JP2019090370A - Electric compressor - Google Patents

Abstract

An axial thrust load acting on an electric motor 3 is reduced, and the configuration is simplified. The electric compressor includes a pair of centrifugal compressors (1, 2), an electric motor (3) at a central portion, and a substantially U-shaped outlet pipe (4) having a single discharge port (5) at the center. Impellers 21 and 22 are fixed to both ends of the rotating shaft 17 of the electric motor 3, respectively, and are combined with the compressor housings 7 and 8. The pair of centrifugal compressors 1 and 2 are configured symmetrically with respect to each other with the central symmetry plane P interposed therebetween. The axial thrust loads generated in the respective centrifugal compressors 1 and 2 act on the rotating shaft 17 in the opposite direction, and therefore cancel each other. [Selection diagram] FIG.

Description

  The present invention relates to an electric compressor used as an air compressor or the like, and more particularly to a centrifugal electric compressor.

  For example, a so-called fuel cell vehicle is known which is equipped with a fuel cell stack and travels with the power generated by the fuel cell stack as one form of the electric vehicle. In such a fuel cell stack for vehicles, air containing oxygen is generally used as an oxidant, and a relatively large amount of compressed air is supplied to the fuel cell stack by an air compressor mounted on the vehicle. It has become.

  Patent Document 1 discloses a centrifugal electric motor in which an impeller of a centrifugal compressor is attached to one end of a rotating shaft of an electric motor as such an air compressor for a fuel cell stack, and the impeller is directly driven to rotate by the electric motor. A compressor is disclosed. A canceller disk that receives the pressure of pressurized air is attached to the other end of the rotary shaft of the electric motor in order to reduce an axial thrust force exerted on the rotary shaft by the impeller.

JP, 2011-214523, A

  Since the centrifugal compressor is configured to feed axially drawn gas (for example, air) in the centrifugal direction by rotation of the impeller, as disclosed in Patent Document 1, axial thrust load as reaction force applied to the impeller Occurs. Therefore, in the configuration in which the impeller is attached to the rotary shaft of the electric motor, axial thrust load acts on the electric motor, which is not preferable.

  In Patent Document 1, the canceller mechanism using the pressure of pressurized air is provided on the other end side of the rotating shaft for the purpose of alleviating axial thrust load, but in such a configuration, it is caused by the canceller mechanism. The construction is complicated and it is difficult to completely cancel the axial thrust load.

  In addition, although this type of electric compressor has a very high rotational speed (for example, 100,000 rpm or more), high precision and durability are required for the bearing that supports the motor rotation shaft, but it is used as an air compressor for fuel cell stack In general, oil lubricated bearings can not generally be used. That is, when an oil lubricated bearing is used, the oil component intrudes into the fuel cell stack with time, which is not preferable. Therefore, the presence of the axial thrust load becomes a larger issue in the fuel cell stack air compressor.

  Furthermore, in fuel cell vehicles, it is necessary for the fuel cell stack to immediately start power generation after the key is turned on, and even in an air compressor that supplies an oxidant, a rapid rise after power on, that is, a rapid pressure rise is required Be done. With respect to such a demand, in the configuration of Patent Document 1, the inertia moment of the rotating body portion (rotor) becomes larger by providing the canceller disk, and the rising of the rotation is deteriorated.

The electric compressor according to the present invention is
A pair of compressor housings each having a suction port at its central portion and an annular diffuser portion and a scroll portion so as to surround the suction port, and symmetrically disposed such that the suction ports face in opposite directions;
An electric motor located between the pair of compressor housings;
A pair of impellers mounted symmetrically on opposite ends of the rotary shaft of the electric motor so as to face in opposite directions, respectively, and constituting a centrifugal compressor in combination with the compressor housing;
An outlet pipe extending in a substantially U-shape so that the outlets of the scroll portions of the pair of compressor housings are assembled together and having a single discharge port at the center, and configured symmetrically;
It is configured with.

  That is, when the electric motor is driven, a pair of impellers attached to both ends of the rotary shaft is rotated and acts as a centrifugal compressor together with the compressor housing to add gas (for example, air) sucked from the suction port. Press to send to the scroll unit. Gases pressurized by these two centrifugal compressors are collected by the outlet pipe and finally discharged from a single discharge port.

  Here, in the two impellers, axial thrust loads in the direction toward the suction port are generated respectively, but these two axial thrust loads are in opposite directions and basically of the same size. Thus, they are mutually offset at the rotation axis. Thus, the electric motor does not receive an axial thrust load in either direction.

  Also, each centrifugal compressor has a small volume, as the necessary flow rates will be supplied by the two centrifugal compressors. Therefore, the diameter of each impeller can be reduced, and the moment of inertia of the rotating body including the pair of impellers is reduced. This is advantageous on a quick start.

  The electric compressor of the present invention is suitable, for example, as an air compressor for supplying air as an oxidant to a fuel cell stack mounted on a vehicle.

  In a preferred aspect of the present invention, the pair of impellers are identical to each other, and attached to the rotation shaft such that the blades of each impeller have different phases.

  In a centrifugal compressor in which an impeller having a plurality of blades rotates, discharge pulsations of a rotation order corresponding to the number of blades occur, and noise is generated accordingly. In the above configuration, the phases of the blades of the two impellers are different from each other, the peaks of the discharge pulsations are shifted, and the pulsations at the discharge port are reduced by overlapping each other. Here, since the outlet pipes connecting the two centrifugal compressors are constructed symmetrically with respect to the discharge port, the pipe lengths from each centrifugal compressor to the discharge port (in other words, the junction) are equal to each other. Therefore, the discharge flows merge with each other in a phase-shifted state of pulsation.

  In another preferred aspect of the present invention, the pair of impellers has the same shape of rotor defined by the outer edge of the wings, and the numbers of the wings are different from each other.

  In such a configuration, since the frequencies of the discharge pulsations generated by the two centrifugal compressors are different from each other, the pulsations at the discharge port are similarly reduced by the two discharge streams merging toward the discharge port. Even if the axial thrust load is different due to the difference in the number of blades, the difference is very small. It is desirable to set each wing shape etc. so that axial direction thrust load may become equal, even if the number of blades differs.

  In one embodiment of the present invention, a cylindrical stator housing accommodating a stator of the electric motor is mounted between the pair of compressor housings, and the stator housing is a cooling fin or a liquid for air cooling. It has a cold water jacket. This cools the stator of the electric motor.

  According to the present invention, each axial thrust load is offset by the pair of centrifugal compressors, and the central electric motor does not receive the axial thrust load. Therefore, the performance required for the bearing at high speed rotation is relatively low.

  In addition, by having a pair of centrifugal compressors, the moment of inertia of the rotating body including the impeller is reduced with respect to the required flow rate, and it is possible to obtain characteristics excellent for the rising of the rotation.

FIG. 1 is a perspective view showing an embodiment of an electric compressor according to the present invention. Sectional drawing along the section which passes along the rotation center of this electric compressor. Sectional drawing which expanded and showed the bearing part of FIG. FIG. FIG. 3 is a cross-sectional view taken along the line A-A of FIG. Sectional drawing similar to FIG. 2 which shows 2nd Example.

  Hereinafter, an embodiment of the present invention will be described in detail based on the drawings.

  FIG. 1 is a perspective view showing an embodiment of an electric compressor according to the present invention, and FIG. 2 is a cross-sectional view taken along a section passing through the rotation center of the electric compressor. The electric compressor of this embodiment is used as an accessory of a fuel cell stack mounted on a fuel cell vehicle, and as an air compressor for supplying air serving as an oxidant to the fuel cell stack.

  As shown in FIGS. 1 and 2, the electric compressor of the embodiment includes a pair of centrifugal compressors 1 and 2 and an electric motor 3 located between the two centrifugal compressors 1 and 2, that is, in the axial center. And an outlet pipe 4 for bringing the discharge flows of the pair of centrifugal compressors 1 and 2 into one another and guiding them to the central discharge port 5. That is, the housing 6 of the main body portion includes a pair of disk-shaped compressor housings 7 and 8 and a substantially cylindrical stator housing 9 located between the two compressor housings 7 and 8. . Both ends of the stator housing 9 are connected to the compressor housings 7 and 8 via disc-shaped end plates 10 and 11, respectively. Specifically, the end of the stator housing 9 is fixed to the inner periphery of the end plates 10 and 11 by a plurality of bolts 12, and the outer peripheral portion of the end plates 10 and 11 is a compressor housing 7 by a plurality of bolts 13. , 8 are fixed. The two compressor housings 7 and 8 are configured symmetrically with respect to a plane of symmetry P (see FIG. 2) passing through the axial center of the entire electric compressor.

  The electric motor 3 has a stator 15 fitted on the inner periphery of the stator housing 9, a rotating shaft 17 supported by a pair of end plates 10 and 11 via bearings 16, and an outer periphery of the rotating shaft 17. It is comprised from the permanent magnet 18 used as the rotor attached to the surface. The electric motor 3 is configured as, for example, a three-phase brushless motor whose rotational speed can be variably controlled by a drive circuit (not shown), and the stator 15 is provided with a stator coil (not shown). The outer peripheral surface of the permanent magnet 18 and the inner peripheral surface of the stator 15 face each other via a slight gap, that is, an air gap.

  Further, as shown in detail in FIG. 3, the bearing 16 is a ball bearing including an inner ring 16a, an outer ring 16b, and rolling elements 16c, and a bearing holding portion 19 formed in a cylindrical shape at the center of the end plates 10 and 11. The outer ring 16b is fitted on the inner peripheral surface of the frame and supported by the end plates 10 and 11, respectively. Further, the rotary shaft 17 has a pair of bearing shaft portions 17a to which the inner ring 16a is fitted, and the flange portion 17b whose diameter is slightly enlarged on the inner side in the axial direction of the pair of bearing shaft portions 17a. The end face of the flange portion 17b is close to the end face of the inner ring 16a.

  The rotating shaft 17 penetrates the pair of bearings 16 and further extends to both sides, and a pair of impellers 21 and 22 is attached to both ends thereof. Specifically, the rotary shaft 17 penetrates the central hole of the impellers 21 and 22, and the screw 23 at the tip of the rotary shaft 17 protruding from the impellers 21 and 22 is screwed with the cone-shaped nut 23 to make the impeller 21. , 22 are tightened and fixed between the bearing shaft 17a and the nut 23.

  The impellers 21 and 22 constitute centrifugal compressors 1 and 2 by being combined with the compressor housings 7 and 8. FIG. 4 is a perspective view showing the impeller 21 corresponding to one compressor housing 7 alone, which is a backward type in which the air taken in along the axial direction is helically twisted so as to send it radially outward. A plurality of wings 24 are provided. In addition, as a rotary-body shape which becomes settled with the outer edge of the wing | blade 24, the impeller 21 has substantially formed the truncated cone shape. Further, in the illustrated example, a half blade type wing 24A whose wing length on the inner diameter side is shortened and a wing 24B of a normal length are alternately arranged, and for example, a total of 12 wings 24 are provided.

  The impeller 22 corresponding to the other compressor housing 8 has a symmetrical shape with the impeller 21 of FIG. 4. That is, the turning direction of the wing 24 of the impeller 22 is in the opposite direction to the wing 24 of the impeller 21 of FIG. 4. The impeller 21 and the impeller 22 have substantially the same shape except for the symmetrical shape. The impellers 21 and 22 can be formed, for example, by precision casting of a metal material such as an aluminum alloy, or may be formed of a hard synthetic resin.

  Here, the pair of impellers 21 and 22 are respectively fixed to the respective end portions of the rotation shaft 17 as described above, but they are mutually offset in the circumferential direction so that the phases of the respective wings 24 are different from each other. It is attached to the rotating shaft 17. For example, in the example of the twelve wings 24, the pitch of the wings 24 is 30 °, but the impeller 21 and the impeller 22 are fixed to the rotating shaft 17 so as to have a phase difference of 15 °. If necessary, each angular position may be defined by a combination of a key and a key groove.

  The impellers 21 and 22 are accommodated in central portions of disk-shaped compressor housings 7 and 8, respectively. The compressor housings 7 and 8 constituting the centrifugal compressors 1 and 2 in combination with the impellers 21 and 22 have a cylindrically extending suction port 26 along the axial direction at the central portion and surround the suction port 26 As such, an annular diffuser portion 27 and a scroll portion 28 are provided. The scroll portion 28 is formed to annularly surround the impellers 21 and 22 at the outer peripheral portions of the compressor housings 7 and 8 and is gradually broken along the rotational direction of the impellers 21 and 22 as shown in FIG. It is formed to expand the area. The diffuser portion 27 is configured as a so-called vaneless diffuser in which a flow path extending from the outer peripheral portions of the impellers 21 and 22 to the scroll portion 28 is formed by two parallel wall surfaces orthogonal to the rotating shaft 17.

  As described above, the two compressor housings 7 and 8 are configured symmetrically with respect to the plane of symmetry P passing through the axial center of the entire electric compressor. Thus, the suction ports 26 face in opposite directions along the axial direction of the rotation shaft 17. The suction port 26 is open to the atmosphere via a piping and an air cleaner (not shown). Since the two compressor housings 7 and 8 are symmetrical with respect to the plane of symmetry P, the starting point 28a (see FIG. 5) in the rotational direction of the scroll portion 28 whose sectional area gradually expands along the rotational direction is the same. In angular position.

  Further, the scroll portion 28 extends tangentially at a position rotated approximately 360 ° from the starting point 28a, and reaches the outlet 28b having the largest cross-sectional area. The both ends 4a of the substantially U-shaped outlet pipe 4 are connected to the pair of outlets 28b.

  The outlet pipe 4 is provided with a single discharge port 5 at the center as described above. The discharge port 5 is connected to the fuel cell stack via a pipe (not shown). The outlet pipes 4 are constructed symmetrically with respect to a plane of symmetry P passing through the axial center of the entire electric compressor. Accordingly, for the two centrifugal compressors 1 and 2, the pipe lengths from the outlet 28b of the scroll portion 28 to the discharge port 5 from the start point 28a to the discharge port 5 are equal to each other. As shown in FIG. 5, the outlet pipe 4 is along a plane including a tangent line toward the outlet 28 b of the two scrolls 28.

  The cylindrical stator housing 9 serving as a housing for housing the electric motor 3 has cooling fins 30 on the outer peripheral surface for promoting cooling by the outside air, that is, heat dissipation to the outside air. The cooling fins 30 annularly extend in the circumferential direction, and are formed in a plurality in the axial direction. The cooling fins 30 effectively cool the electric motor 3, particularly the stator 15.

  In the electric compressor of the embodiment configured as described above, a pair of centrifugal compressors 1 and 2 having basically the same configuration are symmetrically arranged, and these two centrifugal compressors 1 and 2 The electric motor 3 is rotationally driven. Here, in each of the centrifugal compressors 1 and 2, an axial thrust load in a direction to draw the impellers 21 and 22 toward the suction port 26 is generated as the impellers 21 and 22 rotate. However, as a result of the symmetrical arrangement of the pair of centrifugal compressors 1, 2, the axial thrust loads act on the rotating shaft 17 in opposite directions and cancel each other. Therefore, no axial thrust load basically acts on the rotating shaft 17 integrated with the rotor of the electric motor 3. Therefore, no consideration for a large axial thrust load is required, and the structure including the bearing 16 is simplified. In the illustrated example, a general ball bearing capable of bearing a relatively small axial thrust load is used as the bearing 16, and no special thrust bearing is provided. The bearing 16 consisting of a ball bearing is not oil lubricated, so there is no concern that the oil component will be sucked into the fuel cell stack. The impellers 21 and 22, that is, the electric motor 3 rotate at a high speed at a rotational speed of, for example, several tens of thousands of rpm.

  The discharge flows discharged from the two centrifugal compressors 1 and 2 are gathered together and supplied from the discharge port 5 to the fuel cell stack. Therefore, the capacities of the individual centrifugal compressors 1, 2 and hence the diameters of the impellers 21, 22 become smaller compared to the required air flow, and the inertia of the rotating body including the rotating shaft 17 and the pair of impellers 21, 22 The moment becomes smaller. Therefore, the start of the rotation becomes faster, and it becomes possible to quickly supply the fuel cell stack with compressed air serving as an oxidant, for example, at the start of operation of the fuel cell vehicle.

  Further, in each of the centrifugal compressors 1 and 2, discharge pulsation of the rotation order corresponding to the number of the blades 24 of the impellers 21 and 22 occurs, but the two impellers 21 and 22 are shifted by a half pitch, for example. By attaching them to each other, the phases of the discharge pulsations become different. Then, as a result of the two pulsation components joining via the outlet pipe 4, the pulsation contained in the flow obtained from the discharge port 5 becomes small.

  Here, as another embodiment, the number of blades 24 of the two impellers 21 and 22 may be made different in order to reduce discharge pulsation. For example, impeller 21 has twelve wings 24 as described above, while impeller 22 has ten wings 24. When the half blade type wings 24A and the wings 24B of normal length are alternately arranged, the total number of wings 24 is even. The shape of the rotor of the impeller, which is determined by the outer edge of the wing 24, does not have to be the same. However, in one embodiment, the impeller 21 is used to avoid complication of the configuration including the compressor housings 7 and 8. , 22 are equal to one another. That is, only the number of wings 24 is different.

  As described above, if the number of blades 24 is different, the order or frequency of the discharge pulsations of the two centrifugal compressors 1 and 2 will be different from each other, so the amplitude of the pulsation in the discharge port 5 where the two are gathered decreases.

  Here, if the number of blades 24 is different, the displacements of the centrifugal compressors 1 and 2 may change, and the axial thrust loads generated in each may be different. The difference is slight and most of the axial thrust load can be offset. The shapes and the like of the respective wings 24 may be designed so that the axial thrust loads of the two are equal to each other at an appropriate rated rotational speed.

  Next, FIG. 6 shows a second embodiment of the electric compressor of the present invention. In this embodiment, a water jacket 31 for liquid cooling is provided on the stator housing 9 in place of the cooling fins 30 described above. The water jacket 31 is formed as, for example, a spiral passage inside the cylindrical stator housing 9, and is connected to a cooling water circulation system including a cooling water pump and a heat exchanger (not shown) to pass the cooling water. Flow. According to the configuration of the second embodiment, the electric motor 3 and particularly the stator 15 can be cooled more reliably.

  As mentioned above, although one Example which applied this invention as an air compressor for fuel cell stacks was described, it is also possible to apply this invention as a compressor of other uses.

  In the above embodiment, the outlets 28b of the scroll portion 28 are disposed at symmetrical positions, that is, at the same rotational position, but the present invention is not limited to this. Although not shown, the outlets 28b of the scrolls 28 of the two centrifugal compressors 1 and 2 are disposed at positions separated by, for example, 180 ° from each other, and the two are combined by a substantially U-shaped outlet pipe. You can also. In this case, the outlet pipe may have a rotationally symmetrical shape instead of the plane symmetry as in the above embodiment.

1, 2 ... centrifugal compressor 3 ... electric motor 4 ... outlet pipe 5 ... discharge port 7, 8 ... compressor housing 9 ... stator housing 15 ... stator 16 ... bearing 17 ... rotating shaft 18 ... permanent magnet 21, 22 ... impeller 26 ... Intake port 27 ... diffuser part 28 ... scroll part

Claims (5)

A pair of compressor housings each having a suction port at its central portion and an annular diffuser portion and a scroll portion so as to surround the suction port, and symmetrically disposed such that the suction ports face in opposite directions;
An electric motor located between the pair of compressor housings;
A pair of impellers mounted symmetrically on opposite ends of the rotary shaft of the electric motor so as to face in opposite directions, respectively, and constituting a centrifugal compressor in combination with the compressor housing;
An outlet pipe extending in a substantially U-shape so that the outlets of the scroll portions of the pair of compressor housings are assembled together and having a single discharge port at the center, and configured symmetrically;
Electric compressor equipped with The pair of impellers are identical to each other,
The electric compressor according to claim 1, wherein the blades of each impeller are attached to the rotating shaft so that the phases of the blades are different from each other. The pair of impellers have the same shape of rotor defined by the outer edge of the blade, and
The electric compressor according to claim 1, wherein the number of each wing is different from each other. A cylindrical stator housing accommodating the stator of the electric motor is mounted between the pair of compressor housings,
The electric compressor according to any one of claims 1 to 3, wherein the stator housing comprises a cooling fin for air cooling or a water jacket for liquid cooling.   The electric compressor according to any one of claims 1 to 4, which is an air compressor for supplying air as an oxidant to a fuel cell stack mounted on a vehicle.

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