Electric supercharger

Abstract

This electric supercharger comprises: a compressor; and a motor unit that has a motor case joined to the compressor in an axial direction, and imparts torque to a compressor impeller. The joint between the compressor and the motor case is provided with a gap region where the compressor and the motor case face each other in the axial direction with a gap therebetween.

Description

electric supercharger

[0001] The present disclosure relates to an electric supercharger.

[0002] Conventionally, there has been known an electric supercharger having a structure in which a compressor and a motor unit that applies torque to the compressor impeller are connected in the direction of the rotation axis (see Patent Document 1 below). In this type of electric supercharger, heat is generated in the compressor due to adiabatic compression of gas, and some of this heat is conducted from the compressor to the motor side.

[0003] Japanese Patent Application Laid-Open No. 2009-024576

[0004] However, if a large amount of heat is transferred from the compressor to the motor, it can cause the motor's temperature to rise, potentially reducing the motor's operating performance. Furthermore, since the heat from the compressor is ultimately processed by the cooling system that cools the motor, it increases the load on the cooling system. Therefore, this disclosure describes an electric supercharger that suppresses the transfer of heat from the compressor to the motor.

[0005] An electric supercharger according to one aspect of the present disclosure is an electric supercharger including a compressor and a motor unit having a motor case joined to the compressor in the direction of the rotation axis and applying torque to an impeller of the compressor, wherein a gap region is provided at the joint between the compressor and the motor case, where the compressor and the motor case face each other in the direction of the rotation axis with a gap therebetween.

[0006] According to the present disclosure, it is possible to provide an electric supercharger that suppresses heat transfer from a compressor to a motor section.

[0007] Fig. 2 is a cross-sectional view showing an electric supercharger according to an embodiment; Fig. 3 is a cross-sectional view showing an enlarged portion of the electric supercharger of Fig. 1; Fig. 4 is a view of a joint surface of a motor case joined to a compressor, as viewed from an axial direction; Fig. 5 is a view of a modified example of a joint surface of a motor case joined to a compressor, as viewed from an axial direction.

[0008] The gist of the present disclosure lies in the following [1] to [7].

[0009] [1] An electric supercharger comprising: a compressor; and a motor section having a motor case joined to the compressor in the direction of the rotation axis and applying torque to an impeller of the compressor, wherein a gap region is provided at the joint between the compressor and the motor case, where the compressor and the motor case face each other in the direction of the rotation axis with a gap therebetween.

[0010] [2] The electric supercharger according to [1], wherein a radial position of the outermost peripheral portion of the gap region is the same as a radial position of a diffuser outlet of the compressor or is further outward than the radial position of the diffuser outlet, and is the same as a radial position of an outermost peripheral portion of a scroll of the compressor or is further inner than the radial position of the outermost peripheral portion.

[0011] [3] The electric supercharger according to [1] or [2], wherein a radial position of a diffuser outlet of the compressor is on the inner circumferential side of a radial position of an outermost circumferential portion of the gap region and on the outer circumferential side of a radial position of an innermost circumferential portion of the gap region.

[0012] [4] The electric supercharger according to any one of [1] to [3], wherein the gap region is divided into a plurality of regions in the circumferential direction.

[0013] [5] The electric supercharger according to any one of [1] to [4], wherein a projected area of ​​the gap region projected in the direction of the rotation axis is 40% or more of a projected area of ​​the entire joint projected in the direction of the rotation axis.

[0014] [6] The electric supercharger according to any one of [1] to [5], wherein the motor case is formed with a cooling air flow path that connects the outside of the motor case with a space that houses a bearing of the motor section and through which cooling air that cools the bearing circulates, and the gap region is provided at a position that does not overlap with the cooling air flow path when viewed from the direction of the rotation axis.

[0015] [7] The electric supercharger according to any one of [1] to [6], wherein the compressor has a compressor housing and a diffuser plate that forms a diffuser between the compressor housing and the diffuser plate and is joined to the motor case at the joint, and the diffuser plate is made of stainless steel.

[0016] An electric supercharger 1 according to an embodiment of the present disclosure will be described below with reference to the drawings. Identical or equivalent elements in the drawings are designated by the same reference numerals, and redundant description will be omitted. Note that, because characteristic features may be exaggerated in the drawings, the dimensional ratios of the various components may not be consistent between the drawings. In the following description, the terms "axial direction," "radial direction," and "circumferential direction" refer to the direction of the rotational axis of the rotating shaft 15 of the electric supercharger 1 (the direction of the rotational axis H), the rotational radial direction, and the rotational circumferential direction, respectively. In addition, in the direction of the rotational axis H, the turbine 2 side of the electric supercharger 1 (the left side in FIG. 1 ) may be simply referred to as the "turbine side," and the compressor 3 side (the right side in FIG. 1 ) may be simply referred to as the "compressor side."

[0017] Fig. 1 is a cross-sectional view showing an electric supercharger 1, and Fig. 2 is an enlarged cross-sectional view showing a portion thereof. The electric supercharger 1 of this embodiment is an electrically assisted turbocharger mounted on a fuel cell vehicle. The electric supercharger 1 supplies generated compressed air to a fuel cell stack 91 to increase the amount of oxygen involved in chemical reactions in the fuel cell stack 91.

[0018] The electric supercharger 1 includes a turbine 2 and a compressor 3. The electric supercharger 1 further includes a motor unit 20 provided between the turbine 2 and the compressor 3, and an inverter unit 30 that supplies electric power to the motor unit 20.

[0019] The turbine 2 includes a turbine housing 4 and a turbine impeller 6 housed in the turbine housing 4. The turbine housing 4 has a scroll 12 extending circumferentially around the turbine impeller 6. The turbine housing 4 is also provided with an exhaust gas inlet 8 and an exhaust gas outlet 10. The compressor 3 includes a compressor housing 5 and a compressor impeller 7 housed in the compressor housing 5. The compressor housing 5 has a scroll 13 extending circumferentially around the compressor impeller 7. The compressor housing 5 is also provided with an intake port 9 and a discharge port 11. The compressor 3 has a centrifugal compressor structure, and the compressor impeller 7 discharges air introduced axially from the intake port 9 radially outward toward the scroll 13.

[0020] The electric supercharger 1 also includes a rotating shaft 15 that connects the turbine impeller 6 and the compressor impeller 7. That is, the turbine impeller 6 is provided at one end of the rotating shaft 15, and the compressor impeller 7 is provided at the other end of the rotating shaft 15. The turbine impeller 6, the rotating shaft 15, and the compressor impeller 7 integrally form a rotating body 19 that rotates around the rotation axis H.

[0021] The motor section 20 includes a motor 21 and a motor case 23 that houses the motor 21. The motor 21 is, for example, a brushless AC motor, and includes a rotor 27, which is a rotor, and a stator 29, which is a stator. The rotor 27 is fixed to the rotary shaft 15 and is located between the turbine impeller 6 and the compressor impeller 7. The stator 29 is disposed so as to surround the periphery of the rotor 27 and is fixed to the motor case 23.

[0022] The rotating shaft 15 also passes through the motor case 23 in the axial direction. At each portion where the rotating shaft 15 passes through, the motor case 23 is provided with a pair of radial bearings 42, 43 that support the rotating shaft 15. The turbine-side radial bearing 42 is located between the motor 21 and the turbine impeller 6. The compressor-side radial bearing 43 is located between the motor 21 and the compressor impeller 7. The motor case 23 is also provided with a thrust bearing 45 for the rotating shaft 15. The thrust bearing 45 is located between the radial bearing 43 and the compressor impeller 7. The radial bearings 42, 43 and the thrust bearing 45 are air bearings.

[0023] The inverter unit 30 is connected to the motor unit 20 via a connector 31. The inverter unit 30 includes an inverter case 33 disposed outside the motor case 23, and an inverter main body 35 and bus bars 37 housed within the inverter case 33. The inverter main body 35 is electrically connected to the stator 29 of the motor 21 via the bus bars 37 and the connector 31.

[0024] In this electric supercharger 1, exhaust gas discharged from the fuel cell stack 91 flows into the turbine housing 4 through the exhaust gas inlet 8. The exhaust gas then flows into the turbine impeller 6 through the scroll 12, causing the turbine impeller 6 to rotate about the rotation axis H. The exhaust gas then flows out of the turbine housing 4 through the exhaust gas outlet 10. When the turbine impeller 6 rotates as described above, the compressor impeller 7 rotates via the rotary shaft 15. The rotating compressor impeller 7 draws in external air through the intake port 9. This air passes through the compressor impeller 7 and the scroll 13, is compressed, and is discharged from the discharge port 11. The compressed air discharged from the discharge port 11 is supplied to the fuel cell stack 91 described above.

[0025] When the torque of the rotating shaft 15 is insufficient, the motor 21 applies torque to the rotating shaft 15 to make up for the shortage. That is, when a current is supplied from the inverter main body 35 to the coil of the stator 29, a magnetic field is generated around the stator 29, and this magnetic field acts on the permanent magnet of the rotor 27 in the circumferential direction, resulting in the application of torque to the rotating shaft 15.

[0026] Next, the structure of the vicinity of the joint 50 between the compressor 3 and the motor unit 20 will be described. FIG. 2 is an enlarged cross-sectional view showing the vicinity of the joint 50. FIG. 3 is a view of the joint surface 23a of the motor case 23 joined to the compressor 3, viewed from the axial direction. In addition to the compressor housing 5 and compressor impeller 7 described above, the compressor 3 includes a diffuser plate 51. The diffuser plate 51 is located between the compressor housing 5 and the motor case 23. The diffuser plate 51 is joined to the turbine side of the compressor housing 5 and to the compressor side of the motor case 23. A diffuser 53 is formed in a region radially outward of the compressor impeller 7, and is sandwiched in the axial direction between the diffuser plate 51 and the compressor housing 5. The diffuser plate 51 is made of a metal with low thermal conductivity, such as stainless steel. In this embodiment, the diffuser plate 51 is made of stainless steel.

[0027] The motor case 23 is fitted with the aforementioned radial bearing 43 and thrust bearing 45 located around the rotating shaft 15. A cooling air flow path 55 is formed in the motor case 23. The cooling air flow path 55 connects the outside of the motor case 23 with the bearing housing space 52. The bearing housing space 52 houses the radial bearing 43 and thrust bearing 45. The cooling air flow path 55 circulates cooling air sent to the radial bearing 43 and thrust bearing 45 from a cooling air source (not shown) external to the motor section 20. This cooling air cools the radial bearing 43 and thrust bearing 45. After passing through the radial bearing 43 and thrust bearing 45, the cooling air passes through the interior of the motor case 23 and is ultimately discharged from the exhaust gas outlet 10 together with the exhaust gas from the turbine 2. As another structure for cooling the motor 21, the motor case 23 is provided with a cooling water flow path 56 (see FIG. 1 ). The cooling water flow path 56 is formed in a spiral shape within the outer wall of the motor case 23, and cools the motor 21 by flowing cooling water supplied from an external cooling water source (not shown).

[0028] A joint 50 between the diffuser plate 51 and the motor case 23 includes a gap region 57 where the diffuser plate 51 and the motor case 23 face each other in the axial direction with a gap G between them. More specifically, at the joint 50, the diffuser plate 51 and the motor case 23 are joined with the joining surface 23a of the motor case 23 in contact with the joining surface 51a of the diffuser plate 51. A recess 59 is also present in the joining surface 23a of the motor case 23. The recess 59 is formed by slightly recessing a portion of the joining surface 23a toward the turbine. A bottom surface 59a of the recess 59 forms a plane perpendicular to the axial direction and faces the joining surface 51a of the diffuser plate 51 in the axial direction with the gap G between them. The size of the gap G is, for example, approximately 1 mm. The region of the joint 50 where the recess 59 exists is the gap region 57. The recess 59 is indicated by hatching in FIG. 3 .

[0029] When viewed from the axial direction, the gap region 57 extends in a band shape in the circumferential direction with a predetermined radial width along an arc centered on the rotation axis H. When viewed from the axial direction, the gap region 57 is provided at a position that does not overlap with the cooling air flow path 55. The radial position of the outermost peripheral portion 57a ​​of the gap region 57 is outer than a radial position 61 of an outlet of the diffuser 53. Furthermore, the radial position of the outermost peripheral portion 57a ​​is inner than a radial position 62 of the outermost peripheral portion of the scroll 13 of the compressor 3. The radial position of the outermost peripheral portion 57a ​​may be the same as the radial position 61 of the outlet of the diffuser 53 or may be the same as the radial position 62 of the outermost peripheral portion of the scroll 13 of the compressor 3.

[0030] Furthermore, the radial position 61 of the outlet of the diffuser 53 is located on the inner side of the radial position of the outermost peripheral portion 57 a of the gap region 57 and on the outer side of the radial position of the innermost peripheral portion 57 b of the gap region 57 .

[0031] Furthermore, theoretically, there is a point within the diffuser 53 where the compressed air reaches the highest pressure. If the radial position of this point is indicated by reference numeral 63 as shown in Fig. 2 , the axial flow path width of the diffuser 53 is constant on the inner side of the radial position 63, and the axial flow path width of the diffuser 53 increases from the radial position 63 toward the outlet (radial position 61) of the diffuser 53. The radial position 63 is located on the inner side of the radial position of the outermost peripheral portion 57a ​​of the gap region 57 and on the outer side of the radial position of the innermost peripheral portion 57b of the gap region 57.

[0032] An O-ring 67 is disposed near the outermost periphery of the joint 50 and is sandwiched between the diffuser plate 51 and the motor case 23. This O-ring 67 prevents compressed air and the like from leaking to the outside through the joint 50. The outermost periphery 57a of the gap region 57 is located on the inner periphery side of the O-ring 67.

[0033] The projected area of ​​the gap region 57 projected in the axial direction is preferably 40% or more of the projected area of ​​the entire joint 50 projected in the axial direction. In this case, the projected area of ​​the entire joint 50 is the sum of the projected area of ​​the gap region 57 and the projected area of ​​all portions where the diffuser plate 51 and the motor case 23 are in contact. The projected area of ​​the gap region 57 corresponds to the area of ​​the hatched portion (recess 59) in FIG. 3. As shown in FIG. 4, the gap region 57 may be divided into multiple portions in the circumferential direction. In the example of FIG. 4, the gap region 57 is divided into two portions in the circumferential direction, but the gap region 57 may be divided into three or more portions.

[0034] The effects of the electric supercharger 1 described above will now be explained. In this electric supercharger 1, the diffuser plate 51 of the compressor 3 and the motor case 23 of the motor section 20 are joined in the axial direction at the joint 50. In the compressor 3, heat is generated by adiabatic compression of air. If a large amount of this heat is conducted to the motor section 20, it can cause a rise in the temperature of the motor 21, which can reduce the operating performance of the motor 21 due to the heat. In addition, it increases the load on the cooling system, including the cooling air flow path 55 and the cooling water flow path 56.

[0035] In contrast, in the electric supercharger 1, a gap region 57 is provided at the joint 50, where the diffuser plate 51 and the motor case 23 face each other in the rotation direction with a gap G between them. The presence of this gap G reduces heat transfer from the diffuser plate 51 to the motor case 23, that is, suppresses heat transfer from the compressor 3 to the motor section 20. Therefore, a decrease in the continuous operation performance of the motor 21 due to temperature is suppressed. In addition, the load on the cooling system for cooling the motor section 20 can be reduced.

[0036] Furthermore, by making the projected area of ​​the gap region 57 projected in the axial direction 40% or more of the projected area of ​​the entire joint portion 50 projected in the axial direction, as described above, the above-mentioned effects can be efficiently obtained.

[0037] Furthermore, as mentioned above, by using a metal with low thermal conductivity, such as stainless steel, as the material for the diffuser plate 51, the transfer of heat from the compressor 3 to the motor section 20 is suppressed even in the area where the diffuser plate 51 and the motor case 23 come into contact.

[0038] Here, the pressure of the compressed air in the compressor 3 is greatest at a location near the radial position 61 of the outlet of the diffuser 53. Therefore, it is considered that the temperature resulting from the adiabatic compression of the air is also greatest at a location near the radial position 61. In contrast, the radial position of the outermost peripheral portion 57a ​​of the gap region 57 is outer than the radial position 61 of the outlet of the diffuser 53 and inner than the radial position 62 of the outermost peripheral portion of the scroll 13. Thus, although the radial position 61 can be particularly hot, the gap region 57 extends outer circumferentially to a position beyond the radial position 61. This further efficiently reduces heat transfer from the diffuser plate 51 to the motor case 23.

[0039] Furthermore, a radial position 61 of the outlet of the diffuser 53 is located radially inward of the radial position of the outermost peripheral portion 57a ​​of the gap region 57 and radially outward of the radial position of the innermost peripheral portion 57b of the gap region 57. In this way, the presence of the gap region 57 radially straddling the location of the radial position 61, which can become particularly hot, further efficiently reduces heat transfer from the diffuser plate 51 to the motor case 23.

[0040] Furthermore, the radial position 63 at which the air compressed by the compressor 3 theoretically reaches the highest pressure is located more inward than the radial position of the outermost peripheral portion 57a ​​of the gap region 57 and more outward than the radial position of the innermost peripheral portion 57b of the gap region 57. In this way, the existence of the gap region 57 radially straddles the radial position 63, which theoretically can reach particularly high pressure and temperature, thereby more efficiently reducing heat transfer from the diffuser plate 51 to the motor case 23.

[0041] Furthermore, if the cooling air flow path 55 and the recess 59 were provided in the motor case 23 so as to overlap in the axial direction, the wall between the cooling air flow path 55 and the bottom surface 59a of the recess 59 would be too thin. In contrast, in the electric supercharger 1, the gap region 57 is provided in a position that does not overlap with the cooling air flow path 55 when viewed in the axial direction, so that it is possible to ensure a sufficient wall thickness of the motor case 23 in the portion where the cooling air flow path 55 is provided. Furthermore, in this portion, there is no gap region 57 and the diffuser plate 51 and the motor case 23 are in contact, but much of the heat transferred from the diffuser plate 51 to the motor case 23 is removed by the cooling air passing through the cooling air flow path 55.

[0042] The present disclosure can be embodied in various forms, including the above-described embodiment, with various modifications and improvements based on the knowledge of those skilled in the art. Furthermore, modified examples can be constructed by utilizing the technical details described in the above-described embodiment. The configurations of the respective embodiments may be used in appropriate combination. For example, in the embodiment, the clearance region 57 is provided by forming a recess 59 in the joining surface 23 a of the motor case 23. However, the clearance region may be provided by forming a recess in the joining surface 51 a of the diffuser plate 51.

[0043] REFERENCE SIGNS LIST 1 Electric supercharger 3 Compressor 20 Motor section 23 Motor case 50 Joint section 51 Diffuser plate 53 Diffuser 55 Cooling air passage 57 Gap area 57a Outermost periphery section 57b Innermost periphery section 61 Radial position of diffuser outlet 62 Radial position of outermost periphery section of scroll G Gap H Rotation axis

Claims

1. An electric supercharger comprising: a compressor; and a motor section having a motor case joined to the compressor in the direction of the rotation axis and applying torque to an impeller of the compressor, wherein a gap region is provided at the joint between the compressor and the motor case, where the compressor and the motor case face each other in the direction of the rotation axis with a gap therebetween.

2. The electric supercharger according to claim 1, wherein the radial position of the outermost portion of the gap region is the same as the radial position of a diffuser outlet of the compressor or is further outboard than the radial position of the diffuser outlet, and is the same as the radial position of the outermost portion of the scroll of the compressor or is further inboard than the radial position of the outermost portion.

3. The electric supercharger according to claim 1, wherein the radial position of the diffuser outlet of the compressor is on the inner side of the radial position of the outermost peripheral portion of the gap region and on the outer side of the radial position of the innermost peripheral portion of the gap region.

4. The electric supercharger according to claim 1, wherein the gap region is divided into a plurality of regions in the circumferential direction.

5. An electric supercharger as described in claim 1, wherein the projected area of ​​the gap region projected in the direction of the rotation axis is 40% or more of the projected area of ​​the entire joint projected in the direction of the rotation axis.

6. An electric supercharger as described in claim 1, wherein the motor case is formed with a cooling air flow path that communicates between the outside of the motor case and a space that houses a bearing of the motor section, and through which cooling air circulates to cool the bearing, and when viewed from the direction of the rotation axis, the gap region is provided at a position that does not overlap with the cooling air flow path.

7. The electric supercharger according to claim 1, wherein the compressor has: a compressor housing; and a diffuser plate that forms a diffuser between the compressor housing and the diffuser plate and is joined to the motor case at the joint, the diffuser plate being made of stainless steel.

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