Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
OPTIMAL CONTROL OF AIR COMPRESSORS IN A LOCOMOTIVE CONSIST
BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
[0001] The present invention relates to locomotive compressor systems
and, more
particular, to a system for controlling locomotive compressors in a consist.
2. DESCRIPTION OF THE RELATED ART
[0002] In heavy haul freight train operations, there are frequently
multiple locomotives at
the head end of the train, all of which are providing tractive effort to move
the train under lead
control from the front-most locomotive. The locomotives are typically
interconnected into
multiple unit (MU) system by four air pipes, consisting of the brake pipe, 20-
Pipe, 13-Pipe, and
MR Pipe (main reservoir) and a standard "27 Pin" jumper cable. This
combination allows the
driver in the lead locomotive to drive the trailing locomotives as slaves with
MU control of both
propulsion and braking.
[0003] In an MU configuration, the main reservoirs on each of the
locomotives are
interconnected via the MR pipe end hose, making the combined MR volume
available to the
locomotive consist. Each locomotive also includes an air compressor that is
used to pressurize
the main reservoirs. In addition, the 27 pin train line includes a train line
for MU compressor
control (usually train line #22). This allows the compressor governor on the
lead locomotive to
simultaneously start and stop the compressors on all of the locomotives,
resulting in very rapid
filling of the interconnected MR system. In addition, the MU operation of the
compressors
assures uninterrupted, adequate air supply even if the compressor on the lead
locomotive fails.
[0004] While the rapid filling of the MR system is desirable if all the
MRs are at a low
state of charge, or if the train brake system is discharged, because in these
conditions the higher
total air capacity of multiple compressors can be fully utilized. However,
most of the time, the
air system on the locomotives and train brakes are charged, and the air
compressor is cycling
between the compressor governor upper and lower control limits, typically
between 120 psi and
140 psi. As a result, the full capacity of the compressors in the MU is
generally not needed.
[0005] All of the air flow into the train brake pipe is controlled by the
air brake system
on the lead locomotive. The locomotive air brake system includes a nominally
19/64" diameter
choke restricting the flow between the outlet of MR2 and the inlet of the
brake pipe pressure
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control circuit. Brake pipe pressure is typically fully charged at 90 psi. A
full service brake pipe
reduction is typically 26 psi, which corresponds to a 64 psi brake pipe
pressure. To release the
train brakes, the brake pipe is recharged to 90 psi. Because the brake pipe on
the train is the
length of the train, often in excess of 6000 feet, and due to effect of
friction in the pipe, the brake
pipe in the front of the train charges well before the brake pipe in the rear
of the train. As a
result, the brake pipe regulating device (brake pipe relay) in the locomotive
brake system begins
to throttle the air flow based on the brake pipe pressure at the head of the
train before the brake
pipe in the train is fully charged. The net combination of the low head
pressure at recharge,
which is 120 to 140 psi MR pressure flowing into a 64 to 90 psi brake pipe,
the 19/64" charging
choke, and throttling of the brake pipe relay means that the rate of required
air flow is much less
than the air flow capacity of the compressor on just one locomotive.
[0006] In a MU consist, the combined air flow capacity from the
compressors on each of
the locomotives is thus much greater than required and, as a result, the
compressor duty cycle is
very short. For example, in some cases the MR recharge from 120 psi to 140 psi
may take less
than 30 seconds. This is undesirable for several reasons. First, the
compressor start includes high
inrush current, high accelerations, and high torque on the components, all of
which are ultimately
damaging to the compressor. Second, because the compressor runs for so short a
time, it is not
able to achieve optimum, stable operating temperature. As a result, there is
an accelerated wear
of cold parts due to transient thermal expansion issues and the cold
compressor is more prone to
accumulation of condensed water from the product air. Finally, in addition to
issues of
corrosion, the accumulation of liquid water can freeze in winter operation,
thereby causing
blockage of the compressor after cooler and discharge lines.
[0007] Preferably, the compressor has a longer duty cycle, so that the
compressor and
related components are heated due to the heat of compression to more or less
the same
temperature as the discharged air. The normal operating temperature of the
compressor results in
much less condensation in the compressor system, and enough heat in the after
cooler and
discharge lines to prevent any liquid water from freezing in those critical
locations. Thus, while
synchronous control of all the compressors in the locomotive consist might be
an advantage
during dry charge, or in the event of a failure of the compressor on the lead
locomotive,
synchronous control is clearly detrimental to compressor life and problematic
during cold
weather operation because the compressor duty cycle is too short.
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[0008] In some circumstances a lead locomotive in a consist could be set
up to allow for
independent compressor control, so the pressure governor on each locomotive
turns that
compressor on and off independently. This control scheme addresses the issue
of too much
charge capacity because all the main reservoirs are connected by the MR pipe
and therefore the
MR pressure on each locomotive is nominally the same and because there is a
natural tolerance
in the pressure governor settings on each locomotive compressor control.
However, in this
scheme, one compressor in the locomotive consist will turn on at a higher
pressure than the other
compressors in the consist due to tolerance variations of the pressure
governors and will provide
all of the air for the train and, as a result, the compressor utilization and
compressor maintenance
demand is unbalanced. Typically compressor maintenance is done on a planned,
periodic
schedule, with certain maintenance actions occurring at regular calendar
intervals. Thus, the
compressors subject to this control scheme will have done more work during the
maintenance
interval than others, so some compressors will be maintained too late and some
serviced earlier
than needed.
BRIEF SUMMARY OF THE INVENTION
[0009] The present invention comprises a system for controlling multiple
air compressors
in a locomotive consist, where the air compressor of each locomotive is
associated with a
networked controller that can send or receive commands related to the
operation of the
associated compressor. One predetermined controller is programmed issue
commands to the
other controllers so that each compressor is operated more efficiently. For
example, each
compressor may be sequentially enabled for refilling to MR system each time it
needs refilling.
The lead controller may also monitor the total utilization of the other
compressors since a
predetermined point in time or use so that the lead controller can implement a
schedule of
compressor usage that maximizes utilization of each compressor, thereby
ensuring that each
compressor is fully utilized during its scheduled maintenance period. The lead
controller can
also be coupled to thermometers or other sensors to control compressor usage
to avoid freezing
or other temperature related issues.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
[0010] 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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[0011] Fig. 1 is a schematic of a multiple unit consist having a
compressor control
system according to the present invention;
[0012] Fig. 2 is a schematic of a compressor control system for each
locomotive in a
consist according to the present invention;
[0013] Fig. 3 is a schematic of a networked compressor control system
according to the
present invention;
[0014] Fig. 4 is a flowchart of compressor control according to the
present invention; and
[0015] Fig. 5 is a flowchart of compressor system control according to
the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0016] Referring now to the drawings, wherein like reference numerals
refer to like parts
throughout, there is seen in Fig. 1, a smart, distributed locomotive
compressor control system 10
that optimizes compressor life, cold weather operation, and balances
utilization for maintenance
optimization. System 10 interconnects the compressor 12 of each locomotive 14
in a multiple
unit consist. In a multiple unit consist, one locomotive 14 may be designed as
a lead locomotive
14a, while subsequent locomotives 14b through 14n act as slaves. Although Fig.
1 represents
lead locomotive 14a at the head of the consist, locomotive 14 designated to
act as lead
locomotive 14a could be located in any position along the consist.
[0017] As seen in Fig. 2, system 10 is a series of individual locomotive
control systems,
each of which has an individual controller 16 associated with each compressor
12 of each
locomotive 14 in a consist. Controller 16 is networked to other locomotives in
the train consist
via an interface 18 that connects controller 14 to a network 20 spanning the
consist. Network 20
can comprise a wireless network, such as IEEE 802.11 or cellular 3G or 4G
network, or a wired
network, such as Ethernet or IEEE 802.5, or even a custom network employing a
spare wire in
the existing 27 pin train lines used for intra-train communications.
Preferably, interface 18
includes a power line carrier network signal that is overlaid on the existing
27 pin train line
compressor control wire, which is typically wire number 22.
[0018] Controller 16 may monitor the rate of pressure increase in the MR
system while
compressor 12 is operating using a sensor 22 coupled to the MR system, such as
a first main
reservoir 28. Main reservoir 28 may be connected to the main reservoir pipe 36
of the
locomotive. First main reservoir 28 may also be connected via a check valve 30
to a second
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main reservoir 32. Second main reservoir 32 may be connected to the braking
system 34, which
is also connected to the brake pipe 40. A power source 44 may be coupled to
system 10 via
switch 42 that operates in response to pressure in reservoir 28.
[0019] System 10 may also be configured so that each controller 16
includes a
monitoring module 24 that tracks the total utilization of its corresponding
compressor 12 since a
predetermined point in time or use, such as the last overhaul or major
maintenance. Monitoring
module 24 may thus report usage information to lead controller 16, which may
then establish and
implement a schedule of compressor usage that preferentially commands usage of
compressors
in the consist that have the lowest accumulated utilization. System 10 may be
further optimized
by adding a real-time clock to each controller 16 and comparing accumulated
compressor
utilization with the time remaining until the next scheduled maintenance (or
time since last
maintenance), so that system 10 can target compressor usage to achieve 100
percent utilization
of each compressor 12 by the end of the scheduled maintenance interval. For
example, a
compressor having 75 percent accumulated utilization that is 95 percent of the
way through its
maintenance interval would be used preferentially over a compressor having 10
percent
utilization that is only 10 percent of the way through its maintenance
interval. The addition of a
temperature sensor 26 to system 10, will further allow system 10 to manage
compressor
temperatures and avoid related issues. For example, the compressor control
scheme could
preferentially operate only one compressor in the consist to optimize the
compressor temperature
during use of the compressor when the ambient temperature is below freezing.
[0020] As seen in Fig. 3, system 10 includes any number of individual
locomotives, each
of which includes a compressor control system as seen in Fig. 2. As a result,
a designated lead
controller 16a of a lead locomotive 14a can asynchronously control each of the
compressors on
the remaining locomotives 14b through 14n in the consist to optimize charge
rate, compressor
temperature, and balance compressor utilization. Corresponding elements in the
individual
system of each locomotive, with three chosen for illustrative purposes, are
indicated using sub-
numerals (a, b, c).
[0021] In order to avoid maintenance interval issues, system 10 may be
programmed to
manage compressor utilization in several different ways. For example, under
control of lead
compressor controller 16a, the refilling of the main reservoir system may be
done by sequentially
enabling each compressor 12b through 12n in the consist. The first time the MR
system in the
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consist needs to be refilled, compressor 12a on the first locomotive is
utilized. The next time,
compressor 12b on the second locomotive is sent the command to refill the MR
system, with
system 10 sequentially cycling through each of the remaining compressors 12n.
In this way, all
of compressors 12a through 12n in the locomotive consist will undergo the same
amount of
utilization and have an optimized duty cycle.
[0022] As seen in Fig. 4, system 10 may be programmed to preferentially
use the
compressors having the lowest usage time. The first step involves an
identification of all
compressors in the consist 50. Next, a utilization factor is calculated for
each compressor in the
consist 52 based on an assumption of total allowed usage and actual usage. For
example, an
assumption of an eight year useful life between overhauls and 1500 hours of
powered use per
year would result in a 12,000 hour useful life. It should be recognized that
eight years and 1500
hours are exemplary variables and other values could be used by system 10.
Once a utilization
factor is calculated for each compressor 52, the compressors may be ranked
according utilization
54, such as from lowest to highest utilization. When a compressor ON signal is
required 56,
such as when the primary main reservoir is equal to or below about 125 psi, a
command may be
sent to the appropriate compressors 58 using the utilization factor rankings.
When a check 60
determines that the primary main reservoir is equal to or above about 145 psi,
all compressors
may be turned off 62 and the usage hours for each compressor updated
accordingly 64.
[0023] In the event of demand for high air flow, such as during a dry
charge of the
braking system of train, controller 16a of lead locomotive 14a can monitor the
rate of pressure
increase in the MR system while compressor 12a is operating using a sensor 22a
coupled to the
MR system. Sensor 22a can detect the high air flow demand based on the low
rate of pressure
increase in a reservoir 28a of MR system. In this state, controller 16a of
lead compressor 12a
can send a command via interface 18a to slave compressors 12b through 12n on
network 20 to
turn on their corresponding compressors 12b though 12n until the air demand is
satisfied.
Likewise, using the same methodology, controller 16a of lead compressor 12a
can send a
command via network 20 that instructs one or more of compressors 12b though
12n to shut off
when the rate of MR pressure increase is too fast or desired amount has been
achieved. As seen
in Fig. 5, the first step such an approach is to determine that the pressure
in the primary main
reservoir has fallen below a threshold 70, such as 125 psi. The control
compressor, such
compressor 12a, may then be turned ON 72. A check is made 74 to determine
whether the
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pressure remains below a second, lower threshold, such as 120 psi, which may
indicate the need
for additional compressors to be turned on due to extremely low pressure. If
check 74
determines that the pressure is below the second threshold, a rate of
recharging check 76 is made
to determine whether rate of increase of pressure is above a predetermined
rate. If not, a
command is sent 78 to turn on an additional compressor, such as compressor
12n. If check 74
determines that the pressure is not below the second threshold, however, there
is no need for
additional compressors to be turned on and a check 80 is made to determine
whether the primary
main reservoir has been adequately re-pressurized. If so, all compressors are
turned OFF 82.
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