The present invention relates to a power tool and a battery pack capable of preventing an overcurrent from flowing in a secondary battery.
Conventionally, a lithium-ion secondary battery is widely used as a secondary battery for driving a cordless power tool (hereinafter, to be referred to as “power tool”) that requires a large amount of power. However, a battery life of the lithium-ion secondary battery becomes excessively short if an overcurrent flows in the secondary battery. To this effect, a battery pack that detects the occurrence of the overcurrent based on a current flowing in a secondary battery of a power tool and prohibits a power supply to the power tool when the occurrence of the overcurrent is detected, is proposed (See Laid-open Japanese Patent Application Publication No. 2006-281404, for example).
It is an object of the present invention to provide a power tool and a battery pack capable of preventing an overcurrent from flowing in a secondary battery without detecting a current.
In order to achieve the above and other objects, the present invention provides a power tool connectable to a battery pack including a secondary battery. The power tool includes a motor driven with an electrical power supplied from the secondary battery; and a prohibiting unit that prohibits the supply of the electrical power to the motor based on a drop amount of a voltage of the secondary battery.
With this configuration, an overcurrent can be prevented from flowing in the secondary battery without detecting a current.
Preferably, the prohibiting unit prohibits the supply of the electrical power to the motor when the drop amount exceeds a first threshold.
Preferably, the first threshold depends on at least one of a temperature of the secondary battery and a capacity of the secondary battery.
With this configuration, an overcurrent can be prevented from flowing in the secondary battery more appropriately.
Preferably, the power tool further includes a trigger switch that is manually closed to supply the electrical power to the motor. Once prohibiting the supply of the electrical power to the motor, the prohibiting unit continues to prohibit the supply of the electrical power to the motor until the trigger switch is opened.
With this configuration, the supply of the electrical power to the motor can be prevented from being repeatedly permitted and prohibited in a short period of time.
Preferably, the power tool further includes a trigger switch that is manually closed to supply the electrical power to the motor. The prohibiting unit detects the drop amount every predetermined period since the trigger switch has been closed, the predetermined period being set to a value such that the prohibiting unit fails to detect the drop amount occurring due to a starting current.
With this configuration, the supply of the electrical power to the motor can be prevented from being prohibited at the starting time of the motor.
Preferably, the prohibiting unit prohibits the supply of the electrical power to the motor by shutting off a switching unit disposed on a current path between the secondary battery and the motor.
With this configuration, the supply of the electrical power to the motor can be reliably shut down.
Preferably, the secondary battery is a lithium-ion secondary battery.
With this configuration, the overcurrent prevention is more efficient for the lithium-ion secondary battery.
Preferably, the prohibiting unit prohibits the supply of the electrical power to the motor, at least one of when the drop amount exceeds the first threshold and when a capacity of the secondary battery falls below a second threshold for an overdischarge.
With this configuration, the decrease in the battery life of the secondary battery can be suppressed more effectively.
Another aspect of the present invention provides a battery pack connectable to a power tool including a motor. The battery pack includes a secondary battery that supplies an electrical power to the motor to drive the motor; and a prohibiting unit that prohibits the supply of the electrical power to the motor based on a drop amount of a voltage of the secondary battery.
With this configuration, an overcurrent can be prevented from flowing in the secondary battery without detecting a current.
Preferably, the prohibiting unit prohibits the supply of the electrical power to the motor when the drop amount exceeds a first threshold.
Preferably, the first threshold depends on at least one of a temperature of the secondary battery and a capacity of the secondary battery.
With this configuration, an overcurrent can be prevented from flowing in the secondary battery more appropriately.
Preferably, the power tool further includes a trigger switch that is manually closed to supply the electrical power to the motor. Once prohibiting the supply of the electrical power to the motor, the prohibiting unit continues to prohibit the supply of the electrical power to the motor until the trigger switch is opened.
With this configuration, the supply of the electrical power to the motor can be prevented from being repeatedly permitted and prohibited in a short period of time.
Preferably, the power tool further includes a trigger switch that is manually closed to supply the electrical power to the motor. The prohibiting unit detects the drop amount every predetermined period since the trigger switch has been closed, the predetermined period being set to a value such that the prohibiting unit fails to detect the drop amount occurring due to a starting current.
With this configuration, the supply of the electrical power to the motor can be prevented from being prohibited at the starting time of the motor.
Preferably, the prohibiting unit prohibits the supply of the electrical power to the motor by shutting off a switching unit disposed on a current path between the secondary battery and the motor.
With this configuration, the supply of the electrical power to the motor can be reliably shut down.
Preferably, the secondary battery is a lithium-ion secondary battery.
With this configuration, the overcurrent prevention is more efficient for the lithium-ion secondary battery.
Preferably, the prohibiting unit prohibits the supply of the electrical power to the motor, at least one of when the drop amount exceeds the first threshold and when a capacity of the secondary battery falls below a second threshold for an overdischarge.
With this configuration, a decrease in a life of the secondary battery can be suppressed more effectively.
According to the power tool and the battery pack of the present invention, an overcurrent can be prevented from flowing in a secondary battery without detecting a current, thereby suppressing a decrease in a life of the secondary battery.
In the drawings:
a) is a time chart showing timings at which a trigger switch is closed and open when a trigger switch is closed in a state where the battery pack is connected to the power tool;
b) is a time chart showing changes in voltages VA, VB and VC at junctions A, B and C of
c) is a time chart showing a current flowing in each battery cell in correspondence with
a) is a time chart showing timings at which the trigger switch is closed and opened;
b) is a time chart showing changes in the voltages VA and VB at the junctions A and B of
A power tool 1 and a battery pack 5 according to a first embodiment of the present invention will be described with reference to
First, an electrical configuration of the power tool 1 will be described. The power tool 1 (a driver drill, for example) includes a motor 2, a switch unit 3 and a controller 4, as shown in
The motor 2 is connected between the positive terminal 54 and the negative terminal 55 via the switch unit 3 and the controller 4. The switch unit 3 includes a trigger switch 31 and a forward-reverse switch 32. The trigger switch 31 is connected between the motor 2 and the positive terminal 54. The trigger switch 31 is opened/closed in accordance with user's operations. The forward-reverse switch 32 serves to change the rotating direction of the motor 2.
When the battery pack 5 (for example, fully charged battery pack 5) is connected to the power tool 1, a voltage is applied between the positive terminal 54 and the negative terminal 55. When the trigger switch 31 is closed, a closed circuit is formed between the battery pack 5 and the motor 2 via the controller 4, thereby the voltage is applied to the motor 2. Thus, the motor 2 is driven to operate an end bit (not shown) connected to the motor 2.
The controller 4 functions to shut off the closed circuit to stop driving the motor 2 when receiving a signal indicative of prohibition of the power supply from the prohibition signal output terminal 56 of the battery pack 5. A detailed configuration of the controller 4 will be described later.
Next, a configuration of the battery pack 5 will be described. As shown in
The battery 51 is configured of four battery cells 510 (secondary batteries) each connected in series between the positive terminal 54 and the negative terminal 55. In the present embodiment, each battery cell 510 is a lithium-ion secondary battery having a rated voltage of 3.6V. Since the battery 51 has four battery cells 510 of 3.6V connected in series, the battery 51 has a battery voltage of 14.4V. The thermistor 52 is disposed adjacent to the battery 51 to output a signal indicative of a temperature of the battery 51 (battery temperature T). As a variation, two batteries 51 connected in parallel may be connected between the positive terminal 54 and the negative terminal 55 in order to obtain a larger capacity. Alternatively, as the battery 51, more than or less than four battery cells 510 may be connected.
The battery protection IC 53 includes a voltage detecting section 530, an overcharge detecting section 531, an overdischarge detecting section 532, a power supply prohibiting section 533 and a switch 58. In case that the battery protection IC 53 is a microcomputer, a CPU of the microcomputer functions as the voltage detecting section 530, the overcharge detecting section 531, the overdischarge detecting section 532 and the power supply prohibiting section 533.
The voltage detecting section 530 detects respective voltages of the battery cells 510 and outputs the detected voltages to the overcharge detecting section 531, the overdischarge detecting section 532 and the power supply prohibiting section 533. If any one of the voltages of the battery cells 510 exceeds a predetermined value (an overcharge threshold value) during the charge of the battery cells 510, the overcharge detecting section 531 determines that overvoltage has occurred, and outputs a signal indicative of termination of charging to the charger via the overcharge output terminal 57. If any one of the voltages of battery cells 510 falls below a prescribed value (an overdischarge threshold Vth in
The power supply prohibiting section 533 calculates a voltage drop amount ΔV of each battery cell 510 for each sampling time T2 (described later) based on the voltage of each battery cell 510 detected by the voltage detecting section 530. The power supply prohibiting section 533 determines whether or not to prohibit power supply to the motor 2 based on the calculated voltage drop amount ΔV. More specifically, the power supply prohibiting section 533 stores a table 533a (see
If the power supply prohibiting section 533 determines that power should not be supplied to the motor 2, the power supply prohibiting section 533 outputs a close signal to close the switch 58 (to render the switch 58 ON). The determination of the power supply prohibition will be described later in detail. The table 533a may be stored not in the power supply prohibiting section 533 but in a storage unit (not shown), such as a memory. Further, the reference voltages (threshold values α) may correspond to at least one of the battery temperature T and the residual battery capacity C.
When the switch 58 is closed in response to the close signal from the overdischarge detecting section 532 or the power supply prohibiting section 533, the prohibition signal output terminal 56 is connected to the a ground line. Thus, 0V (Lo signal) for prohibiting power supply is outputted to a gate of an FET 410 of the controller 4 (described later) via the prohibition signal output terminal 56.
As shown in
Next, a process to make the power supply prohibition determination according to the first embodiment will be described in detail with reference to
When the trigger switch 31 is closed, in S101 the power supply prohibiting section 533 sets a previous battery voltage Vin−1 to 0V as an initial setting. When a predetermined sampling time T1 has elapsed (S102: YES), in S103 the power supply prohibiting section 533 obtains a present battery voltage Vin(t1) of each battery cell 510 from the voltage detecting section 530. As shown in
Subsequently, in S104 the power supply prohibiting section 533 determines whether or not the present battery voltage Vin(t1) is smaller than the previous battery voltage Vin−1, i.e., whether or not the present battery voltage Vin(t1) has decreased from the previous battery voltage Vin−1.
When the present battery voltage Vin(t1) is greater than or equal to the previous battery voltage Vin−1, which means that the battery voltage has not decreased (S104: NO), it is presumed that the end bit is not working on a workpiece (i.e., an unloaded (idling) state). Therefore, in S105, the power supply prohibiting section 533 resets the previous battery voltage Vin−1 to the present battery voltage Vin(t1), and returns to S102. Note that since the previous battery voltage Vin−1 is set to 0V in S101, the power supply prohibiting section 533 always makes a NO determination in S104 when executing the S104 for the first time.
When the present battery voltage Vin(t1) is smaller than the previous battery voltage Vin−1, which means that the battery voltage has decreased (S104: YES), it is presumed that the end bit is working on the workpiece (i.e., a loaded state) (a region C in
When a predetermined sampling time T2 has elapsed since it is determined to be “YES” in S104 (S106: YES), in S107 the power supply prohibiting section 533 obtains a present battery voltage Vin(t2) of each battery cell 510 from the voltage detecting section 530, the battery temperature Tin from the thermistor 52, and the residual battery capacity C from the residual capacity detection unit 59. The sampling time T2 is set to a value shorter than the sampling time T1 in order to detect the battery voltage accurately.
In S108, the power supply prohibiting section 533 obtains, from the table 533a, the reference voltage (the threshold value α(T)) corresponding to the obtained battery temperature Tin and the obtained residual battery capacity C. In S109, the power supply prohibiting section 533 determines whether or not a voltage drop amount ΔV during the sampling time T2 (a potential difference between the previous battery voltage Vin−1 and the present battery voltage Vin (t2)) is greater than the threshold value α(T). When the voltage drop amount ΔV is smaller than or equal to the threshold value α(T) (S109: NO), the power supply prohibiting section 533 determines that the end bit is working on the workpiece (the loaded state) but the overload (overcurrent) is not occurring (a region C in
On the other hands, when the voltage drop amount ΔV is greater than the threshold value α(T) (S109: YES), it is presumed that the overload (overcurrent) is occurring (a region D in
As described above, the power tool 1 and the battery pack 5 of the present embodiment can prevent an overcurrent from flowing in each battery cell 510 without detecting the current flowing in each battery cell 510, by detecting the voltage drop amount ΔV for each battery cell 510. Therefore, decrease in the life of each battery cell 510 can be suppressed.
Here, assume that the power tool 1 is embodied as a driver drill for fastening a screw onto a workpiece. Relationships between a battery voltage of each battery cell 510 and a current flowing in each battery cell 510 in this example will be described with reference to
When the trigger switch 31 is not closed, the battery voltage does not decrease and the current does not flow (a region A in
When the power tool 1 (the driver tool) starts tightening the screw, a load is generated. Due to the load, the current flowing in each battery cell 510 gradually increases and the battery voltage gradually decreases (a region C in
Upon completion of fastening the screw (time to in
When the trigger switch 31 is opened, the flowchart of
However, normally, under a constant battery temperature, the larger the residual battery capacity C is, the smaller the voltage drop amount ΔV is. Therefore, according to the table 533a of the present embodiment, the threshold value α for “large” amount of the residual battery capacity C is set to a value smaller than those for “medium” and “small” amounts of the residual battery capacity C, as shown in
According to the present embodiment, the threshold value α is selected from among four kinds of threshold values α1 to α4. However, the threshold value α may instead be selected from among an increased number of kinds of threshold values for realizing a more accurate execution of the power supply prohibition. Alternatively, the threshold value α may be set based exclusively on the battery temperature Tin, since the voltage drop amount ΔV tends to be more dependent on the battery temperature Tin rather than the residual battery capacity C.
Next, a detailed configuration of the controller 4 of the power tool 1 according to the first embodiment will be described with reference to
The main current switch circuit 41 includes the Field Effect Transistor (FET) 410, a resistor 411 and a capacitor 412. The FET 410 has a drain connected to the motor 2, the gate connected to the prohibition signal output terminal 56 and a source connected to the negative terminal 55. The resistor 411 is connected between the positive terminal 54 and the gate of the FET 410. The capacitor 412 is connected between the gate and the source of the FET 410. A junction of the gate of the FET 410, the resistor 411 and the capacitor 412 is called as “junction A.”
When the battery pack 5 is connected to the power tool 1, the battery voltage of the battery 51 is applied to the junction A (the gate of the FET 410) via the resistor 411. Therefore, when a power is normally supplied from the battery pack 5 to the motor 2, the FET 410 is turned ON. On the other hand, when 0V (Lo signal) is inputted to the gate of the FET 410 via the prohibition signal output terminal 56, the FET 410 is turned OFF, shutting off the power supply to the motor 2.
The main current switch-off maintaining circuit 42 serves to keep the FET 410 turned OFF even when the switch 58 is opened (OFF). The main current switch-off maintaining circuit 42 includes an FET 420, resistors 421, 422 and a capacitor 423.
The FET 420 has a drain connected to the gate of the FET 410 and the prohibition signal output terminal 56, and a source connected to the negative terminal 55. A gate of the FET 420 is connected to the drain of the FET 410 via the resistor 421, and also to the negative terminal 55 via the resistor 422 or the capacitor 423 which are connected in parallel. A junction of the gate of the FET 420, the resistor 422 and the capacitor 423 is referred to as “junction B.” A junction connecting the drain of the FET 410 with the gate of the FET 420 via the resistor 421 is referred to as “junction C.” When a voltage is generated at the junction B, the FET 420 is turned ON. When the FET 420 is turned ON, the junction A, which is connected to the drain of the FET 420, is connected to the negative terminal 55 (the grand line). As the result, the gate of the FET 410 connected to the junction A is also connected to the negative terminal 55, thereby the FET 410 is turned OFF.
The display section 43 includes a resistor 430 and a display device 431 (LED in the present embodiment) which are connected in parallel between the drain and the source of the FET 410. While the FET 410 is turned ON, no potential difference is generated between the drain and the source of the FET 410, even if the trigger switch 31 is closed. Therefore, the display section 43 connected between the drain and the source of the FET 410 is not illuminated. On the other hands, when the FET 410 is turned OFF in a state where the trigger 31 is closed, a potential difference is generated between the drain and the source of the FET 410, which causes the current to flow in the display device 431 via the resistor 430 to illuminate the display device 431. With the illumination of the display device 431, the user can recognize that the power tool 1 cannot work due to either overdischarge or overcurrent. Further, the display section 43 may also function as the residual capacity display section 59b (
Next, operations of the power tool 1 and the battery pack 5 having the above-described configurations will be described. First, with reference to
a) is a time chart showing timings at which a trigger switch 31 is closed and opened.
In
The power supply prohibiting section 533 of the battery pack 5 determines that the power supply should be prohibited when the voltage drop amount ΔV exceeds the threshold value α (at the time t1 in
When the FET 410 is turned OFF, the voltage VC (voltage at the junction C) starts increasing. At the same time, a voltage VB (voltage at the junction B) also starts increasing. When the voltage VB exceeds the on-voltage of V1 of the FET 420 (t2 in
Suppose here that the power tool 1 is not provided with the main current switch-off maintaining circuit 42. When a predetermined period has elapsed since the FET 410 is turned OFF, the overcurrent state is resolved. When the overcurrent state is resolved, the FET 410 is turned ON to resume the power supply. However, as soon as the power supply starts again, another overcurrent state will result, leading to the FET 410 being again turned OFF.
In contrast, in the power tool 1 according to the present embodiment provided with the main current switch-off maintaining circuit 42, the FET 420 is turned ON when the FET 410 is turned OFF. Since the drain of the FET 420 is connected to the gate of the FET 410, 0V is continuously applied to the gate of the FET 410 as long as the trigger switch 31 is closed even if the switch 58 is opened. Therefore, the FET 410 can maintain to be turned OFF even after the overcurrent has resolved. As the result, the power supply to the motor 2 continues to be shut down.
When the trigger switch 31 is opened (time t3 in
When the voltage VB decreases below the on-voltage V1 (time t4 in
As described above, according to the power tool 1 of the present embodiment, when the power supply to the motor 2 is shut off by the FET 410 in the state that the trigger switch 31 is closed, the main current switch-off maintaining circuit 42 maintains the state where the power supply to the motor 2 is prohibited as long as the trigger switch 31 is closed. This configuration can prevent permission and prohibition of the power supply from being alternately repeated in a short period of time. In case of overdischarge, the main current switch-off maintaining circuit 42 also functions in the same manner as in the case of overcurrent.
Next, with reference to
a) is a time chart showing timings at which the trigger switch 31 is closed and opened.
In
In the present embodiment, the time constant for a circuit configured of the resistor 411 and the capacitor 412 and the time constant for a circuit configured of the resistor 421 and the capacitor 423 are set to values such that the voltage VB increases faster than the voltage VA. More specifically, in the present embodiment, the resistor 411, the capacitor 412, the resistor 421 and the capacitor 423 are set to 1 MΩ, 1 μF, 1 kΩ and 1 μF respectively. When the voltage VB exceeds the on-voltage V1 (time t5 in
When the trigger switch 31 is opened (time t6 in
With this configuration, even if the battery pack 5 is connected to the power tool 1 in a state where the trigger switch 31 is closed, the power supply to the motor 2 is prevented. Therefore, it is prevented that the power tool 1 starts operating as soon as the battery pack 5 is connected to the power tool 1.
According to the power tool 1 and the battery pack 5 of the present embodiment, whether or not to prohibit the power supply is determined based on the voltage drop amount of each battery cell 510. Hence, an overcurrent can be prevented from flowing in the battery 51 without detecting a current, thereby suppressing a decrease in a life of the battery 51.
Further, the threshold value α is determined depending on the battery temperature T and the residual battery capacity C of the battery 51. Therefore, an overcurrent can be prevented from flowing in the battery 51 more appropriately.
Further, even if the power supply to the motor 2 is shut off by the FET 410 in a state the trigger switch 31 is closed, the prohibition of the power supply to the motor 2 can be maintained by the main current switch-off maintaining circuit 42. Therefore, permission and prohibition of the power supply can be prevented from being repeated in a short period of time.
Further, since the lithium-ion battery is used as the battery cell 510, more effective prevention of overcurrent can be realized.
Further, since the motor 2 (discharge) is stopped immediately upon detection of overcurrent, a decrease in the battery life of the secondary battery can be suppressed. Moreover, in the present embodiment, the drastic voltage drop at the time of start-up of the motor 2 (i.e., when the trigger switch 31 is closed) is not determined to be the overcurrent. Therefore, the motor 2 is prevented from stopping immediately after the power tool 1 starts operating, leading to enhancement of workability.
Next, a process to make the power supply prohibition determination according to a second embodiment of the present invention will be described with reference to
In the first embodiment, when the present battery voltage Vin(t1) is smaller than the previous battery voltage Vin−1 (S104 of
Further, in the first embodiment, when a voltage drop amount ΔV during the sampling time T2 (a potential difference between the previous battery voltage Vin−1 and the present battery voltage Vin (t2)) is greater than the threshold value α(T) (S109 of
In the first embodiment, a time different from the sampling time T1 is used as the sampling time T2 (t1>t2). However, in the second embodiment, a single sampling time T is used. More specifically, the sampling time T is set to a value such that the sampling time T elapses after the battery voltage that has decreased due to the drastic voltage drop at the time of start-up of the motor 2 (i.e., when the trigger switch 31 is closed) recovers above the threshold value α.
In the flowchart of
In S204′ the power supply prohibiting section 533 determines whether or not the present battery voltage Vin(t) is smaller than the previous battery voltage Vin−1, i.e., whether or not the present battery voltage Vin(t) has decreased from the previous battery voltage Vin−1. When the present battery voltage Vin(t) is greater than or equal to the previous battery voltage Vin−1, which means that the present battery voltage Vin(t) has not decreased from the previous battery voltage Vin−1 (S204′: NO), in S205 the power supply prohibiting section 533 resets the previous battery voltage Vin−1 to the present battery voltage Vin(t), and returns to S201. Since the previous battery voltage Vin−1 is set to 0V in S201 (at time t0 in
When executing the S204′ for the second time, the present battery voltage Vin(t2) detected at time t2 when the sampling time T has elapsed after the time t1, becomes greater than the battery voltage Vin(t1) detected at the time t1 (i.e., the previous battery voltage Vin−1), as shown in a region B in
In this way, in the second embodiment, the power supply prohibiting section 533 does not makes an YES determination in S204′ (a region B in
On the other hand, when the present battery voltage Vin(t) becomes smaller than the previous battery voltage Vin−1 (at time t3 in
However, minute noises may often cause the battery voltage to decrease. Therefore, in the second embodiment, in S204, the power supply prohibiting section 533 determines whether or not a potential difference between the previous battery voltage Vin and the present battery voltage Vin−1 is greater than a threshold value Va (an absolute value). The threshold Va is set to a value that can ignore the variation in the battery voltage due to the minor noises. Therefore, even if the battery voltage is varied due to minor noises, the power supply prohibiting section 533 does not make an YES determination in S204.
Further, the battery voltage may decrease in a slow pace in the loaded state. In such case, the potential difference between the previous battery voltage Vin−1 and the present battery voltage Vin(t) may not exceed the threshold value Va. Therefore, the steps 204 and 205 are repeated until the time tn in
On the other hand, when the potential difference between the battery voltage Vin−1 (at the time tn in
In S206 the power supply prohibiting section 533 obtains the battery temperature Tin from the thermistor 52, and in S207 obtains the threshold value α(T) corresponding to the obtained battery temperature Tin. In S208 the power supply prohibiting section 533 determines whether or not the voltage drop amount ΔV between the battery voltages Vin−1 and Vin(t) is greater than the threshold value α(T). When the voltage drop amount ΔV between the battery voltages Vin−1 and Vin(t) is greater than the threshold value α(T) (S208: YES), it is presumed that a drastic voltage drop is happening. Therefore, the power supply prohibiting section 533 determines that the overloaded (overcurrent) state has occurred, outputs a signal to close the switch 58 in S218 and terminates the discharge from the battery cells 510.
On the other hand, when the voltage drop amount ΔV between the battery voltage Vin−1 and Vin(t) is smaller than or equal to the threshold value α(T) (S208: NO), after the sampling time T has passed next (S209: YES), in S210 the power supply prohibiting section 533 obtains the latest battery voltage Vin(t) of each battery cell 510 (i.e., a battery voltage Vtn+2 at a time tn+2 in
When the voltage drop amount ΔV1 is greater than the threshold value α(T) (S211: YES) although the voltage drop amount ΔV between the battery voltage Vin-1 and the battery voltage Vin(t) did not exceed the threshold value α(T) (S208: NO), the power supply prohibiting section 533 determines that the overloaded state has occurred and outputs a signal to close the switch 58 in 5218 in order to terminate the discharge.
On the other hand, when the voltage drop amount ΔV1 is smaller than or equal to the threshold value α(T) (S211: NO), the overloaded state has not yet occurred, but there is still a possibility that the battery voltage may gradually decrease (the current may increase) to cause overcurrent. In S212′ the power supply prohibiting section 533 stores the battery voltage Vin(tn+1) (i.e., the battery voltage Vtn+2 at the time tn+2) as the battery voltage Vin(t1). Subsequently, after another sampling time T has passed (S212: YES), the power supply prohibiting section 533 obtains the latest battery voltage Vin(t) (i.e., a battery voltage Vtn+3 at a time tn+3) from the voltage detecting section 530 in 5213. In 5214 the power supply prohibiting section 533 determines whether or not the obtained battery voltage Vin(t) is smaller than the battery voltage Vin(t) detected last time (i.e., the battery voltage Vtn+2 at the time tn+2), that is, whether or not the latest battery voltage Vin(t) (the battery voltage Vtn+3) has decreased from the previous battery voltage Vin(t) (the battery voltage Vtn+2).
When the latest battery voltage Vin(t) (the battery voltage Vtn+3) is greater than or equal to the previous battery voltage Vin(t) (the battery voltage Vtn+2) (S214: NO), which means that the voltage drop is no more occurring, the power supply prohibiting section 533 updates the value of the battery voltage Vin−1 with that of the latest battery voltage Vin(t) (the battery voltage Vtn+3) in S215 and returns to S202. However, there is still a possibility that the battery voltage has stopped dropping only temporarily and may start dropping again. Therefore, as an alternative, the power supply prohibiting section 533 may, after NO determination in S204, compare the battery voltage at the next sampling with the previous battery voltage, and may continue to detect occurrence of overcurrent if there is a voltage drop.
When the battery voltage Vin(t) (the battery voltage Vtn+3) is smaller than the battery voltage Vin(t) (the battery voltage Vn+2) (S214: YES), which means that the battery voltage continues to be falling, the power supply prohibiting section 533 then determines in S216 whether or not a potential difference ΔV2 between the battery voltage Vtn at the time tn when the battery voltage starts falling (the battery voltage Vin−1 stored in S205) and the latest battery voltage Vin(t) at the time tn+3 (the battery voltage Vtn+3) is greater than the threshold value α(T).
When the potential difference ΔV2 is greater than the threshold value α(T) (S216: YES), the power supply prohibiting section 533 determines that the overloaded state is occurring, and outputs a signal to close the switch 58 in S218 in order to terminate the overdischarge. On the other hand, when the potential difference ΔV2 is equal to or smaller than the threshold value α(T) (S216: NO), in S217 the power supply prohibiting section 533 updates the value of the previous battery voltage Vin(t) with the value of the latest battery voltage Vin(t), that is, the battery voltage Vn+2 detected last time at the time tn+2 is replaced with the latest battery voltage Vtn+3 at the time tn+3, and returns to S212. As long as the battery voltage keeps falling down (as long as YES is determined in S214), the processing from S212 to S217 are repeated until a time tn+x in
A the time tn+x, the potential difference ΔV2 between the battery voltage Vtn at the time tn when the voltage drop occurred (corresponding to Vin−1) and the battery voltage Vtn+x at the time tn+x becomes greater than the threshold value α(T). The power supply prohibiting section 533 therefore determines YES in 5216 and terminates discharge.
In the second embodiment, the threshold value α(T) is set in S207 based on only the battery temperature T. However, as the first embodiment, the threshold value α(T) may be set in accordance with both of the battery temperature T and the residual battery capacity C. Further, since the battery temperature T and the residual battery capacity C change during the discharge, the threshold value α(T) may be set appropriately during the processing from S212 to S217 based on the battery temperature T and the residual battery capacity C. This configuration enables overcurrent to be detected with more accuracy, further leading to more reliable suppression of decrease in the secondary batteries.
According to the above-described configuration of the second embodiment, determination on power supply prohibition can be made regardless of the effects of small voltage drops caused by minute noises or load. Further even in case that the amount of voltage drop (current) gradually increases in accordance with gradual increase in the load, the power supply prohibition determination can be reliably made.
The power tool 1 and the battery pack 5 according to the present invention is not limited to the embodiments described above. It will be appreciated by one skilled in the art that a variety of changes and modifications may be made without departing from the scope of the invention.
For example, in the above-described embodiments, the power supply prohibiting section 533 and the switch 58 are provided in the battery pack 5, while the FET 410 is provided in the power tool 1. However, the power supply prohibiting section 533, the switch 58 and the FET 410 may be provided in any combination within the battery pack 5 and the power tool 1. Further, as long as the power supply to the motor 2 can be shut down in response to the output signals from the power supply prohibiting section 533, the switch 58 and the FET 410 may have configurations different from those in the first and second embodiments.
Further, in the foregoing embodiments, the power supply prohibition determination is made based on the voltage drop amount of each battery cell 510 without detecting current flowing through the battery cells 510 (the motor 2). However, the current may also be detected. In the latter case, whether or not to prohibit the power supply is determined based on the voltage drop amount of the battery cells 510, and whether or not overcurrent has occurred is determined based in the detected current. With this configuration, overcurrent can be prevented more reliably.
Further, in the above embodiments, overcurrent is determined to have occurred immediately when the voltage drop amount ΔV exceeds the threshold value α, and the FET 410 is shut down accordingly. However, as shown in
More specifically, with reference to
Given that the period of the initial drastic voltage drop (overcurrent) at the time of turning on the trigger switch 31 is so short (minimal), the prescribed period of time Tth may be set to be longer than the period of the initial voltage drop (for example, twice as long as the period during which the initial drastic voltage drop exceeding the threshold value α continues). In this case, assuming that the sampling time T is minimal, the power supply prohibiting section 533 may determine YES in S104 at the time when the trigger switch 31 is turned ON and also determine YES in S109. However, the drastic voltage drop that occurs upon starting up the motor 2 lasts only for a short period of time, i.e., less than the prescribed period of time Tth. Therefore, the power supply prohibiting section 533 determines NO in S112, and the discharge is never stopped at the time when the motor 2 is started. The period of time Tth may alternatively be set appropriately based on the battery temperature T and the residual battery capacity C.
Further, in the first embodiment, the sampling time T1 at the time of starting-up of the motor 2 and the sampling time T2 that is used once the motor 2 has started are set differently from each other. However, this differentiation of the sampling time may also be employed in the second embodiment. Alternatively, a constant sampling time may be employed in the first embodiment. In other words, the sampling time may be set such that the initial voltage drop can be ignored (tolerated); the FET 410 is never shut off at the time of starting the motor 2; and drops in battery voltages can be detected with certainty.
Further in the above embodiments, the residual capacity detection unit 59 detects and stores the residual battery capacity C of the battery 51 when the user presses the residual capacity confirmation button 59a. However, instead, the residual capacity detection unit 59 may detect and store the residual battery capacity C of the battery 51 when the trigger switch 31 is turned off, or when the battery pack 5 is detached from the power tool 1. Alternatively, the residual capacity detection unit 59 may detect and store the residual battery capacity C of each battery cell 510. Still alternatively, the threshold value α may be set based on the residual battery capacity C and the battery temperature T only when the residual capacity confirmation button 59a is pressed. Unless the residual capacity confirmation button 59a is pressed, the threshold value α may be set based solely on the battery temperature T, or may be set as a fixed value irrespective of the battery temperature T and the residual battery capacity C. When the battery temperature T only is used for determining the threshold value α, the threshold value α should be set so as to be greater as the battery temperature T is lower.
Further, although the power supply prohibiting section 533 obtains the threshold value α(T) in accordance with the battery temperature Tin and the residual battery capacity C in the above embodiments, either one of the battery temperature Tin and the residual battery capacity C may be considered upon obtaining the threshold value α(T).
Further, the lithium-ion battery is used for the battery cell 510 in the above embodiments, but the battery cell 510 is not limited to the lithium-ion battery.
Number | Date | Country | Kind |
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2010-012593 | Jan 2010 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2011/051682 | 1/21/2011 | WO | 00 | 5/25/2012 |