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Title:
ELECTROMOTIVE COMPRESSOR
Document Type and Number:
WIPO Patent Application WO/2019/096890
Kind Code:
A2
Abstract:
The present invention relates to an electromotive compressor comprising: a pair of compressor housings (7, 8) not only providing suction ports (26) in each of the center means thereof, but also an annular diffuser means (27) surrounding these suction ports (26) as well as a scrolling means (28), in addition to said suction port (26) being symmetrically disposed so as to face in opposite directions; and an electric motor (3) disposed between this pair of compressor housings (7, 8); and a pair of impellers (21, 22) attached symmetrically so as to face in mutually opposite directions on both terminal means of the revolving axis (17) of this electric motor (3); and a symmetrically configured exit tube (4) extending in a substantially U shape so as to mutually meet the exits of the scroll means (28) of the above described pair of compressor housings (7, 8), in addition to having a single spew port (5) in the center thereof.

Inventors:
NAOKI MATSUZWA (JP)
HANUO IWANO (JP)
Application Number:
PCT/EP2018/081342
Publication Date:
May 23, 2019
Filing Date:
November 15, 2018
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
MAHLE INT GMBH (DE)
MAHLE FILTER SYSTEMS JP CORP (JP)
International Classes:
F04D17/10; F04D25/06; F04D25/08; F04D25/16; F04D29/051; F04D29/057; F04D29/059; F04D29/26; F04D29/30; F04D29/44; F04D29/66
Foreign References:
JP2011214523A2011-10-27
Attorney, Agent or Firm:
BRP RENAUD UND PARTNER MBB (DE)
Download PDF:
Claims:
Patent claims

Claim 1

An electromotive compressor of the present invention

comprising : a pair of compressor housings not only providing suction ports in each of the center means thereof, but also an annular diffuser means surrounding these suction ports as well as a scrolling means, in addition to said suction port being symmetrically disposed so as to face in opposite directions , and an electric motor disposed between this pair of compressor housings, and a pair of impellers attached symmetrically so as to face in mutually opposite directions on both terminal means of the revolving axis of this electric motor, and a symmetrically configured exit tube extending in a substantially U shape so as to mutually meet the exits of the scroll means of the above described pair of compressor housings, in addition to having a single spew port in the center thereof.

Claim 2

The electromotive compressor claimed in claim 1

characterized by said pair of impellers having mutually identical impellers, in addition to, being attached to said revolving axis so as to have a mutually different phase of each of the impeller blades.

Claim 3

The electromotive compressor claimed in claim 1

characterized by said pair of impellers having mutually equivalent revolving member shapes as determined by the outer edge of the blades, in addition to, the number of blades on each being mutually different.

Claim 4

The electromotive compressor claimed in any one of claims 1 ~ 3 characterized by the attachment of a cylinder shaped stator housing storing the stator of said electric motor between said pair of compressor housings, and these stator housings provide cooling fins for use in air cooling or a water jacket for use in liquid cooling.

Claim 5

The electromotive compressor claimed in any one of claims 1 ~ 4 characterized by being air compressors supplying air as the oxidant to fuel-cell stacks mounted on an automobile.

Claim 6

The electromotive compressor claimed in any of the preceding claims characterized in that the revolving axis comprises a support mounting. Claim 7

The electromotive compressor claimed in claim 6

characterized by the support mounting being configured as a floating support mounting.

Claim 8

The electromotive compressor claimed in claim 6 or 7

characterized by the revolving axis being supported by rolling bearings, preferable by deep groove ball bearings.

Claim 9

The electromotive compressor claimed in one of claims 6 to 8 characterized by the revolving axis being mounted to two end plates, such that the revolving axis is being able to be rotated .

Claim 10

The electromotive compressor claimed in claim 8 or 9, if related to claim 8, characterized in an outer ring of the rolling bearing being fixed at one of the end plates in an axial direction towards the impeller being located close by.

Claim 11

The electromotive compressor claimed in claim 10

characterized in an inner ring of the rolling bearing being fixed on the revolving axis by a first flange means of the revolving axis or by a first locking ring in a direction towards the more far off impeller axially. Claim 12

The electromotive compressor claimed in one of the claims 8 to 11, if related to claim 8, characterized in the bearings being arranged in an x-arrangement.

Claim 13

The electromotive compressor claimed in any of the preceding claims characterized in both of the impellers are each supported by the revolving axis towards the interior of the stator housing, particularly by a flange means of the revolving axis or a locking ring.

Claim 14

The electromotive compressor claimed in claim 13

characterized in the impellers being clamped against the second flange means of the shaft or the second locking ring each by a fastener axially.

Claim 15

The electromotive compressor claimed in claim 14

characterized in an internal thread comprised by the

fastener and an outer thread on the revolving axis exerting an axial force to the respective impeller.

Claim 16

The electromotive compressor claimed in claims 14 or 15 characterized in the fastener comprising an outer contour, which extends off the respective impeller and which is tapered towards the suction port closest by said impeller, wherein the outer contour preferably is reduced towards the shaft in a sharp angle.

Claim 17

The electromotive compressor claimed in claim 16

characterized in the fastener configuring a transition towards the respective impeller by its outer contour, wherein the transition comprises no shoulder, such that the flow of the gas is not influenced by the reduction of the diameter within the transition.

Claim 18

The electromotive compressor claimed in one of the claims 9 to 17 characterized in one of the end plates being connected to the stator housing by screws.

Claim 19

The electromotive compressor claimed in one of the claims 9 to 18 characterized in one of the end plates being screwed to the compressor housing.

Claim 20

The electromotive compressor claimed in any of claims 9 to 19 characterized in the end plates comprising pressure compensation openings which connect the interior of the stator housing to the interior of each of the compressor housings .

Claim 21

The electromotive compressor claimed in claim 20

characterized in the pressure compensation openings being located out of the respective bearing area radially.

Claim 22

The electromotive compressor claimed in any of the claims 10 to 21 characterized in the diffuser means of the compressor housing being sealed against a surrounding by a sealing means located between the compressor housing and the end plate gas-tightly.

Claim 23

The electromotive compressor claimed in any of claims 9 to 22 characterized in the end plates being connectable with the compressor housings by screws.

Claim 24

The electromotive compressor claimed in claim 23

characterized in the screws being arranged

- radially out of the stator housing

- radially within the respective end plate or compressor housing,

wherein the arrangement of the screws is extended in the axial direction. Claim 25

The electromotive compressor claimed in claim 24

characterized in the screws being able to penetrate screw slots which are located in an area out of the stator housing radially and axially within the end plates.

Description:
ELECTROMOTIVE COMPRESSOR

TECHNICAL FIELD

[0001] This invention relates to an electromotive compressor which may be employed in air compressors and the like, in particular to a centrifugal type electromotive compressor.

Prior art technology

[0002] For example, one embodiment of an electric automobile which is known is to mount a fuel cell stack and to generate electricity using this fuel cell stack so as to enable running by means of the electrical power generated thereby. With this type of fuel cell stack for use in automobiles, the configuration is one wherein, normally, air comprising oxygen is used as the oxidant, and a relatively large volume of compressed air is supplied to the fuel cell stack by means of an air compressor which is mounted to the vehicle.

[0003] In Patent Reference 1, there is the disclosure of a centrifugal type electromotive compressor wherein, as the air compressor for use in this type of fuel cell stack, the impeller of a centrifugal type compressor is attached to one terminal means of the revolving axis of an electric motor, so that the impeller is rotationally driven directly by means of an electric motor. Then, a canceller disc is attached to the other terminal means of the revolving axis of the electric motor in order to alleviate the thrust force in the axial direction acting on the revolving axis by means of the impeller. Prior art technology references

Patent References

[0004] Patent Reference 1: Japanese laid open unexamined patent publication 2011-214523

Outline of the invention

Problems to be solved by the invention

[0005] Because a centrifugal style compressor has a configuration sending the gas sucked-in in the axial direction (for example air) in the centrifugal direction by means of the revolving of the impeller, just as disclosed in patent reference 1, there is the generation of a thrust load in the axial direction in reaction to the force of the impeller. Therefore, in the attached configuration of the impeller on the revolving axis of the electric motor there is an axial thrust load acting on the electric motor which is not desirable.

[0006] In patent reference 1, there is the provision of a canceler mechanism on the other terminal means side of the revolving axis employing the pressure of the compressed air in order to alleviate the thrust load in the axial direction, but with this type of configuration, the configuration is complicated by the canceler mechanism, in addition to difficulties in completely canceling the thrust load in the axial direction.

[0007] Moreover, this type of electromotive compressor has an extremely high revolving speed (for example more than 100,000 RPM) , and while the bearings supporting the revolving axis of the motor requires not only high precision but also longevity, in general, when used as an air compressor for use in fuel cell stacks, oil lubricated type bearings cannot be employed. In other words, when oil lubricated type bearings are employed, the oil components seep into the fuel cell stack over time and is not preferable. For that reason, the existence of the thrust load in the axial direction is a great problem in air compressors for use in fuel cell stacks.

[0008] Furthermore, in fuel cell automobiles, there is a need for the fuel cell stack to promptly start generating electricity after the key is switched on, and there is a need for a rapid start-up after the power is switched on, in other words a rapid pressure elevation, even in air compressors supplying oxidants. In that respect, in patent reference 1, the moment of inertia of the revolving member (rotor) provided with the canceler disc is great, such that the startup of the revolution is worsened.

Summary of the invention

[0009] The configuration of the electromotive compressor of the present invention comprises: a pair of compressor housings not only providing suction ports in each of the center means thereof, but also an annular diffuser means surrounding these suction ports as well as a scrolling means, in addition to said suction port being disposed symmetrically so as to face in opposite directions , and an electric motor disposed between this pair of compressor housings, and a pair of impellers attached symmetrically so as to face in mutually opposite directions on both terminal means of the revolving axis of this electric motor, and a symmetrically configured exit tube extending in a substantially U shape so as to mutually meet the exits of the scroll means of the above described pair of compressor housings, in addition to having a single spew port in the center thereof.

In other words, when the electric motor is driven, the pair of impellers attached to both terminal means of the revolving axis revolve, acting as a centrifugal type compressor together with the compressor housing, and the gas sucked in from each of the suction ports (for example air) is compressed and sent to the scroll means. The gas compressed by these two centrifugal type compressors is collected by the exit tube, and is finally spewed out from a single spew port.

[0011] Here, the two impellers generate an axial direction thrust force in the direction facing the respective suction ports, but because these two axial thrust loads have basically the same size but act in opposite directions, they mutually cancel-out in respect of the revolving axis. Therefore, the electric motor is not in receipt of an axial direction thrust load in either direction.

[0012] Moreover, because the required flow rate is supplied by means of the two centrifugal type compressors, the individual centrifugal type compressors may be of relatively smaller capacity. Therefore, each of the impellers may be enabled by a smaller diameter, and the moment of inertia of the revolving member comprising the pair of impellers is thus smaller. By this means, there is the benefit of a quicker startup thereof.

[0013] The electromotive compressors of this invention are suited for air compressors supplying air as the oxidant to fuel cell stacks loaded on automobiles.

[0014] One preferred embodiment of the present invention is where the above described pair of impellers are identical, in addition to the phases of each of the impeller blades being attached to the revolving axis so as to be mutually different .

[0015] In a centrifugal type compressor wherein impellers having multiple blades revolving there about, there is the generation of a spew pulse corresponding to the degree of revolution, and noise generated in tandem there with. In the configuration described above, by the phase of the blades of the two impellers being mutually different, the peaks of each of the spew pulses are mutually staggered, and by the mutual overlap thereof, the pulsation is reduced in respect of the spew port. Here, because the exit tube joined to centrifugal type compressors is symmetrically configured centered on the spew port, the tube lengths from each centrifugal type compressor to the spew port (in other words, the flow merging means) are mutually equal. Therefore, each of the spew flows are mutually merged in a manner so as to stagger the phase of the pulsations thereof. [0016] Another preferred embodiment of the present invention is where the above described pair of impellers have mutually equal revolving member conformations determining the outer edge of the blades, in addition to, the number of blades on each being mutually different.

[0017] In this type of configuration, because the frequency of the spew pulsations generated by the two centrifugal type compressors are mutually different, the two spew flows heading to the spew port have reduced pulsations in the same manner in respect of the spew port. Now, even if, hypothetically, the thrust loads in the axial direction are different resulting from the difference in the number of blades, that difference is minute. It is preferable to set the shape of each of the blades so as to equalize the thrust load in the axial direction, even if the number of blades is different .

[0018] Moreover, in one embodiment of the present invention, the cylinder shaped stator housing storing the stator of the above described electric motor is fitted between the above described pair of compressor housings, and this stator housing provides cooling fins for air cooling or a water jacket for use in liquid cooling. By this means, the stator of the electric motor is cooled.

[0019] Preferable the revolving axis of the electromotive compressor comprises a support mounting. The support mounting minimizes friction when the revolving axis is rotating advantageously, but also defines the locating of the revolving axis opposed to the other elements of the electromotive compressor such as the stator housing. [0020] According to a preferred embodiment of the invention the support mounting of the revolving axis is configured as a floating support mounting, such that the axis has axial play in its support mounting. As an advantage by this configuration of the support mounting as a floating support mounting, length variations of the revolving axis due to thermal or mechanical influences do not result in an unwished tensioning of the support mounting. Such unwished tensioning causes the friction in the support mounting to rise what in turn increases wear and finally accelerates the failure of the support mounting.

[0021] Preferable the revolving axis is supported by rolling bearings. By the use of rolling bearings the friction due to the rotation of the revolving axis is to be minimized. More preferred the rolling bearings are configured as ball bearings, especially deep groove ball bearings. Advantageously by the use of rolling bearings to support the revolving axis the friction resulting of its rotation is to be decreased. Within the species of rolling bearings ball bearings offer the biggest potential of friction reduction. In the case of deep groove ball bearings as an advantage, in addition to the benefits regarding friction, low axial forces are being able to be transmitted by the deep groove ball bearing.

[0022] In a further preferred embodiment of the invention the revolving axis is mounted to two end plates, in a way allowing the rotation of the revolving axis. As an advantage herewith the position of the revolving axis is secured in a way not causing any unwished tensioning leading to an increase of the friction due to the rotation of the revolving axis. The end plates therefore offer the required stiffness for supporting the revolving axis and are being able to be manufactured under rather low costs due to their simple but clever geometry, e.g. in a two piece mold without any cores or slides that are typically needed to transfer complex geometries like undercuts off the mold to the molded piece .

[0023] Within a preferred embodiment of the invention an outer bearing ring of the rolling bearing mentioned before is fixed at one of the end plates. Thereby the axial

location of the outer ring of the rolling bearing is

defined, such that it is not moveable towards the impeller close by in the axial direction. Advantageously the position of the revolving axis is therewith secured and the required stiffness and least possible friction are guaranteed

concomitantly .

[0024] In particular an inner ring of the rolling bearing is fixed on the revolving axis by a first flange means of the revolving axis or a first locking ring. Therewith the inner ring for the rolling bearing is fixed in a direction towards the more far off impeller axially. Advantageously by the fixing being realized by the first flange means no separate fastening element is required, which saves costs. An

advantage of the fixing being realized with the locking ring is to be figured out in the saving of material of which the revolving axis consists, because the diameter of the raw material the revolving axis is manufactured from may be smaller due to an enlargement of the diameter to form the first flange is not required.

[0025] Preferable the rolling bearings which support the revolving axis are arranged in an x-arrangement . This means that the running surfaces, on which rolling elements of the rolling bearing are rolling and by which the radial position of said rolling elements is defined, are tilted by an angle. In the case of the x-arrangement the rolling bearings with the tilted running surfaces are arranged such that two non equal lines perpendicular to one of the running surfaces of one rolling bearing cross each other on the side of the bearing that is closer to the other bearing et vice versa.

As an advantage of the described x-arrangement of the rolling bearings is to be pointed out that the support mounting of the revolving axis is tensioned such that play is to be minimized.

[0026] According to another preferable embodiment of the invention both of the impellers are each supported by the revolving axis towards the interior of the stator housing. This axial support could be realized by a second flange means of the revolving axis or by a second locking ring.

With the use of the second flange means no separate

fastening element is required, which advantageously saves costs. An advantage of the locking ring is to be figured out in the saving of material which the revolving axis consists of, because the diameter of the raw material the revolving axis is manufactured from may be smaller due to an

enlargement of the diameter to form the second flange means is not required.

[0027] Preferable the impellers are clamped against the second flange means or the second locking ring by a fastener axially. Advantageously on the one hand therewith it is secured that the power of the electric motor is being transmitted to the impellers but on the other hand it is possible for the impellers to slip through if a given maximal load is surpassed, such that in this case the impeller itself will not fail and e.g. shatter but the connection of the impeller and the revolving axis will fail. A surpassing of the given maximal load could possibly occur if a non-gaseous material is sucked in the compressor by accident. So the described clamping of the impeller by the fastener is to be subsumed under fail-save features.

[0028] According to another preferred embodiment the

fastener comprises an internal thread and the revolving axis is configured with an outer thread, the threads being designed complementary. This configuration of the fastener could be described as nut-like. By screwing the fastener onto the revolving shaft to clamp the impeller against the second flange means or the second locking ring an axial force is exerted to the respective impeller. This design of the fastener allows a symmetrical application of the

clamping force which stresses the clamped impeller evenly, such that peaks of the mechanical tension within the

material of the impeller resulting of the clamping are to be minimized advantageously.

[0029] An outer contour of the fastener extends preferably off the impeller and is tapered towards the suction port closest by. Further preferred the outer contour of the fastener ends in a tip. This design of the fastener leads to fluidic advantages and therefore improves the efficiency of the electromotive compressor.

[0030] Preferable the outer contour of the fastener

configures a transition towards the respective impeller. The transition comprises no shoulder or flange means or any other discontinuity. As an advantage this configuration of the outer surface of the fastener minimizes the influence of the reduction of the diameter at the ends of the revolving axis and therewith optimizes the efficiency of the

electromotive compressor.

[0031] According to a preferred embodiment of the invention the end plates are screwed to the stator housing by screws. As an advantage the connection between the end plates and the stator housing is to be carried out by screws that are common connecting elements which are relatively inexpensive due to their mass production.

[0032] In particular the end plates are screwed to the compressor housing as well. Above mentioned advantages apply equally .

[0033] Preferable the end plates comprise pressure

compensation openings by which the interior of the stator housing is connected to the each of the interiors of the compressor housings. As an advantage by this the electric motor is being able to be cooled by the gas flowing through the operating compressor to be compressed additionally.

[0034] According to a further preferred embodiment of the invention the pressure compensation openings are located out of the respective bearing area radially. This results in the bearings being shielded off the flow of the gas when the electromotive compressor is operated and therefore a

lubrication of the bearings is not influenced directly.

[0035] In particular the diffuser means of the compressor housing is sealed against a surrounding by a sealing means located between the compressor housing and the end plate gas-tightly. This results in an improvement of the

efficiency of the electromotive compressor due to a

prevention of leaks, such that the output of the compressed gas is maximized.

Preferable the end plates are connectable with the

compressor housings by screws. As an advantage the

connection between the end plates and the compressor

housings is to be carried out by screws that are common connecting elements which are relatively inexpensive due to their mass production.

According to another preferred embodiment of the invention the connecting screws are arranged out of the stator housing radially and within the respective end plate or compressor housing radially. The arrangement of the screws extends axially. This results in advantages regarding the required assembly space.

Preferable the screws are configured to be able to penetrate screw slots. Said screw slots are located in an area out of the stator housing radially and within the end plates axially. This leads to a further saving of required assembly space advantageously.

Effects of the Invention

[0036] By means of the present invention, there is mutual cancellation of each of the axial direction thrust loads by means of a pair of centrifugal type compressors, and the electric motor positioned in the center is not in receipt of an axial direction thrust load. Therefore, the performance required of the bearing in high-speed revolution becomes relatively lower.

[0037] Furthermore, by having a pair of centrifugal type compressors, the moment of inertia of the revolving member comprising the impellers in respect of the required flow rate become smaller, enabling the derivation of superior characteristics resulting from the easier startup of the revolution thereof.

Brief description of the drawings

[0038]

Figure 1 : A perspective view of an embodiment of the electromotive compressor of this invention.

Figure 2: A cross-section view along a cross-section through the revolving center of this electromotive compressor .

Figure 3: A cross-section view representing an exploded view of the bearing part of figure 2.

Figure 4: A perspective view of the impeller.

Figure 5: A cross-section view along the A - A line of figure 2.

Figure 6: A cross-section view along a cross-section through the revolving center of the electromotive compressor in representation of a second embodiment . Embodiments of the present invention

[0039] Hereafter, an embodiment of the present invention is explained in detail based on the figures.

[0040] Figure 1 is a perspective view of an embodiment of the electromotive compressor of this invention, and Figure 2 is a cross-section view along a cross-section through the revolving center of this electromotive compressor. Electromotive compressor of this embodiment is an adjunct apparatus of a fuel cell stack mounted to a fuel cell automobile, and is employed as an air compressor for the purposes of supplying the air which to be the oxidant to the fuel cell stack.

[0041] As illustrated in figures 1 and 2, the electromotive compressor of the embodiment is broadly configured from a pair of centrifugal type compressors 1 and 2, and an electric motor 3 is disposed in the center means of the axial direction between these two centrifugal type compressors 1 and 2, and the exit tube 4 guides the spew flow of the pair of centrifugal style compressors 1 and 2 to the central spew port 5 to mutually merge. In other words, as the housing 6 of the main member parts, there is the provision of a pair of compressor housings 7 and 8, each formed in a disk shape, and a substantially cylinder-shaped stator housing 9 is disposed between these two compressor housings 7 and 8. Both termini of the stator housing 9 are connected to the compressor housings 7 and 8 via mutually disk shaped end plates 10 and 11. Specifically, the terminal means of the stator housing 9 is fixed to the inner periphery of the end plates 10 and 11 by means of multiple bolts 12, and the outer peripheral side parts of the end plates 10 and 11 are fixed to the outer peripheral means of the compressor housings 7 and 8 by means of multiple bolts 13. The two compressor housings 7 and 8 are configured mutually symmetrically sandwiching the symmetrical surface P (refer to figure 2) through the center of the axial direction of the electromotive compressor overall.

[0042] The electric motor 3 is configured from the stator 15 fitted on to the inner periphery of the stator housing 9, and the revolving axis 17 is supported via the respective bearings 16 on a pair of end plates 10 and 11, and the permanent magnet 18 comprises the rotor attached to the outer peripheral surface of the revolving axis 17. This electric motor 3 is configured, for example, from a three- phase brushless motor whose revolving speed can be variably controlled by means of a drive circuit which is not illustrated in the figures, and the stator 15 provides a stator coil which is not illustrated in the figures. The outer peripheral surface of the permanent magnet 18 and the inner peripheral surface of the stator 15 face each other across a minute gap, in other words, an air gap.

[0043] Moreover, as illustrated in detail in figure 3, bearings 16 are comprised of a ball bearing including the inner ring 16a, the outer ring 16b and rolling members 16c, and the outer ring 16b is fitted onto the inner peripheral surface of the bearing holding member 19 formed in the shape of a disk on the center means of the end plates 10 and 11, and is supported on each of the end plates 10 and 11. Moreover, the revolving axis 17 not only has a pair of axis means 17a for use with the bearing to which the inner ring 16a is fitted, but also has the flange means 17b which has a slightly enlarged diameter on the axis direction inner side of this pair of axis means 17a for use with the bearing, and the terminal surface of this flanged means 17b is proximal to the terminal surface of the inner ring 16a.

[0044] The revolving axis 17 extends to both sides perforating through the pair of bearings 16, and a pair of impellers 21 and 22 are attached to these terminal means. Specifically, the revolving axis 17 penetrates through the hole in the center of the impellers 21 and 22, and a cone shaped nut 23 is screwed on to the screw means of the tip terminus of the revolving axis 17 protruding from the impellers 21 and 22 so as to compress and fix the impellers 21 and 22 between the axial means for use on the bearing 17a and the nut 23.

[0045] The impellers 21 and 22 configure the centrifugal type compressors 1 and 2 by being assembled to the compressor housings 7 and 8. Figure 4 is a perspective view representing the impeller 21 on its own in correspondence with one of the compressor housings 7, and provides multiple backward shaped blades 24 twisting in a spiral shape so as to send the sucked in air along the axial direction to the outer peripheral side of the radial direction. Now, as the revolving member shape defining the outer edge of the blades 24, impeller 21 forms a mainly circular truncated conical shape. Moreover, in the embodiment in the figure, there is the alternative disposition of half blade shaped blades 24A which have foreshortened blade length on the inner diameter side blade length and normal length blades 24B, for example, with the provision of a total of 12 of the blades 24. [0046] The impeller 22 corresponding to the other compressor housing 8 is formed in the symmetrically opposite shape to impeller 21 of figure 4. In other words, the screw direction of the blades 24 of impeller 22 is the opposite direction to that of the blades 24 of impeller 21 of figure 4. Other than this point of the opposite symmetrical shape, impeller 21 and impeller 22 comprise the same shape. Impellers 21 and 22 may be formed by means of precision casting of metallic materials, for example, such as aluminum alloys and the like, otherwise, they may also be molded from hard synthetic resin .

[0047] Here, this pair of impellers 21 and 22 are fixed to the respective terminal means of the revolving axis 17 as mentioned above, and are attached to the revolving axis 17 in a mutually staggered shape in the peripheral direction, so as to present mutually different phases of each of the blades 24. For example, in the embodiment where there are 12 of the blades 24, while the pitch of the blades 24 becomes 30°, they are fixed on to the revolving axis 17 so that they have a phase difference of 15° between impeller 21 and impeller 22. Now, if necessary, each of the angular positions may be caused to be regulated by means of a combination of keys and key grooves.

[0048] The impellers 21 and 22 are stored in the center means of the compressor housings 7 and 8 which are each formed in cylindrical shapes. The compressor housings 7 and 8 configuring the centrifugal type compressors 1 and 2 combined with the impellers 21 and 22 not only have a suction port extending in a cylindrical shape along the axial direction of the center means thereof, they also provide an annular diffuser means 27 so as to surround this suction port, as well as a scroll means 28. The scroll means 28 is formed so as to surround the impellers 21 and 22 in an annular shape in respect of the outer peripheral means of the compressor housings 7 and 8, and as illustrated in figure 5, are formed so as to gradually expand the cross- section area along the revolving direction of the impellers 21 and 22. The diffuser means 27 is configured by a so- called vaneless type diffuser formed by means of two parallel wall surfaces orthogonal to the revolving axis 17, configuring a flow path from the outer peripheral means of the impellers 21 and 22 to the scroll means 28.

[0049] As already mentioned, the two compressor housings 7 and 8 are configured to be symmetrically opposite sandwiching the symmetrical surface P through the center of the axial direction of the electromotive compressor overall. Therefore, each of the suction ports 26 are facing in mutually opposite directions along the axial direction of the revolving axis 17. These suction ports 26 are open to the atmosphere via non-illustrated pipes and air cleaners. Because the two compressor housings7 and 8 are mutually mirror opposites sandwiching the symmetrical surface P, the starting point s28a (refer to figure 5) of the revolving direction of the scroll means 28 with a gradually expanding cross-section area along the revolving direction are at the same angular position.

[0050] Moreover, the scroll means 28 extends in the tangential direction 10 at an almost 360° revolved position from the starting point 28a, to the exit 28b with the largest cross-sectional area. Then, the terminal means 4a of substantially U-shaped exit tubes 4 are connected to the pair of exits 28b. [0051] As already mentioned, the exit tube 4 provides a single spew port 5 in the center thereof. This spew port 5 is connected to the fuel cell stack via pipes which are not illustrated in the figures. The exit tubes 4 are configured to be mutually symmetrically sandwiching the symmetrical surface P through the center of the axial direction of the electromotive compressor overall. Therefore, the tube lengths from the exit 28b of the scroll means 28 and from the starting point 28a to the spew port 5, in respect of the two central frugal type compressors 1 and 2, are mutually equal. As illustrated in figure 5, the exit tube 4 is a long a plane including the tangent facing the exit 28b of the two scroll means 28.

[0052] The cylindrical stator housing 9 which is the housing storing the electric motor 3 is air cooled, in other words, it provides the cooling fins 30 on the outer peripheral surface thereof to promote the thermal dissipation to the atmosphere. The cooling fins 30 are formed extending annularly in the peripheral direction, in addition to arraying several in the axial direction. By means of these cooling fins 30, the electric motor 30 comprised of the stator 15 is cooled effectively.

[0053] The electromotive compressor of the embodiment configured as described above disposes a pair of symmetrically opposite central frugal type compressors 1 and 2 having basically the same configuration, and the electric motor 3 at the center of these two central frugal type compressors is rotationally driven. Here, in the individual centrifugal type compressors 1 and 2, they impellers 21 and 22 generate a thrust load in the drawing axial direction to the suction port 26 sides in tandem with the revolution of the impellers 21 and 22. However, as a result of the symmetrical disposition of the pair of centrifugal compressors 1 and 2, each of the thrust loads in the axial direction act in opposite directions on the rotational axis 17, and mutually cancel out. As a result, there is basically no thrust load acting on the axial direction of the revolving axis 17 which is integrated with the rotor of the electric motor 3. Therefore, there is no need to consider a great axial direction thrust load, and the configuration comprising the bearings 16 is simplified. In the embodiment illustrated, as the bearings 16, a normal ball bearing capable of supporting the relatively small axial direction thrust load is employed, and there is no provision of a special thrust bearing. The bearings 16 comprised of a ball bearing is not an oil lubrication type, and therefore there is no fear of suction of the oil components to the fuel cell stack. Now, the impellers 21 and 22, in other words the electric motor 3, revolve at high speed, and for example revolve at a speed of several tens of thousands RPM or more.

[0054] This spew flow spewed out from the two centrifugal type compressors 1 and 2 are mutually merged and supplied from the spew port 5 to the fuel cell stack. Therefore, the capacity of the individual centrifugal type compressors 1 and 2 as well as the diameters of the impellers 21 and 22 are embodied relatively smaller to the required air flow rate, and the moment of inertia of the revolving member including the revolving axis 17 and the pair of impellers 21 and 22 is as a result smaller. Therefore, the startup is more rapid, and for example when the operation of a fuel cell automobile is started up, the rapid supply of the compressed air which is the oxidant to the fuel cell stack is enabled.

[0055] Moreover, with the individual centrifugal type compressors 1 and 2, there is the generation of spew pulses of the revolving rate in correspondence with the 24 blades of the impellers 21 and 22, but by attaching the two impellers 21 and 22, for example, staggered at half pitch worth on the revolving axis 17, the phases of each of the spew pulses become different. Then, as a result of the merging of these two pulse components via the exit tube 4, the pulses included in the derived flow from the spew port 5 become smaller.

[0056] Here, as another embodiment, it is possible to have a different number of blades than the 24 blades on the two impellers 21 and 22, in order to reduce the spew pulses. For example, have 12 of the blades 24 as mentioned above on the impeller 21, and have 10 of the blades 24 on the impeller 22. Now, when alternating the disposition of the half blade shape of blades 24A with the normal long blade 24B, the total number of blades 24 is an even number. As the shape of the revolving member of the impeller as defined by the outer edge of blades 24, there is no necessity to make both of them identical, but in one embodiment, in order to avoid complicating the configuration including the compressor housings 7 and 8 , the shapes of the revolving members of the impellers 21 and 22 are mutually the same. In other words, only the number of blades 24 is different.

[0057] If the number of the blades 24 are different in this manner, because the rate of the spew pulses of the two centrifugal compressors 1 and 2 as well as the frequencies thereof become mutually different, the amplitude of the pulsations in respect of the spew port 5 where they are merged become smaller.

[0058] Here, when the number of the blades 24 are different, the spew capacity of the central frugal compressors 1 and 2 vary, and there is the possibility that the thrust load in the axial direction generated by each would vary, but even in this case, the difference in the thrust load in the axial direction of both is minute, and most of the axial direction thrust load cancels out. Now, it is also possible to design the shape and the like of each of the blades 24 so as to enable a mutually equivalent axial direction thrust load for both in respect of an appropriate rated revolving velocity.

[0059] Next, figure 6 represents the second embodiment of the electromotive compressor of the present invention. This embodiment provides a water jacket 31 for use in liquid cooling of the stator housing 9, instead of the cooling fins 30 mentioned above. The water jacket 31 is formed, for example, in a spiral shaped through path in the interior of the cylinder shaped stator housing, and circulates the cooling water by the connection of a cooling water circulation system including a cooling water pump or a heat exchanger which are not illustrated. By means of this second embodiment, the electric motor 3 comprising the stator 15 is more securely cooled.

[0060] As laid out above, embodiments of the present invention adapted to the air compressors of fuel-cell stacks were explained, but this invention can also be adapted to compressors for other applications. [0061] Now, the exits 28b of the scroll means 28 in the embodiments described above were disposed at mutually symmetrical positions, in other words disposed at the same revolve position, but the present invention is not limited to this. While not illustrated in the figures, the exits 28b of the scroll means 28 of two centrifugal compressors 1 and 2 may be disposed, for example, at positions which are 180° apart from each other, enabling a configuration merging the substantially U-shaped exit tubes thereof. In this case, the exit tubes derive a revolved symmetrical shape, and not a surface symmetrical shape as was in the embodiments described above.

[0062] In the examples of figure 2, 3 and 6 the revolving axis 17 of the electromotive compressor comprises a support mounting. The support mounting of the revolving axis 17 is configured as a floating support mounting, such that the revolving axis 17 has axial play in its support mounting. The revolving axis 17 is supported by rolling bearings 16. The rolling bearings 16 are configured as ball bearings 16 and in the shown examples as deep groove ball bearings 16. The revolving axis 17 is mounted to two end plates 10, 11, in a way allowing the rotation of the revolving axis 17. An outer bearing ring 16b of the rolling bearing 16 mentioned before is fixed at one of the end plates 10, 11. Thereby the axial location of the outer ring 16b of the rolling bearing 16 is defined, such that it is not moveable towards the impeller 21, 22 close by in the axial direction. An inner ring 16a of the rolling bearing 16 is fixed on the revolving axis 17 by a first flange means 17b of the revolving axis 17 or a first locking ring, of which the latter possibility is not shown in the figures. Therewith the inner ring 16a for the rolling bearing 16 is fixed in a direction towards the more far off impeller 21, 22 axially.

[0063] According to another example, which is not shown in the figures, the rolling bearings 16 which support the revolving axis 17 are arranged in an x-arrangement. This means that the running surfaces, on which rolling elements 16c of the rolling bearing 16 are rolling and by which the radial position of said rolling elements 16c is defined, are tilted by an angle. In the case of the x-arrangement the rolling bearings 16 with the tilted running surfaces are arranged such that two non-equal lines perpendicular to one of the running surfaces of one rolling bearing 16 cross each other on the side of the rolling bearing 16 that is closer to the other rolling bearing 16 et vice versa.

[0064] In the examples of figure 2, 3 and 6 the impellers 21, 22 are each supported by the revolving axis 17 towards the interior of the stator housing 9. This axial support could be realized by a second flange means of the revolving axis 17 or by a second locking ring. In the depictured examples said axial support is configured as a second flange means, as to be seen in figure 2 in detail.

[0065] In the examples of figure 2 and 6 the impellers 21,

22 are clamped against the second flange means by a fastener

23 axially. The fastener 23 comprises an internal thread and the revolving axis 17 is configured with an outer thread, the threads being designed complementary. This configuration of the fastener 23 could be described as nut-like. By screwing the fastener 23 onto the revolving axis 17 to clamp the impeller 21, 22 against the second flange means an axial clamping force is exerted to the respective impeller 21, 22. An outer contour of the fastener 23 extends off the impeller 21, 22 and is tapered towards the suction port 26 closest by. The outer contour of the fastener 23 ends in a tip. The outer contour of the fastener 23 configures a transition towards the respective impeller 21, 22. The transition comprises no shoulder or flange means or any other

discontinuity .

[0066] In the example of figure 2 the end plates 10, 11 are screwed to the stator housing 9 by screws 12. The end plates 10, 11 are screwed to the compressor housings 7, 8 as well.

[0067] In the example of figure 3 the end plates 10, 11 comprise pressure compensation openings by which the

interior of the stator housing 9 is connected to the each of the interiors of the compressor housings 7, 8. The pressure compensation openings are located out of the respective bearing 16 area radially.

[0068] In the example of figures 2 and 6 the diffuser means 27 of the compressor housings 7, 8 is sealed against a surrounding by a sealing means located between the

compressor housings 7, 8 and the end plates 10, 11 air tightly. The end plates 10, 11 are connectable with the compressor housings 7, 8 by screws 13. The connecting screws 13 are arranged out of the stator housing 9 radially and within the respective end plate 10, 11 or compressor housing

7, 8 radially. The arrangement of the screws 13 extends axially. The screws 13 are configured to be able to

penetrate screw slots. Said screw slots are located in an area out of the stator housing 9 radially and within the end plates 10, 11 axially. Explanation of the reference numerals

[0069]

1, 2 centrifugal type compressor

3 electric motor

4 exit tube

5 spew port

7, 8 compressor housings

9 stator housing

12, 13 screws

15 stator

16 bearing

16a inner ring

16b outer ring

16c rolling elementl7 revolving axis 17b first flange means

18 permanent magnet

21, 22 impellers

23 fastener

26 suction port

27 diffuser means

28 scroll means