Compressor casings for turbochargers

Abstract: A compressor casing for a turbocharger has an inlet port (6) which communicates with an inlet passage (7), which accommodates an impeller (11) and which communicates with a diffuser (8), which in turn communicates with a scroll (9). An annular chamber (25) is provided between the inlet passage (7) and the scroll (9) and communicates with the inlet passage (7) via a first opening (28) which is directed perpendicular to the impeller axis and optionally also via a second opening (30) which is also directed perpendicular to the impeller axis and is situated upstream of the first opening (28).

Description: The present invention relates to compressor casings for turbochargers. A known turbocharger compressor casing is shown in Figures 1 and 2 which are a diagrammatic longitudinal sectional view of the turbocharger and a scrap longitudinal sectional view of the turbocharger compressor on an enlarged scale, respectively. As is conventional, the turbocharger utilises exhaust gas 2 from an engine 1 to drive a turbine 3 which in turn drives a compressor 4 which is coupled by a common shaft with the turbine 3 and charges compressed air 5 into the engine 1. As shown in Figure 2, the compressor 4 comprises an integrally cast compressor casing 10 which defines an air inlet port 6, an air intake passage 7 extending from the port 6, a diffuser 8 extending radially around the outlet end of the passage 7 and a scroll or volute passage 9 extending around the outer surfaces of the diffuser 8 and passage 7, all of which are in communication with one another in that order. An impeller 11 is rotatably accommodated in the passage 7 and its rotation by the turbine 3 causes the air 5 to be sucked through the port 6 into the passage 7 and its pressure to be increased while flowing through the diffuser 8 and charged through the scroll 9 into the engine 1. When the compressor 4 described above is in the low flow rate range, i.e. when the volume of intake air 5 is low, the air 5, whose pressure is increased by the diffuser 8 may flow back or reverse, causing low-noise vibrations referred to as surging. In order to prevent such surging or to displace the surging range to a lower flow rate range, an annular axially extending space 12 which communicates with the port 6 and extends around the passage 7 is formed when the casing 10 is cast. An annular groove 13 or a plurality of spaced holes are machined through the casing 10 and extend between the passage 7 and the innermost end of the space 12, thereby defining an air passage 14, referred to as a casing treatment passage, whose purpose is to discharge the reversing air 5 into the port 6. Reference numeral 15 denotes reinforcing ribs arranged circumferentially of the space 12. When the engine is operated in the low flow rate range, the reversing air 5 flows out through the passage 14 and when the engine is operated in a high flow rate range the air 5 is also charged through the passage 14 into the engine. This known turbocharger compressor casing has a number of problems: the effect of discharging the reversing air 5 through the passage 14 in the low flow rate range of the engine for the purpose of displacing the surge range to a lower flow rate range is ineffective because the passage 14 is open to the air inlet port 6 and the intake air flow through the port 6 into the passage 7 largely prevents or suppresses the discharge of air 5 out of the passage 14. The manufacturing cost of the compressor casing 10, which defines the annular space 12, is high since the casing 10 is an integral casting and is structurally complicated. The subsequent machining of the groove 13 or the plurality of holes connecting the passage 7 with the innermost end of the space 12 is troublesome and expensive. GB-A-2202585, on which the precharacterising portion of Claim 1 is based, discloses a compressor casing with a slotted ring mounted in contact with a shoulder in the wall of the inlet passage. The slots in the ring bridge the blades of the impeller wheel and reduce the pressure differential across them. A series of axial holes is formed in the ring. Formed in the wall of the compressor casing defining the shoulder is an annular chamber which communicates with the space between the compressor casing and the impeller wheel by means of an annular slot or a series of holes. The annular chamber also communicates with the axial holes formed in the slotted ring. The compressor casing is a one-piece component of complex shape which is therefore complex and expensive to manufacture and to modify, e.g. to different sizes or shapes of the impeller wheel. Accordingly, it is the object of the invention to provide a compressor casing of the type disclosed in GB-A-2202585 which is simpler and cheaper to manufacture and which may be more cheaply modified. According to the present invention, a compressor casing for a turbocharger of the type having an air inlet port, which communicates with an inlet passage, which is adapted to accommodate an impeller therein and which communicates with a diffuser which in turn communicates with a scroll, and an annular chamber defined between the inlet passage and the scroll, the chamber communicating with the inlet passage via a first opening which is directed transversely of the length of the inlet passage is characterised in that the casing comprises a main body and an inner casing member fitted together, and that the main body is itself divided into an outer casing member and a further member, the outer casing member defining the air inlet port, the outer peripheral wall of the scroll and a portion of the inner peripheral wall of the scroll, the further member defining a portion of the inlet passage and the inner casing member defining a wall of the diffuser, the remainder of the inner peripheral wall of the scroll and the remainder of the inlet passage. The chamber may also communicate with the inlet passage via a second opening which is directed transversely of the length of the inlet passage and is closer to the air inlet port than the first opening. It is preferred that a restriction is defined by the inlet passage by a position upstream of the first opening, the restriction being constituted by a progressive decrease in diameter of the inlet passage in the direction from the air inlet port towards the diffuser. Alternatively, a restriction may be defined by the inlet passage at a position upstream of the second opening, the restriction being constituted by a progressive decrease in diameter of the inlet passage in the direction from the air inlet port towards the diffuser. In one embodiment, a second restriction is provided between the first and second openings. Whilst the invention relates principally to compressor casings for turbochargers, it also embraces the entire casing for a turbocharger, that is to say a compressor casing connected to a turbine casing, the compressor casing having the features referred to above. The invention further embraces a turbocharger including a casing as referred to above, the compressor casing containing an impeller and the turbine casing containing a turbine wheel, the impeller and the turbine wheel being connected together by a common shaft. In this event, the first opening referred to above, that is to say the more downstream of the openings if there are two of them, will be positioned abreast of, that is to say directed towards the turbine wheel transversely of or perpendicular to the impeller axis whilst the second opening will be positioned either adjacent the air inlet port or positioned so as to communicate with the inlet passage upstream of the impeller and directed transversely of, preferably perpendicular to, the impeller axis. Further features and details of the present invention will be apparent from the following description of certain preferred embodiments thereof which is given by way of example with reference to Figures 3 to 14 of the accompanying drawings, in which:- Figures 3 and 4 are scrap longitudinal sectional views of two different types of compressor casing which are not in accordance with the present invention; Figure 5 is a sectional view on the line XI-XI in Figure 4; Figures 6 and 7 are scrap longitudinal sectional views of first and second embodiments of the invention, respectively; and Figure 8 is a scrap longitudinal sectional view of a first modification thereof. Components which are similar to those in the known turbocharger casing shown in Figures 1 and 2 are referred to by the same reference numerals and will not be explained again in detail. Referring to Figure 3, the main body 19 of the turbocharger compressor casing, which is not in accordance with the invention, is an integral casting which defines the air inlet port 6, an inlet-side portion 7a of the wall of the air intake passage 7, the outer peripheral wall 16 of the scroll 9 and a portion 18 of the inner peripheral wall 17 of the scroll 9 contiguous with the wall 16. An annular inner casing member 23, which is also an integral casting defines a diffuser wall 20 and a portion 21 of the inner peripheral wall 17 contiguous with the wall 20. The opposed surfaces of the main body 19 and the inner casing member 23 are formed with an annular recess 24 and 26, respectively, which define together a chamber 25. The outer surface of the chamber 25 is defined by a projection 27 which extends from the inner casing member 23 into the recess 24 in the main body 19 and is shrink or cold fitted in place. A gap is defined between the mating main body 19 and inner casing member 23 which constitutes a first opening 28 connecting the air intake passage 7 and the chamber 25. A portion 29 of the wall defining the passage 7 is tapered, i.e. inwardly divergent, and thus constitutes a restriction of the passage 7 downstream of the inlet port 6. The restriction or surface 29 extends inwardly at an angle α to the axis of the port 6 and passage 7. The angle α of the restriction 29 is between 15 and 40 degrees. The first opening 28 opens sideways of the impeller 11, i.e. extends perpendicular to the axis of the impeller 11 and of the passage 7. The mode of operation of the first embodiment is as follows:- The compressor 4 is driven by the turbine 3 which in turn is driven by the exhaust gas from the engine 1 in the conventional manner so that no further explanation of the basic operation is required. If the turbocharger is operated in the low flow rate range, any air 5 whose pressure is increased by the diffuser 8 and then flows back or reverses will escape or flow into the chamber 25, whose capacity is relatively large, and consequently the surge range is displaced to a lower flow rate range. Because the chamber 25 is not open to the air inlet port 6, the escape of air into the chamber is not adversely affected by the flow of air from the port 6 into the intake passage 7 and therefore the effect of displacing the surging-occurring range to the lower flow rate range can be obtained. The characteristics of the escape of the air may be adjusted by varying the capacity and/or shape of the chamber 25. The inner casing member 23 can be connected to the main body 19 simply by fitting the projection 27 on the inner casing member 23 against the outer peripheral wall of the recess 24 in the main body 19 so that, after shrink or cold fitting, deformation of the wall defining the air intake passage 7 due to the fitting pressure is substantially eliminated. As a result, the gap between the wall defining the air intake passage 7 and the impeller 11 can be maintained very small so that a satisfactory supercharging efficiency is ensured. Figures 4 and 5 illustrate a sixth embodiment in which the concept of splitting or dividing the compressor casing 10 as described above is applied to a compressor casing of conventional type, as shown in Figure 2. In this construction, the compressor casing 10 is again divided into a main body 19 and an inner casing member 23. The inner casing member 23 is fitted within the main body 19 to define an air passage 14 therebetween. As a result, no machining is needed after casting. Reference numeral 34 denotes a reinforcing rib and numerals 34 and 35 denote the first and second openings of the passage 14. Figure 6 illustrates the first embodiment of the present invention which is substantially similar to the construction illustrated in Figures 4 and 5 except that the casing main body 19 is further divided into (A) an outer casing member 37 with the air inlet port 6, the outer peripheral wall 16 of the scroll 9 and a portion 18 of the inner peripheral wall 17 of the scroll 9 and (B) a member 38 defining the inlet-side portion 7a of the air intake passage 7. Figures 7 and 8 illustrate a second embodiment of the present invention and a modification thereof which is generally similar to the construction shown in Figure 3 except that the main body 19 is again further divided into (A) an outer casing member 40 with the air inlet port 6, the portion 7a of the air intake passage 7, the outer peripheral wall 16 of the scroll 9 and the portion 18 of the inner peripheral wall 17 of the scroll 9 and (B) a member 41 defining the restriction 29 of the air intake passage 7. If the member 41 is installed as shown in Figure 7 the compressor casing 10 is substantially similar to that shown in Figure 3. Alternatively the member 41 may be installed with a gap defined between it and the inner casing member 23 as shown in Figure 8. If the shape of the impeller 11 is changed as, for example, indicated by the two-dot-chain lines in Figure 3, this will necessitate reshaping the diffuser wall 20 and the chamber 25 as, for instance, indicated by the one-dot-chain lines in Figure 3. Due to the fact that the compressor casing 10 is divided into the main body 19 and the inner casing member 23, it is not necessary to change the design of the main body 19. This means that this design of the compressor housing is very versatile. Both embodiments of the invention have the advantage that, because the compressor casing 10 is divided into a casing main body 19 and an inner casing member 23, the shape of the component parts is simplified which facilitates the manufacturing process and enhances manufacturing productivity. This advantage is further enhanced by the division of the main body 19 into the further portions. It will be understood that the present invention is not limited to the embodiments described above and that various modifications may be effected. For instance, the components may be assembled using screws instead of shrink or force fitting.

Claims: A compressor casing for a turbocharger having an air inlet port (6), which communicates with an inlet passage (7), which is adapted to accommodate an impeller (11) therein and which communicates with a diffuser (8) which in turn communicates with a scroll (9), and an annular chamber (25) defined between the inlet passage (7) and the scroll (9), the chamber (25) communicating with the inlet passage (7) via a first opening (35) which is directed transversely of the length of the inlet passage, characterised in that the casing (10) comprises a main body (19) and an inner casing member (23) fitted together, and that the main body (19) is itself divided into an outer casing member (37, 40) and a further member (38, 41), the outer casing member (37, 40) defining the air inlet port (6), the outer peripheral wall (16) of the scroll (9) and a portion (18) of the inner peripheral wall (17) of the scroll (9), the further member (38, 41) defining a portion (7a, 2a) of the inlet passage (7) and the inner casing member (23) defining a wall (20) of the diffuser (8), the remainder (21) of the inner peripheral wall (17) of the scroll and the remainder of the inlet passage (7) . A casing as claimed in Claim 1, characterised in that the chamber (25) also communicates with the inlet passage (7) via a second opening (30) which is directed transversely of the length of the inlet passage (7) and is closer to the air inlet port (6) than the first opening (28). A casing as claimed in Claim 1, characterised in that a restriction (29) is defined by the inlet passage (7) at a position upstream of the first opening (28), the restriction (29) being constituted by a progressive decrease in diameter of the inlet passage in the direction from the air inlet port (6) towards the diffuser (8). A casing as claimed in Claim 2, characterised in that a restriction (29) is defined by the inlet passage (7) at a position upstream of the second opening (30), the restriction (29) being constituted by a progressive decrease in diameter of the inlet passage in the direction from the air inlet port (6) towards the diffuser (8). A casing as claimed in Claim 2 or Claim 4, characterised by a second restriction (33) between the first and second openings (28, 30). A casing as claimed in Claim 2, characterised by a gap between portions of the main body (19) and the inner casing member (23) which constitutes the second opening (30). A casing as claimed in any one of the preceding claims, characterised by an air passage (14) defined between the main body (19) and the inner casing member (23), the air passage (14) having two open ends (35, 36) which are directed transverse of the length of the inlet passage (7) and adjacent the air inlet port (6), respectively. A casing as claimed in Claim 3, characterised in that the further member (38,41) affords the restriction (29).

Inventors: ASO KAORU, FURUKAWA HIROMU, IWAKAMI AKIRA, KONDO NOBUHIRO, MITSUBORI KEN, NAKAMURA FUSAYOSHI, ONIZUKA KAZUHIRO, SAKIMOTO TATEO, YAMAGUCHI HIROSHI, YAMAGUCHI SATOSHI, ASO, KAORU, FURUKAWA, HIROMU, IWAKAMI, AKIRA, KONDO, NOBUHIRO, MITSUBORI, KEN, NAKAMURA, FUSAYOSHI, ONIZUKA, KAZUHIRO, SAKIMOTO, TATEO, YAMAGUCHI, HIROSHI, YAMAGUCHI, SATOSHI
Applicants: ISHIKAWAJIMA HARIMA HEAVY IND, ISHIKAWAJIMA-HARIMA JUKOGYO KABUSHIKI KAISHA
Application year: 1992
Main classification: F04D29
IPC codes: F04D27, F04D29