Geared gas turbine engine

A turboshaft engine includes a high speed spool that connects a high pressure compressor with a high pressure turbine. A low speed spool connects a low pressure compressor with a low pressure turbine. A speed change mechanism includes an input that is in communication with the low spool and a fixed gear ratio. An output turboshaft is in communication with an output of the speed change mechanism.

BACKGROUND

A gas turbine engine typically includes a compressor section, a combustor section, and a turbine section. Air entering the compressor section is compressed and delivered into the combustion section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive the compressor section. In the case of a turboshaft engine, the engine drives an output shaft to create shaft power instead of thrust. The output shaft may be used to drive devices, such as a rotary wing aircraft, a generator, or a vehicle. There is an increasing desire to improve the power output and fuel efficiency of these engines to extend operating distances for rotary wing aircraft or vehicles and to reduce costs associated with fuel and maintenance.

SUMMARY

In one exemplary embodiment, a turboshaft engine includes a high speed spool that connects a high pressure compressor with a high pressure turbine. A low speed spool connects a low pressure compressor with a low pressure turbine. A speed change mechanism includes an input that is in communication with the low spool and a fixed gear ratio. An output turboshaft is in communication with an output of the speed change mechanism.

In a further embodiment of the above, there is a bypass ratio of zero.

In a further embodiment of any of the above, the speed change mechanism is an epicyclic gear train with a constant gear ratio.

In a further embodiment of any of the above, the epicyclic gear train is a star gear system. The output is fixed to a ring gear and a carrier is fixed from rotation relative to an engine static structure with a gear ratio of about 1.5 to about 2.5.

In a further embodiment of any of the above, the epicyclic gear train is a planet gear system. The output is fixed to a carrier and a ring gear is fixed from rotation relative to an engine static structure with a gear ratio of about 2.5 to 4.0.

In a further embodiment of any of the above, the speed change mechanism is non-epicyclic and includes a gear ratio of about 1.5 to about 2.5.

In a further embodiment of any of the above, an axis of rotation of the output driveshaft is offset from an axis of rotation of the low speed spool.

In a further embodiment of any of the above, the axis of rotation of the output driveshaft is transverse to the axis of rotation of the low speed spool.

In a further embodiment of any of the above, the low pressure compressor includes a pressure ratio of greater than about 1.5 and less than about 6.0. The high pressure compressor includes a pressure ratio of greater than about 4.0 and less than about 10.0.

In a further embodiment of any of the above, a pressure ratio of the low pressure compressor is greater than about 20 and less than about 40.

In a further embodiment of any of the above, the low speed spool is supported by no more than two bearing systems and the high speed spool is supported by no more than two bearing systems.

In a further embodiment of any of the above, the low speed spool and the high speed spool are supported by at least four bearing systems and no more than ten bearing systems.

In a further embodiment of any of the above, the low pressure turbine includes at least one rotor stage and less than four rotor stages.

In one exemplary embodiment, a method of operating a gas turbine engine includes the steps of rotating a high speed spool including a high pressure compressor and a high pressure turbine at between about 48,000 rpms and about 50,000 rpms. A low speed spool is rotated and includes a low pressure compressor and a low pressure turbine at about 40,000 rpms. The rotational speed of the low speed spool is reduced by a ratio of about 1.5 to about 4.0 with a speed change mechanism. An input of the speed change mechanism is attached to the low speed spool and rotates an output driveshaft with an output of the speed change at a reduced rotational speed.

In a further embodiment of any of the above, the gas turbine engine includes a bypass ratio of zero.

In a further embodiment of any of the above, the speed change mechanism is a star gear system. The output turboshaft is fixed to a ring gear and a carrier is fixed from rotation relative to an engine static structure with a gear ratio of about 1.5 to about 2.5.

In a further embodiment of any of the above, the speed change mechanism is a planet gear system and the output turboshaft is fixed to carrier and a ring gear is fixed from rotation relative to an engine static structure with a gear ratio of about 2.5 to 4.0.

In a further embodiment of any of the above, the speed change mechanism is non-epicyclic and includes a gear ratio of about 1.5 to about 2.5.

In a further embodiment of any of the above, the low pressure compressor includes a pressure ratio of greater than about 1.5 and less than about 6.0. The high pressure compressor includes a pressure ratio of greater than about 4.0 and less than about 10.0.

In a further embodiment of any of the above, a pressure ratio of the low pressure compressor is greater than about 20 and less than about 40.

DETAILED DESCRIPTION

FIG. 1schematically illustrates a gas turbine engine20according to a first non-limiting embodiment. The gas turbine engine20is disclosed herein as a two-spool turboshaft engine that generally incorporates an intake section22, a compressor section24, a combustor section26, and a turbine section28. The intake section22accepts air into an intake34and drives the air along a core flow path C into the compressor section24for compression and communication into the combustor section26then expansion through the turbine section28.

In one non-limiting embodiment, the low speed spool30and the high speed spool32are each supported by two separate bearing systems38. In another non-limiting embodiment, the low speed spool30and the high speed spool32are supported by a total of at least four (4) bearing systems38and no more than ten (10) bearing systems38. Furthermore, although the bearing systems38are depicted as ball bearings in the illustrated embodiment, other bearings, such as thrust bearings, roller bearings, journal bearings, or tapered bearings could be used to support the low speed spool30and the high speed spool32.

The low speed spool30generally includes an inner shaft40that interconnects a first (or low) pressure compressor44and a first (or low) pressure turbine46. The inner shaft40is connected to an output driveshaft42through a speed change mechanism, which in exemplary gas turbine engine20is illustrated as a geared architecture48, to turn the output driveshaft42at a lower rotational speed than the low speed spool30. The output driveshaft42is located on an axially forward end of the gas turbine engine20opposite the turbine section28. In another non-limiting embodiment, the output driveshaft42is located at an axially downstream end of the gas turbine engine20. In this disclosure, axial or axially is in relation to the axis A unless stated otherwise.

The high speed spool32includes an outer shaft50that interconnects a second (or high) pressure compressor52and a second (or high) pressure turbine54. A combustor56is arranged in the exemplary gas turbine engine20between the high pressure compressor52and the high pressure turbine54. A mid-turbine frame57of the engine static structure36is arranged generally between the high pressure turbine54and the low pressure turbine46. The inner shaft40and the outer shaft50are concentric and rotate via bearing systems38about the engine central longitudinal axis A which is collinear with their longitudinal axes. In a non-limiting embodiment, the output driveshaft42may also rotate about the axis A. One of the bearing systems38may be located forward or aft of the high pressure turbine54such that one of the bearing systems38is associated with the mid-turbine frame57.

Due to the environment in which the gas turbine engine20may be operating, there is a need to separate particles, such as sand, dirt, or other debris, from the core flow path C entering the gas turbine engine20. Particles entering the intake34traveling through the core flow path C are separated into a particle stream P that enters a particle separator74on a radially outer side of the core flow path C. The particle stream P is formed due to the geometry of the intake34. The intake34includes a component in the radially outer direction upstream of a portion with a component in a radially inward direction. This change in direction forces the particles against a radially outer surface of the intake34and into the particle separator74while the majority of the air is able to continue into the low pressure compressor44along the core flow path C. In this disclosure, radial or radially is in relation to the axis A unless stated otherwise.

In the illustrated embodiment, the gas turbine engine20is a zero bypass engine, such that the gas turbine engine20includes a bypass ratio of zero because the gas turbine engine20includes the core flow path C without having a bypass duct forming a flow path surrounding the gas turbine engine20.

According to one non-limiting embodiment, the geared architecture48is an epicyclic gear train, such as a star gear system or a planet gear system, with a gear reduction ratio of greater than about 1.5 and less than about 4.0. The output rotational speed of the epicyclic gear train would be fixed relative to the rotational speed of the low speed spool30such that a rotational speed of the output driveshaft42would vary with the rotational speed of the low speed spool30by a fixed gear ratio in the epicyclic gear train.

As shown in the non-limiting embodiments ofFIG. 2, the geared architecture48may be a star gear system with a gear ratio of about 1.5 to about 2.5. The star gear system includes a sun gear60mechanically attached to the inner shaft40with a sun gear flexible coupling62and a plurality of star gears64surrounding the sun gear60supported by a carrier66. The carrier66is fixed from rotation relative to the engine static structure36with a carrier flexible coupling68. A ring gear70is located radially outward from the carrier66and the star gears64. The ring gear70is attached to the output driveshaft42, which is supported by drive shaft bearings69, such as roller or ball bearings. The sun gear flexible coupling62and the carrier flexible coupling68provide flexibility into the star gear system to accommodate for any misalignment during operation. Because the geared architecture48is a star gear system, the inner shaft40and the output driveshaft42, rotate in opposite rotational directions.

In another non-limiting embodiment shown inFIG. 3, the geared architecture48may be a planet gear system with a gear ratio of 2.5 to about 4.0. The planet gear system is similar to the star gear system ofFIGS. 1 and 2except where described below or shown inFIG. 3. The planet gear system includes the sun gear60mechanically attached to the inner shaft40with the sun gear flexible coupling62and planet gears65surrounding the sun gear60. The planet gears65are supported by the carrier66. The carrier66is allowed to rotate relative to the engine static structure36. The carrier66drives the output driveshaft42. The ring gear70is located radially outward from the carrier66and the planet gears65and is fixed from rotation relative to the engine static structure36with a ring gear flexible coupling67. The sun gear flexible coupling62and the ring gear flexible coupling67provide flexibility into the planet gear system to accommodate for any misalignment during operation. Because the geared architecture48is a planet gear system, the inner shaft40and the output driveshaft42, rotate in the same rotational direction.

Alternatively, the geared architecture48could be a non-epicyclic gear system including helical, spur, or bevel gears to create a gear reduction ration of greater than about 1.5 and less than about 2.5. The output rotational speed of the non-epicyclic gear system would be fixed relative to the rotational speed of the low speed spool30such that a rotational speed of the output driveshaft42would vary with the rotational speed of the low speed spool30by a fixed gear ratio in the non-epicyclic gear system. Furthermore, with the use of a non-epicyclic gear system, an axis of the output driveshaft42could be offset from the engine axis A or be transverse to the engine axis A. The offset or transverse axis of the output driveshaft42relative to the engine axis A will depend on the packaging requirements for the specific application. However, the flexibility of varying the axis of the output driveshaft42will allow the gas turbine engine20to be utilized in a wide variety of applications. The output driveshaft42could also drive an additional gear train or transmission that would provide a greater range of output orientations.

In the illustrated non-limiting embodiment shown inFIG. 1, the low pressure compressor44includes an array of inlet guide vanes72directing air from the intake34in the intake section22past multiple rotor stages76each including an array of rotor blades78. The rotor stages76are separated by stators80each including an array of vanes82. The vanes82could be variable pitch or fixed from rotating about an axis. In the illustrated non-limiting embodiment, the low pressure compressor44includes three rotor stages76and three stators80and includes a pressure ratio between about 1.5 and about 6.0. In this disclosure, about equates to within ten (10) percent of the stated value unless stated otherwise.

The high pressure compressor52includes an array of inlet guide vanes84axially upstream of a first axial compressor stage86. The first axial compressor stage86includes an axial stage rotor88having an array of rotor blades90. A centrifugal compressor stage92is located downstream and separated from the axial compressor stage86by an array of vanes94. The centrifugal compressor stage92includes an array of blades96that direct compressed air downstream and radially outward and toward the combustor section26. The high pressure compressor52generates a pressure ratio between about 4.0 and about 10.0. This allows the overall pressure ratio of the compressor section24to be greater than about 20 and less than about 40. However, the overall pressure ratio of the compressor section24could reach 60.

The high pressure turbine54includes an array of inlet guide vanes100that direct the core flow path C past a single rotor stage102having an array of rotor blades104upstream of the airfoils59on the mid-turbine frame57.

Furthermore, in the illustrated non-limiting embodiment, the low pressure turbine46includes three rotor stages106each including an array of rotor blades108. Each of the rotor stages108are separated by stators110having an array of vanes112. The vanes112could be variable vanes or fixed from rotation about an axis. In another non-limiting embodiment, the low pressure turbine46includes at least one rotor stage106and less than four rotor stages106. An outlet vane114is located downstream of the low pressure turbine46and directs the core flow path C out of an exhaust nozzle116.

It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines.

During operation of the gas turbine engine20, the high speed spool32rotates at a maximum rotation speed of about 48,000 rpms to about 50,000 rpms while the low speed spool operates a rotational speed of about 40,000 rpms. Because the rotational speed of about 40,000 rpms of the low speed spool is generally much higher than is desired during operation, the input to the geared architecture48is coupled to the low speed spool30to reduce the rotation speed of the low speed spool by a ratio of about 1.5 to about 4.0 at an output of the geared architecture48to drive the output driveshaft42.