Internal combustion engine and exhaust system design method for the same

Abstract

To optimize exhaust system layout so as to obtain good turbine efficiency and fuel consumption in an exhaust system in which a catalytic converter 13 is disposed upstream of a turbine 14 of a turbocharger.SOLUTION: A catalytic converter 13 is connected to an exhaust outlet 12 of a cylinder head 11 of an internal combustion engine 2, and a turbine 14 is disposed on the downstream side thereof. An exhaust system volume between the exhaust outlet 12 of the cylinder head 11 and an exhaust inlet 15 of the turbine 14 is tuned to a best volume that maximizes turbine efficiency at a rated operation point that is a representative operation point. A distance between the exhaust outlet 12 and the exhaust inlet 15 (length of the exhaust system) is tuned to a distance that maximizes a product of the turbine efficiency and a turbine inlet gas temperature at the rated operation point under restriction of obtaining the best volume between the exhaust outlet and the exhaust inlet.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an internal combustion engine equipped with a turbine of a turbocharger in an exhaust passage and a method for designing an exhaust system thereof. [Background technology]

[0002] In a turbocharged internal combustion engine with a turbocharger turbine in the exhaust passage, a typical exhaust system layout is one in which the turbine housing is attached to the exhaust outlet of the cylinder head and the catalytic converter is located directly below the exhaust outlet of this turbine housing. However, in such a configuration in which the turbine is located upstream of the catalytic converter, the catalyst warms up slowly after a cold start and the pumping loss of the internal combustion engine due to exhaust pressure becomes relatively large.

[0003] In response to this, Patent Document 1 discloses a configuration in which a catalytic converter is arranged upstream of a turbine as an exhaust system layout for an internal combustion engine with a turbocharger. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-118050 Summary of the Invention [Problem to be solved by the invention]

[0005] In a configuration in which the catalytic converter is located upstream of the turbine, as in Patent Document 1, there is a disadvantage in that the efficiency of the turbine is reduced compared to when the turbine is located upstream of the catalytic converter, and if the exhaust passage between the exhaust outlet of the cylinder head and the turbine is not properly configured, the efficiency of the internal combustion engine, that is, fuel economy performance, will worsen. Patent Document 1 does not disclose anything about this. [Means for solving the problem]

[0006] This invention relates to an internal combustion engine equipped with a turbocharger turbine in an exhaust passage, A catalytic converter is located between the exhaust outlet of the cylinder head and the exhaust inlet of the turbine; The distance between the exhaust outlet and the exhaust inlet is set at a distance that maximizes the product of the turbine efficiency and the turbine inlet gas temperature, while the exhaust system volume between them has a volume that maximizes the turbine efficiency under a representative operating point.

[0007] Furthermore, the exhaust system design method for an internal combustion engine according to the present invention includes: 1. A method for designing an exhaust system for an internal combustion engine having a turbocharger turbine in an exhaust passage and a catalytic converter located upstream of the turbine, comprising: determining a representative operating point of the internal combustion engine; an exhaust system volume between an exhaust outlet of the cylinder head and an exhaust inlet of the turbine is determined to be an optimal volume that maximizes turbine efficiency at the representative operating point; The distance between the exhaust outlet and the exhaust inlet is determined to be the distance that maximizes the product of the turbine efficiency and the turbine inlet gas temperature within the constraints of the best volume. [Effects of the Invention]

[0008] According to this invention, by optimizing the exhaust system volume and distance between the exhaust outlet of the cylinder head and the exhaust inlet of the turbine, it is possible to reduce pumping loss while ensuring high turbine efficiency, thereby reducing fuel consumption of the internal combustion engine. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is an explanatory diagram of the configuration of a series hybrid vehicle. [Figure 2] FIG. 2 is an explanatory diagram illustrating a schematic layout of an exhaust system. [Figure 3] A characteristic diagram showing the characteristics of PMEP and other parameters relative to the distance between the exhaust outlet of the cylinder head and the exhaust inlet of the turbine. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment in which the present invention is applied to an internal combustion engine for a series hybrid vehicle will be described in detail below with reference to the drawings. First, a series hybrid vehicle using the internal combustion engine of the embodiment will be described. FIG. 1 schematically shows the configuration of the series hybrid vehicle of the embodiment. The series hybrid vehicle is configured to include a power-generating motor-generator 1 that operates primarily as a generator, an internal combustion engine 2 that operates as a power-generating internal combustion engine to drive the power-generating motor-generator 1 in response to power demands, a traction motor-generator 4 that operates primarily as a motor to drive drive wheels 3, and a battery 5 that stores the generated power. Electric power obtained by the internal combustion engine 2 driving the power-generating motor-generator 1 is stored in the battery 5 via an inverter device (not shown). The traction motor-generator 4 is driven and controlled using the power from the battery 5. Electric power generated by the traction motor-generator 4 during regeneration is stored in the battery 5 via an inverter device (not shown).

[0011] The operation of the motor generators 1 and 4, the charging and discharging of the battery 5, and the operation of the internal combustion engine 2 are controlled by a controller 6. The controller 6 is composed of multiple controllers connected to each other so that they can communicate with each other, such as a motor controller 7 that controls the motor generators 1 and 4, an engine controller 8 that controls the internal combustion engine 2, and a battery controller 9 that manages the battery 5. Information such as the accelerator pedal position and vehicle speed (not shown) is input to the controller 6. The battery controller 9 also calculates the SOC of the battery 5 based on the voltage and current of the battery 5. When the SOC drops to a predetermined lower limit, the internal combustion engine 2 is started via the engine controller 8 to generate electricity. Various sensors generally required for controlling the internal combustion engine 2 are connected to the engine controller 8. Such a series hybrid vehicle has two driving modes: an EV mode in which the vehicle runs on power from the battery 5 without combustion operation of the internal combustion engine 2, and an HEV mode in which the vehicle runs while generating electricity through combustion operation of the internal combustion engine 2.

[0012] In one embodiment, the internal combustion engine 2 is a four-stroke cycle spark-ignition internal combustion engine, a so-called gasoline engine, equipped with a turbocharger as a supercharger. The internal combustion engine 2, which is operated to charge the battery 5, is always operated at a specific rated operating point (load and rotational speed) at which thermal efficiency is optimal when power generation is required. The output of the internal combustion engine 2 is used to charge the battery 5, and the maximum required output of the vehicle is basically met by the output of the battery 5. In other words, even in HEV mode, in which the vehicle runs while generating power using the internal combustion engine 2 due to a low battery SOC, the internal combustion engine 2 is basically operated at the rated operating point. Note that, during warm-up of the internal combustion engine 2 or in special circumstances, it may be operated at an operating point other than the rated operating point, but the proportion of time spent operating at an operating point other than the rated operating point is extremely small.

[0013] 2 is an explanatory diagram that schematically shows the layout of the exhaust system of an internal combustion engine 2, in which a catalytic converter 13 using a three-way catalyst is connected to an exhaust outlet 12 of a cylinder head 11 of the internal combustion engine 2, and a turbine 14 of a turbocharger is located downstream of this catalytic converter 13. In other words, the catalytic converter 13 is located between the exhaust outlet 12 of the cylinder head 11 and the exhaust inlet 15 of the turbine 14. Further downstream of the turbine 14, a downstream catalytic converter 16 using a three-way catalyst is located under the floor of the vehicle. The exhaust passage extending downstream from the downstream catalytic converter 16 is finally opened to the outside via a silencer (not shown).

[0014] Although not shown in detail, the turbine 14 has a general configuration including a turbine rotor configured coaxially with the turbocharger compressor, and in one embodiment, is equipped with a wastegate valve that bypasses a portion of the exhaust gas for boost pressure control.

[0015] The catalytic converter 13 is configured with a cylindrical catalyst 13a housed in a substantially cylindrical metal case, and the metal case is equipped with an exhaust inlet pipe 13b including a diffuser section with an expanding diameter, and an exhaust outlet pipe 13c including a section with a decreasing diameter. Therefore, the catalytic converter 13 is connected to the exhaust outlet 12 of the cylinder head 11 via the exhaust inlet pipe 13b, and is connected to the exhaust inlet 15 of the turbine 14 via the exhaust outlet pipe 13c.

[0016] The exhaust system volume between the exhaust outlet 12 of the cylinder head 11 and the exhaust inlet 15 of the turbine 14 is tuned so as to maximize turbine efficiency at the above-mentioned rated operating point, which is a representative operating point. Note that the volume occupied by the catalyst 13a is determined by the required exhaust purification performance, so the tunable volume is mainly the sum of the internal volumes of the exhaust inlet pipe 13b and the exhaust outlet pipe 13c.

[0017] If the exhaust system volume between the exhaust outlet 12 of the cylinder head 11 and the exhaust inlet 15 of the turbine 14 is small, the exhaust pulsation of the exhaust flowing into the turbine 14 will be large, resulting in low turbine efficiency. Increasing the exhaust system volume reduces the exhaust pulsation, thereby increasing turbine efficiency. Furthermore, if the exhaust system volume is excessively large, the turbine efficiency tends to decrease due to a decrease in the dynamic pressure of the exhaust. Therefore, turbine efficiency is maximized when the exhaust system volume is within a certain range. In one embodiment, the smallest volume within this range that maximizes turbine efficiency is determined as the optimal volume. Note that turbine efficiency values ​​for various volumes can be obtained, for example, by appropriate simulations.

[0018] Furthermore, the distance between the exhaust outlet 12 of the cylinder head 11 and the exhaust inlet 15 of the turbine 14 (length of the exhaust system) is tuned to maximize the "product of turbine efficiency and turbine inlet gas temperature" at the rated operating point, which is the representative operating point, within the constraint of obtaining the optimum volume between the two. Within the constraint of maintaining the same volume, for example, reducing the passage diameter increases the distance. The "turbine inlet gas temperature" is the gas temperature at the exhaust inlet 15 of the turbine 14, and can also be calculated by an appropriate simulation.

[0019] 3 is a characteristic diagram showing the characteristics of the "product of turbine efficiency and turbine inlet gas temperature," the characteristics of the turbine inlet gas temperature, and the characteristics of PMEP (pumping mean effective pressure) when the distance between the exhaust outlet 12 of the cylinder head 11 and the exhaust inlet 15 of the turbine 14 is changed under the constraint that the exhaust system volume between them is the above-mentioned optimum volume. As shown in the diagram, the turbine inlet gas temperature decreases as the above-mentioned distance is increased, but the characteristics of the "product of turbine efficiency and turbine inlet gas temperature" have an inflection point that indicates a maximum value. At distance L1 where this maximum value is reached, PMEP, an index indicating low pumping loss, also becomes maximum.

[0020] In other words, by tuning the volume and distance of the exhaust system between the exhaust outlet 12 of the cylinder head 11 and the exhaust inlet 15 of the turbine 14 as described above, the pumping loss of the internal combustion engine 2 is minimized while maintaining high turbine efficiency at the rated operating point, which is the representative operating point, thereby improving the fuel efficiency of the internal combustion engine 2.

[0021] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and various modifications are possible. For example, the above embodiment has been described using an internal combustion engine 2 for generating electricity in a series hybrid vehicle as an example, but the present invention can also be applied to an internal combustion engine that mechanically drives a vehicle, and the operating point at which the engine is operated most frequently can be set as the representative operating point. For example, in the case of an internal combustion engine used in a large trailer, it is expected that the engine will be continuously operated at the maximum power point, so the maximum power point can be set as the representative operating point.

[0022] Furthermore, the present invention can be applied not only to spark ignition internal combustion engines but also to so-called diesel engines that use compression ignition. [Explanation of symbols]

[0023] 1...Power generating motor generator 2...Internal combustion engine 4...Traction motor generator 11...Cylinder head 12...Exhaust outlet 13...Catalytic converter 14...Turbine 15...Exhaust inlet

Claims

1. In an internal combustion engine equipped with a turbocharger turbine in an exhaust passage, A catalytic converter is located between the exhaust outlet of the cylinder head and the exhaust inlet of the turbine; a distance between the exhaust outlet and the exhaust inlet is set to a distance at which, under a representative operating point, an exhaust system volume between the two has a volume at which turbine efficiency is maximized, and at which a product of turbine efficiency and turbine inlet gas temperature is maximized. Internal combustion engine.

2. the internal combustion engine is a power-generating internal combustion engine that drives a generator in a series hybrid vehicle, The representative operating point is the rated operating point at which the thermal efficiency during power generation is optimal.

2. The internal combustion engine according to claim 1.

3. the internal combustion engine is an internal combustion engine that drives a vehicle, The representative operating point is a maximum output point of the internal combustion engine.

2. The internal combustion engine according to claim 1.

4. 1. A method for designing an exhaust system for an internal combustion engine having a turbocharger turbine in an exhaust passage and a catalytic converter located upstream of the turbine, comprising: determining a representative operating point of the internal combustion engine; an exhaust system volume between an exhaust outlet of the cylinder head and an exhaust inlet of the turbine is determined to be an optimal volume that maximizes turbine efficiency at the representative operating point; a distance between the exhaust outlet and the exhaust inlet is determined to be a distance that maximizes the product of turbine efficiency and turbine inlet gas temperature within the constraint of the best volume; A method for designing exhaust systems for internal combustion engines.

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