Abstrict A positive displacement, reciprocating fluid flow meter produces
a digital electrical output signal. The meter includes a piston
which reciprocates within a cylinder for accurately measuring fuel
flow rates over a wide range of rates. The device is particularly
useful in measuring the rate of flow of fuel to an engine, and incorporates
a valve for bypassing the piston to permit resetting of the meter
at the end of each piston stroke.
Claims What is claimed is:
1. A fuel flow meter for series connection in the fuel line of
an engine, comprising:
a cylindrical housing having an inlet and an outlet at opposite
ends, each connected to said fuel line;
a pair of bearings, one mounted at each end of said cylindrical
housing;
a piston including an aperture forming a valve seat, said piston
mounted within said housing on said pair of bearings for reciprocation
along the axis of said cylindrical housing;
flexible sealing means for sealing said piston to said cylindrical
housing during said reciprocation;
a spring positioned between said housing and said piston for biasing
said piston toward said inlet;
a valve member mounted in alignment with said valve seat within
said housing for reciprocation along the axis of said housing, said
valve member closing said piston aperture when positioned against
said aperture; and
over center means mounted on said cylinder for reciprocating said
valve member along the axis of said housing to open and close said
piston aperture in response to the position of said piston along
the axis of said housing.
2. A fuel flow meter as defined in claim 1 wherein said piston
includes a pair of axially aligned guide rods rigidly attached to
said piston for mounting said piston on said pair of bearings for
reciprocation and wherein said valve member is mounted for reciprocation
along one of said pair of guide rods.
3. A fuel flow meter as defined in claim 1 wherein said over center
means for reciprocating said valve member comprises a spring member
mounted on said cylinder for biasing said valve member toward said
piston aperture when said piston is positioned in a first reciprocating
extreme and for biasing said valve member away from said piston
aperture when said piston is in a second reciprocating extreme position.
4. A fuel flow meter for series connection in the fuel line of
an engine, comprising:
a cylindrical housing having an inlet and an outlet at opposite
ends, each connected to said fuel line;
a pair of bearings, one mounted at each end of said cylindrical
housing;
a piston including an aperture forming a valve seat, said piston
mounted within said housing on said pair of bearings for reciprocation
along the axis of said cylindrical housing;
flexible sealing means for sealing said piston to said cylindrical
housing during said reciprocation;
a spring positioned between said housing and said piston for biasing
said piston toward said inlet;
a valve member mounted in alignment with said valve seat within
said housing for reciprocation along the axis of said housing, said
valve member closing said piston aperture when positioned against
said aperture, said valve member including a camming surface adjacent
a camming shoulder; and
means for reciprocating said valve member along the axis of said
housing to open and close said piston aperture in response to the
position of said piston along the axis of said housing, said reciprocating
means comprising a spring member for biasing said valve member toward
said piston aperture when said piston is positioned in a first reciprocating
extreme and for biasing said valve member away from said piston
aperture when said piston is in a second reciprocating extreme position,
said spring member alternately biasing against said camming surface
and said camming shoulder for biasing said valve member toward and
away from said piston aperture respectively.
5. A fuel flow meter as defined in claim 4 additionally comprising:
a stop member positioned on said piston for jarring said bias means
from said camming shoulder to said camming surface when said piston
reaches said second reciprocating extreme.
6. A fuel flow meter as defined in claim 1 wherein said flexible
sealing means comprises an annular rolling diaphragm sealed to said
piston and said cylindrical housing.
7. A fuel flow meter as defined in claim 1 additionally comprising:
a switch mounted on said cylindrical housing and actuated by said
reciprocating piston for permitting monitoring of the reciprocation
of said piston.
8. A fuel flow meter as defined in claim 5 wherein said switch
is a magnetic reed switch mounted externally of said cylindrical
housing, said fuel flow meter additionally comprising:
a magnet mounted on said piston for intermittently actuating said
magnetic reed switch in accordance with the position of said piston.
9. A meter for measuring the rate of flow of a fluid in a conduit,
comprising:
a housing having an inlet and outlet connected in series with said
conduit;
positive displacement reciprocating means mounted within said housing
for separating said housing into an inlet chamber and an outlet
chamber;
means for sealing said reciprocating means to said housing during
motion of said reciprocating means;
means biasing said reciprocating means toward said inlet chamber;
and
flow control means comprising:
a valve for controlling fuel flow through said housing past said
reciprocating means, and
an over center spring mounted on said housing; said spring opening
said valve during motion of said reciprocating means toward said
inlet chamber, said spring closing said valve during motion of said
reciprocating means toward said outlet chamber.
10. A meter for measuring the rate of flow of a fluid as defined
in claim 9 wherein said over center spring is responsive to said
reciprocating means and opens and closes said valve in response
to the relative position of said reciprocating means and said housing.
11. A meter for measuring the rate of flow of a fluid as defined
in claim 10 wherein said valve comprises:
a first valve element mounted on said reciprocating means for reciprocation
with said reciprocating means; and
a second valve element operative to close said first valve element,
said second valve element reciprocating within said housing independently
of said reciprocating means.
12. A meter for measuring the rate of flow of a fluid as defined
in claim 9 additionally comprising:
means for externally monitoring the position of said reciprocating
means within said housing, said monitoring means comprising an electrical
switch activated in response to the position of said reciprocating
means.
13. A meter for measuring the rate of flow of a fluid in a conduit,
comprising:
a housing having an inlet and an outlet connected in series with
said conduit;
positive displacement reciprocating means mounted within said housing
for separating said housing into an inlet chamber and an outlet
chamber; said reciprocating means comprising:
a piston;
a pair of guide rods mounted coaxially on alternate ends of said
piston; and
a passage through said piston concentric with one of said guide
rods;
means for sealing said reciprocating means to said housing during
motion of said reciprocating means;
means biasing said reciprocating means toward said inlet chamber;
and
flow control means permitting fluid flow through said housing past
said reciprocating means during motion of said reciprocating means
toward said inlet chamber, said flow control means prohibiting fluid
flow past said reciprocating means during motion of said reciprocating
means toward said outlet chamber, said permitting means comprising
a valve member for sealing said passage concentric with said guide
rod, said valve member reciprocating on one of said pair of guide
rods independently of said piston.
14. A meter for measuring the flow of a fluid, comprising:
a housing having an inlet and an outlet;
a piston mounted for reciprocation within said housing between
a pair of extremes adjacent said inlet and said outlet;
valve means for bypassing fluid around said piston between said
inlet and said outlet, said valve means closing when said piston
is at said extreme adjacent said inlet and opening when said piston
is at said extreme adjacent said outlet end; said valve means comprising:
an orifice for bypassing fluid around said piston; and
a valve member selectively closing against the downstream end of
said orifice;
means for biasing said piston toward said extreme adjacent said
inlet end; and
means for producing an output signal in response to the position
of said piston within said cylinder.
15. A meter for measuring the flow of fluid as defined in claim
14 wherein said orifice reciprocates with said piston; and wherein
said valve member is mounted within said housing for reciprocation
independent of the reciprocation of said piston but along the same
axis as said piston reciprocation.
16. A meter for measuring the flow of a fluid as defined in claim
15 additionally comprising:
means for biasing said valve member to a position adjacent said
orifice when said piston is at said extreme adjacent said inlet,
said means biasing said valve member away from said orifice when
said piston is at said extreme adjacent to said outlet end.
17. A meter for measuring the flow of a fluid as defined in claim
16 wherein said means for biasing said valve member maintains said
valve member adjacent said orifice after said piston has reached
said extreme adjacent said inlet end and before said piston has
reached said extreme adjacent said outlet end.
18. A meter for measuring the flow of a fluid as defined in claim
14 wherein said means for producing an output signal comprises a
switch mounted externally of said housing.
19. A meter for measuring the flow of a fluid as defined in claim
18 wherein said switch comprises a magnetic reed switch, said meter
additionally comprising:
a magnet mounted for reciprocation with said piston for activating
said magnetic reed switch.
20. A meter for measuring the flow of a fluid comprising:
a housing having an inlet and an outlet;
a piston mounted for reciprocation within said housing between
a pair of extremes adjacent said inlet and said outlet;
valve means for bypassing fluid around said piston between said
inlet and said outlet, said valve means closing when said piston
is at said extreme adjacent said inlet and opening when said piston
is at said extreme adjacent said outlet end, said valve means comprising:
an orifice for bypassing fluid around said piston; and
a valve member selectively closing against the downstream end of
said orifice; and
means for biasing said piston toward said extreme adjacent said
inlet end.
21. A meter for measuring the rate of flow of a fluid comprising:
a housing having an inlet and an outlet;
positive displacement reciprocating means mounted within said housing
for separating said housing into an inlet chamber and an outlet
chamber, said positive displacement reciprocating means including
a through orifice connecting said inlet chamber and said outlet
chamber;
a valve for selectively closing said orifice; and valve-actuating
means for moving said valve toward said outlet end to open said
valve when said reciprocating means is adjacent said outlet end.
22. A meter for measuring the rate of flow of a fluid as defined
in claim 21 wherein said valve-actuating means closes said valve
by moving said valve toward said inlet end when said reciprocating
means is adjacent said inlet end.
23. A meter for measuring the rate of flow of a fluid comprising:
a housing having an inlet and an outlet;
a piston mounted for reciprocating within said housing between
a pair of extremes adjacent said inlet and said outlet;
valve means for bypassing fluid around said piston between said
inlet and said outlet, said valve means having a camming surface;
means for biasing said piston toward said extreme adjacent said
inlet end; and
cam actuated means acting on the camming surface of said valve
means for opening said valve means when said piston is at said extreme
adjacent said outlet end.
24. A meter for measuring the rate of flow of a fluid as defined
in claim 23 wherein said cam actuated means closes said valve means
when said piston is at said extreme adjacent said inlet end.
25. A meter for measuring the rate of flow of a fluid comprising:
a housing having an inlet and an outlet;
a piston;
a piston rod mounting said piston for reciprocating within said
housing between a pair of extremes adjacent said inlet and said
outlet;
valve means reciprocating on said piston rod independent of said
piston reciprocation, said valve means bypassing fluid around said
piston between said inlet and said outlet;
means for closing said valve means when said piston is at said
extreme adjacent said inlet and opening said valve means when said
piston is at said extreme adjacent said outlet end; and
means for biasing said piston toward said extreme adjacent said
inlet end.
Description BACKGROUND OF THE INVENTION
This invention relates to positive displacement digital fluid flow
meters and more particularly to fluid flow meters adapted to measuring
the flow of fuel to an internal combustion engine.
A variety of mechanisms have been used in the past to provide a
measurement of the rate of flow of fuel to engines. Such devices,
in most instances, incorporate a rotating member in the fuel flow
which rotates at a speed governed by the flow rate. Alternatively,
a reciprocating body has been mounted in a fuel line, and fuel flows
around the body to position the mechanism in accordance with the
viscous flow of the fluid over this element. Such fuel flow meters
are generally accurate over a fairly narrow range of flow rates
and are not adapted to measuring fuel flow at extremely low flow
rates. Furthermore, such devices generally connect to monitoring
equipment through complex cabling, conduits or shafts, making their
installation on a vehicle difficult and costly. Due to the nature
of these devices, they are subject to inaccuracies caused by changes
in the viscosity of the fluid being measured which may result, for
example, from temperature changes. They are additionally subject
to inaccuracies resulting from wear of moving parts and the increased
friction caused thereby. Additionally, such meters do not lend themselves
to the rugged construction normally required in a vehicle where
continuous vibration can damage the meters, since such meters often
include lightweight, rapidly rotating elements with low friction
bearings, which fragile elements are easily damaged in a vibrating
environment.
In addition, attempts have been made in the prior art to monitor
the signals within electric fuel pumps to utilize such signals as
an indication of fuel flow rates. Such installations, of course,
require that the automobile or other vehicle being monitored include
an electric fuel pump and that this fuel pump be accurately gaged
so that the amount of fluid per stroke is known. Particularly when
the meter is to be added to an existing vehicle, these factors make
the use of the electric fuel pump as a fuel measuring instrument
unacceptable for a wide range of vehicles.
Other attempts at positive displacement monitoring of fuel flow
have been made by monitoring the extent of the stroke of a mechanical
fuel pump which is a part of the engine being monitored. Each such
device, however, requires a modification of the fuel pump itself
for monitoring purposes, which is both complex and expensive and
therefore impractical for addition to an existing vehicle.
SUMMARY OF THE INVENTION
The present invention alleviates these and other difficulties associated
with the prior art by utilizing a passive, positive displacement
reciprocating meter which produces digital output signals. This
device is rugged in construction and is not susceptible to inaccuracies
due to friction, temperature, or fluid viscosity changes. Furthermore,
the device is easily manufactured to produce output digital signals
corresponding to a precalibrated fuel flow so that the time delay
between successive digital signals may be used as a direct indication
of fuel flow rates. The device, being a passive element in the fuel
flow system, is easily inserted on any vehicle by simply inserting
the device into the fuel flow line at any point which is convenient
to the monitoring devices.
These advantages are accomplished by utilizing as a fuel flow monitoring
system a piston which reciprocates within a cylinder, one end of
the cylinder being connected to the fuel source, such as a fuel
pump, and the other end of the cylinder being connected to the output
fuel flow line. The piston is urged toward the input fuel flow line
within the cylinder by a spring so that, without a pressure differential
across the piston, the piston will move toward the inlet end of
the cylinder. Fuel flowing into the input port under pressure will
move the piston within the cylinder, overcoming the bias of the
spring, so that the piston moves toward the outlet port. When the
piston reaches a predetermined location adjacent the outlet port,
a bypass valve is automatically opened, bypassing fluid from the
inlet port to the outlet port through the piston so that the pressure
differential across the piston is removed. The piston therefore
moves toward the inlet port under the bias of the spring. When the
piston reaches a predetermined location adjacent the inlet port,
the bypass valve is automatically closed to cause the piston to
again move toward the outlet port in response to fluid admitted
through the inlet port.
A magnet is located on the piston structure and magnetic reed switches
are located outside of the cylinder to be actuated by the magnet.
Thus, as the piston reciprocates within the cylinder, the position
of the piston at two extreme positions within the cylinder may be
monitored. The reed switches produce output digital signals indicative
of the beginning and end of each positive displacement stroke of
the piston when the bypass valve is closed and thus produce signals
displaced in time by a delay which is equivalent to the time period
required for the flow of a precalibrated quantity of fuel.
These and other advantages of the present invention are best understood
through a reference to the drawings in which:
FIG. 1 is a perspective view of the fuel flow meter of the present
invention;
FIG. 2 is an exploded perspective view showing the various elements
of the meter of FIG. 1;
FIGS. 3 4 and 5 are sectional views of the fuel flow meter of
FIG. 1 showing the meter in various stages of operation during its
reciprocating cycle; and
FIG. 6 is a partial exploded view of an alternate embodiment monitoring
system for the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring initially to FIGS. 1 2 and 3 the construction of the
fuel flow meter will be described. The meter is mounted within a
cylindrical housing 11 which includes an inlet portion 13 and an
outlet portion 15. The inlet portion 13 is formed as a cylindrical
cup member having an inlet port 17. The port 17 is designed to interconnect
with an inlet conduit, such as a flexible fuel line which may be
connected around the port 17 as by a hose clamp. This inlet conduit
(not shown) typically connects the port 17 to the vehicle fuel pump
outlet.
A bearing plate 19 is positioned within the inlet portion 13 and
is formed as a circular plate covering the inlet port 17. The bearing
plate 19 may be attached to the inlet portion 13 by a pair of screws
21 or any other convenient fastener, and includes a plurality of
inlet orifices 23 for admitting fuel or other fluid from the inlet
port 17 to the inlet portion 13. In addition, the bearing plate
19 includes a central bearing aperture 25 for reciprocally mounting
a guide rod 27 as will be explained in more detail below.
The outlet portion 15 is a cylindrical cup-shaped member similar
to the inlet portion 13 and each of these portions include mating
annular external flanges 29 and 31 respectively, for attaching
the portions 13 15 into a single housing 11. The outlet portion
15 includes an outlet port 33 formed as an extending cylindrical
tube member similar to the inlet port 17 and adapted for interconnection
with a fuel line or other fluid conduit. In a typical installation,
this conduit connects the port 33 to the vehicle carburetor inlet.
As in the case of the inlet port 17 the outlet port 33 mounts a
bearing plate 35 including plural fluid outlet apertures 37 a central
bearing aperture 39 and screws 41 supporting the bearing plate 35
on the outlet portion 15. The bearing aperture 39 reciprocally guides
a second guide rod 43 as will be explained in more detail below.
The inner cylindrical wall 45 of the housing 11 forms a cylinder
for reciprocating movement of a piston 47. The piston 47 may be
formed to fit tightly within the cylinder 45 but in the preferred
embodiment has a smaller diameter than the cylinder 45 to accommodate
a rolling flexible diaphragm 49. This diaphragm 49 positively seals
the piston 47 to the cylinder 45 while permitting free motion of
the piston 47 along the axis of the housing 11.
The piston 47 is formed as a cylindrical cup member including a
flat base portion 51 which is centrally apertured at 53. The central
aperture 53 mounts a cylindrical valve seat 55 formed as a grommet
with an external annular groove 57 which conforms to the aperture
53 to position the valve seat 55 within the aperture 53 and seal
the valve seat 55 to the flat portion 51 of the piston 47. The valve
seat 55 is made of a semiresilient polymer material, such as Viton,
and includes a central aperture 59 which surrounds the second guide
rod 43 but is substantially larger than the guide rod 43 to provide
for the flow of fluid between these members.
The guide rod 27 and second guide rod 43 are formed as a unitary
element with a piston head 61. The piston head 61 is formed as a
cup member having a base flange 63 conforming to the flat portion
51 of the piston 47 and includes a plurality of apertures 65 which
permit the flow of fluid to the valve seat 55.
The rolling diaphragm 49 is formed of flexible, fluid impervious
material in the shape of an annular ring, the sides of the ring
being U-shaped in cross section after the unit is assembled. The
ring includes an external annular flange portion 67 and an internal
annular flange portion 69 which seal the rolling diaphragm 49 to
the housing 11 and piston 47 respectively. In addition, these flanges
67 and 69 form gaskets for the mating portions of the housing 11
and piston 47. Thus, the flange 67 fits between the flanges 29 and
31 of the housing 11 and is pressed between these members by a plurality
of screws 71 positioned at spaced intervals around the housing 11.
Similarly, the internal flange 69 is pressed between the flat portion
51 of the piston 47 and the flange 63 of the piston head 61 by a
plurality of screws 73 positioned at spaced intervals around the
flange 63.
The piston 47 with its connected piston head 61 forms a reciprocating
assembly which is free to move along the axis of the housing 11
guided by the guide rods 27 and 43 bearing on the apertures 25 and
39. This entire assembly is biased toward the inlet port by a spring
75 which is positioned at one end around the bearing plate 35 and
at the other end within the plural screws 73.
A valve bead 77 is formed as a generally conical member having
an axial aperture 79. The aperture 79 has a large enough diameter
to permit this member 77 to reciprocate freely along the second
guide rod 43. This diameter is, however, small enough to provide
a seal between the valve bead 77 and second guide rod 43. The external
conical surface 81 of the valve bead 77 extends to form a spherical
cap 83 at one end of the bead 77. The other end of the bead 77 is
formed as a relatively flat base to provide an annular shoulder
85 and a valve head portion 87. The valve head portion 87 is formed
to fit within the aperture 59 in the valve seat 55 while the shoulder
85 forms a camming surface, as will be described below.
The valve bead 77 is free to reciprocate along the second guide
rod 43 this reciprocation limited at one extreme by the sealing
of the valve head 87 within the valve seat 55 and limited at the
outlet end extreme by contact between the spherical end 83 and a
bead stop 89. This bead stop 89 is formed as a split washer which
fits within an annular external groove in the second guide rod 43.
A pair of spring clips 91 are secured by a pair of the plural screws
41 to the outlet port 33. These spring clips 91 are formed as elongate
leaf springs terminating at one end with a right angle bend to form
a flange portion 93 which is apertured for placement around a screw
41. At the other extremity, the spring clips 91 are bent to form
a V-shaped camming portion 95 extending toward the second guide
rod 43 and valve bead 77. The spring clips 91 are each formed of
spring metal and, when mounted on the screws 41 are biased toward
one another so that, even if the valve bead 77 were removed, the
V-shaped camming portions would bear against the second guide rod
43. Thus, the spring clips 91 are always biased against the conical
camming surface of the valve bead 77 in a direction normal to the
axis of the second guide rod 43.
In order to provide external sensing of the position of the piston
47 within the housing 11 a bar magnet 97 is mounted on the outside
of the skirt of the piston 47. A pair of magnetic reed switches
99 and 101 are mounted on the external cylindrical wall of the housing
11 proximate the position of the magnet 97 so that when the magnet
97 is positioned below either of the reed switches 99 or 101 the
magnet 97 will close that switch to indicate that the piston 47
is at one extreme of its travel. Thus, when the piston 47 has traveled
to its extreme position toward the inlet port 17 the magnet 97
will close the magnetic reed switch 99. Similarly, when the piston
47 has traveled to its extreme position toward the outlet port 33
the magnet 97 will close the magnetic reed switch 101.
Operation of the meter described above will now be explained in
reference to FIGS. 3 through 5. FIG. 3 shows the flow meter at the
beginning of a filling cycle, with the bar magnet 97 positioned
beneath the magnetic reed switch 99 closing the switch 99. The spring
clips 91 are spread apart slightly by their engagement with the
camming surface 81 on the valve bead 77. This biased engagement
of the V-shaped camming portions 95 with the camming surface 81
biases the valve bead 77 to the left, as viewed in FIG. 3 that
is, toward the inlet port 17 since the V-shaped camming portions
95 tend to slide toward the narrower portions of the valve bead
77. The valve bead 77 therefore engages with the valve seat 55
and specifically the valve head portion 87 engages with the aperture
59 to close this aperture and thereby seal the piston 47. Fluid
enters the inlet port 17 flows through the passages 23 and past
the piston head 61 to fill the cavity within the inlet portion 13.
Once this cavity has been filled, it will remain filled throughout
the life of the meter so that it will not interfere with subsequent
measurements. Fluid flows from this cavity within the inlet portion
13 through the apertures 65 to fill the area between the valve seat
55 and piston head 61. This latter area, as with the volume within
the inlet portion 13 once filled, remains filled during the life
of the meter and does not therefore interfere with meter volume
for measurement purposes. Fluid cannot pass through the valve seat
55 since the valve bead 77 is biased toward the inlet passage 17
by the relative camming action of the V-shaped portions 95 of the
spring clip 91 and the camming surface 81. Fluid passing through
the inlet passage 17 therefore generates a pressure differential
between the inlet portion 13 and outlet portion 15 of the housing
11 and specifically across the piston 47 and rolling diaphragm
49. This pressure differential overcomes the bias of the spring
75 so that the piston 47 is displaced toward the outlet passage
33 guided by the guide rods 27 and 43 reciprocating within the
bearing apertures 25 and 39. During this reciprocation, the spring
clips 91 remain biased toward one another so that the camming action
between the V-shaped portions 95 and camming surface 81 maintains
the valve head 87 engaged with the valve seat 55 so that the valve
which bypasses the piston 47 is maintained closed. As soon as this
reciprocating movement is initiated, the magnet 97 is moved from
beneath the reed switch 99 and the reed switch 99 is allowed to
open, signaling the initiation of a measurement.
Referring now to FIG. 4 and specifically to the configuration
of parts shown in solid lines in that figure, it will be seen that
the piston 47 continues to progress in this manner toward the outlet
passage 33 until the V-shaped camming portions 95 of the spring
clips 91 reach the shoulder 85 of the valve bead 77. As the motion
of the piston 47 progresses still farther, the V-shaped camming
surfaces 95 pass over the shoulder 85 so that the inclined surface
103 of these camming elements 95 engages the shoulder 85. This engagement,
shown in phantom lines in FIG. 4 abruptly draws the valve bead
77 toward the outlet passage 33 opening a passage between the valve
head portion 87 and valve seat 55. This permits a flow of fluid
from the inlet portion 13 to the outlet portion 15 and abruptly
reduces the pressure differential across the piston 47 and piston
head 61. The spring 75 is therefore permitted to reciprocate the
piston 47 and piston head 61 toward the inlet passage 17 guided
by the guide rods 27 and 39 with fluid flowing through the apertures
65 in the piston head 61 and the aperture 59 in the valve seat 55.
The shoulder 85 will maintain the valve bead 77 captive within the
V-shaped portion 95 of the spring clips 91 as the piston 47 moves
toward the inlet passage 17.
It will be noted, in addition, that when the piston 47 has reached
the end of its reciprocation toward the outlet passage 33 that
is, when the V-shaped camming portions 95 are adjacent the shoulder
85 of the valve bead 77 the bar magnet 97 has moved to a position
beneath the magnetic reed switch 101 so that this switch is activated
to produce an electrical signal indicating the end of the time period
required to displace the piston 47 through a predetermined stroke,
which in turn signals the end of a period required for the passage
of a predetermined quantity of fluid through the inlet passage 17.
As shown in FIG. 5 and particularly the solid line element positions
of FIG. 5 the valve bead 77 remains captive of the spring clips
91 until the piston 47 along with the piston head 61 and guide
rods 27 and 39 has moved under the force of the spring 75 to a
position adjacent the starting location described in reference to
FIG. 3. Since a free flow of fluid is permitted through the bypass
valve 55 this motion of the piston toward the inlet port 17 is
abrupt and will bring the bead stop 89 into contact with the captive
valve bead 77. The bead stop 89 will impact against the spherical
end 83 of the valve bead 77 the spring 75 providing sufficient
force to jar the V-shaped camming portions 95 and particularly
the camming surface 103 thereof, around the shoulder 85 of the valve
bead 77. The valve bead 77 is thus jarred forward to the broken
line position shown in FIG. 5 so that the V-shaped camming elements
95 reside on the camming surface 81 of the valve bead 77. The spring
bias of the spring clips 91 operates thereafter to cam the valve
bead 77 toward the inlet port 17 until the valve bead 77 closes
the valve seat 55. The structure, at this point in time, once again
resides in the position shown in FIG. 3 to initiate a successive
cycle. Once the piston 47 has returned to this initial position,
the bar magnet 97 will again actuate the switch 99 to signal the
start of another measurement cycle.
It will be understood that the pressure differential which is generated
across the piston 47 when the valve 77 is closed is sufficient to
move this piston 47 overcoming the bias of the spring 75. The differential
is insufficient, however, to overcome the bias of the spring clips
91 acting with the camming elements 95 and 81 to displace the valve
bead 77 from the orifice 59 in the valve seat 55. This is accomplished
through a proper selection of spring constants and pretension of
the springs 75 and 91 and through a proper selection of the size
of the orifice 59.
It will be recognized that a small amount of fluid may pass from
the inlet passage 17 to the outlet passage 33 as the piston 47 is
displaced from its location adjacent the outlet passage 33 as shown
in FIG. 4 to its position adjacent the inlet passage as shown in
FIG. 5. This amount of fluid will be insignificant in relation to
the amount of fluid which passes through the inlet 17 and outlet
33 during the reciprocation when the valve bead 77 is closed against
the valve seat 55. Thus, this small amount of fluid does not substantially
interfere with the total measurement of fluid. The total fluid which
passes through the fluid meter may therefore be determined by counting
the output pulses of either of the magnetic reed switches 99 or
101. The amount of fluid required to displace the piston 47 is accurately
predetermined, so that this quantity may be multiplied by the number
of pulses to produce an accurate measurement of total flow.
Alternatively, if it is desired to operate this meter as a flow
rate meter rather than a total quantity of flow meter, the slight
inaccuracy created by the fluid flowing during retraction of the
piston 47 may be removed altogether. This is accomplished by accurately
measuring the time required for the piston 47 to move from the position
shown in FIG. 3 to the position shown in FIG. 4 and by measuring
the time lag between opening of the magnetic reed switch 99 and
closing of the reed switch 101. If, for example, this meter is to
be used as a portion of a mile-per-gallon indication system in a
vehicle, the time duration between actuation of the magnetic reed
switches 99 and 101 produces an accurate measurement of time per
quantity which may be calibrated, for example, in terms of hours
per gallon. If these signals are used in conjunction with the output
of a vehicle speedometer which measures, for example, in terms of
miles per hour, a simple multiplication of these factors produces
a direct output signal which may be digitally computed in terms
of miles per gallon.
An alternate arrangement for monitoring the flow of fluid through
the meter of the present invention, and of avoiding the slight inaccuracy
created by fluid flowing during the retraction of the piston 47
is shown in FIG. 6. In this alternate embodiment, all of the elements
are identical to those described and shown in reference to FIGS.
1 through 5 except for the valve bead 77. As shown in FIG. 6 the
shoulder 85 of the valve bead 77 includes a circular ring 107 of
electrically conductive material, such as, for example, a ring of
metal which may be adhesively bonded just inside the shoulder 85.
In addition to this modification, a pair of wires 109 and 111 may
be electrically connected to the spring clips 91. Thus, if the valve
bead 77 the bearing plate 35 and the outlet portion 15 of the
housing 11 are constructed of nonconductive material, the spring
clips 91 will normally be electrically isolated from one another.
However, when the valve bead 77 is captive within the V-shaped camming
portions 95 of the spring clips 91 the camming surface 103 of these
portions 95 will contact the conductive ring 107 formed on the valve
bead 77. Thus, electrical continuity will be generated between the
spring clips 91 and their respective lead-in wires 109 and 111.
By monitoring the conductivity or resistance between the lead wires
109 and 111 it is possible to externally monitor the times when
the valve bead 77 is captive within the spring clips 91. A review
of FIGS. 4 and 5 will make it apparent that, during the entire travel
of the piston 47 in a direction toward the outlet passage 33 the
V-shaped camming portions 95 of the spring clips 91 rest on the
camming surface 81 of the valve bead 77. When the piston 47 reaches
the extremity of its stroke toward the outlet passage 33 the valve
bead 77 becomes a captive of the spring clips 91 such that conductivity
is present between the lead-in wires 109 and 111 of FIG. 6. The
valve bead 77 remains captive until the piston has been retracted
to its initial position shown in dotted lines in FIG. 5 and solid
lines in FIG. 3. Thus, during the entire retraction period when
a small amount of fluid passes through the valve, which flow could
otherwise generate a slight inaccuracy in the fluid flow rate measurement,
the valve bead 77 is captive between the spring clips 91. By measuring
the periods of time during which the lead-in wires 109 and 111 of
FIG. 6 are electrically isolated from one another, it is possible
to determine the time period required for a full positive displacement
stroke of the piston 47. This measurement time period may then be
used, as described above, for measuring hours per gallon and for
in turn measuring mileage in a vehicle in terms of miles per gallon.
It should be noted that, since the fluid flow meter of the present
invention is a positive displacement meter, that is, as the measurement
occurs the valve bead 77 is closed against the valve seat 55 so
that no flow occurs past the piston 47 this apparatus is capable
of measuring an extremely wide range of flow rates. In particular,
the apparatus will measure extremely low flow rates since there
is virtually no limitation upon the time which may be required to
reciprocate the piston 47 between the positions shown in FIG. 3
and FIG. 4. |