JPS6114360B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a centrifugal blower such as a vacuum cleaner, and particularly relates to a differential user, and provides a differential user guide vane with high aerodynamic efficiency and low noise.

An example of a conventional electric blower is shown in FIGS. 1 and 2.

In these figures, 1 is an impeller, 2 is a blade of the impeller, and these are rotationally driven by an electric motor 8 via a rotating shaft 7. The impeller 1 is covered by a casing 3, which is connected to a bracket 4, in which guide vanes 5 are installed. Note that a disc 6 is attached behind the impeller 2 and is connected to the guide vane 5.

In Fig. 1, the flow sucked in as the impeller 1 rotates is approximately from the suction port A to A→B→C→
It flows along the path D ₁ →D ₂ →E, passes through the electric motor 8, and is discharged outside the machine. In such a flow path, it is the portion from point B to point E that has a great influence on improving the efficiency of the blower and reducing noise. Between the impeller exit point B and the guide vane entrance point _D , the flow must change its direction by 180 degrees, and in conventional electric blowers, there are no guide vanes in this space, making a sudden change in direction. Therefore, large flow turbulence occurs, high pressure loss occurs, and large noise is generated.

If we look at the average streamline at _{the two} points from point B to D from a different angle, it is as shown in Figure 2, and the flow at point B at the impeller outlet has a velocity component directed outward in the radial direction as well as in the rotational direction of the impeller. It also has a large circumferential velocity component in the same direction as . The flow that has progressed from point C to point _D2 , the entrance of guide vane 5, has changed its radial velocity component inward, while keeping most of its circumferential component, relative to the outer circumferential circle of guide vane 5. and flows into the blade passage at a shallow angle. The role of the guide vane 5 is
D The problem is how to convert the dynamic pressure of the circumferential velocity component at _two points into static pressure without waste. Ideally, it is desirable that the circumferential velocity component be zero at the exit point E of the guide vane. However, in reality, it is normally impossible to change the angle of about 60° to 80° in the air path between the guide vane 5 from point _D2 to point E, and the pressure loss in the air path in this part is If cancer development is to be prevented, a fairly large circumferential velocity component will remain at point E. or,
If we try to forcefully change direction by a large angle so that the circumferential velocity component becomes 0 at point E,
Large pressure loss and large noise generation due to flow turbulence always occur.

In order to consider the flow from point B to point E in more detail, Fig. 3a shows the velocity triangle of the flow at point B at the outlet of impeller 1, and Fig. 3b shows the velocity triangle of the flow at point B at the outlet of impeller 1.
The velocity triangles at the entrance/exit point D ₂ and point E are shown, respectively. In FIG. 3a, the relative velocity at the outlet of the impeller 1 is W _B , which consists of a circumferential component Wθ _B and a radial component C _rB . The absolute velocity at point B is the composite velocity of W _B and the circumferential velocity u=ΩR ₂ at the outer radius R ₂ of the impeller 1 (Ω is the rotational angular velocity of the impeller), and becomes C _B .
C _B consists of a radial component C _rB and a circumferential component Wθ _B , and the angle αB between C _B and the circumferential tangential direction is generally a small angle. It is considered that the flow conserves most of its angular momentum between point B and the entrance point _D of the guide vane 5, and the circumferential component Wθ _D2 of the absolute velocity C _D2 shown by the solid line in FIG. If the outer radius of the blades 5 is equal to the outer radius of the impeller, then Cθ _B ≈Cθ _D2 . In FIG. 3b, a velocity triangle at the exit point E of the guide vane 5 is shown by a chain line. The absolute velocity C _E at point E consists of a circumferential component Cθ _E and a radial component C _rE .

It is desirable that the dynamic pressure of the velocity component Cθ _B at the exit of the impeller 1 is completely and effectively converted into static pressure up to the exit point E of the guide vane 5. However, as shown in Figure 3b, the angle αD ₂ that C _D2 makes with the circumferential tangential direction is generally small, and in order to set Cθ _E to 0, αE must be 90°, and Δa = α
E−αD ₂ becomes extremely large. The length of the passage between the guide vanes 5 is limited, and in order to achieve αE=90° within this length, the guide vanes 5 must be
There is no choice but to increase the number of On the other hand, increasing the number of guide vanes 5 causes an increase in pressure loss due to flow friction, and also increases the manufacturing cost of the guide vanes 5. Therefore, in actual electric blowers, Δa is not set to a sufficient value, and E
The velocity of the flow at the point leaves the circumferential component Cθ _E at a fairly large value, and the dynamic pressure of Cθ _E becomes almost ineffective.

The noise generated in the passage of the guide vane 5 is considered to be proportional to the 5th to 6th power of the inlet velocity C _D2 , and if C _D2 can be reduced to, for example, 2/3, the acoustic energy can be reduced by 8 to 11 dB. can get.

An embodiment of the present invention, which was made to solve the problems of conventional electric blowers as described above, is shown in Figs. 4 and 5.
As shown in the figure.

FIG. 4 is a longitudinal cross-sectional view and an external view, and shows that in the space surrounded by the casing 3 and the bracket 4 between the outlet point B of the impeller 1 and the inlet point D of the guide vane ₅ ,
Axial flow guide vanes 9 were provided. Figure 4 shows Y in Figure 3.
It is a developed view of a cylindrical cross section along -Y, and here,
As an example of the axial flow guide vane 9, a case where the curved surface thereof is formed as a cylindrical surface is shown, but the same effect can be obtained with other curved surfaces. Such an axial flow guide vane 9
is among the streamlines in which the flow changes direction by approximately 180° in the longitudinal section (Fig. ₄ ) from the outlet point B of the impeller 1 to the inlet D point of the guide vane 5.
The part along the cylindrical surface that is almost concentric with the rotation axis (point C →
The purpose is to rectify ₁ point D). Considering that the flow at the outlet point B of the impeller 1 has a circumferential component and a radial component at the same time, placing such an axial guide vane just outside the outlet of the impeller 1 will actually reduce the flow. This could lead to chaos. For the above reasons, it is desirable that the front end of the axial flow guide vane 9 be located behind the surface of the back plate of the impeller 1, and in this case, its inner radius R ₃ is considerably larger than the outer radius R ₂ of the impeller. However, it is necessary to make (R ₃ − R ₂ ) a non-small value.

In addition, the flow at the outlet _D1 of the axial flow guide vane 9 changes direction by 90° in the longitudinal section (Fig. 4),
Considering that the flow flows inward into the guide vane 5 at _two points D, there may be a gap between the rear end of the axial guide vane 9 and the bracket 4. However, the effect of this gap is not necessarily exhibited in all cases, and there may be cases where it is better to eliminate the gap.

FIG. 6 is an explanatory diagram showing the principle of the present invention, a
shows the velocity triangle of the flow at _one point D at the exit of the axial flow guide vane 9, b at _{the second} point D at the inlet of the guide vane 5, and c at the point E at the exit of the guide vane 5. In these figures, the solid line shows the case without the axial flow guide vane 5, and the dotted line shows the case with it. Also, in the letter symbols, those with '' indicate the velocity components when the axial flow guide vanes 9 are present.

In FIG. 6a, since the axial flow guide vanes 9 are provided, if the flow direction is changed even slightly to the axial direction in the passage between the guide vanes, the circumferential component at point _D1 changes from Cθ _D1 to Cθ _D1 ′ can be reduced to a large extent.

As a result, as is clear in FIG. 6b, the absolute velocity at _{the two} entrance points D of the guide vane 5 is C _D2
can be greatly reduced from C D2 ' to C _D2 '. As mentioned above, D ₂
If the absolute velocity at the point is reduced, it can be expected that the noise generation at the guide vanes 5 can be significantly reduced. Also, at point _D2 , Cθ _D1 ′=Cθ _D2 ′, and since the circumferential velocity has already been greatly reduced from Cθ _D2 to Cθ _D2 ′, as is clear in Fig. 6c,
Even if (αE'-αD ₂ ') is approximately the same as (αE-αD ₂ ), only a small circumferential velocity remains at the exit point E of the guide vane 5 as Cθ _E →Cθ _E '. That is, the circumferential velocity component at the outlet of the impeller 1 can be effectively converted into static pressure.

It is desirable for such an axial flow guide vane to have a great effect with a simple shape and manufacturing method, and an example of its structure will be explained with reference to FIG. 7. flow guide vane 9
It is molded in one piece from a material such as ABS, and is fixed to the bracket 4 with screws, etc., and can be easily manufactured.

As explained above, the present invention provides an electric blower having a return flow path, in which the inner diameter of the axial flow guide vane is configured to be larger than the outer diameter of the impeller, and the front end of the axial flow guide vane is positioned behind the rear end of the impeller outlet. Since the guide vanes are located in the same position, it is possible to greatly reduce noise generation in the guide vanes forming the return passage.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a part of a conventional electric blower, Figure 2 is a Z-Z cross-sectional view of Figure 1, and Figure 3 is a velocity diagram of the flow at the impeller outlet and the guide vane outlet. , FIG. 4 is a longitudinal sectional view showing one embodiment of the present invention, FIG. 5 is a YY sectional view of FIG. 4, and FIGS.
FIG. 7 is a velocity diagram of the flow at the inlet and outlet of the guide vane, and is a perspective view showing an example of the structure of the axial flow guide vane according to the present invention. In the figures, the same reference numerals indicate the same or equivalent parts. 1... impeller, 2... impeller blades,
3... Casing, 4... Bracket, 5... Guide vane, 6... Disk, 7... Rotating shaft, 8... Electric motor, 9... Axial flow guide vane.

Claims (1)

[Claims] 1. A disk is disposed in the casing surrounding the impeller to form a return flow path, and a guide vane is located in the return flow path on the front disk, and a guide vane is provided on the inlet side of the return flow path. An electric blower comprising axial flow guide vanes each having a curved front end positioned rearward of the back plate of the impeller and an inner radius larger than the outer radius of the impeller. .