Note: Descriptions are shown in the official language in which they were submitted.
CONSTANT PRESSURE RELIEF VALVE
FOR AN AI R CONTROL VALVE
Th;s invention relates to fluid ac~uated control
valves in general and more particularly to a constant
pressure relief valve for an air control valve.
In order ~o control emissions from internal
combustion engines in motor vehicles, manufacturers have
added secondary air control systems to improve the
combustion and exhaust processes in the engine~ These
secondary air control systems generally include an air
pump which is driven by the engine for supplying air
under pressure and an air control valve responsive to
various operating signals, either electrical, hydraulic
or pneuma~;c ~o direct the output of the pump to various
components in the engine exhaust system~
Due to VariGuS restrictions in the control system
and more particularly in ~he air flow system, various
back pressures are developed~ Further, since the pump is
driven by the vehicle engine, variations in speed of the
pump contribute to pres~ure variations, which if not
limited, can cause damage to the air pump.
2~ Various air control valves such as that described in
U~S. Patent 4,163,543 entitled "A;r Control Valve~ have
provided relie~ valves which are spring biased. The
disadvantage of such a relief valve is that as back
pressures are developed, ~he curve o relie~ pressure
plotted against the pump speed or air flow rate ~s not
flat but increases as speed or air flow rates increase.
It i5 an advantage of the invention to provide a
constant pressure relief valve in an air control valve
wherein the pressure from the air pump does not exceed a
predetermined value regardless of pump speed, air flow
rate, or system back pressures.
These and other ad~antages of the invention will
become apparent in the following detailed description and
drawings wherein.
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Q
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FIGURE 1 is a schematic drawing of the relief valJe
shown in longitudinal cross-section;
E'IGURE 2 is a longitudinal cross-sectional view of
an air control valve embodyihg the relief valve of the
present invention; and
FIGURE 3 is a graph of the relief pxessure plotted
against air pump speed.
Referring ~o ~he FIGURES by the reference
characters, the constant press~re relief valve 10 in
FIGURE 1 comprises a housing 12, a flow restrictor 14 in
the ex~aus~ orifice or por~ 16~ a diaphragm means 18 and
valve means 20.
The housing 12, which is typically molded from a
plastic-type material able to withstand the environmental
conditions found in the engine compartment of a motor
vehiclet has an inlet orifice or por~ 22 and an exhaust
orifice or port 16. The inle~ orifice 22 terminates
within a first chamber 24 of the housing 12 a~ a valve
seat 260
Located within or connected to ~he exhaust orifice
16 of the housing 12 is a flow restrictor 14 which in the
preferred embodiment comprises silencing material not
shown. The purpose of the silencing material is to quiet
the noise of the air exhaus~ing from the housing 1~ but
2S in doing so functions as a restrictor whereby the
pressure in the first chamber 24 of the housing 12
increases.
A diaphragm means 18 comprising a rubber bellows i~
connected to ~he interior walls o~ the housing 12 and
operates ~o divide the housing into a first chamber 24
and a second chamber 28. Both the inlet orifice 22 and
~he exhaust orifice 16 are located in the first chamber
24. Air f~ow is prevented by the diaphragm 18 from
flowing be~wçen the two chambers. A vent ~9 is in the
~all of the second chamber ~8 to main~ain the pressure
therein a~ some pressure being supplied to the vent.
4~
Operatively connected to the diaphraqm 18 is a valve member 20
which extends from the diaphragm 18 and seats against the valve seat 26
on the inlet orifice 22. As shown in FIGURE 1, the valve member 26
mo~es in a direction normal to the valve seat 26 and is guided by means
of a ~uide pin 30 extending from one wall of the housing 12. The guide pin
30 exte~ds into a guide tube in the valve member and both cooperate to
keep t~e valve member 20 normal to the valve seat 26. A spring means 32
bi~ses the valve member 20 against the valve seat 26. In the preferred
enbodiment, there are one or more vents 29 in the wall of housing 12 for
ve~ting the second chamber 28 to atmospheric pressure which becomes the
reference pressure. The pressure therefore requi.red to lift the v~lve
member 20 from the valve seat 26 is the summation of the reference
pressure and the force applied by the spring bias means 32.
. Referring to FIGURE 2 there is illustrated in longitudinal cross-
section, an air control valve 34 including the constant pressure relief
v~lve 10 of FIGURE 1. The air control valve 34 is silllilar to the ai~
control valve of U.~. Patent 4,163,543 entitled "Air Control Valve"
which issued on August 7, 1979. That patent defines and describes the
operation of the air con.rol valve 34 in greater detail.
2Q The air control valve 34 is connected by means of condu.it 36
to an air pump not shown, which provides pressurized air to the input
port 22 of the valve 10. Typically the air pump is a vane pum~ driven
by means of belts from the drive shaft of the engine of a motor vehicl.e~
A vane pump provides a pulsating air flow and the faster the pump runs
~he closer together the air pulses become hence the higher the pressure
of the air. In addition, the flow rate of the pump increases with pump
speed
sd~ 3-
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The air control valve 34 contains a main diverter
valve 38 and its valve member 40 which valve member
operates to cause the air flow from the pump to either be
diverted to the exhaust system or to be discharged to the
atmosphere when the operation of the motor vehicle does
not require ~he use o~ auxiliary air to the exhaust
system. Since air, when it is bl~wn or pushed through an
orifice ~reates a sound~ there is provided in the air
control valve 34 silencing material 42 between the pump
input port 44 of ~he control valve 34 and ~he atmosphere.
When th~ engine control system, which is not shown,
requires that the auxiliary air or secondary air be
applied ~o the exhaust systemt the diverter valve 38
closes the discharge por~ 46 and diverts the air to
either one of the exhaust system ports 48, 49. One port
49 is typically connected to the exhaust manifold of the
engine and the other port 4~ is connected to the exhaust
system near the catalytic converter which is not shown.
In most systems, selection of which exhaust port is to be
used is governed by a vacuum motor controlled by a
temperatur~ operated vacuum switch.
The constant pressure ~elief valve 10 of the present
invention is illuskrated as being in fluid communication
with the pump input port 44 at all times. The input
orifice 22 of the relie~ valve 10 receives ~he air flow
directly from the air pump. The pressure at the face of
the valve member 20 is the pressure which the relief
valve 10 operates to avoid being exceeded beyond a
predetermined value as determined by ~he relief valve 10.
When the relie valve 10 opens, the pressure and the
flow f~om the air pump is communicated between the valve
seat ~5 and the valve member 20 to the first chamber 24
~- of the relie valve 10. The air flows through the first
chamber 24 to the exhaust orifice 16 and therethrough to
the silencing material 42 and to the atmosphere through a
series of vents 50. If the pressure in the first chamber~
starts ~ to build up higher than the pressure which
caused the valve member 20 to lift off the valve seat 26,
this increased pressure operates against the diaphram 18
5 and the valve member 20 causing the valve member 20 to
lift higher. This increased lift, increases the air flow
and an equilibrium is reached which is the pressure which
initially caused the valve member 20 to lit o~f the
valve seat 26.
This increased pres~ure is a back pressure developed
b~ ~he pressure drop throu~h the restriction or silencing
material 42. The combination of reference pressure in
the second chamber 28, the force developed by the spring
bias means 32 and the back pressure produces a constant
pressure in the air being supplied to the exhaus~ systemO
In one application of the preferred embodiment, the
reference pressure in the second chamber 28 is
atmospheric and the constant relief pressure is 2n inches
of mercury~ As illustrated in FIGUR~ ~, the curve of
relief pressure plotted against pump speed or fluid flow
for the relief valve 10 of the present invention is flat.
In prior art devices where the relief valve 10 has only
one chamber which is connected to the exhaust orifice~
the plot of the relief pressure is illustrated by the
dashed curve. The reason for the dashed curve is that
the back pressure is added to the spring bias of the
valve and since the back pressure increases, the relief
preæsure increases.
There has thus been shown and illustrated a constant
pressure relief valve 10 as used in an air control valve
34 found in a seconda~y or auxiliary air system in a
motor vehicle. A cooperation of the diaphragm 18
providing a reference pressure chamber 28 controlling the
valve member 20 and the added lift of the valve member 20
by the system back pressure maintains a constant relie
p~essure.
