JP2014145256A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimize exhaust gas recirculation with an EGR device depending on fuel to be used for combustion in a fuel supply system capable of supplying both gas fuel and liquid fuel.SOLUTION: An internal combustion engine comprises: a first injection valve 21 which injects gas fuel; a second injection valve 22 which injects liquid fuel; and an EGR device which recirculates a portion of exhaust gas, exhausted from a cylinder 24 of an engine 10 to an exhaust passage, to the cylinder 24. A control section 80 executes recirculation of the exhaust gas with the EGR device on the basis of an operation state of the engine. When the engine is in the operation state using the gas fuel, the control device limits execution of the recirculation of the exhaust gas with the EGR device compared to the operation state using the liquid fuel.

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly to a control device for an in-vehicle internal combustion engine provided with a fuel supply system capable of supplying gaseous fuel and liquid fuel, respectively.

  Conventionally, for example, an internal combustion engine that is driven by burning gaseous fuel such as compressed natural gas (CNG) has been put into practical use (see, for example, Patent Document 1). In Patent Document 1, in an internal combustion engine that switches between gaseous fuel and liquid fuel according to the operating state, the opening timing of the intake valve is set to be greater when gaseous fuel is used than when liquid fuel is used. It is disclosed to slow down. By such control, the fuel is supplied to the combustion chamber by taking into account that the intake pressure of the gas fuel mixture becomes higher by the supply pressure of the gas fuel. Optimized according to the nature of the.

  Conventionally, as a control device for an internal combustion engine, one that performs EGR control (exhaust gas recirculation control) for returning a part of the exhaust gas discharged from the combustion chamber to the exhaust passage to the combustion chamber is known. As EGR control, exhaust is introduced into the intake system through a pipe connecting the intake system and the exhaust system, and this is introduced into the combustion chamber from the intake valve together with fresh air. An internal EGR is known in which exhaust gas is returned from an exhaust valve to a combustion chamber by adjusting a lap amount.

Japanese Patent No. 2656181

  Various characteristics such as octane number are different between gaseous fuel and liquid fuel. Therefore, when performing EGR control that uses gas fuel and liquid fuel by switching between them, it can be said that the same effect can be obtained with gas fuel even if the effect of introducing EGR is sufficiently obtained with liquid fuel. Absent. It is also conceivable that the introduction of a gas that does not contribute to combustion causes inconveniences such as a decrease in combustion stability.

  The present invention has been made to solve the above problems, and in a system including a fuel supply system capable of supplying gaseous fuel and liquid fuel, exhaust gas recirculation is performed by an EGR device in accordance with the fuel used for combustion. The main object is to provide a control device for an internal combustion engine that can optimize the engine.

  The present invention employs the following means in order to solve the above problems.

  In the present invention, the first injection means (21) for injecting gaseous fuel, the second injection means (22) for injecting liquid fuel, and the cylinder (24) of the internal combustion engine (10) are discharged into the exhaust passage. The present invention is applied to an internal combustion engine system including an EGR device (28, 29, 30) for recirculating a part of exhaust gas into the cylinder, and the exhaust gas is recirculated by the EGR device based on an operating state of the internal combustion engine. The present invention relates to a control device for an internal combustion engine. According to the first aspect of the present invention, fuel determination means for determining whether or not the fuel used is the gaseous fuel during operation of the internal combustion engine, and the fuel determination means determines that the fuel used is the gaseous fuel. In this case, an EGR limiting means for limiting the recirculation of the exhaust gas by the EGR device as compared with the operation of the internal combustion engine using the liquid fuel is provided.

  In short, in the above configuration, the implementation of exhaust gas recirculation by the EGR device is limited when the gaseous fuel is used compared to when the liquid fuel is used. In general, when liquid fuel such as gasoline fuel is used for combustion, an EGR device is used to suppress NOx generation and knocking, or to reduce pump loss and cooling loss, and promote fuel vaporization. Exhaust gas recirculation is performed. However, gaseous fuel originally does not easily generate NOx due to combustion, and does not easily knock. Further, since it is a gas, the intake negative pressure is not so large, so there is little pump loss, and it is not necessary to consider the promotion of fuel vaporization. Furthermore, since the combustion temperature is lower than that of liquid fuel such as gasoline, cooling loss is less likely to occur. In consideration of such characteristics of the gaseous fuel, the above configuration is adopted, and therefore, exhaust gas recirculation by the EGR device can be appropriately performed according to the fuel used for combustion.

  In addition, as an aspect which restrict | limits implementation of exhaust gas recirculation by an EGR apparatus, the aspect which prohibits implementation of exhaust gas recirculation, the aspect which reduces the introduction amount of exhaust gas, the aspect which restrict | limits the operation area | region which implements exhaust gas recirculation, etc. including.

The block diagram which shows the outline of an internal combustion engine system. The figure which shows an example of the map for EGR rate setting of 1st Embodiment. The flowchart which shows the process sequence of exhaust gas recirculation control of 1st Embodiment. The figure which shows the process sequence of the subroutine at the time of switching of 1st Embodiment. The time chart which shows the specific aspect of exhaust gas recirculation control of 1st Embodiment. The figure explaining the outline | summary of the exhaust gas recirculation control of 2nd Embodiment. The flowchart which shows the process sequence of exhaust gas recirculation control of 2nd Embodiment. The figure which shows the process sequence of the subroutine at the time of switching of 2nd Embodiment. The time chart which shows the specific aspect of exhaust gas recirculation control of 2nd Embodiment. The figure which shows an example of the map for EGR rate setting of other embodiment. The figure explaining the outline | summary of the exhaust gas recirculation control of other embodiment.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. This embodiment is embodied as an internal combustion engine system of a so-called bi-fuel type on-vehicle multi-cylinder engine that uses compressed natural gas (CNG) that is gaseous fuel and gasoline that is liquid fuel as fuel for engine combustion. . An overall schematic diagram of this system is shown in FIG.

  An engine 10 shown in FIG. 1 is an inline three-cylinder spark ignition engine, and an intake system 11 and an exhaust system 12 are connected to an intake port and an exhaust port, respectively. The intake system 11 has an intake manifold 13 and an intake pipe 14. The intake manifold 13 has a plurality of (for the number of cylinders of the engine 10) branch pipe portions 13a connected to the intake port of the engine 10, and a collective portion 13b connected to the intake pipe 14 on the upstream side. ing. The intake pipe 14 is provided with a throttle valve 15 as air amount adjusting means. The throttle valve 15 is configured as an electronically controlled throttle valve whose opening degree is adjusted by a throttle actuator 15a such as a DC motor. The opening degree of the throttle valve 15 (throttle opening degree) is detected by a throttle opening degree sensor 15b built in the throttle actuator 15a.

  Further, the exhaust system 12 has an exhaust manifold 16 and an exhaust pipe 17. The exhaust manifold 16 has a plurality of (for the number of cylinders of the engine 10) branch pipe portions 16a connected to the exhaust port of the engine 10 and a collecting portion 16b connected to the exhaust pipe 17 on the downstream side. ing. Exhaust gas after combustion of the engine 10 is discharged into the exhaust pipe 17 from each cylinder 24 of the engine 10. The exhaust pipe 17 is provided with an exhaust sensor 18 for detecting exhaust components and a catalyst 19 for purifying exhaust. As the exhaust sensor 18, an air-fuel ratio sensor that detects the air-fuel ratio from the oxygen concentration in the exhaust gas is provided.

  The intake port and the exhaust port of the engine 10 are respectively provided with an intake valve 25 and an exhaust valve 26 as engine valves that adjust the amount of air introduced into the cylinder 24 by opening and closing drive. The air / fuel mixture is introduced into the cylinder 24 by the opening operation of the intake valve 25, and the exhaust gas after combustion is discharged into the exhaust passage by the opening operation of the exhaust valve 26. Each of the intake valve 25 and the exhaust valve 26 is provided with an intake side valve drive mechanism 28 and an exhaust side valve drive mechanism 29 as means for variably controlling the opening and closing timings of the intake and exhaust valves 25 and 26. Each of the valve drive mechanisms 28 and 29 adjusts the advance amount (phase angle) of each camshaft on the intake side or the exhaust side with respect to the crankshaft of the engine 10. According to the intake side valve drive mechanism 28, the opening / closing timing of the intake valve 25 is changed to the advance side or the retard side, and according to the exhaust side valve drive mechanism 29, the opening / closing timing of the exhaust valve 26 is advanced or retarded. It is changed to the corner side.

  A spark plug 20 is provided in each cylinder 24 of the engine 10. A high voltage is applied to the ignition plug 20 at a desired ignition timing through an ignition device 20a including an ignition coil. By applying this high voltage, a spark discharge is generated between the opposing electrodes of each spark plug 20, and the fuel introduced into the cylinder 24 (combustion chamber) is ignited and used for combustion.

  Further, the present system is a fuel injection means for injecting and supplying fuel to the engine 10, a first injection valve 21 for injecting gaseous fuel (CNG fuel), and a second injection valve 22 for injecting liquid fuel (gasoline). And have. These injection valves 21 and 22 inject fuel into the branch pipe portion 13 a of the intake manifold 13 in the intake system 11. The second injection valve 22 may be a direct injection type in which fuel is directly injected into the cylinder 24 of the engine 10.

  Each of the injection valves 21 and 22 is an open / close type control valve in which the valve body is lifted from the closed position to the open position by electrically driving the electromagnetic drive unit. Each valve is driven to open by a valve opening drive signal. Each of these injection valves 21 and 22 is opened by energization, closed by energization interruption, and injects an amount of fuel (gaseous fuel, liquid fuel) according to the energization time. In the present embodiment, the injection pipe 23 is connected to the tip of the first injection valve 21, and the gaseous fuel injected from the first injection valve 21 is branched through the injection pipe 23 in the intake manifold 13. It is injected to the part 13a.

  The system includes a gaseous fuel supply unit 40 that supplies gaseous fuel to the first injection valve 21. In the gaseous fuel supply unit 40, a gas tank 42 is connected to the first injection valve 21 via a gas pipe 41. Further, a regulator 43 having a pressure adjustment function for adjusting the pressure of the gaseous fuel supplied to the first injection valve 21 to be reduced is provided in the middle of the gas pipe 41. The regulator 43 is configured so that gaseous fuel in a high pressure state (for example, a maximum of 20 MPa) stored in the gas tank 42 is a predetermined set pressure (for example, in a range of 0.2 to 1.0 MPa) that is an injection pressure of the first injection valve 21. The pressure is adjusted to be constant. Further, the gaseous fuel after the pressure reduction adjustment is supplied to the first injection valve 21 through the gas pipe 41. In the gas pipe 41, the upstream side of the regulator 43 is a high-pressure pipe portion 41a that forms a high-pressure side passage, and the downstream side is a low-pressure pipe portion 41b that forms a low-pressure side passage.

  The gas fuel passage formed by the gas pipe 41 and the like further includes a tank main stop valve 44 (tank outlet valve) disposed in the vicinity of the fuel outlet of the gas tank 42 and a downstream side of the tank main stop valve 44. And a shutoff valve 45 disposed in the vicinity of the fuel inlet of the regulator 43. These valves 44 and 45 allow and block the flow of gaseous fuel in the gas pipe 41. Both the tank main stop valve 44 and the shut-off valve 45 are electromagnetic on-off valves, and are normally closed types in which the flow of gaseous fuel is blocked when not energized and the flow of gaseous fuel is allowed when energized.

  In the gas piping 41, a pressure sensor 46 for detecting the fuel pressure and a temperature sensor 47 for detecting the fuel temperature are provided in the high pressure piping portion 41a, and a pressure sensor 48 for detecting the fuel pressure in the low pressure piping portion 41b. A temperature sensor 49 for detecting the fuel temperature is provided. The shut-off valve 45 and the pressure sensor 46 can be provided integrally with the regulator 43. In this embodiment, a configuration in which the shut-off valve 45 and the pressure sensor 46 are provided integrally with the regulator 43 is adopted. .

  The present system includes a liquid fuel supply unit 70 that supplies liquid fuel to the second injection valve 22. In the liquid fuel supply unit 70, a fuel tank 72 is connected to the second injection valve 22 via a fuel pipe 71. The fuel pipe 71 is provided with a fuel pump 73 that feeds the liquid fuel in the fuel tank 72 to the second injection valve 22.

  This system is provided with a supercharger 50 that compresses air using exhaust gas. The supercharger 50 includes an intake compressor 51 disposed on the upstream side of the throttle valve 15 in the intake pipe 14 and an exhaust disposed on the upstream side of the catalyst 19 near the outlet of the combustion chamber of the engine 10 in the exhaust pipe 17. The turbine 52 and a rotary shaft 53 that connects the intake compressor 51 and the exhaust turbine 52 are configured. When the exhaust turbine 52 is rotated by the exhaust gas flowing in the exhaust pipe 17, the intake compressor 51 is rotated along with the rotation, and the intake air is compressed (supercharged) by the centrifugal force generated by the rotation of the intake compressor 51. Further, the intake pipe 14 is provided with an intercooler (not shown) as a heat exchanger for cooling the supercharged intake air on the downstream side of the intake air compressor 51 so that a decrease in compression efficiency is suppressed. It has become. In the present embodiment, the supercharger 50 can adjust the supercharging pressure of intake air by adjusting the opening of a variable vane (not shown).

  In addition, the present system is provided with an external EGR device 30 as an EGR device for recirculating a part of the exhaust gas to the combustion chamber. The external EGR device 30 includes an EGR pipe 31 that connects the exhaust pipe 17 and the intake pipe 14, an EGR valve 32 that serves as an electromagnetic on-off valve provided in the EGR pipe 31, and exhaust gas that passes through the EGR pipe 31. And an EGR cooler 33 for cooling. By changing the opening degree (EGR opening degree) of the EGR valve 32, the amount of exhaust gas (EGR gas amount) recirculated to the intake system 11 can be adjusted. The EGR pipe 31 is configured to connect the upstream side of the intake compressor 51 in the intake pipe 14 and the downstream side of the catalyst 19 in the exhaust pipe 17, but is not limited to this. Alternatively, the downstream side and the upstream side of the catalyst 19 may be connected. Moreover, it is good also as a structure which changes EGR gas amount by changing the valve-opening time of the EGR valve 32 instead of the structure which changes EGR gas amount by EGR opening degree.

  The control unit 80 includes a CPU 81, a ROM 82, a RAM 83, a backup RAM 84, an interface 85, and a bidirectional bus 86. The CPU 81, ROM 82, RAM 83, backup RAM 84, and interface 85 are connected to each other by a bidirectional bus 86.

  The CPU 81 executes a routine (program) for controlling the operation of each unit in this system. The ROM 82 stores in advance various data such as a routine executed by the CPU 81, maps (including tables, relational expressions, etc. in addition to maps) and parameters referred to when the routine is executed. The RAM 83 temporarily stores data as necessary when the CPU 81 executes a routine. The backup RAM 84 appropriately stores data under the control of the CPU 81 in a state where the power is turned on, and retains the stored data even after the power is shut off.

  The interface 85 includes the throttle opening sensor 15b, the exhaust sensor 18, the pressure sensors 46 and 48, the temperature sensors 47 and 49, and other sensors (crank angle sensor, air flow meter, cooling water temperature sensor) provided in the system. , A vehicle speed sensor, an accelerator sensor, etc.), and outputs (detection signals) from these sensors to the CPU 81. Further, the interface 85 is electrically connected to driving units such as the throttle actuator 15a, the ignition device 20a, the injection valves 21 and 22, the tank main stop valve 44, the shutoff valve 45 and the like, and a drive signal sent from the CPU 81. Are output to the drive unit to drive these drive units. That is, the control unit 80 acquires the operating state of the engine 10 based on the output signals of the above-described sensors, and implements the above-described driving unit control based on the acquired operating state.

  Specifically, for example, the intake air amount of the engine 10 is calculated based on the accelerator operation amount detected by the accelerator sensor, the engine rotation speed detected by the crank angle sensor, and the like, and the throttle actuator 15a of the throttle actuator 15a is calculated based on the calculated value. Control the drive. Further, a fuel injection amount (fuel injection time) is calculated based on the engine speed and the intake air amount detected by the air flow meter, and the driving of the injection valves 21 and 22 is controlled based on the calculated value. Further, the optimal ignition timing is calculated based on the engine rotational speed, the intake air amount, and the like, and the drive of the ignition device 20a is controlled so that ignition is performed at the optimal ignition timing.

  A control signal is input from the control unit 80 to the ignition device 20a, the tank main stop valve 44, the shutoff valve 45, and the EGR valve 32. Specifically, the ignition device 20a outputs a high voltage in response to a control signal from the control unit 80, and generates an ignition spark in the ignition plug. The tank main stop valve 44 and the shut-off valve 45 are independently switched between a valve closing state and a valve opening state in accordance with a control signal from the control unit 80. The opening degree of the EGR valve 32 is changed according to a control signal from the control unit 80. When the EGR opening degree is zero, the EGR valve 32 is fully closed, and the exhaust gas is not recirculated by the external EGR device 30.

  The control unit 80 selectively switches the fuel used for combustion of the engine 10 according to the remaining amount of fuel in the tank, an input signal from a fuel selection switch (not shown), and the like. Specifically, when the remaining amount of the gaseous fuel in the gas tank 42 falls below a predetermined value or when the use of the liquid fuel is selected by the fuel selection switch, the liquid fuel is preferentially used, and the fuel tank 72 When the remaining amount of the liquid fuel is less than a predetermined value or when the use of the gaseous fuel is selected by the fuel selection switch, the gaseous fuel is preferentially used. Moreover, the control part 80 is switching the fuel used according to an engine driving | running state. Specifically, when the engine 10 is started, the engine 10 is basically operated using liquid fuel, and after the start of the engine 10 is completed, the fuel used is switched from liquid fuel to gaseous fuel. Ten operations are performed.

  In this system, the control unit 80 performs exhaust gas recirculation by the external EGR device 30 based on the engine operating state. By returning the exhaust gas into the combustion chamber, the combustion temperature is lowered, thereby suppressing NOx generation, reducing cooling loss, suppressing knocking, or promoting fuel vaporization at low temperatures. Further, exhaust gas recirculation is performed in the middle rotation / medium load region of the engine 10 to reduce pump loss and improve fuel efficiency.

  Specifically, the control unit 80 calculates a target value of the ratio (external EGR rate) of the EGR gas amount to the entire air amount introduced into the combustion chamber of the engine 10 based on the engine operating state every time, and the calculation The EGR opening is controlled so as to achieve the target value. In the present embodiment, the relationship between the engine speed, the engine load, and the external EGR rate is stored in advance in the ROM 82 as an EGR rate setting map. The control unit 80 calculates the target value of the external EGR rate based on the engine rotation speed and the engine load each time by referring to the EGR rate setting map. FIG. 2 shows an example of an EGR rate setting map. According to the figure, the external EGR rate is the largest in the engine operation range of medium rotation / medium load, and the external EGR rate is set to zero in the idle operation region (low rotation / low load region) and in the high rotation / high load region. It has become so.

  By the way, when the engine is operated using liquid fuel, the above-described effects by performing exhaust gas recirculation, that is, NOx generation suppression, cooling loss reduction, knocking suppression, fuel vaporization promotion, pump loss Various effects such as reduction can be sufficiently obtained. However, the effect of exhaust gas recirculation cannot be obtained as much as liquid fuel for gaseous fuel. That is, gaseous fuel (especially CNG fuel) originally has the characteristics that the amount of NOx emission due to combustion is small, the octane number is high, and knocking does not easily occur. Furthermore, it has various characteristics different from those of gasoline fuel, such as the combustion temperature is lower than liquid fuel such as gasoline, it is a gas, the intake negative pressure is relatively small, and it is not necessary to promote vaporization. . Therefore, when gaseous fuel is used, the effect of EGR as described above is diminished or even if the engine is in an operating state where the effect of exhaust gas recirculation can be sufficiently obtained with liquid fuel. Can't get. Conversely, introducing exhaust gas into the combustion chamber may cause a disadvantage that combustion becomes unstable.

  Therefore, in the present embodiment, when the engine 10 is operated using gaseous fuel as the combustion fuel, the exhaust gas is recirculated by the external EGR device 30 rather than when the engine is operated using liquid fuel. Implementation is limited. In particular, in the present embodiment, when gaseous fuel is used, the exhaust gas recirculation by the external EGR device 30 is prohibited regardless of the engine operating state.

  Next, the processing procedure of the exhaust gas recirculation control of the present embodiment will be described using the flowchart of FIG. This process is repeatedly executed at a predetermined cycle by the CPU 81 of the control unit 80 when the engine 10 is in an operating state.

  In FIG. 3, in step S101, the engine rotational speed NE and the engine load detected by the sensor are acquired. In the subsequent step S102, there is a switching request for switching the used fuel from one of the gaseous fuel and the liquid fuel to the other fuel (request determining means), and before the switching of the used fuel accompanying the switching request is completed. It is determined whether or not. If it is determined in step S102 that at least one of the two requirements is negative, that is, if there is no fuel switching request, or if fuel switching associated with the switching request is not being performed, the process proceeds to step S103.

  In step S103, it is determined whether the fuel used is a gaseous fuel (fuel determination means). If the engine is operating using liquid fuel, the process proceeds to step S104, the EGR prohibition flag is turned off, and an EGR rate setting map (see FIG. 2) is used based on the acquired engine speed and engine load. To calculate the target value of the external EGR rate. In the subsequent step S106, a target value (target EGR opening) of the EGR opening is calculated based on the calculated target value, and the EGR valve 32 is set so that the actual opening of the EGR valve 32 becomes the target EGR opening. A drive command is output. Here, the target EGR opening degree is set to a valve opening side value as the target value of the external EGR rate increases. At this time, it is desirable to variably set the target EGR opening based on the engine rotation speed in consideration of the fact that the EGR gas is less easily introduced into the intake system as the engine rotation speed is higher.

  On the other hand, when the used fuel is gaseous fuel, the process proceeds to step S105, the EGR prohibition flag is turned on, and the external EGR rate is set to zero. In step S106, a drive command is output to the EGR valve 32 so that the actual opening of the EGR valve 32 becomes the target EGR opening (zero) (EGR limiting means). During the period when the EGR prohibition flag is on, the exhaust gas recirculation by the external EGR device 30 is prohibited. Then, this process ends.

  Here, in the configuration in which the external EGR rate is made different according to the fuel used, it is necessary to change the EGR opening degree with the switching of the fuel used. On the other hand, after changing the target EGR opening and outputting a drive command to the EGR valve 32, it takes a certain time until the actual opening of the EGR valve 32 becomes the target EGR opening. Therefore, when the fuel used for combustion of the engine 10 is switched from one fuel to the other, if the fuel is switched all at once, the change in the EGR opening cannot catch up with the fuel switching, and the EGR gas amount is excessive or insufficient. If this occurs, the engine operating state may be deteriorated.

  For example, when the engine is operated using liquid fuel (gasoline fuel) and exhaust gas recirculation is performed by the external EGR device 30, the fuel used is changed from liquid fuel (gasoline fuel) to gaseous fuel (CNG fuel). ). At this time, when switching from the injection mode of 100% liquid fuel and 0% gaseous fuel to the injection mode of 0% liquid fuel and 100% gaseous fuel, the switching to gaseous fuel is completed before the EGR opening becomes zero. Doing so may reduce engine output. Further, when the engine is operated using gaseous fuel (CNG fuel) and exhaust gas recirculation by the external EGR device 30 is prohibited, the fuel used is changed from gaseous fuel (CNG fuel) to liquid fuel (gasoline fuel). ). At this time, switching from the injection mode of liquid fuel 0% and gaseous fuel 100% to the injection mode of liquid fuel 100% and gaseous fuel 0% at a stroke completes the change to the appropriate EGR opening when using liquid fuel. If the switching to liquid fuel is completed before starting, knocking may occur.

  Therefore, in the present embodiment, when there is a switching request for switching the fuel to be used from one of the gaseous fuel and the liquid fuel to the other fuel, the other fuel is gradually reduced while the other fuel is being injected. The fuel used is switched by gradually increasing the amount of fuel injection. Further, during the period from the start to the completion of the fuel switching, the EGR gas amount (external EGR rate) is variably controlled in accordance with the usage ratio between one fuel and the other fuel.

  That is, in the exhaust gas recirculation control of FIG. 3 described above, when both of the two requirements are affirmed in step S102, specifically, the timing immediately after the request for switching the fuel or the fuel switching accompanying the switching request is performed. If it is being executed, the process proceeds to step S107, and the switching subroutine shown in FIG. 4 is executed.

  In FIG. 4, in step S201, the injection amounts of gaseous fuel and liquid fuel are calculated. Specifically, for the fuel that was used until immediately before the switch request (fuel before switching), a value obtained by correcting the decrease by a predetermined amount α from the previous injection amount is calculated as the current injection amount, and the other fuel (switching) For the after fuel), a value obtained by correcting the increase by a predetermined amount α from the previous injection amount is calculated as the current injection amount (injection control means). The driving of the first injection valve 21 and the second injection valve 22 based on the calculated injection amount is executed by a separate routine (not shown).

  In the subsequent step S202, a target value of the external EGR rate is calculated according to the fuel usage ratio. In the present embodiment, the external EGR rate Egr1 when using liquid fuel and the external EGR rate Egr2 when using gaseous fuel are linearly interpolated, and a value corresponding to the fuel usage ratio is a target value for the external EGR rate. Get as. Here, the external Egr1 is an external EGR rate corresponding to the current engine speed and engine load in the EGR rate setting map, and Egr2 is zero. The calculation method of the external EGR rate here is not limited to the above. For example, the relationship between the fuel usage ratio and the external EGR rate is stored in the ROM 82 in advance as a map or the like, and is calculated by using the map. May be. According to this map, the higher the liquid fuel usage ratio is, the larger the external EGR rate is set. In step S203, the target EGR opening is calculated based on the calculated target value, and a drive command is output to the EGR valve 32 so that the actual opening of the EGR valve 32 becomes the target EGR opening.

  Next, a specific aspect of the exhaust gas recirculation control according to the present embodiment will be described with reference to the time chart of FIG. In FIG. 5, it is assumed that there is a request for switching to gaseous fuel during operation of the engine using liquid fuel (for example, when a fuel selection switch is switched). FIG. 5 shows a case where the engine operating state (engine speed and engine load) is constant.

  In FIG. 5, during the period when the engine operation using the liquid fuel is performed, the EGR prohibition flag is turned off, and the exhaust gas is recirculated at an external EGR rate corresponding to the engine operation state. In this situation, when there is a switching request to switch the used fuel to gaseous fuel, the liquid fuel injection amount is gradually decreased by a predetermined amount and the gaseous fuel injection amount is reduced during the period after the request timing t11. The amount is gradually increased by a predetermined amount. When changing the injection amount, the gaseous fuel is increased so that the engine output corresponding to the reduced amount of the liquid fuel can be covered by the gaseous fuel so that the engine output does not fluctuate. Further, in the period TA1 from the start of fuel switching to the completion, the EGR valve 32 is gradually closed so that the external EGR rate decreases as the liquid fuel usage ratio decreases. The EGR prohibition flag is turned on at timing t12 when the used fuel is completely switched from the liquid fuel to the gaseous fuel. Thereby, after the timing t12, the recirculation of the EGR gas is prohibited during the period in which the engine operation is performed using the gaseous fuel.

  Note that there is a difference in the optimal ignition timing between the gaseous fuel (CNG fuel) and the liquid fuel (gasoline fuel), and the optimal ignition timing exists on the advance side of the CNG fuel. Considering this point, in this embodiment, the ignition timing is changed according to the fuel used. In addition, in the period TA1 in which two types of fuel are used together with the request for switching the fuel to be used, the ignition timing is gradually changed from the viewpoint of maintaining the output stability of the engine 10 (FIG. 5). Specifically, at the time of switching from gasoline fuel to CNG fuel, the ignition timing is set to an advance side by a predetermined angle from the optimal ignition timing for gasoline fuel to the optimal ignition timing for CNG fuel (see FIG. 5). (Broken line), at the time of switching from CNG fuel to gasoline fuel, the retarded angle is set by a predetermined angle from the optimum ignition timing with CNG fuel to the optimum ignition timing with gasoline fuel. Further, in the period from the start to the completion of the switching of the fuel used (the period in which the external EGR rate is changed) TA1, the optimal ignition timing (set according to the fuel usage ratio) (in order to suppress knocking) Further, the retardation correction may be performed on the broken line in FIG. 5 (solid line in FIG. 5).

  In the period TA1, since two types of fuels having different fuel properties are used in combination, they are different from the normal combustion state. If the ignition retard learning learning update process by knocking is performed under such circumstances, there is a risk of setting the ignition timing inappropriately. Therefore, in the present embodiment, the ignition retard learning update process by knocking is prohibited in the TA1 during the same period. Specifically, the ignition learning permission flag is switched from on to off at timing t11 when there is a switching request for switching the fuel to be used from liquid fuel to gaseous fuel. Further, the ignition learning permission flag is switched from OFF to ON at timing t12 when the fuel switching is completed. As a result, during the period in which the ignition learning permission flag is off, execution of the ignition retard learning update process by knocking is prohibited.

  According to the embodiment described in detail above, the following excellent effects can be obtained.

  When gas fuel is used, the exhaust gas recirculation by the EGR device is restricted compared to when liquid fuel is used. Even when the introduction effect of EGR gas is sufficiently obtained with liquid fuel (gasoline fuel), the effect of introduction of EGR gas is small with gas fuel (CNG fuel) due to its fuel characteristics. In addition, when a gas that does not contribute to combustion is introduced into the combustion chamber, there may be a disadvantage. In this regard, according to the above configuration, exhaust gas recirculation by the EGR device can be appropriately performed according to the fuel used for combustion.

  Since the implementation of the exhaust gas recirculation by the EGR device is prohibited, the implementation is prohibited. Therefore, when the gaseous fuel is used, the deterioration of the combustion stability due to the introduction of the EGR gas into the combustion chamber is ensured. Can be suppressed.

  When there is a switching request to switch the fuel to be used from one of the gaseous fuel and the liquid fuel to the other fuel, the injection amount of the other fuel is gradually decreased while gradually decreasing the injection amount of the one fuel. The fuel used is switched by increasing the amount. If the fuel is switched at once in response to the fuel switching request, for example, knocking may occur due to a difference in octane number or the like. In particular, in the configuration in which the embodiment of the EGR is changed according to the fuel used, it is necessary to change the EGR opening according to the switching of the fuel used. At that time, the change in the EGR opening does not catch up with the fuel switching. It is conceivable that the engine operating state deteriorates due to excessive or insufficient EGR gas amount. On the other hand, in the said structure, since a fuel switch is implemented in steps, a use fuel can be switched in the state which stabilized the engine operating state.

  Further, the external EGR rate (EGR gas amount) is variably controlled in accordance with the usage ratio between one fuel and the other fuel during a period from the start to the completion of the fuel switch in response to the fuel switch request. It was. According to this configuration, even when the fuel is used in combination, the EGR gas amount can be controlled with an appropriate value corresponding to the engine operating state at each time.

  In the engine 10 with a supercharger, the combustion temperature tends to be higher than that of a naturally aspirated engine, and when using gasoline fuel, there are a large operating region and an amount of EGR gas for introducing EGR gas to suppress knocking. On the other hand, if the EGR gas is positively introduced when the gaseous fuel is used in the engine 10 with the supercharger in the same manner as when the gasoline fuel is used, there is a tendency that the combustion becomes unstable. In this regard, according to the above-described embodiment, by applying the present invention to the engine 10 with a supercharger, it is possible to more suitably obtain the effect of suppressing a decrease in combustion stability due to the introduction of EGR gas. .

(Second Embodiment)
Next, a second embodiment of the present invention will be described focusing on differences from the first embodiment. In the first embodiment described above, the case where the exhaust gas recirculation performed by the external EGR device 30 is restricted during the engine operation using the gaseous fuel has been described. In contrast, in the present embodiment, gaseous fuel is used for exhaust gas recirculation by the internal EGR device (intake side valve drive mechanism 28, exhaust side valve drive mechanism 29) that recirculates exhaust gas by adjusting the valve characteristics of the engine valve. It is set as the structure which restrict | limits the implementation during engine operation in use.

  Exhaust gas recirculation control according to this embodiment will be described with reference to FIG. In FIG. 6, it is assumed that the operating state of the engine 10 is a medium load. First, during engine operation using liquid fuel, as shown in FIG. 6A, the valve closing timing of the exhaust valve 26 is made later than the valve opening timing of the intake valve 25 to cause valve overlap. By this overlap, the EGR effect is obtained using the exhaust gas returned from the exhaust port into the combustion chamber. In this embodiment, the actual compression ratio is lowered by separating the closing timing of the intake valve 25 from the compression bottom dead center (compression BDC) in order to further suppress knocking. Specifically, as shown in FIG. 6A, the closing timing of the intake valve 25 is set to the retard side by a predetermined angle θ1 from the compression BDC. In this case, the opening timing of the intake valve is set after the top dead center (TDC) of the intake stroke. Therefore, the valve timing of the exhaust valve 26 is controlled so that the valve closing timing is after the intake TDC and the valve overlap amount is Δθ1.

  On the other hand, the valve timings of the intake valve 25 and the exhaust valve 26 are controlled so that the valve overlap amount is smaller during engine operation using gaseous fuel than during engine operation using liquid fuel. This limits the implementation of exhaust gas recirculation by the EGR device. In this embodiment, as shown in FIG. 6B, when the engine is operated using gaseous fuel, the valve overlap amount is set to zero regardless of the engine operating state, that is, the exhaust gas is returned to the combustion chamber. Avoid it. Further, utilizing the characteristic that gaseous fuel (CNG fuel) is less likely to cause knocking, the intake valve is more effective when the engine is operated using gaseous fuel than when the engine is operated using liquid fuel (gasoline fuel). The actual valve compression ratio of the engine 10 is increased by bringing the valve closing timing of 25 close to the compression BDC. Specifically, as shown in FIG. 6B, the closing timing of the intake valve 25 is set to the retard side by a predetermined angle θ2 (θ1> θ2) from the compression TDC. In this case, the opening timing of the intake valve is set to the intake TDC or the vicinity thereof. Therefore, the valve timing of the exhaust valve 26 is controlled so that the valve overlap amount becomes zero. In FIG. 6B, the closing timing of the exhaust valve 26 is set to the intake TDC or the vicinity thereof, but this is for increasing the scavenging amount of the exhaust as much as possible.

  Next, the processing procedure of the exhaust gas recirculation control according to this embodiment will be described with reference to the flowcharts of FIGS. This process is repeatedly executed at a predetermined cycle by the CPU 81 of the control unit 80 when the engine 10 is in an operating state. In the description of FIGS. 7 and 8, the same processes as those in FIGS. 3 and 4 are denoted by the step numbers in FIGS. 3 and 4 and the description thereof is omitted.

  In FIG. 7, in steps S301 to S303, the same processing as in steps S101 to S103 in FIG. 3 is executed. When the used fuel is liquid fuel, the process proceeds to step S304. In step S304, the EGR prohibition flag is turned off, and the valve overlap amount and the intake valve 25 closing timing (intake closing timing) are set based on the engine operating state. At this time, the valve overlap amount is set to the largest value in the middle rotation / medium load operation region of the engine 10, and the valve overlap amount is smaller as the rotation speed is lower or the load is higher or the rotation speed is higher (the present embodiment). Is set to zero). In addition, the intake closing timing is set to a more retarded angle with respect to the compression BDC in an operation region where knocking is likely to occur (for example, a high rotation / high load operation region).

  On the other hand, when the used fuel is gaseous fuel, the process proceeds to step S305, and the EGR prohibition flag is turned on. In addition, the valve overlap amount is set to zero (EGR restriction means), and the intake closing timing is set closer to the compression TDC (advance angle side) than when liquid fuel is used (compression ratio increasing means). .

  In step S306, the exhaust closing timing is set based on the set intake closing timing and the overlap amount, and the intake side valve drive mechanism 28 and the exhaust valve are closed at the set closing timing. A drive command is output to the exhaust side valve drive mechanism 29.

  Further, when there is a fuel switching request or when the fuel switching accompanying the switching request is being performed, the process proceeds to step S307, and the switching subroutine shown in FIG. 8 is executed. In FIG. 8, in step S401, the same processing as in step S201 of FIG. 4 is executed, and in the subsequent step S402, the valve overlap amount and the intake air closing timing are set according to the fuel usage ratio. Specifically, as the liquid fuel usage ratio increases, the valve overlap amount is set to a larger value, and the intake closing timing is set to the retard side with respect to the compression BDC. In step S403, the exhaust closing timing is set based on the set intake closing timing and valve overlap amount, and a drive command is output to the intake side valve driving mechanism 28 and the exhaust side valve driving mechanism 29.

  Next, a specific aspect of the exhaust gas recirculation control according to the present embodiment will be described with reference to the time chart of FIG. In FIG. 9, it is assumed that there is a request for switching to gaseous fuel during operation of the engine using liquid fuel (for example, when a fuel selection switch is switched). FIG. 9 shows a case where the engine operation state (engine speed and engine load) is constant.

  In FIG. 9, during the engine operation using liquid fuel, the EGR prohibition flag is turned off, and the valve timing is controlled so that the valve overlap amount (EGR gas amount) according to the engine operation state is obtained. Under this circumstance, when there is a switching request to switch the used fuel to the gaseous fuel, after the request timing t21, the injection amount of the liquid fuel is gradually decreased by a predetermined amount and the injection amount of the gaseous fuel is gradually decreased by a predetermined amount. Increase to. Further, in the period TA2 from the start to the completion of fuel switching, the valve overlap amount is gradually reduced so that the EGR gas amount decreases as the liquid fuel usage ratio decreases. Further, the intake closing timing is gradually advanced (side closer to the compression BDC) so that the actual compression ratio of the engine 10 increases as the usage ratio of the liquid fuel decreases (the usage ratio of the gaseous fuel increases). To be changed. Then, the EGR prohibition flag is turned on at a timing t22 when the used fuel is completely switched from the liquid fuel to the gaseous fuel. Thus, after timing t22, recirculation of EGR gas is prohibited while the engine is being operated using gaseous fuel.

  According to the second embodiment described in detail above, the following excellent effects can be obtained in addition to the effects of the first embodiment.

  CNG fuel has a high octane number and is less likely to knock. In view of this point, when the engine is operated using CNG fuel, the actual compression ratio of the engine 10 is increased by bringing the closing timing of the intake valve 25 closer to the compression BDC than when the engine is operated using gasoline fuel. The configuration. By doing so, it is possible to secure the output of the engine 10 when the CNG fuel is used.

  In particular, when the exhaust gas is returned using valve overlap when the gaseous fuel is used, the gaseous fuel is lightweight. Therefore, the air-fuel mixture containing the gaseous fuel introduced from the intake valve 25 into the combustion chamber is used as the intake manifold. It is conceivable that the air is sucked into another cylinder via In addition, the air-fuel ratio may deteriorate due to the combustion of the air-fuel mixture sucked into the other cylinders. In this regard, in the above configuration, when the gaseous fuel is used, the implementation of exhaust gas recirculation by the EGR device is limited, so that the above-described inconvenience can be suppressed.

(Other embodiments)
The present invention is not limited to the description of the above embodiment, and may be implemented as follows, for example.

  -In above-mentioned embodiment, it was set as the structure which restrict | limits implementation of exhaust gas recirculation by prohibiting implementation of exhaust gas recirculation by an EGR apparatus at the time of engine operation using gaseous fuel. On the other hand, in this embodiment, at the time of engine operation using gaseous fuel, the engine operation region in which the exhaust gas recirculation is performed by the EGR device is limited to restrict the exhaust gas recirculation. . In the operation region (low to medium load operation region) where the throttle valve 15 is closed, the intake negative pressure is larger and the pump loss is higher than in the high load operation region. Therefore, during engine operation using gaseous fuel, exhaust gas recirculation is performed for a part of the engine operation region in which exhaust gas recirculation is performed by the EGR device when liquid fuel is used (for example, medium rotation / medium load operation region). To implement. Thereby, a pump loss can be reduced and an improvement in a fuel consumption can be aimed at by extension. Specifically, if applied to the external EGR device 30, in the first embodiment, the EGR rate setting map is configured to use the map of FIG. 10 instead of the map of FIG.

  In the second embodiment, the intake side valve drive mechanism 28 and the exhaust side valve drive mechanism 29 are configured to adjust the valve characteristics by variably controlling the opening / closing timing of the engine valve. The valve characteristic may be adjusted by variably controlling. FIG. 11 shows the exhaust gas recirculation control in this configuration. FIG. 11 illustrates a case where the internal EGR device is applied to a system including an intake side valve drive mechanism 28 that variably controls the operating angle of the intake valve 25.

  For example, when the engine is operated using liquid fuel in a medium load state, the valve overlap between the intake valve 25 and the exhaust valve 26 is increased by widening the operating angle of the intake valve 25 as shown in FIG. Cause it to occur. By this overlap, the EGR effect by the exhaust gas returned from the exhaust port into the combustion chamber is obtained. Further, the actual compression ratio of the engine 10 is lowered by separating the valve closing timing of the intake valve 25 from the compression BDC. Specifically, as shown in FIG. 11A, the intake valve 25 is closed so that the closing timing of the intake valve 25 is retarded from the compression BDC by a predetermined angle θ3, and the valve overlap amount is Δθ2. The side valve drive mechanism 28 is driven.

  In contrast, when the engine is operated using gaseous fuel, the intake valve 25 is set so that the valve overlap amount becomes zero, for example, so that the valve overlap amount becomes smaller than when the engine is operated using liquid fuel. The operating angle is narrowed (see FIG. 11B). Further, when using gaseous fuel, the closing timing of the intake valve 25 is made closer to the compression BDC than when using liquid fuel (gasoline fuel), and the actual compression ratio of the engine 10 is increased. Specifically, as shown in FIG. 11B, the valve closing timing of the intake valve 25 is retarded from the compression TDC by a predetermined angle θ4 (θ3> θ4), and the valve overlap amount is zero. The intake side valve drive mechanism 28 is driven so that

  -As an aspect which restrict | limits implementation of exhaust gas recirculation by an EGR apparatus, it is good also as an aspect which makes EGR gas amount smaller than the time of use of liquid fuel, when comparing in the same operation area | region. At this time, the engine operation region in which exhaust gas recirculation is performed may be the same as that in the case of liquid fuel, or may be part of the case of liquid fuel. For example, in the case of the former, when the gaseous fuel is used, an external EGR rate corresponding to the current engine operating state is calculated using the EGR rate setting map shown in FIG. 2, and a predetermined amount is subtracted from the calculated value. By multiplying by a predetermined coefficient (<1), a value smaller than the calculated value is set as the target value of the external EGR rate. Or it is good also as a structure which has separately the map for liquid fuels, and the map for gaseous fuels.

  In the second embodiment, when the engine using gas fuel is operated, the intake closing timing is set at an angular position where the retardation amount from the compressed BDC is smaller than when the engine is operated using liquid fuel. Thus, the actual compression ratio is increased. The aspect of increasing the actual compression ratio when using the gaseous fuel is not limited to this, and the intake closing timing is more advanced than the compression BDC, and the phase angle from the compression BDC than when using the liquid fuel. It is good also as a structure which increases an actual compression ratio by setting to the angle position where becomes small.

  In the second embodiment, the actual compression ratio is changed according to the fuel used even in the same operating range, but the actual compression ratio may be constant regardless of the fuel used.

  -In above-mentioned embodiment, although this invention was applied to the system provided with a supercharger, you may apply this invention to the system which is not provided with a supercharger. Also in this case, by restricting the exhaust gas recirculation when using the gaseous fuel, it is possible to obtain an effect of suppressing the combustion instability due to the introduction of the EGR gas when using the gaseous fuel.

  In the above embodiment, a plurality of the first injection valves 21 and the second injection valves 22 are provided for each cylinder of the multi-cylinder engine. However, the first injection valve 21 and the second injection are provided in a common part of the plurality of cylinders. A configuration may be provided in which at least one of the valves 22 is provided. For example, it is good also as a structure which injects gaseous fuel and liquid fuel with respect to the collection part of the intake system 11. FIG.

  In the above embodiment, the gaseous fuel is CNG fuel, but other gaseous fuels that are gaseous in the standard state can also be used, for example, fuels mainly composed of methane, ethane, propane, butane, hydrogen, dimethyl ether, etc. It is good also as a structure. Further, liquid fuel is not limited to gasoline fuel. For example, the present invention may be applied to a configuration in which a fuel injection system for gaseous fuel is mounted on a diesel engine using light oil as a liquid fuel for combustion.

  DESCRIPTION OF SYMBOLS 10 ... Engine (internal combustion engine), 14 ... Intake pipe, 17 ... Exhaust pipe, 21 ... 1st injection valve (1st injection means), 22 ... 2nd injection valve (2nd injection means), 24 ... Cylinder, 25 ... Intake valve, 26 ... exhaust valve, 28 ... Intake side valve drive mechanism (EGR device), 29 ... Exhaust side valve drive mechanism (EGR device), 30 ... External EGR device (EGR device), 31 ... EGR piping, 32 ... EGR Valve, 50 ... supercharger, 80 ... control section (fuel determination means, EGR restriction means, request determination means, injection control means, compression ratio increase means).

Claims (7)

Part of the exhaust gas discharged from the first injection means (21) for injecting gaseous fuel, the second injection means (22) for injecting liquid fuel, and the cylinder (24) of the internal combustion engine (10) into the exhaust passage. The internal combustion engine is applied to an internal combustion engine system including an EGR device (28, 29, 30) for recirculating the exhaust gas into the cylinder, and implements recirculation of the exhaust gas by the EGR device based on the operating state of the internal combustion engine A control device of
Fuel determination means for determining whether or not the fuel used is the gaseous fuel during operation of the internal combustion engine;
When the fuel determination means determines that the fuel used is the gaseous fuel, the exhaust gas recirculation by the EGR device is limited compared to when the internal combustion engine is operated using the liquid fuel. EGR limiting means,
A control device for an internal combustion engine, comprising:   2. The control device for an internal combustion engine according to claim 1, wherein the EGR restriction unit restricts the exhaust gas recirculation by prohibiting the exhaust gas recirculation performed by the EGR device.   2. The control device for an internal combustion engine according to claim 1, wherein the EGR restriction unit restricts execution of the exhaust gas recirculation by limiting an operation range of the internal combustion engine in which the exhaust gas recirculation is performed by the EGR device. . Request determining means for determining whether or not there is a switching request for switching the fuel to be used from one of the gaseous fuel and the liquid fuel to the other fuel;
When it is determined by the request determination means that the switching request has been made, the used fuel is switched by gradually increasing the injection amount of the other fuel while gradually decreasing the injection amount of the one fuel. Injection control means for
When the fuel used is switched by the injection control means, the EGR device recycles the fuel during the period from the start to the completion of the fuel switching according to the usage ratio between the one fuel and the other fuel. The control device for an internal combustion engine according to any one of claims 1 to 3, wherein the amount of exhaust gas to be circulated is variably controlled. An intake valve (25) and an exhaust valve (26) as engine valves for adjusting the amount of air introduced into the cylinder;
The EGR device is an internal EGR device (28, 29) for recirculating a part of the exhaust gas into the cylinder by adjusting a valve characteristic of the engine valve.
5. The internal combustion engine according to claim 1, wherein the EGR restriction unit restricts execution of recirculation of the exhaust gas by changing a valve overlap amount between the intake valve and the exhaust valve. 6. Control device.   During operation of the internal combustion engine using the gaseous fuel, the closing timing of the intake valve is closer to the compression bottom dead center of the internal combustion engine than during operation of the internal combustion engine using the liquid fuel. The control apparatus for an internal combustion engine according to claim 5, further comprising compression ratio increasing means for increasing an actual compression ratio of the internal combustion engine. The EGR device includes an EGR passage that connects the exhaust passage and the intake system (11) of the internal combustion engine, and an EGR valve that is disposed in the EGR passage and adjusts the amount of the exhaust gas that is recirculated to the intake system (32). An external EGR device (30) comprising:
5. The control device for an internal combustion engine according to claim 1, wherein the EGR restriction unit restricts the exhaust gas recirculation by changing an opening degree of the EGR valve.

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