Note: Descriptions are shown in the official language in which they were submitted.
V.~HICLE AIR BRAKE
SYS~EM WITH PRESSURE
SEPARATING BRAKE HOU~ING
BACKGROUND OF THE INVENTION
Field of the Invention
This invention pertains to a vehicle brake
system employing two separate air pressure supplies and an
improved brake assembly compatible therewith for connect-
ing to the two supplies and utilizing the pressures
supplied thereby under varying conditions o~ operation.
Description of the Prior Art
Parking, emergency and service air brake systems
that are presently employed on trucks, trailers, truck
tractors, busses and other air-brake equipped vehicles
generally include dual diaphraym brake chambers for all
non-steerable axles and single diaphragm brake chambers on
all steerable axles. The pressure supply systems which
a~e employed in such air brake systems generally comprise
compressors and reservoirs along with multiple valves
employed for the various operating modes of the brake
system. There are generally two separate air systems
employed, namely, a service or primary system, and an
emergency or secondary system. Not only are the valves
numerous, but they vary in complexity of construction.
Variously such valves include service relay valves, spring
brake control valves, quick release valves and others.
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Operationally, treadle valves are commonly used for
service brake applications and pressure-regulated, push-
pull valves are used for parking and emergency applications.
Further, the power or pressure supply equipment utilize
one-way and two-way check valves or other protection
valves to protect one air system from another.
The purposes of having two air systems and the
rather complex valving arrangements that operate therewith
are many. One purpose is to provide safety in the event
that there is a complete loss of air of one of the systems
or at a connection between the tractor and the truck
trailer of a motor truck vehicle. A further feature
provided by such systems is to allow a driver to release
and reapply brakes in the event of pressure loss in one
side of the system. Therefore, it is apparent that safety
and back-up operation are important in air brake systems.
In fact, federal and state highway safety laws require
that air sys-tems meet certain requirements, including not
only having a primary/secondary pressure operation, but
also with regard to providing braking for emergency and
parking operation in the event of complete loss of pressure.
The most prevalent systems employed in the prior
art to meet this latter requirement utilizes a "spring
brake," the operation of which is relatively simple. Such
a spring brake operates in conjunction with a dual diaphragm
brake chamber, namely, a service diaphragm brake chamber
and an emergency diaphragm brake chamber~ During normal
driving operations the emergency diaphragm receives air
pxessure from the emergency reservoir keeping the brake
spring compressed. This brake spring, when not compres-
sed, operates in a direction to actuate the brakes. As
the service brakes are applied, air is applied against the
service diaphragm, causing the push or actuator rod of the
brakes to advance and apply the brakes.
When there is a loss of air in the service
system, the service brakes become inoperable and the
spring is activated by exhausting air from the emergencv
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diaphragm, thereby permitting the brakes to be applied by
the mechanical force of the spring, which is also augment-
ed in some cases by manual effort.
A co~on shortcoming of such a system is evident
when there is a failure of the emergency air system. When
there is a loss of emergency air pressure, the air applied
against the emergency diaphragm will exhaust and the
brakes wiL1 be applied by the spring automatically, even
at highway speeds. Such result can be unexpected and even
cause loss of control of the vehicle.
Another shortcoming of the prior art system just
described is in conjunction with applying the brakes when
parking. When the driver of the vehicle decides to stop
and park the vehicle by applying the parking brake, the
service air is unaffected. The emergency air against the
emergency diaphragm is exhausted to allow the spring to
move the actuator rod foxward to app]y the brakes. The
same separation occurs when a trailer is disconnected from
the tractor or other towing vehicle. That is, the air
supply lines, and especially the emergency air supply
line, is disconnected. This vents or e~hausts the emer-
gency diaphragm and causes the spring to set the brakes.
Brakes are released by restoring the air pressure against
the emergency diaphragm. If it is desired to release the
brakes, there must be an air supply. Otherwise, the
brakes can be manually released only by employing a
special tool that requires considerable effort to operate
and which exposes the user to safety hazards.
In further discussion of the shortcomings of
prior art system, consider also the hazardous nature of
the mechanism. The spring contained in the chamber must
be extremely strong to brake a heavy vehicle. It can be
under as much as 1800 pounds of force. Hence, it can
literally explode from its housing should the housing
corrode and weaken. Further, corrosion cannot be readily
inspected. Moreover, should a mechanic remove the clamp
ring retaining the spring without first taking the
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precaution of suitably externally restraining the housing
parts, the spring will e~plode from the housing. Such an
event has often caused injury and even death.
The chambers are large in size and are heavy.
Because of their proximity to the axle, there is not much
shock absorbing or cushioning of the chambers. Hence, they
are subject to axle vibration, which can cause loss of air
through the connectior.s of the chamber or lines and valve
parts connected thereto. ~s mentioned, high speed lockups
will occur when there is a sudden emergency line pressure
loss, such as with a line rupture.
~ nother disadvantage of the prior art air system
described above is that it can cause severe and premature
brake lining and brake drum wear. This wear results from
i5 brake drag caused by seal leaks between the emergency and
service chambers. That is, when air restraining the
spring leaks into the service chamber, this can cause the
brakes to partially apply. Hence, drum and lining contact
is made, resulting in reduced fuel economy, increased
brake heat that reduces application forces and increased
lining and drum wear.
Therefore, it is a feature of the present
invention to provide an improved air brake system generally
avoiding the safety and maintenance problems associated
with conventional air brake systems employing spring
brakes.
It is another feature of the present invention
to provide an improved air brake assembly utilizing a
single diaphragm with a mechanical locking device without
using a brake-actuation spring.
It is yet another feature of the present invention
to provide an improved air brake assembly utilizing a
simplified two-way check valve in combination with a
single diaphragm assembly i~ such a manner to avoid sudden
brake applications but assuring brake applications in
emergency and parking situation when the power supply
lines are disconnected intentionally or unintentionally.
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SUMMARY OF THE INVENTION
The invention in one broad aspect pertains to a vehicle
brake assembly for opera-ting a brake actuator rod, which brake
assembly includes a pressure housing with a first opening on one
side thereof through which the actuator rod axially operates in a
braking direction and a return direction opposite thereto, and a
diaphragm positioned for actuating the actuator rod in the
braking direction. The pressure housing has a second opening on
the side of the diaphragm opposite from the actuator rod for
receiving pressure for actua-ting the diaphragm. A two-way, open-
center shuttle valve is connected to the second opening having a
first input port on one side of its center for receiving pressure
from a service pressure supply and a second input port on the
other side of its center for receiving pressure from an emergency
pressure supply. A balance of service and emergency pressure
keeps the shuttle of the open-center shuttle valve cen-tered so
that the common pressure of the service and emergency pressures
provide actuating pressure against the diaphragm. An imbalance .
oE the service and emergency pressures closes the two-way valve
input port to the low pressure one of the imbalance service and
emergency pressures while maintaining pressure from -the high
pressure one of the imbalance service and emergency pressures.
The preferred embodiment of the invention includes a
brake assembly at each brake actuator rod whichincludes a single
diaphragm chamber. The diaphragm drives the brake actuator rod
forward to apply the brakes when a sufficient pressure is
supplied to the air receiving inlet side of the chamber.
Otherwise a return spring returns the actuator -to release the
brakes.
The input port to the chamber is connected to a two-
way, open-center shuttle valve, one input to the valve being
connected to the service or primary air supply and the other
input to the valve being connected to the emergency or secondary
air supply. If the supplies are of equal pressure, then the
shuttle valve is centered and both supplies equally enter into
pressurizing the diaphragM chamber. In the service application,
the supply pressure is increased to more than the emergency side,
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thereby closing the emergency lnput side. If there is failure
or loss of pressure on either side, but not both, the valve will
shut off the low pressure side and operate normally with respect
to the remaining pressurized side.
The feature of the brake assembly not requiring air
pressure to actuate the brakes includes a rack and e~ergency
piston having a pawl end which engages and holds the actuator in
place when there is loss of supply pressure and the brakes have
been actuated. Prior to such actuation, an adequate supply of
emergency air pxessure maintains the pawl end in its disengaged
state. After the pawl end is engaged, then a resupply of
pressure applied to the emergency side of the shuttle valve and
to the piston will relieve the holding pressure between rack and
pawl, while lifting the pawl from the rack.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above-recited
features, advantages and objects of the invention, as well
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as others which will become apparent, a~e attained and can
be understood in detail, more particular description of
the invention briefly summarized above may be had by
reference to the embodiment thereof which is illus-trated
in the appended drawings, which drawings form a part of
this specification. It is to be noted, however, that the
appended drawings illustrate only a preferred embodiment
of the invention and are therefore not to be considered
limiting of its scope, for the invention may admit to
other equally effective embodiments.
In the Drawings
Fig. 1 is a cross-sectional side view of a pre-
ferred embodiment of a brake assembly in accordance with
the present invention, with the diaphragm and brake
actuator in the non-applied brake condition.
F-Lg. 2 is a cross-sectional side view of the
embodiment shown in Fig. 1 with the parts shown in the
service or emergency brake application condition.
Fig. 3 is a cross-sectional side vicw of the
embodiment shown in Fig. 1 with the parts shown in the
parking application condition.
Fig. 4 is a cross-sectional view of a two-way
check valve connected to a brake assembly in accordance
with a preferred embodiment of the present invention.
Fig. 5 is a diagram of a preferred fluid supply
system in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
_
- Now referring to the drawings and first Figs.
1-3, a brake assembly 10 in accordance to the present
invention is respectivel~ shown in cross-sectional views
in three operating conditions. A housing 12 defines a
chamber 14 in conjunction with a cover 16. An opening in
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housing 12 accommodates the a~ial movement of brake push
or actuator rod 18. A movement in direction 20 to the
right as shown in the drawing applies the brake which
operates in conjunction with the actuator rod.
The portion of rod 18 which is contained within
chamber 14 includes actuator rod plate 22. A return
spring 24 located between plate 22 and housing 12 internal-
ly within chamber 14 biases actuator rod in the return or
opposite direction from direction 20.
A single diaphragm 26 is held by the joining of
cover 16 to housing 12 and divides chamber 14 into two
sections, namely, the actuator section on the right in the
drawing in which the actuator rod is located and the air
section on the left in the drawing to which air is applied
under pressure. An inlet opening for pressurized air is
established through cover 16 at port 28 at the upper left
portion of the drawing.
In Fig. 1 it is assumed that no service or emer-
gency air is being applied at inlet port 28; therefore,
diaphragm 26 is in its depressurized condition allowing
actuator rod 18 to be at its full left or deactuated
position, as shown.
Fig. 2 shows what happens to the parts upon
application of service or emergency brake air pressure at
inlet port 28. Note that air fills the left portion of
chamber 14 to move the center portion of diaphragm 26 to
the right. Such diaphragm movement causes the diaphragm
to contact actuator rod 18, which causes the actuator rod
to move to the right or direction 20, thereby applying the
brake of the vehicle connected to the rod. At the same
time, return spring 24 is compressed. Spring 24 is not a
powerful spring but is only sufficiently strong to return
the actuator rod to the left upon release of actuating air
pressure from the left side of chamber 14.
Fig. 3 shows the condition of the brake assembly
in the parking application condition. Prior to describing
this condition, further parts of the drawing need to be
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identified. The upper portion of actuator rod 18 is
machined to form a rack having the vertical sides on the
right side of each tooth depression in the ramp side of
each tooth on the left, as shown in the drawing. Hence,
when the pawl end of a piston is inserted at right angles
to the rack, the pawl-and-rack action constrains actuator
rod 18 from moving to the left but allows actuator rod to
move in direction 20 to the right with the application of
additional actuating force on the actuator rod.
Piston rod 30 operates within its piston housing
and includes the conventional parts with O-rings and the
like to permit easy operation in its piston housing. A
bias spring 32 is also included for urging piston 30 in
the downward direction. A port 34 in the piston chamber
or housing below the large center portion of the piston is
connected to an emergency air supply for acting in the
opposing direction to the bias action of spring 32. That
is, if the applied pressure to port 34 is above a predeter-
mined level, the downward force of spring 32 is overcome
and piston 30 will be held so that its pawl end is out of
engagement with the rack previously described. If the
applied pressure at port 34 is below that level, then the
pawl end is pushed into engagement with the rack.
Now referring to Fig. 4, a cross-sectional view
of a check valve 40 with an open-center shuttle valve
mechanism 42 is illustrated. Air pressure from the valve
is applied to port 28 of the brake assembly illustrated in
Figs. 1-3. Check valve 40 has two inputs, namely, ports
44 and 46, input port 44 being connected to the service
air supply system of the overall air brake system and
input port 46 being connected to the emergency or secon-
dary air supply system. Shuttle valve mechanism 42
operates within valve chamber 48 and is free to move
either to the left or to the right of the center position
sho~n depending on the pressure differential appearing at
the inlet ports. Center portion 50 of the shuttle mech-
anism is circumferentially larger than its end portions 52
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and 54 on either side thereof. However the internal
dimension of chamber ~8 in which center portion 50 operates
is larger than the dimension of 50 to permit passage of
air from either direction passing thereby and out port 28,
although applying some side pressure to center portion ~0
as it does so. Port 28 opens into internallv the large
portion of chamber 4~, preferably at center position.
End portions 52 and 54 of the shuttle valve
mechanism operates respectively within portions of chamber
48 which are just slightly larger than these end portions
and hence air passage is permitted to pass by. When
center portion 50 moves to its limit to the left in the
drawing shown, however, the contact of the shuttle valve
mechanism with the shoulders of the reduced portion of the
chamber forms an effective seal with center portion 50
that prevents air flow from entering into the center
portion of chamber 48 from inlet port 44. In similar
fashion movement of center portion 50 of the shuttle
mechanism seals off inlet port 46 when the valve mechanism
is moved to its full righthand position.
In operation it will be seen that when the air
pressure applied at inlet port 44 and inlet port 46 are
the same, the shuttle valve mechanism assumes its center
position. Hence, the pressure in chamber 48 will be equal
to the two inlet pressures. This will also be the pressure
delivered to outlet port 28.
However, if either inlet air pressuxe is greater
than the other, the shuttle valve mechanism will move to
seal off the low pressure side and only the high pressure
will be presented to port 28.
Now turning to a typical alr supply system for a
vehicle operating in conjunction with four brake assemblies
and shuttle valve mechanisms previously discussed, refer-
ence is made to Fig. 5. A service or primary supply
reservoir 60 is shown receiving air from an air comprcssor
~not shownl on line 62 into its input connectlon 64.
Input connection 64 includes a pressure protection valve.
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This valve is set to prevent air pressure to build up in
reservoir 60 until after it has built up to a pre-established
high level pressure setting, normally 70 psi in reservoir 68. In
addition, the valve also includes a one-way check valve that
prevents any air to flow back in line 62 from the reservoir. The
outlet of reservoir 60 is to relay valve 66 from which air is
further distributed in a manner described more fully hereafter.
Relay valve 66 can be of a Type R-12 relay valve manufactured by
the Bendix Corporation Heavy Vehicle Systems Group, or
equivalent. Typically, air applied to the service port of the
valve from service line 76 forces a relay piston down against a
biasing spring to open a supply port connected to reservoir 60 to
permit flow through four delivery ports to lines 72. Varying the
pressure on line 76 causes the opening of the supply and delivery
ports to vary accordingly to regulate the amount of brake
application.
Emergency or secondary air reservoir 68 is
likewise connected to the air compressor via supply line
62. Input connection is made to the reservoir through a
relay emergency valve system 70, also explained more fully
hereafter. Relay emergency valve 70 can be a Type
RE-6 relay emeryency valve manufactured by the Bendix
Corporation Heavy Vehicle Systems Group, or equivalent.
It has several operating modes. The first is when it is
receiving high pressure air from a supply source for
pressurizing reservoir 68 and supplying air to the
delivery ports connected to the respective brake chambers
it is receiving such air through a one-way check valve, so
that no air can escape from reservoir 68 if line 62 is
ruptured. The actual pressure delivered to the brakes is
controlled in the same manner as for relay valve 66
described above. During initial air up, after a
predetermined high level pressure ls supplied to the
delivery ports at the reservoir, for example, 50 psi,
these delivery ports are closed and the excess pressure is
.,
exhausted by an exhaust piston while reservoir pressure
continues to increase. As long as the supply pressure is
maintained above a predetermined low level supply
pressure, for example, 45 psi, a spring is compressed and
operation is in accordance with the above operating mode.
When the supplv pressure decreases to under 45
psi, then the spring e~tend~ and opens air flow from
reservoir 68 to the delivery ports for fully applying the
brakes. At manual operating pressures, the service
function is as stated for a relay valve. That is,
operation is the same as with adequate supply air except
it is with respect to air supplied from reservoir 68. At
the same time, a one-way check valve prevents air in
reservoir 68 from escaping through the supply line,
thereby isolating air in reservoir 68 for emergency and
parking applications.
The output from primary supply
reservoir 60 shows for example, four
brake assemblies 10, which are the same as the brake
assemblies detailed in Figs. 1-3, that are each connected
through a two-way check valve connector 40 via lines 72.
T~wo of these substantially identical brake assemblies are
typically connected to a non-steerable axle. These
connections are made to inlet port 44 of the respective
connectors, as previously discussed in connection with the
detailed description of Fig. 4.
In similar fashion each of the two-way check
valves 40 is connected through relay emergency valve 70 to
receive emergency air via lines 74. Lines 74 are
connected to respective inlet ports 46 of the check
valves.
Service line 76 is connected for application
of pressure by the operator through a mechanism not shown,
but which is typically a piston pump. Service line 76
is connected to both service valve 66 and emergency valve
relay 70,
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The parking capability which was described in
connection with Fig. 3 is provided by lines 78 to the brake
assemblies via relay emergency valve 70 connected to emergency
reservoir 68 or connected directly to reservoir 68. Lines 78
connect respectively to ports 34 leading to the piston chambers.
This pressure is from the same source as the pressure carried in
line 74 (namely, reservoir 68).
In operation, service pressure applied by the operator
on line 76 causes relay valve 66 to connect lines 72 to receive
actuation pressure from reservoir 60 and causes relay emergency
valve 70 to connect lines 74 to receive actuation pressure from
reservoir 68. Assuming that these pressure levels are the same,
the shuttle mechanism of each of the check valves will assume its
center position and the supply of pressure will cause the brake
to actuate as previously described in connection with the
description of Fig. 2. If the pressure of one of the systems is
low or lost because there is a rupture or open connection, the
brakes will still actuate in the desired manner because of the
operation of the two-way check valve as discussed in conjunction
with Fig. 4.
In order to set the emergency or parking brake,
relay emergency valve 70 is operated by means not shown
but separate from reservoir 60, relay valve 66 and lines
72. This is done by a control that effectively opens or
shuts off supply pressure on line 62. The existence of
the one-way check valve at connection 64 prevents air from
reservoir 60 entering line 62 to delay the emergency
braking application. The application of emergency or
parking brakes in this manner causes the relay emergency
valve 70 to be set so that pressure from reservoir 68 is
supplied through lines 74 against diaphragm 26, as discussed
above. Parking is provided by the system by the
application of such air pressure so long as that pressure
is in excess of that which is required to retain spring 32
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in its compressed condition. When the pressure falls
below a predetermined pressure level, the expansion force
supplied by spring 32 causes the pawl end of piston 30 to
engage the rack surface of actuator rod 18 and the brake
holding then becomes mechanical. Subsequent removal of
the remaining air pressure from the left side of diaphragm
26 does not affect the holding condition of the pawl and
rack.
The control mentioned above on a typical air
brake system employed on tractors and trucks for setting
the emergency brakes employs a push-pull pressure
regulated valve. When this valve is pulled, it interrupts
the flow through the supply line and vents the line
pressure to the atmosphere. The same valve is also
designed to automatically disengage the supply line at a
pre-set low pressure, usually 45 psi, to cause the relay
emergency valve to automatically switch over to emergency
operation Eor setting the brakes, as described above.
Any interruption in supply line pressure, no
matter how much pressure is established in reservoir 68,
will establish operation with respect to the emergency air
supply. For example, if a trailer becomes disconnected at
highway speeds, the application would be automatic at full
tank pressure and there would be no loss of air because of
the one-way check valve in relay emergency valve 70.
To release the parki.ng brake mechanism, service
and/or emergency air is applied to the left side of the
respective brake assemblies, as previously discussed,
thereby putting pressure on actuator rods 18 in the
direction 20. This relieves the friction holding of the
pawls and racks. At the same time emergency air is
reestablished to ports 34 to move the piston rods upward
which takes the pawls out of their rack contacts. Now the
brake assemblies are released to operate in the previously
discussed manner.
It will be seen that a two-way valve 40
connected to each of the brake assemblies allows a single
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diaphragm brake with a mechanical locking device to
operate in a superior manner to the prior art assembly
that included a powerful brake actuation spring, as
discussed in the prior art section above. A loss of
pressure on either side of the shuttle valve mechanism
will close that side to prevent air loss from the other
side. Such a two-way check valve offers a further safety
advantage by balancing the air pressure during service
brake application by allowing the shuttle to move in
either direction so to absorb shock received when the
brakes are applied such as when the vehicle is on a rough
surface. Such movement reduces pressure from one chamber
to another; however, because of the double pressuring of
the brake assembly from both supplies there is no locking
up of the brakes, as is a distinctive possibility with the
prior art spring brake.
If there is a complete failure of the system,
please note that the emergency air system can operate as
the service system through the relay emergency valve 70
and the two-way check valves 40 at each of the brake
assemblies.
A further advantage of the two-way check valve
which has been discussed is that the valve allows pressure
build up in a discharged air tank or reservoir by keeping
the reservoir outlets closed until the air has been
pressurized to operating conditions.
Spring 32 which operates in conjunction with
piston 30 applies preferably a pressure of 40 to 60 psi in
order to cause pawl engagement. It has been observed that
this pressure application produces all of the needed force
required to hold a vehicle fully loaded to it axle rating
on a 20 degree grade. Note that this spring tension is
much less than the actuation springs contained in conven-
tional spring brakes which as previously discussed are
under typically 1800 pounds of force.
Although numerous features have been shown and
described, it will be understood that the invention is not
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limited to the particularly embodiment shown since many
modifications may be made and will become apparent to
those skilled in the art.
For example, a large vehicle will typically have
more than two non-steerable axles and, hence, more than
four brake assemblies.
Although not discussed above in connection with
the above operation, a tractor protection valve exists on
towing vehicles such as txuck tractors that protects the
tractor air system if a failure exists in line 62 or line
76. This valve closes when the tractor supply decreases
to an unsafe level.
A truck trailer will also typically include
disconnecting parts wherein the brakes are set and the cab
or tractor portion is removed. In some cases the truck
trailer will include an air system supply, but in many
cases they will not. Therefore, to release the emergency
brake, either an auxiliary air connection will have to be
made or the assemblies will include an auxiliary means for
releasing the piston pawls and, hence, the brakes.
Mechanical means can also be included to reestablish the
piston pawl and rack parking connection.
