AXIAL IMPELLER

Abstract

An axial impeller has a hub and a plurality of blades extending about the hub. Each blade has a root fixed to the hub, a tip spaced away from the hub, a leading edge extending between the root and the tip, and a trailing edge extending between the root and the tip. The root is inclined at a first angle α relative to a first axis B parallel to a rotational axis of the impeller, the tip is inclined at a second angle β relative to the first axis B, and the second angle β is greater than the first angle α. A first end of the trailing edge at the root is located downstream of a second end of the trailing edge at the tip, and a first end of the leading edge at the root is downstream of a second end of the leading edge at the tip.

Claims

1. An axial impeller comprising a hub and a plurality of blades extending about the hub, each blade comprising a root fixed to the hub, a tip spaced away from the hub, a leading edge extending between the root and the tip, and a trailing edge extending between the root and the tip, wherein the root is inclined at a first angle relative to a first axis parallel to a rotational axis of the impeller, the tip is inclined at a second angle relative to the first axis, the second angle being greater than the first angle, and a first end of the trailing edge at the root is located downstream of a second end of the trailing edge at the tip, and a first end of the leading edge at the root is downstream of a second end of the leading edge at the tip.

2. The axial impeller of claim 1, wherein a rate of transition between the first and second angles is irregular between the root and the tip.

3. The axial impeller of claim 1, wherein the second angle is in the region of 25-50% larger than the first angle.

4. The axial impeller of claim 1, wherein the trailing edge comprises a curved profile in a meridional plane established by an axial direction and a radial direction and the leading edge comprises a curved profile in the meridional plane.

5. The axial impeller of claim 4, wherein the curvature of the trailing edge in the meridional plane is greater than the curvature of the leading edge in the meridional plane.

6. The axial impeller of claim 1, wherein a cross-sectional shape of the blades at the root is different to a cross-sectional shape of the blades at the tip.

7. The axial impeller of claim 1, wherein a chord length of the blades at the tip is greater than the chord length of the blades at the root.

8. The axial impeller of claim 7, wherein the chord length of the blades at the tip is greater than the chord length of the blades at the root by between 10-80%.

9. The axial impeller of claim 1, wherein a maximum thickness of the blades is greater at the root than at the tip.

10. The axial impeller of claim 9, wherein the maximum thickness of the blades at the tip is between 30-70% of the maximum thickness of the blades at the root.

11. An electric motor comprising an impeller according to claim 1.

12. A haircare appliance comprising an electric motor as claimed in claim 11.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0030] In order to better understand the present invention, and to show more clearly how the invention may be put into effect, the invention will now be described, by way of example, with reference to the following drawings:

[0031] FIG. 1 is a front perspective view of an axial impeller according to the present invention;

[0032] FIG. 2 is a front view of the axial impeller of FIG. 1;

[0033] FIG. 3 is a rear view of the axial impeller of FIG. 1;

[0034] FIG. 4 is a rear perspective view of the axial impeller of FIG. 1;

[0035] FIG. 5 is a side view of the axial impeller of FIG. 1;

[0036] FIG. 6 is a schematic side view illustrating angles of inclination of blades of the axial impeller of FIG. 1;

[0037] FIG. 7 is a schematic projection of a front view of the blade of FIG. 6 into a plane orthogonal to a rotational axis of the impeller of FIG. 1;

[0038] FIG. 8 is a schematic projection of the blade of FIG. 6 in the meridional plane;

[0039] FIG. 9a is a schematic cross-sectional view of a blade of the impeller of FIG. 1 at the tip of the blade;

[0040] FIG. 9b is a schematic cross-sectional view of a blade of the impeller of FIG. 1 at a radial mid-point of the blade;

[0041] FIG. 9c is a schematic cross-sectional view of a blade of the impeller of FIG. 1 at the root of the blade;

[0042] FIG. 10 is a front perspective view of a known prior art impeller;

[0043] FIG. 11 is a plot of flow rate vs speed comparing the impeller of FIG. 1 vs the impeller of FIG. 10;

[0044] FIG. 12 is an exploded perspective view of an electric motor comprising the impeller of FIG. 1; and

[0045] FIG. 13 is a schematic view of a hairdryer comprising the electric motor of FIG. 12.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0046] An axial impeller according to a first aspect of the present invention, generally designated 10, is shown in FIGS. 1 to 5.

[0047] The axial impeller 10 comprises a hub 12, and a plurality of blades 14 extending circumferentially about the hub 12.

[0048] The hub 12 is substantially cylindrical in form, having a closed upstream end 16 and an open downstream end 18. The hub 12 comprises a central bore 20 which is shaped and dimensioned to receive a shaft 106 of a rotor assembly 102 of an electric motor 100, for example with an interference fit or with sufficient clearance to enable an adhesive fixing. The hub 12 is formed of a metallic material, and in a presently preferred embodiment is formed of brass.

[0049] As mentioned above, the plurality of blades 14 extend circumferentially about the hub 12, with the blades 14 being spaced equidistantly about the circumference of the hub 12. In a presently preferred embodiment there are 13 blades 14 which extend about the hub 12. The blades 14 are formed of a plastic material, and are overmoulded to the hub 12, for example as part of an injection moulding process.

[0050] The geometry of each of the plurality of blades 14 is the same, and hence only a single blade 14 will be described below for the sake of brevity.

[0051] Each blade 14 has a root 22, a tip 24, a leading edge 26, and a trailing edge 28. The root 22 is a radially innermost edge of the blade 14 which is closest to and attached to the hub 12. The tip 24 is a radially outermost edge of the blade 14, spaced apart from the hub 12. The leading edge 26 is a forwardmost edge in a direction of airflow through the impeller 10, for example an edge of the blade 14 which air contacts first as the impeller 10 rotates in use, and extends between the root 22 and the tip 24. The trailing edge 28 is a rearmost edge in a direction of airflow through the impeller 12, for example an edge of the blade 14 which contacts air last as the impeller 10 rotates in use, and extends between the root 22 and the tip 24.

[0052] A first end 30 of the leading edge 26 at the root 22 is attached to the hub 12, whilst a second end 32 of the leading edge 26 at the tip 24 is spaced from the hub 12. The second end 32 of the leading edge 26 is located upstream of the first end 30 of the leading edge 26, for example upstream in a direction of airflow, denoted by arrow A in FIG. 5, through the impeller 10 in use. This gives the leading edge 26 a curved, in this instance concave, profile when the blade 14 is viewed in a meridional plane defined by an axis extending parallel to a rotational axis of the impeller 10 and a radial axis, as seen in FIG. 8. The leading edge 26 also has a curved, in this instance concave, profile when viewed along an axis of rotation of the impeller 10 in a direction of airflow through the impeller 10 in use, as seen in FIG. 7

[0053] A first end 34 of the trailing edge 28 at the root 22 is attached to the hub 12, whilst a second end 36 of the trailing edge 28 at the tip 24 is spaced from the hub 12. The second end 36 of the trailing edge 28 is located upstream of the first end 34 of the trailing edge 28, for example upstream in a direction of airflow, denoted by arrow A in FIG. 5, through the impeller 10 in use. This gives the trailing edge 28 a curved, in this instance convex, profile when the blade 14 is viewed in a meridional plane defined by an axis extending parallel to a rotational axis of the impeller 10 and a radial axis, as seen in FIG. 8. It can also be seen from FIG. 8 that the trailing edge 28 has a greater curvature than the leading edge 26 in the meridional plane. The leading edge 26 also has a curved, in this instance concave, profile when viewed along an axis of rotation of the impeller 10 in a direction of airflow through the impeller 10 in use, as seen in FIG. 7. It can also be seen from FIG. 7 that the trailing edge 28 has a greater curvature than the leading edge 26 when viewed along an axis of rotation of the impeller 10 in a direction of airflow through the impeller 10, ie that the trailing edge 28 is more concave than the leading edge 26 when viewed along an axis of rotation of the impeller 10 in a direction of airflow through the impeller 10. As the second ends 32,36 of the leading 26 and trailing 28 edges respectively are located at the same radial distance from the hub, the trailing edge 28 has a greater distance than the leading edge 26 in light of its greater curvature.

[0054] In the manner described above, the second end 32 of the leading edge 26 at the tip 24 and the second end 36 of the trailing edge 28 at the tip 24 are forward swept, for example swept in a direction opposite to the direction of airflow through the impeller 10 in use. This means that at least a portion of a suction surface of each blade 14 is forward swept.

[0055] As mentioned above, the root 22 of each blade 14 is attached to the hub 12, whilst the tip 24 of each blade 14 is spaced away from the hub 12. The root 22 is inclined relative to an axis, indicated B in FIG. 6, parallel to a rotational axis of the impeller 10, by a first angle α. In a presently preferred embodiment the first angle α is 48.48°. The tip 24 is also inclined relative to axis B by a second angle β. In a presently preferred embodiment the second angle β is 65.41°. Thus it can be seen that the tip 24 has a greater angle of inclination than the root 22, as depicted in FIG. 6.

[0056] In a presently preferred embodiment, an intermediate angle of inclination γ of the blade 14 at a radial mid-point between the root 22 and the tip 24 is 50.81°. Thus it can be seen that the transition from the first angle α to the second angle β is irregular. In particular, the rate of transition from the first angle α to the intermediate angle γ is lower than the rate of transition from the intermediate angle γ to the second angle β.

[0057] Other properties of the blade 14 also vary in a radial direction between the root 22 and the tip 24, as can be seen from FIGS. 9a to 9c. In particular, the blade 14 has a cross-sectional shape that varies between the root 22 and the tip 24.

[0058] The blade 14 has a chord length C of around 5.53 mm at the root 22 (as seen in FIG. 9c), a chord length C of around 6.33 mm at a mid-point between the root 22 and the tip 24 (as seen in FIG. 9b), and a chord length C of around 8.08 mm at the tip 24 (as seen in FIG. 9a). Thus the chord length C of the blade 14 is larger at the tip 24 than the root, and in particular in the presently preferred embodiment the chord length C at the tip 24 is 1.461 times the chord length at the root 22.

[0059] The blade 14 has a maximum thickness D of around 0.99 mm at the root 22 (as seen in FIG. 9c), a maximum thickness D of around 0.66 mm at a mid-point between the root 22 and the tip 24 (as seen in FIG. 9b), and a maximum thickness D of around 0.52 mm at the tip 24 (as seen in FIG. 9a). Thus the maximum thickness D of the blade 14 is smaller at the tip 24 than at the root 22, and in particular in the presently preferred embodiment the maximum thickness D of the blade 14 at the tip 24 is 0.525 times the maximum thickness D of the blade 14 at the root 22.

[0060] It has been found by the inventors of the present application that an impeller 10 having blades 14 with the characteristics provided above can provide advantages relative to known impellers. For example, a plot of the performance of the impeller 10 of the present invention relative to a known impeller 50, the impeller disclosed in published UK patent application GB2557958 and herein reproduced in FIG. 10, is shown in FIG. 11.

[0061] It is clear from FIG. 11 that the impeller 10 can provide the same flow rate as the known impeller 50 whilst rotating at a lower speed. This may provide the impeller 10 with improved operating characteristics, including, for example improved acoustic characteristics and/or a reduction in the level of power needed to operate the impeller 10 to provide a desired flow rate.

[0062] An electric motor 100 comprising the impeller 10 is shown in FIG. 12. The electric motor 100 comprises the impeller 10, a rotor assembly 102 (of which the impeller 10 may form a part), a stator assembly 104, and a frame 105. The rotor assembly 102 comprises a shaft 106 to which the impeller 10 is attached, a bearing assembly 108, and a rotor core permanent magnet 110. The electric motor 100 generally has the form of the electric motor described in published PCT patent application WO2017/098200, and so further details of the electric motor 100 will not be reproduced here for brevity.

[0063] A schematic view of a hair care appliance 200 comprising the electric motor 100 is shown in FIG. 13 in the form of a hairdryer.