Patent Description:
Electrical generators have both an operating temperature range (within which they can operate) and an optimum temperature range (within which they operate most efficiently). In use, electrical generators create heat due to inefficiencies in generation. Electrical generators are typically cooled by a circulating fluid to ensure that they are kept within their operating temperature range, and preferably kept within their optimum temperature range.

Aircraft propulsion systems typically comprise an engine, such as a turbine or jet engine, which may be connected to an electrical generator. The electrical generator is typically formed of an assembly of magnetic circuit components, comprising a rotor and a stator. Generally, aircraft engine electrical generators are cooled using a cooling fluid - typically oil for large aircraft generators - by spraying the cooling fluid out of jets in the rotor to cool the stator. As the rotor rotates, the fluid expelled from the rotor can leave the rotor at very high absolute velocities, carrying significant kinetic energy out of the rotor, which can reduce generator efficiency. To minimise this effect, the fluid is typically ejected backwards, that is, in the opposite direction to the rotation of the rotor, to counteract the circumferential or tangential component of the movement and thus minimise the absolute velocity of the fluid.

The mechanical power consumption of the rotor jets varies with the square of the jet velocity, and so it is also desirable to balance the jet velocity with the rotor velocity in order to minimise the mechanical power consumption of the rotor. In constant speed generators, this is easily achieved by adjusting the hole size and angle of the jets, and thus the mechanical power consumption of the rotor jets in constant speed generators is typically very low - a few hundred watts.

In variable frequency generators, where there is wide range of rotor speeds, the holes of the jets need to be large enough to evacuate a sufficient flow rate of the fluid from the rotor at its minimum speed, and hence minimum centrifugal pumping force. This sets the velocity of the jets relative to the rotor at a low value, due to the larger required diameter of the jets. This results in more residual kinetic energy being left in the fluid, as it leaves the rotor. Consequently, the mechanical power consumption of the rotor is very high, and in certain circumstances can be in the kilowatt range due to the rotor imparting large absolute velocities to the fluid.

Therefore, an improved way of regulating the distribution of fluid to rotor jets is required.

<CIT> relates to a variable speed rotary electric machine comprising a stator having windings and a rotor having windings mounted within the stator for rotation about an axis; a cooling fluid inlet into a first end region of the rotor; at least one first fluid duct having an inlet orifice in the first end region of the rotor and an outlet orifice arranged to discharge fluid onto a first region of the stator windings; and at least one second fluid duct having an inlet orifice in an opposite end region of the rotor and an outlet orifice arranged to discharge fluid onto a second region of the stator windings.

<CIT> relates to a rotor with a cooling mechanism in which a flow of cooling oil sent out from a shaft cooling-oil passage into the inside of an end plate is switched to a first cooling-oil passage or a second cooling-oil passage by using a bimetal wall, thereby effectively cooling a motor-generator without increasing the size of the motor-generator.

<CIT> relates to a method of cooling a rotor wherein, when the rotor rotating speed is low, the number of communication passages that are open when cooling oil flows into a cooling passage from a refrigerant introduction portion into a cooling passage increases.

<CIT> relates to a motor drive unit for a vehicle which suitably distributes a lubricant amount supplied to a motor part and a lubricant amount supplied to a reduction part by using an on-off valve that closes by receiving the centrifugal force or the hydraulic pressure in the rotor oil passage; when the motor rotational speed increases, the on-off valve is set in the closing direction, and when the motor rotational speed decreases, the on-off valve It is set in the opening direction.

A first aspect of the present invention provides a generator arranged to be driven by an aircraft engine, the generator comprising a rotor, the rotor comprising an inlet for receiving a fluid, a plurality of outlets configured to release the fluid from a radially outer region of the rotor, and a fluid distribution arrangement arranged to direct fluid from the inlet to one or more of the plurality of outlets, wherein the fluid distribution arrangement comprises a cavity at a first end of the rotor for receiving fluid from the rotor inlet, and a plurality of inlet openings within the cavity for directing fluid to the plurality of outlets via respective fluid paths, wherein the fluid distribution arrangement is configured to selectively distribute fluid to one or more of the plurality of outlets in dependence on an operational parameter of the rotor, wherein fluid is distributed to a first subset of the plurality of outlets via a first set of inlet openings within the cavity when the operational parameter is above a first threshold value, wherein fluid is further distributed to a second subset of the plurality of outlets) via a second set of inlet openings within the cavity when the operational parameter is below the first threshold value, and wherein the first subset of the plurality of outlets are arranged at different circumferential positions on the rotor to the second subset of the plurality of outlets, and the generator further comprising a restrictor configured to provide a constant flow rate of fluid at the rotor inlet, independent of a velocity at which the rotor is rotating, wherein the constant flow rate of fluid received at the rotor inlet is divided between the first subset of the plurality of outlets, or the first and second subset of the plurality of outlets, such that the velocity at which the fluid is released from the plurality of outlets varies with the operational parameter.

By selectively distributing fluid to the fluid outlets of a fluid, the rate at which fluid is ejected from the rotor can be regulated in order to minimise impact of the fluid on the stator, as well as minimising the mechanical power consumption by the rotor.

The fluid distribution arrangement may then be configured to distribute the fluid to the first subset of outlets when the operational parameter of the rotor is within a first range of values, and distribute the fluid to the second set of outlets when the operational parameter of the rotor is within a second range of values.

The fluid distribution arrangement is preferably configured to distribute the fluid to both the first and second sets of outlets when the operational parameter of the rotor is within the second range of values.

The first range of values may be above a first threshold value, and the second range of values may be below the first threshold value. The second range of values may also be below a different threshold value.

The fluid distribution arrangement may also be configured to distribute the fluid to a third set of outlets when the operational parameter of the rotor is within a third range of values. The third range of values may be below a second threshold value, wherein the second threshold value is below the first threshold value.

It will be appreciated that the fluid distribution arrangement may have any number of further sets of outlets, each set of outlets coming into operation when the operational parameter is in a particular range of values. For example, the fluid distribution arrangement may comprise an outlet for each magnetic pole on the rotor.

The operational parameter of the rotor may be the rotational velocity of the rotor. For example, the fluid distribution arrangement may be configured to distribute the fluid to the first set of outlets when the rotational velocity is above a threshold velocity, and distribute the fluid to the first and second set of outlets when the rotational velocity is below a threshold velocity.

For example, the threshold velocity may be set at the cruising speed for the particular generator. In a four pole variable frequency generator, the cruise speed may correspond to a rotational velocity of approximately <NUM>,<NUM> to <NUM>,<NUM> RPM. In a six pole variable frequency generator, the cruise speed may correspond to a rotational velocity of approximately <NUM>,<NUM> RPM. Setting the threshold velocity so as to correspond to the cruising speed of the generator allows the outlets to be optimised for efficiency at this speed, with the second set of outlets only being used when the generator is operating below this speed (for example, take-off, landing, ground taxiing), which is generally a much smaller proportion of the total time an aircraft is in operation. Where a third set of outlets are used, said third set may come into operation a little below cruise speed.

As such, for a four pole variable frequency generator, the first range of values may be a velocity of <NUM>,<NUM> RPM and above, and the second range of values may be a velocity up to <NUM>,<NUM> RPM. Where the fluid distribution arrangement comprises a third set of outlets, the second range of values may be a velocity of around <NUM>,<NUM> RPM up to <NUM>,<NUM> RPM, and the third range of values may be a velocity up to <NUM>,<NUM> RPM.

For a six pole variable frequency generator, the first range of values may be a velocity of <NUM>,<NUM> RPM and above, and the second range of values may be a velocity up to <NUM>,<NUM> RPM. Where the fluid distribution arrangement comprises a third set of outlets, the second range of values may be a velocity of around <NUM>,<NUM> RPM up to <NUM>,<NUM> RPM, and the third range of values may be a velocity up to <NUM>,<NUM> RPM.

As noted above, the fluid distribution arrangement may have a number of further sets of outlets which come into operation each time the rotational velocity drops below a certain value, such that as the speed decreases, the number of outlets to which fluid is being distributed increases.

As such, the rate at which fluid is released from the outlets can be matched with the rate at which the rotor is rotating. This helps to minimise the impact on the stator by the fluid as it is released at all speeds of the rotor, as well as minimise the mechanical power consumption of the rotor.

In cases where the plurality of outlets comprises a first set of outlets, and a second set of outlets, the fluid distribution arrangement may further comprise a first set of fluid paths configured to direct fluid to the first set of outlets, and a second set of fluid paths configured to direct fluid to the second set of outlets.

The first set of fluid paths may comprise the first set of inlet openings arranged at a first radial position within the cavity, and the second set of fluid paths may comprise the second set of inlet openings arranged at a second radial position within the cavity.

Preferably, the radial distance of the first set of inlet openings from the axis of rotation of the rotor is greater than the radial distance of the second set of inlet openings from the axis of rotation of the rotor. Consequently, when the rotor is moving at high rotational speeds, the centrifugal forces generated by the rotor generate increased outward radial pressure driving the fluid out radially from the rotor through the outlets faster than it can be replenished. This causes the equilibrium position which the surface of the fluid reaches in the cavity to move radially outward beyond the second set of inlet openings such that the fluid only flows into the first set of inlet openings, and thus fluid is only fed to the first set of outlets. As only a subset of the outlets are being fed with fluid, this will increase the speed at which fluid leaves the rotor, reducing the net velocity of the fluid and hence power consumption. When the rotor is moving at slower speeds, the centrifugal forces are weaker and so the fluid will also reach the second set of inlet openings. As such, fluid is fed to both the first and second set of outlets, thereby reducing the rate at which fluid is released from the outlets to better match the rotational velocity of the rotor.

The plurality of outlets may comprise at least one jet configured to eject fluid from the rotor. Each outlet may comprise a jet.

The rotor may comprise a plurality of inlets for receiving fluid.

A second aspect of the present invention provides an aircraft engine comprising a generator as described above.

A third aspect of the present invention provides an aircraft comprising an aircraft engine as described above.

Further features and advantages of the present invention will become apparent from the following description of embodiments thereof, presented by way of example only, and by reference to the drawings, wherein:.

<FIG> illustrates an end of a rotor <NUM> according to the present invention. The rotor <NUM> may be provided in a generator commonly driven by, and in some cases used to drive, i.e. start, an aircraft engine. The rotor <NUM> is arranged to rotate around a central axis <NUM>, for example, in the direction of arrow A. The rotor <NUM> comprises a plurality of jets 104a-d, or some other fluid expulsion means, positioned around the circumference of the rotor <NUM>, generally at or adjacent its outer circumferential surface. Fluid is fed into the jets 104a-d via a number of distribution channels <NUM>, which extend longitudinally along the rotor <NUM>, as shown in more detail by <FIG>. In the illustrated example, there are shown four jets 104a-d and four respective distribution channels <NUM>, however, the rotor <NUM> may comprise two or more jets 104a-d and respective distribution channels <NUM> according to the present invention. It should be appreciated that each distribution channel <NUM> may distribute fluid to a plurality of jets 104a-d, which may be disposed in an array extending along the rotor <NUM> in an axial direction. In this respect, the plurality of jets 104a-d could be located anywhere along the length of the rotor <NUM>, but in most cases would be located toward the ends of the rotor <NUM>, outside of the stator core (not shown) within which the rotor <NUM> is located, since generally it is undesirable to introduce coolant into the air gap between the rotor <NUM> and the stator. In use, the jets 104a-d are arranged to release a fluid in order to cool the stator (not shown) arranged outside the rotor <NUM>. The fluid may be any suitable coolant fluid, for example, oil that has been cooled by a cooling system.

As discussed above, the jets 104a-d are configured so that fluid is released from the rotor <NUM> at an angle, for example, in the opposite direction to the rotation of the rotor <NUM>. For example, in <FIG>, the jets 104a, d are shown as extending from the distribution channel <NUM> at an angle to the radius of the rotor <NUM> (i.e. towards the page). Similarly, in <FIG>, one jet 104c is shown as extending from the distribution channel <NUM> at an angle to the radius of the rotor <NUM> (i.e. away the page), whilst only the jet inlet 104d' in the distribution channel <NUM> can be seen for the specific portion of the rotor <NUM> shown.

As the rotor <NUM> rotates, the fluid is ejected from the jets 104a-d in a non-radial direction, at a non-zero angle to a tangent of the rotor <NUM>, and oriented away from the direction of rotation of the rotor <NUM>, for example, in the direction of arrow B. This partially counteracts the radial component of the rotor velocity, illustrated by arrow C, so as to minimise the absolute velocity of the fluid, illustrated by arrow D, as it is released from the rotor <NUM>. This reduction in the absolute velocity imparted to the fluid leaving the rotor <NUM> helps to reduce the amount of kinetic energy of the rotor <NUM> being lost to the fluid as it leaves the rotor <NUM>, thus minimising the mechanical power consumption by the rotor <NUM>.

As discussed above, in variable frequency generators, it is difficult to vary the jet velocity in order to counteract the continuously varying rotational velocity of the rotor <NUM>. As such, the present invention seeks to provide a way of selectively distributing the fluid to the jets 104a-d in dependence on the rotational velocity of the rotor <NUM>.

One solution to this, not representing the invention, would be for the jet nozzle to dilate at lower speeds, enabling the fluid velocity to be varied in dependence on the rotational speed of the rotor <NUM>. This can help to minimise power consumption. However, in practice, it is likely that the large centrifugal forces generated at high rotational speeds of the rotor <NUM>, in particular in aircraft engine applications, would be likely to damage or render inoperable any such mechanism. An alternative solution, not representing the invention, would be to use a valve mechanism to selectively turn one or more of the jets 104a-d on and off to match the fluid velocity of the operating jets 104a-d to the rotational velocity of the rotor <NUM>. Fewer jets 104a-d operating will result in more fluid flowing through those still in operation, thereby raising the velocity of those jets 104a-d.

However, this is again difficult to put into practice in generators where the rotor speed is constantly changing. Operating a reduced number of jets104 a-d at higher rotational speeds of the rotor <NUM> can therefore be beneficial. However, creating valve mechanisms which can be operated on the rotor <NUM> and which can withstand the high centrifugal forces is challenging.

A further solution is illustrated by <FIG>, in which the rotor <NUM> is provided with an end plate <NUM> which is configured to selectively direct fluid into the jets 104a-d. As shown in <FIG>, the rotor <NUM> comprises an end cap <NUM> and a drive shaft connection <NUM>, which together with the end plate <NUM> enclose a cavity <NUM> within the end of the rotor <NUM>. As such, the end plate <NUM> defines a longitudinally inner wall of the cavity <NUM>. The end cap <NUM> and drive shaft connection <NUM> arrangement define a longitudinally outer wall of the cavity <NUM>, and the outer skirt or sleeve <NUM> of the rotor <NUM> defines a radial wall of the cavity <NUM>.

In the illustrated embodiment, fluid is fed into the cavity <NUM> via one or more inlets <NUM>, which may be in fluid communication with at least one channel <NUM> running through the interior of the rotor <NUM>. However, it will be appreciated that fluid may be fed into the cavity <NUM> from another direction, for example, via the end cap <NUM>.

Fluid in the cavity <NUM> is fed to the distribution channels <NUM> via a number of respective fluid paths <NUM>, <NUM>. Each fluid path <NUM>, <NUM> is provided with an inlet opening <NUM>, <NUM> within the cavity <NUM> and at least one outlet 104a-d, which is in fluid communication with the inlet opening <NUM>, <NUM> via one of the distribution channels <NUM>. In the illustrated embodiment, the fluid paths <NUM>, <NUM> are shown as substantially radially oriented standpipes, however, it will be appreciated that any suitable fluid conduit may be used and its path from its respective radially inwardly located inlet <NUM>, <NUM> to its respective radially outwardly located outlet or outlets 104a-d may not be in the form illustrated.

In prior art systems, the fluid paths feeding the distribution channels <NUM> and jets 104a-d are fed from a point that is equidistant from the rotational axis <NUM> to ensure that all jets 104a-d are given an equal flow rate. However, in variable frequency generators, this can result in very high mechanical power consumption by the rotor <NUM> if sufficient flow rates at low rotational speeds are to be achieved, as discussed above. In embodiments of the present invention, the end plate <NUM> comprises a first set of fluid paths <NUM> and a second set of fluid paths <NUM>, wherein the openings <NUM> of the first set of fluid paths <NUM> are further away from the rotational axis <NUM> than the openings <NUM> of the second set of fluid paths <NUM>. By placing the openings <NUM> of the fluid paths <NUM>, <NUM> at different radial positions on the end plate <NUM>, fluid is distributed to the fluid paths <NUM>, <NUM> in dependence on the rotational velocity of the rotor <NUM>. This is described in further detail in the following.

In the illustrated embodiment, the first set of fluid paths <NUM> are shorter in a radial direction than the second set of fluid paths <NUM> in order to provide the openings <NUM> at different radial positions, with all jets 104a-d being at the same radial position. However, in an alternative configuration, the first set of fluid paths <NUM> and second set of fluid paths <NUM> may be the same length, but with the first set of fluid paths <NUM> instead being set further radially outward than the second set of fluid paths <NUM> to again provide the openings <NUM> at different radial positions.

Generators are typically designed with a restrictor (not shown) on the rotor fluid inlet (not shown) to ensure that the rotor <NUM> receives a constant flow rate of fluid independent of the speed at which the rotor <NUM> is rotating. In the illustrated embodiment, four fluid paths <NUM>, <NUM> are used as as flow dividers, each of which is only partially filled with fluid. The depth of fill will vary with speed, and hence centrifugal pressure, to ensure that a constant jet outlet pressure and hence flow rate is maintained, in order to match the flow into and out of the fluid path <NUM>, <NUM> and jet 104a-d arrangement. As such, the system will use the first set of fluid paths <NUM> as flow dividers until each is fully filled. Once the first set of fluid paths <NUM> are filled, the fluid depth in the cavity <NUM> will increase slightly until the second set of fluid paths <NUM> becomes available to act as an overflow. As the speed continues to drop, the overflow fluid paths <NUM> keep the depth of fluid constant but the centrifugal pressure will drop off, causing the jet velocity in the first set of fluid paths <NUM> to decrease, diverting more of the flow to the second set of fluid paths <NUM>.

When the generator is rotating at high speed, for example, above cruising speed, it will be appreciated that the fluid creates an effective surface within the cavity <NUM>, which is substantially concentric with the outer surface of the generator and cavity <NUM>. As the speed of the rotor <NUM> increases, the centrifugal force created by the rotor <NUM> increases the centrifugal pressure in the cavity <NUM>, which in turn causes the equilibrium position which the surface of the fluid reaches in the cavity <NUM> to move outwards in the radial direction, creating an air bubble in the centre of the cavity <NUM>, as illustrated by circle <NUM> on <FIG>. At sufficiently high speeds, for example, at cruise speed, all of the fluid exits the cavity <NUM> down the first set of fluid paths <NUM> having an inlet opening <NUM> further away from the rotational axis <NUM> and into the jets 104a-b of these shorter fluid paths <NUM>. That is to say, the fluid surface is forced beyond the inlet openings <NUM> of the longer fluid paths <NUM> such that no fluid is fed to the respective jets 104c-d. As only half of the jets 104a-b are being fed with fluid, this will double the speed at which fluid leaves the rotor <NUM>, reducing the net velocity of the fluid and hence power consumption. As will be appreciated, different ratios of overall outlet area between the respective sets of jets 104a-b, 104c-d can be provided to provided differing velocity ratios of the fluid in dependence on whether one or more sets of jets 104a-d are being fed or not.

As the rotor speed is reduced, for example, below cruising speed, the centrifugal force and hence the centrifugal pressure will decrease, thereby reducing the velocity of the jets 104a-b. As the jet velocity decreases, the depth of fill in the first set of fluid paths <NUM> increases until they are completely full, at which point the depth of fluid in the cavity <NUM> will start to increase. As such, the concentric fluid surface created in the cavity <NUM> will move inwardly in the radial direction, reducing the size of the central air bubble in the cavity, as illustrated by circle <NUM> on <FIG>, such that fluid will also reach the openings <NUM> of the longer fluid paths <NUM> and thus be distributed to all four jets, or sets of jets 104a-d. This will reduce the flow rate required through each jet 104a-d in order to maintain a sufficient flow through the rotor <NUM>, thus enable effective cooling of the rotor <NUM> even at the reduced levels of pressure available required to drive the fluid out at lower speeds. This can help to ensure that the velocity at which fluid is expelled is better matched to the rotational velocity of the rotor <NUM> at both higher and lower rotational speeds.

As one example, the fluid paths <NUM>, <NUM> may be configured such that the longer fluid paths <NUM> only come into operation when the rotor <NUM> is rotating below cruising speed. As such, the jets 104a-b are optimised for efficiency at cruising speed, with the outlets 104c-d coupled to the longer fluid paths <NUM> only being used when the rotor <NUM> is operating below this speed (for example, take-off, landing, ground taxiing), which is generally a much smaller proportion of the total time an aircraft is in operation.

In the illustrated example, the rotor <NUM> comprises two sets of jets 104a-d, however, it will be appreciated that the rotor <NUM> may comprises a number of further sets of jets, each being configured to come into operation at different rotational speeds. For example, the rotor <NUM> may comprise a third set of jets connected to a fluid path having an inlet opening that is closer to the rotational axis <NUM> than that of the first and second sets of fluid paths <NUM>, <NUM>.

The difference in the distances from the rotational axis <NUM> to the shorter fluid paths <NUM> and the longer fluid paths <NUM> is relatively small, for example, between <NUM> and <NUM> in some examples, which can ensure that the longer fluid paths <NUM> come into operation almost immediately after the shorter fluid paths <NUM> are fully flooded.

In the illustrated embodiment, four fluid paths <NUM>, <NUM> are shown, however, it will be appreciated that any number of fluid paths may be provided as long as there are at least two sets of fluid paths at two or more different radial positions.

Preferably, the diameter of the jets 104a-d are tuned to match the rate of fluid flow and the depth of the fluid paths <NUM>, <NUM>. For example, , if the hole size of the jets 104a-d is not properly configured to achieve the desired flow from the first and second sets of jets 104a-d, the longer fluid paths <NUM> could come into operation only at or near the minimum speed of the generator, and thus the benefits realised may be minimal. One way to solve this is to reduce the hole diameter of the jets 104a-d slightly, which would also further optimize the jet power consumption. An alternative solution would be to shorten the fluid paths <NUM>, <NUM>, in which case the flow path from the rotor windings to the cavity <NUM> via the inlet <NUM> or inlets needs to be at a point that is radially inwards of the inner most part of the rotor windings to ensure that the windings remain fully submerged in fluid, as shown by fluid level <NUM> in <FIG>. Such an arrangement would therefore act as a weir.

One alternative method of selectively directing fluid to different sets of jets may be to provide at least two sets of jets, each set of jets being fed fluid by a different source. In this respect, the rotor <NUM> may have two or more concentric fluid feeds through the middle <NUM> of the rotor <NUM> and routed to different sets of jets by a valve means located outside of the rotor <NUM>, and thus protected from the centrifugal forces. This routing may be achieved, for example, using a solenoid valve actuated by a control unit measuring the electrical frequency of the generator.

Alternatively, the fluid may be selectively directed to different sets of jets by way of valve means located between the fluid inlet or inlets and the distribution channel of at least one set of jets, whilst at least one other set of jets is continuously fed fluid at all times.

<FIG> illustrate one example valve mechanism <NUM> located between a distribution channel <NUM> of one or more jets and a fluid path <NUM> from the inlet or inlets of the rotor. The valve <NUM> comprises a moveable body <NUM> that is biased towards an open position, as shown in <FIG>, by a biasing means, shown in this example as a spring <NUM>. At high speeds, the centrifugal forces act against the spring <NUM> and push the body <NUM> into a closed position, as shown in <FIG>, such that it blocks the flow of fluid from the inlet fluid path <NUM> to the distribution channel <NUM>. As such, fluid may only be directed to the jet or jets that are not provided with any sort of valve mechanism. As the speed of the rotor decreases, the centrifugal force acting against the valve <NUM> decreases. The force of the spring <NUM> will eventually overcome the centrifugal force, thereby pushing the body <NUM> back towards the open position shown in <FIG> such that fluid then flows from the inlet fluid path <NUM> to the distribution channel <NUM>. Consequently, fluid is directed to all sets of jets in order to compensate for the reduction in rotational velocity.

In certain circumstances, it may be desirable to control the flow to one or more of the sets of jets in dependence on another functional parameter of the rotor, such as a temperature. At low speeds, the rotor may generate more heat than at higher rotational speeds, due to increased currents being required to provide a same power output at relatively lower rotational speeds. <FIG> illustrate a second example valve mechanism <NUM> located between a distribution channel <NUM> of one or more jets and a fluid path <NUM> from the inlet or inlets of the rotor, wherein the valve <NUM> is temperature actuated. The valve <NUM> comprises a moveable body <NUM> comprising a cavity <NUM> between first and second opposing walls <NUM>, <NUM>. The valve <NUM> may comprise a biasing means, shown in this example as a spring <NUM>, which acts upon the second wall <NUM> so as to bias the body <NUM> towards a closed positon, as shown in <FIG>. The valve <NUM> comprises a thermally expanding material <NUM> such as a wax <NUM> adjacent to the first wall <NUM> of the moveable body <NUM>.

The resulting increase in temperature in the rotor can be used to actuate the valve mechanism of <FIG> by causing the volume of the wax <NUM> to increase. The wax <NUM> consequently pushes against the first wall <NUM> so as to compress the spring <NUM>, and thereby pushes the body <NUM> into an open position, as shown in <FIG>, such that fluid then flows from the inlet fluid path <NUM> to the distribution channel <NUM>. Consequently, fluid is directed to one or more additional sets of jets through the valve in order to compensate for the increase in temperature of the rotor.

As the speed increases, or as more fluid flows through the rotor, the temperature of the rotor may decrease and so the wax <NUM> may return to its original volume, thereby allowing the spring <NUM> to bias the body <NUM> into the closed position shown in <FIG>. As such, in this case, fluid may be only directed to the jet or jets that are not closed off by any valve mechanism.

Claim 1:
A generator arranged to be driven by an aircraft engine, the generator comprising:
a rotor (<NUM>), comprising:
a rotor inlet (<NUM>) for receiving a fluid;
a plurality of outlets (104a-d) configured to release the fluid from a radially outer region of the rotor (<NUM>); and
a fluid distribution arrangement arranged to direct fluid from the rotor inlet (<NUM>) to one or more of the plurality of outlets (104a-d), wherein the fluid distribution arrangement comprises a cavity (<NUM>) at a first end of the rotor (<NUM>) for receiving fluid from the rotor inlet (<NUM>), and a plurality of inlet openings (<NUM>, <NUM>) within the cavity (<NUM>) for directing fluid to the plurality of outlets (104a-d) via respective fluid paths (<NUM>, <NUM>);
wherein the fluid distribution arrangement is configured to selectively distribute fluid to the plurality of outlets (104a-d) in dependence on an operational parameter of the rotor (<NUM>), wherein fluid is distributed to a first subset of the plurality of outlets (104a-b) via a first set of inlet openings (<NUM>) within the cavity (<NUM>) when the operational parameter is above a first threshold value, wherein fluid is further distributed to a second subset of the plurality of outlets (104c-d) via a second set of inlet openings (<NUM>) within the cavity (<NUM>) when the operational parameter is below the first threshold value, and wherein the first subset of the plurality of outlets (104a-b) are arranged at different circumferential positions on the rotor (<NUM>) to the second subset of the plurality of outlets (104c-d); and
the generator further comprising a restrictor configured to provide a constant flow rate of fluid at the rotor inlet (<NUM>), independent of a velocity at which the rotor (<NUM>) is rotating, wherein the constant flow rate of fluid received at the rotor inlet (<NUM>) is divided between the first subset of the plurality of outlets (104a-b), or the first and second subset of the plurality of outlets (104a-b), such that the velocity at which the fluid is released from the plurality of outlets (104a-d) varies with the operational parameter.