JP2024063377A - Control device for internal combustion engine - Google Patents

Abstract

[Problem] To provide a control device for an internal combustion engine that can suppress a decrease in the durability of a filter due to abnormal combustion of PM. [Solution] This control device for an internal combustion engine is configured to burn particulate matter accumulated on a filter provided in an exhaust passage by flowing oxygen into the filter through fuel cut control, and includes a first estimation unit that estimates the amount of accumulated particulate matter, a second estimation unit that estimates the amount of condensed water flowing into the filter based on the temperature upstream of the filter, and a fuel cut permission time setting unit that sets the duration during which fuel cut control can be executed based on the amount of accumulated particulate matter estimated by the first estimation unit and the amount of condensed water flowing into the filter estimated by the second estimation unit (step S1). [Selected Figure] Figure 5

Description

The present invention relates to a control device for an internal combustion engine equipped with a filter that collects particulate matter generated by the combustion of an air-fuel mixture.

Patent Document 1 describes a control device for an internal combustion engine that is configured to burn particulate matter (hereinafter referred to as PM) captured on a filter by executing fuel cut control and supplying oxygen to the filter. This control device is configured to prevent excessive PM combustion from damaging the filter. Specifically, when the duration of fuel cut control reaches or exceeds a time determined based on the filter temperature, the amount of PM accumulated on the filter, and the amount of intake air at the start of the fuel cut control, the control device is configured to end the fuel cut control to prevent an excessive increase in filter temperature.

Patent Document 2 describes a device that estimates the amount of PM accumulated in a filter according to the pressure difference between the front and rear of the filter. This estimation device is configured to suppress erroneous determination that the amount of PM accumulation is large when the pressure difference between the front and rear of the filter increases due to condensed water flowing into the filter causing PM captured in the filter to collapse and block the cells. Specifically, when the pressure difference between the front and rear of the filter is equal to or greater than a first predetermined pressure, it is determined that water has been generated, and the amount of PM accumulation estimated from the pressure difference between the front and rear of the filter increases at an abnormal rate, it is configured to determine that at least a portion of the PM has collapsed and blocked the cells. Note that, when it is determined that PM has blocked the cells, the device described in Patent Document 2 is configured to supply unburned fuel to an oxidation catalyst provided upstream of the filter to perform a PM regeneration process that raises the temperature of the exhaust gas flowing into the filter.

JP 2019-190358 A JP 2020-109261 A

The control device for an internal combustion engine described in Patent Document 1 estimates the time until the filter temperature reaches a predetermined temperature while fuel cut control continues, based on factors such as the amount of accumulation on the filter, and sets the estimated time as the upper limit of fuel cut control. However, because PM does not necessarily accumulate evenly on the filter, in areas where the density of accumulated PM is high, the temperature rise associated with the combustion of PM may be higher than in other areas, and in such cases, the filter may be partially damaged.

The estimation device described in Patent Document 2 determines that the differential pressure across the filter is increasing due to PM clogging the cells, and therefore determines that a smaller amount of PM has accumulated than the volume of PM that can be estimated from the differential pressure across the filter. Therefore, when burning the PM trapped in the filter by cutting fuel as in the internal combustion engine control device described in Patent Document 1, the fuel cut time is set long. However, it is believed that the PM accumulation density is higher in the area where PM has clogged the cells than in other areas. Therefore, if the fuel cut time is set long as described above, the area where PM has clogged the cells will become hotter than other areas, and there is a possibility that the filter will be partially damaged.

The present invention was made with a focus on the above technical problems, and aims to provide an internal combustion engine control device that can suppress the deterioration of filter durability caused by abnormal combustion of PM.

To achieve the above object, the present invention provides a control device for an internal combustion engine configured to perform fuel cut control to allow oxygen to flow into a filter provided in an exhaust passage, thereby burning particulate matter accumulated on the filter, and is characterized by comprising a first estimation unit that estimates the amount of accumulated particulate matter, a second estimation unit that estimates the amount of condensed water flowing into the filter based on the temperature upstream of the filter, and a fuel cut permission time setting unit that sets the duration during which the fuel cut control can be executed based on the amount of accumulated particulate matter estimated by the first estimation unit and the amount of condensed water flowing into the filter estimated by the second estimation unit.

According to the present invention, fuel cut control is performed to supply oxygen to the filter and burn particulate matter accumulated on the filter. The duration of the fuel cut control is set based on the amount of condensed water flowing into the filter in addition to the amount of particulate matter accumulated. Therefore, when particulate matter is unevenly accumulated on the rear end side of the filter due to condensed water, the execution period of the fuel cut control can be set to be short. As a result, abnormal combustion can be suppressed in the area where particulate matter is accumulated at a relatively high density, and a decrease in the durability of the filter can be suppressed.

1 is a schematic diagram showing an example of an internal combustion engine and its exhaust system according to an embodiment of the present invention. FIG. 11 is a diagram showing a change in temperature of the GPF according to the amount of PM accumulation. FIG. 2 is a block diagram for explaining functions of a control device according to the embodiment of the present invention. FIG. 4 is a diagram showing changes in intake air amount, exhaust temperature, and inflow amount of condensed water into the GPF during cold start. 4 is a flowchart illustrating an example of control executed by a control device according to an embodiment of the present invention. FIG. 11 is a diagram showing the fuel cut-off permission time and the temperature change of the GPF depending on whether or not condensed water flows into the GPF.

The present invention will be described based on the embodiment shown in the figures. Note that the embodiment described below is merely one example of a specific embodiment of the present invention and does not limit the present invention.

An example of an internal combustion engine and its exhaust system according to an embodiment of the present invention is shown diagrammatically in FIG. 1. The internal combustion engine 1 shown in FIG. 1 is a gasoline engine that generates power by burning a mixture of gasoline and air, and like a conventional gasoline engine, has multiple cylinders 3 formed in an engine body 2. For convenience, only one cylinder 3 is shown in FIG. 1. In the following description, the internal combustion engine 1 will be referred to as engine 1.

Inside the cylinder 3, there is a piston 4 that moves up and down in conjunction with the rotation of a crankshaft (not shown), and the space above the piston 4 is configured to function as a combustion chamber 5. That is, the combustion chamber 5 is formed with an intake port 6 to which outside air and gasoline are supplied, an exhaust port 7 for discharging exhaust gas generated by burning the mixture from the cylinder 3, and an ignition plug 8 for igniting the mixture in the combustion chamber 5. The intake port 6 is provided with an intake valve 9 for opening and closing the intake port 6, and the exhaust port 7 is provided with an exhaust valve 10 for opening and closing the exhaust port 7.

An exhaust passage 11 is provided in communication with the exhaust port 7. This exhaust passage 11 is provided to purify the exhaust gas while discharging it to the outside. In the example shown in FIG. 1, a gasoline particulate filter (hereinafter simply referred to as GPF) 12 for collecting particulate matter (hereinafter simply referred to as PM) contained in the exhaust gas is provided in the exhaust passage 11.

The GPF 12 is constructed in the same way as conventional GPFs, with numerous cells separated by porous partitions arranged along the exhaust flow direction, and the upstream and downstream ends of these cells alternately plugged with plugs.

An exhaust temperature sensor 13 for detecting the temperature of the exhaust gas is provided in the upstream portion of the GPF 12 in the exhaust passage 11, and a bed temperature sensor 15 for detecting the GPF bed temperature is provided in the case 14 that houses the GPF 12.

In the engine 1 configured as described above, the exhaust gas generated by the combustion of the air-fuel mixture in the combustion chamber 5 flows from the exhaust port 7 into the exhaust passage 11, and as it passes through the GPF 12, the PM contained in the exhaust gas is captured in the pores and on the surface of the partition wall.

The exhaust gas also contains water vapor, which also flows from the exhaust port 7 to the exhaust passage 11 and remains in the space between the exhaust port 7 and the GPF 12 in the exhaust passage 11 and inside the GPF 12. Therefore, when the engine 1 is stopped and the temperature in the exhaust passage 11 and the temperature in the GPF 12 drop, the water vapor becomes liquid water. That is, condensed water adheres to the inner wall surface of the exhaust passage 11 and the inside of the cells of the GPF 12. In other words, the condensed water penetrates the PM deposited in the cells. When the engine 1 is started in this state, the condensed water is heated and evaporated by the exhaust gas, which reduces the adhesion between the PM deposited in the cells and the substrate, and the PM flows toward the downstream end of the GPF 12 by the exhaust gas. That is, the density distribution of the PM deposited in the GPF 12 in the exhaust gas flow direction is biased toward the downstream end.

As described above, the GPF regeneration process is periodically performed to burn the PM accumulated in the GPF 12 and restore the collection action of the GPF 12. This GPF regeneration process is a process in which the PM is burned by supplying oxygen when the temperature of the GPF 12 is at or above a predetermined temperature. Specifically, by executing fuel cut control to stop the supply of fuel while the vehicle equipped with the engine 1 is coasting, the air supplied to the cylinder 3 is allowed to flow directly into the exhaust passage 11, thereby supplying oxygen to the GPF 12.

Figure 2 shows the temperature change of the GPF 12 according to the amount of PM accumulation, and shows the results of measuring the temperature at a portion upstream a certain amount from the rear end of the GPF 12. The solid line shows the temperature change at a first PM accumulation amount, the dashed line shows the temperature change at a second PM accumulation amount that is smaller than the first PM accumulation amount, and the dashed line shows the temperature change at a third PM accumulation amount that is even smaller than the second PM accumulation amount. Note that fuel cut control is started at time t1 in Figure 2, and ended at time t2.

As shown in Figure 2, the greater the amount of PM accumulation, the shorter the time for thermal runaway. In other words, even if the amount of PM accumulation in the GPF 12 as a whole is small, if PM accumulates unevenly in one part of the GPF 12, that part will experience thermal runaway in a short time.

Therefore, the control device for the internal combustion engine in the embodiment of the present invention is configured to set the duration for which fuel cut control can be executed according to the amount of PM accumulation and the amount of condensed water inflow. In FIG. 1, an electronic control device (hereinafter referred to as ECU) 16 is provided that sets the duration for which fuel cut control can be executed. This ECU 16 is mainly composed of a microcomputer, and is configured to input signals from the exhaust temperature sensor 13, the bed temperature sensor 15, the intake air volume, etc., and to set the duration for which fuel cut control can be executed based on the input signals and pre-stored maps and calculation formulas.

The ECU 16 shown in FIG. 1 includes a first estimation unit 17 that estimates the amount of accumulated PM, a second estimation unit 18 that estimates the amount of condensed water flowing into the GPF 12, and a fuel cut (F/C) permission time setting unit 19 that sets the duration during which fuel cut control can be executed.

3 is a block diagram for explaining the function of the ECU 16. As shown in FIG. 3, the amount of PM accumulation estimated by the first estimation unit 17, the amount of condensed water flowing into the GPF 12 estimated by the second estimation unit 18, and the temperature detected by the bed temperature sensor 15 (hereinafter referred to as the GPF bed temperature) are input to the fuel cut permission time setting unit 19, and the permission time of the fuel cut control is set. Then, the elapsed time after the fuel cut control is executed (post-F/C counter) is compared with the permission time of the fuel cut control (F/C permission time), and when the post-F/C counter becomes longer than the F/C permission time, the prohibition flag of the fuel cut control is switched on. The GPF bed temperature may be calculated according to the operating state of the vehicle or the engine 1.

The first estimation unit 17 is configured to estimate the amount of PM accumulation based on the difference between the amount of PM emitted by the engine 1 and the amount of PM combusted by the GPF 12. The amount of PM emitted by the engine 1 is found by accumulating the amount of PM emitted based on the operating state of the engine 1, such as the amount of intake air and fuel injection amount to the engine 1, and the ignition timing of the spark plug 8. The amount of PM combusted by the GPF 12 is found by accumulating the amount of PM combusted based on the temperature detected by the bed temperature sensor 15.

The second estimation unit 18 can determine the amount of condensed water flowing into the GPF 12 based on the detection value of the exhaust temperature sensor 13 when the engine 1 is started cold. FIG. 4 is a diagram showing the changes in the intake air volume, the detection value (exhaust temperature) of the exhaust temperature sensor 13, and the amount of condensed water flowing into the GPF 12 during cold start. In the example shown in FIG. 4, the operation (combustion) of the engine 1 starts at time t11, and the intake air volume and exhaust temperature begin to rise accordingly. In addition, water vapor is inevitably generated by the combustion of the mixture by the engine 1. Therefore, it is considered that the amount of moisture contained in the exhaust passage 11 increases according to the driving time of the engine 1, and the theoretical value of the moisture amount can be determined from the volume of the exhaust passage 11, more specifically, the volume between the engine 1 and the GPF 12, and the intake air volume. In FIG. 4, the amount of moisture is indicated as "provisional prediction of condensed water flowing into the GPF".

The exhaust temperature stagnates between time t12 and time t13. This is because the exhaust temperature is absorbed as latent heat when the condensed water remaining in the exhaust passage 11 evaporates. In other words, the temperature stagnation time from time t12 to time t13 and the amount of condensed water are approximately proportional to each other. Therefore, the predicted value of condensed water flowing into the GPF 12 (GPF inflow condensed water actual prediction) is determined based on the temperature stagnation time at time t13 and the provisional predicted value of condensed water flowing into the GPF.

The fuel cut permission time setting unit 19 is configured to set the fuel cut permission time by subtracting a correction time according to the inflow amount of condensed water from the fuel cut permission time (temporary time) for suppressing abnormal combustion of the GPF 12 based on the amount of PM accumulation and the bed temperature of the GPF 12, as in the conventional case. This correction time can be obtained by referring to a predetermined map using the inflow amount of condensed water as a parameter, and the map is set so that the larger the inflow amount of condensed water, the larger the value of the correction time.

Figure 5 is a flow chart for explaining an example of control executed by the ECU 16. First, it is determined whether condensed water has flowed into the GPF 12 (step S1). This step S1 is a step for determining whether condensed water has flowed into the GPF 12 to such an extent that a bias in the amount of PM accumulated in the GPF 12 occurs, and can be determined, for example, based on whether the amount of condensed water that has flowed in estimated by the second estimation unit 18 is equal to or greater than a predetermined flow rate.

If the result of step S1 is negative because condensed water is not flowing into the GPF 12, the routine is terminated. That is, the permitted execution time of the fuel cut control is set based on the amount of PM accumulated in the GPF 12 and the bed temperature, as in the conventional method. In other words, no correction is made according to the amount of condensed water flowing in. On the other hand, if the result of step S1 is positive because condensed water is flowing into the GPF 12, the permitted execution time of the fuel cut control is optimized (step S2), and the routine is terminated. That is, the permitted execution time of the fuel cut control is set by subtracting the correction time from the tentative time during which the fuel cut control can be executed by the fuel cut permission time setting unit 19.

Figure 6 shows the fuel cut-off permission time and the temperature change of GPF 12 when condensed water flows into GPF 12 (solid line), and the fuel cut-off permission time and the temperature change of GPF 12 when condensed water does not flow into GPF 12 (dashed line). As shown in Figure 6, when condensed water flows into GPF 12, the temperature of GPF 12, more specifically, the temperature of the rear end side of GPF 12 rises earlier than when condensed water does not flow into GPF 12.

When condensed water has flowed into the GPF 12, the fuel cut permission time is shortened compared to when condensed water has not flowed into the GPF 12. As a result, it is possible to suppress an excessive increase in the temperature of the GPF 12. In other words, it is possible to suppress abnormal combustion at the rear end of the GPF 12 where the PM deposition density has become high, and to suppress a decrease in the durability of the GPF 12. In other words, by setting the permission time of the fuel cut control based on whether or not condensed water has flowed into the GPF 12, even when condensed water has not flowed into the GPF 12 and abnormal combustion is unlikely to occur, there is no need to shorten the fuel cut permission time assuming a state in which condensed water has flowed into the GPF 12, and the fuel cut control can be executed for a long period of time. As a result, it is possible to suppress the driving period of the engine 1 from becoming longer, such as starting the engine 1 to suppress abnormal combustion, and therefore it is possible to suppress deterioration of fuel efficiency.

1. Engine (internal combustion engine)
11 exhaust passage 12 GPF (gasoline particulate filter)
13 Exhaust temperature sensor 15 Floor temperature sensor 16 ECU (electronic control unit)
17, 18 Estimation section 19 Fuel cut permission time setting section

Claims (1)

A control device for an internal combustion engine configured to perform a fuel cut control to cause oxygen to flow into a filter provided in an exhaust passage, thereby burning particulate matter accumulated in the filter,
A first estimation unit that estimates the accumulation amount of the particulate matter;
A second estimation unit that estimates an amount of condensed water that flows into the filter based on a temperature on an upstream side of the filter;
a fuel cut permission time setting unit that sets a duration during which the fuel cut control can be executed based on the amount of particulate matter accumulated by the first estimation unit and the amount of condensed water inflowing into the filter estimated by the second estimation unit.

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