Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE
HEATER CONTROL 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 having a heating control system for preventing
freezing of valves.
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] The air dryer valves, including any pre-filtration drain valve,
are constantly
subjected to wet air and thus prone to freezing at low temperatures. In order
to counteract
this problem, a heater element may be provided to warm the valves sufficiently
to prevent
freezing. Unfortunately, it takes time to sufficiently warm the valves when
the air supply
system is powered up from a cold temperature. If any of the valves are
commanded open
before they are sufficiently warmed, the valves can freeze in the open
position. If a valve
remains in an open position when it should otherwise be closed, there is a
risk of an
uncontrollable venting of the compressed air from the locomotive air supply
system. Further,
due to the high volume of air flowing through the frozen valve, the heater may
not have
sufficient power to thaw the frozen valve, if it is frozen open. Thus, there
is a need for a
heating control system that ensures that the valves are sufficiently warmed
before they are
operated so that they do not freeze.
BRIEF SUMMARY OF THE INVENTION
[0004] The present invention comprises an air dryer having an inlet for
receiving
compressed air, a series of valves positioned in a valve block for controlling
the movement of
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the compressed air through a dessicant, a heater configured to warm the valve
block, a
temperature sensor for outputting a signal indicating the temperature of at
least a portion of
the air dryer, and a controller piloting the series of valves. To prevent a
risk of the valves
freezing when operated, the controller is programmed to inhibit operation of
the series of
valves until the signal received from the temperature sensor indicates that
the series of valves
are warm enough that they will not freeze when operated. The series of valves
may include a
pair of inlet valves and a pair of exhaust valves associated with a twin-tower
dessicant air
dryer. The series of valves may also include a drain valve associated with a
pre-filtration
stage. The temperature sensor is preferably positioned to determine the
temperature of air
flowing through the air dryer, but may be installed in the valve block or
positioned to detect
the outside temperature.
[0005] The present invention also comprises a method of preventing frozen
air dryer
valves that involves the use of an air dryer comprising an inlet for receiving
compressed air, a
series of valves positioned in a valve block for controlling the movement of
the compressed
air through a dessicant, a heater configured to warm the valve block, a
temperature sensor for
outputting a signal indicating the temperature of at least a portion of the
air dryer, a controller
piloting the series of valves. The signal indicating the temperature in the
air dryer is received
by the controller from the temperature sensor, and then the controller
inhibits operation of the
series of valves if the signal received from the temperature sensor indicates
that any of the
series of valves could freeze when operated.
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:
[0007] FIG. 1 is a schematic of a locomotive air supply system having an
air dryer
having a heated valve block according to the present invention;
[0008] FIG. 2 is a schematic of an air dryer with integral pre-filtration
stage and a
heated valve block according to the present invention;
[0009] FIG. 3 is a schematic of a heated valve block of an air dryer with
pre-filtration
state according to the present invention; and
[0010] FIG. 4 is a flowchart of a heater control process for an air dryer
having a
heated valve block.
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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 heater control 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.
[0012] Referring to FIG. 2, two-tower dessicant air dryer 16 comprises an
inlet 28 for
receiving air from first main reservoir MR1. Inlet 28 is in communication with
pre-filtration
stage 30, shown as comprising 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. Optionally, the temperature, or a second temperature
sensor may be
located in the valve block housing the series of valves. 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. 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 of dessicant towers 46 or 28 may be regenerated
by allowing
dried air to reflow through bypass orifice 62 or 64 and out of exhaust valve
52 or 54 as
needed. 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 drain valve 24, inlet valves 42 and 44 and outlet valves 52
and 54 if the
temperature is below freezing.
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[0013] As seen in FIG. 3, the air dryer pathways seen in FIG. 1 are
arranged so that
drain valve 24, inlet valves 42 and 44, and outlet valves 52 and 54 are
commonly located
along with heater element 70 in a valve block 72. As explained above, air
dryer 16 includes
temperature sensor 50 for determining the approximate temperature of valve
block 72 and
thus drain valve 24, inlet valves 42 and 44, and outlet valves 52 and 54.
Temperature sensor
76 is shown as being positioned to detect the temperature of air passing
through air dryer 16,
but may be positioned to detect the temperature of valve block 72, the
temperature of the inlet
air, the temperature of ambient air, or some combination of the above.
[0014] Referring to FIG. 4, air dryer controller 40 is programmed to
implement a
heater control process 80 to ensure that valve block 72 is sufficiently heated
to a temperature
that avoids the likelihood that drain valve 24, inlet valves 42 and 44, or
outlet valves 52 and
54 can become frozen. First, controller 40 reads the temperature 82 such as by
using
temperature 76 positioned in valve block 72. Next, a check 84 is performed to
determine
whether the temperature is below freezing (or any other predetermined
temperature selected
to be indicative of a risk that drain valve 24, inlet valves 42 and 44, or
outlet valves 52 and 54
will become frozen). If the temperature is below the threshold at check 82,
controller 40
inhibits valve operation 86, such as by inhibiting the operation of drain
valve 24, inlet valves
42 and 44, and/or outlet valves 52 and 54 until such time as the temperature
has risen above
the threshold. Thus, if air dryer 16 is turned on after an extended cold soak
at low
temperature, controller 40 will affirmatively inhibit actuation of drain valve
24, inlet valves
42 and 44, and/or outlet valves 52 and 54 until heater element 70 has warmed
valve block 72
sufficiently to prevent any of drain valve 24, inlet valves 42 and 44, and
outlet valves 52 and
54 from freezing in an open position and causing an undesired venting of
compressed air
from locomotive air supply system 10. Preferably, inlet valves 42 and 44 are
normally open
and exhaust valves 52 and 54 are normally closed in the unpowered state, so
that compressed
air may flow through air dryer 16 to MR2 when all valves are in an unpowered
state. By
using closed loop temperature feedback to control inhibit the operation of the
series of valves,
the start-up time for a cold air dryer is proportional to the starting
temperature. Alternatively,
a simple system which uses a fixed time delay calculated to allow the valve
block to warm to
above freezing for the worst case condition may be provided.
[0015] The same sensor and controller may be used to turn off the heater,
when the
temperature of the valve block is at or above the target temperature, thus
regulating the
temperature of the valve block to a temperature above freezing when the
ambient temperature
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is below freezing; and turning the heater off completely when the ambient
temperature, as
indicated by the temperature of the valve block, is above freezing.
