U.S. patent application number 14/267072 was filed with the patent office on 2014-11-06 for method and system for cooling a device.
This patent application is currently assigned to Control Techniques Limited. The applicant listed for this patent is Control Techniques Limited. Invention is credited to Simon David HART-SHORT, John Paul KURPIEWSKI.
Application Number | 20140326442 14/267072 |
Document ID | / |
Family ID | 48627257 |
Filed Date | 2014-11-06 |
United States Patent
Application |
20140326442 |
Kind Code |
A1 |
KURPIEWSKI; John Paul ; et
al. |
November 6, 2014 |
METHOD AND SYSTEM FOR COOLING A DEVICE
Abstract
There is described a method (20) of cooling a device generating
heat. The method includes (21) monitoring a temperature associated
with the device. The method also includes (25) automatically
operating a cooling means at a first rate if the monitored
temperature rises above a first temperature threshold. The method
also includes (26) automatically operating the cooling means at a
second increased rate if the monitored temperature rises above a
second temperature threshold. There is also described a system (10)
for cooling a device (16) generating heat. The system (10)
comprises means (18) for monitoring a temperature associated with
the device (10), cooling means (14), and a controller (12) for
operating the cooling means (14) at various rates. The controller
(12) is arranged to automatically operate the cooling means (14) at
a first rate if the temperature rises above a first temperature
threshold. The controller (12) is further arranged to automatically
operate the cooling means (14) at a second increased rate if the
temperature rises above a second temperature threshold. According
to the invention, the point at which the monitored temperature
reaches the second threshold may be delayed by operating the
cooling means at a first rate prior to operating the cooling means
at an increased second rate. In applications in which short periods
of relatively high heat generation are experienced, the invention
may delay the point at which the cooling means needs to be operated
at a high level, reducing the overall noise generation of the
cooling means.
Inventors: |
KURPIEWSKI; John Paul;
(Welshpool, GB) ; HART-SHORT; Simon David;
(Welshpool, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Control Techniques Limited |
Newtown |
|
GB |
|
|
Assignee: |
Control Techniques Limited
Newtown
GB
|
Family ID: |
48627257 |
Appl. No.: |
14/267072 |
Filed: |
May 1, 2014 |
Current U.S.
Class: |
165/287 |
Current CPC
Class: |
H02K 9/00 20130101; H05K
7/2089 20130101; G05B 15/02 20130101; G06F 1/206 20130101 |
Class at
Publication: |
165/287 |
International
Class: |
F28F 27/00 20060101
F28F027/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 3, 2013 |
GB |
1308014.8 |
Claims
1. A method of cooling a device generating heat, comprising:
monitoring a temperature associated with the device; automatically
operating a cooling means at a first rate if the monitored
temperature rises above a first temperature threshold; and
automatically operating the cooling means at a second increased
rate if the monitored temperature rises above a second temperature
threshold, wherein the first and/or the second temperature
threshold is a function of a duration and/or an intensity of a peak
power output of the device.
2. The method of claim 1, further comprising: automatically
decreasing the rate of the cooling means if the monitored
temperature drops below the second temperature threshold.
3. The method of claim 2, wherein the rate of the cooling means is
automatically decreased to the first rate if the monitored
temperature drops below the second temperature threshold.
4. The method of claim 1, further comprising: automatically
decreasing the rate of the cooling means if the monitored
temperature drops below the first temperature threshold.
5. The method of claim 4, wherein the rate of the cooling means is
automatically decreased to zero if the monitored temperature drops
below the first temperature threshold.
6. The method of claim 1, wherein the rate of the cooling means is
automatically increased from zero to the first rate if the
monitored temperature rises above the first temperature
threshold.
7. The method of claim 1, wherein the rate of the cooling means is
automatically increased from the first rate to the second increased
rate if the monitored temperature rises above the second
temperature threshold.
8. The method of claim 1, wherein the rate of the cooling means is
automatically increased to a maximum rate if the monitored
temperature rises above the second temperature threshold.
9. The method of claim 1, wherein the first/second rate of the
cooling means is substantially constant if the monitored
temperature is between the first and second temperature thresholds,
or above the second temperature threshold.
10. The method of claim 1, wherein first/second rate of the cooling
means is varied if the monitored temperature is between the first
and second temperature thresholds, or above the second temperature
threshold.
11. The method of claim 1, wherein the second temperature threshold
is higher than the first temperature threshold.
12. The method of claim 1, wherein the second rate of the cooling
means is a maximum rate of the cooling means.
13. The method of claim 1, further comprising; monitoring a current
associated with the device; and automatically operating the cooling
means at the second increased rate if the monitored current rises
above a current threshold.
14. The method of claim 13, wherein the current threshold is from
about 70% to about 90% of a maximum operating current of the
device.
15. The method of claim 1, wherein the first rate is from about 10%
to about 25% of the second rate.
16. The method of claim 1, wherein the first temperature threshold
is from about 80% to about 90% of the second temperature
threshold.
17. The method of claim 1, wherein the first rate and/or the second
rate is a function of a duration and/or an intensity of a peak
power output of the device.
18. The method of claim 1, wherein the first temperature threshold
is independent of the device.
19. A machine-readable medium having instructions stored thereon,
wherein when read by a machine the instructions are configured to
execute the steps of claim 1.
20. A system for cooling a device generating heat, comprising:
means for monitoring a temperature associated with the device;
cooling means; and a controller for operating the cooling means at
various rates, wherein the controller is arranged to automatically
operate the cooling means at a first rate if the temperature rises
above a first temperature threshold, wherein the controller is
further arranged to automatically operate the cooling means at a
second increased rate if the temperature rises above a second
temperature threshold, and wherein the first and/or the second
temperature threshold is a function of a duration and/or an
intensity of a peak power output of the device.
21. The system of claim 20, wherein the device is a motor drive,
and/or the temperature monitoring means is a thermistor, and/or the
cooling means is a fan.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit and priority of Great
Britain Patent Application No. 1308014.8 filed May 3, 2013. The
entire disclosure of the above application is incorporated herein
by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a method of cooling a
heat-generating device, and in particular to a method of cooling a
heat-generating device through controlled use of cooling means such
as a fan. The invention also relates to a system arranged to cool a
heat-generating device.
BACKGROUND TO THE INVENTION
[0003] Motor drives or simply drives are used to control the flow
of power delivered to electric motors for their operation. During
high-intensity bursts of output current, for example when the motor
is being operated at its rated threshold, the heat generated by the
motor drive can become quite high, even for a burst or pulse of
relatively short duration (such as of the order of ten seconds or
so). Increased heat generation can cause a motor or its drive to
operate above its safety threshold, which if sustained can cause
damage to the motor and/or its surroundings.
[0004] A typical method of extracting heat generated in a motor is
to use a fan to cool the drive. Fan cooling, whilst relatively
efficient, generates a substantial amount of noise. In certain
applications, the noise generated by a fan can be especially
undesirable.
[0005] For example, in theatre applications, noise levels must be
kept to a minimum to avoid interfering with the filming, lighting
or stage movements, even when a motor is in use. In another example
application, motors used to operate lifts or elevators are often
located at the top of multi-storey buildings, where property is
typically more expensive. Because of the premium charged for such
properties, the need to keep noise levels to a minimum is therefore
particularly desirable in such locations. Thus, given the proximity
of such properties to the cooling system or fan, it is desirable to
reduce the noise level of the fan to a minimum or at least
acceptable level without also compromising the cooling of the
motor.
[0006] The present invention seeks to address this and other
deficiencies encountered in the prior art.
SUMMARY OF THE INVENTION
[0007] In accordance with a first aspect of the invention, there is
provided a method of cooling a device generating heat. The method
comprises monitoring a temperature associated with the device. The
method also comprises automatically operating a cooling means at a
first rate if the monitored temperature rises above a first
temperature threshold. The method also comprises automatically
operating the cooling means at a second increased rate if the
monitored temperature rises above a second temperature
threshold.
[0008] The device may be any device capable of generating heat. For
example, the device may be an electric motor drive. In particular,
if left unchecked the sustained heat generation may be such that
damage is caused to the device. The monitored temperature may be
monitored substantially continuously or periodically. The
temperature may be an ambient air temperature in close proximity to
the device. In other embodiments, the measured or monitored
temperature may be a measured/monitored temperature of a particular
component of the device, such as a heat sink, and may be designated
an operating temperature of the device. Various types of measuring
equipment may be used to monitor the temperature, such as a
thermistor, a thermometer, etc. In some embodiments, the point at
which the temperature climbs above the first threshold may be
measured using a first temperature measuring means, whilst the
point at which the temperature climbs above the second threshold
may be measured using a second temperature measuring means.
Alternatively, they may be measured using common means.
[0009] The cooling means may take various different forms and in a
preferred embodiment is a cooling fan or other airflow generating
means design to blow, suck or otherwise draw air over the device.
In another embodiment, the cooling means may be a pump arranged to
push or suck a cooling liquid such as cool water or some other
coolant through a jacket. The jacket may be adjacent the device (or
in particular may surround the device) and thereby may be arranged
to extract heat from the device as the device is being run. The
rate of the cooling means may therefore be a speed at which a fan
is operated, or a pumping rate at which a liquid is pumped through
a jacket. Other types of cooling means are contemplated, such as
any cooling means capable of being operated at different rates.
[0010] The first rate may be qualified as a relatively low rate,
and for example may be from about 10% to about 25% of a maximum
rate of the cooling means. In one embodiment, the first rate is
from about 10% to about 85% of a maximum rate of the cooling means.
The second rate may be qualified as a relative high rate and for
example may be from about 50% to about 100% of the maximum rate. In
one embodiment, the second rate is from about 85% to about 100% of
a maximum rate of the cooling means. These rates may depend on
various factors, such as the operating characteristics of the
cooling means. In one embodiment, the second rate may be the
maximum rate of the cooling means. For example, the maximum rate
may be a maximum operating or maximum `safe` rate of the cooling
means. The rate of the cooling means may be automatically increased
to a maximum rate if the monitored temperature rises above the
second temperature threshold. The rate of the cooling means may
also be automatically increased from the first rate to the second
increased rate if the monitored temperature rises above the second
temperature threshold.
[0011] According to the above method, the point at which the
monitored temperature reaches the second threshold may be delayed
by operating the cooling means at a first rate prior to operating
the cooling means at an increased second rate. In applications in
which short periods of relatively high heat generation are
experienced, this can be advantageous as it may delay the point at
which the cooling means needs to be operated at a high level,
reducing the overall noise generation of the cooling means.
Furthermore, by operating the cooling means at a first rate before
it is actually thermally necessary to activate the cooling means,
the duration of time over which the cooling means is operated at a
second, higher rate (which may be a maximum rate) is reduced. This
for example may help to conserve power if operating the cooling
means on maximum power is particularly resource intensive. It may
also entirely avoid the need to operate the cooling means at the
second, increased rate if the second temperature threshold is not
reached, thereby reducing the likelihood of the device
malfunctioning due to excessive heat generation.
[0012] The method may further comprise automatically decreasing the
rate of the cooling means if the monitored temperature drops below
the second temperature threshold. In particular, the rate of the
cooling means may be automatically decreased to the first rate if
the monitored temperature drops below the second temperature
threshold. Advantageously, the noise output from the cooling means
may be minimised by reducing the rate of the cooling means when the
temperature drops below the second threshold. Furthermore, cooling
of the heat-generating device may be maintained at a relatively low
rate so as to minimise noise generation of the cooling means
without compromising on the cooling of the device.
[0013] The method may further comprise automatically decreasing the
rate of the cooling means if the monitored temperature drops below
the first temperature threshold. Thus, if the temperature drops
below the first, `warning` threshold, the system may be configured
such that the cooling rate may be reduced further and in fact the
cooling means may be switched off entirely, to conserve power.
Thus, the rate of the cooling means may be automatically decreased
to zero if the monitored temperature drops below the first
temperature threshold. The rate of the cooling means may be
automatically increased from zero to the first rate if the
monitored temperature rises above the first temperature threshold.
Below the first temperature, there may be no thermal requirement to
operate the cooling means, thereby saving on power.
[0014] In the embodiments described herein, increasing or
decreasing the cooling rate may be a substantially instantaneous
change or else may be effected over a certain timespan. Varying the
cooling rate over a non-trivial time period, according to the
measured temperature, would prevent the system rapidly switching
the cooling means from one rate to another, and would provide a
more gradual rate of change in the cooling rate, as well as more
efficient noise management.
[0015] The first and second rates may be pre-set by the controller,
or else may be dynamically configured. The first and second rates
may represent optimum cooling rates existing between the first and
second thresholds, and above the second threshold. For example, the
first rate may be selected such that the noise generated by the
cooling means is at an acceptable level (e.g. below a certain noise
threshold) whilst providing sufficient cooling to the device to at
least appreciably delay the onset of the second temperature
threshold given a constant power output. The second cooling rate
may be selected such that maximum cooling power is delivered to the
device, to minimise the time spent above the second temperature
threshold. This may be the case for example if the slope of the
temperature increase is relatively high, and if continued
temperature increase at this rate may present a danger to the
device. Alternatively, noise considerations may also be taken into
account when the temperature is above the second threshold, such
that a compromise is arrived at between the noise output and the
cooling efficiency. For example, it may be determined by the system
that the rate of change of the temperature as it passes the second
threshold is relatively low. Therefore, the system may only
moderately further increase the cooling rate to avoid operating the
cooling means at a substantially increased or maximum rate. More
particularly, the system may operate the cooling means at a rate
selected such that the slope of the temperature, given constant
power output, will reverse itself.
[0016] The first rate of the cooling means may be substantially
constant if the monitored temperature is between the first and
second temperatures thresholds. This may be a default setting of
the device, or else may be dynamically configured by the
controller. Similarly, the second rate of the cooling means may be
substantially constant if the monitored temperature is above the
second temperature threshold. Alternatively, there may be a
quantisation in the cooling rate increase, such that the cooling
rate at which the cooling means is operated may be staged as a
function of time and/or measured temperature of the device. For
example, the rate of the cooling means may be ramped so as to
further reduce overall noise output. For example, once the first
temperature threshold has been reached, the rate of the cooling
means may be gradually increased or ramped up to the first rate.
The same may be true for the second rate once the second
temperature threshold has been reached. The ramping may be based on
the rate of change of the temperature, or other factors such as an
output current of the device.
[0017] In addition to monitoring a temperature associated with the
device, a current associated with the device may also be monitored.
The cooling means may be operated at the second increased rate if
the monitored current rises above a current threshold. In one
embodiment, the current threshold may be from about 70% to about
90% of a maximum operating current of the device. Preferably the
current threshold may be about 75% of a maximum operating current
of the device.
[0018] This feature therefore provides a safety mechanism for the
system. For example, irrespective of the monitored temperature, if
the monitored current rises above a pre-set threshold, then the
cooling means may need to be operated at an increased or a maximum
rate to protect the device. The current may be measured using
typical means known in the art, for example an ammeter. Other
current-measuring devices may be used.
[0019] In addition to its temperature, other parameters associated
with the device may be monitored. This may include for example
radiation flux, fuel flow, fluid flow such as hot air flow, latent
heat of such a flow, etc. Measuring such additional parameters may
allow the system to more accurately determine the rate of change of
the temperature and may therefore allow the system to adjust the
rate of change of the cooling means accordingly, with greater
accuracy. The measurement of such additional parameters may also
serve as further safety mechanisms. For example, if it is
determined that hot air flow has reached a critical level then the
cooling means may be operated at a maximum rate.
[0020] The first rate and/or the second rate may be a function of a
duration and/or an intensity of a peak power output of the device.
Thus, the system may adjust the cooling rate based on how long or
at what the level it is known the peak power output will be
experienced. The system may also adjust the rate at which the
desired cooling rate will be reached. For example, if the peak
power output will be experienced for a relatively long period of
time, the system may be configured such that the cooling means is
operated at the first and second cooling rates as soon as the first
and second temperature thresholds, respectively, are reached.
Alternatively, if the peak power output is anticipated as lasting
for a relatively short duration, and/or if the peak output current
is relatively low, then the rate of the cooling means may be
increased only incrementally as and when the first and second
temperature thresholds are reached. Furthermore, the first and/or
second temperature thresholds may be a function of a duration
and/or an intensity of a peak power output of the device. The first
temperature threshold may be independent of the device. Thus, the
first temperature threshold may be set by the programmer and may be
a function of the noise generated by the cooling means when under
operation. The second temperature threshold may be
device-dependent, and may be a function of the operating
characteristics of the device. For example, in the case of a motor,
the second temperature threshold may depend on the motor's rated
threshold.
[0021] In any of the above described embodiments, there may be a
delay incorporated into the algorithm or method such that the
cooling rate is not varied until the temperature reaches a
predetermined point above/below either temperature threshold. Thus,
hysteresis may be incorporated into the method so as to avoid the
cooling means being rapidly operated at two different rates as the
temperature fluctuates above and below a temperature threshold. The
hysteresis may be of the order of 1% of the threshold.
[0022] In a second aspect of the invention, there is provided a
machine-readable medium having instructions stored thereon. When
read by a machine, the instructions are configured to execute the
steps of any of the above methods. Thus, the instructions may be
stored for example on a CD-ROM or other readable disc, a flash
disk, a portable disk drive, or any other medium capable of being
read by a computer or other machine. The instructions may be stored
in firmware embedded in the device itself. The instructions may be
loaded onto a computer configured to control and operate the
cooling means at various rates.
[0023] In a third aspect of the invention, there is provided a
system for cooling a device generating heat. The system includes
means for monitoring a temperature associated with the device. The
system also includes cooling means. The system also includes a
controller for operating the cooling means at various rates. The
controller is arranged to automatically operate the cooling means
at a first rate if the temperature rises above a first temperature
threshold. The controller is further arranged to automatically
operate the cooling means at a second increased rate if the
temperature rises above a second temperature threshold. In one
particular embodiment, the device is a motor drive, and/or the
temperature monitoring means is a thermistor, and/or the cooling
means is a fan.
[0024] Other features of the invention are set out below. Any of
the below features may be combined with the above embodiments by
making the appropriate changes.
[0025] A general aim of the invention is to postpone the need for a
product cooling fan to be turned on to full speed when the product
is used for example in typical theatre applications where fan noise
must be minimised. As part of the thermal management of the
product, the invention may increase the time taken for a
temperature of a heat sink to reach a threshold at which a fan must
be turned on to full speed. This may be achieved by turning the
cooling fan on at a low speed once the heat-sink temperature has
increased to above a lower threshold. This may be done in order to
increase the cooling of the product, and thus reduce the rate at
which the heat sink temperature rises given constant power
dissipation, which in turn delays the point at which the cooling
fan needs to be turned on to full speed. In many theatre
applications, this delay would prevent the cooling fan from ever
being turned on to full speed as the product generally provides
output power for short intervals between which the product will
cool down. The invention may increase the rate of cooling when the
product has stopped providing output power, as the fan may be
operating at a reduced but non-zero rate until the heat-sink
temperature has dropped below the lower threshold. Thus, the
heat-sink may be already cooler when the product is next required
to provide output power.
[0026] In a particular embodiment, the thermal management system
has two inputs: a heat-sink temperature measured using a
thermistor; and a device for measuring the peak output current from
the drive. The thermal management system may use two temperature
thresholds: a `low temperature threshold` used to trigger the
action of the fan turning at low speed; and a `product dependent
threshold` used to trigger the action of the fan turning at full
speed. The low temperature threshold may provide the `theatre/quiet
mode` function trigger. It may be possible for the `low temperature
threshold` to be user selectable. The product dependent threshold
may be determined for each product based on the need to provide
thermal protection.
[0027] The increase in cooling rate may increase the time between
the heat-sink temperature rising from the low temperature threshold
to the product dependent threshold. The fan speed may be increased
to its maximum speed when the temperature is above the product
dependent threshold to provide thermal protection for the product.
The fan at full speed is too loud for certain applications such as
those within theatres. Although the invention may not prevent the
temperature rising to above the product dependent threshold, it
will delay this point. The delay is intended to prevent the fan
having to be set to full given a specific operating duty often
experienced in theatre applications. Thus, by decoupling the
principle of device thermal safety from that of noise reduction,
the present invention is able to satisfy both in an improved
manner.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Preferred embodiments of the invention will now be described
in connection with the accompanying drawings, of which:
[0029] FIG. 1 is a block diagram of a system in accordance with a
first embodiment of the invention;
[0030] FIG. 2 is a flowchart showing the steps taken by a method in
accordance with a first preferred embodiment of the invention
[0031] FIG. 3 is a flowchart showing the steps taken by a method in
accordance with a second preferred embodiment of the invention;
[0032] FIG. 4 is a graph showing temperature management of a device
in accordance with a method of the prior art;
[0033] FIG. 5 is a first graph showing temperature management of a
device in accordance with a preferred embodiment of the invention;
and
[0034] FIG. 6 is a second graph showing temperature management of a
device in accordance with a preferred embodiment of the
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0035] The present invention seeks to provide an improved
algorithm/method for operating a cooling means to cool a device
generating heat. Whilst various embodiments of the invention are
described below, the invention is not limited to these embodiments,
and variations of these embodiments may well fall within the scope
of the invention which is to be limited only by the appended
claims.
[0036] FIG. 1 is a block diagram of a system 10 according to a
preferred embodiment of the invention. System 10 comprises a
controller 12, a cooling means 14, a heat-generating device 16, a
temperature measuring device 18 and a current sensing device 11. In
the present embodiment, cooling means 14 is a fan or other similar
airflow generating means arranged to direct airflow towards
heat-generating device 16. Other types of cooling means are
envisaged. For example, cooling means 14 may comprise a jacket or
other insulation surrounding device 16 and through which a coolant
may be pumped. Heat-generating device 16 may be an electric motor
drive, and temperature measuring means may be a thermistor arranged
in proximity to heat-generating device 16 so as to monitor or
measure a temperature associated with heat-generating device 16.
For example, thermistor 18 may be arranged to measure a temperature
of a heat sink of heat-generating device 16, or else an operating
temperature of device 16 generated when device 16 is in
operation.
[0037] Controller 12 is arranged to control a cooling rate of
cooling means or fan 14. For example, controller 12 may be arranged
to control a speed at which fan 14 operates. If cooling means 14
comprises a jacket or other insulation surrounding device 16, then
controller 12 may be arranged to control a flow rate of a fluid
such as a coolant within the jacket.
[0038] Current-sensing device 11 is also included and is used to
measure a current associated with device 16. Both thermistor 18 and
current-sensing device 11 are in communication with controller 12
such that readings and measurements taken with thermistor 18 and
current sensing device 11 may be transmitted to controller 12 for
controller 12 to process and act thereon.
[0039] FIG. 2 is a flowchart illustrating the steps taken by a
method 20 according to a preferred embodiment of the invention, for
example using system 10. This method may be made active or inactive
by a user of device 16; for example the method may be part of a
mode of operation of device 16 that may be toggled on or off. At
step 21, a temperature associated with device 16 is measured or
otherwise monitored. At step 22, controller 12 determines whether
the measured temperature is less than a first temperature threshold
T1. T1 may be independent of heat-generating device 16. At step 23,
if the measured temperature is less than T1, the fan speed of fan
14 is set to zero. This represents a state in which the heat
generated by device 16 is not sufficient so as to warrant cooling.
Thus, fan 14 may be switched off and noise levels kept to a minimum
as a result.
[0040] If the measured temperature is greater than T1 then, at step
24, controller 12 determines whether the measured temperature is
less than T2. T2 may represent a device-dependent temperature
threshold. For example, T2 may be a product-dependent threshold
above which the heat generated by device 16 is dangerous for device
16 if the temperature level is sustained. If T1>T<T2, then at
step 25 controller 12 sets the speed of fan 14 to a relatively low
speed. A low speed may be a speed at which little or at least
acceptable levels of noise are generated by fan 14 and at which a
minimum of cooling power is provided by fan 14, to reduce the rate
of increase of the temperature. This state represents a state in
which cooling of device 16 is not actually required from a safety
perspective, and yet a state in which the temperature is closer to
the critical threshold T2. Activating fan 14 at step 25 delays the
point in time at which T2 will be reached.
[0041] At step 26, controller 12 determines whether the temperature
has risen above T2, and if so then the fan speed is set to a
maximum (or relatively high) speed so as to reduce the risk of
damage to device 16. In this state, whilst the noise levels of fan
14 are relatively high, the high speed of fan 14 helps ensure that
the temperature will drop below T2 as rapidly as possible.
[0042] T1 and T2 may be set by engineers to protect the motor
drive, and T1 may further be set or altered by the user.
[0043] FIG. 3 is a flow diagram showing an alternative embodiment
of the present invention. The method 30 according to FIG. 3 is
similar to that of FIG. 2 except for the addition of current
measuring steps. At step 31, if it is determined that T<T1,
controller 12 first checks that the operating current of device 16
is below a critical threshold Ic (step 32) before setting the fan
speed to off (step 33). If the current is above critical threshold
Ic, then the fan speed may be set a maximum power (step 34). This
is useful if the temperature of device 16 is not increasing at a
rapid rate but if device 16 is nonetheless providing a high output
power, and thus serves as a safety mechanism. The same steps 35-38
may be taken when it is determined that T1<T<T2. If T>T2,
the fan speed may be set to a maximum speed as in method 20.
Current sensing device 11 may be continuously active, such that
even if controller 12 is not measuring the temperature of device 16
then the fan speed may nonetheless be controlled as a function of
the operating current.
[0044] It should be noted that the flowcharts of FIG. 2 and FIG. 3
are merely representative of particular methods of operation of the
cooling means. Other steps may be taken in-between the steps listed
in FIGS. 2 and 3. For example, in FIGS. 2 and 3, when T is between
T1 and T2, the fan speed may be maintained at a relatively constant
level. Alternatively, controller 12 may measure the gradient of the
temperature curve (by taking multiple readings) and may adjust the
fan speed accordingly. For example, if controller 12 determines
that the temperature is increasing relatively rapidly as it climbs
above T1, then the fan speed may be increased accordingly (perhaps
to a medium or intermediate fan speed). Additionally, the fan speed
may be subjected to hysteresis (for example of the order of 1% of
the threshold) such that if it is determined that the temperature
rises above or drops below a temperature threshold such as T1 or
T2, then the change in fan speed may incorporate a delay to prevent
the rate of change of the fan speed varying too rapidly.
[0045] The table below describes the actions taken by controller 12
based on measured temperature and current, according to a
particular, exemplary embodiment of the invention. An "X" denotes
that the state is independent of the system conditions.
TABLE-US-00001 Device temperature Output current measurement
measurement Resulting action Below low Below 75% Fan is off
temperature maximum drive threshold T1 output current Above low X
Fan is at the low speed unless other temperature state conditions
are met threshold T1 and below critical or product dependent
threshold T2 Above critical or X Fan is full on for at least 20
product dependent seconds threshold T2 X Above 75% Fan is full on
for at least 20 maximum drive seconds output current
[0046] FIG. 4 is a graph showing a temperature profile as a
function of time, in accordance with a prior art method of cooling
a device. When the device is not being used (or else drawing little
power), the fan or other cooling means is off. During a period of
high output current, the temperature of the device rises steadily
to a critical temperature threshold T2. Above this threshold, the
heat levels generated by the device may be detrimental to the
device, and so the fan switched on to a maximum power to cool the
device. Even though the period of high output current is relatively
short, the rapid increase in temperature is sufficient to require
the fan being turned on to a maximum level to avoid damage to the
device. Such a maximum level generates substantial noise.
[0047] A temperature profile according to the inventive
algorithm/method described herein is illustrated in FIGS. 5 and
6.
[0048] In FIG. 5, during a period of operational use, but before
T1, the fan is off. Above T1, the fan is set to a low speed which
delays the point at which the temperature reaches T2. Thus, it can
be seen that the fan is switched on before it being thermally
necessary (e.g. before the temperature reaches a critical,
device-dependent level identified by T2). However, this delay is
sufficient to avoid the need to operate the fan at a maximum rate,
thereby reducing the noise generated by the fan.
[0049] FIG. 6 is similar to FIG. 5 except that whilst the
temperature does reach T2 and thus the fan is eventually set to
maximum power, the duration of this maximum power is reduced due to
the fan being set to a low speed before the temperature reaches T1.
Thus, the time period during which the fan speed generates
excessive levels of noise is reduced when compared to the prior
art.
[0050] It should be noted that these temperature profiles are
merely exemplary profiles and are used to highlight in simple terms
the effect and advantages of the present invention. The profiles
may vary depending on many factors, such as the type of device
being cooled, the settings of T1 and T2, the different speeds at
which the fan is set when the temperature rises above/drops below
the thresholds, etc.
[0051] Any feature of the above-described embodiments may be
combined with the features of another embodiment, by making the
appropriate changes. Whilst the invention has been described in
connection with preferred embodiments, it is to be understood that
the invention is not limited to these embodiments, and that
alterations, modifications, and variations of these embodiments may
be carried out by the skilled person without departing from the
scope of the invention.
* * * * *