Air flow/check valve

An air flow/check valve for an exhaust emission system combines flow and check functions into a single valve which is especially well-suited for use with an electric motor driven air pump. The valving mechanism is operated by a fluid actuator, and pressure conditions in the actuator are controlled by sensing the pressure differential across the valving mechanism to close the valving mechanism when exhaust back pressure is indicative of causing potentially damaging backflow to the air pump. Several embodiments of the invention are disclosed.

FIELD OF THE INVENTION 
This invention relates to internal combustion engine exhaust emission 
control systems of the type wherein an air pump delivers air to the 
exhaust to promote the oxidation of undesirable products of combustion in 
the hot exhaust gases leaving the engine. More specifically, the invention 
relates to a new and unique air flow/check valve that is disposed between 
the air pump and the exhaust to permit air to be delivered from the pump 
to the exhaust but to block backflow of potentially damaging exhaust to 
the air pump. 
BACKGROUND AND SUMMARY OF THE INVENTION 
During operation of an automotive vehicle's internal combustion engine, 
some fraction of the fuel introduced into the engine combustion chambers 
is not fully combusted and remains as an undesirable constituent of the 
exhaust. In order to promote complete combustion of such residual 
constituents, secondary air may be pumped into the exhaust before the 
exhaust is discharged to atmosphere, and typically this is done by means 
of an air pump. In addition to the air pump, a known type of secondary air 
system further comprises an electric ported vacuum valve, an air (flow) 
control valve, and a check valve. 
This known system operates by an electric signal input to the ported vacuum 
valve causing the ported vacuum valve to deliver vacuum to the air valve. 
The air valve opens to allow air to be pumped from the air pump into the 
exhaust. 
Occasionally back pressure from the exhaust can exceed the air pressure 
from the pump, and therefore to protect the pump from the backflow of 
potentially damaging hot exhaust gasses, a one-way (unidirectional) check 
valve is disposed between the air pump and the exhaust to block any 
potentially damaging backflow to the air pump. 
Some embodiments of this known type of system possess certain potential 
disadvantages. One potential disadvantage is that three separate 
assemblies may be required in addition to the air pump; another is that a 
wiring harness is required to connect to the automotive vehicle's 
electrical system; still another is that the operating threshold of the 
check valve can be inconsistent, thereby potentially limiting use to only 
"high" pressure situations; and yet another is that it does not use 
operating parameters (air and exhaust pressures) to optimize performance. 
The present invention provides improvements that can overcome such 
disadvantages. The invention can embody all required protection and 
control functions in a single air flow/check valve assembly. The assembly 
can be entirely mechanical so that there is no need for electrical wiring 
harness connection of the assembly into the electrical system. In a 
general way, the invention may be briefly described as comprising an 
assembly for sensing the pressure differential across a valve seat and 
causing the sensed pressure differential to control a vacuum signal for 
opening and closing a valve member from and against the valve seat to 
thereby perform air flow/check valve functions. The assembly is also 
capable of providing protection of the air pump against a series of 
exhaust pressure surges which collectively, but not individually, may be 
capable of creating potentially damaging backflow from the exhaust to the 
air pump. 
Further features, advantages, and benefits of the invention will suggest 
themselves to the reader as the disclosure of the invention proceeds. 
Drawings accompany the written description, and portray a presently 
preferred embodiment of the invention according to the best mode 
contemplated at the present time for carrying out the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In FIG. 1 an internal combustion engine 10 of an automotive vehicle is 
equipped with an exhaust emission control system 12 embodying the 
invention. Engine 10 comprises an induction air intake system 14 via which 
the engine's combustion chambers 16 are charged and an exhaust system 18 
via which the hot exhaust gases of combustion are carried away from the 
combustion chambers. 
Exhaust emission control system 12 comprises an electric motor driven air 
pump 20 and an air flow/check valve (AFCV) 22. AFCV 22 has an inlet nipple 
24 that is communicated to the air pump outlet by a conduit 26 and an 
outlet nipple 28 that is communicated to exhaust system 18 by a conduit 
30. A flow passage 32 extends between inlet 24 and outlet 28, and flow 
through passage 32 is controlled by a valve mechanism 34. A circular 
annular valve seat 36 internally circumscribes passage 32 and faces flow 
from the air pump. A circular disc-shaped valve head 38 is shown, in its 
solid line position, seated on valve seat 36 closing passage 32 to flow. 
An operating mechanism 40 selectively positions valve head 38 with respect 
to valve seat 36 to open and close passage 32 to flow. In the position 
shown in broken lines, valve head 38 has been unseated from valve seat 36, 
in the direction against the flow from the air pump, by operating 
mechanism 40 thereby allowing flow through passage 32. 
Operating mechanism 40 comprises a vacuum actuating mechanism 42, including 
an actuator shaft 44 that passes through a bushing 46 in the wall of 
passage 32 to attach to the center of valve head 38. The end of shaft 44 
opposite valve head 38 attaches to the center of a two-piece diaphragm 48 
whose outer margin is captured so as to divide vacuum actuating mechanism 
42 into two variable volume chambers 50 and 52. The two-piece construction 
of diaphragm 48 consists of a rigid central hub 54 and a surrounding 
flexible element 56. A helical spring 58 is disposed in chamber 50 and 
acts to resiliently bias diaphragm 48 so as to cause valve head 34 to seat 
on seat 36 and disallow flow through passage 32. 
Chamber 52 is communicated to atmosphere via vents 60 while chamber 50 has 
a nipple 62 that provides for a conduit 64 to communicate the suction of 
engine intake vacuum to chamber 50. Whenever the magnitude of vacuum in 
chamber 50 is sufficiently high in comparison to the atmospheric pressure 
in chamber 52, the bias of spring 58 is overcome causing valve head 34 to 
be unseated from valve seat 36. 
A control mechanism 66 serves to control the magnitude of vacuum in chamber 
50 and hence exercise control over valve mechanism 34. This control 
mechanism senses the pressure differential across valve seat 36 by means 
of two pressure taps 68 and 70. Tap 68 senses the pressure on the side of 
the valve seat that is toward inlet 32, and tap 70 the pressure of the 
side that is toward outlet 28. Mechanism 66 comprises a housing 72 that is 
divided into two variable volume chambers 74 and 76 by a movable wall 78. 
Pressure tap 68 is communicated to chamber 76 via a conduit 80 while 
pressure tap 70 is communicated to chamber 74 via a conduit 82. The path 
of communication between tap 68 and chamber 76 is essentially 
unrestricted; the path of communication between tap 70 and chamber 74 
however, includes a check valve 84 and a bleed 86 whose functions will be 
explained in more detail hereinafter. 
Movable wall 78 is constructed in a similar manner to diaphragm 48 in that 
it comprises a rigid hub and a flexible rim. A helical spring 88 that is 
disposed within chamber 74 serves to bias the hub of movable wall 78 
against the end of a stem 90 of a valve member 92. The body of valve 
member 92 is disposed in a passageway 94 that serves to communicate 
chamber 76 with chamber 50. A helical spring 96 serves to bias the body of 
valve member 92 to close off one end of a hole 98 through which stem 90 
projects from the valve body into chamber 76, and the drawing shows the 
closed position in which the valve blocks communication between chamber 50 
and chamber 76. 
In response to certain pressure differential between chambers 74 and 76, 
movable wall 78 will act on stem 90 to displace valve member 92 away from 
hole 98. There is sufficient clearance between passageway 94 and the outer 
periphery of valve member 92 that flow can occur through the passageway 
when the valve member is displaced away from the hole. 
When valve member 92 is closing passageway 94, the magnitude of vacuum that 
is present in chamber 50 is essentially that of the induction system 
vacuum. At a sufficiently high vacuum, valve mechanism 34 places air pump 
20 in communication with exhaust system 18. When valve member 92 is 
operated to open passageway 94, vacuum present in chamber 50 is bled from 
that chamber via chamber 76, conduit 80, and tap 68 to passage 32. Upon a 
sufficient degree of bleeding of vacuum from chamber 50, operating 
mechanism 40 seats valve head 38 on valve seat 36 to terminate the 
communication between air pump 20 and exhaust system 18. 
The operation of AFCV 22 can now be explained. When engine 10 is started, 
vacuum will be delivered to chamber 50. The characteristics of the AFCV 
are such that this vacuum will open valving mechanism 34. Operation of the 
air pump will be effective to deliver air through the AFCV to the exhaust 
system to promote combustion of undesired constituents in the exhaust 
leaving the engine before the exhaust is discharged from the exhaust 
system to atmosphere. In this operating mode, the pressure at tap 68 will 
be higher than that at tap 70 by a certain amount. Because the open 
valving mechanism 34 is designed to impose a minimum amount of restriction 
on the flow, this pressure differential will be rather small. It is 
however sufficiently large to be effective to cause control mechanism 66, 
acting through operating mechanism 40, to maintain valving mechanism 34 
open. This is because the pressure in chamber 76 will be sufficiently 
large in comparison to that in chamber 74 and the force of spring 88 to 
prevent movable wall 78 from displacing, via stem 90, valve member 92 to 
open hole 98. In other words, the vacuum in chamber 50 cannot be bled off. 
If the engine should operate in such a manner that the pressure in exhaust 
system 18 exceeds that produced by air pump 20, i.e. if the exhaust back 
pressure becomes too large, then the pressure differential sensed by taps 
68 and 70 reverses, becoming such that the pressure at tap 70 exceeds that 
at tap 68. This situation is indicative of potentially damaging backflow 
through the AFCV to the air pump, and it becomes desirable to promptly 
close valving mechanism 34 so that potentially damaging backflow to the 
air pump does not occur. Control mechanism 66 is responsive to this 
condition in the following way. 
The pressure rise at tap 70 is communicated to chamber 74 by the opening of 
check valve 84. The pressure drop at tap 68 is immediately communicated to 
chamber 76. As a consequence, the pressure differential across movable 
wall 78 will expand the volume of chamber 74 and decrease that of chamber 
76, causing the movable wall to displace valve member 92 from hole 98 so 
that passageway 94 now becomes open. The opening of passageway 94 
immediately begins bleeding vacuum from chamber 50 with the result that 
diaphragm 48 is urged to cause valve mechanism 34 to close. As a 
consequence, backflow from the exhaust to the air pump is now prevented. 
When the excessive exhaust backpressure terminates, the contents of 
chamber 74 are allowed to bleed through restricted orifice 86, and when 
the pressure differential between the respective chambers 74 and 76 has 
changed sufficiently, valve member 92 again closes hole 94 to allow vacuum 
to be re-established in chamber 50 for re-opening valve mechanism 34. 
The graph plot 4A of FIG. 4 shows a representative relationship between 
airflow and exhaust pressure for air pressure held at 60 inches H.sub.2 O. 
Maximum air flow occurs when the exhaust pressure is lowest and then 
diminishes as the exhaust pressure increases. Air flow is blocked at a 
predetermined value of exhaust pressure which is less than the air 
pressure to provide added safeguard against damaging backflow. This 
differential pressure is determined by the force of bias spring 88 which 
is disposed in chamber 74. 
A further feature of the AFCV is its ability to respond to a series of 
exhaust pressure surges which collectively, but not individually, are 
capable of creating potentially damaging backflow. Such surges are 
accumulated in chamber 74, and although restricted orifice 86 imposes a 
bleed on the chamber, a series of surges that have a combination of 
sufficiently high frequency and amplitudes will be effective to cause 
valve mechanism 34 to close. In this regard, the operation of the control 
mechanism is somewhat akin to that of a finite memory integrator. 
A few further details should be mentioned. Check valve 84 is an elastomeric 
umbrella type valve having a retention stem that is fitted into a hole. 
The umbrella flexes to uncover holes 100 to establish communication 
between tap 70 and chamber 74. Flow takes place between the periphery of 
the umbrella and a surrounding ridge. A perforated retainer plate 102 is 
fitted to the rim of the ridge to confine the umbrella within the ridge. 
A cylindrical screen 104 is positioned in alignment with and between nipple 
28 and valve seat 36 as an aid to screening particulate exhaust material 
from entering tap 70. 
The connection of chamber 50 to chamber 76 comprises a tubular grommet 106 
fitted over a tubular nipple 108 from chamber 50 and a washer 110 against 
which one end of spring 96 bears. 
The invention is especially advantageous with a low pressure air pump 
because it imposes relatively small restriction to flow from the pump; yet 
it is sufficiently sensitive to perform the necessary air flow control and 
check valve functions. 
The embodiment 118 of AFCV depicted in FIGS. 2 and 3 is in certain respects 
similar to the embodiment of FIG. 1, and so like reference numerals are 
used to designate similar components of the two embodiments without there 
necessarily being a detailed description of those components in connection 
with FIGS. 2 and 3. There are however several significant differences 
between the two embodiments. 
One such difference is that there are two conduits between AFCV 118 and 
engine exhaust system 18. The valve's outlet nipple 28 connects via 
conduit 30 to the inlet of a resonator 120 whose outlet connects via a 
manifold 122 to the exhaust manifold 124 of exhaust system 18 so that an 
individual stream of air can be injected closely adjacent each engine 
exhaust valve. Exhaust manifold pressure is sensed by the AFCV at a 
location that is somewhat further downstream in the exhaust flow where the 
flow will typically be somewhat smoother. 
Another difference between the two embodiments is that the flow passage 32 
which extends between inlet 24 and outlet 28 also includes a 
frustoconically shaped wall portion 126 with which valve head 38 coacts 
when unseated from seat 36. 
Another difference resides in the constructional details of mechanism 66. 
Chamber 74 is communicated to tap 70 by conduit 82, but unlike the first 
embodiment, the second omits check valve 84 and bleed 86. As in the first 
embodiment, chamber 76 is communicated directly to passageway 32 via 
conduit 80, but now the point of communication with that passageway is 
located between wall portion 126 and seat 36, and chamber 76 is not vented 
through valve member 92. While conduit 64 conveys intake manifold vacuum 
through an orifice 128, as in the first embodiment, the orifice is now 
located in the body of mechanism 66 rather than in nipple 62; nipple 62 is 
deleted; and there is a tee 130 which places portions of both mechanisms 
40 and 66 in common communication with intake manifold vacuum. The 
organization of AFCV 118 provides for valve member 92 to controlledly vent 
chamber 50 to atmosphere in accordance with the position to which movable 
wall 78 is operated. 
The mechanism 66 of AFCV 118 retains a stem 90 to which valve member 92 is 
affixed and a small spring 96 which acts to urge valve member 92 toward 
closure of hole 98. Stem 90 is axially guided by a hole in an internal 
wall portion 132 of the mechanism housing, but is unattached to movable 
wall 78. Rather, the end of stem 90 which is opposite valve member 92 will 
merely bear against the center of movable wall 78 when the two are in 
contact. A pin 134 is disposed coaxial with stem 90, but on the opposite 
side of movable wall 78. Pin 134 is guided for axial displacement by a 
hole in another internal wall portion 136 of the mechanism housing and by 
a hole in an annular scraper member 138 which is supported on wall portion 
136 in spaced relation to the first hole. One end of pin 134 is disposed 
in chamber 74 while its other end is disposed in a further chamber 140 of 
mechanism 66 which shares wall portion 136 on the opposite side thereof 
from chamber 74. The remainder of chamber 140 is bounded by a movable wall 
142 which forms a portion of a still further chamber 144 lying on the 
opposite side of movable wall 142 from chamber 140. Chamber 140 is vented 
to atmosphere via an orifice 145 and contains a helical coil spring 146 
that acts to urge movable wall 142 away from pin 134. Chamber 144 is 
communicated to exhaust pressure via a conduit 148, one end of this 
conduit being fitted onto a nipple 150 at mechanism 66 while its opposite 
end is in communication with exhaust manifold 124 downstream of manifold 
122. The venting of manifold vacuum to atmosphere by valve element 92 
takes place through an annular filter element 152 suitably mounted on 
mechanism 66. 
When the engine is not running, the AFCV can assume a condition like that 
shown in the drawings. The force of spring 88 overrides that of spring 96 
causing valve element 92 to vent chamber 50 to atmosphere. Valve head 38 
is therefore forced by spring 58 against seat 36 to close passage 32. 
Upon engine starting, intake manifold vacuum is communicated to the AFCV 
via conduit 64, and exhaust pressure via conduits 30 and 148. Intake 
manifold vacuum will be bled to atmosphere so long as valve element 92 
continues to remain open; consequently, valve head 38 will remain seated 
on seat 36 until air pump 20 begins to deliver a certain pressure output. 
Air pump 20 creates a pressure increase in chamber 76 that generates a 
force on movable wall 78 opposing the combined forces of spring 88 and of 
exhaust pressure in chamber 74 acting on the movable wall. The design of 
spring 88 determines the differential between exhaust pressure and air 
pump pressure which will be effective to displace movable wall 78 from its 
illustrated position in the direction toward scraper member 138. By way of 
example only, a differential of ten inches of water may be required before 
any displacement of the wall occurs, and thereafter the displacement will 
increase with increasing differential. 
The attainment of a certain differential will be sufficient for spring 96 
to close hole 98, and when this happens, intake manifold vacuum ceases to 
be vented to atmosphere. Now vacuum increases in chamber 50 causing valve 
head 38 to be unseated from seat 36 and to move into coactivity with 
frustoconical wall portion 126. 
While the resultant opening of passage 32 enables the pumped air to be 
delivered via the AFCV and resonator 120 into the exhaust system, the 
coaction that is created between valve head 38 and frustoconical wall 
portion 126 takes the form of a restriction whose restrictive effect 
becomes progressively greater the closer the valve head moves toward the 
frustoconical wall portion. In explaining the functioning of the AFCV, let 
it be assumed that for a certain given set of operating conditions, valve 
head 38 occupies a position which imposes a certain degree of restriction 
on the air pump flow. Mechanism 66 is designed to perform a regulating 
function whereby valve head 38 is maintained in this position so long as 
the given set of operating conditions continues unchanged. This regulation 
occurs in the following manner. 
Because valve head 38 moves upstream from tap 68 when it unseats from seat 
36, the pressure differential between tap 68 and tap 70 will be less than 
that which existed before the valve head unseated. Accordingly, movable 
wall 78 will act on stem 90 to unseat valve element 92 and begin venting 
chamber 50 to atmosphere. Orifice 128 prevents chamber from being 
replenished from the manifold faster than it can be bled to atmosphere via 
hole 98, and therefore as a result of these actions, valve head 38 will 
begin to move back toward seat 36. This motion lessens the restriction to 
the air being pumped through the AFCV such that the pressure to chamber 76 
is caused to increase with the result that movable wall 78 now begins to 
move in the opposite direction. These actions that have just been 
described are continuously repeated at a sufficiently fast rate that the 
position of valve head 38 is regulated to a stable position. This 
regulating function is performed over a certain range of exhaust pressure 
so that proper rate of flow occurs. The graph plot 6A of FIG. 6 shows flow 
regulation for a typical range of exhaust pressures measured in inches 
H.sub.2 O. As the exhaust pressure increases the rate of flow increases. 
If the exhaust pressure remains at zero the flow rate regulates at a 
preselected minimum value of approximately 0.75 SCFM as shown on graph 
plot 6B. By comparison, the graph plot 4A represents a non-regulated 
valve. 
The check valve function of AFCV 118 is performed through the action of 
movable wall 78 when the sensed exhaust pressure gets too high. The 
exhaust pressure will act on movable wall 78 in combination with the force 
of spring 88 such that the movable wall will be axially positioned toward 
stem 90 to an extent that is a function of the magnitude of the exhaust 
pressure; specifically, the movable wall is positioned closer to wall 
portion 132 as the exhaust pressure rises. Beyond a preselected pressure, 
the movable wall is positioned to a point where it becomes impossible for 
valve element 92 to regulate due to the fact 78 prevents valve element 92 
from closing hole 98. Such a condition continuously vents chamber 50 to 
atmosphere with the result that valve head 38 is caused to seat on seat 36 
and halt the flow through the AFCV. When exhaust pressure has once again 
dropped below the preselected pressure that initiated the check function, 
the AFCV can return to the regulating function. Hence, the valve provides 
flow regulation from the air pump to the exhaust over a certain range of 
exhaust pressures and flow checking when that pressure range is exceeded. 
The graph plot 5A of FIG. 5 shows a typical response when a constant 
exhaust pressure of 16 inches H.sub.2 O is maintained at outlet 28. At air 
pump pressures below 16 inches H.sub.2 O the combined force of the exhaust 
pressure and spring 88 exerted on movable wall 78 will unseat valve member 
92 and continuously vent chamber 50 to atmosphere. This condition will 
cause valve 38 to seat on seat 36 and halt flow. 
When the air pump pressure exerts a force on movable wall 78 that exceeds 
the combined force of 16 inches H.sub.2 O exhaust pressure and the force 
of spring 88, movable wall 78 will move away from wall 132 causing valve 
element 92 to restrict the bleed of chamber 50 to atmosphere. This will 
cause valve head 38 to move away from seat 36 allowing air flow to the 
exhaust. 
FIG. 7 presents another embodiment 200 of AFCV which possesses a less 
complex construction than the embodiments that have been described up to 
this point. Similar components continue to be identified by like reference 
numerals. The most significant difference between AFCV 200 and the 
previous embodiments is that AFCV 200 does not utilize intake manifold 
vacuum; it is only air pump pressure and exhaust pressure (other than of 
course spring 58) which can exert influence on the operation of valve 
mechanism 34. 
Other significant differences include the following. Inlet 24 is aligned 
with, and outlet 28 is transverse to, operating mechanism 40. Spring 58 is 
disposed in chamber 52. Actuator shaft 44 is tubular. Valve seat 36 and 
valve head 38 are frustoconical. Bushing 46 is provided with 
accommodations for mounting an annular scraper 201 to act on actuator 
shaft 44 during movement thereof for the purpose of dislodging any foreign 
material that might have accumulated on the shaft. 
When the engine is off, AFCV 200 assumes the position illustrated in FIG. 
7. Spring 58 urges movable wall 48 toward chamber 50 such that valve head 
38 seats on seat 36 to close passage 32 to flow. The tubular construction 
of actuator shaft 44 serves to communicate air pump pressure to chamber 
50. A measure of exhaust pressure is communicated to chamber 52 via an 
orifice 202 which is provided between that chamber and a location in 
passage 32 which lies between seat 36 and outlet 28. The orifice controls 
the rate at which flow passes into and out of chamber 52, and hence 
provides a certain damping of the motion of wall 48. 
When the pressure in chamber 50 exceeds that in chamber 52 by an amount 
sufficient to overcome spring 58, valve head 38 unseats to allow flow from 
the air pump to the exhaust. In this mode of operation the AFCV performs a 
regulating function. 
Should the exhaust pressure rise too much relative to air pump pressure, 
the communication provided by orifice 202 will cause chamber 52 to expand 
and re-seat valve head 38 on seat 36. In this way the AFCV performs a 
check function to prevent excessive exhaust pressures from acting on the 
air pump. 
The operating characteristic for AFCV 200 is similar to that of the 
embodiment shown in FIG. 1 and shown in FIG. 4, graph plot 4A. 
The AFCV 300 of FIG. 8 is essentially like AFCV 200, and so corresponding 
parts are designated by like reference numbers. The primary difference 
between the two is that there is a second means of communication of 
passage 32 to chamber 52 in addition to orifice 202. This second means of 
communication comprises a slant passage 302 with which a reed valve 304 in 
chamber 52 coacts. The reed valve functions as a check to allow flow from 
passage 32 to chamber 52 but to block opposite flow. When closing passage 
302, it lies flat against the wall of chamber 52, and when not closing the 
passage, it flexs in cantilever fashion. Preferably a stop 306 is disposed 
to overlie the reed. 
AFCV 300 will respond to exhaust pressure increases more rapidly than it 
will to exhaust pressure decreases because this arrangement enables 
chamber 52 to fill more rapidly than it can exhaust. In other words the 
AFCV will re-open more slowly than it closes, and this capability may be 
useful in some air pump systems. 
The valve 400 of FIG. 9 has the same air flow and check valve functions as 
the valve shown in FIG. 7 and has the added feature of rate of flow 
regulation from an external vacuum source. 
Component parts of valve 400 that correspond to like parts of earlier 
embodiments are identified by the same reference numerals. The following 
is a brief description of the construction and operation of valve 400. 
Air pressure is communicated to the top of diaphragm 48 (i.e. chamber 50) 
via air inlet 24, the passageway in shaft 44 and a valve 402. Valve 402 is 
controlled by a diaphragm 404 which is positioned axially as a function of 
atmospheric air pressure, a spring force, and EVR vacuum. Atmospheric air 
pressure is communicated through an orifice 406 to a chamber 408 on one 
side of diaphragm 404. EVR vacuum from an Electronic Vacuum Regulator (not 
shown) is delivered via a nipple 410 to a chamber 412 on the opposite side 
of diaphrahm 404. Spring force is applied to the diaphragm by a spring 414 
in chamber 412 such that valve 402 is biased closed by the spring force. 
When the vacuum (EVR vacuum) is zero, the force of bias spring 414 acts 
upon diaphragm 404, a shaft 416 and valve 402 to the extent that a valve 
number 418 on shaft 416 will seat against the plate 420 which is attached 
to diaphragm 48. This condition will prevent air flow to chamber 50 
because valve member 418 is closing a hole 422 in plate 420 through which 
shaft 416 passes. 
When the vacuum is at a level that its force on diaphragm 404 will overcome 
the force of bias spring 414, it will unseat valve member 418 from plate 
420 and allow air flow to the top side of the diaphragm. 
When the air pressure is at a level that its force on diaphragm 48 
overcomes the force of bias spring 58, it will unseat valve head 38 and 
allow air flow to the exhaust manifold. Diaphragm 48 will move until its 
plate 420 again seats on valve number 418 and halts the flow of air to the 
top of the diaphragm. The air pressure in chamber 50 will bleed off 
through a filter 424 and orifice 426 in the housing allowing bias spring 
58 to move diaphragm 48 and unseat plate 420 from valve member 418. Air 
flow is again established to the top of the diaphragm and the cycle will 
repeat causing the diaphragm/plate to regulate its position with the 
position of valve 402. 
The level of EVR vacuum determines the position of valve 402 which then 
controls the position of valve head 38 and the flow of air to the exhaust. 
A relationship is now established between the level of vacuum and the rate 
of air flow to the exhaust. 
A check valve function is performed through the action of diaphragm 48 when 
the sensed exhaust pressure gets too high. The exhaust pressure is 
communicated to the lower side of diaphragm 48 via openings 430 in guide 
428, these openings containing an in-line filter element 432. The exhaust 
pressure will act upon diaphragm 48 in combination with the force of 
spring 58 such that it will cause valve head 38 to move toward its seat. 
Beyond a preselected exhaust pressure the diaphragm is positioned to a 
point where it causes valve head 38 to be seated and thereby prevent flow 
between the exhaust 28 and air inlet 24. 
FIG. 10 illustrates an AFCV 500 whose parts that correspond to those of 
earlier embodiments are designated by like reference numberals. Valve head 
38 contains a mesh screen 502 covering the entrance to shaft 44 for 
filtering any particulates greater than a certain size from the flow. 
Spring 58 acting on diaphragm 48 normally biases valve head 38 to close 
the flow path between inlet 24 and exhaust 28. Pump air pressure is 
communicated to the underside of diaphragm 48 though a filter 504 and 
orifice 506. The top face of the diaphragm is communicated to exhaust 
pressure through screen 502 and shaft 44. 
As pump pressure builds relative to exhaust pressure, valve head 38 unseats 
to allow air to flow from the pump to the exhaust manifold. This is 
because there is a sufficiently greater pressure on the underside of the 
diaphragm compared to pressure on the top of the diaphragm. The extent of 
the opening though the AFCV is a function of the relative pressure and the 
spring has acting on the diaphragm. If the exhaust pressure becomes too 
great, its transmission through the shaft to the top of the diaphragm will 
cause valve head 38 to close, thereby checking undesired backflow to the 
air pump. 
While a presently preferred embodiment of the invention has been 
illustrated and described, it should be understood that principles of the 
invention may be practiced in other equivalent embodiments.