JPH0377397B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an electric blower used in a vacuum cleaner or the like.

Conventional technology Conventional electric blowers of this type are, for example,
This is shown in Publication No.-49168.

That is, as shown in FIG. 8, an impeller 2 and an air guide 3 are provided in a casing 1, and the impeller 2 is rotated at high speed by a motor 4 to obtain air volume and vacuum pressure.

Problems to be Solved by the Invention In a structure in which the air guide 3 is provided on the outer periphery of the impeller 2 like the electric blower described above, when the airflow discharged from the impeller 2 flows into the air guide 3, the air guide inlet Noise thought to be caused by collisions was a problem. This is the number of blades Z of impeller 2 and the rotation speed N of impeller 2.
(rpm) and is commonly called the NZ sound.

The present invention solves these problems,
The return passage of the air guide itself has a noise-muffling effect.

Means for Solving the Problems The technical means of the present invention for solving the above-mentioned problems includes a centrifugal impeller driven by a motor, a plurality of differential users through which the airflow sent from the impeller flows, and a motor. The air guide includes a plurality of return passages for guiding the airflow, and a casing that encloses the impeller and the air guide, and the return passage is divided into an inner guide wall and an outer guide wall, and the inner and outer guide walls are divided into an inner guide wall and an outer guide wall. A space is formed in between, and an opening is provided at the inner end of the space.

Effect This technical means works as follows.

In other words, the space formed by the inner guide wall and the outer guide wall constitutes a muffler and serves as a side branch in the acoustic circuit, creating a structure that prevents the noise generated at the air guide entrance from being emitted to the outside. There is.

As a result, an electric blower with low noise level is obtained.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

1 to 4, a centrifugal impeller 11 having a plurality of blades is attached to a shaft 13 of a motor 12, and an air guide 14 is disposed on the blowing side of the impeller 11. be. These impellers 11 and air guides 14 have air intake ports 15 on the top wall.
The lower peripheral wall of the motor frame 16 is surrounded by a casing 17 that is airtightly attached to the motor frame 16.

The air guide 14 has an impeller 1 on its upper surface.
A plurality of differential users 18 receive the airflow sent out from the airflow source 1 and gradually expand the passage area toward the downstream side.
communicates smoothly with the terminal end of the differential user 18 on the lower surface, and the motor intake hole 1 of the motor frame 16.
Each of the return passages 20 has a plurality of return passages 20 that guide airflow to the air passages 9 . In this embodiment, the side of the differential user 18 is closed with a part of the casing 17 and is partitioned from the outside.
Diff user 18 can be formed independently of 7.

Curved guide wall 2 that partitions each return passage 20
1 is divided into an inner guide wall 22 and an outer guide wall 23, and a space 25 with an opening 24 set at the inner end is formed between them. In this embodiment, the outer diameter of the air guide 14 is φ125 mm.
The number of differential users 18 and return passages 20 is 16 each.
In addition, the length of the space 25 is set to 14 mm.

In the above configuration, the airflow sent out from the impeller 11 is decelerated in the process of flowing through the differential user 18 of the air guide 14, and its kinetic energy is
That is, dynamic pressure is replaced with static pressure.
The airflow flowing through the differential user 18 reaches the return passage 20, and then flows through the motor 12 from the motor intake port 19, performs a cooling effect, and is discharged from a predetermined portion.

Next, the function of the space 25 of the guide wall 21 in the air guide 14 will be explained. First, if we consider section A in Figure 1, it can be replaced with a simplified diagrammatic system as shown in Figure 4. This is known as a muffler or side branch in an acoustic circuit. The space 25 of this side branch corresponds to the space 25 of the air guide 14 and has a noise-muffling effect. Here, if the frequency to be muted is f _N (Hz), the theoretical length l (mm) of the same space section 25 is l = (2N-1)・C/(4f _N ) [N (constant) : 1, 2, 3,...C: Speed of sound (mm/
sec)].

As mentioned above, a particularly problematic type of noise from electric blowers is called NZ noise. In this study, the NZ sound occurs at around 5.3KHz, and is extremely harsh to the ears. In order to reduce this NZ sound, an experiment was conducted using a guide wall 21 having the configuration of this embodiment, and as a result, the NZ sound could be reduced. The frequency analysis tables are shown in FIGS. 5 and 6. From the diagram
It can be seen that the NZ sound (around 5.3KHz) has decreased, and the overall noise has also become lower. Using the above formula, l
became 17mm. After that, the actual length L=
I got 14mm. This is considered to be an effect of the curvature of the space 25. Therefore, after further consideration, L
I investigated the relationship between this and the NZ sound. The results are shown in FIG. From the figure, the nz sound is ± with respect to l obtained from the formula.
It was found to be effective in 30% of cases. In this way, this embodiment can be applied to any particularly problematic frequency.
This makes it possible to reduce the NZ sound, and this has a great practical effect. If this ±30% is expressed as the actual length L, then L=(0.7 to 1.3)l.

In this embodiment, the effect obtained is obtained by providing one space composed of an inner guide wall 22 and an outer guide wall 23, but it is also possible to provide another guide wall between the inner guide wall and the outer guide wall. plus 2 to 1 guide wall
Similar effects can be obtained even if two spaces are provided. Therefore, there is no particular limit to the number of guide walls.

Effects of the Invention As described above, according to the present invention, it is possible to reliably reduce noise at a frequency that is a particular problem in electric blowers, and the only structure thereof is to provide a space in the guide wall that forms the return passage. In general, it does not affect fan efficiency, does not require the use of other components in production, and can be implemented without affecting cost.

[Brief explanation of drawings]

FIG. 1 is a back view of an air guide showing an embodiment of the present invention, FIG. 2 is a partially cutaway sectional view of an electric blower,
FIG. 3 is a top view of the air guide, FIG. 4 is an explanatory diagram of its operation, FIG. 5 is a frequency analysis diagram showing the effects of the present invention, and FIG. 6 is a conventional analysis diagram. FIG. 7 is a characteristic diagram of the relationship between the length of the space and the NZ sound, and FIG. 8 is a partial perspective view of a conventional electric blower. 11... impeller, 12... motor, 14...
Air guide, 17...Casing, 18...Diff user, 20...Return passage, 21...Guide wall, 22...Inner guide wall, 23...Outer guide wall,
24...opening, 25...space.

Claims (1)

[Claims] 1. A centrifugal impeller driven by a motor, a plurality of diff users through which the airflow sent out from the impeller flows, and an air guide having a plurality of return passages that guide the airflow to the motor; an impeller and a casing containing an air guide, the return passage is divided into an inner guide wall and an outer guide wall, and a space is formed between the inner and outer guide walls, and an inner end of the space is formed. Electric blower with an opening. 2 When the length from the opening of the space is L (mm) and the frequency you want to mute is f _N (Hz), L = (0.7 to 1.3)・(2N-1)・C/4f _N [N: 1 , 2, 3..., C: sound velocity (mm/sec)] The electric blower according to claim 1, wherein the electric blower is set to the following.