U.S. patent number 3,809,490 [Application Number 05/356,648] was granted by the patent office on 1974-05-07 for compressor surge sensor.
This patent grant is currently assigned to United Aircraft Corporation. Invention is credited to Kermit I. Harner.
United States Patent |
3,809,490 |
Harner |
May 7, 1974 |
COMPRESSOR SURGE SENSOR
Abstract
The disclosure of this invention relates to means for detecting
compressor surge by sensing the pressure downstream of the
compressor of a turbine type power plant for rapidly opening the
compressor bleeds and holding the bleeds open for brief interval
after surge disappears. The sensed pressure is admitted to one side
of the diaphragm through a laminar flow restrictor for obtaining a
lag time constant which increases as pressure decreases.
Inventors: |
Harner; Kermit I. (Windsor,
CT) |
Assignee: |
United Aircraft Corporation
(East Hartford, CT)
|
Family
ID: |
23402333 |
Appl.
No.: |
05/356,648 |
Filed: |
May 2, 1973 |
Current U.S.
Class: |
415/28;
137/625.61; 60/795 |
Current CPC
Class: |
F04D
27/0223 (20130101); F04D 27/001 (20130101); F04D
27/023 (20130101); Y10T 137/8659 (20150401) |
Current International
Class: |
F04D
27/02 (20060101); F01d 017/08 (); F01d 017/20 ();
F02c 009/02 () |
Field of
Search: |
;415/27,28 ;60/39.29
;137/625.6,625.61,15.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Croyle; Carlton R.
Assistant Examiner: Casaregola; Louis J.
Attorney, Agent or Firm: Friedland; Norman
Claims
1. A surge control system for opening a bleed valve of the
compressor section of a turbine type power plant so as to prevent
or eliminate surge therein comprising means for sensing the
pressure at the compressor for producing a signal whenever a
predetermined transitory drop in said pressure occurs, an actuator
connected to said bleed valve for opening and closing said bleed
valve, control means including a servo valve and servo fluid
responsive to said signal for controlling said actuator to position
it to an open position, a relatively unrestricted flow line for
leading said servo fluid to said servo valve to position it from a
normally closed bleed valve condition to an opened bleed valve
condition, said servo valve movable to overtravel null condition
when said servo valve is in the opened bleed valve condition, a
restricted flow line for conducting said servo fluid from said
servo valve to position it to its normally closed bleed valve
condition, said restricted flow line and overtravel being
dimensioned so as to permit said bleed valves to remain open over a
predetermined amount of time subsequent to said transition drop in
pressure returns to substantially its original value, and said
unrestricted flow line being sized to position said servo valve in
the
2. A surge control system as claimed in claim 1 wherein said
sensing means includes a fluid reaction means having opposing
surfaces subjected to the pressure in the compressor, and a laminar
flow restriction disposed
3. A surge control system as claimed in claim 2 wherein said
reaction means
4. A surge control system as claimed in claim 3 including a check
valve disposed in said unrestricted flow line to prevent servo
fluid flowing out
5. A surge control system as claimed in claim 4 including a flapper
valve controlled by said diaphragm for porting and bleeding fluid
to and from
6. A surge control system as claimed in claim 1 wherein said
pressure is
7. A surge controller for an engine comprising in combination,
means for sensing surge condition in said engine by detecting the
rate at which the pressure where surge is occurring drops for
producing a signal, means for subsiding the surge condition by
adjusting the airflow through said engine, an actuator connected to
said means, metering means having a null position for controlling
said actuator by the application of fluid pressure, a controller
responsive to said signal having a restricted and unrestricted flow
line porting and bleeding fluid to and from a reaction surface for
positioning said metering means from its null position, said
unrestricted flow line being sized to port fluid at a rate to
rapidly position said actuator to rapidly effect the flow in said
engine and position said metering means to overtravel the null
position, and said restricted flow line shunting said unrestricted
flow line to reduce the rate in which said metering means returns
to its null position, the extent of overtravel and the dimension of
said restricted flow line being selected to assure that surge
subsides prior to reaching said null
8. A surge controller as claimed in claim 7 wherein said sensing
means includes a diaphragm having one face exposed to unrestricted
communication to the engine and the opposing face exposed to
restricted communication to
9. A surge controller as claimed in claim 8 wherein said restricted
communication includes a laminar flow restrictor.
Description
BACKGROUND OF THE INVENTION
This invention relates to a compressor surge detector for turbine
type power plant and particularly to the means for opening the
compressor bleeds at a rapid rate to eliminate surge in response to
the pressure downstream of the compressor and for holding the
bleeds in the open position until after surge subsides.
As is well known in the art, compressor surge for axial flow types
of compressors utilized in turbine types of power plant has been a
problem that has plagued the aircraft industry since its inception.
Compressor surge is defined as that effect which results from
stalling a sufficient number of compressor blades so that a
momentary reversal of airflow occurs thru the compressor. This
causes compressor discharge pressure to drop very rapidly and
sometimes results in continued pressure oscillations until some
action is taken to eliminate the surge conditions.
While the theory of surge is not readily understood suffice it to
say that this rapid change in pressure and the ensuing pressure
pulsation not only could interfere with the efficiency of the power
plant but can also incur damage or disaster thereto. Thus it is
important that means are incorporated to eliminate or prevent surge
from occurring. One method of preventing surge from occurring is by
opening up bleed valves prior to or at the onset of the oncoming of
the surge condition. In the heretofore known open loop types of
controls the control is designed to schedule the opening of the
bleeds and/or control fuel flow so as to operate the power plant
below the surge line which is well defined for each given
engine.
It is also well known in the art to measure the compressor
discharge pressure and actuate the bleed valves whenever a
predetermined pressure change or rate of change occurs. The problem
with the latter mentioned method is that when the pressure
fluctuation is such to indicate a return to the normal condition
the bleed valves are again returned closed, which may occur prior
to the elimination of the surge condition. Also the condition may
occur where the bleed valves are oscillating between open and
closed during the surge condition.
I have found that I can obviate the problems noted above by sensing
compressor discharge pressure and sizing a control system so that a
predetermined, rapid decrease of sensed pressure will rapidly move
a metering valve which ports flow to the bleed actuator so as to
open the engine bleed ports. The metering valve is designed to
overtravel its null position to supply high pressure to the bleed
actuator to maintain the bleeds open.
By incorporating a combination of restrictor and check valve
judiciously located and sized, the system will move the metering
valve rapidly in a direction to open the engine bleed ports and
will cause the metering valve to return to a position which calls
for closed bleed ports at a much slower rate. Thus sizing the
restrictor and controlling the amount of valve overtravel will
determine the time delay before the actuator returns the bleeds to
their normal closed position and hence allows the surge conditions
to be eliminated before the bleeds are closed.
SUMMARY OF THE INVENTION
An object of this invention is to provide an improved surge
detector for a compressor in a turbine type of power plant.
A still further object of this invention is to provide means for
detecting surge by measuring the pressure downstream of the
compressor of a turbine type power plant, by providing a means for
permitting the bleed actuator metering valve to move at one rate in
the opening direction and at a slower rate in the closing direction
and to build in overtravel in the valve to hold the bleeds open for
a prescribed interval after surge has disappeared.
A still further object of this invention is to provide means for
detecting surge of a turbine type power plant by sensing the
pressure downstream of the compressor and rapidly opening the
engine bleeds upon a predetermined pressure change and then holding
the bleeds open for predetermined interval after the surge
condition disappeared and incorporating a laminar flow restrictor
disposed adjacent one side of the diaphragm sensing the
pressure.
Other features and advantages will be apparent from the
specification and claims and from the accompanying drawings which
illustrate an embodiment of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view, partly in section, showing the details
of the invention.
FIG. 2A is a graph plotting the compressor discharge pressure vs.
time, and
FIG. 2B is a graph plotting metering valve position vs. time.
FIG. 2C is a graph plotting bleed area vs. time.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As can be seen in FIG. 1 the surge detecting control is comprised
of two major assemblies, one being the pneumatic sensing mechanism
generally illustrated by numeral 10 and the other is the hydraulic
control and actuator generally illustrated by numeral 12. The
purpose of the pneumatic sensor is to sense rapid rates of decrease
of compressor discharge pressure (CDP) which exceed the maximum
decrease pressure rates which occur in normal operation and are
indicative of an engine surge. This is accomplished by sensing CDP
in the engine generally illustrated by numeral 14 which is any type
of turbine power plant by suitable pressure sensor 16. Sensor 16
comprises a housing 18 supporting diaphragm 20 extending across
chamber 22 to define a pair of subchambers 24 and 26. Unrestricted
flow from the compressor is admitted into chamber 26 via line 28
and restricted flow, also communicating with the compressor is
admitted through line 28 and branch line 30 via the restrictor 32
to chamber 24. Restrictor 32 in this instance is a laminar flow
restrictor and its purpose will be further described hereinbelow.
One arm of flapper arm 34 suitably pivoted to the housing 18 by
pivot 36 is attached to the diaphragm 20 by the attaching and pivot
member 38. Thus movement of diaphragm 20 is transmitted by the
flapper through housing 18 to open and close the orifice 40 formed
at the end of the pipe 42. Inasmuch as the side externally of
housing 18 is exposed to hydraulic fluid and internally of housing
18 is exposed to pneumatic a suitable seal 44 is incorporated to
prevent the contamination of either side. Spring 48 serves to
preload the flapper to set the value at which the flapper arm will
rotate about pivot 36 and whose value is selected so as to be
coincident with the transition point from where normal operation of
the compressor takes place and where surge occurs. Thus, exceeding
the value selected by the spring 48 (which may be adjustable) will
cause the flapper to rotate about pivot 36 to open and close
orifice 40.
The purpose of the hydraulic actuating system is to control the
position of the bleed valves so as to be opened very quickly and
continue to remain open until after the surge has subsided. This
hydraulic servo system is comprised of a suitable hydraulic
actuator identified by reference numeral 50 which positions bleed
valves 51 schematically illustrated to open and close as desired,
spool valve generally illustrated by numeral 52 and the time delay
mechanism generally illustrated by numeral 54. The hydraulic
actuator 50 may be of any suitable type and a description thereof
is omitted herefrom for the sake of clarity and simplicity. Suffice
it to say that actuator 50 is of the type that includes a piston
having a chamber for admitting hydraulic servo fluid to position
the piston and interconnecting linkage to synchronously position
bleed valves 51. Spool valve 52 includes spool 58, movable
rectilinearly, which serves to direct either high pressure, through
line 68, annulus 66 and line 64 to actuator 50, or drain pressure
from actuator 50 through line 64, annulus 62 and drain line 60.
Obviously land 70, when positioned to the right, communicates line
60 with line 64 and, when positioned to the left, communicates line
64 with supply pressure line 68.
Spool 58 of spool valve 52 is of the half-area type wherein the
end-face 74 equals half the area of end face 72. The high supply
pressure is continuously acting on end face 74 and controlled
pressure acts against end face 72. Thus half of the pressure value
acting on end face 72 is all that is necessary for balancing the
valve. To vary the pressure from the one-half value causes spool 58
to translate. Obviously, flapper 40, serves to regulate the
pressure acting on end-face 72 of spool 58.
As is apparent from the foregoing, the increase in curtain area of
flapper 40 serves to control the pressure drop across fixed
restrictor 80 disposed in line 42 which in turn regulates the
pressure in the branch line 82 which communicates directly with
chamber 84 for acting on the end face 72 of spool valve 58. Thus an
increase in curtain area of flapper valve 40 will increase the
pressure drop across fixed restriction 80 and cause a drop in
pressure in line 82. The high pressure acting on end face 74 in
turn will position spool 58 leftwardly. Conversely, a decrease in
curtain area of flapper 40 serves to decrease the pressure drop
across fixed restriction 80 hence increasing the pressure in line
82 and consequently, the pressure in chamber 84, thus urging the
spool 58 rightwardly. It is therefore apparent that the position of
flapper 40 has direct control over the movement of spool 58 which
in turn positions actuator 50 for opening and closing bleeds
51.
As noted from the sole figure, fixed restriction 90 is disposed in
branch line 82 and serves to restrict the flow passing
therethrough. Thus flow from regulated supply pressure (P.sub.H)
must flow thru orifice 80 and 90 and thru branch line 82 to chamber
84. The orifices 80 and 90 serve to limit the slew rate of the
spool valve 58 when it is moving toward the right. Motion of the
spool valve toward the right will cause the actuators to close
after the spool valve 58 reaches a position where it connects line
64 to drain line 60 thru annulus 62.
When the curtain area of flapper 40 is opened flow is drained from
chamber 84 and spool 58 is moved to the left. Much of the flow is
shunted around fixed restriction 90 through shunt line 92 where it
passes through check valve 94. Since the area of the opening of the
check valve 94 is much larger than the area of the fixed
restriction 90 it offers less resistance to flow and hence the flow
exiting chamber 84 is much faster than flow egressing thereto. Flow
out of chamber 84 moves the spool 58 to the left which will cause
the actuator 50 to open the bleeds when spool 58 has moved
sufficiently far to the left to communicate supply pressure thru
line 68, annulus 66 and line 64 to the actuator. Thus it is
apparent that spool 58 moves rapidly in a direction to open the
bleeds and returns slowly in a direction to close the bleeds by
virtue of the combination orifice 90 and check valve 94 just
described.
Assuming for the moment that a surge in the compressor is imminent
which would occasion a quick reduction in pressure at the discharge
end causing flow to bleed from chamber 26 which will be much faster
than flow out of chamber 24 in view of the fixed laminar restrictor
42. This change in pressure will cause a pressure drop across
diaphragm 20 which, in turn, will cause diaphragm 20 to move in the
upward direction rotating flapper arm 34 in a clockwise direction.
The flapper arm bearing against spring 48 will overcome the force
if the surge signal is strong enough causing the curtain area to
increase. This increase in curtain area causes an increase in flow
in line 42 and hence increases the pressure drop across fixed
restriction 80 which in turn decreases the pressure evidenced in
line 82 and hence in chamber 84. The effect of this is to cause the
spool 58 to translate in the leftward direction and supply high
pressure to the actuator 50 thru line 68, annulus 66 and line 64
and consequently position the bleed valves in the open position.
Because the flow exiting out of chamber 84 is shunted around fixed
restriction 90 bypassing through the line 92 and check valve 94,
the flow is virtually unrestricted and moves at a substantially
fast rate. Of course, check valve 94 is designed to impose as small
a pressure drop as possible. Thus it is apparent that a substantial
drop in pressure in the discharge end of the engine compressor will
cause the actuator to open the bleed valves in as quick a manner as
possible. The problem is to prevent the bleed valves from closing
before surge subsides. Thus if the bleed valves close too quickly
surge would ensue before the bleed valves could be made to
reopen.
Spool 58 in this instance begins metering flow to open the bleed
actuators very quickly and then is permitted to overtravel and thus
continuously supply high pressure to open the bleeds. Thus if
pressure in line 82 cycles, spool valve will cycle slightly, also.
However, it will always remain in the region where it is metering
high pressure to keep the bleeds open. Because spool 58 moves
rapidly in one direction and slowly in the other it will tend to
remain near its saturated position metering high pressure to open
the bleed actuators.
After the surge disappears and compressor discharge pressure
stabilizes spool valve 58 will slowly return to the position which
closes the bleed valve 51. The sizing of the orifice 90 and the
amount of overtravel of spool 58 from the null position will
determine the time required to close the actuator.
From the foregoing it is apparent that this system provides a
simple means for detecting compressor surge, rapidly opening the
engine bleeds to eliminate surge, and then holding the bleeds for a
prescribed interval if the surge disappears. This is exemplified
more fully by referring to the graphs shown in 2A, 2B and 2C which
are plots of CDP, spool valve position, and bleed actuator position
versus time. As noted graph 2A depicts a situation where surge has
occurred and hence the drastic drop in pressure is evidenced in the
discharge end of the compressor is represented by the solid line
curve A. When this pressure reaches a predetermined value say point
B the surge detector triggers the actuator to position the bleed
valves from full closed to full open. As surge subsides where CDP
returns to its stabilized level as evidenced by the dashed line C
spool valve will begin to respond to move actuator 50 and hence
bleed valves 51 to the closed position. However, due to the
overtravel (between points E and G of curve D) built into spool
valve 58, as it proceeds to close along the negative shape of curve
D it will continue to meter servo pressure to actuator 50 to hold
the bleeds opened a predetermined time. Points G to H of curve D
represents the rate of travel of spool 58, which obviously is a
lower rate than the opening value from points E to G. This will
assure that surge has completely subsided before the bleed valves
are allowed to start closing. FIG. 2C shows the resulting bleed
actuator position as represented by the curve K.
As noted above the diaphragm 20 of the surge detector senses CDP
through a lag time constant at one side. This lag time constant is
created by laminar restriction 32 and the volume feeding that side
of diaphragm 20. A laminar restriction is employed because it
causes the lag time constant to increase as pressure decreases.
Although this may be shown by rigorous mathematical derivation, for
purposes of understanding this invention this may be demonstrated
by the following mathematical derivation.
A lag time constant is defined by the equation:
.tau. LAG = (V 128 .mu. L)/(.gamma. D4P)
where
V = volume
.mu. = air viscosity
D = diameter of laminar restriction
.gamma. = ratio of specific heats
P = pressure
L = length of laminar restriction
The force per unit area felt by the diaphragm is:
F/A.sub.D = Ps4 - ] Ps4/(.tau. s + 1)] = (.tau. S/[.tau. S + 1])
Ps4 or F/A.sub.D = [.tau./(.tau. S +1)] (dPs 4/dt)
where
.tau. = volume time constant
Ps4 = compressor discharge pressure
A.sub.D = diaphragm area
Since .tau. is larger at low pressures this tends to cause lower
rates of change of pressure to be detected as surge at the lower
pressure levels and allows a fixed .DELTA.P setting across the
diaphragm to be indicative of surge at both sea level and altitude
conditions.
It should be understood that the invention is not limited to the
particular embodiments shown and described herein, but that various
changes and modifications may be made without departing from the
spirit or scope of this novel concept as defined by the following
claims.
* * * * *