JP2007053899A - Battery pack - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery pack that makes an user recognize the end of discharge of a secondary battery, and prevents an overdischarge of a battery set to enhance a cycle life characteristics. <P>SOLUTION: A microcomputer 60 is designed to interrupt a connection between a battery set 10 and a power tool 200 when a battery voltage becomes equal to a first predetermined voltage or less, while a load current flows, so that the battery set 10 may not be discharged further; and performs a switching control of the load current flowing through the power tool 200 at a fixed frequency to perform the modulation drive of the motor 210 of the power tool 200, when the battery voltage is between the first predetermined voltage and a second predetermined voltage. Consequently, the user of the power tool 200 is able to sense that the battery set 10 is close to overdischarge, and that the battery set 10 has entered into the overdischarge from the stoppage of rotation of the motor 210. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention provides a secondary battery such as a nickel cadmium battery (hereinafter referred to as “Nicad battery”), a nickel metal hydride battery, a lithium ion battery, or the like used as a power source for a cordless power tool (hereinafter simply referred to as “power tool”). The present invention relates to a battery pack composed of batteries.

  In recent years, secondary batteries such as nickel-cadmium batteries, nickel metal hydride batteries, and lithium ion batteries have been remarkably improved in capacity and improved in charge / discharge characteristics due to large currents. For this reason, the secondary battery which performed such performance improvement came to be used as a power supply of high load equipment like an electric tool. Usually, such a secondary battery intended for use takes the form of a battery pack composed of a battery set in which unit cells are connected in series by a connection plate or the like, and the battery pack is mounted on an electric tool to drive a motor and screw. Work such as tightening.

  However, in the case of an electric tool using a battery pack as a power source, the rotation speed of the motor hardly decreases until immediately before the secondary battery is completely discharged, and the rotation of the motor suddenly stops when the secondary battery is completely discharged. The user usually keeps working until the motor stops rotating. For this reason, there existed a problem that the cycle life of a battery pack became short.

  The reason why the cycle life of the battery pack is shortened is that there is a variation in capacity between the unit cells constituting the battery set. If there is a variation in the capacity of the unit cells, the unit cell with a small capacity is likely to be overcharged and overdischarged, and the unit cell has a shorter life than other unit cells. This is a factor that shortens the cycle life.

  FIG. 3 shows the discharge characteristics of the battery set and the unit cells in the battery set. The battery assembly voltage gradually decreases as the discharge progresses, and when the battery capacity is exhausted, the voltage rapidly decreases. At this time, paying attention to the voltage characteristics of the unit cells in the battery set, as described above, the unit cell having a small capacity in the battery set causes a rapid voltage drop first. Further, when the discharge is continued, the voltage of the unit cell having a small capacity becomes 0V or less. This is called a reversal state (reverse charge state). When the inversion state is reached, hydrogen gas starts to be generated from the positive electrode side inside the unit cell and is accumulated in the unit cell. If charging / discharging is repeated, it will eventually cause electrolyte leakage from the inside of the unit cell and reduce the cycle life of the battery set.

  In particular, in applications where the motor is driven with a high load such as an electric tool and screw tightening, etc., there is no function to suppress battery overdischarge and it can be used until the motor stops. Cycle life is shortened.

  An object of the present invention is to eliminate the drawbacks of the prior art described above, to allow the user to recognize the end-of-discharge state of the secondary battery, to prevent overdischarge of the unit cell, and to improve the cycle life characteristics of the battery pack. .

  In order to achieve the above object, the invention according to claim 1 is a battery pack used as a power source of a cordless electric tool, wherein a battery set in which a plurality of unit cells are connected in series, and a battery voltage of the battery set. Battery voltage detecting means for detecting the battery, switching means for turning on and off the current path between the battery set and the cordless power tool, and control means for controlling the switching means based on the output of the battery voltage detecting means. It is characterized by that.

  A second aspect of the present invention is the battery pack according to the first aspect, further comprising current detection means for detecting a load current flowing from the battery set to the cordless power tool, wherein the control means is configured to detect the battery voltage. The switching means is controlled so that the load current changes in a decreasing direction when the output of the means becomes a predetermined voltage or less.

  In the present invention configured as above, when it is detected that the output of the battery voltage detecting means becomes equal to or lower than a predetermined voltage and the capacity of the battery set is reduced to a certain level during use of the electric power tool, the control means switches the switching means. Is controlled to change the current value of the load current flowing from the battery set to the power tool in the decreasing direction. As a result, although the current continues to flow to the electric tool, the current level is reduced or no current flows at all, and the rotation speed of the motor of the electric tool is reduced or the rotation is stopped. The user can know the discharge state of the battery set from the modulation operation of the power tool, and can prevent the battery set from reaching the overdischarge state.

  The method of reducing the load current may be a method of fixing the load current at a low level, or a method of periodically changing the load current within a range lower than the steady load current level. In the former case, the motor of the electric tool rotates at a constant speed at a low speed, and in the latter case, the motor rotates in a roaring manner in which the rotation speed varies periodically. In either case, the alarm is perceptible to the user who is working, and the user's attention can be drawn.

  The predetermined voltage detected by the battery voltage detection means serving as a reference for control may be a voltage corresponding to the voltage when the battery set is about to be overdischarged, or may be a voltage corresponding to the voltage immediately after the overdischarge state is reached. Good. When the predetermined voltage is set based on the latter reference, it is preferable to control so that no electric current flows through the electric tool when it is detected that the battery voltage is equal to or lower than the predetermined voltage.

  A third aspect of the present invention is the battery pack according to the first or second aspect, wherein the control means controls the switching means when the output of the battery voltage detection means becomes equal to or lower than a first predetermined voltage. It is characterized by turning off.

  In the present invention configured as described above, when it is detected that the output of the battery voltage detecting means is equal to or lower than the first predetermined voltage and the capacity of the battery set is reduced to a certain level during use of the electric power tool, the control means The switching means is controlled to interrupt the current flowing from the battery set to the power tool. As a result, the rotation of the motor of the electric tool is stopped, whereby the user can know the discharge state of the battery set and can prevent the battery set from reaching the overdischarge state.

  The first predetermined voltage detected by the battery voltage detecting means serving as a reference for controlling the switching means may be a voltage corresponding to a voltage when the battery set is nearly overdischarged, or a voltage immediately after the overdischarge state is reached. A voltage corresponding to may be used.

  A fourth aspect of the present invention is the battery pack according to the first or second aspect, wherein the control means controls the switching means when the output of the battery voltage detecting means becomes equal to or lower than a second predetermined voltage. It is characterized by being repeatedly turned on and off.

  In the present invention configured as above, when it is detected that the output of the battery voltage detecting means becomes equal to or lower than a predetermined voltage and the capacity of the battery set is reduced to a certain level during use of the electric power tool, the control means switches the switching means. Is controlled to reduce the current flowing from the battery set to the power tool. As a result, although the electric current continues to flow through the electric tool, the current level is reduced, and the motor rotation speed of the electric tool is reduced. The user can know the discharge state of the battery set from the modulation operation of the power tool, and can prevent the battery set from reaching the overdischarge state.

  The second predetermined voltage detected by the battery voltage detecting means serving as a reference for controlling the switching means may be a voltage corresponding to a voltage when the battery set is nearly overdischarged, or a voltage immediately after the overdischarge state is reached. A voltage corresponding to may be used.

  The invention according to claim 5 is the battery pack according to claim 1 or 2, wherein the control means turns off the switching means when the output of the battery voltage detection means becomes equal to or lower than a first predetermined voltage. The switching means is repeatedly turned on and off when the voltage becomes equal to or higher than the first predetermined voltage and equal to or lower than the second predetermined voltage.

  In the present invention configured as described above, the output of the battery voltage detecting means becomes equal to or higher than the first predetermined voltage and equal to or lower than the second predetermined voltage during use of the power tool, and the capacity of the battery set is reduced to, for example, close to overdischarge. Is detected, the control means controls the switching means to reduce the current flowing from the battery set to the power tool. As a result, current continues to flow through the power tool, but the current level decreases, and the motor speed of the power tool decreases. From the modulation operation of the electric power tool, the user can know that the battery set is close to overdischarge. In this state, the use of the electric tool is continued, and the output of the battery voltage detecting means becomes equal to or lower than the first predetermined voltage lower than the second predetermined voltage, and it is detected that the capacity of the battery set has entered, for example, an overdischarge state Then, the control means controls the switching means to cut off the current flowing from the battery set to the electric tool so that the battery set is not overdischarged.

  According to the battery pack of the present invention, when it is detected that the output of the battery voltage detecting means is equal to or lower than the predetermined voltage and the capacity of the battery set is reduced, the current value of the load current flowing from the battery set to the electric tool is Since the control is performed so as to change in the decreasing direction, the user can know the discharge state of the battery set from the accompanying modulation operation of the power tool. If the predetermined voltage is set to a voltage corresponding to the voltage when the battery set is about to be overdischarged, the user can recognize from the modulation operation of the power tool that the battery set is about to be overdischarged. Therefore, the battery pack can be prevented from being overdischarged, and the cycle life can be dramatically improved.

  In addition, when it is detected that the output of the battery voltage detecting means is equal to or lower than the first predetermined voltage and the capacity of the battery set is reduced, the current flowing from the battery set to the power tool is controlled to be cut off. If the predetermined voltage of 1 is set to a voltage corresponding to the overdischarge voltage of the battery set, the overdischarge of the battery set can be reliably prevented and the cycle life can be drastically improved.

  When the output of the battery voltage detecting means falls below the second predetermined voltage during the period when the current detecting means detects the current flowing from the battery set to the power tool, the switching means is pulse-controlled to Since the current flowing in the battery is reduced and the discharge state of the battery set is notified by the accompanying modulation operation of the electric power tool, the user is not discomforted due to a sudden stop of use.

  When the output of the battery voltage detection means falls below the first predetermined voltage during the period when the current detection means detects the current flowing from the battery set to the power tool, the switching means is turned off to switch from the battery set to the power tool. Since the current flowing from the battery set to the power tool is reduced by interrupting the flowing current and when the first predetermined voltage or more and the second predetermined voltage or less, the switching means is pulse-controlled, If the output of the battery voltage detecting means is equal to or lower than the second predetermined voltage, it can be determined that the capacity of the battery set has decreased, for example, to the point of overdischarge, and the output of the battery voltage detecting means is lower than the second predetermined voltage If it becomes below a predetermined voltage, it can be judged that the capacity | capacitance of a battery group has entered into the overdischarge state, for example.

  A battery pack according to an embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a circuit diagram in a state where the battery pack 1 is connected to the electric tool 200. The positive electrode terminal 2 and the negative electrode terminal 3 of the battery pack 1 are respectively connected to a positive electrode terminal 201 and a negative electrode terminal 202 provided in the electric power tool 200. A DC motor 210 and a switch 220 are connected in series between the positive terminal 201 and the negative terminal 202 of the electric tool 200.

  The battery pack 1 includes a battery set 10 in which the cells 11 to 18 are connected in series with connection plates. The battery set 10 is configured using unit cells having the same capacity, but actually, the capacities of the unit cells 11 to 18 vary.

  When the battery pack 1 and the power tool 200 are connected and the switch 220 of the power tool 200 is turned on, a discharge current path flows from the positive terminal of the battery set 10 to the negative terminal of the battery set 10 via the power tool 200. Are connected to a switching unit 20, a constant voltage power supply 30, a battery voltage detection unit 40, and a trigger detection unit 80, and these units are connected to a microcomputer 60 (hereinafter referred to as “microcomputer 60”) as control means. Yes. The battery pack 1 further includes a battery temperature detection unit 50 and a display unit 90, which are also connected to the microcomputer 60.

  The microcomputer 60 includes a central processing unit (CPU) 61, a ROM 62, a RAM 63, a timer 64, an A / D converter 65, an output port 66, and a reset input port 67, which are connected to each other via an internal bus.

  The switching unit 20 is connected between the negative electrode side of the battery set 10 and the negative electrode terminal 3 of the battery pack 1, and is for switching a load current flowing through the electric tool 200 under the control of the microcomputer 60. The switching unit 20 includes an FET 21, a diode 22, and resistors 23 and 24, and a control signal is applied to the gate of the FET 21 from the output port 66 of the microcomputer 60 via the resistor 24. A diode 22 is connected between the source and drain of the FET 21 to form a charging current path when the battery set 10 is charged.

  The current detection unit 70 is for determining whether charging, discharging, or any other state (battery no-load state), and the input side connects the cathode of the diode 22 and the drain of the FET 21. The output side is connected to the A / D converter 65 of the microcomputer 60.

  The current detection unit 70 is configured to include both an inverting amplifier circuit and a non-inverting amplifier circuit. Based on the ON resistance of the FET 21 and the ON voltage of the diode 22, the current detection unit 70 converts the potential generated by the direction of the flowing current to inverting amplification and non-inverting. Amplify. An output is generated in the inverting amplifier circuit or the non-inverting amplifier circuit in response to charging and discharging, and the A / D converter 65 of the microcomputer 60 performs A / D conversion based on this output. If you want to accurately detect the current value during charging and discharging, place a low-resistance current detection resistor in the loop through which the current flows, amplify the potential generated by the magnitude of the current flowing through the resistor with an operational amplifier, The output may be calculated by A / D conversion by the A / D converter 65.

Constant voltage power supply 30, three-terminal regulator (REG.) 31, smoothing capacitors 32 and 33 are composed of a reset IC 34, a constant voltage _{V CC} output from the constant-voltage power supply 30, battery temperature detection unit 50, the microcomputer 60, the current detection unit 70, and the display unit 90. The reset IC 34 is connected to a reset input port 67 of the microcomputer 60, and outputs a reset signal to the reset input port 67 in order to put the microcomputer 60 into an initial state.

  The battery voltage detection unit 40 is for detecting the battery voltage of the battery set 10 and includes resistors 41 to 43. The connection point of the resistors 41 and 42 connected in series between the positive terminal of the battery set 10 and the ground is connected to the A / D converter 65 of the microcomputer 60 via the resistor 43. A digital value corresponding to the detected battery voltage is output from the A / D converter 65, and the CPU 61 of the microcomputer 60 compares the digital value with a first predetermined voltage and a second predetermined voltage described later. The first predetermined voltage and the second predetermined voltage are stored in the ROM 62 of the microcomputer 60.

  The battery temperature detection unit 50 is disposed in the vicinity of the battery set 10 and detects the temperature of the battery set 10, and includes a thermistor 51 as a temperature sensitive element and resistors 52 to 54. The thermistor 51 is connected to the A / D converter 65 of the microcomputer 60 via the resistor 53. A digital value corresponding to the detected battery temperature is output from the A / D converter 65, and the CPU 61 of the microcomputer 60 compares the digital value with a preset predetermined value to determine whether the battery temperature is abnormally high. Make a decision.

  The trigger detection unit 80 includes resistors 81 and 82, and detects the ON operation of the switch 220 of the electric tool 200. When the switch 220 is off, the voltage of the battery set 10 is not applied to the drain of the FET 21, and the potential input to the A / D converter 65 by the resistors 81 and 82 is the GND potential. On the other hand, if the switch 220 is turned on, the DC resistance of the DC motor 210 is very small (several ohms), so that a battery voltage is applied between the drain and source of the FET 21 and this voltage is applied by the resistors 81 and 82. The voltage is divided and input to the A / D converter 65, and the ON operation of the switch 220 is detected.

  The display unit 90 includes an LED 91 and a resistor 92, and controls the lighting and blinking of the LED 91 according to the output of the output port 66 of the microcomputer 60. For example, when the battery temperature detected by the battery temperature detection unit 50 is higher than a predetermined temperature, the display unit 90 performs battery temperature abnormality display.

  Next, the operation will be described with reference to the circuit diagram of FIG. 1 and the flowchart of FIG.

  First, the microcomputer 60 initially sets the output port 66, an overdischarge flag flag indicating that the battery set 10 is overdischarged, and a pulse control start flag indicating that the battery set 10 is close to overdischarge. The battery temperature abnormality flag indicating that the battery temperature has become abnormally high is initially set to 0 (step 301).

  Next, it is determined whether or not the battery temperature abnormality Flag is 1 (step 302). As will be described later, when the battery temperature reaches, for example, 80 ° C., the battery set 10 is determined to be in an abnormally high temperature state. Since the battery set 10 generates Joule heat in proportion to the discharge time, depending on past usage conditions, the battery set 10 may already be at an abnormally high temperature when it is newly used. If the battery set 10 in an abnormally high temperature state is used, the life of the battery set 10 is reduced. In such a case, it is necessary to refrain from using the battery set 10 until the battery temperature decreases.

  Therefore, in step 302, when the battery temperature abnormality flag is 1, that is, when it is determined that the battery set 10 is abnormally high temperature, the display unit 90 displays that the battery temperature is abnormally high ( Step 303) Based on the output of the battery temperature detection unit 50, it is determined whether or not the battery set 10 has been lowered to a predetermined temperature (Step 304). When the temperature does not decrease to the predetermined temperature (step 304: NO), the process returns to step 302 and waits for the battery temperature to decrease. When the battery temperature drops to a predetermined temperature (step 304: YES), the battery temperature abnormality flag is set to 0 (step 305), the battery temperature abnormality display on the display unit 90 is turned off (step 306), and step 302 is performed. Return to.

  If the battery temperature abnormality flag is not 1 in step 302 (step 302: NO), that is, if it is determined that the temperature of the battery set 10 is not abnormally high but usable, the overdischarge flag is next 1. Whether or not (step 307). The overdischarge flag is a flag indicating whether or not the battery set 10 is in an overdischarge state. When the flag is 1, it indicates that the battery set 10 is in an overdischarge state, and when it is 0, it is not in an overdischarge state. Indicates. If it is determined that the overdischarge flag is 1 (step 307: YES), the display unit 90 displays that the battery set 10 is in an overreleased state according to the output from the output port 66 (step 308). The user is prompted to charge the battery set 10.

  Next, it is determined whether or not the battery set 10 is charged based on the output of the current detection unit 70 (step 309). Since the overdischarge flag is 1 (step 307), the battery set 10 cannot be used unless it is charged. Therefore, whether or not the battery has been charged is determined by the direction of the current flowing through the battery set 10. That is, since the charging current flows from the negative electrode side to the positive electrode side of the battery set 10 via the diode 22, it is determined whether or not charging has been performed according to the direction of the current detected by the current detection unit 70. In step 309, it is determined that charging has been performed when charging has been performed for a certain period of time, and the process proceeds to step 310. Charging is performed by removing the battery pack 1 from the electric tool 200 and connecting it to a charger (not shown).

  If it is determined in step 309 that charging has not been performed (step 309: NO), the process returns to step 302 to wait for charging. If it is determined in step 309 that charging of the battery set 10 has been completed (step 309: YES), the overdischarge flag is set to 0 (step 310), and the battery overdischarge display on the display unit 90 is turned off (step 310). 311), the process returns to step 302.

  If the overdischarge flag is not 1 in step 307 (step 307: NO), it is determined whether or not the battery temperature of the battery set 10 has reached an abnormally high temperature state based on the output of the battery temperature detection unit 50 (step 307: NO). Step 312). When the battery temperature of the battery set 10 is abnormally high, for example, exceeding 80 ° C., the battery temperature abnormality Flag is set to 1 (step 313), and the display unit 90 is connected to the battery according to the output of the output port 66. Display that the temperature is abnormally high. In this case, the FET 21 of the switching unit 20 is turned off according to the output of the output port 66 (step 327), and the process returns to step 302.

If the battery temperature of the battery 10 is determined not to be abnormal high temperature condition in the step 312 (step 312: NO), detecting the drain-source voltage _{V DS} of the FET21 of the switching unit 20 (step 315). Next, it is determined whether or not the switch 220 of the electric power tool 200 is turned on based on the output of the trigger detection unit 80 (step 316). When the switch 220 is turned on, a battery voltage is substantially applied between the drain and source of the FET 21, so that the on operation of the switch 220 can be detected based on the drain-source voltage V _DS detected in step 315.

  If the switch 220 is not turned on in step 316 (step 316: NO), the process returns to step 302. When the switch 220 is turned on (step 316: YES), the FET 21 of the switching unit 20 is turned on according to the output of the output port 66 (step 317), and the battery set 10 is being discharged based on the output of the current detection unit 70. It is determined whether or not (step 318). If not, the FET 21 of the switching unit 20 is turned off according to the output of the output port 66 (step 327), and the process returns to step 302.

  If the battery set 10 is discharging (step 318: YES), it is determined whether or not the pulse control start flag is 1 (step 319). If the pulse control start flag is 1 (step 319: YES), the process skips to step 324.

  If the pulse control start flag is not 1 in step 319 (step 319: NO), it is determined whether or not the battery voltage of the battery set 10 has reached a second predetermined value or less based on the output of the battery voltage detector 40. Perform (step 320). In the present embodiment, the determination as to whether or not the battery voltage is equal to or lower than the second predetermined value is a determination as to whether or not the battery set 10 is close to overdischarge. Whether or not it is close to overdischarge depends on the magnitude of the discharge current, etc., but in the case of a nickel-cadmium battery or nickel-metal hydride battery used for an electric tool, it is about 0.9 to 1.0 V with respect to the number of unit cells. In the case of a lithium ion battery of, for example, a 3.6V type, it can be said that the discharge is approaching if it reaches about 2.5 to 2.7V. In the present embodiment, since the number of unit cells is 10, in the case of a nickel-cadmium battery or a nickel-metal hydride battery, a value in the range of 9 to 10 V is set to the second predetermined value.

  Similarly, a first predetermined voltage in step 324, which will be described later, is a reference voltage for determining whether or not the battery set 10 is in an overdischarged state. Therefore, the first predetermined voltage is lower than the second predetermined voltage. Set. The reference voltage for determining whether or not the battery set 10 is in an overdischarged state varies depending on the magnitude of the discharge current or the like, but in the case of a nickel-cadmium battery or a nickel-metal hydride battery used for the power tool, a unit cell If the lithium-ion battery is, for example, a 3.6V battery, the voltage is about 2.3 to 2.5V, and the first predetermined value is based on these values. Should be set.

  If the battery voltage of the battery set 10 is not less than or equal to the second predetermined value (step 320: NO), the discharge may be continued, but the battery temperature rises with the discharge. Based on the output of the unit 50, it is determined whether or not the battery temperature of the battery set 10 has reached an abnormally high temperature state (step 328). This determination is performed based on the same criteria as in step 312. When the battery temperature of the battery set 10 is abnormally high (step 328: YES), the battery temperature abnormality flag is set to 1 (step 329), and the display unit 90 displays the battery temperature abnormality according to the output from the output port 66. (Step 330). Then, the FET 21 of the switching unit 20 is turned off by the output of the output port 66 (step 327), and the process returns to step 302. In step 328, when the battery temperature of the battery set 10 is not abnormally high (step 328: NO), the process returns to step 318.

  In step 320, when the battery voltage of the battery set 10 has reached the second predetermined value or less (step 320: YES), it is determined that the battery set 10 is about to be overdischarged, and the switching unit 20 is output according to the output of the output port 66. The pulse control for switching the FET 21 at a predetermined frequency is started (step 321). When the pulse control starts, the voltage applied to the DC motor 210 decreases, and the rotational speed of the DC motor 210 decreases. The user of the electric power tool 200 can know that the battery set 10 is about to be over-discharged by sensing a change in the rotational speed of the DC motor 210.

  After starting the pulse control in step 321, the pulse control start flag is set to 1 (step 322), and the display of the battery overdischarge is displayed on the display unit 90 by the output of the output port 66 (step 323). As a result, the user of the electric power tool 200 can confirm that the overdischarge is approaching. Next, based on the output of the battery voltage detector 40, it is determined whether or not the battery voltage of the battery set 10 has reached a first predetermined value or less (step 324). When the battery voltage of the battery set 10 is not less than or equal to the first predetermined value (step 324: NO), the process skips to step 328 described above.

  In step 324, when the battery voltage of the battery set 10 has reached the first predetermined value or less (step 324: YES), it is determined that the battery set 10 has entered an overdischarge state, and the battery overdischarge Flag is set to 1. (Step 325). Then, according to the output of the output port 66, the battery overdischarge display is displayed on the display unit 90 (step 326). Next, the FET 21 of the switching unit 20 is turned off according to the output of the output port 66 (step 327), and the process returns to step 302.

  The battery pack according to the present invention is not limited to the above-described embodiment, and various modifications and improvements can be made within the scope described in the claims. For example, in the above-described embodiment, when the battery voltage decreases to the second predetermined value or less during use of the electric power tool 200, the rotational speed of the motor 210 is forcibly decreased by controlling the switching unit 20 ( (First control) Further, when the battery voltage drops below the first predetermined value which is lower than the second predetermined value, the switching unit 20 is controlled to cut off the load current to the motor 210. (Second control), the first control may be omitted and only the second control may be performed. Conversely, the second control may be omitted and only the first control may be performed. Also good. In the case of the latter modification, after the battery voltage drops below the first predetermined value, the number of revolutions of the motor 210 is reduced to such an extent that the operation by the electric power tool 200 cannot be continued, and the user is charged with the battery set 10. It is necessary to prevent overdischarge of the battery caused by continuous use. In the latter modification, the first predetermined value may not be set with reference to the battery voltage at which the battery set 10 is in the overdischarge state, but may be set with reference to the battery voltage that is close to overdischarge.

  In the above embodiment, the determination of the battery voltage during discharge in step 320 and step 324 is such that a large current flows instantaneously when the DC motor is started, and as a result, the battery voltage instantaneously drops accordingly. Although the above steps are not described in the flow, time consideration is necessary.

  In the above embodiment, the battery temperature abnormality display in step 314 and step 330, the battery overdischarge near-up display in step 323, and the battery overdischarge display display method in step 326 are the lighting method of the LED 91, that is, blinking with a different cycle. The number of LEDs corresponding to each status display may be arranged, although not shown in the block circuit diagram of FIG.

  Furthermore, in the above embodiment, the switching unit 20 is connected between the negative electrode side of the battery set 10 and the negative electrode terminal 3 of the battery pack 1, but between the positive electrode side of the battery set 10 and the positive electrode terminal 2 of the battery pack 1. You may connect to.

The circuit diagram which shows the relationship between the battery pack of this invention, and an electric tool. The flowchart for operation | movement description of this invention battery pack. The graph which shows an example of the discharge characteristic of a battery group.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Battery pack 10 ... Battery group 11-18 ... Unit cell 20 ... Switching part 40 ... Battery voltage detection part 60 ... Microcomputer 70 ... Current detection part 80 ... Trigger detection part 90 ... Display part

Claims (5)

In battery packs used as power sources for cordless power tools,
A battery set formed by connecting a plurality of unit cells in series;
Battery voltage detection means for detecting the battery voltage of the battery set;
Switching means for turning on and off a current path between the battery set and the cordless power tool;
Control means for controlling the switching element based on the output of the battery voltage detection means;
A battery pack comprising: Current detection means for detecting a load current flowing from the battery set to the cordless power tool;
2. The battery pack according to claim 1, wherein the control means controls the switching means so that the load current changes in a decreasing direction when the output of the battery voltage detection means becomes a predetermined voltage or less.   3. The battery pack according to claim 1, wherein the control unit turns off the switching unit when the output of the battery voltage detection unit becomes equal to or lower than a first predetermined voltage. 4.   The battery pack according to claim 1 or 2, wherein the control means repeatedly turns on and off the switching means when the output of the battery voltage detection means becomes equal to or lower than a second predetermined voltage.   The control means turns off the switching means when the output of the battery voltage detection means falls below a first predetermined voltage, and repeatedly turns on and off the switching means when it falls above a first predetermined voltage and below a second predetermined voltage. The battery pack according to claim 1 or 2, characterized in that:

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