Patent Description:
Gas turbine engines are known and typically include a fan delivering air into a bypass duct as propulsion air and into a compressor as core air. The air is compressed in the compressor and delivered into a combustor where it is mixed with fuel and ignited. Products of this combustion pass downstream over turbine rotors driving them to rotate. The turbine rotors, in turn, drive the compressor and fan rotor.

As known, the turbine components are exposed to very high temperatures. As such, it is known to deliver cooling air to the turbine.

Historically, the fan rotor rotated as one with a fan drive turbine. However, more recently, a gear reduction is placed between the fan rotor and the fan drive turbine. With this change, the fan may rotate at slower speeds than the fan drive turbine. This allows a designer to increase the speed of the fan drive turbine. This increase results in higher temperatures in the turbine section.

The higher temperatures raise cooling challenges. The higher temperatures also result in higher pressures at an upstream end of the turbine section. This is where one branch of the cooling air is typically delivered. As such, the cooling air must be at a sufficiently high pressure that it can move into this environment.

Historically, air from near a downstream end of the compressor section has been tapped to provide cooling air. However, with the move to a geared gas turbine engine, the efficient use of all air delivered into the core engine becomes more important. As such, utilizing air which has already been fully compressed is undesirable.

Recently, it has been proposed to tap the cooling air from a location upstream of the downstream most location in the compressor. This air is then passed through a boost compressor, which increases its pressure such that it now can move into the turbine section.

<CIT> discloses a prior art gas turbine engine as set forth in the preamble of claim <NUM>.

<CIT> discloses a prior art intercooled cooling air system using cooling compressor as starter.

From a first aspect, the invention provides a gas turbine engine as recited in claim <NUM>.

The geared architecture <NUM> may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about <NUM>:<NUM>.

Gas turbine engine <NUM> is illustrated in <FIG>, which, per se, falls outside the wording of the claims. A fan <NUM> delivers air into a bypass duct <NUM> as propulsion air. The fan <NUM> also delivers air to a low pressure compressor <NUM>. The air then passes into a high pressure compressor <NUM>. A tap <NUM> is shown in the high pressure compressor adjacent a downstream most end <NUM> of the compressor. Another tap <NUM> is shown at a location upstream of the downstream most end <NUM>. Air compressed by the compressor <NUM> passes into a combustor <NUM>. The air is mixed with fuel and ignited and products of this combustion pass over a high pressure turbine <NUM>. In this embodiment, there will typically be at least a second turbine stage. In some embodiments, there may be a third turbine stage which drives the fan <NUM>. A gear reduction <NUM> is shown between a shaft <NUM> driven by a fan drive turbine (which may be the second turbine or the third turbine, if one is included).

Air from the tap <NUM> is utilized as cooling air. It passes through a valve <NUM> to a heat exchanger <NUM>. The air in the heat exchanger <NUM> is cooled by the bypass air in duct <NUM>. Of course, other locations for the heat exchanger may be selected. Downstream of the heat exchanger <NUM> air passes through a boost compressor <NUM> through line <NUM>. The boost compressor <NUM> is driven by an accessory driveshaft or takeoff shaft <NUM> through a gearbox <NUM>. Shaft <NUM> may be driven by the high pressure turbine <NUM>. Also, while bypass air is used to cool the heat exchanger, other fluids, such as fuel, may cool the heat exchanger.

Air downstream of the boost compressor <NUM> passes through a heat exchanger <NUM> through line <NUM>, and then to a mixing chamber <NUM>. It should be understood that while two heat exchangers are illustrated, only one heat exchanger may be needed. In the mixing chamber <NUM>, air from the downstream location <NUM> is mixed with the air from the location <NUM> to arrive at a desired mix of temperature and pressure to be delivered at line <NUM> to cool the high pressure turbine <NUM>.

As an example, at lower power operation, more air from the downstream most location <NUM> may be utilized with limited disadvantage to efficiency. The mixing chamber <NUM> may be a passive orifice feature. As long as the pressure downstream of the boost compressor is higher than the air from location <NUM>, the boost compressor air will flow for cooling. Air from the tap <NUM> will make up any difference in the required flow volume. Alternatively, a control <NUM> may control the mixing chamber <NUM>. Control <NUM> may be a standalone control or may be part of a full authority digital electronic controller (FADEC).

In the <FIG> arrangement, the mixing chamber <NUM> does provide the ability to tailor the air being delivered to the turbine section <NUM>, somewhat. Still, there may be times when demand for the air drops and there could be parasitic losses. In addition, there may be instances where it would be desirable to assist the boost compressor <NUM> in matching the operation of the compressors <NUM> and <NUM> over a larger range of operational conditions. Further, it may be desirable to provide variability in the intercooled cooling air system to match other aircraft system needs. As can be seen, the valve <NUM> is a check valve and thus provides a relatively controlled pressure to the boost compressor <NUM>. However, a second tap <NUM> passes through a controlled valve <NUM>, which may also be controlled by control <NUM>, and into a line <NUM> to mix with the air from tap <NUM>. By controlling the valve <NUM>, the demand on the boost compressor <NUM> can be controlled. That is, should it be desirable to reduce the demand on the boost compressor <NUM> more of the higher pressure air from tap <NUM>, from a location intermediate that of taps <NUM> and <NUM> may be utilized. Further, if the air is passing from tap <NUM> to line <NUM>, that could create a higher pressure downstream of the check valve <NUM>, thus limiting the flow from the tap <NUM>. A worker of ordinary skill in the art would recognize when to actuate the valve <NUM> to achieve the desired controls.

The above arrangement with the valve <NUM> being used to control, if not block, flow downstream of the check valve <NUM> is one way. A separate arrangement might have a valve <NUM> which is able to modulate the pressure, such that a desired pressure can be delivered to the boost compressor. Both embodiments achieve a desired pressure head heading into the boost compressor.

<FIG> shows an embodiment <NUM> wherein a boost compressor <NUM> is provided with several ways to provide variability. As an example, a variable area inlet or vapor core <NUM> may be positioned on a suction side of the compressor <NUM>. This can allow adjustment of a vane or throat quantity to change how much air passes to the compressor <NUM>. In addition, a variable area diffuser <NUM> may be positioned on a downstream end. Again, this can be opened to limit the impact of the compressor <NUM> and reduce downstream pressures.

The control <NUM> may operate here to match conditions with the system. A worker of ordinary care and skill in the art would recognize the various conditions that might desirably indicate a need for controlling operation of the boost compressor.

These embodiments control both inlet pressure head and outlet pressure.

As shown at <NUM>, there is an optional variable tap at a mid-compression point in the boost compressor <NUM>. Tap <NUM> may limit the volume of air passing to the heat exchanger <NUM>. Again, the control <NUM> will control operation of the tap through a valve or other means to achieve a desired and controlled output.

Further, a plurality of taps may be utilized such that desired bleed pressures can be achieved dependent on output needs.

It should be understood that three types of control of <FIG> could be used separately, or in combination.

<FIG> shows yet another arrangement <NUM> falling outside the wording of the claims. Here, a transmission or differential <NUM> is positioned between the gearbox <NUM> and boost compressor <NUM>. This may be a passive control that ensures the boost compressor <NUM> operates at a fixed speed no matter the input speed. Alternatively, the control <NUM> could control the transmission or differential <NUM> to achieve varying speeds for the boost compressor <NUM>.

The passive arrangement could be utilized to keep the boost compressor within a limited speed band, rather than a "fixed speed. " The controlled embodiment can be utilized to achieve a variety of speed bands.

Here again, a worker of ordinary skill in this art would recognize what conditions might indicate a need to control the boost compressor operation.

Claim 1:
A gas turbine engine (<NUM>; <NUM>; <NUM>) comprising:
a compressor section (<NUM>) having a downstream most end (<NUM>) and a cooling air tap (<NUM>) at a location spaced upstream from said downstream most end (<NUM>), air from said cooling air tap (<NUM>) being passed through at least one boost compressor (<NUM>; <NUM>) and at least one heat exchanger (<NUM>; <NUM>), and then passed to a turbine section (<NUM>) to cool said turbine section (<NUM>), said boost compressor (<NUM>; <NUM>) being controlled to provide a desired pressure to said turbine section (<NUM>), wherein said boost compressor (<NUM>) is provided with a controllable output (<NUM>); wherein:
said boost compressor (<NUM>) is provided with a variable area inlet (<NUM>); or
the gas turbine engine further comprises a controlled and variable mid-compression point tap (<NUM>) in said boost compressor (<NUM>); or
said control for said boost compressor (<NUM>) includes a variable area diffuser (<NUM>) at a downstream end of said boost compressor (<NUM>), wherein said variable area diffuser (<NUM>) is operable to control an inlet pressure head and an outlet pressure;
characterised in that:
the gas turbine engine (<NUM>; <NUM>; <NUM>) further comprises a mixing chamber (<NUM>) that receives air downstream of said boost compressor (<NUM>; <NUM>) and selectively receives air from a second location (<NUM>) which has been compressed by said compressor section (<NUM>) to a pressure higher than a pressure of said cooling air tap (<NUM>), wherein said mixing chamber (<NUM>) is configured to control a mixture of said airflow downstream of said boost compressor (<NUM>; <NUM>), and said airflow from said second location (<NUM>) to selectively deliver a mixture of the airflows to said turbine section (<NUM>).