JPS61157794A - Motor driven blower - Google Patents

Abstract

PURPOSE:To provide muffler effect to the return path irself by separating the return path of air guide into inner and outer guide walls to form a space section between them while providing an open section at the inner end of the space section. CONSTITUTION:An air-guide 14 has a return path 20 where the curved guide wall 21 for partitioning respective return path 20 is separated into inner and outer guide walls 22, 23 to form a space section 25 where an open section 24 is set at the inner end between them. The space section 25 will serve as a muffler in acoustic circuit. Consequently, the muffler effect can be provided to the return path itself.

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.

2. Description of the Related Art Conventional electric blowers of this type are known, for example, from Japanese Patent Publication No. 62-49.
This is shown in Publication No. 168.

That is, inside the casing 1 as shown in FIG.

An impeller 2 and an air guide 3 are provided, and the impeller 2t 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, there is a problem at the air guide inlet. The problem was the noise that was thought to be caused by the collision. This occurs as a product of the number of blades Z of the impeller 2 and the rotation speed N (rpm) of the impeller 2, and is commonly called NZ sound.

The present invention is intended to solve these problems.

The return passage of the air guide itself has a noise-muffling effect.

Means to solve problems The technical means of the present invention to solve the above problems is as follows.

Inside the guide wall that forms the air guide return passage.

It is formed of an outer guide wall, and a space having an opening at the inner end is set between these walls.

action This technical means works as follows.

In other words, the space formed by the inner guide and outer guide wall constitutes a muffler, and serves as a side branch in the acoustic circuit.The structure is such that the noise generated at the air guide entrance is not emitted to the outside. There is.

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

Example Embodiments of the present invention will be described below 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.
Also, an air guide 14 is provided on the blowing side of the impeller 11. The impeller 11 and the air guide 14 have an intake port 15 on the top wall, and are surrounded by a casing 17 which is airtightly attached to the motor frame 16 at the lower part of its peripheral wall.

The air guide 14 receives the air flow sent out from the impeller 11 on its upper surface, and has a plurality of diffusers 18 whose path area is gradually expanded by 1 m toward the downstream side, and smoothly communicates with the terminal ends of the diffusers 18 on its lower surface. The airflow is guided to the motor intake hole 19 of the motor frame 16 (each having a plurality of return passages 20). In this embodiment, the side of the diffuser 18 is closed with a part of the casing 17 to separate it from the outside, but if it is a thank you note, the diffuser 18 can be formed independently of the casing 17.

The curved guide wall 21 that partitions each return passage 20 is divided into an inner guide wall 22 and an outer guide wall 23, and a space 26 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 set to φ125ff1m, the number of diffusers 18 and return passages 20 is set to 16 each, and the length of the space 25 is set to 14. In the above configuration, the airflow sent out from the impeller 11 is decelerated in the process of flowing through the diffuser 18 of the air guide 14, and its kinetic energy is reduced.

That is, dynamic pressure is replaced with static pressure.

The airflow flowing through the diffuser 18 then returns to the return passage 2.
0 and then flows through the motor 12 from the motor intake port 19, performs a cooling action, and is discharged from a predetermined portion.

Next, the space 25 of the guide wall 23 in the air guide 14
The effect of this will be explained. First, if we consider the AM shown in Figure 1, we can replace it with a simplified diagrammatic system as shown in Figure 4. This is known as a muffler or side branch in an acoustic circuit. Therefore, this space 25 has the role of muffling the sound. In particular, if the frequency to be silenced is fN, then the theoretical length of the space 25 is β
is given by β=(2N-1)・C/a・fu (N: 1, 2, 3... C: speed of sound).

As mentioned above, a particularly problematic type of noise from electric blowers is called NZ sound. The NZ sound is 5.3 in this study.
KI (occurs in the vicinity of z) and is very harsh to the ears.As a result of the study with the guide wall 21 of this embodiment installed, it was possible to reduce the nz sound.The frequency analysis table is shown in Table 1. It is shown in Figures 5 and 6. From the figure, the nz sound (near 5.3KHz) has decreased.The overall noise has also decreased.When calculated using the above formula, 4 becomes 17#. The actual length L=:14wn was obtained. This is considered to be due to the effect of the curvature of the space portion 26. Therefore, further investigation was performed.

We investigated the relationship between L and nz sounds. The results are shown in FIG.

As shown in the figure, it was found that the L and nz sounds were effective within ±30% of β calculated from the formula. In this way, this embodiment makes it possible to reduce frequencies around any particularly problematic frequency, and this has a great practical effect. If this ±30 inches is expressed as the actual length L, then l, = (0.7 to 1.3)
It becomes 6.

Note that this embodiment has the effect obtained by providing a space, but the same effect can be obtained by adding another guide wall between the inner guide wall and the outer guide wall. Therefore, there is no particular limitation on the number of guide walls.

Effects of the Invention As described above, according to the present invention, it is possible to reliably reduce frequencies that are a particular problem in electric blowers.

In addition, the configuration requires only some modification to the guide wall that forms the return passage, and does not affect fan efficiency.

[Brief explanation of drawings]

FIG. 1 is a back view of an air guide showing an embodiment of the present invention;
Figure 2 is a partially cutaway sectional view of the electric blower. Fig. 3 is a top view of the air guide, Fig. 4 is an explanatory diagram of its operation, and Fig. 5 is a frequency analysis diagram showing the effects of the present invention. FIG. 6 is a conventional analysis diagram. FIG. 7 is a characteristic diagram showing the relationship between the length of the space and the NZ sound, and FIG. 8 is an exploded perspective view showing a conventional electric blower. 11... Inhaler, 12... Motor,
14... Air guide, 17... Casing, 18... Diffuser, 20...
・Return passage, 21... Guide wall. 22: Inner guide wall, 23: Outer guide wall, 24: Opening, 26: Space. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure t4 Air j Ite Figure 2 Figure 3 Figure 4 Figure 4 2r R! A-ku 已、1 澾3 2 み 寫Fig. 7

Claims (2)

[Claims] (1) A centrifugal impeller driven by a motor, a plurality of diffusers 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, these impellers, and the air guide. The return passage is divided into an inner guide wall and an outer guide wall, and the return passage is partitioned by a guide wall with a space formed between the inner and outer guide walls, An electric blower with an opening at the end. (2) When the length from the opening of the space is L and the frequency you want to mute is f_N, L = (0.7 to 1.3)・(2N-1)・C/4f_N
(N: 1, 2, 3..., C: sound speed) The electric blower according to claim 1, wherein the electric blower is set as follows.