MXPA00009388A - Axial flow fan - Google Patents

Abstract

The axial flow fan (1) comprises a central hub (3), a plurality of blades (4), each blade (4) having a root (5) and an end (6) and being delimited also by a convex edge (7), whose projection onto the plane of rotation of the fan is defined by a parabolic segment, and by a concave edge (8) whose projection onto the plane of rotation of the fan is defined by a circular arc. The blades (4) consist of sections having aerodynamic profiles (18) with a face (18a) comprising at least one initial straight-line segment (t) and a blade angle (&bgr;) that decreases gradually and constantly from the root (5) towards the end (6) of the blade (4) according to a cubic law of variation as a function of the fan radius.

Description

AXIAL FLOW FAN TECHNICAL FIELD The present invention relates to a fan with axial flow equipped with inclined vanes in the plane of rotation of the fan. The fan described by the present invention has various applications, for example, moving air through a heat exchanger or radiator in the cooling system of a motor vehicle or similar machine, or moving air through a heat exchanger. in the heating system of the interior compartment of a vehicle. In addition, the fan described by the present invention can be used to move air in fixed installations of air conditioning or heating of buildings. Fans of this type have to satisfy various different requirements, including low noise, high efficiency, compact dimensional character and good load (pressure) and supply values.

BACKGROUND OF THE INVENTION Patent EP 0 553 598 B, in the name of the same applicant as the present invention, describes a fan whose blades have a constant cord length along its entire length. In addition, the front and rear edges of the blades form two curves, which, if projected on the plane of rotation of the fan, are two circular arcs. Fans manufactured in accordance with this patent achieve good results in terms of efficiency and low noise but their ability to achieve high load or pressure values is limited mainly due to their small axial dimensions. The need to achieve high load values has become an increasingly important requirement with respect to thermal units in modern automobiles, which include two or more exchangers ordered in series-for example, the condenser of the air conditioning system, the radiator or the cooling system and the heat exchanger for the air supply of turbine-charged engines - or with respect to the radiators that have become thicker to compensate for the smaller frontal dimensions.

DESCRIPTION OF THE INVENTION The purpose of the present invention is to solve the load or pressure problem of the aforementioned fans and further improve them in terms of efficiency and low noise. The problem is solved by the features described in the independent claim. The dependent claims refer to preferred advantageous embodiments of the invention.

The invention will now be described with reference to the accompanying drawings, which illustrate preferred embodiments of the invention and in which: Figure 1 is a front view of a fan made in accordance with the present invention. Figure 2 illustrates in a front view the geometrical characteristics of a fan blade described by the present invention. Figure 3 shows sections of a fan blade described by the present invention taken at regular intervals starting from the hub to the end of the blade. Figure 4 illustrates a perspective view of other geometric characteristics of a fan blade described by the present invention. Figure 5 shows a detail taken to scale of the fan illustrated in figure 1 and the related conduit. Figure 6 is a front view of another embodiment of the ventilator described by the present invention. Figure 7 shows a diagram representing, in Cartesian coordinates, the convex edge of a fan blade described by the present invention; and Figure 8 is a diagram showing the changes in the angle of the blade in different sections of a blade as a function of the radius of the fan described by the present invention.

The terms used to describe the fan are defined as follows: - the rope (L) is the length of the straight line segment subtended by the arc extending from the leading edge towards the terminal flank through a section aerofoil of the blade obtained by intercepting the blade with a cylinder whose axis coincides with the axis of rotation of the fan and whose radius r coincides at point Q; - the central line or middle string line (MC) of the blade is the line joining the center points of the strings L to the different rays; - the angle of arrow (d) measured at a certain point Q of the characteristic curve of the blade, for example, the curve representing the terminal edge of the blade of the fan, is the angle made by a ray emanating from the center of the fan towards the point Q of interest and the tangent to the curve of the same point Q; - the oblique angle or net angular displacement (a) of a characteristic curve of the blade is the angle between the ray passing through the characteristic curve, for example, the curve representing the line of the central chord of the blade, towards the fan hub, and the ray passing through the characteristic curve towards the end of the blade; - the blade angle (ß) is the angle between the plane of rotation of the fan and the straight line joining the front flank with the terminal flank of the aerofoil of the blade section; - the pitch ratio (P / D) is the ratio between the pitch of the helix, that is, the quantity by which the point Q of interest moves axially, that is, P = 2 • p • r • tan ( ß), in which r is the length of the radius to point Q and ß is the angle of the blade at point Q, and the maximum diameter of the fan; - the curvature of the profile (f) is the longest straight line segment perpendicular to the curdal L, measured from the string L towards the curvature line of the blade; the position of the curvature of profile f in relation to the rope L can be expressed as a percentage of the length of the rope itself; - the inclination (V) is the axial displacement of the blade from the plane of rotation of the fan, including not only the displacement of the entire profile from the plane of rotation but also the axial component due to the curvature of the blade, if it exists, - also in axial direction. With reference to the accompanying drawings, the fan 1 rotates about an axis 2 and comprises a central hub 3 on which are mounted a plurality of blades 4 curved in the plane of rotation XY of the fan 1. The blades 4 have a root 5 and an end 6 and are delimited by a convex flank 7 and a concave flank 8. Since satisfactory results have been obtained in terms of efficiency, noise level and load by rotating the fan made in accordance with the present invention either in a In the other direction, the convex flank 7 and the concave flank 8 may each be the leading edge or the terminal edge of the blade.

In other words, the fan 1 can rotate in such a way that the air to be moved is first with the convex edge 7 and then with the concave edge 8, or vice versa, first with the concave edge 8 and then with the edge convex 7. Obviously, the aerodynamic profile of the cross section of the blade must be oriented in accordance with the operation mode of the fan 1, that is, according to whether the air to be moved first meets the convex edge 7 or the edge Concave 8 first. At the end 6 of the blades 4, a reinforcing ring 9 can be equipped. The ring 9 reinforces the blade assembly 4, avoiding for example that the angle ß of the blade 4 varies in the area at the end of the blade due to the loads aerodynamic Furthermore, the ring 9, in combination with a duct 10, limits the swirling action of the air around the fan and reduces the swirls to the ends 6 of the blades 4, these swirls being created, as is known, by the different pressure in the two faces of the blade 4. For this purpose, the ring has a portion of thick lip 11, which fits in a complementary seat 12 made in conduit 10. The distance (a), very small in the axial direction, between the lip 11 and the seat 12 together with the labyrinth shape of the part between the two elements, reduces the swirl of air at the end of the fan blades. In addition, the special adjustment between the outer ring 9 and the conduit 10 allows the two parts to come into contact with one another while at the same time reducing the axial movements of the fan.

As a total, the ring 9 has the shape of a nozzle, that is, its inlet section is larger than the section through which the air passes towards the end of the blades 4. The larger suction surface maintains the air flowing at a constant speed compensating the resistance to flow. However, as shown in Figure 6, the fan made in accordance with the present invention need not be equipped with the outer reinforcing ring and the related duct. The blade 4, projected towards the plane of rotation XY of the fan 1, has the geometric characteristics that are described below. The angle in the center (B), considering as the center the geometric center of the fan that coincides with the axis of rotation 2 of the fan, corresponding to the width of the blade 4 in the root 5, is calculated using a ratio that takes into account the space that must exist between two adjacent blades 4. In fact, since fans of this type are preferably made of plastic using injection molding, the blades on the die should not be overlap, otherwise the die used to make the fans has to be very complex and production costs inevitably increase as a result. In addition, it should be remembered that, especially in the case of automotive applications, the fans do not work continuously because much of the time that the machine is working, the heat exchangers which are connected to the fans are cooled by the Air flow created by the movement of the vehicle itself. Therefore, air should be allowed to flow easily through it, even when the fan is not on. This is achieved by leaving a relatively large space between the fan blades. In other words, the fan blades should not form a screen that prevents the cooling effect of the air flow created by the movement of the vehicle. The ratio used to calculate the angle (B) in degrees is: B = (360 ° / No. of blades) - K; Kmin = 3 (diameter of the club, height of the blade profile on the club). The angle (K) is a factor that takes into account the minimum distance that must exist between two adjacent blades to prevent them from overlapping during molding and is a function of the diameter of the hub: the larger the diameter of the club , the smaller the angle (K). The value of the angle (K) can also be influenced by the height of the profile of the blade in the hub. The following description, given only by way of example, and without restricting the field of the concept of the invention, refers to a practical application of the ventilator constructed in accordance with the present invention. As shown in the accompanying drawings, the fan has 7 blades, a hub with a diameter of 140 mm and an outside diameter, corresponding to the diameter of the outer ring 9, of 385 mm. The angle (B), corresponding to the width of a blade in the hub, calculated using its values is 44 °.

The geometry of a blade 4 of the fan 1 will be described below: the blade 4 is first defined as a projection on the plane of rotation XY of the fan 1 and the projection of the blade 4 on the plane XY is then transferred into space. Referring to the detail shown in Figure 2, the geometric construction of the blade 4 consists of drawing the bisector 13 of the angle (B) which is in turn bounded by the ray 17 to the left and ray 16 to the right. A ray 14, rotated in the opposite direction to the clock hands at an angle A = 3/11 B relative to the bisector 13, and a ray 15, also rotated in the opposite direction to the clockwise in the angle (A) but relative to ray 16, they are drawn afterwards. The two rays 14, 15 are, thus, rotated at an angle A = 3/11 B, that is, A = 12 °. The intersections of rays 17 and 16 with hub 3 and intersections of rays 14 and 15 with outer ring 9 of the fan or with a circle of diameter equal to outer ring 9), determine 4 points (M, N, S , T) resting on the XY plane, which define the projection of the blade 4 of the fan 1. The projection of the convex edge 7 is also defined, in the hub, by a first tangent 21 inclined at an angle C = 3/4 A, that is, C = 9o, in relation to ray 17 that passes through point (M) in hub 3. As can be seen in figure 2, angle (C) is measured in one direction in the direction of the clock hands relative to the beam 17 and therefore the first tangent 21 is forward of the beam 17 when the convex edge 7 is the first to find the air flow or behind the beam 17 when the convex edge 7 is the last one in meet the air flow, that is, when the edge 8 is the first to meet the flow of air air. In the outer ring 9, the convex edge 7 is also defined by a second tangent 22 which is inclined by an angle (W) equal to 6 times the angle (A), that is, 72 °, relative to the ray 14 that passes through the point (N) in the outer ring 9. As shown in Figure 2, the angle (W) is measured in a direction opposite to the clockwise relative to the spoke 14 and therefore the second tangent 22 is forward when the convex edge 7 is the first to meet the air flow, or behind the beam 14 when the convex edge 7 is the last to meet the air flow, that is, when the edge 8 is the first to meet the air flow. In practice, the projection of the convex edge 7 is tangent with the first tangent 21 and with the second tangent 22 and is characterized by a curve with a single convex portion, without bending. The curve that defines the projection of the convex edge 7 is a parabola of the type: y = a x2 + b x + c. In the illustrated mode, the parabola is defined by the following equation: y = 0.013 x2 - 2.7 x + 95.7. This equation determines the curve illustrated in the Cartesian diagram, shown in Figure 7, as a function of the x and y related variables of the XY plane.

Observing Figure 2 again, the end points of the parabola are defined by the tangents 21 and 22 at points (M) and (N) and the zone of maximum convexity is closest to the mace 3. Experiments have shown that the convex edge 7, with its parabolic projection on the plane of rotation XY of the fan, provides excellent efficiency and noise characteristics. As for the projection of the concave edge 8 of the blade 7 on the XY plane, any curve of the second degree arranged in such a way as to define a concavity can be used. For example, the projection of the concave edge 8 can be defined by a parabola similar to the convex edge 7 and arranged substantially in the same shape. In a preferred embodiment, the curve defining the projection of the concave edge 8 on the XY plane is a circular arc whose radius (Rcu) is equal to the radius (R) of the hub and, in the practical application described in the present invention, the value of this radius is 70 mm. As shown in Figure 2, the projection of the concave edge 8 is delimited by points (S) and (T) and is a circular arc whose radius is equal to the radius of the hub. The projection of the concave edge 8 is thus completely defined in geometric terms. Figure 3 shows eleven profiles 18 representing eleven sections of the blade 4 made at regular intervals from the left to the right, ie from the hub 3 to the outer edge 6 of the blade 4. The profiles 18 may have some characteristics in common but all are geometrically different in order to be able to be adapted to the aerodynamic conditions which are substantially a function of the position of the profiles in the radial direction. The characteristics common to all blade profiles are particularly suitable for high efficiency, low loading and low noise. The first profiles on the left are more arched and have a larger blade angle (ß) because, as they are closer to the rhiza, their linear speed is lower than that of the outer profiles. The profiles 18 have a face 18a comprising an initial straight line segment. This straight line segment is designed to allow airflow to flow smoothly, preventing the blade from "hitting" the air which could interrupt the smooth air flow and thereby increase noise and reduce efficiency. In Figure 3, this straight line tracking is indicated with (t) and its length is from 14% to 17% of the rope length (L). The rest of the face 18a is constituted substantially by circular arcs. Passing from the profiles close to the mace towards those at the end of the blade, the circular arcs constituting the face 18a become increasingly large in radius, that is, the profile curvature (f) of the blade 4 decreases. With respect to the rope (L), the profile curvature (f) is located at a point, indicating with (íf) in figure 3, between 35% and 47% of the total length of the rope (L). This length should be measured from the edge of the profile that meets the air first.

The back part 18b of the blade is defined by a curve in such a way that the maximum thickness (Gma?) Of the profile is located in an area of between 15% and 25% of the total length of the blade rope and preferably at % of the length of the rope (L). In this case too, this length must be measured from the edge of the profile that meets the air first. Moving from the profiles closest to the hub in which the maximum thickness (Gma?) Has its highest value, the thickness of the profile 18 decreases at a constant speed towards the profiles at the end of the blade in which it is reduced by about a quarter of its value. The maximum thickness (Gmax) decreases according to the substantially linear variation as a function of the radius of the fan. The profiles 18 of the sections of the blade 4 in the outermost portion of the fan 1 have the minimum thickness value (Gmax) because their aerodynamic characteristics must make them suitable for high speeds. In this way, the profile is optimized for the linear speed of the blade section, obviously this speed must increase with the increase in the radius of the fan. The rope length (L) of the profiles (18) also vary as a function of the radius. The rope length (L) reaches its maximum value in the middle part of the blade 4 and decreases towards the end 6 of said blade to reduce the aerodynamic load in the outermost portion of the fan blade and also to facilitate the passage of air when the fan is not operating, as indicated above.

The blade angle (ß) also varies as a function of the fan radius. Mainly, the angle of the blade (ß) decreases according to an almost linear law. The law of variation of the angle of the blade (ß) can be chosen according to the aerodynamic load required in the outermost portion of the blade of the fan. In a preferred embodiment, the variation of the blade angle (ß) as a function of the fan radius (r) follows a cubic law defined by the equation (ß) = - 7 • 10"6 • + r3 + 0.0037 • r3 - 0.7602 r + 67.64 The variation law of (ß) as a function of the radius of the fan (r) is represented in the diagram shown in figure 8. Figure 4 shows how the projection of the blade 4 is transferred in the XY plane in space The blade 4 has an inclination V relative to the plane of rotation of the fan 1. Figure 4 shows the segments joining the points (M ', N') and (S, T '') of a aspa (4) .These points (M \ N ', S' T ') are obtained when starting from the points (M, N, S, T) which are located in the XY plane and delineate perpendicular segments (M, M '), (N, N'), (S, S '), (T, T') that determine by thus an inclination (V) or, in other words, a displacement of the blade 4 in the axial direction.

Further, in the preferred embodiment, each blade 4 has a shape defined by the arcs 19 and 20 in FIG. 4. These arcs 19 and 20 are circular arcs whose curvature is calculated as a function of the length of the straight line segments ( M \ N ') and (S \ T'). As shown in Figure 4, the arcs 19 and 20 are offset from the corresponding straight line segments (M ', N') and (S ', T') by the lengths (h1) and (h2) respectively. These lengths (h1) and (h2) are measured on the perpendicular to the plane of rotation XY of the fan 1 and are calculated as a percentage of the length of the segments (M \ N ') and (S', T ') of itself same. The dotted lines in Figure 4 are the curves-parabolic segment and circular arc-related to the convex edge 7 and the concave edge 8. The inclination V of the blade 4, both with respect to its component of axial displacement and with respect to its curvature , makes it possible to correct the deflections of the blade due to the aerodynamic load and to balance the aerodynamic moments in the blade in such a way that a uniform axial air flow is obtained distributed over the entire front surface of the fan. All the characteristic values of the fan blade, according to the modality described, are summarized in the following table, where r is the radius of the generic fan and the following geometric variables that refer to the value of the corresponding radius: L indicates the rope length; f Indicates the curvature of the profile t indicates the initial segment in a straight line of the blade section; 1f indicates the position of the curvature of the profile with respect to the rope L; ß indicates the angle of the profile of the cross section in sexagesimal degrees; x and y indicate the Cartesian coordinates in the XY plane of the parabolic edge of the vane.

Experiments have shown that conventional fans constructed in accordance with the present invention have a noise level of about 25% to 30%, measured in dB (A), lower than that of conventional fans of this type, with considerable improvement in acoustic comfort, meaning that the generated noise was much more "pleasant" than that of conventional fans. Furthermore, under the same air supply conditions, fans constructed in accordance with the present invention develop load values up to 50% higher than conventional fans of this type. In fans constructed in accordance with the present invention, which pass from a subsequent configuration of the blades to a prior configuration thereof, there are no considerable changes in the noise level. Moreover, under certain operating conditions of the fan, particularly in the high load range, the previous configuration of the blades provides 20-25% more than the later configuration of the blades.

Claims (11)

NOVELTY OF THE INVENTION CLAIMS

1. - An axial flow fan (1) rotating in a plane (XY) and comprising a central hub (3), a plurality of blades (4), each blade having a root (5) and one end (6), the vanes (4) being also delimited by a first convex edge (7) and a second concave edge (8), and consisting of sections with aerodynamic profiles (18) with a blade angle (ß) that gradually and steadily decreases from the root (5) towards the end (6) of the blade (4), the blade angle (ß) being defined as the current angle between the plane of rotation (XY) and a straight line joining the leading edge towards the terminal edge of the aerodynamic profile (18) of each blade section, the blades (4) being characterized because the projection of the convex edge (7) on the plane (XY) is defined by a parabolic segment.

2. The fan according to claim 1, further characterized in that the projection of the concave edge (8) on the plane (XY) is defined by a curve segment of the second degree.

3. The fan according to claim 1, further characterized in that the projection of the concave edge (8) on the plane (XY) is defined by a parabolic segment.

4. - The fan according to claim 1, further characterized in that the projection of the concave edge (8) on the plane (XY) is defined by a circular arc.

5. The fan according to any of the preceding claims, further characterized in that the aerodynamic profiles (18) have a face (18a) comprising at least one straight line segment (t).

6. The fan according to claim 5, further characterized in that the aerodynamic profiles (18) have a face (18a) comprising a segment, after the initial segment (t), which is substantially constituted by circular arcs.

7. The fan according to claim 5 or 6, further characterized in that the aerodynamic profiles (18) have a cord length (L) and a backrest (18b) defined by a convex curve which, in combination with the face (18a) determines a maximum thickness value (Gma?) Of the profile in an area between 15% and 25% of the total length of the rope (L) that is measured from the edge that first makes contact with the air.

8. The fan according to any of the preceding claims, further characterized in that each blade (4) projected on the plane (XY) is delimited by four points (M, N, S, T), distributed in the plane (XY) ) and defined as a function of an angle (B) in relation to the width of a single blade (4) subtended at the center of the fan; and characterized further because the four points (M, N, S, T), are determined by the following characteristics: The points (M) and (S) are located in the hub (3) or the root (5) of the blade (4) and are defined by the rays (16, 17) that emanate from the center of the fan and form the angle (B); the point (N) is located at the end 6 of the blade (4) and is displaced counterclockwise by an angle (A) = 3/11 (B) relative to the bisector (13) of the angle ( B); the point (T) is located at the end (6) of the blade (4) and is displaced counterclockwise at an angle (A) = 3/11 (B) with respect to the ray emanating from the center of the fan and what happens through point (S).

9. The fan according to claim 8, further characterized in that the projection of the convex edge (7) on the plane (XY) at the point (M) has a first tangent (21) inclined at an equal angle (C) to three quarters of A with respect to a ray 17 that passes through point (M); and further characterized in that the projection of the convex edge (7) on the XY plane at the point (N) has a second tangent inclined at an angle (W) equal to six times (A) with respect to the ray (14) passing to through point (N); the first and second tangents (21, 22) are forward of the corresponding rays (17, 14) when the direction of rotation of the fan (1) is such that the convex edge (7) is the first to contact the air flow and the first and second tangents (21, 22) are positioned in such a way as to define a curve in the plane (XY) having an individual convex portion with no inflection points.

10. - The fan according to any of the preceding claims from 4 to 9, further characterized in that the circular arc formed by the projection of the concave edge (8) on the plane (XY) has a radius (Rcu) equal to the radius R of the mace (3).

11. The fan according to any of the preceding claims, further characterized in that the blades (4) are formed of sections whose aerodynamic profiles (18) have a blade angle (ß) that decreases gradually and steadily from the root (5). ) towards the end (6) of the blade (4) in accordance with the cubic law of variation as a function of the radius.