Dual area metering valve with variable reaction assembly

The invention relates to a service brake system for towed vehicles and particularly to a service brake system for double trailer combinations and a metering relay valve therefor. According to the invention, a variable reaction amplifying relay valve, controlled by service brake control line pressure, meters reservoir pressure from the leading trailer to the service brake control line in the trailing trailer. Below a predetermined pressure, the metering relay valve provides an amplified pressure output relative to input. Above this predetermined point, the output pressure is substantially one-to-one.

BACKGROUND OF THE INVENTION 
The invention relates to a service brake system for towed vehicles and 
particularly to a service brake system for double trailer combinations. It 
also particularly relates to a metering relay valve for use in such 
systems. 
In known fluid-actuated service brake systems, the service braking is 
effected by pulses of fluid pressure induced in a service brake control 
line controlling a relay valve near the brake actuators. It is well known 
that because of the travel time of the fluid pressure pulses due to the 
distance between the towing vehicle or tractor and the towed vehicle or 
trailer, the brakes of the tractor may be applied prior to the application 
of the brakes in the towed vehicle. This problem is further compounded in 
a following second trailer or a trailing towed vehicle. 
Various attempts have been made to increase the reaction speed to trailer 
braking. One solution has been the use of electrically operated valves 
which open or close by electrical command pulses. However, these known 
values require additional electrical wiring and control features which add 
complexity and greater chance for failure. 
Another approach, taught by Stelzer in the U.S. Pat. No. 3,001,831 
discloses an auxiliary valve interposed in the service brake line near the 
conventional emergency relay valve in order to increase the reaction speed 
of trailer braking. The valving action taught therein is that for a light 
pressure pulse in the service control line, the trailer braking pressure 
is to be brought to a point of nearly full braking pressure and then 
reduced ratio thereafter until at another point the delivered braking 
pressure is again finally approximately one to one with input pressure. 
While this valve reduced the delivery time of air pressure because of the 
amplification in the valve, there is no teaching of intermediate 
responsive control. Bray, in U.S. Pat. No. 4,090,738 teaches a booster air 
assembly including a relay valve having a closely coupled auxiliary air 
tank which may also be incorporated in a double trailer combination. The 
amplification of this valve is in one to one ratio up to a predetermined 
point where it increases to a ratio of 1.3 to 1. Speedup is predicated 
only upon the close proximity of the reservoir tank to the remainder of 
the system. 
SUMMARY OF THE INVENTION 
The present invention provides a desirable quick response of actuation of 
the brakes in a trailing vehicle of a double trailer combination at low 
control pressures in the service line of the leading trailer and at the 
same time there is an intermediate responsive control of pressure whereby 
the pressure to the brake actuators of the following trailer is increased 
in relation to the pressure in the service brake control line. It is only 
after the pressure in the service brake control line of the following 
trailer has reached a predetermined point that the brake pressure will 
correspond in substantially 1:1 ratio with the control pressure. 
In a system according to the invention, a variable-reaction amplifying 
relay is interconnected so as to be controlled by the service brake 
control line of the leading trailer. Air pressure from the conventional 
emergency line and the reservoir of the leading trailer is fed, under the 
control of the variable-reaction amplifying relay valve, to the service 
control line of the following trailer or towed vehicle. For trailing 
vehicle service control line pressure below a predetermined point, the 
variable reaction amplifying relay valve provides an amplified output 
pressure relative to the input pressure. Above this predetermined point 
the trailing vehicle service brake control line pressure is in one-to-one 
ratio with increases in the service brake control pressure. 
In an embodiment of the valve of the invention, a reaction piston is 
disposed in a cavity within an upper valve body. The cavity may be a 
stepped bore having one portion of relatively larger cross section than 
another. The reaction piston then comprises a piston head of relatively 
large cross section, slidingly and sealingly disposed in the portion of 
the stepped bore having the corresponding large cross section and an 
opposing piston head slidingly and sealingly disposed in the other portion 
of the stepped bore having a correspondingly smaller cross-section. In 
combination with a cover and a lower valve body the reaction piston 
divides the cavity into three separate chambers: a service control chamber 
of relatively large cross section between the cover and large piston head, 
a delivery chamber of smaller cross section at the opposite end of the 
stepped bore between the lower valve body and the smaller piston head, and 
a reaction chamber in a space between the piston heads. 
The service control chamber is in pressure communication with the service 
brake control line so that the reaction piston will move in response to 
the pressure in this line. The delivery chamber below the reaction chamber 
is selectively connected to an exhaust port for exhausting pressure from 
the delivery chamber or to a reservoir port for supplying pressure to a 
delivery port also in fluid communication with the delivery chamber. 
The movement of the reaction piston in one direction is operative to 
control a valve member in the lower valve body which serves to both open 
the communication with the reservoir port for supplying fluid pressure to 
the delivery chamber and to maintaining an exhaust valve portion in a 
closed position; movement of the reaction piston in the opposite direction 
will close communication with the reservoir port and open the delivery 
chamber to atmospheric pressure through the exhaust valve portion. The 
position of the reaction piston at one point is such that both the exhaust 
valve and the reservoir port are sealed from the delivery chamber so that 
a given pressure is maintained in the delivery chamber. This balanced 
position is conventionally termed a lapped position. 
In the lapped position, the pressure in the delivery chamber is such that 
the force against the smaller piston head exactly counterbalances the 
force due to the pressure in the control chamber against the large 
reaction piston head. When the reaction piston is force balanced, the 
ratio of pressure in the delivery chamber to the pressure in the control 
chamber is termed the amplification factor of the valve. The valve 
assembly thus enables a fluid pressure output to be amplified by a 
predetermined factor depending in known manner upon the ratio of cross 
sectional areas of the piston heads. That is, upon application of a given 
amount of pressure in the service control chamber, a corresponding 
amplified pressure will be supplied at the delivery port of the variable 
reaction amplifying valve. 
According to the invention, the variable reaction amplifying valve has 
further a reaction chamber defined by the enclosed volume between the 
seals of the large and small piston heads. Fluid pressure in this reaction 
chamber will provide an opposing pressure against the same effective area 
of the reaction piston as that in the service control chamber itself. The 
reaction chamber is in selective fluid communication with the delivery 
chamber so that until a predetermined pressure is reached, the reaction 
chamber is isolated from the delivery chamber. Fluid communication between 
the reaction chamber and the delivery chamber, through, for instance, a 
bore may be controlled by a check valve, which may be biased into a closed 
position by a suitable resilient means so that until a predetermined 
pressure is reached in the delivery chamber, there is no fluid 
communication from the delivery chamber to the reaction chamber. The force 
of the resilient means can be utilized to determine the point at which 
fluid communication will be initiated and also to assure that a pressure 
differential will be maintained between the reaction chamber and the 
delivery chamber. A pressure return check valve arrangement enables fluid 
communication between the reaction chamber and the delivery chamber 
whenever the fluid pressure in the reaction chamber exceeds that of the 
delivery chamber. 
Preferably, in order to establish the selective pressure communication, a 
reaction piston chamber is created within the reaction piston itself. This 
chamber is in open fluid communication with the reaction chamber. A blind 
axial bore extends from the chamber through the interior of the reaction 
piston into the small piston head. The blind axial bore is in fluid 
communication with the delivery chamber. 
A check valve arrangement is disposed in the axial bore to control the 
fluid communication. A resilient plug member is adapted to abut sealingly 
against a shoulder, for example, in this bore and may be biased into the 
closed position by a strong spring whose force may be calculated to 
correspond to the predetermined pressure at which it is desired to change 
the ratio of pressures from an amplified to substantially a one-to-one 
ratio. 
The return check valve may take the form of any well known conventional 
check valve arrangements but preferably, the resilient plug member is a 
hollow cylinder terminating in a pair of flaps on the lower portion of the 
resilient member forming a communicating slot between the reaction piston 
chamber and the blind axial bore. These flaps protrude into the bore so 
that the pressure on the delivery side against the outside of the flaps 
further tends to seal the flaps more tightly while pressure in the 
opposite direction, i.e., when the pressure in the reaction piston chamber 
is greater than the delivery chamber pressure, tends easily to force the 
flaps apart to allow the escape of pressure. 
It will be clear to persons skilled in the art that the variable reaction 
amplifying relay valve will operate so as to have an amplified pressure 
ratio so long as the pressure in the delivery chamber is below the 
predetermined point set by the check valve arrangement and at all higher 
pressures thereafter will provide a substantially one-to-one ratio of 
increases in control pressure to increases in outlet delivery pressure.

Referring to the drawing, the numeral 10 designates the schematic 
representation of the trailer brake system, in which a service line 12 and 
an emergency line 14 have glad hand connectors 16 and 18, respectively, 
for connection to mating connectors of conventional service and emergency 
output lines on a tractor (not shown). The emergency line 14 branches into 
two lines 20 and 22, line 20 being connected to a reservoir 24 and line 22 
leading to a shut-off cock 26. The service line 12 also branches with a 
branch 28 leading to a conventional relay valve 30. Relay valve 30 is 
interposed between the reservoir 24 and conventional service brake 
actuators 32. A line 34 leads from the reservoir 24 to the reservoir port 
36 of the relay valve 30 and the service brake actuators 32 are connected 
through line 38 to the delivery port 40 of this relay valve. 
After the shut-off cock 26, emergency line branch 22 branches again so that 
one branch 42 leads to an output emergency line connector 44 and the 
second branch 46 leads to a reservoir port 48 of the variable reaction 
amplifying relay valve according to the invention shown generally at 50. A 
branch 52 of the service line 12 connects to the service port 54 of valve 
50. The delivery port 56 of the valve 50 connects through line 58 to a 
service line connector 60. 
Preferably, the service line connector 60 and the emergency line connector 
44, respectively substantially match the tractor mating connectors (not 
shown). The connectors 44 and 60 are also adapted to connect to the input 
service and emergency connectors of a second trailing vehicle. Preferably 
the system shown here for one trailer is substantially identical to the 
second trailing vehicle so that the trailer position as either lead or 
following towed vehicle in a double trailering is irrelevant. In the 
system illustrated, the stop cock 26 is open when the trailer is in the 
lead position and closed when the trailer is in a following position, the 
variable reaction amplifying relay valve 50 according to the invention 
being utilized only when the trailer is in a leading position. While valve 
50 is especially adapted for use in connection with a double trailer 
arrangement, the valve may be installed in a tractor in similar manner to 
provide intermediate responsive control of pressure to the brake actuators 
of a single towed vehicle or trailer which does not have a valve 50. 
In FIG. 1 the variable reaction amplifying relay valve is shown generally 
at 50. An upper valve body 62 of suitable metal has a stepped bore having 
a reaction piston 64 slidingly and sealingly disposed therein. The 
reaction piston 64 also of suitable metal comprises a piston head 66 
sealed by sealing annular ring 68, which may conveniently be a neoprene 
O-ring engaged in a slot 69, sliding in a portion 70 of corresponding 
cross-section in the stepped bore. A step 72 of the stepped bore is 
connected to the step 70 by a shoulder 74. A correspondingly stepped 
portion 75 of the reaction piston sealed with sealing ring 76, preferably 
of neoprene, engaged in a slot 77, is slidably sealed within the stepped 
portion 72. 
The steps of the reaction piston 64 and corresponding steps 70 and 72 and 
shoulder 74 of the stepped bore define a reaction chamber 78 between the 
two sealing rings 68 and 76. The reaction piston 64 has an extension 80 
extending into the lower portion of the upper valve body 62. 
A cover 82 having the service port 54 is affixed to the top of the upper 
valve body by conventional means such as a plurality of threaded bolts 
(not shown) and carries a seal 84 in a slot 86 between the upper valve 
body 62 and the cover 82. The valve cover 82 and the reaction piston head 
define a service control pressure chamber 88. 
A lower valve body 90 is affixed to the upper valve body 62 by conventional 
means (not shown). An annular seal 92 seals between the upper 62 and lower 
90 valve bodies to define a delivery chamber 94 between the lower portion 
of the reaction piston at sealing ring 76 and the upper surface of the 
lower valve body 90. Delivery port 56 in the lower valve body 90 is in 
fluid communication with the delivery chamber 94 through a chamber 96. An 
axial bore 98 in the lower valve body 90 houses an exhaust-inlet valve 
assembly 100 further described below and reservoir port 48 is in direct 
fluid communication with this axial bore 98. 
A piston-return spring 102 biases the reaction piston 64 to the upward 
position illustrated in FIG. 1. 
Aperture 104 at the top of the axial bore 98 in the lower valve body 90 
enables downward passage of extension 80 of the reaction piston 64. The 
annular lip 106 of this aperture forms a valve seat for the inlet valve 
portion of the inlet-exhaust valve 100 as described below. The tip 108 of 
extension 80 and a lip 110 of the inlet-exhaust valve assembly 100 
cooperate to form an exhaust valve portion. 
The inlet-exhaust valve assembly 100 comprises an exhaust tube 112 having a 
flanged lip 110 at the top thereof. The tube 112 slides in a valve guide 
114 and is biased into a normally closed position by a valve return spring 
115 between the guide 114 and lip 110. In this normally closed position, 
the reservoir port 48 is sealed from the delivery chamber 94 by the 
sealing abutment of flanged lip 110 against aperture lip 106. The delivery 
chamber 94 is open to atmospheric pressure through the tube 112. Downward 
movement of the reaction piston through aperture 104 brings the lip 108 of 
extension 80 into sealing abutment with the lip 110 of the inlet-exhaust 
valve assembly 100. The sealing abutment seals the delivery chamber 94 
from the exhaust tube 112. Upon further downward movement of the extension 
80, the flanged lip 110 of the exhaust tube is forced from abutment 
against lip 106 which opens the reservoir port 48 to delivery chamber 94. 
A valve guide retainer 116 is sealed in the bore 98 by annular seal 118. An 
O-ring 120 between the exhaust tube 112 and the retainer 116 provides a 
pressure seal for the moveable valve assembly 100. An exhaust shield 122 
and the retainer 116 are held in place against the downward pressure of 
the valve return spring 115 by suitable means such as snap ring 124. 
The top of the reaction piston 64 comprises a cavity portion 126, suitably 
a cylinder of revolution, closed above by a retainer 128 held in place 
against a shoulder of the cavity in suitable manner, conveniently a 
snap-ring 130. A seal 132, suitably neoprene, provides a pressure seal. A 
blind bore 134 extends from the cavity 126 into the extension 80 of the 
reaction piston 64. A small bore 136 connects the delivery chamber 94 with 
the blind bore 134. A second small bore 138 connects the cavity 126 with 
the reaction chamber 78. 
The blind bore 134 has a shoulder 140 on which rests a tubular valve guide 
142 in force fit with the sides of the bore 134. The valve guide 142 
extends nearly to the lower surface of the retainer 128, but is always 
preferably manufactured to be of slightly shorter dimension than this in 
order to avoid a critically tight fit between the valve guide 142 and the 
retainer 128. The valve guide 142 has two small apertures 143 on opposite 
sides thereof opening into the chamber 126. 
A tubular rubber member 144 is slideable within the valve guide 142. 
Shoulders 146 of the tubular rubber member 144 sealingly abut the 
shoulders 140 of the blind bore 134 when normally biased into this 
position by check valve spring 148. The upper end of the check valve 
spring 148 may conveniently rest in a retaining aperture 149 in the 
retainer 128. 
The portion of the tubular rubber member 144 below the shoulders 146 
comprises two flaps 150 extending downward to form a resilient cylindrical 
slot 152 which somoothly changes to circular aperture 154 forming the 
interior of tubular rubber member 144. The top portion of the tubular 
rubber member 144 has a plurality of spaced small spherical proturberances 
156 which allow passage of air even when the resilient member is in 
abutment with the retainer 128. Similarly, the exterior sides of the 
tubular rubber member 144 may have ridges (not shown) parallel to its axis 
to assure passage of fluid from the blind bore 134 through the valve guide 
to apertures 143 whenever the tubular rubber member 144 is not seated. 
For operation of the service brakes when the system of FIG. 1 is installed 
in the leading trailer, the shut-off cock 26 is turned to the open 
position. Emergency fluid pressure is then fed from the mating connector 
(not shown) of a tractor emergency connector 18 to provide fluid pressure 
to the reservoir 24 and line 46 and 42 up to the maximum emergency fluid 
pressure for example 100 psi. Connector 44 then transmits the emergency 
pressure to a similar connector 18 in the following trailer. 
When the system is in use on a trailer in the following position, the 
shut-off valve 26 is placed in the off-position and no fluid pressure is 
transmitted to lines 42 and 46. Thus the portion utilized when the system 
is in the following trailer position is the reservoir 24, relay valve 30 
and brake actuators 32. The relay valve 30 operates upon application of 
service control pressure through line 28 to deliver reservoir pressure to 
brake actuators 32 of the following trailer. The service air delivered to 
the following trailer through glad-hand 60 and line 28 in the following 
trailer is supplied by valve 50 of the leading trailer in accordance with 
the present invention. 
Referring again to FIG. 1, the stop cock 26 is open in the leading trailer 
and service line pressure is delivered to service port 54 of valve 50 
through line 12 and 52 to establish control pressure in chamber 88 of 
valve 50 in the leading trailer when the brakes are actuated in the 
tractor. The pressure in chamber 88 begins to move the reaction piston 64 
in a downward direction until the tip 108 of extension 80 abuts lip 110 of 
the inlet-exhaust valve 100. At this point, delivery chamber 94 is sealed 
off from fluid communication with the exhaust tube 112 of inlet-exhaust 
valve assembly 100. Further downward motion of the reaction piston 64 
compresses valve return spring 115 and opens the inlet valve formed by the 
abutment of lip 110 of the inlet-exhaust valve and lip 106 of the aperture 
104. In this position, the delivery chamber 94 and thereby the delivery 
port 56 are in fluid communication with the reservoir port 48. The 
delivery chamber pressure thus begins to build toward the full emergency 
line pressure. 
As the pressure in the delivery chamber 94 begins to build, the force 
against the lower piston head opposing the downward motion of the reaction 
piston 64 will increase. The effective area of the upper piston head of 
the reaction piston is greater than the effective area of the lower piston 
head of the reaction piston by an amount which provides an amplification 
ratio in a known manner, preferably a ratio of 1.75 to 1. Thus, as the 
pressure in the delivery chamber 94 builds to approximately 1.75 times the 
pressure in the service control chamber 88, the reaction piston 64 moves 
to a position that balances all of the forces upon it. In the balanced 
position, the inlet valve is closed and lip 110 of valve assembly 100 is 
seated on lip 106. When in balance, the force provided by the pressure in 
the service chamber against the larger piston head 66 is counter balanced 
by the force of the air pressure against the lower piston head and the 
force provided by the piston return spring 102. At the balance point, also 
known as the lapped position, the exhaust valve 103,110 remains closed so 
that a pressure of approximately 1.75 times the control pressure is 
maintained in delivery chamber 94. This pressure relationship is 
maintained for delivery chamber pressures up to a predetermined pressure 
point, which may for example, but not as a limitation, be 30 psi. Other 
predetermined points may of course be utilized depending upon such factors 
as the length of conduit connected to the delivery port as well as the 
parameters of the conventional relay valve 30 chosen for use in the 
system. 
Until the predetermined pressure is reached, the tubular rubber member 144 
remains closed by being biased against the shoulder 146 of the blind bore 
134 in the reaction piston 64. The flaps 150 of the tubular rubber member 
remain tightly compressed by the pressure in the delivery chamber 94. The 
pressure in the delivery chamber is finally sufficient to overcome the 
force of check valve spring 148 and the tubular rubber member is opened 
and forced away from the shoulder 140. Fluid pressure is thus transmitted 
through small bore 136 through blind bore 134 and passed through apertures 
143 in the guide member into cavity 126. Cavity 126 is in fluid 
communication with the reaction chamber 78 through small bore 138. Once 
the pressure inside the cavity 126 is sufficient so that the force on the 
tubular rubber member 144 plus that of valve spring 148 matches the force 
on the delivery chamber side of the tubular rubber member, the tubular 
rubber member once again seats against shoulder 140. Thus, a metered 
amount of pressure, with a pressure differential corresponding to the 
force of the chosen valve spring 148, is metered to the reaction chamber 
78. 
The new differential pressure in the reaction chamber 78 acts on an 
additional surface area which when combined with the surface area of the 
reaction piston 64 in the delivery chamber 94 is equal to the full area at 
the top of the reaction piston in service control chamber 88. Thus, above 
the predetermined point, the change in pressure at the delivery chamber 
and thus the delivery port is decreased to a ratio of one-to-one with that 
of the control pressure instead of an amplified ratio. 
When service control line pressure is released, pressure quickly exhausts 
from the service pressure control chamber 88 through service port 54. The 
forces on the reaction piston 64 are thus unbalanced and the reaction 
piston travels rapidly upward impelled by the pressure unbalance as well 
as the piston return spring 102. As the extension 80 lifts from the lapped 
position, the inlet valve portion (106,110) remains closed and the exhaust 
valve portion (110 103) opens to quickly exhaust pressure from the 
delivery port 56 and the delivery chamber 94. As the pressure in the 
delivery chamber decreases below that in the cavity 126 in the reaction 
piston 64, the flaps 150 of the tubular rubber member are forced open by 
the increased pressure in the cavity 126 over that of the delivery chamber 
94 and reaction chamber 78 and cavity 126 are exhausted through the 
exhaust valve (110,103). The reaction piston 64 finally returns to the 
position shown in FIG. 1, awaiting the next cycle of brake application and 
release. 
Service air pressure delivered by valve 50 to the relay valve (30) which 
actuates the brakes in the second following trailer is at first supplied 
in a selected amplified ratio to the service air that actuates the brake 
relay valve in the leading trailer. This gives a quick response to brake 
actuation and an intermediate responsive control of pressure to the brake 
relay valve in the second following trailer until the pressure delivered 
by valve 50 reaches the selected predetermined level. Thereafter service 
air pressure on the relay valve 30 in both trailers is generally equal. 
It will be clear to anyone skilled in this art that the ratios of effective 
areas of the upper and lower piston heads of the reaction piston may be 
varied to provide amplification other than 1.75 to 1. It is also clear 
that various predetermined points for the change from an amplified output 
to a one-to-one ratio output may be made by changing either or both the 
force of the valve return spring 148 or the diameters of the bore 134. 
It will be understood that the claims are intended to cover all changes and 
modifications of the preferred embodiment of the invention, herein chosen 
for the purpose of illustration which do not constitute departures from 
the spirit and scope of the invention.