GB2289090A - Centrifugal fan - Google Patents

Abstract

A centrifugal fan 10 comprises a plurality of longitudinal fan blades 16 around an axis of rotation A. An inlet funnel 18 is attached to and extends away from the fan blades 16 and is shaped to guide air into the fan. In operation the inlet funnel and the fan blades rotate together which permits certain manufacturing body tolerances to be relaxed. The funnel and the fan may also be formed integrally as one piece, for example by moulding, to provide a cost saving over separate components. This fan is particularly suitable for use in a fan heater. <IMAGE>

Description

DESCRIPTION CENTRIFUGAL FAN Rotary fans are well known for providing air flow in a number of applications, for example in fan heaters and air cleaners in the home.

Compact appliances often use a centrifugal style fan as these provide a greater air flow in a given physical space than other types of fan. A typical construction of such an appliance thus comprises an air inlet, a centrifugal fan driven by a motor, heating or filtering components and an air outlet. One difficulty with using a centrifugal fan is that a greater quantity of air is usually desired to be sucked into the centrifugal fan than is readily available at its inlet and a funnel is usually required at that inlet to reduce turbulence and recirculation which adversely affects the efficiency of the fan.

Generally it is desirable to reduce the overall height of the fan and, for aesthetic and safety reasons, a grille is required to cover the mouth of the inlet funnel. Because conventional moulding techniques do not allow the inlet funnel, grille and appliance outer casing to be formed as one piece, an arrangement has been adopted in which the grille is formed integrally with the inlet funnel as a separate piece and an overlap is provided between the inlet funnel and the inlet of the fan to avoid air leaking out between the funnel and the fan inlet.This air seal is critical and presents problems because the shaping of the funnel and fan inlet, the rotation at high speed of the fan and tolerance build ups in the various components make it very difficult to obtain the very small clearance between the fan inlet and the funnel necessary to provide effective sealing and so avoid leakage of air around the fan, so "wasting" air flow. Of course, where it is necessary to meet such very tight tolerance requirements, inevitably manufacturing costs increase. Furthermore, the need for a separate grille or funnel inevitably increases costs.

It is an object of the present invention to reduce or at least mitigate the above disadvantages.

According to the present invention there is provided a centrifugal fan comprising a plurality of longitudinal fan blades arranged around an axis of rotation, and a funnel shaped to guide air into the blades, the funnel extending coaxially away from the fan blades and being arranged to rotate with the blades.

The inlet funnel for the centrifugal fan acts to guide air into the fan so as to reduce turbulence and recirculation which would otherwise result in losses.

In a fan in accordance with the invention, the funnel is arranged to rotate with the blades so that there are no significant air passages between the inlet funnel and the hollow body, without the traditional problems of having to provide a very small clearance between the ends of the blades and the funnel to avoid leakage of air while, at the same time, allowing the blades to be rotated at high speed. The inlet funnel and the fan blades are desirably formed together, for example by moulding as one piece from a suitable plastics material, but may alternatively be separate mouldings closely fitted together.

Generally, the internal surface of the funnel widens out smoothly from the fan blades in any suitable shape. In one example, the funnel surface curves and is bell-shaped. Alternatively the surface may be straight-sided.

The axial length of the funnel may be shorter than, equal to, or greater than the axial length of the fan blades, depending on the requirements of the design.

Generally means will be provided for rotating the fan blades about the axis and a drive hub may be formed integrally with the fan blades for cooperating with the drive means, usually an electric motor, to cause rotation, although the drive hub could be a separate component.

The present invention further relates to a domestic appliance comprising a casing having a first aperture and a second aperture and housing a centrifugal fan, the centrifugal fan comprising a plurality of longitudinal fan blades arranged around an axis of rotation and a funnel extending coaxially between the first aperture and the fan blades, so as to guide air between the first aperture and the fan blades, the funnel being arranged to rotate with the fan blades, and a motor for causing the centrifugal fan to rotate about its rotation axis to provide an air flow between the first and second apertures.

A lip may extend inwardly of the casing to cooperate with a mouth of the funnel. As one possible alterative or additionally, the funnel may have an outwardly extending flange which overlaps with a portion of the casing surrounding the first aperture. Such arrangement enables a good air seal to be provided between the funnel and the casing.

Such a domestic appliance may be a fan heater including a heating element arranged in the air path of the centrifugal fan.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, wherein: Figure 1 shows a perspective view of a centrifugal fan in accordance with the present invention, Figure 2 shows a plan view of the fan shown in Figure 1 looking in the direction of arrow X in Figure 1; Figure 3 shows a vertical section through the centrifugal fan shown in Figure 1; Figure 4 shows a schematic exploded perspective view of a fan heater in accordance with the present invention; Figure 5 shows a diagrammatic part-sectional view of part of the fan heater shown in Figure 4 for illustrating one way of providing an air seal between a casing and funnel of the fan heater; and Figure 6 shows a diagrammatic part-sectional view of part of the fan heater shown in Figure 4 for iliustrating another way of providing an air seal between a casing and funnel of the fan heater.

It should of course be understood that the drawings are merely schematic and are not to scale. Like parts are designated by like reference numerals throughout the drawings.

The fan 10 shown in Figures 1, 2 and 3 is constructed from a suitable plastics material, for example by injection moulding. The fan comprises a plurality of axially extending fan blades 1 6 arranged about an axis of rotation A. In the interests of clarity, the details of the fan blades 1 6 are not shown in Figure 2, rather only an outline of one blade 1 6 is shown. A wide variety of blade shapes may be used as is known in centrifugal fans.

Attached to one end of the fan blades, and supporting them, is a circular funnel 1 8. The internal diameter of the funnel is equal to the internal diametric spacing of the fan blades at this attached end; the internal surface of the funnel 18 smoothly increases in diameter in the axial direction away from the fan blades to form a passageway 30. In this example, the passageway 30 can be considered to be generally bell-shaped. However, any suitable divergent shape or profile for the passageway can be used; for example, a straight-walled divergent funnel could be used.

The funnel 18 and fan blades 16 may be moulded integrally, or may be separate mouldings closely fitted together to retain a smooth internal surface.

As can be seen from Figures 2 and 3, the ends 1 6a of the blades 16 remote from the funnel 18 are connected via a radially inwardly extending flange 21 and spokes 22, four in the example shown, to a central hub 20.

The hub 20 and spokes 22 define a cage or housing for a motor (not shown in Figures 1 to 3) to be used to drive the fan 1 0, that is to cause the fan 10 to rotate about its rotation axis A. The hub 20 and the spokes 22 may be moulded integrally with the blades 16 and funnel 18, or may alternatively be formed separately from the fan, for example as part of the drive shaft of the motor used to drive the fan.

Figure 4 shows an exploded schematic perspective view of a fan heater 30 incorporating a fan in accordance with the invention. The fan heater comprises a casing 31, side walls of which are not shown. The casing may be formed in any appropriate manner and of any suitable material, for example a plastics material or metal. The casing 31 has a lower wall or floor 31a to which is mounted a fan diffusor 32 having an opening 32a opposite a front wall 31 b of the casing. The front wall 31 b has a perforate section 31 c to allow air circulated by the fan 10 to pass through. Generally, the perforate section comprises a slotted grille 31c.

The floor 31a provides a mounting place 31j for a motor 33 within the area defined by the shielding wall of diffusor 32. The fan 1 0 fits within the diffusor 32 so that the motor 33 is received within the cage defined by the spokes 22 with the drive shaft 33a of the motor 33 being engaged within the central hub 20 in known manner so that, in operation, the fan 10 rotates with the drive shaft 33a.

A fan heating device 40 in the form of a wire heating element 41 (only part of which is shown in Figure 4) wound around formers 42 carried by a support 43 is mounted to the floor 31a between the fan and the grille 31c.

A top section 31d of the casing 31 is provided with an opening 31f covered by a further grille 31e which, when the fan heater is assembled, registers with the funnel 1 8 of the fan 1 0.

Figure 5 illustrates schematically one way of avoiding or at least inhibiting air leakage between the funnel 18 and the casing 31. In this example, an inwardly extending lip 319 is provided around the periphery of the opening 31f and the outer edge 18b of the funnel is received within the casing so as to be closely bounded by the lip 319. The interaction of the edge 1 8b and the lip 319 effectively forms an air seal which allows rotation of the funnel 18 relative to the top section 31 d of the casing 31 but inhibits the passage of air between the casing and the funnel 1 8 so that air is only drawn in through the funnel 1 8 and does not leak out significantly between the funnel 1 8 and the casing 31.The clearance between the lip 319 and the edge 18b may be typically 1 to 2 mm (millimetres), 2 mm in this example.

Figure 6 illustrates schematically another way of avoiding or at least inhibiting air leakage. In this example, the outer edge 1 8b of the funnel 1 8 is provided with a radially outwardly extending flange 1 8d of maximum diameter greater than the diameter of the opening 31 f so that the flange 1 8d is located close to and overlaps with the portion 31h of the top section 31d surrounding the opening 31f to enable rotation of the funnel 1 8 about its axis while inhibiting the flow of air into the casing 31 between the casing opening 31f and the funnel 18.

As shown in dashed lines in Figure 6, an inwardly extending lip may also be provided in this example but as an inwardly extending wall 319' spaced back from the periphery of the opening 31 f so that the flange 1 8d is bounded by the lip 319'. The interaction of the flange 1 8d and the portion 31 h (and the lip 319', if present) in effect forms a seal which allows rotation of the funnel 18 relative to the top section 31 d of the casing 31 but inhibits the passage of air between the casing and the funnel 18 so that air is only drawn in through the funnel 18.The provision of both the flange 1 8d and the optional lip 319' should enable an increase in manufacturing tolerance because larger spaces can be allowed between the overlapping flange 1 8d and portion 31 h and between the lip 319' and the edge of flange 18d. Thus, in this example, the spacing between the lip 319' and the edge of flange 18d and the portion 31h of the top section 31d may be as much as 3mm, although generally a spacing of 2mm is preferred. A similar spacing exists between the wall 319' and the edge of the flange 18d, when the wall 31g' is present.

The openings covered by the grilles 31e and 31c form the first and second apertures respectively. The grilles may be integrally formed during the manufacture of the casing by for example forming perforations or slots in the casing or may be defined by separate grids or meshes mounted to the casing in known manner.

In operation of the fan heater 30 shown in Figure 4, the fan 10 is rotated about its axis by the motor 33 so that the fan blades 1 6 cause air to be drawn through the grille 31e in the top of the casing 31 into the funnel 18. The air continues through the fan and is circulated by the fan to pass through the opening 32a and over the heating element 41 which heats the air. The warmed air then passes through the grille 31e. The shape of the funnel allows the fan to draw in an increased quantity of air, as is conventional with funnels for centrifugal fans.

Because the fan includes an integral inlet funnel 18, the clearance between the casing and the funnel (as opposed to the clearance between a fan and a casing mounted funnel) is not particularly critical. This allows greater manufacturing tolerances and design freedom with regard to the mounting of the motor and the fan within the casing.

A fan in accordance with the present invention may also be applied to other domestic appliances which rely upon fan-driven air such as air cleaners as well as other non-domestic applications for which a very compact yet cheap fan is required.

From reading the present disclosure other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the design, manufacture and use of turbine fans and component parts thereof and which may be used instead of or in addition to features already described herein. Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure of the present application also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention. The applicants hereby give notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom.

Claims (11)

1. A centrifugal fan comprising a plurality of longitudinal fan blades arranged around an axis of rotation, and a funnel shaped to guide air into the blades, the funnel extending coaxially away from the fan blades and being arranged to rotate with the blades.

2. A centrifugal fan as claimed in Claim 1, wherein the fan blades and the funnel are formed integrally in one piece.

3. A centrifugal fan as claimed in Claim 1 or Claim 2, wherein the internal surface of the funnel is bell-shaped.

4. A centrifugal fan as claimed in Claim 1 or Claim 2 wherein the internal surface of the funnel is straight-sided.

5. A domestic appliance comprising a casing having a first aperture and a second aperture and housing a centrifugal fan, the centrifugal fan comprising a plurality of longitudinal fan blades arranged around an axis of rotation and a funnel extending coaxially between the first aperture and the fan blades so as to guide air between the first aperture and the fan blades, the funnel being arranged to rotate with the fan blades; and a motor for causing the centrifugal fan to rotate about its rotation axis to provide an air flow between the first and second apertures.

6. A domestic appliance as claimed in Claim 5, wherein the funnel is formed integrally in one piece with the fan blades.

7. A domestic appliance as claimed in Claim 5 or Claim 6, wherein there is first provided around the first aperture an inwardly extending circular lip and the outer edge of the funnel is positioned within said lip.

8. A domestic appliance as claimed in Claim 5 or Claim 6 in which the outer edge of the funnel has an outwardly extending flange of maximum diameter greater than the diameter of the first aperture, and the flange is positioned close to the casing around the first aperture.

9. A domestic appliance as claimed in Claim 8 in which there is further provided around the first aperture an inwardly extending circular lip, and the outer edge of the flange is positioned within said lip.

10. A domestic appliance as claimed in any one of Claims 5 to 9, further comprising at least one heating element arranged in the air path between the first aperture and the second aperture.

11. A centrifugal fan substantially as hereinbefore described with reference to Figures 1, 2 and 3 of the accompanying drawings.

1 2. A domestic appliance substantially as hereinbefore described with reference to Figures 4, 5 or 6 of the accompanying drawings.