A FAN CENTRIFUGAL IMPELLER

Abstract: A fan centrifugal impeller, comprising: a backplate (3), shaped as a surface of revolution having as axis the impeller rotation axis (8), and being tangent along its external circle to a revolution cone (22) with a vertex angle ( alpha ) smaller than or equal to 160 DEG and preferably from 130 DEG to 110 DEG ; blades (2), mounted on the backplate having a leading edge (5) and a trailing edge (6), wherein the distance to the rotation axis (8), along the trailing edge remains substantially constant; a surface of revolution shaped shroud (1), having as axis the impeller rotation axis (8).

Description: χ "A FAN CENTRIFUGAL IMPELLER" Field of invention The present invention relates to centrifugal impellers which can be included in centrifugal fans as well as in in-line fans. Prior art Classic centrifugal impellers are represented in Figs. 1A to IE. They consist of blades 2 attached on the impeller backplate 3, these blades being classically covered by a profiled, conical or even flat shroud 1. They are fixed on a shaft extension through a hub 4 and rotate around the hub axis 8. Usually the impeller backplate 3 is flat and so perpendi¬ cular to the rotation axis 8 as shown in Figs. 1A to ID. Exceptionally it may be profiled as in Fig. IE but even in this case it is tangent along its terminal circle 19 to a plane 20 perpendicular to the rotation axis 8. In most of the cases the blades are developable with generatrices parallel to the rotation axis, the blade trailing edge 6 being classically a generatrix. They can be hollow aero¬ foils as in Fig. 1A or flat as in Figs. IB and IC, or flat with a spoon 21 closed to the leading edge 5. When the generatrices are not parallel with the rotation axis 8 the distance from one point of the trailing edge 6 to the rotation axis 8 remains substantially constant from the shroud 1 to the backplate 3. The blade leading edge 5 presents different variants accor¬ ding to the blade type. It may be a generatrix parallel to the rotation axis 8 as in figures 1A and IB or a flat line as in figure IC or a curved line as in figure ID and IE, the distance from one point of the leading edge 5 to the rotation axis 8 being in these last cases not constant from the shroud 1 to the backplate 3. The invention The object of the invention is to provide a new centrifugal impeller design giving an increased flow with regard to a clas¬ sical centrifugal impeller, the impeller discharge section at every distance from the rotation axis remaining the same. This object is attained by modifying the classical cen¬ trifugal impeller design through the introduction, as backplate, of a truncated revolution cone, which axis is the impeller rotation axis, and by using blades, for which the dis- tance from one point of the trailing edge to the rotation axis is substantially constant from the shroud to the backplate. In a plane passing through the impeller rotation axis, the section of the impeller according to the invention looks like the section of a classical centrifugal impeller which may have been sloped. The fan centrifugal impeller according to the invention is defined by the characterizing features of claim 1. Preferred embodiments of the invention is defined in the subclaims. Brief description of the drawings The invention will now be described more in detail in connection with embodiments shown in the drawings, in which Fig. 1 illustrates different variants of centrifugal impellers according to the prior art, Fig. 2 shows the preferred embodiment of the centrifu¬ gal impeller according to the invention, Fig. 3 shows one embodiment similar to that shown in Fig. 2 but with a further modified backplate, Fig. 4 shows one embodiment similar to that shown in Fig. 2 but with variants for the blade trailing edge, Fig. 5 shows one embodiment similar to that shown in Fig. 2, but with variants for the blade leading edge, Fig. 6 shows a classic centrifugal fan including an impeller according to the invention, Fig. 7 shows an in-line fan including an impeller according to the invention. Description of the preferred embodiments In fig. 2 the centrifugal impeller according to the inven¬ tion, in the simplest design, is illustrated, having blades 2 arranged on the impeller backplate 3 and covered by a shroud 1. The backplate 3 is a truncated revolution cone which belongs to a revolution cone 22 the axis of which is the impeller rotation axis 8, the vertex being 9, and which vertex angle is smaller or equal to 160°, the preferred range being from 130° to 110° for aeraulic characteristics reasons. The blades 2 are developable blades with generatrices parallel to the rotation axis 8, the blade leading edge 5 and the blade trailing edge 6 being generatrices. The shroud 1 is a surface of revolution. Usually the design of centrifugal impellers is based on the hypothesis of a slight evolution of the discharge section area of the impeller from the blades leading edge 5 to the blades trailing edge 6. That involves that the mean shroud slope must be adapted to the slope of the backplate. That is why a section by a plane passing through the impeller rotation axis 8, the section of the impeller according to the invention looks like the section of a classical centrifugal impeller which may have been sloped. Fig. 3 shows that more generally the backplate 3 may be convex or concave or any surface of revolution having as axis the impeller rotation axis 8, at the only one condition to be tangent along its external circle 19 to a revolution cone 22 the axis of which is the impeller rotation axis 8, the vertex being 9 and which vertex angle is smaller than or equal to 160°, the preferred range being from 130° to 110° for aeraulic reasons. Fig. 4 shows that more generally the blades trailing edge 6 may not be generatrices parallel to the impeller rotation axis at the only one condition that the distance to the rotation axis 8 along the trailing edge 6 may remain substantially con¬ stant inside a tolerance of ± 5 % of its value R at the trail- ing edge extremity 19 on the backplate side. Fig. 5 shows that more generally the blades leading edge 5 may not be generatrices parallel to the impeller rotation axis 8 and that the distance to the rotation axis 8 along the leading edge 5 may vary substantially. The leading edge 5 may even be part of a spoon 21. Fig. 6 shows a classical centrifugal fan including an impeller according to the invention. This centrifugal fan con¬ sists of a casing 11, a support 14 attached to the casing 11 and supporting a driving electrical motor 13, an impeller 12 according to the invention and fixed on the shaft extension of the driving electrical motor 13 and an inlet cone 10 attached to the casing 11. The casing backplate 15 is designed to move away adequately the impeller 12 of the casing 11 so that the gasflow leaving the impeller 12 could easily continue to turn inside the casing 11. Fig. 7 shows an in-line fan including an impeller according to the invention. This in-line fan consists of a casing 16, including a downstream guide vane 17, a support 14 attached to the downstream guide vane 17 and supporting a driving elec¬ trical motor 13, an impeller 12 according to the invention and fixed on the shaft extension of the driving electrical motor 13, and an inlet cone 10 attached to the casing 16. A torus 18 attached to the downstream guide vane 17 allows the gasflow, at the outlet of the wheel 12 to easily turn into the downstream guide vane 17.

Claims: Claims 1. A fan centrifugal impeller, comprising a backplate shaped as a surface of revolution having as axis the impeller rotation axis and being tangent along its external circle to a revolution cone with a vertex angle smaller than or equal to 160° and preferably from 130° to 110°, blades mounted on the backplate having a leading edge and a trailing edge, wherein the distance to the rotation axis along the trailing edge of the blades remains substantially constant inside a tolerance of ± 5 % of its value (R) at the trailing edge extremity on the backplate side, a surface of revolution shaped shroud having as axis the impeller rotation axis. 2. An impeller according to claim 1, wherein the backplate is a truncated revolution cone shaped backplate. 3. An impeller according to claim 1, wherein the blades are developable blades. 4. An impeller according to any of claims 1-3, wherein the distance to the rotation axis along the leading edge of the blades varies substantially. 5. An impeller according to any of claims 1 - 4, wherein the blade leading edge and the blade trailing edge are gene¬ ratrices parallel to the rotational axis. 6. A centrifugal fan including an impeller according to any of claims 1 - 5. 7. An in-line fan including an impeller according to any of claims 1 - 5.

Inventors: LONGET CLAUDE, LONGET, CLAUDE
Applicants: FLAEKT AB, LONGET CLAUDE, ABB FLAEKT AB, LONGET, CLAUDE
Application year: 1997
Main classification: F04D29
IPC codes: F04D29