Cordless power tool with overcurrent protection circuit permitting the overcurrent condition during specified time periods
DCFirst Claim
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1. A power tool comprising:
- a battery comprised of a plurality of lithium battery cells connected in series;
a DC motor connected to the battery and supplied with a driving current from the battery; and
means for permitting an overcurrent defined by a current having a value equal to or greater than a predetermined value to flow during a start-up period of the motor and for prohibiting the overcurrent to flow in the current path when the motor is brought into a locked state of operation.
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Abstract
A cordless power tool uses a lithium battery as a power source of a motor and is provided with an overcurrent protection circuit. The circuit allows an overcurrent to instantaneously flow at the start-up time of the motor and shuts off an overcurrent which may flow when the motor is brought into a locked state during the use of the power tool.
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Citations
17 Claims
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1. A power tool comprising:
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a battery comprised of a plurality of lithium battery cells connected in series; a DC motor connected to the battery and supplied with a driving current from the battery; and means for permitting an overcurrent defined by a current having a value equal to or greater than a predetermined value to flow during a start-up period of the motor and for prohibiting the overcurrent to flow in the current path when the motor is brought into a locked state of operation. - View Dependent Claims (2, 6, 8)
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3. The power tool comprising:
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a battery comprised of a plurality of lithium battery cells connected in series; and a DC motor connected to the battery and supplied with a driving current from the battery, wherein an overcurrent defined by a current having a value equal to or greater than a predetermined value is prohibited to flow in the current path for more than a predetermined time period, further comprising; a switching element selectively rendered ON and OFF, wherein the battery, the switching element and the DC motor are connected to provide a current path and the DC motor is supplied with a driving current from the battery through the current path; a current detection section that detects a current flowing in the current path and outputs a detection signal indicative of the current flowing in the current path; and a microcomputer that receives the detection signal from the current detection section and controls the switching element, wherein the microcomputer has a control program that executes a first step wherein determination is made as to whether or not the value of a current flowing in the current path has exceeded a predetermined value, a second step wherein determination is made as to whether or not the current continuously flows in the current path for a first predetermined time period when the value of the current has exceeded the predetermined value, and a third step of generating a control signal to set the switching element in the off state when the current continuously flows in the current path for the first predetermined time period. - View Dependent Claims (4, 7, 9)
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5. The power tool comprising:
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a battery comprised of a plurality of lithium battery cells connected in series; and a DC motor connected to the battery and supplied with a driving current from the battery, wherein an overcurrent defined by a current having a value equal to or greater than a predetermined value is prohibited to flow in the current path for more than a predetermined time period, further comprising; a bit; a speed reduction mechanism having an input side operatively coupled to the motor and an output side operatively coupled to the bit, a rotational speed transmitted by the speed reduction mechanism to the bit being reduced relative to a rotational speed of the motor; a main body that houses the DC motor and the speed reduction mechanism; a handle having one side coupled to the main body; and a battery pack that is attached to another side of the handle, the battery pack housing therein the battery.
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10. A battery pack for use in a power tool including a motor, comprising:
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a battery comprised of a plurality of lithium battery cells connected in series; a pair of connection terminals for connection to the power tool; and means for permitting an overcurrent defined by a current having a value equal to or greater than a predetermined value to flow during a startup period of the motor and for prohibiting the overcurrent to flow from the battery to the motor when the motor is brought into a locked state of operation. - View Dependent Claims (11, 14, 16)
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12. The battery pack for use in a power tool including a motor, comprising:
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a battery comprised of a plurality of lithium battery cells connected in series; and a pair of connection terminals for connection to the power tool; wherein an overcurrent defined by a current having a value equal to or greater than a predetermined value is prohibited to flow from the battery to the motor for more than a predetermined time period, further comprising; a switching element selectively rendered ON and OFF, wherein in use, the DC motor is supplied with a driving current from the battery via the pair of connection terminals; a current detection section that detects a current flowing from the battery to the motor and outputs a detection signal indicative of the current flowing from the battery to the motor; and a microcomputer that receives the detection signal from the current detection section and controls the switching element, wherein the microcomputer has a control program that executes a first step wherein determination is made as to whether or not the value of a current flowing in the current path has exceeded a predetermined value, a second step wherein determination is made as to whether or not the current continuously flows in the current path for a first predetermined time period when the value of the current has exceeded the predetermined value, and a third step of generating a control signal to set the switching element in the off state when the current continuously flows in the current path for the first predetermined time period. - View Dependent Claims (13, 15, 17)
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Specification