WO1996019670A2

WO1996019670A2 - Domestic fan

Info

Publication number: WO1996019670A2
Application number: PCT/NL1995/000437
Authority: WO
Inventors: Augustinus Wilhelmus Maria Bertels
Original assignee: Helpman Intellectual Properties B.V.
Priority date: 1994-12-22
Filing date: 1995-12-20
Publication date: 1996-06-27
Also published as: WO1996019670A3; TW311971B; NL9402187A; AU4401996A

Abstract

The invention relates to a fan (1), comprising: a central hub (2); a plurality of blades (3) connected to this hub (2) and extending at least more or less in radial direction, which blades (3) take a form such that when driven rotatably round the axis of the hub, an air displacement occurs; and drive means (4) for rotatably driving the blades (3) with the hub (2) round the axis of the hub. The invention provides a fan (1) of the stated type which has the feature that the end zones of the blades (3) are connected by a ring (6), which ring (6) is supported rotatably in an annular housing (7); the drive means (4) comprise a motor which is placed at a distance from the hub outside the air flow generated by the driven blades; the axial dimension of the ring and that of the annular housing is a maximum of 0.2 x the diameter; and the annular housing is supported by supporting means, for instance a foot (8, 9) for placing on a surface.

Description

DOMESTIC FAN

The invention relates to a fan comprising: ■ a central hub; a plurality of blades connected to this hub and extending at least more or less in radial direction, which blades take a form such that when driven rotatably round the axis of the hub an air displacement occurs; and drive means for rotatably driving the blades with the hub round the axis of the hub.

Such a fan is known. It is embodied such that the drive means comprise a motor of not inconsiderable diame¬ ter, the output shaft of which motor is joined directly to the hub. The hub likewise has a not inconsiderable diameter adapted to the diameter of the motor.

The drawback of such a known structure is that the central part of the fan does not take part in generating the desired air flow, which is undesirable from the point of view of efficiency.

A further significant aspect limiting efficiency is the flow round the ends of the blades, the so-called tips. It would be desirable to eliminate this flow round the tips.

It is a further object of the invention to embody a fan such that it can be transported with very small volume. This aspect is important particularly for consum- er uses. It is recommended for such applications to make the transport volume as small as possible with a view to bulk transport costs, packaging costs and environmental considerations.

It is therefore an object of the invention to embody a fan such that losses resulting from the presence of an aerodynamically inactive hub are reduced to negligible proportions.

In order to realize this objective the invention provides a fan of the stated type which has the feature that the end zones of the blades are connected by a ring, which ring is supported rotatably in an annular housing; the drive means comprise a motor which is placed at a distance from the hub outside the air flow generated by the driven blades; the axial dimension of the ring and that of the annular housing is a maximum of 0.2 x the diameter; and the annular housing is supported by supporting means, for instance a foot for placing on a surface. A specific embodiment is that in which the ring forms part of the drive means.

This variant can for instance have the special feature that the ring is driven by a motor.

A specific embodiment has the special feature that the ring is the rotor of an optionally collectorless electric motor.

A variant of this latter embodiment has the special feature that the rotor is a linear induction motor.

Use can be made of a mechanical rotating bearing. In an alternative the fan according to the invention has the special feature that during operation the rotor is sus¬ pended magnetically.

A further increase in efficiency is obtained with an embodiment in which the blades possess an aerodynamic form with maximized c_L/c_D at a minimized (c ) , being the coefficient of resistance at c, = 0.

A light but nevertheless mechanically very strong embodiment has the special feature that the blades are connected under bias to the hub and the ring. Yet another variant with a very light rotor has the special feature that the blades each comprise a skin consisting of metal with a thickness of a maximum of 1 mm.

A particular embodiment has the special feature that the blades each comprise a skin consisting of a plastic layer optionally reinforced with fibres having tensile strength. The above two embodiments can have the feature that the skin has a thickness of 0.001-0.03 x the average chord of a blade.

Particularly in the case when bias is applied, this latter variant can make use of a very thin skin. The fan can then for instance have the special feature that the skin has a thickness of (0.2 ± 0.1) mm.

Diverse suitable materials can be envisaged. From considerations of strength on the one hand and price and processing costs on the other, the embodiment is recom¬ mended in which the skin consists of aluminium or stain¬ less steel.

In order to obtain an increased resistance to defor¬ mation through jolts or the like, the fan can have the special feature that the cavity enclosed by the skin is filled with a filler.

This latter embodiment can be manufactured in simple manner. This variant has the special feature that the filler is modelled beforehand in a mould cavity and the skin is subsequently arranged therearound.

A still further increase in efficiency can be ob¬ tained with an embodiment in which the number of blades amounts to more than four. The number of blades can amount for instance to eight or more. When an aerodynamically optimized design is used the efficiency can be very high compared to known fans, while in addition the rotation speed tolerance range is greatly extended. The average thickness of the blades can for instance be in the order of 15% of the chords. In known designs this thickness is in the order of 2 to 3%. With such a design the coefficient of resistance c_D decreases while the lift coefficient c, can be increased for in- stance from 0.8 to 1.6. The efficiency of the fan is related to the quotient c_L/c_β. The fan efficiency can be increased by these steps to the order of magnitude of

90%. In known designs this efficiency lies in the order of magnitude of a maximum of 50%. The decrease of c_D also contributes to a reduction in the generated sound. An advantage of the use of a larger number of blades is that the applied rotation speed can be lower and the noise production can decrease correspondingly.

For an optimized aerodynamic design the blades will taper toward their ends directed toward the ring. The blades can display on the axis a torsion in the order of 15° as seen in the axial direction of the fan, while the blades can have for instance a torsion in the order of 65° at the tips, i.e. the ends adjoining the ring. For the best possible guiding of the air flow gener¬ ated by the fan, the latter can have the special feature that at least the inner surface of the ring has an aero¬ dynamic form.

In preference this embodiment even has the special feature that the ring and the annular housing connect to each other with a small clearance and together display an aerodynamic form. With this embodiment the air is guided correctly in aerodynamic manner not only on the inside of the annular housing but also on the outside of the annu- lar housing. It should be understood that the air flow generated by the fan is not limited to the inner region of the annular housing but that due to induction an air flow develops on the outside of the annular housing.

An embodiment which limits noise and increases efficiency is that in which the end zones of the blades connect smoothly onto the inner surface of the ring.

This embodiment can advantageously display the feature that the end zones have a form widening over the whole periphery with a radius of curvature in the same order of magnitude as the characteristic thickness of the blades.

A variant in which the blades possess an aerodynamic form with maximized c_L/c_D at a minimized c_D)₀, being the coefficient of resistance at c_τ = 0, can moreover advanta- geously have the feature that the blades have a rear edge with a small thickness relative to the aerodynamic bound¬ ary layer during operation of the fan. In a variant in which the blades each comprise a skin of metal or reinforced plastic, the above stated embodiment can have the special feature that the rear edge is formed by one skin layer which connects to a zone in which two skin layers mutually overlap, wherein the skin layer of the rear edge is situated on the convex side.

A specific embodiment has the special feature that the blades carry a thermally active element such as a heating element or a cooling element, to which energy is supplied via the annular housing.

As a result of the preferably aerodynamic form of the blades a thermally active element can be in excellent heat-exchanging contact with the air flowing past without the whooshing sounds occurring which are usual in fan heaters having for instance helically wound heating wires.

A specific embodiment has the special feature of a resistance element operating as electric heating element, for instance comprising resistance wires, a foil resis¬ tance element, a conducting plastic, conducting particles or powder consisting for instance of metal or carbon and embedded in plastic, which resistance element can be connected to or embedded in a preferably thermally resis- tant plastic, or a combination thereof.

An embodiment with a cooling element can advanta¬ geously be provided with a Peltier element. On the basis of a semiconductor junction such an element can extract heat from the environment and transfer it by way of electrical transfer to a heating element placed else¬ where. A cooled air flow can thus be generated.

In order to transfer the energy required for the thermally active element to the blades, use can be made of sliding contacts for transfer of electrical energy present between the ring and the housing, for instance by means of a conducting liquid such as mercury or a con¬ ducting semi-fluid. Another embodiment is provided with a rotating transformer, of which the stator is connected to the housing and the rotor is connected to the ring or they form part thereof. As is known, the efficiency of the transformer increases and the required transformer volume and weight thereby decreases as the frequency used becomes higher. In this respect the embodiment is recommended which is provided with a power supply which can supply electric current to the housing, in which power supply is included a frequency converter which converts the mains supply frequency into a higher frequency, for instance in the range of 400 Hz - 10 kHz.

The smallest possible transport volume can be real- ized with an embodiment in which the supporting means comprise a folding foot, preferably having a shape adapt¬ ed in the folded-away situation to the shape of the rest of the fan.

A preferred embodiment has the special feature that the ring with adjustable position is supported by the foot.

A specific embodiment has the feature that on at least one side the ring carries a protective cover through which air can flow. A preferred variant hereof has the special feature that the protective cover comprises a self-supporting spiral-shaped strip.

A very low noise production is obtained with an embodiment in which the strip has an aerodynamic form. Yet another embodiment has the feature that the ring is supported by the supporting means via a transmission periodically varying the position of the housing.

A very elegant embodiment has the feature that during rotation the ring is mounted for rotation by an air cushion formed by air drawn in through intake aper¬ tures in the blades, which air is blown out via outlet apertures in the ring into the space between ring and annular housing, which space is sufficiently small to form a bearing mounting air cushion. The described struc¬ ture makes unnecessary the use of bearing means suscepti¬ ble to maintenance. The described structure, which can for instance have the action of a centrifugal pump via blades which are hollow or at least provided with contin¬ uous channels, only requires a very small proportion of the drive power, is wholly free of maintenance and not susceptible to ageing.

The invention will now be elucidated with reference to the annexed drawings. Herein: figure 1 shows a perspective view of a domestic fan according to the invention; figure 2 shows a partly broken away perspective view of a second embodiment; figure 3 shows a partly broken away perspective view of a third embodiment; and figure 4 shows a partly broken away, partly perspec¬ tive view of a part of a fan.

Figure 1 shows a domestic fan 1. It comprises a central hub 2, eight blades 3 connected to this hub 2 which extend at least more or less in radial direction and have a form such that during rotary driving round the axis of the hub an air displacement occurs, in addition to a drive motor 4 for rotatably driving the blades 3 round the axis of hub 2. The end zones 4 of blades 3 are joined by a ring 6 which is supported rotatably in an annular housing 7. Motor 4 is placed at a distance from the central hub 2 outside the air flow generated by the driven blades 3. The axial dimensions of ring 6 and those of the annular housing 7 amount to a maximum of 0.1 x the relevant diameter. The annular housing 7 is carried by a foldable foot which consists of two parts 8,9. These parts can be folded up as according to arrows 10,11 respectively and in the folded-away situation have a shape adapted to the rest of the fan.

The motor 4 drives the ring 6 by means of a belt 12. For illustration purposes a telephone 13 is drawn in figure 1 which gives an idea of the possible dimensions of the fan 1.

Figure 2 shows a fan 14. In this embodiment an annular housing 15 supports three motors 15,16,17 of the type with external rotor. The external rotors of these motors drive the ring 6 and therewith the whole rotor 2,3,6.

The housing 22 carries a protective grid 18 which is embodied as a self-supporting spiral, the aerodynamic form of which is not visible due to the scale of figure 2. With a simple pivot bearing the free centre of the grid 18 presses lightly against the free outer end of hub 2. Arrows 19 indicate the air flow direction.

The housing 22 is supported by a foot 20. This carries a control unit 21 for controlling a number of functions of the fan 14.

The housing 22 is supported by the foot 20 through a ball joint 23. Accommodated in the foot is a motor 24 which drives a cross-thread spindle 25. This co-acts with a carriage 26 which is coupled hingedly to the ball 23 such that, when cross-thread spindle 25 is driven, the ball, and thus the housing with components supported thereby, performs a reciprocating movement in the hori¬ zontal plane. This movement is indicated with arrow 27. A vertical corresponding movement is obtained with an analogous construction by means of a motor 28, cross- thread spindle 29 and carriage 30 accommodated in housing 22. The associated reciprocating movement in the vertical plane is shown with arrow 31.

The fan 14 receives its electrical energy via a mains lead 32.

Figure 3 shows a domestic fan 51. In this embodiment the annular housing 52 is sup¬ ported by a foot 55 via a ball joint 53 with toggle lever 54, in which foot is accommodated a control unit 56. Accommodated in housing 52 are electromagnetic stator elements 57 which co-act with electromagnetic rotor elements 58 which are arranged in ring 59 which is supported and driven in turn by motors 15,16,17. The elements 57 and 58 together form a rotating transformer. The electrical energy transferred to the rotor elements 58 via the stator elements 57 during rotation of rotor 2,3,6 is supplied to a heating element which consists of a resistance wire which is embedded in the blades 3 on the surface thereof and thus forms a heating element which can relinquish heat to the air flow 19 occurring during rotation of the rotor.

In the foot 55 is accommodated a frequency converter 60 which converts the mains frequency, normally 50 or 60 Hz, into a considerably higher frequency, for instance in the order of 5 kHz. The volume and weight of the trans¬ former 57, 58 can hereby be limited, while an excellent energy transfer is nevertheless obtained. The frequency converter is of the solid-state type, can be compact and is capable of transferring the required energy to the heating element (not drawn) while taking up little vol¬ ume. A practical power to be transferred lies in the order of 1-2 Kw.

Figure 4 shows a detail of a variant. In this em- bodiment an annular housing 61 carries electromagnetic stator elements 62, while the ring 63, which corresponds functionally with ring 6 in figure 1 and figure 2, accom¬ modates electromagnetic rotor elements. The elements 62 and 64 together form an annular linear induction motor. Figure 5 further shows the structure of the fan blades 3. Each blade 3 comprises a skin 38 modelled to an aerodynamic form such that blade 3 has a convex surface 39 and a concave surface 40. These surfaces connect to each other via a bent front edge 41 with relatively small radius of curvature. In the rear zone 42 the surfaces 39 and 40 mutually overlap. Protruding beyond the overlap zone 43 is that skin part which connects onto the convex surface 39. Thus created is a protruding rear edge 44 consisting of a thin layer corresponding with the thick¬ ness of the skin.

The blade 3 is further filled with foam material 45.

The ring 63 connects at very small distance to a correspondingly formed inner recess in the annular hous¬ ing 61. As shown in figure 4, ring 63 and annular housing 61 together form an aerodynamic shape. This ensures a very low noise production of the fan.

In all the drawn embodiments the end zones 65 of the blades 3 connect smoothly onto the inner surface of the ring 6,63. These end zones have a form widening over the whole periphery with a more or less constant radius of curvature which is in the same order of magnitude as the characteristic thickness of the blades 3.

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Claims

1. Fan comprising: a central hub; a plurality of blades connected to this hub and extending at least more or less in radial direction, which blades take a form such that when driven rotatably round the axis of the hub an air displacement occurs; and drive means for rotatably driving the blades with the hub round the axis of the hub, characterized in that the end zones of the blades are connected by a ring, which ring is supported rotatably in an annular housing; the drive means comprise a motor which is placed at a distance from the hub outside the air flow generated by the driven blades; the axial dimension of the ring and that of the annular housing is a maximum of 0.2 x the diameter; and the annular housing is supported by supporting means, for instance a foot for placing on a surface.

2. Fan as claimed in claim 1, wherein the ring forms part of the drive means.

3. Fan as claimed in claim 2, wherein the ring is driven by a motor.

4. Fan as claimed in claim 2, wherein the ring is the rotor of an optionally collectorless electric motor.

5. Fan as claimed in claim 4, wherein the rotor is a linear induction motor.

6. Fan as claimed in claim 4, wherein during opera¬ tion the rotor is suspended magnetically.

7. Fan as claimed in claim 1, wherein the blades possess an aerodynamic form with maximized c_L/c_D at a minimized (c_D)₀, being the coefficient of resistance at c_L = 0.

8. Fan as claimed in claim 1, wherein the blades are connected under bias to the hub and the ring.

9. Fan as claimed in claim 1, wherein the blades each comprise a skin consisting of metal.

10. Fan as claimed in claim 1, wherein the blades each comprise a skin consisting of a plastic layer op- tionally reinforced with fibres having tensile strength.

11. Fan as claimed in claim 9 or 10, wherein the skin has a thickness of 0.001-0.03 x the average chord of a blade.

12. Fan as claimed in claim 9 or 10, wherein the skin has a thickness of (0.2 ± 0.1) mm.

13. Fan as claimed in claim 9 or 10, wherein the skin consists of aluminium or stainless steel.

14. Fan as claimed in claim 9 or 10, wherein the cavity enclosed by the skin is filled with a filler.

15. Fan as claimed in claim 14, wherein the filler is modelled beforehand in a mould cavity and the skin is subsequently arranged therearound.

16. Fan as claimed in claim 1, wherein the number of blades amounts to more than four.

17. Fan as claimed in claim 1, wherein at least the inner surface of the ring has an aerodynamic form.

18. Fan as claimed in claim 17, wherein the ring and the annular housing connect to each other with a small clearance and together display an aerodynamic form.

19. Fan as claimed in claim 17, wherein the end zones of the blades connect smoothly onto the inner surface of the ring.

20. Fan as claimed in claim 19, wherein the end zones have a form widening over the whole periphery with a radius of curvature in the same order of magnitude as the characteristic thickness of the blades.

21. Fan as claimed in claim 7, wherein the blades have a rear edge with a small thickness relative to the aerodynamic boundary layer during operation of the fan.

22. Fan as claimed in claims 21 and 9 or 10, wherein the rear edge is formed by one skin layer which connects onto a zone in which two skin layers mutually overlap, wherein the skin layer of the rear edge is situated on the convex side.

23. Fan as claimed in claim 1, wherein the blades carry a thermally active element such as a heating ele- ment or a cooling element, to which energy is supplied via the annular housing.

24. Fan as claimed in claim 23, comprising a resis¬ tance element operating as electric heating element, for instance comprising resistance wires, a foil resistance element, a conducting plastic, conducting particles or powder consisting for instance of metal or carbon and embedded in plastic, which resistance element can be connected to or embedded in a preferably thermally resis¬ tant plastic, or a combination thereof.

25. Fan as claimed in claim 23, comprising a Peltier element.

26. Fan as claimed in claim 23, comprising sliding contacts for transfer of electrical energy present be¬ tween the ring and the housing, for instance by means of a conducting liquid such as mercury or a conducting semi¬ fluid.

27. Fan as claimed in claim 23, comprising a rotat¬ ing transformer, of which the stator is connected to the housing and the rotor is connected to the ring or they form part thereof.

28. Fan as claimed in claim 27, comprising a power supply which can supply electric current to the housing, in which power supply is included a frequency converter which converts the mains supply frequency into a higher frequency, for instance in the range of 400 Hz - 10 kHz.

29. Fan as claimed in claim 1, wherein the support¬ ing means comprise a folding foot, preferably having a shape adapted in the folded-away position to the shape of the rest of the fan.

30. Fan as claimed in claim 1, wherein the ring with adjustable position is supported by the foot.

31. Fan as claimed in claim 1, wherein on at least one side the ring carries a protective cover through which air can flow.

32. Fan as claimed in claim 31, wherein the protec- tive cover comprises a self-supporting spiral-shaped strip.

33. Fan as claimed in claim 32, wherein the strip has an aerodynamic form.

34. Fan as claimed in claim 1, wherein the ring is supported by the supporting means via a transmission periodically varying the position of the housing.

35. Fan as claimed in claim 1, wherein during rota¬ tion the ring is mounted for rotation by an air cushion formed by air drawn in through intake apertures in the blades, which air is blown out via outlet apertures in the ring into the space between ring and annular housing, which space is sufficiently small to form a bearing mounting air cushion.

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