Compressor housing and turbocharger including the same

Abstract

A compressor housing accommodating a compressor wheel for compressing intake air supplied to an engine has therein an outer cooling passage extending along a circumferential direction on an outer circumferential side of a scroll passage of a spiral shape through which the intake air compressed by the compressor wheel flows, and an inner cooling passage extending along the circumferential direction on an inner circumferential side of the scroll passage. The inner cooling passage is separated from the outer cooling passage by a separation wall extending along the circumferential direction.

Claims

1. A compressor housing accommodating a compressor wheel for compressing intake air supplied to an engine, wherein the compressor housing has therein: an outer cooling passage extending along a circumferential direction on an outer circumferential side of a scroll passage of a spiral shape through which the intake air compressed by the compressor wheel flows; an inner cooling passage extending along the circumferential direction on an inner circumferential side of the scroll passage, the inner cooling passage being separated from the outer cooling passage by a separation wall extending along the circumferential direction, and wherein when, in a cross-section along a rotational axis of the compressor wheel, a linear direction which passes through a gravity center position of a cross-section of the inner cooling passage and in which the cross-section of the inner cooling passage has a maximum length is defined as a reference longitudinal direction, the reference longitudinal direction is a direction along the rotational axis of the compressor wheel.

2. The compressor housing according to claim 1, wherein the outer cooling passage includes a curved passage portion having a cross-sectional shape curved along a cross-sectional shape of the scroll passage in a cross-section along a rotational axis of the compressor wheel.

3. The compressor housing according to claim 2, wherein the outer cooling passage further includes a flat passage portion having a cross-sectional shape extending flat from at least one of both edges of the curved passage portion in a direction along the cross-sectional shape of the scroll passage in the cross-section along the rotational axis of the compressor wheel.

4. The compressor housing according to claim 1, wherein the inner cooling passage has a cross-sectional shape curved along a cross-sectional shape of the scroll passage in a cross-section along a rotational axis of the compressor wheel.

5. The compressor housing according to claim 1, wherein the compressor housing further has therein a diffuser passage communicating with the scroll passage and extending inward in a radial direction of the compressor wheel from the scroll passage, and wherein, when a direction perpendicular to the reference longitudinal direction is defined as a width direction, a maximum portion of the inner cooling passage in the width direction is positioned on a side of the diffuser passage with respect to the gravity center position.

6. The compressor housing according to claim 1, wherein the compressor housing further has therein a diffuser passage communicating with the scroll passage and extending inward in a radial direction of the compressor wheel from the scroll passage, and wherein, when a direction perpendicular to the reference longitudinal direction is defined as a width direction, a maximum portion of the inner cooling passage in the width direction is positioned on a side opposite to the diffuser passage with respect to the gravity center position.

7. The compressor housing according to claim 1, wherein a width of the inner cooling passage in a direction perpendicular to the reference longitudinal direction is equal to or larger than that of the outer cooling passage.

8. The compressor housing according to claim 1, comprising: at least two first communication holes connecting the outer cooling passage to outside of the compressor housing; and at least two second communication holes connecting the inner cooling passage to outside of the compressor housing.

9. The compressor housing according to claim 8, wherein at least one of the at least two first communication holes and the at least two second communication holes opens vertically upward when the compressor housing is attached to the engine.

10. The compressor housing according to claim 8, wherein openings of the first communication holes make a 90-degree angle with openings of the second communication holes.

11. The compressor housing according to claim 8, wherein one of the at least two first communication holes is an inlet of a coolant flowing through the outer cooling passage, and another one of the at least two first communication holes is an outlet of the coolant flowing through the outer cooling passage, and wherein one of the at least two second communication holes is an inlet of a coolant flowing through the inner cooling passage, and another one of the at least two second communication holes is an outlet of the coolant flowing through the inner cooling passage.

12. The compressor housing according to claim 1, wherein an outlet of a coolant flowing through the outer cooling passage is joined with an outlet of a coolant flowing through the inner cooling passage.

13. The compressor housing according to claim 1, wherein an inlet of a coolant flowing through the outer cooling passage is directly connected to an outlet of a coolant flowing through the inner cooling passage, or an outlet of a coolant flowing through the outer cooling passage is directly connected to an inlet of a coolant flowing through the inner cooling passage.

14. A turbocharger comprising a compressor housing accommodating a compressor wheel for compressing intake air supplied to an engine, wherein the compressor housing has therein: an outer cooling passage extending along a circumferential direction on an outer circumferential side of a scroll passage of a spiral shape through which the intake air compressed by the compressor wheel flows; an inner cooling passage extending along the circumferential direction on an inner circumferential side of the scroll passage, the inner cooling passage being separated from the outer cooling passage by a separation wall extending along the circumferential direction, and wherein when, in a cross-section along a rotational axis of the compressor wheel, a linear direction which passes through a gravity center position of a cross-section of the inner cooling passage and in which the cross-section of the inner cooling passage has a maximum length is defined as a reference longitudinal direction, the reference longitudinal direction is a direction along the rotational axis of the compressor wheel.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a perspective view of a compressor housing according to a first embodiment of the present disclosure.

(2) FIG. 2 is a cross-sectional view taken along line II-II in FIG. 1.

(3) FIG. 3 is a diagram for describing a detailed shape of an inner cooling passage formed in the compressor housing according to the first embodiment of the present disclosure.

(4) FIG. 4 is a graph showing experimental results regarding a compressed air cooling effect in a turbocharger including a compressor housing according to a second embodiment of the present disclosure.

(5) FIG. 5 is a graph showing experimental results regarding a compressor performance improvement effect in a turbocharger including a compressor housing according to the second embodiment of the present disclosure.

(6) FIG. 6 is a cross-sectional view of a compressor housing according to the second embodiment of the present disclosure.

(7) FIG. 7 is a cross-sectional view of a compressor housing according to a third embodiment of the present disclosure.

(8) FIG. 8 is a cross-sectional view of a modification of the compressor housing according to the third embodiment of the present disclosure.

(9) FIG. 9 is a perspective view of an outer cooling passage and an inner cooling passage formed in a compressor housing according to a fourth embodiment of the present disclosure.

(10) FIG. 10 is a perspective view of an outer cooling passage and an inner cooling passage formed in a compressor housing according to a fifth embodiment of the present disclosure.

(11) FIG. 11 is a perspective view of an outer cooling passage and an inner cooling passage formed in a compressor housing according to a sixth embodiment of the present disclosure.

DETAILED DESCRIPTION

(12) Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. However, the scope of the present invention is not limited to the following embodiments. It is intended that dimensions, materials, shapes, relative positions and the like of components described in the embodiments shall be interpreted as illustrative only and not intended to limit the scope of the present invention.

First Embodiment

(13) As shown in FIG. 1, a compressor housing 1 of a turbocharger includes a cylindrical air inlet part 2 into which air to be compressed by a compressor wheel (not shown) flows. The compressor housing 1 has a scroll passage 3 of a spiral shape formed around the air inlet part 2. The compressed air compressed by the compressor wheel flows through the scroll passage 3 and out of the turbocharger and then supplied to an engine (not shown). The cross-sectional area of the scroll passage 3 increases along the flowing direction of the compressed air, i.e., from the inlet side to the outlet side of the scroll passage 3.

(14) As shown in FIG. 2, the compressor housing 1 has a diffuser passage 4 connecting an air passage 2a inside the air inlet part 2 and the scroll passage 3 so as to extend inward in the radial direction of the compressor housing (not shown) from the scroll passage 3. Further, the compressor housing 1 has an outer cooling passage 11 extending along the circumferential direction on the outer circumferential side of the scroll passage 3 and an inner cooling passage 12 extending along the circumferential direction on the inner circumferential side of the scroll passage 3. As cooling water as a coolant flows through each of the outer cooling passage 11 and the inner cooling passage 12, the compressed air flowing through the scroll passage 3 is cooled. The outer cooling passage 11 and the inner cooling passage 12 are separated by a separation wall 13 extending along the circumferential direction in the compressor housing 1.

(15) As shown in FIG. 1, the compressor housing 1 includes four first communication holes 5a, 5b, 5c, 5d connecting the outer cooling passage 11 (see FIG. 2) to the outside of the compressor housing 1 and four second communication holes 6a, 6b, 6c, 6d connecting the inner cooling passage 12 (see FIG. 2) to the outside of the compressor housing 1. Openings of the first communication holes 5a, 5b, 5c, 5d make a 90-degree angle with openings of the second communication holes 6a, 6b, 6c, 6d.

(16) The first communication hole 5a forms an inlet for introducing cooling water into the outer cooling passage 11, and the first communication hole 5b forms an outlet for discharging cooling water from the outer cooling passage 11. The second communication hole 6a forms an inlet for introducing cooling water into the inner cooling passage 12, and the second communication hole 6b forms an outlet for discharging cooling water from the inner cooling passage 12. The first communication hole 5b and the second communication hole 6a are connected by a connection pipe 7. That is, the outer cooling passage 11 and the inner cooling passage 12 are connected via the connection pipe 7.

(17) As shown in FIG. 2, the outer cooling passage 11 includes a curved passage portion 11a having a cross-sectional shape curved along the cross-sectional shape of the scroll passage 3 in a cross-section along the rotational axis L.sub.0 of the compressor wheel, and flat passage portions 11b, 11c having a cross-sectional shape extending flat from both edges 11a1, 11a2 of the curved passage portion 11a in a direction along the cross-sectional shape of the scroll passage 3. The outer cooling passage 11 has a constant width W.sub.0 along the cross-sectional shape of the scroll passage 3. Although in the first embodiment, the width of the outer cooling passage 11 is constant at W.sub.0, in other embodiments, the width of the outer cooling passage 11 may vary in the direction along the cross-sectional shape of the scroll passage 3.

(18) As shown in FIG. 3, when, in a cross-section along the rotational axis L.sub.0 of the compressor wheel, a linear direction which passes through a gravity center position G of a cross-section of the inner cooling passage 12 and in which the cross-section of the inner cooling passage 12 has a maximum length is defined as a reference longitudinal direction L, the reference longitudinal direction L is a direction along the rotational axis L.sub.0 of the compressor wheel. Here, the direction along the rotational axis L.sub.0 of the compressor wheel means that the angle θ between the rotational axis L.sub.0 of the compressor wheel and the reference longitudinal direction L is less than 45°.

(19) In a direction in which the compressed air flows through the scroll passage 3 (see FIG. 2), a cross-section 12a of the inner cooling passage 12 is closer to the outlet of the scroll passage 3, and a cross-section 12b of the inner cooling passage 12 is closer to the inlet of the scroll passage 3. A linear direction which passes through a gravity center position G.sub.a of the cross-section 12a of the inner cooling passage 12 and in which the cross-section 12a of the inner cooling passage 12 has a maximum length is defined as a reference longitudinal direction L1. Further, a linear direction which passes through a gravity center position G.sub.b of the cross-section 12b of the inner cooling passage 12 and in which the cross-section 12b of the inner cooling passage 12 has a maximum length is defined as a reference longitudinal direction L2.

(20) In each of the cross-sections 12a, 12b of the inner cooling passage 12, a direction perpendicular to the reference longitudinal direction L.sub.1, L.sub.2 is defined as a width direction. In each of the cross-sections 12a, 12b, a maximum portion 12a1, 12b1 of the width of the inner cooling passage 12 (respective lengths are represented by W.sub.a, W.sub.b) is positioned on a side of the diffuser passage 4 (see FIG. 2) with respect to the gravity center position G.sub.a, G.sub.b. That is, the maximum portion of the inner cooling passage 12 in the width direction is positioned closer to the diffuser passage 4 over a range from the inlet to the outlet of the scroll passage 3.

(21) Further, the inner cooling passage 12 is configured such that the width of the inner cooling passage 12 is larger than the width W.sub.0 (see FIG. 2) of the outer cooling passage 11. With this configuration, since the inner cooling passage 12 has a larger heat transfer area on a side closer to the diffuser passage 4, it is possible to improve the compressed air cooling effect in the diffuser passage 4.

(22) Next, the cooling operation by cooling water in the compressor housing 1 according to the first embodiment will be described.

(23) As shown in FIG. 1, cooling water flows into the outer cooling passage 11 (see FIG. 2) via the first communication hole 5a which is an inlet of cooling water. The cooling water flows through the outer cooling passage 11 and then flows out of the outer cooling passage 11 via the first communication hole 5b which is an outlet of cooling water. The cooling water out of the outer cooling passage 11 passes through the connection pipe 7 and flows into the inner cooling passage 12 (see FIG. 2) via the second communication hole 6a which is an inlet of cooling water. The cooling water flows through the inner cooling passage 12 and then flows out of the inner cooling passage 12 via the second communication hole 6b which is an outlet of cooling water.

(24) As shown in FIG. 2, air flowing through the air passage 2a is compressed by the compressor wheel (not shown) into compressed air and flows through the diffuser passage 4 into the scroll passage 3. When the compressed air flows through the scroll passage 3 in the compressor housing 1, cooling water flowing through the outer cooling passage 11 cools the air from the outer circumferential side of the scroll passage 3, while cooling water flowing through the inner cooling passage 12 cools the air from the inner circumferential side of the scroll passage 3. The compressed air having passed through the scroll passage 3 then flows out of the compressor of the turbocharger. Then, the compressed air is cooled by an intercooler (not shown) and is supplied to an engine (not shown).

(25) Since the compressed air is cooled by cooling water flowing through the outer cooling passage 11 and the inner cooling passage 12, the compressed air at an appropriate temperature enters the intercooler. Thus, it is possible to reduce the cooling performance required in the intercooler, and it is possible to downsize the intercooler. As a result, it is possible to save the space of the intercooler.

(26) As described above, since the separation wall 13 separates the outer cooling passage 11 from the inner cooling passage 12, a range where the outer cooling passage 11 and the inner cooling passage 12 extend along the cross-sectional shape of the scroll passage 3 is reduced compared with the case where the cooling passage is formed so as to surround the scroll passage 3 from the inner peripheral side to the outer peripheral side of the scroll passage 3. Thus, the formation of a stagnation point is suppressed when cooling water flows through the outer cooling passage 11 and the inner cooling passage 12 each, and a reduction in flow rate of cooling water is suppressed, so that the cooling efficiency for the compressed air is improved. As a result, since the compressed air in the scroll passage 3 is efficiently cooled by cooling water flowing through the outer cooling passage 11 and the inner cooling passage 12 from both the outer circumferential side and the inner circumferential side of the scroll passage 3, it is possible to efficiently cool the compressed air in the turbocharger.

(27) Further, as described above, the outer cooling passage 11 includes the curved passage portion 11a having a cross-sectional shape curved along the cross-sectional shape of the scroll passage 3. Accordingly, since the distance between the curved passage portion 11a and the scroll passage 3 is reduced as much as possible along the cross-sectional shape of the scroll passage 3, it is possible to efficiently cool the compressed air.

(28) Further, as described above, the reference longitudinal direction L in which the length is maximized in a cross-section of the inner cooling passage 12 is along the rotational axis L.sub.0 of the compressor wheel. With this configuration, as shown in FIG. 2, since cooling water flowing through the inner cooling passage 12 reduces heat transfer from the compressed air at high temperature in the scroll passage 3 to air in the air passage 2a, i.e., air to be compressed by the compressor wheel (not shown), it is possible to improve the compressor performance.

(29) Further, as described above, the maximum portion 12a1, 12b1 of the inner cooling passage 12 in the width direction is positioned closer to the diffuser passage 4 over a range from the inlet to the outlet of the scroll passage 3. Thus, it is possible to improve the cooling effect for the compressed air in the diffuser passage 4.

(30) Next, results of experiment regarding the compressed air cooling effect and the compressor performance improvement effect will be described.

(31) Experiment was performed on a turbocharger including a compressor housing 1 according to the second embodiment described later. For each of the operating conditions in which the rotational speed of the compressor wheel is high, middle, or low, the supply condition of air supplied to the air passage 2a (see FIG. 2) was varied so that the compressor works in the vicinity of a surge region, in the vicinity of a choke region, or a peak region with the best compressor efficiency. In the air passage 2a, the atmospheric pressure is kept as much as possible, and the temperature on the turbine side of the turbocharger is fixed at 600° C.

(32) In the operating condition in which the rotational speed of the compressor wheel is high, the temperature of the compressed air discharged from the turbocharger was measured in five cases: cooling water at 50° C. flows through only the inner cooling passage 12 (see FIG. 6) at a flow rate of 6 L/min; the same flows through only the outer cooling passage 11 (see FIG. 2); the same flows through the inner cooling passage 12 and then the outer cooling passage 11; the same flows through the outer cooling passage 11 and then the inner cooling passage 12; and the same flows through neither the outer cooling passage 11 nor the inner cooling passage 12. The measurement results, i.e., experimental results regarding the compressed air cooling effect are shown in FIG. 4.

(33) As seen from FIG. 4, it was revealed that cooling by cooling water flowing through at least one of the outer cooling passage 11 or the inner cooling passage 12 reduces the temperature of the compressed air discharged from the turbocharger compared with not cooling. In addition, it was revealed that the compressed air cooling effect is increased in the case where cooling water flows through both the outer cooling passage 11 and the inner cooling passage 12, compared with the case where cooling water flows through one of the outer cooling passage 11 or the inner cooling passage 12.

(34) Further, the intake pressure ratio, i.e., a ratio of pressure at the outlet to pressure at the inlet of the compressor, against the air supply amount to the compressor is measured for each of the case where cooling water flows through neither the outer cooling passage 11 nor the inner cooling passage 12, and the case where cooling water flows through the outer cooling passage 11 and then the inner cooling passage 12. The measurement results, i.e., experimental results regarding the compressor performance improvement effect are shown in FIG. 5.

(35) Although there is no significant difference when the rotational speed of the compressor wheel is low, when the rotational speed of the compressor wheel is middle or high, the intake pressure ratio is increased in the case where cooling water flows through the outer cooling passage 11 and then the inner cooling passage 12, compared with the case where cooling water flows through neither the outer cooling passage 11 nor the inner cooling passage 12. From these results, it was revealed that the compressor performance is increased by cooling the compressed air.

(36) As described above, since the separation wall 13 separates the outer cooling passage 11 extending along the circumferential direction on the outer circumferential side of the scroll passage 3 from the inner cooling passage 12 extending along the circumferential direction on the inner circumferential side of the scroll passage 3, a range where the outer cooling passage 11 and the inner cooling passage 12 extend along the cross-sectional shape of the scroll passage 3 is reduced compared with the case where the cooling passage is formed so as to surround the scroll passage 3 from the inner peripheral side to the outer peripheral side of the scroll passage 3. Thus, the formation of a stagnation point is suppressed when cooling water flows through the outer cooling passage 11 and the inner cooling passage 12 each, and a reduction in flow rate of cooling water is suppressed, so that the cooling efficiency for the compressed air is improved. As a result, since the compressed air in the scroll passage 3 is efficiently cooled by cooling water flowing through the outer cooling passage 11 and the inner cooling passage 12 from both the outer circumferential side and the inner circumferential side of the scroll passage 3, it is possible to efficiently cool the compressed air in the turbocharger.

(37) In the first embodiment, when the compressed air in the scroll passage 3 is cooled by cooling water flowing through the outer cooling passage 11 and the inner cooling passage 12, the cooling water may boil. In this case, unless the steam is discharged from the outer cooling passage 11 and the inner cooling passage 12, the flow of cooling water is blocked, interrupting cooling of the compressed air. However, in the first embodiment, since the openings of the first communication holes 5a to 5d make a 90 degree angle with the openings of the second communication holes 6a to 6d, in the case where the turbocharger is placed so that the rotational axis L.sub.0 of the compressor wheel is oriented to the vertical direction or the horizontal direction, one of the first communication holes 5a to 5d and the second communication holes 6a to 6d opens vertically upward. By providing, for instance, a pressure control valve in the communication hole that opens vertically upward, the pressure control vale opens as the pressure of the steam increases and allows the steam to be discharged from the outer cooling passage 11 and the inner cooling passage 12 via the communication hole.

(38) As long as the steam is discharged from the outer cooling passage 11 and the inner cooling passage 12, the angle between the openings of the first communication holes 5a to 5d and the openings of the second communication holes 6a to 6d is not limited to 90 degree. If the direction of each communication hole is freely selected, it may be designed so that at least one of the first communication holes 5a to 5d and the second communication holes 6a to 6d opens vertically upward when the compressor housing 1 is attached to the engine.

(39) Further, although the number of the first communication holes and the number of the second communication holes are four each, their numbers are not limited to four. The number of the first communication holes and the number of the second communication holes are at least two each. When each of the outer cooling passage 11 and the inner cooling passage 12 has at least two communication holes, it is possible to arrange the outlets and the inlets of the outer cooling passage 11 and the inner cooling passage 12 in accordance with the layout of an engine room in which the turbocharger is mounted. Further, the first communication hole and the second communication hole are used to hold a core during casting of the compressor housing. When two or more first communication holes and two or more second communication holes exist, it is possible to improve the core holding capacity.

(40) In the first embodiment, as described above, the outer cooling passage 11 includes flat passage portions 11b, 11c having a cross-sectional shape extending flat from both edges 11a1, 11a2 of the curved passage portion 11a in a direction along the cross-sectional shape of the scroll passage 3 in a cross-section along the rotational axis L.sub.0 of the compressor wheel. The compressor housing 1 is produced by filling a mold with powder and heating and solidifying it into the shape of the compressor housing 1. If portions extending from both edges 11a1, 11a2 of the curved passage portion 11a are curved, it is difficult to open the mold. However, if the flat passage portions 11b, 11c having a cross-sectional shape extending flat from both edges 11a1, 11a2 of the curved passage portion 11a are formed, it is easy to open the mold, so that the productivity of the compressor housing 1 is improved.

(41) Although in the first embodiment, the flat passage portions 11b, 11c extend form both edges 11a1, 11a2 of the curved passage portion 11a, the present invention is not limited to this embodiment. The flat passage portion 11b or 11b may extend from one of the edges 11a1, 11a2, or the outer cooling passage 11 may include only the curved passage portion 11a.

(42) Although in the first embodiment, cooling water is configured to flow through the outer cooling passage 11 and then the inner cooling passage 12, the present invention is not limited to this embodiment. Cooling water may flow through the inner cooling passage 12 and then the outer cooling passage 11. In the case where cooling water flows through the inner cooling passage 12 and then the outer cooling passage 11, the first communication hole 5a and the second communication hole 6b are connected by the connection pipe 7.

Second Embodiment

(43) Next, a compressor housing according to the second embodiment will be described. The compressor housing according to the second embodiment is a modification of the first embodiment in that the shape of the inner cooling passage 12 is changed. In the second embodiment, the same constituent elements as those in the first embodiment are associated with the same reference numerals and not described again in detail.

(44) As shown in FIG. 6, in each of the cross-sections 12a, 12b, a maximum portion 12a1, 12b1 of the width of the inner cooling passage 12 is positioned on a side opposite to the diffuser passage 4 with respect to the gravity center position G.sub.a, G.sub.b. The configuration is otherwise the same as that of the first embodiment.

(45) With the configuration in the second embodiment, since a portion of the inner cooling passage 12 with a maximum cooling area (maximum portion 12a1, 12b1) is positioned along the cross-sectional shape of the scroll passage 3, and the cooling area is also effective for the diffuser passage 4, the compressed air cooling effect is improved. Thus, it is possible to efficiently cool the compressed air.

Third Embodiment

(46) Next, a compressor housing according to the third embodiment will be described. The compressor housing according to the third embodiment is a modification of the first embodiment in that the shape of the inner cooling passage 12 is changed. In the third embodiment, the same constituent elements as those in the first embodiment are associated with the same reference numerals and not described again in detail.

(47) As shown in FIG. 7, the inner cooling passage 12 has a cross-sectional shape curved along the cross-sectional shape of the scroll passage 3. Each of the outer cooling passage 11 and the inner cooling passage 12 has a constant width W.sub.0, W.sub.1 along the cross-sectional shape of the scroll passage 3. The widths W.sub.0, W.sub.1 are equal to each other (W.sub.0=W.sub.1). The configuration is otherwise the same as that of the first embodiment. Although in the third embodiment, the widths of the outer cooling passage 11 and the inner cooling passage 12 are constant at W.sub.0, W.sub.1, respectively, in other embodiments, the width of at least one of the outer cooling passage 11 or the inner cooling passage 12 may vary in the direction along the cross-sectional shape of the scroll passage 3.

(48) With the configuration in the third embodiment, since the widths of the outer cooling passage 11 and the inner cooling passage 12 are equal to each other, it is possible to reduce the pressure loss occurring when cooling water flows from the outer cooling passage 11 into the inner cooling passage 12. Thus, stagnation of the cooling water is reduced, and the flow is made uniform. Consequently, it is possible to efficiently cool the compressed air.

(49) Additionally, since the inner cooling passage 12 has a cross-sectional shape curved along the cross-sectional shape of the scroll passage 3, the distance between the inner cooling passage 12 and the scroll passage 3 is reduced as much as possible along the cross-sectional shape of the scroll passage 3. Thus, it is possible to efficiently cool the compressed air.

(50) As shown in FIG. 8, the inner cooling passage 12 in the third embodiment may be shaped such that the maximum portion 12a1, 12b1 is positioned on a side of the diffuser passage 4 with respect to the gravity center position G.sub.a, G.sub.b. With this embodiment, it is possible to efficiently cool the compressed air in the scroll passage 3, and it is also possible to improve the cooling effect for the compressed air in the diffuser passage 4.

(51) However, in the embodiment shown in FIG. 8, since the cross-sectional area closer to the diffuser passage 4 is larger and has smaller pressure loss, the flow of cooling water may be biased toward the diffuser passage 4. In order to avoid such a biased distribution of cooling water, as in the second embodiment shown in FIG. 6, the maximum portion 12a1, 12b1 is preferably positioned on a side opposite to the diffuser passage 4 with respect to the gravity center position G.sub.a, G.sub.b.

Fourth Embodiment

(52) Next, a compressor housing according to the fourth embodiment will be described. The compressor housing according to the fourth embodiment is a modification of the first to third embodiments in that the connection relationship between the outer cooling passage 11 and the inner cooling passage 12 is changed. The following embodiment will be described based on the third embodiment with a modified connection relationship between the outer cooling passage 11 and the inner cooling passage 12. However, the embodiment may be obtained by modifying the connection relationship between the outer cooling passage 11 and the inner cooling passage 12 in the first or second embodiment. In the fourth embodiment, the same constituent elements as those in the first to third embodiments are associated with the same reference numerals and not described again in detail.

(53) As shown in FIG. 9, cooling water enters the outer cooling passage 11 via an inlet 21 and then flows through and out of the outer cooling passage 11 via an outlet 22. Further, cooling water other than the cooling water flowing through the outer cooling passage 11 enters the inner cooling passage 12 via an inlet 23 and then flows through and out of the inner cooling passage 12 via an outlet 24. This embodiment is different from the first embodiment in that the outlet 22 does not communicate with the inlet 23. The configuration is otherwise the same as that of the first embodiment.

(54) In the fourth embodiment, since cooling water separately flows through the outer cooling passage 11 and the inner cooling passage 12, the cooling performance for the compressed air in the scroll passage 3 (see FIG. 7) is improved. Thus, it is possible to more efficiently cool the compressed air.

Fifth Embodiment

(55) Next, a compressor housing according to the fifth embodiment will be described. The compressor housing according to the fifth embodiment is a modification of the first to third embodiments in that the connection relationship between the outer cooling passage 11 and the inner cooling passage 12 is changed. The following embodiment will be described based on the third embodiment with a modified connection relationship between the outer cooling passage 11 and the inner cooling passage 12. However, the embodiment may be obtained by modifying the connection relationship between the outer cooling passage 11 and the inner cooling passage 12 in the first or second embodiment. In the fifth embodiment, the same constituent elements as those in the first to third embodiments are associated with the same reference numerals and not described again in detail.

(56) As shown in FIG. 10, the outer cooling passage 11 and the inner cooling passage 12 are connected on the downstream side so that cooling water flowing into and through the outer cooling passage 11 via an inlet 21 and cooling water flowing into and through the inner cooling passage 12 via an inlet 23 are discharged from a single outlet 22. That is, an outlet of the outer cooling passage 11 joined with an outlet of the inner cooling passage 12. The configuration is otherwise the same as that of the first embodiment.

(57) Since the outer cooling passage 11 and the inner cooling passage 12 share the single outlet 22, it is possible to reduce the cost of a core used for casting the compressor housing 1, and it is possible to improve the core holding capacity, compared with the case where each of the outer cooling passage 11 and the inner cooling passage 12 has an inlet and an outlet.

(58) Further, in the fifth embodiment, like the fourth embodiment, since cooling water separately flows through the outer cooling passage 11 and the inner cooling passage 12, the cooling performance for the compressed air in the scroll passage 3 (see FIG. 7) is improved. Thus, it is possible to more efficiently cool the compressed air.

Sixth Embodiment

(59) Next, a compressor housing according to the sixth embodiment will be described. The compressor housing according to the sixth embodiment is a modification of the first to third embodiments in that the connection relationship between the outer cooling passage 11 and the inner cooling passage 12 is changed. The following embodiment will be described based on the third embodiment with a modified connection relationship between the outer cooling passage 11 and the inner cooling passage 12. However, the embodiment may be obtained by modifying the connection relationship between the outer cooling passage 11 and the inner cooling passage 12 in the first or second embodiment. In the sixth embodiment, the same constituent elements as those in the first to third embodiments are associated with the same reference numerals and not described again in detail.

(60) As shown in FIG. 11, a downstream end of the outer cooling passage 11 is directly connected to an upstream end of the inner cooling passage 12 so that cooling water flowing into and through the outer cooling passage 11 via an inlet 21 flows into and through the inner cooling passage 12 and then are discharged from an outlet 22. The configuration is otherwise the same as that of the first embodiment.

(61) Since the downstream end of the outer cooling passage 11 is directly connected to the upstream end of the inner cooling passage 12, without using either a connection pipe connecting the inlet of the outer cooling passage 11 to the outlet of the inner cooling passage 12 or a connection pipe connecting the outlet of the outer cooling passage 11 to the inlet of the inner cooling passage 12, the outer cooling passage 11 and the inner cooling passage 12 can form a single continuous cooling passage. Thus, it is possible to downsize the turbocharger.

(62) Although in the sixth embodiment, cooling water is configured to flow through the outer cooling passage 11 and then the inner cooling passage 12, the present invention is not limited to this embodiment. Cooling water may flow through the inner cooling passage 12 and then the outer cooling passage 11. In the case where cooling water flow through the inner cooling passage 12 and then the outer cooling passage 11, the component indicated by the reference numeral 22 is the inlet of the cooling water, and the component indicated by the reference numeral 21 is the outlet of the cooling water.

(63) Although in the first to sixth embodiments, a coolant flowing through the outer cooling passage 11 and the inner cooling passage 12 is cooling water, the coolant is not limited to cooling water. As the coolant, any liquid such as oil or any gas such as air may be used.

REFERENCE SIGNS LIST

(64) 1 Compressor housing 2 Air inlet part 2a Air passage 3 Scroll passage 4 Diffuser passage 5a, 5b, 5c, 5d First communication hole 6a, 6b, 6c, 6d Second communication hole 7 Connection pipe 8 Outer cooling passage 11a Curved passage portion 11a1, 11a2 Edge (of curved passage portion) 11b, 11c Flat passage portion 12 Inner cooling passage 12a, 12b Cross-section (of inner cooling passage) 12a1, 2b1 Maximum portion 13 Separation wall 21 Inlet 22 Outlet 23 Inlet 24 Outlet G, G.sub.a, G.sub.b Gravity center position (of cross-section of inner cooling passage) L.sub.0 Rotational axis of compressor wheel L, L.sub.1, L.sub.2 Reference longitudinal direction W.sub.0 Width (of outer cooling passage) W.sub.a, W.sub.b Width (of maximum portion) θ.sub.1, θ.sub.2 Angle