Relay valve

A relay valve for a vehicle brake system having an operating piston which moves in one direction in response to entry of a control pressure into one part of the valve and which by that movement causes an orifice to open whereby working pressure is allowed to enter another part of the valve and pass from there through various outlets. There are six outlets and each is connected to a respective brake assembly of the vehicle brake system. A damping piston is connected to the operating piston so as to move therewith and is subjected to the same pressure as that acting against one side of the operating piston but in a manner such as to provide resistance to movement of the operating piston in the aforementioned one direction.

This invention relates to a relay valve which is operable in response to a 
control signal to open and thereby connect an outlet port or ports thereof 
to a source of pressurized fluid. Such valves are used in vehicle brake 
systems and particularly pneumatic brake systems, and the present 
invention is especially concerned with brake system relay valves. It will 
be convenient to hereinafter describe the relay valve of the present 
invention in relation to vehicle air brake systems, but it may be usable 
in other brake systems. 
The control signal for a relay valve of the foregoing kind is derived from 
a source of pressurized fluid and the pressurized air to be passed to the 
outlet ports when the valve opens is derived from another relatively large 
volume of working supply source. Each outlet port of the valve 
communicates with a respective brake which is to be operated by the 
pressurized air of the working supply. The control source fluid may be air 
also and that source may be of relatively low volume so that the relay 
valve acts to amplify the control signal. 
A particular application for such a relay valve is in the air brake systems 
of semi-trailers where a low volume control signal is applied in response 
to operation of the vehicle brake pedal, and the relay valve then operates 
to connect a high volume source of working compressed air to the brake 
assemblies so as to cause operation of the brakes. The control signal 
pressure is approximately proportional to the foot pressure applied to the 
brake pedal and the relay valve is operable to apply a generally 
proportional pressure of the working compressed air to the brake 
assemblies. 
Relay valves of the foregoing kind have been reasonably satisfactory in air 
brake systems for semi-trailers having two axles and requiring operation 
of four separate brake assemblies. In that particular application, the 
relay valve has four outlets, each of which is connected to a respective 
brake assembly. It is now quite common however, for a semi-trailer to have 
three axles and therefore six separate brake assemblies. Conventional 
relay valves have proven to be inadequate for such applications when 
modified to enable operation of six brake assemblies. One particular 
problem with such modififed valves is that they suffer instability under 
brake applying conditions such that the valve continually "hunts" between 
open and closed positions and that reduces the effectiveness of the brake 
system. 
Because of the foregoing problem, it is common practice to use two 
four-port relay valves in a tri-axle brake system. One valve is connected 
to four of the brake asemblies and the other valve has two of its outlet 
ports closed and the other two are connected to the remaining two brake 
assemblies. 
It is an object of the present invention to provide a relay valve in which 
the problem of "hunting" is overcome or is at least substantially reduced. 
It is a further object of the invention to provide such a relay valve 
which can be connected to six separate brake assemblies. It is yet another 
object of the invention to provide such a valve which incorporates a 
number of parts of a conventional four-port relay valve. 
According to the present invention, there is provided a relay valve for use 
in a vehicle brake system including, a control chamber connectable to a 
source of control pressure, an operating member exposed to said control 
chamber and being movable in one direction under the influence of said 
control pressure, an inlet connectable to a source of working pressure, a 
feed chamber, a plurality of outlets connected to said feed chamber, 
closure means responsive to movement of said operating member in said one 
direction to open communication between said inlet and said feed chamber, 
a damping chamber connectable to a pressure source, and a damping member 
exposed to said damping chamber and being operative in response to 
pressure therein to resist movement of said operating member in said one 
direction. 
The essential features of the invention, and further optional features, are 
described in detail in the following passages of the specification which 
refer to the accompanying drawings. The drawings however, are merely 
illustrative of how the invention might be put into effect, so that the 
specific form and arrangement of the features (whether they be essential 
or optional features) shown is not to be understood as limiting on the 
invention.

The example relay valve 1 shown in the drawings includes a body having 
therein a main cylindrical compartment 3 in which an operating piston 4 is 
movable. The piston 4 divides the compartment 3 into two chambers 5 and 6. 
The chamber 5 is, in use, connected to the control source 7 (FIG. 4) 
through a port 32 and forms a control chamber, and the other chamber 6 
functions as a feed chamber. 
The operating piston 4 is connected to valve operating means which, in the 
particular construction shown, is in the form of a rod 8 extending through 
and beyond the feed chamber 6. The rod 8 is operative to open a valve 
orifice 9 so as to provide a communication path for working fluid between 
an inlet port 10 and a plurality of outlet ports 11 which communicate with 
the feed chamber 6. In use, the inlet port 10 is connected to the working 
supply source 12 and the outlet ports 11 are connected with respective 
brake assemblies 13 (FIG. 4). In operation the operating piston 4 moves 
within the main compartment 3 in response to pressure applied within the 
control chamber 5, and the rod 8 is then operative to open the valve 
orifice 9 and thereby connect the outlet ports 11 with the inlet port 10. 
When the valve 1 is not so operated, the ports 10 and 11 are isolated from 
one another. 
The valve 1 also includes closure member 14 which, in the arrangement 
shown, is biased by a spring 15 towards a valve closing position at which 
it prevents communication between the ports 10 and 11 through the orifice 
9. The closure member 14 is preferfably in the form of a sleeve having a 
head portion 16 which is arranged to engage with an annular valve seat 17 
provided around the orifice 9. The closure member 14 is preferably 
arranged within an inlet compartment 18 which connects with the inlet port 
10 through a passage 19. 
In the construction shown, the body 20 of the closure member 14 is 
cylindrical and is slidably mounted in a cylindrical bore 21 of the valve 
1 for movement towards and away from the valve seat 17. A fluid tight seal 
22 is preferably provided between the body 20 and bore 21 and the bore 21 
is able to communicate with atmosphere through an exhaust port 23. As 
shown, a flap valve 24 operates to close the port 23 against ingress of 
direct and other foreign material. 
The central bore 25 through the closure member 14 provides a passage 
through which the feed chamber 6 may also communicate with atmosphere by 
way of the port 23. That communication is closed under certain conditions 
by a flange 26 connected to the rod 8 for movement therewith and arranged 
to engage the head portion 16 of the closure member 14 at a location 
radially inwardly of the annular valve seat 17. The flange 26 thereby 
functions to close off the feed chamber 6 against communication with 
atmosphere through the bore 25 and exhaust port 23. 
In operation of the relay valve 1 described above, the supply source 12 
does not initially supply pressurized air to the feed compartment 6 
because the operating piston 4 is in the position shown in FIGS. 2 and 5. 
In that position, the flange 26 is lifted from the head portion 16 of the 
closure member 14 and the feed chamber 6 is open to atmosphere through the 
bore 25 in the closure member 14 and the exhaust port 23. At the same 
time, the closure member 14 bears against the valve seat 17 under the 
action of the biasing spring 15 so as to close the orifice 9 such that the 
inlet port 10 is isolated from the feed chamber 6. When a control signal 
in the form of pressurized fluid is applied to the control chamber 5, the 
operating piston 4 moves against its biasing spring 27 so as to bring the 
flange 26 into engagement with the head portion 16 of the closure member 
14 and therby close the feed chamber 6 against communication with 
atmosphere (FIG. 6). Further movement of the operating piston 4 in the 
same direction causes the rod 8, acting through the flange 26, to move the 
closure member 14 away from the valve seat 7 thereby opening the valve and 
allowing the working fluid to pass from the inlet port 10 to the feed 
chamber 6 and thence to the outlet ports 11 (FIG. 7). 
When the valve 1 is opened as described above, the air pressure in the feed 
chamber 6 rapidly rises until its effect exceeds the effect of the 
pressurized fluid in the control chamber 5. The operating piston 4 then 
reverses its direction of movement so that the closure member 4 is able to 
close against the valve seat 17 (FIG. 8), thereby again isolating the feed 
chamber 6 from the working supply. Ideally at this point, the effects of 
the respective presures witin the feed and control chambers are balanced 
so that the valve 1 is in a stable condition and consequently the pressure 
communicated through the outlet ports 11 is constant and proportional to 
the control fluid pressure. 
A valve arrangement as generally described above is in accordance with the 
prior art except that prior valves of that form would not have more than 
four outlet ports 11. As previously advised, such four-port valves have 
not been successfully adapted for tri-axle brake systems so that two such 
valves have been required in such systems and that has naturally added to 
the cost of the braking system. 
A relay valve for semi-trailer brake systems must have certain minimum 
response times for application of working compressed air to the brake 
assemblies and for releasing the compressed air from the brakes by opening 
the feed chamber to atmosphere. In order that a six port relay valve will 
satisfy the desired response times, it has been found necessary to 
substantially increase the dimensions of the closure member bore 25 and 
the flange 26. Under certain conditions however, those changes lead to the 
problem of "hunting", and that problem has been particularly prevalent 
when the ratio of the effective area of the operating piston 4 to the 
effective area of the flange 26 is less than about 30:1. 
The problem of "hunting" occurs when the valve is attempting to reach a 
stable condition but continually over-balances or overshoots that 
condition. When control pressure is applied to the valve and the valve 
operates in a normal manner to relay the working supply to the outlet 
ports, the stable condition as eventually adopted by the valve is that 
shown in FIG. 8. However, if the control pressure is reduced to a lower 
increment, the excess of pressure in the feed chamber 6 will cause the 
operating piston 4 to move so as to lift the flange 26 from the head 
portion 16 of the closure member 14. The feed chamber 6 is thereby opened 
to atmosphere and some pressure will escape from the brake assemblies 13 
through that chamber 6 in order to again approach a balance with the 
control pressure. 
If the closure member bore 25 and the flange 26 are relatively large, it is 
found that excess air may be exhausted to atmosphere before the control 
pressure forces the flange 26 to close the upper end of the closure member 
bore 25. As a result, when the flange 26 does close that bore 25, the 
effect of the control pressure will then exceed the effect of the pressure 
remaining in the feed chamber 6 so that the operating piston will continue 
to move beyond the balance position as shown in FIG. 8 and will thereby 
open the valve to allow working fluid to again enter the feed chamber 6. 
Furthermore, excess pressure build-up may occur in the feed chamber 6 
before the valve has time to reclose so that the operating piston 4 is 
moved to reopen communication between the feed chamber 6 and atmosphere. 
Such continual overbalancing is known as "hunting" and the effect may 
cause a blow down of the air reservoir 12 which forms the working supply 
and will also create a variable feeling at the brakes. 
A relay valve according to the present invention meets that problem by 
inclusion of a damping facility. In the particular construction shown, a 
damping piston 28 is connected to the operating piston 4 and is exposed on 
one side to a damping chamber 29. That chamber 29 is located on the side 
of the piston 28 remote from the flange 26 so that fluid pressure in the 
damping chamber 29 provides a balancing pressure on the damping piston 28 
opposing the pressure on the valve 1 which tends to open the valve. With 
such an arrangement, the pressure acting on the damping piston 28 tends to 
balance the instability producing effects on the flange 26 so that a 
relatively large bore 25 may be provided in the closure member 14 and a 
relatively large flange 26 can be provided without leading to "hunting". 
The damping cylinder may be arranged as shown so as to be at the side of 
the valve body 2 remote from the control chamber 5. Also in the 
arrangement shown, the damping piston 28 is carried by an extension 30 of 
the rod 8 which extends beyond the flange 26 and through both the valve 
orifice 9 and the bore 25 of the closure member 14. 
The damping chamber 29 is preferably connected to the source of control 
pressure and that may be achieved as shown in FIG. 2 by providing 
communication between that chamber and the control chamber 5. In an 
alternative arrangement, the damping chamber 29 may be in communication 
with the feed chamber 6 as shown in FIG. 2A, but is usually preferable for 
the damping chamber 29 to be in communication with the control chamber 5. 
That communication may be effected by means of a passage 31 extending 
through the rod 8, the extension 30, and both the damping piston 28 and 
the operating piston 4. 
The effective surface area of the damping piston 28 which is exposed to the 
pressure in the chamber 29 preferably approximately equal to or slightly 
less than the effective area of the flange 26 which is exposed to pressure 
within the feed chamber 6 when the valve is in the condition of FIGS. 7 or 
8. As a result the pressure effects on the damping piston 28 and the 
flange 26 are substantially balanced and that reduces the possibility of 
instability such as to cause "hunting". That result occurs even in a valve 
having a relatively large bore 25 through the closure member 14 and 
acorrespondingly large flange 26 such that the ratio of the effective area 
of the operating piston 4 to the effective area of the flange 26 is less 
than about 30:1. 
It has been found that a relay valve having the damping facility described 
above can be also provided with six outlet ports 11 and can therefore be 
used for triaxle brake systems. The required application and release times 
can be achieved in such a valve by adopting a suitably large closure 
member bore 25 and flange 26. 
When control pressure is applied to the chamber 5 from the source 7, the 
same pressure is communicated to the underside of the damping piston 28 by 
way of the passage 31. A balancing force is thereby generated within the 
valve 1 and acts against the downward movement of the operating piston 4 
so as to generally balance the downward force on the flange 26 when the 
pressure within the feed chamber 6 has built-up to the required level. 
That is, the valve 1 adds a positive pressure under the piston 4 to offset 
pressure effects on the flange 26 which can lead to instability and 
"hunting". 
The relay valve illustrated in the accompanying drawing is provided with 
six outlet ports 11 extending from the feed chamber 6 and can therefore be 
used with triaxles. The same construction however, can be provided with a 
lesser or greater number of outlet ports 11. A six- port valve as shown 
can be formed by using much of the existing tooling used for production of 
four port relay valves. Also, the overall size of the six-port valve can 
be substantially the same as a conventional four-port relay valve. As a 
result, a six-port relay valve according to the present invention can be 
produced and used in a triaxle system at less cost than that involved in 
the present practice of using two four-port relay valves. 
Various alterations, modifications and/or additions may be made to the 
construction and arrangement of parts as herein described without 
departing from the spirit and scope of the present invention as defined by 
the appended claims.