Method for calculating the oxygen concentration in the intake air of an internal combustion engine.

Abstract

The oxygen concentration of the gas in the intake manifold of an internal combustion engine is calculated simply. 【Solution means】The intake manifold oxygen concentration y of the previous cycle in,o2 s-1 and the exhaust manifold oxygen concentration y ex,o2 s-1 and the supplied air mass m a the fuel injection amount m f and the mass m of the recirculated gas e Based on these, the exhaust manifold oxygen concentration y of the current cycle ex,o2 s is calculated. Next, the recirculated gas oxygen concentration y of the previous cycle egr,o2 s-1 and the exhaust manifold oxygen concentration y of the current cycle ex,o2 s Based on these, the recirculated gas oxygen concentration y of the current cycle egr,o2 s is calculated. Finally, the intake manifold oxygen concentration y of the previous cycle in,o2 s-1 and the recirculated gas oxygen concentration y of the current cycle egr,o2 s Based on these and the exhaust gas recirculation rate egr, the intake manifold oxygen concentration y of the current cycle in,o2 s is calculated.

Description

Technical Field

[0001] The present invention relates to a method for calculating the oxygen concentration of intake air in an internal combustion engine.

Background Art

[0002] In an internal combustion engine, the oxygen concentration and the amount of fuel in the intake air supplied to the cylinder are important parameters in engine control. The combustion state, such as the combustion rate of fuel, changes depending on the oxygen concentration in the intake air, which affects the engine output and the components in the exhaust gas. Therefore, it is desirable to accurately obtain the oxygen concentration in the intake air. Patent Document 1 below discloses a technique for calculating the oxygen concentration of intake air in consideration of fluctuations in exhaust gas recirculation (EGR).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the transient operation of an internal combustion engine, since the fuel supply amount (fuel injection amount), the exhaust gas recirculation amount, etc. change, the composition of the exhaust gas fluctuates over time. As a result, the composition of the recirculation gas and further the composition of the intake gas in the intake manifold also fluctuate over time, and these fluctuate with a delay with respect to the fluctuation of the exhaust gas composition.

[0005] An object of the present invention is to easily obtain the oxygen concentration of intake gas that fluctuates with a delay with respect to the fluctuation of the composition in the exhaust gas.

Means for Solving the Problems

[0006] A method for calculating the oxygen concentration in the intake gas in the intake manifold according to the present invention is, A step of calculating the current cycle exhaust manifold oxygen concentration, which is the oxygen concentration of the gas in the exhaust manifold in the current cycle, based on the previous cycle intake manifold oxygen concentration, which is the oxygen concentration of the gas in the intake manifold in the previous cycle, the previous cycle exhaust manifold oxygen concentration, which is the oxygen concentration of the gas in the exhaust manifold in the previous cycle, and the mass of the supply air, fuel injection amount, and recirculated gas in the current cycle. The steps include: calculating the current cycle recirculating gas oxygen concentration, which is the oxygen concentration of the recirculating gas in the current cycle, based on the previous cycle recirculating gas oxygen concentration, which is the oxygen concentration of the recirculating gas in the previous cycle, and the current cycle exhaust manifold oxygen concentration; A step of calculating the current cycle intake manifold oxygen concentration, which is the oxygen concentration of the gas in the intake manifold in the current cycle, based on the previous cycle intake manifold oxygen concentration, the current cycle recirculated gas oxygen concentration, and the exhaust gas recirculation rate of the current cycle. This method includes [something].

[0007] By using a simplified model that divides the recirculated gas flow into three regions—the exhaust manifold, the recirculation pipe, and the intake manifold—the computational load required to calculate the oxygen concentration in the intake manifold is reduced.

[0008] Furthermore, the step of calculating the current cycle exhaust manifold oxygen concentration may be performed by using the exhaust manifold residual gas ratio, which is the percentage of gas present in the exhaust manifold in the previous cycle that remains until the current cycle, as a constant to calculate the current cycle exhaust manifold oxygen concentration. Furthermore, the step of calculating the current cycle recirculating gas oxygen concentration may be performed by using the recirculating pipe residual gas ratio, which is the proportion of gas present in the recirculating pipe in the previous cycle that remains until the current cycle, as a constant, and calculating the current cycle recirculating gas oxygen concentration. Furthermore, the step of calculating the current cycle intake manifold oxygen concentration may be performed by using the intake manifold residual gas ratio, which is the percentage of gas present in the intake manifold in the previous cycle that remains until the current cycle, as a constant, and calculating the current cycle intake manifold oxygen concentration.

[0009] By treating the residual percentage of the gas from the previous cycle as a constant in the exhaust manifold, recirculation pipe, and intake manifold, the computational load involved in calculating the oxygen concentration can be reduced. [Effects of the Invention]

[0010] The computational load required to calculate the intake manifold oxygen concentration is reduced, making it possible to calculate the intake manifold oxygen concentration using a small processing device such as one installed in a vehicle. [Brief explanation of the drawing]

[0011] [Figure 1] This diagram shows a schematic configuration of a power system including an internal combustion engine. [Figure 2] This is a flowchart for calculating the oxygen concentration of the gas in the intake manifold. [Figure 3] This figure compares the oxygen concentration of the gas in the intake manifold calculated by each model. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will now be described with reference to the drawings. Figure 1 is a diagram showing the schematic configuration of a vehicle drive power unit 10 of this embodiment. The power unit 10 includes a reciprocating internal combustion engine 12. The internal combustion engine 12 may be a compression ignition engine. The internal combustion engine 12 has a plurality of cylinders 14. The illustrated internal combustion engine 12 has four cylinders arranged in series, but the number of cylinders is not limited to this, nor is the cylinder arrangement limited to this. The power unit 10 further includes an intake system 16 related to supplying air to the internal combustion engine 12, an exhaust system 18 related to the discharge of exhaust from the internal combustion engine 12, and an exhaust recirculation device 20 that returns a portion of the exhaust from the internal combustion engine 12 to the intake and circulates it.

[0013] The intake system 16 includes an intake pipe 22 through which intake air to the internal combustion engine 12 flows, a throttle valve 24 arranged along the intake pipe 22, a turbocharger 26, and an intercooler 28. The intake air flowing through the intake pipe 22 passes through the throttle valve 24, the compressor 30 of the turbocharger 26, and the intercooler 28 in that order. The throttle valve 24 is, for example, a butterfly valve, and its operation can change the flow path cross-sectional area of ​​the intake pipe 22. By reducing the flow path cross-sectional area, i.e., by throttling, the pressure of the intake air in the intake pipe 22 downstream of the throttle valve 24 can be reduced. The turbocharger 26 compresses the intake air using the exhaust energy of the internal combustion engine 12. A turbine wheel located inside the turbine 32 of the turbocharger 26 is rotated by the exhaust. A compressor wheel that rotates together with the turbine wheel is located inside the compressor 30 of the turbocharger 26. The compressor 30 functions as a centrifugal compressor to compress the intake air. The compressed and heated intake air is cooled in the intercooler 28 by outside air or the coolant of the internal combustion engine 12. Furthermore, the intake air is distributed and supplied to each cylinder 14 via the intake manifold 36.

[0014] A fuel injector 38 is provided for each cylinder 14, which injects fuel directly into the cylinder 14 at a predetermined timing. The fuel may be a hydrocarbon such as diesel fuel. The injected fuel burns due to the high-temperature gas compressed within the cylinder 14. The exhaust from each cylinder 14 after combustion is combined by an exhaust manifold 40 and sent to a turbocharger 26.

[0015] The exhaust system 18 includes an exhaust pipe 42, a turbocharger 26 installed in the exhaust pipe 42, and an exhaust gas purification device (not shown) installed in the exhaust pipe 42 downstream of the turbocharger 26. The turbocharger 26 has a turbine wheel that is rotated by the exhaust gas as described above, and the rotation of the turbine wheel is transmitted to a compressor wheel. The exhaust gas that has passed through the turbine 32 of the turbocharger 26 is sent by the exhaust pipe 42 to the exhaust gas purification device located further downstream.

[0016] The exhaust gas recirculation device 20 includes a recirculation pipe 44 that guides the exhaust gas from the internal combustion engine 12 from the exhaust manifold 40 or exhaust pipe 42 to the intake pipe 22, and a recirculation valve 46 that adjusts the flow rate of the exhaust gas flowing through the recirculation pipe 44. By adjusting the opening degree of the recirculation valve 46, the amount of exhaust gas mixed with the intake air is adjusted.

[0017] The operation of the power unit 10 is controlled based on a plurality of physical quantities that indicate the operating state of the power unit 10. The power unit 10 includes a control device 48, which controls the operation of the power unit 10 by controlling each operating component of the power unit 10 based on the input physical quantities. For example, the control device 48 receives input such as the amount the driver operates the accelerator pedal 50, engine rotation speed, vehicle speed, coolant temperature, intake air flow rate, intake air temperature, and exhaust air temperature, and the control device 48 controls the amount of fuel injected from the fuel injector 38 and the operation of the recirculation valve 46 so that the output required by the driver is obtained.

[0018] The intake manifold 36 is equipped with an intake manifold gas temperature sensor 52 that detects the intake manifold gas temperature, which is the temperature of the intake air newly supplied into the cylinder 14. The intake manifold 36 is further equipped with an intake pressure sensor 54 that detects the intake pressure (intake manifold internal pressure). The internal combustion engine 12 is equipped with a rotational speed sensor 56 that detects the rotational speed of the internal combustion engine 12. The intake pipe 22 is equipped with an intake flow sensor 58 that detects the intake air flow rate through the intake pipe 22.

[0019] The oxygen concentration of the intake air newly supplied to cylinder 14 affects the combustion state within the cylinder. By calculating the oxygen concentration of the intake air in real time using an on-board device, the internal combustion engine can be controlled with greater precision. The control device 48 has the function of calculating the oxygen concentration of the intake air supplied to cylinder 14 and controls the fuel injection amount, etc., based on the calculated oxygen concentration.

[0020] FIG. 2 is a flowchart showing a process for calculating the oxygen concentration of the air-fuel mixture in the intake manifold 36 in a non-steady state. First, assuming that the internal combustion engine 12 is operating in a steady state, the oxygen concentration of the gas in the intake manifold 36 is calculated, and this value is used as an initial value to calculate the oxygen concentration of the gas in the intake manifold 36 in a non-steady state. Table 1 shows the parameters used below.

[0021]

Table 1

[0022] First, a numerical value s indicating the number of combustion cycles of the internal combustion engine 12 is set to an initial value of 0 (S100). Next, the mass of air supplied to the cylinder per stroke (supply air mass m a [g / stroke]) is calculated based on the following equation (1) (S102). m a =120×G a / rpm ···(1) The supply air flow rate G a is the flow rate of air flowing through the intake pipe 22, which is detected by the intake flow rate sensor 58.

[0023] Assuming that the operating state of the internal combustion engine 12 is steady, the oxygen concentration y ex,o2 of the exhaust gas is calculated (S104). The chemical formula when the fuel (CnHm) is completely burned is as follows equation (2). CnHm+(n+0.25m)O2→ nCO2+0.5mH2O ···(2) (12n+m)[g] 32(n+0.25m)[g] m f [g] 32m f (n+0.25m) / (12n+m)[g] m f is the amount of fuel injected per stroke from the fuel injection valve 38, that is, the fuel injection amount. The fuel injection amount m f can be obtained in relation to the operation control of the fuel injection valve 38. From the law of conservation of mass, the following equation (3) is obtained.

[0024]

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[0025] Equation (3) is used to express the oxygen concentration y of the gas in the exhaust manifold. ex,o2 Solving for this, we obtain equation (4).

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[0026] Assuming the internal combustion engine 12 is operating in a steady state, the oxygen concentration y of the recirculated gas in the recirculation pipe 44 egr,o2 This is the oxygen concentration of the gas in the exhaust manifold. ex,o2 It is equal to (S106). y egr,o2 =y ex,o2 ...(5)

[0027] Furthermore, the exhaust gas recirculation rate egr, which is the ratio of recirculated gas to the gas supplied to the cylinder, is determined by the supply air flow rate G a , gas pressure P in the intake manifold in , and temperature T in Based on this, the following equations (6-1) to (6-4) can be used to determine the supply air flow rate G (S108). a Pressure P in , and temperature T in These are detected by the intake air flow sensor 58, the intake pressure sensor 54, and the intake manifold gas temperature sensor 52, respectively. m a = 120 × G a / rpm ···(6-1) m cyl =η V (W avg P in V in ) / (RT in ) ···(6-2) m e =m cyl -m a ...(6-3) egr=m e / (m a +m e ) ···(6-4) Here, W avg V is the average molecular weight of the gas in the intake manifold. in This is the volume inside cylinder 14 when the intake valve is closed, that is, when the intake of air into cylinder 14 has ended.

[0028] Using the exhaust gas recirculation rate egr, the oxygen concentration y of the gas in the intake manifold is... in,o2 This is given by the following equation (7) (S110).

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[0029] Next, the oxygen concentration y of the gas in the intake manifold during the transient state, i.e., the non-steady state, of the internal combustion engine 12. in,o2 Perform the calculation.

[0030] First, the cycle count value s is updated (S112), and the mass of the supplied air is calculated in the same way as in step S102 (S114). Below, the parameter y related to the oxygen concentration is... ex,o2 ,y egr,o2 ,y in,o2 The superscript attached to a parameter indicates the cycle in which that parameter was calculated.

[0031] Current cycle(s) oxygen concentration y of the gas in the exhaust manifold ex,o2 s Assuming complete combustion, the oxygen concentration y of the gas in the intake manifold from the previous cycle (s-1) is... in,o2 s-1 Using this, we obtain equation (8) from the equation for conservation of mass.

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[0032] In a transient state, the oxygen concentration y of the gas inside the exhaust manifold ex,o2 Because some of the gas from the previous cycle remains in the exhaust manifold 40, the oxygen concentration y, as expressed by equation (8), is... ex,o2 This is not the case. If we let the percentage of gas from the previous cycle remaining in the exhaust manifold 40 (exhaust manifold residual gas percentage) be a constant c1, then the current oxygen concentration y of the gas in the exhaust manifold is... ex,o2 s This is given by the following equation (9) (S116).

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[0033] Similarly, the current oxygen concentration y of the recirculated gas in the recirculation pipe 44 egr,o2 s If the percentage of gas remaining from the previous cycle (recirculation pipe residual gas percentage) is a constant c2, then the following equation (10) is obtained (S118).

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[0034] The exhaust gas recirculation rate egr is calculated in the same way as in step S108 (S120). Furthermore, the current oxygen concentration y of the gas in the intake manifold is calculated. in,o2 s If the percentage of gas remaining from the previous cycle (percentage of residual gas in the intake manifold) is a constant c3, then the following equation (11) is obtained (S122).

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[0035] The system determines whether to continue the calculation for the non-steady state (S124). If it continues, it returns to step S112; otherwise, it terminates. For example, if it is determined that the operation of the internal combustion engine 12 is in a steady state, such as when the rotational speed of the internal combustion engine 12 is within a range that can be considered constant, and the amount of operation of the accelerator pedal 50 is within a range that can be considered constant, the calculation of the oxygen concentration in the non-steady state described above is terminated.

[0036] The constants c1, c2, and c3, which indicate the residual gas percentage, are identified by comparing the oxygen concentration of the gas in the intake manifold, calculated based on a model using commercially available engine simulation software (for example, "GT-POWER" provided by IDAJ Corporation), with the calculation results according to this embodiment. The oxygen concentration of the gas in the intake manifold calculated using the above equation (11) is y in,o2 The constants c1, c2, and c3 are determined so as to minimize the error in the oxygen concentration of the gas in the intake manifold, as calculated by the simulation software.

[0037] Figure 3 shows the oxygen concentration y in the intake manifold for each calculation method during transient operation (non-steady state) of an internal combustion engine. in,o2 This figure shows the oxygen concentration y calculated by formula (11) of this embodiment. in,o2 The transient model is shown as a solid line, and the calculation result calculated by the commercially available software "GT-POWER" (commercial model) is shown as a dashed line. Furthermore, the calculation result of equation (7) above, that is, the calculation result assuming steady-state operation (steady-state model), is shown as a dotted line. It can be seen that the transient model corresponds more closely to the commercial model.

[0038] Typical simulation models are one-dimensional models that consider transient changes in injection and intake conditions, as well as the length and volume of the intake and exhaust systems. The oxygen concentration calculation method in this embodiment uses a simplified model divided into three regions: the exhaust manifold 40, the recirculation pipe 44, and the intake manifold 36. Furthermore, the residual percentage of gas from the previous cycle is treated as a constant in each of the exhaust manifold 40, the recirculation pipe 44, and the intake manifold 36. As a result, the intake oxygen concentration can be calculated in real time using a small processing device that can be mounted on a vehicle. [Explanation of Symbols]

[0039] 10 Power unit, 12 Internal combustion engine, 14 Cylinder, 16 Intake system, 18 Exhaust system, 20 Exhaust recirculation system, 36 Intake manifold, 38 Fuel injector, 40 Exhaust manifold, 44 Recirculation pipe, 48 Control device, 52 Intake manifold gas temperature sensor, 54 Intake pressure sensor, 56 Rotational speed sensor, 58 Intake flow sensor, m a Mass of supplied air per stroke, m cyl Mass of gas inside the cylinder per stroke, m e Mass of recirculated gas per cycle, m f Fuel injection amount per stroke, y ex,o2 Oxygen concentration of gas in the exhaust manifold, y egr,o2 Oxygen concentration of recirculated gas, y in,o2 Oxygen concentration of the gas in the intake manifold.

Claims

1. A method for calculating the oxygen concentration in the intake gas within the intake manifold, A step of calculating the current cycle exhaust manifold oxygen concentration, which is the oxygen concentration of the gas in the exhaust manifold in the current cycle, based on the previous cycle intake manifold oxygen concentration, which is the oxygen concentration of the gas in the intake manifold in the previous cycle, the previous cycle exhaust manifold oxygen concentration, which is the oxygen concentration of the gas in the exhaust manifold in the previous cycle, and the mass of the supply air, fuel injection amount, and recirculated gas in the current cycle. The steps include: calculating the current cycle recirculating gas oxygen concentration, which is the oxygen concentration of the recirculating gas in the current cycle, based on the previous cycle recirculating gas oxygen concentration, which is the oxygen concentration of the recirculating gas in the previous cycle, and the current cycle exhaust manifold oxygen concentration; A step of calculating the current cycle intake manifold oxygen concentration, which is the oxygen concentration of the gas in the intake manifold in the current cycle, based on the previous cycle intake manifold oxygen concentration, the current cycle recirculated gas oxygen concentration, and the exhaust gas recirculation rate of the current cycle. A method that includes this.

2. The method according to claim 1, The step of calculating the current cycle exhaust manifold oxygen concentration is a step of calculating the current cycle exhaust manifold oxygen concentration using the exhaust manifold residual gas ratio, which is the percentage of gas present in the exhaust manifold in the previous cycle that remains until the current cycle, as a constant. The step of calculating the current cycle recirculating gas oxygen concentration is a step of calculating the current cycle recirculating gas oxygen concentration by using the recirculating pipe residual gas ratio, which is the proportion of gas present in the recirculating pipe in the previous cycle that remains until the current cycle, as a constant. The step of calculating the current cycle intake manifold oxygen concentration involves using the intake manifold residual gas ratio, which is the percentage of gas present in the intake manifold from the previous cycle that remains in the current cycle, as a constant, to calculate the current cycle intake manifold oxygen concentration. method.

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