Fluid pump apparatus

Abstract

In an air supply pump, having an electric motor and a blower driven by the electric motor, the blower has an impeller having multiple blades for compressing and pumping out the air. A value (F) obtained by a formula (F=N×S) is made to be higher than the audible frequency band to the human beings, wherein “N” means number of blades of the impeller, and “S” means a number of rotation of the impeller for each second at a normal rotational speed. (“×” is a symbol for a mathematical multiplication.) The frequency (F=N×S) of fan noises at a primary peak appears at higher frequencies out of the audible frequency band, so that the noises audible to the human beings can be reduced.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2004-109909 filed on Apr. 2, 2004, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to a fluid pump apparatus, which compresses and pumps out fluid by rotation of an impeller having multiple blades, and in particular to an air supply pump in which fan noises can be reduced.

BACKGROUND OF THE INVENTION

The following technical features are known in the art to reduce fan noises of an electrical air pump, for example, as disclosed in Japanese Patent Publication No. H9-209997;

• • (1) pitch angles of respective blades are designed to be non-uniform to each other, and
  • (2) positions of blades, which are formed on both sides of an impeller, are designed to be displaced by a half pitch in a rotational direction of the impeller, at a position at which a modulation point is zero.

According to the above conventional technical features, fan noises generated at the both sides of the impeller are interfered with each other to reduce sonic energies and thereby the fan noises.

According to the above conventional method, however, multiple noise peaks are de-concentrated at low frequencies and the noises of such low frequencies may be generated, whereas noise peaks at high frequencies can be suppressed at a normal (constant) rotational speed of the electrical air pump. As a result, the total fan noises in the audible frequency band to human beings can not be reduced.

SUMMARY OF THE INVENTION

The present invention is made in view of the above problems, and it is an object of the present invention to provide a fluid pump apparatus which reduces noises audible to the human beings to a small amount, by moving peak frequency of the noises to a higher value out of the audible frequency band.

According to a feature of the present invention, a value (F) obtained by a calculation of a formula (F=N×S) is made to be higher than the audible frequency band to the human beings, wherein “N” means number of blades of an impeller of the fluid pump apparatus, and “S” means a number of rotation of the impeller for each second at a normal (constant) rotational speed. (“×” is a symbol for a mathematical multiplication.)

The frequency (N×S) of fan noises at a primary peak, according to the above feature, appears at higher frequencies out of the audible frequency band, so that the noises audible to the human beings can be reduced.

According to another feature of the present invention, fin pitch angles of the respective blades are made to be equal to each other.

The peak frequencies of the fan noises can be centralized on one point (frequency) according to such feature, and the variation of the peak frequency at the primary peak is avoided. As a result, the frequency of the fan noises at the primary peak can be completely moved to the higher frequency out of the audible frequency band.

According to a further feature of the present invention, the number of blades of the impeller is so made to be a prime number, so that fan noises are prevented from appearing at other frequencies than that of the primary peak. As a result, the fan noises of 0.5 peak are prevented from generating in the audible frequency band to the human beings. The peak frequencies of the fan noises are prevented from de-concentrating and the peak frequency of the fan noises are prevented from generating in audible frequency band.

According to a still further feature of the present invention, a blower is formed by a vortex flow type blower, which has a vortex flow chamber and an impeller rotatably supported in the vortex flow chamber. A volume decreasing means, such as a groove or an inclined surface, is formed in a partitioning portion, which is formed in the vortex flow chamber between a starting portion and an ending portion of the fluid flow.

According to the volume decreasing means, a cross sectional area of the vortex flow chamber is gradually decreased at the ending portion of the vortex flow chamber in a rotational direction of the impeller (blades), so that pressure variation of the fluid is decreased when the blades come across the partitioning portion, to thereby reduce the fan noise (wind noise). With this arrangement, the fan noises can be reduced, in particular, when the primary peak of the fan noises passes through the audible frequency band during periods of starting and stopping the air pump.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:

FIG. 1 is a cross-sectional view of an air supply pump, according to an embodiment of the present invention;

FIG. 2 is a partial side view of a blower housing of the air supply pump shown in FIG. 1;

FIG. 3A is an enlarged partial front view of an impeller of the air supply pump shown in FIG. 1;

FIG. 3B is a partial side view of the impeller shown in FIG. 3A;

FIG. 4 is a graph showing noise level according to the present invention; and

FIG. 5 is a graph showing noise level according to the conventional apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

The present invention will be explained below with reference to the embodiment, in which the present invention is applied to an electrical air supply pump, as shown in FIGS. 1 to 3.

The air supply pump compresses air and pumps out the compressed air. The air supply pump is used, for example, in a secondary air supply system for an automotive engine, wherein the air supply pump supplies the compressed air into an exhaust pipe of the engine at an upstream side of a catalyst for purifying the exhaust gas.

The air supply pump, which comprises a blower device having a double-blade and vortex flow type impeller, is shown as an example in the first embodiment.

The air supply pump, as shown in FIG. 1, comprises an electric motor 1, the above mentioned blower device 2, and an air duct portion 4 in which a filter 3 is arranged.

(Electric Motor)

The electric motor 1 of this embodiment is a DC motor, which comprises a stator 7 having a cylindrical yoke 5 and multiple permanent magnets 6 fixed to an inner peripheral surface of the yoke 5, a rotor (armature) 8 arranged in the stator 7, a brush assembly 12 arranged in a motor housing 11 and having multiple brushes 10 which are in a sliding contact with a commutator 9 provided in the armature 8.

The armature 8 comprises a rotational shaft 13 rotatably supported by the motor housing 11 and the stator 7, an armature core 14 fixed to the shaft 13, an armature coil wound on the armature core 14, and the commutator 9 electrically connected to the armature coil.

The brush assembly 12 comprises multiple brushes 10 to be brought into the sliding contact with the commutator 9, a brush holder 15 movably holding the brushes 10 therein, multiple springs 16 for urging the brushes 10 toward the commutator 9, and a spacer 17 for firmly supporting the brush holder 15 in the motor housing

(Blower Device)

The blower device 2 has an impeller 21 of a double-blade vortex flow type, and a blower housing 22.

The impeller 21 is formed into a disc shape, wherein multiple blades (fins) 21a are formed at an outer periphery and at both sides of the disc-shaped impeller 21. A center portion of the impeller 21 is connected to an end of the rotational shaft 13 of the electric motor 1 by a connecting means 23, so that the impeller 21 can be rotated integrally with the rotational shaft 13.

The blower housing 22 comprises a first casing 25 fixed to the motor housing 11 by means of screws 24, and a second casing 27 fixed to the first casing 25 by clips 26. A vortex flow chamber (fluid flow chamber) 28 is formed in the blower housing 22, for compressing the air by the rotation of the multiple blades 21a of the impeller 21.

The vortex flow chamber 28 is formed into a C-shaped space formed at the outer peripheral portion of the impeller 21 (along the multiple blades formed at the outer periphery of the impeller), so that the air flows along this vortex flow chamber.

As shown in FIG. 2, an air inlet port 31 is formed in the first casing 25 of the blower housing 22, at a starting portion 28a of the vortex flow chamber 28 (a portion at which the blades 21a come into the vortex flow chamber in accordance with the rotation of the impeller 21). The air inlet port 31 is communicated with a downstream side of the air duct portion 4, as shown in FIG. 1.

An air outlet port 32 is formed in the blower housing 22 at an ending portion 28b of the vortex flow chamber 28 (a portion at which the blades 21a exit from the vortex flow chamber in accordance with the rotation of the impeller), so that the compressed air is discharged through the air outlet port 32.

(Operation of the Electrical Air Pump)

When the electric motor 1 is connected to a battery (not shown) of a vehicle through a relay, the electric power is supplied to the electric motor 1, and the shaft 13 and the impeller 21 are rotated together.

When the impeller 21 is rotated, the multiple blades 21 are circumferentially moved (rotated) so that the air in the vortex flow chamber 28 is compressed, while the air is moved from the starting portion 28a to the ending portion 28b. Since a negative pressure is generated at the air inlet port 31, the air is guided (sucked) from the air duct portion 4 through the air filter 3 toward the air inlet port 31. On the other hand, since a positive pressure is generated at the air outlet port 32, the air compressed in the vortex flow chamber 28 is discharged from the air outlet port 32.

A rotational speed, at which the electric motor 1 is normally operated, is called as “a normal rotational speed”. According to the embodiment, operational modes of the electric motor 1 is either “ON state (supply of the electric power)” or “OFF state (cut off of the electric power)”. When the electric power is supplied to the electric motor 1, and the rotational shaft 13 and the impeller 21 are rotated in a stable condition (at a stable constant speed), the rotational speed of the stable condition corresponds to the “normal rotational speed”.

(Characteristic Features of the Embodiment)

According to the electric motor 1 of the embodiment, a peak frequency of fan noise is moved to a higher frequency side out of an audible frequency band, so that a noise level audible to human beings is reduced.

In the electrical air pump of the embodiment, the multiple blades (fins) 21a are rotated in one direction and each of the blades 21a gives flow velocity to the air. A partitioning portion 33 is formed in the blower housing 22 for partitioning the vortex flow chamber 28 between the starting and ending portions 28a and 28b, as shown in FIG. 2. As a result,

• (1) the pressure of the air is varied each time when the compressed air is guided to the air outlet port 32 by the respective blades 21a, and thereby pulsation noise is generated, and
• (2) a wind noise is generated each time when the respective blades 21a are moved from the ending portion 28b to the partitioning portion 33.

Since the above pulsation noise is generated by variation of the air pressure, when the respective blades 21a come across the air outlet port 32, the frequency of the pulsation noise mainly depends on a cycle during which the blade 21a comes across the air outlet port 32.

In a similar manner, the wind noise is generated by the variation of the air pressure, when the respective blades 21a come across the partitioning portion 33. The frequency of the wind noise mainly depends on a cycle during which the blade 21a comes across the partitioning portion 33.

As above, each of the pulsation noise and the wind noise is such a noise, wherein a frequency of the noise depends on the cycle during which the respective blades come across fixed portions (the air outlet port 32 and the partitioning portion 33). A primary peak of the fan noise (the pulsation noise and the wind noise) appears at the cycle during which the blade 21a comes across the fixed portions 32 and 33).

Namely, the primary peak of the fan noise appears at a frequency F (Hz), calculated by a multiplication of N and S, wherein N is a number of blades 21a, and S is a rotational number of the electric motor for each second (rotation/sec).

In the electrical air pump according to the embodiment, the cycle (frequency) during which the blade 21a comes across the fixed portions 32 and 33 is designed at a higher value than the audible frequency band when the electric motor 1 is operated at the “normal rotational speed” (at which the electric motor 1 is stably rotated at the constant speed with current supply).

Namely, the frequency F is made at a higher value than the audible frequency band Fh (Hz) (N×S=F≧Fh) to the human beings, wherein

• • the frequency “F” is calculated by a formula “F”=“N”דS”,
  • “N” is the number of the blades 21a,
  • “S” is the rotational number of the electric motor 1 for each second (rotation/sec), when the electric motor 1 is operated at the “normal rotational speed”, and
  • × is a symbol for multiplication.

The “audible frequency band” means a range of frequency within which the ordinal human being can hear the noise, whereas “the higher value than the audible frequency band” means a frequency at which the ordinal human being can not hear the noise. For example, the higher value is more than 20 kHz.

FIGS. 4 and 5 show the noise levels with respect to different noise frequencies, wherein FIG. 4 is a graph of the present invention and FIG. 5 is a graph of the conventional apparatus. As understood from those graphs, the frequency of the primary peak appears at a frequency (around 20.5 kHz) higher than 20 kHz, an upper limit of the audible frequency band, as shown in FIG. 4. On the other hand, the frequencies of the primary and 0.5 peaks appear within the audible frequency band, as shown in FIG. 5, respectively at the frequency of 13 kHz and 6.5 kHz. As is also understood from FIG. 4, the frequency of 0.5 peak does not appear in the present invention.

As a result, the fan noise (the pulsation noise and the wind noise) audible to the human beings is reduced to a smaller value.

As described above, the blades 21a are formed at the both sides of the impeller 21. And the fan noise (the pulsation noise and the wind noise) is generated at the both sides of the impeller 21.

The respective numbers of blades 21a of the both (front and back) sides of the impeller 21 are designed to meet the formula (“N”דS”=“F”≧“Fh”). In this embodiment, the number of blades of the front side is made to be the same to that of the back side, wherein the number is 79.

According to the embodiment, fin pitch angles between the neighboring blades 21a on one side (e.g. the front side) are made equal to each other over the entire periphery of the impeller 21, as shown in FIG. 3A. This is also true on the other (back) side.

Further, as shown in FIG. 3B, the position of the blades 21a of one side (the front side) in the rotational direction is the same to that of the other (back) side. However, the position of the blades of one side can be displaced by a half pitch (at a point at which modulation point is zero) from the blades of the other side.

As a result, the peak frequencies of the fan noises can be centralized to one point (frequency) of the primary peak, and the frequency of the primary peak is not varied at the normal (constant) rotational speed of the electric motor 1. And thereby, the frequency of the primary peak can be completely moved to the higher range out of the audible frequency band to the human beings.

According to the embodiment, the number of the blades 21a of the respective sides of the impeller is selected at a prime number, for example at the prime number of 79.

In the embodiment, the frequency “F” calculated by “N”דS”(=79דS”) is designed to be 20.5 kHz. Namely, in the embodiment, the impeller 21 is so designed that the primary peak of the fan noise appears at the frequency of 20.5 kHz.

As a result, the fan noises of a half (½) peak or a one-fourth (¼) peak can be also prevented from appearing in the audible frequency band to the human beings. Namely, the de-concentration of the noise peaks can be prevented and thereby the noise peaks are prevented from appearing in the audible frequency band.

As shown in FIG. 2, multiple (two)grooves 34 are formed in the partitioning portion 33 of the blower housing 22 at a side close to the ending portion 28b of the vortex flow chamber 28, so that the volume of the vortex flow chamber 28 is gradually decreased as the impeller 21 is rotated. In other words, a cross sectional area of the grooves 34 is gradually decreased in a rotational direction of the impeller 21. The grooves 34 are formed in the both partitioning portions 33 respectively opposing to the side of the impeller 21.

The number of grooves 34 shall not be limited to two, and one or three, or any other number of grooves can be formed. The groove or grooves can be further replaced by an inclined surface formed on the partitioning portions 33, at such positions at which the blades 21a and/or the outer periphery of the blades come across the partitioning portions 33.

As a result, the pressure change to be generated when the blades 21a come across the partitioning portions 33 can be suppressed to a smaller amount, and thereby the wind noise can be reduced.

Furthermore, when the fan noises of the primary peak pass through the audible frequency band during periods of starting and stopping the operation of the electrical air pump, the fan noises can be likewise reduced.

The grooves and the inclined surface are collectively referred to as “a volume decreasing means” in this specification.

(Other Modifications)

In the above embodiment, the present invention is applied to the electrical air pump which compresses and pumps out the air. However, the present invention can be used in other pump devices which compress and pump out gas other than the air, or which compress and pump out a mixture of gas and liquid (in a steam phase).

Furthermore, in the above embodiment, the double-blade impeller is used. The present invention can be also applied to the blower having a single-blade impeller, in which multiple blades are formed on one side of the impeller.

The present invention can be further applied to a centrifugal type blower or an axial flow type blower, other than the vortex flow type blower.

Claims

1. A fluid pump apparatus comprising:

an electric motor;

a blower operatively connected to and driven by the electric motor, wherein the blower has a fluid flow chamber and an impeller rotatably supported in the fluid flow chamber, and the impeller has multiple blades,

wherein a value “F” obtained by a formula of “F=N×S” is made to be a higher value than an audible frequency band,

wherein

“N” is a number of blades, and

“S” is a rotational number of the electric motor for each second at its normal rotational speed.

(“×” is a symbol of a mathematical multiplication.)

2. A fluid pump apparatus according to claim 1, wherein

fin pitch angles of the respective blades are made to be equal to each other.

3. A fluid pump apparatus according to claim 1, wherein

the number of the blades is made to be a prime number.

4. A fluid pump apparatus according to claim 1, wherein

the blower has a blower housing forming the fluid flow chamber therein,

a partitioning portion is formed in the fluid flow chamber between a starting portion and an ending portion of the fluid flow, and

a volume decreasing means is formed in the partitioning portion adjacent to the ending portion of the fluid flow chamber, so that across sectional area of the fluid flow chamber is gradually decreased at the ending portion in a rotational direction of the impeller.