Impeller for an axial fan

Abstract

An impeller (2) for an axial fan (1) comprises a hub (3) having a side wall (5) being circumferential with respect to a rotation axis (6) of the impeller (2), a plurality of blades (7) protruding from the side wall (5) with a front edge (12), a rear edge (13) and a peripheral edge (21), wherein a rotation of the impeller (2) generates an air flow in the direction of the rotation axis (6) from a suction side (8) towards a delivery side (9) of the impeller (2), wherein a root portion (10) of the blade (7) creates the connection between the blade (7) and the side wall (5) and forms a connection seam (11) which locally thickens the root (10) with respect to the thickness of the blade (7) adjacent to the root (10), and which extends all about the blade (7), and / or wherein the blades (7) and the side wall (5) of the hub (3) are formed in one piece from fiber-reinforced synthetic material by injection molding.

Description

[0001] The invention relates to an impeller for an axial fan and to an axial fan, in particular for a heat exchanger of a heat pump.

[0002] Although axial fans have a relatively high overall efficiency, in several applications (among which in the heat exchangers of heat pumps) there is a demand for increasingly more energy efficiency and therefore, a reduction in flow resistance and an increased one-way directionality of the axial flow conveyed by the fan. The efficiency and directionality of the air flow of the fan in heat exchangers for heat pumps in turn affect the efficiency and intensity of the heat exchange of the air conveyed and therefore, in a broader manner, the overall coefficient of performance (COP) of the heat pump.

[0003] The axial fans of the prior art comprise a support structure for fastening the fan to an application (e.g., to a heat exchanger housing or an outdoor or indoor heat pump unit), an electric motor having a rotor and a stator supported in a stationary manner by the support structure, as well as a bladed impeller connected to the rotor of the motor and operated in rotation by the motor.

[0004] The shape of the individual blades of the impeller is conventionally curved, in both the radial direction, i.e., in section according to planes which are radial to the rotation axis of the fan, and the circumferential direction, i.e., in section according to planes which are tangent to circumferences with respect to the rotation axis of the fan, in order to direct the air flow along the blades, minimizing the generation of turbulence which gives rise to non-axial secondary flows and energy dispersion which one desires to minimize.

[0005] Blades made of sheared and press-shaped sheet metal as well as blades made of synthetic material molded by injection, are known. It is known to make the blades separately from a hub of the impeller and then to connect them to the latter.

[0006] For example, an impeller is known from EP2823184A1, the hub of which is cast molded from aluminum in order to minimize the weight thereof and the blades of which are made of fiber-reinforced synthetic material in order to curb manufacturing costs, increase mechanical resistance, and reduce weight.

[0007] Making the impeller blades and hub of different materials and / or by different manufacturing processes, as well as the assembly thereof, involve undesirably increased manufacturing costs and times.

[0008] Moreover, the connection of the blades to the hub and, in general, the creation of the transition zone between the blades and the hub, are still not satisfactory from a fluid-dynamic viewpoint. In particular, considerable turbulence in the impellers of the axial fans of the prior art is observable at the roots of the blades, in particular in the regions between the roots of two consecutive blades, respectively. This turbulence reduces the conveying efficiency and increases the fan noise.

[0009] Therefore, it is the object of the present invention to suggest an impeller for an axial fan and an axial fan having features such as to obviate at least partially some of the drawbacks mentioned with reference to the prior art.

[0010] It is a further object of the invention to suggest an impeller for an axial fan and an axial fan which are improved in terms of efficiency, noise reduction, manufacturing costs.

[0011] It is a particular object of the invention to provide an impeller for an axial fan having features such as to simplify and reduce the costs to manufacture it.

[0012] It is a further particular object of the invention to provide an impeller for an axial fan having features such as to reduce the air turbulence during the operation of the fan, in particular the air turbulence in the space between the roots of two consecutive blades, respectively.

[0013] These and other objects are achieved by an impeller for an axial fan according to claim 1 and by an axial fan containing the impeller.

[0014] According to an aspect of the invention, an impeller (2) for an axial fan (1), in particular for a heat exchanger of an outdoor unit of a heat pump, comprises: a hub (3) connectable to an electric motor (4) of the axial fan (1) and having a side wall (5) being circumferential with respect to a rotation axis (6) of the impeller (2), a plurality of blades (7) protruding from the side wall (5) and each being in the shape of a curved shell delimited by a front edge (12) facing in the rotation direction 30 of the impeller (2), a rear edge (13) facing opposite to the rotation direction (30), and a peripheral edge (21), where a rotation of the impeller (2) about the rotation axis (6) generates an air flow in the direction of the rotation axis (6) from a suction side (8) towards a delivery side (9) of the impeller (2), where a root portion (10) of the blade (7) creates the connection between the blade (7) and the side wall (5) and forms a connection seam (11) which locally thickens the root (10) with respect to the thickness of the blade (7) adjacent to the root (10), and which extends all about the blade (7) along the suction side (8), about the front edge (12), along the delivery side (9), and about the rear edge (13), where, with added advantage, the blades (7) and the side wall (5) of the hub (3) are formed in one piece from fiber-reinforced synthetic material by injection molding.

[0015] The connection seam which is thickened with respect to the thickness of the blade adjacent to the root thereof, and extending all around the blade, surprisingly contributes to reducing the vorticity of the air flow in the regions between two consecutive blades, respectively, close to the hub, and also reduces the noisiness of the impeller during the operation of the fan with respect to the same geometry of the impeller, but without a connection seam.

[0016] The formation of the blades together with the side wall of the hub with the same, albeit not necessarily identical, material (injection-moldable synthetic material) and by a single manufacturing process simplifies the manufacturing and reduces the cost of the impeller.

[0017] Moreover, experimental tests with impellers in which the blades were made with a connection seam, but separately from the hub and connected to the hub by a mechanical connection without continuity of material (geometric coupling and fastening via screws), showed losses of efficiency and increased noisiness with respect to the impeller made in a single piece by injection molding.Brief description of the figures

[0018] In order to better understand the invention and appreciate the advantages thereof, some non-limiting embodiments will be described below with reference to the accompanying drawings, in which: Figure 1 is a perspective view of an axial fan, from a suction side, according to an embodiment, Figure 2 is a perspective view of the axial fan in Figure 1, from a delivery side, according to an embodiment, Figure 3 shows the axial fan in Figure 1 without a support structure, Figure 4 shows the axial fan in Figure 2 without a support structure, Figure 5 is an exploded perspective side view - delivery side - of an axial fan, according to an embodiment, Figure 6 shows a detail (suction side) of an impeller of the axial fan according to an embodiment, Figure 7 shows a further detail (suction side) of the impeller of the axial fan according to an embodiment, Figure 8 shows a further detail (side view - delivery side) of the impeller of the axial fan according to an embodiment, Figure 9 is a section view of a root region of a blade of the impeller, according to a section plane tangent to a circumference of the rotation axis, according to an embodiment, Figure 10 is a section view of the impeller according to a section plane X-X of Figure 9, Figure 11 is a section view of the impeller according to a further section plane, not indicated in Figure 9, Figure 12 is a section view of the impeller according to a section plane XII-XII of Figure 9, Figure 13 is a view of a blade of the impeller from a suction side, indicating section planes 13A-13A, 13B-13B, 13C-13C, Figures 13A, 13B, 13C are section views of the blade according to section planes 13A-13A, 13B-13B, 13C-13C. Description of embodiments

[0019] With reference to the drawings, an impeller 2 for an axial fan 1, in particular for a heat exchanger of an outdoor unit of a heat pump (not shown in the drawings), comprises: a hub 3 connectable to an electric motor 4 of the axial fan 1 and having a side wall 5 being circumferential with respect to a rotation axis 6 of impeller 2, a plurality of blades 7 protruding from the side wall 5 and each being in the shape of a curved shell delimited by a front edge 12 facing in the rotation direction 30 of impeller 2, a rear edge 13 facing opposite to the rotation direction 30, and a peripheral edge 21, where a rotation of impeller 2 about the rotation axis 6 generates an air flow in the direction of the rotation axis 6 from a suction side 8 towards a delivery side 9 of impeller 2.

[0020] A root (portion) 10, radially more inwards, of blade 7 which creates the connection between blade 7 and the side wall 5 of hub 3 forms a connection seam 11 which locally thickens root 10 with respect to the thickness of blade 7 adjacent to root 10, and which extends all about blade 7 along the suction side 8, about the front edge 12 of blade 7, along the delivery side 9 and about the rear edge 13 of blade 7.

[0021] With added advantage, the blades 7 (preferably all the blades of impeller 2) and the side wall 5 of hub 3 are formed in one piece from fiber-reinforced synthetic material by injection molding.

[0022] According to an embodiment (Figure 9), the local section thickness of blade 7, at a plane tangent to an outer surface 17 of the side wall 5 (connection plane 14), i.e., a connection thickness 15 of root 10 in the connection plane 14 with the side wall 5, varies along the extension of the root 10 of blade 7.

[0023] A front connection thickness 15_12 of root 10 in the connection plane 14, at the front edge 12, is greater than a rear connection thickness 15_13 of root 10 in the connection plane 14, at the rear edge 13.

[0024] The connection thickness 15 of root 10 in the connection plane 14 gradually increases, moving away from the rear edge 13 up to reaching an intermediate connection thickness value 15_16 in an intermediate region 16 of root 10 between the rear edge 13 and the front edge 12, and locally decreases to a reduced connection thickness value 15_R in a zone between the intermediate region 16 and the region of the front edge 12. The reduced connection thickness value 15_R is advantageously less than the intermediate connection thickness value 15_16 and the front connection thickness value 15_12.

[0025] According to an embodiment, in a radially more outwards zone (or in a section plane tangent to a circumference of the rotation axis 6) with respect to the connection plane 14 or in other words, in the connection regions of the connection seam 11 with an outer surface 18 of blade 7, the connection seam 11 forms one or more reinforced end portions 11_12, 11_13 at at least one of the front edge 12 and rear edge 13 (Figures 7, 8, 9, 11, 12).

[0026] The reinforced end portions 11_12, 11_ 13 have a greater thickness than the thickness of the connection seam 11 in the connection regions with the outer surface 18 of blade 7 furthest from the front 12 and rear 13 edges.

[0027] The reinforced end portion(s) 11_12, 11_ 13 have a connection radius with the outer surface 18 of blade 7 smaller than a connection radius of the connection seam 11 with the outer surface 18 of blade 7 furthest from the front 12 and rear 13 edges.

[0028] According to an embodiment (Figure 9), root 10 is in the shape of an arc section, substantially concave towards the delivery side 9 (or in the rotation direction of impeller 2) and convex towards the suction side 8 (or against the rotation direction of impeller 2), with the exception of a front end segment 25 of root 10 at the front edge 12 and a rear end segment 26 of root 10 at the rear edge 13, which are both bent / curved / oriented in the opposite direction with respect to the curvature of the arc shape.

[0029] According to an embodiment, in a projection on a plane orthogonal to the rotation axis 6, the front edge 12 of blade 7 is more concave and longer than the rear edge 13 and forms, together with the peripheral edge 21 of blade 7, a front tip 22 having an acute angle and facing the rotation direction 30 of impeller 2 (Figure 13).

[0030] Again in a projection on a plane orthogonal to the rotation axis 6, the rear edge 13 of blade 7 is at least approximately straight or rectilinear and forms, together with the peripheral edge 21, a rear angle 23 between 80° and 100°, preferably of 90°.

[0031] According to a further embodiment, the peripheral edge 21 of blade 7, in other words, the radially more outwards outline of blade 7, forms a winglet 24, i.e., an edge bent at an angle towards the suction side 8 (preferred) or towards the delivery side 9.

[0032] All the geometric features described contribute individually and in combination to increasing the efficiency of fan 1, reducing the vorticity and noise and reducing undesired flows of air transverse to the desired axial direction of flow.

[0033] According to an embodiment, the blades 7 form ribs or, more generically, reinforcing geometries 19 which do not coincide with an outer contour 20 of blade 7 (formed by the front 12, rear 13 and peripheral 21 edges), formed for example, by local thickening or steps or discontinuity of surface curvature, curvilinear or by the outline of a region with low / high relief, and which form a distorted triangular or distorted trapezoidal reinforcing pattern having a smaller extension than the extension of the outer contour 20 of blade 7 (Figures 3, 4).

[0034] The reinforcing ribs (geometries) ensure the geometry of impeller 2 is maintained also under harsh conditions of fluid-mechanical stress.

[0035] According to an embodiment (Figures 13, 13A, 13B, 13C), the blades 7 have a bulging plate-like shape with a convex surface facing the delivery side 9 and a concave surface facing the suction side 8.

[0036] The impeller 2 preferably comprises exactly three blades 7.

[0037] The invention also relates to the axial fan 1 comprising a support structure 27 for fastening the axial fan 1 to an application (e.g., a heat exchanger housing or an outdoor or indoor heat pump unit), an electric motor 4 having a rotor 28 and a stator 29 supported in a stationary manner by the support structure 27, as well as impeller 2 connected to rotor 28 of the electric motor 4 and operable in rotation by motor 4.List of reference numerals in the figures

[0038] impeller 2 of axial fan 1, hub 3 electric motor 4 side wall 5 rotation axis 6 blades 7 suction side 8 delivery side 9 root (portion) 10 connection seam 11 reinforced end portions 11_12, 11_13 front edge 12 rear edge 13 connection plane 14 connection thickness 15 of root 10 front connection thickness 15_12 rear connection thickness 15_13 intermediate connection thickness 15_16 reduced connection thickness 15_R intermediate region 16 outer surface 17 of side wall 5 outer surface 18 of blade 7 reinforcing ribs (geometries) 19 outer contour 20 of blade 7 peripheral edge 21 front tip 22 rear angle 23 winglet 24 front end 25 of root 10 rear end 26 of root 10 support structure 27 rotor 28 stator 29 rotation direction 30

Claims

1. An impeller (2) for an axial fan (1), in particular for a heat exchanger of an outdoor unit of a heat pump, comprising: - a hub (3) connectable to an electric motor (4) of the axial fan (1) and having a side wall (5) being circumferential with respect to a rotation axis (6) of the impeller (2), - a plurality of blades (7) protruding from the side wall (5) and each being in the shape of a curved shell delimited by a front edge (12) facing in the rotation direction (30) of the impeller (2), a rear edge (13) facing opposite to the rotation direction (30), and a peripheral edge (21), wherein a rotation of the impeller (2) about the rotation axis (6) generates an air flow in the direction of the rotation axis (6) from a suction side (8) towards a delivery side (9) of the impeller (2), wherein a root portion (10) of the blade (7) creates the connection between the blade (7) and the side wall (5) and forms a connection seam (11) which locally thickens the root (10) with respect to the thickness of the blade (7) adjacent to the root (10), and which extends all about the blade (7) along the suction side (8), about the front edge (12), along the delivery side (9), and about the rear edge (13).

2. An impeller (2) according to claim 1, wherein the blades (7) and the side wall (5) of the hub (3) are formed in one piece from fiber-reinforced synthetic material by injection molding.

3. An impeller (2) according to claim 1 or 2, wherein a connection thickness (15) of the root (10) measured in a connection plane (14) of the blade (7) with the hub (3), tangent to an outer surface (17) of the side wall (5), varies along the extension of the root (10).

4. An impeller (2) according to claim 3, wherein a front connection thickness (15_12) of the root (10) in the connection plane (14), at the front edge (12), is greater than a rear connection thickness (15_13) of the root (10) in the connection plane (14), at the rear edge (13).

5. An impeller (2) according to claim 4, wherein the connection thickness (15) of the root (10) in the connection plane (14) gradually increases, moving away from the rear edge (13) up to reaching an intermediate connection thickness value (15_16) in an intermediate region (16) of the root (10) between the rear edge (13) and the front edge (12), and locally decreases to a reduced connection thickness value (15_R) in a zone between the intermediate region (16) and the region of the front edge (12), said reduced connection thickness value (15_R) being less than the intermediate connection thickness value (15_16) and the front connection thickness value (15_12).

6. An impeller (2) according to any one of the preceding claims, wherein in a transition region between the connection seam (11) and an outer surface (18) of the blade (7), the connection seam (11) forms one or more reinforced end portions (11_12, 11_13) at at least one or both of the front (12) and rear (13) edges.

7. An impeller (2) according to claim 6, wherein the one or more reinforced end portions (11_12), (11_ 13) have a greater thickness than a thickness of the connection seam (11) in the transition regions with the outer surface (18) of the blade (7) furthest from the front (12) and rear (13) edges.

8. An impeller (2) according to claim 6 or 7, wherein the one or more reinforced end portions (11_12), (11_ 13) have a connection radius with the outer surface (18) of the blade (7) smaller than a connection radius of the connection seam (11) with the outer surface (18) furthest from the front (12) and rear (13) edges.

9. An impeller (2) according to any one of the preceding claims, wherein in a projection on a plane orthogonal to the rotation axis (6), the front edge (12) of the blade (7) is more concave and longer than the rear edge (13) and forms, together with the peripheral edge (21), a front tip (22) having an acute angle and facing in the rotation direction of the impeller (2).

10. An impeller (2) according to any one of the preceding claims, wherein in a projection on a plane orthogonal to the rotation axis (6), the rear edge (13) of the blade (7) is substantially straight and forms, together with the peripheral edge (21), a rear angle (23) between 80° and 100°, or of 90°.

11. An impeller (2) according to any one of the preceding claims, wherein the root (10) is in the shape of an arc section, substantially concave towards the delivery side (9) and convex towards the suction side (8), with the exception of a front end segment (25) of the root (10) at the front edge (12) and a rear end segment (26) of the root (10) at the rear edge (13), which are both counter-bent with respect to the curvature of the arc shape.

12. An impeller (2) according to any one of the preceding claims, wherein the peripheral edge (21) of the blade (7) forms a winglet (24) bent at an angle towards the suction side (8).

13. An impeller (2) according to any one of the preceding claims, wherein the blades (7) form ribs or reinforcing geometries (19) which do not coincide with an outer contour (20) of the blade (7), and which form a distorted triangular or distorted trapezoidal reinforcing pattern having a smaller extension than the extension of the outer contour (20) of the blade (7).

14. An impeller (2) according to any one of the preceding claims, comprising exactly three of said blades (7).

15. An axial fan (1) comprising a support structure (27) for fastening the axial fan (1) to an application, an electric motor (4) having a rotor (28) and a stator (29) supported in a stationary manner by the support structure (27), as well as the impeller (2) according to any one of the preceding claims, connected to the rotor (28) of the electric motor (4).

Images