U.S. patent application number 10/954222 was filed with the patent office on 2005-04-07 for methods of discharge control for a battery pack of a cordless power tool system, a cordless power tool system and battery pack adapted to provide over-discharge protection and discharge control.
Invention is credited to Bailey, R. Roby, Brotto, Daniele C., Carrier, David A., Gorti, Bhanuprasad V., Seman, Andrew E. JR., Trinh, Danh Thanh, Watts, Fred S..
Application Number | 20050073282 10/954222 |
Document ID | / |
Family ID | 34437663 |
Filed Date | 2005-04-07 |
United States Patent
Application |
20050073282 |
Kind Code |
A1 |
Carrier, David A. ; et
al. |
April 7, 2005 |
Methods of discharge control for a battery pack of a cordless power
tool system, a cordless power tool system and battery pack adapted
to provide over-discharge protection and discharge control
Abstract
In a cordless power tool system, a battery pack which may
removably attachable to a cordless power tool and to a charger may
include at least one battery cell and a power limiting device. The
power limiting device may be arranged in series with the at least
one battery cell for limiting power output of the battery pack
based on the component that is connected to the pack. Current and
hence power out of the battery pack may be controlled as a function
of total internal impedance in the battery pack, which may be
adjusted depending on the component that is connected to the
pack.
Inventors: |
Carrier, David A.;
(Aberdeen, MD) ; Gorti, Bhanuprasad V.; (Abingdon,
MD) ; Trinh, Danh Thanh; (Parkville, MD) ;
Bailey, R. Roby; (New Park, PA) ; Seman, Andrew E.
JR.; (White Marsh, MD) ; Brotto, Daniele C.;
(Baltimore, MD) ; Watts, Fred S.; (New Freedom,
PA) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 8910
RESTON
VA
20195
US
|
Family ID: |
34437663 |
Appl. No.: |
10/954222 |
Filed: |
October 1, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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60507955 |
Oct 3, 2003 |
|
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60510125 |
Oct 14, 2003 |
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60540323 |
Feb 2, 2004 |
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Current U.S.
Class: |
320/106 |
Current CPC
Class: |
B25F 5/00 20130101; H01M
10/4257 20130101; H02J 2207/20 20200101; Y02E 60/10 20130101; H01M
10/0525 20130101; H01M 10/425 20130101; H01M 10/46 20130101; H02J
7/00304 20200101; H01M 50/20 20210101; H01M 10/482 20130101; H02J
2007/0067 20130101 |
Class at
Publication: |
320/106 |
International
Class: |
H02J 007/00 |
Claims
What is claimed is:
1. A battery pack removably attachable to a cordless power tool and
to a charger, comprising: at least one battery cell; and at least
one power limiting device arranged in series with the at least one
battery cell for limiting at least one of power and current output
of the battery pack based on the component that is connected to the
pack.
2. The battery pack of claim 1, wherein the component is a cordless
power tool, and the battery pack is adapted to provide a one of a
first current and power to drive a first power tool that is
designed to operate with the battery pack and for driving a second
power tool configured to `operate at one of a second current and
power lower than the first current or power, the second power tool
designed for operation with a second battery pack.
3. The battery pack of claim 2, wherein the power limiting device
is adapted to raise internal impedance of the battery pack to match
an internal impedance of the second battery pack, when operatively
connected and providing power to the second power tool, thereby
limiting one of a maximum current within the battery pack and a
maximum power that can be output by the battery pack to the second
power tool.
4. The battery pack of claim 1, wherein the component is a
charger.
5. The battery pack of claim 1, further comprising: an
identification device for identifying the battery pack upon
connection to an external component.
6. The battery pack of claim 1, further comprising: a discharge
control circuit for restricting at least one of a maximum power and
a maximum current that can be output from the battery pack.
7. The battery pack of claim 6, wherein the discharge control
circuit is configured to monitor battery voltage, battery current
and battery temperature.
8. The battery pack of claim 6, further comprising: a temperature
sensor for sensing cell temperature to output a sensed signal to
the discharge control circuit; and a current sensor for sensing
battery current to output a sensed signal to the discharge control
circuit. a voltage monitor circuit for sensing one of individual
cell voltage and total pack voltage of the pack to output a sensed
signal to the discharge control circuit.
9. The battery pack of claim 6, further comprising: at least one
communication terminal for communicating information to, and
sensing information from, an attached external component.
10. The battery pack of claim 1, wherein at least one cell has a
lithium-ion cell chemistry.
11. A cordless power tool system, comprising: a power tool; and a
battery pack removably attachable to the power tool, the pack
including at least one battery cell and at least one power limiting
device arranged in series with the at least one battery cell for
limiting one of power output and current output from the battery
pack.
12. In a cordless power tool system including a battery pack that
is removably attachable to a power tool and to a charger, a method
of limiting one of power and current out of a battery pack,
comprising: limiting one of power and current output of the battery
pack as a function of the component that is connected to the
pack.
13. The method of claim 12, wherein the component is embodied a
power tool, and the battery pack is adapted to provide one of a
first current and first power to drive a first power tool that is
designed to operate with the battery pack and for driving a second
power tool configured to operate at one of a second current and
second power lower than the first current or power, the second
power tool designed for operation with a second battery pack.
14. The method of claim 13, wherein limiting one of power and
current output of the battery pack further comprises: raising
internal impedance of the battery pack to match an internal
impedance of the second battery pack, when operatively connected
and providing power to the second power tool, thereby limiting one
of a maximum current within the battery pack and a maximum power
that can be output by the battery pack to the second power
tool.
15. The method of claim 13, wherein limiting one of power and
current output of the battery pack further comprises: maintaining
internal impedance of the battery pack when operatively connected
and providing power to the first power tool.
16. In a cordless power tool system having a power tool and a
battery pack removably attachable to the power tool, a method of
controlling discharge rate of a plurality of serially connected
cells in the battery pack, comprising: raising total internal pack
impedance of a first battery pack to match an internal impedance of
a second battery pack designed for a given power tool so as to
control discharge rate of the serially-connected cells in the first
battery pack to prevent one or more cells in the first battery pack
from reaching one of an over-discharge state and an over-current
condition, when the first battery pack is operatively connected and
providing power to the given power tool.
17. The method of claim 16, wherein raising total internal pack
impedance includes adding a series resistance between a series
connection of the cells in the first battery back and a terminal
connection point of the first battery pack to increase total
internal impedance of the first battery pack.
18. The method of claim 16, wherein raising total internal pack
impedance includes lengthening connecting wires extending between
each cell and a terminal connection point to increase total
internal impedance of the first battery pack.
19. The method of claim 16, wherein raising total internal pack
impedance includes modifying a cross-sectional area of battery
straps that connect the cells so as to increase total impedance of
the first battery pack.
20. The method of claim 16, wherein raising total internal pack
impedance includes dynamically adding, as a function of power tool
load on the first battery pack, a series resistance between a
series connection of the cells and a terminal connection point of
the first battery pack, so as to increase total internal impedance
of the first battery pack.
21. The method of claim 20, wherein the dynamically adding of
resistance is implemented by at least one semiconductor device of
the first battery pack performing a current limiting function.
22. The method of claim 20, wherein the dynamically adding of
resistance is implemented by a positive temperature coefficient
(PCT) element of the first battery pack.
23. A cordless power tool system, comprising: a power tool; and a
battery pack removably attachable to the power tool, the battery
pack including one or more serially-connected cells therein and at
least one power limiting device in series with at least one of the
serially-connected cells, the at least one power limiting device
adapted to raise total internal pack impedance of the battery pack
to match an internal impedance of a second battery pack that is
designed for operation with the power tool, so as to control
discharge rate of the serially-connected cells and prevent one or
more cells from reaching one of an over-discharge state and an
over-current state, when the battery pack is operatively connected
and providing power to the power tool.
24. The system of claim 23, wherein the power tool encompasses a
first power tool designed for operation with the first battery pack
and a second power tool designed for operation with the second
battery pack, and first battery pack is characterized as providing
a higher current and a higher power at a lower total internal pack
impedance than the second battery pack.
25. A battery pack operatively attachable to differently-rated
cordless power tools, the battery pack adapted for controlling
discharge rate therein, comprising: at least one or more
serially-connected battery cells for providing one of a first
current and first power to drive a first power tool that is
designed to operate with the battery pack and for driving a second
power tool configured to operate at one of a second current and
second power lower than the first current or power; and at least
one power limiting device for raising internal impedance of the
battery pack to match an internal impedance of another, second
battery pack that is designed to operate with the second power tool
to control discharge rate of cells in the battery pack, so as to
prevent one or more cells from reaching one of an over-discharge
state and an over-current state during operation with the second
power tool.
26. The battery pack of claim 25, wherein the at least one power
limiting device includes a passive resistance device to raise total
internal impedance of the battery pack.
27. The battery pack of claim 26, wherein the passive resistance
device is a resistor placed in series with the battery cells
between one of the battery cells and a terminal of the battery
pack.
28. The battery pack of claim 26, wherein the passive resistance
device is embodied by connecting wires extending between each cell
and a terminal, the connecting wires being lengthened to increase
total internal impedance of the battery pack.
29. The battery pack of claim 26, wherein the passive resistance
device is embodied by modifying battery straps connecting the cells
to increase total internal impedance of the battery pack.
30. The battery pack of claim 25, wherein the at least one power
limiting device includes an active resistance device to increase
total internal impedance of the battery pack.
31. The battery pack of claim 30, wherein the active resistance
device dynamically adds a series resistance as a function of tool
load between a series connection of the cells and a terminal
connection point of the battery to increase total internal
impedance of the battery pack.
32. The battery pack of claim 30, wherein the active resistance
device is at least one semiconductor device with current limiting
function in series with at least one of the one or more
serially-connected cells.
33. The battery pack of claim 30, wherein the active resistance
device is at least two semiconductor devices with current limiting
function operating in parallel to form a parallel combination in
series with at least one of the one or more serially-connected
cells.
34. The battery pack of claim 30, wherein the active resistance
device is a positive temperature coefficient (PCT) element.
35. The battery pack of claim 25, wherein the battery pack is a
lithium-ion battery pack, and the second battery pack having an
internal impedance to be matched is a nickel cadmium or nickel
metal hydride battery pack.
36. A battery pack adapted to power one of a first power tool and a
second power tool, the first power tool configured to operate at a
higher current or power than the second power tool, the battery
pack characterized as providing a higher current and a higher power
at a lower internal impedance than that of a second battery pack
designed for operation with the second power tool, the battery pack
comprising: a sensor adapted to selectively add internal impedance
in the battery pack based on a indicator signal indicating that the
battery pack is connected to one of the first or second power
tools, and an active resistance device for dynamically adding a
series resistance to increase total internal impedance of the
battery pack, depending on the indicator signal.
37. The battery pack of claim 36, wherein the active resistance
device is bypassed when the indicator signal indicates that the
first power tool is connected to the battery pack.
38. The battery pack of claim 36, wherein the active resistance
device is activated to add internal impedance in the battery pack
the indicator signal indicates that the second power tool is
connected to the battery pack, facilitating raising of the internal
impedance in the battery pack to match an internal impedance of the
second battery pack that is designed to operate with the second
power tool.
39. The battery pack of claim 36, wherein the sensor is embodied as
one of an inductive pick-up sensor, magnetic sensor, radio
frequency sensor and optical sensor for sensing a corresponding
induction signal, magnetic signal, RF signal or optical signal that
is generated based on engagement of one of the first and second
power tools with the battery pack.
40. A battery pack adapted to power a first power tool configured
to operate at one of a higher current and power than a second power
tool, comprising: a positive terminal; a negative terminal; a third
terminal for sensing power operation of the first or second power
tool to provide a sensed signal, when the pack is attached thereto;
and a control circuit for determining a desired internal impedance
mode for the battery pack based on the sensed signal received from
an attached one of the first and second power tools via the third
terminal.
41. The battery pack of claim 40, wherein the battery pack is
adapted to a higher current and a higher power at a lower total
internal pack impedance than a second battery pack that is designed
to operate with the second power tool.
42. The battery pack of claim 41, wherein the third terminal is a
thermistor contact terminal that is open when the pack is connected
to the second power tool, and the control circuit sets a high
impedance mode based on lack of receipt of the sensed signal,
adding resistance to raise the internal impedance of the pack to
match an internal impedance of the second battery pack that is
designed to operate with the second power tool.
43. The battery pack of claim 42, wherein the thermistor contact
terminal senses a signal from the first power tool when the pack is
connected to the first power tool, and the control circuit sets a
low impedance mode based on the received sensed signal.
44. The battery pack of claim 41, wherein the third terminal is an
additional power contact terminal, and the control circuit is a
current limiting device configured to selectively add resistance to
raise total internal pack impedance based on connective engagement
of the additional power contact terminal with a corresponding power
contact terminal on one of the first and second power tools.
45. The battery pack of claim 44, wherein only the first power tool
has a corresponding power contact terminal, and the current
limiting device maintains a low impedance mode based on a signal
received via the corresponding power contact terminal of the first
power tool.
46. The battery pack of claim 44, wherein the current limiting
circuit selects a high impedance mode for adding resistance to
raise the internal impedance of the pack to match an internal
impedance of the second battery pack designed to operate with the
second power tool, only when the battery pack is connected to the
second power tool.
47. A battery pack adapted to power a first power tool configured
to operate at one of a higher current and power than a second power
tool, the first and second power tools including a motor,
semiconductor device and control circuit, the semiconductor device
and control circuit adapted for providing variable speed control in
the motor of the first or second power tool, the battery pack
comprising: a positive terminal; a negative terminal; a third
terminal for receiving an indicator from the semiconductor device
of one of the first and second power tools; and a current limiting
device connected to the third terminal and configured to select a
desired impedance mode to selectively add resistance to raise
internal impedance of the battery pack, based on the received
indicator.
48. The battery pack of claim 47, wherein the battery pack is
configured to provide a higher current and a higher power at a
lower internal impedance than a second battery pack that is
designed to operate with the second power tool.
49. The battery pack of claim 48, wherein lack of receipt of the
indicator signal when the second power tool is attached causes the
current limiting device to select a high impedance mode for adding
resistance, raising the internal impedance of the pack to match an
internal impedance of the second battery pack.
50. The battery pack of claim 47, wherein receipt of the indicator
signal causes the current limiting device to select a low impedance
mode for the pack, maintaining internal impedance of the pack.
51. The battery pack of claim 50, wherein the indicator generated
by the semiconductor device of the first power tool is embodied as
one of a given resistance value, polarity setting, torque value,
speed, temperature and motor field strength value of the first
power tool.
52. A cordless power tool having a positive terminal, negative
terminal, motor, semiconductor device and control circuit, the
cordless power tool designed to operate with a battery pack having
a positive terminal, negative terminal and a third terminal, the
cordless power tool comprising: a third terminal sending an
indicator generated by the semiconductor device to the
corresponding third terminal of the battery pack indicating an
impedance mode to be selected for the cordless power tool.
53. The cordless power tool of claim 52, wherein the indicator is
embodied as one of a given resistance value, polarity setting,
torque value, speed, temperature and motor field strength value of
the cordless power tool.
54. In a cordless power tool system having a power tool and a
battery pack removably attachable to the power tool, a method of
controlling discharge rate of one or more serially-connected cells
in the battery pack to protect the cells from an over-current
condition, comprising: controlling at least one semiconductor
device in the pack in series with at least one of the one or more
serially-connected cells so as to selectively control total
internal battery pack impedance.
55. The method of claim 54, wherein controlling further includes
controlling at least two semiconductor devices operating in
parallel to form a parallel combination that is in series with at
least one of the one or more serially-connected cells.
56. The method of claim 55, further comprising: sensing current in
the pack during power tool operations, wherein controlling further
includes maintaining the at least one semiconductor device
energized until sensed current meets or exceeds a given maximum
current threshold, pulse width modulating the at least one
semiconductor device to raise an effective internal pack impedance,
as seen by the power tool, until the sensed current has dropped
below the given threshold.
57. A cordless power tool system, comprising: a power tool, and a
battery pack having a plurality of serially-connected cells and
removably attached to the power tool, the pack including a
discharge control circuit controlling at least one semiconductor
device so as to selectively control the average voltage applied to
the tool motor so as to control at least one of power and current
output from the battery pack.
58. The system of claim 57, wherein the at least one semiconductor
device is a field effect transistor in series with at least one of
the plurality of serially-connected cells.
59. The system of claim 57, wherein the battery pack includes at
least at least two field-effect transistors operating in parallel
to form a parallel combination that is in series with at least one
of the serially-connected cells.
60. The system of claim 57, wherein the battery pack includes a
current sensor between a terminal of the pack and at least one of
the cells for sensing battery current and for outputting a sensed
signal to the discharge control circuit, and as the pack is
providing power to a tool motor of the power tool, the discharge
control circuit controls the duty cycle of the at least one
semiconductor device to selectively control the average voltage
applied to the tool motor so as to control at least one of power
and current output from the battery pack.
61. The system of claim 60, wherein the at least one semiconductor
device is a pulse width modulated field-effect transistor (FET),
and as sensed current approaches a maximum current threshold during
pack-tool operations, the discharge control circuit pulse width
modulates the FET to selectively reduce the voltage applied to the
tool motor so as to cause a gradual drop in voltage and current
out-of the pack.
62. The system of claim 61, wherein the gradual reduction in output
voltage causes a drop in motor RPM which changes motor noise,
informing a user of the tool that the tool is approaching one of a
stall and overload condition.
63. The system of claim 60, wherein the discharge control circuit
controls the duty cycle of the at least one FET so that the FET
remains energized until pack current reaches a maximum current
threshold, whereupon the FET is de-energized and current flow,
forced by an inductive nature of the tool motor, is returned back
to the motor by a recirculation path in one of the battery pack and
the power tool.
64. The system of claim 63, wherein the recirculation path is in
the battery pack and includes a diode blocking current when the at
least one FET is energized but allowing current to pass from a
negative terminal of the battery pack to a positive terminal of the
pack.
65. The system of claim 63, wherein the recirculation path is in
the power tool and includes a diode blocking current when the at
least one FET is energized but allowing current to pass from a
negative terminal of the power tool to a positive terminal of the
power tool.
66. The system of claim 60, wherein the at least one semiconductor
device includes first and second pulse width modulated field-effect
transistors (FETs), the second FET operating synchronously with the
first FET, and as sensed current approaches a maximum current
threshold during pack-tool operations, the discharge control
circuit pulse width modulates the first and second FETs to
selectively reduce the voltage applied to the tool motor so as to
cause a gradual drop in voltage and current out of the pack.
67. The system of claim 66, wherein the discharge control circuit
controls the duty cycle of the first and second FETs so that the
first FET remains energized and the second FET de-energized until
pack current reaches a maximum current threshold, whereupon the
first FET is de-energized and the second FET is energized so that
current flow, forced by an inductive nature of the tool motor, is
returned back to the motor by a recirculation path in the battery
pack, the recirculation path including the second FET.
68. The system of claim 67, wherein the first FET reverts to an
energized state and the second FET is de-energized once sensed
current in the pack drops below the current threshold.
69. In a cordless power tool system having a power tool and a
battery pack removably attachable to the power tool, the battery
pack including one or more serially-connected cells, a discharge
control circuit, comprising: a current controlled relay arranged in
a current path of the pack to provide a current limiting function
with hysteresis that limits current out of the pack to a motor of
the tool.
70. The system of claim 69, wherein the current controlled relay
further comprises: a primary coil having N turns, a switch, the
switch and primary coil in series between a negative terminal of
the pack and at least one cell of the pack, a secondary coil having
first and second ends, at least N+1 turns, the first end of the
secondary coil magnetically connected to the switch, and a diode
connected between a positive terminal of the pack and the second
end of the secondary coil, wherein the switch has a first state
which connects the battery pack to a motor of the tool and a second
state which interrupts current to the tool.
71. The system of claim 70, wherein current flow through the pack
during power operations with the tool creates a magnetic field
between the primary and secondary coils, and as current increases
in the pack to a given maximum current threshold for power tool
operations, the magnetic field generated activates the switch to
the second state, interrupting current to the tool.
72. The system of claim 70, wherein the additional turns of the
secondary coil enable the secondary coil to hold the switch in the
second state to enable current within the pack to decay through the
secondary coil and diode, until the current drops to a second
threshold at which the magnetic field is unable to hold the switch
in its second state, the switch returning to the first state to
connect the pack to the tool.
73. A cordless power tool system, comprising: a power tool
including a tool motor, and a battery pack having a plurality of
cells and removably attached to the power tool for providing power
to the motor, wherein a control signal related to speed control
information for the motor of the tool is an input for controlling
the current output from the cells for powering the tool.
74. The system of claim 73, wherein discharge control for current
out of the pack and speed control for controlling speed of the tool
resides in the battery pack.
75. The system of claim 73, wherein the battery pack further
includes: a positive terminal, a negative terminal, a control
terminal, at least one semiconductor device between the negative
terminal and at least one cell for providing variable speed control
for the tool motor, a discharge control circuit operatively
connected to the positive terminal and control terminal, and
operatively connected to the semiconductor device for controlling
the semiconductor device, wherein the power tool further includes:
a pair of power terminals, one power terminal connected to the
positive terminal and the other to the negative terminals of the
pack, a voltage sense device between the power terminals for
sensing a voltage value corresponding to a given tool motor speed
to generate the control signal, and a third terminal connecting the
voltage sense device to the control terminal of the pack, and as
the voltage sense device sends the control signal via the third
terminal and control terminal to the discharge control device, the
discharge control device controls the semiconductor device based on
the control signal to control current out of the pack and speed of
the tool motor.
76. A cordless power tool system, comprising: a power tool having a
tool motor and means for variable speed control of the tool motor,
and a battery pack having a plurality of cells and removably
attached to the power tool, the pack including a discharge control
device controlling a semiconductor device so as to selectively
raise internal battery pack impedance for limiting current out of
the cells of the pack.
77. A cordless power tool system, comprising: a power tool
including a tool motor, and a battery pack having a plurality of
cells and removably attached to the power tool for providing power
to the motor, wherein discharge control for controlling current out
of the pack and speed control for controlling speed of the tool
resides in the power tool.
78. The system of claim 77, wherein the tool includes a
microprocessor for controlling discharge rate of the cells in the
battery pack and for controlling speed of the tool motor.
79. The system of claim 78, wherein the battery pack includes: a
current sensor for communicating a signal representing sensed
current in the pack to the microprocessor, and a semiconductor
device in operative communication with the microprocessor in the
power tool and operable to interrupt current in the battery pack,
and wherein the microprocessor is operable to send a control signal
to de-energize the semiconductor device in the battery pack to
interrupt current, based on the sensed current signal received from
the current sensor in the battery pack.
80. The system of claim 79, wherein the semiconductor device in the
battery pack is further controllable by the microprocessor in the
power tool to provide variable speed control for the tool
motor.
81. In a cordless power tool system including a battery pack that
is removably attachable to a power tool and to a charger, a method
of communicating a fault in the battery pack to the charger,
comprising: detecting a fault in the battery pack, and
communicating the fault to the charger upon pack engagement with
the charger.
82. A cordless power tool system, comprising: a charger; and a
battery pack removably attachable to the charger for receiving a
charge current and to a power tool of the system for powering the
tool, the battery pack including a fault detection device detecting
a fault in the battery pack and communicating the fault to the
charger upon pack engagement with the charger.
83. The system of claim 82, the battery pack further including: a
positive terminal, a negative terminal, an active resistance
circuit for limiting charge current in the battery pack, the fault
detection circuit configured to monitor the active resistance
circuit for a fault therein, and a third terminal operatively
attached to the fault detection circuit, wherein the fault
detection circuit drives the third terminal to a high or low
electrical state if it detects a fault in the active resistance
circuit.
84. The system of claim 83, the charger further including a
microcontroller in operative communication with the third terminal
upon pack to charge engagement to sense the electrical state
indicating the fault, so as to prevent the battery pack from being
charged.
85. The system of claim 83, wherein the third terminal is a
thermistor terminal or a pack identification terminal.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims domestic priority under 35 U.S.C.
.sctn.120 to the following related U.S. Provisional patent
applications filed in the United States Patent & Trademark
Office: U.S. Provisional Application Ser. No. 60/507,955, filed
Oct. 3, 2003, U.S. Provisional Application Ser. No. 60/510,125,
filed Oct. 14, 2003, and U.S. Provisional Application Ser. No.
60/540,323, filed Feb. 2, 2004. The entire contents of the
disclosures for each of these provisional applications are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to methods of discharge
control for rechargeable batteries, to a cordless power tool system
adapted to provide over-discharge protection and discharge control
for an attached battery pack, and to a battery pack including
discharge control and over-discharge protection circuits and
components.
[0004] 2. Description of Related Art
[0005] Over the past few years, lithium-ion (Li-ion) batteries have
begun replacing nickel-cadmium (NiCd), nickel-metal-hydride (NiMH),
and lead-acid batteries in low-voltage, portable electronic devices
such as notebook-type personal computers. As compared to NiCd and
NiMH batteries, Li-ion batteries are lighter but have a larger
capacity per unit volume. For this reason, the Li-ion batteries
have been typically suitable to low-voltage devices that are
preferably light and which are required to endure continuous use
for a long time. In an over-discharged state, however, the Li-ion
batteries deteriorate rapidly, thus Li-ion batteries require
over-discharge protection.
[0006] A battery pack used in a portable electronic device
typically has a plurality of battery cells connected in series. The
maximum number of battery cells connected in series in one battery
pack is determined by the relationship between the output voltage
of the battery pack and a power source voltage supplied from
outside at the time of charging. For instance, the typical output
voltage of one NiCd battery cell or one NiMH battery cell is 1.2 V,
and the power source voltage supplied at the time of charging is
approximately 1.7 V. Assuming that an 18V output voltage from a
battery pack is suitable for most general purpose electronic
devices, the maximum number of NiCd or NiMH battery cells connected
in series in the battery pack is 15. On the other hand, the typical
output voltage of one Li-ion battery cell is approximately 3.6 V.
Accordingly, the maximum number of Li-ion battery cells connected
in series in one fictional 18V Li-ion battery pack would be 5.
[0007] Unlike a NiCd battery pack and a NiMH battery pack, the
Li-ion battery pack may include functionality to protect against
fault conditions inside and outside the Li-ion battery pack. This
prevents cells in the Li-ion battery pack from deteriorating and
shortening useful life of the pack. For instance, if a fault
condition such as short-circuiting occurs inside or outside the
Li-ion battery pack, a fuse may be provided to cut off an
over-discharging current or an overcharging current, if the
discharging current or charging current becomes larger than a given
current level.
[0008] Charge/discharge control and over-discharge protection for
secondary batteries such as Li-ion batteries may be described in
U.S. Pat. No. 6,492,791 to Saeki et al. FIG. 1 is a block diagram
of a prior art battery unit from the '791 patent. The battery unit
1 is mounted on an electronic device 11 and supplies power to the
electronic device 11. The battery unit 1 includes battery cells E1,
E2, and E3, a voltage monitor circuit 101, a fuse 102, p-channel
Field Effect Transistors (FETs) 103 and 104, and power supply
terminals 105 and 106.
[0009] The electronic device 11 includes a DC-DC converter 12, a
device main body 13, a voltage monitor circuit 14, a regulator 15,
a main switch 16, and a reset switch 17. The DC-DC converter 12 is
connected to the power source terminal 105 of the battery unit 1,
and converts the voltage supplied from the battery unit 1 to a
desired voltage. The DC-DC converter 12 is also connected to the
regulator 15, and converts the voltage supplied from the regulator
15 to a desired voltage.
[0010] The voltage converted by the DC-DC converter 12 is supplied
to the device main body 13 via the main switch 16. The main switch
16 is turned on to supply the voltage converted by the DC-DC
converter 12 to the device, main body 13. The main switch 16 is
interlocked with the reset switch 17, so that when the main switch
16 is turned on, the reset switch 17 is also turned on.
[0011] FIG. 2 is a circuit diagram of a voltage monitor circuit for
the prior art battery unit of FIG. 1. As shown in FIG. 2, the
voltage monitor circuit 101 comprises an overcharge monitor circuit
101a and an over-discharge monitor circuit 101b. The overcharge
monitor circuit 101a monitors whether the battery cells E1, E2, and
E3 are in an overcharged state, and switches off the FET 103 when
the battery cells are in an overcharged state. The over-discharge
monitor circuit 101b monitors whether the battery cells E1, E2, and
E3 are in an over-discharged state, and switches off the FET 104
when the battery cells E1, E2, and E3 are in an over-discharged
state.
[0012] The overcharge monitor circuit 101a includes a comparator
121 that compares the voltage of the battery cell E1 with a
reference voltage V.sub.ref1 generated by a reference power source
e.sub.1a. If the voltage of the battery cell E1 is higher than the
reference voltage V.sub.ref1, the comparator 121 outputs "1". If
the voltage of the battery cell E1 is lower than the reference
voltage V.sub.ref1, the comparator 121 outputs "0". Here, "1"
indicates that the output of a comparator is at the high logic
level, and "0" indicates that the output of a comparator is at the
low logic level. Similarly, for cell E2, comparator 122 outputs a
"1" if voltage of the battery cell E2 is higher than reference
voltage V.sub.ref1 generated by reference power source e.sub.1b,
else it outputs a "0". Further, comparator 123 compares the voltage
of battery cell E3, and outputs "1", or "0", depending on whether
the voltage of battery cell E3 is higher or lower than the
reference voltage V.sub.ref1 generated by reference power source
e.sub.1c.
[0013] The outputs of the comparators 121, 122, and 123 are subject
to an OR operation at an OR gate 124, which supplies a result of
the OR operation to the gate of the FET 103. If any of the outputs
of the comparators 121, 122, and 123 is "1", i.e., if any of the
battery cells E1, E2, and E3 is in an overcharged state and the
signal supplied from the OR gate 124 to the gate of the FET 103 is
"1", the FET 103 is switched off so as to prevent overcharge.
[0014] The over-discharge monitor circuit 101b includes a
comparator 111 that compares the voltage of the battery cell E1
with a reference voltage V.sub.ref2 generated by the reference
power source e.sub.2a. If the voltage of the battery cell E1 is
higher than the reference voltage V.sub.ref2, the comparator 111
outputs "0". If the voltage of the battery cell E1 is lower than
the reference voltage V.sub.ref2, the comparator 111 outputs "1".
Similarly, comparator 112 compares the voltage of the battery cell
E2 with a reference voltage V.sub.ref2 generated by the reference
power source e.sub.2b. If the voltage of the battery cell E2 is
higher than the reference voltage V.sub.ref2, the comparator 112
outputs "0". If the voltage of the battery cell E2 is lower than
the reference voltage V.sub.ref2, the comparator 112 outputs "1".
The functions of comparator 113 are also similar; the comparator
113 outputs "0" if voltage of the E3 cell is higher than V.sub.ref2
generated by reference power source e.sub.2c, else comparator 113
outputs "1".
[0015] The outputs of the comparators 111, 112, and 113 are subject
to an OR operation at an OR gate 114, which supplies a result of
the OR operation to the gate of the FET 104. If any of the outputs
of the comparators 111, 112, and 113 is "1", i.e., if any of the
battery cells E1, E2, and E3 is in an over-discharged state and the
signal supplied from the OR gate 114 to the gate of the FET 104 is
"1", the FET 104 is switched off so as to prevent over-discharge of
the battery unit 1.
[0016] FIG. 3 is a circuit diagram of the discharge control circuit
2 in the prior art battery unit of FIG. 1. FIG. 3 is provided to
illustrate the relation between discharge control circuit 2 and
over-discharge monitor circuit 101b.
[0017] The discharge control circuit 2 includes a flip-flop 5 that
has a set terminal and a reset terminal. The output of the
flip-flop 5 is set at "1" when its set terminal is set at "1". The
output of the flip-flop 5 is reset at "0" when its reset terminal
is set at "1". The set terminal 3 is connected to the set terminal
of the flip-flop 5, and the output of an OR gate 6 is supplied to
the reset terminal of the flip-flop 5.
[0018] The OR gate 6 is supplied with a reset signal applied to the
reset terminal 4 and the output of a comparator 8 so as to perform
an OR operation on the reset signal and the output of the
comparator 8. The comparator 8 detects a voltage between the source
and the drain of the charge control FET 103. If the voltage between
the source and the drain is higher than a threshold value, the
comparator 8 outputs a high-level signal. If the voltage between
the source and the drain is lower than the threshold value, the
comparator 8 outputs a low-level signal. In this manner, the
comparator 8 judges whether the charging voltage is higher than a
predetermined level or not from the voltage between the source and
the drain of the charge control FET 103, thereby resetting the
flip-flop 5.
[0019] When the flip-flop 5 is set and the discharge control FET
104 is OFF before charging, the comparator 8 also detects
electrification from the voltage between the source and the drain
of the charge control FET 103. If electrification is detected, the
flip-flop 5 is reset, the output of the flip-flop 5 becomes "low",
and the discharge control FET 104 is turned on.
[0020] When the set terminal 3 becomes "1", the flip-flop 5 outputs
"1". When the output of the reset terminal 4 or the output of the
comparator 8 becomes "1", the flip-flop 5 outputs "0". The output
of the flip-flop 5 is supplied to an OR gate 7. The OR gate 7 is
supplied with the output of the over-discharge control circuit 101b
as well as the output of the flip-flop 5. The OR gate 7 performs an
OR operation on the output of the flip-flop 5 and the output of the
over-discharge control circuit 101b.
[0021] The output of the OR gate 7 is supplied to the discharge
control FET 104. The discharge control FET 104 is OFF when the
output of the OR gate 7 is "1", and is ON when the output of the OR
gate is "0". In other words, when the flip-flop 5 is set, the
discharge control FET 104 becomes "1" and is turned off. When the
flip-flop 5 is reset and outputs "0", the discharge control FET 104
is turned on or off depending on the output of the over-discharge
control circuit 101b.
[0022] The above-described battery unit with charge/discharge
control and over-discharge protection is designed primarily for
low-voltage portable electronic devices such as notebook-type
personal computers, cellular phones, etc., which require voltage
generally on the order of 2 to 4 volts. Such devices are
characterized by using battery packs composed of cells (such as
Li-ion, NiCd, NiMH cells) that provide a maximum output voltage of
about 4.2 volts/cell.
[0023] However, much higher voltages than described above are
required for higher-power electronic devices such as cordless power
tools. Accordingly, higher-power battery packs may be in the
process of being developed for cordless power tools. Such
"high-power" battery packs may provide higher voltage outputs than
conventional NiCd and NiMH battery packs (and substantially higher
power than conventional Li-ion packs used for PCs and cell phones),
and at a much reduced weight (as compared to conventional NiCd or
NiMH battery packs used as power sources in conventional cordless
power tools). A characteristic of these battery packs is that the
battery packs may exhibit substantially lower impedance
characteristics than conventional NiCd, NiMH and/or even the lower
power Li-ion packs.
[0024] However, as this battery technology advances the
introduction of lower impedance chemistries (such as lithium-ion
chemistry) and construction styles to develop secondary batteries
generating substantially higher output voltages then about 4.2
volts/cell may possibly create compatibility issues with existing
cordless power tools. As total internal pack impedance drops, the
pack can supply substantially higher current to an attached
electronic component, such as a power tool. As current through a
tool motor of the attached tool increases, demagnetization forces
(e.g., the number of armature turns of the motor times the current,
ampere-turns) could substantially increase beyond a desired or
design limit in the motor. Such undesirable demagnetization could
thus potentially burn up the tool motor.
[0025] For example, a lower impedance electrical source could cause
damage to a tool's motor when the tool is held at stall condition.
During motor stall, the motor and battery impedances are the only
mechanisms to limit the current since there is no back-EMF created
by the motor. With a lower impedance pack, the currents would be
higher. Higher currents through the motor might cause a stronger
de-magnetization force than what the tool's permanent magnets were
designed to withstand. Additionally, start-up of the tool could
produce excessive starting currents and cause demagnetization of
the motor. Thermal overload could also be a result of using a low
impedance electrical source in an existing power tool, as the new
batteries may be designed to run longer and harder than what the
original cordless tool system was designed. Accordingly,
over-discharge and/or other current limiting controls may need to
be in place before these developing lower-impedance batteries may
be used with existing cordless power tools, for example.
SUMMARY OF THE INVENTION
[0026] In general, exemplary embodiments of the present invention
are directed to a cordless power tool system, battery pack and to
method of providing discharge control in the system and/or battery
pack. In an exemplary cordless power tool system, a battery pack,
which may removably attachable to a cordless power tool and to a
charger of the system, may include at least one battery cell and a
power limiting device. The power limiting device may be arranged in
series with the at least one battery cell for limiting power output
of the battery pack based on the component that is connected to the
pack. Current and hence power out of the battery pack may be
controlled as a function of a total internal impedance of the
battery pack, which may be adjusted depending on the component that
is connected to the pack.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The present invention will become more fully understood from
the detailed description given herein below and the accompanying
drawings, wherein like elements are represented by like reference
numerals and prime and multiple prime notation indicates similar
elements in alternate embodiments, which are given by way of
illustration only and thus are not limitative of the present
invention.
[0028] FIG. 1 is a block diagram of a prior art battery unit.
[0029] FIG. 2 is a circuit diagram of a voltage monitor circuit for
the prior art battery unit of FIG. 1.
[0030] FIG. 3 is a circuit diagram of prior art discharge control
circuit.
[0031] FIG. 4A is a block diagram illustrating an existing,
standard battery pack.
[0032] FIG. 4B is a block diagram illustrating an exemplary
lower-impedance battery pack in accordance with an exemplary
embodiment of the present invention.
[0033] FIGS. 5A-5E illustrate the use of passive resistance to
increase impedance of a lower-impedance battery pack in accordance
with an exemplary embodiment of the present invention.
[0034] FIG. 6 is a block diagram illustrating the use of active
resistance to increase impedance of a lower-impedance battery in
accordance with an exemplary embodiment of the present
invention.
[0035] FIG. 7 is a diagram illustrating a basic concept behind a
dual-mode battery design in accordance with an exemplary embodiment
of the present invention.
[0036] FIG. 8 is a block diagram illustrating a sensor and
impedance adding circuit for a lower-impedance battery in
accordance with an exemplary embodiment of the present
invention.
[0037] FIGS. 9A and 9B are block diagrams illustrating a thermistor
contact arrangement to determine a desired impedance mode for a
given tool in accordance with an exemplary embodiment of the
present invention.
[0038] FIGS. 10A and 10B are block diagrams illustrating additional
contact arrangements for determining a desired impedance mode for a
given tool in accordance with an exemplary embodiment of the
present invention.
[0039] FIGS. 11A and 11B are block diagrams to show a terminal
arrangement for selecting a desired impedance mode in accordance
with an exemplary embodiment of the present invention.
[0040] FIG. 12 is a graph of output voltage versus output current
to describe the different impedance modes of the battery pack.
[0041] FIGS. 13A-13D are block diagrams illustrating discharge
control in accordance with another exemplary embodiment of the
present invention.
[0042] FIG. 14 is a graph of output voltage versus output current
to describe a current profile for stall and start-up
conditions.
[0043] FIG. 15 is a graph of output voltage versus output current
to describe a current profile for a gradual change of total pack
impedance.
[0044] FIG. 16 is a graph of output voltage versus output current
to describe current shaping in accordance with an exemplary
embodiment of the present invention.
[0045] FIG. 17 is a circuit diagram illustrating discharge control
in accordance with another exemplary embodiment of the present
invention.
[0046] FIG. 18 is a block diagram illustrating discharge control of
a battery pack in conjunction with speed control of an attached
tool in accordance with an exemplary embodiment of the present
invention.
[0047] FIG. 19 is a block diagram illustrating discharge control of
a battery pack in conjunction with speed control of an attached
tool in accordance with another exemplary embodiment of the present
invention.
[0048] FIG. 20 is a block diagram illustrating discharge control of
a battery pack in conjunction with speed control of an attached
tool in accordance with another exemplary embodiment of the present
invention.
[0049] FIG. 21 illustrates a detection circuit for providing
over-discharge protection in accordance with an exemplary
embodiment of the present invention.
[0050] FIGS. 22-24 illustrate exemplary cordless power tools of a
cordless power tool system in accordance with an exemplary
embodiment of the present invention.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0051] With general reference to the drawings, a system of cordless
power tools constructed in accordance with the teachings of
exemplary embodiments of the present invention is illustrated.
Exemplary cordless power tools of the system are shown to include,
by way of examples, a circular power saw 10 (FIG. 22), a
reciprocating saw 20 (FIG. 23) and a drill 30 (FIG. 24). The tools
10, 20 and 30 each may include a conventional DC motor (not shown)
adapted to be powered by a power source having a given nominal
voltage rating. In the exemplary embodiments, the tools 10, 20 and
30 may be driven by a removable power source having a nominal
voltage rating of at least 18 volts. It will become evident to
those skilled that the present invention is not limited to the
particular types of tools shown in the drawings nor to specific
voltages. In this regard, the teachings of the present invention
may be applicable to virtually any type of cordless power tool and
any supply voltage.
[0052] With continued reference to the drawings, the removable
power source which may be embodied as a battery pack 40. In the
exemplary embodiments illustrated, the battery pack may be a
rechargeable battery pack 40. Battery pack 40 may include a
plurality of battery cells connected in series, and/or a plurality
of serially-connected strings of cells, in which the strings are in
parallel with one another. For purposes of describing the exemplary
embodiments of the present invention, battery pack 40 may be
composed of cells having a lithium-ion cell chemistry. As the
exemplary embodiments are directed to the cordless power tool
environment, which requires power sources having much higher
voltage ratings than conventional low voltage devices using Li-ion
battery technology, (such as laptop computers and cellular phones)
the nominal voltage rating of the battery pack 40 may be at least
18V.
[0053] However, pack 40 may be composed of cells of another
lithium-based chemistry, such as lithium metal or lithium polymer,
or other chemistry such as nickel cadmium (NiCd), nickel metal
hydride (NiMH) and lead-acid, for example, in terms of the
chemistry makeup of individual cells, electrodes and electrolyte of
the pack 40.
[0054] As used hereafter, the term `lower-impedance battery pack`
may be defined as a battery pack which is intended to supplement or
replace existing, conventional battery packs in a cordless power
tool system. A lower-impedance battery pack, such as the
aforementioned Li-ion battery pack, may occasionally be referred to
as a `first` battery pack hereafter, and may be applicable for the
pack 40 in any of the exemplary cordless power tool systems
illustrated in FIGS. 22-24 and equivalent power tool systems. An
existing battery pack for cordless power tools, such as a
conventional NiCd or NiMH battery pack, may occasionally be
referred to hereafter as a `standard` battery pack or `second`
battery pack hereafter for purposes of clarity and distinction from
the lower impedance battery pack.
[0055] The lower impedance battery pack may produce at least a
similar output voltage (and/or preferably higher voltages) but has
lower internal pack impedance as compared to the standard battery
pack. This lower internal impedance is designed to allow the use of
higher charge and discharge currents with less voltage drop and
thermal heating of the pack, then possible with standard battery
packs currently used in cordless power tool systems. Accordingly,
the lower impedance battery pack may provide higher current and
hence higher power, due to its lower total internal pack impedance
to power a cordless power tool, as compared to its counterpart
standard battery pack.
[0056] The term `new tool` (occasionally also referred to also as a
`first power tool`) may be defined as a cordless power tool that is
designed for and capable of operating with the aforementioned
lower-impedance battery packs as part of a cordless power tool
system as shown in the exemplary FIGS. 22-24, for example. The
first power tool may preferably be compatible with an existing
cordless tool system. Accordingly, the new or first power tools,
when attached to the lower impedance battery pack, may operate at
higher currents, and hence power levels (due to the lower internal
pack impedance in the attached lower-impedance pack) than is
possible in the existing cordless power tool systems, where the
existing power tool is powered by the standard battery pack.
Further, the first power tool may be adapted to communicate one or
more of a power limit, current limit and/or voltage limitation for
the power tool to an attached lower impedance battery pack.
Intelligence or electronics provided in one or both of the lower
impedance battery pack and first power tool may enable such
communication, for example.
[0057] The existing cordless power tool system may consist of a
charger, standard battery pack for a cordless power tool (i.e.,
NiCd, NiMH, etc.) and various power tools that meet each other
components' design specifications and capabilities. The power tools
for the existing cordless power tool system may be occasionally
referred to as an `old` or `second` power tool for purposes of
clarity and distinction from the new or first power tool.
[0058] The second power tool hence is designed to operate with the
standard battery pack at lower currents, which thus may output
lower current and hence power, due to its higher total internal
pack impedance than the first battery pack. Conversely, the first
battery pack may thus be characterized as providing a higher
current and a higher power, because of its lower internal
impedance, than the second, standardized battery pack that is
designed to operate with the conventional, second power tool.
[0059] Several solutions may be possible to allow use of these new
lower-impedance battery packs. Firstly, the new lower-impedance
battery packs could be locked out from an existing power tool base,
perhaps by reconfiguring the pack to tool interface so as to
prevent use with existing tools. Secondly, an upgrade kit could be
sold for integration with the tool motor or tool electronics, so as
to provide a mechanism for enabling the existing power tool to
withstand the new lower-impedance battery pack's more extreme
capabilities. An exemplary upgrade kit might include a new or
replacement tool motor with thicker magnets to handle the higher
magnetic fields that are produced at stall when using a
lower-impedance battery pack.
[0060] Another alternative may be to limit the peak current out of
the lower-impedance battery pack and/or to increase the effective
impedance of the battery pack so that it matches today's design
capabilities for the standard battery pack and existing cordless
power tool system. Limiting the peak current out of a
lower-impedance battery is designed to prevent excessive currents
during heavy loading or start-up conditions.
[0061] Other damage to an attached tool may occur by the excessive
power capability of the lower-impedance battery pack. At a given
current, i.e., 40 amps, a lower-impedance battery pack will have
less voltage drop inside the pack than a standard battery pack.
While the standard battery pack may have an output voltage of 12
volts (from a no-load voltage of 18 volts), the lower-impedance
battery pack (with at least half the internal impedance of the
standard battery pack) would have an output voltage of about at
least 15 volts under the same 40 Amp discharge current. A tool
motor powered by a standard battery pack is controlling about 480
watts of input power, while the same motor powered by a
lower-impedance pack would be controlling about at least 600 watts
of input power.
[0062] Obviously, in this example, the second or old power tool
should be able to handle the higher power capability, if it is to
be used with the lower-impedance battery pack. With this in mind,
it is thus desirable to limit the power that the lower-impedance
battery pack can deliver for existing old tools that have not been
designed for the higher power levels. In an aspect, following
disclosure may detail how peak current out of the lower-impedance
battery pack may be limited, and/or how the effective internal
impedance of the battery pack may be raised so that the
lower-impedance battery pack may be used with both existing and
developing, higher power output tool systems.
[0063] FIG. 4A is a block diagram illustrating an existing,
standard battery pack, and FIG. 4B is a block diagram illustrating
an exemplary lower-impedance battery pack in accordance with an
exemplary embodiment of the present invention. Referring to FIG.
4A, the existing, standard battery pack 400 (such as conventional
NiCd or NiMH packs currently used in cordless power tool systems)
may include a plurality of battery cells 410 which may be connected
in series (five shown for simplicity, pack 400 could have greater
than five cells). The standard pack 400 may also include a Pack ID
420 connected to an output terminal 430 for identification of the
pack 400 when inserted into the charger. The Pack ID 420 may
include the model number, version, cell configuration and the
battery type, such as lithium ion battery, NiCd battery or NiMH
battery, for example. The Pack ID 420 may be embodied as one or
more communication codes received from an output terminal 430 of
the battery pack by an asynchronous full duplex communication
system in the pack 400, such as is described in U.S. Pat. No.
5,680,027 to Hiratsuka et al. However, this is only one example, as
the pack ID may also be embodied by an ID resistor, LED display
that displays identification data of the pack, serial data sent
upon engagement and sensed by the tool/charger, field in a frame of
data sent over an air interface to the tool/charger, etc.
[0064] The standard pack 400 may further include a temperature
sensor 440. The temperature sensor 440 may communicate the
temperature inside the battery pack 400 to a connected charger or
tool (not shown), for example. As such temperature sensors are
known in the art, a detailed explanation of functional operation is
omitted for purposes of brevity.
[0065] Battery pack 450 depicted in FIG. 4B (lower-impedance pack)
may include additional features, and may be part of a cordless
power tool system. Thus, lower-impedance battery pack 450 may be
applicable to and/or designed for cordless power tool systems
comprising at least a cordless power tool, the battery pack and a
charger. Pack 450 may be understood as a removable power source for
high-power, power tool operations. In an example, battery pack 450
may have a nominal voltage rating of at least 18 volts and/or have
a maximum power output of at least about 385 Watts. However, it
should be evident to those skilled in the art that the present
invention is not necessarily limited to the particular types of
tools shown in FIGS. 22-24 nor to specific voltage ratings and/or
power output specifications described above.
[0066] Pack 450 may be comprised of a plurality of
serially-connected cells 410 (five shown for simplicity, pack 450
could have greater than five cells or may be composed of serial
strings of cells with the serial strings in parallel with each
other). In an example, battery pack 450 may be comprised of at
least five serially-connected cells having a Li-ion cell chemistry
and so configured that pack 450 may have a nominal voltage rating
of at least 18 volts and/or may have a maximum power output of at
least 385 Watts. However, pack 450 may be embodied as a pack having
another lithium-based chemistry, or as a nickel cadmium, nickel
metal hydride and/or lead-acid pack, for example, in terms of the
chemistry makeup of individual cells, electrodes and electrolyte of
the pack 450.
[0067] Five (5) terminals are illustrated for the pack 450 in FIG.
4B, although pack 450 may have fewer or greater then five
terminals. Various ones of the terminals may be operatively engaged
to corresponding contacts or terminals when the pack 450 is engaged
to a power tool or charger, as is known in the art, thus a detailed
illustration of the various terminal/contact connections between
pack-tool and pack-charger is omitted in FIG. 4B and may be
occasionally omitted in certain subsequent figures, except where
noted for the purposes of better describing the exemplary
embodiments, for the sake of brevity.
[0068] In addition to the Pack ID and temperature sensor described
above, the lower-impedance battery pack 450 may contain a discharge
control circuit 460 capable of monitoring battery voltage (via a
voltage monitor circuit 415), battery current (through a current
sensor 470), and battery temperature (via temperature sensor 440).
Current sensor 470 may be embodied as known components for current
sensors, such as a shunt resistor, current transformer, etc. which
may provide a signal representing sensed current in pack 450 to
discharge control circuit 460. Voltage monitor circuit 415 may be
embodied by any known voltage monitor circuit, for example, and may
be configured to sense individual cell voltage and/or sense total
pack voltage of the string of cells 410 (`stack voltage`) to
provide a signal representing the individual cell or stack voltage
to discharge control circuit 460.
[0069] Discharge control circuit 460 may be an intelligent device
embodied in hardware or software as a digital microcontroller, a
microprocessor such as a Pentium microprocessor chip, an analog
circuit, a digital signal processor or by one or more digital ICs
such an application specific integrated circuits (ASIC), for
example. Pack 450 may also be configured for communicating and
sensing information from the attached tool (not shown) through
communication terminals 480. In an example, if pack 450 is
operatively connected to the first power tool or a power tool
configured with intelligence (such as a microprocessor) or other
electronic processor, the discharge control circuit 460 of pack 450
may be able to receive, via terminal 480, information related to
one or more of a power limit, current limit and/or voltage
limitation for the first power tool.
[0070] Using combinations of this data, the discharge control
circuit 460 may act to place restrictions of the maximum power and
current through the battery 450. The discharge control circuit 460
may accomplish this by controlling a power limiting device 490
placed in series with the battery cells 410. The power limiting
device 490 may limit current in the battery pack 450 and hence,
power out. Power limiting device 490 may also be understood as,
and/or occasionally referred to as, one or more of a current
limiting means, device or circuit, and/or an impedance matching
means, device or circuit. Hereafter, various configurations for
providing discharge control for the lower-impedance battery pack
450 are described in further detail.
[0071] FIGS. 5A-5E illustrate the use of passive resistance to
increase impedance of a lower-impedance battery pack in accordance
with an exemplary embodiment of the present invention. FIGS. 5A-5E
(and subsequent block or circuit diagrams), may show only a portion
of the pack 450 of FIG. 4B to highlight examples of a power
limiting device 490 and/or other discharge control features, it
being understood that the teachings in these subsequent circuits or
block diagrams are applicable to the lower-impedance pack 450 in
FIG. 4B. Thus, for the sake of brevity and clarity, FIGS. 5A-5E
(and several other subsequent figures), may only show positive and
negative terminals of the pack 450 and a single cell 410 (which may
represent the serially-connected cells 410 of FIG. 4B), with
several of the components in FIG. 4B being omitted for sake of
clarity.
[0072] The power limiting device 490 as shown in pack 450 of FIG.
4B may be embodied, in one aspect, as a passive resistance device.
If it is desired that the lower-impedance battery pack 450 be
permanently de-powered for use with existing power tools (i.e.,
limited to a maximum output current so as not to damage an attached
existing power tool that is specifically designed for operation
with a conventional battery pack), then the total pack impedance of
the lower-impedance battery pack 450 could be raised so as to
substantially match the impedance of an existing, standard battery
pack (i.e., pack 400) that was designed for the old, existing lines
of power tools. Raising the total internal pack impedance of the
lower-impedance battery pack decreases both its output power
capability and its maximum output current, hence de-powering the
lower-impedance battery pack 450 so that it satisfies the design or
operating characteristics of the existing (second) power tool.
[0073] In an exemplary embodiment, raising the internal impedance
of the lower-impedance battery pack 450 may be effected by
utilizing passive resistance in the battery pack. For example, a
series resistor (FIG. 5A) could be added between one or more
battery cells 410 of the lower-impedance battery pack 450 to
increase the total internal battery pack impedance. The proposed
system may include the added resistance between the series
connection of the cells and the positive battery terminal, although
it may be added between either the positive or negative terminal
connection and the serially-connected cells.
[0074] Using a resistor in series as shown in FIG. 5A as the power
limiting device 490 is only one method of increasing impedance in
the lower-impedance battery pack 450 so as to match impedance
characteristics of the standard battery pack, when the
lower-impedance battery pack 450 is operatively attached to an
existing power tool designed for the standard battery pack.
Alternatively, or in addition to adding series resistance, the
power limiting device 490 may be realized by lengthening the
connecting wires from battery cell to terminal block, so as to
increase total pack impedance. As shown in FIG. 5B, connecting
wires 411 between one (or more) cells 410 and a terminal block 412
of the battery pack 450 may be substantially lengthened. As a
further alternative, battery straps 413 shown in FIG. 5C that
connect the individual battery cells 410 of the pack 450 could be
modified to increase the total pack impedance. By reducing the
cross sectional area of the straps 413, the resistance of the strap
increases. Additionally, the strap material may be changed. The
strap material typically may be composed of a low resistance
material (such as nickel). Instead, the straps may be composed of a
less conductive (and hence higher resistance) material such as
steel, for example.
[0075] Further, a printed circuit board (PCB) track could be used
to increase total pack impedance, as shown as FIG. 5D. In lieu of
using battery straps 413, a PCB track 417 may be placed on top of
the cells 410 to not only connect the cells 410, but also to add a
small impedance through the connecting copper traces 418. Even an
illuminating filament 419 in series with the current flow (as shown
as FIG. 5E) may increase the total impedance of the pack. The
illumination intensity of the filament 419 may also be visible to
the user to display the amount of current being used. It should be
readily understood that one or more of the passive resistance
measures described above in FIGS. 5A-5E could be combined to raise
the total pack impedance of pack 450. Each of the above may
represent alternative embodiments of a power limiting device 490
which may be used to increase total pack impedance so as to limit
power output, for example.
[0076] By adding impedance to the lower-impedance cells, the
overall system reliability is not diminished by the lower-impedance
cells' higher current and greater power capability. Accordingly,
discharge control and over-discharge protection for cells of the
lower-impedance battery pack may be provided by raising the
internal impedance of the lower-impedance battery pack in an effort
to reduce the pack's output power capability and maximum output
current.
[0077] FIG. 6 is a block diagram illustrating the use of active
resistance to increase impedance of a lower-impedance battery in
accordance with an exemplary embodiment of the present invention.
The power limiting device 490 as shown in pack 450 of FIG. 4B may
be embodied by an active resistance device 600. If it is desired
that total pack impedance of the lower-impedance battery pack 450
changes as the load changes (i.e., dynamically or adaptively), an
active resistance device 600 may be used. For example, and
referring to FIG. 6, an active resistance device 600 may be placed
between a given cell in the battery pack 450 and the positive
terminal, for example. Accordingly, device 600 may be used to
increase total pack impedance so as to limit power output. Active
resistance device 600 may be embodied as a semiconductor device or
other device or circuit with a current limiting function, as
generally shown in FIG. 6. Alternatively, the active resistance
device 600 may be at least two (or more) semiconductor devices with
current limiting function operating in parallel to form a parallel
combination in series with at least one of the one or more
serially-connected cells. As a further example, there are numerous
off-the-shelf semiconductors ("Smart-FET" Technologies) that
perform an automatic current limit at fixed or programmable
thresholds.
[0078] The active resistance device 600 for limiting power output
may further be embodied as a Positive Temperature Coefficient (PTC)
element or a device which includes a PTC. PTC elements are known as
protective elements for controlling the current which flows through
circuits to be protected, since their resistance value increases as
they give off heat in over-current conditions. For example, PTC
thermistors have been used as an over-current protection element.
When an electric circuit gets overloaded, conductive polymers of a
PTC thermistor, which have PTC properties, emit heat and thermally
expand to become high resistance, thereby reducing the current in
the circuit to a safe, relatively small current level.
[0079] Accordingly, if a PTC device such as described above is
connected in series with the battery, the impedance of the PTC
device, and hence pack impedance, increases with increasing
current. If substantially low impedance is needed and no
commercially available single PTC can offer the desired low
impedance and/or current capability, then multiple PTC's could be
connected in parallel with each other to share the current. It
should be readily understood that the active resistance measures
described above could be combined in a battery circuit of the low
impedance battery pack to dynamically raise the total pack
impedance based on load conditions of a given, attached tool. By
adding impedance to the lower-impedance cells, the overall system
reliability is not diminished by the lower-impedance cells' higher
current capability. Discharge control and over-discharge protection
may thus be in place for the cells 410 of the lower-impedance
battery pack 450.
[0080] FIG. 7 is a diagram illustrating a basic concept behind a
dual-mode battery design in accordance with an exemplary embodiment
of the present invention. FIG. 7 illustrates a principle that while
the lower-impedance battery pack 450 may be desired for use with a
new generation of cordless power tools operable at higher currents
and/or power levels than are currently available, it should also be
useable with existing cordless power tools operating at lower power
levels. In other words, the old power tools may need to be
protected from excessive currents and/or excessive power levels
that could be generated by the lower-impedance battery pack 450 of
FIG. 4B. Accordingly, a dual-mode battery design may be desired
which allows the lower-impedance battery pack 450 to be useable
with both new and old power tools. In an effort to facilitate this
dual use, electronic sense mechanisms may be employed.
[0081] FIG. 8 is a block diagram illustrating a sensor and
impedance adding circuit for a lower-impedance battery in
accordance with an exemplary embodiment of the present invention.
In an effort to provide a lower-impedance battery pack that may be
adapted for use with `new` and `old` power tools, Referring to FIG.
8, the lower-impedance battery pack 450 may contain an impedance
adding circuit 800 (such as a semiconductor device, for example)
that may add series impedance based on a sensed signal received (or
lack thereof) from a sensor 810. The sensor 810 may sense the type
of tool (new or old) upon engagement with the battery pack and/or
as communicated by the power tool, for example, and send the sensed
signal directly to impedance adding circuit 800 indicating that a
new or old power tool is attached. Thus, the impedance adding
circuit 800 is configured to receive the sensed signal from sensor
810 to either add impedance for purposes of limiting maximum
current and output power, or to maintain the lower internal
impedance of the lower-impedance battery pack 450.
[0082] In an alternative, the sensed signal (or lack thereof) may
be used by the discharge control circuit 460 of the lower-impedance
battery pack 450 (or other intelligent device or microprocessor in
pack 450) to control impedance adding circuit 800 for adjusting (or
maintaining) the total pack impedance for the battery pack 450.
Controlling the impedance of the battery pack 450 allows the
benefits of the pack to be maximized in a new cordless power tool
base designed for use with pack 450, while preventing
over-discharge conditions in the pack from occurring, which could
cause corresponding overload damage to the existing or old cordless
power tool base.
[0083] The sensor 810 may be embodied as a magnetic sensor or an
inductive pick-up sensor, for example, which senses signals in the
new tools. It is within the scope of the exemplary embodiments of
the present invention to use radio frequency (RF) communications
and optical sensing as other forms of sensing in order to
distinguish whether a new line of tool (cordless power tool adapted
for use with the lower-impedance battery pack 450) or older
generation of tool (i.e., tool configured for use with the standard
pack 400) is being attached to the lower-impedance battery pack
450, for example.
[0084] FIGS. 9A and 9B are block diagrams illustrating a thermistor
terminal arrangement to determine a desired impedance mode for a
given tool in accordance with an exemplary embodiment of the
present invention. Both figures show only an abbreviated portion of
the circuit of pack 450 for reasons of clarity and/or brevity as
previously discussed. FIGS. 9A and 9B include an impedance varying
circuit 950 that may change or vary the impedance of the
lower-impedance battery pack 450 based on the state of its input,
(i.e., the input from a third terminal 940). The third terminal may
be embodied as a thermistor terminal 940 of a thermistor 970, for
example. The impedance varying circuit 1150 can it be included in,
or controlled by, the discharge control device 460 in FIG. 4B.
[0085] The tools (new or old) may include a motor 910,
semiconductor device 920 and control circuit 930. The semiconductor
device 920 in conjunction with the control circuit 930 may enable
the tool to be used in variable speed modes, for example. The
control circuit 930 may be embodied as a suitable intelligent
device such as a microprocessor chip, for example. It is known that
such a control circuit 930 in a power tool may detect a trigger
switch of the power tool and create a pulse width modulated (PWM)
signal that is input to the semiconductor device 920. The PWM
signal may turn the semiconductor device 920 on and off rapidly
`pulsing` the device, to create an average voltage across the motor
910 that is lower than the applied battery voltage and proportional
to the trigger setting of the power tool. In power tools without
variable speed, only the motor 910 is connected to the terminals
and there is no need for a semiconductor device 920 and control
circuit 930.
[0086] Referring to FIG. 9A, when a new tool is attached to the
lower-impedance battery pack 450, the third (thermistor) terminal
940 may be `pulled` to the positive (+) polarity when a trigger or
power actuator (not shown) of the tool is operated. The
lower-impedance battery pack 450 may further include a sensing
circuit 980, which may be embodied as a circuit component of the
impedance varying circuit 950, for example, to sense whether the
thermistor terminal 940 of the thermistor 970 was pulled high or
left open, in order to determine the desired impedance mode for the
given tool.
[0087] If the battery pack 450 is connected to an old tool, the
thermistor terminal 940 is left connected only to the negative
battery terminal through the thermistor 970. The voltage on the
thermistor terminal 940 will be zero with respect to the battery
negative terminal. In an example, the sensing circuit may be a
comparator 980. The comparator 980 compares this voltage with a
preset reference level 990. Since the thermistor terminal 940
voltage is lower than the reference 990, the comparator output is
low (in FIGS. 9A and 9B, L=higher impedance) and this the pack
should run as a high impedance pack, causing an impedance device
975 of the impedance varying circuit 950 to add a series resistance
so as to raise total internal pack impedance of the pack, thereby
limiting output current and hence power. The impedance device 975
of impedance varying circuit 950 may be another example of the
power limiting device 490 of FIG. 4B, and may be embodied as one or
more of the exemplary embodiments previously discussed (i.e.,
passive resistance (resistor, lengthened connecting wires, modified
straps); active resistance (semiconductor device(s), PTC(s),
etc.).
[0088] If the battery pack 450 were connected to a new tool as in
FIG. 9A, the thermistor terminal 940 is pulled high by terminal
960, which is connected to the battery positive terminal through a
tool trigger switch and resistor 965. The resistance divider
created by resistor 965 and thermistor 970 creates an elevated
voltage at the thermistor terminal 940 which may be greater than
the reference voltage 990. The comparator 980 output will thus be
high (in FIGS. 9A and 9B, H=low impedance) and activates the pack
450 into the low-impedance mode, in which the impedance device 975
of the impedance varying circuit 950 does not add a series
resistance to maintain internal pack impedance at its normal low
impedance level.
[0089] As discussed above, the sensing circuit 980 could be part of
a discharge control circuit 460 shown in FIG. 4B. The sensing
circuit only looks at the "state" of the thermistor terminal 940 to
set the impedance mode of the battery pack 450. As shown in FIG.
9B, when the pack is connected to an existing tool, the thermistor
terminal 940 is not connected to anything. This `floating` state
can be determined by the battery's control circuit, which may (or
may not) be part of the discharge control circuit 460, to set the
mode to high impedance.
[0090] FIGS. 10A and 10B are block diagrams illustrating additional
contact arrangements for determining a desired impedance mode for a
given cordless power tool in accordance with an exemplary
embodiment of the present invention. FIGS. 10A and 10B provide an
additional power contact 1005, so that the battery circuit of the
lower-impedance battery pack 450 consists of two discharge paths.
One path contains an impedance adding circuit 1010, while the other
path does not. The tool side of FIGS. 10A and 10B includes motor
910, semiconductor device 920 and control circuit 930 shown
previously, illustrating a typical variable speed
configuration.
[0091] The impedance adding circuit 1010 is another embodiment of a
power limiting device 490 of FIG. 4B, and may be embodied as one or
more of the exemplary embodiments previously discussed (i.e.,
passive resistance (resistor, lengthened connecting wires, modified
straps); active resistance (semiconductor device(s), PTC(s), etc).
The impedance adding circuit 1010 may be under the control of a
smart or intelligent processor such as discharge control circuit
460, or may have built-in independent control and intelligence,
such as an ASIC, for example.
[0092] The lower-impedance battery pack 450 may include additional
power contacts, if desired. For example, a system as shown in FIGS.
10A and 10B may be envisioned, with an additional power contact
added to the low impedance battery pack 450 in FIG. 10A. With new
tools using a direct battery connection, a low impedance source may
be achieved. The existing `old` tools would still make contact with
the impedance adding circuit 1010 within the low impedance battery
pack 450, and thus be safe from overload because of the added
impedance of the impedance adding circuit 1010.
[0093] FIGS. 11A and 11B are block diagrams to show a terminal
arrangement for selecting a desired impedance mode in accordance
with an exemplary embodiment of the present invention. If an
additional power contact of FIGS. 10A and 10B proves not to be as
feasible as the two-power contact arrangement, then a terminal
arrangement as shown in FIGS. 11A and 11B could be employed. The
battery pack 450 may contain the same impedance adding circuit 1010
as described above, but may employ a third terminal 1120 as an
impedance selection mechanism.
[0094] While the previous example of the new tools shown in FIG.
11A uses a thermistor contact voltage to determine the battery
impedance mode, FIG. 11A illustrates a communication line 1120 that
is arranged between the battery (representative of pack 450) and
the power tool. Electronics provided in new or developing
generations of cordless power tools may provide a given indicator
and/or sense signal via terminal 1120 to the impedance adding
circuit 1010 to establish a given impedance mode in the
lower-impedance battery pack 450, similar to as described with
respect to FIG. 8, for example.
[0095] For example, the terminal indicator may be embodied as a
simple indicator such as an identification (ID) resistor tied to a
specific polarity setting (similar to as described in the
thermistor contact of FIG. 11A). Alternatively, the terminal
indicator may be implemented as actual communication data within a
microprocessor controlled electronic circuit 930' provided in the
new tool. The electronic circuit 930' in the new tool would
communicate the desired impedance mode of the battery based on the
capability of the tool, or motor characteristics of motor 910 such
as speed, torque and/or temperature. If the lower-impedance battery
pack 450 was connected to an old tool as shown in FIG. 11B, there
would be no tool communication over the terminal 1120, thus the
impedance adding circuit 1010 defaults to the high impedance mode
in the battery pack 450.
[0096] FIG. 12 is a graph of output voltage versus output current
to describe a current profile for the low and high impedance states
of the battery output. In low impedance mode, the current out of
the battery cells flows through the motor in the tool and returns
back to the battery cells with very little resistance. The battery
voltage with respect to battery current will have a Slope A, as
shown in FIG. 12. When the pack is in high impedance mode, the
increased impedance causes a loss in battery pack performance and
the V-I curve will have Slope B.
[0097] FIGS. 13A-13D are block diagrams illustrating discharge
control in accordance with another exemplary embodiment of the
present invention. With the aforementioned techniques describing
how to determine the impedance mode, methods of limiting current by
controlling total pack impedance of the low impedance battery pack
should be evaluated. FIGS. 13A-13D only show an abbreviated portion
of an exemplary circuit of the lower-impedance battery pack 450; it
being understood that the teachings of FIGS. 13A-13D may be
applicable to lower-impedance battery pack 450.
[0098] FIG. 13A illustrates one (or more) battery cells
(representing serially-connected cells 410) with output terminals
(+, -) for connection to a tool or charger interface (not shown).
FIG. 13A includes a semiconductor device 1320 and free-wheeling
diode 1330, under the control of discharge control circuit 1310,
which can be used to control current, as shown in FIG. 13A. The
discharge control circuit 1310 may be analogous to the discharge
control circuit 460 of FIG. 4B and may be embodied with
intelligence and/or a processing capability, for example.
[0099] Semiconductor device 1320 is shown as an N-channel MOSFET;
(FET 1320), and occasionally hereafter may be referred to as a
`discharge FET`; however, any semiconductor device capable of
passing/blocking current may be utilized for purposes of discharge
control in accordance with the exemplary embodiments. In general,
in one example, FET 1320 may be set (i.e., at time of manufacture)
to turn ON/OFF at given currents, or may receive a control signal
from the discharge control circuit 1310 to turn ON or OFF at given
current(s), such as when pack current reaches a maximum current
threshold.
[0100] Further, the FET 1320 may be pulsed to provide an average
voltage across the tool motor. When the duty cycle (relationship
between operating time and rest time of the motor) is decreased,
the average voltage drops and the maximum current capability out of
the pack also drops. If the duty cycle of the FET 1320 is
increased, the average output voltage would increase and therefore,
the maximum current capability would increase as well. In this
configuration, the FET 1320 remains fully ON until the current
exceeds some upper limit. The discharge control circuit 1310 could
then reduce the duty cycle on FET 1320 to decrease the average
output voltage provided to the tool motor. This drop in output
voltage reduces the output current. The discharge control device
1310 may thus limit the current provided to the tool to some given
maximum threshold current value by changing the average output
voltage out of the battery pack 450. Since the discharge control
can limit current and voltage out of the battery pack, it is
effectively controlling the battery` pack's total internal
impedance, or `effective impedance`, as seen by the tool. As an
example, if the discharge control circuit 1310 is sensing pack
current during pack-tool operations, directly or via a signal
received from a current sensing device such as current sensor 470
of FIG. 4B, the discharge control circuit 1310 maintains FET 1320
ON until sensed current meets or exceeds a given maximum current
threshold. The discharge control circuit 1310 may then pulse width
modulate FET 1320 to raise an effective internal pack impedance, as
seen by the power tool, until the sensed current has dropped below
the given threshold.
[0101] Because of the inherent inductance found in most motors, the
current cannot change instantaneously when the FET 1320 is turned
OFF based on an over-current condition in the pack. A recirculating
diode 1330 shown in FIG. 13A allows the motor current to
recirculate between negative and positive terminals of the pack and
eventually decay to zero or until the FET 1320 is turned back ON
(i.e., when current drops below the given threshold so that the
over-current condition clears). While the FET 1320 is energized
(ON), the diode 1330 blocks any current trying to bypass the tool
motor.
[0102] FIG. 13B illustrates shows how multiple FETs 1320, 1320'
could be used to help share power dissipation. FETs 1320 and 1320'
are shown in a parallel combination that is in series with the
battery cells. The FETs 1320, 1320' may be activated at the same
time to share the current. During ON state, the power losses are
equal to I.sup.2R. As two semiconductor devices are in parallel,
each device would receive half of the current and one quarter of
the power dissipation. That would yield an overall system
dissipation of one half the single FET 1320 solution of FIG.
13A.
[0103] An alternative placement of the diode 1330 in FIG. 13A is
shown in FIG. 13C. Here, instead of being placed in the pack, a
recirculating diode 1330' could be placed in the tool. Now, the
recirculating path is in the tool and thus the power losses are
moved out of the pack and into the tool. Similar to FIG. 13A, as
FET 1320 is switched OFF based on a sensed over-current condition,
the recirculating diode 1330' allows the motor current to
recirculate between negative and positive terminals of the tool and
eventually decay to zero or until the FET 1320 is turned back ON
(i.e., when current drops below the given threshold so that the
over-current condition clears). The diodes 1330' forward voltage
drop times the current equals its power loss. For example, if the
FET 1320 were at 50% PWM conduction with 40 amps in the tool motor,
and the forward voltage drop in the diode 1330' was 1 volt, the
power loss in the diode 1330' would be 50%*1V*40 A=20 watts. Moving
this power out of the battery pack and into the tool may help
spread out the heat and/or limit power losses.
[0104] In an effort to reduce power losses even further, the
circuit in FIG. 13D could be used. In FIG. 13D, the diode 1330 is
replaced by a second FET 1325, referred to as a `recirculating
FET`. This recirculating FET 1325 is activated out of phase from
the discharge FET 1320, with the duty cycle of both FETs controlled
by the discharge control circuit 1310. The recirculating FET 1325
operates synchronously with the discharge FET 1320. When the
discharge FET 1320 is ON, the recirculating FET 1325 is held OFF
and current flows across the motor and back to the cells. When the
discharge FET 1320 is de-energized (turned OFF), as in the case
described with respect to FIG. 13A, where sensed current has met or
exceeded a given maximum current threshold, the recirculating FET
1325 is energized ON and the motor current is allowed to
recirculate through the recirculating FET 1325 until the current
has dropped to a level below the given threshold, after which FETs
1320 and 1325 revert to ON and OFF states respectively, under
control of the discharge control circuit 1310. The losses through
recirculating FET 1325 may be understood as 12 * "On resistance".
Using a typical FET resistance, for example, recirculating FET 1325
losses may be 50%*40 A.sup.2*0.005 Ohms=4 watts. This power loss is
significantly lower than the diode 1330 that dissipated 20 watts as
described with respect to FIG. 13A. This process is known as
synchronous rectification.
[0105] The discharge control circuits 460/1310 have been described
as including intelligence. If such intelligence is adapted to
monitor the current flowing through the battery cells (via a
current sensor 470 as shown in FIG. 4B or directly), then the
discharge control circuit 460/1310 could change the impedance
dynamically, i.e., "on-the-fly", by switching the semiconductor
state of the FETs 1320 (and/or FETS 1320 and 1320'. Accordingly,
any of FIGS. 13A-13D may include a current sensor such as sensor
470 shown in FIG. 4B, provided between a terminal of the pack and
at least one of the cells for sensing battery current and for
outputting a sensed signal to the discharge control circuit
1310.
[0106] For example, and when attached to an existing `old`'tool for
all normal operations, the battery pack 450 could remain in low
impedance mode with the FET(s) 1320 (or 1320 and 1320') in the ON
state. Only during stall and start-up conditions (when motor
impedance is substantially low and currents get too high) would
there be a need to change total internal pack impedance by reducing
the PWM duty cycle.
[0107] Intelligence in the discharge control circuit 460/1310 (or
possibly in a separate battery control circuit, for example) such
as a microcontroller or DSP controller) could periodically sense
the current through a current sensing device such as the
aforementioned current sensor 470 of FIG. 4B (which may be embodied
as a shunt resistor or current transformer (not shown), for
example) and PWM the FETs 1320 and/or FETS 1320 and 1320' to a
lower duty cycle. The average output voltage of the battery pack
450 would suddenly drop which causes the current to drop in the
attached tool. The lowered duty cycle would remain in effect until
the current drops below a pre-defined or given threshold. The
following describes this example in some more detail.
[0108] FIG. 14 is a graph of output voltage versus output current
to describe a current profile for stall and start-up conditions
where the semiconductor device 1320 in FIGS. 13A-D is pulse width
modulated. For the following description in FIGS. 14, 16, control
is described with respect to FET 1320, it being understood that
such is applicable to the multi-FET example of FIG. 13B. For the
curve defined by Slope C, the current at point 1 is low. As the
load increases, the voltage drops slightly due to the lower pack
impedance. At point 2, the current reaches a given current
threshold and discharge control begins to PWM the FET. Instantly,
the pack voltage is reduced (due to the higher impedance) and
limits the stall current. As the load decreases, the output voltage
follows Slope D back to some pre-defined threshold. At this point,
the FET 1320 is turned on at 100% duty cycle and thereby enables
normal low impedance pack operation. To prevent the circuit from
oscillating at the cut-off threshold, the current at which the FET
1320 turns back on should be lower than the current at the initial
cut-off point. Slope D illustrates a reasonable representation of
the path back to normal operation.
[0109] Referring to the "knee" of FIG. 14, Slope C at point 2, it
is possible that the tool may immediately stall as the PWM is
switched in and the average output voltage of the battery drops.
Without any warning, the tool would lose power and remain at stall
until the load is removed. A user of the tool may not adequately
predict this; thus in this case an alternative design may be
used.
[0110] Just before the knee in FIG. 14, the FET 1320 may be pulsed
to produce an artificial impedance somewhere between slope C and
slope D of FIG. 14. FIG. 15 is a graph of output voltage versus
output current to describe a current profile for a gradual change
of total pack impedance, and illustrates exemplary current profiles
that may be used to gradually change the total internal pack
impedance of pack 450 from low to high and back again.
[0111] The discharge control described in FIGS. 13A-D performs what
is referred to as `current shaping`. Current shaping may be defined
as using active electronic controls to change the V-I curves of a
battery output. With current shaping, the battery output of FIG. 14
can be modified to look like the output of FIG. 15. As the current
increases, (which may be sensed by a current sensor 470 in
communication with discharge control device 1310, for example) the
discharge control device 1310 of FIGS. 13A-D may begin to pulse
width modulate (PWM) the FET 1320, allowing the voltage to drop
somewhere in between slope C and slope D of FIG. 14. The gradual
drop in voltage (shown in FIG. 15 slope E) is perceived to the user
as a small drop in motor RPM. Typically, a user wanting to avoid
stall conditions would back off on the load applied to the tool.
Without their knowledge, professional tool users may become
innately "tuned" to the motor noise and tend to keep the motor
performing at peak power without stalling to motor out.
[0112] Thus, FIG. 15 illustrates that as sensed pack current
approaches a maximum current threshold during pack-tool operations,
the discharge control circuit 1310 may pulse width modulates the
FET 1320 to selectively reduce the voltage applied to the tool
motor, causing a gradual drop in voltage and current out of the
pack
[0113] FIG. 16 is a graph of output voltage versus output current
to describe current shaping in accordance with an exemplary
embodiments of the present invention. The output current in FIG.
13A-D could also be shaped to have the sharp "knee" as in FIG. 16,
at Slope G. This is created by setting a current limit such as the
given maximum threshold current value, for example. Any motor
impedance that is low enough for an over current condition would
cause the immediate drop in average output voltage. The current
would remain fixed at some maximum value, regardless of how low the
motor impedance drops. If a softer "current shape" is desired, the
curve may be rounded to look like Slope H. To round the curve, the
average output voltage should be dropped slightly prior to reaching
the current limit. By dropping the output voltage before the
current limit is reached, the transition between normal ON mode and
a current limiting mode (and hence power limiting mode) is softer
and less abrupt for the user controlling the tool load.
[0114] The circuit in any of FIGS. 13A-13D could also use the FET
1320, (or FETs 1320 and 1320') in a linear mode. For example, the
FET 1320 would not be pulsing, but would be partially on. By
running in linear mode, the FET 1320 may allow some current to pass
while blocking other current at the same time. If a carefully
controlled gate voltage is established on the FET 1320, it will act
like a resistor and limit the current as the tool approaches, and
during, stall conditions. A bipolar transistor may also be used but
these devices are controlled with base to emitter currents.
[0115] The idea of limiting current, and hence power, may be
unnecessary if, once the tool is stalled, the user should turn the
trigger off before the tool will start up again. Such an example of
this case may be where a circular saw binds to a stall in a piece
of wood. If the trigger is held on, the tool will remain stalled
and waste energy heating the motor and pack. If, however, the
current is turned off once the stall threshold is reached, the user
could be forced to release the trigger, remove the saw from the
bind, and then re-trigger to start up again. By holding the FET
1320 in FIGS. 13A-13D OFF until the tool trigger is released, the
wasted energy during stall is avoided.
[0116] FIG. 17 is a circuit diagram illustrating discharge control
in accordance with another exemplary embodiment of the present
invention. FIG. 17 only shows an abbreviated portion of the circuit
of the lower-impedance battery pack 450; it being understood that
the teachings of FIG. 17 may also be applicable to lower-impedance
battery pack 450. A different alternative that doesn't use
semiconductors is a current controlled relay. As will be shown
below, the current controlled relay may be arranged in a current
path of the pack to provide a current limiting function with
hysteresis that limits current out of the pack 450 to a tool motor
of an attached power tool.
[0117] FIG. 17 shows a discharge control circuit for the pack 450
that may be embodied by a current controlled relay 1710. The
current controlled relay 1710 may be composed of two coils, primary
coil 1735 and secondary coil 1740, magnetically connected to a
switch 1750. The switch is connected in series with the primary
coil 1735 and at least one cell (representing cells 410) of the
battery pack 450. The switch may have a first state which connects
the battery pack to a motor of the tool and a second state which
interrupts current to the tool. A free-wheeling diode 1730 is
connected between the positive terminal and the secondary coil
1740. In the example of FIG. 17, the primary coil 1735 of N turns
may be energized by the current flow.
[0118] As is known, current flow through the pack during power
operations with the tool creates a magnetic field between the
primary and secondary coils 1735, 1740. When the magnetic field is
sufficient to activate the switch 1750, the current is diverted
through the diode 1730 and secondary coil 1740 with N+turns.
Because the second branch (secondary coil 1740) has more turns, it
holds the switch 1750 in that position while the current decays
within the battery pack through the diode 1730 and secondary coil
1740. At a second lower threshold, the current through the N+
windings of secondary coil 1740 may have decreased to a point that
is not sufficient to hold the switch state of switch 1750, and it
returns back to the original state, which connects the battery pack
to the tool motor once again. This process thus creates a motor
current limit with hysteresis.
[0119] Alternatively, if a single-pole double-throw (SPDT) relay is
used (an SPDT relay is a general purpose relay for controlling high
current draw devices), the same type of circuit could be employed,
but with each branch of the relay coil connected to separate
contacts. In this alternative embodiment, the large free-wheeling
diode 1730 is no longer needed and the design could be
simplified.
[0120] FIG. 18 is a block diagram illustrating a discharge control
of a battery pack in conjunction with speed control of an attached
tool in accordance with an exemplary embodiment of the present
invention. FIG. 18 only shows an abbreviated portion of the circuit
of the lower-impedance battery pack 450; it being understood that
the teachings of FIG. 18 may also be applicable to lower-impedance
battery pack 450. The discharge control circuit 1815 in FIG. 18 may
be embodied a smart or intelligence device similarly to as
described for any of discharge control circuits 460 and 1310, for
example.
[0121] In FIG. 18, variable speed control is shown residing in the
battery pack. In particular, a third terminal C may be added to the
tool, which may be a tool of the new tool line or an old tool that
has been retrofitted with a third terminal C, in order to provide a
control signal, via control terminal 1805, to control a FET 1820 in
the battery pack. For example, a voltage sense device such as a
potentiometer 1810 or similar device in the tool may sense a
voltage value that corresponds to a desired speed, and forward a
control signal via terminal C and control terminal 1805 to a
discharge control circuit 1815 which controls the FET 1820
accordingly. FET 1820 may be pulse width modulated in a manner
similar to as described for FET 1320 of FIGS. 13A-D at a duty cycle
proportional to the potential at control terminal 1805. By
controlling speed of the tool, current from the battery pack and
hence discharge rate may be controlled.
[0122] FIG. 19 is a block diagram illustrating discharge control of
a battery pack in conjunction with speed control of an attached
tool in accordance with another exemplary embodiment of the present
invention. FIG. 19 only shows an abbreviated portion of the circuit
of the lower-impedance battery pack 450; it being understood that
the teachings of FIG. 19 may also be applicable to lower-impedance
battery pack 450. The discharge control circuit 1915 in FIG. 19 may
be embodied a smart or intelligence device similarly to as
described for any of discharge control circuits 460,1310 and 1815,
for example.
[0123] In FIG. 19 discharge control for the battery pack resides in
the battery pack and variable speed control resides in the tool. A
switch FET 1920 may be employed with a discharge control device
1915 to control discharge rate of the battery pack, as described in
FIGS. 13A-D, for example. A second PWM FET 1912 may be utilized on
the tool side to control variable speed of the tool based on the
user's desired speed. The tool may include a switch 1925 selectable
by the user between ON (bypass position for full speed of tool
motor), OFF and VS (variable speed), for example. The control 1910
may be embodied in hardware and/or software, for example. Control
1910 may be embodied as an intelligent processor or pre-configured
processing device such as a microcontroller, microprocessor chip,
DSP, application specific integrated circuit (ASIC), etc. The
control 1910 in the tool senses a desired speed, such as from a
trigger operation or speed dial, and varies the duty cycle of the
tool PWM FET 1912 to produce the desired motor speed. The tool may
also contain a bypass contact 1930 (the switch 1925 is shown in
bypass position in FIG. 19). The bypass contact 1930 may be engaged
when full speed is desired. Since the tool PWM FET 1912 would be in
an ON state at all times, it may be desirable to bypass the FET
1912 entirely. Thus, current will flow through the bypass contact
1930 when the trigger is pulled to the full throw of the trigger,
i.e., 100%.
[0124] FIG. 20 is a block diagram illustrating discharge control of
a battery pack in conjunction with speed control of an attached
tool in accordance with another exemplary embodiment of the present
invention. FIG. 20 only shows an abbreviated portion of the circuit
of the lower-impedance battery pack 450; it being understood that
the teachings of FIG. 20 may also be applicable to lower-impedance
battery pack 450.
[0125] In FIG. 20, speed control and discharge control may be
controlled via an intelligent device such as a microprocessor 2010
which resides in the tool. Each of the tool and battery pack
illustrate two additional contacts, control terminal 2017 and
contact 2021 on the pack, contacts 2019 and 2020 on the tool. The
microprocessor 2010 may receive sensing signals from a current
sensor 2015 to control current, and hence discharge rate, in the
battery pack. The microprocessor 2010 may also receive variable
resistance signals from a potentiometer 2020 that may be converted
to a voltage value to control speed in the tool. The microprocessor
2010 may further receive a signal from one or more temperature
sensors 2025 in the battery pack and/or tool (shown in FIG. 20 on
the tool side for convenience) to sense and control the battery
pack and/or tool temperature.
[0126] As an example of discharge control, if the current sensor
2015 senses battery power (e.g. I.sup.2/R) above a given threshold,
the current sensor 2015 may send a signal to the microprocessor
2010. The microprocessor 2010 then outputs a control signal, via
contact 2019 to control terminal 2017 and hence to FET 2030 such as
an N-channel MOSFET), to turn off MOSFET 2030 and thus de-energize
the battery pack. The control signal to the MOSFET 2030 may be a
signal to turn the FET ON or OFF, as described previously in FIGS.
13A-13D with supporting explanation in the VI graphs of FIGS. 14-15
and/or the motor current versus motor impedance graph of FIG. 16;
thus a detailed description of FET operations under the control of
microprocessor 2010 is omitted here for the sake of brevity.
[0127] For variable speed control, a measured variable resistance
from a voltage sense device such as a potentiometer 2020 may be
input to the microprocessor 2010 (with suitable A/D conversion, not
shown). The microprocessor 2010 can determine the voltage value
based on the variable resistance and can control speed accordingly
(via a control signal that is sent to the MOSFET 2030). Similarly,
based on a value sensed over the path between contacts 2023 and
2021 and sent by temperature sensor 2025, microprocessor 2010 may
send a signal to turn off the MOSFET 2030 if the sensed value is
outside of a given temperature range, for example. In all cases, a
single MOSFET 2030 may be utilized to perform both variable speed
control and discharge control.
[0128] Additional Over-Discharge Protection
[0129] FIG. 21 illustrates a detection circuit for providing
over-discharge protection in accordance with an exemplary
embodiment of the present invention. Alternatively, if the battery
circuitry contains intelligence that can determine that an internal
device has failed, the battery pack's intelligence could
communicate, to the charger, that it has failed and should not to
be charged.
[0130] Referring to FIG. 21, the lower-impedance battery pack may
have a fault detection circuit 2110 to determine if an active
resistance circuit 2120 has failed (i.e., a shorted FET). If a
fault is detected, the fault detection circuit 2110 drives a third
terminal, which may be embodied as a thermistor terminal 2130 of
thermistor 2125 to a high or low electrical state. When the battery
pack is placed in the charger, a microcontroller 2140 in the
charger senses this high or low state on the thermistor terminal
2130, and prevents the pack from being charged. Likewise, the fault
detection circuit 2110 could also drive a terminal 2130, such as a
pack ID terminal, to a high or low electrical state during a fault
condition. When the battery pack is placed in the charger, a
microcontroller 2140 in the charger senses this high or low state
on the pack ID terminal, and prevents the pack from being
charged.
[0131] In another implementation, the fault detection circuit 2110
could communicate a fault condition to the charger using some type
of data communications over the thermistor terminal 2130 or the
pack id terminal or the positive terminal of the battery pack. A
fault condition in the active resistance circuit 2120 could also be
detected by the charger sensing that a battery pack fuse 2145 has
opened when the battery is inserted into the charger.
[0132] The exemplary embodiments of the present invention being
thus described, it will be obvious that the same may be varied in
many ways. Such variations are not to be regarded as departure from
the spirit and scope of the exemplary embodiments of the present
invention, and all such modifications as would be obvious to one
skilled in the art are intended to be included within the scope of
the following claims.
* * * * *