Engine in-cylinder state quantity prediction device and in-cylinder state quantity prediction method

Abstract

To highly accurately predict an in-cylinder state amount of an engine in an intake / discharge stroke by a quick calculation.SOLUTION: In an ECU 10 of an engine 1 which introduces an EGR into a cylinder by the opening of an exhaust valve 22 in an exhaust stroke and by the simultaneous opening of both the exhaust valve and an intake valve 21 at an intake stroke in a prescribed operation condition, the ECU sets an in-cylinder state amount at the end of a combustion stroke of the engine on the basis of a measurement signal received from a sensor, calculates in-cylinder state amounts in only a plurality of discrete points EOB, SPR and EVO2, including the end of the exhaust stroke of the engine, on the basis of the in-cylinder state amounts at the end of the combustion stroke, and continuously calculates an in-cylinder state amount from the start to the end of the intake stroke at a prescribed calculation step width on the basis of the in-cylinder state amount at the end of the exhaust stroke.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to an in-cylinder state quantity prediction device and an in-cylinder state quantity prediction method for an engine.

Background Art

[0002] Conventionally, for the purpose of improving the fuel efficiency and exhaust gas performance of an engine, techniques for accurately predicting the combustion state in the cylinder of the engine have been proposed in order to precisely control the combustion of the engine. For example, Patent Document 1 discloses a technique for a compression self-ignition engine that uses a linear parameter model to estimate the state quantity in the cylinder (combustion chamber), thereby suppressing the calculation load and improving the estimation accuracy.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, engines that perform premixed charge compression ignition (HCCI) combustion, which achieve high thermal efficiency with low exhaust gas emissions, have attracted attention. In compression ignition combustion such as HCCI combustion, the combustion reaction is strongly influenced by the in-cylinder state quantity and gas composition. On the other hand, since there is no means to directly control the start of combustion like the spark plug in a spark ignition engine or the fuel injection device in a diesel engine, combustion control is difficult. Therefore, in order to obtain a desired combustion reaction, the in-cylinder state is controlled by using exhaust gas recirculation (EGR). To efficiently use EGR, for example, it is conceivable to perform so-called double opening of the exhaust valve, in which the exhaust valve is also opened together with the intake valve during the intake stroke, to draw back the exhaust gas once discharged from the cylinder into the cylinder (internal EGR).

[0005] During engine operation where the engine speed and load change constantly, in order to appropriately control the compression ignition combustion of the engine, it is desirable to predict the in-cylinder state variables of the engine in real time based on an engine control model and perform engine control based on the prediction. However, in conventional technologies such as the above-mentioned Patent Document 1, while emphasis is placed on modeling the combustion process, it cannot be said that gas exchange in the cylinder is sufficiently considered, such as assuming that the in-cylinder pressure in the intake and exhaust strokes is constant. Therefore, for example, when the exhaust valve is opened twice, it is difficult to accurately predict the in-cylinder state variables that affect the internal EGR flowing into the cylinder during the intake and exhaust strokes in a short calculation time, and there is a problem that it is difficult to control the compression ignition combustion based on the engine control model.

[0006] The present invention has been made to solve the above-mentioned problems of the conventional technology, and an object thereof is to provide an in-cylinder state variable prediction device and an in-cylinder state variable prediction method for an engine that can accurately predict the in-cylinder state variables of the engine in the intake and exhaust strokes in a short calculation time.

Means for Solving the Problems

[0007] To achieve the above object, the present invention provides an in-cylinder state variable prediction device for an engine that introduces EGR into the cylinder by opening an exhaust valve in the exhaust stroke and opening both the exhaust valve and the intake valve simultaneously in the intake stroke under predetermined operating conditions. The device includes a sensor attached to the engine and configured to measure a physical quantity related to the in-cylinder state variables of the engine and output a measurement signal, and a processor that receives the measurement signal from the sensor and calculates the in-cylinder state variables of the engine based on the measurement signal. The processor is configured to set the in-cylinder state variables at the end of the combustion stroke of the engine based on the measurement signal, calculate the in-cylinder state variables only at a plurality of discrete points including the end time of the exhaust stroke of the engine based on the in-cylinder state variables at the end of the combustion stroke, and continuously calculate the in-cylinder state variables from the start time to the end time of the intake stroke at a predetermined calculation step width based on the in-cylinder state variables at the end time of the exhaust stroke. In the present invention configured as described above, for the exhaust stroke, the processor calculates the in-cylinder state quantities only at a plurality of discrete points. Therefore, for the exhaust stroke where the exhaust valve only opens and the gas flow in and out of the cylinder is relatively simple, the calculation load can be greatly reduced while ensuring the calculation accuracy. Further, for the intake stroke, the processor calculates the in-cylinder state quantities continuously. Therefore, for the intake stroke where both the exhaust valve and the intake valve open simultaneously and the gas flow in and out of the cylinder is relatively complex, the desired calculation accuracy can be obtained through continuous calculation. Thus, the in-cylinder state quantities of the engine during the intake and exhaust strokes can be predicted with high accuracy in a short calculation time.

[0008] In the present invention, preferably, the discrete points include the blowdown end time when the pressure difference between the cylinder of the engine and the exhaust port reaches 0 after the exhaust valve opens during the exhaust stroke, and the pressure rise start time when the pressure difference between the cylinder and the exhaust port begins to increase after the blowdown end time. In the present invention configured as described above, the processor sets the discrete points in the exhaust stroke at the time when the pressure difference between the cylinder and the exhaust port is 0. Therefore, the in-cylinder pressure of the cylinder can be estimated based on the exhaust port pressure, and the in-cylinder state quantities can be predicted with high accuracy even in discrete calculations.

[0009] In the present invention, preferably, the lower the engine speed of the engine or the larger the valve lift amount of the engine, the smaller the calculation step width is set by the processor. When the calculation step width is larger than a predetermined threshold value, the in-cylinder state quantities in the intake stroke are calculated using a steady flow calculation formula assuming that the gas flow passing through the intake valve and the exhaust valve of the engine is a steady flow. When the calculation step width is equal to or less than the predetermined threshold value, the in-cylinder state quantities in the intake stroke are calculated using an unsteady flow calculation formula assuming that the gas flow passing through the intake valve and the exhaust valve of the engine is an unsteady flow. In the present invention configured as described above, when the valve lift is relatively small or the engine speed is high, that is, when the pressure difference between the pressures in the intake port and exhaust port of the engine and the in-cylinder pressure of the cylinder is relatively large, the in-cylinder state quantity can be accurately predicted with a low computational load by the steady flow calculation formula. Further, when the valve lift is relatively large or the engine speed is low, that is, when the pressure difference between the pressures in the intake port and exhaust port and the in-cylinder pressure of the cylinder is relatively small and the desired calculation accuracy cannot be obtained by the steady flow calculation formula, the in-cylinder state quantity can be accurately predicted by using the unsteady flow calculation formula. Therefore, the in-cylinder state quantity of the engine during the intake and exhaust strokes can be predicted with high accuracy in a short time calculation.

[0010] In the present invention, preferably, the processor calculates the in-cylinder state quantity during the exhaust stroke and intake stroke of the engine under the operating conditions where the engine performs premixed compression ignition combustion. In the present invention configured as described above, in order to appropriately control the premixed compression ignition combustion, the in-cylinder state quantity during the intake and exhaust strokes, which has a great influence on the premixed compression ignition combustion, can be accurately predicted by a short time calculation.

[0011] From another perspective, the present invention is a method for predicting the in-cylinder state quantity of an engine that introduces EGR into the cylinder by opening the exhaust valve in the exhaust stroke and simultaneously opening both the exhaust valve and the intake valve in the intake stroke under predetermined operating conditions. The method includes: measuring, by a sensor attached to the engine, a physical quantity related to the in-cylinder state quantity of the engine and outputting a measurement signal; and receiving, by a processor, the measurement signal from the sensor and calculating the in-cylinder state quantity of the engine based on the measurement signal. The step of causing the processor to calculate the in-cylinder state quantity includes: setting the in-cylinder state quantity at the end of the combustion stroke of the engine based on the measurement signal; calculating the in-cylinder state quantity only at a plurality of discrete points including the end time of the exhaust stroke of the engine based on the in-cylinder state quantity at the end of the combustion stroke; and continuously calculating the in-cylinder state quantity from the start time to the end time of the intake stroke at a predetermined calculation step width based on the in-cylinder state quantity at the end time of the exhaust stroke.

Advantages of the Invention

[0012] According to the in-cylinder state quantity prediction device and the in-cylinder state quantity prediction method of the engine of the present invention, the in-cylinder state quantity of the engine in the intake and exhaust strokes can be predicted with high accuracy by a short-time calculation.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Mode for Carrying Out the Invention

[0014] Hereinafter, with reference to the accompanying drawings, an in-cylinder state quantity prediction device and an in-cylinder state quantity prediction method for an engine according to an embodiment of the present invention will be described.

[0015] <System Configuration> First, with reference to FIGS. 1 and 2, the configuration of the in-cylinder state quantity prediction device for an engine according to the present embodiment will be described. FIG. 1 is a schematic configuration diagram of an engine system to which the in-cylinder state quantity prediction device according to the present embodiment is applied, and FIG. 2 is a block diagram showing the functional configuration of the engine system according to the present embodiment.

[0016] The engine system E is mounted on a vehicle, for example. The engine system E includes an engine 1 and an ECU (Electronic Control Unit) 10 as an arithmetic device and a control device for controlling the engine 1.

[0017] The engine 1 is a four-stroke engine and repeats an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. The engine 1 may be configured to perform HCCI combustion in at least a part of the operating region.

[0018] The engine 1 includes a cylinder block 12 and a cylinder head 13. The cylinder head 13 is placed on top of the cylinder block 12. A plurality (e.g., four) of cylinders 11 are formed in the cylinder block 12.

[0019] A piston 3 is inserted into each cylinder 11. The piston 3 is connected to a crankshaft 15 via a connecting rod 14. The piston 3, cylinder 11, and cylinder head 13 form a combustion chamber 17.

[0020] An intake port 18 is formed in the cylinder head 13 for each cylinder 11. The intake port 18 communicates with the inside of the cylinder 11.

[0021] An intake valve 21 is disposed in the intake port 18. The intake valve 21 opens and closes the intake port 18. The valve timing and / or valve lift of the intake valve 21 are variable by an intake S-VT (Sequential-Valve Timing) 231 or an intake CVVL (Continuously Variable Valve Lift) 232. The intake S-VT 231 continuously changes the rotational phase of the intake camshaft with respect to the crankshaft 15 within a predetermined angle range. The intake CVVL 232 can continuously change the lift amount of the intake valve 21 within a predetermined range.

[0022] Also, an exhaust port 19 is formed in the cylinder head 13 for each cylinder 11. The exhaust port 19 communicates with the inside of the cylinder 11.

[0023] An exhaust valve 22 is disposed in an exhaust port 19. The exhaust valve 22 opens and closes the exhaust port 19. The valve timing and / or valve lift of the exhaust valve 22 is variable by an exhaust S-VT 241 or an exhaust VVL (Variable Valve Lift) 242. The exhaust S-VT 241 continuously changes the rotational phase of the exhaust camshaft with respect to the crankshaft 15 within a predetermined angular range. Although not shown, the exhaust VVL 242 is configured to be able to switch the cam that opens and closes the exhaust valve 22. For example, the exhaust VVL 242 has a first cam, a second cam, and a switching mechanism that switches between the first cam and the second cam. The first cam is configured to open and close the exhaust valve 22 during the exhaust stroke. The second cam is configured to open and close the exhaust valve 22 during the exhaust stroke and to open and close the exhaust valve 22 again during the intake stroke. Note that the second cam may be configured to maintain the opening of the exhaust valve 22 until the intake stroke after opening the exhaust valve 22 during the exhaust stroke. The exhaust VVL 242 can change the lift of the exhaust valve 22 by opening and closing the exhaust valve 22 with either the first cam or the second cam.

[0024] The intake S-VT 231, the intake CVVL 232, the exhaust S-VT 241, and the exhaust VVL 242 control the opening and closing of the intake valve 21 and the exhaust valve 22 to adjust the amount of air introduced into the cylinder 11 and the amount of introduced burned gas (the amount of internal EGR).

[0025] In the cylinder head 13, an injector 6 is attached to each cylinder 11. The injector 6 directly injects fuel into the cylinder 11. A fuel supply system 61 is connected to the injector 6. The fuel supply system 61 includes a fuel tank 63 configured to store fuel, and a fuel supply passage 62 that connects the fuel tank 63 and the injector 6 to each other. The fuel supply passage 62 is provided with a fuel pump 65 and a common rail 64. The fuel pump 65 pumps fuel to the common rail 64. The common rail 64 stores the fuel pumped from the fuel pump 65 at a high fuel pressure. When the injector 6 opens its valve, the fuel stored in the common rail 64 is injected into the cylinder 11 from the nozzle of the injector 6. Note that the configuration of the fuel supply system 61 is not limited to the above configuration.

[0026] In the cylinder head 13, a first spark plug 251 and a second spark plug 252 are attached to each cylinder 11. The first spark plug 251 and the second spark plug 252 each forcibly ignite the air-fuel mixture in the cylinder 11. Note that there may be one spark plug.

[0027] An intake passage 40 is connected to one side of the engine 1. The intake passage 40 communicates with the intake ports 18 of the respective cylinders 11. The air introduced into the cylinder 11 flows through the intake passage 40. An air cleaner 41 is disposed at the upstream end of the intake passage 40. The air cleaner 41 filters the air. A surge tank 42 is disposed near the downstream end of the intake passage 40. The intake passage 40 downstream of the surge tank 42 constitutes an independent intake passage that branches for each cylinder 11. The downstream end of the independent intake passage is connected to the intake port 18 of each cylinder 11.

[0028] A throttle valve 43 is disposed between the air cleaner 41 and the surge tank 42 in the intake passage 40. The throttle valve 43 adjusts the amount of air introduced into the cylinder 11 by adjusting the opening degree of the valve.

[0029] On the other side of the engine 1, an exhaust passage 50 is connected. The exhaust passage 50 communicates with the exhaust ports 19 of each cylinder 11. The exhaust passage 50 is a passage through which the exhaust gas discharged from the cylinder 11 flows. The upstream portion of the exhaust passage 50, although detailed illustration is omitted, constitutes an independent exhaust passage that branches for each cylinder 11. The upstream end of the independent exhaust passage is connected to the exhaust port 19 of each cylinder 11, and the downstream end of the independent exhaust passage is connected to the exhaust pipe collecting portion.

[0030] An exhaust gas purification system having a plurality of catalytic converters is disposed in the exhaust passage 50. The upstream catalytic converter has, for example, a three-way catalyst 511 and a GPF (Gasoline Particulate Filter) 512. The downstream catalytic converter has a three-way catalyst 513. Note that the exhaust gas purification system is not limited to the illustrated configuration. For example, the GPF may be omitted. Also, the catalytic converter is not limited to having a three-way catalyst. Further, the arrangement order of the three-way catalyst and the GPF may be changed as appropriate.

[0031] An EGR passage 52 is connected between the intake passage 40 and the exhaust passage 50. The EGR passage 52 is a passage for refluxing a part of the exhaust gas to the intake passage 40. The upstream end of the EGR passage 52 is connected between the upstream catalytic converter and the downstream catalytic converter in the exhaust passage 50. The downstream end of the EGR passage 52 is connected between the throttle valve 43 and the surge tank 42 in the intake passage 40.

[0032] A water-cooled EGR cooler 53 is disposed in the EGR passage 52. The EGR cooler 53 cools the exhaust gas. An EGR valve 54 is also disposed in the EGR passage 52. The EGR valve 54 adjusts the flow rate of the exhaust gas flowing through the EGR passage 52. When the opening degree of the EGR valve 54 is adjusted, the reflux amount of the external EGR gas is adjusted.

[0033] As shown in Fig. 2, the engine system E includes an ECU 10 as an arithmetic unit and a control unit for controlling the engine 1. The ECU 10 is a controller based on a well-known microcomputer. The ECU 10 is composed of a computer including one or more CPUs (processors) 101, a memory 102 (such as ROM and RAM) for storing various programs, and an I / F circuit 103 for inputting and outputting electrical signals. Note that the ECU 10 corresponds to an example of the "in-cylinder state quantity prediction device of the engine" in the present invention.

[0034] As shown in FIGS. 1 and 2, various sensors SW1 to SW14 are communicably connected to the ECU 10. The sensors SW1 to SW14 output signals to the ECU 10. The air flow sensor SW1 is disposed downstream of the air cleaner 41 in the intake passage 40 and measures the flow rate of the air flowing through the intake passage 40. The intake air temperature sensor SW2 is disposed downstream of the air cleaner 41 in the intake passage 40 and measures the temperature of the air flowing through the intake passage 40. The intake air pressure sensor SW3 is attached to the surge tank 42 and measures the pressure of the air introduced into the cylinder 11. The in-cylinder pressure sensor SW4 is attached to the cylinder head 13 of each cylinder 11 and measures the pressure in each cylinder 11. The water temperature sensor SW5 is attached to the engine 1 and measures the temperature of the cooling water. The exhaust gas temperature sensor SW6 is disposed in the exhaust passage 50 and measures the temperature of the exhaust gas flowing through the exhaust passage 50. The exhaust gas pressure sensor SW7 is attached to the exhaust passage 50 and measures the pressure of the exhaust gas discharged from the cylinder 11. The crank angle sensor SW8 is attached to the engine 1 and measures the rotation angle of the crankshaft 15. The accelerator opening sensor SW9 is attached to the accelerator pedal mechanism and measures the accelerator opening corresponding to the operation amount of the accelerator pedal. The intake cam angle sensor SW10 is attached to the engine 1 and measures the rotation angle of the intake camshaft. The exhaust cam angle sensor SW11 is attached to the engine 1 and measures the rotation angle of the exhaust camshaft. The intake cam lift sensor SW12 is attached to the engine 1 and measures the lift amount of the intake valve 21. The linear O2 sensor SW13 is attached to the exhaust passage 50 and measures the oxygen concentration in the exhaust gas. The fuel pressure sensor SW14 is attached to the common rail 64 and measures the pressure of the fuel injected into the cylinder 11 through the injector 6.

[0035] Based on the signals input from these sensors SW1 to SW14, the ECU 10 predicts, estimates, and determines the operating state of the engine 1 including the in-cylinder state quantity of the cylinder 11, and calculates the control quantity for each device. The ECU 10 outputs an electrical signal related to the calculated control quantity to the injector 6, the first ignition plug 251, the second ignition plug 252, the intake S-VT 231, the intake CVVL 232, the exhaust S-VT 241, the exhaust VVL 242, the fuel supply system 61, the throttle valve 43, and the EGR valve 54.

[0036] <Prediction of In-cylinder State Quantity in Intake and Exhaust Strokes> Next, the prediction of the in-cylinder state quantity of the cylinder 11 in the intake and exhaust strokes of the engine 1 executed by the ECU 10 according to the present embodiment will be described. FIG. 3 is a diagram showing an example of the valve profiles of the intake valve 21 and the exhaust valve 22 when the engine 1 performs HCCI operation. In FIG. 3, the horizontal axis represents the crank angle, the left vertical axis represents the pressure, and the right vertical axis represents the valve lift. In the present embodiment, the top dead center of the combustion stroke is set as the crank angle 0 [deg].

[0037] As shown in FIG. 3, in the present embodiment, the period from the opening timing (EVO) of the exhaust valve 22 to the closing timing (IVC) of the intake valve 21 is defined as the intake and exhaust stroke, and the period from IVC to the next EVO is defined as the combustion stroke. Further, in the intake and exhaust stroke, the period from EVO to the timing (EVO2) when the valve lift of the exhaust valve 22 increases once and then decreases and starts to increase again (i.e., starts the second opening) is defined as the exhaust stroke, and the period from EVO2 to IVC is defined as the intake stroke. In the intake stroke, the intake valve 21 opens and the exhaust valve 22 also performs the second opening, so the exhaust gas discharged in the exhaust stroke is introduced into the cylinder 11 again through the exhaust valve 22.

[0038] In this embodiment, the model used by the ECU 10 to predict the in-cylinder state quantity during the intake and exhaust strokes is composed of a discrete model for the exhaust stroke and a continuous model for the intake stroke. In the discrete model, the in-cylinder state quantity is calculated only for discrete points set during the exhaust stroke. On the other hand, in the continuous model, the in-cylinder state quantity is calculated with a predetermined calculation step width (for example, a crank angle of 1 [deg]). This is because in the exhaust stroke, only the exhaust valve 22 is open, so the gas inflow and outflow to the cylinder 11 are relatively simple, and the necessary calculation accuracy can be obtained even with the calculation of only discrete points. In contrast, in the intake stroke, both the intake valve 21 and the exhaust valve 22 are open simultaneously, so the gas inflow and outflow to the cylinder 11 are complex, and it is necessary to continuously calculate the change in the in-cylinder state quantity in order to obtain the desired calculation accuracy.

[0039] FIG. 4 is a flowchart of the in-cylinder state quantity prediction process executed by the ECU 10 according to this embodiment. The in-cylinder state quantity prediction process is executed, for example, for each combustion cycle of each cylinder 11 of the engine 1 after the end of the combustion stroke and before the end of the intake and exhaust strokes.

[0040] First, in step S1, the ECU 10 acquires various information from the sensors SW1 to SW14.

[0041] Next, in step S2, the ECU 10 sets the in-cylinder state quantity of the cylinder 11 in the EVO. Specifically, the ECU 10 sets the engine speed, intake pressure, exhaust pressure, in-cylinder pressure, in-cylinder temperature, and oxygen mass fraction in the EVO as the initial conditions for predicting the in-cylinder state quantity during the intake and exhaust strokes of the current cycle. These numerical values are set by the ECU 10 based on, for example, the sensor information acquired in step S1 and the in-cylinder state quantity in the EVO estimated by a known model for estimating the in-cylinder state quantity during the combustion stroke.

[0042] Next, in step S3, the ECU 10 calculates the in-cylinder state quantity only at a plurality of discrete points set during the exhaust stroke using the discrete model.

[0043] FIG. 5 is a diagram showing an example of the pressure profiles in the cylinder and the exhaust port during the exhaust stroke. The pressure profile in FIG. 5 was obtained using a simulation tool that numerically analyzes in detail the combustion reaction and gas flow in the cylinder, and the calculation results by the simulation tool have been verified by experiments using an actual machine. As shown in FIG. 5, the exhaust stroke is divided into the following three sub-processes by setting two discrete points in addition to EVO and EVO2.

[0044] (a) Blowdown process (EVO~EOB) In the present embodiment, the process in which high-pressure and high-temperature exhaust gas flows out from the cylinder 11 after EVO is called the blowdown process. The end of the blowdown (EOB) occurs when the pressure difference between the cylinder 11 and the exhaust port 19 becomes almost zero. It is assumed that there is heat loss from the wall of the cylinder 11 in this process.

[0045] (b) Low-pressure-difference exhaust process (EOB~SPR) After the blowdown process, the pressure difference is maintained almost zero, and then the pressure begins to rise. The period from the start of the pressure rise after the blowdown process to the start of the pressure rise (SPR) is called the low-pressure-difference exhaust process. The start of the pressure rise (SPR) refers to the time when the in-cylinder pressure begins to rise to a pressure higher than the exhaust port pressure as the piston 3 rises. It is assumed that there is heat loss from the wall of the cylinder 11 in this process.

[0046] (c) Pressure-rise exhaust process (SPR~EVO2) After the in-cylinder pressure has risen and the piston 3 reaches the top dead center (EVO2), the pressure difference becomes small again. The period from SPR to EVO2 is called the pressure-rise exhaust process. It is also assumed that there is heat loss from the wall of the cylinder 11 in this process.

[0047] In the above EOB and SPR, since the pressure difference between the cylinder 11 and the exhaust port 19 is almost zero, the in-cylinder pressure can be estimated from the exhaust port pressure. Therefore, in addition to EVO and EVO2, these EOB and SPR are used as discrete points. The ECU 10 obtains the exhaust port pressure at each discrete point EOB, SPR, and EVO2, and calculates the in-cylinder pressure, in-cylinder temperature, and in-cylinder mass as in-cylinder state quantities based on the exhaust port pressure.

[0048] FIG. 6 is a diagram showing an example of the pressure pulsation of the exhaust port 19. In the exhaust process, since the high-pressure and high-temperature exhaust gas flows out from the exhaust valve 22, a large pulsation occurs. Therefore, in order to calculate the outflow of the exhaust gas from the cylinder 11, the air column resonance in the exhaust passage 50 is modeled. FIG. 7 is a schematic diagram of the air column resonance model in the exhaust passage.

[0049] As shown in FIG. 7, in the air column resonance model of the present embodiment, one end of the exhaust passage 50 (the cylinder 11 side) is a free end, and the other end (specifically, the exhaust pipe manifold side) is a fixed end with a constant pressure.

[0050] Considering the fundamental vibration, triple vibration, and quintuple vibration, the pressure P of the exhaust port 19 exp is expressed by the following formula (1) as a function of the elapsed time t from EVO. JPEG0007696142000001.jpg9150 Here, P exh is the exhaust pressure (for example, the pressure of the exhaust pipe manifold, which is constant in this embodiment), ΔP n , f n , φ n represent the amplitude, frequency, and phase of the nth mode, respectively.

[0051] The resonance frequency of the air column is expressed by the following formula (2). JPEG0007696142000002.jpg33151

[0052] Here, ΔT n represents the temperature drop from EVO and the term necessary to consider the temperature gradient in the exhaust direction in particular. ΔT nis the three variables that affect the temperature drop, namely the time t from EVO to EVO2 EVO-EVO2 , the in-cylinder temperature T at EVO EVO , and the in-cylinder pressure P at EVO EVO is described as a linear function as follows. JPEG0007696142000003.jpg20150

[0053] The phase is estimated as follows as a function of the three parameters of the engine speed N e , T EVO , P EVO . These parameters are selected considering the exhaust gas velocity and energy. JPEG0007696142000004.jpg20150 These parameters are selected considering the exhaust gas velocity and energy.

[0054] The amplitude of each mode is represented by the following equation (5). JPEG0007696142000005.jpg33150 Here, r n is the amplitude ratio, ΔP total is the total amplitude. The amplitude ratio is the ratio of the amplitude of the fundamental wave or the fifth harmonic vibration to the amplitude of the third harmonic vibration. r1 and r3 are calculated as follows. JPEG0007696142000006.jpg12150

[0055] The definition of the total amplitude is the maximum value of |P exp -P exh | in the exhaust stroke and is predicted as follows. JPEG0007696142000007.jpg9150 Note that in the above equations (3), (4), (6), and (7), α, β, γ, and δ can be values calibrated using the FFT processing results of (P exp -P exh ) in the exhaust stroke.

[0056] Based on the exhaust port pressure calculated using the above-described air column resonance model, the in-cylinder pressure, in-cylinder temperature, and in-cylinder mass at each discrete point EOB, SPR, and EVO2 can be obtained as follows.

[0057] In-cylinder pressure P of EOB EOB is JPEG0007696142000008.jpg9150where ΔP EOB is a preset value, for example, 1 kPa. Also, θ representing the timing of EOB EOB may be obtained in advance using a simulation tool according to the engine speed and the in-cylinder pressure at EVO, and stored in memory as a look-up table, or may be calculated by ECU10 based on the engine speed and the in-cylinder pressure at EVO.

[0058] In-cylinder temperature T of EOB EOB is the temperature T based on the adiabatic process EOB_ad subtracting the temperature drop ΔT due to heat loss from the cylinder wall EOB and calculated as follows. JPEG0007696142000009.jpg20150where ΔT EOB can be calculated as follows using the heat transfer coefficient h given by Woschni's equation (12). JPEG0007696142000010.jpg12150 JPEG0007696142000011.jpg9150where d, P, T, C m are the cylinder diameter (m), in-cylinder pressure (kPa), in-cylinder temperature (K), and cycle-averaged piston speed (m / s), but the average values of these values at EVO and EOB can be used for simplicity of calculation.

[0059] In-cylinder mass m of EOB EOB is based on the ideal gas state equation JPEG0007696142000012.jpg15150

[0060] In-cylinder pressure P of SPR SPR is JPEG0007696142000013.jpg9150where θ representing the timing of SPR SPRis the difference ΔP between the in-cylinder pressure and the exhaust port pressure calculated based on the lift amount of the exhaust valve 22 and the opening area of the exhaust port SPR can be calculated using Bernoulli's equation or the like at the time when it becomes a preset value, for example, 1 kPa. Also, ΔP SPR is the preset value as described above, for example, 1 kPa.

[0061] The in-cylinder temperature T of the SPR SPR is the temperature T based on the adiabatic process SPR_ad subtracting the temperature drop ΔT due to heat loss from the cylinder wall, and is calculated as follows SPR is subtracted and calculated as follows. JPEG0007696142000014.jpg21150 JPEG0007696142000015.jpg14150

[0062] The in-cylinder mass m of the SPR SPR is obtained from the ideal gas state equation JPEG0007696142000016.jpg14150

[0063] The in-cylinder pressure P of the EVO2 EVO2 is JPEG0007696142000017.jpg9150 Here, θ representing the timing of the EVO2 EVO2 is a value preset by the ECU10 based on the engine speed and load. Also, ΔP EVO2 is a value that changes according to the engine speed and the lift amount of the exhaust valve 22. For example, it may be obtained in advance using a simulation tool and stored in the memory as a look-up table, or may be calculated by the ECU10 based on the engine speed and the lift amount of the exhaust valve 22.

[0064] The in-cylinder temperature T of the EVO2 EVO2 is the temperature T based on the adiabatic process EVO2_ad subtracting the temperature drop ΔT due to heat loss from the cylinder wall EVO2 is subtracted and calculated as follows. JPEG0007696142000018.jpg21150 JPEG0007696142000019.jpg15150

[0065] The in-cylinder mass m of EVO2 EVO2 is obtained from the ideal gas equation of state JPEG0007696142000020.jpg14150

[0066] Furthermore, the ECU 10 calculates the in-cylinder EGR rate EGR in EVO2 EVO2 and the EGR outflow mass m to the intake port 18 EGR,inp_EVO2 as well. JPEG0007696142000021.jpg9150The more gas flows into the cylinder from the intake valve 21 to EVO2, the larger ΔEGR EVO2 becomes. Therefore, ΔEGR EVO2 is expressed by Equation (25). JPEG0007696142000022.jpg9150t inflow is the period during which the calculated exhaust port pressure P exp is lower than the intake port pressure P int (set as a constant value in step S2) from IVO to EVO2. To correct t inflow the engine speed N e is taken into account. When the engine speed is high, since the in-cylinder pressure exceeds the exhaust port pressure, it is necessary to shorten t inflow .

[0067] The EGR outflow mass m to the intake port 18 in EVO2 EGR,inp_EVO2 is calculated by Equation (26). JPEG0007696142000023.jpg14150Δm IVO-EVO2 is the absolute change in the mass in the cylinder 11 from IVO to EVO2, max(L iv) is the maximum lift amount of the intake valve 21 during one cycle. As IVO advances with an increase in the lift amount of the intake valve 21, the opening period of the intake valve 21 becomes longer and the opening area becomes larger, so the gas outflow amount from the cylinder 11 increases. Also, when the engine speed is high, the in-cylinder pressure becomes higher than the intake port pressure, so the outflow amount of the EGR gas increases, but the outflow ratio is Δm IVO-EVO2 tends to become smaller as it becomes larger. Equation (26) takes these effects into account.

[0068] When IVO is closer to SPR than EVO2, equation (27) is used, and when it is closer to EVO2, equation (28) is used to obtain m IVO . JPEG0007696142000024.jpg26150

[0069] Returning to FIG. 4, after calculating the in-cylinder state quantities at only a plurality of discrete points in the exhaust stroke using the discrete model in step S3, in step S4, the ECU 10 determines the calculation step width for calculating the in-cylinder state quantities in the intake stroke.

[0070] FIG. 8 is a map showing the calculation step width applied when calculating the in-cylinder state quantities in the intake stroke using the continuous model in the in-cylinder state prediction process according to the embodiment of the present invention. In this map, the horizontal axis represents the maximum intake valve lift, and the vertical axis represents the engine speed.

[0071] The greater the maximum intake valve lift or the lower the engine speed, the smaller the pressure difference between the pressures in the intake port 18 and the exhaust port 19 and the in-cylinder pressure in the cylinder 11 during the intake stroke. In this case, in the steady flow rate calculation formula that determines the gas flow direction for the cylinder 11 based only on the pressure difference between the pressures in the intake port 18 and the exhaust port 19 and the in-cylinder pressure in the cylinder 11, the gas flow direction changes in response to slight pressure fluctuations, and the flow rate cannot be calculated accurately. Therefore, it is desirable to reduce the calculation step width and calculate the gas flow rate using an unsteady flow rate calculation formula that takes into account the unsteady flow as the maximum intake valve lift increases or the engine speed decreases.

[0072] Therefore, as shown in FIG. 8, in the present embodiment, the ECU 10 sets the calculation step width to be smaller as the maximum intake valve lift increases or the engine speed decreases.

[0073] Next, in step S5, the ECU 10 determines whether the calculation step width determined in step S4 is less than or equal to a threshold value. For example, the threshold value is 3 [deg].

[0074] As a result of the determination in step S5, if the calculation step width is greater than the threshold value (step S5: NO), the process proceeds to step S6, and the ECU 10 selects a steady flow rate calculation formula as the calculation formula used to calculate the mass flow rate of the intake valve 21 and the exhaust valve 22 during the intake stroke.

[0075] Assuming that the gas flow passing through the intake valve 21 and the exhaust valve 22 is a steady isentropic flow, the mass flow rate is expressed by the following formula. JPEG0007696142000025.jpg41150 Here, the subscripts up and down mean upstream and downstream, respectively. Also, k is the calculation step, C dThe discharge coefficient is, A is the opening area of the valve, and L is the valve lift. FIG. 9 is a diagram illustrating the results of calculating the mass flow rate of each valve according to this equation (29). In FIG. 9, the upper graph shows each port pressure and the in-cylinder pressure, the middle graph shows the mass flow rate of the exhaust valve 22, and the lower graph shows the mass flow rate of the intake valve 21. Also, the left graph in FIG. 9 shows the case where the valve lift is relatively small and the engine speed is high, and the right graph shows the case where the valve lift is relatively large and the engine speed is low. Further, in the upper graph of FIG. 9, the solid line indicates the in-cylinder pressure, the dotted line indicates the pressure of the exhaust port 19, and the alternate long and short dash line indicates the pressure of the intake port 18. Also, in the middle and lower graphs of FIG. 9, the dotted line indicates the numerical analysis result by the simulation tool, and the solid line indicates the calculation result by the steady flow calculation formula according to this embodiment.

[0076] As shown in the left graph of FIG. 9, when the valve lift is small or the engine speed is high, the pressure difference between the pressures of the intake port 18 and the exhaust port 19 and the in-cylinder pressure of the cylinder 11 becomes large. Therefore, the mass flow rate can be accurately calculated even by the above steady flow calculation formula (29). However, when the valve lift is large or the engine speed is low, the pressure difference between the pressures of the intake port 18 and the exhaust port 19 and the in-cylinder pressure of the cylinder 11 becomes small. As a result, the direction of the flow upstream of the calculation frequently changes, and the calculation result of the mass flow rate vibrates as shown in the right graph of FIG. 9. Therefore, as described above, only when the calculation step width is larger than the threshold value, the ECU 10 selects the steady flow calculation formula as the calculation formula used to calculate the mass flow rates of the intake valve 21 and the exhaust valve 22 during the intake stroke.

[0077] On the other hand, as a result of the determination in step S5, when the calculation step width is equal to or less than the threshold value (step S5: YES), the process proceeds to step S7, and the ECU 10 selects the unsteady flow calculation formula as the calculation formula used to calculate the mass flow rates of the intake valve 21 and the exhaust valve 22 during the intake stroke.

[0078] As an unsteady flow calculation formula, the following unsteady orifice flow equation derived by Kiwan et al. from the Navier-Stokes equation can be used to calculate the flow rate of the EGR valve. JPEG0007696142000026.jpg102150

[0079] Here, the subscripts cyl and port represent the cylinder and the intake port or exhaust port, respectively, and A T is the opening area of the intake valve or exhaust valve. In the continuous model of this embodiment, using the power function of the valve lift amount L, the values of K in each valve and each flow direction are approximated as follows. JPEG0007696142000027.jpg26150 Note that the coefficients α 14~17 and β 14~17 can be preset based on, for example, the detailed numerical analysis results using a simulation tool.

[0080] When the above formula (30) is discretized and deformed, JPEG0007696142000028.jpg14150 Here, the mass flow rate at step k + 1 on the right side is replaced with the following predicted value. JPEG0007696142000029.jpg14150 Here, Δθ is the calculation step width, and m k+1,steady is the mass flow rate at step k + 1 calculated using the steady flow calculation formula (29).

[0081] From the above, the mass flow rate at step k + 1 can be obtained by the following formula. JPEG0007696142000030.jpg14150

[0082] FIG. 10 is a diagram illustrating the calculation results of the mass flow rate of each valve by steady flow calculation and unsteady flow calculation. In FIG. 10, the upper graph shows the mass flow rate of the exhaust valve 22, and the lower graph shows the mass flow rate of the intake valve 21. Also, the left graph in FIG. 10 shows the calculation result by the steady flow calculation formula, and the right graph shows the calculation result by the unsteady flow calculation formula. Further, in FIG. 10, the dotted line indicates the numerical analysis result by the simulation tool, and the solid line indicates the calculation results by the steady flow calculation formula and the unsteady flow calculation formula according to the present embodiment.

[0083] As described above, when the valve lift is large or the engine speed is low, as shown in the left graph of FIG. 10, when the mass flow rate of each valve is obtained using the steady flow calculation formula (29), the calculation result vibrates. On the other hand, when using the unsteady flow calculation formula (37), as shown in the right graph of FIG. 10, the mass flow rate can be calculated with high accuracy. Therefore, as described above, when the calculation step width is equal to or less than the threshold value, the ECU 10 selects the unsteady flow calculation formula as the calculation formula used to calculate the mass flow rate of the intake valve 21 and the exhaust valve 22 during the intake stroke.

[0084] Returning to FIG. 4, in step S6 or S7, after selecting the calculation formula used to calculate the mass flow rate of the intake valve 21 and the exhaust valve 22 during the intake stroke, the process proceeds to step S8, and the ECU 10 calculates the mass flow rate at the calculation step k using the calculation formula selected in step S6 or S7.

[0085] Next, in step S9, based on the mass flow rate calculated in step S8, the in-cylinder state quantity at the next calculation step k + 1 is calculated.

[0086] First, the in-cylinder mass m cyl,k+1 is calculated as follows. JPEG0007696142000031.jpg9150Here, dm ex,k 、dm in,krepresents the mass flowing in through the exhaust valve 22 and the intake valve 21 from the current calculation step to the next calculation step, and is calculated based on the mass flow rate calculated in step S8 and the calculation step width. Also, dm fuel,k is the increase in the fuel mass in the cylinder 11 from the current calculation step to the next calculation step.

[0087] The in-cylinder EGR rate EGR at the calculation step k k is such that the EGR rate at the exhaust port 19 is 1, and assuming that the EGR rate of the outflow gas at the intake port 18 at EVO2 is equal to EGR EVO2 is calculated as follows. JPEG0007696142000032.jpg15150 Here, the first term in the numerator represents the residual gas at EVO2 and the outflow gas to the intake port 18, and the second term represents the re-inflow gas from the exhaust port 19.

[0088] The in-cylinder temperature T at the calculation step k + 1 cyl,k+1 is calculated using the law of conservation of energy JPEG0007696142000033.jpg19150 Here, dH ex,k and dH in,k are the inflow enthalpy values from the exhaust port 19 and the intake port 18 respectively. The heat loss Q from the wall surface of the cylinder 11 loss,k can be estimated using Woschni's formula. JPEG0007696142000034.jpg11150

[0089] The in-cylinder pressure at the calculation step k + 1 is obtained from the ideal gas equation of state JPEG0007696142000035.jpg15150

[0090] The oxygen mass fraction x in the cylinder at IVC O2,IVC is obtained as follows. JPEG0007696142000036.jpg9150 Here, x O2,air is the mass fraction of O2 in the intake air, and x fuel,IVCis the mass fraction of fuel in the IVC. The oxygen mass fraction of the EGR gas is assumed to be equal to the oxygen mass fraction x of the in-cylinder gas in the EVO. O2,EVO Assume equality.

[0091] Next, in step S10, the ECU 10 determines whether the in-cylinder state quantity of the IVC has been calculated. As a result, if the in-cylinder state quantity of the IVC has not been calculated (step S10 : NO), the process proceeds to step S11, and the calculation step of the in-cylinder state quantity in the intake stroke is advanced by one (that is, k + 1 is substituted for the calculation step k). Then, the process returns to step S8, and steps S8 to S11 are repeated until the in-cylinder state quantity of the IVC is calculated.

[0092] In step S10, if the in-cylinder state quantity of the IVC has been calculated, the process proceeds to step S12, and the ECU 10 outputs the calculated in-cylinder state quantity of the IVC. That is, based on the in-cylinder state quantity of the IVC calculated here, the ECU 10 calculates the control quantity of each device of the engine 1.

[0093] After step S12, the ECU 10 ends the in-cylinder state quantity prediction process.

[0094] <Advantages and effects> Next, the advantages and effects of the in-cylinder state quantity prediction device and the in-cylinder state quantity prediction method for an engine according to the above-described embodiment will be described.

[0095] FIG. 11 is a diagram illustrating the calculation results of the in-cylinder state prediction process according to the present embodiment. In FIG. 11, the left graph shows the case where the valve lift is relatively small and the engine speed is high, and the right graph shows the case where the valve lift is relatively large and the engine speed is low. Further, FIG. 11 shows, in order from the top, the in-cylinder pressure, the in-cylinder temperature, the in-cylinder mass, and the in-cylinder EGR rate. Also, the solid line in each graph of FIG. 11 shows the numerical analysis result by the simulation tool, and the dots show the in-cylinder state quantity calculated by the in-cylinder state quantity prediction process of the present embodiment.

[0096] As shown in FIG. 11, according to the in-cylinder state quantity prediction process of this embodiment, in the exhaust stroke, even in the calculation of low load using the discrete model, the in-cylinder state quantity can be accurately predicted at each set discrete point. Further, in the intake stroke, when the valve lift is relatively small and the engine speed is high, that is, when the pressure difference between the pressures of the intake port 18 and the exhaust port 19 and the in-cylinder pressure of the cylinder 11 is relatively large, the in-cylinder state quantity can be accurately predicted with a low calculation load by the steady flow calculation formula. Also, even when the valve lift is relatively large and the engine speed is low, that is, when the pressure difference between the pressures of the intake port 18 and the exhaust port 19 and the in-cylinder pressure of the cylinder 11 is relatively small, the in-cylinder state quantity can be accurately predicted by using the unsteady flow calculation formula.

[0097] Thus, according to this embodiment, since the ECU 10 calculates the in-cylinder state quantity only at a plurality of discrete points in the exhaust stroke, for the exhaust stroke where only the exhaust valve 22 opens and the gas flow in and out of the cylinder 11 is relatively simple, the calculation load can be greatly reduced while ensuring the calculation accuracy. Also, since the ECU 10 continuously calculates the in-cylinder state quantity in the intake stroke, for the intake stroke where both the exhaust valve 22 and the intake valve 21 open simultaneously and the gas flow in and out of the cylinder 11 is relatively complex, the desired calculation accuracy can be obtained by continuous calculation. Therefore, the in-cylinder state quantity of the engine 1 in the intake and exhaust strokes can be accurately predicted with a short-time calculation.

[0098] Further, since the ECU 10 sets the discrete points in the exhaust stroke at the time when the pressure difference between the cylinder 11 and the exhaust port 19 is 0, the in-cylinder pressure of the cylinder 11 can be estimated based on the exhaust port pressure, and the in-cylinder state quantity can be predicted with high accuracy even in discrete calculations.

[0099] Also, when the valve lift is relatively small or the engine speed is high, that is, when the pressure difference between the pressures in the intake port 18 and the exhaust port 19 of the engine and the in-cylinder pressure of the cylinder 11 is relatively large, the ECU 10 can accurately predict the in-cylinder state quantity with a low calculation load by the steady flow calculation formula. Further, when the valve lift is relatively large or the engine speed is low, that is, when the pressure difference between the pressures in the intake port 18 and the exhaust port 19 and the in-cylinder pressure of the cylinder 11 is relatively small and the desired calculation accuracy cannot be obtained by the steady flow calculation formula, the ECU 10 can accurately predict the in-cylinder state quantity by using the unsteady flow calculation formula. Therefore, the in-cylinder state quantity of the engine 1 in the intake and exhaust strokes can be predicted with high accuracy by a short-time calculation.

[0100] Also, in order to appropriately control the HCCI combustion, the ECU 10 can accurately predict the in-cylinder state quantity in the intake and exhaust strokes, which has a great influence on the HCCI combustion, by a short-time calculation.

Explanation of Signs

[0101] 1 Engine 10 ECU (Controller) 11 Cylinder 18 Intake Port 19 Exhaust Port 21 Intake Valve 22 Exhaust Valve E Engine System SW2 Intake Air Temperature Sensor SW3 Intake Air Pressure Sensor SW4 In-Cylinder Pressure Sensor SW5 Water Temperature Sensor SW6 Exhaust Gas Temperature Sensor SW7 Exhaust Gas Pressure Sensor SW8 Crank Angle Sensor SW13 Linear O2 Sensor

Claims

1. An in-cylinder state quantity prediction device for an engine that introduces EGR into the cylinder by opening an exhaust valve during an exhaust stroke and simultaneously opening both the exhaust valve and an intake valve during an intake stroke under predetermined operating conditions, a sensor attached to the engine and configured to measure a physical quantity related to the in-cylinder state quantity of the engine and output a measurement signal; a processor that receives the measurement signal from the sensor and calculates the in-cylinder state quantity of the engine based on the measurement signal, comprising: the processor is configured to: set the in-cylinder state quantity at the end of the combustion stroke of the engine based on the measurement signal; calculate the in-cylinder state quantity only at a plurality of discrete points including the end time of the exhaust stroke of the engine based on the in-cylinder state quantity at the end of the combustion stroke; calculate the in-cylinder state quantity continuously from the start time to the end time of the intake stroke at a predetermined calculation step width based on the in-cylinder state quantity at the end time of the exhaust stroke. An in-cylinder state quantity prediction device for an engine.

2. The discrete points include a blowdown end time when the pressure difference between the cylinder of the engine and the exhaust port reaches 0 after the exhaust valve opens in the exhaust stroke, and a pressure rise start time when the pressure difference between the cylinder and the exhaust port starts to increase after the blowdown end time. The in-cylinder state quantity prediction device for an engine according to claim 1.

3. The processor is configured to: set the calculation step width smaller as the engine speed of the engine is lower or as the valve lift amount of the engine is larger; when the calculation step width is larger than a predetermined threshold value, calculate the in-cylinder state quantity during the intake stroke using a steady flow calculation formula assuming that the flow of gas passing through the intake valve and the exhaust valve of the engine is a steady flow. When the calculation step width is less than or equal to a predetermined threshold value, the in-cylinder state quantity in the intake stroke is calculated using an unsteady flow rate calculation formula assuming that the gas flow passing through the intake valve and the exhaust valve of the engine is an unsteady flow. An in-cylinder state quantity prediction device for an engine according to claim 1 or 2.

4. The in-cylinder state quantity prediction device for an engine according to any one of claims 1 to 3, wherein the processor calculates the in-cylinder state quantity in the exhaust stroke and the intake stroke of the engine under operating conditions in which the engine performs premixed compression ignition combustion.

5. An in-cylinder state quantity prediction method for an engine in which, under predetermined operating conditions, an exhaust valve opens in an exhaust stroke, and EGR is introduced into a cylinder by opening both the exhaust valve and an intake valve simultaneously in the intake stroke, measuring, by a sensor attached to the engine, a physical quantity related to the in-cylinder state quantity of the engine and outputting a measurement signal; receiving, by a processor, the measurement signal from the sensor and calculating the in-cylinder state quantity of the engine based on the measurement signal, The step of causing the processor to calculate the in-cylinder state quantity includes setting the in-cylinder state quantity at the end of the combustion stroke of the engine based on the measurement signal; calculating the in-cylinder state quantity only at a plurality of discrete points including the end time of the exhaust stroke of the engine based on the in-cylinder state quantity at the end of the combustion stroke; continuously calculating the in-cylinder state quantity from the start time to the end time of the intake stroke at a predetermined calculation step width based on the in-cylinder state quantity at the end time of the exhaust stroke. An in-cylinder state quantity prediction method for an engine.

Images