012-09-10 2013-08-29 Power tool WO2014038165A1 (en)

Applications Claiming Priority (2)

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JP2012-198983 2012-09-10
JP2012198983A JP2014050942A (en) 2012-09-10 2012-09-10 Electric power tool

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