Patent Description:
The present technology is related generally to a gas turbine engine for a small aircraft, and more specifically to a multiple spool geared turbofan gas turbine engine with a high spool coupled through a reduction gear box to a low spool shaft with a fan and an integrated starter/generator (ISG). An integrated started/generator operates as a motor to start the engine, and as a generator to deliver electrical power after the engine has been started. The ISG is controlled by a power control module. Document <CIT> discloses a gas turbine engine according to the prior art.

In a gas turbine engine, a compressor is driven by a turbine from a hot gas flow produced in a combustor. A turbofan gas turbine engine is used for aircraft propulsion and typically includes two or three shafts containing compressors, fans, turbines, and other rotating turbomachinery components. Each rotating shaft assembly is called a spool. The spools each turn at different rotor speeds and operate at different pressures in order to improve efficiency. A high spool has the highest compressor pressure and highest turbine inlet temperature and operates at a higher speed. A fan is typically connected to the lower speed spool since the fan operates more efficiently at this lower speed.

<FIG> shows a currently known twin spool gas turbine engine <NUM> with a fan <NUM> (also referred to as a twin spool turbofan engine). The high pressure compressor <NUM>, the combustor <NUM>, and the high pressure turbine <NUM> are formed on the high spool <NUM> or high speed shaft. The low pressure compressor <NUM> and the low pressure turbine <NUM> are formed on the low spool <NUM> or low speed shaft. The low spool <NUM> passes through and is concentric and coaxial with the high spool <NUM>. Each spool <NUM>, <NUM> is supported by bearings <NUM>, <NUM>. The low spool <NUM> or low speed shaft is directly connected to the fan <NUM> without the use of a speed reduction gear box. The currently known twin spool turbofan engine <NUM> of <FIG> uses concentric shafts or spools, with a long low speed shaft <NUM> packaged within the shorter high speed shaft <NUM>. This design suffers from several technical disadvantages when the engine is used in gas turbine engines for small aero vehicles. For example, the diameter of the bearings <NUM> for the high speed shaft <NUM> and bearing speeds are increased due to the larger diameter of the high speed shaft <NUM>, thereby necessitating an increase in required oil flow and bearing complexity. Further, the bearings <NUM> for the high speed shaft <NUM> are located in high-pressure and high-temperature locations within the engine that result in increased leakages, the need for more complex bearings, and buffer cooling air demands. The rotor dynamics (such as bending) of a long low speed shaft <NUM> may require three or more bearings <NUM> to support the low speed shaft <NUM>, which increases the cost and complexity of the engine. The rotor dynamics and packaging constraints reduce the feasibility of integrating a starter/generator directly on the high speed shaft <NUM>. The complexity of the arrangement leads to a costly solution for a small expendable or attritable engine.

Some embodiments advantageously provide a geared turbofan engine with multiple compression and turbine stages on a high speed shaft coupled through a speed reduction gear box to a low speed shaft with a fan and an integrated starter/generator (multi-spool geared turbofan engine with integrated starter/generator). The high speed shaft includes low and high pressure compressors and low and high pressure turbines. The low speed shaft includes the fan and the integrated starter/generator that operates at a lower speed due to the speed reduction gear box positioned between the two shafts. In other embodiments, the high speed shaft includes only one compressor and one turbine as the core of the engine.

According to the claimed invention, a gas turbine engine comprises: a high speed shaft, the high speed shaft including a compressor, a turbine, and a combustor between the compressor and the turbine; a low speed shaft, the low speed shaft including a fan and an integrated starter/generator; and a speed reduction gear box connecting the low speed shaft to the high speed shaft, wherein air flows into the fan and exits as a bypass air flow and a core flow, the core flow entering the compressor, then flows to the combustor to burn with a fuel, and then flows through the turbine, the turbine driving the low speed shaft through the speed reduction gear box.

According to the claimed invention, the high speed shaft is supported by a first bearing located between the speed reduction gear box and the compressor and a second bearing located aft of the turbine.

According to the claimed invention, the low speed shaft is supported by a third bearing located between the fan and the integrated starter/generator and a fourth bearing located between the integrated starter/generator and the speed reduction gear box.

In one aspect of the embodiment, which is not part of the claims, low speed shaft is supported by a third bearing and a fourth bearing, each of the third and fourth bearings being located between the integrated starter/generator and the speed reduction gear box.

According to the claimed invention, the low speed shaft is collinear with the high speed shaft but does not rotate within the high speed shaft.

In one aspect of the embodiment, the speed reduction gear box is located between the integrated starter/generator and the compressor.

In one embodiment, a multiple spool geared turbofan gas turbine engine comprises: a high speed shaft, the high speed shaft including a first compressor, a second compressor downstream of the first compressor, a first turbine, a second turbine located downstream of the first turbine, and a combustor located between the second compressor and the first turbine; a low speed shaft, the low speed shaft including a fan and an integrated starter/generator located downstream of the fan; and a speed reduction gear box mechanically coupling the high speed shaft and the low speed shaft, the first turbine and the second turbine driving the high speed shaft and driving the low speed shaft through the speed reduction gear box.

In one aspect of the embodiment, the speed reduction gear box is located between the integrated starter/generator and the first compressor.

In one aspect of the embodiment, the first compressor is a low pressure compressor; and the second compressor is a high pressure compressor.

In one aspect of the embodiment, the first turbine is a high pressure turbine; and the second turbine is a low pressure turbine.

In one aspect of the embodiment, the low speed shaft is collinear with the high speed shaft but does not rotate within the high speed shaft.

In one aspect of the embodiment, the high speed shaft is supported by a first bearing located between the speed reduction gear box and the first compressor and a second bearing located aft of the second turbine.

In one aspect of the embodiment, the low speed shaft is supported by a third bearing located between the fan and the integrated starter/generator and a fourth bearing located between the integrated starter/generator and the speed reduction gear box.

In one aspect of the embodiment, the low speed shaft is supported by a third bearing and a fourth bearing, each of the third and fourth bearings being located between the integrated starter/generator and the speed reduction gear box.

A more complete understanding of embodiments described herein, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:.

Before describing in detail exemplary embodiments, it is noted that the embodiments reside primarily in combinations of apparatus components and steps related to a multi-spool geared turbofan engine with integrated starter/generator. Accordingly, the system and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

Disclosed herein is a multiple spool geared turbofan gas turbine engine (multi-spool geared turbofan engine with integrated starter/generator) with a low speed shaft having a fan and an integrated starter/generator connected to a high speed shaft through a speed reduction gear box. In one embodiment, the engine as disclosed herein may be used as a power plant for a small aero vehicle. This design reconfigures the high spool and the low spool into an arrangement with two shafts joined by a speed reduction gear box.

<FIG> shows a cross-section view of the multiple spool geared turbofan gas turbine engine <NUM> in accordance with the present disclosure. In one embodiment, the engine <NUM> includes a high speed shaft <NUM> with a low pressure compressor <NUM>, a high pressure compressor <NUM>, a combustor <NUM>, a high pressure turbine <NUM>, and a low pressure turbine <NUM>. In one embodiment, the engine <NUM> further includes a low speed shaft <NUM> with a fan <NUM> and an integrated starter/generator <NUM>. The low speed shaft <NUM> is connected through a speed reduction gear box <NUM> to the high speed shaft <NUM>. The low speed shaft <NUM> is collinear with, but does not rotate within (that is, is not coaxial with), the high speed shaft <NUM>.

Continuing to refer to <FIG>, bearings <NUM>, <NUM> are positioned at locations between the turbomachinery elements to adequately support both shafts <NUM>, <NUM>. Bearings <NUM> support the high speed shaft <NUM> while bearings <NUM> support the low speed shaft <NUM>. In one embodiment, the high speed shaft <NUM> is supported by a first bearing 52A and a second bearing 52B, with the first bearing 52A being located between the speed reduction gear box <NUM> and the low pressure compressor <NUM> and the second bearing 52B being located aft of the low pressure turbine <NUM>. In one embodiment, the low speed shaft <NUM> is supported by a third bearing 54A and a fourth bearing 54B, with the third bearing 54A being located between the fan <NUM> and the integrated starter/generator <NUM> and the fourth bearing 54B being located between the integrated starter/generator <NUM> and the speed reduction gear box <NUM>. In another embodiment, both the third bearing 54A and the fourth bearing 54B are located between the integrated starter/generator <NUM> and the speed reduction gear box <NUM>.

Continuing to refer to <FIG>, in one embodiment air enters the fan <NUM> and then either bypasses the core engine as bypass flow or flows into the low pressure compressor <NUM> as core flow. In one embodiment, a first portion of the total intake air exits the fan <NUM> as bypass flow and a second portion of the total intake air exits the fan <NUM> as core flow. Compressed air from the low pressure compressor <NUM> then flows into the high pressure compressor <NUM> for further compression. The compressed air then flows into the combustor <NUM>, where it is burned with a fuel to produce a hot gas flow that then enters the high pressure turbine <NUM> and then the low pressure turbine <NUM>, from where the hot gas flow exits the engine <NUM> as core exhaust. The high pressure turbine <NUM> and the low pressure turbine <NUM> drive the low pressure compressor <NUM> and the high pressure compressor <NUM> through the high speed shaft <NUM> and also drive the low speed shaft <NUM> through the speed reduction gear box <NUM>.

Referring now to <FIG>, a second embodiment of a multiple spool geared turbofan gas turbine engine 30A in accordance with the present disclosure. The engine 30A of <FIG> is substantially similar to the engine <NUM> of <FIG>, except the core of the engine of <FIG> includes only one compressor <NUM> and one turbine <NUM> on the high speed shaft <NUM> instead of the two compressors <NUM>, <NUM> and the two turbines <NUM>, <NUM> shown in <FIG>. Components that are common to both <FIG> are indicated with the same reference numbers. As shown, the flow of air from the fan <NUM> through the engine 30A is similar to that shown in <FIG>, except that the core flow passes through only one compressor <NUM> and the hot gas flow from the combustor <NUM> passes only through one turbine <NUM>. Further, the turbine <NUM> drives the compressor <NUM> through the high speed shaft <NUM> and also drives the low speed shaft <NUM> through the speed reduction gear box <NUM>. Further, in one embodiment the high speed shaft <NUM> is supported by a first bearing 52A located between the speed reduction gear box <NUM> and the compressor <NUM> and a second bearing 52A located aft of the turbine <NUM>. In some embodiments, the low speed shaft <NUM> is supported by a bearings 54A, 54B as shown and described in <FIG>.

The multiple spool geared turbofan gas turbine engines of <FIG> offer several advantages over the currently known engine of <FIG>. For example, bearing diameters and speeds can be reduced using the engine design of <FIG>. Additionally, the bearings can be positioned within low pressure and temperature locations of the engine away from the combustor <NUM> Shorter shafts, as in <FIG>, improve rotordynamic and stiffness issues, and also enable integration of a higher-capacity starter/generator onto the main (low-speed) shaft <NUM> of the engine <NUM> instead of being driven by a more-limiting power takeoff shaft. Further, multiple pressure ratio and bypass ratio fan designs can be incorporated without change to the core engine. Engine efficiency is improved relative to a conventional two spool design (for example, as shown in <FIG>) of the same size. This arrangement leads to a less costly solution for a small expendable or attritable engine, and allows for growth in overall pressure ratio and turbine inlet temperature.

According to the claimed invention, a gas turbine engine comprises: a high speed shaft, the high speed shaft including a compressor and a turbine; a combustor between the compressor and the turbine; a low speed shaft, the low speed shaft including a fan and an integrated starter/generator; and a speed reduction gear box connecting the low speed shaft to the high speed shaft, wherein air flows into the fan and exits as a bypass air flow and a core flow, the core flow entering the compressor, then flows to the combustor to burn with a fuel, and then flows through the turbine, the turbine driving the low speed shaft through the speed reduction gear box.

In one aspect of the embodiment, which is not covered by the claims, the low speed shaft is supported by a third bearing and a fourth bearing, each of the third and fourth bearings being located between the integrated starter/generator and the speed reduction gear box.

In one aspect of the embodiment, the compressor is a first compressor and the turbine is a first turbine, wherein: the high speed shaft further includes a second compressor downstream of the first compressor and a second turbine located downstream of the first turbine; the combustor is located between the second compressor and the first turbine; the integrated starter/generator is located downstream of the fan; and the speed reduction gear box mechanically couples the high speed shaft and the low speed shaft, the first turbine and the second turbine driving the high speed shaft and driving the low speed shaft through the speed reduction gear box.

Claim 1:
A gas turbine engine (<NUM>) comprising:
a high speed shaft (<NUM>), the high speed shaft (<NUM>) including a compressor (<NUM>, <NUM>) and a turbine (<NUM>, <NUM>);
a combustor (<NUM>) between the compressor (<NUM>, <NUM>) and the turbine (<NUM>, <NUM>);
a low speed shaft (<NUM>), the low speed shaft including a fan (<NUM>) and an integrated starter/generator (<NUM>), the low speed shaft (<NUM>) being collinear with the high speed shaft (<NUM>) but not rotating within the high speed shaft (<NUM>); and
a speed reduction gear box (<NUM>) connecting the low speed shaft (<NUM>) to the high speed shaft (<NUM>),
wherein air flows into the fan (<NUM>) and exits as a bypass air flow and a core flow, the core flow entering the compressor (<NUM>, <NUM>), then flowing to the combustor (<NUM>) to burn with a fuel, and then flowing through the turbine (<NUM>, <NUM>), the turbine driving the low speed shaft (<NUM>) through the speed reduction gear box (<NUM>),
the high speed shaft (<NUM>) being supported by a first bearing (52A) located between the speed reduction gear box (<NUM>) and the compressor (<NUM>, <NUM>) and a second bearing (52B) located aft of the turbine (<NUM>, <NUM>), and
the low speed shaft (<NUM>) being supported by a third bearing (54A) located between the fan (<NUM>) and the integrated starter/generator (<NUM>) and a fourth bearing (54B) located between the integrated starter/generator (<NUM>) and the speed reduction gear box (<NUM>).