Centrifugal multiblade fan

Abstract: A centrifugal multiblade fan comprises a plurality of curved blades which are circularly arranged about a common rotation axis at evenly spaced intervals defining a curved air flow passage between every neighboring blades. Each curved blade has concave front and convex rear surfaces which extend longitudinally in parallel with the rotation axis. A lower annular end plate is provided for putting thereon lower ends of the circularly arranged blades. A radially outside part of each curved blade has a radius of curvature which is greater than that of a radially inside part of the blade.

Description: The present invention relates to a centrifugal multiblade fan according to the preamble part of independent claim 1. In automotive air conditioning devices, there is usually employed a centrifugal multiblade fan which is Installed in an upstream section of an air duct of the air conditioning device. The fan is driven by an electric motor. That is, upon operation of the motor, the fan is rotated to generate an air flow in the air duct in the duct from the outdoor or indoor of an associated motor vehicle toward the passenger cabin of the vehicle. During the flow in the duct, the air passes through an evaporator and/or heater core to adjust temperature thereof to a desired degree. The air thus adjusted in temperature is led into the passenger canbin of the vehicle through air blow openings provided at a downstream end of the air duct. Some of conventional fans of the centrifugal multiblade type are shown in Japanese Patent First Provisional Publications 63-97899 and 60-60299, two of which are schematically shown in Figs. 33 and 34 of the accompanying drawings, respectively. As shown, each fan 1a or 1b comprises a plurality of curved blades 2 which are circularly arranged about a common rotation axis at evenly spaced intervals defining an air flow passage 3 between every neighboring curved blades 2. As is seen from Fig. 35, each curved blade 2 of the fan 1a or 1b has a generally semi-cylindrical shape, that is, the shape having an arcuate cross section. That is, each curved blade 2 has concave front (or leading) and convex rear (or trailing) surfaces 4 and 5 which extend longitudinally in parallel with the rotation axis. Accordingly, each air flow passage 3 curves as it extends radially. The terms "front and rear" are to be understood with respect to the direction "α" in which the fan 1a or 1b rotates under operation of the air conditioning device. When, upon energization of the electric motor, the fan 1a or 1b is rotated in the direction of the arrow "α", air in each air flow passage 3 is forced to move radially outward due to a centrifugal force generated therein. As a result, air is forced to flow radially outward from the inside of the fan 1a or 1b toward the outside through the air flow passages 3. As is known, the fans of the above-mentioned centrifugal multiblade type produce less operation noise than axial fans such as propeller fans. However, sometimes, even the centrifugal multiblade fans fail to provide users with a full satisfaction. That is, when the air conditioning device is in an inner air circulation mode wherein the air blown to the interior of the vehicle is fed from the interior of the vehicle, the noise caused by the fan becomes marked, which makes the passengers uncomfortable. In addition to the above-mentioned fans, other conventional centrifugal multiblade fans have been proposed, which are shown in Japanese Patent First Provisional Publications 62-291498 and 4-203395, and Japanese Utility Model First Provisional Publications 50-76407, 50-76408, 52-2612, 58-94898 and 5-87295. In the fans of these publications, a slit or small opening is formed in each curved blade to improve the performance of the fans. However, even the fans of these publications have failed to provide users with a satisfaction in noise reduction performance particularly in the inner air circulation mode of the air conditioning device. In order to accomplish the present invention, the applicants have carried out various computer simulation tests regarding the structure and arrangement of the curved blades 2 of the fan 1a or 1b. With the tests, the applicants have found the following facts. That is, as is seen from Fig. 36, when the fan 1a or 1b is rotated at a high speed, there is inevitably produced a negative pressure area 6 in each air flow passage 3 at a position facing a radially inside part of the convex rear surface 5. Due to presence of this negative pressure area 6, the air in the air flow passage 3 Is forced to flow radially outward in and along a limited way which is checkered in the drawing. That is, due to presence of the negative pressure area 6, the way for the air is narrowed at that area 6 and thus, not only air flow velocity at such throat area is remarkably increased, but also vortexes are produced in the negative pressure area 6. As Is known, these phenomena bring about a large operation loss of the fan 1a or 1b. According to the simulation tests, the applicants have revealed that the reason for the negative pressure area 6 is a lack of momentum (or energy) possessed by the air which is about to flow in the area 6. That is, as compared with a circumferential velocity of each curved blade 2, the velocity of the air flowing radially outward in that area 6 is small and thus the air flow in the passage 3 becomes separated from the convex rear surface 5. In view of the above-mentioned facts, the applicants have thought out a measure (1X) which is depicted by Fig. 37. As is seen from this drawing, in the measure (1X), the curvature of a radially inside part of each curved blade 2 is greater than that of a radially outside part of the curved blade 2. In other words, the radius of curvature of the inside part is smaller than that of the outside part. That is, in the measure (1X), each curved blade 2 has an arcuate cross section which projects rearward at a portion corresponding to the negative pressure area 6 of Fig. 36. With this measure, the undesired negative pressure area 6 is eliminated or at least minimized, and thus drawbacks caused by such negative pressure area 6 are eliminated. US-A-3 394 876 and JP 61 065095 A disclose a drum rotor blade construction, wherein the blades are substantially longer in axial direction disposed at a circular row between axially spaced end walls and comprises an inner intake portion and an outer discharge portion. Here, the inner intake portion has a smaller radius of curvature than the outer discharge portion. Furthermore, DE 443 163 C, DE 28 50 358 and JP 56 052599 A disclose fans comprising blades which have curvature shapes, a slit, and, accordingly, slats in order to form slits on the blades. The present invention is provided by taking the above-mentioned facts into consideration. Similar to the above-mentioned conventional centrifugal multiblade fan, a fan of the present invention comprises a plurality of curved blades which are circularly arranged about a common rotation axis at evenly spaced intervals defining an air flow passage between every neighboring curved blades. Each curved blade has a generally semi-cylindrical shape, that is, the shape having an arcuate cross section. That is, each curved blade has concave front (or leading) and convex rear (or trailing) surfaces which extend longitudinally in parallel with the rotation axis. The air flow passage thus curves as it extends radially. It is an objective of the present invention to improve a centrifugal multi-blade fan as indicated above so as to eliminate a negative pressure area produced in each air flow passage between respective two adjacent blades. According to the present invention, the objective is solved by a centrifugal multi-blade fan comprising the features of independent claim 1. Further preferred embodiments of the present invention are laid down in the further subclaims. In the following, the present invention is explained in greater detail by means of several embodiments thereof in conjunction with the accompanying drawings, wherein: Fig. 1 is a partial sectional view of two curved blades employed in a centrifugal multiblade fan which is a first preferred embodiment, the view corresponding to 25 the sectional view taken along the line A-A of Fig. 33; Fig. 2 is a view similar to Fig. 1, but showing a way in and along which air is forced to flow under rotation of the fan of the first embodiment; Fig. 3 is a partial sectional view of one of curved blades employed in a fan of a second embodiment which does not relate to the present invention; Fig. 4 is a view similar to Fig. 1, but showing a third embodiment which does not relate to the present invention; Fig. 5A is a view similar to Fig. 1, but showing a conventional centrifugal multiblade fan; Fig. 5B is a view similar to Fig. 1, but showing the fan of the first embodiment; Fig. 6 is a view similar to Fig. 4, but showing a first example of the third embodiment; Fig. 7 is a view similar to Fig. 4, but showing a second example of the third embodiment; Fig. 8 is a partial sectional view of one of curved blades employed in a fan of a fourth embodiment which does not relate to the invention; Fig. 9 is a view similar to Fig. 8, but showing an example of the fourth embodiment; Fig. 10 is a partial sectional view of one of curved blades employed in the conventional centrifugal multiblade fan; Fig. 11 is a view similar to Fig. 10, but showing another conventional centrifugal multiblade fan; Fig. 12 is a partial perspective view of a centrifugal multiblade fan which Is a fifth preferred embodiment; Fig. 13 is a view similar to Fig. 12, but showing a sixth preferred embodiment; Fig. 14 is a view similar to Fig. 12, but showing a seventh preferred embodiment; Fig. 15 is a view similar to Fig. 12, but showing an eighth preferred embodiment; Fig. 16 is a view similar to Fig. 12, but showing a ninth preferred embodiment; Fig. 17 is an enlarged sectional view taken along the line B-B of Fig. 16; Fig. 18 is a view similar to Fig. 12, but showing a tenth preferred embodiment; Fig. 19 is an enlarged sectional view taken along the line C-C of Fig. 18; Fig. 20 is a view similar to Fig. 17, but showing an eleventh preferred embodiment; Fig. 21 is a view similar to Fig. 17, but showing a twelfth preferred embodiment; Fig. 22 is a view showing an arrangement of three microphones used for examining the sound-performance of the fans; Fig. 23 is a graph showing the sound-performance of the preferred embodiments and that of a conventional fan; Fig. 24 is a sectional view of an air blower case In which a fan of a thirteen preferred embodiment is operatively installed; Fig. 25 is an enlarged sectional view of the fan of the thirteen embodiment the fan shown being in a preassembled condition; Fig. 26A is a sectional but half view taken along the line D-D of Fig. 25; Fig. 26B is a sectional but half view taken along the line E-E of Fig. 25; Fig. 27A is an enlarged sectional view taken along the line F-F of Fig. 25; Fig. 27B is a sectional view taken along the line G-G of Fig. 27A; Fig. 27C is a sectional view taken along the line H-H of Fig. 27A; Fig. 28 is a sectional view of a centrifugal multiblade fan which is a fourteenth preferred embodiment; Fig. 29 is a view similar to Fig. 28, but showing a fifteenth preferred embodiment; Fig. 30 is a view similar to Fig. 28, but showing a sixteenth preferred embodiment; Fig. 31 is a view similar to Fig. 28, but showing a seventeenth preferred embodiment; Fig. 32 is a view similar to Fig. 28, but showing an eighteenth preferred embodiment; Fig. 33 is a partial perspective view of a conventional centrifugal multiblade fan for use in an automotive air conditioning device; Fig. 34 is a perspective view of another conventional centrifugal multiblade for the automotive air conditioning device; Fig. 35 is a sectional view of two curved blades employed in the conventional fan; Fig. 36 is a view similar to Fig. 35, but showing a way in and along which air is forced to flow under rotation of the conventional fan; and Fig. 37 is a sectional view of two curved blades employed in the fan which does not relate to the present invention. Referring to Figs. 1 and 2, there is partially shown a centrifugal multiblade fan 1A which is a first embodiment. Similar to the above-mentioned conventional fans of Figs. 33 and 34, the fan 1A of the first embodiment comprises a plurality of curved blades 2 which are circularly arranged about a common rotation axis at even spaced intervals defining an air flow passage 3 between every neighboring curved blades 2. Each curved blade 2 has a generally semi-cylindrical shape, that is, the shape having an arcuate cross section. That is, each curved blade 2 has concave front (or leading) and convex rear (or trailing) surfaces which extend longitudinally in parallel with the rotation axis. The air flow passage 3 thus curves as it extends radially. As is seen from Fig. 1, each curved blade 2 is formed near an inward end with a silt 7 which has parallel upper and lower walls. That is, the slit 7 is formed at a radially Inside part of the curved blade 2 with respect to a diameter of the fan 1A. In other words, the slit 7 is located at an upstream portion of the air flow passage 3 with respect to a direction in which air flows when the fan 1A is rotated in a normal direction "α". Due to provision of the slit 7 at such position, a certain kinetic energy ls applied to any air flowing along the convex rear surface 5 of the blade 2 during rotation of the fan 1A. With such energy, the outward air flow along the convex rear surface 5 is cheered up. That is, through the slit 7, air is blown into the negative pressure area 6 (see Fig. 36) to cheer up the air flow in such area 6. In other words, due to provision of the slit 7, undesired negative pressure area 6 is eliminated in this embodiment. As is understood from Fig. 1, the thickness "W7" of the slit 7 is smaller than 1/5 of that of a part of the air flow passage 3 to which the slit 7 is exposed. That is, the following inequality is established in the first embodiment. W7 ≤ W3/5 If the thickness "W7" is too large, excessive air Is blown into the negative pressure area 6 through the slit 7, which not only deteriorates the air driving efficiency of the fan 1A but also causes generation of noise. Preferably, the thickness "W7" of the slit 7 is larger than 1/20 of that of the part of the air flow passage 3 to which the slit 7 is exposed. That is, the following inequality is established in a preferable example of the first embodiment. W7 ≥ W3/20 As is understood from Fig. 1, each slit 7 curves radially outward as it extends in the curved blade 2 from the concave front surface 4 to the convex rear surface 5. That Is, assuming an angle defined between an imaginary plane "X" evenly passing through the silt 7 and another imaginary plane "Y" flatly contacting an imaginary cylindrical surface coaxially extending around the rotation axis of the fan 1A is denoted by "7", the following inequality is established. 90°<7<180° With this angle "7", elimination of the undesired negative pressure area 6 is much assured. Actually, the angle "7" is determined in accordance with the diameter of the fan 1A, the number of the curved blades 2 and the like. That is, in case of a fan employed In automotive air conditioning devices wherein the outer diameter of the fan is about 150 to about 170 mm, the axial length of the fan is about 70 to about 80 and the number of the curved blades 2 is about 30 to 50, the angle "7" is calculated from the following equation. 7 = π - tan -1 (U/V) wherein: U: radial velocity of air led into the air flow passage 3. V: rotation direction velocity of air flowing In the passage 3 near the slit 7. In view of various correction factors, the angle "7" should be determined to about 100° to about 120°. As is described hereinabove, in the centrifugal multiblade fan 1A of the invention, creation of the undesired negative pressure area 6 in each air flow passage 3 is suppressed or at least minimized. Accordingly, as is seen from Fig. 2, when the fan 1A is rotated at a high speed, there is produced, due to a centrifugal force, in each air flow passage 3 an air flow (which is checked in the drawing) in a direction from a radially inside portion toward a radially outside portion. The air flow is pressed against the concave front surface 4 of each curved blade 2, and thus, part of the air flow is directed to a rear air flow passage 3 through the slit 7. As has been mentioned hereinabove, each slit 7 is arranged to curve radially outward as it extends rearward in the curved blade 2. Accordingly, the air flow passing through the slit 7 can apply a certain kinetic energy to the air flowing in the rear air flow passage 3, and thus, the air flow in the rear air passage 3 is smoothly carried out. As Is described hereinabove, in the fan 1A of the invention, the outward air flow in each air flow passage 3 is smoothly carried out without leaving an undesired negative pressure area therein. Referring to Fig. 3, there is partially shown a centrifugal multiblade fan 1B which is a second embodiment. In this embodiment 1B, a radially inside part 8 of each curved blade 2, that is, the part positioned inside relative to the slit 7, is displaced rearward by a certain distance "δ". The distance "δ" should be smaller than the thickness "T2" of the part 8. That is, the following inequality is established. δ ≤ T2 Preferably, the distance "δ" is smaller than ½ of the thickness "T2" (that is, δ < T2/2). In the preferable example which is not shown in the drawing, a camber line "a" of the inside part 8 extends between the front and rear surfaces 4 and 5 of a radially outside part 9 of the blade 2 and, a camber line "b" of the outside part 9 extends between the front and rear surfaces 4 and 5 of the inside part 8. Referring to Fig. 4, there is partially shown a centrifugal multiblade fan 1C which is a third embodiment. In this embodiment, the thickness of each slit 7 increases gradually with increase of distance from the front surface 4 of the blade 2. As shown, for achieving this, the inclination angle of the upper wall 21 of the slit 7 is made greater than that of the lower wall 22. With such slits 7, elimination of the undesired negative pressure area is much assuredly achieved. The reason of this elimination will be described in the following with reference to Figs. 5A, 5B and 4. Fig. 5A shows radially inside portions of curved blades of a conventional centrifugal multiblade fan, such as the blades shown in Fig. 35, and Fig. 5B shows radially Inside portions of curved blades of the centrifugal multiblade fan 1A of the above-mentioned first embodiment. In the conventional fan of Fig. 5A, the inclination angle of each blade 2 relative to an inscribed cylindrical surface is 30°. In this case, under rotation of the fan, air is led into the air flow passage 3 while defining an entry angle of about 22° relative to the inscribed cylindrical surface. Tests have revealed that such entry angle causes generation of marked vortexes "V" near the rear surface 5 of each blade 2. While, in the fan 1A of Fig. 5B wherein the angle defined between the imaginary plane "X" passing through the slit 7 and the inscribed cylindrical surface is 26°, the entry angle of the air led into the air flow passage 3 is about 32°. Tests have revealed that such entry angle and such arrangement of the slits 7 cause generation of only small vortexes "v" near the rear surface 5 of each blade 2. In fact, such small vortexes "v" tend to appear at a rear end of the upper wall of each slit 7. In the third embodiment 1C of Fig. 4, the rear end of the upper wall 21 of the slit 7 is displaced radially outward for eliminating a portion where such small vortexes "v" tend to appear. Referring to Fig. 6, there is shown a preferred example 1C' of the third embodiment. In this drawing, denoted by reference "r1" is a radius of the inscribed cylindrical surface and denoted by reference "rz" is a distance between the rotation axis of the fan and the outermost end of the lower wall 22 of each slit 7. In this preferred example 1C', the following inequality is established. rz/r1 ≤ 1.08 Furthermore, the angle 22 defined between the lower wall 22 of each slit 7 and the inscribed cylindrical surface satisfies the following inequality in this example 1C'. 22 ≥ tan -1 (U/V) wherein: U: radial velocity of air led into the air flow passage 3. V: rotation direction velocity of air flowing in the passage 3 near the slit 7. Thus, when the fan 1C' is used in an automotive air conditioning device wherein "V" is about 15.27 m/s and "U" is about 3.75 m/s, the following inequality Is established. 22 ≥ 13.8° Referring to Fig. 7, there is shown another preferred example 1C" of the third embodiment. In this example 1C'', the upper and lower walls 21 and 22 of each slit 7 are chamfered at their rear ends 23. If desired, the upper and lower walls 21 and 22 may be chamfered at their front ends. Furthermore, if desired, as is shown in the drawing, each blade 2 has a tapered inner end to allow a smoothed air flow into the air flow passage 3 under rotation of the fan 1C". Referring to Fig. 8, there is partially shown a centrifugal multiblade fan 1D which is a fourth embodiment. In this embodiment, each curved blade 2 comprises a radially outside part 24 having a larger radius of curvature (for example, 18.2 mm) and a radially inside part 25 having a smaller radius of curvature (for example, 6.7 mm) which are united through a smoothly curved portion. With such shape of each blade 2, air can be smoothly led into the air flow passage 3 without making a marked collision against the front surface 4 of the blade 2. Referring to Fig. 9, there is partially shown a centrifugal multiblade fan 1D' which is a modification of the fan 1D of Fig. 8. That is, in this modification, the radius of curvature of the radially outside part 24 of each blade 2 is 21. 7 mm and that of the radially inside part 25 is 5.4 mm. The reason of the advantage possessed by the fans 1D and 1D' of Figs. 8 and 9 will become apparent from the following. In Fig. 10, there is shown one of curved blades 2 employed in a conventional centrifugal multiblade fan. In this blade 2, the radius of curvature of the radially outside part and that of the radially inside part are the same, that is 9.4 mm. The inclination angle of each blade 2 relative to an Inscribed cylindrical surface is 62° which is relatively large. In this arrangement, air led to the air flow passage 3 is forced to collide hard against the concave front surface 4 of each blade 2, which brings about a marked operation loss of the fan. In Fig. 11, there is shown one of curved blades 2 employed in another conventional centrifugal multiblade fan. Each curved blade 2 comprises a radially outside part 24 having a larger radius of curvature (for example, 19.1 mm) and a radially inside part 25 having a smaller radius of curvature (for example, 10.4 mm) which are united through a smoothly curved portion. The inclination angle of each blade 2 relative to an Inscribed cylindrical surface is 62° which is relatively large. Thus, the fan has the drawback possessed by the fan of Fig. 10. However, in case of the above-mentioned fans 1D and 1D' of Figs. 8 and 9, the inclination angle of each blade 2 is only 42° or 25° which is very small. That is, for this reason, air can be smoothly led into the air flow passage 3 without making a hard collision against the front surface 4 of the blade 2. When using the conventional fan of Fig. 10 and the fan 1D of Fig. 8 as test pieces, computer simulation tests have revealed that the static pressure changes from 333.9 (Pa) to 351.7 (Pa), the specific sound level changes from 16.3 (dB-A) to 15.6 (dB-A) and the total pressure efficiency changes from 36.0 % to 36.7 %. From various computer simulation tests, the applicants have found the following facts. That is, if the inclination angle of each curved blade to the inscribed cylindrical surface is smaller than 50°, satisfied function is obtained from the fan. This advantageous fact also takes place irrespective of presence/absence of the sllt 7. Referring to Figs. 12 to 21, there are partially shown other centrifugal multiblade fans 1E to 1L according to preferred embodiments. These fans 1E to 1L satisfy the above-mentioned features. It is further to be noted that these fans 1E to 1L can be produced or injection molded by using a so-called axial draw type mold unit which is simple in construction as compared with a so-called radial draw type mold unit. That is, in the mold unit of axial type, paired molds are displaceable in an axial direction relative to each other. In the fan 1E of Fig. 12, there are employed first and second annular end plates 11 and 13 between which the circularly arranged curved blades 2 are sandwiched. Thus, the fan 1E has a robust structure. As shown, each blade 2 has a lower end whose radially inside part is integrally connected to a radially outside part of the first end plate 11 and has an upper end whose radially outside part is integrally connected to the second end plate 13. The first end plate 11 has a cone-shaped holder part 12 which is connected to an output shaft of an electric motor (not shown). As shown, an inner diameter of the second end plate 13 is greater than an outer diameter of the first end plate 11. With this, the first and second end plates 11 and 13 are not overlapped when viewed from an axial direction of the fan 1E. With this non-overlapped formation of the two end plates 11 and 13, the axial draw type mold unit can be used. As shown, each curved blade 2 is formed with an elongate slit 7 at the radially inside part thereof. Each slit 7 is merged at a lower end thereof with a rectangular opening 14 formed in the first end plate 11. The size of the opening 14 is larger than the cross section area of the slit 7. It is to be noted that the openings 14 are the traces of spacers (not shown) of one mold which have been kept in the mold unit under injection molding. In the fan iF of Fig. 13, there is employed a first annular end plate 11a on which the circularly arranged curved blades 2 are put. The first end plate 11a has a cone-shaped holder part 12 which has an apertured center boss (not shown). Although not shown in the drawing, an output shaft of an electric motor is engaged with the boss to drive the fan 1F. As shown, every other two of the blades 2 have upper portions connected through a bridge 12a which has a curved inside portion. The first annular end plate 11a is formed at portions facing the bridges 12a with openings 20. Each curved blade 2 is formed with an elongate slit 7 at the radially inside part thereof. Each slit 7 is merged at a lower end thereof with the corresponding opening 20. Due to the shape of the fan 1F, injection molding of this fan 1F is relatively easy as compared with that of the above-mentioned fan 1E. The fan 1G of Fig. 14 is substantially the same as the fan 1F of Fig. 13 except for the following. That is, in the fan 1G, in place of the slit 7, two slits 7a and 7b are formed in the radially inside part of each curved blade 2, which are aligned, as shown. That is, the two slits 7a and 7b are aligned leaving a bridge part 2a therebetween. Due to provision of the bridge part 2a, the mechanical strength of each blade 2 is increased as compared with that of the fan 1F. The fan 1H of Fig. 15 is substantially the same as the fan 1G of Fig. 14 except for the following. That is, in the fan 1H, there is further employed a second annular end plate 13 to which an upper end of each blade 2 is integrally connected, like in the manner as the fan 1E of Fig. 12. The fan 1I of Figs. 16 and 17 is similar to the fan 1E of Fig. 12 except for the followings. It is to be noted that Fig. 17 is an enlarged sectional view taken along the line B-B of Fig. 16. That is, in the fan 1I of Fig. 16, in place of the slit 7, two slits 7a and 7b are formed in each curved blade 2. The upper slit 7a has an upper portion crossed by a raised bridge 2b. As shown, each raised bridge 2b is provided at the convex rear surface 5 of the blade 2. The first end plate 11 is formed at portions facing the raised bridges 2b with openings 27. That is, these openings 27 are exposed to the convex rear surfaces 5 of the blades 5. It is to be noted that the openings 27 are the traces of spacers (not shown) of one mode which have been kept in the mold unit under injection molding. Due to provision of the raised bridge 2b, the mechanical strength of each blade 2 is increased. The fan 1J of Figs. 18 and 19 is substantially the same as the fan 1I of Figs. 16 and 17 except for the followings. It is to be noted that Fig. 19 is an enlarged sectional view taken along the line C-C of Fig. 18. That is, in the fan 1J of Fig. 18, half the number of the raised bridges 2b are provided at the concave front surfaces 5 of the blades 2. That is, the raised bridges 2b are provided at the rear and front surfaces 5 and 4 of the blades 2 alternatively. The first end plate 11 is formed at portions facing the raised bridges 2b with openings 28. Each opening 28 extends between adjacent two blades 2. In Fig. 20, there is shown a raised bridge 2b employed In the fan 1K. The fan 1k is substantially the same as the fan 1H of Figs. 16 and 17 except for the following. As shown in Fig. 20, in the fan 1K, each opening 27 of the first end plate 11 extends to a portion 27a which is exposed to the concave front surface 4 of the blade 2. In Fig. 21, there is shown a bridge portion employed in the fan 1L. As is seen from this drawing, in the fan 1L, the bridge portion comprises a first raised bridge 2b formed on the rear surface 5 of each blade 2 and a second raised ridge 2b' formed on the front surface 4 of the blade 2. Each opening 27 of the first end plate 11 extends to a portion 27b which is exposed to the concave front surface 4 of the blade 2. In order to examine the performance of the present invention, the following performance tests were carried out on the conventional fan of Fig. 35, the fan 1X of Fig. 37 according to the invention and the fan 1A of Fig. 1 according to the invention. In the tests, each fan was turned with an electric motor at three speeds to produce three types of air capacities (or airflow) of 7 m3/min, 8 m3/min and 9 m3/min, and the static pressure, input power (demand), efficiency, total pressure, noise level and specific sound level were measured in each air capacity. In all of the fans, the outer diameter was 158 mm, the axial length was 75 mm and the number of blades was 43. The electric motor used was of a 12V-DC motor producing 4.7 Kg·cm in torque, 2955 rpm in rotation speed. As is seen from Fig. 22, for examining the noise level and specific sound level, each fan was set in a blower case 16 connected to a duct 15 and three microphones 17a, 17b and 17c were arranged around the blower case 16 at evenly spaced intervals. The distance between the center of each fan and each microphone 17a, 17b or 17c was 1 m. The results of the tests are shown in Tables I and II (see pages 24 and 25) and the graph of Fig. 23. From the results, the following facts were revealed by the applicants. (a) Performance of blower (static pressure) As is seen from Table-1, the fans 1X and 1A of the Inventions exhibited a slight improvement as compared with conventional one. (b) Noise As Is seen from Table-2 and the graph of Fig. 23, the fans 1X and 1A of the invention exhibited an improvement by a degree of 0.5 to 1.5 dB as compared with the conventional one. Regarding the specific sound level, the fans 1X and 1A of the invention exhibited an improved by a degree 0.8 to 12 dB or 1.5 to 2.0 dB as compared with conventional one. It is to be noted that the performance curves of the graph of Fig. 23 were drawn with reference to the average value of the noise levels. Referring to Figs. 24 to 32, there are shown other centrifugal multiblade fans 1M to 1R according to the present invention. In Figs. 24 to Fig. 27C, there is shown the fan 1M which is a thirteenth embodiment of the invention. As shown In Fig. 24, in practical use, the fan 1M is installed in a case 102 of an air intake unit 101. The case 102 is formed with an outside air inlet opening 105 and an inside air inlet opening 106. These two openings 105 and 106 are selectively closed by an intake door 107. Within the case 102, there is defined a bell-mouth portion 108. Below the bell-mouth portion, the fan 1M is rotatably installed. Denoted by numeral 103 is an electric motor for driving the fan 1M. When, upon energization of the motor 103, the fan 1M is rotated in a given direction, air is led into the fan 1M and blown radially outward therefrom as is Indicated by the arrows. As is best shown in Fig. 25, the fan 1M comprises a first fan part 111 and a second fan part 112 which are coaxially coupled. It is to be noted that the fan 1M shown in Fig. 25 is in a preassembled condition. The first fan part 111 comprises a cone-shaped holder part 114 which has an apertured center boss 113. Although not shown in the drawing, an output shaft of the electric motor 103 is engaged with the apertured center boss 113 to drive the same. Circularly arranged curved blades 115 are integrally formed on a peripheral portion of the holder part 114. That is, as is seen from Figs. 26A and 26B, the curved blades 115 are circularly arranged about a common rotation axis at evenly spaced intervals and have such constructional features as has been described hereinabove. Each curved blade 115 is formed with a slit 118 in such a manner as has been mentioned hereinabove. As is understood from Figs. 25, 26A and 26B, an upper annular end plate 116 is put on and integral with upper ends of the blades 115. The outer diameter D1 of the annular end plate 116 is substantially the same as that of an imaginary circle defined by radially outer ends of the blades 115, while, the inner diameter D2 of the annular end plate 116 is substantially the same as or slightly larger than an outer diameter of cone-shaped holder part 114. With this shape, injection molding for the first fan part 111 is easily carried out through a simple mold unit. As is seen from Fig. 25, the second fan part 112 comprises a lower annular end plate 121 on which circularly arranged curved blades 122 stand. That is, the curved blades 122 are circularly arranged about a common rotation axis at evenly spaced intervals and have such constructional features as has been described hereinabove. Each curved blade 122 Is formed with a slit 125 in such a manner as has been mentioned hereinabove. As is understood from Fig. 25, an upper annular end plate or shroud member 123 is put on and integral with upper ends of the blades 122. As shown, the end plate 123 comprises a skirt part 123a and a tubular part 123b which is to be mated with the bell-mouth portion 108 of the case 102. The outer diameter D3 of the lower annular end plate 121 is substantially the same as or slightly smaller than the inner diameter D2 of the annular end plate 116 of the first fan part 111. That is, the second fan part 112 can be coaxially and snugly put on the first fan part 111 having the end plate 121 mated with the end plate 116. The inner diameter D4 of the end plate 121 is substantially the same as that of an imaginary circle defined by radially inner ends of the blades 122. With this shape, injection molding for the second fan part 112 is easily carried out through a simple mold unit. The manner of coupling between the first and second fan parts 111 and 112 is shown in Fig. 27A which is an enlarged sectional view taken along the line F-F of Fig. 25. Sectional views taken along the line G-G and the line H-H of Fig. 27A are shown in Figs. 27B and 27C respectively. As is understood from these drawings, the annular end plate 116 of the first fan part 111 is formed at an outer side with a plurality of curved grooves 117, while the annular end plate 121 of the second fan part 112 is formed at an outer side with a plurality of curved grooves 124. That is, the curved grooves 117 of the end plate 116 receive lower ends of the curved blades 122 of the second fan part 112, and the curved grooves 124 of the end plate 121 receive upper ends of the curved blades 115 of the first fan part 111. By applying ultrasonic vibration to the mated portions between each blade 116 or 121 and the blades 122 or 115, the mated portions become united. Of course, adhesive may be used in place of such ultrasonic bonding. With usage of the first and second fan parts 111 and 112, various types and sizes are available in the fan 1M of the thirteenth embodiment. That is, by changing the combination between the two fan parts 111 and 112, a fan having a desired shape and size is easily produced. In Fig. 28, there is shown the fan 1N of a fourteenth embodiment of the invention. This fan 1N is the first fan part 111 of the fan 1M of the above-mentioned thirteenth embodiment. In Fig. 29, there is shown the fan 10 of a fifteenth embodiment of the invention. The fan 10 shown is in a preassembled condition. The fan 10 is substantially the same as the above-mentioned fan 1N except that in this fifteenth embodiment a shroud member 131 is employed. That is, the shroud member 131 is integrally connected to the annular end plate 116. In Fig. 30, there is shown the fan 1P of a sixteenth embodiment of the invention. This fan 1P is a modification of the above-mentioned fan 1N of Fig. 28. That is, as is seen from the drawing, the cone-shaped holder part 114 is shallower than that of the fan 1N, so that the apertured center boss 113 is positioned behind the end plate 116. In Fig. 31, there is shown the fan 1Q of a seventeenth embodiment of the invention. Similar to the fan 1M of Fig. 25, the fan 1Q of this embodiment comprises a first fan part 111 and a second fan part 112 which are coaxially coupled. It is to be noted that the fan 1Q shown in Fig. 31 is in a preassembled condition. The first fan part 111 of this fan 1Q is thinner than that of the fan 1M of Fig. 25, while the second part 112 is the same as that of the fan 1M. In Fig. 32, there is shown the fan 1R of an eighteenth embodiment of the invention. As shown in the drawing, the fan 1R of this embodiment comprises a circular plate member 141 and a fan part 112 which is the same as that of the fan 1M of Fig. 25. The fan part 112 is coaxially put on and Integral with the circular plate member 141. The circular plate member 141 is formed with an annular recess 142 into which the annular end plate 121 is snugly received.

Claims: A centrifugal multiblade fan comprising: a plurality of curved blades (2,115,122) which are circularly arranged about a common rotation axis at evenly spaced intervals defining a curved air flow passage (3) between all neighboring blades (2,115,122), wherein each curved blade (2,115,122) has concave front and convex rear surfaces (4,5) which extend longitudinally in parallel with the rotational axis; a lower annular end plate (11,121) with regard to an axial direction of the rotation axis for putting thereon one of the ends of the blades (2,115,122), wherein a radially outside part (9) of each blade (2,115) has a radius of curvature which is greater than that of a radially inside part (8) of the blade (2,115,122), characterized in that the radially inside part (8) of each blade (2,115,122) is formed with a slit (7,118,125) which extends in parallel with the rotation axis, wherein a thickness (W7) of the slit (7,118,125) in radial direction with regard to the rotation axis is smaller than 1/5 of that of a part of the air flow passage (3) to which the slit (7,118,125) has been provided. A centrifugal multiblade fan according to claim 1, characterized in that the thickness (W7) of the slit (7,118,125) in radial direction with regard to the rotation axis is larger than 1/20 of that of the part of the air flow passage (3) to which the slit (7,118,125) has been provided. A centrifugal multiblade fan according to claim 1 or 2, characterized in that the slit (7,118,125) curves radially outward as it extends in the curved blade (2,115,122) from a concave front surface (4) to a convex rear surface (5). A centrifugal multiblade fan according to at least one of the preceding claims 1 to 3, characterized by an angle 7 defined between an imaginary plane (X) evenly passing through the slit (7,118,125) and another imaginary plane (Y) flatly contacting an imaginary cylindrical surface coaxially extending around the rotation axis satisfies a following inequality: 90° < 7 < 180°. A centrifugal multiblade fan according to claim 4, characterized in that the angle 7 is calculated from a following equation: 7 = π - tan -1 (U/V), wherein: U is a radial velocity of air led into the air flow passage (3), V is a rotation direction velocity of air flowing in the air flow passage (3) near the slit (7,118,125). A centrifugal multiblade fan according to claim 4 or 5, characterized in that the angle 7 is about 100° to 160°. A centrifugal multiblade fan according to at least one of the preceding claims 1 to 6, characterized by an upper annular end plate (13,116) with regard to the axial direction of the rotation axis for putting thereon the other ends of the blades (2,115,122). A centrifugal multiblade fan according to claim 7, characterized in that each curved blade (2) has a lower end with regard to the axial direction of the rotation axis, wherein a radially inside part of the lower end is integrally connected to a radially outside part of the lower annular end plate (11), and has an upper end with regard to the axial direction of the rotation axis, wherein a radially outside part of the upper end is integrally connected to the second annular plate (13). A centrifugal multiblade fan according to claim 8, characterized in that the lower annular end plate (11) is formed with a cone-shaped holder part (12) being adapted to be connected to an output shaft of an electric motor (103). A centrifugal multiblade fan according to claim 9, characterized in that an inner diameter of the upper annular end plate (13) is greater than an outer diameter of the lower annular end plate (11). A centrifugal multiblade fan according to claim 10, characterized in that the slit (7) is merged at the lower end of the blade (2) with a rectangular opening (14) formed in the lower annular end plate (11), wherein a size of the rectangular opening (14) is larger than a cross section area of the slit (7). A centrifugal multiblade fan according to at least one of the preceding claims 1 to 6, characterized in that respective two blades (2) have upper portions with regard to the axial direction of the rotation axis wherein the upper portions are connected through a bridge (12a) having a curved inside portion, and the lower annular end plate (11) is formed with openings (20) at portions facing the bridges (12a). A centrifugal multiblade fan according to claim 12, characterized in that the slit (7) of each blade (2) comprises two slit parts (7a,7b) which are aligned and separated by a bridge part (2a) formed by the blade (2). A centrifugal multiblade fan according to claim 12 or 13, characterized by an upper annular end plate (13) with regard to the axial direction of the rotation axis to which upper ends of the blades (2) with regard to the axial direction of the rotation axis are integrally connected. A centrifugal multiblade fan according to claim 11, characterized in that the slit (7) comprises lower and upper slit parts (7a,7b) with regard to the axial direction of the rotation axis, wherein the lower and upper slit parts (7a,7b) are aligned and separated by a bridge portion formed by the blade (2), the upper slit part (7a) has an upper portion with regard to the axial direction of the rotation axis, wherein the upper portion is crossed by a raised bridge (2b) formed by the blade (2), and the lower annular end plate (11) is formed with openings (27,28) at portions facing the raised bridges (2b). A centrifugal multiblade fan according to claim 15, characterized in that the raised bridge (2b) is provided at the convex rear surface (5) of each blade (2). A centrifugal multiblade fan according to claim 15 or 16, characterized in that one half of each raised bridges (2b) are provided at the concave front surface (4) of the blade (2). A centrifugal multiblade fan according to at least one of the preceding claims 15 to 17, c haracterized in that each of the openings (28) formed in the lower annular end plate (11) extends between a rear side exposed to the convex rear surface (5) of the blade (2) and a front side exposed to the concave front side (4) of the blade (2). A centrifugal multiblade fan according to at least one of the preceding claims 15 to 18, characterized in that each raised bridge comprises a first raised part (2b) formed on the convex rear surface (5) of the blade (2) and a second raised part (2b') formed on the concave front surface (4) of the blade (2). A centrifugal multiblade fan according to at least one of the preceding claims 1 to 7, characterized in that the lower annular end plate (121) is formed with a cone-shaped holder part (114) being adapted to be connected to an output shaft of an electric motor (103). A centrifugal multiblade fan according to claim 20, characterized in that the cone-shaped holder part (114) is formed with an aperture center boss (113) to which the output shaft of the motor (103) is mated. A centrifugal multiblade fan according to claim 21, characterized in that the aperture center boss (113) is axially projected outward from one end of the circularly arranged curved blades (115). A centrifugal multiblade fan according to at least one of the preceding claims 20 to 22, c haracterized by a shroud member (123) being integrally connected to the lower annular end plate (121). A centrifugal multiblade fan according to at least one of the preceding claims 21 to 23, characterized in that the aperture center boss (113) is positioned behind the lower annular end plate (121). A centrifugal multiblade fan according to at least one of the preceding claims 1 to 7, c haracterized by a first fan part (111) including a first group of the curved blades (115) and a first annular end plate (116) to which one of the ends of the first group of the blades (115) are integrally connected, and a second fan part (112) including a second group of the curved blades (122) and a second annular end plate (123) to which one of the ends of the second group of the blades (122) are integrally connected, wherein the first and second fan parts (111,112) are coaxially and integrally connected to each other in such a manner that the first and second annular end plates (116,123) are coaxially coupled. A centrifugal multiblade fan according to claim 25, characterized in that the second annular end plate (123) is snugly fitted in the first annular end plate (116). A centrifugal multiblade fan according to claim 26, characterized in that the first annular end plate (116) is formed with a plurality of curved grooves (117) into which one of the ends of the second group of the blades (122) are received, and the second annular end plate (123) is formed with a plurality of curved grooves (124) into which one of the ends of the first group of the blades (115) are received. A centrifugal multiblade fan according to claim 27, characterized in that the first annular end plate (116) and the second group of the blades (122) are integrally connected through a ultrasonic bonding process, and the second annular end plate (123) and the first group of the blades (115) are integrally connected through a ultrasonic bonding process. A centrifugal multiblade fan according to at least one of the preceding claims 1 to 7, characterized in by a circular plate member (141) having a cone-shaped holder part, and a fan part (112) including the circular arranged curved blades (122) and the lower annular end plate (121), wherein the fan part (112) is coaxially put on and integrally connected to the circular plate member (141). A centrifugal multiblade fan according to claim 29, characterized in that the circular plate member (141) is formed with an annular recess (142) into which the lower annular end plate (121) is snugly fitted.

Inventors: KAMIYAMA KAORU, OHASHI TOSHIO, SAEKI NAOFUMI, UOMOTO MANABU, KAMIYAMA, KAORU, OHASHI, TOSHIO, SAEKI, NAOFUMI, UOMOTO, MANABU
Applicants: CALSONIC KANSEI CORP, CALSONIC KANSEI CORPORATION
Application year: 1997
Main classification: F04D29
IPC codes: F04D29