JP6493279B2 - Engine control device - Google Patents

Description

  The technology disclosed herein is an exhaust gas recirculation (hereinafter referred to as “EGR”) in which a part of the exhaust gas is recirculated to the intake air via an exhaust gas recirculation passage that connects the intake passage and the exhaust passage. The present invention relates to an engine control apparatus in which so-called external EGR is performed.

  In this type of engine, an EGR valve is provided in the EGR passage, and the exhaust gas recirculated to the intake passage is adjusted by adjusting the opening of the EGR valve in accordance with the operating state of the engine, for example, the engine speed or the engine load. Is controlled (hereinafter referred to as “EGR flow rate”) (see, for example, Patent Document 1).

JP 2008-163953 A

  In the engine as described above, the difference between the EGR valve upstream pressure, which is the pressure upstream of the EGR valve, and the EGR valve downstream pressure, which is the pressure downstream of the EGR valve, becomes smaller, that is, EGR relative to the EGR valve upstream pressure. As the pressure ratio of the valve downstream pressure approaches 1, the controllability of the EGR flow rate by adjusting the opening degree of the EGR valve becomes worse. Therefore, when the pressure ratio of the EGR valve upstream pressure to the EGR valve downstream pressure is smaller than a predetermined reference value, execution of the external EGR is prohibited, and only when the pressure ratio is larger than the predetermined reference value, the external EGR is prohibited. It is conceivable to allow the execution of.

  However, in such execution control of external EGR, when execution of the external EGR is prohibited during external EGR, the EGR valve is fully closed to stop the external EGR, and the exhaust gas that has been recirculated is The pressure is subtracted from the intake pressure. For this reason, the pressure ratio of the exhaust pressure to the intake pressure suddenly increases and immediately exceeds a predetermined set value, the execution of the external EGR is permitted again, and the external EGR is restarted as soon as it stops. When the external EGR is resumed, the pressure ratio of the exhaust pressure becomes smaller than a predetermined set value, and the execution of the external EGR is prohibited. Thus, there is a possibility that hunting that repeats execution and stop in a short cycle may occur in the control of the external EGR.

  When hunting occurs in the external EGR, there is a concern that engine operation control may be affected and become unstable. In order to prevent the occurrence of hunting in the execution control of the external EGR, it is conceivable that the reference value for switching between the permitted state and the prohibited state for executing the external EGR has a certain width, that is, a so-called hysteresis. . In such hunting countermeasures, it is determined whether or not the prohibition reference value that is a reference value for determining whether or not to prohibit the execution of the external EGR from the state in which the execution of the external EGR is prohibited. It is necessary to set the difference (hysteresis width) between the permission reference value and the prohibition reference value to be relatively large in consideration of the maximum opening of the EGR valve.

  However, if it does so, depending on the operating state of the engine, the controllability of the EGR flow rate does not deteriorate so much, but a situation may occur where external EGR cannot be performed. For example, when the opening of the EGR valve necessary to realize the required EGR flow rate is small and the differential pressure change between the EGR valve upstream pressure and the EGR valve downstream pressure is small even when the external EGR is executed. It falls into a situation. Therefore, the operating state of the engine that is permitted to execute the external EGR is limited, and as a result, the emission performance and the fuel consumption that have been improved by the execution of the external EGR may be reduced.

  The technology disclosed herein has been made in view of such a point, and the purpose thereof is to appropriately control the execution of the external EGR and suppress the occurrence of hunting in the execution control of the external EGR. There is to do.

  In order to achieve the above object, the technique disclosed herein controls the execution of the external EGR in anticipation of a change in the EGR valve downstream pressure when the opening degree of the EGR valve is adjusted.

  Specifically, the technology disclosed herein includes an EGR passage that recirculates the exhaust discharged to the exhaust passage to the intake passage, and an EGR valve that controls the recirculation amount of the exhaust gas flowing through the EGR passage, that is, the EGR flow rate. It is intended for an engine control apparatus in which external EGR is performed to recirculate a part of exhaust gas through an EGR passage by opening an EGR valve.

The engine control device includes: a valve control unit that performs opening / closing control of the EGR valve; a target exhaust partial pressure calculation unit that calculates a target exhaust partial pressure that is a target value of the partial pressure of exhaust gas recirculated by the external EGR; An actual exhaust partial pressure calculation unit that calculates an actual exhaust partial pressure that is a partial pressure of exhaust among the pressures of intake air sucked into the cylinders of the engine when EGR is executed. Then, the valve control unit sets the pressure of the exhaust gas on the exhaust passage side of the exhaust gas recirculation valve to P _ex , the pressure of the intake air mixed with the exhaust gas recirculated by the exhaust gas recirculation, P _in , and the target Assuming that the exhaust partial pressure is Pt _ex and the actual exhaust partial pressure is Pr _ex , the predicted pressure that is the pressure ratio of P _in + (Pt _ex −Pr _ex ) with respect to P _ex in a state where execution of the external EGR is permitted. Execution of external EGR is prohibited when the ratio is greater than or equal to a predetermined permission reference value, and in a state where execution of external EGR is prohibited, the predicted pressure ratio is less than a predetermined prohibition reference value that is smaller than the permission reference value. Sometimes the execution of the external EGR is permitted (execution control of the external EGR by the valve control unit).

According to this configuration, the element P _in + (Pt _ex −P r _ex ) of the EGR valve downstream pressure taking into account the target exhaust partial pressure, that is, the pressure when the opening degree of the EGR valve is adjusted to achieve the target exhaust partial pressure the predicted value of the EGR valve downstream pressure in anticipation of change, based on the predicted pressure ratio which is the ratio of the element P _ex of the EGR valve upstream pressure and so as to permit or prohibit execution of the external EGR, that is, an external EGR In the state where the execution of the external EGR is permitted, the execution of the external EGR is prohibited when the predicted pressure ratio is equal to or greater than the predetermined allowable reference value. In the state where the execution of the external EGR is prohibited, the predicted pressure ratio is the predetermined prohibition standard. since so as to permit the execution of external EGR when it is a value or less, when the prediction pressure ratio is the relationship cause hunting execution control of external EGR is executing external EGR Nitsu Thus, it is possible to keep switching between the permitted state and the prohibited state.

  Thereby, it is possible to suppress the occurrence of hunting in the execution control of the external EGR. In addition, when the opening of the EGR valve necessary to realize the required EGR flow rate is small and the differential pressure change between the EGR valve upstream pressure and the EGR valve downstream pressure is small even when the external EGR is executed, the external EGR The external EGR can be executed on demand even in an engine operating state where external EGR cannot be performed when the reference value for switching between the permitted state and the prohibited state is provided with hysteresis.

It should be noted that the “predicted pressure ratio” and “predetermined permission reference value” used for determining permission or prohibition in the execution control of the external EGR by the valve control unit, and “predicted pressure ratio” and “predetermined In comparison with the “prohibited reference value”, the reciprocal of the predicted pressure ratio (that is, P _in + (Pt _ex -Pr _ex P for _ex Pressure ratio) may be used. In this case, the valve control unit prohibits the execution of the external EGR when the reciprocal of the predicted pressure ratio is equal to or less than a predetermined permission reference value, and in the state where the execution of the external EGR is prohibited, the reciprocal of the predicted pressure ratio. When the value is equal to or greater than a predetermined prohibition reference value larger than the permission reference value, the execution of the external EGR is permitted. Thus, the case where the comparison calculation is performed using the reciprocal of the predicted pressure ratio is also included in the execution control of the external EGR by the valve control unit. In short, “P _ex "And" P _in + (Pt _ex -Pr _ex ) ”, The execution control of the external EGR by the valve control unit based on the predicted pressure ratio may be substantially performed.

The above control device, the EGR rate setting unit for setting a target EGR rate which is a target value of the amount of exhaust gas by the external EGR of the total amount of intake air sucked into the cylinder of the engine, set at E GR ratio setting unit An EGR rate adjustment unit that adjusts the target EGR rate so as to decrease as the predicted pressure ratio increases by multiplying the target EGR rate by an adjustment coefficient of 0 or more and 1 or less that takes a smaller value as the predicted pressure ratio increases And may be further provided. In this case, it is preferable that the valve control unit controls the opening degree of the EGR valve based on the target EGR rate adjusted by the EGR rate adjusting unit.

  The controllability of the EGR flow rate by adjusting the opening of the EGR valve becomes worse as the pressure ratio of the EGR valve downstream pressure to the EGR valve upstream pressure is larger. According to the above configuration, since the target EGR rate is lowered as the predicted pressure ratio of the EGR valve downstream pressure to the EGR valve upstream pressure based on the target exhaust partial pressure is larger, the controllability of the EGR valve becomes worse. The opening degree of the EGR valve can be reduced, and adverse effects on engine operation control due to variations in the EGR rate during execution of external EGR can be reduced. As a result, engine operation control can be further stabilized.

In the control device, the predetermined permission reference value may be set to one or more values.

  According to the engine control apparatus, it is possible to appropriately control the execution of the external EGR and suppress the occurrence of hunting in the execution control of the external EGR. As a result, it is possible to prevent the operation control of the engine including the external EGR from becoming unstable, and to prevent the emission performance and the fuel consumption from being lowered.

1 is a schematic configuration diagram of an engine according to Embodiment 1. FIG. FIG. 2 is a functional configuration diagram of an ECU according to the first embodiment. It is an image figure of the EGR rate adjustment map which concerns on Embodiment 1. FIG. It is a block diagram which shows the adjustment method of the target EGR ratio which concerns on Embodiment 1. FIG. 4 is a flowchart showing execution control of external EGR according to the first embodiment. 10 is a flowchart showing execution control of external EGR according to the second embodiment.

  Hereinafter, exemplary embodiments will be described in detail with reference to the drawings.

Embodiment 1
FIG. 1 shows a schematic configuration diagram of an engine 1 to which the control device according to the first embodiment is applied.

  The engine 1 is a spark ignition direct injection engine with a supercharger. As shown in FIG. 1, the engine 1 mainly burns a mixture of intake air (air) and fuel, and the engine body 3. An intake passage 5 through which intake air introduced into the engine flows, an exhaust passage 7 through which exhaust gas generated by combustion of the air-fuel mixture in the engine body 3 flows, and a turbocharger that supercharges intake air using the energy of the exhaust gas 8, an external EGR mechanism 9 for performing external EGR, sensors for detecting information used for controlling the engine 1, and an ECU (Engine Control Unit) 11 for controlling the engine 1 as a whole. .

<Engine body>
The engine body 3 includes a cylinder block 15 in which a plurality of cylinders 13 (for example, four, only one is shown in FIG. 1) are provided in series, and a cylinder head 17 disposed on the cylinder block 15. Inside the cylinder block 15 and the cylinder head 17, although not shown, a water jacket through which engine coolant flows is provided.

  Each cylinder 13 is fitted with a piston 21 that divides a combustion chamber 19 for burning the air-fuel mixture so as to reciprocate. The piston 21 is connected to the crankshaft 25 via a connecting rod 23. Further, the engine body 3 is provided with a fuel injection device 27 called an injector. The fuel injection device 27 injects fuel (for example, gasoline) toward the combustion chamber 19 at a predetermined timing in accordance with a control signal from the ECU 11.

  Further, the cylinder head 17 is formed with an intake port 29 and an exhaust port 31 that are opened on the ceiling surface of the combustion chamber 19 for each cylinder 13. The intake port 29 is provided with an intake valve 33 that opens and closes the opening on the combustion chamber 19 side. On the other hand, the exhaust port 31 is provided with an exhaust valve 35 for opening and closing the opening on the combustion chamber 19 side.

  The intake valve 33 and the exhaust valve 35 are connected to the crankshaft 25 via a power transmission mechanism (not shown) provided in the engine body 3. The power transmission mechanism reciprocates the intake valve 33 and the exhaust valve 35 between the open position and the closed position in conjunction with the rotation of the crankshaft 25. By this driving, the intake valve 33 opens and closes the intake port 29 and the exhaust valve 35 opens and closes the exhaust port 31 at predetermined timings.

  The cylinder head 17 is further provided with a spark plug 37 for igniting the air-fuel mixture in the combustion chamber 19 for each cylinder 13. The spark plug 37 generates a spark at a predetermined timing in accordance with a control signal from the ECU 11 and causes the air-fuel mixture to explode and burn with the spark. By this explosion combustion, the piston 21 reciprocates in the cylinder 13, and the reciprocating motion of the piston 21 is converted into the rotational motion of the crankshaft 25 and output as torque (rotational power).

<Intake passage>
In the intake passage 5, in order from the upstream side, an air cleaner 39 that purifies the intake air by removing foreign matters such as dust contained in the air intake from the outside, a compressor 41 that boosts the intake air that passes through, and the intake air that passes through An intercooler 43 for cooling, a throttle valve 45 for adjusting the flow rate of intake air introduced into the engine body 3, and a surge tank 47 for temporarily storing intake air supplied to the engine body 3 are provided.

  The intake passage 5 is further provided with an air bypass passage 49 for circulating a part of the intake air supercharged by the compressor 41 to the upstream side of the compressor 41. The air bypass passage 49 is provided with an air bypass valve 51 that adjusts the flow rate of intake air flowing through the air bypass passage 49. The air bypass valve 51 is, for example, a so-called on / off valve that can switch the air bypass passage 49 between a fully closed state and a fully open state.

  The portion of the intake passage 5 downstream of the surge tank 47 is constituted by an intake manifold 52 having a plurality of independent intake passages branched for each cylinder 13 of the engine body 3, although not shown in detail. The surge tank 47 is included in the intake manifold 52.

<Exhaust passage>
In the exhaust passage 7, in order from the upstream side, a turbine 53 that is rotated by exhaust gas passing through, and harmful air pollution such as NOx (nitrogen oxide), CO (carbon monoxide), and HC (hydrocarbon) contained in the exhaust gas. An exhaust purification device 55 for purifying the substance is provided.

  The exhaust purification device 55 is formed by using, for example, two catalytic converters 61 that internally support an exhaust purification catalyst such as a three-way catalyst. The portion of the exhaust passage 7 upstream of the exhaust bypass passage 57 includes an exhaust manifold 60 having a plurality of independent exhaust passages branched for each cylinder 13 of the engine body 3, although not shown in detail.

  The exhaust passage 7 is further provided with an exhaust bypass passage 57 for bypassing the exhaust gas flowing through the exhaust passage 7 by bypassing the turbine 53. The exhaust bypass passage 57 is provided with a waste gate valve 59 for adjusting the flow rate of the exhaust gas flowing through the exhaust bypass passage 57. The waste gate valve 59 is a so-called linear valve that can change the opening of the exhaust bypass passage 57 continuously or in multiple stages between a fully open state and a fully closed state.

<Turbocharger>
The turbocharger 8 includes the compressor 41 provided in the intake passage 5 and the turbine 53 provided in the exhaust passage 7. The compressor 41 and the turbine 53 are connected via a shaft and rotate integrally. In the turbocharger 8, when the turbine 53 rotates in response to the exhaust flow, the compressor 41 sends the intake air to the downstream side using the rotational force of the turbine 53, and compresses (supercharges) the intake air.

<External EGR mechanism>
The external EGR mechanism 9 circulates through the EGR passage 63 that recirculates part of the exhaust discharged to the exhaust passage 7 to the intake passage 5, the EGR cooler 65 that cools the exhaust recirculated through the EGR passage 63, and the EGR passage 63. And an EGR valve 67 for controlling the exhaust gas recirculation amount, that is, the EGR flow rate.

  The EGR passage 63 connects the intake passage 5, specifically the intake manifold 52, downstream of the throttle valve 45, and the exhaust passage 7, specifically exhaust manifold 60, upstream of the turbine 53. Both manifolds 52 and 60 are connected. The EGR cooler 65 and the EGR valve 67 are provided in the EGR passage 63 in order from the upstream side (exhaust passage 7 side). The EGR valve 67 is a linear valve that can change the opening of the EGR passage 63 continuously or in multiple stages between a fully open state and a fully closed state.

<Sensors>
Sensors are provided in the engine main body 3, the intake passage 5, the exhaust passage 7, and the external EGR mechanism 9 described above.

  Specifically, the engine body 3 is provided with a crank angle sensor 69 that detects the rotation angle of the crankshaft 25 and a water temperature sensor 71 that detects the engine water temperature, which is the temperature of the engine coolant in the water jacket. Yes.

  In the intake passage 5, an air flow sensor 73 that detects an intake air flow rate is provided between the air cleaner 39 and the compressor 41. The air flow sensor 73 has a built-in temperature sensor that detects the intake air temperature. Further, the intake air passage 5 between the compressor 41 and the throttle valve 45 and on the downstream side of the intercooler 43 has a first intake pressure that detects the pressure of the intake air compressed by the turbocharger 8, that is, the supercharging pressure. A sensor 75 is provided.

  The intake passage 5 is further provided with a throttle opening sensor 77 that detects the opening of the throttle valve 45. The intake passage 5 on the downstream side of the throttle valve 45, specifically the surge tank 47, is provided with a second intake pressure sensor 79 that detects the intake manifold pressure that is the pressure in the surge tank 47. The second intake pressure sensor 79 includes a temperature sensor that detects the intake manifold temperature, which is the temperature in the surge tank 47.

  In the exhaust passage 7, a WG opening degree sensor 81 that detects the opening degree of the waste gate valve 61 is provided. Further, O2 sensors 83 and 85 are provided in the exhaust passage 7 between the turbine 53 and the exhaust purification device 55 and the exhaust passage 7 between the two catalytic converters 61, respectively. The detection values of these two O2 sensors 83 and 85 are used for feedback control of the air-fuel ratio in the combustion chamber 19.

  The external EGR mechanism 9 is provided with an EGR opening sensor 87 that detects the opening of the EGR valve 67. Further, the EGR passage 63 between the EGR cooler 65 and the EGR valve 67 is provided with an exhaust pressure sensor 89 that detects an EGR valve upstream pressure that is an exhaust pressure upstream of the EGR valve 67.

  The detected values of these various sensors 69 to 89 are output to the ECU 11 during driving of the automobile.

<ECU>
The ECU 11 is activated by a hardware such as an internal memory such as a CPU (Central Processing Unit), a ROM (Read Only Memory) or a RAM (Random Access Memory), a basic control program such as an OS (Operating System), and a specific function activated on the OS. And a computer configured with software including an application program that comprehensively controls the operation of the engine 1 including the external EGR based on the detection values of the sensors. The ECU 11 is an example of a control device for the engine 1.

  FIG. 2 shows a functional configuration diagram of the ECU 11 with a focus on the portion related to the opening degree control of the EGR valve 67. As shown in FIG. 2, the ECU 11 functionally includes a charging efficiency calculation unit 91 that calculates the actual charging efficiency that is the charging efficiency in the current operating state of the engine 1, and the EGR flow rate in the current operating state of the engine 1. The EGR flow rate calculation unit 93 that calculates the actual EGR flow rate, the valve control unit 95 that controls opening and closing of the EGR valve 67, and the storage unit 97 that stores various data.

  The charging efficiency calculation unit 91 is based on the intake air flow rate detected by the air flow sensor 73 and the engine speed obtained from the detected value of the crank angle sensor 69, and is the actual volume that is the volume efficiency in the current operating state of the engine 1. Calculate efficiency. Then, the filling efficiency calculation unit 91 calculates the actual filling efficiency from the actual volume efficiency using the standard atmospheric density (the density of the atmosphere in the standard state: about 1.2 kg [kg / m3]).

  The EGR flow rate calculation unit 93 calculates Bernoulli's theorem based on the EGR valve upstream pressure detected by the exhaust pressure sensor 89, the EGR valve downstream pressure, and the opening degree of the EGR valve 67 detected by the EGR opening degree sensor 87. Use to calculate the basic value of the actual EGR flow rate. Here, the EGR valve downstream pressure corresponds to the pressure in the surge tank 47. For this reason, the intake manifold pressure detected by the second intake pressure sensor 79 is used as the EGR valve downstream pressure. Then, the EGR flow rate calculation unit 93 corrects the basic value according to the temperature of the exhaust gas recirculated by the external EGR, and calculates the corrected value as the final actual EGR flow rate. Here, the temperature of the recirculated exhaust gas is estimated from the engine speed and the engine load.

  The valve control unit 95 sets a target EGR rate setting unit 99 that sets a target EGR rate that is a target value of the EGR rate, and a target that calculates a target exhaust partial pressure that is a target value of the partial pressure of the exhaust gas recirculated by the external EGR. The exhaust partial pressure calculation unit 101 and the actual exhaust for calculating the actual exhaust partial pressure that is the partial pressure of the current exhaust among the pressures of the intake air sucked into the cylinder 13 of the engine 1 when executing the external EGR. A partial pressure calculation unit 103, a target EGR rate adjustment unit 105 that adjusts a target EGR rate, and an EGR execution control unit 107 that permits or prohibits execution of external EGR are provided.

  The target EGR rate setting unit 99 sets a basic value of the target EGR rate based on the EGR control map stored in advance in the storage unit 97. In the EGR control map, the actual charging efficiency, the engine water temperature, and the target EGR rate corresponding to them are defined for each engine speed. The basic value of the target EGR rate includes the actual charging efficiency calculated by the charging efficiency calculation unit 91, the engine speed obtained from the detection value of the crank angle sensor 69, and the engine water temperature detected by the water temperature sensor 71. It is set by checking against the EGR control map.

  Note that various maps used for external EGR execution control, including the EGR control map, are unique to the engine 1 and are obtained in advance by actual measurement or the like. Therefore, the EGR control map and the EGR rate adjustment map described later are merely examples, and may have different characteristics depending on the engine 1.

  The target exhaust partial pressure calculation unit 101 calculates a target exhaust partial pressure by converting a target EGR flow rate, which is a target value of the EGR flow rate, into a pressure based on the intake manifold temperature detected by the second intake pressure sensor 79. . The actual exhaust partial pressure calculation unit 103 converts the actual EGR flow rate calculated by the EGR flow rate calculation unit 93 into a pressure based on the intake manifold temperature detected by the second intake pressure sensor 79, thereby reducing the actual exhaust partial pressure. calculate.

  The target EGR rate adjustment unit 105 adjusts the target EGR rate set by the target EGR rate setting unit 99 based on the EGR rate correction map stored in advance in the storage unit 97. The EGR rate adjustment map includes an EGR valve detected by a predicted intake manifold pressure and an exhaust pressure sensor 89 that is a predicted value of the intake manifold pressure when the target EGR rate is realized, that is, when the target exhaust partial pressure is realized. A predicted pressure ratio, which is a pressure ratio with the upstream pressure, and an adjustment coefficient for the EGR rate corresponding thereto are defined. The predicted pressure ratio in the present embodiment is a pressure ratio of the predicted intake manifold pressure to the EGR valve upstream pressure.

  FIG. 3 shows an image diagram of the EGR rate adjustment map. In the EGR rate adjustment map, as shown in FIG. 3, the EGR rate adjustment coefficient α is a positive value of 0 to 1, and is within a range where the predicted pressure ratio is a certain value or more (for example, 0.8 or more). The predicted pressure ratio decreases as it approaches 1. This is because the controllability of the EGR flow rate by adjusting the opening degree of the EGR valve 67 becomes worse as the pressure ratio of the EGR valve downstream pressure to the EGR valve upstream pressure becomes larger, and the controllability of the EGR valve 67 becomes worse. This is because by reducing the opening of the EGR valve 67, the adverse effect on the operation control of the engine 1 due to the variation in the actual exhaust partial pressure is reduced.

  The target EGR rate adjustment unit 105 obtains the EGR rate adjustment coefficient α by comparing the predicted pressure ratio with such an EGR rate adjustment map. Then, the target EGR rate adjustment unit 105 adjusts the target EGR rate by multiplying the basic value of the target EGR rate by the adjustment coefficient α of the EGR rate.

  The valve control unit 95 sets the final target EGR rate by the functions of the target EGR rate setting unit 99, the target exhaust partial pressure calculation unit 101, the actual exhaust partial pressure calculation unit 103, and the target EGR rate adjustment unit 105. . A method for setting the target EGR rate will be described below with reference to FIG. FIG. 4 is a block diagram showing a method for setting the target EGR rate by the valve control unit 95.

  As shown in FIG. 4, the valve control unit 95 first sets the basic value of the target EGR rate based on the engine speed, the actual charging efficiency, and the engine water temperature by the function of the target EGR rate setting unit 99. Next, the valve control unit 95 calculates the target EGR flow rate by converting the basic value of the target EGR rate into a flow rate based on a throttle passage flow rate that is a flow rate that passes through the throttle valve 45. Here, the throttle passage flow rate is the flow rate of the intake air flowing through the intake passage 5. For this reason, the intake flow rate detected by the air flow sensor 73 is used as the throttle passage flow rate.

  The valve control unit 95 converts the target EGR flow rate thus calculated into a pressure based on the intake manifold temperature by the function of the target exhaust partial pressure calculation unit 101, and acquires the target exhaust partial pressure. Further, the valve control unit 95 converts the actual EGR flow rate calculated by the function of the EGR flow rate calculation unit 93 into a pressure based on the intake manifold temperature by the function of the actual exhaust gas partial pressure calculation unit 103, and acquires the actual exhaust gas partial pressure. To do. The valve control unit 95 subtracts the actual exhaust partial pressure from the target exhaust partial pressure acquired in this manner, thereby obtaining an exhaust value that is a predicted value of the change amount of the actual exhaust partial pressure when the target EGR rate of the basic value is realized. The amount of change in partial pressure is calculated.

  Next, the valve control unit 95 calculates the predicted intake manifold pressure by adding the intake manifold pressure detected by the second intake pressure sensor 79 to the exhaust partial pressure change amount. Subsequently, the valve control unit 95 calculates the predicted pressure ratio by dividing the predicted intake manifold pressure by the EGR valve upstream pressure detected by the exhaust pressure sensor 89.

  Next, the valve control unit 95 obtains the adjustment coefficient α of the EGR rate corresponding to the predicted pressure ratio with reference to the EGR rate adjustment map as shown in FIG. 3 by the function of the target EGR rate adjustment unit 105, and the adjustment The target EGR rate is adjusted by multiplying the basic value of the target EGR rate by the coefficient α. The valve control unit 95 acquires the adjusted value as the final target EGR rate, and executes the external EGR by adjusting the opening degree of the EGR valve 67 so that the target EGR rate is realized.

  The EGR execution control unit 107 permits or prohibits the execution of the above-described external EGR using a predetermined reference value based on the predicted pressure ratio Pr expressed by the following equation.

Pr = {P _in + (Pt _ex −Pr _ex )} / P _ex
Here, P _ex is the EGR valve upstream pressure detected by the exhaust pressure sensor 89. P _in is the intake manifold pressure detected by the second intake pressure sensor 79 (EGR valve downstream pressure). Pt _ex is the target exhaust partial pressure calculated by the target exhaust partial pressure calculation block 101. Pr _ex is the actual exhaust partial pressure calculated by the actual exhaust partial pressure calculation unit 103.

  Specifically, the EGR execution control unit 107 permits the execution of the external EGR when the predicted pressure ratio Pr is less than a predetermined reference value set to a value of 1.0 or more, and the predicted pressure ratio Pr is the predetermined pressure value. Execution of external EGR is prohibited when the value is equal to or greater than the reference value. For example, 1.0 is set as the predetermined reference value.

  The external EGR execution control by the EGR execution control unit 107 will be described below with reference to FIG. FIG. 5 is a flowchart of external EGR execution control.

  As shown in FIG. 5, the EGR execution control unit 107 first determines whether or not the current operating state of the engine 1 is in the external EGR region in step ST01. The external EGR region is a low load to medium load and low rotation to medium rotation operation region where the external EGR is executed if the execution of the external EGR is permitted. Whether or not the operating state of the engine 1 is in the external EGR region is determined based on the engine speed, the charging efficiency, the engine water temperature, and the like.

  At this time, if it is determined that the operating state of the engine 1 is in the external EGR region, it is necessary to determine whether the execution of the external EGR should be permitted or prohibited. move on. On the other hand, if it is determined that the operating state of the engine 1 is not in the external EGR region, there is no need to determine prohibition or permission for the execution of the external EGR because the external EGR is not performed, so the process returns and steps again. ST01 is performed.

  Next, in step ST02, the EGR execution control unit 107 determines whether or not the predicted pressure ratio Pr is equal to or greater than a predetermined reference value (for example, 1.0).

  At this time, if the predicted pressure ratio Pr is greater than or equal to a predetermined reference value, the differential pressure between the EGR valve upstream pressure and the EGR valve downstream pressure is adjusted by adjusting the opening of the EGR valve 67 so as to achieve the target EGR rate. It is expected that the controllability of the EGR flow rate by adjusting the opening degree of the EGR valve 67, that is, the controllability of the EGR rate will be degraded. In particular, when 1.0 is set as the predetermined reference value, the EGR valve downstream pressure is balanced with or larger than the EGR valve upstream pressure, and the EGR rate is controlled by adjusting the opening degree of the EGR valve 67. It is predicted that the property will be significantly worse. Therefore, in this case, it is determined that external EGR execution should not be permitted, and the process proceeds to step ST03.

  In step ST03, the EGR execution control unit 107 prohibits the execution of external EGR.

  On the other hand, if the predicted pressure ratio Pr is less than the predetermined reference value in step ST02, the EGR valve upstream pressure remains the EGR valve downstream pressure even if the opening degree of the EGR valve 67 is adjusted to achieve the target EGR rate. Since the required differential pressure is ensured between the EGR valve upstream pressure and the EGR valve downstream pressure, it is predicted that the controllability of the EGR rate by adjusting the opening degree of the EGR valve 67 is not significantly impaired. Therefore, in this case, the execution of the external EGR should be permitted, and the process proceeds to step ST04.

  In step ST04, the EGR execution control unit 107 permits execution of the external EGR.

  When steps ST03 and ST04 are completed, the process returns, and the steps after step ST01 are repeated.

According to such external EGR execution control, the predicted value P _in + (Pt _ex −P r _ex ) of the EGR valve downstream pressure in anticipation of the pressure change when the opening degree of the EGR valve is adjusted to achieve the target exhaust partial pressure. ) and the pressure ratio of the EGR valve upstream pressure P _ex is, when a relation causing hunting execution control of an external EGR, it not switched enable and disable the execution of external EGR.

  Therefore, according to ECU11 of engine 1 concerning this embodiment 1, it can control suitably that hunting generate | occur | produces in execution control of external EGR. In addition, external EGR can be executed on demand even when the engine 1 is in an operating state where external EGR cannot be performed by providing hysteresis to the reference value for switching between permitting and prohibiting the execution of external EGR. As a result, the operation control of the engine 1 including the external EGR can be avoided from becoming unstable, and the emission performance and fuel consumption can be prevented from being lowered.

<< Embodiment 2 >>
The engine 1 according to the second embodiment is different from the first embodiment in the method of execution control of the external EGR by the ECU. In the second embodiment, the external EGR execution control method is the same as that of the first embodiment except that the external EGR execution control method is different from that of the first embodiment. Therefore, the external EGR execution control method is different from that of the first embodiment. The same configuration and control method will be left to the description of the first embodiment based on FIGS. 1 to 5, and the detailed description thereof will be omitted.

  In the first embodiment, the example in which the prohibition and permission for the execution of the external EGR are switched using the same reference value in the case of prohibiting from the permitted state and in the case of allowing from the prohibited state has been described. In this modification, the EGR execution control unit 107 permits or prohibits the execution of the external EGR using a predetermined reference value (allowed reference value and prohibited reference value) having hysteresis based on the predicted pressure ratio Pr. To do.

  Specifically, the EGR execution control unit 107 determines whether the external EGR is less than a predetermined permission reference value set to a value of 1.0 or more in a state where the execution of the external EGR is permitted. Execution of the external EGR is prohibited when the predicted pressure ratio Pr is equal to or greater than the allowable reference value. For example, 1.0 is set as the permission reference value.

  Further, the EGR execution control unit 107 keeps the execution of the external EGR prohibited when the predicted pressure ratio Pr is larger than a predetermined prohibition reference value smaller than the permission reference value in a state where the execution of the external EGR is prohibited, When the predicted pressure ratio Pr is equal to or less than the prohibition reference value, the execution of external EGR is permitted. For example, a fixed value of 0.2 to 0.4 is set as the prohibition reference value.

  The external EGR execution control by the EGR execution control unit 107 will be described below with reference to FIG. FIG. 6 is a flowchart of external EGR execution control according to this modification.

  As shown in FIG. 6, the EGR execution control unit 107 first determines whether or not the current operating state of the engine 1 is in the external EGR region in step ST11. Since step ST11 is the same as step ST01 in the first embodiment, description thereof is omitted.

  If it is determined in step ST11 that the operating state of the engine 1 is in the external EGR region, it is necessary to determine whether or not the external EGR is being executed. Therefore, the process proceeds to step ST12 for performing such determination. . On the other hand, when it is determined that the operation state of the engine 1 is not in the external EGR region, the process returns as in the first embodiment, and step ST11 is performed again.

  In step ST12, the EGR execution control unit 107 determines whether or not an external EGR is currently being executed.

  Whether or not the external EGR is being executed is determined based on the opening degree of the EGR valve 67 detected by the EGR opening degree sensor 87. Specifically, if the detected value of the EGR opening sensor 87 indicates that the opening of the EGR valve 67 is other than 0, it is determined that the external EGR is being performed because the EGR valve 67 is open. To do. If the detected value of the EGR opening sensor 87 indicates that the opening degree of the EGR valve 67 is 0, it is determined that the external EGR is not executed because the EGR valve 67 is completely closed.

  At this time, if it is determined that the external EGR is being executed, the execution of the external EGR is permitted, and it is necessary to determine whether to prohibit the external EGR from being permitted. Then, the process proceeds to step ST13 for making such a determination. On the other hand, if it is determined that the external EGR is not executed, the execution of the external EGR may be prohibited, and it is necessary to determine whether or not to permit the execution from the state where the execution of the external EGR is prohibited. Therefore, the process proceeds to step ST14 for making such a determination.

  In step ST13, the EGR execution control unit 107 determines whether or not the predicted pressure ratio Pr is equal to or greater than a permission reference value (for example, 1.0).

  At this time, when the predicted pressure ratio Pr is equal to or greater than the permission reference value, it is predicted that the controllability of the EGR rate by adjusting the opening degree of the EGR valve 67 is remarkably deteriorated as described in step ST02 of the first embodiment. Therefore, assuming that the execution of the external EGR should not be permitted, the process proceeds to step ST15.

  In step ST15, the EGR execution control unit 107 prohibits execution of external EGR.

  On the other hand, if the predicted pressure ratio Pr is less than the permitted reference value in step ST13, the controllability of the EGR rate by adjusting the opening of the EGR valve 67 is significantly impaired as described in step ST02 of the first embodiment. Since it is predicted that no external EGR is to be executed, the process proceeds to step ST16.

  In step ST16, the EGR execution control unit 107 permits execution of the external EGR.

  In step ST14, the EGR execution control unit 107 determines whether or not the predicted pressure ratio Pr is equal to or less than the prohibition reference value (for example, a fixed value of 0.2 to 0.4).

  At this time, if the predicted pressure ratio Pr is less than or equal to the prohibition reference value, the EGR valve upstream pressure and the EGR valve downstream pressure are required even if the opening degree of the EGR valve 67 is adjusted to achieve the target EGR rate. Therefore, it is predicted that the controllability of the EGR rate by adjusting the opening degree of the EGR valve 67 is good. Therefore, in this case, the execution of the external EGR should not be prohibited, the process proceeds to step ST16, and the execution of the external EGR is permitted.

  On the other hand, when the predicted pressure ratio Pr is larger than the prohibition reference value, the differential pressure between the EGR valve upstream pressure and the EGR valve downstream pressure is relatively adjusted by adjusting the opening degree of the EGR valve 67 so as to achieve the target EGR rate. It is predicted that the controllability of the EGR rate by adjusting the opening degree of the EGR valve 67 becomes worse. Therefore, in this case, the execution of the external EGR should not be permitted, and the process proceeds to step ST15 to prohibit the execution of the external EGR.

  If the EGR valve 67 is fully closed even when the execution of the external EGR is permitted, the process proceeds to step ST14, but the predicted pressure ratio Pr is larger than the prohibition reference value and permitted. Since it is in the range less than the reference value, the process proceeds to step ST16 and the execution of the external EGR is still permitted.

  When steps ST15 and ST16 are completed, the process returns, and the steps after step ST11 are repeated.

  According to the execution control of the external EGR, in addition to permitting or prohibiting the execution of the external EGR based on the pressure ratio between the EGR valve downstream pressure and the EGR valve upstream pressure in consideration of the target exhaust partial pressure, the execution of the external EGR is performed. Since the reference value for switching between the permitted state and the prohibited state is provided with hysteresis, it is possible to further suppress the occurrence of hunting in the execution control of the external EGR. About the other, the effect similar to the said Embodiment 1 can be acquired.

  As described above, a preferred embodiment has been described as an example of the technique disclosed in the present application. However, the technology in the present disclosure is not limited to this, and can also be applied to embodiments in which changes, replacements, additions, omissions, and the like have been made as appropriate. Moreover, it is possible to form a new embodiment by combining the components and control methods described in the first and second embodiments. In addition, the constituent elements described in the accompanying drawings and the detailed description may include constituent elements that are not essential for solving the problem. For this reason, it should not be immediately recognized that these non-essential components are essential because they are described in the accompanying drawings and detailed description.

  For example, the first and second embodiments may be configured as follows.

  In the first embodiment, the target EGR rate setting unit 99 sets the target EGR rate based on the actual charging efficiency. However, the target EGR rate setting unit 99 is not limited to this, and instead of the actual charging efficiency, a target value of the charging efficiency of the engine 1 is used. It may be set based on a certain target filling efficiency. The target charging efficiency is calculated by a known method based on the required output torque, which is the required value of the output torque corresponding to the depression operation of the accelerator pedal, and the air-fuel ratio and the thermal efficiency obtained from the detected values of the O2 sensors 83 and 85. The

  In the first embodiment, the EGR execution control unit 107 permits the execution of the external EGR by using the target exhaust partial pressure obtained from the basic value of the target EGR rate set by the target EGR rate setting unit 99. Although the control for switching the prohibition is performed, the present invention is not limited thereto, and the target exhaust partial pressure is calculated from the final target EGR rate obtained by adjusting the target EGR rate of the basic value by multiplying by the adjustment coefficient α, The execution control of the external EGR may be performed using the target exhaust partial pressure.

In the first embodiment, the predicted pressure ratio Pr used for the execution control of the external EGR is the pressure ratio of the predicted intake manifold pressure {P _in + (Pt _ex −Pr _ex )} to the EGR valve upstream pressure P _ex , that is, {P _In + (Pt _ex −Pr _ex )} / P _ex , but the reciprocal number P _ex / {P _in + (Pt _ex −Pr _ex )} may be used as the predicted pressure ratio Pr. In short, the valve control unit 95 permits or prohibits the execution of external EGR so that hunting does not occur based on the pressure ratio between the EGR valve upstream pressure Pex and the predicted intake manifold pressure P _in + (Pt _ex −Pr _ex ). It is only necessary to switch to.

  In the first embodiment, the EGR flow rate calculation unit 93 estimates the temperature of the exhaust gas recirculated by the external EGR used to calculate the actual EGR flow rate from the engine speed and the engine load. Not exclusively. For example, the temperature of the exhaust gas may be calculated by correcting the basic value of the actual EGR flow rate according to the temperature detected by the temperature sensor provided between the EGR valve 67 and the EGR cooler 65.

  In the first embodiment, an engine with a turbocharger has been described as an example. However, the present invention is not limited to this, and the technology disclosed herein is applied to an engine control device that does not include a turbocharger. It can also be applied to.

  As described above, the technology disclosed herein is useful for an engine control apparatus in which external EGR is performed.

DESCRIPTION OF SYMBOLS 1 ... Engine, 3 ... Engine main body, 5 ... Intake passage, 7 ... Exhaust passage, 8 ... Turbocharger, 9 ... External EGR mechanism, 11 ... ECU (engine control device), 13 ... Cylinder,
15 ... Cylinder block, 17 ... Cylinder head, 19 ... Combustion chamber, 21 ... Piston,
23 ... Connecting rod, 25 ... Crankshaft, 27 ... Fuel injection device,
29 ... Intake port, 31 ... Exhaust port, 33 ... Intake valve, 35 ... Exhaust valve,
37 ... Spark plug, 39 ... Air cleaner, 41 ... Compressor,
43 ... Intercooler, 45 ... Throttle valve, 47 ... Surge tank,
49 ... Air bypass passage, 51 ... Air bypass valve, 52 ... Intake manifold,
53 ... Turbine, 55 ... Exhaust gas purification device, 57 ... Exhaust gas bypass passage,
59 ... Waste gate valve, 60 ... Exhaust manifold, 61 ... Catalytic converter,
63 ... EGR passage, 65 ... EGR cooler, 67 ... EGR valve,
69 ... Crank angle sensor, 71 ... Water temperature sensor, 73 ... Air flow sensor,
75 ... 1st intake pressure sensor, 77 ... Throttle opening sensor, 79 ... 2nd intake pressure sensor,
81 ... WG opening sensor, 83, 85 ... O2 sensor, 87 ... EGR opening sensor,
89 ... Exhaust pressure sensor, 91 ... Filling efficiency calculation unit, 93 ... EGR flow rate calculation unit,
95 ... Valve control unit, 97 ... Storage unit, 99 ... Target EGR rate setting unit,
101 ... target exhaust partial pressure calculation unit, 103 ... actual exhaust pressure calculation unit,
105 ... target EGR rate adjustment unit, 107 ... EGR execution control unit

Claims (3)

An exhaust gas recirculation passage for recirculating exhaust gas discharged to the exhaust passage to the intake passage;
An exhaust gas recirculation valve for controlling a recirculation amount of exhaust gas flowing through the exhaust gas recirculation passage,
An engine control apparatus that performs exhaust gas recirculation in which a part of exhaust gas is recirculated through the exhaust gas recirculation passage by opening the exhaust gas recirculation valve,
A valve control unit for controlling opening and closing of the exhaust gas recirculation valve;
A target exhaust partial pressure calculation unit that calculates a target exhaust partial pressure that is a target value of a partial pressure of exhaust gas recirculated by exhaust gas recirculation;
An actual exhaust partial pressure calculation unit that calculates an actual exhaust partial pressure that is a partial pressure of exhaust among the pressure of the intake air sucked into the cylinder of the engine when performing exhaust gas recirculation,
The valve control unit is configured such that the exhaust pressure on the exhaust passage side of the exhaust gas recirculation valve is P _ex , the intake air pressure mixed with the exhaust gas recirculated by the exhaust gas recirculation is P _in , and the target exhaust gas When the partial pressure is Pt _ex and the actual exhaust partial pressure is Pr _ex , the pressure ratio of the P _in + (Pt _ex −Pr _ex ) with respect to the P _ex when the exhaust gas recirculation is permitted. Execution of exhaust gas recirculation is prohibited when the predicted pressure ratio is equal to or higher than a predetermined permission reference value, and when the execution of exhaust gas recirculation is prohibited, the predicted pressure ratio is smaller than the permission reference value. An engine control device that permits execution of exhaust gas recirculation when the value is below a reference value . The engine control device according to claim 1,
An exhaust gas recirculation rate setting unit that sets a target exhaust gas recirculation rate that is a target value of the amount of exhaust gas by exhaust gas recirculation out of the total amount of intake air taken into the cylinders of the engine ;
Multiplying the target exhaust gas recirculation rate set in the previous SL exhaust gas recirculation rate setting unit, a 0 or more and 1 or less adjustment factor that takes a smaller value as the predicted pressure ratio is large to the target exhaust gas recirculation rate An exhaust gas recirculation rate adjusting unit that adjusts so as to decrease as the predicted pressure ratio increases.
The valve control unit controls the opening of the exhaust gas recirculation valve based on a target exhaust gas recirculation rate adjusted by the exhaust gas recirculation rate adjusting unit. In the engine control apparatus according to claim 1 or 2,
The engine control device, wherein the predetermined permission reference value is set to a value of 1 or more .

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