Exhaust gas recirculation device

Abstract

An exhaust gas recirculation apparatus includes a high-pressure EGR device, a low-pressure EGR device, and a control device. The high-pressure EGR device has a high-pressure EGR passage connected to a portion of the intake passage downstream of the compressor. The low-pressure EGR device has a low-pressure EGR passage connected to a portion of the intake passage upstream of the compressor. The control device determines an operation region of the internal combustion engine, and calculates a retention amount, which is an estimated value of the amount of condensed water retained in the low-pressure EGR passage. When the retention amount is greater than a determination value corresponding to the operation region, the control device operates the low-pressure EGR device so as to reduce the amount of reflux of the low-pressure EGR gas.

Description

Technical Field

[0001] This disclosure relates to an exhaust gas recirculation device installed in an internal combustion engine. Background Technology

[0002] The exhaust gas recirculation (EGR) device disclosed in Japanese Patent Application Publication No. 2012-163061 includes a high-pressure EGR device, a low-pressure EGR device, and a control device. The high-pressure EGR device includes: a high-pressure EGR passage that allows exhaust gas flowing in the exhaust passage of the internal combustion engine to return as high-pressure EGR gas to the intake passage of the internal combustion engine; and an adjusting valve that adjusts the return flow rate of the high-pressure EGR gas. The high-pressure EGR passage is connected to the downstream portion of the compressor in the intake passage of the turbocharger.

[0003] The low-pressure EGR system includes: a low-pressure EGR passage that allows exhaust gas flowing in the exhaust passage to return as low-pressure EGR gas to the intake passage; a cooling device to cool the low-pressure EGR gas flowing in the low-pressure EGR passage; and an adjusting valve to adjust the return flow rate of the low-pressure EGR gas. The low-pressure EGR passage is connected to the upstream portion of the compressor in the intake passage of the supercharger.

[0004] In the low-pressure EGR passage, condensate is generated by cooling the low-pressure EGR gas through a cooling device. When the flow rate of the low-pressure EGR gas in the low-pressure EGR passage is high, the condensate flows along with the low-pressure EGR gas and is discharged into the intake passage. On the other hand, when the flow rate of the low-pressure EGR gas in the low-pressure EGR passage is low, or when the flow of the low-pressure EGR gas in the low-pressure EGR passage stops, the condensate flows towards the first end of the low-pressure EGR passage due to its own weight. Then, the condensate is discharged into the exhaust passage.

[0005] When the estimated amount of condensate accumulated in the low-pressure EGR passage exceeds a reference value, the control device activates the regulating valves of both the high-pressure EGR unit and the low-pressure EGR passage. This reduces the proportion of low-pressure EGR gas in the total EGR gas returning to the intake passage. Consequently, by discharging condensate from the low-pressure EGR passage to the exhaust passage, the control device reduces the amount of condensate retained in the low-pressure EGR passage.

[0006] Depending on the operating conditions of the internal combustion engine, recirculating low-pressure EGR gas into the intake passage can improve the reduction of NOx in the exhaust gas compared to recirculating high-pressure EGR gas into the intake passage. However, in the aforementioned exhaust gas recirculation device, even under operating conditions where the NOx reduction effect is enhanced by recirculating low-pressure EGR gas into the intake passage, the recirculation rate of low-pressure EGR gas into the intake passage decreases when the amount of condensate exceeds a reference value. Therefore, there is room for improvement in the exhaust gas recirculation device in suppressing the decrease in the reduction effect of NOx in the exhaust gas. Summary of the Invention

[0007] An exhaust gas recirculation (EGR) device is configured to be installed in an internal combustion engine, the internal combustion engine comprising: a cylinder; an intake passage for air flow into the cylinder; an exhaust passage for exhaust gas flow out of the cylinder; and a turbocharger for pressurizing the air flowing in the intake passage, wherein the turbocharger comprises: a turbine disposed in the exhaust passage; and a compressor disposed in the intake passage and operating synchronously with the turbine, the EGR device comprising: a high-pressure EGR device for recirculating exhaust gas flowing in the exhaust passage back into the intake passage as high-pressure EGR gas; a low-pressure EGR device for recirculating exhaust gas flowing in the exhaust passage back into the intake passage as low-pressure EGR gas; and a control device configured to control the high-pressure EGR device and the low-pressure EGR device to adjust the recirculation rate of the high-pressure EGR gas and the recirculation rate of the low-pressure EGR gas, the high-pressure EGR device having a high-pressure EGR passage, the first of the high-pressure EGR passage being... The first end of the high-pressure EGR passage is connected to the portion of the exhaust passage upstream of the turbine, and the second end of the high-pressure EGR passage is connected to the portion of the intake passage downstream of the compressor. The low-pressure EGR device has a low-pressure EGR passage and a cooling device. The first end of the low-pressure EGR passage is connected to the portion of the exhaust passage downstream of the turbine, and the second end of the low-pressure EGR passage is connected to the portion of the intake passage upstream of the compressor. The cooling device cools the low-pressure EGR gas flowing in the low-pressure EGR passage. The control device is configured to perform the following processes: determine the operating range of the internal combustion engine based on the output torque and speed of the internal combustion engine; calculate an estimated value of the amount of condensate retained in the low-pressure EGR passage, i.e., the retention amount; and, if the retention amount is greater than a determination value corresponding to the operating range, operate the low-pressure EGR device by reducing the return flow of the low-pressure EGR gas.

[0008] The exhaust gas recirculation device described above has the following effects: it can suppress the reduction of NOx contained in the exhaust gas and can discharge the condensate generated in the low-pressure EGR passage to the exhaust passage. Attached Figure Description

[0009] Figure 1 This is a schematic structural diagram of an internal combustion engine equipped with an exhaust gas recirculation device in one embodiment.

[0010] Figure 2 It means Figure 1 A diagram showing the operating area of ​​an internal combustion engine.

[0011] Figure 3 It means Figure 2 A graph showing the relationship between multiple operating regions and judgment values.

[0012] Figure 4 It means by Figure 1 The flowchart shows a series of processes performed by the control device of the exhaust gas recirculation system.

[0013] Figure 5 This is a flowchart representing the calculation and processing of condensate. Detailed Implementation

[0014] according to Figures 1-5 One embodiment of the exhaust gas recirculation device will be described.

[0015] <Structure of an Internal Combustion Engine>

[0016] Figure 1 An internal combustion engine 10 equipped with an exhaust gas recirculation device 100 is shown. The internal combustion engine 10 is mounted in a vehicle. The internal combustion engine 10 includes multiple cylinders 11, a crankshaft 12, an intake passage 13, multiple fuel injection valves 14, and an exhaust passage 16.

[0017] The intake passage 13 is a passage for airflow into multiple cylinders 11. An intercooler 21 and a throttle valve 22 are provided in the intake passage 13. The intercooler 21 cools the air flowing in the intake passage 13. The throttle valve 22 is located downstream of the intercooler 21 in the intake passage 13. By adjusting the opening of the throttle valve 22, the amount of air introduced into the multiple cylinders 11 changes.

[0018] Fuel injection valve 14 injects fuel into the corresponding cylinder 11. Within the multiple cylinders 11, a mixture containing air and fuel is burned. This causes crankshaft 12 to rotate. Additionally, exhaust gas is generated within the multiple cylinders 11 through combustion of the mixture. The exhaust gas exiting from the multiple cylinders 11 flows through exhaust passage 16.

[0019] The internal combustion engine 10 includes a turbocharger 30. The turbocharger 30 has a turbine 31 disposed in an exhaust passage 16 and a compressor 32 disposed in an intake passage 13. The turbine 31 operates by means of the flow energy of the exhaust gas flowing in the exhaust passage 16. The compressor 32 is disposed in the portion of the intake passage 13 upstream of the intercooler 21. Furthermore, by operating synchronously with the turbine 31, the compressor 32 is able to pressurize the air flowing in the intake passage 13.

[0020] <Structure of the exhaust gas recirculation system>

[0021] The exhaust gas recirculation device 100 includes a high-pressure EGR device 40, a low-pressure EGR device 50, and a control device 60.

[0022] The high-pressure EGR device 40 redirects the exhaust gas flowing in the exhaust passage 16 as high-pressure EGR gas back to the portion of the intake passage 13 downstream of the compressor 32. The high-pressure EGR device 40 includes a high-pressure EGR passage 41 connecting the exhaust passage 16 and the intake passage 13, and a valve, namely a high-pressure EGR valve 42, disposed within the high-pressure EGR device 40. A first end of the high-pressure EGR passage 41 is connected to the portion of the exhaust passage 16 upstream of the turbine 31. A second end of the high-pressure EGR passage 41 is connected to the portion of the intake passage 13 downstream of the compressor 32. For example, the second end of the high-pressure EGR passage 41 is connected to the portion of the intake passage 13 between the compressor 32 and the intercooler 21.

[0023] The high-pressure EGR valve 42 is an electronically controlled valve. The opening degree of the high-pressure EGR valve 42 can be controlled by the control device 60, described later. The higher the opening degree of the high-pressure EGR valve 42, the greater the backflow of high-pressure EGR gas from the high-pressure EGR device 40 to the intake passage 13. Conversely, when the high-pressure EGR valve 42 is closed, the backflow of high-pressure EGR gas from the high-pressure EGR device 40 to the intake passage 13 stops.

[0024] The low-pressure EGR device 50 redirects the exhaust gas flowing in the exhaust passage 16 back to the portion of the intake passage 13 upstream of the compressor 32 as low-pressure EGR gas. The low-pressure EGR device 50 includes a low-pressure EGR passage 51 connecting the exhaust passage 16 and the intake passage 13, a cooling device 52 disposed in the low-pressure EGR passage 51, and a low-pressure EGR valve 53. A first end of the low-pressure EGR passage 51 is connected to the portion of the exhaust passage 16 downstream of the turbine 31. A second end of the low-pressure EGR passage 51 is connected to the portion of the intake passage 13 upstream of the compressor 32.

[0025] When the internal combustion engine 10 is installed in the vehicle, the first end of the low-pressure EGR passage 51 is located below the second end of the low-pressure EGR passage 51. For example, the low-pressure EGR passage 51 is configured to be located above the intake passage 13 when the internal combustion engine 10 is installed in the vehicle.

[0026] Cooling device 52 cools the low-pressure EGR gas flowing through low-pressure EGR passage 51.

[0027] The low-pressure EGR valve 53 is located in the portion of the low-pressure EGR passage 51 between the connection point with the intake passage 13 and the cooling device 52. The low-pressure EGR valve 53 is an electronically controlled valve. The opening degree of the low-pressure EGR valve 53 can be controlled by the control device 60 described later. The higher the opening degree of the low-pressure EGR valve 53, the greater the return flow of low-pressure EGR gas from the low-pressure EGR device 50 to the intake passage 13. Conversely, when the low-pressure EGR valve 53 is closed, the return flow of low-pressure EGR gas from the low-pressure EGR device 50 to the intake passage 13 stops.

[0028] The low-pressure EGR gas in the low-pressure EGR passage 51 is cooled by the cooling device 52. Therefore, condensate is generated in the low-pressure EGR passage 51 due to the decrease in temperature of the low-pressure EGR gas. When the flow velocity of the low-pressure EGR gas flowing towards the intake passage 13 in the low-pressure EGR passage 51 is relatively high, the condensate is discharged into the intake passage 13 along with the low-pressure EGR gas. On the other hand, when the flow velocity of the low-pressure EGR gas flowing towards the intake passage 13 in the low-pressure EGR passage 51 is relatively low, or when the flow of the low-pressure EGR gas stops, the condensate flows towards the exhaust passage 16 in the low-pressure EGR passage 51 due to its own weight. Then, the condensate is discharged into the exhaust passage 16.

[0029] Control unit 60 controls high-pressure EGR unit 40 and low-pressure EGR unit 50 to adjust the reflux flow rate of high-pressure EGR gas and low-pressure EGR gas. Detection signals are input to control unit 60 from multiple sensors.

[0030] Multiple sensors include crankshaft angle sensor 71, air flow meter 72, water temperature sensor 73, intake air temperature sensor 74, and exhaust air temperature sensor 75.

[0031] Crankshaft angle sensor 71 detects the rotation angle of crankshaft 12. The rotational speed of crankshaft 12 based on the detection signal from crankshaft angle sensor 71 is recorded as "internal combustion engine speed NE". Air flow meter 72 detects the air flow rate in intake passage 13. The air flow rate based on the detection signal from air flow meter 72 is recorded as "intake air volume GA". Coolant temperature sensor 73 detects the temperature of coolant flowing in cooling system 52. The temperature of coolant based on the detection signal from coolant temperature sensor 73 is recorded as "coolant temperature". Intake air temperature sensor 74 detects the temperature of air introduced from intake passage 13 into multiple cylinders 11. The temperature of air based on the detection signal from intake air temperature sensor 74 is recorded as "intake air temperature". Exhaust temperature sensor 75 detects the temperature of exhaust gas flowing in the portion of exhaust gas flowing downstream of turbine 31 in exhaust passage 16. The temperature of exhaust gas based on the detection signal from exhaust temperature sensor 75 is recorded as "exhaust temperature".

[0032] One example of the control device 60 is an electronic control device. In this case, the control device 60 has a CPU 61, a first memory 62, and a second memory 63. The first memory 62 stores the control program executed by the CPU 61. The second memory 63 stores the calculation results of the CPU 61. By executing the control program in the first memory 62 through the CPU 61, the control device 60 can adjust the opening degree of the high-pressure EGR valve 42 and the low-pressure EGR valve 53.

[0033] <Operating range of internal combustion engines>

[0034] Reference Figure 2 The relationship between the operating range of the internal combustion engine 10 and the distribution ratio of high-pressure EGR gas and low-pressure EGR gas is explained. It should be noted that the operating range of the internal combustion engine 10 is determined by the output torque of the internal combustion engine 10, i.e., the engine torque TQ, and the engine speed NE.

[0035] The operating regions of the internal combustion engine 10 can be divided into a first operating region DA1, a second operating region DA2, and a fifth operating region DA5. The second operating region DA2 can be further divided into a third operating region DA3 and a fourth operating region DA4.

[0036] The first operating region DA1 is a high-torque, low-speed operating region. In the first operating region DA1, low-pressure EGR gas is allowed to flow back into the intake passage 13, while high-pressure EGR gas is prohibited from flowing back into the intake passage 13.

[0037] The fifth operating zone, DA5, is a high-torque, high-speed operating zone. In the fifth operating zone, DA5, high-pressure EGR gas is allowed to flow back into the intake passage 13, while low-pressure EGR gas is prohibited from flowing back into the intake passage 13.

[0038] In the second operating zone DA2, both high-pressure EGR gas and low-pressure EGR gas are allowed to recirculate through the intake passages 13 in both directions. The fourth operating zone DA4 is a low-torque, low-speed operating zone. In the fourth operating zone DA4, the temperature of the high-pressure EGR gas is relatively low, and the amount of NOx emitted from the multiple cylinders 11 is not as high. Therefore, in the fourth operating zone DA4, the difference in NOx emission reduction effect from the recirculation of high-pressure EGR gas is smaller than that from the recirculation of low-pressure EGR gas. On the other hand, in the third operating zone DA3, compared to the fourth operating zone DA4, the temperature of the high-pressure EGR gas is higher, and therefore the NOx emission reduction effect from the recirculation of low-pressure EGR gas is greater. That is, it can be said that the fourth operating zone DA4, compared to the third operating zone DA3, is an operating zone where the effect of improving exhaust characteristics by recirculating low-pressure EGR gas into the intake passages 13 is less significant.

[0039] Control of High-Pressure EGR Units and Low-Pressure EGR Units

[0040] The control device 60 calculates an estimated amount of condensate retained in the low-pressure EGR passage 51, namely the retention amount Qwc. Furthermore, if the retention amount Qwc is greater than a predetermined value, the control device 60 operates the low-pressure EGR unit 50 by reducing the return flow rate of the low-pressure EGR gas. For example, the control device 60 controls both the low-pressure EGR unit 50 and the high-pressure EGR unit 40 to reduce the proportion of low-pressure EGR gas in the return flow rate of EGR gas to the intake passage 13. The return flow rate of EGR gas to the intake passage 13 is the sum of the return flow rate of high-pressure EGR gas and the return flow rate of low-pressure EGR gas.

[0041] At this time, the control device 60 compares the judgment value corresponding to the operating area at that time point with the retention amount Qwc. For example, if the operating area is the fourth operating area DA4, the control device 60 operates the low-pressure EGR device 50 by reducing the return flow of the low-pressure EGR gas if the retention amount Qwc is greater than the judgment value QwcThA corresponding to the fourth operating area DA4. For example, if the operating area is the third operating area DA3, the control device 60 operates the low-pressure EGR device 50 by reducing the return flow of the low-pressure EGR gas if the retention amount Qwc is greater than the judgment value QwcThB corresponding to the third operating area DA3. For example, if the operating area is the first operating area DA1, the control device 60 operates the low-pressure EGR device 50 by reducing the return flow of the low-pressure EGR gas if the retention amount Qwc is greater than the judgment value QwcThC corresponding to the first operating area DA1.

[0042] It should be noted that, as Figure 3As shown, multiple judgment values ​​QwcThA, QwcThB, and QwcThC are all less than the upper limit of retention capacity QwcLm. The upper limit of retention capacity QwcLm is the upper limit of condensate that can be retained in the low-pressure EGR passage 51.

[0043] As described above, the fourth operating zone DA4 is an operating zone where the NOx emission reduction effect from low-pressure EGR gas recirculation is relatively low. The third operating zone DA3, compared to the fourth operating zone DA4, is an operating zone where the NOx emission reduction effect from low-pressure EGR gas recirculation is relatively high. The first operating zone DA1, compared to the third operating zone DA3 and the fourth operating zone DA4, is an operating zone where the NOx emission reduction effect from low-pressure EGR gas recirculation is relatively high.

[0044] Therefore, among the three decision values ​​QwcThA, QwcThB and QwcThC, decision value QwcThA is the smallest, decision value QwcThB is the second smallest, and decision value QwcThC is the largest.

[0045]

[0046] Reference Figure 4 This describes a series of processes performed by the control device 60 when the high-pressure EGR device 40 and the low-pressure EGR device 50 are activated. The control device 60 repeats these processes in each predetermined control cycle during the operation of the internal combustion engine 10.

[0047] In step S11, the control device 60 determines from multiple operating regions DA1, DA3, DA4, and DA5 the operating region corresponding to the internal combustion engine torque TQ and internal combustion engine speed NE of the internal combustion engine 10 at the current time point. In the next step S13, the control device 60 determines whether the operating region determined in step S11 is the fifth operating region DA5. If the operating region at the current time point is the fifth operating region DA5 (S13: Yes), the control device 60 moves the process to step S15. On the other hand, if the operating region at the current time point is not the fifth operating region DA5 (S13: No), the control device 60 moves the process to step S21.

[0048] In step S15, the control device 60 operates the low-pressure EGR device 50 by stopping the backflow of low-pressure EGR gas. For example, the control device 60 closes the low-pressure EGR valve 53. Afterward, the control device 60 temporarily terminates a series of processes.

[0049] In step S21, the control device 60 calculates an estimated value, i.e., the retention amount Qwc, of the condensate retained in the low-pressure EGR passage 51. Figure 5The calculation process for the retention amount Qwc will be described later. After calculating the retention amount Qwc, the control device 60 transfers the process to step S23.

[0050] In step S23, the control device 60 determines whether the retention amount Qwc calculated in step S21 is greater than the determination value QwcThA corresponding to the fourth operating region DA4. If the retention amount Qwc is greater than the determination value QwcThA (S23: Yes), the control device 60 moves the process to step S25. On the other hand, if the retention amount Qwc is less than or equal to the determination value QwcThA (S23: No), the control device 60 temporarily terminates the series of processes.

[0051] In step S25, the control device 60 determines whether the operating area at the current time point determined in step S11 is the fourth operating area DA4. If the operating area at the current time point is the fourth operating area DA4 (S25: Yes), the control device 60 moves the process to step S27. On the other hand, if the operating area at the current time point is not the fourth operating area DA4 (S25: No), the control device 60 moves the process to step S31.

[0052] In step S27, the control device 60 operates the low-pressure EGR device 50 and the high-pressure EGR device 40 by reducing the reflux flow rate of the low-pressure EGR gas and increasing the reflux flow rate of the high-pressure EGR gas. Preferably, the control device 60 stops the reflux of the low-pressure EGR gas and increases the reflux flow rate of the high-pressure EGR gas. At this time, the control device 60 closes the low-pressure EGR valve 53 and increases the opening of the high-pressure EGR valve 42. Then, the control device 60 temporarily terminates the series of processes.

[0053] In step S31, the control device 60 determines whether the retention amount Qwc calculated in step S21 is greater than the determination value QwcThB corresponding to the third operating region DA3. If the retention amount Qwc is greater than the determination value QwcThB (S31: Yes), the control device 60 transfers the processing to step S33. On the other hand, if the retention amount Qwc is less than or equal to the determination value QwcThB (S31: No), the control device 60 temporarily terminates the series of processes.

[0054] In step S33, the control device 60 determines whether the operating area at the current time point determined in step S11 is the third operating area DA3. If the operating area at the current time point is the third operating area DA3 (S33: Yes), the control device 60 moves the process to step S35. On the other hand, if the operating area at the current time point is not the third operating area DA3 (S33: No), the control device 60 moves the process to step S41.

[0055] In step S35, the control device 60 operates the low-pressure EGR device 50 and the high-pressure EGR device 40 by reducing the reflux flow rate of the low-pressure EGR gas and increasing the reflux flow rate of the high-pressure EGR gas. Preferably, the control device 60 stops the reflux of the low-pressure EGR gas and increases the reflux flow rate of the high-pressure EGR gas. At this time, the control device 60 closes the low-pressure EGR valve 53 and increases the opening of the high-pressure EGR valve 42. Then, the control device 60 temporarily terminates the series of processes.

[0056] In step S41, the control device 60 determines whether the retention amount Qwc calculated in step S21 is greater than the determination value QwcThC corresponding to the first operating region DA1. If the retention amount Qwc is greater than the determination value QwcThC (S41: Yes), the control device 60 transfers the processing to step S43. On the other hand, if the retention amount Qwc is less than or equal to the determination value QwcThC (S41: No), the control device 60 temporarily terminates the series of processes.

[0057] In step S43, the control device 60 determines whether the operating area at the current time point determined in step S11 is the first operating area DA1. If the operating area at the current time point is the first operating area DA1 (S43: Yes), the control device 60 moves the processing to step S45. On the other hand, if the operating area at the current time point is not the first operating area DA1 (S43: No), the control device 60 temporarily terminates a series of processes.

[0058] In step S45, the control device 60 operates the low-pressure EGR device 50 by reducing the reflux flow of the low-pressure EGR gas. Preferably, the control device 60 stops the reflux of the low-pressure EGR gas. At this time, the control device 60 closes the low-pressure EGR valve 53. Then, the control device 60 temporarily terminates a series of processes.

[0059] <Calculation and processing of retention amount Qwc>

[0060] Reference Figure 5 The calculation and processing of the retention amount Qwc in step S21 above will be explained. The control device 60 repeats the calculation and processing in each predetermined calculation cycle.

[0061] The calculation process includes production calculation process M10, discharge calculation process M20, differential calculation process M30, and cumulative processing M40.

[0062] The generation calculation process M10 calculates the estimated amount of condensate generated in the low-pressure EGR passage 51 per unit time, i.e., the generation amount Qwg. The unit time is, for example, equal to the execution interval of the retention amount Qwc calculation process.

[0063] In the generation calculation process M10, the control device 60 calculates the generation amount Qwg based on factors such as the external gas temperature, intake air volume, fuel injection volume, and moisture content in the air. For example, the control device 60 calculates the moisture content contained in the exhaust gas flowing in the exhaust passage 16 based on the external gas temperature, intake air volume, fuel injection volume, and moisture content in the air. Then, the control device 60 calculates the difference between the moisture content calculated as described above and the moisture content in the exhaust gas with a relative humidity of 100% after being cooled by the low-pressure EGR passage 51 as the generation amount Qwg.

[0064] Discharge calculation process M20 is a process that calculates the estimated amount of condensate discharged from the low-pressure EGR passage 51 per unit time, i.e., the discharge volume Qwd. Discharge calculation process M20 includes a first discharge volume calculation process M21, a second discharge volume calculation process M22, and a total process M23.

[0065] The first discharge volume calculation process M21 is the estimated value of the amount of condensate discharged from the low-pressure EGR passage 51 to the intake passage 13 per unit time, i.e., the first discharge volume Qwd1.

[0066] In the first discharge volume calculation process M21, the control device 60 calculates the first discharge volume Qwd1 based on the flow rate of the low-pressure EGR gas. At this time, the control device 60 calculates the first discharge volume Qwd1 in such a way that the larger the flow rate of the low-pressure EGR gas, the larger the value. It should be noted that the control device 60 can calculate the flow rate of the low-pressure EGR gas based on the exhaust volume flowing in the exhaust passage 16 and the opening degree of the low-pressure EGR valve 53.

[0067] The second discharge volume calculation process M22 is the estimated value of the amount of condensate discharged from the low-pressure EGR passage 51 to the exhaust passage 16 per unit time, i.e., the second discharge volume Qwd2.

[0068] In the second discharge calculation process M22, the control device 60 calculates the second discharge quantity Qwd2 based on the duration of the state in which the low-pressure EGR valve 53 is closed, i.e., the stop time TM.

[0069] Here, the amount of condensate discharged from the low-pressure EGR passage 51 to the exhaust passage 16 is correlated with the stop time TM. Figure 5 The diagram shows a mapping MP representing such a correlation.

[0070] The control device 60 uses such a mapping MP to derive a value based on the stop time TM as the second discharge quantity Qwd2. Thus, the control device 60 can calculate the second discharge quantity Qwd2 in such a way that the longer the stop time TM, the larger the value.

[0071] In the total processing M23, the control device 60 calculates the sum of the first discharge amount Qwd1 and the second discharge amount Qwd2 as the discharge amount Qwd.

[0072] In the differential calculation process M30, the control device 60 calculates the difference ΔQ between the generated quantity Qwg and the discharged quantity Qwd by subtracting the discharged quantity Qwd from the generated quantity Qwg. When the generated quantity Qwg is greater than the discharged quantity Qwd, the difference ΔQ is positive. Conversely, when the generated quantity Qwg is less than the discharged quantity Qwd, the difference ΔQ is negative.

[0073] In the cumulative processing M40, the control device 60 calculates the retention amount Qwc using the cumulative difference ΔQ. However, if the cumulative value of the difference ΔQ is negative, the control device 60 calculates 0 (zero) as the retention amount Qwc.

[0074] <Function and Effects of This Implementation Method>

[0075] (1) The NOx reduction effect of recirculating low-pressure EGR gas into the intake passage 13 varies depending on the operating region of the internal combustion engine 10. Therefore, in operating regions where the NOx reduction effect of recirculating low-pressure EGR gas into the intake passage 13 is relatively low, even if the process of reducing the recirculation flow of low-pressure EGR gas is performed when the amount of condensate retained in the low-pressure EGR passage 51 is relatively small, the NOx reduction effect will not be as significant. On the other hand, in operating regions where the NOx reduction effect of recirculating low-pressure EGR gas into the intake passage 13 is relatively high, if the process of reducing the recirculation flow of low-pressure EGR gas is performed when the amount of condensate retained in the low-pressure EGR passage 51 is relatively small, the NOx reduction effect will be reduced.

[0076] Therefore, the control device 60 determines the operating range of the internal combustion engine 10 based on the internal combustion engine torque TQ and the internal combustion engine speed NE. The control device 60 calculates an estimated value, i.e., the retention amount Qwc, of the amount of condensate retained in the low-pressure EGR passage 51. Furthermore, if the retention amount Qwc is greater than the judgment value corresponding to the determined operating range, the control device 60 operates the low-pressure EGR device 50 by reducing the return flow of the low-pressure EGR gas.

[0077] By comparing the judgment value corresponding to the operating area at the current time point with the retention amount Qwc, the start time for reducing the reflux flow rate of low-pressure EGR gas is determined. Therefore, compared to a case where the judgment value is fixed regardless of the operating area, the exhaust gas recirculation device 100 can appropriately optimize the start time for reducing the reflux flow rate of low-pressure EGR gas. Consequently, the exhaust gas recirculation device 100 can discharge condensate generated in the low-pressure EGR passage 51 to the exhaust passage 16 while suppressing a decrease in NOx reduction effect.

[0078] (2) The first operating zone DA1 is an operating zone that prohibits the backflow of high-pressure EGR gas into the intake passage 13. On the other hand, the second operating zone DA2 is an operating zone that allows the backflow of both high-pressure EGR gas and low-pressure EGR gas into the intake passage 13.

[0079] Therefore, in the exhaust gas recirculation device 100, the judgment values ​​QwcThA and QwcThB corresponding to the second operating region DA2 are less than the judgment value QwcThC corresponding to the first operating region DA1.

[0080] Therefore, when the operating region at the current time point is the first operating region DA1, compared to when the operating region at the current time point is the second operating region DA2, it is difficult to perform the process of reducing the return flow of low-pressure EGR gas during a stage with a small retention volume Qwc. As a result, the exhaust gas recirculation device 100 can suppress the reduction in NOx reduction effect.

[0081] On the other hand, when the operating region at the current time point is the second operating region DA2, compared to the case where the operating region at the current time point is the first operating region DA1, a process is performed to reduce the return flow of low-pressure EGR gas with a smaller retention amount Qwc. As a result, the exhaust gas recirculation device 100 can reduce the amount of condensate retained in the low-pressure EGR passage 51.

[0082] (3) The second operating zone DA2 can be divided into the third operating zone DA3 and the fourth operating zone DA4. The fourth operating zone DA4 is an operating zone with a lower NOx reduction effect caused by the recirculation of low-pressure EGR gas to the intake passage 13 compared with the third operating zone DA3.

[0083] Therefore, in the exhaust gas recirculation device 100, the judgment value QwcThA corresponding to the fourth operating region DA4 is less than the judgment value QwcThB corresponding to the third operating region DA3. Thus, when the operating region at the current time point is the fourth operating region DA4, compared to when the operating region at the current time point is the third operating region DA3, the process of reducing the return flow of low-pressure EGR gas is performed with a smaller retention amount Qwc. Therefore, the exhaust gas recirculation device 100 can suppress the reduction in NOx reduction effect and discharge the condensate generated in the low-pressure EGR passage 51 to the exhaust passage 16.

[0084] (4) The control device 60 calculates the generation amount Qwg and the discharge amount Qwd in each specified control cycle. Then, the control device 60 calculates the retention amount Qwc by accumulating the difference between the generation amount Qwg and the discharge amount Qwd. At this time, the control device 60 calculates the sum of the discharge amount of condensate from the low-pressure EGR passage 51 to the intake passage 13, i.e., the first discharge amount Qwd1, and the discharge amount of condensate from the low-pressure EGR passage 51 to the exhaust passage 16, i.e., the second discharge amount Qwd2, as the discharge amount Qwd. The exhaust gas recirculation device 100 considers both the first discharge amount Qwd1 and the second discharge amount Qwd2 when calculating the discharge amount Qwd, thereby improving the accuracy of calculating the retention amount Qwc.

[0085] <Example of Change>

[0086] The above-described embodiments can be implemented by modification as follows. The above-described embodiments and the following modifications can be combined with each other within the scope of technical inconsistency.

[0087] • When calculating the discharge quantity Qwd, the control device 60 may not calculate the second discharge quantity Qwd2. For example, the control device 60 may also increase the correction for the first discharge quantity Qwd1 based on the execution time of the process of reducing the opening of the low-pressure EGR gas, thereby calculating the discharge quantity Qwd. For example, preferably, the control device 60 calculates the discharge quantity Qwd by correcting the first discharge quantity Qwd1 in such a way that the longer the execution time, the larger the correction amount.

[0088] • The judgment value QwcThA corresponding to the fourth operating region DA4 can also be equal to the judgment value QwcThB corresponding to the third operating region DA3.

[0089] ·exist Figure 4 In steps S27 and S35 shown above, the control device 60 may not close the low-pressure EGR valve 53 as long as it can reduce the return flow of low-pressure EGR gas to the intake passage 13.

[0090] • The control device 60 is not limited to a device with a CPU and ROM to perform software processing. That is, the control device 60 may be any of the structures described in (a), (b) and (c) below.

[0091] (a) The control device 60 includes one or more processors that perform various processes according to a computer program. The processor includes a CPU and memories such as RAM and ROM. The memories store program code or instructions configured to cause the CPU to perform processes. Memory, or computer-readable medium, includes all available media that can be accessed by a general-purpose or special-purpose computer.

[0092] (b) The control device 60 has one or more dedicated hardware circuits for performing various processes. Examples of dedicated hardware circuits include application-specific integrated circuits, i.e., ASICs or FPGAs. ASIC is an abbreviation for "Application Specific Integrated Circuit", and FPGA is an abbreviation for "Field Programmable Gate Array".

[0093] (c) The control device 60 has one or more processors that execute a portion of various processes according to a computer program and one or more dedicated hardware circuits that execute the remaining processes in the various processes.

Claims

1. An exhaust gas recirculation device configured to be installed in an internal combustion engine, the internal combustion engine comprising: a cylinder; an intake passage for air flow into the cylinder; an exhaust passage for exhaust gas flow out of the cylinder; and a turbocharger for pressurizing the air flowing in the intake passage, wherein, The supercharger includes: a turbine disposed in the exhaust passage; and a compressor disposed in the intake passage and operating synchronously with the turbine. The exhaust gas recirculation device includes: A high-pressure EGR device causes the exhaust gas flowing in the exhaust passage to flow back to the intake passage as high-pressure EGR gas. A low-pressure EGR device causes the exhaust gas flowing in the exhaust passage to flow back to the intake passage as low-pressure EGR gas. and The control device is configured to control the high-pressure EGR device and the low-pressure EGR device to adjust the reflux flow rate of the high-pressure EGR gas and the reflux flow rate of the low-pressure EGR gas. The high-pressure EGR device has a high-pressure EGR passage, a first end of which is connected to a portion of the exhaust passage upstream of the turbine, and a second end of which is connected to a portion of the intake passage downstream of the compressor. The low-pressure EGR device includes a low-pressure EGR passage and a cooling device. The first end of the low-pressure EGR passage is connected to the portion of the exhaust passage downstream of the turbine, and the second end of the low-pressure EGR passage is connected to the portion of the intake passage upstream of the compressor. The cooling device cools the low-pressure EGR gas flowing in the low-pressure EGR passage. The control device is configured to perform the following processing: The operating range of the internal combustion engine is determined based on its output torque and speed. The estimated amount of condensate retained in the low-pressure EGR passage is the retention amount. and When the retention ratio is greater than the determination value corresponding to the operating area, the low-pressure EGR device is operated in a manner that reduces the reflux flow rate of the low-pressure EGR gas.

2. The exhaust gas recirculation device according to claim 1, wherein, The operating area includes a first operating area and a second operating area. In the first operating zone, the high-pressure EGR gas is prohibited from flowing back into the intake passage. The second operating zone allows both the high-pressure EGR gas and the low-pressure EGR gas to flow back into the intake passage. The determination value corresponding to the second operating area is less than the determination value corresponding to the first operating area.

3. The exhaust gas recirculation device according to claim 2, wherein, The second operating area includes the third operating area and the fourth operating area. Compared to the third operating region, the fourth operating region is less effective at improving exhaust characteristics by recirculating the low-pressure EGR gas back into the intake passage. The determination value corresponding to the fourth operating region is smaller than the determination value corresponding to the third operating region.

4. The exhaust gas recirculation device according to any one of claims 1 to 3, wherein, The control device is configured such that, The amount of condensate generated in the low-pressure EGR passage and the amount of condensate discharged from the low-pressure EGR passage are estimated in each specified control cycle. The retention amount is derived by accumulating the difference between the generated amount and the discharged amount in each control cycle. The control device is configured to calculate the sum of the amount of condensate discharged from the low-pressure EGR passage to the exhaust passage and the amount of condensate discharged from the low-pressure EGR passage to the intake passage as the discharge amount.

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