EP0467557A1

EP0467557A1 - Blower assembly with impeller for vacuum cleaner

Info

Publication number: EP0467557A1
Application number: EP91306038A
Authority: EP
Inventors: Yukiji Iwase; Shigenori Sato; Masao Sunagawa; Hisanori Toyoshima
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1990-07-20
Filing date: 1991-07-03
Publication date: 1992-01-22
Anticipated expiration: 2011-07-03
Also published as: DE69105845T2; EP0602007B1; JPH0481600A; EP0602007A2; DE69127832D1; EP0467557B2; KR0180742B1; JP2852106B2; DE69127832T2; DE69105845D1; EP0602007A3; EP0467557B1; KR920002084A

Abstract

A vacuum cleaner blower assembly has a blower motor (81), a vaned centrifugal impeller (90) driven by the blower motor (81) and an air diffuser (89) radially beyond the periphery of the impeller. In order to improve air flow efficiency at the impeller inlet and outlet, the impeller (90) has a shroud plate (97) which, as seen in axial section, curves away from the vane inlet region towards its inner edge and the air diffuser (89) has vanes (94) with an inlet angle in the range 1 to 4°.

Description

This invention relates to impellers for vacuum cleaners and to vacuum cleaners having an impeller and a blower motor driving the impeller.
In the field of household vacuum cleaners, JP-A-59-74396 discloses an impeller for an electric blower in which a shroud plate is defined in the vicinity of the inlet of an impeller by a continuous curve, as viewed in an axial plane, having a large curvature as compared to the inner diameter of the impeller. This design can reduce exhaust noise, but is liable to relatively increase the sound transmitted through walls in the vacuum cleaner, due to vibrations transmitted to the walls.
In JP-A-59-74396 also, a covering portion of the blower casing is disposed substantially perpendicularly to the shroud plate of the impeller in the vicinity of the inlet of the impeller. Consequently, when the axial direction of the incoming air flow changes to the radial direction in the inlet region of the impeller, the flow breaks away on the side of the shroud, causing a large loss. Since the aerodynamic condition of the flow is bad in the inlet section of the impeller, noise proportional to the product of the number of vanes and the rotational speed of the impeller tends to increase.
Additionally, since the length of overlap between the impeller inlet and the blower casing is determined by the thickness of the shroud plate of the impeller, the length of a sealing portion is limited to as small as 1 mm; thus, it is difficult to decrease the leakage flow rate between the shroud plate and the casing.
Furthermore, since the leak flow is substantially perpendicular to the main flow at the inlet of the impeller, break-away of the flow is promoted. Since the shroud plate is curved as viewed in the axial plane, the hub plate opposite the shroud plate and the shroud plate tend to be deformed during the fixing of the shroud plate and the vanes together, creating deviation of the impeller from the desired shape. Further, a gap tends to appear at the end surface of the vane inside the impeller, increasing leakage and loss.
In conventional electric blowers such as shown in JP-A-59-74396, the configurations of the diffuser vane, return guide vane, etc. of the centrifugal impeller are analogous to those of a large-size blower or compressor, but such components are limited in size and shape in the case of an electric blower used in the vacuum cleaner. In general in centrifugal blowers or compressors, the angle formed between the flow coming out of the impeller and the circumferential direction is of the order of 10 to 30°, and the inlet angle of the diffuser vane is designed correspondingly. However, the specific speed of the electric blower for use in the vacuum cleaner is low (a small flow rate is provided in spite of a high pressure with respect to a relative rotational speed) and generally, the outlet width of the impeller is designed to be small; therefore, since the friction loss within the impeller becomes large as the outlet width of the impeller is decreased, the width and outlet angle of the vanes are made comparatively large. Accordingly, in the electric blower for use in a household vacuum cleaner, the outlet absolute flow angle of the impeller is designed to be about 6` , and the inlet angle of the diffuser is set to as large as 5 in practice.
The object of the present invention is at least partly to avoid the disadvantages described above, and to improve the air flow efficiency through the blower of a vacuum cleaner.
The present invention is set out in claim 1, and the impeller of the invention in another aspect is set out in claim 2.
Preferably the shroud plate of the impeller is frusto-conical in shape at its region adjacent the impeller vanes. Preferably the extremity of the flange of the shroud plate is at an angle of not more than 30 to the axis, as seen in axial cross-section. Best results are obtained when the ratio of (a) the radius of curvature of the shroud plate, at its region of curvature into said flange, to (b) the vane inlet width in the axial direction, is in the range 0.5 to 1.0.
Embodiments of the invention will now be described by way of non-limitative example with reference to the accompanying drawings, in which:-

Fig. 1 is a side view, partly in cross section, of an electric blower including motor and blower, embodying the present invention;
Fig. 2 is an axial sectional view of part of the blower of Fig. 1;
Figs. 3 and 4 are diagrams illustrating respectively the air flows in the blower of JP-A-59-743986 and the blower of Fig. 2;
Fig. 5 is an axial sectional view showing another embodiment of the blower according to the present invention;
Fig. 6 is an axial view of the impeller and diffuser of the electric blower shown in Fig. 1; and
Fig. 7 is an enlargement of the circled part of Fig. 6 showing the diffuser vanes;
Fig. 8 is a graph showing the characteristic of electric blowers when the inlet angle of the diffuser is varied;
Fig. 9 is a graph showing the characteristic of electric blowers when the ratio of diffuser vane throat width to a diffuser inner diameter is varied;
Fig. 10 is a graph showing the characteristic of electric blowers when the ratio of the total area of the diffuser vane throats to the diffuser inlet area is varied;
Fig. 11 is an axial view showing diffuser vanes of yet another embodiment of the present invention; and
Fig. 12 is a graph showing the aerodynamic characteristic of the embodiment of Fig. 11.

Embodiments of impellers and vacuum cleaner blowers of the invention will now be described. They may be fitted in conventional vacuum cleaners. Examples of vacuum cleaners in which they may be mounted are shown in European Patent Applications 91303152.2 and 91303496.3.
The electric vacuum cleaner blower shown in Fig. 1 and 2 is composed of a blower portion 80 and a motor portion 81. Disposed inside a housing 81 a of the motor portion 81 are a rotor 83 secured to a rotating shaft 82 and a stator 85 including coils 84a and 84b. The housing 81 a has a bearing-retaining portion 81 b formed at the centre of its end wall, and a bearing 86a for rotatably supporting one end of the rotating shaft 82 is disposed in the bearing-retaining portion 81b. The housing 81 a also has exhaust ports 81 c in its peripheral surface. The housing 81 a has an end bracket 87 at the opposite end, and this end bracket 87 connects the blower portion 80 and the motor 81 together.
The end bracket 87 has a bearing retaining portion 87a at its centre and a flat portion 87b around its circumference. The flat portion 87b is formed with suction ports 88 through which the air from the blower 80 is sent into the motor 81 to cool it. Disposed in the bearing-retaining portion 87a is a bearing 86b for rotatably supporting the other end of the rotating shaft 82. The end bracket 87 carries a diffuser 89, and on the upstream side of the diffuser, a centrifugal impeller 90 is secured to the rotating shaft 82 by means of a nut 91. The centrifugal impeller 90 and the diffuser 89 are covered by a blower casing 92 pressure-fitted to the circumference of the end bracket 87. The blower casing 92 has a suction port 93 formed in its central portion to provide an inlet to the central inlet region of the impeller.
The diffuser 89 is composed of a plurality of diffuser vanes 94 arranged radially outside the circumference of the centrifugal impeller 90. A plurality of return guide vanes 95 are arranged on the back of a wall 89a lying adjacent the impeller 90 and supporting the diffuser vanes 94. The wall 89a has a rounded outer peripheral edge to smooth the air flow from the diffuser vanes 94 to the return guide vanes 95, and in conjunction with the wall 89a and the end bracket 87, the return guide vanes 95 define a return guide passage through which the air flow is guided to the suction ports 88.
The general operation of the electric blower in the embodiment will now be described. When the motor 81 is energized so that the impeller 90 is rotated, air flows as indicated by the arrows in the drawing, through the suction port 93 and into the impeller 90. After discharge from the impeller 90, the air passes between the diffuser vanes 94, and after passing through the return guide passage, goes through the suction ports 88 into the housing 81a. The air flow introduced into the housing 81 a cools the rotor 83, passes through an air passage defined by the stator 85 and the inner surface of the housing 81 a, cools the coils 84a and 84b, and goes through the exhaust ports 81 c formed in the periphery of the housing 81 a to the outside.
Fig. 2 shows the configuration of the centrifugal impeller 90 and the diffuser region in more detail. The impeller 90 is composed of a plurality of vanes 96, a shroud plate 97 and hub plate 98. Each vane 96 has on each edge three protrusions which are fitted in holes formed in the shroud plate 97 and the hub plate 98 and then caulked or upset, so that these components are rigidly and tightly secured together at these connection points. As Fig. 6 shows, the vanes 96 are curved as they extend outwardly, but for convenience this is not indicated in Fig. 2.
The outer diameter portion of the shroud plate 97 is frusto-conical, i.e. straight as seen in the axial plane, radially outwardly of the innermost point of connection 99 to the vanes 96. Inwardly of the point 99, the shroud plate 97 is shaped as to define a rounded portion 97a ending in an upwardly turned flange 97b whose end portion is at about 20 to the impeller axis. The radius of curvature of the rounded portion 87a is 0.7 times the vane inlet width. The blower casing 92 is shaped to provide an inwardly bent flange 92a, and a leakage gap 100 is left between the flange 92a and the flange 97b of the impeller 90. As seen in Fig. 2, the flanges 92a and 97b overlap axially (see also Figs. 4 and 5), with the flange 92a radially inside.
By virtue of the pressure difference between the inlet and outlet of the impeller 90, a part of the air flow leaving the impeller 90 passes between the impeller 90 and the blower casing 92 and flows again into the impeller inlet zone. Therefore, the impeller 90 acts on this leak flow too, and if the flow rate of this leakage is large, the performance of the electric blower is considerably degraded; however, since in the illustrated embodiment the length of the gap 100 is larger than the thickness of the shroud plate 97, the friction loss of the leak flow can be increased, thereby decreasing the leak flow rate.
Since the direction of the leak flow is parallel to the axis and in this region the main flow is also parallel to the axis, the leak flow does not have bad influence on the main flow, and since the radius of curvature of the rounded portion 97a of the shroud plate is large, the main flow breaks away from the shroud plate 97 at most only slightly.
From simulation experiments performed on the blower shown in Fig. 3 and blowers similar to the embodiment of Figs. 1 and 2 and using water flows chosen to be identical in terms of the Reynolds number, it has been found that in the case of the known structure as shown in Fig. 3, the flow breaks away considerably on the side of the shroud plate of the impeller, whereas in the case of the impeller of the present invention in which the ratio of the radius of the rounded portion 97a to the impeller vane inlet width (in the axial direction) was 0.5, the flow lies well along the shroud plate as illustrated by Fig. 4. Consequently, it is possible to suppress noise arising at a frequency corresponding to the product of the rotational speed and the number of vanes. Moreover, the energy loss of the impeller of Figs. 1 and 2 is low.
The shroud plate 97 is straight from its outer circumference to the innermost point of connection 99 as viewed in the axial plane, and there is only a small difference in height of the vane 96 between its inlet and outlet. Therefore, although the vane 96 is curved in the circumferential direction in a conventional manner, the force applied in caulking each protrusion of the vane 96 does not vary from one caulking point to another. Accordingly, the deformation of the shroud plate 97 and of the hub plate 98 is minimized even under the force applied to each caulking point. Consequently, hardly any gaps arise between the vanes 96, shroud plate 97 and hub plate 98, and leak flow between the pressure side and suction pressure side of the vane 96 is suppressed. Further, since any face deflection of the shroud plate 97 and of the hub plate 98 is small, unbalance hardly arises; thus, noise based on a frequency corresponding to the rotational speed decreases.
Another embodiment of the present invention will be described with reference to Fig. 5 showing a blower in partial sectional view. The shroud plate 97 is straight in its outer diameter portion, as viewed in the axial plane, and has a rounded portion 97a inwardly from the innermost point of connection 99, as in Fig. 2. The shroud plate 97 in this case is provided with a cylindrical portion 97b extending axially from the end of the rounded portion 97a. Furthermore, the blower casing 101 has an inwardly bent flange 101 a at its inner diameter region, so that the gap 100 is left between the flange 101 a and the cylindrical portion 97b of the impeller 90. Since the length of the gap 100 is much larger than the thickness of the shroud plate 97, the friction loss of the leak flow can be made very large, the leak flow can be reduced remarkably, and the efficiency of the electric blower can be improved.
Figs. 6 and 7 show the diffuser 89 of Figs. 1 and 2 with its vanes 94, as viewed from the suction port 93 of the electric blower. In this embodiment there are seventeen diffuser vanes 94 and eight return guide vanes 95. The inlet angle Q₃ of the diffuser vane 94 as shown in Fig. 7 is 3°. The inlet angle β₃is the angle between the inner face of the vane at its leading edge and the tangential line at this point. The throat width ws is 2.2 mm, and its ratio to the inner diameter of the diffuser is 0.02. The radius of the rounded leading edge of the vane 94 is 0.5 mm. The air flow coming out of the impeller 90 is decelerated in a semi-vaneless space of the vaned diffuser 89 and further decelerated in each passage defined between two vanes 94. In the foregoing embodiment, the air discharge velocity of the blower can be made large, particularly about 0.8 times the peripheral speed of the impeller. Accordingly, the size of the impeller can be reduced. Fig. 8 shows the relative efficiency of an electric blower including the impeller according to the embodiment of Figs. 5 to 7, relative to a varying diffuser inlet angle j83. The efficiency under the condition that the diffuser inlet angle β₃ is 5° was taken as a reference. Where the diffuser inlet angle β₃ is smaller than 2°, the length of the semi-vaneless space is longer, the friction loss increases, and the efficiency decreases. Where the diffuser inlet angle β₃ is larger than 3` , it tends to come out of the flow angle from the impeller; thus, the performance degrades. As will be appreciated, where the diffuser inlet angle β₃ is within the range of 2 to 3` , the efficiency is about 2% greater than that in the prior art based on an angle of 5` , and even where the diffuser inlet angle is within the range of 1 to 2° or within the range of 3 to 4°, the efficiency is 1% greater.
Fig. 9 shows the efficiency of the same electric blower relative to a varying throat width ws. Where the ratio of the throat width ws to the diffuser inner diameter is smaller than 0.017, the deceleration is insufficient in the semi-open portion but increases in the passages defined between two vanes 94; thus, the flow breaks away in such a passage, thereby decreasing the efficiency. Where the ratio of the throat width ws to the diffuser inner diameter is larger than 0.025, the deceleration becomes too significant in the semi-open portion; thus, the flow deviates remarkably as it flows into each passage defined between two vanes, thereby decreasing the efficiency. In the embodiment, where the ratio of the throat width ws to the diffuser inner diameter is 0.02, the efficiency is high. In addition, since the flow angle of the air discharged from the impeller 90 is small and the air discharged from it travels a long distance until it enters the diffuser 89, the inlet diameter of the diffuser can be reduced as shown in Figs. 6 and 7, and the energy loss compared with a diffuser with no vanes can be reduced. Further, since the relative velocity at the outlet of the impeller can be decreased, noise can be reduced. Fig. 10 shows the relative efficiency of this electric blower obtained when varying the ratio
given by
where

Z_Vd = number of diffuser vanes,
b₃ = axial width of diffuser vanes,
ws = diffuser vane throat width,
D₃ = diffuser vane inlet diameter,
Q3 = diffuser vane inlet angle.

When this ratio is smaller than 1.75, since the number of the diffuser vanes increases, the throat width decreases, surging occurs at a low flow rate, and pressure loss increases at a large flow rate, tending to narrow the serviceable range. When this ratio is larger than 3.5, the number of vanes of the diffuser 89 decreases, tending to cause interference with the number of blades of the impeller, so that a peak sound is generated, and the noise level is increased. When this ratio is 2.1 as in the actual embodiment, the efficiency is high.

Fig. 11 shows the diffuser 89 in another embodiment of the present invention. Each passage of the diffuser is defined by the vane portions overlapped. The outer end of each vane 94 is rounded while the inner end is tapered, and by this tapering, the throat width ws can be kept within an optimum range. The air discharged from the impeller 90 flows along the vane 94 at about the set flow rate, but the air flow at a small flow rate breaks away in the semi-vaneless space, as indicated by the arrows in the drawing, on the suction pressure side of the diffuser vane; therefore, the direction of the air stream is forcibly changed by the taper portion on the pressure side of the adjacent vane, thereby alleviating the broken air stream, so that the zone of surge generation is shifted more to the side of a small flow rate.
Fig. 12 shows the result of experiments on the relationship between the flow rate and pressure (static pressure) of the electric blower, in which the solid curve corresponds to the case including a diffuser based on the embodiment of Fig. 11. The broken curve corresponds to the case for comparison including a diffuser whose inlet angle is 5°. Although the comparison case shows the surge generation zone in the vicinity of a design point, the embodiment with a diffuser inlet angle of 3 can shift the surge generation zone to a small flow rate range.

Claims

1. A vacuum cleaner blower assembly having a blower motor (81), a vaned centrifugal impeller (90) driven by the blower motor (81) and an air diffuser (89) radially beyond the periphery of the impeller, characterised in that, to improve air flow efficiency at the impeller inlet and outlet, the impeller (90) has a shroud plate (97) which, as seen in axial section, curves away from the vane inlet region towards its inner edge (97b) and/or the air diffuser (89) has vanes (94) with an inlet angle in the range 1 to 4°.

2. An impeller (90) for a vacuum cleaner having a central air inlet region around its axis of rotation, a plurality of vanes (96) extending outwardly from said inlet region and a shroud plate (97) covering said vanes (96) at one axial side thereof and attached to said vanes, characterised in that said shroud plate (97) extends substantially straight, as seen in axial cross-section, from an innermost point of connection (99) to each said vane to the outer peripheral ends of the vanes, and radially inwardly from said innermost point of connection (99), said shroud plate (97) is curved as seen in axial section, to provide a flange (97b) surrounding said inlet region and directed away from said vanes.

3. An impeller according to claim 2 wherein said shroud plate (97) is frusto-conical in shape at its region adjacent said vanes (96).

4. An impeller according to claim 2 or claim 3 wherein the extremity of said flange (97b) of said shroud plate is at an angle of not more than 30 to the axis, as seen in axial cross-section.

5. An impeller according to any one of claims 2 to 4 wherein the ratio of (a) the radius of curvature of the shroud plate (97), at its region (97a) of curvature into said flange (97b), to (b) the vane inlet width in the axial direction, is in the range 0.5 to 1.0.

6. A vacuum cleaner having an impeller (90) according to any one of claims 2 to 5, a blower motor (81) coupled to said impeller (90) and a casing (92) covering said impeller, the casing (92) having an air inlet passage (93) for flow of air to said inlet region of said impeller, said air inlet passage being provided by an inward annular wall (92a) of said casing which, as seen in axial cross-section, overlaps said flange (97b) of said shroud plate at the radially inner side thereof.

7. A vacuum cleaner having an impeller (90), a blower motor (81) coupled to the impeller (90) and a diffuser (89) having a plurality of diffuser vanes (94) arranged radially outside the impeller, characterised in that the inlet angle of said diffuser vanes (94) is in the range 1 to 4°.

8. A vacuum cleaner according to claim 7 wherein the ratio of the throat width (ws) between adjacent pairs of said diffuser vanes (94) to the inlet diameter of said diffuser vanes (94) is in the range 0.017 to 0.025.

9. A vacuum cleaner according to claim 7 or claim 8 having a return guide passage for guiding air from said diffuser vanes to said blower motor for cooling the motor.

10. A vacuum cleaner according to claim 9 wherein said return guide passage extends radially inwardly and is separated from the region of said impeller (90) and said diffuser vanes (94) by a wall (89a) having a rounded outer peripheral edge.

11. A vacuum cleaner according to any one of claims 7 to 10 wherein the ratio

given by

is in the range 1.75 to 3.5, where

Zy_d = number of diffuser vanes,

b₃ = axial width of diffuser vanes,

ws = diffuser vane throat width,

D₃ = diffuser vane inlet diameter,

Q3 = diffuser vane inlet angle.