Abstrict A flow meter comprising a rotor assembly that is comprised of two
rotors having axis of rotation offset from collinear where the two
rotors define operating chambers that changing volume with respects
to rotation and allow fluid to pass from an inlet port to an outlet
port when the number of rotation is indicated the volumetric flow
therethrough.
Claims Therefore I claim:
1. A flow meter comprising: a housing comprising an inner surface
and an inlet port and an exit port; an inner component have an outer
surface that defines at least part of a sphere; a first rotor mounted
for rotation in the housing about a first axis and having a forward
region and a rearward region and a first outer surface defining
at least part of a sphere and adapted to intimately engages the
inner surface of the housing; a second rotor having a forward portion
and a rearward portion, mounted for rotation in the housing about
a second axis offset from being collinear with the first axis by
an angle .alpha. and intersecting at the common centers of the rotors,
the second rotor including a first inner surface defining at least
part of a sphere having a common center with the center of the first
rotor and is adapted to engage the inner component, a second outer
surface defining at least part of a sphere and having a common center
with the second inner surface and adapted to engage the inner surface
of the housing; the first rotor further having a first contour surface
that is defined by a locus formed by points on the second rotor
as the second rotor rotates about the second axis, and the first
rotor further has a first engagement tip which is positioned in
the forward region of the first rotor; the second rotor further
having a second contour surface that is defined by a locus formed
by points on the first rotor as the first rotor rotates about the
first axis, the second engagement surface having a base region;
the points of each rotor that define the locus lie along an outer
edge of a central axis is essentially a radius extending outward
from the common centers of the rotor at an angle .alpha./2 from
a normal to the axis of the other rotor; a counter engaged to at
least one of the said rotors where the counter is adapted to count
the number of rotations of the rotors; whereas the contour surfaces
of the first and second rotors define operating chambers that change
in volume with respects to rotation of the first and second rotors
where a certain amount of fluid passes from the inlet port to the
outlet port per revolution of the first and second rotors and the
counter indicates the number of rotations.
2. The flow meter as recited in claim 1 further comprising a display
interface that indicates the number of rotations of the first and
second rotor.
3. The flow meter as recited in claim 1 where a first volumetric
value is a product of a volume per rotation coefficient that is
the volumetric throughput per revolution of the first and second
rotors and the number of rotations.
4. The flow meter as recited in claim 3 further comprising an output
component that posts the first volumetric value of the flow meter.
5. The flow meter as recited in claim 4 where the volumetric throughput
through the input port to the output port to the flow meter is measured
for given unit of time and the output portion produces the volumetric
flow rate.
6. The flow meter as recited in claim 3 further comprising; a pressure
differential system that measures a differential pressure from the
input port to the output port; a velocimeter that is in communication
with the counter and indicates the number of rotations per unit
of time and outputs a rotational velocity of the rotors; whereas
the differential pressure and the rotational velocity are used to
determine the volumetric quantity of blow-by.
7. The flow meter as recited in claim 6 where the volumetric quantity
of blow-by is added to the first volumetric quantity to represent
the total volumetric throughput from the inlet port to the output
port.
8. The flow meter as recited in claim 6 where the volumetric quantity
of blow-by is divided by a unit of time to produce a blow-by volumetric
throughput rate value.
9. A method of measuring the volumetric flow of a fluid comprising
the steps of: positioning a rotor assembly in a housing where the
rotor assembly comprises a first rotor and a second rotor that each
have a center axis of rotation where the first rotor and the second
rotors are offset from collinear by and angle a where the first
rotor has a plurality of lobes that comprise tips and contour surfaces
and the second rotor comprises a plurality of lobes that comprises
tips and contour surfaces where the tips each rotor define the corresponding
contour surfaces of the opposing rotor, channeling fluid into an
inlet port of the housing whereby inducing rotation of the rotor
assembly and causing operation chambers of the rotor assembly that
are in communication with the inlet port to increase in volume whereby
drawing in the fluid, passing the fluid past a top dead center location
of the housing to an exist port whereby the chambers reduce in volume
and the fluid thereby exits the rotor assembly, counting the number
of rotations of the rotor assembly to calculate the volumetric throughput
of the fluid.
10. The method as recited in claim 9 where a first volumetric value
is a product of a volume per rotation coefficient that is the volumetric
throughput per revolution of the first and second rotors and the
number of rotations.
11. The method as recited in claim 10 further comprising an output
component that posts the first volumetric value.
12. The method as recited in claim 11 volumetric throughput through
the input port to the output port is measured for given unit of
time and the output portion produces the volumetric flow rate.
13. The method as recited in claim 10 where a pressure differential
system that measures the differential pressure from the input port
to the output port is in communication with the input and output
ports, a velocimeter is used that is in communication with the counter
and indicates the number of rotations per unit of time and outputs
a rotational velocity of the rotors, where the pressure differential
and the rotational velocity are used to determine the volumetric
quantity of blow-by.
14. The method as recited in claim 13 where the volumetric quantity
of blow-by is added to the first volumetric quantity to represent
the total volumetric throughput from the inlet port to the output
port.
15. The method as recited in claim 14 where the volumetric quantity
of blow-by is divided by a unit of time to produce a blow-by volumetric
throughput rate value.
16. A flow meter comprising: a housing comprising an inner surface
and an inlet port and an exit port; a rotor assembly comprising;
a first rotor mounted for rotation in the housing about a first
axis and having a forward region and a rearward region and a first
outer surface defining at least part of a sphere and adapted to
intimately engages the inner surface of the housing and an inner
component that is has an outer surface that is partially spherical;
a second rotor having a forward portion and a rearward portion,
mounted for rotation in the housing about a second axis offset from
being collinear with the first axis by an angle .alpha. and intersecting
at the common centers of the rotors, the second rotor including
a first inner surface defining at least part of a sphere having
a common center with the center of the first rotor and is adapted
to engage the inner component, a second outer surface defining at
least part of a sphere and having a common center with the second
inner surface and adapted to engage the inner surface of the housing;
the first rotor further having a first contour surface that is defined
by a locus formed by points on the second rotor as the second rotor
rotates about the second axis, and the first rotor further has a
first engagement tip which is positioned in the forward region of
the first rotor; the second rotor further having a second contour
surface that is defined by a locus formed by points on the first
rotor as the first rotor rotates about the first axis,the second
engagement surface having a base region; a counter engaged to at
least one of the said rotors where the counter is adapted to count
the number of rotations of the rotors; whereas the points of each
rotor that define the locus lie along an outer edge of a central
axis is essentially a radius extending outward from the common centers
of the rotor at an angle .alpha./2 from a normal to the axis of
the other rotor; the contour surfaces of the first and second rotors
define operating chambers that change in volume with respects to
rotation of the first and second rotors where a certain amount of
fluid passes from the inlet port to the outlet port per revolution
of the first and second rotors and the counter indicates the number
of rotations.
17. The flow meter as recited in claim 16 where a first volumetric
value is a product of a volume per rotation coefficient that is
the volumetric throughput per revolution of the first and second
rotors and the number of rotations.
18. The flow meter in claim 17 where the pressure differential
between the inlet and outlet ports is measured and this value and
the rotational velocity are used to calculate the amount of blow-by
fluid.
19. The flow meter in claim 18 where the amount of blow by fluid
is added to the first volumetric value to obtain the net fluid volume
measured.
Description FIELD OF THE INVENTION
The invention relates to positive displacement machines that convert
energy, namely positive displacement devices that displace fluid
(incompressible or gas) where the device has continuous rotation
to displace fluid contained in operating chambers. The present invention
is particularly advantageous for measuring the flow of fluid passing
through the operating chambers of the machine.
BACKGROUND
Prior flow meters have limitations of only sampling the volumetric
flow or creating excessive head loss of the flow which causes a
pressure drop as a fluid passes through the flow meter.
Traditional flow meters either rely on a tight frictional seal
between the moving parts which causes greater head loss as the fluid
passes therethrough or the moving parts have a loose seal and hence
a greater amount of fluid is not accounted for by the positive displacement
prior art chambers.
The present invention provides an increase in the amount of accuracy
of measured fluid and requires very little pressure differential
to rotate the rotor assembly. The present invention flow meter is
a low friction, low fluid turbulence, positive displacement device
with relatively linear operating characteristics over a wide range
of operating speeds and operating fluid viscosities. This linearity
will enable accurate and predictable flow metering of a wide range
of operating fluids and flow rates with a simple rotational pulse-counter
(as is common to the flow meter industry). There are many applications
where pulse-counter positive displacement flow meters are used and
where a wider flow range, small size, and increased accuracy of
a pulse-counter flow meter would offer significant advantages.
Many other applications exist where even higher accuracy would
be a significant advantage. Electronic flow meter control systems
are common to the flow meter industry. In a second embodiment a
control system which works on a unique set of inputs to refine the
accuracy of the mechanical components. The control system applied
to the rotor assembly has the potential to achieve higher accuracy
then is currently available.
The rotors of the present invention and casing will offer excellent
repeatability due to low friction and the positive displacement
characteristic of the rotors. An obstacle to accurately measure
fluid flow is to account for the changing parameters of viscosity,
flow and system pressure accurately enough to predict how the rotors
will perform under various conditions.
The three main characteristics which will affect the CvR.TM. flow
meter will be fluid viscosity, flow rate, and overall system pressure.
The low flow resistance of the present invention allows higher
viscosity fluids to be metered without damage to the flow meter
and without causing unacceptable changes in the flow meter operating
performance.
The present invention has three distinct advantages which benefit
the accuracy and flow range capability of the device. The first
characteristic is low mechanical friction. The CvR.TM. rotors do
not contact during operation due to a fluid film between the rotors,
and are only limited by the friction of the bearings or bushings.
Even with oversized preloaded bearings, the pressure differential
required to rotate the flow meter of the present invention rotors
has been found to be only 0.5 psi. With low friction bearings, the
pressure required to rotate the rotors can be less than 0.05 psi.
Low mechanical friction allows the flow meter of the present invention
to begin measuring flow with very low pressure differentials providing
high accuracy at low flow rates with very little seepage of fluid
past the rotors. The lower the pressure differential on either side
of the rotors, the less seepage will occur past the rotor seals
and because the rotors have so little resistance to rotation, a
very low pressure differential will cause the rotors to turn. In
other words, the rotors prefer to spin rather then lose fluid (and
accuracy) past the seals.
The second characteristic of the flow meter of the present invention
which is related closely to the flow rate parameter is low flow
resistance that results from the low turbulence characteristic of
the rotors that allows very high rotational speeds without excessively
high pressure differentials across the rotors. This allows for greater
flow rates through a smaller flow meter, and also increases the
flow rate range so fewer models need to be produced. In addition
to accuracy, increased flow range is very desirable as it will greatly
simplify the job of an engineer who needs to account for the performance
parameters of each flow meter in their fluid control system.
The third characteristic of the present invention is the lower
the inertia of the rotors which results in a lower pressure differential
required to cause them to accelerate during sudden changes in flow
rate. The rotor assembly has only two moving parts and can be manufactured
with a very low moment of inertia.
System pressure affects both the inlet and the discharge sides
of the flow meter and therefore has very little effect on the rotors.
The primary effect of system pressure is on the casing as it causes
it to deform and increase seal gap clearances causing increased
seepage and reduced accuracy. The high volume throughput of the
flow meter of the present invention allows the use of a smaller
volume than with other flow meter devices. This allows easier construction
of a less deformable casing structure. In addition, it may be possible
to construct the casing so the deformation which occurs with increased
pressure actually decreases certain clearances making up for other
areas which may increase.
All of the above characteristics are advantages of the flow meter
of the present invention which can be further refined with electronic
optimization. In a second embodiment the controller uses only three
electronic inputs to monitor the changing parameters of fluid viscosity,
flow rate, and system pressure and then to compare these values
to a stored value database to determine the actual flow rate of
fluid through the device at all times. The controller could also
be designed to account for the affect of rotor inertia during sudden
flow rate changes. Further the controller could account for the
effect of temperature on the system with temperature sensors and
calibrating the thermal expansion coefficients of the materials
of the flow meter of the present invention.
As fluid viscosity of the operating fluid increases, the pressure
differential across the flow meter of the present invention will
increase due to increased flow resistance and there will be an increased
tendency of the fluid to seep past the close tolerance seals. At
the same time, however, increased viscosity also decreases the tendency
of the fluid to seep past the seals and the two factors have opposing
effects upon the flow.
In a preferred form, pressure transducers will be located in a
stagnant flow area of the inlet and outlet ports. The viscosity
of the fluid being metered will be determined by comparing the speed
of the rotors determined with a simple pulse counter with the pressure
differential which occurs at this speed. The higher the viscosity
of the fluid at a given speed, the higher the pressure differential.
A speed to pressure differential graph or function (based on empirical
test data) will be stored in the controller and used to determine
the viscosity of the fluid (at a predetermined sample rate).
Once the controller has determined the viscosity of the fluid,
it will compare this viscosity value to another graph (or mathematical
function) which will determine the appropriate flow rate correction
at that rotor speed (based on empirical test data with a wide variety.of
viscosities). The two pressure transducers will also be used to
determine the overall system pressure. This value will be compared
to another graph (based on empirical test data) which will account
for the effect of casing deformation on the flow measurement at
that rotor speed and viscosity.
A special "micro-flow" condition will also be accounted
for by the controller. This condition will be specified any time
a micro-pressure differential is detected.across the rotors but
the rotors are not spinning. In this case, a very low volume of
fluid will be seeping across the rotor seals. Empirical testing
data is used to approximate this flow using the last recorded viscosity
value for the fluid.
SUMMARY OF THE INVENTION
The invention comprises a machine that converts energy such as
a pump to increase the pressure of a fluid, or a motor, turbine,
flow meter or actuator taking a pressure differential in a fluid
to create rotary motion about a shaft or other device that employs
positive displacement of fluid (incompressible or gas). The invention
comprises a housing that has an inner surface. A first rotor is
mounted for rotation in the housing about a first axis and has a
first outer surface that is adapted to intimately engage the inner
surface of the housing. There is further a second rotor having a
forward portion and a rearward portion and is mounted for rotation
and the housing about a second axis that is offset from the first
axis and being collinear by an angle .alpha. and intersects at a
common center of the rotors. The second rotor has a second inner
surface that defines at least part of a sphere having a common center
with the center of the first rotor. There is a second outer surface
that is adapted to engage the inner surface of the housing. The
first rotor further has a first contact face that is defined by
a locus formed by points on the second rotor as the second rotor
rotates about the second axis and the first rotor further has a
first contact surface positioned in the forward region of the first
rotor.
The second rotor further has a second contact face that is defined
by a locus formed by points on the first rotor as the first rotor
rotates about the first axis. The second rotor further has a rearward
surface that is positioned in the rearward portion of the second
rotor. The points of each rotor that define the locus along an outer
edge of a common central axis is essentially a radius extending
outward from the common centers of the rotor at an angle .alpha./2
from the normal to the axis of the other rotor.
A counter is engaged to at least one of the rotors. The counter
is adapted to count the number of rotations of the rotors. The contour
surfaces of the first and second rotors define operating chambers
that change in volume with respects to rotation of the first and
second rotors where a certain amount of fluid passes from the inlet
port to the outlet port per revolution of the first and second rotors
and the counter indicates the number of rotations.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial cross-sectional view of the flow meter assembly;
FIG. 1A is a top view of a spherical master rotor on axial shaft
lying on axis A at an angle .alpha. to axis B prior to modification
of the rotor in accordance with the principles of the invention;
FIGS. 1B and 1C are a side view and isometric view respectively
of the master rotor of FIG. 1A;
FIG. 2A is a top view of a master rotor having material removed
from the side of the rotor opposed to the axial shaft leaving a
conical face with the apex of the cone at the center of the sphere
with its axis aligned with the axis A;
FIGS. 2B and 2C are a side view and isometric view respectively
of the master rotor of FIG. 2A;
FIG. 3A is a top view of the master rotor of FIG. 2A with a vertically
oriented cone of material conceptually overlaid on the front face
of the master rotor, the cone having its apex at the intersection
of axis A and axis B (same as the center of the master rotor sphere);
FIGS. 3B and 3C are a side view and isometric view respectively
of the master rotor of FIG. 3A;
FIG. 4A is a top view of the master rotor of FIG. 3A showing the
movement of the conceptual cone in the frame of reference of the
master rotor as would be traced by the conceptual cone if it were
attached to the front face of an essentially identical rotor (slave
rotor) lying on axis B and having a center at the point of intersection
of axis A and axis B and if the slave rotor was rotated through
180.degree. with the master rotor from the vertical position (the
conceptual cone is shown starting off center but it should be appreciated
that the axis of the cone begins its movement at top dead center,
corresponding to the point of lowest compression in the engine of
this invention);
FIGS. 4B and 4C are a side view and isometric view respectively
of the master rotor of FIG. 4A;
FIG. 4D is an isometric view of the cutting, where the column has
a final apical angle .psi. that is a sum of .psi.1 and .psi.2 wear
.psi.1 is radius of the adjacent engagement tip of the opposing
rotor and the value of .psi.2 is the fluid film thickness gap and
between the adjacent engagement tip and the engagement face being
constructed by the conceptual cone;
FIG. 5A shows the trace of the center of the conceptual cone of
FIG. 3A on the surface of the master rotor while the slave rotor
and master rotor make one revolution about their respective axes;
FIG. 5B shows the trace of FIG. 5A seen in the A axis direction;
FIG. 6A is a top view of the master rotor of FIG. 4A showing an
actual cone of material added to the front face of the master rotor,
the cone having its apex at the intersection of axis A and axis
B, with the axis of the cone lying along the face of the master
rotor whose surface is tangential to a contact face of the master
rotor;
FIG. 6B is a side view of the master rotor of FIG. 6A;
FIG. 6C is an isometric view respectively of the master rotor where
a second conceptual cone traces the base teardrop line as the cone
and master rotors rotate about the B and A axis respectively to
define an opposing engagement face;
FIG. 7A is an isometric view of the second engagement surface with
the engagement tip attached to the forward region of the engagement
surface;
FIG. 7B is an isometric view showing a third engagement face similar
to the first engagement face;
FIG. 7C is an isometric view of the second and third engagement
faces with the material interposed thereinbetween removed;
FIG. 8A is a computer-aided drawing showing the axis A and axis
B offset from being collinear and intersecting at a common intersect
point with a reference axis bisecting the two axis on the obtuse
angle portion of the axes;
FIG. 8B shows an array of the reference axis about the B axis;
FIG. 8C shows the array of reference axis rotated about the axes
A to construct the base reference line;
FIG. 8D shows a base reference line offset toward the origin;
FIG. 8E shows an offset ideal surface from the base reference surface;
FIG. 8F shows a an engagement tip cone attached to the forward
region of the ideal reference surface;
FIG. 9 is a front view of the rotor assembly at the bottom dead
center position;
FIGS. 10A-10B show views of the rotor assembly in one position
but taken from isometric perspectives in approximately twenty degree
increments at the bottom dead center position;
FIG. 11 is a side view of the rotor assembly showing the axis of
each rotor;
FIG. 12 shows in detail the contact surface of the master rotor;
FIG. 13 is another view of one of the contact surfaces of the master
rotor;
FIG. 14 illustrates the contact surface of the slave rotor;
FIG. 15 is a second close-up view of the slave rotor illustrating
the gap that is provided between the same of the master rotor and
the rearward surface of the slave rotor;
FIG. 16 shows the gap which is present between the master and slave
rotors at the bottom dead center position to allow a pressure difference
be distributed therethrough;
FIG. 17 is an isometric view of a symmetric rotor assembly;
FIG. 18 is a side view of a symmetric rotor assembly;
FIG. 19 is a top view of a symmetric rotor assembly;
FIG. 20 is an isometric view of a symmetric rotor that is used
to comprise the rotor assembly of FIGS. 17-19;
FIG. 21 is a cross-sectional view of a symmetric rotor taken at
line 21--21 of FIG. 20;
FIG. 22 is a close-up cross-sectional view showing the central
cavity of the symmetric rotor;
FIG. 23 is an isometric cross-sectional view of a housing of the
flow meter;
FIG. 24 is a cross-sectional view of the housing and a rotor assembly
with the center sphere removed;
FIG. 25 is a graph illustrating the volumetric throughput of fluid
with respects to rotational velocities;
FIG. 26 is a 3-D graph showing the calculated viscosity of the
operating fluid with respects to rotational velocities (.omega.)
and pressure differentials (.DELTA.V) of the fluid passing through
the device;
FIG. 27 is a schematic view illustrating a second embodiment of
the present invention;
FIG. 28 is a partial cross-sectional view showing the second embodiment
of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Throughout this description reference is made to top and bottom,
front and rear. The device of the present invention can, and will
in practice, be in numerous positions and orientations. These orientation
terms, such as top and bottom, are obviously used for aiding the
description and are not meant to limit the invention to any specific
orientation.
Points on a line bisecting the larger angle formed between offset
intersecting axes A and B in the plane defined by axes A and B will
be referred to as being at the "top", while points on
the extension of that line bisecting the acute angle between axes
A and B will be referred to as being at the "bottom".
To ease explanation, two axis systems are defined, one for a first
rotor and a second axis system for a second rotor where the angle
between the axis is defined as .alpha. (see FIG. 11). The axis 10a
is referred to as the longitudinal or axial axis and is defined
as the center of rotation of shaft for the rotor 122. Likewise,
the axis 10b is referred to as the longitudinal or axial axis and
is defined as the center of rotation for shaft of the rotor 124.
The axis indicated at 12a is referred to as the radially lateral
axis for the first rotor and axis 12b is referred to as the radially
lateral axis for the second rotor. Further, the arrow 14a is the
radially transverse axis pointing in a forward direction and the
arrow 14b is a radially transverse axis indicating a forward direction.
The origin of the axis systems is most commonly (and by default)
at the common center of the rotors.
The foundational description of the formation of the rotors is
discussed below with reference to FIGS. 1-8 followed by a description
of the balanced rotor design. Then there is a discussion of the
first embodiment of a flow meter. Finally there is a discussion
regarding a second embodiment of the flow meter.
In general the flow meter 120 as shown in FIG. 1 comprises a casing
123 a rotor assembly 125 and a counter 127.
The construction of the rotor assembly 125 is described referring
to FIGS. 1-8. As shown in FIGS. 1A, 1B and 1C, where a rotor 26
is shown, for example, in an initial stage of construction. The
slave rotor 28 of FIG. 9 is constructed in a similar manner. The
master rotor 26 begins as a sphere with a shaft 30 lying along an
axis A. Axis B is shown at an angle .alpha. to the axis A.
Referring to FIGS. 2A, 2B and 2C, material is removed from the
master rotor 26 to leave a conical funnel section 25 whose apex
is at the center E of the spherical master rotor 26 and whose apical
angle is 180.degree.-.alpha.. The axis of the funnel section 25
lies along the axis 10a.
Referring to FIGS. 3A, 3B and 3C, a conceptual cone 27 is overlaid
on the master rotor 26. This conceptual cone 27 may be thought of
as part of the slave rotor 28 plus a desired gap clearance, as if
the conceptual cone 27 were lying on the equivalent part of the
slave rotor 28 when the slave rotor 28 has its center located at
the center of the master rotor 26 (both at center E of the spherical
housing). As shown in FIG. 9 the conceptual cone 27 is the tip
93 of one of the lobes 84 of the slave rotor 28 minus the desired
fluid film gap radial distance. In one form, the cone 27 has its
apex at the center of the sphere of the master rotor 26 and its
central axis C lies along the surface of the conical face of the
master rotor 20 such that the central axis C is a radius extending
outward from the center of the cavity at an angle .alpha./2 from
a normal to the axis of the other rotor. In effect, the central
axis C of the cone bisects the larger of the two angles formed by
the axis A and the axis B in the plane in which both axes 10a and
10b lie. As shown in FIG. 4D, the cone 27 has an apical angle .psi..
The value of .psi. depends partially on the strength of the material
of which the master rotor 26 and slave rotor 28 are made. The greater
the angle .psi., the lower the stresses on the tips of the vanes
35 and 37 that comprise the lobes 32 and 82 and the lower the pressure
exerted by the lobes 32 and 82 on the engagement 36 38 88 and
90 (see FIG. 9). Large values of .alpha. near 45.degree. requires
smaller values of .psi. to avoid the vanes extending past the axis
of rotation and to avoid removal of too much material, the material
being needed to support the vanes. Smaller values of .alpha. may
have larger values of .psi. for like reason where .alpha. is between
0+.degree. and 45.degree..
Referring back to FIG. 4D, the apical angle .psi. of the conceptual
cutting cone 27 is equal to the apical angle .psi.1 of the adjacent
engagement tip of the opposing rotor that engages the face to be
cut by the cone 44 plus the required apical angle .psi.2 to create
a desirable fluid film gap. The additional angle to create a fluid
film gap can actually be a negative value whereby the cutting cone
has a smaller apical angle than the adjacent engagement tip to create
an interference fit. This is desirable when the rotors are made
from materials that have a lower modulus elasticity and an interference
seal is desired where the lobes of opposing rotors are forcefully
engaging one another.
As shown in FIG. 9 the tip 91 of the opposing rotor that engages
the contour face 36 is referred to as the adjacent engagement tip
with respects to the face. An adjacent tip with a corresponding
contour face are collectively referred to as a "tip-face combination".
As shown in FIG. 16 two adjacent opposing rotor contour faces such
as the first surfaces 36a and 88a for the first and second rotors
26 and 28 are collectively referred to as "adjacent contour
faces of opposite rotors". Further, the rearward and forward
surfaces such as surface 51 a of the second rotor 28 and the forward
surface 42a are collectively referred to as a "slave rearward
surface--power forward surface combination". In a similar manner,
the combination of opposing rotor surfaces for the slave forward
surfaces and the power rearward surfaces such as 76a and 92a are
collectively referred to as a "slave forward surface--power
rearward surface combination".
The value of .psi.2 can change with respects to .rho. (the distance
from the common center of the rotors) to create a variable fluid
film gap with respects to .rho.. For example, the angle .psi.2 can
increase with respect to .rho. to create a consistent fluid film
gap from the radial outward portion of the contact face to the radially
inward portion of the contact face. Likewise, the value of .psi.1
can change with respects to .rho. because the points of engagement
between points on a tip face combination of the opposing rotors
is a constant distance from the common center of the rotors. In
other words, as shown in FIGS. 3C and 4A, the circular region 29
of the cone 27 is at a distance from the common center of the rotors.
The center of the circular region 29 defines a teardrop shaped engagement
line 19 that is a constant distance from the common centerpoint
E. Therefore, at any given distance .rho..sub.i from the centerpoint,
the cutting cone can have a variable radius from the central axis
C of the cone. Thus, the cone can have a variety of shapes such
as a straight cylinder or even an inverted cone.
Referring to FIGS. 4A, 4B and 4C, to create a contour face (or
surface) 38 the conceptual cone 27 is rotated with the master rotor
26 as if the cone were on the slave rotor 28 lying on axis B with
its center at the center of the master rotor 26. The path of the
cone 27 is shown in FIG. 4A where the travel of the center axis
C is defined as the base reference line or teardrop surface 19.
The locus L of the center of the cone at the surface of the rotor
26 in the frame of reference of the master rotor 26 is shown in
FIGS. 5A and 5B. FIG. 5A shows a top view. FIG. 5B shows a view
along the axis A where it will be seen that the locus L is a tear
drop shape. The actual shape 38a removed by the cone 27 is defined
approximately by adding a band .psi./2 wide around the tear drop
shape shown in FIG. 4A. The tear drop is on the surface of a sphere
so that angular distances are readily calculated. A mathematical
description of the locus L is as follows.
If .rho. is the radius of the sphere defining the master rotor
20 and .theta. is the rotational angle from the top, and a is the
angle between the axes 10a and 10b then the trace of a point (x,y,z)
on the axis 10b in the frame of reference of the master rotor 20
for the base reference tear drop 17 has been found to be: ##EQU1##
Rotation of the rotors about 180.degree.-220.degree. around the
axes A and B, with consequential movement of the cone 27 within
the master rotor 26 is required to create the entire engagement
face 36. Rotation less than 180.degree. by a small amount may be
acceptable in some cases, although not preferred. Such a design
may allow some fluid flow between the lobes at the bottom point
of the rotation. This may avoid vibration due to rapid pressure
changes in the chamber between the two contact faces at the bottom
of the rotation. At this position, the contact faces lie adjacent
to one another. If one contact face is constructed by rotation less
than 180.degree., then the corresponding contact face on the other
rotor could be constructed by rotation greater than 180.degree..
The cone could be rotated 360.degree. during construction but as
the surface so created prevents use of interlocking vanes, requiring
subsequent removal of material from the master rotor 26 there is
no need to do so. The contact faces 36 38 88 and 90 of each rotor
26 28 are defined in this manner. There may be any number of contact
faces on each rotor on any number of lobes that can be fit upon.
Effectively, this manner of construction means that each contact
face of one rotor 26 28 is defined by the locus formed as the rotors
26 28 rotate about their respective axes A, B by points on the
other rotor lying along an outer edge of the cone.
Since the contour faces 36 38 88 and 90 (see FIG. 9) of each
rotor are defined by the movement of points on the other rotor as
the two rotors rotate with each other, it can be guaranteed that
there will be points of contact between the two rotors along a radially
extending line R lying along a contact face through at least 180.degree.
of motion (see FIGS. 7A-7C). The lines R shading the contact face
36 38 88 and 90 in FIGS. 4A, 4B, 4C, 6A, 6B, 6C, 7A, 7B and 7C
illustrate the radial lines which define the instantaneous points
of contact as the rotors rotate relative to each other. As the line
defining the points of contact between the rotors reaches its furthest
penetration into the rotor, continuation of contact on that contact
face will mean that the contact face will wrap back on itself as
shown in FIG. 5A. This would allow no part of the slave rotor 28
to penetrate the tear drop shape, unless the opposed faces of the
tear drop cavity swept out by the conceptual cone maintained a sufficient
separation to allow penetration by a vane of the slave rotor. Therefore,
in the case where the vanes are to be symmetrical, it is necessary
for the point of contact between the rotors to switch to a corresponding
contact face on the other rotor. It so happens that when each rotor
is a mirror image of the other, and contact faces are defined as
illustrated in FIGS. 4A, 4B and 4C, then the line of contact switches
from the contact face 36 of one rotor to a contact face of the other
rotor. This switch occurs at the bottom of the housing and at the
top of the housing, namely when the contact faces straddle the line
bisecting the acute angle between the axes A and B. As described
further herein the base region of the slave rotor 28 will not engage
the tip 46 of the master rotor to provide access to a secondary
chamber at bottom dead center (BDC). By construction of all contact
faces 36 38 88 and 90 in the manner described, engagement between
vanes the engagement tips and the contour faces of opposed rotors
may be guaranteed for at least one set of tip-face combinations.
Use of a cone for shaping one rotor, thereby removing material,
however, will leave a gap between the rotors unless material is
added to the other rotor.
FIGS. 6A, 6B and 6C, show how gaps between the rotors at the vane
contacts are avoided. A cone of material 44 corresponding exactly
to the portion of the conceptual cone 27 having an apical radius
of .psi.1 (psi1) as shown in FIG. 4D is added to the rotor. It should
be noted that the values of .psi.1 and .psi.2 can be functions with
respect to .rho. (the radial distance from center E) and .alpha.
(the amount of rotation about the axes 10a and 10b)to produce a
variable tip radius from the center axis of the cone and a variable
gap clearance with respects to row and the amount of rotation of
the rotors. In these figures, the cone of material 27 is shown on
the master rotor 26. Rotation of this cone of material in addition
to the value of .psi.2 to define the gap clearance on the master
rotor 26 while the slave rotor 28 rotates with the master rotor
will create a contour face 90 (FIG. 9) on the slave rotor 28 in
the same manner as the contour face 36 was created on the master
rotor 26. The contour faces 88 and 90 will have the same tear drop
shape as shown in FIGS. 5A and 5B. In order for the correct tear
drop shape to be made, the starting point for the removal of material
from the rotor must be when the axis D of the cone of material 27
lies at the top, namely along the line bisecting the obtuse angle
between the axes A and B. Thus, as shown in FIG. 6A, the cone 27
must be rotated by half of its apical angle before it can be used
to remove material from the slave rotor 28. The .psi.1 inner apical
angle of the cone 27 defines the tip 44 of a vane that is part of
the lobe 32 on the master rotor 26. The extra amount of material
on the tip 28 created by the cone of material 48 compensates for
the loss of material during construction of the master rotors contoured
faces by using the conceptual cone 44. It will be noted that the
cones 27 and 44 need not be exactly conical, nor must the apex of
the cone be exactly at the center of the cavity, but contact portions
between the vanes comprising lobes 32 of the master rotor 26 and
contact faces 88 and 90 on the slave rotor 28 should have a smooth
surface. The closer the apex to the center of the cavity, the smaller
the clearance gap between the contact tips and engagement faces
during the operation of the rotors. The term essentially as used
in the claims is intended to cover an engine whose cone 27 is not
exactly defined in the manner stated, but that embodies the concept
of the invention.
As shown in FIG. 6C a second conceptual cone 27a is used to define
a second contact surface 36 in a similar manner as above, the center
axis D' of the cone 29 travels along the teardrop shape path 31.
Consistent with the foregoing, the teardrop surface 31 is formed
by positioning the forward portion 33 of the teardrop at the top
dead center location and simultaneously rotating the power rotor
26 about the A axis and the reference axis D about the B axis while
having the reference axis D maintain a constant angle of .alpha./2
from the B axis. The major difference between the teardrop surface
31 and the teardrop surface 17 as shown in FIG. 4A is the direction
of rotation of both the A and B axes. In a similar fashion as described
above, the portion of the cone 31 having the inner apical radius
.psi.1 is positioned in a manner as shown in FIG. 7A. It should
be noted that to create the base teardrop line 31 the rotors are
rotated in the opposite direction a value of about 180-220 as to
the direction to create the base teardrop line 17 of FIG. 4A. The
second engagement surface 36 is a part of a second vane 37where
the first and second vanes 35 and 37 comprise a lobe 32. In the
preferred form, the material between the engagement surfaces 34
and 34 remains interposed therein between for strength and rigidity
of the lobe 32.
A third engagement face 38b is created as shown in FIG. 7B. This
engagement face is similar to that as shown in FIG. 6A except for
the rotational location of the engagement face 38b. To put the construction
of the rotor configuration in perspective, reference is made to
FIG. 11 showing a completed rotor set 24 where the base teardrop
surface 17' is shown in and the center of the cone C' runs along
the base teardrop surface 17' during rotation of the rotors.
The next step is removal of the material interposed between the
second and third engagement faces 36a and 38b in a manner as shown
in FIG. 7C. This void allows for the lobe 82a of the slave rotor
to be positioned therein during operation of the engine 20 (see
FIG. 9). The final step after the lobes are created is to manipulate
the rearward surfaces 76 and the forward surfaces 42 to create desirable
compression ratios and ensure that the forward and base surfaces
of the opposing rotors do not crash into one another at BDC.
A variety of mathematical, CAD, and CNC programs can be employed
to construct the aforementioned surfaces. A desirable method of
making the base curve surface and the ideal curve surface can be
executed to a computer-aided design program with reference to FIGS.
8A-8E. As shown in FIG. 8A, two axis are constructed and are offset
from being collinear at angle .alpha. (alpha). A base reference
line (bifurcating line) 39 is constructed which bisects the A 10a
axis and B 10b axis. To construct the base teardrop curve for the
A axis rotor, the base axis is arrayed about the A axis 10a a desirable
number of increments as shown in FIG. 8B. Thereafter, the user coordinate
system is set with reference to the A axis 10a and each arrayed
line is rotated about the A axis 10a an equal amount of degrees
as it was rotated about the B axis 10b. For example, the reference
axis 39' is rotated approximately 160 degrees about the B axis.
Therefore, the reference axis 39' is rotated 160 degrees back around
the A axis to the position as shown in FIG. 8C. Thereafter, computer-aided
drawing tools such as spline, scaling, and offset can be employed
to create the base reference curve as shown in FIG. 8D. In particular,
the end points of the axis as shown in FIG. 8C can be selected using
a spline tool whereby making a continuous line along these points.
Thereafter, this spline can be scaled towards the origin (the common
center of the rotors) and a base surface is created using the original
base reference line and the scaled reference line as shown in FIG.
8E. This surface can be offset using a computer-aided drawing offset
tool where the amount of offset is similar to that as the apical
radius y of the conceptual cone 27 discussed above. Finally, a contact
tip can be attached to the forward portion of the offset line 41
where the radius of the cone tip is equal to .psi.1 the amount
of offset between the base surface and the ideal surface minus the
amount of fluid gap clearance that is desired (see FIG. 8F).
The ideal surface can be exported to a solid modeling program for
constructing the forward and base surfaces and arraying and mirroring
the ideal surface 41 to construct the desired number of lobes for
the rotor.
With the foregoing in mind, there will now be a detailed discussion
of the various aspects and components of the rotors with reference
to FIGS. 9-16 with particular attention being directed towards removal
of material at the base region of the slave rotor to allow a rotationally
balanced design.
As seen in FIG. 9 the rotor assembly 24 comprises a master rotor
26 and a slave rotor 28. The master rotor comprises a shaft 30 and
a plurality of lobes .32a, b, and c (all of which are generally
referred to herein as numeral 32). For ease of discussion, the lobe
32a will be described in detail with the understanding the specification
applies to all of the lobes on the power rotor. Likewise, additional
lobes could be employed without departing from the basic geometry
that create sealed chambers and balanced radial forces (further
discussed herein).
The lobes 32 have a radial outer surface 34 a first surface and
second surface 36 and 38 (described above), a spherical inner surface
40 and a forward surface 42. The lobes 32 further have tips 44
and these tips each have a contact surface 48 and 50. The surfaces
36 38 48 and 50 are described further herein.
The forward portion of surface 34 defines at least part of a sphere
and is adapted to engage the inner surface of the housing 22 (see
FIG. 1). The spherical inner surface 40 also defines a portion of
a sphere and is intimately engaged in a center bearing 23 or is
a unitary piece with a center bearing 23 as shown in a second embodiment
below. In the broader scope the surfaces can converge to the centerpoint
of the rotors whereby removing the need of the center bearing 23.
The surfaces 36 and 38 (as well as the forward portions of surfaces
88 and 90) are described above and thoroughly in U.S. Pat. Nos.
6036463 and 5755196 which are hereby fully incorporated by reference.
The surfaces 36 and 38 comprise a concave and convex continuous
surface with a precisely placed inflection point. As seen in FIG.
12 at the base portion of the lobe 32 the first surface 36 extends
rearwardly to a first concave portion 52 then to a rearward portion
54 and the continuous surface continues forwardly to surface 56.
The aforementioned concave surfaces 52 54 and 56 are defined as
the contour base surface 58.
Best seen in FIG. 12 the base surface 58 extends forwardly to
an inflection point 60. At the inflection point 60 the first surface
36 transforms from a concave to a convex surface. Therefore surface
62 is a convex surface that is also adapted to receive the tip 91
of the slave lobe 82.
Consistent with the foregoing, FIG. 13 shows the second surface
38 extending rearwardly to a first concave portion 64 then to a
rearward portion 66 and the continuous surface continues forwardly
to surface 68. The aforementioned concave surfaces 64 66 and 68
are defined as the contour base surface 70. Best seen in FIG. 13
the contour base surface 70 extends forwardly to an inflection point
72. At the inflection point 72 the first surface 38 transforms
from a concave to a convex surface. Therefore surface 74 is a convex
surface that is also adapted to receive the tip 93 of the slave
lobe 82. A more thorough discussion of the relationships between
the surfaces of the master rotor and the slave rotor will follow
after a thorough description of the slave rotor.
Now referring back to FIG. 9 the rearward surface 76 is positioned
between contour base surfaces 58a and 70b of lobes 32a and 32b.
The rearward surface 76 does not come in contact with the slave
rotor 28 but cooperates with the inner surface of the housing 22
(see FIG. 1), the outer surface of the bearing 23 and the forward
surface 92 of the slave rotor 28 to define an operating chamber
105 that is further discussed herein.
There will now be a detailed discussion of the slave rotor 28 where
reference is made to FIG. 9. The slave rotor 28 comprises a shaft
80 and a plurality of lobes 82. As with the description of the power
rotor 26 only lobe 82a (otherwise referred to as slave lobe or
second lobe) will be described in detail with the understanding
this specification applies to all of the lobes 82 (where 82 collectively
refers to 82a, 82b and 82c). Further, the invention is not limited
to the number of lobes as shown in the preferred embodiment, but
the power and slave rotors 26 and 28 will have an equal number of
lobes.
As seen in FIG. 9 the slave lobes 82 comprise a spherical outer
surface 84 a spherical inner surface 86 (see FIG. 11), a first
surface 88 a second surface 90 and finally a forward surface 92.
Further, the lobes 82 has a first tip 91 and a second tip 93. The
tip 91 has a contact surface 95 and tip 93 has a contact surface
97. The contact surfaces 95 and 97 are adapted to engage surface
88 of the power rotor 26.
In a first embodiment, lobes 82 are symmetrical about the radially
extending plane 94 (see FIG. 9) and hence the first surface 88 will
be described in detail with the understanding the geometry and other
relevant features relates to the second surface 90 has a substantially
mirrored image about plane 94. It should be noted that certain symmetrical
variations could be employed in the lobes 82 about plane 94.
The first surface 88 is shown in FIG. 14 where the rotor assembly
22 is in a bottom dead center position. The first surface 88 comprises
a concave portion 96 and a convex portion 98. The inflection point
line 100 is the location where the surface 88 transforms from a
concave to a convex configuration. As seen in FIG. 15 the concave
surface 96 has a forward portion 99 and a rearward base portion
101. The concave surface 96 further has a loss of fluid film seal
line 102. The loss of engagement line 102 defines the point where
the engagement surface 50 of the vane 46 radially repositions from
the surface 88 and separates (or partially separates) the tip 46
of the power rotor 26 from the rearward base portion 101. It should
be noted that the contact surface 50 and first surface 88 are not
necessarily in direct contact in operation, but rather there is
a thin fluid film thereinbetween. Throughout this text the term
engagement when directed to a contact tip and a contour face is
defined as a fluid film layer between two adjacent surfaces that
provides a fluid film seal and a fluid film layer where there is
not a pressure difference between the engaged surfaces. Further,
engagement covers an embodiment where there is an interference fit
between opposing rotors where it is desired to have the rotors forcefully
engage one another to create a contact type seal. However, as a
contact surface 50 rotates to the bottom dead center position as
seen in FIG. 14 the annular gap 104 is produced. As shown in FIG.
15 the dashed line 106 defines a curved plane that is defined by
contact surface 50 as the power rotor rotates about its axis 10a
(see FIG. 11).
The perpendicular distance between curved plane 106 and rearward
base surface 101 defines the annular gap 104. The distance of this
gap changes with respect to the radial position .theta.. Hence,
as shown in FIG. 16 the open area 110 is defined as the open area
defined between surface 50 of the power rotor 26 surface 101 of
the slave rotor 28 the housing 22 and the-bearing 23. FIG. 16 shows
the open area 110 has a hatched open area where the dashed line
111 indicates the perpendicular distance between contact surface
50 of vane 46 and rearward surface 101. It should be noted that
rearward surface 101 has a greater radius of curvature then contact
surface 50 and hence the narrowest passage between semi-chamber
113 and secondary-chamber or otherwise referred to as semi-chamber
109 (defined further herein) is open area 110. The cross-sectional
area gap of open area 110 could have certain ratios with respect
to the viscosity of the fluid medium that is passed therethrough.
For example, if the engine 20 is designed to pump high viscosity
fluids, open area 110 can be larger to allow the pressure transfer
to happen quickly between semi-chambers 109 and 113. Consistent
with the foregoing communication between semi chambers 113 and 121
have a similar communication means between vane 44 and the base
surface 50 of the slave rotor 28.
The ratio of the distance 101 and the ratio of the contact film
distance between the vane 91 and the base surface 52 54 and 56
can be in the order of 20 to 1 in a preferred form for many fluids.
This ratio is further relevant to the net cross-sectional open area
110 and the net cross-sectional area of the fluid film at location
108. A secondary range for the net cross-sectional areas can be
between 30-1 and 10-1 and the ranges therein between and at certain
ratios with certain fluids. In some cases much lower ratios can
achieve the fluid pressure balancing between semi chambers. For
this patent application, communication is defined as sufficient
open area allowing a desirable pressure equalization between two
rotationally adjacent semi chambers.
It should be noted that a very minimal amount of flow between the
cross-sectional open area 110 is necessary to create a pressure
balancing effect in some conditions. For example, at high speed
and low-pressure, a very low ratio can create desirable balancing
results.
The rotor assembly 24 comprises several chambers and semi-chambers.
A chamber is defined as a substantially sealed and closed area where
leakage of fluid from or to the chamber only occurs due to a passage
through a thin fluid film layer between two surfaces. A secondary-chamber
or semi chamber is defined as a cavity where two adjacent semi-chambers
comprise a chamber; however, the open area 104 allows fluid passage
thereinbetween.
As seen in FIG. 9 the forward surface 92 of lobe 82 and rearward
surface 76 of the power rotor 26 along with the surface of the bearing
and additionally the inner surface of the housing 22 (shown in FIG.
1) create a sealed chamber 105. Now referring to FIG. 16 the first
surface 88 of lobe 82a and the first surface 36 of lobe 32 along
with the outer surface of bearing 23 and inner surface of the housing
define the first semi-chamber 109. The forward surface 42 of lobe
32 and rearward surface 51 in combination with the surface of bearing
23 and the inner surface of housing define the second semi chamber
113. Semi chamber 121 is similar to 109 except on the opposing side
of the open area between two adjacent lobes of a rotor.
Given the foregoing, a balanced slave rotor is advantageous for
greater pressure differentials across the inlet and outlet ports.
However, a preferred embodiment described below employs two identical
rotors such as that shown in FIGS. 17-19. An advantage of using
two identical rotors to comprise a rotor assembly is the simplicity
and lower cost of manufacturing and reduction of inventory. As shown
in FIG. 19 the rotor assembly 125 comprises a first rotor 122 and
a second rotor 124. To eliminate redundant explanation, the first
rotor 122 will be described in detail with the understanding the
description is relevant to the identical rotor 124. As shown in
FIG. 20 the first rotor 122 comprises a plurality of lobes 126
each lobe comprises contoured surfaces 128 and engagement tips 130
that are similar to that as described above with reference to FIGS.
1-8. Each lobe further has an outer spherical surface 132 that defines
at least part of a sphere. FIG. 21 shows a cross-sectional view
of the first rotor 122 and as shown in this figure the surface 140
defines a central cavity 142 that is adapted to house a support
shaft. Because the flow meter has a relatively low pressure differential
from the input to output ports, the shaft for the rotor can have
a smaller diameter because there is less of a load placed thereon.
Further, a smaller shaft is advantageous because it creates lower
rotational friction. For the flow meter application low friction
bearings are advantageous because they create less head loss (for
low load applications such as the flow meter).
FIG. 23 shows a cross-sectional view of the casing. In a preferred
form, the casing (or otherwise referred to as the housing) 123 comprises
two sections 149 and 150 that are identical. In general, the casing
123 comprises an input port 151 and an exit port 151. A central
cavity 153 is positioned between the ports 152 and 151 and is adapted
to house the rotor assembly 125. The operating fluid which the volume
is measured passes through the input port 151 through the chambers
of the rotor assembly is housed in the cavity 153. Therefore, casing
150 will be described in detail and the description is relevant
to the casing section 149.
The casing section 150 has a port 152 that is adapted to allow
fluid to pass therethrough. A cavity region 154 is adapted to house
a shaft 142 of the rotor assembly 125 (see FIG. 18). As shown in
FIG. 24 there is a cross-sectional view of the casing with a rotor
assembly 125 housing therein. In this figure, the central ball is
removed and the radially inward portion of the lobes 126 are visible.
The rearward surface 139 of the rotors 122 and 124 are intimately
engaged to the base surface 156 of the casing sections 150 and 151.
Likewise, the radially outward surfaces of the lobes 132 are intimately
engaged to the radial surface 158 of the casing sections 149 and
150. It should be noted that the portion of the rotors that overlap
with the adjacent rotor must have a spherical outer surface 132.
However, the portion of the rotor (and surface of the casing engaging
the rotor) that is rearward from the intersecting portion of the
lobes of adjacent rotors need not be spherical but should be cylindrically
symmetrical.
FIG. 24 further illustrates the orientation of the rotor assembly
with respects to the housing 123. In a preferred form, the central
axis 143 and 145 of the first and second rotors that are offset
from one another an angle alpha are symmetrically placed within
the housing 123 so the central axis 143 and 145 art each an angle
.alpha./2 with respects to the central axis of the casing. In other
words, the axis 143 and 145 are offset an angle .alpha./2 from the
normal to the plans substantially defining the forward surface 159
of the casing sections. This is advantageous because each casing
section can be symmetrical and hence manufactured from the same
process or procedure.
As shown in FIG. 1 the first embodiment would further comprise
a pulse counter 127 that can be positioned on either shaft 142 or
directly take a reading from either rotor 122 to or 124. For example,
a magnetic conductance typing counter to take a reading of the magnetic
flux shift of the rotors 122 and 124 as they rotate to a position
similar to that as shown in FIG. 19. This is advantageous because
the pulse counter can be attached to the exterior of the casing
if the casing is made of the material that allows the magnetic flux
to pass therethrough. The pulse counter can be a velocimeter that
determines the rotations per unit of time.
As shown in FIG. 25 the graph illustrates the volumetric throughput
rate at given rotational velocities .omega.. The line 160 is the
theoretical volumetric with respects to the rotational velocity
.omega.. However, a certain amount of fluid leaks around the outer
surface 132 and the casing at top dead center and bottom dead center,
between the engagement tips and the contour surfaces. In general,
the fluid that is not accounted for as passing through the operating
chambers but passes through the flow meter device is referred to
as "blow-by". The amount of blow-by is a function of the
gap tolerances between the moving parts of the flow meter, the viscosity
the fluid and the differential pressure between the inlet and outlet
ports. The amount of blow-by can be estimated and simply added to
the calculated value of volume throughput based upon the rotations
of the rotors.
As shown in FIG. 25 for a given rotational velocity the theoretical
throughput of fluid is represented by line 160. However, with a
slight pressure differential from the inlet and outlet ports, a
certain amount of blow-by will occur in the actual fluid throughput
would be a little bit higher such as represented by line 162. Therefore,
for a given .omega. such as .omega.1 the actual fluid throughput
V1.sub.a minus the computed input only given the rotational velocity,
V1.sub.t, is the amount of blow-by which is referred to as .DELTA.V.sub.1.
For a different operating fluid with lower viscosity the amount
of blow-by would be greater. For example, line 164 would represent
the actual fluid flow for a lower viscosity fluid.
Therefore, it can be appreciated that the value of the viscosity
of the operating fluid would be a desirable property to know to
estimate the value of the blow-by. In general, if the viscosity
of the operating fluid is greater than the pressure differential
between the inlet and outlet ports is greater for a given rotational
velocity (value of .omega.). Therefore, given a pressure differential
and a rotational velocity, the viscosity of the fluid can be calculated.
Referring to FIG. 26 the three-dimensional surface 170 represents
the value of the viscosity of the operating fluid with respects
to the rotational velocity of the rotors (.omega.) and the pressure
differential from the input to the output ports (.DELTA.P.sub.1).
For example, if the rotational velocity is relatively high, .omega..sub.2
and the pressure differential between the inlet and outlet ports
is relatively low, .DELTA.P.sub.1 then the viscosity value .mu..sub.21
is a lower value. On the other extreme, if the rotational velocity
is relatively low, a .omega..sub.1 and the pressure differential
is relatively high, .DELTA.P.sub.2 then the viscosity of the operating
fluid must be high (.mu..sub.12).
At a lower rotational velocity .omega..sub.1 with a lower resulting
pressure differential .DELTA.P.sub.1 in intermediate value of viscosity
can be calculating indicated at .mu..sub.11 and further at a higher
rotational velocity .omega..sub.2 with a higher pressure in intermediate
value of viscosity .mu..sub.22 is calculated.
Therefore it can be appreciated that the surface 170 would preferably
be determined by an empirical analysis where certain known viscosity
is a fluid pass through a flow meter at several different rotational
velocities and the pressure differentials will be measured and recorded.
Thereafter, an equation or other function would represent the surface
170 given values of .omega.and .DELTA.P. The surface could look
similar to that as shown by the dashed peripheral lines 172. The
important factor is that the viscosity is calculated is determined
by .DELTA.P and .omega..
Once the viscosity for the fluid has been determined given the
pressure differential and the viscosity, the blow-by can be calculated
based upon a theoretical or empirical analysis based equation using
the viscosity and the pressure differential variables.
FIG. 27 is a schematic view illustrating the underlying principles
of the second embodiment of the present invention. In general, the
second embodiment 180 comprises a rotor casing assembly 182 and
a processing portion 184. The rotor casing 182 showing the schematic
rotors in FIG. 27 comprises an input port 186 and an out port 188.
Three sensors are employed, two pressure sensors and a rotational
sensor. The first and second pressure sensors are schematically
indicated at 190 and 192 and are adapted to read the static pressure
of the input and output lines 200 and 202. The rotational sensor
schematically indicated at 194 and the first and second pressure
sensors 190 and 192 feed inputs processing portion 184. Processor
184 decodes the signals into numeric values to calculate the flow
rate. As described above, the equation for precisely calculating
the flow rate would take into consideration the rate of rotation
of the rotors to determine the volumetric throughput to the chambers
to obtain a first value. Then the pressure differential between
the first and second sensors 198 and 192 and the rotational velocity
indicated by sensor 194 are used to determine the viscosity of the
fluid. The viscosity of the fluid and the pressure differential
are used to calculate a second value, the amount of blow-by. The
first and second values total the net volume throughput.
The processor 184 would preferably have a display portion 196 to
indicate the flow rate or total flow. Of course FIG. 27 is a schematic
figure illustrating the general principles and the rotor assembly
where a production model would preferably have the sensors and display
unit integrated with the casing.
FIG. 28 shows the second embodiment of the present invention where
a first pressure sensor 186 and a second pressure sensor 188 are
embedded in the casing with the inlet and the outlet ports respectively.
The rotational counter 194 tracks a number of rotations of the shaft
142. The output from the pressure sensor is 186 and 188 can extend
through passageways 200 and 202 that can be openings or electrical
conduits to pass a current. Alternatively, the pressure can be measured
at ports 190' and 192'. The above described calculation of determining
the blow-by can be executed on a computer chip or through mechanical
means where mechanical type sensors would indicate the pressure
and rotational speed and a linkage system would indicate the amount
of blow-by.
The embodiment as shown in FIG. 28 further employs a balanced rotor
assembly where the rotor 122' is designed in a manner as described
in FIGS. 9-16. As shown in FIG. 28 the tips of the lobe of the rotor
124' at bottom dead center to not come in contact with the base
portion in between the lobes of the rotor 122'. Therefore, the rotor
122 is rotationally balanced and floats about its axis of rotation.
FIG. 28 shows a further modification showing a shunt assembly.
The shunt assembly 210 comprises a first passageway 211 that is
a communication between the inlet port 152 and the exit port 151.
A flow restriction portion 212 adjusts the fluid resistance between
the inlet and outlet port. In a preferred form, a needle valve or
proportional valve 114 can be employed. In one form, it would be
preferable to only have this valve only accessible at the manufacturing
site of the flow meter of the present invention so the end user
would not tamper with the setting of the fluid restrictor 214. To
calibrate the shunt system, the rotors are rotated at a specific
speed (caused to spin at a predetermined speed). A set fluid at.a
set temperature at a set pressure is then directed through the flow
meter. The exact volumetric throughput of the fluid is known and
the shunt system is adjusted so the output reading of the flow meter
corresponds to the exact volumetric throughput.
A micro flow parameter can be in the controller where as shown
in FIG. 25 at zero rotational velocity with a pressure differential
there will be a small amount of seepage (blow-by). In this case,
the pressure differential is so slight that it is not sufficient
to rotate the rotors. Although the low friction rotors rotate at
very low pressure differentials, in some applications rotational
resistance such as higher friction bearings may cause more resistance
to rotation. In this case, the micro flow can be accounted for in
the controller where a condition is set that if the rotational velocity
is zero and the pressure differential is positive (i.e. higher on
the outlet port than the inlet port) than the microcontroller will
employ a second equation that would account for the seepage past
the rotors and the casing for the given pressure differential. In
a preferred form, the last recorded viscosity of the fluid would
be used to calculate the seepage flow.
A temperature parameter can also be added by using one or two temperature
transducers and using this information to account for dimensional
changes of the casing and rotors. Temperature also affects the viscosity
of fluids, but the viscosity change of the fluid due to temperature
(or any other variable) will already be accounted for by the viscometer
computation which does not require a temperature input.
The effect of temperature would seem to be minor compared to the
effects of viscosity, flow rate and system pressure due to the fact
that all parts should expand at a similar rate. Accounting for temperature
would require one or two thermocouples and an alteration to the
control equation. Temperature could also be compensated for by matching
(or intentionally mismatching) the rotors and casing so the gap
clearance does not change significantly as the parts expand or contract
due to changes in temperature of the fluid or the environment. It
should be noted that larger gap clearances will make the flow meter
more tolerant to temperature variations. It should further be noted
that many of the various corner portions throughout the various
embodiments have tapered corners to allow more desirable fluid flow
therearound.
The cost of manufacturing is reduced to have looser clearances
and tolerances. The consistencies from flow meter to flow meter
will be greater because any inconsistency between the manufactured
part will have a lower percentage effect upon the total gap clearance.
For example, if the tolerances were plus or minus one thousandths
of an inch, a ten thousandths of an inch gap will have less of a
percentage gap variance than a three thousandths of an inch gap.
The flow meter can be employed where the rotors are used in other
engine embodiments (a device that transfers energy such as a motor
or a compressor for example).
While the invention is susceptible of various modifications and
alternative forms, specific embodiments thereof have been shown
by way of example in the drawings and will herein be described in
detail. It should be understood, however, that it is not intended
to limit the invention to the particular forms disclosed, but, on
the contrary, the intention is to cover all modifications, equivalents
and alternatives falling within the spirit and scope of the invention
as expressed in the appended claims.
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