GB2217789A

GB2217789A - Axial flow fan

Info

Publication number: GB2217789A
Application number: GB8907441A
Authority: GB
Inventors: Lorella Annovazzi
Original assignee: Industrie Magneti Marelli SRL; Magneti Marelli SpA
Current assignee: Industrie Magneti Marelli SRL; Marelli Europe SpA
Priority date: 1988-04-01
Filing date: 1989-04-03
Publication date: 1989-11-01
Anticipated expiration: 2009-04-03
Also published as: IT8853036V0; FR2629524A3; ES1009817U; GB8907441D0; ES1009817Y; FR2629524B3; IT214345Z2; DE8903903U1; GB2217789B

Abstract

The fan comprises a hub 2, an outer ring 3 coaxial with the hub 2 and a plurality of blades 4 which extend between the hub 2 and the outer ring 3 and the radially outermost part of which is curved forwards in the direction of rotation of the fan 1. At least the portion of each blade 4 adjacent to the ring 3 forms with respect to the plane of rotation a blade angle W decreasing hyperbolically as a function of the radius. Starting from the hub 2, the median line M of each blade 4, obtained by joining in the projection of the blade 4 on the plane of rotation the points circumferentially equidistant from the edges L, T of the blade 4, has a first section M1, radially innermost, following a rectilinear path along a radial extension less than 25% of the radial distance between the hub 2 and the outer ring 3, a second section M2, radially outermost, joined to the first section M1, and following the path of the arc of a circle. <IMAGE>

Description

Title:Axiai flow fan The present invention relates to axial fans designed to achieve particularly silent operation in the presence of a turbulent air flow. In particular the invention relates to an axial fan intended for operation in conjunction with the radiator of a motor vehicle, of the type comprising a hub, an outer ring coaxial with the hub, and a plurality of blades which extend between the hub and the outer ring and the radially outermost part of which is curved forwards in the direction of rotation of the fan; at least the portion of each blade adjacent to the ring forming with respect to the plane of rotation a blade angle decreasing as a function of the radius.

Such a type of fan is described, for example, in US patent 4,569,631. The blades of the fan described in this prior document have, starting from the hub, a first portion curved backwards with respect to the direction of rotation of the fan and then a radially outermost portion curved forwards. The length of the blades curved in this manner is quite considerable and involves an increase in weight and a reduction in the intrinsic oscillation frequencies of the blades, which may affect the performance of the fan.

The object of the present invention is to provide an axial fan of the specified type, with improved aerodynamic characteristics and in particular a low noise level, which allows the drawbacks of the known fan described above to be avoided.

This object is achieved according to the present invention by means of an axial fan of the type specified above, the main feature of which lies in the fact that, starting from the hub, the median line of each blade, obtained by joining in the projection of the blade on the plane of rotation the points circumferentially equidistant from the edges of the blade, has a first section, radially innermost, following a rectilinear path along a radial extension preferably less than 25% of the radial distance between the hub and the outer ring, and a second section, radially outermost, joined to the first section and following the path of an arc of a circle.

Further characteristic features and advantages of the present invention will emerge from the detailed description which follows, given with reference to the attached drawings provided purely by way of a nonrestrictive example, in which: Figure 1 is an elevation view of a fan according to the invention, Figure 2 is a side view partially sectioned along the line II-II of Figure 1, Figure 3 is a partial view, on an enlarged scale, of Figure 1, and Figures 4, 5 and 6 are views sectioned along the lines IV-IV, V-V and VI-VI of Figure 3.

Referring now to the drawings, 1 denotes in its entirety a fan comprising a central hub 2, an outer ring 3 coaxial with the hub, and a plurality of blades 4 which extend between the hub and this ring.

With reference to Figure 3, each blade 4 in its front view is delimited between two lines L and T which constitute the front projections on the plane of rotation of the leading edge and, respectively, the trailing edge of the blade. A median line M is shown as a broken line between the lines L and T. This line is obtained by joining the points circumferentially equidistant from the lines T and L in Figure 3.

Starting from the hub 2, the median line M has a first section, indicated by M1, following a rectilinear path, along the extension of a radius of the hub 2. The section M1 of the median line of each blade preferably has a radial extension less than 25% and preferably equal to 20% of the radial distance between the hub 2 and the outer ring 3.

The median line M of each blade has, in addition, a second section M2, radially outermost, joined to the first section M1 and following the path of an arc of a circle with the centre 0 which lies on a straight line A passing through the radially outermost end of the first section M1 and perpendicular to this first section.

Each blade, at least in the portion adjacent to the outer ring 3, forms with respect to the plane of rotation a blade angle decreasing as a function of the radius, as is evident from a comparison of Figures 4 and 6, in which the blade angle has been indicated by W. This blade angle preferably decreases as a function of the radius, in accordance with a hyperbolic type function.

With reference again to Figure 3, preferably the angle / formed between the straight line B on which the abovementioned first section M1 of the median line of each blade lies and the straight line C tangential to the median line M at the radially outermost point of the section M2 is between 60 and 75 degrees and is preferably equal to 700.

Fans constructed by the Applicant in accordance with the present invention have demonstrated a very low noise level and a high ventilation efficiency.

Obviously, the invention covers all the embodiments which achieve the same aims as a result of the same innovative ideas.

Claims

1. Axial fan, particularly for motor vehicles, comprising a hub, an outer ring coaxial with the hub, and a plurality of blades which extend between the hub and the outer ring and the radially outermost part of which is curved forwards in the direction of rotation of the fan; at least the portion of each blade adjacent to the ring forming with respect to the plane of rotation a blade angle decreasing as a function of the radius;; characterized in that, starting from the hub, the median line of each blade, obtained by joining in the projection of the blade on the plane of rotation the points circumferentially equidistant from the edges of the blade, has a first section, radially innermost, following a rectilinear path along a radial extension less than 25% of the radial distance between the hub and the outer ring, and a second section, radially outermost, joined to the first section and following the path of an arc of a circle.

2. Fan according to Claim 1, characterized in that the centre of curvature of said second section of the median line of each blade lies on a line passing through the radially outermost end of the first section, and perpendicular to said first section.

3. Fan according to one of the preceding claims, characterized in that the portion of each blade adjacent to the ring forms with respect to the plane of rotation a blade angle decreasing hyperbolically as a function of the radius.

4. Fan according to any one of the preceding claims, characterized in that the angle defined between said first section of the median line and the line tangential to the radially outermost point of the second section of the median line of a blade is between 60 and 750 and is preferably equal to 700.

5. Axial fan, particularly for motor vehicles, substantially in accordance with that described and illustrated in the accompanying drawings and for the purposes specified.