JP2007224802A - Exhaust recirculating device of turbo-compound engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust recirculating device of a turbo-compound engine having high energy recovery efficiency. <P>SOLUTION: This turbo-compound engine has a turbocharger 10 supercharging intake air flowing in an intake passage 8 by the energy of exhaust gas flowing in an exhaust passage 6 and a low pressure turbine 3 rotating by the exhaust gas after passing through a high pressure turbine 14 of this turbocharger, and recovers the energy of the exhaust gas by the turbocharger and the low pressure turbine, and is provided with an exhaust recirculating passage 18 making the exhaust passage 6 communicate with the intake passage 8 on the upstream side of the low pressure turbine. An ejector 30 is arranged in a connecting part of this exhaust recirculating passage and the intake passage. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an improvement in an exhaust gas recirculation device for a turbo compound engine equipped with a turbocharger.

  Conventionally, it has a turbocharger and an exhaust energy recovery device, and the turbocharger includes a high-pressure turbine provided in the exhaust system and a compressor connected to the high-pressure turbine and provided in the intake system. In addition, a turbo compound engine has been proposed in which a high-pressure turbine is rotated by exhaust to rotate a compressor to supercharge intake air into the engine. The exhaust energy recovery device further includes a low-pressure turbine in an exhaust system downstream of the turbocharger, and transmits the rotational force of the low-pressure turbine rotated by exhaust to the engine output shaft. As a result, the turbo compound engine has improved output and fuel efficiency.

  There is also known an exhaust gas recirculation device that reduces part of the engine exhaust gas as EGR gas to the intake manifold and mixes it with the intake air to reduce the combustion temperature, thereby reducing nitrogen oxides in the exhaust gas. . In the conventional exhaust gas recirculation device, depending on the engine operating conditions, the exhaust pressure becomes lower than the intake air pressure, and there is an operation region in which exhaust gas recirculation cannot be performed.

As a technique for solving this problem, there is an EGR passage that connects an exhaust passage upstream of a low-pressure turbo and an intake passage upstream of a compressor of a turbocharger, and enables exhaust gas recirculation regardless of engine operating conditions (patent) Reference 1).
JP 2005-69092 A

  However, since the exhaust gas recirculation device of Patent Document 1 is configured to recirculate part of the exhaust gas to the intake system using the pressure difference between the exhaust passage and the intake passage, the EGR amount can be increased. Although it is possible, there is a problem that the energy of EGR gas cannot be sufficiently recovered.

  In view of the above-described conventional problems, an object of the present invention is to provide an exhaust gas recirculation device for a turbo compound engine with high energy recovery efficiency.

  A first invention includes a turbocharger that supercharges intake air flowing through an intake passage by energy of exhaust gas flowing through an exhaust passage, and a low-pressure turbine that rotates by exhaust after passing through a high-pressure turbine of the turbocharger. In a turbo compound engine that recovers exhaust energy by a charger and the low-pressure turbine, an exhaust gas recirculation passage that connects the exhaust passage upstream of the low-pressure turbine and the intake passage is provided, and a connection portion between the exhaust gas recirculation passage and the intake passage It is characterized by arranging an ejector.

  A second invention includes a turbocharger that supercharges intake air flowing through an intake passage by energy of exhaust gas flowing through an exhaust passage, and a low-pressure turbine that rotates by exhaust after passing through the high-pressure turbine of the turbocharger. In a turbo compound engine that recovers exhaust energy by a charger and the low-pressure turbine, an exhaust gas recirculation passage that communicates an exhaust passage between the high-pressure turbine and the low-pressure turbine and an intake passage upstream of the compressor of the turbocharger is provided. An ejector is disposed at a connection portion between the exhaust gas recirculation passage and the intake passage.

  A third invention is characterized in that, in the second invention, an oxidation catalyst is interposed in an exhaust passage upstream of the high-pressure turbine.

  A fourth invention includes a turbocharger that supercharges intake air flowing through an intake passage by energy of exhaust gas flowing through an exhaust passage, and a low-pressure turbine that rotates by exhaust after passing through the high-pressure turbine of the turbocharger. In a turbo compound engine that collects exhaust energy by a charger and the low-pressure turbine, an exhaust gas recirculation passage is provided that communicates an exhaust manifold of the engine and an intake passage downstream of a compressor of the turbocharger. The exhaust gas recirculation passage and the intake air passage It is characterized in that an ejector is arranged at the connection part.

  According to a fifth invention, in any one of the first to fourth inventions, the variable throttle valve for increasing or decreasing the flow cross-sectional area of the exhaust gas recirculation passage, and the variable throttle valve based on the operating state of the engine. Control means for performing operation control.

  According to a sixth invention, in the fifth invention, the control means controls the operation of the variable throttle valve based on a rotational speed and a load of the engine.

  According to a seventh invention, in any one of the first to sixth inventions, there is provided a cooling means for cooling the exhaust gas flowing through the exhaust gas recirculation passage.

  In an eighth aspect based on the fifth aspect, the high-pressure turbine and the low-pressure turbine are variable nozzle turbines, and the control means controls the nozzle opening according to the operating state of the engine. Features.

  According to a ninth invention, in any one of the first to fourth inventions, the ejector includes a throat portion having a gradually reduced cross-sectional area on the downstream side in the intake air flow direction, and the intake air is circulated through the throat portion. The exhaust air is sucked in.

  According to a tenth aspect of the present invention, in any one of the first to fourth aspects, the ejector includes a throat portion having a gradually decreasing cross-sectional area on the downstream side in the intake flow direction, and exhaust gas recirculated to the throat portion. It is characterized by the fact that it is circulated and sucks in the intake air.

  In the first, second, and fourth inventions, the exhaust gas recirculation passage that connects the exhaust passage upstream of the low-pressure turbine and the intake passage is provided, and the ejector is disposed at the connection portion between the exhaust gas recirculation passage and the intake passage. The internal static pressure is lowered, and the exhaust gas recirculation gas can be recirculated into the intake passage in a large amount.

  In the third invention, the exhaust discharged from the engine first passes through the oxidation catalyst, so that carbon monoxide and hydrocarbons in the exhaust are oxidized and removed. Since the engine exhaust is supplied to the oxidation catalyst before passing through the high-pressure turbine, the temperature drop of the exhaust supplied to the oxidation catalyst is suppressed. As a result, the oxidation catalyst is activated at a high temperature in a short time immediately after the engine 1 is started, so that carbon monoxide and hydrocarbons in the exhaust can be removed quickly and efficiently.

  In the fifth and sixth inventions, since the variable throttle valve is controlled based on the operating state of the engine, the exhaust gas flow rate is controlled in accordance with the supercharging pressure by the turbocharger, and the exhaust gas is purified by the exhaust gas recirculation. Can be achieved.

  In the seventh aspect of the invention, the exhaust gas passing through the exhaust gas recirculation passage is cooled and returned to the engine intake air at a low temperature. Thereby, since the combustion temperature of an engine falls more, the nitrogen oxide in exhaust_gas | exhaustion can be reduced more.

  In the eighth invention, since the nozzle openings of the high-pressure turbine and the low-pressure turbine are controlled according to the operating state of the engine, the output of the engine can be improved.

  In the ninth aspect of the invention, the ejector has a throat portion whose sectional area gradually decreases on the downstream side in the intake flow direction, and the intake air is circulated through the throat portion to suck in the exhaust gas. The static pressure is reduced, and exhaust gas recirculation can be promoted.

  In the tenth aspect of the invention, the ejector has a throat portion whose sectional area gradually decreases on the downstream side in the intake flow direction, and the exhaust gas recirculated to the throat portion is circulated to suck in the intake air. The static pressure of the engine can be reduced, and intake air can be sucked in, and engine output improvement and exhaust energy recovery can be promoted as the intake air amount increases.

  FIG. 1 is a configuration diagram of an exhaust gas recirculation device for a turbo compound engine according to an embodiment of the present invention. A turbo compound engine (hereinafter referred to as an engine) 1 includes an energy recovery device 2, and the energy recovery device 2 includes a low-pressure turbine 3, a speed reduction device 4, and a fluid coupling 5.

  The low-pressure turbine 3 is interposed in the exhaust passage 6 of the engine 1 and rotates by the energy of the exhaust gas that passes through the exhaust passage 6. The reduction gear 4 is connected to the rotating shaft of the low-pressure turbine 3 and decelerates the rotation of the low-pressure turbine 3, and is composed of, for example, a gear mechanism. The fluid coupling 5 connected to the speed reducer 4 rotates from the speed reducer 4 to the output shaft 7 of the engine 1 while absorbing the relative rotation between the output shaft 7 of the engine 1 and the speed reducer 4 due to the rotational fluctuation of the engine 1. Transmit power. Thereby, the energy recovery device 2 can improve the thermal efficiency of the engine 1 by recovering the exhaust energy and adding it to the rotational energy of the engine 1.

  In the intake passage 8 of the engine 1, an air cleaner 9 that removes impurities such as dust from the outside air, a compressor 11 that constitutes a turbocharger 10, and an intercooler 12 that cools the intake air are arranged in order from the upstream in the flow direction of the intake air. ing.

  On the other hand, in the exhaust passage 6, an oxidation catalyst 13 that oxidizes and removes carbon monoxide and hydrocarbons in the exhaust discharged from the engine 1 in order from the upstream in the exhaust flow direction, and a high-pressure turbine that constitutes the turbocharger 10. 14 is arranged upstream of the low-pressure turbine 3. Further, a muffler 15 that silences exhaust noise is interposed in the exhaust passage 6 on the downstream side of the low-pressure turbine 3.

  An EGR passage (exhaust gas recirculation passage) 18 that communicates the exhaust passage 6 between the high-pressure turbine 14 and the low-pressure turbine 3 and the intake passage 8 between the compressor 11 and the air cleaner 9 is provided. An EGR valve (variable throttle valve) 16 and an EGR cooler (cooling means) 17 are installed. The EGR valve 16 increases or decreases the flow path cross-sectional area of the EGR passage 18 according to a signal from a controller (control means) 19 incorporating a microcomputer.

  An ejector 30 is installed at a connection portion between the EGR passage 18 and the intake passage 8, and the static pressure in the intake passage 8 is lowered by the effect of the ejector 30, so that the pressure in the exhaust passage 6 is changed to the pressure in the intake passage 8. It becomes higher, and the EGR gas is efficiently recirculated into the intake passage 8.

  FIG. 2 is a cross-sectional view showing the shape of the ejector 30 provided in the connection portion.

  The ejector 30 shown in FIG. 2 has an integral casting structure that has three openings and forms passages that communicate with each other inside. The first opening 30a is connected to the EGR passage 18, and the second The opening 30b is connected to the intake passage 8 to supply intake air, and the third opening 30c is connected to the intake passage 8 to discharge intake air mixed with EGR gas. In the casing 31 of the ejector 30, the cross-sectional area of the flow path is reduced toward the intake air downstream side, and the throat portion 32 whose end opens to the merging chamber 31 a in the casing 31 communicates with the connected EGR passage 18. The merging chamber 31a communicates the throat portion 32 with the intake passage 8 for introducing intake air. Further, the flow passage cross-sectional area of the intake air supply passage 31b through which intake air is supplied is also formed so as to gradually decrease from the connecting portion to the merge chamber 31a. When the intake air flowing through the intake passage 8 is introduced into the ejector 30, the static pressure in the ejector is reduced, and EGR gas can be efficiently drawn.

  FIG. 3 is a cross-sectional view showing another shape of the ejector 30 provided in the connection portion.

  The ejector 30 shown in FIG. 3 has an integral casting structure that includes three openings and forms passages that communicate with each other inside. The first opening 30a is connected to the EGR passage 18, and the second The opening 30b is connected to the intake passage 8 to supply intake air, and the third opening 30c is connected to the intake passage 8 to discharge intake air mixed with EGR gas. In the casing 33 of the ejector 30, a cylindrical throat portion 34 whose diameter decreases toward the downstream side of the intake air and whose end portion opens to the merge chamber 33 a in the casing 33 is coaxial with the intake passage 8 to be connected. The merging chamber 33a surrounds the throat portion 34 in an annular shape, and an intake air supply passage 33b communicating with the EGR passage 18 is formed. The flow passage cross-sectional area of the intake air supply passage 33b is also formed so as to gradually decrease from the connection portion with the intake passage 8 to the merge chamber 31a. When the intake air flowing through the intake passage 8 is introduced into the ejector 30, the static pressure in the ejector is reduced, and EGR gas can be efficiently drawn.

  Alternatively, the first opening 30a of the ejector 30 shown in FIG. 3 may be connected to the intake passage 8 and the second opening 30b may be the EGR passage 18. In this case, the static pressure of the EGR gas flowing in from the EGR passage 18 is lowered by the effect of the ejector 30, and the intake air is drawn in to increase the intake air amount.

  Returning to the description of the exhaust gas recirculation device, the engine 1 is provided with a rotation speed sensor 20 for detecting the rotation speed and a load sensor 21 for detecting a load such as a fuel supply amount, an intake air flow rate, or a suction negative pressure. It has been. The controller 19 inputs the rotational speed and load of the engine 1 from the rotational speed sensor 20 and the load sensor 21, calculates the EGR flow rate, and duty-controls the EGR valve 16 based on the EGR flow rate.

  For the calculation of the EGR flow rate, the controller 19 stores in advance a map as shown in FIG. 4 in which the EGR flow rate (= EGR valve opening) corresponding to the rotational speed and load of the engine 1 is set. This is done by reading the EGR flow rate corresponding to the rotational speed and load of the engine 1 from this map. FIG. 4 shows a map of the opening degree of the EGR valve 16. The opening degree of the EGR valve 16 increases as the engine load increases. When the engine load is constant, the opening degree increases as the engine speed increases. Is set to be small.

  Next, the operation will be described.

  The exhaust discharged from the engine 1 first passes through the oxidation catalyst 13 to oxidize and remove carbon monoxide and hydrocarbons in the exhaust. Since the exhaust gas from the engine 1 is supplied to the oxidation catalyst 13 before passing through the high-pressure turbine 14, the temperature drop of the exhaust gas supplied to the oxidation catalyst 13 is suppressed. As a result, the oxidation catalyst 13 is activated at a high temperature in a short time immediately after the engine 1 is started, so that carbon monoxide and hydrocarbons in the exhaust gas can be immediately and efficiently removed.

  The exhaust gas that has passed through the oxidation catalyst 13 is supplied to the high-pressure turbine 14. Thereby, the high-pressure turbine 14 rotates and the compressor 11 is rotationally driven. Since all the exhaust of the engine 1 passes through the high-pressure turbine 14, the exhaust energy is efficiently transmitted to the high-pressure turbine 14, and the output of the high-pressure turbine 14 is improved. Thereby, the supercharging effect of the intake air by the turbocharger 10 is enhanced, and the output of the engine 1 is improved.

  The exhaust gas that has passed through the high-pressure turbine 14 passes through the low-pressure turbine 3, then passes through the muffler 15, and is discharged into the atmosphere. The low-pressure turbine 3 is rotationally driven by exhaust energy of exhaust passing therethrough. The rotation of the low-pressure turbine 3 is decelerated by the speed reducer 4 and is transmitted to the output shaft 7 of the engine 1 through the fluid coupling 5 while absorbing rotational fluctuations of the engine 1. As a result, the exhaust energy of the engine 1 is recovered and used for the rotational energy of the engine 1, so that the output and fuel consumption of the engine 1 are improved.

  On the other hand, the outside air as the intake air of the engine 1 is compressed by the compressor 11 of the high-pressure turbine 14 after impurities such as dust are removed by the air cleaner 9. The compressed intake air becomes high temperature, but is cooled by passing through the intercooler 12. Thereby, the volume of the intake air is reduced and the intake efficiency of the engine 1 is improved. The intake air cooled by the intercooler 12 passes through the intake passage 8 and is supplied to the engine 1.

  Part of the exhaust gas that has passed through the high-pressure turbine 14 passes through the EGR passage 18 and is returned to the intake passage 8 upstream of the compressor 11. As a result, exhaust gas recirculation is efficiently performed by the pressure difference between the intake air before being compressed by the compressor 11 and the exhaust gas subjected to back pressure by the low-pressure turbine 3, so that a large amount of exhaust gas is recirculated to the intake air of the engine 1. Thus, the combustion temperature of the engine 1 can be lowered, and nitrogen oxides in the exhaust can be reduced.

  In addition, an ejector 30 is disposed at a connection portion between the intake passage 8 and the EGR passage 18. Due to the effect of the ejector 30, the flow rate of intake air is increased to further reduce the static pressure in the intake air. By increasing the difference between the pressure and the pressure in the intake passage 8 (ejector 30), the exhaust gas recirculation from the EGR passage 18 to the intake passage 8 can be promoted to further increase the exhaust gas flow rate.

  Alternatively, the flow rate of the EGR gas flowing from the EGR passage 18 can be increased to reduce the static pressure of the EGR gas by the effect of the ejector 30, and the intake air can be drawn and the intake air amount can be increased. In this case, the exhaust energy recovery efficiency is improved, the fuel efficiency is improved, and the output of the engine 1 can be expected to be improved due to the increase in the intake air amount.

  In addition, since the carbon monoxide and hydrocarbons are removed by the oxidation catalyst 13 from the exhaust gas recirculated through the EGR passage 18, it is possible to prevent the compressor 11 and the interior of the intercooler 12 provided downstream thereof from being contaminated. Is done.

  The controller 19 controls the operation of the EGR valve 16 based on the rotational speed and load of the engine 1 detected by the rotational speed sensor 20 and the load sensor 21 respectively. In this way, by setting the opening of the EGR valve 16 according to the engine load and the engine speed, the EGR amount can be controlled according to the supercharging pressure by the turbocharger, and the exhaust gas can be cleaned by EGR. . In addition, an optimal exhaust gas recirculation can be performed by using a sensor provided for controlling the engine 1 and the like.

  Further, since the EGR cooler 17 is provided in the EGR passage 18, the exhaust gas passing through the EGR passage 18 is cooled and becomes a low temperature and is returned to the intake air of the engine 1. Thereby, since the combustion temperature of the engine 1 falls more, the nitrogen oxide in exhaust_gas | exhaustion can be reduced more.

  FIG. 5 is a configuration diagram illustrating a configuration of an exhaust gas recirculation device for a turbo compound engine according to the second embodiment. In this embodiment, the EGR passage 18 that connects the exhaust passage 6 and the intake passage 8 is eliminated, the branch pipes of the exhaust manifold are integrated, and the collecting portion 1b that connects to the exhaust passage 6, the intercooler 12, and the intake air An EGR passage 18a that connects the intake passage 8 with the collector portion 1a of the manifold is provided, and an EGR valve 16 and an EGR cooler 17 are installed in the EGR passage 18a. In addition, an ejector 30 is installed at a connection portion between the EGR passage 18a and the intake passage 8, and the high-pressure turbine 14a and the low-pressure turbine 3a of the turbocharger 10 are constituted by variable nozzle turbines. The nozzles of the high-pressure turbine 14a and the low-pressure turbine 3a are controlled based on the load. The second embodiment has such a configuration, and other configurations are the same as those of the first embodiment.

  As shown in FIG. 6, the controller 19 reads the engine load and the engine speed detected by the rotational speed sensor 20 and the load sensor 21, and based on the detected engine load and the engine speed as shown in FIG. In order to control the opening degree of the nozzles of the turbines 3 and 14 using the map, and to control the opening degree of the EGR valve 16 using the map shown in FIG. 4 described above based on the detected engine load and engine speed. The EGR amount can be controlled according to the supercharging pressure by the turbocharger 10 to achieve both the improvement of the output of the engine 1 and the purification of exhaust gas by EGR.

  FIG. 7 shows a map of the variable nozzle openings of the turbines 3 and 14. The opening of the variable nozzles of the turbines 3 and 14 increases as the engine load increases. If the load is constant, the engine speed is increased. Set so that the higher the value, the larger.

  Thus, in the present invention, in the turbo compound engine, the exhaust gas recirculation passage that connects the exhaust passage upstream of the low-pressure turbine and the intake passage is provided, and the ejector is disposed at the connection portion between the exhaust recirculation passage and the intake passage. The internal static pressure is reduced, and a large amount of the reflux gas can be recirculated into the intake passage.

  The present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea.

It is a block diagram of the exhaust gas recirculation apparatus of the turbo compound engine of this embodiment. It is sectional drawing of an ejector. It is other sectional drawing of an ejector. It is an opening degree map of an EGR valve. It is a block diagram of the exhaust gas recirculation apparatus of the turbo compound engine of 2nd Embodiment. It is a flowchart explaining the control content of an exhaust gas recirculation apparatus. It is an opening degree map of a turbine nozzle.

Explanation of symbols

1: Turbo compound engine 1a: Intake manifold collector 1b: Exhaust manifold assembly 3: Low pressure turbine 6: Exhaust passage 8: Intake passage 10: Turbocharger 11: Compressor 13: Oxidation catalyst 14: High pressure turbine 16: EGR valve 17: EGR cooler 18: EGR passage 19: Controller 30: Ejector

Claims (10)

A turbocharger that supercharges the intake air flowing through the intake passage by the energy of the exhaust gas flowing through the exhaust passage;
A low-pressure turbine that rotates by exhaust after passing through the high-pressure turbine of this turbocharger,
In a turbo compound engine that recovers exhaust energy by the turbocharger and the low-pressure turbine,
Providing an exhaust gas recirculation passage communicating the exhaust passage upstream of the low-pressure turbine and the intake passage;
An exhaust gas recirculation device for a turbo compound engine, wherein an ejector is disposed at a connection portion between the exhaust gas recirculation passage and the intake air passage. A turbocharger that supercharges the intake air flowing through the intake passage by the energy of the exhaust gas flowing through the exhaust passage;
A low-pressure turbine that rotates by exhaust after passing through the high-pressure turbine of this turbocharger,
In a turbo compound engine that recovers exhaust energy by the turbocharger and the low-pressure turbine,
Providing an exhaust gas recirculation passage that communicates an exhaust passage between the high-pressure turbine and the low-pressure turbine and an intake passage on the upstream side of the compressor of the turbocharger;
An exhaust gas recirculation device for a turbo compound engine, wherein an ejector is disposed at a connection portion between the exhaust gas recirculation passage and the intake air passage.   The exhaust gas recirculation apparatus for a turbo compound engine according to claim 2, wherein an oxidation catalyst is interposed in an exhaust passage upstream of the high-pressure turbine. A turbocharger that supercharges the intake air flowing through the intake passage by the energy of the exhaust gas flowing through the exhaust passage;
A low-pressure turbine that rotates by exhaust after passing through the high-pressure turbine of this turbocharger,
In a turbo compound engine that recovers exhaust energy by the turbocharger and the low-pressure turbine,
An exhaust gas recirculation passage is provided that communicates the exhaust manifold of the engine and an intake passage downstream of the compressor of the turbocharger;
An exhaust gas recirculation device for a turbo compound engine, wherein an ejector is disposed at a connection portion between the exhaust gas recirculation passage and the intake air passage. A variable throttle valve that increases or decreases the cross-sectional area of the exhaust gas recirculation passage;
Control means for controlling the operation of the variable throttle valve based on the operating state of the engine;
The exhaust gas recirculation device for a turbo compound engine according to any one of claims 1 to 4, characterized by comprising:   6. The exhaust gas recirculation apparatus for a turbo compound engine according to claim 5, wherein the control means controls the operation of the variable throttle valve based on the rotational speed and load of the engine.   The exhaust gas recirculation apparatus for a turbo compound engine according to any one of claims 1 to 6, further comprising cooling means for cooling the exhaust gas flowing through the exhaust gas recirculation passage. The high-pressure turbine and the low-pressure turbine are variable nozzle turbines,
6. The exhaust gas recirculation apparatus for a turbo compound engine according to claim 5, wherein the control means controls a nozzle opening degree according to an operating state of the engine.   5. The ejector according to claim 1, wherein the ejector includes a throat portion whose sectional area gradually decreases on the downstream side in the intake air flow direction, and the intake air is circulated through the throat portion to suck in exhaust gas. 6. The exhaust gas recirculation device for a turbo compound engine according to any one of the preceding claims.   2. The ejector includes a throat portion whose sectional area gradually decreases on the downstream side in the intake flow direction, and circulates exhaust gas recirculated to the throat portion to suck in intake air. 5. The exhaust gas recirculation device for a turbo compound engine according to any one of 4 above.

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