JP7155726B2 - Control device for internal combustion engine - Google Patents

Description

The present invention relates to a control device for a spark ignition internal combustion engine in which a three-way catalytic converter and a filter for trapping particulates are installed in an exhaust passage.

A spark ignition type internal combustion engine performs combustion by igniting a mixture of air and fuel introduced into a cylinder with a spark of an ignition plug. At this time, the combustion of part of the fuel in the air-fuel mixture becomes incomplete, and carbonaceous particulate matter (hereinafter referred to as particulate matter) may be generated.

Patent Document 1 discloses an in-vehicle vehicle equipped with a three-way catalyst device installed in an exhaust passage and a filter for collecting particulates installed in a portion downstream of the three-way catalyst device in the exhaust passage. A spark ignition internal combustion engine is described. In such an internal combustion engine, a filter collects the particulates generated in the cylinder, thereby suppressing the emission of the particulates to the outside air. Since the collected particulates gradually accumulate on the filter, if the accumulation is left unattended, the accumulated particulates may eventually clog the filter.

On the other hand, in the internal combustion engine of the document, filter regeneration control for burning and purifying the particulates deposited on the filter is executed in the following manner. In the filter regeneration control, the fuel is injected while the spark of the ignition plug is stopped, so that the air-fuel mixture is introduced into the three-way catalyst device without being burned in the cylinder. The unburned air-fuel mixture introduced into the three-way catalyst burns inside the three-way catalyst, and the heat generated by the combustion raises the temperature of the gas that flows out of the three-way catalyst and into the filter. be done. The heated gas heats and burns the particulates deposited on the filter.

U.S. Patent Application Publication No. 2014/0041362

If the particulate combustion in the filter becomes active during execution of the filter regeneration control, the heat generated by the combustion may raise the temperature of the filter excessively.

A control device for an internal combustion engine that solves the above problems includes a fuel injection valve, a cylinder into which an air-fuel mixture containing fuel injected by the fuel injection valve is introduced, and an ignition device that ignites the air-fuel mixture introduced into the cylinder with a spark. an exhaust passage through which gas discharged from the cylinder flows; a three-way catalyst device installed in the exhaust passage; and a filter for particulate collection installed in a portion downstream of the three-way catalyst device in the exhaust passage. and an internal combustion engine comprising Then, the control device of the internal combustion engine introduces the air-fuel mixture containing the fuel injected by the fuel injection valve into the three-way catalyst device without burning it in the cylinder, thereby burning and purifying the particulates deposited on the filter. running control.

During execution of the filter regeneration control, the fuel in the air-fuel mixture introduced into the three-way catalyst burns in the three-way catalyst, and the gas heated by the combustion flows out of the three-way catalyst and flows into the filter. will flow into The inflowing high-temperature gas heats and burns the particulates deposited on the filter. During execution of the filter regeneration control, when the particulate is heated to a temperature equal to or higher than the ignition point and oxygen required for combustion is supplied to the filter, the particulate combustion purification is being performed.

After starting the combustion purification of particulates by such filter regeneration control, the filter receives heat from the inflowing high-temperature gas and also receives heat from the combustion of the particulates inside. Combustion of particulates in the filter becomes more active as the temperature of the filter increases. Therefore, if a large amount of particulate remains in the filter when the temperature of the filter rises above a certain level, the amount of heat generated by the burning of the particulate becomes excessive and the filter temperature rises too much. be.

On the other hand, in the control device for the internal combustion engine, when the temperature of the filter is high in a state in which particulate combustion purification is being performed during execution of filter regeneration control, the fuel efficiency is leaner than when the temperature of the filter is low. an air-fuel ratio control unit that controls the air-fuel ratio of the air-fuel mixture so that the value is The more fuel that burns in the three-way catalyst, the more heat the gas receives as it passes through the three-way catalyst. On the other hand, even if the amount of heat received by the gas when passing through the three-way catalyst device is the same, when the flow rate of the gas is high, the heat capacity of the gas is greater than when the flow rate of the gas is low. The amount of temperature rise in the gas of is small. Therefore, the leaner the air-fuel ratio of the air-fuel mixture introduced into the three-way catalyst device, the lower the temperature of the gas flowing out of the three-way catalyst device and flowing into the filter. Therefore, if the air-fuel ratio of the air-fuel mixture is changed to the lean side when the temperature of the filter is high, the temperature of the gas flowing into the filter is lowered, and the temperature rise of the filter is suppressed. Therefore, according to the control device for the internal combustion engine, it is possible to prevent the temperature of the filter from rising excessively during the filter regeneration control.

1 is a schematic diagram showing the configuration of an embodiment of a control device for an internal combustion engine; FIG. 4 is a flowchart of a target air-fuel ratio setting routine executed by an air-fuel ratio control unit included in the control device of the same embodiment; 4 is a graph showing the relationship between the air-fuel ratio of the air-fuel mixture during filter regeneration control, the catalyst outflow gas temperature, the amount of oxygen supplied to the filter, and the filter regeneration speed. 4 is a time chart showing an example of an execution mode of filter regeneration control by the control device of the embodiment;

An embodiment of a control device for an internal combustion engine will be described in detail below with reference to FIGS. 1 to 4. FIG.
As shown in FIG. 1, an internal combustion engine 10 mounted on a vehicle includes a cylinder 12 in which a piston 11 is accommodated so as to reciprocate. Piston 11 is connected to crankshaft 14 via connecting rod 13 . The reciprocating motion of the piston 11 inside the cylinder 12 is converted into the rotational motion of the crankshaft 14 .

The cylinder 12 is connected to an intake passage 15 that is a passage for introducing air to the cylinder 12 . The intake passage 15 is provided with an air flow meter 16 for detecting the flow rate of air flowing through the intake passage 15 (intake air amount GA). A throttle valve 17 is provided in a portion of the intake passage 15 downstream of the airflow meter 16 . A fuel injection valve 18 is installed in a portion of the intake passage 15 downstream of the throttle valve 17 . The fuel injection valve 18 forms a mixture of air and fuel by injecting fuel into the air flowing through the intake passage 15 .

The cylinder 12 is provided with an intake valve 19 that opens and closes the intake passage 15 with respect to the cylinder 12 . Further, the air-fuel mixture is introduced into the cylinder 12 from the intake passage 15 according to the opening of the intake valve 19 . The cylinder 12 is provided with an ignition device 20 that ignites and burns the air-fuel mixture in the cylinder 12 with a spark.

An exhaust passage 21 is connected to the cylinder 12 as an exhaust passage for exhaust gas generated by combustion of the air-fuel mixture. Further, the cylinder 12 is provided with an exhaust valve 22 that opens and closes an exhaust passage 21 with respect to the cylinder 12 . Exhaust gas is introduced into the exhaust passage 21 from inside the cylinder 12 in accordance with the opening of the exhaust valve 22 . The exhaust passage 21 is provided with a three-way catalyst device 23 that oxidizes CO and HC in the exhaust gas and reduces NOx. A filter 24 for trapping particulates is installed in a portion of the exhaust passage 21 downstream of the three-way catalytic converter 23 . Further, an air-fuel ratio sensor 25 for detecting the oxygen concentration of the gas flowing through the exhaust passage 21, that is, the air-fuel ratio ABYF of the air-fuel mixture, is installed in a portion of the exhaust passage 21 upstream of the three-way catalyst device 23. . Further, a catalyst outflow gas temperature sensor 26 for detecting a catalyst outflow gas temperature THC, which is the temperature of the gas outflowing from the three-way catalyst device 23, is provided in the exhaust passage 21 between the three-way catalyst device 23 and the filter 24. is set up.

The control device 27 of the internal combustion engine 10 is configured as a microcomputer having an arithmetic processing circuit that executes arithmetic processing for control and a memory that stores control programs and data. Detection signals from the air flow meter 16 , the air-fuel ratio sensor 25 , and the catalyst outflow gas temperature sensor 26 are input to the control device 27 . A detection signal of a crank angle sensor 28 for detecting a crank angle θc, which is the rotation angle of the crankshaft 14, is input to the control device 27. As shown in FIG. Then, the control device 27 calculates the rotation speed of the internal combustion engine 10 (engine rotation speed NE) from the detection result of the crank angle θc. Furthermore, the controller 27 also receives detection signals from a vehicle speed sensor 29 that detects a vehicle speed V, which is the running speed of the vehicle, and an accelerator position sensor 31 that detects an accelerator opening ACC, which is the operation amount of an accelerator pedal 30. there is Based on the detection results of these sensors, the control device 27 controls the opening of the throttle valve 17, the amount and timing of fuel injection of the fuel injection valve 18, the implementation timing (ignition timing) of the spark of the ignition device 20, and the like. As a result, the operating state of the internal combustion engine 10 is controlled according to the running condition of the vehicle.

In the internal combustion engine 10 configured as described above, the particulates in the exhaust gas are collected by the filter 24, thereby suppressing the release of the particulates to the outside air. Such a filter 24 may become clogged due to accumulation of trapped particulates. Therefore, as part of the control of the internal combustion engine 10, the control device 27 executes filter regeneration control for burning and purifying the particulates deposited on the filter 24. FIG.

Filter regeneration control is performed in the following manner. The control device 27 estimates the amount of particulates deposited on the filter 24 (hereinafter referred to as PM deposition amount) from the operating state of the internal combustion engine 10 . Then, the control device 27 executes filter regeneration control when the PM deposition amount exceeds a certain amount. During filter regeneration control, the control device 27 causes the fuel injection valve 18 to inject fuel while the spark of the ignition device 20 is stopped. It is introduced into the three-way catalyst device 23 without letting it run. The fuel in the air-fuel mixture introduced into the three-way catalyst device 23 at this time is combusted inside the three-way catalyst device 23 . Then, the gas heated to a high temperature by the combustion flows out of the three-way catalyst device 23 and flows into the filter 24 . As a result, the particulates deposited on the filter 24 are heated by the high-temperature gas and are combusted.

During execution of such filter regeneration control, it is necessary to maintain the rotation of the crankshaft 14 in order to send the air-fuel mixture in the cylinder 12 to the exhaust passage 21 while the combustion operation of the internal combustion engine 10 is stopped. Therefore, in the present embodiment, the filter regeneration control is executed during coasting of the vehicle in which the power of the internal combustion engine 10 is not required for running of the vehicle and the rotation of the crankshaft 14 can be maintained by power transmission from the wheels. there is

The control device 27 includes an air-fuel ratio control section 27A that controls the air-fuel ratio of the air-fuel mixture introduced into the three-way catalytic converter 23 during execution of such filter regeneration control. During execution of filter regeneration control, the air-fuel ratio control unit 27A sets a target air-fuel ratio, which is a target value of the air-fuel ratio of the air-fuel mixture to be introduced into the three-way catalytic converter 23, through processing of a target air-fuel ratio setting routine, which will be described later. Subsequently, the air-fuel ratio control unit 27A obtains the mass of air (cylinder inflow air amount) introduced into the cylinder 12 according to the opening of the intake valve 19 from the intake air amount GA and the engine speed NE, and A quotient obtained by dividing the inflow air amount by the target air-fuel ratio is calculated as the value of the required injection amount. Then, the air-fuel ratio control unit 27A controls the air-fuel ratio of the air-fuel mixture introduced into the three-way catalytic converter 23 during filter regeneration control by instructing the fuel injection valve 18 to inject the required amount of fuel. there is

FIG. 2 shows the processing procedure of the air-fuel ratio control section 27A in the target air-fuel ratio setting routine. While the internal combustion engine 10 is running, the air-fuel ratio control section 27A repeatedly executes the processing of this routine at predetermined control cycles.

When the processing of this routine is started, first, in step S100, it is determined whether or not filter regeneration control is being executed. Then, if the filter regeneration control is being executed (YES), the process proceeds to step S110, and if not being executed (NO), the process of this routine is terminated as it is.

When the process proceeds to step S110, it is determined in step S110 whether or not the temperature of the filter 24 (hereinafter referred to as filter temperature THF) is equal to or higher than a predetermined high temperature determination value α. The high temperature determination value α is set to a temperature higher than the regeneration start temperature, which is the lower limit of the filter temperature THF required for particulate combustion, and lower than the heat resistance limit of the filter 24 . In this embodiment, the filter temperature THF is obtained by estimating using a heat balance model of the filter 24 based on the temperature and flow rate of the gas flowing into the filter 24, the temperature of the outside air, and the like.

If the filter temperature THF is less than the high temperature determination value α (S110: NO), the predetermined regeneration promoting air-fuel ratio AF1 is set as the value of the target air-fuel ratio in step S120, and then the processing of this routine ends. be. On the other hand, when the filter temperature THF is equal to or higher than the high temperature determination value α (S110: YES), after the predetermined temperature rise suppression air-fuel ratio AF2 is set as the value of the target air-fuel ratio in step S130, Processing of the routine is terminated. An air-fuel ratio that is leaner than the stoichiometric air-fuel ratio ST is set as a value in the regeneration promoting air-fuel ratio AF1. Further, the value of the temperature rise suppressing air-fuel ratio AF2 is set to an air-fuel ratio that is leaner than the regeneration promoting air-fuel ratio AF1.

The setting of the value of the regeneration promoting air-fuel ratio AF1 and the value of the temperature rise suppressing air-fuel ratio AF2 will be described with reference to FIG. FIG. 3 shows the air-fuel ratio and the catalyst when the filter regeneration control is performed by changing the fuel injection amount and changing the air-fuel ratio of the air-fuel mixture flowing into the three-way catalyst device 23 while the intake air amount GA is constant. The relationship between the outflow gas temperature THC and the oxygen supply of the filter 24 is shown.

The heat and oxygen required for the combustion of particulates in the filter 24 during filter regeneration control are supplied by the gas flowing out of the three-way catalyst device 23 and flowing into the filter 24 (hereinafter referred to as catalyst outflow gas). be done. The amount of heat received by the catalyst outflow gas when passing through the three-way catalyst device 23 increases as the amount of fuel combusted in the three-way catalyst device 23 increases. Therefore, the catalyst outflow gas temperature THC decreases as the air-fuel ratio becomes leaner in the range of the air-fuel ratio leaner than the stoichiometric air-fuel ratio ST. On the other hand, in the air-fuel ratio range richer than the stoichiometric air-fuel ratio ST, the amount of fuel combusted in the three-way catalyst device 23 is determined by the amount of air in the air-fuel mixture, so the catalyst outflow gas temperature THC is substantially constant. .

On the other hand, the catalyst outflow gas contains oxygen surplus due to combustion in the three-way catalyst device 23 . Therefore, the amount of oxygen supplied to the filter 24 during execution of filter regeneration control is substantially zero in the range of the air-fuel ratio on the rich side of the stoichiometric air-fuel ratio ST. On the other hand, in the range of the air-fuel ratio leaner than the stoichiometric air-fuel ratio ST, the leaner the air-fuel ratio becomes, the larger the oxygen supply amount becomes.

FIG. 3 also shows the relationship between the air-fuel ratio and the filter regeneration speed when the filter temperature THF is low and when it is high. Here, the case where the filter temperature THF is higher than the regeneration start temperature and lower than the temperature corresponding to the high temperature determination value α is defined as the case where the filter temperature THF is low. The case where the filter temperature THF is higher than the temperature corresponding to the high temperature determination value α and lower than the heat resistance limit temperature of the filter 24 is defined as the case where the filter temperature THF is high.

When the air-fuel ratio is richer than the stoichiometric air-fuel ratio ST, almost no oxygen is supplied to the filter 24, so the filter regeneration speed is almost zero. On the other hand, in the air-fuel ratio range leaner than the stoichiometric air-fuel ratio ST, the leaner the air-fuel ratio becomes, the more oxygen is supplied to the filter 24, but the more heat is supplied. Therefore, when the air-fuel ratio is changed from the stoichiometric air-fuel ratio ST to the lean side, the filter regeneration speed initially increases with an increase in the oxygen supply amount, but peaks when the air-fuel ratio becomes lean to a certain extent. , and then decreases. Even if the catalyst outflow gas temperature THC is somewhat low, if the filter temperature THF is sufficiently high, the heat of the filter 24 itself can heat the particulates to a temperature necessary for combustion. Therefore, the air-fuel ratio at which the filter regeneration speed peaks becomes leaner as the filter temperature THF increases.

Based on the above, in the present embodiment, the value of the regeneration promoting air-fuel ratio AF1 is set to the air-fuel ratio at which the filter regeneration speed peaks when the filter temperature THF is low. The temperature rise suppressing air-fuel ratio AF2 is an air-fuel ratio that is leaner than the regeneration promoting air-fuel ratio AF1, and the catalyst outflow gas temperature THC is sufficiently lower than the temperature corresponding to the high temperature determination value α. The fuel ratio is set as a value.

The operation and effects of this embodiment will be described.
FIG. 4 shows an embodiment of filter regeneration control by the control device 27 of this embodiment. In the figure, filter regeneration control is started at time t1. Note that, in the example of FIG. 1, the internal combustion engine 10 before time t1 is in combustion operation with the air-fuel ratio set to the stoichiometric air-fuel ratio ST. The filter temperature THF at the start of the filter regeneration control is lower than the regeneration start temperature, and thus lower than the temperature corresponding to the high temperature determination value α. Therefore, the filter regeneration control at this time is started with the air-fuel ratio set to the regeneration promoting air-fuel ratio AF1.

When the filter regeneration control is started and the unburned air-fuel mixture is introduced into the three-way catalyst device 23 and combusted in the three-way catalyst device 23, the heat generated by the combustion increases the catalyst outflow gas temperature THC. Since the filter 24 is heated by the catalyst effluent gas with the increased THF, the filter temperature THF also increases. Then, when the filter temperature THF reaches the regeneration start temperature at time t2, the combustion of particulates in the filter 24 is started.

When the combustion of particulate becomes active, the heat generated by the combustion increases the filter temperature THF. When the filter temperature THF rises, the combustion of particulates becomes more active, and the filter temperature THF may further rise. Therefore, when the filter regeneration control is executed while maintaining the air-fuel ratio constant, there is a possibility that the filter temperature THF may rise excessively during the filter regeneration control.

On the other hand, in this embodiment, when the filter temperature THF becomes equal to or higher than the high temperature determination value α at time t3, the air-fuel ratio of the air-fuel mixture introduced into the three-way catalyst device 23 changes from the regeneration-promoting air-fuel ratio AF1 to the regeneration-promoting air-fuel ratio The temperature rise suppression air-fuel ratio AF2 is changed to be leaner than AF1. As a result, the catalyst outflow gas temperature THC drops, so the filter temperature THF also tends to drop.

At time t4, when the filter temperature THF falls below the high temperature determination value α, the air-fuel ratio of the air-fuel mixture introduced into the three-way catalyst device 23 is again changed from the temperature rise suppressing air-fuel ratio AF2 to the regeneration promoting air-fuel ratio AF1. be done. As a result, the catalyst outflow gas temperature THC rises, and the filter temperature THF goes from decreasing to increasing. Therefore, the filter temperature THF during the filter regeneration control is maintained within a range in which the combustion of particulates can be sustained and the heat resistance limit of the filter 24 is not reached.

This embodiment can be implemented with the following modifications. This embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.
In the above embodiment, the regeneration-promoting air-fuel ratio AF1 is set as the value of the target air-fuel ratio before the combustion purification of particulates during filter regeneration control is started, that is, when the filter temperature THF is less than the regeneration start temperature. Was. The target air-fuel ratio when the filter temperature THF is lower than the regeneration start temperature may be set to a value different from the regeneration-promoting air-fuel ratio AF1, for example, a value closer to the stoichiometric air-fuel ratio than the regeneration-promoting air-fuel ratio AF1.

In the above embodiment, the target air-fuel ratio is set in two stages according to the filter temperature THF in a state where particulate combustion is being purified during execution of filter regeneration control, that is, in a state where the filter temperature THF is equal to or higher than the regeneration start temperature. had changed to The target air-fuel ratio in the above state may be changed in three or more steps according to the filter temperature THF, or may be changed continuously according to the filter temperature THF. In any case, if the target air-fuel ratio is changed such that the higher the filter temperature THF, the leaner the target air-fuel ratio becomes, the filter temperature THF can be prevented from rising excessively.

The air-fuel ratio control section 27A in the above embodiment controls the air-fuel ratio during filter regeneration control by manipulating the fuel injection amount of the fuel injection valve 18. may be used to control the air-fuel ratio. That is, when the filter temperature THF reaches or exceeds the high temperature determination value α, the intake air amount GA is increased by increasing the opening of the throttle valve 17 while maintaining the fuel injection amount constant. The air-fuel ratio of the air-fuel mixture introduced into the device 23 is changed to the lean side. In such a case, the amount of fuel combusted in the three-way catalyst device 23, that is, the amount of heat generated by combustion does not change, but the catalyst outflow gas temperature THC decreases because the heat capacity of the catalyst outflow gas increases. Therefore, even in such a case, when the filter temperature THF rises, it is possible to reduce the catalyst outflow gas temperature THC and suppress the rise in the filter temperature THF.

・In the above embodiment, the filter temperature THF is estimated from the catalyst outflow gas temperature THC, the intake air amount GA, the fuel injection amount, etc., but a temperature sensor is installed in the filter 24 to directly detect the filter temperature THF. You may make it It is also possible to detect the temperature of the gas flowing out of the filter 24 and obtain the filter temperature THF from the temperature of the gas.

In the above-described embodiment, unburned air-fuel mixture is introduced into the three-way catalytic converter 23 by injecting fuel with the spark of the ignition device 20 stopped during filter regeneration control. The timing at which the mixture in the cylinder 12 can be ignited by the spark of the ignition device 20 is limited to the period near the compression top dead center. That is, there is a period during which the air-fuel mixture in the cylinder 12 does not burn even when spark is executed. Therefore, the filter regeneration control may be executed by injecting fuel while sparking the ignition device 20 during such a period to introduce an unburned air-fuel mixture into the three-way catalyst device 23 .

- In the above-described embodiment, the filter regeneration control is performed while the vehicle is coasting. In a hybrid vehicle that includes a motor as a drive source in addition to an internal combustion engine, the crankshaft can be rotated by the power of the motor while the combustion operation of the internal combustion engine is stopped. In the internal combustion engine mounted on such a hybrid vehicle, when the combustion operation of the internal combustion engine is stopped, the power of the motor rotates the crankshaft to execute the filter regeneration control.

In the above embodiment, the filter regeneration control was performed by injecting fuel into the intake passage 15 by the fuel injection valve 18. However, the internal combustion engine is equipped with an in-cylinder fuel injection valve that injects fuel into the cylinder 12. It is also possible to perform filter regeneration control through fuel injection into the cylinder 12 at .

Reference Signs List 10 Internal combustion engine 11 Piston 12 Cylinder 13 Connecting rod 14 Crankshaft 15 Intake passage 16 Air flow meter 17 Throttle valve 18 Fuel injection valve 19 Intake valve 20 ... ignition device, 21 ... exhaust passage, 22
Exhaust valve 23 Three-way catalyst device 24 Particulate-collecting filter 25 Air-fuel ratio sensor 26 Catalyst outflow gas temperature sensor 27 Control device 28 Crank angle sensor 29 Vehicle speed sensor , 30 ... accelerator pedal, 31 ... accelerator position sensor.

Claims (1)

an intake passage that is an air introduction passage; a throttle valve provided in the intake passage; a fuel injection valve; a cylinder into which a mixture containing fuel injected by the fuel injection valve is introduced; an ignition device that ignites the air-fuel mixture with a spark; an exhaust passage through which gas discharged from the cylinder flows; a three-way catalyst device installed in the exhaust passage; and a filter for trapping particulates installed in a portion on the downstream side, and the three-way catalyst is applied to an internal combustion engine comprising: In a control device for an internal combustion engine that executes filter regeneration control for burning and purifying particulates deposited on the filter by introducing into the device,
In a state in which the particulate combustion is purified during execution of the filter regeneration control, when the temperature of the filter is high , the fuel injection amount is set to a leaner value than when the temperature of the filter is low. A control device for an internal combustion engine, comprising an air-fuel ratio control unit that controls the air-fuel ratio of the air-fuel mixture by operating the opening of the throttle valve while maintaining constant the air-fuel ratio.

Images