Patent ID: 12209504

DESCRIPTION OF EMBODIMENTS

Now, with reference to the attached drawings, an embodiment of the present disclosure is described. The dimensions, materials, and other specific numerical values represented in the embodiment are merely examples used for facilitating the understanding of the disclosure, and do not limit the present disclosure otherwise particularly noted. Elements having substantially the same functions and configurations herein and in the drawings are denoted by the same reference symbols to omit redundant description thereof. Further, illustration of elements with no direct relationship to the present disclosure is omitted.

FIG.1is a schematic sectional view for illustrating a turbocharger TC. In the following, description is given while a direction indicated by the arrow L illustrated inFIG.1corresponds to a left side of the turbocharger TC. A direction indicated by the arrow R illustrated inFIG.1corresponds to a right side of the turbocharger TC. As illustrated inFIG.1, the turbocharger TC includes a turbocharger main body1. The turbocharger main body1includes a bearing housing3, a turbine housing5, and a compressor housing7. The turbine housing5is coupled to a left side of the bearing housing3by a fastening mechanism9. The compressor housing7is coupled to a right side of the bearing housing3by a fastening bolt11. The turbocharger TC includes a turbine T and a centrifugal compressor C. The turbine T includes the bearing housing3and the turbine housing5. The centrifugal compressor C includes the bearing housing3and the compressor housing7.

A protrusion3ais formed on an outer peripheral surface of the bearing housing3. The protrusion3ais formed on the turbine housing5side. The protrusion3aprotrudes in a radial direction of the bearing housing3. A protrusion5ais formed on an outer peripheral surface of the turbine housing5. The protrusion5ais formed on the bearing housing3side. The protrusion5aprotrudes in a radial direction of the turbine housing5. The bearing housing3and the turbine housing5are band-fastened by the fastening mechanism9. The fastening mechanism9is, for example, a G coupling. The fastening mechanism9is configured to clamp the protrusion3aand the protrusion5a.

The bearing housing3has a bearing hole3bformed therein. The bearing hole3bpasses through the bearing housing3in a right-and-left direction of the turbocharger TC. A bearing is arranged in the bearing hole3b. A shaft13is inserted through the bearing. The bearing axially supports the shaft13in a rotatable manner. The bearing is a slide bearing. However, the present disclosure is not limited thereto, and the bearing may be a rolling bearing. A turbine impeller15is provided at a left end portion of the shaft13. The turbine impeller15is accommodated in the turbine housing5so as to be rotatable. A compressor impeller17is provided at a right end portion of the shaft13. The compressor impeller17is accommodated in the compressor housing7so as to be rotatable.

An intake port19is formed in the compressor housing7. The intake port19is opened on the right side of the turbocharger TC. The intake port19is connected to an air cleaner (not shown). A diffuser flow passage21is defined by opposed surfaces of the bearing housing3and the compressor housing7. The diffuser flow passage21increases pressure of air. The diffuser flow passage21has an annular shape. The diffuser flow passage21communicates with the intake port19on a radially inner side through intermediation of the compressor impeller17.

A compressor scroll flow passage23is formed in the compressor housing7. The compressor scroll flow passage23has an annular shape. The compressor scroll flow passage23is located, for example, on an outer side with respect to the diffuser flow passage21in a radial direction of the shaft13. The compressor scroll flow passage23communicates with an intake port of an engine (not shown) and the diffuser flow passage21. When the compressor impeller17rotates, the air is sucked from the intake port19into the compressor housing7. The sucked air is pressurized and accelerated in the course of flowing through blades of the compressor impeller17. The air having been pressurized and accelerated is increased in pressure in the diffuser flow passage21and the compressor scroll flow passage23. The air having been increased in pressure is guided to the intake port of the engine.

An exhaust-air discharge port25is formed in the turbine housing5. The exhaust-air discharge port25is opened on the left side of the turbocharger TC. The exhaust-air discharge port25is connected to an exhaust-gas purification device (not shown). In the turbine housing5, a discharge flow passage27, an accommodating portion29, and an exhaust flow passage31are formed. The discharge flow passage27allows communication between the accommodating portion29and the exhaust-air discharge port25. The discharge flow passage27is continuous with the accommodating portion29in a rotation axis direction of the turbine impeller15. The accommodating portion29accommodates the turbine impeller15. The exhaust flow passage31is formed on a radially outer side with respect to the turbine impeller15. The exhaust flow passage31has an annular shape. The exhaust flow passage31includes a turbine scroll flow passage31a. The turbine scroll flow passage31acommunicates with the accommodating portion29. That is, the turbine impeller15is arranged on a radially inner side with respect to the turbine scroll flow passage31a.

The exhaust flow passage31communicates with an exhaust manifold of an engine (not shown). Exhaust gas exhausted from the exhaust manifold of the engine (not shown) is guided to the discharge flow passage27through the exhaust flow passage31and the accommodating portion29. The exhaust gas guided to the discharge flow passage27rotates the turbine impeller15in the course of flowing.

A rotational force of the turbine impeller15is transmitted to the compressor impeller17through the shaft13. When the compressor impeller17rotates, the pressure of the air is increased as described above. In such a manner, the air is guided to the intake port of the engine.

FIG.2is a sectional view taken along the line A-A inFIG.1. InFIG.2, regarding the turbine impeller15, only an outer periphery of the turbine impeller15is indicated by a circle. As illustrated inFIG.2, on a radially outer side of the accommodating portion29(that is, a radially outer side of the turbine impeller15), the exhaust flow passage31is formed. The exhaust flow passage31includes the turbine scroll flow passage31a, a communication portion31b, an exhaust-air introduction port31c, and an exhaust-air introduction passage31d. The exhaust flow passage31allows communication between the accommodating portion29and the exhaust-air introduction port31c.

The communication portion31bis formed into an annular shape over the entire periphery of the accommodating portion29. The turbine scroll flow passage31ais located on the radially outer side of the turbine impeller15with respect to the communication portion31b. The turbine scroll flow passage31ais formed into an annular shape over the entire periphery of the communication portion31b(that is, the entire periphery of the accommodating portion29). The communication portion31ballows communication between the accommodating portion29and the turbine scroll flow passage31a. A tongue portion33is formed in the turbine housing5. The tongue portion33is formed on an end portion of the turbine scroll flow passage31aon a downstream side, and partitions the turbine scroll flow passage31ainto a downstream portion and an upstream portion of the turbine scroll flow passage31a.

The exhaust-air introduction port31cis opened to the outside of the turbine housing5. The exhaust gas exhausted from the exhaust manifold of the engine (not shown) is introduced into the exhaust-air introduction port31c. The exhaust-air introduction passage31dis formed between the exhaust-air introduction port31cand the turbine scroll flow passage31a. The exhaust-air introduction passage31dconnects the exhaust-air introduction port31cand the turbine scroll flow passage31ato each other. The exhaust-air introduction passage31dis formed, for example, into a straight shape. The exhaust-air introduction passage31dguides the exhaust gas introduced from the exhaust-air introduction port31cto the turbine scroll flow passage31a. The turbine scroll flow passage31aguides the exhaust gas introduced from the exhaust-air introduction passage31dto the accommodating portion29through the communication portion31b.

A bypass flow passage35is formed in the turbine housing5. An inlet end of the bypass flow passage35is opened to the exhaust flow passage31(specifically, the exhaust-air introduction passage31d). An outlet end of the bypass flow passage35is opened to the discharge flow passage27(seeFIG.1). The bypass flow passage35allows communication between the exhaust flow passage31(specifically, the exhaust-air introduction passage31d) and the discharge flow passage27while detouring the accommodating portion29. At the outlet end of the bypass flow passage35, a wastegate port WP (seeFIG.1) is formed. At the outlet end of the bypass flow passage35, a wastegate valve WV (seeFIG.1) that can open and close the wastegate port WP is arranged. The wastegate valve WV is arranged in the discharge flow passage27. When the wastegate valve WV opens the wastegate port WP, the bypass flow passage35causes part of the exhaust gas flowing through the exhaust-air introduction passage31dto flow out to the discharge flow passage27while detouring the accommodating portion29(that is, detouring the turbine impeller15).

In the turbine T, opening and closing operations of the wastegate port WP are controlled to adjust a flow rate of the exhaust gas flowing into the turbine impeller15. As described above, the turbine T is a variable capacity turbine.

Here, in the turbine T including the bypass flow passage35, in a branching portion BP between the exhaust flow passage31and the bypass flow passage35(that is, the inlet end of the bypass flow passage35), separation of flow of gas is liable to occur. For example, when the wastegate port WP is closed, part of the exhaust gas flowing through the exhaust-air introduction passage31dflows into the bypass flow passage35from the branching portion BP, and then, returns to the exhaust-air introduction passage31d. At this time, in a portion of the branching portion BP on the downstream side, separation of flow of gas may occur. The separation of flow of gas in the branching portion BP increases pressure loss in the turbine T, which is a cause of a decrease in efficiency of the turbine T.

In view of this, in the turbine T according to the present embodiment, in order to improve the efficiency of the turbine T, the exhaust flow passage31(specifically, the exhaust-air introduction passage31d) is devised in flow passage sectional area. The flow passage sectional area of the exhaust flow passage31is, specifically, the area of the flow passage section orthogonal to a flow direction FD of the exhaust gas (that is, an extending direction of the exhaust flow passage31). In the following, with reference toFIG.2toFIG.5, the flow passage sectional area of the exhaust flow passage31is described in detail.

A position of the exhaust gas in the flow direction FD in the exhaust flow passage31is hereinafter referred to as a flow-direction position Pf. As illustrated inFIG.2, the flow-direction position Pf at the exhaust-air introduction port31cis set to 0, and the flow-direction position Pf at the branching portion BP is set to 1. A region of the exhaust flow passage31in which the flow-direction position Pf is 0 or more and less than 1 corresponds to a region on the exhaust-air introduction port31cside with respect to the branching portion BP. In the example ofFIG.2, the flow-direction position Pf at the branching portion BP is a position of an upstream end portion of the branching portion BP. However, as the flow-direction position Pf at the branching portion BP, a position of a portion other than the upstream end portion of the branching portion BP may be used.

FIG.3is a graph for showing a distribution of a sectional area ratio of the flow passage sectional area of the exhaust flow passage31at each flow-direction position Pf to the flow passage sectional area of the exhaust-air introduction port31cin the turbine T according to the present embodiment. InFIG.3, the distribution of the sectional area ratio in the present embodiment is indicated by the solid line, and the distribution of the sectional area ratio in a comparative example is indicated by the broken line.

As shown inFIG.3, both in the present embodiment and in the comparative example, in the region of the exhaust flow passage31on the exhaust-air introduction port31cside with respect to the branching portion BP, the sectional area ratio decreases as the flow-direction position Pf is closer to the downstream side. That is, in the region of the exhaust flow passage31on the exhaust-air introduction port31cside with respect to the branching portion BP, the flow passage sectional area decreases as the flow-direction position Pf is closer to the downstream side.

In this case, in the comparative example, at the flow-direction position Pf=1, the sectional area ratio is less than 0.6 (specifically, about 0.4). That is, the flow passage sectional area of the branching portion BP is less than 0.6 times the flow passage sectional area of the exhaust-air introduction port31c. Meanwhile, in the present embodiment, at the flow-direction position Pf=1, the sectional area ratio is 0.6 or more (specifically, about 0.6). That is, the flow passage sectional area at the branching portion BP is 0.6 times or more the flow passage sectional area of the exhaust-air introduction port31c.

In the following, description is given with reference toFIG.4,FIG.5, andFIG.6for showing results obtained by flow analysis simulations conducted by the inventor. In the flow analysis simulations, states of the flow of gas (for example, a direction, a speed, and entropy) in the exhaust flow passage31and the efficiency of the turbine T are calculated.

FIG.4is a graph for showing a relationship between a sectional area ratio and an efficiency change amount. The sectional area ratio is a ratio of the flow passage sectional area of the branching portion BP to the flow passage sectional area of the exhaust-air introduction port31c(that is, a ratio of the flow passage sectional area at the flow-direction position Pf=1 to the flow passage sectional area at the flow-direction position Pf=0). The efficiency change amount [%] is a change amount of the efficiency of the turbine T in each sectional area ratio with respect to the efficiency of the turbine T when the sectional area ratio is 0.4. That is, the efficiency change amount [%] is obtained by subtracting the efficiency of the turbine T when the sectional area ratio is 0.4 from the efficiency of the turbine T in each sectional area ratio. The efficiency of the turbine T is a ratio of energy generated by the turbine T to energy input to the turbine T.

According to the graph shown inFIG.4, it is found that, as the sectional area ratio increases, the efficiency of the turbine T increases. In particular, it is found that, when the sectional area ratio is 0.6 or more, the efficiency of the turbine T is improved by at least 0.8% or more as compared to a case in which the sectional area ratio is 0.4. Thus, in the present embodiment, it is found that, when the flow passage sectional area of the branching portion BP is 0.6 times or more the flow passage sectional area of the exhaust-air introduction port31c, the efficiency of the turbine T is remarkably improved.

FIG.5is a diagram for illustrating an entropy distribution obtained by the flow analysis simulation in the comparative example.FIG.6is a diagram for illustrating an entropy distribution obtained by the flow analysis simulation in the present embodiment. InFIG.5andFIG.6, the distribution of entropy in the vicinity of the branching portion BP in the exhaust flow passage31is indicated by contrasting density of hatching. Specifically, inFIG.5andFIG.6, as the density of hatching is higher (that is, as intervals of hatched lines are smaller), the entropy is higher. Further, inFIG.5andFIG.6, a direction of local flow of gas in the vicinity of the branching portion BP is indicated by arrows.

As a result of comparison between the comparative example illustrated inFIG.5and the present embodiment illustrated inFIG.6, it is found that, in the comparative example, entropy increases on the downstream side of the exhaust flow passage31with respect to the branching portion BP (left side inFIG.5andFIG.6) as compared to the present embodiment. Further, in the comparative example, it is found that separation of flow of gas and vortex flow occur on the downstream side of the exhaust flow passage31with respect to the branching portion BP unlike the present embodiment.

In this case, it is conceivable that the efficiency of the turbine T changes in accordance with the size of the flow passage sectional area of the branching portion BP. Specifically, when the flow passage sectional area of the branching portion BP is excessively small, the flow speed of the exhaust gas flowing through the exhaust flow passage31(specifically, the exhaust-air introduction passage31d) excessively increases at the branching portion BP. With this, in the vicinity of the branching portion BP (for example, the downstream side of the exhaust flow passage31with respect to the branching portion BP), separation of flow of gas and vortex flow are liable to occur. For this reason, in the comparative example (that is, when the sectional area ratio is about 0.4), it is assumed that separation of flow of gas and vortex flow occur in the vicinity of the branching portion BP. In contrast, in the present embodiment (that is, when the sectional area ratio is 0.6 or more), the flow passage sectional area of the branching portion BP is large as compared to the comparative example, and hence the flow speed of the exhaust gas is small at the branching portion BP. With this, separation of flow of gas and vortex flow in the vicinity of the branching portion BP are suppressed, and as a result of the reduction of the pressure loss, the efficiency of the turbine T is improved.

In view of improving the flow passage efficiency to improve the turbine efficiency, it is preferred that the sectional area ratio gently decrease as the flow-direction position Pf is closer to the downstream side in the region of the exhaust flow passage31on the exhaust-air introduction port31cside with respect to the branching portion BP. Specifically, in the present embodiment, as shown inFIG.3, in a range in which the flow-direction position Pf is 0 or more and 0.6 or less, the sectional area ratio is 0.9 or more. With this, as shown inFIG.4andFIG.6, improvement of the flow passage efficiency and the turbine efficiency is achieved appropriately. As described above, in view of improving the flow passage efficiency to improve the turbine efficiency appropriately, it is preferred that the flow passage sectional area is 0.9 times or more the flow passage sectional area of the exhaust-air introduction port31cin a region of 60% or more on the exhaust-air introduction port31cside in the flow direction FD of the exhaust gas (that is, the extending direction of the exhaust flow passage31).

An embodiment of the present disclosure has been described above with reference to the attached drawings, but, needless to say, the present disclosure is not limited to the above-mentioned embodiment. It is apparent that those skilled in the art may arrive at various alternations and modifications within the scope of claims, and those examples are construed as naturally falling within the technical scope of the present disclosure.

In the above, an example in which the turbine T is a single scroll type (type in which the number of the turbine scroll flow passage31ais one) has been described, but the type of the turbine T is not limited to the above-mentioned example. For example, the turbine T may be a double scroll type (type in which two turbine scroll flow passages31aare connected to the accommodating portion29at different peripheral direction positions), or may be a twin scroll type (type in which two turbine scroll flow passages31aare arranged side by side in an axial direction).

In the above, an example in which the turbine T is provided in the turbocharger TC has been described. However, the turbine T may be provided in other devices other than the turbocharger TC.