Method for calculating in-cylinder gas temperature of internal combustion engine

Abstract

To calculate an in-cylinder gas temperature at each time point in a compression process of a reciprocating internal combustion engine.SOLUTION: A temperature Tinit of newly suctioned gas is calculated based on a linear combination equation consisting of an intake gas temperature Tbin in an intake manifold, a cooling water temperature Twater, a specific power kPW, and constant terms: Tinit=C1×Tbin+C2×Twater+C3×kPW+C4, C1, C2, C3, C4: constants. A gas temperature Tivc in the cylinder when an intake valve closes is calculated based on the new gas temperature Tinit, and the residual gas temperature Tegrin from the previous cycle. A gas temperature Tca in the cylinder at each time point during a compression process is calculated based on the gas temperature Tivc in the cylinder when the intake valve closes, and a crank angle ca.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for calculating the in-cylinder gas temperature of a reciprocating internal combustion engine.

Background Art

[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 below describes a method for calculating the in-cylinder gas temperature during the compression process based on the in-cylinder gas temperature at the start of compression obtained based on the temperature of the cooling water of the internal combustion engine. Further, in Patent Document 2 below, it is assumed that the in-cylinder gas temperature at the bottom dead center is substantially equal to the intake air temperature.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] The in-cylinder gas temperature during the compression process of a reciprocating internal combustion engine is affected by the in-cylinder gas temperature at the start of the compression process. Therefore, in order to accurately grasp the in-cylinder gas temperature during the compression process, it is important to accurately obtain the in-cylinder gas temperature at the start of the compression process.

Means for Solving the Problems

[0005] A method for calculating the in-cylinder gas temperature (Tca) during the compression process of a reciprocating internal combustion engine according to the present invention is The new gas temperature (Tinit), which is the temperature of the intake gas in the cylinder when the intake valve is closed, is calculated based on a linear combination formula consisting of the intake manifold gas temperature (Tbin) in the intake manifold, the engine coolant temperature (Twater), the specific output (kPW), and constants. Tinit = C1 × Tbin + C2 × Twater + C3 × kPW + C4 Tinit: New gas temperature Tbin: Intake manifold gas temperature Twater: Coolant temperature kPW: Specific output C1, C2, C3, C4: Constants A step of calculating based on the above, Based on the new gas temperature (Tinit) and the residual gas temperature (Tegrin), which is the temperature of the residual gas in the previous cycle, a step of calculating the in-cylinder gas temperature (Tivc) at the time of intake valve closure. Based on the in-cylinder gas temperature (Tivc) at the time of intake valve closure and the crank angle (ca), a step of calculating the in-cylinder gas temperature (Tca) during the compression process. It includes.

[0006] The new gas temperature (Tinit) can be calculated from the intake manifold gas temperature (Tbin), the engine coolant temperature (Twater), and the specific output (kPW), and the in-cylinder gas temperature (Tca) at any crank angle (ca) can be calculated.

[0007] In the above method, when calculating the in-cylinder gas temperature (Tivc) at the time of intake valve closure, the residual gas temperature (Tegrin) may be used as the exhaust gas temperature (Tex).

[0008] In the above method, when calculating the in-cylinder gas temperature (Tivc) at the time of intake valve closure, the residual gas temperature (Tegrin) may be calculated based on the calorific value generated from the fuel injection amount (m f ) and subtracting the piston work and heat loss previously associated with the pair of the engine rotational speed (Ne) and the fuel injection amount (m f ).

[0009] In the above method, the step of calculating the in-cylinder gas temperature (Tivc) at the time of intake valve closure may calculate the in-cylinder gas temperature (Tivc) at the time of intake valve closure based on the fresh gas temperature (Tinit), the residual gas temperature (Tegrin) which is the temperature of the residual gas in the previous cycle, the compression ratio (ε), and the ratio (G egrin ) of the mass (G cyl ) of the residual gas in the previous cycle to the total mass (G egrin / G cyl ) of the gas in the cylinder.

Advantages of the Invention

[0010] By obtaining the in-cylinder gas temperature at the start of the compression process, it has become possible to calculate the in-cylinder gas temperature (Tca) at any crank angle (ca).

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a power unit 10 for driving a vehicle according to the present 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, and the cylinder arrangement is also not limited to this. The power unit 10 further includes an intake system device 16 related to the supply of intake air to the internal combustion engine 12, an exhaust system device 18 related to the discharge of exhaust from the internal combustion engine 12, and an exhaust gas recirculation device 20 that returns a part of the exhaust of the internal combustion engine 12 to the intake air and circulates it.

[0013] The intake system device 16 includes an intake pipe 22 through which intake air to the internal combustion engine 12 flows, 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 in that order. The turbocharger 26 compresses the intake air by the exhaust energy of the internal combustion engine 12. A turbine wheel disposed in a turbine 32 of the turbocharger 26 is rotated by the exhaust. In the compressor 30 of the turbocharger 26, a compressor wheel that rotates integrally with the turbine wheel is disposed. The compressor 30 functions as a centrifugal compressor to compress the intake air. The compressed and heated intake air is cooled by outside air or the cooling water of the internal combustion engine 12 in the intercooler 28. It is distributed and supplied to each cylinder 14 via an intake manifold 36.

[0014] Corresponding to each cylinder 14, a fuel injection valve 38 that directly injects fuel into the cylinder 14 at a predetermined timing is provided. The fuel injected by the high-temperature gas compressed in the cylinder 14 burns. The exhaust from each cylinder 14 after combustion is combined by an exhaust manifold 40 and sent to the turbocharger 26.

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

[0016] The exhaust gas recirculation device 20 includes a recirculation pipe 52 that guides the exhaust gas of the internal combustion engine 12 from the exhaust manifold 40 or the 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 into the intake air is adjusted.

[0017] The operation of the power plant 10 is controlled based on a plurality of physical quantities indicating the operating state of the power plant 10. The power plant 10 includes a control device 56, and the control device 56 controls each operating component of the power plant 10 based on the input physical quantities to control the operation of the power plant 10. For example, the control device 56 receives the operation amount of the driver's accelerator pedal 58, the engine rotation speed, the vehicle speed, the coolant water temperature, the intake air flow rate, the intake air temperature, the exhaust gas temperature, etc., and controls the fuel injection amount from the fuel injection valve 38 and the operation of the recirculation valve 54 so as to obtain an output corresponding to the driver's request.

[0018] FIG. 2 is a diagram schematically showing the configuration of one cylinder 14. The cylinder 14 is defined by a cylinder block 60 in which a cylindrical cavity is formed, a cylinder head 62 disposed so as to close one end of the cylindrical cavity of the cylinder block 60, and a piston 64 disposed at the other end. A water jacket 66 through which the cooling water of the internal combustion engine 12 flows is formed in the cylinder block 60 so as to surround the periphery of the cylinder 14. A flow path for the cooling water is also formed in the cylinder head 62. An intake port 68 connected to the intake flow path of the intake manifold 36 and an exhaust port 70 connected to the exhaust manifold 40 are formed in the cylinder head 62. An intake valve 72 that opens and closes is disposed 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 disposed at the end of the exhaust port 70, and when the exhaust valve 74 opens, exhaust gas is discharged from the cylinder 14.

[0019] Referring to FIG. 1 again. The intake manifold 36 is provided with an intake manifold gas temperature sensor 76 that detects the intake manifold gas temperature Tbit, which is the temperature of the intake air newly sent into the cylinder 14. The intake manifold 36 is further provided with an intake pressure sensor 77 that detects the pressure of the intake air (intake manifold internal pressure P in ). Further, a coolant temperature sensor 78 that detects the coolant temperature Twater, which is the temperature of the engine's cooling water, is provided in the cylinder block 60 or the cylinder head 62. The coolant temperature sensor 78 may be provided in a coolant pipe (not shown) leading from a radiator (not shown) that dissipates heat from the coolant to the internal combustion engine 12. Further, an exhaust temperature sensor 80 that detects the exhaust temperature Tex is provided upstream of the turbocharger 26 in the exhaust manifold 40 or the exhaust pipe 42. Further, a rotational speed sensor 82 that detects the rotational speed of the internal combustion engine 12 is provided.

[0020] The temperature of the intake air flowing into the cylinder 14 from the intake manifold 36 when the intake valve 72 is closed is defined as the fresh gas temperature Tinit, and the temperature of the gas remaining in the cylinder 14 among the exhaust gases generated in the previous cycle is defined as the residual gas temperature Tegrin. The temperature of all the gases in the cylinder 14 when the intake valve is closed is defined as the in-cylinder gas temperature Tivc at the time of intake valve closing. The temperature of the inner wall surface of the cylinder block 60 defining the cylinder 14 is defined as the wall temperature Twall.

[0021] If the compression process of the internal combustion engine 12 is assumed to be adiabatic compression, the gas temperature in the cylinder 14 at a certain point in the compression process (for example, at the start of compression) is known, and the gas temperature at each point in the compression process can be calculated. At the start of compression, that is, when the intake valve is closed, in the cylinder 14, there are fresh gas, which is newly introduced into the cylinder 14, and residual gas, which is a part of the post-combustion gas generated in the previous cycle and remains. Therefore, if the amounts and temperatures of the fresh gas and the residual gas at the time of intake valve closing are known, the gas temperature in the cylinder at each point in the compression process can be calculated. This calculation may be performed by the control device 56 with reference to the temperatures of each part. Hereinafter, the calculation of the gas temperature in the cylinder will be described.

[0022] <Calculation of the fresh gas temperature Tinit> The fresh gas temperature Tinit, which is the temperature of the intake gas in the cylinder when the intake valve is closed, is calculated from the following equation (1), which is a linear combination formula. Tinit = C1×Tbin + C2×Twater + C3×kPW + C4 ···(1) Here, C1, C2, C3, and C4 are constants, and kPW is the specific output.

[0023] The specific output kPW is calculated from the following equation (2). kPW = η glt (Ne / 60.0×0.5)H u m f / (V bdc )×0.001 [kW / L / cylinder] ···(2) Here, Ne is the engine rotational speed [rpm], and V bdc is the cylinder volume at bottom dead center [m3 , H u is the lower calorific value of the fuel [J / kg], m f is the fuel injection amount [kg / cylinder], η glt is the isochoric degree. Note that the isochoric degree η glt may be given by referring to the value associated with the pair of the engine rotational speed Ne and the injected fuel amount m f . The correspondence between the pair of the engine rotational speed Ne and the injected fuel amount m f and the isochoric degree η glt shall be obtained in advance. Also, since the isochoric degree η glt is a value that does not change significantly, it can also be given uniformly as a constant (for example, 0.9).

[0024] Next, the reason why the new gas temperature Tinit can be approximated by the linear combination formula shown in Equation (1) will be explained. The new gas temperature Tinit is the temperature at which the gas inhaled from the intake manifold 36 into the cylinder 14 is heated by receiving heat from the inner wall surface of the cylinder 14. The temperature of the inhaled gas is the intake manifold gas temperature Tbin, and the temperature change of the inhaled gas due to receiving heat from the inner wall surface of the cylinder 14 is ΔT from_wall . If we set it as, the new gas temperature Tinit is expressed by the following Equation (3). Tinit = Tbin + ΔT from_wall ···(3) The temperature change ΔT of the inhaled gas from_wall is expressed by the following Equation (4). ΔT from_wall = Q from_wall / (c v ρ a V cyl ) ···(4) Here, c v is the specific heat of the gas in the cylinder, ρ a is the density of the gas in the cylinder, V cyl is the volume of the gas in the cylinder, and Q from_wall is the amount of heat received by the gas in the cylinder from the inner wall surface of the cylinder 14. The amount of heat received Q from_wall is expressed by the following (5) and (6). Q from_wall = S × h (Twall - Tbin) Δt [J] ···(5) Δt = 0.25×60 / Ne [s] ···(6) Here, S is the surface area of the wall, and h is the heat transfer coefficient. The heat transfer coefficient h is expressed by the following Woschni equation (7). h = C×D B -0.2 P 0.8 U 0.8 T -0.53 ···(7) Furthermore, since U ∝ Ne (the representative velocity is proportional to the engine rotational speed) and P ∝ ρ a T, Equation (7) becomes the following Equation (8). h = C×D B -0.2 ρ a 0.8 Ne 0.8 T 0.27 ···(8)

[0025] In the Woschni equation (7), D B is the bore diameter of the cylinder 14, and U is the representative flow velocity. This equation can be algebraically calculated based on the general equation for the heat transfer coefficient (Nu ∝ Re q , Nu: Nusselt number, Re: Reynolds number, q: model constant), assuming q = 0.8 which holds for most flow fields, and considering the temperature dependence of the physical properties.

[0026] Next, substituting Equations (4) to (6) and (8) into Equation (3), replacing the constant term with a new C, and arranging, we obtain the following Equation (9). Tinit = Tbin + CD B -0.2 ρ a 0.8 Ne 0.8 T 0.27 (Twall - Tbin) / Ne / ρ a = Tbin + C(S / V cyl )D B -0.2 ρ a -0.2 Ne -0.2 T 0.27 (Twall - Tbin) ···(9) In the above equation, (S / V cyl) Assuming the combustion chamber is cylindrical with the height from the piston top surface to the head being L, then (S / V cyl )=(πD B L) / (0.25πD B 2 L) ∝ (1 / D B ) So, substituting into Equation (9) and simplifying (replacing the constant term with a new C), we obtain the following Equation (10). Tinit=Tbin+CD B -1.2 ρ a -0.2 Ne -0.2 T 0.27 (Twall-Tbin) ···(10) Since the bore diameter D B is a constant that does not change with operating conditions, for ρ a -0.2 Ne -0.2 T 0.27 in the above equation, evaluate the degree of change with operating conditions. When the temperature T changes from 253K to 353K, (353K / 253K) 0.27 =1.09 which is within 10%. Also, when the rotational speed Ne or the gas density ρa doubles and changes, 2 -0.2 =0.87 which is within 20%.

[0027] From the above, for the assumed operating conditions, the change amount is at most within 20% and is small. So, this term including D B can be replaced with a constant C, and we obtain the following Equation (11). Tinit=Tbin+C(Twall-Tbin) ···(11)

[0028] On the other hand, the wall temperature Twall is determined by the balance between the heat flowing out from the wall to the cooling water and the heat flowing from the gas to the wall, and is approximately linearly related to these. Furthermore, since the former is approximately linearly related to the cooling water temperature Twater and the latter is approximately linearly related to the specific output kPW respectively, setting A, B, D as constants, it can be expressed as the following Equation (12). Twall = A × Twater + B × kPW + D ···(12) Substituting Equation (12) into Equation (11) and arranging gives Equation (13). Tinit = Tbin + C(A × Twater + B × kPW + D - Tbin) = (1 - C)×Tbin + C×A×Twater + C×B×kPW + C×D··(13) Finally, replacing the constants in Equation (13) with new constants C1 to C4 leads to the aforementioned Equation (1). That is, it becomes clear that the new gas temperature Tinit can be approximated by a linear combination of the intake manifold gas temperature Tbin, the coolant water temperature Twater, and the specific output kPW.

[0029] The constants C1 to C4 in Equation (1) are identified from the obtained new gas temperature Tinit, the intake manifold gas temperature Tbin, the coolant water temperature Twater, and the specific output kPW by conducting tests under various environmental conditions (intake temperature, coolant water temperature) and operating ranges (load, rotational speed). The specific procedures are shown in (i) to (vii).

[0030] The variables used in the description are as follows. G a is the mass [kg] of the gas newly inhaled into cylinder 14 (fresh gas), m f is the fuel injection amount [kg], (A / F) ex is the measured air-fuel ratio, G egr is the mass [kg] of the exhaust gas (external EGR gas) inhaled into cylinder 14 via the exhaust gas recirculation device 20, R egr is the exhaust gas recirculation rate (EGR rate), G egrin is the mass [kg] of the gas remaining in the cylinder (internal EGR gas), ε is the compression ratio, P in is the intake manifold internal pressure [Pa], V bdc is the cylinder internal volume at bottom dead center [m 3 , R is the gas constant, G cyl is the total gas mass [kg] in the cylinder, W avg is the average molecular weight [kg / mol] of the gas in the cylinder. (i) G a = m f (A / F) ex (ii) G egr =R egr G a / (1 - R egr ) (∵R egr =G egr / (G a +G egr )) (iii) G egrin =(1 / ε)(G a +G erg ) / (1 - (1 / ε)) (∵G egrin / (G a +G erg +G egrin ) = 1 / ε) (iv) n=(G a +G erg +G egrin ) / W avg (v) Tivc = P in V bdc / (nR) (vi) Tinit=(Tivc-(G egrin / G cyl )×Tegrin) / (1 - G egrin / G cyl ) (∵Tivc=(G egrin / Gcyl)×Tegrin+(1 - G egrin / G cyl )×Tinit) Here, G cyl =G a +G erg +G egrin and G cyl is calculated from the following equation. G cyl =(P in ·V bdc ) / (R·Tbin) (vii) From the result of (vi), the intake manifold gas temperature Tbin, coolant water temperature Twater, and specific output kPW obtained from experiments, identify the constants C1 to C4.

[0031] Figure 3 is a diagram showing the relationship between the new gas temperature Tinit calculated based on Equation (1) to which the identified constants C1 to C4 are applied and the new gas temperature Tinit obtained by experiments. The vertical axis represents the new gas temperature calculated by Equation (1), and the horizontal axis represents the new gas temperature obtained by experiments. A high correlation between the two was confirmed from Figure 3.

[0032] <Acquisition of the residual gas temperature Tegrin> Since the residual gas temperature Tegrin is approximately equal to the exhaust temperature Tex, it can be obtained as the exhaust temperature Tex detected by the exhaust temperature sensor 80.

[0033] Further, the residual gas temperature Tegrin can be calculated based on the calorific value calculated from the fuel injection amount and the calorific value obtained by subtracting the piston work and the heat loss. The piston work and the heat loss are made clear in advance as a correspondence relationship corresponding to the pair of the rotational speed Ne and the fuel injection amount m f of the internal combustion engine 12, and can be obtained by referring to this correspondence relationship. The correspondence relationship may be represented by a function or may be represented by a correspondence table.

[0034] Furthermore, the residual gas temperature Tegrin can also be calculated theoretically. That is, considering the intake air temperature T0, the heat loss ratio η loss , the isochoric ratio η glt , it is calculated from the following equations (14-1), (14-2), and (14-3). Tegrin = ((3 / 2)nRT0 + H u (1 - η - η loss )m f ) / ((3 / 2)nR) × (P in / ((2 / 3) ((3 / 2)nRT0 + H u (1 - η - η loss )m f ) / V bdc )) (κ-1) / κ ···(14-1) n = P in V bdc / (R Tbin) ···(14-2) η = η glt(1 - 1 / ε (κ-1) ) ···(14 - 3) Here, T0 approximately uses the intake manifold gas temperature Tbin. Also, n is the number of moles of gas in the cylinder, R is the gas constant, Hu is the lower calorific value of the fuel, m f is the fuel injection amount, η is the thermal efficiency, η glt is the isochoric ratio, η loss is the heat loss ratio, V bdc is the cylinder volume at bottom dead center, Tbin is the intake manifold gas temperature, P in is the intake manifold internal pressure, κ is the specific heat ratio of the gas. Note that η glt , η loss can well use the values pre-associated with the pair of the rotational speed Ne and the fuel injection amount m f . Also, as constants, for example, as typical values, η glt = 0.9, η loss = 0.2 may be used.

[0035] Equation (14 - 1) was derived as follows. In the case of an ideal gas, the relationship between the temperature T and the internal energy U is represented by the following equation (15). U = (3 / 2)nRT ···(15) Here, n is the number of moles and R is the gas constant. The thermal efficiency becomes the following equation (16) when using the compression ratio ε, the isochoric ratio η glt , and the specific heat ratio κ of the gas. η = η glt (1 - 1 / ε (κ-1) ) ···(16) And the internal energy U bdc at bottom dead center after combustion ends becomes the following equation (17). U bdc = (3 / 2)nRT0 + H u (1 - η - η loss )m f ···(17) Therefore, the gas temperature Tbdc at bottom dead center becomes the following equation (18) using (16) and (17). Tbdc = U bdc / ((3 / 2)nR) = ((3 / 2)nRT0 + H u (1 - η - ηloss )m f ) / ((3 / 2)nR) ··(18) Here, n is the intake pressure P in , the intake manifold gas temperature Tbin, and the cylinder volume V at bottom dead center bdc . Using these, the following equation (19) is obtained n = P in V bdc / (RTbin) ···(19) η glt , η loss may be determined based on the correspondence relationship with the set of the rotation speed Ne and the fuel injection amount m that have been associated in advance. Also, since it does not change significantly at the operating point, for example, fixed values such as η f -= 0.9, η glt = 0.2 may be used loss

[0036] The pressure P at bottom dead center (exhaust valve closed) is, from the gas state equation bdc PV = nRT = (2 / 3)U Therefore, it is obtained from the following equation (20). P bdc = (2 / 3)(U bdc / V bdc ) = (2 / 3)((3 / 2)nRT0 + Hu(1 - η―η loss )m f ) / V bdc ··(20)

[0037] Assuming that the temperature Tegrin of the residual gas adiabatically expands to the intake pressure (= exhaust pressure) in the above state, the following equation (21) is obtained Tegrin = Tbdc(P in / P bdc ) (κ-1) / κ ···(21) Substituting equations (18) and (20) into equation (21) and arranging gives equation (14 - 1).

[0038] <Calculation of the gas temperature Tivc in the cylinder at the time of intake valve closing> ​​Based on the temperature of the newly inhaled gas (new gas temperature) \(T_{init}\) in the cylinder 14 and the temperature of the gas remaining from the previous cycle (residual gas temperature) \(T_{egrin}\), the in-cylinder gas temperature \(T_{ivc}\) at the intake valve closing is calculated by the following equation (22). \(T_{ivc}=(G\) egrin / G cyl )×T_{egrin}+(1 - G egrin / G cyl )×T_{init} ··(22) Here, G egrin is the mass of the gas remaining in the cylinder (internal EGR gas), and G cyl is the total gas mass in the cylinder 14.

[0039] The ratio of the residual gas to the entire gas in the cylinder 14, G egrin / G cyl can be expressed in terms of the new gas temperature \(T_{init}\) and the residual gas temperature \(T_{egrin}\). The gas mass G init in the cylinder 14 at the intake valve closing is approximately equal to the total gas mass G cyl in the cylinder 14, so the temperature of the total gas is taken as \(T_{init}\). The gas density is inversely proportional to the temperature, and the volume V egrin of the residual gas is approximately equal to the cylinder volume V tdc at the top dead center. Taking the gas volume at the bottom dead center as the cylinder volume V bdc at the bottom dead center, then the ratio of the residual gas to the gas in the cylinder 14, G egrin / G cyl becomes the following equation (23). G egrin / G cyl =(V egrin / T egrin ) / (V bdc / T_{init}) =(V tdc / V bdc )×(T_{init} / T_{egrin}) ···(23) Since V tdc / V bdc = 1 / ε (ε: compression ratio), equation (23) becomes the following equation (24). G egrin / G cyl =(1 / ε)×(T_{init} / T_{egrin}) ···(24) Therefore, the in-cylinder gas temperature Tivc at the intake valve closing can be approximated by the following equation (25). Tivc=(1 / ε)(Tinit / Tegrin) ×Tegrin+(1-(1 / ε)(Tinit / Tegrin))×Tinit ···(25)

[0040] <Calculation of the in-cylinder gas temperature Tca at an arbitrary crank angle ca> When the compression process starts from the bottom dead center, the temperature Tca of the gas in the cylinder 14 at an arbitrary crank angle ca in the compression process is the cylinder volume V at the bottom dead center bdc and the cylinder volume V at the said crank angle ca ca ratio ε ca (=V bdc / V ca ) is used to calculate from the following equation (26). Tca=Tivc×ε ca (κ-1) ···(26)

[0041] When the compression process starts from a certain crank angle after passing the bottom dead center, replace the cylinder volume V at that time with the cylinder volume V at the bottom dead center bdc with the cylinder volume at that time.

[0042] <Calculation of the in-cylinder gas temperature Ttdc at the end of the compression process> The in-cylinder gas temperature Ttdc at the end of the compression process is calculated from the following equation (27) using the adiabatic compression ratio based on the in-cylinder gas temperature Tivc at the intake valve closing. Ttdc=Tivc×ε (κ-1) ···(27)

[0043] <Use for each control variable> From the in-cylinder gas temperature Tca at an arbitrary crank angle calculated as above and the end temperature Ttdc of the compression process, it becomes possible to correct the pilot injection conditions (number of splits, injection amount, injection timing and interval) for injecting a small amount of fuel before the main injection of the fuel, or to correct the exhaust gas recirculation rate.

[0044] <Flow of calculation> FIG. 4 shows a flow of a process for calculating the in-cylinder gas temperature Tca at an arbitrary crank angle ca and the in-cylinder gas temperature Ttdc at the end of the compression process. The control device 56 is configured to execute this process according to a predetermined program.

[0045] First, the rotational speed Ne of the internal combustion engine and the fuel injection amount m f are acquired. The rotational speed Ne is acquired from the rotational speed sensor 82 (S100). The fuel injection amount m f is acquired based on the rotational speed Ne and the operation amount of the accelerator pedal 58. For example, a correspondence relationship between the set of the rotational speed Ne and the operation amount of the accelerator pedal 58 and the fuel injection amount m f is determined in advance, and the fuel injection amount m f is acquired based on this correspondence relationship. Next, the intake manifold gas temperature Tbin is acquired from the intake manifold gas temperature sensor 76, and the intake pressure P in is acquired from the intake pressure sensor 77, and the cooling water temperature Twater is acquired from the cooling water temperature sensor 78 (S102). Based on the acquired variables, the number of moles n of the gas in the cylinder 14 is calculated from Equation (14-2), and the thermal efficiency η is calculated from Equation (14-3) (S104).

[0046] The gas temperature T0 in the cylinder 14 at the initial stage of the compression process is set as the intake manifold gas temperature Tbin (S106), and the isochoric ratio η glt and the heat loss ratio η loss are acquired (S108). The isochoric ratio η glt and the heat loss ratio η loss use values that are previously associated with the set of the rotational speed Ne and the fuel injection amount m f . Next, the residual gas temperature Tegrin is acquired as the exhaust temperature Tex, or is calculated using Equation (14-1) (S110). The specific output kPW is calculated using Equation (2) (S112), and further, the fresh gas temperature Tinit is calculated using Equation (1) (S114). The ratio G egrin / G cylIt is calculated using Equation (23) (S116). The in-cylinder gas temperature Tivc at the time of intake valve closure is calculated using Equation (22) (S118), and further, the in-cylinder gas temperature Tca at an arbitrary crank angle ca and the in-cylinder gas temperature Ttdc at the end of the compression process are calculated using Equations (26) and (27) (S120). Finally, variables related to the control of the internal combustion engine 12, such as the injection conditions of the pilot fuel and the exhaust gas recirculation rate, are corrected according to the calculated in-cylinder gas temperatures Tca and Ttdc.

Explanation of Signs

[0047] 10 Power device, 12 Internal combustion engine, 14 Cylinder, 20 Exhaust gas recirculation device, 36 Intake manifold, 38 Fuel injection valve, 40 Exhaust manifold, 42 Exhaust pipe, 56 Control device, 76 Intake manifold gas temperature sensor, 77 Intake pressure sensor, 78 Cooling water temperature sensor, 80 Exhaust temperature sensor, 82 Rotational speed sensor, G cyl Total gas mass in the cylinder, G egr Mass of recirculated exhaust gas, G egrin Mass of residual gas, G init Mass of fresh gas, H u Lower calorific value of fuel, kPW ratio output, m f Fuel injection amount, n Number of moles of gas in the cylinder, P in Intake manifold pressure, R egr Exhaust gas recirculation rate, R Gas constant, Tbin Intake manifold gas temperature, Tegrin Residual gas temperature, Tex Exhaust temperature, Tinit Fresh gas temperature, Tivc In-cylinder gas temperature at the time of intake valve closure, Twall Wall temperature, Twater Cooling water temperature, T0 Intake temperature, V cyl Volume of gas in the cylinder, V ca Cylinder volume at crank angle ca, V bdc Cylinder volume at bottom dead center, V tdc Cylinder volume at top dead center, W avg Average molecular weight, ε Compression ratio, κ Specific heat ratio of gas, η loss Heat loss ratio, η glt Isometric degree.

Claims

1. A method for calculating the in-cylinder gas temperature (Tca) during the compression process of a reciprocating internal combustion engine, comprising: calculating a fresh gas temperature (Tinit), which is the temperature of the intake gas in the cylinder when the intake valve is closed, based on a linear combination formula consisting of terms of an intake manifold gas temperature (Tbin), which is the temperature of the intake gas in the intake manifold, an engine coolant temperature (Twater), a specific output (kPW), and a constant, Tinit = C1 × Tbin + C2 × Twater + C3 × kPW + C4 where Tinit is the fresh gas temperature; Tbin is the intake manifold gas temperature; Twater is the coolant temperature; kPW is the specific output; C1, C2, C3, and C4 are constants; calculating the in-cylinder gas temperature (Tivc) at the time of intake valve closure based on the fresh gas temperature (Tinit) and a residual gas temperature (Tegrin), which is the temperature of the residual gas from the previous cycle; calculating the in-cylinder gas temperature (Tca) during the compression process based on the in-cylinder gas temperature (Tivc) at the time of intake valve closure and a crank angle (ca). A method comprising the above steps.

2. The method according to claim 1, wherein in the step of calculating the in-cylinder gas temperature (Tivc) at the time of intake valve closure, the residual gas temperature (Tegrin) is set as an exhaust gas temperature (Tex).

3.

4. The method according to claim 1, wherein in the step of calculating the in-cylinder gas temperature (Tivc) at the time of intake valve closing, the residual gas temperature (Tegrin) is determined from the calorific value based on the fuel injection amount (m f ), and is calculated based on the heat amount obtained by subtracting the piston work and heat loss previously associated with the pair of the engine speed (Ne) and the fuel injection amount (m f ). ​ The method according to any one of claims 1 to 3, wherein the step of calculating the in-cylinder gas temperature (Tivc) at the time of intake valve closing calculates the in-cylinder gas temperature (Tivc) based on the new gas temperature (Tinit), the residual gas temperature (Tegrin) which is the temperature of the residual gas in the previous cycle, the compression ratio (ε), and the ratio of the mass (G egrin ), which is the mass of the residual gas in the previous cycle, to the total mass (G cyl ), which is the total mass of the gas in the cylinder, and the ratio (G egrin / G cyl ).

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