A turbine flow meter is disclosed of the type including a turbine
rotor disposed in a fluid flow passage, the turbine receiving the
fluid flow to be measured and mounted so as to restrain rotary movement
in reaction to the change of momentum imposed on the fluid by the
turbine rotor blades. A reactive force sensing arrangement measures
the force acting on the turbine rotor blades and generates signals,
related to the rate of fluid flow. These signals are combined with
downstream pressure and temperature signals to provide a mass rate
of flow output signal. The turbine rotor is disposed downstream
from a shielding stator positioned such that upon increasing fluid
flow and resultant advancing rotary position of the turbine rotor,
a lesser proportion of the total fluid flow in the passage is intercepted
by the turbine rotor. The net result is a linearizing of the relationship
between the fluid flow and the reactive force acting on the turbine
rotor. A coil spring acts to resist the rotary movement of the turbine
rotor while silicone sleeve bearings are employed to damp the rotary
motion of the turbine rotor.
The embodiments of the invention in which an exclusive property
or privilege is claimed are defined as follows:
1. A stalled turbine flow meter comprising:
a housing having an internal bore defining a fluid flow passage;
a turbine rotor;
means mounting said turbine rotor within said housing, said turbine
rotor including at least one turbine blade configured to receive
a portion of fluid flowing through said passage and to impose an
angular momentum change on fluid flowing through said passage and
over said at least one turbine blade developing a reaction force
bias means allowing predetermined angular displacement of said
turbine rotor in response to development of said reaction force
for biasing said turbine rotor against said angular displacement
in response to development of said reaction force;
means varying the proportion of fluid flow directed over said at
least one turbine blade with changing rates of fluid flow in said
flow passage, including at least one shielding stator blade fixedly
mounted within said fluid flow passage and disposed angularly offset
from said at least one turbine rotor blade positioned such that
said turbine rotor blade is advanced into alignment with said stator
blade with increasing fluid flow and causing a lesser rate of increase
in said reaction force resulting from increases in fluid flow; and
means producing an output signal corresponding to said reaction
force on said turbine rotor and said signal varying in a linear
relationship with fluid flow.
A common approach to measure the rate of fluid flow is a turbine
flow meter in which a turbine is caused to rotate in a passage through
which the fluid is directed. The rate of rotation of the turbine
is directly proportional to the velocity of fluid flow, and by measuring
such rate of rotation, a flow rate indication may be obtained.
One application for fluid flow meters which provide a measure of
the mass rate of fluid flow is in automotive air flow sensors for
fuel control systems. In these applications, the rotating turbine
design has the disadvantage of having relatively high inertia such
that the response time of such rotating turbine flow meters is inadequate,
particularly in view of the great range of the rates of air flow
encountered in such applications.
One variation of the turbine type flow meter is the "stalled"
turbine flow meter in which a rotor is provided with turbine blades
and is disposed in the fluid flow passage and mounted for only a
limited degree of angular displacement. The turbine rotor being
restrained, reactive forces are created by the imposition of a change
of angular momentum on the fluid flowing across the turbine blades.
The reactive force is measured by a transducer in order to produce
a signal corresponding to the fluid flow.
The restraining of the turbine allows a relatively rapid response
time since the inertia is much less than the turbine rotating.
In co-pending U.S. Pat. No. 4186602 issued Feb. 5 1980 assigned
to the assignee of the present application, there is disclosed such
a mass rate flow meter. In this design, temperature and pressure
sensors are provided in addition to the reactive force measuring
sensor so as to provide a signal corresponding to the fluid density,
such that the mass rate of fluid flow can be computed from the flow
rate and density signals.
In this design, the turbine blades are configured to receive substantially
the entire fluid flow thereacross such as to provide a high degree
However, a characteristic of fluid flow and the forces generated
by the change in momentum of the fluid is that the reactive force
generated by the air flow corresponds to the square of second power
of the air flow velocity. This nonlinear relationship produces relatively
poor response at very low air flow rates and requires flow meters
having relatively great ranges since the rate of air flow varies
drastically, i.e., a 20:1 air flow range requires a force sensing
transducer with a 400:1 output signal range.
A transducer of this range with good resolution in the lower force
ranges is technically very difficult to achieve.
A poor response at low air flow rates, on the other hand, is very
disadvantageous since the fuel control is more critical due to emission
requirements, i.e., the management of fuel to the engine must be
carefully controlled at low air flow rates in order to maintain
emissions within desired or legal limits.
Accordingly, it is an object of the present invention to provide
a turbine type flow meter in which the relationship between the
reactive force acting on the stalled turbine and the rate of air
flow is more linear with respect to each other such that for increasing
air flow, the reactive forces are increased only moderately with
increasing air flow.
It is another object of the present invention to provide a stalled
turbine type flow meter in which the range of reactive forces which
must be sensed by the force transducer is greatly reduced such as
to enable the use of relatively low cost transducers for measuring
the reactive forces generated by the stalled turbine.
SUMMARY OF THE INVENTION
These and other objects of the present invention, which will become
apparent upon a reading of the following specification and claims,
are achieved by the use of a turbine type flow meter in which a
turbine rotor is disposed in the fluid flow passage through which
the fluid flow is to be measured passes. Turbine blades occupy a
portion of the cross sectional area of the turbine passage such
that a proportion of the fluid flowing through the passage is intercepted
by the turbine blades and the blades are curved so that an angular
momentum change is imposed on the turbine rotor by passage of the
fluid flow along the turbine blades.
The turbine is mounted for a limited excursion in response to the
fluid flow therethrough against a bias force and the reactive forces
are measured with a displacement transducer such as a potentiometer.
Electrical signals corresponding to the excursion of the rotary
turbine are thereby generated to thus provide signals corresponding
to the average velocity of fluid flow through the fluid flow passage.
The turbine bias force is created by a coil spring resisting the
angular displacement thereof such that the rotary position of the
turbine blade corresponds to a reaction force generated by the fluid
flowing through the passage.
In order to offset the second power relationship between fluid
flow and the reactive forces generated on the stalled turbine rotor,
a shielding stator is mounted immediately upstream of the stalled
turbine blade elements and has blade elements oriented with respect
to the turbine blade elements such as to intercept a portion of
the fluid flow in the passage diverting it away from the turbine
rotor blades so as to modify the increase in the reactive force
with increasing rates of air flow.
This thereby produces a more linear relationship between the reactive
forces and the flow rate, which in turn allows good sensitivity
at very low air flow rates to be realized for the automotive applications
described. In addition, this allows the use of relatively low cost
transducers such as a simple potentiometer for measuring the reaction
forces, i.e., as by a potentiometer providing electrical output
signals corresponding to the angular position of the turbine rotor.
The fluid flow meter may also provide a mass rate of flow output
signals by the additional provision of sensors enabling the density
of the fluid to be measured as by pressure and temperature sensors
located downstream of the turbine.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross sectional view of a turbine type flow meter according
to the present invention together with a schematic representation
of the associated sensors and computation circuitry.
FIG. 2 is an endwise view of the stalled turbine type flow meter
depicted in FIG. 1.
FIG. 3 is a developed view of the turbine rotor and shielding stator
depicting the relationship between the shielding stator blades and
the turbine rotor blades with respect to fluid flow through the
fluid flow meter depicted in FIGS. 1 and 2.
In the following detailed description, certain specific terminology
will be employed for the sake of clarity and a particular embodiment
described in accordance with the requirements of 35 USC 112 but
it is to be understood that the same is not intended to be limiting
and should not be so construed inasmuch as the invention is capable
of taking many forms and variations within the scope of the appended
As developed above, the concept according to the present invention
consists of an arrangement of a stalled turbine type fluid flow
meter in which a turbine rotor is provided having one or more turbine
blades adapted to receive a portion of the fluid flow within a fluid
flow passage in which is mounted the turbine rotor.
The turbine blade configuration is curved, preferably helically,
such as to impress an angular momentum change on the fluid flowing
across the blade, which change in angular momentum results in a
reaction force acting on the turbine rotor which is proportional
to the momentum of the fluid flowing in the fluid flow passage,
i.e., corresponds to the fluid flow velocity.
According to the concept of the present invention, there is provided
a means for changing the proportion of fluid flow impinging on the
turbine rotor blades such that with increasing flow rates, a decreasing
proportion of the total flow through the passage acts on the turbine
rotor to offset the increase in reaction force with increasing rates
of fluid flow due to the squared relationship between the reactive
force and the rate of fluid flow thereby allowing a high degree
of sensitivity of the flow meter for relatively low fluid flow rates
and enable the use of wide range, relatively low cost reactive force
Referring to the drawings, the specific means whereby these functions
are contemplated as being achieved may be appreciated and understood.
The fluid flow meter 10 includes a tubular housing 12 and, as installed
in a typical automotive application, the device may be disposed
within an air cleaner. Mounted within the circular section fluid
flow passage defined by the tubular housing 12 is a shielding stator
14 and a turbine rotor 18. The shielding stator 14 is fixed with
respect to the tubular housing 12 by a plurality, i.e., two, opposed
stator blades 20 affixed to a central turbine stator hub 22 on
the inside edge and to the interior of tubular housing 12 on the
The turbine rotor 18 in turn is rotatably mounted on a hub projection
24 extending from the stator hub 22 by means of sleeve bearings
26 which are preferably silicone greased in order to introduce mechanical
damping to reduce the oscillations of the turbine rotor 18.
Bias force means are provided resisting the angular movement of
the turbine rotor 18 in response to the reactive torque generated
by the fluid flow, which means comprises a coil spring 28 affixed
at its outside edge to the interior of the turbine rotor 30 portion
of the turbine rotor 18 and to the hub projection 24 of the stator
The turbine rotor 18 includes a number of helically curved turbine
blades 32 corresponding to the number of stator blades and are affixed
to the turbine rotor 30 which will impress a change in angular momentum
on the fluid flowing thereacross.
In order to provide an output signal corresponding to the angular
position of the turbine rotor 18 a potentiometer shaft 34 is provided
affixed to the turbine rotor 30 and extending through the interior
of the hub projection 24 and to a potentiometer 36 generates an
electrical output signal corresponding to the angular position of
the turbine rotor 18.
As can thus be seen by examination of FIGS. 2 and 3 the position
of corresponding stator blades 20 and turbine blades 32 is such
that the turbine blades 32 are positioned angularly just ahead of
the stator blades 20 with the turbine rotor 18 in the normal relaxed
position such that as the turbine blades 32 are angularly advanced
by fluid flow passing thereover, an increasing shielding or shadowing
of the turbine blades 32 is created by moving behind the corresponding
stator blades 20.
The proportion of shielding is controlled by the shape and size
of the stator shield vane 20 such as to produce a linearizing effect
on the relationship between angular deflection of the turbine rotor
18 and air flow. That is, the shielding effect will reduce the proportion
of the total air flow which is received by the turbine blades 32
with increasing air flow.
An electrical output signal corresponding to the angular position
of the turbine rotor 18 is passed through a suitable position detector
circuit 38 the output of which is transmitted into a computation
In the computation circuit 40 the mass rate of air flow may be
computed by additional signals corresponding to the density of the
fluid including a pressure sensor 42 and a temperature sensor 44
as described in the above-cited patent application.
The relationship between the mass rate of air flow and the downstream
pressure and temperature conditions is fully developed in the above-referenced
patent application, and from which an output signal may be generated
corresponding directly to the mass rate of air flow.
Computation circuit 40 may also take into account the particular
blade and flow proportion geometry in producing a direct output
signal corresponding to the flow rate or mass rate of flow for each
angular position of the turbine rotor 18.
The utilization device such as an electronic fuel control system
46 may then receive the final corresponding output signal for use
in the system.
As also developed in the above-referenced patent application, the
reactive force may also be directed in an axial direction and appropriate
means provided to sense the same.
It should also be understood that other means for creating the
change in proportion of air flow received by the turbine blades
with increasing or varying air flow rates can be incorporated, rather
than the angular system described.
It will further be appreciated that the air flow sensor according
to the present invention differs from that of the above-referenced
patent application in that the total flow in the passage may inherently
not be received by the turbine blades, i.e., the diversion of a
partial flow or portion of the flow within the passage within the
turbine rotor precludes the passing of the entire flow over the
turbine blades. This accordingly represents a potential source of
inaccuracy, but this disadvantage is more than offset by the improved
linearity and low air flow rate response capability and the reduced
excursion ranges of reactive forces which must be measured by the
Other transducing arrangements may also be employed as an alternative
to the potentiometer, but this latter approach offers the advantage
of being of relatively low cost. As noted, this is made possible
by the relatively reduced force range resulting from the diversion
at higher air flow rates of an increasing proportion of the total
The present arrangement also offers the advantage of simplicity
and reliability, rendering it suitable for use in the automotive