JP2015101972A - Engine exhaust gas recirculation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure scavenging residual exhaust gas for recirculation on an upstream side of an air intake throttle valve and suppressing generation of exhaust-gas-containing condensed water at a time of engine stop.SOLUTION: A scavenging passage 15 having one end communicating with an upstream side of a throttle valve 6 and the other end for releasing gas to the atmosphere in an engine is branched off from an air intake passage 3 between the throttle valve 6 and an intercooler 7, and a motor pump 16 having an intake side communicating with the upstream side of the throttle valve 6 and a discharge side communicating with the atmosphere is interposed in this scavenging passage 15. During engine stop, the throttle valve 6 is closed and the motor pump 16 is actuated, thereby ensuring that residual gas resulting from implementation of low-pressure EGR during engine operation is scavenged into the engine and suppressing generation of condensed water containing an exhaust gas component in a low-pressure EGR system, particularly in the intercooler 7.

Description

  The present invention relates to an engine exhaust gas recirculation device that recirculates part of exhaust gas into an intake passage.

  2. Description of the Related Art Conventionally, exhaust gas recirculation (EGR) devices that recirculate part of exhaust gas to intake air have been widely put into practical use for the purpose of reducing NOx in exhaust gas discharged from an engine. As an EGR passage that circulates the exhaust gas, in particular, in a diesel engine, a relatively high pressure EGR that circulates part of the exhaust gas from the exhaust manifold side to the intake manifold side leads to the intake side from the exhaust passage on the downstream side of the catalyst. A relatively low pressure EGR that circulates a portion of the exhaust is known.

  Since this low-pressure EGR circulates exhaust gas that has passed through a turbocharger turbine or catalyst, the gas temperature is low, and moisture contained in the gas may condense, generating condensed water in some cases. Since this condensed water contains sulfur components and the like in the exhaust gas, there is a possibility that each part is corroded to cause a malfunction.

  For this reason, Patent Document 1 discloses a technique for reducing the residual amount of EGR gas in the EGR passage when the internal combustion engine is stopped. In this prior art, by reducing the opening of the nozzle vane before the internal combustion engine is stopped, the boost pressure is increased to keep the pressure in the intake passage downstream from the compressor high, so that the intake passage is stopped when the internal combustion engine is stopped. High pressure air is allowed to flow from the EGR passage toward the EGR passage, and the EGR gas or condensed water remaining in the EGR passage is pushed back to the exhaust passage.

JP 2008-309133 A

  However, in the technique disclosed in Patent Document 1, the EGR gas remaining in the EGR passage is simply pushed back to the exhaust passage, and the EGR gas remaining in the intake passage downstream from the compressor is reliably There is no guarantee that it can be removed.

  In general, air compressed by a compressor is cooled by an intercooler and introduced into the engine through an intake throttle valve. For this reason, if EGR gas remains in the passage from the compressor through the intercooler to the intake throttle valve, particularly in the intercooler, condensed water may be generated depending on the environmental conditions, and there is a concern that problems due to corrosion may occur. Is done.

  The present invention has been made in view of the above circumstances, and is an engine exhaust capable of reliably scavenging the exhaust gas recirculation remaining on the upstream side of the intake throttle valve when the engine is stopped and suppressing the generation of exhaust condensed water. The object is to provide a reflux device.

  An exhaust gas recirculation device for an engine according to the present invention is an exhaust gas recirculation device for an engine having an exhaust gas recirculation system that recirculates a part of exhaust gas purified by a catalyst interposed in an exhaust gas passage to the intake air passage. A scavenging passage where one end is communicated with the upstream side of the interposed intake throttle valve and the other end is opened to the atmosphere, and the scavenging passage is interposed between the suction side and the upstream side of the intake throttle valve. An electric pump whose discharge side communicates with the atmosphere, and when the engine stops, the exhaust throttle valve remaining on the upstream side of the intake throttle valve is reduced by closing the intake throttle valve and operating the electric pump. A scavenging control unit for scavenging to the atmosphere.

  According to the present invention, the exhaust gas recirculation remaining on the upstream side of the intake throttle valve when the engine is stopped can be surely scavenged, and the generation of exhaust condensed water can be suppressed.

Configuration diagram showing the intake and exhaust system of the engine EGR scavenging process flowchart

Embodiments of the present invention will be described below with reference to the drawings.
In FIG. 1, reference numeral 1 denotes an engine, and in this embodiment, a diesel engine. An intake passage 3 is connected to the intake port of the engine 1 via an intake manifold 2, and an exhaust passage 5 is connected to the exhaust port via an exhaust manifold 4.

  A throttle valve 6 as an intake throttle valve is interposed in the intake passage 3, and a compressor 8 a of the turbocharger 8 is interposed upstream of the throttle valve 6 via an intercooler 7. The upstream side of the compressor 8a communicates with an air cleaner 9, and outside air taken in from the air intake is purified by the air cleaner 9 and supplied to the compressor 8a. Cooled by the cooler 7 and introduced into the cylinder of the engine 1.

  Further, a scavenging passage 15 described later is branched from the intake passage 3 between the throttle valve 6 and the intercooler 7. One end of the scavenging passage 15 communicates with the upstream side of the throttle valve 6 and the other end is open to the atmosphere inside the engine chamber. In addition, an electric pump 16 is interposed in the scavenging passage 15, and the suction side of the electric pump 16 communicates with the upstream side of the throttle valve 6 and the discharge side communicates with the atmosphere.

  On the other hand, a turbine 8b of the turbocharger 8 is interposed in the exhaust passage 5, and a part of the exhaust gas is interposed between the exhaust passage 5 upstream of the turbine 8b and the intake passage 3 downstream of the throttle valve 6. An exhaust gas recirculation passage (EGR passage) 20 for recirculating from the exhaust system to the intake system is provided. The EGR passage 20 is a passage that circulates the exhaust gas before the purification process to the intake side. A part of the exhaust gas is transferred from the exhaust passage 5 upstream of the turbine 8b of the turbocharger 8 to the intake passage 3 downstream of the throttle valve 6. This is a high-pressure EGR passage to be circulated. The EGR passage 20 is provided with an EGR cooler 21 for cooling the exhaust gas flowing through the EGR passage 20 and an EGR valve 22 for adjusting the exhaust gas flow rate of the EGR passage 20.

  A catalytic converter 10 as an exhaust treatment device for purifying exhaust gas is interposed downstream of the turbocharger 8 at the turbine 8b. The catalytic converter 10 is disposed on the downstream side of the DOC 10a, for example, a diesel oxidation catalyst (Diesel Oxidation Catalyst; DOC) 10a that mainly oxidizes hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas by a catalytic reaction. Diesel particulate filter that collects particulate matter (Particulate Matter; PM) such as soot, carbon soot (Soot), soluble organic component (SOF), and sulfate (SO4) in exhaust gas Diesel Particulate Filter (DPF) 10b.

  Further, the downstream side of the catalytic converter 10 communicates with the atmosphere from the muffler 12 via the exhaust pressure adjusting valve 11. An EGR passage 30 is provided between the catalytic converter 10 and the exhaust pressure adjusting valve 11 to recirculate a part of the exhaust gas purified by the catalytic converter 10 to the intake side. The EGR passage 30 is a low-pressure EGR passage that circulates a part of the exhaust gas purified by the catalytic converter 10 to the intake side, and an EGR cooler 31 for cooling the exhaust gas flowing through the EGR passage 30, and EGR The turbocharger 8 communicates with the upstream side of the compressor 8a via an EGR valve 32 for adjusting the exhaust flow rate of the passage 30.

  The exhaust pressure adjusting valve 11 is a control valve for introducing the EGR gas into the EGR passage 30 by adjusting the valve opening degree to generate a differential pressure when the low pressure EGR is performed.

  Next, the electronic control system of the engine 1 will be described. A signal from each sensor provided in the engine 1 and a drive signal for the actuator are processed by an electronic control unit (ECU) 50 to control the operation of the engine 1. The ECU 50 is configured to include a peripheral circuit such as an A / D converter, a timer, a counter, and various logic circuits, with a microcomputer including a CPU, a ROM, a RAM, an I / O interface and the like as a center.

  Sensors that output signals to the ECU 50 include an intake air amount sensor 40 that is disposed immediately downstream of the air cleaner 9 and measures the intake air amount, and a water temperature that is exposed to the cooling water passage of the engine 1 and detects the cooling water temperature. Sensor 41, crank angle sensor 42 for detecting the rotational position of the crankshaft, accelerator pedal sensor 43 for detecting the depression amount of the accelerator pedal, and temperature sensors 44, 45 disposed upstream and downstream of the catalytic converter 10 for detecting the exhaust temperature. In addition, there are various sensors not shown.

  The actuators driven by the ECU 50 include a throttle actuator 46 that controls the intake air amount (fresh air amount) and the intake pipe internal pressure by adjusting the opening of the throttle valve 6, the exhaust pressure adjusting valve 11, the electric pump 16, In addition to the EGR valves 22 and 32, there are various actuators (not shown) such as a fuel injection valve for injecting fuel into the cylinder of the engine 1 and an actuator for controlling the supercharging pressure of the turbocharger 8.

  Further, the ECU 50 is connected to an in-vehicle network (not shown) based on a communication protocol such as CAN (Controller Area Network). In addition to the ECU 50, a plurality of ECUs such as a transmission ECU that controls the transmission and a brake ECU that controls the brake are connected to the in-vehicle network, and various information is shared by transmitting and receiving data to and from each other.

  The ECU 50 performs various engine controls such as fuel injection control, intake air control, and supercharging pressure control based on signals from the above-described various sensors that detect the engine operating state and various control information input via the in-vehicle network. The various actuators are driven and executed to maintain the operating state of the engine 1 in the optimum state. In addition, the ECU 50 performs EGR control via the EGR valves 22 and 32 in a predetermined operation region, recirculates a part of the exhaust gas to the intake system, and recombusts it in the cylinder, thereby reducing exhaust emission. I try to plan.

  In the present embodiment, in addition to the high-pressure EGR system that circulates a part of the exhaust from the upstream side of the turbine 8b of the turbocharger 8 to the downstream side of the throttle valve 6, a part of the exhaust gas purified by the catalytic converter 10 is turbocharged. A low-pressure EGR system is provided that circulates from the compressor 8 a of the supercharger 8 to the upstream side of the throttle valve 6 via the intercooler 7. The low-pressure EGR can perform a large amount of EGR at a lower pressure than the high-pressure EGR, but the EGR gas flowing through the EGR passage 30 of the low-pressure EGR system passes through the turbine 8b and the catalytic converter 10 of the turbocharger 8. Therefore, the gas temperature is lower than that of the high pressure EGR EGR gas.

  In particular, in the intercooler 7 through which the EGR gas of the low pressure EGR passes, the internal residual exhaust components are condensed due to the temperature difference between the atmospheric temperature after the engine is stopped and the temperature in the intercooler 7, and condensed water is likely to be generated. When such condensed water is generated, components such as sulfur contained in the condensed water cause corrosion, pitting corrosion and the like in the intercooler 7 and further the compressor 8a of the turbocharger 8, which causes a reduction in life. .

  For this reason, the ECU 50 has a function as a scavenging control unit that executes a process (EGR scavenging process) for scavenging the residual gas of the low pressure EGR into the engine chamber by the electric pump 16 after the engine is stopped. Hereinafter, the EGR scavenging process performed by the ECU 50 will be described with reference to the flowchart shown in FIG.

  The EGR scavenging process is executed at a predetermined time period, and it is determined whether or not the engine 1 is stopped in the first step S1. For example, when the engine speed is 0 based on a signal from the crank angle sensor 42, it is determined that the engine is stopped. When the engine 1 is in operation, the process is exited. When the engine 1 is stopped, the process proceeds from step S1 to step S2.

  In step S <b> 2, it is checked whether or not there is an experience of performing low pressure EGR during engine operation before stopping. Whether or not the low-pressure EGR has been implemented can be determined, for example, by examining the operation history of the EGR valve 32 interposed in the EGR passage 30 of the low-pressure EGR system. If there is no operation history of the EGR valve 32 and the low pressure EGR is not performed, the present process is exited, and if it is determined that there is no operation history of the EGR valve 32 and the low pressure EGR is performed, Proceed from step S2 to step S3.

  In step 3, the throttle actuator 46 is driven to close the throttle valve 6, and the intake manifold 2 side of the intake passage 3 is shut off. In step S4, the electric pump 16 installed between the throttle valve 6 and the intercooler 7 is operated to scavenge residual EGR gas in the intercooler 7 from the scavenging passage 15 into the engine chamber. At this time, a timer is also started to measure the operating time of the electric pump 16.

  The electric pump 16 is stopped during the engine operation, and the scavenging passage 15 is kept closed while the pump is stopped. An opening / closing valve is provided on the suction side of the electric pump 16 in the scavenging passage 15, The valve may be opened only when the electric pump 16 is operated. Also, depending on the capacity of the electric pump 16, engine characteristics, and the low pressure EGR system pipe configuration, the EGR valve 32 is kept open when the residual EGR gas is scavenged by the electric pump 16, and the EGR passage 30 EGR It is also possible to scavenge the inside of the cooler 31.

  Thereafter, in step S5, it is checked whether or not the engine is started. Whether or not the engine is started is checked by, for example, the presence or absence of a starter signal. If there is no starter signal, the process proceeds from step S5 to step S6, and it is checked whether or not a certain time has elapsed since the electric pump 16 was operated. The fixed time is a time during which the residual EGR gas in the pipeline can be substantially discharged, and is set in consideration of the exhaust capacity of the electric pump 16, the pipeline volume, and the like.

  If the predetermined time has not yet elapsed since the operation of the electric pump 16 in step S6, the process is exited. Thereafter, when a certain time has elapsed, the process proceeds from step S6 to step S7, and the electric pump 16 is stopped. Then, in step S8, the throttle valve 6 is opened, and the low-pressure EGR implementation experience is cleared, and the process is exited.

  On the other hand, if the engine is started (with a starter signal) in step S5, the process jumps to step S7 in step S5, and the electric pump 16 is immediately stopped even if a certain time has not elapsed since the electric pump 16 was operated. . Then, in step S8, the throttle valve 6 is opened and the experience of performing the low pressure EGR is cleared. As a result, the engine is started by the rotation of the starter.

  As described above, in the present embodiment, after the engine is stopped, the electric pump 16 installed between the throttle valve 6 and the intercooler 7 is operated, so that the remaining EGR gas can be surely scavenged. Thereby, it is possible to suppress the generation of condensed water containing exhaust components in the low-pressure EGR system, particularly the intercooler 7, and it is possible to prevent the occurrence of problems due to corrosion or the like.

  In the present embodiment, an example in which a high-pressure EGR and a low-pressure EGR are provided has been described. However, the present invention is also applicable to a system in which the high-pressure EGR is eliminated and only the low-pressure EGR is provided. Is possible.

1 Engine 3 Intake passage 5 Exhaust passage 6 Throttle valve (intake throttle valve)
7 Intercooler 8 Turbocharger 8a Compressor 8b Turbine 10 Catalytic converter 15 Scavenging passage 16 Electric pump 30 EGR passage 50 Electronic control unit

Claims (3)

An exhaust gas recirculation device for an engine having an exhaust gas recirculation system for recirculating a part of exhaust gas purified by a catalyst interposed in an exhaust gas passage to an intake air passage,
A scavenging passage where one end communicates with the upstream side of the intake throttle valve interposed in the intake passage and the other end is opened to the atmosphere;
An electric pump interposed in the scavenging passage, the suction side communicating with the upstream side of the intake throttle valve and the discharge side communicating with the atmosphere;
A scavenging control section for scavenging the exhaust gas recirculation remaining on the upstream side of the intake throttle valve to the atmosphere by closing the intake throttle valve and operating the electric pump when the engine is stopped. An exhaust gas recirculation system for engines. The exhaust gas recirculation system passes through an intercooler that cools a part of the exhaust gas discharged from the turbine of the turbocharger interposed in the exhaust passage via the catalyst and the intake air from the compressor of the turbocharger. And a path for recirculation upstream of the intake throttle valve,
2. The engine exhaust gas recirculation device according to claim 1, wherein the scavenging passage is branched from an intake passage between the intake throttle valve and the intercooler.   The scavenging control unit, after operating the electric pump, stops the electric pump after a predetermined time if the engine is not started, and immediately stops the electric pump when the engine is started. The exhaust gas recirculation device for an engine according to claim 1 or 2, wherein the intake throttle valve is opened.

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