GB2624190A

GB2624190A - An impeller

Info

Publication number: GB2624190A
Application number: GB2216681.3A
Authority: GB
Inventors: Kumar Mishra Animesh
Original assignee: Dyson Technology Ltd
Current assignee: Dyson Technology Ltd
Priority date: 2022-11-09
Filing date: 2022-11-09
Publication date: 2024-05-15
Also published as: WO2024100518A1; GB202216681D0

Abstract

An impeller 100 comprises a hub 102’ from which extends a plurality of impeller blades 104. The hub has a varying stiffness around the hub to permit relatively less stiff parts of the hub to deform when respective impeller blades are urged to bend. The hub may have a smoothly varying thickness around the hub to provide the varying stiffness. For each blade, a relatively stiff part 128 of the hub may be provided on an opposite side of the blade from a relatively less stiff part 126. For each blade, the relatively less stiff part may be provided at or towards a suction side of the blade and the relatively stiff part provided at or towards a pressure side of the blade. The impeller may be mixed flow, monolithic, injection moulded and/or made from PEEK or aluminium. A motor may drive the impeller at around 125000 rpm. The impeller may be used in an appliance such as a vacuum cleaner.

Description

AN IMPELLER

Field of the Invention

The present invention relates to impellers.

Background of the Invention

An impeller can be used to generate a fluid flow. For example, an impeller may be used to generate an airflow, for example in an appliance such as a vacuum cleaner or hair care appliance. An impeller typically has a hub supporting a plurality of blades. When the hub is driven to rotate, fluid is moved by the blades to create a fluid flow. It can be desirable for impellers to rotate at relatively high speeds, for example to generate fluid flows having relatively high flow rates and/or relatively high static suction pressures. However, increasing the speed at which the impeller rotates can increase the stresses experienced by the impeller, which may ultimately cause mechanical failure of the impeller.

Summary of the Invention

According to a first aspect of the present invention there is provided an impeller comprising a hub from which extend a plurality of impeller blades. The hub is formed to have a varying stiffness around the hub to permit relatively less stiff parts of the hub to deform when respective impeller blades are urged to bend.

For example, the impeller blades may be urged to bend by a centrifugal force acting on the impeller blades when the impeller rotates. Permitting relatively less stiff parts of the hub to deform when respective impeller blades are urged to bend may allow for stress experienced by the hub associated with bending of the impeller blades to be reduced. Reducing a stress experienced by the hub associated with the bending of the impeller blades may allow for the peak stress experienced by the impeller for a given rotational speed to be reduced. This may, in turn, allow for the impeller to withstand faster rotational speeds before mechanical failure. This may, in turn, allow for high flow rates and/or relatively high static suction pressure differences to be produced by an impeller of a given size.

For example, when the impeller rotates, the centrifugal force acting on the impeller blades may act to bend each impeller blade radially outwardly from the rotational axis of the impeller. This may, in turn, cause an increase in tensile stress of the hub at or near the connection of the blade to the hub (e.g. on a side of the blade away from which the blade is caused to bend). This increased tensile stress may add to the tensile stress already experienced by the hub resulting from the centrifugal force acting on the hub itself. Accordingly, the increase in tensile stress of the hub caused by the bending of the blade by the centrifugal force may result in the peak or maximum stress experienced by impeller overall.

This peak stress may be the limiting factor in how fast the impeller can be rotated before mechanical failure of the impeller. For example, if the peak stress becomes larger than the strength limit of the material from which the impeller is made, then the impeller may fail. However, according to the present invention, the hub is formed to have a varying stiffness around the hub to permit relatively less stiff parts of the hub to deform when respective impeller blades are urged to bend. Accordingly, the tensile stress of the hub associated with the bending of the blade can be reduced. In turn, the peak stress experienced by the impeller can be reduced. The deformation of the relatively less stiff parts may cause the tensile stress associated with the bending of the respective impeller blades to be distributed to other parts of the hub. For example, a part of this tensile stress may be distributed to respective relatively stiff parts of the hub. As another example, a part of the tensile stress may be distributed to a back face of the hub. This distribution of the tensile stress associated with the bending of the blades to other parts of the hub may allow the stress to be borne by the hub while nonetheless reducing the peak stress experienced by the impeller. Reducing the peak stress experienced by the impeller may, in turn, allow for the impeller to withstand faster rotational speeds before mechanical failure. This may, in turn, allow for high flow rates and/or high static suction pressure differences to be produced by an impeller of a given size.

In examples, the impeller is for an appliance. In examples, the impeller is for generating an airflow in an appliance. In examples, the varying stiffness around the hub may comprise a varying stiffness along a path that crosses the impeller blades. In examples, the stiffness of the hub may vary along a path spanning across the impeller blades. In examples, the stiffness may vary around the hub (e.g. along the path) so that there is one relatively less stiff part, and one relatively stiff part, per blade. In examples, the variation in hub stiffness around the hub between relatively less stiff and relatively stiff is repeated for each blade. In examples, the variation in hub stiffness around the hub is rotationally symmetric about the rotational axis of the impeller. In examples, the relatively less stiff parts are each formed to have a reduced stiffness as compared to a baseline stiffness of the hub. This reduced stiffness may help promote the deformation of these relatively less stiff parts of the hub when the respective blades are urged to bend, and hence can help promote the reduction of peak stress described above.

The hub may be formed to have a varying thickness around the hub, thereby to provide the varying stiffness. Varying the thickness of the hub to provide for the different varying stiffness may allow for a simple and cost-effective implementation. For example, this may allow for the hub to be made from one material, which may provide for simpler and more cost-effective manufacturing.

In examples, the relatively less stiff parts are provided by respective relatively less thick parts (that is, relatively thin parts) of the hub. In examples, relatively stiff parts of the hub are provided by respective relatively thick parts of the hub. In examples, the relatively less thick parts are provided by reducing a baseline thickness of the hub. That is, in examples, the relatively less thick parts of the hub each have a reduced thickness as compared to a baseline thickness of the hub. This reduced thickness can help promote the deformation of the relatively less thick parts when the respective blades are urged to bend, and hence can help promote the reduction of peak stress described above. Reducing the thickness of the hub as compared to a baseline thickness in the relatively less stiff parts of the hub may allow for the peak stress to be reduced but without necessarily adding mass or size to the impeller, which may be efficient. In examples, the relatively thick parts of the hub may each have an increased thickness as compared to the baseline thickness of the hub. In examples, the varying thickness may oscillate around the baseline thickness of the hub.

The thickness of the hub may vary smoothly around the hub. This may allow for the concentration of hub stresses to be minimised. Alternatively, or additionally, this may allow for any drag caused by the varying thickness to be minimised. In examples, the variation in thickness around the hub (e.g. along the path) may take the form of one or more arcs, sinusoidal functions, hyperbolic functions and/or smoothed trapezoid functions.

The hub may comprise a front face from which the impeller blades extend, and a back face opposite to the front face, and the varying thicknesses may be provided by undulations in the shape of the back face. This may help to reduce an extent to which the varying thickness impacts the generation of the airflow by the blades. Alternatively, or additionally, this may help for the varying thickness to be provided in a simple and cost-effective manner. For example, the back face may be free of blades and hence relatively simple to form with an undulating shape.

The varying stiffness may be provided at least at or towards a trailing edge of each of the impeller blades. At least for radial flow and mixed flow impellers, peak hub stress is typically experienced at or towards the trailing edge of the blade. This is because the trailing edge of the blade is the furthest distance from the rotational axis. Accordingly, the centrifugal force acting to bend the blade, and hence the tensile stress of the hub caused by blade bending, may be largest at or towards the trailing edge. Moreover, the tensile hoop stress caused by rotation of the hub itself may be largest at or towards the trailing edge of the blade. Providing the varying stiffness at least at or towards the trailing edge of each impeller blade may therefore allow for stress associated with blade bending to be particularly effectively reduced.

The varying stiffness may be provided so as to span the length of each of the impeller blades. This may help provide that the stress associated with blade bending may be reduced for the entire blade. This may help ensure the peak stress for the overall impeller can be effectively reduced.

For each impeller blade, a shape of the relatively less stiff part of the hub may follow a shape of an intersection of the impeller blade with the hub. This may help provide that the stress associated with blade bending may be reduced evenly along the length of the blade. This may help ensure the peak stress for the overall impeller can be effectively reduced. In examples, the shape of the intersection of each of the impeller blades with the hub may be generally helical, and accordingly, the shape of the respective relatively less stiff parts of the hub may follow this helical shape.

For each impeller blade, a relatively stiff part of the hub may be provided on an opposite side of the impeller blade to the relatively less stiff part. As mentioned, for each respective blade, the respective relatively less stiff part of the hub deforms, for example bends, so as to reduce bending of the blade itself. The deformation of the relatively less stiff part of the hub on one side of the blade may cause an increase in tensile stress experienced by the hub on the other side of the blade. Accordingly, having the respective relative stiff part of the hub being provided on the other side of the blade to the relatively less stiff part may allow for the increased tensile stress to be borne on the relatively stiff part of the hub.

This may, in turn, help reduce the impact of the increased tensile stress on the hub, and hence allow for peak stress experienced by the overall impeller to remain relatively low.

For each impeller blade, the respective relatively less stiff part of the hub may be provided at or towards a suction side of the impeller blade and a respective relatively stiff part of the hub may be provided at or towards a pressure side of the impeller blade. In mixed flow impellers, the peak stress, contributed to by the tensile stress associated with blade bending, can occur on the suction side of the blade. Accordingly, providing the relatively less stiff part at or towards the suction side of the impeller blade may help allow reduction of the peak stress in such impellers.

The deformation of the relatively less stiff parts of the hub when respective impeller blades are urged to bend may cause at least a part of a stress associated with bending of the respective impeller blades to be redistributed to respective relatively stiff parts of the hub. For example, as mentioned, the stress associated with the bending of the respective impeller blades may comprise tensile bending stress of the hub, and the deformation of the relatively less stiff parts of the hub may cause at least a part of the tensile bending stress is to be redistributed to the respective relatively stiff parts of the hub. Distributing the stress to the respective relatively stiff parts may allow for the impact of the distribution of the stress on the hub to be reduced. This may, in turn, allow for peak stress experienced by the overall impeller to remain relatively low.

The deformation of the relatively less stiff parts of the hub may cause at least a part of the stress associated with the bending of the respective impeller blades to be redistributed to or towards the back face of the hub. In cases where the peak stress experienced by the hub is otherwise at or towards the trailing edge of the impeller blade, the back face of the hub may be associated with relatively low stress as compared to the peak stress. Accordingly, distributing the stress to the back face of the hub may help allow for the peak stress experienced by the overall impeller to remain relatively low.

The impeller may be monolithic. That is, the hub and the impeller blades may form a single continuous structure or component. This may help provide for the stresses to be distributed relatively smoothly between the impeller blades and the hub, and between parts of the hub. Alternatively, or additionally, this may allow for the impeller to be constructed relatively quickly and efficiently, such as by injection moulding or casting. In examples, the impeller is an injection moulded impeller. For example, the impeller may have been formed by injection moulding.

This may allow for the impeller to be produced relatively quickly and efficiently. In examples, the impeller may be made from poly-ether-ether-ketone (PEEK) or aluminium. PEEK may provide a suitably strong material for the impeller to withstand high rotational speeds, but which is capable of being injection moulded.

Aluminium may provide a suitably strong and light-weight material for certain impeller applications. Aluminium may be cast, forged, or machined from bar stock to produce an impeller.

The impeller may be a mixed flow impeller. A mixed flow impeller may be referred to as one which directs the impelled medium (e.g. fluid such as air) both axially and radially. In other examples, the impeller may be a radial impeller. A radial impeller may be referred to as one which directs the impelled medium only radially. In other examples, the impeller may be an axial impeller. An axial impeller may be referred to as one which directed the impelled medium only axially. A mixed flow impeller can provide an airflow at a relatively high flow rate for a given rotational speed. In conjunction with providing higher rotational speeds and hence a higher airflow rate before failure, the impeller being a mixed flow impeller may also help increase an airflow rate for a given impeller size and/or space taken up by the impeller.

According to a second aspect of the present invention, there is provided an impeller comprising a hub from which extend a plurality of impeller blades, the hub being formed to have a varying stiffness around the hub. As above, the varying stiffness around the hub may reduce peak stress experienced by the hub, for example when the impeller rotates, and hence, for example for an impeller that can withstand larger rotational speeds before failure. In examples, the impeller is for an appliance. In examples, the impeller is for generating an airflow in an appliance.

According to a third aspect of the present invention, there is provided an impeller assembly comprising the impeller according to the first aspect or the second aspect, and a motor for driving rotation of the impeller. The impeller assembly may be controlled to provide the airflow. In examples, the motor may be configured to drive the impeller at rotational speeds to cause the centrifugal and/or other loads to raise the internal stresses of the impeller to the order of the material limit of the impeller. In examples, the motor may be configured to drive the impeller at greater than or equal to around 125000 revolutions per minute. At such relatively high rotational speeds, the centrifugal forces are accordingly relatively high, and the stresses associated with bending of the impeller blades are significant. The deformation of the relatively less stiff first part of the hub to reduce the stress associated with bending of the blade may therefore find particular utility at such rotational speeds.

According to a fourth aspect of the present invention, there is provided an appliance comprising the impeller according to the first aspect or the second aspect, or the impeller assembly according to the third aspect. For example, the appliance may be a domestic appliance. In examples, the appliance may be a vacuum cleaner. In other examples, the appliance may be a haircare appliance. It may be particularly important for such appliances to be of a reasonable size and mass to be easily handled by a person. Accordingly, allowing for high flow rates and/or high static suction pressure differences to be produced by an impeller of a given size may find particular utility in such appliances.

Optional features of aspects of the present invention may be equally applied to other aspects of the present invention, where appropriate.

Brief Description of the Drawings

Figure 1 is a perspective view of an example impeller; Figure 2 is another perspective view of the example impeller of Figure 1; Figure 3 is a side view of the example impeller of Figure 1; Figure 4 is a rear view of the example impeller of Figure 1; Figure 5 is a schematic diagram illustrating a cross section of a part of a known impeller; Figure 6 is a schematic diagram illustrating a cross section of a part of the example impeller of Figure 1; Figure 7 is a rear view of a portion of the example impeller of Figure 1; Figures 8a and 8b illustrate stress simulations in a part of a known impeller; Figures 9a and 9b illustrate the results of stress simulations in a part of an impeller according to an example of the present invention; and Figure 10 is a schematic diagram illustrating an appliance and impeller assembly according to an example.

Detailed Description of the Invention

Referring to Figures 1 to 4, there is illustrated an impeller 100 according to an example. The impeller 100 comprises a hub 102 from which extend a plurality of impeller blades 104.

In the example illustrated in Figures 1 to 4, the impeller is a mixed flow impeller. A mixed flow impeller may be referred to as one which directs the impelled medium (e.g. air) both axially and radially. That is, the blades 104 are arranged such that, when the hub 102 rotates 124 (e.g. by being driven to rotate by a drive shaft or an electric motor (not shown)) the blades 104 force an impelled medium (e.g. air) both in a direction parallel with the rotational axis 106 of the impeller and radially away from the rotational axis 106 of the impeller.

In this example, the hub 102 has a front face 120 from which the impeller blades 104 extend, and a back face 122 opposite to the front face 120. The hub 102 is generally frustoconical in shape, and a diameter of the hub 102 generally increases from a front end 134 of the hub 102 to a rear end 132 of the hub 102.

Each blade 104 comprises a filet 118 at the intersection of the blade 104 with the hub 102. The filet 118 forms a smooth transition between the faces and edges of the blade and the front face 120 of the hub 102. There are nine blades 104 distributed evenly around the hub 102. Each blade 104 is inclined with respect to the font face 120 of the hub 120. Each blade 104 extends from the front end 134 to the rear end 132 of the hub 102, and also extends part way around the hub 102. Accordingly, the intersections of the blades 104 with the hub 102 form a helicoid pattern, such as a generally helical pattern, on the front face 102 of the hub 102. Each blade has a leading edge 112 towards the front end 134 of the hub 102 and a trailing edge 114 towards the rear end 132 of the hub. Each blade 114 has a pressure side 116 and a suction side 110. The pressure side 116 is that at which, when the hub 102 rotates 124, the pressure of the impelled medium is increased. The suction side 110 is that at which, when the hub 102 rotates 124, the pressure of the impelled medium is decreased.

As described in more detail below with reference to Figure 6, the hub 102 is formed to have a varying stiffness around the hub 102 to permit relatively less stiff parts 126 of the hub 102 to deform when respective impeller blades 104 are urged to bend.

In the example of Figures 1 to 4, the stiffness varies around the hub 102 in that different parts of the hub at different locations about the rotational axis 106 of the hub have different stiffnesses. Specifically, the hub 102 has one relatively less stiff part 126 and one relatively stiff part 128 per blade 104. According, in the illustrated example, the hub has nine relatively less stiff parts 126 and nine relatively stiff parts 128. The relatively less stiff parts 126 and the relatively stiff parts 128 alternate around the hub 102. Accordingly, the varying stiffness of the hub forms an oscillatory pattern 130 around the hub 102. The stiffness variation between a relatively less stiff part 126 and a relatively stiff part 128 may repeat for each blade 104. That is, the relatively less stiff part 126 and the relatively stiff part 128 may be the same for each blade 104. Accordingly, the variation in stiffness may be distributed evenly around the hub 102, as are the blades 104.

The variation in hub stiffness around the hub 102 is rotationally symmetric about the rotational axis 106. The variation in hub stiffness between relatively less stiff and relatively stiff is repeated for each blade 104.

In the example of Figures 1 to 4, the varying stiffness around the hub 102 comprises a varying stiffness along a path 108. The path 108 is hypothetical and is used for illustrative purposes. In this example, the path 108 is generally circular and is co-axial with a rotational axis 106 of the hub 102. The path 108 spans across all of the impeller blades 104. Specifically, in this example the path 108 crosses the impeller blades 104. The illustrated path 108 is just an example, and the path 108 may be drawn instead, for example nearer or at the rear side 132 of the hub 102 or for example nearer or at the front side 134 of the hub 102.

In the example of Figures 1 to 4, the varying stiffness around the hub 102 is provided by the hub 102 being formed to have varying thickness around the hub 102. In other words, in this example, the hub 102 is formed to have a varying thickness around the hub 102, thereby to provide the varying stiffness. Accordingly, the relatively less stiff parts 126 are provided by parts of the hub 102 having a relatively small thickness R1. The relatively stiff parts 128 are provided by parts of the hub 102 having a relatively large thickness R2. The thickness of the hub 102 varies smoothly around the hub 102, for example smoothly around the path 108. In this example, the thickness of the hub 102 oscillates smoothly around the hub 102, with one oscillation per blade 104. The distance between consecutive relatively thick parts 128 (or equally consecutive relatively thin parts 126) is the same as the distance between consecutive blades 102. In this example, the varying thickness is provided by undulations in the back face 122 of the hub. In this example the front face 120 of the hub 102 does not have such undulations and is generally conical in shape. Accordingly, in this example, the varying thickness is provided only by undulations in the back face 122 of the hub 102. In this example, the variation in thickness around the hub 102 (e.g. along the path 108) takes the form of two arcs. That is, each undulation is composed of two arcs. A first arc is convex with respect to the rotational axis 106 and provides a respective relatively thick part 128. A second arc is concave with respect to the rotational axis and provides a respective, adjacent, relatively thick part 126. It will be appreciated that in other examples, the variations in thickness (e.g. the undulations in the back face 122 of the hub 102) may take other forms, such as sinusoidal functions, hyperbolic functions, smoothed trapezoid functions and/or any other repeating functions.

As mentioned, in this example, the relatively less stiff parts 126 are provided by respective relatively less thick parts (that is, relatively thin parts) 126 of the hub 102. In examples, the relatively less thick parts 126 may be provided by reducing a baseline thickness of the hub (not shown in Figures 1 to 4, but see the dotted line 109 in Figure 7). That is, the relatively less thick pads 126 of the hub 102 may each have a reduced thickness R1 as compared to a baseline thickness 109 of the hub 102. For example, the baseline thickness 109 of the hub 102 may be that of an otherwise identical impeller but without the varying hub thickness applied. This reduced thickness can help promote the deformation of the relatively less thick parts 126 when the respective blades 104 are urged to bend, and hence can help promote the reduction of peak stress as described in more detail below.

In the example of Figures 1 to 4, the varying stiffness (in this example, varying thickness) is provided at least at or towards the trailing edge 114 of each of the impeller blades 104. Specifically, the varying stiffness is provided so as to span the length of each of the impeller blades 104 along the front face 120 of the hub 102. That is, as perhaps best seen in Figures 2 and 4, the varying thickness is swept from the rear end 132 to the front end 134 of the hub 102. Further, the relatively less stiff parts 106 (and equally the relatively stiff parts 108) each extend, like the blades 104, part way around the hub 102. Specifically, for each impeller blade 104 (see specifically blade 104a in Figures 2 and 4 as an example), a shape of the relatively less stiff part 126 of the hub 102 (and equally the relatively stiff part of the hub 128) may follow a shape of an intersection of the impeller blade 104 with the hub 102. As mentioned above, the intersections of the blades 104 with the hub 102 form a helicoid pattern, specifically a generally helical pattern. Accordingly, the relatively less stiff parts 126 of the hub 102 (and equally the relatively stiff parts of the hub 128) form a helicoid patters, specifically a generally helical pattern.

In this example, for each impeller blade 104, a respective relatively stiff part 128 of the hub 102 is provided on an opposite side of the impeller blade 102 to the relatively less stiff part 126. Further, in this example, for each impeller blade 104, the respective relatively less stiff part 126 of the hub 102 is provided at or towards the suction side 110 of the impeller blade 104 and a respective relatively stiff part 128 of the hub 102 is provided at or towards a pressure side 116 of the impeller blade 104.

In this example, the impeller 104 is monolithic. That is, the hub 102 and the impeller blades 104 form a single continuous structure or component. The impeller 100 may, for example, be an injection moulded impeller 100. For example, the impeller 100 may have been formed by injection moulding. In examples, the impeller 100 may be made from poly-ether-ether-ketone (PEEK), which can, for example, be injection moulded. In examples, the impeller 100 may be made from aluminium, which can, for example, be cast or forged or machined from stock.

With reference to Figures 5, 8a and 8b, there is now described a comparative example to illustrate the stresses that may be experienced by a comparative impeller 500 in which the varying stiffness around the hub is not provided. The hub of the comparative impeller 500 may, for example, have the baseline thickness 109 mentioned above. Referring first to Figure 5, when the hub 502 of the comparative impeller 500 rotates, a centrifugal force 550 acting radially outwardly from the rotational axis (not shown in Figure 5) of the impeller 500 causes the blade 504 to bend radially outwardly from the rotational axis of the impeller 500. The bending of the impeller blade is shown schematically in Figure 5 by the impeller blade 504' drawn with dashed lines. This blade bending causes an increase in tensile stress of the hub on a side of the blade away from which the blade 504 is caused to bend, and an increase in compressive bending stress on the other side of the blade 504. The general location of the tensile bending stress is indicated in Figure 5 as 554, and the general location of the compressive bending stress is indicated in Figures 5 as 552. The increased compressive bending stress 552 corresponds to a relief of the tensile stress already experienced by the hub 502 resulting from the centrifugal force acting on the hub 502 itself (specifically the hub hoop tensile stress, indicated in Figured 5 as 556). However, the increased tensile stress 554 adds to the tensile stress 556 already experienced by the hub 502 resulting from the centrifugal force acting on the hub 502 itself. Accordingly, this increase in tensile stress of the hub 502 caused by the bending of the blade 504 by the centrifugal force 550 may result in the peak or maximum stress experienced by impeller 502 overall.

Specifically, referring to Figures 8a and 8b, there is illustrated the results of a simulation of the stress experienced by the comparative impeller 500 under a given centrifugal loading. Figures 8a and 8b show a pad of the comparative impeller 500 as viewed from the rear end 532 of the hub 502. As can be seen, there is a peak stress of 147 MPa experienced by the hub 502 on the side of the blade 504 away from which the blade 504 is caused to bend by the centrifugal force and towards the trailing edge 514 of the blade. That is, there is a relatively high peak stress experienced by the hub 502 where the tensile bending stress adds to the hub hoop stress (and this is maximised at or towards the trailing edge 514, which is the furthest from the rotational axis and hence experiences the largest centrifugal loading for a given rotational speed). On the other hand, the stress experienced by the hub 502 on the side of the blade 504 towards which the blade is caused to bend by the centrifugal force is relatively low at 100 MPa.

That is, there is a relatively low stress experienced by the hub where the compressive bending stress provides a relief to the hub hoop stress. Further, as shown in Figure 8b, there is a relatively low stress of 114 MPa experienced by the hub at the back face 522 and rear end 532 of the hub.

This peak stress may be the limiting factor in how fast the impeller can rotate before mechanical failure of the impeller. For example, if the peak stress becomes larger than the strength limit of the material from which the impeller is made, then the impeller may fail. For example, is the strength limit of the material from which the comparative impeller 500 is made is less than 147 MPa, then the given centrifugal loading (that is, the given rotational speed of the impeller 500) used in the simulation of Figures 8a and 8b may result in the comparative impeller failing, specifically at the peak stress location.

With reference to Figures 6, 9a, and 9b, there is now described an example to illustrate how the varying stiffness of the hub 102 can reduce peak stress experienced by the impeller 100. Referring first to Figure 6, as was the case for Figure 5, when the hub 102 of the impeller 100 rotates, a centrifugal force 150 acting radially outwardly from the rotational axis (not shown in Figure 6) of the impeller 100 urges the blade to bend radially outwardly from the rotational axis of the impeller 100. However, the hub 102 is formed to have a varying stiffness around the hub 102 to permit relatively less stiff parts 126 of the hub to deform when respective impeller blades 104 are urged to bend. Accordingly, when the centrifugal force 150 urges the blade 104 to bend, in place of the blade 104 bending, the relatively less stiff part 126 of the hub 102 deforms, specifically bends outwards. The deformed configuration of the hub is shown in Figure 6 by the dashed lines 102. The deformation of the hub 102 allows the blade 104 to move as urged by the centrifugal force 150 but without bending or bending to a lesser extent (the position of the blade when the hub deforms is shown by the dashed lines 104' in Figure 6). Accordingly, the tensile bending stress 154 of the hub 102 (that is, the tensile stress on the side of the blade 104 away from which the blade 104 is urged to bend) for a given centrifugal load 150 can be reduced. In turn, the peak stress experienced by the impeller 100 can be reduced. The deformation of the relatively less stiff part 126 causes the tensile bending stress 154 to be redistributed to other parts of the hub 102. Specifically, a part of the tensile bending stress 154 is distributed to the respective relatively stiff part 128 of the hub 102. Further, a part of the tensile bending stress 154 is distributed to a back face 122 of the hub 102.

Specifically, referring to Figures 9a and 9b, there is illustrated the results of a simulation of the stress experienced by the impeller 100 under the same given centrifugal loading (e.g. the same rotational speed) as for Figures 8a and 8b.

Figures 9a and 9b show a part of the impeller 100 as viewed from the rear end 132 of the hub 102. As can be seen, the peak stress experienced by the hub 102 is still on the side of the blade 104 away from which the blade 104 is urged to bend by the centrifugal force and towards the trailing edge 114 of the blade.

However, this peak stress has been reduced from 147 MPa to 132 MPa. The stress experienced by the hub 102 on the side of the blade 104 towards which the blade is urged to bend by the centrifugal force has increased from 100 MPa to 121 MPa. However, this is still less than the now reduced peak stress of 132 MPa. Similarly, as shown in Figure 9b, the stress experienced by the hub 102 at the back face 122 and rear end 132 of the hub 102 has increased from 114 MPa to 126 MPa. However, again, this is still less than the now reduced peak stress of 132 MPa. Accordingly, the peak stress experienced by the impeller 102 is reduced. Reducing the peak stress experienced by the impeller 100, in turn, allows for the impeller 100 to withstand faster rotational speeds before mechanical failure. This may, in turn, allow for high flow rates to be produced by the impeller 100.

The example impeller 100 described above with reference to Figures 1 to 4 has a specific variation in the stiffness around the hub 102 that is optimised for reducing the peak stress for the specific arrangement of the hub 102 and of the blades 100 extending from the hub. However, it will be appreciated that for different hub 102 and blade 104 arrangements, different variation in the stiffness around the hub may be used and/or may be optimal. Figure 7 illustrates some example parameters of the varying stiffness around the hub 102 that may be altered, alone in combination, for example in order to optimise the reduction in peak stress associated with blade bending under centrifugal loading, according to some examples. For example, the amplitude R of the variation in stiffness (e.g. thickness) between the relatively stiff parts 128 and the relatively less stiff parts 126 may be altered and/or optimised. This may, in part, control the extent to which the relatively less stiff parts 126 deform when the blades 104 are urged to bend.

As another example, the arc angle cl) of the relatively stiff parts 128 as compared to the relatively thin parts 126 may be altered. That is, the radial extent of the relatively stiff parts 128 as compared to the relatively thin parts 126 may be altered. This may, in part, control the extent to which the relatively less stiff parts 126 deform when the blades 104 are urged to bend. As another example, the angle 0 of the axial sweep of varying stiffness from back end 132 to the front end of the hub 102 may be altered. For example, where the axial sweep of varying stiffness forms a helical pattern, as is here, the angle 6 of the axial sweep may at least in part define the geometry for the helical pattern. This may, in part, control the positioning of the relatively less stiff parts 126 and the relatively stiff parts 128 relative to the blades 103, and hence, in part, control the distribution of the stress to different parts of the hub 102. As another example, the clocking 4, of the varying thickness around the hub 102 relative to the location 770 of the peak stress (in this case, the hub stress concentration at the trailing edge suction side of the blade 104) may be altered. For example, the clocking may be a radial angle t.t, between the location 770 of the peak stress for a given blade 104 and the respective relatively less stiff part 126 of the hub 102. This may, in part, control the positioning of the relatively less stiff parts 126 and the relatively stiff parts 128 relative to the blades 103, and hence, in part, control the distribution of stress to different parts of the hub 102. Other parameters may be varied. Nonetheless, providing that the hub 102 is formed to have a varying stiffness around the hub 102 to permit relatively less stiff parts 126 of the hub to deform when respective impeller blades 104 are urged to bend. may allow for a reduction in the peak stress experienced by the hub and hence for the impeller 104 to withstand greater centrifugal loading before mechanical failure.

Indeed, it will be appreciated that other examples may be different in other ways to the example impeller 100 described above with reference to Figures 1 to 4. For example, other example impellers (not shown) may have a different type or number or arrangement of blades, may have blades which have different inclination to the hub and/or a different shape, and/or may have a differently shaped hub. Other example impellers may be any one of radial, axial, and mixed flow impellers. In principle, any given impeller design may be used. As another example, the variation in the thickness around the hub need not necessarily be provided by variations in the shape of the back face of the hub, and may, for example alternatively or additionally be provided by variations in the shape of the front face of the hub. As another example, the varying stiffness need not necessarily be provided by varying the thickness of the hub. For example, the varying stiffness may, alternatively or additionally, be provided by forming the hub of different materials having different stiffnesses, distributed around the hub. Other variations are also possible. Nonetheless, in example impellers, the hub is formed to have a varying stiffness around the hub. This allows for relatively less stiff parts of the hub to deform when respective impeller blades are urged to bend, for example under centrifugal loading. This allows for a reduction in the bending of the blade under a given centrifugal loading. This allows for the stress associated with blade bending to be reduced. This allows for a peak stress of the hub, otherwise caused by the bending of the blade, to be reduced. This allows for the impeller to withstand greater centrifugal loading before mechanical failure. This allows the impeller to be rotated at greater speeds before mechanical failure. This allows the impeller to generate a larger flow rate and/or static suction pressure difference.

In examples, the impeller 100 is for an appliance. Referring to Figure 10, there is illustrated schematically an appliance 100 comprising the impeller 100. The appliance 100 may, for example, be a domestic appliance. For example, the appliance 1000 may be a hand-held appliance. For example, the appliance 1000 may be a vacuum cleaner or a haircare appliance, such as a hairdryer. The appliance 1000 comprises an impeller assembly 1002. The impeller assembly 1002 may be used to generate an airflow in the appliance 1000. The impeller assembly 1002 comprises the impeller 100 and a motor 1004 for driving rotation of the impeller 100. The impeller 100 is coupled to the motor by a drive shaft 1006 (which e.g. is affixed to the hub of the impeller and passes through the rotational axis of the impeller). When the motor 1004 is powered (e.g. by a power source such as a battery (not shown), the motor 1004 causes the shaft 1006 to rotate which in turn causes the impeller 100 to rotate to generate the airflow. In examples, the motor 1004 may be configured to drive the impeller 100 at relatively high speeds, for example, greater than or equal to around 125000 revolutions per minute.

In some of the above examples, the impeller 100 is for use with and/or used in an appliance 1000 such as a hairdryer or a vacuum cleaner. In other examples, the impeller may be for use with and/or used in other devices, such as industrial compressors. In examples, the impeller may be for use with and/or used in devices that operate the impeller at relatively high rotational speeds or otherwise operate the impeller in a way that urges the blade to bend. In some of the above examples, the impeller 100 is used to generate an airflow. In other examples, the impeller 100 may be used to generate any fluid flow, such as other gasses, and/or liquids such as oil and water. In examples where the fluid is relatively viscous, such as oil, the fluid may urge the blade 104 to bend when the impeller rotates. Accordingly, the varying stiffness around the hub 102 to permit relatively less stiff 106 parts of the hub 102 to deform when respective impeller blades 104 are urged to bend, as described above, may reduce peak stress experienced by the hub 102 in such examples too.

Whilst particular examples and embodiments have been described, it should be understood that these are illustrative only and that various modifications may be made without departing from the scope of the invention as defined by the claims.

Claims

Claims 1. An impeller comprising a hub from which extend a plurality of impeller blades, the hub being formed to have a varying stiffness around the hub to permit relatively less stiff parts of the hub to deform when respective impeller blades are urged to bend.
2. The impeller according to claim 1, wherein the hub is formed to have a varying thickness around the hub, thereby to provide the varying stiffness.
3. The impeller according to claim 2, wherein the thickness of the hub varies smoothly around the hub
4. The impeller according to claim 2 or claim 3, wherein the hub comprises a front face from which the impeller blades extend, and a back face opposite to the front face, and wherein the varying thickness is provided by undulations in the shape of the back face.
5. The impeller according to any one of the preceding claims the varying stiffness is provided at least at or towards a trailing edge of each of the impeller blades.
6. The impeller according to any one of the preceding claims, wherein the varying stiffness is provided so as to span the length of each of the impeller 25 blades.
7. The impeller according to claim 6, wherein, for each impeller blade, a shape of the relatively less stiff part of the hub follows a shape of an intersection of the impeller blade with the hub.
8. The impeller according to any one of the preceding claims, wherein, for each blade, a relatively stiff part of the hub is provided on an opposite side of the impeller blade to the relatively less stiff pad.
9. The impeller according to any one of the preceding claims, wherein, for each impeller blade, the relatively less stiff part is provided at or towards a suction side of the impeller blade and a relatively stiff part is provided at or towards a pressure side of the impeller blade.
10. The impeller according to any one of the preceding claims, wherein the deformation of the relatively less stiff parts of the hub when respective impeller blades are urged to bend causes at least a part of a stress associated with bending of the respective impeller blades to be distributed to respective relatively stiff parts of the hub.
11. The impeller according to claim 10, wherein the stress associated with the bending of the respective impeller blades comprises tensile bending stress of the hub, and wherein the deformation of the relatively less stiff parts of the hub causes at least a part of the tensile bending stress to be redistributed to respective relatively stiff parts of the hub.
12. The impeller according to claim 10 or claim 11, wherein the deformation of the relatively less stiff parts of the hub causes at least a part of the stress associated with the bending of the respective impeller blades to be redistributed 25 to or towards a back face of the hub.
13. The impeller according to any one of the preceding claims, wherein the impeller is monolithic.
14. The impeller according to any one of the preceding claims, wherein the impeller is an injection moulded impeller.
15. The impeller according to any one of the preceding claims, wherein the impeller is made from poly-ether-ether-ketone, PEEK, or aluminium.
16. The impeller according to any one of the preceding claims, wherein the impeller is a mixed flow impeller.
17. An impeller comprising a hub from which extend a plurality of impeller blades, the hub being formed to have a varying stiffness around the hub.
18. An impeller assembly comprising the impeller according to any one of the preceding claims and a motor for driving rotation of the impeller.
19. The impeller assembly according to claim 18, wherein the motor is configured to drive the impeller at greater than or equal to around 125000 revolutions per minute.
20. An appliance comprising the impeller according to any one of claims 1 to 17 or the impeller assembly according claim 18 or claim 19.
21. The appliance according to claim 20, wherein the appliance is a vacuum cleaner.