VARIABLE CAPACITY RADIAL FLOW TURBINE

Abstract: A variable capacity radial flow turbine includes a turbine housing which incorporates a turbine wheel and which forms a working gas passageway that leads to the turbine wheel and that is divided into two parts. The working gas passageway is provided with a pivotable plate-­ like member, so that the flow rate of the working gas flowing into the turbine wheel can be continuously changed by shifting the position of this member and thus opening or closing part of a working gas intake.

Description: BACKGROUND OF THE INVENTION: Field of the Invention: The present invention relates to an exhaust turbo-charger for use in an internal combustion engine. The present invention also pertains to a radial flow gas turbine which has the same structure as that of an exhaust turbo-charger. Prior Art: Fig. 8 shows the structure of a conventional variable capacity radial flow turbine. A turbine housing 31 of the radial flow turbine incorporates a turbine wheel 32, and forms a passageway 35 for a working gas such as exhaust gas. A vane 33 is provided in a working gas intake 36 of the passageway 35 through which the gas flows into the turbine wheel 32. The turbine flow rate is varied by opening and closing the vane 33. Fig. 9 shows a turbine housing 31 of another radial flow turbine which is not equipped with a capacity varying mechanism and which has an exhaust passageway 35 divided into two chambers by a partition 20. When a variable capacity radial flow turbine of the type shown in Fig. 8 is used with a multicylinder engine, the effect of pulsations in the exhaust is reduced. This reduction in the effect of pulsations has therefore made it difficult to obtain a high charging pressure when the rotational speed of the engine is low. With a turbine having a turbine housing with a partition such as that shown in Fig. 9, the pulsations in the exhaust can be effectively utilized. However, it does not have any capacity varying mechanism, resulting in a narrowing of the suitable matching range. A variable capacity radial flow turbine of the kind defined by the precharacterizing features of the claim is known from the FR-A-1 512 184. The pivot point of the vane of this known turbine is positioned at the center of the vane, which is located in the neighbourhood of the outer circumference of the scroll and always divides the scroll into two parts. In the case, the vane is placed at a neutral position, the flow rate becomes maximum, and when the vane is rotated out of the neutral position, the flow is throttled. However, when upon throttling the flow, the sectional area of the flow passage is abrubtly changed, this inevitably results in lowering of turbine efficiency. From the DE-A-2 044 026, it is known to switch the right and left passageways of the double ported turbine housing, at the entrance thereof, with each other by means of a vane. SUMMARY OF THE INVENTION The object of the present invention is to improve the turbine efficiency of the turbine defined by the precharacterizing features of the claim. This object is attained by the characterizing features of the claim. The sectional area of the flowpassageway changes smoothly at a fixed rate, when the vane is moved. Further, when the vane is opened, the flow attained with the closed vane is maintained and, in addition thereto, the sectional area of the flow passageway is increased. Therefore, the turbine effiency is superior to that one of the prior art discussed above. BRIEF DESCRIPTION OF THE DRAWINGS: Fig. 1 is a cross-sectional view of the first embodiment of the present invention; Fig. 2 is a longitudinal sectional view of the turbine housing of Fig. 1, showing the state in which a vane is closed; Fig. 3 is a longitudinal sectional view of the turbine housing of Fig. 1, showing the state in which the vane is open; Fig. 4 is a perspective view of the vane employed in the first embodiment of the present invention; Fig. 5 is a longitudinal sectional view of the turbine housing, illustrating the scroll design method; Fig. 6 is a graph used to illustrate the scroll design method; Fig. 7 is a perspective view of a vane employed in a second embodiment of the present invention; Fig. 8 is a cross-sectional view of a conventional turbine; and Fig. 9 is a cross-sectional view of a conventional turbine housing which has a passageway divided into two parts. DESCRIPTION OF THE PREFERRED EMBODIMENTS: A first embodiment of the present invention in which the working gas is an exhaust gas will be hereinunder described with reference to Figs. 1 to 6. A turbine housing 31 forms an exhaust passageway 35 which is divided into two parts by a partition 20 and incorporates a turbine wheel 32. An intake 36 of the passageway 35, through which the exhaust gases flow into the turbine wheel, is provided with a vane 33. The vane 33 is supported by a bush 34 in such a manner as to be pivotable about a vane rotary shaft 37 mounted downstream of the exhaust passageway. Fig. 2 shows the turbine housing when the vane is closed and is in surface contact with a portion of the exhaust intake 36 so as to prevent the exhaust gas from flowing into the turbine wheel between the wall and the vane. In this case, the turbine flow rate is reduced, and the area at the entrance of the scroll corresponds to that at the proximal end of the vane 33, expressed as A₁, as shown in Fig. 5. Therefore, a value obtained by dividing the sectional area A of the flow passage at the scroll entrance by the perpendicular distance R from the central axis of the turbine wheel and the centroid of the sectional area A of the flow passage at the scroll entrance (hereinafter referred to as A/R) is a minimum. When the vane 33 is pivoted away from the position at which it is in contact with the exhaust intake 36, exhaust gas flows into the turbine wheel through an opening formed between the vane 33 and the turbine housing 31. At this point, the area at the scroll entrance is A₂, and the ratio A/R therefore increases, increasing the turbine flow rate. Thus, minimum and maximum turbine flow rates can be changed by setting the area of the exhaust passageway 35. Fig. 6 shows an example of the method of designing the area thereof. The area of the scroll changes at a fixed rate in the circumferential direction, that is, as the angle ϑ increases as shown in Fig. 6, when ϑ is a counter clock-wise angle around the central axis of the turbine wheel and ϑ is 0° at the position of A₁. This change enables the designer to select a decrease in the area at a fixed rate or a decrease in the ratio A/R at a fixed rate with respect to the most aerodynamically appropriate angle. Therefore, the minimum turbine flow rate can be set by changing the scroll area A₁, and the maximum turbine flow rate can be set by changing the scroll area A₂. In addition, when the vane 33 is shifted to an open position, the scroll area changes from A₂ to A₃, providing the scroll with a large ratio A/R. The vane 33 of this embodiment consists of a plate member and ribs 38 and 39 disposed at both sides of the plate member, by means of which the exhaust intake is divided into two parts when the vane 33 is open or closed. A second embodiment of the present invention is described below, in which the rib 39 disposed on the side of the vane which is closer to the turbine wheel 32 is removed. In this embodiment, when the turbine flow rate is small (when the vane 33 is closed), the exhaust gases flow into the turbine wheel in the same manner as in the first embodiment. However, when the turbine flow rate is set at its maximum by the pivoting of the vane 33, the exhaust passageway 35 which has been divided into two parts is made into one passage, because the vane 30 has no rib 39. In consequence, the exhaust gas introduced from the engine in one stream is mixed with that in another stream in this exhaust passageway 35, reducing pulsations in the exhaust gases. This produces a state which is close to known hydrostatic supercharging, and enables a lower charging pressure than that of the first embodiment. If the present invention is applied to a turbo-charger, high charging pressure can be provided when the rotational speed of the engine is low by closing the vane 33 and thereby reducing the capacity of the turbine, which increase the torque of the engine at the low rotational speed. Further, if the capacity of the turbine is increased by opening the vane 33 when the engine is operating at a high rotational speed, the pressure of the exhaust gases can be reduced, thereby increasing the maximum output of the engine. These in turn enable the engine performance to be improved over a wider range from a low rotational speed of the engine to a high rotational speed thereof, when compared with the prior art turbo-charger.

Claims: A variable capacity radial flow turbine having a turbine housing (31) which incorporates a turbine wheel (32) and which forms a working gas passageway (35) which leads to said turbine wheel (32) and which is divided into two parts, and a plate-like vane (33) which is pivotable about a vane rotary shaft (37) supported parallel to the axis of said turbine wheel (32) in an upstream portion of said working gas passageway (35), such that the flow rate of a working gas such as an exhaust gas flowing into said turbine wheel (32) can be continuously changed by shifting the position of said vane (33) and thus opening and closing part of an exhaust gas intake (36), characterized in that said vane rotary shaft (37) is mounted at the downstream end of the vane (33) such that in the case when the vane (33) is closed it is in surface contact with the turbine housing (31) forming the upstream end of the working gas passageway (35), whereby exhaust gas from the exhaust gas intake (36) flows over only one side of the vane (33) and in the case the vane (33) is opened the sectional area of the working gas passageway (35) is increased.

Inventors: HAGITA, ATSUSHI SAGAMIHARA MACHINERY WORKS, KYOYA, MICHIO SAGAMIHARA MACHINERY WORKS, MATSUDAIRA, NOBUYASU SAGAMIHARA MACHINERY WORKS, OKAZAKI, YOICHIRO SAGAMIHARA MACHINERY WORKS
Applicants: MITSUBISHI JUKOGYO KABUSHIKI KAISHA
Application year: 1987
Main classification: F01D17
IPC codes: F01D17