JP6267280B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine that estimates an EGR rate of in-cylinder gas filled in a cylinder using in-cylinder pressure detected by an in-cylinder pressure sensor.

  As this type of conventional control device, for example, one disclosed in Patent Document 1 is known. In this control device, assuming that the change in state of the combustion gas during the expansion stroke is adiabatic expansion and the specific heat ratio κexp of the combustion gas is approximated by the polytropic index, κexp = − (lnP2-lnP1) / (lnV2-lnV1) Is calculated by P1 and P2 are in-cylinder pressures detected at two points during the expansion stroke, and V1 and V2 are in-cylinder volumes V1 and V2 at two points. Further, assuming that a certain relationship independent of the air-fuel ratio is established between the specific heat ratio κexp of the combustion gas and the EGR rate, this relationship is mapped in advance and the specific heat ratio of the combustion gas calculated as described above By searching this map according to κexp, the EGR rate is estimated.

Japanese Patent No. 5263184

  In the conventional control device described above, the specific heat ratio of the combustion gas is calculated based on the change in the state of the combustion gas during the expansion stroke. However, the state of combustion gas such as temperature and pressure changes depending on the combustion state in the cylinder, so it is unstable, and the specific heat ratio of combustion gas is further influenced by temperature, so it is very inefficient. It is stable. For this reason, in the conventional method of calculating the specific heat ratio based on the in-cylinder pressure detected at two points during the expansion stroke, it is difficult to stably and accurately calculate the specific heat ratio. Therefore, based on the calculated specific heat ratio. The EGR rate cannot be estimated with high accuracy.

  For this reason, it is preferable to estimate the EGR rate based on the specific heat ratio of the in-cylinder gas before combustion, in which the temperature and pressure are stable compared to the combustion gas. However, since the specific heat ratio of the in-cylinder gas is affected by both the EGR rate and the air-fuel ratio, for example, when the actual air-fuel ratio deviates from the assumed air-fuel ratio, the EGR rate is accurately set. Cannot be estimated.

  The present invention has been made to solve the above-described problems. Even when the actual air-fuel ratio of the in-cylinder gas deviates from the assumed air-fuel ratio, the influence of the air-fuel ratio deviation is affected. It is an object of the present invention to provide a control device for an internal combustion engine that can accurately estimate the EGR rate of in-cylinder gas while appropriately eliminating the exhaust gas.

  In order to achieve the above object, the invention according to claim 1 is a control device for an internal combustion engine that estimates the EGR rate R_EGR of the in-cylinder gas charged in the cylinder 3a, wherein the pressure in the cylinder 3a is controlled by the cylinder. An in-cylinder pressure sensor 51 that detects the internal pressure PCYL, an air-fuel ratio detection unit (LAF sensor 58) that detects an air-fuel ratio of the in-cylinder gas (equivalent ratio KACT in the embodiment (hereinafter the same in this section)), and in-cylinder gas A predetermined reference crank angle during the compression stroke based on the characteristic of the specific heat ratio of the in-cylinder gas in accordance with the detected air-fuel ratio of the in-cylinder gas under the condition that no external EGR gas due to exhaust gas recirculation exists. Reference in-cylinder pressure calculating means (ECU 2, step 6 in FIG. 3, FIG. 4) for calculating the pressure in the cylinder 3a generated in CA_REF as the reference in-cylinder pressure P_REF, and the reference crank angle CA_REF EGR rate estimating means (ECU 2, step of FIG. 3) for estimating the EGR rate R_EGR of the in-cylinder gas based on the pressure difference ΔP between the detected in-cylinder pressure P_CPS detected by the in-cylinder pressure sensor 51 and the calculated reference in-cylinder pressure P_REF. 10 to 11).

  In the control device for an internal combustion engine of the present invention, the cylinder pressure (in-cylinder pressure) is detected by the cylinder pressure sensor, and the cylinder pressure predicted to be generated at a predetermined reference crank angle during the compression stroke is used as the cylinder reference pressure. calculate. Then, based on the pressure difference between the detected in-cylinder pressure detected by the in-cylinder pressure sensor at the reference crank angle and the calculated reference in-cylinder pressure, the EGR rate R_EGR of the in-cylinder gas is estimated.

  Further, according to the present invention, the air-fuel ratio of the in-cylinder gas is detected, and the calculation of the reference in-cylinder pressure is detected under the condition that no external EGR gas due to exhaust gas recirculation exists in the in-cylinder gas. This is performed based on the characteristic of the specific heat ratio of the in-cylinder gas according to the air-fuel ratio of the in-cylinder gas. If the air-fuel ratio of the in-cylinder gas deviates from the assumed air-fuel ratio, the specific heat ratio of the in-cylinder gas changes due to the increase or decrease in the fuel component ratio, and the in-cylinder pressure during the compression stroke changes accordingly. To do. For example, when the air-fuel ratio shifts to the rich side, the specific heat ratio of the in-cylinder gas decreases due to the increase in the ratio of the fuel component, so that the in-cylinder pressure decreases and the air-fuel ratio shifts to the lean side. The reverse of the above. Accordingly, the detected in-cylinder pressure also changes, and the accuracy of estimating the EGR rate based on the pressure difference from the reference in-cylinder pressure is reduced.

  On the other hand, according to the present invention, as described above, the calculation of the reference in-cylinder pressure is performed based on the characteristic of the specific heat ratio of the in-cylinder pressure gas in accordance with the detected in-cylinder gas air-fuel ratio. The change in the in-cylinder pressure due to the deviation can be reflected in the reference in-cylinder pressure. As a result, the pressure difference between the detected in-cylinder pressure and the reference in-cylinder pressure does not include the change in the in-cylinder pressure due to the deviation of the air-fuel ratio, and reflects only the pressure difference due to the EGR rate. Therefore, based on this pressure difference, the EGR rate of the in-cylinder gas can be accurately estimated while appropriately eliminating the influence of the air-fuel ratio shift.

  According to a second aspect of the present invention, in the control device for an internal combustion engine according to the first aspect, the reference in-cylinder pressure calculating means has no external EGR gas in the in-cylinder gas and the air-fuel ratio of the in-cylinder gas is the theoretical sky. Basic value calculating means (ECU 2, step 23 in FIG. 4, FIG. 5) for calculating the pressure in the cylinder generated at the reference crank angle CA_REF as the basic value P_REF_B of the reference in-cylinder pressure P_REF under the condition of the fuel ratio, Correction amount calculation means (ECU2, FIG. 4) for calculating a correction amount (equivalent ratio correction amount P_KACT) of the reference in-cylinder pressure P_REF based on the degree of deviation of the air-fuel ratio of the in-cylinder gas with respect to the air-fuel ratio (equivalence ratio KACT-1). And calculating the reference in-cylinder pressure P_REF by correcting the basic value P_REF_B using the calculated correction amount (step of FIG. 4). 6) and said.

  According to this configuration, the calculation of the reference in-cylinder pressure is performed as follows. First, the basic value of the reference in-cylinder pressure is calculated. This basic value is the in-cylinder pressure generated at the reference crank angle under the condition of in-cylinder gas in which no external EGR gas is present and the air-fuel ratio is the stoichiometric air-fuel ratio, that is, the reference in-cylinder pressure corresponding to the stoichiometric air-fuel ratio. It corresponds to. Next, based on the degree of deviation of the air-fuel ratio of the in-cylinder gas with respect to the stoichiometric air-fuel ratio, that is, the deviation of the actual air-fuel ratio with respect to the stoichiometric air-fuel ratio, the correction amount of the reference in-cylinder pressure is calculated. Then, the reference in-cylinder pressure is calculated by correcting the basic value using the calculated correction amount. As described above, the reference in-cylinder pressure can be accurately calculated while appropriately reflecting the influence of the change in the in-cylinder pressure due to the deviation of the air-fuel ratio with respect to the theoretical air-fuel ratio. Therefore, EGR based on the pressure difference between the detected in-cylinder pressure and the reference in-cylinder pressure. The rate can be estimated with higher accuracy.

  According to a third aspect of the present invention, in the control device for an internal combustion engine according to the second aspect, the air-fuel ratio detecting means detects the equivalent ratio KACT as the air-fuel ratio of the in-cylinder gas, and the correction amount calculating means is detected A correction amount is calculated by multiplying the difference (KACT-1) between the equivalence ratio and the value 1 by a correction coefficient (equivalence ratio correction coefficient KKA) (step 25 in FIG. 4). The reference cylinder pressure P_REF is calculated by adding the calculated correction amount to the value P_REF_B (step 26).

  The difference between the detected equivalence ratio of the in-cylinder gas and the value 1 (hereinafter referred to as “equivalence ratio difference”) represents the deviation (degree of deviation) of the actual air-fuel ratio of the in-cylinder gas with respect to the theoretical air-fuel ratio. As will be described later, under conditions where the EGR rate and the like are constant, the in-cylinder pressure in the compression stroke has a linear relationship with the equivalent ratio of the in-cylinder gas, and decreases as the equivalent ratio increases. Therefore, based on the equivalence ratio-in-cylinder pressure characteristic, for example, when the inclination of the in-cylinder pressure with respect to the equivalence ratio is used as a correction coefficient, the product (multiplication value) of the equivalence ratio difference and the correction coefficient is a difference in the air-fuel ratio. The magnitude of deviation of the reference in-cylinder pressure from the basic value is indicated. Accordingly, by calculating the product of the equivalence ratio difference and the correction coefficient as the correction amount of the reference in-cylinder pressure, the calculation of the correction amount of the reference in-cylinder pressure can be performed easily and accurately based on the above-described equivalent ratio-in-cylinder pressure characteristic. In addition, the reference in-cylinder pressure can be accurately calculated by adding the calculated correction amount to the basic value.

  According to a fourth aspect of the present invention, in the control device for an internal combustion engine according to the third aspect, when the equivalence ratio is in a predetermined range including the value 1, the correction prohibition for prohibiting the correction of the reference in-cylinder pressure P_REF by the correction amount is prohibited. The apparatus further includes means (ECU2, steps 24 and 27 in FIG. 4).

  According to this configuration, when the equivalence ratio is in a predetermined range including the value 1, correction of the reference in-cylinder pressure by the correction amount is prohibited. For example, the air-fuel ratio detection means is configured to detect the air-fuel ratio via the oxygen concentration of the exhaust gas, and the detected air-fuel ratio matches the actual air-fuel ratio of the cylinder pressure gas in the cylinder due to the delay in the detection timing. However, there may be some deviation from the stoichiometric air-fuel ratio. In such a case, if the correction amount is calculated in response to the detected air-fuel ratio, the correction amount may vibrate unnecessarily. On the other hand, according to the above configuration, by prohibiting the correction by the correction amount, unnecessary vibration of the correction amount can be avoided, the correction amount is calculated, the reference in-cylinder pressure is corrected based on the correction amount, and the EGR rate is estimated. Etc. can be performed effectively.

1 is a diagram schematically showing a configuration of an internal combustion engine to which the present invention is applied. It is a block diagram which shows schematic structure of a control apparatus. It is a flowchart which shows the estimation process of an EGR rate. It is a flowchart which shows the subroutine of the calculation process of a reference | standard cylinder pressure. It is a figure which shows the reference in-cylinder pressure map used for calculation of the basic value of a reference in-cylinder pressure, and its input-output relationship. It is a figure which shows the relationship between the pressure difference of a detection cylinder pressure-reference | standard cylinder pressure, and an EGR rate. It is a figure which shows the EGR coefficient map used for calculation of an EGR coefficient, and its input-output relationship. It is a figure for demonstrating the correction method of the reference | standard in-cylinder pressure while showing an example of the relationship between the equivalence ratio of in-cylinder gas and the in-cylinder pressure which generate | occur | produces in the fixed crank angle during a compression stroke. It is a timing chart which shows the operation example by this embodiment with a comparative example. It is a flowchart which shows the control processing of the ignition timing using an EGR rate.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, an internal combustion engine (hereinafter referred to as “engine”) 3 to which the present invention is applied is, for example, a gasoline engine having four cylinders 3a, and is mounted as a power source in a vehicle (not shown). .

  Each cylinder 3a of the engine 3 is provided with a fuel injection valve 4 and a spark plug 5 so as to face a combustion chamber (not shown) of the cylinder 3a. The fuel injection valve 4 is a direct injection type that directly injects fuel into the combustion chamber. The fuel injection amount by the fuel injection valve 4 and the ignition timing IGLOG of the spark plug 5 are controlled by a control signal from an electronic control unit (hereinafter referred to as “ECU”) 2 (see FIG. 2).

  In the embodiment, “in-cylinder gas” refers to all the gas charged in the cylinder 3a and used for combustion. When the external EGR or internal EGR described later is not executed, the fuel and air It corresponds to the air-fuel mixture and, when being executed, further includes an external EGR gas and an internal EGR gas.

  Each cylinder 3a is provided with an in-cylinder pressure sensor 51 for detecting an internal pressure (in-cylinder pressure). In this embodiment, the in-cylinder pressure sensor 51 is integrated with the fuel injection valve 4 and is not shown, but faces the combustion chamber and amplifies the signal from the pressure detection element that picks up the in-cylinder pressure and the pressure detection element. In addition, an output amplifier circuit and the like are integrally assembled with the fuel injection valve 4. A detection signal representing the in-cylinder pressure PCYL detected by the in-cylinder pressure sensor 51 is input to the ECU 2.

  The engine 3 also includes a variable intake phase mechanism 11, a variable exhaust phase mechanism 12, a turbocharger 13, an EGR device 14, and the like.

  The variable intake phase mechanism 11 changes the relative phase (hereinafter referred to as “intake phase”) CAIN of an intake valve (both not shown) with respect to the crankshaft of the engine 3 in a stepless manner. 11a (see FIG. 2) and the like. The intake phase control motor 11a rotates the intake camshaft (not shown) with respect to the crankshaft in response to a control signal from the ECU 2, and changes the relative angle between the two, thereby making the intake phase CAIN stepless. change.

  Similarly, the variable exhaust phase mechanism 12 changes the relative phase (hereinafter referred to as “exhaust phase”) CAEX of an exhaust valve (not shown) with respect to the crankshaft continuously, and the exhaust phase control motor 12a ( Etc.). The exhaust phase control motor 12a rotates the exhaust camshaft (not shown) with respect to the crankshaft in response to a control signal from the ECU 2, and changes the relative angle between the two, thereby making the exhaust phase CAEX stepless. change.

  The variable intake phase mechanism 11 and the variable exhaust phase mechanism 12 control the timing of opening and closing the intake valve and the exhaust valve by changing the intake phase CAIN and the exhaust phase CAEX, respectively, and valve overflow between the intake valve and the exhaust valve. Used to control internal EGR by wrapping.

  The turbocharger 13 includes a compressor 21 provided in the intake passage 6 and a turbine 23 provided in the exhaust passage 7 and integrally connected to the compressor 21 via a shaft 22. The turbine 23 is driven by the exhaust gas flowing through the exhaust passage 7, and the compressor 21 rotates integrally therewith, whereby the intake air is supercharged.

  In the intake passage 6, an intake throttle valve 25, a compressor 21 of the turbocharger 13, an intercooler 26 for cooling intake air whose temperature has been increased by supercharging, and a throttle valve 27 are provided in this order from the upstream side. The intake throttle valve 25 generates a negative pressure for introducing the external EGR gas downstream thereof, and its opening degree is controlled via the LP actuator 25a in accordance with a control signal from the ECU 2.

  The throttle valve 27 is disposed upstream of the intake manifold 6 a in the intake passage 6. The opening degree of the throttle valve 27 is controlled via the TH actuator 27a in accordance with a control signal from the ECU 2, thereby controlling the in-cylinder gas amount sucked into the cylinder 3a.

  A three-way catalyst 28 is provided downstream of the turbine 23 in the exhaust passage 7. In the active state, the three-way catalyst 28 purifies the exhaust gas by oxidizing HC and CO in the exhaust gas and reducing NOx.

  The EGR device 14 recirculates a part of the exhaust gas discharged from the cylinder 3a into the exhaust passage 7 to the intake passage 6 as an external EGR gas via the EGR passage 41. As shown in FIG. 1, the EGR passage 41 is connected downstream of the turbine 23 and the three-way catalyst 28 in the exhaust passage 7 and between the compressor 21 and the intake throttle valve 25 in the intake passage 6. With this configuration, the external EGR gas has a relatively low pressure because the exhaust gas is taken out after the exhaust gas has worked on the turbine 23. That is, the EGR device 14 is configured as a so-called low pressure EGR device.

  In the middle of the EGR passage 41, an EGR valve 42 and an EGR cooler 43 for cooling the external EGR gas are provided. The opening degree of the EGR valve 42 is controlled via the EGR actuator 42a in accordance with a control signal from the ECU 2, thereby controlling the external EGR gas amount.

  Further, the engine 3 is provided with various sensors as described below in addition to the above-described in-cylinder pressure sensor 51 in order to detect the operating state, and these detection signals are input to the ECU 2 ( (See FIG. 2).

  The crank angle sensor 52 outputs a CRK signal and a TDC signal, which are pulse signals, for each predetermined crank angle as the crankshaft rotates. The CRK signal is output every predetermined crank angle (for example, 0.5 degrees). The ECU 2 calculates the engine speed (hereinafter referred to as “engine speed”) NE of the engine 3 based on the CRK signal.

  Further, the TDC signal is a signal indicating that in any cylinder 3a, the piston (not shown) of the engine 3 is at a predetermined crank angle position near the top dead center (intake TDC) at the start of the intake stroke. Yes, when the engine 3 has four cylinders as in this embodiment, it is output every 180 degrees of crank angle. The ECU 2 calculates a crank angle CA based on the output timing of the TDC signal for each cylinder 3a according to the TDC signal and the CRK signal, and a predetermined crank angle (for example, 30) with respect to the calculated crank angle CA. Crank angle stage FISTG (= 0-23) is calculated and assigned for each degree.

  The intake camshaft to which the variable intake phase mechanism 11 is attached and the exhaust camshaft to which the variable exhaust phase mechanism 12 is attached are provided with an intake phase sensor 53 and an exhaust phase sensor 54, respectively. The intake phase sensor 53 outputs a CAMIN signal that is a pulse signal at every predetermined cam angle (for example, 0.5 degrees) as the intake camshaft rotates. The ECU 2 calculates the intake phase CAIN based on the CAMIN signal and the CRK signal. Similarly, the exhaust phase sensor 54 outputs a CAMEX signal at every predetermined cam angle (for example, 0.5 degrees) as the exhaust camshaft rotates. The ECU 2 calculates the exhaust phase CAEX based on the CAMEX signal and the CRK signal.

  Further, in the intake passage 6, an air flow sensor 55 is provided on the upstream side of the intake throttle valve 25, and an intake pressure sensor 56 and an intake air temperature sensor 57 are provided in the intake chamber 6 b on the downstream side of the throttle valve 27. The air flow sensor 55 detects the amount (intake air amount) GAIR of air (fresh air) sucked into the cylinder 3a, the intake pressure sensor 56 detects the intake pressure PBA as an absolute pressure, and the intake air temperature sensor 57 An intake air temperature (intake air temperature) TA including the external EGR gas sucked into the cylinder 3a is detected.

  A LAF sensor 58 is provided between the turbine 23 and the three-way catalyst 28 in the exhaust passage 7. The LAF sensor 58 continuously detects the oxygen concentration in the exhaust gas flowing into the three-way catalyst 28 in a wide air-fuel ratio region including the stoichiometric air-fuel ratio, and outputs a detection signal thereof. The ECU 2 calculates the equivalence ratio KACT as the air-fuel ratio of the in-cylinder gas based on this detection signal.

  Further, the water temperature sensor 59 outputs a detection signal indicating the temperature TW of the cooling water for cooling the engine 3 (hereinafter referred to as “engine water temperature”), and the accelerator opening sensor 60 is used for an accelerator pedal (not shown) of the vehicle. A detection signal representing the depression amount (hereinafter referred to as “accelerator opening”) AP is output.

  The ECU 2 is composed of a microcomputer including a CPU, a RAM, a ROM, an I / O interface (all not shown), and the like. The ECU 2 executes overall engine control including control of the fuel injection amount of the fuel injection valve 4 and the ignition timing IGLOG of the spark plug 5 in accordance with the detection signals of the various sensors described above. Further, particularly in the present embodiment, the ECU 2 executes an estimation process for estimating the EGR rate R_EGR of the in-cylinder gas using the in-cylinder pressure PCYL detected by the in-cylinder pressure sensor 51.

  In the present embodiment, the ECU 2 corresponds to a reference in-cylinder pressure calculating unit, an EGR rate estimating unit, a basic value calculating unit, a correction amount calculating unit, and a correction prohibiting unit.

  FIG. 3 shows an estimation process of the EGR rate R_EGR executed by the ECU 2. The EGR rate R_EGR is defined as the ratio of the EGR gas amount to the total amount of in-cylinder gas. This estimation process is basically the same as that disclosed in detail in the application filed by the present applicant (Japanese Patent Application No. 2015-241446), and is characterized by the calculation of the reference in-cylinder pressure therein.

  This process is repeatedly executed for each cylinder 3a at the same cycle (for example, every 30 degrees of crank angle) as the switching cycle of the crank angle stage FISTG described above. In addition, the process directly related to the in-cylinder pressure PCYL detected by the in-cylinder pressure sensor 51 is executed at the same cycle as the CRK signal generation cycle (for example, every 0.5 degrees of crank angle) separately from the present process. For example, the detected in-cylinder pressure PCYL is stored corresponding to the crank angle CA.

  In the estimation process of FIG. 3, first, in step 1 (illustrated as “S1”, the same applies hereinafter), the crank angle stage FISTG reaches a first predetermined value STG1 corresponding to the top dead center (intake TDC) at the start of the intake stroke. Determine whether they are equal. If the determination result is YES, corresponding to immediately after the cylinder 3a has shifted to the intake stroke, an intake-related parameter is acquired (step 2). Specifically, the detected intake air temperature TA and engine water temperature TW and the calculated intake air phase CAIN and exhaust gas phase CAEX are read out as the intake-related parameters and stored in a predetermined area of the ECU 2 RAM, and this process is terminated. To do.

  When the determination result in step 1 is NO, it is determined whether or not the crank angle stage FISTG is equal to a second predetermined value STG2 corresponding to the bottom dead center (compression BDC) at the start of the compression stroke (step 3). . When the determination result is YES, which corresponds to immediately after the cylinder 3a has shifted to the compression stroke, the compression-related parameters are acquired (step 4). Specifically, the detected intake pressure PBA and in-cylinder pressure PCYL are read out as compression-related parameters, acquired as the compression start intake pressure PBAC and the compression start in-cylinder pressure PCYLC, respectively, and the detected engine speed NE and The ignition timing IGLOG set at that time is read out and stored in a predetermined area of the ECU 2 RAM.

  Next, a reference crank angle CA_REF is set (step 5). This reference crank angle CA_REF predicts the timing immediately before the start of in-cylinder gas combustion, and is represented by the crank angle. In this setting process, a retardation correction amount ΔC_CA is calculated by searching a predetermined map (not shown) according to the compression start intake pressure PBAC and the engine speed NE acquired in step 4, and this The reference crank angle CA_REF is set by subtracting the retard correction amount ΔC_CA from the ignition timing IGLOG acquired in step 4.

  In step 6 following step 5, the reference in-cylinder pressure P_REF is calculated. The reference in-cylinder pressure P_REF is an in-cylinder pressure predicted to be generated at the reference crank angle CA_REF, and is calculated by a subroutine shown in FIG.

  In this process, first, in step 21, the intake valve closing timing (hereinafter referred to as “intake valve closing timing”) IVC is calculated from the intake phase CAIN acquired in step 2. When the intake valve closing timing IVC is set during the compression stroke, it corresponds to the crank angle at the start of compression. Next, by searching a predetermined map (not shown) according to the intake air temperature TA, the intake air phase CAIN, and the exhaust gas phase CAEX acquired in step 2, the initial cylinder that is the temperature in the cylinder 3a at the start of compression. An internal temperature T_STRT is calculated (step 22).

  Next, by searching the reference in-cylinder pressure map shown in FIG. 5 according to the reference crank angle CA_REF set in step 5, the intake valve closing timing IVC, the initial in-cylinder temperature T_STRT, and the compression start intake pressure PBAC, A basic value P_REF_B of the reference in-cylinder pressure is calculated (step 23). This reference in-cylinder pressure map is obtained for various conditions of the above four input parameters under the condition that there is no external EGR gas in the in-cylinder gas and the air-fuel ratio of the in-cylinder gas is the stoichiometric air-fuel ratio. Based on the temperature characteristics of the specific heat ratio of the internal gas, the reference in-cylinder pressure is calculated in advance and mapped as the basic value.

  In the next steps 24 to 27, the above-described basic value P_REF_B is corrected. In this correction process, the basic value P_REF_B is corrected in accordance with the in-cylinder gas equivalent ratio KACT detected by the LAF sensor 58, and the reference in-cylinder pressure P_REF is calculated. FIG. 8 shows the equivalence ratio-in-cylinder pressure characteristic that is the premise of this correction. Specifically, there is no external EGR gas in the in-cylinder gas, and the above-mentioned reference crank angle CA_REF is included. This shows the relationship between the in-cylinder gas equivalent ratio KACT and the in-cylinder pressure PCYL generated at the reference crank angle CA_REF under the same conditions of the four input parameters of the reference in-cylinder pressure map.

  As shown in the figure, the in-cylinder pressure PCYL decreases as the equivalent ratio KACT increases, because the ratio of the fuel component of the in-cylinder gas increases and the specific heat ratio of the in-cylinder gas decreases. Further, the in-cylinder pressure PCYL has a linear relationship with the equivalent ratio KACT, and the inclination thereof is expressed by KKA (negative value). Further, the basic value P_REF_B of the reference in-cylinder pressure P_REF described above is calculated on the condition that the air-fuel ratio of the in-cylinder gas is the stoichiometric air-fuel ratio. Therefore, the in-cylinder pressure PCYL when the equivalent ratio KACT = 1 in FIG. , Corresponding to the basic value P_REF_B.

  The correction processing in steps 24 to 27 is based on the equivalent ratio-in-cylinder pressure characteristic as described above, and corrects the basic value P_REF_B in accordance with the equivalent ratio KACT, thereby changing the reference in-cylinder pressure P_REF to the equivalent ratio on the characteristic line of FIG. A value corresponding to KACT (for example, P_REF in the figure) is set.

  First, in step 24, is the absolute value | KACT-1 | of the difference between the in-cylinder gas equivalent ratio KACT and the value 1 (hereinafter referred to as "equivalent ratio difference" as appropriate) larger than a predetermined threshold value THRESH? Determine whether or not. When the determination result is YES, the equivalent ratio correction amount P_KACT of the reference in-cylinder pressure is calculated by multiplying the equivalent ratio difference (KACT-1) by the equivalent ratio correction coefficient KKA (step 25). This equivalence ratio correction coefficient KKA corresponds to the slope of the characteristic line in FIG. 8 and is represented by a negative value.

  Therefore, the calculated equivalent ratio correction amount P_KACT (= (KACT-1) · KKA) corresponds to the difference between the reference in-cylinder pressure P_REF corresponding to the equivalent ratio KACT and the basic value P_REF_B, and the air-fuel ratio of the in-cylinder gas is When it is richer than the stoichiometric air-fuel ratio, it becomes a negative value, and when it is lean, it becomes a positive value (see FIG. 8). From the above relationship, in the next step 26, the reference in-cylinder pressure P_REF corresponding to the equivalent ratio KACT is calculated by adding the equivalent ratio correction amount P_KACT to the basic value P_REF_B.

  On the other hand, when the determination result of step 24 is NO, and | KACT-1 | ≦ THRESH is satisfied and the equivalence ratio KACT is in a predetermined range centering on the value 1, the calculation of the equivalence ratio correction amount P_KACT is prohibited. In step 27, the reference in-cylinder pressure P_REF is set to the basic value P_REF_B.

  In step 28 following step 26 or 27, a heat transfer correction coefficient K_HT is calculated by searching a predetermined map (not shown) according to the engine speed NE and the engine water temperature TW. The heat transfer correction coefficient K_HT is for compensating for the influence of heat exchanged between the cylinder 3a and the outside. Next, the final reference in-cylinder pressure P_REF is calculated by multiplying the reference in-cylinder pressure P_REF calculated in step 26 or 27 by the heat transfer correction coefficient K_HT (step 29), and the processing in FIG.

  Returning to FIG. 3, in step 7 following the calculation processing of the reference in-cylinder pressure P_REF in step 6, the EGR coefficient C_EGR is calculated, and the processing in FIG. 3 is ended. The EGR coefficient C_EGR has a linear (proportional) relationship as shown in FIG. 6 between a pressure difference ΔP (a difference between a detected in-cylinder pressure P_CPS and a reference in-cylinder pressure P_REF described later) and an EGR rate R_EGR. Therefore, the slope (= R_EGR / ΔP) is defined as the EGR coefficient C_EGR. Further, since this inclination has a characteristic that it changes according to the intake condition and the compression condition, it is calculated in this step 7.

  In this calculation process, as shown in FIG. 7, the same four input parameters (reference crank angle CA_REF, intake valve closing timing IVC, initial in-cylinder temperature T_STRT, and compression start intake pressure as in the reference in-cylinder pressure map of FIG. 5 are used. The EGR coefficient C_EGR is calculated by searching the EGR coefficient map according to (PBAC). This EGR coefficient map is obtained by previously calculating and mapping the EGR coefficient C_EGR for various conditions of these four input parameters.

  When the determination result in step 3 is NO, it is determined whether or not the crank angle stage FISTG is equal to a third predetermined value STG3 corresponding to the top dead center (compression TDC) at the end of the compression stroke (step 8). . When this determination result is NO, this process is terminated as it is. On the other hand, if the determination result in step 8 is YES and the cylinder 3a corresponds to immediately after the end of the compression stroke, the in-cylinder pressure PCYL detected at the reference crank angle CA_REF set in step 5 is read from the RAM, and the reference crank Obtained as the detected in-cylinder pressure P_CPS at the angle CA_REF (step 9).

  Next, a difference (= P_CPS−P_REF) between the detected in-cylinder pressure P_CPS and the reference in-cylinder pressure P_REF is calculated as a pressure difference ΔP (step 10). Then, by multiplying the pressure difference ΔP by the EGR coefficient C_EGR calculated in step 7, the EGR rate R_EGR of the in-cylinder gas is calculated (step 11), and this process is terminated.

  Next, an operation example obtained by the above-described EGR rate estimation process will be described with reference to FIG. 9 together with a comparative example. FIG. 9 shows that the operating condition of the engine 3 including the EGR rate R_EGR (for example, 10%) is constant, and as shown in (a), the equivalence ratio KACT is richer than the value 1.0 corresponding to the stoichiometric air-fuel ratio. In addition, this is an example of a temporary shift between t1 and t2.

  In this case, the basic value P_REF_B of the reference in-cylinder pressure P_REF is calculated on the condition that the air-fuel ratio of the in-cylinder gas is the stoichiometric air-fuel ratio. Therefore, as shown in FIG. , Become constant. On the other hand, when the equivalent ratio KACT shifts to the rich side, the specific heat ratio of the in-cylinder gas decreases and the in-cylinder pressure PCYL decreases, so the detected in-cylinder pressure P_CPS decreases.

  From the above relationship, when the basic value P_REF_B is used as it is as the reference in-cylinder pressure P_REF without being corrected, the pressure between the detected in-cylinder pressure P_CPS and the reference in-cylinder pressure P_REF in accordance with the shift of the equivalence ratio KACT to the rich side. The difference ΔP becomes smaller (broken line (b)). As a result, the EGR rate R_EGR calculated based on the pressure difference ΔP greatly shifts to a smaller side than the actual value (= 10%) (broken line (c)), and the EGR rate R_EGR is calculated with high accuracy. I can't.

  On the other hand, in the estimation process of the embodiment, the reference value P_REF is calculated by correcting the basic value P_REF_B in accordance with the equivalent ratio KACT of the in-cylinder gas. Therefore, the calculated reference in-cylinder pressure P_REF is equivalent to The decrease in the in-cylinder pressure corresponding to the deviation in the ratio KACT is reflected in advance, and the reference in-cylinder pressure P_REF is corrected to a smaller value (solid line in (b)). As a result, the pressure difference ΔP between the detected in-cylinder pressure P_CPS and the reference in-cylinder pressure P_REF is maintained at a large value equivalent to other periods in which the deviation of the equivalence ratio KACT does not occur, so that the EGR rate R_EGR can be accurately obtained. It can be calculated (solid line in (c)).

  Next, an ignition timing control process will be described as an example of engine control using the estimated EGR rate R_EGR with reference to FIG. This process is executed for each cylinder 3a in synchronization with the generation of the TDC signal. In this process, first, in step 41, a basic ignition timing IG_BASE is calculated by searching a predetermined map (not shown) according to the engine speed NE and the required torque TRQCMD. The required torque TRQCMD is calculated based on the accelerator opening AP and the engine speed NE.

  Next, an EGR correction amount ΔIGEGR is calculated by searching a predetermined map (not shown) according to the EGR rate R_EGR (step 42). Next, a correction amount ΔIGTTL due to factors other than the EGR rate R_EGR is calculated according to the engine water temperature TW, the engine speed NE, and the like (step 43). Finally, the ignition timing IGLOG is calculated by adding the EGR correction amount ΔIGEGR and the correction amount ΔIGTTL to the basic ignition timing IG_BASE (step 44), and this processing is terminated.

  As described above, according to the present embodiment, the in-cylinder pressure predicted to occur at the reference crank angle CA_REF during the compression stroke is calculated as the reference in-cylinder pressure P_REF, and the detected in-cylinder pressure detected at the reference crank angle CA_REF is calculated. Based on the pressure difference ΔP between P_CPS and the reference in-cylinder pressure P_REF, the EGR rate R_EGR of the in-cylinder gas is estimated.

  In addition, since the calculation of the reference in-cylinder pressure P_REF is performed based on the characteristic of the specific heat ratio of the in-cylinder pressure gas in accordance with the detected equivalent ratio KACT, the change in the in-cylinder pressure due to the deviation of the air-fuel ratio is used as the reference in-cylinder pressure P_REF. It can be reflected. As a result, the pressure difference ΔP between the detected in-cylinder pressure P_CPS and the reference in-cylinder pressure P_REF does not include the change in the in-cylinder pressure due to the deviation of the air-fuel ratio, and only the pressure difference due to the EGR rate is reflected. Based on the above, it is possible to accurately estimate the EGR rate R_EGR of the in-cylinder gas while appropriately eliminating the influence of the deviation of the air-fuel ratio.

  Further, the basic value P_REF_B of the reference in-cylinder pressure P_REF is calculated under the condition that no external EGR gas is present in the in-cylinder gas and the air-fuel ratio of the in-cylinder gas is the stoichiometric air-fuel ratio (step 23 in FIG. 4), Based on the equivalence ratio-in-cylinder pressure characteristic as shown in FIG. 8, the equivalence ratio correction (KACT-1) representing the degree of deviation of the in-cylinder gas with respect to the theoretical air-fuel ratio is multiplied by the equivalence ratio correction coefficient KKA. The amount P_KACT is calculated (step 25), and the equivalent ratio correction amount P_KACT is added to the basic value P_REF_B to calculate the reference in-cylinder pressure P_REF (step 26).

  As described above, the equivalent ratio correction amount P_KACT and the reference in-cylinder pressure P_REF can be easily and accurately adjusted while appropriately reflecting the influence of the change in the in-cylinder pressure due to the deviation of the air-fuel ratio using the equivalence ratio-in-cylinder pressure characteristic shown in FIG. Therefore, the estimation of the EGR rate R_EGR based on the pressure difference ΔP between the detected in-cylinder pressure P_CPS and the reference in-cylinder pressure P_REF can be performed with higher accuracy.

  Further, when the absolute value | KACT-1 | of the equivalence ratio difference is equal to or smaller than a predetermined threshold value THRESH, the correction of the reference in-cylinder pressure P_REF by the equivalence ratio correction amount P_KACT is prohibited. Thus, unnecessary vibration of the equivalent ratio correction amount P_KACT when the value is relatively small can be avoided, and the calculation of the equivalent ratio correction amount P_KACT, the correction of the reference in-cylinder pressure P_REF, and the estimation of the EGR rate R_EGR can be effectively performed.

  In addition, this invention can be implemented in various aspects, without being limited to the described embodiment. For example, in the embodiment, by using the reference in-cylinder pressure map, a basic value P_REF_B corresponding to the theoretical air-fuel ratio is calculated, and this basic value P_REF_B is corrected according to the equivalent ratio KACT of the in-cylinder gas. P_REF is calculated. The present invention is not limited to such a correction method, and can be implemented by other methods. For example, by adding an equivalent ratio KACT or the like to the input parameters of the reference in-cylinder pressure map, and creating a reference in-cylinder pressure map corresponding thereto in advance, the reference in-cylinder pressure P_REF corresponding to the equivalent ratio KACT is directly calculated from the reference in-cylinder pressure map. You may make it ask.

  In the embodiment, the equivalence ratio KACT is used as a parameter representing the air-fuel ratio of the in-cylinder gas. However, the detected air-fuel ratio is used as it is, and the reference cylinder is used according to the degree of deviation of the air-fuel ratio from the theoretical air-fuel ratio. A correction amount of the internal pressure P_REF may be calculated. Further, in the embodiment, the range of the equivalence ratio KACT that prohibits the correction by the equivalence ratio correction amount P_KACT is set symmetrically on the rich side and the lean side with the value 1 as the center, but even if this is set asymmetrically Good.

  Furthermore, in the embodiment, the ignition timing control is executed in accordance with the estimated EGR rate R_EGR. However, instead of or in addition to this, other engine control, for example, EGR control via the EGR valve 42, throttle valve The intake air amount control via 27, the fuel injection control via the fuel injection valve 4, etc. may be executed.

  Moreover, although the EGR apparatus 14 is comprised with the low voltage | pressure EGR apparatus, it may replace with this and may use a high voltage | pressure EGR apparatus in this case, and this invention can be applied similarly also in that case. Furthermore, the in-cylinder pressure sensor 51 is integrated with the fuel injection valve 4, but it is needless to say that it may be a separate type arranged separately from the fuel injection valve 4.

  Furthermore, in the embodiment, the engine 3 is a vehicle engine, but the present invention can also be applied to an engine for other uses, for example, an engine for an outboard motor in which a crankshaft is arranged in the vertical direction. In addition, the detailed configuration can be changed as appropriate within the scope of the gist of the present invention.

2 ECU (reference in-cylinder pressure calculating means, EGR rate estimating means, basic value calculating means, correction amount calculating means, correction prohibiting means)
3 Internal combustion engine 3a Cylinder 51 In-cylinder pressure sensor 58 LAF sensor (air-fuel ratio detection means)
R_EGR In-cylinder gas EGR rate PCYL In-cylinder pressure KACT Equivalent ratio (in-cylinder gas air-fuel ratio)
CA_REF Reference crank angle P_REF Reference cylinder pressure P_CPS Detection cylinder pressure
ΔP Pressure difference between detected in-cylinder pressure and reference in-cylinder pressure P_REF_B Basic value of reference in-cylinder pressure P_KACT Equivalent ratio correction amount (reference in-cylinder pressure correction amount)
KACT-1 equivalent ratio difference (difference between detected equivalent ratio and value 1)
KKA equivalent ratio correction coefficient (correction coefficient)
THRESH threshold (predetermined range)

Claims (4)

A control device for an internal combustion engine that estimates an EGR rate of in-cylinder gas filled in a cylinder,
An in-cylinder pressure sensor for detecting a pressure in the cylinder as an in-cylinder pressure;
Air-fuel ratio detection means for detecting the air-fuel ratio of the in-cylinder gas;
Based on the characteristic of the specific heat ratio of the in-cylinder gas in accordance with the detected air-fuel ratio of the in-cylinder gas under the condition that the external EGR gas due to exhaust gas recirculation does not exist in the in-cylinder gas, a predetermined value during the compression stroke is obtained. Reference in-cylinder pressure calculating means for calculating the in-cylinder pressure generated at the reference crank angle as a reference in-cylinder pressure;
EGR rate estimating means for estimating an EGR rate of in-cylinder gas based on a pressure difference between a detected in-cylinder pressure detected by the in-cylinder pressure sensor at the reference crank angle and the calculated reference in-cylinder pressure;
A control device for an internal combustion engine, comprising: The reference in-cylinder pressure calculating means includes
The cylinder pressure generated at the reference crank angle is calculated as the basic value of the reference cylinder pressure under the condition that no external EGR gas is present in the cylinder gas and the air-fuel ratio of the cylinder gas is the stoichiometric air-fuel ratio. A basic value calculating means for
Correction amount calculation means for calculating a correction amount of the reference in-cylinder pressure based on the degree of deviation of the air-fuel ratio of the in-cylinder gas with respect to the theoretical air-fuel ratio,
The control apparatus for an internal combustion engine according to claim 1, wherein the reference in-cylinder pressure is calculated by correcting the basic value by using the calculated correction amount. The air-fuel ratio detection means detects an equivalence ratio as the air-fuel ratio of the in-cylinder gas,
The correction amount calculation means calculates the correction amount by multiplying the difference between the detected equivalence ratio and the value 1 by a correction coefficient,
The control apparatus for an internal combustion engine according to claim 2, wherein the reference in-cylinder pressure calculating unit calculates the reference in-cylinder pressure by adding the calculated correction amount to the basic value.   4. The internal combustion engine according to claim 3, further comprising a correction prohibiting unit that prohibits the correction of the reference in-cylinder pressure by the correction amount when the equivalence ratio is in a predetermined range including a value of 1. 5. Control device.

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