Control system for variable exhaust nozzle on gas turbine engines

Information

  • Patent Grant
  • 6402487
  • Patent Number
    6,402,487
  • Date Filed
    Monday, August 14, 2000
    24 years ago
  • Date Issued
    Tuesday, June 11, 2002
    22 years ago
Abstract
The present invention relates to a system that provides independently operated or controlled circuits in a single device. An exemplary application adapts a variable displacement roller pump into an engine geometry control system that uses one circuit of the pump during start-up and then removes the circuit from the system and satisfies other pumping needs with the other circuit of the pump.
Description




BACKGROUND OF THE INVENTION




1. Field of the Invention




The present invention relates to a single device having independently controlled circuits and, more particularly, a pump having first and second independently controlled circuits. It finds particular application as a control system for a variable displacement pump used in an engine geometry control system and, more particularly, to an improved control system for a variable exhaust nozzle on a gas turbine engine and will be described with particular reference thereto. However, it will be appreciated that the present invention is also amenable to other like applications.




2. Discussion of the Art




Engine geometry control systems are in widespread use on modern aircraft turbine engines. Engine geometry controls are used for various actuation of IGV, VSV, VBV, VEN, and other subsystem actuators. Additionally, engine geometry control systems are often required to provide engine start flow.




Engine geometry control systems are generally required to have the capability to control high pressure to either a rod end or piston end of an actuation system. This usually requires the high pressure side of a fluid source to be switched from the rod end to the head end of an actuator, or vice versa.




Switching from one end to the other is generally accomplished by using appropriate control valves to switch the high and low pressure of the fluid supply as demanded by the engine geometry requirements. Depending on the number of actuators to be handled in a given system, the flow change may be accomplished by valves in the supply system or by valves in the actuator. The valves serve to switch the inlet and discharge flow sources.




Generally, the fluid flow source or pumping system must be a variable displacement pump to minimize input power and heat loss due to the high pressures required. The control system response must be fast enough to enable changes from minimum flow to full stroke flow in a very short period. Minimum flow condition is often only needed to supply leakage makeup or cooling flow, whereas full stroke flow is often needed during takeoff or times of maximum actuator movement. The time limitation for the change to occur is dependent on the system needs and the number of actuators being serviced.




Heretofore, high pressure pumps have generally been limited to piston pumps of various configurations. However, these pumps often require extra complexity and expense in order to meet the high pressure and low lubricity fuel requirements of aircraft engine jet fuels. Further, these pumps have not had a history of high reliability.




In any case, the pumping system may be self pressure compensated or externally servo controlled. A pressure compensated pumping system is capable of maintaining a fixed discharge pressure while supplying only the flow needed by the load system. A servo controlled variable displacement pump can vary both the flow and pressure in response to the load system needs.




A variation of a servo control method is to use an over-center servo pump. An over-center servo pump is capable of switching its inlet and discharge porting in response to system demands. A major drawback of the over-center servo pump is that it is normally limited to a piston type pump design and is often unduly complex when discharge pressure requirements reach the 3000-5000 psid range.




Another major drawback of prior art systems is that the components of the system are often numerous, voluminous, heavy and have experienced maintenance problems.




Accordingly, there is a need for an engine geometry control system that does not suffer the disadvantages of the prior art and overcomes the above-referenced drawbacks.




BRIEF SUMMARY OF THE INVENTION




The present invention relates to a system that provides two independently controllable circuits from a single device. An exemplary embodiment of the present invention relates to an improved control system for a variable exhaust nozzle on a gas turbine engine.




In accordance with the present invention, a housing includes a rotor and a split cam ring that defines first and second independent pump circuits. Each circuit is independently controllable.




One advantage of the present invention is the provision of an improved control system for a variable exhaust nozzle on a gas turbine engine which provides a simplified system integration.




Another advantage of the present invention is the provision of an improved control system that enhances performance and stability.




Yet another advantage of the present invention is the provision of an improved control system that enhances service life and reliability.




Still another advantage of the present invention is the provision of an improved control system that is less heavy, less voluminous and less costly than prior art systems.




A still further advantage of the present invention is the provision of an improved control system that reduces system complexity with improved stability.




Another advantage of the present invention is the provision of an improved control system that reduces system temperature.




Further advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiment.











BRIEF DESCRIPTION OF THE DRAWINGS




The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating the presently preferred embodiments and are not to be construed as limiting the invention.





FIG. 1

is a pumping system schematic illustrating a control system for a variable exhaust nozzle on a gas turbine engine in an engine starting mode in accordance with a first preferred embodiment of the present invention.





FIG. 2

is a pumping system schematic illustrating a control system for a variable exhaust nozzle on a gas turbine engine in a variable exhaust nozzle control mode in accordance with a first preferred embodiment of the present invention.





FIG. 3

illustrates another application of the present invention as an alternative to a conventional variable displacement vane pump (VDVP).





FIG. 4

is yet another application of the teachings of the present invention in pumping and metering environment.











DETAILED DESCRIPTION OF THE INVENTION




With reference to

FIGS. 1 and 2

, one application of the present invention that provides independently controllable circuits is shown. Specifically, a control system


10


is provided for the actuation of a jet engine variable exhaust nozzle and for providing engine start flow. The system


10


generally comprises a pump assembly of a variable displacement pump type


12


, a four-way electro-hydraulic servo valve (EHSV)


14


, a full flow boost stage


16


, a high pressure relief valve


18


, a start regulator valve


20


, a de-stroke compensator valve


22


, an actuator


24


, a filter


26


, and a filter bypass valve


28


. The system


10


is capable of being selectively operated in a start-up mode for use during the start-up of an aircraft engine (not shown) and a VEN control mode for use as a variable exhaust nozzle actuation system. Of course, these applications are merely exemplary of the benefits offered by this invention; however, one skilled in the pump art will appreciate the potential use of the assembly in related or similar applications.




The control system


10


preferably uses a variable displacement pump


12


as its primary pump assembly with dual independent pump function capability. The pump has a rotor


30


operatively rotating within opposing cam sections or segments, namely, a start flow cam section


40


and a variable exhaust nozzle (VEN) cam section


42


. The cam sections


40


,


42


are each selectively and independently movable between a zero displacement position and a maximum displacement position with respect to a centerline of the rotor


30


.




More specifically, biasing member(s) or cam section separating springs


44


apply a spring force against the cam sections


40


,


42


and tend to urge cam sections


40


,


42


toward their respective positions of maximum displacement. Opposing pistons, namely, start flow piston


46


for start flow cam section


40


and VEN piston


48


for VEN cam section


42


, are used for moving and maintaining each cam section in a desired position against the springs


44


. Movement of the pistons


46


,


48


depends on the amount of force applied to the pistons against the springs


44


.




For example, if the force applied to piston


46


is less than the spring force, cam section


40


will move toward its position of maximum displacement. If the force applied to piston


46


is greater than the spring force, cam section


40


will move toward its position of minimum displacement. If the force applied to the piston


46


is equal to the spring force, cam section


40


will not move toward either position. The variable displacement pump


12


described herein and further described in co-pending application Serial No. that claims the benefit of U.S. provisional application Serial No. 60/148,828 is but one embodiment of a variable displacement pump for use in conjunction with the present invention.




An outer spool


50


is movably received within the EHSV


14


. The outer spool


50


is selectively moveable between an engine start position (where the outer spool is abutted against pump side stop


52


) and first and second VEN positions. The start position is for use during start-up mode and the VEN positions are for use during the VEN control mode. Movement of the outer spool


50


to the start position or any of the VEN positions is commanded by the EHSV logic


54


.




An inner spool


56


(or tracking servo valve) is movably received within the outer spool


50


of the valve


14


. The inner spool is selectively moveable between a first or maximum stroke stop position and a second position. Movement of the inner spool is controlled by the EHSV logic


54


which responds to an input current.




The actuator


24


serves to apply a force for an associated function, for example, controlling the geometry of an exhaust nozzle. The loading on the actuators is typically unidirectional and exhibits a lighter loading in the extend direction A. The unidirectional load is most significant in the retract direction B of actuator. This skewed load characteristic makes the present invention ideal for providing variable adjustment of the loaded actuators.




At engine start-up (FIG.


1


), the outer spool


50


is moved to its start position for engine start-up mode. In this position, the outer spool


50


causes rod side line


60


of the actuator


24


to be in communication with boost stage pressure through line


62


. The outer spool also prevents any pump discharge flow from entering pump discharge line


64


and being fed to the rod end of the actuator through line


60


during start-up of the aircraft engine. Rather, all available pump discharge flow, from both sides of the pump, exits the pump through start flow pump discharge line


66


. Discharge line


66


is internally connected to line


64


. This pump discharge line


66


communicates with the start regulator valve


20


into the start flow line


68


. Further, the main pump discharge flowing through line


70


is prevented from entering the head side line


72


by the start position of the outer spool.




During the engine starting mode, the inner spool


56


is at the maximum stroke stop position shown in FIG.


1


. As is evident, the maximum stroke stop position is set by the position of the VEN piston


48


. In this position, the inner spool


56


establishes fluid communication between the boost stage line


62


and the inner spool conduit


76


which feeds boost stage pressure to the VEN piston


48


.




Maximum pump output flow is required from the pumping system


10


during the start-up mode to provide fluid to the start flow line


68


of the aircraft engine. Maximum pump output flow for the start flow line


68


is achieved by positioning both cam sections


40


,


42


at their respective maximum displacement positions. The force exerted on the VEN side piston


48


results from the boost stage pressure line


62


as directed by the port provided in the outer spool that communicates with the passage in inner spool


76


. The force is less than the spring force causing cam section


42


to move to its maximum of full displacement position. Likewise, the start side piston


46


has a force acting on the piston


46


that is less than the spring force and moves to its maximum or full displacement position.




Operating with the cam sections


40


,


42


in their maximum displacement positions, the pump


12


provides maximum fluid to the start flow pump discharge line


66


. The fluid in the start flow pump discharge line


66


is routed through the start regulator valve


20


. In a first or closed position shown in

FIG. 1

, all of the fluid entering start valve


20


is directed to the start flow line


68


for satisfying the downstream start flow requirements. The de-stroke compensator valve


22


is also in a first or closed position during the startup mode rendering the valve


22


essentially inactive.




During the starting mode, the position of the actuator is independent of the remainder of the system. Boost stage pressure feeds both the rod and head ends of the actuator so that no net force is exerted thereon.




Once a predetermined pressure has been achieved in the start flow line


68


, the start regulator valve


20


acts to cut-off fluid flowing to the start flow line


68


by moving to an open position. This is accomplished through line


74


that branches from the start flow line


68


and acts on the end of the valve spool


76


and overcomes the biasing force of spring


78


acting on the other end of the spool. In the open position (FIG.


2


), a portion of fluid entering the regulator valve


20


is redirected to line


80


and thereby de-strokes the start flow piston


46


. The start flow cam section


40


is urged toward and held at its position of minimum displacement in response to the increase in the downstream start flow pressure, thereby essentially shutting off the start side of the pump (FIG.


2


). It should be noted that due to the restrictions in the start valve


20


, flow exiting the start valve


20


will be at a slightly lower pressure than the flow exiting the pump


12


.




With the start flow cam section


40


maintained in its minimum displacement position, the system


10


operates solely by the selective movement of the VEN cam section


42


. The VEN cam section


42


of the pump


12


moves between its minimum and maximum displacement positions dependent upon the requirements of the system


10


. The start flow cam section


40


acts only to balance the hydraulic loads within the pump


12


. The system


10


is now in VEN control mode and operates to supply variable flow and pressure to the rod side of the actuator via line


64


, the valve


14


, and line


60


of the system


10


. The fluid in the rod side line


60


acts on the actuator either extend (reference arrow A) or retract (reference arrow B) on the rod.




During the VEN control mode (i.e., after the start regulator has cut off start flow), the outer spool


50


is variable between the first and second positions depending on the desired position of the actuator


24


. The spool position is dependent on the EHSV control. In a first VEN position shown in FIG.


2


, the outer spool


50


is moved toward the VEN side stop


82


. While in this VEN position, the outer spool


50


causes the line


72


that communicates with the head side of the actuator to be connected to the boost stage pressure line


62


. The rod side of the actuator is connected to the VEN side pump discharge


64


through line


60


. The pressure of the fluid flowing into the rod side line


60


is greater than the pressure of the fluid flowing in the head side line


72


thereby causing the actuator


24


to retract, i.e., the actuator piston


24




a


will move into the actuator housing


24




b


. An input current


84


to the EHSV


14


prompts movement of the outer spool


50


thereby controlling the slew direction and rate of movement of the actuator


24


.




In response to an EHSV input current command


84


to retract the actuator


24


, the position of the outer spool


50


is altered. As a result, fluid discharged from the pump


12


through the VEN discharge line


64


is routed to the rod side line


60


of the actuator valve


24


. The pump


12


then produces, in the rod side line


60


, the pressure required to retract the actuator. The head side line


72


of the actuator valve


24


is connected to a low pressure source by the outer spool


50


of the EHSV


14


during a command to retract.




Responsive to a command to extend the actuator, the outer spool


50


moves to a position between the VEN side stop


82


and the start side stop


52


causing the head side line to be connected to the main pump discharge line


70


and causing the rod side line


60


to be connected to the boost stage pressure line


62


. The pressure of the fluid flowing into the head side line


72


is greater than the pressure of the fluid flowing into the rod side line


60


thereby causing the actuator


24


to extend, i.e., the actuator piston


24




a


will move out of the actuator housing


24




b.






The extend rate of the actuator


24


is controlled by throttling flow to the head side line


72


through the EHSV


14


. The retract rates of the actuator are set by positioning the VEN cam section


40


to a desired intermediate position between its maximum and minimum displacement positions. The VEN cam section


40


is moved by the VEN piston


48


which moves proportionally to the input current sent to the EHSV


14


.




During VEN mode, the inner spool


56


moves between first and second positions as required to balance out the pressure in the system


10


. If the pressures become higher than desired, the inner spool


56


connects the inner spool conduit


76


to the main pump discharge pressure line


70


thereby de-stroking the VEN cam section


42


of the pump


12


, i.e., increasing the pressure force on VEN cam piston


48


, such that the VEN cam section


42


moves toward its minimum displacement position. If increased pressure or flow is required, the inner spool


56


communicates with the boost stage pressure line


62


thereby relieving the pressure on the VEN cam piston


48


and causing the VEN cam section


42


to move, toward its maximum displacement position.




To prevent over pressurization of the engine downstream components, pressure relieving safety features are provided in the system


10


. These features include a de-stroke compensator valve


22


and a high pressure relief valve


18


. The de-stroke compensator valve


22


prevents the discharge pressure of pump


12


from becoming too high. The de-stroke compensator valve


22


typically covers all system failures external to the pump


12


such as actuator


24


overload or control system failures which result when the actuator


24


engages physical stops. The high pressure relief valve


18


is provided for preventing over pressurization of the system


10


. The high pressure relief valve


18


provides protection to the system in the event of pump failures which will not allow the de-stoking action of the de-stroke compensator valve


22


to occur.




The de-stroke compensator valve


22


only becomes active with large pump discharge pressures. More specifically, the de-stroke compensator valve


22


limits the pump output pressure to a preset level by “de-stroking” the pump


12


to a reduced displacement. The de-stroke valve


22


does this by providing a high pressure feed through line


86


to the VEN side cam piston


48


of the pump


12


which causes the pump


12


to de-stroke thereby reducing the displacement of cam section


42


and preventing over pressurization. The valve


22


is movable from a normal mode first position to a compensating mode second position.




When the valve


22


is in the first position, the VEN pump discharge pressure in line


66


acts on one end of the valve spool


22




a


but is not great enough to overcome the combined force from boost stage pressure in line


62


and the valve spring


22




b


, which act on the other end of the spool


22




a


. This results in the valve


22


preventing fluid communication between discharge conduit


66


and high pressure feed in line


86


. For this condition, pressure on the VEN side cam piston


48


is kept modulated by the pressure of the main pump discharge


70


that reaches the VEN side cam piston through communicating ports and passages in the outer and inner spools. In the normal mode, the discharge conduit


66


is at the highest pressure, the VEN side cam piston


48


is at an intermediate pressure from main pump discharge


70


, and the boost stage pressure line


62


is at the lowest pressure.




When the valve


22


is in the second position (not shown), the VEN pump discharge pressure of discharge conduit


66


becomes great enough to overcome the force from the boost stage pressure line


62


and the spring


22




b


. This causes the valve


22


to allow fluid communication between discharge conduit


66


and high pressure feed line


86


. Since the VEN side cam piston


48


is now under high pressure, the cam


48


will move and the VEN side of the pump


12


will de-stroke. This de-stroke will reduce the pump displacement and discharge pressure. Also, it will stabilize the compensating valve pressure setting. In the compensating mode, the highest pressure is in the discharge conduit


66


, the VEN side cam piston


48


is at an intermediate pressure, and the boost stage pressure line


62


is at the lowest pressure.




The high pressure relief valve


18


is included as another backup feature to prevent the system


10


from over pressurization. Normally, in the event of system over pressurization, the de-stroke compensator valve


22


would activate and de-stroke the pump


12


, thereby reducing the pump discharge pressure


64


,


66


. If the de-stroke compensator valve


22


fails, or fails to move the VEN side cam


42


on the pump


12


, the high pressure relief valve


18


activates and controls the over pressurization.





FIG. 3

illustrates an application of the variable displacement roller pump (VDRP) for use in performing variable displacement pumping only. Flow from the boost stage


100


passes through a filter


102


before entering a first inlet


104


of the VDRP described in the noted commonly assigned application. Flow also reaches the second inlet


106


. The pressurized flow from the first circuit, or left-hand side of the pump housing as shown, proceeds through outlet


108


and flow also exits via second outlet


110


from the second circuit or right-hand side of the pump housing. Although a portion of the flow from the outlets is used for related actuation uses represented by servo valves


112


, the two circuits essentially act in tandem (as noted by the common control lines that lead from the metering valve delta P regulator


114


to the pistons


116


that control the cam rings associated with the two circuits). The flows from the outlets are combined at juncture


118


before entering a metering valve. Thus, it will be understood from this embodiment that the invention can also be used as an alternative to a conventional variable displacement vane pump. All of the beneficial attributes of the separate and independent circuits associated with a single structure are not used in this embodiment, but can still serve a wide variety of applications.




On the other hand,

FIG. 4

demonstrates the versatility and beneficial advantages offered by the independently controllable circuits of the VDRP. Particularly, flow from the boost stage


120


passes through filter


122


and enters first inlet


124


. The left-hand side of the VDRP, or first circuit, pressurizes the fluid before it exits the first outlet


126


. A portion of the pressurized fluid is again used for related actuation uses as schematically represented by servo valves


128


. The fluid is next directed into second inlet


130


where the right-hand side, or second circuit, is independently operated from the first circuit. Thus, the first circuit provides, for example, high pressure pumping needs for the system and the second circuit serves as an accurate metering device. Although a bearing load is imposed on the VDRP, the bearing design can be preselected to accommodate the bearing needs. Thus, pumping and metering can be achieved with the same device.




The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. The exemplary embodiments should not be construed in any manner that limits the application offered by the VDRP where two independently controllable circuits can be used effectively. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.



Claims
  • 1. A balanced variable displacement roller pump system comprising:a housing having a rotor received therein for rotation about an axis; first and second cam rings received in the housing, the cam rings being independently and selectively movable toward and away from the rotor to define first and second independently variable pumping sections; a control assembly operatively associated with the cam rings for selectively altering positions of the first and second cam rings; and a biasing member urging the cam rings away from the rotor.
  • 2. The pump system of claim 1 wherein the control assembly includes first and second control pistons for independently varying the position of the cam rings relative to the rotor.
  • 3. The pump system of claim 1 further comprising first and second inlets and first and second outlets to the pump housing, the control assembly selectively shutting off flow through one of the outlets in response to a predetermined condition.
  • 4. The pump system of claim 3 wherein the control assembly includes a first and second control pistons for independently varying the position of the cam rings relative to the rotor, the first control piston in selective communication with one of the outlets for altering the position of the first control piston in response to a preselected condition in the outlet.
  • 5. A balanced variable displacement vane pump system comprising:a housing having a rotor received therein for rotation about an axis; first and second cam rings received in the housing and selectively movable toward and away from the rotor to define first and second independent pumping sections; a control assembly operatively associated with the cam rings for selectively using the pumping sections in first and second, different modes of operation, and means for biasing the cam rings toward positions of maximum displacement.
  • 6. The pump system of claim 5 and using only one pumping section during a second mode of operation.
Parent Case Info

This application claims the benefit of and hereby expressly incorporates by reference U.S. Provisional Application Serial No. 60/148,827, filed on Aug. 13, 1999.

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Provisional Applications (1)
Number Date Country
60/148827 Aug 1999 US