U.S. patent application number 11/110407 was filed with the patent office on 2005-11-10 for switch reduction in a cordless power tool.
Invention is credited to Denning, Bruce S..
Application Number | 20050248320 11/110407 |
Document ID | / |
Family ID | 34935926 |
Filed Date | 2005-11-10 |
United States Patent
Application |
20050248320 |
Kind Code |
A1 |
Denning, Bruce S. |
November 10, 2005 |
Switch reduction in a cordless power tool
Abstract
A battery pack may include at least one battery cell, a
discharge switch coupled to the at least one battery cell, and
monitoring and control circuitry responsive to a position of a
trigger of an associated cordless power tool to provide a control
signal to the discharge switch. The discharge switch may be
responsive to the control signal to control a discharge current
provided to a load of the cordless power tool. The load may be a
motor driving an element of the cordless power tool.
Inventors: |
Denning, Bruce S.;
(Fallbrook, CA) |
Correspondence
Address: |
Scott R. Faber
Grossman, Tucker, Perreault & Pfleger, PLLC
55 South Commercial Street
Manchester
NH
03101
US
|
Family ID: |
34935926 |
Appl. No.: |
11/110407 |
Filed: |
April 20, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60568038 |
May 4, 2004 |
|
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|
Current U.S.
Class: |
320/141 |
Current CPC
Class: |
H01M 10/4257 20130101;
Y02E 60/10 20130101; B25F 5/00 20130101; Y10S 388/903 20130101;
H02J 7/0031 20130101; H02J 2007/0067 20130101; H02J 7/0029
20130101; H02J 7/0063 20130101 |
Class at
Publication: |
320/141 |
International
Class: |
H02J 007/02 |
Claims
What is claimed is:
1. A battery pack comprising: at least one battery cell; a
discharge switch coupled to said at least one battery cell; and
monitoring and control circuitry responsive to a position of a
trigger of an associated cordless power tool to provide a control
signal to said discharge switch, said discharge switch responsive
to said control signal to control a discharge current provided to a
load of said cordless power tool.
2. The battery pack of claim 1, wherein said load comprises a motor
to drive an element of said cordless power tool, said motor
receiving said discharge current controlled by said discharge
switch, said discharge switch controlling a speed of said element
driven by said motor by controlling said discharge current.
3. The battery pack of claim 1, wherein said control signal
comprises a pulse width modulated (PWM) signal and said discharge
switch is responsive to a duty cycle of said PWM signal to control
said discharge current.
4. The battery pack of claim 1, wherein said monitoring and control
circuitry monitors said discharge current and open said discharge
switch if said discharge current is greater than or equal to a
maximum discharge current threshold.
5. The battery pack of claim 1, wherein said discharge switch
comprises a field effect transistor (FET).
6. A cordless power tool comprising: a load; a trigger; and a
battery pack comprising at least one battery cell to provide power
to said load, said battery pack further comprising a discharge
switch coupled to said at least one battery cell, and monitoring
and control circuitry responsive to a position of said trigger to
provide a control signal to said discharge switch, said discharge
switch responsive to said control signal to control a discharge
current provided to said load.
7. The cordless power tool of claim 6, wherein said load comprises
a motor to drive an element of said cordless power tool, said motor
receiving said discharge current controlled by said discharge
switch of said battery pack, said discharge switch controlling a
speed of said element driven by said motor by controlling said
discharge current.
8. The cordless power tool of claim 7, further comprising speed
select circuitry responsive to said position of said trigger to
provide an input signal to said monitoring and control circuitry of
said battery pack.
9. The cordless power tool of claim 8, wherein said speed select
circuitry comprises a variable resistor in series with a resistor,
wherein a resistance value of said variable resistor is set in
response to said position of said trigger and is representative of
a desired speed of said element, and wherein a resistance value of
said resistor is representative of a maximum discharge current
rate.
10. The cordless power tool of claim 6, wherein said control signal
comprises a pulse width modulated (PWM) signal and said discharge
switch is responsive to a duty cycle of said PWM signal to control
said discharge current.
11. The cordless power tool of claim 6, wherein said monitoring and
control circuitry monitors said discharge current and opens said
discharge switch if said discharge current is greater than or equal
to a maximum discharge current threshold.
12. A method comprising: monitoring a position of a trigger of a
cordless power tool; and controlling a state of a discharge switch
of a battery pack in response to said position of said trigger to
control a discharge current provided to a load of said cordless
power tool.
13. The method of claim 12, wherein said load comprises a motor to
drive an element of said cordless power tool, said motor receiving
said discharge current controlled by said discharge switch of said
battery pack, said discharge switch controlling a speed of said
element driven by said motor by controlling said discharge
current.
14. The method of claim 12, further comprising: monitoring said
discharge current; and opening said discharge switch of said
battery pack if said discharge current is greater than or equal to
a maximum discharge current threshold.
15. The method of claim 12, further comprising providing a tool
identification signal to said battery pack once said battery pack
is coupled to said cordless power tool, said tool identification
signal representative of data particular to said cordless power
tool.
16. The method of claim of claim 15, wherein said data comprises a
maximum discharge current of said cordless power tool.
17. The method of claim of claim 15, wherein said data comprises a
thermal overload point of said cordless power tool.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of the filing date of
U.S. Provisional Application Ser. No. 60/568,038, filed May 4,
2004, the teachings of which are incorporated herein by
reference.
FIELD
[0002] The present disclosure relates to cordless power tools and,
more particularly, to reduction of switches in a cordless power
tool.
BACKGROUND
[0003] A wide variety of cordless power tools are available that
may be utilized in different applications such as construction
applications, fire and rescue applications, etc. Some examples of
cordless power tools include, but are not limited to, cordless
drills, cordless circular saws, cordless reciprocating saws,
cordless sanders, cordless screwdrivers, and flashlights. Cordless
power tools may utilize a rechargeable battery pack for providing
power to operate the tool. The rechargeable battery pack may be
readily removed from the cordless power tool and coupled to an
external battery charger for charging purposes.
[0004] The battery pack may include one or more battery cells. The
battery pack may also include monitoring circuitry to monitor
parameters such as cell voltage levels, discharge current, and
charging current. The battery pack may also include switches such
as a discharge switch which may be opened in response to the
monitoring circuitry detecting some overload condition. Another
control switch may be utilized in the cordless power tool to
control a level of discharge current supplied to a load of the
cordless power tool. For example, the control switch may be a speed
control switch to control the speed of an element of the cordless
power tool. This switch may be a relatively expensive switch
requiring overload protection. Accordingly, there is a need in the
art to eliminate the speed control switch yet still provide similar
functionality.
BRIEF SUMMARY OF THE INVENTION
[0005] According to one aspect of the invention, there is provided
a battery pack. The battery pack may include at least one battery
cell, a discharge switch coupled to the at least one battery cell,
and monitoring and control circuitry responsive to a position of a
trigger of an associated cordless power tool to provide a control
signal to the discharge switch, the discharge switch responsive to
the control signal to control a discharge current provided to a
load of the cordless power tool.
[0006] According to another aspect of the invention, there is
provided a cordless power tool. The cordless power tool may include
a load, a trigger, and a battery pack. The battery pack may include
at least one battery cell to provide power to the load. The battery
pack may further include a discharge switch coupled to the at least
one battery cell, and monitoring and control circuitry responsive
to a position of the trigger to provide a control signal to the
discharge switch. The discharge switch may be responsive to the
control signal to control a discharge current provided to the
load.
[0007] According to yet another aspect of the invention there is
provided a method. The method may include monitoring a position of
a trigger of a cordless power tool, and controlling a state of a
discharge switch of a battery pack in response to the position of
the trigger to control a discharge current provided to a load of
the cordless power tool.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Features and advantages of embodiments of the claimed
subject matter will become apparent as the following Detailed
Description proceeds, and upon reference to the Drawings, where
like numerals depict like parts, and in which:
[0009] FIG. 1 is a perspective view of a cordless power tool;
[0010] FIG. 2 is a diagram of a power supply system of the cordless
power tool of FIG. 1;
[0011] FIG. 3 is a diagram consistent with FIG. 2 where the load is
a motor driving an element of the cordless power tool;
[0012] FIG. 4 is another diagram a power supply system for the
cordless power tool of FIG. 1;
[0013] FIG. 5 is a diagram of an embodiment of the monitoring and
control circuitry; and
[0014] FIG. 6 is a flow chart of operations consistent with an
embodiment.
[0015] Although the following Detailed Description will proceed
with reference being made to illustrative embodiments, many
alternatives, modifications, and variations thereof will be
apparent to those skilled in the art. Accordingly, it is intended
that the claimed subject matter be viewed broadly.
DETAILED DESCRIPTION
[0016] FIG. 1 is a perspective view of a cordless power tool 100.
The cordless power tool 100 is illustrated as a cordless drill and
may be described as such in relation to embodiments herein.
However, the cordless power tool 100 may be any type of cordless
power tool including, but not limited to, a cordless circular saw,
a cordless reciprocating saw, a cordless sander, a cordless
screwdriver, and a flashlight. The cordless power tool may include
a rechargeable battery pack 102 for providing power to operate the
tool 100. The rechargeable battery pack 102 may be readily removed
from the cordless power tool 100 and coupled to an external battery
charger for charging purposes. The cordless power tool 100 may also
include a trigger 104. For the drill, a user may depress and
release the trigger 104 to control the speed of the chuck 142. For
other tools such as a flashlight, a user may position a trigger to
control a level of illumination from the flashlight.
[0017] FIG. 2 is a diagram of a power supply system 200 of the
cordless power tool of FIG. 1. The power supply system 200 may
include the battery pack 102, a load 240, the trigger 104, and tool
identification (ID) circuitry 230. As used in any embodiment
herein, "circuitry" may comprise, for example, singly or in any
combination, hardwired circuitry, programmable circuitry, state
machine circuitry, and/or firmware that stores instructions
executed by programmable circuitry.
[0018] The battery pack 102 may include one or more battery cells
203 to provide power for the system 200. The battery cells 103 may
be lithium ion cells in one embodiment. The battery pack 102 may
provide power to the load 240 via the discharge switch 209. In one
embodiment, the discharge switch may be a field effect transistor
(FET). The battery pack 102 may also include monitoring and control
circuitry 208. The monitoring and control circuitry 208 may measure
one or more of battery pack current, temperature, and cell voltage
levels for each battery cell.
[0019] The monitoring and control circuitry 208 may compare
measured values to associated threshold levels and identify an
overload condition if one of the measured quantities is greater
than or equal to the associated threshold level. For example, an
overload condition may be a discharge current greater than or equal
to a threshold representative of a maximum discharge current. In
another example, an overload condition may be a charging current
level to the battery cells 203 greater than or equal to a threshold
representative of a maximum charging current. In yet another
example, an overload condition may be a voltage level of a battery
cell greater than or equal to a voltage threshold. In yet another
embodiment, an overload condition may be a temperature of a
component greater than or equal to a temperature threshold. Upon
detection of an overload condition, the monitoring and control
circuitry 208 may provide an output control signal to protect
components of the power supply system 200. The output control
signal may be provided to one or more switches within the battery
pack 102 or may be provided as a control input to other circuitry
located outside the battery pack 102 via path 127. In one
embodiment, the output control signal may be provided to the
discharge switch 209 to open the switch 209 where the overload
condition is a discharge current from the battery cells 203 greater
than or equal to a maximum discharge current threshold.
[0020] The monitoring and control circuitry 208 may also be
responsive to the position of the trigger 104 to provide a control
signal to the discharge switch 209. The control signal may be a
pulse width modulated (PWM) signal 218 in one embodiment and the
discharge switch 209 may be responsive to the duty cycle of the PWM
signal 218 to control the discharge current. The PWM signal 218 may
operate at a fixed frequency, e.g., such as 5 to 10 kilohertz
(KHz). As the duty cycle of the PWM signal is increased, the ON
time of the discharge switch 209 may be increased and hence the
level of discharge current provided to the load 240 may be
increased. Similarly, as the duty cycle of the PWM signal is
decreased, the ON time of the discharge switch may be decreased and
hence the level of discharge current provided to the load 240 may
be decreased.
[0021] The tool ID circuitry 230 may provide a tool identification
signal to the monitoring and control circuitry 208. The tool
identification signal may be representative of data particular to
the cordless power tool such as a variety of power parameters of
the particular cordless power tool. For example, the tool
identification signal may specify a maximum discharge current of
the particular cordless power tool. As another example, the tool
identification signal may specify a thermal overload point of the
cordless power tool. The tool ID circuitry 230 may include
inexpensive passive components such as a paralleled resistor and
capacitor in one embodiment or a simple fixed resistor in another
embodiment. In addition, the tool ID circuitry 230 may provide a
useful secondary indication that the battery pack 102 has been
correctly plugged into the appropriate cordless power tool. In the
absence of a proper tool identification signal, the battery pack
102 may deny discharge thereby improving system safety.
[0022] FIG. 3 is a diagram of a power supply system 300 consistent
with the power supply system 200 of FIG. 2. Components of FIG. 3
similar to FIG. 2 are labeled as such and hence any repetitive
description is omitted herein for clarity. The load 240a in FIG. 3
may be a motor 340 configured to drive an element 142 through an
associated gear train (not illustrated). As one example, the
element 142 may be the chuck of the drill of FIG. 1 that holds a
drill bit. Advantageously, a conventional speed control switch that
may be located in the cordless power tool at the input side to the
motor 340 has been eliminated. In its place, the discharge switch
209 may control a discharge current and hence a speed of the
element 142 driven by the motor 340.
[0023] Speed select circuitry 316 may receive a signal from the
trigger 104 representative of a position of the trigger 104 and
hence a desired speed of the element 142 of the cordless power
tool. The speed select circuitry 316 may then provide an input
signal to the monitoring and control circuitry 208 of the battery
pack 102 representative of the desired speed. The monitoring and
control circuitry 208 may then provide a control signal to the
discharge switch 209 to control the speed of the element 142 by
controlling the discharge current provided to the motor 340.
[0024] In operation, a user of the cordless power tool may depress
the trigger 104 a desired amount to control the speed of the
element 142. In response to the position of the trigger 104, the
speed select circuitry 316 may provide an input signal to the
monitoring and control circuitry 208. The monitoring and control
circuitry 208 may include a PWM generator that modifies the duty
cycle of the PWM signal 218 in response to the input signal from
the speed select circuitry 316. The PWM signal 218 may operate at a
fixed frequency, e.g., such as 5 to 10 KHz. As the duty cycle of
the PWM signal is increased, the ON time the discharge switch 209
may be increased and hence the speed of the element 142 of the
cordless power tool is also increased. Similarly, as the duty cycle
of the PWM signal is decreased, the ON time of the discharge switch
209 may be decreased and hence the speed of the element 142 of the
power tool may be decreased. In one example, the duty cycle of the
PWM signal may vary from about 10% (slow speed) to 75% (fast
speed).
[0025] FIG. 4 is another diagram a power supply system for the
cordless power tool of FIG. 1. The discharge switch 209 may be an
FET Q1. The FET Q1 may be a metal oxide semiconductor field effect
transistor (MOSFET) such as a p-channel MOSFET (PMOS) or n-channel
MOSFET (NMOS). The battery pack 102a may also include a plurality
of battery cells 203-1, 203-2, 203-(n-1), and 203-n. The battery
pack 102a may supply power to a number of loads including a load
240b illustrated as a motor winding. A diode 410 may be connected
in parallel with the FET Q1 to permit charging current flow into
the battery cells 203-1, 203-2, 203-(n-1), and 203-n and to prevent
discharge current from the battery cells. The battery pack 102a may
include optional status indicators 406 to provide indication
signals from the monitoring and control circuitry 208 of various
detected conditions.
[0026] The speed select circuitry 316a may include a variable
resistor 454 in series with another resistor 452. The variable
resistor 454 may be a potentiometer. A resistance value of the
variable resistor 454 may be set in response to the position of the
trigger 104. The resistance value of the variable resistor 454 may
therefore be representative of a desired speed of the element 142
(see FIG. 3). The resistance value of the resistor 452 may be
representative of a maximum discharge current rate. This speed
select circuitry 316a allows for inexpensive discharge limiting
and/or variable power control for low cost cordless power tools
such as flashlights. A third battery pack terminal 422 may be used
by the monitoring and control circuitry 208 to receive information
from the speed select circuitry 316a on the desired speed. In turn,
the monitoring and control circuitry 208 may provide a PWM signal
218 at a particular duty cycle to achieve the desired speed.
[0027] FIG. 5 is one embodiment 208a of the monitoring and control
circuitry 208. The monitoring and control circuitry 208a may
include a switch network 502, an analog to digital converter (ADC)
504, a processor 506, a driver 508, protection circuitry 524, and a
PWM generator 510. The processor 506 may instruct the switch
network 502 to select a particular battery cell 203-1, 203-2,
203-(n-1), or 203-n for monitoring. Individual analog cell voltage
levels for each battery cell may then be sampled through the switch
network 502. The sampled analog signals may then be converted into
associated digital signals by the ADC 504 and provided to the
processor 506. The processor 506 therefore receives digital signals
from the ADC 504 representative of the voltage level of each
battery cell 203-1, 203-2, 203-(n-1), and 203-n and may make
comparisons to various voltage thresholds.
[0028] For example, during charging of the battery pack 102, the
monitoring and control circuitry 208a may monitor the cell voltage
levels to determine if any of the cell voltage levels exceeds an
over voltage threshold. If such a threshold is exceeded, the
processor 506 may instruct some preventative action to be taken. In
one instance, such preventative action may be to stop charging by
providing a signal to the driver 508 to drive a particular switch
open. In another example, during discharging of the battery pack
102, the monitoring and control circuitry 208a may monitor the cell
voltage levels to determine if any of the cell voltage levels is
less than an under voltage threshold. If such an under voltage
threshold level is reached, the processor 506 may instruct some
preventative action to be taken. In one instance, such preventative
action may be to stop discharging by providing a signal to the
driver 508 to drive a particular switch open.
[0029] The processor 506 may also receive other signals from the
protection circuitry 524. The protection circuitry 524 may
generally monitor the current flowing into (charging mode) or out
of (discharging mode) the battery pack 102 for various current
overload conditions, e.g., over current or short circuit
conditions, and alert the processor 506 of such conditions so that
preventative action can be taken. For instance, a current sensing
element such as sense resistor 404 (FIG. 4) may provide the
protection circuitry 524 with a signal representative of the
current level to or from the battery pack as that current level
varies. The protection circuitry 524 may compare the current level
to various thresholds and provide a signal to the processor
notifying the processor of an over current condition or a short
circuit condition so the processor 506 can take preventative
action.
[0030] The PWM generator 510 may receive a signal from the speed
select circuitry 316, 316a and provide an output PWM signal to the
discharge switch such as FET Q1 (see FIG. 4). The processor 506 may
allow the PWM signal to control the state of the discharge switch
until an overload condition occurs. When the overload condition
occurs, e.g., excessive discharge current, the processor 506 may
disable the PWM generator 510 and may instruct the driver 508 to
open the discharge switch. As such, the monitoring and control
circuitry 208a can advantageously enable the PWM generator 510 to
control the discharge switch 209 when appropriate and it can also
disable the PWM generator 510 and open the discharge switch if an
overload condition is detected.
[0031] FIG. 6 illustrates operations 600 according to an
embodiment. Operation 602 may include monitoring a position of a
trigger of a cordless power tool. Operation 604 may include
controlling a state of a discharge switch of a battery pack in
response to the position of the trigger to control a discharge
current provided to a load of the cordless power tool.
[0032] Advantageously, elimination of a conventional speed control
or load control switch provides cost savings and simplifies
configuration complexity. Such speed or load control may be
accomplished by a discharge switch in the battery pack. In
addition, a cordless power tool may include tool ID circuitry. The
tool ID circuitry may enable the battery pack to receive data about
a particular tool that it may otherwise not be aware. Such data may
include data of the maximum discharge current of the particular
cordless power tool or a thermal overload point of the particular
tool to name a couple. In addition, the tool ID circuitry could
provide a useful secondary indication that the battery pack has
been correctly plugged into the appropriate cordless power tool. In
the absence of a proper tool identification signal, the battery
pack could deny discharge thereby improving system safety
[0033] The terms and expressions which have been employed herein
are used as terms of description and not of limitation, and there
is no intention, in the use of such terms and expressions, of
excluding any equivalents of the features shown and described (or
portions thereof, and it is recognized that various modifications
are possible within the scope of the claims. Other modifications,
variations, and alternatives are also possible.
* * * * *