Abstract:
An integrated bleed air and engine starting system for an engine utilizes an innovative flow multiplier air turbine starter to provide bleed air supply to an ECS as well as starting an engine. The technique reduces bleed air consumption by mixing fan stage air and high stage air for ECS fresh air usage. It also can eliminate or reduce the size of the precooler heat exchanger. The system includes an air turbine starter subsystem and an air flow subsystem. The air turbine starter subsystem includes a compressor, a turbine, and a common shaft fixed between the compressor and turbine. Also provided is a gear coupled to a gearbox which links the engine with a shaft, as well as a variable nozzle valve intermediate the turbine and engine. The air flow subsystem comprises a diverter valve downstream of the turbine, an isolation valve intermediate the turbine and an auxiliary power unit, and a check valve downstream of the compressor and turbine. A fan is in air flow communication with the compressor and engine.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to systems for supplying air to start an engine and fresh air to a cabin, such as in aircraft. More specifically, the present invention relates to an integrated bleed air and engine starting system that minimizes fuel penalties associated with the use of bleed air. 
     Efficiency in aircraft design remains an ever-present concern. Yet, future aircraft designs remain focused on reducing unit costs and operating costs. The design trend is to integrate system functions to reduce duplicate components to thereby reduce the unit cost. An approach to reducing operating costs is to lower the fuel consumption by designing a higher efficiency system. 
     In terms of operating efficiency, anti-ice systems and environmental control systems of aircraft typically operate with bleed air at intermediate or high pressures from gas turbine engines. But utilizing bleed air to operate these systems and their components results in operating penalties or, in other words, reduced engine efficiency. In particular, the penalty is increased fuel consumption. For instance, bleed air taken from an engine compressor is usually cooled and the pressure regulated before its ultimate use. Typically, engine fan air or ram air is used to cool the bleed air through a heat exchanger, which will have a negative impact to the engine and aircraft performance. The heat exchanger imposes a weight penalty to the aircraft. The bleed air taken from the engine for environmental control system (ECS) usage usually has a pressure higher than what the ECS needs. Thus, the pressure is regulated in a pressure regulator and throttled at a flow control valve to meet the ECS demand. Throttling the bleed pressure, however, means a waste of energy and imposes a fuel penalty to the aircraft. 
     A past attempt to lower the unit cost by integrating engine starting and thermal management is found in U.S. Pat. No. 5,363,641 wherein a starter compressor and a starter turbine are linked through a shaft to an engine. An auxiliary power unit provides air to the starter compressor which, in turn, provides compressed air to an auxiliary burner during a start mode or a heat exchanger during an operating mode. In the start mode, fuel is also fed to the auxiliary burner for combustion, with the combustion products then being flowed to the starter turbine. As the starter turbine accelerates, the starter compressor, in turn, accelerates. The starter compressor then accelerates the shaft to a high compressor in the engine until the engine becomes self-sustaining. In the operating mode, the shaft between the starter compressor and the engine are disengaged via a clutch. The compressed air from the starter compressor is flowed into a heat exchanger. From the heat exchanger, the air moves to the starter turbine, expanded, and then flowed to cool engine components. A disadvantage to this design, however, includes the fact that the turbine discharge air cannot be used for passenger breathing because of contamination during the starting mode. 
     In U.S. Pat. Nos. 5,143,329 and 5,125,597, during ground start operation of one engine, a starting turbine receives compressed air from a starting air supply such as bleed air from another engine and discharges the air overboard. The starting turbine consequently cranks a high pressure turbine shaft within the engine until the engine can continue operation off of an engine compressor and without assistance from the starter turbine, although the starter turbine remains connected to the turbine shaft. During flight, a primary heat exchanger of an ECS receives an outlet flow from the starting turbine. The flow from the primary heat exchanger moves through a compressor, a secondary heat exchanger, and then an ECS turbine. From the ECS turbine, the air can be used to cool a cabin. A drawback of this design is that the pressure of the compressed boundary layer flow is too low for ECS operation and, thus, does not offer bleed air reduction for fuel savings. 
     Boundary layer bleed air is used in U.S. Pat. No. 5,136,837; to feed a compressor. During cruise operation, the compressor provides compressed air to a turbine and the outlet from the turbine is then used for cooling. During start-up, air to the turbine can be supplied from a ground supply or auxiliary power unit. The turbine outlet flow can then pass into the engine. Limitations in this design, however, include the fact that the turbine cooling flow is unmixed and is supplied for engine cowl cooling. Also, there is no mention in reducing the bleed air penalty associated with cabin fresh air supply. 
     Other related disclosures include U.S. Pat. Nos. 5,490,645; 5,414,992; 4,916,893; and 4,684,081. 
     As can be seen, there is a need for an improved integrated system for supplying bleed air and starting an engine. Also needed is a system that supplies air not only to start an engine but also to supply air to an environmental control system. Another need is for a system that can start an engine while minimizing associated fuel penalties. In that latter regard, there is a need for an engine starting system that minimizes fuel penalties by maximizing the use of existing aircraft components. A further need is for a system that can multiply an air flow to supply an environmental control system, thereby lowering flow mixing temperatures and reducing a high stage bleed penalty. A particular need is for an integrated system of bleed air supply and engine starting. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention, an integrated bleed air and engine starting system for an engine comprises an air turbine starter subsystem having a compressor and a turbine coupled to one another and to the engine; and an air flow subsystem that optionally directs the bleed air through the turbine or around the turbine and to an environmental control system and that also enables an auxiliary air flow from an auxiliary power unit to be optionally received by the turbine. 
     In another aspect of the invention, an integrated bleed air and engine starting system for an engine comprises an air turbine starter subsystem having a compressor, a turbine, a common shaft fixed between the compressor and turbine, a gear fixed between the common shaft and engine, and a variable nozzle valve intermediate the turbine and engine; an air flow subsystem having a diverter valve downstream of the turbine, an isolation valve intermediate the turbine and an auxiliary power unit, and a check valve downstream of the compressor and turbine; and a fan in air flow communication with the compressor and engine. 
    
    
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of a prior art system for providing bleed air and a separate engine starting system; and 
     FIG. 2 is a schematic diagram of one embodiment of the present invention that provides integrated bleed air and an engine starting system. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While a preferred embodiment of the present invention is described below in the context of aircraft, the present invention is not intended to be so limited. Further, while the present invention is described, in part, by contrasting it to a particular prior art design, the advantages achieved by the present invention are not intended to be limited to those described in relation to such prior art design. 
     To better illustrate some of the advantages of the present invention, FIG. 1 is provided to schematically show a frequently used design in the art that provides air to an environmental control system and air to start an engine. The prior art design includes a bleed air system  10  (marked with dashed lines in FIG. 1) that is separate from an engine start system  11  (marked with separately dashed lines). 
     During an aircraft cruising mode, an intermediate pressure (Ip) air  18  or a high pressure (Hp) air  19  flows from an engine  12 . The Ip air  18  passes through a check valve  20 , a shut off valve  23 , a pressure regulator  24 , a temperature sensor  25 , and then cooled in a heat exchanger  17 . From the heat exchanger  17 , the Ip air  18  passes a temperature sensor  26  and a pressure sensor  27 . Alternatively, the Hp air  19  moves through a high pressure valve  21 , a pressure sensor  22 , and then into the shut off valve  23 . Thereafter, the Hp air  19  flows the same as the Ip air  18  until reaching the pressure sensor  27 . If the Ip air  18  or the Hp air  19  require cooling, the flow from a fan  15  moves through a fan air valve  16 , to the heat exchanger  17 , and then overboard. Whether from the Ip air  18  or the Hp air  19 , the flow moves into a flow control valve  29  and then to an air cycle system  14  of an environmental control system. 
     During a start mode in the prior design shown in FIG. 1, a high pressure pneumatic air from an auxiliary power unit  13  flows through a shut off valve  28 , eventually through the pressure regulator  24 , and then another shut off valve  32 . The outlet from the shut off valve  32  leads to an air turbine starter  30  that is coupled to an engine gearbox  33  by a gear shaft assembly  31  which is linked to the engine  12 , thereby enabling the engine  12  to be started. 
     In contrast to the prior art design depicted in FIG. 1, the present invention provides a single or integrated bleed air and engine starting system (IBANESS)  40 , as shown by the dashed lines in FIG.  2 . The system  40  includes an air turbine starter (ATS) subsystem  46  and an air flow subsystem  67 . As further described below, the air turbine starter subsystem  46  generally includes a compressor  47  that is mechanically coupled to a turbine  49 . Upstream of the turbine  49  inlet is a variable nozzle  50 . The air flow subsystem  67 , as further described below, includes various valves, sensors, and ducts that control the air flow between the ATS subsystem  46 , an air cycle system (ACS)  43  of an environmental control system, and an auxiliary power unit (APU)  42  with one another. Thereby, the IBANESS  40  can operate in a first bleed air mode, a second bleed air mode, and an engine start mode. 
     According to the preferred embodiment shown in FIG. 2, the air flow (AF) subsystem  67  includes a bleed air source—specifically an intermediate pressure (Ip) air  52  and a high pressure (Hp) air  53 —coming from an aircraft engine  41 . The Ip air  52  passes through an intermediate pressure (Ip) valve  54  that supplies a flow to either the variable nozzle  50  or to a cowl/wing anti-ice system or engine start system via a temperature sensor  59  that senses the temperature of the flow. The cowl/wing anti-ice starter system does not form a part of the present invention and can be of any well known design in the art. 
     Through varying the opening of the variable nozzle  50 , the pressurized air (i.e., the Ip air  52  or the Hp air  53 ) is controlled in terms of amount of flow and pressure into the turbine  49  of the ATS subsystem  46 . The turbine  49  expands and thereby cools the pressurized air flow to produce an expanded air flow. The expanded flow mixes with a compressed air flow from the compressor  47  and moves into a diverter valve  57  that can be in one of two positions. In an overboard position, the diverter valve  57  diverts the mixed flow to overboard  62 . In a feed position, the diverter valve  57  diverts the mixed flow to the supply of the ACS  43 . 
     An air flow entering the compressor  47  is produced from a fan  44  that is part of the AF subsystem  67  and engine  41 . The fan  44 , however, need not always be operating in accordance with the present invention. When operating, the fan  44  produces a fan air flow through a fan air valve  45  that regulates the amount of flow passing therethrough. The fan air flow then moves into the compressor  47 . 
     The compressor  47  compresses the fan air flow to provide a compressed air flow that can mix with an outlet or expanded flow from the turbine  49 , as described above. A mixed air flow from the combination of expanded and compressed air flows moves through a check valve  66  that controls the passage of the flow. The flow then passes through a shut off valve  64  or through an isolation valve  58  that is part of the AF subsystem  67  and that can isolate the inlet of turbine  49  from receiving a flow. 
     If the mixed flow is to move through the shut off valve  64 , the isolation valve  58  is in a closed position. The mixed flow can then pass a temperature sensor  60  that senses flow temperature and also a pressure sensor  61  that senses flow pressure. Once past the pressure sensor  61 , the mixed flow moves through the shut off valve  64 , then past a flow sensor  65  that controls the amount of flow, and finally into the ACS  43 . The ACS  43  does not form an integral part of the present invention and can be constructed according to well know designs in the art. 
     When the mixed flow moves through the variable nozzle  50  and into the turbine  49 , it can be seen in FIG. 2 that the turbine  49  mechanically drives the compressor  47  via a common shaft  48 . The rotation of the common shaft  48 , in turn, drives a gear shaft assembly  51 . A gearbox  68  is actuated by the gear/shaft  51  to drive the engine  41  components needed to start the engine  41 . Although not shown in FIG. 2, the gear shaft assembly  51  may be decoupled from the engine  41 , such as by means of a sprag over-running clutch. 
     The operation of the integrated system  40  of the present invention can be characterized as being in one of three modes—a first bleed air mode, a second bleed air mode, and an engine start mode. In the first bleed air mode or aircraft cruising condition, the diverter valve  57  is in the mixing position, the isolation valve  58  is in the closed position, and the gear shaft assembly  51  is decoupled from the engine  41 . Thereby, the Ip air  52  or the Hp air  53  is routed through the turbine  49 . The turbine  49  drives the compressor  47  that, in turn, raises the pressure of the fan air. The fan air and expanded air from the turbine  49  are mixed and flowed to the ACS  43 . The variable nozzle  50  controls the flow and pressure demands of the ACS  43  as a result of controlling the area of the variable geometry nozzle  50  of the turbine  49 . 
     In the second bleed air mode or aircraft idle descent condition, the Ip air  52  will typically be deficient for operation of the ACS  43  and, therefore, the Hp air  53  is used. The variable nozzle  50  is in a fully closed position and the isolation valve  58  is in an open position. Doing so allows the Hp air  53  to bypass the ATS subsystem  46 , including the turbine  49 , and flow into the ACS  43 . 
     The Ip air  52  is the primary source for use to the anti-ice system. However, if the Ip air  52  temperature is lower than the anti-ice system demands, the Hp air  53  can be mixed in by moving it through a high pressure valve  55  and past a pressure sensor  56 . 
     In the engine start mode, the diverter valve  57  is in the overboard position, the variable nozzle  50  is in an open position, and the isolation valve  58  is in the open position. An auxiliary air flow from an auxiliary power unit  42  can then flow through a shut off valve  63  and to the turbine  49 . In turn, the turbine  49  can drive the shaft  48  and gear/shaft assembly  51  which is coupled to an engine gearbox  68  for engine starting. The discharge from the turbine  49  mixed with the compressor air is then sent to overboard  62 . 
     In contrast to the prior art design in FIG. 1, the present invention eliminates the separately provided engine start system  11 , including the air turbine starter  30 . In the prior art design, it can be seen that during aircraft operation, other than start-up, the engine start system  11  remains idle. In other words, the turbine starter  30  is not performing any useful work. If the engine start system  11  remains idle, but still results in fuel consumption because of the added weight, removing it eliminates a fuel penalty. 
     As also provided in the prior art design of FIG. 1, the heat exchanger  17  is used to cool air. By using the turbine  49  in the present invention to cool air, the heat exchanger  17  is eliminated and replaced by a component that is smaller in size and weight. This reduction in size and weight leads to a reduction in fuel consumption. 
     It can also be seen in the prior art design of FIG. 1 that the fan air from the fan  15  is dumped overboard after passing through the heat exchanger  17 . In contrast, the present invention utilizes the fan air by mixing it with the expanded air from the turbine  49  to eventually supply the ACS  43 . From the mixing, a flow multiplication effect results. In other words, since the fan air provides a cooling component to the mixed flow, the amount of expanded air that would be needed in the absence of the fan air is reduced. The reduction of needed expanded air reduces the amount of bleed air needed. Therefore, the penalties associated with the use of bleed air is necessarily reduced. 
     For those skilled in the art, it can be appreciated that the present invention provides an integrated system for supplying bleed air and starting an engine. The present system supplies air not only to start an engine but also to supply air to an environmental control system. In particular, the system of the present invention can start an engine while maximizing the use of existing aircraft components and thus minimizing associated fuel penalties. The present invention multiplies an air flow to supply an environmental control system, thereby lowering flow mixing temperatures and ram drag. 
     It should be understood, of course, that the foregoing relates to preferred embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.