Improved aircraft engine fuel pump

Abstract

A fuel pump (1) for an aircraft engine comprising an impeller (10) and a wheel (20) fixed together and having an axis of rotation (X), an annular space (E) axially spacing the impeller (10) and the wheel (20), and two contact portions between the impeller (10) and the wheel (20) located radially outside the annular space (E), a first plenum (C1) and a second plenum (C2) in which the impeller (10) and the wheel (20) are axially spaced from each other, each plenum being disposed between the two contact portions, the plenums (C1, C2) being symmetrical to each other with respect to the axis of rotation (X) and in fluid communication with the annular space (E), the wheel (20) comprising a plurality of axial balancing holes (26) distributed around the axis of rotation (X) and opening at one end into the annular space (E) and at the other end into a downstream space (70) of the wheel (20).

Description

Technical Field

[0001] This disclosure relates to the field of fuel pump technology. In particular, this disclosure relates to fuel pumps for aircraft engines, and aircraft including such pumps. Background Technology

[0002] The fuel pump is one of the key components regulating aircraft engines, especially airplane engines. It allows fuel to be supplied from the aircraft's fuel tanks to the combustion chamber. Its flow rate and pressure are also used to generate hydraulic power to drive the engine's variable geometry.

[0003] The main fuel pump typically consists of a low-pressure (LP) stage and a high-pressure (HP) stage. The low-pressure stage usually comprises a guide vane, a centrifugal impeller, and a volute. The HP stage of the main fuel pump typically includes an external gear pump mechanically driven by the shaft of the engine power gearbox.

[0004] Typically, fuel pumps are sized to meet the requirements of ensuring flow rates greater than those needed under all operating conditions. Currently, centrifugal pumps with guide vanes, impellers, and volutes are known to be used in LP classes.

[0005] To ensure the normal operation of the low-pressure stage of the fuel pump, it is necessary to understand and control the hydraulic pressure generated at different operating points. These hydraulic pressures can be divided into two parts: axial force and radial force.

[0006] Axial force is difficult to determine because the balance problem is directly related to the knowledge of the pressure field at the guide vane outlet. If the guide vane is placed in front of the centrifugal impeller, the pressure generated by the guide vane will be applied to the rear of the impeller. The axial force is also related to the diameter of the guide vane. A reduction in the latter makes it less sensitive to poorly controlled pressure. However, force control remains essential for the normal operation of the pump's LP stage.

[0007] Therefore, to promote axial balance in the LP stage of a fuel pump, it is known to use an "open" type centrifugal impeller without an upstream flange, which has orifices called "balance holes". The function of these orifices is to allow fluid to flow from the high-pressure area to the low-pressure area, thereby reducing axial forces.

[0008] However, in configurations with guide vanes and "closed" impellers, the blades are positioned between the upstream and downstream flanges, completely covering the impeller blades (from leading to trailing edge), and the balancing holes may be located between the guide vane blades, making it very difficult to understand the pressure field. Furthermore, the impeller's rotation shears the airflow, resulting in a significant pressure drop that varies depending on the operating point. These drawbacks affect pump performance.

[0009] Therefore, in the case of a "closed" impeller, it is necessary to at least partially overcome the above-mentioned disadvantages. Summary of the Invention

[0010] This disclosure relates to a fuel pump for an aircraft engine, comprising:

[0011] Including the guide wheel on the axis of rotation,

[0012] A centrifugal impeller is coaxial with the guide vane, the guide vane being fixed upstream of the centrifugal impeller to define an annular interface between the guide vane and the impeller about the axis of rotation. The annular interface includes an annular space axially separating the guide vane and the impeller, and two contact portions located radially outside the annular space between the guide vane and the impeller. A first pressurization chamber and a second pressurization chamber are also present, in which the guide vane and the impeller are axially spaced apart from each other. Each pressurization chamber is circumferentially disposed between the two contact portions. The pressurization chambers are symmetrical about each other with respect to the axis of rotation and are in fluid communication with the annular space.

[0013] The impeller includes a plurality of axial balancing holes, which are circumferentially distributed around the axis of rotation and open at one end to the annular space and at the other end to the downstream space of the impeller.

[0014] In some embodiments, the upstream flange is fixed to the impeller upstream of it so as to at least partially cover the blades of the impeller.

[0015] Typically, axial direction corresponds to the axis of rotation of the fuel pump, while radial direction is the direction perpendicular to that axis of rotation. Circumferential direction corresponds to the direction describing the ring around the axial direction. Furthermore, upstream and downstream are defined relative to the normal flow direction of fluid through the pump (from upstream to downstream), with the fluid first reaching the guide vane and then the impeller. Finally, unless otherwise specified, the adjectives "inner" and "outer" are used to refer to the radial direction, so the inner (i.e., radially inner) portion of an element is closer to the axis of rotation than the outer (i.e., radially outer) portion of the same element.

[0016] Preferably, both the impeller and the guide vane include an orifice coaxial with the axis of rotation. Axial fixing devices are respectively disposed through the orifices of the impeller and the guide vane, allowing the impeller and guide vane to be axially fixed together. For example, a threaded screw can be inserted through the orifices of the guide vane and the impeller and screwed into a threaded hole provided in the impeller. Furthermore, the assembly can be driven by a rotating shaft via a spline located on the impeller. The profile of the spline can be selected as needed.

[0017] Therefore, when the guide wheel and the impeller are fixed together, an annular interface is formed between the two components. This interface has a ring shape around the axis of rotation; in other words, it is an axial fixing device.

[0018] The guide vane and impeller do not contact each other across the entire surface of the annular interface. The annular interface includes an annular space in which the impeller and interface are not in contact but are axially spaced apart. The annular space preferably extends around the axis of rotation over the entire circumference of the interface, but not over the entire radial width of the annular interface, and the surface of the annular interface also includes contact portions.

[0019] The contact portion is radially positioned outside the annular space. In other words, the contact portion at least partially surrounds the annular space.

[0020] Therefore, the contact surfaces between the guide vane and the impeller are discontinuous. In other words, the guide vane and the impeller do not contact each other across the entire circumference of the interface. More specifically, the guide vane and the impeller only contact each other at the annular interface through contact portions, and this contact is axial. Thus, two circumferentially spaced portions are formed between the two contact portions, wherein the guide vane and the impeller are axially spaced apart from each other. These spaced portions form a first and a second pressurization chamber, which are radially arranged symmetrically with respect to each other relative to the axis of rotation outside the annular space. In this way, the contact portions are also arranged symmetrically with respect to each other with respect to the axis of rotation.

[0021] In addition, axial balancing holes are provided in the impeller to allow axial passage, and these holes are radially arranged inside the contact portion and the booster chamber to provide access to the annular space.

[0022] Therefore, the circulating fluid from the guide vane and impeller, as well as the fluid returning to the space downstream of the impeller, can be reinjected into the annular space through the balancing orifice. This allows for the balancing of pressure between the upstream and downstream of the impeller, thereby reducing axial force.

[0023] Furthermore, the fluid present in the annular space can be radially ejected from the annular space via pressurization chambers. These pressurization chambers allow for the calming of crossflows, particularly through the normalization of the velocity field. More specifically, the pressurization chambers allow for the limitation of turbulence and shearing of the fluid passing through the balancing orifice, generated by the impeller's rotation, before the fluid reaches the downstream region of the guide vane.

[0024] Calming the crossflow before it merges with the main flow leaving the guide vane can reduce its impact on the pressure field, thereby reducing its impact on the velocity field between the guide vane and the centrifugal impeller.

[0025] Furthermore, the symmetrical arrangement of the booster chambers allows for the normalization of the pressure of the fluid escaping through these chambers, thereby further limiting the influence on the mainstream, i.e., the fluid flowing from upstream to downstream between the guide vane and the impeller.

[0026] In some embodiments, the first and second pressurization chambers each extend circumferentially over at least a quarter of the circumference of the annular interface.

[0027] This configuration allows for maximizing the calming effect of the fluid exiting the balance hole and being radially ejected to the outside of the impeller, while maintaining sufficient contact surface between the guide vane and the impeller, thus allowing for good structural stability of the assembly.

[0028] In some embodiments, the guide wheel includes a first annular surface with two first protrusions projecting axially relative to the remainder of the first annular surface. When the impeller and the guide wheel are fixed together, the first protrusions are symmetrical about each other with respect to the axis of rotation and contact the second annular surface of the impeller.

[0029] The contact between the first protrusion of the guide vane and the second annular surface of the impeller corresponds to the contact portion, thus forming a discontinuous annular contact surface between the guide vane and the impeller.

[0030] In some embodiments, the second annular surface of the impeller includes two second protrusions that project axially relative to the remainder of the second annular surface, the second protrusions being symmetrical about each other with respect to the axis of rotation, and circumferentially arranged between the first protrusions when the impeller and the guide wheel are fixed together.

[0031] In other words, the first protrusion forms two gaps between them, each gap containing a second protrusion, and the second protrusion also forms two gaps between them, each gap containing a first protrusion. Therefore, the first and second protrusions are nested within each other. This configuration allows for limiting the relative circumferential displacement of the guide vane relative to the impeller about its axis of rotation.

[0032] Preferably, the length of the arc formed by each first protrusion is substantially equal to the length of the gap between the two second protrusions. Similarly, the length of the arc formed by each second protrusion is substantially equal to the length of the gap between the two first protrusions. This configuration allows for further restriction of the relative circumferential displacement of the guide vane relative to the impeller about the axis of rotation.

[0033] In some embodiments, the height of the first protrusion is greater than the height of the second protrusion, such that the first protrusion contacts the second annular surface of the impeller, and the second protrusion does not contact the first annular surface of the guide wheel.

[0034] According to this configuration, when the guide vane and impeller are fixed together, the first protrusion of the guide vane abuts against the second annular surface of the impeller, but a space remains between the second protrusion of the impeller and the first annular surface of the guide vane. These spaces form a first pressurization chamber and a second pressurization chamber. Therefore, the implementation of these pressurization chambers is simple and inexpensive.

[0035] Optionally, in some embodiments, the height of the second protrusion is greater than the height of the first protrusion, such that the second protrusion contacts the first annular surface of the guide wheel, and the first protrusion does not contact the second annular surface of the impeller.

[0036] In some embodiments, the balancing holes are circumferentially distributed at regular intervals around the axis of rotation.

[0037] This configuration allows for the standardization of the distribution of circulating fluid returning from the downstream space of the impeller to the upstream space of the impeller, thereby improving the pressure balance efficiency between the upstream and downstream of the impeller.

[0038] In some embodiments, the centrifugal impeller includes sixteen axial balancing holes.

[0039] The presence of sixteen balance holes allows a large amount of circulating fluid to be transferred from the downstream to the upstream of the impeller, thereby improving the pressure balance between the upstream and downstream of the impeller.

[0040] In some embodiments, the distance between the balancing hole and the main shaft is less than 20% of the impeller radius, preferably less than 15%, and more preferably less than 10%.

[0041] The fact that the balancing orifice is positioned as close as possible to the axis of rotation and thus as far away as possible from the mainstream fluid exiting the guide vane allows for a reduction in the shear effect of the fluid leaving the balancing orifice on that mainstream. This reduces pressure drop, thereby improving pump performance.

[0042] In some embodiments, the ratio L / D between the length L and diameter D of the balancing hole is greater than or equal to 2.

[0043] In particular, a ratio greater than or equal to 2 allows for a substantially constant emission coefficient of 0.8, which enables the maximization of the volume of fluid transferred from the downstream space of the impeller to the upstream space of the impeller while minimizing the pressure drop.

[0044] This disclosure also relates to an aircraft that includes a pump according to any of the foregoing embodiments.

[0045] Aircraft can be, in particular, airplanes or helicopters. Attached Figure Description

[0046] The invention and its advantages will be better understood by reading the following detailed description of various embodiments of the invention given by way of non-limiting examples. This description refers to the accompanying drawings, in which:

[0047] Figure 1 This is a perspective view of a fuel pump according to an embodiment of the present disclosure;

[0048] Figure 2 yes Figure 1 Exploded view of the fuel pump;

[0049] Figure 3 It is along Figure 1 A cross-sectional view of section A of the centrifugal pump;

[0050] Figure 4 yes Figure 3 A top view of the centrifugal impeller of a centrifugal pump on plane BB;

[0051] Figure 5 yes Figure 1 Perspective bottom view of the guide vane of the fuel pump;

[0052] Figure 6 This is a perspective view of a fuel pump according to an embodiment of the present disclosure, wherein the upstream flange is concealed and the booster chamber is visible. Detailed Implementation

[0053] A fuel pump according to an embodiment of the present invention will be referred to in the following description. Figures 1 to 6 Describe it.

[0054] Figure 1 This is a perspective view of an example fuel pump 1. More specifically, it shows the low-pressure stage of this pump, extending about and capable of rotating about the axis of rotation X. The environment of this component (volute, high-pressure stage, etc.) is not shown.

[0055] The low-pressure stage includes a guide vane 10 and a centrifugal impeller 20 fixed downstream of the guide vane 10.

[0056] The guide vane 10 includes a tubular hub 11 from which a plurality of blades 12 extend radially. The upstream end of the hub 10 includes an aperture 110 through which a fixing device (e.g., a threaded screw 60) is inserted.

[0057] The centrifugal impeller 20 includes a body 21, with a plurality of blades 22 extending axially upstream and radially outward from the body 21. The impeller 20 includes a tubular portion 23 at its central portion for insertion into a cavity 13 formed within a tubular hub 11 of the guide vane 10, thereby forming a cylindrical contact surface between the guide vane and the impeller 20. Furthermore, the tubular portion 23 of the impeller 20 includes, at its center, an orifice 230 coaxially disposed with an orifice 110 of the hub 11 of the guide vane 10, and orifices 110 and 230 themselves are coaxial with the axis of rotation X. The orifice 230 is also configured to receive a threaded screw 60. The radially outer surface of the downstream end of the impeller 20 may include a labyrinth seal, thereby ensuring a seal between the downstream end of the impeller 20 and the pump housing (not shown).

[0058] More specifically, the threaded screw 60 includes a screw head 61 abutting against the upstream end of the hub 11, with a bearing washer 50 inserted between the screw head 61 and the upstream end. The downstream end of the screw 60 is disposed in the tubular portion 23 of the impeller 20 and includes a threaded portion 62 configured to be threadedly connected to a threaded portion disposed within the tubular portion 23. Thus, the guide vane 10 and the centrifugal impeller 20 are axially fixed to each other. The assembly can be driven by a rotating shaft via a spline (not visible in the figure).

[0059] The upstream flange 30 is also secured upstream of the centrifugal impeller 20 by a plurality of screws 40. This upstream flange 30 allows at least partial coverage of the blades 22 of the impeller 20, thereby forming a closed enclosure between the flange 30 and the body 21 of the impeller 20. "Closed" should be understood as the impeller blades 22 being at least partially axially enclosed between the flange 30 and the body 21, thus at least partially isolated upstream and downstream of the impeller 20 by the flange 30 and the body 21, respectively. The radially outer end of the flange 30 may also include a labyrinth seal, thereby ensuring a seal between the flange 30 and the pump housing (not shown).

[0060] In addition to the cylindrical interface mentioned above, when the guide wheel 10 and the centrifugal impeller 20 are fixed together, there is also an annular interface between the two components, the guide wheel 10 and the centrifugal impeller 20.

[0061] More specifically, the guide vane 10 includes a first annular surface 14 formed at the downstream end of the hub 11 of the guide vane 10 and surrounding the end of the cavity 13. Similarly, the centrifugal impeller 20 includes a second annular surface 24 formed at the upstream end of the body 21 of the impeller 20 and surrounding the tubular portion 23. When the guide vane 10 and the impeller 20 are fixed together, the first annular surface 14 and the second annular surface 24 are axially opposite to each other. Some portions of these surfaces 14, 24 are in contact with each other, and other portions of these surfaces are spaced apart from each other, as described below.

[0062] The first annular surface 14 of the guide wheel 10 includes two first protrusions 141 and 142 that extend axially relative to the remainder of the first annular surface. These protrusions have the form of arcuate serrations projecting from the remainder of the first annular surface 14 and extend circumferentially and axially symmetrically with respect to the central axis X, but only on a portion of the circumference of the first annular surface 14. Each of the first protrusions 141 and 142 forms an arc whose dimension is substantially equal to one-quarter of the total circumference of the first annular surface 14. Furthermore, the first protrusions 141 and 142 are arranged symmetrically with respect to the central axis X. Figure 5In the example shown, the portion of the first annular surface 14 other than the protrusions 141 and 142 is represented at two different levels. However, this example is not limiting, and the surface may be uniform. It should also be noted that the protrusions 141, 142 do not extend radially across the entire width of the first annular surface 14, but are positioned at their radially outer ends to leave space between these protrusions 141 and 142 and the cavity 13. This space allows the formation of the annular space E, described later, when the guide wheel is fixed to the impeller 20.

[0063] The second annular surface 24 of the centrifugal impeller 20 includes two second protrusions 241 and 242 that extend axially relative to the remainder of the second annular surface 24. The second protrusions 241 and 242 have substantially the same features as the first protrusions 141 and 142, and therefore will not be described further. However, the second protrusions 241 and 242 differ from the first protrusions 141 and 142 in that their axial dimensions are smaller. That is, the second protrusions 241 and 242 project upstream in the axial direction by a smaller distance than the first protrusions 141 and 142 project downstream in the axial direction.

[0064] Therefore, when the guide wheel 10 and the impeller 20 are fixed together, the first protrusions 141 and 142, which are respectively inserted between the two second protrusions 241 and 242, abut against the second annular surface 24 of the impeller 20, thereby forming a discontinuous annular contact surface around the rotation axis X. A space is maintained between the second protrusions 241 and 242 inserted between the two first protrusions 141 and 142 and the first annular surface 14. The two spaces formed thereby form a first pressurization chamber C1 and a second pressurization chamber C2, which have the same shape and size and are arranged symmetrically with respect to the rotation axis X.

[0065] However, this example is not limiting. Alternatively, the second protrusions 241 and 242 may be axially longer than the first protrusions 141 and 142, thus providing two pressurization chambers C1 and C2.

[0066] Furthermore, when the guide vane 10 and the impeller 20 are fixed together, the radial portion of the first annular surface 14 located within the first protrusions 141 and 142 and the radial portion of the second annular surface 24 located within the second protrusions 241 and 242 form an annular space E. This annular space E is disposed radially inside the first protrusions 141 and 142, the second protrusions 241 and 242, and the booster chambers C1 and C2, and surrounds the tubular portion 23 of the impeller 20 on its entire circumference. The axial thickness of this annular space E is greater than the axial thickness of the booster chambers C1 and C2.

[0067] The centrifugal impeller 20 also includes a plurality of balancing holes 16 circumferentially distributed around the axis of rotation X at regular intervals. These holes are radially disposed between the second protrusions 241, 242 and the tubular portion 13. They extend axially along length L through the entire thickness of the body 21 of the impeller 20, such that a first end of each of these holes 26 opens into a downstream space 70 downstream of the impeller 20, and a second end opens into an annular space E. The balancing holes 16 have a diameter D, which is determined such that the ratio L / D is greater than or equal to 2. According to this embodiment, the impeller 20 includes 16 balancing holes 26. However, this example is not limiting and can be adjusted according to the dimensions of the impeller 20.

[0068] Figure 3 This shows the path of fluid (e.g., liquid) flow in centrifugal pump 1 (see...). Figure 3 (Black arrow in the diagram). The fluid first flows in the guide vane 10 and then in the centrifugal impeller 20. The flow along the guide vane 10 and impeller 20 is the main flow. The fluid is then discharged in the volute (not shown). A portion of this fluid, referred to as "recirculated fluid," can also return to the downstream space 70. This fluid can then be transferred from the downstream space 70 to the annular space E through the balance orifice 26, and then radially injected from the annular space E toward the main flow at the height of the outlet of the guide vane 10, passing through the pressure chambers C1 and C2. The fluid passing through these pressure chambers C1 and C2 calms this crossflow, thereby limiting the shear effect generated on the main flow. It should be noted that a portion of the fluid (not shown) leaving the impeller 20 can also return from the impeller 20 to the guide vane 10 along the outer wall of the flange 30. This portion is then drawn into the main flow by the guide vane 10 and impeller 20.

[0069] Although the invention has been described with reference to specific exemplary embodiments, it will be apparent that modifications and changes may be made to these examples without departing from the general scope of the invention as defined in the claims. In particular, individual features of different illustrated / mentioned embodiments may be combined in additional embodiments. Therefore, the specification and drawings should be considered in an illustrative rather than restrictive sense.

Claims

1. A fuel pump (1) for an aircraft engine, comprising: Includes a guide wheel (10) with a rotation axis (X). A centrifugal impeller (20) is coaxial with the guide wheel (10), the guide wheel (10) being fixed upstream of the centrifugal impeller (20) to define an annular interface between the guide wheel (10) and the impeller (20) about the axis of rotation (X). The annular interface includes an annular space (E) that is axially spaced between the guide wheel (10) and the impeller (20), and two contact portions (141, 142) located radially outside the annular space (E) between the guide wheel (10) and the impeller (20). The first pressurization chamber (C1) and the second pressurization chamber (C2) are axially spaced apart from each other. Each pressurization chamber is circumferentially disposed between the two contact portions (141, 142). The pressurization chambers (C1, C2) are symmetrical about each other with respect to the axis of rotation (X) and are in fluid communication with the annular space (E). The centrifugal impeller (20) includes a plurality of axial balancing holes (26) which are circumferentially distributed around the axis of rotation (X) and open at one end to the annular space (E) and at the other end to the downstream space (70) of the impeller (20).

2. The fuel pump (1) according to claim 1, wherein, The first pressurization chamber (C1) and the second pressurization chamber (C2) each extend circumferentially at least one-quarter of the circumference of the annular interface.

3. The fuel pump (1) according to claim 1 or 2, wherein, The guide wheel (10) includes a first annular surface (14) with two first protrusions (141, 142) axially projecting relative to the rest of the first annular surface (14). When the impeller (20) and the guide wheel (10) are fixed together, the first protrusions (141, 142) are symmetrical to each other with respect to the axis of rotation (X) and contact the second annular surface (24) of the impeller (20).

4. The fuel pump (1) according to claim 3, wherein, The second annular surface (24) of the impeller (20) includes two second protrusions (241, 242) that axially protrude relative to the rest of the second annular surface (24). The second protrusions (241, 242) are symmetrical to each other with respect to the axis of rotation (X), and when the impeller (20) and the guide wheel (10) are fixed together, the second protrusions are circumferentially arranged between the first protrusions (141, 142).

5. The fuel pump (1) according to claim 4, wherein, The height of the first protrusion (141, 142) is greater than the height of the second protrusion (241, 242), such that the first protrusion (141, 142) contacts the second annular surface (24) of the impeller (20), and the second protrusion (241, 242) does not contact the first annular surface (14) of the guide wheel (10).

6. The fuel pump (1) according to claim 1, wherein, The balancing holes (26) are circumferentially distributed at regular intervals around the axis of rotation (X).

7. The fuel pump (1) according to claim 1, wherein, The centrifugal impeller (20) includes sixteen axial balancing holes (26).

8. The fuel pump (1) according to claim 1, wherein, The distance between the balancing hole (26) and the axis of rotation (X) is less than 20% of the radius of the impeller (20).

9. The fuel pump (1) according to claim 8, wherein, The distance between the balancing hole (26) and the axis of rotation (X) is less than 15% of the radius of the impeller (20).

10. The fuel pump (1) according to claim 8, wherein, The distance between the balancing hole (26) and the axis of rotation (X) is less than 10% of the radius of the impeller (20).

11. The fuel pump (1) according to any one of claims 1 to 10, wherein, The ratio L / D between the length L and diameter D of the balancing hole (26) is greater than or equal to 2.

12. An aircraft comprising a fuel pump according to any one of claims 1-11.

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