BLOWER AND FAN FRAME

- Panasonic

The blower includes a fan blade 5 extending in a centrifugal direction from an outer peripheral surface of a hub part having a cylindrically-shaped outer peripheral surface, a driving part for supporting and driving the fan blade 5, and a fan frame 2a which supports the driving part and has an intake port 4, and is characterized in that the fan frame 2a includes legs 9a to 9c for connecting a drive side inner peripheral end of the intake port 4 to an outer peripheral end, and a side of the outer peripheral end of the fan frame 2a is provided with slits 10 for extending the legs 9a to 9c.

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Description
BACKGROUND

1. Field of the Invention

The present invention relates to a blower and a fan frame used in a cooler of a heating element such as a CPU mounted inside a cabinet of, for example, an electronic device.

2. Description of the Related Art

A conventional blower includes a device as shown in (JP2001-057493A), and a diameter of an intake port provided in a fan frame is limited to a certain range by a relation between static pressure and air volume flowing into a fan case from the intake port. That is, it is necessary to largely provide the diameter of the intake port in order to ensure the air volume required for cooling of a heat-generating component in the case of being used for cooling of the heat-generating component. However, when the intake port is too larger, the static pressure becomes low, and the blower cannot be installed in a device with a high mounting density or a device with a narrow flow path. Therefore, the diameter of the intake port is limited to the certain range in which the air volume and the static pressure are combined, so that a length of a diameter of legs for connecting the fan frame to a motor part is also provided in the same diameter in conjunction with the diameter of the intake port.

However, when the length of the diameter of the legs for connecting the fan frame to the motor part for driving a fan blade is limited to a certain range, rigidity of the leg becomes high. As a result, a natural frequency of the leg becomes a value close to a frequency of vibration by a magnetic pole dependent on the number of rotations of the motor part, and vibration of a motor is resonated and amplified in the fan frame and a noise problem of a device incorporated as noise from the vibration is caused.

Hence, the invention has been implemented in view of the problem described above, and an object of the invention is to provide a blower capable of reducing noise by preventing a natural frequency of a leg from becoming a value close to a frequency of vibration of a motor by adjusting the natural frequency of the leg.

SUMMARY

Hence, the invention has been implemented in order to solve the problem described above, and is a blower including a fan blade extending in a centrifugal direction from an outer peripheral surface of a hub part having a cylindrically-shaped outer peripheral surface, a driving part for supporting and driving the fan blade, and a fan frame which supports the driving part and has an intake port, characterized in that the fan frame includes a leg for connecting a drive side inner peripheral end of the intake port to an outer peripheral end opposed to the inner peripheral end, and a side of the outer peripheral end of the fan frame is provided with a slit for extending the leg.

By the configuration described above, the invention can decrease rigidity and adjust a natural frequency of the leg by extending the legs and increasing a diameter of the legs. As a result, an object of the invention is to reduce noise by being prevented from becoming a value close to a frequency of vibration of a motor.

Another object of the invention is that the notch is parallel to a longitudinal direction of the leg and thereby a metallic mold for molding is simplified and manufacture is facilitated.

A further object of the invention is that a situation in which vibration of the motor is resonated and amplified in the fan frame and noise from the vibration is caused is prevented and the amount of air sucked from the intake port is adjusted freely and the air in the vicinity of an exhaust port is decreased and adjusted and noise is reduced.

A further object of the invention is that a cabinet for installing the blower generally has rigidity higher than that of the blower and accordingly, rigidity of the fixing part becomes high, so that a resonance point of the fixing part greatly deviates from a resonance point of the leg, so that it is made difficult for vibration to propagate to the cabinet and noise is reduced.

A further object of the invention is that the blower can be tightly fixed to the cabinet having rigidity higher than that of the blower, so that a resonance point of the fixing part greatly deviates from a resonance point of the leg, so that it is made difficult for vibration to propagate to the cabinet and noise is reduced. Also, the object is that as the area of connection to the cabinet is large, the resonance point of the fixing part greatly deviates from the resonance point of the leg, so that it is made difficult for vibration to propagate to the cabinet and the noise is reduced.

A further object of the invention is that occurrence of an eddy is reduced and a flow can be smoothed, so that noise is reduced.

A further object of the invention is that the natural frequency is decreased while increasing strength of the side of the notch of the leg.

A further object of the invention is that thicknesses of both ends of the leg change obliquely so as to become thin from a side of the notch toward a side of the driving part and thereby a sudden change in the thickness is prevented and strength of the leg is improved.

A further object of the invention is that thicknesses of both ends of the leg change stepwise so as to become thin from a side of the notch toward a side of the driving part and thereby the thickness of the leg in a wider range is thin constructed. Also, the object is that the natural frequency of the leg is made lower and further is distanced from the value of the integral multiple of the fundamental frequency of vibration of the motor.

A further object of the invention is that thicknesses of both ends of the leg change in a portion notched in the leg so as to become thin from a side of the notch toward a side of the driving part and thereby an influence of intake air by change in the thickness is prevented.

A further object of the invention is that lengths of the leg and the notch are maximized with respect to the diameter of the certain legs by extending in a tangential direction of the drive side inner peripheral end of the intake port. As a result, rigidity of the leg is minimized and the natural frequency of the leg can be prevented from becoming the value close to the integral multiple of the fundamental frequency of vibration of the motor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view seen from the side of a fan frame of a centrifugal fan device in a first embodiment,

FIG. 2 is a perspective view seen from the side of a fan blade of the centrifugal fan device in the first embodiment,

FIG. 3(a) is a top view of the fan frame in the first embodiment and FIG. 3(b) is a sectional view of the fan frame in the first embodiment,

FIG. 4 is an enlarged view of a connection between the fan frame and a leg in a region A of FIG. 1,

FIG. 5 is a diagram showing a relation between a natural frequency of the legs and a size Wd of a diameter of the legs in the first embodiment,

FIG. 6 is a diagram showing a relation between a sound pressure and a rotational speed of a motor in the case of changing the diameter of the legs in the first embodiment,

FIG. 7 is a diagram showing a relation between the natural frequency of the legs and a width Ws of the legs in the first embodiment,

FIG. 8 is a diagram showing a relation between the natural frequency of the legs and a thickness Wt of the legs in the first embodiment,

FIG. 9(a) is a top view of a fan frame provided with a notch substantially perpendicular to and a notch parallel to a longitudinal direction of the leg in the first embodiment and FIG. 9(b) is a top view of a fan frame provided with plural layers of notches in the whole periphery of the intake port in the first embodiment,

FIG. 10 is a perspective view seen from the side of a fan frame of a centrifugal fan device in a second embodiment,

FIG. 11 is a perspective view seen from the side of a fan cover of the centrifugal fan device in the second embodiment,

FIG. 12 is a top view of a centrifugal fan device in which a part of the centrifugal fan device of FIG. 10 is changed,

FIG. 13 is a top view of a centrifugal fan device in which a part of the centrifugal fan device of FIG. 10 is changed,

FIG. 14 is a diagram showing a noise level every the number of rotations of a motor in the centrifugal fan device of FIG. 10 and a centrifugal fan device without a notch,

FIG. 15 is a diagram showing FFT analysis of noise in the centrifugal fan device of FIG. 10 and the centrifugal fan device without the notch,

FIG. 16 is a perspective view of a centrifugal fan device in a third embodiment,

FIG. 17(a) is a top view of the centrifugal fan device in the third embodiment and FIG. 17(b) is a sectional view taken on line A-A in FIG. 17(a), and

FIG. 18(a) is a top view of a conventional centrifugal fan device and FIG. 18(b) is a sectional view taken on line A-A in FIG. 18(a).

 DETAILED DESCRIPTION

Embodiments of the invention will hereinafter be described with reference to the drawings.

First Embodiment

In a first embodiment, the case of using a blower of the invention for cooling of a heat-generating component will be described.

FIG. 1 is a perspective view seen from the side of a fan frame of a centrifugal fan device in the first embodiment. A fan case 2 of a centrifugal fan device 1 is constructed of a fan frame 2a positioned in a lower portion and a fan cover (not shown) positioned in an upper portion of the fan frame. Here, a bottom surface and side surfaces of the fan frame 2a are integrally formed by, for example, resin molding or die casting of aluminum alloy. An exhaust port 3 for exhausting the sucked air is arranged in one side surface of the fan frame and an intake port 4 is arranged in the bottom surface. Also, the fan cover is molded in a plate shape by resin molding or punching molding of a metal material such as aluminum or stainless steel, and an intake port 4 with substantially a circular shape for sucking air is arranged in the center of the fan cover.

Then, a fan blade 5 is placed so as to be received with the fan blade pinched by the fan frame 2a and the fan cover.

FIG. 2 is a perspective view seen from the side of the fan blade of the centrifugal fan device in the first embodiment. In FIG. 2, the fan blade 5 is constructed of a hub part 6 having a cylindrically-shaped outer peripheral surface and plural blade parts 7 substantially radially extending in a centrifugal direction from its outer peripheral surface. Also, a motor part is disposed inside the hub part 6.

Also, the fan blade 5 is rotated and driven by the motor part, and a surface shape of a rotary shaft direction in a predetermined region of a surface (a positive pressure surface) of a rotational direction of the blade part 7 is formed in a shape in which both side ends in a vertical direction of the blade part 7 are positioned to the side of the rotational direction than the center of the blade part 7. Further, an upper side annular plate 8 continuously joined to upper side ends in the rotary shaft direction in outer peripheral parts of the blade parts 7 is provided.

When the fan blade 5 rotates at high speed, air is sucked from the intake port 4 arranged in the bottom surface of the fan frame 2a and the intake port 4 arranged in the center of the fan cover as opposed to an upper surface of the hub part 6. At that time, the air is sucked from a direction of a rotary shaft (not shown) of the fan blade 5 described below and further, a direction of the sucked air is changed in the centrifugal direction of the blade parts 7 inside the fan case 2 by rotational motion of the plural blade parts 7. Therefore, while most of the sucked air collides with an inner wall of a cover 2b or the frame 2a, the air is supplied along the inner wall in the same direction as the rotational direction of the fan blade 5 and is exhausted from the exhaust port 3.

Next, the fan frame 2a which is a feature of the invention will be described in detail.

FIG. 3(a) is a top view of the fan frame in the first embodiment, and FIG. 3(b) is a sectional view of the fan frame in the first embodiment. Also, FIG. 4 is an enlarged view of a connection between the fan frame and a leg in a region A of FIG. 1.

Legs 9a, 9b, 9c connect an outside end 13 of the intake port 4 opposed to a connection hole 11 to a drive side inner peripheral end 14 in the side of the connection hole 11 for connecting the fan frame 2a to the motor part in an end of the intake port 4. The fan frame 2a supports the motor part for supporting the fan blade 5. By providing the fan frame 2a with notches 10 for extending the legs 9a to 9c, a diameter Wd of the legs 9a to 9c is made longer than a diameter of the outside end 13 of the intake port 4. The fan frame 2a is connected to the motor part by the connection hole 11, and is connected to the fan cover by plural connections 12. In addition, the notch 10 in the present application includes all such as a slit or a groove as shown in FIG. 1.

Also, as shown in FIG. 3(a), it is preferable to provide the legs 9a to 9c so that the connections 12 are not placed as extensions of longitudinal directions of the legs 9a to 9c. That is, since vibration of the motor part propagates to the legs 9a to 9c along the longitudinal directions of the legs 9a to 9c, when the connections 12 are disposed as the extensions, it becomes easy for the vibration to propagate from the connections 12 to the fan cover and noise increases. Therefore, the increase in the noise from the vibration of the motor can be reduced further by placing the connections 12 in positions other than the extensions of the longitudinal directions of the legs 9a to 9c as described in the first embodiment.

Also, a shape of the notches 10 is a shape parallel to the longitudinal directions of the legs 9a to 9c as shown in FIG. 4 and thereby, a metallic mold for molding is simplified and manufacture is facilitated, but the shape is not necessarily the parallel shape. That is, by making lengths of the legs 9a to 9c longer than a distance between the outer peripheral end 13 and the drive side inner peripheral end 14 of the intake port 4 through the notches 10, rigidity of the legs 9a to 9c could be decreased to adjust a natural frequency of the legs 9a to 9c. For example, the vicinity of the connection between the notch 10 and the fan frame 2a may be formed so as to expand outward in a shape. By being constructed thus, the connection between the legs 9a to 9c and the fan frame 2a can be strengthened without influencing the natural frequency of the legs 9a to 9c. Therefore, an angle α of the notch 10 in the connection between the legs 9a to 9c and the fan frame 2a is preferably about 0 to 60° and in the first embodiment, a width d is about 1 to 5 mm. When the angle α of the notch 10 is small and is about 0 to 30° (the width d is about 1 mm in the first embodiment), there is little change in area of the intake port 4 and thus in static pressure, so that air can be sucked at the static pressure at which even a device with a high mounting density or a device with a narrow flow path is not influenced. Also, when the angle α of the notch 10 is large and is about 30 to 60° (the width d is about 5 mm in the first embodiment), occurrence of cavity noise can be reduced. The cavity noise means that when wind blows on a narrow groove, the wind whirls and results in the noise.

In the first embodiment, a diameter of the outside end 13 of the intake port 4 is 35 mm, but the diameter of the intake port 4 is not limited to 35 mm since the diameter depends on a size of the fan blade 5. For example, as a cooler of an electrical device of a notebook PC, the diameter of the outside end 13 of the intake port 4 is generally 30 to 46 mm, and the coolers with other sizes may be adopted. In addition, Wd in FIG. 3 represents a diameter of a circle obtained by connecting the ends, at which the legs 9a to 9c are connected to the fan frame 2a, of the legs 9a to 9c, and Ws shows a width of the legs 9a to 9c, and Wt shows a thickness of the legs 9a to 9c.

Next, a relation between a natural frequency of the legs 9a to 9c and a vibration frequency of the motor part will be described. The motor part includes a rotor and a stator. The rotor is provided with the blade parts 7 of the fan blade 5 and a rotor magnet for disposing plural magnetic poles in an inner periphery. In the stator, a winding is wound on an insulator and insert molding is performed so as to be inserted into the insulator and a metallic electronic steel plate is provided. In order to rotate this rotor, the stator is turned on and off according to the magnetic poles of the rotor magnet and thereby, vertical vibrations in a thrust direction (a direction parallel to a rotary shaft of the rotor) of the rotor by variations in a magnetic force are generated.

Therefore, a fundamental frequency of the vibration frequency of the motor is expressed as a value in which the number of rotations of the motor is multiplied by the magnetic poles of the rotor magnet. When an integral multiple of this fundamental frequency becomes a value close to the natural frequency of the legs 9a to 9c, vibration of the motor is resonated and amplified in the fan frame 2a and noise from the vibration increases. Normally, in a band of the fundamental frequency, resonance and amplification do not become a problem and when a frequency two to three times the fundamental frequency becomes the value close to the natural frequency of the legs 9a to 9c, resonance and amplification are maximized. Therefore, it becomes important to set the natural frequency of the legs 9a to 9c at a value distant from the frequency two to three times the fundamental frequency.

In addition, generally, when the motor rotates at, for example, 2000 to 6000 r/min, the fundamental frequency of the vibration frequency of the motor becomes 133 to 400 Hz. As described above, this band has a low possibility that vibration of the motor is resonated and amplified in the fan frame 2a and noise from the vibration becomes the problem. In this case, it becomes necessary to set the natural frequency of the legs 9a to 9c at a value distant from the frequency (500 to 1200 Hz) two to three times the fundamental frequency.

Next, a relation between a size Wd of the diameter of the legs 9a to 9c and the natural frequency of the legs 9a to 9c will be described. FIG. 5 is a diagram showing the relation between the natural frequency of the legs and the size Wd of the diameter of the legs in the first embodiment. In addition, a graph a in FIG. 5 is the case where a width of the legs 9a to 9c is 3 mm and a thickness of the legs 9a to 9c is 1.2 mm and a material of the legs 9a to 9c is a resin such as PBT in the first embodiment. A graph b is the case where the width of the legs 9a to 9c is 3 mm and the thickness of the legs 9a to 9c is 0.4 mm and the material of the legs 9a to 9c is an iron material such as SECC in the embodiment.

As a length of the legs 9a to 9c becomes long, rigidity of the legs 9a to 9c becomes low generally and the natural frequency of the legs 9a to 9c becomes low. Also, as the length of the legs 9a to 9c becomes short, the rigidity of the legs 9a to 9c becomes high generally and the natural frequency of the legs 9a to 9c becomes high. This is because the natural frequency is proportional to the square root of the rigidity (spring constant). That is, for example, a wavelength of vibration propagating from the motor part to the legs 9a to 9c is determined by the length of the legs 9a to 9c and the wavelength also becomes long when the legs 9a to 9c are long, with the result that a speed of propagation of vibration does not change, so that the natural frequency becomes low.

Therefore, as shown in FIG. 5, as the diameter Wd of the legs 9a to 9c becomes large, the natural frequency of the legs 9a to 9c becomes low.

As described above, a situation in which vibration of the motor is resonated and amplified in the fan frame 2a and noise from the vibration is caused is prevented by providing the notches 10 to extend the diameter of the legs 9a to 9c.

FIG. 6 is a diagram showing a relation between a sound pressure and a rotational speed of the motor in the case of changing the diameter of the legs in the first embodiment. In addition, graphs shown in FIG. 6 are the case where a width Ws of the legs 9a to 9c is 1 mm and a thickness Wt of the legs 9a to 9c is 1.2 mm and a diameter of the intake port 4 is 35 mm.

The graph a in FIG. 6 is a state in which the diameter of the legs 9a to 9c is 35 mm equal to the diameter of the intake port 4 and the notch 10 is not provided. In this case, it is apparent from comparison with the graphs b to e in the case of providing the notches 10 to lengthen the legs 9a to 9c that vibration of the motor is resonated and amplified in the fan frame 2a and noise from the vibration increases.

In the graph b, the diameter of the legs 9a to 9c is 40 mm which is larger than the diameter of the intake port 4 by 5 mm, and it is apparent that vibration of the motor is not resonated and amplified too much in the fan frame 2a and the motor is stable. Also, in the graph c, the diameter of the legs 9a to 9c is 44 mm which is larger than the diameter of the intake port 4 by 9 mm, and it is apparent that vibration of the motor is not resonated and amplified too much in the fan frame 2a and the motor is stable like the graph b. Also, in the graph d, the diameter of the legs 9a to 9c is 46 mm which is larger than the diameter of the intake port 4 by 11 mm, and it is apparent that noise is lower than that of the graph a but vibration of the motor is slightly resonated and amplified at a motor rotational speed of about 4300 r/min and is not resonated and amplified too much in the fan frame 2a at the other rotational speeds and the motor is stable. Further, in the graph e, the diameter of the legs 9a to 9c is 48 mm which is larger than the diameter of the intake port 4 by 13 mm, and it is apparent that noise is lower than that of the graph a like the graph d but vibration of the motor is slightly resonated and amplified at the motor rotational speed of about 4400 r/min and is not resonated and amplified too much in the fan frame 2a at the other rotational speeds and the motor is stable. Also, it is apparent that the sound pressure is low in the case where the diameter of the legs 9a to 9c is 40 mm or 44 mm at any motor rotational speed as a whole. This result is similar in the case where the diameter of the intake port 4 is 34 to 36 mm as well as 35 mm, and the sound pressure is low in the case where the diameter of the legs 9a to 9c is 40 mm or 44 mm. Also, the diameter of the intake port 4 is 34 to 36 mm and thereby, it becomes easy to prevent the natural frequency of the legs from becoming a value close to a frequency of vibration of the motor and the noise can be reduced further.

Also, the natural frequency of the legs 9a to 9c depends on the width Ws and the thickness Wt as well as the length of the diameter Wd of the legs 9a to 9c.

FIG. 7 is a diagram showing a relation between the natural frequency of the legs and the width Ws of the legs in the first embodiment, and this graph shows the case where the thickness Wt of the legs 9a to 9c is 1.2 mm and the diameters Wd are respectively 35 mm, 40 mm and 46 mm. Also, FIG. 8 is a diagram showing a relation between the natural frequency of the legs and the thickness Wt of the legs in the first embodiment, and this graph shows the case where the diameter Wd of the legs 9a to 9c is 40 mm and the width Ws is 3 mm.

It is apparent from FIG. 7 that the natural frequency of the legs 9a to 9c becomes low as the width Ws of the legs 9a to 9c becomes small. This is because rigidity of the legs 9a to 9c becomes low as the width Ws of the legs 9a to 9c becomes small. Also, it is apparent from FIG. 8 that the natural frequency of the legs 9a to 9c becomes low as the thickness Wt of the legs 9a to 9c becomes thin. This is because rigidity of the legs 9a to 9c becomes low as the thickness Wt of the legs 9a to 9c becomes thin.

Next, other forms of the notches 10 and the legs 9a to 9c will be described. FIG. 9(a) is a top view of a fan frame provided with a notch substantially perpendicular to and a notch parallel to a longitudinal direction of the leg in the present embodiment, and FIG. 9(b) is a top view of a fan frame provided with plural layers of notches in the whole periphery of the intake port in the first embodiment.

By providing the fan frame with the notches 10 substantially perpendicular to and the notches 10 parallel to the longitudinal directions of the legs 9a to 9c as shown in FIG. 9(a), a direction of vibration propagating from the motor part to the longitudinal directions of the legs 9a to 9c is converted in substantially the perpendicular direction and thereby it can be made more difficult for the vibration to propagate to the connections 12 or the outside of the fan frame 2a. As a result, noise from the vibration of the motor part of the fan frame 2a can be reduced. Also, like the form of FIG. 3(a) described above, it is very easy to mold the form of FIG. 9(a), so that manufacture is simplified. Also, by providing the fan frame with the plural layers of notches 10 in the whole periphery of the intake port 4 as shown in FIG. 9(b), a direction of vibration propagating from the motor part to the longitudinal directions of the legs 9a to 9c is converted toward the whole periphery of the intake port 4 and thereby it can be made more difficult for the vibration to propagate to the connections 12 or the outside of the fan frame 2a. As a result, noise from the vibration of the motor part of the fan frame 2a can be reduced. Also, it is preferable to dispose the connections 12 so that the connections 12 are not placed as extensions of the longitudinal directions of the legs 9a to 9c in any form.

As described above, by providing the connections between the fan frame 2a and the legs 9a to 9c with the notches 10, the diameter Wd of the legs 9a to 9c is constructed longer than the diameter of the outside end 13 of the intake port 4 and rigidity is decreased and the natural frequency of the legs 9a to 9c can be decreased. By being constructed thus, the natural frequency of the legs 9a to 9c can be prevented from becoming a value close to an integral multiple of the fundamental frequency of vibration of the motor, and a situation in which vibration of the motor is resonated and amplified in the fan frame 2a and noise from the vibration is caused can be prevented.

Second Embodiment

In a blower in a second embodiment, a shape of the blower shown in the first embodiment is partially changed. Therefore, the same numerals show the same components in the first embodiment and the second embodiment.

FIG. 10 is a perspective view seen from the side of a fan frame of a centrifugal fan device in the second embodiment, and FIG. 11 is a perspective view seen from the side of a fan cover of the centrifugal fan device 1 in the second embodiment.

Numeral 2b is a fan cover. A fan case 2 is constructed of the fan cover 2b and a fan frame 2a. Here, a bottom surface and side surfaces of the fan frame 2a are integrally formed by, for example, resin molding or die casting of aluminum alloy. The fan cover 2b is molded in a plate shape by resin molding or punching molding of a metal material such as aluminum or stainless steel, and an intake port 4 with substantially a circular shape for sucking air is arranged in the center of the fan cover 2b. Then, a fan blade 5 is placed so as to be received with the fan blade pinched by the fan frame 2a and the fan cover 2b. Also, in a fixing part 15, the centrifugal fan device 1 of the second embodiment is fixed to an electronic device installed. Also, in the fan case 2, a thickness of the side of an exhaust port 3 is formed thicker than a thickness of the portion in which the fan blade 5 is positioned, and the exhaust port 3 is increased.

In the second embodiment, a diameter of an outside end 13 of the intake port 4 is 42 mm and a diameter Wd of legs 9a to 9c is 46 mm and thicknesses Wt are 1.0 to 1.8 mm. Also, a width of a notch 10 is 1 mm. A width Ws of the legs 9a and 9c is 4.2 mm and a width of the leg 9b is 6 mm. The reason why the thicknesses Wt have a range of 1.0 to 1.8 mm is because an inner peripheral end 14 of the side of a connection hole 11 of the intake port 4 requires a thick thickness. The thickness Wt of the inner peripheral end 14 is 1.8 mm, but the outside end 13 does not require the thickness Wt of 1.8 mm and is formed as thin as possible in order to decrease rigidity further. By thick forming the thickness Wt in the side of the inner peripheral end 14 of the side of the connection hole 11 of the intake port 4 and thin forming the thickness Wt in the side of the outside end 13 thus, rigidity of the legs 9a to 9c is decreased while maintaining strength and thereby, a natural frequency of the legs 9a to 9c can be prevented from becoming a value close to an integral multiple of a fundamental frequency of vibration of a motor, and a situation in which vibration of the motor is resonated and amplified in the fan frame 2a and noise from the vibration is caused can be prevented.

Also, the reason why the width Ws of the legs 9a and 9c differs from the width Ws of the leg 9b is because blade pass noise is caused in the vicinity of the exhaust port 3. That is, both of air sucked from the intake port 4 and air exhausted from the exhaust port 3 gather in the vicinity of the exhaust port 3 in the fan frame 2a. As a result, the amount of air increases and a turbulent flow tends to occur in a flow of air. Therefore, by making the leg 9b near to the exhaust port 3 thicker than the other legs 9a and 9c, the air sucked from the intake port 4 is decreased and adjusted and noise can be reduced. Thus, by providing the side of the outer peripheral end 13 of the fan frame 2a with the notches 10 for extending the legs 9a to 9c and further making the leg 9b, near to the exhaust port 3, of the plural legs 9a to 9c thicker than the other legs 9a and 9c, rigidity of the legs 9a to 9c is decreased without increasing the intake port 4 from a certain or more size, and the natural frequency of the legs 9a to 9c can be prevented from becoming the value close to the integral multiple of the fundamental frequency of vibration of the motor. As a result, the situation in which vibration of the motor is resonated and amplified in the fan frame 2a and noise from the vibration is caused can be prevented. Further, the amount of air sucked from the intake port 4 can be adjusted freely, so that the air in the vicinity of the exhaust port 3 is decreased and adjusted and noise can be reduced.

FIG. 12 is a top view of a centrifugal fan device in which a part of the centrifugal fan device of FIG. 10 is changed, and while the number of legs 9a to 9c is three, the number of fixing parts 15 is two and is smaller than the number of legs 9a to 9c.

Also, the fixing part 15 is disposed as an extension of the leg 9a. Generally, a cabinet for installing the blower has rigidity higher than that of the blower and accordingly, rigidity of the fixing part 15 becomes high. As a result, a resonance point of the fixing part 15 greatly deviates from a resonance point of the leg 9a, so that it becomes difficult for vibration to propagate to the cabinet and noise can be reduced.

FIG. 13 is a top view of a centrifugal fan device in which a part of the centrifugal fan device of FIG. 10 is changed, and while the number of legs 9a to 9c is three, the number of fixing parts 15 is four and is larger than the number of legs 9a to 9c. By making the number of fixing parts 15 larger than the number of legs 9a to 9c thus, the blower can be tightly fixed to the cabinet having rigidity higher than that of the blower. Therefore, a resonance point of the fixing part 15 greatly deviates from a resonance point of the legs 9a to 9c, so that it becomes difficult for vibration to propagate to the cabinet and noise can be reduced. Further, as the area of connection to the cabinet is large, the resonance point of the fixing part 15 greatly deviates from the resonance point of the legs 9a to 9c, so that it becomes difficult for vibration to propagate to the cabinet and the noise can be reduced.

Also, by forming a shape of the end of a notch 10 in substantially a circular arc shape, occurrence of an eddy is reduced and a flow can be smoothed. That is, when the end of the notch 10 is angular, the eddy tends to occur and a flow of air is inhibited and noise is caused. On the other hand, when the shape of the end of the notch 10 is formed in substantially the circular arc shape as described in the second embodiment, the occurrence of the eddy is reduced and the flow can be smoothed, so that the noise can be reduced.

Also, in the second embodiment, lengths of the notches 10 are the same (4 mm) in all the legs 9a to 9c. By equalizing the lengths of the notches 10 in all the plural legs 9a to 9c thus, rigidity can be decreased equally in all the legs 9a to 9c. As a result, the natural frequency of the legs 9a to 9c can be decreased equally, so that a good balance is achieved. By such a configuration, all the natural frequencies of the legs 9a to 9c can be prevented from becoming the value close to the integral multiple of the fundamental frequency of vibration of the motor, and the situation in which vibration of the motor is resonated and amplified in the fan frame 2a and noise from the vibration is caused can be prevented.

Also, in the second embodiment, widths of the notches 10 are the same (1 mm) in all the legs 9a to 9c. By equalizing the widths of the notches 10 in all the plural legs 9a to 9c thus, the natural frequency and rigidity of the legs 9a to 9c can be adjusted with a good balance. By such a configuration, all the natural frequencies of the legs 9a to 9c can well be prevented from becoming the value close to the integral multiple of the fundamental frequency of vibration of the motor, and the situation in which vibration of the motor is resonated and amplified in the fan frame 2a and noise from the vibration is caused can be prevented.

Also, in the second embodiment, the leg 9b differs from the legs 9a and 9c in the width Ws, so that the length of the notch 10 of the leg 9b with a wide width Ws may be set so as to differ from those of the other legs 9a and 9c. By such a configuration, rigidity can be decreased equally more precisely in all the legs 9a to 9c and the natural frequency of the legs 9a to 9c can be decreased equally, so that a better balance is achieved. Then, all the natural frequencies of the legs 9a to 9c can be prevented from becoming the value close to the integral multiple of the fundamental frequency of vibration of the motor, and the situation in which vibration of the motor is resonated and amplified in the fan frame 2a and noise from the vibration is caused can be prevented.

Also, when all the legs 9a to 9c have the same width Ws, it becomes easy to equally decrease rigidity in all the legs 9a to 9c and the natural frequency of the legs 9a to 9c can be decreased equally, so that it is easy to adjust the balance. As a result, all the natural frequencies of the legs 9a to 9c can be prevented from becoming the value close to the integral multiple of the fundamental frequency of vibration of the motor, and the situation in which vibration of the motor is resonated and amplified in the fan frame 2a and noise from the vibration is caused can be prevented.

FIG. 14 is a diagram showing a noise level every the number of rotations of a motor in the centrifugal fan device of FIG. 10 and a centrifugal fan device without a notch, and FIG. 15 is a diagram showing FFT analysis of noise in the centrifugal fan device of FIG. 10 and the centrifugal fan device without the notch. In addition, FIG. 15(a) shows the FFT analysis of noise in the centrifugal fan device without the notch and FIG. 15(b) shows the FFT analysis of noise in the centrifugal fan device of FIG. 10.

As is evident from FIGS. 14 and 15, the noise level of the centrifugal fan device with the notch 10 is lower than that of the centrifugal fan device without the notch 10. Particularly, the noise level reduces when the number of rotations is 3000 to 4000 r/min in FIG. 14. In addition, the notch 10 is constructed so that the diameter of the outside end 13 of the intake port 4 is 42 mm and the diameter Wd of legs 9a to 9c is 46 mm and the thicknesses Wt of the legs 9a to 9c are 1.0 to 1.8 mm and the width of the notch 10 is 1 mm and the width Ws of the legs 9a and 9c is 4.2 mm and the width of the leg 9b is 6 mm. Also, it is apparent that regions A1, B1, C1 have sharp values in FIG. 15(a) but the level reduces in regions A2, B2, C2 of FIG. 15(b). This is because connections between the fan frame 2a and the legs 9a to 9c are provided with the notches 10 and thereby the diameter Wd of the legs 9a to 9c is constructed longer than the diameter of the outside end 13 of the intake port 4 and rigidity is decreased and the natural frequency of the legs 9a to 9c is decreased. By being constructed thus, the natural frequency of the legs 9a to 9c can be prevented from becoming the value close to the integral multiple of the fundamental frequency of vibration of the motor, and the situation in which vibration of the motor is resonated and amplified in the fan frame 2a and noise from the vibration is caused can be prevented. Particularly, by being constructed so that the diameter of the outside end 13 of the intake port 4 is 42 mm and the diameter Wd of legs 9a to 9c is 46 mm and the thicknesses Wt of the legs 9a to 9c are 1.0 to 1.8 mm and the width of the notch 10 is 1 mm and the width Ws of the legs 9a and 9c is 4.2 mm and the width of the leg 9b is 6 mm, the situation in which vibration of the motor is resonated and amplified in the fan frame 2a and noise from the vibration is caused can well be prevented.

Third Embodiment

In a blower in a third embodiment, a shape of the blower shown in the first embodiment is partially changed. Particularly, a centrifugal fan device of the third embodiment is miniaturized as a whole since a fan blade becomes smaller than that of the first embodiment. Also, the same numerals show the same components in the first embodiment and the third embodiment.

FIG. 16 is a perspective view of the centrifugal fan device in the third embodiment, and FIG. 17(a) is a top view of the centrifugal fan device in the third embodiment and FIG. 17(b) is a sectional view taken on line A-A in FIG. 17(a). Also, in order to describe comparison with the third embodiment, FIG. 18(a) is a top view of a conventional centrifugal fan device and FIG. 18(b) is a sectional view taken on line A-A in FIG. 18(a).

In the third embodiment, a diameter of an outside end 13 of an intake port 4 is 26 mm and a diameter Wd of legs 9a to 9c is 37.5 mm and thicknesses Wt are 1.0 to 1.2 mm. Also, a width of a notch 10 is 1 mm.

The third embodiment is formed so that the thicknesses Wt have a range of 1.0 to 1.2 mm and the inside of the intake port 4 is 1.0 mm and the side of the notch 10 is 1.2 mm. Also, in the portion of formation of the notch 10 in the legs 9a to 9c, the thickness Wt changes from the thickness Wta (1.0 mm) of the inside of the intake port 4 to the thickness Wtb (1.2 mm) of the side of the notch 10. That is, the thickness Wt does not change in the range of formation of the intake port 4. By being constructed thus, an influence of intake air by change in the thickness Wt can be prevented. Also, the thickness Wt of the legs 9a to 9c in a wider range can be constructed thin, so that a natural frequency of the legs 9a to 9c is made lower and can be distanced from a value of an integral multiple of a fundamental frequency of vibration of a motor. In addition, the thickness Wt may be changed from the thickness Wta (1.0 mm) of the inside of the intake port 4 to the thickness Wtb (1.2 mm) of the side of the notch 10 over all the legs 9a to 9c. By being constructed thus, a sudden change in the thickness Wt can be prevented and strength of the legs 9a to 9c can be improved.

Also, the change in the thickness Wt is oblique in the third embodiment, but may be stepwise. The oblique shape can prevent the sudden change in the thickness Wt and improve the strength of the legs 9a to 9c. Also, the stepwise shape can thin construct the thickness Wt of the legs 9a to 9c in a wider range. Therefore, the natural frequency of the legs 9a to 9c is made lower and can be distanced from the value of the integral multiple of the fundamental frequency of vibration of the motor.

Also, in the miniature centrifugal fan device as shown in the third embodiment, a fan frame 2a itself is small, so that the legs 9a to 9c become very short and rigidity becomes high. As a result, the natural frequency of the legs 9a to 9c becomes a value closer to a frequency of vibration by a magnetic pole dependent on the number of rotations of a motor part, and vibration of the motor is resonated and amplified in the fan frame 2a and a noise problem of a device incorporated as noise from the vibration is caused.

Therefore, as shown in FIG. 17, in a circle made of a drive side inner peripheral end of the intake port 4, the legs 9a to 9c are formed along a tangential direction (a dotted line B of FIG. 17) of this circle and extend in the tangential direction (the dotted line B of FIG. 17) and thereby, lengths of the legs 9a to 9c can be maximized. As a result of this, lengths of the notches 10 can also be maximized with respect to the diameter Wd of the certain legs 9a to 9c.

That is, in order to provide the notches 10 and extend the legs 9a to 9c in the fan frame 2a with, a limited size, in the circle made of the drive side inner peripheral end of the intake port 4, the legs 9a to 9c could be formed along the tangential direction (the dotted line B of FIG. 17) of this circle and the notches 10 parallel to the legs 9a to 9c could be provided.

Also, in the third embodiment, the thickness Wt of the legs 9a to 9c changes from 1.0 mm to 1.2 mm by about 0.2 mm. In the third embodiment, changes of 0.2 to 0.4 mm could be made.

Next, a difference between natural frequencies of the third embodiment and a conventional embodiment will be described.

Table 1 shows the natural frequencies of the respective legs 9a to 9c in the case of respectively changing the thickness Wta of the inside of the intake port 4 of the legs 9a to 9c and the thickness Wtb (thickness of the fan frame 2a) of the side of the notches 10 of the legs 9a to 9c.

TABLE 1 THICKNESS THICKNESS NATURAL FREQUENCY No. Wta Wtb OF LEG 1 0.8 mm 0.8 mm 416.88 Hz 2 1.2 mm 0.8 mm 388.63 Hz 3 1.2 mm 1.0 mm 474.19 Hz 4 1.2 mm 1.2 mm 545.85 Hz

In Table 1, No. 2 and No. 3 are the centrifugal fan device of the third embodiment shown in FIG. 17, and No. 1 and No. 4 are the conventional centrifugal fan device shown in FIG. 18.

In FIG. 18, notches for extending legs 9a to 9c are not formed and the legs 9a to 9c extend toward a radial direction from the center of a circle formed by a drive side inner peripheral end of an intake port 4. Therefore, a length of the legs 9a to 9c becomes short and rigidity becomes high, so that a natural frequency becomes high.

As is evident from Table 1, as the thickness Wta becomes thick, rigidity of the drive side inner peripheral end of the intake port 4 becomes high and as the thickness Wtb becomes thin, rigidity in the fan frame 2a becomes high. As a result, as is evident from comparison between No. 1 and No. 2, rigidity of the legs 9a to 9c becomes low and the natural frequency can be decreased.

Also, as is evident from comparison between No. 2 and No. 3, the thinner thickness Wtb can decrease the natural frequency of the legs 9a to 9c. Also, as is evident from comparison between No. 1 and No. 4, the thinner thickness Wt as a whole can decrease the natural frequency.

As described above, a fan blade extending in a centrifugal direction from an outer peripheral surface of a hub part having a cylindrically-shaped outer peripheral surface, a driving part for supporting and driving the fan blade, and a fan frame which supports the driving part and has an intake port are included, and the fan frame includes plural legs for connecting a drive side inner peripheral end of the intake port to an outer peripheral end opposed to the inner peripheral end, and a side of the outer peripheral end of the fan frame is provided with a notch for extending the leg, and thicknesses of both ends of the leg are formed so that the thickness of a side of the driving part becomes thinner than the thickness of a side of the notch and thereby, a natural frequency can be made lower than the case of forming a leg with a constant thickness. As a result, the natural frequency can be prevented from becoming a value close to an integral multiple of a fundamental frequency of vibration of a motor. Also, the natural frequency can be decreased while increasing strength of the side of the notch of the leg.

Also, thicknesses of both ends of the leg change obliquely so as to become thin from a side of the notch toward a side of the driving part and thereby, a sudden change in the thickness can be prevented and strength of the leg can be improved.

Also, thicknesses of both ends of the leg change stepwise so as to become thin from a side of the notch toward a side of the driving part and thereby, the thickness of the leg in a wider range can be thin constructed. Therefore, the natural frequency of the leg is made lower and can further be distanced from a value of the integral multiple of the fundamental frequency of vibration of the motor.

Also, thicknesses of both ends of the leg change in a portion notched in the leg so as to become thin from a side of the notch toward a side of the driving part and thereby, an influence of intake air by change in the thickness can be prevented.

Also, the leg and the notch extend in a tangential direction of the drive side inner peripheral end of the intake port and thereby, lengths of the leg and the notch can be maximized with respect to the diameter of the certain legs. As a result, rigidity of the leg is minimized and the natural frequency of the leg can be prevented from becoming the value close to the integral multiple of the fundamental frequency of vibration of the motor.

The invention is a blower including a fan blade extending in a centrifugal direction from an outer peripheral surface of a hub part having a cylindrically-shaped outer peripheral surface, a driving part for supporting and driving the fan blade, and a fan frame which supports the driving part and has an intake port, characterized in that the fan frame includes a leg for connecting a drive side inner peripheral end of the intake port to an outer peripheral end opposed to the inner peripheral end, and a side of the outer peripheral end of the fan frame is provided with a notch for extending the leg, and by extending the legs and increasing a diameter of the legs, rigidity is decreased and a natural frequency of the leg can be adjusted, so that the natural frequency of the leg can be prevented from becoming a value close to a frequency of vibration of a motor and noise can be reduced.

Also, the fan frame is provided with a connection for connecting the fan frame to a fan cover for pinching and supporting the fan blade together with the fan frame, and the connection is placed in a position other than an extension of the leg and thereby, an increase in noise from the vibration of the motor can be reduced further.

Also, the notch is parallel to a longitudinal direction of the leg and thereby, a metallic mold for molding is simplified and manufacture is facilitated.

Also, the leg near to an exhaust port among the plural legs is formed thicker than the other legs and thereby, rigidity of the legs is decreased without increasing the intake port from a certain or more size, and the natural frequency of the legs can be prevented from becoming a value close to an integral multiple of a fundamental frequency of vibration of the motor. As a result, a situation in which vibration of the motor is resonated and amplified in the fan frame and noise from the vibration is caused can be prevented. Further, the amount of air sucked from the intake port can be adjusted freely, so that the air in the vicinity of the exhaust port is decreased and adjusted and noise can be reduced.

Also, a length of the slit with which the leg near to the exhaust port is provided differs from that of the slit with which the other leg is provided and also an end of the slit has substantially a circular arc shape and thereby, occurrence of an eddy is reduced and a flow can be smoothed, so that noise can be reduced.

Also, in thicknesses of both ends of the leg, the thickness of a side of the driving part is thinner than the thickness of a side of the slit and thereby, the natural frequency can be made lower than the case of forming a leg with a constant thickness. As a result, the natural frequency can be prevented from becoming the value close to the integral multiple of the fundamental frequency of vibration of the motor. Also, the natural frequency can be decreased while increasing strength of the side of the notch of the leg.

Also, thicknesses of both ends of the leg change obliquely so as to become thin from a side of the slit toward a side of the driving part and thereby, a sudden change in the thickness can be prevented and strength of the leg can be improved.

Also, thicknesses of both ends of the leg change stepwise so as to become thin from a side of the slit toward a side of the driving part and thereby, the thickness of the leg in a wider range can be thin constructed. Therefore, the natural frequency of the leg is made lower and can further be distanced from the value of the integral multiple of the fundamental frequency of vibration of the motor.

Also, thicknesses of both ends of the leg change in a portion notched in the leg so as to become thin from a side of the slit toward a side of the driving part and thereby, an influence of intake air by change in the thickness can be prevented.

Also, the leg and the slit extend in a tangential direction of the drive side inner peripheral end of the intake port and thereby, lengths of the leg and the notch can be maximized with respect to the diameter of the certain legs. As a result, rigidity of the leg is minimized and the natural frequency of the leg can be prevented from becoming the value close to the integral multiple of the fundamental frequency of vibration of the motor.

Also, the invention includes a fan blade extending in a centrifugal direction from an outer peripheral surface of a hub part having a cylindrically-shaped outer peripheral surface, a driving part for supporting and driving the fan blade, and a fan case which supports the driving part and has an intake port and an exhaust port, and the fan case includes plural legs for connecting a drive side inner peripheral end of the intake port to an outer peripheral end opposed to the inner peripheral end, and a side of the outer peripheral end of the fan frame is provided with a slit for extending the leg and thereby, rigidity is decreased by extending the legs and increasing a diameter of the legs and a natural frequency of the leg can be adjusted, so that the natural frequency of the leg can be prevented from becoming a value close to a frequency of vibration of a motor and noise can be reduced.

Also, the fan case includes a fixing part for fixing the blower to a cabinet for installing the blower, and the fixing part is positioned as an extension of the leg and thereby, the cabinet for installing the blower generally has rigidity higher than that of the blower and accordingly, rigidity of the fixing part becomes high. As a result, a resonance point of the fixing part greatly deviates from a resonance point of the leg, so that it becomes difficult for vibration to propagate to the cabinet and noise can be reduced.

Also, the fan case includes a fixing part for fixing the blower to a cabinet for installing the blower, and the number of legs is smaller than the number of fixing parts and thereby, the blower can be tightly fixed to the cabinet having rigidity higher than that of the blower. Therefore, a resonance point of the fixing part greatly deviates from a resonance point of the leg, so that it becomes difficult for vibration to propagate to the cabinet and noise can be reduced. Further, as the area of connection to the cabinet is large, the resonance point of the fixing part greatly deviates from the resonance point of the leg, so that it becomes difficult for vibration to propagate to the cabinet and the noise can be reduced.

Also, the plural slits are provided and all the plural slits have substantially the same length and thereby, the natural frequencies of the respective legs can be adjusted with a good balance.

Also, the plural slits are provided and all the plural slits have substantially the same width and thereby, rigidities of the respective legs can be decreased equally, so that the natural frequencies can be adjusted with a good balance.

According to the blower of the invention, rigidity is decreased by increasing the diameter of the legs and the natural frequency of the leg is made lower than the frequency of vibration of the motor and noise can be reduced, so that the invention is useful as the blower for cooling an electrical device such as a notebook PC.

The disclosure of Japanese Patent Application No. 2010-045159 filed Mar. 2, 2010, Japanese Patent Application No. 2010-174122 filed Aug. 3, 2010, and Japanese Patent Application No. 2010-184601 filed Aug. 20, 2010, including specification, drawings and claims is incorporated herein by reference in its entirety.

Claims

1. A blower including:

a fan blade extending in a centrifugal direction from an outer peripheral surface of a hub part having a cylindrically-shaped outer peripheral surface;
a driving part for supporting and driving the fan blade; and
a fan frame which supports the driving part and has an intake port, characterized in that the fan frame includes a leg for connecting a drive side inner peripheral end of the intake port to an outer peripheral end opposed to the inner peripheral end, and a side of the outer peripheral end of the fan frame is provided with a slit for extending the leg.

2. The blower as claimed in claim 1, wherein the fan frame is provided with a connection for connecting the fan frame to a fan cover for pinching and supporting the fan blade together with the fan frame, and the connection is placed in a position other than an extension of the leg.

3. The blower as claimed in claim 1, wherein the slit is parallel to a longitudinal direction of the leg.

4. The blower as claimed in claim 1, wherein the leg near to an exhaust port among the plural legs is formed thicker than the other legs.

5. The blower as claimed in claim 4, wherein a length of the slit with which the leg near to the exhaust port is provided differs from that of the slit with which the other leg is provided.

6. The blower as claimed in claim 1, wherein an end of the slit has substantially a circular arc shape.

7. The blower as claimed in claim 1, wherein in thicknesses of both ends of the leg, the thickness of a side of the driving part is thinner than the thickness of a side of the slit.

8. The blower as claimed in claim 6, wherein thicknesses of both ends of the leg change obliquely so as to become thin from a side of the slit toward a side of the driving part.

9. The blower as claimed in claim 7, wherein thicknesses of both ends of the leg change stepwise so as to become thin from a side of the slit toward a side of the driving part.

10. The blower as claimed in claim 7, wherein thicknesses of both ends of the leg change in a portion notched in the leg so as to become thin from a side of the slit toward a side of the driving part.

11. The blower as claimed in claim 1, wherein the leg and the slit extend in a tangential direction of the drive side inner peripheral end of the intake port.

12. A blower including:

a fan blade extending in a centrifugal direction from an outer peripheral surface of a hub part having a cylindrically-shaped outer peripheral surface;
a driving part for supporting and driving the fan blade, and
a fan case which supports the driving part and has an intake port and an exhaust port, characterized in that the fan case includes plural legs for connecting a drive side inner peripheral end of the intake port to an outer peripheral end opposed to the inner peripheral end, and a side of the outer peripheral end of the fan frame is provided with a slit for extending the leg.

13. The blower as claimed in claim 12, wherein the fan case includes a fixing part for fixing the blower to a cabinet for installing the blower, and the fixing part is positioned as an extension of the leg.

14. The blower as claimed in claim 12, wherein the fan case includes a fixing part for fixing the blower to a cabinet for installing the blower, and the number of legs is smaller than the number of fixing parts.

15. The blower as claimed in claim 1, wherein the plural slits are provided and all the plural slits have substantially the same length.

16. The blower as claimed in claim 1, wherein the plural slits are provided and all the plural slits have substantially the same width.

17. A fan frame for housing a fan blade, including an intake port for sucking air by the fan blade, wherein the fan frame includes a leg for connecting an inner peripheral end of the intake port to an outer peripheral end opposed to the inner peripheral end, and a side of the outer peripheral end of the fan frame is provided with a slit for extending the leg.

18. A blower including:

a fan blade extending in a centrifugal direction from an outer peripheral surface of a hub part having a cylindrically-shaped outer peripheral surface, and
a fan frame which receives the fan blade and has an intake port, wherein the fan frame includes a leg for connecting a drive side inner peripheral end of the intake port to an outer peripheral end opposed to the inner peripheral end, and a side of the outer peripheral end of the fan frame is provided with a slit for extending the leg.
Patent History
Publication number: 20110217161
Type: Application
Filed: Feb 28, 2011
Publication Date: Sep 8, 2011
Applicant: PANASONIC CORPORATION (Osaka)
Inventor: Koji YOSHIOKA (Oita)
Application Number: 13/037,070
Classifications
Current U.S. Class: Scroll-type Casing (415/204)
International Classification: F01D 25/24 (20060101);