Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE
BRAKE CYLINDER MAINTAINING REFERENCE
BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
[0001] The present invention relates to rail car braking systems and, more
specifically, to
a system for providing an accurate brake cylinder reference pressure and
improved pressure
regulation.
2. DESCRIPTION OF THE RELATED ART
[0002] The quick service limiting valve of an Association of American
Railroads (AAR)
type braking system controls the supply of brake pipe air to the brake
cylinder during quick
service operations. Recent advancements in quick service limiting valves
include
modifications to the quick service limiting valve that assist in the
replenishment of brake
cylinder pressure that may be lost, such as through leakage. For example, one
approach is to
use a brake cylinder reference pressure based on the actual brake cylinder
pressure that
pressurizes one side of the diaphragm in the quick service limiting valve so
that if brake
cylinder pressure leaks below a threshold set by the pressure on the opposing
side of the
diaphragm, the resulting force imbalance will cause movement that opens
communication
between the brake pipe and the brake cylinder, thus replenishing any lost
brake cylinder
pressure, until the force balance is re-established.
[0003] In order for this arrangement to work effectively, however, the
brake cylinder
reference pressure must accurately represent the desired target brake cylinder
pressure in all
possible scenarios. Current approaches work very well in the situation where
the brake
cylinder develops a leak after it has been fully pressurized to the desired
level. These
approaches are not as effective when the brake cylinder has a pre-existing
leak such that the
brake cylinder leaks while the brake cylinder pressure is being charged. In
this situation, the
actual brake cylinder pressure is not likely to achieve the desired pressure
value. As a
consequence, the brake cylinder maintaining reference pressure will not
achieve the desired
target value and there will not be a desired force imbalance across the quick
service limiting
valve diaphragm that opens communication between the brake pipe and the brake
cylinder to
replenish lost brake cylinder pressure.
BRIEF SUMMARY OF THE INVENTION
[0004] The present invention comprises a system for maintaining pressure in
a brake
cylinder that includes a valve responsive to a source of brake pipe pressure
and a source of
auxiliary reservoir pressure to provide a brake cylinder reference pressure
based on the
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difference between the brake pipe pressure and the auxiliary reservoir
pressure. The valve
may be an independent poppet style valve, it may be driven by the main service
piston, or it
may be incorporated as a port positioned in a slide-valve style control valve.
In any case, the
brake cylinder reference pressure is fed to a choke having a reference area
for restricting the
flow of the brake cylinder reference pressure and then to a volume in
communication with the
choke for storing the restricted brake cylinder reference pressure. The ratio
of the reference
area of the choke to the volume of stored brake cylinder reference pressure is
substantively
equal to the ratio of a brake cylinder charging valve area to the brake
cylinder volume.
[0005] The reference pressure may be incorporated into a braking system by
providing it
to a brake cylinder maintaining charging check valve that selectively allows
the brake
cylinder reference pressure to be in communication a quick service limiting
valve so that the
quick service limiting valve operates in response to a difference between the
brake cylinder
reference pressure and the pressure in the brake cylinder. Alternatively, the
reference
pressure may be provided to a control port of a relay so that relay is
moveable between a first
position where a source of brake pipe pressure is connected to the source of
brake cylinder
pressure and a second position where a source of brake cylinder pressure is
connected to an
exhaust. The relay will move to the first position if the brake cylinder
reference pressure
exceeds the brake cylinder pressure and the relay will move to the second
position if the
brake cylinder pressure exceeds the brake cylinder reference pressure.
[0006] BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
[0007] The present invention will be more fully understood and appreciated
by reading
the following Detailed Description in conjunction with the accompanying
drawings, in
which:
[0008] Fig. 1 is a schematic of one embodiment of a brake cylinder
maintaining reference
system according to the present invention that includes a separate brake
cylinder reference
pressure valve and reference volume coupled to a quick service limiting valve
of a braking
system for integration into a braking system;
[0009] Fig. 2 is a schematic of another embodiment of a brake cylinder
maintaining
reference system according to the present invention that includes a separate
brake cylinder
reference pressure valve and reference volume coupled to a brake cylinder
maintaining relay
for integration into a braking system;
[0010] Fig. 3 is a perspective view of a slide valve modified according to
the present
invention to provide a brake cylinder reference pressure according to the
present invention;
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[0011] Fig. 4 is a perspective view of a slide valve bushing to be modified
according to
the present invention to provide a brake cylinder reference pressure according
to the present
invention;
[0012] Fig. 5 is a cross-sectional view of a slide valve bushing modified
according to the
present invention to provide a brake cylinder reference pressure according to
the present
invention;
[0013] Fig. 6 is a schematic of a further embodiment of a brake cylinder
maintaining
reference system according to the present invention integrated into slide-
valve style control
valve according to the present invention; and
[0014] Fig. 7 is a schematic of an exhaust cut-off valve for use with the
brake cylinder
maintaining reference system according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0015] Referring now to the drawings, wherein like reference numerals refer
to like parts
throughout, there is seen in Fig. 1 a schematic of a brake cylinder
maintaining system 10
according to the present invention. System 10 provides a reference pressure
for brake
cylinder maintaining in an independent and redundant manner so that the brake
cylinder
maintenance reference is unaffected by any pre-existing leaks in the brake
system, thereby
providing greater pressure regulating accuracy across many different scenarios
that result in a
loss of brake cylinder BC pressure.
[0016] System 10 comprises a brake cylinder reference pressure valve 12
that operates in
response to the same influences as the main service piston 14 of the service
portion 16 of a
rail car braking system, shown in Fig. 1 as a detailed schematic of a DB-10
Service Portion
available from New York Air Brake, LLC of Watertown, New York. More
particularly,
brake cylinder reference pressure valve 12 has an actuator 18 that is
responsive to movement
of a diaphragm 20 that separates a first chamber 22 that is in communication
with a source of
brake pipe BP pressure and a second chamber 24 that is in communication with a
source of
auxiliary reservoir AUX pressure. When auxiliary reservoir pressure acting in
chamber 20 is
greater than the brake pipe pressure acting in chamber 22. Actuator 18 opens a
communication between auxiliary reservoir AUX pressure and brake cylinder
reference BC
Ref volume 28. When the auxiliary reservoir and brake pipe pressures in
chambers 20 and 22
are substantively equal, actuator 18 moves to lap position, where the
communication between
the auxiliary reservoir and brake cylinder reference BC Ref volume 28 is
severed. In a
similar way, when the BP pressure exceeds auxiliary reservoir pressure acting
across
diaphragm 20. actuator 18 moves downward to exhaust brake cylinder reference
BC Ref
3
,
volume 28. Thus, valve 12 provides a brake cylinder reference BC Ref pressure
when
actuator 18 moves in response to a reduction in brake pipe BP pressure
relative to
auxiliary reservoir AR pressure, or to vent the brake cylinder reference BC
Ref pressure to
an exhaust EX when the brake pipe BP pressure is greater than auxiliary
reservoir AUX
pressure. The valve is in lap, where brake cylinder reference BC Ref volume is
in
communication with neither auxiliary reservoir AUX or exhaust when brake pipe
BP and
auxiliary reservoir AUX are in balance. Thus, valve 12 mimics the operation of
the main
service piston. While Fig. 1 illustrates a separate actuating diaphragm for
valve 12, it
could be actuated directly by the main service piston 14 as it operates in a
parallel manner.
[0017] The brake cylinder reference BC Ref pressure is passed through
a suitably
sized choke 26 into a brake cylinder reference volume 28. The ratio of the
reference area
of choke 26 (Areference choke) to brake cylinder reference volume 28
(Vreference volume) is
substantively equal to the ratio of the area of the brake cylinder charging
valve 30 (ABC
Charging VIv) of the service piston 14 to the volume of the brake cylinder 32
(VBC volume), so
that the brake cylinder reference volume 28 and the brake cylinder BC
pressurize at the
same rate and to the same value, as set forth in the following formula:
Areterence choke / Vreference volume = ABC Charging Vlv VBC volume
As a result, volume 28 provides an accurate measurement of what the brake
cylinder BC
pressure should be as volume 28 will operate according to what should be
occurring in the
brake cylinder in the absence of any leakage.
[0018] In a first embodiment of the present invention, valve 12 may
be integrated into
a conventional braking system by putting brake cylinder reference pressure
volume 28 into
communication with the brake cylinder BC reference chamber 34 of a quick
service
limiting valve 38. For example, volume 28 may be placed into communication
with a
brake cylinder maintaining charging check valve 42. Instead of bottling a
reference
pressure for use in maintaining the brake cylinder BC pressure, as described
in U.S. Pub.
No. 2014/0102558, brake cylinder maintaining charging check valve 42 will
bottle brake
cylinder reference BC Ref pressure in reference chamber 34 of quick service
limiting
valve 38. As the other side of diaphragm 40 of quick service limiting valve 38
has a
chamber 44 that is in communication with brake cylinder BC pressure, quick
service
limiting valve 38 will operate according to the difference between actual
brake cylinder
BC pressure and brake cylinder reference BC Ref pressure. Quick service
limiting valve
38 will release brake pipe BP pressure into the quick service chamber 46 when
the
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actual brake cylinder BC pressure is below the brake cylinder reference BC Ref
pressure
(which is the brake cylinder BC pressure that is supposed to occur), thereby
addressing the
issue of under-pressurization of brake cylinder BC pressure on a real-time
basis.
[0019] Because the brake cylinder reference BC Ref pressure is determined
in response to
a change in brake pipe BP pressure relative to auxiliary reservoir AUX
pressure, the
reference pressure released from valve 12 accurately represents the desired
brake cylinder BC
pressure that has been ordered via a brake pipe BP pressure reduction,
regardless of whether
brake cylinder BC has actually achieved the desired pressure. Valve 12 thus
determines an
intended brake cylinder pressure instead of relying on a feedback of the
actual brake cylinder
BC pressure achieved during initial brake cylinder charging to determine
whether additional
charging of the brake cylinder BC is necessary to compensate for leakage. As
the brake
cylinder reference BC Ref pressure is then provided to quick service limiting
valve 38, any
under-pressurization of brake cylinder BC relative to the intended brake
cylinder BC Ref
pressure will be compensated by the operation of quick service limiting valve
38, which
would otherwise disconnect brake pipe BP pressure from the quick service
chamber only in
response to the brake cylinder BC achieving a threshold pressure that is
predetermined to
indicate a fully charged brake cylinder BC.
[0020] In a second embodiment of the present invention, valve 12 may be
integrated into
a conventional braking system by putting volume 28 into communication with a
brake
cylinder maintaining relay 50, as seen in Fig. 2. Relay 50 includes a control
port 52 for
receiving brake cylinder reference BC Ref pressure and allowing the reference
pressure to
communicate with a brake cylinder reference BC Ref pressure chamber 54
positioned on one
side of a diaphragm 56. The other side of diaphragm 56 includes a chamber 58
in
communication with a source of brake cylinder BC pressure. Movement of
diaphragm 56 in
response to higher pressure in brake cylinder reference BC Ref pressure
chamber 54 than in
brake cylinder BC pressure chamber 58 opens communication between a brake pipe
BP
pressure connection 60 and brake cylinder BC pressure connection 62. Movement
of
diaphragm 56 in response to lower pressure in brake cylinder reference BC Ref
pressure
chamber 54 than in brake cylinder BC pressure chamber 58 opens communication
between
brake cylinder BC pressure connection 62 and an exhaust EX. Thus, relay 50 can
address
both under-pressurization and over-pressurization. It should be recognized
various
conventional valve structures, such as a 3-way valve, may be used, in lieu of
the relay
structure seen in Fig. 2 to provide brake cylinder maintaining against both
brake cylinder
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leakage and brake cylinder overcharge in response to brake cylinder reference
BC Ref
pressure.
[0021] When a brake application is made, brake pipe BP pressure is reduced
and
auxiliary reservoir pressure moves brake cylinder reference BC Ref pressure
valve 12 to open
the connection between auxiliary reservoir AUX pressure and brake cylinder
reference
volume 28 through brake cylinder reference choke 26. Because the brake
cylinder reference
volume 28 charges at the same time and same rate as brake cylinder BC, the
resulting
pressure in brake cylinder reference volume 28 will accurately reflect the
pressure in brake
cylinder BC even if there is brake cylinder leakage. The brake cylinder
reference BC Ref
pressure is directed to control port 52 of brake cylinder maintaining relay
50. Actual brake
cylinder BC pressure is fed back to the underside of control diaphragm 56. If
the brake
cylinder BC pressure leaks, the feedback pressure on the underside of
diaphragm 56 is
reduced, and the maintaining relay piston 64 moves downward to open the valve
connection
between brake pipe BP pressure source 60 and brake cylinder BC source 62, thus
allowing
brake pipe BP pressure to replenish the leaking brake cylinder BC. Valve 12
closes when
brake cylinder BC pressure is restored to nominally the same value as the
brake cylinder
reference BC Ref pressure. In a similar manner, if brake cylinder BC pressure
increases due
to high pressure leakage into brake cylinder BC, then brake cylinder relay
valve 50 will move
upward and connect brake cylinder BC to exhaust EX until brake cylinder BC
pressure
nominally equals the brake cylinder reference BC Ref pressure at control port
52.
[0022] Although not explicitly shown in the accompanying figures, it is
clear that it is
desirable that the brake cylinder reference BC Ref pressure have a small and
intentional
offset (lower) than the actual brake cylinder BC pressure (when there is no
leak). That small
pressure offset provides operating hysteresis and valve stability. The
pressure offset may be
created by bias springs in brake cylinder reference valve 12 and/or brake
cylinder
maintaining relay 50, by a check valve in the output of brake cylinder
reference valve 12
having a cracking pressure equal to the desired pressure offset, or by other
means known to
those skilled in the art.
[0023] In a third embodiment of the present invention, a brake cylinder
reference BC Ref
pressure may be developed using a slide-valve type control valve 70, such as
the Wabtec
ABDX control valve available from Wabtec Corporation of Wilmerding,
Pennsylvania.
As seen in Figs. 3 through 6, this type of control valve 70 uses a slide valve
72 connected to a
service piston 76 to perform the valving functions, rather than the poppet
valve typical of the
NYAB DB-600 described above. The basic service portion 74 operates in a
similar fashion
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as service piston 76 will move under the influence of brake pipe BP pressure
and auxiliary
reservoir AUX pressures. As seen in Fig. 3, slide valve 72 is connected to
service piston 76
and provisioned with multiple ports 78 that align with corresponding ports 80
in a fixed
mating valve body bushing 82. Ports 78 and 80 are connected and disconnected
as service
piston 76 translates through its operating range under the influence of the
pressure differential
between brake pipe BP pressure and auxiliary reservoir AUX pressure. For
example, one
existing port in slide valve 72 connects the brake cylinder BC to the
auxiliary reservoir AUX
pressure when service piston 76 is in the brake applied position, and connects
the brake
cylinder BC to exhaust EX when service piston 76 is in the brakes released
position. For this
embodiment, an additional port 84 is added to service slide valve 72 and a
corresponding port
86 is added to corresponding main body bushing 82, as seen in Figs. 4 and 5.
Referring to
Fig. 6, the output of pressure reference port 84 connects to a brake cylinder
reference volume
88 through a brake cylinder reference choke 90. The resulting brake cylinder
reference BC
Ref pressure may then be directed to control port 52 of brake cylinder
maintaining relay 50
described above. Additional port 84 of service slide valve 72 will connect
brake cylinder
reference volume 88 to auxiliary reservoir pressure when service piston 76 is
in the brake
applied position, and to connect brake cylinder reference volume 88 to exhaust
when service
piston 76 is in the brakes released position.
[0024] In a fourth embodiment of the present invention, slide valve 72 may
be modified
as discussed above. In this embodiment, however, brake cylinder reference BC
Ref pressure
may be connected to and used to pilot a quick service limiting valve 38 in the
manner
described above with respect to the first embodiment.
[0025] System 10 may include a nominally 20 psi exhaust cut-off valve 92 to
allow an
AAR compliant retainer valve to function as intended when relay 50 is used to
implement the
present invention. For example, as seen in Fig. 7, the inlet 94 of exhaust cut-
off valve 92
may be coupled to the exhaust port EX of relay 50. Valve 92 includes a pilot
96 in
communication with brake cylinder BC pressure that acts against a valve spring
98 to
selectively connect relay 50 to exhaust EX. Valve spring 98 is configured to
provide a
biasing force equal to about 20 psi and thus will close exhaust cut-off valve
92 if brake
cylinder pressure BC falls below about 20 psi. As conventional AAR brake
systems include
a retainer valve that, when manually activated, will bottle up the brake
cylinder pressure by
sealing the brake cylinder exhaust. This allows a train driver to bottle up
the brakes on the
cars, and then make a release and recharge of the brake pipe and all of the
control valves on
the train while the retainer bottles brake cylinder BC pressure. Retainers are
typically used
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while descending long grades. By AAR standard, the retainer will bottle 20 psi
in the high
pressure setting. Exhaust cut-off valve 92 thus disables the exhausting of the
brake cylinder
BC pressure via present invention during retainer operations to comply with
AAR standards.
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