FAN

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 (2) an air displacement occurs; and drive means (7, 8, 9) for rotatably driving the blades with the hub round the axis of the hub. The invention provides a fan of the stated type which has the feature that the end zones (4) of the blades are connected by a ring (5), which ring (5) is supported rotatably in a housing; and the drive means comprise a motor (7) which is placed at a distance from the hub outside the air flow generated by the driven blades (3).

Description: 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. Another drawback of the known fan is that the motor shaft and the hub are directly and rigidly connected to each other. As a result of this inseparable coupling, the known fan lacks any flexibility in the choice of the type of motor and the motor design is wholly determined by the desired rotation speed. 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. A further object of the invention is to embody a fan such that a greater flexibility is obtained in respect of the choice of the or each drive motor, wherein the trans- mission between the rotor, comprising hub and blades, and the motor can be designed such that both the rotor and the motor rotate at the most favourable possible rotation speed. 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 a housing; and the drive means comprise a motor which is placed at a distance from the hub outside the air flow generated by the driven blades. 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 rotatable mounting. In an alternative the fan according to the invention has the special feature that during operation the rotor is suspended magnetically. A further increase in efficiency is obtained with an embodiment in which the blades possess an aerodynamic form with maximized c τ /c„ at a minimized (c „, being the shape resistance at c L = 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 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 on the other, the embodiment is recommended in which the skin consists of aluminium or stainless 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 aerodynami- cally optimized design is used the efficiency can be very high compared to known fans, while in addition the rota¬ tion 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 L can be increased for instance from 0.8 to 1.6. The efficiency of the fan is related to the quotient c L /c D . 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 ) 0 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 torsion of the blades can display at 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. 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. I-i/c-,J at a minimized c- U can moreover advantageously have the feature that the blades have a rear edge with a small thickness relative to the aerody¬ namic boundary 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 onto a zone in which two skin layers mutually overlap, wherein the skin layer of the rear edge is situated on the convex side. The invention will now be elucidated with reference to the annexed drawings. Herein: figure 1 shows a partly broken away perspective view of a fan according to the invention in a first embodi¬ ment; 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; figure 4 shows a longitudinal section through a fourth embodiment; and figure 5 shows a partly broken away, partly perspec¬ tive view of a part of the fan. Figure 1 shows a fan 1 comprising a central hub 2, eight blades 3 connected to this hub 2 and extending at least more or less in radial direction and having a form such that during rotary driving round the axis of hub 2 an air displacement occurs. The end zones 4 of blades 3 are mutually joined by a ring 5 which is supported rota¬ tably and drivably in a housing 6. Serving to drive the rotor 2,3,4,5 is a motor 7 which drives a drive roller 9 via a transmission 8. In turn the roller 9 drives the ring 5 by frictional con¬ tact. The latter is further supported by two free guide rollers 10,11 which are arranged spring-mounted in hous¬ ing 6 for movement away from and toward ring 5. The inner surface 12 of ring 5 has a rounded aerody¬ namic design. Figure 2 shows a fan 12, the housing 13 of which is adapted to accommodate two rotors 2,3,4,5. The motor 7 drives both rotors. To this end use is made of a toothed belt 15 which is driven by a tooth wheel 14 driven by motor 7 and which co-acts with a pinion 16 arranged round each ring 5. Two free-turning tooth wheels 17,18 are mounted fixedly relative to housing 13 and serve for correct positioning of both rotors 2,3,4,5 in combination with the tensile stress in toothed belt 15. Space saving is achieved by using two free-turning deflecting rollers 19,20 whereby the toothed belt engages in substantially horizontal direction on both the upper part and the lower part of the rotors. Figure 3 shows a fan 21, the housing 22 of which is rotatably supported by frame 23. The housing 22 takes a tubular form and has an aerodynamic form on its inner surface 24. A rotor 2,3,4,5 is fixed to this inner sur¬ face 24. It is noted that the ring 15 can be used for production purposes. This could also be omitted, particu¬ larly in the case where the blades 3 are joined directly, for instance under bias, to inner surface 24. Via schematically designated electrical connections 25,26 electrical energy is supplied to a stator winding 27 forming part of the frame 23. The housing 22 which, as stated, is rotatable relative to frame 23, carries a crown 28 of magnet means which together with the stator winding 27 form a collectorless electric motor. If de¬ sired, this motor can be embodied such that during opera¬ tion the housing 22 is suspended electrically. Figure 4 shows a fan 29 with a plastic housing 30 and a guard 31 of metal gauze. The rotor 2,3,4,5 carries magnets 32 which co-act with a stator winding 33 analogously of the embodiment of figure 3. The blades 3 comprise a foam core 34, for instance of plastic such as PUR, with stainless steel skin plates with a thickness in the order of 0.2 mm. In order to obtain a sufficiently great mechanical strength and stiffness the wall of housing 30 comprises a plurality of metal rods 36 glued thereto. In the zone of the rotor 2-5 the inner surface of housing 30 has a streamlined form as shown in the top left-hand corner of figure 4. For the sake of a low weight use is made of a foam material filling 37. In an embodiment in which the blades comprise a skin, this skin has a thickness which is preferably related to the span width and the chord of these blades. Figure 5 shows in partly broken away perspective view 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 sur¬ face 40. These surfaces are joined to each other via a bent front edge 41 with relatively small radius of curva- ture. 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 thickness of the skin. The blade 3 is further filled with foam material 45. In the embodiments according to figures 1, 2 and 5 the end zones of the fan blades connect smoothly onto the inner surface of the ring. These end zones have a form widening over their whole periphery. The radius of curva- ture is more or less constant and has a value in the same order of magnitude as the characteristic thickness of the fan blades. *****

Claims: 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 a housing; and the drive means comprise a motor which is placed at a distance from the hub outside the air flow generated by the driven blades. 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 a maximized c L /c D at a minimized (c D ) 0 , being the shape 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 rein¬ forced 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 end zones of the blades connect smoothly onto the inner surface of the ring. 19. Fan as claimed in claim 18, 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. 20. 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. 21. Fan as claimed in claim 20, 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. *****

Inventors: BERTELS AUGUSTINUS WILHELMUS M, BERTELS, AUGUSTINUS, WILHELMUS, MARIA
Applicants: BERTELS AUGUSTINUS WILHELMUS M, HELPMAN INTELLECTUAL PROPERTIE, BERTELS, AUGUSTINUS, WILHELMUS, MARIA, HELPMAN INTELLECTUAL PROPERTIES B.V.
Application year: 1995
Main classification: F04D25
IPC codes: F04D25, F04D29