Method and device for estimating EGR in an internal combustion engine

Abstract

This EGR estimation method for an internal combustion engine 1 is for estimating an EGR rate in intake and exhaust systems 10, 20 of the internal combustion engine 1 provided with: the intake system 10 which includes an air cleaner 12 and an intake passage 11; the exhaust system 20 which includes an exhaust passage 21; and a supercharger 30. The internal combustion engine 1 is also provided with an EGR device 40 including an EGR passage 41 and an EGR valve 43. The intake system 10 is provided with an intake bypass passage 18 and a R / V 19. The EGR estimation method for the internal combustion engine 1 includes estimating the EGR rate on the basis of the reverse flowrate of an EGR gas flowing back to the air cleaner 12 side as a result of opening of the R / V 19, in the case where the R / V 19 is opened and the EGR valve 43 is fully closed during supercharging.

Description

[Technical field]

[0001] The present invention relates to EGR estimation in an internal combustion engine. [Background technology]

[0002] JP2013-7268A and WO2012 / 176490A1 disclose an intake device for a supercharged internal combustion engine that prevents fresh air containing EGR gas from blowing back to the air flow meter when the recirculation valve is opened. The recirculation valve releases the pressure downstream of the compressor to the upstream of the compressor when the throttle valve is closed. Summary of the Invention

[0003] When the recirculation valve is opened during supercharging, gas may flow back up to the vicinity of the air cleaner. In this case, it is considered to fully close the EGR valve to prevent the EGR gas from flowing back. However, even if the EGR is stopped in this way, the EGR gas already present in the intake passage will flow back through the intake passage and then into the cylinder of the internal combustion engine. For this reason, it is desirable to understand how the backflowing EGR gas flows into the cylinder and to estimate the EGR rate more accurately.

[0004] The present invention has been made in consideration of the above problems, and has an object to estimate a more accurate EGR rate when the recirculation valve is opened and the EGR valve is fully closed during supercharging.

[0005] An embodiment of the present invention provides an EGR estimation method for an internal combustion engine, the method comprising: estimating an EGR amount of an intake passage for an internal combustion engine including an intake system including an air cleaner and an intake passage connecting the air cleaner and the internal combustion engine; an exhaust system including an exhaust passage connected to the internal combustion engine; and a supercharger provided in the intake passage and the exhaust passage, the intake system including an intake bypass passage connecting an upstream pressure portion and a downstream pressure portion of the supercharger in the intake system, and a recirculation valve provided in the intake bypass passage; to an EGR junction to which the EGR passage is connected. The method for estimating an EGR rate in an intake passage for an internal combustion engine estimates the EGR rate in an intake passage based on the EGR rate in the intake passage before the recirculation valve is opened during supercharging so that EGR gas flows back to the air cleaner side, and the EGR valve is fully closed.

[0006] According to another aspect of the present invention, there is provided an EGR estimation device for an internal combustion engine corresponding to the above-described EGR estimation method for an internal combustion engine. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram showing the main parts of a vehicle. [Figure 2A] FIG. 2A is a first diagram illustrating the flow pattern of EGR gas. [Figure 2B] FIG. 2B is a second diagram illustrating the flow pattern of EGR gas. [Figure 2C] FIG. 2C is a third explanatory diagram of the flow pattern of EGR gas. [Figure 2D] FIG. 2D is a fourth explanatory diagram of the flow pattern of EGR gas. [Diagram 3] FIG. 3 is a diagram illustrating a method for estimating the EGR rate. [Figure 4] FIG. 4 is a control block diagram showing a process for estimating the EGR rate. [Diagram 5]FIG. 5 is a flowchart showing a process for estimating the EGR rate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0009] 1 is a diagram showing a main part of a vehicle. The vehicle includes an internal combustion engine 1, an intake system 10, an exhaust system 20, a supercharger 30, an EGR device 40, and a controller 50.

[0010] The intake system 10 includes an intake passage 11, an air cleaner 12, an air flow meter 13, an intake throttle valve 14, an intercooler 15, a throttle valve 16, a collector 17, a compressor 31, an intake bypass passage 18, and a recirculation valve (hereinafter referred to as R / V) 19. The intake passage 11 connects the air cleaner 12 to the internal combustion engine 1, and distributes the intake air to be introduced into the internal combustion engine 1. In the intake passage 11, the air cleaner 12, the air flow meter 13, the intake throttle valve 14, the compressor 31, the intercooler 15, the throttle valve 16, and the collector 17 are provided in this order from the upstream side.

[0011] The air cleaner 12 removes foreign matter contained in the intake air. The air flow meter 13 measures the flow rate of the intake air. The intake throttle valve 14 is provided in a portion of the intake passage 11 upstream of an EGR junction 11a to which an EGR passage 41 (described later) is connected. The intake throttle valve 14 increases the amount of exhaust gas recirculated through the EGR passage 41 by decreasing the opening degree.

[0012] The intercooler 15 cools the supercharged intake air. The throttle valve 16 adjusts the amount of intake air introduced into the internal combustion engine 1. The collector 17 temporarily stores the intake air. The compressor 31 is a compressor of the supercharger 30, and compresses the intake air.

[0013] The exhaust system 20 includes an exhaust passage 21, an upstream catalyst 22, a downstream catalyst 23, and a turbine 32. The exhaust passage 21 is connected to the internal combustion engine 1, and allows the exhaust gas discharged from the internal combustion engine 1 to flow therethrough. In the exhaust passage 21, the turbine 32, the upstream catalyst 22, and the downstream catalyst 23 are provided in this order from the upstream side. The upstream catalyst 22 and the downstream catalyst 23 purify the exhaust gas. The turbine 32 is a turbine of the turbocharger 30, and recovers energy from the exhaust gas.

[0014] The supercharger 30 compresses the intake air and supplies it to the internal combustion engine 1. The supercharger 30 is a turbocharger and includes a compressor 31, a turbine 32, and a shaft 33. The supercharger 30 is provided in the intake passage 11 and the exhaust passage 21, with the compressor 31 and the turbine 32 being provided in the intake passage 11 and the exhaust passage 21, respectively. In the supercharger 30, the turbine 32 is rotated by exhaust air, which causes the compressor 31 to rotate via the shaft 33 and compress the intake air. In the compressor 31, a pair of compressor wheels arranged back to back are provided on the shaft 33, and the intake air is compressed by the pair of compressor wheels. The turbine 32 is provided with an exhaust bypass passage, and the exhaust bypass passage is provided with a wastegate valve (not shown) that adjusts the flow rate of the exhaust gas flowing therethrough.

[0015] The EGR device 40 includes an EGR passage 41, an EGR cooler 42, and an EGR valve 43. The EGR device 40 recirculates exhaust gas from the exhaust passage 21 to the intake passage 11.

[0016] The EGR passage 41 connects the exhaust passage 21 and the intake passage 11. The EGR passage 41 recirculates a portion of the exhaust gas flowing through the exhaust passage 21 to the intake passage 11 as EGR gas. An EGR cooler 42 and an EGR valve 43 are provided in the EGR passage 41. The EGR cooler 42 cools the EGR gas flowing through the EGR passage 41. The EGR valve 43 adjusts the flow rate of the EGR gas flowing through the EGR passage 41.

[0017] The EGR device 40, specifically the EGR passage 41, connects the portion of the exhaust passage 21 downstream of the turbocharger 30, i.e. the turbine 32, to the portion of the intake passage 11 upstream of the turbocharger 30, i.e. the compressor 31. The EGR passage 41 thus connecting the intake passage 11 and the exhaust passage 21 forms an LPL, i.e. low pressure loop, EGR path. More specifically, the EGR passage 41 connects the portion of the exhaust passage 21 between the upstream catalyst 22 and the downstream catalyst 23 to the portion of the intake passage 11 between the intake throttle valve 14 and the compressor 31.

[0018] The intake bypass passage 18 connects an upstream pressure portion and a downstream pressure portion of the turbocharger 30 in the intake system 10. The upstream pressure portion is the intake passage 11 upstream of the turbocharger 30 and downstream of the EGR junction 11a. The downstream pressure portion is the intake passage 11 downstream of the turbocharger 30 and upstream of the intercooler 15. Connecting to the downstream pressure portion of the turbocharger 30 in the intake system 10 includes connecting to the compressor 31 so that compressed intake air can flow into the intake bypass passage 18.

[0019] The R / V 19 is provided in the intake bypass passage 18. The R / V 19 is configured with an on-off valve. During supercharging, the downstream pressure is higher than the upstream pressure of the turbocharger 30. For this reason, when the R / V 19 opens during supercharging, the intake air compressed by the compressor 31 is returned to the intake passage 11 at the upstream side of the turbocharger 30 via the intake bypass passage 18.

[0020] The controller 50 is an electronic control device, and receives signals from various sensors and switches, such as the air flow meter 13, a crank angle sensor 71, an accelerator opening sensor 72, a boost pressure sensor 73, and an atmospheric pressure sensor 74. The crank angle sensor 71 generates a crank angle signal for each predetermined crank angle. The crank angle signal is used as a signal representing the rotation speed NE of the internal combustion engine 1. The accelerator opening sensor 72 detects the depression amount of the accelerator pedal of the vehicle. The depression amount of the accelerator pedal is used as a signal representing the load on the internal combustion engine 1. The boost pressure sensor 73 detects the downstream pressure of the supercharger 30 in the intake passage 11, and the atmospheric pressure sensor 74 detects the atmospheric pressure.

[0021] The controller 50 controls the internal combustion engine 1, the intake throttle valve 14, the throttle valve 16, the R / V 19, and the EGR valve 43, based on input signals from the various sensors and switches described above. The controller 50 controls the internal combustion engine 1 by controlling the ignition timing and the fuel injection amount according to the engine operating conditions. The engine operating conditions are, for example, the rotation speed NE and the load.

[0022] However, if the R / V 19 is opened during supercharging, gas may flow back up to the vicinity of the air cleaner 12. In this case, therefore, it is conceivable to fully close the EGR valve 43 to prevent the EGR gas from flowing back. However, even if the EGR is stopped in this way, the EGR gas already present in the intake passage 11 will flow back through the intake passage 11 and then into the cylinders of the internal combustion engine 1.

[0023] For this reason, in this embodiment, the manner in which the backflowing EGR gas flows into the cylinder is grasped, and the EGR rate (actual EGR rate) is estimated based on the grasped inflow pattern.

[0024] Figures 2A to 2D are explanatory diagrams of the flow patterns of EGR gas. In Figures 2A to 2D, the air flow meter 13, the R / V 19, etc. are omitted. Figure 2A shows the state immediately before the R / V 19 is opened during supercharging. At this time, the intake passage 11 downstream of the EGR junction 11a is filled with EGR gas at a target EGR rate, which is a gas mixture with the intake air.

[0025] 2B shows a state in which the R / V 19 is opened during supercharging and the EGR valve 43 is fully closed. At this time, the mixed gas compressed by the compressor 31 is returned to the intake passage 11 upstream of the compressor 31 via the intake bypass passage 18, and then flows back toward the air cleaner side, i.e., upstream of the EGR junction 11a, and blows through to the air cleaner 12. As a result, the mixed gas becomes diluted with air in the air cleaner 12. As a result, the EGR rate drops stepwise at the outlet position of the air cleaner 12, and then gradually drops further upstream.

[0026] 2C shows a state when a flow rate Q2 equivalent to the volume of the intake passage 11 from the EGR junction 11a to the connection with the air cleaner 12 (hereinafter referred to as the upstream piping volume) is re-inhaled. At this time, the diluted mixed gas arrives just before the EGR junction 11a, so that a step where the EGR rate decreases stepwise is located just before the EGR junction 11a.

[0027] 2D shows a state in which the diluted mixture gas passes through the EGR junction 11a and is re-absorbed. At this time, the EGR rate at the EGR junction 11a gradually decreases due to the diluted mixture gas.

[0028] In consideration of such a flow state of the mixed gas, in this embodiment, the EGR rate at the EGR junction 11a is estimated based on the amount of gas that flows back to the air cleaner 12 (hereinafter, referred to as the backflow amount of EGR gas).

[0029] 3 is a diagram illustrating a method for estimating the EGR rate. The dashed line indicates the target EGR rate.

[0030] At timing T1, the R / V 19 is opened. At this time, the EGR valve 43 is fully closed and EGR is stopped, but the mixed gas blows back as described above with reference to Fig. 2B. As a result, the EGR rate at the EGR junction 11a does not become zero as indicated by the broken line, but remains at the same value at timing T1.

[0031] At timing T2, the flow rate Q2 of the upstream piping volume is re-inhaled. As described above with reference to Fig. 2C, the EGR rate of the EGR junction 11a remains the same until timing T2 when the flow rate Q2 of the upstream piping volume is re-inhaled.

[0032] If the amount of backflow of EGR gas is large, the time until the flow rate Q2 of the upstream piping volume is re-inhaled becomes longer. Therefore, timing T2 changes according to the amount of backflow of EGR gas. As a result, the predetermined time α, which is indicated as the time between timing T1 and timing T2, becomes longer as the amount of backflow of EGR gas becomes larger. The predetermined time α is the time from when R / V 19 opens until the flow rate Q2 of the upstream piping volume is re-inhaled, and is changed according to the amount of backflow of EGR gas.

[0033] For this reason, in this embodiment, from timing T1 to timing T2, the estimated EGR rate is set by the first profile Prof1 that holds the EGR rate at the EGR junction 11a to the target EGR rate immediately before the R / V 19 is opened, with the upstream piping volume as an adaptation element, until the predetermined time α has elapsed, even if the R / V 19 is opened and the EGR valve 43 is fully closed.

[0034] 2C and 2D, immediately after timing T2, the EGR rate at the EGR junction 11a is represented by the EGR rate in the air cleaner 12 when the EGR gas flows back into the air cleaner 12. Therefore, immediately after timing T2, the EGR rate at the EGR junction 11a is estimated based on the EGR rate in the air cleaner 12 described above.

[0035] Immediately after timing T2, the EGR rate at the EGR junction 11a drops stepwise as described above with reference to FIG. 2C. The EGR rate at this time is higher as the amount of mixed gas blown back into the air cleaner 12 is larger, because the mixed gas is less likely to be diluted. Also, the amount of mixed gas blown back into the air cleaner 12 is larger as the amount of backflow of EGR gas is larger. Therefore, the EGR rate at this time is higher as the amount of backflow of EGR gas is larger.

[0036] For this reason, in this embodiment, the amount of backflow of EGR gas is used as an adaptation element, and the estimated EGR rate is set according to the second profile Prof2 in which the EGR rate is reduced in a stepped manner following the first profile Prof1, and the greater the amount of backflow of EGR gas, the higher the EGR rate that is reduced in a stepped manner.

[0037] After the EGR rate is reduced stepwise, the EGR rate at the EGR junction 11a is gradually reduced by the diluted mixed gas as described above with reference to Fig. 2D. The amount of reduction in the EGR rate at this time varies depending on the flow rate of the rebreathed gas, and the greater the flow rate of the rebreathed gas, the greater the reduction in the EGR rate. This is because the greater the flow rate of the rebreathed gas, the earlier the diluted mixed gas passes through the EGR junction 11a, and the earlier the reduction in the EGR rate becomes.

[0038] For this reason, in this embodiment, the estimated EGR rate is set by a third profile Prof3 that reduces the EGR rate over time following the second profile Prof2 with the rebreathed gas flow rate as an adaptation element, and reduces the amount of reduction in the EGR rate according to the rebreathed gas flow rate.

[0039] The third profile Prof3 is a profile that changes the EGR rate with a temporary response delay according to the rebreathed gas flow rate. The amount of reduction in the EGR rate in the third profile Prof3 can be changed by changing the time constant according to the rebreathed gas flow rate.

[0040] 4 is a control block diagram showing the EGR rate estimation process performed by the controller 50. A passing amount calculation unit 51 calculates the passing amount of gas passing through the R / V 19. The passing amount is calculated by multiplying the passing flow rate of gas passing through the R / V 19 by the JOB period of the estimation process, and is set to a negative value when blowback occurs. The passing flow rate of gas passing through the R / V 19 can be calculated based on, for example, the supercharging pressure and atmospheric pressure of the compressor 31, and the cross-sectional area of ​​the intake bypass passage 18. The calculated passing amount of gas is input to an integrated value calculation unit 52.

[0041] The integrated value calculation unit 52 calculates the integrated value QS of the amount of backflow. The integrated value QS of the amount of backflow is calculated by adding together the input amount of passing gas and the integrated value QS of the amount of backflow of gas calculated previously. The calculated integrated value QS of the amount of backflow is input to the first determination unit 53, the integrated value peak value calculation unit 56, and the forward flow rate calculation unit 57.

[0042] The first determination unit 53 determines whether the input cumulative value QS of the amount of blowback is smaller than zero. If blowback is occurring, the cumulative value QS of the amount of blowback is a negative value, and a positive determination is made. In this case, a signal is input from the first determination unit 53 to the AND circuit unit 54.

[0043] The AND circuit unit 54 inputs an AND signal to the EGR rate hold unit 55 when signals are input from the first determination unit 53 and a second determination unit 58 described later. The signal from the first determination unit 53 indicates that spit-back is occurring, and the signal from the second determination unit 58 indicates that the flow rate Q2 of the upstream piping volume has not yet been re-inhaled since the R / V 19 was opened. Therefore, the AND signal indicates that spit-back is occurring and that the flow rate Q2 of the upstream piping volume has not yet been re-inhaled.

[0044] The EGR rate hold unit 55 sets the EGR rate to be held, that is, sets the EGR rate based on the first profile Prof1. The EGR rate hold unit 55 selects the target EGR rate when the AND signal is not input. As a result, the EGR rate is set to the target EGR rate.

[0045] When the AND signal is input, the EGR rate hold unit 55 selects the previously set EGR rate and stops processing. This sets the EGR rate to be held. The set EGR rate is input to the step change setting unit 59 and the EGR rate selection unit 60.

[0046] The integrated value peak value calculation unit 56 calculates an integrated value peak value QSmax, which is the peak value of the integrated value QS of the amount of backflow air. When the input integrated value QS of the amount of backflow air is equal to or less than the integrated value peak value QSmax calculated last time (when the absolute value is equal to or more than the integrated value peak value QSmax), the integrated value peak value calculation unit 56 selects the input integrated value QS of the amount of backflow air. This updates the selected integrated value QS of the amount of backflow air as the new integrated value peak value QSmax, and calculates a provisional integrated value peak value QSmax.

[0047] When the input cumulative amount QS is larger than the cumulative amount peak value QSmax calculated previously (when the absolute value is smaller than the cumulative amount peak value QSmax), the cumulative amount peak value calculation unit 56 selects the cumulative amount peak value QSmax calculated previously and stops processing. As a result, the cumulative amount peak value QSmax calculated previously is calculated and determined as the true cumulative amount peak value QSmax in the calculation. In other words, the true cumulative amount peak value QSmax is the backflow amount of EGR gas, and indicates the total backflow amount of the mixed gas. The calculated cumulative amount peak value QSmax is input to the forward flow amount calculation unit 57 and the step change setting unit 59.

[0048] The forward flow rate calculation unit 57 calculates the backflow divided forward flow rate Q1. In other words, the backflow divided forward flow rate Q1 is the flow rate of gas re-inhaled, and is calculated based on the integrated value peak value QSmax and the backflow amount integrated value QS. Specifically, the backflow divided forward flow rate Q1 is calculated by adding the backflow amount integrated value QS with the positive and negative signs remaining the same to the integrated value peak value QSmax with the positive and negative signs reversed. The calculated backflow divided forward flow rate Q1 is input to the second judgment unit 58.

[0049] The second determination unit 58 determines whether the backflow distribution flow rate Q1 is equal to or less than the flow rate Q2 for the upstream piping volume. The backflow distribution flow rate Q1 becomes equal to or less than the flow rate Q2 for the upstream piping volume when the flow rate Q2 for the upstream piping volume has not yet been re-inhaled since the R / V 19 was opened. If the determination is positive, the second determination unit 58 inputs a signal to the AND circuit unit 54, the EGR rate selection unit 60, and the response delay calculation unit 62.

[0050] The step change setting unit 59 calculates the step rate (degree of decrease) of the EGR rate based on the integrated value peak value QSmax and the rotation speed NE. The step rate of the EGR rate is calculated to be smaller as the integrated value peak value QSmax is larger, and is calculated to be smaller as the rotation speed NE is smaller. This is because when a step change occurs in the EGR rate in the air cleaner 12, the amount of the mixed gas blown back into the air cleaner 12 depends on the backflow amount of the EGR gas and further on the rotation speed NE of the internal combustion engine 1 that performs the intake.

[0051] The step change setting unit 59 further multiplies the calculated step rate by the EGR rate input from the EGR rate holding unit 55. As a result, a step change is set in the EGR rate, and the EGR rate based on the second profile Prof2 is set. The set EGR rate is input to the EGR rate selection unit 60.

[0052] When a signal is input from the second determination unit 58, that is, when the flow rate Q2 corresponding to the upstream piping volume has not yet been re-inhaled since the R / V 19 was opened, the EGR rate selection unit 60 selects the EGR rate input from the EGR rate hold unit 55. Therefore, in this case, the EGR rate based on the first profile Prof1 is selected.

[0053] When no signal is input from the second determination unit 58, that is, when the flow rate Q2 corresponding to the upstream piping volume is re-inhaled, the EGR rate selection unit 60 selects the EGR rate input from the step change setting unit 59 and stops the process. As a result, the EGR rate based on the second profile Prof2 is selected in a manner switching from the EGR rate based on the first profile Prof1. The selected EGR rate is input to a response delay calculation unit 62.

[0054] The response delay filter setting unit 61 calculates the time constant of the response delay filter of the EGR rate based on the rotation speed NE and the fresh air flow rate. The fresh air flow rate can be detected based on a signal from the air flow meter 13. The response delay of the EGR rate is set to be smaller as the rotation speed NE is higher and as the fresh air flow rate is larger. This is because the higher the rotation speed NE and the larger the fresh air flow rate, the larger the re-inhaled gas flow rate is and the earlier the diluted mixed gas passes through the EGR junction portion 11a, so the decrease in the EGR rate is accelerated. The calculated time constant of the response delay filter is input to the response delay calculation unit 62.

[0055] When no signal is input from the second determination unit 58, that is, when the flow rate Q2 corresponding to the upstream piping volume is re-inhaled, the response delay calculation unit 62 applies the time constant of the response delay filter input from the response delay filter setting unit 61 to the EGR rate input from the EGR rate selection unit 60. This causes the response delay of the EGR rate to be calculated and reflected in the EGR rate. The EGR rate reflecting the response delay is input to an EGR rate determination unit 63.

[0056] When a signal is input from the second determination unit 58, that is, when the flow rate Q2 corresponding to the upstream piping volume has not yet been re-inhaled since the R / V 19 was opened, the response delay calculation unit 62 does not calculate the response delay of the EGR rate. In this case, the EGR rate input from the EGR rate selection unit 60 is input to the EGR rate determination unit 63 as it is.

[0057] The EGR rate determination unit 63 determines the input EGR rate as the EGR rate of the EGR junction 11a. As a result, the EGR rate at the EGR junction 11a when the R / V 19 is opened and the EGR valve 43 is fully closed during supercharging is estimated according to the first profile Prof1 to the third profile Prof3.

[0058] 5 is a flowchart showing the process of estimating the EGR rate performed by the controller 50. The controller 50 is programmed to execute the process shown in this flowchart, and is configured to have a control unit.

[0059] In step S1, the controller 50 calculates the integrated amount of blowback air QS. The integrated amount of blowback air QS can be calculated as described above with reference to FIG.

[0060] In step S2, the controller 50 determines whether the R / V 19 is in operation, that is, whether the R / V 19 is open or not. If the determination in step S2 is negative, the process proceeds to step S6.

[0061] In step S6, the controller 50 determines whether or not the integrated value QS of the amount of backflow is less than zero. In step S6, if the integrated value QS of the amount of backflow is less than zero, it is determined that backflow is occurring.

[0062] When the R / V 19 is closed, no backflow is occurring. Therefore, if the process proceeds to step S6 following a negative determination in step S2, a negative determination is made in step S6, and the process proceeds to step S7.

[0063] In step S7, the controller 50 sets the EGR rate at the EGR junction 11a to the target EGR rate. As a result, the EGR rate at the EGR junction 11a is set to the target EGR rate before the R / V 19 opens. After step S7, the process ends.

[0064] If the R / V 19 is opened in the subsequent routine, an affirmative determination is made in step S2, and the process proceeds to step S3.

[0065] In step S3 and the following step S4, the controller 50 calculates the integrated peak value QSmax and the backflow divided flow rate Q1. The integrated peak value QSmax and the backflow divided flow rate Q1 can be calculated as described above with reference to FIG.

[0066] In step S5, the controller 50 judges whether the flow rate Q1 of the backflow is equal to or less than the flow rate Q2 of the upstream piping volume. If the judgment in step S5 is positive, it is judged that the flow rate Q2 of the upstream piping volume has not yet been re-inhaled since the R / V 19 was opened, and the process proceeds to step S6.

[0067] If the process proceeds to step S6 following the positive determination in step S5, the cumulative amount of backflow QS becomes smaller than zero, and the positive determination is made in step S6. In this case, the process proceeds to step S8.

[0068] In step S8, the controller 50 holds the EGR rate in the EGR junction 11a at the previous value. That is, in step S8, the first profile Prof1 is applied to estimate the EGR rate. After step S8, the process temporarily ends.

[0069] In the subsequent routine, while the R / V 19 is in operation and the flow rate Q1 of the backflow gas becomes larger than the flow rate Q2 of the upstream piping volume, the determinations in steps S2 and S5 are affirmative, and the determination in step S6 is also affirmative. As a result, the EGR rate in the EGR junction 11a is held at the previous value.

[0070] If the R / V 19 is in operation and the flow rate Q1 of the backflow is greater than the flow rate Q2 of the upstream piping volume, it is determined that the flow rate Q2 of the upstream piping volume has been re-inhaled since the R / V 19 was opened, and the result of the determination in step S5 is negative. In this case, the process proceeds to step S9.

[0071] In step S9, the controller 50 determines whether or not a step change was set in the EGR rate in the previous routine. If the determination in step S9 is negative, the process proceeds to step S10.

[0072] In step S10, the controller 50 sets a step change in the EGR rate at the EGR junction 11a. That is, in step S10, the second profile Prof2 is applied to estimate the EGR rate. After step S10, the process ends. In this case, in the next routine that is one job after the routine in which the process of step S10 is performed, a positive determination is made in step S9, and the process proceeds to step S11.

[0073] In step S11, the controller 50 reduces the EGR rate with a first-order response delay. That is, in step S11, the third profile Prof3 is applied to estimate the EGR rate. After step S11, the process of this flowchart ends once.

[0074] Next, the main effects of this embodiment will be described.

[0075] The EGR estimation method for the internal combustion engine 1 according to the present embodiment estimates an EGR rate at an EGR junction 11a in the intake and exhaust systems 10, 20 of the internal combustion engine 1, which include an intake system 10 including an air cleaner 12 and an intake passage 11, an exhaust system 20 including an exhaust passage 21, and a turbocharger 30, and which is provided with an EGR device 40 including an EGR passage 41 and an EGR valve 43, and the intake system 10 includes an intake bypass passage 18 and an R / V 19. The EGR estimation method for the internal combustion engine 1 estimates the EGR rate at the EGR junction 11a based on the amount of EGR gas that flows back to the air cleaner 12 side by opening the R / V 19 when the R / V 19 is opened and the EGR valve 43 is fully closed during turbocharging.

[0076] According to this method, in light of the flow patterns of the EGR gas described above with reference to Figures 2A to 2D, a more accurate EGR rate can be estimated when the R / V 19 is opened and the EGR valve 43 is fully closed during supercharging.

[0077] In the EGR estimation method for the internal combustion engine 1, even if the R / V 19 is opened and the EGR valve 43 is fully closed, the EGR rate is estimated by using the EGR rate before the EGR valve 43 is fully closed as the EGR rate at the EGR junction 11a, which is the estimated EGR rate, until the predetermined time α has elapsed. In other words, the first profile Prof1 is applied to estimate the EGR rate.

[0078] According to this method, the EGR rate can be held in light of the flow pattern of the EGR gas described above with reference to FIGS. 2B and 2C, thereby making it possible to estimate the EGR rate more accurately.

[0079] In this method, the predetermined time α is changed depending on the amount of backflow of EGR gas.

[0080] According to this method, the EGR rate can be held for an appropriate period of time, so that the EGR rate can be estimated more accurately.

[0081] In the EGR estimation method for the internal combustion engine 1, after the predetermined time α has elapsed, the EGR rate is estimated based on the EGR rate in the air cleaner 12 when the EGR gas flows back into the air cleaner 12. That is, the second profile Prof2 or the third profile Prof3 is applied to estimate the EGR rate.

[0082] According to this method, the EGR rate at the EGR junction 11a can be appropriately estimated in light of the flow pattern of the EGR gas described above with reference to FIGS. 2C and 2D, so that the EGR rate can be estimated more accurately.

[0083] In this method, the EGR rate estimated based on the EGR rate in the air cleaner 12 is stepped down and is increased as the amount of backflow of EGR gas increases. That is, the second profile Prof2 is applied to estimate the EGR rate.

[0084] According to this method, in light of the flow pattern of the EGR gas described above with reference to FIG. 2C , the EGR rate can be reduced in a stepwise manner and the step rate of the EGR rate when the EGR rate is reduced in a stepwise manner can be set appropriately, so that a more accurate EGR rate can be estimated.

[0085] Furthermore, in this method, the EGR rate estimated based on the EGR rate in the air cleaner 12 is decreased over time, and the amount of decrease in the EGR rate is changed according to the rebreathed gas flow rate. That is, the third profile Prof3 is further applied to estimate the EGR rate.

[0086] According to this method, in light of the flow pattern of the EGR gas described above with reference to FIG. 2D, the EGR rate when the mixed gas diluted in the air cleaner 12 passes through the EGR junction 11a can be appropriately reflected, so that a more accurate EGR rate can be estimated.

[0087] Although the embodiments of the present invention have been described above, the above-mentioned embodiments merely show some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above-mentioned embodiments.

[0088] For example, in the above embodiment, the case of estimating the EGR rate at the EGR junction 11a has been described. However, the estimated EGR rate may be, for example, the EGR rate of the gas flowing into the cylinder of the internal combustion engine 1, or an EGR rate at a predetermined position from the intake passage 11 downstream of the EGR junction 11a to the internal combustion engine 1. Such an EGR rate can be estimated, for example, by correcting the timing at which a step change in the EGR rate arrives, depending on the distance from the EGR junction 11a, etc.

[0089] The estimated EGR rate may be, for example, the EGR rate at a predetermined position in the intake passage 11 upstream of the EGR junction 11a. Such an EGR rate can be estimated, for example, by correcting the timing at which the mixed gas that filled the intake passage 11 just before the R / V 19 opens reaches the intake passage 11, depending on the distance from the EGR junction 11a or the like. In such a case, the EGR rate at the EGR junction 11a is also included in estimating the EGR rate based on the backflow amount of the EGR gas that flows back to the air cleaner 12 side by opening the R / V 19 when the R / V 19 is opened and the EGR valve 43 is fully closed during supercharging. Therefore, the estimated EGR rate can be the EGR rate at a predetermined position from the intake passage 11 to the internal combustion engine 1.

Claims

1. An intake and exhaust system of an internal combustion engine including an intake system including an air cleaner and an intake passage connecting the air cleaner and an internal combustion engine, an exhaust system including an exhaust passage connected to the internal combustion engine, and a supercharger provided in the intake passage and the exhaust passage, wherein an EGR device including an EGR passage connecting the intake passage and the exhaust passage and an EGR valve provided in the EGR passage is provided, and the intake system includes an intake bypass passage connecting an upstream pressure portion and a downstream pressure portion of the supercharger in the intake system and a recirculation valve provided in the intake bypass passage, the method comprising the steps of: estimating an EGR rate at any position within a range from the supercharger in the intake passage to an EGR junction connected to the EGR passage, The recirculation valve is opened and the EGR valve is fully closed during supercharging so that the EGR gas flows back to the air cleaner side. An EGR estimation method for an internal combustion engine, which estimates the EGR rate of the intake passage based on the EGR rate of the intake passage before the recirculation valve is opened, during a predetermined time period after the EGR valve is fully closed.

2. 2. The method for estimating EGR in an internal combustion engine according to claim 1, The predetermined time is changed depending on the amount of backflow of the EGR gas flowing back to the air cleaner side. A method for estimating EGR in an internal combustion engine.

3. 3. The method for estimating EGR in an internal combustion engine according to claim 1, After the predetermined time has elapsed, the EGR rate is estimated based on the EGR rate in the air cleaner when the EGR gas flows back into the air cleaner. A method for estimating EGR in an internal combustion engine.

4. 4. The method for estimating EGR in an internal combustion engine according to claim 3, The EGR rate estimated based on the EGR rate in the air cleaner is decreased in a stepwise manner and is increased as the amount of EGR gas flowing back to the air cleaner side increases. A method for estimating EGR in an internal combustion engine.

5. 5. The method for estimating EGR in an internal combustion engine according to claim 4, The EGR rate estimated based on the EGR rate in the air cleaner is reduced over time, and the amount of reduction in the EGR rate is changed according to a flow rate of gas re-inhaled. A method for estimating EGR in an internal combustion engine.

6. An intake and exhaust system of an internal combustion engine including an intake system including an air cleaner and an intake passage connecting the air cleaner and an internal combustion engine, an exhaust system including an exhaust passage connected to the internal combustion engine, and a supercharger provided in the intake passage and the exhaust passage, wherein an EGR device including an EGR passage connecting the intake passage and the exhaust passage and an EGR valve provided in the EGR passage is provided, and the intake system includes an intake bypass passage connecting an upstream pressure portion and a downstream pressure portion of the supercharger in the intake system and a recirculation valve provided in the intake bypass passage, the EGR estimation device for an internal combustion engine estimating an EGR rate at any position within a range from the supercharger in the intake passage to an EGR junction where the EGR passage is connected, The recirculation valve is opened and the EGR valve is fully closed during supercharging so that the EGR gas flows back to the air cleaner side. a control unit that estimates an EGR rate in the intake passage based on an EGR rate in the intake passage before the recirculation valve is opened during a predetermined time period after the EGR valve is fully closed, An EGR estimation device for an internal combustion engine.

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