Patent Description:
Continuously variable transmission (CVT) systems are well known in the art for adjusting ratios of input speed to output speed in a machine or vehicle. Typically, a mechanism for adjusting the ratio of an output speed to an input speed in a CVT is known as a variator. In a belt-type CVT, the variator consists of two adjustable pulleys coupled to one another by a belt. Typically, a governor is used to control the variator so that the desired speed ratio can be achieved in operation.

In an aircraft gas turbine engine, overall system sizing can drive opposing sizing points for fuel pumps, making an optimized engine package difficult to achieve. For example, a positive displacement pump that is sized for high engine power conditions such as take-off may not provide sufficient fuel flow at engine start and at low engine shaft speed. In contrast, sizing fuel pumps only for engine start conditions can result in excess fuel pumping capability at high engine shaft speeds.

Larger or oversized fuel pump volumes can result in undesirable design consequences that can have a negative impact on system integrity, weight, envelope and thermal management. <CIT> describes a fuel system. <CIT> describes aircraft fuel pump systems.

The invention is defined in claim <NUM> and directed to a new and useful fuel delivery system for a gas turbine engine which includes a continuously variable drive assembly having a driving portion operatively associated with a gearbox of the gas turbine and a driven portion operatively associated with a fuel pump of the gas turbine, and a governor for controlling a drive ratio of the drive assembly to vary fuel pump flow performance over a range of engine operating conditions. The drive assembly includes a driving pulley assembly including a fixed pulley sheave and a movable pulley sheave, a driven pulley assembly including a fixed pulley sheave and a movable pulley sheave, and a drive belt operatively connecting the driving pulley assembly to the driven pulley assembly. The drive assembly is governed to drive the fuel pump faster than the gearbox in a start mode wherein engine fuel flow demand is relatively high, and it is governed to drive the fuel pump slower than the gearbox in a cruise mode wherein engine fuel flow demand is relatively low.

It is envisioned that the fuel pump would be sized to meet engine fuel flow demand for a specific engine operating condition. In a preferred embodiment of the subject invention, the fuel pump is sized to meet engine fuel flow demand in a take-off mode.

The driving portion of the drive assembly is connected to an input shaft driven by the gearbox and the driven portion of the drive assembly is connected to a drive shaft of the fuel pump.

The subject invention is also directed to a fuel delivery system for a gas turbine engine that includes a gearbox operatively associated with the gas turbine engine, a fuel pump sized to meet engine fuel flow demand for a specific engine operating condition (e.g., a take-off mode), a continuously variable drive assembly having a driving portion operatively associated with the gearbox and a driven portion operatively associated with the fuel pump, and a governor for controlling a drive ratio of the drive assembly to vary fuel pump flow performance over a range of engine operating conditions. The drive assembly is governed to drive the fuel pump faster than the gearbox in a start mode wherein engine fuel flow demand is relatively high, and to drive the fuel pump slower than the gearbox in a cruise mode wherein engine fuel flow demand is relatively low.

The subject invention is also directed to a fuel delivery method for a gas turbine engine which includes the steps of providing a continuously variable drive assembly between a gearbox of the gas turbine engine and a fuel pump of the gas turbine engine, and varying a drive ratio of the drive assembly to adjust fuel pump flow to the gas turbine engine over a range of engine operating conditions in response to input from the gearbox.

In an embodiment of the invention, varying the drive ratio of the drive assembly involves requesting or otherwise scheduling a reduction of the drive ratio from start mode to maximum engine power. In another embodiment of the invention, varying the drive ratio of the drive assembly involves requesting or otherwise scheduling a reduction of the drive ratio immediately after start mode. This can be accomplished by the governor.

The method further includes sizing the fuel pump to meet fuel flow demand for a specific engine operating condition (e.g., a take-off mode). The step of varying the drive ratio of the drive assembly involves driving the fuel pump faster than the gearbox in a start mode wherein engine fuel flow demand is relatively high, and driving the fuel pump slower than the gearbox in a cruise mode wherein engine fuel flow demand is relatively low.

These and other features of the subject invention will become more readily apparent to those having ordinary skill in the art to which the subject invention appertains from the detailed description of the preferred embodiments taken in conjunction with the following brief description of the drawings.

So that those having ordinary skill in the art will readily understand how to make and use the subject invention without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to the figures wherein:.

Referring now to the drawings wherein like reference numerals identify similar structural features or elements of the subject invention, there is illustrated in <FIG> a fuel delivery system <NUM> for a gas turbine engine <NUM> employed on an aircraft or the like.

The fuel delivery system <NUM> of the subject invention includes a continuously variable drive assembly <NUM> having a driving portion <NUM> operatively associated with a gearbox <NUM> of the gas turbine engine <NUM> and a driven portion <NUM> operatively associated with a main fuel pump <NUM> of the gas turbine engine <NUM>, and a governor <NUM> for controlling a drive ratio of the drive assembly <NUM> to vary fuel pump flow performance over a range of engine operating conditions.

By way of non-limiting example, the fuel pump <NUM> can be configured as a positive displacement gear pump or the like. Furthermore, those skilled in the art will readily appreciate that the governor <NUM> that controls the drive assembly can be configured as an electronic controller, a mechanical controller or an electro-mechanical controller.

The driving portion <NUM> of the drive assembly <NUM> is connected to a drive shaft <NUM> driven by the gearbox <NUM> and the driven portion <NUM> of the drive assembly <NUM> is connected to an input shaft <NUM> of the fuel pump <NUM>. The driving portion <NUM> of drive assembly <NUM> includes a fixed pulley sheave <NUM> and a movable pulley sheave <NUM>. The driven portion <NUM> of the drive assembly <NUM> includes a fixed pulley sheave <NUM> and a movable pulley sheave <NUM>. A drive belt <NUM> operatively connect the driving portion <NUM> of drive assembly <NUM> to the driven portion <NUM> of drive assembly <NUM>. The drive belt <NUM> is preferably a V-shaped drive belt made from rubber or a similar material, which increases the frictional grip of the belt.

In accordance with a preferred embodiment of the subject invention, the fuel pump <NUM> is sized to meet engine fuel flow demand in a take-off mode. Moreover, the main gear stage of fuel pump <NUM> is sized for optimum operational efficiency during take-off. It follows that the gearbox <NUM> is designed to operate most efficiently at a speed that coincides with the take-off mode.

Thus, in the take-off mode shown in <FIG>, the movable pulley sheave <NUM> of the driving portion <NUM> of drive assembly <NUM> and the movable pulley sheave <NUM> of the driven portion <NUM> of drive assembly are aligned in a neutral position. Consequently, the speed of the drive shaft <NUM> associated with the gearbox <NUM> is equal to the speed of the input shaft <NUM> associated with the fuel pump <NUM>.

Referring now to <FIG>, in a start mode wherein engine fuel flow demand is relatively high, the governor <NUM> will adjust the drive assembly <NUM> to drive the fuel pump <NUM> faster than the gearbox <NUM>. To accomplish this result, the movable pulley sheave <NUM> of the driving portion <NUM> of drive assembly <NUM> remains in a neutral position while the movable pulley sheave <NUM> of the driven portion <NUM> of drive assembly <NUM> is displaced from the fixed pulley sheave <NUM>. As a consequence, the speed of the input shaft <NUM> associated with the fuel pump <NUM> is increased, so that it is faster than the speed of the drive shaft <NUM> of the gearbox <NUM>.

Referring to <FIG>, in a cruise mode wherein engine fuel flow demand is relatively low, the governor <NUM> will adjust the drive assembly <NUM> to drive the fuel pump <NUM> slower than the gearbox <NUM>. To accomplish this result, the movable pulley sheave <NUM> of the driving portion <NUM> of drive assembly <NUM> is displaced from the fixed pulley <NUM> of the driving portion <NUM>, while the movable pulley sheave <NUM> of the driven portion <NUM> of drive assembly <NUM> remains in a neutral position. Consequently, the speed of the drive shaft <NUM> associated with the fuel pump <NUM> is reduced, so that it is slower than the speed of the gearbox <NUM>.

While it is desirable in this instance for the fuel pump <NUM> to be sized to meet engine fuel flow demand in a take-off mode, those skilled in the art will readily appreciate that the size of the fuel pump could be optimized to meet engine fuel flow demand for any operating condition over a range of engine operating conditions, including, but not limited to a take-off mode.

The subject invention is also directed to a fuel delivery method for a gas turbine engine <NUM> which includes the steps of providing a continuously variable drive assembly <NUM> between a gearbox <NUM> of the gas turbine engine <NUM> and a main fuel pump <NUM> of the gas turbine engine <NUM>, and varying a drive ratio of the drive assembly <NUM> to adjust fuel pump flow to the gas turbine engine <NUM> over a range of engine operating conditions in response to input from the gearbox <NUM>.

The method further includes sizing the fuel pump <NUM> to meet fuel flow demand in a take-off mode, as best seen in <FIG>. The step of varying the drive ratio of the drive assembly <NUM> involves driving the fuel pump <NUM> faster than the gearbox <NUM> in a start mode wherein engine fuel flow demand is relatively high, as shown in <FIG>, and driving the fuel pump <NUM> slower than gearbox <NUM> in a cruise mode wherein engine fuel flow demand is relatively low, as shown in <FIG>.

It is envisioned that using the continuously variable drive assembly <NUM> to increase pump shaft speed at initial start-up conditions and subsequently varying the drive ratio of the drive assembly <NUM> down at higher engine power, enables the use of a fuel pump <NUM> that is optimally sized for take-off conditions. In this regard, varying the drive ratio of the drive assembly <NUM> can involve requesting or otherwise scheduling a reduction of the drive ratio from engine start to maximum engine power. Alternatively, varying the drive ratio of the drive assembly <NUM> can involve requesting or otherwise scheduling a reduction of the drive ratio immediately after engine start. This can be accomplished by the governor <NUM>.

Those skilled in the art will readily appreciate that the subject invention provides several benefits. These benefits include an optimized fuel pump package (i.e., minimal operational volume, size and weight); minimized fuel pump bearing sizing and internal leakage(s); and more precise tailoring between the engine shaft input speed and the operational envelope of the fuel pump throughout the flight cycle of the aircraft. In addition, the on-demand nature of the system of the subject invention enables more accurate pressure regulation and flow metering of fuel to the engine.

There are also fuel system thermal benefits achieved by the system of the subject invention. For example, with an optimized fuel pump, there will be less return-to-tank fuel flow, which will make the system more fuel efficient. Another benefit involves easier engine re-start following an engine In-Flight Shut Down (IFSD) event, since the CVT would allow higher rotational speed of the fuel pump for a given gearbox drive shaft rotational speed. Moreover, since the gearbox drive shaft rotational speed is proportional to the engine's N2 shaft rotational speed, it becomes critical that following an IFSD, the free wind-milling of the shut-down engine is sufficient to drive the gearbox, which in turn, drives the main fuel pump to provide sufficient fuel flow and pressure to facilitate combustor light-up.

There will also be less residual kinetic heat deposited into the fuel by having a smaller pump. Consequently, there will be more opportunity to use the fuel in the system as a waste heat sink for other onboard systems (e.g., mechanical, electrical, electro-mechanical, electronic, hydraulic, lubricating, pneumatic, etc.) which are rejecting waste heat into the fuel. Additional benefits of the subject invention include improved overall on-board power thermal management capabilities.

Claim 1:
A fuel delivery system for a gas turbine engine (<NUM>) comprising:
a) a fuel pump (<NUM>); a gearbox (<NUM>) and
b) a continuously variable drive assembly (<NUM>) in operable communication with both the fuel pump (<NUM>) and the gas turbine engine through the gearbox (<NUM>) and being configured to adjust fuel pump (<NUM>) output to align with fuel demand of the gas turbine engine, and wherein the drive assembly (<NUM>) includes a driving pulley assembly including a fixed pulley sheave (<NUM>) and a movable pulley sheave (<NUM>), a driven pulley assembly including a fixed pulley sheave (<NUM>) and a movable pulley sheave (<NUM>), and a drive belt operatively connecting the driving pulley assembly to the driven pulley assembly; and
further comprising a governor for controlling a drive ratio of the drive assembly (<NUM>) to vary fuel pump flow performance over a range of engine operating conditions, and wherein the drive assembly (<NUM>) is governed to drive the fuel pump (<NUM>) faster than the gearbox (<NUM>) in a start mode wherein engine fuel flow demand is relatively high and governed to drive the fuel pump (<NUM>) slower than the gearbox (<NUM>) in a cruise mode wherein engine fuel flow demand is relatively low.