GB2265420A

GB2265420A - Air-blower in which the fan is fixed on a motor shaft having rotation speed control means.

Info

Publication number: GB2265420A
Application number: GB9300778A
Authority: GB
Inventors: Kenji Umetsu
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 1992-03-13
Filing date: 1993-01-15
Publication date: 1993-09-29
Anticipated expiration: 2013-01-15
Also published as: GB2265420B; KR960016528B1; KR930020033A; JPH05256299A; GB9300778D0

Abstract

An air blower having a speed control circuit has a fan (3) incorporating a vibration damping arrangement (4, 5A, 5B, 6) between the blades (7) and the motor shaft (1). The circuit (10) controls the rotation speed of the motor by controlling the wave-number or phase of AG power voltage. The fan (3) comprises a boss portion (4) attached to the shaft (2), a surrounding hub portion (6) and two groups of interconnecting bridge ribs (5A, 5B). The air-blowing blades (7) are integrally formed on the outer periphery of the hub portion (6). The two groups of bridge ribs (5A, 5B) are spaced in the axial direction of the rotation shaft (2). Each bridge rib of one of the groups is positioned to face a pitch gap between two adjacent ribs of the other group such that the bridge ribs of one of the groups are displaced circumferentially from the bridge ribs of the other group by 45 DEG . In a second embodiment bridging ribs extend between an intermediate hub portion and both the boss and hub portions. <IMAGE>

Description

"AIR-BLOWER IN WHICH FAN IS FIXED ON ROTATION SHAFT OF MOTOR HAVING ROTATION SPEED CONTROL MEANS" The present invention relates to an air-blower in which a fan is fixed on a rotation shaft of a motor having rotation speed control means, which air-blower is situated, for example, in an air conditioner.

For example, an air conditioner is provided with an air blower for blowing heat-exchanged air to a heat exchanger. The air blower is constructed such that a propeller fan or a sirocco fan is fixed on a rotation shaft of a motor.

In this type of air conditioner, it is desirable that the fan rotation speed (i.e. the number of rotations of the fan) be designed to be adjustable, in order to achieve an air blow amount corresponding to a heat exchange amount.

In order to vary the fan rotation speed of the air blower, the rotation speed of a motor for driving the fan must be controlled.

Methods of controlling the rotation speed of a motor, which is, for example, an induction type motor, include a power supply voltage control method, a power supply frequency control method, a switching control method using a motor winding tap, a power supply frequency wave-number control method, and a phase control method.

In particular, in the field of air blowers used in the air conditioner, power supply control by means of a thyristor has recently becomes easier, and therefore the wave-number control method and phase control method have been widely used.

The wave-number control method and phase control method can provide finer, lower-cost control than the power supply voltage control method. In addition, in these methods non-stepwise control can be performed, in contrast to the switching control method using the motor winding tap.

In the wave-number control method, as shown in Fig. 9A, a wave of a specified ratio (1/3 in Fig. 9A) is not output. Accordingly, the voltage is set at zero and only waves of 2/3 are output. Thereby, the maximum number of rotations can be reduced to 2/3.

In the phase control method, as shown in Fig. 9B, the output voltage is set at zero for a predetermined time period of a single wave of a power supply waveform (about 1/4 of the single wave in Fig. 9B), the voltage is output only in the other time period (3/4 of the wave). Thus, the maximum number of rotations is reduced to about 3/4.

However, in the control of the number of rotations of the motor by means of the above wave-number control method and phase control method, the waveform is forcefully made unstable, unlike the other control methods wherein the motor is driven in the mode of stable sine waveform.

Owing to such distortion of waveform, a pulsatile variation would occur in torque of the motor, or abnormal vibration or resonance would occur. Such undesirable vibration or resonance is transmitted to the fan to produce noise.

To overcome these drawbacks, Published Examined Japanese Utility Model Application (PEJUMA) No. 55-53749, for example, teaches a prior-art technique wherein a rotation shaft of a motor is coupled to a boss of a fan to be fixed on the rotation shaft, by means of an elastic member such as rubber member.

According to this type of structure, pulsatile torque of the motor is absorbed by the elastic member, and noise is reduced to a certain degree.

However, the elastic member is easily degraded, and there is a considerable variation in quality of manufactured elastic members. Consequently, the number of manufacturing steps increases, and the productivity lowers.

The object of the present invention is to provide an air blower wherein a fan is fixed on a rotation shaft of a motor having rotation speed control means, and vibration and noise caused by the motor driven by a power supply capable of varying the rotation speed is damped and absorbed with high efficiency. Thereby, the material quality of the air blower is not deteriorated, and the productivity is not adversely affected.

According to the present invention, there is provided an air blower wherein a fan is fixed to a rotation shaft of a motor having rotation speed control means, the air blower comprising: a motor having rotation speed control means and driven by a power supply for varying the rotation speed of the motor, and a fan fixed to the rotation shaft of the motor and having vibration damping means at a location where the fan is attached to the rotation shaft of the motor.

This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Figs. 1 to 4 show an embodiment of the present invention, in which Fig. 1 is a perspective view of an air blower in which a fan is fixed on a rotation shaft of a motor having rotation speed control means, Fig. 2 is a partially omitted, front view of a fan, Fig. 3 is a partially omitted, cross-sectional side view of an air blower, and Fig. 4 is a perspective view of a bridge hub; Fig. 5 is a view showing dimensions of the bridge hub; Figs. 6 to 8 show a modification example of the present invention, in which Fig. 6 is a partially omitted, front view of a fan, Fig. 7 is a partially omitted, cross-sectional side view of the fan, and Fig. 8 is a view for describing the structure of the bridge hub;; Fig. 9A shows a waveform associated with a wave number control method which is one of methods of controlling the number of rotations of a motor; and Fig. 9B shows a waveform associated with a phase control method which is one of methods of controlling the number of rotations of a motor.

An embodiment of the present invention will now be described with reference to the accompanying drawings.

As shown in Fig. 1, a fan 3 (a propeller fan 3 in this embodiment) is fixed on a rotation shaft 2 of a motor 1, thereby constituting an air blower.

The motor 1 is a generally employed induction motor. The motor 1 is electrically connected to an AC power supply 11 via a rotation speed control circuit 10.

The rotation speed control circuit 10 controls the number of rotations of the motor 1 by a wave-number control method, in which the wave number of an AC power supply voltage supplied from the motor 1 is controlled, or a phase control method, in which the phase of the AC power supply voltage from the motor 1 is controlled.

As shown in Figs. 2 and 3, the propeller fan 3 comprises a boss portion 4 tightly fitted or screwed on the rotation shaft 2 of the motor 1, a hub portion 6 provided around the boss portion 4 via two groups of bridge ribs 5A and 5B functioning as vibration-damping means (described later), and blades 7 formed on the outer peripheral surface of the hub portion 6.

The propeller fan 3 is integrally molded of, e.g.

AS (acryl-styrene) resin containing glass fibers. For example, the fan 3 is an integral mold product manufactured by a resin molding machine such as an injection machine. Thus, it is relatively easy to increase the number of products, and therefore the fan 3 is suitable for mass production. In addition, the fan 3 has a high strength and a high precision. It is possible to provide the propeller fan having high reliability, with low vibration and noise.

The boss portion 4 and hub portion 6 have concentric cylindrical shapes and have the same axial length. Only the boss portion 4 has a large wall thickness, since it is attached to the rotation shaft 2.

The hub portion 6 has such a wall thickness as to provide sufficient strength to support the blades 7 which perform an actual air blow function.

The two sets of bridge ribs 5A and 5B for coupling the outer peripheral surface of the boss portion 4 and the inner peripheral surface of the hub portion 6 are displaced from each other both in the axial direction and in the circumferential direction.

The bridge ribs 5A are situated at one axial end and the bridge ribs 5B are situated at the other axial end.

The number of bridge ribs 5A is four, and also the number of bridge ribs 5B is four (eight in total). The bridge ribs 5A and 5B are arranged at regular angular intervals of 90 .

For example, when the bridge ribs 5A are situated in horizontal and vertical directions, the bridge rib 5B are situated in oblique directions.

Since the positional relationship between the bridge ribs 5A and bridge ribs 5B is constant, the ribs 5A are always displaced circumferentially from the ribs 5B by 45 .

Even if the number of bridge ribs 5A and 5B is varied, each rib 5A (SB)is always situated to face the pitch gap between two adjacent ribs 5B (5A) of the opposed group.

The narrowest portion of each bridge rib 5A, 5B in the axial direction has a dimension t2, as shown in Fig. 3, and the narrowest portion of each bridge rib 5A, 5B in the circumferential direction has a length t2, as shown in Fig. 2.

The position of the narrowest portion of each bridge rib 5A, 5B in the axial direction coincides with the position of the narrowest portion of each bridge rib 5A, 5B in the circumferential direction. Thus, the bridge ribs 5A and 5B are provided with the thinnest portions 8 and 9 with the least cross sectional area.

Fig. 4 shows the bridge ribs 5A and 5B which are separated from the boss portion 4 and hub portion 6.

Fig. 5 shows the positional relationship between the thinnest portions 8 of the bridge ribs 5A and the thinnest portions 9 of the bridge ribs 5B.

The thinnest portion 8 of each bridge rib 5A is situated at a distance 2Da from the axis. The distance 2Da is double or more the diameter DX (equal to the diameter of that part of the rotation shaft 2 which is fitted in the boss portion 4) of a bore 4a for insertion of the rotation shaft 2.

Specifically, the diameter 4DaX of a circle described by connecting the thinnest portions 8 and 9 of the bridge ribs 5A and 5B is more than four times the diameter DX of that part of the rotation shaft 2 which is fitted in the boss portion.

Referring back to Fig. 2, the thinnest portion 8, 9 of the bridge rib 5A, 5B is formed at a substantially middle portion between the proximal end portion of the rib coupled to the boss portion 4 and the distal peripheral portion of the rib coupled to the hub portion 6.

The propeller fan 3 having bridge ribs 5A and 5B as one body, as described above, is rotated by the motor 1, thereby flowing air.

The rotation speed control circuit 10 controls the rotation speed (i.e. the number of rotations) of the motor 1 by a power supply frequency wave-number control method in which the wave-number of AC power supply voltage applied to the motor 1 is controlled, or a phase control method in which the phase of AC power supply voltage applied to the motor 1 is controlled.

Owing to distortion of waveform, pulsatile variation of torque of the motor 1, abnormal vibration or resonance may occur, and this is transmitted to the propeller fan 3.

Specifically, such pulsatile torque variation, abnormal vibration or resonance is transmitted from the boss portion 4, which is formed with the rotation shaft 2 as one body, to the hub portion 6 and blades 7.

However, since the bridge ribs 5A and 5B for coupling the boss portion 4 and hub portion 6 have the above-described structure, vibration, etc. is absorbed and not transmitted to the blades 7. Thus, occurrence of noise is prevented.

More specifically, since the bridge ribs 5A and 5B have thin middle portions 8 and 9 having the least axial and circumferential dimensions, the torque M applied to the portions 8 and 9 is given by M = F1 x D/2 = F2 x d/2 where D: the diameter of that part of the rotation shaft 2 which is fitted in the boss portion, F1: the torque applied to the rotation shaft 2, d: the cross-sectional area of the thinnest portion 8 and 9 of each bridge rib 5A, 5B, F2: the force applied to the thinnest portion 8 and 9 of each bridge rib 5A, 5B.

From the above, when 4D < d, it follows that F1 > 4F2 and accordingly F2 < 1/4F1.

Thus, the force applied to the bridge ribs 5A and 5B can be made less than the force applied to the outer periphery of the rotation shaft 2.

Specifically, the force applied to each of the eight bridge ribs 5A and 5B is not 1/8 of the force applied to the rotation shaft 2, but less than 1/8.

Even if the force applied to the bridge ribs 5A and 5B is summed, the sum is less than the force applied to the rotation shaft 2.

The bridge ribs 5A are displaced axially and circumferentially from the bridge ribs 5B such that each rib 5A (SB)is situated to face the pitch gap between two adjacent ribs 5B (5A) of the opposed group.

Accordingly, the propeller fan 3 has high strength, in particular, against the bending force F indicated by a curved arrow in Fig. 3.

In other words, the vertical flexural strength of the fan with respect to the axis is very high, and even if the bridge ribs 5A and 5B are considerably thinned, vibration produced by the motor 1 can be absorbed with high efficiency.

In conclusion, by virtue of the above-described bridge ribs 5A and 5B, the vibration of the motor 1 can be absorbed with high efficiency, even if non-sine waveform power is supplied to the motor 1 when the rotation speed is controlled by the wave-number control method or phase control method. Thus, transmission of vibration to the propeller fan 3 can be prevented and the vibration noise of the motor 1 can be reduced.

In addition, since the propeller fan 3 is an integral molded product made of glass fiber-containing AS (acryl-styrene) resin, etc., the material quality of the fan 3 does not deteriorate for a long time, and productivity is not adversely affected.

Figs. 6 and 7 show another type of propeller fan 3A according to the invention.

The blades 7 may be the same as are used in the above embodiment.

An intermediate hub portion 12 is provided between a boss portion 4A and a hub portion 6A. Bridge ribs 15A and 15B are interposed between the boss portion 4A and the intermediate hub portion 12. The bridge ribs 15A are displaced axially and circumferentially from the bridge ribs 15B such that each rib 15A (15B)is situated to face the pitch gap between two adjacent ribs 15B (15A) of the opposed group.

The number of bridge ribs 15A is four, and also the number of bridge ribs 15B is four (eight in total). The bridge ribs 15A and 15B are arranged at regular angular intervals of 90".

When the bridge ribs 15A are situated horizontally and vertically, the bridge ribs 15B are situated obliquely. Accordingly, the bridge ribs 15A are displaced from the bridge ribs 15B by 45".

In addition, bridge ribs 25A and 25B provided between the intermediate hub portion 12 and the hub portion 6A. The number of bridge ribs 25A is four, and also the number of bridge ribs 25B is four (eight in total). The bridge ribs 25A and 25B are arranged at regular angular intervals of 90 . The bridge ribs 25A are displaced axially from the bridge ribs 25B by 45".

The bridge ribs 25A and 25B are circumferentially displaced by 45O from the above-described bridge ribs 15A and 15B provided between the boss portion 4A and the intermediate hub portion 12.

Fig. 8 is a schematic view for easy understanding of the positional relationship between the bridge ribs 15A and 15B, on the one hand, and the bridge ribs 25A and 25B, on the other hand.

The vibration damping means comprising the bridge ribs 15A, 15B, 25A and 25B constitutes a so-called zigzag path of vibration. Thus, even when vibration of the motor 1 is transmitted via the rotation shaft 2, vibration can be absorbed more effectively.

In the case of the propeller fan 3 shown in Figs. 2 and 3, as well as the propeller fan 3A shown in Fig. 6, a mold structure required for integral molding can be obtained with no problem, and therefore there is no problem in manufacturing.

If the bridge pieces are formed, as independent pieces, of a softer molding material, the vibration of the motor 1 can be absorbed more effectively.

Claims

Claims:

1. An air blower wherein a fan is fixed to a rotation shaft of a motor having rotation speed control means, the air blower comprising: a motor having rotation speed control means and driven by a power supply for varying the rotation speed of the motor, and a fan fixed to the rotation shaft of the motor and having vibration damping means at a location where the fan is attached to the rotation shaft of the motor.

2. A machine according to claim 1, wherein said motor is an induction motor and employs, as rotation speed control means, one of means for controlling the wave-number of AC power supply voltage applied to the motor and means for controlling the phase of AC power supply voltage applied to the motor.

3. A machine according to claim 1, wherein said fan comprises: a cylindrical boss portion fixed to the rotation shaft of the motor; a cylindrical hub portion situated around the boss portion with a gap; a blade having a proximal end portion integrally attached to the outer periphery of the hub portion, for performing an air-blowing function in accordance with the rotation of the rotation shaft; and vibration damping means interposed between the boss portion and the hub portion.

4. A machine according to claim 3, wherein said vibration damping means comprises a plurality of groups of bridge ribs interposed between the outer periphery of the boss portion and the inner periphery of the hub portion, and a first group of the bridge ribs are displaced axially and circumferentially from a second group of the bridge ribs such that each bridge rib of one of the first and second group is situated to face a pitch gap between two adjacent ribs of the opposed group.

5. A machine according to claim 4, wherein the boss portion, the hub portion, the blades and the bridge ribs are integral mold products formed of a selected AS resin material containing glass fibers by means of an injection molding machine.

6. A machine according to claim 4, wherein said bridge ribs consist of two groups, and one group is provided at first axial end portions of the boss portion and the hub portion, and the other group is provided at second axial end portions of the boss portion and the hub portion.

7. A machine according to claim 4, wherein the number of the bridge ribs of each of the first and second groups is four, and each bridge rib of one of the first and second group is situated to face a pitch gap between two adjacent ribs of the opposed group such that the bridge ribs of the first group are displaced circumferentially from the bridge ribs of the second group by 450.

8. A machine according to claim 4, wherein each bridge rib is provided with an axially narrowest portion and a circumferentially narrowest portion.

9. A machine according to claim 8, wherein the axially narrowest portion and the circumferentially narrowest portion of each bridge rib are located at the same position, thereby forming a thinnest portion with the least cross-sectional area.

10. A machine according to claim 9, wherein the thinnest portion of each bridge rib is situated at a distance from the axis, which is double or more the diameter DX (equal to the diameter of the rotation shaft) of a bore for insertion of the rotation shaft, and accordingly the diameter of a circle described by connecting the thinnest portions of the bridge ribs is more than four times the diameter DX of the rotation shaft.

11. A machine according to claim 9, wherein the thinnest portion of each bridge rib is formed at a substantially middle portion between the proximal end portion of the rib coupled to the boss portion and the distal peripheral portion of the rib coupled to the hub portion.

12. A machine according to claim 3, wherein said vibration damping means comprises a plurality of groups of bridge ribs integrally having intermediate hub portions between the boss portion and the hub portion, the bridge ribs being provided between the boss portion and the intermediate hub portion and between the intermediate hub portion and the hub portion and being displaced axially and circumferentially.

13. A machine according to claim 12, wherein two groups of the bridge ribs are provided between the boss portion and the intermediate hub portion and two groups of the bridge ribs are provided between the intermediate hub portion and the hub portion, the bridge ribs being displaced from one another by 90 , and the bridge ribs provided between the boss portion and the intermediate hub portion being circumferentially displaced from the bridge ribs provided between the intermediate hub portion and the hub portion by 450.

14. A machine according to claim 13, wherein the bridge ribs provided between the boss portion and the intermediate hub portion are circumferentially displaced from the bridge ribs provided between the intermediate hub portion and the hub portion by 45".

15. An air-blower in which fan is fixed on rotation shaft of motor having rotation speed control means, substantially as hereinbefore described with reference to the accompanying drawings.