Patent Description:
In gas turbine engines, it is known to drive a propeller or a fan rotor through a gearbox defining a single ratio between the input and output rotational speeds of the gearbox; this ratio typically defines a speed reduction from the input speed to the output speed. This ratio may be selected based on predetermined flight conditions, but however may not be optimal for other flight conditions. Prior art includes <CIT>, <CIT>, <CIT>, <CIT> and <CIT>.

In one aspect of the invention, there is provided a gas turbine engine as claimed in claim <NUM>.

In a further aspect of the invention, there is provided a method of rotating a rotor of a gas turbine engine through a gearbox as claimed in claim <NUM>.

<FIG> illustrates a gas turbine engine <NUM> of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan <NUM> through which ambient air is propelled, a compressor section <NUM> for pressurizing the air, a combustor <NUM> in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section <NUM> for extracting energy from the combustion gases.

The gas turbine engine includes low pressure and high pressure shafts <NUM>, <NUM> which are rotatable independently from one another. The two shafts <NUM>, <NUM> are coaxial and the low pressure shaft <NUM> extends within the high pressure shaft <NUM>. The high pressure shaft <NUM> is connected to rotor(s) <NUM> of a high pressure portion of the turbine section <NUM>, so as to be driven by the high pressure turbine rotor(s) <NUM>. The low pressure shaft <NUM> is connected to rotor(s) <NUM> of a low pressure portion of the turbine section <NUM>, so as to be driven by the low pressure turbine rotor(s) <NUM> located downstream of the high pressure turbine rotor(s) <NUM>.

The high pressure shaft <NUM> is drivingly engaged to one or more rotor(s) <NUM> of a high pressure portion of the compressor section <NUM>; in the embodiment shown in solid lines, the high pressure compressor rotors <NUM> are directly connected to the high pressure shaft <NUM> so as to rotate at the same rotational speed. The low pressure shaft <NUM> is drivingly engaged to the fan <NUM>, and to one or more rotor(s) <NUM> of a low pressure portion of the compressor section <NUM>, e.g. boost compressor rotor(s), located upstream of the high pressure compressor rotor(s) <NUM> and downstream of the fan <NUM>.

The gas turbine engine includes a gearbox <NUM>, <NUM>, <NUM>, <NUM> through which one of the shafts <NUM>, <NUM> of the gas turbine engine <NUM> is drivingly engaged to a rotatable load, such as a drivable rotor. As will be further described below, the gearbox <NUM>, <NUM>, <NUM>, <NUM> has two configurations allowing the shaft to drive the rotatable load either through a direct drive (i.e., speed ratio of <NUM>) or through a drive having a speed ratio different from <NUM>, i.e. providing a speed increase or speed decrease.

In the embodiment shown in solid lines, the gearbox <NUM>, <NUM>, <NUM>, <NUM> provides the driving engagement between the low pressure shaft <NUM> and the low pressure or boost compressor rotor <NUM>. It is understood that the gearbox <NUM>, <NUM>, <NUM>, <NUM> may additionally or alternately provide the driving engagement between the low pressure shaft <NUM> and any other suitable drivable rotor or rotatable element of the gas turbine engine, including, but not limited to, the fan <NUM>. The gearbox <NUM>, <NUM>, <NUM>, <NUM> may alternately provide the driving engagement between the high pressure shaft <NUM> and any suitable drivable rotor or rotatable element, including, but not limited to, one or more high pressure compressor rotor(s) <NUM> (as shown in dotted lines), and accessories <NUM>. The engine may include more than two rotatable shafts, and the gearbox <NUM>, <NUM>, <NUM>, <NUM> may be used for example to provide the driving engagement between an intermediate shaft and a drivable rotor or other rotatable element of the gas turbine engine <NUM>.

In a particular embodiment where the gearbox <NUM>, <NUM>, <NUM>, <NUM> is used to drive a boost compressor rotor <NUM> from the low pressure shaft <NUM>, the gearbox <NUM>, <NUM>, <NUM>, <NUM> provides access to increased power for the gas turbine engine <NUM> by increasing the rotational speed of the boost compressor rotor <NUM> in certain conditions, e.g., one engine operation, hot temperature, high altitude operation. The gearbox <NUM>, <NUM>, <NUM>, <NUM> can be switched from a direct drive to a speed increase configuration to provide for an increased rotational speed of the boost compressor rotor <NUM>.

Although the gas turbine engine <NUM> has been shown as a turbofan engine, it is understood that the gas turbine engine <NUM> may have any other suitable configuration, including, but not limited to, a turboprop and a turboshaft configuration. The gearbox <NUM>, <NUM>, <NUM>, <NUM> may be used in such engines similarly as shown in <FIG>. For a turboprop engine where the gearbox <NUM>, <NUM>, <NUM>, <NUM> is used to drive a boost compressor rotor <NUM>, switching from a direct drive to a speed increase configuration allows for a propeller speed reduction in certain flight regimes (i.e. rotational speed reduction of the low pressure shaft and accordingly of the input shaft) while maintaining the rotational speed or minimizing the speed reduction of the boost compressor rotor <NUM>.

Moreover, for a turboprop engine <NUM> and as shown in <FIG>, the gearbox <NUM>, <NUM>, <NUM>, <NUM> may be used in the driving engagement between the low pressure/power shaft <NUM> and the propeller <NUM>, for example in series with a reduction gearbox <NUM>. In such an embodiment, the gearbox <NUM>, <NUM>, <NUM>, <NUM> can be used to change the propeller speed in certain flight regimes without changing the rotational speed of the driving power turbine rotor(s) <NUM>, for example for noise reduction purposes.

Referring now to <FIG>, <FIG> and <FIG>, a particular embodiment of the gearbox <NUM> is generally shown, which drivingly engages input and output shafts <NUM>, <NUM>. The input shaft <NUM> is connected to the driving shaft of the gas turbine engine <NUM>, for example the low pressure shaft <NUM> (<FIG>). The input shaft <NUM> may be connected to the driving shaft in any suitable manner, including removable connections (e.g. spline connection, bolted connection) and permanent connections (e.g. integrally formed therewith).

The output shaft <NUM> is connected to the drivable rotor or other rotatable load, for example the low pressure or boost compressor rotor <NUM> (<FIG>). The output shaft <NUM> may be connected to the drivable rotor or other rotatable load in any suitable manner, including removable connections (e.g. spline connection, bolted connection) and permanent connections (e.g. integrally formed therewith).

The gearbox <NUM> is a planetary gear set, and has a gear assembly including a ring gear <NUM> and a sun gear <NUM> in driving engagement with each other through planet gears <NUM>, <NUM> supported by a rotatable carrier <NUM>. In the particular embodiment shown, the ring gear <NUM> is the input component and is connected to the input shaft <NUM>, the sun gear <NUM> is the output component and is connected to the output shaft <NUM>, and the carrier <NUM> is an intermediate component. Other configurations are possible, as will be further detailed below.

The particular embodiment of the gearbox <NUM> shown is selectively configurable between a speed change configuration where the output shaft <NUM> rotates faster than the input shaft <NUM>, and a direct drive configuration where the input and output shafts <NUM>, <NUM> rotate together as a single shaft.

As can be best seen in <FIG>, in order for the input and output shafts <NUM>, <NUM> (ring and sun gear <NUM>, <NUM>) to have the same direction of rotation, the planet gears include a first set of planet gears <NUM> in meshed engagement with the sun gear <NUM> and a second set of planet gears <NUM> in meshed engagement with the ring gear <NUM>, with corresponding planet gears <NUM>, <NUM> of the first and second sets being meshed together. Although each set of planet gears <NUM>, <NUM> is shown as including three planet gears, it is understood that alternately more or less planet gears may be provided.

Referring back to <FIG>, the gearbox <NUM> further includes a blocking member <NUM> which in an engaged position (<FIG>) impedes (i.e. prevents) the rotation of the planet gears <NUM>, <NUM> about their respective central axis C. In the embodiment shown, the blocking member <NUM> is a clutch which in the engaged position connects the carrier <NUM> (i.e., the intermediate component) to the output shaft <NUM> so that they are rotatable together at the same rotational speed. In the embodiment shown, the clutch <NUM> connects the carrier <NUM> and output shaft <NUM> by engaging a shaft of the carrier <NUM> and the output shaft <NUM>. Alternately, the clutch <NUM> can connect the carrier <NUM> and output shaft <NUM> by engaging or any other element connected to the carrier <NUM> and rotatable therewith at the same rotational speed and/or any other element connected to the output shaft <NUM> and rotatable therewith at the same rotational speed (including, but not limited to, the sun gear <NUM>). By forcing the carrier <NUM> and output shaft <NUM> to rotate at the same rotational speed, the clutch <NUM> prevents the planet gears <NUM>, <NUM> from rotating about their axes C. The clutch <NUM> also has a disengaged position (<FIG>) where it is disengaged from one or both of the carrier <NUM> and the output shaft <NUM>, so they can rotate relative to each other.

The gearbox also includes a brake <NUM> which in a brake position (<FIG>) is engaged the shaft of the carrier <NUM> (i.e., the intermediate component) to impede (i.e. prevent) its rotation. The brake <NUM> also has a release position (<FIG>) where it is disengaged from the carrier <NUM> to allow its rotation.

Is it understood that in the present specification, including claims, the term "clutch" is intended to include any mechanism for selectively engaging two rotatable components to each other so that they become rotatable together as a single component at a same rotational speed, while the term "brake" is intended to include any mechanism for selectively engaging a rotatable component to impede its rotation. Both terms are intended to include mechanisms that can be engaged automatically and mechanism that require actuation to be engaged. For example, the clutch <NUM> and brake <NUM> can be similar or identical mechanisms, differing in what they are interconnecting: two rotatable components for the clutch <NUM>, and a rotatable component to a fixed structure for the brake <NUM>.

As shown in <FIG>, in the speed change configuration, the clutch <NUM> is in its disengaged position, to allow the output shaft <NUM> and the carrier <NUM> to rotate with respect to each other. The brake <NUM> is in its brake position, engaged to the shaft of the carrier <NUM> to impede the rotation of the carrier <NUM>. The input shaft <NUM> rotates the ring gear <NUM>, which drives rotation of the planet gears <NUM>, <NUM> about their respective axis. The axes of the planet gears <NUM>, <NUM> remain stationary since the carrier <NUM> is not rotating. The rotating planet gears <NUM>, <NUM> drive rotation of the sun gear <NUM> and accordingly of the output shaft <NUM>. In this configuration, the gearbox <NUM> defines a speed ratio different than <NUM> between the rotational speeds of the input and output shafts <NUM>, <NUM>; as mentioned above, in the particular embodiment shown the gearbox <NUM> provides for a speed increase between the input and output shaft <NUM>, <NUM>. In other words, the ratio of the rotational speed of the input shaft <NUM> on the rotational speed of the output shaft <NUM>ωIN/ωOUT is smaller than <NUM>.

As shown in <FIG>, in the direct drive configuration, the brake <NUM> is in its release position, disengaged from the carrier <NUM> and thus allowing the carrier <NUM> to rotate. As the torque is applied to the ring gear <NUM> by the input shaft <NUM>, the carrier <NUM> and sun gear <NUM> both start to rotate about their central axis. Since the sun gear <NUM> is connected to the load and the carrier <NUM> is not, the carrier <NUM>, if free, would accelerate faster than the sun gear <NUM>. The clutch <NUM>, which in a particular embodiment is a one-way clutch, is in its engaged position and connects the output shaft <NUM> to the carrier <NUM> so that they are rotatable together at the same rotational speed. Since the sun gear <NUM> and carrier <NUM> are both connected to the output shaft <NUM> and rotate together at the same rotational speed due to the engaged clutch <NUM>, the planet gears <NUM>, <NUM> do not rotate about their respective axis. The ring gear <NUM>, carrier <NUM> and sun gear <NUM> thus all rotate at the same rotational speed, defining a direct drive between the input and output shafts <NUM>, <NUM> - the input and output shafts <NUM>, <NUM> rotate together as a single shaft. In other words, the ratio of the rotational speed of the input shaft <NUM> on the rotational speed of the output shaft <NUM>ωIN/ωOUT is <NUM>.

Referring now to <FIG>, <FIG> and <FIG>, another particular embodiment of the gearbox <NUM> is generally shown, where elements similar to that of the gearbox <NUM> of <FIG>, <FIG> and <FIG> are designated with the same reference numerals. Similarly to the gearbox <NUM>, the input shaft <NUM> is connected to the ring gear <NUM>. However, in this embodiment, the output shaft <NUM> is connected to the carrier <NUM>. The sun gear <NUM> is thus the intermediate component which is selectively engageable by the brake <NUM>, either directly or (as shown here) by having the brake <NUM> engaging a shaft connected to the sun gear <NUM>. The blocking member <NUM> is a clutch which in the engaged position connects the shaft of the sun gear <NUM> (i.e., the intermediate component) to the output shaft <NUM> so that the sun gear <NUM> and output shaft <NUM> are rotatable together at the same rotational speed. It is understood that the clutch <NUM> could alternately engage the sun gear <NUM> directly or any other component connected to the sun gear <NUM> and rotatable therewith, and/or any other component connected to the output shaft <NUM> and rotatable therewith (including, but not limited to, the carrier <NUM>).

This gearbox <NUM> is also selectively configurable between a speed change configuration where the output shaft <NUM> rotates faster than the input shaft <NUM>, and a direct drive configuration where the input and output shafts <NUM>, <NUM> rotate together as a single shaft. As can be best seen in <FIG>, in order for the input and output shafts <NUM>, <NUM> (ring gear <NUM> and carrier <NUM>) to have the same direction of rotation, the planet gears <NUM> are each in meshed engagement with both the sun gear <NUM> and the ring gear <NUM>. Although three planet gears <NUM> are shown, it is understood that alternately more or less planet gears may be provided.

As shown in <FIG>, in the speed change configuration, the clutch <NUM> is in its disengaged position, to allow the output shaft <NUM> and the sun gear <NUM> to rotate with respect to each other. The brake <NUM> is in its brake position, engaged to the shaft of the sun gear <NUM> to impede its rotation. The input shaft <NUM> rotates the ring gear <NUM>, which drives rotation of the planet gears <NUM> about their respective axis. The rotating planet gears <NUM> drive rotation of the carrier <NUM> and accordingly of the output shaft <NUM>. In this configuration, the gearbox <NUM> defines a speed ratio different than <NUM> between the rotational speeds of the input and output shafts <NUM>, <NUM>; as mentioned above, in the particular embodiment shown the gearbox <NUM> provides for a speed increase between the input and output shaft <NUM>, <NUM>, i.e., the ratio of the rotational speed of the input shaft <NUM> on the rotational speed of the output shaft <NUM>ωIN/ωOUT is smaller than <NUM>.

As shown in <FIG>, in the direct drive configuration, the brake <NUM> is in its release position, disengaged from the shaft of the sun gear <NUM> and thus allowing for the sun gear <NUM> to rotate. As the torque is applied to the ring gear <NUM> by the input shaft <NUM>, the carrier <NUM> and sun gear <NUM> both start to rotate about their central axis. Since the carrier <NUM> is connected to the load and the sun gear <NUM> is not, the sun gear <NUM>, if free, would accelerate faster than the carrier <NUM>. The clutch <NUM> is in its engaged position and connects the output shaft <NUM> to the shaft of the sun gear <NUM> so that they are rotatable together at the same rotational speed. Since the sun gear <NUM> and carrier <NUM> are both connected to the output shaft <NUM> and rotate together at the same rotational speed due to the engaged clutch <NUM>, the planet gears <NUM> do not rotate about their respective axis. The ring gear <NUM>, carrier <NUM> and sun gear <NUM> thus all rotate at the same rotational speed, defining a direct drive between the input and output shafts <NUM>, <NUM>. The input and output shafts <NUM>, <NUM> rotate together as a single shaft, i.e. the ratio of the rotational speed of the input shaft <NUM> on the rotational speed of the output shaft <NUM>ωIN/ωOUT is <NUM>.

Referring now to <FIG> and <FIG>, another particular embodiment of the gearbox <NUM> is generally shown, where elements similar to that of the gearboxes <NUM>, <NUM> are designated with the same reference numerals. Similarly to the gearbox <NUM>, the output shaft <NUM> is connected to the carrier <NUM>. However, in this embodiment, the input shaft <NUM> is connected to the sun gear <NUM>. The ring gear <NUM> is thus the intermediate component which is selectively engageable by the brake <NUM>. The blocking member <NUM> includes a second brake engaging the planet gears <NUM> to directly impede their rotation about their respective axis.

This gearbox <NUM> is selectively configurable between a speed change configuration where the output shaft <NUM> rotates more slowly than the input shaft <NUM>, and a direct drive configuration where the input and output shafts <NUM>, <NUM> rotate together as a single shaft. Similarly to the gearbox <NUM> and as illustrated in <FIG>, in order for the input and output shafts <NUM>, <NUM> (sun gear <NUM> and carrier <NUM>) to have the same direction of rotation, the planet gears <NUM> are each in meshed engagement with both the sun gear <NUM> and the ring gear <NUM>.

As shown in <FIG>, in the speed change configuration, the planet brake <NUM> is in its disengaged position, to allow the planet gears <NUM> to rotate about their respective axes. The ring gear brake <NUM> is in its brake position, engaged to the ring gear <NUM> to impede its rotation. The input shaft <NUM> rotates the sun gear <NUM>, which drives rotation of the planet gears <NUM> about their respective axis. The rotating planet gears <NUM> drive rotation of the carrier <NUM> and accordingly of the output shaft <NUM>. In this configuration, the gearbox <NUM> defines a speed ratio different than <NUM> between the rotational speeds of the input and output shafts <NUM>, <NUM>; as mentioned above, in the particular embodiment shown the gearbox <NUM> provides for a speed decrease between the input and output shaft <NUM>, <NUM>, i.e. the ratio of the rotational speed of the input shaft <NUM> on the rotational speed of the output shaft <NUM>ωIN/ωOUT is greater than <NUM>.

As shown in <FIG>, in the direct drive configuration, the ring gear brake <NUM> is in its release position, allowing for the ring gear <NUM> to rotate. As the torque is applied to the sun gear <NUM> by the input shaft <NUM>, the carrier <NUM> and ring gear <NUM> both start to rotate about their central axis. Since the carrier <NUM> is connected to the load and the ring gear <NUM> is not, the sun gear <NUM>, if free, would accelerate faster than the carrier <NUM>. The planet brake <NUM> is in its engaged position blocks rotation of the planet gears <NUM> about their respective axes, thus forcing the carrier <NUM> and ring gear <NUM> to rotate together at the same rotational speed. The ring gear <NUM>, carrier <NUM> and sun gear <NUM> thus all rotate at the same rotational speed, defining a direct drive between the input and output shafts <NUM>, <NUM>. The input and output shafts <NUM>, <NUM> rotate together as a single shaft, i.e. the ratio of the rotational speed of the input shaft <NUM> on the rotational speed of the output shaft <NUM>ωIN/ωOUT is <NUM>.

It is understood that the embodiments shown are exemplary only and that variations are possible. In a particular embodiment, various configurations may be obtained by having one of the ring gear <NUM>, sun gear <NUM> and carrier <NUM> as the input component connected to the input shaft <NUM>, another one of the ring gear <NUM>, sun gear <NUM> and carrier <NUM> as the output component connected to the output shaft <NUM>, and the remaining one of the ring gear <NUM>, sun gear <NUM> and carrier <NUM> as the intermediate component which is engaged by the brake <NUM>, <NUM>, <NUM> in the speed change configuration. The blocking member (e.g., clutch <NUM>, brake <NUM>) impedes rotation of the planet gears about their respective axis in the direct drive configuration, either by directly engaging the planet gears to impede their rotation, or by connecting the intermediate component with the output shaft <NUM> so that they rotate together at the same speed. Examples of such configurations are illustrated in the table below (where configuration <NUM> is the configuration of <FIG>, configuration <NUM> is the configuration of <FIG>, and configuration <NUM> is the configuration of <FIG>) :.

Other variations are also possible, including, but not limited to, having the blocking member configured as a brake engageable to the planet gears for configurations <NUM>-<NUM> and as a clutch to connect the intermediate and output components for configurations <NUM>-<NUM>. A single set of planet gears as shown in <FIG> or dual sets of planet gears as shown in <FIG> may be used with any of the configurations to obtain the desired relative direction of rotation of the input and output shafts <NUM>, <NUM>.

In the embodiment shown, the input and output shafts <NUM>, <NUM> are coaxial, and the gearbox <NUM> is configured to be used coaxially with the centerline of the gas turbine engine <NUM>.

Referring now to <FIG>, <FIG> and <FIG>, another particular embodiment of the gearbox <NUM> is generally shown, which drivingly engages input and output shafts <NUM>, <NUM>. In this embodiment, the gearbox <NUM> includes first and second sun gears <NUM>, <NUM> in driving engagement with each other through planet gears <NUM>, <NUM> supported by a rotatable carrier <NUM>. In the particular embodiment shown, the first sun gear <NUM> is the input component and is connected to the input shaft <NUM>, the second sun gear <NUM> is the output component and is connected to the output shaft <NUM>, and the carrier <NUM> is an intermediate component. Other configurations are possible, as will be further detailed below.

As can be best seen in <FIG>, in order for the input and output shafts <NUM>, <NUM> (sun gear <NUM>, <NUM>) to have the same direction of rotation, the planet gears include pairs of interconnected planet gears <NUM>, <NUM> rotatable together about a common axis. The pairs of interconnected planet gears <NUM>, <NUM> each include a smaller planet gear <NUM> meshed with the input sun gear <NUM> and a larger planet gear <NUM> meshed with the output sun gear <NUM>, and the input sun gear <NUM> is larger than the output sun gear <NUM>. This configuration allows for the speed change configuration to define a speed increase between the input and output shaft <NUM>, <NUM>; it is understood that the proportions of the gears <NUM>, <NUM>, <NUM>, <NUM> can be changed to have an embodiment where the speed change configuration allows for the output shaft <NUM> to rotate slower than the input shaft <NUM>. Although three pairs of planet gears <NUM>, <NUM> are shown, it is understood that alternately more or less pairs of planet gears may be provided.

Referring back to <FIG>, the gearbox <NUM> further includes a blocking member <NUM> which in an engaged position (<FIG>) impedes the rotation of the planet gears <NUM>, <NUM> about their respective central axis C. In the embodiment shown, the blocking member <NUM> is a clutch which in the engaged position connects the carrier <NUM> (i.e., the intermediate component) to the output shaft <NUM> so that they are rotatable together at the same rotational speed. In the embodiment shown, the clutch <NUM> connects the carrier <NUM> and the output shaft <NUM> by engaging a shaft of the carrier <NUM> and the output shaft <NUM>. Alternately, the clutch <NUM> can engage any other element connected to the carrier <NUM> and rotatable therewith at the same rotational speed and/or any other element connected to the output shaft <NUM> and rotatable therewith at the same rotational speed (including, but not limited to, the output sun gear <NUM>). By forcing the carrier <NUM> and output shaft <NUM> to rotate at the same rotational speed, the clutch <NUM> prevents the planet gears <NUM>, <NUM> from rotating about their axes C. The clutch <NUM> also has a disengaged position (<FIG>) where it is disengaged from one or both of the carrier <NUM> and the output shaft <NUM>, so they can rotate relative to each other.

The gearbox also includes a brake <NUM> which in a brake position (<FIG>) is engaged the shaft of the carrier <NUM> (i.e., the intermediate component) to impede its rotation. The brake <NUM> also has a release position (<FIG>) where it is disengaged from the carrier <NUM> to allow its rotation.

As shown in <FIG>, in the speed change configuration, the clutch <NUM> is in its disengaged position, to allow the output shaft <NUM> and the carrier <NUM> to rotate with respect to each other. The brake <NUM> is in its brake position, engaged to the shaft of the carrier <NUM> to impede the rotation of the carrier <NUM>. The input shaft <NUM> rotates the input sun gear <NUM>, which drives rotation of the planet gears <NUM>, <NUM> about their respective axis. The axes of the planet gears <NUM>, <NUM> remain stationary since the carrier <NUM> is not rotating. The rotating planet gears <NUM>, <NUM> drive rotation of the output sun gear <NUM> and accordingly of the output shaft <NUM>. In this configuration, the ratio of the rotational speed of the input shaft <NUM> on the rotational speed of the output shaft <NUM>ωIN/ωOUT is different from <NUM>.

As shown in <FIG>, in the direct drive configuration, the brake <NUM> is in its release position, disengaged from the carrier <NUM> and thus allowing for the carrier <NUM> to rotate. As the torque is applied to the input sun gear <NUM> by the input shaft <NUM>, the carrier <NUM> and output sun gear <NUM> both start to rotate about their central axis. Since the output sun gear <NUM> is connected to the load and the carrier <NUM> is not, the carrier <NUM>, if free, would accelerate faster than the output sun gear <NUM>. The clutch <NUM> is in its engaged position and connects the output shaft <NUM> to the carrier <NUM> so that they are rotatable together at the same rotational speed. Since the output sun gear <NUM> and carrier <NUM> are both connected to the output shaft <NUM> and rotate together at the same rotational speed due to the engaged clutch <NUM>, the planet gears <NUM>, <NUM> do not rotate about their respective axis. The ring gear <NUM>, carrier <NUM> and sun gear <NUM> thus all rotate at the same rotational speed, defining a direct drive between the input and output shafts <NUM>, <NUM> - the input and output shafts <NUM>, <NUM> rotate together as a single shaft, with the ratio of the rotational speed of the input shaft <NUM> on the rotational speed of the output shaft <NUM>ωIN/ωOUT being <NUM>.

In a particular embodiment, various configurations may be obtained by having one of the sun gears <NUM>, <NUM> and carrier <NUM> as the input component connected to the input shaft <NUM>, another one of the sun gears <NUM>, <NUM> and carrier <NUM> as the output component connected to the output shaft <NUM>, and the remaining one of the sun gears <NUM>, <NUM> and carrier <NUM> as the intermediate component which is engaged by the brake <NUM> in the speed change configuration. The blocking member (e.g., clutch <NUM>) impedes rotation of the planet gears about their respective axis in the direct drive configuration, either by directly engaging the planet gears to impede their rotation, or by connecting the intermediate component with the output shaft <NUM> so that they rotate together at the same speed. Similar configurations can be obtained with the two sun gears <NUM>, <NUM> being replaced by two ring gears. Examples of two sun gear configurations and of two ring gear configurations are illustrated in the table below (where configuration <NUM> is the configuration of <FIG>) :.

Other configurations are also possible, including, but not limited to, having the blocking member configured as a brake engageable to the planet gears for the configurations set forth above. For configurations where the relative direction of rotation of the input and output shafts <NUM>, <NUM> needs to change, each planet gear may be replaced by two meshed planet gears each meshed with a respective one of the sun/ring gears, similarly to the embodiment shown in <FIG>.

In a particular embodiment, failure, malfunction or wear of the brakes <NUM>, <NUM>, <NUM>, <NUM> can be detected by the control system of the engine <NUM> (electronic engine controller or EEC) through detection of the resulting increased rotational speed of the output shaft <NUM>. Malfunction or wear of the blocking member (e.g. clutch <NUM>, <NUM>, brake <NUM>) can be detected by the EEC through detection of the resulting inconsistencies between the rotational speed of the input shaft <NUM> and the rotational speeds of the output shaft <NUM>.

In a particular embodiment and in use, a rotor (e.g. boost compressor rotor <NUM>, propeller <NUM>) of the gas turbine engine <NUM> is thus rotated in accordance with the following. The input shaft <NUM> is rotated with a turbine section <NUM> of the gas turbine engine <NUM>, for example through a direct connection between one or more rotor(s) of the turbine section <NUM> and a gas turbine shaft (e.g. low pressure turbine rotor(s) <NUM> and shaft <NUM>) and a direct connection between the gas turbine shaft and the input shaft. One component between the sun/ring gears <NUM>, <NUM>, <NUM>, <NUM> and the carrier <NUM>, <NUM> is rotated with the input shaft <NUM> while another one of the sun/ring gears <NUM>, <NUM>, <NUM>, <NUM> and the carrier <NUM>, <NUM> is connected to the output shaft <NUM> and the remaining one of the sun/ring gears <NUM>, <NUM>, <NUM>, <NUM> and the carrier <NUM>, <NUM> defines the intermediate component.

When the direct drive configuration is selected, the rotation of the planet gears <NUM>, <NUM>, <NUM>, <NUM>, <NUM> is impeded while allowing rotation of the intermediate component so that the input and output shafts <NUM> rotate together as a single shaft at a same rotational speed. When the second configuration is selected, the rotation of the intermediate component is impeded while allowing rotation of the planet gears <NUM>, <NUM>, <NUM>, <NUM>, <NUM> so that the input and output shafts <NUM>, <NUM> rotate with different rotational speeds. The output shaft <NUM> is then driven by the input shaft <NUM> through the gearbox <NUM>, <NUM>, <NUM>, <NUM> in the selected configuration, and the rotor is rotated with the output shaft <NUM>.

Although the gearbox <NUM>, <NUM>, <NUM>, <NUM> has been described as part of a gas turbine engine <NUM>, it is understood that the gearbox <NUM>, <NUM>, <NUM>, <NUM> may alternately be used in other suitable applications where an alternate direct drive/speed change drive is beneficial.

Claim 1:
An aircraft gas turbine engine (<NUM>) comprising:
an input shaft (<NUM>) drivingly engaged to a turbine rotor (<NUM>);
an output shaft (<NUM>) drivingly engaged to a driveable rotor (<NUM>, <NUM>, <NUM>);
a gearbox (<NUM>, <NUM>, <NUM>, <NUM>) drivingly engaged with the input shaft (<NUM>) and the output shaft (<NUM>), the gearbox (<NUM>, <NUM>, <NUM>, <NUM>) further comprising:
a gear assembly including first and second gears (<NUM>, <NUM>, <NUM>, <NUM>) in driving engagement through planet gears (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>), the planet gears (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) rotatable about a respective central axis (C) and supported by a carrier (<NUM>, <NUM>), the assembly connected to the input and output shafts (<NUM>, <NUM>) and including at least one rotatable intermediate component (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>);
a brake (<NUM>, <NUM>, <NUM>, <NUM>) configured to selectively impede rotation of the intermediate component (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>); and
a blocking member (<NUM>, <NUM>, <NUM>) configured to selectively impede rotation of the planet gears (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) about their central axes (C);
wherein the gearbox (<NUM>, <NUM>, <NUM>, <NUM>) is selectively configurable between:
a speed change configuration wherein the input shaft (<NUM>) drivingly engages the output shaft (<NUM>), the brake (<NUM>, <NUM>, <NUM>, <NUM>) is configured to impede the rotation of the intermediate component (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) and the blocking member (<NUM>, <NUM>, <NUM>) is configured to allow the rotation of the planet gears (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) about their central axes to define a speed ratio different than <NUM> between rotational speeds of the input and output shafts (<NUM>, <NUM>); and a direct drive configuration wherein the input shaft (<NUM>) drivingly engages the output shaft (<NUM>), the brake (<NUM>, <NUM>, <NUM>, <NUM>) is configured to allow the rotation of the intermediate component (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) and the blocking member (<NUM>, <NUM>, <NUM>) is configured to impede the rotation of the planet gears (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) about the central axes so that the input and output shafts (<NUM>, <NUM>) are rotatable together at a same rotational speed; characterized in that
the driveable rotor is a compressor rotor (<NUM>,<NUM>) of the gas turbine engine compressor section (<NUM>), T
or the driveable rotor is a propeller (<NUM>).