CN1974140B - Battery pack and cordless electric tool using said battery pack - Google Patents

Abstract

A compact battery pack having high handling capability and limiting degradation of battery cell performance. The battery pack includes: an insertion portion that is inserted into a handle portion of the cordless power tool; and an accommodating part accommodating all the battery cells therein. A protection plate having a protection circuit is installed in the insertion portion for preventing overcharge and overdischarge of the secondary battery. The switching element is connected between the battery unit and a drive motor of the electric power tool. An air passage is formed in the handle and the main housing of the cordless power tool in communication with the battery pack. The switching element is disposed at the air passage.

Description

Battery pack and cordless electric tool using said battery pack

technical field

The present invention relates to a battery pack for a cordless power tool, and more particularly to a battery pack for storing rechargeable or secondary lithium battery cells. The invention also relates to a cordless power tool having said battery pack.

In cordless electric tools such as screwdrivers and drills, and impact tools, the rotation of a motor is decelerated by a deceleration mechanism, and the decelerated rotation is transmitted to an end tool. Generally, a commercial power source (AC power source) is used as the power source of the motor. Recently, however, rechargeable alkaline storage batteries such as nickel-cadmium storage batteries and nickel-metal hydride storage batteries are used as power sources for cordless electric tools.

According to the increase in voltage required in the cordless electric tool, the number of storage battery cells accommodated in the battery pack has increased. For example, since the nominal voltage of a nickel-cadmium battery cell is 1.2V, if the desired voltage is 14.4V, 12 cells must be accommodated in the battery pack, and if the desired voltage is 24V, then 12 cells must be accommodated in the battery pack. There must be room for 20 battery cells, and the battery pack must be connected to the cordless power tool. Therefore, according to the increase in required voltage, the overall weight of the electric tool increases.

On the other hand, organic electrolyte rechargeable batteries such as lithium cells and lithium ion battery cells offer higher voltage ratings. Therefore, the number of battery cells is reduced. Therefore, a compact cordless power tool can be provided.

Here, the lithium battery cell is a general term for a vanadium-lithium secondary battery and a manganese-lithium secondary battery, and has a negative electrode made of lithium-aluminum alloy by using an organic electrolyte. In addition, the lithium ion storage battery cell has a positive electrode formed of cobaltate lithium and a negative electrode formed of graphite by using an organic electrolyte. Throughout the specification, organic electrolyte rechargeable batteries such as lithium cells and lithium ion storage cells will be simply referred to as "lithium cells".

The lithium battery cell provides a high rated voltage, such as 3.6V equivalent to a three-cell nickel-cadmium battery cell. That is, the number of storage battery cells can be reduced by using lithium battery cells. This is beneficial for increased capacity and reduced size and weight requirements. However, if overcharging and/or overdischarging is performed, or if an overcurrent flows through the lithium battery cell, the performance of the lithium battery cell decreases. As a result, the service life of the lithium battery cells will be reduced. In addition, if overcharging is performed, gas may be generated due to decomposition of the electrolyte. Furthermore, due to overdischarging, performance degradation can occur, whereby an electrical short circuit of the battery cells can occur during the subsequent charging process.

In order to avoid this problem, Japanese Patent Application Laid-Open No. 2003-164066 discloses a protection circuit and a control process for protecting a storage battery unit. The circuit includes switching elements such as field effect transistors (FETs) connected between the battery pack and the DC motor. For protection, the switching element is switched off before overdischarging. Related techniques are also described in Japanese Patent Applications Kokai Nos. H11-55866, H04-75430, 2002-223525 and 2000-12107.

Summary of the invention

However, if the FETs are placed on the current path between the battery cell group and the DC motor, new disadvantages will be found by the present invention. That is, typically, with lithium battery cells, the level of current flowing through personal computers and cellular phones is quite low. In contrast, relatively high current levels flow through cordless power tools. For example, a typical current level of 3OA flows through the DC motor of the power tool. If a switching element such as a FET is provided on this current path for avoiding excessive discharge and preventing excessive current from flowing, heat will be generated in the FET. In particular, if the end tool penetrates or penetrates into the workpiece during operation, the motor locks up so that an overload current flows through the motor. This load current is also applied to the FET so that overheating will occur in the FET.

If a fault such as an electrical short circuit between source and drain occurs in the FET due to overheating, the FET does not work anymore, which in turn causes a serious degradation in the performance of the lithium battery cell due to over-discharge or over-current flow.

It is therefore an object of the present invention to provide a cordless power tool which avoids overheating of the switching element and thus avoids performance degradation of the lithium battery cell.

Another object of the present invention is to provide a compact battery pack capable of avoiding performance degradation of lithium battery cells having a high processing capacity stored therein.

These and other objects of the present invention will be achieved by a cordless power tool including a main housing, a handle portion, a DC motor, a fan, a battery pack and a switching element. The main housing has an inner housing space. The handle portion protrudes from the main housing and has an inner handle space communicating with the housing space. The DC motor is placed in the housing space. The fan is placed in the housing space and can be driven to rotate by a DC motor. A battery pack may be mounted within the free end portion of the handle portion. At least one rechargeable battery cell may be accommodated within the battery pack. An air passage is defined from the battery pack, through the handle space to the housing space. With the fan rotating, an air flow is generated in the air channel. A switching element is connected between the at least one rechargeable battery cell and the DC motor and is positioned at the air passage.

In another aspect of the present invention, there is provided a cordless power tool including a main housing, a handle portion, a DC motor, a fan and a battery pack. The battery pack includes an accommodating portion, an insertion portion, and a switching element. The housing portion is adapted to receive at least one battery cell therein and is formed with a vent hole for fluid communication between the atmosphere and the interior space of the housing portion. The insertion portion protrudes from the receiving portion and is connectable to the free end portion of the handle portion. The insertion portion is in fluid communication with the receiving portion, and a vent hole for fluid communication between the insertion portion and the handle space is formed to define an air passage inside the battery pack. The switching element is connected between at least one rechargeable battery cell and the DC motor and is positioned at an air passage in the battery pack.

In another aspect of the present invention, there is provided a battery pack accommodating a plurality of battery cells therein and assembled in an electric power tool having a portion having an inner space, the battery pack including an insertion portion, an accommodating portion and protection board. The insertion portion is insertable into the inner space. The accommodating portion is connected to the inserting portion, and is disposed outside the power tool when the inserting portion is inserted into the inner space. All battery cells are housed in the housing portion. The protection board has a protection circuit. At least a portion of the protective plate is located within the insertion portion.

Description of drawings

In the attached picture:

FIG. 1 is a schematic partially cut-away side view of an electric power tool according to a first embodiment of the present invention;

Fig. 2 is a cross-sectional front view of a handle portion and a main body portion of the power tool according to the first embodiment;

3 is a cross-sectional view of a battery pack in the electric tool according to the first embodiment;

4 is a circuit diagram showing electrical connections between a battery pack and a motor in the electric tool according to the first embodiment;

5 is a flowchart showing a control process in the battery pack mounted in the electric tool according to the first embodiment;

FIG. 6(a) is a side view of an electric tool to which a battery pack according to a second embodiment of the present invention is assembled;

6(b) is a cross-sectional side view of a battery pack according to a second embodiment;

Fig. 6 (c) is the front view of the battery pack according to the second embodiment;

FIG. 6( d) is a plan view of a battery pack according to a second embodiment;

7 is a circuit diagram showing electrical connections in a battery pack according to a second embodiment;

Fig. 8(a) is a side view of an electric tool to which a battery pack according to the related art is assembled;

8(b) is a cross-sectional side view of a battery pack according to the related art;

FIG. 8(c) is a front view of a battery pack according to the related art;

FIG. 8( d ) is a plan view of a battery pack according to the related art;

Fig. 9(a) is a side view of an electric tool to which a battery pack according to another related art is assembled;

FIG. 9(b) is a cross-sectional side view of a battery pack according to another related art;

FIG. 9(c) is a front view of a battery pack according to another related art; and

FIG. 9(d) is a plan view of a battery pack according to another related art.

Detailed ways

A cordless electric tool having a battery pack according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 5 . Portable fastening drivers, drills, impact drills and power wrenches are examples of cordless power tools. The power tool 1 includes a main barrel portion or housing 10 and a handle portion 20 extending therefrom. The housing 10 has an inner housing space, and the handle part 20 has an inner handle space communicating with the housing space.

A battery pack 30 accommodating therein a lithium battery cell group 31 including lithium battery cells 32 to 35 is attached to the free end portion of the handle portion 20 . The casing 10 is formed to have a plurality of ventilation holes 10a on diametrically opposite sides thereof as shown in FIG. 2 .

Inside the casing 10, there is a DC motor 11 as a drive source. This DC motor 11 has a motor case 12 formed to have ventilation holes 12a on diametrically opposite sides substantially aligned with the ventilation holes 10a. A terminal bit (not shown) such as a drill bit is provided at the front end of the housing 10 . Furthermore, a reduction mechanism 13 for reducing the rotation speed of the DC motor 11 is accommodated in the housing 10 . For an impact screwdriver, an impact mechanism (not shown) including a hammer is provided between the reduction mechanism 13 and the end bit.

The fan 14 is connected to the rotating shaft of the DC motor 11 to generate a positive air flow in the casing 10 and a suction flow in the battery pack 30 and the handle portion 20 as indicated by arrows in FIG. 2 .

A switch 40 is disposed within the handle portion 20 . The switch 40 is electrically connected to the DC motor 11 . A partition plate 21 formed with a ventilation hole 21 a is located inside the handle portion 20 . The partition plate 21 divides the inner handle space into a switch accommodating space and a battery pack connection space. Lead terminals 51 extend through the separator plate 21 for electrically connecting the battery pack 30 to the switch 40 . The connection space has an engaging portion (not shown) to be engaged with the battery pack 30 . In the handle portion 20 , an air passage is defined which fluidly connects the interior of the battery pack 30 to the interior of the housing 10 .

The battery pack 30 includes: a battery cell accommodating portion 36 for accommodating the battery cell group 31 therein; and a cylindrical connection portion or insertion portion 37 inserted into the connection space of the handle portion 20 and engageable with the engagement portion. A plurality of lithium battery cells 32 - 35 each having a rated voltage of 3.6V are accommodated in the accommodation portion 36 . If the electric tool operates at a voltage of 14.4V, four battery cells are connected in series to form a battery cell group 31 .

As shown in FIG. 3 , in the battery pack 30 , the storage battery cells 32 - 35 are connected one by one by connecting members 38 , 39 . The driving voltage of the electric tool is 14.4V, so that four lithium battery cells are connected in series. As a variant, in order to increase the current capacity, two battery cell groups are connected in parallel, each group having four battery cells connected in series.

The receiving portion 36 has a front portion (the end tool of the power tool) with a working section 41 biased by a spring 42 . Use the hook 43 and the working section 41 to be set as one. When the working section 41 is pushed against the biasing force of the spring 42 , the hook 43 is engaged with an engaging portion (not shown) of the handle portion 20 . As shown in FIG. 2 , the width of the upper portion of the receiving portion 36 is greater than that of the connecting portion 37 so that the upper portion of the receiving portion 36 can be easily formed with a ventilation hole 36 a to introduce air into the receiving portion 36 .

For example, the accommodating portion 36 has a rear wall portion formed with a vent hole 36 a for fluid communication between the atmosphere and the inside of the accommodating portion 36 . In order to prevent dust and foreign objects from entering the accommodating portion 36 through the vent 36a, the vent 36a is covered with a filter (not shown).

The connecting portion 37 has an upper end portion provided with a terminal holding portion 44 whose surface is formed with a terminal 45 . DC power from lithium battery cells 32 - 35 is supplied to DC motor 11 through terminal 45 , lead terminal 51 and switch 40 .

The circuit board 52 on which the FETs 53A, 53B are mounted is placed in the connection portion 37 . In the circuit diagram shown in FIG. 4, a single FET 53 is shown as a switching element for the sake of simplicity. However, in the embodiment shown in FIG. 3, two FETs 53a, 53b are connected in parallel to increase the current capacity.

As shown in FIG. 2, a heat sink (heat sink) 54 is directly mounted on the FET53 to accelerate heat radiation from the FET53. As shown in FIG. 2, the connection portion 37 has an upper wall formed with a vent 37a. The air in the receiving portion 36 is introduced into the inside of the housing 10 through the vents 37 a and 21 a, and then through the air passage 20 a provided in the handle portion 20 . Thus, the circuit board 52 is positioned in the air flow path.

As described above, the DC voltage from the battery pack 30 is supplied to the DC motor 11 through the switching element (FET) 53 , the lead terminal 51 and the switch 40 . If the lithium battery cell voltage becomes not more than a predetermined voltage, the switching element 53 is controlled to appear OFF in order to avoid excessive discharge. Similarly, if an overcurrent flows through the DC motor 11, the switching element 53 is controlled to appear OFF. The ON/OFF control of the FET 53 according to the battery voltage can avoid excessive discharge of the battery unit group 31 . For this effect, the motor drive current must flow continuously through FET 53 during the discharge phase of battery pack 30 . Here, the current level flowing through the DC motor 11 is as large as 30A. If such a high-level current flows through the FET 53 for a long time, excessive heat will be generated in the FET 53 . Therefore, in this embodiment, the FET 53 is positioned in the air flow path.

Next, a circuit and a control process for avoiding excessive discharge of the storage battery unit group 31 will be described. This circuit is basically the same as that described in Japanese Patent Application Laid-Open No. 2003-164066.

FIG. 4 is a circuit diagram showing a battery pack 30 connected to the handle portion 20 of the electric tool 1 . The battery pack 30 has a positive terminal 60 and a negative terminal 61 . The positive terminal 60 is connected to the positive terminal 15 of the power tool 1 , and the negative terminal 61 is connected to the negative terminal 16 of the power tool 1 . The DC motor 11 and the switch 40 are connected in series between the positive terminal 15 and the negative terminal 16 of the electric tool 1 .

The battery pack 30 includes a battery cell group 31 , a switch section 65 , a constant voltage power supply 70 , a battery voltage detector 75 , a battery temperature detector 80 , a microcomputer 85 , a current detector 93 , a trigger detector 94 and a display 97 . When the switch 40 of the electric tool 1 is turned on while the battery pack 30 is connected to the electric tool 1 , discharge current flows from the positive terminal of the battery cell group 31 to the negative terminal of the battery cell group 31 through the electric tool 1 . The battery voltage detector 75 , the constant voltage power supply 70 , the trigger detector 94 and the switch section 65 are connected to the discharge path, and the microcomputer 85 is connected to these and other elements included in the battery pack 30 .

The microcomputer 85 includes a central processing unit (CPU) 86, a read-only memory (ROM) 87, a random access device (RAM) 88, a timer 89, an analog-to-digital (A/D) converter 90, an output port 91 and a reset Set the input port 92. The components of this microcomputer 85 are connected to each other by an internal bus.

The switch section 65 is connected between the negative terminal of the battery cell group 31 and the negative terminal 61 of the battery pack 30 , and includes a field effect transistor (FET) 53 , a diode 66 and resistors 67 , 68 . A control signal from the output port 91 of the microcomputer 85 is applied to the gate of the FET 53 via the resistor 68 to perform switching control of the load current flowing through the electric tool 1 . A diode 66 connected across the source and drain of the FET 53 serves as a charging current path in which the charging current flows while charging the battery cells using a battery charger (not shown) connected to the battery pack 30. Group 31 charges.

The current detector 93 is used to determine whether the battery cell group 31 is being charged, discharged or in other conditions, such as no load is placed on the battery cell group 31 . The input of current detector 93 is connected to the cathode of diode 66 and the drain of FET 53 . The output of this current detector 93 is connected to the A/D converter 90 of the microcomputer 85 .

Although not shown, the current detector 93 includes an inverting amplifier circuit and a non-inverting amplifier connected in parallel, which selectively amplifies the voltage applied to the current detector 93 . The polarity of the voltage applied to the current detector 93 is determined depending on the direction of the current, that is, whether the charging current flows into the diode 66 or the discharging current flows into the FET 53 . The voltage level applied to this current detector 93 is determined depending on the ON resistance of the FET 53 and the ON voltage of the diode 66 . As a result, an output is generated depending on whether the storage battery cell group 31 is charged or discharged by the inverting amplifier circuit or the non-inverting amplifier circuit. The output from the current detector 93 is A/D converted by the A/D converter 90 of the microcomputer 85 . If it is desired to accurately detect the current value during charging and discharging, a low resistance current sense resistor can be placed in the loop of this current. In this case, a voltage generated depending on the level of current flowing through the resistor can be amplified by an operational amplifier. The A/D converter 90 performs A/D conversion on the output from the operational amplifier, and calculates a current value based on the obtained digital output.

The constant voltage power supply 70 includes a three-terminal regulator (REG.) 71 , smoothing capacitors 72 and 73 , and a reset IC 74 . The constant voltage V _CC output from the constant voltage power supply 70 is used as a power source for the battery temperature detector 80 , the microcomputer 85 , the current detector 93 and the display 97 . Connect the reset IC 74 to the reset input port 92 of the microcomputer 85 and output a reset signal to the reset input port 92 to initialize the settings of the microcomputer 85 .

The battery voltage detector 75 is used to detect the voltage of the battery cell group 31 and includes resistors 76 to 78 . The resistors 76, 77 are connected in series between the positive terminal of the battery cell group 31 and ground. The A/D converter 90 of the microcomputer 85 is connected through the resistor 78 to the connection point connecting the resistors 76, 77 together, thereby outputting a digital value corresponding to the detected battery voltage. The CPU 86 of the microcomputer 80 compares the digital value from the A/D converter 90 with first and second predetermined voltage values described later. The first and second predetermined voltages are stored in the ROM 87 of the microcomputer 8.

A battery temperature detector 80 is positioned adjacent to the battery cell group 31 to detect the temperature of the battery cell group 31 . The temperature detected by the battery temperature detector 80 is not the temperature of the battery cell group 31 in the strict sense, but is substantially equal to the temperature of the battery cell group 31 . The battery temperature detector 80 includes a thermistor 81 and resistors 82 to 84 . This thermistor 81 is connected to an A/D converter 90 of a microcomputer 85 through a resistor 83 . Therefore, the A/D converter 90 outputs a digital value corresponding to the battery temperature detected by the battery temperature detector 80 . The CPU 86 of the microcomputer 80 compares the digital value with a predetermined value to judge whether the battery temperature is abnormally high.

The trigger detector 94 includes resistors 95, 96, and detects when the switch 40 of the electric tool 1 is turned ON. When the switch 40 is OFF, the voltage of the battery cell group 31 is not applied to the drain of the FET 53 . Therefore, the input of the A/D converter 90 connected to the trigger detector 94 is kept at ground potential. On the other hand, since the DC resistance of the DC motor 11 is very small, for example, only a few ohms, a voltage substantially identical to the battery voltage is generated between the drain and the source of the FET 53 while the switch 40 is ON. . This voltage is divided at resistors 95, 96, and the voltage developed across resistor 96 is applied to A/D converter 90 so that the ON state of switch 40 can be detected.

The display 97 includes a light emitting diode (LED) 98 and a resistor 99 . The LED 98 is controlled to emit light or to be turned OFF according to the output from the output port 91 of the microcomputer 85 . This display 97 is controlled, for example, to display a warning that the temperature of the battery unit group 31 is too high when the battery temperature detector 80 detects a battery temperature higher than a predetermined temperature.

Next, with reference to the circuit diagram of FIG. 4 and the flowchart in FIG. 5 , a control process for avoiding excessive discharge of the storage battery unit group 31 will be described. The control program is stored in the ROM 87 of the microcomputer 85 and executed by the CPU 86 .

First, in S101, the microcomputer 85 initializes the settings at its output port 91, and also initializes the overdischarge flag to zero, and then activates the pulse control flag. The overdischarge flag indicates that the storage battery unit group 31 is overdischarged. The start pulse control flag indicates that the battery cell group 31 is almost over-discharged.

In S102, the microcomputer 85 judges whether or not the overdischarge flag is set to one. The over-discharge flag indicates whether the battery cell group 31 is over-discharged, and indicates that the battery cell group 31 is over-discharged when set to one, and is not over-discharged when set to zero .

In S101, the overdischarge flag is initially set to zero. If it is judged as No in S102, that is, if the overdischarge flag is not one, the program proceeds to S103 where the voltage V _DS between the drain and source of the FET 53 of the switch section 65 is detected. Next, in S104 , it is determined based on the output from the trigger detector 94 whether the switch 40 of the electric tool 1 is ON. When switch 40 is turned ON, a voltage substantially equal to the battery voltage is developed between the drain and source of FET 53 . Therefore, whether the switch 40 is turned ON can be detected based on the voltage V _DS detected in S103 .

When the switch 40 is not turned ON (S104: NO), the procedure returns to S102. If the switch 40 is turned ON (S104: YES), then in S105, the FET53 of the switch section 65 is turned ON according to the output from the output port 91. Then, in S106, it is judged whether the start pulse control flag is set to one. If the start pulse control flag is set to one (S106: YES), the procedure jumps to step S111.

If the starting pulse control flag is not set to one (S106: NO), then in S107, based on the output from the battery voltage detector 75, it is judged whether the voltage of the battery unit group 31 has reached the second predetermined value or lower than the second predetermined value. predetermined value. In this embodiment, whether the battery voltage is at or lower than the second predetermined value is to know whether the battery unit group 31 is close to an over-discharged state. The battery voltage indicating that the battery cell group 31 is in a state close to overdischarge differs depending on the level of the discharge current. In the case of a lithium battery cell with a rated voltage of 3.6V used in an electric tool, it can be said that it is close to an overdischarged state when the voltage of the battery cell is about 2.5V to 2.7V.

The first predetermined voltage described below with respect to the process in S111 is used as a reference voltage for judging whether or not the storage battery unit group 31 has accurately reached the overdischarged state. Therefore, the first predetermined voltage is lower than the second predetermined voltage. The reference voltage for indicating that the storage battery unit group 31 has reached an over-discharged state also differs according to the level of the discharge current. In the case of a lithium battery cell having a rated voltage of 3.6V used in an electric tool, it can be said that the battery cell is in an overdischarged state when the voltage of the battery cell is about 2.3V to 2.5V. If the battery voltage exceeds the second predetermined voltage (S107: NO), discharging continues.

If it is judged that the voltage of the battery cell group 31 does not exceed the second predetermined voltage (S107: YES), it means that the battery cell group 31 is almost in an over-discharged state. Therefore, in S108, the pulse control is started in accordance with the output from the output port 91, so that the switching operation of the FET 53 of the switching portion 65 is performed at a predetermined frequency. When the control pulse is activated, the average voltage applied to the DC motor 11 drops, causing the DC motor 11 to rotate at a low speed. The operator of the electric tool 1 can sense the speed change of the DC motor 11 and understand that it indicates that the battery unit group 31 has almost reached an over-discharged state.

After the pulse control has been started in S108, the start pulse control flag is set to one in S109. Then, in S110, the display 97 is controlled through the output of the output port 91 to display that the storage battery is almost over-discharged. The operator of the electric tool 1 can look at the display 97 to confirm that the reason why the DC motor 11 is rotating more and more slowly is because the battery unit group 31 is almost exhausted. Then, at S111, it is judged based on the output from the battery voltage detector 75 whether or not the voltage across the battery unit group 31 has reached a first predetermined value or less. If the voltage across the battery cell group 31 is not at the first predetermined value or less (S111: NO), the procedure jumps to S108.

If the voltage across the battery cell group 31 is at the first predetermined voltage or less (S111: YES), it is judged that the battery cell group 31 has entered an over-discharged state. Therefore, the battery overdischarge flag is set to one in S112, and based on the output from the output port 91, the display is displayed to indicate the battery overdischarge state in S113. Therefore, the operator is aware of the need for charging. Next, in S114, the FET53 of the switch section 65 is turned OFF, and therefore, the procedure returns to S102.

On the other hand, when it is judged that the overdischarge flag is set to one (S102: YES), it is judged in S115 based on the output from the current detector 93 whether to charge the storage battery unit group 31 or not. Since the overdischarge flag is set to have a value of "one" as judged in S102, the battery cell group 31 cannot be used until the battery cell group 31 has been charged. Incidentally, charging is performed by removing the battery pack 30 from the electric power tool 1, and by connecting the battery pack 30 to a battery charger (not shown). Whether or not the battery cell group 31 is charged is determined based on the direction of current flowing through the battery cell group 31 . That is, the charging current flows from the positive terminal of the battery cell group 31 to the negative terminal through the diode 66 . Therefore, according to the direction of the current detected by the current detector 93, it is determined whether the battery unit group 31 is being charged. Once it is judged in S115 that charging has continued for a fixed period of time (S115: YES), the procedure proceeds to S116.

If it is judged that the storage battery unit group 31 has not been sufficiently charged (S115: NO), the procedure returns to S102 until the charging is completed. Once it is judged that the battery unit group 31 has been fully charged (S115: YES), the over-discharge flag is reset to zero in S116, and the display 97 is controlled to stop displaying that the battery unit group 31 is over-discharged in S117, and then The program returns to S102.

In this way, if the output of the battery voltage detector 75 becomes not greater than the first predetermined voltage so that a decrease in battery capacity is detected, the current flowing from the battery cell group 31 to the electric power tool 1 is cut off. Therefore, by setting the over-discharge voltage of the battery cell group 31 to the first predetermined voltage, overcharging of the battery cell group 31 can be prevented, thereby providing an extended cycle life of the battery cells.

According to the above-described control process, when the battery voltage is at or below the second predetermined voltage during use of the electric power tool 1, the switching portion 65 is controlled to forcibly reduce the speed of the DC motor 11 (first control) . In addition, when the battery voltage is lower than the second predetermined voltage and also equal to or lower than the first predetermined voltage, the switch portion 65 is controlled to cut off the load current supplied to the DC motor 11 (second control).

However, the embodiment described above may be modified in such a way that the first control is removed and only the second control is implemented. Alternatively, this embodiment can be modified in such a way that the second control is removed and only the first control is implemented.

Using the above-described geometric arrangement within housing 10 and handle portion 20, during rotation of DC motor 11, fan 14 is rotated so that the resulting airflow exits housing 10 through vent holes 12a and 10a. This air flow sucks the air in the air passage 20a in the handle portion 20 to generate the air flow in the handle portion 20 and the battery pack 30 as indicated by the arrows in FIG. 2 .

Since the FET53 serving as a switching element is placed in the air flow path, effective heat radiation can be performed to avoid overheating of the FET53. In addition, since the heat sink 54 is mounted on the FET 53, the heat release capability is further improved. As a result, a short circuit of the FET 53 due to overheating can be avoided, which prevents excessive discharge of the battery cell group 31 .

Furthermore, when the current detector 93 detects an overcurrent, the FET 53 is turned off. With this connection, as long as the short-circuit fault of the FET53 is eliminated, the overcurrent flowing through the battery unit group 31 due to the overheating of the FET53 can be avoided. Therefore, occurrence of overcurrent discharge in the FET 53 and overheating during overcurrent discharge can be avoided, thereby avoiding performance degradation of the lithium battery cell.

Next, a battery pack according to a second embodiment of the present invention will be described with reference to FIGS. 6( a ) to 7 .

The electric tool 101 includes a handle portion 101a and a drive mechanism mounting portion 101b in which a motor and a reduction mechanism connected to a drive shaft of the motor are accommodated. The handle portion 101 a defines an inner space in which the battery pack 110 is assembled. The interior space has a joint area (not shown).

The battery pack 110 includes an insertion portion 111 and an accommodating portion 112 integrally formed with the insertion portion 111 . The insertion part 111 is to be inserted into the inner space of the handle part 101a, and has a structure conforming to the shape of the inner space. A protection plate 114 ( FIG. 7 ) having a protection circuit 200 is accommodated in the insertion portion 111 . It is especially necessary to protect the circuit 200 for safety during charging and discharging when a lithium battery cell is used. That is, performance degradation and ignition may occur in lithium ion storage cells due to overcharge and overdischarge. To avoid this problem, protection circuit 200 is required. In the illustrated embodiment, an integral protective plate 114 is received within the insert portion 111 . Although, a part of the protective plate 114 may be accommodated in the insertion portion 111 , and the remaining portion of the protective plate 114 may be accommodated in the accommodation portion 112 .

A dedicated IC circuit can be used as the protection circuit 200 . Alternatively, overcharging or overdischarging can be monitored by a microcomputer. In any case, if the voltage level in the Li-ion battery cells falls below a predetermined lower limit or exceeds a predetermined upper limit, the charge or discharge in the battery pack 110 is cut off by a cut-off unit such as a FET 205 ( FIG. 7 ) disposed on the path. path.

As shown in FIG. 6( c ), the positive terminal 115 and the negative terminal 116 are connected on opposite walls of the insertion portion 111 . In addition, as shown in FIG. 6( d ), the battery cell information transmission terminal 117 is exposed to the air at the top surface of the insertion portion 111 . This terminal 117 is adapted to communicate the condition of the battery cell to external elements. Conditions of the battery cells include overcharge, overdischarge, overcurrent, and temperature of the battery cells.

When the insertion portion 111 is inserted into the inner space of the handle portion 101a in the direction indicated by the arrow in FIG. All lithium battery cells 113 (four battery cells in the illustrated embodiment) are accommodated in the accommodation portion 112 . All lithium battery cells 113 are connected in series with the positive poles of the leading end battery cells connected to the positive terminal 115 and the negative poles of the trailing end battery cells connected to the negative terminal 116 .

The accommodating portion 112 has an upper portion pivotably supporting a pin 118 engageable with an engaging area in the inner space when the insertion portion 111 is fully inserted into the inner space of the handle portion 101a. Therefore, the battery unit group 110 is held by the electric power tool 101 .

Since the lithium battery unit 113 is not accommodated in the insertion portion 111 , the size of the handle portion 101 a of the electric tool 101 can be freely determined regardless of the diameter of the lithium battery unit 113 . Therefore, the degree of freedom in design of the handle portion 101a is increased, and the grip performance can be mainly focused.

In addition, since all or a part of the protection plate 114 is installed in the insertion portion 111 not accommodating the battery cell, the installation space for the protection plate 114 can be reduced in the accommodation portion 112 except for the insertion portion 111 . Therefore, the overall volume of the electric tool 101 and the battery pack 110 when the latter is assembled into the electric tool 101 can be reduced. Thus, operability can be improved.

In addition, since the battery cell information transmission terminal 117 is provided at the insertion portion 111 of the battery pack 110, a plurality of terminals may be collectively arranged at a distal portion of the insertion portion.

Comparative examples are shown in Figs. 8(a) to 8(d). 8( a ) to 8( d ) show a first comparative example in which the battery pack 120 is mounted to the electric tool 101 in a sliding motion as indicated by the arrow in FIG. 8( a ).

The battery pack 120 includes a connecting portion 121 to be connected to the handle portion 101 a of the electric tool 101 , and an accommodating portion 122 integrally formed with the connecting portion 121 . The accommodation portion 122 accommodates therein a plurality of lithium battery cells 123 (four storage battery cells) and a protection plate 124 having a protection circuit. The positive end 125 , the negative end 126 and the information transmission end 127 are embedded in the connecting portion 121 , and the pin 128 protrudes from the upper portion of the connecting portion 121 to prevent the battery pack 120 from coming out of the power tool 101 .

FIGS. 9( a ) to 9 ( d ) show a second comparative example in which the battery pack 130 is attached to the electric tool 101 with an insertion motion as indicated by the arrow in FIG. 9( a ). The battery pack 130 includes an insertion portion 131 inserted into the handle portion 101a and an accommodating portion 132 integrally formed therewith. Three lithium battery cells 133a are accommodated in the accommodating portion 132 , and one lithium battery unit 133b is accommodated in the insertion portion 131 . The positive terminal 13 and the negative terminal 136 are disposed on opposite sides of the insertion portion 131 .

According to the first comparative example, only the limited mass of the battery pack 120 is disposed in the inner space of the handle portion 101a due to the sliding installation type, and thus, almost all parts of the battery pack 120 are located outside the handle portion 101a. Therefore, when the battery pack 120 is mounted to the electric tool 101 , the combined shape of the electric tool 101 and the battery pack 120 is bulky. In other words, the battery pack 120 cannot take advantage of using compact lithium battery cells.

According to the second comparative example, a greater mass of the battery pack 130 can be inserted into the handle portion 101a compared to the first comparative example. However, temperature fluctuations occur in the lithium battery cells 133a and 133b due to the separate arrangement of these battery cells. This temperature fluctuation leads to a rapid degradation of the performance of the battery cells. Performance degradation due to temperature fluctuations in battery cells is more likely to occur in lithium cells than in nickel-cadmium cells and nickel hydride cells.

On the other hand, according to the above-mentioned embodiment, the lithium battery cells are only concentrated in the containing portion 112, so that temperature fluctuation among the battery cells is not easy to occur, so as to avoid performance degradation of the battery cells. In addition, part or all of the protection plate 114 is placed inside the insertion portion 111 . Since the insertion portion 111 is not provided with the battery unit 113 but only with the protection plate 114, the degree of freedom in design of the handle portion can be improved.

Next, the circuits within the battery pack 110 will be described with reference to FIG. 7 . The circuit includes a protection board 114, four lithium battery cells 113, a positive terminal 115, a negative terminal 116, a battery cell information transmission terminal 117, a protection circuit 200 and FETs 205 as described above. Protection circuit 200 includes battery voltage detector 201, overcurrent determination unit 202 connected to positive terminal 115 and FET 205, overcharge determination unit 203 connected to battery voltage detector 201, and overcharge determination unit 203 connected to battery voltage detector 201 and FET 205. A discharge determination unit 204 . A terminal of each battery cell 113 is connected to a battery voltage detector 201 . Each voltage of each battery cell 113 is monitored at the battery voltage detector 201 .

The battery unit information transmission terminal 117 includes a battery temperature transmission terminal 117a, a battery type transmission terminal 117b, and an overcharge transmission terminal 117c. The battery temperature transmission terminal 117a is connected to the FET 205 through a temperature sensing element 208 such as a thermistor. The thermistor 208 is located near the battery unit 113 to detect the temperature of the battery unit 113 . In addition, the battery type transmission terminal 117 b is connected to the FET 205 through the resistor 206 . Furthermore, a resistor 207 is connected between the positive terminal 115 and the leading battery cell of the battery cell 113 .

When the tool 101 is used continuously, the voltage of the battery unit 113 decreases. The battery voltage detector 201 monitors each voltage level of each battery cell 113 so that the monitored signal is input to the over-discharge determination unit 204 . If the over-discharge determination unit 204 determines that the voltage of the storage battery pack 113 becomes not greater than the allowable lower limit, the determination unit 204 outputs a cutoff signal to the FET205 to turn off the FET205 to cut off the discharge current path. In the circuit diagram shown in Figure 7, two FETs are connected in parallel to suppress heat generation from the FETs. Alternatively, only a single FET may be used.

When the electric power tool 101 becomes locked, a high-level current flows through the battery unit 113 . This current is detected at the current detection resistor 207 so that the overcurrent determination unit 202 outputs an off signal to the FET 205 to turn off the FET 205 .

On the other hand, when the battery pack 110 is connected to the battery charger, the battery voltage detector 201 monitors the voltage level of each battery cell 113 . A signal indicating the temperature of the battery unit 113 is input to the battery charger through the battery temperature transmission terminal 117a.

When the voltage of the storage battery unit 113 rises due to charging, and the voltage level becomes not less than the allowable upper limit, the overcharge determination unit 203 outputs a cutoff signal to cut off the charging current path. Incidentally, in addition to providing the FET 205, a FET for charge control may also be provided. In the latter case, the FET for charge control is connected in series in the opposite direction with respect to the FET 205 .

Although the present invention has been described in detail with reference to specific embodiments thereof, it should be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. For example, the number of battery cells is not limited to four, and a required number of battery cells can be accommodated as long as the structure of the accommodation portion is changed.

In the embodiment shown in FIG. 3 , a ventilation hole 36 a is formed at the rear wall of the receiving portion 36 . However, the ventilation holes may be formed at any part of the accommodation portion 36 , such as its front wall beside the working section 41 .

In addition, in the above-described embodiments, the switching element is provided within the battery pack. However, the switching element may be provided separately from the battery pack. In the latter case, the switching element can also be arranged in the gas flow path.

Claims (15)

1. A battery pack accommodating a plurality of storage battery cells therein and installed in an electric tool to supply electric power from the battery pack to the electric tool, the electric tool being provided with a portion having an internal space, the battery pack comprising : an insertion portion capable of being inserted into the interior space; an accommodating portion connected to the insertion portion and disposed outside the electric tool when the insertion portion is inserted into the inner space, the plurality of battery cells being accommodated only in the accommodating portion such that no battery cell is accommodated in the insertion portion; as well as a circuit board having a protection circuit controlling switching elements for electrically protecting the plurality of battery cells, at least a portion of the circuit board being located within the insertion portion; Wherein, if the battery cell voltage becomes not more than a predetermined voltage, the switching element is controlled to be turned OFF. 2. The battery pack of claim 1, wherein the circuit board is entirely located within the insertion portion. 3. The battery pack according to claim 1, wherein the insertion portion has a tip portion, and the storage battery unit further includes an information transmission terminal provided at the tip portion for transmitting a condition of the storage battery unit. 4. The battery pack according to claim 1, wherein the insertion part is provided integrally with the receiving part. 5. The battery pack of claim 1, wherein the portion of the power tool is a handle portion. 6. The battery pack according to claim 1, wherein the protection circuit controls the switching element to open/close a current path connected to the electric tool. 7. The battery pack of claim 1, wherein the protection circuit controls the switching element according to a voltage condition of the battery cell. 8. The battery pack of claim 1, wherein the switching element comprises a FET. 9. The battery pack of claim 1, wherein the switching element comprises two FETs connected in parallel. 10. The battery pack according to claim 8 or 9, further comprising a heat sink that radiates heat generated by the FET. 11. A cordless power tool having a main housing, a handle portion, a DC motor, and a fan, the cordless power tool being equipped with a battery pack, the cordless power tool comprising: a power tool comprising a portion having an interior space; a battery pack accommodating a plurality of battery cells therein and mounted in the portion having an interior space so as to supply electric power from the battery pack to the motor, The battery pack includes: an insertion portion capable of being inserted into the interior space; an accommodating portion connected to the insertion portion and disposed outside the electric tool when the insertion portion is inserted into the inner space, the plurality of battery cells being accommodated only in the accommodating portion such that no battery cell is accommodated in the insertion portion; as well as a circuit board having a protection circuit controlling switching elements for electrically protecting a plurality of battery cells, at least a portion of the circuit board being located within the insert portion; Wherein, if the battery cell voltage becomes not more than a predetermined voltage, the switching element is controlled to be turned OFF. 12. The electric tool according to claim 11, wherein the protection circuit controls the switching element so as to open/close a current path connected to the motor. 13. The electric tool according to claim 11, wherein said switching element comprises a FET. 14. The electric tool according to claim 11, wherein the switching element comprises two FETs connected in parallel. 15. The electric tool according to claim 13 or 14, further comprising a heat sink that radiates heat generated by the FET.

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