JP2007154684A - Two-stage supercharging type engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a two-stage turbo supercharging engine which includes a bypass pipe line in an exhaust passage and controls the actuation of a turbo supercharger in high pressure/low pressure stages in according to an operating state, wherein both turbo superchargers are effectively actuated by achieving compact layouts by the simplification of a composition of an exhaust passage. <P>SOLUTION: A high pressure bypass pipe 5 for bypassing a high pressure stage turbine HT and a low pressure bypass pipe 9 for bypassing a low pressure stage turbine LT are provided at an exhaust passage of an engine 1 which keeps the high pressure stage turbine HT and the low pressure stage turbine LT arranged in series. An inlet of the low pressure bypass pipe 9 is connected to an outlet of the high pressure bypass pipe 5. A bypass valve is mounted in the connection part so as to control both bypass pipes by one valve. The low pressure bypass pipe 9 is opened to reduce back pressure in the high pressure stage turbine HT at low speed and a low load of the engine 1, thereby enhancing the efficiency of the turbo supercharge in the high pressure stage to reduce a fuel consumption rate of the engine. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a two-stage turbocharged engine, that is, a low-pressure stage compressor and a high-pressure stage compressor that are arranged in series in an intake passage of the engine, and a low-pressure turbine and a high-pressure turbine that drive these compressors in the exhaust passage of the engine. The present invention relates to an engine having a supercharging system that is installed and pressurizes air supplied to an engine cylinder by a two-stage turbocharger.

  In order to increase the intake air amount of the engine, an exhaust turbo supercharger that is driven by a turbine provided with an intake air pressurizing compressor in the intake passage and installed in the exhaust passage may be used as a means for increasing the engine output. It is known and widely used for the purpose of reducing the size and weight and improving the fuel economy (reducing the fuel consumption rate) even in the engine for vehicles. In particular, a diesel engine is an engine that supplies only air instead of supplying an air-fuel mixture to an engine cylinder, unlike a gasoline engine, and does not adjust output by increasing or decreasing the amount of intake air. Compared with the engine, the compatibility with the exhaust turbocharger is good, and the output can be improved without causing the deterioration of the efficiency due to the blow-through of the fuel or the output adjustment.

  In recent years, in order to further improve the output or fuel consumption rate of an engine equipped with an exhaust turbocharger, a two-stage turbocharger in which a low-pressure turbocharger and a high-pressure turbocharger are arranged in series Development is underway to apply the aircraft to vehicle engines. Generally, a compressor used in a turbocharger or the like has a characteristic in which efficiency changes according to an air (volume) flow rate and a pressure ratio, and the characteristic is expressed as a so-called compressor map. When a two-stage turbocharger is used, the compressor for the low-pressure turbocharger is a large-capacity type with a large flow rate and high efficiency, and the compressor for a high-pressure stage is a small-capacity type with a small flow rate and high efficiency. By using the engine, it becomes possible to more effectively utilize the exhaust energy of the engine.

  Furthermore, in the two-stage turbocharger, it is possible to select a supercharging system that matches various characteristics of the engine. For example, when the engine is operating at a low speed and a low load, the intake air amount is small, so a high-efficiency high-pressure turbocharger with a small flow rate is activated, and the low-pressure turbocharger is substantially deactivated. As a result, the efficiency of the supercharger increases, and as a result, the fuel consumption rate of the engine decreases. When the engine enters a high-speed and high-load operation state, the engine exhaust gas bypasses the high-pressure stage turbocharger's high-pressure stage turbine so that only the large-capacity low-pressure stage turbocharger operates. Ensure sufficient intake air volume to meet engine output increase.

  A supercharging system equipped with a two-stage turbocharger and controlling the operation of the low-pressure turbocharger and the high-pressure turbocharger in accordance with the operating state of the engine will be described with reference to FIG. The engine 1 has a large-capacity low-pressure turbocharger HTC and a small-capacity high-pressure turbocharger LTC installed in series, and the outlet of the low-pressure compressor LC of the low-pressure turbocharger LTC is high-pressure. It is connected to the inlet of the high-pressure stage compressor HC of the stage turbocharger HT. The outlet of the high-pressure compressor HC is connected to an intake manifold 3 of the engine 1 via an air cooler 2 that cools compressed air. On the other hand, a high-pressure stage turbine HT and a low-pressure stage turbine LT are connected in series to the exhaust manifold 4 of the engine 1, and a bypass pipe that bypasses the high-pressure stage turbine HT and directly leads the exhaust gas to the low-pressure stage turbine LT. 5 is provided, and a bypass valve 51 is disposed in the pipeline. Reference numeral 6 denotes a conduit for recirculating (EGR) the exhaust gas to the engine cylinder, and an EGR control valve 61 and an EGR cooler 62 are disposed in the middle thereof.

When the engine is operated at a low speed and a low load, the bypass valve 51 of the bypass line 5 connected to the exhaust manifold is closed. As a result, the exhaust gas expands mainly in the high-pressure stage turbine HT to drive the high-pressure stage compressor HC, and the amount of work generated in the low-pressure stage turbine LT becomes substantially zero. Since the high-pressure compressor HC is highly efficient in a small flow rate region, the exhaust energy of the engine is used efficiently and the fuel consumption rate is reduced. As the engine load increases, the opening degree of the bypass valve 51 increases, and when the engine enters a high speed and high load operation state, the exhaust gas is directly introduced into the low pressure turbine LT and the intake air is substantially compressed by the low pressure compressor LC. As a result, a large amount of air is efficiently supplied to the engine 1.
A method of using such a two-stage turbocharger is disclosed in Japanese Utility Model Publication No. 6-48119 as an example. Japanese Patent Laid-Open No. 2002-276382 discloses a method for controlling a bypass valve that bypasses a high-pressure turbine.

Incidentally, in the technical field of diesel engines, a technology that combines a two-stage turbocharger and a premixed compression self-ignition combustion system (HCCI <Homogeneous Charge Compression Ignition>) has recently attracted attention. HCCI is a combustion method that suppresses particulate matter (PM) and the like that are subject to exhaust gas regulations in the combustion process, and injects fuel early into the engine cylinder and compresses it in a premixed state with air. This is a combustion method in which combustion is rapidly completed after compression ignition. In this combustion method, it is necessary to prevent pre-ignition of the fuel previously mixed with air, and therefore, a high rate of EGR is performed. When a two-stage turbocharger is applied to an HCCI combustion type diesel engine and the high-pressure stage turbocharger is substantially operated, air is efficiently generated even in an engine cylinder containing a large amount of exhaust gas due to high supercharging. It is supplied and good combustion can be performed.
No. 6-48119 JP 2002-276382 A

  In a vehicle engine equipped with a two-stage turbocharger, a high-efficiency high-pressure turbocharger is operated in a small flow rate range at low speed and low load operation. At this time, it is desirable to increase the pressure of the air supplied to the engine, that is, boost by increasing the pressure ratio of the high-pressure compressor. For example, when a two-stage turbocharger is applied to an HCCI combustion type engine, the supply state of air into the engine cylinder is improved by increasing the boost, and the operating range in which HCCI combustion is performed is expanded. It becomes possible.

  Increasing the pressure ratio of the high-pressure compressor can increase the boost and increase the amount of supplied air, but also increases the pressure difference acting on the high-pressure turbocharger, leading to an increase in engine exhaust pressure. An increase in engine exhaust pressure results in an increase in so-called pumping loss, which is a loss associated with engine cylinder gas exchange, and deteriorates the fuel consumption rate. In particular, in a two-stage turbocharger, a low-pressure stage turbine is connected downstream of the high-pressure stage turbine, and pressure loss occurs when exhaust gas passes through the low-pressure stage turbine, so that the engine exhaust pressure further increases. It will be.

In order to eliminate the pressure loss of the exhaust gas caused by the fluid resistance of the low-pressure turbine, an exhaust pipe that bypasses the low-pressure turbine and a low-pressure bypass valve that opens and closes the exhaust pipe are provided. It is conceivable to bypass. That is, as shown by a broken line in FIG. 6, the low pressure bypass pipe 71 that bypasses the low pressure stage turbine LT is connected to the inlet and the outlet of the low pressure stage turbine LT, and the low pressure bypass valve 71 installed in the middle is connected to the low speed and low load. Open during operation. In this way, it is possible to avoid the pressure loss caused by the fluid resistance of the low-pressure turbine LT, but two pipe lines of the bypass pipe 5 and the low-pressure bypass pipe 7 that bypass the high-pressure turbine HT are required, Two valves are required to open and close each pipeline. A vehicle engine has a limited mounting space and is strongly demanded to be light in weight. Therefore, it is necessary to avoid a complicated layout of pipes as much as possible.
The present invention is a supercharged engine equipped with a two-stage turbocharger and controlling the operation of a high-pressure / low-pressure stage turbocharger according to an operating state, and is provided with a pipe line and a valve for bypassing the low-pressure stage turbine, And it makes it the subject to make the structure simple and to operate both turbochargers efficiently by a compact layout.

In view of the above problems, the present invention provides a low-pressure turbine in an exhaust passage of an engine provided with a two-stage turbocharger, from a connection portion of an exhaust passage to which an outlet of a high-pressure bypass pipe that bypasses the high-pressure turbine is connected. The low-pressure bypass pipe that bypasses the turbine is branched, and the operating state of both turbines is controlled by a single bypass valve installed at the connecting portion. That is, the present invention
“A supercharged engine with a two-stage turbocharger,
A low-pressure compressor and a high-pressure compressor are arranged in series in the engine intake passage, and a high-pressure turbine that drives the high-pressure compressor and a low-pressure turbine that drives the low-pressure compressor are arranged in the exhaust passage of the engine. ,
In the exhaust passage of the engine, a connected exhaust pipe connecting the outlet of the high-pressure stage turbine and the inlet of the low-pressure stage turbine, a high-pressure bypass bypassing the high-pressure stage turbine and connecting the outlet to the connected exhaust pipe A low-pressure bypass pipe for bypassing the pipe and the low-pressure turbine, and
An inlet of the low pressure bypass pipe is connected to a connection portion of the connection exhaust pipe to which an outlet of the high pressure bypass pipe is connected, and the connection portion controls the flow rates of the high pressure bypass pipe and the low pressure bypass pipe. Bypass valve is installed "
The supercharged engine is characterized by this.

  The bypass valve has a valve body that rotates about a valve shaft, and the valve body closes an outlet of the high-pressure bypass pipe and opens an inlet of the low-pressure bypass pipe. The high pressure stage turbine operating position, the high pressure bypass pipe outlet is opened and the low pressure bypass pipe outlet is closed, and the high pressure bypass pipe outlet opening is adjustable. It is preferable to configure.

  According to a third aspect of the present invention, there is provided a supercharged engine according to the present invention having an exhaust gas recirculation device and a diesel engine having a fuel injection control device for advancing fuel injection timing in a load region smaller than a predetermined load. Is preferred.

  In the supercharged engine of the present invention including the two-stage turbocharger, a high-pressure bypass pipe that bypasses the high-pressure turbine is provided, and a low-pressure bypass pipe that bypasses the low-pressure turbine is further provided. When the engine is operating at low speed and low load, the high pressure bypass pipe is closed and a high efficiency turbocharger is operated in a small flow rate range to increase the engine boost. By opening the bypass pipe, the exhaust gas flows bypassing the low-pressure turbine. Therefore, pressure loss based on the fluid resistance of the low-pressure turbine can be avoided to suppress an increase in engine exhaust pressure, and the fuel consumption rate at the time of engine low load can be reduced. By the way, the applicant has confirmed through experiments and the like that a fuel consumption rate can be reduced by several percent by installing a low-pressure bypass pipe and setting the back pressure of the high-pressure turbine to almost atmospheric pressure. Yes.

  The exhaust passage of a supercharged engine equipped with a two-stage turbocharger is provided with a connected exhaust pipe that connects the outlet of the high-pressure turbine and the inlet of the low-pressure turbine. Then, the inlet of the low-pressure bypass pipe that bypasses the low-pressure turbine is connected to the connection portion of the connection exhaust pipe to which the outlet of the high-pressure bypass pipe is connected. By comprising in this way, a bypass valve is installed in the connection part of a connection exhaust pipe line, and the flow volume of the exhaust gas which flows through both a high pressure bypass pipe and a low pressure bypass pipe is controlled by one common bypass valve. Is possible. As a result, the configuration of the bypass pipe and the bypass valve becomes compact, and the installation space is also reduced.

  According to a second aspect of the present invention, a rotary valve having a valve body that rotates around a valve shaft is adopted as a bypass valve, and the outlet of the high-pressure bypass pipe is closed at both ends of rotation of the valve body to reduce the pressure. The high pressure stage turbine operating position for opening the inlet of the bypass pipe and the low pressure stage turbine operating position for opening the outlet of the high pressure bypass pipe and closing the inlet of the low pressure bypass pipe occupy the high pressure bypass pipe in the middle region of the valve body rotation. It can be made to be an adjustment position for changing the opening degree (opening area) of the outlet. In this way, the configuration of the bypass valve becomes even more compact.

  According to a third aspect of the present invention, a diesel engine that performs HCCI combustion at a low load, that is, a diesel engine that has an exhaust gas recirculation device and a fuel injection control device that accelerates fuel injection timing in a low load region. When the supercharged engine of the present invention is applied, the fuel economy at the time of low load can be improved and the operating range of HCCI combustion can be expanded.

  Hereinafter, a supercharged engine equipped with a two-stage turbocharger and embodying the present invention will be described with reference to the drawings. FIG. 1 schematically shows a supercharged engine according to the present invention. However, components corresponding to the parts and apparatus of FIG. 6 showing a conventional engine equipped with a two-stage turbocharger are denoted by the same reference numerals. Is attached.

  The configuration of the low-pressure stage and high-pressure stage turbocharger of the supercharged engine, the configuration of the engine intake passage, and the like are basically the same as those of the conventional engine shown in FIG. That is, the engine 1 is provided with a large-capacity low-pressure turbocharger LTC and a small-capacity high-pressure turbocharger HTC in series, and the outlet of the low-pressure compressor LC in the intake passage of the engine is a high-pressure compressor. Connected to HC inlet. An air cooler 2 is placed between the intake manifold 3 and the high-pressure compressor HC, and an EGR pipe 6 is connected. The high-pressure compressor HC is provided with an intake bypass passage 8 and a bypass throttle valve 81 that bypass the high-pressure compressor HC.

  In the supercharged engine of the present invention, the high-pressure stage turbine HT and the low-pressure stage turbine LT are connected in series to the exhaust manifold 4, and the high-pressure bypass pipe 5 that bypasses the high-pressure stage turbine HT is provided. A low-pressure bypass pipe 9 that branches from the outlet and bypasses the low-pressure turbine LT is installed. That is, the outlet of the high-pressure bypass pipe 5 is connected to a connection exhaust pipe 10 that connects the outlet of the high-pressure stage turbine HT and the inlet of the low-pressure stage turbine LT. The low-pressure bypass pipe 9 is connected and branched from the connection portion 11 so as to guide the exhaust gas downstream of the low-pressure stage turbine LT.

  A bypass valve 12 is placed in the connection portion 11, and its specific structure is shown in FIG. As can be seen from FIG. 2 (a), the bypass valve 12 has a valve casing 121 having a rectangular cross section, and each of the four outer surfaces of the valve casing 121 has a high-pressure turbine HT outlet pipe, The bypass pipe 5, the pipe of the inlet of the low pressure turbine LT and the low pressure bypass pipe 9 are connected. The connection state of these pipe lines corresponds to the arrangement state of each pipe in the connection portion 11 of FIG. 1, and the piping of the outlet of the high-pressure turbine HT and the piping of the inlet of the low-pressure turbine LT are: The connected exhaust pipe 10 is configured.

  A valve chamber 122 having a cylindrical cross section is formed inside the valve casing 121, and four circular holes corresponding to the connected pipelines are opened in the valve chamber 122. In the valve chamber **, an arcuate valve body 123 that closes these openings is rotatably installed. As shown in FIG. 2B, fan-shaped connecting plates 125 attached to the shaft 124 are fixed to both ends of the arc-shaped valve body 123. The shaft 124 is connected to an actuator (not shown) via a link mechanism or the like, and rotates in response to a command from an engine control device to control the flow of exhaust gas. At the position of the valve body 123 in FIG. 2, the high pressure bypass pipe 5 is fully closed and the low pressure bypass pipe 9 is opened, and the exhaust gas flows through the high pressure stage turbine HT and bypasses the low pressure stage turbine LT. Become.

  Next, the operation of the supercharged engine equipped with the two-stage turbocharger of the present invention and the control method of the bypass valve and the like will be described with reference to FIGS. These figures show the position of the bypass valve 12 corresponding to the operating state of the engine and the flow of intake air and exhaust gas of the engine.

  When the engine 1 is operating at a low speed and a low load, as shown in FIG. 3, the bypass valve 12 is placed at a position where the high pressure bypass pipe 5 is closed and the low pressure bypass pipe 9 is opened. The entire amount of exhaust gas of the engine 1 passes through the high-pressure turbine HT and generates work to drive the high-pressure compressor HC. At this time, the low pressure bypass pipe 9 is opened, and substantially all exhaust gas discharged from the high pressure turbine HT flows through the low pressure bypass pipe 9. The exhaust gas is not subjected to fluid resistance by the low-pressure turbine LT, and the back pressure of the high-pressure turbine HT is almost atmospheric pressure. That is, the expansion ratio of the high-pressure turbine HT increases and the amount of work generated increases, resulting in efficient driving of the high-pressure compressor HC.

  The intake air enters the high-pressure compressor HC via the low-pressure compressor LC, where it is compressed and boosted. After being cooled by the air cooler 2, it is supplied into the engine cylinder. Since the high-pressure compressor HC has a small flow rate and high efficiency, when the engine 1 is at a low speed and a low load, it is possible to effectively use the exhaust energy, and exhaust based on the bypass of the low-pressure turbine LC. Since the use of energy becomes more efficient, the fuel consumption rate of the engine is further reduced.

  In a diesel engine that performs HCCI combustion, early fuel injection is performed for fuel premixing during operation at low speed and low load, for example, fuel injection is performed at a time earlier than 20 ° before top dead center, and A high rate of EGR is performed from the EGR line 6. In the supercharged engine of the present invention, the amount of work generated by the high-pressure turbine HT increases and the pressure ratio of the high-pressure compressor HC increases, so that sufficient air can be supplied into the engine cylinder even in such a case. This is possible, and the operating range in which HCCI combustion is performed can be expanded.

  When the engine 1 is operated at a high speed and a high load, as shown in FIG. 4, the bypass valve 12 is placed at a position where the high pressure bypass pipe 5 is opened and the low pressure bypass pipe 9 is closed. Due to the fluid resistance of the high-pressure turbine HT, the entire exhaust gas of the engine 1 is basically led directly to the low-pressure turbine LT, bypassing the high-pressure turbine HT, where it generates work and the low-pressure compressor LC Drive. The low-pressure compressor LC is a high-efficiency compressor with a large flow rate, and operates efficiently in accordance with the intake air amount when the engine is heavily loaded, and the output of the engine 1 is ensured. At this time, the air compressed by the low pressure compressor LC passes through the intake bypass pipe 8 and bypasses the high pressure compressor HC and is supplied to the engine 1. By bypassing the high-pressure compressor HC, a pumping loss due to the fluid resistance of the small-capacity high-pressure compressor HC can be avoided.

  When the operating state of the engine 1 is in an intermediate transition region between the low speed and low load and the high speed and high load, the bypass valve 12 closes the low pressure bypass pipe 9 and closes the high pressure bypass pipe 5 as shown in FIG. The opening area (opening degree) of the high pressure bypass pipe 5 is controlled according to the operating state by the engine control device. The exhaust gas branches and flows into the high-pressure stage turbine HT and the low-pressure stage turbine LT at the inlet of the high-pressure bypass pipe 5, and work is generated in both turbines. The distribution of work of both turbines changes corresponding to the opening area of the high-pressure bypass pipe 5, and as a result, the pressure ratio of the low-pressure stage compressor LC and the high-pressure stage compressor HC pressure ratio are adjusted. When the shape or the like of the opening of the high-pressure bypass pipe 5 in the bypass valve 12 is changed, the characteristics of the opening degree in the transition region can be changed. In the transition region, the amount of air that bypasses the high-pressure compressor HC is adjusted according to the operating state of the high-pressure turbocharger HTC, that is, the work amount of the high-pressure turbine HT.

  Incidentally, the engine control device stores a map for determining the fuel supply amount (load) of the engine based on the depression amount of the accelerator pedal operated by the vehicle driver and the engine speed. The engine control device controls the fuel injection amount, the injection timing, and the like in the case of a diesel engine based on the map based on the input signal of the accelerator pedal depression amount and the engine speed representing the operating state of the engine. The operation areas of the low speed and low load, the high speed and high load, and the transition area in the above embodiment are also determined based on this map.

  As described above in detail, in the supercharged engine equipped with the two-stage turbocharger, the present invention is provided with a high-pressure bypass pipe that bypasses the high-pressure turbine and a low-pressure bypass pipe that bypasses the low-pressure turbine in the exhaust passage. The operation state of both turbines is controlled by a single bypass valve installed at the connection portion, and the turbocharger is efficiently operated by a compact layout. In the above embodiment, a diesel engine for a vehicle is mainly described, but the present invention can also be applied to a gasoline engine. Further, it is obvious that various modifications can be made to the configuration of the embodiment, such as applying a valve other than the rotary valve of the embodiment as a bypass valve.

It is a schematic diagram which shows the pipe line structure etc. of the two-stage supercharging engine by this invention. It is a figure which shows an example of this invention bypass valve. It is a figure which shows the action | operation at the time of the low speed low load of the two-stage supercharged engine of this invention. It is a figure which shows the action | operation at the time of the high-speed high load of the two-stage supercharged engine of this invention. It is a figure which shows the operation | movement in the transition area of the two-stage supercharging engine of this invention. It is a schematic diagram which shows the pipe line structure etc. of the conventional 2-stage supercharged engine.

Explanation of symbols

HTC High-pressure stage turbocharger HC High-pressure stage compressor, HT High-pressure stage turbine LTC Low-pressure stage turbocharger LC Low-pressure stage compressor, LT Low-pressure stage turbine 5 High-pressure bypass pipe 9 Low-pressure bypass pipe 12 Bypass valve

Claims (3)

A supercharged engine with a two-stage turbocharger,
A low-pressure compressor (LC) and a high-pressure compressor (HC) are arranged in series in the intake passage of the engine to drive the high-pressure turbine (HT) that drives the high-pressure compressor (HC) and the low-pressure compressor (LC). A low-pressure stage turbine (LT) that is disposed in the exhaust passage of the engine,
The exhaust passage of the engine is connected to an exhaust pipe (10) connecting the outlet of the high-pressure stage turbine (HT) and the inlet of the low-pressure stage turbine (LT), and bypasses the high-pressure stage turbine (HT) and exits. Is provided with a high pressure bypass pipe (5) connected to the connection exhaust pipe and a low pressure bypass pipe for bypassing the low pressure stage turbine (LT),
An inlet of the low-pressure bypass pipe (9) is connected to a connection part (11) of the connection exhaust pipe to which an outlet of the high-pressure bypass pipe (5) is connected, and the connection part (11) includes the high-pressure bypass pipe (9). A supercharged engine comprising a bypass pipe (5) and a bypass valve (12) for controlling a flow rate of the low-pressure bypass pipe (9). The bypass valve (12) has a valve body (123) that rotates about a valve shaft (124), and the valve body (123) closes an outlet of the high-pressure bypass pipe (5) to thereby reduce the low pressure. A high pressure turbine operating position for opening the inlet of the bypass pipe (9), a low pressure turbine operating position for opening the outlet of the high pressure bypass pipe (5) and closing the inlet of the low pressure bypass pipe (9), and the high pressure bypass The supercharged engine according to claim 1, wherein the supercharged engine is configured to be movable to an adjustment position for changing an opening degree of an outlet of the pipe (5). 3. The engine according to claim 1, wherein the engine is a diesel engine, has an exhaust gas recirculation device, and has a fuel injection control device that advances fuel injection timing in a load region smaller than a predetermined load. Supply engine.

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