Note: Descriptions are shown in the official language in which they were submitted.
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PNEUMATIC VALVE WITH AN ENHANCED EXHAUST FLOW CONTROL FEATURE
Statement RegazduzgFederally Sponsored Research & Development
[0001] This invention was not made by an agency of the United States
Government
nor under contract with an agency of the United States Government.
Back round of the Invention
[0003] The present invention relates to a valve for quick release of pneumatic
pressure
in a pneumatic fluid system. It finds particular application with air brakes
used in
conjunction with heavy or commercial vehicles and will be described with
particular
reference thereto. The invention may be used in other applications without
departing from
the spirit and scope of the invention.
[0004] Some air brake valves used in the industry today (e.g., in Europe) do
not meet
release timing requirements of Federal Motor Vehicle Safety Standard (FMVSS)
121, Air
Brake Systems. The release timing requirements relate to how quickly the
brakes release
after the brake pedal is allowed to return to its normal position. In order to
use these
valves in the worldwide market, the release timing must be improved to meet
the
requirements of this market. As shown in FIGURE 1, current brake system valves
utilize
a fixed inlet orifice I to generate a pressure differential across an exhaust
diaphragm 2 to
enhance the release timing.
[0005] When the actuator 3 for the brake valve is released (e.g., foot lifted
from a
brake pedal), the air flows from the brake chamber 4 to the actuator 3 through
a fixed inlet
orifice 1. While the fixed inlet orifice does provide some pressure
differential across the
exhaust diaphragm, relatively little air, less than 50%, actually is exhausted
through the
CA 02508745 2008-11-24
exhaust port, and only slight improvements are realized for the release
timing. Moreover,
this method restricts the inlet capacity of the valve. Furthennore, this
method does not
sufficiently :improve the release timing to meet the FMVSS 121 requirements.
[0006] Patent disclosure DE3938101A1 discusses reducing the vent time of a
pressure
control valve for improved release timing. In this disclosure a "reflux" valve
is placed
directly in the inlet flow path, thus restricting the inlet flow. Inclusion of
a reflux valve
that restricts inlet flow doesn't, however, provide both apply and release
timing sufficient
to meet, for example the requirements of FMVSS 121. Apply timing relates to
how
quickly the brakes are applied after pressing the brake pedal. The enhancement
for the
release timing in disclosure DE3938101A1 degrades the performance of the valve
for the
apply timing. With the current sizing requirements of the antilock brake
system (ABS)
valve, it is not capable to meet both apply and release timing of FMVSS 121
using the
"reflux" valve design. .
Summary of the Invention
[0007] The present invention provides a new and improved apparatus and method
which addresses the above-referenced problems.
In accordance with one aspect of the present invention, there is provided a
method of controlling air flow in an air brake valve having a supply cavity,
an
exhaust port and a delivery cavity, comprising: communicating a majority of
the air
from the supply cavity to the delivery cavity approximately across a generally
central
axis of a flow diverter when the pressure of the air in the supply cavity is
greater than
the pressure of the air in the delivery cavity; diverting communication of the
air when
the pressure of the air in the delivery cavity is greater than the pressure of
the air in
the supply cavity so that a majority of the air from the delivery cavity flows
to the
exhaust port and the remaining air returns to the supply cavity traversing the
flow
diverter.
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In accordance with another aspect of the present invention, there is provided
an air brake valve having a supply cavity, an exhaust port and a delivery
cavity
comprising: a generally cylindrical bore between the supply cavity and the
delivery
cavity, a flow diverter with an at least two legs portion wherein the flow
diverter is
placed in the bore such that the flow diverter freely moves to a first
position when the
pressure of the air in the supply cavity is greater than the pressure of the
air in the
delivery cavity, thereby restricting a minority of the air flow from the
supply cavity
to the delivery cavity through the at least two legs portion, and wherein the
flow
diverter with a restrictor portion freely moves to a second position when the
pressure
of the air in the delivery cavity is greater than the pressure of the air in
the supply
cavity, thereby diverting a majority of air from the delivery cavity to an
exhaust port
and allowing a minority of air to pass from the delivery cavity to the supply
cavity
traversing the restrictor portion.
Brief Description of the Drawings
[0008] In the accompanying drawings which are incorporated in and constitute a
part
of the specification, embodiments of the invention are illustrated, which,
together with a
general description of the invention given above, and the detailed description
given below,
serve to exemplify the embodiments of this invention.
[0009] FIGURE 1 illustrates a prior art valve;
[0010] FIGURE 2 illustrates a flow diverter as positioned during a brake
application in
accordance with one embodiment of the present invention; and
[0011] FIGURE 3 illustrates a flow diverter as positioned during a brake
release in
accordance with one embodiment of the present invention;
[0012] FIGURE 4 illustrates a perspective view of the flow diverter in
accordance
with one embodiment of the present invention; and
[0013] FIGURE 5 illustrates a graph showing test data.
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Detailed Description of Illustrated Embodiment
[0014] In order to provide decreased release timing, such as to meet the FMVSS
121
release timing requirements, the delivery air of the air brake system valve is
diverted to the
exhaust port in order to limit the amount of air returning through the inlet
port of the
valve. In this manner, the release timing is improved without significantly
increasing the
apply timing. The feature described below meets the required release timing of
FMVSS
121 without significantly restricting the inlet capacity of the valve (see
Figures 2 and 3)
such that the required apply timing of FMVSS 121 is met. The invention is not
limited to
features requiring compliance with FMVSS 121 release and apply timing
requirements,
but is discussed below in relation to features that will meet these
requirements.
[0015] As used herein, "apply timing" means the time from the first movement
of the
brake valve actuator (brake pedal) for the brake chamber to reach 60 psi with
an initial
service reservoir pressure of 100 psi. As used herein, "release timing" means
the time
from initial brake pedal movement (release) for a set of brake chambers
initially at 95 psi
to reach 5 psi. Unless otherwise specified, use of the term "or" herein is the
inclusive,
and not the exclusive, use. See BRYAN A. GARNER, A DICTIONARY OF MODERN LEGAL
USAGE 624 (2d Ed. 1995).
[0016] The release timing of a brake valve correlates to how quickly the
pressure of
the pneumatic fluid therein, often air, is released from the brake chamber 4
(see Fig. 1).
The more quickly the pneumatic fluid pressure applied to the brake chamber 4
is released,
the more quickly the brake will release. The present invention provides for a
restriction in
the fluid flow from the brake chamber 4 to more quickly begin fluid
communication with
an exhaust port and to redirect more of the fluid to the exhaust port after
the actuator 3 is
released. This creates a pressure differential across the exhaust diaphragm 2
to unseat the
exhaust diaphragm 2 and exhaust fluid. The greater the pressure differential,
the more
quickly the exhaust diaphragm 2 is unseated and the greater is the quantity
and speed of
the fluid exhausted. Unlike conventional valves that have some restriction,
however, the
present invention provides a restriction that does not significantly reduce
the incoming
fluid flow upon application of the actuator 3 to engage the brake. Therefore,
there is
minimal reduction of the apply timing due to the restriction.
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[00171 Generally, the restriction device, herein called a flow diverter, has
at least two
positions-a first or open position when the pneumatic fluid flows to actuate
the brake and
a second or closed position when the brake is released. When in the first
position, the flow
diverter does not significantly restrict fluid flow to actuate the brake. When
in the second
position, the flow diverter diverts fluid flow to the exhaust by restricting
the flow back in
the direction of the actuator 3. The flow diverter may divert all or a portion
of the fluid to
the exhaust. Thus, the flow diverter does not significantly reduce the apply
timing, as
does a conventional fixed inlet orifice 1.
[0018] FIGURE 2 illustrates a flow diverter 20 as positioned during a brake
application, in accordance with one embodiment of the present invention.
FIGURE 3
illustrates the flow diverter 20 as positioned during a brake release
operation, in
accordance with the embodiment illustrated in FIGURE 2. Air flow paths of the
delivery
air during brake application and release are shown by arrows in FIGURES 2 and
3,
respectively. Flow diverter 20 moves freely within a bore 22 according to
relative air
pressures in a supply (inlet) cavity 24 and a delivery cavity 26.
[0019] As shown in FIGURE 2, air from a service reservoir (not shown) enters
the
supply (inlet) cavity 24 via an inlet/outlet port 30 when a brake valve 32 is
actuated via,
for example, a foot pedal 34. The air creates pressure in the supply cavity 24
and passes to
a control side 36 of an exhaust diaphragm 40. The pressure created by the air
at the
control side 36 creates a stronger force on the exhaust diaphragm 40 than the
pressure on
the other side of the exhaust diaphragm 40 and urges the exhaust diaphragm 40
to seat
against a housing wall 42 at a point 44. Typically, the exhaust diaphragm 40
will be
biased to seat against the housing wall 42 at point 44. A portion of the other
side of the
exhaust diaphragm 40 is exposed to the pressure of delivery cavity 26 and a
portion is
exposed to the pressure of an exhaust port 46. The pressure of the exhaust
port 46 is
generally atmospheric pressure. As will be discussed in more detail below, the
seating of
the exhaust diaphragm 40 at the point 44 creates a seal between the delivery
cavity 26 and
the exhaust port 46. At the same time, the air creating pressure in the supply
cavity 24
also passes through a passage 48 between a supply (hold) diaphragm 50 and a
housing
wall 52.
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[0020] After passing through the passage 48, the air passes into the bore 22.
A flow
diverter 20, which is described in more detail below, is positioned within the
bore 22. The
air exits the bore 22 via a passage (not shown) into the delivery cavity 26.
Because of the
seal created between the delivery cavity 26 and the wall 42 at point 44, the
air entering the
delivery cavity 26 from the bore 22 does not pass to the exhaust port 46;
instead, the air
passes from the delivery cavity 26 to a delivery port 56 and then to a brake
chamber 60.
[0021] As shown in FIGURES 2 and 4, the flow diverter 20 includes a restrictor
portion 100 and a spacer portion 102. In the illustrated embodiment, the
restrictor portion
100 is flat; furthermore, the spacer portion includes a plurality (e.g., four)
of legs 102a,
102b, 102c, 102d. Additionally, an outer diameter of the restrictor portion
100 is sized to
be smaller than an inner diameter of the bore 22. In one embodiment, the outer
diameter
of the restrictor portion 100 is about 0.475 inches while the inner diameter
of the bore 22
is about 0.490 inches. The flow diverter 20 illustrated in FIGURES 2 and 4
represents
only one embodiment and other embodiments including other designs, shapes,
and/or
dimensions of the flow diverter 20 relative to the bore 22 are contemplated.
[0022] For example, the surface of restrictor portion 100 may be of any shape
suitable
for use, including regular or irregular polygons, such as rectangular,
pentagonal,
hexagonal, octagonal, or dodecahedral polygons. Preferably, the restrictor
portion 100 is
circular, if the cross-section of the bore 22 is circular. The diameter of the
restrictor
portion 100 is dimensioned relative to the diameter of the bore 22 such that
the restrictor
portion 100 provides sufficient resistance to the flow of air to divert a
sufficient amount,
preferably at least about 50%, of the air in the delivery cavity 26 to the
exhaust port 46.
The flow diverter 20 also is dimensioned so that there is minimal restriction
in the flow of
air from supply cavity 24 to delivery cavity 26. The restriction is such that
the desired
apply timing may still be obtained. Preferably, the flow diverter 20 provides
a restriction
in the flow in this direction of no more than about 25%. Therefore, one of
skill in the art
may determine the optimum diameter of the restrictor portion 100 without undue
experimentation.
[0023] Moreover, while the spacer portion 102 is illustrated with four legs
102a,
102b, 102c, 102d, there may be any number of legs, including three legs, so
long as there
is sufficient stability to enable the flow diverter 20 to divert the requisite
air to the exhaust
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port 46 without significantly restricting the flow of air from the supply
cavity 24 to the
delivery cavity 26 when the brake valve 32 is actuated. The number of legs may
be
chosen without departing from the spirit and scope of the invention.
[0024] The shape of the legs 102a, 102b, 102c, 102d is illustrated as
rectangular
prisms, but any suitable shape is contemplated, such as any suitable regular
or irregular
polygon, and is within the spirit and scope of the invention. The shape of the
legs 102a,
102b, 102c, 102d is to be selected such that there is minimal interference
with air flow
between the supply cavity 24 and the delivery cavity 26, while providing
sufficient
support for the restrictor portion 100. For example, the shape of the legs
102a, 102b,
102c, 102d may be selected to have tapering or curved portions to reduce the
turbulent
flow characteristics of the air and to reduce stress points on the flow
diverter 20. In one
design, the legs 102a, 102b, 102c, 102d have a triangular cross section. There
may also
be ribs between the legs or otherwise provided, for example, to provide
additional strength
for the legs.
[0025] The specific dimensions of the restrictor portion 100 and the spacer
portion 102
may be selected based on the circumstances and parameters of each particular
application
without departing from the spirit and scope of the invention. Suitable
dimensions may be
determined without undue experimentation based on the measurement of the
release
timing and apply timing of the brake.
[0026] Also, the flow diverter 20 may be a spherical ball or a cylindrical
slug or other
shape dimensioned such that, for example, the pressure of the air in the
supply cavity 24 is
sufficient to move the ball or slug substantially out of the way of the flow
of air from the
supply cavity 24 to the delivery cavity 26, but the ball or slug interposes
restriction in the
flow of air from the delivery cavity 26 to the supply cavity 24. Thus, the
flow diverter 20
need not have both a restrictor portion 100 and a spacer portion 102, but may
be provided
as one portion.
[0027] Although the flow diverter 20 has been discussed thus far as
restricting flow of
air from the supply cavity 24 to the delivery cavity 26, but allowing some
flow of air in
this direction, the flow diverter 20 may also completely restrict any flow of
air from the
supply cavity 24 to the delivery cavity 26. There need not be any leak by or
flow of air
back into the supply cavity 24 around or through the flow diverter 20. For
example, a
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flapper or check valve may be placed in or near the passage 48 that is in an
open position
when air is flowing from the supply cavity 24 to the delivery cavity 26, but
is in a closed
position when air is no longer flowing in that direction.
[0028] The material from which the flow diverter 20 is made may be any
conventional
material selected, for example, based on cost, availability, weight, or any
other parameter
without departing from the spirit and scope of the invention. Preferably, the
material is
plastic, but metals, such as aluminum, are also suitable. The specific
material chosen may
affect the restriction of fluid flow because of, for example, weight or
surface smoothness,
but the appropriate shape and dimensions for the chosen material may be
determined
without undue experimentation.
[0029] As illustrated in FIGURE 2, the flow diverter 20 is positioned in the
bore 22
upon a brake application such that the flow diverter 20 does not substantially
interfere
with the flow of air from the supply cavity 24 to the delivery cavity 26 via
the bore 22.
For example, the restrictor portion 100 is above the passage (not shown) from
the bore 22
to the delivery cavity 26. The legs 102a, 102b, 102c, 102d are designed such
that they do
not substantially interfere with the flow of air from the bore 22 to the
delivery cavity 26
upon brake application.
[0030] As shown in FIGURE 3, when the brake valve 32 is no longer actuated
(e.g.,
when the brake valve or foot pedal is released), air begins to flow from the
control side 36
of the exhaust diaphragm 40 into the supply cavity 24. Air in the supply
cavity 24 is
exhausted via the inlet/outlet port 30, thereby causing a pressure drop in the
supply cavity
24. Once the pressure in the supply cavity 24 drops, air begins to flow from
the delivery
cavity 26 to the supply cavity 24 via the bore 22. The flow diverter 20 is
then positioned
as shown in FIGURE 3. The restrictor portion 100 reduces the amount of air
that flows
from the delivery cavity 26 to the supply cavity 24 via the bore 22 and
passage 48.
[0031] Because a restricted amount of air is permitted to escape from the
delivery
cavity 26 via the bore 22 and, furthermore, because of the reduced pressure at
the control
side 36 of the exhaust diaphragm 40, the pressure of air in the delivery
cavity 26 urges the
exhaust diaphragm 40 to become unseated from the wall 42 at the point 44.
Consequently,
air passes from the delivery cavity 26 to the exhaust port 46 via a channel 62
defined
between the exhaust diaphragm 40 and wall 42. More specifically, the higher
pressure in
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the delivery cavity 26 unseats the exhaust diaphragm 40, directing the major
portion of the
delivery air flow out the exhaust port 46. The combination of low pressure on
the control
side 36 of the exhaust diaphragm 40 and high pressure on the seat side speeds
the opening
of the exhaust valve and the release timing of the valve.
[0032] As shown in FIGURES 2 and 3, the flow diverter 20 allows minimally-
restricted inlet flow during brake application and meters back flow during
brake release.
The metering of back flow quickly induces a differential pressure across the
exhaust
diaphragm triggering the opening of the exhaust seat. This unseating results
in the
improved release timing that meets the FMVSS 121 timing requirements.
[0033] The flow diverter 20 is a flow-activated device having two positions of
operation. During a brake application the flow diverter is moved by the
application air to
its minimally restricted open position. This allows the ABS valve to meet the
FMVSS 121
apply timing requirement. During the brake application release, the flow of
delivered air
carries the flow diverter 20 to its metering position (see FIGURE 3). At this
position the
flow diverter 20 diverts the majority of the air in the delivery cavity to the
exhaust port 46
and restricts the amount of air returning to the inlet/outlet 30 of the valve
32 through the
clearance between its outside diameter and the housing bore's inside diameter.
[0034] A valve available from Knorr Bremse with a part number of BR9164 was
fitted
with a flow restrictor 20 having three legs with substantially triangular
cross sections. In
this embodiment, the inner diameter of the bore 22 was about 0.490 inches and
the outer
diameter of the restrictor portion 100 was about 0.481 inches. FIGURE 5
illustrates a
graph 200 of test data showing a reduction in the amount of time for releasing
pressure in
the delivery cavity 26 (see FIGURES 2 and 3) from 95 psi to 5 psi. A line 202
shows that,
for these dimensions, it took about 0.564 seconds to release the pressure
without the flow
diverter according to the present invention. Furthermore, a line 204 shows
that, for the
same embodiment, it took about 0.267 seconds to release the pressure with the
flow
diverter according to the present invention. The reduction in flow area for
the air passing
from the supply cavity 24 to the delivery cavity 26 imposed by the flow
diverter 20 for
three different tests was about 23.3%, about 23.8%, and about 23.9%, with an
average of
about 23.7%, or less than 25%.
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[0035] While the present invention has been illustrated by the description of
embodiments thereof, and while the embodiments have been described in
considerable
detail, it is not the intention of the applicants to restrict or in any way
limit the scope of the
appended claims to such detail. Additional advantages and modifications will
readily
appear to those skilled in the art. Therefore, the invention, in its broader
aspects, is not
limited to the specific details, the representative apparatus, and
illustrative examples
shown and described. Accordingly, departures may be made from such details
without
departing from the spirit or scope of the applicants' general inventive
concept.
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