Control device for internal combustion engine

Abstract

This control device controls an internal combustion engine by estimating an in-cylinder gas temperature (Tgas) during compression from an in-cylinder gas temperature (Tivc) of the internal combustion engine during intake valve closure IVC, which is when compression starts. The control device calculates the in-cylinder gas temperature (Tivc) as a weighted average of a temperature (Tegrin) of internal EGR gas and a new gas temperature (Tinit) during intake valve closure IVC of the valve through which gas is drawn in. During a warm-up process, which is the period following the start of the internal combustion engine in which the combustion chamber wall temperature has not yet reached a steady-state value and is still rising, the control device calculates the in-cylinder gas temperature (Tivc n) at time n step using the new gas temperature (Tinit n) and the combustion chamber wall temperature (Twall n) at the time n step.

Description

Control device for internal combustion engine

[0001] The present invention relates to a control device for an internal combustion engine.

[0002] The in-cylinder gas temperature during the compression process of a reciprocating internal combustion engine is an important factor in the control of the internal combustion engine. Patent Document 1 discloses an invention related to a control device for an internal combustion engine that improves the estimation accuracy of the in-cylinder temperature. In this invention, an engine control unit (ECU) calculates the in-cylinder temperature at the start of compression based on the engine coolant temperature, obtains the first in-cylinder pressure (PB) detected at the start of compression, and obtains the second in-cylinder pressure (P g ) detected at a predetermined crank angle during the compression stroke. Based on this information, a process of calculating the in-cylinder temperature (T g ) at a predetermined crank angle is performed.

[0003] Japanese Patent Application Laid-Open No. 2008-309006

[0004] In the prior art, the process is performed on the premise that the internal combustion engine is in a steady state, that is, the combustion chamber wall temperature is constant. However, under transient conditions, the combustion chamber temperature that affects the in-cylinder gas temperature during the intake stroke is different from that under steady conditions. Therefore, there is a problem that the in-cylinder gas temperature T ivc at the start of compression cannot be predicted with high accuracy.

[0005] One aspect of the present invention is a control device that estimates the in-cylinder gas temperature T ivc at the start of compression (intake valve closing IVC) of an internal combustion engine to the in-cylinder gas temperature T gas during compression and controls the internal combustion engine. The in-cylinder gas temperature T ivc is calculated as the weighted average of the temperature T egrin of the internal EGR gas and the temperature T init of the fresh gas at the intake valve closing IVC of the intake gas, and T ivc =(G egrin / G cyl )×T egrin +(1-G egrin / G cyl )×T init (where G egrin : mass of the internal EGR gas, G cyl : total mass of the gas in the cylinder) T init =C1×Tbin +C2×T water +C3×kPW+C4 (where T egrin : Internal EGR temperature, constant: C1 to C4, T bin : Intake manifold gas temperature, T water Calculated from the cooling water temperature (kPW: specific power), the compression start gas temperature T at time step n is calculated during the warm-up process, which is the process from the start of the internal combustion engine when the combustion chamber wall temperature has not yet reached a steady state and is rising. ivcn T at time step n init n Combustion chamber wall temperature T wall n Using T ivc n =( G egrin / G cyl )×T egrin +(1-G egrin / G cyl )×T init n T init n =T initst -α×(1-C1)×(T wall_st -T wall n ) (Here, T wall_st This is a control device for an internal combustion engine, characterized by calculating the steady-state combustion chamber wall temperature under those operating conditions (α: adjustment coefficient).

[0006] Here, the combustion chamber wall temperature T wall n Q c =Const,1×(T g -T wall n-1 ) Q out =Const,2×(T wall n-1 -T water ) T wall n =T wall n-1 +ZF(Q c -Q out )Δt (Here, Q c : The heat flow per unit time into the combustion chamber wall, Q out : The heat flow per unit time outflowing from the combustion chamber wall to the cooling water side, T g: (using the unsteady heat conduction equation of cylinder gas temperature T, Z: a constant representing the ease of warming of the combustion chamber, Δt: time step) and calculating the cylinder gas temperature T g using the maximum temperature T max within the cycle, T g =E×T max (where E: constant) to obtain, and using the cylinder gas temperature T g as a constant value to calculate the combustion chamber wall temperature T wall n is preferably calculated.

[0007] Also, the maximum temperature T max is calculated as T max =(x o2_in / 0.21) H ×T​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​total : Total fuel injection amount, G cylinder : Cylinder gas mass, F, G: Constant) T tdc =T ivc n-1 ×ε (1-κ) This is a control device for an internal combustion engine, characterized by its ability to determine the following from (where ε is the compression ratio and κ is the specific heat ratio).

[0009] This technology allows for highly accurate prediction of the compression start temperature inside the cylinder, even during transient conditions such as the warm-up process or acceleration of an internal combustion engine, enabling appropriate correction of injection conditions for each cycle.

[0010] This figure shows the schematic configuration of the power unit of this embodiment. This figure shows the main components of the cylinder. This figure illustrates the heat transfer on the combustion chamber wall. This is a correlation diagram of the maximum temperature showing the validity of the constant identification in this embodiment. This is a correlation diagram of the heat flow showing the validity of treating the gas temperature as a constant value in this embodiment. This is a correlation diagram of the heat flow showing the validity of the constant identification in this embodiment. This figure shows the change in wall temperature from immediately after startup in this embodiment. This figure shows the change in compression start temperature from immediately after startup in this embodiment. This is a flowchart showing the calculation flow of this embodiment.

[0011] 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. The power unit 10 further includes an intake system 16 related to the supply of intake 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 air and circulates it.

[0012] The intake system 16 includes an intake pipe 22 through which intake air to the internal combustion engine 12 flows, and a turbocharger 26 and an intercooler 28 arranged along the intake pipe 22. The intake air flowing through the intake pipe 22 passes through the compressor 30 of the turbocharger 26 and then the intercooler 28. 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 hot intake air is cooled in the intercooler 28 by outside air or the cooling water of the internal combustion engine 12. It is then distributed and supplied to each cylinder 14 via the intake manifold 36.

[0013] A fuel injector 38 is provided for each cylinder 14, which injects fuel directly into the cylinder 14 at a predetermined timing. The injected fuel is burned by the high-temperature gas compressed within the cylinder 14. The exhaust gases from each cylinder 14 after combustion are combined by an exhaust manifold 40 and sent to a turbocharger 26.

[0014] 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.

[0015] The exhaust gas recirculation device 20 includes a recirculation pipe 52 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 54 that adjusts the flow rate of the exhaust gas flowing through the recirculation pipe 52. By adjusting the opening degree of the recirculation valve 54, the amount of exhaust gas mixed with the intake air is adjusted.

[0016] 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 56, 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 amount the driver operates the accelerator pedal 58, engine rotation speed, vehicle speed, coolant temperature, intake air flow rate, intake air temperature, exhaust air temperature, etc. are input to the control device 56, and the amount of fuel injected from the fuel injector 38 and the operation of the recirculation valve 54 are controlled so that the output can be obtained according to the driver's requirements.

[0017] Figure 2 is a schematic diagram showing the configuration of one cylinder 14. The cylinder 14 is defined by a cylinder block 60 with a cylindrical cavity, a cylinder head 62 positioned to close one end of the cylindrical cavity of the cylinder block 60, and a piston 64 positioned at the other end. The cylinder block 60 has a water jacket 66 formed around the cylinder 14 through which the cooling water of the internal combustion engine 12 flows. The cylinder head 62 also has a cooling water passage. The cylinder head 62 has an intake port 68 connected to the intake passage of the intake manifold 36 and an exhaust port 70 connected to the exhaust manifold 40. An intake valve 72 that opens and closes is positioned at the end of the intake port 68, and when the intake valve 72 opens, intake air is supplied into the cylinder 14. An exhaust valve 74 that opens and closes is positioned at the end of the exhaust port 70, and when the exhaust valve 74 opens, exhaust gas is discharged from inside the cylinder 14.

[0018] Refer to Figure 1 again. The intake manifold 36 has an intake manifold gas temperature T, which is the temperature of the intake air newly supplied into the cylinder 14. bin An intake manifold gas temperature sensor 76 is provided to detect the intake pressure (intake manifold internal pressure P). in An intake pressure sensor 77 is provided to detect the following: The cylinder block 60 or cylinder head 62 is equipped with a coolant temperature sensor T, which is the temperature of the engine's coolant. waterA coolant temperature sensor 78 is provided to detect the coolant temperature. The coolant temperature sensor 78 may be provided in the coolant piping (not shown) from the radiator (not shown) that dissipates heat from the coolant to the internal combustion engine 12. Furthermore, upstream of the turbocharger 26 in the exhaust manifold 40 or exhaust pipe 42, the exhaust temperature T ex An exhaust temperature sensor 80 is provided to detect the temperature. Furthermore, a rotational speed sensor 82 is provided to detect the rotational speed of the internal combustion engine 12.

[0019] The temperature inside cylinder 14 of the intake air that flows into cylinder 14 from intake manifold 36 when the intake valve 72 is closed is called the new gas temperature T. init The temperature of the gas remaining in cylinder 14 from the exhaust generated in the previous cycle is defined as the residual gas temperature T. egrin The temperature of the total gas inside cylinder 14 at the time when the intake valve 72 is closed (IVC - Inlet valve closure) is defined as the in-cylinder gas temperature T at the start of compression. ivc The temperature of the inner wall surface of the cylinder block 60 that defines cylinder 14 is defined as wall temperature T. wall Let's assume that.

[0020] <In-cylinder gas temperature T at the start of compression> ivc Calculation method > Compression start time, i.e., the time when the intake valve 72 closes, and the in-cylinder gas temperature T of the IVC internal combustion engine. ivc The internal EGR gas temperature T egrin The new gas temperature T is the temperature of the gas drawn in at the IVC when the intake valve is closed. init It is calculated from these two terms by equations (1) and (2). Here, the new gas temperature T init This refers to the intake manifold gas temperature T in the intake manifold 36. bin Unlike this, the intake manifold gas temperature T is affected by the exchange of heat from the combustion chamber wall during the intake stroke. bin It changes from T. ivc =( G egrin / G cyl )×T egrin +(1-G egrin / G cyl )×T init ... (1) Here, G egrin : Mass of internal EGR gas, G cyl : This is the total mass of gas inside the cylinder.init =C1×T bin +C2×T water +C3 × kPW + C4 ... (2) Here, T bin : Intake manifold gas temperature, T water : Cooling water temperature, kPW: Specific power, C1 to C4: Constants.

[0021] <Wall temperature T wall Changes in the new gas temperature T init Influence on the new gas temperature T under steady-state conditions init and wall heating wall The relationship is expressed by formula (3) according to formula (11) in Japanese Patent Publication No. 2025-104780 (Japanese Patent Application No. 2023-222831). init =T bin +C(T wall -T bin ) ... (3)

[0022] On the other hand, the wall temperature T wall This is determined by the balance between the amount of heat flowing from the wall into the cooling water and the amount of heat flowing from the gas into the wall, and is linearly related to these two factors. Furthermore, the former is related to the cooling water temperature T water Since the latter has an approximately linear relationship with the relative power kPW, it can be expressed as shown in equation (4) if A, B, and D are constants. wall =A×T water +B × kPW + D ... (4)

[0023] Substituting equation (4) into equation (3) and rearranging gives equation (5). init =T bin +C(A×T water +B×kPW+D-T bin ) = (1-C)×T bin +C×A×T water +C × B × kPW + C × D ... (5)

[0024] Intake manifold gas temperature T bin Comparing equations (2) and (5) regarding the coefficients, we obtain equation (6). C1=(1-C) C=1-C1・・・(6)

[0025] In other words, wall temperature change ΔT wall In contrast, the new gas temperature T init The change is approximately (1-C1)ΔTwall In practice, considering the adjustment range, in transient cases, formula (7) is used to determine the new gas temperature T. init Corrected the new gas temperature T at time step n. init n We can find T init n =T initst -α×(1-C1)×(T wall_st -T wall n ) ... (7) Here, T initst : Steady-state new gas temperature T under those operating conditions init , T wall_st : The steady-state combustion chamber wall temperature under those operating conditions, α: the adjustment coefficient.

[0026] <Combustion chamber wall temperature T wall n Calculation method: In-cylinder gas temperature T g How to calculate it > Figure 3 shows a schematic diagram of the heat transfer between the combustion chamber walls in steady and transient states. During transient (transient) conditions, the wall temperature T at time step n is... wall n This is derived from the energy conservation equation as equations (8a), (9a), and (10). Q c =S1h1(0.5N e / 60)(T g -T wall n-1 )... (8a) Q out =S2h2(T wall n-1 -T water ) ... (9a) T wall n =T wall n-1 +ZF(Q c -Q out )Δt...(10) Here, Q c : The heat flow per unit time into the combustion chamber wall, Q out : The heat flow per unit time outflowing from the combustion chamber wall to the cooling water side, T g : Cylinder gas temperature, T water : Cooling water temperature, Z: A constant representing how easily the combustion chamber heats up (equivalent to the reciprocal of the heat capacity of the wall), Δt: Time step.

[0027] In equations (8a) and (9a), h1 and h2 are the heat transfer coefficients of the wall boundary on the combustion chamber side (Hot boundary) and the wall boundary on the cooling side (Cold boundary), respectively. ,2 These represent the surface areas of the walls at the combustion chamber side wall boundary (Hot boundary) and the cooling side wall boundary (Cold boundary), respectively. The heat transfer coefficient can be given, for example, from Woschni's equation, as will be discussed later.

[0028] The gas temperature T inside the cylinder in formula (8a) g The internal combustion engine changes with each crank angle during the compression and expansion strokes. Therefore, when calculating equation (10), if we assume an engine speed of 2000 rpm and calculate for every 1° crank angle, then Δt = 8.3 × 10 －５ It needs to be reduced to such an extent that it is difficult to perform the calculation in the implemented ECU. Therefore, the in-cylinder gas temperature T g The maximum temperature T in the cycle max It is calculated using formula (11) in relation to T. g =E×T max ... (11) Here, E is a constant.

[0029] This allows the in-cylinder gas temperature T to be controlled within the same cycle. g Calculations become possible by treating as a constant value, and Δt = 6. × 10 －２ It can be enlarged to a certain extent. Therefore, calculations on the onboard implemented ECU become easier.

[0030] <Combustion chamber wall temperature T wall n Calculation method: Maximum temperature T max How to calculate it > First, the maximum temperature T in a cycle without EGR max,noegr In contrast, EGR leads to a decrease in oxygen concentration, resulting in poor combustion and a decrease in the specific heat ratio, leading to a maximum temperature T. max Formula (12) that takes into account the effect on the maximum temperature T max Calculate T max =(x o2_in / 0.21) H ×T max,noegr ... (12) Here, x o2_in : Mole fraction of inhaled oxygen, H: constant.

[0031] Next, the maximum temperature T within the cycle. max,noegr This is calculated using formula (13) as the sum of the two effects of the piston's compression work and the temperature rise due to combustion. max,noegr =T tdc +F × (η) glt ×Q total ×G cylinder ) G ... (13) Here, η glt : Isovolubility, Q total : Total fuel injection amount, G cylinder : Mass of gas inside the cylinder, F,G: constants. tdc This is calculated from equation (14), assuming a polytropic change. tdc =T ivc n-1 ×ε (1-κ) ... (14) Here, ε is the compression ratio and κ is the specific heat ratio.

[0032] Based on equations (12) to (14), the maximum temperature T max This is expressed by formula (15). max =(x o2_in / 0.21) H ×(T ivc n-1 ×ε (1-κ) +F × (η) glt ×Q total ×G cylinder ) G )...(15)

[0033] Note that the maximum temperature T max This can be used to monitor and control the state of an internal combustion engine. For example, the maximum temperature T max This can be used for processes such as predicting NOx emissions from internal combustion engines.

[0034] <Method for identifying constants> Under steady-state conditions, equations (8a) and (9a) are expressed as equations (8b) and (9b). Q c_st =S1h1(0.5N e / 60)(T g -T wall_st )...(8b) Q out_st =S2h2(T wall_st -T water ) ... (9b) Here, Twall_st This is the wall temperature in a steady state.

[0035] In equation (8b), S1h1 and S2h2 are given by equations (16) and (17), respectively, by obtaining the heat transfer coefficient from Woschni's formula. S1h1 = A(ρ air,ivc T g ) B (N e (2000) C T g -0.53 ... (16) Here, ρ air,ivc : Gas density inside the cylinder, A, C: Constants. S2h2=D(N e (2000) C ... (17) Here, D is a constant.

[0036] Wall surface area S 1、 S2 is included in the constants A and D respectively, N e The engine speed is non-dimensionalized at 2000 rpm and used as the representative flow velocity in the Woschni equation. The constant C is set to 0.8 from the Woschni equation.

[0037] Next, identify the other constants in Steps 1 and 2 shown below.

[0038] [Step 1: Identification of A, B, E, H, F, G] Substituting equation (16) into equation (8b) yields equation (18). Q c_st =A(ρ air,ivc T g ) B (N e (2000) C T g -0.53 (0.5N e / 60)(T g -T wall_st )...(18)

[0039] Also, the gas temperature inside the cylinder T g From equations (11) and (15), we obtain equation (19). g =E × (x o2_in / 0.21) H ×(T ivc n-1 ×ε (1-κ) +F × (η) glt ×Qtotal ×G cylinder ) G )...(19)

[0040] On the other hand, heat Q flows into the wall of the combustion chamber. c This can be obtained separately, for example, from experiments (Reference 1: Kazuhisa Inagaki et al., "Theoretical Study on Spray Design for Small Bore Diesel Engines (Part 4)", Transactions of the Society of Automotive Engineers of Japan, Vol. 47, No. 6, pp. 1297-1303, 2016) or cycle simulations (Reference 2: Kazuhisa Inagaki et al., "Improvement of Accuracy of Diesel Combustion Simulation UniDES", Transactions of the Society of Automotive Engineers of Japan, Vol. 45, No. 1, pp. 35-41, 2014).

[0041] The heat Q flowing into the combustion chamber wall, determined by these methods. c The correct value is Q c_true Therefore, A, B, E, H, F, and G are identified from the data set with changed operating conditions in such a way that the cumulative error defined by formula (20) is minimized. error=Σ(Q c,st,i -Q c_true,i ) 2 ... (20)

[0042] [Step 2: D(A st ,B st ,D st Identification of ) Substituting equation (17) into equation (9b) yields equation (21). Q out_st =D(N e (2000) C (T wall_st -T water )...(21)

[0043] Under steady-state conditions, as shown in the left diagram of Figure 3, Q c_st and Q out_st These are equal. Here, the steady wall temperature is defined by equation (22). T wall_st =A st ×T water +B st ×kPW+D st ... (22) Here, A st ,B st ,D st : It is a constant.

[0044] From the data set with changed operating conditions, D,A are selected so that the cumulative error defined by formula (23) is minimized. st ,B st ,D st Identify error=Σ(Q c_st,i -Q out_st,i ) 2 ... (23)

[0045] <Woschni equation> The Woschni equation is h = C・D B -0.2 P 0.8 U 0.8 T -0.53 It is represented as follows: Here, D B is the bore diameter of the cylinder, and U is the typical flow velocity. This equation is a general equation for the heat transfer coefficient (Nu∝Re n Based on the Nusselt number (Nu), Re (Reynolds number), and model constant (n), and assuming n=0.8 which holds true for most flow fields, the temperature dependence of the material properties can be calculated algebraically.

[0046] <Combustion chamber wall temperature T wall n Method of calculation: Solution of non-stationary equations > Substituting equations (8a) and (9a) into equation (10) yields equation (10-2). wall n =T wall n-1 +Z×(S1h1(0.5N e / 60)(T g -T wall n-1 )-S2h2(T wall n-1 -T water ))Δt...(10-2)

[0047] S1h in the above equation 1、 S2h2 can be calculated from equations (16) and (17), respectively, and all constants can be identified in Step 1.2 above, so from equation (10-2), the combustion chamber wall temperature T at time step n can be calculated. wall n These can be obtained sequentially.

[0048] The above refers to the combustion chamber wall temperature T at time n-1, which is the previous step in the calculation of equations (8a) and (9a). walln-1 This method is used. This is a so-called explicit method. However, in general, with explicit methods, the solution will not converge unless the time step Δt is made small, and the computation time tends to increase. Therefore, in order to avoid this, the combustion chamber wall temperature T at time step n-1 on the right-hand side of equations (8a) and (9a) is used. wall n-1 The current step wall temperature T wall n By substituting this, the solution can be obtained more stably. This is called the implicit method. In this case, equations (8a) and (9a) are expressed as equations (8c) and (9c).

[0049] Q c =S1h1(0.5N e / 60)(T g -T wall n )... (8c) Q out =S2h2(T wall n -T water )...(9c)

[0050] Substitute equations (8c) and (9c) into equation (12) to obtain the combustion chamber wall temperature T at time step n. wall n Solving for gives the equation (10-3). wall n =( T wall n-1 +Z(S1h1T g (0.5N e / 60)+S2h2T water )Δt / (1+ZS1h1(0.5N e / 60)Δt+ZS2h2Δt) ・・・(10-3)

[0051] Since onboard control requires calculations to be performed quickly, formula (10-3), which allows for a larger Δt than formula (10-2), is preferable.

[0052] [Example: Identification of Constants] First, a specific example of constant identification is shown. Thirty conditions were considered by varying the operating conditions: coolant temperature, ambient temperature, rotational speed, and load (fuel injection amount).

[0053] As shown in Step 1 above, the constants A, B, E, H, F, and G were first identified to minimize the error defined by equation (20) for these conditions. The heat flow Q per unit time flowing into the combustion chamber wall used at this time c_true,i This was calculated using the cycle simulation method described in reference 2 above (hereinafter simply referred to as "cycle simulation"). The results are shown in Table 1.

[0054] Figure 4 shows the maximum temperature T within the cycle, calculated using equation (15) with the identified constants. max (PredictedT max ) and the maximum temperature T calculated by cycle simulation max (TrueT max The correlation between these factors is shown. These factors exhibit a high correlation with a coefficient of determination R² = 0.993, confirming the validity of equation (15).

[0055] Figure 5 shows the heat flow Q calculated using equation (18) with the identified constants. c_st (PredictedQ c_st ) and the heat flow Q calculated by cycle simulation c_st (TrueQ c_st The correlation between the two is shown. The coefficient of determination R² = 0.995 indicates a high correlation, and as shown in equation (11), the gas temperature T changes with the crank angle. ｇ The maximum temperature T max It was confirmed that the method of treating it as a constant value in relation to it is appropriate.

[0056] Next, with respect to the operating conditions targeted in Step 1, the constants D and A are used to minimize the error defined by the formula (23) shown in Step 2. st ,B st ,D st The results were identified. The results are shown in Table 2.

[0057] Figure 6 shows the heat flow Q calculated using equation (18) with the identified constants. c_st The heat flow Q calculated by formula (21) out_stThe correlation is shown. The coefficient of determination R² = 0.995 indicates a high correlation, meaning the error defined by formula (23) is almost negligible, confirming the validity of the constant.

[0058] [Example 1: Calculation of Transient Wall Temperature] This example shows a concrete example of the change in wall temperature during transient conditions. The change in wall temperature is calculated from immediately after starting, when transitioning from a stopped internal combustion engine state to the operating conditions shown in Table 3.

[0059] Figure 7 shows the time variation of the wall temperature calculated from equation (10⁻³) using the identified constants. The constant Z in equation (10⁻³), which represents how easily the combustion chamber heats up, corresponds to the reciprocal of the heat capacity of the wall. Immediately after starting, the wall temperature rises sharply from the initial temperature, then the rate of increase gradually decreases, and finally converges to the steady wall temperature shown in equation (22).

[0060] In this study, we calculated the constant Z for two cases. As the constant Z decreases, the response time increases. In practice, transient experiments are conducted to measure the time it takes to reach a steady state (response time) from the time changes in heat generation rate and noise, and the constant Z is determined to correspond to this. Since the constant Z is equivalent to the reciprocal of the engine's heat capacity, it does not depend on the operating conditions. Therefore, it is sufficient to identify it from one to several cases of transient experiments.

[0061] <Example 2: Transient in-cylinder gas temperature T ivc Changes > If we give 0.65 and 1.0 as C1 and α respectively in equation (7), we obtain equation (7-2). init n =T initst -0.35 × (T wall_st -T wall n ) ... (7-2)

[0062] Using the constants shown in Table 2 as the constants in equation (22), we obtain equation (22-2). wall_st = 0.967 × T water +1.23 × kPW + 16.7 ... (22 - 2)

[0063] Furthermore, if we provide constants identified from experiments, etc., for the constants in equation (2), then the new gas temperature T initst This becomes equation (2-2). initst= 0.65 × T bin +0.3×T water +0.37 × kPW + 33.3 ... (2 - 2)

[0064] Under the transient conditions shown in Table 2, and assuming no internal EGR for simplification, the in-cylinder gas temperature T ivc = new gas temperature T init Assuming this, the new gas temperature T at the start of transient compression can be calculated based on equations (7-2), (22-2), and (2-2). init n We seek.

[0065] Figure 8 shows the new gas temperature T at the start of compression. init n The calculation results are shown below. New gas temperature T at the start of compression. init The temperature rises sharply immediately after startup and then converges to a steady state. Also, the response time increases as Z decreases. Thus, the new gas temperature T at the start of compression immediately after startup is... init By improving the accuracy of the compression end temperature calculated from this point forward, it will become possible to appropriately correct and control the fuel injection conditions.

[0066] <Processing Flow> Figure 9 shows the new gas temperature T at the start of compression of the internal combustion engine in an embodiment of the present invention. init and the gas temperature inside the cylinder T ivc The following shows the process flow for calculating [the value]. The control device 56 is configured to execute this process according to a predetermined program.

[0067] When the internal combustion engine is started, the time step n is reset to 0. Wall temperature T wall Initial value of wall temperature T wall 0 The current wall temperature T wall The value is set (step S10). Subsequently, the time step n is incremented by 1 (step S12).

[0068] Cylinder gas temperature T at the end of the compression process tdc Formula (14) shows the maximum temperature T in the cycle when EGR is absent. max,noegr Formula (13), maximum temperature T max Formula (12), the gas temperature inside the cylinder T gThe value is calculated based on formula (11) (step S14). Also, S1h1 is calculated based on formula (16) and S2h2 is calculated based on formula (18) (step S16). Based on these calculation results, the combustion chamber wall temperature T at time step n is calculated. wall n This is calculated based on the formula (10-3) (step S18).

[0069] Next, it is determined whether or not the internal combustion engine has been stopped (step S20). If the internal combustion engine has not been stopped, the process returns to step S12; if the internal combustion engine has been stopped, the process ends.

[0070] Thus, the wall temperature T of the combustion chamber at each time step n wall n By calculating the wall temperature T, wall n Based on the in-cylinder gas temperature T of the internal combustion engine ivc The control device 56 can calculate the in-cylinder gas temperature T of the internal combustion engine. ivc It becomes possible to control the internal combustion engine accordingly. For example, the calculated in-cylinder gas temperature T ivc Accordingly, variables related to the control of the internal combustion engine, such as the injection conditions of pilot fuel and the exhaust gas recirculation rate, can be corrected.

[0071] [Configuration of the Invention] [Configuration 1] The in-cylinder gas temperature T of the internal combustion engine when the intake valve is closed, which is at the start of compression. ivc From the gas temperature inside the cylinder during compression T gas A control device that estimates the in-cylinder gas temperature T and controls the internal combustion engine, ivc The temperature of the internal EGR gas T egrin The new gas temperature T at the IVC when the intake valve is closed for the inhaled gas init As a weighted average of T ivc =( G egrin / G cyl )×T egrin +(1-G egrin / G cyl )×T init (Here, G egrin : Mass of internal EGR gas, G cyl (Total mass of gas inside the cylinder) T init =C1×T bin +C2×Twater +C3×kPW+C4 (where T egrin : Internal EGR temperature, constant: C1 to C4, T bin : Intake manifold gas temperature, T water Calculated from the cooling water temperature (kPW: specific power), the in-cylinder gas temperature T at time step n is calculated during the warm-up process, which is the process from the start of the internal combustion engine when the combustion chamber wall temperature has not yet reached a steady state and is rising. ivc n T at time step n init n Combustion chamber wall temperature T wall n Using T ivc n =( G egrin / G cyl )×T egrin +(1-G egrin / G cyl )×T init n T init n =T initst -α×(1-C1)×(T wall_st -T wall n ) (Here, T wall_st A control device for an internal combustion engine, characterized in that it calculates the steady-state combustion chamber wall temperature T under the operating conditions (α: adjustment coefficient). [Configuration 2] A control device for an internal combustion engine according to Configuration 1, wherein the combustion chamber wall temperature T wall n Q c =Const,1×(T g -T wall n-1 ) Q out =Const,2×(T wall n-1 -T water ) T wall n =T wall n-1 +ZF(Q c -Q out )Δt (Here, Q c : The heat flow per unit time into the combustion chamber wall, Q out : The heat flow per unit time outflowing from the combustion chamber wall to the cooling water side, T gThe transient heat conduction formula (where : is the gas temperature inside the cylinder, Z: is a constant representing how easily the combustion chamber heats up, and Δt: is the time step) is used to calculate the gas temperature inside the cylinder T g The maximum temperature T in the cycle max Using the following equation T g =E×T max (Here, E is a constant) The in-cylinder gas temperature T is calculated from this and within the same cycle g Using this as a constant value, the combustion chamber wall temperature T wall n A control device for an internal combustion engine, characterized by calculating the maximum temperature T. [Configuration 3] A control device for an internal combustion engine according to Configuration 2, wherein the maximum temperature T max T max =(x o2_in / 0.21) H ×T max,noegr (Here, x o2_in : Inhaled O2 mole fraction, T max,noegr : Maximum temperature without EGR, H: constant) T max,noegr =T tdc +F × (η) glt ×Q total ×G cylinder ) G (Here, η glt : Isovolubility, Q total : Total fuel injection amount, G cylinder : Cylinder gas mass, F, G: Constant) T tdc =T ivc n-1 ×ε (1-κ) A control device for an internal combustion engine, characterized by determining from (where ε: compression ratio, κ: specific heat ratio). [Configuration 4] A control device for an internal combustion engine, wherein the maximum temperature T of the in-cylinder gas temperature max T max =(x o2_in / 0.21) H ×T max,noegr (Here, x o2_in : Inhaled O2 mole fraction, T max,noegr : Maximum temperature without EGR, H: constant) T max,noegr =T tdc +F × (η) glt ×Q total ×G cylinder ) G (Here, η glt : Isovolubility, Qtotal : Total fuel injection amount, G cylinder : Cylinder gas mass, F, G: Constant) T tdc =T ivc n-1 ×ε (1-κ) A control device for an internal combustion engine, characterized by being determined from (where ε: compression ratio, κ: specific heat ratio).

[0072] 10 Power unit, 12 Internal combustion engine, 14 Cylinder, 16 Intake system, 18 Exhaust system, 20 Exhaust recirculation system, 22 Intake pipe, 26 Turbocharger, 28 Intercooler, 30 Compressor, 32 Turbine, 36 Intake manifold, 38 Fuel injector, 40 Exhaust manifold, 42 Exhaust pipe, 52 Recirculation pipe, 54 Recirculation valve, 56 Control device, 58 Accelerator pedal, 60 Cylinder block, 62 Cylinder head, 64 Piston, 66 Water jacket, 68 Intake port, 70 Exhaust port, 72 Intake valve, 74 Exhaust valve, 76 Intake manifold gas temperature sensor, 77 Intake pressure sensor, 78 Coolant temperature sensor, 80 Exhaust temperature sensor, 82 Rotational speed sensor.

Claims

1. A control device for an internal combustion engine, which estimates the in-cylinder gas temperature T of the internal combustion engine at the time of intake valve closing IVC at the start of compression, controls the internal combustion engine, and calculates the in-cylinder gas temperature T initst , wall_st , wall from the in-cylinder gas temperature T gas during compression, controls the internal combustion engine, and calculates the in-cylinder gas temperature T ivc as the weighted average of the temperature T egrin of the internal EGR gas and the fresh gas temperature T init at the intake valve closing IVC of the intake gas, so that T ivc = (G egrin / G cyl ) × T egrin + (1 - G egrin / G cyl ) × T init (where G egrin : mass of the internal EGR gas, G cyl : total mass of the gas in the cylinder) T init = C1 × T bin + C2 × T water + C3 × kPW + C4 (where T egrin : internal EGR temperature, constants: C1 to C4, T bin : intake manifold gas temperature, T water : coolant temperature, kPW: specific output), and calculates, in the warm-up process, which is a process in which the combustion chamber wall temperature has not reached a steady value and is rising from the start of the internal combustion engine, the in-cylinder gas temperature T ivc n at the nth step of time using the T init <00,00024>at the nth step of time and the combustion chamber wall temperature T wall n so that T ivc n = (G egrin / G cyl ) × T egrin + (1 - G egrin / G cyl ) × T init n T init n = T initst - α × (1 - C1) × (T wall_st - T wall n ) (where T<OOOO042>: steady combustion chamber wall temperature under the operating conditions, α: adjustment coefficient).

2. A control device for an internal combustion engine according to claim 1, wherein the combustion chamber wall temperature T wall n Q c =Const,1×(T g -T wall n-1 ) Q out =Const,2×(T wall n-1 -T water ) T wall n =T wall n-1 +ZF(Q c -Q out )Δt (Here, Q c : The heat flow per unit time into the combustion chamber wall, Q out : The heat flow per unit time outflowing from the combustion chamber wall to the cooling water side, T g The transient heat conduction formula (where : is the gas temperature inside the cylinder, Z: is a constant representing how easily the combustion chamber heats up, and Δt: is the time step) is used to calculate the gas temperature inside the cylinder T g The maximum temperature T in the cycle max Using the following equation T g =E×T max (Here, E is a constant) The in-cylinder gas temperature T is calculated from this and within the same cycle g Using this as a constant value, the combustion chamber wall temperature T wall n Calculate.

3. A control device for an internal combustion engine according to claim 2, wherein the maximum temperature T max T max =(x o2_in / 0.21) H ×T max,noegr (Here, x o2_in : Inhaled O2 mole fraction, T max,noegr : Maximum temperature without EGR, H: constant) T max,noegr =T tdc +F × (η) glt ×Q total ×G cylinder ) G (Here, η glt : Isovolubility, Q total : Total fuel injection amount, G cylinder : Cylinder gas mass, F, G: Constant) T tdc =T ivc n-1 ×ε (1-κ) (Here, ε is the compressibility ratio and κ is the specific heat ratio.) 4. An internal combustion engine control device, wherein the maximum temperature T of the in-cylinder gas max is calculated as T max =(x o2_in / 0.21) H ×T max,noegr (where x o2_in : intake O2 molar fraction, T max,noegr : maximum temperature without EGR, H: constant) T max,noegr =T tdc +F×(η glt ×Q total ×G cylinder ) G (where η glt : isochoric ratio, Q total : total fuel injection amount, G cylinder : in-cylinder gas mass, F, G: constants) T tdc =T ivc n-1 ×ε (1-κ) (where ε: compression ratio, κ: specific heat ratio), and is obtained therefrom.

Images