Reflux gas flow rate estimation device

Abstract

Provided is a reflux gas flow rate estimation device capable of accurately estimating the flow rate of a reflux gas flowing into a cylinder of an internal combustion engine.　A processor of an ECU 21: performs a process for deriving a first flow rate (EGR gas flow rate GEGR(k)) of EGR gas passing through a recirculation passage 10 on the basis of the opening degree of an EGR valve 11 for each stroke of an internal combustion engine 1; derives a second flow rate (EGR gas flow rate GEGR(k−α)) of EGR gas flowing into an intake passage 4 on the basis of the first flow rate derived through a plurality of instances of the aforementioned process; derives a first ratio (intake inlet EGR rate EGRREXin(k)), which is the ratio of the second flow rate to a fresh air flow rate at an inlet of the intake passage 4, on the basis of the second flow rate; and derives a second ratio (cylinder inflow EGR rate EGRREXcyl(k)), which is the ratio of the EGR gas flow rate to the flow rate of fresh air introduced into a cylinder 1a, on the basis of the first ratio.

Description

[Technical Field]

[0001] This invention relates to a reflux gas flow rate estimation device. [Background technology]

[0002] Patent Document 1 describes a surge tank in which fresh air is introduced from the intake system of an engine, while EGR (Exhaust Gas Recirculation) gas is recirculated from the exhaust system of the engine according to the opening degree of the EGR valve, and the fresh air and EGR gas are mixed internally; branches of an intake manifold connecting the surge tank to each cylinder of the engine; a first EGR rate calculation means that calculates the EGR rate in the surge tank each time the mixed gas from the surge tank is transferred through the branches in conjunction with the intake of the engine; an EGR rate storage means that stores the EGR rate of the internal mixed gas as the previous value for each region of the branch that is divided in advance by the transfer stroke of the mixed gas associated with the intake; and the EGR rate calculation means that stores the EGR rate of the internal mixed gas as the previous value for each region of the branch that is divided in advance by the transfer stroke of the mixed gas associated with the intake. The EGR rate estimation device for an internal combustion engine is described, comprising: a second EGR rate calculation means that calculates the EGR rate of the mixed gas in each region after transfer and the EGR rate of the mixed gas introduced into the cylinder, based on the EGR rate in the surge tank calculated by the first EGR rate calculation means, the previous value of the EGR rate of each region stored in the storage means, and a volume change correlation value that correlates with the volume change of the mixed gas in the branch, for each transfer of the mixed gas; and an EGR rate update means that updates the EGR rate in the storage means with the calculated EGR rate of the mixed gas in each region for each calculation by the second EGR rate calculation means. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2004-011618 [Overview of the project] [Problems that the invention aims to solve]

[0004] The technology of the present disclosure aims to provide a recirculation gas flow rate estimation device that can accurately estimate the recirculation gas flow rate flowing into the cylinder of an internal combustion engine.

Means for Solving the Problems

[0005] A recirculation gas flow rate estimation device according to one aspect of the technology of the present disclosure is a recirculation gas flow rate estimation device for estimating the recirculation gas flow rate flowing into the cylinder of an internal combustion engine provided with a recirculation gas valve for adjusting the amount of recirculation gas recirculated from the exhaust passage of the internal combustion engine to the intake passage through the recirculation passage, comprising a processor, and the processor performs a process of deriving a first flow rate of the recirculation gas passing through the recirculation passage based on the opening degree of the recirculation gas valve for each step of the internal combustion engine. It was performed before the prescribed number of times. Based on the first flow rate derived by the plurality of times of the above processing, a second flow rate of the recirculation gas flowing into the intake passage is derived, and based on the second flow rate, a first ratio which is the ratio of the second flow rate to the fresh air flow rate at the inlet of the intake passage is derived, and based on the first ratio, a second ratio which is the ratio of the recirculation gas flow rate to the fresh air flow rate introduced into the cylinder is derived. Based on the second ratio and the total flow rate of the cylinder introduced into the cylinder, the processor estimates the flow rate of recirculating gas flowing into the cylinder. When the space of the intake passage connecting the outlet of the recirculating passage and the cylinder is divided into multiple regions, the processor derives the ratio of recirculating gas in the gas flowing into the most upstream region based on the first ratio. Based on the value of the ratio from one step prior, the processor derives the ratio of recirculating gas in the gas flowing into each region downstream of the most upstream region, and the ratio derived for the most downstream region is set as the second ratio. That's what it is.

Effects of the Invention

[0006] According to the technology of the present disclosure, it is possible to provide a recirculation gas flow rate estimation device that can accurately estimate the recirculation gas flow rate flowing into the cylinder of an internal combustion engine.

Brief Description of the Drawings

[0007] [Figure 1] FIG. 1 is an overall configuration diagram of an internal combustion engine 1 including an ECU 21 as a recirculation gas flow rate estimation device according to an embodiment of the technology of the present disclosure. [Figure 2] FIG. 2 is a diagram schematically showing the connection state between one cylinder and each gas flow path in the internal combustion engine shown in FIG. 1. [Figure 3] FIG. 3 is a schematic diagram showing a spatial model of the intake passage. [Figure 4]Figure 4 is a flowchart illustrating the method for deriving the cylinder inflow EGR rate. [Modes for carrying out the invention]

[0008] Figure 1 is an overall diagram of an internal combustion engine 1, including an ECU 21 as a recirculating gas flow rate estimation device, which is one embodiment of the technology of this disclosure. Figure 2 is a schematic diagram showing the connection state between one cylinder and each gas flow path in the internal combustion engine shown in Figure 1.

[0009] As shown in Figure 1, the internal combustion engine 1 is configured as an intake manifold injection type inline four-cylinder engine. The space in which the piston 13 (see Figure 2) of each cylinder 1a of the internal combustion engine 1 moves is connected to a surge tank 3 common to each cylinder 1a via a branch 2 of the intake manifold (hereinafter also referred to as the intake manifold). The surge tank 3 is connected to an air cleaner 5 via an outside air passage 7.

[0010] The outside air (fresh air) introduced into the outside air passage 7 via the air cleaner 5 is then introduced into the surge tank 3 after its flow rate is adjusted according to the opening degree of the throttle valve 6. Below, the flow rate of the fresh air flowing into the surge tank 3 is referred to as the fresh air flow rate G. TH The gas introduced into the surge tank 3 moves through each branch 2 of the intake manifold, and after fuel is injected from fuel injectors (not shown) provided in each branch 2, it is introduced into each cylinder 1a as the intake valves 12a (see Figure 2) provided in each cylinder 1a open. The surge tank 3 and each branch 2 constitute the intake passage 4 of the internal combustion engine 1. In the following, the total flow rate of gas flowing into the cylinder 1a in one stroke of the internal combustion engine 1 is defined as the total cylinder flow rate G. CYL It is stated that the volume of cylinder 1a is V. CYL It should be written as follows.

[0011] The interior of each cylinder 1a is connected to an exhaust passage 9 via an exhaust manifold 8. The exhaust passage 9 and the surge tank 3 are connected by a recirculation passage 10. The recirculation passage 10 is provided with an EGR valve 11 for adjusting the amount of recirculation gas (hereinafter referred to as EGR gas) that is recirculated from the exhaust passage 9 through the recirculation passage 10 to the intake passage 4.

[0012] The injected fuel introduced into the cylinder 1a together with the gas present in the intake passage 4 is ignited at a predetermined timing by the ignition plug 12 (see FIG. 1) of each cylinder 1a. The exhaust gas after combustion of the injected fuel is discharged from the inside of the cylinder 1a as the exhaust valve 12b shown in FIG. 2 opens. A part of this exhaust gas is discharged to the outside through the exhaust manifold 8, the exhaust passage 9, and a catalyst (not shown). The remainder of this exhaust gas is recirculated as EGR gas from the recirculation passage 10 into the surge tank 3 according to the opening degree of the EGR valve 11. The control of opening the EGR valve 11 to recirculate the EGR gas to the intake passage 4 is referred to as EGR control.

[0013] Hereinafter, the flow rate of the EGR gas recirculated into the surge tank 3 for each stroke of the internal combustion engine 1 during EGR control is denoted as the EGR flow rate G EGR Also, the total flow rate of the gas flowing into the intake passage 4 for each stroke of the internal combustion engine 1 (the sum of the fresh air flow rate G TH and the EGR flow rate G EGR during the execution of EGR control) is denoted as the intake total flow rate G IN Also, the flow rate of the fresh air excluding the EGR gas out of the cylinder total flow rate G CYL is denoted as the cylinder fresh air flow rate G AIRCYL Also, the flow rate of the EGR gas out of the cylinder total flow rate G CYL is denoted as the cylinder EGR flow rate G EGRCYL

[0014] ​An ECU (Electronic Control Unit) 21 is installed in the passenger compartment of a vehicle equipped with an internal combustion engine 1. The ECU 21 comprises an input / output device, a storage device such as RAM (Random Access Memory), ROM (Read Only Memory), SSD (Solid State Drive), or HDD (hard disk drive), and a processor such as a CPU (Central Processing Unit). The ECU 21 performs various processes by having the processor execute programs stored in the storage device. The ECU 21 controls the intake valve 12a, exhaust valve 12b, spark plug 12, and EGR valve 11. The ECU 21 controls the volumetric efficiency η of the internal combustion engine 1 by variably controlling the opening and closing timing of the intake valve 12a and exhaust valve 12b. V The volumetric efficiency η (an index indicating the intake capacity of internal combustion engine 1) can be changed. V The larger the value of , the greater the amount of gas flowing into cylinder 1a in one stroke of internal combustion engine 1, and therefore the greater the distance the gas in intake passage 4 travels in one stroke.

[0015] ECU21 is cylinder fresh airflow G AIRCYL Based on this, the ignition timing of the spark plug 12 is determined, thereby optimizing the combustion air-fuel ratio in the internal combustion engine 1. The above-mentioned EGR control can be switched on and off by the ECU 21 as needed. Even during the transition period when this EGR control switches from off to on, or when it switches from on to off, the cylinder fresh air flow rate G AIRCYL Accurately estimating this is crucial for optimizing the combustion air-fuel ratio.

[0016] The internal combustion engine 1 is equipped with a sensor group 22, which includes a sensor for detecting the rotational speed of the internal combustion engine 1, a sensor for detecting the pressure PBA in the intake passage 4, and a sensor for detecting the temperature TA in the intake passage 4. The output of the sensor group 22 is transmitted to the ECU 21. Information on the opening degree of the EGR valve 11 and the opening degree of the throttle valve 6 is also transmitted to the ECU 21.

[0017] The ECU 21 estimates the flow rate of EGR gas flowing into cylinder 1a by deriving the cylinder inflow EGR rate EGRREXcyl, which is the proportion of EGR gas in the gas flowing into cylinder 1a, based on information from sensor group 22, information on the opening degree of EGR valve 11, and information on the opening degree of throttle valve 6. Using this cylinder inflow EGR rate EGRREXcyl, the cylinder fresh gas flow rate G AIRCYL It is possible to estimate this.

[0018] In this configuration, the space of the intake passage 4 connecting the outlet 10A of the recirculation passage 10 (the connection point between the recirculation passage 10 and the surge tank 3) and each cylinder 1a (space SP shown in Figure 2) is divided into N regions (where N is a natural number greater than or equal to 2) as shown in Figure 3 (in the example of Figure 3, there are three regions: R1, R2, and R3). A spatial model is adopted in which the EGR gas G flowing into space SP is sequentially transported to adjacent regions while diffusing with each stroke of the internal combustion engine 1. In other words, the EGR gas G that flows into region R1 at the end of one stroke moves to region R2 by diffusing with fresh air after the next stroke of the internal combustion engine 1 is completed. The EGR gas G that flows into region R2 moves to region R3 by further diffusing with fresh air after the next stroke of the internal combustion engine 1 is completed. Then, when the next stroke of the internal combustion engine 1 is started, the gas present in region R3 is introduced into the cylinder 1a.

[0019] Furthermore, as mentioned above, the volumetric efficiency η V As the volumetric efficiency η increases, the distance the gas moves (diffusion) in each step within the spatial SP increases. Therefore, by reducing the number of divisions of the spatial SP in the above spatial model, a spatial model suitable for the operating conditions of the internal combustion engine 1 can be created. In other words, the number of divisions of the spatial SP is equal to the volumetric efficiency η. V It is preferable to make it inversely proportional to. Below, the proportion of EGR gas in the gas at the inlet of this space SP (i.e., region R1 shown in Figure 3) will be referred to as the intake inlet EGR rate EGRREXin. Also, the volume of space SP is V IN It should be written as follows.

[0020] (Cylinder fresh air flow rate G) AIRCYL (Derivation of) In the following explanation, the flow rates and EGR rates at the start of a stroke of internal combustion engine 1 are denoted by the subscript (k), and the flow rates and EGR rates at the start of the stroke immediately preceding that stroke are denoted by the subscript (k-1).

[0021] Total cylinder flow rate G CYL (k) is obtained by solving the ideal gas law in cylinder 1a and the ideal gas law in space SP. The total flow rate G of this cylinder. CYL By multiplying (k) by (1-EGRREXcyl(k)), the cylinder fresh air flow rate G is obtained. AIRCYL (k) can be derived.

[0022] The ideal gas law in cylinder 1a is given by equation (A) below.

[0023]

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[0024] Differentiating both sides of equation (A) yields equation (B), where R is the gas constant.

[0025]

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[0026] The ideal gas law in space SP is given by equation (C) below.

[0027]

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[0028] Differentiating both sides of equation (C) yields equation (D) below.

[0029]

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[0030] Solving equation (D) for the derivative of pressure PBA yields the following equation (E).

[0031]

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[0032] Substitute equation (E) into equation (B) to get the total cylinder flow rate G CYL Solving for (k), we obtain the following equation (F).

[0033]

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[0034] Here, cylinder fresh air flow rate G AIRCYL (k-1) is the total cylinder flow rate G in equation (F). CYL Since this is the value obtained by multiplying (k-1) by (1-EGRREXcyl(k-1)), the relationship in equation (G) holds.

[0035]

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[0036] Also, new airflow G TH (k) is the total intake flow rate G in equation (F). IN Since (k) is the value obtained by multiplying it by (1-EGRREXin(k)), the relationship in equation (H) holds.

[0037]

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[0038] Formula (G) represents the total flow rate of the cylinder G CYL Solve for (k-1) and express equation (H) as the total intake flow rate G IN Solving for (k) and substituting each of them into the equation obtained by multiplying both sides of equation (F) by (1-EGRREXcyl(k)), we obtain the following equation (I).

[0039]

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[0040] Therefore, if the intake inlet EGR rate EGRREXin(k) and the cylinder inlet EGR rate EGRREXcyl(k) can be accurately estimated, then the cylinder fresh air flow rate G AIRCYL (k) can be derived with high accuracy. Next, the method for deriving the intake inlet EGR rate EGRREXin and the cylinder inlet EGR rate EGRREXcyl will be explained.

[0041] (Derivation of intake inlet EGR rate EGRREXin and cylinder inlet EGR rate EGRREXcyl) The intake inlet EGR rate EGRREXin and the cylinder inlet EGR rate EGRREXcyl are calculated using the following formulas (J) and (K), respectively.

[0042]

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[0043] In the internal combustion engine 1, there is a time lag between the opening of the EGR valve 11 and the arrival of the EGR gas in the return passage 10 at region R1 in Figure 3. Therefore, when the ECU 21 derives the intake inlet EGR rate EGRREXin(k), the EGR flow rate G is obtained based on the most recent information on the opening degree of the EGR valve 11. EGR Instead of using (k), the EGR flow rate G is obtained based on the information of the opening degree of the EGR valve 11 a predetermined number of times before the process, taking into account the time lag. EGR We use (k-α). The value of α can be any value greater than or equal to 1, but in the following explanation, we will assume α=1.

[0044] To achieve this, the ECU21 controls the EGR flow rate G for each process. EGR When this value is obtained, it is stored in memory, and the EGR flow rate G for the past multiple processes is recorded. EGR Keep this value. And the EGR flow rate G for these multiple processes. EGRBased on this, the flow rate of EGR gas flowing into the intake passage 4 (space SP) before the start of the current process is derived. Specifically, as described above, the ECU21 calculates the EGR flow rate G for multiple processes. EGR From among these, the EGR flow rate G obtained at the end of the process α times earlier EGR This is defined as the flow rate of EGR gas that will enter the space SP during the next process. The ECU21 then derives the intake inlet EGR rate EGRREXin(k) by performing the calculation shown in the following equation (Ka). In this way, by considering the recirculation delay of the EGR gas, the cylinder inlet EGR rate EGRREXcyl(k) can be derived with high accuracy.

[0045]

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[0046] Figure 4 is a flowchart illustrating the method for deriving the cylinder inflow EGR rate EGRREXcyl(k). The ECU21 adjusts the fresh air flow rate G based on the information of the throttle valve 6 opening. TH (k) is obtained (step S1). Also, based on the information of the opening degree of the EGR valve 11, the EGR flow rate G is obtained. EGR (k) is obtained and stored in memory (step S2).

[0047] ECU21 retrieves the EGR flow rate G from memory. EGR (k-1) is read and obtained, and this EGR flow rate G EGR (k-1) and new airflow G TH Based on (k), the calculation of equation (Ka) is performed to derive the intake inlet EGR rate EGRREXin(k) (step S3).

[0048] Next, ECU21 controls the EGR flow rate G EGR (k-1) and new airflow G TH Based on (k) and various information regarding the space SP, a delay coefficient C(k) is derived by the calculation of the following equation (L) in order to consider the movement and diffusion of gas in the space SP for each process (step S4).

[0049]

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[0050] Next, the ECU21 uses the intake inlet EGR rate EGRREXin(k), the EGR rate R1(k-1) of region R1 one stroke prior, and the delay coefficient C(k) to derive the current EGR rate R1(k) of region R1 by the calculation of the following equation (M) (step S5).

[0051] R1(k) =(1-C(k))×R1(k-1)+C(k)×EGRREXin(k) ···(M)

[0052] Next, the ECU21 uses the EGR rate R2(k-1) of region R2 from the previous step, the EGR rate R1(k-1) of region R1 from the previous step, and the delay coefficient C(k) to derive the current EGR rate R2(k) of region R2 by performing the calculation shown in equation (N) below (step S6).

[0053] R2(k) =(1-C(k))×R2(k-1)+C(k)×R1(k-1) ···(N)

[0054] Next, the ECU21 uses the EGR rate R3(k-1) of region R3 from the previous step, the EGR rate R2(k-1) of region R2 from the previous step, and the delay coefficient C(k) to derive the current EGR rate R3(k) of region R3 by performing the calculation shown in equation (O) below (step S7). The EGR rate R3(k) derived in step S7 is the EGR rate of the gas flowing into cylinder 1a in the next step, and is the cylinder inflow EGR rate EGRREXcyl(k).

[0055] R3(k) =(1-C(k))×R3(k-1)+C(k)×R2(k-1) ···(O)

[0056] ECU21 uses the intake inlet EGR rate EGRREXin(k) derived in step S3, the cylinder inlet EGR rate EGRREXcyl(k) derived in step S7, and the cylinder fresh air flow rate G derived in the previous process. AIRCYL (k-1) and volume V IN , volume V CYL Pressure PBA, gas constant R, temperature TA, and volumetric efficiency η V By performing the calculation in equation (I) using and, the cylinder fresh air flow rate G AIRCYL (k) is derived. Then, ECU21 determines the new airflow rate G of this cylinder. AIRCYL Ignition control is performed based on (k).

[0057] As described above, this embodiment derives the cylinder inflow EGR rate by considering the time it takes for the EGR gas that has passed through the EGR valve 11 to flow into the cylinder 1a, and the delay in the response of the change in the amount of EGR gas that has passed through to the change in the EGR gas flowing into the cylinder. This improves the accuracy of the estimation of the cylinder inflow EGR rate. This improved estimation accuracy leads to an optimized combustion air-fuel ratio and ignition timing, thereby improving marketability.

[0058] Furthermore, in this configuration, a divided space model is formed by dividing the intake passage 4 downstream of the connection point between the recirculation passage 10 and the surge tank 3 into multiple sections. Using this model, in which the EGR gas diffuses within the space SP and flows into the cylinder 1a with each stroke of the internal combustion engine, the cylinder inflow EGR rate is derived, taking into account the wasted time for EGR gas inflow and the delay in tracking changes. As a result, the estimation accuracy of the cylinder inflow EGR rate is improved. Improved estimation accuracy leads to an optimized combustion air-fuel ratio and ignition timing, thereby improving marketability.

[0059] Furthermore, according to this form, the volume efficiency η V Since the number of divisions in the spatial SP is changed accordingly, it becomes possible to estimate an appropriate cylinder inflow EGR rate according to the operating status of the internal combustion engine 1.

[0060] This specification contains at least the following information. Note that the components etc. in parentheses indicate those corresponding to the embodiments described above, but are not limited thereto.

[0061] (1) A recirculating gas flow rate estimation device (ECU21) for an internal combustion engine (internal combustion engine 1) is equipped with a recirculating gas valve (EGR valve 11) that adjusts the amount of recirculated gas that is recirculated from the exhaust passage (exhaust passage 9) of the internal combustion engine (internal combustion engine 1) through the recirculation passage (recirculation passage 10) to the intake passage (intake passage 4), and estimates the recirculating gas flow rate into the cylinder (cylinder 1a) of the internal combustion engine. Equipped with a processor, The aforementioned processor, For each stroke of the internal combustion engine, based on the opening of the recirculating gas valve, the first flow rate (EGR flow rate G) of the recirculating gas passing through the recirculating passage is controlled. EGR Perform the process to derive (k), Based on the first flow rate derived by the multiple processes described above, the second flow rate (EGR flow rate G) of the recirculating gas flowing into the intake passage is determined. EGR Derive (k-α), Based on the second flow rate, the first ratio (intake inlet EGR rate EGRREXin(k)), which is the ratio of the second flow rate to the fresh air flow rate at the inlet of the intake passage, is derived. A recirculating gas flow rate estimation device that derives a second ratio (cylinder inflow EGR rate EGRREXcyl(k)), which is the ratio of the recirculating gas flow rate to the fresh gas flow rate introduced into the cylinder, based on the first ratio.

[0062] According to (1), the second flow rate of recirculated gas flowing into the intake passage is derived based on the first flow rate derived through multiple processes, and the second ratio is derived based on this second flow rate, thereby improving the accuracy of the second ratio. By improving the accuracy of the second ratio, the combustion air-fuel ratio can be optimized. In particular, the combustion air-fuel ratio can be optimized even during the transient period when switching between executing and not executing the control to recirculate the recirculated gas into the intake passage, improving the marketability of vehicles equipped with internal combustion engines.

[0063] (2) (1) The reflux gas flow rate estimation device described above, The processor divides the space (space SP) of the intake passage connecting the outlet of the recirculation passage and the cylinder into a plurality of regions (region R1, region R2, region R3), derives the proportion of recirculated gas (EGR rate R1(k)) of the gas flowing into the upstreammost region (region R1) based on the first proportion, derives the proportion of recirculated gas (EGR rate R2(k), EGR rate R3(k)) of the gas flowing into each region (region R2, region R3) downstream of the upstreammost region based on the value of the proportion one step prior (EGR rate R1(k-1)), and sets the proportion (EGR rate R3(k)) derived for the downstreammost region (region R3) as the second proportion, thereby determining the recirculation gas flow rate estimation device.

[0064] According to (2), the second ratio is derived by simulating the process in which the recirculated gas diffuses with each stroke of the internal combustion engine, thus improving the estimation accuracy of the second ratio when switching between executing and not executing the control to recirculate the recirculated gas into the intake passage. This improved estimation accuracy allows for optimization of the combustion air-fuel ratio, improving the marketability of vehicles equipped with internal combustion engines.

[0065] (3) (2) The reflux gas flow rate estimation device described above, The aforementioned processor, The opening and closing timing of the valves (intake valve 12a and exhaust valve 12b) connected to the cylinder is variably controlled. An index value (volumetric efficiency η) indicating the suction capacity of the internal combustion engine, determined based on the opening and closing timing. V A recirculating gas flow rate estimation device that changes the number of divisions of the space based on ).

[0066] According to (3), even when the load on the internal combustion engine is transient when the valve opening and closing timing is variable, the number of spatial divisions is optimized according to the load, thereby improving the estimation accuracy of the second ratio. [Explanation of symbols]

[0067] 1. Internal combustion engine 1a Cylinder 4 Intake passage 9 Exhaust passage 10 Reflux passage 11 EGR valve 21 ECU

Claims

1. A recirculating gas flow rate estimation device for estimating the recirculating gas flow rate into a cylinder of an internal combustion engine, which is equipped with a recirculating gas valve that adjusts the amount of recirculating gas recirculated from the exhaust passage of the internal combustion engine through a recirculation passage to the intake passage, Equipped with a processor, The aforementioned processor, For each step of the internal combustion engine, a process is performed to derive a first flow rate of the recirculating gas passing through the recirculating passage based on the opening degree of the recirculating gas valve. Based on the first flow rate derived by the multiple processes performed before a predetermined number of times, a second flow rate of recirculating gas flowing into the intake passage is derived. Based on the second flow rate, a first ratio is derived, which is the ratio of the second flow rate to the fresh air flow rate at the inlet of the intake passage. Based on the first ratio, a second ratio is derived, which is the ratio of the recirculated gas flow rate to the fresh gas flow rate introduced into the cylinder. Based on the second ratio and the total flow rate of the cylinder introduced into the cylinder, the flow rate of the recirculating gas flowing into the cylinder is estimated. The processor divides the space of the intake passage connecting the outlet of the recirculation passage and the cylinder into a plurality of regions, derives the proportion of recirculated gas in the gas flowing into the most upstream region based on the first proportion, derives the proportion of recirculated gas in the gas flowing into each region downstream of the most upstream region based on the value of the proportion one step prior, and sets the proportion derived for the most downstream region as the second proportion.

2. A reflux gas flow rate estimation device according to claim 1, The aforementioned processor, The opening and closing timing of the valve connected to the cylinder is variably controlled. A recirculating gas flow rate estimation device that changes the number of divisions of the space based on an index value indicating the suction capacity of the internal combustion engine, which is determined based on the opening and closing timing.

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