JPS61182500A - Centrifugal multiblade blower - Google Patents

Abstract

PURPOSE:To reduce the absolute value of a noise with an nz-sound being as the center, by connecting a cavity part of predetermined volume, provided in a nose part of a casing, with an opening part of small size, provided in an external surface of the nose part brought into contact with a flow of air, through a pipe line having an opening section area. CONSTITUTION:A nose part 14 generates a turbulence being hit by air immediately after coming out from a multiblade impeller 11, and a blower, providing an opening part 15 of sectional area S in the depth directional center of an external surface of the nose part 14 opposed to the multiblade impeller 11 while a cavity part 16 of volume V in a position L from the opening part 15, connects the opening part 15 with the cavity part 16 through a pipe line 17 of sectional area S. In this way, the blower, reducing a sound level of frequency with an nz-sound being as the center while also a reverberating sound due to a space surrounded by the impeller 11 and a casing 13, enables also the absolute value of a noise to be reduced. Further the blower, in which a substantially limited position and shape of the multiblade impeller 11, air guider 12 and the casing 13 can be more freely designed because the nz-sound is decreased than usual, can obtain large contribution to the improvement of performance of efficiency or the like of the blower.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a centrifugal multi-blade blower that is widely used as a blower for air conditioners.

BACKGROUND OF THE INVENTION In recent years, blowers using multi-purpose impellers have been widely used as blowers for air conditioners, but as efficiency increases, the frequency of noise increases by the product n of the number of rotations n and the number of blades 2.
-z, which is generally called nz sound, is required to design a blower system under conditions where a high level of noise occurs. Various attempts have been made to suppress the nz sound without reducing it. Furthermore, as disclosed in Japanese Patent Application No. 125049/1982, a multi-blade impeller is manufactured in which the pitch angle between the blades of the impeller is arranged randomly without periodicity.

An example of a centrifugal multi-blade blower using the above-mentioned conventional multi-blade impeller will be described below with reference to the drawings.

Figures 6, 7, and 8 show the configuration of a conventional centrifugal multi-blade blower, the cross-section of a multi-blade impeller in which the pinch angle between the blades is randomly arranged without any periodicity, and the noise level. This shows the frequency characteristics of

In FIG. 6, 1 is a multi-blade impeller. Reference numeral 2 denotes an air guider, which forms an introduction path for air flowing into the multi-blade impeller 1. 3 is a casing that rectifies the air flowing out from the multi-blade impeller 1 and improves the blowing performance of the multi-blade impeller 1. Reference numeral 4 denotes a nose portion, which is the end of the casing 3 and is closest to the multi-blade impeller 1.

In FIG. 7, reference numeral 5 denotes blades constituting the multi-blade impeller 1, and the pitch angle θ of these blades 5 is not uniform but randomly arranged. Here, the pitch is the angle between the blades 5 in the circumferential direction.

Regarding the centrifugal multi-blade blower configured as above,
The operation will be explained below.

When the multi-blade impeller 1 equipped with the air guider 2 and the casing 3 is rotated, a peculiar sound (generally called nz sound), which is characterized by the product n・2 of the number of rotations n and the number of blades 2, is generated at a high rate. Instead, like the frequency characteristic factor in Figure 8,
The nz sound is divided into a plurality of types of frequency components and the wave height is lowered, so that the perceptible nz sound can be reduced.

Problems to be Solved by the Invention However, with the above configuration, the nz sound with a single frequency is dispersed into multiple frequencies by randomly arranging the pinch angle of the blade, which makes it difficult to hear. n
Although it is possible to reduce the z sound, it becomes a nz sound in which frequencies that are very close to each other change continuously, so it does not sound like a continuous sound with a constant frequency, but as a continuous sound with a periodically changing frequency. Although it is not a loud sound, it is noticeable as an abnormal sound. In particular, in a centrifugal multi-blade blower that uses a spiral casing to improve its performance, the space surrounded by the multi-blade impeller and the casing causes reverberations that result in extremely poor acoustics.

In view of the above-mentioned problems, it is an object of the present invention to reduce the NZ sound and to simultaneously reduce noises other than the NZ sound, and to avoid creating new noise with changing frequencies.

Means for Solving the Problems In order to solve the above-mentioned problems, the centrifugal multi-blade blower of the present invention has a cavity with a predetermined volume in the nose of the casing, and a cavity in the nose that is in contact with the air flow. It has a configuration in which a small diameter opening is provided on the outer surface, and the cavity and the opening are connected by a conduit having an opening cross-sectional area.

Effect of the present invention With the above-described configuration, by matching the frequency at which the acoustic impedance of the cavity provided in the nose portion is the lowest to the frequency of the nz sound, the nz sound is reduced, and the nz sound is reduced. The sound is mixed with other noise and becomes almost inaudible.

Example Below, regarding a centrifugal multi-blade blower according to an example of the present invention,
This will be explained with reference to the drawings.

FIGS. 1 and 2 show an embodiment of a centrifugal multi-blade blower according to the present invention.

In FIGS. 1 and 2, 11 is a multi-blade impeller. 1
2 is an air guide, and 13 is a spiral-shaped synthetic resin casing. Reference numeral 14 denotes a nose portion, which is a part of the casing 13, and is a portion where the beginning and end of the spiral shape overlap.

At the center in the depth direction of the outer surface facing the multi-blade impeller 11 of the nose portion 14, where the air flowing inside the spiral-shaped casing 13 collides with the air that has just exited the multi-blade impeller 11 and causes turbulence, there is a groove with a cross-sectional area S. An opening 15 is provided, a cavity 16 having a volume V is provided at a distance from the opening 15, and the opening 1
5 and the cavity 16 are connected by a conduit 17 having a cross-sectional area S.

The acoustic impedance of the nose portion 14 having the above structure is expressed as follows, where p is the density of air and C is the speed of sound. However, H=lZT. If this equation is graphed, it will look like Figure 3. Moreover, this frequency f. By matching the frequency n'z of the nz sound, noise centered on the nz sound can be reduced.

FIG. 4 shows an opening 15 in the nose portion 14, a cavity 16,
It shows the frequency characteristics of noise when the pipe line 17 is not provided. In such a structure, no measures are taken against the nz sound, so the nz sound has a high peak.

On the other hand, in the frequency characteristics of the noise in this example shown in FIG. 5, although there is a peak, it is not higher than other frequencies, so the former sounds audibly like a high-pitched whistle. On the other hand, the latter is mixed with other noise and becomes almost inaudible.

In addition, the centrifugal multi-blade blower according to the present invention reduces the level of sound at frequencies centered around the rIz sound, and also reduces the echoes of the noise caused by the space surrounded by the impeller 11 and the casing 13. The absolute value of No increase in sound or decrease in air blowing performance was observed.

Therefore, not only can the nz sound generated at the nose section where the flow is disturbed, which has traditionally been considered a major drawback of centrifugal multi-blade blowers, be significantly reduced, but it also eliminates any increase in other noise or decrease in efficiency caused by it. First, the overall noise level can be reduced. Moreover, it is now possible to design the positions and shapes of the multi-blade impeller 11, air guider 12, and casing 13 more freely, which had previously been significantly restricted in order to reduce the nz sound, thereby improving the efficiency and other performance of the blower. This greatly contributes to the improvement of

Effects of the Invention As described above, the present invention provides a cavity with a predetermined volume in the nose portion of the casing, and also provides a small diameter opening on the outer surface of the nose portion that is in contact with the air flow. This configuration reduces noise, including NZ sound, which was considered a serious drawback of centrifugal multi-blade blowers, and enables quiet and highly efficient air blowing. It has the effect of

[Brief explanation of the drawing]

Fig. 1 is a perspective view schematically showing a centrifugal multi-blade blower according to an embodiment of the present invention, Fig. 2 is a partial perspective view of a nose portion showing an embodiment of the present invention, and Fig. 3 is a perspective view showing an outline of a centrifugal multi-blade blower according to an embodiment of the present invention. FIG. 4 is an acoustic impedance characteristic diagram of a cavity in the nose section showing an embodiment of the present invention, FIG. 4 is a frequency characteristic diagram of noise when no cavity is provided in an embodiment of the present invention, and FIG. 5 is a diagram of an embodiment of the present invention. Figure 6 is a perspective view showing the shelf of a conventional centrifugal multi-blade blower, and Figure 7 is a diagram of the multi-blade blades of a conventional centrifugal multi-blade blower. FIG. 8, a cross-sectional view of the vehicle, is a frequency characteristic diagram of noise generated by a conventional centrifugal multi-blade blower. 11...Multi-blade impeller, 12...Air guider, 13・Casing, 14...Nose part, 15...Opening part, 16...Cavity part, 1.・・・
・Pipeline. Name of agent: Patent attorney Toshio Nakao and 1 other person11
Shishi in Good Car I2 Air Guy Z'' I5・Opening L Otsudo Shime Iwage I7 Throat Figure 3 Figure 6

Claims (1)

[Claims] An air guider and a casing are disposed before and after the multi-blade impeller, and a small diameter opening is provided on the outer surface of the casing in contact with the air flow at the nose portion of the casing, and a conduit having an opening cross-sectional area is connected to the opening. A centrifugal multi-blade blower with a built-in cavity that is continuous and has a predetermined volume.