JP2010048171A - Misfire detection device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect misfire in an internal combustion engine which continues to combust even after opening the exhaust valve. <P>SOLUTION: The history of the heat generation rate before opening the exhaust valve is detected. A model equation expressing the history of the heat generation rate over the combustion period is then determined based on the history of the heat generation rate before opening the exhaust valve. Then, the amount of generated heat is calculated by integrating the model equation over at least the combustion period. On the basis of the calculation, if the amount of generated heat is smaller than a threshold value, misfire is determined to occur. If the amount of generated heat is lager than the threshold value, misfire is determined not to occur. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a misfire detection apparatus for an internal combustion engine.

  Calculate the in-cylinder pressure history in the crank angle range including the combustion period, calculate the actual heat generation rate history from the in-cylinder pressure history, and compare the actual heat generation rate history with the theoretical heat generation history. An internal combustion engine that detects the occurrence of knock is known (see Patent Document 1). In this internal combustion engine, the heat release rate history is calculated from the in-cylinder pressure using a thermodynamic energy conservation law.

JP 2007-170345 A

  By the way, for example, if the ignition timing or fuel injection timing is retarded, the combustion period is retarded, and as a result, combustion may continue even after the exhaust valve is opened, and heat generation may continue.

  However, after the exhaust valve is opened, the energy conservation law no longer holds between the in-cylinder pressure and the heat generation rate. As a result, if combustion continues even after the exhaust valve is opened, the actual heat release rate history cannot be accurately detected from the in-cylinder pressure history using the energy conservation law. There is a possibility that it cannot be detected accurately.

  In order to solve the above problems, according to the present invention, in an internal combustion engine in which combustion can continue even after the exhaust valve is opened, means for obtaining a heat release rate history before the exhaust valve is opened, and after the exhaust valve is opened, Means for estimating the heat generation rate history based on the heat generation rate history before opening the exhaust valve, means for estimating the heat generation amount based on the heat generation rate history after opening the exhaust valve, and the heat generation Means for determining that a misfire has occurred when the amount is less than the threshold value.

  Misfire can be accurately detected in an internal combustion engine in which combustion can continue even after the exhaust valve is opened.

  FIG. 1 shows a case where the present invention is applied to a spark ignition type internal combustion engine. However, the present invention can also be applied to a compression ignition type internal combustion engine.

  Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an intake valve, 7 is an intake port, 8 is an exhaust valve, 9 is an exhaust port, Reference numeral 10 denotes a spark plug. The intake port 7 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to an air cleaner 14 via an intake duct 13. An air flow meter 15 for detecting the amount of intake air and a throttle valve 17 driven by an actuator 16 are disposed in the intake duct 13. An electronically controlled fuel injection valve 18 is attached to the intake port 7. These fuel injection valves 18 are connected to a fuel pump 20 through a common rail 19, and the fuel pump 20 is connected to a fuel tank 21. On the other hand, the exhaust port 9 is connected to a catalytic converter 24 via an exhaust manifold 22 and an exhaust pipe 23, and the catalytic converter 24 is connected to an exhaust pipe 25.

  The electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31. A ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port 35 and an output port 36. It comprises. A water temperature sensor 26 for detecting the engine cooling water temperature is attached to the cylinder block 2. An oil temperature sensor 27 for detecting the engine oil temperature is attached to the engine body 1. Further, a load sensor 40 for detecting the amount of depression of the accelerator pedal is attached to the accelerator pedal 39. The output signals of the air flow meter 15, the water temperature sensor 26, the oil temperature sensor 27, and the load sensor 40 are input to the input port 35 via the corresponding AD converters 37. Further, a crank angle sensor 41 that generates an output pulse every time the crankshaft rotates by a certain angle, for example, 30 crank angles, is connected to the input port 35. The intake air amount detected by the air flow meter 15, the engine cooling water temperature Tw detected by the water temperature sensor 27, the engine oil temperature To detected by the oil temperature sensor 27, and the crank angle θ detected by the crank angle sensor 41 are constant time. Each time as a function of time t. The CPU 34 calculates the engine speed based on the output pulse from the crank angle sensor 41. On the other hand, the output port 36 is connected to the spark plug 10, the actuator 16, the fuel injection valve 18, and the fuel pump 20 through corresponding drive circuits 38.

  Next, a first embodiment according to the present invention will be schematically described first with reference to FIG. In FIG. 2, dQ (θ) / dθ represents the heat generation rate, θ represents the crank angle, and θEVO represents the valve opening timing of the exhaust valve 8.

  In the first embodiment according to the present invention, first, the history dQ (θ) / dθ of the heat generation rate before the exhaust valve is opened, that is, a plurality of data sets (θ, dQ (θ) / dθ) for each crank angle interval Δθ. Detected. An example of the heat release rate history dQ (θ) / dθ before opening the exhaust valve is shown in the form of a plot in FIG. Next, a model formula M representing the heat generation rate history dQ (θ) / dθ over at least the combustion period is determined based on the heat generation rate history dQ (θ) / dθ before opening the exhaust valve. An example of the model formula M is shown by a solid line in FIG. Next, the heat generation amount Qt is calculated by integrating the model formula M at least over the combustion period. This heat generation amount Qt is shown in the form of a hatched area in FIG.

  In addition, it is determined that misfire has occurred when the heat generation amount Qt is smaller than, for example, a certain threshold value Qmf, and that no misfire has occurred when the heat generation amount Qt is larger than the threshold value Qmf. To be judged.

  In the first embodiment according to the present invention, the heat generation rate dQ (θ) / dθ is calculated using the following equation (1) obtained from the thermodynamic energy conservation law.

  Here, γ represents the specific heat ratio of the in-cylinder gas, Pc (θ) represents the in-cylinder pressure, and V (θ) represents the in-cylinder volume.

  The specific heat ratio γ is a constant value. The specific heat ratio γ may be a function of temperature.

  The in-cylinder volume V (θ) is stored in advance in the ROM 32 in the form of a map shown in FIG. 3 as a function of the crank angle θ. Further, the change rate dV (θ) / dθ of the in-cylinder volume is calculated from the in-cylinder volume V (θ).

  The in-cylinder pressure Pc (θ) can be detected by, for example, an in-cylinder pressure sensor, but is calculated using the following equation (2) in the first embodiment according to the present invention.

  Here, TQp (θ) represents an in-cylinder pressure torque that is a torque generated by the force exerted on the piston 4 by the in-cylinder pressure Pc (θ).

  The in-cylinder pressure torque TQp (θ) is calculated using the following equation (3) derived from the equation of motion for the crankshaft.

  Here, J (θ) is the moment of inertia of the engine body 1, ω (θ) is the crank angular velocity as a function of the crank angle θ, and TQm (θ) is caused by the inertia of a moving member such as a piston of the engine body 1. Inertial mass torque that is torque, TQf (θ) represents mechanical loss torque that is torque generated by mechanical loss of the engine body 1.

  The inertia moment J (θ) and the inertia mass torque TQm (θ) are stored in advance in the ROM 32 in the form of maps shown in FIGS. 4 and 5 as a function of the crank angle θ.

  The crank angular velocity ω (θ) is calculated by converting the crank angular velocity ω (t) as a function of time t into a function of the crank angle θ. The crank angular velocity ω (t) is calculated from the crank angle θ (t) as a function of time t using the following equation (4).

  Mechanical loss torque TQf (θ) is a function of crank angular velocity ω (θ), engine load factor KL (θ) as a function of crank angle θ, and engine oil temperature To (θ) as a function of crank angle θ. It is stored in advance in the ROM 32 in the form of a map shown in FIG.

  The engine load factor KL (θ) represents the ratio of the engine load to the total load. In the first embodiment according to the present invention, the engine load factor KL (t) as a function of time t is calculated in advance based on the intake air amount detected by the air flow meter 15, and this KL (t) is calculated as the crank angle. KL (θ) is calculated by converting θ (t) into a function of the crank angle θ.

  The engine oil temperature To (θ) is calculated by converting the engine oil temperature To (t) as a function of time t into a function of the crank angle θ using the crank angle θ (t).

  That is, the crank angular velocity history ω (θ) is calculated from the crank angle history θ (t), and the mechanical loss torque is calculated from the crank angular velocity history ω (θ), the engine load factor history KL (θ), and the engine oil temperature history To (θ). A history TQf (θ) is calculated. Next, in-cylinder pressure torque history TQp (θ) using equation (3) from inertia moment history J (θ), crank angular velocity history ω (θ), inertia mass torque history TQm (θ), and mechanical loss torque history TQf (θ). ) Is calculated. Next, the in-cylinder pressure history Pc (θ) is calculated from the in-cylinder pressure torque history TQp (θ) and the in-cylinder volume history V (θ) using Equation (2). Next, the heat release rate history dQ (θ) / dθ is calculated from the in-cylinder pressure history Pc (θ) and the in-cylinder volume history V (θ) using Equation (1).

  Here, in the first embodiment according to the present invention, the heat release rate history dQ (θ) / dθ is calculated for each crank angle interval Δθ from the timing before combustion start, for example, from the ignition timing θSA to the exhaust valve opening timing θEVO. The This is because, of course, no heat is generated before the start of combustion, and after the exhaust valve 8 is opened, the energy conservation law expressed by the equation (1) is not established. However, the heat release rate history dQ (θ) / dθ may be calculated from, for example, the intake valve closing timing θIVC before the start of combustion. The other crank speed history ω (θ), engine load factor history KL (θ), etc. may be calculated as long as necessary for calculating the heat generation amount Qt.

  On the other hand, various function expressions can be used as the model expression M. In the first embodiment according to the present invention, the Wiebe function represented by the following equation (5) is used as the model equation M.

  Here, a is a constant (for example, 6.9), Qf is the amount of heat of the fuel supplied into the cylinder, k is an efficiency parameter indicating the efficiency with which the amount of heat Qf of fuel is converted into heat, and θp is expressed by the crank angle width. The combustion period, m is a shape parameter representing the shape of the heat release rate curve, and θb is the heat generation start crank angle.

  The heat quantity Qf of the fuel is stored in advance in the ROM 32 as a function of the fuel injection time TAU as shown in FIG. 7, for example. The heat quantity Qf of the fuel may be obtained based on one or both of the fuel injection time TAU and the fuel injection timing.

  Then, the model equation M can be determined by calculating the four parameters of the efficiency parameter k, the combustion period θp, the shape parameter m, and the heat generation start crank angle θb.

  In the first embodiment according to the present invention, first, the above-described heat release rate history dQ (θ) / dθ, that is, n data sets (θ, dQ (θ) / dθ) are substituted into equation (5), n equations are created. These equations are expressed by the following equation (6).

  Next, by solving these equations using, for example, the least square method, four parameters k, θp, m, and θb are calculated. Therefore, the model formula M is determined.

  Since the number of unknown parameters is 4, it means that the number of equations or data sets necessary for determining the model formula M is n4 or more.

  When the model formula M is determined, the heat generation amount Qt is calculated by integrating the model formula M to the formula (5) from the timing before combustion occurrence, for example, the ignition timing θSA, to the timing after completion of combustion, for example, exhaust top dead center θTDCE. Is done. That is, the heat generation amount Qt is expressed by the following equation (7).

  Qt calculated in this way accurately represents the amount of heat generated even when combustion continues even after the exhaust valve is opened. Therefore, it is possible to accurately determine whether or not misfire has occurred.

  Therefore, in general terms, the heat generation rate history before opening the exhaust valve is obtained, the heat generation rate history after opening the exhaust valve is estimated based on the heat generation rate history before opening the exhaust valve, and the exhaust valve This means that the heat generation amount is estimated based on the heat generation rate history after the valve is opened. In this case, the in-cylinder pressure history before opening the exhaust valve is obtained, and the heat release rate history before opening the exhaust valve is obtained based on the in-cylinder pressure history before opening the exhaust valve. Furthermore, at least a model formula representing the heat release rate history after the exhaust valve is opened is determined based on the heat release rate history before the exhaust valve is opened, and the heat generation amount is estimated using the model formula.

  FIG. 8 shows a flowchart for executing the misfire detection routine of the first embodiment according to the present invention. This routine is executed by interruption every predetermined time.

  Referring to FIG. 8, first, at step 100, a routine for calculating the heat release rate history dQ (θ) / dθ is executed. This routine is illustrated in FIG. In the subsequent step 200, the routine for determining the model formula M is executed. This routine is illustrated in FIG. In the subsequent step 300, a routine for calculating the heat generation amount Qt is executed. This routine is illustrated in FIG. In the following step 400, it is determined whether or not the heat generation amount Qt is smaller than the threshold value Qmf. When Qt <Qmf, the routine proceeds to step 500 where it is determined that a misfire has occurred. In contrast, when Qt ≧ Qmf, the routine proceeds to step 600 where it is determined that no misfire has occurred.

  Referring to FIG. 9 showing a routine for calculating the heat release rate history dQ (θ) / dθ, in step 101, the moment of inertia history J (θ) is calculated using the map of FIG. In the subsequent step 102, the crank angle history θ (t) detected by the crank angle sensor 41 is acquired, that is, read. In the subsequent step 103, the crank angular velocity history ω (t) is calculated using equation (4). In the subsequent step 104, the crank angular velocity history ω (θ) is calculated from ω (t). In the subsequent step 105, the change rate history dω (θ) / dt of the crank angular velocity ω (θ) is calculated. In the subsequent step 106, an inertia mass torque history TQm (θ) is calculated using the map of FIG. In the subsequent step 107, the engine load factor history KL (t) calculated based on the intake air amount is acquired. In the subsequent step 108, the engine load factor history KL (θ) is calculated from KL (t) and θ (t). In the subsequent step 109, the engine oil temperature history To (t) detected by the oil temperature sensor 27 is acquired. In the subsequent step 110, the engine oil temperature history To (θ) is calculated from To (t) and θ (t). In the subsequent step 111, the mechanical loss torque history TQf (θ) is calculated using the map of FIG. In the following step 112, in-cylinder pressure torque history TQp (θ) is calculated using equation (3). In the following step 113, the cylinder volume history V (θ) is calculated using the map of FIG. In the following step 114, the change rate history dV (θ) / dθ of the in-cylinder volume V (θ) is calculated. In the following step 115, in-cylinder pressure history Pc (θ) is calculated using equation (2).

  In the following step 116, the change rate history dPc (θ) / dθ of the in-cylinder pressure Pc (θ) is calculated. In the following step 117, the specific heat ratio γ is obtained. In the subsequent step 118, the ignition timing θSA is acquired. In the following step 119, the exhaust valve opening timing θEVO is acquired. In the following step 120, the heat release rate history dQ (θ) / dθ from the ignition timing θSA to the exhaust valve opening timing θEVO is calculated using equation (1).

  Referring to FIG. 10 showing the routine for determining the model formula M, in step 201, the heat quantity Qf of the fuel is calculated using the map of FIG. In the following step 202, an equation is created using the heat release rate history dQ (θ) / dθ. In the next step 203, unknown parameters (k, θp, m, θb) are calculated by solving the equations. In this way, the model formula M is determined.

  Referring to FIG. 11 showing the calculation routine of the heat generation amount Qt, in step 301, the exhaust top dead center θTDCE is acquired. In the subsequent step 302, the heat generation amount Qt is calculated by integrating the model equation M from the ignition timing θSA to the exhaust top dead center θTDCE.

  Next, a second embodiment according to the present invention will be described.

  The change in the amount of heat of the in-cylinder gas can be caused not only by combustion but also by heat transfer or heat loss between the in-cylinder gas and the cylinder wall. That is, when the above-described dQ (θ) / dθ is referred to as an apparent heat generation rate dQ (θ) / dθ, the apparent heat generation rate dQ (θ) / dθ is expressed by the following equation (8). .

  Here, dQcomb (θ) / dθ represents a combustion heat generation rate that is a heat generation rate due to combustion, and dQth (θ) / dθ represents a heat loss rate from the in-cylinder gas to the cylinder wall.

  Therefore, the combustion heat generation rate dQcomb (θ) / dθ is expressed by the following equation (9).

  In the second embodiment according to the present invention, first, the history dQcomb (θ) / dθ of the combustion heat generation rate before the exhaust valve is opened is calculated. Next, a model formula M representing the combustion heat generation rate history dQcomb (θ) / dθ over at least the combustion period is determined based on the combustion heat generation rate history dQcomb (θ) / dθ.

  In this case, the following equation (10) representing the combustion heat generation rate dQcomb (θ) / dθ is used as the model equation M.

  Next, the heat generation amount Qt is calculated by integrating the model formulas M to (10) at least over the combustion period.

  Further, when the heat generation amount Qt is smaller than the threshold value Qmf, it is determined that misfire has occurred, and when the heat generation amount Qt is larger than the threshold value Qmf, it is determined that no misfire has occurred. .

  The heat generation amount Qt in this case accurately represents the heat generation amount due to combustion, and misfire detection is performed based on the heat generation amount Qt, so that misfire detection can be performed more accurately. Further, since the Weibé function simulates heat generation by combustion, the model heat generation rate dQcomb (θ) / dθ is used to accurately calculate the combustion heat generation rate dQcomb (θ) / dθ. Therefore, the heat generation amount Qt can be accurately calculated.

  Specifically, in the second embodiment according to the present invention, as in the first embodiment, the history of the apparent heat generation rate dQ (θ) / dθ from the ignition timing θSA to the exhaust valve opening timing θEVO is recorded. Calculated. Further, a heat loss rate history dQth (θ) / dθ from the ignition timing θSA to the exhaust valve opening timing θEVO is calculated. Next, the combustion heat generation rate history dQcomb (θ) / dθ from the ignition timing θSA to the exhaust valve opening timing θEVO is calculated using Equation (9).

  The heat loss rate dQth (θ) / dθ is calculated using the following equation (11) in the second embodiment of the present invention.

  Here, k represents a heat transfer coefficient between the in-cylinder gas and the cylinder wall or engine cooling water, Tc (θ) represents the in-cylinder gas temperature, and Tw represents the engine cooling water temperature (θ).

  The in-cylinder gas temperature Tc (θ) is calculated using the following equation (12) derived from the equation of state.

  Here, R represents a gas constant.

  The engine coolant temperature Tw (θ) is calculated by converting the engine coolant temperature Tw (t) as a function of time t into a function of the crank angle θ.

  For the heat transfer coefficient k, the in-cylinder gas temperature Tc (θSA), the engine cooling water temperature Tw (θSA) and the heat loss rate dQth (θSA) / dθ at the timing before the start of combustion, for example, the ignition timing θSA, are substituted into the equation (11). It is calculated using the formula (13) obtained by the above.

  The heat loss rate dQth (θSA) / dθ at the ignition timing θSA corresponds to the negative value (−dQ (θSA) / dθ) of the apparent heat generation rate dQ (θSA) / dθ at the ignition timing θSA. 14).

  That is, the heat transfer coefficient k is calculated from the in-cylinder gas temperature Tc (θSA), the engine cooling water temperature Tw (θSA), and the heat loss rate dQth (θSA) / dθ at the ignition timing θSA, using the equation (13). The heat loss rate history dQth (θ) / dθ is calculated from the coefficient k, the in-cylinder gas temperature history Tc (θ), and the engine cooling water temperature history Tw (θ) using Equation (11). Next, the combustion heat generation rate history dQcomb (θ) / dθ is calculated from the apparent heat generation rate history dQ (θ) / dθ and the heat loss rate history dQth (θ) / dθ using Equation (9).

  Next, a plurality of equations are created by substituting the combustion heat generation rate history dQcomb (θ) / dθ from the ignition timing θSA to the exhaust valve opening timing θEVO into the equation (10). These equations are expressed by the following equation (15), for example.

  Then, the model equation M is determined by solving these equations using, for example, the least square method.

  Next, the heat generation amount Qt is calculated by integrating the model formula M to formula (10), for example, from the ignition timing θSA to the exhaust top dead center θTDCE. That is, the heat generation amount Qt is expressed by the following equation (16).

  Therefore, in general terms, the heat loss rate history before opening the exhaust valve is obtained, and the combustion heat generation rate before opening the exhaust valve based on the heat release rate history and the heat loss rate history before opening the exhaust valve. Obtain the history, estimate the combustion heat generation rate history after opening the exhaust valve based on the combustion heat generation rate history before opening the exhaust valve, and heat generation amount based on the combustion heat generation rate history after opening the exhaust valve It means that is estimated.

  FIG. 12 shows a flowchart for executing the misfire detection routine of the second embodiment according to the present invention. This routine is executed by interruption every predetermined time.

  Referring to FIG. 12, first, in step 100, an apparent heat generation rate history dQ (θ) / dθ calculation routine is executed. This routine is illustrated in FIG. In the subsequent step 140, a routine for calculating the heat loss rate history dQth (θ) / dθ is executed. This routine is illustrated in FIG. In the following step 160, the combustion heat generation rate history dQcomb (θ) / dθ is calculated using the equation (9).

  In the subsequent step 200, the routine for determining the model formula M is executed. This routine is illustrated in FIG. However, in the second embodiment according to the present invention, the model equation M determined by this routine is expressed by equation (10). In step 202, an equation is created using the combustion heat generation rate history dQcomb (θ) / dθ.

  In the subsequent step 300, a routine for calculating the heat generation amount Qt is executed. This routine is illustrated in FIG. However, in the second embodiment according to the present invention, the model equation M integrated in step 302 is expressed by equation (10).

  In the following step 400, it is determined whether or not the heat generation amount Qt is smaller than the threshold value Qmf. When Qt <Qmf, the routine proceeds to step 500 where it is determined that a misfire has occurred. In contrast, when Qt ≧ Qmf, the routine proceeds to step 600 where it is determined that no misfire has occurred.

  Referring to FIG. 13 showing a routine for calculating the heat loss rate history dQth (θ) / dθ, in step 141, in-cylinder gas temperature history Tc (θ) using Pc (θ) and V (θ) using equation (12). Is calculated. In the subsequent step 142, the engine cooling water temperature history Tw (t) detected by the water temperature sensor 26 is acquired. In the following step 143, the engine coolant temperature history Tw (θ) is calculated from Tw (t) and θ (t). In the following step 144, the in-cylinder gas temperature history Tc (θSA) at the ignition timing θSA is calculated. In the following step 145, the engine coolant temperature history Tw (θSA) at the ignition timing θSA is calculated. In the following step 146, the heat loss rate dQth (θSA) / dθ at the ignition timing θSA is calculated using the equation (14). In the following step 147, the heat transfer coefficient k is calculated using equation (13). In the following step 148, the heat loss rate history dQth (θ) / dθ is calculated from the heat transfer coefficient k, the in-cylinder gas temperature history Tc (θ), and the engine cooling water temperature history Tw (θ) using equation (11). .

  Since the other configuration and operation of the second embodiment according to the present invention are the same as those of the first embodiment according to the present invention, description thereof is omitted.

  Next, a third embodiment according to the present invention will be described.

  In the first and second embodiments according to the present invention described so far, the threshold value Qmf is set to a constant value.

  However, the amount of heat generated by combustion, particularly the lower heating value of the fuel, can vary depending on the type of fuel such as gasoline, alcohol, or light oil.

  Therefore, in the third embodiment according to the present invention, the fuel property indicating the type of fuel is detected, and the threshold value Qmf is set based on the fuel property. As a result, misfire detection can be performed accurately regardless of the type of fuel.

  More specifically, in the third embodiment according to the present invention, the threshold value Qmf is calculated using the following equation (17).

  Here, kmf represents the misfire determination margin allowance coefficient, and Qbs represents the lower heating value of the fuel.

  The misfire determination margin allowance coefficient kmf is a value from 0 to 1, and is preferably 0.2 to 0.3, for example.

  The lower heating value Qbs is stored in advance in the ROM 32 in the form of a map shown in FIG. 14 as a function of the fuel property representative value I determined according to the fuel property.

  The fuel property representative value I is calculated as follows. That is, when the combustion speed at the time when the laminar combustion ends or at the time tLE is referred to as a laminar combustion speed SL, the laminar combustion speed SL is previously stored in the ROM 32 in the form of a map shown in FIG. Is stored within. In the third embodiment according to the present invention, the laminar combustion speed SL is calculated, and I giving the SL closest to the laminar combustion speed SL is the fuel property representative value I.

  The laminar combustion speed SL is calculated as follows. That is, first, the combustion speed history Sf (t) is calculated. Next, a laminar combustion end time tLE is calculated. Next, the combustion speed Sf (tLE) at the laminar combustion end time tLE is set to the laminar combustion speed SL. That is, the laminar combustion speed SL is calculated using the following equation (18).

  The combustion speed Sf (t) is calculated as follows. That is, assuming that a spherical burned gas portion Pb and surrounding unburned gas portion Pub are formed in the cylinder during the combustion period, as shown in FIG. Pb expands. Accordingly, the combustion speed Sf (t) is calculated from the radius rb (t) of the burned gas portion Pb using the following equation (19).

  The burnt gas portion Pb radius rb (t) is calculated from the volume Vb (t) of the burnt gas portion Pb using the following equation (20).

  The burnt gas partial volume Vb (t) is calculated using the following equation (21).

  Here, V (t) represents the in-cylinder volume as a function of time t, and xb (t) represents the combustion ratio.

  The in-cylinder volume V (t) is calculated from the in-cylinder volume V (θ) and the crank angle θ (t). The in-cylinder volume V (θ) is calculated using the map shown in FIG.

  The combustion ratio xb (t) is calculated using the following equation (22).

  Here, t (θ) represents the time when the crank angle is θ.

  In Expression (22), the denominator represents the heat generation amount Qt from the start of combustion to the end of combustion, that is, the total heat generation amount as described above. On the other hand, the numerator represents the integral of the heat generation rate dQ (θ) / dθ from the ignition timing θSA to the crank angle θ, that is, the amount of heat generation from the start of combustion to time t (θ). Therefore, the combustion ratio xb (t) represents the degree of progress of combustion at time t (0 ≦ xb (t) ≦ 1).

  That is, the combustion rate history xb (t) is calculated from the heat release rate history dQ (θ) / dθ and the crank angle history θ (t) using Equation (22). Next, the burned gas partial volume history Vb (t) is calculated from the in-cylinder volume history V (t) and the combustion ratio history xb (t) using Equation (21). Next, the burnt gas partial radius history rb (t) is calculated from the burnt gas partial volume history Vb (t) using the equation (20). Next, the combustion speed history Sf (t) is calculated from the burned gas partial radius history rb (t) using Equation (19).

  On the other hand, the laminar combustion end time tLE is calculated as follows. That is, the combustion speed history Sf (t) as a function of time t draws a downward convex curve while laminar combustion is performed after the start of combustion, and rises upward when laminar combustion ends. Assuming that this curve is drawn, the laminar combustion end time tLE is the time t at which an inflection point occurs in the combustion speed history Sf (t) for the first time after the start of combustion. Therefore, in the third embodiment according to the present invention, the laminar combustion end time tLE is calculated using the following equation (23).

  Here, the function min {x | y, z} is a function that gives the smallest one of x that satisfies the conditions y and z simultaneously. That is, the minimum one of the times t for which the twice differential value of the combustion speed history Sf (t) is made zero is the laminar combustion end time tLE.

  When the laminar combustion end time tLE is calculated, the laminar combustion speed SL is calculated using Equation (18). Next, the fuel property representative value I is calculated from the laminar combustion speed SL using the map of FIG. Next, the lower heating value Qbs of the fuel is calculated from the fuel property representative value I using the map of FIG. Next, the threshold value Qmf is calculated from the lower heating value Qbs of the fuel using the equation (17).

  FIG. 17 shows a flowchart for executing the misfire detection routine of the third embodiment according to the present invention. This routine is executed by interruption every predetermined time.

  Referring to FIG. 17, first, at step 100, a routine for calculating the heat release rate history dQ (θ) / dθ is executed. This routine is illustrated in FIG. In the subsequent step 200, the routine for determining the model formula M is executed. This routine is illustrated in FIG. In the subsequent step 300, a routine for calculating the generation amount Qt is executed. This routine is illustrated in FIG. In the subsequent step 320, a routine for calculating the threshold value Qmf is executed. This routine is illustrated in FIG. In the following step 400, it is determined whether or not the heat generation amount Qt is smaller than the threshold value Qmf. When Qt <Qmf, the routine proceeds to step 500 where it is determined that a misfire has occurred. In contrast, when Qt ≧ Qmf, the routine proceeds to step 600 where it is determined that no misfire has occurred.

  Referring to FIG. 18 showing the routine for calculating the threshold value Qmf, in step 321, the combustion rate history xb () is calculated from the heat release rate history dQ (θ) / dθ and the crank angle history θ (t) using equation (22). t) is calculated. In the subsequent step 322, the in-cylinder volume history V (t) is calculated from the in-cylinder volume V (θ) and the crank angle θ (t). In the subsequent step 323, Vb (t) is calculated from the in-cylinder volume history V (t) and the combustion ratio history xb (t) using the equation (21). In the following step 324, the burned gas partial radius history rb (t) is calculated from the burned gas partial volume history Vb (t) using the equation (20). In the following step 325, the combustion speed history Sf (t) is calculated from the burned gas partial radius history rb (t) using the equation (19). In the following step 326, the laminar combustion end time tLE is calculated from the combustion speed history Sf (t) using the equation (23). In the following step 327, the laminar combustion speed SL is calculated from the laminar combustion end time tLE using the equation (18). In the following step 328, the fuel property representative value I is calculated from the laminar combustion speed SL using the map of FIG. In the following step 329, the lower heating value Qbs of the fuel is calculated from the fuel property representative value I using the map of FIG. In the subsequent step 330, the threshold value Qmf is calculated from the lower heating value Qbs of the fuel using the equation (17).

  The remaining structure and operation of the third embodiment according to the present invention are the same as those of the first embodiment according to the present invention, so description thereof will be omitted. Further, the third embodiment according to the present invention can be combined with the second embodiment.

1 is an overall view of an internal combustion engine. It is a figure for demonstrating 1st Example by this invention. It is a figure which shows the map of cylinder internal volume V ((theta)). It is a figure which shows the map of inertia moment J ((theta)). It is a figure which shows the map of inertia mass torque TQm ((theta)). It is a figure which shows the map of mechanical loss torque TQf ((theta)). It is a figure which shows the map of the calorie | heat amount of fuel Qf. It is a flowchart which shows the misfire detection routine of 1st Example by this invention. It is a flowchart which shows the calculation routine of heat release rate log | history dQ ((theta)) / d (theta). It is a flowchart which shows the determination routine of the model formula M. It is a flowchart which shows the calculation routine of the heat generation amount Qt. It is a flowchart which shows the misfire detection routine of 2nd Example by this invention. It is a flowchart which shows the calculation routine of heat loss rate log | history dQth ((theta)) / d (theta). It is a figure which shows the map of the low calorific value Qbs of a fuel. It is a figure which shows the map of the laminar flow combustion speed SL. It is a figure for demonstrating the burnt gas part Pb. It is a flowchart which shows the misfire detection routine of 3rd Example by this invention. It is a flowchart which shows the calculation routine of threshold value Qmf.

Explanation of symbols

1 Engine Body 5 Combustion Chamber 8 Exhaust Valve 41 Crank Angle Sensor

Claims (5)

  In an internal combustion engine in which combustion can continue even after the exhaust valve is opened, a means for obtaining a heat release rate history before the exhaust valve is opened, and a heat release rate history after the exhaust valve is opened are the heat release history before the exhaust valve is opened. A means for estimating based on the generation rate history, a means for estimating the heat generation amount based on the heat generation rate history after opening the exhaust valve, and a misfire occurs when the heat generation amount is smaller than a threshold value A misfire detection device comprising: means for determining that the   Obtaining the heat loss rate history before opening the exhaust valve, and based on the heat release rate history before the exhaust valve opening and the heat loss rate history, The combustion heat generation rate history before opening the exhaust valve is obtained, the combustion heat generation rate history after opening the exhaust valve is estimated based on the combustion heat generation rate history before opening the exhaust valve, and the exhaust valve opening The misfire detection device for an internal combustion engine according to claim 1, wherein the heat generation amount is estimated based on a combustion heat generation rate history after the valve.   The misfire detection device for an internal combustion engine according to claim 1 or 2, wherein a fuel property is obtained, and the threshold value is set based on the fuel property.   4. The in-cylinder pressure history before the exhaust valve is opened, and the heat release rate history before the exhaust valve is opened based on the in-cylinder pressure history before the exhaust valve is opened. The misfire detection device for an internal combustion engine according to one item.   A model equation representing at least a heat release rate history after the exhaust valve is opened is determined based on a heat release rate history before the exhaust valve is opened, and the heat generation amount is estimated using the model equation. The misfire detection apparatus for an internal combustion engine according to any one of 1 to 4.

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