Improved oil filtration system and method

Abstract: The pressurized oil flow of an engine (not shown) is rerouted from a primary filter (14) to a secondary filter (18) in the event of a first sensed pressure differential across the primary filter (14) which exceeds an allowable pressure differential, the excessive differential indicative of a primary filter (14) obstruction. In the event of a subsequent second sensed pressure differential which exceeds a second and higher pressure differential across the secondary filter (18), the oil flow is then diverted through a pump relief valve (19) toward the oil reservoir (26), away from an engine bearing compartment (50). The system (10) also provides sequenced first and second level warnings (40, 42) to the controller/flight crew, said warnings responsive to the operating status of the system (10).

Description: Technical Field This invention relates to lubrication filtration systems, and more particularly to a lubricant filtration system for turbines. Background Art In pressurized lubrication systems, a lubricant flow is directed through a network of conduits to specified regions of a machine to serve numerous functions, such as lubrication and cooling. This lubricant flow may carry a residual quantity of particulate matter, such as metallic filings, sediments, or other undesirable solids generated by, for example, the material wear occurring at sliding or impacting surfaces of numerous internal components. The lubrication system of a turbine engine directs a substantial volume of a lubricant to its engine bearing compartments to provide the ongoing necessary lubrication and cooling of the bearings contained therein. It is well known that by effectively filtering abrasive and undesirable particulate matter from the lubrication flow, additional wear to the machine's components may be minimized, and especially at the shaft bearings in a gas turbine engine. According to the prior art, a lubricant filter element is disposed in a lubrication system conduit upstream of the bearing compartments of a turbine engine and prevents the introduction of undesirable particulate matter to the engine bearings, adversely affecting bearing wear and engine performance. An indicated pressure differential between an upstream inlet and a downstream outlet of the filter element is indicative of several important operating parameters. One such parameter is the degree of flow obstruction by captured particulate matter within the filter element. In general, a substantial capture of particulate matter will result in an increased pressure differential across the filter element. Pressure differential sensors, which are well known in the art, inform the engine controller or flight crew of a substantial or complete obstruction of the filter element. In response to a pressure differential indication (whether actual or erroneous) which exceeds a predetermined maximum differential, the controller is then required to initiate a throttleback or engine shutdown procedure to avoid damage to the engine due to decreased lubricant flow. Thus, an important problem facing engine controllers/flight crews is the necessity of throttling back or shutting down an engine due to an apparent but unverified excessive pressure differential indication, especially in the instance of an erroneous pressure indication. One solution used in the current art is the diversion of the unfiltered lubricant flow to the bearing compartments through a bypass valve in response to an actual or indicated (but erroneous) obstructing event, resulting in an unfiltered, but continuing, lubricant flow throughout the engine. While permitting the engine to continuous operation, the unfiltered diverted flow may deliver contaminants to the bearing compartment. Reference is made to EP-A-0 337 851 which discloses another prior art filtration system having a secondary filter in a primary filter bypass line to ensure filtered lubricant flow to the engine bearings when the lubricant flow is rerouted around the primary filter. A one-way check valve disposed in the bypass line upstream of the secondary filter opens when the pressure upstream of the primary filter reaches a predetermined threshold value indicating obstruction of the primary filter. Means are provided for reversing the lubricant flow direction through the secondary filter when lubricant flow through the primary filter is resumed, after replacement or cleaning thereof. The secondary filter is cleaned by the reversed lubricant flow therethrough. Another prior art filtration system is disclosed in GB-A-820 878. This system has a coarse filter and a fine filter in parallel or series arrangement for supplying different engine components which require coarse oil filtration or fine oil filtration. If the fine filter is blocked, the engine components requiring fine oil filtration are supplied with oil from the coarse filter and if the coarse filter is also blocked unfiltered oil is supplied to the engine components. Summary of the Invention The object of the present invention is to prevent an unfiltered lubricant flow from reaching the engine in the instance of complete filter blockage of the primary and secondary filters. In accordance with the invention this is achieved by the method of providing filtered lubricant flow in an engine, according to independent claim 1, or by the lubricant filtration system according to independent claim 4. The present invention provides an improved lubricant filtering system for engines, and especially for the turbine engines used in many aircraft applications. This system provides a filtered secondary lubricant flowpath to the engine and its bearing compartments in the event of an obstructed or otherwise disrupted primary flowpath. This redundancy thereby allows for the continuing operation of the engine at normal power settings in the event of either a substantial obstruction of the primary filter of in the event of an erroneous indication of an obstructed primary filter. This condition is indicated to the engine controller by a first level warning indicator. A pump relief valve is activated in the event of a complete obstruction of both filters. The pressurized flow of lubricant is directed away from the obstructed filters and returned to the main oil tank, thereby preventing the introduction of undesirable particulate matter, carried by the unfiltered oil flow, to the engine. This condition is indicated to the controller by a second level warning indicator. More specifically, the system of the present invention reroutes the oil flow, through a first valve, from a primary conduit having a primary filter to a secondary filter, which may be housed together with or separately from the primary filter, in response to a detected pressure differential across the primary filter which exceeds a predetermined maximum allowable pressure differential, the excessive reading indicative of a partial or complete obstruction of the primary filter. A second, pressure return, valve disposed upstream of both filters allows for the return of an unfiltered oil flow to the main oil reservoir in the event of a subsequent partial or complete obstruction of the secondary filter, which is indicated by either an associated excessive pressure differential across that filter or by a pressure sensor disposed upstream of the bearing compartment. Operation of the valves is monitored and controlled by the engine controller and/or flight crew through either manual or automatic indicating and switching means. The invention thus allows the engine operator/flight crew to continue operation of the engine at normal power in the event of a first level indication, whether actual or erroneous, of an obstructed primary filter. This new filtration system also eliminates contamination of selected regions of an engine such as its bearing compartments by preventing an unfiltered lubricant flow to these regions in the event of a total filtration system obstruction. Advantageous features of the method and filtration system according to the invention are recited in the dependent claims. Brief description of the drawings Figure 1 is a flow diagram of the oil filtration system of the present invention. Figure 1a is an alternative embodiment of the present invention. Detailed Disclosure Figure 1 schematically represents, within the dashed box, a redundant oil filtration system 10 according to the present invention for a gas turbine engine (not shown). The filtration system 10 is disposed downstream of a main oil pump 24 which provides pressurization to a lubricant flow originating from an oil reservoir 26. The lubricant needed for engine requirements is flowed from the oil reservoir 26 through a conduit 11 to the oil pump 24 using either gravity or pressurized means. The pressurized oil from the pump 24 is then flowed to an engine bearing compartment 50 through the filtration system 10, and, depending on the particular engine installation, through an air/oil heat exchanger 30, a fuel/oil heat exchanger 32, and/or a last chance screen 28. The pressurized circuit initiated at the oil pump 24 and terminating at the bearing compartment 50 will henceforth be termed the pressure side of the lubrication system. The oil flow exiting from the bearing compartment 50 through a scavenge pump 25 and returning to the oil reservoir 26 will henceforth be termed the scavenge side of the lubrication system. More specifically, this system 10, according to the present invention, reroutes the pressurized oil, which normally flows through a primary conduit 12 housing a primary filter 14 to a secondary filter 18 in response to a detection of an excessive pressure differential across the primary filter 14. The secondary filter 18 may be disposed either downstream of, or in parallel with, the primary filter 14. The differential pressure is detected by a first pressure sensor 20. A bypass valve 15 disposed upstream of the primary filter 14 reroutes the oil flow to the secondary filter 18 in response to a sensed excessive pressure differential indication. This excessive pressure differential is indicative of a partially or completely clogged primary filter 14 or primary conduit 12. According to the present invention, sensory detection by the first pressure differential sensor 20 of an excessive pressure across the primary filter element 14 provides a first level warning 40 to the cockpit crew or engine controller. In an aircraft context, an amber warning light or other suitable indication provides the first level warning indication of the clogged primary filter 14 to the crew, which can then activate the bypass valve 15, which allows the oilflow to reenter the conduit upstream of the secondary filter 18, thus allowing continued operation of the engine through the use of the secondary filter 18. In the event of a subsequent substantial or complete blockage of both filters 14, 18, the oil flow is rerouted back to the oil reservoir 26 through a pump relief valve 19. This condition is indicated by an insufficient pressure in the main oil pressure line 17 disposed immediately upstream of the bearing compartment 50, as detected by a second pressure sensor 48 therein disposed. In the event of a subsequent blockage to the secondary filter 18, a second level warning indication 42, which is detected by second sensor 48, is made to the flight crew or controller via a red warning light or other like indicating means. The pump relief valve 19 is then operated to return the unfiltered oil flow to the oil reservoir 26 via a conduit 13 disposed upstream of the filtering system 10, thereby preventing unfiltered oil from flowing to the bearing compartment 50. Alternatively, detection of a subsequent blockage of both filters 14, 18, may be indicated by an excessive pressure differential across the secondary filter 18, as sensed by yet another pressure differential sensor 22. In either of these configurations, diversion of the unfiltered oil through the pump relief valve 19 in response to a secondary pressure indication 48, 22 prevents its introduction to the bearing compartment 50. Figure 1a shows an alternative configuration of the system 10 wherein a secondary conduit 16, housing the secondary filter 18, is physically separate from the primary conduit 12. Unlike the configuration of Fig. 1, the lubricant is not sequentially flowed through the secondary filter 18 after passing through the primary filter 14 in the normal operation of the lubrication system and the filtration system 10 incorporated therein. However, this alternative configuration still provides the continuing filtered lubricant flow to the engine (not shown) in the event of an actual or erroneous indication of a primary filter 14 blockage. The primary and secondary filters 14, 18 may be installed together or in separate housings as required by a particular engine configuration and/or access requirements. The filtering media, provided by Aircraft Porous Media, Inc. (Pinellas Park, Florida), has a primary filter porosity of nominally 30 microns, or generally within a range of 10 to 60 microns. The porosity of the secondary filtering media is nominally 150 microns. The pressure sensors 20, 22, 48, of the present invention may be of any design having the ability to accurately and precisely detect an anticipated pressure differential exceeding a maximum allowable level or range. In general, the primary filter 14 causes a 0.345 bar (5 psi) differential between its inlet and outlet during normal, relatively unobstructed, operation of the filtration system. According to the present invention, a first level warning indication 40 is made to the controller, as previously discussed, when the first sensor 20 detects a pressure differential of about 2.4 bar (35 psi), the warning provided to the operator via an amber light or another effective indicator. The engine controller is prompted by this indication 40 to further monitor the system 10 for a continuing and undesirable increase in oil pressure above 2.4 bar (35 psi). The bypass 15 is opened when the oil pressure reaches about 3.45 bar (50 psi), diverting the oil flow to the secondary filter 18. Operation of the bypass valve 15 is activated manually, by the engine controller/flight crew, or by an automated system, as is more fully described below. A second level warning 42, provided to the operator by a red light or another effective indicator, is indicated when the second sensor 22 either detects an excessive pressure differential [nominally 28 bar (410 psi)] across the secondary filter 18, or when a third pressure sensor 48 detects an insufficient supply pressure (indicating insufficient lubricant flow) immediately upstream of the bearing compartment 50. Should either condition be met, the pump relief valve 19 then opens to cause the unfiltered oil to recirculate back to the oil reservoir 26, and away from the bearing compartment 50. The oil filtration system 10 of the present invention may also be disposed in the scavenge side of the oil delivery system, as shown in phantom in Figure 1. According to both configurations, the system 10 is disposed downstream of the bearing compartment 50, with pressurization of the oil flow provided by a scavenge pump 25. Generally, a deaerator (not shown) will be disposed between the bearing compartment 50 and the system 10 in this configuration. Cockpit indicators of pressure and pressure differential may be of analog, digital, alphanumeric, or any other type of display, which sufficiently indicates contemporaneous oil pressure within the system 10 and upstream of the bearing compartments 50 of the engine (not shown). This invention further contemplates automatic filtration system control which is responsive to pressure differential changes in the system. Pressure detection analysis and sequencing of the bypass valves may be included in a larger automated system such as a F.A.D.E.C. (Full Authority Digital Electronic Control) which generally monitors and manages operational engine parameters. Furthermore, such a controlling process might include an alarm or other indicator means, registration of sensed pressure changes, recording means of those sensed changes, or means for inspecting the system.

Claims: Method for providing a filtered lubricant flow in an engine having an engine bearing compartment (50), comprising the steps of: flowing lubricant to the engine bearing compartment (50) across a primary filter (14) disposed in a lubricant conduit (12), generating a first signal responsive to an excessive threshold pressure across the primary filter (14) indicating a predetermined obstruction of the primary filter (14), diverting the lubricant flow in response to the first signal from the primary filter (14) to a secondary filter (18) disposed downstream of the primary filter (14) or in parallel flow relationship therewith, generating a second pressure signal when there is also a predetermined obstruction of said secondary filter (18), diverting the lubricant flow, in response to the second pressure signal, around the primary and secondary filters (14, 18) and the engine bearing compartment (50). Method according to claim 1, wherein said second pressure signal is generated responsive to an excessive threshold pressure across the secondary filter (18). Method according to claim 1, wherein said second pressure signal is generated responsive to insufficient lubricant supply pressure downstream of the primary and secondary filters (14, 18). Lubricant filtration system for carrying out the method according to claim 1 in an engine having an engine bearing compartment (50) connected to a pressurized lubricant conduit (12), the system comprising: a primary lubricant filter (14) disposed in the lubricant conduit (12) a first differential pressure sensor (20) disposed in a parallel circuit arrangement across the primary filter (14) for sensing a first pressure differential across said primary filter (14), a secondary lubricant filter (18) disposed downstream of the primary filter (14) or in parallel flow relationship therewith, means (15) for diverting the lubricant flow from the primary filter (14) to the secondary filter (18) in response to the first sensed pressure differential exceeding a first preselected value indicating blockage of said first filter (14), and means (19), responsive to a second sensed pressure indicating blockage of both said primary and secondary filters (14, 18), for rerouting the lubricant flow away from the primary and secondary filters (14, 18) and the engine bearing compartment (50). Lubricant filtration system according to claim 4, wherein a second differential pressure sensor (22) is disposed in a parallel circuit arrangement across the secondary filter (18) for sensing a second pressure differential across the secondary filter (18), and the means for rerouting the lubricant flow is responsive to the second sensed pressure differential across the secondary filter (18) exceeding a second preselected value higher than said first preselected value. Lubricant filtration system according to claim 4, wherein a pressure sensor (48) is disposed downstream of the primary and secondary filters (14, 18) for sensing the lubricant supply pressure in the lubricant conduit (12), and that the means for rerouting the lubricant flow is responsive to a sensed insufficient lubricant supply pressure downstream of the primary and secondary filters (14, 18). Lubricant filtration system according to claim 5 or 6, wherein a bypass valve (15) is disposed upstream of both filters (14, 18) for diverting the lubricant flow from the primary filter (14) to the secondary filter (18), and the means for rerouting comprises a pump relief valve (19) and a bypass line (13) for diverting the flow around the primary and secondary filters (14, 18) and the engine bearing compartment (50), said pump relief valve (19) being responsive to said second sensed pressure indicating blockage of both said primary and secondary filters (14, 18). Lubricant filtration system according to claim 7, wherein the bypass valve (15) is responsive to the pressure differential across the primary filter (14) exceeding about 2.4 bar (35 pounds per square inch). Lubricant filtration system according to claim 7 when depending from claim 5, wherein the pump relief valve (19) is responsive to the pressure differential across the secondary filter (18) exceeding about 28 bar (410 pounds per square inch). Lubricant filtration system according to claim 4, wherein the secondary filter (18) is housed together with the primary filter (14). Lubricant filtration system according to claim 4, wherein the filtration system is disposed upstream of the engine bearing compartment (50). Lubricant filtration system according to claim 4, wherein the filtration system is disposed downstream of the engine bearing compartment (50), the system further comprising a lubricant pump (25) disposed therebetween.

Inventors: FULLER WILLIAM E, MAKOWSKI ROBERT J, SLAYTON RICHARD M, SNYDER JAMES G, FULLER, WILLIAM E., MAKOWSKI, ROBERT J.(DECEASED), SLAYTON, RICHARD M., SNYDER, JAMES G.
Applicants: UNITED TECHNOLOGIES CORP, UNITED TECHNOLOGIES CORPORATION
Application year: 1992
Main classification: F16N39
IPC codes: F16N39, F01D25, F01M13, F02C7, F01M1, F01M11, F16N29