Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
SLEEP MODE FOR AN AIR DRYER
BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
[0001] The present invention relates to railway air system air dryers
and, more
particularly, to an air dryer control system having a sleep mode to prevent
the depletion of air
and power during idling times.
2. DESCRIPTION OF THE RELATED ART
[0002] A typical "twin-tower" desiccant-type air dryer includes two
drying circuits
that are controlled by valves. Wet inlet air flows through one circuit to
remove water vapor,
while dry product air counter flows through the other circuit to remove the
accumulated water
and regenerate the desiccant. Inlet and outlet valves for each pneumatic
circuit are
responsive to controlling electronics to switch the air flow between the two
circuits so that
one circuit is always drying while the other is regenerating. The air dryer
may include a pre-
filtration stage with a water separator and/or coalescer positioned upstream
of the drying
circuits. The pre-filtration stage removes liquid phase and aerosol water and
oil that can
accumulate in air supply system as a result of the compression of ambient air
by the
locomotive air compressors. A pre-filtration stage includes a drain valve that
is used to
periodically purge any accumulated liquid. For example, a typical pre-
filtration drain valve
actuation cycle might command a purge (open) for two seconds every two
minutes.
[0003] When a locomotive is parked, the driver will usually open the main
circuit
breaker and shut down the auxiliary electrically powered equipment, which
includes the air
dryer. Under certain circumstances, however, the locomotive may be parked or
idled for an
extended period with the electrical power left on. If the diesel engine or air
compressor is
turned off, the pre-filtration drain valve and desiccant regeneration valves
will continue to
cycle and will eventually deplete the main air reservoir and/or the locomotive
battery. Some
air supply systems address the problem of electrical power depletion by only
operating the air
dryer valves when the air compressor is running. This solution, however, does
not fully
address the problem, as it can result in inefficient drying of the air when it
is operating. For
example, air can still flow through an air dryer when the compressor is off In
addition, there
are many instances when the compressor is turned on but no air is actually
flowing through
the air dryer such that operation of the valves is wasteful. Finally, in a
multiple locomotive
consist where all of the locomotives are coupled together by a main reservoir
trainline, the
other locomotives in the consist can be supplying compressed air to the
locomotive whose
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compressor is off. Accordingly, there is a need in the art for an air dryer
control system
prevents the air dryer from unnecessarily venting compressed air or wasting
electricity when
the locomotive air supply system is intended to be idle.
BRIEF SUMMARY OF THE INVENTION
[0004] The present invention comprises an air dryer for a locomotive air
supply
system having a set of valves for controlling the flow of air from an inlet
through one of two
dessicant towers to an outlet and a controller for piloting the set of valves.
More specifically,
the controller is programmed to inhibit operation of the valves in response to
a determination
that the locomotive air supply system is not in use. The locomotive air supply
system is
determined to not be in use if the air compressor supplying air to the air
dryer is not in
operation for a predetermined period of time, if the electrical state of a
diesel locomotive
coupled to the air dryer indicates a lack of usage, if there is a lack of air
flow through the air
dryer over a predetermined period of time, if first main reservoir lacks
sufficient pressure for
a predetermined period of time, if the second main reservoir has a sufficient
amount of
pressure in the second main reservoir relative to the first main reservoir, or
if the humidity in
the air exiting the air dryer over a predetermined period of time indicates a
lack of use of the
air supply system. Accordingly, the air dryer may include a humidity sensor
coupled to the
controller, and the controller may be interconnected to the air compressor,
the locomotive
electrical system, pressure sensors in the first and second main reservoirs.
The controller
may also be interconnected to a check valve positioned between the first and
second main
reservoirs and, optionally, a flow meter positioned to measure air flow volume
in the inlet to
the air dryer.
[0005] The method of the present invention comprises a sleep mode control
for an air
dryer having a series of valves for controlling the flow of air from an inlet
through at least
one dessicant tower to an outlet and a controller for piloting the set of
valves. The controller
of the air dryer determines whether the locomotive air supply system is not in
use and, if not,
inhibits the series of valves during the time period the locomotive air supply
system is not in
use. The controller may restore normal operations periodically, or after
detecting an
indication that the locomotive air supply system is back in use.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
[0006] The present invention will be more fully understood and
appreciated by
reading the following Detailed Description in conjunction with the
accompanying drawings,
in which:
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[0007] FIG. 1 is a schematic of a locomotive air supply system having an
air dryer
with sleep mode according to the present invention;
[0008] FIG. 2 is a schematic of an air dryer with a sleep mode according
to the
present invention;
[0009] FIG. 3 is a schematic of an air dryer with a sleep mode according
to the
present invention interconnected to various elements of a locomotive air
supply system; and
[0010] FIG. 4 is a flowchart of a sleep mode implementation process for
an air dryer
according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0011] Referring now to the drawings, wherein like reference numerals
refer to like
parts throughout, there is seen in FIG. 1 a locomotive air system 10 having an
air compressor
12, aftercooler 14, first and second main reservoirs MR1 and MR2, and a two-
tower dessicant
air dryer 16 having a sleep mode according to the present invention, as more
fully described
below. Second main reservoir MR2 is coupled to the braking system 18 and a
check valve 20
is positioned between the first and second main reservoirs MR1 and MR2. A pre-
filtration
stage 22 is associated with air dryer 16 and includes a drain valve 24 that is
operated
according to a drain valve purge cycle time. Optionally, a flow meter 26 may
be positioned
in the inlet air to the air dryer.
[0012] Referring to FIG. 2, a two-tower dessicant air dryer 16 comprises
an inlet 28
for receiving air from first main reservoir MR1. Inlet 28 is in communication
with an
integral pre-filtration stage 30, shown as including a water separator 32, a
coarse coalescer
34, and a fine coalescer 36. Any accumulated liquids in water separator 32,
coarse coalescer
34, and fine coalescer 36 are expelled through drain valve 24. A pair of inlet
valves 42 and
44 are positioned downstream of pre-filtration stage 30 for diverting incoming
air between
one of two pathways, each of which is associated with one of two dessicant
towers 46 and 48.
A temperature sensor 50 is positioned upstream of inlet valves 42 and 44 and
downstream of
pre-filtration stage 30. The first pathway downstream of first inlet valve 42
leads to an
exhaust valve 52 and first dessicant tower 46. The second pathway downstream
of second
inlet valve 44 leads to a second exhaust valve 54 and second dessicant tower
48. The first
pathway further includes a first check valve 58 and first bypass orifice 62
downstream of first
dessicant tower 46, and the second pathway further includes a second check
valve 60 and
bypass orifice 64 downstream of second dessicant tower 48. A single outlet 66
is coupled to
the end of the first and second pathways, and a humidity sensor 68 is
positioned upstream of
outlet 66. Inlet valves 42 and 44 and outlet valves 52 and 54 are piloted by
controller 40.
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Controller 40 operates inlet valves 42 and 44 and outlet valves 52 and 54 so
that compressed
air provided at inlet 28 is directed through one of dessicant towers 46 or 48
for drying. The
other dessicant towers 46 or 28 may be regenerated by allowing dried air to
reflow through
bypass orifice 62 or 64 by opening the corresponding exhaust valve 52 or 54
for a given
period of time. Controller 40 is also in communication with temperature sensor
50 and
humidity sensor 68. A heating element 70 may also be coupled to controller 40
and
positioned in air dryer 16 to warm inlet valves 42 and 44 and outlet valves 52
and 54 is the
temperature is below freezing.
[0013] In addition to executing the normal operation of inlet valves 42
and 44 and
outlet valves 52 and 54, controller 40 is programmed to determine whether the
operation of
air dryer 16 should be inhibited, such as when the locomotive is idle of if
there is no demand
for drying because air is not flowing through air dryer 16. When controller 40
determines the
locomotive air system 10 is not in use, controller 40 is programmed to
activate a sleep mode
where actuation of drain valve 38 and/or inlet valves 42 and 44 and outlet
valves 52 and 54
are suspended until controller 40 receives a signal indicating that air system
10 is in use
again. When controller 40 determines that air system 10 is again in use,
controller 40 may
resume normal actuation of the valves. Once sleep mode is initiated,
controller can de-
energize the normally closed drain valve 24, the normally open inlet valves 42
and 44 and
and the normally closed outlet valves 52 and 54 to avoid undesirable leakage
of air from air
supply system 10.
[0014] Referring to FIG. 3, controller 40 may be interconnected to
compressor 12 to
receive an input reflecting when compressor 12 is being operated. For example,
controller 40
may receive a signal reflecting the status of the compressor motor driver
current, the
unloader, or the motor control contactors. Similarly, controller 40 may be
interconnected to
the locomotive electrical system 72 to determine the status of the locomotive.
For example,
controller 40 may be interconnected to the output of the auxiliary generator
74 to determine
whether the diesel locomotive is off Controller 40 may also be interconnected
to the
locomotive battery 76 to determine whether the battery voltage has dropped
below a
predetermined threshold, thereby indicating that the diesel engine of the
locomotive is not
running and battery 76 is not being recharged. Any or all of these detected
events may be
used as a trigger for controller 40 to initiate sleep mode. Controller 40 may
implement sleep
mode for a predetermined period of time, or until controller 40 detects an
event indicative of
the resumption of use of the locomotive air supply system 10.
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[0015] Instead of, or in addition to, detecting locomotive status events,
controller 40
may also be programmed to determine whether there is any air flow through air
dryer 16, or
even the quality and amount of air flow through air dryer 16, as a trigger for
entering sleep
mode. For example, a binary reading may be taken from check valve 20 to
provide an
indication whether check valve 20 is open or closed, thereby allowing
controller 40 to
determine whether air is flowing from MR1 to MR2. Similarly, a proportional
reading may
be taken from check valve 20 to determine how far check valve 20 has opened.
The size of
the opening of check valve 20 is proportional to the pressure difference
across check valve 20
and the spring rate and preload of the bias spring in check valve 20 are
known. As a result,
the amount of displacement of check valve 20 can be used to calculate the
instantaneous flow
rate across check valve 20. The total air flow volume can then be calculated
by a simple
integration of the instantaneous air flow rate over a given period of time.
Lastly, the system
may include flow meter 26 to directly measure the flow rate. Controller 40 may
then be
programmed to enter into sleep mode to inhibit valve actuation if there is
zero air flow or if
the air flow is below a predetermined threshold over a particular time period,
such as twenty-
four hours.
[0016] Controller 40 may also be interconnected to MR1 or MR2 to
determine the
pressure in either or both of those reservoirs. Controller 40 may then
initiate sleep mode if the
pressure in MR1 is less than the low pressure governor set point used to
trigger air
compressor 12 to recharge system 10 as this would indicate that the locomotive
is not in a
state where air compressor 12 needs to replenish MR1. Similarly, controller 40
may be
programmed to initiate sleep mode if the pressure in MR2 is greater than the
pressure in MR1
for a predetermined number of hours, thereby indicating that MR1 is not being
recharged.
The pressure in MR1 or MR2 may be determined by a pressure transducer or
pressure switch
that is interconnected to controller 40.
[0017] Controller 40 may also be programmed to measure the output of air
dryer 16
to determine whether the sleep mode should be initiated. For example, a lack
of change in
humidity at the output of air dryer 16 may be used to infer that air supply
system 10 is not in
active use. For example, if the humidity remains sufficiently dry within a
predetermined
tolerance while the air dryer purge cycle time is at a maximum duration
setting and
temperature at inlet 28 is warm enough that the humidity should otherwise be
increasing if
there was air flow through the air dryer, controller 40 may initiate sleep
mode.
[0018] Controller 40 may also be programmed to determine whether the
outlet
humidity reflects the expected saturation level for air flowing through air
dryer 16 and, if not,
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initiate sleep mode. If the compressed air in MR1 is assumed to be saturated
due to the
compression pressure, the current air temperature and corresponding water
vapor saturation
level may be used to calculate the volume of air that, over time, would
saturate one of
desiccant towers 46 or 48 in air dryer 16. For example, at the measured
temperature,
controller 40 might calculate that 500 cubic feet of air from MR1 would
saturate the
desiccant of air dryer 16. At a flow rate of 90 standard cubic feet per minute
(SCFM)
saturation should occur in as little as 5.5 minutes. If the humidity of outlet
66 does not reflect
saturation after the expected time to saturation has passed, controller can
initiate sleep mode.
[0019] Instead of measuring the expected saturation time, controller 40
may instead
by programmed to initiate sleep mode if the default regeneration cycle time
has been reached
a predetermined number of times without an increase in humidity. For any air
dryer 16
having a variable regeneration cycle, controller 40 may be programmed to
initiate sleep mode
if the variable regeneration cycle has been extended a predetermined number of
times without
any resulting increase in humidity in the air passing through air dryer 16. A
subesequent
increase in humidity at outlet 66 may be used to trigger controller 40 to
return to normal
valve control.
[0020] Once controller 40 has initiated sleep mode, a change in the
various triggering
conditions identified above may be used by controller 40 to terminate sleep
mode and to
return to normal valve operation. For example, the turning on of air
compressor 12, the
detection of air flow through air dryer 16, an increase in MR1 pressure above
a
predetermined threshold, power at the auxiliary generator, a recharge of the
locomotive
battery above a predetermined number of volts, and/or a change in the humidity
at the air
dryer outlet 66 may trigger a return to normal operations. Alternatively, or
in addition
thereto, controller 40 may be programmed to return to normal valve operations
periodically,
such as once every twenty-four hours, and then reenter valve control sleep
mode if the
conditions of air supply system 10 for initiating sleep mode are still
present.
[0021] Referring to FIG. 4, controller 40 may thus implement a sleep mode
process
80 that begins with air dryer 16 in normal valve operation 82. Controller 40
then performs a
check 82 to determine whether locomotive air supply system 10 is intended to
be at idle using
one or more of the approaches discussed above. For example, controller 40 can
check
locomotive electrical system 72, air compressor 12, first main reservoir MR1,
check valve 20,
air dryer 16, or second main reservoir MR2 for relevant status data and then
perform any
necessary calculations as described above to determine if system 10 is idle
such that air dryer
16 should be placed into sleep mode and all valves de-energized. If a check 84
indicates that
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the locomotive air supply system is not in use, such as by being idle for a
predetermined
period of time, controller 40 inhibits air dryer valves 86, thus putting air
dryer 16 into sleep
mode. Controller 40, according to a predetermined schedule, performs a
subsequent check 88
of the relevant aspects of system 10 to determine whether locomotive air
supply system 10 is
back in use. If so, controller 40 restores normal valve operation 90.
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