Centrifugal air blower

Abstract

The centrifugal fan (2) has upright first blades (2c1) with inequidistant circumferential spacing on a main plate (2b) extending radially outward from a hub (2a) integrally formed with a rotor yoke (3b), and has second blades (2c2) that are shorter than the first blades (2c1) and are formed upright between the first blades (2c1) at inequidistant circumferential distances from adjacent first blades (2c1). In one partial circumferential region (Z1), the radial length of the inner portions of the second blades (2c) is shorter than that of the second blades in another region (Z2), such that the center of gravity of the centrifugal fan coincides with the pivot point.

Description

Technical field The present disclosure relates to a centrifugal blower which is used in a device such as a seat climate control system or an HVAC (heating, ventilation and air conditioning) system. State of the art A typical centrifugal blower is equipped with a motor with a rotating shaft, an impeller driven by the motor for blowing air, and a housing containing these components. The housing has a spiral section containing the impeller, which forms a spiral airflow path on the outside of the impeller, and a blower section with an air outlet through which air is blown out of the spiral. A partition called a "tongue" (see 4h in Fig. 2) is located at the boundary between the spiral section, which winds around the circumference of the impeller, and the blower section, which is connected to the spiral section and separates the air blown to the air outlet from the circulating air (see patent document 1; Japanese publication no. 2017-125405). Although impellers of various shapes are used, a multitude of blades are configured to be mounted axially on a main plate connected to a cup-shaped hub that forms the base. The outer edges of the multitude of blades are connected to one another by an annular connecting element (or "collar"). The collar improves blowing efficiency when air drawn in from the radial center of the casing is blown outwards in a radial direction. The blades mounted on the main plate are all of the same shape and are evenly distributed circumferentially around the main plate (see patent document 2; Japanese patent application no. 2020-63679). Summary of the invention Technical task Typical centrifugal fans require noise reduction and improved blowing performance. However, the impeller configurations described in patent documents 1 and 2 mentioned above are unable to reduce the peak noise level that occurs due to pressure fluctuations in the air passing through the so-called tongue area at (number of centrifugal fan blades × rotational speed). It was found that the peak noise level occurring at (number of blades 50 of the centrifugal fan × rotational speed) can be reduced by using, as shown in Fig. 8, first blades 52, which are long in one radial direction and arranged at uneven (inequidistant) intervals on the main plate 51, and second blades 53, which are short in one radial direction and arranged at uneven (inequidistant) intervals between the first blades 52. However, if the distance between the first blades 52 and the second blades 53 is set inequidistant (where X1 ≠ X2), as shown in Fig. 8, the center of gravity of the centrifugal fan 50 shifts from the pivot point (i.e., the rotor shaft 54), thus making the rotation of the centrifugal fan 50 unbalanced.To solve this problem, an attempt was made to compensate for the imbalance by adding counterweights to the underside of the main plate 51, corresponding to the imbalance. However, it turned out that this generated frequency noise (first to third order rotational components) in addition to the peak noise. Solution to the problem The present disclosure was designed to solve the problems described above and aims to provide a centrifugal blower that reduces noise by decreasing the peak noise level that occurs at (number of blades of the centrifugal fan × rotational frequency) and that stabilizes the rotational balance by preventing the center of gravity of the centrifugal fan from being displaced from the axis of rotation (the rotor shaft). The embodiment described below has the following configuration. That is, a centrifugal blower has a centrifugal fan and a motor for driving the centrifugal fan, which are housed in a casing body, and air is drawn in from a center in a radial direction of the casing body and expelled from an outlet opening provided on an outer side in a radial direction of the casing body, wherein the casing body comprises: a first housing assembled to cover the centrifugal fan, provided with an intake opening in the center in a radial direction, and having a first air channel that is annular and formed on an outer side in a radial direction;and a second housing comprising a second annular air duct combined with the first air duct and formed further outwards in a radial direction than an outer circumferential end of the centrifugal fan on an outer circumference of a base plate rotatably mounting the motor, wherein the centrifugal fan: comprises a plurality of first blades formed inequidistantly in the circumferential direction, such that they are mounted on a main plate extending continuously outwards in a radial direction from a hub integrally connected with a rotor yoke;and has a plurality of second blades that are shorter than the first blades and are formed upright between the first blades, such that a distance to an adjacent first blade is inequidistant in the circumferential direction, wherein a length of inner end parts in a radial direction of a plurality of the second blades is shorter than a length of the second blades in another area, so that a center of gravity position of the centrifugal fan coincides with the pivot point. With the above configuration, the inequidistant spacing between the blades makes it possible to provide a centrifugal blower that operates more quietly by distributing peak noise occurring at (number of blades of the centrifugal fan × rotational frequency), and that has a stabilized rotational balance by preventing the center of gravity of a centrifugal fan from being displaced from the axis of rotation (the rotor shaft). The radial length of the second blades in the circumferential region is preferably determined such that the length of the end sections located further inward radially than a collar connecting the outer edges of the first blades and the second blades in an annular manner is shorter than the radial length of the second blades in another region. This stabilizes the rotational equilibrium by preventing the center of gravity of a centrifugal fan from shifting from the pivot point (the rotor shaft), and the airflow performance remains unaffected even if the second blades in one circumferential region are configured such that the radial length of the inner end sections is shorter than the radial length of the second blades in another region. Advantageous effects of the invention By using the centrifugal blower described above, it is possible to provide a centrifugal blower that has quieter operation by reducing the peak noise that occurs at (number of blades of the centrifugal fan × rotational frequency) and that has a stabilized rotational balance by preventing the center of gravity position of a centrifugal fan from shifting away from the axis of rotation (the rotor shaft). Brief description of the drawings Fig. 1 is a perspective view of a centrifugal fan. Fig. 2 is a top view of a state in which the first casing has been removed from the centrifugal fan shown in Fig. 1. Fig. 3 is an axial cross-sectional view of the centrifugal fan shown in Fig. 1. Figs. 4A, 4B, and 4C are a top view, a front view, and a perspective view of a centrifugal fan. Fig. 5A is a top view of the centrifugal fan, and Fig. 5B is an explanatory partial view of the inequidistant spacing of the first and second blades. Fig. 6A is an FFT analysis plot of the noise generated in an inequidistant impeller, and Fig. 6B is an FFT analysis plot of the noise generated in an equidistant impeller. Fig. 7 is a diagram comparing the PQ properties of an inequidistant impeller and an equidistant impeller.Figure 8 is a top view of a centrifugal fan with first and second blades arranged inequidistantly on a main plate. Description of the embodiments An embodiment of a centrifugal blower according to the present invention is described below with reference to the accompanying drawings. First, the overall configuration of the centrifugal blower is described with reference to Figures 1, 2, 3, 4, 5, 6 to 7. A brushless DC motor is used as the motor M. In the present embodiment, an external rotor motor is used. It should be noted that the motor can also be an internal rotor motor. As shown in Fig. 3, the centrifugal blower 1 comprises a centrifugal fan 2 (impeller) and a rotor 3, which are integrally assembled, and the motor M, which drives these components, is housed in a casing 4. As shown in Fig. 1, the centrifugal blower 1 draws in air from the center in a radial direction within the casing 4 and expels compressed air from a side face in a radial direction. The casing 4 is formed from a first housing 4a, which is connected to and covers the centrifugal fan 2, and a second housing 4b, which rotatably mounts the motor M (i.e., the rotor 3 and a stator 5, see Fig. 3). In Fig. 1, an inlet opening 4c is provided in the center of the first housing 4a, and an annular first air channel 4d is formed on the outside in a radial direction. In Fig. 2, an annular second air channel 4e, combined with the first air channel 4d, is formed on the outside in a radial direction of the second housing 4b. The first housing 4a and the second housing 4b are assembled such that they form an annular air channel 4f on the outside in a radial direction of the housing body 4 (see Fig. 3). As shown in Fig. 2, a partition, referred to as the "tongue section 4h", is provided on the second housing 4b at the boundary between the second air channel 4e, which forms the annular air channel 4f, and the outlet opening 4g.Although not shown, the same applies to the boundary in the first housing 4a between the first air duct 4d, which forms the annular air duct 4f, and the outlet opening 4g. As shown in Fig. 3, a bearing housing 6 and a motor board 7 are mounted in the center of the second housing 4b. The output wires of the stator coil 5b are connected to the motor board 7, and a Hall sensor or similar detects the position of a rotor magnet 3d, which is also mounted. If the motor M is a sensorless model, this position detection sensor can be omitted. A stator core 5a is integrally attached to the outer circumference of the bearing housing 6, which is formed as a metal tube and held upright on the second housing 4b. A rotor shaft 3a is rotatably mounted in a shaft bore of the bearing housing 6 via a pair of bearings 6a. A retaining washer 6c is fitted to an axial end of the rotor shaft 3a and limits the axial movement of the bearing 6a at its lower end. A stator coil 5b is wound around pole teeth formed on the stator core 5a via an insulator 8, with the tips of the pole teeth facing the rotor magnet 3d. One end of the rotor shaft 3a is integrally connected to the hub 3c of a cup-shaped rotor yoke 3b by a press fit, shrink fit, adhesive bond, or a combination of these methods. The other end of the rotor shaft 3a is supported by a shaft bracket 6b provided on the second housing 4b.The rotor magnet 3d is integrally attached to an inner circumferential surface of the rotor yoke 3b. It should be noted that the center of the inlet opening 4c does not need to be precisely aligned with the axis of the rotor shaft 3a of the motor M, but that it is sufficient if the inlet opening 4c is located radially near the center of the housing body 4 within a range in which the centrifugal fan 2 operates without loss of efficiency. As shown in Fig. 4C, the centrifugal fan 2 has a dome-shaped main plate 2b, which is formed such that it extends radially outwards from the hub 2a. The main plate 2b, which is connected to the hub 2a, extends radially outwards and is inclined towards the downstream side in the direction of the airflow. A plurality of first blades 2c1 and second blades 2c2, which are curved radially from the inside out, are formed alternately such that they are mounted on the main plate 2b. As shown in Figs. 4A and 4B, an annular cover 2d is connected to the outer edges of the first blades 2c1 and the second blades 2c2. The air, pressurized by the rotation of the first blades 2c1 and the second blades 2c2, is directed and guided to the annular airflow channel 4f on the outer circumference (see Fig. 3). Furthermore, as shown in Fig. 4A, several first blades 2c1 are configured such that they are arranged circumferentially on the outside of the dome-shaped main plate 2b at inequidistant intervals. Second blades 2c2, which are shorter than the first blades 2c1, are arranged upright between the first blades 2c1, so that the distance to an adjacent first blade 2c1 is inequidistant in the circumferential direction. As shown in Fig. 5A, in a section Z1, several second blades 2c2 are arranged circumferentially such that the length of the inner end sections in one radial direction is shorter than the length of the second blades 2c2 in the other section Z2. This results in the center of gravity of the centrifugal fan 2 coinciding with the center of rotation. In this way, the uneven spacing between the first blades 2c1 and a second blade 2c2, as shown in Fig. 5B (see Fig. 5B where X1 ≠ X2), distributes the location where the peak noise occurs at (number of blades of the centrifugal fan 2 × rotational speed), leading to quieter operation. Furthermore, by preventing the center of gravity of the centrifugal fan 2 from shifting away from the pivot point (of the rotor shaft 3a), it is possible to provide a radial blower 1 whose rotation compensation is stabilized. As shown in Fig. 5A, the radial length of the second blades 2c2, which are provided in one section Z1 in the circumferential direction of the centrifugal fan 2, is shorter than the radial length of the inner end sections of the second blades 2c2 provided in the other section Z2. This prevents the center of gravity of the centrifugal fan 2 from shifting from the pivot point (the rotor shaft 3a), thus stabilizing the rotational balance. Even though the radial length of the inner end sections of the second blades 2c2 in section Z1 is shorter in the circumferential direction than the length of the second blades 2c2 in the other section Z2, this has no effect on the fan performance. As shown in Fig. 3, the hub 2a of the centrifugal fan 2 and the main plate 2b connected to the hub 2a form a dome-shaped chamber 4i on the side opposite the inlet opening 4c. This dome-shaped chamber 4i can be used to accommodate tall components (such as an electrolytic capacitor 7a) mounted on the motor M and the motor board 7, allowing the centrifugal fan 2 and the motor M to be assembled compactly. The rotor 3 and the stator 5 of the motor M are housed in the dome-shaped chamber 4i and are arranged coaxially. This reduces the axial dimension of the centrifugal fan 1, enabling a smaller, flatter structure, even for a centrifugal fan 1 of the same size. As shown in Fig. 1, the first housing 4a and the second housing 4b are integrally assembled by placing the housings 4a and 4b on top of each other with their openings facing each other and engaging the locking elements 4j provided on the outer circumferential side of the first housing 4a with the locking elements 4k provided on the outer circumferential side of the second housing 4b. A wiring connection 4m, through which wires connected to the motor board 7 can be led out of the housing, is also provided on the first housing 4a and the second housing 4b. The cable connection 4m is formed by fitting a counter plate 4m1, which projects from the side of the first housing 4a, into a corresponding channel 4m2, which projects from the opposite side of the second housing 4b (see Fig. 1 and Fig. 2). It should be noted that for the first blades 2c1 and the second blades 2c2, which are arranged inequidistantly on the main plate 2b, the optimal arrangement for noise reduction is determined by measuring the noise level and performing an FFT analysis while varying the number of blades and the blade spacing. This is achieved by dispersing the locations of the peak noise level, which occurs at (number of blades of the centrifugal fan 2 × rotational frequency). However, due to the inequidistant arrangement of the first blades 2c1 and the second blades 2c2, which are positioned between the first blades 2c1, the rotational balance of the centrifugal fan 2 remains unbalanced in this state. For this reason, in the sub-region Z1, the length of the inner end sections in the radial direction of the second blades 2c2 is shorter than the length of the inner end sections in the radial direction of the second blades 2c2 in the other sub-region Z2.Shortening the radial length of the outer end sections of the first blades 2c1 and the second blades 2c2 to correct the balance would significantly affect the airflow static pressure properties (the "PQ properties"). Even shortening the radial length of the inner end sections of the first blades 2c1, which are located near the center of the centrifugal fan 2, would have only a minor effect on correcting the rotational balance. Therefore, shortening the radial length of the inner end sections of the second blades 2c2 allows for a correction of the rotational balance without affecting the airflow static pressure properties (the "PQ properties"). This prevents the center of gravity of the centrifugal fan 2 from shifting away from the pivot point (the rotor shaft 3a), thus stabilizing the rotational balance. Fig. 6A is an FFT analysis diagram of the noise generated by the centrifugal fan 2, which has an impeller with inequidistant spacing, and Fig. 6B is an FFT analysis diagram of the noise generated by the centrifugal fan 2, which has an impeller with equidistant spacing, for comparison purposes. In both cases, the noise measurement was performed on a centrifugal fan 2 with 50 blades (i.e., 25 first blades 2c1 and 25 second blades 2c2) at various rotational frequencies, and an FFT analysis (Fast Fourier Transform, frequency analysis) was carried out. For the impeller with equidistant blade spacing shown in Fig. 6B, a peak noise level (the area marked by the dotted oval) was observed at a frequency of 4685 Hz and a rotational speed of 5622 rpm. However, no peak noise level was observed in the impeller with inequidistant blade spacing shown in Fig. 6A. Fig. 7 shows the airflow-static pressure characteristic (PQ characteristic) for the centrifugal fan 2 with an inequidistantly spaced impeller shown in Fig. 6A and the centrifugal fan 2 with an equidistantly spaced impeller shown in Fig. 6B. In the diagram in Fig. 7, the dashed line shows the airflow-static pressure characteristics (PQ characteristics) of the centrifugal fan 2 with an inequidistantly spaced impeller, and the solid line shows the airflow-static pressure characteristics (PQ characteristics) of the centrifugal fan 2 with an equidistantly spaced impeller. As indicated by the dashed line, the centrifugal fan 2 with the inequidistantly spaced impeller exhibits slightly improved airflow static pressure (PQ) characteristics in the low to medium flow range compared to the centrifugal fan 2 with the equidistantly spaced impeller. As described above, by adjusting the distances between the first blades 2c1 and the second blades 2c2 to an equidistant distance, it is possible to provide a centrifugal fan 1 that achieves quieter operation by distributing the points where a peak noise level occurs, which occurs at (number of blades of the centrifugal fan × rotational frequency), and that stabilizes the rotational balance by preventing the center of gravity of the centrifugal fan 2 from shifting from the pivot point (of the rotor shaft 3a). It should be noted that, although the first blades 2c1 and the second blades 2c2 provided on the main plate 2b of the centrifugal fan 2 are arranged alternately, a plurality of second blades 2c2 can be arranged in a non-uniform arrangement between the first blades 2c1. The region in which the length of the inner end portions is shorter in a radial direction of the second blades 2c2 is not limited to a single region, and several such regions can be provided in the circumferential direction of the impeller fan 2. Although an external rotor motor used in a centrifugal blower for HVAC (heating, ventilation, and air conditioning) systems has been described as an example in the present embodiment, the present disclosure is not limited thereto, and the motor can also be used as a drive source for other devices. QUOTES INCLUDED IN THE DESCRIPTION This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature JP 2017-125405

[0002] JP 2020-63679

[0003]

Claims

A centrifugal blower (1) in which a centrifugal fan (2) and a motor (M) for driving the centrifugal fan are housed in a housing body (4) and air is drawn in from a center in a radial direction of the housing body (4) and expelled from an outlet opening (4g) provided on an outside in a radial direction of the housing body (4), wherein the housing body (4) comprises: a first housing (4a) which is assembled to cover the centrifugal fan (2), is provided with an inlet opening (4c) in the center in a radial direction and has a first air channel (4d) which is annular and is formed on an outside in a radial direction;and a second housing (4b) comprising a second annular air duct (4e) combined with the first air duct (4d) and extending radially further outward than an outer circumferential end of the centrifugal fan (2) in an outer circumference of a base plate rotatably supporting the motor (M), and wherein the centrifugal fan (2) comprises a plurality of first blades (2c1) formed inequidistant in the circumferential direction, such that they are mounted on a main plate (2b) extending continuously outward in a radial direction from a hub (2a) integrally connected with a rotor yoke (3b);and has a plurality of second blades (2c2) that are shorter in length than the first blades (2c1) and are formed upright between the first blades, such that the circumferential distance to an adjacent first blade (2c1) is equidistant, and in one sub-region (Z1) circumferentially a plurality of the second blades (2c2) are formed in a length of inner end parts that is shorter in the radial direction than the length of the second blades in another region (Z2), such that the center of gravity of the centrifugal fan (2) coincides with the pivot point. The centrifugal blower (1) according to claim 1, wherein the length in the radial direction of the second blades (2c2) in the partial region (Z1) is defined in the circumferential direction such that a length of end parts which are located further inwards in the radial direction than a collar (2d) which connects outer edge sections of the first blades (2c1) and the second blades (2c2) in a ring-like manner is formed shorter than a length in a radial direction of the second blades (2c2) in another region.

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