U.S. patent number RE31,835 [Application Number 06/562,793] was granted by the patent office on 1985-02-19 for pneumatic supply system having variable geometry compressor.
This patent grant is currently assigned to United Technologies Corporation. Invention is credited to George C. Rannenberg.
United States Patent |
RE31,835 |
Rannenberg |
February 19, 1985 |
Pneumatic supply system having variable geometry compressor
Abstract
In a compressed air supply system utilizing a shaft-driven
compressor (10,16), the flow capacity of the compressor is changed
by varying the compressor outlet stator geometry (16) by an
actuator (18) which controls the outlet stator geometry to provide
an optimum match between the compressor flow capacity and the
requirements of the load. The result is a compressed air supply
system which satisfies wide variations in demanded flow by the
load, while supplying air at maximum pressure with minimum input
shaft horsepower.
Inventors: |
Rannenberg; George C. (Canton,
CT) |
Assignee: |
United Technologies Corporation
(Hartford, CT)
|
Family
ID: |
26904772 |
Appl.
No.: |
06/562,793 |
Filed: |
December 19, 1983 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
210071 |
Nov 24, 1980 |
04405290 |
Sep 20, 1983 |
|
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Current U.S.
Class: |
417/282;
415/27 |
Current CPC
Class: |
F04D
29/462 (20130101); F04D 27/0246 (20130101) |
Current International
Class: |
F04D
27/02 (20060101); F04D 29/46 (20060101); F04B
027/02 () |
Field of
Search: |
;415/1,15,17,27,28
;417/20,22,282 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Casaregola; Louis J.
Attorney, Agent or Firm: Swiatocha; John
Claims
I claim:
1. A pneumatic supply system characterized by:
a compressor including a variable geometry stator portion included
in an outlet portion of said compressor, for providing delivery by
said compressor of an airflow of varying magnitude in accordance
with demands of a load;
actuator means for operating said variable geometry stator
portion;
a dump valve disposed in fluid communication with said compressor
outlet and sequentially operated with said variable geometry stator
portion by said actuator means; and
control means responsive to the flow demand of said load, the flow
output of said compressor, the power input and maximum allowable
power input to said compressor and the position of said variable
geometry stator portion for controlling said actuator means,
thereby controlling the actuation of said variable geometry stator
portion and said dump valve.
2. The pneumatic supply system of claim 1 characterized by said
compressor being of a centrifugal variety and said variable
geometry stator portion comprising a plurality of diffuser vanes
disposed radially outwardly of said compressor rotor and pivotally
connected to a movable member driven by said actuator means,
whereby driving of said movable member by said actuator means
pivotally displaces said diffuser vanes thereby adjusting the flow
capacity of said compressor.
3. The pneumatic supply system of claim 1 characterized by said
dump valve being operably connected to said variable geometry
stator portion by a lost motion connection, said lost motion
connection accommodating a predetermined amount of diffuser vane
displacement prior to transmission of said actuator displacement to
said dump valve for actuation thereof whereby said dump valve is
only opened subsequent to said stator being set by said actuator
means to a position corresponding to minimum flow through said
outlet.
4. The pneumatic supply system of claim 1 characterized by said
control means including means for determining a flow error between
the flow demand of said load and the flow output of said
compressor, means for determining a power error between the input
power to said compressor and the maximum allowable input power to
said compressor, means for determining .[.an outlet geometry error
between an actual.]. .Iadd.a desired .Iaddend.setting of the
variable geometry stator portion .[.and a setting of the variable
geometry stator portion required to achieve said flow demand of
said load.]. .Iadd.for operation of said compressor at an optimal
efficiency thereof.]..Iaddend., said flow.[.,.]. .Iadd.and
.Iaddend.power .[.and outlet geometry.]. errors .Iadd.and said
desired variable geometry setting .Iaddend.being applied to at
least select means, said least select means selecting .Iadd.as an
output signal thereof, .Iaddend.the least of said errors .Iadd.and
desired geometry setting .Iaddend.and providing .[.an.]. .Iadd.said
.Iaddend.output .[.control.]. signal to .Iadd.means for providing a
signal indicative of a geometry error between said output signal
and a signal indicative of the actual setting of said actuator
means, said geometry error signal being applied to .Iaddend.said
actuator means .[.corresponding to said least error..]. .Iadd.for
adjusting said variable geometry to minimize said geometry error.
.Iaddend.
5. The pneumatic supply system of claim 4 characterized by means to
monitor the speed of said compressor and a surge schedule
responsive to flow output of said compressor and the speed thereof
for formulating variable geometry stator portion settings required
to achieve said flow demand while said compressor operates along a
surge line thereof.
Description
DESCRIPTION
1. Technical Field
This invention relates to pneumatic supply systems in which
compressed air is supplied to a load by a shaft-driven compressor,
and including control means having a variable geometry compressor
outlet for automatically satisfying the demands of varying
pneumatic loads with improved efficiency.
2. Background Art
Certain prior art, pneumatic supply systems employing shaft driven
compressors use actuator systems to vary the compressor outlet
geometry to adjust system output. The present invention overcomes
various limitations and disadvantages of the prior art by utilizing
a variable geometry outlet in the compressor stator in combination
with a control, including an actuator which adjusts the outlet
stator geometry in accordance with load demands and other operating
conditions, for maximum overall efficiency (minimal compressor
output dumping) and maximum pressure rise of the pneumatic supply
system.
It is therefore an object of the present invention to provide a
pneumatic supply system, the output of which is adapted for
delivery to a varying pneumatic load at maximum supply pressure and
at maximum overall compressor efficiency.
It is another object of the present invention to provide in a
pneumatic supply system, the combination of a variable geometry
compressor outlet downstream of the compressor rotor, a variable
surge dump valve, and actuator means responsive to operating
conditions to operate both variable elements in a predetermined
mechanical sequence.
It is a further object of the present invention to provide a
pneumatic control system having a control means for modulating the
compressor outlet geometry to continuously maintain the compressor
operation on its surge control line over a very wide range of flow
required by the load.
It is another object of the present invention to provide a
pneumatic supply system in which the shaft horsepower absorption of
the compressor is limited by limiting the geometry of the variable
compressor outlet in response to a signal indicative of shaft power
overload.
DISCLOSURE OF THE INVENTION
In accordance with the present invention there is provided a
pneumatic supply system employing a compressor which delivers air
to a load, the compressor having variable outlet geometry to
provide the effect of a variable compressor without actually
changing the geometry of the compressor rotor itself. By varying
the flow capacity of the outlet geometry disposed in the stator in
the preferred embodiment, the flow capacity of the compressor is
varied while the pressure rise remains relatively unaffected. The
pressure rise of the variable compressor is therefore, determined
only by the speed of the rotor. Additionally, a control means is
employed to vary the compressor outlet geometry, and consists of a
single actuator positioned in response to the output from a
comparator which receives signals from sensors which measure the
flow through the compressor, and a signal from a referenc which is
indicative of desired flow to the load. The comparator signals the
actuator to control the compressor geometry to produce a flow which
satisfies the desired load flow while at the same time preventing
surge. As flow demand of the load decreases, the effective size of
the compressor is reduced by decreasing the capacity of the
variable outlet geometry by operating with the geometry scheduled
to maintain the compressor directly on its surge control line. This
results in maximum pressure rise and maximum efficiency. If flow to
the load is completely shut off, or decreases so far that surge
cannot be prevented by decreasing diffuser geometry, a surge pump
valve is then opened. The surge dump valve is operated in
mechanical sequence with the diffuser geometry, both being driven
by the single actuator.
Additional control means, such as means for protecting the
compressor shaft power source from overloading may be employed.
These protecting means measure a signal from the shaft power source
indicative of its having reached its power limit, such signal being
motor temperature, motor current or power, shaft torque, or any
other indicia of overload. The overload signal is compared to a
maximum permissible signal, and if overload is indicated the
actuator is actuated to reduce weight flow, and therefore, torque
absorption of the compressor, to avoid continued overloading of the
shaft power source.
The foregoing, and other features and advantages of the present
invention, will become more apparent from the following description
and accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plot of the pressure ratio versus airflow
characteristics of typical prior art fixed geometry centrifugal
compressors.
FIG. 2 is a plot of the pressure ratio versus airflow
characteristics of a centrifugal compressor using variable geometry
outlet diffuser vanes.
FIG. 3 is a schematic diagram showing a preferred implementation of
a pneumatic supply system using the variable compressor geometry
and control system of the present invention.
FIG. 4 is a cross-sectional view of a preferred implementation of a
variable geometry compressor diffuser using movable diffuser
vanes.
FIG. 5 is a plot of the sequential relationship between diffuser
vane position as implemented in the diagram of FIG. 3, actuator
stroke, and surge dump valve area.
FIG. 6 is a functional schematic diagram showing the control system
of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring to FIGS. 1 and 2, there is shown a comparison between the
performance of a prior art fixed geometry centrifugal compressor
(FIG. 1), and that of a variable outlet stator geometry (diffuser
vane) centrifugal compressor of equal size (FIG. 2). In the
Figures, .eta.=efficiency. The Figures are in fact maps of
compressor performance in which pressure ratio is plotted against
airflow. In FIG. 1, at any given operating speed of the compressor,
a limited flow range is available between the point of compressor
surge (to the left of the surge line), and the choked condition
where no more airflow can pass. It should be noted that as
operating conditions move away from the surge line, compressor
efficiency drops off rather quickly. The capacity range or
operating range of the compressor at acceptably high efficiencies
is typically about 1.25 to 1. The same size compressor is shown in
FIG. 2 with movable vanes employed in the compressor outlet
geometry. As shown, the variable geometry flow or capacity range
for this compressor is 6 to 1, over four times that of the
equivalent sized fixed geometry compressor. The broad, high
efficiency range also results in significant savings in system
weight and power dissipation. The surge line of FIG. 2 is far to
the left, indicating a wide compressor operating range without risk
of surge.
The pneumatic supply system of the present invention provides a
means for effectively utilizing the high efficiency, broad
operating range characteristics of variable outlet geometry
compressors. FIG. 3 shows the elements essential to practicing the
present invention including a compressor rotor 10 driven via a
shaft 12 from a source of power 14 such as an electric motor,
variable outlet stator geometry 16 at the exit of the compressor
rotor 10, and a control means including an actuator 18 responsive
to a controller 20 for modulating the geometry of the diffuser 16
to produce operation of the compressor driven pneumatic supply
system at maximum efficiency and maximum pressure rise. It will be
recognized that the stator outlet recovers as increased pressure,
the velocity energy imparted to the flow by the compressor rotor.
In the preferred embodiment, this variable geometry outlet
comprises a plurality of adjustable diffuser vanes which vary the
outlet flow area. However, it will be understood that any means
such as variably positioned diffuser walls which vary the stator
outlet geometry to achieve a desired flow, may be employed without
departing from the present invention. Also employed is a surge dump
valve 22 driven in conjunction with the variable outlet 16 by
actuator 18.
Air to be delivered by the pneumatic supply system enters the
compressor at the inlet 24. The air entering the inlet will
generally, but not necessarily, be at approximately atmospheric
pressure, one exception being when the system is used with an
aircraft environmental control system for cabin pressurization
wherein the compressor inlet air may be pressurized by the motion
of the aircraft relative to ambient. After leaving the compressor
rotor 10 the air enters the variable diffuser 16. Variable vanes 16
as shown in the preferred embodiment, and data on their performance
and construction are disclosed in ASME publication 77-ENAs-7, July
11, 1977, pp. 1-5, in an article entitled "Variable Geometry Air
Cycle Machine" by J. Tseka and G. C. Letton, Jr. The performance
data in FIGS. 1 and 2, and the compressor diffuser vane
construction of FIGS. 4 and 5, are derived from this
publication.
Referring again to FIG. 3, the position of diffuser vanes 16 is
determined by the stroke position of the actuator 18 which is
connected to the vanes via connecting shaft 26. The air, after
passing through the diffuser vanes 16, enters compressor discharge
housing 28 and is delivered to the load, not shown, via duct
30.
The construction of the actuator 18 is not shown in detail since
any of various well known types of actuators could be used, for
example, a solenoid operated motor or servo which provides rotary
motion to shaft 26 which in turn is connected to vanes 16. The
basic criterion is that the actuator, in response to a signal from
controller 20 fed to the actuator via line 32, vary the position of
shaft 26 so as to position vanes 16. A feedback signal indicative
of actuator (diffuser vane) setting is provided to controller 20
from actuator 18 through line 33.
To prevent surge at very low weight flow (a flow represented in the
area to the left of surge line B of FIG. 2), the surge dump valve
22 is opened to let whatever portion of compressor flow escape to
ambient through conduit 34 as is necessary to prevent compressor
surge. The surge dump valve 22 is operated in conjunction with
movement of variable compressor vanes 16 in the sequence shown in
FIG. 5. Mechanically, vanes 16 are hingedly connected to a drive
ring 36 by pins 38 and pinned to any suitable compressor stator
structure by pins 40 received through cam slots 42 provided in the
vanes (FIG. 4) whereby movement of one of the vanes or the ring
causes movement of the remainder of the vanes. Actuator 18 is
connected to the vanes in any suitable manner as determined by the
type of actuator employed. In the preferred embodiment, ring 36 is
provided with teeth 43 engaging pinion 44 rotatably powered by the
actuator to drive the ring. Rotation of the vanes by the actuator
adjusts both the mutual spacing and relative angular orientation of
the vanes to achieve a desired weight flow. The drive ring and
vanes are connected to dump valve 22 via crank assembly 45
comprising crank shaft 46 which engages ring 36 through cam slot 47
therein, the cam slot providing a lost motion connection between
the ring and the surge dump valve 22. The lost motion connection
moves the surge dump valve only after the vanes 16 have reached
positions defining a minimum capacity diffuser geometry. The
schedule, shown in FIG. 5, indicates that when the actuator 18 has
moved the vanes to any position between the maximum and minimum
compressor diffuser geometries, the surge dump valve is closed.
However, at lower flows (those that would be to the left of the
surge line of FIG. 2), the surge dump valve begins to open, and
reaches its fully open position at minimum or zero flow to the
load. In other words, surge is prevented by actuator 18, in
response to a signal on line 32 from controller 20, first sending
the compessor diffuser geometry toward a smaller compressor
capacity, and then after the smallest geometry compressor is
reached, gradually opening surge valve 22.
The function of determining when the surge valve must open and how
far it must open is determined by controller 20. The controller 20
receives a signal from a compressor flow sensor located in load
supply flow duct 30, the flow sensor preferably consisting of a
total pressure sensor 60 P.sub.t and a static pressure sensor 62
P.sub.s which enable controller 20 to determine flow to the load.
Other locations for pressure taps, and/or other means for sensing
compressor flow, may be used.
Also supplied to controller 20 is a flow demand signal from the
load on line 64. This signal could be produced by a flow selector
rheostat manually positioned by the operator of the pneumatic
supply system, or from any number of automatically generated flow
demand signals such as ventilation flow required to satisfy the
controls of an aircraft ventilating air system such as that
described in U.S. Pat. No. 3,699,777 entitled "Capacity Control for
Gas Turbine Powered Air Cycle Refrigeration System" and assigned to
the assignee of the present invention. An alternate source of flow
demand signal 64 could be a simple load supply pressure signal,
e.g., controller 20 could modulate the position of the diffuser
vanes 16 to satisfy a selected value of pressure in the load supply
duct 30 as provided via compressor discharge housing 28. The choice
of load demand signal is determined by design details of the
pneumatic supply system.
Also fed to controller 20 is a signal indicative of shaft power
supplied to the compressor. This signal, from sensor 66 attached to
power source 14, is fed to controller 20 via a signal line 67. The
power sensor may take the form of a current sensor, electrical
power sensor, torque sensor, temperature sensor, or any other
device which would indicate the power produced by power source 20
to drive compressor rotor 10. As will be described, when an
overload is sensed, the stator outlet geometry is set to .[.its
highest.]. .Iadd.a lower .Iaddend.flow capacity position to reduce
the load on the compressor.
The details of the controller 20 are shown in schematic fashion in
FIG. 6, the controller being enclosed in dashed lines. The
controller receives various input signals as shown in FIG. 3, and
produces an output signal one line 32 which directs or schedules
the position of actuator 18 and thereby controls the diffuser
geometry and dump valve area. The controller can be implemented in
various ways, although preferably it is composed of electronic or
hydraulic elements. The best mode presently contemplated will be
described.
Referring to FIG. 6, controller 20 receives input signals of actual
power consumed by the compressor and maximum allowable compressor
power input, air flow required by the load, static and total
pressures of the compressor discharge air and the position of the
compressor outlet (diffuser vane) geometry. The controller includes
a flow calculator 68 which calculates the weight flow output of the
compressor from the static and total pressure P.sub.s and P.sub.t
sensed in duct 30. This weight flow output signal is fed to
comparator 70 which compares this signal with weight flow required
by the load. The output of the comparator represents an air-flow
error or difference between these signals and is fed to least
selector 72. The actual weight flow output signal from flow
calculator 68 is also fed to surge schedule 74 which, from that
signal and a compressor speed signal from speed sensor 76
determines or schedules a desired compressor outlet (diffuser)
geometry which causes the compressor to run in its highest
efficiency (along the surge line). This desired outlet geometry
signal from schedule 74 is fed .[.to comparator 78 which compares
that signal with the signal indicative of actual compressor outlet
geometry (line 33) and determines a geometry error signal which is
also fed.]. to least selector 72. An error signal indicating the
difference between signals representing the maximum allowable
compressor input power and the actual compressor input power (from
power sensor 66) is calculated by comparator 80 and fed to least
selector 72. As its name implies, least selector 72 selects the
error signal of least magnitude from the power, airflow and
diffuser position error signals. This least error signal is fed to
.Iadd.comparator 78 which compares that signal with the signal
indicative of actual compressor outlet geometry (line 33) and
determines a geometry error signal which is also fed to
.Iaddend.actuator 18 .[.which.]. .Iadd.. Actuator 18 .Iaddend.sets
the dump valve and variable outlet geometry to eliminate this least
error in accordance with the dump valve and diffuser position
operating schedules of FIG. 5.
In operation, assuming that the load demand is at a steady state,
high weight flow value, corresponding to maximum compressor output,
the power error signal is zero (maximum compressor power input
equal to actual power input) and therefore, the least selector will
pass a zero error signal to the actuator despite any further
increase in flow demand. As load demand diminishes to a value less
than that of the actual compressor output, a negative airflow error
signal is applied to least selector 72 which passes this signal to
actuator 18. Actuator 18 adjusts (closing down) the diffuser vanes
to achieve the desired airflow. This airflow is input with the
compressor speed to surge schedule 74 in the manner described
hereinabove, schedule 74 providing a signal indicative of a
diffuser position adapted to achieve the desired airflow at optimal
efficiency. The error between this signal and the actual diffuser
position is passed to the actuator by least selector 72 wherein the
actuator sets the diffusers to the optimal setting determined by
schedule 74.
Referring to FIG. 5, the adjustment of the diffuser vanes to
achieve the desired (reduced) flow is indicated by segments A and B
of the dump valve area and diffuser vane position curves. As shown
in the dump valve area curve, the lost motion connection between
crank 46 and ring 36 allows a substantial adjustment in the
diffuser vanes without opening surge dump valve 22. Thus, the
output of the supply system is delivered at optimal efficiency
(maximum pressure rise) since no energy is expended in pressurizing
air which in prior art supply systems would be dumped through valve
22 when not required by the load.
As flow demand continues to decrease, the vanes will effectually
close to an extent that further closure without dumping of a
portion of the flow to meet minimal flow demands would result in
compressor surge. At these operating conditions, further
displacement (stroke) of actuator 18 is transmitted to crank 46 by
the lost motion connection, thereby opening surge dump valve 22.
Such valve opening dumps a portion of the compressor output thereby
preventing compressor surge at such minimal flow demand conditions.
The opening of the dump valve is indicated by line segment C of the
surge dump valve area curve of FIG. 5. As shown in the diffuser
vane position curve (segment D) of FIG. 5, the opening of the surge
dump valve is accompanied by no further movement of the diffuser
vanes. It will be understood that such stationary disposition of
the diffuser vanes is achieved by an orientation of cam slows 42
generally parallel to the direction of drive ring rotation when the
diffuser vanes are in their most closed orientation.
Accordingly, it will be appreciated that the present invention
provides a pneumatic supply system which delivers a required
airflow efficiently, at a maximum possible pressure rise. Dumping
is only required at minimal required flows and therefore, does not
represent a significant deterioration of system efficiency. It will
be further appreciated that such efficiency is maintained despite
system safeguards which prevent both compressor surge and
overload.
Although this invention has been shown and described with respect
to detailed embodiments thereof, it will be understood by those
skilled in the art that various changes in form and detail thereof
may be made without departing from the spirit and scope of the
claimed invention.
* * * * *