GB2610218A

GB2610218A - Fan for a generator

Info

Publication number: GB2610218A
Application number: GB2112302.1A
Authority: GB
Inventors: Zhihua Yang; Jinjin Jian; Patil Sunil; Qianyun Chen; Guoqing Hu; Dong Hua
Original assignee: Cummins Generator Technologies Ltd
Current assignee: Cummins Generator Technologies Ltd
Priority date: 2021-08-27
Filing date: 2021-08-27
Publication date: 2023-03-01
Also published as: GB202112302D0

Abstract

A fan is disclosed for use with a generator which is arranged to be coupled to a prime mover via a coupling disc. The fan 40 comprises a plurality of fan blades 42 and a backplate 46. The backplate comprises a plurality of recesses 50 which allow insertion of a tool for connecting the coupling disc to the prime mover. This may allow the amount of space between the fan and the coupling disc to be reduced, while still allowing the coupling disc to be connected to the prime mover.

Description

FAN FOR A GENERATOR

The present invention relates to a fan for a generator, and in particular a fan for use with a generator in a power generation system.

Power generation systems typically comprise a prime mover such as an internal combustion engine connected to a generator. In operation the prime mover is used to drive the generator, in order to generate the output power. This is achieved by mechanically connecting rotating parts of the prime mover and the generator. An adaptor may be used to connect non-rotating parts, in order to prevent movement between the prime mover and the generator.

When a generator is in operation, currents passing through stator and/or rotor windings, as well as other factors such as friction and windage losses, may cause it to heat up. Therefore, many generators require some form of cooling. This may be achieved by providing a fan for forcing airflow through the machine. The cooling fan is typically mounted on the generator shaft, inside the adaptor. Airflow through the machine is in a generally axial direction, with the main paths for the airflow being through a rotor/stator airgap and through a stator/frame airgap.

Generators for power generation systems may be supplied with a coupling disc for coupling the generator to a prime mover. The coupling disc is typically provided on the generator shaft and is arranged to be bolted to a rotating component such as an engine flywheel. Openings or windows are provided in the adaptor to allow an operator access to the coupling disc so as to bolt the coupling disc to the flywheel. Typically, a fastening tool such as a socket wrench is used to tighten the bolts. The openings in the adaptor also allow airflow to exit the machine.

It is generally desirable to desirable to minimise the amount of space occupied by a generator for a given power output. In particular, it may be desirable to minimise the axial length of the generator to reduce the amount of space required for shipping and to allow the generator to be used in applications with space constraints.

In existing generator designs, sufficient clearance needs to be provided between the fan and the coupling disc to allow an operator to connect the disc to the prime mover. This tends to result in an adaptor with a relatively large axial length, which adds to the overall length of the generator. Attempts to reduce the axial length of the adaptor have typically involved the use of a smaller fan. However, this may reduce the thermal performance of the generator.

WO 2021/023985, the subject matter of which is incorporated herein by reference, discloses a fan for an electrical generator, the fan comprising a plurality of fan blades and an inlet ring. The inlet ring is angled so as to direct airflow from the stator/frame airgap towards stator end windings.

GB 2590610 A, the subject matter of which is incorporated herein by reference, discloses a fan for a rotating electrical machine where the fan is mounted to a plurality of field winding support bars which extend axially through the rotor.

The arrangements disclosed in WO 2021/023985 and GB 2590610 may help to improve the cooling efficiency of the generator using fewer parts and may allow a more compact design than with previous approaches. However, these arrangements may still require a relatively long adaptor to facilitate connection of the generator to the prime mover.

It would therefore be desirable to provide a generator design in which the overall length of the generator can be minimized, without comprising thermal performance. In other situations, it may be desirable to enhance thermal performance by using larger fan blades, without the need to increase the length of the adaptor.

According to one aspect of the present invention there is provided a fan for a generator, wherein the generator is arranged to be coupled to a prime mover via a coupling disc, the fan comprising: a plurality of fan blades; and a backplate, wherein the backplate comprises a plurality of recesses which allow insertion of a tool for connecting the coupling disc to the prime mover.

The present invention may provide the advantage that, by providing the back plate with a plurality of recesses which allow insertion of a tool for connecting the coupling disc to the prime mover, it may be possible to reduce the amount of space between the fan and the coupling disc, while still allowing the coupling disc to be connected to the prime mover. This may allow the axial length of the adaptor to be reduced, thereby reducing the overall length of the generator.

Furthermore, it has been found that this can be achieved with significantly less impact on the thermal performance of the generator than if the length of the fan were reduced. In addition, the amount of material required for the adaptor and the generator shaft may be reduced, leading to cost savings. Alternatively, a larger fan could be provided for the same sized adaptor, thereby improving thermal performance.

The fan is preferably mounted on a generator shaft. The fan may be a centrifugal fan which may be arranged to dispel air radially outwards under centrifugal force as the fan rotates. Thus, the fan blades may be centrifugal blades, which may be arranged to dispel air radially outwards under centrifugal force. Preferably the fan blades are connected to the backplate. However, if desired, other types of fan could be used instead.

The backplate is preferably arranged to help direct airflow from a substantially axial direction to a substantially radial direction. This may allow airflow which has passed through the generator in a generally axial direction to be exhausted in a generally radial direction, for example, through openings in an adaptor.

The backplate may be substantially annular. For example, the backplate may be in the form of a substantially annular disc with a plurality of protrusions extending radially outwards. In this case each protrusion may be formed between two adjacent recesses.

Preferably the recesses are open on a radially outwards periphery of the backplate. This may allow radial insertion of the tool into a recess when the coupling disc is being connected to or disconnected from the prime mover. Thus, the fan may be arranged such that the tool can be inserted a radial direction into a recess.

Preferably the recesses allow the tool to pass through them in an axial direction.

For example, the recesses may be sized and positioned such that a rotating part of a tool, such as the socket part of a socket wrench, can pass through them in an axial direction. This can allow rotation of the tool in order to tighten or loosen bolts which are used to connect the coupling disc to the prime mover.

Preferably each recess is located between two adjacent fan blades in a circumferential direction. This can allow rotation of the socket wrench between the two fan blades while tightening or loosening bolts which connect the coupling disc to the prime mover.

Preferably the fan further comprises a front plate connected to the fan blades. In this case, the fan blades may be connected between the front plate and the backplate. The front plate may be in the form of an annular disc. The front plate may function as an inlet ring and may help to guide airflow into the fan. Thus, the front plate may help to direct airflow towards the fan blades. The front plate may also help to prevent exhaust air from re-entering the air intake during operation.

In one embodiment, the front plate lies in a plane which is substantially perpendicular to the axis of rotation. In other embodiments, the front plate may be angled (have a non-zero angle) with respect to the axis of rotation. This may allow the front plate to divert airflow exiting the generator in a substantially axial direction to a more radial direction. This may help with cooling of the machine, for example, by diverting airflow more towards stator end windings.

A notch may be provided in the front plate at a location where a fan blade meets the front plate. Preferably a notch is provided on each side of the front plate where it meets a fan blade. The notches may reduce the stress at the junction of the fan blade and the front plate during operation. This may help to avoid defects occurring at the junction during use, without the need to add additional material to strengthen the junction.

Preferably the front plate and the backplate are substantially concentric and spaced apart axially. Preferably the fan is arranged such that the tool can be inserted into the fan in a radial direction through a gap between the front plate and the backplate.

Preferably the backplate is located radially inwards of the front plate. Preferably, the outer periphery of the backplate is substantially aligned with the inner periphery of the front plate. For example, when viewed axially, there may be a relatively small annular gap between front plate and the backplate, or the outer periphery of the backplate may be approximately aligned with the inner periphery of the front plate, or there may be some overlap between the outer periphery of the backplate and the inner periphery of the front plate. This may help to ensure that there is sufficient space for connecting the coupling disc to the prime mover, while minimising or avoiding direct axial airflow paths through the fan, and thus minimising any impact on thermal performance.

The fan blades may have a decreasing thickness with increasing distance in an axial direction from the front plate. This may help to provide additional strength where it is needed, while allowing the fan blades to use less material and be lighter elsewhere. Thus, this may help to optimise the weight and strength of the fan.

Providing recesses in the backplate may potentially reduce its strength in comparison to the case where no recesses are provided. In order to help compensate for any potential loss of the strength, the backplate may comprise a plurality of ribs. The ribs may be areas of increased thickness in an axial direction. Preferably the ribs are provided on a rear surface of the backplate. The ribs may be radial ribs and/or circumferential ribs, or any other type of rib.

Preferably at least some of the ribs are provided in portions of the backplate between two adjacent recesses. For example, where the backplate comprises a plurality of protrusions extending radially outwards, the ribs may be provided on the protrusions. The ribs may be for example radial and/or circumferential and may be provided on the rear of the protrusions. This may help to strengthen the protrusions.

The fan may further comprise a hub portion to which the fan blades and/or the backplate are connected. The hub portion is preferably located at the centre of the fan radially. This may facilitate connection of the fan to a rotating part of the generator such as a generator shaft or a hub on the generator shaft. However, if desired, the fan could be connected to another component such as bars which extend through the rotor.

Preferably the fan blades have a decreasing thickness (cross-sectional area) with increasing distance in a radial direction from the hub portion. This may help to ensure that the fan blades have sufficient strength where it is needed, while being lighter elsewhere.

Preferably the fan blades extend forwards from the hub portion in an axial direction (towards the generator). Thus, the front plate may be axially displaced with respect to the hub portion. This may help to position the front plate in a suitable location such as facing an exit of a stator/frame airgap.

The recesses are preferably aligned axially with bolt holes in the coupling disc. This can allow a rotating part of the tool to pass through a recess and rotate in order to tighten or loosen bolts in the coupling disc.

The fan blades are preferably positioned such that a handle of the tool can rotate between two adjacent fan blades when tightening or loosening a bolt which connects the coupling disc to the prime mover. In order to achieve this, it would be possible to provide the fan with the same number of fan blades as recesses, and to position each recess circumferentially between two adjacent fan blades.

However, in some circumstances it may be desirable to provide a larger number of fan blades than recesses to improve the thermal performance.

Thus, in a preferred embodiment, the fan comprises a larger number of fan blades than recesses. This may be achieved, for example, by arranging the fan 35 such that some adjacent recesses have a single fan blade located between them in a circumferential direction and some adjacent recesses have two fan blades located between them in a circumferential direction. For example, when viewed circumferentially around the fan, the number of fan blades between two adjacent recesses may alternative between one and two. Thus, the ratio of fan blades to recesses may be 3 to 2. In a preferred embodiment the fan comprises eight recesses and twelve fan blades, although other arrangements such as six recesses and nine fan blades, ten recesses and fifteen fan blades, or an equal number of recesses and fan blades, or any other appropriate combination, could be used instead.

According to another aspect of the invention there is provided a generator assembly comprising: a generator; a fan in any of the forms described above; and a coupling disc for coupling the generator to a prime mover.

The fan and/or the coupling disc are preferably mounted on a generator shaft.

The coupling disc preferably comprises a plurality of holes (such as bolt holes) for connecting the coupling disc to a rotating component of the prime mover such as an engine flywheel. In this case each recess in the backplate may be aligned axially with a hole in the coupling disc.

The generator assembly may further comprise an adaptor for connecting the generator to a prime mover. The adaptor may comprise a plurality of openings which allow access to the coupling disc. The openings may also allow airflow from the fan to be exhausted.

The generator preferably comprises a rotor and a stator inside a generator frame.

In this case the adaptor may be connected to the generator frame. The adaptor may be used to connect the generator to a flywheel housing.

In any of the above arrangements, the tool may be a fastening tool which is arranged to be rotated in order to connect the coupling disc to the prime mover. 35 For example, the tool may be a wrench such as a socket wrench, and may comprise a rotating part and a handle for applying torque. The tool may be used to fasten and/or loosen bolts on the coupling disc. However, other types of fastener and other types of tool may be used instead or as well.

Corresponding methods may also be provided. Thus, according to another aspect of the present invention there is provided a method of connecting a generator to a prime mover, the method comprising: inserting a fastening tool into a recess in a backplate of a fan; and using the tool to connect a generator coupling disc to the prime mover.

Features of one aspect of the invention may be provided with any other aspect. Apparatus features may be provided with method aspects and vice versa.

In the present disclosure, terms such as "radially", "axially' and "circumferentially" are generally defined with reference to the axis of rotation of the fan and/or generator unless the context implies otherwise.

Preferred embodiments of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which: Figure 1 shows schematically a generating set; Figure 2 shows parts of a generator; Figure 3 illustrates how a coupling disc is connected to an engine flywheel in an existing design; Figure 4 is a perspective view of a fan in one embodiment of the invention; Figure 5 is an end view of a generator with the fan of Figure 4; Figure 6 is a perspective view of the fan, viewed from the front; Figure 7 shows in more detail part of the fan; Figure 8 shows parts of a generator with the fan in place; Figure 9 shows the generator of Figure 8 connected to an engine flywheel; Figure 10 shows an end view of a fan in another embodiment; and Figure 11 is a perspective view of a fan in a further embodiment.

Figure 1 shows schematically a generating set comprising an engine 10 coupled to a generator (alternator) 12. The engine 10 is typically an internal combustion engine such as a petrol or diesel engine. The generator 12 may be any type of electrical generator, such as a synchronous generator with field coils or permanent magnets, and is typically housed in a generator frame. The engine 10 and generator 12 are both mounted on a bed frame 14. The crankshaft of the engine (not shown) is mechanically coupled to the rotor of the generator (not shown). In operation, mechanical energy produced by the engine 10 is transferred to the generator 12 in order to generate the electrical output.

In the arrangement of Figure 1 the engine 10 comprises a flywheel located in a fly wheel housing 16. An adaptor 18 is used to connect the engine 10 to the generator 12. Typically, the adaptor is connected between the flywheel housing and the generator frame. The adaptor 18 helps to prevent relative movement between the engine and the generator. Openings 20 are provided in the adaptor, which provide exit paths for airflow through the generator. The openings 20 also allow an operator to connect the rotating parts once the generator has been brought into alignment with the engine.

Figure 2 shows parts of a generator prior to assembly to an engine. Referring to Figure 2, the generator 12 comprises a rotor and stator (not shown) inside a generator frame 22. The generator frame is connected to an adaptor 18, which is used to connect the generator to a flywheel housing. The generator also comprises a fan 26 and a coupling disc 28 mounted on a generator shaft 24. The fan 26 is located inside the adaptor 18. Openings 20 in the adaptor provide exit paths for airflow. During assembly, the generator 12 and adaptor 18 are brought into alignment with the engine. The openings 20 in the adaptor allow an operator to access to the coupling disc 28 as illustrated in Figure 2. This allows the operator to bolt the coupling disc 28 to the engine flywheel.

Figure 3 illustrates how the coupling disc is connected to the engine flywheel in the existing generator design. Referring to Figure 3, a plurality of bolts 30 are used to connect the coupling disc 28 to the engine flywheel (not shown). A socket wrench 32 is used to apply torque to the bolts in order to tighten them. The socket wrench 32 comprises a socket part 34 which passes axially through the end of the adaptor and engages with the bolts. The handle of the socket wrench passes radially through a gap between the end of the fan 26 and the end of the adaptor 18. The handle is used to apply torque to tighten or loosen the bolts.

From Figure 3 it can be seen that sufficient clearance needs to be left between the fan 26 and the end of the adaptor 18 to allow the operator to insert the socket wrench 32. This adds to the axial length of the adaptor 18, which in turn adds to the overall length of the generator. While it may be possible to reduce the length of the adaptor by using a smaller fan, this tends to compromise thermal performance, which may limit the overall rating of the generator.

Figure 4 is a perspective view of a fan in one embodiment of the invention. In Figure 4 the fan is viewed from the rear in the direction of air flow. The fan is designed for use with a generator such as that described above with reference to Figures 1 to 3.

Referring to Figure 4, the fan 40 comprises a plurality of fan blades 42, a front plate 44, a backplate 46 and a hub portion 48. The fan blades 42 are centrifugal blades which are arranged to dispel air radially (and tangentially) outwards under centrifugal force as they rotate. The fan blades 42 are spaced circumferentially around the fan and are mounted on the hub portion 48 at the centre of the fan radially. The fan blades 42 are also connected to the front plate 44 at the front of the fan and to the backplate 46 at the rear of the fan (in the direction of air flow).

The front plate 44 is in the form of an annular disc and is located at the front of the fan. The front plate 44 is connected to the radially outwards ends of the fan blades 42. The fan blades 42 have a length in an axial direction which increases with increasing distance from the axis of rotation, so as to position the inlet fan forwards of the backplate 46 and the hub portion 48 in the direction of airflow (towards the generator). The front plate 44 acts as an inlet ring and is used to guide airflow from the generator into the fan. The front plate 44 also helps prevent exhaust air from re-entering the air intake.

The backplate 46 is in the general form of an annular disc and is located at the rear of the fan. The backplate 46 is sized and positioned so as to be generally radially inwards of the front plate 44. The back plate 46 is connected to the radially inwards ends of the fan blades 42. The backplate 46 is also connected to the hub portion 48. The backplate 46 curves slightly from a more axial direction to a more radial direction with increasing distance from the hub portion 48 (increasing distance from the axis of rotation). The backplate 46 is used to help direct airflow from a substantially axial direction as it enters the fan to a substantially radial direction as it exits the fan. The front plate and the backplate are substantially concentric, and are spaced apart axially, leaving a gap between the two.

The hub portion 48 is located at the centre of the fan radially. It is used to mount the fan to the generator shaft as well as provide some support for the fan blades.

In the arrangement of Figure 4, a plurality of notches or recesses 50 are provided in the backplate 46. The recesses are U-shaped, and open on the radially outwards side of the backplate 46. As a consequence, the backplate has a radially inwards part in the form of a substantially annular disc, and a radially outwards part which consists of a series of radial protrusions or "petals'. The petals are spaced circumferentially about the fan, each petal being formed between two adjacent recesses in a circumferential direction. The recesses 50 are located between the fan blades 42 in a circumferential direction. The recesses 50 are used to allow a socket wrench to connect the coupling disc to an engine flywheel.

Figure 5 is an end view of a generator with the fan of Figure 4, looking axially into the adaptor. In Figure 5 the generator is shown without a coupling disc to illustrate how a socket wrench can be used to connect the coupling disc to the engine flywheel. Referring to Figure 5, the fan 40 is mounted on a hub 25 on the generator shaft inside the adaptor 18. A socket wrench 32 is inserted through a window in the adaptor. A plurality of recesses 50 are provided at spaced locations around the periphery of the backplate 46. The recesses 50 are sized and positioned such that the socket part of the socket wrench 32 fits at least partially into the recesses. The socket wrench 32 can then be used to tighten bolts which are used to connect the coupling disc to the engine flywheel.

In use, when the coupling disc is to be connected to the engine flywheel, the socket wrench 32 is inserted radially through an opening 20 in the adaptor 18. The socket wrench is inserted radially into the fan 40 in the gap between the front plate 44 and the backplate 46. The socket part 34 of the socket wrench is inserted into one of the recesses 50 in a radial direction. When the socket wrench is in position, the handle of the wrench is located between the front plate 44 and the backplate 46 in an axial direction. The socket part 34 of the wrench passes axially through the recess 50, and engages with a bolt on the coupling disc. The socket wrench 32 can then be used to tighten the bolt. This may be facilitated by using a ratcheting socket wrench, which allows the bolt to be tightened with a reciprocating motion as indicated by the arrow in Figure 5.

The coupling disc comprises a number of bolt holes spaced circumferentially about the disc, which are used to bolt the disc to the flywheel. The recesses 50 are aligned with the holes in the coupling disc. As the bolt is being tightened, the socket wrench moves between two fan blades 42 on the fan. The fan blades are therefore positioned circumferentially so that they do not overlap with the holes in the coupling disc, and to allow reciprocating motion of the socket wrench.

It one possible configuration, the fan could be provided with the same number of fan blades as there are holes in the coupling disc. In this case, each recess in the backplate could be located centrally between two adjacent fan blades in a circumferential direction. This would allow the socket wrench to turn between two adjacent fan blades. For example, a typical coupling disc comprises eight bolt holes, in which case the fan could be provided with eight fan blades and eight recesses, with each recess located circumferentially between two adjacent blades. However, in some situations a better thermal performance may be achieved with a greater number of fan blades. Therefore, it may be desirable to provide the fan with more fan blades than there are recesses.

In the arrangement of Figures 4 and 5 the fan comprises eight recesses 50 in the backplate 46 and twelve fan blades 42. When viewed in a circumferential direction around the fan, there are alternately a single fan blade between two adjacent recesses and two fan blades between two adjacent recesses. Where a single fan blade is located between two adjacent recesses, the fan blade is located centrally (in a circumferential direction) between those two recesses. Where two fan blades are located between two adjacent recesses, one fan blade is located next to one of the recesses and the other fan blade is located next to the other recess. This arrangement can allow the fan to be provided with a greater number of fan blades than there are recesses, while avoiding overlap of the fan blades with the recesses and the bolt holes, Referring back to Figure 4, the backplate 46 has a number of protrusions or petals, with each petal being formed between two adjacent recesses 50 in a circumferential direction. In this configuration, some of the petals span two adjacent fan blades 42, while the other petals extend each side of a single fan blade in a circumferential direction. The petals alternate between one and the other in a circumferential direction about the fan. This arrangement allows twelve fan blades 42 to be provided with a backplate having eight recesses 50.

Of course, it will be appreciated that the coupling disc may have a different number of bolt holes, and the number and positioning of the fan blades may be adjusted accordingly.

Still referring to Figure 4, it can be seen that the petals on the backplate 46 have ribs 52 on their rear side axially. The ribs are provided in those areas where additional strength is needed. The ribs 52 extend in a generally radial direction adjacent to the area where the fan blades 42 meet the backplate 46. In addition, a circumferential rib 53 is provided on the radially inward side of the backplate 46, just inside the recesses 50. The ribs 52, 53 help to compensate for any loss of strength caused by the recesses 50, without requiring a significant increase in the amount of material. In particular, the ribs 52, 53 help the backplate 46 resist the force of airflow against it.

From Figure 4 it can also be seen that the fan blades 42 have a varying cross section. The blades are thicker at the front of the fan where they meet the front plate 44 and decrease in thickness in an axial direction towards the rear of the fan. The fan blades 42 are also thicker at their radially inwards ends where they meet the backplate 46 and the hub 48 and decrease in thickness with increasing distance from the axis of rotation. By varying the thickness of the fan blades in this way, the blades can be thicker where more strength is needed (particularly at the junctions with the front plate 44, backplate 46 and hub portion 48) and thinner elsewhere to save weight.

Figure 6 is a perspective view of the fan, viewed from the front in the direction of air flow. Referring to Figure 6, the front plate 44 has a rim 54 at its outer periphery. The rim 54 extends forwards of the front plate 44 in an axial direction. The front plate also has a plurality of ribs 56 on its front surface. The ribs 56 provide strength to the front plate, and also help direct airflow towards the air inlet at the centre of the fan.

Figure 7 shows in more detail part of the fan where a fan blade meets the front plate. Referring to Figure 7, notches 58 are provided in the front plate 44 on either side of the fan blade 42 at the point where the fan blade meets the front plate 44. The notches 58 reduce the stress at the junction of the fan blade and the front plate during operation. This can help to avoid failure of the junction without the need to add additional material to strengthen the junction.

The fan of Figures 4 to 7 may be manufactured from any suitable material such as metal or plastic. For example, in one embodiment, the fan is moulded from a temperature resistant plastic. This may avoid the need to machine the part and reduce its weight.

Figure 8 shows parts of the generator with the fan in place. Referring to Figure 8, the generator comprises a rotor 60 mounted on a shaft 24 and arranged to rotate inside a stator 62. Stator end windings 63 extend axially out of the stator. The stator 62 is located inside a generator frame 22. An adaptor 18 is connected to the generator frame 22 using bolts 64. The fan 40 is located inside the adaptor 18. The generator shaft 24 comprises a hub 25 at one end, on which the fan 40 is mounted using bolts 65. The coupling disc 28 is mounted on the end of the hub 25. The front plate 44 of the fan faces an exit of the stator/frame airgap. The adaptor 18 includes openings 20 which allow airflow from the fan to exit the machine. Figure 8 also shows a grill which covers the openings. The grill can be removed to allow an operator access to the coupling disc 28 through the openings 20.

Figure 9 shows the generator of Figure 8 connected to an engine flywheel. Referring to Figure 9, an engine flywheel 66 is located on an engine shaft 67. The engine shaft and flywheel are housed in a flywheel housing 68. A plurality of bolts 30 are used to connect the coupling disc 28 to the flywheel 64. This is achieved by removing the grill which covers the adaptor opening 20 and inserting a socket wrench through the opening 20. The end of the socket wrench fits into the recesses 50 in the fan 40, in the manner shown in Figure 5. The socket wrench can then be used to tighten the bolts 30. Similarly, if the generator is to be disassembled from the engine, then the socket wrench can be used to loosen the bolts 30.

Figure 9 also shows airflows through the machine. In operation, as the fan rotates, it draws airflow though the generator. Airflow is in a generally axial direction, with the main paths for the airflow being through an airgap between the stator and the frame and through an airgap between the rotor and the stator. As airflow exits the generator, it flows over the stator end windings 63, and is guided by the front plate 44 into the fan 40. The airflow is then diverted from a substantially axial direction to a substantially radial direction by the centrifugal force of the fan blades, assisted by the backplate. Airflow exits the machine through the openings 20 in the adaptor 18, as shown by the arrows in Figure 9.

If desired, rather than mounting the fan 40 on a hub, the fan could be mounted directly to the shaft, or to the rotor in the manner disclosed in GB 2590610 A. Furthermore, if desired, the front plate 44 could be angled so as to direct airflow from the stator/frame airgap towards the stator end windings and/or positioned above the stator end windings in the manner disclosed in WO 2021/023985.

The arrangement of Figures 4 to 9 can allow a smaller gap to be left between the fan and the coupling disc than would otherwise be the case. This can allow the axial length of the adaptor to be reduced. thereby reducing the overall length of the generator. This may allow the generator to packaged more efficiently during shipping and allow use of the generator is application where the space is constrained. Furthermore, it has been found that this can be achieved without a significant impact on the thermal performance of the machine. Alternatively, a larger fan could be provided for the same size of adaptor, thereby improving the thermal performance. In general, the disclosed arrangement may allow an optimization of thermal performance and axial length of the adaptor.

Figure 10 shows an end view of a fan in another embodiment. The fan of Figure is designed for use with a generator in a similar way to the fan described above with reference to Figures 4 to 9.

Referring to Figure 10, the fan comprises a plurality of fan blades 42, a front plate 44, a backplate 46 and a hub portion 48. The backplate 46 is provided with a plurality of recesses 50, in a similar way to the fan described above. However, in the fan of Figure 10, the backplate 46 is smaller in a radial direction than that of the fan of Figure 4. As a consequence, when viewed axially, there is a gap between the backplate 46 and the front plate 44. This gap may provide additional space for the socket wrench when attaching the coupling disc to the engine flywheel, although at the expense of some potential loss in thermal performance.

In the fan of Figure 10, the backplate 46 has ribs on its rear side, in a similar way to the fan of Figure 4. The ribs are provided in those areas where additional strength is needed. However, as the backplate of Figure 10 is smaller than that of Figure 4, fewer ribs are required.

Figure 11 shows a perspective view of a fan in a further embodiment. Referring to Figure 11, the fan comprises a plurality of fan blades 42, a front plate 44, a backplate 46 and a hub portion 48. The backplate 46 is provided with a plurality of recesses 50, in a similar way to the fans described above. However, in the fan of Figure 11, the backplate 46 is larger in a radial direction than that of the fans of Figures 4 and 10. Thus, when viewed axially, the backplate 46 overlaps slightly with the front plate 44. The larger backplate can help with thermal performance of the machine by helping direct airflow radially outwards, although at the cost of potentially reducing the amount of space available for connecting the coupling disc to the engine flywheel.

In the fan of Figure 11, the backplate 46 has ribs on its rear side, in a similar way to the fans of Figures 4 and 10. The ribs are provided in those areas where additional strength is needed. However, as the backplate of Figure 11 is larger than those of Figures 4 and 10, an enhanced rib pattern is provided.

The fan designs described above may provide one or more of the following 5 advantages: * Improvement in thermal performance by allowing the size of the fan blades to be increased.

* Increase in size of the fan can allow the fan to be made from a less expensive material such as plastic.

* The generator is easy to connect to the flywheel by virtue of the recesses on the backplate.

* The overall length of the generator can be reduced, which may be desirable for logistic purposes such as shipping.

* The amount of material needed for the adaptor and shaft can be reduced, leading to a cost reduction.

* Manufacturing is facilitated as it is easy to install the fan with bolts.

It will be appreciated that embodiments of the present invention have been described above by way of example only, and variations in detail are possible.

For example, features of one embodiment may be used with any of the other embodiments. The generator may be connectable to any appropriate type of prime mover and not necessarily to an engine flywheel. Other variations in detail will be apparent to the skilled person within the scope of the appended claims.

Claims

CLAIMS1. A fan for a generator, the generator arranged to be coupled to a prime mover via a coupling disc, the fan comprising: a plurality of fan blades; and a backplate, wherein the backplate comprises a plurality of recesses which allow insertion of a tool for connecting the coupling disc to the prime mover.
2. A fan according to any of the preceding claims, wherein the backplate is arranged to direct airflow from a substantially axial direction to a substantially radial direction.
3. A backplate according to claim 1 or 2, wherein the backplate is in the form of a substantially annular disc with a plurality of protrusions extending radially outwards.
4. A fan according to any of the preceding claims, wherein the recesses are open on the radially outwards periphery of the backplate.
5. A fan according to any of the preceding claims, wherein the fan is arranged such that the tool can be inserted a radial direction into a recess.
6. A fan according to any of the preceding claims, wherein the recesses allow a tool to pass through them in an axial direction.
7. A fan according to any of the preceding claims, wherein each recess is located between two adjacent fan blades in a circumferential direction.
8. A fan according to any of the preceding claims, further comprising a front plate connected to the fan blades.
9. A fan according to claim 8 wherein the fan blades are connected between the front plate and the backplate.
10. A fan according to claim 8 or 9, wherein the front plate is an inlet ring which guides airflow into the fan.
11. A fan according to any of claims 8 to 10, wherein a notch is provided in the front plate at a location where a fan blade meets the front plate.
12. A fan according to any of claims 8 to 11, wherein the front plate and the backplate are substantially concentric and spaced apart axially.
13. A fan according to any of claims 8 to 12, wherein the backplate is located radially inwards of the front plate.
14. A fan according to any of claims 8 to 13, wherein the fan blades have a decreasing thickness with increasing distance in an axial direction from the front plate.
15. A fan according to claim any of the preceding claims, wherein the backplate comprises a plurality of ribs.
16. A fan according to claim 15, wherein at least some of the ribs are provided in portions of the backplate between two adjacent recesses.
17. A fan according to any of the preceding claims, further comprising a hub portion to which the fan blades and/or the backplate are connected.
18. A fan according to claim 17, wherein the fan blades have a decreasing thickness with increasing distance from the hub portion.
19. A fan according to any of the preceding claims, wherein the fan comprises a larger number of fan blades than recesses.
20. A fan according to claim 19, wherein some adjacent recesses have a single fan blade located between them in a circumferential direction and some adjacent recesses have two fan blades located between them in a circumferential 35 direction.
21. A fan according to claim 19 or 20, wherein the ratio of fan blades to recesses is 3:2.
22. A generator assembly comprising: a generator; a fan according to any of the preceding claims; and a coupling disc for coupling the generator to a prime mover.
23. A generator assembly according to claim 22, wherein the coupling disc comprises a plurality of holes for connecting the coupling disc to a rotating component of a prime mover, and each recess in the backplate is aligned with a hole in the coupling disc.
24. A generator assembly according to claim 22 or 23, further comprising an adaptor for connecting the generator to a prime mover, the adaptor comprising a plurality of openings which allow access to the coupling disc.
25. A method of connecting a generator to a prime mover, the method comprising: inserting a fastening tool into a recess in a backplate of a fan; and using the tool to connect a generator coupling disc to the prime mover.