JP2009275673A - Egr system and controlling method of egr system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide: an EGR system capable of efficiently evaporating condensate water generated by cooling moisture in exhaust gas led to an EGR passage of an internal combustion engine with an EGR cooler, with the heat of the exhaust gas by using supercharging pressure; and a controlling method of the EGR system. <P>SOLUTION: In the EGR system 1 of the internal combustion engine 10 with a turbocharger equipped with the EGR cooler 20, a condensate water collecting portion 22 provided between a downstream side of the EGR cooler 20 of the EGR passage 19 and an EGR valve 21, and an exhaust passage 15 are connected by a condensate water discharging passage 23. A bypass opening/closing valve 27 is provided on a high-pressure gas bypass passage 26 provided so as to connect an upstream side of a turbine 13b of the turbocharger 13 in the exhaust passage 15, the downstream side of the EGR cooler 20 of the EGR passage 19, and the condensation water collecting portion 22. The bypass opening/closing valve 27 is controlled to temporally open before the supercharging pressure P5 is increased and a waste gate valve 13c of the turbocharger is controlled to open. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an EGR system for evaporating condensed water generated by moisture in exhaust gas guided to an EGR passage of an internal combustion engine by an EGR cooler by heat of the exhaust gas, and a control method for the EGR system.

  In order to satisfy the recent exhaust gas regulations, it is an important means to recirculate the exhaust gas to the intake air in the internal combustion engine and to suck the mixed gas of the intake air and the exhaust gas into the cylinder. In this exhaust gas recirculation EGR system, the EGR gas to be recirculated is cooled in order to suppress the temperature rise of the intake air and to control the ignition in the cylinder. This EGR gas is cooled by the EGR cooler from the high temperature state discharged from the cylinder, and depending on the cooling medium of the EGR cooler, in the normal case of using engine cooling water, 70 to 80 ° C. at the outlet of the EGR cooler. It is cooled to the extent.

  At the time of cooling the EGR gas, the water present in the EGR gas becomes condensed water by cooling and accumulates in the piping on the outlet side of the EGR cooler. Depending on the arrangement of the piping, the condensed water accumulates in the EGR valve portion and becomes sludge or the like due to soot in the exhaust gas, thereby fixing the EGR valve. Also, condensed water enters the intake system and causes corrosion and the like. For this reason, it is important to appropriately treat the condensed water generated after cooling the EGR gas.

  As one countermeasure against the condensed water, a turbocharger, a low pressure EGR passage, a low pressure EGR cooler, an exhaust throttle valve, a low pressure EGR passage downstream of the low pressure EGR cooler, and an exhaust passage downstream of the exhaust throttle valve are provided. And the exhaust throttle valve is closed to increase the pressure of the low pressure EGR passage, thereby generating a differential pressure between the EGR passage side and the exhaust passage side of the communication passage. There has been proposed an exhaust gas recirculation device for an internal combustion engine provided with condensed water discharge means for discharging condensed water in a low pressure EGR passage to an exhaust passage (see, for example, Patent Document 1).

  In this exhaust gas recirculation device for an internal combustion engine, the timing of injecting the condensed water in the low pressure EGR passage is a state in which the exhaust temperature is relatively low such as during vehicle deceleration, idling operation of the internal combustion engine, and immediately before the engine stops. Since the condensed water injected into the inside does not necessarily evaporate, there is a problem that the vicinity of the outlet of the exhaust passage and the portion of the device may be contaminated.

  In addition, the exhaust throttle generates a differential pressure at both ends of the communication passage to discharge condensed water. However, in a state where low pressure EGR is required, the exhaust throttle valve is basically fully open. On the other hand, when the low pressure EGR cooler is arranged, there is a possibility that the pressure on the low pressure EGR passage side of the communication passage is higher than the pressure on the exhaust passage side. In addition, when the low pressure EGR cooler is fouled by use, the pressure in the low pressure EGR passage further increases, so that the EGR gas that has not been cooled through the communication passage does not pass through the low pressure EGR cooler and enters the low pressure EGR valve. The possibility of being supplied increases. In such a case, a serious disadvantage occurs in the performance of the internal combustion engine.

  As other measures against condensed water, an intake passage for supplying an air-fuel mixture to an engine combustion chamber, an exhaust passage for exhausting exhaust gas after combustion to the outside, and an exhaust gas recirculation passage for connecting the exhaust passage and the intake passage In the exhaust gas recirculation apparatus equipped with the above, the heat exchange means for cooling is provided in the middle of the exhaust gas recirculation passage, and the moisture separation means is provided downstream of the heat exchange means, so that condensation occurs downstream of the heat exchange means. An exhaust gas recirculation device for separating water has been proposed (see, for example, Patent Document 2).

  In this exhaust gas recirculation device, as one of the water separation means, exhaust gas is caused to flow through the exhaust bypass passage by the exhaust throttle, and condensed water is sucked by the pressure drop of the throttle portion provided in the exhaust bypass passage, forcibly. An example of discharging into the exhaust passage is described.

  In this exhaust gas recirculation device, since exhaust throttling is performed, exhaust resistance is increased by the exhaust throttling, so that the pumping loss of the engine increases, which is not preferable in terms of engine performance. Also, recent diesel engines are equipped with exhaust aftertreatment devices, and there is a problem that the performance of these exhaust aftertreatment devices changes depending on the location where the exhaust throttle valve or the like is attached. Further, since the post-processing device is attached, there is a problem that a negative pressure difference due to a throttle portion such as an exhaust throttle valve is hardly generated, and suction of condensed water due to a negative pressure action becomes extremely difficult.

  As another countermeasure against condensed water, an exhaust manifold (exhaust manifold) and an intake manifold (intake manifold) are connected by an EGR pipe, and a condensed water discharge port is provided on the downstream side of the heat exchanger in the EGR pipe. An EGR device for a diesel engine with a supercharger has been proposed in which a drain pipe connected to the condensed water discharge port is connected to an exhaust pipe, and condensed water generated downstream of the EGR cooler is discharged to the exhaust pipe and evaporated (for example, (See Patent Document 3).

In the case of this EGR device, the condensed water is injected by the pressure in the exhaust manifold or the pressure difference between the pressure in the intake manifold and the exhaust pipe. In this case, the condensed water is used even when the turbocharger is operating. Therefore, in a normal turbocharged engine, the state is similar to the state in which the wastegate valve is opened, and there is a problem that the state becomes inappropriate from the viewpoint of engine performance.
JP 2008-002351 A Japanese Utility Model Publication No. 61-110859 JP 2000-027715 A

  The present invention has been made in view of the above-described situation, and an object of the present invention is to provide condensed pressure generated by cooling water in the exhaust gas guided to the EGR passage of the internal combustion engine by the EGR cooler. It is an object to provide an EGR system and an EGR system control method capable of efficiently evaporating with the heat of exhaust gas by using the above.

  In order to achieve the above object, an EGR system according to the present invention is an EGR system for a turbocharged internal combustion engine equipped with an EGR cooler, wherein a condensed water reservoir is provided between the EGR passage downstream of the EGR cooler and the EGR valve. The condensed water reservoir and the exhaust passage are connected by a condensed water discharge passage, and the upstream side of the turbine of the turbocharger in the exhaust passage, the downstream side of the EGR cooler in the EGR passage, and the condensed water reservoir A high-pressure gas bypass passage that connects between the two, and a bypass on-off valve is provided in the high-pressure gas bypass passage to increase the supercharging pressure before performing control to open the wastegate valve of the turbocharger. Bypass opening / closing valve control means for performing control to temporarily open the bypass opening / closing valve is provided.

  That is, the condensed water generated after passing through the EGR cooler is separated from the EGR gas and temporarily stored in the condensed water storage part provided in the piping part of the EGR passage, and the engine operating conditions and the boost pressure (boost pressure) are stored. The condensed water is evaporated by sensing the pressure in the exhaust passage and the like and injecting the condensed water into the exhaust passage using the pressure in the exhaust passage at a predetermined timing. As this predetermined timing, select when the exhaust pressure just before opening the wastegate valve is high in order to prevent the turbocharger from exceeding, the turbocharger from over-rotating, etc., and at this timing, the bypass on-off valve is temporarily opened. The condensed water accumulated in the condensed water reservoir is injected into the exhaust passage and evaporated by the heat of the exhaust gas. In addition, this wastegate valve has an exhaust gas when the boost pressure reaches a certain level (judgment value) in order to prevent the boost pressure from becoming too high and causing knocking or destruction of the cylinder. Is a valve that bypasses the turbine, and is attached to the turbine housing or the exhaust manifold (exhaust manifold).

  According to this configuration, it is possible to prevent the condensed water generated by the exhaust gas being cooled by the EGR cooler from accumulating in the EGR passage, and further, the exhaust gas is discharged to the exhaust passage side due to the increase of the supercharging pressure and becomes unnecessary. The condensed water can be injected into the exhaust passage by using the section, and can be evaporated with the heat of the exhaust gas having a relatively high temperature so that the supercharging pressure becomes high.

  In other words, exhaust pressure that is unnecessary in an internal combustion engine with a turbocharger is released by the wastegate valve, etc., but the pressure in the exhaust manifold that is unnecessary just before the wastegate valve is opened is used. Then, the condensed water generated downstream of the EGR cooler is injected into the downstream exhaust passage such as the DPF, so that the condensed water can be treated without impairing the performance of the internal combustion engine.

  Condensed water discharge timing is generated in the EGR passage by detecting the state of operation of the turbocharger's wastegate valve, etc. at relatively high speed and high load, and using the pressure of the exhaust gas immediately before the operation. The condensed water is injected into the exhaust passage. Since the exhaust gas pressure at this time is used, drivability and performance on the internal combustion engine side are not adversely affected. In addition, at the timing of discharging condensed water, the temperature of the exhaust gas in the exhaust passage to be discharged is sufficiently high at high speed and high load, so that the heat of the exhaust gas is injected into the exhaust passage. The discharged condensed water can be sufficiently evaporated. Note that while the wastegate valve is opened and a portion of the exhaust gas is bypassed through the turbine, the bypass on-off valve returns to the closed state.

  In the above EGR system, a check valve is provided in the condensed water discharge passage to allow a fluid flow only from the condensed water storage portion to the exhaust passage side. According to this configuration, the condensed water stored in the condensed water storage unit can be prevented from entering the EGR cooler and the EGR valve side of the EGR passage.

  And the control method of the EGR system for achieving the above-mentioned object is to provide a condensed water storage part between the EGR cooler downstream side of the EGR passage and the EGR valve, and between the condensed water storage part and the exhaust passage. A high-pressure gas bypass passage that connects the condensed water discharge passage, connects the upstream side of the turbine of the turbocharger of the exhaust passage, the downstream side of the EGR cooler of the EGR passage, and the condensed water storage section; In the EGR system for an internal combustion engine with a turbocharger in which the high-pressure gas bypass passage is provided with a bypass opening / closing valve, the bypass opening / closing valve is temporarily opened before the boost pressure is increased and the wastegate valve of the turbocharger is opened. The condensed water stored in the condensed water reservoir is discharged to the exhaust passage.

  According to this method, the condensed water generated when the exhaust gas is cooled by the EGR cooler can be prevented from accumulating in the EGR passage, and further, the exhaust gas that is discharged to the exhaust passage side due to the increase of the supercharging pressure is unnecessary. The condensed water is injected into the exhaust passage by using the section, and the evaporation pressure can be evaporated with the heat of the exhaust gas having a high supercharging pressure and a relatively high temperature.

  In the above EGR system control method, the EGR valve is controlled to be closed when the bypass on-off valve is opened. By this method, it is possible to prevent the condensed water from flowing into the EGR valve side.

  According to the control method of the EGR system and the EGR system according to the present invention, by installing a condensed water collecting part for collecting condensed water generated after the EGR gas passes through the EGR cooler on the downstream side of the EGR cooler, It is possible to easily collect condensed water. In addition, in order to treat the collected condensed water, the state immediately before opening the wastegate valve of the turbocharger is monitored by a sensor, and the high pressure in the exhaust manifold immediately before this love valve is used. By discharging condensed water to the exhaust passage, it avoids abrupt changes in the operating state of the engine and sufficiently evaporates the condensed water with exhaust gas having a sufficiently high temperature without deteriorating the feeling of operation. Can be processed.

  Hereinafter, an EGR system and an EGR system control method according to embodiments of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, an engine 10 (internal combustion engine: E) using the EGR system 1 generates an intake passage 11 for sucking fresh air A and supplying it into a cylinder of the engine 10, and is generated in the cylinder. An exhaust passage 15 for discharging combustion gas into the atmosphere as exhaust gas G, an EGR passage 19 for performing EGR (exhaust gas recirculation), and a control device 30 for controlling the operation of the engine 10 are provided. Composed.

  In the intake system of the engine 10, an air cleaner 12, a compressor 13a of a turbocharger 13, and an intercooler 14 are provided in the intake passage 11 connected to the intake manifold 11a in order from the upstream side. Further, in the exhaust system, the turbine 13b of the turbocharger 13, the oxidation catalyst (DOC) 16 constituting the exhaust gas purification system, and the diesel particulate filter (in order) from the upstream side to the exhaust passage 15 connected to the exhaust manifold 15a. DPF) 17 and selective reduction catalyst (SCR) 18 are provided. The exhaust gas purification system is merely an example, and an exhaust gas purification system having another configuration may be used.

  An exhaust passage 15 between the exhaust system diesel particulate filter 17 and the selective reduction catalyst 18 and an intake passage 11 between the air cleaner 12 and the compressor 13 a are connected by an EGR passage 19. The EGR passage 19 is a passage for introducing the EGR gas Ge branched from the exhaust system of the engine 10 into the intake system, and the EGR passage 19 is an EGR cooler which is a cooling device for cooling the introduced EGR gas Ge. 20 and an EGR valve 21 for adjusting and controlling the flow rate of the EGR gas Ge according to the operating state of the engine 1.

  In the present invention, the bent pipe 19a is formed between the EGR cooler 20 and the EGR valve 21 so that condensed water generated on the outlet side of the EGR cooler 20 does not easily reach the EGR valve 21. A condensed water collection tank (condensed water storage unit) 22 for collecting condensed water Wc is provided in the portion 19a. One end side of the condensed water discharge passage 23 is connected to the lower portion of the condensed water collecting tank 22, and the other end side is connected to the exhaust passage 15 between the diesel particulate filter 17 and the selective catalytic reduction catalyst 18.

  This condensed water collection tank 22 is for separating and temporarily storing water droplets of condensed water Wc condensed in the EGR passage 19 from the EGR gas Ge, and from the outlet of the EGR cooler 20 to the EGR valve 21. Install between. Thereby, the condensed water Wc condensed in the EGR passage 19 is prevented from adhering to the piping of the EGR passage 19 on the downstream side of the EGR cooler 20. The installation location of the condensed water collection tank 22 is a downwardly bent pipe 19a between the EGR cooler 20 and the EGR valve 21 so that the condensed water Wc can be easily collected, and the outside (lower side) of the bent pipe 19 It is preferable that the condensed water collection tank 22 is connected to the bent portion. By providing the condensed water collection tank 22 at the outer bent portion, the condensed water Wc can be guided to the condensed water collection tank 22 by utilizing the centrifugal force of the exhaust gas.

  The condensed water discharge passage 23 is provided with a check valve (one-way valve) 24 for making the flow of the condensed water Wc one-way from the condensed water collection tank 22 to the exhaust passage 15, and the condensed water Wc is exhausted. Prevent backflow from the passage 15 side to the EGR passage 19 side. Further, an injection port 25 is provided on the tip side protruding into the exhaust passage 15 so that the condensed water Wc can be injected into the exhaust passage 15.

  When the gas pressure P4 in the exhaust passage 15 is higher than the gas pressure P3 in the EGR passage 19 between the EGR cooler 20 and the EGR valve 21, the check valve 24 is closed due to the pressure difference (P4-P3). The valve is opened only when the pressure P3 on the EGR passage 19 side is higher than the pressure P4, and the condensed water Wc is guided from the EGR passage 19 side only in one direction on the exhaust passage 15 side. The check valve 24 can prevent the condensed water Wc stored in the condensed water collecting tank 22 from entering the EGR cooler 20 and the EGR valve 21 side of the EGR passage 19.

  Further, the high pressure gas bypass passage 26 connecting the upstream side of the turbine 13 b of the turbocharger 13 in the exhaust passage 15, the EGR passage 19 between the downstream side of the EGR cooler 20 in the EGR passage 19 and the condensed water collection tank 22. Is provided. Further, a bypass opening / closing valve 27 is provided in the high-pressure gas bypass passage 26.

  The first pressure sensor 31 is connected to the exhaust manifold 11a, the second pressure sensor 32 is connected to the EGR passage 19 upstream of the EGR cooler 20, the third pressure sensor 33 is connected to the EGR passage 19a downstream of the EGR cooler 20, and A four pressure sensor 34 is provided in the exhaust passage 15 between the diesel particulate filter 17 and the selective catalytic reduction catalyst 18, and a fifth pressure sensor 35 is provided in the intake passage 11 upstream of the intercooler 15.

  Outputs of these sensors 31 to 35 are input to a control device 30 called an engine control unit (ECU). The control device 30 controls the overall operation of the engine 10, obtains data indicating the operation state of the engine 10 from sensors provided in the engine 10, calculated values of the control device 30, etc., and selects with the diesel particulate filter 17. Control for purifying the exhaust gas G in the reduction catalyst 18 and regeneration of the devices 17 and 18 is also performed.

  Next, EGR control and control of the bypass opening / closing valve 27 in the EGR system 1 of the engine 10 will be described. First, when the engine 10 is in an engine operation state in which the generation of NOx or the like needs to be suppressed, the EGR valve 21 is opened by the instruction from the control device 30 and the EGR gas Ge which is a part of the exhaust gas G is changed. While adjusting the flow rate, the EGR gas Ge is guided from the branch portion of the EGR passage 19 provided in the exhaust passage 15 to the EGR passage 19 on the EGR cooler 20 side.

  In the state in which the EGR is performed, the EGR gas Ge is rapidly cooled from the temperature state of the exhaust gas G by the EGR cooler 20 through which the engine cooling water W circulates, and the temperature according to the engine cooling water W (for example, , 70 ° C. to 80 ° C.) and supplied to the intake passage 11 on the downstream side of the air cleaner 12 via the EGR passage 19a, the EGR valve 21 and the like. In the EGR gas Ge that has passed through the EGR cooler 20, the water present in the EGR gas Ge condenses due to rapid cooling and becomes water droplets or water, which adheres to the piping of the EGR passage 15a. The water droplets and condensed water Wc that has become water are temporarily stored in the condensed water collecting tank 22 to prevent the condensed water Wc from flowing out to the EGR valve 21 side.

  The condensed water Wc temporarily collected in the condensed water collection tank 22 is injected into the exhaust passage 15 at the following timing. Regarding the timing of the injection of the condensed water Wc, supercharging is performed using the pressure (supercharging pressure) P5 detected by the fifth pressure sensor 35 installed upstream of the intercooler 14 in the intake passage 15 during engine operation. The pressure (boost pressure) is monitored, and a predetermined pressure Pc2 immediately before the supercharging pressure P5 reaches the pressure value Pc1 when the wastegate valve 13c (or the exhaust bypass valve) of the turbine 13b of the turbocharger 13 is opened. Is selected, and at this time, the control device 30 of the engine 10 controls the bypass on-off valve 27 installed in the high-pressure exhaust gas bypass passage 26 to open. The opening instruction time of the bypass opening / closing valve 27 is 1 second or less per opening instruction.

  Alternatively, the bypass opening / closing valve 27 is temporarily opened before the opening operation of the wastegate valve 13c, and then the bypass opening / closing valve 27 is closed after an extremely short time of 1 second or less. Then, the waste gate valve 13c is controlled to open.

  By opening the bypass opening / closing valve 27, the high-pressure exhaust gas Gp in the exhaust manifold 15a is introduced into the EGR passage 19 between the EGR cooler 20 outlet and the EGR valve 21 through the high-pressure exhaust gas bypass passage 26. By this introduction, the gas pressure in this portion is temporarily increased, and the condensed water Wc in the condensed water collection tank 22 is injected into the exhaust passage 15 with this gas pressure. That is, the bypass on-off valve 27 is temporarily opened when the exhaust pressure P5 immediately before opening the wastegate valve 13c is high in order to prevent the turbocharger 13 from over-rotating due to the supercharging pressure P5 being exceeded. The condensed water Wc stored in the condensed water collecting tank 22 is discharged to the exhaust passage 15.

  The opening / closing operation of the bypass opening / closing valve 27 is performed so that the condensed water Wc does not flow out to the EGR cooler 20 side, and the second downstream side of the EGR cooler 20 from the detection value P2 of the second pressure sensor 32 upstream of the EGR cooler 20. 3 Only when the detected value P3 of the pressure sensor 33 is lower.

  In the present invention, the pressure values of the pipes detected by the pressure sensors 31 to 35 are taken into the control device 30, and the bypass on / off valve control means 30 a incorporated in the control device 30 based on these data is used to detect excessive pressure. Before the supply pressure P5 increases and the control for opening the wastegate valve 13c is performed, the bypass on-off valve 27 is temporarily opened to temporarily increase the pressure P3 in the EGR passage 19 by the exhaust gas Gp. The condensed water Wc accumulated in the condensed water collecting tank 22 is discharged into the exhaust passage 15 by injection from the injection port 25. When the waste gate valve 13c is opened, the bypass opening / closing valve 27 is returned to the closed state. That is, the bypass opening / closing valve 27 is in a closed state when the wastegate valve 13c is opened and during opening.

  According to the EGR system 1 and the control method of the EGR system, the condensed water Wc generated by the EGR cooler 20 being cooled by the EGR gas Ge can be prevented from accumulating in the EGR passage 19, and the supercharging pressure P5 is increased. The condensed water Wc is injected into the exhaust passage 15 by using a part of the exhaust gas G which is discharged to the exhaust passage 15 side and becomes unnecessary, and is evaporated with the heat of the exhaust gas G having a relatively high temperature Can do.

It is a figure which shows the structure of the EGR system of embodiment of this invention.

Explanation of symbols

1 EGR system 10 Engine (internal combustion engine)
DESCRIPTION OF SYMBOLS 11 Intake passage 13 Turbocharger 13b Turbine 13c Wastegate valve 14 Intercooler 15 Exhaust passage 15a Exhaust manifold 19 EGR passage 19a Curved piping 20 EGR cooler 21 EGR valve 22 Condensed water collection tank (condensed water storage part)
23 Condensed water discharge passage 24 Check valve (one-way valve)
25 Injection port 26 High-pressure gas bypass passage 27 Bypass on-off valve 30 Control device (ECU)
30a Bypass on-off valve control means 31-35 Pressure sensor A Fresh air G Exhaust gas Ge EGR gas Gp Exhaust gas in exhaust manifold P1-P5 Gas pressure W Engine cooling water Wc Condensed water

Claims (4)

  In an EGR system of an internal combustion engine equipped with a turbocharger equipped with an EGR cooler, a condensed water reservoir is provided between the EGR passage downstream of the EGR cooler and the EGR valve, and condensed water is provided between the condensed water reservoir and the exhaust passage. A high-pressure gas bypass passage that is connected to the upstream side of the turbine of the turbocharger in the exhaust passage, the downstream side of the EGR cooler in the EGR passage, and the condensed water storage portion; A bypass opening / closing valve is provided in the bypass passage to perform control to temporarily open the bypass opening / closing valve before the boost pressure is increased and the waste gate valve of the turbocharger is opened. An EGR system provided with a valve control means.   The EGR system according to claim 1, wherein a check valve is provided in the condensed water discharge passage to allow a fluid flow only from the condensed water storage portion to the exhaust passage side.   A condensed water reservoir is provided between the EGR cooler downstream of the EGR cooler and the EGR valve, the condensed water reservoir and the exhaust passage are connected by a condensed water discharge passage, and the upstream of the turbine of the turbocharger in the exhaust passage. A turbocharged internal combustion engine provided with a high-pressure gas bypass passage connecting between the EGR passage and a downstream side of the EGR cooler of the EGR passage and the condensed water storage portion, and provided with a bypass on-off valve in the high-pressure gas bypass passage In the EGR system of the present invention, before the boost pressure is increased and the wastegate valve of the turbocharger is opened, the condensed water stored in the condensed water reservoir is temporarily opened by opening the bypass on-off valve. A control method for an EGR system, characterized by discharging to the exhaust passage.   The EGR system control method according to claim 3, wherein when the bypass on-off valve is opened, the EGR valve is controlled to be closed.

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