U.S. patent application number 13/169453 was filed with the patent office on 2011-10-20 for battery pack and cordless power tool having the same.
Invention is credited to Takao ARADACHI, Kazuhiko FUNABASHI, Hiroyuki HANAWA, Tomomasa NISHIKAWA, Masayuki OGURA, Nobuhiro TAKANO.
Application Number | 20110253402 13/169453 |
Document ID | / |
Family ID | 37070902 |
Filed Date | 2011-10-20 |
United States Patent
Application |
20110253402 |
Kind Code |
A1 |
ARADACHI; Takao ; et
al. |
October 20, 2011 |
Battery Pack and Cordless Power Tool Having The Same
Abstract
A compact battery pack with high handling ability and
restraining degradation of battery cells. The battery pack includes
an insertion portion to be inserted into a handle portion of a
cordless power tool and an accommodation portion in which all
battery cells are accommodatable. A protection board with a
protection circuit that protects batteries against overcharge and
over-discharge is installed in the insertion portion. A switching
element is connected between the battery cells and a drive motor of
the power tool. An air passage in communication with the battery
pack is formed within the handle and a main housing of the cordless
power tool. The switching element is positioned at the air
passage.
Inventors: |
ARADACHI; Takao;
(Hitachinaka-shi, JP) ; TAKANO; Nobuhiro;
(Hitachinaka-shi, JP) ; NISHIKAWA; Tomomasa;
(Hitachinaka-shi, JP) ; HANAWA; Hiroyuki;
(Hitachinaka-shi, JP) ; OGURA; Masayuki;
(Hitachinaka-shi, JP) ; FUNABASHI; Kazuhiko;
(Hitachinaka-shi, JP) |
Family ID: |
37070902 |
Appl. No.: |
13/169453 |
Filed: |
June 27, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11396681 |
Apr 4, 2006 |
7969116 |
|
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13169453 |
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Current U.S.
Class: |
173/46 ;
429/97 |
Current CPC
Class: |
H01M 10/613 20150401;
H01M 10/623 20150401; H01M 10/6563 20150401; H02J 7/0031 20130101;
H01M 50/213 20210101; H01M 10/643 20150401; H01M 10/482 20130101;
H01M 10/052 20130101; Y02E 60/10 20130101; H01M 10/425 20130101;
B25F 5/008 20130101; H02J 7/00309 20200101 |
Class at
Publication: |
173/46 ;
429/97 |
International
Class: |
B25F 5/00 20060101
B25F005/00; H01M 2/10 20060101 H01M002/10 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 4, 2005 |
JP |
P2005-107059 |
Apr 6, 2005 |
JP |
P2005-110351 |
Claims
1. A power pack to be assembled into a power tool provided with a
portion having an internal space for receiving a part of the power
pack having a plurality of battery cells so as to supply electrical
power from the power pack to the power tool, the power pack
comprising: an insertion portion insertable into the internal space
through an open end of the portion of the power tool, the insertion
portion delimiting an elongated space extending in an elongated
direction from the open end of the portion of the power tool,
wherein the insertion portion does not accommodate a battery cell
therein; a terminal holding portion accommodated in a part of the
elongated space of the insertion portion which is at a position
away from the open end of the portion of the power tool when the
insertion portion is inserted into the internal space; an
accommodation portion having a bottom surface and side walls
connected to the insertion portion and disposed outside of the
power tool when the insertion portion is inserted into the internal
space, the accommodation portion having the plurality of battery
cells accommodated therein for supplying the electrical power to
the power tool, each of the plurality of battery cells having a
positive terminal and a negative terminal and a longitudinal axis,
wherein all of the plurality of battery cells of the power pack
only being accommodated into the accommodation portion so that none
of the plurality of battery cells of the power pack is accommodated
in the insertion portion, each of the plurality of battery cells of
the power pack having the longitudinal axis thereof oriented
substantially parallel to the bottom surface of the accommodation
portion and in a substantially perpendicular extending direction at
least with respect to the elongated extending direction of the
elongated space of the insertion portion; and an electrical circuit
board disposed in the elongated space of the insertion portion at
least at a position between the terminal holding portion and the
accommodation portion, the electrical circuit board extending in
the elongated extending direction of the elongated space, and the
electrical circuit board having a circuit which controls a
switching element for electrical protection of at least one of the
plurality of battery cells, at least a major portion of the circuit
board being located in the insertion portion.
2. The power pack as claimed in claim 1, wherein the electrical
circuit board in its entirety is located in the insertion
portion.
3. The power pack as claimed in claim 1, wherein the insertion
portion has a tip end portion, and the power pack further
comprising an information transmission terminal provided at the tip
end portion for transmitting a condition of the plurality of
battery cells.
4. The power pack as claimed in claim 1, wherein the insertion
portion is provided integrally with at least part of the
accommodation portion.
5. The power pack as claimed in claim 1, wherein the portion of the
power tool is a handle portion.
6. The power pack as claimed in claim 1, wherein the circuit
controls the switching element so as to turn ON/OFF a current path
connected to the power tool.
7. The power pack as claimed in claim 1, wherein the circuit
controls the switching element in accordance with a condition of
the plurality of battery cells.
8. The power pack as claimed in claim 1, wherein the switching
element includes at least one FET.
9. The power pack as claimed in claim 1, wherein the switching
element includes two FET connected in parallel.
10. The power pack as claimed in claim 8, further comprising a heat
sink which radiates heat generated by the at least one FET.
11. The power pack as claimed in claim 1, wherein the electrical
circuit board is disposed within the insertion portion so as to be
spaced from a housing of the insertion portion which surrounds the
electrical circuit board.
12. The power pack as claimed in claim 1, further comprising an
electrical terminal connected with the electrical circuit board and
located above the electrical circuit board between the electrical
circuit board and an upper surface of a housing of the insertion
portion.
13. The power pack as claimed in claim 1, wherein the circuit of
the circuit board which controls a switching element for electrical
protection includes two FET switches connected in parallel and
positioned at an air flow passage of at least the major portion of
the circuit board which is located in the insertion portion.
14. The power pack as claimed in claim 1, wherein the insertion
portion extends in a longitudinal direction transverse to a
direction of extension of the accommodation portion so as to be
inserted in a longitudinal extension direction of the portion of
the power tool having the internal space therein, at least the
major portion of the circuit board which is located in the
insertion portion extending in the longitudinal direction of the
insertion portion.
15. The power pack as claimed in claim 14, wherein the circuit
board is located in the insertion portion so as to be spaced from a
housing of the insertion portion to enable air flow around the
circuit board.
16. The power pack as claimed in claim 15, wherein the housing of
the insertion portion includes vent holes enabling air flow
therethrough so as to enable cooling of the circuit of the circuit
board.
17. The power pack as claimed in claim 13, wherein the elongated
extending direction of the internal space of the insertion portion
is a vertical extending direction, the part of the elongated
internal space which extends in the vertical direction at which the
terminal holding portion is accommodated is an upper part thereof,
the substantially perpendicular extending direction of each of the
plurality of battery cells of the power pack is a horizontally
extending direction, the position of the electrical circuit board
between the terminal holding portion and the accommodation portion
is a position below the terminal holding portion so that the
electrical circuit board extends in the vertical extending
direction of the internal space, and wherein the terminology of (a)
vertical, (b) upper, (c) horizontally, and (d) below are utilized
based upon an orientation of the power tool in which the power tool
is located above the power pack when the power pack is assembled
into the power tool.
18. The power pack as claimed in claim 13, wherein the terminal
holding portion is supported by the circuit board.
19. A combination of a power tool and a power pack comprising: the
power tool having a motor and a receiving portion; the power pack
having a plurality of battery cells being assembled into the
receiving portion so as to supply electric power from the power
pack to the motor; the power pack comprising: an insertion portion
insertable into the receiving portion through an open end of the
receiving portion, the insertion portion delimiting an elongated
space therein extending in an elongated direction away from the
open end of the receiving portion, wherein the insertion portion
does not accommodate a battery cell therein; a terminal holding
portion accommodated in a part of the elongated space which is at a
position away from the open end of the receiving portion when the
insertion portion is inserted into the receiving portion; an
accommodation portion having a bottom surface and side walls
connected to the insertion portion and disposed outside of the
power tool when the insertion portion is inserted into the
receiving portion; the accommodation portion having the plurality
of battery cells accommodated therein for supplying the electrical
power to the motor, each of the plurality of battery cells having a
positive terminal and a negative terminal and a longitudinal axis,
wherein all of the plurality of battery cells of the power pack
only being accommodated into the accommodation portion so that none
of the plurality of battery cells is accommodated in the insertion
portion, each of the plurality of battery cells of the power pack
having the longitudinal axis thereof oriented substantially
parallel to the bottom surface of the accommodation portion and in
a substantially perpendicular extending direction at least with
respect to the elongated extending direction of the elongated space
of the insertion portion; and an electrical circuit board disposed
in the elongated space of the insertion portion at least at a
position between the terminal holding portion and the accommodation
portion, the electrical circuit board extending in an elongated
direction of the elongated space, and the electrical circuit board
having a circuit which controls a switching element for electrical
protection of at least one of the plurality of battery cells, at
least a major portion of the circuit board being located in the
insertion portion.
20. A combination of a power tool and a power pack as claimed in
claim 19, wherein the circuit controls the switching element so as
to turn ON/OFF a current path connected to the motor in accordance
with a condition of a current for the motor.
21. A combination of a power tool and a power pack as claimed in
claim 19, wherein the switching element includes at least one
FET.
22. A combination of a power tool and a power pack as claimed in
claim 21, wherein the switching element includes two FET connected
in parallel.
23. A combination of a power tool and a power pack as claimed in
claim 21, further comprising a heat sink which radiates heat
generated by the at least one FET.
24. A combination of a power tool and a power pack as claimed in
claim 19, wherein the circuit of the circuit board which controls a
switching element for electrical protection includes two FET
switches connected in parallel and positioned at an air flow
passage of at least the major portion of the circuit board which is
located in the insertion portion.
25. A combination of a power tool and a power pack as claimed in
claim 19, wherein the insertion portion extends in a longitudinal
direction transverse to a direction of extension of the
accommodation portion so as to be received along a longitudinal
extension direction of the receiving portion of the power tool, at
least the major portion of the circuit board which is located in
the insertion portion extending in the longitudinal direction of
the insertion portion.
26. The combination of a power tool and a power pack as claimed in
claim 25, wherein the circuit board is located in the insertion
portion so as to be spaced from a housing of the insertion portion
to enable air flow around the circuit board.
27. The combination of a power tool and a power pack as claimed in
claim 26, wherein the housing of the insertion portion includes
vent holes enabling air flow therethrough so as to enable cooling
of the circuit of the circuit board.
28. The combination of a power tool and a power pack as claimed in
claim 26, wherein the elongated extending direction of the
elongated space of the insertion portion is a vertical extending
direction, the part of the elongated space which extends in the
vertical direction at which the terminal holding portion is
accommodated is an upper part thereof, the substantially
perpendicular extending direction of each of the plurality of
battery cells of the power pack is a horizontally extending
direction, the position of the electrical circuit board between the
terminal holding portion and the accommodation portion is a
position below the terminal holding portion so that the electrical
circuit board extends in the vertical extending direction of the
elongated space, and wherein the terminology of (a) vertical, (b)
upper, (C) horizontally, and (d) below are utilized based upon an
orientation of the power tool in which the power tool is located
above the power pack when the power pack is assembled into the
power tool.
29. The combination of a power tool and a power pack as claimed in
claim 26, wherein the terminal holding portion is supported by the
circuit board.
30. A power pack to be assembled into a power tool provided with a
portion having an internal space for receiving a part of the power
pack having a plurality of battery cells so as to supply electrical
power from the power pack to the power tool, the power pack
comprising: an insertion portion insertable into the internal
space, the insertion portion delimiting an elongated space
extending in an elongated direction, wherein the insertion portion
does not accommodate a battery cell therein; a terminal holding
portion accommodated in an upper portion of the insertion portion;
an accommodation portion having a bottom surface and side walls
connected to the insertion portion and disposed outside of the
power tool when the insertion portion is inserted into the internal
space, the accommodating portion having the plurality of battery
cells accommodated therein for supplying the electrical power to
the power tool, each of the plurality of battery cells having a
positive terminal and a negative terminal and a longitudinal axis,
wherein the plurality of battery cells of the power pack are
accommodated into the accommodation portion so that none of the
plurality of battery cells of the power pack is accommodated in the
insertion portion, each of the plurality of battery cells of the
power pack having the longitudinal axis thereof oriented
substantially parallel to the bottom surface of the accommodation
portion and in a substantially perpendicular extending direction at
least with respect to the elongated extending direction of the
elongated space of the insertion portion; and an electrical circuit
board disposed in the insertion portion and extending between the
plurality of battery cells and the terminal holding portion, the
electrical circuit board having a circuit which controls a
switching element for electrical protection of at least one of the
plurality of battery cells, the circuit board being located in the
insertion portion; wherein the term of upper is utilized based upon
an orientation of the power tool in which the power tool is located
above the power pack when the power pack is assembled into the
power tool.
31. A combination of a power tool and a power pack comprising: the
power tool having a motor and a receiving portion; the power pack
having a plurality of battery cells being assembled into the
receiving portion so as to supply electrical power from the power
pack to the motor; the power pack comprising: an insertion portion
insertable into the receiving portion, the insertion portion
delimiting an elongated space extending in an elongated direction,
wherein the insertion portion does not accommodate a battery cell
therein; a terminal holding portion accommodated in an upper
portion of the insertion portion; an accommodation portion having a
bottom surface and side walls connected to the insertion portion
and disposed outside of the power tool when the insertion portion
is inserted into the receiving portion; the accommodating portion
having the plurality of battery cells of the power pack
accommodated therein for supplying the electrical power to the
power tool so that none of the plurality of battery cells of the
power pack is accommodated in the insertion portion, each of the
plurality of battery cells having a positive terminal and a
negative terminal and a longitudinal axis, each of the plurality of
battery cells of the power pack having the longitudinal axis
thereof oriented substantially parallel to the bottom surface of
the accommodating portion and in a substantially perpendicular
extending direction at least with respect to the elongated
extending direction of the elongated space of the insertion
portion; and an electrical circuit board disposed in the insertion
portion and extending between the plurality of battery cells and
the terminal holding portion, the electrical circuit board having a
circuit which controls switching element for electrical protection
of at least one of the plurality of battery cells, the circuit
board being located in the insertion portion; wherein the term of
upper is utilized based upon an orientation of the power tool in
which the power tool is located above the power pack when the power
pack is assembled into the power tool.
32. A power pack comprising: a housing including an upper portion
extending in a first direction so as to delimit an elongated space
extending in an elongated direction and a lower portion, and an
accommodating portion connected to the lower portion, the
accommodating portion having a bottom surface and side walls, and
having a width extending in a second direction which is transverse
to the first direction and which is greater than a width extending
in the second direction of the upper portion, wherein the upper
portion does not accommodate a battery cell therein; a plurality of
battery cells of the power pack accommodated in the accommodating
portion of the housing; a circuit board extending in the first
direction and positioned above the plurality of battery cells of
the power pack accommodated in the accommodating portion, the
circuit board being at least partially accommodated in the upper
portion of the housing; a terminal positioned above the circuit
board in the first direction; a switching element fixed to the
circuit board; and a heat sink connected to the switching element
and extending in the first direction, at least a part of the heat
sink being accommodated in the upper portion; wherein all of the
plurality of battery cells of the power pack are accommodated in
the accommodating portion so that none of the plurality of battery
cells of the power pack is accommodated in the upper portion of the
housing, each of the plurality of battery cells having a positive
terminal and a negative terminal and a longitudinal axis; and
wherein the plurality of battery cells of the power pack include a
first battery cell having the longitudinal axis thereof extending
in the second direction substantially in parallel to the bottom
surface of the accommodating portion and substantially
perpendicularly to the extending first direction of the circuit
board, a second battery cell having the longitudinal axis thereof
extending in the second direction substantially in parallel to the
bottom surface of the accommodating portion and substantially
perpendicularly to the extending first direction of the circuit
board, and a connection piece connecting the first lithium ion
battery cell to the second lithium ion battery cell.
33. The power pack as claimed in claim 32, further comprising an
operation segment provided at the housing, the operation segment
and the circuit board having a partial overlapping relationship
with each other when viewed in the second direction.
34. The power pack as claimed in claim 33, wherein the first
battery cell and the operation segment have a partial overlapping
relationship with each other when viewed in the second
direction.
35. The power pack as claimed in claim 32, wherein the switching
element and the heat sink are in surface contact with each
other.
36. The power pack as claimed in claim 32, wherein the first
direction is a vertical direction and the second direction is a
horizontal direction.
37. A power tool comprising: the power pack as claimed in claim 32;
a motor; and a switch provided between the motor and the power
pack.
38. The power tool as claimed in claim 37, wherein the power pack
further comprises an operation segment provided at the housing, the
operation segment and the circuit board having a partial
overlapping relationship with each other when viewed in the second
direction.
39. The power tool as claimed in claim 38, wherein the first
lithium ion battery cell and the operation segment have a partial
overlapping relationship with each other when viewed in the second
direction.
40. The power tool as claimed in claim 37, wherein the switching
element and the heat sink are in surface contact with each
other.
41. The power tool as claimed in claim 37, wherein the first
direction is a vertical direction and the second direction is a
horizontal direction.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. application Ser.
No. 11/396,681, filed Apr. 4, 2006, the contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a battery pack for a
cordless power tool, and more particularly, to a battery pack that
stores rechargeable or secondary lithium battery cells. The present
invention also relates to a cordless power tool having the battery
pack.
[0003] In a cordless power tool such as a driver, a drill, and an
impact tool, rotation of a motor is decelerated by a deceleration
mechanism, and the decelerated rotation is transmitted to an end
tool. Conventionally, a commercial power source (alternating
current source) is used as a power source to the motor. However
recently, rechargeable alkaline batteries such as nickel-cadmium
battery cells and nickel hydride battery cells are used as a power
source of a cordless power tool.
[0004] In accordance with an increase in a required voltage in the
cordless power tool, the number of battery cells to be accommodated
in a battery pack is increased. For example, since a nominal
voltage of nickel-cadmium battery cell is 1.2V, 12 battery cells
must be accommodated in the battery pack if the required voltage is
14.4V, and 20 battery cells must be accommodated in the battery
pack if the required voltage is 24V, and the battery pack must be
attached to a cordless power tool. Therefore, in accordance with an
increase in required voltage, entire weight of the power tool is
increased.
[0005] On the other hand, an organic electrolyte rechargeable
battery such as a lithium battery cell and lithium ion battery cell
provides a higher nominal voltage. Therefore, the number of the
battery cells can be reduced. As a result, a compact cordless power
tool can be provided.
[0006] Here, the lithium battery cell is a generic term over a
vanadium-lithium battery and a manganese-lithium battery, and has a
negative electrode made from a lithium-aluminum alloy employing
organic electrolyte. Further, the lithium ion battery cell has a
positive electrode formed of cobaltate lithium and a negative
electrode formed of graphite employing organic electrolyte.
Throughout the specification, organic electrolyte rechargeable
battery such as the lithium battery cell and the lithium ion
battery cell will be simply referred to as "lithium battery
cell".
[0007] The lithium battery cell provides high nominal voltage, for
example, 3.6V equivalent to three nickel-cadmium battery cells.
That is, the number of battery cells can be reduced by employing
lithium battery cells. This is advantageous in terms of a demand of
an increase in capacity, and reduction in size and weight. However,
degradation of lithium battery cell occurs if excessive charging
and/or excessive discharging is performed, or if excessive electric
current flows through the lithium battery cell. As a result a
service life of the lithium battery cell will be reduced. Further,
gas may be generated due to the decomposition of the electrolyte if
excessive charging is performed. Moreover, degradation of
characteristic occurs due to excessive discharging, which in turn
causes electricalshort-circuit in the battery cell upon subsequent
charging.
[0008] To avoid this problem, Japanese Patent Application
Publication No.2003-164066 discloses a protection circuit and
control process for protecting the battery cells. The circuit
includes a switching element such as a field effect transistor
(FET) connected between the battery pack and a DC motor. For the
protection, the switching element is shut off prior to the
excessive discharging. Relevant technique is also described in
Japanese Patent Application Kokai Nos. H11-55866, H04-75430,
2002-223525, and 2000-12107.
SUMMARY OF THE INVENTION
[0009] However, a new drawback will be found by the present
inventors if FET is disposed at an electrical current path between
the battery cell group and the DC motor. That is, conventionally,
electrical current level flowing through a personal computer and a
cellular phone is quite low by the employment of the lithium
battery cell. In contrast, relatively high current level flows
through a cordless power tool. For example, a current level of 30A
ordinarily flows through the DC motor of the power tool. If the
switching element such as FET is disposed at the current path for
avoiding excessive discharging and for protection against the
excessive current flow, heat generation in FET will occur.
Particularly, if the end tool bites or digs into a workpiece during
operation, motor locking occurs so that excessive load current
flows through the motor. This load current is also applied to the
FET so that overheating in FET will occur.
[0010] If breakdown such as electrical short circuit between a
source and a drain occurs in FET due to the overheating, FET does
not work any more, and the lithium battery cell may be severely
degraded due to the excessive discharging or excessive current
flowing.
[0011] It is therefore, an object of the present invention is to
provide a cordless power tool capable of avoiding overheating to a
switching element, thereby avoiding degradation of the lithium
battery cells.
[0012] Another object of the present invention is to provide a
compact battery pack capable of avoiding degradation of the lithium
battery cells stored therein with high handling ability.
[0013] These and other objects of the present invention will be
attained 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 internal housing space. The handle
portion extends from the main housing and has an internal handle
space in communication with the housing space. The DC motor is
disposed in the housing space. The fan is disposed in the housing
space and is rotatable by the DC motor. The battery pack is
assembleable in a free end portion of the handle portion. At least
one rechargeable battery cell is accommodatable in the battery
pack. An air passage is defined from the battery pack to the
housing space through the handle space. An air flow is produced in
the air passage upon rotation of the fan. The switching element is
connected between the at least one rechargeable battery cell and
the DC motor and is positioned at the air passage.
[0014] In another aspect of the invention, there is provided a
cordless power tool including the main housing, the handle portion,
the DC motor, the fan, and a battery pack. The battery pack
includes an accommodation portion, an insertion portion, and a
switching element. The accommodation portion is adapted for
accommodating therein at least one battery cell and is formed with
a vent hole for fluid communication between an atmosphere and an
internal space of the accommodation portion. The insertion portion
extends from the accommodation portion and is attachable to a free
end portion of the handle portion. The insertion portion is in
fluid communication with the accommodation portion and is formed
with a vent hole for fluid communication between the insertion
portion and the handle space to define an air passage in an inside
of the battery pack. The switching element is connected between the
at least one rechargeable battery cell and the DC motor and is
positioned at the air passage in the battery pack.
[0015] In still another aspect of the invention, there is provided
a battery pack accommodating therein a plurality of battery cells
and to be assembled into a power tool provided with a portion
having an internal space, the battery pack including an insertion
portion, an accommodation portion, and a protection board. The
insertion portion is insertable into the internal space. The
accommodation portion is connected to the insertion portion and is
disposed outside of the power tool when the insertion portion is
inserted into the internal space. All battery cells are
accommodatable into the accommodation portion. The protection board
has a protection circuit. At least a part of the protection board
is located in the insertion portion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] In the drawings;
[0017] FIG. 1 is a schematic side view partially cut away of an
electric power tool according to a first embodiment of the present
invention;
[0018] 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;
[0019] FIG. 3 is a cross-sectional view of the battery pack in the
power tool according to first embodiment;
[0020] FIG. 4 is a circuit diagram showing an electrical connection
between the battery pack and a motor in the power tool according to
the first embodiment;
[0021] FIG. 5 is a flowchart showing a control processing in the
battery pack assembled in the power tool according to the first
embodiment;
[0022] FIG. 6(a) is a side view of a power tool to which a battery
pack according to a second embodiment of the present invention will
be assembled;
[0023] FIG. 6(b) is a cross-sectional side view of the battery pack
according to the second embodiment;
[0024] FIG. 6(c) is a front view of the battery pack according to
the second embodiment;
[0025] FIG. 6(d) is a plan view of the battery pack according to
the second embodiment;
[0026] FIG. 7 is a circuit diagram showing an electrical connection
in a battery pack according to the second embodiment;
[0027] FIG. 8(a) is a side view of a power tool to which a battery
pack according to a related art will be assembled;
[0028] FIG. 8(b) is a cross-sectional side view of the battery pack
according to the related art;
[0029] FIG. 8(c) is a front view of the battery pack according to
the related art;
[0030] FIG. 8(d) is a plan view of the battery pack according to
the related art;
[0031] FIG. 9(a) is a side view of a power tool to which a battery
pack according to another related art will be assembled;
[0032] FIG. 9(b) is a cross-sectional side view of the battery pack
according to the other related art;
[0033] FIG. 9(c) is a front view of the battery pack according to
the other related art; and
[0034] FIG. 9(d) is a plan view of the battery pack according to
the other related art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] A cordless power tool having a battery pack according to a
first embodiment of the present invention will be described with
reference to FIGS. 1 through 5. A portable fastener driver, a
drilling machine, an impact drilling machine and a power wrench are
examples of a cordless power tool. The power tool 1 includes a main
barrel portion or a housing 10 and a handle portion 20 extending
therefrom. The housing 10 has an internal housing space, and the
handle portion 20 has an internal handle space in communication
with the housing space.
[0036] A battery pack 30 accommodating therein a group 31 of
lithium battery cells including lithium battery cells 32 through 35
is attachable to a free end portion of the handle portion 20. The
housing 10 is formed with a plurality of vent holes 10a at
diametrically opposite sides thereof as shown in FIG. 2.
[0037] Within the housing 10, a DC motor 11 serving as a drive
source is provided. The DC motor 11 has a motor housing 12 formed
with vent holes 12a at diametrically opposite sides and generally
in alignment with the vent holes 10a. An end bit (not shown) such
as a drill bit is positioned at a front end of the housing 10.
Further, a deceleration mechanism 13 is housed in the housing 10
for decelerating the rotation speed of the DC motor 11. in case of
an impact driver, an impact mechanism (not shown) including a
hammer is provided between the deceleration mechanism 13 and the
end bit.
[0038] A fan 14 is connected to the rotation shaft of the DC motor
11 to cause a positive air flow within the housing 10 and a suction
flow within the battery pack 30 and the handle portion 20 as shown
by arrows in FIG. 2.
[0039] A switch 40 is disposed in the handle portion 20. The switch
40 is electrically connected to the DC motor 11. A partition plate
21 formed with a vent hole 21a is provided in the handle portion
20. The partition plate 21 partitions the interior handle space
into a switch accommodation space and a battery pack attachment
space. A lead terminal 51 extends through the partition plate 21
for electrically connecting the battery pack 30 to the switch 40.
The attachment space is provided with an engagement portion (not
shown) to be engaged with the battery pack 30. In the handle
portion 20, air passages are defined that fluidly connects an
interior of the battery pack 30 to the interior of the housing
10.
[0040] The battery pack 30 includes a battery cell accommodation
portion 36 for accommodating therein the battery cell group 31, and
a cylindrical attachment portion or insertion portion 37 to be
inserted into the attachment space of the handle portion 20 and
engageable with the engagement portion. A plurality of lithium
battery cells 32-35 each having nominal voltage of 3.6V are
accommodatable into the accommodation portion 36. If the power tool
is operated under the voltage of 14.4V, four battery cells are
connected in series as a battery cell group 31.
[0041] As shown in FIG. 3, in the battery pack 30, the battery
cells 32-35 are connected one after another by connection pieces
38, 39. Driving voltage of the power tool is 14.4V, so that four
lithium battery cells are connected in series. As a modification,
in order to increase electric current capacity, two battery cell
groups are connected in parallel, each group having four battery
cells connected in series.
[0042] The accommodation portion 36 has a front portion (end tool
side of the power tool) provided with an operation segment 41
biased by a spring 42. A hook 43 is provided integrally with the
operation segment 41. Upon pushing the operation segment 41 against
the biasing force of the spring 42, the hook 43 is engageable with
the engagement portion (not shown) of the handle portion 20. As
shown in FIG. 2, a width of an upper portion of the accommodation
portion 36 is greater than that of the attachment portion 37, so
that the upper portion of the accommodation portion 36 can be
easily formed with vent holes 36a in order to introduce air into
the accommodation portion 36.
[0043] For example, the accommodation portion 36 has a rear wall
portion formed with the vent holes 36a for fluid communication
between an atmosphere and an interior of the accommodation portion
36. In order to avoid entry of the dust and foreign objects into
the accommodation portion 36 through the vent holes 36a, the vent
holes 36a are covered with a filter (not shown).
[0044] The attachment portion 37 has an upper end portion provided
with a terminal holding portion 44 whose surface is formed with a
terminal 45. Direct current from the lithium battery cells 32-35 is
supplied to the DC motor 11 through the terminal 45, the lead
terminal 51 and the switch 40.
[0045] A circuit board 52 on which FETs 53A, 53B are mounted is
provided in the attachment portion 37. In the circuit diagram shown
in FIG. 4, a single FET 53 is shown as a switching element for
simplicity. However, in the embodiment shown in FIG. 3, two FETs
53a 53b are connected in parallel in order to increase electric
current capacity.
[0046] As shown in FIG. 2, a heat sink 54 is mounted directly onto
the FET 53 in order to accelerate heat radiation from the FET 53.
As shown in FIG. 2, the attachment portion 37 has an upper wall
formed with vent holes 37a. Air in the cell accommodation portion
36 passes through the vent holes 37a and 21a and is introduced into
the interior of the housing 10 through the air passage 20a provided
in the handle portion 20. Thus, the circuit board 52 is positioned
at the air flow passage.
[0047] As described above, DC voltage from the battery pack 30 is
supplied to the DC motor 11 through the switching element (FET) 53,
lead terminal 51, and switch 40. If the lithium battery cell
voltage becomes not more than a predetermined voltage, the
switching element 53 is controlled to be rendered OFF in order to
avoid excessive discharging. Similarly, if excessive current flows
through the DC motor 11, the switching element 53 is controlled to
be rendered OFF. Excessive discharging of the battery cell group 31
is avoidable by ON/OFF control to the FET 53 in accordance with a
battery voltage. To this effect, motor driving current must be
continuously flowed through the FET 53 during discharging phase of
the battery pack 30. Here, the current level flowing through the DC
motor 11 is as large as 30A. If such high level current is flowed
through the FET 53 for a long period of time, excessive heat
generation occurs in the FET 53. Thus, in the present embodiment,
the FET 53 is positioned at the air flow passage.
[0048] Next, an electrical circuit and control process for avoiding
over-discharge of the battery cell group 31 will be described. The
circuit is basically the same as that described in Japanese Patent
Application Publication No.2003-164066.
[0049] FIG. 4 is a circuit diagram showing the battery pack 30
connected to the handle portion 20 of the power tool 1. The battery
pack 30 has a positive terminal 60 and a negative terminal 61. The
positive terminal 60 is connected to a positive terminal 15 of the
power tool 1 and the negative terminal 61 is connected to a
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 power tool 1.
[0050] The battery pack 30 includes the battery cell group 31, a
switching portion 65, a constant voltage power source 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 power tool 1 is turned on
while the battery pack 30 is connected to the power tool 1, a
discharge current flows from the positive terminal of the battery
cell group 31 through the power tool 1 to the negative terminal of
the battery cell group 31. The battery voltage detector 75, the
constant voltage power source 70, the trigger detector 94, and the
switching portion 65 are connected to the discharge current path,
and the microcomputer 85 is connected to these and other components
contained in the battery pack 30.
[0051] The microcomputer 85 includes a central processing unit
(CPU) 86, a read-only memory (ROM) 87, a random access memory (RAM)
88, a timer 89, an analog-to-digital (A/D) converter 90, an output
port 91, and a reset input port 92. The components of the
microcomputer 85 are connected to each other through an internal
bus.
[0052] The switching portion 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 the 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 for
the load current flowing through the power tool 1. The diode 66
connected across the source and drain of the FET 53 serves as a
charge current path in which a charge current flows while the
battery cell group 31 is being charged with a battery charger (not
shown) connected to the battery pack 30.
[0053] The current detector 93 serves to judge whether the battery
cell group 31 is being charged, discharging, or in other
conditions, such as when no load is being placed on the battery
cell group 31. The input of the current detector 93 is connected to
the cathode of the diode 66 and to the drain of the FET 53. The
output of the current detector 93 is connected to the A/D converter
90 of the microcomputer 85.
[0054] Although not shown, the current detector 93 includes an
inverting amplifier circuit and a non-inverting amplifier connected
in parallel which selectively amplify 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
current, that is, whether a charge current flowing in the diode 66
or a discharge current flowing in the FET 53. The level of the
voltage applied to the current detector 93 is determined depending
on an ON resistance of the FET 53 and an ON voltage of the diode
66. As a result, an output is generated by either the inverting
amplifier circuit or the non-inverting amplifier circuit depending
on whether the battery cell group 31 is being charged or
discharged. The output from the current detector 93 is subject to
A/D conversion by the A/D converter 90 of the microcomputer 85. If
it is desired to accurately detect the current value during charge
and discharge, then a low-resistance current detecting resistor can
be disposed in the loop followed by the current. In this case, the
voltage developed according to the level of the current flowing
through the resistor can be amplified by an operational amplifier.
The A/D converter 90 performs an A/D conversion on the output from
the operation amplifier and the current value is calculated based
on the resultant digital output.
[0055] The constant voltage power source 70 includes a
three-terminal regulator (REG.) 71, smoothing capacitors 72, 73,
and a reset IC 74. The constant voltage V.sub.cc output from the
constant voltage power source 70 serves as the power source for the
battery temperature detector 80, the microcomputer 85, the current
detector 93, and the display 97. The reset IC 74 is connected to
the reset input port 92 of the microcomputer 85 and outputs a reset
signal to the reset input port 92 in order to initialize settings
in the microcomputer 85.
[0056] The battery voltage detector 75 is provided for detecting a
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 where the resistors 76, 77 are
connected together, and outputs a digital value that corresponds to
the detected battery voltage. The CPU 86 of the microcomputer 85
compares the digital value from the A/D converter 90 with first and
second predetermined voltages to be described later. The first and
second predetermined voltages are stored in the ROM 87 of the
microcomputer 85.
[0057] The battery temperature detector 80 is located adjacent to
the battery cell group 31 to detect 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
a 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. The thermistor 81 is
connected to the A/D converter 90 of the microcomputer 85 through
the resistor 83. Accordingly, the A/D converter 90 outputs a
digital value that corresponds to the battery temperature detected
by the battery temperature detector 80. The CPU 86 of the
microcomputer 85 compares the digital value with a predetermined
value to judge whether the battery temperature is abnormally
high.
[0058] The trigger detector 94 includes resistors 95, 96 and
detects when the switch 40 of the power tool 1 is turned ON. While
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 held at
ground potential. On the other hand, because the DC resistance of
the DC motor 11 is extremely small, for example, only a few ohms, a
voltage substantially the same as the battery voltage is developed
between the drain and the source of the FET 53 while the switch 40
is ON. This voltage is divided at the resistors 95, 96 and the
voltage developed across the resistor 96 is applied to the A/D
converter 90 so that the ON condition of the switch 40 can be
detected.
[0059] The display 97 includes a light emitting diode (LED) 98 and
a resistor 99. The LED 98 is controlled to illuminate or turn OFF
in accordance with output from the output port 91 of the
microcomputer 85. The display 97 is controlled to display, for
example, a warning that the temperature of the battery cell group
31 is too high when the battery temperature detector 80 detects a
battery temperature that is higher than the predetermined
temperature.
[0060] Next, control process for avoiding excessive discharge of
the battery cell group 31 will be described with reference to the
circuit diagram of FIG. 4 and the flowchart of FIG. 5. A control
program is stored in the ROM 87 of the microcomputer 85 and is
executed by the CPU 86.
[0061] First, in S101 the microcomputer 85 initializes settings at
its output port 91 and also initializes to zero its over-discharge
flag, and start pulse control flag. The over-discharge flag
indicates that the battery cell group 31 is over-discharged. The
start pulse control flag indicates that the battery cell group 31
is nearly over-discharged.
[0062] In S102, the microcomputer 85 judges whether or not the
over-discharge flag is set to one. The over-discharge flag
indicates whether or not the battery cell group 31 is
over-discharged, and indicates the battery cell group 31 is
over-discharged when set to one and not over-discharged when set to
zero.
[0063] In S101, the over-discharge flag is initially set to zero.
If the judgment in S102 falls No, that is, if the over-discharge
flag is not one, the routine goes into S103 where the voltage
V.sub.DS between the drain and source of the FET 53 of the
switching portion 65 is detected. Next, in S104 it is judged
whether or not the switch 40 of the power tool 1 is ON based on the
output from the trigger detector 94. A voltage substantially equal
to the battery voltage is developed between the drain and the
source of the FET 53 when the switch 40 is turned ON. Therefore,
whether or not the switch 40 is turned ON can be detected based on
the voltage V.sub.DS detected in S103.
[0064] When the switch 40 is not turned ON (S104:NO), then the
program returns to S102. If the switch 40 is turned ON (S104:YES),
then in S105 the FET 53 of the switching portion 65 is turned ON in
accordance with output from the output port 91. Then, in S106 it is
judged whether or not the start pulse control flag is set to one.
If the start pulse control flag is set to one (S106:YES), then the
program jumps to the step of S111.
[0065] If the start pulse control flag is not set to one (S106:NO),
then in S107 it is judged, based on output from the battery voltage
detector 75, whether or not the voltage of the battery cell group
31 has reached the second predetermined value or lower. In the
present embodiment, whether or not battery voltage is at or lower
than the second predetermined value is to know whether or not the
battery cell group 31 is near an over-discharged condition. The
battery voltage that indicates that the battery cell group 31 is
near an over-discharged condition differs depending on the level of
the discharge current. In the case of a lithium battery cell having
a nominal voltage of 3.6V used in a power tool, a near
over-discharged condition can be said when the voltage of a battery
cell falls to about 2.5V to 2.7V.
[0066] A first predetermined voltage to be described later with
respect to process in S111 serves as a reference voltage for
judging whether or not the battery cell group 31 has actually
reached an over-discharged condition. Accordingly, the first
predetermined voltage is lower than the second predetermined
voltage. The reference for indicating that the battery cell group
31 has reached an over-discharged condition also differs depending
on the level of the discharge current. In the case of the lithium
battery cell having nominal voltage of 3.6V used in a power tool,
an over-discharged condition can be said when the voltage of the
battery cell is about 2.3V to 2.5V. If the battery voltage is more
than the second predetermined voltage (S107:NO), discharge is
continued.
[0067] If it is judged that the voltage of the battery cell group
31 is not more than the second predetermined voltage (S107:YES),
then this means that the battery cell group 31 is nearly in an
over-discharged condition. Therefore, in S108 a pulse control is
started, in accordance with output from the output port 91, to
perform switching action of the FET 53 of the switching portion 65
at a predetermined frequency. When the pulse control is started, an
average voltage applied to the DC motor 11 drops so that the DC
motor 11 rotates at a slower speed. The operator of the power tool
1 can perceive the change in speed of the DC motor 11 and
understands that it means that the battery cell group 31 has nearly
reached an over-discharged condition.
[0068] After the pulse control has started in S108, the start pulse
control flag is set to one in S109. Then, in S110 the display 97 is
controlled by the output of the output port 91 to display that the
battery is nearly over-discharged. The operator of the power tool 1
can view the display 97 to confirm that the reason the DC motor 11
is rotating more slowly is because the battery cell group 31 is
nearly used up. Then, in S111, it is judged, based on the output
from the battery voltage detector 75, whether or not the voltage
across the battery cell group 31 has reached the first
predetermined voltage or less. If the voltage across the battery
cell group 31 is not at the first predetermined voltage or less
(S111:NO), then the program jumps to S108.
[0069] If the voltage across the battery cell group 31 is at the
first predetermined voltage or less (S111:YES), then it is judged
that the battery cell group 31 has entered an over-discharged
condition. Therefore, the battery over-discharge flag is set to one
in S112 and, in accordance with output from the output port 91, the
display 97 is displayed to indicate a battery over-discharge
condition in S113. Therefore, the operator recognizes the necessity
of charging. Next, the FET 53 of the switching portion 65 is turned
OFF in S114, whereupon the program returns to S102.
[0070] On the other hand, when it is judged that the over-discharge
flag is set to one (S102:YES), then in S115 it is judged whether or
not the battery cell group 31 is charged based on the output from
the current detector 93. Because the over-discharge flag is set
with 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 power tool 1, and by connecting the battery pack 30 to a
battery charger (not shown). The judgment of whether or not the
battery cell group 31 is charged is made based on the direction of
current flowing through the battery cell group 31. That is, charge
current flows from the positive terminal to the negative terminal
of the battery cell group 31 through the diode 66. Therefore,
whether or not the battery cell group 31 is being charged is judged
according to the direction of the current detected by the current
detector 93. The program proceeds to S116 once it is judged in S115
that charging has continued for a fixed period of time
(S115:YES).
[0071] If it is judged that the battery cell group 31 has not yet
been fully charged (S115:NO), then the program returns to S102
until charging is completed. Once it is judged that the battery
cell group 31 has been completely charged (S115:YES), then in S116
the over-discharge flag is reset to zero and in S117 the display 97
is controlled to stop displaying that the battery cell group 31 is
over-discharged, whereupon the program returns to S102.
[0072] In this way, if the output from the battery voltage detector
75 becomes not more than the first predetermined voltage so that
the decrease in battery capacity is detected, electrical current
flowing from the battery cell group 31 to the power tool 1 is shut
off. Therefore, by setting the over-discharge voltage of the
battery cell group 31 as the first predetermined voltage,
over-discharge of the battery cell group 31 can be prevented to
provide a prolonged cyclic life of the battery cells.
[0073] According to the above-described control process, when the
battery voltage is at the second predetermined voltage or less
during use of the power tool 1, the switching portion 65 is
controlled to compulsorily lower the speed of the DC motor 11
(first control). Further, when the battery voltage is lower than
the second predetermined voltage and also equal to or lower than
the first predetermined voltage, then the switching portion 65 is
controlled to cut off load current supplied to the DC motor 11
(second control).
[0074] However, the above-described embodiment may be modified in
such a manner that the first control is dispensed with and only the
second control is performed. The embodiment may alternatively be
modified in such a manner that the second control is dispensed with
and only the first control performed.
[0075] With the above-described geometrical arrangement within the
housing 10 and handle portion 20, upon rotation of the DC motor 11,
the fan 14 is rotated so that air flow is generated flowing out of
the housing 10 through the vent holes 12a and 10a. The air flow
sucks air in the air passage 20a in the handle portion 20 to
generate air flow in the handle portion 20 and in the battery pack
30 as shown by arrows in FIG. 2.
[0076] Since the FET 53 serving as the switching element is
disposed at the air flow passage, effective heat radiation is
performed to avoid overheating to the FET 53. Further, since the
heat sink 54 is mounted on the FET 53, heat releasing function is
further promoted. As a result, short circuit of FET 53 due to
overheating can be avoided, so that excessive discharge of the
battery cell group 31 can be prevented.
[0077] Further, the FET 53 is rendered OFF when excessive current
is detected by the current detector 93. In this connection
excessive current flowing through the battery cell group 31 due to
damage to the FET 53 by overheating can be obviated as long as the
trouble of short circuit of FET 53 is eliminated. Thus, excessive
current discharge and overheating at the time of excessive current
discharge can be avoided in FET 53, thereby avoiding degradation of
lithium battery cells.
[0078] Next, a battery pack according to a second embodiment of the
present invention will be described with reference to FIGS. 6(a)
through 7.
[0079] A power tool 101 includes a handle portion 101a and a drive
mechanism installing portion 101b in which a motor and a
deceleration mechanism connected to a drive shaft of the motor are
accommodated. The handle portion 101a defines an internal space in
which a battery pack 110 is assembled. The internal space has an
engagement region (not shown).
[0080] The battery pack 110 includes an insertion portion 111 and
an accommodation portion 112 provided integrally with the insertion
portion 111. The insertion portion 111 is to be inserted into the
internal space of the handle portion 101a and has a configuration
in conformance with the shape of the internal space. A protection
board 114 having a protection circuit 200 (FIG. 7) is accommodated
in the insertion portion 111. The protection circuit 200 is
particularly required in case of the employment of lithium battery
cell in terms of safety at a time of charging and discharging. That
is, degradation and ignition may occur in the lithium ion battery
cell as a result of excessive charging and excessive discharging.
The protection circuit 200 is required to avoid this problem. An
entire protection board 114 is accommodated in the insertion
portion 111 in the depicted embodiment. However, a part of the
protection board 114 can be accommodated in the insertion portion
111 and a remaining part of the protection board 114 can be
accommodated in the accommodation portion 112.
[0081] An exclusive IC circuit is available as the protection
circuit 200. Alternatively, overcharge or over-discharge can be
monitored by a microcomputer. In any event, charging or discharging
path in the battery pack 110 is shut off by a shut off unit such as
a FET 205(FIG. 7) provided at the path if a voltage level in
lithium ion battery cell is reduced below a predetermined lower
limit or exceeds a predetermined upper limit.
[0082] As shown in FIG. 6(c), a positive terminal 115 and a
negative terminal 116 are attached at opposing walls of the
insertion portion 111. Further, as shown in FIG. 6(d), a battery
cell information transmission terminals 117 are exposed to an
atmosphere at a top face of the insertion portion 111. The
terminals 117 are adapted for transmitting a condition of the
battery cell to an external component. The condition of the battery
cell includes overcharge, over-discharge, over-current, and
temperature of the battery cell.
[0083] The accommodation portion 112 protrudes out of the power
tool 101 when the insertion portion 111 is inserted into the
internal space of the handle portion 101a in a direction indicated
by an arrow in FIG. 6(a). All lithium battery cells 113 (four
battery cells in the depicted embodiment) are accommodated into the
accommodation portion 112. All lithium battery cells 113 are
connected in series, and a positive electrode of a leading end
battery cell is connected to the positive terminal 115, and a
negative electrode of a trailing end battery cell is connected to
the negative terminal 116.
[0084] The accommodation portion 112 has an upper portion pivotally
movably supporting a latch 118 engageable with the engagement
region in the internal space of the handle portion 101a when the
insertion portion 111 is fully inserted into the internal space.
Thus, the battery pack 110 is held by the power tool 101.
[0085] Since the lithium battery cells 113 are not accommodated in
the insertion portion 111, size of the handle portion 101a of the
power tool 101 can be freely determined regardless of a diameter of
the lithium battery cell 113. Thus, degree of freedom in a design
of the handle portion 101a can be enhanced, and a gripping
performance can be a primary attention.
[0086] Further, since entire or a part of the protection board 114
is installed in the insertion portion 111 where no battery cell is
accommodated, a layout space for the protection board 114 can be
reduced in the accommodation portion 112, which is other than the
insertion portion 111. As a result, an entire volume of the power
tool 101 and the battery pack 110 when the latter is assembled into
the power tool 101 can be reduced. Consequently, improved handling
ability can result.
[0087] Furthermore, since the battery cell information transmission
terminals 117 are provided at the insertion portion 111 of the
battery pack 110, a plurality of terminals can be aggregatedly
disposed at the distal end portion of the insertion portion.
[0088] Comparative examples are shown in FIGS. 8(a) through 8(d).
FIGS. 8(a) through 8(d) show a first comparative example in which a
battery pack 120 is assembled to the power tool 101 with a sliding
motion as indicated by an arrow in FIG. 8(a).
[0089] The battery pack 120 includes an attachment portion 121 to
be attached to a handle portion 101a of the power tool 101, and an
accommodation portion 122 integral with the attachment portion 121.
The accommodation portion 122 accommodates therein a plurality of
lithium battery cells 123 (four battery cells) and a protection
board 124 having a protection circuit. A positive terminal 125, a
negative terminal 126 and an information transmission terminal 127
are embedded in the attachment portion 121, and a latch 128
protrudes from the upper portion of the attachment portion 121 for
preventing the battery pack 120 from being released from the power
tool 101.
[0090] FIGS. 9(a) through 9(d) show a second comparative example in
which a battery pack 130 is assembled to the power tool 101 with
inserting motion as indicated by an arrow in FIG. 9(a). The battery
pack 130 includes an insertion portion 131 to be inserted into the
handle portion 101a and an accommodation portion 132 integral
therewith. A three lithium battery cells 133a are accommodated in
the accommodation portion 132 whereas one lithium battery cell 133b
is accommodated in the insertion portion 131. A positive terminal
135 and a negative terminal 136 are provided at opposite sides of
the insertion portion 131.
[0091] According to the first comparative example, due to
slide-assembly type, only a limited mass of the battery pack 120 is
disposed within an internal space of the handle portion 101a, and
as a result, almost all portion of the battery pack 120 is
positioned outside of the handle portion 101a. Thus, a bulky
combined shape of the power tool 101 and the battery pack 120
results when the battery pack 120 is assembled to the power tool
101. In other words, the battery pack 120 cannot utilize the
advantage of using compact lithium battery cells.
[0092] According to the second comparative example, a greater mass
of the battery pack 130 can be inserted into the handle portion
101a in comparison with the first comparative example. However,
temperature fluctuation occurs among lithium battery cells 133a and
133b due to separate layout of these battery cells. This
temperature fluctuation causes rapid degradation of the battery
cells. The degradation due to the temperature variation among
battery cells occurs particularly in lithium battery cells rather
than in nickel-cadmium battery cells and nickel hydride battery
cells.
[0093] On the other hand, according to the above described
embodiments, lithium battery cells are aggregated only in the
accommodation portion 112, temperature fluctuation among battery
cells does not easily occur, to avoid degradation of the battery
cells. Further, a part of or the entire protection board 114 is
disposed in the insertion portion 111. Since the insertion portion
111 does not dispose the battery cells 113 but disposes only the
protection board 114, a degree of design freedom on the handle
portion can be improved.
[0094] Next, electrical circuit in the battery pack 110 will be
described with reference to FIG. 7. The circuit includes the
protection board 114, the four lithium battery cells 113, the
positive terminal 115, the negative terminal 116, the battery cell
information transmission terminal 117, the protection circuit 200
and the FET 205 those described above. The protection circuit 200
includes a battery voltage detector 201, an excessive current
determining unit 202 connected to the positive terminal 115 and to
the FET 205, an over-charge determining unit 203 connected to the
battery voltage detector 201, and an over-discharge determining
unit 204 connected to the battery voltage detector 201 and to the
FET 205. Terminals of each battery cell 113 are connected to the
battery voltage detector 201. Each voltage of each battery cell 113
is monitored at the battery voltage detector 201.
[0095] The battery cell information transmission terminal 117
includes a battery temperature transmission terminal 117a, a
battery kind transmission terminal 117b, and an over-charge
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
positioned in the vicinity of the battery cells 113 for detecting
temperature of the battery cells 113. Further, the battery kind
transmission terminal 117b is connected to the FET 205 through a
resistor 206. Further, a resistor 207 is connected between the
positive terminal 115 and a leading end battery cell of the battery
cells 113.
[0096] When the tool 101 is continuously operated, voltage of the
battery cells 113 is decreased. 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 determining unit
204. If the over-discharge determining unit 204 determines that the
voltage of the battery cell 113 becomes not more than an allowable
lower limit, the determining unit 204 outputs a shut off signal to
the FET 205 to turn off the FET 205 in order to shut off a
discharge current path. In the circuit diagram shown in FIG. 7, two
FETs are connected in parallel in order to restrain heat generation
of the FET. Only a single FET can be used instead.
[0097] If the power tool 101 becomes a locking state, high level
current flows through the battery cells 113. This current is
detected at the current detection resistor 207, so that the
excessive current determination unit 202 outputs a shut off signal
to the FET 205 to turn off the FET 205.
[0098] 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 indicative of
temperature of the battery cells 113 is input to the battery
charger through the battery temperature transmission terminal
117a.
[0099] When the voltage of the battery cells 113 is elevated by
charging and the voltage level becomes not less than an allowable
upper limit, the over-charge determining unit 203 outputs a shut
off signal for shutting off the charge current path. Incidentally,
an FET for charging control can be provided instead of the FET 205.
In the latter case, the FET for the charging control is connected
in series in a reverse direction with respect to the FET 205.
[0100] While the invention has been described in detail and with
reference to specific embodiments thereof, it would be apparent to
those skilled in the art that various changes and modifications may
be made therein without departing from the spirit and scope of the
invention. For example, the number of battery cells is not limited
to four, but a desired number of battery cells can be accommodated
as long as a configuration of the accommodation portion is
modified.
[0101] In the embodiment shown in FIG. 3, the vent holes 36a are
formed at the rear wall of the accommodation portion 36. However,
vent holes can be formed at any portion of the accommodation
portion 36 such as a front wall thereof beside the operation
segment 41.
[0102] Further, in the above described embodiment, the switching
element is disposed within the battery pack. However, the switching
element can be disposed separately from the battery pack. In the
latter case, also, the switching element is positioned at the air
flow passage.
* * * * *